Microwave Encoders with Synchronous Reading and Direction Detection for Motion Control Applications

A microwave system based on electromagnetic encoders useful for motion control applications is presented in this paper. The encoders are implemented by etching two chains (one acts as a clock for synchronous reading and the other one contains the identification) of rectangular patches, on a dielectric substrate. For motion control, the encoder must be in relative movement with regard (and in close proximity) to the reader, an element able to detect the presence of patches through microwaves. The specific developed reader (sensitive part) consists of a microstrip line conveniently loaded with three resonant elements tuned at different frequencies. By injecting three harmonic signals (tuned to the resonator frequencies) to the input port of the reader line, the chains modulate the amplitude of such signals, provided the encoder is in relative motion with regard to the reader. The envelope functions of such AM signals thus contain the clock information (as peaks in the envelope function), the ID code (with maxima or minima in the envelope function), and the motion direction information (the lag or lead between the clock signal and the redundant signal). In order to demonstrate the potential of the approach, a prototype encoder/reader is designed, fabricated, and validated.