Radiolucent Robotic Joint Actuation Without Cable Backlash

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Solution Overview

Problem

Current surgical robotics rely on cable-actuated end effectors that cause backlash, hysteresis, and coupled motion, leading to imprecise and unpredictable motion, and are incompatible with MRI and CT imaging, limiting their use in microsurgery and 3D image-guided surgery.

Innovation Solution

The Micra-Arm utilizes electroactive polymer (EAP) flexor extensor muscles powered by non-metallic conductive transmission wires, enabling precise and controlled articulation within MRI and CT bores, eliminating backlash and hysteresis through inverse proportional muscle pairs and elastic biasing mechanisms.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If cable-actuated end effectors are used for surgical robotics, then the system can achieve mechanical actuation and articulation, but the system experiences backlash, hysteresis, and coupled motion that reduce precision and predictability

Engineering Contradiction:

Improvemechanical actuationVSAvoidmotion precision

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent replaces the traditional cable-actuated mechanical system with a magnetic field-based actuation system. Permanent magnets and electromagnetic coils generate magnetic forces to articulate the end effector, eliminating the mechanical cable transmission that causes backlash and hysteresis. This substitution maintains mechanical actuation capability while removing the sources of imprecision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Strength

If metallic components are used in surgical robotics, then the system achieves structural strength and electrical conductivity, but the system creates artifacts in MRI and CT imaging

Engineering Contradiction:

Improvestructural strengthVSAvoidimaging artifacts

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent employs composite material construction for the end effector, combining non-metallic materials (such as polymers and ceramics) with embedded magnetic components. This composite approach provides the necessary structural strength while the non-metallic matrix prevents imaging artifacts. The permanent magnets and coils are strategically positioned and shielded to maintain mechanical integrity without compromising imaging compatibility.

Inventive Principle:

Principle #40Composite materials

3Ease of operation

If cable actuation is used for joint articulation, then the system can transmit force and motion, but the system requires continuous clutching and resetting to manage cable tension and slack

Engineering Contradiction:

Improveforce transmissionVSAvoidresetting time

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

The patent eliminates the cable tension management problem by replacing the mechanical cable system with a magnetic field system. The permanent magnets and electromagnetic coils can dynamically adjust forces without physical contact, eliminating the need for clutching and resetting operations. Magnetic forces can be modulated in real-time to maintain optimal tension without mechanical slack or binding.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Ease of operation

If rotational wire/cable means are used for articulation, then the system achieves joint movement capability, but the system experiences slippage and unexpected backlash motion

Engineering Contradiction:

Improvejoint movementVSAvoidmotion control

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent replaces the rotational wire/cable articulation mechanism with a magnetic field-based articulation system. The interaction between permanent magnets and electromagnetic coils produces controlled rotational and translational movements of the end effector joints. This magnetic system eliminates slippage and unexpected backlash by providing direct, contactless force transmission with precise controllability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution provides stable, smooth, and precise actuation, replicating natural joint movements, allowing for advanced microsurgery with real-time MRI and CT guidance, overcoming the limitations of cable-actuated systems.

Implementation Method 1

The Micra-Arm utilizes electroactive polymer (EAP) flexor extensor muscles powered by non-metallic conductive transmission wires, enabling precise and controlled articulation within MRI and CT bores

Methodology Applied

Scientific EffectElectroactive polymer: Electroactive Polymer