Servo-Controlled Manipulator Arms With Clutch-Based Energy Release
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Solution Overview
Problem
Robotic manipulator arms often experience discrepancies between commanded and actual states, leading to abrupt movements and potential collisions when they are unable to immediately follow commands, as the buildup of this discrepancy can go unnoticed by operators, especially in scenarios where the arm is blocked or externally back-driven.
Innovation Solution
A computer-assisted control system that includes a non-clutch mode and a clutch mode, where in non-clutch mode, the system servo-controls joints by updating the commanded state with an offset to reduce errors below a threshold, and in clutch mode, the joints are allowed to float, preventing excessive energy buildup and allowing for safe external manipulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the controller continuously servo-controls the joint to maintain precise position, then positioning accuracy is improved, but energy buildup occurs when the arm is blocked or externally manipulated
Solution Approach 1:
The controller dynamically switches between non-clutch mode (continuous servo-control for precision) and clutch mode (floating joints for energy release) based on operational conditions. This allows the system to adapt its control characteristics in real-time, maintaining precision when needed while preventing energy buildup during external manipulation or blocking events.
Solution Approach 2:
The system changes the control parameter from rigid position control (non-clutch mode) to compliant floating control (clutch mode) by activating/deactivating the clutch mechanism. This parameter change allows the joint to transition between maintaining precise positioning and allowing free movement to dissipate energy, resolving the contradiction between precision and energy management.
2Measurement precision
If the controller maintains a rigid commanded state to ensure precise movement, then movement precision is improved, but abrupt movements and collisions occur when the arm encounters obstacles
Solution Approach 1:
The clutch mechanism acts as a pre-prepared energy release mechanism that prevents harmful abrupt movements before they can occur. When the arm encounters an obstacle or external manipulation, the clutch can be activated to allow the joint to float, cushioning the impact and preventing collisions rather than allowing the rigid servo-control to cause abrupt movements.
Solution Approach 2:
The system transitions from a static rigid control mode to a dynamic compliant mode when obstacles are detected or during external manipulation. This dynamic adaptation allows the controller to maintain precision during normal operation while switching to a compliant floating mode to prevent harmful effects when obstacles are encountered.
3Speed
If the system uses continuous servo-control to respond to commanded states, then responsiveness is improved, but the discrepancy between commanded and actual states builds up when movement is blocked
Solution Approach 1:
The clutch mechanism extracts or separates the energy accumulation problem from the servo-control system. By providing a dedicated path for energy release through the floating joint mode, the system removes the harmful effect of state discrepancy buildup while maintaining the responsive servo-control for normal operation. The clutch acts as a separate safety mechanism that handles the discrepancy issue independently.
Data Source
AI summary
A computer-assisted medical system includes a manipulator arm and a controller. The controller includes a computer processor. The controller is configured to servo at least one joint associated with at least one manipulator arm segment of the manipulator arm, the servoing including executing a servo loop. Executing the servo loop includes obtaining an actual state of the manipulator arm, computing a difference between a commanded state and the actual state, where the commanded state is used for the servoing the at least one joint, and determining whether the difference exceeds an error threshold. Based on determining that the difference does exceed the error threshold, the commanded state is updated using an offset to reduce the difference, and. Based on determining that the difference does not exceed the error threshold, the commanded state is not updated. The controller is further configured to apply the commanded state to control the actual state.