Pedal shaft

Abstract

A pedal shaft (100) for a pedal-type power meter is provided with: a hollow shaft (10) to which a pedal is rotatably mounted; strain gauges (SGX, SSG) attached to the outer peripheral surface of the hollow shaft; and a processing circuit (20) which is disposed in the inner space of the hollow shaft and processes the output from the strain gauge.

Description

Technical Field

[0001] The present invention relates to a pedal shaft. Background Art

[0002] A power meter is known which is mounted on a bicycle or the like and measures the magnitude, direction, and position of the force applied by a user to step on a pedal. The power meter is generally classified into a pedal-type power meter having a measuring portion provided on a pedal, a crank-type power meter having a measuring portion provided on a crank, and a hub-type power meter having a measuring portion provided on a tire hub.

[0003] Patent Document 1 discloses a pedal-type power meter. In Patent Document 1, four elongation measurement pieces are attached to a pedal shaft.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 8-145824 Summary of the invention

[0007] Problems to be solved by the invention

[0008] It is difficult to say that the pedal shaft described in Patent Document 1 can detect strain generated in the pedal shaft with sufficient accuracy.

[0009] An object of the present invention is to provide a pedal shaft for a pedal-type power meter, which can detect strain generated in the pedal shaft with high accuracy.

[0010] Solutions for solving problems

[0011] According to one aspect of the present invention, there is provided a pedal shaft for a pedal-type power meter, wherein the pedal shaft comprises:

[0012] A hollow shaft for the pedal to be mounted in a rotatable manner;

[0013] a strain gauge mounted on the outer circumference of the hollow shaft; and

[0014] The processing circuit is disposed in the inner space of the hollow shaft and processes the output from the strain gauge.

[0015] Effects of the Invention

[0016] The pedal shaft of the present invention can detect the strain generated by the pedal shaft with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a perspective view of a power meter according to one embodiment of the present invention.

[0018] Figure 2It is a perspective view of a pedal shaft according to one embodiment of the present invention.

[0019] Figure 3 It is a plane passing through the central axis X and extending radially. Figure 2 A sectional view obtained by cutting through the pedal shaft. Figure 3 The illustration of the strain gauge is omitted.

[0020] Figure 4 In the figure, (a) is along Figure 3 The cross-sectional view of the hollow shaft along the IVa-IVa line, (b) is a cross-sectional view of the hollow shaft along the IVa-IVa line. Figure 3 The cross-sectional view of the hollow shaft along the IVb-IVb line, (c) is a cross-sectional view of the hollow shaft along the IVb-IVb line. Figure 3 A cross-sectional view of the hollow shaft along line IVc-IVc.

[0021] Figure 5 In the figure, (a) is a top view when observing the first strain surface from the radial outside, showing the structure of the four strain gauges installed on the first strain surface, (b) is a top view when observing the second strain surface from the radial outside, showing the structure of the four strain gauges installed on the second strain surface, (c) is a top view when observing the third strain surface from the radial outside, showing the structure of the four strain gauges installed on the third strain surface, (d) is a top view when observing the fourth strain surface from the radial outside, showing the structure of the four strain gauges installed on the fourth strain surface. Figure 5 (a)~ Figure 5 In each figure of (d), the left side is the base end side and the right side is the tip end side.

[0022] Figure 6 is along Figure 5 (a) is a cross-sectional view taken along line VI-VI.

[0023] Figure 7 In the figure, (a) to (d) are circuit diagrams of a Wheatstone bridge composed of strain gauges mounted on a hollow shaft.

[0024] Figure 8 It is a top view of a strain gauge provided in a pedal shaft according to a modified example.

[0025] Fig. 9 In the figure, (a) is a top view when observing the first strain surface from the radial outside, showing the structure of the strain gauge of the modified example assembled on the first strain surface, (b) is a top view when observing the second strain surface from the radial outside, showing the structure of the strain gauge of the modified example assembled on the second strain surface, (c) is a top view when observing the third strain surface from the radial outside, showing the structure of the strain gauge of the modified example assembled on the third strain surface, (d) is a top view when observing the fourth strain surface from the radial outside, showing the structure of the strain gauge of the modified example assembled on the fourth strain surface.

[0026] Fig.10 In FIG. 1 , (a) to (d) are circuit diagrams of a Wheatstone bridge composed of a strain gauge according to a modified example mounted on a hollow shaft. DETAILED DESCRIPTION

[0027] <Implementation Method>

[0028] Reference Figure 1 to Figure 7 , the pedal shaft 100 and the power meter PM according to the embodiment of the present invention will be described.

[0029] [Power meter PM]

[0030] like Figure 1 As shown, the power meter PM is a pedal-type power meter including a pedal shaft 100 and a pedal P rotatably mounted on the pedal shaft 100 .

[0031] [Pedal shaft 100]

[0032] like Figure 2 , Figure 3 As shown, the pedal shaft 100 mainly comprises: a hollow shaft (hollow main shaft) 10 having a central axis X; sixteen strain gauges (details will be described later) mounted on the outer peripheral surface 10 of the hollow shaft 10; OUT and a circuit substrate 20 disposed in the inner space of the hollow shaft 10. The pedal shaft 100 further includes: a power supply unit 30 disposed in the inner space of the hollow shaft 10; and a flexible printed wiring board (FPC) 40 connecting the sixteen strain gauges to the circuit substrate 20.

[0033] In the following description, the direction of the central axis X is referred to as the axial direction of the hollow shaft 10 and the pedal shaft 100. In addition, the radial direction centered on the central axis X is referred to as the radial direction of the hollow shaft 10 and the pedal shaft 100, and the circumferential direction centered on the central axis X is referred to as the circumferential direction of the hollow shaft 10 and the pedal shaft 100.

[0034] In the axial direction, the crank threaded portion 11 (described later) side of the hollow shaft 10 is called the base end side, and the pedal threaded portion 16 (described later) side of the hollow shaft 10 is called the front end side. In the circumferential direction, the clockwise direction when the front end side is viewed from the base end side in the axial direction is called the positive direction, and the counterclockwise direction is called the negative direction.

[0035] [Hollow shaft 10]

[0036] The hollow shaft 10 has a substantially cylindrical shape having a through hole TH extending in the axial direction. As an example, the hollow shaft 10 is formed of metal such as stainless steel.

[0037] The hollow shaft 10 is divided into a crank threaded portion 11 , a bolt head 12 , a strain gauge mounting portion 13 , a middle diameter portion 14 , a small diameter portion 15 , and a pedal threaded portion 16 in order from the base end side along the central axis X.

[0038] The crank threaded portion 11 is located at the end portion on the base end side of the hollow shaft 10. OUT With external thread MS 11 . External thread MS 11 The hollow shaft 10 is used when being mounted on a crank of a bicycle or the like.

[0039] The bolt head 12 is adjacent to the crank threaded portion 11 and is provided on the axial front end side of the crank threaded portion 11. OUT A hexagonal bolt head 121 and a flange 122 are provided. The flange 122 is provided on the external thread MS. 11 Between the hexagonal bolt head 121. It should be noted that a two-angle bolt head or a four-angle bolt head may be provided instead of the hexagonal bolt head.

[0040] The strain gauge mounting portion 13 is adjacent to the bolt head 12 and is provided on the axial front end side of the bolt head 12 .

[0041] like Figure 2 , Figure 4 As shown in (a), in the strain gauge mounting portion 13, the outer peripheral surface 10 of the hollow shaft 10 OUT A first strain surface 131, a second strain surface 132, a third strain surface 133 and a fourth strain surface 134 are provided, each extending in a plane orthogonal to the radial direction of the hollow shaft 10. Figure 5 (a)~ Figure 5 As shown in (d), the first to fourth strain surfaces 131 to 134 are rectangular flat surfaces with the axial direction as the long side direction and the circumferential direction as the short side direction. The first to fourth strain surfaces 131 to 134 are strain gauge mounting surfaces for mounting the strain gauge.

[0042] like Figure 4 As shown in (a), the first strain plane 131 and the third strain plane 133 are parallel to each other, and the second strain plane 132 and the fourth strain plane 134 are parallel to each other. The first strain plane 131 and the third strain plane 133 are orthogonal to the second strain plane 132 and the fourth strain plane 134.

[0043] The long side of the circumferential positive side of the first strain surface 131 is connected to the long side of the circumferential negative side of the second strain surface 132 through a curved surface CS1 with a circular arc cross section. The long side of the circumferential positive side of the second strain surface 132 is connected to the long side of the circumferential negative side of the third strain surface 133 through a curved surface CS2 with a circular arc cross section. The long side of the circumferential positive side of the third strain surface 133 is connected to the long side of the circumferential negative side of the fourth strain surface 134 through a curved surface CS3 with a circular arc cross section. The long side of the circumferential positive side of the fourth strain surface 134 is connected to the long side of the circumferential negative side of the first strain surface 131 through a curved surface CS4 with a circular arc cross section.

[0044] In other words, the outer peripheral surface of the hollow shaft 10 in the strain gauge mounting portion 13 has a shape in which four D-shaped cut surfaces are provided at equal intervals in the circumferential direction on the cylindrical surface (cylindrical surface).

[0045] like Figure 3 , Figure 4 As shown in (b), a groove G extending over the entire circumferential area of ​​the hollow shaft 10 is provided at the substantially central portion of the strain gauge mounting portion 13 in the axial direction. Figure 6 As shown in FIG. 1 , rounded corners are respectively applied to the upper edge Ge1 (i.e., the connection between the side surface Gs and the first to fourth strain surfaces 131 to 134) and the lower edge Ge2 (i.e., the connection between the side surface Gs and the bottom surface Gb) of the groove G. Therefore, the cross-sectional shape formed by the surface orthogonal to the circumferential direction in the upper edge Ge1 and the lower edge Ge2 of the groove G is a curved surface.

[0046] like Figure 2 and Figure 4 As shown in (c), a connection hole CH is provided in the region of each of the curved surfaces CS1 to CS4 closer to the front end than the groove G. The connection hole CH extends in the radial direction of the hollow shaft 10 and connects the outer peripheral surface 10. OUT With the inner surface 10 IN Connected to the internal space IS. In this embodiment, the four connection holes CH are long holes (grooves) with the axial direction as the long dimension. One of the four connection holes CH is configured with FPC40, and the other three connection holes CH are not configured with FPC40 (details will be described later).

[0047] The middle diameter portion 14 is adjacent to the strain gauge mounting portion 13 and is provided at the axial front end side of the strain gauge mounting portion 13. The outer diameter of the hollow shaft 10 at the middle diameter portion 14 is smaller than the outer diameter of the hollow shaft 10 at the strain gauge mounting portion 13 (the outer diameters of two opposing curved surfaces among the curved surfaces CS1 to CS4).

[0048] The small diameter portion 15 is adjacent to the middle diameter portion 14 and is provided at the axial front end side of the middle diameter portion 14. The outer diameter of the hollow shaft 10 at the small diameter portion 15 is smaller than the outer diameter of the hollow shaft 10 at the middle diameter portion 14.

[0049] The pedal threaded portion 16 is adjacent to the small diameter portion 15 and is provided at the axial front end side of the small diameter portion 15. The pedal threaded portion 16 is located at the end of the front end side of the hollow shaft 10. In the pedal threaded portion 16, an external thread MS is provided on the outer peripheral surface of the hollow shaft 10. 16 . External thread MS 16 It is used when the pedal P is mounted on the hollow shaft 10 .

[0050] like Figure 3 As shown, inside the hollow shaft 10 , an internal space IS is defined by the through hole TH.

[0051] The through hole TH is divided into a first portion TH1, a second portion TH2, a third portion TH3, and a fourth portion TH4 along the central axis X from the base end side. The diameter of the through hole TH at the second portion TH2 (the inner diameter of the hollow shaft 10) is smaller than the diameter of the through hole TH at the first portion TH1. The diameter of the through hole TH at the third portion TH3 is smaller than the diameter of the through hole TH at the second portion TH2. The diameter of the through hole TH at the fourth portion TH4 is smaller than the diameter of the through hole TH at the third portion TH3.

[0052] The first portion TH1 is located between the base end of the hollow shaft 10 and the vicinity of the axial center of the crank threaded portion 11. The second portion TH2 is located between the vicinity of the axial center of the crank threaded portion 11 and the vicinity of the axial center of the bolt head 12. The third portion TH3 is located between the vicinity of the axial center of the bolt head 12 and the base end of the small diameter portion 15. The fourth portion TH4 is located between the base end of the small diameter portion 15 and the front end of the hollow shaft 10.

[0053] [Strain gauge]

[0054] The strain gauges SG are mounted on the first to fourth strain surfaces 131 to 134 of the strain gauge mounting portion 13. 11 ~SG 14 , strain gauge SG 21 ~SG 24 , strain gauge SG 31 ~SG 34 And strain gauge SG 41 ~SG 44 ( Figure 5 (a)~ Figure 5 (d)). Hereinafter, the strain gauge SG 11 ~SG 14 , strain gauge SG 21 ~SG 24 , strain gauge SG 31 ~SG 34 And strain gauge SG 41 ~SG44 Collectively referred to as strain gauge SG X .

[0055] Each strain gauge SG X The device includes a base material BM formed of a resin film and a metal resistor RS provided on the base material BM.

[0056] The resistor RS includes a strain sensing portion SS and a pair of connection protrusions (connection terminals) T1 and T2 for connecting the strain sensing portion SS to the circuit board 20 .

[0057] In the strain sensing portion SS, the linear resistor RS is folded back in a zigzag shape. In the following description, the extension direction of the linear portion defined between the folding points is referred to as the grid direction (strain sensing direction), and the direction in which the linear portion is arranged is referred to as the grid width direction. The grid direction and the grid width direction are orthogonal to each other. Each strain gauge is configured to sense the strain generated in the grid direction.

[0058] Each strain gauge SG X The strain sensing portion SS is arranged so that the grid direction thereof is consistent with the axial direction.

[0059] Strain gauge SG 11 The strain gauge SG is provided on the base end side and the circumferential negative side of the third strain surface 133. 12 Provided on the proximal end side and the circumferential positive side of the third strain surface 133. Strain gauge SG 13 The strain gauge SG is provided on the base end side and the circumferential negative side of the first strain surface 131. 14 Provided on the base end side and the circumferential positive side of the first strain surface 131. Strain gauge SG 11 ~SG 14 The connection protrusions T1 and T2 are provided so as to be located closer to the front end side than the sensing portion SS.

[0060] Strain gauge SG 21 The strain gauge SG is provided on the base end side and the circumferential negative side of the second strain surface 132. 22 Provided on the base end side and the circumferential positive side of the second strain surface 132. Strain gauge SG 23 The strain gauge SG is provided on the base end side and the circumferential negative side of the fourth strain surface 134. 24 Provided on the proximal end side and the circumferential positive side of the fourth strain surface 134. Strain gauge SG 21 ~SG 24 The connection protrusions T1 and T2 are provided so as to be located closer to the front end side than the sensing portion SS.

[0061] Strain gauge SG 31 The strain gauge SG is provided at the front end side and the circumferential negative side of the third strain surface 133. 32It is provided at the front end side and the positive side in the circumferential direction of the third strain surface 133. Strain gauge SG 33 The strain gauge SG is provided at the front end side and the circumferential negative side of the first strain surface 131. 34 It is provided at the front end side and the positive side in the circumferential direction of the first strain surface 131. Strain gauge SG 31 ~SG 34 The connection protrusions T1 and T2 are provided so as to be located closer to the base end side than the sensing portion SS.

[0062] Strain gauge SG 41 The strain gauge SG is provided at the front end side and the circumferential negative side of the second strain surface 132. 42 It is provided at the front end side and the positive side in the circumferential direction of the second strain surface 132. Strain gauge SG 43 The strain gauge SG is provided at the front end side and the circumferential negative side of the fourth strain surface 134. 44 It is provided at the front end side and the positive side in the circumferential direction of the fourth strain surface 134. Strain gauge SG 41 ~SG 44 The connection protrusions T1 and T2 are provided so as to be located closer to the base end side than the sensing portion SS.

[0063] In the first strain surface 131, when viewed in the radial direction, the strain gauge SG 13 SG 14 The connection tabs T1, T2 and strain gauge SG 33 SG 34 The connecting tabs T1 and T2 are both arranged inside the groove G. Strain gauge SG 13 SG 14 SG 33 SG 34 The base material BM is not bonded to the first strain surface 131 in the region where the connecting protrusions T1 and T2 are formed, but is arranged in the inner part of the groove G when viewed in the radial direction in a state away from the bottom surface Gb of the groove G ( Figure 6 ). In addition, the base material BM is bent in the radial direction so that the connecting protrusions T1 and T2 are located inside the groove G when viewed in the circumferential direction. By utilizing this bending to absorb the strain of the hollow shaft 10, the generation of strain at the connecting protrusions T1 and T2 can be suppressed (details will be described later).

[0064] On the other hand, the strain gauge SG 13 SG 14 SG 33 SG 34 The base material BM is bonded to the first strain surface 131 in the region where the sensing portion SS is formed and fixed to the first strain surface 131. Therefore, when the first strain surface 131 is strained, the sensing portion SS is also strained in accordance with the strain.

[0065] The same is true for the second strain surface 132 to the fourth strain surface 134. The base material BM of the strain gauge mounted on each strain surface is not bonded to the second strain surface 132 to the fourth strain surface 134 in the area where the connecting protrusions T1 and T2 are formed, but is arranged inside the groove G when viewed in the radial direction in a state away from the bottom surface of the groove G. In addition, the base material BM is bent in the radial direction so that the connecting protrusions T1 and T2 are located inside the groove G when viewed in the circumferential direction. On the other hand, the base material BM of each strain gauge is bonded to each strain surface in the area where the sensing portion SS is formed and fixed to each strain surface.

[0066] [Circuit Board 20, Power Supply Unit 30, FPC 40]

[0067] The circuit board 20 is a printed circuit board assembly (PCBA) provided with a processing circuit 21 for processing the output of each strain gauge, a communication circuit 22 for communicating with the outside, etc. In the present embodiment, the circuit board 20 is arranged in the area defined by the second portion TH2 of the internal space IS.

[0068] The processing circuit 21 includes a strain gauge SG 11 ~SG 14 , strain gauge SG 21 ~S 24 , strain gauge SG 31 ~SG 34 And strain gauge SG 41 ~SG 44 The output of the amplifier is amplified by an amplifier circuit and / or using a strain gauge SG 11 ~SG 14 , strain gauge SG 21 ~S 24 , strain gauge SG 31 ~SG 34 And strain gauge SG 41 ~SG 44 A computing circuit that uses the output of the

[0069] The communication circuit 22 includes a transmission circuit and the like for transmitting the processing result of the processing circuit 21 to the outside.

[0070] The power supply unit 30 is a power supply to the strain gauge SG X The part that supplies power to the circuit board 20 is, for example, a battery. Any secondary battery can be used as the power supply unit 30. In the present embodiment, the power supply unit 30 is arranged in the area defined by the second portion TH2 of the internal space IS.

[0071] FPC40 will strain gauge SG X The FPC 40 further connects the four Wheatstone bridge circuits to the circuit board 20 and the power supply unit 30 .

[0072] The FPC 40 has a structure in which a first wiring substrate 41 , a second wiring substrate 42 , a third wiring substrate 43 , and a fourth wiring substrate 44 are connected to each other as one.

[0073] The first wiring substrate 41 ( Figure 2 , Figure 6 ) extends along the circumference of the hollow shaft 10 and is connected to the strain gauge SG 11 ~SG 14 , strain gauge SG 21 ~SG 24 , strain gauge SG 31 ~SG 34 And strain gauge SG 41 ~SG 44 The first wiring substrate 41 is arranged on the radially outer side of the groove G.

[0074] The first wiring substrate 41 is in a strip shape with the circumferential direction of the hollow shaft 10 as the long dimension direction. The first wiring substrate 41 is provided with four grooves SL penetrating the first wiring substrate 41 in the thickness direction and extending in the long dimension direction at the center portion in the width direction (the axial direction of the hollow shaft 10). The four grooves SL are respectively arranged between the connecting protrusions of two strain gauges arranged in the axial direction in one of the first strain surfaces 131 to the fourth strain surface 134.

[0075] The second wiring substrate 42 ( Figure 2 ) extends in the axial direction from a portion of the circumference of the first wiring substrate 41. The second wiring substrate 42 is provided on the curved surface CS1.

[0076] The third wiring substrate 43 ( Figure 2 ) extends radially from the circumferential end of the second wiring substrate 42. The third wiring substrate 43 extends from the curved surface CS1 to the internal space IS through the connection hole CH provided in the curved surface CS1.

[0077] The fourth wiring substrate 44 ( Figure 3 ) extends axially from the radially inner end of the third wiring substrate 43. The fourth wiring substrate 44 extends from the third wiring substrate 43 along the inner circumferential surface 10 of the hollow shaft 10. IN The connector extends to and is connected to the circuit board 20 and the power supply unit 30 .

[0078] By using FPC40 to connect the strain gauge SG 11 ~SG 14 connected to form the first Wheatstone bridge WSB1 ( Figure 7 (a)). Similarly, by using FPC40 to connect the strain gauge SG 21 ~SG 24 Connect to form the second Wheatstone bridge WSB2 ( Figure 7 (b)) by using FPC40 to connect the strain gauge SG 31 ~SG 34 Connect to form the third Wheatstone bridge WSB3 ( Figure 7 (c)) by using FPC40 to connect the strain gauge SG 41 ~SG 44 connect to form the fourth Wheatstone bridge WSB4 ( Figure 7 (d)).

[0079] An input voltage Ei is applied to each of the Wheatstone bridges WSB1 to WSB4 through the power supply unit 30 . An output voltage Eo of each of the Wheatstone bridges WSB1 to WSB4 is output to the circuit board 20 .

[0080] The pedal P is in the shape of a thick plate having a through hole (not shown) inside which the pedal shaft 100 is inserted. The pedal P is assembled to the pedal shaft 100 by inserting the pedal shaft 100, in which a ball bearing (not shown) is arranged near the base end of the middle diameter portion 14 and the small diameter portion 15, into the through hole of the pedal P, and a nut (not shown) is assembled to the pedal threaded portion 16 to restrict the axial movement of the pedal P. In addition, the pedal P can be assembled to the pedal shaft 100 by any known method.

[0081] Next, a method of using the power meter PM will be described.

[0082] When using the power meter PM, first attach the power meter PM to the crank CR ( Figure 1 The power meter PM is assembled to the crank CR by engaging a tool such as a wrench with the bolt head 12 of the pedal shaft 100 and screwing the crank thread 11 into the internal thread (not shown) of the crank CR.

[0083] When a bicycle user steps on pedals P with power meter PM attached to crank CR, a load corresponding to the position of pedal P is applied to pedal shaft 100 from the user's legs. Wheatstone bridges WSB1 to WSB4 detect strain of pedal shaft 100 caused by the load and output it to circuit board 20 .

[0084] The processing circuit 21 of the circuit board 20 calculates the magnitude, direction, position, etc. of the force (pedaling force) of the user of the bicycle or the like stepping on the pedal P based on the strain detected via the Wheatstone bridges WSB1 to WSB4. The calculated values ​​are sent to an external device, such as a display device (not shown) mounted on the handlebars of the bicycle, via the communication circuit 22. The display device displays the values ​​calculated by the pedal meter PM to the user of the bicycle or the like.

[0085] Hereinafter, advantageous effects of the pedal shaft 100 and the power meter PM of the present embodiment will be summarized.

[0086] In the pedal shaft 100 of the present embodiment, the strain gauge SG X The outer peripheral surface 10 of the hollow shaft 10 is arranged OUT The circuit board 20 is arranged in the internal space IS of the hollow shaft 10, and the strain gauge SG X The FPC 40 connected to the circuit substrate 20 extends inside the internal space IS through the connection hole CH.

[0087] By placing the strain gauge SG X The outer surface 10 is provided at a position where the maximum strain will occur in the hollow shaft 10. OUT , can improve the strain gauge SG X In addition, each strain gauge SG X The output signal is weak and easily affected by external noise, but by arranging the circuit substrate 20 and the FPC 40 in the internal space IS of the hollow shaft 10, the hollow shaft 10 can be used to block external noise, and the signal transmission by the FPC 40 and the various processes by the circuit substrate 20 can be well performed. Based on these aspects, the pedal shaft 100 of this embodiment can detect strains, etc., by the circuit substrate 20 with high precision.

[0088] In the pedal shaft 100 of the present embodiment, since the circuit board 20 and the FPC 40 are arranged in the internal space IS of the metal hollow shaft 10 , the circuit board 20 and the FPC 40 can be well protected from external water, dust, and the like.

[0089] Since the pedal shaft 100 of the present embodiment is configured using the metal hollow shaft 10 having the internal space IS, the pedal shaft 100 has sufficient strength and is lightweight.

[0090] In the pedal shaft 100 of the present embodiment, the outer peripheral surface 10 of the hollow shaft 10 OUT The first to fourth strain surfaces 131 to 134 are provided at equal intervals in the circumferential direction as flat surfaces orthogonal to the radial direction. X Assembled on the first strain surface 131 to the fourth strain surface 134. In this way, by X Set on a flat surface parallel to the axial direction, each strain gauge SG XThe strain generated in the axial direction of the hollow shaft 10 can be detected with high accuracy, and the burden of calculation processing in the circuit substrate 20 is also reduced. In addition, by arranging a plurality of strain surfaces of the same shape at equal intervals (i.e., rotationally symmetrical) in the circumferential direction, the strain generated in the hollow shaft 10 is uniformed in the circumferential direction, and the magnitude of the pedaling force in the circuit substrate 20 can be calculated with higher accuracy.

[0091] In the pedal shaft 100 of the present embodiment, the strain gauge mounting portion 13 of the hollow shaft 10 is provided with a groove G. X The connecting tabs T1 and T2 are arranged inside the recess G when viewed in the radial direction in a manner away from the bottom surface of the recess G, and are not bonded to the hollow shaft 10. In addition, the base material BM is bent in the radial direction so that the connecting tabs T1 and T2 are located inside the groove G when viewed in the circumferential direction. Therefore, even if the hollow shaft 10 is strained, the connecting tabs T1 and T2 will only move in the radial direction, and the connecting tabs T1 and T2 will not be strained. Therefore, it is possible to prevent the deterioration of the connection state between the connecting tabs T1 and T2 and the FPC 40 that may be caused by the generation of strain at the connecting tabs T1 and T2 or even the strain of the connecting tabs T1 and T2.

[0092] In the pedal shaft 100 of the present embodiment, the slot SL is provided in the first wiring substrate 41 of the FPC 40. Therefore, the influence of the strain generated by the connection tabs T1 and T2 of the strain gauges arranged on one axial side of the slot SL can be suppressed from affecting the connection tabs T1 and T2 of the strain gauges arranged on the other axial side of the slot SL. That is, even if there is a difference in the strain amount (displacement amount) of the hollow shaft 10 and the strain gauges on one axial side and the other side of the slot SL, the influence of the difference is absorbed by the slot SL, so it is possible to suppress the strain generated on one axial side of the slot SL from causing the connection tabs T1 and T2 of the strain gauges on the other axial side of the slot SL.

[0093] In the pedal shaft 100 of the present embodiment, four connection holes CH having the same shape are provided at equal intervals along the circumferential direction in the strain gauge mounting portion 13 of the hollow shaft 10. Thus, although only one connection hole CH is sufficient for the FPC 40 to pass through, by providing a plurality of connection holes CH having the same shape in a rotationally symmetrical manner in the circumferential direction, the strain generated by the hollow shaft 10 is uniformed in the circumferential direction, and the magnitude of the pedaling force in the circuit substrate 20 can be calculated with higher accuracy.

[0094] In the pedal shaft 100 of the present embodiment, each strain gauge SG mounted on the strain gauge mounting portion 13 of the hollow shaft 10 X The grid direction of the WSB1 is consistent with the axial direction of the hollow shaft 10. Therefore, each of the Wheatstone bridges WSB1 to WSB4 can be made into a full-bridge circuit, and high-precision sensing can be performed.

[0095] In the pedal shaft 100 of the present embodiment, the processing circuit 20 and the power supply unit 30 are arranged in the internal space IS of the hollow shaft 10. Therefore, the power meter PM having the pedal shaft 100 is functionally complete, and when the power meter PM is mounted on the crank CR of a bicycle or the like, there is no need to set wiring across the power meter PM and the crank CR. Therefore, the power meter PM including the pedal shaft 100 of the present embodiment is easy to handle, and can be mounted and dismounted from the crank CR with less effort.

[0096] <Modification>

[0097] The pedal shaft 100 of the above-described embodiment may also be subjected to the following modifications.

[0098] In the pedal shaft 100 of the above embodiment, all sixteen strain gauges SG X , so that the grid direction of the sensing part SS is consistent with the axial direction of the hollow shaft 10. However, it is not limited to this, and the grid direction of a part of the sensing part can also be consistent with the axial direction of the hollow shaft 10 and the grid direction of another part of the sensing part can be consistent with the circumferential direction of the hollow shaft 10.

[0099] Specifically, for example, using Figure 8 The strain gauge SSG shown in FIG. 1 includes a base material BBM formed of a resin film and a metal resistor RRS provided on the base material BBM. The resistor RRS includes a strain sensing portion SS A SS B1 SS B2 and for the strain sensing part SS A SS B1 SS B2 Connected to the connection tabs TT1 , TT2 , and TT3 of the circuit board 20 .

[0100] In the strain sensing part SS A SS B1 SS B2 In the figure, the linear resistor RRS is folded back in a zigzag shape. A The grid direction and strain sensing part SS B1 SS B2 The grid directions are orthogonal to each other. B1 SS B2 In the strain sensing part SS A The strain sensing portion SS is separated from the grid direction in a direction perpendicular to the grid direction (grid width direction). A Configuration.

[0101] like Fig. 9 (a)~ Fig. 9As shown in (d), eight strain gauges SSG are mounted in pairs on the first strain surface 131 to the fourth strain surface 134. The eight strain gauges SSG are mounted in the following manner: the strain sensing portion SS A The grid direction is consistent with the axial direction of the hollow shaft 10, and the strain sensing part SS B1 SS B2 The grid direction is consistent with the circumferential direction of the hollow shaft 10.

[0102] The strain gauges SSG mounted on the base end side of the first to fourth strain surfaces 131 to 134 are connected to the protruding pieces TT1 to TT3 and are located at the relative strain sensing portion SS A SS B1 SS B2 The strain gauges SSG mounted on the front end of the first to fourth strain surfaces 131 to 134 are arranged so that the connecting protrusions TT1 to TT3 are located closer to the strain sensing portion SS. A SS B1 SS B2 The connection protrusions TT1 to TT3 of the eight strain gauges SSG are arranged inside the groove G when viewed in the radial direction.

[0103] The strain sensing portion SS of the strain gauge SSG mounted on the base end side of the third strain surface 133 is A SS B1 SS B2 The strain sensing part SS 11 SS 131 SS 132 The strain sensing portion SS of the strain gauge SSG mounted on the base end side of the first strain surface 131 is A SS B1 SS B2 The strain sensing part SS 14 SS 121 SS 122 At this time, these strain sensing parts can be connected by FPC40 to form Fig.10 The Wheatstone bridge WSB5 shown in (a).

[0104] The strain sensing portion SS of the strain gauge SSG mounted on the base end side of the second strain surface 132 is A SS B1 SS B2 The strain sensing part SS 21 SS 231 SS 232 The strain sensing portion SS of the strain gauge SSG mounted on the base end side of the fourth strain surface 134 is A SSB1 SS B2 The strain sensing part SS 24 SS 221 SS 222 At this time, these strain sensing parts can be connected by FPC40 to form Fig.10 (b) shows the Wheatstone bridge WSB6.

[0105] The strain sensing portion SS of the strain gauge SSG mounted on the front end side of the third strain surface 133 is A SS B1 SS B2 The strain sensing part SS 31 SS 331 SS 332 The strain sensing portion SS of the strain gauge SSG mounted on the front end side of the first strain surface 131 is A SS B1 SS B2 The strain sensing part SS 34 SS 321 SS 322 At this time, these strain sensing parts can be connected by FPC40 to form Fig.10 (c) shows the Wheatstone bridge WSB7.

[0106] The strain sensing portion SS of the strain gauge SSG mounted on the front end side of the second strain surface 132 is A SS B1 SS B2 The strain sensing part SS 41 SS 431 SS 432 The strain sensing portion SS of the strain gauge SSG mounted on the front end side of the fourth strain surface 134 is A SS B1 SS B2 The strain sensing part SS 44 SS 421 SS 422 At this time, these strain sensing parts can be connected by FPC40 to form Fig.10 (d) shows the Wheatstone bridge WSB8.

[0107] In this way, by using the strain gauge SSG formed with a half bridge, the degradation of the temperature characteristics caused by the internal wiring length can be reduced. In more detail, since all or most of the wirings constituting the Wheatstone bridges WSB5 to WSB8 can be formed on the strain gauge SSG instead of the FPC40, the temperature characteristic change caused by the resistance difference between the wiring pattern (e.g., copper pattern) of the strain gauge and the wiring pattern of the FPC40 can be suppressed. Therefore, the sensing error caused by the temperature change can be suppressed.

[0108] In addition, in this modification, a strain gauge SSG is used in which a plurality of strain sensing parts are formed on a single substrate BBM. Therefore, the strain gauge can be arranged in a smaller area, and the first strain surface 131 to the fourth strain surface 134 and even the pedal shaft 100 can be miniaturized. In addition, since the strain sensing parts are connected to each other on the strain gauge SSG, the number of connecting tabs required to form a Wheatstone bridge can be reduced to six. Since the number of connecting tabs required to form a Wheatstone bridge is reduced, the size of the connecting tab can be increased, and the workability related to the electrical connection with the FPC40 can be improved.

[0109] The strain gauge SSG can also be understood as two separate strain gauges, namely, a strain gauge having a strain sensing portion SS A The strain gauge and the strain sensing part SS B1 SS B2 In addition, two separate strain gauges, i.e., a strain sensing portion S SA The strain gauge and the strain sensing part SS B1 SS B2 The strain gauge is used to replace the strain gauge SSG.

[0110] In the pedal shaft 100 of the above-mentioned embodiment, the first to fourth strain surfaces 131 to 134 are provided on the strain gauge mounting portion 13 of the hollow shaft 10, but the present invention is not limited thereto. The number of flat strain surfaces orthogonal to the radial direction provided on the strain gauge mounting portion 13 is arbitrary. In the case of having a plurality of strain surfaces, by setting them to have the same shape as each other and arranging them at equal intervals along the circumferential direction, the strain generated by the hollow shaft 10 can be made uniform in the circumferential direction. It is also possible to mount the strain gauge on the outer circumferential surface 10 of the hollow shaft 10 instead of providing the flat strain surfaces orthogonal to the radial direction. OUT (For example, a cylindrical surface). In this case, the outer peripheral surface 10 OUT It is actually a strain surface.

[0111] In the pedal shaft 100 of the above embodiment, the hollow shaft 10 has a through hole TH, and the internal space IS is defined by the through hole TH inside the hollow shaft 10, but the present invention is not limited thereto. The hollow shaft 10 may also have a center hole (a recessed hole extending in the axial direction) instead of the through hole TH, wherein the center hole adopts a structure in which the end of the through hole TH on the base end side and / or the end of the front end side is closed. In this case, the internal space IS is defined by the center hole.

[0112] In the present invention, "hollow shaft" refers to any member that is shaft-shaped and has a space inside. In addition, in the present invention, "internal space of the hollow shaft" refers to any space defined inside the hollow shaft. The space may be connected to the outside of the hollow shaft, or may be a sealed space defined inside the hollow shaft.

[0113] In the pedal shaft 100 of the above embodiment, the hollow shaft 10 has a substantially cylindrical shape, but the present invention is not limited thereto. The shape of the cross section of the hollow shaft 10 formed by a plane perpendicular to the axial direction is arbitrary.

[0114] In the pedal shaft 100 of the above embodiment, sixteen strain gauges SG X The number of strain gauges mounted on the hollow shaft 10 is arbitrary.

[0115] In the pedal shaft 100 of the above embodiment, four connection holes CH are arranged at equal intervals in the circumferential direction in the hollow shaft 10 , and the four connection holes CH are long holes with the axial direction as the long dimension, but the present invention is not limited thereto. The shape, number, and arrangement of the connection holes CH are arbitrary.

[0116] Specifically, for example, only the FPC 40 may be provided from the outer peripheral surface 10 OUT The single connection hole CH required to extend to the internal space IS. In addition, the shape of the cross section formed by the plane orthogonal to the radial direction of each connection hole CH may be circular, quadrilateral, or the like.

[0117] When a plurality of connection holes CH are arranged at equal intervals in the circumferential direction, the shapes of the cross sections formed by the surfaces orthogonal to the radial direction of the plurality of connection holes CH do not have to be the same. In this case, by arranging the connection holes CH at equal intervals in the circumferential direction, the strain generated by the hollow shaft 10 can also be made uniform in the circumferential direction.

[0118] In the pedal shaft 100 of the above embodiment, sixteen strain gauges SG are connected by FPC 40. X The connection with the circuit board 20 is not limited thereto. Sixteen strain gauges SG XThe connection with the circuit board 20 can be performed by any wiring structure such as a lead wire. In addition, the groove SL of the first wiring board 41 of the FPC 40 can also extend in any direction intersecting the axial direction of the hollow shaft 10.

[0119] In the pedal shaft 100 of the above-mentioned embodiment, an adhesive with low adhesive force may be arranged in the groove G of the strain gauge mounting portion 13 of the hollow shaft 10 (i.e., between the base material BM and the bottom surface Gb). The adhesive with low adhesive force refers to an adhesive with an adhesive force weaker than that of the adhesive used in the region having the sensing portion SS and having an adhesive force to such an extent that the connecting protrusions T1 and T2 will not generate strain corresponding to the strain when the hollow shaft 10 generates strain. The scheme in which the strain gauge is not fixed to the hollow shaft 10 includes the scheme in which the base material BM is bonded to the hollow shaft 10 by the adhesive with low adhesive force. In addition, the scheme in which the connecting protrusions T1 and T2 of the base material BM are not bonded to the hollow shaft 10 without providing the groove G, or the scheme in which the connecting protrusions T1 and T2 of the base material BM are bonded to the hollow shaft 10 by the adhesive with low adhesive force.

[0120] Such a structure can also suppress the generation of strains in the connection protrusions T1 and T2 corresponding to the strains of the hollow shaft 10 , and further suppress damage to the connection between the connection protrusions T1 and T2 and the FPC 40 .

[0121] As long as the characteristics of the present invention are maintained, the present invention is not limited to the above-described embodiments, and other embodiments that can be conceived within the scope of the technical concept of the present invention are also included in the scope of the present invention.

[0122] Description of Reference Numerals

[0123] 10: Hollow shaft; 11: Crank threaded part; 12: Bolt head; 13: Strain gauge assembly part; 14: Middle diameter part; 15: Small diameter part; 16: Pedal threaded part; 20: Circuit board; 30: Power supply part; 40: FPC; 100: Pedal shaft; PM: Pedal meter; SG X ,SSG: strain gauge.

Claims

1. A pedal shaft for a pedal-type power meter, wherein: The pedal shaft comprises: A hollow shaft for the pedal to be mounted in a rotatable manner; a strain gauge mounted on the outer circumference of the hollow shaft; and The processing circuit is disposed in the inner space of the hollow shaft and processes the output from the strain gauge.

2. The pedal shaft according to claim 1, wherein: The hollow shaft is provided with a connection hole for connecting the outer peripheral surface with the inner space. Wiring that connects the strain gauge and the processing circuit is arranged in the connection hole and the internal space.

3. The pedal shaft according to claim 2, wherein: A plurality of the connection holes are arranged at equal intervals along the circumference of the hollow shaft.

4. The pedal shaft according to claim 2 or 3, wherein: The connecting hole is a long hole with the axial direction of the hollow shaft as the long dimension direction.

5. The pedal shaft according to any one of claims 2 to 4, wherein: The strain gauge comprises two strain gauges arranged along the axial direction of the hollow shaft, The wiring includes a flexible printed wiring substrate connected to the two strain gauges, The flexible printed wiring substrate has a groove extending in a direction intersecting the axial direction in a region located between the two strain gauges.

6. The pedal shaft according to any one of claims 1 to 5, wherein: The hollow shaft is cylindrical. The internal space is defined by a recessed hole or a through hole extending in the axial direction of the hollow shaft.

7. The pedal shaft according to any one of claims 1 to 6, wherein: A plurality of flat surfaces are provided on the outer peripheral surface of the hollow shaft, and the plurality of flat surfaces extend in planes orthogonal to the radial direction of the hollow shaft, respectively. The plurality of flat surfaces are arranged at equal intervals along the circumference of the hollow shaft. The strain gauges are respectively mounted on the plurality of flat surfaces.

8. The pedal shaft according to claim 7, wherein: The plurality of flat surfaces are four flat surfaces.

9. The pedal shaft according to any one of claims 1 to 8, wherein: The strain gauge comprises: a strain sensing portion; A connecting terminal, used to connect the strain sensing part to the processing circuit; and a substrate, on which the strain sensing portion and the connecting terminal are formed, The substrate is fixed to the hollow shaft in a region where the strain sensing portion is formed, and is not fixed to the hollow shaft in a region where the connecting terminal is formed.

10. The pedal shaft according to claim 9, wherein: A groove is provided on the outer peripheral surface of the hollow shaft. When viewed in a radial direction of the hollow shaft, the connection terminal of the strain gauge is located inside the groove.

11. The pedal shaft according to any one of claims 1 to 10, wherein: A threaded portion for assembling the pedal shaft to a crank is provided at one end of the hollow shaft, and a threaded portion for assembling the pedal to the pedal shaft is provided at the other end of the hollow shaft.

12. The pedal shaft according to any one of claims 1 to 11, wherein: The strain gauges are a plurality of strain gauges each having a strain sensing portion, The strain sensing direction of the strain sensing portion of each of the plurality of strain gauges is consistent with the axial direction of the hollow shaft.

13. The pedal shaft according to any one of claims 1 to 11, wherein: The strain gauges are a plurality of strain gauges each having a strain sensing portion, The plurality of strain gauges include: a first strain gauge group, wherein the strain sensing direction of each strain sensing portion thereof is consistent with the axial direction of the hollow shaft; and a second strain gauge group, wherein the strain sensing direction of each strain sensing portion thereof is consistent with the circumferential direction of the hollow shaft.

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