In the past, operators of a boring machine in an underground potash mine were responsible for controlling a device called a bridge conveyor that drops ore onto a long main conveyor. The main conveyor hauls the ore to the loading pocket and from there it is transported to the surface by the skip. The operators had many other jobs to do, so the conveyor was often loaded unevenly, which could create spills that took hours to clear. Another problem was that the mine operators had no way of knowing how much potash was loaded on the conveyor, which made it challenging to plan shift changes that minimized downtime for the skip.
Recently, the mining company installed a system developed by Hinz, a Rockwell Automation company based in Saskatoon, Sask., that uses machine vision to automatically measure the amount and distribution of potash on the main conveyor as it is loaded by the bridge conveyor. A laser projects a line of light across the main conveyor and a Cognex In-Sight Micro 1050 vision system reads the profile of the line three times every second. This information is used by the mine control system to automatically move the bridge conveyor to correct any imbalance.
“We selected the Cognex Micro 1050 vision system because it is self-contained and rugged, communicates well with programmable logic controllers (PLCs), and provides a powerful programming environment that we were able to easily use to determine the complete profile of the top of the ore pile,” said Scott Huckerby, senior process consultant for Hinz.
Hinz engineers set up the laser so it would project a line onto the top of the pile of ore and set up the vision system so that it pointed at that line. The vision system subtracts the position of the actual line projected on a full conveyer from the position of the line on an empty conveyor to determine the amount and distribution of ore on the conveyor. This information is transmitted to the PLC, which determines if the load on the conveyor is unbalanced and, if so, issues a command to the bridge conveyor to dump more ore on the lighter side.
Efforts in the past to address these challenges with machine vision have run up against very difficult lighting conditions underground. For example, one second the vision system will be operating with only its controlled lighting, and the next second the controlled lighting will be overwhelmed by the bright headlights of a truck or the headlamp of a miner. The mine is also a very dusty and harsh environment where vibrations driven by powerful equipment or rock falls can easily destroy all but the toughest vision systems.
The vision system has already demonstrated its ability to survive in the rugged mining environment without downtime.
“The camera is mounted on the bridge conveyor, and while I was underground commissioning the vision system, a big hunk of rock went through the conveyor and become lodged in the chute that feeds the main conveyor,” said Huckerby. “The mine operators utilized the hydraulics on the bridge conveyor, itself a 10-ton piece of equipment, to slam the bridge conveyor repeatedly into the ceiling of the mine to clear the rock. After the dust settled, the vision system continued operation without any interruption.”
The vision system has eliminated spills and associated downtime, and the mining company now knows exactly how much potash is on the conveyor at any point in time, so they can plan shift breaks to avoid skip downtime.