Surgical Robot Joint Velocity Limiting Near Singular Poses
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Solution Overview
Problem
Conventional robotic manipulator control systems face challenges in managing joint velocities, particularly when certain poses lead to singularities, making it difficult to move the end effector in all directions with finite joint velocities, and there is a need for an improved control system to efficiently limit joint velocities without relying on commanded movements.
Innovation Solution
A method is introduced to determine a common joint velocity limit for multiple joints based on their permitted range of motion and maximum deceleration, allowing for efficient velocity limiting without needing access to commanded joint movements, which is calculated using joint states and applied to all joints to prevent excessive velocities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional inverse kinematics control is used to calculate joint motions for end effector positioning, then the end effector can be moved to desired positions, but the system becomes problematic at singular poses where it is impossible to make subsequent movements with finite joint velocities
Solution Approach 1:
The control system performs preliminary action by anticipating singular configurations before the robot reaches them. The method calculates the time to reach singular poses and proactively reduces joint velocity limits before the singularity is encountered, preventing the control breakdown that would otherwise occur at singular poses.
Solution Approach 2:
The system dynamically adjusts joint velocity limits based on the robot's current configuration and predicted trajectory. Rather than using fixed velocity limits, the control method continuously monitors proximity to singular poses and adapts velocity constraints in real-time, allowing optimal performance across the entire workspace including near singular configurations.
2Reliability
If individual joint velocity limits are derived from each joint's permitted range of motion, then each joint can operate within its safe limits, but the system complexity increases and computation becomes more intensive
Solution Approach 1:
The method merges individual joint velocity considerations into a unified control approach. By calculating a common velocity limit based on the minimum permitted range of motion across all joints and the maximum deceleration requirement, the system achieves comprehensive velocity safety without managing separate complex limit calculations for each joint independently.
Solution Approach 2:
A single common velocity limit parameter serves multiple functions: it ensures all joints operate within their permitted ranges of motion, guarantees safe stopping from any configuration, and simplifies the control architecture. This universal parameter replaces what would otherwise require multiple joint-specific velocity limit calculations and coordination mechanisms.
3Device complexity
If a common joint velocity limit is selected from the minimum of k joints' velocity limits, then all k joints are effectively limited with a single parameter, but the permitted range of motion for individual joints may be more restrictive than necessary
Solution Approach 1:
The system performs preliminary action by anticipating the needs of all joints before motion begins. The common velocity limit is calculated based on the most restrictive joint's requirements, ensuring that when this limit is applied to all joints, none will exceed their individual velocity capabilities or require unsafe deceleration distances, thus maintaining adaptability through proactive constraint setting.
Data Source
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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.