Surgical Haptic Joint Layout for Stiff Motion Boundaries

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 position of the stops dynamically.

Engineering Contradictions & Design Principles

VSEngineering 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 surgeons from forcing the instrument past the virtual boundary

Engineering Contradiction:

Improvelightness during free space movementVSAvoidconstraint stiffness

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The system dynamically switches between passive joint mode (allowing free movement) and active joint mode (providing stiff constraints) based on the surgical task requirements. The controller transitions joints between these modes to optimize both ease of operation and constraint reliability as needed during different phases of the surgical procedure

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The robotic system divides its joints into separate passive and active segments. Passive joints provide unpowered degrees of freedom for natural, light movement during approach and positioning, while active joints provide powered, stiff constraints when boundary enforcement is required. This segmentation allows the system to exhibit different mechanical characteristics in different parts of the kinematic chain

Inventive Principle:

Principle #1Segmentation

2Reliability

If admittance-based haptic constraints are used to provide stiff boundaries, then the constraints effectively prevent movement beyond boundaries, but the device feels heavy during free space movement and requires force sensors

Engineering Contradiction:

Improveconstraint stiffnessVSAvoidlightness during free space movement

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The system dynamically switches between passive joint mode (allowing free movement) and active joint mode (providing stiff constraints) based on the surgical task requirements. The controller transitions joints between these modes to optimize both ease of operation and constraint reliability as needed during different phases of the surgical procedure

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system extracts the constraint function from the entire robotic arm and implements it only at specific active joints where boundary enforcement is needed. This allows the majority of the robotic system to remain passive and lightweight during free space movement, while providing stiff constraints only when and where required

Inventive Principle:

Principle #2Taking out (Extraction)

3Power

If the robotic arm has limited power output in actuators, then the system can maintain control, but it cannot generate boundaries as stiff as those generated by admittance devices

Engineering Contradiction:

Improveactuator power outputVSAvoidboundary stiffness

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The system dynamically switches between passive joint mode (allowing free movement) and active joint mode (providing stiff constraints) based on the surgical task requirements. The controller transitions joints between these modes to optimize both ease of operation and constraint reliability as needed during different phases of the surgical procedure

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the mechanical impedance parameters of the robotic arm by switching between passive and active joint configurations. This allows the same actuator to provide both lightweight free-space movement (passive mode) and stiff boundary enforcement (active mode) by fundamentally altering the system's mechanical properties rather than relying solely on actuator force output

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11123881B2Surgical system with passive and motorized joints

Publication Date: 2021.09.21 MAKO SURGICAL CORP

AI summary

A surgical system includes a motor, a first link movable by operation of the motor, a plurality of non-driven, revolute joints coupled to the first link such that the first link separates the plurality of revolute joints from the motor, and an end effector coupled to the first link via the plurality of non-driven, revolute joints.