NONLINEARITY COMPENSATION AND ACCURACY IMPROVEMENT METHOD FOR AN OPTICAL ROTARY ENCODER

This paper presents a method for the nonlinearity compensation of an optical rotary encoder. The proposed method is based on the application of 1) a special 4-bit mixed analog-digital circuit used for the generation of a quasi-linear signal, and 2) a two-stage nonlinear ADC which performs linearization and digital conversion of the quasi-linear signal at the same time. The quasi-linear signal is obtained by combining fragments of phase-shifted sinusoidal signals, where each fragment is presented with a 4-bit digital code. In the continuation, the quasi-linear signal is linearized with the two-stage nonlinear ADC of a compact design based on the application of a single flash ADC in both conversion stages. Additionally, the design of the flash ADC is modified so that the number of employed comparators is equal to the resolution of the flash ADC. For instance, by linearizing an optical rotary encoder using the 4-bit mixed analog-digital circuit and the 20-bit two-stage nonlinear ADC containing 10 comparators, the maximal value of the absolute measurement error can be reduced to 3.23·10-5°

A METHOD OF REDUCING THE ERROR IN DETERMINING THE ANGULAR DISPLACEMENTS WHEN USING INDUCTIVE SENSORS

Goal. Representation of a special mathematical software for determining the angular displacements of the rotor of the induction angle sensor – resolver (rotating transformer) for applications in which the speed of the sensor's rotor is close to zero. As well as performing its experimental verification. Methodology. The presented method is based on the determination of the phase shift angle of the output signals of the induction sensor, which is determined by comparing the obtained arrangements of signal values with a circular discrete convolution in order to achieve the most precise approximation of the obtained signal values to cosine and sine. The conversion of orthogonal components to an angle is based on the use of a digital phase detector which is use of a software comparator and inverse trigonometric functions. Results. Based on the obtained results of mathematical modeling and experimental research, the characteristic dependencies of the angle of rotation of the rotor of the induction sensor relative to its stator, the nature of which is linear, were obtained. In addition, the estimation of measurement errors of angular displacements is carried out that occur when defining such angles by the method offered. The obtained results of the computer simulation taking into account the high signal noise, as well as the results of experimental investigations, confirm the high precision of this method and the fact that it can be used in systems where high positioning accuracy is required and the speed of the sensor shaft is close to zero. Originality. This article introduces, for the first time, special mathematical software for a new method of determining the angular displacements of the rotor of an induction sensor, which is based on the determination of the orthogonal components of the signal in combination with the use of a circular discrete convolution in the determination of the phase shift angle of the induction sensor signals. Practical meaning. The proposed method does not require the use of demodulators, counters and quadrant tables associated with conventional methods for determining the phase shift of signals. The presented method can be used to measure the full range of 0-2p angular displacements in real time, is simple and can be easily implemented using digital electronic circuitry

A resolver-to-digital conversion method based on third-order rational fraction polynomial approximation for PMSM control

—In this paper, a cost-effective and highly accurate resolver-to-digital conversion (RDC) method is presented. The core of the idea is to apply a third-order rational fraction polynomial approximation (TRFPA) for the conversion of sinusoidal signals into the pseudo linear signals, which are extended to the range 0-360° in four quadrants. Then, the polynomial least squares method (PLSM) is used to achieve compensation to acquire the final angles. The presented method shows better performance in terms of accuracy and rapidity compared with the commercial available techniques in simulation results. This paper describes the implementation details of the proposed method and the way to incorporate it in digital signal processor (DSP) based permanent magnet synchronous motor (PMSM) drive system. Experimental tests under different conditions are carried out to verify the effectiveness for the proposed method. The obtained maximum error is about 0.0014° over 0-360° , which can usually be ignored in most industrial applications. Index Terms—Arc tangent function, Analog processing circuits, Pseudo linear signals, Resolver-to-digital conversion (RDC), Third-order rational fraction polynomial approximation (TRFPA)

A resolver-to-digital conversion method based on third-order rational fraction polynomial approximation for PMSM control

In this paper, a cost-effective and highly accurate resolver-to-digital conversion (RDC) method is presented. The core of the idea is to apply a third-order rational fraction polynomial approximation (TRFPA) for the conversion of sinusoidal signals into the pseudo linear signals, which are extended to the range 0-360° in four quadrants. Then, the polynomial least squares method (PLSM) is used to achieve compensation to acquire the final angles. The presented method shows better performance in terms of accuracy and rapidity compared with the commercial available techniques in simulation results. This paper describes the implementation details of the proposed method and the way to incorporate it in digital signal processor (DSP) based permanent magnet synchronous motor (PMSM) drive system. Experimental tests under different conditions are carried out to verify the effectiveness for the proposed method. The obtained maximum error is about 0.0014° over 0-360°, which can usually be ignored in most industrial application

A novel PLL resolver angle position indicator

This paper describes a novel and high-performance phase-locked loop (PLL) resolver converter for the measurement of mechanical angles. The proposed method does not require the use of demodulators, voltage-controlled oscillator, digital-to-analog converter, counter, and lookup tables, that are associated with conventional PLL converters. The proposed method employs full-wave rectifiers to obtain the absolute values of the modulated resolver signals. This scheme results in a triangular output voltage and two binary outputs that represent a measure of the input angle. The required sine and cosine of the estimated angle, which are needed for PLL converters, are determined using simple approximation techniques. The proposed method can be used to measure angles in the full 360° range, is simpler than the available techniques, and may be easily implemented using digital or basic analog electronic circuitry. This paper describes the proposed method, full details of its implementation using standard electronic components, and experimental results. The performance of the proposed converter is comparable with that of a commercial product.Scopu