Abstract:
A grinding arrangement for sharpening knives carried by a chopper drum includes a movement arrangement for moving a grinding stone along the chopper drum during a grinding process. A force measurement arrangement is provided which measures the force applied to the knife by the grinding stone, during the grinding process, and provides a signal representing this force for controlling a movement arrangement which moves the grinding stone as a function of the signal received from the force measurement arrangement. The manner of measuring the force is by way of a force measurement cell inserted in the power flux connection between the grinding stone and the chopper drum.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention concerns a grinding arrangement with a grinding stone for grinding at least one knife of a chopper arrangement, a movement arrangement for moving the grinding stone along the chopper arrangement, a measurement arrangement for the provision of a signal that contains information regarding the force applied by the grinding stone of the knife during the grinding process and a control arrangement that controls the movement arrangement as a function of the signal of the measurement arrangement.  
       BACKGROUND OF THE INVENTION  
       [0002]     During the operation of a forage harvester, the knives fastened to the chopper arrangement wear over time. It is possible that individual knives wear at different rates. While the knives around the circumference of the chopper arrangement as a ruled wear at approximately uniform rates, the wear along the width of the chopper arrangement may vary considerably. Thereby, the diameter of the enveloping circle described by the cutting edges of the knives can vary in the axial direction of the shaft of the chopper arrangement. A cylindrical or slightly concave shape is desired as a target shape in order to simplify the automatic repositioning of the shearbar or in order to make this possible depending upon the repositioning system. A parallel and precise in-feed of the shearbar towards the circumference of the chopper arrangement is indispensable for a effective chopper process.  
         [0003]     To avoid this problem, U.S. Pat. No. 6,503,135 proposes that the actual shape of the enveloping circle described by the knives of a chopper arrangement be detected before a grinding process and to thereupon move the grinding stone on the basis of the results of the measurement in such a way that a desired shape of the enveloping circle is attained. The shape of the enveloping circle is detected by means of a knock sensor or by a magnetic sensor associated with the grinding stone or with the shearbar. As an alternative, the force applied to the shearbar is measured.  
         [0004]     The disadvantage of a measurement of the spacing between the shearbar and the knives by means of magnetic sensors, knock sensors or force sensors is seen I the fact that an additional information about the immediate angle of rotation of the chopper arrangement is required in order to be able to associate the immediate measurement value of the spacing with the particular knife. Moreover, at high rotational speeds, the association with the proper knife may be problematic. In addition, an improper positioning of the shearbar that is not parallel to the shaft of the chopper arrangement may adversely affect the validity of the measurement. If the spacing at the grinding stone is detected inductively or by a knock sensor, there are problems with the association of the measurement values with an actual spacing, since the vibratory performance of the grinding stone and the noises generated by it are a function of its worn condition. Inductive measurement processes depend upon the condition of the knives and are therefore also problematic.  
         [0005]     The problem underlying the invention is seen in the need to make available a grinding arrangement that is improved relative to the state of the art, in which the problems cited above do not exist or do so only to a lesser degree.  
       SUMMARY OF THE INVENTION  
       [0006]     According to the present invention, there is provided an improved grinding arrangement for grinding knives of a chopper arrangement.  
         [0007]     An object of the invention is to provide a grinding stone arrangement which has its movement relative to cutting knives controlled by signals representing the force applied by the grinding stone to the knives.  
         [0008]     The invention proposes that a force measurement cell be attached to any desired location in the connecting line or power flux connection between the grinding stone and the chopper arrangement. The force measurement detects the load or the pressure exerted by the grinding stone on the knife or knives of the chopper arrangement during the grinding process. The value measured by the force measurement cell is all the greater when the enveloping curve of the knives is closer to the grinding stone and the smaller when the knives are separated from the grinding stone.  
         [0009]     In this way, the result is an absolute and exact measurement value that contains information about the actual shape of the knife. The chopper arrangement can be brought into an optimum shape tat makes possible the repositioning to a sufficiently small cutting gap. Thereby the energy required for the chopper operation can be reduced or at a constant energy level a higher throughput can be attained. Furthermore, the quality of the chopper operation or the length of cut is improved (that is, the uniformity and precision of the cut). The proportion of uncut components, such as husks or leaves, is sharply reduced or even eliminated.  
         [0010]     The movement arrangement for the grinding stone is controlled by the control arrangement in such a way that the grinding stone brings the cutting edge of the knife into a certain target shape which may be a predetermined shape or a shape that can be selected from several inputs or from any desired input shape. In order to attain the target shape of the cutting edge of the knife, the control arrangement can perform a comparison between the information made available by the measurement arrangement regarding the actual present shape of the cutting edge and the target shape and control the movement arrangement as a function of the result of the comparison. Thereby, the grinding stone is controlled by the movement arrangement that transports the grinding stone across the width of the chopper arrangement and provides an in-feed as a function of the signal of the measurement arrangement and brings about a movement of the grinding stone in such a way that any deviation in the shape of the cutting edges of the knives is automatically equalized.  
         [0011]     The chopper arrangement may include a chopper drum in open or closed form to which several knives are attached. The chopper drum is arranged on a shaft that is brought into rotation during the grinding and in its normal operation, as a rule, rotates in the opposite direction compared to the normal chopper operation. In the case of chopper drums of this type, the measurement arrangement detects information about the distance between the shaft and the cutting edges of the knives, that is, the radius of the enveloping circle described by the cutting edges. However, the invention can also be applied to chopper arrangements with web disk wheel choppers. There it is not the radius of the cutting edges of the knives that is detected, but their axial position.  
         [0012]     The force measurement cell can be attached between the grinding stone retainer of the grinding stone and a frame to which the grinding stone retainer is fastened and that also carries the chopper arrangement. As a rule, the grinding stone retainer can be traversed across the width of the chopper arrangement and is supported in bearings on a shaft. The force measurement cell may be arranged between the shaft and the frame or between the shaft and the grinding stone retainer.  
         [0013]     Alternatively, or in addition, there is the possibility of arranging the force measurement cell between the grinding stone and the grinding stone retainer.  
         [0014]     Furthermore, the control arrangement can make an error signal available in case the measured force that is applied to the grinding stone exceeds a threshold value. This error signal can be provided to the operator optically or acoustically and points to a knife projecting too far outward. Moreover, in this case the grinding process can be stopped automatically. Thereby, damage (breaking out) or unusual wear of the grinding stone can be avoided, since in the case of excessive force between the grinding stone and the drum countermeasures are taken.  
         [0015]     The present invention can be applied to a multitude of arrangements with knives that must be sharpened. It can be used in particular on self-propelled or towed harvesting machines with chopper drums or web disk wheel choppers. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     The drawings show two embodiments of the invention that shall be described in greater detail in the following.  
         [0017]      FIG. 1  is a schematic left side view of a harvesting machine with a chopper arrangement.  
         [0018]      FIG. 2  is a front view of a first embodiment of a grinding arrangement.  
         [0019]      FIG. 3  is a front view of a second embodiment of a grinding arrangement. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]     The harvesting machine  10  shown in  FIG. 1  in the form of a self-propelled forage harvester is supported on a frame  12  that is carried by front and rear wheels  14  and  16 . The harvesting machine  10  is controlled from an operator&#39;s cab  18  from which a harvested crop take-up arrangement  20  can be seen. Crop taken up from the ground by means of the take-up arrangement  20  can be seen. Crop taken up from the ground by means of the take-up arrangement  20 , for example, corn, grass or the like, is conducted to a chopper arrangement  22  in the form of a chopper drum, which chops it into small pieces and delivers it to a conveyor arrangement  24 . The crop leaves the harvesting machine  10  to an accompanying trailer over a discharge duct  25  mounted for being selectively rotated about an upright axis. A post-chopper reduction arrangement  28  extends (during the corn harvest) between the chopper arrangement  22  and the conveyor arrangement  24  through which the crop to be conveyed is conducted tangentially to the conveyor arrangement  24 .  
         [0021]      FIG. 2  shows a schematic view of a chopper arrangement  22  and a grinding arrangement  26  associated with it, as it is seen when looking at the harvesting machine  10  in  FIG. 1  from the front (relative to the direction of operation). The chopper arrangement  22  is provided with a number of knives  38  distributed over its width at its circumference which cut harvested crop taken up by the harvested crop take-up arrangement  20  in interaction with a rigid shearbar  46 . The chopper arrangement  22  includes a central shaft  32 , that can be driven in rotation by means of a belt pulley  36  at its end face and belts, not shown, by a motor of the harvesting machine  10 . The shaft  32  is supported by two rolling contact bearings  56  arranged on both sides of the chopper arrangement  22  on the frame  12  of the harvesting machine  10 .  
         [0022]     In order to be able to sharpen the knives  38  after a certain operating time, without having to disassemble the individual knives  38  or the entire chopper arrangement  22 , the grinding arrangement  26  is provided above the chopper arrangement  22  near the enveloping circle described by the knives  38 . The grinding arrangement  26  essentially includes a grinding stone  42 , a grinding stone retainer  40  associated with it and a support shaft  44  oriented parallel to the shaft  32 , on which the grinding retainer  40  is supported in bearings, free to slide.  
         [0023]     If the knives  38  are to be sharpened, the chopper arrangement  22  is brought into rotation, as a rule in the opposite direction of rotation and/or at a reduced rotational speed, compared to the normal chopper operation. The grinding stone retainer  40  with the grinding stone  42  attached to it is shifted across the entire width of the chopper arrangement  22  by means of a movement arrangement  48  from a rest or park position, not shown, in which it is arranged at the side alongside the chopper arrangement  22 . Thereby, the underside of the grinding stone  42  is in contact with the knives  38  and sharpens them. During the grinding process, the grinding stone  42  traverses several times across the width of the chopper arrangement  22 . The end points of this sliding movement are illustrated in  FIG. 2  by the grinding stone retainers with the part number call-out  40  at the left reversal point and  40 ′ at the right reversal point.  
         [0024]     Between the sliding traverse movements, an in-feed of the grinding stone  42  can be performed, that is a small movement of the grinding stone  42  towards the knives  38 . In the embodiment shown for this purpose, a mechanical element (ratchet wheel) is used that interacts with an element fixed to the frame when one or both of the reversal points of the grinding stone retainer  40  are reached. The rotation of the mechanical element is converted into a sliding movement by means of a screw thread, so that the grinding stone  42  is provided with an in-feed towards the chopper arrangement  22 . When the grinding stone  42  is shifted only over a limited sideways shift region, an in-feed movement can be avoided, since then the mechanical element does not come into contact with the stationary element. A grinding of this type without in-feed is appropriate for the honing at the end of the grinding process.  
         [0025]     The movement arrangement  48  of the grinding arrangement  26  is controlled by a control arrangement  52 , shown schematically in  FIG. 2  which controls the shifting of the grinding stone  42  by the movement arrangement  48  as well as the in-feed in the manner described above. The control arrangement  52  is supplied with information about the immediate position of the grinding stone  42 , this can be provided by a corresponding sensor  58 , which detects the immediate position of the movement arrangement  48 , or that the control arrangement  52  has been supplied with information into which position it has brought the grinding stone retainer  40 . For this purpose, for example, the number of impulses can be stored in memory that have been delivered to a stepper motor of the movement arrangement  48 . In addition, the control arrangement  52  can control the drive of the chopper arrangement  22 .  
         [0026]     It should be noted that the in-feed could also be performed by a separate motor, particularly an electric motor or a hydraulic motor, that would also have to be connected with the control arrangement  52 . In place of an in-feed by moving the grinding stone  42 , the entire grinding stone retainer  40  or the shaft  44  could be moved in the in-feed direction.  
         [0027]     The control arrangement  52  is connected with a memory  54  and with two force measurement cells  50 , that are used as a measurement arrangement. The force measurement cells  50  are arranged close to both ends of the shaft  44  between the shaft  44  and the frame  12  or an element connected to it. The force measurement cells  50  may be of any desired configuration, such as piezo-electric sensors or strain gages. They deliver a measurement value to the control arrangement  52 , that is proportional to the force applied to the knives  38  by the grinding stone  42  or the reverse. this force contains information regarding the enveloping curve described by the knives  38  on the immediate position of the grinding stone  42 . If the grinding stone retainer  40  is supported on two parallel shafts  44 , each of the shafts  44  can be associated with two force measurement cells  50  at the ends, or the two shafts  44  are connected to each other at both ends and supported in each case on the frame over a single force measurement cell  50 . The use of a single shaft  44  is also conceivable that has a non-circular cross section (for example, a rectangular cross section).  
         [0028]     A grinding process can take place as described in the aforementioned U.S. Pat. No. 6,503,135. After the beginning of the grinding process, the control arrangement  52  brings about a traverse across the width of the chopper arrangement  22  by the grinding stone  42  by means of the movement arrangement  48 , and then is again traversed back into the original position. Thereby, the grinding stone  42  can remain in the position into which it was brought during the preceding grinding process, or, if necessary, provided with an in-feed towards the chopper arrangement  22 . This process can be used to determine whether an in-feed of the grinding stone  42  is required. This is the case if no signal (or a relatively minor signal) is generated by the force measurement cell  50  in at least one location of the chopper arrangement  22 . In this case, there is an indentation, recess or the like in the knives  38 , that cannot be removed or equalized without an in-feed. This process can also be omitted, particularly if a control is performed subsequently to determine whether the grinding process was successful.  
         [0029]     During the traverse of the width of the chopper arrangement  22 , the force measurement cell  50  generates a signal that is a function of the spacing between the cutting edges of the knives  38  and the grinding stone  42 . The control arrangement  52  is supplied with information over an appropriate analog digital converter about the amplitude of this signal.  
         [0030]     At first, the grinding stone  42  is not in-fed any further and is brought to a first position at the chopper arrangement  22 , as a rule at the left or right outside. It remains in this position until the force measurement cell  50  generates an output signal that corresponds to a desired force between the grinding stone  42  and the cutting edges of the knives  38 , so that a sufficient sharpness is attained by the parts of the knives  38  that interact with the grinding stone  42 . After that, the grinding stone  42  is transported by the movement arrangement  48  through a distance corresponding to its width further to the left or the right and grinds the knives there. In this way, the entire width of the chopper arrangement  22  is processed successively. As a rule, the process described is repeated and/or performed multiple times at a reversed direction of movement. At the conclusion of the grinding process, a normal grinding and/or honing of the entire chopper arrangement  22  can be performed in a manner known in itself. Finally, the grinding stone  42  is brought into its park position.  
         [0031]     A grinding process alternative to that described above is performed in such a way that the grinding stone  42  continuously traverses the entire width of the chopper arrangement  22 , until a constant spacing between the shaft  32  and the cutting edges of the knives  38  is attained. The control arrangement  52  can recognize from the output signal of the force measurement cell  50 , whether a constant spacing between the shaft  32  and the cutting edges of the knives  38  has been reached, and that corresponding thereto the grinding process can be ended. In this move, and in-feed of the grinding stone  42  can be performed, if the force measurement cell  50  does not detect a contact between the grinding stone  42  and the knives  38  at one or more places of the chopper arrangement  22 .  
         [0032]     To control the success of the operation or since the grinding stone  42  wears down during the grinding, which can result in an unsatisfactory result of the grinding process, the control arrangement can traverse the grinding stone retainer  40  one more time before the honing or during a subsequent normal grinding process across the width of the chopper arrangement  22  and detect the space in between the shaft  32  and the cutting edges of the knives  38  by means of the force measurement cell  50 . If the shape of the cutting edges of the knives  38  is unsatisfactory here, a new grinding process is performed in the manner described above.  
         [0033]      FIG. 3  shows a second embodiment of a grinding arrangement  26  according to the invention. Components that correspond to those of the first embodiment are designated by the same part number call-outs. There is a difference regarding the force measurement cell  50  that is arranged between the grinding stone  42  and the grinding stone retainer  40  in the embodiment according to  FIG. 3 . Here the force measurement cell  50  also delivers information regarding the force applied by the grinding stone  42  to the knives  38 . The control arrangement  52  controls the movement arrangement  48  as a function of this information in the manner described above. The electrical connection between the force measurement cell  50  and the control arrangement  52  can be performed by a flexible cable or by a contact strip located on the shaft  44  connected with the control arrangement  52 , which is fixed to the frame and electrically insulated from the shaft  44 , with which a second contact strip on the grinding stone retainer  40  interacts, this is connected with the force measurement cell  50 . Alternatively, a radio frequency connection is provided between the force measurement cell  50  and the control arrangement  52 .  
         [0034]     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.