Robot Calibration Using Artificial Neural Networks
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Abstract
Robot calibration is an integrated procedure of measurement and data processing to improve and maintain robot positioning accuracy. Existing robot calibration techniques require extensive human intervention and off-line processing, which preclude the techniques from being used to perform on-site calibration in an industrial environment at regular intervals. This thesis investigates and develops intelligent calibration processing algorithms and a novel measurement method toward rapid autonomous robot calibration in a shop-floor environment.Artificial Neural Network (ANN) techniques have been vigorously investigated for calibration data processing (modelling, identification and compensation). A new identification algorithm has been developed for estimating robot kinematic parameter errors using Hopfield continuous-valued type Recurrent Neural Network (RNN). The RNN-based algorithm is computationally more efficient and robust compared with conventional optimisation approaches.A generic accuracy model which accounts for various error sources was introduced. A higher-order neural network was used for implementation of the generic accuracy model. Due to the ANN learning capability, computational power and adaptability, the ANN-based accuracy representation offers an appealing solution to the complex modelling problem.Efficient and robust accuracy compensation algorithms have been developed under the framework of artificial neural networks. The ANN-based algorithms provide constant-time inverse compensation therefore are suitable for on-line implementation. Both path compensation and compensation near robot singularity were tackled using the new algorithm.A novel autonomous calibration tool was developed using a trigger probe and a constraint plane. The new method eliminates any use of external measuring devices to determine robot end-effector location measurements, enabling the robot to perform self-calibration on a production line. Robot accuracy was improved to the level of its repeatability within the local calibration volume using the new calibration scheme, which is consistent with the results from using a precision external measuring device, in this case a Coordinate Measuring Machine (CMM)