Pedal shaft

Abstract

To provide a pedal shaft capable of accurately detecting strain arising therein.SOLUTION: A pedal shaft for pedal power meters is provided, comprising a hollow shaft configured to allow a pedal to rotatably attached thereto, a strain gauge attached to an outer peripheral surface of the hollow shaft, and a processing circuit disposed in an internal space of the hollow shaft and configured to process an output from the strain gauge.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a pedal shaft. [Background technology]

[0002] Power meters are known devices that are attached to bicycles and other vehicles to measure the magnitude, direction, and position of the force applied by the user when pedaling. Power meters are broadly classified into pedal-type power meters, which have a measuring unit on the pedal; crank-type power meters, which have a measuring unit on the crank; and hub-type power meters, which have a measuring unit on the tire hub.

[0003] Patent Document 1 discloses a pedal-type power meter. In Patent Document 1, four elongation measuring pieces are attached to the pedal shaft. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-145824 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The pedal shaft described in Patent Document 1 cannot be said to be able to detect the strain occurring in the pedal shaft with sufficient accuracy.

[0006] The present invention aims to provide a pedal shaft for a pedal-type power meter that can detect strain occurring in the pedal shaft with high accuracy. [Means for solving the problem]

[0007] According to one aspect of the present invention, A pedal axle for a pedal-type power meter, A hollow shaft on which the pedal is rotatably mounted, A strain gauge attached to the outer surface of the hollow shaft, A pedal shaft is provided, comprising a processing circuit disposed within the internal space of the hollow shaft and processing the output from the strain gauge. [Effects of the Invention]

[0008] The pedal shaft of the present invention can detect strain occurring in the pedal shaft with high precision. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a perspective view of a power meter according to one embodiment of the present invention. [Figure 2] Figure 2 is a perspective view of the pedal shaft of one embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional view of the pedal shaft shown in Figure 2, cut by a plane passing through the central axis X and extending radially. The strain gauges are not shown in Figure 3. [Figure 4] Figure 4(a) is a cross-sectional view of the hollow shaft along the line IVa-IVa in Figure 3. Figure 4(b) is a cross-sectional view of the hollow shaft along the line IVb-IVb in Figure 3. Figure 4(c) is a cross-sectional view of the hollow shaft along the line IVc-IVc in Figure 3. [Figure 5] Figure 5(a) is a plan view of the first strain surface viewed from the radial outside, showing the configuration of four strain gauges attached to the first strain surface. Figure 5(b) is a plan view of the second strain surface viewed from the radial outside, showing the configuration of four strain gauges attached to the second strain surface. Figure 5(c) is a plan view of the third strain surface viewed from the radial outside, showing the configuration of four strain gauges attached to the third strain surface. Figure 5(d) is a plan view of the fourth strain surface viewed from the radial outside, showing the configuration of four strain gauges attached to the fourth strain surface. In each of Figures 5(a) to 5(d), the left side is the base end and the right side is the tip end. [Figure 6] Figure 6 is a cross-sectional view along the line VI-VI in Figure 5. [Figure 7] Figures 7(a) to 7(d) are circuit diagrams of Wheatstone bridges, each consisting of strain gauges mounted on a hollow shaft. [Figure 8] Figure 8 is a plan view of the strain gauges installed in the modified pedal shaft. [Figure 9] Figure 9(a) is a plan view of the first strain surface viewed from the radial outside, showing the configuration of a modified strain gauge attached to the first strain surface. Figure 9(b) is a plan view of the second strain surface viewed from the radial outside, showing the configuration of a modified strain gauge attached to the second strain surface. Figure 9(c) is a plan view of the third strain surface viewed from the radial outside, showing the configuration of a modified strain gauge attached to the third strain surface. Figure 9(d) is a plan view of the fourth strain surface viewed from the radial outside, showing the configuration of a modified strain gauge attached to the fourth strain surface. [Figure 10] Figures 10(a) to 10(d) are circuit diagrams of Wheatstone bridges constructed using modified strain gauges mounted on hollow shafts, respectively. [Modes for carrying out the invention]

[0010] <Embodiment> A pedal shaft 100 and power meter PM according to an embodiment of the present invention will be described with reference to Figures 1 to 7.

[0011] [Power Meter PM] As shown in Figure 1, the power meter PM is a pedal-type power meter having a pedal shaft 100 and a pedal P rotatably mounted on the pedal shaft 100.

[0012] [Pedal axis 100] As shown in Figures 2 and 3, the pedal shaft 100 consists of a hollow shaft (hollow spindle) 10 having a central axis X, and the outer circumferential surface 10 of the hollow shaft 10 OUT The pedal shaft 100 mainly consists of 16 strain gauges (details described later) attached to the shaft and a circuit board 20 arranged in the internal space of the hollow shaft 10. The pedal shaft 100 further includes a power supply unit 30 arranged in the internal space of the hollow shaft 10 and a flexible printed circuit board (FPC) 40 that connects the 16 strain gauges to the circuit board 20.

[0013] In the following explanation, the direction of the central axis X will be referred to as the axial direction of the hollow shaft 10 and the pedal shaft 100. Furthermore, the radial direction centered on the central axis X will be 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 will be referred to as the circumferential direction of the hollow shaft 10 and the pedal shaft 100.

[0014] In the axial direction, the side of the hollow shaft 10 with the crank thread portion 11 (described later) is called the base end, and the side of the hollow shaft 10 with the pedal thread portion 16 (described later) is called the tip end. In the circumferential direction, the clockwise direction when viewed from the base end to the tip end in the axial direction is called the positive direction, and the counterclockwise direction is called the negative direction.

[0015] [Hollow shaft 10] The hollow shaft 10 is substantially cylindrical in shape and has a through hole TH extending in the axial direction. The hollow shaft 10 is formed of a metal such as stainless steel, as an example.

[0016] The hollow shaft 10 is divided along the central axis X into, in order from the base end, a crank threaded section 11, a bolt head section 12, a gauge mounting section 13, a medium diameter section 14, a small diameter section 15, and a pedal threaded section 16.

[0017] The crank thread portion 11 is located at the base end of the hollow shaft 10. In the crank thread portion 11, the outer circumferential surface 10 of the hollow shaft 10 OUT Male screw MS 11 A male screw MS is provided. 11 This is used when attaching the hollow shaft 10 to the crank of a bicycle or the like.

[0018] The bolt head portion 12 is located adjacent to the crank thread portion 11 and is provided on the axial end side of the crank thread portion 11. In the bolt head portion 12, the outer circumferential surface 10 of the hollow shaft 10 OUT A hexagonal bolt head 121 and a flange 122 are provided. The flange 122 has a male thread MS 11 It is provided between the hexagonal bolt head 121. Alternatively, a two-sided or square bolt head may be used instead of the hexagonal bolt head.

[0019] The gauge mounting portion 13 is located adjacent to the bolt head portion 12 and is provided on the axial end side of the bolt head portion 12.

[0020] As shown in Figures 2 and 4(a), the outer circumferential surface 10 of the hollow shaft 10 is located in the gauge mounting portion 13. OUT The hollow shaft 10 is provided with a first strain surface 131, a second strain surface 132, a third strain surface 133, and a fourth strain surface 134, each extending in a plane perpendicular to the radial direction of the hollow shaft 10. As shown in Figures 5(a) to 5(d), each of the first strain surface 131 to the fourth strain surface 134 is a rectangular flat surface with the axial direction as the longer side and the circumferential direction as the shorter side. Each of the first strain surface 131 to the fourth strain surface 134 is a gauge mounting surface to which a strain gauge is attached.

[0021] As shown in Figure 4(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 perpendicular to the second strain plane 132 and the fourth strain plane 134.

[0022] The long side on the positive circumferential side of the first strain surface 131 and the long side on the negative circumferential side of the second strain surface 132 are connected by a curved surface CS1 with a circular arc cross-section. The long side on the positive circumferential side of the second strain surface 132 and the long side on the negative circumferential side of the third strain surface 133 are connected by a curved surface CS2 with a circular arc cross-section. The long side on the positive circumferential side of the third strain surface 133 and the long side on the negative circumferential side of the fourth strain surface 134 are connected by a curved surface CS3 with a circular arc cross-section. The long side on the positive circumferential side of the fourth strain surface 134 and the long side on the negative circumferential side of the first strain surface 131 are connected by a curved surface CS4 with a circular arc cross-section.

[0023] In other words, the outer circumferential surface of the hollow shaft 10 in the gauge mounting portion 13 has a cylindrical surface with four D-cut surfaces provided at equal intervals in the circumferential direction.

[0024] As shown in FIGS. 3 and 4(b), a concave groove G extending over the entire circumferential direction of the hollow shaft 10 is provided at a substantially central portion in the axial direction of the gauge mounting portion 13. As shown in FIG. 6, R surface finishing is performed on the upper edge Ge1 (i.e., the connection portion between the side surface Gs and each of the first to fourth starting distortion surfaces 131 to 134) and the lower edge Ge2 (i.e., the connection portion between the side surface Gs and the bottom surface Gb) of the concave groove G. Therefore, the upper edge Ge1 and the lower edge Ge2 of the concave groove G have a curved cross-sectional shape by a surface orthogonal to the circumferential direction.

[0025] As shown in FIGS. 2 and 4(c), in the region on the tip side of each of the curved surfaces CS1 to CS4 with respect to the concave groove G, a connection hole CH extending in the radial direction of the hollow shaft 10 and connecting the outer peripheral surface 10 OUT and the inner peripheral surface 10 IN and the internal space IS is provided. In the present embodiment, each of the four connection holes CH is a long hole (slot) having the axial direction as the longitudinal direction. The FPC 40 is disposed in one of the four connection holes CH, and the FPC 40 is not disposed in the other three of the four connection holes CH (details will be described later).

[0026] The middle diameter portion 14 is provided adjacent to the gauge mounting portion 13 on the tip side in the axial direction of the gauge mounting portion 13. The outer diameter of the hollow shaft 10 in the middle diameter portion 14 is smaller than the outer diameter of the hollow shaft 10 in the gauge mounting portion 13 (the outer diameter passing through two opposing ones of the curved surfaces CS1 to CS4).

[0027] The small diameter portion 15 is provided adjacent to the middle diameter portion 14 on the tip side in the axial direction of the middle diameter portion 14. The outer diameter of the hollow shaft 10 in the small diameter portion 15 is smaller than the outer diameter of the hollow shaft 10 in the middle diameter portion 14.

[0028] The pedal screw portion 16 is provided adjacent to the small diameter portion 15 on the tip side in the axial direction of the small diameter portion 15. The pedal screw portion 16 is located at the tip side end portion of the hollow shaft 10. In the pedal screw portion 16, a male screw MS 16 is provided on the outer peripheral surface of the hollow shaft 10. The male screw MS 16 is used when attaching the pedal P to the hollow shaft 10.

[0029] As shown in Figure 3, the internal space IS is defined within the hollow shaft 10 by through holes TH.

[0030] The through-hole TH is divided into a first section TH1, a second section TH2, a third section TH3, and a fourth section TH4 along the central axis X from the base end. The diameter of the through-hole TH in the second section TH2 (the inner diameter of the hollow shaft 10) is smaller than the diameter of the through-hole TH in the first section TH1. The diameter of the through-hole TH in the third section TH3 is smaller than the diameter of the through-hole TH in the second section TH2. The diameter of the through-hole TH in the fourth section TH4 is smaller than the diameter of the through-hole TH in the third section TH3.

[0031] The first part TH1 is located between the base end of the hollow shaft 10 and the vicinity of the axial center of the crank thread portion 11. The second part TH2 is located between the vicinity of the axial center of the crank thread portion 11 and the vicinity of the axial center of the bolt head portion 12. The third part TH3 is located between the vicinity of the axial center of the bolt head portion 12 and the base end of the small diameter portion 15. The fourth part TH4 is located between the base end of the small diameter portion 15 and the tip of the hollow shaft 10.

[0032] [Strain Gauge] Strain gauges SG are attached to the first strain surface 131 to the fourth strain surface 134 of the gauge mounting section 13. 11 ~SG 14 , strain gauge SG 21 ~SG 24 , strain gauge SG 31 ~SG 34 , and strain gauge SG 41 ~SG 44 It is installed (Figures 5(a) to 5(d)). Below, 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 These are collectively called strain gauges SG X This may be written as follows.

[0033] Strain gauge SG X Each of these comprises a base material BM formed of a resin film and a metal resistor RS provided on the base material BM.

[0034] The resistor RS has a strain-sensitive section SS and a pair of connection tabs (connection terminals) T1 and T2 for connecting the strain-sensitive section SS to the circuit board 20.

[0035] In the strain-sensing section SS, a linear resistor RS is folded back in a zigzag pattern. In the following description, the direction of extension of the linear portion defined between the folding points is called the grid direction (strain-sensing direction), and the direction in which these linear portions are aligned is called the grid width direction. The grid direction and the grid width direction are orthogonal to each other. Each strain gauge is configured to detect strain occurring in the grid direction.

[0036] Strain gauge SG X Each of these is positioned such that the grid direction of the strain-sensitive part SS coincides with the axial direction.

[0037] Strain gauge SG 11 It is provided on the base end side and circumferential negative side of the third strain surface 133, and the strain gauge SG 12 It is provided on the base end side and circumferentially positive side of the third strain surface 133. Strain gauge SG 13 It is provided on the base end side and circumferential negative side of the first strain surface 131, and the strain gauge SG 14 It is provided on the base end side and circumferentially positive side of the first strain surface 131. Strain gauge SG 11 ~SG 14 In each case, the connection tabs T1 and T2 are positioned towards the tip of the sensing element SS.

[0038] Strain gauge SG 21 It is provided on the base end side and circumferential negative side of the second strain surface 132, and the strain gauge SG 22 It is provided on the base end side and circumferentially positive side of the second strain surface 132. Strain gauge SG 23It is provided on the base end side and circumferential negative side of the fourth strain surface 134, and strain gauge SG 24 It is provided on the base end side and circumferentially positive side of the fourth strain surface 134. Strain gauge SG 21 ~SG 24 In each case, the connection tabs T1 and T2 are positioned towards the tip of the sensing element SS.

[0039] Strain gauge SG 31 It is provided on the tip side and circumferentially negative side of the third strain surface 133, and the strain gauge SG 32 It is provided on the tip side and circumferentially positive side of the third strain surface 133. Strain gauge SG 33 It is provided on the tip side and circumferentially negative side of the first strain surface 131, and the strain gauge SG 34 It is provided on the tip side and circumferentially positive side of the first strain surface 131. Strain gauge SG 31 ~SG 34 Each of these is provided such that the connection tabs T1 and T2 are located on the base end side of the sensing part SS.

[0040] Strain gauge SG 41 It is provided on the tip side and circumferentially negative side of the second strain surface 132, and strain gauge SG 42 It is provided on the tip side and circumferentially positive side of the second strain surface 132. Strain gauge SG 43 It is provided on the tip side and circumferentially negative side of the fourth strain surface 134, and the strain gauge SG 44 It is provided on the tip side and circumferentially positive side of the fourth strain surface 134. Strain gauge SG 41 ~SG 44 Each of these is provided such that the connection tabs T1 and T2 are located on the base end side of the sensing part SS.

[0041] In the first strain surface 131, strain gauge SG 13 SG 14 Connection tabs T1, T2, and strain gauge SG 33 SG 34 The connecting tabs T1 and T2 are both located inside the groove G when viewed radially. Strain gauge SG 13 SG14 SG 33 SG 34 In the region where the connecting tabs T1 and T2 are formed, the base material BM is not bonded to the first strain surface 131, but is positioned inside the groove G viewed radially, spaced apart from the bottom surface Gb of the groove G (Figure 6). Furthermore, the base material BM deflects radially, positioning the connecting tabs T1 and T2 inside the groove G viewed circumferentially. By absorbing the strain of the hollow shaft 10 through this deflection, the generation of strain in the connecting tabs T1 and T2 is suppressed (details will be described later).

[0042] On the other hand, strain gauge SG 13 SG 14 SG 33 SG 34 The base material BM is bonded to and fixed to the first strain surface 131 in the region where the sensing portion SS is formed. Therefore, if strain occurs in the first strain surface 131, strain corresponding to that strain will also occur in the sensing portion SS.

[0043] The same applies to the second strain surface 132 to the fourth strain surface 134. The base material BM of the strain gauge attached to each strain surface is not bonded to the second strain surface 132 to the fourth strain surface 134 in the region where the connecting tabs T1 and T2 are formed, but is positioned inside the groove G viewed in the radial direction, spaced apart from the bottom surface of the groove G. Furthermore, the base material BM flexes radially, positioning the connecting tabs T1 and T2 inside the groove G viewed in the circumferential direction. On the other hand, the base material BM of each strain gauge is bonded to and fixed to each strain surface in the region where the sensing part SS is formed.

[0044] [Circuit board 20, power supply unit 30, FPC 40] The circuit board 20 is a printed circuit board assembly (PCBA) equipped with a processing circuit 21 for processing the output of each strain gauge, a communication circuit 22 for communicating with the outside, and the like. In this embodiment, the circuit board 20 is located in the region defined by the second portion TH2 of the internal space IS.

[0045] The processing circuit 21 uses 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 An amplification circuit for amplifying the output of and / or 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 This includes calculation circuits and the like that perform various calculations using the output.

[0046] The communication circuit 22 includes a transmission circuit and the like for transmitting the processing results of the processing circuit 21 to an external source.

[0047] The power supply unit 30 is for strain gauge SG X This is the part that supplies power to the circuit board 20, and is, for example, a battery. The power supply unit 30 can be any secondary battery. In this embodiment, the power supply unit 30 is located in the region of the internal space IS defined by the second part TH2.

[0048] FPC40 is a strain gauge SG X These are connected to form four Wheatstone bridge circuits. The FPC40 also connects the four Wheatstone bridge circuits to the circuit board 20 and the power supply unit 30.

[0049] The FPC40 has a configuration in which a first wiring board 41, a second wiring board 42, a third wiring board 43, and a fourth wiring board 44 are integrally connected.

[0050] The first wiring board 41 (Figures 2 and 6) extends in the circumferential direction of the hollow shaft 10 and connects to the strain gauge SG. 11 ~SG 14 , strain gauge SG 21 ~SG 24 , strain gauge SG 31~SG 34 and strain gauges SG 41 ~SG 44 are connected to the connection tabs T1 and T2. The first wiring board 41 is provided on the radially outer side of the concave groove G.

[0051] The first wiring board 41 is in a strip shape with the circumferential direction of the hollow shaft 10 as the longitudinal direction. The first wiring board 41 is provided with four slots SL that penetrate the first wiring board 41 in the thickness direction and extend in the longitudinal direction at the central portion in the width direction (the axial direction of the hollow shaft 10). Each of the four slots SL is disposed between the connection tabs of two strain gauges arranged axially in any one of the first to fourth strained surfaces 131 to 134.

[0052] The second wiring board 42 (FIG. 2) extends axially from a part of the circumferential direction of the first wiring board 41. The second wiring board 42 is provided on the curved surface CS1.

[0053] The third wiring board 43 (FIG. 2) extends radially from the circumferential end of the second wiring board 42. The third wiring board 43 extends from the curved surface CS1 into the internal space IS through the connection hole CH provided on the curved surface CS1.

[0054] The fourth wiring board 44 (FIG. 3) extends axially from the radially inner end of the third wiring board 43. The fourth wiring board 44 extends along the inner peripheral surface 10 of the hollow shaft 10 from the third wiring board 43 and is connected to the circuit board 20 and the power supply unit 30. IN and is connected to the circuit board 20 and the power supply unit 30.

[0055] Strain gauge SG 11 ~SG 14 By connecting the strain gauges SG with the FPC 40, the first Wheatstone bridge WSB1 (FIG. 7(a)) is formed. Similarly, by connecting the strain gauges SG 21 ~SG 24 with the FPC 40, the second Wheatstone bridge WSB2 (FIG. 7(b)) is formed, and by connecting the strain gauges SG 31 ~SG 34 with the FPC 40, the third Wheatstone bridge WSB3 (FIG. 7(c)) is formed, and by connecting the strain gauges SG41 ~SG 44 By connecting them with FPC40, the fourth Wheatstone bridge WSB4 (Figure 7(d)) ​​is formed.

[0056] Each of the Wheatstone bridges WSB1 to WSB4 is supplied with an input voltage Ei by the power supply unit 30. The output voltage Eo of each of the Wheatstone bridges WSB1 to WSB4 is output to the circuit board 20.

[0057] Pedal P is a thick, plate-like structure with a through-hole (not shown) inside into which pedal shaft 100 is inserted. Pedal P is attached to pedal shaft 100 by inserting pedal shaft 100, which has ball bearings (not shown) placed near the base end of the medium-diameter portion 14 and in the small-diameter portion 15, into the through-hole of pedal P, and attaching a nut (not shown) to the pedal threaded portion 16 to restrict the axial movement of pedal P. In addition, pedal P can be attached to pedal shaft 100 by any known method.

[0058] Next, we will explain how to use the power meter PM.

[0059] When using the Power Meter PM, first attach the Power Meter PM to the crank CR (Figure 1) of a bicycle or similar device. The Power Meter PM is attached to the crank CR by engaging a tool such as a wrench with the bolt head portion 12 of the pedal axle 100 and screwing the crank screw 11 into the female thread (not shown) of the crank CR.

[0060] When a user of a bicycle or similar device pedals P with the power meter PM attached to the crank CR, a load corresponding to the position of pedal P is applied from the user's leg to the pedal axle 100. The Wheatstone bridges WSB1 to WSB4 detect the strain generated in the pedal axle 100 due to this load and output it to the circuit board 20.

[0061] The processing circuit 21 of the circuit board 20 calculates the magnitude, direction, and position of the force (pedaling force) applied by the user of a bicycle or the like when pressing down on the pedal P, based on the strain detected via the Wheatstone bridges WSB1 to WSB4. The calculated values ​​are transmitted via the communication circuit 22 to an external device, such as a display device (not shown) attached to the handlebars of the bicycle. The display device shows the values ​​calculated by the pedal meter PM to the user of the bicycle or the like.

[0062] The advantageous effects of the pedal shaft 100 and power meter PM in this embodiment are summarized below.

[0063] In the pedal shaft 100 of this embodiment, strain gauge SG X the outer circumferential surface 10 of the hollow shaft 10 OUT The circuit boards 20 are each placed in the internal space IS of the hollow shaft 10, and strain gauges SG X The FPC 40, which connects to the circuit board 20, extends through the connection hole CH into the interior of the internal space IS.

[0064] The outer surface 10 is the location where the greatest strain occurs in the hollow shaft 10. OUT Strain gauge SG X By installing the strain gauge SG, X This can improve the detection accuracy of strain gauges SG. X The signals output by each of these components are weak and susceptible to external noise. However, by arranging the circuit board 20 and FPC 40 in the internal space IS of the hollow shaft 10, external noise is blocked by the hollow shaft 10, allowing for smooth signal transmission by the FPC 40 and efficient processing by the circuit board 20. Therefore, the pedal shaft 100 of this embodiment enables high-precision distortion detection by the circuit board 20.

[0065] In this embodiment, the pedal shaft 100 has the circuit board 20 and FPC 40 arranged in the internal space IS of the hollow metal shaft 10, thus providing good protection for the circuit board 20 and FPC 40 from external water, dust, and the like.

[0066] The pedal shaft 100 in this embodiment is constructed using a hollow metal shaft 10 having an internal space IS, and is therefore lightweight while possessing sufficient strength.

[0067] In the pedal shaft 100 of this embodiment, the outer circumferential surface 10 of the hollow shaft 10 OUT The first strain surface 131 to the fourth strain surface 134, which are flat surfaces perpendicular to the radial direction, are provided at equal intervals in the circumferential direction. Strain gauge SG X These are mounted on the first strain surface 131 to the fourth strain surface 134. In this way, the strain gauge SG X By providing it on a flat surface parallel to the axial direction, the strain gauge SG X Each of these can detect the strain occurring in the axial direction of the hollow shaft 10 with high accuracy, and the burden on the calculation processing on the circuit board 20 is also reduced. Furthermore, by providing multiple strain-generating surfaces of the same shape at equal intervals in the circumferential direction (i.e., rotationally symmetric), the strain occurring in the hollow shaft 10 is equalized in the circumferential direction, allowing for more accurate calculation of the magnitude of the pressing force on the circuit board 20.

[0068] In the pedal shaft 100 of this embodiment, a groove G is provided in the gauge mounting portion 13 of the hollow shaft 10. And strain gauge SG X Each of the connecting tabs T1 and T2 is positioned within the recess G, viewed in the radial direction, spaced apart from the bottom surface of the recess G, and is not bonded to the hollow shaft 10. Furthermore, the base material BM flexes radially, positioning the connecting tabs T1 and T2 within the groove G, viewed in the circumferential direction. Therefore, even if strain occurs in the hollow shaft 10, the connecting tabs T1 and T2 only move radially, and no strain occurs in the connecting tabs T1 and T2. Thus, the occurrence of strain in the connecting tabs T1 and T2, and consequently the deterioration of the connection between the connecting tabs T1 and T2 and the FPC 40 that could occur due to the strain in the connecting tabs T1 and T2, can be prevented.

[0069] In the pedal shaft 100 of this embodiment, a slot SL is provided on the first wiring board 41 of the FPC 40. Therefore, the influence of strain generated in the connection tabs T1 and T2 of the strain gauge located on one axial side of the slot SL can be suppressed from affecting the connection tabs T1 and T2 of the strain gauge located on the other axial side of the slot SL. In other words, even if there is a difference in the amount of strain (displacement) of the hollow shaft 10 or the strain gauge between one axial side and the other side of the slot SL, the effect is absorbed by the slot SL, so that the generation of strain in the connection tabs T1 and T2 of the strain gauge on the other axial side of the slot SL caused by strain generated on one axial side of the slot SL is suppressed.

[0070] In the pedal shaft 100 of this embodiment, four connection holes CH of the same shape are provided at equal intervals in the circumferential direction on the gauge mounting portion 13 of the hollow shaft 10. In this way, even though only one connection hole CH is sufficient for passing the FPC 40 through, by providing multiple connection holes CH of the same shape in a rotationally symmetrical manner in the circumferential direction, the strain generated in the hollow shaft 10 is equalized in the circumferential direction, and the magnitude of the pressing force on the circuit board 20 can be calculated with higher accuracy.

[0071] In the pedal shaft 100 of this embodiment, a strain gauge SG is attached to the gauge mounting portion 13 of the hollow shaft 10. X The direction of each grid coincides 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, enabling high-precision detection.

[0072] In this embodiment, the pedal shaft 100 has the processing circuit 20 and power supply unit 30 located 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 attached to the crank CR of a bicycle or the like, there is no need to provide wiring that spans between the power meter PM and the crank CR. Therefore, the power meter PM including the pedal shaft 100 of this embodiment is easy to handle, and can be attached to and detached from the crank CR with minimal effort.

[0073] <Variation> In the pedal shaft 100 of the above embodiment, the following modified forms can also be used.

[0074] In the pedal shaft 100 of the above embodiment, 16 strain gauges SG are attached to the hollow shaft 10. X In all cases, the grid direction of the sensing element SS is aligned with the axial direction of the hollow shaft 10. However, this is not the only option; the grid direction of some sensing elements may be aligned with the axial direction of the hollow shaft 10, while the grid direction of other sensing elements may be aligned with the circumferential direction of the hollow shaft 10.

[0075] Specifically, for example, the strain gauge SSG shown in Figure 8 is used. The strain gauge SSG has a base material BBM formed of a resin film and a metal resistor RRS provided on the base material BBM. The resistor RRS is a strain-sensitive part SS A , SS B1 , SS B2 And, the strain-sensitive part SS A , SS B1 , SS B2 It has connection tabs TT1, TT2, and TT3 for connecting to the circuit board 20.

[0076] Strain-sensitive part SS A , SS B1 , SS B2 In this configuration, the linear resistor RRS is folded back in a zigzag pattern. Strain-sensitive section SS A The grid direction and the strain-sensitive part SS B1 , SS B2 The grid directions are mutually orthogonal. Strain-sensitive part SS B1 , SS B2 This is the strain-sensitive part SS A In the direction perpendicular to the grid direction (grid width direction), the strain-sensitive part SS A They are positioned with one in between.

[0077] As shown in Figures 9(a) to 9(d), eight strain gauges SSG are attached, two to each of the first strain surface 131 to the fourth strain surface 134. Each of the eight strain gauges SSG has a strain sensing element SS A The grid direction coincides with the axial direction of the hollow shaft 10, and the strain-sensitive part SS B1 , SS B2 Install it so that the grid direction coincides with the circumferential direction of the hollow shaft 10.

[0078] The strain gauge SSG attached to the base end side of the first strain surface 131 to the fourth strain surface 134 has connection tabs TT1 to TT3 which are strain sensing parts SS A , SS B1 , SS B2 It is mounted so as to be located towards the tip. The strain gauge SSG mounted on the tip side of the first strain surface 131 to the fourth strain surface 134 has connection tabs TT1 to TT3 which are the strain sensing part SSG A , SS B1 , SS B2 It is mounted so as to be located closer to the base end. Each of the eight strain gauges SSG has connecting tabs TT1 to TT3 that are located inside the groove G when viewed radially.

[0079] Strain sensing part SS of strain gauge SSG attached to the base end side of the third strain surface 133 A , SS B1 , SS B2 Each of the strain-sensitive parts SS 11 , SS 131 , SS 132 The strain sensing part SS of the strain gauge SSG attached to the base end side of the first strain surface 131 A , SS B1 , SS B2 Each of the strain-sensitive parts SS 14 , SS 121 , SS 122 In this case, these strain-sensitive parts can be connected by FPC40 to form the Wheatstone bridge WSB5 shown in Figure 10(a).

[0080] Strain sensing part SS of strain gauge SSG attached to the base end side of the second strain surface 132A , SS B1 , SS B2 Each of the strain-sensitive parts SS 21 , SS 231 , SS 232 The strain-sensing part SS of the strain gauge SSG attached to the base end side of the fourth strain surface 134 A , SS B1 , SS B2 Each of the strain-sensitive parts SS 24 , SS 221 , SS 222 In this case, these strain-sensitive parts can be connected by FPC40 to form the Wheatstone bridge WSB6 shown in Figure 10(b).

[0081] Strain sensing part SS of strain gauge SSG attached to the tip side of the third strain surface 133 A , SS B1 , SS B2 Each of the strain-sensitive parts SS 31 , SS 331 , SS 332 The strain sensing part SS of the strain gauge SSG attached to the tip side of the first strain surface 131 A , SS B1 , SS B2 Each of the strain-sensitive parts SS 34 , SS 321 , SS 322 In this case, these strain-sensitive parts can be connected by FPC40 to form the Wheatstone bridge WSB7 shown in Figure 10(c).

[0082] Strain sensing part SS of strain gauge SSG attached to the tip side of the second strain surface 132 A , SS B1 , SS B2 Each of the strain-sensitive parts SS 41 , SS 431 , SS 432 The strain-sensing part SS of the strain gauge SSG attached to the tip side of the fourth strain surface 134 A , SS B1 , SS B2 Each of the strain-sensitive parts SS 44 , SS 421, SS 422 In this case, these strain-sensitive parts can be connected by FPC40 to form the Wheatstone bridge WSB8 shown in Figure 10(d).

[0083] Thus, by using strain gauge SSGs with half-bridges formed on them, the degradation of temperature characteristics due to the internal wiring length can be reduced. More specifically, since all or most of the wiring constituting the Wheatstone bridges WSB5 to WSB8 can be formed on the strain gauge SSG instead of the FPC40, temperature characteristic changes due to the resistance difference between the wiring pattern of the strain gauge (e.g., copper pattern) and the wiring pattern of the FPC40 are suppressed. Therefore, detection errors caused by temperature changes can be suppressed.

[0084] Furthermore, this modified example uses a strain gauge SSG in which multiple strain-sensing elements are formed on a single base material BBM. Therefore, the strain gauges can be arranged in a smaller area, making it possible to miniaturize the first strain surface 131 to the fourth strain surface 134, and consequently the pedal shaft 100. Also, since the strain-sensing elements are connected on the strain gauge SSG, the number of connection tabs required to form one Wheatstone bridge can be reduced to six. Because the number of connection tabs required to form the Wheatstone bridge is reduced, the size of the connection tabs can be increased, improving the workability of electrical connection with the FPC 40.

[0085] The strain gauge SSG consists of two separate strain gauges, namely the strain sensing part SS. A A strain gauge having a strain sensing element SS B1 , SS B2 It can also be considered as a structure in which strain gauges having the following properties are combined as a single unit. Alternatively, instead of the strain gauge SSG, two separate strain gauges, namely the strain sensing part S, can be used. SA A strain gauge having a strain sensing element SS B1 , SS B2 A strain gauge having the following characteristics may be used.

[0086] In the pedal shaft 100 of the above embodiment, the gauge mounting portion 13 of the hollow shaft 10 is provided with first strain surfaces 131 to fourth strain surfaces 134, but is not limited to this. The number of radially perpendicular flat strain surfaces provided on the gauge mounting portion 13 is arbitrary. If there are multiple strain surfaces, the strain generated in the hollow shaft 10 can be made uniform in the circumferential direction by arranging them at equal intervals in the circumferential direction with identical shapes. OUT A strain gauge may be attached to (for example, a cylindrical surface). In this case, the outer surface 10 OUT This becomes the effective strain-generating surface.

[0087] 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 inside the hollow shaft 10 by the through hole TH, but it is not limited to this. The hollow shaft 10 may have a central hole (a recessed hole extending in the axial direction) in which the through hole TH is closed at the base end and / or the tip end. In this case, the internal space IS is defined by the central hole.

[0088] In this invention, "hollow shaft" means any member that is axial and has a space inside. In this invention, "internal space of a hollow shaft" means any space defined inside the hollow shaft. This space may be in communication with the outside of the hollow shaft, or it may be a sealed space defined inside the hollow shaft.

[0089] In the pedal shaft 100 of the above embodiment, the hollow shaft 10 is substantially cylindrical, but is not limited to this. The shape of the cross-section of the hollow shaft 10, determined by a plane perpendicular to the axial direction, is arbitrary.

[0090] In the pedal shaft 100 of the above embodiment, 16 strain gauges SG are attached to the hollow shaft 10. X While this is the case, it is not limited to this. The number of strain gauges attached to the hollow shaft 10 is arbitrary.

[0091] In the pedal shaft 100 of the above embodiment, four connection holes CH, each being an elongated hole with its longitudinal direction axially, are arranged at equal intervals in the circumferential direction on the hollow shaft 10, but this is not limited to this configuration. The shape, number, and arrangement of the connection holes CH are arbitrary.

[0092] Specifically, for example, FPC40 outer surface 10 OUT Only a single connecting hole CH necessary for extending from the internal space IS may be provided. Furthermore, the cross-sectional shape of each connecting hole CH, with planes perpendicular to the radial direction, may be circular, square, or the like.

[0093] When multiple connection holes CH are provided at equal intervals in the circumferential direction, the cross-sectional shapes of the multiple connection holes CH formed by planes perpendicular to the radial direction do not necessarily have to be identical. In this case as well, by providing the connection holes CH at equal intervals in the circumferential direction, the strain generated in the hollow shaft 10 can be made uniform in the circumferential direction.

[0094] In the pedal shaft 100 of the above embodiment, 16 strain gauges SG X The connection between the components and the circuit board 20 is made by an FPC 40, but this is not the only method. 16 strain gauges SG X The connection between these components and the circuit board 20 can be made by any wiring structure such as lead wires. In addition, the slot SL of the first wiring board 41 of the FPC 40 may extend in any direction perpendicular to the axial direction of the hollow shaft 10.

[0095] In the pedal shaft 100 of the above embodiment, an adhesive with low adhesive strength may be placed in the groove G of the gauge mounting portion 13 of the hollow shaft 10 (i.e., between the base material BM and the bottom surface Gb). An adhesive with low adhesive strength means an adhesive with weaker adhesive strength than the adhesive used in the region having the sensing portion SS, and having an adhesive strength such that when strain occurs in the hollow shaft 10, a strain corresponding to that strain does not occur in the connecting tabs T1 and T2. The embodiment in which the base material BM is bonded to the hollow shaft 10 with an adhesive with low adhesive strength is also included in the embodiment in which the strain gauge is not fixed to the hollow shaft 10. Alternatively, the connecting tabs T1 and T2 of the base material BM may not be bonded to the hollow shaft 10 without providing a groove G, or they may be bonded with an adhesive with low adhesive strength.

[0096] This structure also suppresses the generation of strain in the connecting tabs T1 and T2 in response to the strain in the hollow shaft 10, and consequently suppresses damage to the connection between the connecting tabs T1 and T2 and the FPC 40.

[0097] As long as the features of the present invention are maintained, the present invention is not limited to the embodiments described above, and other forms conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention. [Explanation of Symbols]

[0098] 10 Hollow shaft; 11 Crank threaded section; 12 Bolt head section; 13 Gauge mounting section; 14 Medium diameter section; 15 Small diameter section; 16 Pedal threaded section; 20 Circuit board; 30 Power supply section; 40 FPC; 100 Pedal shaft; PM Pedal meter; SG X SSG strain gauge

Claims

1. A pedal shaft for a pedal-type power meter, a hollow shaft to which the pedal is rotatably mounted; a strain gauge attached to an outer circumferential surface of the hollow shaft; A pedal shaft comprising: a processing circuit disposed in the internal space of the hollow shaft and configured to process an output from the strain gauge.

2. a connection hole that connects the outer circumferential surface and the internal space is provided in the hollow shaft, 2. The pedal shaft according to claim 1, wherein a wiring that connects the strain gauge and the processing circuit is disposed in the connection hole and the internal space.

3. The pedal shaft according to claim 2 , wherein a plurality of the connection holes are provided at equal intervals along the circumferential direction of the hollow shaft.

4. 3. The pedal shaft according to claim 2, wherein the connection hole is an elongated hole whose longitudinal direction is in the axial direction of the hollow shaft.

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

6. The hollow shaft is cylindrical; 2. The pedal shaft according to claim 1, wherein the internal space is defined by a recess or a through hole extending in the axial direction of the hollow shaft.

7. a plurality of flat surfaces are provided on the outer circumferential surface of the hollow shaft, each flat surface extending in a plane perpendicular to a radial direction of the hollow shaft; The flat surfaces are provided at equal intervals along a circumferential direction of the hollow shaft, 2. The pedal shaft according to claim 1, wherein the strain gauge is attached to each of the plurality of flat surfaces.

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

9. the strain gauge includes a strain sensing part, a connection terminal for connecting the strain sensing part to the processing circuit, and a substrate on which the strain sensing part and the connection terminal are formed; A pedal shaft as described in any one of claims 1 to 4 and 6 to 8, wherein the base material 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 connection terminal is formed.

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

11. 2. The pedal shaft according to claim 1, wherein one end of the hollow shaft is provided with a threaded portion for attaching the pedal shaft to a crank, and the other end of the hollow shaft is provided with a threaded portion for attaching the pedal to the pedal shaft.

12. The strain gauge is a plurality of gauges each having a strain sensing part, 2. The pedal shaft according to claim 1, wherein each of the plurality of strain gauges has a strain sensing direction of a strain sensing portion that coincides with the axial direction of the hollow shaft.

13. The strain gauge is a plurality of gauges each having a strain sensing part, 2. The pedal shaft according to claim 1, wherein the plurality of gauges include a first gauge group, in which the strain sensing direction of each strain sensing portion coincides with the axial direction of the hollow shaft, and a second gauge group, in which the strain sensing direction of each strain sensing portion coincides with the circumferential direction of the hollow shaft.

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