Screw tightening device

Abstract

To provide a screw fastening device which can prevent damage of a chuck unit and a screw guide.SOLUTION: A screw fastening device 10 includes: a screw fastening tool 30 which has a driver bit 34 rotatable by receiving driving of a rotary drive source and a screw guide 36 which houses the driver bit 34 and is configured to be slidable with respect to the driver bit 34; a position control mechanism 20 which reciprocatingly moves the screw fastening tool 30; a chuck unit 40 which is arranged on an axis line of the driver bit 34; damage prevention means which detects that the screw guide 36 or the driver bit 34 excessively presses the chuck unit 40; and a control section 50 which is configured to control driving of the position control mechanism 20 on the basis of a signal from the damage prevention means.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a screw tightening device for fastening a screw to a workpiece.

Background Art

[0002] As a conventional screw tightening device, as shown in Patent Document 1, there is known a screw tightening device including a driver bit that can be fitted to a screw, and a chuck unit that is disposed on the axis of the driver bit and temporarily holds a screw supplied from an external screw supply device. The chuck unit of this screw tightening device includes a chuck body in which a guide hole for guiding the screw guide 36 to reciprocate in the axial direction is formed, a chuck claw that is swingably attached to the chuck body and divides and forms a holding hole on the axis of the driver bit, and an opening / closing cylinder that is an example of a swing restricting mechanism for restricting the swing of the chuck claw. Further, the opening / closing cylinder is configured to forcibly close the chuck claw when supplying a screw and when fitting the screw to the driver bit, and prevent the screw from jumping out of the chuck due to the momentum of the pressure-fed screw or the screw from falling off the chuck before fitting to the driver bit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the conventional screw tightening device was configured to restrict the swing of the chuck jaws by a swing restricting mechanism, when a supply defect such as the presence of two screws in the chuck occurred, the driver attempting to descend to the fitting position with the screw might collide with the second screw. After this collision, the driver bit or the screw guide that further descends might excessively press the second screw, resulting in problems such as damage to the driver bit, the screw guide, the screw, or the chuck jaws that come into contact with the screw.

Means for Solving the Problems

[0005] The present invention was created in view of the above problems, and an object thereof is to provide a screw tightening device capable of preventing breakage of a chuck, a driver bit, or the like. To achieve this object, the present invention includes a screw tightening tool having a driver bit rotatable by receiving the drive of a rotary drive source and a screw guide that encloses the driver bit and is configured to be slidable with respect to the driver bit, a position control mechanism for reciprocating the screw tightening tool, a chuck unit disposed on the axis of the driver bit, breakage prevention means for preventing breakage of the screw tightening tool or the chuck unit that moves by receiving the drive of the position control mechanism, and a control unit configured to control the drive of the position control mechanism based on a signal from the breakage prevention means. The chuck unit includes a chuck body in which a guide hole for guiding the screw guide is formed, a pair of chuck jaws that are swingably attached to the chuck body and that divide and form a holding hole for holding a screw on an extension line of the guide hole, a hose fitting that intersects the swing surface of the chuck jaw and extends obliquely rearward, and a supply pipe disposed between the hose fitting and the chuck jaw and swingable in a direction away from the swing surface of the chuck jaw. Further, the breakage prevention means is configured to detect excessive pressing of the screw guide of the screw tightening tool or the driver bit against the chuck unit that moves by receiving the drive of the position control mechanism, and it is preferable that the control unit is configured to interrupt the drive of the position control mechanism when the breakage prevention means detects excessive pressing. Furthermore, the position control mechanism includes a lifting motor and a ball screw connected to the lifting motor, and it is preferable that the breakage prevention means measures the load current value of the lifting motor and, if the load current value reaches a predetermined collision current value set in advance, determines that the screw tightening tool is pressing the chuck unit and interrupts the drive of the lifting motor. Moreover, the breakage prevention means is preferably a contact type sensor attached to any one of the chuck jaws, the supply pipe, the screw guide, and the driver bit.

[0006] Further, the breakage prevention means is configured to operate between a collision confirmation start position set above the height at which the lower end of the screw guide abuts against the supply pipe and a collision confirmation end position set below the height at which the screw guide abuts against the head of the screw normally supplied to the chuck jaw. Further, the breakage prevention means is configured to determine the posture of the screw supplied to the holding hole, and it is preferable that the control unit is configured to drive the position control mechanism when the breakage prevention means determines that the posture of the screw in the holding hole is normal. Moreover, the breakage prevention means is a non-contact sensor arranged such that the detection range comes within the screw passage area set on the supply pipe side from the head of the screw normally supplied in the holding hole, or imaging means arranged to image the screw passage area.

Advantages of the Invention

[0007] According to the present invention, since the position control mechanism is driven based on the signal of the breakage prevention means, it is possible to prevent breakage of the screw tightening tool that moves under the drive of the position control mechanism and the chuck unit that contacts the screw tightening tool. Also, in order to prevent excessive pressing, there are advantages such as being able to prevent breakage of the screw guide, chuck unit, etc. due to the pressing. Especially when the chuck unit includes chuck jaws, a supply pipe, etc. in the moving path of the screw guide, there are also advantages such as being able to prevent breakage of these. Further, since the breakage prevention means is configured to measure the load current of the lifting motor and measure the pressing force based on the magnitude of the load current, there is also an advantage such as being able to immediately obtain the force with which the screw guide presses the chuck unit. On the other hand, when the breakage prevention means is a contact sensor provided separately from the position control mechanism, there are advantages such as the position control mechanism may have a configuration other than a ball screw mechanism.

[0008] In addition, when the damage prevention means is configured to be able to detect the posture of the screw in the holding hole, and the control unit is configured to control the driving of the position control mechanism based on the signal from the damage prevention means, it is possible to detect a supply failure of the screw before the screw guide starts to move toward the chuck unit. For this reason, there are advantages such as preventing a screw with a supply failure or the like from colliding with the screw guide and being damaged. Further, if the damage prevention means is a non-contact sensor that detects the screw passing area or an imaging means that images the screw passing area, there are also advantages such as the screw not coming into contact with the sensor and not inhibiting the passage of the screw.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 10 denotes a screw tightening device for tightening a screw S having a head and a shaft with respect to a workpiece. This screw tightening device 10 includes a position control mechanism 20, a screw tightening tool 30 that moves up and down under the drive of the position control mechanism 20, a chuck unit 40 disposed on the movement path of the screw tightening tool 30, and a control unit 50 that controls the drive of the position control mechanism 20 and the screw tightening tool 30.

[0011] The position control mechanism 20 includes a frame 21 extending in the vertical direction, and upper and lower plates 211 and 212 extending in the horizontal direction are integrally fixed to the upper and lower ends of the frame 21. Between the upper plate 211 and the lower plate 212, a guide rod 22 extending parallel to the frame 21 is provided, and a driver base 23 configured to be slidable is mounted on the guide rod 22 so as to be movable up and down. Further, an elevating AC servo motor 24 (hereinafter referred to as an elevating motor 24), which is an example of an elevating drive source, is placed on the upper plate 211, and a ball screw 25 is integrally rotatably connected to the output shaft of the elevating motor 24. This ball screw 25 is provided between the upper plate 211 and the lower plate 212, and the driver base 23 is connected to the ball screw 25 via a drive nut (not shown) that moves up and down by the rotation of the ball screw 25. With these structures, the driver base 23 can move up and down along the guide rod 22 under the rotational drive of the elevating motor 24. Note that the elevating motor 24 is provided with an encoder (not shown), which is an example of position detection means capable of detecting the amount of rotation of the output shaft.

[0012] The housing 31 of the screwing tool 30 is connected to the driver base 23, and an AC servo motor 32 (hereinafter referred to as the tightening motor 32), which is an example of a rotational drive source, is placed on the housing 31 with its output shaft (not shown) facing downward. A connecting shaft 33 that penetrates the housing 31 rotatably is connected to the output shaft of the tightening motor 32, and a driver bit 34 is attached to the connecting shaft 33. The lower end of the driver bit 34 is configured to be able to fit with the head of the screw S. Further, a hollow cylindrical screw guide 36 that encloses the connecting shaft 33 and the driver bit 34 is installed at the lower part of the housing 31. An air hose joint 37 to which an intake hose (not shown) continuous to an intake means such as a compressor (not shown) is connected is attached to the upper part of the screw guide 36, and the screw S can be adsorbed and held at the lower end opening of the screw guide 36 when the intake means is driven. Further, a cushion spring (not shown) is provided between the screw guide 36 and the housing 31, and the screw guide 36 is constantly biased downward by this cushion spring with a predetermined force. That is, the screw guide 36 is configured to be axially relatively movable with respect to the housing 31 and the driver bit 34 in conjunction with the expansion and contraction of the cushion spring.

[0013] Further, the chuck unit 40 has a chuck body 41 fixed through the lower plate 212. As shown in Fig. 2(a), a guide hole 411 having a hole diameter larger than the maximum diameter of the screw guide 36 is formed through the chuck body 41, and the screw guide 36 is configured to be axially insertable through this guide hole 411. A pair of the chuck jaws 42, 42 are swingably mounted on both side surfaces of the chuck body 41 so as to sandwich the guide hole 411, and the chuck jaws 42, 42 are always urged by a claw spring (not shown) sandwiched between the chuck body 41 and the tip side to close. Holding holes 421 are formed in a split manner on the opposing surfaces of the chuck jaws 42, 42 on the extension line of the guide hole 411. The holding holes 421 are formed with a hole diameter larger than the head diameter of the screw S, and a guide hole 422 having a hole diameter larger than the shaft diameter of the screw S and smaller than the head diameter is continuous in front of the holding holes 421. Thereby, as shown in Fig. 3(a), the chuck jaws 42, 42 hold the screw S by bringing the head seating surface into contact with the boundary portion between the holding holes 421 and the guide holes 422.

[0014] Further, inclined holes 412 that are inclined with respect to the guide hole 411 and whose extension lines intersect are formed in the chuck body 41, and a hose mounting fitting 43 to which a supply hose 61 extending from an external screw supply device (not shown) is connected is installed in the inclined holes 412. The hose mounting fitting 43 is a cylindrical member configured to allow the screw S to pass through, and a supply pipe 44 is connected between the hose mounting fitting 43 and the chuck jaws 42, 42. The supply pipe 44 is also a cylindrical member configured to allow the screw S to pass through, and is swingably mounted in a direction away from the swing surface of the chuck jaws 42, 42 with set screws 45 arranged on both side surfaces of the chuck body 41 as pivot shafts. The supply pipe 44 is always in communication with the hose mounting fitting 43, and the tip end thereof is urged by a torsion coil spring 46 so as to be continuous with the rear end portion of the holding hole 421 of the chuck jaws 42, 42, and the end portion of the torsion coil spring 46 is wound around the set screw 45.

[0015] Furthermore, as an example of a swing restricting mechanism that restricts the swing of the chuck claws 42, the chuck unit 40 has a swing plate 47 that interlocks with the supply pipe 44. This swing plate 47 is configured to be swingable about the set screw 45 as an axis of rotation, similar to the supply pipe 44, and is constantly biased toward the chuck claws 42, 42 by the torsion coil spring 46. The swing plate 47 is formed with bifurcated fitting portions 48, 48. As shown in Fig. 2(a), when the supply pipe 44 is located on the extension line of the guide hole 411, the fitting portions 48, 48 engage with the chuck claws 42, 42, contact the outside of the chuck claws 42, 42, and can forcibly restrict the opening. As shown in Fig. 2(b), the fitting portions 48, 48 are dimensioned to disengage from the chuck claws 42, 42 before the chuck claws 42, 42 are pushed open by the screw guide 36.

[0016] The control unit 50 is connected to the lifting motor 24, the tightening motor 32, the intake means continuous with the screw guide 36, the screw feeder, etc., and is configured to receive various signals output from these and control the operation of each unit based on the signals. The control unit 50 is configured to be able to process the pulse signal output by the encoder of the lifting motor 24, and is configured to be able to calculate the movement amount of the screw tightening tool 30, that is, the movement position of the driver bit 34 and the screw guide 36, from the pulse signal (the rotation amount of the lifting motor 24) and the lead of the ball screw 25.

[0017] In addition, as control data, the control unit 50 stores data on the standby position of the screw tightening tool 30 shown in Fig. 3(a), the amount of movement of the screw tightening tool 30 from the standby position to the position immediately before the screw guide 36 shown in Fig. 3(b) contacts the supply pipe 44 (hereinafter referred to as the collision discrimination start position), data on the amount of movement of the screw tightening tool 30 from the collision discrimination start position to the position where the driver bit 34 or the screw guide 36 shown in Fig. 3(c) contacts the screw S supplied correctly in the holding hole 421 of the chuck (hereinafter referred to as the collision discrimination end position), and data on the amount of movement of the screw tightening tool 30 from the standby position to the position immediately before the screw guide 36 contacts the workpiece (hereinafter referred to as the pre-workpiece position) are preset.

[0018] Note that the lifting motor 24 is an example of a damage prevention means. This lifting motor 24 is configured to transmit to the control unit 50 a load current value corresponding to the load generated by the movement of the screw tightening tool 30 between the collision confirmation start position and the collision discrimination end position. Further, the control unit 50 has also registered in advance a load current value (collision current value) of the lifting motor 24 corresponding to the load generated when the screw tightening tool 30 collides with the chuck unit 40 and stops. When the load current value reaches the collision current value while the lifting motor 24 is driving, it is configured to determine that the screw tightening tool 30 has collided with the chuck unit 40.

[0019] As shown in Fig. 6, the control unit 50 S01: Wait for the input of the start signal. S02: Send a downward drive command to the lifting motor 24 and output a drive command to the intake means. S03: Wait for the screw tightening tool 30 to reach the collision discrimination start position. S04: Obtain the load current value of the lifting motor 24. S05: Check whether the load current value of the lifting motor 24 has reached the collision current value. If it has reached, output an abnormal signal and proceed to S12. S06: Check whether the screw tightening tool 30 has reached the collision discrimination end position. If it has not reached, return to S04. S07: Wait for the screw tightening tool 30 to reach the collision determination end position. S08: Drive the tightening motor 32. S09: Wait for the tightening to be completed. S10: Output a drive stop command to the intake means and the tightening motor 32, and send an upward drive command to the lifting motor 24. S11: Wait for the screw tightening tool 30 to reach the standby position. S12: End. It is configured to process as follows. Although omitted in FIG. 6, the control unit 50 has a step of operating the screw supply device immediately after the start signal is input (between S01 and S02 in FIG. 6) and pumping the screw S toward the chuck unit 40.

[0020] Next, the operation of the screw tightening device 10 configured as described above will be described. When a start signal is input, the control unit 50 drives the screw supply device and pumps the screw S toward the chuck unit 40. The pumped screw S is supplied through the supply hose 61 and the supply pipe 44 to the holding holes 421 of the chuck claws 42, 42. At this time, the chuck claws 42, 42 are restricted by the fitting portions 48, and the chuck claws 42, 42 are prevented from being greatly pushed open by the impact when the screw S changes direction at the pressure feed air for pumping the screw S, the connection portion between the supply pipe 44 and the chuck claw 42, and the impact when the head seating surface of the pumped screw S contacts the boundary portion between the holding hole 421 and the guide hole 422. Since the swinging of the chuck claws 42, 42 is thus prevented, the screw S stops with its head contacting the boundary portion between the holding hole 421 and the guide hole 422 as shown in the figure. As a result, the screw S is held inside the chuck claws 42, 42 in a correct posture where the head is guided by the holding hole 421 and the shaft portion is guided by the guide hole 422.

[0021] As described above, when the screw S is supplied to the holding hole 421, the control unit 50 drives the lifting motor 24 to lower the screw tightening tool 30 and drives the intake means to start intake from the tip opening of the screw guide 36. Then, when the screw tightening tool 30 reaches the collision determination start position, the damage prevention means is activated. When the supply pipe 44 swings in a direction away from the swing surfaces of the chuck claws 42, 42 by being pushed by the screw guide 36 of the screw tightening tool 30 that descends in this way, the swing plate 47 also swings in a direction away from the swing surfaces of the chuck claws 42, 42 in conjunction with the supply pipe 44. As a result, the fitting portions 48, 48 of the swing plate 47 are disengaged from the chuck claws 42, 42, so that the chuck claws 42, 42 can swing freely. After that, the screw guide 36 of the further lowered screw tightening tool 30 reaches the collision determination end position after its tip portion enters the holding hole 421. At this time, since the intake means has already been driven as described above, the screw S in the holding hole 421 is adsorbed and held at the tip opening of the screw guide 36. Also, since the screw S is held in the correct posture in the holding hole 421 as described above, it is possible to surely adsorb and hold the screw S at the tip of the screw guide 36. After that, as the screw guide 36 further descends, the chuck claw 42 is pushed open.

[0022] When the screw guide 36 that has passed through the chuck unit 40 reaches the position immediately before the workpiece as described above, the control unit 50 drives the tightening motor 32 to rotate forward. As a result, the driver bit 34 starts to rotate. Then, when the further lowered screw guide 36 abuts against the surface of the workpiece, the cushion spring is deflected and only the driver bit 34 advances. At this time, since the driver bit 34 is rotating under the drive of the tightening motor 32, the driver bit 34 and the screw S are fitted in the screw guide 36, and the screw S is fastened to the workpiece. After the screw fastening is completed, the control unit 50 stops the intake means and the tightening motor 32, and drives the lifting motor 24 in reverse to return the screw tightening tool 30 to the standby position.

[0023] In the supply of the screw S to the screw guide 36 described above, as shown in Fig. 4(a), the fed screw S may stop at a position straddling the boundary between the supply pipe 44 and the holding hole 421, or as shown in Fig. 4(b), two screws S, S may be supplied simultaneously, etc., causing the screw S to bite into the supply pipe 44 and inhibiting the oscillation of the supply pipe 44. At this time, after the screw guide 36 collides with the supply pipe 44 in a non-oscillating state, it descends toward the collision determination end position, thus pressing the supply pipe 44. When pressing, if the oscillation amount of the oscillation plate 47 is small and the fitting portion 48 has not come off from the chuck claw 42, the screw guide 36 tries to descend toward the collision determination end position, thereby pressing up to the chuck claw 42 via the supply pipe 44 and the screw S. When such a supply defect occurs, in the conventional screw tightening device, since the descending screw guide 36 excessively presses the supply pipe 44, a strong force is applied to the lower end of the screw guide 36, the supply pipe 44, the screw S, and the chuck claw 42, and these components may be damaged. However, in the present invention, the control unit 50 monitors the load current value of the lifting motor 24, and when the load current value of the lifting motor 24 reaches the collision current value, the control unit 50 reversely drives the lifting motor 24 to return the screw tightening tool 30 to the standby position. As a result, before the screw guide 36 excessively presses the supply pipe 44, the screw S, the chuck claw 42, etc., the descent of the screw tightening tool 30 by the lifting motor 24 can be interrupted, and damage to various components can be prevented. When the screw guide 36 collides with the supply pipe 44, the screw S, etc., the cushion spring that biases the screw guide 36 bends, absorbing the impact caused by the collision, and damage to various components is prevented. Also, depending on the length of the screw S, even if the above-mentioned simultaneous supply defect occurs, the supply pipe 44 may be able to oscillate. In this case, the screw guide 36 collides with the screw S before reaching the collision determination end position as shown in Fig. 4(c). At this time, depending on the posture of the screw S, a force is applied in a direction in which the chuck claw 42 does not oscillate, and the chuck claw 42 and the screw guide 36 are in a state of pressing against each other with the screw S sandwiched therebetween.Even in such a state, as described above, when the load current value of the lifting motor 24 reaches the collision current value, the lowering of the screw guide 36 is stopped, so that damage to each component can be prevented. Note that while the screw tightening tool 30 moves from the collision determination start position to the collision determination end position, the damage prevention means is set to operate, so that the working time is shortened and the cycle time can be improved.

[0024] Note that the screw tightening device 10 according to the present invention is not limited to the above-described one, and various modifications are possible without departing from the gist of the invention. For example, in the screw tightening device 10, the chuck unit 40 includes a swing plate 47 as an example of a swing restriction mechanism, but as long as it is configured to be able to restrict the swing of the chuck jaws 42, as shown in Japanese Patent No. 3718349, a chuck jaw having a cylindrical protrusion formed on the side surface, an operation plate having a figure-eight-shaped hole that meshes with the protrusion of the chuck jaw, and an air cylinder that moves this operation plate up and down. It may be a chuck unit or the like. Further, the processing procedure of the control unit 50 shown in FIG. 6 is merely an example, and can be appropriately changed according to the initial position of the screw tightening tool 30 and the like. For example, when the standby position of the screw tightening tool 30 is very close to the collision determination start position, a configuration may be adopted in which a start signal is input, the lifting motor 24 is started, and at the same time, monitoring of the load current value thereof is started. Further, the position of the collision determination end position is such that when the fitting portion 48 of the swing plate 47 is disengaged from the chuck jaw 42 and the screw guide 36 excessively presses the chuck jaw 42 via the screw S, the chuck jaw 42 swings and the screw S can be discharged to the outside, or the dimension from the lower end of the holding hole 421 to the lower end of the screw guide 36 is equal to or less than the dimension of the screw S, and it is set to satisfy at least one of the positions where it can be determined that the screw S is normally supplied, and it can be appropriately changed according to the length and shape of the screw S, or the length of the fitting portion 48 of the swing plate 47.

[0025] Also, the configuration for monitoring the load current value of the lifting motor 24 as described above is an example of the damage prevention means, and there is no problem with other configurations. For example, a displacement sensor capable of detecting the relative movement between the screw guide 36 and the driver bit 34. If the relative descent amount of the driver bit 34 with respect to the screw guide 36 is greater than the normal descent amount, it means that the driver bit 34 is descending while the screw guide 36 is in contact with the supply pipe 44 or the like and stopped, that is, the screw guide 36 is pressing the supply pipe 44 or the like excessively. A configuration for making such a determination may be used. Additionally, a pressure sensor (not shown) attached to any one of the chuck claws 42 of the chuck unit 40, the supply pipe 44, or the screw guide 36 and the driver bit 34 of the screwing tool 30 may be used. If the pressure is above a predetermined value, a configuration for determining that the screwing tool 30 is pressing the chuck unit 40 excessively may be used. In cases where, as described above, a configuration for monitoring whether the screwing tool 30 is pressing the chuck unit 40 excessively while the screwing tool 30 moves from the collision determination start position to the collision determination end position, the control unit 50 may be configured to receive the output signal of a predetermined damage prevention means in the process of S04 in FIG. 6 and determine whether the value of the output signal is a normal value in the process of S05 in FIG. 6.

[0026] Furthermore, the damage prevention means is not limited to a configuration that detects that the screw guide 36 has collided with the supply pipe 44 or the like, and may be a configuration that detects the posture of the screw S in the holding hole 421. For example, as shown by the two-dot chain lines in FIGS. 5(a) and 5(b), a space 423 (hereinafter referred to as a screw passage area 423) located above the head of the screw S normally supplied in the holding hole 421 may be a sensor 424 such as an optical sensor or a proximity sensor capable of detecting that the screw S has passed through, or a camera (not shown) capable of photographing the screw passage area 423. The damage prevention means for detecting an abnormality before the screw guide 36 descends in this way can detect whether or not the screw S exists in the screw passage area 423 before the control unit 50 outputs a drive signal to the position control mechanism 20 (between S01 and S02 in FIG. 6). Further, the control unit 50 is configured to drive the position control mechanism 20 after receiving a detection signal from the damage prevention means. When the screw S is normally supplied to the holding hole 421 as shown in FIG. 5(a), the position control mechanism 20 is driven, while when a supply defect such as two screws S being supplied occurs as shown in FIG. 5(b), an abnormal signal is output without driving the position control mechanism 20. As a result, as described above, the screw guide 36 driven by the position control mechanism 20 does not collide with the supply pipe 44 or the like in a state where it cannot swing due to the defective screw S, and damage to various components is prevented.

Explanation of Reference Numerals

[0027] 10 … Screw tightening device 20 … Position control mechanism 24 … Lifting motor 25 … Ball screw 30 … Screw tightening tool 34 … Driver bit 36 … Screw guide 40 … Chuck unit 41 … Chuck body 411… Guide hole 42 … Chuck jaw 421… Holding hole 44 … Supply pipe 50 … Control unit S... screw

Claims

1. A screw tightening tool comprising a driver bit rotatable by receiving the drive of a rotational drive source, and a screw guide that encloses the driver bit and is configured to be slidable with respect to the driver bit, a position control mechanism for reciprocating the screw tightening tool, a chuck unit disposed on the axis of the driver bit, a breakage prevention means for preventing breakage of the screw tightening tool or the chuck unit that moves by receiving the drive of the position control mechanism, and a control unit configured to control the drive of the position control mechanism based on a signal from the breakage prevention means. The screw tightening device has, The breakage prevention means is configured to detect excessive pressing of the screw guide of the screw tightening tool or the chuck unit of the driver bit that moves by receiving the drive of the position control mechanism, The control unit is configured to interrupt the drive of the position control mechanism when the breakage prevention means detects excessive pressing. A screw tightening device characterized by this.

2. The position control mechanism includes a lifting motor and a ball screw connected to the lifting motor, The breakage prevention means measures the load current value of the lifting motor, and if the load current value reaches a predetermined collision current value set in advance, it determines that the screw tightening tool is pressing the chuck unit, and interrupts the drive of the lifting motor. The screw tightening device according to claim 1, characterized in that it is configured as such.

3. The chuck unit includes a chuck body in which a guide hole for guiding the screw guide is formed, a pair of chuck jaws that are swingably attached to the chuck body and that divide and form holding holes for holding a screw on an extension line of the guide hole, a hose mounting fitting that intersects the swing surface of the chuck jaws and extends obliquely rearward, and a supply pipe that is disposed between the hose mounting fitting and the chuck jaws and is swingable in a direction away from the swing surface of the chuck jaws. The anti-breakage means is a contact sensor attached to any one of the chuck jaws, supply pipe, screw guide, or driver bit, according to the screw tightening device of claim 1 or claim 2.

4. The anti-breakage means is configured to operate between a collision confirmation start position set above the height at which the lower end of the screw guide abuts against the supply pipe and a collision confirmation end position set below the height at which the screw guide abuts against the head of the screw normally supplied to the chuck jaw, according to the screw tightening device of claim 3.

5. The anti-breakage means is configured to determine the posture of the screw supplied to the holding hole. The control unit is configured to drive the position control mechanism when the anti-breakage means determines that the posture of the screw in the holding hole is normal, according to the screw tightening device of claim 3.

6. The anti-breakage means is a non-contact sensor disposed such that the detection range comes within the screw passing area set on the supply pipe side from the head of the screw normally supplied in the holding hole, or imaging means disposed to image the screw passing area, according to the screw tightening device of claim 3 or claim 4.

Images