TITLE: Single Point Load Cell Measuring Apparatus

Inventors: Jeffrey D. Watkins and Michael L. Kochersperger Cross Reference to Applications

[0001] This application is related to, and claims priority from, U.S.

Provisional Patent application no. 60/988,449 filed on November 16, 2007, by J. Watkins et al., entitled "Integrated Single Point Load Cell Technology into Process and Bioprocess Systems", the entire contents of which are hereby incorporated by reference. Technical Field

[0002] The present invention relates to methods and apparatus for weighing vessels using load cells, and more particular to methods and apparatus for using one single point load cell to weigh a vessel using a cantilevered vessel support structure. Background Art

[0003] Fig. 1 shows a prior art implementation of a vessel weighing device using three single point load cells 10. The vessel weighing devices that use three single point load cells 10 typically include a vessel support collar 12, three support legs 14, three single point load cells 16 and three ground supports 18. A vessel 22 may be supported in the vessel support collar 12 which may be connected to the single point load cells 16 by the support legs 14. The support legs 14 may then be connected to one end of the single point load cells 16, while the ground supports 18 are connected to the other end of the single point load cells 16, anchoring the vessel weighing device to a floor 20.

[0004] The vessel weighing device using three single point load cells 10 is a multi-cell approach that tends to increase system costs, system complexity, and typically requires significant calibration, including accurate leveling, to avoid measurement instability and possible other inaccuracies.

Disclosure of Invention

[0005] The present invention relates to methods and devices for weighing vessels, particularly vessels being used in a process or bioprocess.

[0006] In a preferred embodiment, the weighing device uses a single load cell that is attached at one end to a structural support, and at the other is rigidly connected to a vessel. The center of gravity of the vessel is off-set from a primary load axis of the load cell.

[0007] The load cell may be a single point load cell having a specified load platform and the center of gravity of the vessel may be substantially orthogonal to a plane of the specified load platform and lie within the range of the specified load platform.

[0008] The weighing device may include a cantilever vessel support that is rigidly attached to the load cell, and which supports the vessel.

[0009] These and other features of the invention will be more fully understood by references to the following drawings.

Brief Description of Drawings

[0010] Fig. 1 shows a prior art implementation of a vessel weighing device using three single point load cells.

[0011] Fig. 2 shows an exemplary experimental implementation of a vessel weighing device using a single point load cell.

[0012] Fig. 3 shows an exemplary experimental implementation of a vessel weighing device using a single point load cell and a cantilever, vessel support. [0013] Fig. 4 shows the loading range of a single point load cell with a weighing pan.

[0014] Fig. 5 shows an exemplary implementation of a vessel weighing device using a single point load cell and a cantilever, vessel support of the present invention. [0015] Fig. 6 shows a 3-D view of an exemplary implementation of a vessel weighing device using a single point load cell and a cantilever, vessel support of the present invention.

Best Mode for Carrying Out the Invention

[0016] A device that only uses one single point load cell may overcome many of the difficulties typically associated with multi-point load cell devices, including high system cost, system complexity and calibration requirements by, for instance, reducing system cost, reducing system complexity and eliminating redundant level sensing to determine fluid level or vessel volume. A device that only uses one single point load cell may also eliminate measurement instability and calibration accuracy. A device that only uses one single point load cell may readily detect small changes in vessel biomass, fluid level and vessel volume throughout a process run without necessitating the requirement of keeping the applied force normal to the load cell plenum as in the traditional approach exemplified by vessel weighing device using three single point load cells 10.

[0017] Fig. 2 shows an exemplary experimental implementation of a vessel weighing device using only one single point load cell 21. The vessel weighing device using only one single point load cell 21 shown in figure 2 tends to be unstable. Even

if the support leg 14 and the ground support 18 are made wider, the stability of this design is typically limited by the width of the attachment plate of the single point load cell 16 in relation to the size of the vessel 22.

[0018] Fig. 3 shows an exemplary experimental implementation of a vessel weighing device using a single point load cell and a cantilever, vessel support 31. [0019] The vessel 22 may be supported by a cantilever vessel support 24. The cantilever vessel support 24 may be attached by a pivot bearing 30 to a support structure 26. The support structure 26 may in turn be rigidly attached to a structural support 28 that may in turn rest on the floor 20. The single point load cell 16 may be attached at one end to the structural support 28. A load bearing element 32 may be rigidly attached to the cantilever vessel support 24 and used to transfer the weight to be measured to the single point load cell 16.

[0020] The vessel weighing device using a single point load cell and a cantilever, vessel support 31 may not be as accurate as required for a particular process or bioprocess because of shortcomings such as friction in the pivot bearing 30 or the vessel 22 center of gravity changing during the process and thereby altering the leverage of the cantilever vessel support 24.

[0021] Fig. 4 shows the loading range of a single point load cell with a weighing pan 41. One end of the single point load cell 16 may be connected to the floor 20 by a structural support 28, while the other end of the single point load cell 16 may be attached to a weighing pan 44 via a pan support element 46. If the internal structure of the single point load cells 16 is perfectly symmetrical, the single point load cell 16 will register the same reading irrespective of where on the weighing pan 44 the force is applied, i.e., the same force applied at point 48 will register as exactly

the same as if the force is applied at point 50 or point 52. In practice, however, the elements of a single point load cell 16 are not usually perfectly symmetrical, and there may be both off-center and off-axis loading errors. There are, however, ways of minimizing these errors as described in, for instance, US Patent 7,342,185 issued on March 11, 2008 to Haggstrom entitled "Compression Column Load Cell with Compensation for Center loading errors", the contents of which are hereby incorporated by reference. Single point load cells, therefore, usually have a specified platform size that is an indicates a weighing pan 44 or load platform area over which the load cell will provide an accurate measurement of weight to within a predetermined error range. For instance a 60 kg CPB planer beam load cell made by Flintec Inc. of Hudson MA is rated to be accurate over a 300 mm by 300 mm platform size, while their 200 kg single point load cell type PCl is rated to be accurate over a 600 x 600 mm platform size.

[0022] A preferred embodiment of the invention will now be described in detail by reference to the accompanying drawings in which, as far as possible, like elements are designated by like numbers.

[0023] Although every reasonable attempt is made in the accompanying drawings to represent the various elements of the embodiments in relative scale, it is not always possible to do so with the limitations of two-dimensional paper. Accordingly, in order to properly represent the relationships of various features among each other in the depicted embodiments and to properly demonstrate the invention in a reasonably simplified fashion, it is necessary at times to deviate from absolute scale in the attached drawings. However, one of ordinary skill in the art

would fully appreciate and acknowledge any such scale deviations as not limiting the enablement of the disclosed embodiments.

[0024] Fig. 5 shows an exemplary implementation of a vessel weighing device using a single point load cell having a cantilever, vessel support 51 of the present invention. The single point load cell having a cantilever, vessel support 51 includes a single point load cell 16 that may be attached to the floor 20 via a structural support 28. The other end of the single point load cell 16 may be rigidly attached to a cantilever vessel support 24 that holds the vessel 22.

The center of gravity 23 of the vessel 22 and what ever contents are in the vessel 22 and/or whatever elements are attached to the vessel 22, may be offset from the primary load axis 25 of the load cell, but be located within the specified load platform 17 of the single point load cell 16. Such a single point load cell having a cantilever, vessel support 51 may then readily detect small changes in vessel biomass, fluid level and vessel volume throughout a process run.

[0025] Fig. 6 shows a 3-D view of an exemplary implementation of a vessel weighing device using a single point load cell and a cantilever, vessel support 51 of the present invention.

[0026] The single point load cell 16 may be any suitable load cell having a sufficient specified load platform 17 for the application including, but not limited to, a suitable planar beam load cell and a single point load cell 16.

[0027] The one end of the single point load cell 16 may be rigidly connected to a structural support 28 while the other end of the single point load cell 16 may be rigidly attached to a cantilever support mounting 36 that may in turn be attached to a cantilever vessel support 24. The vessel 22 may be held in a cylindrical collar 40 that

may be rigidly attached to the cantilever vessel support 24 by one or more collar attachment elements 38. The vessel 22 may have external elements such as, but not limited to, lifting lugs 42.

[0028] Although the invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed invention. Modifications may readily be devised by those ordinarily skilled in the art without departing from the spirit or scope of the present invention. Industrial Applicability

[0029] In the field of pharmaceutical research and production there is significant interest in methods and apparatus for weighing vessels using load cells. Such using one single point load cell to weigh a vessel using a cantilevered vessel support structure would be of considerable utility as, for instance, a means to monitor fluid weights during research and production processes and bioprocesses.