JPH055624B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention is a method for monitoring breakage and abnormalities of tools in machine tools using acoustic emission (hereinafter referred to as AE) that occurs during cutting and breakage.
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 was developed in consideration of the fact that the AE signal at the time of tool breakage attenuates with the same attenuation characteristics regardless of the type of tool.
The attenuation characteristics are determined by comparing the amplitude levels of the AE signal at two times. and
This method identifies the similarity between the attenuation characteristics of the AE signal and the AE signal at the time of tool breakage, and uses this as a condition for detecting tool breakage. In this way, by adding a detection condition based on the amplitude attenuation characteristic that is independent of other breakage detection conditions such as frequency detection, the reliability of tool breakage detection can be improved.

[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 breakage of tools in machine tools, conventional methods have been to
A device has been proposed that includes an AE sensor and detects tool breakage based on the AE signal obtained from the sensor.

However, according to the conventional tool breakage detection device, tool breakage is detected based on the average value of the amplitude of the signal obtained from the AE sensor or a specific frequency. Therefore, it is not possible to sufficiently separate the AE signal obtained from other causes, such as signals generated from chips on the workpiece, electrical noise associated with the opening and closing of a solenoid, and impact noise when an object comes into contact with the workpiece. There was a problem in that the reliability of breakage detection was extremely low.

[Purpose of the invention]

The present invention has been 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 of the present invention is to provide a highly reliable tool breakage detection device.

[Structure and effects of the invention]

The present invention is an AE installed near the tool of a machine tool.
A tool breakage detection device that has a sensor and detects breakage based on the AE signal obtained when the tool breaks, the amplitude of the AE signal of the AE sensor at a certain time and the amplitude of the AE signal a certain time before that time. Compare the
a damping characteristic identifying means that outputs an output when the ratio of the amplitudes is within a range of the damping characteristic at the time of breakage; a signal processing section that identifies tool breakage based on the output signal of the AE sensor; and a damping characteristic identifying means and a signal. The present invention is characterized by comprising a logical output means for outputting a tool breakage detection output based on the logical product output of the processing section.

According to the present invention having such characteristics, the attenuation characteristic of the AE signal at the time of tool breakage is used as one of the conditions for detecting tool breakage. The attenuation characteristic of the AE signal at the time of breakage is also not affected by the attenuation of the AE signal from the tool to the AE sensor. Therefore, tool breakage can be reliably detected by the AND condition together with other detection conditions, such as the determination of breakage based on the power spectrum distribution of the AE signal or the determination based on the rising edge of the breakage signal. Therefore, according to the present invention, there is no possibility of malfunction due to signals such as chips of the workpiece or electrical noise, and it is possible to greatly improve the reliability of tool breakage detection.

[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 installed on a drilling machine, and the workpiece 1 is fixed on the base of the drilling machine, and the drill 2 is rotated from the top of the workpiece 1 and pushed down at a predetermined speed to open the workpiece 1. will be provided. Here, before cutting the workpiece at the position where the drill bit on the top of workpiece 1 makes contact, the AE sensor
A pseudo-breakage signal generator 3 made of PZT or the like is attached. The level setter 4 sets the drive level of the pseudo-breakage signal generator 3, sets a drive level determined according to the size and type of the tool used, and transmits it to the drive circuit 5. The drive circuit 5 drives the pseudo-breakage signal generator 3, and drives the pseudo-breakage signal generator 3 in advance with a drive waveform that is similar to and has the same power spectrum distribution as the AE output waveform when the tool breaks. It is something. An AE sensor 6 for detecting an AE 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 the AE signal from a tool such as the drill 2 or the AE signal from the pseudo-breakage signal generator 3, and its output is given to the analog switch 7. The analog switch 7 connects and disconnects the analog signal using an external output, and the output is applied to the amplifier 8. The amplifier 8 is an amplifier whose amplification factor can be arbitrarily set by adjusting a variable resistor 9, and provides its output to two band pass filters 10, 11 and a cutting level indicator 12. The bandpass filter 10 is a filter with a center frequency of 300KHz, and the bandpass filter 11 is a filter with a center frequency of 50KHz, and only signals near the respective center frequencies are transmitted to the next-stage detectors 13 and 14. The detectors 13 and 14 each detect the input signal and obtain an output according to the amplitude, and the output of the detector 13 is given to a differentiating circuit 15 and a delay circuit 16. Further, the outputs of the detectors 13 and 14 are provided to a comparator 17, respectively. These bandpass filters 10, 11, detectors 13, 14, and comparator 1
7 forms a frequency identification means for identifying the AE signal at the time of breakage. Differentiating circuit 15 transmits only steep changes in the input signal to level determiner 18 at the next stage. 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 19 and the abnormal cutting detection circuit 20. The delay circuit 16 delays the input signal by a predetermined time ΔT, and provides its output to the attenuator 21. Attenuator 21
As will be described later, the attenuator attenuates the input signal at a predetermined ratio, and its output is applied to one input terminal of the window comparator 22. Further, the output of the wave detector 13 is directly applied to the other input terminal of the window comparator 22 without going through the delay circuit 16. The window comparator 22 outputs an output when the difference between two input signals falls within a predetermined range, and transmits the output to the breakage detection circuit 19. Here, the delay circuit 16, the attenuator 21, and the window comparator 22 form an attenuation characteristic identifying means for identifying the attenuation characteristic at the time of breakage. The comparator 17 also compares the outputs of the wave detectors 13 and 14, and transmits the output to the breakage detection circuit 19 only when the output of the wave detector 13 is large. Breakage detection circuit 1
Reference numeral 9 denotes a logic circuit that detects tool breakage by calculating the logical product of these inputs, and closes the analog switch 7 based on the detection signal, and also closes the output circuit 23.
Output to the outside via. Also, abnormal cutting detection circuit 2
0 detects abnormal cutting based on the output of the level determiner 18, and outputs the output to the output circuit 2.
4 to the outside.

(AE Sensor Sensitivity Setting Operation) Next, the operation when installing the AE sensor of this tool breakage detection device in a machine tool, in this case a drilling machine, will be explained in this embodiment. First, the AE sensor 6 is installed at a predetermined position, and then the level setter 4 is set to a predetermined level depending on the type of tool, etc., and the drive circuit 5 is operated. Then, the AE signal is transmitted from the pseudo-breakage signal generator 3 to the AE sensor 6 via the workpiece 1 and the base. At this time, the pseudo-breakage signal obtained from the AE sensor 6 has the same power spectrum as when the tool breaks, and also has a waveform similar to the waveform when the tool breaks in the time domain. Therefore, the variable resistor 9 is adjusted according to the level determined by the level setter 4, and the amplification factor of the amplifier 8 is changed to provide an AE signal of an appropriate level to the signal processing section during work. be able to do so. In this way, even if the attenuation rate of the AE signal is unknown due to the mounting condition between the tool and the AE sensor 6, it is possible to provide the signal processing unit with a signal at the same level as when the tool is broken.

(Operation of the signal processing unit) Now, the distribution of the power spectrum of the AE signal given by the AE sensor 6 during normal cutting is the second
As shown by curve b in the figure, it is concentrated around the frequency of 50 KHz, and the distribution is monotonically attenuated in the higher frequency range. Also, as is known from many experiments, the power spectrum distribution when a tool breaks is represented by curve a in Figure 2, and the frequency is 300K.
It has become clear that it has a peak around 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, the two bandpass filters 10 and 11 extract only the AE signals near the respective frequency components and send them to the detector 1.
3 and 14, and by comparing their output levels, it is possible to distinguish between normal conditions and tool breakage conditions. That is, during normal cutting, the power of the AE signal near a frequency of 50 KHz is greater than the power near a frequency of 300 KHz, and when a tool breaks, the power near a frequency of 300 KHz is greater than the power near a frequency of 50 KHz. The comparator 17 compares these outputs and sends a signal only when the tool breaks to the breakage detection circuit 19.
is giving to

On the other hand, a signal similar to the power spectrum distribution shown by curve a in FIG. 2 may be generated due to contact and friction between chips and tools or workpieces generated during cutting. In this case, a bandpass filter 10,
Even if the center frequency and Q value of 11 and the threshold level of comparator 16 are set appropriately, a signal caused by contact between chips and the tool or workpiece or friction may be mistakenly judged as a tool breakage signal. . Therefore, in this example, the AE observed when the tool breaks
We also focused on the time domain waveforms of the signals and separated these signals. That is, obtained when the tool breaks.
As shown in Figure 3a, the AE signal waveform is a signal with a sharp rise at the time of breakage.
As shown in FIG. 3b, the signal has a waveform that does not show a sharp rise but continues for a certain period of time. Therefore, as shown in FIG. 1, the output of the detector 13 is applied to a differentiating circuit 15, which separates only steep signals such as those caused by breakage, and provides the separated signal to a level determiner 18. The input level is then compared with a predetermined reference value to detect a steep rise.
When the AE signal is obtained, a signal is given from the level determiner 18 to the breakage detection circuit 19.

(Operation of attenuation characteristic identification means) Next, there is a possibility that a signal that is not a breakage signal is generated because the rising edge is sharp and the power spectrum distribution is the same as that at the breakage signal. Therefore, in the present invention, the reliability of breakage detection is improved by focusing on the rising waveform of the breakage signal, that is, the attenuation characteristic, and identifying those having the attenuation characteristic at the time of breakage and using this as a breakage determination condition. Figure 4 shows the AE at the time of breakage obtained from the detector 13 at the time of breakage.
It is a figure which shows an example of the envelope waveform of a signal. As shown in this figure, at the time of breakage, the E signal rises sharply and is attenuated according to a predetermined attenuation characteristic. This attenuation has the same waveform regardless of the type or size of the tool. Therefore, the output level of the breakage signal of the AE sensor 6 adjusted to the optimum sensitivity is almost the same,
Moreover, it has become clear from many experiments that the time Ta required for the signal to exceed the average signal level and return to the normal level does not exceed 5 mS. Therefore, if the time when the signal rises and reaches its peak is t1, and the time after a certain period of time ΔT (for example, 3 mS) has elapsed from time t1 is t2, then the ratio of the amplitudes A1 and A2 at times t1 and t2 is and identify the damping characteristics. That is, the delay time of the delay circuit 16 is set to ΔT, and the attenuation rate of the attenuator 21 is set to A2/A1. Then the delay circuit 16
The delayed output of is attenuated to A2/A1 by the attenuator 21. A range in which these outputs are considered to be substantially the same is determined by the window comparator 22. Then the detector 13
When the obtained AE signal has attenuation characteristics as shown in FIG. The signal is applied to the breakage detection circuit 19. The breakage detection circuit 19 detects tool breakage based on these AND signals. In this way, by using the attenuation characteristic of the signal at the time of breakage as one of the conditions at the time of breakage and combining it with other breakage detection conditions, for example, breakage detection in the frequency domain and breakage detection in the time domain, it is possible to reliably detect only tool breakage. It becomes possible to detect.

(Overall operation of this embodiment) In this way, other signals seen in the machine tool, such as spike-like electrical noise caused by the opening and closing of a solenoid, can be removed by the bandpass filter 10 and the detector 1.
3 from the differentiating circuit 15 to the level judger 18, but its power spectrum has a monotonically decreasing distribution as shown by curve c in FIG. 2, and the output from the comparator 17 I can't get it.
Another possibility is the shock wave generated when an object collides with workpiece 1 or the base of workpiece 1, but in this case as well, the power spectrum is concentrated at low frequencies due to mechanical vibration, and is greatly attenuated at frequencies around 300KHz. Therefore, no output is obtained from the comparator 17, and no tool breakage signal is generated. Furthermore, it has a power spectrum as shown in curve a in Fig. 2 and a sharp rise as shown in Fig. 3 a.
Even when the AE signal is applied, the output from the window comparator 22 will not be applied to the breakage detection circuit 19 unless there is an attenuation characteristic as shown in FIG. Therefore, there is no risk of erroneously detecting such a signal as a breakage signal, and it is possible to improve the accuracy of breakage detection. In this way, only the breakage of the tool is detected and a breakage signal is provided from the output circuit 23, and the analog switch 7 is turned off so that no AE signal is transmitted to the amplifier 8 thereafter. This is to prevent the cutting level display 12 from displaying a large AE signal generated by abnormal contact or friction between the broken tool and the workpiece after the tool breaks, so that the signal level at the time of breakage can be recognized.

In this embodiment, as attenuation characteristic identification means, a delay circuit, an attenuator that attenuates the delayed signal at a predetermined ratio, and comparison means that compares the attenuated signal with the signal before the delay are provided. It is also possible to amplify and compare, or to directly compare the ratio of the two. Furthermore, it is also possible to detect the attenuation characteristic by sequentially storing the output of the AE sensor and comparing the data before a predetermined time ΔT with the data at that time.

Furthermore, in this embodiment, in addition to the attenuation characteristic identification means, breakage detection in the frequency domain and breakage detection in the time domain are both used to detect breakage by the logical product of these. It is also possible to use a combination of other types of breakage detection.

Furthermore, 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 drawings]

FIG. 1 is a block diagram showing an embodiment of the tool breakage detection device according to the present invention, and FIG. 2 is a diagram showing the power spectrum of the AE signal obtained from the AE sensor 6.
Figure 3a shows the AE signal waveform obtained when the tool breaks.
FIG. 3b is a diagram showing the AE signal waveform obtained when chips are generated, and FIG. 4 is a diagram showing the envelope waveform of the breakage signal obtained from the detector 13. 1... Work, 2... Drill, 3... Pseudo-breakage signal generator, 4... Level setting device, 5... Drive circuit, 6... AE sensor, 7... Analog switch,
8...Amplifier, 10, 11...Band pass filter, 13, 14...Detector, 15...Differentiating circuit,
16...Delay circuit, 17...Comparator, 18...Level determiner, 19...Breakage detection circuit, 21...Attenuator, 22...Window comparator,
23, 24...output circuit.

Claims (1)

[Claims] 1. A tool breakage detection device that has an AE sensor installed near a tool of a machine tool and detects breakage based on an AE signal obtained when the tool breaks, comprising: Compare the amplitude of the AE signal and the amplitude of the AE signal a certain time before the time,
attenuation characteristic identification means that outputs an output when the ratio of the amplitudes is within the range of the attenuation characteristics at the time of breakage; a signal processing section that identifies tool breakage based on the output signal of the AE sensor; and the attenuation characteristic identification means. and logic output means for outputting a tool breakage detection output based on the AND output of the signal processing section. 2 The signal processing section is obtained when the tool breaks.
Tool breakage detection according to claim 1, characterized in that it is a frequency identification means that outputs an output when an AE signal of a frequency component having a strong correlation with a frequency component of the AE signal is given from the AE sensor. Device. 3. The tool breakage detection device according to claim 1, wherein the signal processing section is a rising signal detection means that outputs an output when a signal that rises rapidly is given from the AE sensor. 4 The signal processing section is obtained when the tool breaks.
a frequency identification means that outputs an output when the AE sensor receives an AE signal having a frequency component having a strong correlation with the frequency component of the AE signal, and outputs an output when a signal that rises rapidly is provided from the AE sensor. 2. The tool breakage detection device according to claim 1, wherein the detection means outputs an output based on a logical product of the rising signal detection means.