Apparatus for measuring and determining the force, the torque and the power on a crank, in particular the pedal crank of a bicycle

Abstract

The invention relates to an apparatus for measuring and determining the force, the torque and the power on a crank, in particular the pedal crank of a bicycle, comprising an evaluation device, in particular a bicycle computer, and at least one pedal, wherein the force and angular speed variables are converted into electrical signals and supplied to the evaluation device, the pedal comprises a pedal body, a deformation element, a pedal shaft and an angle transmitter, and wherein the force variable is determined by measuring the deformation of the deformation element using strain gauges, preferably by measuring the individual normal strains of the strain gauges, and wherein four pairs of strain gauges assigned to each other are arranged at different angles, preferably +/45, with respect to the pedal shaft.

Claims

1. An apparatus for measuring and determining the force, the torque and the power on the pedal shaft of a bicycle, wherein the pedal shaft extends along a pedal shaft axis, comprising: at least one pedal having a pedal body; a deformation body contained within the pedal body, wherein the deformation body is stationarily connected to the pedal body at a first location and is rotatably supported by the pedal shaft at a second location spaced from the first location, wherein the deformation body includes a cantilevered section that extends between the first and second locations and wherein the deformation body connects the deformation body to the pedal body at the second location, wherein pedaling forces applied to the pedal body by a user are transferred from the pedal body through the cantilevered section of the deformation body to the pedal shaft; an angle sensor associated with the deformation body, wherein the angle sensor measures an angle of orientation of the deformation body relative to the pedal axis; and a strain sensing arrangement on the cantilevered section of the deformation body for measuring strain experienced by the cantilevered section of the deformation body due to forces applied to the pedal.

2. Apparatus according to claim 1, further comprising a bicycle computer and a signal transmission arrangement for transmitting signals to the bicycle computer from the strain sensing arrangement.

3. Apparatus according to claim 2, wherein the pedal and the bicycle computer each has an inclination angle sensor.

4. Apparatus according to claim 1, wherein a force variable from the strain sensing arrangement is converted into electrical signals by means of Resistor-to-Digital-Converters (RDC).

5. Apparatus according to claim 2, wherein pedal force characteristics are determined by the bicycle computer by means of the angle of a pedal crank to which the pedal shaft is mounted.

6. Apparatus according to claim 2, wherein the signal transmission, arrangement comprises a wireless signal transmission arrangement by which signals are transmitted to the bicycle computer.

7. Apparatus according to claim 1, wherein torsional moments, such as the loss moments due to friction, are determined on the pedal shaft via the pedal.

8. Apparatus according to the claim 2, wherein the signal transmission arrangement transmits signals relating to force components from the pedal to the bicycle computer, wherein riding styles such as out of saddle pedaling, sprinting, or downhill riding can be identified and be compared against riding styles stored in the bicycle computer.

9. Apparatus according to claim 2, wherein the bicycle computer determines the inclination of a road surface for recalibrating data corresponding to signals transmitted by the signal transmission arrangement.

10. Apparatus according to claim 1, wherein the pedal has a mechanically adjustable zero point position for the angle.

11. Apparatus according to claim 10, further comprising an adjusting tool for adjusting the zero point position for the angle, and wherein the adjusting tool is also a transport locking device for the pedal.

12. Apparatus according to claim 2, wherein data corresponding to signals transmitted by the signal transmission arrangement are retrieved from a left and a right pedal of the bicycle.

13. Apparatus according to claim 12, wherein the bicycle computer evaluates, compares and displays power separately from the left and the right pedals.

14. Apparatus according to claim 1, wherein the strain sensing arrangement on the deformation body of the pedal comprises two pairs of strain gages to determine vertical and horizontal components of a force applied to the pedal.

15. Apparatus according to claim 1, further comprising a pedal crank to which the pedal shaft is mounted, and wherein an angle of the pedal crank and an angle speed of the pedal crank are determined from a pedal-periodic and terrestrial signal.

16. Apparatus according to claim 1, wherein a determination of forces on the pedal in three spatial directions and a loss moment due to friction are performed via linking of strains on the deformation body.

17. Apparatus according to claim 16 wherein a measurement of normal strains on the deformation body is performed by means of pairs of strain gages applied on the deformation body less than 45 in relation to the pedal shaft axis in two directions placed perpendicular on top of each other.

18. Apparatus according to claim 1, further comprising a pedal crank to which the pedal shaft is mounted, and wherein a relative angle between the crank and the pedal body is determined from a transit time signal.

19. Apparatus according to claim 1, further comprising a pedal crank to which the pedal shaft is mounted, and wherein a radial and a tangential component of a force on the crank and a resulting force with an effective angle is determined by means of pedal force characteristics.

20. Apparatus according to claim 1, further comprising a pedal crank to which the pedal shaft is mounted, and wherein the pedal links the accuracy of a relative angle between the crank and the pedal body with a number of trigger points.

21. Apparatus according to claim 1, wherein an axial force and a loss moment due to friction are determined with two pairs of strain gages on the deformation body.

Description

(1) The drawing shows:

(2) FIG. 1 is a system diagram with a bicycle computer (FC) as evaluation unit 17 and a left and a right pedal, where a resistor-to-digital converter (RDC) is arranged after the strain gauge

(3) FIG. 2 is a side elevation of the crank 20 with the pedal 16, representing the angle positions in dependence of the ground and the road surface

(4) FIG. 3 is a coordinate transformation regarding the configuration of the strain gages

(5) FIG. 4 is a side elevation of the crank 20 with the pedal 16 by representing the effective crank forces

(6) FIG. 5 is a cross-section through the pedal 16, consisting of a pedal body 11, a deformation body 9, a trigger element 14, a pedal shaft 10, two bearings 13, and an angle sensor 12

(7) FIG. 6 is a cross-section (front elevation) through the pedal body 11 by representing the configuration of the strain gages on the deformation body 9

(8) FIG. 7 is a cross-section (side elevation) through the pedal body 11 by representing the configuration of the strain gages on the deformation body 9

(9) FIG. 8 are the signs of the shear distortion on the facing side as well as on the side facing away, as a result of loads F.sub.z and M.sub.x in the direction of the positive coordinates

(10) FIG. 9 is the single V and the double V configuration of the strain gages

(11) In the following, an embodiment of the invention is described in detail by means of the drawings:

(12) FIG. 5 shows a pedal 16 comprising a pedal body 11, a deformation body 9, a trigger element 14, a pedal shaft 10, two bearings 13, a locking screw 19, and an angle sensor 12. The left and the right pedal 16 are constructed identically. For this reason, only one pedal is described in terms of measuring technology and structural design. The deformation body 9 is rotatably pivoted on two positions on the pedal shaft 10. The strain gages 1-8 are applied on the cantilevered sections which connects the deformation body 9 with the pedal body 11. The flux of force from the pedal body 11 via the joint to the deformation body 9 up to the thread of the pedal shaft 10, i.e. all effective forces and moments acting on the pedal body 11, occurs non-branched and completely via the strain gages.

(13) Four pairs of assigned strain gages 1-8 at an orientation angle of 45 to the pedal shaft 10 are used, of which respectively two pairs each are reciprocally opposed on the periphery of the deformation body 9. Two reciprocally opposed pairs serve for the determination of the shear force component perpendicular to the plane which connects the pairs, and because the strain gauge pairs are applied reciprocally in two vertical planes, one of which is the tread plate plane, the vertical and horizontal components on the tread plate of the pedal body 11 can be determined in this manner. In this connection, the selection of a position angle of +45 in relation to the pedal shaft produces the biggest strain signals, which is desirable for the purpose of maximum resolution. This configuration has the known advantage that bending moments acting upon the deformation body 9, irrespective of their origin, by forming the average value of the resulting tensile and compressive stress within the strain gages resulting therefrom, have the tendency to let the bending moments disappear.

(14) Particularly the x-shaped configuration of the reciprocally opposed strain gauge pairs 1-4, see FIG. 6, offers the possibility to also be able to separate the axial force and the loss moment on the pedal shaft 10, with suitable algebraic linkage beyond the measured strains across the said shear force components (vertically and horizontally).

(15) For the straight determination of shear force, also one-sided applied single v or also double v configurations are suitable, for example. This is shown and represented in FIG. 9.

(16) The back calculation of the distortions from .sub.x,.sub.y,.sub.xy from strains .sub.,.sub. which were measured below 45 to the pedal shaft 10, results from the coordinate transformation of the reciprocally rotated coordinate systems (see FIG. 2):
D.sup.=T.Math.D.sup.xy.Math.T.sup.T in which is

(17) $D^{\mathrm{xy}}=\left[\begin{array}{cc}{\mathrm{.Math.}}_x& 1/2{}_{\mathrm{xy}}\\ 1/2{}_{\mathrm{xy}}& {\mathrm{.Math.}}_y\end{array}\right]$$D^n=\left[\begin{array}{cc}{\mathrm{.Math.}}_{}& 1/2{}_n\\ 1/2{}_n& {\mathrm{.Math.}}_n\end{array}\right]$$T=\left[\begin{array}{cc}\cos & \sin \\ -\sin & \cos \end{array}\right]$
D.sup.xy: is a distortion tensor in the x, y coordinate system
D.sup.: is a distortion tensor in the , coordinate system
T: is the rotation matrix (transformation matrix)
T.sup.T: is the transposed rotation matrix

(18) The strain components of interest of D.sup. when written out, are for =45:
.sub.=(.sub.x+.sub.y)+.sub.xy and .sub.=(.sub.x+.sub.y).sub.xy.

(19) These correlations must be addressed for each strain gauge 1-8 applied, noting any signs of distortions, i.e. which direction the distortions .sub.x,.sub.y,.sub.xy assumes by means of the sought-for loads (shear force, axial force, loss moment). The shear distortion y.sub.xy, as a result of shear force and torsional moment, is composed of Y.sub.xy.sup.F and Y.sub.xy.sup.M.

(20) The normal strain .sub.x is made up of the axial force and the bending moment percentages .sub.x.sup.Fx and .sub.x.sup.Fy together, the second of which disappears as a result of averaging within the strain gages 1-8. In addition, for a purely axial load in the X direction, .sub.x+.sub.y=.sub.x.Math..sub.x is applicable.

(21) The transfer to the coordinate system of the strain gages 1-8 from FIG. 6 results by taking into account the signs of the distortions as a result of F.sub.z and M.sub.x from FIG. 8 and F.sub.x from FIG. 6 for the strain gauge 1, for example:

(22) ${\mathrm{.Math.}}_1={\mathrm{.Math.}}_{}^{}=\frac{1-v}{2}{\mathrm{.Math.}}_x^{\mathrm{Fx}}+1/2\left({}_{\mathrm{xz}}^{\mathrm{Fz}}+{}_{\mathrm{xz}}^{\mathrm{Mx}}\right)$
.sub.x.sup.Fx: =>strain as a result of axial force F.sub.x (strain from bending moment M.sub.y averages to zero)
.sub.xz.sup.Fz: =>shear as a result of shear force F.sub.z
.sub.xz.sup.Mx: =>shear as a result of torsional moment M.sub.x, (loss moment)
: =>Poisson ratio
If this is performed for the strain gages 1-4, then the following information can be gained (analogously for the strain gages 5-8):
.sub.1.sub.2+.sub.3.sub.4=2.sub.xz.sup.Fz=>shear force F.sub.z
.sub.1.sub.2+.sub.4.sub.3=2.sub.xz.sup.Mx=>loss moment M.sub.x
.sub.1+.sub.2+.sub.3+.sub.4=2(1).sub.x.sup.Fx=>axial force F.sub.x
.sub.5.sub.6+.sub.7.sub.8=2.sub.xy.sup.Fy=>shear force F.sub.y

(23) These four equations are the actual characteristics of the invention for the evaluation of the strain gages, because they show that the simple algebraic relationship of the individual normal strains provides all four sought-for variables. While a Wheatstone circuit according to the prior art with the strain gages 1-4 can determine only the first variable (F.sub.z), the first three variables from the strain gages 1-4 can be determined with only one RDC circuit. This is considered to be a particular advantage.

(24) The calculation of the force effects from the distortions is done using the law of elasticity:
F.sub.x=E.Math.A.Math.s.sub.x F.sub.z=G.Math.A.sub.S.Math..sub.xz.sup.Fz F.sub.y=G.Math.A.sub.S.Math..sub.xy.sup.Fy M.sub.x=G.Math.W.sub.x.Math..sub.xz.sup.Mx

(25) Here, A, A.sub.S and W.sub.x are the stress-defining cross-sectional variables.

(26) After the strain gages 1-8 have been applied, the deformation body 9 can be uniquely positioned mechanically in the pedal body 11, by an indexing pin 15, for example, which is inserted through a sufficiently precise bore in the pedal body 11 and in the deformation body 9. Therefore it is ensured that the x,y-plane mounted from the strain gages 1-4 is positioned exactly parallel in relation to the tread plate plane (see FIGS. 6 and 7), as a consequence of which no further force calibrations will be required.

(27) In an alternative option for a Wheatstone circuit, the arrangement produces the biggest signals below 45, which is important for the use of so-called Resistor-to-Digital-Converters (RDC), because no stress signals must be evaluated.

(28) The trigger element 14 which is needed for detecting the relative angle between the pedal body 10 and the crank 20 is designed as a sleeve in FIG. 5, which supports two trigger points in the form of radial bores provided at 180 spacing on a raised annulus. Therefore two impulses per revolution are given. The zero trigger of the trigger element 14 will here be designed particularly by a bore of a varying diameter. By a relative rotation of the pedal shaft 10, the trigger points sweep past the relative angle sensor 12 and will be detected as a result; for that purpose, the relative angle sensor 12 is fixed at a suitable distance to the trigger annulus in the deformation body 9.

(29) To establish the zero point of the trigger element 14 in relation to the crank 20, the trigger element 14 must be mechanically aligned to any optional position of the crank 20, such as when this points perpendicular to the top. The selected position is advantageously programmed permanently in the bicycle computer 17. As a result, after arranging the crank 20 in this position and having adjusted the zero trigger relative to it, the bicycle computer 17 requires no further input.

(30) The mechanical adjustment to crank zero is performed in a first step, in that the indexing pin 15 is inserted through the pedal body 11 and the deformation body 9 until touching the trigger annulus, and in that the pedal shaft 10 together with the trigger element 14 is subsequently turned into the push-through position. The indexing pin 15 can now be completely inserted as shown in FIG. 5 and must be fixed. Because of the different bore diameters, any mix-up with the bore of the zero point trigger 21 is therefore impossible. The second step comprises loosening the trigger element 14 by means of the indicated positioning screw 19. If the crank 20 is in its defined zero position and the pedal 16 is screwed-in, the tread plate plane of the pedal body 11 can be turned into a horizontal position, for example, which means that the loosened trigger element 14 co-rotates. The positioning screw 19 must subsequently be re-tightened, the indexing pin must be removed, which means that the adjustment is finalized. This adjustment will be retained until the arrangement needs to be taken apart, i.e. even if the pedal is screwed-off and screwed-on again temporarily, the adjustment will not change.

(31) The swept relative angle (t) between the crank 20 and the pedal body 11, measured from the zero point trigger 21 can be calculated from the angular speed .sub.i-1=.sub.i-1/t.sub.i-1 of the preceding trigger segment and the transit time t=tt.sub.i-1 since the last trigger point, on the assumption that the angular speed and the current angle segment has not changed compared to the preceding one, to:

(32) $\left(t\right)={\left(t-t_{t-1}\right)}^0.Math.{}_{i-1}+{}_{i-1}.Math.\left(t-t_{i-1}\right){\mathrm{where}\left(t-t_{i-1}\right)}^0=\{\begin{array}{cc}0,& t{t}_{i-1}\\ {\left(t-t_{i-1}\right)}^0=1,& t>t_{i-1}\end{array}$
.sub.i-1 180 for the trigger element 14 with two equidistant trigger points
t.sub.i-1 transit time between the preceding triggers

(33) With each pass of the zero point trigger 21, the time is recorded anew. For additional information, the relative angle sensor 12 can provide the cadence n.sub.i-1 from the angular speed .sub.i-1=2.Math..Math.n.sub.i-1.

(34) The relative angle (t) determined between the pedal body 11 and the crank 20 alone is not sufficient to be able to calculate the characteristics of forces, moment, or the power via the crank angle. In order to be able of not having to use any external crank angle sensors because of the additional components required, the crank angle information can be determined by calculation from the relative angle (t), the pedal inclination , and the incline of the road surface .sub.FC. For this purpose, the inclination angle sensor 18 is integrated in the pedal 16 in the present embodiment, which measures the pedal inclination in relation to the ground surface. But because the signal also contains the incline of the road surface .sub.FC, an inclination angle sensor of the same type must be attached stationary (e.g. integrated in the bicycle computer 17), to measure the current incline separately and from which it is corrected by means of the microcontrollers, e.g. in the bicycle computer.

(35) The following circumstances refer to FIG. 2 (positive angles, turning clockwise):

(36) The following is applicable for the pedal body 11: =tilting angle of the pedal body 11 measured relative to the road surface and =
results in the following: =.sub.FC; =.sub.PR=.sub.FC und =(t)

(37) Because of the positive direction of rotation for , the following applies:

(38) =.sub.FC<0 with a positive incline of the road surface and

(39) <0 the pedal body rotates in reverse in relation to a forward motion of the crank (>0)

(40) In this context, is the crank angle, .sub.FC is the incline of the road surface measured at the bicycle computer 17, is the pedal inclination measured at the pedal 16. = is the relative angle measured in pedal 16. In order to be able to use .sub.FC as a correction quantity on the bicycle computer 17, an offset determination of the installation position of the bicycle computer 17 is required.

(41) The drive torque M.sub.A which is relevant for propulsion is derived from the equilibrium on the crank 20 (see FIG. 4) in relation to:
M.sub.A=F.sub.T.Math.1M.sub.x; M.sub.x: loss moment on the pedal bearing
and equilibrium of forces on pedal 16 (see FIG. 4) produces:
F.sub.T=F.sub.z.Math.sin +F.sub.y.Math.cos ; F.sub.T: tangential force on the crank 20
F.sub.R=F.sub.z.Math.cos F.sub.y.Math.sin ; F.sub.R: radial force on the crank 20

(42) The relative angle between crank 20 and pedal 16 is measured directly. As a result of the angular relationships described above, the force characteristics about the crank angle are also available.

(43) If required, the resultant F.sub.TR and its effective angles .sub.TR are derived from (FIG. 4).
F.sub.TR={square root over (F.sub.T.sup.2+F.sub.R.sup.2)} and tan .sub.TR=F.sub.T/F.sub.R

(44) FIG. 1 shows a system diagram of the embodiment of the signal recovery and signal processing for both pedals. Here, the left and the right are constructed identically. On the bicycle computer 17, only one measuring pedal can be operated, as a low-cost variant, for example. The strain measurement is illustrated by means of two RDCs, the digitalized signals of which are combined with the signals of the relative angle sensor 12 and the inclination angle sensor 18 (NW) in a separate microcontroller (MC), are pre-processed and transmitted to the bicycle computer (FC) via the RF module (RF) using a highly energy-saving, digital transmission protocol.

(45) The strain gages 1-8 are not externally connected into the bridge circuit, but can be individually measured by the RDC, which makes it possible, as shown by the four equations above, that all shear forces of interest, the axial force, and the loss moment on the pedal shaft 10, can be determined by simple algebraic linkage of the strain information in the microcontroller (MC). The measurement of the shear forces of one plane (e.g. vertical) is performed by one of each set of strain gages (comprising two strain gage pairs), e.g. set 1-4; the strain gage set 5-8 measures the horizontal component. For determining the axial force and moment information, only one of the two strain gage sets needs to be associated. An embodiment is also possible in which, by leaving out the axial force and loss moment information, a single RDC is sufficient.

(46) The bicycle computer 17 then takes over the correction of the road surface ascent through its inherent inclination angle (NW), to make it possible to later represent crank angle related characteristics correctly, performs all contemplated calculations, stores the determined data and displays selected data, such as the current overall power, power and/or force balances left/right, etc. If any further evaluations are envisaged on the PC, the RF transmits the data to a PC interface.