Compensated multiple load cell scale

• US 4,804,052 A
• Filed: 11/30/1987
• Issued: 02/14/1989
• Est. Priority Date: 11/30/1987
• Status: Expired due to Term

• Current Assignee: Mettler-Toledo Incorporated (Mettler-Toledo International Inc.)
• Original Assignee: Toledo Scale Corp. (Mettler-Toledo International Inc.)
• Inventors: Griffen, Neil C.
• Primary Examiner(s): MILLER JR, GEORGE
• Application Number:
  US07/126,271
• Time in Patent Office: 442 Days
• Field of Search: 177/25.14, 177/211, 177/134, 177/255, 177/163, 177/50, 73/1 B
• US Class Current: 177/25.14
• CPC Class Codes: G01G 19/021 having electrical weight-sensitive devices G01G19/04 - G01G19/07 take precedence
• CPC Class Codes: G01G 23/3714 with feedback means

Abstract

Multiple digital load cells forming one or more weighing scales are connected together and to a common master controller in a local area network. The digital load cells are polled by and provide weight readings to the master controller. The weight readings are combined with a load position correction factor for each load cell and summed to provide a weight indication corrected for load position. The values of the load position correction factors are determined during set up of the scale and stored at the master controller. An individual load cell can be diagnosed remotely and replaced if defective. A new load position correction factor is determined and stored for a replacement load cell.

Claims

1. Weighing apparatus comprising a plurality of load cells, load receiving means supported by said load cells, means associated with said load cells for providing a digital representation of a load on each load cell, means for storing a mathematical expression for load corrected for load position, and means for applying said mathematical expression to said digital load representations to produce a digital representation of the total load on said load receiving means corrected for load position.

2. Weighing apparatus as claimed in claim 1 wherein said mathematical expression includes a load position correction factor for at least one of said load cells, and wherein said correction factors are combined with the corresponding digital representations to produce corrected digital representations, and any uncorrected digital representations and said corrected digital representations are combined to produce the total load on said load receiving means corrected for load position.

3. Weighing apparatus as claimed in claim 2 including control means for receiving said digital representations from each of said load cells, combining said load position correction factors with the corresponding digital representations to produce corrected digital representations and combining the corrected digital representations and any uncorrected digital representations to produce the total load on said load receiving means corrected for load position.

4. Weighing apparatus as claimed in claim 1 wherein each load cell includes a counterforce and an analog to digital conversion means associated with the counterforce.

5. Weighing apparatus as claimed in claim 1 including control means for interrogating said load cells to receive said digital representations.

6. Weighing apparatus as claimed in claim 5 including means connecting said load cells and said control means in a local area network.

7. A method for compensating a multiple load cell scale for load position, said scale including means for providing a digital representation of a load on each load cell, the method comprising the steps of determining a mathematical expression for load corrected for load position, storing said mathematical expression, interrogating each of said load cells to receive said digital load representations, and applying said mathematical expression to said digital load representations to produce a digital representation of the total load on the scale corrected for load position.

8. A method as claimed in claim 7 wherein said mathematical expression includes a correction factor for at least one of said load cells, and including the steps of determining the load position correction factors, storing the load position correction factors, combining the load position correction factors with the respective digital load representations to provide corrected digital load representations, and combining any uncorrected digital representations and said corrected digital load representations to provide a digital representation of the total load on the scale corrected for load position.

9. A method as claimed in claim 8 wherein the step of determining the load position correction factors for each load cell includes the steps of positioning a load at different locations on said scale, determining the responses of said load cells to said load, and utilizing said responses and said mathematical expression to determine the load position correction factors.

10. A method as claimed in claim 8 including the step of determining a fresh load position correction factor for a replacement load cell and storing said fresh load position correction factor.

11. A method as claimed in claim 10 wherein said fresh load position correction factor is determined by positioning a load on said replacement load cell, obtaining digital representations from each of the load cells, positioning the same load at another location and obtaining load representations from each of the load cells, and utilizing said load representations and the known correction factors from all but the replaced load cell to determine the value of the load position correction factor for the replacement load cell, and storing said load position correction factor for the replacement load cell.

12. In a multiple digital load cell scale having a load position correction factor stored for each load cell, a method of recompensating said scale after replacement of a load cell, comprising the steps of positioning a load on the replacement load cell and obtaining load representations from each of the load cells, positioning the same load at another location and obtaining load representations from each of the load cells, utilizing said load representations and the known correction factors from all but the replaced load cell to determine the value of the load position correction factor for the replacement load cell, and storing said new load position correction factor for the replacement load cell.

13. A method as claimed in claim 12 wherein said load placed on said replacement load cell has an unknown value.

14. Weighing apparatus comprising a plurality of load cells, each load cell including a counterforce, means associated with the counterforce for providing digital representations of loads on the counterforce, and means responsive to external commands for transmitting said digital representations, load receiving means supported by said load cells, control means for interrogating said load cells to receive said digital representation, means associated with said control means for storing a predetermined load position correction factor for at least one of said load cells, means associated with said control means for combining said digital representations with corresponding ones of said load position correction factors to produce corrected digital load representations, and means for combining any uncorrected digital representations and said corrected digital load representations to produce a digital representation of the total load on said platform corrected for load position.

15. Weighing apparatus as claimed in claim 14 including means connecting said load cells and said control means in a local area network.

16. A method for compensating a multiple load cell scale for load position, said scale including means for providing a digital representation of a load on each load cell, the method comprising the steps of positioning the same load at different locations on said scale, obtaining digital load representations from each load cell at each load position, utilizing said digital load representations to determine a load position correction factor for at least one of said load cells, and storing said load position correction factor for combination with digital load representations from corresponding ones of said load cells during use of the scale.

17. A method as claimed in claim 16 wherein said load has an unknown value.