A high-resolution interpolator for incremental encoders by two-phase type PLL method

Incremental type high-resolution encoders are widely used in NC machines to detect rotary angle or linear displacement. However, since the maximum speed of the high-resolution encoder is very low due to the limitation of response-frequency, we can not use it for high-speed NC machines. The authors solved this problem of the response frequency by using an encoder of which the wavelength is extremely long but the pitch accuracy is high enough. In general, long wave encoders require high-accuracy, high-resolution interpolators to obtain a high-accuracy, high-resolution pulse. However, the maximum input frequency of high-resolution interpolators is too low to be used for the high-speed NC machine. Therefore, the two-phase type PLL proposed by T. Emura was used to raise the input frequency of the interpolator. This two-phase type PLL has reversible characteristic for phase angle of input signal and strong ability for noise reduction. Using a long-wave, high-accuracy magnetic scale and an induction type magnetic head, we succeeded in detecting the angular position with extremely high resolution at the maximum input frequency of 360 kHz. This paper describes a high-accuracy, high-resolution, highspeed interpolator realized by two-phase type PLL