Tool moving device and screw fastening device including the same

Abstract

To provide a tool moving device.SOLUTION: A tool unit 30 that performs a predetermined operation on a workpiece, a driver base 26 that holds the tool unit 30, a ball screw that reciprocates the driver base 26 in a direction toward or away from the workpiece, a moving motor that drives the ball screw, and a control unit that controls driving of the moving motor, wherein the control unit has a torque command section that performs feedback control so that the moving motor outputs a preset command torque, the command torque is set to a value obtained by adding a desired thrust, a thrust for canceling a driving load of the reciprocating unit, and a thrust for canceling a self-weight of the tool unit 30 so that the desired thrust can be applied to the tool unit 30.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tool moving device that moves a tool unit that performs a predetermined task, and a screw tightening device that includes the same device. [Background technology]

[0002] A screw tightening device disclosed in Patent Document 1 is known as an example of a tool movement device including a tool unit with a tool for performing a predetermined operation on a workpiece and a reciprocating movement unit for moving the tool unit. This screw tightening device includes a screw tightening unit including a driver bit that engages with the screw and a tightening motor that rotates and drives the driver bit, and a tool movement device that moves the screw tightening unit back and forth in the axial direction of the driver bit. The tool movement device includes a driver base that holds the screw tightening unit, a ball screw that moves the driver base toward or away from the workpiece, and a movement motor that drives the ball screw. The tool movement device of this screw tightening device limits the torque of the movement motor so that it does not output rotational torque that is abnormal to a predetermined limit torque, and is controlled so that the driver bit does not press the screw against the workpiece with excessive thrust. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4148445 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because the conventional tool movement device is configured to limit the rotational torque of the movement motor as described above, the weight of the tool unit, the drive nut of the ball screw, etc. is transmitted to the screw tightening tool, which poses a problem of being unable to apply a thrust force that is less than the weight of the tool unit, etc.

[0005] Therefore, an object of the present invention is to provide a tool moving device that can impart a desired thrust to a tool unit. [Means for solving the problem]

[0006] To achieve this object, the present invention provides a tool movement device that moves a tool unit that performs a predetermined operation on a workpiece, comprising: a reciprocating movement unit that moves the tool unit toward or away from the workpiece; a movement motor that drives the reciprocating movement unit; and a control unit that can control the drive of the movement motor, wherein the control unit has a torque command section that controls torque so that the movement motor outputs a predetermined command torque, and the command torque is set to a value obtained by adding together the desired thrust, a thrust that offsets the drive load of the reciprocating movement unit, and a thrust that offsets the weight of the tool unit, so that a desired thrust can be applied to the tool unit. Preferably, the control unit divides the entire movable range of the reciprocating unit into a number of minute sections, and obtains a thrust force for offsetting the drive load for each minute section. It is also preferable that the reciprocating movement unit has a ball screw that rotates when driven by the movement motor, and a driver stand that moves when driven by this ball screw, and that the tool unit is held on the driver stand. Furthermore, a tool movement device for moving a tool unit that performs a predetermined operation on a workpiece includes: a reciprocating movement unit that moves the tool unit toward or away from the workpiece; a movement motor that drives the reciprocating movement unit; and a control unit that can control driving of the movement motor, wherein the control unit has: a torque command unit that controls torque so that the movement motor outputs a predetermined command torque; a position command unit that controls the position of the tool unit by controlling the amount of rotation of the movement motor; and an operation command unit that outputs an operation command to either the torque command unit or the position command unit to control the movement motor, wherein the operation command unit outputs an operation command to the position command unit while the tool unit is moving from a position where it is separated from the workpiece to a predetermined switching position, and when the tool unit reaches the switching position, outputs an operation command to the torque command unit to switch control of the movement motor from position control to torque control. It is preferable that the torque command unit has a limit on the movement speed of the tool unit, and the position command unit controls the drive of the movement motor so that the movement speed of the tool unit gradually decelerates from just before the switching position to the switching position, and that when the tool unit reaches the switching position, the movement speed of the tool unit has decreased to the limit speed set in the torque command unit.

[0007] A second object of the present invention is to provide a screw tightening device that can impart a desired thrust force to a tool unit. Therefore, the present invention provides a screw tightening device comprising a screw tightening tool that can be engaged with a screw, a tool unit having a tightening motor that rotates and drives the screw tightening tool, a reciprocating movement unit that moves the tool unit toward or away from a workpiece, a movement motor that drives the reciprocating movement unit, and a control unit that can control the drive of the movement motor, wherein the control unit has a torque command section that controls the torque so that the movement motor outputs a predetermined command torque, and the command torque is set to a value that is the sum of the desired thrust, a thrust that offsets the drive load of the reciprocating movement unit, and a thrust that offsets the weight of the tool unit, so that the desired thrust can be applied to the tool unit. The present invention also provides a screw tightening device comprising: a screw tightening tool engageable with a screw; a tool unit having a tightening motor for rotating the screw tightening tool; a reciprocating movement unit for moving the tool unit toward or away from a workpiece; a movement motor for driving the reciprocating movement unit; and a control unit capable of controlling the driving of the movement motor, wherein the control unit has a torque command unit for torque control so that the movement motor outputs a predetermined command torque, and the control unit has a position command unit for position-controlling the tool unit by controlling the amount of rotation of the movement motor; and an operation command unit for outputting an operation command to either the torque command unit or the position command unit to control the movement motor, wherein the operation command unit outputs an operation command to the position command unit while the tool unit is moving from a position where it is separated from the workpiece to a predetermined switching position, and when the tool unit reaches the switching position, outputs an operation command to the torque command unit and switches control of the movement motor from position control to torque control. [Effects of the Invention]

[0008] According to the above invention, since the movement motor for moving the tool unit is feedback-controlled to output a predetermined command torque, a desired thrust can be applied to the tool unit, and further, since the command torque is set to a value obtained by adding together the desired thrust, a thrust for offsetting the drive load of the reciprocating unit, and a thrust for offsetting the weight of the tool unit so that the desired thrust can be applied to the tool unit, when the command torque is output, the weight of the tool unit is not applied to the workpiece, thereby preventing damage to the workpiece, etc. Similarly, since there is no torque loss due to the drive load, there is also the advantage that thrust is not insufficient. The command torque is calculated by dividing the stroke of the ball screw into minute sections and obtaining the driving load for each minute section, so that it can also accommodate changes in the driving load for each position, making it possible to accurately apply only the desired thrust to the tool unit. Furthermore, the control unit has a position command section and an operation command section, and the operation command section switches between position control, which can move the tool unit at high speed, and torque control, which can impart a desired thrust force to the tool unit, at a switching position, which has the advantage of shortening the cycle time and making it possible to impart a desired thrust force. Furthermore, when the switching position is reached, the position command unit slows down the movement speed of the tool unit to the speed limit set in the torque command unit, which has the advantage of preventing the tool unit from suddenly stopping or accelerating when control is switched.

[0009] Furthermore, according to the second aspect of the present invention, the thrust force applied by the screw tightening tool to the screw and the workpiece can be reduced, which has the advantage of preventing damage to the screw and the workpiece. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a front view showing the structure of a screw fastening device according to the present invention; [Figure 2] 1 is a side view showing the structure of a screw fastening device according to the present invention. [Figure 3]1 is a partially cross-sectional side view showing the structure of a screw fastening device according to the present invention. [Figure 4] 2 is a block diagram showing the configuration of a torque command unit of the screw fastening device according to the present invention; FIG. [Figure 5] 4 is an enlarged, partially cutaway cross-sectional view of a main portion illustrating the operation of the screw fastening device according to the present invention. FIG. [Figure 6] 6 is a graph showing changes in various parameters of the screw fastening device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will now be described with reference to the drawings. In Fig. 1, reference numeral 10 denotes a screw tightening device that tightens a screw S into a workpiece W. This screw tightening device 10 comprises a reciprocating unit 20, which is the essential part of the present invention; a screw tightening unit 30 that is held by the reciprocating unit 20 and can be moved to any position; and a control unit 50 that controls the driving of the reciprocating unit 20 and the screw tightening unit 30.

[0012] In this embodiment, the screw S is a general screw S having a head portion with a cross-recessed driving hole formed therein and a shaft portion with a thread formed on the outer circumferential surface integrally formed therewith, and is configured to be able to thread into the internal thread W1 formed in the workpiece W.

[0013] The reciprocating unit 20 includes a base plate 21 fixed to a frame (not shown) of the screw fastening device 10. The base plate 21 extends vertically, and a motor base 22 and a chuck base 23, which extend horizontally, are fixed to the top and bottom ends of the base plate 21. A ball screw 24 is rotatably held between the motor base 22 and the chuck base 23. A drive nut 25, which is axially movable by rotation of the ball screw 24, is threadedly engaged with the ball screw 24. A driver base 26 is fixed to the drive nut 25, and the driver base 26 is axially slidably guided by a guide rod 27 extending parallel to the ball screw 24. An elevating AC servo motor 28 (hereinafter referred to as the moving motor 28) that rotates the ball screw 24 is mounted on the motor base 22. With this structure, when the moving motor 28 is driven, the drive nut 25 and the driver base 26 move up and down along the ball screw 24.

[0014] In addition, the movement motor 28 has an encoder 281 that can emit a pulse signal corresponding to the rotation angle of the output shaft of the movement motor 28, and a torque sensor 282 that can measure the rotational torque, and these encoder 281 and torque sensor 282 are connected to the control unit 50.

[0015] As shown in FIG. 3 , the screw tightening unit 30 has an AC servo motor 31 (hereinafter referred to as the tightening motor 31) mounted on the driver stand 26, with its output shaft passing through the driver stand 26. The tightening motor 31 has a torque sensor that measures the output torque of the tightening motor 31, and this torque sensor is connected to the control unit 50. A driver bit 33, which is an example of a tool, is connected to the output shaft of the tightening motor 31 via a shaft coupling 32, and a fitting portion 331 that can fit into a drive hole of the screw S is formed at the tip of the driver bit 33. An insertion hole 321 into which the base end of the driver bit 33 is inserted is formed in the shaft coupling 32, and a cushion spring 322 that constantly urges the driver bit 33 downward is enclosed within the insertion hole 321. Therefore, when a force is applied in the direction of the tightening motor 31 , the driver bit 33 can move axially relative to the tightening motor 31 and the shaft coupling 32 while deflecting the cushion spring 322 .

[0016] A retaining sleeve 34 is fixed to the underside of the driver base 26. A hollow cylindrical screw guide 35, which rotatably houses the driver bit 33, is inserted into the retaining sleeve 34 so as to be movable relative to the retaining sleeve 34 in the axial direction, and a hose coupling 36 is attached to the screw guide 35. An intake hose (not shown) is connected to the hose coupling 36, and the other end of the intake hose is connected to an intake means such as an external vacuum generator. Therefore, when the intake means is driven, a negative pressure is generated inside the screw guide 35, and the screw S can be attracted and held at the opening at the lower end of the screw guide 35. The screw guide 35 is constantly biased downward by a guide spring 37 enclosed therein, and is configured to be movable relative to the retaining sleeve 34 and the driver bit 33 in the axial direction as the guide spring 37 deflects.

[0017] Further, below the screw tightening unit 30, a chuck unit 40 capable of holding screws S pressure-fed from an external parts supply device is provided. The chuck unit 40 has a chuck body 41 fixed on the movement path of the screw guide 35 and the driver bit 33. A guide hole 42 that accommodates the tip of the screw guide 35 is formed through the chuck body 41. A pair of chuck jaws 43, 43 are swingably attached to the chuck body 41. A holding hole 44 that can hold the screw S is formed separately on the opposing surfaces of the chuck jaws 43, 43 and is positioned on an extension of the guide hole 42. Further, the chuck body 41 is provided with a supply pipe 45 that can swing in a direction perpendicular to the swing plane of the chuck jaws 43, 43. The tip of this supply pipe 45 is continuous with the holding hole 44 and is configured to close the opening of the guide hole 42, while the base end is connected to a screw supply hose fitting 46 to which a screw supply hose (not shown) is connected, and the screw supply hose continues to a component supply device (not shown). Therefore, the screws S pressure-fed from the component supply device can pass through the screw supply hose and supply pipe 45 and be supplied to the holding hole 44.

[0018] A restricting plate 47 is attached to the chuck body 41 and can swing in conjunction with the supply pipe 45. The tip of the restricting plate 47 is provided with restricting claws 48, which abut against the outer surfaces of the chuck jaws 43 when the jaws are closed and restrict the swinging of the jaws 43. The restricting claws 48, 48 gradually move away from the chuck jaws 43 as they swing along the supply pipe 45, so that they can completely move away from the chuck jaws 43, 43 before the screw guide 35 begins to push the jaws 43, 43 open. The supply pipe 45 and the restricting plate 47 are constantly biased toward the chuck jaws 43, 43 by a torsion coil spring 49, which elastically deforms when the supply pipe 45 and the restricting plate 47 swing.

[0019] The screw tightening unit 30 also has a cable carrier 38, as shown in FIG. 2. This cable carrier 38 houses wiring and intake hoses that connect the movement motor 28 and the control unit 50. One end of this cable carrier 38 is fixed to the driver stand 26, while the other end is fixed to the circuit board 21. The cable carrier 38 is configured to deform as shown by the two-dot chain line in FIG. 2 as the screw tightening unit 30 and the driver stand 26 are raised and lowered. Because the wiring and intake hoses are inserted into this cable carrier 38, the postures of the wiring and intake hoses remain constant whenever the screw tightening unit 30 is raised and lowered. As a result, the load on the wiring and intake hoses that occurs when the screw tightening unit 30 is raised and lowered can be kept constant every time.

[0020] The control unit 50 is composed of a drive control unit 51 that outputs various signals, a movement control unit 52 that controls the drive of the movement motor 28 of the movement means, and a tightening control unit 53 that controls the drive of the tightening motor 31 of the screw tightening unit 30. The drive control unit 51 is connected to the movement control unit 52, the tightening control unit 53, the component supply device, the suction means, and external devices such as an input device that can input various data. The drive control unit 51 is configured to input and output various signals to and from these devices to control their drive. The drive control unit 51 also stores operating programs and various control parameters.

[0021] 4, the movement control unit 52 has an operation command unit 521 that drives the movement motor 28, and a position command unit 522 and a torque command unit 523 that are provided in parallel between the operation command unit 521 and the movement motor 28, and the operation command unit 521 is configured to output an operation command to either the position command unit 522 or the torque command unit 523 to control the drive of the movement motor 28. The operation command unit 521 is connected to the encoder 281 and torque sensor 282 of the movement motor 28, and is configured to be able to determine the amount of movement of the driver table 26, i.e., the movement position of the screw tightening unit 30, from the pulse signal (rotation angle of the movement motor 28) output by the encoder 281 and the lead of the ball screw 24. In addition, the operation command unit 521 is configured to control the driving of the tightening motor 31 via the position command unit 522 while the screw tightening unit 30 moves from the upper end of the ball screw 24 as shown in Figure 1 to position Z1 (hereinafter referred to as switching position Z1) shown in (Z1) of Figure 6, which is just before the tip of the screw guide 35 collides with the workpiece W, and to control the driving of the tightening motor 31 via the torque command unit 523 while the screw tightening unit 30 moves from the switching position Z1 to a stop position Z4 set a predetermined distance below the position where the screw S is seated as shown in (Z3) of Figure 6 (hereinafter referred to as seating position Z3).

[0022] The position command unit 522 controls the position of the driver's stand 26 by controlling the amount of rotation of the movement motor 28, and is configured to move the driver's stand 26 at high speed from the standby position toward the target position Z1b set on the stop position Z4 side from the switching position Z1.

[0023] The position command unit 522 is configured to gradually decelerate the movement speed from a deceleration start position Z1a, which is set above the target position Z1b as shown in FIG. 5, to the target position Z1b at a predetermined deceleration rate in order to stop the screw tightening unit 30 at the target position Z1b. The deceleration start position Z1a and the target position Z1b are set using the deceleration rate so that the screw tightening unit 30, upon reaching the switching position Z1, decelerates to a speed limit value set by a torque command unit 523 (described later). Because the target position Z1b and the deceleration start position Z1a are set in this manner, when the screw tightening unit 30 reaches the switching position Z1, the control of the movement motor 28 can be switched from position control to torque control without stopping the screw tightening unit 30. This allows the screw tightening unit 30 to move faster by the hatched area H, as shown by the two-dot chain line in FIG. 5, compared to a control method in which the screw tightening unit 30 is temporarily stopped at the switching position Z1 and then switched. This shortens the cycle time and improves work efficiency.

[0024] The torque command unit 523 controls the torque so that the movement motor 28 outputs a rotational torque according to a torque table created in advance, and is configured to move the driver stand 26 to the target position Z1b with a desired axial thrust. In addition, the torque command unit 523 controls the rotational speed of the movement motor 28 so that it does not exceed a predetermined speed limit value so that the screw tightening unit 30 does not move at an excessively high speed.

[0025] The torque table is one of the control parameters that is set in advance, and divides the movable range of the ball screw 24 into a large number of minute sections, and sets a rotational torque (hereinafter referred to as command torque) to be output by the movement motor 28 for each of these minute sections. This command torque is set to a value obtained by dividing the product of the lead of the ball screw 24 and the desired thrust by the product of 2π and the efficiency of the ball screw 24, and is expressed as "command torque = (lead of ball screw 24 × desired thrust) / (2π × torque transmission efficiency of ball screw 24)."

[0026] Furthermore, the desired thrust is set to a value obtained by adding together the desired screw tightening thrust and a thrust (hereinafter referred to as an offsetting thrust) that offsets loads due to the weight of the screw tightening unit 30 and the dynamic frictional force and spring reaction force that the screw tightening unit 30 receives when moving through the minute section, so that only the desired screw tightening thrust can be applied to the driver bit 33 in the minute section. Furthermore, the desired thrust is set to gradually increase from the switching position Z1 as shown in Fig. 5 so that the descent speed of the screw tightening unit 30 does not exceed the speed limit due to excessive torque being output immediately after switching with the position command unit 522. The screw tightening thrust is set so that the driver bit 33 does not cam out of the screw S when tightening is complete.

[0027] The tightening control unit 53 is connected to the tightening motor 31, and is configured to switch between driving and stopping the tightening motor 31 according to the load current value of the tightening motor 31. In other words, when tightening the screw S, the tightening control unit 53 determines whether the screw S has been tightened to a predetermined tightening torque based on the load current value of the tightening motor 31, which increases in proportion to an increase in the tightening torque, and when this value reaches the predetermined value, it stops driving the tightening motor 31.

[0028] The teaching process for teaching the position of the workpiece W will be described below. During teaching, the torque command unit 523 controls the drive of the movement motor 28 throughout the entire movable range of the ball screw 24, and sets the screw tightening thrust of the torque table to 0. This ensures that the weight, drive load, and command torque of the screw tightening unit 30 are balanced regardless of where the screw tightening unit 30 is located on the ball screw 24. Therefore, the screw tightening unit 30 remains stationary in its initial position until an external force is applied. However, if an operator applies a thrust force to the screw tightening unit 30 in the vertical direction, the balance is lost and the screw tightening unit 30 can move in the direction of the applied thrust. In other words, the operator can move the screw tightening unit 30 with a weak force without being affected by the screw tightening unit 30's own weight, drive load, etc. Furthermore, this prevents the screw tightening unit 30 from falling and colliding with the workpiece W if the operator lets go of it.

[0029] Next, the operation of the screw fastening device 10 configured as described above will be described. When a drive signal is input, the control unit 50 drives the component supply device to pressure-feed the screw S to the chuck unit 40. Once the screw S has been pressure-fed to the chuck unit 40, the operation command unit 521 of the control unit 50 drives the movement motor 28 via the position command unit 522, causing the screw tightening unit 30, which is waiting at the standby position, to descend toward the target position Z1b. At the same time, the control unit 50 drives the tightening motor 31 to rotate the driver bit 33 and drives the vacuum generator to suck air from inside the screw guide 35. This creates a negative pressure inside the screw guide 35, sucking air through the opening at its lower end. Therefore, when the screw tightening unit 30 descends as described above and the tip of the screw guide 35 enters between the chuck jaws 43, the screw S held by the chuck jaws 43 is attracted and held inside the screw guide 35 and engages with the driver bit 33.

[0030] As described above, when the screw tightening unit 30, which has adsorbed and held the screw S, further descends, the screw guide 35 protrudes from the chuck unit 40. Thereafter, when the screw tightening unit 30 reaches the deceleration start position Z1a, the reciprocating unit 20 gradually decelerates the descending speed of the screw tightening unit 30. As a result, when the decelerated screw tightening unit 30 reaches the switching position Z1, the operation command unit 521 switches control of the movement motor 28 from the position command unit 522 to the torque command unit 523. At this time, because the speed of the screw tightening unit 30 is decelerated to below the speed limit of the torque command unit 523 before reaching the switching position Z1, sudden braking is not applied immediately after switching, and the movement speed of the screw tightening unit 30 is not decelerated below the speed limit set in the torque command unit 523. Furthermore, because the torque command unit 523 is configured to gradually increase the torque after switching, sudden acceleration is not performed immediately after switching, and the screw tightening unit 30 is prevented from colliding with the workpiece W. As a result, the control of movement motor 28 can be smoothly switched from position command unit 522 to torque command unit 523.

[0031] Thereafter, as the screw tightening unit 30 further descends, the lower end of the screw guide 35 comes into contact with the workpiece W as shown in (Z2) of FIG. 6, and only the screw guide 35 stops descending. As a result, the driver bit 33 descends inside the screw guide 35 while deflecting the guide spring 37. As a result, the driver bit 33 comes into contact with the screw S held in the screw guide 35 and presses the screw S toward the workpiece W. At this time, because the driver bit 33 is rotating, the fitting portion 331 of the driver bit 33 fits into the head of the screw S. Thereafter, the screw S comes into contact with the workpiece W and rotates integrally with the driver bit 33, thereby being fastened to the workpiece W.

[0032] During the screw tightening described above, the movement motor 28 is feedback-controlled to output the command torque stored in the torque table. At this time, as described above, the command torque is set to the resultant force of the desired screw tightening thrust and a counter-thrust that counteracts loads due to the weight of the screw tightening unit 30, dynamic friction, spring reaction force, and the like. This allows the desired screw tightening thrust to be applied to the driver bit 33. Since the weight of the screw tightening unit 30 is prevented from being applied to the screw S, damage to the threads of the screw S or the workpiece W can be prevented. Furthermore, the screw S is prevented from slipping out obliquely due to excessive thrust, such as the weight of the screw tightening unit 30, being applied to the screw S via the driver bit 33 immediately after the screw S begins to thread into the workpiece W. Furthermore, since loads due to dynamic friction, spring reaction force, and the like are also counter-balanced, the thrust applied to the screw S is prevented from changing due to fluctuations in the load. Moreover, the wiring and intake hose connecting the movement motor 28 and control unit 50 are housed in the cable carrier 38 and are configured to curve integrally, so the reaction force from the wiring and intake hose does not change with each tightening. As a result, the driver bit 33 does not cam out of the screw S, and the screw can be tightened with an appropriate screw tightening thrust that does not damage the workpiece W or the screw S. Furthermore, because the screw tightening unit 30 is set so that it can descend to the stop position Z4, which is set below the seating position Z3, it can be tightened without any problems even if the workpiece W is misaligned in the vertical direction or is warped.

[0033] Thereafter, when the screw S is seated on the workpiece W, the tightening torque of the tightening motor 31 reaches a predetermined value. When it is determined that the screw has been tightened, the operation command unit 521 drives the moving motor 28 in the reverse direction using the torque command unit 523, thereby raising the screw tightening unit 30 to the switching position Z1. When the screw tightening unit 30 has risen to the switching position Z1, the operation command unit 521 switches control of the moving motor 28 from the torque command unit 523 to the position command unit 522, thereby raising the screw tightening unit 30 to the standby position. Note that the torque command unit 523 also drives the moving motor 28 in the reverse direction to raise the screw tightening unit 30 to the standby position when the workpiece W is not positioned in the predetermined position and the screw tightening unit 30 has descended to the stop position Z4 as shown in (Z4) of FIG. 6 .

[0034] The specific configuration of each part of the present invention is not limited to the above, and various modifications are possible without departing from the spirit of the invention. For example, the screw fastening device 10 is an example of a tool movement device that moves a tool unit that performs a predetermined operation on the workpiece W, and the tool unit is not limited to the screw fastening unit 30, but may be a drill unit equipped with a drill that forms a female thread in the workpiece W, or a pin insertion unit that inserts a pin into a hole formed in the workpiece W. Furthermore, although the reciprocating unit 20 of the screw fastening device 10 is fixed to a frame (not shown), the present invention is not limited to this, and there is no problem if the reciprocating unit 20 is held by a robot arm or the like and has a movable structure. [Explanation of symbols]

[0035] 10...Screw tightening device 20...Reciprocating unit 24... Ball screw 26... Driver's stand 28...Movement motor 281... Encoder 282... Torque sensor 30...Screw tightening unit 31 ... Fastening motor 33... Driver bit 40...Chuck unit 50 ... control unit 51 ... Drive control unit 52 ... Movement control section 521...Operation command section 522...Position command section 523... Torque command unit 53 ... Tightening control section

Claims

1. A tool moving device that moves a tool unit that performs a predetermined operation on a workpiece, a reciprocating unit that moves the tool unit toward or away from the workpiece; a movement motor that drives the reciprocating movement unit; a control unit capable of controlling the driving of the movement motor; the control unit has a torque command section that controls torque so that the movement motor outputs a preset command torque, the command torque is set to a value obtained by adding together a desired thrust, a thrust for offsetting a drive load of the reciprocating unit, and a thrust for offsetting the weight of the tool unit, so that a desired thrust can be applied to the tool unit.

2. 2. The tool movement device according to claim 1, wherein the control unit divides the entire movable range of the reciprocating movement unit into a number of minute sections, and obtains a thrust force for offsetting the drive load for each minute section.

3. the reciprocating movement unit has a ball screw that rotates when driven by the movement motor, and a driver base that moves when driven by the ball screw, 3. The tool moving device according to claim 2, wherein the tool unit is held on the driver's stand.

4. A tool moving device that moves a tool unit that performs a predetermined operation on a workpiece, a reciprocating unit that moves the tool unit toward or away from the workpiece; a movement motor that drives the reciprocating movement unit; a control unit capable of controlling the driving of the movement motor; the control unit includes a torque command section that controls the movement motor to output a predetermined command torque; a position command unit that controls the position of the tool unit by controlling the rotation amount of the movement motor; an operation command unit that outputs an operation command to either the torque command unit or the position command unit to control the movement motor; the operation command unit outputs an operation command to the position command unit while the tool unit moves from a position away from a workpiece to a predetermined switching position, and when the tool unit reaches the switching position, outputs an operation command to the torque command unit to switch control of the movement motor from position control to torque control.

5. 5. The tool movement device according to claim 4, wherein the torque command unit has a limit set to a movement speed of the tool unit, and the position command unit controls driving of the movement motor so that the movement speed of the tool unit gradually decreases from just before the switching position to the switching position, so that when the tool unit reaches the switching position, the movement speed of the tool unit decreases to the limit speed set in the torque command unit.

6. a tool unit having a screw tightening tool that can be fitted with a screw and a tightening motor that rotates and drives the screw tightening tool; a reciprocating unit that moves the tool unit toward or away from a workpiece; a movement motor that drives the reciprocating movement unit; a control unit capable of controlling the driving of the movement motor; In a screw fastening device, the control unit has a torque command unit that controls torque so that the movement motor outputs a preset command torque, the command torque is set to a value obtained by adding together a desired thrust, a thrust that offsets the drive load of the reciprocating unit, and a thrust that offsets the weight of the tool unit, so that the desired thrust can be applied to the tool unit.

7. a tool unit having a screw tightening tool that can be fitted with a screw and a tightening motor that rotates and drives the screw tightening tool; a reciprocating unit that moves the tool unit toward or away from a workpiece; a movement motor that drives the reciprocating movement unit; a control unit capable of controlling the driving of the movement motor; In a screw fastening device, the control unit has a torque command unit that controls torque so that the movement motor outputs a preset command torque, a position command unit that controls the position of the tool unit by controlling the rotation amount of the movement motor; an operation command unit that outputs an operation command to either the torque command unit or the position command unit to control the movement motor; the operation command unit outputs an operation command to the position command unit while the tool unit moves from a position away from a workpiece to a predetermined switching position, and when the tool unit reaches the switching position, outputs an operation command to the torque command unit to switch control of the movement motor from position control to torque control.

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