PORTABLE POWER METER FOR CALCULATING POWER APPLIED TO A PEDAL AND CRANK ARM BASED DRIVE MECHANISM AND A METHOD OF CALCULATING THE POWER

• US 20070245835A1
• Filed: 03/17/2006
• Published: 10/25/2007
• Est. Priority Date: 03/17/2006
• Status: Active Grant

• Current Assignee: Gunter Hauschildt
• Original Assignee: Gunter Hauschildt
• Inventors: Hauschildt, Gunter
• Granted Patent: US 7,599,806 B2
• Time in Patent Office: Days
• US Class Current: 73/862.391
• CPC Class Codes: A43B 3/44 with sensors, e.g. for detecting contact or position
• CPC Class Codes: A43B 5/14 Shoes for cyclists
• CPC Class Codes: A61B 5/221 Ergometry, e.g. by using bicycle type apparatus
• CPC Class Codes: A61B 5/224 Measuring muscular strength
• CPC Class Codes: A61B 5/6807 Footwear
• CPC Class Codes: A61B 5/6829 Foot or ankle
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A63B 22/0605 performing a circular movement, e.g. ergometers
• CPC Class Codes: A63B 2220/51 Force
• CPC Class Codes: A63B 2220/833 Sensors arranged on the exercise apparatus or sports implement
• CPC Class Codes: A63B 2220/836 Sensors arranged on the body of the user
• CPC Class Codes: A63B 69/16 for cycling , i.e. arrangements on or for real bicycles
• CPC Class Codes: A63B 71/0619 Displays, user interfaces and indicating devices, specially adapted for sport equipment, e.g. display mounted on treadmills
• CPC Class Codes: G01L 5/225 to foot actuated controls, e.g. brake pedals
• CPC Class Codes: G06F 3/011 Arrangements for interaction with the human body, e.g. for user immersion in virtual reality blind teaching G09B21/00

Abstract

A power meter for power a pedal and crank arm based drive mechanism measures and displays athletic performance information as a measure of a physical quantity, power, using a flexible force sensor inserted into a cycling shoe. Mathematical cycling models and data from the flexible force sensor are used to calculate the power.

Claims

1. A power meter for calculating power applied to a pedal and crank arm based drive mechanism, comprising:

a flexible force sensor inside a shoe worn by a person applying force to a pedal of the pedal and crank arm based drive mechanism, the flexible force sensor being placed within the shoe so that at least a representative proportion of a total force applied by the person to the pedal and crank arm based drive mechanism is sensed; and

a processor for receiving force signals from the force sensor and for using the force signals in mathematical models to calculate the power.

2. The power meter as claimed in claim 1 further comprising an analog interface connected to the flexible force sensor, the analog interface generating an output voltage that has a predetermined relationship to the force sensed by the flexible force sensor.

3. The power meter as claimed in claim 2 further comprising a variable reference circuit for adjusting a range of the output voltage in dependence on a determination by the processor of whether the cyclist is seated or standing.

4. The power meter as claimed in claim 1 further comprising an analog-to-digital converter for digitally sampling the output voltage received from the analog interface and outputting the digital samples to the processor.

5. The power meter as claimed in claim 1 further comprising a user interface for accepting user input and for displaying information about the calculated power applied to the pedal and crank arm based drive mechanism.

6. The power meter as claimed in claim 5 comprising a first electronics unit connected to the flexible force sensor, and a second electronics unit comprising a processor for controlling a display for displaying the information about the calculated power, the first and second electronics units being interconnected by a data interface that does not inhibit the person from applying force to the pedal and crank arm based drive mechanism.

7. The power meter as claimed in claim 5 wherein the first and second electronics units respectively include calibration ports for interconnecting the first and second electronics units to permit calibration variables to be entered using the user interface.

8. The power meter as claimed in claim 6 wherein the first electronics unit comprises a radio frequency transmitter and an antenna, and the second electronics unit comprises a radio frequency receiver and an antenna, and the data interface comprises a radio frequency data channel.

9. A method of calculating power applied to a pedal and crank arm based drive mechanism, comprising:

receiving force signals from a flexible force sensor inside a shoe worn by a person applying force to the pedal and crank arm based drive mechanism, the flexible force sensor being placed within the shoe so that at least a representative proportion of a total force applied by the person is sensed; and

using the force signals in mathematical models to calculate the power.

10. The method as claimed in claim 9 further comprising:

calculating an integral of a square of a derivative of a frequency of rotation of the crank arm based drive mechanism versus time, and comparing a result to a threshold to determine whether the crank arm based drive mechanism is being rotated or is at rest; and

if the crank arm based drive mechanism is at rest, setting cadence to zero and calculating average force as an average of all force samples.

11. The method as claimed in claim 10 wherein if it is determined that the crank arm based drive mechanism is not at rest, performing a rest-of-foot correction by adding to the force signals an assumed proportion of applied force contributed by the rest of the foot of the person.

12. The method as claimed in claim 11 further comprising:

performing a Fast Fourier Transform (FFT) to convert the force signals to a frequency domain;

down-sampling the converted signals samples by a predetermined down-sampling factor;

windowing the samples using a trapezoidal function; and

performing a first approximation of cadence to determine a fundamental frequency of the force signals.

13. The method as claimed in claim 12 further comprising:

determining actual crank arm rotation periods by searching for local minima in a range predicted by the FFT, and if local minima are found, assuming the results of the FFT are valid and that a valid crank arm rotation was found between the local minima;

locating a peak between the minima; and

determining cadence using the minima.

14. The method as claimed in claim 13 further comprising:

comparing a crank arm angle where the peak and the minima were located; and

if a difference is greater than a predetermined threshold, then assuming the person is seated;

else assuming the person is standing.

15. The method as claimed in claim 14 wherein:

if it is assumed that the person is seated, selecting one of a slow cadence model and a normal cadence model to be used in an effective force calculation;

else

selecting a standing cycling model to be used in the effective force calculation.

16. The method as claimed in claim 15 wherein:

the effective force calculation comprises calculating F_EFFECTIVE and F_NEGATIVE from F_PEDAL, using;

F_EFFECTIVE=F_CYCLIST*cos Θ

 

 

Eq.4

where;

F_CYCLIST=magnitude of the force applied by the person; and

, Θ

=the angle of the applied force with respect to the crank arm; and

F_CYCLIST=F_PEDAL/cos φ

Eq.5

where;

F_PEDAL is the force measured by the flexible force sensor; and

, φ

=the angle of applied force with respect to the pedal;

wherein φ and

Θ

are derived from one of a table for the slow cadence model, a table for the normal cadence model and a table for the standing cycling model.

17. The method as claimed in claim 16 further comprising:

performing an average force calculation using;

F_AVERAGE=2·

{[Σ

F_EFFECTIVE−

Σ

F_NEGATIVE]/n}  

 

Eq. 7

where;

n=number of samples in the crank arm rotation period; and

, F_AVERAGE=an average force that propelled the pedal an crank arm mechanism during a selected period, wherein the factor of 2 is required only if a single force sensor is used.

18. The method as claimed in claim 17 further comprising:

converting F_AVERAGE to known units by multiplying a value of F_AVERAGE by M_BINARY2_NETWONS, which is determined using;

M_BINARY2_NETWONS=(Known_Force_NEWTONS)/A_TO_—

D_Output_BINARY  

 

Eq. 10

where;

Known_Force_NEWTONS is a predetermined force applied to the force sensor, and A_TO_D_Output_BINARY is a binary output of the analog-to-digital converter when the predetermined force is applied.

19. The method as claimed in claim 17 further comprising:

retrieving a length ‘

r’

of the crank arm from memory and calculating T_AVERAGE using;

T_AVERAGE=F_AVERAGE˜

r  

 

Eq. 8

where;

r=the length of the crank arm from crank arm shaft to pedal axis spindle; and

converting cadence in RPM to cadence in RADs per second by multiplying cadence in revolutions per minute by 2π

/360.

20. The method as claimed in claim 18 further comprising:

calculating P_AVERAGE for each crank arm rotation using;

P_AVERAGE=T_AVERAGE·

{acute over (ω

)} Eq. 9.

21. The method as claimed in claim 19 further comprising:

using hysteresis to smooth data associated with the power applied to the pedal and crank arm based drive mechanism to decrease display jitter, and displaying the data for observation by the person.