Open Cut » Overburden Removal
The aim of this project was to develop modifications that can be installed in a dragline cabin to assist the operator in achieving maximum productivity and safety.
The most important developments were concerned with providing the operator real-time feedback of relevant operational and production data. The feedback mechanisms were of two distinct types:
Visual feedback devices, eg analogue bargraph modules mounted on the periphery of the operator's windscreen.
Tactile feedback in the operator's controls ie direct physical feedback in the drag master switch control lever that allowed an operator to 'feel' the duty on the machine / bucket.
This project has shown that
it is possible to influence productivity
by supplying real-time feedback to the operator.
The visual system used hoist motor amps as its input and supplied a conditioned signal to a strip-like display module. Since motor torque is directly proportional to current, this feedback equated to hoist rope load. Using the feedback system to minimise hoist rope load during hoist dependent cycles, two major effects occurred:
Hoisting speed increased thus reducing overall cycle times
Peak half-cyclic stresses on all hoist drive machinery and suspended components were reduced thus increasing component fatigue life.
Experiments were carried out on both Dragline Technologies' training dragline and Dragline 304 at Curragh in Central Queensland. These test quantified the effects described above.
Cycle times reduced by 2 to 6 seconds depending upon the pit geometry and conditions.
The amount of time spent at high hoist motor current levels (>90% of stall amps) was typically halved.
The tactile system used drag motor amps as its input and ultimately applied an active proportional torque to the drag master switch control lever via a servo motor. This torque was only applied as drag stall conditions were approached during the digging part of a cycle.
Experiments were carried out on Dragline Technologies' training dragline. Results included:
Reductions in the size of maximum levels of drag motor current (approximately 5%)
Reductions in time spent at high levels of drag motor current (>90% of drag stall amps reduced by two thirds).
The tactile system used drag motor amps as its input and ultimately applied an active proportional torque to the drag master switch control lever via a servo motor This torque was only applied as drag stall conditions were approached during the digging part of a cycle.
Experiments were conducted on Dragline Technologies' training dragline. Results included.
Reductions in the size of maximum levels of drag motor current (approx 5%)
Reductions in the time spent at high levels of drag motor current (> 90% of drag stall amps reduced by 2/3)
The first point leads to similar effects as those described above with respect to increased mechanical fatigue life. The second result implies an increase in drag motor lifetime due to a reduction in RMS temperature which directly affects insulation breakdown.
Operator Response to both feedback systems was extremely positive. Acceptance levels for the technology was high. All operators agreed that the systems would assist trainees in learning good operating techniques. Most operators agreed that the systems would assist them in optimising their own actions.
The major benefits to the industry include:
Direct methods of improving dragline productivity by utilising the maximum talents of an operator.
Providing superior training aids for novice operators.
Improved safety to both men and machines by real-time feedback of operational data.
Determine what forms of feedback would be of benefit to operators
Design, construct and install prototype feedback systems
Test the systems and quantify their effects on dragline production and operator performance
Determine whether these effects are of benefit
Ensure that the level of operator acceptance of the final systems was as high as possible to assist in the implementation of feedback systems.
Discussion of Results
The first trial for the drag feedback system involved four operators digging in an underhand geometry across a normal digging face in swing dependent cycles.(ie, no hoist or drag-payout dependent cycles). The average swing angle for these trials was 88.5 degrees.
The operators were first asked to dig normally without any tactile feedback. These results were used as a benchmark. The second part of the exercise was a repeat of the first with the feedback system energised. The operators were instructed in the expected 'feel' that they would experience but were not told what, if any, operational effects may arise.
For the first trial, the feedback torque was programmed to become active at approximately 50% of drag stall amps. The feedback torque would linearly increase from zero to maximum corresponding to 50% and 100% of drag stall amps respectively.
The second trial involved another group of four operators digging under similar conditions with an average swing angle of 94.5 degrees. In this case, the feedback torque was programmed to become active at 75% of drag stall amps. The torque would also increase linearly from zero at 75% stall amps to maximum at 100% stall amps. The maximum torque value reached was increased by 10% from the first group of operators.
Operators were consistently positive towards the feedback system both in their perceived use of the device and its benefits. Not one operator was of the view that a reduction in productivity would result if the system were installed.
Most operators believed that the system would be of significant benefit to trainees, especially in reducing overdrag and unnecessary damage to the dragline.
Most operators who used the system were enthusiastic towards having a programmable system where different levels of feedback could be tailored to individual needs and/or situations.
Recommendations for Further Work in this Area
Testing of other operational inputs to the existing feedback systems
Development and testing of a visual feedback system that does not require LEDs (eg Head-Up display)
Installation of tactile feedback system on a production dragline and monitoring of the effects.