Grain Harvesting Machinery

1.1 Introduction

Seeds come in an immense variety of shapes and sizes. Small grains include wheat and
rice as well as small and slippery oilseeds such as flax and canola. Large seeds include
grain corn with seed on ears, soybeans, and other beans in pods. Plant height varies from
ground-hugging peas to elevated ears on tall cornstalks. Such wide variations create unique
demands for harvesting machinery. All these crops from oilseeds, grass, and clover seeds
through to large fava beans are mechanically harvested with combines and mechanical
threshers. The term “grain” will be used here to include all types of seeds.

1.2 History

Until the nineteenth century, most grain was harvested by cutting with a sickle or scythe,
then manually flailed or beaten to break the bond of the grain with the stalk, then winnowed
to separate the grain from material other than grain (MOG). In the developing
world, these practices or the use of small stationary threshers are still in use for rice and
other grain harvesting. Stationary threshers emerged at the time of the Industrial Revolution.
The design generally used a tangentially-fed rotating cylinder to beat material and
break the bond between grain and stalk, followed by a screen or sieve that allowed smaller
grain pieces to pass through and separate grain from MOG. Those threshers were powered
by humans, animals, or water and later by engines.
During the nineteenth century, mechanical reapers and binders were developed to cut
and windrow grain for field drying. The sheaves were then hauled to stationary threshers.
Around the start of the twentieth century animal-drawn machines, “combines,” were
developed that integrated cutting, threshing, and separating wheat and small grains. The
necessities of World War II hastened the adoption of self-propelled combines.
Corn was initially harvested by hand picking ears after drying in the field. Such
manual corn harvest was labor intensive. Early in the twentieth century, Grandpa Sallee
hand picked about 0.4 acres per day. The important job of harvest was a family affair
(Grandma Sallee would get a kiss if she found a rare ear of corn with red grain during
hand picking).
Mechanical ear corn pickers were commercialized in the United States during the 1930s
and had been commonly adopted by World War II when labor was scarce. Prior to World
War II, the processing components on small grain combines were not yet rugged enough
to harvest corn. Corn pickers were either pulled by tractor or tractor mounted. Snapping
stalk rolls that pulled down cornstalks and snapped off ears were necessarily aggressive
but not shielded. Many farmers lost an arm or hand or were caught in the rolls while trying
to unplug stalks with the picker still running. Snapping rolls were later shielded by
stripper or deck plates. Ear corn was commonly stored and further dried by natural air in
a crib with gaps between side boards. Corn was fed locally to livestock or threshed by a
stationary thresher before entering the commercial grain trade. Although seed corn is still
commonly mechanically harvested by ear followed by carefully-controlled storage, then
stationary threshing of seeds from the ear at a central location, handling the full ear doubles
the amount of material that must be stored and handled. In the 1960s, advances in artificial
corn grain drying, and more rugged threshing and separation components in combines,
transformed corn harvest from ears to field-shelled grain.

1.3 Machine Design: Pre-harvest Issues

Harvest equipment design criteria and operation are affected not only by the type of
crop but by the limited time available for harvest and cultural practices associated with
the crop. Grain and oilseeds rapidly mature in just a few days before harvest. Grain moisture
content drops rapidly as the plant matures. Unless the grain is artificially dried, harvest
is delayed until moisture content is low enough to avoid spoilage during the time the grain
will be in storage. However, if seeds and plants are left in the field too long, pre-harvest
field losses occur from storms, lodging plants, or grain falling on the ground. Also, growers
are financially penalized for selling grain if moisture content is less than that of official
market grain grades. In some crops, re-wetting by rain also can create storage and/or
quality problems. Optimal field harvest conditions are governed by the weather. This
creates considerable pressure to complete harvest in a short time period before the crop is
lost in the field or spoilage occurs. For rice, that optimum period may be just three days.
Cultural practices affect harvest conditions. Stalk strength (small grains, corn) or seed
placement on the plant (beans) differs with variety or hybrid. The date of planting and
approximate days to plant maturity affects how quickly a crop will be ready to harvest.
Densely planted populations may promote stalk lodging. Row spacing determines corn
head geometry. If weed management strategies have not been effective, large green weeds
can overload and plug harvest equipment. Machine design has to cater for all these
conditions.
Grain end-user requirements also influence harvesting equipment design and settings.
Grain may be used for livestock feed, human food, fuel (e.g., ethanol production), seed,
industrial, or other purposes. Grain damage occurs during threshing, separating, and handling. Unless grain is used immediately for livestock feed, most grain buyers want damage
limited to a prescribed standard. Besides a general market standard, the buyer may require
a lower damage level for particular uses. Grain may also need to be segregated or “identity-
preserved” for some uses (e.g., seed, food, higher-value industrial uses) and that
demands a thorough clean-out of the combine before harvesting another crop.

1.4 Performance Factors

Aside from cost, grain harvesting machinery is rated by the following five performance
factors: throughput capacity, losses, grain quality, ease of operator use, and economics.
Throughput is the time rate of plant material processed by the equipment, usually measured
in tons of grain or MOG per hour. Loss is the percentage of grain processed that exits
the machine without being captured as harvested grain. As throughput increases to high
levels, loss increases due to inefficiencies in collection or separation. The American
Society of Agricultural and Biological Engineers (ASABE) defines combine capacity as
throughput at a specific grain loss level (e.g., 1% corn loss, 3% rice loss; ASABE, 2005).
Grain quality may be defined by grain grading standards (such as amounts of foreign
material and cracked or broken grain) or also include visible damage to the seed coat.
Field efficiency, the percentage of time the combine is actually harvesting in the field, is
used along with combine width and speed to determine acres per hour of field capacity.
Operator performance is affected by machine comfort, controls, noise, visibility, ease of
settings, etc. Finally, economic factors such as the cost of capital, repair/maintenance, and
fuel costs are used to estimate total operating costs.
Functional components of a combine include the crop gathering system, conveyors,
thresher, and separator (often combined) to separate threshed grain from stems and stalks,
the cleaning shoe to remove small/light material, and a storage bin to hold clean grain
until it is unloaded on to a transport vehicle to be moved from the field. Materials handling
equipment (conveyors) are required to move crop material throughout the machine.
Engine power is required for all these functions as well as significant amounts for the
ground drive system, straw chopper, unloading auger, and cab air conditioner

1.5 Heads: Grain Platforms, Corn Heads, and Strippers

Gathering head capacity determines combine throughput. Because threshing, separating,
and cleaning mechanisms must operate at constant speeds, travel speed is adjusted by
a variable speed drive to the crop intake capacity of the head while the engine throttle is
fixed by requirements of the separator and shoe. The head must gather all grain into the
combine and enough other plant material to cushion the grain during threshing.
Direct cutting grain platforms consist of a cutterbar, reel, and platform auger The cutterbar has a series of knife sections oscillating back and forth through knife
guards. Standard knife and guard sections are 3 inches wide with each knife oscillating
from directly under one guard to directly under an adjacent guard (i.e., knives are “in register”).
If the cutterbar is not linearly adjusted so the knife sections stop directly under
guards, it is out of register and rough cutting of plant stems will occur. A variation is the

Kwik-cut style of cutterbar using 1.5-inch knives and guards with a 3-inch stroke for
double cutting.
Cutterbar height affects the amount of plant material entering the combine. Small grain
cutterbars are fixed on the grain platform and the operator endeavors to cut the crop just
under the plant heads. For soybean harvest with bean pods close to the ground, a floating
cutterbar is used with height control to sense ground position and flexibility, to follow
ground contours on wider heads. Forward travel speed can be limited by cutterbar speed,
as the cutterbar must oscillate more quickly to cut plant stems as the head moves forward
at faster ground speeds.
The reel controls feeding of the upper part of plants into the grain platform. Bats on the
reel push the top of plants over the cutterbar to aid cutting and sweep the material across
the platform. For soybean or rice crops, pick-up fingers are often added to the reel to help
lift and pick up lodged crop. The center of the reel is slightly ahead of the cutterbar. If
pick-up fingers are used, the reel should be positioned so that fingers clear the cutterbar
by at least 1 inch for all conditions (also in the uppermost flexed position of flexible
cutterbars).
Peripheral reel speed should be slightly faster than ground speed in good harvesting
conditions. The dimensionless ratio of peripheral reel speed to ground speed is the reel

index. An average setting is about 1.25, but reel speed controllers should have the ability
to vary the reel index from about 1.1 to 2.0, with faster speeds being used to more aggressively
gather lodged crop into the head.
The platform auger takes cut crop material away from the cutterbar and moves it into
the feederhouse for feeding into the threshing area. Retractable fingers in the center alternately
pull the crop into the center and retract for release to the feeder. Ability to adjust
the auger position can help feeding. The auger should be low enough to efficiently move
crop material without plugging. However, too low a position may damage grain pinched
between the platform and steel auger flights. Moving the auger slightly forward may be
beneficial in short crops to aggressively pull material away from the cutterbar area.
A windrow pick-up header using conveying belts may be used in crops that have been
previously cut and windrowed for additional drying before threshing. Draper platforms
(using rubberized belts to cross convey instead of an auger) are popular for small grains
as they increase capacity by smoother heads-first feeding.
Stripper heads are sometimes used for rice and small grains. The stripper rotor has a set
of combing teeth, which literally comb grain heads from stems. The rotor is covered by a
hood to prevent grain flying away from the head. A platform auger gathers material into
the feederhouse to the threshing area. The advantage of the stripper head is that it greatly
reduces MOG entering the combine. This allows greater throughput and forward speed.
A corn head has individual row units designed to strip the ear from the stalk and gather
it into the machine . Six-, eight-, and twelve-row corn heads are common, but larger and smaller heads are also made, by short-line manufacturers. The head should be
matched to row spacing (commonly 30 inches) to avoid machine losses during gathering.
Cornstalks are pulled down by stalk rolls and the ears are snapped off as they strike stripper
plates (also called deck or snapping plates) that shield the stalk rolls . Gathering
chains on top of the stripper plates pull the snapped ears to the platform cross auger
with the auger feeding ears into the feederhouse. Snouts of lightweight plastic or sheet
metal divide crop rows and cover operating parts. Gear boxes under the platform drive
individual snapping rolls and gathering chains.
Several adjustments and options affect corn head operation. Stripper plates should be
adjusted to cover enough of stalk rolls to avoid butt-shelling of kernels from ears but not
so close as to pinch and break off upper portions of corn stalks. Stalk roll speed should
be adjusted to travel speed so that ears are stripped about halfway up the stripper plates.
Gathering chain speed should match ground speed to bring stalks uniformly into the head.
The leading edges of the head, or snouts, should operate a few inches above the ground
unless lodged corn requires them to float on the surface for dividing the crop. Newer equipment
offers in-cab controls for many of these manual adjustments and one manufacturer
makes spring-loaded stripper plates that automatically compensate for stalk size
on-the-go.
Options available with many heads include variable speed operation (to match crop
gathering with travel speed), a head reverser to help dislodge or unplug crop, slip clutches,
and other various safety and/or functional features. Automated steering helps to increase
field efficiency when using wider heads or to stay centered on the row. Row-crop heads
to harvest individual plant rows similar to a corn head have also been used to harvest soybeans
and grain sorghum. Because of the toughness and size of corn stalks, stalk shredders

are sometimes used under the corn head. Shredding is done by separate rotary knife
units, or limited additional shredding may be done by knife-type stalk rolls. An aftermarket
reel is occasionally mounted above the corn head in lodged crop conditions.

1.6 Feeder house

The feeder house or “feeder”  transports grain from the head to the threshing
area. Large chains with cross slats fastened to them pull material along the bottom of
the housing of the feeder house into the threshing area. Chain position, tension, and speed
should be adjusted to uniformly take material from the head. The height position of the
front drum around which the feeder chains operate should be adjustable to accommodate
different crop sizes (e.g., wheat versus corn) and crop volumes due to yield or the amount
of plant material moved through the combine. Many combines have a rock trap in the
feeder house or close to the top end of the feeder house.

1.7 Cylinder or Rotor and Concave

Action in the threshing area both detaches (threshes) grain from other plant material by
impact and rubbing and separates the detached free grain from other crop material. Both
major styles of threshing mechanism move the crop between the surface of a rotating cylinder
and an open-mesh concave. Cylinder threshing  is sometimes termed conventional
threshing as it is used on all types of crops and early forms of the design were
used in the first stationary mechanical threshers. The crop is tangentially fed between
the underside of a rotating cylinder and a crescent-shaped, open-mesh concave surface

wrapped around the underside of the cylinder . The cylinder axis is perpendicular
to crop flow. Grain is rapidly threshed near the entry point and separates from straw
(i.e., other plant material) as it progresses along the concave path. In good conditions,
70–90% of the grain may be separated at the concave. The rate of separation decreases
near the rear sections of the concave as considerable amounts of free grain have already
been separated. A rotating beater strips material flow at the rear of the concave to prevent
back feeding of the cylinder. This material falls on to straw walkers for further separation.
In some variants, multiple cylinders are used in place of straw walkers for separation and
threshing of un threshed heads.
Rotary threshing uses a larger-diameter rotor surrounded by an open-mesh concave
 Crop material travels in a spiral path (may be guided by vanes in
the concave) several times around the rotor during processing. Most rotor designs areaxially-fed with the rotor axis parallel to main crop flow. Transitioning crop flow from the
feeder chain into the entry of the axial flow rotor is often aided by some means to redirect
the flow path into the rotating spiral (e.g., guiding vanes, rotor extensions, or a beater).
Variations are to use two rotors or to feed the single rotor tangentially with the rotor axis
perpendicular to the crop flow path at the rotor entry point. Centrifugal action during a
longer flow path is used to separate grain after threshing. The front section of the rotor is
used for threshing, whereas the middle and rear sections perform centrifugal separation.
On the cylinder surface or on the front threshing section of the rotor, a series of rasp
bars are mounted to strike and feed the crop material. In tougher, greener stem harvest
conditions, spiked tooth rasp bars (or specialty rotor sections) are commonly used—for
example, in rice—to move material through the threshing area between rotor/cylinder and
concave. Threshing occurs by impact of grain at high speed with metal surfaces and by
rubbing of grain against other grain and crop material. Grain damage is reduced when this
“grain-on-grain” or other crop material threshing occurs rather than grain being struck by
metal.
Grain quality is directly impacted by rotor or cylinder speed and concave clearance settings.
Appropriate peripheral thresher tip speed varies for different crops and field conditions.
Typical peripheral speeds are 50 feet per second for corn or soybeans and 100 feet
second for small grains such as wheat and oats. A general recommendation is to increase
cylinder or rotor speed to just below the point where grain quality is adversely affected.
Concave clearance should be narrowed to just the point where threshing is satisfactory
without adversely impacting grain damage. Although threshing increases with increased
rotor/cylinder speed and decreased concave clearance, grain damage greatly increases in
order to thresh the most resistant grain heads. Grain damage increases with the square of
rotor/cylinder speed. To quickly adjust speeds a variable speed drive (e.g., belt or hydrostatic
transmission) is used.
Rotary type threshing mechanisms have been widely adopted since the 1980s on corn,
soybean, and rice, where grain damage may be less affected across a somewhat wider
range of rotor speeds (Newberry et al., 1980; Paulsen and Nave, 1980). Lower centrifugal
force can be used with a larger-diameter rotor and longer concave. Cylinder type
threshers have been more frequently used over a wide range of crops and conditions that
may have difficulty in feeding at the rotor entry point or have excessive straw breakage
in rear sections of the rotor. The amount of separation generally increases with concave
length along the cylinder, but straw breakage increases, which results in a greater load on
the cleaning system. Cylinder width is limited by road travel requirements of the combine
chassis to about 5.5 feet. Feeding of non-uniform or “slugged” material can be impacted
by rotor/cylinder moment of inertia (i.e., size and configuration). Both types of threshing
mechanisms have advantages and limitations depending upon the harvest situation.
Threshing performance criteria include throughput, separation, grain damage, threshing
loss, and straw breakup.

1.8 Separation: Straw Walkers and Rotary Separation

Although much of the grain has been separated from other crop material in the threshing
zone, MOG leaving the threshing area still must be processed to remove further grain
in order to reach the performance criteria the customer expects (e.g., 1% or 3% total grain
losses). There are two separation processes commonly used: gravity-dependent straw
walkers or rotary separation.
Straw walkers  are sieve sections that oscillate up and down to literally shake
remaining grain from the mat of MOG. Each section may be about 10 to 14 inches wide
and 25 to 45 inches long, with a rake of teeth projecting above each side to help keep
larger straw above the sieve. MOG enters the straw walkers from the beater stripping the
threshing cylinder. MOG then passes over four to eight oscillating perforated sections over
a distance of up to 16 or 18 feet before exiting the rear of the combine. The number of
sections across the width or along the length of the straw walkers is limited by the chassis
size of the combine, which in turn is limited by road transport width and length.
Grain is separated from MOG in the straw walkers by gravity as the individual shakers
oscillate on crankshafts at about 200 rpm with a throw of 2 to 3 inches. Larger straw, stems,
and other material “walk” toward the rear exit of the combine, while heavier grain falls
through the sieves. This grain is routed to the cleaning shoe by augers or a stationary,
sloped grain pan underneath the straw walkers.
Rotary separation is commonly used in conjunction with rotary threshing and accomplished
in the mid- and rear-sections of the rotor or rotor pair, as MOG continues to spiral
between rotor and concave. Rotary action results in centrifugal separation as heavier grain
flies through the concave. Forces can be 50 g to 100 g or more, with orders of magnitude
higher than in straw walkers. Rotary separators often use helical transport vanes to guide
MOG in a spiral movement. Directed flow by the vanes helps to avoid plugging and if
vanes are adjustable, they may be used to increase or decrease the number of spirals or
amount of time MOG spends traveling around the rotor.
Rotary separators require more power than straw walkers as they grind away on the
straw but grain damage may be acceptable over a wider range of speeds, and separation
forces are greater. The greater propensity for straw breakage in rotary separators is usually
not a problem in corn, soybeans, or rice, but for this reason a rotary separator may not be
as versatile in some other small grain conditions with drier straw (e.g., wheat, oats, barley)
when excessive straw break-up can overload the cleaning shoe. Compared with straw
walkers, rotary separators have high separation capacity within a smaller machine chassis,
reduced moving parts and drives, lower vibration, and lower combine weight. The high
moment of inertia of a large rotor can help if crop flow becomes non-uniform with “slugs,”
but if a rotor becomes plugged with crop material it can be more tedious to unplug and
clean than straw walkers, unless a powered rotor reversing system is incorporated.

5.9 Cleaning Shoe

Grain from the threshing or separating areas still contains smaller pieces of broken straw,
chaff, weed seeds, and dirt. To further clean grain by separating it from these smaller
pieces, material is processed by the cleaning shoe. The cleaning shoe consists of a grain
pan or bed of clean grain augers, fan, two or three oscillating screens or sieves and a tailings return system. Grain is conveyed (often in a bed of augers) by the grain pan under the thresher into an air stream generated by the fan and on to the op sieve(chaffer).
Grain is separated from chaff and other materials by both pneumatic and mechanical
forces. Cleaning makes use of the greater density and terminal velocity of grain than chaffy
materials. Air flow from the fan should be greatest near the front of the chaffer screen and
reduce as it reaches the rear of the sieves. Air flow is directed by a wind board. Newer
cleaning shoes have split air streams so that an initial higher velocity air stream is channeled
in a pre-winnowing process to the front of the chaffer to help fluidize the mat of
grain entering the sieves.
Air flow is critical and should be increased as crop flow increases to fluidize the crop
mat, allowing grain to work its way downward through the mat to the sieve openings. Too
high air flow allows grain to be blown out through the rear of the shoe. Too low air speed
does not allow chaff to separate but keeps it embedded with grain in bulk flow of the
crop mat.
Heavier grain falls through the top chaffer sieve and lower sieve to a clean grain cross
auger at the bottom of the combine. Heavy particles that have not been blown out the rear
of the shoe but that fall through an extended sieve at the rear end of the chaffer drop into
the tailings return cross auger for re-threshing. Tailings material should be primarily
unthreshed grain with minimal whole grain present, otherwise threshed grain is subjected
to additional damage.
Proper setting adjustments for the cleaning shoe involve fan air flow and direction as
well as adjustments in sieve openings. Setting air flow is key and should normally be the
first adjustment. Air speed should be reduced from a relatively high level to the point where
grain is not blown out the rear of the shoe. Then the opening of the chaffer sieve should
be reduced until further closing would cause excessive grain in the tailings return. Finally,
the lower sieve opening should be set in the same manner as the chaffer sieve. Air velocity
at the fan may be 20 to 25 feet per second. Air flow is more effective for separation
with an increasing vertical angle, although machine envelopes limitations restrict this
angle. Air flow should be uniform across the width of the shoe. Sieve openings are
adjustable either manually from the rear or by automatic control. Sieve opening is measured
between the faces of adjacent vanes. Openings of both sieves should be related to
grain size, with the chaffer having a slightly larger opening.
Typical values for sieve oscillations have a frequency of 4 to 6Hz with an amplitude
of 0.75–1.5 inches. The fluidized crop mat should evenly diffuse grain and chaff. As the
mat is subjected to upward air flow and oscillating sieves, heavier grain moves to the sieve
openings in a convection-like process. A separation theory in the cleaning shoe by diffusion
and convection has been developed (Kutzbach and Quick, 1999).
When the combine is operated on slopes, the crop mat tends to gravitate to the lower
side and become non-uniform. Separating ability is reduced as thickness of the crop mat
affects air flow and the distance grain must fall to sieve openings. In thin mats, excess air
flow can blow grain out the rear of the shoe before it drops through the sieves. In thick
mats, air flow is reduced and the crop mat ceases to be fluid. Instead it becomes bulk flow
over the top chaffer sieve with little separation and a resulting overload on the tailing
return system. Combine leveling systems on hillside combines or self-leveling cleaning
shoes can be used on sloping ground to correct this problem.

1.10 Elevators: Clean Grain and Tailing

From the cleaning shoe area, clean grain is transported horizontally by auger to one side
of the combine chassis and then up to a clean grain storage tank  at the top
of the combine. Grain falling into the tailings return system at the rear of the cleaning shoe
is transported horizontally by auger to one side of the combine and then delivered back
to the front of the thresher for re-threshing.

1.11 Grain Bin and Unloading Auger

Ever increasing crop yields have resulted in larger clean grain tanks (i.e., mobile storage
bin) on combines. Grain tanks hold at least 150 bushels, but may hold over 400 bushels
 depending on which combine class the machine fits into. Panels (extensions
or hungry boards) attached to the top edges of the grain tank are often used to increase
grain tank capacity and the distance the combine may be driven before unloading. Some
extensions are designed to be folded down to prevent rain wetting the grain or when not
in use. A loaded grain tank adds considerable weight to the combine, almost all of which
is carried over the powered front axle. This impacts structural and drive requirements as
well as size of tires and wheels. Tires are overloaded and for that reason a combine should
never be operated in road gear speed with a full grain tank. Wide, floatation-type tires or
dual tires “straddling” rows or even rubber tracks are sometimes used to avoid excessive
soil compaction in wet conditions and field damage that could adversely affect subsequent
crops.
A high-capacity unloading auger  is required to quickly empty the grain
tank. If field conditions allow, unloading “on-the-go” into an accompanying truck or grain
cart traveling alongside, greatly enhances field efficiency. As combine threshing and separation
capacity has increased, wider gathering heads have been needed to keep the
combine fully loaded. To allow clearance for grain transport vehicles alongside combines,
the auger must reach somewhat beyond the edge of the head when extended for unloading.
Unloading auger lengths now commonly exceed 20 feet. For safety and road transport,
the auger must pivot to fold alongside the combine when not being used for
unloading.

1.12 Other Attachments

Several attachment options are commonly used in different crop situations. For wider
heads and heavier crop material (e.g., cornstalks) a stalk spreader  with rotating vanes or fingers is used to more evenly spread MOG across the soil surface. If straw will not be picked up or baled, but instead is to decompose on the surface, a straw chopper  with rotating knives at the rear of the combine shreds and sizes stems. A lodged crop with downed stems in the field is more difficult to get underneath with the grain platform cutterbar. In such cases, sloping extensions called crop lifters may be periodically mounted along the cutterbar to help lift stems. A pneumatic device known as an
air reel uses directed air near the front of the grain platform to blow small grain material
on to the platform. Wet field conditions, particularly common with rice harvest, reduces
the tractive ability of combine drive wheels. Specialized “rice” tires may improve traction
in wet, plastic soil conditions. To add to floatation and traction in muddier soil, tracks are
an option.

1.13 Operator’s Station, Adjustments

and Monitoring Systems

Nowaday, numerous control and monitoring systems are used to facilitate a safe efficient
grain harvest and maintain grain quality. Electronic systems control hydraulic or
mechanically actuated adjustments. A microprocessor within the system can be used to
both control settings and direct information to archival storage. In some cases, archived
information may be used to store successful machine settings so that they may be used
later in an operator or even machine learning process. Touch-screens used in some newer
combines can be customized to display a subset of 40 or more operating parameters so
that they can be conveniently monitored and adjusted.
Adjustments of head functions are often combined into a single operator joystick. Cutterbar
height may be controlled by mechanical or ultrasonic sensors below the cutterbar.
Automated or “hands-free” steering for wide grain platforms or to stay centered on corn
rows reduces operator fatigue, allows faster overall speed, and reduces overlapping. Grain
loss sensors at the rear of the cleaning shoe convert grain impact on sensor pads to electrical
signals showing relative grain loss. Audible or visual warnings may be set to accommodate
operation within a defined range for critical sensors.
Grain yield is commonly sensed near the top of the clean grain elevator by the force of
grain striking an impact plate. A speed sensor and head width sensor can be used to calculate

area harvested. Global positioning system (GPS) equipment can record field position
and also sense speed. Data storage can hold information on grain yield, moisture
content, and field position to create yield maps useful to the grower for crop management
decisions.

1.14 Field Performance

Desirable performance of grain harvesting equipment is usually evaluated in terms of
least machine losses, lower grain damage, and maximizing crop throughput. Unfortunately
these are conflicting goals. Optimal machine performance involves trading off acceptable
machine grain loss levels in the adjustment of threshing and separating equipment while
maintaining grain quality for customer specifications. For specific crop conditions there is
often a “sweet spot” of combine throughput, with enough crop material being processed
by the combine so that crop-on-crop threshing minimizes grain damage, but not so much
material that separation efficiency is sacrificed and crop is lost (Quick and Hanna, 2004).
Theoretical combine rate of work or field capacity (acres per hour) can be estimated by
harvested head width and combine travel speed but actual field capacity is often 60 to 70%
of this due to time spent unloading, turning on ends, operator delays, etc. A narrow time
window for optimal harvest puts a premium on high combine field capacity and machine
reliability. High combine field capacities with large combines may be limited not by the
combine but by the transport capacity of trucks and wagons available to remove grain
from the field. For corn, if the artificial drying capacity of the crop is harvested at a moisture
content much higher than needed for storage, this may limit harvesting rate.

1.15 Grain Damage

In the industrialized world, grain damage is most frequently assessed against government
market standards. There are specific end uses and end-use customers (e.g., food
processors) who have other requirements. Within bulk commodity market channels regulated
by government standards, the presence of both larger stems and unthreshed grain,
and smaller material at levels above standards, dock grain grade and quality. Grain protein
levels are another criterion for quality. Extremely small material that is not easily identified
(broken grain pieces, dirt, weed seed) is lumped into the category of foreign material.

Besides large residue and foreign material, for some grain varieties smaller pieces of
identifiable broken or misshapen grain comprise one or more other categories (e.g., split
soybean seeds).
Government commodity grain standards assess damage by segregating different sizes
of particles with sieves or laboratory cleaning machines. Damage to the seed coat or invisible
internal grain damage is more difficult to quickly assess, but is particularly important
to some customers (e.g., the seed industry and food-grade processors). Significant machine
grain damage and loss also occurs when extremely small particles of ground-up grain dust
are blown from the rear of the combine. Such loss is invisible to standard measuring techniques.
However, it may be approximated by comparing hand-harvested yield to machine
yield plus visible machine losses.

1.16 Combine Trends

Modern combines continue to increase in size and power. Class 9 combines are now
marketed with engines exceeding 500HP to meet harvest timeliness demands, custom contractor
requirements, and increasing farm sizes.