Abstract
High precision position control is essential in the process of parts manufacturing and assembling, where eddy current displacement sensors (ECDSs) are widely used owing to the advantages of non-contact sensing, compact volume, and resistance to harsh conditions. To solve the nonlinear characteristics of the sensors, a high-accuracy calibration method based on linearity adjustment is proposed for ECDSs in this paper, which markedly improves the calibration accuracy and then the measurement accuracy. After matching the displacement value and the output voltage of the sensors, firstly, the sensitivity is adjusted according to the specified output range. Then, the weighted support vector adjustment models with the optimal weight of the zero-scale, mid-scale and full-scale are established respectively to cyclically adjust the linearity of the output characteristic curve. Finally, the final linearity adjustment model is obtained, and both the calibration accuracy and precision are verified by the established calibration system. Experimental results show that the linearity of the output characteristic curve of ECDS adjusted by the calibration method reaches over 99.9%, increasing by 1.9–5.0% more than the one of the original. In addition, the measurement accuracy improves from 11–25 m to 1–10 m in the range of 6mm, which provides a reliable guarantee for high accuracy displacement measurement.
Highlights
Online precise displacement measurement and positioning are important parts of the manufacturing process quality inspection system [1]
The linearity adjustment model established in this paper is divided into the following steps: (a) Firstly, adjust the sensitivity of the original calibration result by regulating the voltage u to the required output range; (b) partition adjustment is adopted on the account of targeted adjustments to the deviations of different regions; mid-scale, zero-scale and full-scale adjustments are determined for operation convenience and universality; (c) the iterate adjustment function to perform overall fine-tuning until the sensitivity, linearity and required voltage output range meet the requirements
ΜSVM is adopted for two reasons: firstly, support vector machine (SVM) method can adjust the nonlinearity moderately avoiding overfitting, due to the introduction of slack variable; secondly, targeted nonlinearity adjustment is achieved by the determination of weight coefficient μ
Summary
Online precise displacement measurement and positioning are important parts of the manufacturing process quality inspection system [1]. In order to obtain better performance of the sensor, much research has been conducted for improving the sensitivity, optimizing the circuit design and high-accuracy calibration. A high accuracy calibration method based on linearity adjustment has been proposed, which combines the weighted support vector machine and the cyclical linearity adjustments of the output characteristic curve, consist of mid-scale adjustments, zero-scale adjustments and full-scale adjustments. Both accuracy and precision of ECDs are discussed.
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