WO1990008945A1

WO1990008945A1 - Improvements to load sensing apparatus

Info

Publication number: WO1990008945A1
Application number: PCT/AU1990/000030
Authority: WO
Inventors: Peter Thomas Goodier
Original assignee: Masstech Scientific Pty. Ltd.
Priority date: 1989-01-26
Filing date: 1990-01-25
Publication date: 1990-08-09

Abstract

Load sensing apparatus (10) including a substantially rigid load receiving member (12) incorporating a stress beam (24), the load receiving member (12) being supported on a base (11) by knife edge connectors (16) or solid flexural connectors and a load platform (13) supported on the load receiving member (12) via similar connectors (26) at a position spaced from the connectors (16) so that load applied to the platform (13) is transferred through the connectors (16 and 26) to the stress beam (24) to cause stress therein, stress in the beam (24) being sensed to provide an indication of applied load.

Description

IMPROVEMENTS TO LOAD SENSING APPARATUS Technical Field

THIS INVENTION relates to improvements to load sensing apparatus and in one particular aspect to apparatus incorporating a weighing platform so as to function as bathroom scales, floor platform scales, weighbridges or any other weighing device. Background Art

Many different configurations of weighing apparatus are presently in use. In the case of bathroom scales or similar weighing devices, a load carrying platform is supported via knife edge connections and on a leverage assembly mounted on a base such that when a load is applied to the platform, movement of the leverage system occurs. Movement of the leverage system can be sensed by a number of different devices, for example load cells or by linkage systems which cause rotation of a member in accordance with the amount of load applied with such rotation being sensed to provide an indication of load. Most of the load sensing devices are supported on the lower base surface of the weighing apparatus so that in the case where the base is placed on an uneven surface inaccurate load measurement is obtained.

Similarly the base can expand or retract with changes in temperature so that again inaccuracies can occur.

Further inaccuracies occur also in the use of the various leverage assemblies. Such leverage assemblies generally include rigid lever members which extend from one side of the base of the apparatus and hanger members which extend from the opposite side of the apparatus base and which hang from the rigid members. Such an arrangement is particularly susceptible to damage if for example the apparatus is dropped. Disclosure of Invention

The present invention aims to overcome or alleviate one or more of the above disadvantages by providing load sensing apparatus which does not employ the conventional leverage systems and which therefore is much more reliable and sturdy in use. The present invention also aims to provide apparatus which eliminates the abovementioned disadvantages associated with mounting the load sensing element on the base. Other objects and advantages of the invention will become apparent from the following description.

The present invention thus provides in a first preferred aspect, load sensing apparatus including substantially rigid load receiving means, said load receiving means including a load sensitive region, supporting means spaced from said load sensitive region for suspending said load receiving means, means for applying a load to said load receiving means at a position spaced from said supporting means whereby to cause stress in said load sensitive region, said stress in said load sensitive region being indicative of load applied to said load receiving means.

Preferably, the means for applying a load to said load receiving means comprises platforms means, said platform means being suitably supported in a floating manner on said load receiving means at said positions spaced from said supporting means.

The support means for said load receiving means and said platform means suitably comprises knife edge connections or solid flexural connections which will provide the necessary floating and suspension support of said load receiving means and said platform means, such connections not impeding the transfer of load from said platform means to said load sensitive region. The load receiving means may comprise a one-piece member integrally defining said load sensitive region. Alternatively, the load sensitive region may comprise a separate stress beam rigidly secured to at least two support arms to define said load receiving means, said support arms being supported by said support means. In either case, the load receiving means suitably includes a pair of opposed U-shaped parts, the arms of which are supported on said support means and the bases of which are rigidly connected to or integral with a stress beam defining said load sensitive region. The apparatus also suitably includes base means upon which said load receiving means is mounted via said support means. For this purpose, the base means may be provided with a peripheral flange defining supports for knife edge connectors or alternatively provided with brackets for supporting said flexural connectors.

The stress in the load sensitive region may be sensed by a strain gauge or any other element such as a vibration type force sensor which alters its vibration frequency in accordance with applied stress. Brief Description of the Drawings

In order that the invention may be more readily understood and put into practical effect reference will now be made with the accompanying drawings which illustrate a preferred embodiment of the invention and wherein:-

Fig. 1 illustrates in perspective view, a preferred form of load sensing apparatus according to the present invention;

Fig. 2 is a cut-away perspective view illustrating components of the load sensing apparatus of Fig. 1;

Fig. 3 illustrates in enlarged view one arrangement for supporting the load receiving member of the load sensing apparatus;

Fig. 4 illustrates one form of hanger for supporting the platform of the apparatus;

Fig. 5 is a plan view of the load receiving means of the apparatus; Figs. 6 and 7 are respective end elevational views of the load receiving means of Fig. 5;

Fig. 8 illustrates an alternative load receiving means incorporating a load sensitive element;

Fig. 9 is a sectional view showing an alternate method of supporting the load receiving means;

Fig. 10 is an end sectional view along line A-A of Fig. 9 showing the engagement between the arm of the load receiving means and support saddle;

Fig. 11 is a plan view showing the engagement of an arm of the load receiving means with a supporting saddle of the embodiment of Fig. 9;

Fig. 12 illustrates in plan view an alternative engagement arrangement between an arm and flexural connector;

Fig. 13 is a sectional view showing an alternative method of supporting the pl tform and load receiving means; Figs. 14 A, B and C illustrate alternative flexural connectors in front elevation, side elevation and plan views for the embodiment of Fig. 13;

Figs. 15 A, B, C_τ D, E and F illustrate alternative flexural connectors in front elevation, side elevation and plan view for the embodiment of Figs. 9 to 11. Best Mode for Carrying Out the Invention

Referring to the drawings and firstly to Figs. 1 to 4 there is illustrated load sensing apparatus 10 according to the present invention which in this instance is in the form of platform scales including a base member 11 which supports via a load receiving and sensitive member 12 a platform 13 to which load to be measured or sensed is applied. The base member 11 includes upwardly extending side flange portions 14 and defines adjacent its four corners respective mounts 15 for supporting respective hangers 16 of somewhat U or V-shaped form upon which the load sensitive member 12 is supported. Each mount 15 as shown more clearly in Fig. 3 includes a pair of opposite

V-sectioned recesses 17 and each hanger 16 includes opposite knife edges 18 for location in the respective recesses 17 so that the hangers 16 are free for rocking movement. Each hanger

16 also includes between the knife edge 18 and facing in the opposite direction a further knife edge 19 upon which the load sensitive member 12 is supported in the manner described below.

The load sensitive member 12 as shown more clearly in Figs. 5 to 7 includes a pair of generally U-shaped end parts 20 each of which includes a main channel sectioned part 21 provided at each end with a pair of outwardly extending arms 22 which are adapted to be supported on the hangers 16. For this purpose the outer ends of the arms 22 are formed with V-shaped cut-out portions 23 which seat in use upon the knife edges 19 of the hangers 16 in the manner shown in Fig. 2.

The load sensitive member 12 also includes a stress beam 24 which extends normal to the U-shaped parts 20 and which is formed integrally and rigidly therewith so that the parts 20 and beam 24 form a substantially rigid load receiving member. As shown, the beam 24 is U- or channel sectioned form in cross section so as to form a substantially rigid member and suitably the member 12 comprises a sheet metal pressing of suitable properties such as 7075 aluminium, 2024 aluminium or low creep steel .

The arms 22 of the parts 20 are also provided adjacent their ends and opposite the cut-out portions 23 with further V-shaped cut-out portions 25 which define mounts for further hangers 26 (see Fig. 4), the latter each having a central knife edge 27 which seats within the V-shaped cut-out 25 in the manner shown in Fig. 1 so as to be free for rocking movement in a similar manner to the hangers 16. Each hanger 26 also includes oppositely disposed knife edges 28 upon which the weighing platform 13 may be supported. For this purpose the platform 13 is provided with respective U-shaped saddles 29, opposite arms 30 of which include V-shaped cut-outs 31 which seat upon the opposite upwardly directed knife edges 28 of the hangers 26. It will be apparent that in the above described arrangement, the load receiving member 12 is fully suspended and floating on the base 11 via the recesses 23 and hangers 16 such that when load is applied to the platform 13, it is transferred through the respective hangers 26 and 16 and support parts 20 to the stress beam 24 whereby to apply a load thereto. The platform 13 is also supported in a floating manner on the load receiving member 12.

Associated with or mounted to the underside of the stress beam 24 is a load sensing element which may for example comprise a vibratory type force sensor 32 such as disclosed in US Patent No. 4773493 which senses stress in the beam 24 as a result of load applied to the platform 13. The element 32 incorporates a piezo-electric driver to which a signal is applied to cause the element 32 to vibrate and a piezo-electric receiver which detects the frequency of vibration of the element 32, changes in frequency of vibration being proportional to stress applied to the load beam 24 and thus to the element 32. Indicating means may be associated with the sensor 32 to provide a visual readout of load, or for example in the case of bathroom scales, weight. Conventional electronic circuitry and displays ⁵ may be used for this purpose with the display in the case of bathroom scales being mounted on the platform 13. Many alternative means may be employed for sensing stress in or applied to the beam 24 such as by means of a strain gauge or gauges attached to the stress beam. ¹⁰ The amount of load or stress applied to the stress beam

24 varies with the spacing between the hangers 16 and 26 and the calibration of the load sensing element is varied in accordance with this spacing to provide a correct load reading on a load readout device. -^■-^■ The suspension of the load sensing member 12 on the outer flanges of the base member 11 reduces additive or subtractive influences introduced into the apparatus due to flexing of the base member 11 where for example the base member 11 may be supported on an uneven surface or subject to flexing ⁰ due to temperature conditions. Thus the stress beam 24 will be substantially free from such influences and will enable accurate reading of a load applied to the platform.

In a preferred form, both the base member 11 and platform 13 are formed of a plastics material and suitably a ⁵ relatively rigid plastics material. The member 11 and platform 13, however, may be formed of metal such as cast aluminium if desired.

Fig. 8 illustrates an alternative load receiving member 12' wherein the stress beam 24' may be formed of an extruded ⁰ length of material such as aluminium cut to the required thickness for rigid attachment to opposite U-shaped supports 20' by any suitable fasteners. Alternatively, the stress beam 24 may be formed integrally with the supports 20'. The beam 24 may also be supported in any other manner and by supports other than ⁵ of the form described above. For example, where a circular weighing or load sensing apparatus is to be used, the beam 24 may be supported by three equally spaced arms 22. More than four arms may also be used for supporting the beam 24 in certain circumstances.

Whilst the preferred arrangement for applying load to the stress beam 24 is via hangers and knife edge supports which provide point loadings, solid flexural members may be used at the respective connection points to transfer the load in a similar manner. One such arrangement is shown in Figs. 9 to 11 where, in this case, the arms 22' of the load receiving member 12 are stepped at their outer ends and are slit and pressed and threaded at 33 and 34 to define mounts for solid flexural members 35 and 36.

Adjacent the corners of the platform 13 and base 11 and secured thereto are respective upper and lower U-shaped supports or saddles 37 which define in their opposite arms V-shaped recesses 38 for receiving hexagonal sectioned blocks 39, the latter being centrally apertured and threaded at 40 for engagement with the flexural member 35 or 36.

Each flexural member 35 or 36 includes opposite end threaded portions 41 and 42 joined by a reduced thickness or necked portion 43 which serves as the flexing part of the joint. In the flexural member 35, the necked portion 43 is offset from the centreline of the member 35 for a purpose which will hereinafter become apparent.

As shown, the respective flexural members 35 and 36 are screw-threadably engaged with the arm 22' and a hexagonal block 39, with the platform 13 seating through the inner supports 37 on the block 39 associated with the flexural member 36 whilst the outer end of the arm 22' is suspended through the flexural member 35 and block 39 on the outer supports 37 as shown in Fig. 10. Suitably also, a spring or springs 44 are provided to urge the platform 13 towards the base 11 so as to hold the components together.

The offset nature of the necked portion 43 of the flexural member 35 permits adjustment and calibration of the apparatus. Thus rotation of the member 35 will cause the point of load transfer from the platform to be varied inwardly or outwardly because of the repositioning of the necked portion 43 to thereby vary the point of leverage.

The threads of the threaded portion of the members 36 may also be made of opposite hand so that screwing in or out thereof allows adjustment of the zero setting of the apparatus, rotation of the member 36 causing the platform 13 to move towards or away from the load receiving member 12.

Fig. 11 illustrates an alternative arrangement for forming the threads in the arm 22', with the area 45 being pressed out of the arm 22' and threaded to accept the flexural member 36. Alternatively and as shown in Fig. 12, the arm 22' may be turned back upon itself to define an aperture 46 which may be threaded for engagement with a flexural member.

Fig. 13 illustrates yet a further embodiment of the invention wherein the platform 13 is supported on the arm 22" of the load receiving member 12 by means of an arrangement similar to that described in Figs. 1 to 7 including a saddle 29 and hanger 16. In this case, however, the end of the arm _.22" is secured at 46 to a further generally planar solid flexural member 47, the latter being fixed via mounting blocks 48 and a fastener 49 to the base 11.

The flexural member 478 in this case may be of the form shown in Figs. 14 A, B or C including a pair of necked portions 50 or simply comprise a flexural member with a single "necked" portion. Fig. 15 illustrates alternative forms of flexural member which may replace the members 35 or 36 for use in the embodiment of Fig. 9 with each member having alternative necked configurations and in some cases double necked portions.

The apparatus 10 may be used with any combination of flexural elements or alternative knife edge supports as described above. Other means for providing point transfer of the load applied to the platform 13 to the stress beam 24 may also be used. For example ball socket connections may be employed for this purpose. In all cases however, the connections are such as to permit in the case of the load receiving members 12, free deflection thereof when subject to applied load with the connections having no influence on the transmitted load. The above has been given by way of illustrative embodiment of the invention, however, it will be realized that many variations and modifications as would be apparent to persons skilled in the art may be made to the invention without departing from the broad scope and ambit therof.

Claims

1. Load sensing apparatus including substantially rigid load receiving means, said load receiving means including a load sensitive region, supporting means spaced from said load sensitive region for suspending said load receiving means, means for applying a load to said load receiving means at a position spaced from said supporting means whereby to cause stress in said load sensitive region, said stress in said load sensitive region being indicative of load appl ed to said load receiving means.

2. Load sensing apparatus according to claim 1 wherein said means for applying a load to said load receiving means comprises platforms means, said platform means being supported in a floating manner on said load receiving means at said positions spaced from said supporting means'.

3. Load sensing apparatus according to claim 1 wherein said supporting means for said load receiving means comprises knife edge connections providing said floating support of said load receiving means.

4. Load sensing apparatus according to claim 2 wherein said platform means is supported on said load receiving means via knife edge connections.

5. Load sensing apparatus according to claim 1 wherein said load sensitive region is defined by a substantially rigid stress beam.

6. Load sensing apparatus according to claim 4 wherein said load receiving means includes a plurality of support arms supported on said support means, said support arms being formed integrally with said stress beam or rigidly secured thereto.

7. Load sensing apparatus according to claim 5 wherein said support arms comprise the arms of generally U- shaped brackets, and wherein the bases of said U-shaped brackets are secured to or formed integrally with said stress beam.

8. Load sensing apparatus according to claim 1 and including base means upon which said load receiving means is mounted via said support means.

9. Load sensing apparatus according to claim 8 wherein said base means includes a peripheral flange defining supports for knife edge connectors, the latter comprising said support means.

10. Load sensing apparatus according to claim 1 wherein said supporting means for said load receiving means comprise flexural connectors.

11. Load sensing apparatus according to claim 10 wherein said flexural connectors comprise opposite end portions interconnected by a reduced thickness portion.

12. Load sensing apparatus according to claim 11 wherein said opposite end portions of said flexural connectors are threaded for engagement with said load receiving means and a supporting block.

13. Load sensing apparatus according to claim 12 and including base means, said base means including bracket means for supporting said support block.

14. Load sensing apparatus according to claim 12 wherein said reduced thickness portion or portions is/are axially offset from said threaded portions whereby rotation of said flexural members varies the position of support of said load receiving means.

15. Load sensing apparatus according to claim 10 and including platform means supported on said load receiving means via flexural connectors.