Method for determining the wear state

Abstract

This invention relates to a method for determining a wear state of a chisel, a chisel holder, and/or a chisel holder replacement system equipped with a chisel and chisel holder. For this method to give the user qualitative and quantitative information about the wear, according to one embodiment of this invention, a position of at least one point of the chisel and/or the chisel holder is determined by a contactless measurement method and a corresponding measurement result is compared in a switching unit to a reference value stored in a memory device.

Claims

1. A measurement system for determining a wear state of at least one milling tool of a milling roller of a road milling machine or a surface miner machine, the measurement system comprising: a sensor associated with the machine and arranged to provide at least a sensor output that varies in relation to a distance between the sensor and the milling tool; and a processor configured to determine the wear state of the milling tool at least in part by comparing the sensor output to a reference value.

2. The measurement system of claim 1, wherein the sensor is a distance-measuring sensor.

3. The measurement system of claim 1, wherein the sensor is a proximity sensor.

4. The measurement system of claim 1, wherein the sensor is mounted on the machine.

5. The measurement system of claim 1, wherein the sensor output corresponds to a current distance between the sensor and the milling tool.

6. The measurement system of claim 5, wherein the reference value is a previously determined value of the sensor output corresponding to a distance between the sensor and the milling tool in an unworn new state of the milling tool.

7. The measurement system of claim 1, wherein the sensor operates upon a magnetic measurement principle.

8. The measurement system of claim 1, wherein the sensor operates upon an acoustic measurement principle.

9. The measurement system of claim 1, wherein the sensor operates upon an optical measurement principle.

10. The measurement system of claim 1, wherein the sensor operates upon a mechanical measurement principle.

11. The measurement system of claim 1, wherein the sensor is configured to operate based upon a runtime measurement principle.

12. The measurement system of claim 1, wherein the sensor is configured to operate based upon a phase shifting principle.

13. The measurement system of claim 1, wherein the sensor is configured to operate based upon a triangulation principle.

14. The measurement system of claim 1, the milling roller including a plurality of milling tools, wherein: the sensor is arranged to inspect multiple ones of the plurality of milling tools.

15. The measurement system of claim 1, further comprising an angle detection sensor configured to detect a rotation angle of the milling roller.

16. A method for determining a wear state of a milling tool including a chisel, the method comprising; providing, using a sensor, a sensor output corresponding to a distance of the sensor from the chisel; and comparing the sensor output in a processor to at least one reference value for the sensor output stored in a memory device to determine the wear state of the milling tool.

17. The method of claim 16, wherein in the providing step a contactless method is used to provide the sensor output.

18. The method of claim 16, wherein the reference value is a sensor output corresponding to a distance of the sensor from the chisel in an unworn new state of the chisel.

19. The method of claim 16, further comprising determining a rotational position of a milling roller that supports the chisel.

20. The method of claim 16, wherein in the providing step the sensor is a distance measuring sensor.

21. The method of claim 16, wherein in the providing step the sensor is a proximity sensor.

22. The method of claim 16, wherein in the providing step the sensor operates on a magnetic measurement principle.

23. The method of claim 16, wherein in the providing step the sensor operates on an acoustic measurement principle.

24. The method of claim 16, wherein in the providing step the sensor operates on an optical measurement principle.

25. The method of claim 16, wherein in the providing step the sensor operates on a mechanical measurement principle.

26. The method of claim 16, wherein in the providing step the sensor is configured to operated based on a runtime measurement principle.

27. The method of claim 16, wherein in the providing step the sensor is configured to operated based on a phase shifting principle.

28. The method of claim 16, wherein in the providing step the sensor is configured to operated based on a triangulation principle.

29. A method for determining a wear state of a milling tool mounted on a milling roller of a milling machine, using a measurement system mounted on the milling machine, the measurement system including a proximity sensor, the method comprising: (a) sensing a proximity of the milling tool to the proximity sensor of the measurement system, and providing an output signal from the proximity sensor, the output signal having a current value; and (b) determining the wear state of the milling tool by comparing the current value to a reference value.

30. The method of claim 29, wherein step (a) comprises detecting the current value without contacting the milling tool.

31. The method of claim 29, wherein in step (b) the reference value is a previously determined value of the output signal when the milling tool was in an unworn new state.

32. The method of claim 29, wherein: step (a) further comprises determining a rotational position of the milling roller and based upon the rotational position of the milling roller determining a position of the milling tool on the milling roller.

33. The method of claim 29, wherein in step (a) the proximity sensor operates on a magnetic measurement principle.

34. The method of claim 29, wherein in step (a) the proximity sensor operates on an acoustic measurement principle.

35. The method of claim 29, wherein in step (a) the proximity sensor operates on an optical measurement principle.

36. The method of claim 29, wherein in step (a) the proximity sensor operates on a mechanical measurement principle.

37. The method of claim 29, wherein in step (a) the proximity sensor is configured to operated based on a runtime measurement principle.

38. The method of claim 29, wherein in step (a) the proximity sensor is configured to operated based on a phase shifting principle.

39. The method of claim 29, wherein in step (a) the proximity sensor is configured to operated based on a triangulation principle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This invention is explained in greater detail below in view of exemplary embodiments shown in the drawings, wherein:

(2) FIG. 1 shows a side view of a chisel, such as a round-shafted chisel, which is for a road surface milling machine, a mining machine, a surface miner, or the like, and is inserted into the holder of a replaceable holder tool for such machines;

(3) FIG. 2 shows the chisel head of the chisel from FIG. 1, shown in a graph;

(4) FIGS. 3 through 7 show various wear states of the chisel head, depicted in graphs;

(5) FIG. 8 is a schematic side view of a road surface milling machine;

(6) FIG. 9 shows a milling roller of the road surface milling machine according to FIG. 8, with a measuring device that functions based on the principle of triangulation; and

(7) FIG. 10 shows the milling roller according to FIG. 9, with an alternative embodiment of the measuring device that functions based on a shadow-casting method.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows an example of a chisel 10 of the type known from the prior art and described, for example, in German Patent Reference DE 38 18 213 A1. The chisel 10 has a chisel head 12 and a chisel shaft 15 integrally formed onto the chisel head 12. The chisel head 12 supports a chisel tip 11 composed of a hard material, for example hard metal.

(9) The chisel tip 11 is usually soldered to the chisel head 12 along a contact surface. A circumferential extraction groove 13 is in the chisel head 12. This extraction groove 13 serves as a tool receptacle because a removing tool is placed onto it, enabling removal of the chisel 10 from a chisel holder 70.

(10) The chisel shaft 15 supports a longitudinally slit, cylindrical clamping sleeve 21. This sleeve is secured so that it cannot be detached in the direction of the longitudinal span of the chisel 10, but is able to freely rotate in the circumferential direction on the chisel shaft 15. In the region between the clamping sleeve 21 and the chisel head 12, a wear-prevention disk 20 is provided. When installed, the wear-prevention disk 20 rests against a counterpart surface of a chisel holder 70 and, on the side oriented away from the chisel holder 70, rests against the underside of the chisel head 12.

(11) The chisel holder 70 has an attachment 71 in which a chisel receptacle 72 in the form of a cylindrical bore is provided. In the chisel receptacle 72, the clamping sleeve 21 is secured with its outer circumference clamped against the inner wall of the bore. The chisel receptacle 72 opens out into the ejection opening 73. An ejecting pin, not shown, can be inserted through this opening in order to remove the chisel 10. It acts on the end of the chisel shaft 15 so that by overcoming the clamping force of the clamping sleeve 21, the chisel 10 is slid out from the chisel receptacle 72.

(12) As shown in FIG. 1, the attachment 71 has two circumferential grooves in a cylindrical region below the wear-prevention disk 20. The grooves serve as wear markings 74. During operational use, the wear prevention disk 20 rotates and in so doing, can produce wear, chisel holder wear, on the supporting surface of the attachment 71. When the supporting surface abrades down until it reaches the second wear marketing, the chisel holder 70 is worn down to the point that it must be replaced.

(13) The chisel holder 70 has an insertion attachment 75 that can be inserted into an insertion receptacle 82 of a base part 80 and can be clamped there by a clamping screw 83.

(14) The clamping screw 83 thus presses a contact surface 76 of the chisel holder 70 against a supporting surface 84 of the base part 80. In a manner not shown in detail in FIG. 1, the underside 81 of the base part 80 itself is welded to the milling roller tube of a milling roller.

(15) To determine the wear state of the chisel 10 mounted on the chisel holder, a contactless measurement of the chisel head 12 is performed. In this instance, a specified point or a plurality of points of the chisel head 12 each is measured and/or determined as position values. FIG. 2 shows the contour of an unworn chisel head 12, in a side view. This contour is shown in a graph, with the span of the chisel head 12 in the direction of the longitudinal axis of the chisel 10, the x-axis, plotted over the span in the width direction, perpendicular to the central longitudinal axis, such as the y-axis. The contour of the chisel head 12, including the chisel tip 11, is composed of a multitude of measured points. The linear border or contour line represents an interpolation of these position values.

(16) The measurement on a milling roller 35, as shown in FIGS. 9 and 10, can be performed when the chisel 10 is in the unworn state or in a partially worn state. Then these points, such as the calculated chisel head contour, or also only a single measurement point can be determined and stored as reference values or as a reference value in a memory device.

(17) FIG. 3 shows various measurement images of a chisel 10. The chisel head 12 here is shown in the unworn state and in three measured wear states V1 through V3. The wear state V3 represents the state in which the chisel 10 is no longer suitable for further operation and must be replaced. The wear can be determined by comparing the reference value, the contour in the unworn state, to the respectively measured current chisel head contour, such as wear states V1, V2, or V3, that represent the position value.

(18) The contours must be aligned with one another. Due to holder wear or other error sources, unworn contour regions are not necessarily situated at the same absolute positions, such as relative positions in relation to the rotational axis of the roller. Setting the contours into relation with one another again requires reference features that are clearly identifiable and appear in both the unworn and worn state, thus permitting an alignment and an exclusive evaluation. The extraction groove 13, the wear markings 74, the wear-prevention disk 20, or other prominent regions that are subject to only slight wear or to no wear at all can be used as reference features.

(19) As shown in FIG. 3, the length of the chisel head 12 decreases during operational use. Through subtraction of the contour lines in a switching unit, it is possible to obtain information about the wear state, which is visually depicted for the user on a display unit, for example. Instead of measuring the entire contour of the chisel head 12, it is also possible for only a part of the contour or a single point, in particular the front end of the chisel tip 11, to be detected as a position value. More detailed information about the wear state can be obtained if the wear on the chisel tip 11 and on the chisel head 12, without the chisel tip 11, are determined separately.

(20) This is easily possible with the previously known position of the attachment, such as the attachment point TP/attachment line 18, of the chisel tip 11 to the chisel head 12 in the unworn state.

(21) If the measured wear states V1 through V3 are superimposed on the unworn contour of the chisel head 12, as shown in FIG. 2, then the total wear volume can be determined through integration of the measured contours along the x-axis. In FIG. 4, the wear volume is depicted as a shaded region.

(22) Consequently, the wear volume can be used as a position value and compared to a reference value. The reference value in this case can comprise a functional correlation or a characteristic field. Different wear volumes are correlated with associated wear states, for example a mm.sup.3 of wear volume corresponds to b % wear. Based on the previously known position of the attachment point TP/attachment line 18, the tip wear 16 and the head wear 17 can then be separately determined through subtraction. This wear determination gives the user qualitative information, for example, about whether the chisel 10 is still suitable for certain milling tasks. Thus, a chisel that has not in fact reached its wear limit yet, but does have a certain degree of tip wear, can no longer be used for fine milling work, for example.

(23) In the method according to FIGS. 3 and 4, the measured position values are superimposed with the reference values. During the machining process, wear occurs not only on the chisel head 12, but also on the chisel holder. The chisel holder wears down in the direction of the central longitudinal axis of the chisel 10. The isolated determination of the longitudinal wear on the chisel holder in this direction then succeeds simply because the degree of shifting of the position value toward the reference value required to reach the superimposed positions shown in FIGS. 3 and 4, shifting of the chisel head 12 in the direction of the x-axis until, for example, the extraction grooves of the individual wear states are congruent, constitutes an absolute wear value of the chisel holder. The total shifting of the chisel tip 11 minus this wear value is then a separate indication of the chisel wear.

(24) FIG. 5 shows a method variant in which information about wear is obtained based on measuring a clearly identifiable feature on the chisel. The feature and the surroundings of this feature should be subject to only slight wear or to no wear at all. According to FIG. 5, the extraction groove 13, a part of the extraction groove 13, or a point, for example the groove bottom, of the extraction groove 13 is used as a definite feature and reference criterion.

(25) Furthermore, this feature is then used for determining the distance to the position of the free end of the chisel tip 11, such as the position value. This makes it easily possible to determine the longitudinal wear in a simple way. If the position of the chisel tip 11 is known, then as described above, it is once again possible to determine the chisel holder wear. Alternatively or in addition, as specified in conjunction with FIG. 4, it is also possible to determine the volume wear and the associated wear lengths, such as where X=total wear.

(26) The relative measurement through the use of a definitely identifiable feature as a reference point has the advantage that a wear determination can also be made in the absence of a reference measurement because, for example, the length of the replaced chisel 10 or the wear state of the chisel 10 or chisel holder is not known.

(27) FIG. 3 shows the change in the chisel head contour as the wear increases. The decreasing length of the chisel head 12 is clearly visible. If the chisel head contours are respectively shifted toward the point of the maximum length of the chisel 10, such as shown in FIG. 6, then through the changing head angle the angle becomes flatter as chisel wear increases and through the increasing volume of the chisel head 12 the increasing wear state of the chisel 10 becomes evident when the area under the contour curve, starting from the respective tip over a certain length, is integrated. It is thus possible to establish a functional correlation between the head volume/area and the absolute chisel length for a certain chisel type, for example by experiments carried out in advance to determine reference values.

(28) If this correlation is known, then the length of the chisel 10 can be determined through measurement/integration of the respective head volume currently present. This method, however, is based on the assumption that the chisel tip 11 has a cross-section that increases in the longitudinal direction of the chisel. The integration method is preferably established so that even with completely worn chisels 10, the integration does not extend into the head region because erosion in the head region distorts the result.

(29) This method has the advantage of not requiring a reference point that is subject to little wear. Sometimes such a reference point is not present or is very difficult to identify.

(30) In order to determine the asymmetry factor of the wear, it is possible, for example, to calculate the average between the upper and lower contour lines. FIG. 7 shows the contour lines and their averages for a new chisel tip 11, for a chisel tip 11 with rotationally symmetrical wear R1, and for a chisel tip 11 with non-rotationally symmetrical wear R2. It is clear that with the asymmetrically worn chisel 10, the average line M2 of the two contour lines has a certain slope in relation to the longitudinal axis of the chisel. The angular position could be easily evaluated in order to determine the asymmetry factor of the wear. It is also possible, however, to directly ascertain/determine the position/deviations of several contour lines.

(31) According to the same method, it is possible to determine an asymmetrical wear on the chisel head 12. Usually, however, an asymmetrically worn chisel head 12 is accompanied by an asymmetrically worn chisel tip 11. It is thus sufficient to analyze the chisel tip 11.

(32) FIG. 8 symbolically depicts a road surface milling machine 30 in which a machine body 32 is supported by four column-like traveling units 31. The road surface milling machine 30 can be controlled from a control center 33. A milling roller 35 is mounted in a milling roller housing 34.

(33) In order to measure the wear state using one of the above-described methods, a light source 50 and a camera 40 are associated with the milling roller 35. The milling roller 35 is shown in greater detail in FIG. 9. Numerous chisel holder replacement systems, each having a respective chisel holder 70, are fastened to the surface of a milling roller tube 35.1 of the milling roller 35. A chisel 10 is mounted in each chisel holder 70. In the current example, the chisel holders 70 are welded directly to the milling roller 35.

(34) It is possible to use the chisel holder replacement system according to FIG. 1. Then, the base part 80 is welded to the milling roller 35.

(35) As the apparatus for measuring the chisel contours, an optical system is used in which a type of scanning operation is used to measure a contour line of the roller surface. The measurement principal used here can, for example, be a triangulation method in which the roller surface is illuminated for example by a light source 50 such as a laser line. The laser line produced in this way is observed by a camera 40 at a different angle, as a result of which height differences on the roller surface, for example produced by the chisels 10, produce shifts in these projection lines. With a known differential angle between the camera 40 and the light source 50, it is possible to calculate the height coordinates. By rotating the milling roller 35, it is thus possible to establish a height profile of the circumference surface of the roller, from which the contour line of the individual chisels 10 can be read.

(36) Another optical measurement principal for measuring the height and/or geometry of the chisels 10 is the shadow-casting method according to FIG. 10. This method takes advantage of the fact that as they move through a light curtain produced by a light source 50, the chisels 10 produce a shadow contour that can be observed by a camera 40 and evaluated. The significant advantage of this method is that it is possible to work with a single camera line using the same principle as a document scanner. It is thus possible, even for measurements of milling rollers 35 with large diameters and high rotation speeds, to be carried out with a sufficient resolution.

(37) According to an alternative embodiment of this invention, it is possible to modify the method described in relation to FIG. 10. In this case, a light curtain in the form of a light plane is again produced by the light source 50. This light plane extends parallel to the central longitudinal axis of the milling roller 35 and tangential to the roller surface. In this case, the light plane is oriented so that when the milling roller 35 rotates, the chisel tips of the chisels 10 initially pass through the light plane.

(38) They then throw shadows that can be detected by the camera 40. The chisels 10 are conveyed across the light plane over a certain rotation angle of the roller until they dip below the light plane again.

(39) A reference measurement can be performed with unworn chisels 10 and/or chisel holders 70. In this case, the time at which the chisel 10 passes through the light plane, an entry or exit, is detected and the associated rotation angle of the milling roller 35 is detected. After an operational use, a corresponding measurement is carried out on the worn or partially worn chisel 10. Due to the reduction in length, the chisel 10 breaks through the light plane later and dips below it earlier in comparison to an unworn system. The corresponding rotation angles of the milling roller 35 can then be determined as position values. The rotation angles are then compared to the rotation angles of the unworn system, such as reference values. It is then possible to calculate the wear state through subtraction using the differential angle or the differential angle is used directly as a wear criterion.

(40) During the milling process, the measurement system is suitably stowed in a corresponding protective device during phases in which no measurement is performed. When a second camera 40 is used, it is possible, for example, to perform a direct measurement of the height geometry without an additional light source.

(41) Alternatively, through appropriate positioning of a second camera, additional measurements of the contours can be performed, thus increasing the overall information density and increasing the probability of detecting asymmetrical wear states.

(42) Alternatively, the position of the chisel tip 11 and the position of the chisel head contour can also be detected in at least one step by other distance-measuring sensors, for example ultrasonic sensors, proximity switches.

(43) German Patent Reference 10 2008 045 470.2, filed 3 Sep. 2008, the priority document corresponding to this invention, to which a foreign priority benefit is claimed under Title 35, United States Code, Section 119, and its entire teachings are incorporated, by reference, into this specification.