GB2041549A

GB2041549A - Measuring tension in chains

Info

Publication number: GB2041549A
Application number: GB7903799A
Authority: GB
Original assignee: Post Office
Current assignee: Post Office
Priority date: 1979-02-02
Filing date: 1979-02-02
Publication date: 1980-09-10
Also published as: GB2041549B

Abstract

A device for measuring the tension in a chain comprised of a plurality of connected links comprises a pair of link plates 10, 11 which are mounted in spaced-apart relationship on articulator blocks 12, 14. Each plate is profiled as indicated by sections 20, 21, 22, 24, 25 and at least one of the plates carries a strain gauge. The device is arranged to form one link in a chain and the profile of each plate is such that when it is under tension that part carrying the strain gauge deforms. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the measurement of tension in chains This invention relates to the measurement of tension in chains.

A known device for measuring tension in a chain, particularly a chain of a chain conveyor, is arranged to constitute one link of the chain. The device comprises a pair of planar side plates which are mounted in parallel spaced relationship by articulators located at each end of the plates. Each plate carries strain indicating means which may take the form of two strain gauges, one extending laterally and the other longitudinally of the plate. The four strain gauges are connected together to form a bridge network and the electrical output from the bridge is sensed to provide an indication of the tension in the chain..

A drawback of this arrangement is that, when the chain is under tension, the strain in each plate is relatively low because the forces generated operate within the plane of each plate. The signal produced by each strain gauge is low and thus the signal to noise ratio of the device is poor.

We propose to profile at least one of the plates so that when the plate is under tension at least part of the plate deforms, strain indicating means being carried by that part of the plate which deforms.

Thus according to the present invention there is provided a device for measuring tension in a chain comprised of a plurality of connected links, said device being arranged to form a link of the chain and comprising a pair of link plates mounted in spaced relationship on mounting members located towards the ends of the plates, at least one of said plates being profiled such that when the plate is under tension at least a part of the plate deforms, and strain indicating means carried by said plate part.

The strain indicating means may comprise a strain gauge carried by said plate part and means for sensing the strain gauge signal.

Preferably each plate is profiled and carries two strain gauges, one on each side of said plate. Each strain gauge may form one arm of a bridge network.

The bridge network may be connected to an electrical indicating instrument which is arranged to indicate the tension in the chain.

Each plate may be profiled to define a central planar portion, two planar end portions parallel to but displaced from the plane of the central portion and intermediate portions extending at an acute angle to the end portions and the central portion which connect the central portion to the end portions. Alternatively each plate may have two planar end portions and a smoothly curved central portion extending between and integral with the end portions.

Due to the profile of the plate when tension is applied to it, the central portion is subjected to a bending strain which results in a substantial signal being generated in the strain gauges.

The invention will be described now by way of example only with particular reference to the accmpanying drawings. In the drawings: Figure 1 is a plan view of a device in accordance with the present invention; Figure 2 is a side elevation of the device of Figure 1,and Figure 3 is a circuit diagram illustrating the way in which the strain gauges of the device are connected together.

The device shown in the drawings has been designed for use in measuring the tension in a chain of a chain conveyor which is used in postal sorting offices. The tension measuring device comprises a pair of link plates 10, 11 which are mounted in spaced apart relationship on articulator blocks 12, 14 located one at each end of the plates. The plates are secured to the blocks by means of nuts 15 which engage the ends of a two piece spindle comprising a bearing sleeve keyed to one of the plates 10, 11 and a central draw spindle. Wheels 16 are located between each nut 15 and the respective end of the plates 10, 11.

Each articulator block 12, 14 comprises a first generally cylindrical portion 17 which is coaxial with the nuts 15 and a second generally cylindrical portion 18 which is integral with the first portion and whose axis extends perpendicular to the first portion 17. The second portion 18 has a central through aperture 19 and is provided to allow the tension measuring device to be connected to links in a chain in a conventional manner.

Each plate comprises first and second planar end portions 20, 21 which are disposed adjacent respective wheels 16, a central planar portion 22 which extends parallel with the end portions 20, 21 but whose plane is displaced inwardly of the device relative to the end portions, and intermediate portions 24, 25 which are integral with the end and central portions and extend at a small acute angle to the end and central portions.

The device includes upper and lower plates 26A, 26B which are mounted on end plates 27 which are loosely pinned or keyed into the link plates 10, 11.

The upper, lower and end platestogetherform a box which is loosely mounted around the link plates and gives protection to electrical components contained within it. The upper plate 26A supports a switching block 29 which contains means by which the position of the device can be sensed electromagnetically at positions along the length of the chain. These sensing means are known and will not be described.

Each side plate 10, 11 carries a pair of strain gauges which are located one on each side of the plate at positions indicated generally at 28. Each strain gauge is bonded to the respective surface of the plate by a resin-based glue. The four strain gauges are connected together in a bridge formation as illustrated in Figure 3. The four strain gauges are represented at 30,31,32 and 33. The bridge arrangement is connected to a terminal plug 35 in a conventional manner. Power is supplied to the bridge via terminals 36,37 and the signal appearing across the bridge appears across terminals 38,39.

The terminals 38,39 are connected to an electrical measuring instrument (not shown) in a conventional manner. The instrument provides an indication of the strain in the plates 10,11.

It will be appreciated that when the device illustrated in Figures 1 and 2 is connected as one link in a chain consisting of a plurality of links and tension is applied to the chain, the central portion 22 of each plate bows which compresses the strain gauge on one side of the plate whilst elongating the strain gauge on the other side. Thus a signal appears across the bridge network and this signal is applied via the terminals 38, 39 to the electrical measuring instrument to indicate the tension in the chain. By profiling the plates as shown in the drawings the signal obtained from the strain gauges is significantly greater than that obtained in the prior art arrangementwhere purely planar side plates were employed.

As an alternative to strain gauges the central section of each link plate may be coated with a brittle lacquer e.g. "Stresscoat". This technique for indicating stress is well known.

Claims

1. A device for measuring tension in a chain comprised of a plurality of connected links, said device being arranged to form a link of the chain and comprising a pair of link plates mounted in spaced relationship on mounting members located towards the ends of the plates, at least one of said plates being profiled such that when the plate is under tension at least a part of the plate deforms, and strain indicating means carried by said plate part.

2. A device as claimed in claim 1 wherein said strain indicating means comprises a strain gauge carried by said plate part, and means for sensing the strain gauge signal.

3. A device as claimed in claim 2 wherein each plate is profiled and carries two stran gauges, one on each side of said plate.

4. A device as claimed in claim 3 wherein said strain gauge forms one arm of a bridge network.

5. A device as claimed in claim 4 wherein the bridge network is connected to an electrical indicating instrument which is arranged to indicate the tension in the chain.

6. A device as claimed in any one of claims 3 to 5 wherein each plate is profiled to define a central planar portion, two planar end portions parallel to but displaced from the plane of the central portion and intermediate portions extending at an acute angle to the end portions and the central portion which connect the central portion to the end portions.

7. A device for measuring tension in a chain substantially as hereinbefore described with reference to and as shown in the accmpanying drawings.