Robot Tool Calibration Using Vision-Based Absolute Positioning
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Solution Overview
Problem
Current calibration methods for robot arms lack precision, particularly in determining the absolute position of tool working points, leading to potential damage or stagnation in production due to manufacturing tolerances, geometric deviations, and wear, with existing methods relying on human intervention or incomplete non-contact calibration.
Innovation Solution
A calibration system using a robot arm with a first coordinate system and an imaging device with a second coordinate system, where the imaging device sets an image sensing area, allowing the robot arm to move the tool's working point into this area, record its gesture and position, and calculate the absolute position using a transformation matrix between the two coordinate systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If manual tutoring calibration is used, then the robot arm can be calibrated to reach desired positions, but the calibration accuracy depends on operator experience and skill, resulting in unsatisfactory precision
Solution Approach 1:
The patent replaces manual mechanical positioning and visual judgment with an automated vision-based measurement system. The imaging device captures images of the tool working point, and image processing algorithms automatically determine its coordinates, eliminating dependence on operator skill and experience while significantly improving calibration precision.
Solution Approach 2:
The patent creates a digital copy (image) of the tool working point position rather than relying on manual physical positioning. By capturing the position through imaging and processing the image data to obtain coordinates, the system transforms physical positioning into digital measurement, achieving high precision without manual intervention.
2Measurement precision
If contact type calibration is used, then the tool working point touches calibration blocks to obtain directional offsets, but the tool experiences wearing during calibration, which is especially problematic for high precision tools
Solution Approach 1:
The patent replaces mechanical contact-based calibration with a non-contact vision measurement system. The imaging device optically captures the tool working point position without physical contact, and image processing algorithms calculate the coordinates. This eliminates tool wearing while maintaining high calibration precision.
Solution Approach 2:
The patent introduces an intermediary (imaging device and light field) between the measurement system and the tool working point. Instead of direct mechanical contact, the measurement is performed through optical fields and image processing, serving as a non-contact intermediary that preserves tool integrity while achieving precise measurement.
3Object-affected harmful factors
If non-contact type calibration is used, then tool wearing is avoided, but the method can only establish deviation amount between TWP and flange, not obtaining absolute position of TWP in robot arm coordinate system
Solution Approach 1:
The patent introduces a coordinate transformation matrix as an intermediary that bridges the imaging device coordinate system and the robot arm coordinate system. This matrix enables conversion of relative deviation measurements into absolute position information, allowing the system to obtain both the benefits of non-contact measurement and complete positional data.
Solution Approach 2:
The patent adds a dimensional transformation layer by establishing a coordinate transformation matrix between two different coordinate systems. This transformation enables the system to convert measurements from the imaging device's coordinate framework into the robot arm's coordinate framework, thereby obtaining absolute position information while maintaining non-contact measurement advantages.
4Object-affected harmful factors
If non-contact calibration is used, then tool wearing is avoided, but sample needs to be established again and new deviation amount is needed when tool is replaced, which is cumbersome
Solution Approach 1:
The patent creates a universal calibration system where the coordinate transformation matrix and measurement methodology remain consistent across different tool replacements. The imaging device and processing algorithms serve multiple tools without requiring sample re-establishment, making the calibration process tool-agnostic and significantly reducing calibration time when tools are changed.
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 enhances calibration precision by eliminating manual tutoring and tool wear, providing accurate absolute positioning of tool working points without the need for sample setup, thus improving production accuracy and efficiency.
Implementation Method 1
an imaging device adopting a second coordinate system, where the imaging device sets an image sensing area
Implementation Method 2
recording a current gesture of the robot arm and a specific coordinate of the TWP of the tool in the second coordinate system
Data Source
AI summary
A calibration system for robot tool including a robot arm adopting a first coordinate system, a tool arranged on a flange of the robot arm, and an imaging device adopting a second coordinate system is disclosed, wherein an image sensing area is established by the image device. A calibration method is also disclosed and includes steps of: controlling the robot arm to move for leading a tool working point (TWP) of the tool enters the image sensing area; recording a current gesture of the robot arm as well as a specific coordinate of the TWP currently in the second coordinate system; obtaining a transformation matrix previously established for describing a relationship between the first and the second coordinate systems; and importing the specific coordinate and the current gesture to the transformation matrix for calculating an absolute position of the TWP in the first coordinate system.