Open Cut » General
Automatic dump trucks have the potential to increase productivity and reduce maintenance costs without major uncontrolled risks.
Pacific Coal and Komatsu developed and tested various autonomous dump truck (ADT) prototype systems at Tarong between 1996 and 1998. Limited operational testing showed encouraging results.
Following on from the prototype development work, Rio Tinto Ltd, Komatsu Ltd and Modular Mining Systems conducted a development project at Tarong between July 2000 and March 2001. The project sought to demonstrate the extended operation of the two Komatsu HD785-3 ADTs, assess their operational performance and the impacts on current mine practices.
The specific objectives were to address:
- Loading practices between ADTs and manually operated loading machines
- ADT dumping practices, including ADT and dump dozer interaction
- Safe work practices for mine personnel working in the vicinity of ADT operations
- Interaction of ADTs with other mobile equipment (such as graders, water trucks and light vehicles)
- Interaction with current mine practices
- Comparison of operational characteristics between manned trucks and ADTs
- Haul road design, operation and maintenance
- Manning implications
- Impact of environmental conditions on ADT operations
Each ADT is fitted with a high precision global positioning system (GPS) system which, together with a dead reckoning system comprising a gyroscope and wheel encoders, accurately controls the navigation of the ADTs.
Each ADT is also fitted with onboard controllers linked to its computer system to control the operating functions including engine, steering, braking, dumping, and obstacle detection. The computer system is, in turn, linked by a UHF communications system to the central control computer where a GPS ground station is also located.
Before autonomous operation is possible, a pit database needs to be compiled by the central computer operator. This database consists of the loading area boundary, dumping area boundary, haul road edge boundaries, and travel course for the trucks. The boundary data is acquired using an equipped manual vehicle (EMV) - a light vehicle fitted with a high precision GPS system - and data communications system. The EMV is simply driven around each boundary perimeter recording the coordinate data, which is then transmitted to the central computer. The travel course data is acquired by manually driving an ADT along the required course and, at the required speed (the teaching run), allowing the onboard computer to record data for the course, including position, speed and direction.
Productivity testing on the King 4 East prestrip haul circuit (3.5km haul cycle) revealed a cycle time increase between 20 percent and 23 percent for ADTs compared with manual operation and an increase of 10.6 percent on the Ramp 7 coal haul circuit (haul cycle 7km). This improvement in productivity is related to the longer haul cycles and the larger radius curves on the coal haul circuit.
ADTs are capable of dumping to a single dump position, such as a dump hopper, or to multiple dump positions. The project only used multiple dump positions on a paddock dump (low dumping) because the ADTs are not yet capable of dumping over the edge of a dump face (high dumping) and operational constraints prevented dumping to a hopper. The ADTs provided precise dumping to a pre-determined dump pattern, demonstrated by tight, regular rows of dumps, when paddock dumping.
A risk management study was conducted using an independent risk professional. The study concluded that a substantial risk reduction is possible through the application of autonomous haulage. No major uncontrolled risks were highlighted by the study although, in some cases, additional investigation was recommended. A package of safe work procedures was developed for the project, suitable as a basis for subsequent autonomous haulage activities.
The research also found that a single repeater could not provide adequate coverage across the mine site. Two repeaters were installed to aid in cross-site UHF coverage. One of them was installed as a fixed unit located on the main mine communications tower (channel 1), and the other (channel 2) was a mobile trailer-mounted unit. Testing, by driving each of the trucks on all haul roads, ramps and pits, revealed that the use of the fixed and mobile repeaters resulted in acceptable UHF performance on one of the two available channels across the entire mine site. Flexibility was enhanced by the use of the mobile repeater.
The project has successfully demonstrated the technical and operational feasibility of autonomous haulage. However, there was insufficient operational testing to determine commercial feasibility. In addition, the final version tested was the pre-commercial version 0.3 autonomous system. This system has significant limitations including inability for high dumping, inability for use with wheeled loader, inability for concurrent road grading and production, database limited to a single loading area and a single dump area. These limitations, together with many others, are expected to be addressed with the first commercial system.