Electric driver and automatic machine system, method for performing direct teaching of automatic machine system, and method for fastening of screw member in automatic machine system

Abstract

To provide an electric driver which can solve problems during direct teaching and after completion of fastening in an electric driver for an automatic machine.SOLUTION: An electric driver 100 for an automatic machine includes: an electric motor 110; a speed reduction gear mechanism 112 connected to the electric motor 110; a drive shaft 114 connected to the speed reduction gear mechanism; and a bit holder 116 which is held so as to be rotatable around a rotation axis R. The drive shaft 114 is driven to rotate around the rotation axis R through the speed reduction gear mechanism 112 by the electric motor 110. The bit holder 116 engages with the drive shaft 114 in a rotation direction and rotates with the drive shaft 114. Further, the bit holder 116 may rotate relative to the drive shaft 114 in a range of a predetermined rotation angle.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electric screwdriver, an automated machine system including an electric screwdriver, a method for performing direct teaching in an automated machine system, and a method for tightening a screw member in an automated machine system. [Background technology]

[0002] There is known an electric screwdriver for tightening various fastening members such as screws, hexagonal bolts, nuts, etc. Such an electric screwdriver is sometimes attached to an articulated robot arm of an automatic machine and used, as shown in Patent Document 1, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-146904 Summary of the Invention [Problem to be solved by the invention]

[0004] When an electric screwdriver is used in an automatic machine, various problems may occur, particularly when the electric screwdriver is fixed to a multi-joint robot arm or the like. For example, when direct teaching is adopted in which the operation of the multi-joint robot arm is taught by manually moving the multi-joint robot arm to memorize the operation, a problem may occur in that the rotational position of the driver bit attached to the electric screwdriver does not match the direction of the cross hole of the screw, and the electric screwdriver cannot be moved to a position where the driver bit is properly engaged with the cross hole of the screw. In this case, it is necessary to turn the driver bit by hand, but since a gear structure with a large reduction ratio is usually arranged between the electric motor and the bit holder that holds the driver bit, a large force is required to turn the driver bit, and in some cases it is practically impossible to turn the driver bit by hand. In addition, immediately after performing a tightening operation with the electric screwdriver, the driver bit is strongly pressed against the cross hole of the screw in the rotational direction, so if you try to remove the driver bit from the screw in this state, the screw will be pulled by the driver bit, and the workpiece to which the screw is tightened will move together with the screw. This may cause a problem. In this case, the driver bit can be rotated slightly in the reverse direction to release the engagement between the driver bit and the cross recess of the screw in the rotation direction. However, if the amount of rotation in the reverse direction is too large even slightly, the screw may rotate in the reverse direction and be loosened, or the driver bit and the cross recess of the screw may be strongly engaged in the reverse direction, which may end up moving the workpiece. In order to release the engagement without loosening the screw, it is necessary to perform extremely precise reverse rotation control of the driver bit, but there are mechanical parts such as a gear structure between the electric motor and the driver bit, and due to the influence of backlash and play of these parts, it is difficult to accurately reverse the driver bit so as not to cause the above-mentioned problems.

[0005] Therefore, the present invention provides an electric screwdriver, an automatic machine system equipped with an electric screwdriver, a method for direct teaching of an automatic machine system, or a method for tightening a screw-type member in an automatic machine system, which are capable of solving at least one of the above-mentioned problems in electric screwdrivers for automatic machines. [Means for solving the problem]

[0006] That is, the present invention provides: An electric screwdriver for an automatic machine, An electric motor; a reduction gear mechanism connected to the electric motor; a drive shaft connected to the reduction gear mechanism and rotated about a rotation axis by the electric motor via the reduction gear mechanism; a bit holder that is rotatably held around the rotation axis and engages with the drive shaft in a rotational direction to rotate together with the drive shaft; Equipped with The bit holder is adapted to be rotatable relative to the drive shaft within a predetermined range of rotation angles in an electric screwdriver.

[0007] In the electric screwdriver for an automatic machine, the bit holder is rotatable relative to the drive shaft within a predetermined rotation angle range. As a result, for example, when performing direct teaching of an automatic machine system in which the electric screwdriver is attached to an automatic machine, the driver bit attached to the bit holder can be rotated by hand to be oriented so as to be properly engaged with the fastening engagement portion of the screwing member, such as the cross recess of a screw. Therefore, in direct teaching, it is possible to move the electric screwdriver to a position where the driver bit is properly engaged with the fastening engagement portion of the screwing member. In addition, by rotating the drive shaft in the reverse direction within a predetermined rotation angle range after fastening the screwing member in the automatic machine system, it is possible to rotate only the drive shaft and not the bit holder, so that the engagement between the driver bit and the screwing member in the rotation direction can be easily released.

[0008] Also, The drive shaft and the bit holder are arranged side by side in the front-rear direction along the rotation axis, the drive shaft has a front end surface and a first engagement protrusion protruding forward from the front end surface, the bit holder has a rear end surface facing the front end surface of the drive shaft and a second engagement protrusion protruding rearward from the rear end surface, The first engaging protrusion and the second engaging protrusion may be adapted to engage with each other in the rotational direction.

[0009] moreover, the first engagement protrusion has two sector-shaped protrusions arranged at positions symmetrical with respect to the rotation axis, each sector-shaped protrusion has two side surfaces extending in a radial direction of the rotation axis, and an angle between the two side surfaces in the rotation direction is approximately 45 degrees; the second engagement protrusion has two sector-shaped protrusions arranged at positions symmetrical with respect to the rotation axis, each sector-shaped protrusion has two side surfaces extending in a radial direction of the rotation axis, and the angle between the two side surfaces in the rotation direction is approximately 45 degrees; The side surface of the first engagement protrusion and the side surface of the second engagement protrusion may be adapted to engage with each other in the rotational direction.

[0010] Furthermore, the tool may further include a spacer disposed between the drive shaft and the bit holder to prevent the drive shaft and the bit holder from coming into direct contact with each other in the direction of the rotation axis.

[0011] Since the drive shaft and the bit holder do not come into direct contact with each other in the direction of the rotation axis, it is possible to reduce the frictional force that occurs between the drive shaft and the bit holder during relative rotation.

[0012] The machine may further include a magnetostrictive sensor configured to detect twist in the rotational direction of the output shaft of the electric motor, the drive shaft, the bit holder, or a member connecting them.

[0013] Or, a housing having a fixing portion for fixing at least one of the electric motor and the reduction gear mechanism in the rotational direction, an attachment portion for attaching the electric screwdriver to an external member, and a sensor attachment portion between the fixing portion and the attachment portion; A strain gauge attached to the sensor attachment portion; The above configuration may further include:

[0014] The present invention also provides An automated machine having a multi-degree-of-freedom robot; Any of the electric drivers described above attached to a movable part of the multi-degree-of-freedom robot; An automated machine system is provided.

[0015] Further, the present invention relates to A method for directly teaching a fastening operation of a screw member in the above-mentioned automated machine system, comprising: A step of manually moving the electric screwdriver while displacing the movable part includes a step of moving the electric screwdriver to a fastening completion position where a tip end of a driver bit attached to the bit holder of the electric screwdriver is engaged with a screw member that is screwed into a predetermined position, The method further includes manually rotating the driver bit together with the bit holder relative to the drive shaft within the predetermined rotation angle range, such that the moving step includes engaging a tip of the driver bit with a tightening engagement portion of the threaded member.

[0016] Further, the present invention relates to A method for tightening a screw member using the automated machine system described above, comprising the steps of: A step of attaching a screw member to a driver bit attached to the bit holder of the electric screwdriver; a step of automatically driving the movable part and the electric screwdriver to tighten the screw member at a predetermined screw position; After the screw member is tightened, the drive shaft is rotated in a reverse direction within the range of the predetermined rotation angle to release the engagement between the drive shaft and the bit holder in the rotational direction; The present invention provides a method comprising:

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an electric screwdriver and an automatic machine system according to the present invention will be described with reference to the accompanying drawings. [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of an automated machine system according to an embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view of a power screwdriver according to a first embodiment of the present invention. [Diagram 3] FIG. 3 is a perspective view of a drive shaft of the power screwdriver of FIG. 2. [Figure 4] 3 is a perspective view of a bit holder of the power screwdriver of FIG. 2. [Diagram 5] FIG. 13 is a diagram showing the rotation angle of the bit holder relative to the drive shaft. [Figure 6] 10 is a flowchart showing a method for directly teaching a tightening operation of a screw member in an automated machine system. [Figure 7] 13 is a flowchart showing a method for tightening a threaded member using an automated machine system. [Figure 8] FIG. 5 is a cross-sectional view of a power screwdriver according to a second embodiment of the present invention. [Figure 9] FIG. 11 is a cross-sectional view of a power screwdriver according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] 1, an electric screwdriver 100 according to a first embodiment of the present invention is an electric screwdriver 100 for an automatic machine that is attached to a vertical articulated robot arm (a movable part of a multi-degree-of-freedom robot) 104 of an automatic machine 102 for use. The electric screwdriver 100 and the automatic machine 102 constitute an automatic machine system 106. Various driver bits 108 can be detachably attached to the electric screwdriver 100 in accordance with the target screw-fitting members (screws, hexagonal bolts, nuts, etc.).

[0020] 2, the electric screwdriver 100 includes an electric motor 110, a reduction gear mechanism 112 connected to an output shaft 111 of the electric motor 110, a drive shaft 114 connected to the reduction gear mechanism 112, and a bit holder 116 arranged to rotate together with the drive shaft 114. The driver bit 108 is detachably attached to the bit holder 116. In this embodiment, the reduction gear mechanism 112 is a planetary gear mechanism.

[0021] The electric screwdriver 100 further includes a housing 118 having a first housing portion 118a and a second housing portion 118b. The first housing portion 118a holds the electric motor 110 and the reduction gear mechanism 112 in a fixed manner and holds the drive shaft 114 in a rotatable manner. The second housing portion 118b is fixed to the first housing portion 118a and holds the bit holder 116 in a rotatable manner. The drive shaft 114 and the bit holder 116 are held in a state in which they are aligned in the front-rear direction (up-down direction as viewed in the figure) along the rotation axis R by the housing 118. A cover 120 that houses the electric motor 110 is attached to the rear of the housing 118 (upper as viewed in the figure). When the electric motor 110 is driven, the drive shaft 114 is rotated around the rotation axis R via the reduction gear mechanism 112. Furthermore, the bit holder 116 is rotationally engaged with the drive shaft 114 as described below, and is rotated together with the drive shaft 114 .

[0022] As shown in Fig. 3, the drive shaft 114 has a first engagement protrusion 124 that protrudes forward (downward as viewed in the figure) on its front end surface 122. This first engagement protrusion 124 is made up of two sector-shaped protrusions 126. The two sector-shaped protrusions 126 are disposed in positions symmetrical with respect to the rotation axis R, i.e., at positions 180 degrees opposite each other with respect to the rotation axis R. Each sector-shaped protrusion 126 has two side surfaces 126a, 126b that extend in a radial direction of the rotation axis R.

[0023] As shown in Fig. 4, the bit holder 116 has a second engagement protrusion 130 similar to the first engagement protrusion 124 of the drive shaft 114. The bit holder 116 has the second engagement protrusion 130 protruding rearward (upward as viewed in the figure) on a rear end surface 128 of the bit holder 116. This second engagement protrusion 130 is made up of two sector-shaped protrusions 132. The two sector-shaped protrusions 132 are disposed in symmetrical positions with respect to the rotation axis R, i.e., in positions 180 degrees opposite each other with respect to the rotation axis R. Each sector-shaped protrusion 132 has two side surfaces 132a, 132b extending in a radial direction of the rotation axis R.

[0024] As shown in FIG. 5, the drive shaft 114 and the bit holder 116 are arranged such that the sector-shaped protrusion 132 of the bit holder 116 is located between the sector-shaped protrusions 126 of the drive shaft 114. The angle between the two side surfaces 126a, 126b of the sector-shaped protrusion 126 is 45 degrees in the rotational direction. Similarly, the angle between the two side surfaces 132a, 132b of the sector-shaped protrusion 132 is 45 degrees in the rotational direction. When the bit holder 116 rotates 45 degrees counterclockwise as viewed in the figure from the state in which the bit holder 116 is in the position of FIG. 5(a) relative to the drive shaft 114, one side surface 132a of the sector-shaped protrusion 132 engages with one side surface 126a of the sector-shaped protrusion 126 as shown in FIG. 5(b). 5(a) with respect to the drive shaft 114, the other side surface 132b of the sector-shaped projection 132 engages with the other side surface 126b of the sector-shaped projection 126, as shown in FIG. 5(c). Therefore, the bit holder 116 is capable of rotating relative to the drive shaft 114 within a rotation angle range of 90 degrees.

[0025] 2, the drive shaft 114 and the bit holder 116 are formed with holes 134, 136, respectively, that extend along the rotation axis R, and needle rollers 138 are disposed therein. In addition, a spacer 140 is disposed between the drive shaft 114 and the bit holder 116, so that the drive shaft 114 and the bit holder 116 do not come into direct contact with each other in the direction of the rotation axis R.

[0026] When the electric motor 110 is not driven, the bit holder 116 can be manually rotated relative to the drive shaft 114 within a range of a predetermined rotation angle (90 degrees). When the electric motor 110 is driven to rotate the drive shaft 114, one of the two side surfaces 126a, 126b of the first engagement protrusion 124 engages with one of the side surfaces 132a, 132b of the second engagement protrusion 130 in the rotational direction. This causes the bit holder 116 to rotate together with the drive shaft 114. In this embodiment, a fan 142 is provided between the electric motor 110 and the reduction gear mechanism 112, and the reduction gear mechanism 112 is connected to the electric motor 110 via the fan 142. This fan 142 rotates with the rotation of the electric motor 110 to generate cooling air for cooling the electric motor 110.

[0027] A method for directly teaching a screw tightening operation in an automatic machine system 106 in which an electric screwdriver 100 is attached to a multi-joint robot arm 104 of an automatic machine 102 will be described below. In this method, the electric screwdriver 100 is manually moved while displacing the multi-joint robot arm 104 so that the driver bit 108 attached to the electric screwdriver 100 is brought to a tightening completion position where it engages with a screw-threaded member that is screwed into a predetermined position, and the tightening completion position is taught to the automatic machine system 106. Specifically, as shown in FIG. 6, first, the electric screwdriver 100 is moved until the tip of the driver bit 108 is positioned near the screw (S100). Next, if the tip of the driver bit 108 and the cross hole of the screw (the tightening engagement portion of the screw-threaded member) are not aligned, the bit holder 116 is manually rotated so that the tip of the driver bit 108 can engage with the cross hole of the screw (S102). Then, the electric screwdriver 100 is manually moved toward the screw so that the tip of the driver bit 108 is appropriately engaged with the cross hole of the screw (S104). The position of the electric screwdriver 100 at this time is taught to the automatic machine system 106 as the tightening completion position (S106). As described above, in the electric screwdriver 100, the bit holder 116 is rotatable with respect to the drive shaft 114 within a range of a predetermined rotation angle (90 degrees), so that the driver bit 108 attached to the bit holder 116 can be easily rotated together with the bit holder 116. Therefore, it is possible to easily align the tip of the driver bit 108 with the cross hole of the screw. The step (S102) of rotating the driver bit 108 so that the tip of the driver bit 108 is oriented to align with the cross hole of the screw may be performed before or during the step (S100) of moving the electric screwdriver 100 so that the tip of the driver bit 108 is positioned near the screw.

[0028] A method for tightening a screw by the automated machine system 106 in which the electric screwdriver 100 is attached to the articulated robot arm 104 of the automated machine 102 will be described below with reference to FIG. 7. First, a screw is attached to the tip of the driver bit 108 attached to the electric screwdriver 100 (S200). The screw is attached to the tip by forming the tip of the driver bit 108 with a magnet and magnetically attracting the screw with magnetic force, or by providing a vacuum suction mechanism around the tip of the driver bit 108 and vacuum-attracting the screw. Next, the articulated robot arm 104 and the electric screwdriver 100 are automatically driven to tighten the screw to a predetermined screwing position (S202). In the electric screwdriver 100, the current flowing through the electric motor 110 is detected, and the torque applied to the electric motor 110 is calculated from the magnitude of this current, so that the tightening force of the screw is controlled and the seating of the screw-engaging member is detected. Immediately after the tightening of the screw is completed, the tip of the driver bit 108 is pressed against the cross hole of the screw in the tightening direction. Therefore, in order to release the pressing force of the driver bit 108 against the screw, the drive shaft 114 is rotated in the opposite direction to the fastening direction within a range of a predetermined rotation angle (90 degrees) (S204). For example, the drive shaft 114 is rotated by approximately 45 degrees. As described above, the drive shaft 114 and the bit holder 116 can rotate relatively within a range of a predetermined rotation angle (90 degrees), so when the drive shaft 114 is rotated in the opposite direction within that range after fastening is completed, the bit holder 116 remains in that position and only the drive shaft 114 rotates. Then, the force that has been pressing the driver bit 108 attached to the bit holder 116 against the screw in the rotation direction is released, while almost no force in the reverse direction acts on the screw. After that, the electric screwdriver 100 is moved away from the fastened screw (S206). In this method using the electric screwdriver 100, the magnitude of the rotation angle when rotating the drive shaft 114 in the reverse direction after tightening the screw only needs to be within a specified range of rotation angle (90 degrees) that can be rotated between the drive shaft 114 and the bit holder 116, so there is no need to precisely control the rotation angle of the drive shaft 114.This makes it possible to prevent a situation in which the rotation angle in the reverse direction is too small to fully release the engagement between the driver bit 108 and the screw in the rotational direction, or a situation in which the rotation angle is too large to rotate a tightened screw in the reverse direction and loosen it.

[0029] The electric screwdriver 200 according to the second embodiment of the present invention shown in FIG. 8 has a similar configuration to the electric screwdriver 100 according to the first embodiment, but the configuration of the drive shaft 214 is different. The drive shaft 214 in this embodiment is composed of a front part 250 having a first engagement protrusion 224 and a rear part 252 extending between the front part 250 and the reduction gear mechanism 212. The front part 250 and the rear part 252 are fixed in the rotation direction. The rear part 252 is formed of a magnetostrictive material having magnetostrictive properties, and has two enlarged diameter parts 254. These enlarged diameter parts 254 are formed with a plurality of spiral grooves inclined in different directions with respect to the rotation axis R. In addition, a detection coil 256 is arranged around each enlarged diameter part 254. When a torque is applied to the drive shaft 214 by tightening the screw member or the like and the drive shaft 214 is twisted, the magnetic permeability of the enlarged diameter part 254 in which the spiral grooves are formed changes. The change in magnetic permeability is detected as an electric quantity by the detection coil 256, so that the direction and magnitude of the torque applied to the drive shaft 214 can be detected. That is, the rear part 252 of the drive shaft 214 and the detection coil 256 constitute a magnetostrictive sensor that detects the torque applied to the drive shaft 214. In the electric screwdriver 200, the tightening force of the screw member can be controlled and the seating of the screw member can be detected based on the torque detected by the magnetostrictive sensor. The magnetostrictive sensor can also be arranged and configured to detect the twist in the rotation direction of other rotating members, such as the output shaft 211 of the electric motor 210, the fan 242, the bit holder 216, etc., to detect the torque applied thereto. Alternatively, another member that connects these members may be further provided, and the magnetostrictive sensor may be configured to detect the twist of that member.

[0030] The electric screwdriver 300 according to the third embodiment shown in FIG. 9 has a similar configuration to the electric screwdriver 100 according to the first embodiment, but has a different configuration of the housing 318. The housing 318 has a fixed portion 360 that fixes the reduction gear mechanism 312 in the rotational direction, an attachment portion 362 to which the cover 320 is attached, and a sensor attachment portion 364 between the fixed portion 360 and the attachment portion 362. A strain gauge 366 is attached to the sensor attachment portion 364. An arm attachment portion 368 for attachment to the vertical articulated robot arm 104 of the automatic machine 102 is provided at the front end portion of the cover 320. Thus, the housing 318 is attached to the vertical articulated robot arm (external member) 104 at the attachment portion 362 via the cover 320. When torque is applied to the driver bit 108 during screw tightening or the like with the electric screwdriver 300 attached to the vertical articulated robot arm 104, the torque is applied to the fixed part 360 of the housing 318 via the bit holder 316, the drive shaft 314, and the reduction gear mechanism 312. Meanwhile, since the mounting part 362 of the housing 318 is fixed to the vertical articulated robot arm 104, a twist corresponding to the magnitude of the torque is generated between the fixed part 360 and the mounting part 362 of the housing 318. The strain caused by this twist is detected by a strain gauge 366 attached to a sensor mounting part 364 of the housing 318. In the electric screwdriver 300, the torque applied to the driver bit 108 is calculated from the amount of strain of the housing 318 detected by the strain gauge 366, and the tightening force of the screw member can be controlled or the seating of the screw member can be detected based on the torque.

[0031] In this way, in the electric screwdriver for an automatic machine according to the present invention, the bit holder is rotatable relative to the drive shaft within a predetermined rotation angle range. This makes it possible to rotate the driver bit attached to the bit holder by hand and orient it so that it properly engages with the fastening engagement portion of the screwing member, for example, when performing direct teaching of the automatic machine system. In addition, by rotating the drive shaft in the reverse direction within a predetermined rotation angle range after fastening the screwing member in the automatic machine system, it is possible to rotate only the drive shaft and not the bit holder, so that the engagement between the driver bit and the screwing member in the rotational direction can be easily released.

[0032] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, the screw member to be fastened in the electric screwdriver of the present invention and the automatic machine system equipped with the same is not limited to a screw having a cross recess, but may be a screw member having a fastening engagement portion of another form, such as a bolt having a hexagonal hole or a nut having a hexagonal outer peripheral surface. In addition, the first engagement protrusion of the driver bit and the second engagement protrusion of the bit holder may be in a shape other than a sector-shaped protrusion. In this regard, the magnitude of the rotation angle that can be relatively rotated between the driver bit and the bit holder may be any other size other than 90 degrees, such as 120 degrees or 60 degrees. The electric screwdriver may also be attached to a movable part of a multi-degree-of-freedom robot of another form, such as a horizontal articulated robot, a parallel link robot, and an orthogonal robot, and used. [Explanation of symbols]

[0033] 100 Electric screwdriver 102 Automatic Machine 104 Vertical multi-joint robot arm (moving part of multi-degree-of-freedom robot, external parts) 106 Automated Machine System 108 Driver Bit 110 Electric motor 111 Output shaft 112 Reduction gear mechanism 114 Drive shaft 116 Bit Holder 118 Housing 118a 1st housing section 118b Second housing section 120 Cover 122 Front end surface 124 First engaging protrusion 126 Fan-shaped protrusion 126a, 126b side 128 Rear end surface 130 Second engagement protrusion 132 Fan-shaped protrusion 132a, 132b side 134, 136 holes 138 Needle Roller 140 Spacer 142 Fans 200 Electric screwdriver 210 Electric Motor 211 Output shaft 212 Reduction gear mechanism 214 Drive shaft 216 Bit Holder 224 First engaging protrusion 242 Fans 250 front part 252 Rear part 254 Expanded diameter part 256 detection coils 300 Electric screwdriver 312 Reduction gear mechanism 314 Drive shaft 316 Bit Holder 318 Housing 320 Cover 360 Fixed part 362 Mounting part 364 Sensor mounting part 366 Strain Gauge 368 Arm attachment part R Rotation axis

Claims

1. An electric screwdriver for an automatic machine, An electric motor; a reduction gear mechanism connected to the electric motor; a drive shaft connected to the reduction gear mechanism and rotated about a rotation axis by the electric motor via the reduction gear mechanism; a bit holder that is rotatably held around the rotation axis and engages with the drive shaft in a rotational direction to rotate together with the drive shaft; Equipped with The bit holder is rotatable relative to the drive shaft within a predetermined range of rotation angles.

2. The drive shaft and the bit holder are arranged side by side in the front-rear direction along the rotation axis, the drive shaft has a front end surface and a first engagement protrusion protruding forward from the front end surface, the bit holder has a rear end surface facing the front end surface of the drive shaft and a second engagement protrusion protruding rearward from the rear end surface, The electric screwdriver according to claim 1 , wherein the first engagement protrusion and the second engagement protrusion are adapted to engage with each other in the rotational direction.

3. the first engagement protrusion has two sector-shaped protrusions arranged at positions symmetrical with respect to the rotation axis, each sector-shaped protrusion has two side surfaces extending in a radial direction of the rotation axis, and an angle between the two side surfaces in the rotation direction is approximately 45 degrees; the second engagement protrusion has two sector-shaped protrusions arranged at positions symmetrical with respect to the rotation axis, each sector-shaped protrusion has two side surfaces extending in a radial direction of the rotation axis, and an angle between the two side surfaces in the rotation direction is approximately 45 degrees; The electric screwdriver according to claim 2 , wherein the side surface of the first engagement protrusion and the side surface of the second engagement protrusion are adapted to engage with each other in the rotational direction.

4. The power screwdriver according to claim 2 , further comprising a spacer disposed between the drive shaft and the bit holder to prevent the drive shaft and the bit holder from coming into direct contact with each other in the direction of the rotation axis.

5. The electric screwdriver according to claim 1 , further comprising a magnetostrictive sensor configured to detect a twist in the rotational direction of the output shaft of the electric motor, the drive shaft, the bit holder, or a member connecting them.

6. a housing having a fixing portion for fixing at least one of the electric motor and the reduction gear mechanism in the rotational direction, an attachment portion for attaching the electric screwdriver to an external member, and a sensor attachment portion between the fixing portion and the attachment portion; A strain gauge attached to the sensor attachment portion; The power driver of claim 1 further comprising:

7. An automated machine having a multi-degree-of-freedom robot; The electric screwdriver according to any one of claims 1 to 6, which is attached to a movable part of the multi-degree-of-freedom robot; An automated machine system comprising:

8. 8. A method for directly teaching a fastening operation of a screw member in an automated machine system according to claim 7, comprising the steps of: A step of manually moving the electric screwdriver while displacing the movable part includes a step of moving the electric screwdriver to a fastening completion position where a tip end of a driver bit attached to the bit holder of the electric screwdriver is engaged with a screw member that is screwed into a predetermined position, The method, wherein the moving step includes manually rotating the driver bit together with the bit holder relative to the drive shaft within the predetermined rotation angle range so that a tip of the driver bit engages a tightening engagement portion of the threaded member.

9. A method for tightening a screw member using the automated machine system according to claim 7, comprising the steps of: A step of attaching a screw member to a driver bit attached to the bit holder of the electric screwdriver; a step of automatically driving the movable part and the electric screwdriver to tighten the screw member at a predetermined screw position; After the screw member is tightened, the drive shaft is rotated in a reverse direction within the range of the predetermined rotation angle to release the engagement between the drive shaft and the bit holder in the rotational direction; A method comprising:

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