JPS61132858A - Tool breakage detecting device - Google Patents

Abstract

PURPOSE:To improve the reliability of a detection by constituting a titled device so that an output of an acoustic emission (AE) sensor is provided to a signal processing part only in the course of an actual work. CONSTITUTION:At the time of a regular cutting, a power spectrum distribution of an AE signal from an AE sensor 9 is concentrated to around 50kHz, and a power spectrum distribution of the time when a tool is broken has a peak in the vicinity of 300kHz. Therefore, when only the AE signal of the vicinity of the respective frequency components is fetched by two BPFs 13, 14, detected by detectors 16, 17, and its output levels are compared by a comparator 19, the normal time and the time when the tool is broken can be discriminated exactly. Therefore, by applying a signal to a breakage detecting circuit 21 only when the tool is broken, a wrong detection is eliminated, and the reliability for detecting a breakage is improved.

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 includes an AE sensor installed near the workpiece and a contact detection means for detecting contact of the tool with the workpiece, and a gate is opened only while the tool is in contact with the workpiece. The sensor is opened to transmit the output from the AE sensor to the signal processing section. In this way, an erroneous tool breakage signal will not be output based on various signals generated from the tool, the workpiece, or their surroundings, and a highly reliable tool breakage detection device can be achieved.

[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
A device has been proposed that includes a sensor and detects tool breakage based on an AE flaw signal obtained from the sensor.

By the way, it is impossible for the tool to break while the tool and the workpiece are not in contact. However, according to the conventional tool breakage detection device, the signal obtained from the AE sensor is sent to the signal processing unit to constantly detect tool breakage. I try to do that.

Therefore, various signals generated from the workpiece, the workbench, and its surroundings are applied to the signal processing section via the AE sensor, so there is a risk that a tool breakage signal may be erroneously output even though cutting is not in progress.

[Purpose of the invention]

The present invention has been made in view of the problems of the conventional tool breakage detection device, and improves the reliability of the tool breakage detection device by providing the output of the AE sensor to the signal processing section only during actual machining. The purpose is to improve

[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 part of a machine tool and detects breakage based on an AE flaw signal obtained when a tool breaks. a signal processing unit that identifies tool breakage; a contact detection unit that detects contact of the tool with the workpiece;
A while the contact detection signal is being given by the contact detection means.
The device is characterized by comprising a gate means for transmitting the output of the E-sensor to a signal processing section.

According to the present invention having such characteristics, the gate is opened only while the tool and the workpiece are in contact with each other, and the AE flaw signal is transmitted to the signal processing section. Therefore, if the tool is broken as a result of processing by the signal processing section, a breakage signal can be output.

However, if the tool is not in contact with the workpiece, the output of the AE sensor will not be transmitted to the signal processing section, which eliminates the possibility of erroneously outputting various signals from the workpiece or workbench as a tool breakage signal. Therefore, the present invention makes it possible to 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 attached to a drilling machine, and the workpiece 1 is fixed on the base 2 of the drilling machine, and a drill 4 is attached to the drill support part 3 from above, and an opening is provided in the workpiece 1. . A limit switch 5 is provided on the side of the drill support part 3, as shown in the figure, which operates when the tip of the drill 4 comes into contact with the workpiece 1. Before cutting the work 1, a pseudo-breakage signal generator 6 is installed in advance on the work 1 at a position where the drill 4 comes into contact with the work 1. As will be described later, the pseudo-breakage signal generator 6 generates a pseudo-breakage signal that is similar to the AE output waveform when the tool breaks and has the same power spectrum distribution. Further, the level setter 7 sets the drive level of the pseudo-breakage signal generator 6, and transmits to the drive circuit 8 signals of drive levels set according to the two sizes of the tools used. The drive circuit 8 drives the pseudo-breakage signal generator 6 with a drive waveform that is similar to the AE flaw signal at the time of tool breakage and has the same power spectrum distribution.

An AE sensor 9 for detecting AE flaw signals is provided near the tool on which the workpiece 1 is placed, for example, on the base 2 as shown in FIG. This is a wideband AE sensor that detects an AE flaw signal from a signal generator 6, and its output is given to a gate circuit 10. The gate circuit 10 intermittents the analog signal using an external output, and its output is given to the amplifier 11. The amplifier 11 is an amplifier whose amplification factor can be arbitrarily set by adjusting the variable resistor 12, and its output is passed through two band-pass filters 13.1.
4 and the cutting level indicator 15. The bandpass filter 13 has a center frequency of 300 Kb, and the bandpass filter 14 has a center frequency of 50KHz, and only signals near the respective center frequencies are transmitted to the next-stage detectors 16 and 17. The detectors 16 and 17 each detect the input signal and obtain an output according to the amplitude, and the output of the detector 16 is sent to a differentiating circuit 18,
The outputs of 7 are respectively given to a calibrator 19. These bandpass filters 13, 14, detectors 16, 17, and comparator 19 form a frequency identification means for identifying an AE flaw signal at the time of breakage. Differentiating circuit 18 transmits only steep changes in the input signal to level determiner 20 at the next stage.

The level determiner 20 compares the input signal with a predetermined reference level, and if the input signal is large, transmits the output to the breakage detection circuit 21 and the abnormal cutting detection circuit 22. Comparison 8
19 compares the outputs of the detectors 1116 and 17, and
The output is transmitted to the breakage detection circuit 21 only when the output is large. The breakage detection circuit 21 is a logic circuit that takes the AND of these inputs to detect a breakage of the tool, and outputs a breakage detection signal to the outside via the output circuit 23. The abnormal cutting detection circuit 22 detects abnormal cutting based on the output of the level determiner 20, and transmits the output to the outside via the output circuit 24.

(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, the pseudo-breakage signal generator 6
As shown in Figure 1, install the tool at the location where it will be opened with a drill on workpiece 1, and select the type of tool.

For example, a pseudo-breakage signal level is set by the level setter 7 according to the diameter of the drill. Then, by driving the pseudo-breakage signal generator 6 via the drive circuit 8, a pseudo-breakage signal is applied to the AE sensor 9 through the work l and the base 2. At this time, the gate circuit 10 is closed regardless of the operating state of the limit switch 5, so that the output of the AE sensor 9 is applied to the amplifier 11. Then, the amplifier 11 is set so that the display level of the cutting level indicator 15 becomes a predetermined value.
The amplification factor of is adjusted by the variable resistor 12.

This allows the AE flaw signal to be transmitted from the AE sensor 9 to the signal processing section at an appropriate level.

(Monitoring operation) Next, when opening the workpiece 1 using this drilling machine,
The pseudo-breakage signal generator 6 is removed from the workpiece 1 and the drill support part 3 is pushed down to open the workpiece 1. At this time, as shown in FIG. 2, when the drill support 3 is pushed down and the tip of the drill 4 reaches the workpiece 1, the actuator of the limit switch 5 is pushed down and a gate signal is transmitted to the gate circuit 10. Then, the gate is opened and the AE flaw signal is transmitted from the AE sensor 9 to the amplifier 11 through the gate circuit 10. Furthermore, when raising the drill support part 3 to change the opening position of the workpiece, the drill support part 3 does not come into contact with the actuator of the limit switch 5, so the gate circuit 1
0 is closed and is not transmitted to the AE flaw signal signal processing section. Therefore, the AE flaw signal is transmitted to the signal processing unit only when the drill 4 actually opens the hole.

(Operation of the signal processing section) Now, the A given by the AE sensor 9 during normal cutting
The distribution of the power spectrum of the E-flaw signal is concentrated around a frequency of 50 KHz, as shown by the curve in FIG. 3, and the distribution is monotonically attenuated in a frequency range higher than that. 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 is clear that it has a peak at frequency 300 and around 11z.

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
3.14, 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 16 and 17, and comparing their output levels. . In other words, during normal cutting, the frequency is 50K.
The AE multiplied signal power near Hz is larger than the power near the frequency 300KHz, and when the tool breaks, the frequency is 300K.
This is because the power near Hz is greater than the power near a frequency of 50 KHz. The comparator 19 compares these outputs and provides a signal to the breakage detection circuit 21 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 filter 13°14,
Even if the threshold level of the comparator 19 is set appropriately, contact between the chips and the tool or workpiece9. - Signals caused by friction may be mistakenly interpreted as tool breakage signals.

Therefore, in this example, the AE observed when the tool breaks
We also focused on the waveform in the double signal time domain and separated these signals. 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 16 is fed to the differentiating circuit 18, and only steep signals such as those caused by breakage are separated to determine the level! Give 520. Then, the input level is compared with a predetermined reference value, and when an AE multiplied signal with a steep rise is obtained, the breakage detection circuit 21
give a signal to The breakage detection circuit 21 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 improve the reliability of tool breakage.

In addition, as shown in the block diagram of Fig. 1, the output of the amplifier 11 is directly displayed as a cutting level display 815 to indicate the cutting level, and furthermore, abnormal contact between chips and workpieces and friction conditions are detected by tool breakage 1. It is possible to separate the signal as a processed signal.

In this embodiment, a limit switch is used to obtain a signal when actually cutting a workpiece, but when the tool breakage detection device of the present invention is applied to a device that processes a workpiece using a numerical control device, The numerical control device sends a signal when cutting the tool to the gate circuit, and based on that signal, the AE is activated only during machining.
It is also possible to detect tool breakage by transmitting the multiplied signal to the signal processing unit.

Furthermore, in this embodiment, the signal processing section detects breakage by the AND of breakage detection in the frequency domain and breakage detection in the time domain. 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 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 side view showing the positional relationship between the drill support part and the limit switch during machining of the tool breakage detection device of the present embodiment. , FIG. 3 shows the AE obtained from the AE sensor 9.
FIG. 4(a) is a diagram showing a double signal power spectrum. FIG. 4(a) is a diagram showing an AE signal waveform obtained when a tool breaks, and FIG. 4(a) is a diagram showing an AE signal waveform obtained when chips are generated. 1.-----1~-Work 2----------Base 3----------Drill support part 4--
--------Drill 5---Limit switch 6・---------Pseudo-breakage signal generator 7-
・------Level setter 8--------Drive circuit 9------A E sensor 10--
-----------Gate circuit 11・------・Amplifier 13, 14---Band pass filter 15---------Cutting level indicator 16.
17---1--Detector 18--1 Differential circuit 19---1 Comparator 20---Level judge 21--1 Breakage detection circuit 23
．． 24・-1---- Output circuit patent applicant Tateishi Electric Co., Ltd. (1 representative) Patent attorney Yoshiyoshi Okamoto (1 other person) Figure 2 Figure 3

Claims (3)

[Claims] (1) In a tool breakage detection device that includes an AE sensor provided on a tool support part of a machine tool and detects breakage based on an AE signal obtained when the tool breaks, the tool is detected based on an output signal of the AE sensor. a signal processing unit that identifies breakage of the tool; a contact detection unit that detects contact of the tool with the workpiece; and a contact detection unit that detects the output of the AE sensor while the contact detection unit is applying a contact detection signal to the signal processing unit. A tool breakage detection device comprising: a gate means for transmitting a signal to the tool. (2) Tool breakage detection according to claim 1, wherein the contact detection means is a limit switch that is provided in a movable range of a tool support part of a machine tool and detects contact with an object of the tool. Device. (3) 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.