Auto tensioner and belt drive mechanism equipped therewith

Abstract

The present invention provides an auto tensioner and a belt transmission mechanism equipped therewith, which ensure sufficient spring biasing force regardless of the pulley layout of the belt transmission mechanism, and apply appropriate tension to the belt via two tension rollers. [Solution] The auto tensioner 5 includes a first swing arm 56 and a second swing arm 57 that swing around a swing axis 53 and intersect with the central axis R of the swing axis 53 as the intersection point, a first tension roller 51 provided at one end 561 of the first swing arm 56, a second tension roller 52 provided at one end 571 of the second swing arm 57, and a spring 54 provided between the other end 562 of the first swing arm 56 on the opposite side of the swing axis 53 from the one end 561 of the first swing arm 56 and the other end 572 of the second swing arm 57 on the opposite side of the swing axis 53 from the one end 571 of the second swing arm 57, and biasing the other end 562 of the first swing arm 56 and the other end 572 of the second swing arm 57 in a direction that pulls them towards each other.

Description

Technical Field

[0001] The present invention relates to an auto-tensioner for automatically maintaining an appropriate tension of a belt when transmitting the rotational force of a driving pulley to a driven pulley via the belt, which is incorporated in a robot arm of an industrial robot, etc., and a belt transmission mechanism provided with the same.

Background Art

[0002] In recent years, industrial robots such as vertical articulated robots and horizontal articulated robots such as scara robots have been widely used for automobile manufacturing, semiconductor manufacturing, smartphone manufacturing, etc. In industrial robots, for the drive of the robot arm and the drive of the wrist part (hereinafter referred to as "robot arm drive"), in order to achieve miniaturization, high speed, weight reduction, etc., instead of gear drive, drive by a toothed belt (hereinafter abbreviated as "belt transmission mechanism for robot arm drive") is being adopted.

[0003] Generally, in a belt transmission mechanism without an auto-tensioner, after attaching a toothed belt (hereinafter sometimes simply abbreviated as "belt"), a tension adjustment operation for adjusting the tension of the belt is required to correct the tension reduction of the belt that occurs at the initial stage of running when starting the operation by performing so-called running-in by idling operation. However, in the belt transmission mechanism for robot arm drive, due to its structure and manufacturing process, it is impossible to perform idling operation only by attaching a toothed belt to the pulley in the robot arm. Therefore, after the robot is assembled, a tension adjustment operation by idling operation called aging is performed. Aging must be carried out over several hours to reach the correct control state of the robot through tension adjustment operations such as straightening the belt by adjusting the axial distance, which is the distance between the driving pulley and the driven pulley, and tightening operations of various bolts, etc., which has been a factor causing a large loss cost.

[0004] Furthermore, since the robot arm is driven by frequent forward and reverse rotation, the tension and slack sides of the belt reverse with each forward and reverse rotation. This makes it easy for excessive tension to act on the tension side of the belt and for slack to occur on the slack side when switching between forward and reverse rotation, i.e., when starting and stopping forward and reverse rotation. When the belt becomes excessively tensioned or slack in this way, the difference in rotation angle between the drive pulley and the driven pulley increases, making synchronous transmission between the drive pulley and the driven pulley uncertain. This makes it impossible to accurately move the arm, wrist, etc., to the predetermined position, affecting the positioning accuracy of the arm, etc.

[0005] Furthermore, in belt drive mechanisms where the distance between pulleys is narrow and the reduction ratio (the ratio of pulley diameters) is large, the contact angle of the belt becomes smaller at the smaller diameter drive pulley. If the belt is loose, there is a concern that the belt teeth will be more likely to skip.

[0006] In synchronous power transmission using toothed belts, to address the above problem, it is necessary to automatically adjust for the tension drop that occurs at least at the beginning of travel, and to maintain an appropriate belt tension so that the belt does not loosen during travel.

[0007] Therefore, conventional belt transmission mechanisms for robot arm drives employ an auto-tensioner that incorporates two tension rollers, each rotatably mounted on either side of the pulley centerline connecting the rotation centers of the drive pulley and the driven pulley, and uses a spring or similar mechanism to bring these rollers into contact with the outer or inner surface of the belt with appropriate biasing force.

[0008] For example, in the belt transmission mechanism incorporated into the robot arm of an industrial robot described in Patent Document 1, an auto tensioner that automatically adjusts the tension of a belt wrapped between a drive pulley and a driven pulley has a spring provided between the base shafts of two tension rollers that swing around a pivot axis in order to apply tension to the belt. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2023-134367 [Overview of the project] [Problems that the invention aims to solve]

[0010] However, in an auto tensioner as described in Patent Document 1, which has a spring between the base shafts of two tension rollers that swing around a pivot axis, if the diameters of the drive pulley and the driven pulley are relatively small relative to the distance between the axes of the drive pulley and the driven pulley, the distance between the base shafts of the two tension rollers may become relatively small. In such cases, the length of the spring becomes relatively small relative to the distance between the axes of the drive pulley and the driven pulley, so sufficient expansion and contraction of the spring cannot be secured, and the biasing effect of the spring that applies tension to the belt does not work sufficiently, making it impossible to apply an appropriate tension that does not cause the belt to loosen.

[0011] Therefore, the present invention aims to provide an auto tensioner used in a belt drive mechanism incorporated into a robot arm of an industrial robot, which ensures sufficient spring biasing force regardless of the pulley layout of the belt drive mechanism and applies appropriate tension to the belt via two tension rollers, as well as a belt drive mechanism equipped therewith. [Means for solving the problem]

[0012] The present invention relates to an auto tensioner that automatically adjusts the tension of a belt via two tension rollers that contact a belt wrapped between a drive pulley and a driven pulley, A first swing arm and a second swing arm are configured to swing freely around a pivot axis and are positioned to intersect with the pivot axis as an intersection point. A first tension roller, which is one of the two tension rollers, is provided at one end of the first swing arm so as to contact the belt, A second tension roller, which is the other of the two tension rollers, is provided at one end of the second swing arm so as to contact the belt, The invention is characterized by comprising a spring provided between the other end of the first rocking arm, which is on the opposite side of one end of the first rocking arm with respect to the rocking axis, and the other end of the second rocking arm, which is on the opposite side of one end of the second rocking arm with respect to the rocking axis, and the spring being configured to be expandable and contractible so as to bias the other end of the first rocking arm and the other end of the second rocking arm in a direction that pulls them together or in a direction that separates them from each other.

[0013] According to the above configuration, the spring is positioned on the first and second oscillating arms, on opposite sides of the oscillating axis from the first and second tension rollers. Therefore, depending on the pulley layout, the length from the intersection to the other end of the first oscillating arm to which the spring is attached, the length from the intersection to the other end of the second oscillating arm to which the spring is attached, the length from the intersection to one end of the first oscillating arm to which the first tension roller is attached, and the length from the intersection to one end of the second oscillating arm to which the second tension roller is attached can be adjusted to adjust the distance between the first and second tension rollers and the distance between the other end of the first oscillating arm and the other end of the second oscillating arm, thereby adjusting the length of the spring relative to the axial distance between the drive pulley and the driven pulley. This allows the expansion and contraction range of the spring to be adjusted according to the pulley layout. Depending on the pulley layout, the length of the spring may be adjusted to be greater than the distance between the first and second tension rollers, less than the distance between the first and second tension rollers, or the same as the distance between the first and second tension rollers. Also, depending on the pulley layout, the number of driven pulleys around which the belt is wound is at least one, and there may be one or more driven pulleys, but there is only one drive pulley. Therefore, the auto tensioner used in a belt drive mechanism incorporated into the robot arm of an industrial robot according to the present invention can ensure sufficient spring biasing action and apply appropriate tension to the belt via two tension rollers, regardless of the pulley layout of the belt drive mechanism.

[0014] Furthermore, in the above-mentioned auto tensioner, Viewed in the direction of the axis of the aforementioned pivot shaft, The length of the spring may be greater than the distance between the rotation center of the first tension roller and the rotation center of the second tension roller.

[0015] According to the above configuration, the auto tensioner is configured such that the length of the spring is greater than the distance between the rotation center of the first tension roller and the rotation center of the second tension roller when viewed in the axial direction of the pivot axis. For example, in a pulley layout where the diameters of the drive pulley and the driven pulley are relatively small relative to the distance between the axes of the drive pulley and the driven pulley, the expansion and contraction range of the spring can be sufficiently increased compared to a conventional auto tensioner in which the spring is placed between the base axis of the first tension roller and the base axis of the second tension roller. As a result, the auto tensioner used in a belt drive mechanism incorporated into the robot arm of an industrial robot according to the present invention can ensure sufficient spring biasing action and apply appropriate tension to the belt via the two tension rollers, regardless of the pulley layout of the belt drive mechanism. Note that the length of the spring referred to here means the length of the spring when no external force is applied to the auto tensioner.

[0016] Furthermore, in the above-mentioned auto tensioner, Viewed in the direction of the axis of the aforementioned pivot shaft, The distance between the other end of the first swing arm and the intersection is greater than the distance between the intersection and one end of the first swing arm. The distance between the other end of the second swing arm and the intersection point may be greater than the distance between the intersection point and one end of the second swing arm.

[0017] According to the above configuration, the auto tensioner is configured such that, when viewed in the axial direction of the pivot axis, the length of the spring provided between the other end of the first pivot arm and the other end of the second pivot arm is greater than the distance between the first tension roller provided at one end of the first pivot arm and the second tension roller provided at one end of the second pivot arm. As a result, in a pulley layout in which the diameters of the drive pulley and the driven pulley are relatively small relative to the distance between the axes of the drive pulley and the driven pulley, the expansion and contraction range of the spring can be sufficiently increased compared to an auto tensioner configured in which the length of the spring provided between the other end of the first pivot arm and the other end of the second pivot arm is smaller than the distance between the first tension roller provided at one end of the first pivot arm and the second tension roller provided at one end of the second pivot arm. As a result, the auto tensioner used in the belt drive mechanism incorporated into the robot arm of an industrial robot of the present invention can ensure sufficient spring biasing action and apply appropriate tension to the belt via two tension rollers, regardless of the pulley layout of the belt drive mechanism. Furthermore, the distance between the other end of the first rocking arm and the intersection point, as viewed in the axial direction of the rocking axis, may be the distance from the intersection point as viewed in the axial direction of the rocking axis to the other end of the first rocking arm. Also, the distance between the intersection point as viewed in the axial direction of the rocking axis and one end of the first rocking arm may be the distance from the intersection point as viewed in the axial direction of the rocking axis to one end of the first rocking arm. Furthermore, the distance between the other end of the second rocking arm and the intersection point, as viewed in the axial direction of the rocking axis, may be the distance from the intersection point as viewed in the axial direction of the rocking axis to the other end of the second rocking arm. Also, the distance between the intersection point as viewed in the axial direction of the rocking axis and one end of the second rocking arm may be the distance from the intersection point as viewed in the axial direction of the rocking axis to one end of the second rocking arm.

[0018] Furthermore, in the above-mentioned auto tensioner, Viewed in the direction of the axis of the aforementioned pivot shaft, The distance between the other end of the first swing arm and the intersection point is the same as the distance between the other end of the second swing arm and the intersection point. It may be characterized in that the distance between the intersection point and one end of the first swing arm is the same as the distance between the intersection point and one end of the second swing arm.

[0019] According to the above configuration, when viewed in the axial direction of the swing axis, the autotensioner is configured such that the line connecting the central axis of the first tension roller and the central axis of the second tension roller is parallel to the axis of the spring. Here, making the line connecting the central axes of the two tension rollers parallel to the axis of the spring means that the angle formed by the line connecting the central axes of the two tension rollers and the axis of the spring is not limited to 0 degrees, but includes about 0 degrees ± 10 degrees. As a result, the biasing action of the spring on the two tension rollers becomes uniform, and the tension of the belt applied from the first tension roller and the tension of the belt applied from the second tension roller become uniform. And, for example, it is possible to ensure a higher level of responsiveness of the autotensioner with respect to the driving when switching the forward and reverse directions of the running direction of the belt (at the start / stop of forward and reverse). Even when the speed of the operation involving forward and reverse rotation increases, synchronous transmission can be made more reliable. That is, it is possible to maintain an appropriate belt tension while preventing a decrease in tension that occurs at the initial stage of running. As a result, in the autotensioner used in the belt transmission mechanism incorporated in the robot arm or the like of the industrial robot of the present invention, regardless of what kind of pulley layout the belt transmission mechanism has, the biasing action of the spring can be sufficiently ensured, and an appropriate tension can be applied to the belt via the two tension rollers.

[0020] Further, the present invention is the above autotensioner, The spring is a tension spring that biases the other end of the first swing arm and the other end of the second swing arm in a direction of attracting each other. It may be characterized in that the first tension roller and the second tension roller are provided so as to contact the outer peripheral surface of the belt.

[0021] According to the above configuration, the distance between the first tension roller and the second tension roller can be reduced. As a result, in the belt transmission mechanism, even when the layout with a relatively small distance between the first tension roller and the second tension roller is adopted, the biasing action of the spring can be sufficiently ensured, and an appropriate tension can be applied to the toothed belt via the first tension roller and the second tension roller.

[0022] Further, the present invention includes the drive pulley fixed to the drive shaft that can be driven to rotate forward and backward by a drive source, the driven pulley rotatably supported by the driven shaft, the belt wound around between the drive pulley and the driven pulley, the auto-tensioner described above, and is characterized by comprising the above. It is a belt transmission mechanism.

[0023] According to the above configuration, in the auto-tensioner of the belt transmission mechanism, the spring is disposed on the opposite side of the first tension roller and the second tension roller with respect to the swing axis of the first swing arm and the second swing arm. Therefore, according to the pulley layout, the length from the intersection point to the other end of the first swing arm to which the spring is attached, the length from the intersection point to the other end of the second swing arm to which the spring is attached, the length from the intersection point to the one end of the first swing arm to which the first tension roller is attached, and the length from the intersection point to the one end of the second swing arm to which the second tension roller is attached are adjusted, and the distance between the first tension roller and the second tension roller and the distance between the other end of the first swing arm and the other end of the second swing arm are adjusted, thereby adjusting the length of the spring with respect to the axial distance between the drive pulley and the driven pulley. As a result, according to the pulley layout, the expansion and contraction allowance of the spring can be adjusted. Therefore, the belt transmission mechanism incorporated into the robot arm of an industrial robot according to the present invention can apply appropriate tension to the belt via two tension rollers of an auto-tensioner that ensures sufficient spring biasing action, regardless of the pulley layout. [Effects of the Invention]

[0024] Regardless of the pulley layout of the belt drive mechanism incorporated into the robot arm of an industrial robot, an auto tensioner and a belt drive mechanism equipped therewith can be provided that ensures sufficient spring biasing force and applies appropriate tension to the belt via two tension rollers. [Brief explanation of the drawing]

[0025] [Figure 1] This is an explanatory diagram of the belt transmission mechanism according to this embodiment. [Figure 2] This is a plan view of a belt drive mechanism equipped with an auto tensioner according to this embodiment, and is a schematic diagram illustrating the state in which the drive pulley is stopped. [Figure 3] This is a cross-sectional view taken along line A-A in Figure 1. [Figure 4] This is a cross-sectional view taken along line B-B in Figure 1. [Figure 5] This is a plan view of the belt drive mechanism according to this embodiment, and is a schematic diagram illustrating the operating state of the auto tensioner during forward / reverse switching. [Figure 6] This is a cross-sectional perspective view of the toothed belt included in the belt transmission mechanism according to this embodiment. [Figure 7] This is an explanatory diagram of a belt transmission mechanism equipped with an auto-tensioner, relating to a comparative example. [Figure 8] This is an explanatory diagram of the responsiveness evaluation test machine used in the responsiveness test for evaluating the belt transmission mechanism according to the embodiment. [Figure 9] This is an explanatory diagram of the test pattern for a responsiveness test to evaluate a belt transmission mechanism according to an embodiment. [Modes for carrying out the invention]

[0026] (Embodiment) The present invention will be described in detail below with reference to the drawings based on embodiments, but the present invention is not limited to these embodiments. The belt transmission mechanism 1 of this embodiment is an example in which the auto tensioner 5 of this embodiment is applied to a belt transmission mechanism 1 for driving a robot arm (hereinafter sometimes simply referred to as "belt transmission mechanism 1") which is incorporated into the robot arm of a horizontal articulated robot 10 called a SCARA robot, a type of industrial robot. Specifically, in the belt transmission mechanism 1 of this embodiment which is incorporated into the second arm 11 of the horizontal articulated robot 10, the auto tensioner 5 of this embodiment is added to automatically maintain the tension of the toothed belt 4 at an appropriate level when transmitting the rotational force of the drive pulley 2 to the driven pulley 3 via the toothed belt 4.

[0027] For example, as shown in Figure 1, the belt transmission mechanism 1 of this embodiment is incorporated as a belt-type reduction mechanism for driving a ball screw spline shaft 13, which extends vertically and is provided at the tip of the second arm 11 of a horizontal articulated robot 10 so as to be able to move vertically and rotate coaxially together with a wrist portion 12 that is detachably attached to the lower end, in forward and reverse rotation via a driven shaft 31 that is coaxial with the ball screw spline shaft 13. The vertical movement of the ball screw spline shaft 13 is performed by a vertical movement drive mechanism 14. The belt transmission mechanism 1, incorporated as a belt-type reduction mechanism, can drive the ball screw spline shaft 13 in forward and reverse rotation while allowing the vertical movement of the ball screw spline shaft 13 by the vertical movement drive mechanism 14 and keeping it in a rotation-preventing state.

[0028] (Belt transmission mechanism 1) As shown in Figures 1 and 2, the belt drive mechanism 1 of this embodiment consists of a drive pulley 2, a driven pulley 3, a toothed belt 4, and an auto tensioner 5. The drive pulley 2 transmits the driving force of the servo motor 20, which is the drive source, via the drive shaft 21 at the rear side of the second arm 11. Here, the servo motor 20 is the servo motor provided in the first-stage belt-type reduction mechanism when applied to the second-stage mechanism of a two-stage reduction system. The drive shaft 21 is the drive shaft of the second-stage belt-type reduction mechanism, extending coaxially with the driven shaft (not shown) of the first-stage belt-type reduction mechanism when applied to the second-stage mechanism of a two-stage reduction system. The driven pulley 3 transmits the driving force to the driven shaft 31, which is connected to the ball screw spline shaft 13 to which the wrist portion 12 is attached, at the front side of the second arm 11. The toothed belt 4 is wound endlessly between the drive pulley 2 and the driven pulley 3. The auto tensioner 5 automatically maintains the tension of the toothed belt 4 at an appropriate level via a first tension roller 51 and a second tension roller 52, which are rotatably mounted.

[0029] In Figure 1, the base end of the second arm 11 is considered the rear side, and the tip end of the second arm 11 is considered the front side. The base end is the side that connects to the first arm 15, and the tip end is the side that connects to the ball screw spline shaft 13 to which the wrist portion 12 is attached. The front side is one side, and the rear side is the other side. Furthermore, in Figure 2, the left side is defined as the front, i.e., one side, and the right side is defined as the rear, i.e., the other side. Also, the radial direction around the central axis R of the pivot axis 53 is simply defined as the radial direction, and the circumferential direction around the central axis R is simply defined as the circumferential direction.

[0030] (Drive pulley 2 and driven pulley 3) The drive pulley 2 is fixed to the drive shaft 21, which is driven by the driving force of the servo motor 20 so as to be able to rotate in both forward and reverse directions. The driven pulley 3 is fixed to the driven shaft 31, to which the ball screw spline shaft 13 is connected.

[0031] The drive pulley 2 and the driven pulley 3 are toothed pulleys. Grooves (not shown) are formed on the outer circumference of the drive pulley 2 and the driven pulley 3, with a shape corresponding to the tooth shape of the teeth of the toothed belt 4. The tooth shape is, for example, a straight tooth shape. In this embodiment, the grooves formed on the outer circumference of the drive pulley 2 and the driven pulley 3 have a shape corresponding to the straight teeth and extend along the direction of the driven shaft 31.

[0032] The distance between the drive pulley 2 and the driven pulley 3 is fixed and cannot be adjusted, for example, to about 80 mm to 300 mm. In this embodiment of the belt transmission mechanism 1, the distance between the drive pulley 2 and the driven pulley 3 is 220 mm. The speed ratio between the drive pulley 2 and the driven pulley 3 is, for example, about 1 to 4. Here, the speed ratio between the drive pulley 2 and the driven pulley 3 is the diameter of the driven pulley 3 divided by the diameter of the drive pulley 2. In this embodiment, the driven pulley 3 has a pitch diameter approximately twice that of the drive pulley 2 so that the speed ratio, or reduction ratio, is 2. When the drive pulley 2 is stopped, the resting belt tension of the toothed belt 4 is at a level that prevents the toothed belt 4 from loosening, for example, about 1 to 5 N per 1 mm of belt width. In the belt transmission mechanism 1 of this embodiment, the resting belt tension of the toothed belt 4 is 5 N per 1 mm of belt width. The allowable range of the rotational angle difference between the drive pulley 2 and the driven pulley 3 is determined by the design. The "rotational angle difference" mentioned above is a surrogate characteristic that represents responsiveness, and refers to "the magnitude of the difference in rotational angle (°) between the drive pulley and the driven pulley." Furthermore, the rotational angle difference is maximum during forward / reverse switching.

[0033] (Toothed belt 4) As shown in Figure 6, the toothed belt 4 has a back portion 43 in which a core wire 42 is spirally embedded along the longitudinal direction of the belt, and a plurality of teeth 44 arranged at predetermined intervals along the longitudinal direction of the belt on the inner circumferential surface of the back portion 43. In this embodiment, the plurality of teeth 44 are integrally molded on the inner circumferential surface of the back portion 43. The teeth 44 also extend along the belt width direction. In other words, the teeth 44 are straight teeth. Furthermore, the inner circumferential surface of the toothed belt 4, i.e., the surface of the teeth 44, and a part of the inner circumferential surface of the back portion 43 where teeth 44 are not provided, are covered with toothed fabric 45. The outer circumferential surface of the back portion 43 is not covered with backing fabric such as cloth.

[0034] The tooth pitch Pt, which is the distance between adjacent teeth 44 in the longitudinal direction of the belt, is preferably a relatively small value from the viewpoint of ensuring repeated positioning accuracy and reliable synchronous transmission even when the speed of operation involving forward and reverse rotation increases, for example, it is preferably around 2 mm to 5 mm. In this embodiment, it is set to 3 mm. The value of the tooth pitch Pt also corresponds to the scale size of the teeth 44. The scale of the teeth 44 is the length of the teeth 44 in the longitudinal direction of the belt and the tooth height Ht of the teeth 44. In other words, the larger the tooth pitch Pt, the larger the scale of the teeth 44 becomes.

[0035] The circumference of the toothed belt 4, which is the length in the longitudinal direction of the belt, is, for example, about 200 mm to 800 mm. In the belt transmission mechanism 1 of this embodiment, the circumference of the toothed belt 4 is about 600 mm. The width of the toothed belt 4, which is its length in the belt width direction, is, for example, about 6 mm to 35 mm. In the belt transmission mechanism 1 of this embodiment, the width of the toothed belt 4 is 10 mm.

[0036] (Back portion 43 and teeth portion 44) The back portion 43 and teeth portion 44 of the toothed belt 4 are made of a rubber composition, and the rubber components of this rubber composition include chloroprene rubber (CR), nitrile rubber, hydrogenated nitrile rubber (HNBR), ethylene-propylene copolymer (EPM), ethylene-propylene-diene terpolymer (EPDM), styrene-butadiene rubber, butyl rubber, chlorosulfonated polyethylene rubber, etc. These rubber components can be used individually or in combination. From the viewpoint of low cost, chloroprene rubber is preferred for the rubber component of the rubber composition constituting the back portion 43 and teeth portion 44. In the belt transmission mechanism 1 of this embodiment, the rubber component of the rubber composition constituting the back portion 43 and teeth portion 44 is chloroprene rubber. Note that the rubber composition constituting the teeth portion 44 and the back portion 43 may use the same rubber composition or different rubber compositions. The rubber composition constituting the back portion 43 and teeth portion 44 may contain various conventional additives or compounding agents as needed. The hardness of the tooth rubber, which is the rubber composition constituting the teeth 44, is preferably about 73 to 83°, as measured using a Type A durometer at an ambient temperature of 23°C (23±2°C) in accordance with JIS K6253 (2012), from the viewpoint of ensuring the transmission performance of the toothed belt 4, particularly its resistance to tooth skipping.

[0037] (Tooth shape of tooth 44) The tooth shape of the teeth 44 of the toothed belt 4 may be a straight tooth shape, which is a general term for straight teeth, or a bevel tooth shape, which is a tooth shape, where the contact angle of the tooth surface is oblique, as long as synchronous transmission by meshing is possible. The toothed belt 4 used in the belt transmission mechanism 1 of this embodiment has straight teeth.

[0038] As for tooth shapes belonging to straight teeth, in addition to the known tooth shapes listed below, variations thereof, or special shapes can be selected as appropriate to suit the application of the belt transmission mechanism. For example, there are shapes called H-shaped teeth, which have a roughly semi-circular cross-section; T-shaped teeth, which have a trapezoidal cross-section; and S-shaped teeth of the STPD type, which have two sides made of outwardly bulging convex curved surfaces, i.e., arc surfaces, connected by a flat surface. From the viewpoint of ensuring the transmission performance of the toothed belt 4, particularly its transmission capacity and resistance to tooth skipping, it is preferable to increase the rigidity of the teeth 44, and an H-shaped tooth (a roughly semi-circular cross-section) is preferred. The toothed belt 4 used in the belt transmission mechanism 1 of this embodiment is also an H-shaped tooth.

[0039] (Core wire 42) The core wire 42 is composed of a twisted cord formed by twisting together multiple strands. Each strand may be formed by bundling and aligning long filaments. From the viewpoint of improving responsiveness to driving during forward / reverse switching in the belt transmission mechanism 1, the material of the filaments is preferably high-strength, high-modulus, and low-elongation, such as alkali-free glass fiber (E glass fiber), high-strength glass fiber, or carbon fiber. From the viewpoint of low cost, alkali-free glass fiber (E glass fiber) is more preferable. The diameter of the core wire 42 is preferably small from the viewpoint of improving the flexibility of the toothed belt 4, that is, from the viewpoint of suppressing speed unevenness of the toothed belt 4 due to vertical movement of the belt pitch line and ensuring high positioning accuracy. Here, the flexibility of the toothed belt 4 refers to the suppleness of the toothed belt 4 when it is wrapped around the drive pulley 2 or driven pulley 3. The diameter of the core wire 42 is, for example, about 0.15 mm to 0.60 mm. The toothed belt 4 used in the belt transmission mechanism 1 of this embodiment has core wire types of E glass fiber and K glass fiber with a core wire diameter of 0.35 mm, and carbon fiber with a core wire diameter of 0.53 mm.

[0040] Examples of high-strength glass fibers include those with a tensile strength of 300 kg / cm². 2 The above materials, in particular, glass fibers with compositions shown in Table 1 that have a higher Si component than alkali-free glass fibers (E glass fibers), can be suitably used. Table 1 also includes the composition of E glass fiber for comparison. Examples of such high-strength glass fibers include K glass fiber, U glass fiber (both manufactured by Nippon Glass Fiber Co., Ltd.), T glass fiber (manufactured by Nitto Boseki Co., Ltd.), R glass fiber (manufactured by Vetrotex), S glass fiber, S-2 glass fiber, and ZENTRON glass fiber (all manufactured by Owens Corning Fiberglass).

[0041] [Table 1]

[0042] Examples of carbon fibers include pitch-based carbon fibers, polyacrylonitrile (PAN)-based carbon fibers, phenolic resin-based carbon fibers, cellulose-based carbon fibers, and polyvinyl alcohol-based carbon fibers. Commercially available carbon fibers include, for example, "Torayca®" manufactured by Toray Industries, Inc., "Tenax®" manufactured by Toho Tenax Co., Ltd., and "Dialead®" manufactured by Mitsubishi Chemical Corporation. These carbon fibers can be used individually or in combination of two or more types. Among these carbon fibers, pitch-based carbon fibers and PAN-based carbon fibers are preferred, and PAN-based carbon fibers are particularly preferred.

[0043] It is preferable that the stranded cord used as the core wire 42 be subjected to an adhesive treatment to enhance adhesion with the back portion 43. As an adhesive treatment, for example, a method is employed in which the stranded cord is immersed in a resorcinol-formaldehyde-latex treatment solution (RFL treatment solution), and then heated and dried to form a uniform adhesive layer on the surface. The RFL treatment solution is a mixture of a resorcinol-formaldehyde initial condensate with latex, and examples of latex used here include chloroprene, styrene-butadiene-vinylpyridine terpolymer (VP latex), hydrogenated nitrile, and NBR. As an adhesive treatment, there are also methods such as pre-treatment with epoxy or isocyanate compounds followed by treatment with the RFL treatment solution.

[0044] The core wires 42 are embedded in the back portion 43 in a spiral pattern along the longitudinal direction of the belt, with predetermined intervals in the belt width direction. In other words, the core wires 42 are arranged in the back portion 43 with predetermined intervals in the belt width direction.

[0045] (Toothcloth 45) From the viewpoint of abrasion resistance and other factors, the tooth fabric 45 is preferably composed of a woven fabric in which warp and weft threads are interwoven vertically and horizontally according to a certain rule. For the tooth fabric 45, it is preferable to arrange the warp threads of the woven fabric so that they extend in the belt width direction and the weft threads so that they extend in the belt longitudinal direction. This ensures the elasticity of the tooth fabric 45 in the belt longitudinal direction. Alternatively, the tooth fabric 45 may be arranged so that the weft threads extend in the belt width direction and the warp threads extend in the belt longitudinal direction. In this case, elastic yarn with elasticity may be used as the warp threads. The material of the fibers constituting the tooth fabric 45 can be nylon, aramid, polyester, polybenzoxazole, cotton, or a combination thereof. The woven fabric used as the tooth cloth 45 may be treated with an adhesive coating to enhance its adhesion to the back portion 43 and the tooth portion 44. A common adhesive coating method involves immersing the woven fabric in resorcinol-formaldehyde-latex (RFL solution), followed by heating and drying to form a uniform adhesive layer on the surface.

[0046] (Auto Tensioner 5) As shown in Figures 2 to 5, the auto tensioner 5 according to this embodiment automatically adjusts the tension of the toothed belt 4 via a first tension roller 51 and a second tension roller 52 that contact the toothed belt 4 wrapped between the drive pulley 2 and the driven pulley 3. The auto tensioner 5 is configured to swing freely around a pivot shaft 53 and includes a first swing arm 56 and a second swing arm 57, which are provided so as to intersect with the central axis R of the pivot shaft 53 as the intersection point; a first tension roller 51 provided on one end 561 of the first swing arm 56 so as to contact the toothed belt 4; a second tension roller 52 provided on one end 571 of the second swing arm 57 so as to contact the toothed belt 4; and a spring 54 provided between the other end 562 of the first swing arm 56, which is on the opposite side of the pivot shaft 53 from the one end 561 of the first swing arm 56, and the other end 572 of the second swing arm 57, which is on the opposite side of the pivot shaft 53 from the one end 571 of the second swing arm 57, and is configured to expand and contract so as to bias the other end 562 of the first swing arm 56 and the other end 572 of the second swing arm 57 in a direction that pulls them towards each other. The first tension roller 51 and the second tension roller 52 correspond to two tension rollers. Furthermore, the first tension roller 51 corresponds to one of the two tension rollers, and the second tension roller 52 corresponds to the other of the two tension rollers.

[0047] (Oscillating axis 53) As shown in Figure 3, the pivot shaft 53 is a metal part formed integrally with a cylindrical body portion 531 extending in the vertical direction, a flange portion 532 extending radially outward from the upper end of the body portion 531, and a fastening portion 533 extending downward from the center of the lower end surface of the body portion 531.

[0048] As shown in Figure 2, the pivot shaft 53 has a central axis R that extends parallel to the drive shaft 21. The pivot shaft 53 extends from the intersection of the roller center line RL, which connects the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52, and the pulley center line PL, which connects the rotation center 22 of the drive pulley 2 and the rotation center 32 of the driven pulley 3, through a point on the pulley center line PL or a point on the extension of the pulley center line PL, spaced apart towards the drive pulley 2, and through a point parallel to the drive shaft 21. The fastening portion 533 (male thread portion) is fastened to the female thread portion of the housing of the second arm 11 of the horizontal articulated robot 10. Furthermore, the outer circumferential surface of the body portion 531 and the lower end surface of the flange portion 532 of the pivot shaft 53 make surface contact with the inner circumferential surface of the sliding member 55, so that the sliding member 55, which will be described later, acts as a bearing and rotatably supports the first pivot arm 56 and the second pivot arm 57.

[0049] (First oscillating arm 56) The first oscillating arm 56 is a flat plate made of a rectangular aluminum alloy casting or the like, viewed in the axial direction of the oscillating shaft 53. One end 561E and the other end 562E of the first oscillating arm 56 are machined into a U-shape when viewed in the axial direction of the oscillating shaft 53. As shown in Figure 4, the first swing arm 56 has a cylindrical projection 561A formed below one end 561. The first swing arm 56 has a female threaded hole 561B that penetrates the one end 561 and the projection 561A in the same axial direction as the rotation center 51C. Furthermore, as shown in Figure 3, the first swing arm 56 is provided with a cylindrical first spring locking shaft portion 563 extending in the same axial direction as the swing shaft 53 below the other end 562. Below the first spring locking shaft portion 563, a first flange portion 564 is formed, having an outer diameter larger than the diameter of the first spring locking shaft portion 563. The first flange portion 564 serves to prevent one end 541B of the spring 54, which is locked to the first spring locking shaft portion 563, from coming off downward from the first spring locking shaft portion 563. Furthermore, the first swing arm 56 has a first pivot point 566 into which a swing hole 565 is formed, into which the body portion 531 of the swing shaft 53 is inserted via a sliding member 55. As a result, the inner circumferential surface of the swing hole 565 of the first swing arm 56 makes surface contact with the outer circumferential surface of the sliding member 55, so that the sliding member 55 acts as a bearing, and the first swing arm 56 is rotatably supported with respect to the swing shaft 53.

[0050] Here, the first swing arm 56 is rotatably supported on the central axis R of the swing shaft 53 such that, when viewed in the axial direction of the swing shaft 53, the distance between the other end 562 of the first swing arm 56 and the central axis R is greater than the distance between the central axis R and the one end 561 of the first swing arm 56. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, the distance between the other end 562 of the first swing arm 56 and the central axis R may be the same as the distance between the central axis R and one end 561 of the first swing arm 56, or it may be smaller than the distance between the central axis R and one end 561 of the first swing arm 56.

[0051] More specifically, as shown in Figure 2, the first swing arm 56 is rotatably supported on the central axis R of the swing shaft 53 such that the distance 56B between the center 563C of the first spring locking shaft portion 563 provided at the other end 562 of the first swing arm 56 and the central axis R is greater than the distance 56A between the central axis R and the rotation center 51C of the first tension roller 51 provided at one end 561 of the first swing arm 56. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, distance 56B may be the same as distance 56A, or it may be smaller than distance 56A.

[0052] Furthermore, the first swing arm 56 is rotatably supported on the central axis R of the swing shaft 53 such that, when viewed in the axial direction of the swing shaft 53, the distance between the other end 562E of the first swing arm 56 and the central axis R is greater than the distance between the central axis R and one end 561E of the first swing arm 56. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, the distance between the other end 562E of the first swing arm 56 and the central axis R may be the same as the distance between the central axis R and one end 561E of the first swing arm 56, or it may be smaller than the distance between the central axis R and one end 561E of the first swing arm 56.

[0053] (Second oscillating arm 57) The second oscillating arm 57, like the first oscillating arm 56, is a flat plate made of a rectangular aluminum alloy casting or the like, when viewed in the axial direction of the oscillating shaft 53. One end 571E and the other end 572E of the second oscillating arm 57 are machined into a U-shape when viewed in the axial direction of the oscillating shaft 53. As shown in Figure 3, the second oscillating arm 57 has a cylindrical projection 571A formed above one end 571. The second oscillating arm 57 has a female threaded hole 571B that penetrates the one end 571 and the projection 571A in the same axial direction as the rotation center 52C. Furthermore, as shown in Figure 4, the second swing arm 57 is provided with a cylindrical second spring locking shaft portion 573 extending in the same axial direction as the swing shaft 53 above the other end 572 of the second swing arm 57. Above the second spring locking shaft portion 573, a second flange portion 574 is formed, having an outer diameter larger than the diameter of the second spring locking shaft portion 573. The second flange portion 574 serves to prevent the other end 541A of the spring 54, which is locked to the second spring locking shaft portion 573, from coming out upward from the second spring locking shaft portion 573. Furthermore, the second swing arm 57 has a second pivot point 576 into which a swing hole 575 is formed via a sliding member 55 into which the body 531 of the swing shaft 53 is inserted. As a result, the inner circumferential surface of the swing hole 575 of the second swing arm 57 makes surface contact with the outer circumferential surface of the sliding member 55, so that the sliding member 55 acts as a bearing, and the second swing arm 57 is rotatably supported with respect to the swing shaft 53.

[0054] The second swing arm 57 is rotatably supported on the central axis R of the swing shaft 53 such that, when viewed in the axial direction of the swing shaft 53, the distance between the other end 572 of the second swing arm 57 and the central axis R is greater than the distance between the central axis R and the one end 571 of the second swing arm 57. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, the distance between the other end 572 of the second swing arm 57 and the central axis R may be the same as the distance between the central axis R and one end 571 of the second swing arm 57, or it may be smaller than the distance between the central axis R and one end 571 of the second swing arm 57.

[0055] More specifically, the second swing arm 57 is rotatably supported on the central axis R of the swing shaft 53 such that the distance 57B between the center 573C of the second spring locking shaft portion 573, which is provided at the other end 572 of the second swing arm 57, and the central axis R is greater than the distance 57A between the central axis R and the rotation center 52C of the second tension roller 52, which is provided at one end 571 of the second swing arm 57. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, distance 57B may be the same as distance 57A, or it may be smaller than distance 57A.

[0056] Furthermore, the second swing arm 57 is rotatably supported on the central axis R of the swing shaft 53 such that, when viewed in the axial direction of the swing shaft 53, the distance between the other end 572E of the second swing arm 57 and the central axis R is greater than the distance between the central axis R and one end 571E of the second swing arm 57. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, the distance between the other end 572E of the second swing arm 57 and the central axis R may be the same as the distance between the central axis R and one end 571E of the second swing arm 57, or it may be smaller than the distance between the central axis R and one end 571E of the second swing arm 57.

[0057] With the auto tensioner 5 configured as described above, the length of the spring 54 provided between the other end 562 of the first swing arm 56 and the other end 572 of the second swing arm 57 can be configured to be greater than the distance between the first tension roller 51 provided at one end 561 of the first swing arm 56 and the second tension roller 52 provided at one end 571 of the second swing arm 57, when viewed in the axial direction of the swing shaft 53. As a result, in a pulley layout in which the diameters of the drive pulley 2 and the driven pulley 3 are relatively small relative to the distance between their axes, the extension and contraction range of the spring 54 can be made sufficiently large compared to an auto tensioner configured such that the length of the spring 54 provided between the other end 562 of the first swing arm 56 and the other end 572 of the second swing arm 57 is smaller than the distance between the first tension roller 51 provided at one end 561 of the first swing arm 56 and the second tension roller 52 provided at one end 571 of the second swing arm 57. As a result, the auto tensioner 5 with the above configuration can ensure sufficient biasing action of the spring 54 regardless of the pulley layout, and can apply appropriate tension to the toothed belt 4 via the first tension roller 51 and the second tension roller 52.

[0058] In the auto tensioner 5 configured as described above, the first swing arm 56 and the second swing arm 57 are configured to swing freely with the swing axis 53 as the pivot point. A spring 54 functions as the point of force application, biasing the other end 562 of the first swing arm 56 and the other end 572 of the second swing arm 57 in a direction that pulls them towards each other. The biasing force of this spring 54, via the swinging motion of the first swing arm 56 and the second swing arm 57, applies tension to the toothed belt 4, with the first tension roller 51 provided at one end 561 of the first swing arm 56 and the second tension roller 52 provided at one end 571 of the second swing arm 57 as the points of application. In this way, by utilizing the principle of levers, with the spring 54 as the point of force application, the oscillating shaft 53 as the pivot point, and the first tension roller 51 and the second tension roller 52 as the points of application, the biasing force of the spring 54 can be effectively transmitted to the first tension roller 51 and the second tension roller 52, thereby applying appropriate tension to the toothed belt 4. This makes it possible to automatically and stably maintain the tension of the toothed belt 4, suppressing loosening and overtension during forward and reverse rotation, and improving the transmission accuracy of the belt transmission mechanism 1.

[0059] (First swinging arm 56 and second swinging arm 57) The first swing arm 56 and the second swing arm 57 intersect with the central axis R of the swing shaft 53 as their intersection point, and are supported on the swing shaft 53 via bearings so that the first swing arm 56 and the second swing arm 57 can swing freely about the central axis R of the swing shaft 53.

[0060] Furthermore, in this embodiment, the first swing arm 56 and the second swing arm 57 are such that, when viewed in the axial direction of the swing axis 53, the distance between the other end 562 of the first swing arm 56 and the central axis R is the same as the distance between the other end 572 of the second swing arm 57 and the central axis R, and the distance between the central axis R and one end 561 of the first swing arm 56 is the same as the distance between the central axis R and one end 571 of the second swing arm 57.

[0061] Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, the distance between the other end 562 of the first swing arm 56 and the central axis R does not have to be the same as the distance between the other end 572 of the second swing arm 57 and the central axis R, and the distance between the central axis R and one end 561 of the first swing arm 56 does not have to be the same as the distance between the central axis R and one end 571 of the second swing arm 57.

[0062] More specifically, in the auto tensioner 5 of this embodiment, the first swing arm 56 and the second swing arm 57 are such that, when viewed in the axial direction of the swing axis 53, the distance 56B between the center 563C of the first spring locking shaft portion 563 provided at the other end 562 of the first swing arm 56 and the central axis R is the same as the distance 57B between the center 573C of the second spring locking shaft portion 573 provided at the other end 572 of the second swing arm 57 and the central axis R, and the distance 56A between the central axis R and the rotation center 51C of the first tension roller 51 provided at one end 561 of the first swing arm 56 is the same as the distance 57A between the central axis R and the rotation center 52C of the second tension roller 52 provided at one end 571 of the second swing arm 57. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, distance 56B does not have to be the same as distance 57B, and distance 56A does not have to be the same as distance 57A.

[0063] Furthermore, in the first and second swing arms 56 and 57, when viewed in the axial direction of the swing axis 53, the distance between the other end 562E of the first swing arm 56 and the central axis R is the same as the distance between the other end 572E of the second swing arm 57 and the central axis R, and the distance between the central axis R and one end 561E of the first swing arm 56 is the same as the distance between the central axis R and one end 571E of the second swing arm 57. Depending on the layout of the auto tensioner 5 in the belt transmission mechanism 1, the distance between the other end 562E of the first swing arm 56 and the central axis R does not have to be the same as the distance between the other end 572E of the second swing arm 57 and the central axis R, and the distance between the central axis R and one end 561E of the first swing arm 56 does not have to be the same as the distance between the central axis R and one end 571E of the second swing arm 57.

[0064] With the above configuration, the roller centerline RL, which connects the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52, can be made parallel to the axis SL of the spring 54 when viewed in the axial direction of the oscillating shaft 53. Here, making the roller centerline RL and the axis SL of the spring 54 parallel means that the angle between the roller centerline RL and the axis SL of the spring 54 is not limited to 0 degrees, but includes approximately 0 degrees ± 10 degrees. As a result, the biasing force of the spring 54 on the first tension roller 51 and the second tension roller 52 becomes equal, and the tension of the toothed belt 4 applied by the first tension roller 51 and the tension applied by the second tension roller 52 become equal. Furthermore, it becomes possible to ensure a higher level of responsiveness of the auto tensioner 5 to the drive during forward and reverse starting / stopping, for example, when the forward and reverse direction of the toothed belt 4 is switched, and synchronous transmission can be made more reliable even when the speed of the operation involving forward and reverse rotation increases. In other words, it is possible to maintain an appropriate tension in the toothed belt 4 while preventing the tension drop that occurs in the initial stages of travel. As a result, in the auto tensioner 5, regardless of the pulley layout, sufficient biasing force from the spring 54 can be ensured, and appropriate tension can be applied to the toothed belt 4 via the first tension roller 51 and the second tension roller 52.

[0065] (First support section 566 and second support section 576) The first pivot point 566 of the first swing arm 56 has an upwardly extending flange shape and is formed in a cylindrical shape when viewed from above. Specifically, as shown in Figure 3, the upper end surface of the first pivot point 566 extends upward to a position where it can contact the lower end surface of the flange portion 551B that extends radially outward from the upper end of the vertically extending cylindrical portion 551A of the upper cylindrical sliding portion 551 of the sliding member 55, which will be described later, and the lower end surface of the first pivot point 566 is in contact with the upper end surface of the plate-shaped sliding portion 552 of the sliding member 55, which will be described later. Furthermore, the first pivot point 566 extends radially inward to a position where it can contact the outer circumferential surface of the vertically extending cylindrical portion 551A of the upper cylindrical sliding portion 551. As shown in Figure 3, the diameter (inner diameter) of the radially inner end face of the first pivot point 566 is the same as or slightly larger than the diameter (outer diameter) of the outer circumferential surface of the cylindrical portion 551A of the upper cylindrical sliding portion 551.

[0066] The second pivot point 576 of the second swing arm 57 has a flange shape that extends downward and is formed in a cylindrical shape when viewed from above. Specifically, as shown in Figure 3, the lower end surface of the second pivot point 576 extends downward to a position where it can contact the upper end surface of the flange portion 553B that extends radially outward from the lower end of the vertically extending cylindrical portion 553A of the lower cylindrical sliding portion 553 of the sliding member 55, which will be described later, and the upper end surface of the second pivot point 576 is in contact with the lower end surface of the plate-shaped sliding portion 552 of the sliding member 55, which will be described later. Furthermore, the second pivot point 576 extends radially inward to a position where it can contact the outer circumferential surface of the vertically extending cylindrical portion 553A of the lower cylindrical sliding portion 553. As shown in Figure 3, the diameter (inner diameter) of the radially inner end face of the second pivot point 576 is the same as or slightly larger than the diameter (outer diameter) of the outer circumferential surface of the cylindrical portion 553A of the lower cylindrical sliding portion 553.

[0067] With the above configuration, the first pivot point 566 of the first swing arm 56 and the second pivot point 576 of the second swing arm 57 are rotatably supported on the swing shaft 53 with the sliding member 55 (described later) as a bearing, independently in the vertical direction.

[0068] (Sliding member 55) As shown in Figure 3, the sliding member 55 has an upper cylindrical sliding portion 551, a plate-shaped sliding portion 552, and a lower cylindrical sliding portion 553, which are formed separately. The upper cylindrical sliding portion 551 and the lower cylindrical sliding portion 553 have the same configuration (shape and dimensions).

[0069] The upper cylindrical sliding portion 551 has a cylindrical portion 551A that extends vertically and a flange portion 551B that extends radially outward from the upper end of the cylindrical portion 551A. The plate-shaped sliding portion 552 has a plate-shaped portion 552A formed in the shape of an annular plate, and a cylindrical portion 552B extending upward and downward on the radially inner side of the plate-shaped portion 552A. The lower cylindrical sliding portion 553 has a cylindrical portion 553A that extends in the vertical direction and a flange portion 553B that extends radially outward from the lower end of the cylindrical portion 553A.

[0070] The sliding member 55 is externally fitted onto the body 531 of the pivot shaft 53. More specifically, from above, the upper cylindrical sliding part 551, the first pivot part 566, the plate-shaped sliding part 552, the second pivot part 576, and the lower cylindrical sliding part 553 are externally fitted onto the body 531 of the pivot shaft 53 in that order, and the upper cylindrical sliding part 551, the plate-shaped sliding part 552, and the lower cylindrical sliding part 553 are fixed in such a manner that they are sandwiched vertically between the flange part 532 of the pivot shaft 53 and the housing of the second arm 11.

[0071] The sliding member 55 functions as a sliding bearing that slides against the first oscillating arm 56, with the cylindrical portion 551A of the upper cylindrical sliding portion 551 and the cylindrical portion 552B of the plate-shaped sliding portion 552 making surface contact with the inner circumferential surface of the first pivot portion 566, the flange portion 551B of the upper cylindrical sliding portion 551 making surface contact with the upper end surface of the first pivot portion 566, and the upper end surface of the plate-shaped portion 552A of the plate-shaped sliding portion 552 making surface contact with the lower end surface of the first pivot portion 566.

[0072] Similarly, the sliding member 55 functions as a sliding bearing that slides against the second oscillating arm 57, with the cylindrical portion 553A of the lower cylindrical sliding portion 553 and the cylindrical portion 552B of the plate-shaped sliding portion 552 making surface contact with the inner circumferential surface of the second pivot portion 576, the flange portion 553B of the lower cylindrical sliding portion 553 making surface contact with the lower end surface of the second pivot portion 576, and the lower end surface of the plate-shaped portion 552A of the plate-shaped sliding portion 552 making surface contact with the upper end surface of the second pivot portion 576.

[0073] With the above configuration, the first swing arm 56 and the second swing arm 57 are each independently supported on the swing shaft 53 so as to be rotatable, with the sliding member 55 acting as a bearing.

[0074] In this embodiment, the sliding member 55 is formed by injection molding of a hard thermoplastic resin (e.g., polyacetal resin) having a Rockwell R scale (compliant with JIS K7202-2:2001) of 80 to 130, from the viewpoint of low friction sliding properties and wear resistance.

[0075] (First tension roller 51 and second tension roller 52) The first tension roller 51 is a cylindrical roller member. The first tension roller 51 is rotatably supported around a rotation center 51C via a rolling bearing on a first base shaft portion 51A, which is provided at one end 561 of the first swing arm 56 and has the same axial direction as the swing shaft 53. As shown in Figure 4, the first base shaft portion 51A is the base end portion that rotatably supports the first tension roller 51 around the rotation center 51C via a rolling bearing. The first base shaft portion 51A has a male threaded portion 51A1 extending downward for screwing into a threaded hole 561B provided at one end 561 of the first swing arm 56. As a result, the first base portion 51A is fixed to the first swing arm 56 by screwing the male thread portion 51A1 into the female thread hole 561B of the first swing arm 56. The second tension roller 52 is also a cylindrical roller member with the same shape as the first tension roller 51. The second tension roller 52 is rotatably supported around the rotation center 52C via a rolling bearing on a second base shaft portion 52A, which is provided at one end 571 of the second swing arm 57 and has the same axial direction as the swing shaft 53. As shown in Figure 3, the second base shaft portion 52A is the base end portion that rotatably supports the second tension roller 52 around the rotation center 52C via a rolling bearing. The second base shaft portion 52A has a male threaded portion 52A1 extending downward for screwing into a threaded hole 571B provided at the tip portion 571 of the second swing arm 57. As a result, the second base portion 52A is fixed to the second swing arm 57 by screwing the male thread portion 52A1 into the female thread hole 571B of the second swing arm 57.

[0076] As shown in Figures 2 and 5, the first tension roller 51 and the second tension roller 52 are rotatably supported on the first base shaft portion 51A and the second base shaft portion 52A, respectively, at positions on either side of the pulley center line PL connecting the rotation center 22 of the drive pulley 2 and the rotation center 32 of the driven pulley 3, and the first tension roller 51 and the second tension roller 52 are capable of contacting the outer circumferential surface of the toothed belt 4.

[0077] (Spring 54) In the auto tensioner 5 of this embodiment, the spring 54 is a tension spring. The tension spring 54 is stretched in a direction that makes it longer than its natural length, that is, in a state where a self-elastic recovery force acts in the direction of compression. One end 541B of the hook-shaped spring 54 is locked to a first spring locking shaft portion 563 provided below the other end 562 of the first swing arm 56, and the other end 541A of the hook-shaped spring 54 is locked to a second spring locking shaft portion 573 provided above the other end 572 of the second swing arm 57. In other words, as shown in Figures 3 and 4, the spring 54 is stretched between a first spring locking shaft portion 563 provided below the other end 562 of the first swing arm 56 and a second spring locking shaft portion 573 provided above the other end 572 of the second swing arm 57, such that the locking positions of the other end 541A and the one end 541B are on the same plane in a side view without shifting vertically, and the other end 541A and the one end 541B cannot fall off. As a result, the tension spring 54 biases the first spring locking shaft portion 563 and the second spring locking shaft portion 573 in a direction that pulls them towards each other along the axis SL of the spring 54. That is, the spring 54, via the first swing arm 56 and the second swing arm 57, biases the first tension roller 51 and the second tension roller 52 in a direction that pulls them towards each other along the roller centerline RL.

[0078] In this embodiment of the auto tensioner 5, the length of the spring 54 is greater than the distance between the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52, when viewed in the axial direction of the pivot shaft 53. In detail, as shown in Figure 2, when the drive pulley 2 is stopped, that is, when the first tension roller 51 and the second tension roller 52 and the outer surface of the toothed belt 4 are in contact with each other and in balance, a spring 54 is used whose length is greater than the distance between the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52. Note that the length of the spring 54 referred to here means the length of the spring 54 when no external force is applied to the auto tensioner 5.

[0079] In this way, by making the length of the spring 54 greater than the distance between the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52, the expansion and contraction range of the spring 54 can be sufficiently increased compared to a conventional auto tensioner in which the spring is placed between the base axis of the first tension roller and the base axis of the second tension roller, in a pulley layout in which the diameters of the drive pulley 2 and the driven pulley 3 are relatively small relative to the distance between the axes of the drive pulley 2 and the driven pulley 3. As a result, the auto tensioner 5 according to this embodiment can ensure sufficient biasing action of the spring 54 regardless of the pulley layout, and can apply appropriate tension to the toothed belt 4 via the first tension roller 51 and the second tension roller 52.

[0080] Furthermore, in the case of spring 54, the tension spring is used in a manner in which the first tension roller 51 and the second tension roller 52 are in contact with the outer circumferential surface of the toothed belt 4, as shown in Figure 2.

[0081] In this embodiment, the auto tensioner 5 may use a spring other than a tension spring. For example, a compression spring may be used for spring 54. In this case, the compression spring 54 is stretched between the first spring locking shaft portion 563, which is provided at the other end 562 of the first swing arm 56, and the second spring locking shaft portion 573, which is provided at the other end 572 of the second swing arm 57, in a state where it is compressed in a direction shorter than its natural length, that is, in a state where a self-elastic recovery force acts in the direction of extension. With this configuration, the compression spring 54 can bias the first spring locking shaft portion 563 and the second spring locking shaft portion 573 in a direction that separates them from each other along the axis SL of the spring 54. For example, a compression spring 54 is used in a configuration where the first tension roller 51 and the second tension roller 52 are positioned on the inner circumference side of the toothed belt 4, and the first tension roller 51 and the second tension roller 52 are in contact with the inner surface of the toothed belt 4.

[0082] As in the auto tensioner 5 of this embodiment, if a tension spring is used for the spring 54, the first tension roller 51 and the second tension roller 52 can be positioned on the outer circumference side of the toothed belt 4 (see Figure 5). Therefore, the distance between the first tension roller 51 and the second tension roller 52 can be reduced compared to the case where the spring 54 is a compression spring and the first tension roller 51 and the second tension roller 52 are positioned on the inner circumference side of the toothed belt 4. As a result, even in a belt transmission mechanism 1 where the distance between the first tension roller 51 and the second tension roller 52 is relatively small, the biasing effect of the spring 54 can be sufficiently ensured, and appropriate tension can be applied to the toothed belt 4 via the first tension roller 51 and the second tension roller 52.

[0083] Furthermore, the spring 54 is preferably a coil spring so that a predetermined spring characteristic can be repeatedly obtained for each belt transmission mechanism 1, and a coil spring is also used in this embodiment. The spring wire is preferably an oil-tempered spring wire with a circular cross-section, conforming to JIS G3560:1994, and the auto tensioner 5 of this embodiment uses an oil-tempered spring wire with a circular cross-section conforming to the above standard. The natural length of the spring wire, as well as the spring's coil diameter and coil length, are designed and determined so that a predetermined spring characteristic is repeatedly obtained for each belt transmission mechanism, particularly for each level of belt tension.

[0084] In the auto tensioner 5 of this embodiment, in order to facilitate tensioning the spring 54 between the first spring locking shaft portion 563 and the second spring locking shaft portion 573, one end 541B and the other end 541A of the spring 54, which correspond to approximately one turn of the end of the spring 54, are bent horizontally by approximately 90° in the same direction.

[0085] In the auto tensioner 5 configured as described above, the spring 54 is positioned on the first swing arm 56 and the second swing arm 57, on the opposite side of the swing axis 53 from the first tension roller 51 and the second tension roller 52. Therefore, depending on the pulley layout of the belt transmission mechanism 1, the length of the spring 54 relative to the axial distance between the drive pulley 2 and the driven pulley 3 can be adjusted by adjusting the distance between the first tension roller 51 and the second tension roller 52, and the distance between the other end 562 of the first swing arm 56 and the other end 572 of the second swing arm 57, which is the point where the first swing arm 56 and the second swing arm 57 intersect, from the central axis R of the swing arm 53 to the other end 572 of the second swing arm 57, which is the point where the spring 54 is attached, from the central axis R of the swing arm 53 to the one end 561 of the first swing arm 56 to which the first tension roller 51 is attached, and from the central axis R of the swing arm 53 to the one end 571 of the second swing arm 57 to which the second tension roller 52 is attached. This allows the expansion and contraction range of the spring 54 to be adjusted according to the pulley layout of the belt transmission mechanism 1. Furthermore, depending on the pulley layout of the belt transmission mechanism 1, the length of the spring 54 may be adjusted to be greater than the distance between the first tension roller 51 and the second tension roller 52, less than the distance between the first tension roller 51 and the second tension roller 52, or the same as the distance between the first tension roller 51 and the second tension roller 52. Furthermore, depending on the pulley layout of the belt transmission mechanism 1, the number of driven pulleys around which the toothed belt 4 is wound is at least one, and there may be one or more driven pulleys, but there is only one drive pulley. Therefore, the auto tensioner 5 with the above configuration can ensure sufficient biasing action of the spring 54 and apply appropriate tension to the toothed belt 4 via the first tension roller 51 and the second tension roller 52, regardless of the pulley layout.

[0086] (Operation of auto tensioner 5: Tensioning side of toothed belt 4) (operation) In a belt transmission mechanism 1 for driving a robot arm, i. When the drive pulley 2 is stopped, as shown in Figure 2, the first tension roller 51 and the second tension roller 52 are in contact with the outer surface of the toothed belt 4 and are in balance when viewed in the axial direction of the swing shaft 53, with the roller centerline RL and the pulley centerline PL being perpendicular to each other (see Figure 2).

[0087] ii. When switching between forward and reverse: When starting / stopping forward / reverse The case where the drive pulley 2 rotates in the direction of arrow Z in Figure 5 will be explained. First, as shown in Figure 5, on the tensioned side of the toothed belt 4, the tension of the toothed belt 4 increases, and the first tension roller 51, which is one of the tension rollers located on the tensioned side of the toothed belt 4, is pushed by the toothed belt 4 due to the tension of the toothed belt 4 and displaced in the direction of tension of the toothed belt 4. As the tension of the toothed belt 4 increases, the first tension roller 51 is pushed by the toothed belt 4 and displaced in the direction of tension of the toothed belt 4, while rotating in the direction of arrow X around the pivot axis 53. The first tension roller 51, via the first swing arm 56, begins to rotate in the direction of arrow (1) around the central axis R of the swing shaft 53 on a trajectory whose swing radius is between the rotation center 51C of the first tension roller 51 and the central axis R of the swing shaft 53, as viewed in the axial direction of the swing shaft 53. While resisting the biasing force of the spring 54, it swings in the direction of arrow (1) around the central axis R of the swing shaft 53, and quickly displaces to the equilibrium position, that is, the position where the toothed belt 4 reaches a tensioned state on the tensioned side (see Figure 5).

[0088] (action) In this configuration, when the tension of the toothed belt 4 increases on the tensioned side of the toothed belt 4, and the first tension roller 51 located on the tensioned side of the toothed belt 4 is pushed by the toothed belt 4 due to the tension of the toothed belt 4 and displaced in the tension direction of the toothed belt 4, the spring 54 is located on the first spring locking shaft portion 563 provided on the other end 562 of the first swing arm 56, opposite to the first tension roller 51 provided on one end 561 of the first swing arm 56, which straddles the swing shaft 53, and on one end of the second swing arm 57, which straddles the swing shaft 53. The first spring locking shaft portion 563 is stretched between the second spring locking shaft portion 563 and the second spring locking shaft portion 573, which is located on the opposite side of the second tension roller 52 provided on 571 and the other end 572 of the second swing arm 57. Since the first spring locking shaft portion 563 and the second spring locking shaft portion 573 are biased to pull each other along the axis SL of the spring 54, the spring 54 biases the first tension roller 51 and the second tension roller 52 to pull each other along the roller centerline RL via the first swing arm 56 and the second swing arm 57. Furthermore, since the first tension roller 51 and the second tension roller 52 are configured to swing freely around the central axis R of the pivot shaft 53, the first tension roller 51 can swing together with the second tension roller 52 along the trajectory of the swing radius of the first tension roller 51 and the swing radius of the second tension roller 52 in the tension direction of the toothed belt 4, that is, in the direction of arrows (1) and (2) in Figure 5, around the central axis R of the pivot shaft 53, while resisting the biasing force of the spring 54. This allows the first tension roller 51 to be quickly displaced to the equilibrium position.

[0089] Therefore, on the tensioned side of the toothed belt 4, the first tension roller 51 can quickly displace to the equilibrium position by oscillating around the central axis R of the oscillating axis 53 via the first oscillating arm 56, which rotates in the direction of arrow X around the oscillating axis 53, while suppressing damping by the spring 54, that is, displacement in the direction of the biasing force of the spring 54. As a result, the responsiveness of the first tension roller 51 on the tensioned side of the toothed belt 4, specifically the operating speed of the first tension roller 51, is improved with forward and reverse rotation, and it is possible to suppress overtension of the toothed belt 4, thereby keeping tension fluctuations low.

[0090] (Operation of auto tensioner 5: Loosening side of toothed belt 4) (action, effect) iii. Next, on the loose side of the toothed belt 4, the tension of the toothed belt 4 decreases, causing the toothed belt 4 to loosen. However, in the above operation (ii) on the tensioned side of the toothed belt 4, the first tension roller 51 on the tensioned side, while resisting the biasing force of the spring 54, oscillates together with the first tension roller 51 and the second tension roller 52 along the trajectory of the oscillation radius of the first tension roller 51 and the oscillation radius of the second tension roller 52 in the direction of the tension of the toothed belt 4, as shown by arrow (1) in Figure 5. Consequently, on the loose side of the toothed belt 4, the other second tension roller 52 is naturally biased by the spring 54 in a direction that eliminates the loosening of the toothed belt 4, and oscillates around the central axis R of the oscillation axis 53 via the second oscillation arm 57, which rotates in the direction of arrow X around the central axis R of the oscillation axis 53, causing it to quickly displace in the direction of arrow (2) (see Figure 5).

[0091] Therefore, even on the slack side of the toothed belt 4, the responsiveness (operating speed) of the second tension roller 52 is improved, and the second tension roller 52 can be kept in contact with the outer surface of the toothed belt 4. As a result, the tension of the toothed belt 4 can be automatically maintained at an appropriate level without causing slack in the toothed belt 4.

[0092] The case where the drive pulley 2 rotates in the opposite direction to the arrow Z in Figure 5 will be explained. Next, when the drive pulley 2 is rotated in the opposite direction to the arrow Z in Figure 5, the positions of the tensioned and loosened sides of the toothed belt 4 become the opposite of those when the drive pulley 2 is rotated in the direction of arrow Z in Figure 5, as described above. In this case, on the tensioned side of the toothed belt 4, when the second tension roller 52 is pushed by the toothed belt 4 and displaced in the direction of tension of the toothed belt 4, it swings via the second swing arm 57, which rotates around the central axis R of the swing shaft 53 in the opposite direction to the direction of arrow X, while resisting the biasing force of the spring 54, and is quickly displaced from the position shown in Figure 5 to the equilibrium position in the opposite direction to the direction of arrow (2) in Figure 5. In conjunction with this, the first tension roller 51 is naturally biased by the spring 54 in the direction of spring biasing, which is the direction that eliminates the slack in the toothed belt 4, and swings via the first swing arm 56, which rotates around the central axis R of the swing shaft 53 in the opposite direction to the direction of arrow X, and is quickly displaced from the position shown in Figure 5 in the opposite direction to the direction of arrow (1) in Figure 5. As a result, on the tension side of the toothed belt 4, the responsiveness of the second tension roller 52, specifically its operating speed, is improved, preventing the toothed belt 4 from becoming overtightened and keeping tension fluctuations low. Furthermore, on the slack side of the toothed belt 4, the responsiveness of the first tension roller 51, specifically its operating speed, is improved, and the first tension roller 51 can be kept in contact with the outer surface of the toothed belt 4. This allows the tension of the toothed belt 4 to be automatically maintained at an appropriate level without causing slack in the toothed belt 4.

[0093] By using the above-described auto tensioner 5, in the belt transmission mechanism 1 for driving the robot arm, regardless of whether the drive pulley 2 rotates in forward or reverse direction, it is possible to ensure a high level of responsiveness to the drive during forward / reverse switching, that is, when starting / stopping forward / reverse. In other words, it is possible to sufficiently suppress the difference in rotational angle between the drive pulley 2 and the driven pulley 3 during forward / reverse switching, ensuring reliable synchronous transmission even when the speed of operation involving forward and reverse rotation increases, automatically adjusting for the tension drop that occurs at least at the beginning of travel, and maintaining the tension of the toothed belt 4 at an appropriate level so as not to loosen.

[0094] Furthermore, in the belt transmission mechanism 1 using the auto tensioner 5 configured as described above, the spring 54 is positioned on the opposite side of the first tension roller 51 and the second tension roller 52 of the first swing arm 56 and the second swing arm 57, with the swing shaft 53 in between. Therefore, depending on the pulley layout of the belt transmission mechanism 1, the length of the spring 54 relative to the distance between the axes of the drive pulley 2 and the driven pulley 3 can be adjusted by adjusting the distance between the first tension roller 51 and the second tension roller 52, and the distance between the other end 562 of the first swing arm 56 and the other end 572 of the second swing arm 57, which is the point where the first swing arm 56 and the second swing arm 57 intersect, from the central axis R of the swing arm 53 to the other end 562 of the second swing arm 57, which is the point where the spring 54 is attached, from the central axis R of the swing arm 53 to the other end 561 of the first swing arm 56 to which the first tension roller 51 is attached, and from the central axis R of the swing arm 53 to the other end 571 of the second swing arm 57 to which the second tension roller 52 is attached. This allows the expansion and contraction range of the spring 54 to be adjusted according to the pulley layout of the belt transmission mechanism 1. Therefore, the belt transmission mechanism 1 using the auto tensioner 5 with the above configuration can ensure sufficient biasing action of the spring 54 and apply appropriate tension to the toothed belt 4 via the first tension roller 51 and the second tension roller 52, regardless of the pulley layout.

[0095] (Other embodiments) In the above embodiment, a toothed belt 4 was used as an example of the belt wrapped between the drive pulley 2 and the driven pulley 3, but the type of belt is not particularly limited. In particular, the auto tensioner 5 according to the present invention can be suitably applied to meshing transmission belts.

[0096] In the above embodiment, the first tension roller 51 and the second tension roller 52 are provided on the driven pulley 3 side, but they may also be provided on the drive pulley 2 side. Here, the provision of the first tension roller 51 and the second tension roller 52 on the driven pulley 3 side means that the intersection point of the roller centerline RL and the pulley centerline PL is on the driven pulley 3 side of the center of the pulley centerline PL.

[0097] In the above embodiment, the central axis R of the oscillating shaft 53 is configured to pass through a point on the pulley centerline PL, which is spaced apart from the intersection of the roller centerline PL (which connects the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52) toward the drive pulley 2, and extends in a direction parallel to the drive shaft 21. However, the central axis R of the oscillating shaft 53 may be configured to pass through a point on the extension of the pulley center line PL, spaced apart on the drive pulley 2 side from the intersection of the roller center line RL, which connects the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52, and the pulley center line PL. Specifically, the drive shaft 21 may be positioned between the first tension roller 51 and the second tension roller 52, which are the two tension rollers of the auto tensioner 5, and the oscillating shaft 53.

[0098] Furthermore, the central axis R of the oscillating shaft 53 may be a point on the pulley centerline PL, spaced apart toward the drive pulley 2 from the intersection of the roller centerline PL, which connects the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52, and the oscillating shaft R may pass through the rotation center 22 of the drive pulley 2, which is the central axis of the drive shaft 21, and extend in a direction parallel to the drive shaft 21, that is, the drive shaft 21 may also serve as the oscillating shaft 53. In this case, the first oscillating arm 56 and the second oscillating arm 57 will be rotatably supported on the drive shaft 21, which simplifies the belt transmission mechanism 1, that is, reduces the number of parts and improves ease of assembly.

[0099] In the above embodiment, the auto tensioner 5 has the first tension roller 51 and the second tension roller 52 positioned on the driven pulley 3 side and the spring 54 positioned on the drive pulley 2 side. However, the first tension roller 51 and the second tension roller 52 may be positioned on the drive pulley 2 side and the spring 54 may be positioned on the driven pulley 3 side.

[0100] In the above embodiment, the belt transmission mechanism according to the present invention was described as a belt transmission mechanism for driving a robot arm, but it is not limited to this. For example, the belt transmission mechanism according to the present invention can be applied to belt transmission mechanisms in injection molding machines and other general industrial equipment and devices. An injection molding machine is a belt transmission mechanism section in which each operating part, such as injection, metering, and mold opening / closing, is electrically driven by an independent motor. [Examples]

[0101] In the auto tensioner and belt transmission mechanism of the present invention, it is necessary to eliminate the need for aging and achieve good responsiveness regardless of the pulley layout. Aging, as described above, refers to the tension adjustment work performed by readjusting the belt tension by adjusting the distance between shafts, etc., after the break-in period which is dry running.

[0102] Therefore, in this embodiment, belt transmission mechanisms equipped with auto tensioners according to the embodiment and comparative example (hereinafter referred to as "each test specimen") were fabricated, and a comparative verification of their tension application performance was performed. The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0103] [Belt transmission mechanism] The comparative example belt drive mechanism (see Figure 7) has a configuration similar to that of Example 1 of Patent Document 1, in which the spring of the auto tensioner is stretched between two tension rollers, and the length of the spring (spring length) and the distance between the centers of the two tension rollers (hereinafter abbreviated as "roller center distance") are the same. In the belt drive mechanism of this embodiment (see Figure 2), the spring of the auto tensioner is stretched on the opposite side of the pivot axis from the two tension rollers, and the spring and the two tension rollers are connected via two pivot arms, so that the length of the spring is greater than the distance between the centers of the two tension rollers.

[0104] [Toothed belt: Figure 6] (Toothed belt A) • Tooth shape: The tooth shape was determined to be an H-shaped tooth (with a roughly semi-circular cross-section), which belongs to the category of straight teeth. • Number of teeth: 200 • Tooth pitch: 3mm Belt length: 600mm • Belt width: 10mm (Toothed belt B) Except for changing the number of teeth to 179 and the belt length to 537 mm, the configuration was the same as toothed belt A.

[0105] [Materials used in toothed belts] (Core wire) • Construction: A twisted cord with the configuration shown in Table 2 was fabricated. The core stranded cord was created using the following procedure. Three strands of glass fiber (E-glass fiber) filaments (9 micron diameter) designated as ECG-150, as described in JIS R 3413 (2012), were bundled and aligned. These three strands were immersed in an RFL solution with the composition shown in Table 3 at 18-23°C for 3 seconds, and then heated and dried at 200-280°C for 3 minutes to form a uniform adhesive layer on the surface. After this bonding treatment, the three strands were under-twisted 12 times / 10 cm, without any over-twisting, to prepare a single-strand twisted cord with a diameter of approximately 0.35 mm.

[0106] [Table 2]

[0107] (Elastic modulus of the core wire) Here, we will explain the method for measuring the elastic modulus of the core wire, that is, the tensile elastic modulus in the longitudinal direction of the core wire, as shown in Table 2. A chuck (gripping device) is attached to the lower fixing part and the upper load cell connection part of the autograph ("AGS-J10kN" manufactured by Shimadzu Corporation), and both ends of the core wire are gripped with the chuck. Next, in the stress-strain curve measured when the core wire was pulled at a speed of 250 mm / min until it broke, the slope of the line in the region of 100-200 N, which is a relatively linear relationship, was calculated as the tensile modulus of the core wire.

[0108] (Tooth cloth) The teeth of the toothed belt are made of a twill weave fabric, with the warp threads of the fabric positioned to extend in the direction of the belt width and the weft threads in the direction of the belt length. The weft of the woven fabric was made of elastic 66 nylon yarn (woolly processed yarn), and the warp was made of 66 nylon yarn. The fineness of the yarns was 44 dtex for both the weft and warp. The tooth fabric with the above configuration was then subjected to RFL treatment with the RFL treatment solution shown in Table 3. Subsequently, the same rubber composition as the unvulcanized rubber sheet shown in Table 4 was bonded using rubber glue dissolved in toluene, and then a rubber composition sheet with the composition shown in Table 4 was laminated and coated.

[0109] [Table 3]

[0110] (Rubber composition) The rubber composition shown in Table 4 [rubber component: chloroprene rubber (CR)] was mixed in a Banbury mixer, and this mixed rubber was passed through a calender roll to produce a rolled rubber sheet of a predetermined thickness. Unvulcanized rubber sheets for forming the back and teeth of each toothed belt of each specimen were then prepared. The hardness of the vulcanized rubber sheet obtained by press-vulcanizing the prepared rubber composition, an unvulcanized rubber sheet, at 165°C for 30 minutes was approximately 81, measured using a Type A durometer at an ambient temperature of 23°C (23±2°C) in accordance with JIS K 6253 (2012). • The ingredients marked with an asterisk (*) in Table 4 are as follows:

[0111] [Table 4] *1 Denka's "PM-40" *2 "Nocrack MB" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *3 "N-cyclohexyl-2-benzothiazole sulfenamide" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *4 Tokai Carbon Co., Ltd.'s "Seast 3" *5 "Zinc Oxide 3 Types" manufactured by Seido Chemical Industry Co., Ltd.

[0112] [Manufacturing of toothed belts] Using the core wire (adhesive-treated), tooth cloth (adhesive-treated), and rubber composition (unvulcanized rubber sheet) described above, toothed belts were fabricated for each test specimen using the conventional press-fitting method described in the above embodiment. Vulcanization was performed at 161°C for 25 minutes. In order to configure the back portion to a predetermined thickness, the back portion of the belt sleeve obtained after vulcanization was polished to a certain thickness, then cut to a certain width to obtain toothed belts for each test specimen. Since the toothed belts were manufactured using a standard press-fitting method, the back and teeth are made of the same rubber composition. Therefore, in each toothed belt, the hardness of the rubber composition constituting the back and the hardness of the rubber composition constituting the teeth are approximately the same.

[0113] [Pulley layout] The belt transmission mechanisms in both the examples and comparative examples all feature a two-axis layout with straight-toothed pulleys for both the drive pulley and the driven pulley, and are equipped with a load cell, which is an axial load sensor that can be connected to the rotating shaft of the drive pulley.

[0114] (Pulley layout A) • Number of teeth on the drive pulley / pulley diameter: 21 teeth / 20.054 mm • Driven pulley teeth count / pulley diameter: 84 teeth / 80.216 mm • Reduction ratio: 4. In other words, the driven pulley has a pitch diameter four times larger than the drive pulley. • Belt mounting tension: The required belt mounting tension level was set at 5 N / mm width, or approximately 5 N per 1 mm of belt width. In this specification, the pulley diameter is assumed to be the core wire line. Furthermore, the belt tension measured in a stationary state after a break-in run (no load) immediately before actual operation is treated as the "belt mounting tension". The belt mounting tension was calculated from the axial load detected by a load cell, which is an axial load sensor connected to the rotating shaft of the drive pulley. The distance between the drive pulley and the driven pulley was set to 220 mm as the standard value.

[0115] (Pulley layout B) The configuration was the same as pulley layout A, except that the driven pulley had 42 teeth / 40.108 mm in diameter and the reduction ratio was set to 2.

[0116] [Auto Tensioner] (Comparative example) The configuration is similar to Embodiment 1 of Patent Document 1, and as shown in Figure 7, the spring of the auto tensioner is stretched between two tension rollers, and the spring length and the distance between the roller centers are the same. (Examples) As shown in Figure 2, the spring of the auto tensioner is tensioned on the opposite side of the tension roller from the pivot axis, and the spring and tension roller are connected via a pivot arm, resulting in a configuration where the spring length is greater than the distance between the roller centers.

[0117] [Evaluation of Belt Transmission Mechanisms: Items, Methods, Criteria] For each test specimen (example, comparative example), in order to determine whether a belt transmission mechanism capable of solving the problem of the present invention was obtained, a layout in which toothed belt A was mounted on pulley layout A was designated as condition A, and a layout in which toothed belt B was mounted on pulley layout B was designated as condition B. For each condition, the tension application performance was verified as the ability to automatically adjust or automatically correct the decrease in tension at the beginning of belt travel, and the responsiveness was verified as the responsiveness to drive during forward and reverse switching.

[0118] [Tension-applying performance] (Method, criteria) If the specified belt mounting tension (approximately 5 N / mm width) could be secured without aging, it was evaluated as being able to automatically adjust (correct) the tension drop during the initial stages of belt operation, and was given an "a" rating. If aging was necessary to ensure the specified belt mounting tension (approximately 5 N / mm width), it was evaluated that the system could not automatically adjust for the initial tension drop during belt operation, resulting in a rating of "b," and subsequent responsiveness tests were postponed. From the perspective of suitability based on tension application performance for actual use in this application, belt transmission mechanisms with a rating of A were deemed to be at an acceptable level.

[0119] [Responsiveness] (Test name) Responsiveness Test (Test machine) A responsiveness evaluation tester was used for the test (see Figure 8). The test machine is configured to detect the time-series change in the rotation angle difference during operation by running a toothed belt, which is wrapped between two pulleys, in a cycle pattern involving frequent forward and reverse rotations, and outputting rotation pulse signals from a pair of rotary encoders (rotation angle detectors) attached to each shaft. The rotation angle difference is defined as the rotation angle of the drive shaft minus the rotation angle of the driven shaft. The pulley layout is the same as that of the belt drive mechanism described above (Figure 2). In other words, the pulley layout of the test machine consists of a drive pulley and a driven pulley, with the distance between the shafts fixed at 220 mm. Furthermore, a flywheel was attached to the driven side to enable the application of a predetermined load torque, as intended for use in driving a robot arm. Furthermore, considering its intended application as a robot arm drive, a pair of rotary encoders (CANON R-1L) with an angular resolution of 0.0044°, which is excellent for detecting the rotation angle of both the drive pulley and the driven pulley with high precision, were used.

[0120] (Test method) Under normal temperature conditions, a toothed belt, wrapped between pulleys with a fixed distance between shafts and a belt mounting tension of approximately 5 N / mm width, was run under the test conditions shown in Table 5, with only the rotational speed of the drive pulleys being varied, and in a cycle pattern as shown in Figure 9, repeating frequent forward and reverse rotations for 250 cycles. From the resulting time-series graph of the rotational angle difference (not shown), the level of the rotational angle difference (maximum absolute value) was read as a test result for each varied rotational speed of the drive pulleys (1, 2, 5 rps). Furthermore, the rotational angle difference, when viewed over time, experiences overshoot and undershoot during forward / reverse switching, i.e., during forward / reverse starting (acceleration) and stopping (deceleration). Therefore, its absolute value is maximum during forward / reverse switching. The frequency of forward / reverse switching is four times per cycle. The acceleration / deceleration during forward / reverse switching corresponding to each rotational speed of the drive pulley are shown in Table 6.

[0121] [Table 5]

[0122] (Judgment criteria) For this application, the most important aspect of a belt drive mechanism is responsiveness during forward / reverse switching. To determine this responsiveness, the difference in rotational angle between the drive pulley and the driven pulley during forward / reverse switching is used as an indicator. A smaller absolute value indicates higher responsiveness, allowing for repeated positioning accuracy and reliable synchronous transmission. If the absolute value of the difference in rotational angle of the drive pulley for each rotational speed is consistently within 0.2°, it is classified as "a," and if it exceeds 0.2° even once, it is classified as "b." From the perspective of appropriate responsiveness for actual use in this application, a belt transmission mechanism with a rating of A was deemed to be at an acceptable level.

[0123] [Overall assessment] The criteria for ranking belt transmission mechanisms that can solve this problem based on an overall assessment are as follows: Based on the results of the evaluation of the two test items mentioned above, tension application performance and responsiveness, the following conclusions were reached. Rank A: If both the tension application performance and responsiveness evaluations above received an "a" rating, the solution was deemed satisfactory and passed the test. Rank B: If even one of the evaluations of tension application performance and responsiveness was rated as "b," the solution was deemed insufficient and therefore failed.

[0124] [Verification Results and Discussion] The verification results are shown in Table 6. [Table 6]

[0125] (Comparison of modified auto-tensioner configurations: Examples, comparative examples) In a comparative example where the auto tensioner spring is stretched between two tension rollers and the spring length matches the distance between the roller centers, layout A achieved an 'a' rating for both tension application performance and responsiveness. However, in layout B, the reduced distance between the roller centers prevented sufficient expansion and contraction of the spring, resulting in insufficient biasing action from the spring to apply tension to the toothed belt. Consequently, after a break-in period without load, it was not possible to secure a belt mounting tension of approximately 5 N / mm width, resulting in a 'b' rating for tension application performance and an overall rank of B. In an embodiment where the auto tensioner spring is tensioned on the opposite side of the oscillating axis from the tension roller, and the spring length is greater than the distance between the roller centers, sufficient expansion and contraction of the spring can be ensured even when the distance between the roller centers is small, and the biasing effect of the spring that applies tension to the toothed belt can be elicited. Therefore, regardless of the pulley layout, the tension application performance was judged as "a" under both conditions A and B, and sufficient responsiveness to the drive during forward and reverse switching was also ensured, resulting in a "a" rating in the responsiveness evaluation as well, and an overall rank of A.

[0126] (Effects obtained) From the verification results above, it can be seen that in the belt transmission mechanism of the embodiment, the spring of the auto tensioner is stretched on the opposite side of the tension roller from the oscillating axis, and the spring length is greater than the distance between the roller centers. This addresses the problem, and even without regard to the pulley layout, sufficient expansion and contraction range of the auto tensioner spring can be secured, and sufficient tension-applying performance of the auto tensioner that applies tension to the toothed belt can be obtained. As a result, it can be seen that a belt transmission mechanism with no aging requirement and excellent responsiveness can be obtained. [Explanation of Symbols]

[0127] 1. Belt transmission mechanism 2 Drive pulley 3. Driven pulley 4 Toothed belt 5 Auto Tensioner 51. First Tension Roller 52 Second Tension Roller 53. Oscillating axis 54 springs 56 First oscillating arm 561 One end 562 Other end 57 Second oscillating arm 571 One end 572 Other end R: The central axis (intersection) of the oscillation axis. PL pulley centerline RL roller centerline SL spring axis

Claims

1. An auto tensioner that automatically adjusts the tension of a belt via two tension rollers that contact the belt wrapped between a drive pulley and a driven pulley, A first swing arm and a second swing arm are configured to swing freely around a pivot axis and are positioned to intersect with the pivot axis as an intersection point. A first tension roller, which is one of the two tension rollers, is provided at one end of the first swing arm so as to contact the belt, A second tension roller, which is the other of the two tension rollers, is provided at one end of the second swing arm so as to contact the belt, A spring is provided between the other end of the first swing arm, which is on the opposite side of one end of the first swing arm with respect to the swing axis, and the other end of the second swing arm, which is on the opposite side of one end of the second swing arm with respect to the swing axis, and is configured to be expandable and contractible so as to bias the other end of the first swing arm and the other end of the second swing arm in a direction that pulls them together or in a direction that separates them from each other. An auto-tensioner characterized by having the following features.

2. Viewed in the direction of the axis of the aforementioned pivot shaft, The auto tensioner according to claim 1, characterized in that the length of the spring is greater than the distance between the rotation center of the first tension roller and the rotation center of the second tension roller.

3. Viewed in the direction of the axis of the aforementioned pivot shaft, The distance between the other end of the first swing arm and the intersection is greater than the distance between the intersection and one end of the first swing arm. The auto tensioner according to claim 1, characterized in that the distance between the other end of the second swing arm and the intersection is greater than the distance between the intersection and one end of the second swing arm.

4. Viewed in the direction of the axis of the aforementioned pivot shaft, The distance between the other end of the first swing arm and the intersection is the same as the distance between the other end of the second swing arm and the intersection. The auto tensioner according to any one of claims 1 to 3, characterized in that the distance between the intersection and one end of the first swing arm is the same as the distance between the intersection and one end of the second swing arm.

5. The spring is a tension spring that biases the other end of the first swing arm and the other end of the second swing arm in a direction that pulls them together. The auto tensioner according to any one of claims 1 to 4, wherein the first tension roller and the second tension roller are provided so as to be in contact with the outer circumferential surface of the belt.

6. The drive pulley is fixed to a drive shaft that is driven by a drive source so as to be able to rotate in both forward and reverse directions, The driven pulley is rotatably supported on the driven shaft, The belt is wrapped around the drive pulley and the driven pulley, An auto tensioner according to any one of claims 1 to 5, A belt transmission mechanism characterized by having the following features.

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