Lift cyclinder and mast assembly of forklift

摘要

An ultrasonic sensor (26) detects whether a piston (30) is at the lowest position. The sensor (26) is not affected by the environment or damaged by contact with other objects. The sensor (26) is located in the bottom of a mast cylinder (10), transmits ultrasonic waves to the bottom of a piston (30) and receives ultrasonic waves reflected by the piston (30). The sensor (26) then outputs electric signals based on the received ultrasonic waves. The ultrasonic sensor (26) is electrically connected to a transmitter-receiver (47), which, in turn, is electrically connected to a controller (48). The transmitter-receiver (47) includes an ultrasonic wave generator and sends ultrasonic wave transmitting signal having a predetermined frequency to the ultrasonic sensor (26) based on control signals from the controller (48). The controller (48) measures time from when it outputs the ultrasonic wave transmitting signal to when the sensor (26) receives a reflected wave. The controller (48) then compares the measured time with a threshold value thereby judging whether the piston (30) is at the lowest position.