(a) A position sensor is used in a microprocessor-based feedback control system for accurately moving the cutter blades of an automated meat-cutting machine. The machine is an integral part of the production line of a meat processing plant. What are the primary considerations in selecting the position sensor for this application? Discuss the advantages and disadvantages of using an optical encoder in comparison with an LVDT in this context.
(b) Figure P6.50 illustrates one arrangement of the optical components in a linear incremental encoder.
The moving code plate has uniformly spaced windows as usual, and the fixed masking plate has two groups of identical windows, one above each of the two photodetectors. These two groups of fixed windows are positioned in a half-pitch out of phase so that when one detector receives light from its source directly through the aligned windows of the two plates, the other detector has the light from its source virtually obstructed by the masking plate. Explain the purpose of the two sets of photodiode-detector units, giving a schematic diagram of the necessary electronics. Can the direction of motion be determined with the arrangement shown in Figure P6.50? If so, explain how this could be done. If not, describe a suitable arrangement for detecting the direction of motion.