Manipulator Arm Servo Control for Limiting Energy Buildup
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Solution Overview
Problem
Robotic manipulator arms in medical and surgical systems often face discrepancies between commanded and actual states, leading to potential collisions and unexpected movements due to obstacles or external back-driving, which can be hazardous and disrupt workflow.
Innovation Solution
A computer-assisted control system with a non-clutch mode that servo-controls joints by calculating and updating the commanded state to reduce discrepancies between actual and commanded states, using an error threshold to prevent abrupt movements and allow for safe external manipulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the controller continuously updates the commanded state to reduce discrepancies between commanded and actual states, then the positioning precision is improved, but energy buildup increases leading to abrupt movements
Solution Approach 1:
The controller applies partial correction by only updating the commanded state when the discrepancy exceeds a threshold, rather than continuously correcting. This partial action approach reduces energy buildup while maintaining acceptable positioning precision by tolerating small errors that would otherwise generate continuous correction forces
Solution Approach 2:
The threshold mechanism acts as a cushioning buffer that prevents excessive energy accumulation. By allowing discrepancies to reach a certain level before triggering correction, the system cushions against rapid energy buildup and abrupt movements, enabling smoother energy management while maintaining positioning accuracy
2Ease of operation
If the controller allows external manipulation by not updating the commanded state, then ease of operation is improved, but positioning precision deteriorates due to drift from commanded position
Solution Approach 1:
The controller dynamically switches between two operational modes based on real-time conditions: updating the commanded state when precision is needed, and maintaining the current commanded state when external manipulation is detected. This dynamic adaptation allows the system to optimize between positioning precision and ease of operation depending on the operational context
3Reliability
If the controller detects obstacles and stops updating the commanded state, then safety is improved by preventing collisions, but productivity decreases due to workflow disruption
Solution Approach 1:
The controller takes preliminary anti-action by detecting obstacles and proactively stopping commanded state updates before collisions can occur. This preventive approach prioritizes safety by eliminating the possibility of collision-driven energy buildup, while the system later recovers by resuming normal operation once the obstacle is cleared
Solution Approach 2:
The obstacle detection mechanism, while interrupting workflow, converts a potentially harmful situation (collision) into a beneficial safety feature. The workflow disruption is temporary and prevents much larger disruptions from collisions, ultimately improving overall system reliability and safety
Data Source
Figure 1A
Figure 1B
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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.