WO2001023846A1

WO2001023846A1 - Shear beam load cell

Info

Publication number: WO2001023846A1
Application number: PCT/AU2000/001188
Authority: WO
Inventors: Arthur Kellenbach
Original assignee: Kellco Technologies Pty. Limited
Priority date: 1999-09-28
Filing date: 2000-09-28
Publication date: 2001-04-05
Also published as: AUPQ313099A0

Abstract

A shear beam load cell includes a beam (10) with a webbed portion (18) to which is attached a strain measuring device for determining the shear applied to the beam by a load means (16). A plurality of support means (12, 14) are spaced along the beam, with the axes of at least the support means extending horizontally transverse to the longitudinal beam for supporting the beam in equilibrium. Preferred support means include rigid members such as horizontal pins extending through apertures (12, 14) horizontally transverse to the longitudinal axis of the beam, or external ledges or flanges (112) extending across the width or thickness of the beam.

Description

SHEAR BEAM LOAD CELL

FIELD OF THE INVENTION

The present invention relates to a shear beam load cell in which the cell is supported by pins or other horizontal rigid members rather than bolts extending vertically through the beam.

BACKGROUND OF THE INVENTION

In the prior art, for example, as shown in Fig. 1, a shear beam load cell comprises a beam fixed to a surface by bolts A and B and bearing a load L applied to the cantilever portion of the beam at C. A thinned or webbed portion E of the beam carries strain measuring devices for determining the shear applied by the load. In forming the free end of the beam the beam is shaved creating a point of high compression at D. High compression at D in addition to compression caused by the bolt B, requires considerable strength of the portion of the loadcell at location D.

This arrangement of shear beam load cell has many disadvantages among which are: that the bolts precompress the load cell; that the cell has to be wide enough to accommodate the bolts; a large amount of vertical space is required for mounting and loading the load cell; considerable machining is required in order to drill the holes and to provide the step in the free end of the load cell; the mounting is considerably inflexible; the load forces are carried on the threads of the bolts and bear considerable stress; as the load cell is supported by bolts and threads in tension the likelihood of fracture is greater than if the supports were in shear for example; in order to support the load cell a hardened flat bearing surface is required adding to the overall cost and difficulties with this form of load cell.

These defects follow from the fact that the main axis of mounting fittings and/or load fittings is in the same plane as the load line for the load cell; the axis of fitting is at right angles to the load cell support surface and the axes of the fittings are in the same plane and in the same direction as the main forces which are transferred by the fittings.

SUMMARY OF THE INVENTION

The present invention seeks to overcome these disadvantages in the prior art, or to ameliorate them or to provide an alternative thereto.

According to a broad aspect of the invention there is provided a shear beam load cell including a beam having a webbed portion to which is attached strain measuring means for determining the shear applied to the beam by a load means, and a plurality of support means spaced along the beam, the axes of at least said support means extending horizontally transverse to the longitudinal axis of the beam for supporting the beam in equilibrium. Preferably, there are two support means and one load means arranged along the length of the beam and said support means are rigid members such as pins extending through apertures in or externally of the beam; or external ledges or flanges extending across the width or thickness of the beam.

The load means may apply a load to the beam in a number of ways, for example, through a vertically extending bolt or pin, or alternatively, through a horizontally extending pin passing through an aperture in, or resting externally of but in contact with, the beam; or an external ledge or flange extending across the width or thickness of the beam.

According to a second aspect of the invention there is provided a shear beam load cell including a beam having a webbed portion to which is attached strain measuring means for determining the shear applied to the beam by a load, and a plurality of slots or apertures in the beam extending horizontally transverse to the longitudinal axis of the beam for accommodating pins therethrough for supporting the beam and said load. Preferably, there are three pins arranged along the length of the beam and the pins supporting the beam are supported externally of the beam, for example by separate plates having cooperating apertures.

Each pin can be fitted into a slot or aperture loosely fitting, tightly fitting or pressed into the slot, for example surrounded by a bushing. In addition where the ends of the pins are supported by external plates, the support may be in an aperture holding the pin tightly, loosely or via a bushing. The pins may extend either side of the beam so that the beam is supported bi-laterally or alternatively the beam may be supported on one side only. Pins may ride on a flat, grooved, hard, rigid or elastomeric surface. The bushing may be made of an elastomeric material.

In another form of the invention, the end of the beam to which the load is applied may be proved with an elastomeric body for receiving the load, instead of a rigid pin or the like.

The use of bushings in the instant invention is distinguished over that described in the prior art of Australian patent 590,520 in that the latter relates to a bending beam in which the force must be transferred by the bushing without impeding moment in torsion whereas no such requirements exist for the instant invention, a shear beam. The bushing according to the invention may or may not be present and, if present, simply allows the pin supports to adjust for small distortions induced in the shear beam by temperature, load misalignment or other local environmental factors.

In this way a cell can be made which is narrow, requires only two machine orientations in order for the apertures or web to be formed, instead of the four required in the prior art. The apertures only require short holes to be drilled and only shallow pockets are needed to form the webbed area, if at all.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described with respect to the following figures in which: Fig. 1 shows a shear beam load cell of the prior art;

Fig. 2 shows a first embodiment according to the invention in schematic form;

Fig. 3 shows a second embodiment of the invention in a schematic form;

Fig. 4 shows a third embodiment according to the invention in a schematic form;

Fig. 5 shows a fourth embodiment according to the invention in a schematic form; and

Figs. 6(a)-(f) show schematically further embodiments of the invention; and Fig. 7 shows an alternative embodiment to that of the embodiment of Fig. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 2 a thin beam 10 is provided with three apertures 12, 14, 16 arranged along the centre line 20 of the beam 10. A web 18 is formed in the beam 10 by a thinned section of the beam. The web 18 accommodates a strain measuring device on either side of the web.

Pins (not shown) extend through the apertures 12,14 or 16 either side of the bar 10 and are supported on a support structure (not shown). The pins may sit tightly in the apertures 12, 14, 16, or may be a loose fit with or without a bushing between the pin and its aperture. In practice, it is difficult to ensure that the pins are dimensioned to match the apertures 12, 14, 16 and the pins will tend to sit differently within the apertures 12, 14, 16 depending upon the force that they experience, locally. For example, if a load is attached to a pin through aperture 16 with the bar 10 supported by pins in apertures 12 and 14, then for the pin in aperture 12 the force may extend downwardly with the pin resting at the bottom of the aperture 12. In aperture 14 the pin may sit towards the top half of the aperture due to a force acting upwardly at that point. Similarly the pin in aperture 16 may sit at the lower half of the slot 16 due to a perceived downwardly directed force. A force diagram connecting the force transfer points indicates that the cell is "self aligning" under load. This allows for example loose fitting of cells; the adaptation to and following of mis-alignment and distortions of load receiving and/or load support structures under variations in load, temperature, or small movements; and the pins to slide in the apertures 12, 14, 16 allowing the force transfer points to be adaptive dimensionally, that is not only in the vertical plane but also in the horizontal plane.

A variation of Fig. 2 is shown in Fig. 3 where the beam 10 is supported by plates 30, 32 either side of the beam 10 with the pins through apertures 12, 14 extending through associated apertures in the plates 30, 32. A load is supported by the pin through aperture 16 while the load cell is supported through a pinned aperture 34 in the top corner of the plates 30, 32. In this form a very safe and simple as well as economic suspension is provided which can be used in suspension weighing.

Referring to Fig. 4, a third embodiment is shown where the web 48 is located along the longitudinal centre line of the beam 40. The apertures 42, 44 and 46 are located off the centre line with apertures 42, 46 being above the centre line and aperture 44 being below the centre line. The web 48 is located much as before towards one end of the beam. In this embodiment by varying the location of the force transfer points manipulation of the shape and or orientation of the field of shear strain to be measured is allowed.

Fig. 5 shows yet a further embodiment of the invention in which the beam is T-shaped with the apertures 51, 52, 54 arranged at the vertices of the T whilst strain is measured in a web or strain measuring area 56 along the "vertical" arm of the T although the beam is horizontally arranged as shown. This configuration can be associated in a very narrow layout due to the support of the T-shaped beam 50 by pins rather than by bolted fixtures, which would be more complex and expensive to effect.

The T-shaped beam 50 may be supported by a stand having a single or a pair of upstanding arm(s) with associated apertures through which the pins of the T-shaped beam extend leaving the third aperture 54 free to bear the load that is to be measured. A single sided support is shown. The pin may be connected rigidly to the arm of the beam 50 or the force acting thereon may be conveyed through an elastomeric support whereby the degree of rigidity and or flexibility of the assembly can be adjusted for the application to which the load cell it is to be applied.

Referring to Fig. 6, six further embodiments of the invention are shown. The shear beam load cell according to the invention includes two support points and one load point on the beam. In place of apertures with pins through the beam acting as the support or load points, the support or load points may be replaced on the beam by a number of alternatives including an external ledge support, pins supporting the beam externally resting on the surface of the beam directly or with an elastomeric material therebetween (as a bushing or a separate single layer), pins in grooved or channeled sections, or stepped external ledge or flange supports, with the external supports whether of pins, flanges or ledges being supported on the beam directly or on elastomeric material, as will now be described.

In Figs. 6(a), (b), (c) and (f) one support point corresponding to and substituting for pinned aperture 12 of Fig. 2 or Fig. 3 is made up by a fixed external support 112. A load depending from pinned aperture 16 (in Figs. 6(a), (b), (c))produces a strain in strain measuring means 118. The beam 110 has a further support at 14, 124 or 134 corresponding respectively in Figs. 6(a), (b) or (c) to a pinned aperture, a pin supporting the beam externally, or a pin in a channeled or grooved depression 136 in the beam 110.

Equally the two pinned support apertures 12, 14 may both be replaced by external ledge supports, for example, by sliding the beam 110 into channelled or tubular section.

In the embodiment of Fig. 6(d) both load support points are made up of pins 144, 146 in respective channeled or grooved depressions 148, 150 along the beam. Similarly, the load may be applied, as shown in Fig. 6(e), through a pin 160 in a channeled or grooved depression 162. In Fig 6(f), the load L is applied through a fixed external point 166 and, in addition, the beam at that point may be cut or stepped at 170 to better configure the strain field as measured by the strain measuring device 118.

Thus the present invention contemplates means acting along the length of the beam at the load or support points which are other than pins extending through apertures in the beam (pinned apertures).

In each of the alternate embodiments of Figs. 6(a) - (f) the support or load point is a rigid member such as a pin or an external ledge or flange extending transversely of the beam, that is, approximately perpendicular to the longitudinal axis of the beam. Otherwise stated, the rigid member is across the width or thickness of the beam and the beam can be made thin, according to the invention, as it does not have to bear threaded bolts through the thickness thereof. The pin or external ledge or flange whether at its point of intersection with the beam or at its single or double sided support post or flange may include a bushing or layer of elastomeric material interfacing between such pin, external ledge or flange and such beam or post, as the case may be.

A further embodiment of the invention involves the load point being replaced by a vertically extending rigid means such as a bolt or a pin instead of being applied to the beam through a transversely extending rigid means such as described above with respect to the variations of Figs. 6(a)-(f) or Figs. 2-5. The bolt or the pin can extend through a vertical aperture in the beam and may be affixed to a ledge or post external of the beam.

In the case of a bolt, the bolt may be screw threaded into the post or ledge whereas in the case of a pin, the pin may be integral with or welded to the flange or post.

The bolt or pin in this case does not (or does not have to) bear the full force and hence can be made of a smaller diameter than as required for bolts in prior art shear beam load cells. Equally, the size of the apertures required to accommodate the bolt or pin can be made smaller with the consequence that the width of the shear beam can be less than that necessary for prior art shear beam load cells. In this form of the invention the support means are as described above with respect to any of the embodiments of Figs. 2-6. With this form of the invention a platform load cell can be constructed.

Although the invention has been described above with respect to preferred embodiments thereof, variations are contemplated within the knowledge of a person skilled in the art.

Claims

CLAIMS.

1. A shear beam load cell including a beam having a webbed portion to which is attached strain measuring means for determining the shear applied to the beam by a load means, and a plurality of support means spaced along the beam, the axes of at least said support means extending horizontally transverse to the longitudinal axis of the beam for supporting the beam in equilibrium.

2. A shear beam load cell according to claim 1 including two support means and one load means arranged along the length of the beam, said support means being rigid members extending through apertures in the beam

3. A shear beam load cell according to claim 1 including two support means and one load means arranged along the length of the beam, said support means being external ledges or flanges extending across the width or thickness of the beam.

4. A shear beam load cell including a beam having a webbed portion to which is attached strain measuring means for determining the shear applied to the beam by a load, and a plurality of slots or apertures in the beam extending horizontally transverse to the longitudinal axis of the beam for accommodating pins therethrough for supporting the beam and said load.

5. A shear beam load cell according to claim 4 including three pins arranged along the length of the beam, the pins supporting the beam and being supported externally of the beam.