Motion Control System for Industrial Scenarios Based on Electromagnetic Encoders

In this article, a complete system useful for the measurement of the absolute position, velocity, and acceleration of moving objects in industrial scenarios (such as conveyor transport devices, elevators, escalators, and other mechanical systems) is presented. The proposed system contains an electromagnetic encoder consisting of a pair of chains of metallic patches screen-printed on a rubber belt. In one of the chains (designated as clock/velocity chain), the patches are printed at predefined periodic positions. Such clock chain also generates the clock signal necessary to read the other chain (position chain), with patches either present (binary state "1") or absent (binary state "0") at their predefined positions. The system includes a reader based on a transmission line with three resonators etched on the ground plane and fed with three harmonic signals. Such three elements are complementary split ring resonators (CSRRs), which are sensitive to the presence of patches at short distance on top of them, and therefore, they are used to detect the patches as the encoder moves with regard to the reader. By encoder motion, the patches generate three amplitude modulation (AM) signals, providing the velocity (and acceleration), the absolute encoder position, and the motion direction. A prototype system, including the encoder, the reader, and the associated electronics, is designed, fabricated, and validated.