Surgical Robotic Joint Testing for Stiffness and Backlash Mapping
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Solution Overview
Problem
Existing tests for characterizing the performance of robotic joints are complex, unreliable, and unable to fully observe a range of joint configurations and forces, limiting the acquisition of comprehensive data points for thorough performance investigation.
Innovation Solution
A method for characterizing the performance of a joint in a surgical robotic arm involves sending command signals to position the arm and apply forces, measuring configurations and torque at predefined intervals, calculating elongation, and comparing these values to generate an output indicating joint performance, including stiffness characteristics and potential backlash regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external test equipment and sensors are used to characterise joint performance, then measurement capability is improved, but device complexity and reliability issues increase
Solution Approach 1:
The robotic arm uses its own integrated sensors and control systems to characterize joint performance without requiring external test equipment. The system performs self-diagnosis by utilizing existing actuators, encoders, and control hardware already present in the robotic arm, thereby eliminating the need for complex external measurement apparatus while maintaining measurement capability
Solution Approach 2:
The control system is designed to perform multiple functions: it controls the robotic arm's operation during normal use and simultaneously characterizes joint performance during testing phases. The same actuators and sensors used for operation are repurposed for performance characterization, reducing the need for dedicated test equipment and simplifying the overall system
2Loss of information
If known test methods are used to characterise joint performance, then some performance data is obtained, but a full spectrum of data points across all joint configurations and forces cannot be collected
Solution Approach 1:
The test method dynamically adjusts the operational parameters of the robotic arm, varying joint configurations, forces, and velocities across the full range of motion. Rather than using static or limited test positions, the system continuously changes operating conditions to capture performance data across all possible joint states, ensuring complete coverage of the performance spectrum
Solution Approach 2:
The system systematically varies multiple parameters including joint angles, applied forces, velocities, and accelerations to generate a comprehensive dataset. By changing these parameters across their full ranges and observing joint performance at each combination, the method captures the complete spectrum of operational characteristics without being constrained by fixed test protocols
3Extent of automation
If manual force application methods are used to test joints, then some torque data is obtained, but automation and standardisation are reduced
Solution Approach 1:
The system employs closed-loop feedback control where sensors continuously monitor joint configuration, applied forces, and actuator performance. This feedback is fed back to the control system which automatically adjusts test parameters and records data, ensuring consistent and repeatable testing conditions. The automated feedback mechanism eliminates manual intervention variability and standardizes the test procedure across different joints and configurations
Data Source
AI summary
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.