Clutch Designs for Equipment Controls Optimization

Farmershave long been aware that they are losing money by double planting on end rows,point rows, around terraces and by planting unsuitable areas such as waterways.With seed corn at $200 a bag, the amount of money wasted in dropping seed whereit is not needed is substantial. Another concern is double planted areas oftenrun out of moisture and nutrients, resulting in yield loss.

Somefarm equipment OEMs have addressed this concern by providing the operator withthe ability to manually turn off sections of the planter. This approachprovides significant benefits, however, it places an additional burden on theoperator, and controlling planting at the section rather than the individualrow level still wastes a considerable amount of seeds.

Adoption of automatedcontrol
Overthe past few years, there has been rapid adoption of automated control forsprayers applying fertilizer and chemicals. A number of companies offerautomated control of the three to five sections into which most sprayers aredivided, and a few companies have introduced control at the individual nozzlelevel.

Now,OEMs are working on upgrading planters to automatically control individual rowunits while planting. The basic idea is to automatically turn rows off as theyenter covered areas, or areas that are marked not to plant on the coverage map.This requires the GPS system be integrated with a control system that comparesthe planter's location to the coverage map, and sends a signal to disengage aclutch integrated with the seed meter drives at appropriate times.

Normallythe seed meters for the individual rows are driven by flexible cables through agearhead. Controlling the seed meters requires that, for each row, a clutch beadded that can engage or disengage the power from that row's seed meter.

Froma mechanical standpoint, this application requires the seed meters be turned onand off with very little delay in order to deliver seeds exactly where they areneeded without overplanting. From a standpoint of reducing the development,manufacturing and operating costs, the drive system should be as small, lightand power-efficient as possible. In addition, the rigors of operating in thefarming environment of course require a very rugged design and one that isprotected from the elements.

Upto now, the normal approach has been to retrofit pneumatically-powered clutchesto existing seed meter gearheads so that individual rows can be turned on andoff. One weakness of this approach is that a pneumatic power system needs to beadded to the planter. This adds cost and weight, as well as another type ofpower system that needs to be maintained and supported over the life of theequipment. Pneumatic systems also consume power whether or not they are beingused. The use of a separate clutch with its own enclosure also increases thesize and weight of the installation. In many cases, extensive modificationswill have to be made to install this type of device such as cutting andre-welding the frame.

Wrap Spring Clutches
Thomsonis a supplier of wrap spring clutches (Deltran brand) and also a major supplierof gearheads (Micron brand). The company recently took advantage of itscapabilities in these two areas to integrate a wrap spring clutch and gearhead intoa single enclosure to provide a complete row control solution for planter OEMs.

Thebasic wrap spring clutch consists of three elements: an input hub, an outputhub and a spring whose inside diameter is slightly smaller than the outsidediameter of the two hubs. In its basic form, the wrap spring clutch operates asan overrunning clutch. When the input hub is rotated, the spring wraps down toengage the two hubs. If the input is stopped or reversed, the spring unwraps torelease the output hub, allowing the load to overrun. The greater the force ofrotation, the more tightly the spring grips the hubs. The torque capacity ofthe spring clutch is a direct function of the diameter of the hub and thetensile strength of the spring.

Theaddition of a stop collar and a control tang on the spring lets the output hubstart and stop while the input hub spins. Stop collars come with one or morestops, up to 24/rev or 15 degrees between stops. The control tang anchors tothe stop collar, which surrounds the spring and hubs. An external mechanismengages a lug on the stop collar OD. Halting the collar unwraps the spring andreleases the output hub. The arrangement applies no braking to the output hub.

Wrapspring clutches provide several advantages in planter row control applications.For example, wrap spring clutches are considerably lighter and smaller, andrequire only 1/10 to 1/5 of the power of a friction clutch for a given amountof torque. Wrap spring clutches also provide faster response than frictionclutches by rapidly syncing up loads with the drive motor within a predictabletime or rotation angle. Unlike friction

clutches that can slip under certainconditions,  wrap-spring clutches won't slip when engaged. The reverse logic approachneeded for this application was developed by modifying a standard wrap spring clutchso that it is normally engaged and only disengages when the control tang isactivated.

User ROI
Theability to shut off individual rows can generate substantial cost savings. Atypical planter working on corn acres plants 12 to 20 seeds per sec per row,representing a cost of about 50 cents per sec for a 12 row planter. Someestimate that the ability to individually control rows based on a coverage mapand GPS data can provide savings of over $2,000 compared to a planter withoutswath control, and just under $1,000 compared to a planter with manual swathcontrol on an approximately 1,400 acre operation. Some estimate that yieldimprovements are closer to $4,000 in value compared to the planter withoutswath control, and around $1,500 compared to the planter with manual swathcontrol.

Clint Trenor is global accountmanager, John Pieri is Deltran product line manager and Mike Leone is seniorapplications engineer at Thomson Industries Inc.

Formore information, visit: www.thomsonlinear.com.