US 4,491,918 AGranted

Method and system for horizontally controlling a fork for a fork lift truck

AssigneesKabushiki Kaisha Toyoda Jidoh Shokki Seisakusho, Meidensha Corporation

InventorsKatsumi Yuki, Susumu Yoshida, Mineo Ozeki, Yasuyuki Miyazaki, Masaru Kawamata

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Abstract

A method and system for horizontally controlling a fork for a fork lift truck to be positioned at a position parallel with respect to the ground, according to the loads mounted on the fork. The target backward tilting angle of the upright is previously determined as a function of the load on the fork and stored in a memory of a microcomputer. Therefore, the microcomputer outputs an upright forward/backward tilting operation command signals to a tilt servo mechanism on the basis of signals outputted from a load sensor and a potentiometer to detect upright tilt angles. The tilt servo mechanism according to the present invention can adjust and stop the upright at a target backward tilting angle at a low speed without applying a shock to the load.

Claims12

Dependent claims

A method of controlling a fork movably supported by an upright of a fork lift truck to attain, by means of a microcomputer, a position parallel with respect to the ground according to loads mounted on the fork, which comprises the steps of:

(a) predetermining target upright backward tilting angles according to various loads mounted on the fork for keeping the fork parallel with respect to the ground;
(b) storing the predetermined target upright backward tilting angles into a memory of the microcomputer;
(c) detecting an actual load mounted on the fork;
(d) selecting a target upright backward tilting angle stored in the microcomputer memory corresponding to the detected actual load;
(e) detecting an actual upright tilt angle with respect to a neutral position vertical to the ground;
(f) comparing the detected actual upright tilt angle with the stored target upright backward tilting angle;
(g) outputting an upright backward tilting operation command signal when the detected actual upright tilt angle is less than the stored target upright backward tilting angle, outputting an upright forward tilting operation command signal when the detected actual upright tilt angle is greater than the stored target upright backward tilting angle, and outputting an upright neutral position command signal when the detected actual upright tilt angle is equal to the stored target upright backward tilting angle;
and
(h) adjusting the upright position in response to the outputted upright tilting operation command signals to provide an actual upright tilt angle substantially equal to the target upright backward tilting angle,
whereby the fork of the fork lift truck is kept parallel with respect to the ground.

7 more elements

A system for controlling a fork movably supported by an upright of a fork lift truck attain a position parallel with respect to the ground, according to loads mounted on the fork, which comprises;

(a) a hydraulic tilt cylinder (7) for adjusting the vertical position of the upright;
(b) a hydraulic lift cylinder (6) for lifting or lowering the fork;
(c) a first potentiometer (21) mechanically linked with said hydraulic tilt cylinder for detecting upright forward or backward tilt angles and for outputting signals (I.sub.1) corresponding thereto;
(d) a load sensor (24) mechanically linked with said hydraulic lift cylinder for detecting the load mounted on the fork and for outputting signals corresponding thereto;
(e) an A-D converter (22) connected to said first potentiometer for converting the analog signal indicative of upright tilt angle into the digital signal corresponding thereto;
(f) a microcomputer (23) including:
(1) an input interface (231) connected to said A-D converter for inputting the converted digital tilt angle signals into said microcomputer, and connected to said load sensor for converting the detected analog load signals into the corresponding digital load signals and inputting the signals into said microcomputer;
(2) a RAM (235);
(3) a ROM (234) for storing preestablished program sequences and target upright backward tilting angles to be previously set for keeping the fork parallel with respect to the ground according to various loads mounted on the fork;
(4) a CPU (233) for selecting a target upright backward tilting angle from among the ones stored in said ROM in accordance with the detected digital load signal, comparing the detected digital upright backward tilt angle with the selected target upright backward tilting angle, and outputting an upright forward tilting operation command signal a when the detected upright backward tilt angle is beyond the selected target upright backward tilt angle, an upright backward tilting operation command signal b when the detected upright backward tilt angle is below the selected target upright backward tilt angle, and an upright neutral position command signal when both the angles are equal to each other;
(5) an output interface (232) for outputting the upright tilting command signals a or b from the microcomputer;
(g) a tilt control valve (27) connected between said microcomputer and said hydraulic tilt cylinder for switching the direction of flow of hydraulic fluid supplied into said hydraulic tilt cylinder in order to tilt the upright backward or forward in response to the upright forward/backward tilting command signals a and b outputted from said microcomputer.

9 more elements

Dependencies are inferred from the claim text.