Redundant Robot Arm Torque Control for Surgical Precision
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Solution Overview
Problem
In medical and industrial applications, robot arms face challenges in avoiding collisions and minimizing forces on sensitive openings due to unpredictable environments and limited spaces, where traditional position or force control methods are inadequate.
Innovation Solution
A method using a robot arm with redundant joints, equipped with torque sensors to detect and control external torque, allowing for active control and zero moment control to reduce collision risks and forces on openings, employing impedance, admittance, and impedance projection control methods to manage dynamic behavior in Cartesian coordinates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional position control or force control is used in medical robot applications, then the control system is simple, but collision avoidance capability is insufficient due to unpredictable environments and limited spaces
Solution Approach 1:
The patent implements a feedback mechanism where torque sensors continuously monitor external torques acting on the robot arm, and the control system adjusts actuator commands in real-time based on detected torques to maintain zero moment at the elbow joint, enabling dynamic collision avoidance in unpredictable medical environments
Solution Approach 2:
The system transitions from static position control to dynamic torque control, where the robot arm actively adapts its mechanical impedance in real-time based on external forces, allowing the elbow joint to dynamically evade collisions while maintaining end effector position through redundant degree of freedom
2Reliability
If the robot base and end effector are fixed to avoid collisions, then collision risk is reduced, but the robot cannot perform evasion movements when collisions are imminent
Solution Approach 1:
The robot arm utilizes its redundant degree of freedom (elbow joint) to dynamically change configuration in real-time, allowing the arm to move the elbow away from potential collision zones while keeping the end effector fixed in position and orientation, thus providing both collision avoidance and evasion capability
Solution Approach 2:
The robot arm is divided into segments (base, elbow, end effector) that can move independently, where the elbow segment can be repositioned to avoid collisions while the end effector segment maintains its operational position, enabling localized evasion without affecting overall task performance
3Manufacturing precision
If the robot arm maintains fixed position and orientation at the opening site, then surgical precision is maintained, but forces tangential to the patient surface cannot be minimized
Solution Approach 1:
Torque sensors provide real-time feedback on forces acting on the robot arm, enabling the control system to detect and minimize tangential forces at the opening site while maintaining the end effector's precise position and orientation through active torque compensation
Solution Approach 2:
The system changes the mechanical impedance parameters of the robot arm by actively controlling joint torques, allowing the arm to present a compliant interface that minimizes harmful forces on the patient while maintaining positioning precision through redundant degree of freedom
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces collision risks and forces on sensitive openings, enabling safe and flexible operation of robot arms in dynamic environments, providing haptic feedback and allowing for controlled movement without interrupting end effector operations, particularly in minimally invasive surgeries.
Implementation Method 1
A torque sensor detects an external torque acting in at least one joint
Data Source
AI summary
In a method for controlling a robot arm, which is particularly suitable for use in medical applications, a robot arm (10) with a redundant number of joints is used. A torque acting in at least one joint (12a, 12b) is sensed. By means of a control device, the torque acting in this joint (12a, 12b) is controlled to become substantially 0.