Methods for refining original robot command signals

• US 4,763,276 A
• Filed: 03/21/1986
• Issued: 08/09/1988
• Est. Priority Date: 03/21/1986
• Status: Expired due to Fees

• Current Assignee: Actel Partnership
• Original Assignee: Actel Partnership
• Inventors: Tucker, Michael, Perreirra, Noel D.
• Primary Examiner(s): Lastova, John R.
• Application Number:
  US06/842,173
• Time in Patent Office: 872 Days
• Field of Search: 364/513, 364/167, 364/170, 364/191-193, 364/474, 318/568, 901/2, 901/3, 901/15, 901/9
• US Class Current: 700/262
• CPC Class Codes: B25J 9/1653 parameters identification, estimation, stiffness, accuracy, error analysis
• CPC Class Codes: B25J 9/1692 Calibration of manipulator
• CPC Class Codes: G05B 2219/37619 Characteristics of machine, deviation of movement, gauge,
• CPC Class Codes: G05B 2219/41206 Lookup table, memory with certain relationships
• CPC Class Codes: G05B 2219/45083 Manipulators, robot
• CPC Class Codes: G05B 2219/49195 Slide, guideway, robot arm deviation

Abstract

A method for refining an original command signal which is intended to locate a robot at a desired position and orientation (pose) comprising the steps of identifying the actual system parameters of the robot; predicting, through utilization of those actual system parameters the anticipated pose of the robot which would actually be obtained as the result of the original command signal; calculating corrected command signals required to minimize the difference between the predicted anticipated pose and the desired pose; and employing the corrected command signals to place the robot. Preferably, a plurality of desired calibration pose command signals are used in the step of identifying the actual system parameters to place the robot in a plurality of actual calibration poses in the measuring range of at least one pose sensor. The differences between the desired calibration poses and the correponding actual poses are calculated and these differences are used to solve a set of equations which relates those differences to the actual system parameters of the robot, to thereby obtain the actual system parameters of the robot.

Claims

1. A method for refining original command signals which are intended, by conversion to corresponding pair variable signals, to place, in response to said pair variable signals, a robot having mechanical linkage and joint actuators at a desired position and orientation (pose), comprising the steps of:

a. identifying actual system parameters of said robot which describe said mechanical linkage and joint actuators of said robot;

b. predicting, through the utilization of said actual system parameters and said original command signals, a predicted anticipated pose of said robot which would actually be obtained as a result of said original command signals;

c. calculating, as a function of the difference between said desired pose and said predicted anticipated pose, corrected command signals required to minimize the difference between said desired pose and said predicted anticipated pose; and

d. employing said corrected command signals to place said robot in said desired pose.

2. A method of claim 1 wherein said step of predicting includes utilizing forward kinematics of said robot based upon said actual system parameters.

3. A method of claim 1 wherein said actual system parameters include parameters which locate placement of said robot.

11. A method of claim 1, 4 or 5 wherein said step of identifying the actual system parameters includes locating said robot at a plurality of desired calibration poses as a function of nominal system parameters of said robot.

12. A method of claim 1 or 4 wherein said step of calculating corrected command signals includes employing an actual inverse Jacobian of said robot, while using the difference between said desired pose and/said predicted anticipated pose.

13. A method of claim 1 or 4 wherein said step of identifying the actual system parameters includes use of a least squares technique.

14. A method of claim 13 wherein said least squares technique comprises the substeps of:

i. employing a plurality of calibration pose command signals which, based upon nominal system parameters of said robot, would place said robot in a plurality of desired calibration poses, to place said robot in a plurality of corresponding actual calibration poses, each of which desired and actual calibration poses is within the measuring range of at least one pose sensor;

ii. measuring said actual calibration poses of said robot by operation of said pose sensors;

iii. calculating differences between said plurality of said desired calibration poses and said corresponding measured actual calibration poses and summing the squares of said differences over all said poses to obtain resultant sums;

iv. solving a set of equations which relate said resultant sums to said actual system parameters of said robot to obtain said actual system parameters of said robot.

15. The method of claim 14 wherein said substep of solving said set of equations includes the sub-substeps of:

A. employing said set of equations to determine pairs, if any, of said actual system parameters which cause said set of equations to be singular;

replacing selective ones of said actual system parameters in said set of equations with new actual systems parameters which are each the sum of a respective one of said pairs; and

C. partially solving said set of equations to thereby obtain said actual system parameters, except for said pairs, and to thereby obtain said sums of said pairs.

16. A method of claim 15 wherein said substep of solving said set of equations includes the further sub-substeps of:

D. employing previously solved sets of equations for actual system parameters and related sums of said pairs to determine said sets of equations which remain singular; and

E. repeating said substep of solving said set of equations using previously obtained actual system parameters and said pairs and thereafter solving said set of equations to obtain all of said actual system parameters at times when said equations become non-singular.

17. A method of claims 1 or 4 wherein said step of calculating corrected command signals comprises calculating corrections required of said original command signals and combining said corrections and said original command signals to obtain said corrected command signals.

18. A method of claim 1 or 4 wherein said step of employing includes converting said corrected command signals to corresponding pair variable signals without any alteration of said step of converting based upon said actual system parameters.

4. A method for refining original command signals which are intended, by conversion to corresponding pair variable signals, to place, in response to said pair variable signals, a robot having mechanical linkage and joint actuators at a desired position and orientation (pose), comprising the steps of:

a. identifying actual system parameters of said robot, which describe said mechanical linkage and joint actuators of said robot, by;

i. employing a plurality of calibration pose command signals which, based upon nominal system parameters of said robot, would place said robot in a plurality of desired calibration poses, to place said robot in a plurality of corresponding, actual calibration poses, each of which desired and actual calibration poses is within the measuring range of at least one pose sensor;

ii. measuring said actual calibration poses of said robot by operation of said pose sensors;

iii. calculating the differences between said plurality of said desired calibration poses and said corresponding measured actual calibration poses;

iv. solving a set of equations which relate said differences to said actual system parameters of said robot to obtain said actual system parameters of said robot;

b. predicting, through utilization of said actual system parameters and said original command signal, a predicted anticipated pose of said robot which would actually be obtained as a result of said original command signals;

c. calculating, as a function of the difference between said desired pose and said predicted anticipated pose, corrected command signals required to minimize said difference between said desired, pose and said predicted anticipated pose; and

d. employing said corrected command signals to place said robot in said desired pose.

5. A method of claim 4 wherein said step of identifying the actual system parameters includes the substep of positioning a plurality of said pose sensors and said robot adjacent to each other.

6. A method of claim 5 wherein said step of identifying the actual system parameters includes the substep of locating said robot in a plurality of desired calibration poses, with each of said desired calibration poses falling within the measuring range of at least one of said plurality of pose sensors.

7. A method of claim 4 wherein said substep of solving said set of equations includes the sub-substeps of:

A. employing said set of equations to determine pairs, if any, of said actual system parameters which cause said set of equations to be singular;

replacing selective ones of said actual system parameters in said set of equations with new actual system parameters which are each the sum of a respective one of said pairs;

C. partially solving said set of equations to thereby obtain said actual system parameters, except for said pairs, and to thereby obtain said sums of said pairs.

8. A method of claim 7 wherein said substep of solving said set of equations includes the further sub-substeps of:

D. employing previously solved sets of said equations for actual system parameters and related sums of said pairs to determine said sets of equations which remain singular; and

E. repeating said substep of solving said set of equations using previously obtained actual system parameters and said pairs and thereafter solving said set of equations to obtain all of said actual system parameters at times when said equations become non-singular.

9. A method of claim 4 wherein said robot remains within the measurement range of said pose sensors during said step of employing said corrected command signals to place said robot, and wherein said pose sensors during said step of employing provide additional measurement of the difference between the actual pose of said robot and the desired pose of said robot in the form of additional difference signals, and wherein said step of calculating corrected command signals required to minimize the difference between said predicted anticipated pose and said desired pose includes utilization of said additional difference signals.

10. A method of claim 4 wherein said actual system parameters include parameters which locate placement of said robot relative to said at least one pose sensor.