Lift truck control systems

• US 4,942,529 A
• Filed: 05/26/1988
• Issued: 07/17/1990
• Est. Priority Date: 05/26/1988
• Status: Expired due to Term

• Current Assignee: The Raymond Corporation (Toyota Motor Corporation)
• Original Assignee: The Raymond Corporation (Toyota Motor Corporation)
• Inventors: Allen, Ralph, Radley, David J., Kellogg, David L., Avitan, Isaac, Page, Stephen L.
• Primary Examiner(s): Black, Thomas G.
• Application Number:
  US07/199,782
• Time in Patent Office: 782 Days
• Field of Search: 364/424.07, 364/463, 364/550, 364/571, 340/685, 414/636, 180/282, 180/290
• US Class Current: 701/50
• CPC Class Codes: B60L 15/20 for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
• CPC Class Codes: B60L 2200/42 Fork lift trucks
• CPC Class Codes: B60L 2240/12 Speed
• CPC Class Codes: B60L 2260/46 by self learning
• CPC Class Codes: B66F 17/003 for fork-lift trucks
• CPC Class Codes: B66F 9/24 Electrical devices or systems
• CPC Class Codes: F15B 15/2838 with out using position sensors, e.g. by volume flow measurement or pump speed
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility

Abstract

A travel speed limiting control system for lift trucks, particularly of the "orderpicker" type, having an extendible mast, is disclosed. The truck travel speed which the operator can command is limited by factors including load weight, load elevation, heading angle and direction of truck travel (forward or reverse) . Optionally, other factors may be involved, such as lateral tilt and load moment. An algorithm including the desired input factors is continually processed by an on-board microcomputer to provide an instantaneous speed limit signal. In addition to its normal operating mode, the microcomputer is also arranged to operate in a "learn" mode, whereby it runs through the ranges of various input signals and develops a set of stored values which indicate the allowable ranges of the inputs, as well as offset or bias values which compensate for manufacturing tolerances occurring in the components of the system.

Claims

1. In a lift truck having a steerable base frame, a mast, a hydraulic lift system operable to move a load carriage along said mast to raise and lower a payload, a traction motor system for driving said truck, and an operator control for generating a speed request signal for requesting variation of the speed of said traction motor system, the combination comprising:

(a) means for deriving a first signal commensurate with the position of said load carriage along said mast;

(b) means for deriving a second signal commensurate with the steering angle of said base frame;

(c) means for deriving a third signal commensurate with the weight of the payload on said load carriage; and

(d) means responsive to said first, second, third, and speed request signals for providing a speed limit signal, said speed limit signal being supplied to said traction motor system to limit the speed of said truck.

2. The lift truck as claimed in claim 1, wherein said means for providing the speed limit signal includes a microcomputer.

3. A lift truck as claimed in claim 1, wherein said means for deriving said first signal comprises means for sensing fluid flow into and out of said hydraulic lift system.

4. The lift truck of claim 3 wherein said means for sensing fluid flow is operative to provide quadrature encoded pulse trains for detecting direction of flow and flow rate.

5. The apparatus of claim 3, wherein the fluid flow sensing means is a quadrature flow sensor.

6. The apparatus of claim 3, wherein the hydraulic lift system includes a lift cylinder, the fluid flow sensing means is in fluid communication with the lift cylinder, and the fluid flow sensing means includes a means for generating a pulse each time a first volume of hydraulic fluid passes into or out from the lift cylinder.

7. A lift truck as claimed in claim 1, wherein said means for deriving said third signal includes means for sensing the pressure in said hydraulic lift system.

8. In a lift truck having a steerable base frame, a mast, a hydraulic lift system operable to move a load carriage along said mast to raise and lower a payload, a traction motor system for driving said truck, and an operator control for generating a speed request signal for requesting variation of the speed of said traction motor system, the combination comprising;

(a) means for deriving a first signal commensurate with the position of said load carriage along said mast;

(b) means for deriving a second signal commensurate with the steering angle of said base frame;

(c) means for deriving a third signal commensurate with the weight of the payload on said load carriage;

(d) means for deriving a fourth signal commensurate with the direction of travel of said truck; and

(e) means responsive to said first, second, third, fourth, and speed request signals for providing a speed limit signal, said speed limit signal being supplied to said traction motor system to limit the speed of said truck.

9. A lift truck having an operator control to provide an output voltage, a converter means for converting said output voltage to a digital signal, sensors for generating sensor signals indicative of operating states of the lift truck, and a computer connected to the converter means and the sensors, wherein the computer includes a non-volatile memory, and wherein the computer is programmed to generate signals for instructing an operator to position said operator control to a plurality of successive position, to generate signals for sampling said digital signal and said sensor signals when said operator control is at each of said successive positions, to generate respective digital operating state signals, and to store said digital operating state signals in the non-volatile memory, so that the stored digital operating state signals may be further processed during generation of a truck speed limit signal.

10. A control system for a lift truck having a fork, comprising:

a plurality of sensors each providing a respective output voltage,

converter means for converting the output voltages to digital signals,

a computer, programmed with a learning program for prompting the sampling of successive ones of said sensors to provide a first group of output voltages from said sensors and a corresponding first group of digital signals,

non-volatile storage means for storing said first group of digital signals, wherein the computer is also programmed to generate operating digital signals for controlling operation of the lift truck, in accordance with selected ones of said first group stored in said non-volatile storage means.

11. The system of claim 10, wherein a first one of the sensors emits electrical pulses indicative of the height of the fork, and also including:

pulse counter means for counting said electrical pulses to provide a first digital signal, wherein the computer is programmed to prompt said operator to operate a control device to cause said first one of the sensors to emit said electrical pulses, and means for storing the digital signal from said pulse counter means in said non-volatile storage means.

12. A method of operating a lift truck, including the steps of:

operating a series of controls aboard said truck to generate signals indicative of operating parameters of the truck in a learning mode;

digitizing the signals to provide a first plurality of digital signals;

storing said first plurality of digital signals in a non-volatile memory;

generating normal mode signals indicative of operating parameters of the truck in a normal operating mode;

digitizing the normal mode signals while said truck is operating in said normal operating mode to provide a second plurality of digital signals;

comparing signals of said second plurality with corresponding signals of said first plurality stored in said non-volatile memory and limiting the maximum speed of said truck in accordance with the results of said comparison.

13. In a lift truck having a mast, a load carriage for supporting a payload, and hydraulic power means for raising and lowering said load carriage and payload along said mast, the combination comprising;

(a) means for sensing the weight imposed on said hydraulic power means with a given payload supported on said load carriage to provide a first data value;

(b) means for determining the position of said load carriage along said mast to provide a second data value;

(c) data storage means containing a group of data values each representing the weight imposed on said hydraulic power means with said load carriage at a predetermined position along said mast and with a reference payload weight on said load carriage;

(d) means responsive to said second data value for selecting a data value from said group;

(e) means comprising microcomputer means for combining said selected data value and said first data value to provide a third data value commensurate with the weight of the given payload on said load carriage; and

(f) means responsive to said third data value for generating a speed limit signal for limiting the speed of said truck.

14. The combination as claimed in claim 13, also including a pair of switches for sensing the presence of said load carriage at a predetermined position along said mast, and means responsive to the operation of said switches for resetting said second data value to a predetermined value.

15. The combination as claimed in claim 13, wherein said hydraulic power means includes a lift cylinder, and said means for sensing the weight imposed on said hydraulic power means includes a pressure transducer responsive to the hydraulic pressure in said lift cylinder.

16. The combination as claimed in claim 15, wherein said means for determining the position of said load carriage includes means for sensing fluid flow into and out of said lift cylinder to provide said second data value.

17. The combination as claimed in claim 13, also including means for updating the data values of said group.

18. A method of generating speed limit values for a lift truck, comprising the steps of:

in a learning mode, storing a first set of data values representing operating parameters of the truck;

in a normal operating mode in which the truck supports a payload, deriving a second set of data values representing operating parameters of the truck, including a data value representing the weight of the payload;

processing the first and the second set of data values to generate an instantaneous truck velocity signal and an instantaneous dynamic speed limit signal, and controlling the speed of said truck in accordance with the value of said instantaneous dynamic speed limit signal.

19. In a lift truck having a mast, a load carriage for supporting a payload, power means for raising and lowering said load carriage and payload along said mast, and a traction motor control system, the combination comprising:

means for storing a first set of data values indicative of operating parameters of the truck in a learning mode;

means for determining the height of said load carriage and payload in a normal operating mode of the truck, and for deriving a height data value representing said height; and

means governed by said height data value and said first set of data values for governing said traction motor control system to limit the acceleration of the truck as a function of the height of the load carriage.

20. In a control system including a displacement sensitive manual control, means for providing a predetermined non-linear relationship between the position of the manual control at the mid-range of displacement of said control, and a control output signal comprising means for generating a first set of data values representing a plurality of positions of said control in each direction from its neutral or midpoint of travel, data modifying means for modifying said first set of data values to provide a second set of data values having a desired non-linear relationship to said first set of data values and means for generating a control output signal from said second set of data values.

21. In a lift truck having a steerable base frame, a mast, a hydraulic lift system operable to move a load carriage along said mast to raise and lower a payload, a traction motor system for driving said truck, and an operator control for generating a speed request signal for requesting variation of the speed of said traction motor system, the combination comprising;

(a) means for deriving a first signal commensurate with the position of said load carriage along said mast;

(b) means for deriving a second signal commensurate with the steering angle of said base frame;

(c) means for deriving a third signal commensurate with the weight of the payload on said load carriage;

(d) means for deriving a fourth signal commensurate with the instantaneous location of the center of gravity for said truck; and

(e) means responsive to said first, second, third, fourth, and speed request signals for providing a speed limit signal, said speed limit signal being connected to said traction motor system to limit the speed of said truck.

22. The apparatus of claim 21, wherein the fourth signal is generated from the first, second third, and speed request signals.