Belt transmission mechanism

Abstract

The present invention pertains to a belt transmission mechanism comprising: a drive pulley which is fixed to a drive shaft driven by a drive source so as to be rotatable forward and backward; a driven pulley which is supported rotatably; a toothed belt which is wound around the drive pulley and the driven pulley; and an auto tensioner which automatically and moderately maintains the tension of the toothed belt through two tension rollers that are provided rotatably about respective base shaft parts at positions on both sides of a pulley center line connecting the center of rotation of the drive pulley and the center of rotation of the driven pulley, and that are in contact with the toothed belt. The belt transmission mechanism is characterized in that: the auto tensioner has a swing shaft provided so as to extend in the direction parallel to the drive shaft, through a point which is separated from an intersection point between the pulley center line and a roller center line connecting the rotation centers of the two tension rollers and which is on the pulley center line or a point on an extension line of the pulley center line, and has a spring for biasing the two tension rollers in a direction of being pulled to each other or in a direction of being separated from each other; and the two tension rollers are configured to swing freely about the swing shaft. The belt transmission mechanism is also characterized: by further comprising a regulation means for regulating the swings of the two tension rollers; and in that the regulation means is positioned to regulate the swinging of the two tension rollers about the swing shaft in a direction reverse to the biasing direction of the spring from the balanced position in which the driving pulley and the driven pulley are in a suspended state.

Description

Belt transmission mechanism

[0001] The present invention relates to a belt transmission mechanism that is incorporated into the arm of an industrial robot or the like and is equipped with an auto-tensioner that automatically maintains an appropriate tension in the toothed belt when transmitting the rotational force of a drive pulley to a driven pulley via the toothed belt.

[0002] In recent years, industrial robots such as vertical articulated robots and horizontal articulated robots (SCARA robots) have been widely used in automobile manufacturing, semiconductor manufacturing, smartphone manufacturing, etc. For driving the arms and wrists of industrial robots (hereinafter referred to as "robot arm drives"), toothed belt drives (hereinafter referred to as "robot arm drive belt transmission mechanisms") are increasingly being adopted instead of gear drives in order to achieve smaller size, higher speed, and lighter weight.

[0003] Belt transmission mechanisms without an auto-tensioner typically require a toothed belt (hereinafter simply referred to as "belt") to be installed and then run idle (break-in) to adjust (correct) any loss of belt tension that occurs during initial operation (running). However, due to the structure and manufacturing process, belt transmission mechanisms for driving robot arms cannot be run idle simply by installing a toothed belt on the pulleys inside the robot arm. Therefore, after the robot is assembled, a tension adjustment process called "wearing" is performed by running the belt idle. This requires several hours of work to properly control the robot, including adjusting the gap (center distance) between the drive pulley and driven pulley (tension adjustment work) and retightening bolts, resulting in significant loss costs.

[0004] Furthermore, because the drive of a robot arm involves frequent forward and reverse rotation (the tight and slack sides of the belt are reversed with each forward and reverse rotation), excessive tension is likely to act on the tight side of the belt when switching between forward and reverse (when starting and stopping the forward and reverse directions), and slack is likely to occur on the slack side of the belt. If the belt becomes overtensioned or the slack becomes large in this way, synchronous transmission becomes uncertain (the difference in rotation angle between the drive pulley and driven pulley becomes large), making it impossible to accurately move the arm, wrist, etc. to the specified position (affecting the positioning accuracy of the arm, etc.).

[0005] Furthermore, in a belt transmission mechanism in which the spacing between pulleys is narrow and the reduction ratio (ratio of pulley diameters) is large, the contact angle of the belt on the smaller diameter drive pulley becomes small, and if the belt is loose, there is a concern that the belt may be more susceptible to tooth skipping.

[0006] In order to address the above issues in synchronous (meshing) transmission using toothed belts, it is necessary, in principle, to automatically maintain the belt tension at a moderate level (to the extent that the belt does not slacken) (including adjusting for the drop in tension that occurs at the beginning of running).

[0007] Specifically, in a belt transmission mechanism for driving a robot arm using a toothed belt, even if the tight and slack sides of the belt are reversed with each forward and reverse rotation, the tight side of the belt does not need to have a very high tension at startup (as in the case of friction transmission), so it is necessary to keep tension fluctuations low without applying a damping force, while on the slack side of the belt, it is necessary to prevent slack in the belt (as in the case of friction transmission).

[0008] To achieve this, it is conceivable to adopt a belt transmission mechanism for driving a robot arm that is equipped with an auto-tensioner that can automatically and appropriately maintain belt tension (to the extent that the belt does not become loose) (including adjusting for the decrease in tension that occurs at the beginning of travel) even if the tight and loose sides of the belt reverse with each forward and reverse rotation, by bringing two tension rollers, each rotatably mounted on either side of the pulley center line connecting the rotation centers of the drive pulley and driven pulley, into contact with the belt (its outer or inner surface) with an appropriate biasing action such as a spring.

[0009] (Prior Art) For example, Patent Document 1 discloses an auto-tensioner provided in a belt transmission mechanism for driving a robot arm, in which two support arms 18A, 18B (members connecting the base shaft of the tension roller to the swing shaft) each having a tension roller at its tip are provided so as to be able to swing independently, and a spring is stretched between the support arms (see FIG. 2 of Patent Document 1).

[0010] According to this, by bringing two tension rollers, which are freely rotatable on either side of the pulley center line connecting the rotation centers of the drive pulley and the driven pulley, into contact with the belt with an appropriate biasing action from a spring or the like, it appears possible to automatically and appropriately maintain the tension of the belt even if the tight and loose sides of the belt are reversed with each forward and reverse rotation.

[0011] Japan Utility Model Publication No. 2-110494

[0012] However, according to the configuration of Patent Document 1, when the load on the driven pulley increases (for example, when the load torque on the driven pulley increases from about 1 N·m to about 3 N·m in a belt transmission mechanism for driving a robot arm), the moment of inertia of the driven pulley also increases. As a result, the driven pulley cannot stop quickly immediately after the drive pulley stops when switching between forward and reverse (when forward and reverse are stopped), and the time (damping time) from when the drive pulley stops to when the driven pulley stops when switching between forward and reverse (when forward and reverse are stopped) becomes long. In other words, there is a concern that the "damping characteristic" of the driven pulley will deteriorate when switching between forward and reverse (when forward and reverse are stopped).

[0013] This is because the belt tension is kept relatively low (low enough that the belt does not become loose), and the two tension rollers are configured to be able to swing freely around the swing axis, so the biasing force of the springs, etc. is set relatively weak. As a result, compared to when the load on the driven pulley (and therefore the moment of inertia of the driven pulley) is not very large (for example, when the load torque of the driven pulley in a belt transmission mechanism for driving a robot arm is about 1 N-m), the tension of the toothed belt increases on the tight side of the toothed belt and decreases on the slack side of the toothed belt (the toothed belt becomes too loose) immediately after the drive pulley stops when switching between forward and reverse (when forward and reverse stops). For this reason, immediately after the drive pulley stops, the two tension rollers connected (biased) by springs are unable to quickly displace (converge) to the balanced position (the state shown in Figure 9 described below), that is, the belt position where the tight side of the toothed belt reaches a state of tension, and the belt position where the slack side of the toothed belt is eliminated. Instead, both tension rollers repeatedly oscillate in short forward and reverse directions around the oscillation axis for a while, with the tight side and slack side of the toothed belt frequently alternating. In conjunction with this, as shown in the circled area in Figure 16 (a graph showing the time-series changes in the rotation speed of the drive pulley and the driven pulley when switching between forward and reverse directions (when starting / stopping forward and reverse directions)), the driven pulley also repeatedly rotates in short forward and reverse directions after overshooting or undershooting.

[0014] For this reason, in a belt transmission mechanism, in order to repeatedly ensure positioning accuracy (ensuring synchronous transmission) even when the load on the driven pulley (for example, the mass of an object driven by a robot arm) increases, it is important to "ensure a high level of damping of the driven pulley when switching between forward and reverse (when the forward and reverse are stopped) [and further, to ensure a high level of responsiveness to drive when switching between forward and reverse (in other words, to sufficiently suppress the difference in rotation angle between the drive pulley and driven pulley when switching between forward and reverse)]."

[0015] This is particularly important in belt transmission mechanisms, such as those for driving robot arms, where the speed of operations involving forward and reverse rotation is increasing dramatically compared to the past due to dramatically increased demands for improved productivity in automobile manufacturing, semiconductor manufacturing, smartphone manufacturing, and other industries.

[0016] In response to this issue, it is important to avoid simply increasing the biasing force of springs or the like, which would make it impossible to maintain an appropriate belt tension (enough to prevent the belt from loosening) (i.e., the belt tension would become excessive).

[0017] Therefore, an object of the present invention is to provide a belt transmission mechanism that can reliably perform synchronous transmission even when the load on the driven pulley increases.

[0018] The present invention provides a belt transmission mechanism having: a drive pulley fixed to a drive shaft that is driven by a drive source to be rotatable in both directions; a rotatably supported driven pulley; a toothed belt wound between the drive pulley and the driven pulley; and auto-tensioners that are rotatable about their respective base shafts at positions on either side of a pulley center line connecting the rotation centers of the drive pulley and the driven pulley, and that automatically maintain an appropriate tension in the toothed belt via two tension rollers that contact the toothed belt, wherein the auto-tensioner comprises: a swing shaft that is disposed so as to extend in a direction parallel to the drive shaft and that passes through a point on the pulley center line or a point on an extension of the pulley center line, spaced from the intersection of the pulley center line and a roller center line connecting the rotation centers of the two tension rollers; and a spring that biases the two tension rollers in a direction that draws them together or moves them away from each other; The two tension rollers are configured to be freely oscillating around the oscillating shaft, and the belt transmission mechanism further includes a regulating means for regulating the oscillation of the two tension rollers, and the regulating means is located at a position that regulates the two tension rollers from oscillating around the oscillating shaft from a balanced position in which the drive pulley and the driven pulley are stopped in a direction opposite to the biasing direction of the spring.

[0019] With the above-described restricting means, in the autotensioner, the two tension rollers cannot oscillate around the oscillating axis from a balanced position, in which the drive pulley and driven pulley are stationary, in a direction opposite to the spring biasing direction (for example, in the direction that would move the two tension rollers away from each other if the springs are tension springs), but can oscillate only in the spring biasing direction. Therefore, in a belt transmission mechanism that includes an auto-tensioner in which the spring force is set to be relatively weak and two tension rollers are configured to oscillate around an oscillating axis and that is configured to keep the tension of the toothed belt relatively low (low enough that the toothed belt does not become loose), even if the load on the driven pulley (and therefore the moment of inertia of the driven pulley) increases, even if the tension of the toothed belt increases on the tight side of the toothed belt and decreases on the slack side of the toothed belt (even if the toothed belt becomes too loose) immediately after the drive pulley stops during forward / reverse switching (when forward / reverse rotation is stopped), the tension roller located on the tight side of the toothed belt can be prevented from being pushed by the toothed belt and displacing (oscillating around the oscillating axis) toward the tight side of the toothed belt.

[0020] As a result, the tension roller located on the tight side of the toothed belt can be prevented from swinging around the swing axis together with the two tension rollers connected (biased) by the spring in the direction of displacement toward the tight side of the toothed belt. In addition, the addition of the regulating means prevents the tension roller located on the tight side from displacing toward the tight side, so that the amount of displacement from the neutral position of the tension roller located on the slack side to a position where the belt slack can be eliminated is small compared to a configuration in which the regulating means is not added. Therefore, even if the spring biasing force is set relatively weak so that the tension of the toothed belt is kept relatively low, the tension roller located on the slack side of the toothed belt can be quickly displaced (swinged around the swing axis) to a position where the toothed belt slack can be eliminated while being biased by the spring in the direction of eliminating the slack of the toothed belt (spring biasing direction). Therefore, with this configuration, in the belt transmission mechanism, even if the load on the driven pulley increases, immediately after the drive pulley stops when switching between forward and reverse (when forward and reverse are stopped), the two tension rollers will repeatedly oscillate forward and reverse in small increments for a while around the oscillating axis, with the tight and slack sides of the toothed belt alternating in small increments, and the driven pulley will also be prevented from overshooting or undershooting and then repeatedly rotating forward and reverse in small increments.

[0021] In other words, this configuration ensures a high level of damping of the driven pulley when switching between forward and reverse (when forward and reverse are stopped) [and thus ensures a high level of responsiveness to drive when switching between forward and reverse (i.e., sufficiently suppresses the difference in rotation angle between the drive pulley and driven pulley when switching between forward and reverse)]. In other words, this configuration ensures the positioning accuracy of the belt transmission mechanism repeatedly (ensuring synchronous transmission) even if the load on the driven pulley increases.

[0022] Furthermore, in the above-described belt transmission mechanism, the present invention may be characterized in that the autotensioner has: a first swing arm having one end provided with the base shaft portion of one of the tension rollers and the other end supported rotatably on the swing shaft; and a second swing arm having one end provided with the base shaft portion of the other tension roller and the other end supported rotatably on the swing shaft; the two tension rollers are configured to swing about the swing shaft via the first swing arm and the second swing arm; and the regulating means is provided in a position where it can come into contact with the first swing arm and the second swing arm.

[0023] According to the above configuration, each of the two oscillating arms (first oscillating arm and second oscillating arm), which have the base shafts of the two tension rollers biased by springs at one end (tip end), is freely rotatable around the oscillating axis, so that the two tension rollers oscillate around the oscillating axis in addition to the biasing action of the springs, and the regulating means specifically regulates the two tension rollers from swinging around the oscillating axis in the direction opposite to the biasing direction of the springs from the balanced position in which the drive pulley and driven pulley are stopped.

[0024] Furthermore, in the belt transmission mechanism of the present invention, the spring may be stretched on the roller center line between the base shaft portions of the two tension rollers and bias the two tension rollers.

[0025] Compared to a configuration in which a spring is not tensioned between the base shafts of the two tension rollers, the above configuration makes it easier to apply the spring's biasing force responsively in a direction (spring biasing direction) that eliminates slack in the toothed belt, for example, to the point of contact (point of application) between the tension roller and the toothed belt on the slack side of the toothed belt. This further improves the responsiveness (operating speed) of the two tension rollers to the drive pulley. Furthermore, this configuration (spring tensioning structure) can be formed relatively simply.

[0026] In the belt transmission mechanism of the present invention, the swing shaft may be spaced away from the intersection of the roller center line and the pulley center line toward the driven pulley.

[0027] According to the above configuration, the drive pulley, two tension rollers, swing shaft, and driven pulley can be arranged in this order. In this case, it is easier to set the tension of the toothed belt low compared to when the order is drive pulley, swing shaft, two tension rollers, and driven pulley, which makes it easier to ensure the ease of wearing the toothed belt, the synchronous power transmission performance of the toothed belt, and the tooth skip resistance of the toothed belt.

[0028] In addition, in the above-mentioned belt transmission mechanism, the present invention may be characterized in that the two tension rollers are provided on the drive pulley side or on the side of the pulley having a smaller diameter out of the drive pulley and the driven pulley.

[0029] In a belt transmission mechanism, the diameter of the drive pulley is generally smaller than that of the driven pulley (when the mechanism functions as a so-called speed reduction mechanism) to ensure that the rotational torque of the driven pulley is at a predetermined level, but the diameters of the drive pulley and the driven pulley may also be the same. For example, in a belt transmission mechanism in which the distance between the pulleys is narrow and the reduction ratio (ratio of pulley diameters) is large, there is a concern that the contact angle of the toothed belt at the drive pulley on the smaller diameter side becomes small, and if the toothed belt is loose, tooth jumping of the toothed belt is more likely to occur. However, with this configuration, the contact angle of the toothed belt at the drive pulley (including when the drive pulley and the driven pulley have the same diameter) or at the pulley on the smaller diameter side (regardless of whether it is a drive pulley or a driven pulley) can be prevented from becoming small, thereby making tooth jumping of the toothed belt less likely to occur.

[0030] Furthermore, in the belt transmission mechanism of the present invention, the spring may be a tension spring, and the two tension rollers may be provided so as to contact an outer peripheral surface of the toothed belt.

[0031] According to the above configuration, both sides of the belt (tight side and slack side) are sandwiched between two tension rollers by the biasing action of a single spring (tension spring). Therefore, compared to a configuration in which the spring is a compression spring and two tension rollers are provided to contact the inner circumferential surface of the toothed belt (a configuration in which both sides of the belt are pushed apart by two tension rollers by the biasing action of a single compression spring), the contact angle of the belt (the central angle with respect to the arc where the belt and pulley are in contact) is larger, thereby making it possible to suppress belt tooth jumping.

[0032] In the belt transmission mechanism of the present invention, the diameter of the drive pulley may be smaller than the diameter of the driven pulley.

[0033] With the above configuration (i.e., when the belt transmission mechanism is a reduction mechanism), the degree of displacement caused by the two tension rollers swinging about the swing shaft during forward / reverse switching is greater than when the diameter of the drive pulley is the same as that of the driven pulley. Therefore, compared to a configuration in which the two tension rollers cannot swing about the swing shaft (i.e., a configuration in which only the spring biasing force acts on the two tension rollers) and the two tension rollers can only be displaced in a direction perpendicular to the pulley center line when viewed parallel to the drive shaft, this configuration allows one of the tension rollers on the tension side of the belt to swing about the swing shaft while suppressing spring damping (displacement in a direction against the spring biasing force), thereby enhancing the effect of enabling quick displacement. This ultimately ensures a higher level of responsiveness to drive during forward / reverse switching (starting / stopping forward / reverse) in the belt transmission mechanism.

[0034] Furthermore, in the belt transmission mechanism of the present invention, the driving pulley and the driven pulley may be fixed to a robot arm and drive the robot arm.

[0035] According to the above configuration, when driving the robot arm, even if the load on the driven pulley increases in the belt transmission mechanism, a high level of damping of the driven pulley can be ensured when switching between forward and reverse (when forward and reverse are stopped), and the positioning accuracy of the robot arm can be repeatedly ensured (in other words, the magnitude of the difference in rotation angle between the drive pulley and driven pulley can always be kept within an allowable range), ensuring synchronous transmission.

[0036] It is possible to provide a belt transmission mechanism that can ensure synchronous transmission even when the load on the driven pulley increases.

[0037] 2 is an explanatory diagram of a robot arm drive belt transmission mechanism according to the present embodiment, which is incorporated into the robot arm of a horizontal articulated robot. FIG. 3 is a plan view of the robot arm drive belt transmission mechanism according to the present embodiment (a diagram illustrating a state in which the drive pulley is stopped). FIG. 4 is a cross-sectional view / left side view taken along line A-A of FIG. 2. FIG. 5 is a cross-sectional view taken along line B-B of FIG. 2. FIG. 6 is a plan view of the robot arm drive belt transmission mechanism according to the present embodiment (a diagram illustrating the operating state of an auto-tensioner when switching forward and reverse (at startup)). FIG. 7 is a plan view of the robot arm drive belt transmission mechanism according to the present embodiment (a diagram illustrating the operating state of an auto-tensioner when switching forward and reverse (at shutdown)). FIG. 8 is a plan view of the robot arm drive belt transmission mechanism according to Comparative Example 1 (a diagram illustrating a state in which the drive pulley is stopped). FIG. 9 is a plan view of the robot arm drive belt transmission mechanism according to Comparative Example 1 (a diagram illustrating the operating state of the auto-tensioner when switching forward and reverse (at startup)). FIG. 10 is a plan view of the robot arm drive belt transmission mechanism according to Comparative Example 1 (a diagram illustrating the operating state of the auto-tensioner when switching forward and reverse (at shutdown)). 18 is a plan view of a belt transmission mechanism for driving a robot arm according to Example 2 (a view illustrating a state in which the drive pulley is stopped). FIG. 19 is a plan view of a belt transmission mechanism for driving a robot arm according to another embodiment ... using a pin as a regulating means. FIG. 20 is a cross-sectional perspective view of a toothed belt according to the present embodiment. FIG. 21 is an explanatory diagram of a responsiveness evaluation tester used in the evaluation of the examples (damping and responsiveness tests). FIG. 22 is an explanatory diagram of a test pattern (cycle pattern) for the responsiveness test used in the evaluation of the examples (damping and responsiveness tests). FIG. 23 is a graph of time series changes in the rotation speed of a drive pulley and the rotation speed of a driven pulley when switching between forward and reverse (when starting / stopping forward and reverse) in a conventional (comparative) belt transmission mechanism. FIG. 24 is a graph of time series changes in the rotation speed of a drive pulley and the rotation speed of a driven pulley when switching between forward and reverse (when starting / stopping forward and reverse) in a belt transmission mechanism of the present embodiment. FIG. 25 is a plan view and a side view of a regulating member according to the present embodiment. FIG. 26 is a cross-sectional view of the regulating member shown in FIG. 25, and a front view of the regulating member shown in FIG.

[0038] (Embodiment) This embodiment is an example in which the present invention is applied to a belt transmission mechanism 1 for driving a robot arm (hereinafter, may be simply referred to as "belt transmission mechanism 1") that is incorporated into a second arm 11 of a horizontally articulated robot 10 (industrial robot) known as a SCARA robot, and that is equipped with an auto-tensioner 5 for automatically maintaining an appropriate tension in the toothed belt 4 when transmitting the rotational force of the drive pulley 2 to the driven pulley 3 via the toothed belt 4.

[0039] For example, as shown in Fig. 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 in the vertical direction and is provided at the tip end of a second arm 11 of a horizontal articulated robot 10 so as to be movable up and down and rotatable coaxially with a wrist unit 12 (details not shown) detachably attached to the lower end thereof, in forward and reverse rotation via a driven shaft 31 coaxial with the ball screw spline shaft 13. The ball screw spline shaft 13 is moved up and down 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 ball screw spline shaft 13 to move up and down by the vertical movement drive mechanism 14 and preventing it from rotating.

[0040] (Belt transmission mechanism 1) As shown in Figs. 1 and 2, the belt transmission mechanism 1 is provided at the rear side (one end) of the second arm 11 with a drive pulley 2 that transmits the driving force of a servo motor 20 (drive source: when applied to a second-stage mechanism of a two-stage reduction system, a servo motor provided in a first-stage belt-type reduction mechanism) via a drive shaft 21 (when applied to a second-stage mechanism of a two-stage reduction system, a drive shaft of a second-stage belt-type reduction mechanism that extends coaxially with a driven shaft (not shown) of the first-stage belt-type reduction mechanism), and at the front side (the other end) of the second arm 11 with a drive pulley 2 that transmits the driving force of a servo motor 20 (drive source: when applied to a second-stage mechanism of a two-stage reduction system, a servo motor provided in a first-stage belt-type reduction mechanism) via a drive shaft 21 (when applied to a second-stage mechanism of a two-stage reduction system, a drive shaft of a second-stage belt-type reduction mechanism that extends coaxially with a driven shaft (not shown) of the first-stage belt-type reduction mechanism). The device is comprised of a driven pulley 3 that transmits driving force to a driven shaft 31 that is connected to a ball screw spline shaft 13 to which a wrist portion 12 is attached, a toothed belt 4 that is endlessly wound between the drive pulley 2 and the driven pulley 3, an auto-tensioner 5 that automatically maintains an appropriate tension on the toothed belt 4 via a first tension roller 51 and a second tension roller 52 that are rotatably provided, and a regulating member 6 (regulating means) that regulates the oscillation of the first tension roller 51 and the second tension roller 52.

[0041] 1, the base end side of the second arm 11 (the side connected to the first arm 15) is defined as the rear side (one side), and the tip end side of the second arm 11 (the side connected to the ball screw spline shaft 13 to which the wrist unit 12 is attached) is defined as the front side (the other side). Also, in FIG. 2, the left side is defined as the front (the other side), and the right side is defined as the rear (one side). Also, in FIG. 3, the radial direction centered on the central axis R of the swing shaft 53 is simply defined as the radial direction, and the circumferential direction centered on the central axis R is simply defined as the circumferential direction. Also, in FIGS. 3 and 4, the up-down direction is defined as the up-down direction, and the left-right direction is defined as the horizontal direction.

[0042] (Drive Pulley 2 and Driven Pulley 3) The drive pulley 2 is fixed to a drive shaft 21 that is driven to be rotatable forward and reverse by the driving force of a servo motor 20. The driven pulley 3 is fixed to a driven shaft 31 to which the ball screw spline shaft 13 is connected.

[0043] The drive pulley 2 and the driven pulley 3 are toothed pulleys. Grooves (not shown) having a shape corresponding to the tooth shape of the toothed belt 4 (for example, a tooth shape generally called a straight tooth) are formed on the outer periphery of the drive pulley 2 and the driven pulley 3. In this embodiment, the grooves formed on the outer periphery of the drive pulley 2 and the driven pulley 3 have a shape corresponding to the straight tooth and extend along the driven shaft 31.

[0044] The center distance between the drive pulley 2 and the driven pulley 3 is fixed and unadjustable, and is, for example, approximately 80 mm to 300 mm (220 mm in this embodiment). The speed ratio between the drive pulley 2 and the driven pulley 3 (diameter of the driven pulley 3 / diameter of the drive pulley 2) is, for example, approximately 1 to 4. In this embodiment, the driven pulley 3 has a pitch diameter approximately four times larger than that of the drive pulley 2 so that the speed ratio (reduction ratio) is 4. The belt tension of the toothed belt 4 when stationary (belt tension when the drive pulley 2 is stopped) is, for example, approximately 1 to 5 N / 1 mm width of the belt (5 N / 1 mm width of the belt in this embodiment), which is a level that does not cause the toothed belt 4 to slacken. The allowable range of the rotation angle difference between the drive pulley 2 and the driven pulley 3 (maximum when switching between forward and reverse) is determined by the design. The "rotation angle difference" is an index (substitute characteristic) that indicates responsiveness, and refers to the "magnitude of the difference in rotation angle (°) between the driving pulley and the driven pulley."

[0045] (Toothed Belt 4) As shown in FIG. 13 , the toothed belt 4 has a back portion 43 in which a core wire 42 is embedded spirally along the belt longitudinal direction, and a plurality of teeth 44 arranged at predetermined intervals along the belt longitudinal direction on the inner circumferential surface of the back portion 43 (corresponding to one 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 extend along the belt width direction (i.e., the teeth 44 are straight teeth). The inner circumferential surface of the toothed belt 4, i.e., the surfaces of the teeth 44, and a portion of the inner circumferential surface of the back portion 43 (a portion where the teeth 44 are not provided) are configured (covered) with a tooth cloth 45. The outer circumferential surface of the back portion 43 (corresponding to the other surface of the back portion 43) is not covered with a cloth or the like (back cloth).

[0046] From the viewpoint of repeatedly ensuring positioning accuracy (ensuring synchronous transmission) even when the speed of forward and reverse rotation increases, the interval between adjacent tooth portions 44 in the belt longitudinal direction (tooth pitch Pt) should be a relatively small value, for example, approximately 2 mm to 5 mm (3 mm in this embodiment). The value of the tooth pitch Pt also corresponds to the size of the scale of the tooth portions 44 (the length of the tooth portions 44 in the belt longitudinal direction and the tooth height Ht of the tooth portions 44). In other words, the larger the tooth pitch Pt, the larger the scale of the tooth portions 44.

[0047] The length (circumferential length) of the toothed belt 4 in the belt longitudinal direction is, for example, about 200 mm to 800 mm (about 600 mm in this embodiment), and the length (width) of the toothed belt 4 in the belt width direction is, for example, about 6 mm to 35 mm (10 mm in this embodiment).

[0048] (Back Portion 43 and Toothed Portion 44) The back portion 43 and toothed portion 44 of the toothed belt 4 are made of a rubber composition. Examples of the rubber component 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, and chlorosulfonated polyethylene rubber. These rubber components can be used alone or in combination. Chloroprene rubber is preferred as the rubber component of the rubber composition constituting the back portion 43 and toothed portion 44, particularly from the viewpoint of cost (chloroprene rubber is also used in this embodiment). The rubber compositions constituting the toothed portion 44 and the back portion 43 may be the same or different. The rubber compositions constituting the back portion 43 and toothed portion 44 may contain various conventional additives (or compounding agents) as necessary. From the viewpoint of ensuring the power transmission performance (particularly tooth skipping resistance) of the toothed belt 4, the hardness of the rubber composition (tooth rubber) constituting the tooth portion 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).

[0049] (Tooth Shape of Tooth Portion 44) The tooth shape of the tooth portion 44 of the toothed belt 4 may be a tooth shape known as a general straight tooth (suguba) or a tooth shape known as a helical tooth (teeth with an oblique contact angle on the tooth surface) as long as synchronous transmission (meshing transmission) is possible. The toothed belt 4 used in the belt transmission mechanism 1 of this embodiment has straight teeth.

[0050] As for the straight tooth profile, any of the following known tooth profiles, as well as modified or special shapes thereof, can be selected as appropriate for the application of the belt transmission mechanism. Examples include an H-tooth profile with a substantially semicircular cross section, a T-tooth profile with a trapezoidal cross section, and an S-tooth profile (STPD type) with two outwardly bulging convex curved surfaces (arcuate surfaces) connected by a flat surface. From the viewpoint of ensuring the power transmission performance (particularly transmission capacity and tooth skip resistance) of the toothed belt 4, it is preferable to increase the rigidity of the tooth portion 44, and therefore an H-tooth profile (with a substantially semicircular cross section) is preferred (the present embodiment also uses an H-tooth profile).

[0051] (Core Wire 42) The core wire 42 is a twisted cord formed by twisting together multiple strands. A single strand may be formed by bundling and aligning filaments (long fibers). To improve responsiveness to drive during forward / reverse switching in the belt transmission mechanism 1, the filament material is preferably high-strength (high elastic 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 (the flexibility of the toothed belt 4 when wound around the drive pulley 2 or the driven pulley 3), i.e., suppressing speed fluctuations of the toothed belt 4 due to vertical movement of the belt pitch line and ensuring high positioning accuracy. The diameter of the core wire 42 is, for example, about 0.15 mm to 0.60 mm (in this embodiment, the core wire types are 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).

[0052] The high-strength glass fiber is, for example, a glass fiber having a tensile strength of 300 kg / cm 2The above-mentioned glass fibers, particularly those having a composition shown in Table 1, which has a higher Si content than alkali-free glass fibers (E-glass fibers), can be preferably used. For comparison, the composition of E-glass fibers is also shown in Table 1. Examples of such high-strength glass fibers include K-glass fibers, U-glass fibers (both manufactured by Nippon Glass Fiber Co., Ltd.), T-glass fibers (manufactured by Nitto Boseki Co., Ltd.), R-glass fibers (manufactured by Vetrotex), S-glass fibers, S-2 glass fibers, and ZENTRON glass fibers (all manufactured by Owens Corning Fiberglass).

[0053]

[0054] 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 "Torayca (registered trademark)" manufactured by Toray Industries, Inc., "Tenax (registered trademark)" manufactured by Toho Tenax Co., Ltd., and "Dialead (registered trademark)" manufactured by Mitsubishi Chemical Corporation. These carbon fibers can be used alone or in combination of two or more. Of these carbon fibers, pitch-based carbon fibers and PAN-based carbon fibers are preferred, and PAN-based carbon fibers are particularly preferred.

[0055] The twisted cord used as the core wire 42 is preferably subjected to an adhesive treatment to enhance adhesion to the spine 43. For example, an adhesive treatment may involve immersing the twisted cord in a resorcinol-formalin-latex treatment solution (RFL treatment solution), followed by heating and drying to form a uniform adhesive layer on the surface. The RFL treatment solution is a mixture of a precondensate of resorcinol and formalin with latex. Examples of latex used here include chloroprene, styrene-butadiene-vinylpyridine terpolymer (VP latex), hydrogenated nitrile, and NBR. Another adhesive treatment method involves pretreating the cord with an epoxy or isocyanate compound, followed by treatment with the RFL treatment solution.

[0056] The core wires 42 are embedded in a spiral shape along the belt longitudinal direction at predetermined intervals in the belt width direction in the spine portion 43. That is, the core wires 42 are arranged in the spine portion 43 at predetermined intervals in the belt width direction.

[0057] (Tooth Cloth 45) From the viewpoint of abrasion resistance, etc., the tooth cloth 45 is preferably composed of a woven fabric woven by interlacing warp and weft threads vertically and horizontally according to a certain rule. The tooth cloth 45 is preferably arranged so that the warp threads of the woven fabric extend in the belt width direction and the weft threads extend in the belt longitudinal direction. This ensures the tooth cloth 45's elasticity in the belt longitudinal direction. The tooth cloth 45 may also be arranged so that the weft threads of the woven fabric extend in the belt width direction and the warp threads extend in the belt longitudinal direction. In this case, elastic warp threads having elasticity may be used as the warp threads. The fiber material constituting the tooth cloth 45 may be any of nylon, aramid, polyester, polybenzoxazole, cotton, etc., or a combination thereof. The woven fabric used as the tooth cloth 45 may be subjected to an adhesive treatment to enhance adhesion between the back portion 43 and the tooth portion 44. A typical adhesive treatment involves immersing the woven fabric in resorcinol-formalin-latex (RFL liquid) and then heating and drying it to form a uniform adhesive layer on the surface.

[0058] (Method of Manufacturing Toothed Belt 4) The toothed belt 4 according to this embodiment is produced, for example, by the following method (press-fit method). First, a fiber fabric that forms the tooth cloth 45 is wound around the outer peripheral surface of a cylindrical mold having a plurality of grooves (recesses) that correspond to the tooth portions 44 of the toothed belt 4. Next, a twisted cord that forms the core wires 42 is wound spirally at a predetermined pitch (so as to have a predetermined pitch in the axial direction of the cylindrical mold) around the outer peripheral surface of the wound fiber fabric. Furthermore, an unvulcanized rubber sheet that forms the spine portion 43 and the tooth portions 44 is wound around the outer peripheral side of the wound fiber fabric to form an unvulcanized belt molded body (unvulcanized laminate).

[0059] Next, the unvulcanized belt molded body is placed around the outer periphery of a cylindrical mold, and a rubber jacket, which functions as a vapor barrier, is then placed on the outside. The jacketed belt molded body and the cylindrical mold are then placed inside a vulcanizing device such as a vulcanizer. When the belt molded body is heated and pressurized inside the vulcanizing device, the rubber composition and woven fiber fabric of the unvulcanized rubber sheet are pressed into the grooves (concave strips) of the cylindrical mold, forming a toothed portion of the desired shape. The rubber composition of the unvulcanized rubber sheet is then vulcanized to form a sleeve-shaped vulcanized molded body (vulcanized belt sleeve) in which the rubber composition, woven fiber fabric, and cord are integrated. At this time, the woven fiber fabric stretches to conform to the contour of the toothed portion 44, forming tooth cloth 45 on the surface of the toothed portion 44. The vulcanized belt sleeve is then removed from the cylindrical mold and cut to a predetermined width to obtain multiple toothed belts 4. In this construction method (press-fitting method), the same rubber composition is used to construct the spine portion 43 and the toothed portion 44.

[0060] (Autotensioner 5) As shown in FIGS. 2 to 4, the autotensioner 5 includes a swing shaft 53 fixed to the housing of the second arm 11, a first base shaft 51A having a tip end 561 (corresponding to one end of the first swing arm 56) on which the first tension roller 51 is rotatably supported, a base end 562 (corresponding to the other end of the first swing arm 56) on which the first swing arm 56 is rotatably supported relative to the swing shaft 53, and a tip end 571 (corresponding to one end of the second swing arm 57) on which the second swing arm 57 is rotatably supported. A second base shaft portion 52A is provided on which the tension roller 52 is rotatably supported, and the base end portion 572 (corresponding to the other end of the second oscillating arm 57) has a second oscillating arm 57 that is rotatably supported relative to the oscillating shaft 53, and a spring 54 that urges the first base shaft portion 51A and the second base shaft portion 52A in a direction that draws them toward each other along the roller center line RL that connects the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52.

[0061] In this embodiment, the autotensioner 5 has two tension rollers (first tension roller 51 and second tension roller 52) provided on the drive pulley 2 side, not on the driven pulley 3 side. Note that the autotensioner 5 may have two tension rollers (first tension roller 51 and second tension roller 52) provided on the side of the drive pulley 2 or the driven pulley 3, whichever has a smaller diameter. Here, "two tension rollers provided on the drive pulley 2 side" means that the intersection of the roller center line RL and the pulley center line PL is located closer to the drive pulley 2 than the center of the pulley center line PL.

[0062] (First tension roller 51 and second tension roller 52) The first tension roller 51 is a cylindrical roller member supported on the first base shaft portion 51A via a rolling bearing (not shown) so as to be rotatable (swingable) about the central axis R2. The second tension roller 52 is also a cylindrical roller member supported on the second base shaft portion 52A via a rolling bearing (not shown) so as to be rotatable (swingable) about the central axis R3.

[0063] As shown in Figure 2, the first tension roller 51 and the second tension roller 52 are located on the drive pulley 2 side, on both sides 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 are rotatable around the first base shaft portion 51A and the second base shaft portion 52A, respectively, and the first tension roller 51 and the second tension roller 52 are capable of contacting the outer peripheral surface of the toothed belt 4.

[0064] (First Base Shaft Portion 51A and Second Base Shaft Portion 52A) As shown in FIGS. 3 and 4 , the first base shaft portion 51A is a base end portion that supports the first tension roller 51 rotatably about the central axis R2 via a rolling bearing (not shown). The first base shaft portion 51A has a male thread extending downward for insertion into a hole (female thread) provided in the tip end portion 561 of the first swing arm 56 (described later). Similarly, as shown in FIG. 3 , the second base shaft portion 52A is a base end portion that supports the second tension roller 52 rotatably about the central axis R3 via a rolling bearing (not shown). The second base shaft portion 52A has a male thread extending downward for insertion into a hole (female thread) provided in the tip end portion 571 of the second swing arm 57 (described later). A spring 54 (described later) is tensioned between the first base shaft portion 51A and the second base shaft portion 52A.

[0065] (Oscillating shaft 53) As shown in FIG. 3, the oscillating shaft 53 is a metal part that has a cylindrical body portion 531 that extends in the vertical direction, a flange portion 532 that extends radially outward from the upper end of the body portion 531, and a fastening portion 533 that extends downward from the center of the lower end face (lower end face) of the body portion 531, and these are integrally formed.

[0066] 2 , the oscillation shaft 53 is fixed to the housing (internal thread portion) of the second arm 11 of the horizontal articulated robot 10 via a fastening portion 533 (external thread portion) so that the central axis R (center point of oscillation) of the oscillation shaft 53 passes through a point on the pulley center line PL (or may be a point on an extension of the pulley center line PL) that is spaced toward the drive pulley 2 from the intersection of the pulley center line PL and a roller center line RL that connects the rotation center 51C of the first tension roller 51 and the rotation center 52C of the second tension roller 52), and extends in a direction parallel to the drive shaft 21. Furthermore, the outer peripheral surface of the body portion 531 and the lower end surface of the flange portion 532 of the oscillation shaft 53 are in surface contact with a sliding member 55 (bearing), and the first oscillation arm 56 and the second oscillation arm 57 are rotatably supported via this sliding member 55 (bearing).

[0067] (Spring 54) In this embodiment, a tension spring is used as the spring 54. The tension spring is stretched on the roller center line RL between the first base shaft portion 51A and the second base shaft portion 52A while being pulled in a direction longer than its natural length (a state in which the self-elastic recovery force acts in the contracting direction). The spring 54 biases the first base shaft portion 51A and the second base shaft portion 52A toward each other along the roller center line RL. That is, the spring 54 biases the first tension roller 51 rotatably mounted on the first base shaft portion 51A and the second tension roller 52 rotatably mounted on the second base shaft portion 52A toward each other along the roller center line RL.

[0068] The tension spring is employed when the first tension roller 51 and the second tension roller 52 are used in a manner that they come into contact with the outer peripheral surface of the toothed belt 4, as shown in FIG.

[0069] A compression spring may be used for the spring 54. The compression spring is attached between the first base shaft portion 51A and the second base shaft portion 52A in a compressed state in a direction that shortens the spring length (a state in which the self-elastic recovery force acts in the extension direction), and is used when biasing the first base shaft portion 51A and the second base shaft portion 52A in a direction that separates them from each other along the roller center line RL. Specifically, a compression spring is used when the first tension roller 51 and the second tension roller 52 are disposed on the inner periphery of the toothed belt 4 and are used in a manner in which the first tension roller 51 and the second tension roller 52 are in contact with the inner periphery of the toothed belt 4.

[0070] If a tension spring is used for the spring 54 as in this embodiment, the biasing action of a single spring 54 (tension spring) causes two tension rollers (first tension roller 51 and second tension roller 52) to sandwich both sides (tight side and slack side) of the toothed belt 4. Therefore, compared to a configuration in which the spring 54 is a compression spring and two tension rollers (first tension roller 51 and second tension roller 52) are provided so as to contact the inner circumferential surface of the toothed belt 4 (a configuration in which the biasing action of a single compression spring causes two tension rollers to spread apart both sides of the toothed belt 4), the contact angle of the toothed belt 4 (the central angle with respect to the arc where the belt and pulley are in contact) is larger, thereby making it possible to suppress tooth jumping of the toothed belt 4.

[0071] The spring 54 is preferably a coil spring so that predetermined spring characteristics 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 having a circular cross section or the like that conforms to JIS G3560:1994, and this embodiment uses an oil-tempered spring wire having a circular cross section that conforms to the above standard. The diameter of the spring wire, as well as the coil diameter and coil length (natural length) of the spring are designed and determined so that predetermined spring characteristics can be repeatedly obtained for each belt transmission mechanism 1 (particularly for each level of belt tension).

[0072] In this embodiment, in order to make it easier to tension the spring 54 between the first base shaft portion 51A and the second base shaft portion 52A, both ends of the spring 54 (hereinafter referred to as "spring ends 541A, 541B"), which correspond to approximately one turn at the end of the spring 54, are bent by approximately 90 degrees in the same direction. In this way, this configuration (tensioning structure of the spring 54) can be formed relatively simply.

[0073] (First Oscillating Arm 56 and Second Oscillating Arm 57) The first oscillating arm 56 and the second oscillating arm 57 are independent metal components made of aluminum alloy casting (e.g., ADC12) or the like. As shown in FIG. 3, a base end 562 of the first oscillating arm 56 is rotatably supported on the oscillating shaft 53 (via a sliding member 55 (bearing) described later). Similarly, as shown in FIG. 3, a base end 572 of the second oscillating arm 57 is rotatably supported on the oscillating shaft 53 (via a sliding member 55 (bearing) described later). As shown in FIG. 2, the first oscillating arm 56 and the second oscillating arm 57 are formed so as to have a generally C-shape when viewed from above when installed in the belt transmission mechanism 1 as the autotensioner 5.

[0074] (Tip Portion 561 and Tip Portion 571) As shown in FIG. 4 , the tip portion 561 of the first swing arm 56 is formed with a cylindrical protrusion 561A that protrudes downward (below the lower end surface of the arm portion between the tip portion 561 and the base end 562) around axis R2 (the central axis of the first tension roller 51). A female thread is formed in a hole that penetrates the tip portion 561 in the vertical direction around axis R2, including the protrusion 561A. Furthermore, the spring end portion 541A of the spring 54 is inserted into the protrusion 561A from below and engaged with the outer periphery of the upper end (base) of the protrusion 561A. As a result, the first base shaft portion 51A (mainly the male thread portion) is fixed from above to the tip portion 561 of the first swing arm 56, and the spring end portion 541A is engaged with the first base shaft portion 51A via the protrusion 561A.

[0075] As shown in FIG. 3 , the tip end 571 of the second swing arm 57 is formed with a cylindrical protrusion 571A that protrudes upward (beyond the upper end surface of the arm portion between the tip end 571 and the base end 572) around axis R3 (the central axis of the second tension roller 52). A female thread is formed in a hole that penetrates the tip end 571 in the vertical direction around axis R3, including the protrusion 571A. The spring end 541B of the spring 54 is inserted from above into the protrusion 571A and engaged with the outer periphery of the lower end (base) of the protrusion 571A. As a result, the second base shaft 52A (mainly the male thread) is fixed from above to the tip end 571 of the second swing arm 57, and the spring end 541B is engaged with the second base shaft 52A via the protrusion 571A.

[0076] With the above configuration, the first base shaft 51A, on which the first tension roller 51 is rotatably supported, is immovably fixed (hinged) to the tip 561 of the first swing arm 56. Similarly, the second base shaft 52A, on which the second tension roller 52 is rotatably supported, is immovably fixed (hinged) to the tip 571 of the second swing arm 57. The spring end 541A is inserted into the first base shaft 51A, and the spring end 541B is inserted into the second base shaft 52A. As a result, the spring 54 is tensioned between the first base shaft 51A and the second base shaft 52A such that the engagement positions of the spring ends 541A, 541B are on the same plane in side view (there is no vertical displacement) and the spring ends 541A, 541B cannot fall off (see FIG. 3 ).

[0077] (Base End 562 and Base End 572) The base end 562 of the first swing arm 56 has a flange shape extending upward and is formed into a cylindrical shape when viewed from above. Specifically, as shown in Fig. 3, the upper end surface of the base end 562 extends upward to a position where it can contact a lower end surface of a plate-like portion 551B extending radially outward from the upper end of a cylindrical portion 551A extending in the vertical direction in an upper cylindrical sliding portion 551 of a sliding member 55 (described later), and the lower end surface of the base end 562 contacts the upper end surface of the plate-like sliding portion 552 of the sliding member 55 (described later). Furthermore, the base end 562 extends radially inward to a position where it can contact the outer circumferential surface of the cylindrical portion 551A extending in the vertical direction in the upper cylindrical sliding portion 551. The diameter (inner diameter) of the radially inner end surface of the base end portion 562 is the same as or slightly larger than the diameter (outer diameter) of the outer peripheral surface of the cylindrical portion 551A of the upper cylindrical sliding portion 551 (see FIG. 3).

[0078] The base end 572 of the second swing arm 57 has a flange shape extending downward and is formed cylindrically when viewed from above. Specifically, as shown in FIG. 3 , the lower end surface of the base end 572 extends downward to a position where it can contact the upper end surface of a plate-like portion 553B extending radially outward from the lower end of a cylindrical portion 553A extending in the vertical direction of a lower cylindrical sliding portion 553 of a sliding member 55 (described later), and the upper end surface of the base end 572 contacts the lower end surface of the plate-like sliding portion 552 of the sliding member 55 (described later). The base end 572 also extends radially inward to a position where it can contact the outer peripheral surface of the cylindrical portion 553A extending in the vertical direction of the lower cylindrical sliding portion 553. The diameter (inner diameter) of the radially inner end surface of the base end 572 is the same as or slightly larger than the diameter (outer diameter) of the outer peripheral surface of the cylindrical portion 553A of the lower cylindrical sliding portion 553 (see FIG. 3 ).

[0079] With the above configuration, the base end 562 of the first swing arm 56 and the base end 572 of the second swing arm 57 are independently supported in the vertical direction and rotatably supported on the swing shaft 53 via the sliding member 55 (bearing) described below.

[0080] 3, the sliding member 55 has an upper cylindrical sliding portion 551, a plate-like 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, dimensions).

[0081] The upper cylindrical sliding part 551 has a cylindrical part 551A extending in the vertical direction and a plate-like part 551B extending radially outward from the upper end of the cylindrical part 551A. The plate-like sliding part 552 has a plate-like part 552A formed in the shape of an annular plate and a cylindrical part 552B extending upward and downward radially inside the plate-like part 552A. The lower cylindrical sliding part 553 has a cylindrical part 553A extending in the vertical direction and a plate-like part 553B extending radially outward from the lower end of the cylindrical part 553A.

[0082] The sliding member 55 is fitted onto the trunk 531 of the swing shaft 53. In detail, the upper cylindrical sliding portion 551, the base end portion 562, the plate-shaped sliding portion 552, the base end portion 572, and the lower cylindrical sliding portion 553 are fitted onto the trunk 531 of the swing shaft 53 in this order, and the upper cylindrical sliding portion 551, the plate-shaped sliding portion 552, and the lower cylindrical sliding portion 553 are fixed in a manner such that they are sandwiched between the flange portion 532 of the swing shaft 53 and the housing of the second arm 11 in the vertical direction.

[0083] The sliding member 55 functions as a sliding bearing that slides against the first swing 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 surface of the base end portion 562, the plate-shaped portion 551B of the upper cylindrical sliding portion 551 making surface contact with the upper end surface of the base end portion 562, 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 base end portion 562.

[0084] Similarly, the sliding member 55 functions as a sliding bearing that slides against the second swing 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 surface of the base end portion 572, the plate-shaped portion 553B of the lower cylindrical sliding portion 553 making surface contact with the lower end surface of the base end portion 572, 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 base end portion 572.

[0085] With the above-described configuration, the first swing arm 56 and the second swing arm 57 are each independently rotatably supported on the swing shaft 53 via the sliding member 55 (bearing).

[0086] The sliding member 55 (bearing) of this embodiment is formed by injection molding from a hard thermoplastic resin (e.g., polyacetal resin) having a Rockwell R scale (in accordance with JIS K7202-2:2001) of 80 to 130, from the viewpoint of low-friction sliding properties, wear resistance, etc.

[0087] 2, 3, 18, and 19, the regulating member 6 is a block-shaped metal part that extends in the up-down direction and has a U-shape in a plan view. Specifically, as shown in Fig. 2 and 18, the regulating member 6 is a metal part that is integrally formed with a main body portion 61 that extends in a direction perpendicular to the pulley center line PL, a first swing arm regulating portion 62 that extends forward from one end of the main body portion 61 and has a contact surface 62a that can come into contact with the side surface 56a of the first swing arm 56, and a second swing arm regulating portion 63 that extends forward from the other end of the main body portion 61 and has a contact surface 63a that can come into contact with the side surface 57a of the second swing arm 57.

[0088] The regulating member 6 is fixed between the oscillating shaft 53 and the drive pulley 2 by bolts 64, 65 (see Figure 19) passed through bolt holes 66, 67 to the housing of the second arm 11 at a position (a position where the regulating member 6 can contact the first oscillating arm 56 and the second oscillating arm 57) that regulates the first tension roller 51 and the second tension roller 52 from oscillating about the oscillating shaft 53 in a direction opposite to the biasing direction of the spring 54 (see Figure 2) from the balanced position (state in Figure 2) in which the drive pulley 2 and the driven pulley 3 are stopped.

[0089] Specifically, the contact surface 62a of the first swing arm restricting portion 62 has a shape (inclined surface) and is positioned such that it comes into surface contact with the side surface 56a of the first swing arm 56 at the balanced position where the drive pulley 2 and the driven pulley 3 are stationary. When the first tension roller 51 moves in the biasing direction due to the bias of the spring 54, the surface contact between the contact surface 62a of the first swing arm restricting portion 62 and the side surface 56a of the first swing arm 56 is released. Similarly, the contact surface 63a of the second swing arm restricting portion 63 has a shape (inclined surface) and is positioned such that it comes into surface contact with the side surface 57a of the second swing arm 57 at the balanced position where the drive pulley 2 and the driven pulley 3 are stationary. When the second tension roller 52 moves in the biasing direction due to the bias of the spring 54, the surface contact between the contact surface 63a of the second swing arm restricting portion 63 and the side surface 57a of the second swing arm 57 is released.

[0090] The regulating member 6 is preferably formed with a shape, dimensions, and material (e.g., steel material) that can ensure sufficient rigidity so that it does not bend when there is a significant increase in belt tension (the force exerted by the toothed belt 4) on the tension side of the toothed belt 4.

[0091] The restricting member 6 allows the first tension roller 51 and the second tension roller 52 to swing about the swing shaft 53 from a balanced position where the drive pulley 2 and the driven pulley 3 are stationary only in the biasing direction of the spring 54 (only in the direction that draws the first tension roller 51 and the second tension roller 52 toward each other if the spring 54 is a tension spring). In other words, the first tension roller 51 and the second tension roller 52 cannot swing about the swing shaft 53 from a balanced position where the drive pulley 2 and the driven pulley 3 are stationary only in the direction opposite to the biasing direction of the spring 54 (only in the direction that separates the first tension roller 51 and the second tension roller 52 from each other if the spring 54 is a tension spring).

[0092] The configuration (form) of the regulating member 6 is not limited as long as it can regulate the first tension roller 51 and the second tension roller 52 from swinging about the swing shaft 53 in the direction opposite to the biasing direction of the spring 54 (see FIG. 2) from the balanced position (state in FIG. 2) in which the drive pulley 2 and the driven pulley 3 are stopped. For example, as shown in FIG. 12, the regulating members 261 and 262 may be formed in a pin shape and disposed on either side of the pulley center line PL.

[0093] Furthermore, in this embodiment, the regulating member 6 is fixed to the housing of the second arm 11 by bolts 64, 65 (see Figure 19) passed through bolt holes 66, 67, but it may also be fixed to the housing of the second arm 11 via the oscillating shaft 53 by connecting the regulating member 6 to the oscillating shaft 53 via a connecting member (not shown) (not shown).

[0094] (Method of Mounting the Restricting Member 6) (1) Mounting the Toothed Belt 4 For a belt transmission mechanism 1 that is provided with an autotensioner 5 but does not have a restricting member 6, the toothed belt 4 is wound around the drive pulley 2 and the driven pulley 3 (with a fixed center distance) with a predetermined belt mounting tension (e.g., 5 N / mm width) so that the first tension roller 51 and the second tension roller 52 contact the toothed belt 4. In other words, this is a state in which the restricting member 6 has not yet been mounted (corresponding to the state shown in FIG. 7 ). With the drive pulley 2 and the driven pulley 3 stationary, the roller center line RL and the pulley center line PL are perpendicular to each other when viewed in a direction parallel to the drive shaft 21 (hereinafter, viewed from above), and the first tension roller 51 and the second tension roller 52 and the outer peripheral surface of the toothed belt 4 are in contact with each other and in balance (see FIG. 7 ).

[0095] (Fixing of Restricting Member 6) With the drive pulley 2 and the driven pulley 3 stationary as described above, the restricting member 6 is fixed at a predetermined position within the belt transmission mechanism 1, thereby completing the belt transmission mechanism 1 of this embodiment. Here, the predetermined position refers to a position where, under a predetermined belt installation tension (e.g., 5 N / mm width), the roller center line RL and the pulley center line PL are perpendicular to each other when viewed from above, the first tension roller 51 and the second tension roller 52 are in contact with and balanced against the outer peripheral surface of the toothed belt 4, and the contact surface 62 a of the first swing arm restricting portion 62 of the restricting member 6 can come into surface contact with the side surface 56 a of the first swing arm 56 without load, and the contact surface 63 a of the second swing arm restricting portion 63 of the restricting member 6 can come into surface contact with the side surface 57 a of the second swing arm 57 without load.

[0096] As a result, even when the regulating member 6 is attached to the belt transmission mechanism 1 (when the drive pulley 2 and driven pulley 3 are stopped), the first tension roller 51, the second tension roller 52 and the outer surface of the toothed belt 4 are in contact with each other and maintained in a balanced state, with the roller center line RL and the pulley center line PL perpendicular to each other when viewed from above, just as when the regulating member 6 is not yet attached (corresponding to the state in Figure 7) (see Figure 2).

[0097] (Operation of autotensioner 5) (1: Before activation) In the belt transmission mechanism 1 for driving a robot arm, before the drive pulley 2 starts to rotate, i.e., when the drive pulley 2 is stopped, when viewed in a direction parallel to the drive shaft 21 (hereinafter, viewed from above), the roller center line RL and the pulley center line PL are perpendicular to each other, the two tension rollers (first tension roller 51 and second tension roller 52) and the outer peripheral surface of the toothed belt 4 are in contact with each other and balanced, and the contact surface 62a of the first swing arm regulating portion 62 of the regulating member 6 is in surface contact with the side surface 56a of the first swing arm 56 without load, and the contact surface 63a of the second swing arm regulating portion 63 of the regulating member 6 is in surface contact with the side surface 57a of the second swing arm 57 without load (see Figure 2).

[0098] (2: At the time of forward / reverse switching (at the time of start-up) (when the drive pulley 2 starts to rotate in the direction of the arrow Z in FIG. 5)) (2-1: On the tension side of the toothed belt 4) As shown in FIG. 5 , when the drive pulley 2 starts to rotate in the direction of the arrow Z, the tension of the toothed belt 4 increases on the tension side of the toothed belt 4, and the first tension roller 51, which is one of the tension rollers located on the tension side of the toothed belt 4, is pushed by the toothed belt 4 due to the tension of the toothed belt 4 and attempts to displace in the tension direction of the toothed belt 4. At this time, the contact surface 62 a of the first swing arm regulating portion 62 of the regulating member 6 comes into surface contact with the side surface 56 a of the first swing arm 56 on which the first tension roller 51 is supported, thereby regulating the displacement of the first tension roller 51 in the tension direction of the toothed belt 4. This prevents the two tension rollers (first tension roller 51 and second tension roller 52) connected (biased) by the spring 54 from swinging around the swing shaft 53 (center axis R).

[0099] 5, when the drive pulley 2 starts to rotate in the direction of the arrow Z, the tension of the toothed belt 4 decreases on the slack side of the toothed belt 4, causing the toothed belt 4 to become slack. However, the second tension roller 52, which is the other tension roller located on the slack side of the toothed belt 4, is displaced in the X direction in FIG. 5 by the biasing force of the spring 54, thereby attempting to eliminate the slack in the toothed belt 4. At this time, on the tight side of the toothed belt 4, the contact surface 62a of the first swing arm regulating portion 62 of the regulating member 6 comes into surface contact with the side surface 56a of the first swing arm 56 on which the first tension roller 51 is supported, thereby regulating the displacement of the first tension roller 51 in the tension direction of the toothed belt 4. This suppresses displacement of the first tension roller 51 in the tension direction of the toothed belt 4, and therefore, compared to a configuration not provided with the regulating member 6 (FIG. 8), only a small amount of displacement is required from the neutral position of the second tension roller 52 located on the slack side to a position where slack in the toothed belt 4 can be eliminated. Specifically, in the configuration provided with the regulating member 6 (FIG. 5), the amount of displacement of the second tension roller 52 located on the slack side is only about 1 / 10 of the amount required in a configuration not provided with the regulating member 6 (FIG. 8).

[0100] Therefore, even if the spring force of the spring 54 is set relatively weak so that the tension of the toothed belt 4 is kept relatively low, the second tension roller 52 located on the slack side of the toothed belt 4 can be quickly displaced (swinged around the swing axis 53) to a position where the slack of the toothed belt 4 can be eliminated while being urged by the spring 54 in the direction of eliminating the slack of the toothed belt 4 (the urging direction of the spring 54).

[0101] (3: When switching between forward and reverse directions (when stopped) (when the drive pulley 2 stops while rotating in the direction of arrow Z in FIG. 6)) (3-1: On the tension side of the toothed belt 4) As shown in FIG. 6, when the drive pulley 2 stops while rotating in the direction of arrow Z, the tension of the toothed belt 4 increases on the tension side of the toothed belt 4 (the lower side in FIG. 6), and the second tension roller 52, which is the other tension roller located on the tension side of the toothed belt 4, is pushed by the toothed belt 4 due to the tension of the toothed belt 4 and attempts to displace in the tension direction of the toothed belt 4. At this time, the contact surface 63a of the second swing arm regulating portion 63 of the regulating member 6 comes into surface contact with the side surface 57a of the second swing arm 57 on which the second tension roller 52 is supported, thereby regulating the displacement of the second tension roller 52 in the tension direction of the toothed belt 4. This prevents the two tension rollers (first tension roller 51 and second tension roller 52) connected (biased) by the spring 54 from swinging around the swing shaft 53 (center axis R).

[0102] 6, when the drive pulley 2 stops while rotating in the direction of the arrow Z, the tension of the toothed belt 4 decreases on the slack side of the toothed belt 4 (the upper side in FIG. 6), causing the toothed belt 4 to become slack. However, the first tension roller 51, which is one of the tension rollers located on the slack side of the toothed belt 4, is displaced in the X direction in FIG. 6 by the biasing force of the spring 54, thereby attempting to eliminate the slack in the toothed belt 4. At this time, on the tight side of the toothed belt 4, the contact surface 63a of the second swing arm regulating portion 63 of the regulating member 6 comes into surface contact with the side surface 57a of the second swing arm 57 on which the second tension roller 52 is supported, thereby regulating the displacement of the second tension roller 52 in the tension direction of the toothed belt 4. This suppresses displacement of the second tension roller 52 in the tension direction of the toothed belt 4, and therefore, compared to a configuration not provided with the regulating member 6 (FIG. 9), the amount of displacement required from the neutral position of the first tension roller 51 located on the slack side to a position where slack in the toothed belt 4 can be eliminated is small. Specifically, in the configuration provided with the regulating member 6 (FIG. 6), the amount of displacement required of the first tension roller 51 located on the slack side is only about 1 / 10 of the amount required in a configuration not provided with the regulating member 6 (FIG. 9).

[0103] Therefore, even if the spring force of the spring 54 is set relatively weak so that the tension of the toothed belt 4 is kept relatively low, the first tension roller 51 located on the slack side of the toothed belt 4 can be quickly displaced (swinged around the swing axis 53) to a position where the slack of the toothed belt 4 can be eliminated while being urged by the spring 54 in the direction of eliminating the slack of the toothed belt 4 (the urging direction of the spring 54).

[0104] (4: Operation of the spring 54 stretched between the first base shaft portion 51A and the second base shaft portion 52A) In addition, in this configuration, the spring 54 is stretched between the first base shaft portion 51A and the second base shaft portion 52A of the two tension rollers (the first tension roller 51 and the second tension roller 52). For this reason, even in a configuration in which the two tension rollers (first tension roller 51 and second tension roller 52) are freely oscillating about the oscillation axis 53 (along a plane perpendicular to the oscillation axis 53), the distance between the center of oscillation (central axis R: the "fulcrum" on the slack side of the toothed belt 4) and the point where the biasing force of the spring 54 is applied on the slack side of the toothed belt 4 (i.e., the "point of force" on the slack side of the toothed belt 4) is longer when viewed in a direction parallel to the drive shaft 21, compared to a configuration in which the spring 54 is not stretched between the base shafts of the two tension rollers [for example, a configuration in which a spring is stretched between each member connecting the base shafts of the two tension rollers to the oscillation axis (between two independent arm members) ( FIG. 10 : equivalent to FIG. 2 of Patent Document 1)]. As a result, a larger force acts on the slack side of the toothed belt 4 at the point where the first tension roller 51 or the second tension roller 52 contacts the toothed belt 4 on the slack side (i.e., the "point of application" on the slack side of the toothed belt 4), further improving the responsiveness (operating speed) of the first tension roller 51 or the second tension roller 52 on the slack side of the toothed belt 4. This makes it easier to apply the biasing force of the spring 54 responsively in the direction that eliminates slack in the toothed belt 4 (the biasing direction of the spring 54), and ultimately further improves the responsiveness (operating speed) of the two tension rollers (the first tension roller 51 and the second tension roller 52) to the drive pulley 2.

[0105] (Effect) With the regulating member 6 configured as described above (FIG. 2), in the autotensioner 5, the two tension rollers (first tension roller 51 and second tension roller 52) are both unable to oscillate around the oscillating shaft 53 (center axis R) from a balanced position in which the drive pulley 2 and driven pulley 3 are stopped in a direction opposite to the biasing direction of the spring 54 (in the case where the spring 54 is a tension spring, the direction that separates the first tension roller 51 and the second tension roller 52 from each other), but can only oscillate in the biasing direction of the spring 54. Therefore, in the belt transmission mechanism 1 in which the biasing force of the spring 54 is set to be relatively weak and the autotensioner 5 is provided in which two tension rollers (a first tension roller 51 and a second tension roller 52) are configured to swing about a swing shaft 53, and the tension of the toothed belt 4 is kept relatively low (low enough that the toothed belt 4 does not become loose), when the load on the driven pulley 3 (and thus the moment of inertia of the driven pulley 3) increases (for example, in the belt transmission mechanism 1 for driving a robot arm, when the load torque of the driven pulley 3 becomes 1 N· Even if the tension of the toothed belt 4 increases on the tight side of the toothed belt 4 and decreases on the slack side of the toothed belt 4 (even if the toothed belt 4 becomes too loose) immediately after the drive pulley 2 stops during forward / reverse switching (when the forward / reverse rotation is stopped), the tension roller located on the tight side of the toothed belt 4 (the second tension roller 52 when the forward / reverse rotation is stopped) can be prevented from being pushed by the toothed belt 4 and displacing (swinging around the swing shaft 53) toward the tight side of the toothed belt 4 (FIG. 6).

[0106] As a result, the tension roller located on the tight side of the toothed belt 4 (the second tension roller 52 when stopped in the forward and reverse directions) can be prevented from swinging around the swing shaft 53 together with the two tension rollers (the first tension roller 51 and the second tension roller 52) connected (biased) by the spring 54 in a direction that would displace the tension roller on the tight side of the toothed belt 4 toward the tight side of the toothed belt 4. In addition, the addition of the regulating member 6 can prevent the tension roller located on the tight side (the second tension roller 52 when stopped in the forward and reverse directions) from displacing toward the tight side, so that the tension roller located on the slack side can be prevented from swinging more easily than in a configuration without the regulating member 6 (FIG. 7). Since only a small amount of displacement is required from the neutral position (or the first tension roller 51 when stopped in forward or reverse direction) to a position where the slack in the toothed belt 4 can be eliminated, even if the biasing force of the spring 54 is set relatively weak so that the tension in the toothed belt 4 is kept relatively low, the tension roller (or the first tension roller 51 when stopped in forward or reverse direction) located on the slack side of the toothed belt 4 can be quickly displaced (oscillated around the oscillation axis 53) to a position where the slack in the toothed belt 4 can be eliminated while being biased by the spring 54 in the direction (the biasing direction of the spring 54) that eliminates the slack in the toothed belt 4.

[0107] Therefore, with this configuration, as shown in the circled area in Figure 17 (a graph showing time-series changes in the rotation speed of the drive pulley and the rotation speed of the driven pulley when switching between forward and reverse directions (when starting / stopping forward and reverse directions)), even if the load on the driven pulley 3 increases in the belt transmission mechanism 1, immediately after the drive pulley 2 stops when switching between forward and reverse directions (when stopping forward and reverse directions), the two tension rollers (first tension roller 51 and second tension roller 52) each repeatedly oscillate in short forward and reverse directions around the oscillation shaft 53 for a while, with the tight side and slack side of the toothed belt 4 repeatedly alternating in short steps, and the driven pulley 3 can be prevented from overshooting or undershooting and then repeatedly rotating in short forward and reverse directions. In other words, this configuration ensures a high level of damping of the driven pulley 3 when switching between forward and reverse (when forward and reverse are stopped) [and thus ensures a high level of responsiveness to drive when switching between forward and reverse (i.e., sufficiently suppresses the difference in rotation angle between the drive pulley 2 and the driven pulley 3 when switching between forward and reverse)]. In other words, this configuration ensures the positioning accuracy of the belt transmission mechanism 1 repeatedly (ensuring synchronous transmission) even if the load on the driven pulley 3 increases.

[0108] In the above embodiment, the autotensioner 5 has two tension rollers (first tension roller 51 and second tension roller 52) provided on the drive pulley 2 side, not on the driven pulley 3 side (note that the autotensioner 5 may have two tension rollers (first tension roller 51 and second tension roller 52) provided on the side of either the drive pulley 2 or the driven pulley 3, whichever has a smaller diameter). In the belt transmission mechanism 1, the diameter of the drive pulley 2 is generally smaller than the diameter of the driven pulley 3 (when the belt transmission mechanism 1 functions as a so-called speed reduction mechanism) in order to ensure that the rotational torque of the driven pulley 3 is at a predetermined level, but the diameters of the drive pulley 2 and the driven pulley 3 may also be the same. For example, in a belt transmission mechanism in which the distance between the drive pulley 2 and the driven pulley 3 is narrow and the reduction ratio (ratio of pulley diameters) is large, there is a concern that the contact angle of the toothed belt 4 becomes small at the drive pulley 2 on the smaller diameter side, and if the toothed belt 4 is significantly loose, tooth jumping of the toothed belt 4 becomes more likely. However, with this configuration, the contact angle of the toothed belt 4 can be prevented from becoming small at the drive pulley 2 (including when the drive pulley 2 and driven pulley 3 are the same diameter) or at the pulley on the smaller diameter side (regardless of whether it is drive or driven), thereby making tooth jumping of the toothed belt 4 less likely to occur.

[0109] Furthermore, when the diameter of the drive pulley 2 of the belt transmission mechanism 1 is smaller than the diameter of the driven pulley 3 (i.e., when the belt transmission mechanism 1 is a speed reduction mechanism), the degree of displacement caused by the two tension rollers swinging about the swing shaft 53 during forward / reverse switching is greater than when the diameter of the drive pulley 2 is the same as the diameter of the driven pulley 3. Therefore, with this configuration, the first tension roller 51 swings about the swing shaft 53 on the tension side of the toothed belt 4, while suppressing damping by the spring 54 (displacement in a direction against the swing force of the spring 54), which is more effective than a configuration in which the two tension rollers (the first tension roller 51 and the second tension roller 52) cannot swing about the swing shaft 53 (a configuration in which only the biasing force of the spring acts on the two tension rollers) and the two tension rollers can only be displaced in a direction perpendicular to the pulley center line PL when viewed in a direction parallel to the drive shaft. As a result, in the belt transmission mechanism 1, a higher level of responsiveness to drive when switching between forward and reverse directions (when starting / stopping forward and reverse directions) can be ensured.

[0110] The belt transmission mechanism 1 also drives the second arm 11 of the horizontal articulated robot 10. Therefore, even if the load on the driven pulley 3 increases when driving the second arm 11, a high level of damping of the driven pulley 3 can be ensured when switching between forward and reverse (when forward and reverse are stopped), and the positioning accuracy of the second arm 11 can be repeatedly ensured (i.e., the magnitude of the difference in rotation angle between the drive pulley 2 and the driven pulley 3 can always be kept within an allowable range), thereby ensuring synchronous transmission.

[0111] Other Embodiments In the above embodiment, the central axis R (center point of oscillation) of the oscillation shaft 53 passes through a point on the pulley center line PL, spaced toward the drive pulley 2 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, and extends in a direction parallel to the drive shaft 21. However, as shown in Figure 11, the central axis R (center point of oscillation) of the oscillation shaft 53 may also be configured to pass through a point on the pulley center line PL, spaced toward the driven pulley 3 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, and extend in a direction parallel to the drive shaft 21.

[0112] In this case, as shown in Figure 11, the regulating member 6 is fixed by bolts 64, 65 (see Figure 19) passed through bolt holes 66, 67 to the housing of the second arm 11 at a position between the oscillating shaft 53 and the driven pulley 3 that regulates the first tension roller 51 and the second tension roller 52 from swinging around the oscillating shaft 53 in a direction opposite to the biasing direction of the spring 54 from the balanced position in which the driving pulley 2 and the driven pulley 3 are stopped (a position in which the regulating member 6 can come into contact with the first oscillating arm 56 and the second oscillating arm 57).

[0113] According to the above configuration, the arrangement from rear to front can be the drive pulley 2, two tension rollers (the first tension roller 51 and the second tension roller 52), the swing shaft 53, the regulating member 6, and the driven pulley 3. In this case, compared to when the arrangement is in the order of the drive pulley 2, the regulating member 6, the swing shaft 53, two tension rollers (the first tension roller 51 and the second tension roller 52), and the driven pulley 3, it is easier to set the tension of the toothed belt 4 low, which makes it easier to ensure the ease of wearing the toothed belt 4, the synchronous power transmission performance of the toothed belt 4, and the tooth skip resistance of the toothed belt 4.

[0114] Furthermore, the central axis R (center point of oscillation) of the oscillation shaft 53 may be configured to pass through a point on an extension of the pulley center line PL, away from the intersection of the pulley center line PL and a roller center line RL connecting 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. Specifically, the drive shaft 21 may be configured to be located between the oscillation shaft 53 and the two tension rollers (the first tension roller 51 and the second tension roller 52) of the autotensioner 5.

[0115] Furthermore, the central axis R (center point of oscillation) of the oscillation shaft 53 may be a point on the pulley center line PL that is spaced toward the drive pulley 2 from the intersection of the pulley center line PL and a roller center line RL that connects the rotation centers 51C of the first tension roller 51 and the rotation centers 52C of the second tension roller 52 with each other, and may pass through the central axis of the drive shaft 21 (the rotation center 22 of the drive pulley 2) and extend in a direction parallel to the drive shaft 21 (i.e., the drive shaft 21 may also serve as the oscillation shaft 53). In this case, the first oscillation arm 56 and the second oscillation arm 57 are rotatably supported on the existing drive shaft 21 via the sliding members 55 (bearings), which simplifies the belt transmission mechanism 1 (reduces parts and improves assembly).

[0116] In the above embodiment, the belt transmission mechanism according to the present invention has been described as a belt transmission mechanism for driving a robot arm, but the present invention is not limited to this. For example, the belt transmission mechanism according to the present invention can be applied to an injection molding machine (a belt transmission mechanism in which each operating unit, such as injection, metering, mold opening and closing, is electrically driven by an independent motor), other belt transmission mechanisms of general industrial machinery and equipment, etc.

[0117] In the belt transmission mechanism of the present invention, even if the load on the driven pulley increases, it is necessary to ensure a high level of damping of the driven pulley when switching between forward and reverse (when stopping forward and reverse) [and thus to ensure a high level of responsiveness to drive when switching between forward and reverse (when starting / stopping forward and reverse), in other words, to always keep the difference in rotation angle between the drive pulley and driven pulley when switching between forward and reverse within an acceptable range], repeatedly ensure positioning accuracy, and ensure synchronous transmission [automatically (including adjustment for the drop in tension that occurs at the beginning of running) and maintain an appropriate belt tension (to the extent that the belt does not slacken)].

[0118] Therefore, in this example, belt transmission mechanisms according to Examples 1 to 4 and Comparative Examples 1 to 4 (hereinafter referred to as "test specimens") were fabricated, and a damping test [evaluation of damping of the driven pulley when switching between forward and reverse (when stopping forward and reverse)] and a responsiveness test [evaluation of responsiveness to drive when switching between forward and reverse (when starting / stopping forward and reverse)] were conducted for comparative verification. Note that the present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0119] [Belt transmission mechanism] (Common to all test specimens) (Toothed belt: Figure 13) Tooth shape: The tooth shape was an H-tooth type belonging to straight teeth (cross section is roughly semicircular). Number of teeth: 200 Tooth pitch: 3 mm Belt length: 600 mm Belt width: 10 mm

[0120] [Materials Used] (Core Wire) - Configuration: Twisted cords A1 to A3 with the configuration shown in Table 2 were prepared as the core wire used in each toothed belt of each test specimen. - The core wire (twisted cord) of A1 was prepared using the following procedure. Filaments (9 micron diameter) of glass fiber (E-glass fiber) designated ECG-150 as described in JIS R 3413 (2012) were bundled and pulled together to form three strands. These three strands were immersed in an RFL liquid (18-23°C) with the composition shown in Table 3 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 adhesive treatment, the three strands were first twisted 12 times per 10 cm without any final twist to prepare a twisted cord with a diameter of approximately 0.35 mm. The core wire (twisted cord) A2 was produced in the same manner as A1, except that the glass fiber was changed to KCG 150. The core wire (twisted cord) A3 was produced in the same manner as the core wires A1 and A2, except that the strand used was a single strand made by bundling and paralleling carbon fiber filaments (3K), and was a single-twisted twisted cord with a diameter of 0.53 mm.

[0121]

[0122] (Elastic Modulus of Core Wire) Here, we will explain the method for measuring the elastic modulus (tensile modulus) of the core wire (longitudinal direction) shown in Table 2. Chucks (gripping tools) were attached to the lower fixing part and the upper load cell connecting part of an autograph ("AGS-J10kN" manufactured by Shimadzu Corporation), and both ends of the core wire were grasped with the chucks. Next, the core wire was pulled at a speed of 250 mm / min until it broke, and the measured stress-strain curve was used to calculate the tensile modulus of the core wire from the slope of the straight line in the relatively linear region (100 to 200 N).

[0123] (Tooth Fabric) The fiber woven fabric used for the tooth fabric of each specimen was of one of the following types: The weft was made of 66 nylon and the warp was made of 66 nylon. The yarn structure was a 44 dtex woolly processed weft and a 44 dtex warp. The weave structure was a twill weave. The tooth fabric with the above structure was subjected to an RFL treatment using the RFL treatment solution shown in Table 3. Thereafter, it was subjected to an adhesive treatment using a rubber glue prepared by dissolving the same rubber composition as the unvulcanized rubber sheet shown in Table 4 in toluene, and then a rubber composition sheet with the composition shown in Table 4 was laminated and coated.

[0124]

[0125] (Rubber Composition) - A rubber composition having the composition shown in Table 4 [rubber component: chloroprene rubber (CR)] was kneaded in a Banbury mixer, and this kneaded rubber was passed through a calendar roll to form a rolled rubber sheet of the specified thickness, to prepare unvulcanized rubber sheets for forming the back and tooth portions of each toothed belt of each test specimen. - The prepared rubber composition (unvulcanized rubber sheet) was press-vulcanized at 165°C for 30 minutes to obtain a vulcanized rubber sheet. The hardness of the vulcanized rubber sheet was approximately 81, as measured using a Type A durometer at an ambient temperature of 23°C (23±2°C) in accordance with JIS K 6253 (2012). - The components marked with an asterisk in Table 4 are as follows.

[0126] *1 "PM-40" manufactured by Denka *2 "Nocrac MB" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *3 "N-cyclohexyl-2-benzothiazole sulfenamide" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. *4 "Seast 3" manufactured by Tokai Carbon Co., Ltd. *5 "Zinc oxide type 3" manufactured by Seido Chemical Industry Co., Ltd.

[0127] [Manufacturing of Toothed Belts] Each toothed belt specimen was manufactured using the core wire (adhesive-treated), tooth cloth (adhesive-treated), and rubber composition (unvulcanized rubber sheet) described above in the Materials Used section, using the standard press-fitting method described in the above embodiment. Vulcanization was performed at 161°C for 25 minutes. To achieve a predetermined thickness for the back portion, the back surface of the vulcanized belt sleeve was polished to a predetermined thickness and then cut to a predetermined width to obtain each toothed belt specimen. Since the toothed belts were manufactured using the standard press-fitting method, the back portion and the toothed portion were made of rubber compositions with the same composition. Therefore, in each toothed belt, the hardness of the rubber composition constituting the back portion and the hardness of the rubber composition constituting the toothed portion were approximately the same.

[0128] (Pulley Layout) In the belt transmission mechanisms of Examples 1 to 4 (see FIG. 2 for Examples 1, 3, and 4, and FIG. 10 for Example 2) and Comparative Examples 1 to 4 (not shown for Comparative Examples 2 to 4, and FIG. 7 for Comparative Example 1), the drive pulley and driven pulley were straight-tooth pulleys, and the two-axis layout was fixed between the axes. An axle load detector (load cell) was attached to the rotating shaft of one of the pulleys (the drive pulley). Number of teeth / pulley diameter of the drive pulley (assuming a core line): 21 teeth / 20.054 mm Number of teeth / pulley diameter of the driven pulley (assuming a core line): 84 teeth / 80.214 mm Reduction ratio: 4 (the driven pulley has a pitch diameter four times larger than that of the drive pulley). Belt installation tension: The required level of belt installation tension was approximately 5 N / mm width (5 N per 1 mm width of the belt). In this specification, the belt tension measured in a stationary state immediately before actual running [after idling (break-in)] is treated as the "belt installation tension." The belt installation tension was calculated from the shaft load detected by the shaft load detector (load cell) connected to one of the rotating shafts (drive pulley). The center distance was set to 220 mm (standard value).

[0129] (Autotensioner and Regulating Means (Regulating Member)) (Examples 1, 3-4) The autotensioner and regulating means (regulating member) described in the above embodiment (see FIGS. 3 and 4) were attached to a belt transmission mechanism in the manner shown in FIG. 2. In other words, the autotensioners and regulating means in Examples 1, 3, and 4 all had the same configuration: an autotensioner configured so that the biasing action of a spring (tension spring) stretched between the base shafts of the two tension rollers and the oscillation action around the oscillation shaft act together on the two tension rollers; and a regulating means provided so as to be able to come into contact with the first oscillation arm and the second oscillation arm after the toothed belt is installed between the pulleys (fixed (bolted) to the table of the evaluation testing machine described below). The regulating means was a metal part made of aluminum alloy casting (ADC12) and formed into a single block shape in plan view.

[0130] (Example 2) As shown in Figure 10, an autotensioner and a regulating means were fabricated and attached to a belt transmission mechanism, with the same configuration as in Examples 1, 3 and 4 (see Figure 2), except that a spring (tension spring) was tensioned between two arm members (between one swing arm and the other swing arm).

[0131] Comparative Example 1 As shown in FIG. 7, assuming a configuration in which the belt transmission mechanism does not have a regulating means, an autotensioner having the same configuration as in Examples 1, 3, and 4 (see FIG. 2) was manufactured and attached to the belt transmission mechanism.

[0132] (Comparative Example 2) Assuming that the belt transmission mechanism does not have a regulating means, an autotensioner (not shown) was manufactured based on the autotensioner of Example 1 (see Figure 2) and configured so that only the biasing action of the spring (tension spring) acts on the two tension rollers, and no oscillation action around the oscillation axis acts, and was attached to the belt transmission mechanism.

[0133] Comparative Example 3 The belt transmission mechanism did not have an autotensioner or a restricting means (that is, it was configured with only a drive pulley, a driven pulley, and a toothed belt) (not shown).

[0134] (Comparative Example 4) Assuming that the belt transmission mechanism does not have a regulating means, an autotensioner (not shown) was manufactured based on the autotensioner of Example 1 (see Figure 2) and configured so that the spring biasing action does not work on the two tension rollers, but only the oscillation action around the oscillation axis works, and this was attached to the belt transmission mechanism.

[0135] [Evaluation of Belt Transmission Mechanism: Items, Methods, and Criteria] For each test specimen (Examples 1 to 4, Comparative Examples 1 to 4), in order to determine whether a belt transmission mechanism capable of solving the problem of the present application was obtained, the necessity of aging (whether or not automatic adjustment (correction) of the decrease in tension at the beginning of belt running can be performed), damping (damping of the driven pulley when stopped in forward and reverse), and responsiveness (responsiveness to drive when switching between forward and reverse) were verified.

[0136] [Necessity of Aging] (Method, Evaluation Criteria) If the specified belt installation tension (approximately 5 N / mm width) could be secured without aging [belt readjustment (tension adjustment work) by adjusting the center distance after idle running (break-in)], it was evaluated as being able to automatically adjust (correct) the decrease in tension at the beginning of belt running, and was given a rating of a. If aging [belt readjustment (tension adjustment work) by adjusting the center distance after idle running (break-in)] was required to secure the specified belt installation tension (approximately 5 N / mm width), it was evaluated as being unable to automatically adjust (correct) the decrease in tension at the beginning of belt running, and was given a rating of b, and subsequent testing (responsiveness testing) was not carried out. From the perspective of suitability for practical use in this application (necessity of aging), belt transmission mechanisms rated a were deemed to pass.

[0137] [Damping and Response] (Test Name) Damping and Response Test (Testing Machine) A responsiveness evaluation testing machine was used for the test (see Figure 14). The responsiveness evaluation testing machine runs a toothed belt wound around two pulleys in a test pattern (cycle pattern) involving frequent forward and reverse rotation. A pair of rotary encoders (rotation angle detectors) attached to each shaft output rotation pulse signals to detect time-series changes in the rotation speed of each pulley during operation, as well as time-series changes in the rotation angle difference (drive shaft rotation angle - driven shaft rotation angle) during operation. The pulley layout was the same as that of the belt transmission mechanism described above (Figure 2). That is, the pulley layout of the responsiveness evaluation testing machine included a drive pulley and a driven pulley, with a fixed center distance of 220 mm. In addition, considering the intended use (driving a robot arm), a flywheel was attached to the driven side to apply a predetermined load torque. Furthermore, considering the intended use (driving a robot arm), a pair of rotary encoders with excellent resolution for the rotation angle (encoder with an angular resolution of 0.0044° (CANON R-1L)) were used so that the rotation angle of the drive pulley and the rotation angle of the driven pulley could be detected with high accuracy.

[0138] (Test Method) At room temperature, a toothed belt wound around pulleys (with a fixed center distance) at a predetermined belt installation tension (approximately 5 N / mm width) was run under the test conditions shown in Table 5 (only the rotation speed of the drive pulley was varied) and under the test pattern (cycle pattern) shown in Fig. 15, with frequent forward and reverse rotation repeated for 250 cycles. From the obtained graphs (not shown) of the time series changes in the rotation speed of each pulley (drive pulley, driven pulley) and the obtained graphs (not shown) of the time series changes in the rotation angle difference, the test results were read as to whether or not the driven pulley reversed when stopped in the forward and reverse directions, and the level of the rotation angle difference (maximum absolute value), for each of the varied load torques of the driven pulley (0.8, 3 N m) and the varied rotation speeds of the drive pulley (2, 5 rps). In addition, the rotation angle difference, when viewed over time, overshoots and undershoots when switching between forward and reverse directions [when starting (accelerating) and when stopping (decelerating)], so its absolute value is greatest when switching between forward and reverse directions (frequency: 4 times per cycle). The acceleration and deceleration rates when switching between forward and reverse directions corresponding to each rotation speed of the drive pulley are shown in Tables 6 and 7.

[0139]

[0140] (Judgment Criteria [Damping Performance]) To judge damping performance (damping performance of the driven pulley when stopped in forward and reverse directions), the presence or absence of a reversal of the driven pulley (from forward rotation to reverse rotation, or from reverse rotation to forward rotation) when stopped in forward and reverse directions was used as an indicator (if there is no reversal, a high level of damping can be ensured, and therefore a high level of responsiveness to drive when switching between forward and reverse can be ensured). When switching between forward and reverse directions (when stopped in forward and reverse directions), if no reversal of the driven pulley was observed for each load torque of the driven pulley and each acceleration / deceleration of the drive pulley (in other words, if the driven pulley only overshoots or undershoots when stopped in forward and reverse directions), it was judged to be rated a, and if reversal of the driven pulley was observed even once for each load torque of the driven pulley and each acceleration / deceleration of the drive pulley, it was judged to be rated b. From the perspective of suitability (damping performance) for practical use in this application, a belt transmission mechanism rated a was deemed to be at the pass level.

[0141] (Judgment Criteria [Responsiveness]) To judge responsiveness (responsiveness to drive when switching between forward and reverse), the difference in rotation angle between the drive pulley and the driven pulley when switching between forward and reverse was used as an index (the smaller the absolute value, the higher the responsiveness, and the more repeatable the positioning accuracy and the more reliable the synchronous transmission), and when switching between forward and reverse (when starting / stopping forward and reverse), the following were assigned: A rating of "a" was given if the difference in rotation angle (absolute value) for each load torque of the driven pulley and each acceleration / deceleration of the drive pulley was always within 0.1°; A rating of "b" was given if the difference in rotation angle (absolute value) for each load torque of the driven pulley and each acceleration / deceleration of the drive pulley exceeded 0.1° even once but was always within 0.2°; and A rating of "c" was given if the difference in rotation angle (absolute value) for each load torque of the driven pulley and each acceleration / deceleration of the drive pulley exceeded 0.2° even once. From the perspective of suitability (responsiveness) for actual use in this application, belt transmission mechanisms rated "a" and "b" were deemed to be pass levels.

[0142] [Overall Judgment] The criteria for the overall judgment (ranking) of a belt transmission mechanism as a solution to this problem were determined as follows, based on the results of the judgments in the above three evaluation items (necessity of aging, damping, and responsiveness). Rank A: If all of the above evaluation items were rated a, it was judged to have no practical problems and was ranked as the best. Rank B: If both the evaluation items for necessity of aging and damping were rated a, and the evaluation item for responsiveness was rated b, it was ranked as having no practical problems but was slightly inferior. Rank C: If even one of the evaluation items for necessity of aging and damping was rated b, and / or the evaluation item for responsiveness was rated c, it was ranked as insufficient (failed) as a solution to this problem.

[0143] [Verification Results] The verification results are shown in Tables 6 and 7. (Comparison of autotensioner configurations and whether or not restriction means is installed)

[0144] (Examples 1 and 2, Comparative Examples 1 to 4) Based on the belt transmission mechanism of Example 1 (equipped with an auto-tensioner configured so that the biasing action of a spring stretched between the base shafts of two tension rollers and the swinging action around the swing shaft work together for two tension rollers, and with a regulating means), the configuration of the auto-tensioner (including whether or not an auto-tensioner is installed) or whether or not a regulating means is installed was changed and compared.

[0145] In cases where the belt transmission mechanism has an auto-tensioner in which a spring biasing action acts on the two tension rollers (Examples 1-2, Comparative Examples 1-2), aging is not required (rating a). In Examples 1-2, in which the two tension rollers are biased not only by the spring but also by an oscillation action about the oscillation shaft, and in which a regulating means is installed, the damping performance was also rated a. However, in Comparative Example 1, in which the two tension rollers are biased not only by the spring but also by an oscillation action about the oscillation shaft, but which is not equipped with a regulating means, the damping performance deteriorated as the load on the driven pulley increased (from 0.8 N m to 3 N m), and the damping performance was rated b (failure level). As a result, the responsiveness was rated c (rank C in the overall rating). Of Examples 1 and 2, Example 1, in which a spring was tensioned between the base shafts of the two tension rollers, also received an a rating for responsiveness (rank A in the overall assessment), but Example 2, in which a spring was not tensioned between the base shafts of the two tension rollers but was tensioned between the two arm members, received a b rating (rank B in the overall assessment), which was at an acceptable level for responsiveness but slightly inferior to Example 1 (rated a).On the other hand, Comparative Example 3, which did not have an auto-tensioner in the belt transmission mechanism, and Comparative Example 4, which had an auto-tensioner in which the biasing action of a spring did not act on the two tension rollers but only caused them to oscillate around the oscillating shaft, required aging (rated b) and received a rank C in the overall assessment.

[0146] (Comparison of different core wire types in toothed belts)

[0147] (Examples 1, 3 to 4) The fiber material (filament material) constituting the core wire of the toothed belt was changed and compared based on the toothed belt (E glass fiber: A1) of Example 1. Example 3 used a core wire of high-strength glass fiber (K ​​glass fiber: A2) with a higher elastic modulus than Example 1, and Example 4 used a core wire of carbon fiber (A3) with an even higher elastic modulus than Example 3. As the core wire (i.e., the belt) became higher in elastic modulus and lower in elongation, the level of the rotation angle difference (maximum absolute value) per load torque of the driven pulley and per rotation speed of the drive pulley became smaller, and responsiveness (responsiveness to drive when switching between forward and reverse) tended to become higher, and under these conditions (Examples 1, 3 to 4), they were ranked A.

[0148] (Effects Obtained) From the above verification results, when the belt transmission mechanisms of Examples 1 to 4 are applied to a belt transmission mechanism that is driven to be capable of forward and reverse rotation, such as for driving a robot arm, the auto-tensioner is configured so that the biasing action of the springs (tension springs) and the swinging action about the swing shaft work together on the two tension rollers, and the mechanism is provided with a restricting means that restricts the two tension rollers from swinging about the swing shaft from a balanced position in which the drive pulley and driven pulley are stopped in a direction opposite to the biasing direction of the springs. Therefore, a predetermined belt installation tension (approximately 5 N / mm width) can be secured without aging (re-tensioning the belt by adjusting the center distance, etc., after idling (break-in)), and a decrease in tension at the beginning of belt running can be automatically adjusted (corrected), and the speed of operation involving forward and reverse rotation (acceleration / deceleration of the drive pulley) can be reduced to 10 to 25 revolutions / s. 2 Even when the load on the driven pulley increased from 0.8 N m to 3 N m at a relatively large level, the presence or absence of reverse rotation of the driven pulley, which is an indicator of the damping ability of the driven pulley when stopped in forward and reverse, could be kept in a "no reverse" state, and furthermore, the rotation angle difference (absolute value), which is an indicator of the responsiveness to drive when switching between forward and reverse, could be kept within the allowable range (within 0.2°), so even if the load on the driven pulley increased, positioning accuracy could be repeatedly ensured, making it easier to ensure reliable synchronous transmission.

[0149] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-124260 filed on July 31, 2023 and Japanese Patent Application No. 2024-115605 filed on July 19, 2024, the contents of which are incorporated herein by reference.

[0150] REFERENCE SIGNS LIST 1 Belt transmission mechanism 11 Second arm 2 Drive pulley 21 Drive shaft 22 Rotation center 3 Driven pulley 31 Driven shaft 32 Rotation center 4 Toothed belt 5 Auto tensioner 51 First tension roller 51A First base shaft portion 52 Second tension roller 52A Second base shaft portion 53 Swing shaft 54 ​​Spring 55 Sliding member 56 First swing arm 561 Tip portion 562 Base end portion 57 Second swing arm 571 Tip portion 572 Base end portion 6 Restricting member (restricting means) 61 Main body portion 62 First swing arm restricting portion 63 Second swing arm restricting portion R Central axis PL Pulley center line RL Roller center line

Claims

1. A belt transmission mechanism comprising: a drive pulley fixed to a drive shaft that is driven by a drive source to be rotatable in both directions; a rotatably supported driven pulley; a toothed belt wound between the drive pulley and the driven pulley; and an auto-tensioner that is rotatable about its respective base shafts at both sides of a pulley center line that connects the rotation centers of the drive pulley and the driven pulley, and that automatically maintains an appropriate tension in the toothed belt via two tension rollers that contact the toothed belt, wherein the auto-tensioner comprises: a swing shaft that is provided to extend in a direction parallel to the drive shaft, passing through a point on the pulley center line or a point on an extension of the pulley center line, spaced from the intersection of the pulley center line and a roller center line that connects the rotation centers of the two tension rollers; and a spring that biases the two tension rollers in a direction that draws them together or moves them away from each other; and The two tension rollers are configured to be freely oscillating around the oscillating shaft, and the belt transmission mechanism further includes a regulating means for regulating the oscillation of the two tension rollers, the regulating means being provided at a position that regulates the two tension rollers from oscillating around the oscillating shaft in a direction opposite to the biasing direction of the spring from a balanced position in which the drive pulley and the driven pulley are stopped.

2. The belt transmission mechanism described in claim 1, wherein the autotensioner has a first swing arm, one end of which is provided with the base shaft portion of one of the tension rollers and the other end of which is supported for free rotation on the swing shaft, and a second swing arm, one end of which is provided with the base shaft portion of the other tension roller and the other end of which is supported for free rotation on the swing shaft, the two tension rollers are configured to swing about the swing shaft via the first swing arm and the second swing arm, and the regulating means is provided in a position where it can come into contact with the first swing arm and the second swing arm.

3. A belt transmission mechanism as described in claim 1 or 2, characterized in that the spring is tensioned on the roller center line between the base shaft portions of the two tension rollers and biases the two tension rollers.

4. A belt transmission mechanism as set forth in any one of claims 1 to 3, characterized in that the oscillating shaft is spaced away from the intersection of the center line of the roller and the center line of the pulley toward the driven pulley.

5. A belt transmission mechanism as described in any one of claims 1 to 4, characterized in that the two tension rollers are provided on the drive pulley side, or on the side of the drive pulley or driven pulley whichever has a smaller diameter.

6. A belt transmission mechanism as claimed in any one of claims 1 to 5, characterized in that the spring is a tension spring, and the two tension rollers are arranged so as to contact the outer circumferential surface of the toothed belt.

7. A belt transmission mechanism according to any one of claims 1 to 6, characterized in that the diameter of the driving pulley is smaller than the diameter of the driven pulley.

8. A belt transmission mechanism according to any one of claims 1 to 7, characterized in that the driving pulley and the driven pulley are fixed to a robot arm and drive the robot arm.

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