The Pit, The Bit, and the Benefit
Open pit mines present a harsh and dangerous environment- for machinery and for workers. They also pose a particular challenge for global navigation satellite system (GNSS) technology-especially regarding the issue of blocked and reflected satellite signals that increase as mining equipment nears the steep pit walls (Figure 1).
Nonetheless, mining is an industry that demands operational reliability, consistency, and the kind of precision that GNSS brings. This is particularly true when it comes to blast hole drilling operations: the better a mine can control quality at the tip of the drill, the less time and handling of mined material that is needed-not to mention reduced wear and tear on downstream processing equipment.
Most mines attempt to blast holes within 20-30 centimetres (8-12 inches) of the mine plan, both horizontally and vertically. Horizontal hole spacing is critical to controlling rock fragmentation. The service life of the crushers used in processing the blasted materials (ore and waste rock) can be reduced if fragments are too large or if too much fine material is produced. Hole depth is important for creating a flat bench for subsequent mining activities. Designing the bench with a slight slope helps to improve water drainage, while a relatively flat bench reduces machine wear.
Flanders and ARDVARC®
Flanders Inc., is an Evansville, Indiana-based privately owned, third-generation manufacturer of motors, power systems, and automation solutions used in industrial operations around the world. Flanders developed its ARDVARC (Advanced Rotary Drill Vector Automated Radio Control) kit to give mine operators reliable, consistent automated drilling capabilities to ensure quality control. The advanced drilling system relies on NovAtel's GNSS receiver technology for ultra-precise positioning of drill holes-a major factor in optimizing the processing of mined materials.
Jarrid Cima, manager of software development for Flanders, points out that the development of the ARDVARC® system was driven by two factors. The first is safety: if no human operator is physically operating the drill onboard, it avoids exposure to an unsafe, collapse- prone environment. The second is productivity: an improvement of up to 30 percent can be realized.
The ARDVARC system's built-in intelligence is engineered to optimize machine movements and drill positioning. Above all, the system can be used to optimize a mine's operational profitability. It stores data related to the amount of energy required to create each blast hole. The data is then used to refine blasting procedures and optimize fragmentation of the materials being mined, which in turn affects the rest of the mining process.
The ARDVARC® operator can call up an overhead view of the drill and X cursors indicating the location of nearby target hole coordinates and the current drill steel location (Figure 2). For most of the ARDVARC® kits deployed, the operator stops the drill with the two cursors aligned as closely as possible before simply pressing a button to drill.
The system handles any of the various maneuvers required in drilling. These include raising the drill onto its corner jacks and leveling it, lowering the drill bit to detect the elevation of the surface, “collaring the hole” (a technique used to stabilize the borehole during drilling), backing out and re-drilling to clear any clogs, retracting the drill steel and drill bit once the hole is completed, and lowering the drill off of the jacks for tramming-that is, relocation of equipment between holes.
While drilling, the system records the precise position of the hole, its exact elevation, and foot-by-foot readings on the amount of required drilling force. This data reveals the geotechnical information about the rock being drilled, which can then be used to design blast patterns in the future.
By removing variables that might otherwise be introduced by operators, the system maximizes production quantity and quality. The system also optimizes the use of human resources, especially at remote mines where attracting the necessary semi-skilled talent is difficult.
“ARDVARC® can be installed drill,” Flanders sales manager Jim Elkins says, another plus for Flanders customers because most mines operate more than one type of drill. The ARDVARC® system monitors hole profile data and hole quality and integrity. The system also tracks production and records and builds reports for immediate display at the control center.
NovAtel's GNSS receivers are critical components of Flanders' ARDVARC® system. Flanders' system can perform all drill functions up to and including full autonomy for major efficiency and safety improvements. The ARDVARC® control center allows monitoring of up to five GNSS-guided drills.
The control center operator directs drill movements by creating waypoints on the blast-pattern map that are transmitted via radio to update motion files in the drill's system. The machine's GNSS system guides drills to the intended positions as defined by the blast plan.
The system provides Flanders customers with several benefits. Key maintenance points ar constantly monitored and alarmed to provide near instantaneous data. Drills controlled by the system minimize inefficient tramming by moving in a direct path from one position to the next, which minimizes stress on moving components of the drill machinery.
GNSS on Drills
Precise positioning and heading are fundamental to successful drilling. NovAtel's Advance® RTK positioning (centimetre level-Figure 3) is used for positioning of the drill, and its ALIGN® (0.3 degree, 95% for a 3-4 metre antenna separation) for drill heading and measured offsets from the antennas to the drill steel (Figure 4). Heading accuracy is critical, as distance from antennas to drill steel is typically two to three times the distance between the antennas. Generally, every 0.1 degrees of heading error results in 1.75 centimetre of error in the drill steel.
Flanders normally uses NovAtel's DL-V3 high-performance GNSS receiver as the RTK base station to broadcast corrections to the drill-mounted ProPak-V3s. Typical reference station-to-equipment baselines for real-time kinematic GNSS operations in a mine are 2-10 kilometres or (1.6 to 6 miles) miles. Both types of NovAtel receivers are “off-the-shelf” products that incorporate NovAtel's OEMV-3 receiver board. In some cases, a customer's existing base station is used.
The solution's precision positioning system includes a single “full feature” ProPak® to provide the RTK position and a “heading” ProPak to provide the precise heading. Each receiver is connected to its own GPS-702-GG antenna. Don Treadaway, a Flanders GIS project manager, said that Flanders likes the fact that the heading version is firmware-upgradable, which saves its customers money, and helped make the ProPak-V3 the company's standard rover receiver.
Flanders mounts two arms off of the left and right of the mast support onto which the GNSS antennas are installed. This is necessary as that portion of the drilling equipment is exposed to the movement of heavy components, such as the lowering and raising of the mast, and requires access for frequent maintenance. The NovAtel ProPak-V3s are mounted in a stainless steel enclosure, usually along a handrail on the side of the drill.
To determine the combined position of the drill steel, Flanders applies basic geometry to the position and heading provided by the GNSS receivers provide. Once an ARDVARC® kit is installed on a drill, Flanders captures the static offsets needed to calculate the geometry of the drill itself. The offsets are measured from each GNSS antenna to the center line of the drill; from that intersection point, along that center line, to the center of the drill steel; from the horizontal plane of the antennas down to the stops; and from the stops to the tip of the drill bit, when the steel is fully retracted.
The position and heading from the two GNSS receivers are imported into the ARDVARC® system. Flanders uses a custom application to continuously derive the current location of the drill bit using this geometry. Most mines use local coordinates, occasionally based upon historical surveys from the 19th or early 20th century, notes Treadaway, adding that mines usually retain the local coordinates to maintain their historical accounting processes. So, Flanders configures its system to incorporate these coordinates.
Treadaway points out that mining offers unique satellite signal reception challenges that are addressed by the ProPak-V3's multi-constellation reception capability.
“The ability to use both GPS and GLONASS is critical for open pit mining, since the higher number of GNSS signal sources increases the probability of being able to determine a solution while in a deep pit, with its restricted view of the sky,” he says.
The ProPak-V3's design makes it highly reliable when equipment is powered up at the start of a shift, Treadaway says. Furthermore, the unit's design allows the antenna and receiver to be located separately. This provides much more flexibility in placement, more physical and environmental protection of the most expensive components, and greater ease of maintenance.
The multi-constellation DL-V3s are better suited for base station duty than mounting on the drills, as far as Flanders is concerned.
“The DL-V3 is used whenever we provide a base station and is excellent at filling that role,” Treadaway says. “Because of the complexities of GNSS and radio in many mine pits, positioning systems have proven to be an Achilles' Heel of the automation system; so, we have developed special activities centered around this product.”
These include using a DL-V3 for mobile field work to collect on-site coordinates for use in deriving ARDVARC's own local coordinate conversion algorithms, if required. Also, Flanders has used it to validate the conversion algorithm, whether provided by the mine or derived by Flanders' system.
In blast hole drilling operations, success at the tip of the drill is everything. NovAtel and Flanders engineers have worked closely together to develop OEM solutions that solve the multitude of equipment and environmental challenges that affect safety of life, efficiency, and profitability within the demanding, highstakes mining industry.