Patent ID: 6463009
Filing Date: 2002-10-08
Classification: B66F,F15B,G01S,Y10S

Abstract:
A position detecting device for detecting a position of a movable member, which moves within a hydraulic cylinder, by using an ultrasonic wave, the device comprising:an ultrasonic wave sensor which emits the ultrasonic wave toward the movable member and receives the ultrasonic wave reflected by the movable member; position calculating means for counting a time elapsed from an emission of the ultrasonic wave to a reception of the reflected ultrasonic wave by the ultrasonic wave sensor to calculate a position of the movable member relative to the ultrasonic wave sensor on the basis of the time elapsed thus counted; a temperature sensor which detects a temperature of fluid through which the ultrasonic wave is propagated within the cylinder; and reception sensitive level setting means for variably setting a reception sensitive level for the ultrasonic wave received by the ultrasonic wave sensor, wherein the reception sensitive level setting means sets the reception sensitive level for the ultrasonic wave based on the temperature of the fluid detected by the temperature sensor, so as to include a range in which it is made consecutively higher as the temperature of the fluid detected by the temperature sensor is made higher.