JPS61173155A - Tool fracture detector - Google Patents

Abstract

PURPOSE:To obtain a signal which does not saturate even if an AE signal level is high and to detect exactly the fracture, etc. of a tool by attaching an AE sensor to be installed near the tool of a machine tool by way of an attenuating plate interposed between said sensor and the installation surface thereof. CONSTITUTION:The facture, etc. of the tool 3 of the machine tool is detected by the AE sensor 7 installed near the tool 3 thereof and the work 1. The sensor 7 is so formed as to be housed in a case 31 by attaching the attenuating plate 34 having the high resistance to oil and oscillation to the bottom of the body 30 thereof. The detection signal thereof is applied to a signal processing part including a means for discriminating frequency which consists of band pass filters 11, 12, detectors 14, 15 and a comparator 17 and a means for detecting a rise signal which consists of a differentiation circuit 16. The result thereof is displayed on a display device 19. The signal of the sensor 7 is thus properly attenuated and the exact detection of the tool fracture as the unsaturating signal is made possible.

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.

The present invention relates to a tool breakage detection device that automatically detects tool breakage, and in particular to a tool breakage detection device that is characterized by the mounting structure of the AE sensor.

[Summary of the invention]

In view of the possibility that the AE signal level obtained by the AE sensor may become saturated depending on the mounting position of the AE sensor, the tool breakage detection device according to the present invention inserts a damping plate between the AE sensor and the vicinity of the tool to attenuate the signal by a factor of AE. It was designed to do so. In this way, by attaching an attenuation plate as necessary, an AE multiplied signal without saturation can be obtained from the AE sensor, so it is possible to perform reliable signal processing by adjusting the sensitivity of the AE sensor to the desired level. Become.

[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
An apparatus has been proposed that includes a sensor and detects tool breakage based on an AE multiplied signal obtained from the sensor.

However, depending on the type of machine tool, the AE sensor may only be installed in the immediate vicinity of the tool position on the machine tool. At this time, during the work, a large level AE multiplied signal is transmitted to the AE sensor, so the AE sensor may not be able to convert the large amplitude signal into an electrical signal and may become saturated. Furthermore, when a large diameter drill or the like is attached, the AE sensor is also likely to become saturated. Tool breakage is usually detected by determining the breakage signal level, so if the AE sensor is saturated, accurate signal processing cannot be performed, making it impossible to reliably detect tool breakage. was there.

[Purpose of the invention]

The present invention was made in view of the problems of the conventional tool breakage detection device, and is capable of appropriately attenuating the AE multiplied signal obtained from the AE sensor, and even when the AE signal level is high, the AE multiplied signal obtained from the AE sensor can be It is an object of the present invention to provide a tool breakage detection device that can obtain an AE multiplied signal without saturation.

[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 obtained when the tool breaks. A damping plate is inserted between the machine tool and the machine tool to attenuate the AE multiplied signal propagating through the machine tool and transmits it to the AE sensor, and a signal processing unit that identifies tool breakage based on the AE multiplied signal obtained from the AE sensor. It is characterized by:

According to the present invention having such characteristics, even when the tool position and the AE sensor need to be installed close to each other depending on the type of machine tool, the damping plate can be installed in contact between the AE sensor and the machine tool. The signal can be attenuated by AE times and converted into an electrical signal. Therefore, saturation does not occur within the AE sensor, and by appropriately amplifying its output, an appropriate AE sensor sensitivity can be set and signal processing can be performed. Therefore, there is no fear that tool breakage cannot be detected depending on the mounting position of the AE sensor, and it is possible to improve the reliability of tool breakage.

Furthermore, since the tool breakage detection device according to the present invention can detect tool breakage regardless of the AE signal level, it can be applied to various machine tools.

[Explanation of Examples]

(Overall Configuration of Embodiment) FIG. 1 is a block diagram showing the overall configuration of 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 the workpiece 1 is fixed on the base 2 of the drilling machine. An opening is provided. Here, before cutting the workpiece at the position where the drill bit on the upper part of workpiece 1 comes into contact,
Pseudo-breakage signal generator 4 made of PZT, etc., which is the same as the sensor
is installed. The level setter 5 sets the drive level of the pseudo-breakage signal generator 4, sets a predetermined drive level according to one type of tool size, and transmits it to the drive circuit 6. The drive circuit 6 generates a pseudo-breakage signal having a power spectrum distribution similar to and the same as the AE output waveform when the tool breaks, and drives the pseudo-breakage signal generator 4. Now, an AE sensor 7 for detecting the AE multiplied signal is provided near the tool on which the work l is placed, for example, on the base 2 as shown in FIG. As will be described later, the AE sensor 7 has a damping plate inserted between the AE sensor body and the base 2, and attenuates the AE multiplied signal from the AE multiplied signal of a tool such as a drill 3 or the like and the AE multiplied signal from the pseudo-breakage signal generator 4 and converts it into an electrical signal. It is a wideband AE sensor that converts, 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 set at will by adjusting a variable resistor IO, and its output is given to two band pass filters If, 12 and a cutting level indicator 13. The band pass filter 11 is a filter with a center frequency of 300 KHz, and the band pass filter 12 is a filter with a center frequency of 50 Kllz, and only signals near the respective center frequencies are passed to the next stage detector 1.
4, 15. Detector 14. ．． Reference numerals 15 and 15 respectively detect the input signals and obtain outputs corresponding to the amplitudes.The output of the detector 14 is applied to a differentiating circuit 16, and the outputs of the detectors 14 and 15 are applied to a comparator 17, respectively. These bandpass filters 11, 12, detectors 14, 15, and comparators 17
This forms a frequency identification means for identifying the AE multiplied signal at the time of breakage. The differentiating circuit 16 transmits only the steep changes in the input signal to the next level level judger 1 and the breakage/abnormal level indicator 19. The level determiner 18 compares the input signal with a predetermined reference level, and if the input signal is large, transmits the output to the breakage detection circuit 20 and the abnormal cutting detection circuit 21. Further, the comparator 17 compares the outputs of the wave detectors 14 and 15, and transmits the output to the breakage detection circuit 20 only when the output of the wave detector 14 is large. The breakage detection circuit 20 is a logic circuit that takes the logical product of these inputs to detect a breakage of the tool, and closes the analog switch 8 based on the detection signal and outputs the signal to the outside via the output circuit 22. Further, the abnormal cutting detection circuit 21 detects abnormal cutting based on the daily output of the level judger, and the output is sent to the output circuit 23.
The information is communicated to the outside through the .

(Configuration of AE Sensor and Damping Plate) FIG. 2 is a sectional view showing the configuration of the AE sensor 7 according to this embodiment. In this figure, the AE sensor 7 is the sensor body 30.
is inserted into the case 31.

The case 31 houses the AE sensor and is fixed on the base 2, and a permanent magnet is attached below the case 31 to hold the AE sensor main body 30 therein on the base 2. The upper opening of the case 31 has a screw groove as shown in the figure, and the case 31 is closed with a lid 32. and lid 3
A spring 33 is inserted between the base 2 and the AE sensor body 30, and when the lid 32 is closed, the spring 33 contracts to fix the AE sensor body 30 on the base 2. Now, in the present invention, as shown in the figure, a damping plate 34 is provided between the AE sensor main body 30 and the base 2.
Insert. The damping plate 34 is made of various materials having excellent oil resistance and vibration resistance, such as alloys such as iron and copper, synthetic resin, and ceramic resin, and is a circular plate having the same diameter as the AE sensor body 30. The AE multiplied signal attenuation rate by the attenuation plate 34 is predetermined for each of the plurality of attenuation plates, and is set to, for example, 5 dB, 10 dB, and 20 dB. When installing the AE sensor 7, a damping plate having a predetermined damping rate is selected depending on its position. That is, when the AE sensor 7 is installed very close to the drill 3, a damping plate with a high attenuation rate is used, and when it is placed a predetermined distance from the drill 3, a damping plate with a small attenuation rate is used. In this way, the AE sensor main body 30 is housed in the case 31 on the base 2 via the damping plate 34, and the AE sensor 7 is fixed on the base 2 by closing the case 31 from above using the lid 32.

(AE Sensor Sensitivity Setting Operation) Next, the operation when installing the tool breakage detection device according to this embodiment in a machine tool, in this case a drilling machine, will be explained.

First, after installing the AE sensor 7 at a predetermined position, the level setter 5 is set to a predetermined level according to the type of tool, that is, the diameter of the drill, and the pseudo-breakage signal generator 4 is driven via the drive circuit 6. Then, while monitoring the display on the breakage/abnormality level indicator 19, the variable resistor 10 is adjusted so that the level is set according to the setting of the level setting device 5, and the amplification factor of the amplifier 9 is changed. Appropriate level of A for the signal processing section
Allow E times signal to be given. If the AE sensor 7 is installed in the immediate vicinity of the tool 3, the large level of the AE multiplied signal transmission signal may become saturated. Therefore, as shown in FIG. The output of the inserted AE sensor 7 is prevented from being saturated, and the amplification factor of the amplifier 9 is changed so that an appropriate level of the AE multiplied signal is transmitted to the signal processing section. In this way, tools and AE
Even if the AE multiplied signal attenuation rate is unknown depending on the mounting condition between the sensors 7, it is possible to provide the signal processing section with a signal at the same level as when the sensor is broken.

(Operation of Signal Processing Unit) After setting the sensitivity of the AE sensor, the drill 3 is pushed down onto the workpiece to perform cutting. The distribution of the power spectrum of the AE multiplied signal given by the AE sensor 7 during normal cutting is concentrated around a frequency of 50 KIIz, as shown by the curve in Figure 3, and the distribution monotonically attenuates in the higher frequency range. It has become. Furthermore, as is known from many experiments, the distribution of the power spectrum when a tool breaks is represented by curve a in FIG. 3, 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, only the AE multiplied signals near the respective frequency components are extracted by the two bandpass filters 11 and 12 and sent to the detector 14.
15, and by comparing the output levels, it is possible to clearly distinguish between a normal situation and a broken tool. 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, contact between chips generated during cutting and tools and workpieces,
Friction may generate a signal similar to the power spectral distribution shown by curve a in FIG. Therefore, in this embodiment, attention is paid to the waveform of the AE multiplied signal time domain which is observed when a tool breaks, and these signals are separated. That is, the AE signal waveform obtained when the tool breaks is a signal that has a sharp rise at the time of breakage, as shown in FIG. 4(a).
On the other hand, the AE multiplied signal generated by contact and friction between chips and a tool or workpiece has a waveform that does not show a sharp rise and continues for a predetermined period of time, as shown in FIG. 4 (bl).

Therefore, as shown in FIG. 1, the output of the detector 14 is applied to a differentiating circuit 16, and only steep signals such as those caused by breakage are separated and applied to a level determiner 18. The input level is then compared with a predetermined reference value, and when an AE multiplied signal with a steep rise is obtained, a signal is provided from the level determiner 18 to the breakage detection circuit 20. The breakage detection circuit 20 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 2
2 provides a broken output, and the analog switch 8 is turned off so that the signal is not transmitted to the AE multiplier signal amplifier 9 thereafter. This is to make it possible to check the signal level at the time of breakage by not displaying the large AE multiplier signal display 13.19 that occurs due to abnormal contact or friction between the broken tool and the workpiece after the tool breaks. be.

In this embodiment, the signal processing section detects breakage by the logical product of breakage detection in the frequency domain and breakage detection in the time domain, but breakage may be detected by using either one of these. It is also possible to use or combine other breakage detection methods.

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

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of the tool breakage detection device according to the present invention, FIG. 2 is a sectional view showing the structure of the AE sensor according to the present invention, and FIG. 3 is a block diagram showing the AE sensor 7 obtained from the AE sensor 7.
FIG. 4 (al is the AE signal waveform obtained when the tool breaks, the fourth output) is a diagram showing the double signal power spectrum, and is a diagram showing the AE signal waveform obtained when chips are generated. 1-・-・-Work 2-・-・-Base 3-・
−11−−−Drill 4−−−−−−−Pseudo-breakage signal generator 5−−−−−−−Level setter 6−・−・−
Drive circuit 7・------A E sensor 8------
--Analog switch 9-・-Amplifier 11.1
2---・-Band pass filter 14.15----
---1 detector 16---1--differentiator circuit 17
-------Comparator 18...Level determiner 20---Breakage detection circuit 22, 2
3--------One output circuit 30--A E sensor body 31-----Case 32-3--・
- Lid 33 - - - Spring 34 - - Damping plate Patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (1 person) Figure 2 Figure 3

Claims (2)

[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 an AE signal obtained when the tool breaks, the AE sensor and the AE sensor installation surface of the machine tool are provided. is inserted between the
A tool breakage detection device comprising: an attenuation plate that transmits information to an E sensor; and a signal processing unit that identifies tool breakage based on an AE signal obtained from the AE sensor. (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.