JPS61117449A - Tool breakage detecting device - Google Patents

Abstract

PURPOSE:To detect the breakage of a tool securely without the influence of the size of a tool, a chip, other signals, etc., by providing AE sensors and signals processing means, a position decision means and a breakage decision means, etc. CONSTITUTION:The respective AE sensors 6A-6D detect AE signals from tools such as a drill 2a and an artificial breakage signal generator 6 and their outputs are supplied to AE signal processing parts 7A-7D. Those signals are amplified to a specific level and the signal of the breakage of a tool, etc., is detected and sent to a CPU 9. The storage means consisting of an ROM 10 and an RAM 11 stored with sensitivity information on the AE sensors 6A-6D corresponding to tools used by a numerical controller 3 is connected to the CPU 9 and an event timer 12 stored with the time when breakage signals are obtained from the processing parts 7A-7D is connected. Then, the CPU 9 calculates the position where a breakage signal is obtained on the basis of those signals and also outputs the breakage signal through a display part 14. Thus, the breakage of the tool is detected with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention is directed to the acoustic emission (acoustic emission) that occurs during cutting and tool breakage in machine tools.
(hereinafter referred to as AE) for monitoring.

This invention relates to a tool breakage detection device that automatically detects tool breakage.

[Summary of the invention]

The tool breakage detection device according to the present invention arranges at least three AE sensors on a workpiece at a predetermined interval,
The position of the signal source is calculated based on the time difference between the breakage detection signals obtained from each AH sensor. By comparing the position of the tool at the moment when the breakage detection signal was obtained and the position of the signal source, it is determined that the tool is truly broken only when the breakage detection signal is obtained from the position where the tool is present. I am trying to output a signal. The reliability of tool breakage is improved by eliminating signals similar to the AE multiplied signal at the time of tool breakage that occur from locations where the tool does not exist.

[Prior art and its problems]

When cutting a workpiece using a tool in a machine tool, the tool may break for some reason or become clogged with chips, resulting in abnormal cutting. With the recent progress in factory automation, there is a strong demand for automatic detection of tool breakage and abnormal cutting. As a method for detecting tool breakage in machine tools, a device has been proposed that installs an AE sensor near the tool or workpiece of the machine tool and detects tool breakage based on the AE multiplied signal obtained from the AE sensor. There is.

However, conventional tool breakage detection devices detect tool breakage based on the average amplitude of the signal obtained from the AE sensor or a specific frequency. There was a problem in that reliability was low because it was not possible to sufficiently separate signals generated from chips, electrical noise associated with opening and closing of solenoids, and impact noise when an object came into contact with a workpiece.

[Purpose of the invention]

The present invention was made in view of the problems of conventional tool breakage detection devices, and is capable of reliably detecting tool breakage without being affected by tool size, chips, other signals, etc. The purpose is to provide a highly reliable tool breakage detection device.

[Structure and effects of the invention]

The present invention is a tool breakage detection device that detects breakage based on an AE multiplied signal obtained when a tool of a machine tool breaks. A plurality of signal processing means each outputting a tool breakage detection signal based on the AE multiplied signal obtained from the sensor, and a position determining means that determines the position of the breakage signal source based on the time difference between the breakage signals obtained from each signal processing means. The tool position when a breakage detection signal is obtained from the signal processing means is compared with the position determined by the position determining means, and a breakage signal is output when a breakage signal is obtained from the tool position. The present invention is characterized by comprising a determining means.

According to the present invention having such characteristics, the position of the signal source is specified on the workpiece from the difference in arrival time of the AE multiplied signal to each AE sensor using a plurality of AE sensors, and is compared with the position of the tool. ing. In this way, even if a signal extremely similar to a broken signal is obtained from a location other than the location where the tool is present, it will not be mistakenly determined that the tool is broken. Therefore, only the AE multiplied signal generated from the position where the tool exists can be used as the tool breakage signal, making it possible to significantly improve the reliability of tool breakage. Such a tool breakage detection method according to the present invention can be set as one AND condition independent of the detection of tool breakage based on the frequency characteristics and time domain characteristics of the breakage signal, and it is possible to combine each of these conditions. This makes it possible to further improve the reliability of tool breakage detection.

[Explanation of Examples]

FIG. 1 is a block diagram showing an embodiment of a tool breakage detection device according to the present invention. This embodiment shows a tool breakage detection device attached to a drilling machine controlled using a numerical control device, in which a workpiece 1 is fixed on the base of the drilling machine, and a drill 2 is inserted from the top of the workpiece 1. The workpiece I is opened by rotating and pushing down at a predetermined speed. The operation of the drill 2 is controlled by a numerical control device 3. It is assumed that the drill used here is automatically replaced by an automatic tool changer (not shown). Now, before cutting the workpiece 1, a pseudo-breakage signal generator 4 made of the same material as the AE sensor (PZT, etc.) is installed in advance at the position where the drill bit comes into contact with the upper part of the workpiece 1.The drive circuit 5 receives this pseudo-breakage signal. It drives the generator 4, and is configured in advance to oscillate a drive waveform that is similar to and has the same power spectrum distribution as the AE output waveform when the tool breaks, and its amplitude level is given from the outside. As shown in Fig. 1, four AE sensors 6A, 6B, 6G, and 6D are arranged at the vertices of a square on the top of the workpiece 1, and the lengths between 6A and 6B and between 6C and 6D are respectively 2C. do.

Each AE sensor 6A to 6D detects AE from a tool such as drill 2.
It is a wideband AE sensor that detects the AE multiplied signal from the multiplied signal pseudo-breakage signal generator 4, and its output is sent to each AE signal processing section. Given to A, 7B, 7C, 7D.

AE signal processing units 78-7D are AE sensors 6A-6D, respectively.
The input/output interface 8 amplifies the signal from the
It is provided to a central processing unit (hereinafter referred to as CPU) 9 via the CPU. The CPU 9 has a read-only memory (hereinafter referred to as ROM) 1 that stores the system control program.
0 and a random access memory (hereinafter referred to as RAM) 11 containing sensitivity information of the AE sensor corresponding to the tool used by this numerical control device 3 are connected, and each AE signal processing unit 7A to 7D outputs a breakage signal. An event timer 12 is connected to store the time at which the event is obtained. The CPU 9 further includes, via an input/output interface 13, a display section 14 that displays the AE signal level during cutting, abnormal cutting or breakage of the tool, and input keys that set the tool number, type, and standard AE sensor sensitivity. 15 are connected. Further, a numerical control device 3 is connected via a signal transmission line 16. As described later, the CPU 9 calculates the position where the breakage signal is given based on the signals of the four AE signal processing units 7A to 7D, and displays the breakage signal on the display unit 14 when the position is a position where a tool exists. It outputs more.

Next, FIG. 2 is a block diagram showing the detailed configuration of the AE signal processing section 7A. The other AE signal processing sections 7B to 7D also have the same configuration. Now, in this figure, the output of the AE sensor 6A is first given to the analog switch 20. The analog switch 20 is a switch that connects and disconnects analog signals based on a control signal from the CPU 9, and its output end is connected to a variable gain amplifier 21. The amplifier 21 is a variable gain amplifier whose amplification factor can be set based on control input from the CPU 9, and provides its output to the CPU 9 via two bandpass filters 22, 23 and the input/output interface 8. It is. Bandpass filter 22 has a center frequency of 300KHz
, bandpass filter 23 is a filter with a center frequency of 50 KHz, and transmits only signals near the respective center frequencies to the next-stage detectors 24 and 25. The detectors 24 and 25 each detect the input signal and obtain an output according to the amplitude, and the output of the detector 24 is sent to the differentiator 26 and
The outputs of 4.25 are given to comparators 27, respectively. These bandpass filters 22, 23, detectors 24, 25, and comparator 27 form a frequency identification means for identifying the AE multiplied signal at the time of breakage. Differentiating circuit 26 transmits only steep changes in the input signal to level determiner 28 at the next stage. The level determiner 28 compares the input signal with a predetermined reference level, and if the input signal is large, transmits the output to the breakage detection circuit 29 and the abnormal cutting detection circuit 30.

Also, the comparator 27 compares the outputs of the detectors 24 and 25, and sends the output to the breakage detection circuit 2 only when the output of the detector 24 is large.
Tell 9. The breakage detection circuit 29 is a logic circuit that performs the logical product of these inputs to detect tool breakage, and transmits a detection signal to the CPU 9 via the input/output interface 8. Further, the abnormal cutting detection circuit 30 detects abnormal cutting based on the output of the level determiner 28 and transmits the detected abnormal cutting to the CPU 9 via the input/output interface 8.

Next, the operation of this embodiment will be explained. First, enter the oysters - 1
When the data of the tool used by the numerical control device 3 is input from 4 to the CPU 9, the CPU 9 sends a reference input to the drive rotation 5, and at that time, variable amplification is performed based on the signal level obtained from each AE sensor 6A to 6D. Rate increase @ vessel 2
The amplification factor of j is adjusted and the sensitivity of all AE sensors 6A to 6D is set to the optimum value.

Next, the process for identifying the signal source of this embodiment will be explained with reference to the flowchart of FIG. In this flowchart, the numbers indicated using leader lines are CPU
This is the 9th operational step.

First, when the operation is started, the value V of the sound velocity at that time is read from the input key 15 in step 40. stop.

Then, in step 41, the operation of the event marker 12 connected to the CPU 9 is started. Then routine 4
Proceed to steps 2 to 45 and receive AE from each AE signal processing unit 7A to 7D.
Signal processing of the outputs of the sensors 6A to 6D is performed. This signal processing is executed by the hardware of each of the signal processing units 7A to 7D shown in FIG. 2, and when a breakage detection signal is detected, it is transmitted to the CPU 9 via the input/output interface 8. Therefore, the CPU 9 checks whether or not a breakage detection signal is given from each AE signal processing unit 7A to 7D (steps 46 to 49), and if a breakage signal is detected from a certain AE signal processing unit, it indicates that the work is on the same workpiece. Breakage signals are also detected from the signal processing units of other AE sensors with a predetermined time difference. Therefore, when a breakage signal is detected, in steps 50 to 53, the timer values Ta and Tb of the event timer 12 at the time of detection are determined.

Tc and Td are each stored in RAM II. Then, proceed to step 54 and select the AE signal processing section? A, 7B and 7C and 7
The timer values obtained from D are rearranged in order of earliest.

Each of the AE sensors 6A to 6D detects signals from the same signal source with a slight time difference, and at this time, a hyperbola with a constant distance from the AE sensor is determined due to the arrival time difference from the signal source as shown in the figure. The intersection of these hyperbolas is the signal source P. Therefore, the distance differences ΔLl and ΔL2 are calculated from the following equations.

ΔLl = ΔT1-V = l Ta -Tb l
V------=(1) ΔL2 = ΔT2・V = l
Tc -Td l v---------(2) Now, the fourth
In the figure, each AE sensor 6A to 6D is connected to the origin O.
at symmetrical positions, i.e. 6A (0°c), 6B (0, -
c), 6C (c, 0), and 6D (-c, 0), the AE sensor 6A.

The hyperbolas S1 and S2 with 6B as the focal point are determined by the following equations.

However, ΔLl=2a,,b,=F? = Similarly, hyperbola S3. with the AE sensors 6G and 6D as focal points. S4 is determined by the following equation.

However, ΔL2-2az, bz=i Therefore, equation f3), (From simultaneous equations 41, Xs = ±
a+bxn) Finished Ys evening ± a, b, Hama 7 stones, however, d = b, b, -a, a3≠0. Here, the signal source P is located under the following conditions than the timer value.

When Ta<Tb, the first. 2nd quadrant Ta > Tb 3rd and 4th quadrants Tc < Td 1st and 4th quadrants Tc > Td 2.3rd quadrant From this condition, it is possible to identify the signal source P (Xs, Ys) at one point. can. (If jlJ, Ta < Tb, Tc
<Td, the signal source P is in the first quadrant as shown in FIG. In this way, in step 56, the position of the signal source P, that is, Xs, Ys, is calculated based on the above equation. Then, the position of this signal #P and any of the AE sensors 6A~
The time TO when the signal actually occurs is calculated based on the breakage time Ta=Td obtained in step 6D (step 57). Next, in step 58, data on the signal generation time To is sent to the numerical control device 3, and the tool coordinates Po(
Xo.

Yo ) data is received. Then, the distance S between the tool coordinate PO and the signal source P (Xs, Ys) is calculated based on the following equation (step 59).

S = (Xo −Xs)” + (Yo −Ys
)''---(5) The process further advances to step 60 to determine whether the distance S between the tool and the signal source is less than or equal to the sum of the tool diameter and the allowable measurement error E. If the distance S is greater than this value, it is considered that the AE multiplied signal was generated from a location other than the location where the tool existed, so even if a breakage signal is given from each AE signal processing unit 7A to 7D, it is determined that it is an incorrect signal. Therefore, it is not determined that the tool is broken, and the process returns to step 41 to repeat the same process. However, if the distance S is less than or equal to the sum of the tool diameter and the measurement error E in step 6o, the range where the tool existed is determined. Since a breakage signal is obtained from inside, it is determined that the tool is broken.Therefore, the process proceeds to step 61, where the display section 14 displays the tool breakage and the operation is stopped.

Next, detection of a broken signal in each AE signal processing section in routines 42 to 45 will be explained based on the AE signal processing section 7A. Now AE double signal analog switch 2 from AE sensor 6A
0, it is amplified by amplifier 21 and provided to bandpass filters 22 and 23. Now, the AE given by the AE sensor 6A during normal cutting
The distribution of the doubled signal power spectrum is concentrated around a frequency of 50 KHz, as shown by the curve in FIG. 5, and is monotonically attenuated in the higher frequency range.

Furthermore, as is known from many experiments, the distribution of the power spectrum when a tool breaks is represented by curve a in FIG. 5, and it has been revealed that it has a peak around a frequency of 300 KHz. This is considered to be because the signal source is not caused by mechanical vibration, but a phenomenon unique to ultrasonic waves of 1i occurs during non-plastic fracture of the tool. Therefore, the two band-pass filters 22 and 23 reduce the AE near each frequency component.
By extracting the doubled signal, detecting it by the detectors 24 and 25, and comparing the output levels, it is possible to clearly distinguish between normal conditions and tool breakage conditions. In other words, during normal cutting, the AE multiplied signal power at a frequency of around 50 KHz is
It is larger than the power near 00 K llz, and when the tool breaks, the power near 300 K Hz becomes a frequency of 50 KH.
This is because it is larger than the power near z. The comparator 27 compares these outputs and provides a signal to the breakage detection circuit 29 only when the tool breaks.

On the other hand, a signal similar to the power spectrum distribution shown by curve a in FIG. 5 may be generated due to contact or friction between the chips and the tool workpiece generated during the machining process. In this case, even if the center frequency and Q value of the band-pass filters 22 and 23, the threshold level of the comparator 27, etc. are set appropriately, the signal due to contact and friction between chips and the tool or workpiece cannot be used as the tool breakage signal. may be mistakenly judged. Therefore, in the present invention, attention is also paid to the waveform in the time domain of the AE multiplied signal that is observed when a tool breaks, and these signals are separated.

That is, the AE signal waveform obtained when the tool breaks is shown in Figure 6 (a
), the signal has a sharp rise at the time of breakage, while the AE multiplied signal generated by contact and friction between the chip and the tool or workpiece does not show a sharp rise and remains for a specified period of time, as shown in Figure 6(b). The signal has a continuous waveform.

Therefore, as shown in the block diagram of FIG. 2, the output of the detector 24 is applied to a differentiating circuit 26, and only steep signals such as those caused by breakage are separated and applied to a level determiner 28. Level determiner 28
gives an output to the breakage detection circuit 29 and the abnormal cutting detection circuit 30 when the input signal is large.

The breakage detection circuit 29 detects tool breakage based on the AND of the comparator 27 and the level determiner 28, and transmits a breakage detection signal to the CPU 9 from the input/output interface 8 when the tool breaks. Based on this, the CPU 9 stores the time Ta at the time of breakage and performs the signal processing described above.

As described above, in this embodiment, each AE signal processing section outputs a breakage detection signal by the AND of the AE multiplied signal frequency detection and the rising signal detection in the time domain, and calculates the breakage detection signal according to the breakage detection time given from each E sensor signal processing section. Based on this, the signal source of the breakage signal is calculated, and if the position is equal to the position where the tool was present, it is determined that the tool is broken. Therefore, there is no possibility that a breakage signal will be output based on an erroneous signal, and tool breakage can be detected with extremely high accuracy.

In this embodiment, the signal source of the breakage signal is calculated using four AE sensors and an AE signal processing section, but three AE sensors are arranged at each vertex of a triangle, and one of the three AE sensors is arranged at one vertex. It is also possible to calculate the signal source from two hyperbolas using the AE sensor as a common sensor.

Furthermore, in this embodiment, the position of the tool breakage signal is detected in addition to the detection of breakage in the frequency domain and the time domain, but the position of the tool breakage signal is detected only in either the frequency domain or the time domain. It is also possible to detect tool breakage in combination with detection.

Furthermore, although this embodiment applies this breakage signal detection device to a pole machine using a numerical control device, the present invention is also applicable to other machine tools used in combination with a numerical control device, such as a lathe, a milling cutter, etc. It is also possible to apply it to various machine tools and large-scale machining centers.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the tool breakage detection device according to the present invention, FIG. 2 is a block diagram showing the detailed configuration of the AE signal processing section, and FIG. 3 is a block diagram showing the detailed configuration of the AE signal processing section, and FIG. 3 is a block diagram showing an embodiment of the tool breakage detection device according to the present invention. Fig. 4 is a graph showing the four AE sensors and the signal source P of hyperbola and tool breakage, Fig. 5 is a drawing showing the AE multiplied signal power spectrum obtained from the AE sensor, Fig. 6 ( Fig. 6(a) shows the AE signal waveform obtained when the tool breaks, and Fig. 6(a) shows the AE signal waveform obtained when chips are generated. 1--------Work 2--Drill 3--
----One numerical controller 4---Pseudo breakage signal generator 5---Drive circuit 6A, 6B,
6C, 6D----1・-AE sensor 7 A,
7 B, 7 C,? D--------A E signal processing ff! 8.12・---1-・Input/output interface 9-------CPU 10------R
OM 11------RAM 12--i
-Event timer 14-...-Display section 15--
・−・Input key 20−・−−−−−Analog switch
21---Variable gain amplifier 22゜23--
−・Band pass filter 24.25・・−・−Detector 26−−−−−−One differential circuit 27−−−−−
・=Comparator 28−・−Level judger 29−・−・Breakage detection circuit Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Yoshiki Okamoto (and one other person) Fig. 5 100K 200K 300K 400K H7
Figure 6 (a3 Figure 6 (b)

Claims (5)

[Claims] (1) In a tool breakage detection device that detects breakage based on an AE signal obtained when a tool of a machine tool breaks, at least three
a plurality of signal processing means each outputting a tool breakage detection signal based on the AE signal obtained from each of the AE sensors; and a plurality of signal processing means each outputting a breakage detection signal based on a time difference between the breakage signals obtained from each of the signal processing means a position determining means for determining the position of the tool, and comparing the position of the tool when the breakage detection signal is obtained from the signal processing means with the position determined by the position determining means, and detects a breakage signal from the position of the tool. A tool breakage detection device comprising: a breakage determination unit that outputs a breakage signal when a breakage signal is obtained. (2) Each of the plurality of signal processing means has a frequency identification means, and outputs a breakage detection signal when an AE signal having a frequency component that has a strong correlation with the frequency component of the AE signal obtained at the time of tool breakage is given. A tool breakage detection device according to claim 1, wherein the tool breakage detection device is characterized in that: (3) Each of the plurality of signal processing means includes a rising signal detecting means that outputs a breakage detection signal when a rapidly rising signal is applied from the AE sensor. The tool breakage detection device described. (4) The plurality of signal processing means include frequency identification means that outputs an output when an AE signal having a frequency component that has a strong correlation with the frequency component of the AE signal obtained when the tool breaks; The tool breakage detection device according to claim 1, wherein the tool breakage detection signal is output based on the AND output of the rising signal detection means which outputs an output when a rising signal is given. . (5) The tool breakage detection device according to claim 1, wherein the AE sensors are four AE sensors arranged at each vertex of a square on the workpiece.