JP3575719B2 - Silk hat-type flexible meshing gear device with torque detector - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a silk hat type flexible meshing gear device in which a flexible external gear has a silk hat shape. More specifically, the present invention relates to a silk hat-type flexible meshing gear device having a torque detecting portion capable of accurately detecting torque transmitted through the device.
[0002]
[Prior art]
For a joint drive mechanism of a robot or the like, a flexible meshing gear device that can obtain a high reduction ratio, has a simple structure, and can perform accurate positioning is used. The flexible meshing gear device generally includes an annular rigid internal gear, a flexible external gear disposed inside the ring internal gear, and a wave generator fitted inside the internal ring gear. . The wave generator generally has an elliptical profile, and the flexible external gear is bent into an elliptical shape by the wave generator, and the outer peripheral gears located at both ends in the major axis direction of the elliptical shape. The teeth are engaged with the internal teeth of the rigid internal gear.
[0003]
High-speed rotation is input to the wave generator from a motor output shaft or the like. When the wave generator rotates at high speed, the meshing position of the external teeth of the flexible external gear with the internal teeth also moves in the circumferential direction. The number of external teeth of the flexible external gear is set to 2N (N is a positive integer) with respect to the number of internal teeth of the rigid internal gear, and is usually set to a number of teeth smaller by two. Therefore, when the meshing position rotates in the circumferential direction, a relative rotation occurs between the two gears. If the gear on one side, generally a rigid internal gear, is fixed so as not to rotate, the other gear, generally a flexible external gear, rotates at a speed that is significantly reduced compared to the input rotation. I do. This decelerated rotation is transmitted to the load side.
[0004]
The flexible meshing gear device having this configuration is classified into a flat type, a cup type, and a silk hat type according to the shape of a flexible external gear incorporated therein. The device to which the present invention is directed is a silk hat type flexible meshing gear device.
[0005]
In this silk hat type flexible meshing gear device, a silk hat-shaped flexible external gear is incorporated. The top hat-shaped flexible external gear has a cylindrical torso, external teeth formed on the outer periphery of the distal opening, and a radially outer portion continuous with the opening at the base end of the torso. It has a configuration in which an annular diaphragm that extends is provided and an annular boss that is continuous with the outer peripheral edge of the diaphragm.
[0006]
[Problems to be solved by the invention]
A mechanism using a strain gauge is known as a torque detection mechanism for detecting a torque transmitted via the silk hat type flexible meshing gear device. In the torque detecting mechanism, a strain gauge for torque detection is attached to a diaphragm portion of a flexible external gear having a top hat shape. Since the diaphragm portion is continuous with the body portion which is repeatedly bent in the radial direction by the wave generator, the diaphragm portion is deformed along with this deformation to generate bending stress. Therefore, it is necessary to measure the transmitted torque by attaching a strain gauge to the diaphragm portion having the lowest bending stress other than the shearing force generated by the torque transmitted through the diaphragm portion.
[0007]
However, in a portion including a position where the bending stress is minimized, the generated stress varies greatly depending on the position. Therefore, accurate torque detection cannot be performed unless the strain gauge is accurately attached to a position where the bending stress is minimized.
[0008]
SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a silk hat-type flexible meshing gear device having a torque detecting portion capable of accurately detecting torque even when the position where the strain gauge is attached is slightly shifted. It is to realize.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the present invention, an annular rigid internal gear, a flexible external gear disposed inside the annular internal gear, and a flexible external gear which is fitted inside the internal gear, A radial wave generator that radially bends and meshes with the rigid internal gear at a plurality of locations and moves the meshing position in the circumferential direction, and the flexible external gear has a cylindrical shape. -Shaped trunk, external teeth formed on the outer periphery of the distal opening end of the trunk, and an annular diaphragm extending radially outward continuously to the proximal opening of the trunk, In a silk hat-type flexible meshing gear device having a shape having an annular boss continuous to the outer peripheral end of the diaphragm, a radial direction generated in the diaphragm of the flexible external gear during operation. Bending stress distribution cuts from tensile stress to compressive stress The portion of the diaphragm including the switching point is used as a torque detecting portion for detecting the transmitted torque, and the thickness of the torque detecting portion is controlled so that a change in stress in the torque detecting portion along the radial direction can be suppressed. The configuration is such that the thickness is set to be relatively thicker than the adjacent part.
[0010]
Here, the thickness of the torque detecting portion can be set to be substantially the same along the radial direction.
[0011]
As described above, instead of making the thickness of the torque detecting portion thicker than an adjacent portion, a configuration is adopted in which the thickness of the torque detecting portion is set to be substantially constant along the radial direction. Is also good.
[0012]
In the silk hat type flexible meshing gear device of the present invention having the above configuration, the torque detecting portion of the diaphragm to which the strain gauge is attached is thicker than the adjacent portion. Therefore, it is possible to suppress the amount of change in bending stress along the radial direction in the torque detection portion including the point where the bending stress switches from the tension side to the compression side. Therefore, even if the attachment position of the strain gauge is slightly shifted, it is possible to suppress a decrease in torque detection accuracy.
[0013]
Similarly, even when the torque detection portion is set to a constant thickness, fluctuations in the radial stress distribution in this portion can be reduced, so that even if the position where the strain gauge is attached is slightly shifted, A decrease in torque detection accuracy can be suppressed.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0015]
FIG. 1 shows the configuration of a silk hat type flexible meshing gear device to which the present invention can be applied. As shown in this figure, a silk hat type flexible meshing gear device 1 has an annular rigid internal gear 2, a flexible external gear 3 disposed inside the ring internal gear 2, and a wave generation fitted inside the ring. Vessel 4. The wave generator 4 generally has an elliptical contour, and the flexible external gear 3 is bent into an elliptical shape by the wave generator 4, and is located at both ends in the major axis direction of the elliptical shape. The portions 31a and 31b of the external teeth 31 are engaged with the internal teeth 21 of the rigid internal gear 2.
[0016]
High-speed rotation is input to the wave generator 4 from, for example, a motor output shaft (not shown). When the wave generator 4 rotates at high speed, the positions (31a, 31b) at which the external teeth 31 of the flexible external gear 3 mesh with the internal teeth 21 also move in the circumferential direction. The number of external teeth of the flexible external gear is set to 2N (N is a positive integer) with respect to the number of internal teeth 21 of the rigid internal gear 2, and is usually set to a number of teeth smaller by two. . Therefore, when the meshing position rotates in the circumferential direction, a relative rotation occurs between the two gears. If one of the gears, generally the rigid internal gear 2 is fixed so as not to rotate, the other gear, generally the flexible external gear 3, will have a significantly reduced rotational speed compared to the input rotation. Rotate with. This decelerated rotation is transmitted to the load side.
[0017]
The flexible external gear 3 has a silk hat shape as a whole. The top hat-shaped flexible external gear 3 is continuously connected to a cylindrical body 32, external teeth 31 formed on the outer periphery of the distal opening, and an opening on the base end side of the body 32. An annular diaphragm 33 extending radially outward and an annular boss 34 connected to the outer peripheral edge of the diaphragm 33 are provided. The portion of the boss 34 is fastened and fixed to the load side member by a fastening bolt or the like.
[0018]
In the operating state, a bending stress is generated in a portion of the diaphragm 33 of the flexible external gear 3 along the radial direction as shown in FIG. FIG. 2 shows a bending stress distribution appearing in a diaphragm portion of a silk hat-shaped flexible external gear generally used in the related art (FIG. 2 shows a flexible external gear of this example). Parts corresponding to the tooth gears are denoted by the same reference numerals.) As can be seen from this bending stress distribution state, a switching point at which the tensile stress switches to the compressive stress appears at a position in the middle of the diaphragm 33 in the radial direction. If a strain gauge is attached to a position where no bending stress is generated or a position 331 where the bending stress is minimized, it is possible to accurately detect the transmission torque based on the detection output.
[0019]
However, as can be seen from the distribution of the bending stress in the radial direction including the position 331, in the region including the position 331, the stress fluctuation accompanying the movement in the radial direction is severe. Therefore, if the attachment position of the strain gauge is displaced in the radial direction, the influence of bending stress greatly affects the output of the strain gauge, and accurate torque measurement cannot be expected. In other words, the influence on the torque detection accuracy based on the error in the position where the strain gauge is attached is large.
[0020]
Therefore, in the flexible external gear 3 of the present embodiment, as shown in a half cross section in FIG. 3, the thickness of the cross section in the radial direction is set. As a whole, the thickness of the diaphragm 33 is thick at the inner peripheral portion 332 that is continuous with the body 32 and the outer peripheral portion 333 that is continuous with the boss 34, and the radial center position (substantially at the position 331) (A position corresponding to). For example, such a thickness is set by defining the rear surface 33a of the diaphragm 33 as a flat surface and defining the front surface 33b side as a curved surface.
[0021]
However, in this example, a portion having a constant width in the radial direction of the diaphragm 33 including the position 331 is defined as a torque detecting portion 334, and the thickness t1 of the portion 334 is set to the thickness t2, t3 of the adjacent diaphragm portion. It is set to be thicker than that. Normally, the thickness t1 of the torque detecting portion 334 is set to a predetermined width and a constant thickness, and is smoothly connected to an adjacent thin portion in an arc shape.
[0022]
In the thus configured silk hat type flexible meshing gear device 1 of this embodiment, a strain gauge (not shown) is provided on the surface of the annular torque detection position 334 formed on the diaphragm 33 of the flexible external gear 3. And the transmission torque is detected based on the detection output from the above. Since the torque detection position 334 is thicker than the portion of the adjacent diaphragm, the fluctuation of the bending stress in this portion in the radial direction is suppressed. Therefore, even when the position where the strain gauge is attached is slightly shifted, it is possible to suppress a decrease in torque detection accuracy.
[0023]
FIG. 4 shows another example of the cross-sectional shape of the diaphragm 33. In the example shown in this figure, a flat portion having a constant thickness is formed as the torque detection portion 334 including the position 331 at the center position in the radial direction of the diaphragm 33. That is, the overall cross-sectional shape of the diaphragm 33 is set such that the center position in the radial direction is thinnest by defining the back surface side by a flat surface and the front surface side by a curved surface. At this radial center position, a portion of constant width, including the point 331 at which the stress switches from tension to compression, is defined by a plane rather than a curved surface, thereby providing an annular flat portion of constant width. Are formed as a torque detecting portion 334. Even in the case of having such a cross-sectional shape, the radial variation of the bending stress can be suppressed even at the radially intermediate portion of the diaphragm 33. Therefore, it is possible to reduce the influence on the accuracy of the detected torque due to the error in the position where the strain gauge is attached.
[0024]
【The invention's effect】
As described above, in the silk hat type flexible meshing gear device of the present invention, the sectional shape of the diaphragm of the flexible external gear having the silk hat shape is changed by the radial bending stress generated in the diaphragm during operation. A portion of the diaphragm including a point at which the distribution switches from tensile stress to compressive stress is used as a torque detecting portion for detecting a transmission torque, and a change in stress in the torque detecting portion along a radial direction can be suppressed. In addition, a configuration is adopted in which the thickness of the torque detecting portion is set to be relatively thicker than the adjacent portion. Alternatively, a configuration is adopted in which the thickness of the torque detection portion is set to be constant at a constant width. Therefore, according to the present invention, since the fluctuation of the bending stress generated at the portion including the switching point of the bending stress located at the radially intermediate portion of the diaphragm is small, the torque caused by the error in the position where the strain gauge is attached can be reduced. A decrease in detection accuracy can be avoided or suppressed.
[Brief description of the drawings]
FIGS. 1A and 1B are a cross-sectional view including a shaft and a front view, respectively, showing the outline of the configuration of a silk hat type flexible meshing gear device to which the present invention can be applied.
FIG. 2 is an explanatory view showing a bending stress distribution along a radial direction generated in a diaphragm portion of a general silk hat-shaped flexible external gear.
FIG. 3 is a half sectional view showing a sectional shape along a radial direction of a diaphragm portion of the flexible hat-shaped external gear shown in FIG. 1;
FIG. 4 is a half sectional view showing another sectional shape of a diaphragm portion of the flexible external gear shown in FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Silk-hat type flexible meshing gear device 2 Rigid internal gear 21 Internal teeth 3 Silk-hat-shaped flexible external gear 31 External teeth 32 Body 33 Diaphragm 331 Bending stress switching point 332 Inner peripheral edge of diaphragm 333 Peripheral edge portion of diaphragm 334 Torque detecting portion 34 formed in middle of diaphragm in radial direction Boss 4 Wave generator

Claims (3)

An annular rigid internal gear, a flexible external gear disposed on the inner side thereof, and fitted into the inner side thereof, and bending the flexible external gear in a radial direction at a plurality of locations to thereby form the rigid internal gear at a plurality of locations. A wave generator that meshes with the gears and moves these meshing positions in the circumferential direction, wherein the flexible external gear has a cylindrical body, and a distal open end of the body. External teeth formed on the outer periphery of the ring, an annular diaphragm extending radially outward continuously with the base end side opening of the body, and an annular boss continuous with the outer peripheral end of the diaphragm. In the silk hat type flexible meshing gear device having a shape provided with: a switch in which a radial bending stress distribution generated in the diaphragm of the flexible external gear during operation switches from tensile stress to compressive stress. Part of the diaphragm including the point Is used as a torque detecting portion for detecting a transmission torque, and the thickness of the torque detecting portion is made relatively smaller than that of an adjacent portion so that a change in stress in the radial direction in the torque detecting portion can be suppressed. A silk hat-type flexible meshing gear device characterized in that it is set to be thicker. 2. The silk hat type flexible meshing gear device according to claim 1, wherein the thickness of the torque detecting portion is set to be substantially the same along the radial direction. 2. The method according to claim 1, wherein the thickness of the torque detecting portion is set to be substantially constant along the radial direction instead of making the thickness of the torque detecting portion thicker than an adjacent portion. Silk hat type flexible meshing gear device.

Images