Robot Path Control for Singularity-Avoiding Tool Orientation

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Solution Overview

Problem

Robotic mechanisms face challenges in maintaining smooth motion and avoiding damage due to singularities, which occur when joint axes align, leading to excessive joint movement rates and potential damage, particularly in applications like welding and painting where precise control is crucial.

Innovation Solution

A robot-mechanism controller is introduced that identifies and modifies paths to avoid singularities by incorporating a virtual three-axis wrist element and a final virtual joint, allowing for the minimization of tool orientation changes and joint rate limitations, ensuring smooth motion and precise control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the robot follows the original path through a singularity, then the tool position and orientation can be maintained, but excessive joint movement rates occur causing disruption or damage

Engineering Contradiction:

Improvetool position controlVSAvoidjoint movement stability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The controller proactively identifies singularities along the planned tool path before execution and pre-computes modified path segments that circumvent these singularities. By performing path modification in advance rather than reacting to singularities during execution, the system maintains tool position accuracy while preventing excessive joint velocities from occurring

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention introduces an intermediate computational layer between the desired tool path and the actual joint commands. This intermediary path modification process calculates alternative joint trajectories that achieve the same tool position and orientation goals while avoiding singularity regions where joint velocities would become excessive

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the robot avoids singularities by modifying the path, then joint movement rates are controlled, but tool orientation may deviate from the desired path

Engineering Contradiction:

Improvejoint movement stabilityVSAvoidtool orientation accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The path modification process dynamically adjusts the tool orientation along the modified path segment while maintaining the primary task objectives. Rather than using a fixed or simplified orientation approach, the system continuously optimizes orientation to minimize deviation from the desired path while still avoiding singularities, adapting to the local geometric constraints at each point along the modified trajectory

Inventive Principle:

Principle #15Dynamics

3Reliability

If the robot slows down joints to avoid singularity damage, then joint safety is improved, but productivity decreases due to disrupted motion

Engineering Contradiction:

Improvejoint protectionVSAvoidoperation continuity

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The invention replaces the mechanical constraint of slowing down joint movements with a computational solution. Instead of physically limiting joint velocities or adding mechanical protection systems, the controller uses software-based path modification to redirect the tool through alternative trajectories that naturally avoid singularity regions, thereby maintaining both joint safety and operational efficiency without actual speed reductions

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS11667035B2Path-modifying control system managing robot singularities

Publication Date: 2023.06.06 WISCONSIN ALUMNI RES FOUND

AI summary

A controller for robot arms and the like having mechanical singularities identities paths near the singularities and modifies those paths to avoid excessive joint movement according to a minimization of tool orientation deviation to produce alternative paths that minimize changes in the tool orientation such as can affect application such as welding, sealant application, coating and the like.