Wassenaar, Netherlands--Using a custom-designed variable-speed drive, engineers from John Deere have created an air seeder cart that allows for "on-the-fly" setting changes. The cart, which seeds and fertilizes farmland, enables users to quickly adjust to variations in crops or soil. In contrast, previous systems called for users to disassemble and reassemble the chains and sprockets on the feeding mechanisms, which sometimes took hours.
The new variable speed drive is especially important when used in conjunction with Deere's GreenStar yield-mapping system. GreenStar, which employs satellite-based global positioning (GPS) and computer control, enables farm machinery to vary seed rates for specific geographic locations on the land. But GreenStar's value would be diminished if users needed to repeatedly change the sprockets and drives each time the situation called for it.
"The chain drive systems usually had three or four different sprockets driving the seed augers," notes Lyle Gerads, president of Zero-Max, Inc., the company that designed the new variable speed drive for Deere. "Every time they changed seeds or fertilizers, they had to move the chains and sprockets for each auger."
To design a variable drive system, Zero-Max engineers worked with their counterparts at Deere. The result: an adjustable drive mechanism that eliminates the problems of earlier V-belt and chain-and-sprocket drive devices.
The four-bar drive mechanism consists of control linkages, connecting rods, eccentrics, and clutches. During operation, the cart's crankshaft turns a journal that serves as the input power for the drive. To vary the output, users merely turn a crank, which swings a control link to a different point within the arc of its prescribed motion envelope. Doing so produces a different output, because the position of the system's connecting rod is altered from vertical (which corresponds to 0 rpm output) to horizontal (which corresponds to maximum output). Movement of the connecting rod varies the length of the strokes delivered to the unit's overrunning clutches, which, in turn, determines the speed of the seed mechanism.
Deere engineers initially selected Zero-Max's Model ZX for its first prototype Model 1900 Air Carts. The ZX offered a 4:1 speed ratio, however, standard ZX drives were designed for higher speed inputs and lower torques than called for in the Deere application. As a result, Zero-Max's design team produced a customized version of the ZX drive.
The customized drive employs the four-bar linkage of the ZX, but incorporates compact roller clutches. The roller clutches were critical to the design because they allowed for additional travel distance of the linkages. The additional travel, in turn, enabled the system to achieve a 1.6:1 speed ratio, which was better suited to the application than the original 4:1 ratio.
The Model 1900 Air Carts are available in manually-adjusted versions and motor-adjusted models. Both can be set for a range of dispensing levels by referencing a metered scale on the variable speed drive unit. The motor-driven version provides "on-the-go" adjustment, and allows users to alternate from conventional to map-based seeding and feeding using the GreenStar system.
"The really nice thing about the design is that unlike competitive models, the John Deere system can be adjusted manually in the event of computer failure," notes Ronald Pratt, staff engineer for Deere. "Keeping the system operating is extremely important for seeding where the time window for best seeding conditions is very narrow."
Most important, the variable speed drive unit eliminates the need to change sprockets and chain drives, or in some cases, to hammer away at the system's bolts in an effort to change the settings. "If you change to a different terrain or soil, and you want to change the output from 15 pounds per acre to 40 pounds, you just dial it in," Gerads says. "With the old chain-and-sprocket system, it was never that simple."
Additional details...Contact Martin Blaauw, Koppe Europe bv, Postbus 112-2240 AC Wassenaar, Ban Hallstraat 6-8 - 2241 KT Wassenaar, Netherlands (P).
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