Fujishima, Kazuo (Kasumigaura-shi, JP)
Ishii, Akinori (Ushiku-shi, JP)
Plaque It!
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1. A construction machine, comprising: a work arm rotatably mounted at a construction machine main body; a work tool mounted at the work arm; an attitude decision device that decides an attitude of the work arm or the work tool relative to the construction machine main body; a follow-up enabling device that allows the work arm or the work tool to follow a displacement of a contacting object that comes into contact with the work tool and applies an external force to the work tool, by adjusting the attitude of the work arm or the work tool decided by the attitude decision device; and a switching device that selects whether or not to allow the work arm or the work tool to follow the displacement of the contacting object via the follow-up enabling device.
2. A construction machine according to claim 1, wherein: the attitude decision device is a hydraulic cylinder that decides the attitude of the work arm or the work tool by extending/contracting a cylinder rod; and the follow-up enabling device is an accumulator that adjusts the attitude of the work arm or the work tool by causing the cylinder rod to extend/contract as pressure oil supplied to the hydraulic cylinder is absorbed into or released from the accumulator.
3. A construction machine according to claim 2, wherein: the follow-up switching device is a switching valve disposed in an oil passage connecting the hydraulic cylinder with the accumulator, by which a flow of the pressure oil between the hydraulic cylinder and the accumulator is allowed or disallowed.
4. A construction machine according to claim 2, further comprising: an oil chamber selecting device that selects one of a bottom oil chamber and a rod oil chamber at the hydraulic cylinder where the pressure oil has a higher pressure and connecting the selected oil chamber to the accumulator.
5. A construction machine according to claim 1, further comprising: a traveling carriage rotatably supports the construction machine main body.
6. A construction machine according to claim 1, further comprising: a follow-up characteristics adjusting device that adjusts follow-up characteristics achieved with the follow-up enabling device.
7. A construction machine according to claim 1, wherein: the attitude decision device is a hydraulic cylinder that decides the attitude of the work tool by extending/contracting a cylinder rod; and the construction machine further comprises: oil passages that communicate with a bottom-side oil chamber and a rod-side oil chamber at the hydraulic cylinder; and a switching valve that opens or blocks the oil passages.
8. A construction machine, comprising: a work arm rotatably mounted at a construction machine main body; a work tool mounted at the work arm; an attitude adjusting device that adjusts an attitude of the work arm or the work tool relative to the construction machine main body; an adjustment enabling device that allows the attitude of the work arm or the work tool to be adjusted by the attitude adjusting device so as to assume an attitude corresponding to an external force applied to the work tool at the work arm or the work tool; an operating state determining device that determines an operating state of the construction machine main body; and a switching device that selects, based upon the operating state determined by the operating state determining device, whether or not the adjustment enabling device is to allow the attitude adjusting device to adjust the attitude of the work arm or the work tool.
9. A construction machine according to claim 8, wherein: the operating state determining device determines the operating state based upon at least one of; an operating state of an operation lever by which operation instructions for the work arm or the work tool are issued, a work load applied to the work arm or the work tool and the attitude of the work arm or the work tool.
10. A construction machine according to claim 9, wherein: the work tool is a gripping device that grips a target object; the operating state determining device determines the operating state based upon an operating state of an operation lever by which operating instructions for the gripping device are issued; and if the operating state determining device determines that the operation lever has been operated so as to grip the target object with the gripping device, the switching device switches the adjustment enabling device so as to allow the attitude adjusting device to adjust the attitude of the work arm or the work tool.
11. A construction machine according to claim 9, wherein: the work tool is a gripping device that grips a target object; the construction machine further comprises a detection device that detects a physical quantity corresponding to a gripping force imparted by the gripping device; the operating state determining device determines the operating state based upon the physical quantity detected by the detection device; and if the operating state determining device determines that the physical quantity detected by the detection device is smaller than a predetermined value, the switching device switches the adjustment enabling device so as to allow the attitude adjusting device to adjust the attitude of the work arm or the work tool.
12. A construction machine according to claim 9, wherein: if the operating state determining device determines, based upon the attitude of the work tool, that the work tool is positioned facing downward substantially along a vertical direction, the switching device switches the adjustment enabling device so as to allow the attitude adjusting device to adjust the attitude of the work tool.
13. A construction machine, comprising: a first work arm and a second work arm rotatably mounted at a construction machine main body; a first work tool mounted at the first work arm; a second work tool mounted at the second work arm; a first operation device to be operated by an operator to adjust an attitude of the first work arm or the first work tool relative to the construction machine main body; a second operation device to be operated by the operator to adjust an attitude of the second work arm or the second work tool relative to the construction machine main body; a first attitude decision device that decides the attitude of the first work arm or the first work tool relative to the construction machine main body based upon an operation of the first operation device by the operator; a second attitude decision device that decides the attitude of the second work arm or the second work tool relative to the construction machine main body based upon an operation of the second operation device by the operator; a follow-up enabling device that allows the first work arm or the first tool, or the second work arm or the second work tool to follow a displacement of a contacting object that comes into contact with the first work tool or the second work tool and applies an external force to the first work tool or the second work tool, by adjusting the attitude of the first work arm or the first work tool decided by the first attitude decision device or adjusting the attitude of the second work arm or the second work tool decided by the second attitude decision device; and a switching device that selects whether or not to allow one of the first work arm or the first work tool and the second work arm or the second work tool to follow the displacement of the contacting object via the follow-up enabling device.
14. A construction machine according to claim 13, wherein: the follow-up enabling device comprises; a first follow-up enabling device that allows the first work arm or the first work tool to follow the displacement of a contacting object that comes into contact with the first work tool and applies an external force to the first work tool by adjusting the attitude of the first work arm or the first work tool decided by the first attitude decision device; and a second follow-up enabling device that allows the second work arm or the second work tool to follow the displacement of a contacting object that comes into contact with the second work tool and applies an external force to the second work tool by adjusting the attitude of the second work arm or the second work tool decided by the second attitude decision device.
15. A construction machine according to claim 14, wherein: the switching device is capable of selecting whether or not to allow the first work arm or the first work tool to follow the displacement of the contacting object via the first follow-up enabling device in response to an operation performed by the operator and is also capable of selecting whether or not to allow the second work arm or the second work tool to follow the displacement of the contacting object via the second follow-up enabling device in response to an operation performed by the operator.
16. A construction machine according to claim 13, wherein: the switching device selects whether or not to allow the first work arm or the first work tool to follow the displacement of a contacting object that comes into contact with the first work tool and applies an external force to the first work tool based upon an operation of the second operation device performed by the operator and selects whether or not to allow the second work arm or the second work tool to follow the displacement of a contacting object that comes into contact with the second work tool and applies an external force to the second work tool based upon an operation of the first operation device performed by the operator.
17. A construction machine according to claim 16, wherein: the first work tool is a first gripping tool; the second work tool is a second gripping tool; and if the first work arm and the second work arm are judged to have been adjusted to assume substantially identical attitudes based upon operations of the first operation device and the second operation device performed by the operator, the switching device selects a setting at which at least one of; the first work arm, the first gripping tool, the second work arm and the second gripping tool, is allowed to follow the displacement of the contacting object.
18. A construction machine according to claim 13, wherein: the first work arm and the second work arm are each allowed to rotate to a left/right direction relative to the construction machine main body; the first operation device and the second operation device are respectively operated by the operator to adjust rotational attitudes assumed by the first work arm and the second work arm along the left/right direction relative to the construction machine main body; the first attitude decision device and the second attitude decision device respectively decide the rotational attitudes of the first work arm and the second work arm relative to the construction machine main body based upon operations of the first operation device and the second operation device performed by the operator; and the follow-up enabling device allows the first work arm and the second work arm to follow the displacement of the contacting object that comes into contact with the first work tool or the second work tool and applies an external force to the first work tool or the second work tool by adjusting the rotational attitudes assumed by the first work arm and the second work arm along the left/right direction relative to the construction machine main body, respectively decided by the first attitude decision device and the second attitude decision device.
INCORPORATION BY REFERENCE
The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Publication No. 2006-285163 filed Oct. 19, 2006
Japanese Patent Publication No. 2006-310261 filed Nov. 16, 2006
Japanese Patent Publication No. 2007-097269 filed Apr. 3, 2007
Japanese Patent Publication No. 2007-233799 filed Sep. 10, 2007
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a construction machine that includes a work arm.
2. Description of Related Art
There is a construction machine known in the related art capable of performing various types of work with different work tools attached to a base constituted with a hydraulic excavator. As disclosed in Japanese Laid Open Patent Publication No. H 5-295901, a work tool mounted at such a construction machine may include a spring device for reducing the load applied from the work tool to the arm of the construction machine so as to prevent damage to the arm due to an overload.
However, there is a problem to be addressed with regard to work tools in the related art in that the response of the operating force is slow and the work tool operability becomes poor to result in low work efficiency.
SUMMARY OF THE INVENTION
A construction machine according to a 1st aspect of the present invention includes: a work arm rotatably mounted at a construction machine main body; a work tool mounted at the work arm; an attitude decision device that decides an attitude of the work arm or the work tool relative to the construction machine main body; a follow-up enabling device that allows the work arm or the work tool to follow a displacement of a contacting object that comes into contact with the work tool and applies an external force to the work tool, by adjusting the attitude of the work arm or the work tool decided by the attitude decision device; and a switching device that selects whether or not to allow the work arm or the work tool to follow the displacement of the contacting object via the follow-up enabling device.
According to a 2nd aspect of the present invention, in the construction machine according to the 1st aspect, it is preferable that the attitude decision device is a hydraulic cylinder that decides the attitude of the work arm or the work tool by extending/contracting a cylinder rod; and that the follow-up enabling device is an accumulator that adjusts the attitude of the work armor the work tool by causing the cylinder rod to extend/contract as pressure oil supplied to the hydraulic cylinder is absorbed into or released from the accumulator.
According to a 3rd aspect of the present invention, in the construction machine according to the 2nd aspect, it is preferable that the follow-up switching device is a switching valve disposed in an oil passage connecting the hydraulic cylinder with the accumulator, by which a flow of the pressure oil between the hydraulic cylinder and the accumulator is allowed or disallowed.
According to a 4th aspect of the present invention, the construction machine according to the 2nd aspect may further include an oil chamber selecting device that selects one of a bottom oil chamber and a rod oil chamber at the hydraulic cylinder where the pressure oil has a higher pressure and connecting the selected oil chamber to the accumulator.
According to a 5th aspect of the present invention, the construction machine according to the 1st aspect may further includes a traveling carriage rotatably supports the construction machine main body.
According to a 6th aspect of the present invention, the construction machine according to the 1st aspect may further include a follow-up characteristics adjusting device that adjusts follow-up characteristics achieved with the follow-up enabling device.
According to a 7th aspect of the present invention, in the construction machine according to the 1st aspect, the attitude decision device may be a hydraulic cylinder that decides the attitude of the work tool by extending/contracting a cylinder rod; and the construction machine may further include: oil passages that communicate with a bottom-side oil chamber and a rod-side oil chamber at the hydraulic cylinder; and a switching valve that opens or blocks the oil passages.
A construction machine according to a 8th aspect of the present invention includes: a work arm rotatably mounted at a construction machine main body; a work tool mounted at the work arm; an attitude adjusting device that adjusts an attitude of the work arm or the work tool relative to the construction machine main body; an adjustment enabling device that allows the attitude of the work arm or the work tool to be adjusted by the attitude adjusting device so as to assume an attitude corresponding to an external force applied to the work tool at the work armor the work tool; an operating state determining device that determines an operating state of the construction machine main body; and a switching device that selects, based upon the operating state determined by the operating state determining device, whether or not the adjustment enabling device is to allow the attitude adjusting device to adjust the attitude of the work arm or the work tool.
According to a 9th aspect of the present invention, in the construction machine according to the 8th aspect, the operating state determining device may determine the operating state based upon at least one of; an operating state of an operation lever by which operation instructions for the work arm or the work tool are issued, a work load applied to the work arm or the work tool and the attitude of the work arm or the work tool.
According to a 10th aspect of the present invention, in the construction machine according to the 9th aspect, it is preferable that: the work tool is a gripping device that grips a target object; the operating state determining device determines the operating state based upon an operating state of an operation lever by which operating instructions for the gripping device are issued; and if the operating state determining device determines that the operation lever has been operated so as to grip the target object with the gripping device, the switching device switches the adjustment enabling device so as to allow the attitude adjusting device to adjust the attitude of the work arm or the work tool.
According to a 11th aspect of the present invention, in the construction machine according to the 9th aspect, it is preferable that: the work tool is a gripping device that grips a target object; the construction machine further comprises a detection device that detects a physical quantity corresponding to a gripping force imparted by the gripping device; the operating state determining device determines the operating state based upon the physical quantity detected by the detection device; and if the operating state determining device determines that the physical quantity detected by the detection device is smaller than a predetermined value, the switching device switches the adjustment enabling device so as to allow the attitude adjusting device to adjust the attitude of the work arm or the work tool.
According to a 12th aspect of the present invention, in the construction machine according to the 9th aspect, it is preferable that if the operating state determining device determines, based upon the attitude of the work tool, that the work tool is positioned facing downward substantially along a vertical direction, the switching device switches the adjustment enabling device so as to allow the attitude adjusting device to adjust the attitude of the work tool.
A construction machine according to a 13th aspect of the present invention includes: a first work arm and a second work arm rotatably mounted at a construction machine main body; a first work tool mounted at the first work arm; a second work tool mounted at the second work arm; a first operation device to be operated by an operator to adjust an attitude of the first work arm or the first work tool relative to the construction machine main body; a second operation device to be operated by the operator to adjust an attitude of the second work arm or the second work tool relative to the construction machine main body; a first attitude decision device that decides the attitude of the first work arm or the first work tool relative to the construction machine main body based upon an operation of the first operation device by the operator; a second attitude decision device that decides the attitude of the second work arm or the second work tool relative to the construction machine main body based upon an operation of the second operation device by the operator; a follow-up enabling device that allows the first work arm or the first tool, or the second work arm or the second work tool to follow a displacement of a contacting object that comes into contact with the first work tool or the second work tool and applies an external force to the first work tool or the second work tool, by adjusting the attitude of the first work arm or the first work tool decided by the first attitude decision device or adjusting the attitude of the second work arm or the second work tool decided by the second attitude decision device; and a switching device that selects whether or not to allow one of the first work arm or the first work tool and the second work arm or the second work tool to follow the displacement of the contacting object via the follow-up enabling device.
According to a 14th aspect of the present invention, in the construction machine according to the 13th aspect, it is preferable that the follow-up enabling device includes a first follow-up enabling device that allows the first work arm or the first work tool to follow the displacement of a contacting object that comes into contact with the first work tool and applies an external force to the first work tool by adjusting the attitude of the first work arm or the first work tool decided by the first attitude decision device and a second follow-up enabling device that allows the second work arm or the second work tool to follow the displacement of a contacting object that comes into contact with the second work tool and applies an external force to the second work tool by adjusting the attitude of the second work arm or the second work tool decided by the second attitude decision device.
According to a 15th aspect of the present invention, in the construction machine according to the 14th aspect, it is preferable that the switching device is capable of selecting whether or not to allow the first work arm or the first work tool to follow the displacement of the contacting object via the first follow-up enabling device in response to an operation performed by the operator and is also capable of selecting whether or not to allow the second work arm or the second work tool to follow the displacement of the contacting object via the second follow-up enabling device in response to an operation performed by the operator.
According to a 16th aspect of the present invention, in the construction machine according to the 13th aspect, it is preferable that the switching device selects whether or not to allow the first work arm or the first work tool to follow the displacement of a contacting object that comes into contact with the first work tool and applies an external force to the first work tool based upon an operation of the second operation device performed by the operator and selects whether or not to allow the second work arm or the second work tool to follow the displacement of a contacting object that comes into contact with the second work tool and applies an external force to the second work tool based upon an operation of the first operation device performed by the operator.
According to a 17th aspect of the present invention, in the construction machine according to the 16th aspect, it is preferable that: the first work tool is a first gripping tool; the second work tool is a second gripping tool; and if the first work arm and the second work arm are judged to have been adjusted to assume substantially identical attitudes based upon operations of the first operation device and the second operation device performed by the operator, the switching device selects a setting at which at least one of; the first work arm, the first gripping tool, the second work arm and the second gripping tool, is allowed to follow the displacement of the contacting object.
According to a 18th aspect of the present invention, in the construction machine according to the 13th aspect, it is preferable that: the first work arm and the second work arm are each allowed to rotate to a left/right direction relative to the construction machine main body; the first operation device and the second operation device are respectively operated by the operator to adjust rotational attitudes assumed by the first work arm and the second work arm along the left/right direction relative to the construction machine main body; the first attitude decision device and the second attitude decision device respectively decide the rotational attitudes of the first work arm and the second work arm relative to the construction machine main body based upon operations of the first operation device and the second operation device performed by the operator; and the follow-up enabling device allows the first work arm and the second work arm to follow the displacement of the contacting object that comes into contact with the first work tool or the second work tool and applies an external force to the first work tool or the second work tool by adjusting the rotational attitudes assumed by the first work arm and the second work arm along the left/right direction relative to the construction machine main body, respectively decided by the first attitude decision device and the second attitude decision device.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an external view of a construction machine;
FIG. 2 shows the structure of a gripping device;
FIG. 3 is a circuit diagram pertaining to the hydraulic circuits that drive a boom cylinder and a work tool cylinder of the construction machine;
FIG. 4 is a circuit diagram pertaining to the hydraulic circuits that drive the boom cylinder and the work tool cylinder of the construction machine achieved in a second embodiment;
FIG. 5 is a circuit diagram pertaining to the hydraulic circuits that drive the boom cylinder and the work tool cylinder of the construction machine achieved in a third embodiment;
FIG. 6 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 7 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 8 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 9 presents an example of a variation;
FIG. 10 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 11 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 12 is an external view of the construction machine achieved in a fourth embodiment;
FIG. 13 shows the structure of the gripping device;
FIG. 14 is a circuit diagram pertaining to the hydraulic circuits that drive the boom cylinder and the work tool cylinder of the construction machine;
FIG. 15 presents a flowchart of the control processing operation executed to control the electromagnetic switching valve;
FIGS. 16A and 16B provide conceptual illustrations showing how the attitude of the front work arm changes when gripping a target object, with FIG. 16A showing a state after only one of the gripping claws comes into contact with the target object and 16 B showing how the attitude of the front work arm changes as the gripping claws close with one of them remaining in contact with the target object;
FIG. 17 is a circuit diagram pertaining to the hydraulic circuits that drive the boom cylinder and the work tool cylinder of the construction machine achieved in a fifth embodiment;
FIG. 18 presents a flowchart of the control processing operation executed to control the electromagnetic switching valve in the fifth embodiment;
FIG. 19 is a circuit diagram of the hydraulic circuit that drives the work tool cylinder of the construction machine achieved in a sixth embodiment;
FIG. 20 presents a flowchart of the control processing operation executed to control the electromagnetic switching valve in the sixth embodiment;
FIG. 21 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 22 presents an example of a variation;
FIG. 23 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 24 is an external view of the construction machine achieved in a seventh embodiment;
FIG. 25 is a plan view of the construction machine;
FIG. 26 shows the structure of the gripping devices;
FIG. 27 shows the hydraulic circuit in the construction machine;
FIG. 28 is a perspective of an operator's seat;
FIG. 29 is a top view of the area around operation levers;
FIG. 30 illustrates the construction machine engaged in operation to grip a gripping target object;
FIG. 31 schematically illustrates the state of the gripping devices and the gripping target object as the second front work arm B is rotated along the forward/rearward direction without moving the first front work arm A;
FIG. 32 presents a flowchart of the control processing operation executed to control the control valves in the work load follow-up devices;
FIG. 33 is a circuit diagram of the hydraulic circuit in the construction machine achieved in an eighth embodiment;
FIG. 34 presents a flowchart of the control processing operation executed to control the control valves in the work load follow-up devices in the eighth embodiment;
FIG. 35 presents a flowchart of the control processing operation executed to control the control valves in the work load follow-up devices in a ninth embodiment;
FIG. 36 shows an example of a variation that may be adopted in the hydraulic circuits;
FIG. 37 shows an example of a variation that may be adopted in the hydraulic circuits; and
FIG. 38 shows an example of a work operation.
DESCRIPTION OF PREFERRED EMBODIMENTS
First Embodiment
In reference to FIGS. 1 through 3, the first embodiment of the construction machine according to the present invention is explained. As shown in FIG. 1, a revolving superstructure 11 is rotatably mounted at a traveling carriage 12 in a construction machine 100 that includes as its base unit a hydraulic excavator. An operator's cab 11 a is disposed at the front of the revolving superstructure 11 . Behind the operator's cab 11 a , a main drive device 11 b , which includes an engine and a hydraulic pump, is disposed.
A front work arm 10 constituted with an articulated arm is mounted at the revolving superstructure 11 . The front work arm 10 includes a boom 13 attached to the revolving superstructure 11 so as to swing up/down freely via a boom cylinder 14 , an arm 15 connected to the boom 13 and mounted so as to swing up/down freely via an arm cylinder 16 and a gripping device 101 , which is a work tool connected to the front end of the arm 15 so as to rotate freely along the up/down direction via a work tool cylinder 18 .
FIG. 2 shows the structure of the gripping device 101 . The gripping device 101 includes a gripping device body 17 attached to the front end of the arm 15 , a pair of gripping claws 19 disposed facing opposite each other so as to be able to grasp and hold a target object between the front ends thereof and a cylinder 20 that drives the gripping claws 19 to engage them in opening/closing operation.
FIG. 3 is a circuit diagram pertaining to the hydraulic circuits that drive the boom cylinder 14 and the work tool cylinder 18 in the construction machine 100 . While an explanation is given below on the hydraulic circuit that drives the boom cylinder 14 , the hydraulic circuit that drives the work tool cylinder 18 assumes an identical structure. A main pump 31 , a control valve 30 , a main relief valve 33 , a hydraulic operating fluid reservoir 32 and a work load follow-up device 200 are installed to form this hydraulic circuit. In addition, the hydraulic circuit includes a pilot pump (not shown) and an operation lever 34 used to control the control valve 30 .
As the main pump 31 , by which pressure oil is supplied to the various actuators of the construction machine 100 , is driven by an engine (not shown), the hydraulic operating fluid in the hydraulic operating fluid reservoir 32 is delivered to the boom cylinder 14 via the control valve 30 . The pressure oil from the main pump 31 is also delivered to the arm cylinder 16 , the work tool cylinder 18 and the cylinder 20 via corresponding control valves (not shown). The maximum pressure in this hydraulic circuit is defined via the main relief valve 33 .
The work load follow-up device 200 includes an electromagnetic switching valve (or solenoid controlled directional control valve) 35 , a control valve 38 , an accumulator 39 and a relief valve 40 . The work load follow-up device 200 further includes a drive circuit 36 and an ON/OFF switch 37 , by which the operating position of the electromagnetic switching valve 35 is switched. The electromagnetic switching valve 35 , disposed so as to intersect oil passages 41 and 42 , communicates the upstream side (oil passages 41 a and 42 a ) of the oil passages 41 and 42 with the downstream side (oil passages 41 b and 42 b ) or cuts off the upstream side from the downstream side. The oil passage 41 a is connected with a bottom-side oil chamber 14 a of the boom cylinder 14 , whereas the oil passage 42 a is connected to a rod-side oil chamber 14 b of the boom cylinder 14 .
The control valve 38 switches the state of connection of the oil passages 41 b and 42 b to oil passages 45 and 46 by selecting a spool position in correspondence to the pressures in the oil passages 41 b and 42 b . Namely, the pressure oil from an oil passage 43 connected to the oil passage 41 b and from an oil passage 44 connected to the oil passage 42 b as pilot pressure oil at the control valve 38 to drive the spool. When the pressures in the oil passages 41 b and 42 b are both low or when the pressures in the oil passages 41 b and 42 b are substantially equal to each other, the spool at the control valve 38 assumes the neutral position, disconnecting the oil passages 41 b and 42 b from the oil passages 45 and 46 .
As the pressure in the oil passage 41 b increases and the pressure in the oil passage 42 b decreases, the spool at the control valve 38 shifts from the neutral position and, as a result, the oil passage 41 b becomes connected to the oil passage 45 and the oil passage 42 b becomes connected to the oil passage 46 . If, on the other hand, the pressure in the oil passage 41 b becomes lower and the pressure in the oil passage 42 b becomes higher, the spool at the control valve 38 shifts from the neutral position to connect the oil passage 41 b to the oil passage 46 and the oil passage 42 b to the oil passage 45 . In other words, when the pressure in either the oil passage 41 b or the oil passage 42 b becomes high and the pressure in the other oil passage becomes low, the oil passage where the pressure is high is connected to the oil passage 45 and the oil passage where the pressure is low is connected to the oil passage 46 via the control valve 38 .
The accumulator 39 is connected to the oil passage 45 to absorb the pressure oil in the oil passage 45 or release pressure oil it has absorbed into the oil passage 45 . Once the pressure in the oil passage 45 exceeds a preset pressure level, the pressure oil in the oil passage 45 is released into the oil passage 46 via the relief valve 40 . The pressure level set for the relief valve 40 is lower than the pressure level setting selected for the main relief valve 33 . It is to be noted that the oil passage 46 is connected to the hydraulic operating fluid reservoir 32 .
The drive circuit 36 switches the operating position of the electromagnetic switching valve 35 based upon the ON/OFF state of the ON/OFF switch 37 installed in the operator's cab 11 a . As the ON/OFF switch 37 enters an ON state in response to an operator operation, the drive circuit 36 excites the solenoid at the electromagnetic switching valve 35 and drives the solenoid so as to communicate the oil passages 41 a and 42 a with the oil passages 41 b and 42 b respectively. As the ON/OFF switch 37 enters an OFF state in response to an operator operation, the drive circuit 36 demagnetizes the solenoid at the electromagnetic switching valve 35 . As a result, the spool is driven with the force of the spring at the electromagnetic switching valve 35 to disconnect the oil passages 41 a and 42 a from the oil passages 41 b and 42 b.
As a specific operation lever is operated in the construction machine 100 structured as described above, the spool of the control valve corresponding to the relevant hydraulic cylinder is driven and the hydraulic cylinder is driven at a speed reflecting the extent to which the operation lever is operated. For instance, as the operation lever 34 corresponding to the boom cylinder 14 is operated, the spool at the control valve 30 is driven with the pilot pressure oil from a pilot pump (not shown) assuming a pressure level corresponding to the extent to which the operation lever 34 has been operated and thus, the boom cylinder 14 is driven at a speed reflecting the extent to which the operation lever 34 has been operated.
As pressure oil is delivered into the bottom-side oil chamber 14 a at the boom cylinder 14 , the boom 13 is driven to swing upward relative to the revolving superstructure 11 , whereas if pressure oil is delivered into the rod-side oil chamber 14 b at the boom cylinder 14 , the boom 13 is driven to swing downward relative to the revolving superstructure 11 . As pressure oil is delivered into a bottom-side oil chamber (not shown) at the arm cylinder 16 , the arm 15 is driven to swing downward relative to the boom 13 , whereas if pressure oil is delivered into a rod-side oil chamber (not shown) at the arm cylinder 16 , the arm 15 is driven to swing upward relative to the boom 13 .
As pressure oil is delivered into a bottom-side oil chamber 18 a at the work tool cylinder 18 , the gripping device 101 is driven to swing downward relative to the arm 15 , whereas if pressure oil is delivered into a rod-side oil chamber 18 b , the gripping device 101 is driven to swing upward relative to the arm 15 . As pressure oil is delivered to a bottom-side oil chamber (not shown) at the cylinder 20 , the pair of gripping claws 19 are driven along the gripping direction, whereas if pressure oil is delivered into a rod-side oil chamber (not shown) at the cylinder, the pair of gripping claws 19 are driven along the releasing direction.
--Operations of the Work Load Follow-Up Device 200 and the Boom Cylinder 14 --
As described above, when the ON/OFF switch 37 is in the ON state, the oil passages 41 a and 42 a are made to communicate with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , and thus, the pressure oil in the bottom-side oil chamber 14 a and the rod-side oil chamber 14 b at the boom cylinder 14 flows into the downstream side of the electromagnetic switching valve 35 . In this situation, the behavior of the boom cylinder 14 is affected by the operations of the control valve 38 and the accumulator 39 . As explained earlier, when pressure oil is delivered into the bottom-side oil chamber 14 a in response to an operation of the operation lever 34 , the boom 13 is driven to swing upward relative to the revolving superstructure 11 , whereas when pressure oil is delivered into the rod-side oil chamber 14 b , the boom is driven to swing downward relative to the revolving superstructure 11 .
As the gripping claws 19 come into contact with the work target object and the swinging motion of the boom 13 stops with the operation lever 34 remaining in the operating state, the pressure in either the oil chamber 14 a or the oil chamber 14 b , to which the pressure oil is supplied via the control valve 30 , rises in correspondence to the force (work load) with which the gripping claws 19 contact the work target object. Then, as the pressure in either of the oil passages 41 b and 42 b in communication with the oil chambers 14 a and 14 b becomes high and the pressure in the other oil passage becomes low, the oil passage where the pressure has risen to a high level is connected with the oil passage 45 and the oil passage where the pressure has decreased is connected to the oil passage 46 via the control valve 38 . As a result, the pressure oil in either the oil chamber 14 a or the oil chamber 14 b (hereafter referred to as the “high-pressure side oil chamber”) communicating with the oil passage where the pressure has risen is absorbed by the accumulator 39 . Since this allows the accumulator 39 to function as a spring element against the work load, a sudden increase in the work load is prevented.
If the operation lever 34 remains in the operating state after the gripping claws 19 contact the work target object, the pressure oil in the high-pressure side oil chamber (or the pressure oil flowing from the control valve 30 toward the high-pressure side oil chamber) is absorbed and collected at the accumulator 39 until the pressure rises to the pressure level setting selected for the relief valve 40 . The pressure oil in the high-pressure side oil chamber (or the pressure oil flowing from the control valve 30 toward the high-pressure side oil chamber) is released via the relief valve 40 into the hydraulic operating fluid reservoir 32 once the pressure rises to the pressure level set for the relief valve 40 . Namely, the accumulator 39 is protected via the relief valve 40 which regulates the pressure of the pressure oil applied to the accumulator 39 . In addition, the relief valve 40 allows the gripping claws 19 to contact the work target object with a workload (contact force) corresponding to the pressure setting selected for the relief valve 40 .
If a swinging motion of the arm 15 , for instance, causes the gripping claws 19 to contact the work target object while the operation lever 34 is in a non-operating state, the pressure in either the oil chamber 14 a or the oil chamber 14 b at the boom cylinder 14 rises to a level corresponding to the work load. When the operation lever 34 is in the non-operating state, the pressure oil in the high-pressure side oil chamber does not flow to the outside via the control valve 30 . However, since the oil passages 41 a and 42 a are in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , the pressure oil in the high-pressure side oil chamber flows into the accumulator 39 via the control valve 38 , as explained earlier.
As a result, the pressure oil in the high-pressure side oil chamber is absorbed and collected at the accumulator 39 in correspondence to the work load, and the boom cylinder 14 extends/contracts in correspondence to the quantity of pressure oil accumulated at the accumulator 39 to cause a swinging motion of the boom 13 . As the work load is lessened, the pressure oil having been collected at the accumulator 39 flows back into the high-pressure side oil chamber and thus, the boom cylinder 14 extends/contracts. In other words, the boom 13 swings to an extent corresponding to the level of the workload. Namely, the swinging motion of the boom 13 occurring as the pressure oil in the high-pressure side oil chamber is absorbed and collected at the accumulator 39 and then released from the accumulator 39 in correspondence to the work load, allows the gripping device 101 to follow the displacement of the work target object coming into contact with the gripping claws 19 to apply an external force to the gripping claws 19 .
If the pressure in the oil passage 45 is equal to or less than the pressure level setting selected for the relief valve 40 at the time of the work load application, the pressure oil in the high-pressure side oil chamber will not have flowed back into the hydraulic operating fluid reservoir 32 via the relief valve 40 . Under these circumstances, as the work load application stops and the pressure oil having been collected at the accumulator 39 flows back to the high-pressure side oil chamber, the cylinder rod at the boom cylinder 14 resumes the pre-work load application extension position.
If the pressure in the oil passage 45 exceeds the pressure level setting selected for the relief valve 40 at the time of the work load application, the pressure oil in the high-pressure side oil chamber flows back into the hydraulic operating fluid reservoir 32 via the relief valve 40 . Under these circumstances, as the work load application stops and the pressure oil having been collected at the accumulator 39 flows back into the high-pressure side oil chamber, the cylinder rod at the boom cylinder 14 moves back closer to the pre-work load application extension position but stops at a position short of the full pre-work load application extension position by an extent matching the quantity of pressure oil having flowed back into the hydraulic operating fluid reservoir 32 .
As described above, when the oil passages 41 a and 42 a are set in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , the work load follow-up device 200 is able to affect the operation of the boom cylinder 14 . In other words, the ON/OFF switch 37 should be turned on to make the movement of the boom 13 follow the displacement of the work target object which constitutes the work load.
As described above, communication between the oil passages 41 a and 42 a and the oil passages 41 b and 42 b is cut off via the electromagnetic switching valve 35 when the ON/OFF switch 37 is in the OFF state, and thus, the pressure oil in the bottom-side oil chamber 14 a and the rod-side oil chamber 14 b at the boom cylinder 14 does not flow into the downstream side of the electromagnetic switching valve 35 . In this situation, the behavior of the boom cylinder 14 is not affected by operations of the control valve 38 or the accumulator 39 . Thus, if pressure oil is delivered into the bottom-side oil chamber 14 a the boom 13 is driven to swing upward relative to the revolving superstructure 11 in response to an operation of the operation lever 34 , but if pressure oil is delivered into the rod-side oil chamber 14 b , the boom is driven to swing downward relative to the revolving superstructure 11 as explained earlier.
As the gripping claws 19 come into contact with the work target object and the swinging motion of the boom 13 stops with the operation lever 34 remaining in the operating state, the pressure of the pressure oil supplied to the boom cylinder 14 rises to the level defined by the main relief valve 33 . If a swinging motion of the arm 15 , for instance, causes the gripping claws 19 to contact the work target object while the operation lever 34 is in the non-operating state, the pressure in either the oil chamber 14 a or the oil chamber 14 b at the boom cylinder 14 rises to a level corresponding to the work load. When the operation lever 34 is in the non-operating state, the flow of pressure oil in the oil chambers 14 a and 14 b at the boom cylinder 14 to the outside is blocked at the control valve 30 and the electromagnetic switching valve 35 and thus, the boom 13 does not swing.
As described above, when the oil passages 41 a and 42 a are cut off from the oil passages 41 b and 42 b by the electromagnetic switching valve 35 , the work load follow-up device 200 is not able to affect the operation of the boom cylinder 14 . In other words, the ON/OFF switch 37 should be turned off if the movement of the boom 13 is not to follow the displacement of the work target object which constitutes the work load.
The hydraulic circuit that drives the work tool cylinder 18 also includes a work load follow-up device 200 in the construction machine 100 achieved in the embodiment. Since the operation of the work tool cylinder 18 is similar to the operation of the boom cylinder 14 described above, its explanation is omitted. A setting for allowing/not allowing the operation of the boom cylinder 14 to follow the displacement of the work target object which constitutes the work load and a setting for allowing/not allowing the operation of the work tool cylinder 18 to follow the displacement of the work target object which constitutes the work load can be individually selected as desired. For instance, when the operations of both the boom cylinder 14 and the work tool cylinder 18 are set to follow the displacement of the work target object which constitutes the work load, two articulating joints are allowed to rotate in conformance to the displacement of the work target object, doubling the level of freedom of movement. In this case, the front work arm 10 is able to follow a wider range of work target object displacement.
By selecting the settings that allow neither the boom cylinder 14 nor the work tool cylinder 18 to follow the displacement of the work target object which constitutes the work load, the construction machine can be engaged in work operation in much the same way as work machines in the related art that do not include work load follow-up devices 200 . In addition, the operation of either the boom cylinder 14 or the work tool cylinder 18 alone may be allowed to follow the displacement of the work target object which constitutes the work load. In short, optimal settings should be selected by operating the individual ON/OFF switches 37 in correspondence to the specific details of the work to be performed.
The following operational advantages can be achieved with the construction machine 100 in the first embodiment of the present invention described above.
(1) The construction machine includes the work load follow-up devices 200 , which allow the movement of the front work arm 10 to follow the displacement of the work target object which constitutes the work load and the settings for allowing/not allowing the movement of the front work arm 10 to follow the displacement of the work target object which constitutes the work load can be selected by turning on/off the ON/OFF switches 37 . As a result, damage to the front work arm 10 due to an overload is prevented and, at the same time, a delay in the operating force response is prevented, which, in turn, assures the desired level of operability. Thus, the work efficiency is not compromised. In addition, since the movement of the front work arm 10 can follow the displacement of the work target object which constitutes the work load, the gripping device 101 can be engaged in a force following operation over the contour of a wall surface, a base surface or the like to assure a higher level of convenience. For instance, a force following operation such as ground leveling can be executed with ease by mounting a bucket instead of the gripping device 101 as the work tool.
(2) The boom 13 is allowed to follow the displacement of the work target object which constitutes the work load via the work load follow-up device 200 connected to the hydraulic circuit that drives the boom cylinder 14 . In addition, the gripping device 101 is allowed to follow the displacement of the work target object which constitutes the work load via the work load follow-up device 200 connected to the hydraulic circuit that drives the work tool cylinder 18 . When a work tool includes a spring device attached thereto in the related art, greater load capacity needs to assured and the operability of such a work tool is bound to be poorer due to the presence of the spring device. As a result, a high level of work efficiency cannot be achieved. The operation of the construction machine according to the present invention, however, is not affected by such negative factors. In addition, since damage to the front work arm 10 attributable to the work load applied to the gripping claws 19 is prevented through a simple structure, an increase in the cost can be minimized. It is to be noted that since the present invention may be adopted in an existing construction machine simply by connecting the work load follow-up device 200 in the oil passage to a hydraulic cylinder, a function of following the displacement of the work target object which constitutes the work load can be added at low cost in the existing construction machine.
(3) The setting for allowing/not allowing the operation of the boom cylinder 14 to follow the displacement of the work target object which constitutes the work load and the setting for allowing/not allowing the operation of the work tool cylinder 18 to follow the displacement of the work target object which constitutes the work load can be individually selected as desired. Thus, by selecting the settings for allowing the operations of both the boom cylinder 14 and the work tool cylinder 18 to follow the displacement of the work target object which constitutes the work load, two articulating joints are allowed to rotate in conformance to the displacement of the work target object, doubling the level of freedom of movement. Consequently, the front work arm 10 is able to follow a wider range of work target object displacement and the risk of damage to the front work arm 10 can be greatly reduced. In addition, depending upon the specific details of the work to be performed, the operation of either the boom cylinder 14 or the work tool cylinder 18 alone may be set to follow the displacement of the work target object which constitutes the work load, or the settings not allowing either the boom cylinder 14 or the work tool cylinder 18 to follow the displacement of the work target object which constitutes the work load may be selected. In short, optimal settings can be selected with a high level of flexibility to best suit the specific details of the work to be performed.
(4) As the pressure oil in the high-pressure side oil chambers at the boom cylinder 14 and the work tool cylinder 18 is absorbed and collected in the respective accumulators 39 and then is released from the accumulators 39 , the movement of the front work arm 10 is allowed to follow the displacement of the work target object which constitutes the work load. In addition, the setting for allowing or not allowing the pressure oil in a high-pressure side oil chamber to be absorbed at the corresponding accumulator 39 is selected via the electromagnetic switching valve 35 . Thus, the cylinder rods of the boom cylinder 14 and the work tool cylinder 18 are allowed to extend/contract so as to follow the displacement of the work target object which constitutes the work load and also the extend/contract allow/disallow settings for the cylinder rods of the boom cylinder 14 and the work tool cylinder 18 to follow the displacement of the work target object which constitutes the work load can be selected through hydraulic circuits adopting a simple circuit structure. This means that stable and reliable operation is assured at low cost.
(5) Since the pressure oil in a high-pressure side oil chamber is guided to the accumulator 39 via the control valve 38 , only a single accumulator 39 is required, which contributes to cost reduction. Furthermore, since the spool at the control valve 38 is driven with the pressure oil from the high-pressure side oil chamber used as the pilot pressure oil, a high level of operational reliability is assured through a simple structure.
Second Embodiment
In reference to FIG. 4, the second embodiment of the construction machine according to the present invention is explained. The same reference numerals are assigned to structural elements identical to those in the first embodiment and the following explanation focuses on the differences from the first embodiment. Structural elements that are not specially noted in the following explanation are identical to those in the first embodiment. The second embodiment differs from the first embodiment in that an additional set of an accumulator and a relief valve is disposed between the oil passage 45 and the oil passage 46 within the work load follow-up device 200 .
FIG. 4 is a circuit diagram pertaining to the hydraulic circuits that drive the boom cylinder 14 and the work tool cylinder 18 in the construction machine 100 achieved in the second embodiment. While an explanation is given below on the hydraulic circuit that drives the boom cylinder 14 , the hydraulic circuit that drives the work tool cylinder 18 assumes an identical structure. The work load follow-up device 200 in the embodiment includes an electromagnetic switching valve 35 , a control valve 38 , an accumulator 39 , a relief valve 40 , an electromagnetic switching valve 301 , an accumulator 302 and a relief valve 303 . The work load follow-up device 200 further includes a drive circuit 36 and ON/OFF switches 37 and 304 , by which the operating positions of the electromagnetic switching valves 35 and 301 are switched.
In an oil passage 47 connecting an oil passage 45 and an oil passage 46 , the electromagnetic switching valve 301 and the relief valve 303 are disposed in this order in series starting from the side toward the oil passage 45 . The accumulator 302 is connected to the oil passage 47 at a position between the electromagnetic switching valve 301 and the relief valve 303 . In other words, the electromagnetic switching valve 301 , the accumulator 302 and the relief valve 303 are disposed between the oil passage 45 and the oil passage 46 , in parallel to the accumulator 39 and the relief valve 40 .
The electromagnetic switching valve 301 is a switching valve which allows/disallows a pressure oil flow from the oil passage 45 to the accumulator 302 and the relief valve 303 . The operating position of the electromagnetic switching valve 301 is switched by the drive circuit 36 in correspondence to the ON/OFF state of the ON/OFF switch 304 installed in the operator's cab 11 a . The accumulator 302 , connected to the oil passage 45 via the electromagnetic switching valve 301 , absorbs the pressure oil in the oil passage 45 or releases pressure oil having been absorbed to the oil passage 45 . The accumulator 302 has operating characteristics such that it absorbs pressure oil at a lower pressure compared to the accumulator 39 .
The main function of the relief valve 303 is similar to that of the relief valve 40 , which is to protect the accumulator 39 , i.e., the relief valve 303 is disposed mainly to protect the accumulator 302 . The pressure level setting selected for the relief valve 303 is lower than the pressure level setting selected for the relief valve 40 .
When the ON/OFF switch 37 is in the ON state and the ON/OFF switch 304 is in the OFF state in the work load follow-up device 200 in the embodiment structured as described above, the oil passages 41 a and 42 a are set in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , but the oil passage 45 is disconnected from the part of the oil passage 47 located further on the downstream side relative to the electromagnetic switching valve 301 . Under these circumstances, the work load follow-up device 200 in the embodiment engages in an operation identical to that executed by the work load follow-up device 200 in the first embodiment.
When both ON/OFF switches 37 and 304 are in the ON state, the oil passages 41 a and 42 a are set in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 and also, the oil passage 45 is made to communicate with the part of the oil passage 47 located further on the downstream side relative to the electromagnetic switching valve 301 . As a result, the pressure oil in the oil passage 45 is allowed to flow into the accumulator 302 . Since the accumulator 302 absorbs the pressure oil at a lower pressure level than the accumulator 39 , as described earlier, the pressure oil in the oil passage 45 is absorbed more readily at the accumulator 302 than at the accumulator 39 .
In addition, since the pressure level setting selected for the relief valve 303 is lower than the pressure level setting selected for the relief valve 40 , the pressure oil in the oil passage 45 is released into the oil passage 46 via the relief valve 303 as the pressure in the oil passage 45 rises.
Thus, when the ON/OFF switches 37 and 304 are both in the ON state, it is possible to operate the boom 13 in conformance to the displacement of the work target object which constitutes the work load over a smaller work load range compared to the work load range over which the boom 13 is operated in conformance to the displacement of the work target object when the ON/OFF switch 37 is in an ON state and the ON/OFF switch 304 is in the OFF state. Namely, by opening/closing the electromagnetic switching valve 301 in response to an on/off operation of the ON/OFF switch 304 , the follow-up characteristics of the boom 13 with which the boom 13 operates in correspondence to the work load can be switched or adjusted.
As in the first embodiment, the hydraulic circuit that drives the work tool cylinder 18 also includes a work load follow-up device 200 connected therein in the construction machine 100 achieved in the embodiment. Since the operation of the work tool cylinder 18 is similar to that of the boom cylinder 14 explained above, its explanation is omitted.
In the construction machine 100 achieved in the embodiment, the operating characteristics of the accumulator 39 and the pressure level setting selected for the relief valve 40 may be set over a relatively high pressure range so as to effectively prevent damage to the front work arm 10 attributable to the work load. In addition, the operating characteristics of the accumulator 302 and the pressure level setting selected for the relief valve 303 may be set over a relatively low pressure range so as to effectively prevent damage to the gripping target object and enable the work tool to perform an effective force following operation, that is, an effective positional error absorption.
In addition to the advantages of the first embodiment, the following operational advantages can be achieved in the construction machine 100 in the second embodiment of the present invention.
(1) The addition of the electromagnetic switching valve 301 , the accumulator 302 and the relief valve 303 allows the movement of the front work arm 10 to follow the displacement of the work target object which constitutes the work load over an even smaller work load range. This means that the operator is able to adjust the follow-up characteristics with which the front work arm 10 operates in correspondence to the work load by operating the ON/OFF switch 304 as appropriate under specific work conditions, which achieves improvements in the operability and the work efficiency.
(2) By selecting optimal operating characteristics for the accumulators 39 and 302 and optimal pressure level settings for the relief valves 40 and 303 to suit specific purposes of use, the durability and the ease of use of the construction machine 100 can be improved.
Third Embodiment
In reference to FIG. 5, the third embodiment of the construction machine according to the present invention is explained. The same reference numerals are assigned to structural elements identical to those in the first and second embodiments and the following explanation focuses on the differences from the first and second embodiments. Structural elements that are not specially noted in the following explanation are identical to those in the first and second embodiments. The third embodiment differs from the first embodiment mainly in that an electromagnetic switching valve is disposed between the oil passage 45 and the oil passage 46 in the work load follow-up device 200 and in that the work load follow-up device 200 is installed only in the hydraulic circuit for driving the work tool cylinder 18 .
FIG. 5 is a circuit diagram of the hydraulic circuit that drives the work tool cylinder 18 in the construction machine 100 achieved in the third embodiment. As explained earlier, the work load follow-up device 200 is installed in the hydraulic circuit that drives the work tool cylinder 18 alone. The work load follow-up device 200 in the embodiment includes an electromagnetic switching valve 35 , a control valve 38 , an accumulator 39 , a relief valve 40 and an electromagnetic switching valve 301 . The work load follow-up device 200 further includes a drive circuit 36 and ON/OFF switches 37 and 304 used to select the operating positions of the electromagnetic switching valves 35 and 301 . It is to be noted that the work load follow-up device 200 in this embodiment differs from the work load follow-up device 200 in the second embodiment described earlier in that it does not include an accumulator 302 or a relief valve 303 .
An oil passage 47 connects the oil passage 45 and the oil passage 46 . The electromagnetic switching valve 301 is a switching valve that allows/disallows a flow of pressure oil from the oil passage 45 to the oil passage 46 through the oil passage 47 . The operating position of the electromagnetic switching valve 301 is switched by the drive circuit 36 in correspondence to the ON/OFF state of the ON/OFF switch 304 installed in the operator's cab 11 a.
When the ON/OFF switch 37 is in the ON state and the ON/OFF switch 304 is in the OFF state in the work load follow-up device 200 in the embodiment structured as described above, the oil passages 41 a and 42 a are set in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , but the oil passage 45 is disconnected from the part of the oil passage 47 located further on the downstream side relative to the electromagnetic switching valve 301 . Under these circumstances, the work load follow-up device 200 in the embodiment engages in an operation identical to that executed by the work load follow-up device 200 in the first embodiment.
When both ON/OFF switches 37 and 304 are in the ON state, the oil passages 41 a and 42 a are set in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 and also, the oil passage 45 is set in the communication with the oil passage 46 , thereby allowing the pressure oil in the oil passage 45 to flow into the oil passage 46 .
When a pressure difference occurs between the pressure in the bottom-side oil chamber 18 a and the pressure in the rod-side oil chamber 18 b at the work tool cylinder 18 , the control valve 38 sets the oil passage 41 in communication with either the oil passage 45 or the oil passage 46 and sets the oil passage 42 in communication with the other oil passage 45 or 46 that is not in communication with the oil passage 41 . Since the oil passage 41 is in communication with the bottom-side oil chamber 18 a and the oil passage 42 is in communication with the rod-side oil chamber 18 b , the bottom-side oil chamber 18 a comes into communication with either the oil passage 45 or the oil passage 46 and the rod-side oil chamber 18 b comes into communication with the other oil passage 45 or 46 that is not in communication with the oil passage 41 if there is a pressure difference between the bottom-side oil chamber 18 a and the rod-side oil chamber 18 b . In this situation, the bottom-side oil chamber 18 a and the rod-side oil chamber 18 b at the work tool cylinder 18 are made to communicate with each other through the oil passage 47 .
Thus, if the gravitational center of the gripping device 101 is set at a position other than that directly under the rotational center of the gripping device 101 at the front end of the arm 15 , a difference occurs between the pressure in the bottom-side oil chamber 18 a and the rod-side oil chamber 18 b due to the weight of the gripping device 101 . Under these circumstances, the pressure oil in the oil chamber with the higher pressure is allowed to travel through the electromagnetic valve 35 and the control valve 38 and then be released into the oil passage 46 from the oil passage 45 via the oil passage 47 and the electromagnetic switching valve 301 . Since the weight of the gripping device 101 causes the work tool cylinder 18 to extend/contract, the gripping device 101 becomes suspended directly under the front end of the arm 15 due to its own weight. Namely, the gripping device 101 is invariably positioned to face downward along the vertical direction regardless of the attitudes of the boom 13 and the arm 15 .
Accordingly, when the ON/OFF switches 37 and 304 are both in the ON state, the construction machine 100 is in the optimal condition to perform a lowering operation to lower the gripping target object by the gripping device 101 . When the ON/OFF switch 37 is in the ON state and the ON/OFF switch 304 is in the OFF state, the gripping device 101 can be operated in conformance to the displacement of the work target object which constitutes the work load, as in the first embodiment. When neither the ON/OFF switch 37 nor the ON/OFF switch 304 is in the ON state, the gripping device 101 does not follow the displacement of the work target device which constitutes the work load, just as in construction machines in the related art.
In addition to the advantages of the first and second embodiment, the following operational advantage can be further achieved in the construction machine 100 in the third embodiment described above.
(1) The construction machine includes the oil passage 47 connecting the oil passages 45 and 46 with each other and the electromagnetic switching valve 301 by which a pressure oil flow through the oil passage 47 is allowed or disallowed. The electromagnetic switching valve 301 is opened/closed via the ON/OFF switch 304 . Thus, regardless of the attitudes assumed by the broom 13 and the arm 15 , the gripping device 101 can always be positioned to face downward along the vertical direction under its own weight, to engage in a lowering operation to lower the gripping target object with improved operability and work efficiency.
--Examples of Variations--
(1) While the explanation is given above on an assumption that the spool at the control valve 30 is driven as the pilot pressure oil is controlled with the operation lever 34 , the present invention is not limited to this example. For instance, a control valve 50 may be controlled via an electric lever as shown in FIGS. 6 and 7. Reference numeral 51 indicates an electric operation lever and reference numeral 136 indicates a control circuit in the example presented in FIG. 6. The control circuit 136 outputs a command value corresponding to the extent to which the electric operation lever 51 is operated to the solenoid at the control valve 50 and selects the operating position of the electromagnetic switching valve 35 in correspondence to the ON/OFF state of the ON/OFF switch 37 . Reference numeral 51 indicates an electric operation lever and reference numeral 336 indicates a control circuit in the example presented in FIG. 7. The control circuits 336 outputs a command value corresponding to the extent to which the electric operation lever 51 is operated to the solenoid at the control valve 50 . It is to be noted that while the work load follow-up device 200 in FIG. 6 represents an example of a variation of the work load follow-up device 200 in the first embodiment and the work load follow-up device 200 in FIG. 7 represents an example of a variation of the work load follow-up device 200 in the second embodiment, the present invention is not limited to these examples.
(2) While the pressure oil in the high-pressure side oil chamber is absorbed and collected at a single accumulator 39 in the explanation provided above, the present invention is not limited to this example. For instance, the present invention may be adopted in a structure such as that shown in FIG. 8 with accumulators 60 and 61 disposed respectively in parallel to pilot check valves 62 and 63 at the oil passages 41 b and 42 b on the downstream side of the electromagnetic switching valve 35 and relief valves 64 and 65 disposed in series at the accumulators 60 and 61 respectively on the downstream side of the accumulators 60 and 61 . In this case, as the oil passages 41 a and 42 a come into communication with the oil passages 41 b and 42 b , the oil chambers 14 a and 14 b at the boom cylinder 14 become connected to the accumulators 60 and 61 respectively. When the pressure in either oil chamber increases, the pressure oil in the high-pressure side oil chamber is absorbed and collected at the corresponding accumulator 60 or 61 . Namely, the accumulators 60 and 61 functioning as spring elements in the work load follow-up device 201 allow the movement of the boom 13 to follow the displacement of the work target object which constitutes the work load. As a result, advantages similar to those explained earlier are achieved. It is to be noted that the work load follow-up device 201 assuming the structure shown in FIG. 8 does not require a control valve 38 .
(3) While no special mention is included in the explanation above with regard to the type of accumulator that should constitute the accumulator 39 , the accumulator 39 may be, for instance, a bladder-type hydro-pneumatic accumulator, a spring-loaded accumulator or a piston-type accumulator.
(4) While the workload follow-up devices 200 are each connected to one of the hydraulic circuits through which the pressure oil is supplied to the boom cylinder 14 and the work tool cylinder 18 in the explanation above, the present invention is not limited to this example. For instance, the present invention may be adopted in a structure such as that shown in FIG. 9 with a special follow-up cylinder 82 fixed to a frame 80 of the revolving superstructure 11 . The structure further includes a bracket 81 that allows a base end portion 13 a of the boom 13 to slide toward the front and the rear (along the left/right direction in the figure) of the construction machine 100 through a slide groove 83 . The cylinder rod front end of the follow-up cylinder 82 is connected to the base end portion 13 a of the boom 13 with a pin and a work load follow-up device 200 is connected to a hydraulic circuit through which pressure oil is supplied to the follow-up cylinder 82 .
The structure described above allows the base end portion 13 a of the boom 13 to move along the slide groove 83 so as to adjust the attitude of the boom 13 in correspondence to the displacement of the work target object which constitutes the work load. As a result, advantages similar to those described earlier are achieved.
(5) While the spool at the control valve 38 is driven by using the pressure oil from the oil passage 43 connected to the oil passage 41 b and the pressure oil from the oil passage 44 connected to the oil passage 42 b as the pilot pressure oil in the explanation provided above, the present invention is not limited to this example. The present invention may instead be adopted in structures such as those shown in FIGS. 10 and 11, with an electromagnetic control valve 138 disposed in place of the control valve 38 and pressure sensors 91 and 92 installed respectively at the oil passages 41 and 42 . In the examples shown in FIGS. 10 and 11, a control circuit 236 excites/demagnetizes the solenoid at the control valve 138 in correspondence to the pressures detected via the pressure sensors 91 and 92 and the ON/OFF state of the ON/OFF switch 37 to select the optimal spool position at the control valve 138 . In these examples too, advantages similar to those described earlier are achieved. A workload follow-up device 202 assuming the structure shown in either FIG. 10 or FIG. 11 does not require the electromagnetic switching valve 35 . It is to be noted that while the work load follow-up device 202 in FIG. 10 represents an example of a variation of the work load follow-up devices 200 in the first embodiment and the work load follow-up device 202 in FIG. 11 represents an example of a variation of the work load follow-up devices 200 in the second embodiment, the present invention is not limited to these examples.
(6) While the pressure oil in the high-pressure side oil chamber is absorbed and collected and the pressure oil having been collected is then released in the hydraulic circuit which supplies the pressure oil to the hydraulic cylinder in order to operate the front work arm 10 in conformance to the displacement of the work target object which constitutes the work load in the explanation provided above, the present invention is not limited to this example. For instance, the present invention may be adopted in a structure with a mechanical spring disposed between the cylinder and the front work arm 10 so as to operate the front work arm 10 in conformance to the displacement of the work target object which constitutes the work load as the spring extends/contracts.
(7) While the pressure oil in the high-pressure side oil chamber is absorbed and collected and the pressure oil having been collected is then released via the work load follow-up devices 200 engaged in operation in conjunction with the boom cylinder 14 and the work tool cylinder 18 in the explanation provided above, the present invention is not limited to this example. The work load follow-up devices 200 may instead be engaged in operation to absorb and collect the pressure oil in the high-pressure side oil chambers and then release the pressure oil having been collected in conjunction with the boom cylinder 14 and the arm cylinder 16 , or the work load follow-up devices 200 may be engaged in operation to absorb and collect the pressure oil in the high-pressure side oil chambers and then to release the pressure oil having been collected in conjunction with the arm cylinder 16 and the work tool cylinder 18 .
(8) While the electromagnetic switching valve 35 is electrically operated in response to an on/off operation of the ON/OFF switch 37 in the explanation provided above, the present invention is not limited to this example. For instance, a manual switching valve instead of the electromagnetic switching valve 35 , may be utilized to allow the operator to directly operate the switching valve manually. In addition, the structure shown in FIG. 3 may be modified to include pressure sensors each installed at either the oil passage 41 a or the oil passage 42 a so as to enable the drive circuit 36 to switch the electromagnetic switching valve 35 based upon the pressure values detected via the pressure sensors. In this case, the pressure sensors, the drive circuit 36 and the electromagnetic switching valve 35 together function as a switching means for selecting either to follow or not follow the work load.
(9) While the pressure oil in the oil passage 45 is released into the oil passage 46 via the relief valve 40 in the explanation provided above, the present invention is not limited to this example and a proportional electromagnetic pressure control valve may be installed in place of the relief valve 40 . The use of the proportional electromagnetic pressure control valve allows any value to be set as the maximum value for the pressure of the pressure oil applied to the accumulator 39 and thus, a high level of versatility is assured for the construction machine 100 with regard to the type of work it performs.
(10) It is to be noted that a work load follow-up device 200 structured as described earlier may be connected to the hydraulic circuit through which pressure oil is supplied to the cylinder 20 . In this case, when the ON/OFF switch 37 is in the ON state and the pressure in the bottom-side oil chamber (not shown) at the cylinder 20 increases as the work target object (gripping target object) becomes gripped, the bottom chamber comes into communication with the accumulator 39 via the electromagnetic switching valve 35 and the control valve 38 . Since this prevents a sudden increase in the gripping force after the gripping claws 19 grip the work target object, damage to the gripping target object due to an excessive gripping force is prevented. In other words, the gripping target object can be gripped gently. In addition, even if the work target object comes into contact with a gripping claw 19 inadvertently, damage to the work target object or the gripping claw 19 can be prevented since the gripping claw 19 will move along the closing direction or the opening direction in correspondence to the contact force.
(11) While the work load follow-up device 200 is installed only in the hydraulic circuit for driving the work tool cylinder 18 in the third embodiment described above, the present invention is not limited to this example and the work load follow-up device 200 may instead be installed in the hydraulic circuit for another hydraulic cylinder, such as the arm cylinder 16 , which drives the work arm 10 . In addition, a plurality of hydraulic circuits that drive hydraulic cylinders may each include a work load follow-up device 200 .
(12) The embodiment and variations described above may be adopted in various combinations.
The present invention is not limited to the embodiments described above in any way whatsoever and may be adopted in construction machines assuming various structures, as long as they include a structural element that absorbs and collects the pressure oil in an oil chamber where the pressure has risen in response to a work load and releases the pressure oil having been absorbed and collected once the work load is eliminated (or reduced) to allow the pressure oil to flow back into the initial oil chamber and a structural element that allows/disallows absorption and collection of the pressure oil.
By adopting any of the first through third embodiment of the present invention and the variations thereof described above, damage to the work armor the work tool due to an overload can be prevented and a delay in the operating force response can be avoided to assure good operability and sustain the desired level of work efficiency.
Fourth Embodiment
In reference to FIGS. 12 through 16, the fourth embodiment of the construction machine according to the present invention is explained. As shown in FIG. 12, a revolving superstructure 11 is rotatably mounted at a traveling carriage 12 in a construction machine 100 that includes as its base unit a hydraulic excavator. An operator's cab 11 a is disposed at the front of the revolving superstructure 11 . Behind the operator's cab 11 a , a main drive device 11 b , which includes an engine and a hydraulic pump, is disposed.
A front work arm 10 constituted with an articulated arm is mounted at the revolving super structure 11 . The front work arm 10 includes a boom 13 attached to the revolving superstructure 11 so as to swing up/down freely via a boom cylinder 14 , an arm 15 connected to the boom 13 and mounted so as to swing up/down freely via an arm cylinder 16 and a gripping device 101 , which is a work tool connected to the front end of the arm 15 so as to rotate freely along the up/down direction via a work tool cylinder 18 .
FIG. 13 shows the structure of the gripping device 101 . The gripping device 101 includes a gripping device body 17 attached to the front end of the arm 15 , a pair of gripping claws 19 disposed facing opposite each other so as to be able to grasp and hold a target object between their front ends and a cylinder 20 that drives the gripping claws 19 to engage them in opening/closing operation.
FIG. 14 is a circuit diagram pertaining to the hydraulic circuits that drive the boom cylinder 14 and the work tool cylinder 18 in the construction machine 100 . While an explanation is given below on the hydraulic circuit that drives the boom cylinder 14 , the hydraulic circuit that drives the work tool cylinder 18 assumes an identical structure. In addition, while an electromagnetic switching valve 35 and a work load follow-up device 200 to be detailed later in the description of the hydraulic circuits for driving the boom cylinder 14 and the work tool cylinder 18 are not included in the hydraulic circuit that drives the cylinder 20 , the hydraulic circuit adopts a structure which is otherwise similar to that of the hydraulic circuits for driving the cylinders 14 and 18 .
A main pump 31 , a control valve 30 , a main relief valve 33 , a hydraulic operating fluid reservoir 32 , an electromagnetic switching valve 35 and a work load follow-up device 200 are installed to form the hydraulic circuit. In addition, the hydraulic circuit includes an operation lever 34 and a control circuit 36 for controlling the control valve 30 . The operation lever 34 is an electrically operated lever normally referred to as an electric lever. An ON/OFF switch 601 installed in the operator's cab 11 a is connected to the control circuit 36 .
As the main pump 31 , by which pressure oil is supplied to the various actuators of the construction machine 100 , is driven by an engine (not shown), the hydraulic operating fluid in the hydraulic operating fluid reservoir 32 is delivered to the boom cylinder 14 via the control valve 30 . The pressure oil from the main pump 31 is also delivered to the arm cylinder 16 , the work tool cylinder 18 and the cylinder 20 via corresponding control valves (not shown). The maximum pressure in this hydraulic circuit is defined via the main relief valve 33 .
The work load follow-up device 200 includes a control valve 38 , an accumulator 39 and a relief valve 40 . Via the electromagnetic valve 35 , installed in the oil passages 41 and 42 connecting the boom cylinder 14 and the control valve 38 , the upstream side (oil passages 41 a and 42 a ) of the oil passages 41 and 42 are allowed to communicate with the downstream side (oil passages 41 b and 42 b ) of the oil passages 41 and 42 or the upstream side of the oil passages 41 and 42 is disconnected from the downstream side of the oil passages 41 and 42 . The electromagnetic switching valve 35 is connected with the control circuit 36 , which selects the operating position of the electromagnetic switching valve 35 . The oil passage 41 a is connected to a bottom-side oil chamber 14 a at the boom cylinder 14 , whereas the oil passage 42 a is connected to a rod-side oil chamber 14 b at the boom cylinder 14 .
The control valve 38 switches the state of connection of the oil passages 41 b and 42 b to the oil passages 45 and 46 by selecting a spool position in correspondence to the pressures in the oil passages 41 b and 42 b . Namely, the pressure oil from an oil passage 43 connected to the oil passage 41 b and from an oil passage 44 connected to the oil passage 42 b as pilot pressure oil at the control valve 38 to drive the spool. When the pressures in the oil passages 41 b and 42 b are both low or when the pressures in the oil passages 41 b and 42 b are substantially equal to each other, the spool at the control valve 38 assumes the neutral position, disconnecting the oil passages 41 b and 42 b from the oil passages 45 and 46 .
As the pressure in the oil passage 41 b increases and the pressure in the oil passage 42 b decreases, the spool at the control valve 38 shifts from the neutral position and, as a result, the oil passage 41 b becomes connected to the oil passage 45 and the oil passage 42 b becomes connected to the oil passage 46 . If, on the other hand, the pressure in the oil passage 41 b becomes lower and the pressure in the oil passage 42 b becomes higher, the spool at the control valve 38 shifts from the neutral position to connect the oil passage 41 b to the oil passage 46 and the oil passage 42 b to the oil passage 45 . In other words, when the pressure in either the oil passage 41 b or the oil passage 42 b becomes high and the pressure in the other oil passage becomes low, the oil passage where the pressure is high is connected to the oil passage 45 and the oil passage where the pressure is low is connected to the oil passage 46 via the control valve 38 .
The accumulator 39 is connected to the oil passage 45 to absorb the pressure oil in the oil passage 45 or release pressure oil it has accumulated into the oil passage 45 . Once the pressure in the oil passage 45 exceeds a preset pressure level, the pressure oil in the oil passage 45 is released into the oil passage 46 via the relief valve 40 . The relief valve 40 , the pressure level setting for which is lower than the pressure level setting selected for the main relief valve 33 , is installed mainly for purposes of protecting the accumulator 39 . It is to be noted that the oil passage 46 is connected to the hydraulic operating fluid reservoir 32 .
The control circuit 36 outputs a command value corresponding to the extent to which the operation lever 34 is operated to the solenoid at the control valve 30 and selects the operating position of the electromagnetic switching valve 35 based upon the ON/OFF state of the ON/OFF switch 601 and the operating state of the operation lever 34 . Conditions set with regard to the selection of the operating position of the electromagnetic switching valve 35 by the control circuit 36 are to be described in detail later. As the solenoid at the electromagnetic switching valve 35 becomes excited by the control circuit 36 , the spool is driven so as to set the oil passages 41 a and 42 a in communication with the oil passages 41 b and 42 b . As the solenoid at the electromagnetic switching valve 35 becomes demagnetized by the control circuit 36 , the spool is driven with the force of the spring at the electromagnetic switching valve 35 , thereby disconnecting the oil passages 41 a and 42 a from the oil passages 41 b and 42 b.
As a specific operation lever is operated in the construction machine 100 structured as described above, the spool of the control valve corresponding to the relevant hydraulic cylinder is driven and the hydraulic cylinder is driven at a speed reflecting the extent to which the operation lever is operated. For instance, in response to an operation of the operation lever 34 installed in conjunction with the boom cylinder 14 , the control circuit 36 outputs a control signal so as to drive the spool at the control valve 30 in correspondence to the extent to which the operation lever 34 is operated. As a result, the boom cylinder 14 is driven at a speed reflecting the extent to which the operation lever 34 is operated.
As pressure oil is delivered into the bottom-side oil chamber 14 a at the boom cylinder 14 , the boom 13 is driven to swing upward relative to the revolving superstructure 11 , whereas if pressure oil is delivered into the rod-side oil chamber 14 b at the boom cylinder 14 , the boom 13 is driven to swing downward relative to the revolving superstructure 11 . As pressure oil is delivered into a bottom-side oil chamber (not shown) at the arm cylinder 16 , the arm 15 is driven to swing downward relative to the boom 13 , whereas if pressure oil is delivered into a rod-side oil chamber (not shown) at the arm cylinder 16 , the arm 15 is driven to swing-upward relative to the boom 13 .
As pressure oil is delivered into a bottom-side oil chamber 18 a at the work tool cylinder 18 , the gripping device 101 is driven to swing downward relative to the arm 15 , whereas if pressure oil is delivered into a rod-side oil chamber 18 b , the gripping device 101 is driven to swing upward relative to the arm 15 . As pressure oil is delivered to a bottom-side oil chamber (not shown) at the cylinder 20 , the pair of gripping claws 19 are driven along the gripping direction, whereas if pressure oil is delivered into a rod-side oil chamber (not shown) at the cylinder 20 , the pair of gripping claws 19 are driven along the releasing direction.
--Flowchart--
FIG. 15 presents a flowchart of the control processing operation executed to control the individual electromagnetic switching valves 35 . As an ignition switch (not shown) is turned on at the construction machine 100 , the program in conformance to which the processing shown in FIG. 15 is executed is started up and is executed in the control circuit 36 . In step S 701 , information indicating the states assumed at various components of the construction machine 100 is obtained. More specifically, information indicating the extent to which the operation lever 34 has been operated to drive the cylinder 20 for the gripping device 101 and information indicating the state of the ON/OFF switch 601 are obtained. Once step S 701 is executed, the operation proceeds to step S 702 to make a decision based upon the information having been obtained in step S 701 as to whether or not the ON/OFF switch 601 is currently in the ON state.
If an affirmative decision is made in step S 702 , the operation proceeds to step S 703 to determine the operating state of the construction machine 100 . More specifically, a decision is made as to whether or not the operation lever 34 , which is operated to drive the cylinder 20 , has been operated beyond the dead zone so as to grip the target object with the gripping device 101 . If an affirmative decision is made in step S 703 , the operation proceeds to step S 704 to output an open command for the electromagnetic switching valve 35 , i.e., to excite the solenoid at the electromagnetic switching valve 35 , before the operation makes a return. If a negative decision is made in step S 702 or in step S 703 , the operation proceeds to step S 705 to output a close command for the electromagnetic switching valve 35 , i.e., to demagnetize the solenoid at the electromagnetic switching valve 35 , before the operation makes a return.
--Operations of the Work Load Follow-Up Device 200 and the Boom Cylinder 14 --
As the electromagnetic switching valve 35 is controlled as described above, the work load follow-up device 200 and the boom cylinder 14 are engaged in operation as follows. If the ON/OFF switch 601 is in the ON state (an affirmative decision is made in step S 702 ) and the operation lever 34 by which the cylinder 20 is driven has been operated beyond the dead zone so as to grip the target object with the gripping device 101 (an affirmative decision is made in step S 703 ), the solenoid at the electromagnetic switching valve 35 is excited (step S 704 ).
As a result, the oil passages 41 a and 42 a are set in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , allowing the pressure oil in the bottom-side oil chamber 14 a and the rod-side oil chamber 14 b at the boom cylinder 14 to flow into the downstream side of the electromagnetic switching valve 35 . In other words, when the ON/OFF switch 601 is in the ON state and the operation lever 34 by which the cylinder 20 is driven has been operated beyond the dead zone along the gripping direction, the behavior of the boom cylinder 14 is affected by the control valve 38 and the accumulator 39 . As explained earlier, when pressure oil is delivered into the bottom-side oil chamber 14 a , the boom 13 is driven to swing upward relative to the revolving superstructure 11 in response to an operation of the operation lever 34 by which the boom 13 is operated, whereas when pressure oil is delivered into the rod-side oil chamber 14 b , the boom 13 is driven to swing downward relative to the revolving superstructure 11 in response to an operation of the operation lever 34 .
With the operation lever 34 , by which the boom 13 is operated, remaining in the operating state, the pressure in either the oil chamber 14 a or the oil chamber 14 b , to which the pressure oil is supplied via the control valve 30 , rises as the gripping claws 19 come into contact with the work target object, in correspondence to the force (work load) with which the gripping claws 19 contact the work target object. Then, as the pressure in either of the oil passages 41 b and 42 b in communication with the oil chambers 14 a and 14 b becomes high and the pressure in the other oil passage becomes low, the oil passage where the pressure has risen to a high level is connected with the oil passage 45 and the oil passage where the pressure has decreased is connected to the oil passage 46 via the control valve 38 . As a result, the pressure oil in either the oil chamber 14 a or the oil chamber 14 b (hereafter referred to as the “high-pressure side oil chamber”) communicating with the oil passage where the pressure has risen is absorbed by the accumulator 39 . Since this allows the accumulator 39 to function as a spring element against the work load, a sudden increase in the work load is prevented.
If the operation lever 34 , by which the boom 13 is operated, remains in the operating state after the gripping claws 19 contact the work target object, the pressure oil in the high-pressure side oil chamber (or the pressure oil flowing from the control valve 30 toward the high-pressure side oil chamber) is absorbed and collected at the accumulator 39 until the pressure rises to the pressure level setting selected for the relief valve 40 . The pressure oil in the high-pressure side oil chamber (or the pressure oil flowing from the control valve 30 toward the high-pressure side oil chamber) is released from the relief valve 40 into the hydraulic operating fluid reservoir 32 once the pressure rises to the pressure level set for the relief valve 40 . Namely, the accumulator 39 is protected via the relief valve 40 which regulates the pressure of the pressure oil applied to the accumulator 39 . In addition, the relief valve 40 allows the gripping claws 19 to contact the work target object with a work load or contact force corresponding to the pressure setting selected for the relief valve 40 .
If a swinging motion of the arm 15 , for instance, causes the gripping claws 19 to contact the work target object while the operation lever 34 , by which the boom 13 is operated, is in a non-operating state, the pressure in either the oil chamber 14 a or the oil chamber 14 b at the boom cylinder 14 rises to a level corresponding to the work load. When the operation lever 34 , by which the boom 13 is operated, is in the non-operating state, the pressure oil in the high-pressure side oil chamber does not flow to the outside via the control valve 30 . However, since the oil passages 41 a and 42 a are in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , the pressure oil in the high-pressure side oil chamber flows into the accumulator 39 via the control valve 38 as explained earlier.
As a result, the pressure oil in the high-pressure side oil chamber is absorbed and collected at the accumulator 39 in correspondence to the work load, and the boom cylinder 14 extends/contracts in correspondence to the quantity of pressure oil accumulated at the accumulator 39 to cause a swinging motion of the boom 13 . As the work load is lessened, the pressure oil having been collected at the accumulator 39 flows back into the high-pressure side oil chamber and thus, the boom cylinder 14 extends/contracts. In other words, a swinging motion of the boom 13 corresponding to the level of the work load is induced. Namely, the swinging motion of the boom 13 occurring as the pressure oil in the high-pressure side oil chamber is absorbed and collected at the accumulator 39 and then released from the accumulator 39 in correspondence to the work load, allows the attitude of the front work arm 10 to be adjusted so as to follow the displacement of the work target object coming into contact with the gripping claws 19 to apply an external force to the gripping claws 19 . Thus, the attitude of the gripping device 101 is adjusted in correspondence to the external force applied to the gripping claws 19 .
If the pressure in the oil passage 45 is equal to or less than the pressure level setting selected for the relief valve 40 at the time of the work load application, the pressure oil in the high-pressure side oil chamber will not have flowed back into the hydraulic operating fluid reservoir 32 via the relief valve 40 . Under these circumstances, as the work load application stops and the pressure oil having been collected at the accumulator 39 flows back to the high-pressure side oil chamber, the cylinder rod at the boom cylinder 14 resumes the pre-work load application extension position.
If the pressure in the oil passage 45 exceeds the pressure level setting selected for the relief valve 40 at the time of the work load application, the pressure oil in the high-pressure side oil chamber flows back into the hydraulic operating fluid reservoir 32 via the relief valve 40 . Under these circumstances, as the work load application stops and the pressure oil having been collected at the accumulator 39 flows back into the high-pressure side oil chamber, the cylinder rod at the boom cylinder 14 moves back closer to the pre-work load application extension position but stops at a position short of the full pre-work load application extension position by an extent matching the quantity of pressure oil having flowed back into the hydraulic operating fluid reservoir 32 .
As described above, when the oil passages 41 a and 42 a are set in communication with the oil passages 41 b and 42 b via the electromagnetic switching valve 35 , the work load follow-up device 200 is able to affect the operation of the boom cylinder 14 . In other words, the ON/OFF switch 601 simply needs to be turned on to adjust the attitude of the boom 13 in conformance to the external force applied to the gripping claws 19 when gripping the target object with the gripping device 101 .
For instance, if the gripping target object assumes a position offset from the midpoint between the two gripping claws 19 facing opposite each other, the gripping target object first contacts one of the gripping claws 19 as shown in FIG. 16A. In other words, only one of the gripping claws