A PLD based encoder interface with accurate position and velocity estimation

Several industrial applications require accurate displacement resolution and high accuracy speed estimates. This paper describes a new architecture to process pulses coming from an optical incremental encoder, deriving information about absolute position and velocity. Encoder interface circuitry has been implemented in VHDL by a programmable device and can be easily interfaced with low-cost microcontrollers. The time elapsed between two subsequent readouts is managed by the processor according to previous estimates. In this way it is possible to obtain high accuracy even at low rotational speed. If needed, acceleration estimates could be obtained by digital differentiation. The use of low-cost microcontrollers has led to the development of an adequate division algorithm that allows a ±0.5 Hz resolution over a range from MHz to a few Hz, being upper limited by position counter and lower limited by time counter size. The main goal of this solution is the simplicity despite of the high accuracy.