Sugar cane is conventionally harvested by manually first burning the cane to remove the leaves, then hand cutting and piling the cane, and finally mechanical grab loading the piled cane into a transport vehicle. When a cane field that has not been burned (green cane) is cut by hand, the output of cut and piled cane is only approximately one-third of that which is achievable by hand cutting burned cane. Therefore, the cost of hand cutting green cane is uneconomical for most applications. As the economies of sugar cane producing areas improves, hand labor for cutting cane becomes difficult to justify. Accordingly, mechanical cane harvesters are being increasingly used to supplement and replace the vanishing hand cutters.
Their are two basic types of machines for mechanically harvesting cane: (1) a soldier-type harvester, and (2) a chopper harvester. A soldier harvester is used for harvesting erect cane, and takes the erect cane into a center carrier where the cane is conveyed through the body of the harvester while remaining vertical. While the cane is erect in the field, the tops of the cane are removed and the cane is base cut at ground level. If the cane is not standing erect, the soldier-type harvester is designed so that its front end lifts the cane to an erect position prior to the cane entering the center carrier for progressing through the harvester in the erect position. The cane is thus lifted into the center carrier and, while held by the center carrier, is topped, base cut, and passed through the carrier in the body of the harvester. After being carried in its vertical position through at least a portion of the body of the harvester, the cane is piled in one or multiple row heaps, where the cane is later conventionally burned to remove the dead leaves on the millable cane stalks. The cut cane is loaded whole stalk into transports by grab loaders. Solider-type cane harvesters are disclosed in U.S. Pat. Nos. 5,379,577, 5,303,533, 4,483,130, 4,380,281, 4,232,775, 4,165,596 and 3,090,183.
While the soldier harvester works quite efficiently in conditions where cane varieties allow the cane to be easily moved to an erect position without burning, the soldier harvester does not work as well in cane fields where burning of the cane on the ground is not allowed. Since the cane is transversely piled whole stalk, a large row spacing is desired to stack the relatively long whole cane stalks. As a practical matter, Louisiana has the only significant location which has the type of cane varieties and field conditions which allow for the effective use of a soldier-type harvester.
Conventional tropical cane harvesters or chopper harvesters are characterized by their bottom first feeding of the cane stalks into the mouth of the harvester. This is followed by a chopper cleaning mechanism which cuts the passing cane and leaves into short pieces. A forced air current is used to remove the free leaves. The chopped cane is conventionally passed through a side loading conveyor and loaded directly into the transport. While a conventional bottom first chopper harvester works reasonably well in a burned cane field where most of the cane is erect, it has more difficulty working in a green, unburned cane field, and also has difficulty working a field with much of the cane in a semi-erect or lodged condition.
Those familiar with cane harvesting operations recognize that as the yield per area of harvested cane increases, more of the cane is fallen and is either semi-erect or lodged, and less of the cane remains erect. While chopper harvesters theoretically are designed to work in green cane fields where cane varieties result in a high yield with more cane stalks being semi-erect or lodged, conventional chopper harvesters are almost never used to harvest green cane, and instead harvest cane predominantly from burned cane fields. Burning standing cane in the field removes most of the leaves, thereby facilitating harvesting of the cane without the harvester becoming plugged with material as it moves through the field. Cane burning is environmentally undesirable, however, since clouds of ash from a burnt field may drift over residential areas, thereby making breathing difficult and creating a significant nuisance by covering patio furniture, automobiles and outdoor plants with a layer of ash.
Those familiar with processing cane have long recognized that burning the cane has a significant and undesirable effect upon the amount and quality of the sugar produced from the cane. From a cane processing standpoint, cane should desirably be brought to the processing plant whole stock and green, with little dirt and cane leaf or top matter. Conventional chopper harvesters which operate in burned cane fields cut the stalks of cane into billets which are typically from eight to ten inches long, thus increasing the likelihood that at least some of the sugar in the cane stalk adjacent the end cuts will become lost or will decompose before processing.
Even when harvesting burned cane, conventional bottom first chopper harvesters have problems when the cane is semi-erect or lodged, including substantial damage to the field and to the planted cane as a result of harvester operations (resulting in future crop yield losses and requiring manual replanting of a higher percentage of total cane area), and substantial harvesting costs due to low production rates and high initial costs of conventional single-row, bottom first copper harvesters. Due to the above problems, the overall cost of mechanical harvesting burned cane can be higher than a reasonable hand cutting operation.
A primary problem for bottom first chopper harvesters working in green cane field is the abundance of leaves on the cane. This effects the harvester in two distinct places, namely the front end of the harvester and the body of the harvester. Once cane is in the body of a harvester, the harvester must clean the cane without choking by first removing the leaves from the cane stalks and then removing the leaves from the body of the harvester.
Most chopper harvesters do not have adequate mechanical devices to separate the leaves from the cane stalks while the green cane passes through the harvester. These harvesters remove leaves from the cane within the harvester by chopping simultaneously through both the cane and leaves. Conventional chopper harvesters blow away free cut leaves, but cannot blow away that part of the leaf which is still attached to the stalk or is trapped by the passing cane. Therefore, the cleaning efficiency of a conventional chopper harvester becomes a function of how short the cane billets are cut. As cane billets are shortened in length, the cane is cleaner. However, shorter billets result in more juice loss and juice deterioration adjacent the many cut ends. Also, more pieces of good millable cane get sucked out of the harvester with the leaves.
U.S. Pat. Nos. 3,603,064, 3,705,481, 3,791,114, 4,270,337, 4,295,325, 4,512,142, 4,574,567, 4,702,423, 4,722,174, 5,379,578, and 5,488,820 disclose various types of sugar cane harvesters. For most sugar cane harvesters which cut cane into billets of a selected length, the cane cutters or knife blades are provided on drums which rotate about a shaft at a selected speed. Rollers act to hold back the cane stalks which pass between the rollers, and thus the rotational speed of the powered rollers is adjusted to obtain the desired billet length. As discussed above, the length of the billets may be shortened to remove excess leaves and thus improve cleaning, although shorter billets experience greater sugar loss and degradation. The speed of the powered rollers thus effectively determines billet length, since the speed of the rotating drum on which the knife blades are positioned remains fixed.
In one early type of sugar cane harvester, the speed of the machine passing through the field determined the length of the billets, since the cane was cut into billets immediately as it was fed into the mouth of the harvester. In this early embodiment, rotating knives were provided on the drum which rotated at a fixed speed, and the cane was not supported when it was passed into the cutter knives. The operator thus regulated the speed of the harvester passing through the field to adjust the length of the billets. This type of harvester is not used in most harvesting operations, and instead has been replaced by the harvesters of the type described earlier wherein the cane stalks are held between rollers as the cane is fed into the cutting knives, with the rollers retarding the cane from freely feeding into the cutters. Other devices for adjusting the billet length of sugar cane are disclosed in U.S. Pat. Nos. 4,483,129, 4,550,552, and 5,414,981.
A significant problem with prior art harvesters when cutting cane into selected billet lengths concerns the "choking effect" as cane is fed into the cutters. In an exemplary application, the harvester may be moving through a field at 5 miles per hour in a field containing 40 tons of sugar cane per acre. If the rollers which hold the sugar cane for feeding into the cutters are effectively slowed down to a rate whereby the cane is progressing toward the cutters at only three miles per hour in order to secure a desired billet length of 9 inches, then the chopper mechanism is being "choked off" since it is effectively handling cane at the rate of approximately 67 tons per acre due to the 5:3 ratio of harvester ground speed compared to the feed rate of cane to the choppers. To minimize this effect, some harvesters such as those disclosed in U.S. Pat. No. 5,622,034 have proposed using a fly wheel to minimize this undesirable choking effect.
Another problem associated with retarding or slowing down the cane as it is fed into the cutters concerns the ability of the harvester to remove leaves from the cut billets. Such a cleaning system is disclosed, for example, in U.S. Pat. No. 5,092,110. If the chopper mechanism for the harvest effectively is handling cane at a rate equivalent to a 67 per acre field because the cane is slowed down as it is fed into the chopper mechanism, the cleaning system must be designed to remove leaves from the billets at this very heavy rate.
The disadvantages of the prior art are overcome by the present invention. An improved chopper-type harvester is hereafter disclosed suitable for harvesting tropical cane. Most importantly, the harvester of the present invention is able to move efficiently through unburned or green tropical cane fields with semi-erect or lodged cane, and outputs cane in billet form which may be more efficiently used by the cane processing facility.