AU660232B2

AU660232B2 - Shear beam loadcell

Info

Publication number: AU660232B2
Application number: AU46269/93A
Authority: AU
Inventors: Arthur Kellenbach
Original assignee: Kelba (australia) Pty Ltd
Current assignee: Kelba (australia) Pty Ltd
Priority date: 1992-09-11
Filing date: 1993-09-09
Publication date: 1995-06-15
Anticipated expiration: 2013-09-09
Also published as: AU4626993A

Description

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AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT "Shear Beam Loadcell" The following statement is a full description of this invention, including the best method of performing it known to me -2- 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 20 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.

25 According to the invention, a shear beam loadcell including a mounting portion having a lower surface 0 which provides a mounting surface engagable with a support and a strain sensing portion having a free lower surface, the strain sensing portion being 30 provided with means sensing shear strain therein and being adapted to receive a load force, is characterised in that said free surface is substantially coplanar with said mounting surface, a lateral groove being provided between said surfaces.

In use the cell is preferably mounted on a support 8 surface, with the mounting surface being engaged with -3the support surface, the support surface extending beyond the end of the mounting surface in the direction of the free surface and terminating bplow 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 10 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 is made of a suitable material such as heat treated tool steel. The loadcell 10 is attached by bolts 20 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.

o. :25 A groove 23 extends across the width of the loadcell 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.

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 -4the loadcell 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).

10 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 th, art. For example, where the loadcell 10 is to replace a conventional loadcell, 15 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.

0 20 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.

25 It will be understood that references in the description and claims 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.

Claims

1. A shear beam loadcell including a mounting portion having a Jower surface which provides a mounting surface engagable with a support and a strain sensing portion having a free lower surface, the strain sensing portion being provided with means sensing shear strain therein and being adapted to receive a load force, characterised in that 10 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 15 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 S' *terminating below said groove.

3. A shear beam loadcell according to claim 2 wherein said support surface is stepped downwardly along a line located below said groove. 25

4. A shear beam loadcell according to claim 2 wherein said support surface is the upper 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. DATED this 8th day of September 1993 ARTHUR KELLENBACH Patent Attorneys for the Applicant: HALFORD CO.

-6- ABSTRACT 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 seperated by a 0*0@ groove (23). 0* 0@ 0 0000 0@ S 00 S Os 0. 0 0 ~*0 0 0000 *0 SO 0 0 0 000@ 5* 00 0005 0* *0 0 0 0* 05 S