DE3828101A1 - DEVICE FOR MONITORING ROTATING TOOLS - Google Patents

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

The invention relates to a device for over monitoring of rotating tools and in particular of Twist drills.

The effective monitoring of rotating tools special of twist drills in multi-spindle drilling machines a problem that has not yet been solved in practice.

In the scientific field there are a wide variety Approaches have been undertaken, for example, by a drill monitoring by force-torque or vibration analysis perform. Please refer to the review article by F. Quante and H. Fehrenbach in QZ quality technology, year gang 1984, Issue 3, pages 75-78.

The Hypo thesis that especially asymmetrical Cutting edge wear due to strong deflections and vibrations conditions of the drill. Accordingly, so far has been sought, asymmetrical cutting edge wear by force and / or vibration sensors.

Another approach to drilling monitoring, the one if mentioned in the review article mentioned, the drill contour is recorded with a distance sensor and the detected contour to detect damage or breakage of the drill is evaluated.

Similarly, Feutlinske suggested using a shadow sensor or one based on the tri-angulation Principle working optical sensor the contour of a  Cutter and back from the contour measurement conclude about the condition of the rotating tool pull.

According to the invention, however, it has been recognized that the known suggestions, where using a distance sensor the contour of the tool is detected in "rough use" especially on industrial multi-spindle drilling systems are hardly usable:

For example, an optically working distance sensor relatively quickly by drilling chips, drilling fluid or the like. become unusable or at least inaccurate.

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

It has been recognized as the cause of this that in particular "thin" drills, i.e. Drills whose diameter is more typical is less than 6 mm during operation can deflect comparatively strongly without them would be damaged. Through such short-term Deflections changes that of the "distance sensor" ge delivered signal very strong. Therefore it is necessary the threshold on the basis of which, for example, a damaged The drill is differentiated from a drill that is still usable will set very insensitive so as not to go through short-term deflections of the drill during operation a signal indicating a damaged drill bit, the under certain circumstances to switch off the multi-spindle drilling system leads to get. This insensitive threshold firm  but leads to certain damage to the Drill that can disrupt the operation is not recognized can be.

The invention has for its object a device for monitoring rotating tools and in particular to specify those of twist drills with which, for example reliable damage to a multi-spindle drilling machine of the tool that requires replacement make, can be recognized.

An inventive solution to this problem is with their Developments characterized in the claims.

Surprisingly, this task is solved by that continues from a device according to the Ober Concept of claim 1, that is, from one with one Distance sensor working device is assumed as for example in the overview mentioned in the introduction item is described.

In contrast to the known devices according to the The preamble of claim 1 is the distance sensor but designed so that the area covered by the distance sensor detects or scans large against typical shapes changes of the tool. Typically, one Drill with a diameter of 6 mm a measuring spot from Ab use a level sensor with a diameter of approx. 4 mm det.

Such a distance sensor does not deliver a signal that in a direct connection with the contour of the tool stands, because the measuring spot for example for a twist drill typical cross-sectional profile for each  Time areas with a different distance from the reference surface of the distance sensor.

Surprisingly, this cannot be done - in a simple way Relation to the geometry of the rotating tool standing - output signal for recognizing the wear status and in particular to detect drill breaks use.

It is preferred if the according to the invention direction from the output signal of the distance sensor for a specific one, for example in a multi-spindle drilling plant used tool that generates thresholds, based on which the condition of the tool is assessed.

For this purpose, the distance sensor is fixed according to claim 2 arranged such that it is due to the advance of the Tool this before, during and after the procedure sums up. 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 correction the signal change frequency and the signal change amplitude (not filtered and / or high pass filtered) the device according to the invention generates evaluation thresholds on the basis of which the decision can be made reliably can be met whether a tool is still in the system can remain or must already be replaced.

The invention is based on execution examples with reference to the drawing wrote in the show:  

Fig. 1 shows schematically an apparatus according to the invention,

Fig. 2 is an illustration of the sensor measuring surface on a tool,

FIGS. 3a to 3c, the signal processing and typical sensor signals,

Fig. 4a and 4b, a comparison of the sensor signals with damaged and undamaged tool,

FIGS. 5a and 5b, the sensor signal and the filtered sensor signal when hochpaßge tool breakage,

Figs. 6a and 6b the sensor signal and the filtered sensor signal when hochpaßge tool breakage due to high load,

Fig. 7, the high-pass filtered sensor signal before the tool engagement,

Fig. 8a and 8b the sensor signal and the hochpaßge filtered sensor signal when faults occur,

Fig. 9a and 9b, the sensor signal at an undamaged and damaged tool,

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

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

Fig sensor signal and the sensor signal hochpaßgefil shouldered coagulation disorders. 12a and 12b in the occurrence of Zerspa.

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

In a manner known per se, a drill guide plate 15 is spring-mounted on guide columns 13 and 14 and 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, Determine in the direction of the coordinates x and 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. In Fig. 2a is a side view and a cross-section through the tip of a typical twist drill. The size of the measuring spot of one of the radial displacement sensors 21 to 24 is also entered in FIG. 2a. As can be seen from Fig. 2a, the measuring spot has a diameter which is comparable to typical drill diameters. The output signal of the displacement sensor thus 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 measuring spot, as 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 to an average, weighted distance, the sensor output signal additionally relative to the type of the displacement sensor and its displacement in the direction parallel to its scanning spot depends on the drill.

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

M 61 EDDY PROBE (eddy current sensor) ⌀ 5 mm from Sientific Atlanta Inc. PO Box 23575 San Diego California 921230575
U1 sensor (eddy current sensor) ⌀ 4 mm from Micro Epsilon Messtechnik GmbH & Co.KG Königsbergerstrasse 15 Postfach 90 D-8359 Ortenburg-Dorfbach
5SU sensor (eddy current sensor) ⌀ 2 mm from Kaman Instrumentation Corporation Measurement Systems Group PO box 7463 Colorado Springs CO 80933.

Surprisingly, however, it has been found that it is possible with such displacement sensors, more reliable and more precise statements about possible confirmations of the Get tool than this with known Vorrich in which the sensor "exactly the contour of the work stuff recorded ", is possible.  

Fig. 3a shows again a drill, for example, the drill bit 17 and associated sensor 22. The output connection of the sensor 22 is connected to a preamplifier 30 , the output connection of which is applied directly to an evaluation circuit, for example a commercially available microcomputer 31 and once via a high-pass filter 32 to the evaluation circuit 31 . The evaluation circuit 31 , which - as already stated, a microcomputer, but can also be a corresponding analog circuit - evaluates the signal alternating frequency and the signal amplitude of the (amplified) sensor output signal and the high-pass filtered signal alternating frequency and the high-pass filtered signal amplitude and links the evaluated signals in the manner explained below.

FIG. 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.

Further, 3b and 3c the time is shown in Figs. Is indicative net required for 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 means the contour of the drill.

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

Fig. 4A shows the sensor signal at an undamaged tool before the tool engagement, while Fig. 4b shows the sensor signal with damaged tool before the tool engagement. As can be seen in FIG. 4a, the underside of the following maxima or successive minima differs by a certain value in the case of an undamaged tool, but this is comparatively small. In addition, the curve indicating the mean distance, ie 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, ie if - as shown in this case - the drill tip is broken.

Fig. 5a and 5b show the sensor output signal and the high pass filtered sensor output signal in Tool breakage due to low load, ie at break of a vorbe damaged tool. Fig. 5a can be seen that the change of the non-filtered sensor signal indicative of an average weighted distance is comparatively small. However, there is a clear change in the highly 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 damaged tool at low load.

Fig. 6a and 6b show the resulting signal, which occurs due to high load in a broken tool. Fig. 6b shows that the high-pass filtered output signal is not particularly meaningful at high load even when the tool is initially undamaged. In the non-high-pass filter 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 tool intervention can also be determined from the high-pass filtered sensor signal which can be interpreted as an oscillation path. Before the tool intervenes, the signal is typically characterized in that it has a high amplitude at a low frequency. In contrast, a high amplitude at high frequency occurs during the tool engagement.

Figs. 8a and 8b show that it is possible to distinguish errors by the correlation of the two signals disorders, which are caused by environmental conditions, of tools.

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 for the occurrence of chips, which - as a rule - have nothing to do with damage to the tool, that extreme values occur simultaneously in both signals.

Figs. 9a and 9b show again that Werkzeugbe damage, in this case, damage to a cutting corner, can be determined by comparison of successive extreme values, ie of successive maxima or successive minima.

Fig. 9a shows that in the case of an undamaged tool, consecutive minima differ only slightly, as a reference point in the figure are 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, however, differ consecutive minima significantly.

As a side note, it should be noted that the sensor in FIG. 9 is adjusted so that the "signal maxima are saturated", so that no meaning is given to them.

FIGS. 10a to 10c show the differences between the high-pass filtered sensor signal during a work-producing procedure in a series of successive tool operations. In Fig. 10a is the fourth hole, in Fig. 10b the fiftieth and Fig. 10c is the three hundredth hole with the same tool Darge. 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 aufeinan also bores of the following, namely Fig. 11a the frequency response during the sixty-fourth bore and Fig. 11b the frequency response during the zweihundertdreiundzwanzigsten bore.

The figures show that the frequency responses - as long as the tool is not damaged but only used abge - are topologically the same, so they can also be used to determine a tool confirmation.

Finally, FIGS. 12a and 12b show the sensor signal or the high-pass filtered sensor signal when material inclusion occurs, ie when machining problems occur.

These disorders also differ from other errors and especially those of damaged ones Signals occurring with tools.

The invention is based on typical signal progress has been assessed. It goes without saying that it is possible for the average specialist, based on the above description depends on the respective Tool to find out the evaluation criteria for the respective application are decisive. Yourself understandable, it is also possible for all reviewers tions, as exemplified above are united in one device.

Claims (17)

1. A device for monitoring rotating tools and in particular twist drills, with at least one distance sensor which detects 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 sensor detected area of the rotating tool is large compared to typical shape changes of the tool, so that the output signal of the sensor corresponds to a "mean" distance. 2. Device according to claim 1, characterized in that the distance sensor fixed such is arranged that the tool before, during and after the intervention detected. 3. Device according to claim 1 or 2, characterized in that the evaluation unit from the Output signal of the sensor the signal change frequency averages. 4. Device according to one of claims 1 to 3, characterized in that the evaluation unit from the Output signal of the sensor the signal change amplitude determined. 5. Device according to one of claims 1 to 4, characterized in that the evaluation unit the Aus output signal of the sensor high-pass filters and out of the high pass-filtered signal to determine the signal change frequency telt. 6. Device according to one of claims 1 to 5, characterized in that the evaluation unit the Aus output signal of the sensor high-pass filters and out of the high pass-filtered signal to determine the signal change amplitude telt. 7. Device according to one of claims 1 to 6, characterized in that the evaluation unit from the signal received before the intervention thresholds for the Evaluation of the signal received during the procedure generates or adjusts thresholds that have already been set.   8. Device according to one of claims 1 to 7, characterized in that the evaluation unit the evaluator during the engagement of the rotating tool correct the ratings received outside of the procedure liert. 9. The device according to claim 7 or 8, characterized in that the evaluation unit a Operating condition rated as "drill break", if the same the high-pass filtered signal change amplitude one first generated threshold during a time that is large against the rotation time of the drill and not consecutive extreme values of the filtered signal change amplitude by a value below divide that is greater than a second generated threshold is. 10. The device according to claim 7 or 8, characterized in that the evaluation unit a Operating status as "external fault" and not as "feh learner's tool "rated when the high pass filtered Signal change amplitude a first generated threshold only during a time comparable to that Revolution time of the drill is, exceeds and itself at the same time successive extreme values of the filtered signal change amplitude by a value below divide that is greater than a second generated threshold is. 11. The device according to one of claims 1 to 10, characterized in that the evaluation unit the Sig waveforms of the high-pass filtered signal change amplitude  who saves during the procedure and the one at the beginning a series of tool interventions recorded compared with later courses. 12. The device according to one of claims 1 to 11, characterized in that the evaluation unit the evaluator due to the signal amplitude and the signal frequency correlated. 13. The device according to one of claims 1 to 12, characterized in that the evaluation unit ver different valued sizes compared. 14. The device according to one of claims 1 to 13, characterized in that the evaluation unit ver different sizes determined during the procedure and the Change tracked over a number of holes. 15. The apparatus according to claim 14, characterized in that the evaluation unit from the Resizing over a number of new holes Barriers generated for the evaluation. 16. The device according to one of claims 1 to 15, characterized in that the displacement sensors on a Sensor carrier plate on the tool holder facing side are attached. 17. The apparatus of claim 16, characterized in that the displacement sensors in radial Direction can be shifted.