AU2016200790B2

AU2016200790B2 - Mitigating the Consequences of Conveyor Belt Wander

Info

Publication number: AU2016200790B2
Application number: AU2016200790A
Authority: AU
Inventors: Barry Charles Brown
Original assignee: Bemo Pty Ltd
Current assignee: Bemo Pty Ltd
Priority date: 2015-02-13
Filing date: 2016-02-08
Publication date: 2020-06-04
Anticipated expiration: 2036-02-08
Also published as: AU2020203474A1; AU2016200790A1

Abstract

A method and apparatus for ameliorating the consequences of belt wander in troughed conveyor belts is disclosed. The location of the belt edges is measured or sensed by ultrasonic probes (1, 2) or proximity switches (9-14). Only when the wander to the left equals the wander from the right is a usable measurement taken (to avoid belt edge defects). A belt wander factor is then calculated using a microprocessor (8). A hierarchy of belt wander factors is used to determine whether remedial action should be taken before having to stop the belt (3). 5004M-AU ru o(D C) 'NJ)

Description

Mitigating the Consequences of Conveyor Belt Wander

Field of the Invention

The present invention relates to conveyor belts.

Background Art

Conventional troughed belt conveyors are universally used for the conveyance of bulk materials and they represent a very efficient and cost-effective transport solution over short to medium distances. However, as with most mechanical devices, this type of conveyor system can suffer from challenging operational issues.

One such operational issue is belt wander, also known as mistracking or belt drift.

A traditional belt conveyor has the belting supported in a generally V or U configuration by troughing idler rollers while conveying the product in the ‘carry path’. In the “return path” the belt can have either a flat configuration or ‘V’ configuration, being supported by return idler rollers.

At the load point (Tail) and discharge point (Head) of the conveyor, there are a number of pulleys where the belt is flat. These pulleys allow for the belt to be driven, permit the application of background tension, and allow for any desired change of direction.

In a perfect world, the running belt would track along the lateral centre of the support structure, in both the laden or unladen conditions.

This is often not the case.

When a new belt conveyor is installed, the support structure is carefully aligned so that the empty running belting sits in the centreline of the structure, all the way on its endless journey around the conveyor path. This is commonly achieved using laser alignment tools and/or ‘toe in’ of the wing troughing idler rollers, and/or a “V” in the return rollers.

There may also be tracking devices fitted to the conveyor structure.

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Also, any splices in the endless belting are checked for ‘straightness’ as splices which do not transfer belt tension across the splice along the centreline of the belting can give rise to belt wander in the region of such splices.

Over time, belt tracking characteristics often change due to movement of components (eg. by subsidence of support foundations) , and/or component wear, and/or increasing build up of conveyed product on the various conveyor elements. Wet belting, temperature changes and wind are all additional factors. The end result is that a running belt, even when empty, can wander significantly from the centreline of the structure.

The primary driver for belt tracking is thought to be interference between the belt and its support structure.

When product is loaded onto the belt, this interference is thought to increase significantly, particularly in the carry path.

When the product is of high density, like iron ore, copper ore, bauxite ore, etc., if it is not loaded uniformly and centrally onto the receiving conveyor, belt wander can be exacerbated. In many conveyor belt arrangements, the conveyor belt is used as a blender to blend different grades of material. Often this incorporates side loading or sequential loading of material having different densities and coming from different sources.

The centre of gravity of the conveyed product tends to act through the vertical centreline of the structure. Off-centre product loading can cause the belt to assume a lateral position on the structure, which is not co-incident with the centreline of the structure, ie. belt wander is created or exacerbated.

A small amount of belt wander is common and generally accepted, up to say, 50mm either side of the normal position of the edge of the belt, but often the wander is much more.

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Excessive belt wander can lead to any or all of (i) gross product spillage, (ii) damage to the belt, and (iii) damage to the conveyor structure.

It is normal to have belt wander detection systems fitted to this type of conveyor. Typically the belt has to have wandered by some ‘critical’ amount before these systems are activated. Activation of a belt wander detection system usually results in the conveyor being stopped, in order to minimise the three above-mentioned negative effects. Stopping the conveyor belt is very undesirable as it causes un-scheduled downtime in the plant, with consequent loss of production and financial loss.

In particular, in some installations where, for example, material is being reclaimed from a stockpile to be loaded onto a ship, or is being received from a train or truck dump station for stockpiling, multiple conveyors in series may be used to transport the material. If any one of these is stopped because of belt wander, then it is necessary to stop all the upstream conveyors. To restart the series of conveyors requires a scheduled or sequential restarting procedure to be carried out. This can be a time consuming procedure.

Genesis of the Invention

The genesis of the present invention is a desire to sense and then measure the degree of the wander in any particular conveyor and if the wander continues towards the critical state, implement one or more remedial procedures to allow the conveyor to continue to run and return to an acceptable location on the structure. Such a desirable state of affairs may result in a partial interruption in the product stream, but not unscheduled downtime. Thus the negative impacts of belt wander can be to some extent mitigated or ameliorated

Summary of the Invention

In accordance with a first aspect of the present invention there is disclosed an apparatus to ameliorate the effects of belt wander of an endless loop conveyor belt having side edges and a nominal belt position from which the belt deviates in use, said apparatus comprising a plurality of digital proximity switches arranged intermediate the nominal belt edge positions and in a sequence transverse to the direction of travel of the belt to detect the presence or absence of said belt at each location corresponding

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2016200790 21 Jan 2020 to one of said proximity switches, the outputs of said proximity switches forming a digital word indicative of the belt position and being connected as an input to digital processing apparatus having an output used to signal that intervention in the belt operation is required.

In accordance with a second aspect of the present invention there is disclosed amethod of ameliorating the effects of belt wander of an endless loop conveyor belt having side edges and a nominal belt position from which the belt deviates in use, said method comprising the steps of positioning a plurality of digital proximity switches intermediate the nominal belt edge positions and in a sequence transverse to the direction of travel of the belt to thereby detect the presence or absence of said belt at each location corresponding to one of said proximity switches, forming a digital word indicative of the belt position from the outputs of said proximity switches and inputting same to digital processing apparatus having an output used to signal that intervention in the belt operation is required.

Brief Description of the Drawings

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is a transverse cross-sectional view through the carry run of a trough conveyor belt on which the apparatus of the preferred embodiment has been installed, and

Fig. 2 is a schematic transverse cross-sectional view through the return run of a conveyor belt on which the apparatus of a second embodiment has been installed, the apparatus on the left of the belt and the apparatus on the right of the belt being substantially longitudinally coincident.

Detailed Description

Fig 1 shows a conveyor belt (3) sitting centrally on an idler set (4), while conveying product (6).

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In the preferred embodiment of the invention, two ultrasonic distance-measuring probes (1) and (2) are fitted to the conveyor structure (7), one on either side of the running conveyor belt. Each of the probes (1) and (2) is an analogue output 4-20mA device, with a typical measurement range of 100mm - 1,000mm. The neutral (that is without any belt wander being present) conveyor belt edge-to-probe distance is typically 300mm.

The preferred location for the probes (1) and (2) in the conveyor path is just after the last load point in the belt carry path, for example 20 - 50 m downstream from the last load point. However, other locations in the conveyor path may be chosen instead, or in addition.

The probes (1) and (2) are aligned so that they use the actual belt edge as their targets. As either belt edge moves closer to, or further away from, a probe, the output of the probe changes, either up or down, depending on the direction of movement.

The probes (1) and (2) should be longitudinally located close to idler rollers (5) so that the plane of belt sideways movement is predictable and uniform. Preferably, in this way belt flutter and sag is at a minimum at the location of the probes. This locating arrangement ensures the probes (1) and (2) do not lose their targets.

The 4-20mA output from the two probes is connected to a corresponding input of a microprocessor (8).

After calibration during commissioning, the 4-20mA probe outputs are converted to millimetres by the microprocessor (8). Probe 1 provides a distance measurement D1 and probe 2 provides a distance measurement D2.

The apparatus is ‘zeroed’ by the microprocessor (8) with the belt (3) in its central position.

The current values of DI and D2 are monitored in the microprocessor. When the DI and D2 values change inversely and equally, a ‘Wander Factor’ is calculated within

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2016200790 21 Jan 2020 the microprocessor (8). The “Wander Factor” includes a direction of wander and its magnitude in mm.

A variation in DI and D2 values which does not satisfy the above inverse and equal change condition is likely to be the result of belt edge damage such as a bight in the belt edge, or some other spurious effect, and is therefore ignored by the microprocessor (8).

Multiple thresholds are then entered by the end-user into the microprocessor (8) and these thresholds are compared by the microprocessor (8) with the Wander Factor. There are preferably five (5) thresholds and as each threshold is violated an appropriate Command issues into the Site Supervisory Control & Data Acquisition (SCADA) system.

The Threshold / Action Table of the first embodiment is preferably the following:

Threshold	Wander Value	Action
T1	+/- 50mm	Flag Only - Conveyor X has wandered 50mm to the Left/Right
T2	+- 100mm	Flag Only- Conveyor X continues to wander to the Left/Right
T3	+/- 200mm	Action - Potential Wander Event, apply remedial procedure(s)
T4	+/- 250mm	Action - Wander Event turn off feed
T5	+/- 300mm	Action - Wander Event Critical - Stop Conveyor

In this way there is the opportunity to apply at least one remedial action to halt the belt wander before it becomes critical and leads to a belt stop. Such remedial actions

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2016200790 21 Jan 2020 can include applying a sideways force to the belt, for example immediately before the tail pulley, and altering the direction, and/or speed, and/or angle of loading of material onto the conveyor.

The foregoing describes only a first embodiment of the present invention and modifications, obvious to those skilled in the conveyor belt arts, can be made thereto without departing from the scope of the present invention.

For example, in the other embodiments of the invention, the probe outputs are made directly available to a Site PLC as 4-20mA retransmitted signals and the Site PLC then controls the appropriate response.

Alternatively, the microprocessor (8) can be used to drive the operation of a servocontrolled belt tracking device whereby belt lateral position information defined by the Wander Factor completes a feedback loop.

Similarly, where multiple pairs of probes (1 & 2) are used, each pair of probes will have its own microprocessor (8) which is thus connected into the site SCADA. In this connection adjacent pairs of probes may be many hundreds of metres or kilometres apart.

A second embodiment of the invention, as illustrated in Fig. 2, can be utilised where space is restricted and locating Probes 1 and 2 of Fig. 1 in the preferred positions may be impractical or impossible. Under these conditions, a number of discrete proximity switches (not analogue devices) (9), (10), (11), (12), (13) and (14) can be employed adjacent the underside and towards the outer edges of the conveyor belt (3). The distance away from the belt surface is determined by the type of proximity switches being employed and the distance away from the belt edges is determined by the degree of belt wander that can be tolerated.

The proximity switches (9), (10) and (11) are located adjacent the left-hand edge of the belt (3) and are connected to a “left” Preamp - L (15). The proximity switches (12), (13) and (14) are located adjacent the right hand edge of the belt (3) and are connected to a “right” Preamp - R (16). Each proximity switch has two states, ON

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2016200790 21 Jan 2020 and OFF. When covered by the belt a switch is ON and when in free space the switch is OFF.

This enables the creation of a 6-bit digital “word” to define the lateral position of the belt.

Depending on the state of each switch, the Preamps (15) and (16) produce a current output in the range 4-20mA, which is delivered to the Microprocessor (8).

It can be seen from Fig. 2 that when the conveyor belt (3) is in its neutral position (A) on the structure, (indicated by solid lines in Fig. 2), all six switches are covered by the belt and are therefore ON. When the belt wanders to the right and is at location (B), (indicated by dashed lines in Fig. 2), switch (9) is OFF, while the remaining switches continue to be ON. Further wandering to the right places the belt into location (C), (again indicated by dashed lines in Fig. 2), thereby forcing switch (10) OFF. If the wander continues, this places the belt at location (D) and forces switch (11) OFF. Again, the location (D) of the belt is indicated by dashed lines in Fig. 2. Switches (12), (13) and (14) remain ON for belt locations (A) through (D) inclusive.

The Preamps convert the digital ‘word’ as determined by the states of the switches into an analogue output. The outputs from the Preamps conform with the following Table, depending on belt lateral location

Preamp - L (15)

Belt Position (A)

Belt Position (B)

Belt Position (C)

Belt Position (D)

Preamp - R (16)

Belt Position (A)

Belt Position (B)

Belt Position (C)

Belt Position (D)

Output in mA

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It will be apparent that if the belt wanders to the left, the Preamp outputs will be reversed.

The Microprocessor (8) interprets the output currents of Preamp - L and Preamp - R and is able to determine the direction and magnitude of belt wander. This information is able to be passed on to the site SCADA which invokes remedial action(s) as appropriate, or is able to be used directly to drive a servo-controlled belt tracking or aligning device.

Claims

1. An apparatus to ameliorate the effects of belt wander of an endless loop conveyor belt having side edges and a nominal belt position from which the belt deviates in use, said apparatus comprising a plurality of digital proximity switches arranged intermediate the nominal belt edge positions and in a sequence transverse to the direction of travel of the belt to detect the presence or absence of said belt at each location corresponding to one of said proximity switches, the outputs of said proximity switches forming a digital word indicative of the belt position and being connected as an input to digital processing apparatus having an output used to signal that intervention in the belt operation is required.

2. The apparatus as claimed in claim 1 wherein said proximity switches are arranged adjacent the underside of said belt.

3. The apparatus as claimed in claim 1 or 2 wherein said digital processing apparatus incorporates two thresholds, a first lower threshold indicative of the requirement that at least one remedial procedure needs to be applied to the belt operation, and a second upper threshold indicative of the need to stop operation of the belt.

4. The apparatus as claimed in any one of claims 1-3 wherein a first plurality of said proximity switches is located adjacent a first edge of said belt and a second plurality of said proximity switches is located adjacent a second edge of said belt.

5. The apparatus as claimed in any one of claims 1-4 wherein the numbers of said first and second pluralities of proximity switches are equal.

6. The apparatus as claimed in claim 5 wherein the total of said proximity switches is six.

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7. The apparatus as claimed in any one of claims 1-6 wherein said digital processing apparatus comprises a pair of pre-amplifiers and a microprocessor.

8. The apparatus as claimed in any one of claims 1-7 wherein the output of said digital processing apparatus is connected to a Site Supervisory Control & Data Acquisition (SCADA) system.

9. A method of ameliorating the effects of belt wander of an endless loop conveyor belt having side edges and a nominal belt position from which the belt deviates in use, said method comprising the steps of positioning a plurality of digital proximity switches intermediate the nominal belt edge positions and in a sequence transverse to the direction of travel of the belt to thereby detect the presence or absence of said belt at each location corresponding to one of said proximity switches, forming a digital word indicative of the belt position from the outputs of said proximity switches and inputting same to digital processing apparatus having an output used to signal that intervention in the belt operation is required.

10. The method as claimed in claim 9 including the step of positioning said proximity switches adjacent the underside of said belt.

11. The method as claimed in claim 9 or 10 including the step of providing said digital processing apparatus with two thresholds, a first lower threshold indicative of the requirement that at least one remedial procedure needs to be applied to the belt operation, and a second upper threshold indicative of the need to stop operation of the belt.

12. The method as claimed in any one of claims 9-11 including the further steps of positioning a first plurality of said proximity switches adjacent a first edge of said belt and positioning a second plurality of said proximity switches adjacent a second edge of said belt.

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13. The method as claimed in any one of claims 9-12 including the step of making the numbers of said first and second pluralities of proximity switches equal.

14. The method as claimed in claim 13 wherein the total of said proximity switches is six.

15. The method as claimed in any one of claims 9-14 wherein said digital processing apparatus comprises a pair of pre-amplifiers and a microprocessor.

16. The method as claimed in any one of claims 9-15 including the step of connecting the output of said digital processing apparatus to a Site Supervisory Control & Data Acquisition (SCADA) system.