BEST MODE FOR CARRYING OUT THE INVENTION

[0089] In the following, a hand-held powered wrench used in an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0090] FIG. 1 is a vertically sectioned side view of a principal part of an powered wrench designed to produce rebound on impact, which is an example of a hand-held powered wrench used in the present invention. It is to be noted that all powered wrenches and nut runners mentioned below, including an impact wrench and an impulse wrench, means those of hand-held type.

[0091] In the diagram, 1 denotes an impact wrench used in the present invention. 2 denotes an air motor disposed in an interior of a casing 1b of a gripping portion 1a of a rear part of the impact wrench 1 at the bottom. 3 denotes a driving shaft of the air motor 2. 4 denotes a cylindrical rotary member integrally coupled with a front end of the driving shaft 3. A disk-like rear wall panel 4a of the cylindrical rotary member is integrally coupled with the driving shaft 3 at the center thereof via the fitted structure comprising a quadrangular projection and a complementary depression.

[0092] The impact wrench 1 is one embodied form of the hand-held impact wrench as recited in claims and is a tool designed for both screw tightening and screw loosening. The air motor 2 is one embodied form of the torque generating means as recited in claims. The cylindrical rotary member 4 is one embodied form of the rotary member as recited in claims.

[0093] The air motor 2 is structured to revolve at high velocity in a clockwise direction or an counterclockwise direction by compressed air fed thereto from outside through an air feed passage (not shown) arranged in the gripping portion 1a by a switching operation of a control lever 20 and a selector valve (not shown), as already known. The torque of the cylindrical rotary member 4 which is driven to rotate together with the driving shaft 3 of the air motor 2 revolved is transmitted, through a hammering force transmission mechanism 5 mentioned later, to a driven shaft 6 called an anvil block having a front end projecting forward from a front end of the casing 1b and, in turn, to a socket (not shown) attached to the front end of the driven shaft 6, so as to tighten a screw member fitted to the socket in the known manner.

[0094] A rear portion of the driven shaft 6 is formed into a trunk 6a of the body having a large diameter, and the trunk 6a is mounted to the center of the cylindrical rotary member 4. The cylindrical rotary member 4 is rotated around the trunk 6a of the driven shaft 6, and the torque is transmitted to the driven shaft 6 through a hammering force transmission mechanism 5, as mentioned above.

[0095] The hammering force transmission mechanism 5 comprises, as shown in FIGS. 1 and 3, a hammering boss 5a projecting inwardly from a proper location of an inner periphery of the cylindrical rotary member 4 and the anvil block 5b which is supported in a semi-circular support groove 6b formed on the trunk 6a of the driven shaft 6 in such a manner as to freely sway from side to side. The anvil block 5b is put in the state in which it is inclined with respect to a horizontal direction and then the hammering boss 5a is collided with one upswept end face of the anvil block 5b, so as to transmit the torque of the cylindrical rotary member 4 to the driven shaft 6 side.

[0096] The hammering force transmission mechanism 5 is one embodied form of the torque transmission mechanism as recited in claims.

[0097] As shown in FIG. 4, when a cam plate 5c at a front end of the anvil block 5b is positioned within a concave portion 5d having a given circular length circumferentially formed in the inner periphery of the cylindrical rotary member 4 at the front end thereof, the anvil block is kept in its neutral position in which it is not allowed to engage with the hammering boss 5a. When the cam plate comes out from the concave portion 5d and moves in contact with the inner periphery of the cylindrical rotary member 4, the anvil block takes an inclined position to collide with the hammering boss 5a. The anvil block 5b is under pressure in the direction for the anvil block 5b to be always kept in the neutral position from an anvil block pressing member 5e, a spring 5f and a spring receiving member 5g which are provided in the trunk 6a of the driven shaft 6. The spring receiving member 5g is in contact with an inner cam surface 4b of the cylindrical rotary member 4. Further, a concave portion 5h for allowing the anvil block 5b to be inclined is formed in the inner periphery of the cylindrical rotary member 4 at both sides of the hammering boss 5a. As this structure of the impact wrench is already known, the detailed description thereon is omitted.

[0098] While in the embodiment of the present invention, the hammering is produced once for each rotation of the cylindrical rotary member 4, it is needless to say that the present invention is also applicable to the hand-held impact wrench designed to produce the hammering twice or third times or more for each rotation of the cylindrical rotary member.

[0099] A rotary detecting member 7 comprising a gear having a predetermined number of teeth 7a around its outer periphery is fixedly mounted to the cylindrical rotary member 4 at the rear end thereof to be integral therewith, as shown in FIG. 2. On the other hand, a pair of detecting sensors 8a, 8b comprising semi-conducting magneto-resistive elements are mounted around an inner periphery of the non-revolving casing 1b so as to confront the rotary detecting member 7, leaving a given circumferential space therebetween. The rotation of the rotary detecting member 7 is detected by the detecting sensors 8a, 8b, and the output signals are input to an input circuit 10 electrically connected to the detecting sensors 8a, 8b. The input circuit 10 is connected to a solenoid valve 19 arranged in a compressed air supply hose 18 through an amplifying part 11, a waveform shaping part 12, a central processing part 13, a rotation angle signal outputting part 14, a completed screw tightening detecting part 15, a solenoid valve controlling part 16 and an output circuit 17.

[0100] It is noted here that a completed screw loosening detecting part 15B shown in FIG. 1 is used to make a screw loosening control of the impact wrench 1.

[0101] The rotary detecting member 7 and the detecting sensors 8a, 8b form one embodied form of the detecting means as recited in claims.

[0102] In the arrangement mentioned above, electric components provided between the input circuit 10 and the output circuit 17 are disposed in a controller (not shown) located at the outside of the impact wrench. The controller and the solenoid valve 19 can be housed in the impact wrench. The solenoid valve 19 and the solenoid valve controlling part 16 can be substituted by a compressed air supply shut-down device and an adequate controlling part.

[0103] Now, the method of reading a rotation angle of screw member, such as bolt and nut, in the impact wrench thus constructed will be described below.

[0104] First, a screw member 9 to be tightened is fitted to the socket mounted on the front end portion of the driven shaft 6 and a predetermined screw tightening angle is previously input to the completed screw tightening detecting part 15. Then, when the solenoid valve 19 is opened and the control lever 20 of the impact wrench is pressed to feed compressed air to the impact wrench, so as to rotate the air motor 2 in the screw tightening direction (in the clockwise direction for the right-hand screw member), the driving shaft 3 and the cylindrical rotary member 4 are then rotated together. This rotation causes the cam plate 5c to shift from the concave portion 5d, while contacting with the inner periphery of the cylindrical rotary member 4, so that the anvil block 5b is tilted. The frictional resistance between the spring receiving member 5g and the inner cam surface 4b causes the cylindrical rotary member 4 and the driven shaft 6 to rotate together, so as to rotatively propel the screw member 9 at high velocity in the tightening direction until the screw member is seated.

[0105] While the screw member 9 is rotatively propelled, in other words, before the screw member 9 seats on a bearing surface, little load is applied to the driven shaft 6 side, so that the rotary detecting member 7 comprising the gear that rotates together with the cylindrical rotary member 4 revolves at high velocity in the direction of tightening the screw member 9 and the teeth 7a runs through over the detecting sensors 8a, 8b continuously. Then, pulse signals of waveform of out-of-phase are generated by the detecting sensors 8a, 8b, but the pulse signals are not used for arithmetical operation to detect the rotation angle of the screw member until the screw member is seated.

[0106] The driven shaft 6 is driven to revolve together with the cylindrical rotary member 4 at high velocity through the hammering force transmission mechanism 5 comprising the hammering boss 5a and the anvil block 5b. When the screw member 9 is seated on the bearing surface, a resistance torque (load) generates in the driven shaft 6 and the rotation of the driven shaft 6 slows down to nearly standstill rapidly. Then, the hammering boss 5a and the anvil block 5b come into collision with each other to start hammering. After the end of the hammering, an elastic force of the spring 5f pressing the anvil block 5b overcomes a force to bring the hammering boss 5a and the anvil block 5b into engagement, so that the engagement therebetween is released and the cylindrical rotary member 4 is allowed to run freely around the trunk 6a of the driven shaft 6.

[0107] While the cylindrical rotary member 4 is running freely, the cylindrical rotary member 4 is accelerated by the driving torque of the air motor 2, while on the other hand, the cam plate 5c is brought into contact with the inner periphery of the cylindrical rotary member 4, so that the anvil block 5b is tilted, as shown in FIGS. 5 and 6. After the end of the free running of the cylindrical rotary member 4, the hammering boss 5a is brought into engagement with the anvil block 5b with impact, as shown in FIG. 7. This hammering causes the torque of the cylindrical rotary member 4 to be transmitted to the driven shaft 6 so as to rotate the driven shaft 6 in the tightening direction by a certain angle only. Then, the screw tightening angle is detected by the rotary detecting member 7 and the detecting sensors 8a, 8b in the manner mentioned later.

[0108] When the screw member 9 is tightened up, a resistance force larger than the torque of the air motor 2 is generated at the driven shaft 6 side. At the moment when the driven shaft 6 is finished rotating by a certain angle in the tightening direction by the hammering force of the hammering boss 6a, the cylindrical rotary member 4 rebounds in the opposite direction to the tightening direction and then runs freely in the tightening direction through the driving torque of the air motor 2, as shown in FIG. 8. This brings the hammering boss 5a into engagement with the anvil block 5b again with impact in the same manner as above, so as to rotate the driven shaft 6 in the screw tightening direction further. The screw tightening angle at that time is read by the rotary detecting member 7 and the detecting sensors 8a, 8b. Subsequently, after the free running of the cylindrical rotary member 4, the screw tightening angle is detected every time the hammering boss 5a comes into collision with the anvil block 5b. When the cumulative total of screw tightening angle reaches a predetermined screw tightening angle, the feed of the compressed air is automatically stopped to complete the tightening of the screw member 9.

[0109] Referring now to FIGS. 9-15, the method of detecting the screw tightening angle by use of the rotary detecting member 7 and the detecting sensors 8a, 8b will be described.

[0110] The detecting sensors 8a, 8b are so structured that when a tooth of the rotary detecting member 7 rotating together with the cylindrical rotary member 4 passes through the detecting sensors, the detecting sensors can detect one pulse and measure the velocity of the cylindrical rotary member 4 from the number of passing teeth per unit of time. In each of the diagrams above, (a) shows the operative relation between the cylindrical rotary member 4 and the driven shaft 6; (b) illustrates a screw tighening angle of the screw member 9; and (c) plots a time shift in rotation velocity of the cylindrical rotary member 4 and screw tightening angle of the screwing member 9 every time the hammering is provided. It is noted that the screw member 9 used is a right-hand thread to be tightened in the clockwise direction.

[0111] FIG. 9 is a view showing the free running state of the cylindrical rotary member 4. In this state, the torque of the cylindrical rotary member 4 is not transmitted to the driven shaft 6 from the hammering force transmitting mechanism 5 comprising the hammering boss 5a and the anvil block 5b, so that the cylindrical rotary member 4 gradually accelerates, while freely running {circle over (1)} in the clockwise direction, as depicted by an upward-sloping line in FIG. 9(c) and FIG. 15.

[0112] The detecting sensors 8a, 8b are structured to output pulse signals of different in phase by 90 degree from each other, as mentioned above. While the rotary detecting member 7 is rotating in the screw tightening direction (in the clockwise direction), the waveform of the pulse signal is output from one detecting sensor 8a, whose phase is more advanced by 90 degree than that of the other detecting sensor 8b, as shown in FIG. 15. On the other hand, when the hammering boss 5a collides with the anvil block 5b, for the hammering, and then the rotary detecting member 7 rebounds in the counterclockwise direction together with the cylindrical rotary member 4, the phases of the signals from the both detecting sensors 8a, 8b are reversed. In other words, the waveform of the pulse signal is output from the other detecting sensor 8b, whose phase is more advanced by 90 degree than that of the one detecting sensor 8a.

[0113] When the rotary detecting member 7 is rotating in the screw tightening direction (in the clockwise direction), the waveform from the one detecting sensor 8a comes to be at a high level (H) when the waveform from the other detecting sensor 8b is upended (↑). When the rotary detecting member 7 is rotating in the rebounding direction (in the counterclockwise direction), the waveform from the one detecting sensor 8a comes to be at a low level (L). Q₀ is the detection signal indicating the rotation direction. The waveform (H) or (L) is kept at the high level or at the low level until the rotation direction is changed. On the other hand, the signal Q₁ maintains exactly the opposite state to the signal Q₀. The central processing part 13 is constituted to discriminate between the tightening direction (clockwise direction) or the rebounding direction (counterclockwise direction) by the signal Q₀ or Q₁ and detect the respective directional pulse signal. Thus, the free running {circle over (1)} is detected by detecting the pulse signal in the normal rotation direction (clockwise pulse signal).

[0114] Then, at the moment at which the hammering boss 5a collides with the anvil block 5b after the free running of the cylindrical rotary member 4, the rotation velocity of the cylindrical rotary member 4 becomes maximum {circle over (2)}, as shown in FIG. 10(c). From this state, the tightening of the screw member 9 by the hammering is started. At this time of screw tightening, the driven shaft 6 rotated in the tightening direction via the hammering force transmission mechanism 5 consumes energy for tightening the screw member 9, so that when the first screw tightening is provided, the cylindrical rotary member 4 is decelerated {circle over (3)} from the maximum velocity {circle over (2)}, as indicated by a downward-sloping line shown in FIG. 11(c) and FIG. 15. Thereafter, the cylindrical rotary member 4 rebounds {circle over (4)} in the counterclockwise direction, as shown in FIG. 12(c).

[0115] A point of time at which the deceleration {circle over (3)} is started from the maximum velocity {circle over (2)} is determined by detecting the state of rotation of the rotary detecting member 7 by use of the detecting sensors 8a, 8b, as shown in FIG. 15. Specifically, as the cylindrical rotary member 4 is accelerated in the free running, the widths of the pulse signals detected by the detecting sensors 8a, 8b gradually decreases, and at the moment at which the hammering boss 5a collides with the anvil block 5b, the widths of the pulse signals becomes minimum. Thereafter, during the time from after the start of deceleration of the cylindrical rotary member 4 to the end of hammering (the start of rebounding), the widths of the pulse signals in the clockwise direction increase gradually. These pulses of gradually decreasing widths and those of gradually increasing widths are output from the detecting sensors 8a, 8b. They are detected by the central processing part 13 as the clockwise pulse signals to judge the point of time at which the pulse widths are narrowed to minimum as the starting point of tightening of the screw member 9 by hammering (starting point of deceleration), as mentioned above.

[0116] Thus, after the detection of the starting point of deceleration of the cylindrical rotary member 4, the rotation angle of the rotary detecting member 7 is detected by the detecting sensors 8a, 8b throughout the deceleration {circle over (3)} or during the period from the start of deceleration to the end of hammering. In other words, the screw tightening angle ΔH₁ of the screw member 9 is determined from the number of pulses equivalent to the number of teeth of the rotary detecting member 7 passing through the detecting sensors 8a, 8b during the deceleration. Then, the cylindrical rotary member 4 rebounds {circle over (4)} in the counterclockwise direction, as mentioned above. The pulses generated at the time of rebound {circle over (4)} are used for determination of the starting point of control and for judgment of bad tightening such as a unitary rotation of bolt and nut.

[0117] As shown in FIG. 12, after the rebound {circle over (4)} of the cylindrical rotary member 4 gradually decelerates to the stop, the cylindrical rotary member 4 runs freely {circle over (1)} again with acceleration in the clockwise direction by the torque from the air motor 2, as shown in FIG. 13. Then, the hammering boss 5a is brought into collision with the anvil block 5b, from the moment of which the rotation velocity of the cylindrical rotary member 4 is decelerated {circle over (3)}, as shown in FIG. 14. The rotation angle of the rotary detecting member 7 or the screw tightening angle ΔH₂ of the screw member 9 formed during the deceleration {circle over (3)} from the start of deceleration to the end of hammering is detected by the rotary detecting member 7 and the detecting sensors 8a, 8b in the same manner as that mentioned above.

[0118] Thereafter, every time when the cylindrical rotary member 4 is decelerated {circle over (3)} by the hammering after the free running {circle over (1)}, the screw tightening angles ΔH of the screw member 9 formed during the deceleration {circle over (3)} from the start of deceleration to the end of hammering are integrated in sequence by the central processing part 13 in the same manner. Then, when the integrated angle of the screw tightening angles reaches a preset screw tightening angle of the screw member 9, the rotation angle signal outputting part 14 outputs signals to the solenoid valve controlling part 16 through the completed screw tightening detecting part 15, to stop the solenoid valve 19 via the output circuit 17. This operation can also be realized by use of a logical circuit or software.

[0119] Thus, the screw tightening angle of the screw member 9 is determined by detecting the deceleration of the cylindrical rotary member 4 after the hammering and the rotation angle of the rotary detecting member 7 formed during the time from the start of deceleration to the end of hammering (the start of rebound). For example, when the hammering is provided 20 times till a preset screw tightening angle (e.g. 50°) is formed; the working time from the start to the end is 1 sec.; and the average time for the cylindrical rotary member 4 to decelerate every time the hammering is provided is 0.001 sec., it follows that the total time for the screw member 9 to be tightened is 0.001×20=0.02 sec. It follows from this that even if a wobbling of e.g. 30° is caused in a 1 second of screw tightening work, an angle error given to the screw tightening angle is 30°×0.02/1=0.6°, which is very limited (1.2%), as compared with the preset screw tightening angle (50°), and can be said that the proportion of the error caused by the wobbling is very minute.

[0120] The rotation angle of the rotary detecting member 7 during the deceleration of the cylindrical rotary member 4 may be detected by a different method than the method mentioned above. Specifically, the rotation angle formed when the rotary detecting member 7 is rotated in the tightening direction only or the free running angle formed every time the cylindrical rotary member 4 rotates in the tightening direction, and the rotation angle formed when it rotates in the tightening direction until one screw tightening is completed, including the free running angle, are detected by the detecting sensors.

[0121] FIGS. 16 and 17 illustrate the alternative detecting method. After the cylindrical rotary member 4 gradually accelerates, while running freely {circle over (1)} in the clockwise direction, as indicated by an upward-sloped line, the hammering boss 5a collides with the anvil block 5b and the cylindrical rotary member 4 decelerates {circle over (3)}, as indicated by a downward-sloped line, and rebounds {circle over (4)}. In this process, one screw tightening is provided. When A₁ is a starting point of the free running {circle over (1)}; A₂ is a point of time at which the hammering is performed (maximum velocity); A₃ is a point of time at which the tightening is completed; and A₄ is a point of time at which the rebound is started, the rotation of the cylindrical member 4 is represented as shown in FIG. 17.

[0122] From FIG. 17, the screw tightening angle (screwing angle) is given by:

ΔH=F−J Eq. 2

[0123] where F is a clockwise rotation angle of the cylindrical rotary member 4 per rotation of the same, J is a clockwise free running angle of the same per rotation thereof, and ΔH is the screw tightening angle (screwing angle). The screw tightening angle can be calculated by detecting the clockwise rotation angle F and the clockwise free running angle J by use of the rotary detecting member 7 and the detecting sensors 8a, 8b. In other words, the screw tightening angle is calculated by detecting the number of teeth of the rotary detecting member 7 passing through the detecting sensors 8a, 8b. In this method, even when a wobbling is caused in the course of the detection of the clockwise free running angle J and the clockwise rotation angle F, since the angle of the wobbling generated at a point of time within the free running from the point of time A₁ to the point of time A₂ is included in both of those angles, the angle of wobbling is balanced out by the both angles. Thus, even when the wobbling is caused, since the influence is limited to only a very short time (from the point of time A₂ to the point of time A₃) during which the screw member 9 is tightened by the driven shaft 6, it is substantially a negligible level, and as such can provide the screw tightening work with little error.

[0124] Next, an impulse wrench that is so structured that the rebound is not produced at the time of hammering or torque impulse will be described as another example of the hand-held powered wrench used in the present invention.

[0125] Shown in FIGS. 18 and 19 is an embodied form thereof. The impulse wrench is provided with an air motor 2A in an interior of a casing 1A at the rear portion thereof having an integrally provided grip portion 1a in the bottom. A center portion of a rear wall panel of an oil cylinder 4A is integrally coupled with a front end portion of a rotational driving shaft 3A of the air motor 2A via their fitted structure comprising a hexagonal projection and a complementary depression.

[0126] The impulse wrench is one embodied form of the hand-held powered wrench as recited in claims and is a tool designed for both screw tightening and screw loosening. The air motor 2A is one embodied form of the torque generating means as recited in claims. The oil cylinder 4A is one embodied form of the rotary member as recited in claims.

[0127] The air motor 2A is structured to revolve at high velocity in a clockwise direction or an counterclockwise direction by compressed air fed thereto from outside through an air feed passage (not shown) arranged in the gripping portion la by a switching operation of a control lever 20 and a selector valve (not shown), as in the same manner as the impact wrench.

[0128] The torque of the oil cylinder 4A which is rotated together with the driving shaft 3A of the air motor 2A revolved is transmitted to a driven shaft 6A having a front end projecting forward from a front end of the casing 1A and, in turn, to a socket (not shown) attached to the front end of the driven shaft 6A, through a hammering force transmission mechanism 5A arranged in the oil cylinder 4A, so as to tighten a screw member fitted to the socket.

[0129] The hammering force transmission mechanism 5A has sealing surfaces 51, 51, 52, 52 formed at a plurality of locations (four locations in the diagram) in the inner periphery of the oil cylinder 4A, as shown in FIG. 19. On the other hand, the driven shaft 6A side has a blade insertion groove 53 in which at least one blade 55 (two blades are shown in the diagram) which is put in always contact with the inner periphery of the oil cylinder 4A by an elastic force of a spring 54 is received in a radially retractable manner. The rotation of the oil cylinder 4A brings the blades 55 and projected portions 56, 56 projecting from the driven shaft 6A with different phases of 180° into close contact with their respective sealing surfaces 51, 52 in a oil-tight manner. When the oil cylinder 4A is rotated slightly from this state, a low pressure chamber L and a high pressure chamber H are produced by oil in the oil cylinder 4A between the neighboring sealing surfaces 51 and 52. The differential pressure therebetween permits the hammering torque to be transmitted to the driven shaft 6A side through the both blades 55, 55, so as to generate the tightening force in the same rotation direction as that of the oil cylinder 4A.

[0130] The hammering force transmission mechanism 5A is one embodied form of the torque transmission mechanism as recited in claims. While in this example, the high-pressure chamber H is formed once for each rotation of the oil cylinder 4A, it may be formed twice for each rotation of the same.

[0131] In the impulse wrench thus constructed, the rotary detecting member 7 comprising a gear having a predetermined number of teeth 7a is fixedly mounted to the outer periphery of the oil cylinder 4A so as to be integral therewith.

[0132] On the other hand, the pair of detecting sensors 8a, 8b comprising semi-conducting magneto-resistive elements are mounted around an inner periphery of the non-revolving casing 1A so as to confront the rotary detecting member 7, leaving a given circumferential space therebetween. As the control circuit for the signals generated by the rotation of the rotary detecting member 7 to be transmitted from the input circuit to the solenoid valve is identical to that of the impact wrench mentioned above, the description thereon is omitted.

[0133] Now, description on the method of reading a rotation angle of screw member, such as bolt and nut, by the impulse wrench thus constructed will be given below. A screw member 9 to be tightened is fitted to the socket mounted on the front end portion of the driven shaft 6A and a predetermined screw tightening angle is previously input to the completed screw tightening detecting part 15. Then, when the control lever 20 is pressed to feed compressed air to the impulse wrench, so as to rotate the air motor 2A in the screw tightening direction (in the clockwise direction for the right-hand screw member), the driving shaft 3A and the oil cylinder 4A are rotated together. This rotation is transmitted to the driven shaft 6A through the hammering force transmission mechanism 5A to cause the oil cylinder 4A and the driven shaft 6A to rotate together, so as to rotatively propel the screw member 9 at high velocity in the screw tightening direction.

[0134] When the screw member 9 is seated on a bearing surface, a resistance torque (load) is generated at the driven shaft 6A, to cause rotation of the driven shaft 6A to decelerate to a nearly stop rapidly, while on the other hand, the oil cylinder 4A is rotated in the tightening direction at a accelerated rate by a driving torque from the air motor 2A side. After the blades 55 and the projected portions 56 are brought into close contact again with the sealing surfaces 51, 52 in the oil-tight manner, respectively, the high pressure chamber H is produced to transmit the rotational tightening force to the driven shaft 6A side with impact, so as to rotate the driven shaft 6A in the tightening direction by a certain angle.

[0135] At this time, the oil cylinder 4A is started decelerating through the oil-tight contact with the driven shaft side and, in the middle of deceleration, the rotation angle of the oil cylinder 4A, or the screw tightening angle of the screw member 9 through the driven shaft 6A, is detected by the rotary detecting member 7 and the detecting sensors 8a, 8b, as mentioned later.

[0136] The screw tightening angle of the screw member 9 is measured in the middle of deceleration of the oil cylinder 4A. Though the deceleration is also caused before the screw member 9 is seated on the bearing surface, the deceleration of the oil cylinder 4A before the screw member 9 is seated is not included in the screw tightening angle of the screw member 9. The judgment on whether the screw member 9 is seated or not is performed in the manner as shown in FIGS. 20(a< /italic>), (b). Specifically, before the screw member 9 is seated, some acceleration and deceleration is generated in rotation velocity of the oil cylinder 4A, as shown in FIG. 20(a). In the rotation of the oil cylinder 4A, a value T_k obtained when the rotation velocity becomes maximum and a value V_k obtained when the rotation velocity becomes subsequent minimum are detected.

[0137] When the minimum value V_k of rotation velocity is over a preset lower limit (e.g. ⅓ of the maximum value T_k of rotation velocity), in other words, when only a slight deceleration is generated, the screw member 9 is judged to be not yet seated, so that this slightly decelerated rotation of the oil cylinder 4A is not used for the calculation of the screw tightening angle of the screw member 9.

[0138] When the screw member 9 is seated, the difference between the maximum value T_k+1 and the subsequent minimum value V_k+1 of the rotation velocity of the oil cylinder 4A becomes significant, as shown in FIG. 20(b). When the minimum value V_k+1 is under a preset lower limit (e.g. ⅓ of the maximum value T_k+1 of rotation velocity), in other words, when a significant deceleration is generated, the screw member 9 is judged to be already seated, so that this significantly decelerated rotation of the oil cylinder 4A is used for the calculation of the screw tightening angle of the screw member 9.

[0139] A point of time when the rotation velocity becomes maximum is detected in the same manner as that described on FIG. 15. Also, a point of time when the rotation velocity becomes minimum is detected in the same manner as that described on FIG. 15. Specifically, in this embodiment, the width of the pulse signals detected by the detecting sensors 8a, 8b gradually broadens to the maximum and thereafter gradually narrows. The point of time at which the width of the pulse signal became maximum before it starts gradually narrowing is judged as the point of time when the rotation velocity of the oil cylinder 4A became minimum.

[0140] The screw member is tightened when the oil cylinder 4A is in the middle of significantly decelerating, as mentioned above. The detection and calculation of the screw tightening angle in the middle of that deceleration will be described below.

[0141] The oil-tight state is produced when the oil cylinder 4A inclines rearwards at a certain angle M to the driven shaft 6A, and the oil-tight state is released when the oil cylinder 4A inclines forwardly at a certain angle N thereto, as shown in FIGS. 21(a< /italic>), (b). These angles M, N are the angles determined in design of the impulse wrench, and the interrelation between these angles is formed even when the oil cylinder 4A and the driven shaft 6A rotate together in the middle of the oil-tight state to tighten the screw member 9.

[0142] Description on the rotation of the driven shaft 6A in the middle of the deceleration of the oil cylinder 4A will be given with reference to FIGS. 22 and 23.

[0143] At A₂, the oil-tight state is produced by the oil cylinder 4A and the driven shaft 6A and the oil cylinder 4A starts decelerating. At this time, the driven shaft 6A is kept in its halt condition. From that point of time, the oil cylinder 4A starts compressing oil. When the oil cylinder rotates at the angle M to correspond in phase to the driven shaft 6A, first, and then rotates further at an angle g₁ to compress the oil, an impact torque exceeding the load torque of the driven shaft 6A is generated. From this point of time A₃, the oil cylinder 4A and the driven shaft 6A rotate together at an identical angle ΔG₁, respectively, while keeping the angular phase difference g₁. A magnitude of the angular phase difference g₁ varies in accordance with the load torque of the driven shaft 6A side. The angle is small in an early stage of the seating of the screw member 9, and it increases as the tightening of the screw member 9 proceeds.

[0144] While the angular phase difference gi is represented by an angle formed with respect to the screw tightening direction (clockwise rotation angle) in FIG. 23, there may be cases where the angle g₁ is zero or its absolute value is a negative value smaller than M.

[0145] In other words, there may be cases where at the point of time when or before the oil cylinder 4A and the driven shaft 6A correspond in phase to each other after the oil-tight state is produced, the oil cylinder 4A and the driven shaft 6A rotate together.

[0146] At the point of time A₄ when the load torque at the driven shaft 6A side increases so much as to exceed the impact torque generated by the differential pressure between the high pressure chamber H and the low pressure chamber L produced in the interior of the oil chamber 4A, the driven shaft 6A stops rotating and the oil cylinder 4A remains rotating with deceleration until a point of time A₅ at which the oil-tight state is released.

[0147] At the point of time A₄, the oil cylinder 4A is in the phase that is advanced by the angle g₁ than that of the driven shaft 6A. Accordingly, the oil cylinder 4A is just required to rotate at an angle (N−g₁) until a point of time A₅ at which the oil-tight state is released.

[0148] Thus, after rotating at an angle (M+g₁) in the angle Z₁ ranging from the point of time A₂ to the point of time A₅ that can be detected by the above-mentioned method, the oil cylinder 4A is rotated together with the driven shaft 6A at the angle ΔG₁. Thereafter, only the oil cylinder 4A is rotated further at the angle (N−g₁).

[0149] A total sum of these angles is the rotation angle Z₁ of the oil cylinder 4A ranging from the point of time A₂ to the point of time A₅, which is expressed by:

Z₁=(M+g₁ )+ΔG₁+(N−g₁)=M+N+ΔG₁ Eq. 3

[0150] As mentioned above, the angles M and N are the values that can be determined in design. Where δ is the sum of these angles, the rotation angle of the driven shaft 6A from the point of time A₂ to the point of time A₅, in other words, the screw tightening angle ΔG₁ of the screw member 9, can be determined by subtracting the sum of the angles δ from the rotation angle Z₁ of the oil cylinder 4A ranging from the point of time A₂ to the point of time A₅.

[0151] Referring now to FIGS. 24-30, description will be given on the concrete method of detecting the screw tightening angle of the screw member 9 defined by the driven shaft 6A by use of the rotary detecting member 7 and the detecting sensors 8a, 8b.

[0152] In each of those diagrams, (a) is an illustration of the screw tightening angle of the screw member 9 and (b) is a diagram plotting a time shift in detecting the rotation velocity of the oil cylinder 4A and the screw tightening angle of the screwing member 9 every time the hammering is provided. The direction for the screw member 9 to be tightened illustrated in the diagrams is a clockwise direction.

[0153] FIG. 24 is a diagram showing the state in which the oil cylinder 4A runs freely with acceleration. In this state, the oil cylinder 4A rotates in the clockwise direction with acceleration, as depicted by an upward-sloping line {circle over (1)} in the diagram. After the oil cylinder 4A runs freely, the blades 55 and the projected portions 56 come into close contact with the sealing surfaces 51, 52 in the oil-tight manner, respectively, at the moment of which the velocity of the free running becomes maximum, as shown in FIG. 25. From that point of time A₂, compression of the oil is started.

[0154] When the oil is compressed, the oil cylinder 4A is decelerated, as depicted by a downward-sloping line {circle over (2)} in FIG. 26. In the early stage of the deceleration, the torque for urging the driven shaft 6A to rotate through the both blades 55, 55 by means of the differential pressure between the high pressure chamber H and the low pressure chamber L is smaller than the torque on the load side, so that the driven shaft 6A and the screw member 9 are kept in their stationary state.

[0155] As shown in FIG. 27, the oil cylinder 4A rotates further with deceleration, to compress the oil further, at a point of time A₃ of which the impact torque applied to the driven shaft 6A via the differential pressure between the high pressure chamber H and the low pressure chamber L exceeds the torque on the load side. From that point of time, the oil cylinder 4A and the driven shaft 6A cooperate to tighten the screw member 9 at a certain angle, while maintaining the phase difference in angle therebetween. After the screw member 9 is tightened up, the torque on the load side is higher than the impact torque applied to the driven shaft 6A via the differential pressure between the high pressure chamber H and the low pressure chamber L, so that the driven shaft 6A is stopped at a point of time A₄, while the oil cylinder 4A is rotated with deceleration to a point of time A₅ at which the oil-tight state is released, as shown in FIG. 28.

[0156] After a point of time of A₅, the oil-tight resistance is eliminated from the oil cylinder 4A, so that the oil cylinder restarts the free running {circle over (1)} with acceleration, as shown in FIG. 29. Then, the oil cylinder 4A is put into the oil-tight contact with the driven shaft 6A again and is decelerated {circle over (2)}, as shown in FIG. 30. In the middle of the deceleration, the oil cylinder 4A and the driven shaft 6A re-cooperate to tighten the screw member 9 at a certain angle, while maintaining the phase difference in angle therebetween. Thereafter, the oil cylinder 4A is decelerated until the oil-tight state is released.

[0157] The rotation angle of the driven shaft 6A in the middle of deceleration of the oil cylinder 4A, i.e., the rotation angle of the screw member 9, is an angle formed in the period from the point of time A₃ to the point of time A₄. The screwing angle ΔG₁ of the screw member 9 in this period is calculated as the angle (Z₁−δ) after the angle Z₁ is detected in the above-mentioned manner.

[0158] Subsequently, the same process is taken that the oil cylinder 4A runs freely and decelerates and the screw member 9 is tightened in the middle of the deceleration. The screw tightening angle ΔG formed in the middle of the deceleration is integrated by the central processing part 13. When the integrated value of the screw tightening angle reaches a preset screw tightening angle of the screw member 9, signals are output from the rotation angle signal outputting part 14 to the solenoid valve controlling part 16 through the completed screw tightening detecting part 15, to stop the solenoid valve 19 via the output circuit 17.

[0159] In addition to the method mentioned above, the detection of the rotation angle of the driven shaft 6A formed in the middle of deceleration of the oil cylinder 4A by use of the rotary detecting member 7 can be performed by another method that the free running angle formed every time the oil cylinder 4A rotated in the screw tightening direction and the rotation angle formed until the completion of each deceleration, including the free running angle, are detected by the detecting sensors.

[0160] FIGS. 31, 32 are illustration of the detecting method. After running freely {circle over (1)} with acceleration, as indicated by an upward-sloped line, the oil cylinder 4A comes into the oil-tight with the driven shaft 6A and decelerates {circle over (2)} to perform one screw tightening in the middle of the deceleration, as indicated by a downward-sloped line. The state of rotation of the oil cylinder 4A is represented as shown in FIG. 32, where A₁ is a starting point of the free running {circle over (1)}, A₂ is a point of time at which the oil-tight is produced (maximum velocity), A₃ is a point of time at which the screwing is started, A₄ is a point of time at which the screwing is stopped, and A₅ is a point of time at which the deceleration of the oil cylinder 4A is ended and the next acceleration is started.

[0161] From FIG. 32, the screw tightening angle (screwing angle) is given by:

ΔG=Z−δ=(F′−J′)−δ Eq.4

[0162] where F′ is a clockwise rotation angle per cycle of the oil cylinder 4A, J′ is a clockwise free running angle per rotation of the same, Z is a deceleration angle of the oil cylinder 4A, and ΔG is the screw tightening angle (screwing angle).

[0163] The screw tightening angle is calculated by detecting the clockwise rotation angle F′ and the clockwise free running angle J′ by use of the rotary detecting member 7 and the detecting sensors 8a, 8b. In this method, even when a wobbling is caused in the course of the detection of the clockwise free running angle J′ and the clockwise rotation angle F′, since the angle of the wobbling generated at a point of time within the free running from the point of time A₁ to the point of time A₂ is included in both of those angles, the angle of wobbling is balanced out by the both angles. Thus, even when the wobbling is caused, since the influence is limited to only a very short time (from the point of time A₂ to the point of time A₅) during which the oil cylinder 4A decelerates, it is substantially a negligible level, and as such can provide the screw tightening work with little error.

[0164] In the following, description will be given on the method of detecting the degree of generation of the wobbling, for the purpose of evaluating the tightening work.

[0165] For the study of an actual quality of the practical work, it is necessary to confirm reliability of the screw tightening work and accordingly it is necessary to grasp the degree of wobbling in the screw tightening work.

[0166] Reference will be first given to an impact wrench designed to generate the rebound.

[0167] In this type of impact wrench, as shown in FIG. 33, when the cylindrical rotary member 4 provides one hammering per rotation of the same, the number of pulses detected in accordance with and derived from the rotation angle in one cycle from one hammering to the next hammering, in other words, the number of pulses obtained by subtracting the number of pulses (R_p) corresponding to the rebound angle from the number of pulses (F_p) corresponding to the rotation angle in the tightening direction, are the sum of the number of pulses per rotation with no wobbling (which is expressed by Pd_p, the number of pulses corresponding to 360 degree in this case), the number of pulses (ΔH_p) corresponding to the tightening angle and the number of pulses (h_p) generated by the wobbling. The number of pulses (h_p) generated by the wobbling can take any one of a positive value, a negative value and zero, depending on the direction of the wobbling, as mentioned later.

[0168] The number of pulses detected and derived from the rotation of the cylindrical rotation member from the start to the end of the screw tightening work (which is called the total number of pulses, which is represented as a value obtained by subtracting the cumulative total number of pulses (R_p) of the opposite direction to the screw tightening direction from the cumulative total number of pulses (F_p) in the tightening direction) can be expressed as the sum of the cumulative total number of pulses corresponding to the actual screw tightening angle (which is represented as ΔH_p, which is called the number of advance pulse angle), the cumulative total number of design pulses (Pd_p) preset under design corresponding to the number of hammerings until the end of work (=the number of design pulses×the number of hammering n), and the cumulative total number of wobbling pulses (h_p) corresponding to the wobbling angle until the end of work. The number of design pulses is a characteristic value prescribed for the concerned impact wrench. In the case of the wrench wherein the cylindrical rotary member provides the m number of hammerings per rotation of the same, the number of design pulses is the number of pulses corresponding to an angle of 360°/m. In the case of the wrench wherein the cylindrical rotary member 4 provides one hammering per rotation of the same, the number of design pulses is the number of pulses corresponding to the angle of 360°. In the case of the wrench wherein the cylindrical member provides two hammerings per rotation of the same, the number of design pulses is the number of pulses corresponding to the angle of 180®.

Total number of pulses=the cumulative total number of advance pulses+the cumulative total number of design pulses+the cumulative total of wobbling pulses Eq. 5

[0169] Second, reference is given to an impact wrench designed not to generate the rebound w