EMBEDDED ARM STRAIN SENSORS

• US 20110175745A1
• Filed: 01/14/2011
• Published: 07/21/2011
• Est. Priority Date: 01/20/2010
• Status: Abandoned Application

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Atwell, Paul C., Stokes, Burnham
• Application Number:
  US13/006,461
• Publication Number:
  US 20110175745A1
• Time in Patent Office: Days
• US Class Current: 340/665
• CPC Class Codes: G01B 11/007 feeler heads therefor
• CPC Class Codes: G01B 21/047 Accessories, e.g. for positioning, for tool-setting, for measuring probes
• CPC Class Codes: G01B 5/012 Contact-making feeler heads therefor
• CPC Class Codes: G05B 19/401 characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes G05B19/19 takes precedence
• CPC Class Codes: G05B 19/406 characterised by monitoring or safety G05B19/19 takes precedence
• CPC Class Codes: G05B 2219/24067 Processor stores variables, events and date in eeprom, for external monitor
• CPC Class Codes: G05B 2219/37193 Multicoordinate measuring system, machine, cmm
• CPC Class Codes: G05B 2219/40233 Portable robot
• CPC Class Codes: G05B 2219/40596 Encoder in each joint
• CPC Class Codes: G05B 2219/45061 Measuring robot

Abstract

A portable articulated arm coordinate measurement machine (AACMM) can include a manually positionable articulated arm portion, a measurement device attached to the first end, a structural component of the AACMM, wherein the structural component has an axial direction, at least three strain gage sensors, each having a sensitive axis, coupled to the structural component, wherein the sensitive axis of each strain gage sensor is oriented approximately parallel to the axial direction, each strain gage sensor is approximately intersected by a transverse plane perpendicular to the axial direction, each strain gage sensor produces an analog strain gage signal, and the strain gage sensors are disposed to provide data sufficient to determine a bending strain at any point residing on both the structural component and the transverse plane and an electronic circuit that receives the position signal and provides data corresponding to a position of the measurement device.

Claims

1. A portable articulated arm coordinate measurement machine (AACMM) for measuring coordinates of an object in space, comprising:

a manually positionable articulated arm portion having opposed first and second ends, the arm portion including a plurality of connected arm segments, the plurality of connected arm segments including an arm segment adjacent the first end, each arm segment including at least one position transducer that produces a position signal;

a measurement device attached to the first end;

a structural component of the AACMM, wherein the structural component has an axial direction;

at least three strain gage sensors, each having a sensitive axis, coupled to the structural component, wherein the sensitive axis of each strain gage sensor is oriented approximately parallel to the axial direction, each strain gage sensor is approximately intersected by a transverse plane perpendicular to the axial direction, each strain gage sensor produces an analog strain gage signal, and the strain gage sensors are disposed to provide data sufficient to determine a bending strain at any point residing on both the structural component and the transverse plane; and

an electronic circuit that receives the position signal and provides data corresponding to a position of the measurement device.

2. The AACMM of claim 1 further comprising an analog-to-digital converter circuit that converts some combination of the analog strain gage signals into a plurality of digital strain gage signals, wherein the electronic circuit receives the plurality of digital strain gage signals.

3. The AACMM of claim 2 wherein the electronic circuit calculates the magnitude and direction of maximum bending of the structural component.

4. The AACMM of claim 3 wherein the electronic circuit uses the digital strain gage signals from the at least three strain gage sensors to modify the provided data corresponding to the position of the measurement device.

5. The AACMM of claim 4 further comprising a capture signal, wherein the position signal and the digital strain gage signals are collected in response to the capture signal.

6. The AACMM of claim 4 further comprising parameters obtained from a compensation procedure and stored in the electronic circuit, wherein the parameters are obtained in part by a collecting of data by the AACMM in response to movement of the arm segments.

7. The AACMM of claim 6, wherein the electronic circuit uses the parameters and the calculated magnitude and direction of maximum bending to modify the provided data corresponding to the position of the measurement device.

8. The AACMM of claim 3 wherein the structural component has a coefficient of thermal expansion and the strain gage sensor is selected to match the coefficient of thermal expansion of the structural component.

9. The AACMM of claim 3, further comprising a fourth strain gage sensor.

10. The AACMM of claim 3 wherein the electronic circuit produces a warning in response to the strain gage signals.

11. The AACMM of claim 10 wherein the warning is one of a visual warning and an audible warning.

12. The AACMM of claim 10 wherein the warning is produced when the bending strain has a value that falls outside pre-determined limits.

13. A method for measuring strain in an articulated arm coordinate measurement machine (AACMM) comprising the steps of:

providing a manually positionable articulated arm portion having opposed first and second ends, the arm portion including a plurality of connected arm segments, each attached to at least one bearing cartridge, the plurality of connected arm segments including an arm segment adjacent to the first end, each arm segment including at least one position transducer that produces a position signal;

a measurement device attached to the first end;

a structural component of the articulated arm coordinate measurement machine, wherein the structural component has an axial direction;

at least a first strain gage sensor disposed on the structural component, each strain gage sensor producing an analog strain gage signal;

converting a combination of the analog strain gage signals into at least one digital strain gage signal;

sending the at least one digital strain gage signal through at least one of the at least one bearing cartridges to an electronic circuit that receives the position signal and the at least one digital strain gage signal;

providing and storing data corresponding to a position of the measurement device; and

storing the at least one digital strain gage signal.

14. The method according to claim 13 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of providing a second strain gage sensor on the structural component and a third strain gage sensor on the structural component, wherein the first, second, and third strain gage sensors produce analog strain gage signals;

converting some combination of the analog strain gage signals into a plurality of digital strain gage signals;

sending the plurality of digital strain gage signals through at least one of the at least one bearing cartridges to the electronic circuit, wherein the electronic circuit stores the digital strain gage signals.

15. The method according to claim 14 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the steps of:

coupling the first, second, and third strain gage sensor, each having a sensitive axis, to the structural component, wherein the sensitive axis of each strain gage sensor is oriented approximately parallel to the axial direction;

disposing each strain gage sensor on the structural component to be approximately intersected by a transverse plane perpendicular to the axial direction of the structural component; and

disposing the first, second, and third strain gage sensor to provide data sufficient to determine a bending strain at any point residing on both the structural component and the transverse plane.

16. The method according to claim 15 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of calculating the magnitude and direction of maximum bending of the structural component.

17. The method according to claim 16 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of using the plurality of digital strain gage signals to modify the provided data corresponding to the position of the measurement device.

18. The method according to claim 17 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the steps of

providing a capture signal;

and

collecting the position signal and the digital strain gage signals in response to the capture signal.

19. The method according to claim 18 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of obtaining parameters from a compensation procedure, wherein the parameters are obtained in part by the collecting of data by the articulated arm coordinate measurement machine in response to movement of the arm segments.

20. The method according to claim 19 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of using the parameters and the calculated magnitude and direction of maximum bending of the structural element to modify the provided data corresponding to the position of the measurement device.

21. The method according to claim 15 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of selecting a coefficient of thermal expansion for each strain gage sensor to match a coefficient of thermal expansion of the structural component.

22. The method according to claim 14 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of producing a warning in response to the strain gage signals.

23. The method according to claim 22 for measuring strain in an articulated arm coordinate measurement machine (AACMM), wherein the warning is one of a visual warning and an audible warning.

24. The method according to claim 16 for measuring strain in an articulated arm coordinate measurement machine (AACMM), further comprising the step of producing a warning in response to the strain gage signals when the bending strain has a value that falls outside pre-determined limits.