There’s no doubt lasers are a must for high-productivity grading work.
But with a diverse and growing range of products in the marketplace contractors need to carefully match their needs with the equipment available.
“It can be difficult for a contractor to get it right unless he asks the appropriate questions,” says Bob Ford, sales director, 2D machine automation, for Leica-Geosystems. “You don’t want to oversell them, but you don’t want to undersell them either. You want to sit down with them and ask some key questions about their machines, their work and what they want to accomplish.”
Indicate only vs. automatic blade control
There are two basic types of systems for laser grade control, indicate only and automatic blade control.
An indicate-only system consists of a laser transmitter that’s set up over a surveyed reference point on the worksite and a receiver that is mounted typically on a mast on top of the machine’s blade facing the operator. The laser transmitter shoots out a perfectly flat, 360-degree plane of light, which when it strikes the receiver, activates lights on the receiver that tell the operator whether his blade is too high, too low or right on target. The operator eyeballs the lights and raises and lowers his blade accordingly.
“Indicate-only systems are generally sufficient for rough grading applications,” says Mike Bank with Apache Technologies. “Not that you can’t do fine grading with indicate systems but you will get better speed and accuracy with automatic blade control.” In a simulator demo the company sets up at trade shows, contractors are challenged to try and keep up with an automatic blade control system running over the same virtual site. “All it takes is about a minute and a half before they give up in frustration,” Bank says.
Conversely, automatic systems are sometimes too precise for rough grading. “A lot of guys will do their rough grading with a bigger piece of equipment on indicate only or use just the indicate portion of an automatic system,” Bank says. Then they’ll come back and do the final grading using automatic blade control. It’s also a good idea to put the automatic system on your newest machine, he says, because jerky controls or worn linkages may defeat the precision you’re trying to achieve with automatic systems.
The big difference between the indicate-only systems and automatic blade control is the latter taps directly into the machine’s hydraulics and moves the blade up and down without any operator input to keep the cutting edge level with the desired final grade. Given you’re adding a valve assembly and controls to the machine’s hydraulics, the automated blade control systems cost more. A typical indicate-only system runs $1,300 to $2,500. For automatic blade control, prices go from $10,000 to as high as $28,000 for top-of-the-line units for big graders and dozers.
If you start with an indicate-only system you may want to seriously consider one that will allow you to upgrade to an automatic blade control system later without having to purchase a new transmitter or receiver. Another feature to consider: some receivers can be switched from grading machines to digging machines to measure trench depth and make it easier to keep a consistent depth.
Set up your blade with dual receivers and you can grade slopes.
Bang-bang, two-stage or proportional
With automatic blade control systems there are three different types of hydraulics to choose from:
Bang-bang hydraulics, as the name implies, are either all the way on or all the way off. “It’s the least expensive option and it gives you a rougher finish,” Bank says. “We use some software to make the valve act a little smoother,” he adds. But for land leveling this is the least expensive hydraulic option.
Two-stage hydraulics have a coarse spool and a fine spool, Ford says. “When we get close to finish grade we close off the coarse spool and let the fine spool take over,” he says.
Proportional hydraulics give you the most refined control. “As you get closer to grade, the spool slows down,” Ford says. “You can change how fast your blade reacts. If you’re working in sand you may want to slow it down because the level of the blade isn’t changing much. If you’re in rock and banging around the blade in going up and down a lot you would want to speed it up for a faster reaction time.” Another reason to consider proportional hydraulics is should you decide to upgrade GPS systems will only work with proportional hydraulics.
Grading slopes
If your work involves more than flat building pads you will want a laser transmitter that can give you dual-grade capability, as opposed to a single grade. Dual-grade lasers can be tilted and thus produce a slanted plane of light that matches the slope you want to grade. Then you put two receivers on masts on your blade. With two receivers and a dual-slope laser your blade will maintain the proper angle even if you’re turning up or down the slope.
Lasers with this capability express the amount of slope they can convey in a percentage of grade with most going up to 25 percent. For steeper grades manufacturers offer what they call steep-slope lasers. A certain amount of slope can also be calibrated by attaching a tilt meter on the blade and then maintaining that angle throughout each pass.
Blade control systems tap directly into your machine’s hydraulics and keep the blade on grade automatically.
Achieving accuracy
The accuracy standard for construction grade lasers is typically 10 arc seconds or less, which translates to 1/16th of an inch per 100 feet, Bank says. But accuracy in the field can be affected by numerous variables. The wind or vibration from heavy machinery nearby can shake the laser transmitter. On hot days convection currents rising off the ground can affect the transmission of the laser beam.
The newer laser transmitters spin at faster rates and advances in receiver microprocessors enable the systems to handle more data, which means better chances to overcome these sources of distortion in the field.
A good receiver on an automatic blade control system will also allow you to change accuracy settings in response to changing jobsite conditions and/or the speed of the machine. “You don’t want it to be constantly correcting itself, bouncing the blade up and down,” Bank says. “You don’t want to be chasing the laser all over the place. You want to find a setting that adds some stability to it. Otherwise you’ll start washboarding.”
Sales and installation
Laser systems are typically sold through laser dealers. And installation of automatic blade control systems is most often best handled by the dealers. Thanks to the booming market in automated systems a lot of survey equipment dealers are transforming themselves into machine automation dealers, Ford says.
Contractors rarely do the installs. “The biggest issue is that there is a fair amount of time spent fine tuning the control box, especially when you’re applying the equipment across a broad range of machines – motor graders, skid steers, dozers and drag boxes,” Bank says. “That’s something a technician is best suited to do.”
