Adjustable Positive Stops for Surgical Haptic Motion Constraints
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Solution Overview
Problem
Conventional haptic devices in computer-aided surgery lack an adjustable positive stop mechanism that can provide sufficient constraint forces to prevent erroneous movements while allowing flexibility of motion, leading to potential tissue damage.
Innovation Solution
A mechanical positioner with controllable first and second stops, driven by a mechanism to constrain movement within a predetermined range, allowing free motion within that range and preventing movement outside it, using actuators and tracking devices to adjust the stops dynamically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If an impedance device is used to provide haptic constraints, then the device feels relatively light to the user during free space movement, but the output force is finite and cannot generate boundaries as stiff as admittance devices, allowing the user to potentially overcome the constraints and force the instrument past the virtual boundary
Solution Approach 1:
The system dynamically switches between impedance mode (for free space movement with light perception) and positive stop mode (for constrained movement with strong force). The mechanical positioner can be positioned at different locations along the range of motion, allowing the control system to activate appropriate constraint forces only when needed, thus providing both lightness during free movement and strong constraints when boundaries are approached
Solution Approach 2:
A mechanical positioner acts as an intermediary component that can be positioned between the user input and the surgical instrument. This positioner serves as a physical mediator that can provide positive stop constraints at specific locations, bridging the gap between the lightweight impedance interface and the need for strong constraint forces without requiring the entire system to be heavy
2Force
If an admittance device is used to provide haptic constraints, then the device can provide stiff boundaries that prevent user movement, but the device feels heavy to the user as the user moves the device through free space
Solution Approach 1:
The system uses dynamic positioning of the mechanical positioner to provide stiff boundaries only when and where needed. During free space movement away from boundaries, the positioner is positioned such that it does not engage, allowing lightweight operation. When approaching virtual boundaries, the positioner is automatically positioned to engage and provide strong constraint forces, thus achieving stiff boundaries without continuous heaviness
3Force
If a fixed positive stop is used to constrain movement, then the device provides strong constraint forces that cannot be overcome by the user, but the stop cannot be adjusted to different positions in space
Solution Approach 1:
The mechanical positioner is made dynamically adjustable along the range of motion of the haptic interface. It can be automatically repositioned by the control system based on the virtual environment parameters, allowing the positive stop location to adapt to different surgical scenarios while maintaining the ability to provide strong constraint forces when engaged
Solution Approach 2:
The mechanical positioner serves multiple functions: it can be positioned at different locations to provide constraints at various points in the workspace, it can be adjusted to accommodate different virtual boundary configurations, and it maintains the capability to provide strong positive stop forces regardless of position, thus making the system versatile for different surgical applications
Data Source
AI summary
An apparatus for providing haptic guidance during manipulation of an end-effector includes a robotic arm. The robotic arm has at least one actuated joint, at least one other joint connected to the at least one actuated joint, and a physical constraint movable by actuation of the at least one actuated joint. The physical constraint limits the motion of the at least one other joint in at least one direction. The apparatus further includes an end-effector configured to be manipulated by an application of external forces and connected to the at least one other joint.