NZ248606A - Shear beam loadcell: lateral groove present between lower surface of mounting portion and lower surface of coplanar free strain sensing portion - Google Patents

Description

Patents Form# 5 24 86 0 6 Priority Date(s): .0". 37* Complete Specification Filed: Class: Publication Date: .. 2 6.JUU995 P.O. ..'.V-.-rnr'. No: . . <.

•V % '30NOVI993^j ■> ** 'W I, Arthur Kellenbach, an Australian citizen, of 15 Awatea Road, Stives, NSW 2075, Australia, do hereby declare the invention for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: The following page is numbered "la" NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION Shear Beam Loadcell PF05JWP FEE CODE - 1050 248606 -la- A shear beam loadcell (10) in which the lower surface of the mounting portion (14) and of the strain sensing portion (13) are coplanar, and are separated by a groove (23).

The following page is numbered "lb" >, 248606 -lb- The present invention relates to shear beam loadcells.

A typical and well-known form of prior art load cell is shown in Fig. 1, and comprises a bar 10 of steel or aluminium from which a portion of material has been removed in the region 11, to form a line 12 beyond which the portion 13 of the loadcell is free to deflect downwardly.

In use, the support portion 14 of the bar is secured by bolts 15 and 16 to a support 17. In the sensing portion 13 cylindrical bores form a thin wall structure 19 to each face of which is attached a strain gauge (not shown). A load L applied at some point towards the end of the loadcell is measured by the shear forces acting upon the two strain gauge.

Such shear beam cells are machined to close tolerances from high grade materials in order to obtain necessary performance in terms of linearity and repeatability. As a result of the cost of machining, the wastage of material and the cost of subsequent heat treatment, these devices are expensive.

According to the invention, a shear beam loadcell includes a shear beam loadcell including a mounting portion and a strain sensing portion, the mounting portion having a mounting surface engagable with a support, the strain sensing portion being adapted to receive a load force and being provided with means sensing shear strain therein, the strain sensing portion also having a free surface facing substantially the same direction as the mounting surface, characterised in that said free surface is substantially coplanar with said mounting surface, a 248606 lateral groove being provided between said surfaces.

In use the cell is preferably mounted on a support surface, with the mounting surface being engaged with the support surface, the support surface extending beyond the end of the mounting surface in the direction of the free surface and terminating opposite the groove.

We have found that with such a construction, a load cell can be manufactured with satisfactory performance while requiring less machining than prior art designs. A further advantage of such a construction is the reduction which is achieved in the profile of the device, which need be no higher than the required section depth of the strain-sensing area.

A preferred embodiment of the invention will now be described with reference to Figs. 2 and 3.

In the embodiment illustrated in Fig. 2 the loadcell 10 is made of a suitable material such as heat treated tool steel. The loadcell 10 is attached by bolts 15 and 16 to a support 17 which is stepped downwardly at 21. A pair of strain gauges (not shown) are mounted on either side of a wall 19 as in the prior art described above.

A groove 23 extends across the width of the loadcell 10 dividing its lower surface into a mounting surface which engages the support 17 and a free surface which is spaced from the support 17 by virtue of the step 21. The loadcell is mounted so that the step 21 lies beneath the groove 23, so that the mounting surface and the free surface of the cell are clear of the edge 24 of the mounting plate 21. — *4860 The profile of the groove 23 may take any suitable form, including a smooth curve or a triangular or polygonal shape. Preferably, the profile is a smooth curve in order to avoid stress points or areas within the loadcell 10.

Throughout this specification the term "groove" is to be read as including functionally equivalent formations by which a surface region across the loadcell between the mounting surface and the free surface is disposed upwardly (in the orientation assumed in this specification).

Though the invention has been described above with respect to a preferred embodiment thereof, other variations are contemplated within the knowledge of a person skilled in the art. For example, where the loadcell 10 is to replace a conventional loadcell, instead of employing a step 21 the loadcell may be mounted on a filler plate 25 (Fig. 3) the end of which lies below the groove 23 to provide the free area 11 for deflection of the loadcell.

Other approaches to the design of loadcells incorporating the principle of the invention will occur to the reader and are within the scope of the invention.

It will be understood that references in the description which assume a particular orientation of the loadcell are for convenience only, and are not to be taken as limiting the scope of the invention to such an orientation. 1 *muvigg 4*7

Claims (5)

-4- WHAT I CLAIM IS:

1. A shear beam loadcell including a mounting portion and a strain sensing portion, the mounting portion having a mounting surface engagable with a support, the strain sensing portion being adapted to receive a load force and being provided with means sensing shear strain therein, the strain sensing portion also having a free surface facing substantially the same direction as the mounting surface, characterised in that said free surface is substantially coplanar with said mounting surface, a lateral groove being provided between said surfaces.

2. A shear beam loadcell according to claim 1 mounted on a support surface, said mounting surface being engaged with said support surface, said support surface extending beyond the end of said mounting surface in the direction of said free surface and terminating opposite said groove.

3. A shear beam loadcell according to claim 2 wherein said support surface is stepped away from said groove along a line located below said groove.

4. A shear beam loadcell according to claim 2 wherein said support surface is a surface of a filler plate mounted between said mounting surface and a mounting body.

5. A shear beam loadcell substantially as described herein with reference to Figs. 2 or 3 of the accompanying drawings. James W Piper & Co Attorneys For: Arthur Kellenbach