Sandvik Mining finds a unique use for a linear position sensor
Sandvik Mining is a drilling solutions provider focused on the design and manufacturing of a wide range of underground in-the-hole (ITH), and geo-technical drilling equipment. The company’s products are distributed globally, and its main markets are the United States, Canada, Africa, South America, and Australia.
Sandvik’s DU421-C ITH drill is an underground production drill that produces long, straight holes at depths from 65 ft to greater than 330 ft—making them suitable for many mining methods. The articulated, rubber-tired ITH production drills offer high mobility with a heavy-duty platform and high-pressure, on-board booster (350 psi) made for heavy use in production drilling.
The two-stage hydraulic feed cylinders move the top drive, feeding the drill string as it penetrates into the rock. The operating environment is wet and muddy with falling debris and drill pipe being loaded and unloaded in close quarters, according to Scott Dalrymple, Design Engineering Manager–Sandvik Mining PU Winnipeg.
“Optimizing drill penetration rates and minimizing tool wear requires constant monitoring and adjustment of feed force and rotation speed, balanced against the ever-changing rock mechanics,” he said.
The challenge, in this underground environment, is to monitor the position of the drill head in spite of the dust generated while drilling. The issues with cable reels in this environment are:
• They stretch, requiring re-calibration
• Dust and build up prevents the wire from being retracted
The other option discussed, optical sensors, has issues “seeing” through the dust; therefore often gives erratic readings.
The solution came from Rota Engineering, a manufacturer of position sensors with internal and external solutions. In this application, the cylinders had a very long stroke and the cost to gun drill the cylinder rod for an internal solution was cost prohibitive. An external design, where the sensor was mounted stationary (colored red in the image below) in the drill mast while a magnet traveled with the drill head, solved the problem.
When using Hall effect sensors, there are two components—the sensor and a permanent magnet. One component is generally stationary while the other component moves. The output is proportional to the positional relationship of the two components. While drilling in rock, it is desired that the vertical speed of the drill head be monitored so the operator knows what kind of rock formation he is dealing with. The sensor for this application provides a digital (CANBUS J1939) output indicating the position of the drill head but also computes the velocity of the drill head. The velocity of the drill head is inserted into unused bits of the digital signal stream, which is understood by the machine’s electronics. The velocity information is then displayed in an operator usable interface.
Rota’s linear transducers were developed for applications where robustness is required. They can be designed up to 140-ft in length, for use 20,000 ft below the surface of the ocean, for hazardous environments, and feature voltage, current, PWM, CANBUS, and CANOPEN output options.
Dalrymple said that the Rota sensor provides the operator the instantaneous penetration rate (speed) in addition to the hole depth. This data is collected and analyzed by mining engineers and geologists, to aid with production planning.
“Having a non-contact sensor mounted within the existing structure is a much more reliable solution,” he said. “We don’t have sufficient data but we can safely say the Rota sensor solution is at least 300% more robust for our application.”