Screw fastening device

Abstract

To provide a screw fastening device having small loads to a workpiece and a screw.SOLUTION: A screw fastening device includes a driver unit 30 for rotating a bit 35 engageable with a screw S head by a bit rotation motor 33, a position control unit 20 capable of moving the driver unit 30 in the axial direction of the bit 35, and a control unit 40 for controlling the driving of the driver unit 30 and the position control unit 20. The driver unit 30 has a cushion spring 36 for energizing the bit 35 in a direction separated from the bit rotation motor 33, and the control unit 40 controls the position of the driver unit 30 so that the cushion spring 36 is compressed between the bit 35 and the bit rotation motor 33 by a preset arbitrary dimension.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Conventionally, as a screw tightening device for tightening a screw onto a workpiece, what is disclosed in Patent Document 1 is known. This screw tightening device includes a driver unit having a bit that rotates under the drive of a motor, and a thrust applying means for reciprocating the driver unit in the axial direction of the bit. Further, in the screw tightening process, the thrust applying means presses the driver unit toward the workpiece with a predetermined thrust to prevent the bit and the screw from coming out of engagement.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional screw tightening device, not only the pressing force toward the workpiece by the thrust applying means but also the self-weight of the driver unit was loaded on the bit. For this reason, the bit presses the screw and the workpiece with a large force including the self-weight of the driver bit, and there is a problem that the burden on the screw and the workpiece is large.

[0005] Therefore, an object of the present invention is to provide a screw tightening device with a small burden on the workpiece and the screw during the screw tightening process.

Means for Solving the Problems

[0006] To achieve this object, the present invention includes a driver unit that rotates a bit engageable with a screw head by a bit rotation motor, a position control unit that can move the driver unit in the axial direction of the bit, and a control unit that controls the driving of the driver unit and the position control unit. The driver unit has a cushion spring that biases the bit in a direction away from the bit rotation motor, and the control unit controls the position of the driver unit so that the cushion spring is compressed by an arbitrary dimension preset between the bit and the bit rotation motor. Further, a pressing force such that the bit does not come off from the head of the screw when tightening the screw and the spring constant of the cushion spring are preset in the control unit, and it is preferable that the control unit controls the position of the driver unit so that the cushion spring is compressed to such an extent that it exerts a spring reaction force corresponding to the pressing force. Further, a lead of a screw to be tightened to a workpiece is preset in the control unit, and the control unit calculates a screwing speed at which the screw is screwed into the workpiece from the product of the rotation speed of the bit rotation motor and the lead of the screw, and preferably controls the driving of the position control unit so that the driver unit moves at the same speed as the screwing speed.

Advantages of the Invention

[0007] According to the above invention, since the position control unit controls the position of the driver unit, the dimension by which the cushion spring is compressed can be adjusted, so that the spring reaction force of the cushion spring that biases the bit can be adjusted. As a result, there are advantages such as it is possible to tighten a screw with a small burden on the workpiece and the screw without applying the self-weight of the driver unit to the bit. Further, the position control unit controls the position of the driver unit so that the cushion spring exerts a spring reaction force equal to the pressing force that does not cause the cam-out required immediately before the completion of the screw fastening. For this reason, the bit is biased toward the work side by the pressing force of the cushion spring. Therefore, it has advantages such as preventing cam-out and enabling screw tightening with a small load on the screw and the work. In addition, since the control unit calculates the screwing speed at which the screw is screwed into the work from the product of the rotational speed of the bit rotation motor and the lead of the screw, and controls the drive of the position control unit so that the driver unit moves at the same speed as the screwing speed, it has advantages such as enabling screw tightening while maintaining a constant pressing force.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 10 denotes an automatic fastening device 10 for tightening a screw S1 to a workpiece W. This automatic fastening device 10 includes a position control unit 20, a driver unit 30 held by the position control unit 20 and movable to an arbitrary position, a control unit 40 for controlling the driving of the position control unit 20 and the driver unit 30, and a supply device (not shown) for supplying the screw S1 to a predetermined receiving position set within the movement range of the driver unit 30 by the position control unit 20. In the present embodiment, the screw S1 is a general screw having a head and a shaft, and a driving portion in the shape of a cross hole is formed on the upper surface of the head, and is tightened to a tapped screw W1 formed in the workpiece W.

[0010] As shown in FIG. 1, the position control unit 20 of the automatic fastening device 10 includes a frame 21 extending in the vertical direction. At the upper and lower ends of this frame 21, a horizontally extending upper plate 22 and a lower plate 23 are integrally fixed. Between this upper plate 22 and the lower plate 23, a guide rod 24 extending parallel to the frame 21 is provided, and a driver base 25 configured to be slidable is mounted on this guide rod 24 so as to be movable up and down. Further, an AC servo motor 26 for lifting and lowering (hereinafter referred to as the lifting motor 26), which is an example of a lifting drive source, is placed on the upper plate 22, and a ball screw 27 is integrally and rotatably connected to the output shaft of this lifting motor 26. This ball screw 27 is provided between the upper plate 22 and the lower plate 23, and a drive nut 28, which is an example of a moving part that moves up and down by its rotation, is screwed onto this ball screw 27. The driver base 25 is connected to this drive nut 28 so as to move up and down integrally. Therefore, the driver base 25 moves up and down in response to the rotational drive of the lifting motor 26. Furthermore, the lifting motor 26 has an encoder 261 capable of transmitting a pulse signal corresponding to the rotation angle of the output shaft of the lifting motor 26, and this encoder 261 is connected to the control unit 40.

[0011] As shown in FIG. 1, the driver unit 30 has a connection plate 31 connected to the driver base 25 of the position control unit 20. A hollow cylindrical housing 32 is fixed to the connection plate 31. An AC servo motor 33 (hereinafter referred to as the bit rotation motor 33) is fixed to the housing 32 such that its output shaft is inserted into the housing 32. The bit rotation motor 33 has an encoder 331 capable of transmitting a pulse signal corresponding to the rotation angle of the output shaft of the bit rotation motor 33, and this encoder 331 is connected to the control unit 40. Further, a shaft coupling 34 that can rotate integrally is connected to the output shaft of the bit rotation motor 33, and an insertion hole 341 is formed at the lower end of the shaft coupling 34. A long hole 342 extending in the axial direction intersects the insertion hole 341, and a connection pin 343 configured to be movable up and down along the long hole 342 is inserted through the long hole 342. A bit 35 that can rotate integrally with the shaft coupling 34 is suspended from the connection pin 343. The bit 35 has a fitting portion 351 at its lower end that can be fitted with a screw S1, and an annular magnet 352 capable of holding the screw S1 by magnetic force is mounted near the fitting portion 351.

[0012] Further, a cushion spring 36 that constantly biases the bit 35 downward is disposed between the bottom surface of the insertion hole 341 and the bit 35. The cushion spring 36 is dimensioned such that it is slightly compressed even when the connection pin 343 abuts against the lower end of the long hole 342 of the shaft coupling 34 so as to constantly bias the bit 35 in a direction away from the bit rotation motor 33. For this reason, while the cushion spring 36 biases the connection pin 343 to constantly abut against the lower end of the long hole 342, the bit 35 bends when an upward pressing force is applied to the bit 35, and as shown in FIGS. 2(a) and 2(b), the bit 35 and the connection pin 343 can be relatively raised with respect to the shaft coupling 34 and the bit rotation motor 33.

[0013] The control unit 40 is connected to an external device and includes a transceiver unit that transmits and receives various signals, a storage unit that stores an operation program and the like, and an arithmetic processing unit that performs arithmetic operations based on the information of the transceiver unit and the storage unit and compares and determines the arithmetic operation results. The bit rotation motor 33 and the lifting motor 26 are connected to the transceiver unit.

[0014] The storage unit has a screw parameter, a spring parameter, a taught position L, an offset parameter, and a speed parameter as control parameters necessary for the tightening operation of the screw S1. These can be configured to input predetermined numerical values on an input screen as shown in FIG. 3.

[0015] The screw parameter includes the axial length J1 of the screw S1, the distance J2 that the screw S1 advances in the axial direction when it makes one revolution (hereinafter referred to as the lead J2), and the pressing force J3 (hereinafter referred to as the fastening thrust J3) such that the fitting portion 351 does not come off from the head of the screw S1 when the screw S1 is tightened.

[0016] The spring parameter includes the spring constant K1 of the cushion spring 36, the length K2 of the cushion spring 36 before compression, the maximum compression amount K3 of the cushion spring 36, and the compression amount K4 (hereinafter referred to as the compression dimension K4) necessary to exert the fastening thrust J3. The maximum compression amount K3 of the cushion spring 36 is the compression amount of the cushion spring 36 when the connecting pin 343 abuts against the upper end of the long hole 342 of the shaft joint 34 (the cushion spring 36 is bent 100%) as shown in FIG. 2(b), and the value obtained by subtracting the diameter of the connecting pin 343 from the axial dimension of the long hole 342 is input. The compression dimension K4 is a dimension calculated by dividing the value of the fastening thrust J3 by the value of the spring constant K1 of the cushion spring 36. In the present embodiment, as exemplarily shown in FIG. 2(a), it is set to a dimension such that the connecting pin 343 is located at the axial center of the long hole 342 (the cushion spring 36 is bent 50%). In this way, when the cushion spring 36 is compressed by the compression dimension K4, the bit 35 is biased by the fastening thrust J3.

[0017] The teaching position L is composed of the coordinates and orientation of the driver unit 30 when the fitting portion 351 of the bit 35 is fitted to the screw S1 in a state of being seated on the workpiece W in advance. In addition, the coordinates of the driver unit 30 in a state where the cushion spring 36 is not compressed are taught at this teaching position L.

[0018] The offset parameter is composed of a collision avoidance offset dimension L1, a rotation start offset dimension L2, and a compression start offset dimension L3. The collision avoidance offset dimension L1 is a value set so that when the driver unit 30 moves horizontally, the bit 35 and the screw S1 do not contact components or the like installed around the female thread W1 of the workpiece W, and is set in consideration of the height of the components around the fastening portion and the total length of the screw S1. The rotation start offset dimension L2 is a value set so that the screw S1 and the workpiece W do not collide when the driver unit 30 is moving at high speed, and is set in consideration of the dimensional tolerances of the screw S1 and the workpiece W. A dimension of at least twice the lead J2 of the screw S1 is set for the compression start offset dimension L3.

[0019] In addition, as operation switching points in the screw tightening operation for tightening a screw onto the workpiece, a collision avoidance position, a rotation start position, a compression start position, a compression completion position, and a seating position are set in the control unit 40, and their coordinates are calculated from the teaching position L and the value of the offset parameter. The collision avoidance position is a position set above the workpiece W, and as shown in FIG. 4(a) (Z-1), it is determined to be above the teaching position L by the sum of the shaft length J1 and the collision avoidance offset dimension L1. Further, the rotation start position is a position immediately before the tip of the screw S1 contacts the workpiece W, as shown in FIG. 4(a) (Z-2), and is determined to be above the teaching position L by the sum of the shaft length J1 and the rotation start offset dimension L2. Moreover, the compression start position is a position when the screw S1 is threadedly engaged with the workpiece W by several turns, as shown in FIG. 4(a) (Z-3), and is determined to be above the teaching position L by the amount obtained by subtracting the compression start offset dimension L3 from the shaft length J1. The compression completion position is a position immediately before the screw S1 seats on the workpiece W, as shown in FIG. 4(a) (Z-4), and is determined to be above the teaching position L by the value of the rotation start offset dimension L2. In the screw tightening operation, when the screw S1 reaches the compression completion position, the cushion spring 36 is compressed by the compression dimension K4. The seating position is determined to be the same position as the teaching position L at the position where the screw S1 seats, as shown in FIG. 4(a) (Z-5). Similar to the compression completion position, in the screw tightening operation, when the screw S1 reaches the seating position, the cushion spring 36 is compressed by the compression dimension K4. Therefore, at the compression completion position and the seating position, the control unit 40 performs position control so that the driver unit 30 is positioned below the screw S1 by the compression dimension K4. Also, as shown in FIG. 4(a) (Z-6), a target position is defined below the seating position by the rotation start offset dimension L2. When the driver unit 30 reaches the target position, the control unit 40 is configured to determine that there is a tightening abnormality and return the driver unit 30 to the initial position.

[0020] The speed parameter is composed of a fast feed speed which is the moving speed from the origin or the component supply device to the collision avoidance position, and an approach speed which is the moving speed from the collision avoidance position to the rotation start position.

[0021] Note that the control unit 40 constantly monitors the driving amounts of the bit rotation motor 33 and the lifting motor 26. Therefore, it is configured such that the positions of the bit rotation motor 33 and the shaft coupling 34 of the driver unit 30 can be grasped from the driving amount of the lifting motor 26, and the positions of the screw S1 and the bit 35 in contact with the screw S1 can be grasped from the driving amount of the bit rotation motor 33. Therefore, the control unit 40 can calculate the relative position of the bit 35 with respect to the shaft coupling 34, and can calculate the compression amount of the cushion spring 36 based on the calculation result.

[0022] Further, as shown in FIG. 4(b), the control unit 40 calculates the screwing speed of the screw S1 from the product of the rotation speed of the bit rotation motor 33 and the lead J2 of the screw S1 between the rotation start position and the compression start position and between the compression completion position and the seating position, and rotates the lifting motor 26 at a rotation speed obtained by dividing the calculated screwing speed by the lead J2 of the ball screw 27 input in advance. As a result, the lowering speed of the driver unit 30 becomes the same speed as the screwing speed of the screw S1 (hereinafter referred to as the synchronous speed). When the driver unit 30 descends at the synchronous speed in this way, during the synchronous speed, the cushion spring 36 is not compressed or extended, and the thrust acting on the screw S1 becomes constant. Further, when the driver unit 30 reaches the compression start position, the control unit 40 is configured to control the drive of the lifting motor 26 so that the driver unit 30 descends at a compression speed set higher than the synchronous speed. This compression speed is maintained until the compression amount of the cushion spring 36 reaches the compression dimension K4 or the driver unit 30 reaches the compression completion position. Note that when the compression amount of the cushion spring 36 reaches the same dimension as the compression dimension K4, the control unit 40 switches the lowering speed of the driver unit 30 to the synchronous speed. On the other hand, when the driver unit 30 reaches the compression completion position and the compression amount of the cushion spring 36 is less than the compression dimension K4, the rotation drive of the bit rotation motor 33 is temporarily stopped, and the driver unit 30 is lowered until the compression amount of the cushion spring 36 reaches the compression dimension K4.

[0023] Next, the operation of the automatic fastening device 10 configured as described above will be described. When a start signal is input, the control unit 40 drives the position control unit 20 to move the driver unit 30 to the receiving position of the supply device, which waits at the origin. When the driver unit 30 reaches the receiving position, the control unit 40 drives the bit rotation motor 33. As a result, since the bit 35 is rotationally driven, the screw S1 fits into the fitting portion 351, and the screw S1 is magnetically held on the bit 35 by the magnet 352. After that, when the screw S1 is magnetically held on the fitting portion 351 of the bit 35, the control unit 40 drives the position control unit 20 to move the driver unit 30 to the collision avoidance position at a fast feed speed.

[0024] When the driver unit 30 reaches the collision avoidance position shown in Fig. 4(a)(Z-1), the control unit 40 lowers the driver unit 30 to the rotation start position shown in Fig. 4(a)(Z-2) at an approach speed. When the driver unit 30 reaches the rotation start position, the control unit 40 drives the bit rotation motor 33 in a temporary tightening operation at high speed and low torque, and synchronizes the rotation of the lifting motor 26 with the rotation of the bit rotation motor 33 to lower the driver unit 30 at a synchronous speed. In this way, when the driver unit 30 descends at the same synchronous speed as the screwing speed of the screw S1, almost no impact occurs when the screw S1 contacts the workpiece W. Therefore, when the tip of the screw S1 descending at the synchronous speed abuts against the workpiece W, it is prevented that the screw S1, which is excessively pressed from above against the bit 35, falls down or the like. After that, the screw S1 gradually engages with the female screw W1. By lowering the driver unit 30 at the synchronous speed in this way, when the screw S1 and the female screw W1 start to engage, the cushion spring 36 is hardly compressed. As a result, since the downward force applied to the screw S1 is only the self-weight of the bit 35, damage to the screw S1 and the female screw W1 is prevented.

[0025] Further, when the driver unit 30 reaches the compression start position, the control unit 40 switches the descending speed of the bit 35 from the synchronization speed to the compression speed. As a result, since the bit rotation motor 33 and the shaft coupling 34 descend faster than the screw S1 and the bit 35, the cushion spring 36 is compressed. At this time, the compression start position is set at a position where the screw S1 and the female screw W1 are screwed together for two or more pitches. When the cushion spring 36 is compressed, the reaction force of the suddenly rising cushion spring 36 is dispersed and applied to a plurality of screw threads, thereby preventing the screw S1 and the female screw W1 from being damaged.

[0026] Also, when the driver unit 30 descending at the compression speed relatively moves by the compression dimension K4 with respect to the bit 35 descending at the screwing speed, the control unit 40 returns the descending speed of the driver unit 30 to the synchronization speed and tightens until the screw S1 seats on the work W.

[0027] Thereafter, when the screw S1 seats on the work W and the bit rotation motor 33 torque - ups, the control unit 40 switches the rotation of the bit rotation motor 33 to a low - speed and high - torque final tightening operation. At this time, since the cushion spring 36 biases the bit 35 toward the work W with the fastening thrust J3, the bit 35 does not come off the screw S1. Also, during the final tightening operation, since the screw S1 has already seated and the rotation of the bit rotation motor 33 is almost zero, the lifting motor 26 also hardly rotates and continues to maintain the relative position between the shaft coupling 34 and the bit 35. Thereafter, when the bit rotation motor 33 torque - ups again, the control device stops the drive of the bit rotation motor 33 and reversely drives the lifting motor 26 to retract it to the standby position at the retraction speed.

[0028] As described above, in the automatic fastening device 10 of the present application, the control unit 40 controls the position of the driver unit 30 to adjust the spring reaction force of the cushion spring 36, and the bit 35 is configured to apply a fastening thrust force such that it does not come off from the screw S1. In this way, the cushion spring 36 is compressed within a range smaller than the maximum compression amount K3, and the bit 35 is urged by the spring reaction force thereof, so that the self-weight of the bit rotation motor 33, the connecting plate, etc. is not applied to the bit 35 and the screw S1. Therefore, while preventing damage to the screw S1 and the work W, it is possible to apply an appropriate thrust force and prevent the cam-out between the screw S1 and the bit 35.

[0029] Next, a second embodiment will be described in which a bolt S2 having a fitting convex portion with a non-circular shape formed on its head is tightened with respect to the screw W1 formed on the work W. In this third embodiment, as a difference, a socket 353 that can be fitted to the outer diameter of the head of the bolt S2 is provided at the tip of the bit 35. Also, in the control unit 40, the same value as the shaft length J1 is set for the compression start offset dimension L3, and the fastening thrust force is set to 0. In addition, other control parameters are changed to appropriate values according to the bolt S2, the work W, etc. As a result, the compression start position and the compression completion position are determined to be the same position as the teaching position L.

[0030] With the above configuration, in the automatic fastening device 10 of the second embodiment, after the driver unit 30 reaches the rotation start position shown in Fig. 5(a)(Z-2), the driver unit 30 is lowered at a synchronous speed until it reaches the seating position shown in Fig. 5(a)(Z-5). Therefore, as shown in Fig. 5(b), the cushion spring 36 can fasten the bolt to the work with almost no compression. As a result, when tightening the bolt S2 with the socket 353, which has a large contact area and is less likely to cam out compared to the screw S1 and the bit 35, it is possible to fasten the work W with almost no thrust force applied.

[0031] Next, a third embodiment will be described in which a tapping screw S3 that is tightened while forming a female screw W1 in a lower hole W2 formed in a workpiece W is tightened. The basic configuration of this third embodiment is the same as that of the automatic fastening device 10 for the screw S1, but the values of the rotation start offset L2 and the compression start offset L3 stored in the control unit 40 are set to 0 as a difference. Also, various control parameters are changed to appropriate values according to the tapping screw S3, the workpiece W, etc. As a result, both the rotation start position and the compression start position are determined at the same position above the teaching position L by the shaft length J1.

[0032] With the above configuration, in the automatic fastening device 10 of the third embodiment, when the tip of the tapping screw S3 reaches the upper surface of the workpiece W as shown in Fig. 6(a) (Z-2), the bit rotation motor 33 rotates the bit 35, and the lifting motor 26 lowers the driver unit 30 by the compression dimension K4 at the compression speed. As a result, the tapping screw S3 is in a state of being pressed by a predetermined tightening thrust immediately after rotation, so the tapping screw S3 is screwed in while cutting the female screw W1 in the lower hole W2. Also, when the tapping screw S3 is screwed in, the lifting motor 26 lowers the driver unit 30 at the synchronous speed until the tapping screw S3 is seated and the bit rotation motor 33 torques up as shown in Fig. 6(a) (Z-5). As a result, as shown in Fig. 6(b), it becomes possible to continuously apply a constant thrust to the tapping screw S3. As a result, it is possible to prevent excessive thrust from being applied and the thrust from weakening and the bit 35 from coming out of the tapping screw S3, and it becomes possible to tighten the tapping screw S3 with high precision.

[0033] Note that the automatic fastening device 10 according to the present invention is not limited to the above-described one, and various modifications are possible without departing from the spirit of the invention. For example, the shape of the fitting portions of the above-described screw S1, bolt S2, and tapping screw S3 is not limited to a cross shape or a hexagonal shape, and other shapes such as a hexalobe shape are also acceptable. Further, in the above-described embodiment, the screw tightening device 10 is configured such that the bit 35 reciprocates in the vertical direction. However, the present invention is not limited to this, and the bit 35 may reciprocate in the horizontal direction to tighten a screw against a wall or the like, or the bit 35 may be inclined. Furthermore, the position control mechanism 20 is not limited to a structure that reciprocates the driver unit 30 by the rotation of the ball screw 27, and may be an orthogonal robot that combines a plurality of drive units that drive in the orthogonal directions, or an articulated robot that includes a plurality of arm portions and an indirect portion that swings or rotates the arm portions, or other structures of the position control mechanism.

[0034] Also, as described in detail in Japanese Patent Application No. 2018-079554 disclosed by the present applicant, there is no problem even if a chuck unit capable of supplying the screw S1 pressure-fed from a supply device on the axis of the bit 35 and a screw guide that covers the bit 35 and adsorbs and holds the screw S are provided. By providing such a chuck unit, the operation of receiving the screw S1 becomes unnecessary and the cycle time is improved. Further, by adsorbing and holding the screw S1 by the negative pressure of the screw guide instead of the magnet 352, it becomes possible to tighten the screw without any problem even for products that dislike magnetism such as electronic substrates. Furthermore, advantages such as the ability to perform a screw floating inspection by measuring the relative position between the screw guide and the bit 35 are generated. Also, the collision avoidance position restricts the return of the driver unit 30 to the origin when sequentially tightening screws against a plurality of workpieces W having the same shape or when tightening a plurality of screws S1 against one workpiece W, and is set so that the operation can quickly shift to the screw tightening operation at the next screw tightening point. When a chuck unit or a screw guide as described above is provided and the screw can be tightened only by the lifting operation, it may be replaced with the origin.

Explanation of Reference Numerals

[0035] 10 … Automatic fastening device 20 … Position control unit 30 … Driver unit 33 … Bit rotation motor 34 … Shaft coupling 35 … Bit 36 … Cushion spring 40 … Control unit

Claims

1. A driver unit that rotates a bit engageable with a screw head by a bit rotation motor, A position control unit that can move the driver unit in the axial direction of the bit, A control unit that controls the driving of the driver unit and the position control unit, The driver unit has a cushion spring that biases the bit in a direction away from the bit rotation motor, The control unit controls the position of the driver unit so that the cushion spring is compressed by an arbitrary dimension preset between the bit and the bit rotation motor. A screw tightening device characterized by this.

2. The control unit is preset with a pressing force such that the bit does not come off the head of the screw when tightening the screw and the spring constant of the cushion spring, The control unit controls the position of the driver unit so that the cushion spring is compressed to the extent that it exerts a spring reaction force corresponding to the pressing force. The screw tightening device according to claim 1, characterized by this.

3. The lead of the screw to be tightened on the workpiece is preset in the control unit, The control unit calculates the screwing speed at which the screw is screwed into the workpiece from the product of the rotation speed of the bit rotation motor and the lead of the screw, and controls the driving of the position control unit so that the driver unit moves at the same speed as the screwing speed. The screw tightening device according to claim 1, characterized by this.

Images