Abstract:
A method of operating a self-propelled harvesting machine includes continuously separating a crop-material flow into a useful-material flow and a remaining-material flow, in a separating step of the machine, capturing at least a portion of the useful-material flow from the separating step in a measurement channel, weighing the useful material contained in the measurement chamber and determining a density based on a weight that was measured, and optimizing operational patrameters of the separating step based on the weight that was determined.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
   The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2005 047 filed on Sep. 30, 2005. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a method for operating a self-propelled harvesting machine such as a combine harvester and a harvesting machine designed for operating according to this method. 
   A combine harvester typically includes a threshing step, in which a flow of harvested stalks is separated into straw, which is discarded, and into a flow that contains the threshed-out grain and contaminants such as stalk pieces, non-threshed-out ear pieces, husks, etc., and a cleaning step, in which the contaminants are removed using sieves and a blower, in order to obtain a useful-material flow composed nearly exclusively of threshed-out grain. 
   Contaminants that remain in this useful material make it difficult to process the grain further, which is why the yields that can be attained for inadequately cleaned grain can be much lower than the yields of well-cleaned grain. 
   Although it is technically easy to adjust the large number of changeable operating parameters of the threshing and cleaning step such that a highly pure useful-material flow is attained, when a set of operating parameters is optimized without compromise and solely with regard for purity-related results, high losses of useful material result. This means that, the more that contaminants in the harvested grain are suppressed, the more the amount of grain increases that is removed as residual material and is therefore not utilized, or is at least not utilized in the most economical manner. An optimal yield can therefore be attained only when a reasonable compromise is found between purity and grain loss. 
   It is difficult even for an experienced user to pre-select the various operating parameters that result in a useful compromise of this type, because they depend on the type of material harvested and on the environmental conditions under which the crop material has grown, e.g., ground conditions, the climate during the growing period, the moisture content of the harvested material, etc. It is therefore desirable to be able to dynamically adapt the operating parameters of a harvesting machine to the properties of the crop material. 
   A method is made known in DE 10147733A1, with which a harvesting machine such as a combine harvester is operated with different settings of operating parameters in succession; the combine harvester is acted upon with a quantity of crop material that remains the same, working results are obtained for the various parameter settings, and the parameter setting at which the best working result was obtained is ultimately selected. The cleanliness of the grain is a criterium for evaluating the working result. 
   The publication calls for the operator to carry out a subjective evaluation of the cleanliness by assigning it a rating from “adequate” to “very good”. In order to rate the cleanliness of the grain, the operator must be able to see the harvested material. This task can therefore not be carried out while the combine harvester is operating. The publication states that the cleanliness of the grain is linked to the density of the harvested grain, and that a grain density sensor can be located on a grain elevator, but it does not state how a grain density sensor of this type could be designed. It is difficult, in fact, to perform a reliable measurement of grain density of grain that moves constantly between the output of the cleaning step and the grain tank. Weighing flowing grain directly does not yield reproducible results; an indirect estimate of the density based, e.g., on optical detection, requires laborious calibration which would have to be carried out separately for every harvesting run, due to the above-mentioned environmental variables, which influence the optimum operating parameter values of the threshing and cleaning steps. 
   SUMMARY OF THE INVENTION 
   The object of the present invention is to create a method for operating a self-propelled harvesting machine that makes it possible to easily optimize the operating parameters of the harvesting machine during operation, so that useful material is obtained in a good yield and with good purity. 
   In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a method of operating a self-propelled harvesting machine, comprising the steps of continuously separating a crop-material flow into a useful-material flow and a remaining-material flow, in a separating step of the machine; capturing at least a portion of the useful-material flow from the separating step in a measurement channel; weighing the useful material contained in the measurement chamber and determining a density based on a weight that was measured; and optimizing operational parameters of the separating step based on the weight that was determined. 
   Given that at least a portion of the useful-material flow out of the separating step is delayed in a measurement chamber, the non-reproducible influences are eliminated, which typically make it difficult to perform a density measurement of a moving flow of material. 
   In an initial approach, the fill level and weight of the useful material in the measurement chamber are determined, and this information is used to calculate the density. This approach is suited, in particular, for use with a large measurement chamber, which requires large quantities of material to be filled. By determining the fill level, a determination can be made regarding the density of the useful material even before the measurement chamber is filled completely. 
   If the harvesting machine is a combine harvester, the measurement chamber can be the grain tank itself of the combine harvester. 
   According to a second approach, to determine the density, the weight of the measurement chamber that has been filled to a specified level is measured. The weight determined in this manner is always directly proportional to the density, which means it is also possible to compare densities determined with different operating parameters when the volume of the specified level is not known exactly. 
   According to a preferred refinement of this second approach, at least a portion of the useful-material flow is fed continually to the measurement chamber, and a flow conveyed out of the measurement chamber is regulated in order to hold the filling of the measurement chamber to a specified level. A method of this type is practicable in particular with a combine harvester that continually transfers harvested grain to an accompanying vehicle and has only a small intermediate tank, which can be used as a measurement chamber. 
   According to a particularly simple embodiment, the specified level is the complete filling of the measurement chamber, and useful material fed to the measurement chamber after it is completely filled is directed away via an overflow. 
   To ensure that a measured density value is obtained that reflects the quality of the useful material this is being obtained currently, it must be ensured that the useful material in the measurement chamber is replaced continually. This is easily attainable when useful material flows continually out of the measurement chamber and is continually replaced by the incoming useful-material flow. In addition, the incoming useful-material flow should be stronger than the continually outflowing flow. This ensures that the measurement chamber is always full during non-stop operation, while excess useful material fed to the measurement chamber leaves via the overflow. 
   To obtain good purity of the useful material, the optimization of the operating parameters of the separating step preferably includes changing at least one operating parameter of the separating step in a direction that results in an increase in the density of the useful material that was separated out. 
   A change of this type is preferably carried out only when the density of the useful material obtained is below a reference density by more than a specified amount. When the density of the useful material is below the reference density by less than the specified amount, it can be assumed that a good purity of the useful material has been attained, and making any further changes to operating parameters with the goal of increasing density further would result in a disproportionately high increase in the losses of useful material. 
   It is therefore advantageous when the optimization also includes changing at least one operating parameter of the separating step in a direction toward reducing the remaining portion of useful material in the remaining-material flow. More specifically, in the case in which the harvesting machine is a combine harvester, this results in a reduction of grain losses, particularly when the density of the useful material deviates from the reference density by less than a specified amount. 
   A high degree of flexibility is attained when a direction of the change of the operating parameter that results in an increase in the density of the useful-material flow or a reduction in the remaining portion is determined via experimentation. 
   When the change of a first selected parameter of the separating step does not result in an expected increase in the density of the useful-material flow or a reduction in the remaining portion, a second parameter is advantageously selected and changed. By iterating the steps of determining density and changing the parameters, an optimal—or at least nearly optimal—parameter setting can be found over time. 
   The reference density used in a given iteration can be derived from a density measured in a previous iteration. As a result, the method becomes largely independent of fluctuations in the density of the useful material, which can occur from one harvesting run to another due to different crop qualities, moisture contents, etc. 
   As an alternative, the reference densities can be measured in advance with a specified fine setting of the separating step, i.e., at a setting that is known to deliver a highly pure useful-material flow, but also high losses of useful material. 
   Values of operating parameters set at the beginning of every harvesting run are preferably specified depending on the type of crop to be harvested. 
   The subject of the present invention is also a harvesting machine, with which a method of the type described above can be carried out. 
   The novel features of the which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows an agricultural working machine in the form of a schematic side view of a combine harvester; 
       FIG. 2  shows a schematic sectional view through a grain-density measuring device according to a first embodiment of the present invention; 
       FIG. 3  shows a schematic, perspective view of a grain-density measuring device according to a second embodiment of the present invention; 
       FIG. 4  shows a flow chart of a working procedure carried out by a control of the combine harvester; and 
       FIG. 5  shows a flow chart of a modified working procedure. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A schematicized side view of a combine harvester  1  is shown in  FIG. 1 . The object of a combine harvester  1  is to pick up the crop material growing on stalks from a field  32  and separate it from the straw and other admixtures. A grain cutting device  2 , which is used to pick up the crop material, is shown in  FIG. 1  as an example. It cuts the crop stalks with the crop material in the ears out of field  32  and combines them across the width of feeder  3 . Located in feeder  3  are rotating feed chains  4  with transverse segments that feed the crop material to downstream threshing units  5 ,  6 . The crop material is removed by preacceleration cylinder  5  at the end of feed rake  3  and is accelerated around the circumference of preacceleration cylinder  5  between preacceleration cylinder  5  and concave  8 . 
   The accelerated crop material is then transferred to cylinder  6 . The crop material is separated from the ears and straw via the striking and rubbing effect of preacceleration cylinder  5  and cylinder  6 , and via the centrifugal force acting on the crop material. The crop material then travels through concave  8 , which allows the crop material to pass, and reaches grain pan  27 . The straw output by cylinder  6  is redirected by impeller  7  to several shakers  9  located next to each other across the working width. The oscillating motion of shakers  9  and their stepped design cause the straw to be conveyed to the back end of the combine harvester, and they cause the crop material remaining in the straw to be removed. This remaining quantity is also transferred via return pan  28  and an oscillation motion thereof to grain pan  27 . 
   The crop material with the remaining admixtures, e.g., straw pieces, chaff and ear pieces, located on grain pan  27  is separated via an oscillating motion of grain pan  27  and its stepped design, and is conveyed to downstream cleaning units  10 ,  11 ,  24 . The transfer takes place via a straw walker step  34  ventilated by cleaning fan  24  to upper sieve  10 . Upper sieve  10  and lower sieve  11  located below it are usually chaffers with separately-adjustable opening widths; upper sieve  10  in the rear region can be adjusted with a opening width that differs from the remaining opening widths of upper sieve  10 . A flow of air created by cleaning fan  24  passes through upper sieve  10  and lower sieve  11 . The oscillating motion of sieves  10 ,  11  and the air flow cause the crop material and its admixtures to be directed toward the back end of the harvesting machine. 
   By way of straw walker step  34 , large and lightweight admixtures are captured by the air flow before they reach upper sieve  10  and are ejected out of combine harvester  1 . Smaller and heavier crop components travel from grain pan  27  via straw walker step  34  to upper sieve  10 . Depending on the setting of the upper sieve width, the individual crop grains and further components of the crop material fall through it, thereby reaching lower sieve  11 . Straw and non-threshed-out ears are moved past the front sieve area and, in the rear region of upper sieve  10 , fall through upper sieve  10  directly into the “tailings”. Lower sieve  11  typically has a finer plate structure than upper sieve  10 , and is normally set with a smaller opening width than upper sieve  10 . Larger and lighterweight crop components, such as crop grains with husks, ear parts or stalk parts—provided they have traveled through upper sieve  10  and reached lower sieve  11 —are transferred via the oscillating motion and air flow into the tailings. The cleaned crop material itself falls directly through lower sieve  11  and is conveyed to grain tank  33  using a feed auger and grain elevator  13 . The crop material that reaches the tailings is returned via a feed auger and tailings elevator  12  above preacceleration cylinder  5  to the threshing process. 
   Combine harvester  1  is equipped with a driver&#39;s cab  35 , in which a control and monitoring device  29  and an operating and display device  30  are located. In addition, devices for specifying the driving direction and ground speed of combine harvester  1  are provided, although they are not shown and they are known to one skilled in the art. Control and monitoring device  29  and display and operating device  30  are connected with individual sensors and actuators located on combine harvester  1  at various points. They allow the operator of combine harvester  1  to adjust and monitor the operation of combine harvester  1 . In  FIG. 1 , arrows point to the individual points in combine harvester  1  where a sensor is located for determining process and adjustment parameters. The particular actuators for adjusting combine harvester  1  are adequately known to one skilled in the art; the particular element will therefore not be depicted in  FIG. 1 . A cutting-height measuring device  22  is assigned to header  2 . This device  22  serves to determine the actual distance between header  2  and field surface  32 . The sensed value can be displayed to the operator using monitoring device  29  or display device  30 , and can also be used as the actual value for the automatic regulation of cutting height. A crop-quantity measuring device  20  is installed in feed rake  3  to detect harvested quantity M. It determines the deflection of a feed chain  4 , which depends on harvested quantity M. A further sensor system is located on concave  8 . This concave-width measuring device  21  is provided singly or in plurality, and determines the distance between preacceleration cylinder  5  and concave  8  and/or cylinder  5  and concave  8  at one or more points. Preacceleration cylinder  5 , cylinder  6  and impeller  7  are usually driven by a common drive, it being possible to vary the speeds of cylinders  5 ,  6 ,  7  using a servo drive. A cylinder-speed measuring device  31  for detecting at least one of the cylinder speeds is assigned to these cylinders  5 ,  6 ,  7 . To produce different air flows through the cleaning device, the drive of cleaning fan  24  has a variable-speed design. The actual speed of cleaning fan  24  is detected using a cleaning-fan measuring device  25 . Additional sensors can be assigned to the cleaning device. In this manner, the particular sieve opening width can also be detected using an upper-sieve width measuring device  18  and a lower-sieve width measuring device  26 . These measuring devices  18 ,  26  can be part of the particular not-shown adjustment device, or they can be separate therefrom, and they can be located on sieve  10 ,  11 . An upper-sieve loss measuring device  17  is located on the back end of upper sieve  10 . This device is used to detect the portion of crop grains that leave combine harvester  1  via the cleaning device and that are considered losses. Sensors of this type are known to one skilled in the art and extend over part or all of the working width of the cleaning device. They are normally designed as a baffle plate or tube and evaluate the oscillations that are produced by the impact of crop grains on the plate or tube. This sensor technology can also be used and located at any other point in a combine harvester  1 . This sensor technology allows flows of crop grains to be detected and makes it possible to obtain a determination—that is comparative and relative, at the least—of the quantities of grain present at a particular site. This sensor technology is also used in shakers  9  to detect the separation. 
   To obtain a determination of the amount of crop grains remaining in the straw, a shaker-loss sensor  19  is attached at least to the back end of a shaker  9 . This sensor  19  detects the portion of crop grains separated at the end of shaker  9 . To also evaluate the quantity of crop grains in the tailings, a baffle plate sensor system of this type can also be located at the end of lower sieve  11  or at the point at which the tailings are returned to the threshing process. 
   To evaluate the crop components located in the tailings, a tailings measuring device  16  is located on the upper end of tailing elevator  12 . It is used to determine the tailings volume, the portion of grain, and the portion of damaged grain. Optical light barriers, optical sensors or transillumination sensors (NIR sensors) are known for use for this purpose. Grain elevator  13  is equipped with a yield measuring system  14 . 
   Devices for measuring grain density can be located at different points on the combine harvester, e.g., at the points indicated by dotted circles  36 ,  37  in  FIG. 1 . 
     FIG. 2  shows a schematic cross section through a grain density measuring device, which can be located, e.g., at the point indicated by circle  36 . An opening  40  is formed in a slanted plate  39  located beneath lower sieve  11 , on which grain that has passed through lower sieve  11  slides to grain elevator  13 . A bucket  41  is located beneath opening  40 . Bucket  41  is held on a frame using force sensors  42 , which deliver a measured signal representative of the weight of the contents of bucket  41  to a control and monitoring device  29 . An outlet opening  43  is formed at the lowest point in the base of bucket  41 , and under this is located a slide  44  that leads to grain elevator  13 . 
   During operation, grain that slides on plate  39  fills bucket  41  to the rim. Grain that cannot fit into bucket  41  slides past it. Outlet opening  43  is dimensioned such that the quantity of grain flowing through it is less than that which flows past opening  40 , thereby ensuring that bucket  41  is always full, but also ensuring that the contents of bucket  41  are continually replaced, so that the grain contained therein is representative of the quality of the grain currently being harvested. The grain practically comes to rest in bucket  41 , so that it can settle, and the measured weight of bucket  41  truly allows the grain density to be reliably determined. The dwell time of the grain in bucket  41  is determined by the ratio between its volume and the cross-section of outlet opening  43 ; the dwell time can be, e.g., a few minutes. 
   A second configuration of a grain-density measuring device is shown in  FIG. 3  in a perspective view; this configuration can be installed at points in the combine harvester where the grain falls freely, e.g., at the outlet of grain elevator  13 . A bucket  46  and a cover  47  are mounted on a carrier wall  45  that is exposed to the flow of the falling grain. Bucket  46  and cover  47  are equipped with force sensors. The force sensors installed on bucket  46  detect the weight of bucket  46 , and the force exerted by its contents and by grain falling onto it from above. The sensor on cover  47  detects its mass and the force of grain falling onto it. The cross-sectional surface of bucket  46  and cover  47  are the same, and the contour of cover  47  resembles a heaped cone that is formed by the grain in bucket  46  during operation. 
   As long as the density of the grain “rain” to which bucket  46  and cover  47  are exposed is the same, they both therefore detect the same force of falling grain, regardless of fluctuations in the density of the grain flow, shaking of the combine harvester, or the like. Similar to bucket  41  in  FIG. 2 , bucket  46  also includes an outlet opening  43 , through which the grain can flow continually, so that the contents of bucket  46  are continually replaced. By determining the difference between the forces detected by bucket  46  and cover  47 , control and monitoring device  29  evaluates the weight of grain in bucket  46  and, since the volume of the bucket contents can be assumed to be constant, it also evaluates its density. 
   According to a third, not-shown configuration, grain tank  33  itself is designed as a measurement chamber for determining the grain density by the fact that it is equipped with sensors for determining the weight of grain contained in the tank and the fill level of the tank. When the weight and fill level are known, control and monitoring device  29  is able to calculate the density of the grain in the tank. 
   According to a fourth configuration, the feed rate of a (not shown) elevator used to transfer grain from tank  33  using an arm  48  into an accompanying vehicle can be regulated as a function of the detected fill level of tank  33 , in order to keep its fill level at a constant value. When the fill level of tank  33  is held constant in this manner during operation, the measured mass of the grain in tank  33  is a direct measure of its density. 
     FIG. 4  shows a flow chart of an operating procedure carried out by control and monitoring device  29 . 
   Control and monitoring device  29  is designed to control the various above-mentioned operating parameters of the combine harvester that influence the grain purity and grain losses, e.g., the rotational speeds of cylinders  5 ,  6 ,  7  of the threshing mechanism, the gap width of concave  8 , the width of upper sieve  10  and lower sieve  11 , the speed of cleaning fan  24 , etc. In a method step  51  at the beginning of a harvesting procedure, control and monitoring device  29  adjust the threshing mechanism and/or the cleaning step of the combine harvester to a “fine” setting in order to obtain grain that is, with certainty, free of contaminants. In the case of the threshing mechanism, for example, a fine setting of this type means the rotational speeds of cylinder  6  are high and the gap width of concave  8  is small. 
   A setting of this type delivers—at the outlet of the threshing mechanism—a material flow to be cleaned in which the grain is largely separated from husks and ear pieces adhering thereto, but which also contains an undesired, high portion of damaged grain. In the case of the cleaning step, the fine setting is characterized by a high speed of blower  24  and a small gap width of sieve  10 ,  11 , and results in separation of components such as grain with husks, ear pieces and stalk sections that one wants to separate out anyway, but also in the separation of a large quantity of good grain, which reaches the tailings or is ejected. Higher grain losses resulting from the fine setting are tolerated temporarily. It is not necessary to retain this setting for a long period of time or to hold the crop-material flow fed to the threshing mechanism constant for a longer period of time; it suffices to obtain a quantity of grain that suffices to perform a density measurement in step  52 . The density value obtained in this manner serves as a reference value D ref  for use in subsequent operation. 
   Subsequently, an economical setting of the operating parameters of the combine harvester is implemented, i.e., parameter values are set that have been proven via experience to be suitable for the material to be harvested, and can be saved, e.g., as default settings in control and monitoring device  29  matched to the type of crop. 
   A measurement  54  of grain density D akt  resulting from this economical setting is carried out. 
   Next, in step  55 , a check is carried out to determine whether the difference D ref −D akt  between the two density values is above or below a specified tolerance threshold  8 . When the difference is above it, an operating parameter is selected in step  56  that should be changed in order to obtain a higher density of the harvested grain. The selected operating parameter can be an operating parameter of the cleaning step or the threshing mechanism, because the setting of the threshing mechanism also influences the grain density via the quality of the threshing: “Soft” threshing delivers a high portion of grain with husks or ear pieces still attached which, if this material is not separated out, reduces the density of the harvested grain; “hard” threshing delivers a large quantity of small non-grain fragments, which also have a lesser density than the grain. 
   The extent of the change of the parameter selected in step  57  can be predetermined and fixed; it is also possible to select the change to be proportional to difference D ref −D akt , in order to quickly obtain a favorable value of the parameter. Another density measurement  58  is carried out, and results in density value D neu . In step  59 , it is evaluated whether D neu &gt;D akt , that is, whether the parameter change has resulted in an increase in density. If it has not, the parameter change is discarded in step  60 , and the direction of the parameter change is changed and the method returns to step  57 , or, if this was already attempted and did not result in an improvement, the method returns to step  56 , so that a new parameter can be selected. If it is determined in step  59 , however, that the density increased, stored value D akt  is replaced with D neu , and the method returns to step  55 . 
   The individual parameters are therefore optimized in order, until difference D ref −D akt  falls below ε. If this is detected in step  55 , it is assumed that an adequately good approximation of reference value D ref  of the density has been attained, so that the harvested grain is adequately clean. Now, the grain losses can be optimized. To do this, a parameter to be changed is also selected, in step  61 , from among the operating parameters of the combine harvester. Before this parameter is changed in step  63 , current grain loss rate V akt  is determined. 
   The extent of the parameter change in step  63  can be predetermined and fixed for the individual operating parameters. If difference D ref −D akt  is greater than a limiting value specified for each parameter, however, it is advantageous to specify the extent of the parameter change as a proportion of the difference, so that a small difference value can be attained in a few change steps. 
   After the change is carried out, the new grain loss rate V neu  is determined (step  64 ), and the two loss rates are compared in step  65 . A worsening of the loss rate results in the change being discarded (step  66 ), followed by the same parameter being changed in the opposite direction in step  63  or, if this has not already been successful, a new parameter to be changed is selected in step  61 . If an improvement in the loss rate is attained in step  65 , however, the method returns to step  54 , in order to measure the current density and determine whether it is still located at the permitted distance s from reference value D ref . 
   The method described forms an endless loop that results in the density of the grain fluctuating continually only slightly around D ref −ε during non-stop operation. As an alternative, a comparison of difference D ref −D akt  with two tolerance thresholds ε1, ε2, with ε1&lt;ε2, could be provided in step  55 ; the method would branch off to step  56  only if D ref −D akt &gt;ε2, and to step  61  only if D ref −D akt &lt;ε1. Otherwise, it would be assumed that the optimal setting has been found. 
   A modification of the working method is explained with reference to  FIG. 5 . In this case, first step  71  is to set a set of operating parameters known to be suitable for the crop to be processed, corresponding to step  53  in  FIG. 4 . 
   Resultant density D ref  of the crop material is measured in  72 ; it is not necessarily optimal, but will not be too far from the optimium, so it can be assumed that it is possible to find the optimum by systematically varying the operating parameters in close proximity to the values that were set. An operating parameter to be varied is then selected ( 73 ) and changed ( 74 ). Resultant density D neu  is measured in  75  and compared with D ref  in  76 . If difference D neu −D −ref  is greater than positive number ε, the change is retained, and D ref  is overwritten with D neu  in step  77 , and the method returns to step  74 . If the difference is negative, the change was carried out in the wrong direction; if it is positive or less than ε, it is considered to be not worthwhile and is discarded ( 78 ). Next, a decision is reached in  79  as to whether the parameter can be retained and the direction of its change can be changed, in which case the method returns to step  74 . If the decision is whether a parameter has still not been varied, the method returns to step  73 . 
   If neither of these cases applies, it can be provided that the method ends, or the method illustrated in  FIG. 4  can be carried out from step  61  onward. 
   The method illustrated in  FIG. 5  is based on the idea that a strict optimization of the density must result in a fine setting of the operating parameters with high grain losses. If, starting with a setting known to be useful, one attempts to optimize the density only to the extent that the density increases attainable using further optimization steps become small, an excessively fine setting is not attained, although it can be simultaneously assumed that the grain losses will be small, which cannot be assumed with an optimization based on a randomly selected initial setting. Steps  71  through  79  are therefore sufficient for attaining a good setting. It is possible, however, to optimize the grain losses separately using steps  61  ff. 
   It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods and constructions differing from the type described above. 
   While the invention has been illustrated and described as embodied in a self-propelled harvesting machine and operating method thereof, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
   Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, be applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 
   What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.