Surgical Tool Joint Stops for Stiff Motion Boundary Control
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Solution Overview
Problem
Conventional haptic devices in computer-aided surgery lack an effective mechanism to prevent surgeons from inadvertently moving surgical instruments beyond defined boundaries, leading to potential tissue damage due to the inability to generate stiff enough constraints.
Innovation Solution
A haptic system with adjustable positive stops, comprising a mechanical positioner and controllable stops, allows movement within a predetermined range while constraining the end-effector from exceeding this range, using a drive mechanism and linkage joints to adjust the stops dynamically in response to the end-effector's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If impedance-based haptic constraints are used to limit surgical instrument movement, then the device feels relatively light during free space movement, but the constraints are not stiff enough to prevent the surgeon from forcing the instrument past the virtual boundary
Solution Approach 1:
The system dynamically switches between passive joint mode (allowing free movement) and active motorized joint mode (providing stiff constraints) based on the surgical instrument's proximity to the virtual boundary. The motorized joints can be activated to provide additional constraint forces when the passive mechanical constraints are insufficient, thereby resolving the contradiction between light operation and reliable constraint enforcement.
2Reliability
If admittance-based haptic constraints are used to provide stiff boundaries, then the constraints are sufficiently rigid to prevent boundary violation, but the device feels heavy during free space movement and requires force sensors
Solution Approach 1:
The robotic arm joints dynamically transition between passive (mechanical-only) and active (motorized) modes. During free space movement, the joints remain passive providing light operation. When constraint enforcement is needed near the virtual boundary, the motorized joints activate to provide admittance-based stiff constraints, thus achieving both light operation and reliable constraints at different times.
Solution Approach 2:
The system uses the surgeon's own manipulation forces to trigger constraint enforcement. When the surgeon applies force to move the instrument toward or beyond the virtual boundary, the motorized joints detect this and automatically activate to provide the necessary constraint forces, eliminating the need for separate force sensors while maintaining reliable constraints.
3Reliability
If motorized joints are used to provide active constraint forces, then stiff boundaries can be enforced, but the device complexity increases and the output force is limited by actuator capabilities
Solution Approach 1:
The system uses a hybrid passive-active joint configuration where only necessary joints are motorized. The passive joints provide mechanical constraints without motors, while motorized joints are strategically placed to provide active constraint forces only when needed. This dynamic configuration reduces overall system complexity compared to fully motorized systems while maintaining reliable constraint enforcement capability.
Data Source
AI summary
A method includes obtaining an implant plan, defining a range of motion for a surgical tool based on the implant plan, adjusting, by an actuator and based on the range of motion, a passive joint coupled between the actuator and the surgical tool, and allowing manual movement of the surgical tool through the range of motion via rotation at the passive joint.