Surgical Robot Joint Velocity Limiting Near Singular Poses
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Solution Overview
Problem
Conventional robotic manipulators face challenges in controlling joint velocities, particularly when inverse kinematics becomes singular, making it difficult to move the end effector in all directions with finite joint velocities, leading to undesirable high joint speeds and potential collisions.
Innovation Solution
A method is introduced to limit joint velocities by determining a common joint velocity limit based on the permitted range of motion and maximum deceleration of each joint, applied uniformly across multiple joints to prevent excessive movement and ensure smooth stopping, using joint states and a Jacobian matrix for Cartesian space translation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inverse kinematics control is used, then the end effector can be positioned at desired locations, but joint velocities become unbounded near singular poses causing high-speed issues and potential collisions
Solution Approach 1:
The control system pre-calculates velocity limits for each joint based on current pose and singularities before executing motion commands. By anticipating problematic configurations and setting appropriate velocity constraints in advance, the system prevents unbounded joint velocities near singular poses while maintaining positioning accuracy through the inverse kinematics solver.
2Ease of operation
If individual joint velocity limits are applied, then each joint can be controlled independently, but the system complexity increases and processing becomes more difficult
Solution Approach 1:
The patent combines individual joint velocity limits into a unified control framework where all joint limits are calculated simultaneously based on the current pose and singularities. This merging approach maintains the benefits of individual joint control while reducing overall system complexity through a coordinated velocity limiting strategy that processes all joints in a single control loop.
Data Source
AI summary
A method for limiting joint velocity of a plurality of joints of a surgical robotic system, the surgical robotic system comprising a robot having a base and an arm extending from the base to an attachment for an instrument, the arm comprising a plurality of joints whereby the configuration of the arm can be altered, the method comprising: obtaining joint states for a first group of k joints of the arm, where k>1; for each of the k joints: determining from the obtained joint state a permitted range of motion for that joint; deriving, using the permitted range of motion, a joint velocity limit for that joint; selecting the minimum joint velocity limit of the k joints to be a common joint velocity limit used to limit each of the k joints individually; and calculating drive signals for driving the k joints wherein the velocity of each of the k joints is limited using the common joint velocity limit.