Robotic End Effector Position Control via Virtual Constraint Sliding
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Solution Overview
Problem
Robotic systems in orthopedic surgeries face challenges in controlling end effectors with respect to arbitrarily shaped virtual constraints, leading to sticking issues and limited tool movement range, which affects the smoothness of tool control and user experience.
Innovation Solution
A robotic system with a navigation system and controller that computes a target position to avoid collisions with virtual constraints, allowing the end effector to slide along the constraint and prevent sticking, thereby expanding the range of tool movement and improving control smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the end effector is constrained by a virtual constraint surface, then the tool movement is restricted to prevent collisions, but the end effector may stick to the constraint for an extended period, limiting range of movement and decreasing smoothness of control
Solution Approach 1:
The system dynamically adjusts the end effector's movement behavior when approaching virtual constraints. Instead of rigidly preventing all contact, the controller enables the end effector to slide along the constraint surface when contact occurs, transitioning from a static collision-avoidance mode to a dynamic sliding mode that maintains both safety and operational smoothness
Solution Approach 2:
The controller modifies motion parameters in real-time based on the end effector's proximity to and contact with virtual constraints. By adjusting position and velocity parameters dynamically, the system allows controlled sliding along constraint surfaces, preventing sticking while maintaining collision avoidance
2Reliability
If the robotic system uses traditional collision avoidance methods, then safety is maintained, but the range of tool movement relative to constraints is limited
Solution Approach 1:
When the end effector contacts a virtual constraint surface, the system transitions from preventing movement in the normal direction to enabling movement along the tangent plane of the constraint surface. This dimensional shift allows the tool to slide along the constraint rather than being completely restricted, expanding the accessible workspace while maintaining safety
3Extent of automation
If the robotic system requires minimal interaction by the surgeon, then automation is improved, but the system is suitable only for interventions performed frequently
Solution Approach 1:
The system continuously monitors the end effector's position relative to virtual constraints and provides real-time feedback control. When contact is detected, the controller automatically adjusts motion commands to enable sliding along the constraint surface, allowing the highly automated system to adaptively handle varied surgical scenarios without surgeon intervention
Data Source
AI summary
A robotic device includes one or more actuators to position an end effector in a plurality of degrees of freedom. A navigation system tracks an actual position of the end effector. A controller identifies a condition wherein the actual position of the end effector contacts a virtual constraint. The controller determines that an anticipated movement of the end effector from an actual position to the home position would cause a collision between the end effector and a virtual constraint and computes a target position of the end effector that avoids the collision. The target position is spaced from the actual position and computed with respect to the virtual constraint. The one or more actuators are controlled to move the end effector from the actual position to target position along the virtual constraint.