Gear device and method for manufacturing gear device

Abstract

The purpose of the present invention is to provide a gear device capable of suppressing a decrease in rotation accuracy while achieving a light weight. The gear device (100) is provided with an internal gear (18) and an external gear (14) meshed with the internal gear (18), the internal gear (18) is made of resin, the external gear (14) is made of a material with the linear expansion coefficient smaller than that of the resin, and before the gear device is used, the PCD of the internal gear (18) and the PCD of the external gear (14) are set to be larger than the PCD of the internal gear (18) and the PCD of the external gear (14). The idle stroke is set to 0 min or more and 15 min or less on the basis of the difference in the amount of thermal expansion between the internal gear (18) and the external gear (14) when the gear device is used.

Description

[0001] This application is a divisional application of the invention patent application with the application number 202010195643.1 and the title "Gear Device and Manufacturing Method of Gear Device".

[0002] This application claims priority based on Japanese Patent Application No. 2019-074120 filed on April 9, 2019. The entire content of this Japanese application is incorporated herein by reference. Technical Field

[0003] The present invention relates to a gear device and a manufacturing method of a gear device. Background Art

[0004] There is known a gear device having an external gear and an internal gear. The applicant has disclosed in Patent Document 1 a gear device for preventing gear heating. This gear device is a flexural engagement type gear device including a flexurally deformable external gear and an internal gear meshing with the external gear, wherein one of the external gear and the internal gear is made of resin, and the other gear is made of a highly heat-conductive material having a higher thermal conductivity than that of the resin.

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2018-155313

[0006] If one of the external gear and the internal gear is made of resin in order to achieve the light weight of the gear device, based on the difference in the linear expansion coefficients between metal and resin, when the gear device is used, the clearance between the gears becomes wider, resulting in a decrease in the rotational accuracy. Summary of the Invention

[0007] The present invention has been made in view of such circumstances, and one of its objects is to provide a gear device capable of achieving light weight while suppressing a decrease in rotational accuracy.

[0008] In order to solve the above problems, a gear device according to an embodiment of the present invention includes an internal gear and an external gear meshing with the internal gear. In this gear device, the internal gear is made of resin, the external gear is made of a material having a linear expansion coefficient smaller than that of the resin, and the PCD of the internal gear and the PCD of the external gear before using this gear device are set so that the backlash is 0 min or more and 15 min or less based on the difference in the thermal expansion amounts between the internal gear and the external gear when using this gear device.

[0009] In addition, any combination of the above constituent elements or a manner of mutually replacing the constituent elements and expressions of the present invention between methods, systems, etc. is also effective as a manner of the present invention.

[0010] According to the present invention, there is provided a gear device capable of achieving light weight while suppressing a decrease in rotational accuracy. Description of the Drawings

[0011] Figure 1 FIG. 1 is a side cross-sectional view showing a gear device according to the first embodiment.

[0012] Figure 2 For explaining Figure 1 the backlash of the gear device.

[0013] Figure 3 For showing Figure 1 the relationship between the difference in PCD between the external gear and the internal gear of the gear device and the backlash.

[0014] Figure 4 For showing Figure 1 the relationship between the difference in PCD between the external gear and the internal gear of the gear device and the tooth surface pressure.

[0015] In the figure: 12 - vibration generating body, 14 - external gear, 16 - vibration generating body bearing, 18 - internal gear, 20 - supporting member, 22 - bearing housing, 24 - main bearing, 26 - bearing, 100 - gear device, S200 - manufacturing method. Detailed Description of the Invention

[0016] First, the reason for proposing the present invention will be described. The present inventors have studied a gear device having an external gear and an internal gear meshing with each other and obtained the following insights. Regarding a gear device in which an internal gear made of resin meshes with an external gear made of a material having a coefficient of linear expansion smaller than that of the resin, in a state where the temperature rises as the gear device is used (hereinafter referred to as "during use"), due to the difference in thermal expansion amount, the circumferential clearance between the gears increases, which causes an increase in backlash. In a gear device, if the backlash during use is large, it may sometimes be difficult to cope with applications requiring high precision, and thus its applications are limited.

[0017] The present inventors have found that as long as the backlash of the gear device during use is in the range of 0 min or more and 15 min or less, it is possible to cope with applications requiring high precision.

[0018] Furthermore, the present inventors have repeatedly studied and found that when the internal gear is made of resin, even when the internal gear and the external gear are meshed in an interference fit state before the temperature rises as the gear device is used (hereinafter referred to as "before use"), it can be started as well as in the case of a clearance fit. The reason can be considered as follows: The resin-made internal gear has high flexibility, so its surface will elastically deform based on the compressive stress. From this, it can be seen that the backlash (or, it can also be expressed as the meshing state) before the temperature rises can be set relatively flexibly.

[0019] It is also confirmed that if the previous internal gear and external gear are meshed in an interference fit manner, the backlash during use can be reduced.

[0020] Based on these insights, the inventors of the present invention proposed a structure of the present invention in which the PCD of the internal gear and the PCD of the external gear before using the gear device are set based on the backlash during use in order to enable the gear device to also cope with applications requiring high precision. Hereinafter, the content of the present invention will be described with reference to specific embodiments.

[0021] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the embodiments and variations, the same or equivalent components and parts are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. Also, in each drawing, for ease of understanding, the dimensions of the components are appropriately enlarged or reduced. Also, in each drawing, a part of the components that are not important for explaining the embodiments is omitted.

[0022] Also, terms including ordinal numbers such as first, second, etc. are used to describe various components, but this term is only for the purpose of distinguishing one component from other components, and this term is not used to limit the components. Also, for each component having a common point, the words "first, second" etc. are marked at the beginning of the name and the words "-A, -B" etc. are marked at the end of the reference numeral for distinction, and these words are omitted when collectively referred to.

[0023] [First Embodiment]

[0024] First, the overall structure of the gear device 100 according to the first embodiment will be described. Figure 1 FIG. is a side cross-sectional view showing the gear device 100 of the first embodiment. The gear device 100 is a flexure engagement type gear device that rotates while causing the external gear 14 meshing with the internal gears 18-A and 18-B to flexurally deform so that the external gear 14 rotates self-reliantly and outputs its self-rotation component. The gear device of the present embodiment is a so-called cylindrical flexure engagement type gear device that decelerates the rotation of the vibrating body 12 using the reduction internal gear 18-A and the output internal gear 18-B and then outputs it.

[0025] The gear device 100 mainly includes: a vibrating body 12; an external gear 14; vibrating body bearings 16-A and 16-B; internal gears 18-A and 18-B; a support member 20; and bearing housings 22-A and 22-B. Hereinafter, the direction along the rotation center line of the vibrating body 12 may be simply referred to as the "axial direction X", and the circumferential direction and the radial direction centered on the rotation center line La may be simply referred to as the "circumferential direction" and the "radial direction".

[0026] The oscillation body 12 is a cylindrical member having rigidity, which functions as an input shaft for input rotation. The rotational input from a driving device such as a motor is input to the oscillation body 12. An axial hole 12a for inserting wiring or the like is formed on the inner peripheral side of the oscillation body 12. The oscillation body 12 rotates about its own axis by the rotation of the drive shaft. In addition, the driving device is disposed on one side (the right side in the figure) of the oscillation body 12 in the axial direction X. Hereinafter, one side in the axial direction X is referred to as the input side, and the other side (the left side in the figure) is referred to as the input opposite side.

[0027] The oscillation body 12 has an intermediate shaft portion 12b, an input side shaft portion 12c located on the input side closer to the input side than the intermediate shaft portion 12b, and an input opposite side shaft portion 12d located on the input opposite side closer to the input opposite side than the intermediate shaft portion 12b. The outer peripheral shape of the cross section of the intermediate shaft portion 12b orthogonal to the axial direction X is elliptical. The outer peripheral shapes of the cross sections of the input side shaft portion 12c and the input opposite side shaft portion 12d orthogonal to the axial direction X are circular. The "ellipse" in this specification does not only refer to an ellipse in the strict geometric sense, but also includes a substantially elliptical shape.

[0028] The external gear 14 is disposed on the outer peripheral side of the intermediate shaft portion 12b of the oscillation body 12. The external gear 14 is a cylindrical member having flexibility. The external gear 14 has a cylindrical base portion 14a, a first external tooth portion 14b formed integrally with the base portion 14a on the outer peripheral side of the base portion 14a, and a second external tooth portion 14c. The first external tooth portion 14b is disposed on the input side in the axial direction X and meshes with a reduction internal gear 18-A described later. The second external tooth portion 14c is disposed on the input opposite side in the axial direction X and meshes with an output internal gear 18-B described later. The portions of the first external tooth portion 14b and the second external tooth portion 14c corresponding to both sides in the major axis direction of the intermediate shaft portion 12b of the oscillation body 12 mesh with the internal gear 18.

[0029] When the oscillation body 12 rotates, the intermediate shaft portion 12b of the oscillation body 12 causes the external gear 14 to flexurally deform into an elliptical shape via the oscillation body bearing 16. At this time, the external gear 14 flexurally deforms in such a manner that the meshing position between it and the reduction internal gear 18-A changes in the circumferential direction and conforms to the shape of the intermediate shaft portion 12b of the oscillation body 12.

[0030] The oscillation body bearing 16 is disposed between the intermediate shaft portion 12b of the oscillation body 12 and the external gear 14. The oscillation body bearing 16 includes a first oscillation body bearing 16-A disposed between the first external tooth portion 14b of the external gear 14 and the oscillation body 12, and a second oscillation body bearing 16-B disposed between the second external tooth portion 14c of the external gear 14 and the oscillation body 12. The oscillation body 12 supports the external gear 14 via the oscillation body bearing 16 so as to be rotatable.

[0031] Each oscillation body bearing 16 has a plurality of first rolling elements 16a, a first inner ring 16b, and a first outer ring 16c. The first rolling element 16a of the present embodiment is a sphere, but it may also be a roller or the like. The first inner ring 16b of the present embodiment is constituted by the outer peripheral surface of the intermediate shaft portion 12b of the oscillation body 12, but it may also be constituted by another component different from the oscillation body 12. The first outer ring 16c has flexibility. When the oscillation body 12 rotates, the intermediate shaft portion 12b of the oscillation body 12 causes the first outer ring 16c to be flexurally deformed into an elliptical shape via the first rolling element 16a.

[0032] The internal gear 18 is a rigid ring-shaped member. The internal gear 18 is disposed on the outer peripheral side of the first external tooth portion 14b and the second external tooth portion 14c of the external gear 14. The internal gear 18 of the present embodiment includes: a reduction internal gear 18-A (first internal gear) disposed on the input side in the axial direction X; and an output internal gear 18-B (second internal gear) disposed on the opposite side of the input in the axial direction X.

[0033] The reduction internal gear 18-A has a first internal tooth portion 18a that meshes with the first external tooth portion 14b of the external gear 14. The number of internal teeth of the first internal tooth portion 18a is 2i (i is a natural number of 1 or more) more than the number of external teeth of the first external tooth portion 14b. Thus, when the oscillation body 12 rotates, the rotation of the oscillation body 12 is decelerated at a reduction ratio corresponding to the tooth number difference between the first internal tooth portion 18a and the first external tooth portion 14b and then causes the external gear 14 to rotate self. In addition, the reduction internal gear 18-A has a connection portion 18b formed with a bolt hole into which a bolt B1 is screwed. The bolt B1 is used to connect the reduction internal gear 18-A to the input side bearing housing 22-A.

[0034] The output internal gear 18-B has a second internal tooth portion 18c that meshes with the second external tooth portion 14c of the external gear 14. The number of internal teeth of the second internal tooth portion 18c is the same as the number of external teeth of the second external tooth portion 14c. Thus, when the oscillation body 12 rotates, a rotation at the same speed as the self-rotation component of the external gear 14 is output to the output internal gear 18-B.

[0035] The support member 20 has an outer cylinder portion 20a that rotatably supports the output internal gear 18-B via a main bearing 24. The outer cylinder portion 20a is disposed more radially outward than the first internal tooth portion 18a of the reduction internal gear 18-A. The support member 20 of the present embodiment and the reduction internal gear 18-A are formed as a part of a single member and are integrally formed. An insertion through-hole 20b through which a bolt (not shown) for connecting to an external component is inserted is formed in the outer cylinder portion 20a. The external component is disposed outside the gear device 100 and has a function of supporting the gear device 100.

[0036] The main bearing 24 has a plurality of second rolling elements 24a, a second inner ring 24b, and a second outer ring 24c. The second rolling element 24a of the present embodiment is a sphere, but it may also be a roller or the like. The second inner ring 24b of the present embodiment is constituted by the outer peripheral surface of the output inner gear 18-B, but it may also be constituted by another component different from the output inner gear 18-B. The second outer ring 24c is constituted by the inner peripheral surface of the outer cylindrical portion 20a of the support member 20, but it may also be constituted by another component different from the support member 20.

[0037] The bearing housing 22 is arranged at intervals along the axial direction X of the vibration exciter 12. The bearing housing 22 includes: an input-side bearing housing 22-A, which is arranged on the input side in the axial direction X; and an input-opposite-side bearing housing 22-B, which is arranged on the input-opposite side in the axial direction X.

[0038] The input-side bearing housing 22-A is connected to the reduction inner gear 18-A by bolts B1 and thus becomes integral with the reduction inner gear 18-A. The input-side bearing housing 22-A functions as a first abutting member that is connected to the reduction inner gear 18-A and abuts against the input-side end surface of the outer gear 14.

[0039] The input-opposite-side bearing housing 22-B is connected to the output inner gear 18-B by bolts B2 and thus becomes integral with the output inner gear 18-B. The input-opposite-side bearing housing 22-B functions as a second abutting member that is connected to the output inner gear 18-B and abuts against the input-opposite-side end surface of the outer gear 14.

[0040] Bearings 26 are arranged between the input-side bearing housing 22-A and the input-side shaft portion 12c of the vibration exciter 12 and between the input-opposite-side bearing housing 22-B and the input-opposite-side shaft portion 12d of the vibration exciter 12. The pair of bearing housings 22-A and 22-B double-support the vibration exciter 12 via the bearings 26 so as to be rotatable freely. Each bearing 26 has a plurality of third rolling elements 26a, a third inner ring 26b, and a third outer ring 26c.

[0041] The input-opposite-side bearing housing 22-B and the output inner gear 18-B are connected to the driven device by bolts (not shown). The driven device is arranged on the input-opposite side in the axial direction X relative to the vibration exciter 12. An insertion hole 22a for inserting the shaft portion of the bolt (not shown) is formed in the input-opposite-side bearing housing 22-B. An internal threaded hole 18d for screwing in the bolt is formed in the output inner gear 18-B.

[0042] Next, the operation of the above-described gear device 100 will be described. When the vibrating body 12 rotates as the drive shaft of the drive device rotates, the outer gear 14 continuously flexes and deforms in such a manner that the meshing position between it and the inner gear 18 changes circumferentially and conforms to the shape of the intermediate shaft portion 12b of the vibrating body 12. Each time the vibrating body 12 rotates once, the first outer tooth portion 14b rotates relative to the reduction inner gear 18-A (self-rotates) by an amount corresponding to the difference in the number of teeth between it and the first inner tooth portion 18a of the reduction inner gear 18-A. At this time, the rotation of the vibrating body 12 is decelerated by a reduction ratio corresponding to the difference in the number of teeth between the first outer tooth portion 14b and the first inner tooth portion 18a, and then the outer gear 14 rotates self. The number of teeth of the second inner tooth portion 18c of the output inner gear 18-B is the same as the number of teeth of the second outer tooth portion 14c. Therefore, before and after the rotation of the vibrating body 12, the meshing position between the output inner gear 18-B and the second outer tooth portion 14c does not change, and it rotates synchronously with the second outer tooth portion 14c with the same self-rotation component. The rotation of this output inner gear 18-B is transmitted from the output inner gear 18-B to the driven device. As a result, the rotation of the vibrating body 12 is decelerated and then output from the output inner gear 18-B to the driven device.

[0043] Here, the gear device 100 of the present embodiment is characterized in that the inner gear 18 is made of resin, and the outer gear 14 is made of a material (hereinafter, "low-expansion material") having a linear expansion coefficient smaller than that of the resin of the inner gear 18. That is, both the reduction inner gear 18-A and the output inner gear 18-B are made of resin. In addition, in the present embodiment, the reduction inner gear 18-A including the support member 20 is made of resin. As an example, general engineering plastics such as polyvinyl fluoride, polyamide, and PEEK can be used as the resin for manufacturing the inner gear 18, and composite materials with carbon fiber and phenolic resin materials can also be used.

[0044] Moreover, the outer gear 14 is made of a low-expansion material. Specifically, the entire outer gear 14 (that is, the base portion 14a, the first outer tooth portion 14b, and the second outer tooth portion 14c) is made of a low-expansion material. As an example, metals such as iron and aluminum can be used as the low-expansion material for manufacturing the outer gear 14. The outer gear 14 can also be made of other resins having a linear expansion coefficient smaller than that of the resin of the inner gear 18.

[0045] In addition, the materials of other components other than the internal gear and the external gear are not particularly limited. In the present embodiment, the input-side bearing housing 22-A and the input-opposite-side bearing housing 22-B are made of resin, and the vibration generating body 12, each bearing, and each bolt are made of metal. In particular, in addition to the external gear 14 being made of metal, the vibration generating body 12 and the vibration generating body bearing 16 are also made of metal. Therefore, the heat generated at the meshing portion between the internal gear 18 and the external gear 14 can be transferred in the order of the external gear 14 with a high thermal conductivity → the vibration generating body bearing 16 → the vibration generating body 12 and released to the outside.

[0046] When the gear device 100 is in use, if the meshing portion between the internal gear 18 and the external gear 14 generates heat, the thermal expansion amount of the internal gear 18 becomes larger than that of the external gear 14. Therefore, based on the difference in thermal expansion amounts, the difference in PCD (Pitch Circle Diameter) between the internal gear 18 and the external gear 14 becomes larger. If this PCD difference becomes larger, the circumferential clearance between the internal teeth of the internal gear 18 and the external teeth of the external gear 14 increases, resulting in a larger backlash.

[0047] Next, the PCD of the internal gear 18 and the external gear 14 will be described. In this specification, the PCD of a gear refers to the diameter of the circle passing through the center between the tooth tip and the tooth root.

[0048] Next, the backlash of the gear device 100 will be described. Figure 2 FIG. is for explaining the backlash. In this specification, the definition of the backlash is as follows. If, with the vibration generating body 12 (high-speed shaft) of the gear device fixed, a load is slowly applied from the input-opposite-side bearing housing 22-B (low-speed shaft) side until the rated torque and the load and the displacement (torsion angle) of the low-speed shaft are measured until unloading, and the relationship therebetween is shown, a rigid hysteresis curve as shown in Figure 2 can be obtained. The backlash is defined as the torsion angle at the rated torque ±3% point.

[0049] Next, the backlash of the present embodiment will be described. As described above, as long as the backlash of the gear device 100 during use is in the range of 0 min or more and 15 min or less, it is possible to cope with applications requiring high precision. Therefore, in the present embodiment, the difference ΔD in PCD between the internal gear 18 and the external gear 14 before using the gear device 100 is set so that the backlash during use becomes 0 min or more and 15 min or less. In addition, the difference ΔD is the difference obtained by subtracting the PCD of the external gear 14 from the PCD of the internal gear 18. If this difference is positive, it means that the PCD of the internal gear 18 is larger than the PCD of the external gear 14, and if this difference is negative, it means that the PCD of the internal gear 18 is smaller than the PCD of the external gear 14.

[0050] Next, an example of a method for setting the difference ΔD between the PCDs of the internal gear 18 and the external gear 14 so that the backlash during use is within a specified range will be described. In addition, if the backlash during use is less than 0 min, the torque loss of the gear unit 100 will increase, so the backlash during use is set to 0 min or more. In addition, the PCD in the present embodiment is the PCD in the state before the internal gear 18 and the external gear 14 are assembled into the gear unit 100 (the state of individual components).

[0051] Figure 3 It is a graph showing the relationship between the difference ΔD between the PCDs of the internal gear 18 and the external gear 14 before use and the backlash RM during use. The difference ΔD between the PCDs and the backlash RM in this curve graph are obtained through simulation tests. The horizontal axis of this curve graph represents the ratio ΔD / Dt obtained by dividing the difference ΔD between the PCDs of the internal gear 18 and the external gear 14 before use (at 20°C in the present embodiment) by the PCD of the internal gear 18 (i.e., Dt). The vertical axis of this curve graph represents the magnitude of the backlash RM of the gear unit 100 during use (at 50°C in the present embodiment). As can be seen from Figure 3 it, when the ratio ΔD / Dt before use is 0 or less, the backlash during use becomes 15 min or less.

[0052] In addition, the ratio ΔD / Dt before use can be determined from the design values of the internal gear and the external gear. The temperature rise amount during use can be obtained through experiments. In addition, in the present embodiment, regarding the temperature of the gear unit 100, the temperature of the outer periphery of the component integrated with the internal gear was measured. Specifically, the temperature of the outer periphery of the support member 20 was measured. This point is the same in other embodiments. In this example, the temperature rise amount is 20°C to 30°C, and 30°C was adopted in the simulation test.

[0053] Similarly, the ratio ΔD / Dt before use that makes the backlash during use 0 min or more can be obtained. In this example, the ratio ΔD / Dt before use is determined to be -0.0011 or more. And the ratio ΔD / Dt before use that makes the backlash during use 15 min or less can be obtained. In this example, the ratio ΔD / Dt before use is determined to be 0 or less. Thus, by setting the ratio ΔD / Dt before use in the range of -0.0011 to 0, the backlash during use can be made 0 min or more and 15 min or less. This setting method is an example, and as long as the backlash during use can be made 0 min or more and 15 min or less, other methods can also be used to set the ratio ΔD / Dt before use.

[0054] As described above, by reducing the PCD of the internal gear 18 relative to the PCD of the external gear 14 (= reducing ratio ΔD / Dt), the backlash during use can be reduced. However, depending on the ratio ΔD / Dt, the tooth surface pressure Pf applied to the tooth surface becomes excessive, sometimes resulting in a decrease in the reliability of the gear device 100. Therefore, the inventors of the present invention studied the relationship between the ratio ΔD / Dt and the tooth surface pressure Pf.

[0055] Figure 4 It is a graph showing the relationship between the difference ΔD in PCD between the internal gear 18 and the external gear 14 and the tooth surface pressure Pf applied to the tooth surface. In this graph, the temperature before use was set to 20°C, and the ratio ΔD / Dt and the tooth surface pressure Pf at this time were obtained through a simulation test. The horizontal axis of this graph represents the ratio ΔD / Dt. The vertical axis of this graph represents the magnitude of the tooth surface pressure Pf applied to the tooth surface of the internal gear 18, and the higher its position in the graph, the higher the tooth surface pressure Pf, and the lower its position, the lower the tooth surface pressure Pf.

[0056] As Figure 4 shown, if the ratio ΔD / Dt increases, the number of engaged teeth decreases accordingly. Therefore, the pressure borne by one tooth increases, resulting in a higher tooth surface pressure Pf. If the ratio ΔD / Dt decreases, the number of engaged teeth increases accordingly. Therefore, the pressure borne by one tooth decreases, resulting in a lower tooth surface pressure Pf. However, in the region where the ratio ΔD / Dt is negative, the internal gear 18 and the external gear 14 are in an interference fit, so the interference amount increases, resulting in a higher tooth surface pressure Pf.

[0057] Therefore, the ratio ΔD / Dt is preferably set within a range where the tooth surface pressure Pf does not become excessive. From the viewpoint of this tooth surface pressure Pf, the difference ΔD in PCD between the internal gear 18 and the external gear 14 can be set within a range where the tooth surface pressure Pf before use does not exceed a specified value. As an example, the ratio ΔD / Dt before use can be set within the range of -0.0015 to 0. In addition, when this range is different from the range set from the viewpoint of the backlash during use, the ratio ΔD / Dt can be set within the overlapping range of these two ranges.

[0058] In the present embodiment, by setting the PCD of the internal gear 18 and the external gear 14 before use in this way, even if the temperature rises as the gear device 100 is used, the backlash can be suppressed within the range of 0 min or more and 15 min or less. At this time, it is possible to cope with applications requiring high precision.

[0059] In the gear device 100 with the above structure, before use, the PCD of the external gear 14 can also be larger than the PCD of the internal gear 18. It has been confirmed that even if the PCD of the external gear 14 is larger than the PCD of the internal gear 18, the gear device can operate no less than when in a clearance fit. In this structure, the external gear 14 and the internal gear 18 are in an interference fit state before use. Therefore, even when the temperature rises during use, the backlash can be suppressed within a specified range.

[0060] [Second Embodiment]

[0061] Next, the gear device 100 according to the second embodiment of the present invention will be described. In the drawings and descriptions of the second embodiment, the same reference numerals are given to the constituent elements and components that are the same as or equivalent to those of the first embodiment. The description of the content that is repeated with the first embodiment will be omitted as appropriate.

[0062] The gear device 100 of the present embodiment includes an internal gear 18 and an external gear 14 that meshes with the internal gear 18. The internal gear 18 is made of resin, and the external gear 14 is made of a material having a linear expansion coefficient smaller than that of the resin. The PCD of the external gear 14 at a temperature of 20°C of the gear device 100 is set to be larger than the PCD of the internal gear 18 so that the backlash is 0 min or more and 15 min or less within the range where the temperature of the gear device 100 is 40°C or more and 50°C or less.

[0063] For example, based on the linear expansion coefficients of the materials of the external gear 14 and the internal gear 18, the temperature difference between 20°C (low temperature) and 40°C or more and 50°C or less (high temperature), and the backlash of the gear device 100 at high temperature (0 min or more and 15 min or less), the PCD of the external gear 14 and the PCD of the internal gear 18 at low temperature are determined. At this time, the PCD of the external gear 14 at low temperature is set to be larger than the PCD of the internal gear 18. The relationship between the PCDs of the external gear 14 and the internal gear 18 and the backlash can be determined through simulation tests or experiments as in the example shown Figure 3 shown.

[0064] According to the present embodiment, the external gear 14 and the internal gear 18 are in an interference fit state at 20°C. Therefore, even when the temperature during use rises to 40°C or more and 50°C or less, the backlash can be suppressed within the range of 0 min or more and 15 min or less. At this time, it can meet general applications.

[0065] The above is the description of the second embodiment.

[0066] [Third Embodiment]

[0067] Next, a manufacturing method S200 of the gear device according to the third embodiment of the present invention will be described. In the drawings and description of the third embodiment, the same or equivalent components and parts as those of the first embodiment are denoted by the same reference numerals. The description of the content repeated with the first embodiment is appropriately omitted. The manufacturing method S200 of the present embodiment is a method for manufacturing the above-described gear device 100, and includes an embedding step of embedding the external gear 14 into the internal gear 18 in an interference fit manner.

[0068] According to this method, since the external gear 14 is embedded into the internal gear 18 in an interference fit manner, even if thermal expansion occurs during use, the backlash can be suppressed to a small value.

[0069] In the above embedding step, the internal gear 18 can be heated and then embedded. At this time, if the internal gear 18 is heated, the PCD of the internal gear 18 becomes larger due to thermal expansion, and thus the embedding becomes easier. And since the embedding can be easily performed, damage to the internal gear 18 and the external gear 14 during embedding can be prevented. The internal gear 18 can be heated using a dryer or an oven. The heating temperature of the internal gear 18 can be set through simulation tests or experiments.

[0070] In the above embedding step, the external gear 14 can also be cooled and then embedded. At this time, if the external gear 14 is cooled, it shrinks and the PCD of the external gear 14 decreases, and thus the embedding becomes easier. And since the embedding can be easily performed, damage to the internal gear 18 and the external gear 14 during embedding can be prevented. The external gear 14 can be cooled using liquid nitrogen or dry ice. The cooling temperature of the external gear 14 can be set through simulation tests or experiments.

[0071] The above is the description of the third embodiment.

[0072] The above has described in detail examples of the embodiments of the present invention. The above embodiments are merely specific examples of the present invention. The content of the embodiments does not limit the technical scope of the present invention, and many design changes such as changes, additions, and deletions of components can be made without departing from the idea of the invention defined in the technical solution. In the above embodiments, for the content that can be subjected to such design changes, words such as "of the embodiment" and "in the embodiment" are added for explanation, but this does not mean that design changes are not allowed for the content without such words. And the hatching marked in the cross-section of the drawings does not limit the material of the object marked with the hatching.

[0073] Hereinafter, a modified example will be described. In the drawings and description of the modified example, the same reference numerals are given to the constituent elements and components that are the same as or equivalent to those in the embodiment. The description of the content that duplicates the embodiment will be appropriately omitted, and the structures different from the embodiment will be mainly described.

[0074] [Modified Example]

[0075] In the description of the first embodiment, an example is shown in which the PCD of the external gear before assembly (single-piece state) is larger than the PCD of the internal gear, but the present invention is not limited thereto. For example, when the main bearing 24 has an inner ring, the PCD of the external gear before assembly can also be set to be smaller than the PCD of the internal gear. In this case, the inner ring of the main bearing 24 can be externally fitted to the output-side internal gear 18-B in an interference fit manner so that the internal gear 18-B deforms radially inward, thereby making the PCD of the external gear after assembling the gear device larger than the PCD of the internal gear.

[0076] In the description of the first embodiment, an example is shown in which the gear device is a flexure engagement type reduction gear (sometimes referred to as a harmonic gear device) having a cylindrical external gear, but the present invention is not limited thereto. For example, the gear device can also be a cup-shaped or top-hat-shaped flexure engagement type reduction gear.

[0077] In the description of the first embodiment, an example is shown in which the gear device is a flexure engagement type reduction gear, but the present invention is not limited thereto, and the present invention can be applied to various gear devices having internal and external gears that mesh with each other. For example, the gear device can also be a so-called center crank type eccentric swing type gear device, a so-called distributed eccentric swing type reduction gear in which a plurality of crankshafts are arranged at positions offset from the center axis of the internal gear, or a simple planetary gear device, etc.

[0078] In the third embodiment, the method of embedding the external gear 14 after cooling and the method of embedding the internal gear 18 after heating are described, but the cooled external gear 14 can also be embedded in the heated internal gear 18. In this case, the embedding can be performed more easily.

[0079] The above-described modified examples also have the same effects as the above-described embodiments.

[0080] Any combination of the above-described embodiments and modified examples is also effective as an embodiment of the present invention. The new embodiment generated by the combination has the effects of each of the combined embodiments and modified examples.

Claims

1. A gear device includes an internal gear and an external gear meshing with the internal gear. The gear device is characterized in that: the internal gear is made of resin; the external gear is made of a material having a coefficient of linear expansion smaller than that of the resin; before using the gear device, the PCD of the internal gear and the PCD of the external gear are set such that the backlash during use of the gear device becomes greater than the backlash before using the gear device and is 0 min or more and 15 min or less based on the difference in the amount of thermal expansion between the internal gear and the external gear during use of the gear device; the backlash is defined as the torsional angle at the rated torque ±3% point in the hysteresis curve showing the load and the torsional angle of the low-speed shaft until the rated torque is slowly applied from the low-speed shaft side while fixing the high-speed shaft of the gear device until the load is removed.

2. The gear device according to claim 1, characterized in that: the PCD of the internal gear and the PCD of the external gear are set in a state where the internal gear and the external gear are assembled into the gear device and before using the gear device.

3. The gear device according to claim 2, characterized in that: in a state where the internal gear and the external gear are assembled into the gear device and before using the gear device, the PCD of the external gear is greater than the PCD of the internal gear.

4. The gear device according to any one of claims 1 to 3, characterized in that: in a state before the internal gear and the external gear are assembled into the gear device, the PCD of the external gear is greater than the PCD of the internal gear.

5. The gear device according to any one of claims 1 to 3, characterized in that: the difference between the PCD of the internal gear and the PCD of the external gear before use is represented as ΔD, the PCD of the internal gear is represented as Dt, and the ratio thereof, i.e., ΔD / Dt, is in the range of -0.0015 to 0.

6. The gear device according to any one of claims 1 to 3, characterized in that: in a state where the temperature of the gear device is 20 °C, the PCD of the external gear is set to be greater than the PCD of the internal gear so that the backlash becomes greater than the backlash before using the gear device and is 0 min or more and 15 min or less when the temperature of the gear device reaches 40 °C or more and 50 °C or less.

7. A method for manufacturing a gear device, the gear device being the gear device according to claim 1 or 3, and including an internal gear and an external gear meshing with the internal gear, the internal gear being made of resin, and the external gear being made of a material having a coefficient of linear expansion smaller than that of the resin. The method for manufacturing the gear device is characterized in that: it includes: an embedding step of embedding the external gear into the internal gear in an interference fit manner.

8. The method for manufacturing a gear device according to claim 7, characterized in that: in the embedding step, the internal gear is heated and then embedded.

9. The method for manufacturing a gear device according to claim 7, characterized in that: In the embedding step, the external gear is embedded after being cooled.

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