Abstract:
A kernel cracking assembly comprises two frames each supporting a respective one of two rollers between which kernels are crushed. A hydraulically operated actuator acts to move the frame relative to frame to set the separation of the rollers. A position sensor coupled to the actuator forms part of a closed-loop feedback circuit which serves to maintain a predetermined separation of the rollers.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     This Patent Application claims priority under 35 U.S.C. § 119 to GB0411825.3, filed on May 27, 2004 titled, “Kernel Cracking Assembly”, the full disclosure of which is hereby fully incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     This invention relates to agricultural vehicles and more specifically to forage harvesters which cut down and process maize or grass to be used for animal feed.  
       BACKGROUND OF THE INVENTION  
       [0003]     Forage harvesters are machines which handle the cutting down of crops in the field and subsequent processing of the relevant crop into a state suitable for animal consumption. This may involve picking up crops, such as grass or alfalfa, which have been pre-cut and allowed to dry off in the sun, or it may require the forage harvester to cut crops, such as maize, directly from the fields.  
         [0004]     The crop, whether cut maize or gathered grass, is fed into a rotating knife drum or cutter which chops the product to a suitable length. With grass crops, cutting alone is sufficient to produce the desired forage. When harvesting maize for silage purposes, the cutting alone does not yield enough grain due to the presence of kernels in the crop. The kernels need to be cracked in order to extract the grain as un-cracked kernels are difficult for animals to digest. As cutting alone is insufficient to crack all the kernels, it is supplemented by a further process which passes the cut crop through a kernel cracking assembly, also known as a crop processor. This consists of two close, adjacent rollers, typically having fluted or serrated surfaces, which rotate such that there is slippage between the adjacent surfaces. The gap between the rollers is tailored to the desired diameter of grain passing through and the speed, rotational energy of the rollers, relative movement and fluting of the surfaces ensures that any un-cracked kernels are cracked.  
         [0005]     The kernel cracking assembly performs best when the distance between the rollers is small and constant. The performance of the crop processor decreases when the separation of the rollers increases because fewer kernels are cracked. For optimal performance this distance needs to be monitored and adjustable by the operator of the machine.  
         [0006]     A crop processor known from U.S. Pat. No. 6,290,599 attempts to solve this problem by controlling the relative positions of the rollers by means of two adjustable stops in the form of plungers which are movably guided in hydraulic cylinders, each arranged at a respective axial end of rollers.  
         [0007]     These are problematic in that the rollers are actively moved at both ends by different plungers which, despite being hydraulically coupled, are prone to leak at different rates, causing their displacement to differ slightly from one another. This in turn leads to the rollers being non-parallel and thus less efficient at cracking kernels.  
         [0008]     There is therefore a need to carefully control the separation of the rollers and their alignment in order to maintain the efficiency of the kernel cracking assembly.  
       SUMMARY OF THE INVENTION  
       [0009]     With a view to mitigating the foregoing problem, the present invention provides a kernel cracking assembly comprising two frames each supporting a respective one of two rollers between which kernels are crushed; and a hydraulically operated actuator for moving the frames relative to one another to set the separation of the rollers; characterized by a position sensor coupled to the actuator and forming part of a closed-loop feedback circuit which serves to maintain a predetermined separation of the rollers.  
         [0010]     The present invention avoids the problem of leakage from hydraulic actuators and other components by virtue of its feedback system. This operates on the error generated from the difference between the desired position and the actual position and moves the actuator accordingly to minimize this. This way the increased leakage of a worn actuator does not affect the accurate placement of the rollers relative to one another.  
         [0011]     The actuator may be in the form of a wedge. As the wedge reciprocates, its tapered surface pushes against the frame to move it relative to the direction of reciprocation. This may be similarly achieved when the actuator is in the form of a cam, rotation of which serves to move the frames relative to one another. A further option is the use of a screw, or any device which yields a mechanical distance multiplier advantage.  
         [0012]     The separation of the rollers controlled in this way can be more accurately determined if the frames on which they are mounted are pivoted relative to one another.  
         [0013]     The actuator functions to separate the frames and hence the rollers by a predetermined amount. This may be achieved by having one suitably shaped actuator (wedge, cam etc.) disposed at one end of the frames. This arrangement can be improved by providing actuators at both ends of the rollers, which may be suitably connected so that the hydraulic action of one actuator is transmitted to the other actuator, so that the separation of the frames and rollers is controlled at both axial ends. The actuators may be hydraulically controlled, either separately or together.  
         [0014]     Some known kernel cracking assemblies do not have sufficient structural rigidity to maintain their parallel arrangement relative to one another. It is therefore preferable to use two frames that have sufficient rigidity to maintain the rollers, supported thereby, parallel at all times. With this in mind, the cracking assembly benefits from frames, the structural integrity of which is not dependent upon having the rollers mounted to them. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The invention will now be described further by way of example with reference to the accompanying drawings in which:  
         [0016]      FIG. 1  is a right side line drawing of a crop processor according to the present invention;  
         [0017]      FIG. 2  is a left side line drawing of the crop processor of  FIG. 1 ; and  
         [0018]      FIG. 3  is a schematic representation of a position feedback sensor. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]      FIG. 1  shows an end on view of a kernel cracking assembly (also known as a crop processor) as used in forage harvesters for cracking kernels of maize. The kernel cracking assembly is arranged downstream of the main cutter (not shown) of the forage harvester in the crop flow path, just prior to the blower which urges the crop up a discharge chute and into a suitable vessel normally driven alongside the forage harvest.  
         [0020]     In reference to  FIG. 1 , the assembly  10  consists of two frames  12  and  14  pivotable relative to one another about a pivot pin  16 . Each frame supports one of two rollers  18  and  20  along their axial end. An arrow on  FIGS. 1 and 2  indicates the path of the crop flow between the two rollers  18  and  20 . The rollers  18  and  20  rotate relative to one another at different speeds so that crop passing between them is sheared causing any remaining kernels unaffected by the main cutter to crack open releasing their nutrient.  
         [0021]     The separation of the rollers is related to the size of the kernels and maintaining this separation is important to the efficient operation of the kernel cracking assembly.  
         [0022]     In the embodiment shown in  FIGS. 1 and 2 , the separation of the frames  12  and  14 , and hence the rollers they support  18  and  20 , is determined by actuators, in this case wedges  22  and  24 . At respective axial ends of the rollers  18  and  20 , the wedges  22  and  24  are sandwiched between the frames  12  and  14 , the latter being urged towards one another by means of springs  38 . The wedges  22  and  24  are pivotally attached by means of cranks  30  and  32  to a transition shaft  34 . The crank  30  is further pivotally attached to hydraulic ram  36 , which serves to raise or lower both wedges  22  and  24  simultaneously by virtue of their connection through the cranks  30  and  32  and the transition shaft  34 .  
         [0023]     The wedges  22  and  24 , have tapering ramp surfaces  26  and  28 , respectively. As the ram  36  forces the wedges to translate relative to a plane containing the axes of the rollers  18  and  20 , the ramp surfaces  26  and  28  push against bearings  40  arranged on the frame  12 , forcing the frame  12  to separate against the action of the springs  38 . Thus, the vertical position of wedges  22  and  24 , governs the separation of the roller  18  with regard to roller  20 .  
         [0024]     In order to determine the position of the wedges or actuators, the wedge  24  is pivotally connected via a tie rod  42  to sensor arm  44 . As the wedge  24  translates, tie rod  42  causes sensor arm  44  to rotate relative to the frame  14 . This rotation is monitored by a rotational sensor  46  and is indicative of the separation of the rollers.  
         [0025]     The position of the hydraulic ram  36 , and hence the separation of the rollers  18  and  20 , is controlled by the feedback circuit shown in  FIG. 3 . The hydraulic fluid used to power the ram  36  is provided by hydraulic pump  58 , which is connected via control valve  54  to hydraulic cylinder  56 . This may be a dedicated pump, or as is more likely to be the case, a pressurized oil supply already employed in the vehicle for other purposes. A control unit  50 , having a control panel located for easy access by the vehicle operator, is connected to rotational sensor  46  and control valve  54 . The control valve  54  is biased into a central position in which no fluid can flow into or out of cylinder  56  of the hydraulic ram  36 . Thus, in the absence of any signal from the control unit  50 , the position of the ram  36 , and thus the separation of the rollers  18  and  20 , remains constant.  
         [0026]     The rotational sensor  46  delivers a signal to the control unit indicative of the position of the rollers. At any point the control unit  50  is preset with a desired separation input by the operator of the vehicle. The control unit  50  creates an error signal from the difference between the desired and measured separation of the rollers. The control unit then operates the control valve  54  to minimize this error.  
         [0027]     As with any closed loop feedback system, a dead band must be programmed into the control unit  50  in order to prevent the system from oscillating. The dead band dictates the margin of error permitted by the control unit.  
         [0028]     The dead band has little effect on the accurate placement of the rollers  18  and  20  due to the mechanical advantage provided by the shape of the actuator  24 , be it a screw, wedge or cam. Their use in this application ensures that a significant amount of movement is required by the hydraulic ram  36  in order to produce a relatively small movement in the rollers. The mechanical advantage also means that a relatively small ram  56  will suffice to overcome the force of the springs  38  urging the rollers together.  
         [0029]     If the position of the hydraulic ram  36  should change as a result of some leakage of hydraulic fluid past the piston of the ram  56 , the resulting movement of the rollers will be detected by the rotational sensor  46  and automatically be compensated for by the feedback circuit.  
         [0030]     Though the actuators  22 ,  24  limit the distance that the rollers can move toward one another, they do not inhibit separation of the rollers. Thus, if a stone should be present in the crop, the two frames will pivot to increase the distance between the rollers to allow the stone to pass without causing permanent damage to the kernel cracking assembly.