Cutting sharpness detection device

Abstract

A detection arrangement for detecting a wear status of a chopping knife arrangement of a chopping device provided for processing a product flow, wherein the chopping device has a revolving chopping drum receiving the chopping knife arrangement and at least one shear bar which cooperates with the chopping knives, with a sensor arrangement which has a magnetic exciter arrangement and a flux conducting device magnetically coupled thereto. The sensor arrangement provides a pole arrangement which forms at least one magnetic pole with a pole surface for conducting magnetic flux, wherein at least a portion of the chopping knife passes the pole arrangement during a rotation of the chopping drum. A voltage induced when a chopping knife arrangement passes the sensor arrangement forms the measured magnetic value, which is used by the evaluation unit to determine the state of wear of the chopping knife arrangement.

Claims

1. A detection arrangement for detecting a wear status of a chopping knife arrangement of a chopping device provided for processing a product flow, wherein the chopping device has a revolving chopping drum receiving the chopping knife arrangement and at least one shear bar which cooperates with chopping knives of the chopping knife arrangement, wherein the detection arrangement comprises: at least one sensor arrangement which has a magnetic exciter arrangement and a flux conducting device magnetically coupled thereto, wherein the sensor arrangement provides a pole arrangement which forms at least one magnetic pole with a pole surface for conducting magnetic flux, wherein the sensor arrangement is configured such that at least a portion of the chopping knife passes the pole arrangement during a rotation of the chopping drum, the chopping knife passing the pole arrangement forms an air gap arrangement with at least one air gap with respect to the pole arrangement, and at least one magnetic circuit excited by the exciter arrangement is accordingly closed via the respective chopping knife, a measuring arrangement, and an evaluating unit, wherein the measuring arrangement is configured to detect at least one measured magnetic value pertaining to the magnetic flux in at least one magnetic circuit excited by the exciter arrangement, wherein voltage induced when a chopping knife arrangement passes the sensor arrangement forms the measured magnetic value, and wherein the evaluating unit is configured to determine the wear status of the respective chopping knife from the at least one detected measured magnetic value by determining the induced voltage and recording the induced voltage as a voltage signal, resolving the voltage signal into its frequency components by means of frequency analysis, separating the frequency components into frequency components of a fundamental oscillation and into frequency components of a superposed oscillation which cause signal distortion, inverse-transforming the separated frequency components of the superposed oscillation which cause a signal distortion in a time domain, and deriving a measurement for the wear status or cutting sharpness of the chopping knife from the inverse-transformed frequency components of the superposed oscillation.

2. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 1, wherein the frequency components comprise the amplitude and the phase of the respective voltage signal.

3. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 1, wherein the frequency analysis of the voltage signal is carried out by means of Fourier analysis.

4. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 1, wherein a plurality of induction sensors are associated with each sensor arrangement, and each induction sensor generates a voltage signal, wherein each of the generated voltage signals is analyzed separately, and wherein a plurality of voltage signals, or all of the voltage signals, of a detected chopping knife are combined to form one or more voltage signals prior to an analysis.

5. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 1, wherein the respective voltage signal is classified into frequency components of a fundamental oscillation and frequency components of a superposed oscillation which cause signal distortions, and wherein the frequency components representing the fundamental oscillation are not taken into account in the derivation of the wear status or of the cutting sharpness of the respective chopping knife.

6. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 5, wherein an amplitude of the respective voltage signal of the frequency components causing a signal distortion forms a measurement for assessing the wear status and/or cutting sharpness of the respective chopping knife.

7. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 1, wherein the at least one sensor arrangement is configured to be positioned at a circumference of the chopping drum such that every chopping knife of the chopping drum is detected by means of the at least one sensor arrangement.

8. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 7, wherein right-hand-side and left-hand-side chopping knife arrangements are associated with the chopping drum, and at least one sensor arrangement is associated with each of said chopping knife arrangements.

9. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 1, wherein a reference value indicating a sharp knife is stored in the evaluating unit or in another data processing device, and wherein when the wear status of a chopping knife falls below this reference value, the detection arrangement is configured to generate a grinding signal, and wherein the reference value forms an amplitude of a voltage signal indicating a sharp knife.

10. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 9, wherein the generation of a grinding signal includes the generation of an informatory signal that comprises a visualization of that chopping knife that falls below the reference value.

11. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 9, wherein the generation of a grinding signal further includes a triggering of a grinding process.

12. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 1, wherein the assessment of the cutting sharpness or wear status is effected by means of evaluation criteria selected from the group consisting of grinding surface length of the respective chopping knife, roundness of the chopping knife tip, general knife wear, camber of the chopping knife and relative distance of the shear bar from the chopping knife.

13. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 12, wherein the reference value is an amplitude of a voltage signal indicating roundness of the chopping knife tip.

14. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 12, wherein the reference value is an oscillation period of a voltage indicating grinding surface length of the respective chopping knife.

15. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 12, wherein the reference value comprises an amplitude and an oscillation period of a voltage signal indicating general knife wear.

16. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 12, wherein the reference value is an amplitude of a voltage signal indicating camber of the chopping knife or relative distance of the shear bar from the chopping knife.

17. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 12, wherein a reference value is stored in the evaluating unit and/or some other data processing device for every evaluation criterion, and ii wherein the detection arrangement is configured to generate a grinding signal or a knife change signal when the wear status falls below this reference value, wherein the reference value being an amplitude of a voltage signal indicating grinding or a knife change.

18. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 17, wherein the generation of a grinding signal includes the generation of an informatory signal in the form of a visualization of that chopping knife falling below the reference value.

19. The detection arrangement for detecting a wear status of a chopping knife arrangement according to claim 18, wherein the generation of a grinding signal further comprises a triggering of a grinding process or a signal to exchange a chopping knife.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantageous configurations are the subject of further subclaims and are described in the following with reference to an embodiment example shown in the figures. In the drawings:

(2) FIG. 1 shows a forage harvester with cutting sharpness detection device according to the invention;

(3) FIG. 2 shows a detailed view of the forage harvester according to FIG. 1 with cutting sharpness detection device according to the invention;

(4) FIG. 3 shows a detailed view of the inductive sensor arrangement;

(5) FIG. 4 shows a schematic view of the frequency analysis according to the invention;

(6) FIG. 5 shows a detailed view of the frequency analysis according to the invention;

(7) FIG. 6 shows a further detailed view of the frequency analysis according to the invention; and

(8) FIG. 7 shows a schematic view of a use of the frequency analysis according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) FIG. 1 schematically shows an agricultural work machine 1 which is constructed as a forage harvester 2 and which receives a harvesting header 3 in the front area thereof. Gathering and pre-compacting rollers 4 which accept the crop flow 5 coming from the harvesting header 3, compress it and transfer it to a chopping device 6 in the rear area is associated with the header 3 in the rear area thereof. In a manner to be described further, the chopping device 6 comprises a chopping drum 7 which is outfitted with chopping knives 8 of a chopping knife arrangement 9. In the feed-in area 10 of the chopping drum 7, the revolving chopping knives 8 are moved past a shear bar 11 by means of which the crop flow 5 to be comminuted is conveyed. In the rear area of the chopping drum 7, the comminuted crop 5 is then transferred either to an after-comminution device 13 constructed as a so-called cracker 12 or directly to an after-acceleration device 14. While the after-comminution device 13 further comminutes the grain constituents of the crop flow 5, e.g., corn kernels, the after-acceleration device 14 accelerates the crop flow 5 such that this crop flow 5 can be moved through a deflector 15 and exit from the forage harvester 2 at the end in the area of a deflector flap 16 and can be transferred to a transport vehicle, not shown.

(10) According to FIG. 2, the chopping knife arrangement 9 comprises right-hand-side and left-hand-side chopping knife arrangements 9a, 9b. Each chopping knife arrangement 9a, 9b comprises a plurality of chopping knives 8 positioned oblique to the rotational axis 20 of the chopping drum 7 at the circumference of the chopping drum 7. The chopping drum 7 is sheathed on the underside by a drum base 21 preferably comprising stainless steel. At the upper side, the chopping drum 7 is enclosed by a rear drum wall 22 which likewise preferably comprises stainless steel. The sensor arrangement 23 according to the invention which will be described in more detail later can be positioned either at the rear drum wall 22 according to the embodiment example shown in FIG. 2 or at the drum base 21. It is also conceivable that a sensor arrangement 23 is arranged both at the drum base 21 and the rear drum wall 22 at the same time. Regardless of the specific position, at least two sensor arrangements 23a, 23b are associated with every chopping drum 7 in such a way that one of the sensor arrangements 23a, 23b is associated in each instance with the associated chopping knife arrangement 9a, 9b, respectively. Each sensor arrangement 23a, 23b completely covers the cutting edge 24 of the respective chopping knife 7 so that each cutting edge 24 can be detected over its entire length by the respective sensor arrangement 23a, 23b. Further, it lies within the scope of the invention that the respective sensor arrangement 23a, 23b is positioned either parallel to the rotational axis 20 of the chopping drum 7 or parallel to the cutting edge 24 of the chopping knives 8 at the drum base 21 and/or rear drum wall 22. The view at lower right in FIG. 2 shows the possible orientations of the sensor arrangements 23a, 23b depicted individually merely by way of example. All of the sensor arrangements 23a, 23b are preferably positioned either parallel to the rotational axis 20 of the chopping drum 7 or parallel to the cutting edge 24 of the chopping knives 8. In the depicted embodiment example, the sensor arrangements 23a, 23b are constructed as induction sensors 25 to be described more fully in the following. Each sensor arrangement 23 comprises one or more magnetic exciter arrangements 26 and, in each instance, a pole arrangement 27 cooperating with the latter.

(11) FIG. 3 depicts some characteristics of the sensor arrangements 23a, 23b which are key to understanding the invention. The further details of the sensor arrangements are given in DE 10 2017 103 537 A1, the disclosure of which is hereby incorporated by reference in its entirety herein. The detection arrangement 28 according to the invention for detecting a wear status of a chopping knife arrangement 9a, 9b comprises a plurality of sensor arrangements 23a, 23b, preferably for each chopping knife arrangement 9a, 9b. Every sensor arrangement 23a, 23b is formed by a plurality of magnetic exciter arrangements 26 which are coupled with a flux conducting device 29. The respective sensor arrangement 23a, 23b provides a pole arrangement 27 which forms at least one magnetic pole 30, preferably five magnetic poles 30, with a pole surface 31 in each instance for conducting magnetic flux. During a rotation of the chopping drum 7, a chopping knife 8 passes the respective pole arrangement 27, and the chopping knife 8 passing the pole arrangement 27 forms an air gap arrangement 32 with at least one air gap 33 with respect to the pole arrangement 27, and at least one magnetic circuit 34 excited by the exciter arrangement 26 is accordingly closed via the respective chopping knife 8. The detection arrangement 28 further has a measuring arrangement 35 and an evaluating unit 36. In a manner according to the invention which will be described more fully later, the measuring arrangement 35 detects at least one measured magnetic value 37 pertaining to the magnetic flux, preferably an induced voltage 38 in at least one magnetic circuit 34 excited by the exciter arrangement 26, and the evaluating unit 36 determines the wear status 39 of the respective chopping knife 8 from the at least one detected measured value 37.

(12) Details of the device according to the invention will now be described referring to FIG. 4. During operation of the chopping drum 7, the chopping knives 8 are guided past the respective sensor arrangement 23a, 23b according to the rotational direction 40 of the chopping drum 7. Owing to the virtually non-magnetic properties of the rear drum wall 22 or of the drum base 21 which preferably comprises stainless steel, the magnetic circuits 34 formed by adjacent magnetic poles 30 penetrate the chopping knife 8 passing over the sensor arrangement 23a, 23b, respectively. In the depicted embodiment example, four magnetic circuits 34 which penetrate the respective chopping knife in four sections L1 to L4 are formed between the five poles 30. For each of these sections L1 to L4, a voltage 38, i.e., the measured magnetic value 37, is induced in the measuring arrangement 35 associated with each section L1 to L4. The evaluating unit 36 associated with the detection arrangement 28 determines and records the section-by-section induction voltage 38a-e in each instance. In this respect, it lies within the scope of the invention that the respective sensor arrangement 23 has more or less than the disclosed five magnetic poles 30 so that there can also be more or less than five induced voltages 38a-e. It also lies within the scope of the invention that the voltage signals 38a-e can be combined to form one or more voltage signals 38 for each chopping knife 8 detected.

(13) The respective voltage signal 38a . . . e is converted in the evaluating unit 36 into a voltage signal 49a . . . e which can be further processed. This voltage signal 49a . . . e which can be further processed is formed in such a way that the induced voltage 38, i.e., the reference value 38 of the induced voltage, is initially determined for a sharp, unworn chopping knife 8, the induction voltage 38a . . . e which changes contingent on wear is then determined during the operation of the chopping knife 8 and, lastly, the voltage signals 49a . . . e which can be further processed are determined from the difference of the wear-dependent change in induction voltage 38a . . . e minus the reference value 38 of the induced voltage of an unworn chopping knife 8.

(14) The respective voltage signals 49a . . . e is then resolved into its frequency components 42, preferably oscillation period or phase 43 and amplitude 44, in the evaluating unit 36 in a manner known per se by means of frequency analysis 41, preferably by means of Fourier analysis 47. In doing so, the respective induced voltage signal 49a . . . e is separated into frequency components 42 of a fundamental oscillation 45 and into frequency components 42 of a superposed oscillation 46 which cause signal distortions. The separated frequency components 42 causing a signal distortion, i.e., the so-called superposed oscillation 46, are then inverse-transformed in the time domain 48 in a manner to be described more fully later and, lastly, a measurement for the cutting sharpness, i.e., the wear status 39, of a chopping knife 8 is derived from the inverse-transformed frequency components 42 in a manner which will likewise be described more fully later.

(15) The frequency analysis 41 carried out according to the invention by the evaluating unit 36 is shown schematically in detail in FIG. 5. The voltage signal 49a-e derived in each instance from the induced voltage 38a-e is initially derived in the manner described above. The respective voltage signal 49a . . . e is then resolved into its frequency components 42 by means of Fourier analysis 47. In this case, as has already been described, a fundamental oscillation 45 and one or more superposed oscillations 46, so-called harmonics 50, causing the signal distortions are separated. When a chopping knife 8 moves past the sensor arrangement 23a,b formed as induction sensor 25, the respective chopping knife 8 changes the permeability in the air gap 33 in front of the sensor arrangement 23a,b. Consequently, the magnetic induction changes. This change can be measured by means of the respective induced voltage 38a . . . e. Regardless of whether its cross-sectional shape is curved or planar, a typical chopping knife 8 comprises essentially three characteristic areas. The first area 51 defines the roundness of the knife tip 52 and is determined by its radius; the smaller its radius, the sharper a chopping knife 8 is. The so-called grinding surface length 54 defines a further area 53. An increasing grinding surface length 54 is a measurement for increasing wear 39 of the respective chopping knife 8. Lastly, the so-called knife back 56 is distinguished as the third area 55; its shape and quality can be utilized as a measurement for describing the general wear status 39 of the respective chopping knife 8. The general wear status and wear are both denoted in the following as wear 39 for reasons of simplicity.

(16) The voltage signal 49a . . . e shown at bottom right in FIG. 5 results for the curved chopping knife 8 in the depicted embodiment example. Voltage signal 49a . . . e is shown here over the angle position 57 of the chopping knife 8 relative to the respective sensor arrangement 23a,b, and the angle position 0° describes the central position of the chopping knife 8 in front of the respective sensor arrangement 23a,b.

(17) It will be noted that the described characteristic areas 51, 53, 55 induce voltages 49a . . . e of different levels. The area 51, 52 describing the roundness of the knife tip induces the highest total voltage 49a . . . e. It will be noted at the same time that the size of the air gap 33 has an influence on the induced voltage 49a . . . e. As expected, the value of the induced voltage 49a . . . e decreases as air gap 33 increases. The signal shape of the induced voltage 49a . . . e is acquired and separated for every knife. This means that a plurality of voltage signals 49a . . . e are available for each chopping knife 8 depending on the configuration of the sensor arrangement 23a,b. According to FIG. 3, every magnetic pole 30 of the pole arrangement 27 generates an induced voltage 38a . . . e. These induced voltages 38a . . . e are then subjected to the frequency analysis 41 according to the invention by means of Fourier analysis 47 in the evaluating unit 36 after conversion into the voltage signals 49a . . . e described above. As has already been described, the Fourier analysis 47 separates these voltage signals 49a . . . e into frequency components 42 of a fundamental oscillation 45 and frequency components 42 of one or more superposed oscillations 46, or harmonics 50, which cause the signal distortion.

(18) FIG. 6 describes the individual steps of the frequency analysis 41 in detail. In the first analysis step 58, the induced voltages 38a . . . e are subjected to a Fourier analysis 47 as voltage signals 49a . . . e in the manner already described, and the fundamental oscillation 45 and superposed oscillation 46 determine approximately one or more of the harmonics 50. The frequency analysis 60 shown in a further analysis step 59 shows that the amplitudes 61 of sharp knives 62 differ only insignificantly from those of blunt knives 63 regardless of whether the oscillation is a fundamental oscillation 45 or a superposed oscillation 46. In the subsequent analysis step 64, the determined fundamental oscillation 45 is no longer taken into account according to the invention, and only the frequency components 42 of the superposed oscillations 46 causing a signal distortion are inverse-transformed in the time domain 48. The results of this inverse-transformation are visualized in an exemplary manner in analysis step 64 with the example of three chopping knives 8 with chopping performance of different lengths. Chopping knife 8a has the highest chopping performance, while chopping knife 8b delivered approximately 40% of the chopping performance of chopping knife 8a, and chopping knife 8c delivered only approximately 10% of the chopping performance of chopping knife 8a. Consequently, the wear status 39 and, therefore, the cutting sharpness 65 of each chopping knife 8 can be deduced from the inverse-transformed frequency components 42 of the superposed oscillations 46.

(19) FIG. 7 schematically shows the implementation of a cutting sharpness adjustment. As already stated, the amplitude 44 of the respective induced voltage 38a . . . e and the voltage signal 49a . . . e derived therefrom form a measurement for the wear status 39 and, analogously, the cutting sharpness 65 of a chopping knife 8. Usually, a chopping knife 8 counts as sharp when the roundness (the radius) of the knife tip 52 amounts to approximately 0.04 mm. The amplitudes 44 of the chopping knives 8a . . . c shown by way of example in FIG. 7 correspond to radii of the knife tip 52 of approximately 0.1 mm-0.25 mm-0.6 mm, and an increasing roundness 52 corresponds to an increasing wear 39 and a decreasing cutting sharpness 65. In the simplest case, a “sharp knife” reference value 66 can now be stored in the evaluating unit 36 or other data processing device, including an external data processing device. In the simplest case, this reference value is a stored reference value 66 of the amplitude 44 of the induced voltage 38a . . . e, 49a . . . e. If the value falls below reference value 66, a grinding signal 67 is then generated. In this case, as will be explained in the following, this grinding signal 67 can conceivably be generated in different ways. In the simplest case, the chopping knife or chopping knives 8 which have fallen below the “sharp knife” threshold value can be displayed to an operator 68 on a display 69. In this case, the operator decides when a grinding process 70 of the chopping knives 8 is to be initiated. However, it is also conceivable that a control device 71 monitors the adherence to the “sharp knife” reference value 66 and automatically initiates the grinding process 70. The automatic initiation of the grinding process 70 is preferably defined such that a minimum number of chopping knives 8 must fall below the reference value 66 before a grinding process 70 is activated. In a manner known per se, it is also taken into account that the forage harvester 2 is not in a working mode in that crop 5 is moved through the forage harvester 2.

(20) Alternatively or additionally, the assessment of the wear status 39 or of the cutting sharpness 65 can also be coupled to evaluation criteria 72. Preferably, the evaluation criteria can be one or more of the evaluation criteria comprising “grinding surface length 54 of the respective chopping knife 8” 72a, “roundness of the chopping knife tip 52” 72b, “general knife wear 39” 72c and/or “camber of the chopping knife 8” 72d or “relative distance of the shear bar 11 from the chopping knife 8” 72e. Analogous to the preceding description, a reference value 73 can also be stored in the evaluating unit 36 or other data processing device, including an external data processing device, with respect to the evaluation criteria 72a . . . e. In the simplest case, this is a stored reference value 73 of the amplitude 44 of the induced voltage 38a . . . e, 49a . . . e. Depending on the selected evaluation criterion or individual stored evaluation criterion 72a . . . e, the stored reference value 73 is then either a measurement for the wear status 39 of the respective chopping knife 8 in total or for the sharpness of the cutting edge 24. If the value falls below the reference value 73, the grinding signal 67 described above is generated. This grinding signal 73 can then conceivably be generated in different ways. In the simplest case, the chopping knife or chopping knives 8 which have fallen below the reference value 73 can be displayed to an operator 68 on a display 69. In this case, the operator decides when a grinding process 70 of the chopping knives 8 is to be initiated. However, it is also conceivable that a control device 71 monitors the adherence to reference value 73 and automatically initiates the grinding process 70. The automatic initiation of the grinding process 70 is preferably defined such that a minimum number of chopping knives 8 must fall below the reference value 73 before a grinding process 70 is activated. It is also taken into account in a manner known per se that the forage harvester 2 is not in a working mode in that crop 5 is moved through the forage harvester 2.

(21) Alternatively or additionally, when the value falls below the reference value 66 or reference value 73, replacement of a chopping knife 8 can be suggested, namely, preferably when measurements fall below reference value 66, 73 to such an extent that it can be inferred that the respective chopping knife 8 is at the end of its usable range.

(22) In view of the fact that the induced voltage 38a . . . e, i.e., the voltage signal 49a . . . ederived therefrom increases with increasing roundness 52 of the cutting edge 24 of the chopping knives 8, it is provided that the reference value 73 is an amplitude 44 of the determined voltage signal 49 when the “roundness of the chopping knife tip 52” evaluation criterion 72b is selected.

(23) Since the oscillation period 43 of the induced voltage 38a . . . e increases with increasing grinding surface length 54 of the chopping knife 8, the reference value 73 is an oscillation period 43 of the derived voltage signal 49a . . . e when the “grinding surface length 54 of the respective chopping knife 8” evaluation criterion 72a is selected.

(24) Due to the fact that the oscillation period 43 and the amplitude 44 of the induced voltage 39a . . . e both increase significantly with increasing general wear 39 of chopping knife 8, reference value 73 is an amplitude 44 and an oscillation period 43 of the determined voltage signal 49a . . . e when the “general knife wear” evaluation criterion 72c is selected.

(25) The distance of the chopping knife 8 from the shear bar 11 increases and the amplitude 44 of the induced voltage 38a . . . e decreases significantly with increasing wear 39 of the chopping knife 8 so that when the “camber of the chopping knife 8” or “relative distance of the shear bar 11 from the chopping knife 8” evaluation criterion 72d, e is selected, reference value 73 is an amplitude of the determined voltage signal 49a . . . e.

REFERENCE CHARACTERS

(26) 1 agricultural work machine

(27) 2 forage harvester

(28) 3 header

(29) 4 gathering and pre-compacting rollers

(30) 5 crop flow

(31) 6 chopping device

(32) 7 chopping drum

(33) 8 chopping knife

(34) 9 chopping knife arrangement a . . . b

(35) 10 feed-in area

(36) 11 shear bar

(37) 12 cracker

(38) 13 after-comminution device

(39) 14 after-acceleration device

(40) 15 deflector

(41) 16 deflector flap

(42) 20 rotational axis of the chopping drum

(43) 21 drum base

(44) 22 rear drum wall

(45) 23 sensor arrangement a . . . b

(46) 24 cutting edge

(47) 25 induction sensor

(48) 26 magnetic exciter arrangement

(49) 27 pole arrangement

(50) 28 detection arrangement

(51) 29 flux conducting device

(52) 30 magnetic pole

(53) 31 pole surface

(54) 32 air gap arrangement

(55) 33 air gap

(56) 34 magnetic circuit

(57) 35 measuring arrangement

(58) 36 evaluating unit

(59) 37 measured magnetic value

(60) 38 reference value of induced voltage

(61) 38a.e induced voltage

(62) 39 wear status

(63) 40 rotational direction

(64) 41 frequency analysis

(65) 42 frequency component

(66) 43 oscillation period/phase

(67) 44 amplitude

(68) 45 fundamental oscillation

(69) 46 superposed oscillation

(70) 47 Fourier analysis

(71) 48 time domain

(72) 49 voltage signal a . . . e

(73) 50 harmonic

(74) 51 first area

(75) 52 roundness of the knife tip

(76) 53 further area

(77) 54 grinding surface length

(78) 55 third area

(79) 56 back of knife

(80) 57 angle position

(81) 58 first analysis step

(82) 59 further analysis step

(83) 60 frequency analysis

(84) 61 amplitude

(85) 62 sharp knife

(86) 63 blunt knife

(87) 64 analysis step

(88) 65 cutting sharpness

(89) 66 “sharp knife” reference value

(90) 67 grinding signal

(91) 68 operator

(92) 69 display

(93) 70 grinding process

(94) 71 control device

(95) 72 evaluation criterion a . . . e

(96) 73 reference value

(97) L1.L4 sections