US 6,296,081 B1Granted

Lift cylinder and mast assembly of forklift

AssigneeKabushiki Kaisha Toyoda Jidoshokki Seisakusho

InventorsKatsumi Nagai, Takaki Ogawa, Yasuhiko Naruse

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Abstract

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

Claims8

Dependent claims

A lift cylinder comprising:

a cylinder body, the cylinder body being occupied by oil;
a piston that is moved axially in the cylinder body by oil pressure within a limited range of movement;
a transducer device located near one end of the cylinder body out of the range of movement of the piston, wherein, in response to an electric signal, the transducer device transmits an ultrasonic signal toward a reflective surface that moves integrally with the piston, and the transducer device receives an ultrasonic signal reflected from the reflective surface and produces an electric signal corresponding to the received ultrasonic signal;
a temperature sensor located in the cylinder body to detect the temperature of the oil;
and
a controller for judging whether the piston is fully retracted, wherein the controller derives a current threshold value from the currently detected oil temperature based on a predetermined relationship between oil temperatures and threshold values, and wherein the controller produces a measured value that represents the time period from when an ultrasonic signal is sent to when a reflection of the ultrasonic signal is received by the transducer device and wherein the controller compares the current threshold value to the measured value to determine whether the piston is fully retracted.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 09/287,835Filed 7 Apr 1999
Priority: JP 10-09899910 Apr 1998
Granted: 2 Oct 2001
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

B66F 9/08
Constructional features or details: masts; Guides; Chains
B66F 9/20
Constructional features or details: means for actuating or controlling masts, platforms, or forks
F15B 15/2884
Position sensing, i.e. means for continuous measurement of position, e.g. LVDT: using sound, e.g. ultrasound
G01S 15/88
Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems: sonar systems specially adapted for specific applications