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C.R. Kennedy fine tunes the control of bucket wheel trenching

Bucket wheel trenchers are notoriously difficult to guide using GNSS. However, with GNSS and some lateral thinking C.R. Kennedy now has a Victorian contractor’s trencher working super-efficiently.

C.R. Kennedy, by dollar value Australia’s largest importer and distributor of surveying equipment, has installed automatic guidance systems on earthmoving equipment all over Australia. In an industry first however, the company has just installed a GNSS system on an articulated bucket wheel trencher. In northern Victoria, Goulburn-Murray Water is well advanced with its $2billion G-MW Connections Project to improve the region’s irrigation network. Many open channels are being replaced with HDPE pipe, and new control systems will allow irrigators to log-in by mobile phone to order the volumes they require. Solar powered, computer controlled gate valves will then open automatically to send the volumes ordered.

Rubicon Water is supplying the control systems, and Retic Water, a subsidiary of Rubicon, is currently laying 230 km of 500mm HDPE pipewest of Echuca. They are using a Trencor T1360 bucket wheel trencher which is articulated, with a tractor at the front towing a bucket wheel behind. Looking to increase its pipe laying speed and efficiency, Retic Water contacted C.R. Kennedy. [The pipeline industry is probably most familiar with C.R. Kennedy’s lines of Leica and Riegl products.]

Traditionally a bucket wheel trencher’s operator steers the machine by eyeballing sighting poles placed ahead of the machine, while a surveyor walks alongside the machine continually checking the trench level and telling the operator to go up a bit or down a bit. With machine control technology, you would imagine some GNSS system would be available off-the-shelf to simplify operations. There are good reasons why there isn’t. Scott Craik of C.R. Kennedy’s Survey Division explained why.

“The biggest issue is with the machine being articulated,” Mr Craik said. “It’s a bit like reversing a trailer. GNSS can’t steer for you because the orientation and path of the tow vehicle are often nothing like those of the trailer, and it takes time for the trailer to react to steering movements. You’re in the same boat with an articulated trencher,” he said.

The other issue relates to the trencher’s slow travel speed. According to Mr Craik, a machine needs to maintain a certain minimum speed for GNSS to track its position, to understand the machine’s orientation and to know what direction the machine is moving.

GNSS control of a trencher’s steering is yet to be mastered by anyone; however C.R. Kennedy has already raised Retic Water’s productivity enormously with a GNSS system that has sped up and improved the accuracy of trench depth control. For most GNSS work of this kind, a base station would be set up on site to correct the positional data sourced by GNSS antennas on the machine. C.R. Kennedy’s first initiative was to source the correction data from SmartNetAus, a national network of GNSS reference stations that offers the necessary +/-25mm tolerance on height. Now, with positioning corrections available 24/7, the trencher’s operator doesn’t spend time setting up the base station. He focuses on the trenching work.

On the machine itself, two Leica CGA60GNSS antennas have been fitted laterally across the width of the bucket wheel’s frame. One provides information on the bucket wheel’s position, while the two antennas combined give the orientation of the machine, its direction of travel and trench cross fall. As the wheel digs deeper, the frame rises, thereby tilting the masts, so a Leica SP14 tilt sensor has also been fitted, to provide corrections related to the machine’s geometry. A Leica iCON Total Station was used to map that geometry.

The brains of the whole package is a Leica iCG82 GNSS Receiver. It has a circuit board for each antenna and is tied into the existing hydraulic control system that raises and lowers the bucket wheel. The connection has been done in such a way that the automated system works independently of the original system while still giving the operator manual control for over-ride if needed. The iCG82 computes the position of the cutting edge, applies the satellite corrections provided by SmartNetAus and sends the data to a screen in the cabin, where the operator gets a real time, 3-D view of the bucket’s position in relation to the trench design depth at that chainage. Retic Water is now able to consistently achieve a tolerance of +/-25mm on its trench level and more frequently +/-15mm. The operator still uses the tried and true sighting poles for steering but can refer to his screen to confirm the machine is on the pipe’s centreline. 

Through the on-board iCON Telematics service, the operator can record in real time the position and depth of the cutting edge and send the recorded data back to the project office at the end of each shift for quality assessment by the survey team.
Retic Water is working on several fronts of the project simultaneously and is swapping the GNSS system between the trencher and several excavators. It’s early days yet, but according to Will Spence, Survey Manager at Retic Water, using C.R. Kennedy’s system on the excavators is improving productivity by a massive 50%. He doesn’t yet have a measure on the productivity improvement of the trencher, but he said the system has halved the surveyors’ workload and, because the trencher is working so accurately, the three excavators that were previously required to support the trencher are now free for other work.

C.R. Kennedy has offices with service centres in most Australian capital cities and professional staff with a level of knowledge and expertise that matches the calibre of the brands they carry.

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