Industrial Robot Calibration Using Automated Optical Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current calibration methods for industrial robot systems are time-consuming and dependent on operator skill, leading to inaccuracies and complications when replacing robots or positioners, especially in multi-robot and multi-station setups, where precise alignment of coordinate systems is required for high-accuracy processing tasks like welding.
Innovation Solution
A method involving at least three calibration objects with known positions in the object coordinate system, using a calibration tool to determine their positions in the robot coordinate system, rotating the positioner to establish the rotational axis direction, and performing a best-fit transformation to define the positioner and object coordinate systems, allowing for automated and skill-independent calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If manual jogging of TCP to reference points is used to define coordinate systems, then the process is simple to perform, but calibration accuracy deteriorates due to operator skill dependency
Solution Approach 1:
The patent replaces manual mechanical jogging of the TCP with an automated optical measurement system. A measurement device with cameras captures images of calibration objects, and a computer automatically calculates positions and orientations, eliminating operator skill dependency while improving accuracy.
Solution Approach 2:
The patent introduces calibration objects (spheres, planes, or cylindrical features) as intermediaries between the measurement device and the robot system. These objects provide precisely measurable reference features that facilitate accurate coordinate system definition without direct manual intervention.
2Ease of manufacture
If conventional calibration methods are used, then the process is straightforward, but calibration time increases and productivity decreases
Solution Approach 1:
The patent performs calibration operations automatically after the robot cell is assembled but before production begins. The measurement device captures images and the computer calculates coordinate transformations in advance, enabling fast production startup without time-consuming manual calibration during production setup.
Solution Approach 2:
The calibration system is self-calibrating through automated image capture and computer-based calculation of coordinate systems. The system performs its own calibration without requiring extensive manual intervention, reducing calibration time and enabling faster production deployment.
3Speed
If robot replacement is performed without precise calibration, then the replacement process is fast, but path accuracy with respect to workpiece deteriorates
Solution Approach 1:
The patent defines coordinate systems with respect to the fixture and workpiece rather than the robot, creating a universal reference framework. This allows different robots to work on the same workpiece using the same coordinate system, enabling quick robot replacement without reprogramming while maintaining path accuracy.
4Speed
If positioner replacement is performed without recalibration, then the replacement is quick, but coordinate system alignment accuracy deteriorates
Solution Approach 1:
The patent defines the positioner coordinate system with respect to the rotational disc and fixture rather than the positioner motor assembly. This creates a universal reference that remains valid when the positioner is replaced, allowing quick replacement while maintaining coordinate system alignment accuracy through automated recalibration.
Data Source
AI summary
An industrial robot system has at least one robot (1) having a robot coordinate system (xr1, yr1, zr1) and a positioner (2) having a positioner coordinate system (xp, yp, zp) and adapted to hold and change orientation of a workpiece by rotating about a rotational axis. Target points for the robot are programmed with respect to an object coordinate system (xo1, yo1, zo1). A robot controller (3), at least three calibration objects (24a-c) arranged on the positioner, and a calibration tool (26) held by the robot are provided. The positions of the calibration objects are determined for at least three different angles of the rotational axis of the positioner, to determine the direction of the rotational axis of the positioner and relation between the object coordinate system and the positioner coordinate system by performing a best fit between known and determined positions of the calibration objects.