Direct velocity estimation for encoders using nonlinear period measurement

Abstract

A method and apparatus for providing a direct velocity of a moving object using nonlinear period measurement. A pulse signal from an encoder indicates the detection of a passage of a point on a moving sensor element, such as a mark on an encoder disk. A counter is then made to count down from a higher value to a lower value, where counts by the counter are made at a variable, nonlinear rate. The rate is faster when the count begins and gets slower as the count continues, reducing the possibility that the counter will overflow before the next encoder signal is received. The counter value is output and the counter is reset when another encoder signal is received, where the output value is directly related to the velocity of the object. In a different method and apparatus, first and second values, such as PWM or DAC commands, are provided to an actuator to output as forces. The values are differenced a rate of change of the force values is determined. A force is output according to the rate of change until another force value is received, allowing more stable and continuous force output.