Increasing precision of encoder output

Abstract

An output of a rotary or linear encoder of lower-precision (a subject encoder) is corrected according to that of higher-precision (a reference encoder) to provide higher precision output signals. In the present invention, a frequency multiplied pulse signal is obtained by multiplying a low precision output of a subject encoder by a multiplier. The number of pulses comprised in a portion of the multiplied pulse signal corresponding to a unit movement length of an object connected to the subject encoder is obtained by a hardware operation or by a program stored into a memory. A higher-precision output signal is obtained by dividing the frequency of the multiplied-frequency pulse signal of the subject encoder by a variable divisor corresponding uniquely to the number of high precision reference pulses between low precision subject encoder pulses when the object and the subject encoder are connected and moved. The various divisors can be stored as binary data consisting of high and low states corresponding to a unit movement length obtained by dividing the frequency of an output of the reference encoder at each pulse occurrence of the multiplied frequency pulse signal of the subject encoder. The storage for the divisors is preferably an EPROM which, along with the subject encoder, is connected to a calibration device for determining the high precision divisors. The EPROM and the subject encoder are removable from the calibration device for connection to an image reproduction device.