November 2008: Cover Story

Signals from the Sky
Machine Control Grading Systems Provide Jobsite Guidance
By Jason Morgan

When the ancients looked to the stars, patterns in the sky emerged — scenes mimicking their everyday experiences and myths. Today, new constellations are still being discovered. On a quiet, dark jobsite, as the machines rest after a long, hard day’s work, you can see one of the newest constellations, if you look closely. Machina Gradus is its proper name, but in layman’s terms it’s the Machine Grader; instead of being made up of stars, it’s formed by a cluster of orbiting satellites.

The satellites that make up this grading constellation are of the global positioning system (GPS). Just as automakers have leveraged this technology for navigation systems, machine manufacturers have adapted the technology for machine control grading. Using the signal from the stars, GPS grading systems from the likes of Topcon, Leica Geosystems and Trimble offer a three-dimensional (3-D) map of the jobsite in the cab of your grader, dozer, excavator, backhoe loader or skid steer.

“In machine control, one-dimensional [1-D] or two-dimensional [2-D] systems control basic depth or a simple slope, but have no link to the point on the jobsite in the horizontal directions. Satellite-based mapping systems most people see in automobiles provide a map view with the horizontal location but not the depth.

Modern 3-D machine control systems provide both the horizontal location of where you are on the site in addition to the depth accuracy required for grading,” explains Rich Calvird, Program Manager of Machine Control for Leica Geosystems Inc., a company founded in Aarau, Switzerland in the early 1800s that began with surveying equipment but evolved into grading control in the 1980s. “So you start with a 2-D map and then, for any point on that map, you have a given elevation. That way you know not only the X and the Y, but also the Z. The system will give the operator guidance, allowing him or her to see where the trench needs to be and how deep and how wide it should be.”

Although GPS machine control grading is starting to gain momentum, 2-D grading systems — laser and sonic — have been around since the 1970s (and earlier in surveying equipment applications). Laser and sonic systems use a physical reference point. Laser systems are able to dial in a grade and have it projected by the laser in a 360-degree dome light stream that the machine sensors can pick up. Sonic systems use sound sensors to find the ground, curb or stringline and allow machines to work in both vertical and horizontal grades. While earlier systems were bulky and expensive, today’s laser and sonic systems are precision tools.

“Laser-based systems are straightforward,” says Calvird. “They are easy to set up and the concept is easy to grasp with the analogy between using a laser and a simple builder’s level. Laser machine control systems may be as simple as a magnetic-mounted laser sensor that can provide grade information. You set it to where grade is and dial in a slope on the laser transmitter — something like a 1 or 2 percent slope that’s lined up with your trench. The laser detector has a bright LED display that’s easily visible from the cab to tell the operator when he or she is on grade.”

Grading Major

While stars in constellations fade from the night sky as the Earth continues its yearly orbit, GPS satellites are clearly seen by machine control GPS grading systems all year round. The machine uses the cosmos data to provide more than just trench specifications and indications. Sonic and laser systems need physical references — so they are mainly used for finishing work, after the bulk of earth moving is done — but GPS grading systems can be used for more than just grading.

The sensors on the machine relay data back to the control computer to let the system know where the machine is on the jobsite. In the case of an excavator, you may have up to four or five sensors — the cab, bucket, boom and arm, and a fifth sensor on a tilting bucket, as seen here.

“You can use GPS throughout the entire project and that’s why it’s really taken off,” says Murray Lodge, Vice President of Sales for Topcon, a developer and manufacturer of precision positioning equipment such as precision GPS systems, laser, optical surveying and machine control products. “That’s from a culmination of things. First, it’s getting hard to find skilled operators. The older generation is retiring and the younger guys don’t have the experience or the same amount of time to learn the skill as the older guys did. Second, a grading job that used to take a week or two, now needs to be done in five days.

And plus or minus a tenth [on the grade] isn’t close enough, you need plus or minus a few hundredths. So you have to figure out how to take a less-experienced operator and have him produce quality results.

“With a machine control GPS grading system, you know the elevation and the slope anywhere on the jobsite. You can run the machine manually using the indicator system when you’re roughing in the line or [in the case of a dozer or grader with automatic grade control] you put the grader in automatic and it goes right to the pre-programmed elevation and slope.”

The jobsites of yesteryear were a webbed maze of stakes and strings for grades and trenches. Surveyors often visited the jobsite checking and critiquing the grade. The jobsite of the future, however, is nearly stakeless. GPS grading systems eliminate the grade markers that are commonly knocked out or moved during an initial rough grade and take out much of the grading guesswork. Keep in mind that it doesn’t eliminate the need to check the grades — you still have to comply with all the regional and local rules and regulations. But it does increase the odds of success that the first pass by the operator is the right pass and that puts the grade where it needs to be on the first check, not the third or fourth.

The basic hardware may seem complicated at first, but it can be broken down into understandable segments. Typically, you have a GPS receiver (to receive the GPS signal from satellites), sensors on the machine (be it an excavator, dozer or grader) and the control box (to receive and interpret the data). The number of sensors depends on the type of machine. On a dozer, for example, you’ll typically have one sensor for the tilt and slope of the blade; whereas on an excavator, you may have up to four or five sensors — the cab, bucket, boom and arm, and a fifth sensor on a tilting bucket, if applicable. Generally, the control boxes can be moved from machine to machine to maximize the system’s versatility and productivity.

After dialing in your specific grading or excavation requirements, the sensors mounted onto the dozer blade or excavator boom will let the system know exactly where the blade or bucket cutting edge is. Then the system is able to alert the operator to the grade through a series of colored lights or a graphical display, depending on the system.

Automatic grade control is a popular option on dozers and graders. By patching into the machine’s control functions, you can pre-set the grade and allow the system to automatically adjust the blade as the operator drives the machine.

“You can’t beat an automatic system,” says Lodge. “Even if my operator is great, he can keep control of both sides of the blades and match them up. But that might be good from 7 a.m. to 10 a.m. and then after lunch he’s a little worn out — no one can maintain that level of accuracy all day, every day. But you put it on automatic and it controls both sides of the blade. No one can outperform an automatic grade control day in and day out.”

Mapping Minor

It may seem like a mystical process — gathering info from the sky to work on your terrestrial jobsite, but there’s a method to machine grading mapping. The first and most important step is to convert the 2-D file (the blueprints) into a 3-D digital terrain model. Many grading systems come with software that takes the 2-D model from IOCAD and translates it into 3-D for the model.

In-cab displays alert the contractor to the grade. While some are simple alert displays (like this one), more in-depth systems offer full-color LCD displays.

After you have the digital model, you have to localize the jobsite. This means that you are taking the jobsite and tying its physical position with that of the satellites. This is done by walking around the jobsite and placing the handheld GPS rover for a short amount of time on control points put in by the surveyor. The number of points depends upon the size and layout of the jobsite, but you need to provide at least four.

You then take the file from the rover unit and put it into the GPS control box on the machine to be controlled. Now, the GPS system knows where the machine is on the jobsite and its activity in the programmed job.

“Operators would have access to the data, where to pinpoint the spot they need to be digging at and see the surrounding area — giving them a more complete picture of the job, so they can think beyond just controlling the blade to stay on grade,” says Calvird. “Operators have indications or full automatic control to help them do that, so they can think at a higher level of ‘What’s the best way to do this job?’ and ‘How does this fit in with all the other construction going into this job?’”

Although getting the information to the machine is the primary goal of the rover, it can be used for more than just machine data.

“Just about everyone uses the rover before they start moving material,” says Lodge. “I might go out and do a quick topography before I bid a job, but usually you bid on what the engineer sends out. But before moving any material, I go out and do a good topo of the existing surface and compare it to what the engineer provided. If they match up — great, I’m going to work. But a lot of times you’ll find out the existing ground topo was based on an aerial survey or material has moved in or out and you find that you have an additional 20,000 or 50,000 more yards to move that you didn’t anticipate. You want to make sure you will be compensated before you move the dirt because once you start, it’s pretty hard to get after the fact.”
Beyond the initial bidding, you can also use GPS grading systems to plan beyond the initial stages of the project. For example, an operator might pile material up on a jobsite during a rough grade and then find out in the next phase that the material has to move to another spot. By analyzing the job with the GPS system first and planning the job ahead of time, the operator can move the material to the proper place the first time.

When dialing in your grading work specifications, you can also map the location of known utilities to show on the screen — giving the operator yet another layer of visibility. Being able to mark these utilities on a display that can alert the operator that he or she is digging near an established utility line is more than just a feature — it’s peace of mind

The Vastness of Grading

Not one star in the sky looks the same. Some twinkle brighter than others, while some seem unattainable in the distance, but they come together in a cluster to create an image that is greater than any individual part. Grading systems work in a similar way. While a contractor may start with a simple laser or sonic-based system for finish grading, adding a GPS-based system to the mix is as simple as glancing at another part of the sky when looking for more stars.

Those antennas aren’t for receiving the hottest satellite radio stations. They receive and send positioning data to allow the operator to rock the jobsite with productivity.

For many contractors, it comes down to price when getting into grading systems. A basic flat laser, sonic or site recognition system can range from $5,000 to $15,000 depending on the options such as the display system. GPS, on the other hand, is a larger investment running $30,000 to $55,000, not including the $20,000 base station. The tradeoff is that once the major investment is made, you can add components such as a laser or sonic system at a fraction of the starting cost. And there’s the added value you get out of maximizing your productivity and bid preparation.

“Even though it costs five times as much as a conventional 2-D system, the payback from a 3-D GPS system is five times quicker,” says Lodge. “In reality, everyone is going to have some system or else you’re not going to be able to compete. If you have two contractors bidding the same job and you have one that can increase his productivity 40 to 50 percent or more, then the other guy can’t compete.”

With technology moving at such a rapid pace, new features and options are well stocked. For applications where the GPS equipment cannot pick up signals from the sky, such as inside a building or in a heavy tree canopy, a robotic total station known as a Local Positioning System (LPS) or Theodolite Positioning System (TPS) can be used to send the position information. The robot tracks the machine as it moves and wirelessly sends X, Y and Z data to the control box, letting it know where it is on the jobsite.

For greater jobsite visibility, Leica Geosystems subsidiary Cable Detection Ltd. offers an excavator-mounted utility detection system that alerts the operator when he digs close to metallic, buried utilities. While not exactly a part of a grading system, it can provide the operator with added underground and grade knowledge.

Greater jobsite direction and knowledge is an important edge to have over the competition. With job costs skyrocketing, a system that lets you plan the job ahead of time, conserving fuel, time and money, is well worth the investment. Where generations of old have used star charts for navigation, today’s contractor looks to the sky to chart his own course of productivity and profitability.

Jason Morgan is Associate Editor of Utility Contractor.