Robot Workpiece Frame Calibration Using a Virtual Image Sensor
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Solution Overview
Problem
Conventional automated calibration methods for robot workpiece coordinate frames are prone to inaccuracies due to human error, require external image sensors that can be obstructed, and involve potential damage to the workpiece, making them time-consuming and inefficient.
Innovation Solution
An automated calibration system using a physical image sensor on a robot's flange and a controller to create a virtual image sensor, allowing the robot to move characteristic points between the two image axes for precise calibration without direct contact or additional sensors, enabling single-step calibration and improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If external image sensors are used to monitor the robot and measure distances to target points, then automated calibration can be achieved, but images of designated points may be blocked by the robot itself or other objects
Solution Approach 1:
Instead of using external image sensors that may be blocked, the patent inverts the approach by mounting the image sensor on the robot's end effector itself. This allows the sensor to capture images of designated points on the workpiece from the robot's operational position, eliminating the blocking problem while maintaining automated calibration capability
Solution Approach 2:
The patent introduces a virtual image sensor as an intermediary concept. By constructing a virtual image sensor through coordinate transformation and mathematical modeling based on the physical sensor's data, the system can perform calibration measurements without requiring direct line-of-sight to all points, overcoming physical blocking limitations
2Measurement precision
If image sensors are mounted to measure in advance or a control center directly touches the workpiece to confirm relative positions, then calibration can be performed, but the workpiece may be damaged and human operation errors occur
Solution Approach 1:
The patent replaces mechanical contact-based calibration methods with an optical measurement system. The image sensor mounted on the end effector captures images of designated points on the workpiece, and the controller calculates relative positions through image processing and coordinate transformation, eliminating direct mechanical contact and the associated damage risk
Solution Approach 2:
The system performs self-calibration by using the robot's own mounted image sensor to capture workpiece features and automatically calculate position relationships through the controller, eliminating the need for external operators to manually touch or measure the workpiece, thereby preventing human error and damage
3Measurement precision
If a CAD file is applied to obtain relative distances between the robot and calibration device or workpiece, then measurements can be made, but the operation is time-consuming and the workpiece shall have obvious characteristic points
Solution Approach 1:
The patent applies preliminary action by pre-defining multiple designated points on the workpiece with known coordinates in the workpiece coordinate system. During calibration, the robot simply needs to move to these pre-defined points and capture images, eliminating the need for time-consuming CAD file processing and real-time coordinate calculations
Solution Approach 2:
The system changes the measurement parameters from requiring obvious characteristic points on the workpiece to using artificially marked designated points with known coordinates. This parameter change allows the use of simple geometric markers instead of complex workpiece features, speeding up the calibration process while maintaining precision
4Measurement precision
If human teaching is used to overlap the TCP and designated points on the workpiece and record coordinates, then calibration can be completed, but operational performance is highly influenced by user experience and tool center may collide with the workpiece
Solution Approach 1:
The patent replaces manual human teaching operations with an automated optical measurement system. The image sensor mounted on the end effector automatically captures images of designated points, and the controller automatically calculates TCP position and workpiece coordinates through image processing and coordinate transformation, eliminating human error and collision risks
Solution Approach 2:
The system implements feedback by using the image sensor to continuously monitor the position of the end effector relative to designated points on the workpiece. The controller processes these images and provides real-time feedback on positioning accuracy, automatically adjusting the TCP position until precise alignment is achieved, thereby eliminating the need for manual trial-and-error teaching
Data Source
AI summary
An automated calibration system for a workpiece coordinate frame of a robot includes a physical image sensor having a first image central axis, and a controller for controlling the physical image sensor adapted on a robot to rotate by an angle to set up a virtual image sensor having a second image central axis. The first and the second image central axes are intersected at an intersection point. The controller controls the robot to repeatedly move back and forth a characteristic point on the workpiece between these two axes until the characteristic point overlaps the intersection point. The controller records a calibration point including coordinates of joints of the robot, then the controller moves another characteristic point and repeats the foregoing movement to generate several other calibration points. According to the calibration points, the controller calculates relative coordinates of a virtual tool center point and the workpiece to the robot.