JPS61164765A - Detecting device of tool breakage - Google Patents

Abstract

PURPOSE:To improve reliability of detecting breakage by detecting unusual cutting from the abrupt rise of an AE (acoustic emission) signal while detecting the breakage of a tool from the frequency in the issuance of an unusual cutting signal. CONSTITUTION:At the time of cutting operation, the peak in the distribution of power spectrum of the AE signal of an AE sensor 7, is around a frequency of 300kHz when a tool is broken. This is detected by detectors 14, 15 and compared with the frequency 50kHz at the time of ordinary cutting operation, by means of a comparator 17 and the resulting signal is given to a breakage detecting circuit 19 only at the time of breakage of the tool 3, to detect the breakage of tool and give a signal to an OR circuit 21. On the other hand, when an unusual cutting signal is given to an unusual signal counter 23, a one-shot signal is generated. And, the unusual cutting signal which is continuously generated from a circuit 20 during this time, is transmitted to a shift register and shifted, and the resulting output on the final stage is transmitted to an output circuit 22 and a switch 8 as a tool breakage detected output, via the OR circuit 21.

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 detects an abnormality based on a rising signal indicating an instantaneous rise in the output of the AE sensor, and detects a tool breakage when an abnormal cutting output is continuously obtained within a predetermined period. Even if no breakage is detected, it is assumed that there is a breakage and a breakage signal is output. This makes it possible to detect tool breakage without fail even when various signals are generated, such as when no clear breakage signal is generated when the tool breaks.

[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, 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, and the AE multiplied signal obtained from other causes, such as It was not possible to sufficiently distinguish the noise from 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 are also variations in the characteristics of the AE multiplied signal that occurs when a tool breaks, and there are cases where an AE multiplied signal is generated that cannot be clearly determined to be a breakage. Therefore, for such breakage, a certain breakage detection process alone is not sufficient, and there is also a problem that the breakage may be overlooked.

[Purpose of the invention]

The present invention has been made in view of the problems of conventional tool breakage detection devices, and the present invention detects tool breakage by detecting tool breakage even when abnormal cutting occurs continuously in a short period of time. It is an object of the present invention to provide a tool breakage detection device that has an expanded range.

[Structure and effects of the invention]

The present invention is a tool breakage detection device that has an AE sensor installed in a tool support of a machine tool and detects breakage based on an AE multiplied signal obtained when a tool breaks, and the device an abnormal cutting detection circuit that detects an abnormality in tool cutting based on a rising signal indicating an increase; a counting means that counts abnormal cutting signals given within a predetermined time based on an output signal of the abnormal cutting detection circuit; and an AE sensor. A signal processing unit that identifies tool breakage based on the characteristics of the output signal of and detects tool breakage when the count value of the counting means reaches a predetermined value. be.

According to the present invention having such features, abnormal cutting is detected based on the sudden rise of the AE multiplied signal obtained from the AE sensor, and tool breakage is detected based on the frequency of occurrence of the abnormal cutting signal. Therefore, even if a tool breaks due to generation of signals such as frequency characteristics and rise characteristics that are different from normal breakage signals, the present invention makes it possible to detect the breakage and improve the reliability of breakage. can.

[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 1. Here, before cutting the workpiece, a pseudo-breakage 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 contacts the upper part of the workpiece 1. The level setter 5 sets the drive level of the pseudo-breakage signal generator 4, and transmits a drive level signal set according to one type of tool size to the drive circuit 6. 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. AE sensor 7 is drill 4
This is a wideband AE sensor that detects the AE multiplied signal from the pseudo-breakage signal generator 4 from tools such as tools, and its output is given to the 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 30
0KHz, bandpass filter 12 center frequency 50K
Hz filter, and transmits only signals near the respective center frequencies to the next stage detector 14.15. Detector 14.
15 detects the input signal and obtains an output according to the amplitude, and the output of the detector 14 is sent to a differentiating circuit 16.
The outputs of the detectors 14 and 15 are provided to comparators 17, respectively. These band pass filters 11, 12, detector 14
．． 15 and the comparator 17 form a frequency identification means for identifying the AE multiplied signal at the time of breakage. Differentiating circuit 16 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.

Also, the comparator 17 compares the outputs of the detectors 14 and 15, and sends the output to the breakage detection circuit 1 only when the output of the detector 14 is large.
Tell 9. The breakage detection circuit 19 is a logic circuit that performs the logical product of these inputs to detect a breakage of the tool, and provides a breakage detection signal to the OR circuit 21. Further, the abnormal cutting detection circuit 20 is made up of a monostable multi-bi-break circuit that outputs a predetermined pulse based on the rising signal of the level determiner 18, and detects abnormal cutting, and its output is sent to the abnormal signal counter 23 and the output circuit. 24. The abnormal signal counting section 23 counts the output of the abnormal cutting detection circuit 20, and outputs an output when the counted value is equal to or greater than a predetermined value, and provides the output to the OR circuit 21.

The OR circuit 21 provides a breakage detection output to the output circuit 22 by ORing with the output of the breakage detection circuit 19, and closes the analog switch 8.

(Configuration of Abnormal Signal Counting Unit) Next, the detailed configuration of the abnormal signal counting unit 23, which is a feature of the present invention, will be described with reference to FIG.

First, the output of the abnormal cutting detection circuit 20 is given to the gate circuit 31 and the rising edge detection section 32. The rising edge detecting section 32 is composed of, for example, a differentiating circuit, etc., which detects the rising edge of the abnormal cutting signal, and its output is sent to the blank shot signal generating section 33.
tell to. The one-shot signal generator 33 is a generator that uses the signal from the rise detector 32 as a trigger input and generates a pulse with a predetermined time width, for example, 1 second, and its output is given to the gate circuit 31 and the fall detector 34. It will be done. The gate circuit 31 uses the output of the one-shot signal generator 33 as a gate to transmit an abnormal cutting signal given from the abnormal cutting detection circuit 20 to the shift register 35. Further, the falling detection section 34 detects the falling edge of the one-shot signal and transmits a trigger signal to the reset signal generation section 36. The reset signal generator 36 generates a predetermined width signal based on the input signal and transmits it to the shift register 35.

The shift register 35 has, for example, a 5-bit configuration, and its serial output end is connected to the OR circuit 21.

As described above, the output of the breakage detection circuit 19 is transmitted to the OR circuit 21, and the OR output thereof is outputted to the output circuit 22 as a breakage signal.

(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. Then, if the pseudo-breakage signal generator 4 is driven via the drive circuit 6, the pseudo-breakage signal will be transmitted through the workpiece 1 and the base 2 to generate an AE signal.
is applied to sensor 7. Then, the AE multiplied signal is transmitted to the amplifier 9 via the analog switch 8.

Therefore, the output of the amplifier 9 is adjusted by the variable resistor 10 so that the display level of the cutting level indicator 13 becomes a predetermined value. 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 a frequency of 50 KHz, as shown by the curve in FIG. 3, and the distribution is monotonically attenuated in a higher frequency region. 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, 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. . In other words, during normal cutting, the frequency is 50
AE multiplied signal power near KHz frequency is 300KHz
Thicker than the nearby power (frequency 30 when the tool breaks)
This is because the power near 0 KHz is greater than the power near a frequency of 50 KHz. The comparator 17 compares these outputs and provides a signal to the breakage detection circuit 19 only when the tool breaks.

On the other hand, a signal similar to the power spectrum distribution shown by curve a in FIG. 3 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. That is, the AE signal waveform obtained when the tool breaks, as shown in Figure 4(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 4), the waveform does not show a sharp rise and continues for a predetermined period of time. 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 19. The breakage detection circuit 19 detects tool breakage based on these AND signals and transmits the signal to the OR circuit 21.

Further, even if the tool has a sharp rise as shown in FIG. 4(a), it may not be determined as a tool breakage by the breakage detection in the frequency domain, and the breakage detection circuit 19 may not give a breakage signal. Therefore, in the present invention, the output of the abnormal cutting detection circuit 20 is also provided to the abnormal signal counting section 23. As shown in FIG. 5(a), when the abnormal cutting signal is applied to the abnormal signal counting diagram 23, its rising edge is detected by the rising signal detecting section 32, and as shown in FIG. 5(b), the one-shot signal generating section A one-shot signal is generated from 33 and applied as a gate signal to the gate circuit 31 and fall detection section 34. If an abnormal cutting signal is subsequently transmitted from the abnormal cutting detection circuit 20 during that time, it is sequentially transmitted to the shift register 35 via the gate circuit 31 and shifted. For example, as shown in FIG.
If five abnormal cutting signals are transmitted during the signal time, the output of the final stage of the shift register 35 is transmitted via the OR circuit 21 to the output circuit 22 and the analog switch 8 as a tool breakage detection output. In this way, the present invention combines both frequency-domain breakage detection and time-domain breakage detection, and also detects that the tool has broken even without frequency-domain breakage detection if abnormal cutting signals are continuously transmitted within a predetermined time. As a result, a breakage signal is output. Therefore, it becomes possible to identify tool breakage in response to various abnormal breakage signals.

Although this embodiment uses a shift register to count abnormal signals, abnormal cutting signals within a predetermined time are detected by a control means using a CPU in a tool breakage detection device integrated with a numerical control device. It is also possible to do so. In this case, the output of the abnormal cutting detection circuit is first input to the CPU via the input/output interface, as shown in the flowchart of FIG. In the flowchart of FIG. 6, the CPU monitors an abnormal cutting signal (step 41), and if this signal is given, the process proceeds to step 42 and starts a timer. This timer is a timing means for a predetermined period of time corresponding to the one-shot signal generator, and then the process goes to the loop of steps 43 and 44 to check whether an abnormal cutting signal is continuously obtained before time amplification. If an abnormal cutting signal is subsequently obtained during this period, the process proceeds to step 45 and the count value is incremented, and if the count value is less than a predetermined value N, for example 5, the process returns to the loop of steps 43 and 44. If the time is up before the number of abnormal cutting signals reaches the predetermined value N,
From step 44, the process proceeds to steps 47 and 48, where the count value and timer are reset, and the process returns to step 41.

If the abnormal cutting signal reaches the predetermined value N before time-up, the process proceeds from step 46 to step 49, where a broken tool is output and the subsequent operation is stopped. In this way, the abnormal cutting signal can be realized by both hardware and software using the CPU.

Furthermore, in the signal processing section according to this embodiment, breakage is detected by logical product of breakage detection in the frequency domain and breakage detection in the time domain for normal breakage detection, but other breakage detection methods may be used or combined. It is also possible.

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, FIG. 2 is a block diagram showing the detailed configuration of the abnormal signal counting section of the tool breakage detection device of this embodiment, and FIG. A diagram showing the AE multiplied signal power spectrum obtained from the AE sensor 7, Fig. 4 (a) shows the AE obtained when the tool breaks.
Signal waveform (Fig. 4) is A obtained when chips are generated.
FIG. 5 is a waveform diagram showing the waveforms of each part of the abnormal signal counting section 23, and FIG. 6 is a flowchart showing the abnormal signal counting operation according to another embodiment of the present invention. 1---------Work 2---------Base
3--11--Drill 4--Pseudo breakage signal generator 5--Level setter 6--
-------Drive circuit 7--AE sensor 8--Analog switch 9--------
-1 amplifier 11, 12--Band pass filter 14.15-...-Detector 1
6.--Differential circuit 17-.-Comparator 18-
------・-Level judger 19-・-1111 breakage detection circuit 20-・-・−・-Abnormal cutting detection circuit
21--OR circuit 23---Abnormal signal counting section 31---Gate circuit 32---
-Rise detection section 33--One-shot signal generation section
31-- Fall detection section 35-- Shift register 36-- Reset signal generation section Patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Kanki Okamoto (1st person) Fig. 2 Fig. 5 Figure 3 Figure 7↑ 100K 200K 300K 400K H
2 Figure 4 (a) Figure 4 (1)) , 1

Claims (2)

[Claims] (1) In a tool breakage detection device that has an AE sensor provided on a tool support of a machine tool and detects breakage based on an AE signal obtained when a tool breaks, an instantaneous increase in the output of the AE sensor an abnormal cutting detection circuit that detects an abnormality in tool cutting based on a rising signal indicating the AE; a counting means that counts abnormal cutting signals given within a predetermined time based on an output signal of the abnormal cutting detection circuit; The present invention is characterized by comprising a signal processing unit that identifies tool breakage based on the characteristics of the output signal of the sensor and detects tool breakage when the count value of the counting means reaches a predetermined value. Tool breakage detection device. (2) The signal processing unit is configured to control the AE obtained when the tool breaks.
Frequency identifying means that outputs an output when an AE signal having a frequency component that has a strong correlation with the frequency component of the signal is given, and rising signal detecting means that outputs an output when a signal that rises rapidly from the AE sensor is given. and logic output means for identifying tool breakage based on the AND output of the frequency identification means and the rising signal detection means. Device.