GB2101753A

GB2101753A - Load cell

Info

Publication number: GB2101753A
Application number: GB08121492A
Authority: GB
Inventors: Kenneth Harry Stedman
Original assignee: DEFIANT WEIGHING Ltd
Current assignee: DEFIANT WEIGHING Ltd
Priority date: 1981-07-13
Filing date: 1981-07-13
Publication date: 1983-01-19
Also published as: DE3226046A1; FR2509464A1; IT1156046B; GB2101753B; IT8267870A0; FR2509464B3; DE3226046C2

Abstract

A load cell has a pair of parallel, facing portions (1, 2) with means (15) for securing respectively to a support and a load receiving member, for measurement of a load in a plane parallel to the portions (1, 2). The portions are joined together to form a parallel motion unit by mutually parallel transverse portions (5, 6, 7, 8) at least one of which is fitted with strain gauges (11, 12, 13, 14) to measure the load. <IMAGE>

Description

SPECIFICATION Load cell The present invention relates to load cells.

According to the present invention there is provided a load cell comprising a pair of parallel, facing portions with means for securing respectively to a support and a load receiving member to measure a load in a direction parallel to said portions, the portions being joined together to form a parallel motion unit by a plurality of mutually parallel transverse portions at least one of which is fitted with at least one strain gauge arranged for measurement of said load.

In a preferred arrangement, the facing portions are joined at their ends by two mutually parallel transverse portions, to form a rectangular structure, and in a central region by a further transverse portion upon which the strain gauge(s) is/are mounted.

In one embodiment, the central portion comprises a pair of members each disposed between the centre-line of the cell and a respective one of the end portions and having gauges on its surface facing that end portion, the gauges being responsive to the bending strains in the members resulting from shear loading of the cell, whilst in another arrangement, the central portion is a single member of I-section, with strain gauges on the web of the I-section to measure the shear strain therein.

Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of one form of load cell according to the invention; Figure 2 is a cross-section on line ll-ll of Fig. 1; Figure 3 is a view taken in the direction of the arrow Ill in Fig. 1; Figure 4 is a side elevation of a second embodiment of load cell according to the invention; and Figure 5 is a cross-section on line V-V of Fig. 4.

The load cell shown in Fig. 1 to 3 is of generally rectangular shape with a pair of parallel face portions 1, 2 with plane fixing faces 3, 4. The face portions are joined by upper and lower transverse members 5, 6 which extend the full width of the cell, and a central transverse portion with upper and lower members 7, 8 having, as can be seen from Fig. 2, a width of about one-third of that of the cell. The regions at which the transverse members join the face portions are radiused as shown at 9, partly to reduce the danger of stress concentrations occuring; but also to weaken the transverse members at two specific points, to give defined bending points. The inwardly directed faces of the face portions 1, 2 have arcuate recesses 10 in the central region of the cell.This structure is formed as an integral unit, e.g. by machining, and may be of any suitable material such as aluminum alloy or steel, according to the particular application.

The upper and lower members 7, 8 each have, fitted respectively to their upper and lower surfaces, a pair of strain gauges 11, 12, 13, 14, one at each end.

It will be appreciated that the cell construction described operates as parallel motion unit. In use, one of the plane faces-e.g., the face 3 is secured to a support such as a wall, bracket or staunchion and the load to be measured is applied by suitable means secured to the other face 4, such as a hopper or jib arm for changing a load to be measured.

Each of the faces has four bores 15, either tapped or (as shown) fitted with helical inserts 1 6 for receiving securing bolts. It will be appreciated that the provision of the faces 3, 4 for attachment directly to a support surface, and to loading means, provides a particularly compact and convenient arrangement, especially where space is limited. For some applications it may be convenient to employ 2, 3 or more load cells for supporting a load or load-bearing member.

The load to be measured acts downwardly as viewed in Fig. 1, giving rise to distortion of the cell in parallelogram fashion, and the shear force on the cell causes bending of the central transverse portion 7, 8 particularly since the radiused weakened regions 9 coincide with the flexure regions. The sense of the bending moment is different at its two ends: the gauges may suitably be connected in a bridge circuit with the pair of gauges 11, 1 2 on the one hand and the pair of gauges 1 2, 1 3 on the other hand being connected in respective bridge arms. In this way the differential changes in gauge resistance can be measured whilst sensitivity to tensile or compressive loads and to bending moments applied to the cell is minimised since these give rise to similar resistance changes in the two gauges of a pair.

In principle, the gauges could be mounted on the outer members 5, 6, but positioning on the central member 7, 8 provides a better insensitivity to torsional of loads, and again reduces sensitivity to externally applied bending moments since these members are closer to the neutral axes.

The alternative form of load cell shown in Figs. 4 to 6 is similar to that described above, but has a single central portion 1 7 with recesses in its lateral faces to form a connecting member of I-section. Here the force measurement is achieved by a pair of strain gauges 1 9 disposed so as to measure the shear strain in the web 20 of the I-section. An aperture 20 is provided for lead-out wires for the gauges.

Claims

1. A load cell comprising a pair of parallel, facing portions with means for securing respectively to a support and a load receiving member to measure a load in a direction parallel to said portions, the portions being joined together to form a parallel motion unit by a plurality of mutually parallel transverse portions at least one of which is fitted with at least one strain gauge arranged for measurement of said load.

2. A load cell according to claim 1 in which the facing portions are joined at their ends by two mutually parallel transverse portions, to form a rectangular structure, and in a central region by a further transverse portion upon which the stain gauge(s) is/are mounted.

3. A load cell according to claim 2, in which the central portion comprises a pair of members each disposed between the centreline of the cell and a respective one of the end portios and having gauges on its surface facing that end portion, the gauges being responsive to the bending strains in the members resulting from shear loading of the cell.

4. A load cell according to claim 2, in which the central portion is a single member of I-section, with strain gauges on the web of the I-section to measure the shear strain therein.

5. A load cell substantially as herein described with reference to the accompanying drawings.