Power transmission device and drive unit

Abstract

The present invention provides a power transmission device that can reduce the torque required for unlocking while suppressing the occurrence of jerking phenomena. [Solution] The power transmission device comprises a fixed component, an output shaft having a concave surface, an input shaft having a pressing portion, a pair of first rolling elements arranged on both sides of the pressing portion in the circumferential direction, and a pair of intermediate objects arranged between the first rolling elements and the pressing portion. The concave surface has a bottom surface and a pair of pressed surfaces. The bottom surface has a cam surface on the radially outward side where the first rolling elements are arranged, and a guide surface on the radially outward side where the intermediate objects are arranged. The distance between the cam surface and the inner circumferential surface increases as it approaches the pressed surfaces. In the portion of the cam surface closer to the guide surface, the distance between it and the inner circumferential surface is smaller than the diameter of the first rolling elements. The intermediate objects are sandwiched between the first rolling elements, the guide surface, and the pressing portion. When the pressing portion moves from its position in the circumferential center to the circumferential outward side, the pressing portion pushes the intermediate objects between the first rolling elements and the guide surface.

Description

Technical Field

[0001] The present disclosure relates to a power transmission device and a drive unit.

Background Art

[0002] A power transmission device is a device that transmits torque generated by a motor or the like. Such a power transmission device is used, for example, in a drive unit that drives an arm of an industrial robot. The power transmission device includes an input shaft to which torque is input and an output shaft that outputs torque. An object to be driven is connected to the output shaft. Therefore, the weight of the object or the like (hereinafter referred to as an external force) may act on the output shaft. Here, when the output shaft rotates due to an external force, the position of the object is not maintained. Therefore, in the power transmission device of Patent Document 1, the output shaft does not rotate even when an external force acts on the output shaft.

[0003] The details of the power transmission device of Patent Document 1 will be described. The power transmission device of Patent Document 1 includes an annular fixed part, an output shaft having a cam surface facing the inner peripheral surface of the fixed part, a cylindrical roller disposed between the fixed part and the cam surface, and an input shaft having a pressing part disposed in the circumferential direction of the cylindrical roller. When an external force acts on the output shaft and the output shaft rotates, the cylindrical roller is sandwiched between the fixed part and the cam surface, and the rotation of the output shaft is restricted. Further, when torque is input to the input shaft, the pressing part presses the cylindrical roller. As a result, the cylindrical roller sandwiched between the fixed part and the cam surface moves, and the locked state is released.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, at the start of torque input to the input shaft, an external force acting on the output shaft in the same direction as the torque may be present. In this case, even if a cylindrical roller sandwiched between the fixed part and the cam surface is pressed and moved by the pressing part, the cam surface may move in the same direction, potentially causing the cylindrical roller to become sandwiched between the fixed part and the cam surface again. In other words, the unlocked and locked states may repeatedly occur alternately, potentially resulting in intermittent rotation of the input and output members. Therefore, there is a need for the development of a power transmission device that is less prone to the phenomenon of repeated unlocking and locking (hereinafter referred to as the jerking phenomenon). Furthermore, reducing the torque required to unlock the device has been a long-standing desire.

[0006] This disclosure has been made in view of the above, and aims to provide a power transmission device and drive unit that can reduce the torque required for unlocking while suppressing the occurrence of the jerking phenomenon. [Means for solving the problem]

[0007] To achieve the above objective, a power transmission device according to one aspect of the present disclosure includes: an annular fixed part having an inner circumferential surface; an output shaft having an outer circumferential surface facing the inner circumferential surface and a concave surface recessed radially inward from the outer circumferential surface; an input shaft having a pressing portion housed inside the concave surface; a pair of first rolling elements housed inside the concave surface and arranged on both sides of the pressing portion in the circumferential direction; and a pair of intermediate objects arranged between the first rolling elements and the pressing portion. The concave surface has a bottom surface extending in the circumferential direction and facing the inner circumferential surface in the radial direction; and a pair of pressed surfaces extending radially outward from both ends of the bottom surface in the circumferential direction. The bottom surface has a pair of cam surfaces on which the first rolling elements are arranged radially outward, and a pair of guide surfaces on which the intermediate objects are arranged radially outward. The distance between the cam surfaces and the inner circumferential surface gradually increases as they approach the pressed surfaces. The portion of the cam surfaces closer to the guide surfaces has a distance from the inner circumferential surface that is smaller than the diameter of the first rolling elements. The portion of the cam surface closer to the pressed surface has a distance from the inner circumferential surface that is greater than the diameter of the first rolling element. The intermediate object is sandwiched between the first rolling element, the guide surface, and the pressing portion. When the pressing portion moves from its position in the circumferential center of the concave surface to the circumferential outward direction, the pressing portion pushes the intermediate object between the first rolling element and the guide surface. The intermediate object is either a second rolling element with a smaller diameter than the first rolling element, or a wedge-shaped body having a wedge surface that gradually narrows in the direction in which it is pushed into the pressing portion.

[0008] Furthermore, in order to achieve the above objective, a drive unit according to one aspect of this disclosure includes a motor and the power transmission device described above. Torque generated by the motor is input to the input shaft. [Effects of the Invention]

[0009] According to the power transmission device and drive unit of this disclosure, the occurrence of jerking phenomena is suppressed, and the torque required to unlock is also reduced. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic diagram of the power transmission device of Embodiment 1, viewed from the axial direction. [Figure 2] Figure 2 is a cross-sectional view taken along the line II-II in Figure 1. [Figure 3] Figure 3 is a magnified view of one of the concave surfaces in Figure 1. [Figure 4] Figure 4 is a magnified view of a portion of Figure 3. [Figure 5] Figure 5 is a diagram illustrating the operating state of the power transmission device of Embodiment 1, and more specifically, it shows the state at the start of torque input. [Figure 6] Figure 6 is a diagram illustrating the operating state of the power transmission device of Embodiment 1, and more specifically, it shows the state when the lock state is released. [Figure 7] Figure 7 is a diagram illustrating the operating state of the power transmission device of Embodiment 1, and more specifically, it shows the state in which the first roller is in contact with the pressed surface. [Figure 8] Figure 8 is a diagram illustrating the operating state of the power transmission device of Embodiment 1, and more specifically, it shows the point in time when the first roller begins to return to the second rotation direction. [Figure 9] Figure 9 shows the power transmission device of Embodiment 1 at the point when an external force (first rotation direction) is acting on the output shaft and torque (first rotation direction) is started to be input to the input shaft. [Figure 10] Figure 10 shows the power transmission device of Embodiment 1 at the point when an external force (second rotation direction) is acting on the output shaft and torque (first rotation direction) is started to be input to the input shaft. [Figure 11] Figure 11 is a magnified view of one of the concave surfaces of the power transmission device in Modification Example 1. [Figure 12] Figure 12 shows the power transmission device of Modified Example 1, in which the pressing part is pressing the surface to be pressed via the first roller. [Figure 13] Figure 13 is a magnified view of one of the concave surfaces of the power transmission device in the modified example 2. [Figure 14]FIG. 14 is a view showing a state in which the pressing portion presses the pressed surface via the second roller and the first roller in the power transmission device of Modification 2. [Figure 15] FIG. 15 is a partial cross-sectional view showing an enlarged view of the vicinity of the pressed surface in the power transmission device of Modification 3. [Figure 16] FIG. 16 is an enlarged view showing an enlarged view of one of the concave surfaces of the power transmission device of Modification 4. [Figure 17] FIG. 17 is a schematic view of one of the concave surfaces of the power transmission device of Modification 5 viewed from the axial direction. [Figure 18] FIG. 18 is a schematic view for explaining the configuration of the drive unit of Embodiment 2. [Figure 19] FIG. 19 is a schematic view for explaining the configuration of the drive unit of Modification 6.

MODE FOR CARRYING OUT THE INVENTION

[0011] Embodiments for carrying out the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by the contents described in the following description. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and substantially the same ones. Furthermore, the constituent elements described below can be combined as appropriate.

[0012] (Embodiment 1) FIG. 1 is a schematic view of the power transmission device of Embodiment 1 viewed from the axial direction. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1. As shown in FIG. 1, the power transmission device 100 of Embodiment 1 includes a fixed component 1, an output shaft 2, an input shaft 3, a plurality of first rollers (first rolling elements) 4, and a plurality of second rollers (second rolling elements) 5.

[0013] The fixed component 1 is an annular component. The inner peripheral surface 10 and the outer peripheral surface 11 of the fixed component 1 are formed in a circular shape centered on the central axis X. Hereinafter, the direction parallel to the central axis X of the inner peripheral surface 10 is referred to as the axial direction. The direction orthogonal to the central axis X is referred to as the radial direction. The direction of rotation about the central axis X is referred to as the circumferential direction.

[0014] As shown in Figure 2, the output shaft 2 comprises an inner ring portion 20 located inside the fixed component 1 and an output shaft body 21 protruding from the inner ring portion 20 in one axial direction. The input shaft 3 comprises a torque transmission portion 30 located inside the fixed component 1 and an input shaft body 31 protruding from the torque transmission portion 30 in the other axial direction.

[0015] Regarding the axial direction, the direction in which the input shaft body 31 protrudes when viewed from the torque transmission section 30 is referred to as the first direction X1. The direction in which the output shaft body 21 protrudes when viewed from the inner ring section 20 is referred to as the second direction X2. Furthermore, regarding the circumferential direction, the explanation will be based on the view from the second direction X2, as shown in Figure 1. The counterclockwise direction when viewed from the second direction X2 is referred to as the first rotation direction L1. The clockwise direction when viewed from the second direction X2 is referred to as the second rotation direction L2.

[0016] As shown in Figure 1, the outer circumferential surface 22 of the inner ring portion 20 faces the inner circumferential surface 10 of the fixing component 1. The diameter of the outer circumferential surface 22 is approximately the same as the diameter of the inner circumferential surface 10 of the fixing component 1. Furthermore, the inner ring portion 20 is rotatably positioned on the inner circumference side of the fixing component 1.

[0017] Three concave surfaces 23 are formed on the outer circumferential surface 22 of the inner ring portion 20, recessing radially inward. Inside one of the concave surfaces 23 are the pressing portion 34 of the input shaft 3 (described later), two (a pair) of first rollers 4, and two (a pair) of second rollers 5.

[0018] As shown in Figure 2, the outer diameter of the torque transmission section 30 is approximately the same as the diameter of the inner circumferential surface 10 of the fixed part 1. The torque transmission section 30 is rotatably positioned on the inner circumferential side of the fixed part 1. The torque transmission section 30 also has a disc-shaped disc portion 33 positioned in a first direction X1 relative to the inner ring portion 20, and a pressing portion 34 protruding from the disc portion 33 in a second direction X2.

[0019] As shown in Figure 1, the first roller 4 and the second roller 5 are cylindrical rollers formed in a cylindrical shape. The diameter of the first roller 4 is H1 (see Figure 1). The second roller 5 has a diameter of H2 (see Figure 1), which is smaller than that of the first roller 4.

[0020] The three imaginary lines W1, W2, and W3 shown in Figure 1 are straight lines extending radially from the central axis X and are spaced at 120° intervals. The internal shape of the fixed component 1 is three-fold rotationally symmetric with respect to the central axis X. In other words, if the fixed component 1 is divided into three parts circumferentially along the imaginary lines W1, W2, and W3, the shape of one of the divided parts is identical to the other shapes. The following explanation will describe one of the three divided parts.

[0021] Figure 3 is an enlarged view of one of the concave surfaces in Figure 1. The dashed line W4 in Figure 3 passes through the circumferential center of the concave surface 23 from the central axis X. The concave surface 23 is formed symmetrically with respect to the dashed line W4. More specifically, the concave surface 23 has a bottom surface 24 and a pair of pressure surfaces 25. The bottom surface 24 has a central surface 26 located in the circumferential center of the bottom surface 24, a pair of cam surfaces 27 located at both ends of the bottom surface 24 in the circumferential direction, and a pair of guide surfaces 28 located between the central surface 26 and the cam surfaces 27. Hereinafter, the direction in which the cam surfaces 27 are positioned when viewed from the central surface 26 in the circumferential direction will be referred to as the circumferential outer direction. Also, the direction in which the central surface 26 is positioned when viewed from the cam surfaces 27 in the circumferential direction will be referred to as the circumferential inner direction.

[0022] The first roller 4 is positioned radially outward of the cam surface 27. The diameter M1 from the central axis X to the cam surface 27 gradually decreases as it approaches the pressed surface 25. Therefore, the distance M2 between the inner circumferential surface 10 of the fixed part 1 and the cam surface 27 gradually increases as it approaches the pressed surface 25.

[0023] When the first roller 4 moves closer to the guide surface 28, the first roller 4 is sandwiched between the cam surface 27 and the inner circumferential surface 10, causing the output shaft 2 to lock. In other words, the distance M2 from the part of the cam surface 27 closer to the guide surface 28 to the inner circumferential surface 10 is smaller than the diameter H1 of the first roller 4 (see Figure 1).

[0024] On the other hand, when the first roller 4 moves closer to the pressed surface 25, the first roller 4 is not sandwiched between the cam surface 27 and the inner circumferential surface 10 but is loosely fitted (unlocked). In other words, the distance M2 from the part of the cam surface 27 closer to the pressed surface 25 to the inner circumferential surface 10 is greater than the diameter H1 of the first roller 4 (see Figure 1).

[0025] To explain the locked state in detail, when the first roller 4 positioned in the first rotation direction L1 is gripped against the pressing part 34, the rotation of the output shaft 2 in the first rotation direction L1 is restricted. On the other hand, when the first roller 4 positioned in the second rotation direction L2 is gripped against the pressing part 34, the rotation of the output shaft 2 in the second rotation direction L2 is restricted.

[0026] As shown in Figure 3, the central surface 26 is formed in a straight line perpendicular to the imaginary line W4. However, in this disclosure, the central surface 26 may be formed in an arc shape around the central axis X instead of being a straight line.

[0027] Figure 4 is an enlarged view of a portion of Figure 3. The second roller 5 is positioned radially outward from the guide surface 28. The second roller 5 is also in contact with the guide surface 28. The circumferential position of the second roller (second rolling element) 5 is between the first roller (first rolling element) 4 and the pressing portion 34 (intermediate). In the following, the second roller (second rolling element) 5 may be referred to as the intermediate object.

[0028] The guide surface 28 is positioned radially inward as it moves circumferentially outward. Therefore, as the second roller 5 moves circumferentially outward along the guide surface 28, the amount it sinks radially inward increases.

[0029] Furthermore, the shortest distance between the locked first roller 4 and the guide surface 28 (see Figure 4) is H3. This shortest distance H3 is smaller than the diameter H2 of the second roller 5 (see Figure 1). The center X5 of the second roller 5 is located radially outward from the line indicating the shortest distance H3. Also, when the first roller 4 moves circumferentially outward, the shortest distance H3 moves radially inward (circumferentially outward) as indicated by arrow Y in Figure 4. In other words, the second roller 5 becomes capable of moving radially inward (circumferentially outward).

[0030] The pressed surface 25 is the surface that the first roller 4 contacts. The pressed surface 25 is linear from its radial inner end 25a to its radial outer end 25b. Furthermore, the outer end 25b is positioned circumferentially outward from a hypothetical line W5 drawn from the central axis X to the inner end 25a. In other words, the pressed surface 25 is tilted circumferentially outward.

[0031] An elastic coil spring 50 is provided between the pressed surface 25 and the first roller 4. The coil spring 50 is positioned in a state that is compressed from its natural length. The first roller 4 is constantly biased inward in the circumferential direction by the coil spring 50. Therefore, even without an external force being applied to the output shaft 2, the first roller 4 becomes trapped (locked) between the inner circumferential surface 10 and the cam surface 27.

[0032] A hole 51 is formed in the pressed surface 25. A portion of the coil spring 50 is housed in the hole 51. When the first roller 4 moves outward in the circumferential direction, the coil spring 50 is housed in the hole 51, and the first roller 4 comes into contact with the pressed surface 25 (see Figure 7). Also, as shown in Figure 1, the hole 51 penetrates the pressed surface 25 of another concave surface 23 located on the back side of the pressed surface 25. In other words, the hole 51 communicates the interiors of adjacent concave surfaces 23 in the circumferential direction. One coil spring 50 biases two first rollers 4.

[0033] As shown in Figure 4, the pressing portion 34 has a pair of side surfaces 35 facing outward in the circumferential direction, an inner surface 36 facing inward in the radial direction, and a pair of intermediate object pressing surfaces 37 formed at the corners where the side surfaces 35 and the inner surface 36 intersect.

[0034] The side surface 35 has an inner surface 351 positioned radially inward with respect to the radial center of the side surface 35, and an outer surface 352 positioned radially outward. The outer surface 352 is positioned circumferentially outward as it extends radially outward, and protrudes circumferentially outward more than the inner surface 351.

[0035] The imaginary line W6 shown in Figure 4 is a straight line perpendicular to the imaginary line W4 (see Figure 3). The inner surface 36 extends along the imaginary line W6. The pressing surface 37 for the intermediate object is formed in a straight line. When the pressing portion 34 is positioned in the circumferential center, the pressing surface 37 for the intermediate object is in contact with the second roller 5. When the pressing portion 34 moves outward in the circumferential direction, the pressing surface 37 for the intermediate object presses against the second roller 5. The pressed second roller 5 is then pushed between the first roller 4 and the guide surface 28.

[0036] Furthermore, the orientation of the intermediate object pressing surface 37 is such that the pressed second roller 5 moves between the first roller 4 and the guide surface 28. In this embodiment, the intermediate object pressing surface 37 is positioned radially outward as it moves circumferentially outward, and is inclined to intersect with the imaginary line W6.

[0037] Next, the operation of the power transmission device of Embodiment 1 will be described. First, the initial state of the power transmission device 100 (a state in which no torque or external force is input) will be described.

[0038] As shown in Figure 3, the pair of first rollers 4 are pressed by the coil spring 50 and move inward in the circumferential direction. The first rollers 4 are sandwiched between the inner circumferential surface 10 and the cam surface 27. In other words, the output shaft 2 is locked in the initial state.

[0039] Furthermore, in the initial state, the side surface 35 of the pressing portion 34 is not in contact with the first roller 4. The pressing surface 37 for intermediate objects of the pressing portion 34 is in contact with the second roller 5. Also, the second roller 5 is in contact with both the first roller 4 and the guide surface 28.

[0040] Next, we will explain the case where torque is input to the input shaft body 31 (see Figure 2) of the power transmission device 100 in its initial state. In the following explanation, we will first describe the state in which no external force is acting on the output shaft 2. Also, the direction of the input torque behaves the same way whether it is in the first rotational direction L1 or the second rotational direction L2. Therefore, the following explanation will describe the case in which the direction of the torque is in the first rotational direction L1.

[0041] Figure 5 is a diagram illustrating the operating state of the power transmission device of Embodiment 1, and more specifically, it shows the state at the start of torque input. As shown in Figure 5, when torque in the first rotational direction L1 is input to the input shaft body 31 (see Figure 2), a load A in the first rotational direction L1 is transmitted to the pressing part 34. In the initial state, the side surface 35 of the pressing part 34 is not in contact with the first roller 4. Therefore, at the start of torque input, the pressing part 34 does not press the first roller 4.

[0042] On the other hand, the pressing portion 34 is in contact with the second roller 5. Therefore, the pressing portion 34 presses the second roller 5 with the pressing surface 37 for the intermediate object, and the second roller 5 receives a load B from the pressing portion 34. As a result, the second roller 5 is pushed between the first roller 4 and the guide surface 28. Then, loads B1 and B2 act on the first roller 4 and the guide surface 28, causing them to be pulled apart from each other. When the load B1 acting on the first roller 4 is divided into components, it includes a component in the first rotational direction L1 in addition to a component in the radially outward direction.

[0043] Figure 6 is a diagram illustrating the operating state of the power transmission device of Embodiment 1, and more specifically, it shows the state when the lock state is released. As shown in Figure 6, the first roller 4 moves in the first rotation direction L1, and the state in which it is sandwiched between the inner circumferential surface 10 and the cam surface 27 (lock state) is released.

[0044] Furthermore, the load B2 acting on the guide surface 28 (see Figure 5) includes a component in the second rotational direction L2, and a torque in the second rotational direction L2 acts on the output shaft 2. This torque is such that it moves the cam surface 27 in the second rotational direction L2 relative to the first roller 4. From the above, it can be seen that the load B2 includes a torque that unlocks the mechanism, and the torque required to unlock it becomes small.

[0045] When the lock state is released, the pressing part 34 begins to move in the first rotational direction L1. At the same time, the second roller 5 begins to move radially inward along the guide surface 28. As the second roller 5 moves radially inward, the distance between the first roller 4 and the pressing part 34 decreases, and as shown in Figure 6, the side surface 35 of the pressing part 34 comes into contact with the first roller 4. Therefore, after the lock state is released, the first roller 4 receives a load C from the pressing part 34 and moves in the first rotational direction L1 while compressing the coil spring 50. Note that even after the lock state is released, the first roller 4 continues to receive a load B1 (see Figure 5) from the second roller 5 for a while.

[0046] Figure 7 illustrates the operating state of the power transmission device of Embodiment 1, and more specifically, shows the state in which the first roller is in contact with the surface to be pressed. As shown in Figure 7, when the first roller 4 moves to a certain extent in the first rotational direction L1, it comes into contact with the surface to be pressed 25. After contact with the first roller 4, the pressing part 34 presses the surface to be pressed 25 via the first roller 4 (see arrows D1 and D2 in Figure 7). As a result, torque in the first rotational direction L1 is transmitted to the output shaft 2, and the output shaft 2 rotates in the first rotational direction L1.

[0047] Furthermore, when the pressing portion 34 presses the surface to be pressed 25 via the first roller 4, the portion of the side surface 35 that contacts the first roller 4 is the outer surface 352, not the inner surface 351. The outer surface 352 is formed to be approximately parallel to the surface to be pressed 25. Therefore, the load D1 acting on the first roller 4 from the outer surface 352 is the normal vector of the surface to be pressed 25. As a result, the amount of torque loss transmitted from the pressing portion 34 to the output shaft 2 is extremely small, and torque is transmitted efficiently.

[0048] Furthermore, because the pressed surface 25 is inclined, the first roller 4 is pressed against the pressed surface 25 and moves radially outward (see arrow E in Figure 7). As a result, the clearance between the inner circumferential surface 10 of the fixed part 1 and the first roller 4 is small.

[0049] Furthermore, as shown in Figure 7, when the amount of radial inward sinking of the second roller 5 increases, it separates from the intermediate object pressing surface 37. Therefore, when the pressing portion 34 is pressing the surface to be pressed 25 via the first roller 4, the second roller 5 does not receive a load from the pressing portion 34.

[0050] Figure 8 is a diagram illustrating the operating state of the power transmission device of Embodiment 1, and more specifically, it shows the point in time when the first roller begins to return to the second rotation direction. As shown in Figure 8, when the torque input to the input shaft body 31 is released, the first roller 4 is pressed by the coil spring 50 and moves in the second rotation direction L2 (see arrow F in Figure 8). Then, once the first roller 4 has moved to a certain extent in the second rotation direction L2, it becomes trapped between the cam surface 27 and the inner circumferential surface 10 (locked state), as shown in Figure 3.

[0051] Incidentally, an oil film of a certain thickness is formed on the inner circumferential surface 10 of the fixing part 1. In other words, an oil film is also interposed between the inner circumferential surface 10 of the fixing part 1 and the first roller 4. Here, in order to lock the output shaft 2, the first roller 4 needs to shear the oil film. If the thickness of the oil film between the inner circumferential surface 10 and the first roller 4 is large, the first roller 4 may not be able to easily shear the oil film, and the output shaft 2 may not be locked.

[0052] As shown in Figure 7, when the first roller 4 is pressed against the pressure surface 25, the clearance between the inner circumferential surface 10 and the first roller 4 decreases. In other words, the thickness of the oil film interposed between the inner circumferential surface 10 and the first roller 4 decreases. Therefore, according to this embodiment, the first roller 4 easily shears the oil film interposed between the inner circumferential surfaces 10, and the output shaft 2 is securely locked.

[0053] Furthermore, when the first roller 4 moves in the second rotation direction L2, the second roller 5, which is in contact with the first roller 4, receives a load in the second rotation direction L2. The second roller 5 is lifted radially outward along the guide surface 28 (see arrow G in Figure 8). As a result, the second roller 5 comes into contact with the intermediate object pressing surface 37 of the pressing section 34 (see Figure 3).

[0054] Figure 9 shows the power transmission device of Embodiment 1 at the point when an external force (first rotation direction) is acting on the output shaft and torque (first rotation direction) is started to be input to the input shaft. Next, we will explain the case when an external force in the same direction (first rotation direction L1) is acting on the output shaft 2 at the point when torque is started to be input to the input shaft 3. The reason why the jerking phenomenon occurs is that when the first roller 4 moves in the first rotation direction L1 and the locked state is released, the output shaft 2 also rotates in the first rotation direction L1 due to the external force (see arrow J1 in Figure 9), and the first roller 4 is once again sandwiched between the inner circumferential surface 10 and the cam surface 27.

[0055] As shown in Figure 9, when the pressing part 34 pushes the second roller 5 between the first roller 4 and the guide surface 28 at the start of torque input to the input shaft 3, a load B2 acts on the guide surface 28. This load B2 includes a component in the second rotational direction L2. Therefore, rotation of the output shaft 2 in the first rotational direction L1 is suppressed. In other words, the first roller 4 is prevented from being squeezed again between the inner circumferential surface 10 and the cam surface 27, and the occurrence of the jerking phenomenon is avoided.

[0056] Figure 10 shows the power transmission device of Embodiment 1 at the point when an external force (second rotation direction) is acting on the output shaft and torque (first rotation direction) is started to be input to the input shaft. On the other hand, as shown in Figure 10, when an external force in the opposite direction (second rotation direction L2) is acting on the output shaft 2 and torque (first rotation direction L1) is started to be input to the input shaft 3, the pressing part 34 presses the first roller 4 via the second roller 5 (see arrows B and B1). Then, the first roller 4 moves and presses the pressed surface 25 in the first rotation direction L1. As a result, the output shaft 2 rotates in the first rotation direction L1 (see arrow J2). From the above, the first roller 4 is not caught between the inner circumferential surface 10 and the cam surface 27, and the jerking phenomenon does not occur.

[0057] The power transmission device 100 of Embodiment 1 has been described above, but this disclosure is not limited to the example described in Embodiment 1. Next, a modified example in which a part of the power transmission device 100 of Embodiment 1 is modified will be described. Furthermore, the following description will focus on the differences from the power transmission device 100 described above.

[0058] (Variation 1) Figure 11 is an enlarged view of one of the concave surfaces of the power transmission device of Modification 1. The power transmission device 100A of Modification 1 differs from Embodiment 1 in that all of the side surface 35A of the pressing portion 34 is flat. In other words, the side surface 35A of Modification 1 does not have an outer surface 352 that protrudes circumferentially outward from the inner surface 351.

[0059] Even in the power transmission device 100A of Modified Example 1, when torque is first applied to the input shaft 3, the pressing part 34 presses against the second roller 5 (see arrow B). Then, loads B1 and B2 act on the first roller 4 and the guide surface 28, causing them to be pulled apart from each other. Therefore, even if an external force acting on the output shaft 2 is in the same direction as the torque applied to the input shaft 3, rotation of the output shaft 2 in the first rotational direction L1 is suppressed. From the above, the power transmission device 100A of Modified Example 1, like Embodiment 1, suppresses the first roller 4 from being sandwiched between the inner circumferential surface 10 and the cam surface 27 again, and the occurrence of the jerking phenomenon is avoided. Furthermore, according to Modified Example 1, like Embodiment 1, the torque required to unlock can be reduced.

[0060] Figure 12 shows the power transmission device of Modified Example 1 in a state where the pressing part is pressing the surface to be pressed via the first roller. In Modified Example 1, the side surface 35A of the pressing part 34 that presses the surface to be pressed via the first roller 4 is not parallel to the surface to be pressed 25. In other words, the load K acting on the first roller 4 from the side surface 35A is not the normal vector of the surface to be pressed 25. Therefore, compared to Embodiment 1, the amount of torque loss transmitted from the pressing part 34 to the output shaft 2 is large.

[0061] (Modification 2) Figure 13 is an enlarged view of one of the concave surfaces of the power transmission device of Modification 2. As shown in Figure 13, the power transmission device 100B of Modification 2 differs from Modification 1 in that the shape of the guide surface 28B is different. The guide surface 28B of Modification 2 is formed in an arc shape centered on the central axis X. The dashed line W7 is the extension of the load B2 acting on the guide surface 28B. In this Modification 2 as well, the load B2 acting on the guide surface 28B includes the second rotation direction L2, and rotation in the first rotation direction L1 by the output shaft 2 is suppressed. In other words, the jerking phenomenon is less likely to occur in Modification 2 as well. Furthermore, according to Modification 2, the torque required for unlocking can be reduced, similar to Embodiment 1.

[0062] Furthermore, comparing the load B2 of Modification 2 (see Figure 13) with the load B2 of Embodiment 1 (see Figure 5), the load B2 in Embodiment 1 is more oriented in the circumferential direction. In other words, the torque in the second rotational direction L2 acting on the output shaft 2 is greater in Embodiment 1 than in Modification 2. Therefore, Embodiment 1 is preferable because it is less likely to cause jerking phenomena and the torque required to unlock can be reduced.

[0063] Figure 14 shows the power transmission device of Modification 2, in which the pressing part presses the surface to be pressed via the second roller and the first roller. Furthermore, according to the guide surface 28B of Modification 2, the second roller 5, which is pressed by the pressing surface 37 for the intermediate object, does not sink (move) radially inward even when it moves circumferentially outward. In other words, the distance between the pressing part 34 and the first roller 4 does not decrease, so the side surface 35A does not come into contact with the first roller 4. Therefore, as shown in Figure 14, torque is transmitted to the output shaft 2 by the pressing part 34 pressing the first roller 4 via the second roller 5.

[0064] (Variation 3, Variation 4) Figure 15 is a partially cross-sectional view of the vicinity of the pressed surface in the power transmission device of Modification 3. Figure 16 is a magnified view of one of the concave surfaces of the power transmission device of Modification 4. As shown in Figure 15, the power transmission device 100C of Modification 3 differs from Embodiment 1 in that the hole 51C does not go all the way through. Also, as shown in Figure 16, the power transmission device 100D of Modification 4 differs from Embodiment 1 in that it does not have a coil spring 50. Even with such Modifications 3 and 4, the occurrence of the jerking phenomenon is avoided, just as with Embodiment 1 and the like.

[0065] The above describes four modified examples. In addition, although three concave surfaces 23 are formed on the output shaft 2 of Embodiment 1, this disclosure does not particularly limit the number of concave surfaces 23. Furthermore, in Embodiment 1, the pressing portion 34 and the first roller 4 are separated in the initial state, but in this disclosure, the pressing portion 34 may be in contact with the first roller 4. In this case, the first roller 4 receives a load B1 (see Figure 5, etc.) acting from the second roller 5, as well as a load from the pressing portion 34, and moves outward in the circumferential direction, releasing the locked state.

[0066] Furthermore, while Embodiment 1 provides an example using cylindrical rollers as the rolling elements (first rolling element, second rolling element), this disclosure may also use balls. Regarding the intermediate object, Embodiment 1 describes an example using a second roller (second rolling element) 5, but this disclosure may also use a wedge-shaped body having a wedge surface that gradually narrows in the direction in which it is pressed into the pressing portion 34 (see arrow B in Figure 11) as the intermediate object. Hereinafter, Modification 5 will describe an example using a wedge-shaped body.

[0067] (Variation 5) Figure 17 is a schematic diagram of one of the concave surfaces of the power transmission device of Modification 5, viewed from the axial direction. The power transmission device 100E of Modification 5 differs from Embodiment 1 in that it uses a wedge body 105 instead of the second roller (second rolling element) 5. The wedge body 105 is a rectangular prism when viewed from the axial direction. Therefore, the wedge body 105 has four planes (first surface 111, second surface 112, third surface 113, and fourth surface 114).

[0068] The first surface 111 faces the pressing portion 34 and is opposite the pressing surface 37 for the intermediate object. In modified example 5, as shown in Figure 17, a small gap is formed between the first surface 111 and the pressing surface 37 for the intermediate object, but in this disclosure, the first surface 111 may be in contact with the pressing surface 37 for the intermediate object. The second surface 112 is the back surface of the first surface 111. The third surface 113 is in contact with the guide surface 28. When the wedge body 105 is pressed into the pressing portion 34 (see arrow N in Figure 17), it moves while sliding along the guide surface 28.

[0069] The fourth surface 114 is the back surface of the third surface 113 and is in contact with the first roller (first rolling element) 4. The fourth surface 114 is not formed parallel to the third surface 113. The fourth surface 114 is inclined such that the distance Z between the third surface 113 and the fourth surface 114 (see Figure 17) gradually decreases from the first surface 111 towards the second surface 112. In other words, the third surface 113 and the fourth surface 114 constitute a wedge surface 110 that gradually narrows in the direction in which it is pressed into the pressing portion 34 (see arrow N in Figure 17).

[0070] According to the modified example 5 described above, for example, when the pressing portion 34 moves in the first rotational direction L1, the wedge body 105 receives a load from the pressing portion 34 (see arrow N in Figure 17). As a result, the wedge body 105 is pushed between the first roller 4 and the guide surface 28. Consequently, similar to Embodiment 1, loads N1 and N2 act on the first roller 4 and the guide surface 28, causing them to be pulled apart from each other.

[0071] From the above, even in Modification 5, which uses the wedge body 105, the first roller 4 is prevented from being sandwiched between the inner circumferential surface 10 and the cam surface 27 again, just as in Embodiment 1, and the occurrence of the jerking phenomenon is avoided. Furthermore, according to Modification 5, the torque required to unlock can be reduced, just as in Embodiment 1.

[0072] Although Modification 5 has been described above, the present disclosure is not limited to the rectangular prism (square when viewed from the axial direction) wedge body 105 shown in Modification 5. The present disclosure only needs to have a wedge surface 110 (third surface 113, fourth surface 114). In other words, the present disclosure may be a polygonal prism (polygon when viewed from the axial direction), such as a triangular prism (triangle when viewed from the axial direction) or a pentagonal prism (pentagon when viewed from the axial direction). Furthermore, although the third surface 113 and fourth surface 114 constituting the wedge surface 110 are flat in Modification 5, they only need to be formed to gradually narrow in the direction in which they are pressed into the pressing part 34 (see arrow N in Figure 17), and the third surface 113 and fourth surface 114 may be curved surfaces (arc-shaped when viewed from the axial direction).

[0073] Next, a drive unit 5000 equipped with the power transmission device 100 of Embodiment 1 will be described.

[0074] (Embodiment 2) Figure 18 is a schematic diagram illustrating the configuration of the drive unit of Embodiment 2. As shown in Figure 18, the drive unit 5000 comprises a motor 5001 and the power transmission device 100 described above. The motor 5001 is a device for generating torque. The output shaft (not shown) of the motor 5001 is connected to the input shaft body 31 (not shown in Figure 18; see Figure 2) of the power transmission device 100.

[0075] Such a drive unit 5000 can be used, for example, in electric sliders, robot arms, lifting devices, transport robots, electric carts, electric assist bicycles, electric mobility devices, trolleys, and strollers. In other words, an electric slider or the like is connected to the output shaft body 21 of the power transmission device 100. Then, when the motor 5001 of the drive unit 5000 is driven, torque is transmitted to the electric slider or the like via the power transmission device 100.

[0076] On the other hand, even if an external force acts on an electric slider or the like and that force is transmitted to the output shaft 2, the output shaft 2 does not rotate. Therefore, the electric slider connected to the output shaft 2 does not rotate, move, or change its posture due to the external force. Thus, with the drive unit 5000, an electromagnetic brake to restrict rotation due to external forces is unnecessary, and the amount of power used can be reduced.

[0077] Embodiment 2 has been described above. The drive unit 5000 of Embodiment 2 is equipped with the power transmission device 100 described in Embodiment 1, but the present disclosure may also be equipped with the power transmission device described in Modification 1 to Modification 5.

[0078] Figure 19 is a schematic diagram illustrating the configuration of the drive unit of Modification 6. While the drive unit 5000 of Embodiment 2 includes a motor 5001 and a power transmission device 100, this disclosure may also include a drive unit 5000A of Modification 6, as shown in Figure 19, which includes a motor 5001, a power transmission device 100, a reduction gear 5002, and a sensor 5003 for detecting the rotation angle of the output shaft of the motor 5001. The reduction gear 5002 is a device for increasing torque. Furthermore, in Modification 6, an electric slider or the like is connected to the output shaft 5004 of the reduction gear 5002.

[0079] In the modified example 6, the drive unit 5000A is configured to transmit the torque generated by the motor 5001 to the power transmission device 100 and then to the reduction gear 5002. However, the present disclosure may change the arrangement of the power transmission device 100 and the reduction gear 5002 so that the torque is transmitted to the reduction gear 5002 and then to the power transmission device 100.

[0080] Furthermore, this disclosure may also be a combination of the following configurations. (1) An annular fixing part having an inner circumferential surface, An output shaft having an outer circumferential surface facing the inner circumferential surface and a concave surface recessed radially inward from the outer circumferential surface, An input shaft having a pressing portion housed inside the concave surface, A pair of first rolling elements housed inside the concave surface and arranged on both sides in the circumferential direction relative to the pressing portion, A pair of intermediate objects disposed between the first rolling element and the pressing portion, Equipped with, The aforementioned concave surface is Extending in the circumferential direction, the bottom surface facing the inner circumferential surface in the radial direction, A pair of pressure surfaces extending radially outward from both ends in the circumferential direction of the bottom surface, It has, The aforementioned bottom surface is A pair of cam surfaces on which the first rolling element is arranged radially outward, A pair of guide surfaces on which the intermediate object is positioned radially outward, It has, As the cam surface approaches the pressed surface, the distance between it and the inner circumferential surface gradually increases. The portion of the cam surface closer to the guide surface has a distance from the inner circumferential surface that is smaller than the diameter of the first rolling element. The portion of the cam surface closer to the pressed surface has a distance from the inner circumferential surface that is greater than the diameter of the first rolling element. The intermediate object is sandwiched between the first rolling element, the guide surface, and the pressing portion. When the pressing portion moves from its position in the circumferential center of the concave surface to the circumferential side, the pressing portion pushes the intermediate object between the first rolling element and the guide surface. The aforementioned intermediate object is A second rolling element having a smaller diameter than the first rolling element, It is either a wedge body having a wedge surface that gradually narrows in the direction in which it is pressed into the pressing portion, or a wedge body having a wedge surface that gradually narrows in the direction in which it is pressed into the pressing portion. Power transmission device. (2) The guide surface is positioned radially inward as it approaches the cam surface. (1) The power transmission device described above. (3) The pressing portion has a side surface facing outward in the circumferential direction, At least a portion of the aforementioned side surface is parallel to the surface to be pressed when the first rolling element is pressing against the surface to be pressed. (2) The power transmission device described above. (4) The guide surface is formed in an arc shape around the central axis of the inner circumferential surface. (1) The power transmission device described above. (5) The radial outer end of the surface to be pressed is positioned outside the circumferential direction relative to a virtual line drawn from the central axis of the inner circumferential surface to the radial inner end of the surface to be pressed, and the surface to be pressed is inclined outward in the circumferential direction. A power transmission device as described in any one of (1) to (4). (6) The elastic body is positioned between the pressed surface and the first rolling element and biases the first rolling element toward the pressing portion. A power transmission device as described in any one of (1) to (5). (7) Motor and, A power transmission device as described in any one of items (1) to (6), It has, The torque generated by the motor is input to the input shaft. Drive unit. [Explanation of symbols]

[0081] 1. Fixing parts 2 Output shafts 3 Input axes 4. First roller (first rolling element) 5. Second roller (second rolling element, intermediate object) 10 Inner surface 20 Inner ring section 23 Concave 24 Bottom 25 Pressed surface 26 Central plane 27 Cam surface 28, 28B Guide surface 30 Torque transmission section 34 Pressing part 35, 35A side 37 Pressing surface for intermediate objects 50 coil springs 51, 51C hole 100, 100A, 100B, 100C, 100D, 100E Power transmission devices 105 Wedge-shaped body (intermediate object) 110 Cuneiface 113 3rd page 114 Page 4 351 Inner surface 352 External surface 5000, 5000A drive unit

Claims

1. An annular fixing part having an inner circumferential surface, An output shaft having an outer circumferential surface facing the inner circumferential surface and a concave surface recessed radially inward from the outer circumferential surface, An input shaft having a pressing portion housed inside the concave surface, A pair of first rolling elements housed inside the concave surface and arranged on both sides in the circumferential direction relative to the pressing portion, A pair of intermediate objects disposed between the first rolling element and the pressing portion, Equipped with, The aforementioned concave surface is Extending in the circumferential direction, the bottom surface facing the inner circumferential surface in the radial direction, A pair of pressure surfaces extending radially outward from both ends in the circumferential direction of the bottom surface, It has, The aforementioned bottom surface is A pair of cam surfaces on which the first rolling element is arranged radially outward, A pair of guide surfaces on which the intermediate object is positioned radially outward, It has, As the cam surface approaches the pressed surface, the distance between it and the inner circumferential surface gradually increases. The portion of the cam surface closer to the guide surface has a distance from the inner circumferential surface that is smaller than the diameter of the first rolling element. The portion of the cam surface closer to the pressed surface has a distance from the inner circumferential surface that is greater than the diameter of the first rolling element. The intermediate object is sandwiched between the first rolling element, the guide surface, and the pressing portion. The guide surface is positioned radially inward as it approaches the cam surface. When the pressing portion moves from its position in the circumferential center of the concave surface to the circumferential side, the pressing portion pushes the intermediate object between the first rolling element and the guide surface. When the pressing portion is pressed, the intermediate object moves radially inward along the guide surface, and the pressing portion comes into contact with the first rolling element. After the pressing portion contacts the first rolling element, it moves further outward in the circumferential direction, pressing the surface to be pressed via the first rolling element. The intermediate object does not receive a load from the pressing portion when the pressing portion is pressing the surface to be pressed via the first rolling element. The aforementioned intermediate object is A second rolling element having a smaller diameter than the first rolling element, It is either a wedge body having a wedge surface that gradually narrows in the direction in which it is pressed into the pressing portion, or a wedge body having a wedge surface that gradually narrows in the direction in which it is pressed into the pressing portion. Power transmission device.

2. The pressing portion has a side surface facing outward in the circumferential direction, At least a portion of the aforementioned side surface is parallel to the surface to be pressed when the first rolling element is pressing against the surface to be pressed. The power transmission device according to claim 1.

3. An annular fixing part having an inner circumferential surface, An output shaft having an outer circumferential surface facing the inner circumferential surface and a concave surface recessed radially inward from the outer circumferential surface, An input shaft having a pressing portion housed inside the concave surface, A pair of first rolling elements housed inside the concave surface and arranged on both sides in the circumferential direction relative to the pressing portion, A pair of intermediate objects disposed between the first rolling element and the pressing portion, Equipped with, The aforementioned concave surface is Extending in the circumferential direction, the bottom surface facing the inner circumferential surface in the radial direction, A pair of pressure surfaces extending radially outward from both ends in the circumferential direction of the bottom surface, It has, The aforementioned bottom surface is A pair of cam surfaces on which the first rolling element is arranged radially outward, A pair of guide surfaces on which the intermediate object is positioned radially outward, It has, As the cam surface approaches the pressed surface, the distance between it and the inner circumferential surface gradually increases. The portion of the cam surface closer to the guide surface has a distance from the inner circumferential surface that is smaller than the diameter of the first rolling element. The portion of the cam surface closer to the pressed surface has a distance from the inner circumferential surface that is greater than the diameter of the first rolling element. The intermediate object is sandwiched between the first rolling element, the guide surface, and the pressing portion. When the pressing portion moves from its position in the circumferential center of the concave surface to the circumferential side, the pressing portion pushes the intermediate object between the first rolling element and the guide surface. The aforementioned intermediate object is A second rolling element having a smaller diameter than the first rolling element, It is either a wedge body having a wedge surface that gradually narrows in the direction in which it is pressed into the pressing portion, The guide surface is formed in an arc shape around the central axis of the inner circumferential surface. Power transmission device.

4. The radial outer end of the surface to be pressed is positioned outside the circumferential direction relative to a virtual line drawn from the central axis of the inner circumferential surface to the radial inner end of the surface to be pressed, and the surface to be pressed is inclined outward in the circumferential direction. A power transmission device according to any one of claims 1 to 3.

5. The elastic body is positioned between the pressed surface and the first rolling element and biases the first rolling element toward the pressing portion. A power transmission device according to any one of claims 1 to 3.

6. Motor and, A power transmission device according to any one of claims 1 to 3, It has, The torque generated by the motor is input to the input shaft. Drive unit.

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