Automated dream nearer to reality

AUTOMATED bolting and mesh handling on a continuous miner is considered by some to be the Holy Grail of roadway development in underground mines. A team at the University of Wollongong has prepared a prototype that could help realise that vision. By Lou Caruana.
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The rib bolt manipulator is designed to be as compact as possible.

Staff Reporter

The project, which is being conducted under the Australian Coal Association Research Program, aims to contribute to the Australian underground coal industry’s goal of achieving rapid roadway development production rates from a continuous miner of at least 10 metres per operating hour and utilisation rates of 20 hours per day.

It would also help realise that other mine manager’s dream: an underground longwall system capable of mining 10 million tonnes per annum, University of Wollongong dean of engineering Professor Chris Cook said.

“It’s almost the difference between pit ponies and longwall mines,” he told Australian Longwall Magazine.

“The next great leap forward is going to need a lot more automation than we have now.

“The arithmetic is very straight forward. You cannot get to 10 million tonnes per annum with existing manually based methods. We think seven million tonnes is where most mines would get to with existing methods.

“ACARP is aiming even higher – at 15 million tonnes per annum.”

The results so far now allow the laboratory test facility to be redesigned for a more substantial trial within an underground production environment, according to the University of Wollongong research team on the project, which included Stephen van Duin, Peter Donnelly, Ian Oxley, and Luke Meer.

“Roadway development in underground coal mines is a unique process,” van Duin said.

“The methods used to extract coal and support the exposed strata have evolved over the past century in a way that has taken the fundamentals of major machinery and incrementally modified the designs and processes to make limited improvement.

“As a result the process has become very restrictive for further innovation, especially in the areas of automatic operation and control.

“The existing machinery used to support operations has been specifically designed to accommodate the harsh and challenging environment that it operates within and any changes to their fundamental design can be counterproductive to increased output.

“Subsequently, today’s roadway development rates are failing to keep pace with modern longwall systems, and the methods currently used are proving to be inadequate if the industry is to progress to higher and more profitable production.

“Through a series of industry surveys, the bottlenecks which restrain improved production and safety of operators, have been identified and the manual strata support activities on a continuous miner have been acknowledged to be a major contributor to these constraints.”

One of the big constraints – to meet the industry targets – is that the team had six minutes per cycle time to do all the roof and rib bolts and the roof and rib mesh, Cook said.

“There is a lot going on and you can’t do it in parallel because things would hit each other,” he said.

“So we had to be quite careful how this was to happen and be integrated. The bolting machinery has got a life of its own, it’s already there. So we have had to feed that.”

Cook said the project automated the primary roof and rib support activities associated with roadway development.

It draws together a system integrated into a continuous miner platform that, when taken to production, will fully automate the process of self-loading and installing rib and roof bolts as well as steel mesh or other alternative roof confinement material, including the associated materials handling systems.

The team developed prototype automatic machinery to be used in a set of laboratory surface trials that demonstrate a solution to automatic primary strata support on a continuous miner.

A retrofit approach has been used to limit the amount of project risk in adversely affecting the fundamental operations of continuous miner equipment.

The automation developed includes roof/rib bolt and mesh handling manipulators as well as plate handling equipment.

Successful results indicate that a satisfactory solution for automatic control and manipulation of roof and rib support materials has been achieved and that the designed machinery can be potentially used to support and improve cycle times in an underground production environment.

Prototype designs and simulation have significantly reduced the technical risk in proceeding forward.

When taken to full fruition, cycle times, and therefore overall development rates, are expected to be improved in line with the target of 10 metres per operating hour.

The results of the project have completed the first step of progressive stages with the next phase consisting of full underground trial of automation equipment by the end of 2012.

Results from a laboratory demonstration have confirmed that there is at least a solution for automated roof and rib support activities and that the achievable cycle times are consistent with higher development rates.

“This project builds upon the recent advances of SDB [self drill bolt] technology by manipulating consumables on a continuous miner,” van Duin said.

The time saving benefits of a complete system will be realised from three distinct operations, which include the transportation, storage and delivery of consumables to the development face and interface of the continuous miner with little or no disruption to the roadway development process.

“It also builds upon the automatic retrieval and insertion of consumables by the drilling and meshing system during the roof support sequence [and] the integration of the manipulation sequences into other automation processes occurring on the continuous miner – such as coal cutting, CM steering and auto drill cycles,” van Duin said.

The project also exploits existing technology from other industries to use the latest advances in industrial automation and robotic technology to deal with the specific challenges of the underground coal mine environment.

Some of these challenges include using sensors, actuators, manipulators and controllers that are compatible with vibration, gaseous, dusty and/or wet conditions and developing a cost-effective system within the confined space limitations of the continuous miner and the immediate area surrounding each drilling machine.

Other challenges include creating a robust system whose component design ensures machine reliability and longevity, designing for easy operation and maintenance, and integration of control systems into a common automation protocol.

To limit the scope of work of the project the design of the automation manipulation equipment has specifically been made to suit a JOY12CM30/32 frame.

However, in principle each manipulator is designed to generically fit on any frame with the relevant modifications.

The rib bolt manipulator is designed to be as compact as possible and is located on the side of the hydraulic rib bolting rig.

The hydraulic rig requires at least a homing position for the bolt to be loaded. For this unit, the rib bolter has three positions.

One bolt is installed above horizontal and one below.

The third position is the horizontal, and is used for loading the rig.

The design of the rib bolt manipulator also uses pneumatic control for all actuation.

Similar to the roof bolt manipulator, the rib bolt manipulator uses a set of pneumatically controlled roller mechanisms to longitudinally convey a bolt from the common centreline.

Once a rib bolt is delivered to the rear of the manipulator, a set of rollers convey the bolt through a rib washer.

The mechanism then extends horizontally upwards to swipe the washer out of a holder, before being rotated 90 degrees inline with the hydraulic rib bolter.

The bolt is lowered into the centreline of the hydraulic rig and the roller mechanism then feeds the bolt into the drill chuck.

Drill clamps automatically hold and secure the bolt using a programmed movement of the hydraulic head plate.

The clamps don’t require any actuated control other than the hydraulic movement of the head plate. The clamps support the bolt during the drilling cycle and release as the drill chuck approaches the retracted position.

Each rib bolt can be loaded within 20 seconds before returning to its home position.

Manual methods for roof mesh installation are physically demanding.

Mesh is typically lifted from the rear of the machine up over the centre conveyor before being rotated normal to the roadway and up onto the drill rig head plates.

Alternatively for some frames, onboard storage requires mesh to be retrieved from a stack of mesh stored above the centre conveyor, rotated and placed upon the temporary roof support (TRS).

Both of these processes are required to transverse the mesh forward to the drill rig operator’s platform before rotating the mesh and placing it in a bolting position.

Cook said there were limitations to automating underground that were not found in other industrial environments such automobile manufacture.

“It’s under the ground, its dirty, there can be a lot of moisture and dirt lying around, it’s very restrictive in terms of space,” he said.

“It’s not like a factory floor.”

“You can’t disrupt production because they are working day and night. There are very strict regulations in what can you install in an environment with methane.”

Due to the restrictions, the manipulator design only allows for one roof mesh sheet to be loaded and manipulated at any time.

The manipulator is divided into two sections to allow space to avoid obstruction of the rib bolters during backslide operation.

The rear section simultaneously conveys the mesh forward while the supporting carriage extends to the front of the machine by approximately 700mm.

Manual methods for rib mesh installation are also physically demanding.

Mesh is typically carried from the rear of the machine along the side of the continuous miner before being held in place by an operator.

The rib mesh manipulator replaces this manual activity using a series of integrated servomechanisms.

Typically, only one piece of mesh is required on each side of the miner for a one metre advance.

However, for the purpose of a demonstration and testing, the rib mesh manipulator has been designed to store up to 10 pieces in a storage unit.

Each piece of mesh can be automatically dispensed on demand.

The storage unit separates a single piece of mesh onto a transfer arm.

A chain conveyor located under the walkway conveys the mesh alongside the machine and in front of a modified rib crash barrier.

The rib crash barrier has pneumatic gripping cylinders that grab the mesh once the transfer arm has conveyed the mesh into position.

Once secured, the mesh is extended upwards while the crash barrier extends towards the rib.

This allows the mesh to be positioned within the corner of the rib and roof and prevents any fouling with existing roof and rib anchored bolts.

At this point the rib bolt is then positioned within the rib bolter and the drilling cycle commences.

The project has given the Roadway Development Task Group a better understanding of the requirements needed to automate the development process.

Van Duin said the laboratory equipment would be further modified so that more detailed underground trials could be carried out.

The project has also revealed further constraints for a future automated system, such as the standardisation of consumables, the tight control of consumable condition and the preferred requirement of pneumatic services at the face.

It has also identified safety or no-go zones on the continuous miner that would need to be controlled during a production environment.

The results have identified critical interface points at the rear of the continuous miner for where consumables are supplied to the onboard automation equipment, which affects how materials are handled and presented downstream of the cutting process and all the way to the mine surface.

The work has also identified the potential time savings that can be achieved through automated repeatability.

The cycle times for each modular section of the automation are well defined and further refinement can be made through future small incremental design changes.

The researchers point out that the systems developed and manufactured to date represent a prototype example of a potential solution, and in its current form it does not satisfy the strict regulatory approval for underground use.

An underground trial has been planned to progress the concept to an industrial application.

It is envisaged that the results of the underground trial will be sufficient for original equipment manufacturers to incorporate the findings into commercial equipment.

“Because of the achievements of Stage 1 project C17018 [ACARP’s code for the project], it is recommended that the project be extended to an underground trial,” van Duin said.

“Secondly, it is recommended that the focus of the automation equipment should now extend beyond the immediate continuous miner and include the entire development panel, the required systems used to support the automation, and the integration of other automation technologies such as continuous miner self steering, and continuous haulage.”

The next stage proposes a further two-year project that will expand the scope of the existing project to include further modification and improved design to allow underground trials of the system in a production environment.

This new proposed project is split into two distinct parts: firstly, to build upon the outcomes of Project C17018 by further developing the prototype systems to conform to an underground production standard; and secondly, the design of a preferred integrated logistics system that will be used to take consumables from the mine surface to the continuous miner in a way that is conducive with high rate roadway development, and in particular, to facilitate automated bolt and mesh handling activities on the miner.

Other challenges will include defining and agreeing on the preferred actuation and power source required for the final design of manipulation equipment and taking existing prototype proof-of-concept bolt and mesh manipulation designs from Stage 1 and modifying them to comply with underground intrinsically safe requirements.

This would include the design and transfer of all control and electronics into flame proof enclosure and rewiring and installation of intrinsically safe DCVs, electric motors, and FRAS-rated materials.

Future work would also centre on making any required modifications to a continuous miner platform and attach the new equipment for the purpose of underground trials through SDB modifications, saddle tanks and removal of whole side platforms of the machine, automation or at least remote operation of hydraulic controls for drilling rigs, and making high risk components more rugged.

An integration of the control and operation of the automated bolt and mesh manipulators into the existing coal cutting process would be achieved through developing a workable control operator interface and integrating automation processes with miner operation.

Underground trials will be needed to test the automation system in conjunction with a continuous miner’s operation and analyse options for batch or continuous materials delivery of roof support materials.

Lastly a logistics system would need to be designed including mechanical hardware, such as cassettes, mining attachments or integrated conveyance, required to facilitate the system.

Cook believes an engineer can always solve a problem but the question is if he or she solve it a reasonable cost for the industry.

“It is going to take a lot of good will from mining suppliers, mining companies and researchers to come up with a practical solution, but I think we have shown the way now with this project,” Cook said.

“To the credit of the industry, it has an extremely strong system to ensure that researchers come up with a practical solution.

“There‘s a strong team spirit.

“Initially our original proposal was that we would use commercially available robots because that was quite a cheap option. But it turned out the commercially available robots weren’t strong enough, weren’t compact enough and couldn’t survive in that environment.

“And they were probably too complex technically in that environment. So part of the challenge was to provide a robust, tough but not complex computer-controlled mechanism to handle rock bolt and mesh.

“After several iterations what we have now is pretty straight forward and easily maintainable mechanisms that combine to do the job.

“There were a range of technical issues – things couldn’t be done quickly enough, or the actuators weren’t powerful enough or the machines didn’t have enough room."

There were also social issues.

“Putting a fine computer controlled machine in an environment where people aren’t IT graduates and aren’t computer literate and an environment where you can’t see much ... we have to take that all in to account,” Cook said.

“It had to be both usable by the actual operators and acceptable by them.

“We have to understand that human beings come in different sizes and have certain limits on precision.”

Cook said one of the obvious benefits of the project was increased safety.

“If that doesn’t happen then it’s failed,” he said.

“In many ways one of the most dangerous places is right at the face, where you haven’t supported the roof yet.

“At the moment human beings have to be there doing the rock bolts and putting the mesh in. It’s obviously safer not to be there than to be there.”

Published in the September 2011 Australian Longwall Magazine

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