GB2237381A

GB2237381A - Apparatus and method for monitoring particulate material

Info

Publication number: GB2237381A
Application number: GB9019298A
Authority: GB
Inventors: Derek William Robert Covacic
Original assignee: PRISECTER SAMPLING PLC
Current assignee: PRISECTER SAMPLING PLC
Priority date: 1989-09-05
Filing date: 1990-09-04
Publication date: 1991-05-01
Anticipated expiration: 2010-09-04
Also published as: GB9019298D0; GB2237381B; GB8920056D0

Abstract

Apparatus for monitoring characteristics of particulate material comprises a vibratory feeder 32 arranged to receive particulate material, e.g. from a sample splitter 20, and an electro-optical imaging device such as a video camera 52 arranged to view the particulate material on the vibratory feeder. The vibratory feeder separates the particles of the particulate material and the video camera produces electronic signals from which information regarding the required characteristics may be derived. e.g. in the form of a particle size distribution curve. The vibratory feeder may have a transparent or translucent portion 46, the particulate material being backlit by light tubes 50. Alternatively the vibratory feeder is reflective and the particulate material is lit from above. <IMAGE>

Description

APPARATUS AND METHOD FOR MONITORING PARTICULATE MATERIAL The invention relates to apparatus and methods for monitoring characteristics of particulate material and has particular but not exclusive relevance to the monitoring of the size and size distribution of particles of particulate materials such as aggregate.

It is commonly a requirement in the production of particulate material that specific characteristics be maintainea, e.g. that the size or size distribution of particles in the material be within a particular range.

Commonly, this is achieved in the manufacture or selection of particulate material by screening particulate material through a series of sieves of different mesh and selecting that fraction having the desired size characteristics.

A failure in one of the meshes used may allow particulate material to pass through which is not of the correct size.

To guara against this, it is the practice to monitor the size characteristics of the material produced at the end of the process. This is conventionally done by taking a representative sample periodically and passing this through a series of analytical sieves manually. Weight measurements are then taken and the size and size distribution of the particles calculated as appropriate. This kind of quality control is laborious and time consuming. During the time taken to perform the analysis, large quantities of sub-standard material may be produced. This material may have to be discarded or may have to be recycled.

It woula be aesirable to have a system of monitoring characteristics of particulate material as it is produced which is adapted to provide more rapidly information relating to important characteristics of the material.

Optical systems for measuring particle size distributions have been described but these have not in practice been adopted by the industry. Generally, such systems attempt to separate particles in a sample for analysis by dropping the particles in a curtain from an upper conveyor to a lower one. The optical device used views the falling curtain of particles. This type of teaching is exemplified by EP-A-0059115 (Etats Francais).

We have appreciated that a drawback of such systems is that the free falling particles will not all present their largest area to the optical device ana so the size distribution measured is unlikely to correlate well with that measured by seiving.

EP-A-0147802 relates to measuring the size distribution of tobacco leaf laminae and describes separating laminae from one another using a viDrating conveyor which drops the separated laminae on to an endless conveyor upon which they are optically measured.

We have found that a system of this kind provides inadequate separation of particulates such as aggregate and yields poor information.

We nave discoverea that particulates such as aggregate can be separated adequately for optical measurement using a vibratory feeder, provided that the optical viewing step is carried out whilst the particulates are still on the vibratory feeder. We have further discovered that substantially improved information can be obtained if the particulates on the vibratory feeder are back lit for viewing.

The present invention provides apparatus for monitoring characteristics of a particulate material, which apparatus comprises a vibratory feeder arranged to receive said particulate material and an electro-optical imaging device arranged to view said vibratory feeder and said particulate material sample carried thereon in use ana adapted to produce electronic signals from which information regarding said characteristics may be derived. The use of a vibratory feeder to convey the sample through the field of view of the imaging device serves to present the particles of sad sample to saiaimaging device with the particles in said sample substantially all separated from one another.

The vibratory feeder will normally be a vibratory tray feeder.

The apparatus may further comprise means for illuminating particulate material on said vibrating feeder for viewing by said imaging device.

Said illuminating means is preferably suitable for backlighting said particulate material.

To this end said vibratory feeder may have a translucent or transparent portion viewed by said imaging device and said illuminating means may be arranged to backlight said particulate material through said portion.

The apparatus may further comprise means for separating fines from said particulate material prior to viewing by said imaging device.

Said fines separating means may comprise a mesn portion providea in said vibratory feeder over wnich mesh or grid potion the particulate material is passed in use prior to said viewing, and means for collectinq fines passing through said mesh portion.

The apparatus may further comprise means for weighing collected fines.

Air flow through the mesh or grid may be provided to assist in the removal of fines, and especially of dust, e.g. by a vacuum source.

The average particle size of the particulate material may be from 3 to 40 mm, e.g. from 10 to 30 mm.

Typically, the particles within a sample will be such as to pass through a mesh having 50mm or smaller openings (e.g. 30 mm) but such as not to pass through a mesh having 3 mm openings or larger (e.g. 10 mm). Examples of particulate material which may be monitored include aggregate, e.g. roadstone, coal, minerals and animal feed. The particulate material may be a starting material, an intermediate or a final product.

Data processing systems are known which are capable of performing a size analysis on particles viewed by a video camera but it is generally necessary that the particles be presented to the camera are all separated from one another. Where particles touch, they will generally be interpreted by the data processing system as being a single larger particle.

The characteristics to be monitored may be the sizes of particles in said material or the distribution of said sizes and said imaging device may be adapted to produce electronic signals trom which information regarding particle size or size distribution may be derived.

However, the apparatus may be intended to provide information relating to characteristics of the particulate material other than size.

The mode of operation of vibratory feeders is such that the individual particles of particulate material placed on such a feeder tend to move apart from one another as they progress along the feeder which assists materially in presenting the particles to an imaging device with the particles substantially all separated from one another.

Ideally, the particles will all be separated from one another but it will generally be acceptable for a small proportion of the particles to touch. Preferably, at least 90% of the particles are separate from any other particle, more preferably more than 95%, e.g.

998.

The apparatus may further comprise means for producing a representative sample for monitoring from a supply of particulate material and for depositing said representative sample on said vibratory feeder for monitoring.

The sampling means may comprise a sample splitter for receiving a representative bulk sample of said particulate material, splitting off a representative sample thereof and supplying said representative sample for monitoring to said vibratory feeder.

Various forms of sample splitter suitable for this purpose are known.

The sample splitter may be adjustable to vary the fraction of said material split off as said representative sample (the split ratio).

Typically, such a sample splitter has an inlet for material, a pair of outlets for material ana a aeflector plate with an aperture therein which serves normally to deflect material from the inlet to the first of the outlets through which the bulk of the sample material is expelled. The aeflector plate rotates in use and when the aperture therein is aligned with the second outlet of the splitter, a fraction of the sample material is allowed to pass through to the second outlet as a sample for monitoring.

The sample splitter may be adjustable to provide a representative sample for monitoring having a volume between l/lOth and 2 of the bulk sample volume.

The sample splitter split ratio may be settable in conjunction with the rate of material transport along the vibratory feeder for the representative sample for monitoring so that suitably sized batches of material deposited on to the feeder for the representative sample monitoring do not overlap.

Ideally a small gap should be present between each batch of sample material on the vibratory feeder.

The sampling means may further comprise means for removing said representative bulk sample from a supply of said particulate material and a bulk sample conveying means arranged to supply said bulk sample progressively to said sample splitter.

The bulk sample conveying means may be a further vibratory feeder. A sample loaded onto the starting end of a vibrating tray feeder will be gradually spread and separated and will be fed progressively from the discharge ena of the feeder to the sample splitter.

The rate of material transport along the bulk sample conveying means preferably can be controlled independently of the rate of material transport along the vibratory reefer for the sample for monitoring.

The rate of material transport along the vibratory feeder for the sample for monitoring may be adjustable between 1/3 and t of the rate of material transport along the bulk sample conveying means.

The vibrating tray of a vibrating tray feeder used as the vibratory feeder for the material for monitoringmay include an optical viewing area below the imaging device which may be provided with a polished surface to assist in the production of a high quality image.

The imaging means may be a video camera.

The imaging means may be provided with means for producing shadowless illumination of particles on said conveying means for said sample for monitoring.

The imaging means may be mounted at the apex of a generally downwardly directed hood and the means for producing shadowless illumination may comprise one or more light sources contained within the hood, the hood serving to reflect light from said light sources down onto the conveying means. However, backlighting as described above is preferred.

The apparatus may further comprise data processing apparatus adapted to derive information relatinq to said characteristics from signals produced in use by said imaging means.

The data processing apparatus may be adapted to derive information relating to the size and/or size distribution of said material.

The invention includes a method for monitoring characteristics of a particulate material comprising conveying said particulate material on a vibratory feeder to an electro-optical imaging device arranged to view said sample on said feeder, the particles within said sample as presented being substantially all separated from one another and deriving electronic signals from which information regarding said characteristics may be derived.

The invention further includes a method of producing particulate material including monitoring characteristics of the particulate material by a monitoring method as described above.

The invention includes also particulate material produced by such a manufacturing method, e.g.

aggregate.

The invention will be illustrated by the following description of a preferred embodiment with reference to the accompanying drawing in which: Figure 1 shows a schematic side view of apparatus incorporating a first embodiment of the invention; and Figure 2 shows a similar view of apparatus including a second embodiment.

As shown in Figure 1, a first hopper 1 is arranged to receive a sample of particulate material from a supply of such material. Hopper 1 has an outlet positioned above the inlet end of a vibrating tray feeder 2. The discharge end of tray feeder 2 is positioned above a second hopper 3 having an outlet communicating with the interior of a sample splitter 4.

Sample splitter 4 has a first outlet 5 discharging to waste and a second outlet 6 positioned above the inlet end of a second vibrating tray feeder 7.

Each of the vibrating tray feeders is provided with an electrical actuator, that for tray feeder 2 is not shown.

In a first section of the length of the vibrating tray feeder 7, the floor of the feeder is formed as a mesh or grid at 8 to allow dust and fine particles to fall through to be collected and to be discharged.

A video camera 9 is positioned at the apex of a downwardly directed hood 10 around the rim of which are provided light sources 11.

Immediately below tne video camera 9 is a portion of the tray feeder 7 which has a polished surface.

Data processing apparatus (not shown) is connected to the video camera 19 for processing the image from the camera to provide information relating to size ana size distribution of particles.

In use, particulate material is removed from a supply, e.g. a belt conveyor, and is introduced as a representative sample into hopper 1 from which it falls on to tray feeder 2. The sample is spread out and discharged progressively from the tray feeder 2 to hopper 3 of the sample splitter. An adjustable fraction of the sample is discharged through the outlet 6 of the sample splitter on to the inlet end of tray feeder 7.

The sample is further spread out as it progresses along the tray feeder 7, fines such as dust associated with the sample falling through the grid 8 to waste.

Alternatively these may be collected and weighed. As the sample passes under the video camera 9 it is illuminated in a shadowless manner against the reflective surface of the polished portion of the tray feeder to provide a good image of the particles which at this point are separated such that substantially all of them do not touch another particle.

It may be desirable to select the colour or darkness of the background to enhance the contrast according to the lightness or darkness of the colour of the particulate material.

By standard data processing techniques, it is possible to derive the number or weight percentage of particles within an allowable range of size, e.g. within an allowable range of oversize above a target range. It is possible to determine the percentage of particles below a particular bottom size. The system may be arrangea to provide a warning if more than an allowable fraction of oversize material is found. The system may be arranged to provide the elongation factor of the particulate materials, i.e. the ratio of their length to breadth.

The apparatus described with reference to the drawing is adapted to operate in a continuous real-time mode to provide the required size information substantially instantaneously so that in the event of a mesh failure in the production process, the process may be halted or switched to an alternative set of production meshes whilst repairs are carried out before any substantial volume of particulate material is processed through the aefective mesh.

The apparatus shown in Figure 2 differs from that shown in Figure 1 principally in providing for backlighting of the particulate material during monitoring. The apparatus comprises a sample splitter 20 having an inlet hopper 22 and having a first outlet for the bulk of the material passed through the splitter at 24. The splitter has a second outlet for the representative sample selected by the splitter at 26 which directs a selected sample via a cascade including baffle plates 28 and 30 to the upstream end of a vibratory feeder in the form of a vibrating tray conveyor 32. Moving downstream along the vibratory feeder one comes first to a metal grid portion 34 of the floor of the feeder through which fines such as dust fall in use to a weighing chamber 36 incorporating a load cell 38.Fines falling through the grid 34 are collected by a hopper 40 and directed to the weighing chamber 36.

At its base, the weighing chamber 36 has an outlet valve 42 which when openec releases the fines from the weighing chamber 36 to the upstream end of a second vibratory feeder in the form of a vibrating tray feeder 44.

On the vibrating tray feeder 32, downstream from the metal grid portion 34 is a translucent floor area 46 beneath which is situated a light box 48 containing light tubes 50 for backlighting particulate material on the translucent area 46. Above the translucent area 46 is situated a video camera 52. The vibrating tray feeder 32 is provided with an electrical acuator 54 and the second vibrating tray feeder 44 is provided with an electrical acuator 56.

In use, a bulk sample of particulate material is introduced into the hopper 22 of the sample splitter 20 and a representative sample for monitoring is produced at the outlet 26 of the sample splitter 20. The particles within the representative sample are separated by the action of the vibrating tray feeder 32, fines being lost through the metal grid 34 into the weighing chamber 36. The remaining particulate material is monitored by the video camera 52 backlit by the light box 48. This provides excellent contrast whether the particulate material is light or dark in appearance.

The size distribution of the particulate material may be derived from the video image of the particulate material. The measured weight of the fines may be used to complete the distribution curve to take account of the whole of the weight of the sample.

Whilst the invention has been described with reference to the specific embodiment, many variations and modifications thereof are possible within the scope of the invention.

The invention includes a vibrating tray feeder in which a portion of the conveying surface is transparent or translucent so as to provide a good support for backlighting material on the feeder for imaging by a video camera.

Claims

1. Apparatus for monitoring characteristics of a particulate material, which apparatus comprises a vibratory feeder arranged to receive said particulate material and an electro-optical imaging device arranged to view said vibratory feeder and said particulate material sample carried thereon in use and adapted to produce electronic signals from which information regarding said characteristics may be aerived.

2. Apparatus as claimed in Claim 1, wherein the vibratory feeder is a vibrating tray feeder.

3. Apparatus as claimed in Claim 1 or Claim 2, further comprising means for illuminating particulate material on said vibratory feeder for viewing by said imaging device.

4. Apparatus as claimed in Claim 3, wherein said illuminating means is suitable for backlighting said particulate material.

5. Apparatus as claimed in Claim 4, wherein said vibratory feeder has a translucent or transparent portion viewed by said imaging device and said illuminating means is arranged to backlignt said particulate material through said portion.

6. Apparatus as claimed in any preceding claim, wherein the characteristics to be monitored are the sizes of particles in said material or the distribution of said sizes and said imaging device is adapted to produce electronic signals from which information regarding particle size or size distribution may be derived.

7. Apparatus as claimed in any preceding claim, wherein the operating frequency of the vibratory feeder is adjustable to vary the rate of conveying of particles thereon in use.

8. Apparatus as claimed in any preceding claim, further comprising means for separating fines from said particulate material prior to viewing by said imaging device.

9. Apparatus as claimed in Claim 8, wherein said fines separating means comprises a mesh portion provided in said vibratory feeder over which mesh portion the particulate material is passed in use prior to said viewing, and means for collecting fines passing through said mesh portion.

10. Apparatus as claimed in Claim 9, further comprising means for weighing collected fines.

11. Apparatus as claimed in any preceding claim, wherein said imaging means is a video camera.

12. Apparatus as claimed in any preceding claim, further comprising data processing means adapted to derive information relating to said characteristics from signals produced in use by said imaging means.

13. Apparatus as claimed in Claim 12, wherein the data processing apparatus is adapted to derive information relating to the size and/or size distribution of said material.

14. Apparatus as claimed in any preceding claim further comprising means for producing a representative sample for monitoring from a supply of particulate material and for depositing said representative sample on said vibratory feeder for monitoring.

15. Apparatus as claimed in Claim 14, wherein said sampling means comprises a sample splitter for receiving a representative bulk sample of said particulate material and splitting off a said representative sample thereof for monitoring.

16. Apparatus as claimed in Claim 15, wherein the sample splitter can be adjusted to vary the fraction of said material split off as said representative sample (the split ratio).

17. Apparatus as claimed in Claim lOr, wherein the sample splitter is adjustable to provide a sample for monitoring having a volume between l/lOth and 1 of the bulk sample volume.

18. Apparatus as claimed in Claim 16 or Claim 17, wherein the sample splitter split ratio is settable in conjunction with the rate of material transport along the vibratory feeder for the representative sample for monitoring so that suitably sized batches of material deposited on to the vibratory feeder for the representative sample for monitoring do not overlap.

19. Apparatus as claimed in any one of Claims 15 to 18, wherein said sampling means further comprises means for removing said representative bulk sample from a supply of said particulate material and a bulk sample conveying means arranged to supply said bulk sample progressively to said sample splitter.

20. Apparatus as claimed in Claim 19, wherein the bulk sample conveying means is a vibrating tray feeder.

21. Apparatus as claimed in Claim 19 or Claim 20, wherein the rate of material transport along the bulk sample conveying means can be controlled independently of the rate of material transport along the vibratory feeder for the representative sample for monitoring.

22. Apparatus as claimed in any one of Claims 19 to 21, wherein the rate of material transport along the vibratory feeder for the representative sample for monitoring is adjustable to be between 1/3 and t of the rate of material transport along the bulk sample conveying means.

23. Apparatus for monitoring characteristics of a particulate material substantially as hereinbefore described with reference to and as illustrated in Figure 1 or Figure 2.

24. A method for monitoring characteristics of a particulate material comprising conveying said particulate material on a vibratory feeder to an electro-optical imaging device arranged to view said sample on said feeder, the particles within said sample as presented being substantially all separated from one another and deriving electronic signals from which information regarding said characteristics may be derived.

25. A method as claimed in Claim 24, including a preliminary step producing a representative sample of said particulate material for monitoring.

26. A monitoring method as claimed in Claim 24 or Claim 25, wherein the particulate material is aggregate.

27. A method of producing particulate material including a monitoring method as claimed in any one of Claims 24 to 26.

28. Particulate material produced by a method as claimed in Claim 27.

29. A vibrating tray feeder in which a portion of the conveying surface of the feeder is transparent or translucent.