Remote-Center Tool Positioning With Infinite Roll and Low Inertia
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Solution Overview
Problem
Conventional apparatuses for positioning surgical tools in minimally invasive surgical procedures suffer from high total inertia, reduced precision, and increased bulkiness due to actuators mounted on the end-effector, which complicates the system and limits its degree of freedom.
Innovation Solution
The apparatus employs three spherical arms with first and second spherical linkages, connected by revolute joints, which intersect at a remote centre of motion. This configuration allows for three degrees of freedom without the need for actuators on the platform or tool, reducing inertia and complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If actuators are mounted on the end-effector to provide rotational movement, then the tool can be rotated about the tool axis, but the total inertia of the system increases and precision decreases
Solution Approach 1:
The patent removes the rotational actuator from the end-effector (platform) and relocates it to the base. This extraction eliminates the added inertia and complexity at the end-effector while maintaining the rotational capability through the spherical parallel mechanism's kinematic chains, directly resolving the precision-inertia contradiction.
Solution Approach 2:
Instead of mounting actuators on the moving end-effector to achieve rotation, the patent inverts the approach by mounting actuators on the stationary base and using the spherical parallel mechanism's passive kinematic chains to achieve the rotational motion at the end-effector. This inversion transfers the active components away from the moving parts, reducing inertia.
2Adaptability or versatility
If actuators are mounted on the end-effector to provide rotational movement, then the tool can be rotated about the tool axis, but the system becomes bulkier and more complex
Solution Approach 1:
The patent extracts the rotational actuator from the end-effector assembly, eliminating the need for additional transmission components, cables, and mounting structures at the platform. This extraction directly reduces the bulkiness and complexity of the end-effector while maintaining rotational capability through the base-mounted actuator and spherical mechanism.
Solution Approach 2:
The patent merges the rotational actuation function into the base structure, combining the actuator with the existing spherical parallel mechanism's kinematic chains. This consolidation eliminates separate rotational actuation components at the end-effector, reducing overall system complexity and bulkiness.
3Adaptability or versatility
If actuators are mounted on the end-effector to provide translational and rotational motion, then four degrees of freedom are achieved, but the total inertia increases
Solution Approach 1:
The patent extracts one actuator from the end-effector and relocates it to the base. The spherical parallel mechanism's three passive kinematic chains, combined with the base-mounted actuators, provide the necessary four degrees of freedom (three rotations and one translation) without the added inertia of end-effector-mounted actuators.
Solution Approach 2:
The patent inverts the conventional approach by mounting actuators on the stationary base rather than on the moving end-effector. The spherical parallel mechanism's kinematic chains passively transmit the motion from the base actuators to achieve four degrees of freedom at the end-effector, eliminating the inertia penalty of moving actuators.
Data Source
AI summary
An apparatus for positioning a tool, the apparatus comprising a base, a platform for supporting the tool, and three spherical arms each connecting the platform to the base. Each spherical arm comprises a first spherical linkage and a second spherical linkage. Each first spherical linkage is connected to the base by a primary joint, and all primary joints are coaxial with one another. Each first spherical linkage is connected to the respective second spherical linkage by a first revolute joint. Each second spherical linkage is connected to the platform by a second revolute joint. Axes of the primary joints, first revolute joints and second revolute joints intersect at a remote centre of motion that is remote from the platform. The apparatus further comprises rotary inputs arranged on the base to receive rotary drive to rotate each first spherical linkage about the respective primary joint so as to move the platform over a portion of the surface of a notional sphere and rotate the platform about a tool axis that is normal to the surface of the platform. Particularly, the platform can have infinite rolling motion about the tool axis in any achievable orientation.