Estimation of Acceleration with an AC Tachogenerator and its Application for Servo Control

In order to control an electric servo motor precisely, the state variables of the motor should be known exactly. For that purpose, position sensor, velocity sensor and current sensor are mainly used. However sufficient control performance is not always obtained when the fluctuations of the parameters such as torque constant and inertia moment are excited, or when a large step-like load is imposed. In particular, these problems are serious in the robot controller or the numerical controller in the machine tools. To overcome these problems, an advanced control method which also utilizes the information of the acceleration has been proposed recently. Since the practical angular accelerometer is not available, the differentiation of the speed signal is carried out to obtain the acceleration signal. This method does not give the precise acceleration signal to the controller due to the noise problem in the high frequency area. More effective method should be developed. In this paper, a method which estimates an accurate acceleration by using both a position sensor and an AC tachogenerator is proposed. In the proposed method, the higher harmonic component except the fundamental component in the AC tachogenerator outputs is cancelled out by the proposed method based on the Fourier analysis. Because of a considerable amount of the comprehensive calculation, the digital signal processor (DSP) will be applied to the real applications. Several experimental results based on the proposed method with DSP are also shown.