GB2160985A - Weighing machine - Google Patents

Abstract

A checkweighing machine has a rotating scroll feed 32 and a main conveyor 31 and a weigh-cell conveyor in the form of two light chains 34,35, both conveyors travelling at identical speeds. Cans 40 are accelerated by the rotating scroll 32 and transferred to the weigh-cell conveyor over a low-friction guide 36. Each can 40 is weighed by weigh cell 39 which supports the conveyor 34,35 via another guide 38. After weighing the cans are transferred to conveyor 31 by guides 37. <IMAGE>

Description

SPECIFICATION Weighing machines The invention relates to weighing machines.

More particularly the invention relates to a form of check-weighing machine in which articles whose weights are to be checked are arranged to pass at substantially constant intervals of time and spacing over a weighing device hereafter called a "weigh cell", the output of the weigh cell being used to represent the weight or by suitable processing the volume or other characteristics of the article or to determine its acceptance by or rejection from the conveyor line by suitable means.

These means are not the subject of this invention.

The invention applies particularly but not exclusively to high speed machines where articles are required to be checkweighed at a rate, for example, of 500 to 1 200 per minute when the linear speed across the conveyors used is so high as to cause severe problems in maintaining positional stability and a consistent attitude of the articles at any point in the conveying means but particularly when on the weigh cell itself. To illustrate some of the problems which occur in such handling, a typical system is described with reference to Figs. 1 and 2 of the accompanying drawings which show diagrammatically in elevational and plan views respectively the relevant features of an existing machine.

A supply chute or conveyor 1 which acts as a temporary store for articles to be weighed and is kept substantially full is arranged by gravity feed, for example, to supply articles, e.g. cans, continuously one at a time to a conveyor 2 where they are gathered up by a rotating scroll 3. By suitable design of the scroll, an item which is well known in the art of conveying cans, the cans 20 are accelerated to the required speed of processing and simultaneously separated to the required spacing. The conveyor 2 may be a linked metal or fabric continuous belt running on rollers 4 and 5 and separate from succeeding apparatus. The cans are carried forward by their own momentum on to a further conveyor 6 which consists of a pair of chains, for example, running on sprockets 7 to 14.The chains are further fitted with toothed brackets or dogs which are fitted precisely opposite to each other as at 1 5. As the chains travel the next pair of dogs gathers the respective can and carries it across a support or slide 1 6 and then on to a weigh cell platform 1 7 where the weight of the can is intended to be measured.

The arrangement is such that the chains themselves do not bear on the weigh cell platform and only the dogs may remain in contact with the can. The cans pass from the weigh cell platform to a further support or slide 1 8 and finally on to an exit conveyor 19 which transports the cans for further handling as required by the processor. Drive means are suitably arranged for the scroll 3 and the conveyors 2, 6 and 1 9 as convenient to the machine manufacturer.

The deficiencies of a machine with such a method of conveying are such as to cause serious perturbations in the attitude and stability of the can while on the weigh cell whereby false readings of weight will occur. In particular, for example, the dogs 1 5 may change their vertical position slightly as the chains move and due to the frictional force between the dogs and can may impart a force small but significant in this application to the can which will give an apparent change in weight.

Again the can as it moves from support 1 6 on to the weight platform 1 7 may either foul slightly the leading edge of the platform or drop on to it depending on the accuracy to which the weigh cell has been positioned.

Furthermore, there may be small changes in the nature of the can base so that as it slides over the platform 1 7 slightly varying frictional forces occur leading again to small changes in the positions of the respective dogs and as above may give further changes in apparent weight.

According to the invention there is provided a check-weighing machine having a rotating scroll feed and a multiplicity of conveyors one of which is used for transporting articles to be weighed over a weigh cell, wherein the scroll transfers the articles directly to said weigh cell conveyor.

Preferably the transporting means of the weigh cell conveyor supports each article throughout the weighing process, the transporting means itself being supported by the weigh cell.

It is also preferred that the scroll feed overlaps the weigh cell conveyor and is associated with another of the conveyors which precedes the weigh cell conveyor, the transporting means of the weigh cell conveyor running in guide means whose entry is depressed below the surface of said preceding conveyor and whose guide tract is gradually elevated to a level sufficient to lift the article being transported clear of the preceding conveyor. The overlap of the scroll and the weigh cell conveyor is preferably such that the transfer of the article is just complete when the article is lifted clear of the preceding conveyor.

The transporting means of the weigh cell conveyor may comprise a pair of chains running in guide slots, the article being weighed resting on the chains. Within the overlap zone the slots may be conveniently inclined at about 5" to the horizontal.

The weigh cell conveyor preferably has an exit guide of similar characteristics to the entry guide but of opposite hand whereby the article having been weighed is transferred to a take-off conveyor. The conveyor preceding the weigh cell conveyor and the take-off conveyor may be a single conveyor extending the full length of the machine.

By way of example, a specific embodiment will now be described with reference to Figs.

3 to 6 of the accompanying diagrammatic drawings in which: Figure 3 is an elevational view of a checkweighing machine in accordance with the invention; Figure 4 is a plan view of the checkweighing machine of Fig. 3; Figure 5 is an enlarged elevational view of part of the checkweighing machine of Fig. 3; and Figure 6 is a transverse view showing the weigh cell conveyor and the preceding conveyor.

Referring to Figs. 3 to 6, a checkweighing machine has a chute or conveyor 30 acting as a temporary store for articles, which in this embodiment are cans. The chute or conveyor 30, is inclined downwardly to supply, by gravity feed, cans 40 continuously but one at a time to a main conveyor 31. In this embodiment the conveyor 31 traverses the whole length of the machine but may of course be sub-divided for manufacturing purposes. As described below the conveyor takes no part in the transfer of cans over the weigh cell itself.

Each can 40 is gathered by a rotating scroll 32 and again, as before, it accelerates and spaces each can and transfers it to a second conveyor 33. However, the method of transfer has been simplified and yet significantly improved over the existing machine described above with reference to Figs. 1 and 2.

The nature of the scroll 32 is now described. It may be compared to a screw thread in which at the can entry end the first one or one and a half threads are of substantially constant pitch but thereafter the threads are of rapidly increasing pitch up to the final one or one and a half threads which are again of constant but very much greater pitch than at the entry end. For example, the pitch of the thread at the entry end may be approximately equal to the diameter of the largest of the range of cans to be handled by the machine but the pitch at the scroll exit will be at least equal to the length of the weigh cell platform which again will be related to the required rate of can weighing and the response time of the weigh cell.

The weigh cell conveyor 33 is now described. Two light chains 34 and 35 one on either side of the conveyor 31 and travelling at identical linear speeds and at the linear speed of conveyor 31 and again at the linear speed of the point of contact of the can and scroll exit thread surface, pass over mechanically separate pairs of low friction guides 36, 37, 38, the outer pairs 36, 37 being fixed to the machine frame while the central pair 38 are supported by a weigh cell 39 and can move freely vertically to an extent required by the weigh cell. When situated on the weigh cell the can is supported by the chains 34, 35 which are themselves supported by the weigh cell and as described below the can is held clear of conveyor 31 so that any random movement of the conveyor 31 is not transmitted to the cell.

A novel feature of this embodiment is the contouring in the vertical plane of the pairs of guides 36 and 37 and the horizontal positioning of the contoured section of the guides 36 in relation to the exit section of the scroll 32.

It is considered important that the can or other article to be weighed is transferred from the scroll 32 to the conveyor 33 with the minimum of impact or drag between can and conveyor 33 so that the can being transferred is not caused to tumble in any way and so that negligible impact or drag exists to cause a lesser or greater tension in the chains which may cause perturbation of a can which may be on the weigh cell. In this embodiment each guide 36 is of such a length and design that its upwardly inclined portion is overlapped by the exit end of the scroll 32, this length of overlap being equivalent to about two can diameters. Thereby the overlap of the scroll 32 and the weigh cell conveyor 33 is such that the transfer of each can 40 is just complete when the can is lifted clear of the preceding or upstream section of the main conveyor 31.The set of guides 37 is contoured in the same way but of opposite hand so that the can is transferred from conveyor 33 to conveyor 31 again with the minimum of impact or drag. As indicated above the linear speeds of both conveyors 33, 31 and the speed of scroll thread advancement in the zone of transfer are identical and it is preferred to use a single motor drive with suitable gearbox and shaft transmissions to provide uniform drive speeds for the various items above instead of, for example, a multiplicity of chains, sprocket drives and gearboxes. The contouring of the guides 36 and the guides 37 of opposite hand is shown in Fig. 5. The guides may be made of metal or materials known as P.T.F.E. or DELRIN(RTM) but a low friction material is desirable and it is preferred to use DELRIN. The guides are slotted throughout their length. In the case of each guide 36, the slot is inclined below the horizontal over the first half of its length. The inclination is of the order of 5 degress, the requirement being that the distance of the respective chain below the horizontal when in the slot must be sufficient to allow for tolerances in manufacturing and bought-out materials used so that until the leading edge of the can reaches a limited zone opposite the exit end of the scroll its contact with conveyor 33 is prevented. It will further be noted that as the front end of the can is raised by the chains 34, 35 to bring it clear of conveyor 31 and to transport it over the weigh cell platform, the can 39 tends to be rotated in an anti-clockwise direction as shown in this particular diagram but it is restrained from doing so since within this zone it is still in contact with the leading edge of the scroll thread, a feature which further assists in maintaining stability of the can.

Claims (8)

1. A checkweighing machine having a rotating scroll feed and a multiplicity of conveyors one of which is used for transporting articles to be weighed over a weigh cell, wherein the scroll transfers the articles directly to said weigh cell conveyor.

2. A checkweighing machine as claimed in Claim 1, wherein the transporting means of the weigh cell conveyor supports each article throughout the weighing process, the transporting means itself being supported by the weigh cell.

3. A checkweighing machine as claimed in Claim 1 or Claim 2, wherein the scroll feed overlaps the weigh cell conveyor and is associated with another of the conveyors which precedes the weigh cell conveyor, the transporting means of the weigh cell conveyor running in guide means whose entry is depressed below the surface of said preceding conveyor and whose guide track is gradually elevated to a level sufficient to lift the article being transported clear of the preceding conveyor.

4. A checkweighing machine as claimed in Claim 3, wherein the transporting means of the weigh cell conveyor comprises a pair of chains running in guide slots, the article being weighed resting on the chains.

5. A checkweighing machine as claimed in Claim 4, wherein within the overlap zone the guide slots are inclined at about 5" to the horizontal.

6. A checkweighing machine as claimed in any one of Claims 3 to 5, wherein the weigh cell conveyor has an exit guide of similar characteristics to the entry guide but of opposite hand whereby the article having been weighed is tranferred to a take-off conveyor.

7. A checkweighing machine as claimed in Claim 5, wherein the conveyor preceding the weigh cell conveyor and the take-off conveyor are a single conveyor extending the full length of the machine.

8. A checkweighing machine substantially as hereinbefore described with reference to and as shown in Figs. 3 to 6 of the accompanying drawings.