Penguin/Codelco team up to use robotics to solve an age-old problem in cave mining – hang-up assessment and removal
The removal of rock blockages in mining operations has long been a risky undertaking, especially in high overhead conditions. In fact, the assessment of where to place charges has been difficult due to the lack of visibility and safe access to the area. Thus, the traditional practice of wedging long poles with explosives on them, keeping the operator in as safe a location as possible, has been one of the tried and true methods in attempting to remove blockages. Unfortunately, this is less than perfect and it usually takes several attempts to remove the blockage. Each attempt can result in even more dangerous conditions for the worker and/or damage to the mine due to successively larger amounts of explosives.
Over the years, different ideas have been attempted to change this process and reduce the inherent safety risks. Some of the solutions that have been attempted include projectiles fired at the hang-up, large cumbersome arms and massive amounts of explosives, each of which come with their own safety risks resulting in dangerous situations for the miner and the mine.
We have reached a point where combining mining problems with gaming technology and robots can produce results that the mining industry has so far struggled to achieve. The safe assessment and removal of hang-ups and oversize has been made possible by combining Penguin’s proprietary GPS-denied positioning system with a six degrees of freedom telerobot, virtual gaming and teleoperation over a wireless network. Penguin Automated Systems has developed a robot system that is capable of working in a rock blockage safely.
The idea draws on the latest in telerobotics technology combined with 3D scanning and underground geospatial positioning. The hang-up removal is performed by scanning the inside of the hang-up to rapidly develop a geospatially placed 3D model for the operator to use. The 3D model is detailed enough to attempt to pick the ‘keystone’. A blasting engineer or the operator can then determine the exact position where the explosive charge should be placed in the 3D model and thus the actual hang-up. The operator-controlled robot arm then uses the 3D virtual reality model of the robot system and the actual drawpoint information model to display the location information. The robot arm reaches into the hang-up to position the charge using the kinematic model of the robot system. The 3D model is then used to provide views inside the hang-up for the operator to move the arm. This process allows the operator to place the charge within the 3D representation of the drawpoint from a long distance away. As the process continues, the end of the arm, which has a 3D vision system, drills the rock and the explosives are loaded precisely. The robot then returns the blasting cable to the command station located in a truck a safe distance away from the blockage.
Cave mining and the issue of hang-ups
Cave mining is one of the major methods employed by mining companies today. When performed properly in the right orebody, cave mining is the lowest-cost underground mining method. There are many parameters to make a low-cost cave mine work according to Laubscher (1994) and Chitombo (2010). These parameters include: cavability, drawpoint spacing, draw control, dilution entry, layouts, undercutting, ground support and fragmentation. Most importantly, caving operations depend on size distribution, as discussed by Laubscher (1994). Rock blockages or hang-ups in underground drawpoints and drawpoint structures are typically caused by oversize issues and the arching of rocks to form a blockage. This makes caving dependent on the rapid, safe removal of hang-ups and oversize. Rock blockages due to oversize and hang-ups create and/or cause many problems in all forms of mining. Production rock blockages cause dilution and recovery problems if not dealt with promptly. Furthermore, the removal of these blockages, regardless of type, creates potential safety issues for those involved.
What does a hang-up assessment and removal robotic system need to do?
The hang-up assessment and removal robotic system safely allows any operator to assess and remove rock blockages from a safe location. The hang-up assessment and removal robot system was envisaged to do two very important tasks:
- assess a blockage or hang-up to understand the nature of the problem
- determine how to deal with the problem.
Entering past the drawpoint collar can be an unsafe task. The potential for rock to fall and roll out of the collar is high. Therefore, current visual assessment of the hang-up can only be done from the side of the collar of the drawpoint, allowing for a partial view at best. This technique then uses concussion charges on poles, gradually increasing in size until the hang-up is removed. While this typically solves the problem, it continuously puts the operator at risk and usually causes damage to the mine. However, there has not been a better way to try to safely remove a hang-up.
Penguin’s GPS-denied positioning system, demonstrated at Codelco, provides a better way by creating a 3D model of the inside of the hang-up using optical and laser-scanning techniques. This model is then used by the operator or blasting engineer to determine where to place a charge for maximum effectiveness while protecting the operator and reducing damage to the opening. Moreover, if the exact position of the 3D model can be matched with the machine position, it is possible to reach a robotic arm to the exact location needed to drill, load and blast the charge to shatter or substantially move the keystone to free the hang-up.
What would it take to accomplish a system such as this for removing hang-ups? The main need was to create a rugged, mathematical machine that could be telerobotically operated with accurate position control and a communication system capable of moving multiple video scanners and data streams in a closed-loop fashion with the machine and arm control. At first, this appeared to be an impossible system to develop for underground mining because the technologies of positioning and high-bandwidth networking didn’t exist.
The first task to complete is the assessment function. Assessment requires the creation of a 3D model of the hang-up. Today, miners can only get a limited view of a hang-up due to the difficulty of looking into a drawpoint. Since a drawpoint is basically an open flow of rock, personnel should not enter the area to assess the hang-up. However, this assessment process is not a problem with a robot because the robot can enter the drawpoint if absolutely necessary. Therefore, a clearer picture can be captured to gather point cloud data of the hang-up, giving a much superior look into the drawpoint. The patented subsystem consists of a subsurface positioning system and a kinematic model of the machine and robot arms to support mathematical measuring and imaging of the hang-up.
With the image generated in the assessment stage, the robot needs to position and extend the lower and upper arm sections to get the drill and explosive to the precise location determined by the blasting engineer or operator. Once positioned, the location is drilled and readied for explosive insertion, pulling the leg wire back to the centre of the drift. The leg wire will be connected to allow multiple blasts at cross shift. The robot drills and inserts a charge at each deployment.
The development and patenting of a new optical communication network made this concept even more feasible as its capability far exceeded current best performance in radio networking. This supported teleoperation control of an assessment system with scanners, cameras and data control. Furthermore, it allowed the creation of a precise robot arm and mobile delivery system. The data transfer system could then support the kinematic modeling of a six degrees of freedom robot with an arm and an end effector consisting of a rock drill and explosives loading device. This meant that a dangerous brute force task could be performed safely if a mobile computer numerically controlled machine with accurate position control could be built.
Hang-up robot system
The hang-up robot is a 5530 kg (12 191 lbs) electric machine consisting of an undercarriage, power system, two-stage robot arm, hang-up scanning system, end effectors, camera system, control system, wireless networking, safety system and diagnostic system. While the system has been especially designed for hang-up assessment and removal, the end effectors can be modified to handle any number of power tools.
The system consists of:
- A Normet RBO housing a telecommand centre, hydraulic generator, robot battery charger and explosive transportation container. The telecommand centre is wirelessly connected to the robot using radio frequency (RF) and optical techniques.
- A geospatially operated robot and high-reach, two-stage arm capable of reaching into and building a 3D image of the hang-up to assess the optimal means to remove it.
- An end effector for drilling and loading explosives into the hang-up to blast the rock blockages imaged in the 3D scans from the assessment.
The robot undercarriage is a powerful electric machine. The unit is a waterproof tub with sealed external gearboxes for operation in difficult environments and has a grade ability of 30°. The undercarriage has four external gearboxes with solid rubber tires and four electric motors with 9 HP continuous operation and 32 HP on peak requirements achieved through 30:1 gearboxes. The unit has independent braking systems, including two spring-applied electromagnetic disc brakes and three piston stabilisers.
The robot arm consists of a two-stage, telescoping lower arm with an electric drive motor capable of extending 5 m (16’ 4.8”) horizontally. The lower arm is capable of pivoting to 30° to support the opening of the arm in 3.6 m (11’ 9.7”) back height. The upper arm is connected to the lower arm and is capable of pivoting to 135° and extending to 10 m (32’ 9.7”). A stinger is attached to the lower arm to support the weight of the arms at their full extension.
When the robot is reversed, two lower stingers can be extended to raise the rear of the robot so that the upper arm can be extended to 0.6 m (1’ 11.6”) from the ground for secondary blasting of chunks.
The robot system has an end effector that is capable of drilling, loading explosives and blasting at a precise location for hang-up breakage. The end effector uses an electric rock drill and bit selected to drill a hole 305 mm (12”) in length with a 34 mm (1.34”) diameter. The drill is mounted on a table with a screw feed to thrust the drill into the rock. Once the hole is drilled, the table is rotated to thrust the explosives into the hole. The end effector holds a 3D camera system to allow the operator to track the progress of the drilling and the insertion of the explosives. Power and ethernet at the end effector support the use of any other power tool.
Additional end effectors are currently under development. These include the ability to glue the charge to the hang-up and adding other potential systems, such as a water cannon.
The robot, multi-stage arm and end effector are all electric. At the heart of the system are two lithium-iron phosphate batteries, which give the robot a shift of operating time before charging. This power system allows the design of a highly reliable robot.
System control and communications
The RBO telecommand/robot control system consists of many components. The most crucial system is the wireless networking system. Without the wireless system, this robot would be impossible to build and operate. Penguin’s proprietary Wireless Optical System (WOS) is the key component that allows this system to work. The WOS is capable of 100 MB/s to support the low latency requirements of the camera, data and scanning systems, which are needed to run the components of the hang-up assessment and removal robot system.
The WOS combines with a local wi-fi system to support long- and short-range operation. The WOS is located on the front of the RBO and on all four sides of the robot. The system has several light-emitting panels and light-receiving devices. Configuration of these panels is important to the full operation of the system.
The RBO telecommand centre has several devices for the operator interface, including:
- multiple video system operation interface
- a pair of multifunction joysticks
- computers mounted in a rack in the RBO.
- The visualisation system accesses all cameras onboard and runs the proprietary machine software. Joysticks run all the drive and arm functions.
Robot control system
The robot control system is linked to the RBO command centre via wireless optical and RF networking. The system on board the robot consists of the following components:
- hardened, military-grade industrial computer
- a military-grade positioning unit
- the robot control system
- the arm control system
- the laser scanning system
- four pan–tilt–zoom cameras
- two infrared drive cameras
- an on-board computer for local control
- a CAN bus network
- a safety system.
Robot computer and positioning system
At the heart of the system is a hardened military/industrial computer platform. This system is linked to the underground positioning unit, cameras and sensors and actuators in real time via a CAN bus network using Penguin’s software control system.
A prototype of a new mining robot system has been created to allow miners to safely remove hang-ups and rock blockages from mines, in particular caving-type mines. The hang-up assessment and removal robotic system has been created, developed, tested and commissioned by Penguin Automated Systems Inc of Naughton, Ontario, Canada.
Key features include:
- teleremote operator control of the system to ensure that workers can stay out of harm’s way when removing rock blockages such as hang-ups and oversize
- the ability to display a 3D image of the hang-up without the operator needing to expose themselves to potential falling rock hazards
- a robot arm mounted on the body of the robot that is capable of reaching 3 m (9’ 10.11”) horizontally and 10 m (32’ 9.7”) vertically
- an end effector that is capable of drilling a hole and loading the hole with explosives in the precise position required.
These features have been tested underground in Sudbury. The photo at left shows the unit in an underground drift during commissioning and testing.
Chitombo G P, 2010. Cave mining – 16 years after Laubscher’s 1994 paper ‘Cave Mining – state of the art’, in Proceedings Second International Symposium on Block and Sublevel Caving, pp 45–61 (Australian Centre for Geomechanics: Perth).
Laubscher D H, 1994. Cave mining – the state of the art, Journal of the South African Institute of Mining and Metallurgy, 94(100):279–293.