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.