Sand belt tensioning device

Abstract

This invention provides a movable side sanding belt tensioner (101) that stably maintains the sanding belt in an active and inactive state through a simple structure. The movable side sanding belt tensioner (101) includes: a fixed part (10); a rod (30); a movable part (20) that moves the sanding belt (105) between an active and inactive state according to the operation of the rod (30), and has a cam part (32); and a torsion spring (34). The follower (40) is pressed towards the cam surface (33) by the torsion spring (34) and is displaced relative to the cam part (32) according to the rotation of the rod (30). When the follower (40) is at points P1 and P5, viewed from point P2, the relative directions of the resultant force X acting on the follower (40) through the cooperation of the torsion spring (34) and the cam surface (33) relative to the cam part (32) are respectively towards the X1 side (point P1 side) and the X2 side (point P5 side).

Description

Technical Field

[0001] This invention relates to a strainer device for a drum. Background Technology

[0002] Generally, the snappy tensioning device used in drums such as snare drums has a fixed part attached to the drum body and a movable part that moves relative to the fixed part. Snappy is mounted on the movable part, and by rotating a lever, the movable part can be moved to an engaged position where the snappy contacts the drumhead, and a disengaged position where the snappy leaves the drumhead. During transport, the drum body may tilt or flip. If the lever rotates due to its own weight, the position of the snappy may unintentionally change.

[0003] Therefore, Patent Document 1 provides a mechanism for maintaining the position of the snarewire in both the active and deactivated positions. For example, in the active position, the active position is maintained by inserting a locking pin into a recess. In the deactivated position, the deactivated position is maintained by providing a spring that presses the snarewire away from the drumhead.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Patent No. 4977161 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, in Patent Document 1, in order to keep the sand belt in the active and inactive positions respectively, it is necessary to set up independent components such as locking pins and springs, and the structure is not simple.

[0009] One object of the present invention is to provide a sanding belt tensioning device that can stably maintain the sanding belt in both active and inactive states through a simple structure.

[0010] means for solving problems

[0011] According to one aspect of the present invention, a sanding belt tensioning device is provided, comprising: a fixing part fixed to the drum barrel of a drum; an operating part rotatable relative to the fixing part about a rotation center; a movable part that moves relative to the fixing part according to the operation of the operating part, thereby transferring the sanding belt between an active state in contact with the drumhead and a deactivated state away from the drumhead; a pressing member; a cam part disposed on either the movable part or the operating part and having a cam surface; and a follower member disposed on the other of the movable part and the operating part, pressed by the pressing member toward the cam surface side of the cam part, and adjusting according to... The follower is relatively displaced relative to the cam portion between a first position and a second position on the cam portion according to the rotation of the operating part. When the follower is in the first position, viewed from the middle position of the relative movement stroke of the follower relative to the cam portion, the force acting on the follower by the cooperation of the pressing member and the cam surface is directed towards the first position side relative to the cam portion. And when the follower is in the second position, viewed from the middle position, the force acting on the follower by the cooperation of the pressing member and the cam surface is directed towards the second position side relative to the cam portion.

[0012] Invention Effects

[0013] According to one aspect of the present invention, the sand belt can be stably maintained in both active and inactive states through a simple structure. Attached Figure Description

[0014] Figure 1 It is a three-dimensional diagram of a percussion instrument that uses a sanding belt tensioning device.

[0015] Figure 2 This is a rear view of the movable side belt tensioner.

[0016] Figure 3 This is a side view of the movable side belt tensioner.

[0017] Figure 4 It means along Figure 2 A three-dimensional view of the cross-section of the movable side belt tensioner of the AA line.

[0018] Figure 5 It is a schematic diagram showing the positional relationship between the fixed part, the movable part, and the rod.

[0019] Figure 6 It is a schematic diagram showing the positional relationship between the fixed part, the movable part, and the rod.

[0020] Figure 7 This is a magnified view of a portion of the cam section.

[0021] Figure 8 This is a magnified view of a portion of the cam section.

[0022] Figure 9 This is a magnified view of a portion of the cam surface.

[0023] Figure 10 This is a rear view of the movable side belt tensioner of a modified example.

[0024] Explanation of reference numerals in the attached figures

[0025] 10 Fixed part, 20 Movable part, 30 Rod, 32 Cam part, 33 Cam surface, 34 Torsion spring, 40 Follower, 41, 42 Bearings, 101 Movable side belt tensioner Detailed Implementation

[0026] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0027] Figure 1 This is a perspective view of a percussion instrument 100 using a snare wire tensioning device according to an embodiment of the present invention. As an example, the percussion instrument 100 is a snare drum. The percussion instrument 100 has a drum body 103. A batter head is disposed at one (surface side) opening in the cylindrical shape of the drum body 103, and a resonance head 104 is disposed at the other (rear side) opening. A plurality of lugs (not shown) are fixed at equal intervals on the outer circumferential surface of the drum body 103. Snappy wire 105 is disposed on the outer surface of the resonance head 104. Snappy wire 105 is also referred to as snare wire.

[0028] On the outer circumference of the drum 103, at symmetrical positions along the diameter direction of the drum 103, a pair of abrasive belt tensioning devices are arranged. The abrasive belt tensioning devices consist of a movable abrasive belt tensioner 101 and a fixed abrasive belt tensioner 102. They are positioned away from the drum lugs. The movable abrasive belt tensioner 101 and the fixed abrasive belt tensioner 102 can also be referred to as abrasive belt tensioning devices. The two ends of the abrasive belt 105 are connected to the abrasive belt tensioners 101 and 102 via rope components, tape material, or the like.

[0029] The movable-side sanding belt tensioner 101 will be described below. The movable-side sanding belt tensioner 101 has a fixed part 10, a movable part 20, and a lever 30 (operating part) as its main components. The fixed part 10 is fixed to the drum 103. The movable part 20 is configured to move relative to the fixed part 10 in the direction of the central axis (vertical direction) of the drum 103. As will be explained in detail later, the movable part 20 moves relative to the fixed part 10 according to the user's rotation operation of the lever 30. By moving the movable part 20, the sanding belt 105 can be switched between an active state (contacting the resonant drumhead 104) and a deactivated state (away from the resonant drumhead 104).

[0030] Figure 2 This is a rear view of the movable side belt tensioner 101. Note that the side of the movable side belt tensioner 101 opposite to the drum 103 is designated as the back side. Figure 3 This is a side view of the movable side belt tensioner 101. Figure 4 It means along Figure 2 A perspective view of the cross-section of the movable side belt tensioner 101 of the AA line. Among them, in Figure 2 , Figure 3 In the middle, lever 30 is in the rotational position corresponding to the activated state, in Figure 4 In the middle, lever 30 is in the rotational position corresponding to the enabled state and the disabled state.

[0031] The fixing part 10 includes a housing 13 and mounting parts 11 and 12. The mounting parts 11 and 12 are fixed to the housing 13. The fixing part 10 is mounted on the drum 103 by fixing the mounting parts 11 and 12 to the drum 103 using screws.

[0032] like Figure 4 As shown, the movable part 20 mainly includes a first movable body 21, a second movable body 22, an adjustment knob 25, and an adjustment bolt 24. A rope component (not shown) extending from the sanding belt 105 is fixed to the first movable body 21 by screws 23. The adjustment knob 25 and the adjustment bolt 24 are fixed together by a nut 28. The adjustment bolt 24 is rotatable within the second movable body 22. Rotating the adjustment knob 25 causes the adjustment bolt 24 to rotate accordingly. The external thread 29 of the adjustment bolt 24 engages with the internal thread of the first movable body 21. The axial direction of the adjustment bolt 24 is parallel to the central axis of the drum 103. Rotating the adjustment bolt 24 changes the position of the first movable body 21 relative to the adjustment bolt 24 along its axial direction. Therefore, the user can adjust the tension of the sanding belt 105, for example, by rotating the adjustment knob 25 in the active state.

[0033] A spring 27 is disposed between the outer periphery of the adjusting bolt 24 and the second movable body 22. The spring 27 presses the first movable body 21 downward, suppressing the wobble between the first movable body 21 and the second movable body 22. An O-ring 26 is provided near the neck of the adjusting bolt 24. The O-ring 26 is embedded in the outer peripheral groove formed on the adjusting knob 25 and contacts the inner peripheral surface of the second movable body 22. No threads are formed on the inner peripheral surface of the second movable body 22 in contact with the O-ring 26. When the adjusting knob 25 is rotated, it slides relative to the inner peripheral surface of the second movable body 22 through the O-ring 26. The O-ring 26, due to its elasticity, presses against the inner peripheral surfaces of the adjusting knob 25 and the second movable body 22, thus preventing the adjusting knob 25 from loosening. Generally, the external thread 29 of the adjusting bolt 24 is locked at its engagement point with the internal thread of the first movable body 21. However, in this embodiment, since the O-ring 26 is provided, the loosening of the adjustment knob 25 and the adjustment bolt 24 relative to the second moving body 22 in the rotational direction can be suppressed.

[0034] With the position of the first movable body 21 relative to the second movable body 22 adjusted, the first movable body 21 and the second movable body 22 move together by rotating the lever 30. The user typically switches between the active and deactivated states by rotating the movable part 20 after adjusting the position of the first movable body 21 relative to the adjusting bolt 24 to the desired state.

[0035] A screw 35 and a nut 43 are fixed to the rod 30. The shaft of the screw 35 is rotatably supported on the housing 13 via bearings 41 and 42. Therefore, the rod 30 is rotatably supported on the housing 13 about the central axis of the bearings 41 and 42 as the rotation center C1. By providing bearings 41 and 42, stable rotation of the rod 30 is achieved. In addition, the bearings 41 and 42 are located at two points in the direction of the rotation center C1, thus suppressing the swaying of the rod 30 relative to the rotation center C1 and achieving stable rotation.

[0036] A cam component 31 is fixed to the rod 30 using multiple screws. Figure 2 The cam component 31 rotates integrally with the rod 30. The cam component 31 is made of resin or the like. A cam portion 32 is formed on the cam component 31, extending through the rotation center C1. Figure 2 The cam portion 32 includes a cam surface 33.

[0037] A screw 37 is fixed to the back side of the second moving body 22. A follower 40 and a spring-loaded retainer 38 are fixed to the screw 37. An O-ring 39 is installed around the spring-loaded retainer 38, and one end 34a of a torsion spring 34 is attached to the spring-loaded retainer 38. The spring-loaded retainer 38 is an integral part (fixed together) with the follower 40. On the other hand, a spring-loaded screw 36 is fixed to the cam part 31. The other end 34b of the torsion spring 34 is attached to the spring-loaded screw 36. The spring-loaded screw 36 is an integral part (fixed together) with the cam part 32. The torsion spring 34 is an example of a pressing member that presses the follower 40 against the cam surface 33. Instead of the torsion spring 34, other pressing members such as leaf springs or other elastic members can also be used.

[0038] Figure 5 , Figure 6 This is a schematic diagram showing the positional relationship between the fixed part 10, the movable part 20, and the rod 30. In particular, Figure 5 The diagram shows an intermediate state between the enabled and disabled states of the movable side belt tensioner 101. Figure 6 The device is shown to be disabled. Note that... Figure 2 The enabled status is shown in the image.

[0039] The follower 40 is pressed against the cam surface 33 and displaces relative to the cam portion 32 according to the rotation of the rod 30. Since the follower 40 is fixed to the second moving body 22, it moves integrally with the movable part 20 in the axial direction of the adjusting bolt 24. If the rod 30 moves from the activated state ( Figure 2 )Towards Figure 2 If the rotation is counterclockwise, the follower 40 slides on the cam surface 33, and the movable side belt tensioner 101 shifts to the intermediate state. Figure 5 If lever 30 rotates further counterclockwise, follower 40 slides on cam surface 33, and movable side belt tensioner 101 transitions to the disengaged state. Figure 6 The following uses... Figures 7-10 The specific structure of the cam section 32 and the relationship between the cam section 32 and the follower 40 are explained.

[0040] Figure 7 , Figure 8 This is a magnified view of a portion of the cam section 32. Figure 7 , Figure 8 The cam component 31 is observed from the rear side. The active position Fon and the deactivated position Foff are the center positions of the follower 40 corresponding to the active and deactivated states, respectively.

[0041] like Figure 7As shown, the continuous surface from point P1 to P5 is the cam surface 33. The cam portion 32 has limiting portions 32a and 32b at both ends along its length. By abutting the O-ring 39 against the limiting portions 32a and 32b, the movement range of the follower 40 relative to the cam portion 32 is limited. Therefore, in terms of the contact range of the follower 40 with respect to the cam surface 33, the range from point P1 to P5 is the relative movable range of the follower 40. The follower 40 itself does not contact the limiting portions 32a and 32b. Noise is suppressed by abutting the O-ring 39 against the limiting portions 32a and 32b.

[0042] Points P2, P3, Pm, and P4 are all intermediate positions on the cam surface 33 during the relative movement stroke of the follower 40 relative to the cam portion 32. Specifically, point P2 is a protrusion (peak), which, as described later, is the point where the clicking sensation is generated. When the center of the follower 40 is in the active position Fon and the deactivated position Foff, the contact points between the follower 40 and the cam surface 33 are points P1 (first position) and P5 (second position), respectively. When the center of the follower 40 is in the intermediate positions Q2 and Qm0, the contact points between the follower 40 and the cam surface 33 are points P2 and Pm, respectively.

[0043] The follower 40 is pressed against the cam surface 33 by the torsion spring 34, thus a resultant force X is exerted on the follower 40 through the cooperation of the pressing force from the torsion spring 34 and the reaction force at the cam surface 33. The relative direction of the resultant force X with respect to the cam portion 32 switches between the X1 side and the X2 side at point P2. Taking the line segment connecting point P2 and the intermediate position Q2 as the boundary, the X1 side is the side where point P1 is located when viewed from point P2 (point P1 side; first position side), and the X2 side is the side where point P5 is located when viewed from point P2 (point P5 side; second position side).

[0044] In particular, considering the contact area between the cam surface 33 and the follower 40, when the follower 40 is at point P1, viewed from point P2, the relative direction of the resultant force X on the cam portion 32 is towards X1. Furthermore, when the follower 40 is at point P5, viewed from point P2, the relative direction of the resultant force X on the cam portion 32 is towards X2. Therefore, the follower 40 is subjected to a force that maintains its active state in the active state and a force that maintains its deactivated state in the deactivated state. Thus, the active and deactivated states are the same as the locked state, respectively. Therefore, the active and deactivated states of the sand belt 105 can be stably maintained.

[0045] In other words, when the follower 40 is closer to X1 than the intermediate position Q2 (in other words, when the contact point is within the range of point P1 to point P2), the relative direction of the resultant force X, viewed from point P2, is towards X1. When the follower 40 is closer to X2 than the intermediate position Q2 (in other words, when the contact point is within the range of point P2 to point P5), the relative direction of the resultant force X, viewed from point P2, is towards X2. Thus, the relative direction of the resultant force X switches with the intermediate position Q2 as the boundary, allowing for a smooth transition to the active or deactivated state without requiring excessive force to operate the lever 30, resulting in high operability.

[0046] The function of the torsion spring 34 will be explained. The torsion spring 34 has a structure in which one end 34a and the other end 34b extend from the ring-shaped portion into two branches. Figure 2 The degree of opening of the torsion spring 34 in its free state is not shown, but it is approximately 90 degrees. The degree of opening of the torsion spring 34 is minimized when the center of the follower 40 is at the intermediate position Q2. For example, in Figure 5 In the middle position, the center of the follower 40 is located near the intermediate position Q2, and the opening degree of the torsion spring 34 is negative when measured in terms of angle. When the center of the follower 40 is in the active position Fon or the deactivated position Foff, the opening degree of the torsion spring 34 is angle α1 and α2 respectively. Figure 2 , Figure 6 These opening degrees are all smaller than the opening degree of the torsion spring 34 in its free state, but larger than the opening degree of the follower 40 when its center is in the intermediate position Q2. Through this structure, after passing the intermediate position Q2, the necessary operating force to the activated position Fon and the deactivated position Foff is reduced, thus improving operability.

[0047] Furthermore, point P2 is a convex part, and when the follower 40 moves on this convex part, a clicking sensation is generated on the follower 40. Also, point P2 is closer to point P1 than point P5. Therefore, during the operation of the lever 30, a clicking sensation can be generated near the activated position. Thus, after the clicking sensation is generated when passing the intermediate position Q2, the operation becomes lighter. From this perspective, operability and the feel of operation are also improved.

[0048] use Figure 8 The specific shape of the cam surface 33 is described. In particular, the characteristics of the area between points P3 and P4 on the cam surface 33 are described. Figure 8 In this diagram, the follower 40, whose center positions are at the intermediate positions Qm1 and Qm2, is denoted as follower 40-1 and 40-2. The trajectory curve R is the relative trajectory curve of the center position of follower 40 with respect to cam surface 33 in the range of points P3 to P4. In the range of points P3 to P4, the trajectory curve R lies on an equiangular spiral (logarithmic spiral) centered on the rotation center C1.

[0049] Straight lines L1 and L2 are the radius vectors (radius vectors) passing through the contact points (Qm1 and Qm2) between the follower elements 40-1 and 40-2 and the cam surface 33 at their intermediate positions Qm1 and Qm2, respectively. Tangents S1 and S2 are the tangents between the follower elements 40-1 and 40-2 and the cam surface 33. Angles θ1 and θ2 are the angles (refer to) between straight lines L1 and L2 and tangents S1 and S2 within the cam portion 32 and on the X1 side. Figure 7 The angle formed by the points P3 and P4. Within the range of points P3 to P4, the trajectory curve R is an equiangular spiral, therefore angle θ1 = angle θ2. With this structure, the component force acting on the follower 40 is constant. Therefore, it is easier to design a uniform operating force for the rod 30 within the range of points P3 to P4.

[0050] Figure 9 This is a magnified view of a portion of the area near point P2 on cam surface 33. Figure 7 The text describes how the relative direction of the resultant force X acting on the follower 40 switches with point P2 as the boundary. This will be explained by referring to... Figure 9 Examine it from other perspectives.

[0051] exist Figure 9 In the diagram, point P1-2 is the contact point between point P1 and point P2 on cam surface 33, and between follower 40 and cam surface 33. Point P2-5 is the contact point between point P2 and point P5 on cam surface 33, and between follower 40 and cam surface 33. Normals N1, N2, and N3 represent the normals of cam surface 33 passing through points P1-2, P2, and P2-5, respectively. Vectors V1, V2, and V3 represent the vectors of the (pressing) force exerted by torsion spring 34 on follower 40.

[0052] The normal N1 and vector V1, viewed from the cam surface 33, form an angle β1 on the rotation center C1 side (vector direction). The normal N3 and vector V3, viewed from the cam surface 33, form an angle β2 on the rotation center C1 side (vector direction). Regarding angles β1 and β2, their formation directions relative to the normal are opposite. The angle formed by the normal N2 and vector V2, viewed from the cam surface 33 on the rotation center C1 side, is 0 degrees.

[0053] That is, when the follower 40 contacts the cam surface 33 at point P2, vector V2 is parallel to the normal N2. Furthermore, within the range of points P1 to P2, vector V1, viewed from the cam surface 33, is closer to the X1 side than the normal N1 on the rotation center C1 side. Within the range of points P2 to P5, vector V3 is closer to the X2 side than the normal N3 on the rotation center C1 side. With this structure, the necessary operating force towards the active position Fon and the deactivated position Foff side is reduced when the follower 40 passes point P2, thus improving operability.

[0054] According to this embodiment, when the follower 40 is at point P1, viewed from the middle position (point P2), the resultant force X acting on the follower 40 is directed towards the X1 side relative to the cam portion 32. Furthermore, when the follower 40 is at point P5, viewed from the middle position, the resultant force X is directed towards the X2 side relative to the cam portion 32. Therefore, the sand belt 105 can be stably maintained in both its active and inactive states with a simple structure.

[0055] In Patent Document 1, the spring constantly presses the sandbag towards the deactivated position, so when the lever is rotated towards the activated position, the force from the spring acts as resistance throughout the entire stroke. Therefore, there is room for improvement in the operability of the lever. In contrast, in this embodiment, the follower 40 is subjected to forces that maintain the activated and deactivated states, respectively, in the activated and deactivated states.

[0056] In contrast, in this embodiment, when the follower 40 is within the range of points P1 to P2, the relative direction of the resultant force X, viewed from point P2, is towards the X1 side; when the follower 40 is within the range of points P2 to P5, the relative direction of the resultant force X, viewed from point P2, is towards the X2 side. That is, the aforementioned relative direction of the resultant force X switches between the X1 and X2 sides at point P2 (the intermediate position Q2). From other perspectives, vectors V1 to V3 are parallel to normals N1 to N3 at point P2. Figure 9 Therefore, the lever 30 can be smoothly switched to the active or inactive state without requiring excessive force, thus improving operability.

[0057] Furthermore, when the center of the follower 40 is in the active position Fon or the deactivated position Foff, the degree of opening of the torsion spring 34 is smaller than in the free state, but larger than when the center of the follower 40 is in the intermediate position Q2. Therefore, the necessary operating force is reduced by the intermediate position Q2, thus improving operability. In addition, point P2, which is closer to point P1, is a convex part, producing a click-like sensation on the follower 40 near the active position, thus improving operability and the feel of operation.

[0058] In addition, the rod 30 is rotatably supported by bearings 41 and 42 located at two points in the direction of the rotation center C1, which can suppress the swaying of the rod 30 and achieve stable rotation.

[0059] In addition, the cam surface 33 includes a region (points P3 to P4) on an equiangular spiral centered on the rotation center C1, where the relative trajectory curve R of the follower 40 with respect to the cam portion 32 is located. Therefore, it is easier to design a uniform operating force for the lever 30.

[0060] Figure 10 This is a rear view of the movable side belt tensioner 101 in a modified example. Figure 2 In the example shown, the cam portion 32 is disposed on the rod 30, and the follower 40 is disposed on the movable portion 20. However, it can also be the opposite, such as... Figure 10 As shown in the modified example, a structure is adopted in which a cam portion 32 is provided on the movable portion 20 and a follower 40 is provided on the rod 30. That is, it can be that the cam portion having a cam surface is provided on either the movable portion or the operating portion, and the follower is provided on the other side of the movable portion and the operating portion.

[0061] exist Figure 10 In the modified example shown, the rod 30 can rotate relative to the fixed part 10 about the rotation center C1. Figure 10 The enabled status is shown in the image. Figure 10 The clockwise direction is the rotation direction to the off state. The spring-loaded latching component 38 is integrated with the follower 40, and the spring-loaded latching screw 36 is integrated with the cam portion 32. The torsion spring 34 is latched onto the spring-loaded latching component 38 and the spring-loaded latching screw 36. Using the torsion spring 34, the follower 40 is pressed against the cam surface 33 of the cam portion 32. Other basic structures are similar to... Figure 2 The example shown is the same.

[0062] Note that Figure 2 Regarding the structure used in the example shown (the shape and features of the cam surface 33, etc.), as long as there is no contradiction, it is still possible to maintain the modified example ( Figure 10 (This is used in the context of )

[0063] The present invention has been described in detail above based on preferred embodiments, but the present invention is not limited to these specific embodiments, and various methods without departing from the spirit of the invention are also included in the present invention.

Claims

1. A belt tensioning device, characterized in that, have: A fixing part, which is fixed to the drum cylinder, includes a housing and a mounting part, wherein the mounting part is fixed to the housing; The operating part is capable of rotating about the rotation center relative to the fixed part. The movable part moves relative to the fixed part according to the operation of the operating part, so that the sand belt moves between an activated state in contact with the drumhead and a deactivated state away from the drumhead. Pressing component; A cam portion, disposed on either the movable portion or the operating portion, and having a cam surface; and A follower, disposed on the other side of the movable part and the operating part, is pressed against the cam surface side of the cam part by the pressing member, and displaces relative to the cam part between a first position and a second position on the cam part according to the rotation of the operating part. When the follower is in the first position, viewed from the middle position of the relative movement stroke of the follower relative to the cam part, the force acting on the follower by the cooperation of the pressing member and the cam surface is directed towards the first position side relative to the cam part. And when the follower is in the second position, viewed from the middle position, the force acting on the follower by the cooperation of the pressing member and the cam surface is directed towards the second position side relative to the cam part. The force acting on the follower, relative to the cam portion, switches between the first position side and the second position side at the intermediate position. The first position corresponds to the activated state of the sand belt, and the second position corresponds to the deactivated state of the sand belt.

2. The sand belt tensioning device as described in claim 1, characterized in that, When the follower is closer to the first position than the intermediate position, the relative direction of the force acting on the follower is towards the first position when viewed from the intermediate position; when the follower is closer to the second position than the intermediate position, the relative direction of the force acting on the follower is towards the second position when viewed from the intermediate position.

3. The sand belt tensioning device as described in claim 1 or 2, characterized in that, The pressing component is a torsion spring. The degree of opening of the torsion spring when the follower is in the first position and the degree of opening of the torsion spring when the follower is in the second position are both smaller than the degree of opening of the torsion spring in its free state, and larger than the degree of opening of the torsion spring when the follower is in the intermediate position.

4. The sand belt tensioning device as described in claim 3, characterized in that, One end of the torsion spring is in contact with the part that is integral with the follower, and the other end of the torsion spring is in contact with the part that is integral with the cam portion.

5. The sand belt tensioning device as described in claim 1 or 2, characterized in that, The middle position on the cam surface is closer to the first position than the second position, and it is a convex part. When the follower moves on the protrusion, a clicking sensation is generated on the follower.

6. The sand belt tensioning device as described in claim 1 or 2, characterized in that, The operating part is rotatably supported on the fixed part via a bearing.

7. The belt tensioning device as described in claim 6, characterized in that, The bearing is positioned at two points along the axial direction of the rotation center.

8. The sand belt tensioning device as described in claim 1 or 2, characterized in that, The cam surface includes the region where the relative trajectory curve of the follower with respect to the cam portion lies on an equiangular spiral centered on the rotation center.

9. The sand belt tensioning device as described in claim 1, characterized in that, The vector of the force applied by the pressing component to the follower and the normal passing through the contact point between the follower and the cam surface are parallel at the midpoint of the relative movement stroke of the follower relative to the cam portion.

10. The belt tensioning device as described in claim 9, characterized in that, When the follower is closer to the first position than the intermediate position, the vector is closer to the first position than the normal at the rotation center. When the follower is closer to the second position side than the intermediate position, the vector is closer to the second position side than the normal on the rotation center side.

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