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Industrial vision system checks for missing teeth

Motion Metrics uses Matrox 4Sight in Missing Tooth Detection System (MTDS) for hydraulic mining shovel buckets

By Dr. Shahram Tafazoli, Motion Metrics Inc.

Motion Metrics Inc. of Vancouver, British Columbia, in collaboration with the Alberta Research Council (ARC) in Edmonton, Alberta, has developed an embedded, intelligent, machine vision system for monitoring hydraulic mining shovel buckets to detect missing teeth.

A specialized algorithm embedded in a Matrox 4Sight industrial computer processes the digital images acquired by a protected monochrome CCD camera to find out whether there are any teeth missing on the machine's bucket. If so, an alarm is triggered to warn the machine operator of the breakage so that precautionary measures may be taken.

A prototype of the Missing Tooth Detection System from Motion Metrics.

The problem

Motion Metrics became aware of this dental problem during a meeting with research engineers from a leading mine in Canada. The problem occurs when the machine bucket comes into contact with rough material while digging in a surface mine. Since the bucket's teeth are made of hardened steels, a lost or broken tooth can cause serious damage to tools, conveyor belts, pumps, screens, the crusher and other equipment in the plant as it enters the processing system downstream.

In particular, the crusher unit can be adversely damaged and may require several shifts to repair, thus causing serious delays in a key part of the mining and processing operation. In fact, some crusher units specify that no hard material of any kind be permitted into the system while others specify a maximum size of the objects to be fed to the machine (e.g., six inches).

Various investigations revealed that the problem might occur more often in certain mines than others, such as iron ore, copper and oilsand mines, depending on the roughness of the material being excavated. On average, several incidents are reported each year.

There are two cost factors associated with the tooth breakage problem - downtime cost and repair cost. In some cases, the whole operation of the open pit mine or quarry comes to a complete halt to enable the workers to find the broken shovel tooth. This sometimes means dumping all haulage trucks that the shovel had recently loaded material into to see if the tooth is in the load. Costs incurred by a typical tooth breakage incident are wide-ranging, anywhere from tens to hundreds of thousands of dollars.

The O&K RH400 is the largest hydraulic mining shovel in the world. Due to significant wear experienced by shovel teeth during their 24-hour use, they need to be replaced with new ones regularly. Thus, the implemented solution must be able to differentiate between tooth wear (a slow process) and tooth breakage (a sudden process).

The solution

Since the operators cannot see all of the teeth while seated in the machine's cab, they only examine the machine tooth status periodically during operation, thereby increasing the chance of a broken tooth entering the system. To resolve this, Motion Metrics and the Alberta Research Council implemented a solution that is based on remote and non-contact monitoring of the bucket teeth using machine vision.

A monochrome CCD camera is installed on the shovel arm with its output connected to an embedded computer located inside the machine cab. A specialized, intelligent proprietary algorithm analyzes the captured digital images in real time and determines whether a tooth is lost or broken (either partial or full breakage).

The entire set of teeth is analyzed in each upswing of the shovel arm and the status of each tooth is determined by employing several computational and decision-making algorithms. After every upswing of the arm, the operator panel displays detailed information regarding the status of each tooth. When a broken or damaged tooth is detected, an audio alarm is activated to warn the machine operator. In addition, green, yellow and red lights on the panel are used to visually inform the operator of the current breakage status of the other teeth. When it is confirmed that a tooth is broken or lost, the machine operator informs the truck dispatcher and the truckload is simply dumped.

The Missing Tooth Detection System (MTDS), which is currently being field-tested by the ARC at a surface mine in Canada, includes a vibration-resistant video camera, the Matrox 4Sight image processing computer, a display panel with LED indicators and control buttons, a high-intensity light source, a customized support mount to fit various shovel types and custom-made and fully moulded connectors for rugged application. The display panel is connected to the Matrox 4Sight via RS232.

Why Matrox 4Sight?

In Motion Metrics' investigation of a hardware/software platform for the MTDS, various providers of rugged platforms for machine vision systems were contacted. Most of the vendors evaluated only provided individual components of the integrated system they were looking for.

In the search for a turnkey (one-stop) solution provider, Motion Metrics noticed Matrox Imaging's 4Sight industrial computer. This stand-alone system's unique combination of compact size, leading-edge technology, ruggedness, software support and price - along with the Matrox Imaging Library (MIL-Lite) - made Matrox 4Sight the ideal solution for the MTDS project.

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