The technological evolution of combine harvesters
Combine harvesters are operating machines that have been manufactured in their current configuration since the first half of the 1900s. They have their origins in fixed-point threshers. As a matter of fact, their development has been uninterrupted, both mechanically and from the (more recent) mechatronic point of view. The current models are highly sophisticated, resulting in a combination of high work capacity and high-quality results
In the early days of grain species cultivation, harvesting and threshing were managed separately: plants were cut in the field and grouped into sheaves, which were later threshed manually, either through a stick or by animal trampling.
Following the development of mechanization, fixed-point threshing machines appeared on the market around the 1830s. They were made up of a beater, and a concave, sieves, fan and straw walker, driven by a belt drive moved by stationary steam or endothermic engines or, more recently, directly by farm tractors. The latter also enabled the machinery to be moved from farmhouse to farmhouse; a task performed until then by animal traction.
In 1836 the first combine harvester was built in the United States. This machine was designed to cut plants in the field and separate the grain from the chaff, albeit still inaccurately. This combine harvester had a cutting width of about five meters and was pulled by about twenty horses. However, the lack of an adequate drive unit and the tendency of harvested grain to deteriorate from excessive moisture limited its spread.
In 1915, International Harvester of Canton (Illinois, USA) released the first line of trailed harvesters equipped with an engine to drive the threshing system. Case and John Deere introduced the first tractor-drawn models a few years later. The demand for these machines overgrew, particularly after World War I, even though the presence of combine harvesters in Italy remained confined to a few large cereal farms until after the war. In 1942, an outstanding expert in agricultural mechanics even wrote about combine harvesters "...this category of equipment does not present a real and concrete interest from the point of view of the possible widespread application in Italy.”.
Despite this pessimistic prediction, the spread of the combine harvester domestically grew after the end of World War II as the economy recovered. Major import brands included Massey Harris, McCormick, Claas, John Deere and International Harvester. The first Italian combined harvester model was manufactured by Pietro Laverda of Breganze (VI) and presented at the 1956 Verona Fair. That model, named "M60," was equipped with a 35-Hp Fiat diesel engine, the mowing apparatus was 1.98 m wide single-body with the machine with mechanical ratchet lift equipped with an articulated reel, and was provided, as threshing apparatus, with an 8-bar beater and concave that could also be adjusted while working. The Laverda M60 was produced until 1963, with a total of 974 units sold in Italy and Europe.
The diffusion of this new machine entailed some problems related to both threshing efficiency and quality. These were solved by developing the two main categories by which combined harvesters are still commonly classified today: conventional, also known as "tangential-flow," and axial-flow.
A large footprint characterizes the former due to alternating motion straw walkers, an adequate operating capacity, relatively low diesel consumption, and the ability to recover undamaged straw.
The latter, however, are characterized by a higher working capacity, being able to process a high input biomass flow. They have a smaller footprint, but they do not provide for the reuse of straw since, due to more energetic action, the straw is shredded excessively before being released on the ground. An interesting solution - which is actually in between the two mentioned above - is that of the so-called "hybrid" harvesters. A conventional thresher/counter-thresher is followed by a separation apparatus generally composed of a pair of counter-rotating rotors, which process the crop in an axial pattern. Regardless of the threshing device installed, these machines were initially designed to be used on flat land since, especially for conventional models, it is necessary to ensure the best uniformity of biomass distribution between the thresher and concave and then on the walkers. If this were not the case, grain losses would increase unacceptably due to the inevitable overloading of the related working organs. Since Italy has a high percentage of hilly and mountainous land cultivated with cereals, so-called "leveling" and later "self-leveling" models appeared in the late 1960s, i.e., equipped with hydraulic actuators at the individual wheels. These were designed to keep the machine body horizontal in both the turntable and retractor gears, allowing the cleaning system to work correctly under all conditions.
Once again, Laverda was the progenitor of the production, with the M 100 AL model produced starting in 1971. These systems, which can be adjusted automatically through dedicated inclinometers, allow correct work on slopes up to about 25 percent uphill, 10 percent downhill and over 35 percent transversely.
High mechanical complexity
From a technological point of view, combined harvesters were immediately characterized by high mechanical complexity due to the numerous moving parts and having to ensure their own self-displacement at the same time. As of today, several types of transmission enable the operation of the various components, with a certain preponderance for the hydraulic ones, which are more capable of making continuous and precise adjustments.
As far as the sensor part is concerned, it should be mentioned that it was precisely combined harvesters that were among the first machines implemented for precision agriculture purposes, thanks to the installation of systems for geo-localized mapping of production, already described in a previous article (see Machinery World no. 11/2021).
On-board sensing and automation.
The most innovative features include: 1. the position of the mowing bar: the header frame can move vertically, employing hydraulic actuators, to define an optimal distance of the cutting apparatus from the ground surface. A very interesting solution also consists in the possibility of making the cutter bar flex (thanks to its sectional conformation) and thus following, in a more reliable way, the profiles of even considerably irregular soils. This is very useful for threshing prostrate bearing crops such as soybean, bean, pea, etc. 2. in the case of threshing autumn/winter cereals, adjust the reel position according to the development and density of biomass in the field. Precisely, a laser sensor controls the depth and horizontal position of the reel according to the plant material in the bin. This results in a uniform feed of product, which improves threshing performance and optimizes the utilization of engine power; 3. threshing equipment adjustment: it is possible to automatically adjust the distance between the beater and concave (both in and out of the crop flow), the speed of rotation of the beater, and the position of the ginning bar, and the opening/closing of the concave blinders. To constantly optimize machine performance, some specific solutions make use of data from a high-definition color camera mounted on the grain elevator header. The resulting images identify parts other than caryopses, i.e., straw, glumes and glumettes, and broken grains. The resulting image processing can alert the operator if threshold values are exceeded so as to improve crop cleanliness; 4. the fan speed can be modulated according to the slope of the ground on which the machine works.
Specifically, the speed automatically decreases when working uphill (to avoid excessive leakage from the rear of the combine) and increases instead when proceeding downhill to avert clogging of the threshing apparatus. In addition to fan speed, some systems improve grain cleaning by automatically managing the opening of the upper and lower sieves or by directly adjusting the machine's forward speed; 5. residue distribution in the field: through 2D radar, it is possible to obtain an accurate picture of the distribution profile of residue particles ejected from the machine by detecting the position and speed of airborne residues before they fall back to the ground so that an actual distribution profile can be obtained. This results in uniform residue coverage behind the combine without specific operator intervention.
Combining harvesters' spread and continuous technological improvement make them absolute protagonists of modern agriculture.
The latest sales data also confirm this belief: in the 2020/21 season, the sale of these machines in Italy increased by about 30 percent, from 290 units in the previous year to 376 in the most recent harvesting campaign.Specifically, axial combines made up 37 percent of the total, conventional ones 35 percent, and self-leveling 28 percent, a figure the latter of which testifies the importance of hill and mountain agriculture in the Italian reality.