JPS6188147A - Broken loss detector of tool - Google Patents

Abstract

PURPOSE:To detect the broken loss of a tool precisely by setting the sensitivity of an AE sensor automatically to an optimum value in accordance with the tool used. CONSTITUTION:A false AE signal generator 4 is arranged on a position where the knife of a drill arranged on the upper part of a work 1 contacts. The output of the AE sensor 6 arranged close to the tool is applied to an AE signal processing part 7 and amplified with a prescribed level and a signal indicating the broken loss or abnormal cutting of the tool is detected and applied to a CPU9 through an I/O interface 8. The CPU9 applies a prescribed driving level of the generator 4 to a driving circuit 5 on the basis of the kind of the tool, detects the optimum sensitivity on the basis of an AE signal level obtained from the AE signal processing part 7 and controls the sensitivity so as to be set to the optimum sensitivity.

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.

[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 progress of factory automation in recent years, there is a strong demand for automatically detecting such folding and abnormal cutting of tools. As a method for detecting tool breakage in machining &'M, t=4, conventionally an AE sensor is installed near the machine tool or workpiece, and the AE multiplied signal obtained from the sensor is used to detect tool breakage. A device for detecting has been proposed.

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 multiplied signal at the time of tool breakage can only be obtained at the time of breakage, it is difficult to confirm the mounting position and mounting condition of the E sensor, making it difficult to reliably detect tool breakage. Furthermore, the AE signal level changes when the type of tool is changed, such as when the drill diameter or cutting conditions are changed, making adjustment difficult and difficult to use.

In addition, 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, and the AE multiplied signal obtained from other causes, such as chips from the workpiece, is detected. Electrical noise associated with generated signals and opening/closing of solenoids.

What if an object comes into contact with the workpiece? IT ``There was a problem that it could not be sufficiently separated from the A sound, etc., and reliability was low.

[Purpose of the invention]

The present invention was made in view of the problems of the conventional tool breakage detection device, and it automatically sets the sensitivity of the AE sensor to the optimum value corresponding to the tool being used. size and chips.

It is an object of the present invention to provide a highly reliable tool breakage detection device that can reliably detect tool breakage without being influenced by other signals.

[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 the AE multiplied signal obtained when the tool breaks. A condensed AE signal generating means that generates a pseudo AE multiplied signal including frequency, a variable amplification amplifier that amplifies the AE sensor's AE multiplied signal by changing the amplification factor based on external input, and a drive level corresponding to the tool used. Drives the condensed AE signal generating means to amplify the variable amplification factor amplifier.
AE sensitivity setting means for setting B to the optimum value; storage means for storing the optimum amplification factor for each tool set by the ΔE sensitivity setting means; and a strong correlation with the AE multiplied signal frequency component obtained when a tool breaks. AE multiplied signal of frequency component A frequency identification means that outputs an output when a variable amplification amplifier set to the optimum amplification factor is given, and a rising signal that outputs when a rapidly rising signal is given from the AE sensor. The present invention is characterized by comprising a detection means, and logic output means for outputting a tool breakage detection output based on the logic and product output of the frequency identification means and the rising signal detection means.

According to the present invention having such features, the AE is adjusted for each tool used in a machine tool according to the usage environment.
Describe the optimum sensitivity of the sensor.1. I'm kicking.

Therefore, even when using any tool, it is possible to automatically adjust the sensitivity of the AE sensor to the optimum value. After adjusting in this way, the AE that has a strong correlation with the AE multiplied signal power spectrum obtained at the time of tool breakage is determined by the frequency identification means.
The multiplication signal is identified, and at the same time, the detection of a steep rise of the AE multiplication signal, which is observed at the time of breakage, is independently determined by the rising signal detection means, and the breakage of the tool is detected based on the logical product condition. Therefore, there will be no malfunction caused by signals such as chips from the workpiece or electrical noise, and there will be no effect of AE multiplied signal attenuation from the tool to the AE sensor, greatly improving the reliability of tool breakage detection. becomes possible.

[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. 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 1 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 AE signal generator 4 made of PZT or the like, which is the same as the AE sensor, is installed in advance at the position where the drill blade comes into contact with the upper part of the workpiece 1. The drive circuit 5 drives the pseudo AE signal 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. Its amplitude level is given externally. An AE sensor 6 for detecting the AE multiplied signal is provided near the tool on which the workpiece 1 is placed, for example, on the base as shown in FIG. The AE sensor 6 is a wideband AE sensor that detects an AE multiplied signal from a tool such as a drill 2 or the like, and an AE multiplied signal from the AE signal generator 4, and its output is given to an AE signal processing section 7. The AE signal processing unit 7 amplifies the signal from the AE sensor 6 to a predetermined level, detects a signal indicating tool breakage or abnormal cutting, and provides the signal to a central processing unit (hereinafter referred to as CPU) 9 through an input/output interface 8. be. The CPU 9 includes a read-only memory (hereinafter referred to as ROM) 10 that stores a system control program.
Random access memory containing sensitivity information of the AE sensor corresponding to the tool used by this numerical control device 3
A storage means (hereinafter referred to as RAM) consisting of 11 is connected. The CPU 9 also has an input/output interface 12.
A display 13 for displaying the AE signal level during cutting, abnormal cutting or breakage of the tool, and an input key 14 for setting the number and type of tool and the sensitivity of the standard AE sensor are connected. Furthermore, a numerical control device 3 is connected via a signal transmission line 15. Based on these inputs, the CPU 9 applies a predetermined drive level of the pseudo AE signal generator 4 to the drive circuit 5, detects the optimum sensitivity based on the AE signal level obtained from the AE signal processing section 7, and selects the optimum sensitivity. are sequentially held in the RAM 1l, and the sensitivity is controlled to be set to that sensitivity when the corresponding tool is used thereafter.

Next, FIG. 2 is a block diagram showing the detailed configuration of the AE signal processing section 7. As shown in FIG. In this figure, the output of the AE sensor 6 is first given to an 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.

The bandpass filter 22 has a center frequency of 300KHz.

The 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 corresponding to the amplitude, and the output of the detector 24 is sent to the differentiator 26 and
．． The outputs of 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 comparator 27
compares the outputs of the wave detectors 24 and 25, and transmits the output to the breakage detection circuit 29 only when the output of the wave detector 24 is large.

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 CP tJ 9 via the input interface 8. In addition, the abnormal cutting detection circuit 30 is level 2: (based on the output of 28, detects abnormal cutting and outputs the input/output interface 8.
The information is transmitted to the CPU 9 via the .

Next, the operation of this embodiment will be explained. First, the sensitivity setting method for each tool according to the present invention will be explained with reference to the flowchart of FIG. - When the operation is started, first, in step 40, data (magazine number) corresponding to the size of the tool being used at the time, input by the user, is read from the input key 14. and step 4
1 and a pseudo AE signal generator 4 corresponding to the magnitude.
A drive level of 1 is applied to the drive circuit 5. Then, in order for the drive circuit 5 to drive the pseudo AE signal generator 4, the AE multiplied signal is transmitted from the pseudo AE signal generator 4 to the AE sensor 6 via the work 1 and the HASE. At this time, the approximate AE signal obtained from the AE sensor 6 has the same power spectrum as that at the time of tool breakage, and also has a waveform similar to the waveform at time of breakage in the time domain. This AE multiplied signal AE
The signal is transmitted to the signal processing section 7, and is transmitted from the input/output interface 8 to the CPU 9 via the analog switch 20 and the variable gain amplifier 21. The CPU 9 adjusts the signal level of the AE sensor using the amplification factor of the variable amplification factor amplifier 21 in step 42, and proceeds to step 43 to check whether the output level is appropriate. If this level is not appropriate, a necessary increase or decrease in the amplification factor is calculated in step 44, and the process returns to step 42 to change the amplification factor of the variable amplification factor amplifier 21. and steps 42 to 4
Repeat loop 4 and adjust the amplification factor appropriately. The optimal amplification factor thus obtained is stored in a predetermined area of RAMII together with the magazine number (step 45). Next, the process advances to step 46 to check whether the settings for all tools have been completed, and if the settings have not been completed, the process returns to step 40 to repeat the same process with other tools. In this way, the sensitivity values of all the tools used by the numerical control device 3 are adjusted, and as shown in the memory map shown in FIG. Save and end the sensitivity setting process.

Next, a description will be given of a monitoring operation for monitoring tool breakage using the optimal sensitivity data corresponding to each tool set in this way. FIG. 5 is a flowchart showing this monitoring operation. When the monitoring operation is started, first, in step 50, the optimum value of the amplification factor corresponding to the tool is read out from the RAM II, and is sent to the AE signal processing unit 7 via the input/output interface 8. The amplification factor of the variable amplification factor amplifier 21 is set. Then, depending on the cutting of the workpiece 1, the AE sensor 6 will
The E signal is applied via the analog switch 20, amplified by an optimal amplification factor, and applied to two bandpass filters 22 and 23. Now, during normal cutting, AE
The distribution of the power spectrum of the AE multiplied signal given by the sensor 6 is concentrated around a frequency of 50 KHz, as shown by the curve in FIG. 6, and has a monotonically attenuated distribution 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. 6, 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 peculiar to ultrasonic waves that occurs during non-plastic fracture of a tool occurs. Therefore, the two band-pass filters 22 and 23 extract only the AE-multiplied signals near the respective frequency components and send them to the detector 2.
4.25, and by comparing the output levels, it is possible to clearly distinguish between normal times and tool break times. In other words, during normal cutting, the AE multiplied signal power at a frequency of around 50 K Ilz increases to a frequency of 300 K Ilz.
Higher power than nearby, 300KH when tool breaks
This is because the power near the frequency 50 KHz is greater than the power near the frequency 50 KHz. 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. 6 may be generated due to contact or friction between chips and the tool workpiece during cutting. In this case, even if the center frequency of the band-pass filters 22, 23, the value of Q2, the threshold level of the comparator 27, etc. are set appropriately, the signal due to the contact between chips and the tool or workpiece, or the friction of the tool may be It may be mistakenly judged as a broken signal. 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.

In other words, the E signal waveform obtained when the tool breaks is shown in Figure 7 (a).
), the signal has a sharp rise at the time of breakage, while the AE multiplied signal caused 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 7). is 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 judge 2
8 provides an output to the breakage detection circuit 29 and the abnormal cutting detection circuit 30 when the input signal is large. Abnormal cutting detection circuit 3
0 notifies the CPU 9 of abnormal cutting from the human output interface based on the output of the level determiner 28. In the flowchart shown in FIG. 5, the CPU 9 checks whether an abnormal cutting signal is transmitted from the abnormal cutting detection circuit 30 (step 51), and if there is no signal, normal cutting operation is being performed, so step 52 Then, the cutting level is displayed on the display 13. and step 50
The process returns to , and the same process is repeated, and cutting abnormalities are monitored while executing the processes of steps 50 to 52. Now, if an abnormal cutting signal is transmitted from the abnormal cutting detection circuit 30, the process proceeds to step 53, and it is checked whether or not a breakage signal is supplied from the breakage detection circuit 29. The breakage detection circuit 29 detects tool breakage based on the logic of the comparator 27 and the level determiner 28, and when the tool breaks, it transmits the breakage output to the CPU 9 through the input/output interface. Therefore, it is checked in step 53 whether or not a breakage signal is given, and if this is not given, abnormal cutting is being performed, so in step 54 the display 13 displays abnormal cutting, and the process returns to step 50. If a breakage detection signal is given in step 53, the tool breakage is detected, so the process proceeds to step 55, where the display 13 displays the tool breakage, and the data is transmitted to the numerical control device 3 to stop the operation. . Then, the process proceeds to step 56, where the analog switch 20 of the AE signal processing section 7 is turned off, and the process ends.

In this way, other signals found in machine tools, such as spike-like electrical noise associated with opening and closing of solenoids, are filtered through the bandpass filter 20. Differentiator circuit 26 via detector 24
However, the power spectrum thereof has an R-key decreasing distribution as shown by curve C in FIG. 6, and no output is obtained from the comparator 27. Also, an equilibrium wave that is generated when an object collides with the base of the workpiece L or the base of the workpiece L can be considered, but in this case as well, the power spectrum is concentrated at a low frequency due to mechanical vibration, and the frequency is 300 KHz. Since it is thick (attenuated) in the vicinity, no output is obtained from the comparator 27 and no tool breakage signal is generated.In this way, both frequency domain breakage detection and time domain breakage detection can be combined. This makes it possible to reliably detect only tool breakage.If tool breakage is detected in this manner, the analog switch 20 is turned off and input of the AE multiplication signal is subsequently stopped.

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 this embodiment, breakage is detected by analog processing in the AE signal processing section 7, but it is also possible to sample the output of the AE sensor after A/D conversion and perform all subsequent processing by digital signal processing. It is. In this case, it is conceivable to replace the bandpass filter with a digital filter, replace the differential circuit with a difference calculation, etc., and perform signal processing using the CPU.

Furthermore, in this embodiment, the magazine number for each tool and the corresponding amplification factor data are held in the memory in the tool breakage detection device, but even if this data is held in the memory in the numerical control device, good.

Furthermore, although this embodiment describes a breakage detection device applied to a numerical control device, the present invention can also be applied to other machine tools, such as various machine tools such as lathes and milling machines, and even large-scale machining centers. It is possible.

[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 tool breakage detection device according to the present embodiment. A flowchart showing the automatic sensitivity setting process, Figure 4 is a memory map showing the state in which the amplification factor obtained at that time is stored, and Figure 5 is the process when monitoring the cutting situation based on the sensitivity data obtained in this way. FIG. 6 is a diagram showing the AE multiplied signal power spectrum obtained from the AE sensor 6, FIG. 7(a) is the AE signal waveform obtained when the tool breaks +i, and FIG. 7(b) is when chips are generated. FIG. 3 is a diagram showing an AE signal waveform obtained in this case. 1--------Work 2--Drill 3--
---1 Numerical controller 4.-----1 Pseudo AE signal generator 5-.-=Drive circuit 6-----A
E-sensor 7-・-A E-transmission/processing section 8.1
2- - Human output interface! L---
-----CPU 1 0------・-ROM
11------RAM L3-・-
Display device 14...-Person key-20--Analog switch 21--Variable gain amplifier 22,
-23---Band pass filter 24. 2
5--------・-Detector 26-------Differential circuit 27-----Comparator 28・--1---
Level judger 29----One-break rhyme detection circuit 3
0・-～----Abnormal cutting detection circuit Patent applicant Tateishi Electric Co., Ltd. Agent Patent attorney Kanki Okamoto (1 person) Fig. 3 Fig. 4 Fig. 5 Fig. 6 100K 200K BOOK 400K H1
Fig. 7(a) b Fig. 7tt. Small procedure amendment (voluntary) 1932
November 9, 9

Claims (3)

[Claims] (1) In a tool breakage detection device that has an AE sensor installed near the tool of a machine tool and detects breakage based on the AE signal obtained when the tool breaks, the frequency of the AE signal obtained when the tool breaks is Contains pseudo A
pseudo AE signal generating means for generating an E signal; and A of the AE sensor by changing an amplification factor based on external input.
a variable amplification factor amplifier that amplifies the E signal; and an AE sensitivity setting device that drives the pseudo AE signal generating means at a drive level corresponding to the tool used and sets the amplification factor of the variable amplification factor amplifier to an optimum value; a storage means for storing an optimum amplification factor for each tool set by the AE sensitivity setting means; and an AE signal having a frequency component having a strong correlation with a frequency component of an AE signal obtained at the time of tool breakage is set to the optimum amplification factor. a frequency identifying means that outputs an output when a signal that rises rapidly is given from the AE sensor; a rising signal detecting means that outputs an output when a signal that rises rapidly is given from the AE sensor; and the frequency identifying means and the rising signal. A tool breakage detection device comprising: logic output means for outputting a tool breakage detection output based on a logical product output of the detection means. (2) The frequency identification means compares the output level of each band-pass filter with a band-pass filter whose center frequency is the maximum value of the frequency obtained when detecting tool breakage and the frequency obtained during normal cutting. 2. The tool breakage detection device according to claim 1, further comprising a comparator, from which a tool breakage signal is obtained. (3) The rising signal detection means includes a differentiating circuit that differentiates the AE signal, and detects rapid amplitude fluctuations based on the differentiated output. tool breakage detection device.