GB2062256A - Measuring Stress in Chains Etc. - Google Patents

Abstract

In a moving chain conveyor etc. stress is measured by a means constraining the chain to a curved path over a portion of its travel and measuring the force of the constraining means. The means may comprise a straight section track (18) and a curved section (17), the width of a gap between the sections, being varied by the stress and monitored by a force transducer (21). The transducer (21) is mounted, at the gap, between a yoke (30) and a flange (25) of the section (18). The yoke (30) is pivotably mounted on the track sections (17, 18) at bearing points (23, 22) so as to pivot about point (23) on section 17. An embodiment using a gap separating two straight sections each joined to a curved section is also described. The device may operate an excess tension alarm or control. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Chain Conveyors This invention relates to an improved stress measuring device for measuring the stress in a chain or flexible elongate member which is contrained to move in a track for part or all of its length.

One use of such a chain is in a chain conveyor system. In such a system the chain is required to move in a track which can be arranged in three dimensions. The system is used for conveying articles around an area such as a factory or store.

The articles are suspended from the chain and as the chain is driven round its track, by a drive unit, the articles move with it.

Chain tension measurements in such a system are used inter alia as a guide for maintenance and a guide for design of track layout.

Known tensometers measure the tension in the chain by direct sensing and use a sensor mounted in a chain test link. The sensor is commonly either of hydraulic, pneumatic or electric strain gauge type and is monitored by apparatus suspended from the test link. Thus the link and monitoring apparatus move round the chain circuit during the time the measurements are made.

Such a moving tensometer/monitor arrangement usually restricts its use to nonoperational periods. Also, such a tensometer is diffucilt to use as an excess tension alarm or as a sensing element to control the tension in the chain via the chain drive units, both of which would be desirable features.

According to the present invention there is provided an apparatus for measuring stress in a flexible elongate member while said member is in motion along and constrained to an at least partially curved path, said apparatus comprising a length of track having a first section and a second section separated by a gap, said track disposed on said path, said first and second sections mounted such that motion of said first section relative to said second section is permitted in a direction tangential to said path at said gap so as to tend to change the gap width, means at said gap for sensing forces between said two sections, said two sections arranged so that when said elongate member is in motion along said path stress in said elongate member tends to change the gap width without causing substantial displacement of said gap.

Two embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a diagram of a rope or chain constrained by a straight track Fig. 2 is a diagram of a chain constrained to move in a curved track; Fig. 3. is a schemmatic diagram of the forces acting when the chain is under tension; Fig. 4. shows the mounting of a sensor on the track.

It is to be noted that the drawings are not to scale and are merely to illustrate embodiments of the present invention.

A first embodiment is illustrated in Fig. 1 Referring to Fig. 1 a rope or chain 32 is constrained by two track sections 30 and 31 which have a gap 33 between their adjacent ends.

A weight 34 is suspended by rope or chain 32, which is constrained to curve round a freely rotatable wheel 35, after emerging from track section 31. The wheel 35 is attached to track section 31 by a support 36. The rope or chain 32 is gripped by a pair of wheels 37, 39 which are attached by supports 38 to track section 32.

In order to raise or lower the weight 34 wheel 37 is rotated in a clockwise or anti-clockwise direction respectively and wheel 39 is rotated in an anti-clockwise or clockwise direction respectively. The rotation of wheels 37, 39 may be effected by a motor or other mechanism (not shown).

The tension in the rope or chain 32 is applied to track section 30 via the wheels 37, 39 and the supports 38, and to track section 31 via the wheel 35 and support 36 owing to the rope or chain curving round wheel 35. Thus when the rope or chain 32 is in tension, the gap 33 tends to close.

A tensometer mounted across, and maintaining the gap 33 therefore provides a measure of the tension in rope or chain 32.

In a second embodiment the tension, in an elongate tension supporting member constrained by a track, is applied to the track by using a curved section of track. This second embodiment will now be described by way of example with reference to Figs. 2, 3 and 4.

Referring to Fig. 2, a chain is shown which is constrained to move in a track comprising two straight sections (10 and 11) and a section 12 which curves through 900.

The chain comprises a plurality of links, each link comprises wheels 14 and a pair of parallel link plates 13. Axles 40 protrude through and are fastened to holes in the link plates 13. The wheels 14 are freely rotatable about the protruding parts of axles 40. Consecutive links are connected by a universal joint (not shown). The universal joint comprises a block containing two mutually perpendicular non intersecting bearing holes in which axles 40 are freely rotatable. Thus the link plates 1 3 of consecutive links lie in planes which are mutually perpendicular as shown in Fig. 1. The universal joints also have bearing surfaces for the link plates 13.

The motion along its length of straight section 11 is substantially prohibited by its mounting.

The curved section 12 is structurally rigid 900 horizontal bend which is mounted so that it is substantially freely floating (i.e. able to move in all directions).

A gap 1 5 is maintained between sections 12 and 11 by a force transducer. As section 12 is free to move in the horizontal plane the application of forces E and H to the chain would move section 12 so as to reduce the gap 1 5. This compression force across the gap 15 is opposed by a force transducer maintaining the gap, and the output from the force transducer gives a measure of the compression force across the gap.

Fig. 3 is a schemmatic representation of the chain and inner side of the track shown in Fig 2.

The figure shows the forces acting on the inner surface of the track due to the application of the tensional forces FE and FH to the chain. The forces act on the inner track surface via the wheels. They are shown in Fig. 3 resolved into their components along the axes parallel to FE (components a, b, c, d, e, f) and parallel to FH (components g, hj, k, I, m). As the bend is in the horizontal plane and is a 900 bend, the sum of the components parallel to FE are equal to FE, similarly the sum of the components parallel to FH are equal to FH. Thus, the compressive force across gap 15 (in Fig. 1) which is the sum of the components parallel to FH, is equal to the tension in the chain at that point (which is FH).

Fig. 4 shows the mounting of the sensor.

Tracks 1 6 and 1 8 represent the tracks 10 and 11 in Fig. 2 respectively. Track 1 7 represents track 12 in Fig. 2 and represents the 900 bend of the track. It should be noted that no bolts hold the track sections 1 8 and 1 7 together. The sections 16 and 1 7 are positioned such that there is a small gap between the adjacent flanges, 26 of track section 1 7 and 25 of track section 18, when there is no tension in the chain.

A rigid yoke 20 is provided to transfer track forces which operate between flanges 26 and 25 to a transducer 21. The rigid yoke 20 is attached to flange 25 of track section 18 by two needle bearings which are located symmetrically with respect to the axis of the track, one bearing 22 is shown. The rigid yoke 20 is also attached to flange 26 of track section 17, by two needle bearings, located symmetrically with respect to the axis of track section 1 7, one bearing 23 is shown. One end of the force transducer is fastened to yoke 20 and the other end of the force transducer is fastened to flange 25 of track section 18 at point 24. The yoke and the mounting of the transducer thus provide a force multiplying factor equal to the vertical distance between needle bearings 22 and 23 divided by the vertical distance between needle bearing 22 and transducer mounting 24.The yoke lever arrangement in this embodiment has been designed such that the line joining needle bearings 23 cuts the axis of the chain.

A spring adjustment 19 is provided which operates between yoke 20 and flange 25. This spring arrangement is used to adjust the gap and to set the tensometer reading to zero when the chain is not in tension.

The force transducer selected for the tensometer is of a rigid type such that zero to full compressive load causes a movement which is negligible in comparison with the gap width. In a tensometer for a conveyor system designed for a chain tension of 1000 Ib., the force transducer had a movement of approximately 0.002" under a 2000 Ib. force. The selection of such a force transducer ensures that the adjustment of the spring 19 and of the bend section 1 7 to create the required gap, can be neglected and assumed to have no effect on the compression measurements indicated by the force transducer. The compressive force as measured by the transducer multiplied by the reciprocal of the aforementioned multiplying factor (due to the yoke leverage) provides a measure of the chain tension.

The needle bearings are all provided with additional thrust bearings so that track alignment is maintained. The yoke and associated bearings together with the mounting of the force transducer are arranged to allow only one degree of mechanical freedom so that the only force on the force transducer is the compressive force across the gap and no force transverse to the gap axis is transmitted to the force transducer.

It will be realised that the particular embodiments described above are just an example. Alternative designs of the mounting of the force sensor could be used, for example, a structure involving no multiplying factor. Bends of other than 900 could be employed and the sensor could be calibrated by calculation or experiment, to give a direct reading of the tension.

It will also be realised that compression measurements could be made in a similar manner. For example, in the second embodiment, if compression was applied to the chain ends shown in Fig. 2, the wheels 14 would transfer the compression force to the track and the gap 1 5 would tend to open. A sensor across the gap 1 5 would therefore provide a measure of the compression.

It will be understood that a chain tension measuring apparatus constructed on the principles described above can be used in a chain conveyor system to provide an alarm for excess chain tension. The alarm could be used to turn off the chain drive and it could also be used to control the chain tension. In the latter case an output from the tension measuring apparatus would be provided which would be used to control the driving force applied to the chain by the chain drive.

Claims (12)

Claims

1. An apparatus for measuring stress in a flexible elongate member while said member is in motion along and constrained to an at least partially curved path, said apparatus comprising a length of track having a first section and a second section separated by a gap, said track disposed on said path, said first and second sections mounted such that motion of said first section relative to said second section is permitted in a direction tangential to said path at said gap so as to tend to change the gap width, means at said gap for sensing forces between said two sections, said two sections arranged so that when said elongate member is in motion along said path stress in said elongate member tends to change the gap width without causing substantial displacement of said gap.

2. Apparatus according to claim 1 wherein at least one of said sections is a curved section.

3. An apparatus according to claim 1 wherein said first section is a straight section and is mounted so that motion of said first section in said direction is inhibited, and said second section is a curved section and is mounted so that motion of said second section in said direction is permitted.

4. An apparatus according to claims 2 or 3 wherein said curved section is a 900 bend.

5. An apparatus according to any of the preceding claims wherein said means at said gap for sensing forces between said two sections comprises a member which is pivotably mounted on said first section at a first bearing point and is pivotably mounted on said second section at a second bearing point such that a line joining said bearing points is not parallel to said direction, a force transducer mounted between one or other of said track sections and said member.

6. An apparatus according to any of the preceeding claims for measuring tension in an elongate tension supporting member.

7. An apparatus according to any of the preceeding claims wherein said elongate member is a chain.

8. An apparatus according to any of the preceding claims wherein said means at said gap for sensing forces between said two sections comprises an electric strain gauge.

9. An apparatus according to any of the preceeding claims wherein said means at said gap for sensing forces between said two sections designed for a range of said forces is such that application of the maximum value of said range causes a negligible variation of the gap width.

10. An apparatus for measuring stress in a chain substantially as herein before described with reference to the accompanying figures 2, 3 and 4.

11. An apparatus for measuring stress in an elongate member substantially as hereinbefore described with the reference to the accompanying figure 1.

12. A chain conveyor system comprising a chain tension measuring apparatus in accordance with any of the preceeding claims.