At present, tomato harvesters are very expensive, their price, as of 1982, approaching $200,000.00 per harvester. One reason why they are expensive is that a large proportion of the cost of each harvester is the cost of the engine, its support structure, and its related parts for propelling the harvester and its moving parts; for all current commercial tomato harvesters are self-propelled, partly so that the operator controlling the tractor's forward movement through the field can also control the depth at which the tomato plant stems are severed and the amount of dirt taken up by the harvester's pickup.
The high cost of harvesters has meant that farmers with relatively small areas planted in tomatoes have been unable to take advantage of efficient mechanical harvesting, unless they could do so cooperatively or from someone who owned a harvester and was willing to lease it or rent it to them or to use it for them in their fields. (Currently available tow-type harvesters, such as there are, have been small, low capacity machines.) Since all the tomatoes in a given agricultural area tend to ripen at about the same time for mechanical harvest, this has caused difficulties in scheduling and allocating harvesters among the smaller farms. Even for the larger farms the numbers of harvesters that could be afforded for large plantings of tomatoes was limited by the cost of the harvesters and by the cost of operating them.
Another problem of the self-propelled harvester, has been that they have had to be very heavy. Their weight made it expensive to freight them from one location to another, increased the fuel cost during operation, and also caused the harvesters to bear heavily on the soil in the field, especially, when that soil had been softened by a rain.
Even when the conditions were good for harvesting, the axles for the wheels of the harvester were low to the ground and could easily sink down into contact with the ground. Furthermore, the self-propelled harvesters have had numerous cross members, including not only the wheel axles but other parts which have often been so low as to lie only 12 to 18 inches above the ground on hard soil, and since the wheels are usually run in furrows on each side of a raised bed, and since the furrows are typically six to eight inches deep, the cross members are often as low as four to twelve inches above the ground in the bed, and when the wheels sink into the dirt in the furrows, this distance is even further lowered. It has therefore been difficult to complete harvesting when the soil has been softened as by rain, and even worse when the soil is somewhat muddy, for then the mud has tended to build up on these cross members and rather frequent stops had to be made to clean them off.
Another problem with the self-propelled harvesters has been that they have had a long turning radius, because of their long wheelbases. Farmers like to utilize their fields to the full, but when harvesters require a substantial amount of maneuvering room, some crop acreage has to be sacrificed and also time is wasted during the maneuvering when moving from the end of one row to the beginning of a succeeding row.
The height or depth control problem for the pickup elevator and its cutting device has been recently ameliorated or solved by the use of an automatic distance-measuring device coupled with the raising and lowering mechanism for the harvester's pickup unit, which supports the sickle blade and also supports the elevating conveyor carrying the tomato plants back to the separator unit. As shown in co-pending patent application, Ser. No. 363,642, filed Mar. 30, 1982, it has been found that ultrasonic distance-measuring apparatus makes possible automatic control of the level at which the sickle or other cutting device rides below the soil and cuts off the stems of the tomato plant, and that variations in soil surface can be accommodated by coupling these ultrasonic devices to the raising and lowering mechanisms for the pickup unit. Use of these automatic devices frees the driver from watching the height of the forward end of the pickup unit, so that he has to think only of steering and speed, and therefore also makes it more attractive than it would otherwise be to separate the propelling device from the harvester, although even without automatic height control this separation can be obtained.