Robot Calibration Using Visual Sensor Error Compensation
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Solution Overview
Problem
Conventional robot calibration methods fail to adequately account for operational errors such as mechanical and assembly errors, leading to inaccuracies in the control of a robot's position and orientation, especially when using a multi-jointed arm with a visual sensor.
Innovation Solution
A robot calibration apparatus and method that calculates a calibrating function based on the difference between the ideal and actual positions and orientations of a robot body, using a visual sensor to adjust command values and improve accuracy by accounting for operational errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional coordinate calibrating methods are used, then the calibration process is simple, but operational errors such as mechanical error and bending at an arm cannot be sufficiently suppressed, preventing accuracy from being improved in control of the position and orientation of the robot body
Solution Approach 1:
The patent introduces a calibration object with known geometric features as an intermediary between the robot body and the measurement coordinate system. This calibration object serves as a mediator that enables accurate determination of the relationship between coordinate systems while accounting for operational errors. The calibration object's known geometry allows the system to calculate correction values that compensate for mechanical errors and arm bending, thereby improving measurement precision without significantly increasing system complexity
Solution Approach 2:
The patent replaces purely mechanical calibration methods with a hybrid approach that combines visual measurement (camera-based) with mathematical calculation. Instead of relying solely on mechanical positioning and physical alignment, the system uses image processing to detect the calibration object's position and orientation, then calculates the coordinate transformation relationships. This substitution of mechanical methods with optical and computational methods enables more accurate error compensation while maintaining operational simplicity
2Measurement precision
If hand-eye calibration method is used to acquire relationship between coordinate systems, then the calibration can be performed, but operational errors and assembly errors cannot be sufficiently suppressed, preventing accuracy improvement
Solution Approach 1:
The patent implements a feedback mechanism where the actual position and orientation of the robot body (measured through the camera and calibration object) are compared with the commanded position and orientation. The difference (error) is calculated and used to generate correction values that are applied to the coordinate transformation. This closed-loop feedback approach enables the system to compensate for operational errors and assembly errors, significantly improving both measurement precision and reliability of the coordinate transformation
Solution Approach 2:
The patent changes the parameters used in coordinate transformation from simple geometric relationships to error-compensated parameters. By measuring the actual positions and orientations during calibration and calculating the differences from ideal values, the system derives correction parameters that account for operational errors and assembly errors. These modified parameters are then used in the coordinate transformation, improving both accuracy and reliability
Data Source
AI summary
A robot calibrating apparatus calibrating a command value for a robot body 2 whose position and orientation is controlled based on the command value, includes an operating unit configured to calculate a calibrating function of calibrating the command value, based on the difference between an ideal position and orientation of the robot body 2 and an actual position and orientation of the robot body 2. The ideal position and orientation is operated based on a command value RHTcom for calibration used during calibration or on a control result value which is a result of control according to the command value. The actual position and orientation is operated based on a measurement value RHT′meas for calibration acquired by a camera 3 arranged at a prescribed relative position and orientation with respect to the robot body 2 during the robot body 2 being controlled according to the command value for calibration.