Dynamic Scaling for Teleoperated Surgical Slave Devices
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Solution Overview
Problem
Existing master-slave robotic systems for medical or surgical teleoperation, particularly those with unconstrained master devices, face challenges in maintaining usability and intuitive control when the slave device approaches its physical limits or when the target pose is outside its workspace, leading to inconsistent user experience and potential mapping issues.
Innovation Solution
A method and system that dynamically adjusts the scale factor and translational offset of the slave device's trajectory to keep it within a predefined convex volume, using dynamic scaling functions and translational offsets to maintain the slave device within its workspace, even when approaching physical limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the master device maps to a nominal target pose outside the slave device workspace, then the operator can command any position freely, but the slave device cannot reach the target and loses control coherence
Solution Approach 1:
The patent applies dynamics by making the scale factor dynamic rather than fixed. The scale factor is continuously adjusted based on the slave device's proximity to workspace boundaries, allowing the system to adapt between free operation (when workspace is available) and constrained operation (when approaching limits). This resolves the contradiction by providing both operator freedom and control coherence through context-dependent scaling.
Solution Approach 2:
The patent changes the parameter of scale factor from a constant value to a variable that depends on the slave device's position relative to workspace boundaries. When the slave device approaches limits, the scale factor is reduced to prevent mapping to unreachable poses. This parameter change maintains control coherence while preserving operator freedom to command positions within the adjusted mapping.
2Device complexity
If a fixed scale factor is used for master-slave mapping, then the control relationship is simple and intuitive, but the slave device may exceed workspace boundaries near motion limits
Solution Approach 1:
The patent implements feedback by continuously monitoring the slave device's position relative to workspace boundaries and using this information to adjust the scale factor. The system calculates the distance to boundaries and dynamically modifies the mapping scale to prevent exceeding limits. This feedback mechanism maintains reliability while keeping the control algorithm relatively simple through geometric calculations.
3Reliability
If the slave device is constrained to stay within workspace boundaries, then boundary compliance is maintained, but the operator perceives distorted or reduced control authority near limits
Solution Approach 1:
The dynamic scale factor creates a smooth transition between full control authority (when far from boundaries) and reduced scaling (when approaching boundaries). This dynamic adjustment maintains perceived control authority by only applying scaling when necessary, rather than continuously distorting the control relationship. The operator experiences natural control most of the time with minimal perceptible distortion.
Data Source
AI summary
A method for controlling a robotic system slave device for medical or surgical teleoperation, is close to physical motion limits of the slave device. The robotic system includes a master device movable by an operator, controlling a slave device having a surgical instrument. For each master trajectory of the master device, a respective slave target trajectory is determined in a slave reference coordinate system, with slave device movements being reduced by a scale factor with respect to master device movements. Determining the slave trajectory includes defining an edge region and an inner region of a convex volume. When a slave device nominal target trajectory is outside the inner region the modified scale factor is greater than a predetermined maximum scaling factor, the scale factor or the translational offset are dynamically varied so the target slave trajectory remains within the convex volume.