The Bottom Line: Entry Points to Machine Control - Paul F. Hahn

Written by Paul F. Hahn

Created on Saturday, 02 May 2009 19:54

Lasers have been used to improve earth-moving operations and agricultural applications since the 1970’s. They deliver excellent results, especially in fine grading and finish grading applications, due to their high-accuracy at short to medium distances. (Specialized laser systems are also used to augment 3D machine control, improving the vertical element of GPS-guided machines-but more on that later.) Their utilization eliminates a lot of staking (and re-staking) and allows you to get to grade much faster and with more accuracy. They do not give you horizontal position, but with some alignment staking and elevation benchmarks, they certainly get you to grade more quickly than with conventional methods. Laser-based machine control can be useful in rough grading operations utilizing scrapers and big dozers, as the operator has clear guidance of where the design grade is at all times. This prevents over-cut and under-cut and the additional passes needed to correct them.  Since they can cut very close to the design grade, smaller dozers and motor graders can then move in and do the fine and finish work more efficiently.  Lasers provide exceptional accuracy at close range, more than sufficient for finish grading, providing excellent control of materials with fewer passes, less personnel and reduced staking costs.  These systems are relatively inexpensive and very versatile.  They typically pay for themselves on just one job.  The application where lasers are most commonly used is site prep jobs. Depending on the accuracy of the laser you select and the job specifications, lasers can provide machine guidance up to 1000 feet from the laser transmitter. Lasers can be purchased that provide a single (flat) reference plane which are useful for pouring slabs and other horizontal surface or provide single-slope or dual-slope reference planes.  The dual-slope, or dual-grade, lasers allow you to dial in a percent of grade and cross slope information and provide reference planes to guide your grading activities. A useful example is grading a roadway with a certain fall and cross-slope, or other applications like ditches and berms.  The typical configuration is a laser transmitter, a laser receiver (mounted on the machine) and a display, viewable by the operator. The display will indicate whether the cutting edge is above, below or on grade.  The operator then makes the manual adjustments necessary to get to the blade on grade.  These types of machine control systems are called “indicate” or “guidance” systems.  Although they do not provide the same magnitude of return-on-investment that 3D automated systems do, they greatly improve productivity, accuracy, save on materials costs and reduce manpower requirements and with their lower acquisition cost, provide a quick ROI.

Site Management Systems
These systems are relatively new to the machine control, market but provide many benefits. They utilize some of the components of a fully automated 3D system, but allow for a lower-cost entry point. One of the main benefits of these systems is the fast and accurate measurement of earthwork quantities at any point in time for inspection and progress payment purposes. They do require a 3D digital terrain model (DTM) of the design surface (also referred to as the data model) to yield results. This is a good thing, especially if you are not using 3D machine control today. You will be able to get up to speed on utilizing 3D data models and get your people trained on their usage and quirks. A quick example may help you understand how these systems can be of benefit:

Let’s say you have a GPS base station established for surveying purposes.  You also would have a GPS rover available for the same purposes. But now you add the 3D data model to your tools and special site management software. You can now use the GPS rover to check grade anywhere on the site. You can use the results to see how close you are to grade or compare these sets of measurements to the last ones you took to determine progress payments. The rover can be mounted to a truck (or other vehicle) or a on a GPS rod used as a walkabout. If vehicle mounted, you can obtain the data quite quickly. You are not controlling machines, but checking the results for your purposes.

Site management systems provide other benefits.
•    Bid Verification
•    You can topo the site before you bid it- errors are sometimes found on the old topo maps provided –this can greatly impact the earthwork quantities, which can make a break a project
•    Cut/Fill for every square inch – in real time
•    Collect/Stake Points
•    Daily, weekly and anytime volumes
•    Stationing & Offset in real time
•    Spot check elevations and horizontal positions
•    Warning and watch zones
•    Usually scalable to indicate and automatic machine control

These systems are an excellent entry point and easily scalable for those of you who want to migrate to 3D automated machine control. Your people will gain experience working with GPS and 3D data models. The learning curve will then be shortened when it’s time to automate your operation to include full-blown 3D machine control. In the meantime, you will realize productivity improvements in your inspection and earthwork quantity determinations. If you don’t have GPS equipment yet, there will be costs associated with this move, but you will need this equipment later on anyway to fully automate your machines. If you have the GPS equipment already, the cost for the site management software is very reasonable.

There are other positioning solutions that will increase productivity with a lower-cost initial investment, including those that utilize sonic tracers. We will discuss those solutions in future articles. It is a good time to consider some of these solutions if you don’t already employ them. Yes, jobs and money are tight, but now is an opportune time to get through the learning curves and get your personnel trained. Once that is done, your bids will be more competitive and your jobs can be much more profitable.

Also visit Paul's blog