Bringing a high-end control system, programming and mechanical design to FireFly's automated turf harvesting machine proves technology and automation work well in agriculture applications. Not only is the FireFly ProSlab 155 more efficient and productive compared to what was originally available in industry, it also connects to the Internet of Things (IoT) to bring even more technology to the field (Figure 1).
Things started slowly but moved quickly for FireFly in North Salt Lake, Utah. "We started in business in 2010 building aftermarket parts for the turf farming industry," says Steve Aposhian, CTO and president at FireFly Equipment. "Having grown up on a farm and with my brothers identifying problems with existing harvesting equipment, we designed in some improvements. Feedback from customers in the industry triggered the design of the ProSlab 155 machine." FireFly made the leap of using advanced controls to solved a number of problems customers were facing in the industry.
Aposhian is a mechanical engineer with an emphasis in software development and controls design. Using engineering knowledge, the FireFly team observed that there were machines out there dedicated to cutting flat slabs of turf that worked under some conditions. However, the machines weren't very productive; they were slow and had reliability issues requiring high maintenance. The existing turf machines were also not very flexible.
There are a wide range of conditions in the field. "Sod is perishable and is grown all over the country and close to most metropolitan areas, so there are different soils and different grass types," says Aposhian. "The industry needed a machine that worked in a wide variety of field conditions."
Instead of a turf harvesting system based on hydraulic activation and simplistic control algorithms, a higher level of control was needed, continues Aposhian. "Looking at the needs of the industry, we determined the use of advanced controls, including servo systems, was the solution, even though it is not normally done on mobile equipment,” he says (Figure 2).
A new design begins
FireFly started the design of a high-performance servo motor control system for its turf stacker movements, which addressed two needs of the market—neatness and durability. "The precision motion of our machine made it easy to create neat pallet stacks," says Aposhian. "It also helped durability when the system was sped up. When original manufacturers tried to speed up, the result was rough, moving mechanisms that didn't place the turf accurately in a stack. This rough, jerky motion also tended to tear up the turf square. The servo motion provided excellent positioning capability and speed and was gentle with the turf due to the smooth velocity control. This smooth control also helped the durability of the equipment that could see millions of cycles a year."
That's a lot of 450-sq-foot pallets—a common size—that can be stacked in a little over 2 minutes.
Another benefit of the servo control is it is much more fuel efficient, says Aposhian. "Taking a look at the industry and with the team’s background in other areas of automation, we saw the opportunity to bring a higher level of control design to an industry that really needed it," he says.
The first machine
"We started design in 2010 on a part-time basis and went to full-time design with me and three other engineers in June 2011," notes Aposhian. "We completed the design and build of the first machine and brought it to a trade show in April 2012. There were a lot of long hours in completing it in less than a year."
Aposhian focused on the software, electrical and hydraulics, and three other engineers focused on the mechanical and motion during this rapid development cycle. Six machines were built, and then a revision created an improved model as part of the development cycle, and more machines were built during the first year.
The control system helped speed the development cycle. "Part of the testament to the National Instruments platform used is that it allowed us a rapid development cycle when implementing some fairly sophisticated controls," says Aposhian. "Having a strong background with National Instruments helped with the choice of the control system, but there where many reasons. I had been doing LabView for 14 years, but, more importantly, the LabView CompactRIO platform was ideally suited for the requirements we were faced with. The turf machine is really a collection of small machines all on one piece of equipment."
An up-close look
In the front, the machine cuts and singulates the sod (Figure 3). The cutter extricates the grass from the ground consisting of two different processes. One process controls the blade that cuts underneath the grass—the skim cut—and one that cuts vertically to cut the piece to length similar to a flying cutoff process. These cutting mechanisms feed the conveyor, which delivers and positions the turf for the stacker to grab.
The turf is positioned at the high-speed stacker using encoders on the conveyors and photo-eyes to register the position and coordinate pickup with the servo-controlled stacker mechanism. This provides some buffering, and the turf can be picked up on the fly without stopping the conveyor.
The stacker has the servo motion control hardware to pick the pieces off the conveyor, move them to the pallet and stack them. This is a very high-speed and high-performance pick and place. At the pallet, there are forks and an empty magazine system for up to 20 pallets. The forks and magazine work in tandem, lowering the pallet incrementally as the turf is stacked and then placing a completed pallet on the field.
The tractor itself is another major system including the drive system, propulsion and steering that the control system can monitor and control. This self-propelled tractor moves all the automated systems through the field.
All of the systems must work in parallel since this is a continuous flow operation. "While the stacker is stacking, the cutter in front cannot stop cutting," says Aposhian. "The LabView CompactRIO is well-suited in handling these parallel systems, simultaneously. It also enables very rich transfer of data between each system. There is significant coordination between each parallel system, where synchronizing conveyor speed with tractor propulsion speed is one of many examples."