WO2020126211A1

WO2020126211A1 - Grain cleaning system and method of controlling such

Info

Publication number: WO2020126211A1
Application number: PCT/EP2019/080722
Authority: WO
Inventors: Dan Hermann; Morten Bilde
Original assignee: Agco International Gmbh
Priority date: 2018-12-20
Filing date: 2019-11-08
Publication date: 2020-06-25
Also published as: GB201820875D0

Abstract

A photoelectric sensing device is mounted proximate to a sieve of screening apparatus and is arranged to generate a light beam directed above and across the sieve. An ECU is configured to generate control signals for the control of one of a cleaning fan and upstream processing systems in dependence upon detection signals generated by the photoelectric sensing device.

Description

GRAIN CLEANING SYSTEM AND METHOD OF CONTROLLING SUCH

FIELD OF THE INVENTION

[0001] The invention relates to grain cleaning systems and particularly, but not exclusively, to grain cleaning systems provided in combine harvesters for the screening of clean grain from material other than grain in a harvested crop material stream. The invention also relates to a method of controlling a grain cleaning system.

BACKGROUND OF THE INVENTION

[0002] The process of harvesting grain from crop fields has not changed substantially for many decades. Farmers use combine harvesters to cut a standing crop, thresh the crop material, separate the grain from the stem and clean the grain whilst returning the crop material residue onto the field. Typically, combine harvesters include threshing apparatus, separating apparatus and a grain cleaning system.

[0003] Grain cleaning systems utilise screening apparatus which typically includes one or more sieves driven in an oscillating motion. A mixture of grain, chaff, unthreshed heads and straw is delivered to an uppermost sieve upon which the mixture is conveyed across the surface thereof. Hereinafter the chaff and straw will be referred to as‘MOG’, Material Other than Grain.

[0004] Generally speaking, clean grain finds its way down through the sieves to a collection trough. A fan is provided to generate a cleaning airstream through the cleaning apparatus. The cleaning airstream is directed through and/or over the sieves so as to lift and carry the MOG away from the surface of the sieves and eject it from the cleaning system. The sieves are generally set up to screen the unthreshed heads which are‘returned’ as tailings to a rethreshing system.

[0005] Today it is known to provide combines with control systems that automatically adjust settings of the various crop processing apparatus. Such “auto-setting” functionality relieves the operator of making manual adjustments to optimise the harvesting process, wherein the optimum settings continuously change as harvest conditions vary. However, for reliable auto-setting operation an accurate representation of the current conditions within the various processing apparatus is required.

[0006] One situation that has a detrimental impact on the cleaning effectiveness is when the sieve becomes overloaded and MOG and grain piles up on the surface thereof. This is commonly referred to as“collapse” of the shoe and prevents the grain from falling through the upper sieve. Collapse of the shoe is often caused by an insufficient speed of the cleaning airstream. Monitoring for collapse of the shoe is challenging because the resultant grain loss is often not indicated by the conventional grain loss sensors located behind the sieve.

SUMMARY OF THE INVENTION

[0007] According to a first aspect of the invention there is provided a grain cleaning system comprising screening apparatus, a fan arranged to generate a cleaning airstream through the screening apparatus, an electronic control unit (ECU), and a photoelectric sensing device in communication with the ECU, wherein the photoelectric sensing device is mounted proximate to the screening apparatus and is arranged to generate a light beam directed above and across the screening apparatus, wherein the ECU is configured to generate control signals for the control of one of the fan and upstream processing systems in dependence upon detection signals generated by the photoelectric sensing device.

[0008] According to a second aspect of the invention there is provided a method of controlling a grain cleaning system comprising generating and directing a light beam above and across screening apparatus, detecting the light beam and generating detection signals, generating control signals from the detection signals, and controlling one of a fan and an upstream processing system based upon the control signals.

[0009] In operation the light beam is broken by the presence of material, especially MOG. The light beam passes above and over the screening apparatus and, as such, any piling up of material thereon can be detected by appropriate processing of the detection signals. Control algorithms for the fan and any upstream processing system may use the detection signals as inputs so as to make appropriate adjustments or trigger operator alerts in the event of a shoe collapse. Even in the absence of a shoe collapse (i.e. under normal working conditions) the detection signals may be representative of a MOG load of the grain cleaning system, wherein the detection signals are used as control inputs for the fan or upstream processing systems.

[0010] The screening apparatus typically comprises a sieve mounted to a sieve frame that is coupled to an oscillating drive mechanism, wherein the fan is located at an upstream end of the sieve, and wherein the cleaning airstream is directed through and/or over the sieve. The sieve frame, often referred to as a‘shoe frame’, may be mounted on hangers from a machine main frame (a chassis in the case of a combine harvester) wherein the hangers permit an oscillating movement of the sieve frame with respect to the main frame. One or more sieves may be mounted to the sieve frame so that they oscillate as one unit. Furthermore, one or more pans (having a continuous surface) may be mounted to the sieve frame for the same reason.

[0011] The oscillating motion of the shoe frame is typically in a generally fore and aft direction with respect to a longitudinal material conveyance direction.

[0012] The photoelectric sensing device is preferably mounted to the sieve frame, wherein the light beam is directed in a transverse direction with respect to material conveyance direction. In other words, the light beam passes across the path of the conveyed material from one side to another. As such the light beam is momentarily broken as material is conveyed in the conveyance direction.

[0013] The sieve frame may comprise a pair of opposing side frame members disposed along outboard edges of the sieve. The photoelectric sensing device can then be mounted to the side frame members. In this case the photoelectric sensing device may comprise a light source mounted to a first one of the side frame members and a photodiode mounted to a second one of the side frame members so that the light beam passes across the width of the sieve from one side to the other.

[0014] In an alternative arrangement the photoelectric sensing device comprises a light source and a photodiode mounted to a first one of the side frame members and wherein a reflective surface is provided on the second one of the side frame members for reflecting the light beam. As such the light beam passes across the width of the sieve twice as it is reflected by the reflective An advantage of this arrangement is that the light source and photodiode can be mounted or encased in a single module thus reducing component count and reducing the number of electrical harnesses required. [0015] Crop dividers are often placed on the upper surface of the sieve to reduce effects of operating on sidehills. The crop dividers typically comprise a fin that is aligned longitudinally and extends upward from the sieve. In an embodiment in which the photoelectric sensing device is mounted at outboard edges of the sieve, any crop dividers located in the path of the light beam should include a hole through which the light beam passes.

[0016] In another embodiment one or more crop dividers serve as a mounting location for part or all of the photoelectric sensing device. For example, in one arrangement like this the screening apparatus comprises two crop dividers disposed on an upper surface of the sieve, wherein the crop dividers are aligned parallel to one another, and wherein the photoelectric sensing device comprises a light source mounted to a first one of the crop dividers and a photodiode mounted to a second one of the crop dividers. As such the light beam passes across a gap defined between two crop dividers. Alternatively the photoelectric sensing device comprises a light source and a photodiode mounted to a first one of the crop dividers and wherein a reflective surface is provided on the second one of the crop dividers for reflecting the light beam.

[0017] The photoelectric device preferably comprises a plurality of light sources spaced from one another and arranged in a vertical stack so as to generate a light curtain having a plurality of light beams. The multiple light beam arrangement provides more data on the state of material in the cleaning system. For example, a collapse event is more easily identified by the detection of multiple broken light beams, especially when those light beams are the lower ones.

[0018] The light sources are preferably LEDs or lasers that can be detected by photo-sensors spaced therefrom.

[0019] The grain cleaning system is preferably embodied in a combine harvester. However, it is envisaged that aspects of the invention may be embodied in alternative machines including stationary grain cleaning systems.

[0020] A combine harvester embodying an aspect of the invention preferably further comprises threshing apparatus and separating apparatus located upstream to the grain cleaning system with respect to a crop material flow.

[0021] Although control of the fan speed or sieve opening by control signals delivers significant advantages as described above, it is envisaged that the control signals may in addition, or instead, serve to control one of a concave adjustment and a rotor speed.

[0022] In another embodiment the combine harvester is provided with a display device that is in communication with the ECU. The display device may be configured to display a representation of the MOG load determined from the detection signals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further advantages of the invention will become apparent from reading the following description of specific embodiments with reference to the appended drawings in which:

Fig. 1 is a schematic side elevation of a combine harvester shown with the side panels removed to reveal the inside processing systems;

Fig. 2 is a top-down view of a grain cleaning system in accordance with a first embodiment for use in the combine harvester of Fig. 1 ;

Fig. 3 is a block diagram of the grain cleaning system of Fig. 2;

Fig. 4 is a perspective view of the rear end of the upper sieve embodied in the grain cleaning system of Fig. 2;

Fig. 5 is a top-down view of the grain cleaning system in accordance with a second embodiment for use in the combine harvester of Fig. 1 ;

Fig. 6 is a perspective view of the rear end of the upper sieve embodied in the grain cleaning system of Fig. 5; and,

Fig. 7 is a schematic side view of a photoelectric sensing device for use in embodiments of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0024] Aspects of the invention will now be described in connection with various preferred embodiments implemented on a combine harvester. Relative terms such as front, rear, forward, rearward, left, right, longitudinal and transverse will be made with reference to the longitudinal vehicle axis of the combine harvester travelling in the normal direction of travel. The terms“direction of conveyance”,“upstream” and “downstream” are made with reference to the general flow of crop material through the combine harvester, or to the cleaning airstream through the screening apparatus.

[0025] Although the embodiments described relate to a grain cleaning system in a combine harvester, it should be appreciated that aspects of the invention can be embodied in other grain cleaning systems such as stationary systems that may, for example, be located at a grain processing plant.

[0026] With reference to Figure 1 a combine harvester 10 includes a frame or chassis 12, front wheels 14 and rear steerable wheels 16. A cutting header 17 is detachably supported on the front of a feederhouse 18 which is pivotable about a transverse axis to lift and lower the header 17 in a conventional manner.

[0027] The combine 10 is driven in a forward direction F across a field of standing crop in a known manner. The header 17 serves to cut and gather the crop material before conveying such into feederhouse 18 and elevator 19 housed therein. At this stage the crop stream is unprocessed. It should be understood that combine harvesters are employed to harvest a host of different crops including cereal, rice, corn and grass seed. The following description will make reference to various parts of the cereal crop stream but it should be understood that this is by way of example only and does not by any means limit the applicability of the invention to harvester other harvesting crops.

[0028] The cut crop stream is conveyed rearwardly from the feederhouse 18 to a processor designated generally at 20. In the illustrated embodiment the processor 20 is of the axial rotary type having a pair of axial-flow threshing and separating rotors 22 which are each housed side-by-side inside a respective rotor housing 23 and are fed at their front end by a feed beater 25. It should be appreciated that the right-hand rotor is hidden from view in Fig. 1. The rotors serve to thresh the crop stream in a front‘threshing’ region, separate the grain therefrom in a rear‘separating’ region, and eject the straw residue through the rear of the machine 26 either directly onto the ground in a windrow or via a straw chopper.

[0029] Each rotor housing 23 is generally cylindrical and is made up of an opaque upper section and a foraminous lower section which includes a set of side-by-side arcuate concave grate segments 26 extending the length of the front threshing region and which allow the threshed material to fall by gravity onto a grain collection pan 28 located below for onward conveyance to a grain cleaning system which is designated generally at 30. Guide vanes (not shown) are secured to the inside of the rotor housing and serve, in conjunction with the crop engaging elements on the rotor 22, to convey the stream of crop material in a generally rearward spiral path from front to rear.

[0030] The rear separating region of rotors 22 comprises plural crop engaging elements to separate the residual grain from the stream of crop material. A grain return pan 32 is provided underneath the separating region to collect the separated grain and convey it forwardly for delivery onto the grain collection pan 28. Both the collection pan 28 and return pan 32 are driven so as to oscillate in a known manner.

[0031] Although described as a rotary axial type, the processor 20 may be of an alternative type such as known conventional, hybrid or transverse types without departing from the scope of the invention. For example, in the case of a conventional type processor, a transverse cylindrical beater may be provided as threshing apparatus and a set of straw-walkers provided as separating apparatus.

[0032] The grain cleaning system 30 comprises a fan 34 housed in a fan housing 35. The fan 34 may be of a known type such as a crossflow or centrifugal fan that rotates on a transverse axis and draws in air either tangentially or axially through air intake openings. A cleaning airstream generated by the fan 34 and exhausted from the fan housing 35 is represented in Fig. 1 by arrows‘X’.

[0033] The fan 34 is driven by a fan drive system (not shown) which may derive its power via a mechanical drive coupled to the processor 20. Alternatively, the fan 34 may be driven by a hydraulic or electric motor. In any case, the fan drive system is operable to drive the fan 34 with an adjustable speed determined by a fan speed controller 134 (Fig. 3) that is in communication with the fan drive system.

[0034] The grain cleaning system further comprises screening apparatus 36 which includes an upper sieve 38 (alternatively referenced‘chaffer’) and a lower sieve 39. The sieves 38,39 are driven with an oscillating motion in a known manner. For example, the sieves 38,39 may form part of a unitary‘shoe’ which is suspended on hangers (not shown) from the frame 12 and driven in an oscillating motion. [0035] The sieves 38,39 each may comprise a plurality of transverse louvres 85 (Fig. 4) which can be adjusted either manually or remotely to adjust the coarseness of the screen provided. A pair of vertical sidewalls 40,41 (Fig. 2) bound either side of the sieves 38,39. The sidewalls 40,41 form part of the frame 12.

[0036] Grain collection pan 28, upper sieve 38 and lower sieve 39 are mounted to a sieve frame 87 which comprises a pair of side frame members 88,89 located along outboard side edges of the pan and sieves 28,38,39. The sieve frame 87 is mounted on hangers (not shown) from the side walls 40,41 which permits the shoe to oscillate in a generally fore and aft direction.

[0037] The upper sieve 38 is provided with a pair of crop dividers 91 ,92 disposed on the upper surface thereof. The crop dividers 91 ,92 extend in a spaced longitudinal direction and each comprise an upstanding fin. During sidehill operation the crop dividers 91 ,92 prevent the conveyed material from moving sideways.

[0038] The threshed material comprising a mixture of grain and MOG is conveyed by the grain collection pan 28 in a rearward direction until it falls from a rear edge 28' and into the grain cleaning system 30. The cleaning airstream is directed through and over the sieves 38,39 in a known manner so as to lift the lighter material, primarily MOG, away from the surface of upper sieve 38 and in a rearward direction for ejection at a rear outlet 42.

[0039] In a known manner, the screening apparatus 36 is operable to allow the clean grain to pass through the sieves 38,39, wherein the clean grain is collected in a transverse clean grain trough 44 and conveyed onwards to an on-board grain tank (not shown). The louvres 85 of upper sieve 38 may be set to allow unthreshed heads to pass through a rear region of the upper sieve 38 into a tailings collection trough 46. Likewise, any material screened out by lower sieve 39 falls from the rear edge thereof into the tailings collection trough 46 from where the‘returns’ are fed back to the processor 20 or a dedicated rethreshing system (not shown).

[0040] With reference to Figure 3, an electronic control unit (hereinafter termed ‘ECU’) 101 is provided and is in communication (via a databus) with an operator console 105, a photoelectric sensor 160, a concave controller 126, a rotor speed controller 122, a sieve controller 136, and the fan speed controller 134. The ECU 101 comprise control circuitry 102 which may be embodied as custom made or commercially available processor, a central processing unit or an auxiliary processor among several processors, a semi-conductor based micro-processor (in the form of a micro-chip), a macro processor, one or more applications specific integrated circuits, a plurality of suitably configured digital logic gates, and/or other well-known electrical configurations comprising discrete elements both individually and in various combinations to coordinate the overall operation of the combine 10.

[0041] The ECU 101 further comprises memory 103. The memory 103 may include any one of a combination of volatile memory elements and non-volatile memory elements. The memory 103 may store a native operating system, one or more native applications, emulation systems, emulated applications for any of a variety of operating systems and/or emulated hardware platforms, emulated operating systems etc. The memory 103 may be separate from the controller 101 or may be omitted.

[0042] The operator console 105 comprises a display 106 which may be integrated as part of a terminal having user interface devices such as buttons, levers and switches. The console 105 is mounted proximate to a drivers work station in the cab 52.

[0043] The concave controller 126, rotor speed controller 122, sieve controller 136, and fan speed controller 134 each serve to control adjustments of respective working units of the combine 10 and may each comprise a local standalone processor and/or memory, or may be integrated into the central ECU 101. Control signals generated by the ECU 101 are communicated to the respective working unit controllers 126,122,136,134 which are then translated into an adjustment of the associated working unit including the concave 26, processing rotor 22, sieves 38,39 and fan 34.

[0044] In operation, the cleaning airstream velocity is ideally of a sufficient magnitude and direction to lift the MOG away from the upper sieve 38 whilst still allowing the grain-rich material to settle thereon. The speed of fan 34 significantly influences the cleaning airstream velocity. If the fan speed is insufficient to lift the MOG then material may accumulate on the upper sieve 38. This‘collapse’ of the shoe can occur rapidly as a positive feedback loop results from the initial blockage preventing the cleaning airstream from passing through the louvres 85. The required fan speed is proportional to, inter alia, the MOG load or throughput.

[0045] In accordance with the invention, and with reference to Figures 2 and 4, a photoelectric sensor 160 is mounted to the side frame members 88,89 close to a rear edge of the upper sieve 38, 5-10cm therefrom for example. The photoelectric sensor 160 comprises a light source portion 161 mounted to an inside face of the right-hand side frame member 88, and a sensing portion 161 mounted to the inside face of the left-hand side frame member 89.

[0046] The light source portion 161 comprises a vertical stack of twelve LEDs 164 which are spaced from one another in a line extending from just above the upper surface of the upper sieve 38 to just short of an upper edge of the right-hand side frame member 88. The sensing portion 162 includes a vertical stack of twelve photodiodes 166 which are spaced from one another in a line extending from just above the upper surface of the upper sieve 38 to just short of an upper edge of the left-hand side frame member 89.

[0047] Each LED 164 generates a beam of light 165 which is directed in a transverse direction, right-to-left, toward a corresponding one of the photodiodes 166. The crop dividers 91 ,92 (if present) are provided with holes 168 through which the light beams 165 pass.

[0048] It should be appreciated that the LEDs 164 may emit light in several directions but that at least a portion of the light emitted thereby is‘visible’ by the corresponding photodiode 166. It should also be understood that alternative forms of light sources may be employed such as compact lasers.

[0049] Both portions 161 ,162 of the photoelectric device are connected by an appropriate electrical harness for power. Furthermore, at least the photodiodes 166 are connected to the ECU 101.

[0050] During operation, material including grain and MOG passes through the channel defined between the side frame members 88,89 in a generally rearward direction. When passing between a light source 164 and associated photodiode 166 the light beam 165 is broken. The ECU 101 interprets detection signals from the respective photodiodes 166 to detect for material load and potential collapse events. In turn, the control algorithms for at least one of the concave controller 126, rotor speed controller 122, sieve controller 136, fan speed controller 134 and a ground speed controller (not shown) use the detection signals from the photodiodes as inputs for the generation of control signals.

[0051] In one working example, several of the light beams 165 may be broken for a period of time that exceeds a predetermined threshold, thus indicating a collapse event (i.e. piling up of MOG and grain on the upper sieve 38). The fan speed controller 134 may, in response, increase the speed of fan 34 and/or the sieve controller 136 may adjust the upper sieve 38 so as to open it further. Of course, this is merely one example of an adjustment that may be made in response to received detection signals from the photodiodes.

[0052] In a second embodiment illustrated in Figures 5 and 6, the photoelectric sensing device 260 is mounted to facing surfaces of two adjacent crop dividers 91 ,92. A light source portion 261 comprises a vertical stack of twelve LEDs 264 which are spaced from one another in a line extending from just above the upper surface of the upper sieve 38 to just short of an upper edge of a first crop divider 91. A sensing portion 262 includes a vertical stack of twelve photodiodes 266 which are spaced from one another in a line extending from just above the upper surface of the upper sieve 38 to just short of an upper edge of a second crop divider 92.

[0053] Each LED 264 generates a beam of light 265 which is directed in a transverse direction, right-to-left, toward a corresponding one of the photodiodes 266. The stack of light beams 265 provides a vertical sensing curtain that is transverse to the general crop material stream. MOG and grain passing through the curtain momentarily interrupts one or more of the light beams 265, wherein the interruptions are detected by the ECU 101.

[0054] The above-described embodiments employ photoelectric sensing devices 160,260 having separate portions for the light sources and the photodiodes wherein the portions are transversely spaced on the screening apparatus 36. However, in an alternative arrangement the light sources and photodiodes are encapsulated in a single sensing module 360 as shown in Figure 7. The sensing module 360 is mounted to one of the side frame members 88,89 and the crop dividers 91 ,92, wherein a reflective (mirror) surface is provided on an opposing face of one of the other side frame members 88,89 and crop dividers 91 ,92.

[0055] In operation light beams generated and transmitted by the light sources 364 are directed across the upper sieve 38 toward the reflective surface and‘bounced back’ toward a corresponding one of the photodiodes 366. As such, each light beam makes two passes across the‘gap’ between the sensing module and the reflective surface. Any interruption to the light beam, caused by the passage of grain or MOG, is detected by the ECU 101. [0056] The sensing module 360 may comprise a printed circuit board (PCB) 369 having the LEDs 364 and photodiodes 366 mounted thereon. A power supply 371 is mounted to the PCB 369 and allows for wireless communication between the sensing module 360 and the ECU 101. Also mounted on the PCB 371 is a micro-controller 372 and an LED driver 373.

[0057] The sensing module 360 may be itself encapsulated in the structure of a side frame member 88,89 or a crop divider 91 ,92.

[0058] As explained previously, detection signals generated by the sensing devices 160,260,360 are received by the ECU and interpreted to determine a state of material presence on the surface of the upper sieve 38. From the determined state control signals or algorithm inputs are generated to control or adjust the speed of the fan, the sieve opening, a forward ground speed of the combine 10, a concave setting, or a rotor speed.

[0059] From reading the present disclosure, other modification will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the field of grain cleaning systems, component parts, and automatic setting systems therefore, and which may be used instead of or in addition to features already described herein.

Claims

1. A grain cleaning system comprising screening apparatus, a fan arranged to generate a cleaning airstream through the screening apparatus, an electronic control unit (ECU), and a photoelectric sensing device in communication with the ECU, wherein the photoelectric sensing device is mounted proximate to the screening apparatus and is arranged to generate a light beam directed above and across the screening apparatus, wherein the ECU is configured to generate control signals for the control of one of the fan and upstream processing systems in dependence upon detection signals generated by the photoelectric sensing device.

2. A grain cleaning system according to Claim 1 , wherein the screening apparatus comprises a sieve mounted to a sieve frame that is coupled to an oscillating drive mechanism, wherein the fan is located at an upstream end of the sieve, and wherein the cleaning airstream is directed through and/or over the sieve.

3. A grain cleaning system according to Claim 2, wherein the photoelectric sensing device is mounted to the sieve frame and wherein the light beam is directed in a transverse direction with respect to a fore and aft oscillating motion of the sieve.

4. A grain cleaning system according to Claim 3, wherein the sieve frame comprises a pair of opposing side frame members disposed along outboard edges of the sieve, wherein the photoelectric sensing device is mounted to the side frame members.

5. A grain cleaning system according to Claim 4, wherein the photoelectric sensing device comprises a light source mounted to a first one of the side frame members and a photodiode mounted to a second one of the side frame members.

6. A grain cleaning system according to Claim 4, wherein the photoelectric sensing device comprises a light source and a photodiode mounted to a first one of the side frame members and wherein a reflective surface is provided on the second one of the side frame members for reflecting the light beam.

7. A grain cleaning system according to Claim 5 or 6, wherein the screening apparatus comprises a crop divider disposed on an upper surface of the sieve, wherein the crop divider comprises a fin that is aligned longitudinally and extends upward from the sieve, and wherein the fin comprises a hole through which the light beam passes.

8. A grain cleaning system according to Claim 2, wherein the screening apparatus comprises a crop divider disposed on an upper surface of the sieve, wherein the crop divider comprises a fin that is aligned longitudinally and extends upward from the sieve, and wherein the photoelectric sensing device is mounted to the crop divider and wherein the light beam is directed in a transverse direction with respect to a fore and aft oscillating motion of the sieve.

9. A grain cleaning system according to Claim 8, wherein the screening apparatus comprises two crop dividers disposed on an upper surface of the sieve, the crop dividers aligned parallel to one another, wherein the photoelectric sensing device comprises a light source mounted to a first one of the crop dividers and a photodiode mounted to a second one of the crop dividers.

10. A grain cleaning system according to Claim 8, wherein the screening apparatus comprises two crop dividers disposed on an upper surface of the sieve, the crop dividers aligned parallel to one another, wherein the photoelectric sensing device comprises a light source and a photodiode mounted to a first one of the crop dividers and wherein a reflective surface is provided on the second one of the crop dividers for reflecting the light beam.

11. A grain cleaning system according to any preceding claim, wherein the photoelectric device comprises a plurality of light sources spaced from one another and arranged in a vertical stack.

12. A combine harvester comprising a grain cleaning system according to any preceding claim.

13. A combine harvester according to Claim 12, and further comprising threshing apparatus and separating apparatus located upstream to the grain cleaning system with respect to a crop material flow.

14. A combine harvester according to Claim 13, wherein the control signals serve to control one of a concave adjustment, a rotor speed and a ground drive.

15. A combine harvester according to any one of Claims 12 to 14, further comprising a display device that is in communication with the ECU, wherein the display device is configured to display a representation of a MOG load determined from the detection signals.

16. A method of controlling a grain cleaning system comprising generating and directing a light beam above and across screening apparatus, detect the light beam and generate detection signals, generate control signals from the detection signals, and control one of a fan and an upstream processing system based upon the control signals.