JPH066252B2 - Pseudo breakage signal generator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to tool breakage detection for monitoring and automatically detecting breakage or abnormality of a tool in a machine tool by using acoustic emission (hereinafter referred to as AE) that occurs during cutting and breakage. The present invention relates to a pseudo breakage signal generation device used for adjusting the sensitivity of an AE sensor of the device.

[Outline of Invention]

The pseudo breakage signal generator according to the present invention is provided with a conversion element for receiving waves in addition to the conversion element for wave transmission in the pseudo breakage signal converter, and based on the output thereof, the pseudo breakage signal has a predetermined value corresponding to the tool diameter. Discrimination is made in comparison with the above, and the drive level of the pseudo breakage signal is adjusted based on the result, so that the pseudo breakage signal level given to the attachment target is made appropriate.
Therefore, it becomes possible to accurately set the sensitivity of the AE sensor using the pseudo breakage signal generator.

[Prior art and its problems]

When a machining target (hereinafter referred to as a work) is cut using a tool in a machine tool, the tool may be broken or clogged with chips for some reason and abnormal cutting may be performed. With the progress of factory automation in recent years, it is strongly required to automatically detect such breakage of tools and abnormal cutting. As a method of detecting the breakage of the tool of the machine tool, AE has been conventionally performed near the tool or the work of the machine tool.
An apparatus has been proposed which is provided with a sensor and detects breakage of a tool based on an AE signal obtained from the sensor.

However, according to the conventional tool breakage detection device, the AE sensor is mounted so as to come into contact with the vicinity of the tool or the work, but the level of the AE signal becomes large depending on the mounting position. Therefore, in the conventional tool breakage detection device, the sensitivity of the AE sensor is set to a standard value that is predetermined according to the size of the tool, and the attenuation rate between the tool of each machine tool and the AE sensor is corrected by trial and error. It was However, since the AE signal at the time of breakage of the tool is obtained only at the time of breakage, it is difficult to confirm the attachment position and the attachment state of the AE sensor, and it is difficult to reliably detect the breakage of the tool. Further, since the AE signal level is different even when the type of tool, for example, the drill diameter is changed or the cutting conditions are changed, there is a drawback that adjustment is difficult and it is difficult to use.

[Object of the Invention]

The present invention has been made in view of the problems of the conventional tool breakage detection device, and has the same characteristics as the AE signal at the time of tool breakage in order to adjust the sensitivity of the AE sensor.
An object of the present invention is to provide a pseudo breakage signal generator capable of generating an E signal and generating a pseudo breakage signal having a correct level corresponding to an object to which a pseudo breakage signal converter is attached.

[Constitution and effect of the invention]

The present invention is a pseudo breakage signal generation device having an AE sensor provided in the vicinity of a tool of a machine tool and used for adjusting the sensitivity of a tool breakage detection device that detects a breakage based on an AE signal when a tool breaks. And a pseudo breakage signal converter having a conversion element for generating a pseudo breakage signal including a frequency of an AE signal obtained when the tool is broken according to a level set corresponding to the tool and sending the pseudo breakage signal converter. Drive means for driving the wave conversion element, receiving means for amplifying the pseudo breakage signal obtained in the wave receiving conversion element of the pseudo breakage signal converter, and the reception wave level of the reception means for the pseudo breakage signal level corresponding to the tool It is characterized by comprising: a discriminating means for discriminating by means of: and a display means for displaying the excess or deficiency of the pseudo breakage signal level discriminated by the discriminating means.

According to the present invention having such a feature, a conversion element that receives the pseudo-breakdown signal as it is and converts it into an electric signal is provided in the pseudo-breakage signal converter, and the pseudo-breakdown signal of the pseudo-breakage signal is generated based on the received level. The suitability is displayed. Therefore, if the level of the pseudo breakage signal is not proper, the level of the pseudo breakage signal can always be accurately adjusted by changing the drive level based on it. By using the pseudo breakage signal of the level thus adjusted, the sensitivity of the AE sensor can be adjusted to an optimum value, and the frequency characteristic of the signal processing unit of the tool breakage detection device connected to the subsequent stage of the AE sensor can be properly adjusted. The effect is that it can be adjusted.

[Explanation of Examples]

(Structure of Pseudo Breakage Signal Generator) FIG. 1 is a block diagram showing the overall structure of the pseudo breakage signal generator according to the present invention, and FIG. 2 is a sectional view showing the structure of the pseudo breakage signal converter. In these figures,
The pseudo breakage signal converter 1 is connected to the pseudo breakage signal generation circuit unit 2. Then, as shown in FIG. 2, two piezoelectric elements 4 and 5 are attached to the lower surface of the case 3. The piezoelectric element 4 is a conversion element for converting a pseudo breakage signal given from the circuit unit 2 into an ultrasonic signal and transmitting it to an attachment target.
The piezoelectric element 5 is a conversion element that receives a pseudo breakage signal obtained by reflecting from a bottom surface of an attachment target to which the pseudo breakage signal converter is attached and converts the pseudo breakage signal into an electric signal. Pseudo breakage signal converter 1
Shall be mounted on the work 6 as shown.

Next, FIG. 1 is a block diagram showing the overall configuration of the pseudo breakage signal generator. In the figure, the level setter 10 is a setting means for setting the level based on the tool used. For example, when the pseudo breakage signal generator is attached to a drilling machine, the level is set according to the diameter of the drill. . Then, the signal of the set level is given to the drive circuit 11. The drive circuit 11 oscillates a drive waveform similar to the AE signal at the time of tool breakage and having the same power spectrum distribution based on the level set by the level setter 10, and its output is a pseudo breakage signal. Converter 1
Is applied to the piezoelectric element 4 for transmitting the wave. On the other hand, an amplifier 12 for amplifying the converted pseudo breakage signal is connected to the wave receiving piezoelectric element 5 of the pseudo breakage signal converter 1. In the amplifier 12, the feedback resistors R1 to Rn are selected based on the opening and closing of the analog switches 13-1 to 13-n as shown in the figure, and the pseudo breakage signal is generated by the amplification factor determined by the ratio of the selected feedback resistor and the input resistance. An amplifier for amplifying, the output of which is a counter 14 and two comparators 1.
Passed to 5,16. The clock generator 17 is an oscillator that generates a clock signal of a predetermined cycle, and the clock signal is given to the attachment target setting unit 18. The attachment target setting unit 18 directly selects the attachment target, for example, the material of the work, and the selection data is given to a read only memory (hereinafter referred to as ROM) 19. ROM1
9 is the acoustic impedance of the attachment target, that is, the density ρ and the sound velocity c of the sound waves propagating through the attachment target, and a value corresponding to a constant determined by each material is stored for each material and selected by the attachment target setting unit 18 Is read as appropriate. The attachment target setting unit 18 reads the value, appropriately divides the output of the clock generator 17, and transmits it to the counter 14.
The counter 14 is an n-bit binary counter that counts the pulses given from the attachment target setting unit 18, and based on its parallel output, the analog switches 13-1 to 13-n.
Is opened and closed. The values of the resistors R1 to Rn are set so that the resistance value between the input and output of the amplifier 12 opened and closed by the count value of the counter 14 increases logarithmically. On the other hand, the comparators 15 and 16 are each provided with a reference voltage at one terminal. It is assumed that these reference voltages are appropriately switched so that the values of the resistors Rc1 and Rc2 are changed by the level setting in the level setter 10 and the reference level becomes higher as the tool diameter increases. The comparators 15 and 16 compare the amplified signal with the reference level, and the output thereof is given to the excess / deficiency indicator 20. The excess / deficiency indicator 20 indicates to the user whether the level of the pseudo breakage signal is proper or excess / deficient by a display such as a light emitting diode.

(Structure of Tool Breakage Detection Device) Next, FIG. 3 is a block diagram showing the overall structure of a tool breakage detection device to which this pseudo breakage signal generator is applied. In the figure, the above-mentioned pseudo breakage signal converter 1 is attached in advance to the position where the blade of the drill 30 contacts the upper part of the work 6 before cutting the work 6. An AE sensor 31 for detecting an AE signal is provided near the tool on which the work 6 is arranged, for example, on the base as shown in FIG. A
The E sensor 31 is a broadband AE sensor that detects an AE signal from a tool such as the drill 30 and a pseudo breakage signal from the pseudo breakage signal converter 1, and its output is given to the analog switch 32. The analog switch 32 interrupts an analog signal by an external output, and its output is given to the amplifier 33. The amplifier 33 is an amplifier whose amplification factor can be arbitrarily set by adjusting the variable resistor 34, and the output of the amplifier 33 is set to two band pass filters 35,
36 and the cutting level indicator 37. The bandpass filter 35 is a filter having a center frequency of 300 KHz, and the bandpass filter 36 is a filter having a center frequency of 50 KHz. Only the signals near the respective center frequencies are detected by the detector 3 in the next stage.
Tell 8, 39. The detectors 38 and 39 respectively detect the input signals and obtain outputs corresponding to the amplitudes. The output of the detector 38 is given to the differentiating circuit 40, and the outputs of the detectors 38 and 39 are given to the comparator 41, respectively. To be The differentiating circuit 40 transmits only the steep change of the input signal to the level determiner 42 at the next stage. The level determiner 42 compares a predetermined reference level with the input signal. If the input signal is large, the level determiner 42 sends the output to the breakage detection circuit 43 and the abnormal cutting detection circuit 44. Further, the comparator 41 compares the outputs of the wave detectors 38 and 39, and outputs the output only when the output of the wave detector 38 is large.
Tell. The breakage detection circuit 43 is a logic circuit that detects the breakage of the tool by taking the logical product of these inputs, and outputs it to the outside via the output circuit 45 according to the breakage detection signal.
The abnormal cutting detection circuit 44 detects abnormal cutting based on the output of the level determiner 42, and transmits the output to the outside via the output circuit 46.

(Operation of Pseudo Breakage Signal Generator) Next, the amplitude adjusting operation of the pseudo breakage signal generator of the present embodiment will be described. First, the pseudo breakage signal converter 1 is fixed to the upper portion of the work 6 as shown in FIG. 1, and the pseudo breakage signal level is set by the level setter 10 according to the type of tool used, for example, the drill diameter. At the same time, the material of the workpiece 6 to which the pseudo breakage signal converter 1 is attached is set by the attachment target setting unit 18 at the same time. Then, the reference levels of the comparators 15 and 16 are adjusted based on the output. Then, the wave-transmitting piezoelectric element 3 of the pseudo breakage signal converter 1 is driven by the set level via the drive circuit 11, and the pseudo breakage signal is transmitted into the fixed work as shown by the broken line in FIG. Here, the attenuation rate of the pseudo breakage signal is determined by the sound velocity c of the medium through which the signal propagates, the density ρ, and the propagation distance x, and the output level P at the distance x has the following equation P = Po exp (−ρcx ) …… Given in (1). Therefore, in order to adjust the pseudo breakage signal level, it is necessary to consider this attenuation rate. As described above, the user selects the attachment target of the pseudo breakage signal converter 1, that is, the material of the workpiece 6 from the attachment target setting unit 18. Therefore, for example, the product ρc of the sound velocity and the density corresponding to the type of iron, aluminum, etc. is read from the ROM 19,
A clock signal having a corresponding clock width is given to the counter 14 from the attachment target setting unit 18. Now, letting t be the time until the signal is reflected on the bottom surface of the workpiece 6 to be attached and is received by the wave receiving piezoelectric element 5, t is given by the following equation.

t = 2d / c (2) (d: thickness of work 6) Therefore, in this embodiment, in order to compensate for the attenuation of the pseudo breakage signal, the amplification factor G of the amplifier 12 is expressed by the following expression G (t) = Go exp ( −ρct / 2) (3) In dB display, G _dB (t) = Go′ρct (4) The value is continuously increased with the passage of time. The broken line in FIG. 4 is a curve showing this increase in the amplification factor G _dB . This increase in the amplification factor actually increases in accordance with the count value counted by the counter 14 by the opening and closing of the analog switches 13-1 to 13-n according to the count value of the amplifier 12. This is achieved by changing the amplification factor as shown in the figure. If the amplification factor of the amplifier 12 is sequentially increased in this way, an output corresponding to the pseudo breakage signal level sent out can be obtained from the amplifier 12 without depending on the thickness d of the work 6. If the amplifier 12 detects the reflected wave at time t1, the counter 14
A hold signal is given to stop counting. Comparator 1
Reference numerals 5 and 16 are provided with a reference signal corresponding to the level set by the level setter 10 at one input end of each, and the other input end depends on the thickness of the work 6 amplified by the amplifier 12. A false breakage signal of a generation level that does not occur is transmitted. Therefore, the comparator 15 detects an excessive level signal and the comparator 16 detects an excessive level signal, and the pseudo breakage signal converter 1 generates an appropriate pseudo breakage signal level only when no signal is obtained from either of them. Either of them is displayed by the excess / deficiency indicator 20. Then, the user can appropriately adjust the drive level of the drive circuit 11 based on the display, and adjust the pseudo breakage signal level so as to be an appropriate level.

(Operation of Tool Breakage Detection Device) If the pseudo breakage signal of the pseudo breakage signal generator is adjusted to an appropriate level in this way, the sensitivity of the AE sensor of the tool breakage detection device becomes a predetermined value on the cutting level display 37. Thus, the amplification factor of the amplifier 33 is adjusted by the variable resistor 34. This makes it possible to transmit the AE signal from the AE sensor 31 to the signal processing unit at an appropriate level.
When a tool breaks, a break signal with a peak near a frequency of 300 KHz is obtained.
The level is detected by the comparator 31 and the breakage of the tool is detected by comparing with the signal having the frequency component of 50 KHz by the comparator 31. Further, when the signal is rapidly raised by the differentiating circuit 15, if the level is equal to or higher than a predetermined value, the comparator 42 outputs an output, and the breakage detecting circuit 43 detects the breakage of the tool based on the logical product condition. . As described above, in the tool breakage detection device, the reliability of the tool breakage is improved by combining both the frequency domain breakage detection and the time domain breakage detection.

In this embodiment, the mounting target to which the pseudo breakage signal converter 1 is mounted is set by its material. However, the acoustic impedance itself of the mounting target, that is, the product of the sound velocity and the density is input as it is to set the clock width. It is also possible to set it. Further, in the present embodiment, it is displayed whether the breakage detection signal level generated by the comparators 15 and 16 is proper or excessive. However, the drive level of the drive circuit 11 is automatically determined based on these outputs. It is also possible to adjust so that the pseudo breakage signal level automatically becomes the optimum level according to the type of the set tool and work.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a circuit portion of a pseudo breakage signal generator according to the present invention, FIG. 2 is a sectional view showing the structure of a pseudo breakage signal converter of this pseudo breakage signal generator, and FIG. FIG. 4 is a block diagram showing an example in which the pseudo breakage signal generator of the present invention is applied to a tool breakage detection device, and FIG. 4 is a graph showing a change in amplification factor of an amplifier when the level of the pseudo breakage signal generator is adjusted. 1 ... Pseudo breakage signal converter 2 ... Pseudo breakage signal generation circuit section 3 ... Case 4, 5 ... Piezoelectric element 6
…… Work 10 …… Level setter 11 …… Driving circuit 12 …… Amplifier 13-1 to 13-n …… Analog switch 14 …… Counter 15, 16 …… Comparator 17 …… Clock generator 18 …… Mounting Target setting section 19: ROM 20: Excess / shortage indicator

Claims (2)

[Claims] 1. A pseudo breakage signal generation device for use in adjusting the sensitivity of a tool breakage detection device having an AE sensor provided in the vicinity of a tool of a machine tool and detecting a breakage based on an AE signal at the time of tool breakage, Pseudo breakage signal converter having a transducer element for transmitting and receiving, and a pseudo breakage signal converter for generating a pseudo breakage signal including a frequency of an AE signal obtained at the time of breakage of the tool according to a level set corresponding to the tool Driving means for driving the wave conversion element, receiving means for amplifying the pseudo breakage signal obtained in the wave receiving conversion element of the pseudo breakage signal converter, and the reception level of the reception means corresponding to the tool. Pseudo breakage signal generation, comprising: discrimination means for discriminating based on the pseudo breakage signal level; and display means for displaying an excess or deficiency of the pseudo breakage signal level discriminated by the discrimination means. Location. 2. The receiving means includes a selecting means for selecting an object to which the pseudo breakage signal converter is attached, and the receiving means while varying an amplification factor according to a change rate based on an acoustic impedance of the selected object. The pseudo breakage signal generating device according to claim 1, further comprising: an amplifier that amplifies an output of the wave piezoelectric element.