Load cell

Details Load cell Load cell

1999-10-01

2001-06-19

Fuller, Benjamin R. (Department: 2856)

Measuring and testing

Dynamometers

Responsive to multiple loads or load components

Reexamination Certificate

active

06247372

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the field of load cells, specifically load cells that measure torsion or shear.
Load cells are used for measuring forces and moments along certain directions. Measurement of loads and moments about multiple axes can be beneficial in various research and manufacturing applications. Current multi-axis load cells, however, require complex machining and mechanical linkages to isolate loads along multiple axes. Loads that manifest only through shear stress at the load cell typically require especially complex machining or linkages for isolation. See, e.g., Meyer et al., U.S. Pat. No. 4,640,138; Meyer et al., U.S. Pat. No. 5,315,882; Mullin, U.S. Pat. No. 5,339,697; Rieck et al., U.S. Pat. No. 4,259,863; Ruoff, Jr. et al., U.S. Pat. No. 4,138,884. Current multi-axis load cells are consequently expensive to manufacture, and can be readily damaged by overloading. The frequency response of current load cells is also limited by the characteristics of the machining and mechanical linkages, precluding their use in applications with rapidly varying loads.
Many applications that might benefit from multi-axis load measurements are precluded by the high cost of current multi-axis load cells. Also, applications such as many robotics applications encounter widely varying loads. Some encounter unknown loading, making load cell damage due to overloading likely. Also, existing load cells can not be integrated into a robot link, complicating the robotic system.
There is a need for a multi-axis load cell that is simple and inexpensive to manufacture, that is unlikely to be damaged by widely varying loads, and that can be readily incorporated into a robotic system.
SUMMARY OF THE INVENTION
The present invention provides an improved load cell that is simple and inexpensive to manufacture, and that is capable of measuring a wide range of loads. The present invention uses strain gauges, mounted in novel arrangements on free surfaces of a load cell body, to measure loads.
Generally, six load components are of interest: axial load, axial moment (torsion), two loads at angles to the axis (typically along two axes mutually orthogonal and orthogonal to the cell axis), and moments about two axes at angles to the cell's axis (typically about two axes mutually orthogonal and orthogonal to the cell axis). Strain gauges measure axial surface strain along a given axis, and accordingly do not directly measure any of the six loads of interest. Placing sets of strain gauges at certain locations on free surfaces of the cell, however, can allow the gauge outputs to be combined to measure any of the six load components of interest individually. Specific placements of the strain gauges, described herein, can provide coupled, linearly-independent relationships among strain gauge outputs and load components. Individual load components can be determined from the strain gauge outputs and the coupled linearly-independent relationships.
Advantages and novel features will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.


REFERENCES:
patent: 4138884 (1979-02-01), Ruoff, Jr. et al.
patent: 4493220 (1985-01-01), Carnigan et al.
patent: 4640138 (1987-02-01), Meyer et al.
patent: 4733571 (1988-03-01), Ormond
patent: 5315882 (1994-05-01), Meyer et al.
patent: 5339697 (1994-08-01), Mullin
patent: 5850044 (1998-12-01), Spletzer
patent: 5889214 (1999-03-01), Kang et al.
patent: 5969268 (1999-10-01), Sommerfield et al.

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