JPS61105462A - Tool breakage detecting device - Google Patents

Abstract

PURPOSE:To easily set the sensitivity of an AE (acoustic emission) sensor without depending upon the shape, etc., of a work by providing the tool fitting part of a machine tool with a pseudo AE signal generating means and the tool support part with the AE sensor. CONSTITUTION:The pseudo AE signal generator 4 is fitted at the drill fitting position of a drill support part 3 before the work 1 is cut. The generator 4 generates a pseudo AE signal which is similar to an AE output waveform in the breakage of a tool and has the same power spectrum distribution. Further, the AE sensor 5 is provided on the flank of the support part 3 to detect an AE signal from a tool such as a drill and an AE signal from the generator 4 over a wide range. Then, a means which discriminates the AE signal in the breakage is composed of BPFs 9 and 10, detectors 12 and 13, and a comparator 15. Further, a breakage detecting circuit 18 detects the breakage of the tool and an abnormal cutting detecting circuit 19 detects abnormal cutting on the basis of the output of a level deciding device 16 and reports that to the outside through an output circuit 21.

Description

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

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

[Summary of the invention]

The present invention has a mounting portion having a shape corresponding to the tool, and a pseudo AE signal generating means that generates a pseudo AE multiplied signal including the AE multiplied signal frequency obtained at the time of breakage and at the same level as that at the time of breakage, is mounted on the tool of a machine tool. At the same time, an AE sensor is provided on the tool support. Pseudo AE installed in this way
If the AE sensor sensitivity is adjusted using a signal generating means, even when a tool breaks, the pseudo AE multiplied signal will be transmitted through the same transmission path, so the sensitivity adjustment of the AE sensor will be reliable, resulting in a highly reliable tool breakage detection device. It can be done.

[Prior art and its problems]

When a machine tool uses a tool to cut an object to be machined (hereinafter referred to as a workpiece), 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 such tool breakage and abnormal cutting. As a method for detecting breakage of tools in machine tools, conventional methods have been to
A device has been proposed that includes an E sensor and detects tool breakage based on an AE multiplied signal obtained from the E sensor.

However, according to the conventional tool breakage detection device, since the AE sensor is provided near the workpiece, the AE multiplied signal level varies greatly depending on the mounting position. Therefore, in conventional tool breakage detection devices, the sensitivity of the AE sensor is set to a predetermined standard value depending on the size of the tool, and the sensitivity of the AE sensor is set to a predetermined standard value depending on the size of the tool.

The reduction rate between AE sensors was corrected through trial and error.

However, (1) since the AE multiplied signal at the time of tool breakage can only be obtained when the AE sensor is broken, it is difficult to confirm the mounting position and mounting state of the AE sensor, making it difficult to reliably detect tool breakage. Furthermore, when changing the type of tool, for example, when changing the drill diameter or cutting conditions such as rotation speed, the AE multiplication signal level differs for each workpiece with a different shape and material, making adjustment difficult and difficult to use (reliable). The disadvantage was that he had problems with his sexuality.

[Purpose of the invention]

The present invention has been made in view of the problems of the conventional tool breakage detection device, and it is an object of the present invention to extremely easily set the sensitivity of the AE sensor without depending on the shape of the workpiece or the surface condition of the material. The purpose of the present invention is to provide an easy-to-use tool breakage detection device.

[Structure and effects of the invention]

The present invention is a tool breakage detection device that has an AE sensor installed in a tool support part of a machine tool and detects breakage based on an AE multiplied signal obtained when a tool breaks. a pseudo AE signal generating means which has a mounting part shaped corresponding to the shape of the tool and generates a pseudo AE multiplied signal at a predetermined level according to the type of tool, including the AE multiplied signal frequency obtained when the tool breaks; It is equipped with a display that displays the output level of the sensor, and a sensitivity setting means that sets the sensitivity of the AE sensor, and is based on a pseudo AE multiplied signal obtained when the pseudo AE signal generating means is attached to the tool mounting position. This feature is characterized in that the sensitivity of the AE sensor is set by

According to the present invention having such characteristics, the sensitivity of the AE sensor can be adjusted by generating a pseudo AE multiplied signal at the time of tool breakage using the pseudo (JJAE signal generating means) before machining with the machine tool. At this time, a pseudo AE signal generating means is provided in the tool mounting part of the machine tool, and an AE sensor is provided in the tool support part.
When a pseudo AE multiplied signal is generated by the E signal generating means, the pseudo AE multiplied signal is transmitted to the AE sensor through the same transmission path as the AE multiplied signal transmitted when the tool breaks. At this time, adjust the sensitivity of the A/E sensor so that an appropriate signal is received. In this way, the mounting position and sensitivity of the AE sensor can be optimally adjusted very easily.

If the tool is attached after completing the adjustment in this way, when the tool breaks, the pseudo AE multiplied signal is transmitted to the AE sensor through the same route. Therefore, it is not affected by the type, shape, surface condition, or material of the workpiece, and is not affected by AE multiplied signal attenuation from the tool to the AE sensor, greatly improving the reliability of tool breakage detection. This makes it possible to provide an easy-to-use tool breakage detection device.

[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 state in which the workpiece 1 is attached to a pole machine, and a workpiece 1 is fixed on a base 2 of the drilling machine, and a drill is attached to a drill support part 3 from above to provide an opening in the workpiece. Before cutting the workpiece, the pseudo AE signal generator 4 is attached to the drill attachment position of the drill support section 3. As described later, the pseudo AE signal generator 4 generates a pseudo AE signal that is similar to the AE output waveform when the tool breaks and has the same power spectrum distribution.
This generates a double signal. An AE sensor 5 is provided on the side surface of the drill support portion 3 as shown in the figure. The AE sensor 5 is a broadband AE sensor that detects an AE flaw signal from a tool such as a drill and an AE flaw signal from the pseudo AE signal generator 4, and its output is given to an analog switch 6. The analog switch 6 connects and disconnects the analog signal using an external output, and the output is given to the amplifier 7. The amplifier 7 is an amplifier whose amplification factor can be arbitrarily set by adjusting a variable resistor 8, and its output is sent to two band pass filters 9° 10 and a cutting level indicator 1.
1. The bandpass filter 9 has a center frequency of 300Kk.

The bandpass filter 10 is a filter with a center frequency of 50 KHz, and transmits only signals near the respective center frequencies to the next-stage detectors 12 and 13. The detectors 12 and 3 respectively detect the input signals and obtain an output according to the amplitude, and the output of the detector 12 is sent to the differentiating circuit 14,
．． The outputs of 13 are respectively given to comparators 515. These bandpass filters 9, 10, detectors 12, 13, and comparators 15 form frequency identification means for identifying the AE flaw signal at the time of breakage. Differentiator circuit 14 transmits only the steep changes in the input signal to the next level level judger 16 and the broken/abnormal level indicator 17.The level judger 16 compares the input signal with a predetermined reference level, and If the signal is large, the output is transmitted to the breakage detection circuit 18 and the abnormal cutting detection circuit 19.

Also, the comparator 45 compares the outputs of the detectors 12 and 13, and transmits the output to the breakage detection circuit 18 only when the output of the detector 12 and 13 is large.The breakage detection circuit 18 takes the AND of these inputs and detects the tool. This is a logic circuit for detecting breakage of the cutter, and the detection signal closes the analog switch 6 and outputs the signal to the outside via the output circuit 20.The abnormal cutting detection circuit 19 detects an abnormality based on the output of the level determiner 16. It detects cutting and transmits its output to the outside via the output circuit 21.

FIG. 2 is a sectional view showing an example of the pseudo AE signal generator 4, and FIG. 3 is a block diagram showing its electrical configuration.

In these figures, a battery 31 is provided within a housing 30 of the pseudo AE signal generator 4. Also on the side is a selection switch 3 for selecting the level of the AE damage signal generated.
2 is provided, and its switch output and power supply are applied to the drive circuit 33. As shown in FIG. 3, the drive circuit 33 includes a clock generator 34 that generates a square wave clock signal at a predetermined timing and a differentiation circuit 3 that differentiates the output thereof.
5 is provided. The differentiating circuit 35 generates a substantially triangular waveform output, and the output is given to a multiplier 36. Further, the drive circuit 33 is provided with a noise generator 37 that generates white noise having a uniform frequency distribution, and a bandpass filter 38 that extracts only signals around a frequency of 300 Kb from the noise output. The output and the output of the differentiating circuit 35 are multiplied by a multiplier 36. Then, the multiplier 36 generates a pseudo AE multiplied signal in which the differentiated output of the differentiating circuit 35 is an envelope.The output of the 0 multiplier 3G is amplified by the amplifier 39 with the amplification factor selected by the level selection switch 32. Ru. The amplified output is attached to the upper part of the inner surface of the case 30,
This is a piezoelectric element that transmits a pseudo AE double signal to the tool support of a machine tool. The upper part of the case 30 of the pseudo AE signal generator 4 is made of a metal member that easily transmits the AE flaw signal, and the upper part has a cylindrical member 41 having a constant diameter corresponding to the diameter of the drill used. I try to make it stand out.

FIG. 4 is a partial cross-sectional view showing a state in which the pseudo AE signal generator 4 is attached to a tool support part. A chuck 52 for attaching a drill is provided at the tip of the main shaft 51. Normally, a drill of a desired diameter is attached to the tip of the chuck 52, but when operating this tool breakage detection device, the above-mentioned pseudo AE signal generator is first placed at the attachment position of the drill in order to adjust the sensitivity of the AE sensor 5. The upper cylindrical member 41 of No. 4 is fixed.

It is assumed that the AE sensor 5 is attached to the side surface of the tool support section 3 as shown in the figure.

Next, the operation when installing the tool breakage detection device of this embodiment in a machine tool will be explained. First, pseudo AE signal generator 4
After attaching the tool to the chuck 52, the level setting switch 32 is operated to set the level of the pseudo AE signal depending on the type of tool, for example, the diameter of the drill. After operating the pseudo AE signal generator 4, the machine tool is driven. Since the pseudo-image AE signal generator 4 has a battery 31 inside, it operates without being supplied with power from an external part. Therefore, by rotating the main shaft 51, a pseudo AE multiplied signal can be obtained in a state close to the actual operating state of the tool. At this time, the amplification factor is adjusted by the variable resistor 8 of the amplifier 7 which amplifies the AE multiplied signal so that the display on the cutting level indicator 11 becomes a predetermined level. By setting this for each tool used, it becomes possible to adjust the sensitivity of the AE sensor 5, that is, the output of the amplifier 7, to a constant level. At this time, the pseudo AE multiplied signal is transmitted from the main shaft 51 through the tool support 3 to the AE sensor 5, but even when a drill is attached to the chuck 52, the AE multiplied signal is transmitted through the same transmission path when the drill breaks, so the workpiece Therefore, when the tool breaks, a signal at the same level as the pseudo AE multiplied signal AE output is transmitted to the signal processing section.

Now, during normal cutting, the distribution of the AE multiplied signal power spectrum given by the AE sensor 5 is concentrated around a frequency of 50 KHz, as shown by the curve in Figure 5, and monotonically attenuates in the higher frequency range. distribution. Furthermore, as is known from many experiments, the power spectrum distribution when a tool breaks is represented by curve a in Figure 5.
It is clear that the frequency has a peak near 300 Hz.

This is considered to be because the signal source is not caused by mechanical vibration, but a phenomenon peculiar to ultrasonic waves that occurs during non-plastic fracture of a tool occurs. Therefore, two bandpass filters 9
．． 10 extracts only the AE multiplied signals near the respective frequency components and detects them using the detectors 12 and 13. By comparing the output levels, it is possible to clearly distinguish between normal conditions and tool breakage. In other words, during normal cutting, the frequency is 50KH.
The AE multiplied signal power near z has a frequency of 300 K.
It is larger than the power near Hz, and 300 when the tool breaks.
This is because the power near a frequency of 50 KHz is greater than the power near a frequency of 50 KHz. The comparator 15 compares these outputs and provides a signal to the breakage detection circuit 18 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 chips and a tool workpiece during cutting. In this case, even if the center frequency and Q value of the bandpass filter 9.10, the threshold level of the comparator 15, etc. are set appropriately, the signal due to contact between chips and the tool or workpiece, or friction may cause the tool to break. It may be mistaken for a signal. Therefore, in this embodiment, attention is 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. 1, the output of the detector 12 is applied to a differentiating circuit 14, and only steep signals such as those caused by breakage are separated and applied to a level determiner 16. Then, the input level is compared with a predetermined reference value, and when an AE multiplied signal with a steep rise is obtained, the breakage detection circuit 1
Give a signal to 8. The breakage detection circuit 18 detects tool breakage based on these AND signals. In this way, by combining both frequency domain breakage detection and time domain breakage detection, it is possible to reliably detect only tool breakage.

If only tool breakage is detected in this way, the output circuit 1
A broken output is given from 9, and the analog switch 6 is turned off so as not to be transmitted to the AE multiplier signal amplifier 7 thereafter. This is to prevent a large AE multiplied signal generated due to abnormal contact or friction between the broken tool and the workpiece that occurs after the tool is broken, and to prevent it from being determined as broken. In addition, as shown in the block diagram of Fig. 1, the output of the amplifier 7 is directly displayed on a cutting level indicator 11 to indicate the cutting level, and furthermore, abnormal contact friction between chips and workpieces can be detected by tool breakage, 2 normal conditions, etc. It is possible to separate it as a processed signal. Abnormal cutting detector 1 is detected by the output of level determiner 16.
Since the abnormal cutting output is given to the outside from the output circuit 22 via the output circuit 9, it is also possible to detect abnormal cutting at the same time.

In this embodiment, the pseudo AE signal generator is provided with a level setting switch, and by setting the setting switch appropriately according to the type of tool, a pseudo AE signal multiple of the reference level is generated. It is also possible to use a pseudo AE signal generator having a predetermined level for each type of AE signal.

Further, although this embodiment describes a drill breakage detection device for a drilling machine, the present invention can be applied to other machine tools, such as various machine tools such as lathes and milling machines.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the tool breakage detection device according to the present invention, FIG. 2 is a sectional view of the pseudo AE signal generator 4 according to the present embodiment, and FIG. 3 is a block diagram showing its electrical configuration. , Fig. 4 is a side view showing the state in which the pseudo AE signal generator 4 and the AE sensor 5 are installed on the machine tool, and Fig.
FIG. 6 is a diagram showing the AE multiplied signal power spectrum obtained from the sensor 5 (al is the AE signal waveform obtained when the tool breaks, in FIG. 6) is a diagram showing the AE signal waveform obtained when chips are generated. . 1---------Work 2----Drill 3
---1---Tool support part 4----1 Pseudo AE signal generator 5----AE sensor 7--
・-・Analog switch 7-・-41 width switch 9.
10・---Band pass filter 12.13
−・−−−−1 detector 14−・−−−−−・Differential circuit 15−−−1−・−Comparator 16−・−・−Level judger 18−・−−−m=Breakage detection circuit 20
, 21-----One output circuit 30----
-Case 31--Battery 3
2−・−−−−・Level setting switch 33−・−
-1--Drive circuit 40---1--Piezoelectric element patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Kanki Okamoto (and one other person) Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Ca) Figure 6 (b)

Claims (3)

[Claims] (1) In a tool breakage detection device that has an AE sensor installed on the tool support of a machine tool and detects breakage based on the AE signal obtained when the tool breaks, the shape of the tool that is attached to the tool attachment position is determined. It has a mounting part with a shape corresponding to
a pseudo AE signal generating means for generating an E signal; a display for displaying the output level of the AE sensor; and a sensitivity setting means for setting the sensitivity of the AE sensor; A tool breakage detection device characterized in that the sensitivity of the AE sensor is set based on a pseudo AE signal obtained when the tool is mounted at a mounting position. (2) The tool breakage detection device according to claim 1, wherein the pseudo AE signal generating means has an internal power source and generates the pseudo AE signal when the machine tool is driven. (3) The tool breakage detection device according to claim 1, wherein the pseudo AE signal generating means includes level setting means for setting an AE signal level according to the type of tool.