System and method for three dimensional calibration of force plates

• US 9,459,173 B2
• Filed: 09/27/2012
• Issued: 10/04/2016
• Est. Priority Date: 10/14/2011
• Status: Active Grant

• Current Assignee: Advanced Mechanical Technology Incorporated
• Original Assignee: Advanced Mechanical Technologies, Inc.
• Inventors: Ruland, Fred, Drueding, Albert, Glass, Gary, Taylor, Jonathan, White, Bruce F., Carignan, Forest J.
• Primary Examiner(s): Toatley, Jr., Gregory J
• Assistant Examiner(s): QUIGLEY, KYLE ROBERT
• Application Number:
  US13/628,433
• Publication Number:
  US 20130298633A1
• Time in Patent Office: 1,468 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 2562/0247 Pressure sensors
• CPC Class Codes: A61B 5/1036 Measuring load distribution, e.g. podologic studies
• CPC Class Codes: A61B 5/1038 Measuring plantar pressure during gait
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: A61B 5/112 Gait analysis
• CPC Class Codes: A61B 5/4023 Evaluating sense of balance
• CPC Class Codes: A61B 5/6887 mounted on external non-worn devices, e.g. non-medical devices
• CPC Class Codes: A61B 5/7235 Details of waveform analysis A61B5/349 takes precedence
• CPC Class Codes: G01G 23/01 Testing or calibrating of weighing apparatus
• CPC Class Codes: G01L 25/00 Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency

Abstract

A method for calibrating a force platform includes, providing a force platform and applying an n×m grid on a top surface of the force platform via a computing device. Next, applying p known loads on each of the n×m grid points of the top surface along a Z-axis being perpendicular to the X and Y axes and along the X and Y axes. Next, taking multipoint measurements at each grid point and for each applied known load along the X, Y and Z axes and generating six measured output signals, exact position coordinates and applied known load magnitude for each grid point. Next, assembling an array of n×m×p of six equations with six unknown for each grid point and applied known load and then solving the assembled equations and deriving a position and load specific calibration matrix for each grid point.

Claims

1. A method for calibrating a force platform comprising:

providing a force platform and applying a grid of points on a top surface of the force platform via a computing device, wherein said top surface extends along an X-axis, and along a Y-axis of said force platform;

applying p known loads on each of the grid points of the top surface along a Z-axis being perpendicular to said X and Y axes and along said X and Y axes;

taking multipoint measurements at each grid point and for each applied known load along said X, Y and Z axes;

generating six measured output signals, exact position coordinates and applied known load magnitude for each grid point;

assembling an array of six equations with six unknowns for each grid point and applied known load;

solving the assembled equations and deriving a position and load specific calibration matrix for each grid point and applied known load; and

entering the derived position and load specific calibration matrices for all grid points in a calibration table and storing the calibration table in a non-volatile memory.

2. The method of claim 1 wherein said p known loads are applied via a 3-D Cartesian load apparatus.

3. The method of claim 1 wherein said applied p known loads comprise magnitudes in the range of zero to Full Scale Capacity (FSC) at increments of 10%.

4. The method of claim 1, wherein said grid of points comprises n and m points extending along said X and said Y axis, respectively, and wherein said n and m points comprise values in the range of 2 to 20.

5. The method of claim 1, wherein said six measured output signals comprise three force components Fx, Fy, Fz and three moment components Mx, My, Mz.

6. The method of claim 1, further comprising providing an estimate algorithm and storing a global platform calibration matrix in said non-volatile memory, wherein the estimate algorithm is configured to generate first estimates of magnitude and position of an unknown applied load on the force platform by applying the global platform calibration matrix onto measured platform outputs for the unknown applied load.

7. The method of claim 6, wherein the first estimates of magnitude and position of the unknown applied load are used to determine a position and load specific calibration matrix in the calibration table.

8. The method of claim 7, further comprising generating accurate measures of the magnitude and position of the applied unknown load by applying the determined position and load specific calibration matrix onto the measured platform outputs for the unknown load.

9. The method of claim 1, further comprising verifying said derived position and load specific calibration matrices by applying NIST traceable dead weights onto the top surface grid points.

10. The method of claim 1, further comprising measuring secondary characteristics at eight grid points using a calibration protocol.

11. A system for calibrating a force platform comprising:

a force platform;

a computing device comprising a processor and a memory storing instructions that when executed cause to apply a grid of points on a top surface of the force platform, wherein said top surface extends along an X-axis, and along a Y-axis of said force platform;

a 3-D Cartesian load apparatus comprising an actuator and a memory storing instructions that when executed cause to apply p known loads on each of the grid points of the top surface along a Z-axis being perpendicular to said X and Y axes and along said X and Y axes;

a sensor configured to take multipoint measurements at each grid point and for each applied known load along said X,Y and Z axes and to generate six measured output signals, exact position coordinates and applied known load magnitude for each grid point;

an algorithm for solving an assembled array of six equations with six unknowns for each grid point and applied known load and for deriving a position and load specific calibration matrix for each grid point and applied known load; and

a non-volatile memory configured to store a calibration table comprising the derived position and load specific calibration matrices for all grid points.

12. The system of claim 11 wherein said applied p known loads comprise magnitudes in the range of zero to Full Scale Capacity (FSC) at increments of 10%.

13. The system of claim 11, wherein said grid of points comprises n and m points extending along said X and said Y axis, respectively, and wherein said n and in points comprise values in the range of 2 to 20.

14. The system of claim 11, wherein said six measured output signals comprise three force components Fx, Fy, Fz and three moment components Mx, My, Mz.

15. The system of claim 11, further comprising an estimate algorithm and a global platform calibration matrix, wherein the estimate algorithm is configured to generate first estimates of magnitude and position of an unknown applied load on the force platform by applying the global platform calibration matrix onto measured platform outputs for the unknown applied load.

16. The system of claim 15, wherein the first estimates of magnitude and position of the unknown applied load are used to determine a position and load specific calibration matrix in the calibration table.

17. The system of claim 16, further comprising a correction algorithm generating accurate measures of the magnitude and position of the applied unknown load by applying the determined position and load specific calibration matrix onto the measured platform outputs for the unknown load.