GB2180357A

GB2180357A - Loadcell mounting

Info

Publication number: GB2180357A
Application number: GB08522433A
Authority: GB
Inventors: Michael Hughes; Trevor Monk
Original assignee: MASTERWEIGH Ltd
Current assignee: MASTERWEIGH Ltd
Priority date: 1985-09-10
Filing date: 1985-09-10
Publication date: 1987-03-25
Also published as: GB8522433D0

Abstract

A load, e.g. that exerted by a weighting pan 11, is transmitted to a loadcell 12, through a mounting device including two plates 15,16 urged towards one another by a spring system 17,18, the plates 15,16 being in contact through 20 spaced fulcrums, in the form of balls 20. Excessive or uneven loading causes the plates 15,16 to tilt, thus compressing the spring 18 and protecting the loadcell 12. <IMAGE>

Description

SPECIFICATION Loadcell mounting This invention relates to loadcells used for measuring or detecting deflections between members and usually producing electrical or other output signals. They are, for example, useful in weighing machines, the electrical signal providing a readout and/or the means to control other apparatus.

Loadcells are easily damaged by overloading and require care in handling and use. They are usually designed for operation over a relatively small load range and overloading even by a relatively small margin from the designed loads can result in permanent damage. Not only is the load range often small but the limits of travel are also often very small. To overcome this problem it has been proposed to mount the loadcell in such a way that a direct overload in the direction of normal operation of the loadcell compresses a spring. Although this is satisfactory where too great a load is applied in the normal direction, the application to the loadcell of loads in other directions can still cause damage.

It is the object of the invention to provide a loadcell mounting in which the loadcell is protected from damaging loadings which might be applied in various ways.

In accordance with the present invention there is provided a loadcell mounting comprising a fixture to which the loadcell is fixed, in use, and a member, of which movement relatively to said fixture is to be detected, said member or said fixture being connected to the loadcell through a mounting including two separate parts spring urged into contact with one another, contact between these parts being through multiple spaced fulcrums.

Preferably the fulcrums are spaced generally equally about a point at which the spring force acts.

With this arrangement the loadcell is protected against simple overload in the normal direction of application of the load to be detected but also against loads applied to the mounting in any other direction.

Conveniently, the two separate parts are plates which are connected together with a spring system and having fulcrums through which the two parts are in contact.

The fulcrums may be represented by re- spective balls positioned between the parts. In a particularly advantageous arrangement, three balls are positioned equidistantly around a point through which the spring force acts.

The invention will now be described by way of example with reference to the accompanying drawing, the single figure of which is a diagrammatic representation of a loadcell mounting constructed in accordance with the invention.

The drawing illustrates a typical application for a loadcell used, in this instance, in weighing apparatus and in which the loadcell is intended to provide an electrical output signal to a readout and/or control device indicated at 10. The loadcell is intended to detect loads through a predetermined load range as applied to a weighing pan 11 or other equivalent device. It is to be understood that the device may be a simple weighing machine or, alternatively, it may be part of other apparatus such as a weighing and packaging apparatus in which the loadcell is intended to signal the receipt in the weighing pan 11 of a predetermined quantity of product, whereupon the supply of product is stopped and possibly also the pan is tipped or other mechanism actuated to empty the pan ready for receipt of a further supply of product.It will be clear that the loadcell can be used in a number of different applications.

The loadcell, which is indicated at 12, is of the kind having strain detecting means arranged to transmit electrical signals and these are mounted on a deflectable beam. One end of the loadcell is securely fixed and mounted on a fixture indicated at 13. The other end is attached to the weighing pan 11 through a protection device. The weighing pan in this instance is carried on a support arm 14 which is fixed on or rests on a portion of the protection device.

The protection device comprises two parallel generally flat plates 15, 16. The plate 15 is secured to the loadcell 12 and the plate 16 has secured to it or resting on it the arm 14 for the pan 11. The two plates 15, 16 are connected through a spring system comprising a pintle 17 surrounded by a coiled compression spring 18 of predetermined rating. The pintle engages in the plate 15 through a chamfered hole so that the pintle can rock relatively to the plate 15. It passes through a relatively large clearance hole in the other plate 16. The opposite end of the pintle 17 has a head engaging an abutment plate 19.

The spring 18 acts between the abutment plate 19 and the adjacent plate 16.

The two plates 15, 16 are urged together by the action of the spring 18 but are held apart by balls 20 which are engaged in re spective cups or recesses in the opposite surfaces of the plates 15 and 16. In this example there are three balls situated equidistantly about the centre represented by the spring system. The balls 20 act as fulcrums for the plates. If the plates 15, 16 are tilted relatively to one another, the upper plate 16 will rise from one or two of the balls and will pivot about the contact of the other ball. Application of load to the pan 11 and arm 14 in any but the normal direction will tend to tilt or separate the plates relatively to one another, thus compressing the spring 18 and protect ing the loadcell 12 from direct application of that load.

The plates 15, 16 may be of triangular or other shape and the number and positioning of the balls may be varied, though the three ball arrangement is particularly advantageous in minimising friction and thus providing the greatest protection to the loadcell against accidental or other overloads in various directions.

If the weighing pan 11 is overloaded in the normal direction, for example by the application of excessive amounts of the product to be weighed, the loadcell deflects in the normal manner until some part of the loadcell or the protection device comes into contact with one or more fixed stops 21.

Other types of loadcell or load detecting or measuring devices not producing electrical signals, or producing electrical signals in a way different from the type of loadcell referred to, can also advantageously be protected by means of the protection device described.

Claims

1. A loadcell mounting between a fixture to which the loadcell is fixed, in use, and a member, of which movement relatively to said fixture is to be detected, said member or said fixture being, in use, connected to the loadcell through a mounting including two separate parts which are spring urged towards one another, contact between these parts being through multiple spaced fulcrums.

2. A loadcell mounting as claimed in Claim 1 in which the fulcrums are spaced generally equally about an axis through which the spring force acts.

3. A loadcell mounting as claimed in either of Claims 1 and 2 in which the two separate parts are plates which are connected together through a spring system and having fulcrums through which the parts are normaily in contact.

4. A loadcell mounting as claimed in any one of the proceeding claims in which the fulcrums are represented by respective balls positioned between the parts.

5. A loadcell mounting as claimed in Claim 4 in which three balls are positioned equidistantly around an axis through which the spring force acts.

6. A loadcell mounting as claimed in Claim 3 in which the spring system comprises a coiled compression spring, one end of which acts on one of the plates, at its side remote from the other plate, and a pintle passing through the spring and the plates, and pintle having an abutment at one end acting on the other of the plates and an abutment at the other end acting on the other end of the spring.

7. A loadcell mounting as claimed in Claim 6 in which one of the plates is arranged to act on the loadcell, at a position spaced from the spring system and the other plate is arranged to carry a load, at a further position also spaced from the spring system, whereby loads other than in a normal direction will tend to tilt one plate relatively to the other to compress the spring system and separate the plates at least at one of the fulcrums.

8. A loadcell mounting substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.