Comprising a radically new bucket rigging and control system, the UDD is set to revolutionise open cut coal mining and will redefine the key performance indicators for this kind of mining operation. For instance, the UDD system increases the economic changeover point between dragline and truck/shovel overburden removal.

The new system eliminates over half of the rigging associated with a conventional bucket (which can be subsequently replaced with increased payload) and allows the bucket to be disengaged from the dig face as soon as it is full (thus reducing total cycle time).

The first dragline to be fitted with the new technology is a Bucyrus 1370W machine – Dragline 23 - at the BHP Billiton Mitsubishi Alliance (BMA) Peak Downs mine in Queensland.

The machine was converted to UDD configuration between January and March this year and then subjected to extensive commissioning and testing. Comparisons between the conventional configuration prior to retrofit and the Universal configuration showed an improvement from 2021 bcm/operating hour to 2654 bcm/op hour in a carefully quantified production trial; effectively a huge 31% productivity increase.

The site trials were conducted in a sidecasting operation, selected because sidecast operations are not subject to large variations in dig rate and provided a good test of digging performance. The 31% productivity increase was attributed to the following:

Elimination of 10 tonnes of rigging;

Decrease in average fill time from 15.1 to 10.6 seconds;

Decrease in average spot time from 2.2 to 0.4 seconds due to increased stability of the bucket being ready to dig when it returns to the cut;

Decrease in average swing time by 1.7 seconds for similar average swing angles due to increased flexibility in digging method.

Increase in available operating hours due to a decrease in time associated with pad preparation and wait-on-dozer.

Researchers observed several other improvements that were not quantified during the trials. One of these is greater speed and accuracy in cleaning the coal seam due to the ability to set and control the bucket angle.In response to these early results, Peak Downs has already adjusted sections of its mine plan with an increased overall digging depth, reducing pre-strip requirements.

The main observable difference between a conventional dragline system and the UDD system is the innovative way the hoist ropes are used.

The bucket of a conventional dragline is suspended by two hoist ropes on either side of the bucket, which means the bucket’s carry angle is determined by where it is in space and by the geometry of the rigging. A conventional dragline must drag its bucket close to the house of the machine before lifting to reduce loss of payload from the front face of the bucket. This also means that the payload must be dumped at the perimeter of the boom.

The UDD system replaces the conventional system by attaching the two suspension ropes separately to the front and rear of the bucket. The hoist ropes are individually controlled by a robust computerized system.

The result allows the operator to pick up a load at any point without losing payload and without overdragging the bucket. Material can be dumped at virtually any point under the boom.

While the idea seems obvious, the complexity resides in the control system. UDD inventor, Dr Jeff Rowlands said the key problem was to perfect a robust and safe control system that adjusts the carry angle of the bucket through all modes of dragline operations: digging, chopping, disengaging, carrying (anywhere under the boom), cleaning top of coal, and dumping. Covering all these scenarios requires algorithms that solve a continually changing, statically indeterminate geometry.

Work on the new concept began in 1999 with researchers from the Cooperative Research Centre for Mining Technology and Equipment (CMTE) at Brisbane’s University of Queensland, led by Dr Rowlands.

A mini version of the system was installed on a one-tenth scale dragline at CMTE’s Pinjarra Hills site in Brisbane.

Strong industry backing followed, with initial support from the Australian Coal Association Research Program (ACARP) fast-tracked to quantify the effects of the new rigging on productivity. Tests of the scale unit were conducted by an experienced dragline operator, Greg Sheppard, who has since been closely involved with training the UDD dragline operators at Peak Downs.

“The UDD requires a different approach to operating the machine,” Sheppard said. “It has more flexible operating limits so for example dig sequencing methods have to be looked at differently.”

By March 2000 an ACARP report was released, showing indicative increases in dragline productivity of 18% to 29%, depending on various operating parameters.

Detailed information about the new system – such as the retrofit - was kept confidential until last month when BMA held a very well attended open-day at Peak Downs to demonstrate the technology to industry.

The UDD system is expected to be commercially available from December 2002 for a cost of around $7 million to $10 million for a similar dragline. Each retrofit requires a 120 day design phase, Dr Rowlands said, which first had to take into account the duty cycle and mining conditions related to the specific machine. In time, a standardised retrofit package for the various dragline models will be developed, cutting down design time.

For the Bucyrus 1370, the retrofit has reconfigured the main hoist machinery including splitting the hoist drum into two independent winches, repositioning the hoist motors, adding a new gearbox and auxiliary AC motor and variable frequency drive.

The exercise involved contributions from companies including Team Engineering, Hatch, Hofmann Engineering, P&H MinePro Services, REB Engineering, DLE Electrical Services and Tritronics. Some 90% of the revenue generated by the project went to Australian companies and over 150 jobs were supported for engineers, operators and technical personnel.

One of the long lead time items was the new boom point assembly which was fabricated by P&H MinePro Services in Mackay using special high-grade steel pipe sourced out of the USA. Dr Rowlands said the 30 tonne, 15m x 7m structure was subjected to extremely rigid fabrication controls. Continues .