Robot End Effector Calibration Using Local Positioning System
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Solution Overview
Problem
In robotic systems used for composite non-destructive inspection and assembly, accurately determining the location of a workpiece relative to the robot base is challenging due to variations in support fixturing and 3D coordinate changes, leading to the need for re-programming motion paths for each new workpiece, which is time-consuming and costly.
Innovation Solution
A local positioning system (LPS) is used to calibrate the location of the end effector relative to the workpiece, allowing for relative location feedback to adjust the robot's position and orientation, enabling the reuse of pre-programmed motion paths by measuring target markers on both the workpiece and the robot base, and modifying the motion plan program accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motion paths are re-programmed for each new workpiece to compensate for position and orientation variations, then inspection accuracy is improved, but production time and cost increase
Solution Approach 1:
A calibration workpiece with known geometric features is used to pre-determine the transformation matrix between the workpiece coordinate system and robot base coordinate system before actual inspection. This preliminary calibration step allows the robot to accurately locate subsequent workpieces without requiring full re-programming, thus maintaining inspection accuracy while reducing production time.
Solution Approach 2:
The system uses measured positions of alignment features on the calibration workpiece to compute and apply a transformation matrix that compensates for variations in workpiece location and orientation. This feedback mechanism enables the robot to adapt to position variations automatically, eliminating the need for time-consuming manual re-programming while maintaining precision.
2Measurement precision
If motion paths are re-programmed for each new workpiece to account for support fixturing variations, then positioning accuracy is improved, but operational complexity increases
Solution Approach 1:
A calibration workpiece with precisely manufactured alignment features serves as an intermediary between the robot and the variable support fixturing. By measuring features on this intermediate calibration piece, the system indirectly determines the transformation matrix needed for accurate positioning, simplifying the operation compared to direct measurement and programming for each workpiece.
Solution Approach 2:
The calibration workpiece creates a copy or representation of the ideal coordinate system transformation. By using this calibrated reference, the system can replicate the correct positioning approach for multiple subsequent workpieces without repeating the complex measurement and programming process each time, thus reducing operational complexity while maintaining accuracy.
3Manufacturing precision
If 3D coordinates of workpiece features are measured and used to adjust motion paths, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The system replaces complex mechanical measurement and adjustment mechanisms with an optical/laser-based measurement approach. By using a laser scanner or vision system to measure alignment features on the calibration workpiece, the transformation matrix is computed automatically, eliminating the need for complex mechanical gauges, fixtures, and manual measurement procedures while achieving high motion path accuracy.
Data Source
AI summary
Systems and methods for calibrating the location of an end effector-carrying apparatus relative to successive workpieces before the start of a production manufacturing operation. The location calibration is performed using a positioning system. These disclosed methodologies allow an operator to program (or teach) the robot motion path once and reuse that path for subsequent structures by using relative location feedback from a measurement system to adjust the position and orientation offset of the robot relative to the workpiece. When each subsequent workpiece comes into the robotic workcell, its location (i.e., position and orientation) relative to the robot may be different than the first workpiece that was used when developing the initial program. The disclosed systems and methods can also be used to compensate for structural differences between workpieces intended to have identical structures.