Surgical Robot Instrument Control With Static Pretension
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Solution Overview
Problem
Surgical robotic systems face challenges in precisely controlling surgical instruments due to backlash, friction, and compliance in the transmission between the tool drive and end effector, especially under varying external loads.
Innovation Solution
Implementing a control algorithm that uses redundant actuators to create static pretension by applying an opposite direction bias during the homing stage, maintaining this bias throughout operation to compensate for backlash and compliance, and transitioning to position control mode to ensure precise movement of the end effector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple actuators are used to control the end effector, then the force or torque applied by one actuator may not make its way to the second actuator due to internal friction and compliance, but adding more actuators increases device complexity
Solution Approach 1:
The system applies a static pretension force through the actuators before operation to pre-compress the transmission elements. This preliminary action eliminates backlash and reduces the effects of compliance and friction, ensuring that subsequent actuator forces are effectively transmitted without loss.
Solution Approach 2:
The control system dynamically adjusts the pretension level based on operational requirements. By changing the pretension parameter, the system optimizes the balance between eliminating transmission errors (backlash, compliance) and managing the complexity of the multi-actuator system.
2Ease of operation
If the transmission has large compliance to allow for mechanical coupling, then precise control of the end effector becomes difficult under varying external loads
Solution Approach 1:
The system applies a static pretension force through the actuators before operation to pre-compress the transmission elements. This preliminary action eliminates backlash and reduces the effects of compliance and friction, ensuring that subsequent actuator forces are effectively transmitted without loss.
Solution Approach 2:
The control system continuously monitors the positions and forces of multiple actuators and adjusts their output to maintain precise end effector control. Feedback from position sensors and force measurements allows the system to compensate for compliance effects in real-time under varying external loads.
3Force
If actuators operate in torque control mode to apply force, then position precision is reduced under external loads
Solution Approach 1:
The system applies a static pretension force through the actuators before operation to pre-compress the transmission elements. This preliminary action eliminates backlash and reduces the effects of compliance and friction, ensuring that subsequent actuator forces are effectively transmitted without loss.
Solution Approach 2:
The control system dynamically switches between torque control and position control modes based on operational requirements. During phases requiring force application, torque control is used; during phases requiring precise positioning, the system transitions to position control while maintaining the static pretension to ensure accurate force transmission.
Data Source
AI summary
For control of a surgical instrument in a surgical robotic system, multiple actuators establish a static pretension by actuating in opposition to each other in torque control. The static pretension reduces or removes the compliance and elasticity, reducing the backlash width. To drive the tool, the actuators are then moved in cooperation with each other in position mode control so that the movement maintains the static pretension while providing precise control.