Dragline Automation through Automatic Control of Bucket Carry Angle

The aims of dragline automation are to:

• increase average bucket content by maximising fill and reducing spillage,
• decrease average cycle time, by improving repeatability,
• reduce maintenance down-time by reduction of dynamic overloads.

Automation allows individual portions of the digging cycle to be tuned, with respect to: precise bucket positioning, winch speeds and accelerations. Thus, peak loads in the digging cycle may be smoothed out. High repeatability possible from the automated system allows the digging process to be optimised with respect to a productivity index, which considers the costs of production and maintenance down-time along with the need to meet a production quota.

Scope of work

The following report describes the theory and experimental implementation of a carry angle control strategy used for the automation of a dragline's digging cycle. This strategy uses a feedback loop, which automatically actuates the drag-rope of a conventionally rigged machine, to regulate bucket carry angle and hence control the bucket trajectory. The drag rope automatically tracks and responds to changes in hoist rope length, in order to maintain a desired carry angle whilst the bucket is in flight. Feedback is obtained from a bucket mounted instrumentation package which continuously monitors and transmits carry angle data to the drag rope motor controller.

The objectives of this research project are to:

• devise and tune a feedback controller for automatic control of bucket carry angle,
• integrate the carry angle control strategy into an automation system for the digging cycle,
• demonstrate the technology using a laboratory scale model,
• design and field test a prototype bucket carry angle sensor package.

Results

This research has yielded the following outcomes:

• a theoretical understanding of the statics, dynamics and automatic control of a dragline's bucket carry angle.
• development of mathematical modeling and experimental techniques. These have been applied to a laboratory scale model, but are equally applicable to a full size machine. These techniques are a precursor to the implementation of a carry angle control automation strategy on a full-scale machine's digging cycle.
• evidence, on a laboratory scale model, that the automation strategy, using automatic control of carry angle, is successful. It has been shown that the strategy requires only two data inputs from the operator (drag haul and hoist lift distances) in order to define the entire automatic digging cycle. /li>
• computer hardware and software capable of implementing the automation strategy. This is based on a MATLAB/Simulink/dSPACE digital controller.
• a robust, self powered, instrumentation package has been created to transmit data from the bucket to the cab of the dragline. The onboard sensors (inclinometers and gyroscopes) continuously measure and transmit at 20 Hz : bucket carry angle and rate, bucket roll angle and rate, plus battery voltage.
• field trials at Peak Downs mine, have provided evidence that bucket mounted sensors work reliably on an operating dragline, continuously for periods up to 25 days (ie transmitter battery life) duration. These sensors can accurately measure carry and roll angles and transmit data from the bucket to a receiver located at the cab.