JPS61173154A - Tool fracture detector - Google Patents

Abstract

PURPOSE:To stabilize the sensitivity adjustment of an AE sensor to be installed near the tool of a machine tool by using a pseudo fracture signal by processing the output from the AE sensor in a signal processing part having a means for discriminating frequency and a means for detecting a rise signal. CONSTITUTION:A pseudo fracture signal generator 4 consisting of a PZT, etc. is attached in the position where the tool 3 contacts with a work 1 in order to adjust the sensitivity of the AE sensor 7. The detection signal from the AE sensor is applied to the signal processing part including the means for discriminating frequency which consists of band pass filters 11, 12, detectors 14, 15 and a comparator 17 and the means for detecting the rise signal which consists of a differentiation circuit 16. The output thereof is integrated in an integration circuit 19 and the result thereof is displayed on a fracture abnormal level display device 24. The non-flickering output is thus obtd. and the exact sensitivity adjustment of the AE sensor is made possible. The reliability of the fracture detection of the tool is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention solves the problem of tool breakage and abnormality in machine tools by acoustic emissions (
(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 generates a pseudo-breakage signal having the same properties as the breakage signal waveform obtained when a tool breaks in order to adjust the sensitivity of the AE sensor. An integrating circuit is used to stabilize the level display when adjusting sensitivity.

This prevents the level display from flickering and allows the sensitivity of the AE sensor to be adjusted accurately.

[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 tool breakage and abnormal cutting. As a method for detecting tool breakage in machine tools, conventional methods have been to
There is a device in use that is equipped with a sensor and detects tool breakage based on the AE multiplied signal obtained from the sensor.

However, according to the conventional tool breakage detection device, the AE sensor is mounted near the tool or in contact with the workpiece, but 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 according to the size of the tool, and the attenuation rate between the tool and AE sensor of each machine tool is corrected by trial and error. Ta. However, since the AE multiplier signal cannot be obtained when the tool breaks, it is difficult to confirm the mounting position and mounting state of the AE sensor, making it difficult to reliably detect tool breakage. Furthermore, the type of tools,
For example, when the drill diameter is changed or the cutting conditions are changed, the AE signal level changes, making adjustment difficult and making it difficult to use.

[Purpose of the invention]

The present invention was made in view of the problems of the conventional tool breakage detection device, and in order to adjust the sensitivity of the AE sensor, an AE multiplied signal having the same characteristics at the time of tool breakage is used.
To provide a tool breakage detection device which can adjust the sensitivity of an AE sensor by giving an E-fold signal to a machine tool and display the signal level without flickering when adjusting the sensitivity of the AE sensor using a pseudo-breakage signal. The purpose is to

[Structure and effects of the invention]

The present invention is a tool breakage detection device that has an AE sensor installed near the tool of a machine tool and detects breakage based on an AE multiplied signal when the tool breaks. a pseudo-breakage signal generating means for generating a pseudo-breakage signal including an AE multiplied signal frequency; a signal processing section for detecting tool breakage based on the output of the AE sensor;
A including the AE multiplied signal frequency at the time of breakage obtained from the sensor
The present invention is characterized by comprising an integrating circuit that integrates the E signal output, and a breakage level display means that displays the output level of the integrating circuit.

According to the present invention having such characteristics, the AE at the time of breakage
It is possible to adjust the sensitivity of the AE sensor using a pseudo-breakdown signal that includes a doubled signal frequency.

Furthermore, when the pseudo-breakage signal is transmitted from the AE sensor to the signal processing section, its output is once integrated to eliminate sudden signal changes and to be displayed on the level indicator. In this way, even if pseudo-breakage signals are continuously applied, the level display on the display will be stable, making it possible to easily set the sensitivity of the AE sensor. In this way, accurately AE
If the sensitivity of the sensor can be adjusted, the reliability of tool breakage can be improved.

[Explanation of Examples]

(Overall Configuration of Embodiment) 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 drilling machine, and a workpiece 1 is fixed on a base 2 of the drilling machine, and a drill 3 is attached from above to form an opening in the workpiece l. Here, a pseudo-breakage signal generator 4 consisting of <PZT, etc., which is the same as the AE sensor, is installed in advance at a position on the upper part of the workpiece 1 where the drill blade comes into contact with the workpiece before cutting the workpiece. The level setter 5 sets the drive level of the pseudo-breakage signal generator 4, and transmits to the drive circuit 6 drive level signals set according to two types of tool sizes. The drive circuit 6 drives the pseudo-breakage signal generator 4 with a drive waveform that is similar to the AE multiplied signal at the time of tool breakage and has the same power spectrum distribution. An AE sensor 7 for detecting the AE multiplied signal is provided near the tool on which the workpiece 1 is placed, for example, on the base 2 as shown in FIG. The AE sensor 7 is a wideband AE sensor that detects an AE multiplied signal from a tool such as a drill 3 and an AE multiplied signal from the pseudo-breakage signal generator 4, and its output is given to an analog switch 8. The analog switch 8 connects and disconnects the analog signal using an external output, and the output is given to the amplifier 9. The amplifier 9 is an amplifier whose amplification factor can be arbitrarily set by adjusting a variable resistor 10, and provides its output to two band pass filters 11, 12 and a cutting level indicator 13. The bandpass filter 11 has a center frequency of 3
00 K Ilz , the bandpass filter 12 is a filter with a center frequency of 50 KHz, and transmits only signals near the respective center frequencies to the next-stage detector 14.15. The detectors 14 and 15 each detect the input signal and obtain an output according to the amplitude.The output of the detector 14 is given to a differentiating circuit 16, and the output of the detectors 14 and 15 is given to a comparator 17, respectively. It will be done. These bandpass filters 11, 12,
The detectors 14, 15 and the comparator 17 form frequency identification means for identifying the AE multiplied signal at the time of breakage. The differentiating circuit 16 transmits only steep changes in the input signal to the next stage level determiner 18 and integrating circuit 19. The level determiner 18 compares the input signal with a predetermined reference level,
If the input signal is large, the output is transmitted to the breakage detection circuit 20 and the abnormal cutting detection circuit 21. Also, the comparator 17 is the detector 14,
The outputs of the detector 15 are compared, and the output is transmitted to the breakage detection circuit 20 only when the output of the detector 14 is large. Breakage detection circuit 2
0 is a logic circuit that performs the logical product of these inputs to detect tool breakage, and provides a breakage detection signal to the output circuit 22 and transmits it to the analog switch 8. Further, the abnormal cutting detection circuit 21 detects abnormal cutting based on the rising signal of the level determiner 18, and transmits its output to the output circuit 23. Further, the integrating circuit 19 integrates the output of the differentiating circuit 16 with a large time constant, and transmits the output to the breakage/abnormality level indicator 24.

FIG. 2 is a circuit diagram showing an example of the integrating circuit 19. In this figure, the display signal of the differentiating circuit 16 is applied to an integrator consisting of a resistor R25 and a capacitor C26, and the output of the integrator is applied via a resistor R27 to a non-inverting amplifier 28 consisting of an operational amplifier.

The non-inverting amplifier 28 compensates for the output reduced by the integrating circuit, amplifies the integrated output to a predetermined level, and transmits the output to the breakage/abnormality level indicator 24 shown in FIG.

(Configuration of a drive circuit for a pseudo-breakage signal) FIG. 3 is a block diagram showing the configuration of a drive circuit for a pseudo-breakage signal according to this embodiment. In this figure, the noise generating circuit 30 is a generating circuit that generates white noise having a uniform spectrum up to a frequency exceeding 300 KHz, and its output is passed through a bandpass filter that passes components around the frequency of 300 KHz. Given to 31. Further, the rectangular wave oscillator 32 is an oscillator that oscillates a rectangular wave signal with a constant period, and its output is given to the multiplier 34 via the differentiating circuit 33. The multiplier 34 multiplies these outputs to generate a pseudo-breakage signal whose envelope is the differential signal. The amplifier 35 amplifies this pseudo-breakage signal based on the level setting of the level setter 5 (using an amplification factor), and its output is sent to the power amplifier 36.
The signal is applied to the pseudo-breakage signal generator 4 via.

(AE Sensor Sensitivity Setting Operation) Next, the operation when installing the tool breakage detection device of this embodiment in a machine tool will be described. First, pseudo-breakage signal generator 4
As shown in FIG. 1, it is attached to the workpiece 1 at a position where it will be opened by a drill, and a level setting device 5 sets a pseudo-breakage signal level according to the type of tool, for example, the diameter of the drill. When the drive circuit 6 is driven, the noise generating circuit 30 generates white noise as shown in the waveform diagram in FIG. 4(a), and the rectangular wave oscillator 32 generates a rectangular wave as shown in is generated.Then, the rectangular wave is shown in Fig. 4 tc+
The white noise is differentiated by the differentiating circuit 33 as shown in FIG.
given to 4. Therefore, a pseudo-breakage signal is obtained from the multiplier 34, as shown in FIG. 4 (d+), which periodically rises sharply and then attenuates. It is not necessarily constant.Therefore, the pseudo-breakage signal is transmitted through the workpiece 1 and the base 2.
Although the peak value is transmitted to the sensor 7, the peak value is not constant and varies every cycle. The AE multiplied signal is then transmitted to the amplifier 9 via the analog switch 8 . Then, the signal is detected via the pan-pass filter 11 and the detector 14, and differentiated by the differentiating circuit 16. This differential output is integrated with a long time constant and averaged by the integrator of the integration circuit 19, as shown in FIG. FIG. 4 (el is a waveform diagram showing the integrator input and its output of this integration circuit 19.The level lowered by the integration is corrected by the non-inverting amplifier 2, and is displayed by the broken/abnormal level indicator 24. Therefore, the output of the amplifier 9 is connected to the variable resistor 10 so that the display level of the display 24 becomes a predetermined value.
Adjust by. In this way, it becomes possible to transmit the AE multiplied signal from the AE sensor 7 to the signal processing section at an appropriate level.

(Operation of the signal processing unit) Now, the A given by the AE sensor 7 during normal cutting
The distribution of the E-times signal power spectrum is concentrated around the frequency 50KFIz, as shown by the curve in FIG. 5, and the distribution is monotonically attenuated in the higher frequency range. Furthermore, as is known from many experiments, the power spectrum distribution when a tool breaks is represented by curve a in Figure 5.
It has been revealed that the peak frequency is around 300 KHz.

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 1
1.12, it is possible to clearly distinguish between normal conditions and tool breakage by extracting only the AE multiplied signals near each frequency component, detecting them with detectors 14 and 15, and comparing their output levels. . The comparator 17 compares these outputs and provides a signal to the breakage detection circuit 20 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 or workpiece during cutting. In this case, the center frequency and Q value of the bandpass filters 11 and 12,
Even if the threshold level and the like of the comparator 17 are set appropriately, a signal caused by contact or friction between chips and a tool or workpiece may be mistakenly determined to be a tool breakage 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. In other words, the AE signal waveform obtained when the tool breaks, as shown in Figure 6(a), is a signal with a sharp rise at the time of breakage, while the AE multiplied signal waveform generated by contact and friction between chips and the tool or workpiece. As shown in Figure 6 (bl), the waveform does not show a sharp rise and the signal continues for a predetermined period of time.Therefore, as shown in Figure 1, the output of the detector 14 is fed to the differentiating circuit 16, and the waveform does not show a sharp rise. The input level is then compared with a predetermined reference value, and when an AE multiplied signal with a steep rise is obtained, the level determiner 18 sends a signal to the breakage detection circuit 20. The breakage detection circuit 20 detects tool breakage based on these AND signals and outputs the detected tool to the outside via the output circuit 22, and closes the analog switch 8.

In this way, in this embodiment, tool breakage is detected by combining both frequency domain breakage detection and time domain breakage detection. Therefore, it becomes possible to identify tool breakage in response to various abnormal breakage signals.

Although the integrator of this embodiment uses a CR integrator, it is also possible to use a similar type of integrator such as a Miller integrator. Although the signal processing section according to this embodiment detects breakage by ANDing the breakage detection in the frequency domain and the time domain, it is also possible to use or combine other breakage detection methods.

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

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the tool breakage detection device according to the present invention, FIG. 2 is a circuit diagram showing the detailed configuration of the integrating circuit, and FIG. 3 is the configuration of the pseudo-breakage signal drive circuit 6. 4 is a waveform diagram showing the waveforms of each part of this embodiment, FIG. 5 is a diagram showing the AE multiplied signal power spectrum obtained from the AE sensor 7, and FIG. Signal waveform, FIG. 6 (bl is a diagram showing the AIE signal waveform obtained when chips are generated. 1-.- Work 2-- Base 3--
---Drill 4-----Pseudo breakage signal generator 5
・-1--Level setter 6--11 Drive circuit 7-----A E sensor 8--Analog switch 9--1 Amplifier 11.1
2-...-Band pass filter 14.15-
~----Detector 16---Differential circuit 17--
--- Comparator 18 --- Level judger 19 --- Integrating circuit 20 ---
-Breakage detection circuit 24--Breakage abnormality level indicator R25, 27--Resistor C26--
--- Capacitor 28 --- Non-inverting amplifier Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Yoshiki Okamoto (and one other person) Figure 2 Figure 3 Figure 5 100K 200K 300K 400K Hz
Figure 6 (al Figure 6 (b)

Claims (2)

[Claims] (1) A tool breakage detection device that has an AE sensor installed near the tool of a machine tool and detects breakage based on an AE signal when the tool breaks. pseudo-breakage signal generating means for generating a pseudo-breakage signal including a frequency of the signal; a signal processing section for detecting tool breakage based on the output of the AE sensor; and a frequency of the AE signal at the time of breakage obtained from the AE sensor. A pseudo-breakage signal generating device comprising: an integrating circuit that integrates an AE signal output including: and a breakage level display means that displays an output level of the integrating circuit. (2) The signal processing unit is configured to control the AE obtained when the tool breaks.
A frequency identification means that outputs an output when an AE signal having a frequency component having a strong correlation with the frequency component of the signal is given, and a rising signal detection means that outputs an output when a signal that rises suddenly from the AE sensor is given. 2. The tool breakage detection device according to claim 1, further comprising logic output means for identifying tool breakage based on the AND output of the frequency identification means and the rising signal detection means.