Medical Robot Joint Controller with Programmable Error Dynamics

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Solution Overview

Problem

Medical robotic systems used in minimally invasive surgeries face challenges in accurately and efficiently positioning surgical instruments due to the need for manual handling of slave manipulators, which can be difficult and unfriendly for assistants, especially when optimized for tracking purposes, leading to unsafe forces and overshooting issues.

Innovation Solution

A joint controller and method that utilize motor-driven joints with a processor-controlled movement system, incorporating feedback and feedforward motor torque terms, limiting forces and velocities to ensure optimal tracking performance and safe instrument positioning.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the slave manipulator is optimized for tracking purposes with high control gains, then the tracking performance is improved, but the manipulator becomes difficult to manually position and may exert unsafe forces

Engineering Contradiction:

Improvetracking performanceVSAvoidmanual positioning difficulty

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The control system dynamically adjusts between two modes: a first control mode during manual positioning that reduces control gains to facilitate easy manual manipulation, and a second control mode during surgical procedures that increases control gains for high-precision tracking. This dynamic switching resolves the contradiction by adapting the system characteristics to the current operational phase.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the control parameters (control gains) based on the operational state. During manual positioning, lower control gains are used to reduce the effort required by the assistant. During surgical procedures, higher control gains are applied to achieve precise tracking of master manipulator movements, thus resolving the trade-off between ease of operation and tracking performance.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the slave manipulator is manually positioned by an assistant, then the initial positioning is achieved, but the process is difficult and unfriendly for the assistant

Engineering Contradiction:

Improvepositioning efficiencyVSAvoidassistant operation difficulty

Core Design Contradiction:

ProductivityVSEase of operation

Solution Approach 1:

The control system incorporates feedback mechanisms that monitor the position and movement of the slave manipulator. During manual positioning, this feedback allows the system to assist the assistant's movements by providing force feedback and reducing mechanical impedance, making the manipulator easier to position while maintaining awareness of the assistant's intended actions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system replaces pure mechanical manual positioning with a hybrid approach where the control system actively assists the assistant's manual inputs. The controller processes the assistant's movements and generates appropriate motor commands, substituting complex mechanical impedance matching with intelligent control algorithms that make positioning easier while maintaining precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If high control gains are used for tracking optimization, then the tracking accuracy is improved, but overshooting and unsafe forces occur

Engineering Contradiction:

Improvetracking accuracyVSAvoidsafety of forces exerted

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The control system dynamically adjusts control gains based on the operational phase. During manual positioning, lower control gains prevent overshooting and unsafe forces. During surgical procedures when tracking accuracy is critical, higher control gains are applied but with appropriate safety limits and force constraints to prevent harmful forces, thus resolving the contradiction between accuracy and safety.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control system implements preliminary constraints and safety limits on the motor commands before they can cause unsafe forces or overshooting. By pre-programming force limits and rate-of-change constraints, the system prevents harmful effects while still allowing high control gains for accurate tracking during surgical operations.

Inventive Principle:

Principle #9Preliminary anti-action

Data Source

PatentUS7741802B2Medical robotic system with programmably controlled constraints on error dynamics

Publication Date: 2010.06.22 INTUITIVE SURGICAL OPERATIONS INC

AI summary

A medical robotic system has a robot arm holding an instrument for performing a medical procedure, and a control system for controlling movement of the arm and its instrument according to user manipulation of a master manipulator. The control system includes at least one joint controller that includes a controller having programmable parameters for setting a steady-state velocity error and a maximum acceleration error for the joint's movement relative to a set point in response to an externally applied and released force.