Robot Arm Tool Center Point Calibration Using Stereo Vision

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Solution Overview

Problem

Traditional contact-type calibration methods for robot arms are prone to high human influence factors, are time-consuming, and unable to accurately calibrate three-dimensional rotations, leading to decreased machine tool usage rates and frequent recalibration needs.

Innovation Solution

A non-contact tool center point calibration method using a hand-eye calibration algorithm and stereoscopic reconstruction to establish a space coordinate system, with multiple cameras capturing images of a robot arm and a replaceable member to record feature and flange surface coordinates, determining the transformation relationship between the tool center point and flange surface, and updating this relationship into the robot arm's control program.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If contact-type calibration method is used, then calibration can be performed with simple equipment, but calibration time is long and machine tool usage rate decreases

Engineering Contradiction:

Improvecalibration equipment complexityVSAvoidcalibration time

Core Design Contradiction:

Device complexityVSLoss of time

Solution Approach 1:

The patent replaces the mechanical contact-type calibration method with an optical non-contact measurement system. Multiple cameras capture images of the robot arm and replaceable member, and a computing host processes these images to calculate coordinate transformations and determine the tool center point. This substitution of mechanical contact measurement with optical field measurement eliminates the need for physical contact and manual operations, thereby significantly reducing calibration time while maintaining equipment simplicity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of operation

If contact-type calibration method is used, then calibration process is simple, but human error is high and measurement precision is low

Engineering Contradiction:

Improvecalibration operation simplicityVSAvoidcalibration accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent uses multiple cameras to create optical copies (images) of the robot arm and replaceable member from different viewpoints. These image copies are then processed by the computing host to extract precise coordinate information and calculate transformation relationships. By working with optical copies rather than direct physical contact, the system eliminates human error in manual measurement while maintaining operational simplicity through automated image processing algorithms.

Inventive Principle:

Principle #26Copying

3Device complexity

If contact-type calibration method is used, then calibration can be performed without additional sensors, but three-dimensional rotation calibration is impossible

Engineering Contradiction:

Improvecalibration system configurationVSAvoidthree-dimensional rotation calibration capability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent transitions from two-dimensional contact point measurement to three-dimensional spatial coordinate measurement by introducing multiple cameras positioned at different locations. The computing host processes images from multiple viewpoints to reconstruct three-dimensional coordinates of feature points on the robot arm and replaceable member. This multi-dimensional optical measurement approach enables accurate calibration of three-dimensional rotations while maintaining relatively simple system configuration without requiring additional specialized sensors.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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

This method enables quick and accurate calibration of robot arms, reducing human error and time consumption, allowing for efficient recalibration and improved machine tool usage by eliminating the need for manual contact calibration.

Implementation Method 1

constructing a space coordinate system according to the coordinate transformation relationship by a stereoscopic reconstruction method

Methodology Applied

Scientific EffectStereoscopic reconstruction: Photogrammetry

Data Source

PatentUS11247340B2Method and apparatus of non-contact tool center point calibration for a mechanical arm, and a mechanical arm system with said calibration function

Publication Date: 2022.02.15 IND TECH RES INST

AI summary

This disclosure is related to a non-contact tool center point calibration method for a robot arm, and the method comprises: obtaining a coordinate transformation relationship between a flange surface of the robot arm and cameras by a hand-eye calibration algorithm; constructing a space coordinate system by a stereoscopic reconstruction method; actuating a replaceable member fixed with the flange surface to present postures in a union field of view of the cameras sequentially, recording feature coordinates of the replaceable member in the space coordinate system, and recording flange surface coordinates which is under the postures in the space coordinate system; obtaining a transformation relationship between a tool center point and the flange surface; and updating the transformation relationship into a control program of the robot arm. Moreover, the disclosure further discloses a calibration device performing the calibration method and a robot arm system having the calibration function.