Q: What is automation?

A: Equipment repetitively performing consistent sequences of required tasks without human intervention.

Q: But how about longwall automation? There are lots of people who use the term “fully automated longwall”. What are the requirements for a longwall to be fully automated?

A: The equipment should repetitively perform consistent sequences (shears) without human intervention. This means at the very least:

• Manual controls are never used to advance roof supports;
• String line straightening cuts and wedge cuts are never required;
• Desired face alignment is maintained to ± 100mm;
• Creep distance is zero;
• Chainage distance is logged continuously to 10mm resolution;
• There is no shearer driver;
• Horizon control is according to plan to within ± 50mm.

Q: If that’s what a fully automated longwall is, how automated is your longwall? And even if you want full automation, how automated can a longwall get?

A: Several automation products have been around for a number of years and go some of the way to full automation. The first general automation area is roof supports:

Shearer position initiated roof support advance. As the shearer moves, the roof supports automatically advance a set distance behind the shearer and also push the AFC pans. This functionality is supported by the major longwall OEMs and has gone a long way towards removing the need for manual control of overall face advance.

Automated roof support advance in gate ends. The roof supports automatically advance and push the AFC drives based on shearer position. Operates effectively and is supported by major OEMs.

Automated wedge cuts. If the face needs to turn, a partial advance profile or wedge cut can be automatically executed by the roof support system. This is a major advance in roof support automation, meaning the individual supports can move a preset distance. Supported by major OEMs.

Even with these developments, the overall problem with the current state of roof support automation is that there is no effective way to measure the actual distance each support moves its corresponding AFC pan when it advances and pushes. So we can’t automatically calculate where the face actually is.

It is the pan position that determines the path the shearer will move along during the next shear and the shearer path determines the face profile. The only distance that can be measured accurately is the D/A ram movement and errors creep in over a few shears when trying to estimate pan position from D/A ram information because of slop in linkages, pile up of coal etc. This means face alignment gets out of control and manual straightening cuts guided by a string line are needed to correct it.

Q: So with existing automation systems, face alignment cannot currently be fully automated.

A: The second major area for automation is the shearer. Current mature automation products are:

Shearer Speed control. The major OEMs all have basic speed zone control that limits the speed of the shearer in set zones across the face. This feature is widely used as the speed of the shearer is directly proportional to tonnes per hour output of the longwall.

Automatic gate end stops. All shearers are fitted with a function to automatically stop the shearer before it smashes into the mechanical end stop. Unfortunately not all shearers do this well.

AFC overload. When the AFC or other related equipment is in overload the shearer automatically slows or even stops.

Shearer to roof support collision avoidance. The shearer will automatically stop if a roof support is in a collision zone. This technology is based on leg pressures and D/A ram extension. The same problems occur here as with face alignment. The relative position of shearer and roof supports is not an accurate measurement due to errors between pan position and D/A ram measurements.

Shearer auto steering or memory cut. This is the automatic positioning of the shearer arms. An arm can be automatically controlled to cut the floor, the roof or idle at a set height to create a bench. All the major shearer OEMs claim to have this functionality but the systems vary greatly from one OEM to the next. The major problem with memory cut is similar to face alignment in that with the transducers currently used it is very difficult to measure the actual positions of the shearer drums and so the drums cannot be guided accurately. So, like face alignment, horizon control cannot be “fully automated”.

Shearer State Based Automation. This is a new development. At the moment not all OEMs have a working and tested system. State based automation allows mine operators to design a detailed cutting sequence that the shearer will follow. The operators only have to press “auto” on the shearer control system and the machine will automatically haul and position the ranging arms. This feature is the most powerful of the OEM automation systems for shearers and allows full automation of all shearer functions including gate-end cut-outs. However, even though the ranging arms can be moved to nominal set points, their actual positions are very difficult to measure to sufficient accuracy for consistent horizon control.

Shearer Pause. If you have a shearer that is cutting coal automatically, it must be sequenced to the coal clearance system. If the conveyor stops, you want the shearer to stop hauling and even shut down the cutters automatically. Then when the conveyors start, you want the shearer to automatically resume cutting with no operator input.

So the current score for longwall automation is:...click here to read on.