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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.
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| 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. |
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“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.”
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