JPH055618B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention is a method for monitoring tool breakage and abnormalities in machine tools 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.

[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 recent progress in factory automation, there is a strong demand for automatic detection of tool breakage and abnormal cutting. As one method for detecting tool breakage in machine tools, a device has been proposed that installs an AE sensor near the tool or workpiece of the machine tool and detects tool breakage based on the AE signal obtained from the AE sensor. There is.

However, according to conventional tool breakage detection devices, the AE sensor is installed near the tool or in contact with the workpiece, but depending on the installation position,
The level of the AE signal is significantly different. 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 signal when a tool breaks can only be obtained when the tool breaks, it is difficult to confirm the mounting position and mounting condition of the AE sensor, making it difficult to reliably detect tool breakage. Furthermore, the AE signal level varies 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 value of the amplitude of the signal obtained from the AE sensor or a specific frequency. There was a problem in that reliability was low because it could not be sufficiently separated from the signals generated by the process, the electrical noise associated with the opening and closing of the solenoid, and the impact sound caused when an object comes into contact with the workpiece.

[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 an AE installed near the tool of a machine tool.
A tool breakage detection device that has a sensor and detects breakage based on an AE signal obtained when a tool breaks, and generates a pseudo AE signal that includes the frequency of the AE signal obtained when a tool breaks. a variable amplification factor amplifier that amplifies the AE signal of the AE sensor by changing the amplification factor based on an external input;
Simulated by drive level corresponding to the tool used
AE sensitivity setting means for driving the AE signal generation means and setting the amplification factor of the variable amplification factor amplifier to an optimum value;
A storage means for storing the optimum amplification factor for each tool set by the sensitivity setting means, and a variable means for storing the optimum amplification factor for the AE signal of a frequency component that has a strong correlation with the frequency component of the AE signal obtained when the tool breaks. A frequency identification means that outputs an output when a signal is given from the amplification factor amplifier, a rising signal detection means that produces an output when a rapidly rising signal is given from the AE sensor, and the logic of the frequency identification means and the rising signal detection means. The present invention is characterized by comprising logic output means for outputting a tool breakage detection output based on the product output.

According to the present invention having such characteristics, the optimum sensitivity of the AE sensor is stored in advance for each tool used in a machine tool according to the usage environment.
Therefore, even when using any tool, AE is automatically performed.
It becomes possible to adjust the sensitivity of the sensor to an optimal value. After adjusting in this way, the frequency identification means identifies the AE signal that has a strong correlation with the power spectrum of the AE signal obtained at the time of tool breakage, and at the same time, the rising signal detection means identifies the AE signal observed at the time of tool breakage.
Detection of a steep rise in the signal is determined independently, and tool breakage is detected based on the logical product condition. Therefore, there is no possibility of malfunction due to signals such as chips from the workpiece or electrical noise, and there is no AE from the tool.
Since it is not affected by the attenuation of the AE signal up to the sensor, it is possible to greatly improve the reliability of tool breakage detection.

[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, like 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 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 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 AE signals from tools such as the drill 2 and AE signals from the pseudo AE signal generator 4, and its output is given to the AE signal processing section 7. The AE signal processing unit 7 amplifies the signal from the AE sensor 6 to a predetermined level, detects signals of tool breakage and abnormal cutting, and connects the input/output interface 8 to the input/output interface 8.
It is provided to the central processing unit (hereinafter referred to as CPU) 9 through the CPU. The CPU 9 has a read-only memory (hereinafter referred to as "read-only memory") that stores system control programs.
Random access memory (hereinafter referred to as RAM) containing sensitivity information of the AE sensor corresponding to the tool used by this numerical control device 3
11) is connected to the storage means. CPU9 also has input/output interface 1
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 through the terminal 2. Furthermore, signal transmission line 1
A numerical control device 3 is connected via 5.
The CPU 9 performs a predetermined pseudo AE based on these inputs.
Applying the drive level of the signal generator 4 to the drive circuit 5,
It detects the optimum sensitivity based on the AE signal level obtained from the AE signal processing section 7, stores it sequentially in the RAM 11, and controls the sensitivity to be set to that sensitivity when the corresponding tool is used from now on. be.

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 cuts off and on the analog signal based on the control signal from the CPU 9, and its output end is connected to the variable gain amplifier 21. The amplifier 21 is a variable amplification factor amplifier whose amplification factor can be set based on the 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 something.
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. Detector 2
Reference numerals 4 and 25 each detect the input signal and obtain an output according to the amplitude.The output of the detector 24 is applied to a differentiating circuit 26, and the outputs of the detectors 24 and 25 are applied to a comparator 27, respectively. These bandpass filters 22, 23, detectors 24, 25, and comparator 27 form a frequency identification means for identifying the AE 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, the comparator 27 is the detector 24,
The outputs of the wave detector 25 are compared, and the output is transmitted 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 CPU 9 via the input interface 8. The abnormal cutting detection circuit 30 detects abnormal cutting based on the output of the level determiner 28 and transmits the detected abnormal cutting to the CPU 9 via the input/output interface 8.

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 starts, the input key 14 is first pressed in step 40.
Then, the data (magazine number) corresponding to the size of the tool being used at the time inputted by the user is read. The process then proceeds to step 41, where a drive level of the pseudo AE signal generator 4 corresponding to the magnitude is applied to the drive circuit 5. Then, the drive circuit 5 generates a pseudo AE signal generator 4 to drive the pseudo AE signal generator 4.
An AE signal is transmitted from the AE signal generator 4 to the AE sensor 6 via the workpiece 1 and the base. At this time
The pseudo AE 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. This AE signal is transmitted to the AE signal processing section 7, where it is connected to an analog switch 20 and a variable gain amplifier 2.
1 to the CPU via input/output interface 8
9 will be informed. CPU9 at step 42
Variable amplification factor amplifier 21 for the signal level of the AE sensor
The output level is adjusted according to the amplification factor, and the process 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. Then, the loop of steps 42 to 44 is repeated to adjust the amplification factor appropriately. The optimal amplification factor thus obtained is stored in a predetermined area of the RAM 11 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 for all the tools used by the numerical control device 3 are adjusted, and as shown in the memory map in FIG. are stored in sequence and the sensitivity setting process is completed.

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 manner. FIG. 5 is a flowchart showing this monitoring operation. When the monitoring operation starts, first, in step 50, the optimum value of the amplification factor corresponding to the tool is read out from the RAM 11, and the AE signal is processed via the input/output interface 8. The amplification factor of the variable amplification factor amplifier 21 of the section 7 is set. Then, depending on the cutting of workpiece 1, the AE sensor 6 will
A signal is applied via an analog switch 20,
The signal is amplified by an optimum amplification factor and provided to two bandpass filters 22 and 23. Now, the distribution of the power spectrum of the AE signal given by the AE sensor 6 during normal cutting is concentrated around the frequency of 50 KHz, as shown by curve b in Figure 6, and the distribution monotonically attenuates in the higher frequency range. It is becoming. 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 become clear 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 filter out frequencies near the respective frequency components.
By extracting only the AE signal, detecting it by the detectors 24 and 25, and comparing the output levels, it is possible to clearly 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 300 KHz is greater than the power near a frequency of 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 a tool workpiece during cutting. In this case, the bandpass filters 22, 2
Even if the center frequency and Q value of 3, the threshold level of the comparator 27, etc. are set appropriately, a signal caused by contact or friction between chips and a tool or workpiece may be mistakenly judged as a tool breakage signal. . Therefore, in the present invention, attention is also paid to the time-domain waveform of the AE signal seen when a tool breaks, and these signals are separated. That is, the AE signal waveform obtained when the tool breaks is a signal with a sharp rise as shown in Figure 7a, while the AE signal generated by contact and friction between chips and the tool or workpiece has a sharp rise. As shown in FIG. 7b, the waveform does not show a sharp rise and continues for a predetermined period of time. Therefore, as shown in the block diagram of FIG. 2, the output of the wave detector 24 is applied to a differentiating circuit 26, which separates only steep signals such as those caused by breakage, and provides the separated signal to a level determiner 28. The level determiner 28 provides an output to the breakage detection circuit 29 and the abnormal cutting detection circuit 30 when the input signal is large. The abnormal cutting detection circuit 30 is connected to the input/output interface based on the output of the level judger 28.
Inform CPU9 of abnormal cutting. In the flowchart shown in FIG. 5, the CPU 9 checks whether or not an abnormal cutting signal is transmitted from the abnormal cutting detection circuit 30 (step 51). If there is no abnormal cutting signal, normal cutting operation is being performed, so the CPU 9 checks whether the abnormal cutting signal is transmitted from the abnormal cutting detection circuit 30 or not.
Proceeding to step 52, the cutting level is displayed on the display 13. Then, the process returns to step 50 and repeats the same process, and while the processes in steps 50 to 52 are executed, cutting abnormalities are monitored. Now, the abnormal cutting detection circuit 30
If an abnormal cutting signal is transmitted, the process advances to step 53 to check whether the breakage detection circuit 29 provides a breakage signal. The breakage detection circuit 29 detects tool breakage based on the AND of the comparator 27 and the level determiner 28, and when the tool breaks, it transmits the breakage output to the CPU 9 via the input/output interface. Therefore, it is checked in step 53 whether or not a breakage signal is given. If not, abnormal cutting is being performed, so in step 54 the display 13 displays abnormal cutting, and the process returns to step 50. Also, if a breakage detection signal is given in step 53, tool breakage has been detected, so step 55 is performed.
Then, the broken tool is displayed on the display 13, 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 seen in machine tools, such as spike-like electrical noise caused by the opening and closing of a solenoid, can be removed by the bandpass filter 20 and the detector 2.
4 from the differentiating circuit 26 to the level determiner 28, but its power spectrum has a monotonically decreasing distribution as shown in curve c in FIG. 6, and the output from the comparator 27 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 27 and no tool breakage signal is generated. 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 tool breakage is detected in this manner, the analog switch 20 is turned off and input of the AE signal is subsequently stopped. This is to prevent a large AE signal generated due to abnormal contact or friction between the broken tool and the workpiece that occurs after the tool breaks from being further determined as a breakage.

In this embodiment, breakage is detected by analog processing in the AE signal processing section 7, but the AE
It is also possible to sample the sensor output after A/D conversion and perform all subsequent processing by digital signal processing. In this case, it is conceivable to replace the bandpass filter with a digital filter, replace the differentiation circuit with a difference operation, 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 a flowchart showing the state in which the amplification factor obtained at that time is stored. A flowchart showing the process, Fig. 6 shows the power spectrum of the AE signal obtained from the AE sensor 6, Fig. 7a shows the AE signal waveform obtained when the tool breaks, and Fig. 7b shows the AE signal waveform obtained when chips are generated. FIG. 3 is a diagram showing an AE signal waveform. 1... Work, 2... Drill, 3... Numerical control device, 4... Pseudo AE signal generator, 5... Drive circuit, 6... AE sensor, 7... AE signal processing section,
8, 12...I/O interface, 9...
CPU, 10...ROM, 11...RAM, 13...
...Display device, 14...Input key, 20...Analog switch, 21...Variable gain amplifier, 22,2
3...Band pass filter, 24, 25...Detector, 26...Differentiating circuit, 27...Comparator, 28...
...Level judger, 29...Breakage detection circuit, 30...
...Abnormal cutting detection circuit.

Claims (1)

[Claims] 1. In 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, the AE obtained when the tool breaks. A pseudo AE signal generating means for generating a pseudo AE signal including a signal frequency; a variable amplification amplifier for amplifying the AE signal of the AE sensor by changing the amplification factor based on an external input; and a drive corresponding to the tool used. AE sensitivity setting means for driving the pseudo AE signal generation means according to a level and setting the amplification factor of the variable amplification factor amplifier to an optimum value; and a memory for storing the optimum amplification factor for each tool set by the AE sensitivity setting means. and frequency identification means that outputs an output when an AE signal having a frequency component having a strong correlation with a frequency component of an AE signal obtained when a tool breaks is given by the variable amplification factor amplifier set to the optimum amplification factor. , a rising signal detecting means that outputs an output when a signal that rises suddenly from the AE sensor is given, and a logical output means that produces a tool breakage detection output based on the AND output of the frequency identifying means and the rising signal detecting means. A tool breakage detection device comprising: 2 The frequency identification means includes a bandpass filter whose center frequency is the maximum value of the frequency obtained when detecting tool breakage and the frequency obtained during normal cutting, and a comparator that compares the output level of each of the bandpass filters. 2. The tool breakage detection device according to claim 1, wherein the tool breakage detection device has a comparator and obtains a tool breakage signal from the comparator. 3. The tool according to claim 1, wherein the rising signal detection means includes a differentiation circuit that differentiates the AE signal, and detects rapid amplitude fluctuations based on the differential output. Breakage detection device.