Abstract:
A forage harvester includes a cutting drum equipped with a plurality of cutting knives. A grinding arrangement is provided for sharpening the knives. Different embodiments of a wear sensing device are provided which include sensing circuit elements that are either embedded in the sharpening stone or carried by the backing plate of the sharpening stone assembly. In either case, the sensing circuit elements are located so as to make or break a circuit when a predetermined amount of the sharpening stone has worn away.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a grinding arrangement with a grinding stone for the grinding of a knife. 
     On harvesting machines and harvest preparation machines such as, for example, a forage harvester, knives are employed for chopping of plant material and other materials. These knives become dull when so employed and must be ground. In the state of the art, various manual and automatic grinding mechanisms are known. 
     In the known grinding mechanisms, grinding stones of the most diverse shapes and materials are employed. As a rule, the grinding stone is fastened to a grinding stone retainer and is moved over the width of the knives during the grinding process and successively fed towards the knives. In addition to the knives that are being sharpened, the grinding stone also wears during the grinding process. It is therefore possible for the grinding stone retainer to come into contact with the knives that are to be sharpened when the grinding stone is completely worn and thereby damages the knives. 
     The problem underlying the invention is seen in the aforementioned disadvantages in the state of the art. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a novel way of preventing damage to the cutting knives of a forage harvester coming into contact with a grinding stone retainer, during the sharpening process, after the grinding stone is worn away. 
     A broad object of the invention is to preventing possible damage to the knives by the grinding arrangement by constructing a grinding stone such that its worn condition can be easily detected so that a worn stone can be replaced promptly by a new one. 
     A more specific object of the invention is to provide a knife grinding stone and detection arrangement constructed for use with each other so that an electrical signal is transmitted when the wear limit of the grinding stone is reached, the signal being used for the control of an indicator arrangement that informs the user of the need to replace the grinding stone. 
     A alternative or additional object of the invention is to provide knife grinding stone and detection arrangement wherein the detection arrangement may also control the grinding arrangement in such a way that grinding is possible only with a grinding stone that has not yet reached its wear limit. 
     Yet another object of the invention is to provide a further alternate construction wherein the indicator arrangement is loaded with another message that warns the user shortly before reaching the wear limit that the grinding stone must soon be replaced, this being performed by a detection arrangement that senses a second wear condition of the grinding stone, that lies just ahead of the wear limit. 
     Another more specific object of the invention is to provide a grinding stone arrangement including a conductive element embedded into the grinding stone that is, in one case, destroyed upon reaching the wear limit, and in another case, becomes exposed, with the detection arrangement being constructed in accordance with the particular case to sense the condition of this element. The detection arrangement may include a microprocessor that forms a component of the control arrangement of the grinding and/or cutting arrangement. 
     A further alternative or additional object of the invention is to provide an optical sensor whose output signal changes as soon as the wear limit of the grinding stone is reached. For this purpose, for example, an optical sensor is located at a cavity provided in the grinding stone into which ambient light falls upon reaching the wear limit, this light being sensed by the optical sensor. 
     These and other objects of the invention will become apparent from a reading of the ensuing description together with the appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic right side elevational view of a harvesting machine including a chopper drum with which a grinding arrangement constructed in accordance with the present invention is particularly suited for use. 
     FIG. 2 is a front elevational view of a chopper drum with parts in section shown together with a grinding arrangement including a grinding stone shown in end positions assumed during the grinding operation. 
     FIG. 3 shows an unused grinding stone according to a first embodiment of the invention. 
     FIG. 4 shows the grinding stone of FIG. 3 worn to its wear limit. 
     FIG. 5 shows an unused grinding stone according to a second embodiment of the invention. 
     FIG. 6 shows the grinding stone of FIG. 5 worn to its wear limit. 
     FIG. 7 shows an unused grinding stone according to a third embodiment of the invention. 
     FIG. 8 shows the grinding stone of FIG. 7 worn to its wear limit. 
     FIG. 9 shows an unused grinding stone according to a fourth embodiment of the invention. 
     FIG. 10 shows the grinding stone of FIG. 9 worn to its wear limit. 
     FIG. 11 shows a grinding stone connected to a detector circuit. 
     FIG. 12 shows a grinding stone connected to a different detector circuit. 
     FIG. 13 shows a grinding stone in a park position connected to a test element forming part of a third detector circuit embodiment. 
     FIG. 14 is a view like FIG. 13 but showing a different test element and detector circuit for detecting the wear of a grinding stone of a construction like that shown in FIGS.  7  and  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, there is shown a harvesting machine  10  in the form of a self-propelled forage harvester supported on a frame  12  that is carried on front and rear wheels  14  and  16 . The operation of the harvesting machine  10  is controlled from an operator&#39;s cab  18  from which a crop recovery or pickup arrangement  20  can be controlled visually. Crop taken up from the ground by means of the crop recovery arrangement  20 , for example, corn, grass or the like is conducted to a chopper drum  22  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 (not shown) through a pivoted discharge pipe  26 . A post-chopper reducing arrangement  28  extends between the chopper drum  22  and the conveyor arrangement  24  by means of which the crop conveyed is delivered tangentially to the conveyor arrangement  24 . Further details of the harvesting machine  10  do not require description since these are known in themselves. However, the position of the post-chopper reducing arrangement  28  is not critical, so that it can also be provided downstream of the conveyor arrangement  24 . 
     FIG. 2 is a schematic view of a chopper drum  22  and a grinding arrangement associated with it, as it is seen from the view of the harvesting machine  10  in FIG. 1 (with respect to the direction of operation) from the front. The chopper drum  22  comprises a central shaft  32  supported on two bearings  34  arranged at opposite ends of the chopper drum and carried by the frame  12  of the harvesting machine  10  in a well known manner, not shown. The chopper drum  22  can be brought into rotation by a belt drive including a pulley  36  fixed to an end of the shaft  32  and to which power is delivered by belts extending from a drive pulley, not shown, that is driven from a motor of the harvesting machine  10 . The chopper drum  22  is provided with a number of knives  38  distributed over its width and circumference which cut the crop taken up by the crop recovery arrangement  20  in interaction with a fixed shear bar  39 . Critical to the proper cutting of the crop is the spacing of the knives  38  from the shear bar  39  and the sharpness of the knives  38 . If the distance to the shear bar  39  is too small, the knives  38  rapidly become dull or even damaged. If the spacing is too large, the harvested crop is not cut properly. The present invention refers to the second problem area, the sharpness of the knives  38 . In order to be able to sharpen the knives  38  after a certain operating time, without having to disassemble the knives  38  or the entire chopper drum  22 , a grinding arrangement is provided above the chopper drum  22 , close to the enveloping circle described by the knives  38 , that generally comprises a grinding stone retainer  40 , an associated grinding stone  40  and a guide rail  44 , on which the grinding stone retainer  40  is supported in bearings so that it can move axially. 
     When the knives  38  are to be sharpened, the chopper drum  22  is set into rotation, as a rule in the opposite direction of rotation and/or at reduced rotational speed compared to normal chopper operation. The grinding stone retainer  40 , with the grinding stone  42  fastened to it, is moved from a rest or park position, not shown, in which it is located to the side next to the chopper drum  22 , over the entire width of the chopper drum  22 . Here the underside of the grinding stone  42  is in contact with, and sharpens, the knives  38 . The grinding process is performed in such a way that the grinding stone  42  is moved several times back and forth over the width of the chopper drum  22 . The end points of this movement are illustrated in FIG. 2, with the grinding stone retainer  40  and associated grinding stone  42  being shown in solid lines at the left reversal point and being shown in dashed linse at the right reversal point. Between the movements, the grinding stone  42  is fed, that is, it is given a minute advance of the grinding stone  42  towards the knives  38 . The feed motion in itself is known and either can be performed by movement of the grinding stone or the entire retainer arrangement. 
     In order to prevent the knives  38  from coming into contact with the grinding stone retainer  40  when the grinding stone  42  is worn to its wear limit, sensors are applied according to the invention that detect this wear limit. FIG. 3 shows an unused or factory fresh, grinding stone  42 , in which is embedded an electrical conductor, here shown as a u-shaped wire loop  50 . The wire loop  50  can be embedded during the manufacture of the grinding stone  42  that is performed, for example, by sintering or compacting of abrasive grinding material and an adhesive filler. A plate  48  of the grinding stone retainer  40 , to which the grinding stone  42  is fastened, as a rule by an adhesive connection, is a non-conductor at least in the region through which the ends of the wire loop  50  are routed. In this region, the plate  48  may be provided with a sufficiently large hole or it may be an electrical insulator entirely. The plate  48  is preferably fastened so that it can be removed from the usual grinding stone retainer  40 , shown in FIG. 2, in order to permit replacement of both components, grinding stone  42  and plate  48 , if required. For this purpose, a screw connection is particularly appropriate. 
     In FIG. 3, the grinding stone  42  is new and the wire loop  50  is intact, hence, an electrical current may flow between its ends. FIG. 4 illustrates the same grinding stone  42  which has been worn to its predetermined wear limit. Along with the abrasive material, the central portion of the wire loop  50  has also been ground away and there is no electrical connection between the opposite ends. By measurement of the conductivity, or resistance, of the wire loop  50 , the attainment of the wear limit of the grinding stone  42  can be indicated. 
     FIG. 5 shows a second embodiment of a grinding stone  42  according to the invention. Two wires  52  are integrated into the grinding stone  42  as electrically conducting elements, which extend in the direction in which the grinding stone  42  is fed towards the knives  38 . When the grinding stone  42  is worn, as is shown in FIG. 6, the ends of the wires  52  facing the knives  38  become exposed. These exposed ends can come into contact with the knives  38 , or another conductor forming part of a detector circuit which measures the resistance or the conductivity between the wires  52  and in that way senses when the wear limit of the grinding stone  42  has been occurred. 
     FIG. 7 shows a third embodiment of a grinding stone according to the invention. In this embodiment, only a single wire  54  is integrated into the grinding stone  42  as an electrically conducting element. When the grinding stone  42  has reached its wear limit, as is illustrated in FIG. 8, the end of the wire  54  facing the knives  38 , shown at the bottom in the drawing, becomes exposed and can come into contact with the knives  38  when the knife drum rotates. By measuring the resistance between the chopper drum  22 , which as a rule lies at the level of a mass potential, and the upper end of the wire  54 , the wear limit of the grinding stone can be detected; in this case, the resistance becomes significantly less than before at certain angular positions of the chopper drum  22  at which the wire  54  makes contact with a knife  38 . It is also possible to move the grinding stone retainer  40  to a position alongside the chopper drum  22  and to bring the under side of the grinding stone  42  into contact with another conducting test element and to measure the corresponding resistance. 
     FIG. 9 shows a grinding stone according to a fourth embodiment of the invention. On the upper side of the grinding stone  42  facing away from the knives  38 , a cavity  60  is provided in which an optical sensor  56  is arranged. When the grinding stone  42  has reached its wear limit, as shown in FIG. 10, the material covering the cavity  60  in the grinding stone  42  will have been ground away, so that the cavity  60 , and therewith the optical sensor  56 , is exposed to incoming light  58 . In this way, the wear limit can be detected without any problem. 
     FIG. 11 shows a first embodiment of a detector circuit that can be applied in connection with grinding stones  42  constructed in accordance with FIGS. 3 through 6. The grinding stone retainer  40  with the attached grinding stone  42  is provided with a pair of flexible cables  66 , first ends of which are respectively connected to the wires  50  or  52 , which are integrated into the grinding stone  42 . One of the cables  66  is connected with its other end to a certain potential (in the drawing, the vehicle mass), and the other cable is connected to a microprocessor  62 , which for its part controls an indicator arrangement  64 . The microprocessor  62  is stationary, that is, it is not moved over the width of the chopper drum  22 . 
     In place of the microprocessor  62 , a relay or the like could also be applied. On the basis of the potential at the cable  66 , the microprocessor  62  is provided with information that indicates whether the grinding stone  42  has reached its wear limit (then the cable lies at 0 V potential) or not (then the cable lies at any other potential). In this embodiment, the grinding stone  42  is monitored continuously. In a grinding stone  42  as shown in FIG. 3, the resistance increases when the grinding stone is worn by interruption of the wire loop  50 . On the other hand, the resistance decreases in the case of a grinding stone  42  shown in FIG. 5 when the wear limit is reached since then the knives  38  generate a contact between the wires  52 , at corresponding angular positions, while previously the resistance was higher. 
     FIG. 12 shows a second embodiment of a detector circuit that can be applied together with the grinding stone  42  shown in FIGS. 7 and 8. The wire  54  integrated into the grinding stone  42  is connected over a flexible cable  66  to a stationary microprocessor  62 , which controls the indicator arrangement  64 . If the grinding stone  42  has reached its wear limit, a circuit is intermittently completed between the wire  54 , and hence between the cable  66 , and the mass of the vehicle when respective ones of the knives  38  are positioned in engagement with the stone  42 , and hence with the exposed wire  54 . The microprocessor  62  could be replaced by a simpler device, such as a relay or toggle switch. Both devices are constructed such that they respond to the contact of a given knife  38  with the wire  54  and energize the indicator arrangement  64 . In this embodiment, the sensing of the condition of the grinding stone  42  is also continuous. 
     FIG. 13 shows a third embodiment of a detector circuit that can be used with the grinding stones of FIGS. 3 and 5. For use with this detector circuit, the grinding stone  42  is moved to a position alongside the chopper drum  22 , for example, after completion of a grinding process. If the grinding stone  42  has not been worn to its wear limit, neither the loop  50  or the wires  52  will come into contact with a test element in the form of a wire loop  70 . The upper end of one of the two ends of the wire loop  50  or of the wires  52  is connected over a cable  68  to a certain potential and the upper end of the other of the two ends of the wire loop  50  or of the wires  52  is connected over a further cable  72  to the microprocessor  62  which controls the indicator arrangement  64 . The wire loop  70  and the cables  68  and  72  are stationary. When the grinding stone  42  has reached its wear limit, the wire loop  70  comes into contact, in the one case, with the wires left after the central part of the loop  50  has been worn away, and in the other case with the lower ends of the exposed wires  52  in the grinding stone  42 , so that the potential at the input of the microprocessor  62  changes. If the grinding stone  42  is worn only little, no contact is made between the wire loop  70  and the loop  50  or the wires  52  in the grinding stone  42 . 
     Finally, in FIG. 14, a fourth embodiment of a detector circuit is illustrated that can be applied in connection with the grinding stone  42  shown in FIGS. 7 and 8. The contacts of the detector circuit are also arranged stationary alongside the chopper drum  22 . To test the grinding stone  42  after a grinding process, it must therefore be moved to a position alongside the chopper drum  22 . A conductor  70 ′, used as a test element, is connected to mass potential and a cable  72  is connected to the microprocessor  62  which controls the indicator arrangement  64 . When the grinding stone  42  is positioned above a contact forming an end of the conductor  70 ′, the cable  72  is attached to the top end of the conductor  54 . If the grinding stone  42  has not reached its wear limit, no electrical path is made between the wire  54 , in the grinding stone  42 , and the conductor  70 ′. If, on the other hand, the grinding stone  42  has reached its wear limit, then the electrical conductor  70 ′, which is at mass potential, comes into electrical connection with the wire  54 , so that the cable  72  is also at mass potential, and the microprocessor  62  is supplied with a corresponding signal. The microprocessor  62  then controls the indicator unit  64  and warns the user that the grinding stone  42  has reached its wear limit. 
     As a result, the wires  50 ,  52 ,  54  embedded in the grinding stone  42  together with the cables or contacts  66 ,  68 ,  70 ,  70 ′,  72 , the microprocessor  62  and the indicator unit  64  form a detector arrangement with which the attainment of the wear limit of the grinding stone  42  can be detected.