Environmental Engineering Reference
In-Depth Information
technology captures images from one or more cameras at a time interval preset by
the user or in response to a trigger signal. Its software architecture is object-oriented.
Split-Online applications include rock fragmentation size with an estimation for fine
material, determination of agglomeration quality using texture classification, auto-
matic image acquisition of fragmentation bucket-by-bucket, and size distribution
curve averaging for each truckload on cable shovels.
VisioRock [10] is a vision technology that can determine the texture and color
separately for each size class and discriminate between ore types and size distribu-
tion for different types of particles. The hardware comprises one or several cameras
and their associated lighting systems, camera-computer communication hardware
and one or more computers. The vision software is part of the vision module in the
optimization control system (OCS
©1
) software. The OCS
©
vision module embeds
numerous image processing algorithms.
VisioRock applications include evaluation of rock size distribution on conveyor
belts, the most common situations being:
1. crusher product - automatic help for setting the crusher gap;
2. semi-autogenous (SAG) or autogenous (AG) mill feed - information on feed size
to enable more highly optimized mill operation;
3. screen undersize - detecting holes in the screen or abnormal operation; and
4. feed to critical equipment - detecting wood logs or other abnormal objects on the
conveyor belt that may damage equipment or disturb production.
The size distribution of grinder feed ore is one of the main disturbances affect-
ing the mill process. The measurements provided by these sensors can therefore be
usefully incorporated as a feed-forward variable in automatic mill control strategies.
Since the sensors extract the data from the image analysis of surface ore, the mea-
surements may not be sufficiently representative of the material as a whole. This
factor led to the development of certain variants using, for example, 3-D laser scan-
ning [11].
7.2.2 Mill Operating Condition Sensors
Variables such as power draw that are typically measured for supervising and con-
trolling grinding mills only partially describe the operating condition of these in-
stallations, particularly if they are autogenous or semi-autogenous. This shortcom-
ing explains the efforts made to develop sensors or instrumentation systems that
measure other variables. The results of some of these efforts are outlined below.
The Electric Ear (Metso Minerals) [6] consists of a microphone mounted adja-
cent to the mill, with an amplifier and controller installed remotely. The microphone
converts the sound into electrical energy and transmits it to the controller. The sound
1
OCS is copyright of Metso Minerals Cisa BP 6009, 45060 Orlans Cedex 2, France, www.svedala-
cisa.com
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