WO1990002022A1

WO1990002022A1 - Device for monitoring rotating tools

Info

Publication number: WO1990002022A1
Application number: PCT/DE1988/000616
Authority: WO
Inventors: Philipp KÜHBAUCH
Original assignee: Kuehbauch Philipp
Priority date: 1988-08-18
Filing date: 1988-10-06
Publication date: 1990-03-08
Also published as: DE3828101A1; DE3828101C2; EP0429443A1

Abstract

A device for monitoring rotating tools, in particular twist drills, has at least a distance sensor that detects the distance between a plane of reference and the area of the tool that is acquired by the sensor, and a control unit that evaluates the output signal of the sensor. The device is characterized by the fact that the area of the rotating tool acquired by the sensor is large in comparison with typical deformation of the tool, so that the output signal of the sensor corresponds to an ''average'' distance.

Description

Device for monitoring rotating tools

Description

Technical field

The invention relates to a device for monitoring rotating tools and in particular twist drills.

State of the art

The effective monitoring of rotating tools, in particular of twist drills in multi-spindle drilling systems, is a problem that has so far not been solved in practice.

A wide variety of approaches have been taken in the scientific field, for example to carry out drill monitoring by force-torque or vibration analyzes. For this, reference is made to the review article by F. Quante and H. Fehrenbach in QZ-Quality Technology, year 1984, volume 3, pages 75-78 ^' .

As has been explained in more detail there, the hypothesis has hitherto been assumed that, in particular, asymmetrical cutting wear leads to strong deflections and vibrations of the drill. Accordingly, attempts have so far been made to detect asymmetrical cutting edge wear by force and / or vibration sensors.

In another approach to drilling monitoring, which is also addressed in the review article mentioned, the drill contour is recorded with a distance sensor and the detected contour is evaluated to detect damage or breakage of the drill.

In a similar way, Feutlinske proposed using a shadow sensor or an optical sensor working according to the tri-angulation principle to record the contour of a milling cutter and to draw conclusions about the state of the rotating tool from the contour measurement.

According to the invention, however, it has been recognized that the known proposals, in which the contour of the tool is detected by means of a distance sensor, are hardly usable in "rough use", particularly on industrial multi-spindle drilling systems:

For example, an optically operating distance sensor will become unusable or at least inaccurate relatively quickly due to drilling chips, drilling fluid or the like.

Also inductive or magnetic distance sensors, whose measuring spot allows the drill contour to be recorded, i.e. whose measuring spot typically has a diameter of less than 1 mm, fail in the harsh environmental conditions of an industrial multi-spindle drilling system.

The cause of this has been recognized to be that, in particular, "thin" drills, ie drills whose diameter is typically less than 6 mm, can bend comparatively strongly during operation without being damaged thereby. Due to such short-term deflections, however, the signal delivered by the "distance sensor" changes very strongly. It is therefore necessary to set the threshold on the basis of which, for example, a damaged ter drill is distinguished from a still usable drill, very insensitive, so as not to receive a signal indicating a damaged drill due to short-term deflections of the drill during operation, which may lead to the shutdown of the multi-spindle drilling system. However, this insensitive setting of the threshold means that certain damage to the drill, which can disrupt operation, cannot be detected.

Presentation of the invention

The invention is based on the object of specifying a device for monitoring rotating tools and in particular twist drills with which, for example on a multi-spindle drilling system, damage to the tool which necessitates replacement can be reliably detected.

A solution to this problem according to the invention is characterized by its developments in the claims.

Surprisingly, a solution to this problem is achieved by proceeding from a device according to the preamble of claim 1, that is to say a device working with a distance sensor, as described, for example, in the overview article mentioned in the introduction.

In contrast to the known devices according to the preamble of claim 1, the distance sensor is designed such that the area which the distance sensor detects or scans is large compared to typical changes in the shape of the tool. Typically, with a drill with a diameter of 6 mm, a measuring spot of the level sensor with a diameter of approx. 4 mm is used.

Such a distance sensor does not provide a signal which is directly related to the contour of the tool, since the measuring spot detects areas with a different distance from the reference surface of the distance sensor at any time due to the cross-sectional profile typical of a twist drill, for example.

Surprisingly, this output signal - which has no simple connection with the geometry of the rotating tool - can be used to detect the state of wear and, in particular, to detect drill fractures.

It is preferred if the device according to the invention generates the thresholds from the output signal of the distance sensor for a specific tool, for example used in a multi-spindle drilling system, on the basis of which the condition of the tool is evaluated.

For this purpose, according to claim 2, the distance sensor is arranged such that it detects it before, during and after the engagement due to the advance of the tool. The inventive method generates from the evaluation of the signal change frequency, the high-pass filtered signal change frequency and the signal change amplitude and / or the high-pass filtered signal change amplitude, but preferably from the correlation of the signal change frequency and the signal change amplitude (not filtered and / or high-pass filtered) Device evaluation thresholds, based on which the decision can be reliably made as to whether a tool is still in the system can remain or already has to be replaced:

Various strategies are possible, which will be briefly addressed in the following:

During the ongoing drilling cycle, the sensors first record the drill tip and then, one after the other, the areas of the drill helix between the drill tip and drill shank. The signals measured in the "pre-process phase, process phase and post-process phase" are correlated with one another and enable a statement to be made about the condition of the tool and a statement about the trend, i.e. the "normal tool wear". In addition, the immediate detection of tool damage is possible.

Brief description of the drawing

The invention is described in more detail below on the basis of exemplary embodiments with reference to the drawing, in which:

Fig. 1 shows schematically a device according to the invention, Fig. 2 shows the sensor measuring surface on a

Tool, Fig. 3a to 3c the signal processing or typical

4a and 4b a comparison of the sensor signals in the case of damaged and undamaged tools, FIGS. 5a and 5b the sensor signal and the high-pass filtered sensor signal in the event of tool breakage, FIGS. 6a and 6b the sensor signal and the high-pass filtered sensor signal in the event of tool breakage due to high 7, the high-pass filtered sensor signal before

Tool intervention, 8a and 8b the sensor signal and the high-pass filtered sensor signal when interference occurs,

9a and 9b, the sensor signal with undamaged and damaged tool,

10a to 10c a comparison of the high-pass filtered sensor signals in a series of successive tool interventions,

11a and 11b the frequency response of the high-pass filtered sensor signal during the tool engagement in a series of successive tool interventions,

12a and 12b show the sensor signal and the high-pass filtered sensor signal when machining problems occur.

Description of exemplary embodiments

FIG. 1 schematically shows a device according to the invention for monitoring rotating tools, which is integrated in a two-spindle drill head 1 with spindles 11 and 12.

On guide columns 13 and 14, a drill guide plate 15 is spring-mounted in a manner known per se, which also carries a catch bolt 16.

On the drill guide plate 15, each drill 17 or 18 is assigned radial displacement sensors 21, 22, 23, 24, which each have a signal which - as will be explained later - depends on an average weighted distance of the drill contour of a reference surface , in the direction of the coordinates x or y of the coordinate system shown in FIG. 1, that is to say perpendicular to the drill feed direction z. FIG. 2 explains the term “average weighted distance” introduced above. FIG. 2a shows a side view or a cross section through the tip of a typical twist drill. The size of the measurement spot of one of the radial displacement sensors 21 to 24 is also entered in FIG. 2a. As can be seen in FIG. 2a, the measuring spot has a diameter that is comparable to typical drill diameters. The output signal of the displacement sensor therefore does not correspond to the distance between the reference surface of the displacement sensor and a "point of the drill contour", as is the case with the known devices. The output signal of the displacement sensor, as used according to the invention, is rather dependent on the course of the drill contour within the measurement spot, as is shown in FIGS. 2b and 2c. Of course, the evaluation or the sensitivity of the displacement sensor is also included over its entire "scanning spot". For this reason, the sensor output signal does not correspond to the distance of a "point on the drill contour" from the displacement sensor, but rather to an average, weighted distance, the sensor output signal additionally also depending on the type of the displacement sensor and its displacement in the direction parallel to its scanning spot is dependent on the drill.

Displacement sensors that can be used for this purpose are available, for example, under the following names

M 61 EDDY PROBE (eddy current sensor) measuring spot 5 mm from Sientific Atlanta Inc. PO Box 23575 San Diego California 921230575 Ul sensor (eddy current sensor) measuring spot 0 4 mm

Micro Epsilon Messtechnik GmbH & Co.KG

Königsbergerstrasse 15

Box 90

D-8359 Ortenburg-Dorfbach

5SU sensor (eddy current sensor) measuring spot 0 2 mm

Kaman Instrumentation Corporation

Measurement Systems Group

P.O. box 7463

Colorado Springs CO 80933

Surprisingly, however, it has been found that it is possible with such displacement sensors to obtain more reliable and more accurate statements about possible confirmations of the tool than with known devices in which the sensor "detects the exact contour of the tool" - , is possible.

FIG. 3a again shows a drill, for example the drill 17 and the associated sensor 22. The output connection of the sensor 22 is connected to a preamplifier 30, the output connection of which is connected directly to an evaluation circuit, for example a commercially available microcomputer 31, and once via a High-pass filter 32 is applied to the evaluation circuit 31. The evaluation circuit 31, which - as already stated, can be a microcomputer, but can also be a corresponding analog circuit - evaluates, on the one hand, the signal alternating frequency and the signal amplitude of the (amplified) sensor output signal and, on the other hand, the high-pass filtered signal Alternating frequency and the high-pass filtered signal amplitude and links the evaluated signals in the manner explained below. Figure 3b shows a typical sensor signal. The time in seconds is plotted on the abscissa, while the sensor signal is plotted in arbitrary units on the ordinate.

FIG. 3c shows a typical high-pass filtered sensor signal. The time in seconds is plotted on the abscissa, while the high-pass filtered signal is plotted in arbitrary units on the ordinate.

3b and 3c show the time it takes the drill to complete a full revolution.

The high-pass filtered sensor signal shown in FIG. 3c can also be interpreted "clearly" as the vibration path of the drill. It is expressly pointed out, however, that this descriptive interpretation is not exactly correct due to the measuring spot, which is averaged over the contour of the drill.

Nevertheless, it is possible to determine exact statements about the condition of the drill from these averaged signals through different evaluations.

FIG. 4a shows the sensor signal for an undamaged tool before the tool engagement, while FIG. 4b shows the sensor signal for a damaged tool before the tool engagement. As can be seen in FIG. 4a, in the case of an undamaged tool, successive maxima or successive minima differ by a certain value, which is, however, comparatively small. In addition, it has the mean distance, ie the curve indicating the distance averaged over the drill contour has a comparatively "smooth" course.

However, as FIG. 4b shows, this is not the case if the tool is damaged, i. H. if - as shown in this case, the drill tip is broken.

FIGS. 5a and 5b show the sensor output signal and the high-pass filtered sensor output signal in the event of tool breakage due to low loads, i.e. H. if a damaged tool breaks. FIG. 5a shows that the change in the unfiltered sensor signal, which indicates an average weighted distance, is comparatively small. However, there is a clear change in the high-pass-filtered sensor output signal which can be interpreted as an "oscillation path". By generating or specifying the threshold shown in FIG. 5b, it can thus be determined whether a drill break occurs in particular as a result of "fatigue" or pre-damaged tools at low loads.

FIGS. 6a and 6b show the resulting signal that occurs when a tool breaks due to high loads. FIG. 6b shows that the high-pass filtered output signal is not particularly meaningful at high loads even when the tool is initially undamaged. In the non-high-pass filtered output signal, which is shown in FIG. 6a, the appearance of large extreme values (in this case minimum values) clearly shows that the tool is broken.

FIG. 7 shows that the occurrence of the tool engagement can also be determined from the high-pass filtered sensor signal which can be interpreted as an oscillation path. Before the tool intervention, the signal is typically characterized in that it has a high amplitude at a low frequency. In contrast, a high amplitude occurs at high frequency during the tool engagement.

FIGS. 8a and 8b show that it is possible to distinguish faults caused by environmental conditions from tool errors by correlating the two signals.

As an example of this, FIGS. 8a and 8b show the case where there are chips between the drill and the sensor. It is typical of the occurrence of chips, which - as a rule - have nothing to do with damage to the tool, is that extreme values occur simultaneously in both signals.

FIGS. 9a and 9b again show that tool damage, in this case damage to a cutting corner, by comparing successive extreme values, i.e. H. can be determined from successive maxima or from successive minima.

FIG. 9a shows that in the case of an undamaged tool, successive minima differ only slightly, the reference point in the figure being 75 μm. However, it should be expressly pointed out that this drill output signal corresponding to a certain displacement does not correspond to an actual path difference due to the averaging over the contour.

If the cutting corner is damaged, consecutive minima differ considerably. As a side note, it should be pointed out that the sensor in FIG. 9 is adjusted so that the "signal maxima are saturated" so that these are not relevant.

FIGS. 10a to 10c show the differences between the high-pass filtered sensor signal during a tool intervention in a series of successive tool interventions. FIG. 10a shows the fourth hole, FIG. 10b the fiftieth and FIG. 10c the three hundredth hole with the same tool. As can be seen from the figures, the high-pass filtered sensor signals differ considerably due to the increasing wear of the tool and can therefore be used to determine normal wear without direct damage to the tool.

FIG. 11a shows the frequency response of successive bores, namely FIG. 11a the frequency response during the sixty-fourth bore and FIG. 11b the frequency response during the two hundred and twenty-third bore.

It can be seen from the figures that the frequency responses - as long as the tool is not damaged, but only worn - are topologically the same, that is, they can also be used to determine a tool confirmation.

Finally, FIGS. 12a and 12b show the sensor signal and the high-pass filtered sensor signal when

Inclusion of material, ie when machining errors occur. These faults also distinguish characteristically from other faults and in particular from the signals occurring when the tools are damaged.

The invention has been evaluated above on the basis of typical signal profiles. It goes without saying that, on the basis of the above description, it is possible for the average person skilled in the art to find out, depending on the respective tool, the evaluation criteria which are decisive for the respective application. Of course, it is also possible to combine all the evaluations, as explained above by way of example, in one device.

Claims

Patent claims

1. Device for monitoring rotating tools and in particular twist drills, with at least one distance sensor, which determines the distance between a reference plane and the area of the tool detected by the sensor, and whose output signal evaluates a control unit, characterized in that the The area of the rotating tool detected by the sensor is large compared to typical changes in shape of the tool, so that the output signal of the sensor corresponds to an "averaged" distance.

2. Device according to claim 1, characterized in that the distance sensor is fixedly arranged such that it detects the tool before, during and after the engagement.

3. Apparatus according to claim 1 or 2, characterized in that the evaluation unit from the output signal of the sensor determines the signal change frequency.

. Device according to one of claims 1 to 3, characterized in that the evaluation unit determines the signal change amplitude from the output signal of the sensor.

5. Device according to one of claims 1 to 4, characterized in that the evaluation unit high-pass filters the output signal of the sensor and detects the signal change frequency from the high-pass filtered signal.

6. Device according to one of claims 1 to 5, characterized in that the evaluation unit high-pass filters the output signal of the sensor and determines the signal change amplitude from the high-pass filtered signal.

7. Device according to one of claims 1 to 6, characterized in that the evaluation unit from the signal received before the intervention generates thresholds for evaluating the signal received during the intervention or adapts already set thresholds.

8. Device according to one of claims 1 to 7, characterized in that the evaluation unit corrects the evaluations during the engagement of the rotating tool with the evaluations obtained outside the engagement.

9. Apparatus according to claim 7 or 8, characterized in that the evaluation unit evaluates an operating state as a "drill break" when at the same time the high-pass filtered signal change amplitude exceeds a first generated threshold during a time which is large compared to the rotation time of the drill and successive extreme values of the unfiltered signal change amplitude differ by a value that is greater than a second generated threshold.

10. The device according to claim 7 or 8, characterized in that the evaluation unit evaluates an operating state as an "external fault" and not as a "faulty tool" when the high-pass filtered Signal change amplitude only exceeds a first generated threshold during a time that is comparable to the rotation time of the drill, and at the same time successive extreme values of the unfiltered signal change amplitude differ by a value that is greater than a second generated threshold.

11. The device according to one of claims 1 to 10, characterized in that the evaluation unit stores the signal curves of the high-pass filtered signal change amplitudes during the intervention and compares the curve recorded at the beginning of a series of tool interventions with later curves.

12. Device according to one of claims 1 to 11, characterized in that the evaluation unit correlates the evaluations on the basis of the signal amplitude and the signal frequency.

13. The device according to one of claims 1 to 12, characterized in that the evaluation unit compares the various evaluated variables with each other.

14. Device according to one of claims 1 to 13, characterized in that the evaluation unit determines the various sizes during the intervention and tracks the change over a number of bores.

15. The apparatus according to claim 14, characterized in that the evaluation unit generates new barriers for the evaluation from the change in sizes over a number of holes.

16. The device according to one of claims 1 to 15, characterized in that the displacement sensors are mounted on a sensor carrier plate on the side facing the tool holder.

17. The apparatus according to claim 16, characterized in that the displacement sensors are displaceable in the radial direction.