Characterising the performance of a robotic joint
A method for characterising the performance of a joint in a surgical robotic arm, the joint being driven by a drivetrain which transfers power from a drive source to the joint, the method comprising: sending a first command signal to position the robot arm into an initial configuration; sending a second command signal to apply a force to the joint to displace the joint from a steady state; for a plurality of predefined time intervals: receiving a first measurement indicating the configuration of the drive source at a first end of the drivetrain; receiving a second measurement indicating the configuration of the joint at a second end of the drivetrain; calculating a value of elongation using the first and second measurements; and receiving a third measurement indicating the torque experienced by the joint at the second end of the drivetrain; comparing the values of elongation with corresponding values of torque at each of the predefined time intervals; and generating an output from the comparison indicating the performance of the joint.
1. A method for characterising the performance of a joint in a surgical robotic arm, the joint being driven by a drivetrain which transfers power from a drive source to the joint, the method comprising:
sending a first command signal to position the robot arm into an initial configuration;
sending a second command signal to apply a force to the joint to displace the joint from a steady state;
for a plurality of predefined time intervals:
receiving a first measurement indicating the configuration of the drive source at a first end of the drivetrain;
receiving a second measurement indicating the configuration of the joint at a second end of the drivetrain;
calculating a value of elongation using the first and second measurements; and
receiving a third measurement indicating the torque experienced by the joint at the second end of the drivetrain;
comparing the values of elongation with corresponding values of the measured torque at each of the predefined time intervals; and
generating an output from the comparison indicating the performance of the joint.
2. The method as described in claim 1 , wherein generating the output comprises calculating a graph of elongation against torque to define a stiffness characteristic for the joint.
3. The method as claimed in claim 1 , further comprising comparing the values of elongation and corresponding values of torque to a predetermined characteristic for the joint.
4. The method as claimed in claim 1 , wherein the method comprises:
sending a command signal to apply an instantaneous force to the displace the joint from the steady state; and
receiving the first, second and third measurements at a plurality of predefined time intervals whilst the joint returns to the steady state.
5. The method as claimed in claim 1 , wherein the method further comprises:
sending a command signal to consistently increase the frequency of the force applied to the joint; and
receiving the first, second and third measurements at a plurality of predefined time intervals.
6. The method as claimed in claim 1 , wherein the method further comprises:
sending a command signal to consistently vary the direction of the force to be applied to the joint; and
receiving the first, second and third measurements at a plurality of predefined time intervals.
7. The method as claimed in claim 1 , wherein the second command signal indicates a desired configuration for the joint.
8. The method as claimed in claim 1 , wherein elongation is characterised as the difference between the measured configuration of the drive source q i and the measured configuration of the joint q o .
9. The method as claimed in claim 2 , further comprising calculating one or more regression lines on the graph of elongation against torque, each regression line having a corresponding gradient.
10. The method as claimed in claim 9 , wherein the method further comprises analysing the gradients of the one or more regression lines to identify a plurality of distinct regions.
11. The method as claimed in claim 10 , wherein the method further comprises identifying a backlash region from the graph, the backlash region being characterised a regression line with a near-zero gradient.
12. The method as claimed in claim 8 , wherein the method further comprises identifying one or more linear stiffness regions from the graph, each linear stiffness region being identified by a regression line with a gradient that is above a predetermined threshold.
13. The method as claimed in claim 9 , the method further comprising analysing the graph to establish the accuracy of the one or more regression lines.
14. The method as claimed in claim 13 , wherein analysing the graph comprises performing an R-squared analysis.
15. The method as claimed in claim 10 , wherein the plurality of distinct regions are identified by applying signal conditioning to the received sensor measurements.
16. The method as claimed in claim 1 , wherein the drive source is a motor.
17. The method as claimed in claim 1 , wherein the initial configuration of the arm is selected from a set of predetermined arm configurations.
18. The method as claimed in claim 1 , wherein the drivetrain comprises one or more gears.
19. The method as claimed in claim 1 , wherein the drivetrain is a harmonic drive.