Method and system for estimating payload weight with hydraulic fluid temperature compensation

• US 9,200,432 B1
• Filed: 06/09/2014
• Issued: 12/01/2015
• Est. Priority Date: 06/09/2014
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Shatters, Aaron
• Primary Examiner(s): Trammell, James
• Assistant Examiner(s): Stroud, James E
• Application Number:
  US14/299,419
• Publication Number:
  US 20150354176A1
• Time in Patent Office: 540 Days
• US Class Current: 1/1
• CPC Class Codes: E02F 3/36 Component parts
• CPC Class Codes: E02F 3/40 Dippers; Buckets ; Grab devices, e.g. manufacturing processes for buckets, form, geometry or material of buckets devices to connect tools to arms or booms E02F3/3604; teeth therefor E02F9/28
• CPC Class Codes: E02F 9/2264 Arrangements or adaptations of elements for hydraulic drives
• CPC Class Codes: E02F 9/24 Safety devices , e.g. for preventing overload E02F9/226 takes precedence
• CPC Class Codes: E02F 9/264 Sensors and their calibration for indicating the position of the work tool
• CPC Class Codes: F15B 19/007 Simulation or modelling
• CPC Class Codes: G01G 19/083 lift truck scale

Abstract

A system for estimating the weight of a payload in a bucket of a machine is provided. The system includes a lift linkage supporting the bucket and a hydraulic lift cylinder assembly connected to the lift linkage. A pressure sensor is arranged remotely from the lift cylinder assembly. A payload measurement system is configured to monitor pressure data from the pressure sensor, hydraulic fluid temperature data and cylinder extension velocity data. The payload measurement system estimates a weight of the payload in the bucket based on the pressure data as adjusted by an estimate of a pressure drop between the lift cylinder assembly and the pressure sensor, the estimate of the pressure drop being determined based on a mathematical model that has been fitted to empirical data.

Claims

1. A system for estimating the weight of a payload in a bucket of a machine, the system comprising:

a pivotable lift linkage supporting the bucket;

a lift cylinder assembly connected to the lift linkage and configured to be movable by pressurized hydraulic fluid between extended and retracted positions for pivoting the lift linkage to move the bucket between raised and lowered positions;

a pressure sensor arranged remotely from the lift cylinder assembly and configured to provide pressure data relating to pressure in the lift cylinder assembly; and

a payload measurement system configured to monitor the pressure data from the pressure sensor, temperature data relating to a temperature of the hydraulic fluid in the lift cylinder assembly and extension velocity data relating to velocity of extension of the lift cylinder assembly, the payload measurement system being configured to estimate a weight of the payload in the bucket based on the pressure data as adjusted by an estimate of a pressure drop between the lift cylinder assembly and the pressure sensor, the payload measurement system being configured to determine the estimate of the pressure drop based on the temperature data, the extension velocity data and a mathematical model that has been fitted to empirical data relating to pressure loss between the lift cylinder assembly and the pressure sensor at different hydraulic fluid temperatures and lift cylinder assembly extension velocities.

2. The system of claim 1 wherein the mathematical model has been fit to the empirical data using a regression analysis.

3. The system of claim 1 wherein the payload measurement system determines the estimate of the weight of the payload from a table stored in the payload measurement system using the pressure data as adjusted by the pressure loss data.

4. The system of claim 1 wherein the mathematical model uses an equation including:

5. The system of claim 1 wherein the mathematical model uses an equation including:

6. The system of claim 1 wherein the mathematical model uses an equation including:

Δ

P_C=C

where Δ

P_C is a pressure drop resulting from the pressure sensor, and

C is a coefficient the value of which is determined by fitting the empirical data to the mathematical model.

7. The system of claim 1 wherein the pressure sensor is located adjacent a control valve for the lift cylinder assembly.

8. A method for estimating by a payload measurement system, the weight of a payload in a machine, the machine including a bucket, a lift linkage connected to the bucket, a lift cylinder assembly connected to the lift linkage and configured to be movable by pressurized hydraulic fluid between extended and retracted positions for pivoting the lift linkage, and a pressure sensor arranged remotely from the lift cylinder assembly and configured to provide pressure data relating to pressure in the lift cylinder assembly, the method comprising the steps of:

monitoring the pressure data from the pressure sensor;

monitoring temperature data relating to a temperature of the hydraulic fluid in the lift cylinder assembly;

monitoring extension velocity data relating to velocity of extension of the lift cylinder assembly;

determining an estimate of the pressure drop between the lift cylinder assembly and the pressure sensor based on the temperature data, the extension velocity data and a mathematical model that has been fitted to empirical data relating to pressure loss between the lift cylinder assembly and the pressure sensor at different hydraulic fluid temperatures and lift cylinder assembly extension velocities; and

adjusting the pressure data with the estimate of the pressure drop; and

estimating the weight of the payload in the bucket using the pressure data as adjusted by the estimate of the pressure drop.

9. The method of claim 8 wherein the mathematical model has been fit to the empirical data using a regression analysis.

10. The method of claim 8 wherein the step of estimating the weight of the payload includes looking up an estimated weight from a table stored in a payload measurement system using the pressure data as adjusted by the pressure loss data.

11. The method of claim 8 wherein the mathematical model uses an equation including:

12. The method of claim 8 wherein the mathematical model uses an equation including:

13. The method of claim 8 wherein the mathematical model uses an equation including:

Δ

P_C=C

where Δ

P_C is a pressure drop resulting from the pressure sensor, and

C is a coefficient the value of which is determined by fitting the empirical data to the mathematical model.

14. A machine comprising:

a chassis;

a bucket for holding a payload;

a lift linkage pivotally attached to the chassis and to the bucket;

a lift cylinder assembly connected to the chassis and the lift linkage and configured to be movable by pressurized hydraulic fluid between extended and retracted positions for pivoting the lift linkage to move the bucket between raised and lowered positions;

a pressure sensor arranged remotely from the lift cylinder assembly and configured to provide pressure data relating to pressure in the lift cylinder assembly; and

a payload measurement system configured to monitor the pressure data from the pressure sensor, temperature data relating to a temperature of the hydraulic fluid in the lift cylinder assembly and extension velocity data relating to velocity of extension of the lift cylinder assembly, the payload measurement system being configured to estimate a weight of the payload in the bucket based on the pressure data as adjusted by an estimate of a pressure drop between the lift cylinder assembly and the pressure sensor, the payload measurement system being configured to determine the estimate of the pressure drop based on the temperature data, the extension velocity data and a mathematical model that has been fitted to empirical data relating to pressure loss between the lift cylinder assembly and the pressure sensor at different hydraulic fluid temperatures and lift cylinder assembly extension velocities.

15. The system of machine of claim 14 wherein the mathematical model has been fit to the empirical data using a regression analysis.

16. The machine of claim 14 wherein the payload measurement system determines the estimate of the weight of the payload from a table stored in the payload measurement system using the pressure data as adjusted by the pressure loss data.

17. The machine of claim 14 wherein the mathematical model uses an equation including:

18. The machine of claim 14 wherein the mathematical model uses an equation including:

19. The machine of claim 14 wherein the mathematical model uses an equation including:

Δ

P_C=C

where Δ

P_C is a pressure drop resulting from the pressure sensor, and

C is a coefficient the value of which is determined by fitting the empirical data to the mathematical model.

20. The machine of claim 14 wherein the pressure sensor is arranged adjacent a control valve for the lift cylinder assembly.