JP2016038353A - Torque detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a torque detector having a structure for eliminating an influence on a strain causing unit that is disposed on a rotation shaft and detects a rotation torque by sensing strain.SOLUTION: The torque detector includes a rotation shaft that can transmit power to a loading device in conjunction with an output unit of a speed reducer and can detect the rotation torque. A strain causing unit for detecting the rotation torque by sensing strain is disposed on the rotation shaft, and the position is closer to the loading device side than a bearing supported from a housing side. Due to this arrangement, detection of the friction torque of the bearing caused by assembling can be eliminated, and accurate rotation torque value can be acquired.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a torque detector that is connected to a motor and a speed reducer to enable torque detection.

  Conventionally, as shown in FIG. 2, as a means for detecting the rotational torque while transmitting the power of the motor to the load device, a reduction gear is connected to the output shaft of the motor to reduce the rotational speed and simultaneously increase the torque. Generally, a torque detector capable of measuring torque is connected via a shaft coupling such as a ring, and the output shaft of the torque detector is connected to a load device. With this configuration, each unit is independent, and maintenance such as component replacement is advantageous, but there are limitations on the application because the length in the axial direction is long and the electrical wiring is complicated. It was.

  On the other hand, the invention which comprises a motor, a reduction gear, and a torque detector by integral structure is disclosed (patent document 1, patent document 2). In both inventions of Patent Document 1 and Patent Document 2, the output rotating shaft after being decelerated has a hollow structure, and there is a bearing that supports the rotating shaft from the inside, while the rotating shaft is supported from the outside. Bearings are provided concentrically. That is, in this configuration, the output rotation shaft from the speed reducer is sandwiched between the inner and outer bearings, and the inner ring of the bearing that supports this rotation shaft from the inside of the shaft is also configured to rotate. It is expected that smooth rotation cannot be obtained unless the shape accuracy of the parts is increased and the dimensional management of the assembly is tightened.

  On the other hand, in the torque detection, there is no description of a detailed embodiment in the invention of Patent Document 2, and when a means for measuring the magnetostriction of the rotating shaft is used, although it can be measured even at high speed rotation, a continuous load is applied to the shaft. In some cases, it is difficult to maintain highly accurate measurements because the shaft itself causes creep deformation over time. In Patent Document 1, there is a description in which a strain gauge is provided. However, according to this structure, an accurate torque value cannot be obtained due to the stress generated in the torque detection portion or the occurrence of creep deformation due to screw fastening at the time of assembly. However, wiring from strain gauges can only be made, and there is a problem that the application range is limited.

  Patent Document 3 discloses a wave gear device with a torque detection mechanism that detects torque by attaching a strain gauge inside a reduction gear. Here, the strain gauge is attached to a fixed member instead of a rotating member, and the torque of the rotating body is indirectly measured in the vicinity of the bending portion in the speed reducer, so the responsiveness is poor. There was a difficulty in measurement accuracy.

JP 2013-215081 A Japanese Patent No. 4581543 Japanese Patent No. 3512160

  Basically, a unit composed of a single unit as shown in FIG. 2, when these are configured as an integral type, a strain generating portion 2 a provided to detect strain on the rotating shaft 2 as shown in FIG. 3 is provided. The structure located in the intermediate part of the bearing 3 and a reduction gear can be considered. A plurality of strain gauges are affixed to the strain generating portion 2a, the rotational torque of the rotating shaft can be measured, and the torque is detected by wireless transmission of data from the rotating side substrate to the fixed side substrate. Even in such a configuration, when the rotary shaft 2 is assembled by the bearing 3, the rotary shaft 2 is distorted and affects the strain generating portion 2a, so that an accurate torque value cannot be obtained. That is, since the friction torque generated in the bearing 3 is detected by the strain generating portion 2a of the rotating shaft 2, there is a problem that an accurate torque value cannot be obtained.

  An object of the present invention is to obtain a torque detector that compensates for the above-described drawbacks and can detect torque with high responsiveness and high accuracy.

A torque detector according to the present invention is connected to a speed reducer mechanically connected to a motor, and has a means for detecting rotational torque of a speed reducer output unit.
A rotating shaft that is mechanically connected to the reduction gear output and transmits power to the load device;
A bearing that rotatably supports the rotating shaft at an intermediate position in the axial direction of the rotating shaft of the reduction gear output unit and the load device;
The strain generating portion provided on the rotating shaft so as to detect the torque generated by detecting the distortion on the rotating shaft is positioned closer to the load device than the portion supported by the bearing of the rotating shaft in the axial direction of the rotating shaft. It consists of

  It is preferable to detect the strain of the strain generating portion with a strain gauge provided in the strain generating portion of the rotating shaft.

  Moreover, it is preferable that a reduction gear is a wave gear reduction gear.

1 is a cross-sectional structural view of a torque detector showing a first embodiment of the present invention. A diagram showing the configuration of a conventional torque detector, reducer, and motor Cross-sectional structure diagram of a conventional torque detector Cross-sectional structure diagram of a torque detector showing a second embodiment of the present invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional structural view showing a first embodiment of the present invention. In FIG. 1, the torque detector 1 is formed by integrating a reduction gear portion and a torque detection portion.

  The rotating shaft 2 is rotatably supported, transmits power decelerated by a speed reducer, and also includes a strain generating portion 2a for detecting rotational torque. The strain generating portion 2a is provided with a small diameter at the central portion in the axial direction of the rotary shaft 2, and has no strength and does not deform in the axial direction of the rotary shaft 2, and deforms in the twist direction. A strain gauge is affixed to this surface, and a rotational torque is detected by detecting a twist generated in the strain generating portion 2a. The shape of the strain generating portion 2a is not limited to a cylindrical shape, and an optimal one is selected depending on the amount of rotational torque to be measured. On the load side of the rotary shaft 2, it is mechanically connected to a load device (not shown), and the rotational torque is detected while rotating together with the load device.

  On the other hand, the motor shaft 101 is rotatably supported by a bearing 102 provided in a motor housing (not shown), and is connected to a wave generator 14 of a speed reduction mechanism to transmit rotational power.

  The bearing 3 is, for example, a cross roller bearing that receives a load by line contact with a cylindrical roller, and its outer ring is fixed to a connection portion 17 that also serves as a housing, and rotatably supports the rotary shaft 2. It is provided as follows. Accordingly, the bearing 3a is an outer ring, and the bearing 3b facing the bearing 3a is an inner ring, and the rotary shaft 2 is rotatable by being fixed to the rotary shaft 2 with screws.

  The primary side core 7 and the primary side coil 8, and the secondary side core 6 and the secondary side coil 5 form a rotary transformer structure. The rotating shaft 2 includes rotating-side substrates 4a and 4b that rotate together with the rotating shaft 2. The rotating-side substrates 4a and 4b include a Wheatstone bridge circuit that includes a strain gauge attached to the cylindrical surface of the strain generating portion 2a. It is mounted and power is supplied to this circuit without contact.

  Hereinafter, the flow of electric power and electric signals in this circuit will be described. The fixed-side substrate 10 is supplied with power from an external DC power supply device, converts this DC to AC, and is used to supply power to an electric circuit provided on the rotating shaft 2 and rotating together. A circuit is provided.

  The primary core 7 is a ferrite having a U-shaped cross section with protrusions at both ends, and is attached to the fixed substrate 10 via a core holder 9. A primary coil 8 formed by winding a copper wire is provided between both protrusions of the primary core 7. Electric power is supplied to the primary coil 8 from the switching circuit of the fixed substrate 10.

  On the other hand, the secondary side of the transformer is configured on the rotating shaft 2 so as to face the primary side core 7 and the primary side coil 8 at a predetermined interval. A secondary side core 6 made of a ferrite sheet is provided on the surface of the rotary shaft 2, and a secondary side coil 5 formed by winding a copper wire is provided on the outer periphery of the secondary side core 6.

  Accordingly, when power is supplied from the external DC power supply device to the fixed side substrate 10 and the current converted to AC by the switching circuit on the fixed side substrate 10 is passed through the primary side coil 8, an AC magnetic field is generated. This alternating magnetic field passes through the secondary core 6 on the rotating shaft 2 side, so that a current is induced in the secondary coil 5. The induced current is supplied to a strain gauge constituting a Wheatstone bridge circuit through a rectification circuit and a stabilization circuit in the rotation side substrates 4a and 4b.

  In actual torque detection, when torque is applied to the rotating shaft 2, the strain generating portion 2a of the rotating shaft 2 is distorted according to the magnitude of the torque, and the magnitude of this distortion is the magnitude of the change in the resistance value of the strain gauge. Detected as Detection is performed by a detection circuit provided in the rotation side substrates 4a and 4b, and the detected analog signal is digitized and modulated by A / D conversion.

  This digitized signal is transmitted by the LED that performs infrared communication provided on the rotation side substrates 4a and 4b, and is received by the light receiving element provided on the fixed side substrate 10, and is digital corresponding to the torque value. A signal can be obtained. The fixed board 10 is provided with a demodulation circuit so that a voltage signal corresponding to the detected torque value can be output. The output voltage signal is displayed on a display or the like by known means and used for controlling the motor.

  The rotation-side substrates 4a and 4b are fixed to the rotation shaft 2 by the substrate fixing column 19 and have a ring shape, and the arrangement positions of the electronic components are considered on the substrate so as to maintain the balance during rotation. Has been. In this embodiment, the rotation-side substrates 4a and 4b are composed of two substrates. However, depending on the diameter dimension of the rotating shaft 2, the substrate area can be widened and may be composed of one substrate, which is appropriately selected. The

  On the other hand, a wave gear reducer is connected to the drive side with respect to the rotating shaft 2. The wave gear reducer includes a flex spline 13 having a thin cup shape and gear teeth on the outer periphery of the opening, and a circular spline having gear teeth on the inner peripheral surface corresponding to the outer peripheral gear teeth of the flex spline 13. 12 and a wave generator 14 which is located on the inner periphery of the flex spline 13 and which is coupled to the motor shaft 101.

  The wave generator 14 is a component in which a thin ball bearing is combined on the outer periphery of an elliptical cam. The inner ring of the bearing is fixed to the cam, and the outer ring is elastically deformed via the ball. The flex spline 13 is a thin cup-shaped metal elastic body. The bottom of the thin cup of the flex spline 13 is called a diaphragm and functions as a reduction gear output. The circular spline 12 is a rigid ring-shaped part, and has an internal tooth structure having two more teeth than the flex spline 13.

  The flex spline 13 is bent into an elliptical shape by the wave generator 14, and the teeth are engaged with the circular spline 12 at the major axis of the ellipse, and the teeth are not meshed at the minor axis. When the circular spline 12 is fixed and the wave generator 14 is rotated clockwise, the flex spline 13 is elastically deformed, and the meshing position of the teeth with the circular spline 12 is sequentially moved. When the wave generator 14 rotates once, the flex spline 13 moves counterclockwise by the difference in the number of teeth. Therefore, the diaphragm of the flex spline 13 of the wave gear reducer serves as an output unit, and the speed is reduced by the reduction ratio of the wave gear reducer.

  The rotating shaft 2 is fastened to the diaphragm portion of the flex spline 13, that is, the reducer output portion by screws. An oil seal 11 is provided in the middle of the flexpline 13, the secondary core 6, and the secondary coil 5 in the axial direction in order to prevent the oil on the reduction gear side from being scattered. The oil seal 11 is inserted into the cover 16 and brought into contact with the rotating shaft 2 to be sealed.

  On the other hand, the rotating shaft 2 is fixed to the bearing inner ring 3b by a flange portion 2b projecting in the radial direction. The bearing outer ring 3a provided so as to face the bearing inner ring 3b is fixed to the connecting portion 17 that also serves as an exterior portion, and becomes the fixed side when viewed from the whole.

  FIG. 4 is a cross-sectional structural view showing a second embodiment of the present invention. In the second embodiment, the bearing 3 is constituted by a radial deep groove ball bearing. In this case, since the bearing 3 is not a high-rigidity cross roller bearing, a bearing 18 is provided in the vicinity of the flex spline 13 of the reduction gear with the rotation side substrates 4a and 4b and the secondary side coil 5 interposed therebetween. This bearing 18 is a radial deep groove ball bearing with a seal, which also serves as a seal for oil in the speed reducer. In the second embodiment as well, it is the same that the strain generating portion 2a of the rotating shaft 2 is provided closer to the load device than the bearing 3.

  In FIG. 3 showing the conventional embodiment, the strain generating portion 2a of the rotating shaft 2 is located at an intermediate position between the bearings 3a and 3b and the reduction gear output, that is, the flex spline 13. Therefore, in order to secure the axial length of the strain generating portion 2a, it is inevitable that the axial length becomes longer as a whole. On the other hand, in the present invention, the rotating shaft 2 is connected to the flex spline 13 at one end, receives the reduced power, and is supported by the exterior fixing portion by the bearing 3, and is closer to the load device side in the axial direction than the supporting portion. The structure is provided with a strain generating portion for detecting strain. With this arrangement, it is possible to reduce the occurrence of stress due to fastening of screws and bolts during assembly in the strain generating portion 2a. That is, since the friction torque of the bearing 3 generated by assembly is not detected, an accurate torque value can be obtained. Moreover, since the freedom degree of arrangement | positioning of the strain generation part 2a is high, it is also easy to suppress the length of an axial direction. Furthermore, in the first embodiment, since there is no mutual interference due to a plurality of bearings, smooth movement of the rotating shaft 2 can be realized without increasing the assembly accuracy and the component accuracy.

  As an application example of the present invention, it can be applied to an actuator that generates power while controlling torque, that is, a robot or the like.

DESCRIPTION OF SYMBOLS 1 Torque detector 2 Rotating shaft 2a Strain part 2b Collar part 3 Bearing 3a Bearing outer ring 3b Bearing inner ring 4a, 4b Rotation side board 5 Secondary side coil 6 Secondary side core 7 Primary side core 8 Primary side coil 9 Core holder DESCRIPTION OF SYMBOLS 10 Fixed side board | substrate 11 Oil seal 12 Circular spline 13 Flex spline 14 Wave generator 15 Shaft cover 16 Cover 17 Connection part 18 Bearing 19 Board | substrate fixed support | pillar 20 Torque detector 101 Motor shaft 102 Bearing 103 Reduction gear 104 Motor 105 Shaft coupling

Claims (3)

In a torque detector connected to a reduction gear mechanically connected to a motor and having means for detecting rotational torque of a reduction gear output unit,
A rotary shaft that is mechanically connected to the reduction gear output and transmits power to a load device;
A bearing that rotatably supports the rotating shaft at an intermediate position in the axial direction of the rotating shaft of the speed reducer output unit and the load device;
The strain generating portion provided in the rotating shaft so as to detect the torque generated by detecting the distortion generated in the rotating shaft is more load than the portion of the rotating shaft supported by the bearing in the axial direction of the rotating shaft. A torque detector located on the apparatus side.   The torque detector according to claim 1, wherein the strain of the strain generating portion is detected by a strain gauge provided in the strain generating portion of the rotating shaft. The torque detector according to claim 1, wherein the speed reducer is a wave gear speed reducer.