HYDRAULIC WEIGHT DETERMINATION

Abstract

A method and device for weight determination of a load lifted by an actuator in a hydraulic lifting device are disclosed. A pressure signal is generated using a pressure gauge, a deviation signal is generated based on a flow signal and a setpoint, and a regulation signal is generated based on the deviation signal to regulate the actuator. An inclination signal is generated using an inclination gauge. The weight of the load is determined based on the pressure signal, the deviation signal, the regulation signal, and the inclination signal.

Claims

1. A method for weight determination of a load lifted by an actuator, comprising: performing at least one upward displacement of the actuator and at least one downward displacement of the actuator, wherein displacing the actuator comprises initiating a flow in a hydraulic tubing system of the actuator; generating a pressure signal based on a hydraulic pressure in the hydraulic tubing system, wherein the hydraulic pressure is determined using a pressure gauge; generating a deviation-dependent parameter via a flow signal and a setpoint, wherein the flow signal is based at least in part on a displacement speed of the actuator; generating a regulation parameter based at least in part on the deviation-dependent parameter; determining a weight of the load based at least in part on the deviation-dependent parameter and the regulation parameter; and outputting the weight of the load.

2. The method according to claim 3, further comprising determining a position-dependent parameter of the actuator using a position gauge and a position sensor, wherein determining the weight of the load is further based at least in part on the position-dependent parameter of the actuator.

3. The method according to claim 1, further comprising performing controlling a pressure relief system to reduce pressure and power consumption, and wherein the weight determination is performed using the pressure relief system to reduce the power consumption.

4. The method according to claim 3, further comprising determining an oscillation-dependent parameter based on a pressure signal or an inclination signal, wherein determining the weight of the load is further based at least in part on the oscillation-dependent parameter.

5. The method according to claim 1, further comprising determining a temperature-dependent parameter based at least in part on a hydraulic fluid temperature, wherein determining the weight of the load is further based at least in part on the temperature-dependent parameter.

6. The method according to claim 1, further comprising measuring an actuator inclination relative to a direction of the gravity to determine an inclination-dependent parameter, and wherein determining the weight of the load is further based at least in part on the inclination-dependent parameter.

7. A weighing device comprising: an actuator comprising a hydraulic tubing system; a pressure gauge; and a processor configured to: initiate a flow in a hydraulic tubing system of the actuator, wherein displacing the actuator comprises initiating a flow in a hydraulic tubing system of the actuator; generate a pressure signal based on a hydraulic pressure in the hydraulic tubing system using the pressure gauge; generate a deviation-dependent parameter via a flow signal and a setpoint, wherein the flow signal is based at least in part on a displacement speed of the actuator; generate a regulation parameter based at least in part on the deviation-dependent parameter; determine a weight of the load based at least in part on the deviation-dependent parameter and the regulation parameter; and output the weight of the load.

8. The weighing device according to claim 7, further comprising: a position gauge and a position sensor configured to measure a position-dependent parameter of the actuator; wherein the processor is configured to determine the weight of the load further based at least in part on the position-dependent parameter.

9. The weighing device according to claim 7, further comprising: a pressure relief valve configured to reduce actuator pressure and power consumption.

10. The weighing device according to claim 7, wherein the processor is further configured to determine an oscillation-dependent parameter based on a pressure signal or an inclination signal, wherein determining the weight of the load is further based at least in part on the oscillation-dependent parameter.

11. The weighing device according to claim 7, further comprising a temperature sensor, wherein the processor is further configured determine a temperature-dependent parameter based at least in part on a hydraulic fluid temperature using the temperature sensor, wherein determining the weight of the load is further based at least in part on the temperature-dependent parameter.

12. The weighing device according to claim 7, further comprising an inclination gauge configured to measure an actuator inclination relative to a direction of gravity to generate an inclination signal, and wherein the processor is configured to record the inclination signal and perform the determining of the weight based at least in part on the inclination signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Examples of the principles of the present disclosure will be explained with reference to the accompanying drawings, of which:

[0029] FIG. 1 is a diagram of a system for hydraulic weight determination in a neutral position in which a weight determination function is not in operation and where a lifting device is used in the customary way; and

[0030] FIG. 2 is a diagram of a system for hydraulic weight determination in a weighing position in which a weight determination is performed together with a hydraulic lifting device comprising an actuator carrying a load.

DETAILED DESCRIPTION

[0031] FIG. 1 is a diagram of a system for hydraulic weight determination in a neutral position in which a weight determination function is not in operation and where a lifting device is used in the customary way. In the neutral position in FIG. 1, the weight determination function is not in operation whereby the flow 20 merely passes through the tubing of the system along the flow route marked by the unbroken line. As a result of this, the flow 20 enters the tubing through a bypass valve 15 and through a gauge 18 measuring the flow to an actuator 27 whereby the load 2 is lifted.

[0032] FIG. 2 is a diagram of a system for hydraulic weight determination in a weighing position in which a weight determination is performed together with a hydraulic lifting device comprising an actuator carrying a load. In the weighing position in FIG. 2, the weight determination procedure relies on the circumstance that the load 2, which is lifted by the actuator 27, is subjected to at least one upward and one downward displacement and that the hydraulic pressure in the actuator 27 is measured by means of a pressure gauge 16.

[0033] The weighing procedure is initiated by activation of the display unit 1, which supplies a solenoid 17 with current thereby closing the bypass valve 15; this establishes a flow route marked by the unbroken line. Following this, a flow 20 equivalent to at least the magnitude of a flow as set by means of a pre-defined setpoint 3 is fed to the hydraulic lifting device. As a result of this, the flow passes into the tubing through a flow regulator 13 and through the flow gauge 18 to an actuator 27 that lifts the load 2. If the flow fed is larger than the flow set using the setpoint 3, the excessive flow 24 will pass through a pressure relief valve 22 and return to the tank 23, which reduces the power loss in the flow regulator 13 when the load 2 is lifted.

[0034] During the displacement of the actuator 27 a flow signal 11 proportional to the actuator displacement speed is sent to a summation point 6 where the flow signal 11 is compared with the setpoint 3 flow which is equivalent to a given actuator displacement speed. Thereby a deviation-dependent signal 9 is generated which via a process unit 10 and a regulation signal 12 controls that the flow regulator 13 maintains the actuator displacement speed which is set by the setpoint 3. In an alternative example, where connections 4 and 5 are established, parts of or the entire regulation circuit, consisting of 3, 6 and 10, can be performed by the display unit 1. The deviation-dependent signal 9 is transmitted to the display unit 1, where it is used as a criterion to determine when a constant and desired actuator speed has been reached and when the display unit 1 should start recording the hydraulic pressure. When the criterion has been met, the display unit 1 records the pressure for a few seconds and then demands the load 2 to be lowered, whereby the flow 25 returns from the actuator 27 along the exact same route as during the lift, only in the opposite direction.

[0035] During the lowering procedure, the actuator displacement speed is controlled in the same manner as during the lifting procedure; the flow signal 11, however, changes operational sign which can be allowed for in various ways. After a period of time equivalent to the one for the lifting procedure, the display unit 1 has recorded the pressure for the actuator displacement in both directions and the display unit 1 can now perform the weight determination procedure. During the above weighing process, the inclination of the actuator 27 is recorded via a dual-axis inclination gauge 14 and an inclination signal is generated which is used in the weight determination in order to render it more accurate.

[0036] Improvement is achieved through a process whereby a position gauge 7 detects the position of the actuator 27 via one or more position sensors 8 and generates a position signal which is used in the weight determination. As an example, the hydrostatic pressure generated by the hydraulic medium 26 depends on the position of the actuator, and on forklift trucks the varying length of chains and hydraulic tubing contributes to a variable pressure, in addition to the pressure generated by the load 2. In another method, the weight determination always starts at the same actuator position which can be performed by means of a simple position gauge in only a single point. Using the position-dependent signal, the above error contributions can be determined and eliminated.

[0037] Another improvement has been achieved by introducing a pressure relief valve 22, which reduces the hydraulic pressure thereby avoiding unnecessary power consumption during upward actuator displacement. If the flow fed when lifting the load 2 is larger than necessary in order to obtain the lifting speed defined using the setpoint 3, the excess flow 24 will return to the tank 23 through a pressure relief valve 22 at exactly the pressure necessary to lift the load 2 and defined by the pilot pressure 21.

[0038] One more improvement has been achieved in that natural oscillations in the lifting devices are detected, either via variations in the signal from the pressure gauge 16 or from the inclination gauge 14, in order to postpone the weighing process until the oscillations have stopped. The weighing accuracy is improved by measuring and compensating for temperature changes in the hydraulic system. The temperature is measured via a temperature gauge which may form an integral part of the pressure gauge 16. This way, temperature-dependent measuring errors produced by the pressure gauge can be reduced considerably.

[0039] To determine the dead load of various components of the lifting device, for example the actuator piston rod 19, a special weight determination procedure is performed without load resetting; this is done only once. In subsequent weight determination procedures, the above dead load is subtracted thereby producing the weight of the load.

[0040] The system comprising components 28, a display unit 1 and a position sensor 8 can either be provided in a single unit or be decentralised such that certain components of the system, such as flow regulator 13, pressure relief valve 22 or similar, can form part of the structure of the hydraulic lifting device.

[0041] A skilled person would be able to apply the principles described herein by following these instructions and on their own develop functions to realise variants of the principles described herein.