Yamaguchi, Jinichi (Tokyo, JP)
Miyamoto, Atsushi (Kanagawa, JP)
Plaque It!
Sponsored by: Flash of Genius |
2. A motion controlling apparatus for a legged mobile robot according to claim 1, characterized in that said third means includes: landed location searching means for searching for a landed location upon tumbling of said legged mobile robot based on the variation per time Δt of the area S of the support polygon formed from the landed points of said body and the floor; target landing point setting means for setting a target landing point at which the location selected by said landed location searching means should be landed so that the variation ΔS/Δt per time Δt of the area S of the support polygon formed from the landed points of said body and the floor may be minimized; and location landing means for landing the location selected by said landed portion searching means at the target landing point set by said target landing point setting means.
3. A motion controlling apparatus for a legged mobile robot according to claim 2, further comprising: support polygon expansion means for moving the landed portion so that the support polygon newly formed by landing of the location selected by said location landing means may be further expanded.
4. A motion controlling apparatus for a legged mobile robot according to claim 2, characterized in that the landing operation of the portion by said landed portion searching means and said target landing point setting means and/or the expansion operation of the support polygon by said support polygon expansion means are performed repetitively.
5. A motion controlling apparatus for a legged mobile robot according to claim 2, characterized in that said legged mobile robot is formed from a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and said target landing point setting means sets a location at which a link with which the number of non-landed links is maximized exists as a target.
6. A motion controlling apparatus for a legged mobile robot according to claim 1, characterized in that said legged mobile robot is formed from a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and said third means includes: means for searching, when said legged mobile robot returns from its tumbling state, for the narrowest support polygon formed from the least number of links from among landed polygons formed, in an on-floor posture of said legged mobile robot in which two or more links including a gravity center link positioned at the center of gravity of said body are landed on the floor, from the landed links; means for taking off the landed links in the landed polygons except those of the searched out support polygon; means for bending two or more continuous ones of non-landed links until end portions of the end links land onto the floor to form a narrower landed polygon; and means for taking off a number of links greater than a first predetermined number from one end side of said link structure to stand said body uprightly in response to that the support polygon is sufficiently narrow.
7. A motion controlling apparatus for a legged mobile robot according to claim 6, characterized in that said means for searching for the support polygon extracts a landed link which can be taken off from the floor while a zero moment point remains plannable.
8. A motion controlling apparatus for a legged mobile robot according to claim 6, characterized in that said means for searching for the support polygon searches for a narrower support polygon while keeping the gravity center link in the landed state.
9. A motion controlling apparatus for a legged mobile robot according to claim 6, characterized in that said means for standing said body uprightly determines whether or not the gravity center link can be taken off in a state wherein the end portions of the opposite end links of the landed polygon are landed thereby to determine whether or not the support polygon is sufficiently narrow.
10. A motion controlling apparatus for a legged mobile robot according to claim 6, characterized in that said means for standing said body uprightly includes: means for taking off the gravity center link from the floor in a state wherein the end portions of the opposite end links of the support polygon are landed; means for reducing the distance between the end portions of the opposite end links of the support polygon in a state wherein the gravity center link is taken off to move a zero moment point to the other end side of said link structure; and means for taking off, in response to that the zero moment point enters a landed polygon formed only from a number of landed links smaller than a second predetermined number from the other end of said link structure, a number of links greater than a first predetermined number from the one end side of said link structure while the zero moment point is kept accommodated in the landed polygon to expand the non-landed links in the lengthwise direction.
11. A motion controlling apparatus for a legged mobile robot according to claim 10, characterized in that said means for expanding the non-landed links in the lengthwise direction operates positively using a joint degree-of-freedom having a comparatively great mass operation amount.
12. A motion controlling apparatus for a legged mobile robot according to claim 6, characterized in that said link structure includes at least shoulder joint pitch axes, a trunk pitch axis, hip joint pitch axes and knee pitch axes connected to each other in the heightwise direction of said body.
13. A motion controlling apparatus for a legged mobile robot according to claim 12, characterized in that said means for searching for the support polygon extracts two or more continuous links extending from one end side of said link structure which includes at least the shoulder joint pitch axes as links which can be taken off from the floor while the zero moment point remains plannable.
14. A motion controlling apparatus for a legged mobile robot according to claim 12, characterized in that said means for searching for the support polygon searches for a narrower support polygon while a link which interconnects said trunk pitch axis and said hip joint pitch axes is kept as the gravity center link in the landed state.
15. A motion controlling apparatus for a legged mobile robot according to claim 12, characterized in that said means for forming a narrower landed polygon bends the non-landed links around said shoulder joint pitch axes to land the hands which are an end portion of one of the end links onto the floor.
16. A motion controlling apparatus for a legged mobile robot according to claim 15, characterized in that, where the length of the upper arms is represented by l1, the length of the forehands by l2, the shoulder roll angle by α, the elbow pitch angle by β, the length from the shoulders to the hands by l12, the angle defined by a line interconnecting each of the shoulders and a corresponding one of the hands by γ, and the height of the shoulders by h, each of the arm parts operates so as to satisfy the following expressions:
l12=l1 cos α+l2 sin (α+β−90)
l12 sin γ<h
17. A motion controlling apparatus for a legged mobile robot according to claim 12, characterized in that said means for searching for the support polygon extracts two or more continuous links extending from the other end side of said link structure and including at least said knee joint pitch axes as the links which can be taken off from the floor while the zero moment point remains plannable.
18. A motion controlling apparatus for a legged mobile robot according to claim 12, characterized in that said means for forming a narrower landed polygon bends the non-landed links around said knee joint pitch axes to land the soles which are end portions of the end links of said link structure.
19. A motion controlling apparatus for a legged mobile robot according to claim 12, characterized in that said means for standing said body uprightly determines whether or not the gravity center link which interconnects said trunk pitch axis and said hip joint pitch axes can be taken off from the floor in a state wherein the hands and the soles as the end portions of the opposite end links of the landed polygon to determine whether or not the support polygon is sufficiently narrow.
20. A motion controlling apparatus for a legged mobile robot according to claim 12, characterized in that said means for standing said body uprightly includes: means for taking off the gravity center link which interconnects said trunk pitch and said hip joint pitch axes from the floor in a state wherein the hands and the soles as the end portions of the opposite end links of the landed polygon are landed; means for contracting the distance between the hands and the soles as the end portions of the opposite end links of the landed polygon in a state wherein the gravity center link is taken off from the floor to move the zero moment point to the soles; and means for taking off, in response to that the zero moment point enters the landed polygon formed from the soles, the links from said shoulder pitch axes to said knee pitch axes while the zero moment point is kept accommodated in the landed polygon to expand the non-landed links in the lengthwise direction to stand said body uprightly.
21. A motion controlling apparatus for a legged mobile robot according to claim 20, characterized in that said means for expanding the non-landed links in the lengthwise direction operates positively using said knee joint pitch axes having a comparatively great mass operation amount.
22. A motion controlling apparatus for a legged mobile robot according to claim 6, characterized in that said means for producing a narrower landed polygon selectively utilizes one of a step changing motion and a dragging motion on the floor of the hand parts or the foot parts in response to whether it is possible to take off two or more of the links which do not relate to the smallest support polygon from the floor to form a narrower landed polygon.
23. A motion controlling method for a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, characterized in that said legged mobile robot has a plurality of postures or states, and that said motion controlling method comprises: a first step of calculating an area S of a support polygon formed from landed points of a body of said legged mobile robot and a floor; a second step of calculating the variation ΔS/Δt of the area S of the support polygon per time Δt; and a third step of determining a motion of said body when the posture or state is to be changed based on the area S of the support polygon or the variation rate ΔS/Δt of the area S.
24. A motion controlling method for a legged mobile robot according to claim 23, characterized in that said third step includes: a landed location searching step for searching for a landed location upon tumbling of said legged mobile robot based on the variation per time Δt of the area S of the support polygon formed from the landed points of said body and the floor; a target landing point setting step of setting a target landing point at which the location selected at the landed location searching step should be landed so that the variation ΔS/Δt per time Δt of the area S of the support polygon formed from the landed points of said body and the floor may be minimized; and a location landing step of landing the location selected at the landed portion searching step at the target landing point set at the target landing point setting step.
25. A motion controlling method for a legged mobile robot according to claim 24, further comprising: a support polygon expansion step for moving the landed portion so that the support polygon newly formed by landing of the location selected at the location landing step may be further expanded.
26. A motion controlling method for a legged mobile robot according to claim 24, characterized in that the landing operation of the portion at the landed portion searching step and the target landing point setting step and/or the expansion operation of the support polygon at the support polygon expansion step are performed repetitively.
27. A motion controlling method for a legged mobile robot according to claim 24, characterized in that said legged mobile robot is formed from a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and the target landing point setting step sets a location at which a link with which the number of non-landed links is maximized exists as a target.
28. A motion controlling method for a legged mobile robot according to claim 23, characterized in that said legged mobile robot is formed from a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and the third step includes the steps of: searching, when said legged mobile robot returns from its tumbling state, for the narrowest support polygon formed from the least number of links from among landed polygons formed, in an on-floor posture of said legged mobile robot in which two or more links including a gravity center link positioned at the center of gravity of said body are landed on the floor, from the landed links; taking off the landed links in the landed polygons except those of the searched out support polygon; bending two or more continuous ones of non-landed links until end portions of the end links land onto the floor to form a narrower landed polygon; and taking off a number of links greater than a first predetermined number from one end side of said link structure to stand said body uprightly in response to that the support polygon is sufficiently narrow.
29. A motion controlling method for a legged mobile robot according to claim 28, characterized in that, at the step of searching for the support polygon, a landed link which can be taken off from the floor while a zero moment point remains plannable is extracted.
30. A motion controlling method for a legged mobile robot according to claim 28, characterized in that, at the step of searching for the support polygon, a narrower support polygon is searched for while keeping the gravity center link in the landed state.
31. A motion controlling method for a legged mobile robot according to claim 28, characterized in that it is determined at the step of standing said body uprightly whether or not the gravity center link can be taken off from the floor in a state wherein the end portions of the opposite end links of the landed polygon are landed thereby to determine whether or not the support polygon is sufficiently narrow.
32. A motion controlling method for a legged mobile robot according to claim 28, characterized in that, at the step of standing said body uprightly, the gravity center link is taken off from the floor in a state wherein the end portions of the opposite end links of the support polygon are landed, and the distance between the end portions of the opposite end links of the support polygon is reduced to move a zero moment point to the other end side of said link structure, and, in response to that the zero moment point enters a landed polygon formed only from a number of landed links smaller than a second predetermined number from the other end of said link structure, a number of links greater than a first predetermined number from the one end side of said link structure are taken off from the floor while the zero moment point is kept accommodated in the landed polygon to expand the non-landed links in the lengthwise direction.
33. A motion controlling method for a legged mobile robot according to claim 32, characterized in that, at the step of expanding the non-landed links in the lengthwise direction, a joint degree-of-freedom having a comparatively great mass operation amount is positively used for the operation.
34. A motion controlling method for a legged mobile robot according to claim 28, characterized in that said link structure includes at least shoulder joint pitch axes, a trunk pitch axis, hip joint pitch axes and knee pitch axes connected to each other in the heightwise direction of said body.
35. A motion controlling method for a legged mobile robot according to claim 34, characterized in that, at the step of searching for the support polygon, two or more continuous links extending from one end side of said link structure which includes at least the shoulder joint pitch axes are extracted as links which can be taken off from the floor while the zero moment point remains plannable.
36. A motion controlling method for a legged mobile robot according to claim 34, characterized in that, at the step of searching for the support polygon, a narrower support polygon is searched for while a link which interconnects said trunk pitch axis and said hip joint pitch axes is kept as the gravity center link in the landed state.
37. A motion controlling method for a legged mobile robot according to claim 34, characterized in that, at the step of forming a narrower landed polygon, the non-landed links are bent around said shoulder joint pitch axes to land the hands which are an end portion of one of the end links onto the floor.
38. A motion controlling method for a legged mobile robot according to claim 37, characterized in that, where the length of the upper arms is represented by l1, the length of the forehands by l2, the shoulder roll angle by α, the elbow pitch angle by β, the length from the shoulders to the hands by l12, the angle defined by a line interconnecting each of the shoulders and a corresponding one of the hands by γ, and the height of the shoulders by h, each of the arm parts operates so as to satisfy the following expressions:
l12=l1 Cos α+l2 sin (α+β−90)
l12 sin γ<h
39. A motion controlling method for a legged mobile robot according to claim 34, characterized in that, at the step of searching for the support polygon, two or more continuous links extending from the other end side of said link structure and including at least said knee joint pitch axes are extracted as the links which can be taken off from the floor while the zero moment point remains plannable.
40. A motion controlling method for a legged mobile robot according to claim 34, characterized in that, at the step of forming a narrower landed polygon, the non-landed links are bent around said knee joint pitch axes to land the soles which are end portions of the end links of said link structure.
41. A motion controlling method for a legged mobile robot according to claim 34, characterized in that it is determined at the step of standing said body uprightly whether or not the gravity center link which interconnects said trunk pitch axis and said hip joint pitch axes can be taken off from the floor in a state wherein the hands and the soles as the end portions of the opposite end links of the landed polygon to determine whether or not the support polygon is sufficiently narrow.
42. A motion controlling method for a legged mobile robot according to claim 34, characterized in that, at the step of standing said body uprightly, the gravity center link which interconnects said trunk pitch and said hip joint pitch axes is taken off from the floor in a state wherein the hands and the soles as the end portions of the opposite end links of the landed polygon are landed and the distance between the hands and the soles as the end portions of the opposite end links of the landed polygon is reduced in a state wherein the gravity center link is taken off from the floor to move the zero moment point to the soles, and, in response to that the zero moment point enters the landed polygon formed from the soles, the links are taken off from said shoulder pitch axes to said knee pitch axes while the zero moment point is kept accommodated in the landed polygon to expand the non-landed links in the lengthwise direction to stand said body uprightly.
43. A motion controlling method for a legged mobile robot according to claim 42, characterized in that, at the step of expanding the non-landed links in the lengthwise direction, said knee joint pitch axes having a comparatively great mass operation amount are used positively for the operation.
44. A motion controlling method for a legged mobile robot according to claim 28, characterized in that, at the step of producing a narrower landed polygon, one of a step changing motion and a dragging motion on the floor of the hand parts or the foot parts is selectively utilized in response to whether it is possible to take off two or more of the links which do not relate to the smallest support polygon from the floor to form a narrower landed polygon.
45. A legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, comprising: external force detection means for detecting application of an external force to a body of said legged mobile robot; zero moment point trajectory planning means for disposing a zero moment point at which moments applied to said body balance each other on or on the inner side of a side of a support polygon formed from a sole landed point and a floor based on a result of the detection by said external force detection means; and tumbling motion execution means for executing a tumbling motion of said body in response to that the disposition of the zero moment point in the support polygon by said zero moment point trajectory planning means is rendered difficult or impossible by the external force applied to said body.
46. A legged mobile robot according to claim 45, characterized in that said external force detection means detects the external force applied to said body using a floor reactive force sensor or an acceleration sensor disposed on each of the soles or an acceleration sensor disposed at a position of the waist of the body.
47. A motion controlling method for a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, comprising: an external force detection step of detecting application of an external force to a body of said legged mobile robot; a zero moment point trajectory planning step of disposing a zero moment point at which moments applied to said body balance each other on or on the inner side of a side of a support polygon formed from a sole landed point and a floor based on a result of the detection at the external force detection step; and a tumbling motion execution step of executing a tumbling motion of said body in response to that the disposition of the zero moment point in the support polygon by said zero moment point trajectory planning means is rendered difficult or impossible by the external force applied to said body.
48. A motion controlling method for a legged mobile robot according to claim 47, characterized in that, at the external force detection step, the external force applied to said body is detected using a floor reactive force sensor or an acceleration sensor disposed on each of the soles or an acceleration sensor disposed at a position of the waist of the body.
49. A motion controlling apparatus for a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, comprising: means for calculating an impact moment applied to a body of said legged mobile robot at each stage upon tumbling of said body; means for calculating an impact force applied to said body from the floor at each stage upon tumbling; means for calculating an area S of a support polygon formed from a landed point of said body and the floor; first landed location searching means for selecting a next landed location so that the area S of the support polygon may be minimized or fixed; and second landed location searching means for selecting a next landed location so that the area S of the support polygon may be increased.
50. A motion controlling apparatus for a legged mobile robot according to claim 49, characterized in that a tumbling motion of said body is performed by said second landed location searching means if the impact force applied to said body from the floor is within a predetermined tolerance, but a tumbling motion of said body is performed by said first landed location searching means if the impact force is outside the predetermined tolerance.
51. A motion controlling method for a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, comprising: a step of calculating an impact moment applied to a body of said legged mobile robot at each stage upon tumbling of said body; a step of calculating an impact force applied to said body from the floor at each stage upon tumbling; a step of calculating an area S of a support polygon formed from a landed point of said body and the floor; a first landed location searching step of selecting a next landed location so that the area S of the support polygon may be minimized or fixed; and a second landed location searching step of selecting a next landed location so that the area S of the support polygon may be increased.
52. A motion controlling method for a legged mobile robot according to claim 51, characterized in that a tumbling motion of said body is performed by the second landed location searching step if the impact force applied to said body from the floor is within a predetermined tolerance, but a tumbling motion of said body is performed by the first landed location searching step if the impact force is outside the predetermined tolerance.
53. A motion controlling apparatus for controlling a series of motions relating to tumbling and standing up of a body of a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, characterized in that said legged mobile robot is formed from a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and said motion controlling apparatus comprises: means for searching for the narrowest support polygon formed from a minimum number of links from among landed polygons formed from landed links in an on-floor posture wherein two or more links including a gravity center link at which the center of gravity of said body is positioned are landed on a floor upon tumbling of said legged mobile robot; means for setting a zero moment point at a location at which the number of links which do not relate to the smallest support polygon is maximized to perform a tumbling motion; means for searching for a link or links which can be taken off from the floor in the tumbling posture of said body; and means for taking off all of the links which can be taken off from the floor to perform a standing up motion.
54. A motion controlling method for controlling a series of motions relating to tumbling and standing up of a body of a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, characterized in that said legged mobile robot is formed from a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and said motion controlling method comprises the steps of: searching for the narrowest support polygon formed from a minimum number of links from among landed polygons formed from landed links in an on-floor posture wherein two or more links including a gravity center link at which the center of gravity of said body is positioned are landed on a floor upon tumbling of said legged mobile robot; setting a zero moment point at a location at which the number of links which do not relate to the smallest support polygon is maximized to perform a tumbling motion; searching for a link or links which can be taken off from the floor in the tumbling posture of said body; and taking off all of the links which can be taken off from the floor to perform a standing up motion.
55. A robot apparatus having a trunk part, leg parts connected to said trunk part and arm parts connected to said trunk part, comprising: support polygon detection means for detecting a first support polygon formed from a plurality of end portions of said leg parts, trunk part and/or arm parts at which said leg parts, trunk part and/or arm parts are landed on a floor; support polygon changing means for bending said leg parts toward said trunk part to reduce the area of the first support polygon; zero moment point motion controlling means for determining whether or not a zero moment point which is positioned in the changed first support polygon can be moved into a landed polygon formed from the soles of said leg parts; and control means for moving, when said zero moment point motion controlling means determines that the zero moment point can be moved, the zero moment point from within the first support polygon into the landed polygon formed by the soles and changing the posture of said robot apparatus from a tumbling posture to a basic posture while the zero moment point is maintained within the landed polygon.
56. A robot apparatus which includes at least a body, one or more arm links connected to an upper portion of said body each through a first joint (shoulder), a first leg link connected to a lower portion of said body through a second joint (hip joint), and a second leg link connected to an end of said second leg link through a third joint (knee), comprising: means for landing ends of said arm links and a foot part at an end of said second leg link to form a first support polygon; means for moving said second joint upwardly higher than said third joint in a normal direction to the floor while the ends of said arm links and said foot part are kept landed, decreasing the area of the first support polygon and moving a zero moment point into a landed polygon formed from said foot part; and means for standing a body of said robot apparatus uprightly while the zero moment point is kept in the landed polygon formed from said foot part.
TECHNICAL FIELD
The present invention relates to a motion controlling apparatus and a motion controlling method for a legged mobile robot having a great number of joint degrees of freedom, and a robot apparatus, and more particularly to a motion controlling apparatus and a motion controlling method for a legged mobile robot which includes a plurality of movable legs and has a basic standing posture, and a robot apparatus.
More specifically, the present invention relates to a motion controlling apparatus and a motion controlling method for a legged mobile robot wherein a ZMP (Zero Moment Point) is used as a posture stability determination criterion to stabilize and control the position of the body during movement, and more particularly to a motion controlling apparatus and a motion controlling method for a legged mobile robot wherein the damage which may otherwise be given to the robot is reduced as far as possible by motion control of the entire body during tumbling (fall down) or dropping and a standing posture is restored from an on-floor posture such as a supine posture or a prone posture by a stable motion with comparatively low torque, and a robot apparatus.
BACKGROUND ART
A mechanical apparatus which performs movements similar to motions of a human being using mechanical or magnetic actions is called “robot”. It is said that the word “robot” originates from a word ‘ROBOTA’ (slave machine) of a Slavic language. Here in Japan, robots began to be popularized at the end of the nineteen sixties. Most of them, however, were industrial robots such as manipulators or transport robots intended for automation and unmanning of manufacturing works in a factory.
Recently, research and development regarding legged mobile robots such as pet type robots which copy body mechanisms and motions of animals that perform four-leg walking like a dog or a cat, or robots (humanoid robot) called “human-type” or “humanoid” robots which are designed by modeling body mechanisms and motions of animals which perform bipedal upright walking such as a human being have proceeded, and also expectation that they be placed into practical use is increasing.
The significance in research and development of legged mobile robots of bipedal locomotion type called human-like or humanoid robots can be grasped, for example, from the following two points of view.
One of them is a human scientific point of view. In particular, a mechanism of a natural motion of a human being beginning with walking can be clarified in an engineering sense through a process that a robot having a structure similar to the lower limbs and/or the upper limbs of a human being is produced and a controlling method for the robot is devised to simulate a walking motion of a human being. It is expected that results of such research can be fed back significantly to the progress in various other research fields which handle a movement mechanism of a human being such as the human engineering, rehabilitation engineering or sports engineering.
Another point is development of a robot for practical use which supports the life of a human being as a partner of the human being, that is, which supports human activities in dwelling environments and other various scenes in everyday life. It is necessary for a robot of the type just described to learn a method of adaptation to human beings having individually different identities and to environments while being taught by human beings in various phases of life environments of human beings. It is considered that, in this instance, if the robot is a “human type” robot, that is, if the robot has a same configuration or a same structure as that of the human being, then the robot functions effectively in smooth communication between a human being and the robot.
For example, in such a case that it is tried to actually teach to a robot a method of passing through a room while bypassing an obstacle which must be kept off, where the robot which is an object of teaching is a bipedal locomotion robot having a similar configuration to that of a user (operator), it is much easier for the user to teach the robot and also it is easier for the robot to learn than where the robot has a structure quite different from the user such as a crawler type robot or a four-legged robot (refer to, for example, TAKANISHI, “Control of a Bipedal locomotion Robot”, the Kanto Branch of the Society of Automotive Engineers of Japan <Koso>, No. 25, April, 1996).
A great number of proposals have been made for a technique for posture control or stable walking relating to a robot of the type which performs legged movement by bipedal locomotion. The stable “walking” here can be defined as “traveling without tumbling through use of the legs”.
Posture stabilization control of a robot is very important in order to prevent tumbling of a robot. This is because tumbling of a robot signifies interruption of a work being performed and considerable labor and time are required until the robot stands up uprightly from the tumbling state and resumes the work. Above all, there is the possibility that the tumbling may critically damage the robot body itself or also damage a substance with which the tumbling robot collides. Accordingly, in research and development of legged mobile robots, posture stabilization control upon walking or upon any other legged operation is considered one of the most significant technical subjects.
Upon walking of a robot, the gravity and the force of inertia and moments of them originating from the gravity and an acceleration generated by the walking movement act from the walking system of the robot upon the road surface. According to the “d'Alembert's principle”, they are balanced with a floor reactive force and a floor reactive force moment as a reaction from the road surface to the walking system. As a consequence of mechanical inference, a point at which the pitch axis moment and the roll axis moment are zero, that is, a “ZMP (Zero Moment Point)”, is present on or on the inner side of a side of a support polygon formed by landed points (contact points) of the soles and the road surface.
Most of proposals regarding posture stabilization control of legged mobile robots and prevention of tumbling upon walking uses the ZMP as a criterion for determination of the stability of walking. Production of a bipedal locomotion pattern based on the ZMP criterion is advantageous in that a sole landing point can be set in advance and it is easy to take a kinetic restriction condition of the sole according to a shape of the road surface into consideration. Further, to adopt the ZMP as a stability determination criterion does not signify to handle not a force but a trajectory as a target value on motion control, and therefore, it technically raises the feasibility. It is to be noted that a concept of the ZMP and application of the ZMP to a stability determination criterion for a walking robot are disclosed in Miomir Vukobratovi'c, “LEGGED LOCOMOTION ROBOTS” (Ichiro KATO et al., “Walking Robot and Artificial Feet”, the Nikkan Kogyo Shimbun, Ltd.).
Normally, a bipedal locomotion robot such as a humanoid robot is higher in the position of the center of gravity and narrower in the ZMP stable region upon walking than a four-legged walking robot. Accordingly, the problem of a posture variation caused by a variation of the road surface condition is significant particularly with a bipedal locomotion robot.
Several proposals are already available which use the ZMP as a posture stability determination criterion for a bipedal locomotion robot.
For example, a legged mobile robot disclosed in Japanese Patent Laid-Open No. Hei 5-305579 performs stable walking by making a point on a floor at which a ZMP is zero coincide with a target value.
Meanwhile, another legged mobile robot disclosed in Japanese Patent Laid-Open No. Hei 5-305581 is configured such that a ZMP is positioned in the inside of a supporting polyhedron (polygon) or, upon landing or upon taking off, the ZMP is positioned at a position having at least a predetermined margin from an end portion of the support polygon. In this instance, even if the legged mobile robot is subject to some disturbance, it has a margin for the ZMP by the predetermined distance, and the stability of the body upon walking is improved.
Further, Japanese Patent Laid-Open No. Hei 5-305583 discloses that the walking speed of a legged mobile robot is controlled depending upon a ZMP target position. In particular, walking pattern data set in advance is used, and a leg part joint is driven so that a ZMP may coincide with a target position whereas a slope of the upper part of the body is detected and the discharging rate of the set walking pattern data is changed in response to the detection value. If the robot steps on an unknown concave or convex place and tilts forwardly, then the posture thereof can be restored by raising the discharging rate. Further, since the ZMP is controlled to the target position, there is no trouble even if the discharging rate is changed within a double support phase.
Japanese Patent Laid-Open No. Hei 5-305585 discloses that the landing position of a legged mobile robot is controlled in accordance with a ZMP target position. In particular, the legged mobile robot disclosed in the patent document mentioned detects a displacement between a ZMP target position and an actually measured position and drives one or both of the leg parts so that the displacement may be canceled. Or, the legged mobile robot detects a moment around a ZMP target position and drives the leg parts so that the moment may be reduced zero. The legged mobile robot thereby achieves stabilized walking.
Japanese Patent Laid-Open No. Hei 5-305586 discloses that a tilting posture of a legged mobile robot is controlled in accordance with a ZMP target position. In particular, a moment around a ZMP target position is detected, and if a moment appears, then the leg parts are driven so that the moment may be reduced to zero thereby to achieve stabilized walking.
Posture stabilization control of a robot which adopts a ZMP as a stability determination criterion basically resides in search for a point at which a moment is zero on or on the inner side of a side of a support polygon formed from landed points of the soles and the road surface.
As described hereinabove, for a legged mobile robot, possible much effort has been made to prevent the robot from tumbling during walking or during execution of some other motion pattern by taking such a countermeasure as to introduce a ZMP as a posture stabilization criterion.
Naturally, the state of tumbling of a robot signifies interruption of a work being performed by the robot and considerable labor and time are required until the robot stands up uprightly from the tumbling state and resumes the work. Further, there is the possibility that, above all, the tumbling may critically damage the robot body itself or also damage a substance with which the tumbling robot collides.
Although the possible best posture stabilization control is performed in order to prevent tumbling of a robot, the robot may still lose its stability in posture because of some defect in control, some unpredictable external factor (such as, for example, accidental collision with another substance, a road surface situation such as a projection or a depression on the floor, appearance of an obstacle or the like) to such a degree that it cannot be supported only with the movable legs thereof, resulting in tumbling.
Particularly in the case of a robot which performs bipedal legged traveling such as a human-type robot, since the position of the center of gravity is high and an uprightly standing stationary state itself of the robot is originally instable, the robot is likely to tumble. If the robot tumbles, then there is the possibility that critical damage may be applied to the robot itself or to the other party side with which the robot collides by the tumbling.
For example, Japanese Patent Laid-Open No. Hei 11-48170 discloses a control apparatus for a legged mobile robot by which, when the legged mobile robot is in a situation wherein it seems to tumble, the damage which may be given to the robot by the tumbling or the damage to the other party side with which the robot may collide upon the tumbling can be reduced as far as possible.
However, the patent document merely proposes control by which the center of gravity of the robot when landing upon tumbling is merely lowered, but does not make such an argument that, in order to minimize the possible damage when the robot actually tumbles, in what manner the entire body including not only the leg parts but also the body and the arm parts should operate.
In the case of a legged mobile robot of the uprightly standing walking type, a posture which makes a reference when a movement of a body such as walking is taken into consideration is a standing posture in which the robot stands uprightly with the two feet. For example, a state in which the robot is most stable among various standing postures (that is, a point at which the instability is in the minimum) can be positioned as a basic standing posture.
Such a basic standing posture as just described requires generation of torque by joint axis motors for the leg parts and so forth by execution of posture stabilization control and control instruction. In other words, in a no-power supply condition, no standing posture is stable. Therefore, it is considered preferable that the robot starts activation thereof from an on-floor posture in which the robot is physically most stable such as a supine posture or a prone posture.
However, even if power supply to the robot in such an on-floor posture as just described is made available, if the robot cannot stand up autonomously, then an operator must give a hand to lift the body, which is cumbersome to the operator.
Further, when the robot once assumes a standing posture and performs walking or some other autonomous legged operation, it basically makes an effect to travel using the legs without tumbling. However, the robot may sometimes tumble unfortunately. “Tumbling” is inevitable when a robot operates under dwelling environments of human beings which involve various obstacles and unforeseeable situations. In the first place, a human being also tumbles. Also in this instance, it still is cumbersome if an operator must give a hand to lift the body.
If the robot cannot stand up by itself every time it assumes an on-floor posture, then it cannot be operated in unmanned environments after all, and the operation lacks in self-conclusion. Thus, the robot cannot be placed into fully self-contained environments.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a superior legged mobile robot and a superior tumbling motion (fall down motion) controlling method for a legged mobile robot by which damage which may otherwise be given to the robot can be reduced as far as possible by motion control of an entire body including not only the leg parts but also the body and the arm parts during tumbling and dropping.
It is another object of the present invention to provide a superior motion controlling apparatus and motion controlling method for a legged mobile robot and a superior robot apparatus by which the robot can autonomously restore its standing posture from an on-floor posture such as a supine posture or a prone posture.
It is a further object of the present invention to provide a superior motion controlling apparatus and motion controlling method for a legged mobile robot and a superior robot apparatus by which the robot can restore its standing posture from an on-floor posture such as a supine posture or a prone posture through a stabilized motion with comparatively low torque.
The present invention has been made in view of the subjects described above, and according to a first aspect of the present invention, there is provided a motion controlling apparatus or a motion controlling method for a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, characterized in that
-
- the legged mobile robot has a plurality of positions or states, and that
- the motion controlling apparatus or method includes:
- first means for or a first step of calculating an area S of a support polygon formed from landed points (contact points to the floor) of a body of the legged mobile robot and a floor;
- second means for or a second step of calculating the variation ΔS/Δt of the area S of the support polygon per time Δt; and
- third means for or a third step of determining a motion of the body when the position or state is to be changed based on the area S of the support polygon or the variation rate ΔS/Δt of the area S.
In many legged mobile robots, a ZMP is utilized as a stability determination criterion so that the posture stability of the body within a period of a particular legged operation such as walking may be maintained. With the motion controlling apparatus or the motion controlling method for a legged mobile robot according to the first aspect of the present invention, when the robot changes the posture or the state thereof such as when the robot which is in a walking or uprightly standing state or when the robot stands up from a horizontally lying position after tumbling or the like, the motion pattern of the body is successively determined based on the area S of the support polygon formed by the landed points of the body and the floor or the variation rate ΔS/Δt of the area S. By this, a tumbling motion or a standing up motion can be realized such that they may be performed more efficiently with a reduced load.
Here, the third means or step may include:
-
- landed location searching means (means for searching contacting part) for or a landed location searching step (step of searching contacting part) of searching for a landed location (part) upon tumbling of the legged mobile robot based on the variation per time Δt of the area S of the support polygon formed from the landed points of the body and the floor;
- target landing point (target contacting point) setting means for or a target landing point setting step of setting a target landing point at which the location selected by the landed location searching means should be landed (contacting to the floor) so that the variation ΔS/Δt per time Δt of the area S of the support polygon formed from the landed points of the body and the floor may be minimized; and
- location landing means for landing the location selected by the landed portion searching means or at the landed portion searching step, at the target landing point set by the target landing point setting means or at the target landing point setting step.
While the legged mobile robot performs a legged operation in the standing posture, it detects an external force applied to the body by means of floor reactive force sensors, acceleration sensors disposed on (mounted on) the soles or acceleration sensors disposed at the position of the waist of the body or the like. Then, the legged mobile robot establishes a ZMP balance equation based on the thus detected external forces to normally plan a ZMP trajectory so that a ZMP at which moments applied to the body balance with each other may be disposed on or on the inner side of a side of the support polygon formed from the landed points of the soles and the floor to perform posture stabilization control.
However, if a moment error on the ZMP balance equation cannot be canceled due to such a situation that the external force applied to the body is excessively high or the situation of the road surface is not favorable, then it sometimes becomes difficult or impossible to dispose the ZMP in the support polygon in accordance with the ZMP trajectory plan. In such an instance, the legged mobile robot according to the present invention gives up the posture stabilization control of the body and executes a predetermined tumbling motion to minimize the damage to the body upon dropping onto the floor.
In particular, upon tumbling, the legged mobile robot searches for a location (part) at which the variation ΔS/Δt per time Δt of the area S of the support polygon formed from the landed points of the body and the floor is minimized and sets a target landing point at which the selected location should be landed so that the variation ΔS/Δt per time Δt of the area S of the support polygon formed from the landed points of the body and the floor may be minimized, and then lands the location onto the floor. Then, the legged mobile robot further expands the support polygon formed newly by the landing.
Then, the legged mobile robot repetitively executes the motion of searching for a location at which the variation ΔS/Δt is minimized and landing the location at the target landing point at which the variation ΔS/Δt is minimized and the motion of expanding the newly formed support polygon until after the potential energy of the body becomes minimum and the tumbling motion comes to an end.
Where the variation ΔS/Δt per time Δt of the area S of the support polygon is minimized and the support polygon upon dropping onto the floor is maximized in this manner, the impact applied from the floor upon dropping can be dispersed to the whole body thereby to suppress the damage to the body to the minimum. Where the legged mobile robot is regarded as a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, moderation of the impact force can be achieved by setting a location at which a link with which the number of non-landed links (non-contacting to the floor) is maximized exists as a target.
Further, the legged mobile robot may be formed from, for example, a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and
-
- the third means or step may include:
- means for or a step of searching, when the legged mobile robot returns from its tumbling state, for the narrowest support polygon formed from the least number of links from among landed polygons (contacting to the floor) formed, in an on-floor posture of the legged mobile robot in which two or more links including a gravity center link positioned at the center of gravity of the body are landed on (contacted to) the floor, from the landed links (contacting to the floor);
- means for or a step of taking off the landed links in the landed polygons except those of the searched out support polygon;
- means for or a step of bending two or more continuous ones of non-landed links until end portions of the end links onto the floor to form a narrower landed polygon; and
- means for or a step of taking off a number of links greater than a first predetermined number from one end side of the link structure to stand the body uprightly in response to that the support polygon is sufficiently narrow.
- the third means or step may include:
Here, the link structure includes at least shoulder joint pitch axes, a trunk pitch axis, hip joint pitch axes and knee pitch axes connected to each other in the heightwise direction of the body. Naturally, the body of the legged mobile robot may include an additional joint pitch axis or axes other than them. Further, each joint location may include a rotational degree-of-freedom around a roll axis and a yaw axis other than the pitch axis.
A polygon formed from a plurality of end portions of the body which are landed on the floor is called landed polygon. Meanwhile, a landed polygon in which a ZMP is present is called support polygon. A stable region of the ZMP is a region in which the posture and so forth of the robot can be controlled stably in the support polygon.
In a basic on-floor posture of the legged mobile robot such as a supine posture or a prone posture, all links which interconnect the joint pitch axes, trunk pitch axis, hip joint pitch axes and knee pitch axes are landed on the floor. On the other hand, in a basic standing posture or a walking posture, all links which interconnect the joint pitch axes, trunk pitch axis, hip joint pitch axes and knee pitch axes are taken off from the floor and aligned in a substantially vertical direction.
Upon standing up in transition from an on-floor posture to a standing posture of the robot, a higher torque output is required for the relating joint actuators when compared with a case wherein the robot maintains an ordinary standing posture or performs a walking motion. According to the present invention, by performing a standing up motion making use of a posture in which the ZMP support polygon is minimized, a standing up operation is realized with reduced driving torque.
First, in an on-floor posture wherein almost all links of the robot are landed on the floor, the narrowest support polygon is searched for from among landed polygons formed from the landed links. At this time, it is determined whether or not a ZMP can be planned when at least two or more links from one end side of the body are taken off from the floor.
For example, a narrower support polygon is searched for while a link which interconnects the trunk pitch axis and the hip joint pitch axes is selected as a gravity center link and keeping the landed link (contacting to the floor). The plannability of the ZMP can be determined taking movable angles of the link structure, torque values of the joint actuators interconnecting the links, joint forces, angular speeds, angular accelerations and so forth into consideration. Then, it is tried to take off two or more continuous links from one end side including the shoulder joint pitch axes.
Then, while the landed links which form the support polygon are left, two or more continuous links from the one end side of the landed polygon are taken off from the floor. Then, one or more non-landed links from the one end side are bent to land the end portions of the end links to form a narrower landed polygon.
For example, two or more links from the one end side of the link structure including the shoulder joints are taken off as links which do not relate to the support polygon from the floor. Then, in a state wherein two or more links including the shoulder joints are taken off from the floor, the shoulder joint pitch axes are bent so that the hands which are end portions of the end links are landed on the floor. Then, the hands are gradually moved toward the trunk pitch axis side which is the position of the center of gravity of the body to form a landed polygon narrower than that in the original on-floor posture.
Further, in the landed polygon, the narrowest support polygon is searched for. Now, at least two or more links from the other end are taken off from the floor, and it is determined whether or not a ZMP is plannable. The plannability of the ZMP can be determined taking movable angles of the link structure, torque values of the joint actuators interconnecting the links, joint forces, angular speeds, angular accelerations and so forth into consideration.
For example, while the gravity center link which interconnects the trunk pitch axis and the hip joint pitch axes is kept in the landed state (contacting to the floor), it is attempted to take off two or more continuous links from the other end side including the knee joint pitch axes from the floor.
For example, while the landed links which make the support polygon are left, two or more continuous links from the other end side of the landed polygon are taken off from the floor. Then, one or more non-landed links from the other end side are bent to land the end portions of the end links to form a narrower landed polygon.
For example, in a state wherein two or more links including the knee joints are taken off from the floor, the knee joint pitch axes are bent so that the soles which are end portions of the end links are landed onto the floor. Then, the soles are gradually moved toward the hip joint pitch axes side which is the position of the center of gravity of the body to form a landed polygon narrower than that in the original on-floor posture.
Thereafter, it is determined whether or not the gravity center link can be taken off from the floor in a state wherein the end portions of the opposite end links of the landed polygon remain landed on the floor to determine whether or not the support polygon is sufficiently narrow. Whether or not the gravity center link can be taken off from the floor can be determined taking movable angles of the link structure, torque values of the joint actuators interconnecting the links, joint forces, angular speeds, angular accelerations and so forth into consideration.
For example, it is determined whether or not the gravity center link which interconnects the trunk pitch axis and the hip joint pitch axes can be taken off from the floor in a state wherein the hands and the soles as the end portions of the opposite end links of the landed polygon to determine whether or not the support polygon is sufficiently narrow.
Then, in response to that the support polygon of the body is sufficiently narrow, the gravity center link is taken off from the floor in a state wherein the end portions of the opposite link ends of the support polygon are kept landed on the floor, and the distance between the end portions of the opposite end links of the support polygon is reduced while the ZMP is maintained in the support polygon formed from the landed links at the opposite end links to move the ZMP to the other end side of the link structure. At this time, whether or not the ZMP can be moved to the other end side can be determined taking movable angles of the link structure, torque values of the joint actuators interconnecting the links, joint forces, angular speeds, angular accelerations and so forth into consideration.
For example, in a state wherein the hands and the soles as the end portions of the opposite end links of the landed polygon are kept landed on the floor, the gravity center link which interconnects the trunk pitch axis and the hip joint pitch axes is taken off from the floor, and the distance between the hands and the soles is gradually reduced to move the ZMP toward the soles.
Then, in response to that the ZMP enters the landed polygon formed only from a number of non-landed links smaller than a second predetermined number from the other end of the link structure, a number of links greater than a first predetermined number from the one end side of the link structure are taken off from the floor while the ZMP is kept accommodated in the landed polygon to expand the landed polygons in the lengthwise direction to complete the standing up motion.
For example, in response to that the ZMP enters the landed polygon formed from the soles, the links from the shoulder pitch axes to the knee pitch axes are taken off from the floor while the ZMP is kept accommodated in the landed polygon, and the non-landed links are expanded in the lengthwise direction to complete the standing up motion.
When the non-landed links are expanded in the lengthwise direction at the final stage of standing up, it assures a high efficiency in motion of the body to positively use the knee joint pitch axes having a comparatively great mass operation amount to perform the motion.
It is to be noted that, in order to form a narrower landed polygon, when the non-landed links are bent around the shoulder joint pitch axes to land the hands which are the end portions of the end links onto the floor, each of the arm parts may operate so as to satisfy the following expressions. It is to be noted that the length of the upper arms is represented by l1, the length of the forehands by l2, the shoulder roll angle by α, the elbow pitch angle by β, the length from the shoulders to the hands by l12, the angle defined by a line interconnecting each of the shoulders and a corresponding one of the hands by γ, and the height of the shoulders by h.
l12=l1 Cos α+l2 sin (α+β−90)
l12 sin γ<h
In particular, by causing the elbow pitch axes to perform bending movement in place of rendering the shoulder roll axis operative, the left and right hands can be landed with a smaller use volume rearward of the body.
The means for or step of producing a narrower landed polygon may selectively utilize one of a step changing motion and a dragging motion on the floor of the hand parts or the foot parts in response to whether it is possible to take off two or more of the links which do not relate to the smallest support polygon from the floor to form a narrower landed polygon.
If only a step changing motion of the hand parts or the foot parts is utilized in the process of such successive formation of a smaller landed polygon, then in order to realize the step changing motion, it is necessary for the hand parts or the foot parts to be taken off from the floor, and two or more links which do not relate to the support polygon must be present. Depending upon the posture of the body, however, it is sometimes impossible to perform a step changing motion. In this instance, the standing up motion itself results in failure. In contrast, where a dragging movement of the hand parts or the foot parts is utilized, the possibility that a standing up motion may result in failure can be reduced.
According to a second aspect of the present invention, there is provided a motion controlling apparatus and a motion controlling method for a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, including:
-
- means for or a step of calculating an impact moment applied to a body of the legged mobile robot at each stage upon tumbling of the body;
- means for or a step of calculating an impact force applied to the body from the floor at each stage upon tumbling;
- means for or a step of calculating an area S of a support polygon formed from a landed point (contact point) of the body and the floor;
- first landed location searching means for or a first landed location searching step of selecting a next landed location so that the area S of the support polygon may be minimized or fixed; and
- second landed location searching means for or a second landed location searching step of selecting a next landed location so that the area S of the support polygon may be increased.
In such an instance, an impact moment applied to the body can be warded off by minimizing or fixing the area S of the support polygon by means of the first landed location searching means. In this instance, the body may be moved forward or backward to move the supporting face itself. Meanwhile, an impact force applied from the floor to the body upon tumbling can be moderated by selecting the landed location by means of the second landed location searching means so that the area S of the support polygon may be increased suddenly. Accordingly, a tumbling motion of the body should be performed by the second landed location searching means or step if the impact force applied to the body from the floor is within a predetermined tolerance, but a tumbling motion of the body should be performed by the first landed location searching means or step if the impact force is outside the predetermined tolerance.
According to a third aspect of the present invention, there is provided a motion controlling apparatus or a motion controlling method for controlling a series of motions relating to tumbling and standing up of a body of a legged mobile robot which includes movable legs and performs a legged operation in a standing posture thereof, characterized in that
-
- the legged mobile robot is formed from a link structure wherein a plurality of substantially parallel joint axes having a joint degree-of-freedom are connected to each other in a lengthwise direction, and
- the motion controlling apparatus or method includes:
- means for or a step of searching for the narrowest support polygon formed from a minimum number of links from among landed polygons formed from landed links in an on-floor posture wherein two or more links including a gravity center link at which the center of gravity of the body is positioned are landed on a floor upon tumbling of the legged mobile robot;
- means for or a step of setting a ZMP at a location at which the number of links which do not relate to the smallest support polygon is maximized to perform a tumbling motion;
- means for or a step of searching for a link or links which can be taken off from the floor in the tumbling position of the body; and
- means for or a step of taking off all of the links which can be taken off from the floor to perform a standing up motion.
Where the center of gravity of the body exists at the waist portion, the ZMP can be set to a location at which the number of links which do not relate to the smallest support polygon is maximized. After such tumbling and landing motions, all those links which can be take off from the floor are taken off from the floor, that is, both of the lower limbs and the trunk are lifted to take off the upper part of the body and the lower limbs simultaneously from the floor. Then, the foot parts, the hand parts and so forth are landed. By this, a smaller landed polygon can be formed at a reduced number of steps. Consequently, an efficient standing up motion can be realized at a higher speed.
According to the third aspect of the present invention, there is provided a robot apparatus having a trunk part, leg parts connected to the trunk part and arm parts connected to the trunk part, including:
-
- support polygon detection means for detecting a first support polygon formed from a plurality of end portions of the leg parts, trunk part and/or arm parts at which the leg parts, trunk part and/or arm parts are landed on a floor;
- support polygon changing means for bending the leg parts toward the trunk part to reduce the area of the first support polygon;
- ZMP motion controlling means for determining whether or not a ZMP which is positioned in the changed first support polygon can be moved into a landed polygon formed from the soles of the leg parts; and
- control means for moving, when the ZMP motion controlling means determines that the ZMP can be moved, the ZMP from within the first support polygon into the landed polygon formed by the soles and changing the position of the robot apparatus from a tumbling position to a basic posture while the ZMP is maintained within the landed polygon.
According to a fourth aspect of the present invention, there is provided a legged mobile robot which includes at least a body, one or more arm links connected to an upper portion of the body each through a first joint (shoulder), a first leg link connected to a lower portion of the body through a second joint (hip joint), and a second leg link connected to an end of the second leg link through a third joint (knee), including:
-
- means for landing ends of the arm links and a foot part at an end of the second leg link to form a first support polygon;
- means for moving the second joint upwardly higher than the third joint in a normal direction to the floor while the ends of the arm links and the foot part are kept landed, decreasing the area of the first support polygon and moving a ZMP into a landed polygon formed from the foot part; and
- means for standing a body of the robot apparatus uprightly while the ZMP is kept in the landed polygon formed from the foot part.
With the robot apparatus according to the present invention, the body returns from a tumbling position to a standing posture while reducing the area of the support polygon. Consequently, joint actuators for the leg parts and so forth can perform a standing up motion with comparatively low torque.
The above and other objects, features and advantages of the present invention will become apparent from the following description based on an embodiment of the present invention and the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic view showing a legged mobile robot to which the present invention is applied when it is in an uprightly standing state as viewed from obliquely forward;
FIG. 2 is a perspective view showing the legged mobile robot to which the present invention is applied when it is in an uprightly standing state as viewed from obliquely backward;
FIG. 3 is a schematic view showing a joint degree-of-freedom configuration of the legged mobile robot;
FIG. 4 is a diagrammatic view schematically showing a basic control system configuration of the legged mobile robot 100;
FIG. 5 is a diagrammatic view illustrating basic state transitions of a movement system of the legged mobile robot 100 has;
FIG. 6 is a view showing a basic supine posture of the legged mobile robot 100;
FIG. 7 is a view showing a basic prone posture of the legged mobile robot 100;
FIG. 8 is a view showing a basic standing posture of the legged mobile robot 100;
FIG. 9 is a view showing a basic walking posture of the legged mobile robot 100;
FIG. 10 is a schematic diagrammatic view showing a multiple mass point approximation model of the legged mobile robot 100;
FIG. 11 is an enlarged view showing a portion around a waist portion of the multiple mass point approximation model;
FIG. 12 is a flow chart illustrating a processing procedure for producing a body movement with which the legged mobile robot 100 can walk stably;
FIG. 13 is a flow chart illustrating a general processing procedure for motion control of the body when the legged mobile robot 100 performs a legged operation;
FIG. 14 is a schematic view illustrating a principle of maintaining a supporting area when the body tumbles;
FIG. 15 is a diagrammatic view illustrating a principle that a support polygon becomes maximum when the body drops onto the floor;
FIG. 16 is a view illustrating a motion of maintaining the supporting area upon tumbling when the legged mobile robot 100 tumbles rearwardly to be a supine posture;
FIG. 17 is a view illustrating the motion of maintaining the supporting area upon tumbling when the legged mobile robot 100 tumbles rearwardly to be a supine posture;
FIG. 18 is a view illustrating a motion of maintaining the supporting area upon tumbling when the legged mobile robot 100 tumbles forwardly to be a prone posture;
FIG. 19 is a view illustrating the motion of maintaining the supporting area upon tumbling when the legged mobile robot 100 tumbles forwardly to be a prone posture;
FIG. 20 is a flow chart illustrating a processing procedure of the legged mobile robot 100 according to the present embodiment for performing a tumbling motion because the foot parts are unplannable;
FIG. 21 is a view illustrating motions of the legged mobile robot 100 when, where it is modeled as a link structure including a plurality of substantially parallel axes connected in a vertical direction such as a shoulder joint pitch axis 4, a trunk pitch axis 9, a hip joint pitch axis 12 and a knee joint pitch axis 14, it tumbles to be a supine posture with the joint pitch axes driven synchronously and cooperatively;
FIGS. 22 to 38 are side elevational views illustrating a manner wherein the legged mobile robot 100 tumbles from its standing posture into a supine posture;
FIGS. 39 to 55 are perspective views illustrating the manner wherein the legged mobile robot 100 tumbles from its standing posture into a supine posture;
FIG. 56 is a view illustrating motions of the legged mobile robot 100 when, where it is modeled as a link structure including a plurality of substantially parallel axes connected in a vertical direction such as the shoulder joint pitch axis 4, trunk pitch axis 9, hip joint pitch axis 12 and knee joint pitch axis 14, it tumbles to be a prone posture with the joint pitch axes driven synchronously and cooperatively;
FIGS. 57 to 73 are side elevational views illustrating a manner wherein the legged mobile robot 100 tumbles from its standing posture into a prone posture;
FIGS. 74 to 90 are perspective views illustrating the manner wherein the legged mobile robot 100 tumbles from its standing posture into a prone posture;
FIG. 91 is a flow chart illustrating a processing procedure when the legged mobile robot 100 according to the embodiment of the present invention performs a standing up motion through synchronous and cooperative driving of the shoulder joint pitch axis 4, trunk pitch axis 9, hip joint pitch axis 12 and knee joint pitch axis 14;
FIG. 92 is a view illustrating a manner wherein the legged mobile robot 100 according to the embodiment of the present invention performs a standing up motion from its supine posture through synchronous and cooperative driving of the shoulder joint pitch axis 4, trunk pitch axis 9, hip joint pitch axis 12 and knee joint pitch axis 14 in the form of a joint link model;
FIG. 93 is a view illustrating a manner wherein a legged mobile robot of the type which does not include a trunk pitch axis performs a standing up motion from its supine posture through synchronous driving of a plurality of joint pitch axes;
FIGS. 94 to 111 are side elevational views illustrating a manner wherein the legged mobile robot 100 stands up from its basic supine posture;
FIGS. 112 to 129 are perspective views illustrating the manner wherein the legged mobile robot 100 stands up from its basic supine posture;
FIG. 130 is a view illustrating a modification to a series of motions when the left and right hands are contacted with the floor rearward of the body;
FIG. 131 is a view illustrating the modification to the series of motions when the left and right hands are contacted with the floor rearward of the body;
FIG. 132 is a diagrammatic view illustrating the motions of an arm illustrated in FIGS. 130 and 131;
FIG. 133 is a diagrammatic view showing the legged mobile robot shown in FIG. 92 but in a generalized form wherein it is replaced with a link structure;
FIG. 134 is a view illustrating a manner wherein the legged mobile robot 100 according to the embodiment of the present invention performs a standing up motion from its prone posture through synchronous and cooperative driving of the shoulder joint pitch axis 4, trunk pitch axis 9, hip joint pitch axis 12 and knee joint pitch axis 14 in the form of a joint link model;
FIG. 135 is a side elevational view illustrating a manner wherein the legged mobile robot 100 stands up from its basic spine posture;
FIGS. 136 to 153 are side elevational views illustrating a manner wherein the legged mobile robot 100 stands up from its basic spine posture;
FIGS. 154 to 172 are perspective views illustrating the manner wherein the legged mobile robot 100 stands up from its basic prone posture;
FIG. 173 is a flow chart illustrating a processing procedure for determining whether or not a sufficiently narrowed support polygon is obtained;
FIG. 174 is a flow chart illustrating a standing up operation which makes use of a dragging motion and a step changing motion of hand parts and foot parts;
FIGS. 175 to 191 are side elevational views illustrating a manner wherein the legged mobile robot 100 stands up from its basic prone posture while making use of a dragging motion and a step changing motion of the hand parts and the foot parts;
FIGS. 192 to 198 are views illustrating a series of motions of the body when a standing up motion is performed continuously to a tumbling motion; and
FIG. 199 is a flow chart illustrating a processing procedure for searching for a link and a location of the link at which the number of links which do not relate to the smallest support polygon is maximum.
BEST MODE FOR CARRYING OUT THE INVENTION
In the following, an embodiment of the present invention is described in detail with reference to the drawings.
A. Mechanical Configuration of the Legged Mobile Robot
Referring to FIGS. 1 and 2, a “human-like” or “humanoid” legged mobile robot 100 to which the present invention is applied is shown in a manner wherein it stands uprightly as viewed from obliquely forward and obliquely rearward, respectively. As shown in FIGS. 1 and 2, the legged mobile robot 100 includes a body part, a head part, left and right upper limb parts, and left and right lower limb parts used for legged traveling. A control section (not shown) is built, for example, in the body part and generally controls action of the body.
Each of the left and right lower limb parts is composed of a femoral region, a knee joint, a shin part, an ankle and a foot and is connected to a substantially lowermost end of the trunk part by a hip joint. Meanwhile, each of the left and right upper limb parts is composed of an upper arm, an elbow joint and a front arm and is connected to a left or right side edge of an upper portion of the trunk part by a shoulder joint. Further, the head part is connected to a middle portion of a substantially uppermost end of the trunk part by a neck joint.
The control section includes a housing in which a controller (main control section) for controlling driving of various joint actuators of the legged mobile robot and processing external inputs from various sensors (hereinafter described) and like elements, a power supply circuit and other peripheral apparatus are accommodated. The control section may additionally include a communication interface or a communication apparatus for remote control.
The legged mobile robot having the configuration described above can achieve bipedal locomotion through whole-body cooperative motion control by the control section. Such bipedal locomotion as just mentioned is usually performed by repetitions of a walking cycle divided into the following motion periods. In particular,
-
- (1) A single support phase within which the legged mobile robot walks using the left leg with the right leg lifted;
- (2) A double support phase within which the right foot is contacted with the ground;
- (3) Another single support phase within which the legged mobile robot walks using the right leg with the left leg lifted; and
- (4) Another double support phase within which the left foot is contacted with the ground.
Walking control of the legged mobile robot 100 is achieved by planning a target trajectory of each of the lower limbs in advance and correcting the planned trajectory within each of the periods described above. In particular, within each double support phase, the correction of the lower limb trajectories is stopped and the height of the waist is corrected with a fixed value using a total correction amount for the planned trajectories. On the other hand, within each single support phase, a corrected trajectory is produced so that the relative positional relationship between the ankle of a leg with regard to which correction has been performed and the waist may be returned to the planned trajectory.
For stable control of the posture of the body beginning with trajectory correction in a walking motion, interpolation calculation in which a five-dimensional polynomial is used is usually used so that the position, speed and acceleration for minimizing the deviation with respect to a target ZMP (Zero Moment Point) may be continuous. A ZMP is used as a criterion for determination of the stability in walking. The stability determination criterion by a ZMP is based on the “d'Alembert's principle” that the gravity and inertial force which act from a walking system to the road surface and the moment of them are balanced with the floor reaction force as a reaction from the road surface to the walking system and the floor reaction force moment. As a consequence of mechanical inference, a point at which the pitch axis moment and the roll axis moment are zero, that is, a “ZMP”, is present on or on the inner side of a side of a support polygon (that is, a ZMP stable region) formed by the landing points of the soles and the road surface.
FIG. 3 schematically shows a joint degree-of-freedom configuration of the legged mobile robot 100. As seen from FIG. 3, the legged mobile robot 100 has a structure having a plurality of limbs including upper limbs including two arm parts and a head part, lower limbs including two leg parts for achieving traveling motion and a trunk part for interconnecting the upper limbs and the lower limbs.
The neck joint (Neck) for supporting the head part has a 4 degree-of-freedom including a neck joint yaw axis 1, first and second neck joint pitch axes 2A and 2B, and a neck joint roll axis 3.
Meanwhile, each arm part includes a shoulder joint pitch axis 4 of a shoulder, a shoulder joint roll axis 5, an upper arm yaw axis 6, an elbow joint pitch axis 7 of an elbow, a wrist joint yaw axis 8 of a wrist, and a hand part as a degree-of-freedom thereof. The hand part actually is a multi-joint, multi-degree-of-freedom structure including a plurality of fingers.
On the other hand, the trunk part (Trunk) has a 2 degree-of-freedom including a trunk pitch axis 9 and a trunk roll axis 10.
Each of the leg parts which form the lower limbs includes a hip joint yaw axis 11, a hip joint pitch axis 12 and a hip joint roll axis 13 of the hip joint (Hip), a knee joint pitch axis 14 of the knee, an ankle joint pitch axis 15 and an ankle joint roll axis 16 of the ankle, and a foot part.
It is to be noted that the legged mobile robot 100 directed for entertainment need not necessarily have all of the degrees of freedom described above or not necessarily have only the degrees of freedom described above. Naturally, it is possible to suitably increase or decrease the degree of freedom, that is, the number of joints, in accordance with restrictive conditions or required specifications in design or manufacture.
The degree of freedom of the legged mobile robot 100 having such a configuration as described above is actually achieved using actuators. Preferably, the actuators are small in size and light in weight from such requirements that the legged mobile robot be approximated to a natural shape of a human being by removing surplus swelling in an outer appearance and that posture control be performed for an unstable structure which performs bipedal locomotion. In the present embodiment, a small size AC servo actuator of the direct-geared type and of the type wherein a servo control system is formed as a single chip and built in a motor unit is incorporated (an AC servo actuator of the type mentioned is disclosed, for example, in Japanese Patent Laid-Open No. 2000-299970 assigned already to the applicant of the present application). In the present embodiment, a low speed reducing gear is adopted as the direct gear to achieve a passive characteristic of a driving system required for a robot of the type with regard to which importance is attached to physical interactions with a human being.
B. Control System Configuration of the Legged Mobile Robot
FIG. 4 schematically shows a control system configuration of the legged mobile robot 100. Referring to FIG. 4, the legged mobile robot 100 includes mechanism units 30, 40, 50R/L and 60R/L which represent the limbs of a human being, and a control unit 80 which performs adaptive control for achieving a cooperative motion of the mechanism units (it is to be noted that reference characters R and L are added as suffixes for representing the distinction between the right and the left. This similarly applies to the following description).
A motion of the entire legged mobile robot 100 is generally controlled by the control unit 80. The control unit 80 includes a main control section 81 formed from principal circuit components (not shown) such as a CPU (Central Processing Unit) and a memory, and a peripheral circuit 82 including a power supply circuit, an interface (both not shown) for performing transmission and reception of data and commands to and from the components of the legged mobile robot 100 and other required elements.
The location of the control unit 80 is not particularly limited when the present invention is embodied. Although the control unit 80 is incorporated in the trunk part unit 40 in FIG. 4, it may otherwise be incorporated in the head part unit 30. Alternatively, the control unit 80 may be located outside the legged mobile robot 100 and communicate with the body of the legged mobile robot 100 by wire or wireless communication.
Each joint degree-of-freedom in the legged mobile robot 100 shown in FIG. 3 is implemented by an individually corresponding actuator. In particular, the head part unit 30 has disposed therein a neck joint yaw axis actuator A1, first and second neck joint pitch axis actuators A2A and A2B and a neck joint roll axis actuator A3 which represent the neck joint yaw axis 1, first and second neck joint pitch axes 2A and 2B and neck joint roll axis 3, respectively.
The trunk part unit 40 has disposed therein a trunk pitch axis actuator A9 and a trunk roll axis actuator A10 which represent the trunk pitch axis 9 and the trunk roll axis 10, respectively.
The arm part units 50R/L are subdivided into upper arm units 51R/L, elbow joint units 52R/L and forearm units 53R/L, respectively. Each of the arm part units 50R/L has disposed therein a shoulder joint pitch axis actuator A4, a shoulder joint roll axis A5, an upper arm yaw axis actuator A6, an elbow joint pitch axis actuator A7 and a wrist joint yaw axis actuator A8 which represent the shoulder joint pitch axis 4, shoulder joint roll axis 5, upper arm yaw axis 6, elbow joint pitch axis 7 and wrist joint yaw axis 8, respectively.
The leg part units 60R/L are subdivided into femoral region units 61R/L, knee units 62R/L and ankle part units 63R/L, respectively. Each of the leg part units 60R/L has disposed therein a hip joint yaw axis actuator A1l, a hip joint pitch axis actuator A12, a hip joint roll axis actuator A13, a knee joint pitch axis actuator A14, an ankle joint pitch axis actuator A15 and an ankle joint roll axis actuator A16 which represent the hip joint yaw axis 11, hip joint pitch axis 12, hip joint roll axis 13, knee joint pitch axis 14, ankle joint pitch axis 15 and ankle joint roll axis 16, respectively.
Each of the actuators A1, A2, A3, . . . used for the joints can be formed from a small size AC servo actuator (described hereinabove) preferably of the direct-geared type and of the type wherein a servo control system is formed as a single chip and incorporated in a motor unit.
Sub control sections 35, 45, 55 and 65 for actuator driving control are disposed for individual mechanism units such as the head part unit 30, trunk part unit 40, arm part units 50 and leg part units 60, respectively.
Acceleration sensors 95 and a posture sensor 96 are disposed on the trunk part unit 40 of the body. The acceleration sensors 95 are disposed in the X, Y and Z axis directions. Where the acceleration sensors 95 are disposed at the waist portion of the body, it is possible to set the waist portion, which has a great mass operation amount, as a control target point and directly measure the posture or an acceleration at the position of the waist portion to perform posture stabilization control based on a ZMP.
Meanwhile, landing confirmation sensors 91 and 92 and acceleration sensors 93 and 94 are disposed on the leg part units 60R and 60L, respectively. The landing confirmation sensors 91 and 92 are formed from, for example, pressure sensors mounted on the soles and can each detect whether or not the sole is contacted with the floor depending upon the presence or absence of floor reactive force. Meanwhile, the acceleration sensors 93 and 94 are disposed at least in the X and Y axis directions. By disposing the acceleration sensors 93 and 94 on the left and right foot parts, a ZMP equation can be established directly with that one of the foot parts which is nearest to the ZMP position.
Where acceleration sensors are disposed only at the waist portion which is a portion having a great mass operation amount, only the waist portion is set as a control target point, and a state of each foot part must be calculated relatively based on a result of the calculation of the control target point. In this instance, it is a prerequisite that the following conditions are satisfied between the foot part and the ground surface.
-
- (1) The ground surface does not move at all whatever force or toque acts thereupon.
- (2) The coefficient of friction of the road surface against translation is sufficiently high and does not allow a slip.
In contrast, in the present embodiment, a reactive force sensor system (floor reactive force sensor or the like) for directly detecting a ZMP and force is disposed on the foot part, which is a contact portion with the ground surface, and a local coordinate system and acceleration sensors for directly measuring the coordinate are disposed on the foot part. As a result, a ZMP equation can be established directly at the foot part which is nearest to the ZMP position, and more strict posture stabilization control which does not rely upon such a prerequisite as described above can be achieved at a high speed. As a result, stable walking (movement) of the body can be secured also on a gravel place or a thick-piled carpet on which the road surface moves if force or torque acts thereupon or a tiled place of a house on which a slip is likely to occur because a sufficient coefficient of friction against translation cannot be assured.
The control unit 80 can dynamically correct the control target in response to outputs of the sensors 91 to 96. More particularly, the control unit 80 adaptively controls each of the sub control sections 35, 45, 55 and 65 to realize a gross movement pattern wherein the upper limbs, trunk and lower limbs of the legged mobile robot 100 are cooperatively driven.
For a gross movement on the body of the robot 100, movements of the foot parts, a ZMP (Zero Moment Point) trajectory, a trunk movement, upper limb movements and the height of the waist portion are set, and commands indicating motions in accordance with the set contents are transferred to the sub control sections 35, 45, 55 and 65. Each of the sub control sections 35, 45, . . . interprets a command received from the main control section 81 and outputs driving control signals to the actuators A1, A2, A3, . . . The “ZMP” here defines a point on the floor at which the moment by floor reactive force during walking is zero, and the “ZMP trajectory” signifies a trajectory along which the ZMP moves, for example, during a period of a walking motion of the robot 100.
C. Movement System Basic State Transitions of the Legged Mobile Robot
The control system of the legged mobile robot 100 according to the present embodiment defines a plurality of basic postures. Each of the basic postures is defined taking the stability of the body, energy consumption and transition to a next state into consideration, and a body movement can be controlled efficiently through a form of transition between the basic postures.
FIG. 5 illustrates basic state transitions by the movement system of the legged mobile robot 100 according to the present embodiment. Referring to FIG. 5, for the legged mobile robot, a basic supine posture, a basic standing posture, a basic walking posture, a basic sitting posture and a basic prone posture are defined taking the stability of the body, energy consumption and transition to a next state when the robot lies with the face upward, stands, is ready for walking, sits and lies with the face downward into consideration.
These basic postures are positioned to a platform of a motion control program for the body. Further, when the legged mobile robot is in its standing posture or the like, it performs various performances making uses of a gross movement such as walking, jumping or dancing, and apparatus control programs for them are positioned as applications which operate on the platform. The application programs are loaded suitably from an external storage and executed by the main control section 81.
FIG. 6 illustrates the basic supine posture of the legged mobile robot 100. In the present embodiment, when the power supply to the body is made available, the legged mobile robot 100 assumes the basic supine posture and can be activated from a state wherein it is kinetically most stable without the possibility of tumbling (fall down) or the like. Further, not only upon activation but also upon ending of system operation, the legged mobile robot returns to the basic supine posture. Accordingly, since the legged mobile robot 100 starts its operation in a state wherein the body is kinetically most stable and ends its operation in the most stable state, the motion operation of the legged mobile robot is self-completed.
Naturally, also when the body tumbles, if a prescribed standing up motion is executed after the basic supine posture is restored once through a predetermined motion on the floor, then the original posture taken upon interruption of the operation can be restored through the basic standing posture.
Further, the legged mobile robot 100 according to the present embodiment includes, as one of the basic postures on the floor, such a basic prone posture as shown in FIG. 7. The basic prone posture is a state wherein the body is kinetically most stable similarly to the basic supine posture, and can maintain the posture stability also in a strength-gone state wherein the power supply is interrupted. For example, if the body tumbles due to inadvertent external force during a legged operation, then since it is unknown whether it drops in a supine posture or in a prone posture, in the present embodiment, two different on-floor basic postures are defined in this manner.
The legged mobile robot 100 can change its posture reversibly between the basic supine posture and the basic prone posture through various on-floor postures. Conversely speaking, the legged mobile robot 100 can smoothly change its posture to various on-floor postures with reference to the basic supine posture and the basic prone posture.
The basic supine posture is the kinetically most stable basic posture. However, where a legged operation is taken into consideration, a smooth state transition cannot be performed from the basic supine posture. Therefore, such a basic standing posture as shown in FIG. 8 is defined. Where the basic standing posture is defined, the legged mobile robot 100 can proceed to a later legged operation smoothly.
The basic standing posture is the most stable state among various standing states and is a posture in which the computer load for posture stabilization control and the power consumption are the lowest or are minimized. In the basic standing state, the knees are stretched straightforwardly to minimize the motor torque for keeping the uprightly standing state. The legged mobile robot 100 can change its posture smoothly from the basic standing posture to various standing postures to play, for example, a dance performance which makes use of the upper limbs.
On the other hand, although the basic standing posture is superior in the posture stability, it is not optimized so as to immediately enter a legged operation such as walking. Therefore, the legged mobile robot according to the present embodiment defines, as another basic posture in a standing state with the legs, such a basic walking posture as seen in FIG. 9.
When the legged mobile robot is in its basic standing posture, the pitch axes 12, 14 and 15 for the hip joints, knee joints and ankle joints are driven so that the legged mobile robot may have a posture wherein the position of the center of gravity of the body is lowered a little so as to enter the basic walking posture. The basic walking posture allows smooth transition to various legged motions beginning with an ordinary walking motion. However, since the knees are bent, additional torque for keeping the posture is required as much, and therefore, the basic walking posture requires increased power consumption when compared with the basic standing posture.
In the basic standing posture, the ZMP position of the body exists in the proximity of the center of a ZMP stable region, and the bent angle of the knees is small and the energy consumption is low. In contrast, in the basic walking posture, although the ZMP position is in the proximity of the stable region, the bent angle of the knees is comparatively great in order to secure high adaptability to the road surface and external force.
Further, in the legged mobile robot 100 according to the present embodiment, a basic sitting posture is defined. The basic sitting posture (not shown) is defined as a posture wherein, when the legged mobile robot 100 sits on a predetermined chair, the computer load for posture stabilization control and the power consumption are the lowest or are minimized. The legged mobile robot 100 can change its posture reversibly from the basic supine posture, basic prone posture and basic standing posture described hereinabove to the basic posture. Further, the legged mobile robot 100 can smoothly change its posture from the basic sitting posture or the basic standing posture to various sitting postures, in which it can play various performances, for example, using only the upper part of the body.
D. Posture Stabilization Control of the Legged Mobile Robot
Subsequently, a procedure of the posture stabilization control of the legged mobile robot 100 according to the present embodiment in a legged operation, that is, a procedure of a stabilization process of the posture of the legged mobile robot 100 when it executes a gross cooperative movement including movements of the foot parts, waist, trunk and lower limbs, is described.
The posture stabilization control according to the present embodiment uses a ZMP for posture stabilization control. The posture stabilization control of a robot wherein the ZMP is used as a stabilization determination criterion basically resides in search for a point at which the moment is zero on or on the inner side of a side of a support polygon formed from the landing points of the soles and the road surface. In particular, a ZMP equation which describes a balancing relationship of various moments applied to the body of the robot is introduced, and the target trajectory of the body is corrected so that a moment error appearing on the ZMP equation may be canceled.
In the present embodiment, as a control target point on the body of the robot, a location (part) at which the mass operation amount is maximum, for example, the waist portion, is set as a local coordinate system origin. Then, a measuring element such as an acceleration sensor is disposed at the control target point to directly measure a posture or an acceleration at the position to perform posture stabilization control based on the ZMP. Further, an acceleration sensor is disposed at each of the foot parts which are contacting portions with the road surface to directly measure a local coordinate system to be used for the control and coordinates of the local coordinate system, and a ZMP equation is produced directly at the foot part which is nearest to the ZMP position.
D-1. Introduction of a ZMP Equation
The legged mobile robot 100 according to the present embodiment is an aggregate of infinite, that is, continuous mass points. Here, however, the legged mobile robot 100 is replaced into an approximation model formed from a finite number of discrete mass points to reduce the amount of calculation for a stabilization process. More particularly, the legged mobile robot 100 which has such a multiple joint degree-of-freedom configuration as shown in FIG. 3 is physically replaced into and handled as such a multiple mass point approximation model as shown in FIG. 10. The approximation model shown is a linear and non-interacting multiple mass point approximation model.
Referring to FIG. 10, an O-XYZ coordinate system repre