When does a wheel loader make more sense than a skid steer? By embracing the technology of external machine control systems, all four of the remaining North American manufacturers of asphalt milling machines (Astec’s Roadtec, BOMAG, Caterpillar, and Wirtgen) have made it simpler for customers to manage milling depth.
These GPS- and software-driven systems have evolved into plug-and-play essentials for clever managers on milling (and later paving) works, much like systems for earthmoving equipment.
Accuracy is the aim, just like when executing earthwork to grade. Cost savings, speed, and efficiencies come next. The limits of traditional milling using stringlines and marks.
According to Matthias Schmidt, senior product portfolio manager, machine control division, Leica Geosystems, “the operator needs to work to the design for the new surface, removing the proper depths in the right spots.” Traditionally, a surveyor would manually follow sprayed markers that he or she had laid down. This preliminary process takes time and has a chance of error. The road must be blocked for the work to be done safely, and the surveyor frequently has to work at night to reduce inconvenience.
This makes the job challenging, as does the weather; spraymarks can be washed away by rain, and wind might result in erroneous marking, according to Schmidt. “Once the design has been marked, it may be challenging for operators to view since it may be obscured by nearby machinery or challenging to read from their machine. Any errors cause the machine operator to either remove too much asphalt, which necessitates additional filling costs and makes the project more expensive than it needs to be, or not remove enough asphalt, which results in lower-quality new surface layers. When milling deeper than necessary, there is also a risk of harming the structural subbase layers.
Leica is one of three significant businesses that offer milling machine 3D machine control systems. As a first step toward milling that is managed digitally, it offers a technology called Leica iCon site milling pilot application.
“As the cold planer goes over the area that is being milled, the milling pilot calculates the difference between the existing and the design surface using positional data from a GNSS receiver such as the iCON gps 60 and iCON gps 70 on the machine,” adds Schmidt. The iCon site software displays a two-step preview of set and cross slope values at expected places, ahead of the present position, on the iCon CC80 field controller in the cabin. The operator must enter the appropriate settings into the leveling controller of the machine because this operation is manual.
Then, managers can advance to the quicker and more precise 3D machine control solution. According to Schmidt, this is where the cold planer’s machine control technology, which regulates how much to grind, is installed. “3D technologies can more correctly duplicate road grades and slopes, making it simpler to achieve complex designs and, eventually, enhancing the smoothness of the finished pavement. The two 3D stringless milling options offered by Leica Geosystems are differential milling and profile milling.
According to Schmidt, the 3D solution in profile milling modifies milling depth and slope based on information provided from a total station.
The digital design file for the road is uploaded into the Leica MC1 machine control software by the surveyor or the machine operator, according to him. “The software supports the operator in positioning the machine to accomplish the anticipated design by comparing the design model to the actual position of the machine’s cutting edge. The cold planer’s position is tracked in three dimensions by an active total station, and MC1 on the machine checks the elevation and slope against the plan. The machine controller receives the amount of asphalt that has to be cut. It is shown on the tablet interface that the operator uses in the cab and manages the machine’s hydraulic reaction. This does away with the requirement for a surveyor to mark out any stringlines or marks on the ground, or for the operator to regulate changes by following man-made markers.
The iCon site milling pilot allows for automatic differential milling, and it employs two data sources to do so: the road’s design and the as-built model of the road, which describes the present surface.
According to Schmidt, “the as-built model’s source could be measurements made using a total station, a 3D laser scanner, or a mobile mapping solution.” “Fitting a mobile mapping system to a vehicle and driving it down the road that has to be resurfaced is a rapid way to create the as-built model. An alternative is to use a ground penetrating radar system, which offers information on the various layers and the details that are crucial for carrying out the project correctly, such as the depth and thickness of the reinforcement cover, the thickness of the concrete slab, the thickness of the asphalt, the detection of areas affected by corrosion, and the detection of rebars.
The iCon program analyzes the difference between the design and the as-built model and determines what must be eliminated to obtain the required surface. The milling machine’s location and its position in relation to the design are determined using the Leica iCon GPS 60 or GPS 70 smart antenna, according to Schmidt. The iCon site milling pilot app uses the changes in design to determine the milling depth values and the cross slope at the position of the machine. The milling machine controller, which manages the hydraulic reaction on the machine, receives this information from the app via the Leica iCon CC80 tablet.
With Topcon’s 3D-MC Milling, milling depth may be determined and controlled by a 3D design model. It has a 2,400-meter working range horizontally and a 40-meter working range vertically, allowing millimeter-level accuracy. In the same zone, many users can mill vertically, horizontally, or with combined transitions.
How do milling machines for asphalt control their operations?
The system is demonstrated via a runway restoration project at Toledo, Ohio Express Airport.
Mike Kreig, project manager for Gerken Paving in Toledo, states that the project mostly comprises a mill/fill to design grade. “We must achieve a design grade on the finished surface, per the engineer. Additionally, there is a design grade to mill to, thus there are two courses totaling around three inches: a leveling course and a surface course.
The person utilizing the technique is Tim Winch, Gerken’s grading foreman. He frequently strolls alongside the milling machine, quickly glancing at a monitor to assess accuracy and progress. When all is said and done, “They demand a super smooth surface, which is why we’re doing it with a 3D millimeter system. It is significantly more accurate than what we can obtain with our standard technique, he claims.
The benefit, according to Kreig, “something we realized right away was that you can just let the machines do the work.” If you need a surface grade for your pavement or a cut grade for the mill, you can virtually go anywhere on the project and discover your grade. As opposed to stringline, where you are allows you to catch grade; a parallel line is not necessary.
At the ground level, managers will discover cost savings and other efficiencies.
Some of those stringlines can droop, and Winch advises that you double-check. Whereas they don’t lie with this—those satellites. Although I have no idea how it accomplishes so, it is extremely effective.
Using the millimeter GPS also has the benefit of removing the need for a stringline, which saves time and money on this project, according to Kreig. “We only really need to update the batteries in a couple of the transmitters so that we can go out and set everything up in the morning and operate all day. Instead of needing to move the stringline, reset the grading, and stop our operation, we may work nonstop all day long. So, only by using millimeter technology, our output significantly increased.
Winch listed mental tranquility as still another benefit. “It was just so pleasant to be able to stroll without worrying about a bump. There wouldn’t be any lumps in [the outcome] if it hadn’t all been carried away or if my ski had crossed over it. It improved our quality of life somewhat on the ground, he said.
In order to use the milling machine for the paving task, Gerken was able to remove the machine control equipment from it.
The benefits of paving are “quite comparable to the milling benefits, where there is no stoppage, we always carry grade, and we are able to continue at the same speeds and even faster production rates with the process of paving,” adds Kreig.
According to Winch, “[The system] is directing that machine what to do and where to do it, and it’s really accurate.” It is good to not have to worry about a hiccup in the road when you’re down to the last course. All they had to do was come in and lay an inch and a half. While they were in their final [laydown], it was already ideal.
In order to mill at a set or variable depth, depending on the work parameters, Trimble PCS 900 for milling machines uses a 3D design model, the company’s SPS930 Universal Total Station, and add-on machine sensors.
The milling machine operator sees the 3D design, which highlights any places that are on, above, or below the ideal grade. The technology automatically guides the milling drum to cut the correct depth and slope without manual adjustments or stringlines by comparing the actual drum position and slope with the digital design.