Screw fastening machine and torque sensor

Abstract

Provided is a screw fastening machine capable of suppressing noise from affecting a detection signal of a torque input to an amplification circuit. The screw fastening machine includes a motor, an output shaft driven by the motor and capable of mounting a tool head, a hollow torsion portion that is transmitted with a torque applied to the output shaft via a transmission element and is indirectly twisted with the torque applied to the output shaft, a plate-shaped portion integrally formed with the torsion portion, a strain gauge disposed on the torsion portion, and an amplification circuit disposed on the plate-shaped portion and input with a signal from the strain gauge.

Description

Technical Field

[0001] This invention relates to a screw fastening machine and a torque sensor. Background Technology

[0002] In the technical field of screw fastening machines, the tool disclosed in Patent Document 1 is known. In Patent Document 1, the tool includes a torque sensor.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-122429 Summary of the Invention

[0006] In the product assembly process, screw fastening machines are used to perform screw tightening operations. For product management, it is sometimes necessary to record the torque detection signal applied to the output shaft. Additionally, an amplifier circuit for amplifying the torque detection signal is sometimes installed in the screw fastening machine. To accurately record the torque detection signal, it is necessary to suppress the influence of noise on the torque detection signal input to the amplifier circuit.

[0007] The purpose of this invention is to suppress the noise affecting the detection signal of the torque input to the amplifier circuit.

[0008] According to the present invention, a screw fastening machine is provided, comprising: a motor; an output shaft driven by the motor and capable of mounting a tool head; a hollow torsion section that transmits torque applied to the output shaft by means of a transmission element and is indirectly torsioned by the torque applied to the output shaft; a plate-shaped section integrally formed with the torsion section; a strain gauge disposed in the torsion section; and an amplification circuit disposed in the plate-shaped section and receiving a signal from the strain gauge.

[0009] According to the present invention, it is possible to suppress the situation where the detection signal of the torque input to the amplifier circuit is affected by noise. Attached Figure Description

[0010] Figure 1 This is a perspective view of the screw fastening machine according to the first embodiment, viewed from the front.

[0011] Figure 2 This is a side view showing the screw fastening machine according to the first embodiment.

[0012] Figure 3 This is a cross-sectional view showing the screw fastening machine according to the first embodiment.

[0013] Figure 4This is a perspective view showing the structure near the planetary gear mechanism involved in the extracted first embodiment.

[0014] Figure 5 This is a perspective view of the torque sensor according to the first embodiment, viewed from the left front.

[0015] Figure 6 This is a perspective view of the torque sensor according to the first embodiment, viewed from the right front.

[0016] Figure 7 This is a perspective view of the torque sensor according to the first embodiment, viewed from the left rear.

[0017] Figure 8 This is a right view showing the torque sensor according to the first embodiment.

[0018] Figure 9 This is a left view showing the torque sensor according to the first embodiment.

[0019] Figure 10 This is a cross-sectional view showing the torque sensor according to the first embodiment.

[0020] Figure 11 This is a perspective view, viewed from the left front, showing the state after the cover of the torque sensor according to the first embodiment has been removed.

[0021] Figure 12 This is a perspective view, viewed from the left front, showing the flexible substrate with the strain gauge fixed thereon and the flexible substrate with the amplifier circuit fixed thereon, according to the first embodiment.

[0022] Figure 13 This is a perspective view, viewed from the right front, showing the flexible substrate with the strain gauge fixed thereon and the flexible substrate with the amplifier circuit fixed thereon, according to the first embodiment.

[0023] Figure 14 This is a perspective view of the flexible substrate with a strain gauge fixed thereon, as shown in the first embodiment, viewed from the left front.

[0024] Figure 15 This is a perspective view of the flexible substrate with a strain gauge fixed according to the first embodiment, as seen from the front right.

[0025] Figure 16 This is a perspective view of the flexible substrate according to the first embodiment, viewed from the left front.

[0026] Figure 17 This is a perspective view of the flexible substrate according to the first embodiment, viewed from the front right.

[0027] Figure 18 This is a circuit diagram showing the strain gauge and amplification circuit according to the first embodiment.

[0028] Figure 19 This is a cross-sectional view showing the screw fastening machine according to the second embodiment.

[0029] Explanation of reference numerals in the attached figures

[0030] 1… Screw fastener, 2… Housing, 2L… Left housing, 2R… Right housing, 2S… Screw, 4… Gearbox, 5… Battery assembly, 6… Motor, 6F… Front end, 7… Planetary gear mechanism, 8… Output shaft, 8R… Rear end, 9… Torque sensor, 9F… Front end, 9R… Rear end, 11… First lead, 12… Second lead, 13… Fan, 14… Trigger switch, 14A… Trigger component, 14B… Switch body, 15… Forward / reverse switching lever, 16… Control circuit base 16P…board, 17…control circuit board housing, 18…intake port, 19…exhaust port, 20…battery pack, 21…motor housing, 22…grip, 23…control circuit board housing, 31…first connector, 32…second connector, 33…lead wire, 40…hole, 61…stator, 61A…stator core, 61B…front insulator, 61C…rear insulator, 61D…coil, 61E…sensor circuit board, 61F…short-circuit component, 62…rotor, 62A… Rotor core, 62B…permanent magnet, 63…rotary shaft, 64…bearing, 65…bearing, 67…bearing retainer, 70…internal gear, 71C…carrier, 71P…planetary gear, 71S…pinion, 72C…carrier, 72P…planetary gear, 72S…sun gear, 81…spindle, 81A…insertion hole, 82…chuck, 83…bearing, 84…bearing, 90…torsion section, 90A…hole, 91…plate-like section, 91A…front surface, 91B…rear surface, 91C…outer periphery Surface, 91G… Gear, 92… Plate-shaped part, 92A… Front surface, 92B… Rear surface, 92C… Outer peripheral surface, 93… Strain gauge, 94… Amplifier circuit, 94A… Operational amplifier, 95… Flexible substrate, 96… Flexible substrate, 97… Cover, 98… Bridge circuit, 101… Screw fastener, 951… Part 1, 951A… Support part, 951B… Bend part, 951C… Opening, 951D… Terminal, 952… Part 2, 952A… Terminal, AX… Rotating shaft. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The present invention is not limited to these embodiments. The constituent elements of the embodiments described below can be appropriately combined. Furthermore, sometimes some constituent elements are not used.

[0032] In the implementation, terms such as "left," "right," "front," "back," "up," and "down" are used to describe the positional relationships of the various parts. These terms indicate the relative position or direction with the center of the screw fastening machine as a reference.

[0033] Screw fastening machines use a motor as their power source. The direction parallel to the motor's rotation axis AX is appropriately called the axial direction, the direction around the rotation axis AX is appropriately called the circumferential direction or rotational direction, and the radial direction of the rotation axis AX is appropriately called the radial direction.

[0034] The axis of rotation AX extends along the front-to-back direction. The axial direction and the front-to-back direction are aligned. One side of the axial direction is the front, and the other side is the rear. Furthermore, regarding the radial direction, the position closer to or near the axis of rotation AX is appropriately called the radial inner side, and the position farther from or away from the axis of rotation AX is appropriately called the radial outer side.

[0035] [First Implementation]

[0036] The first embodiment is described.

[0037] <Screw Fastening Machine>

[0038] Figure 1 This is a perspective view of the screw fastening machine 1 according to this embodiment, viewed from the front. Figure 2 This is a side view of the screw fastening machine 1 according to this embodiment. Figure 3 This is a cross-sectional view showing the screw fastening machine 1 according to this embodiment. The screw fastening machine 1 is an industrial electric screwdriver used in an assembly plant. During the product assembly process, the screw fastening machine 1 is used to perform screw fastening operations. An example of an assembly plant is an automobile assembly plant. An example of a product is an automobile.

[0039] like Figure 1 , Figure 2 ,as well as Figure 3 As shown, the screw fastening machine 1 includes: a housing 2, a gearbox 4, a battery assembly 5, a motor 6, a planetary gear mechanism 7, an output shaft 8, a torque sensor 9, a first lead 11, a second lead 12, a fan 13, a trigger switch 14, a forward / reverse switching lever 15, a control circuit board 16, and a control circuit board housing 17.

[0040] The outer casing 2 is made of synthetic resin. The outer casing 2 includes a left outer casing 2L and a right outer casing 2R. The left outer casing 2L and the right outer casing 2R are fixed together by screws 2S. The outer casing 2 is formed by fixing the left outer casing 2L and the right outer casing 2R.

[0041] The housing 2 includes: a motor housing 21, a gripping part 22, and a control circuit board housing 23.

[0042] The motor housing 21 houses the motor 6. The motor housing 21 has a cylindrical portion. The motor housing 21 is positioned above the gripping portion 22.

[0043] The grip 22 is provided for the operator to hold. The grip 22 is positioned below the motor housing 21. The grip 22 protrudes downward from the motor housing 21. A trigger switch 14 is disposed on the grip 22.

[0044] The control circuit board receiving portion 23 houses the control circuit board 16. The control circuit board receiving portion 23 is positioned downwards from the grip portion 22. The control circuit board receiving portion 23 is connected to the lower end of the grip portion 22. In each of the front-back and left-right directions, the external dimensions of the control circuit board receiving portion 23 are larger than the external dimensions of the grip portion 22.

[0045] The gearbox 4 houses a torque sensor 9, a planetary gear mechanism 7, and a portion of an output shaft 8. The gearbox 4 is positioned forward of the motor 6. The gearbox 4 is cylindrical and made of metal. In this embodiment, the gearbox 4 is made of aluminum. The gearbox 4 is configured to cover the front opening of the motor housing 21. The gearbox 4 is fixed to the motor housing 21. The rear portion of the gearbox 4 is located inside the motor housing 21. At least a portion of the motor housing 21 is disposed around the gearbox 4. The front portion of the gearbox 4 is positioned forward of the motor housing 21.

[0046] A battery assembly 5 is formed at the lower part of the control circuit board receiving portion 23. The battery assembly 5 is connected to the battery pack 20. The battery pack 20 is assembled to the battery assembly 5. The battery pack 20 can be installed and removed relative to the battery assembly 5. The battery pack 20 includes a secondary battery. In this embodiment, the battery pack 20 includes a rechargeable lithium-ion battery. The battery pack 20 can supply power to the screw fastener 1 via the battery assembly 5. The motor 6 is driven based on the power supplied from the battery pack 20. The control circuit board 16 operates based on the power supplied from the battery pack 20.

[0047] Motor 6 is the power source for screw fastening machine 1. Motor 6 is an electric motor. Motor 6 is an internal rotor type brushless motor. Motor 6 is housed in motor housing 21. Motor 6 has a stator 61 and a rotor 62. The stator 61 is arranged around the rotor 62. The rotor 62 rotates about the rotation axis AX.

[0048] The stator 61 includes: a stator core 61A, a front insulator 61B, a rear insulator 61C, a coil 61D, a sensor circuit board 61E, and a short-circuit component 61F.

[0049] The stator core 61A is cylindrical. The stator core 61A includes multiple stacked steel plates. A front insulator 61B is disposed at the front of the stator core 61A. A rear insulator 61C is disposed at the rear of the stator core 61A. Multiple coils 61D are provided. The multiple coils 61D are wound around the stator core 61A by means of the front insulator 61B and the rear insulator 61C. The sensor circuit board 61E has multiple rotation detection elements for detecting the rotation of the rotor 62. The sensor circuit board 61E is supported by the rear insulator 61C. A short-circuit component 61F connects the multiple coils 61D via fuse terminals. The short-circuit component 61F is supported by the rear insulator 61C. The short-circuit component 61F is connected to the control circuit board 16 via leads (not shown).

[0050] The rotor 62 has: a rotor core 62A, a permanent magnet 62B, and a rotating shaft 63.

[0051] The rotor core 62A is disposed inside the stator core 61A and the coil 61D. The rotor core 62A is cylindrical. The rotor core 62A is disposed around the rotating shaft 63. The rotor core 62A includes multiple stacked steel plates. Multiple permanent magnets 62B are provided. The permanent magnets 62B are held in the rotor core 62A. The rotor core 62A has through holes extending along the axial direction. Multiple through holes are formed in the circumferential direction. The permanent magnets 62B are respectively disposed in the multiple (four in this embodiment) through holes of the rotor core 62A.

[0052] The rotation detection element of the sensor circuit board 61E detects the rotation of the rotor 62 by detecting the magnetic field of multiple (four in this embodiment) permanent magnets 62B. The control circuit board 16 supplies drive current to the coil 61D based on the detection signal from the rotation detection element.

[0053] The rotary shaft 63 extends axially. The rotary shaft 63 rotates about a rotation axis AX. The rotation axis AX of the rotary shaft 63 coincides with the rotation axis of the output shaft 8. The front portion of the rotary shaft 63 is rotatably supported by a bearing 64. The rear portion of the rotary shaft 63 is rotatably supported by a bearing 65. The bearing 64 is held by the torque sensor 9. The bearing 65 is held by a bearing retainer 67 provided in the motor housing 21. The front end of the rotary shaft 63 is positioned forward of the bearing 64. The front end of the rotary shaft 63 is located inside the gearbox 4.

[0054] A pinion 71S is provided at the front end of the rotary shaft 63. The rotary shaft 63 is connected to the planetary gear mechanism 7 by means of the pinion 71S.

[0055] Planetary gear mechanism 7 is housed in gearbox 4. Planetary gear mechanism 7 connects rotary shaft 63 to output shaft 8. Planetary gear mechanism 7 slows the rotation of rotary shaft 63 and rotates output shaft 8 at a lower speed than rotary shaft 63. Planetary gear mechanism 7 functions as a power transmission mechanism that transmits the rotational force generated by motor 6 to output shaft 8. Planetary gear mechanism 7 has multiple (three in this embodiment) gears. Planetary gear mechanism 7 is positioned forward of torque sensor 9.

[0056] Figure 4 This is a perspective view showing the structure near the planetary gear mechanism 7 involved in this embodiment. (See diagram below.) Figure 3 as well as Figure 4 As shown, the planetary gear mechanism 7 includes: planetary gear 71P, carrier 71C, sun gear 72S, planetary gear 72P, carrier 72C, and internal gear 70.

[0057] Multiple planetary gears 71P are provided. Multiple (three in this embodiment) planetary gears 71P are arranged around the pinion 71S. Each planetary gear 71P meshes with the pinion 71S. A carrier 71C supports the multiple planetary gears 71P for rotation. A sun gear 72S is arranged in front of the carrier 71C. The diameter of the sun gear 72S is smaller than the diameter of the carrier 71C. The carrier 71C and the sun gear 72S are integrated. The carrier 71C rotates together with the sun gear 72S. Multiple planetary gears 72P are provided. Multiple planetary gears 72P are arranged around the sun gear 72S. Each planetary gear 72P meshes with the sun gear 72S. A carrier 72C supports the multiple planetary gears 72P for rotation. An internal gear 70 is arranged around the multiple planetary gears 72P. The internal gear 70 is located inside the gearbox 4. The internal gear 70 does not rotate. The internal gear 70 is connected to the torque sensor 9.

[0058] The rotating shaft 63 is connected to the sun gear 72S via a pinion 71S, planetary gears 71P, and a carrier 71C. The sun gear 72S rotates due to the rotational force generated by the motor 6. An internal gear 70 is arranged around the sun gear 72S. Multiple planetary gears 72P are radially arranged between the sun gear 72S and the internal gear 70. Each planetary gear 72P meshes with the sun gear 72S. Each planetary gear 72P meshes with the internal gear 70. The carrier 72C supports the multiple planetary gears 72P so that they can rotate. The carrier 72C is connected to the output shaft 8. The carrier 72C rotates about the rotation axis AX.

[0059] When the rotary shaft 63 is rotated by the drive of the motor 6, the pinion gear 71S rotates, and the planetary gear 71P revolves around the pinion gear 71S. Through the revolution of the planetary gear 71P, the carrier 71C and the sun gear 72S rotate at a lower speed than the rotary shaft 63. When the sun gear 72S rotates, the planetary gear 72P revolves around the sun gear 72S. Through the revolution of the planetary gear 72P, the carrier 72C rotates at a lower speed than the carrier 71C. Thus, when the motor 6 is driven, the carrier 72C rotates at a lower speed than the rotary shaft 63.

[0060] The output shaft 8 is driven by the motor 6. A tool head (front-end tool) can be mounted on the output shaft 8. The output shaft 8 rotates with the tool head mounted due to the rotational force generated by the motor 6. The output shaft 8 rotates based on the rotational force transmitted from the motor 6 via the planetary gear mechanism 7. At least a portion of the output shaft 8 is positioned forward of the planetary gear mechanism 7.

[0061] The output shaft 8 includes a spindle 81 and a chuck 82.

[0062] The spindle 81 rotates around the rotation axis AX based on the rotational force transmitted from the motor 6. The spindle 81 is supported by bearings 83 and 84 to enable rotation. The spindle 81 is connected to the carrier 72C. The spindle 81 rotates around the rotation axis AX by rotating the carrier 72C. The spindle 81 has an insertion hole 81A, also with a roughly hexagonal cross-section, into which a tool head with a roughly hexagonal cross-section is inserted. The tool head is fixed to the spindle in the rotational direction by the roughly hexagonal shape of the tool head and the insertion hole. The insertion hole 81A is formed to extend rearward from the front end of the spindle 81. A chuck 82 prevents the tool head inserted into the insertion hole 81A from falling forward by means of balls. The chuck 82 is disposed around the front part of the spindle 81. The tool head, fixed in the rotational direction and prevented from falling forward, rotates by rotating the spindle 81.

[0063] Torque sensor 9 detects the torque applied to output shaft 8. The torque applied to output shaft 8 is the shaft torque applied centered on the rotation axis AX. With the tool head mounted on output shaft 8, a screw tightening operation is performed. The torque detected by torque sensor 9 includes the tightening torque of the screw applied to output shaft 8 during the screw tightening operation. The detection signal output from torque sensor 9 represents the detection signal of the torque applied to output shaft 8.

[0064] The torque sensor 9 includes: a torsion section 90, a plate-shaped section 91, a plate-shaped section 92, a strain gauge 93, an amplifier circuit 94, and a cover 97.

[0065] Torque sensor 9 is connected to output shaft 8. In this embodiment, the plate-shaped portion 91 of torque sensor 9 is connected to the internal gear 70 of planetary gear mechanism 7. Torque sensor 9 is connected to output shaft 8 via planetary gear mechanism 7.

[0066] Torque sensor 9 is housed in gearbox 4. Torque sensor 9 is positioned forward of stator 61. Torque sensor 9 is positioned rearward of output shaft 8. That is, in the front-rear direction, torque sensor 9 is positioned between the front end 6F of stator 61 and the rear end 8R of output shaft 8. In this embodiment, torque sensor 9 is positioned between fan 13 and planetary gear mechanism 7.

[0067] Torque sensor 9 is disposed around rotary shaft 63. The front end of rotary shaft 63 is positioned forward of the front end 9F of torque sensor 9. Pinion gear 71S is disposed at the front end of rotary shaft 63. Pinion gear 71S is positioned forward of the front end 9F of torque sensor 9. Fan 13 and motor 6 are positioned rearward of the rear end 9R of torque sensor 9.

[0068] Multiple first leads 11 are provided. The amplifier circuit 94 is connected to multiple first leads 11. The first leads 11 are connected to the first connector 31.

[0069] The gearbox 4 has a hole 40. The hole 40 is formed to connect the interior and exterior of the gearbox 4. A first lead 11 is led out from the hole 40. One end of the first lead 11 is disposed inside the gearbox 4 and connected to the amplifier circuit 94. The other end of the first lead 11 is disposed outside the gearbox 4 and connected to the first connector 31.

[0070] Multiple second leads 12 are provided. Multiple second leads 12 are connected to the control circuit board 16. The second leads 12 are connected to the second connector 32.

[0071] The first connector 31 is connected to the second connector 32.

[0072] Fan 13 is positioned in front of stator 61. Fan 13 generates airflow to cool motor 6. Fan 13 is fixed to rotating shaft 63. Fan 13 rotates as rotating shaft 63 rotates. Motor housing 21 has intake port 18 and exhaust port 19. Intake port 18 is positioned rearward than exhaust port 19. As fan 13 rotates, air from outside housing 2 flows into housing 2 through intake port 18. The air flowing into housing 2 cools motor 6 by circulating within housing 2. The air circulating within housing 2 exits to outside housing 2 through exhaust port 19.

[0073] The trigger switch 14 is operated to start the motor 6. The trigger switch 14 is disposed in the grip portion 22. The trigger switch 14 includes a trigger member 14A and a switch body 14B. The switch body 14B is housed in the grip portion 22. The trigger member 14A protrudes forward from the upper part of the front of the grip portion 22. The trigger member 14A is operated by the operator. By operating the trigger member 14A, the driving and stopping of the motor 6 are switched.

[0074] A forward / reverse switching lever 15 is located on the upper part of the handle 22. The lever 15 is operated by the operator. By operating the lever 15, the rotation direction of the motor 6 is switched between forward and reverse directions. Switching the rotation direction of the motor 6 also switches the rotation direction of the output shaft 8.

[0075] The control circuit board 16 includes a computer system. The control circuit board 16 outputs control commands for controlling the motor 6. The control circuit board 16 is housed in the control circuit board housing section 23. The control circuit board 16 includes a board 16P on which multiple electronic components are mounted. Examples of electronic components mounted on the board 16P include: a processor such as a CPU (Central Processing Unit), non-volatile memory such as ROM (Read Only Memory) or RAM (Random Access Memory), transistors, capacitors, and resistors.

[0076] The control circuit board housing 17 houses the control circuit board 16. The control circuit board housing 17 is disposed within the internal space of the control circuit board housing portion 23. At least a portion of the control circuit board 16 is housed within the control circuit board housing 17.

[0077] <Torque Sensor>

[0078] Figure 5 This is a perspective view of the torque sensor 9 involved in this embodiment, viewed from the left front. Figure 6 This is a perspective view of the torque sensor 9 involved in this embodiment, viewed from the right front. Figure 7 This is a perspective view of the torque sensor 9 involved in this embodiment, viewed from the left rear. Figure 8 This is a right-side view of the torque sensor 9 according to this embodiment. Figure 9 This is a left-side view of the torque sensor 9 according to this embodiment. Figure 10 This is a cross-sectional view showing the torque sensor 9 according to this embodiment, and... Figure 5 The A-A line view is equivalent. Figure 11This is a perspective view, viewed from the left front, showing the state after the cover 97 of the torque sensor 9 involved in this embodiment has been removed.

[0079] like Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 ,as well as Figure 11 As shown, the torque sensor 9 includes: a torsion portion 90, a plate-shaped portion 91, a plate-shaped portion 92, a strain gauge 93, an amplifier circuit 94, a flexible substrate 95, a flexible substrate 96, a cover 97, a first lead 11, and a first connector 31.

[0080] The torsion section 90 is torsiond by a torque applied to the output shaft 8. The torsion section 90 is hollow and cylindrical. The central axis of the torsion section 90 coincides with the rotation axis AX. The torsion section 90 has a hole 90A for mounting the rotation shaft 63. The hole 90A is a through hole that passes through the front and rear ends of the torsion section 90. The hole 90A extends in the front-rear direction. The bearing 64 is held at the rear of the hole 90A. The front of the rotation shaft 63 is positioned inside the hole 90A of the torsion section 90.

[0081] A plate-shaped portion 91 is disposed around the front end of the torsion portion 90. The plate-shaped portion 91 is integrally formed with the torsion portion 90. The plate-shaped portion 91 is substantially circular in shape. The outer diameter of the plate-shaped portion 91 is larger than the outer diameter of the torsion portion 90. The plate-shaped portion 91 has a front surface 91A, a rear surface 91B, and an outer peripheral surface 91C. The front surface 91A faces forward. The front surface 91A is orthogonal to an axis parallel to the rotation axis AX. The rear surface 91B faces rearward. The rear surface 91B is orthogonal to an axis parallel to the rotation axis AX. A gear 91G is provided on the outer peripheral surface 91C. An internal gear 70 is disposed around the plate-shaped portion 91. The gear 91G meshes with the internal gear 70. The torque sensor 9 is connected to the internal gear 70 via the plate-shaped portion 91.

[0082] A plate-shaped portion 92 is disposed around the rear end of the torsion portion 90. The plate-shaped portion 92 is integrally formed with the torsion portion 90. The plate-shaped portion 92 is substantially circular in shape. The outer diameter of the plate-shaped portion 92 is larger than the outer diameter of the torsion portion 90. The outer diameter of the plate-shaped portion 92 is larger than the outer diameter of the plate-shaped portion 91. The plate-shaped portion 92 has a front surface 92A, a rear surface 92B, and an outer peripheral surface 92C. The front surface 92A faces forward. The front surface 92A is orthogonal to an axis parallel to the rotation axis AX. The rear surface 92B faces rearward. The rear surface 92B is orthogonal to an axis parallel to the rotation axis AX. The plate-shaped portion 92 is disposed in front of the fan 13. The plate-shaped portion 92 is fixed to the gearbox 4.

[0083] A strain gauge 93 is disposed on the torsion section 90. The strain gauge 93 indirectly detects the torque applied to the output shaft 8. Here, when the torque is large, the output signal (voltage) is large, and when the torque is small, the output signal (voltage) is small. The signal (voltage) output from the strain gauge 93 includes a detection signal of the torque applied to the output shaft 8. The strain gauge 93 is fixed to the surface of the torsion section 90. The torsion section 90 transmits the torque applied to the output shaft 8 via a planetary gear mechanism 7. That is, the torsion section 90 is torsionally transmitted by the torque applied to the output shaft 8. The torque applied to the output shaft 8 is transmitted via the planetary gear mechanism 7, and the strain of the torsion section 90, which is indirectly torsionally transmitted by the torque applied to the output shaft 8, is detected by the strain gauge 93. In addition, although the planetary gear mechanism 7 is set as the transmission element for transmitting the torque applied to the output shaft 8 to the torsion section 90, any element capable of transmitting torque may be any element other than a planetary gear mechanism.

[0084] An amplifier circuit 94 is disposed on the plate-shaped portion 92. In this embodiment, the amplifier circuit 94 is disposed on the front surface 92A of the plate-shaped portion 92. The amplifier circuit 94 is disposed inside the gearbox 4. The signal (voltage) from the strain gauge 93 is input to the amplifier circuit 94. The amplifier circuit 94 amplifies the signal from the strain gauge 93.

[0085] The flexible substrate 95 is a flexible printed circuit (FPC). The flexible substrate 95 has a base film and wiring disposed on the base film. The base film is formed of an insulating material. The wiring is formed of a conductive material. The base film is flexible. The flexible substrate 95 is bendable.

[0086] Like the flexible substrate 95, the flexible substrate 96 is a flexible printed circuit (FPC). The flexible substrate 96 has a base film and wiring disposed on the base film.

[0087] The flexible substrate 95 has a first portion 951 disposed on the surface of the torsion portion 90 and a second portion 952 connected to the flexible substrate 96. The first portion 951 is disposed on the surface of the torsion portion 90 in a bent state. The first portion 951 is fixed to the surface of the torsion portion 90 using, for example, an adhesive.

[0088] like Figure 11As shown, a flexible substrate 96 is disposed on a portion of the front surface 92A of the plate-shaped portion 92. In a plane orthogonal to the rotation axis AX, the flexible substrate 96 is arc-shaped. The flexible substrate 96 is disposed on the front surface 92A of the plate-shaped portion 92 without being bent. The flexible substrate 96 is fixed to the front surface 92A of the plate-shaped portion 92 using, for example, an adhesive. A second portion 952 of the flexible substrate 95 is connected to the flexible substrate 96.

[0089] The strain gauge 93 is fixed to the flexible substrate 95. The strain gauge 93 is fixed to the surface of the torsion section 90 by means of the flexible substrate 95.

[0090] The amplifier circuit 94 is fixed to the flexible substrate 96. The amplifier circuit 94 is fixed to the front surface 92A of the plate-shaped portion 92 by means of the flexible substrate 96.

[0091] Four strain gauges 93 are arranged circumferentially. The four strain gauges 93 are arranged side by side in the circumferential direction of the torsion portion 90 by bending the first portion 951 of the flexible substrate 95. The four strain gauges 93 are arranged at equal intervals of 90° in the circumferential direction.

[0092] The amplifier circuit 94 is disposed on the plate-shaped portion 92 without being bent. The flexible substrate 96 is disposed on the front surface 92A of the plate-shaped portion 92 without being bent.

[0093] The cover 97 is configured to cover the amplifier circuit 94 and the flexible substrate 96. The cover 97 is fixed to the plate-shaped portion 92 while covering the amplifier circuit 94 and the flexible substrate 96. The cover 97 protrudes forward from the front surface 92A of the plate-shaped portion 92.

[0094] Multiple first leads 11 are provided. The upper end of the first lead 11 is fixed to the flexible substrate 96. The upper end of the first lead 11 is connected to the amplifier circuit 94 via wiring on the flexible substrate 96. The lower end of the first lead 11 is connected to the first connector 31. The first connector 31 is connected to the second connector 32. The second connector 32 is connected to the control circuit board 16 via the second lead 12.

[0095] When the torsion section 90 is torsiond by the torque applied to the output shaft 8, the strain gauge 93 outputs a signal corresponding to the torque. The signal from the strain gauge 93 is input to the amplifier circuit 94. The amplifier circuit 94 sends the amplified signal from the strain gauge 93 to the control circuit board 16. The signal output from the amplifier circuit 94 is a detection signal of the torque applied to the output shaft 8. The detection signal from the torque sensor 9 includes the signal from the strain gauge 93 amplified by the amplifier circuit 94.

[0096] The amplifier circuit 94 sends the amplified signal from the strain gauge 93 to the control circuit board 16. The signal (voltage) input from the amplifier circuit 94 to the control circuit board 16 is higher than the signal (voltage) input from the strain gauge 93 to the amplifier circuit 94. The signal from the strain gauge 93, amplified by the amplifier circuit 94, is sent to the control circuit board 16 via the first lead 11, the first connector 31, the second connector 32, and the second lead 12.

[0097] Figure 12 This is a perspective view, viewed from the left front, showing the flexible substrate 95 on which the strain gauge 93 is fixed and the flexible substrate 96 on which the amplifier circuit 94 is fixed, as per this embodiment. Figure 13 This is a perspective view, viewed from the right front, showing the flexible substrate 95 on which the strain gauge 93 is fixed and the flexible substrate 96 on which the amplifier circuit 94 is fixed, as per this embodiment. Figure 14 This is a perspective view of the flexible substrate 95 on which the strain gauge 93 is fixed, as shown in this embodiment, viewed from the left front. Figure 15 This is a perspective view of the flexible substrate 95 on which the strain gauge 93 is fixed, as shown from the right front. Figure 16 This is a perspective view of the flexible substrate 95 involved in this embodiment, viewed from the left front. Figure 17 This is a perspective view of the flexible substrate 95 involved in this embodiment, viewed from the right front.

[0098] Part 951 is disposed around a portion of the torsion portion 90. Part 951 is disposed on a portion of the surface of the torsion portion 90 in a bent state. Part 951 has a support portion 951A and a bent portion 951B.

[0099] A strain gauge 93 is supported on a support portion 951A. Four support portions 951A are spaced apart circumferentially. The surface of the support portion 951A is flat. Each support portion 951A has an opening 951C and a terminal 951D. The terminal 951D is connected to the wiring of the flexible substrate 95. At least a portion of the strain gauge 93 is disposed inside the opening 951C. With at least a portion of the strain gauge 93 disposed inside the opening 951C, the strain gauge 93 is fixed to the surface of the support portion 951A. At least a portion of the strain gauge 93 is fixed to the surface of the torsion portion 90 via the opening 951C. With at least a portion of the strain gauge 93 disposed inside the opening 951C, the strain gauge 93 is connected to the terminal 951D. Through the connection between the strain gauge 93 and the terminal 951D, the strain gauge 93 is connected to the wiring of the flexible substrate 95.

[0100] A bend 951B is disposed between two adjacent support portions 951A. Three bends 951B are provided at intervals in the circumferential direction. The bends 951B are bent into an arc shape in such a way that they contact the surface of the torsion portion 90.

[0101] Part 2 952 is configured to project radially outward from a portion of the rear end of Part 1 951. The surface of Part 2 952 is flat. Part 2 952 has a terminal 952A connected to wiring on flexible substrate 96. Terminal 952A is connected to wiring on flexible substrate 95. The wiring on flexible substrate 95 is connected to the wiring on flexible substrate 96 via the wiring on flexible substrate 96 and terminal 952A.

[0102] Amplifier circuit 94 is supported on flexible substrate 96. The surface of flexible substrate 96 is flat. Amplifier circuit 94 is connected to wiring on flexible substrate 96. Strain gauge 93 is connected to amplifier circuit 94 via terminal 951D, wiring on flexible substrate 95, terminal 952A, and wiring on flexible substrate 96.

[0103] Figure 18 This is a circuit diagram showing the strain gauges 93 and the amplifier circuit 94 involved in this embodiment. The resistance of each of the four strain gauges 93 is R. g1 R g2 R g3 R g4 A bridge circuit 98 is formed by four strain gauges 93. The four strain gauges 93 are connected in a so-called four-resistance strain gauge configuration.

[0104] When the torsion section 90 is torsionped, the strain gauge 93 deforms, and the resistance R... g1 R g2 R g3 R g4 A change occurs. The bridge voltage V is input to the bridge circuit 98. e Under these conditions, the resistance R g1 R g2 R g3 R g4 When the resistance R changes, g1 With resistance R g2 The voltage V between b1 and resistor R g3 With resistance R g4 The voltage V between b2 The change occurs. The output voltage V1 of the bridge circuit 98 is: Voltage V b1 With voltage V b2 The difference (V1 = V) b2 -V b1 ).

[0105] The amplifier circuit 94 includes resistors R1, R2, R3, and R4, and an operational amplifier 94A. Resistors R1, R2, R3, and R4, and the operational amplifier 94A are respectively supported on the substrate film of the flexible substrate 96. As the first input signal, the voltage V... b1 The signal is input to operational amplifier 94A via resistor R1 as the second input signal, voltage V. b2 The voltage is input to operational amplifier 94A via resistor R3. The amplified voltage V output from operational amplifier 94A... o Voltage V o This is equivalent to an amplified signal from strain gauge 93. Voltage V o The signal is transmitted to the control circuit board 16 via the first lead 11 and the first connector 31. Furthermore, the amplifier circuit 94 is not limited to the circuit shown in the figure; for example, it could be a PGA (Programmable Gain Amplifier). Additionally, a filter circuit can be provided between the bridge circuit 98 and the amplifier circuit 94. In this case, the noise effects described later can be further suppressed.

[0106] <Action>

[0107] During screw tightening, the control circuit board 16 starts the motor 6 to rotate the output shaft 8 based on the operation signal of the trigger switch 14. During screw tightening, the torque applied to the output shaft 8 increases as the screw is screwed into the workpiece. The torque applied to the output shaft 8 is transmitted to the internal gear 70 via the carrier 72C and the planetary gear 72P. The torque transmitted to the internal gear 70 is then transmitted to the torque sensor 9 via the plate-shaped portion 91. The torque applied to the output shaft 8 is detected by the torque sensor 9.

[0108] The plate-shaped portion 92 of the torque sensor 9 is fixed to the gearbox 4. The torsion portion 90 of the torque sensor 9 is torsionally rotated along the rotational direction via the internal gear 70. Furthermore, although the plate-shaped portions 91 and 92 are also subjected to torque, their diameters are larger than the diameter of the torsion portion 90. Therefore, the torsional deformation of the plate-shaped portions 91 and 92 is less than that of the torsion portion 90. When the torsion portion 90 of the torque sensor 9 is torsionally rotated along the rotational direction, the four strain gauges 93 disposed on the surface of the torsion portion 90 deform. The deformation of the strain gauges 93 generates a signal (voltage) indicating the torque applied to the torsion portion 90, which is then input to the amplifier circuit 94. The amplifier circuit 94 amplifies the signal from the strain gauges 93. The amplified signal from the strain gauges 93 is then transmitted to the control circuit board 16 via the first lead 11, the first connector 31, the second connector 32, and the second connector 32.

[0109] The control circuit board 16 acquires the detection signal from the torque sensor 9. Based on the detection signal from the torque sensor 9, the control circuit board 16 calculates the torque applied to the output shaft 8. The target torque is recorded on the control circuit board 16. Based on the detection signal from the torque sensor 9, the control circuit board 16 controls the motor 6 so that the screw is tightened to the workpiece at the target torque.

[0110] Based on the detection signal from the torque sensor 9, the control circuit board 16 determines that the torque applied to the output shaft 8 has reached the target torque, and then stops the drive of the motor 6. Accordingly, the control circuit board 16 can control the motor 6 based on the detection signal from the torque sensor 9 so that the screw is tightened to the work object with the target torque.

[0111] In this embodiment, the screw fastener 1 includes a wireless communication device (not shown). The wireless communication device is disposed at a designated location on the housing 2. The wireless communication device is capable of short-range wireless communication in a communication method that does not require a wireless license. The wireless communication device can implement wireless communication in a communication method that, for example, conforms to the IEEE 802.15.1 standard established by the Institute of Electrical and Electronics Engineers (IEEE).

[0112] The control circuit board 16 transmits the detection signal from the torque sensor 9 to a wireless communication device. The wireless communication device then transmits the detection signal from the torque sensor 9 to a management computer externally configured on the screw fastening machine 1. The management computer records the detection signal from the torque sensor 9 during the screw fastening operation.

[0113] <Effect>

[0114] As explained above, according to this embodiment, the strain gauge 93 is disposed on the torsion section 90. The amplifier circuit 94 is disposed on the plate-shaped section 92. The plate-shaped section 92 and the torsion section 90 are integrally formed. The amplifier circuit 94 is disposed near the strain gauge 93. The distance between the strain gauge 93 and the amplifier circuit 94 is shortened, thereby suppressing the situation where the signal input from the strain gauge 93 to the amplifier circuit 94 is affected by noise.

[0115] Both the strain gauge 93 and the amplifier circuit 94 are fixed to the flexible substrates (95, 96). The signal from the strain gauge 93 is input to the amplifier circuit 94 via the wiring of the flexible substrates 95 and 96. Since the signal from the strain gauge 93 is input to the amplifier circuit 94 via the wiring of the flexible substrates (95, 96), it is possible to suppress the influence of noise on the signal input from the strain gauge 93 to the amplifier circuit 94.

[0116] Four strain gauges 93 are configured. The four strain gauges 93 are arranged side by side in the circumferential direction of the torsion section 90 by bending the first portion 951 of the flexible substrate 95. After the strain gauges 93 are fixed to the support portion 951A of the first portion 951, the four strain gauges 93 are arranged in the circumferential direction of the torsion section 90 by bending the bending portion 951B.

[0117] The amplifier circuit 94 is disposed on the front surface 92A of the plate-shaped portion 92 in a manner in which the flexible substrate 96 is not bent. Accordingly, stress on the amplifier circuit 94 can be suppressed. After the amplifier circuit 94 is fixed to the flexible substrate 96, the amplifier circuit 94 is disposed on the plate-shaped portion 92 by connecting the flexible substrate 96 to the front surface 92A of the plate-shaped portion 92.

[0118] The amplifier circuit 94 is connected to a plurality of first leads 11. Each first lead 11 is connected to a first connector 31. The control circuit board 16 for controlling the motor 6 is connected to a plurality of second leads 12. Each second lead 12 is connected to a second connector 32. The first connector 31 is connected to the second connector 32. Accordingly, the signal from the strain gauge 93, amplified by the amplifier circuit 94, is transmitted to the control circuit board 16 via the first leads 11, the first connector 31, the second connector 32, and the second leads 12.

[0119] Furthermore, the first lead 11 and the second lead 12, which connect the amplifier circuit 94 to the control circuit board 16, are less likely to be affected by significant noise. This is because, when the same level of noise acts on the flexible substrate (95, 96) and the leads (11, 12) respectively, the impact on the voltage before amplification is relatively large, while the impact on the voltage after amplification (a higher voltage) is relatively small. Therefore, when the torque sensor 9 is separated from the control circuit board 16 by a specified distance, a shorter distance between the strain gauge 93 and the amplifier circuit 94 becomes important, while a shorter length of the leads (11, 12) connecting the amplifier circuit 94 to the control circuit board 16 becomes relatively less important.

[0120] The torque sensor 9 is connected to the output shaft 8 via a planetary gear mechanism 7. Accordingly, the torque applied to the output shaft 8 is transmitted to the torque sensor 9 via the planetary gear mechanism 7.

[0121] The planetary gear mechanism 7 includes: a sun gear 72S that rotates due to the rotational force generated by a motor 6; an internal gear 70 disposed around the sun gear 72S; a plurality of planetary gears 72P disposed between the sun gear 72S and the internal gear 70; and a carrier 72C that supports the planetary gears 72P. The carrier 72C is connected to an output shaft 8. The internal gears 70 are connected to a torque sensor 9. Accordingly, the rotation generated by the motor is transmitted to the output shaft 8, and the torque applied to the output shaft 8 is transmitted to the torque sensor 9.

[0122] The torque sensor 9 is cylindrical and disposed around the rotary shaft 63. The front end of the rotary shaft 63 is connected to the sun gear 72S via a pinion 71S, a planetary gear 71P, and a carrier 71C. Accordingly, it is possible to prevent the size of the screw fastener 1 from increasing in the front-to-back direction.

[0123] A plate-shaped portion 91 is connected to the front end of the torsion section 90, and a plate-shaped portion 92 is connected to the rear end of the torsion section 90. The internal gear 70 meshes with a gear 91G provided on the plate-shaped portion 91. The torsion section 90 is connected to the internal gear 70 by means of the plate-shaped portion 91. The plate-shaped portion 92 is fixed to the gearbox 4. Therefore, when a torque is applied to the output shaft 8, the torsion section 90 can receive the torque from the internal gear 70 in a torsion manner along the rotation direction. Therefore, the strain gauge 93 provided on the torsion section 90 can effectively detect the torque applied to the output shaft 8.

[0124] [Second Implementation]

[0125] The second embodiment will be described. In the following description, the same or equivalent components as those in the above embodiment will be given the same reference numerals, and the description of these components will be simplified or omitted.

[0126] Figure 19 This is a cross-sectional view showing the screw fastening machine 101 according to this embodiment. The screw fastening machine 101 includes: a housing 2, a gearbox 4, a battery assembly 5, a motor 6, a planetary gear mechanism 7, an output shaft 8, a torque sensor 9, a first lead 11, a second lead 12, a fan 13, a trigger switch 14, a forward / reverse switching lever 15, a control circuit board 16, and a control circuit board housing 17.

[0127] The gearbox 4 houses a torque sensor 9, a planetary gear mechanism 7, and a portion of the output shaft 8. The torsion section 90 of the torque sensor 9 is housed within the gearbox 4. The torsion section 90 is twisted by a torque applied to the output shaft 8. Similarly to the embodiment described above, a strain gauge 93 is disposed on the torsion section 90.

[0128] The amplifier circuit 94 is located inside the gearbox 4. Figure 19In the example shown, the amplifier circuit 94 is disposed in the lower part of the interior of the gearbox 4. In this embodiment, the amplifier circuit 94 is fixed to the inner surface of the gearbox 4. The signal from the strain gauge 93 is input to the amplifier circuit 94 via the lead 33.

[0129] The gearbox 4 has a hole 40. The hole 40 is configured to connect the interior of the gearbox 4 to the exterior. The amplifier circuit 94 is connected with a plurality of first leads 11. The first leads 11 are led out from the hole 40. One end of the first lead 11 is disposed inside the gearbox 4 and connected to the amplifier circuit 94. The other end of the first lead 11 is disposed outside the gearbox 4.

[0130] The other end of the first lead 11 is connected to the first connector 31. The control circuit board 16 is connected to a plurality of second leads 12. The second leads 12 are connected to the second connector 32. The first connector 31 is connected to the second connector 32. The signal from the strain gauge 93, amplified by the amplification circuit 94, is transmitted to the control circuit board 16 via the first lead 11, the first connector 31, the second connector 32, and the second leads 12.

[0131] As explained above, according to this embodiment, the torsion section 90 is disposed inside the gearbox 4. The strain gauge 93 is disposed inside the torsion section 90. The amplifier circuit 94 is disposed inside the gearbox 4. The amplifier circuit 94 is disposed near the strain gauge 93. Because the distance between the strain gauge 93 and the amplifier circuit 94 is shortened, it is possible to suppress the situation where the signal input from the strain gauge 93 to the amplifier circuit 94 is affected by noise.

[0132] Furthermore, even in this embodiment, the first lead 11 and the second lead 12, which connect the amplification circuit 94 to the control circuit board 16, are less likely to be affected by significant noise. This is because, when the same level of noise acts on lead 33 and leads (11, 12) respectively, the impact on the voltage before amplification is relatively large, while the impact on the voltage after amplification (a higher voltage) is relatively small. Therefore, when the torque sensor 9 and the control circuit board 16 are separated by a predetermined distance, a shorter distance between the strain gauge 93 and the amplification circuit 94 becomes important, while a shorter length of the leads (11, 12) connecting the amplification circuit 94 to the control circuit board 16 becomes relatively less important.

[0133] [Other implementation methods]

[0134] In the above embodiments, the amplifier circuit 94 may also be disposed on the rear surface 91B of the plate-shaped portion 91.

[0135] In the above embodiments, the amplifier circuit 94 may also be disposed on the surface of the twisted portion 90.

[0136] In the above embodiments, an electric screwdriver was used as an example to describe the screw fastening machine (1, 101). Any screw fastening machine (1, 101) that has a motor 6 and an output shaft 8 that rotates due to the rotational force generated by the motor 6 is acceptable. The screw fastening machine (1, 101) can also be at least one of the following: a vibratory screwdriver, an angle drill, an impact screwdriver, a hammer drill, a circular saw, and an electric reciprocating saw.

[0137] In the above embodiment, a battery pack 20 assembled in the battery assembly 5 is used as the power source for the screw fastening machine (1, 101). Commercial power (AC power) can also be used as the power source for the screw fastening machine (1, 101).

[0138] In the above embodiments, motor 6 is an electric motor, and the screw fastening machine (1, 101) is a power tool powered by motor 6. The screw fastening machine (1, 101) may also be powered by an air motor. Furthermore, the power source of the screw fastening machine (1, 101) is not limited to an electric motor or an air motor; it can be other power sources. For example, the power source of the screw fastening machine (1, 101) may be a hydraulic motor or a motor driven by an engine.

Claims

1. A screw fastening machine characterized by comprising: a motor having a rotor and a stator; an output shaft driven by the motor and capable of mounting a tool head; a hollow torsion portion disposed around a rotation axis of the rotor, transmitted torque applied to the output shaft by a transmission element, and indirectly twisted around a center axis using torque applied to the output shaft; a first plate-shaped portion disposed around a front end portion of the torsion portion, formed integrally with the torsion portion, and linked to the output shaft; a strain gauge disposed in the torsion portion; an amplification circuit disposed behind the strain gauge and inputted with a signal from the strain gauge; and a second plate-shaped portion having a front surface facing forward orthogonally to the center axis, disposed around a rear end portion of the torsion portion, formed integrally with the torsion portion, and fixed to a gear case housing the strain gauge and the amplification circuit. The amplification circuit is disposed on the front surface of the second plate-shaped portion.

2. The screw fastening machine according to claim 1, characterized in that the strain gauge and the amplification circuit are both fixed to a flexible substrate.

3. The screw fastening machine according to claim 2, characterized in that the strain gauge is disposed in four, and disposed side by side in a circumferential direction of the torsion portion by bending the flexible substrate.

4. The screw fastening machine according to claim 2, characterized in that the amplification circuit is not disposed in a bent manner on the plate-shaped portion.

5. The screw fastening machine according to any one of claims 1 to 4, characterized in that the amplification circuit is connected to a plurality of first lead wires, the first lead wires are connected to a first connector, a control circuit substrate for controlling the motor is provided, the control circuit substrate is connected to a plurality of second lead wires, the second lead wires are connected to a second connector, and the first connector is connected to the second connector.

6. A screw fastening machine characterized by comprising: a motor; an output shaft disposed at a position further forward than the motor, driven by the motor, and capable of mounting a tool head; a torque sensor disposed between a stator of the motor and the output shaft, detecting torque applied to the output shaft; and a gear case disposed at a position further forward than the motor, housing a planetary gear mechanism, the torque sensor is disposed around a rotation axis of the motor, connected to the output shaft by the planetary gear mechanism disposed at a position further forward than the torque sensor, a front end portion of the rotation axis is disposed at a position further forward than a front end portion of the torque sensor, the torque sensor comprises: a hollow torsion portion twisted by torque applied to the output shaft; a first plate-shaped portion disposed around a front end portion of the torsion portion, formed integrally with the torsion portion, and linked to the output shaft by the planetary gear mechanism; and a second plate-shaped portion disposed around a rear end portion of the torsion portion, formed integrally with the torsion portion, and fixed to the gear case. ​ ​ ​ ​ ​ ​ The torsion portion and a part of the output shaft are housed in the gear case, A strain gauge is provided in the torsion portion, An amplification circuit to which a signal from the strain gauge is input is provided inside the gear case.

7. The screw fastening machine according to claim 6, wherein A hole is formed in the gear case, A plurality of first lead wires are connected to the amplification circuit, The first lead wires are drawn out from the hole.

8. A torque sensor, comprising: a hollow torsion portion that is twisted about a center axis by a torque applied to an output shaft; a first plate-shaped portion that is provided around a front end portion of the torsion portion, is formed integrally with the torsion portion, and is coupled to the output shaft; a strain gauge that is provided in the torsion portion; an amplification circuit that is provided behind the strain gauge, to which a signal from the strain gauge is input, and that is provided in a gear case that houses the strain gauge and the amplification circuit; and a second plate-shaped portion that has a front surface facing forward in a direction orthogonal to the center axis, is provided around a rear end portion of the torsion portion, is formed integrally with the torsion portion, and is fixed to the gear case, The amplification circuit is provided on the front surface of the second plate-shaped portion. ​

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