Input circuit of a fork lift truck control system for a fork lift truck

摘要

An improved fork lift truck control system using a microcomputer, which comprises a sensing unit including a first sensor for detecting a lift height of a fork above its lowest position and a second sensor for detecting a tilting angle of an upright with respect to a neutral position of the upright including an input interface circuit for interfacing the sensing unit and control unit which has: (a) a lifting height counting circuit which counts the number of pulses produced on a basis of two photo-converted electrical signals fed from two photocouplers constituting the first sensor, the signals having a phase difference of 90 DEG from each other, so that an accurate measurement of the lifting height of the fork can be made; (b) an analog-to-digital converter which produces a bit string according to an output signal from the second sensor; and (c) an abnormal detection facility which detects a defective analog-to-digital converter and second sensor by comparing the bit string presently outputted from the analog-to-digital converter with each of predetermined bit strings that would be produced if the analog-to-digital converter operates normally.