GB2219654A

GB2219654A - Aggregate quality monitoring

Info

Publication number: GB2219654A
Application number: GB8812237A
Authority: GB
Inventors: Anthony Richard Hyde
Original assignee: B & H Specialist Products Limi
Current assignee: B & H Specialist Products Limi
Priority date: 1988-05-24
Filing date: 1988-05-24
Publication date: 1989-12-13
Also published as: GB8812237D0

Abstract

An apparatus for monitoring the quality of aggregate delivered from an aggregate processing system comprises means for generating an image of a sample of the delivered aggregate, and means for deriving data representative of the size of particles within the sample and of the distribution of particle sizes within the sample. The aggregate processing system is then controlled to maintain the particle size and particle size distribution within predetermined limits. The monitoring may be carried out by passing the aggregate in a continuous stream beneath a television camera and storing individual frames of the camera. Means may also provide for stopping the aggregate processing system automatically in the event of the predetermined size and size distribution limits being exceeded.

Description

AGGREGATE QUALITY MONITORING The present invention relates to a method and apparatus for monitoring the quality of aggregate delivered by an aggregate processing system. The term aggregate1 is used herein to mean particulate material formed from broken stones.

Aggregate is produced for a variety of purposes such as road building, concrete production and the like. Stone is crushed in appropriate processing equipment and the crushed output of that equipment is sorted on the basis of particle size. Sorting is generally acheived by passing the processing equipment output over a series of sieves of progressively decreasing mesh size. The quality of the resultant product in terms of particle size uniformity is essentially a function of the efficiency of the sieving equipment and the effectiveness of the operators of that equipment.

For example if a particular sieve is allowed to become clogged small particles which should have passed through that sieve continue to the subsequent sieve in the series and the material passed by that sieve includes relatively small particles which should have been previously removed.

In many applications the particle size is not really critical. For example if one is concerned with the manufacture of bulk concrete a fairly tolerant attitude can be taken to variations in the size of aggregate incorporated in that concrete.

There are however certain applications where particle size is of very considerable importance. For example the particle size of aggregate used for high quality flooring must be carefully controlled if the resultant flooring is to meet acceptable standards.

Some method is accordingly required for checking the size of particles in batches of aggregate and for monitoring the size distribution within that batch.

The traditional aproach to obtaining the required information is to take a small sample from a batch of aggregate and then to sieve that batch using various sieve mesh sizes. Such an approach is time consuming and generally not very reliable. It is difficult on the basis of a very small sample to convince a supplier that large volumes of aggregate that have been provided do not have the required particle size and particle size distribution.

Laboratory equipment is known which enables the characteristics of particulate material to be monitored on the basis of an image of a sample batch of particulate material spread out on a support surface. The image is electronically processed to derive information related to the size of individual particles and the distribution of sizes within the imaged sample. The known equipment has however been used only in a laboratory enviroment.

It is an object of the present invention to provide a method and apparatus for monitoring the quality of aggregate.

According to the present invention there is provided a method for monitoring the quality of aggregate delivered from an aggregate processing system, wherein an image is generated of a sample of the delivered aggregate, the generated image is electronically processed to produce data representative of the size of particles within the sample and the distribution of particle sizes within the sample, and the aggregate processing system is controlled to maintain the particle size and particle size distribution within predetermined limits.

The present invention also provides an apparatus for monitoring the quality of aggregate delivered from an aggregate processing system, comprising means for generating an image of a sample of the delivered aggregate, means for deriving from the generated image data representative of the size of particles within the sample and the distribution of particle sizes within the sample, and means for controlling the aggregate processing system to maintain the particle size and particle size distribution within predetermined limits.

The aggregate may be sampled substantially continuously by passing it in a continuos stream beneath a television camera and storing individual frames of the camera output for subsequent processing. Such an arrangement would enable automatic control of the aggregate processing system, for example the system being stopped automatically in the event of the predetermined size and size distribution limit being exceeded. Alternatively the system can be controlled by a human operator on the basis of the derived data. The aggregate may be held stationary instantaneously beneath the television camera to facilitate capture of an image of a sample.

In one embodiment of the present invention aggregate is produced by a limestone crushing machine and delivered to a conveyor belt which transports the crushed stone to a series of sieves. Each of the sieves is recipricated so that as the stone flows over it particles which are small enough to pass through the mesh size of the particular sieves do so. Each seive thus divides the aggregate it receives into two streams of aggregate in separate channels.

If a particular quality is required for a category of aggregate such as that used in high quality flooring it is necessary in accordance with the present invention to monitor the aggregate passing through the channels into which aggregate of the appropriate nominal size falls. A camera is accordingly located on one side of the channel so that aggregate falling into that channel passes in front of the camera. The camera output is sampled periodically such that an image of the particles immediately in front of the camera at the sampling instant is stored as a single frame image. That image is then processed to produce data indicative of the size and shape of individual particles and the distribution of sizes and shapes within the sample.

For example it may be that it is very important to maintain a maximum possible particle size. The system could then be set up to provide an output if that maximum size is exceeded. A minimum particle size may also be defined but this is in many circumstances less important. It is however important to ensure that the range of particle sizes is maintained within acceptable limits, for example by indicating that the average particle size should be a predetermined percentage less than the maximum particle size. The system incorporates software which enables the maximum particle size and a range of acceptable average particle sizes to be preset.

The system can then be left to monitor the aggregate passing through the channel to which its camera is allocated. The system may also be set up to detect particles of undesirable shape.

If a sieve is broken, oversized particles will start to appear in the respective one of the channels. The system can then automatically stop the delivery of fresh aggregate until the cause of the problem has been located. Simiiarly, if a sieve becomes clogged the effective mesh size will reduce and the average particle size passing through the sieve will reduce. Again the system can be set up to stop the delivery of further aggregate in the event of the average size dropping below preset limits so that the cause of the problem can be investigated.

In assessing the shape of particles to ensure detection of particles that are for example insufficiently close to being spherical, the Zform factor" of individual particles may be calculated as follows: Form factor = 4 (Projected area)/(Perimeter)2 The closer the shape is to spherical, the greater is the form factor.

Size can be estimated simply by monitoring the projection of the perimeter of a particle onto mutually perpendicular axes X, Y.

Equipment suitable for use in a system in which samples to be monitored are stationary at least for the time taken to store an image of the sample maybe made up from the following components, all available from Analytical Measuring Systems Limited of Shire Hill Industrial Estate, Soffron Walden, Essex, CBll 3AU.

1. AMS OPTOMAX Image Analyser 2. AMS Micro Stand 3. Video Camera 4. Personal Computer 5. A digitising pad for X, Y image editing

Claims

CLAIMS:

1. A method for monitoring the quality of aggregate delivered from an aggregate processing system, wherein an image is generated of a sample of the delivered aggregate, the generated image is electronically processed to produce data representative of the size of particles within the sample and the distribution of particle sizes within the sample, and the aggregate processing system is controlled te maintain the particle size and particle size distribution within predetermined limits

2.An apparatus for monitoring the quality of aggregate delivered from an aggregate processing system, comprising means for generating an image of a sample of the delivered aggregate, means for deriving from the generated image data representative of the size of particles within the sample and the distribution of particle sizes withir the sample, ar.

means for controlling the aggregate processing system to maintain the particle size and particle size distribution within predetermined limits.

3. An apparatus according to claim 2, comprising means for passing the aggregate substantially in a continuous stream beneath a television camera and storing individual frames of the camera output for subsequent processing.

4. An apparatus according to claim 3, comprising means for stopping the aggregate processing system automatically in the event of the predetermined size and size distribution limit being exceeded.

5. An apparatus according to claim 2, 3 or 4, comprising means for holding the aggregate stationary instantaneously beneath the television camera to facilitate capture of an image of a sample.

6. An apparatus substantially as hcrelnbefoLe described for monitoring the particle size and particle size distribution of aggregate delivered from an aggregate processing system.