AU427671B2 - Flexure plate scale with hydraulic load cell - Google Patents

Description

359 7171' This invention pertain generally to weighing

devices and more particularly to a scale of the type having

a platform for receiving a load to be weighed.

Most platform scales heretofore provided utilize

conventional pivots and bearings throughout their lever

systems. These pivots and bearings are subject to wear

which can impair the accuracy of the scale, and they require

frequent maintenance and/or replacement.

Heretofore, there have been some attempts to re-

place the pivots and bearings of platform scales with flexible

members such as plates, straps and cables. However, none

of these attempts has provided entirely satisfactory results.

There is, therefore, a need for a new and improved

scale which overcomes the foregoing and other disadvantages

of scales heretofore provided.

FIGURE 1 is a perspective view of one embodiment

of a platform scale incorporating the present invention,

with the platform removed for clarity of illustration.

FIGURE 2 is a cross-sectional view taken along

line 2-2 in FIGURE 1.

FIGURE 3, is a cross-sectional view taken along

line 3-3 in FIGURE i.

In the preferred embodiment, the scale of the pre-

sent invention includes a platform for receiving loads to

be weighed a generally rectangular base assembly, a framework

disposed within the base assembly for supporting the platform,

a pair of lever arms mounted within the base assembly,

flexure plates connecting the lever arms to the platform

supporting framework in such manner that forces applied to

24797L7 by a load are transmitted to the lever arms, a hydraulic load

3 947 71 cell, and flexible cable means connecting the lever arms to

the load cell in such manner that the load cell produced a

hydraulic output signal corresponding to the load on the

platform.

The platform comprises a generally planar member

disposed in a substantially horizontal position above the

base of the scale. A skirt 11, fabricated of rigid angle

stock, extends around the outer periphery of the platform

member 10. Alternatively, if desired, the skirt can be

fabricated of channel stock, box beam stock, or stock having

another structural shape. This skirt adds strength and rigid-

ity to the platform and it also provides means far enclosing

the upper portion of the scale. It is attached Ca the

platform member 10 by conventional means such as bolting,

brazing, or welding. Other structural cross-members are

included in the platform and attached to planar member

and skirt 11 to provide structural rigidity as required by

the size and capacity of the scale.

The base assembly includes end members 13 and

side members 14 which are joined together at their ends by

conventional means such as brazing or welding. These members

extend in a horizontal direction and are substantially

greater in length than in height, thereby forming a rectan-

gular base of low profile. A cross-member 16 extends between

the side members 14 at a position intermediate the end mem-

bers 13. In the preferred embodiment, the end and side

members are fabricated of a rigid channel stock, and the

cross-member is a flat plate. Gusset plates 17 are attached

to the lower surfaces of the end and side members at the

corners of the base assembly. 26 .427671

3 5 9 4 7/71 The supporting framework includes a plurality of

vertically extending posts '18 having generally flat upper

surfaces upon which the platform rests. The posts 18 are

mounted at opposite ends of structural cross-members 19 which

extend in a direction generally parallel to the base end

members 13 and in proximity thereto. Tie-bars 21 extend in

a direction generally parallel to the' frame side members 14

and interconnect the posts at corresponding ends of the cross-

bars 19. Thus, the posts 18, structural members 19 and tie-

bars 21 form a rigid framework which lies substantially

within the region defined by the end and side members of the

base assembly.

A pair of simple lever arms 22 is provided for

transferring forces produced by a load on the platform to

the load cell. Each of these lever arms includes a torque

transmitting member 23 disposed generally parallel and

proximate to one of the base assembly end members and a pair

of arm portions 24 which extend from the torque transmitting

member in a direction generally perpendicular thereto. Each

of the arm portions 24 has a free end 24a generally proximate

to the load cell. One or more bracing members 26 extend

between the arm portions of each of the lever arms to provide

strength and rigidity to the lever arms. The arm portions of

the lever arms are spaced apart by different distances to

provide clearance between the free ends. As is most clearly

illustrated in FIGURE 3, the free ends of the arm portions of

each lever arm are substantially equidistant from the load

cell.

Forces are transmitted from the platform and platform

supporting framework to the lever arms through a plurality

4 427797 1 ir' of flexure plate assemblies 31. One such assembly is provided at each of the ends of the torque transmitting members 23 of the lever arms. Each flexure plate assembly includes a fulcrum flexure plate 32 extending between the base assembly and the torque transmitting member and a load flexure plate 33 extending between the torque transmitting member and the platform supporting framework. Each of these flexure plates is a generally rectangular member fabricated of a flexible material such as a steel alloy. The base assembly is formed to include a vertically extending post 34 at each of its corners, and the upper portion in each of the fulcrum flexure plates 32 is secured to one of these posts by-means of bolts

36, a spacer block 37, and a clamping block 38. Rectangular

mounting blocks 41 are provided at each end-of the torque

transmitting portions of the lever arms. Each of these

mounting blocks includes a lower ear portion 42 to which the

lower portion of the fulcrum flexure plate 32 is secured by

means of bolts 44 and a clamping block 46. Each of the moun-

ting blocks 41 also includes an upper ear portion 47 to which

the upper portion of the load flexure plate 33 is secured by

means of bolts 48 and a clamping block 49. The lower portion

of the load flexure plate 33 is secured to the cross-arm 19

of the platform supporting framework by means of bolts 51 and

a clamping block 52.

The load cell, designated by the reference numeral

56, is a hydraulic transducer which is mounted on the cross-

member 16 of the base assembly. This load cell comprises

a cylinder containing a hydraulic fluid and a movable piston

which varies the pressure intensity of the .fluid in accordance

with the force applied to theiston. The load cell can be connected by a conventional hydraulic line to a conventional pressure gauge which can be located remotely of the remainder of the scale. The pressure gauge can be calibrated in units of weight to provide a direct indication of the weight of an object on the platform of the scale.

Forces are transferred from the lever arms to the

load cell piston by means of a load transfer bar 57 and flex-

ible cables 58. The transfer bar rests upon the. piston of the

load cell, and the cables 58 extend vertically between the

transfer bar and the free ends 24a of the arm portions of the

lever arms. The cables connected to the free ends of the arm

portions of each lever arm equally spaced from the load cell,

and the cables are positioned to flex about centers located

in the same general horizontal plane as the flexure plates 32

and 33. Alternatively, if desired, the transfer bar can be

connected to the lever arms by rigid members, such as bolts

or tie rods, rather than flexing cables.

Check links are provided to reduce the effects of

side forces applied to the scale and to prevent lateral

motion or swaying of the platform member. 9ach of these check links include a flat elongate member 61 which is attached at

its ends to the tie-bars 21 of the platform supporting frame-

work by blocks 62 and at its center to the cross-member 16

of the base assembly by a post 63.

Operation and use of the scale can now be described

briefly. A load placed on the platform member 10 exerts a

downward force which is applied to the platform supporting

framework through the post 18. This force-is transmitted to the lever arms 22 through the flexure plate assemblies 31

and produces a downward force at the free ends of the arm 427 7f vJ S I portions 24a. This downward force is applied to the load cell

56 through the flexible cables 58 and the transfer bar 57 to

produce a change in pressure intensity in the hydraulic fluid

in the load cell corresponding to the weight of the load

applied to the platform member. This hydraulic signal is

applied to a conventional pressure gauge to provide a direct

reading of the weight of the load.

utilizing the techniques of the present invention,

a scale having a capacity on the order of 20,000 pounds can

be constructed in a unit having a height on the order of 6

inches and a length and width on the order of 30 inches. Such

a scale has an accuracy on the order of 0.1 per cent.

It is apparent from the foregoing that a new and

improved scale has been provided. While only the presently

preferred embodiment has been described, as will be apparent

to those familiar with the art, certain changes and modifica-

tions can be made without departing from the scope of the

invention as defined by the following claims.

427 f71

THE CLAIMS DEFINING THE INVENTION AE AS FOLLOWS:- 4 7/7

1. In a weighing scale, a rigid framework, a load

supporting member for receiving a load to be weighed in such manner that the load exerts a force on said member, lever

means for translating the forces exerted by a load on-said

load supporting member to output transducer means for indi-

cating the weight of the load, said lever means including

a pair of levers each having a fulcrum portion and an arm

portion, a transfer member connected to the arm portions of

said pair of levers for transferring forces from said arm

portions to the output transducer means, and flexure means

connecting each of said levers to said load supporting member

and said framework in such manner that a force exerted on

said supporting member by a load produces a torque in the

fulcrum portion and a force in the-lever, said flexure means

including first and second generally rectangular flexure

plates disposed in substantially parallel vertical planes on

opposite sides of the fulcrum portion of said lever, means

rigidly affixing the upper and lower portions of the first

flexure plate to said framework and said fulcrum portion inc

such manner that the central portion of said flexure plate is

free to flex without contacting either said framework or said

lever, and means rigidly affixing the upper and lower por-

tions of the second flexure plate to said fulcrum portion

and said load supporting member in such manner that the central portion 6f said second flexure plate is free to flex

without contacting either said lever or said supporting member.

2. A scale as in Claim 1 wherein the output trans- ducer means includes a hydraulic load cell adapted for producing a hy_drau icpressurecorresponding-to-the-force--

427 71

9 47/7 exerted by the transfer member.

3. A scale as in Claim 1 wherein the transfer

member comprises a load plate connected to the lever arm

portions by means of flexible cables.

4. A scale as in Claim 3 wherein the output

transducer means includes a hydraulic load cell comprising

a cylinder portion carried by said framework and a piston

portion connected to said load plate, said piston portion

being disposed for movement within said cylinder portions.

A scale substantially as herein described with

reference to and shown in the accompanying drawings.

6. A scale as in any preceding claim including

check links connected to the load supporting member and the

framework.

Dated this 18th day of November, 1971

NATIONAL CONTROLS, INC.

By its Patent Attorneys

DAVIES COLLISON

V5 1JIll7

3 5 i 4 '1/71

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II :7 47 A9, 7 97

9 4 7 /71

13 427971

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14 47 6 7 1 A-2

35.947/7f

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427671

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