JPS62193750A - Multi-blade tool damage detecting device - Google Patents

Abstract

PURPOSE:To detect damage of a multi-blade tool, by applying the rectified output of an AE sensor to second band-pass filters having a pass frequency determined by the product of the rotational speed of a spindle and the number of blades of the tool, and by adding the levels thereof together so that the obtained value is compared with the the output level of a first band-pass filter having the pass frequency determined by the product of the rotational speed of the spindle and the number of blades of the tool. CONSTITUTION:During cutting of a workpiece 2, an AE signal detected by an AE sensor 6 is amplified by an amplifier 8 and is delivered to a full-wave rectifying circuit 9 for delivering frequency signals in accordance with the rotational speed of a spindle and the number of a multi-blade tool 4. If any chipping or damage is there in a part of the multi-blade tool 4, the frequency component in accordance with the rotational speed of the spindle 5 and higher harmonic frequency components may be simultaneously produced in addition to the frequency corresponding to the product of the rotational speed of the spindle 5 and the number of blades of the multi-blade tool 4. Accordingly, by comparing the sum of odd- number mode harmonic frequency components corresponding to the rotational speed of the spindle 5, with the frequency corresponding to the product of the rotational speed of the spindle and the number of the blade of the tool, tool damage may be detected. Accordingly, it is possible to detect damage of a multi-blade tool with a high degree of accuracy on a real time base.

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention is used in a machine tool such as a milling machine that uses a multi-blade tool having a plurality of blades, and utilizes acoustic emissions (hereinafter referred to as AE) generated during machining. The present invention relates to a multi-blade tool damage detection device that automatically detects damage to a multi-blade tool.

[Summary of the invention]

The multi-blade tool damage detection device according to the present invention is based on the rotational speed and number of teeth of the spindle to which the multi-blade tool is attached during normal cutting, when a signal obtained by rectifying the output of an AE sensor installed near the multi-blade tool of a machine tool is used. Focusing on the fact that when a multi-blade tool is damaged, it has a frequency component and its harmonics determined by the rotational speed, Damage to a multi-blade tool is detected by comparing the sum of signal levels with the output level of a frequency component determined based on the rotational speed and number of teeth.

[Prior art and its problems]

When cutting an object to be machined (hereinafter referred to as a workpiece) using a machine tool, chipping or damage may occur where the tip of the tool is chipped, and in such cases, precise machining cannot be performed. Therefore, in order to detect such damage to the tool, it is necessary for an operator to periodically inspect the tip of the tool.

However, with the recent progress in factory automation, etc., there is a need to automatically detect damage to tools of machine tools. Therefore, in order to automatically detect damage to the tool of a machine tool during machining, an apparatus has been proposed in which an AE sensor is attached near the tool and the damage to the tool is detected based on the signal from the AE sensor. Such conventional tool damage detection devices detect when the AE multiplied signal suddenly rises or the average value exceeds a predetermined threshold level, or when the maximum value of the probability density function of the AE multiplied signal output exceeds a predetermined level. This is to detect tool damage.

However, multi-edged tools with multiple blades have a
Since the E signal level is high and buried in sudden type AE multiplied signal noise during chipping, there is a problem in that it is difficult to detect minute damage with such a conventional detection device.

[Purpose of the invention]

The present invention was made in view of the problems of the conventional tool damage detection device, and detects damage to a multi-blade tool by detecting damage to a multi-blade tool by changing the frequency spectrum of the rectified AE specific output signal during cutting. The purpose of this invention is to provide a multi-edge tool damage detection device that can detect damage in real time during machining.

[Structure and effects of the invention]

The present invention is a multi-blade tool damage detection device used in a machine tool having a multi-blade tool, and comprises: an AE sensor provided near the tool; a rectifier circuit for rectifying the AE multiplied signal obtained from the AE sensor; a first band-pass filter group including a band-pass filter to which an output is applied and whose pass frequency is substantially equal to the product of the rotation speed of the main shaft of the machine tool and the number of teeth of the multi-blade tool; and the output of the rectifier circuit. is given, and a second bandpass filter group whose passing frequency is substantially equal to the rotational speed of the main shaft of the machine tool and its harmonics, unlike the passing frequency of the first bandpass filter group, and the first bandpass filter group. The first bandpass filter group and the second bandpass filter group are added together. The present invention is characterized by comprising a second addition circuit and comparison means for detecting damage to the tool by comparing the outputs of the first and second addition circuits.

In a machine tool with a multi-edge tool, when normal cutting is being performed, the A
The rectified signal of the E-sensor has a high signal level of the frequency of the product of the rotational frequency of the spindle and the number of teeth of the multi-blade tool and its harmonic components. Among the rectified signals of the AE sensor, the signal level of the frequency corresponding to the rotation speed of the main shaft and its harmonics becomes high.

Therefore, in the present invention, the rectified output is applied to a second band-pass filter group having a pass frequency corresponding to the rotation speed of the spindle and its harmonics, and the levels are added. Damage to the multi-blade tool is detected by comparison with the output level of the first band-pass filter whose pass frequency is determined by the product of . In this way, damage to multi-edge tools can be detected in real time with high accuracy. Since damage is detected by comparing two signal levels, there is no need to set a threshold level for each multi-blade tool, and the device can be operated easily. Therefore, by constantly performing such detection during the cutting operation and immediately stopping the machining if the tool is damaged, it is possible to prevent unnecessary machining without machining the workpiece with a damaged tool.

[Explanation of Examples]

FIG. 1 is a block diagram showing an embodiment of a multi-blade tool damage detection device according to the present invention. In this figure, a vice 3 that holds a workpiece 2 to be machined on a table 1 of a machine tool
is fixed. From the top of this work 2, a multi-blade tool,
For example, a tool 4 such as an end mill is attached to the main shaft 5, and a predetermined machining is performed on the workpiece 2. Now, in the present invention, an AE sensor 6 is attached near the multi-blade tool 4 of the machine tool, for example, on the side wall of the vise 3 as shown. The AE sensor 6 is a sensor that detects a broadband AE multiplied signal from frequencies IKIIz to IMHz generated during cutting and converts it into an electrical signal, and its output is given to a bandpass filter. The band pass filter 7 has a frequency of 100 KHz to 1 MH, for example.
This is a filter that passes AE multiplied signals up to z, and removes noise components associated with mechanical vibrations and the like. The output of the bandpass filter is passed through an amplifier 8 to a full-wave rectifier circuit 9.
given to. The full-wave rectifier circuit 9 performs full-wave rectification on the applied signal and sends its output to the second . It is applied to the first variable bandpass filter group 10, 11.12 and 13.14. Now, a rotation speed detector 15 is attached to the main shaft 5 of the machine tool.

The rotation speed detector 15 is composed of, for example, a photoelectric switch that detects a mark attached to the spindle 5, a proximity switch that detects a protrusion on the spindle, etc., and detects the rotation speed based on pulses accompanying the rotation of the spindle 5. . and rotation speed detector 1
The output of 5 is given to a conversion circuit 16. The conversion circuit 16 converts a pulse signal obtained by the rotation speed of the main shaft into an analog voltage of a level corresponding to the rotation speed, and its output is sent to the variable band pass filter 10 and the multiplier 1.
Give on 7, 18, 19. The number of blades detection device 20 is a device that includes a proximity switch or a photoelectric switch and detects the number of blades of the multi-blade tool 4 at the time of tool exchange, and its output is sent to the multiplier 17.1.
Given on 8.19. The multiplier 17 multiplies the number of cutting edges - 1 given by the number of cutting edges detection device 20 by the conversion output given from the conversion circuit 16 and outputs the variable bandpass filter 1 .
1, and the multiplier 18 multiplies the number of cutting edges + 1 by the output of the conversion circuit 16 to generate the variable bandpass filter 1.
2.

Also, the multiplier 19 directly multiplies the number of cutting edges by the conversion output of the conversion circuit 16, and then outputs the variable bandpass filter 13 and the multiplier 2.
Give to 1. The multiplier 21 multiplies its output by 2 and provides the result to the variable bandpass filter 14. The variable bandpass filters 10 to 14 change their passing frequencies in response to the applied analog signals. The variable band-pass filter 10 is controlled so that its pass frequency is substantially the same as the rotation speed of the main shaft 5, and the variable band-pass filters 11.12 have a frequency equal to the product of the rotation speed of the main shaft 5 and the number of blades, and It is controlled so that frequencies different from the high frequency, for example, harmonics three times and five times higher, respectively, are used as the passing frequencies. The variable band pass filter 13 is controlled so that its pass frequency is substantially the same as the product of the rotation speed of the main shaft 5 and the number of blades, and the variable band pass filter 14 passes harmonic components twice that frequency. frequency. And these first band pass filter groups 10~
12 and the second group of bandpass filters 13 and 14 are provided to rectifier/smoothing circuits 22 to 26, respectively. The rectification/smoothing circuits 22 to 24 convert the applied signals to a DC level, and give their outputs to the adder 27, and the rectification/smoothing circuits 25 and 26 send their outputs to the adder 28.
give to The division circuit 29 divides the output of the adder 27 into the adder 2.
The ratio is calculated by dividing by the output of 8, and the output is given to the comparator 30.

The comparator 30 is supplied with the output of a threshold setting circuit 31 that sets a constant threshold level. The division circuit 29, the comparator 30, and the threshold value setting circuit 31 constitute comparison means for comparing the outputs of the adders 27 and 28. If the output of the adder 30 is higher than the output level, damage to the multi-blade tool is detected and the output is provided to the damage output circuit 32 and the display circuit 33.

Next, the operation of this embodiment will be explained with reference to a frequency spectrum diagram. When the workpiece 2 is being cut using the aforementioned machine tool, the AE multiplied signal is detected by the AE sensor 6, amplified by the amplifier 8, and a signal with a frequency corresponding to the rotational speed of the spindle and the number of blades is sent to the full-wave rectifier circuit. 9. For example, when cutting the workpiece 2 using a four-blade end mill as the multi-blade tool 4 with the rotation speed of the spindle 5 at 637 rpm, the frequency corresponding to the rotation speed of the spindle 5 multiplied by the number of blades is I get a signal. FIG. 2 is a diagram showing the frequency spectrum of the output of the full-wave rectifier circuit 9 during normal cutting. As shown in this figure, a harmonic component P c+ (42,4 Hz) that is four times the frequency (10,6 Hz) corresponding to the rotational speed of the main shaft 5 and a harmonic component P that is twice that frequency. A spectrum with a peak at w (84,8 Hz) was obtained.

Now, if there is chipping or damage in a part of the multi-blade tool 4, in addition to the frequency determined by the product of the rotation speed of the spindle 5 and the number of teeth, as shown in FIG. frequency component PH1 (10,6Hz) and its harmonic component PNt (21,2Hz); Ps3 (31,
It was found that harmonic components such as 8 Hz) and PN5 (53 Hz) occur simultaneously. The present invention was made in view of the change in the frequency spectrum of the rectified signal when the tool is damaged, and is based on the sum of odd harmonic components of the frequency corresponding to the rotation speed of the spindle 5, the rotation speed of the spindle 5, and the number of teeth. Damage to the tool is detected by comparing the product frequencies.

Now, when the multi-blade tool 4 is not damaged and cutting is being performed normally, the AE multiplied signal is full-wave rectified via the AE sensor 6, band-pass filter, and amplifier 8; Since the output has a frequency spectrum as shown in Fig. 2, the first variable bandpass filter group 13.14
The signal is converted to a DC level and sent to an adder 28.
is added. Bandpass filter group 10 for solution 2
12 is adder 2 because only the noise level signal passes through.
The output level of No. 7 is an extremely low level.

Therefore, the output of the divider circuit 29 is extremely low (the comparator 30 does not output a tool damage output and cutting continues).

Now, if the multi-blade tool 4 is damaged, the full-wave rectifier circuit 9
A signal having a frequency spectrum as shown in FIG. 3 is applied to variable bandpass filters 10 to 14. Therefore, when the tool is damaged, the components passing through the variable bandpass filters 10 to 12 become dramatically larger than during normal machining as shown in FIG. 2, and the output level of the divider circuit becomes high. By setting the threshold level of the intermittent value setting circuit 31 to an appropriate value, damage such as chipping or chipping of the multi-blade tool can be detected. The output of the comparator 30 is provided to a damage output circuit 32 and a display circuit 33 to provide an output to the outside and to be displayed. Therefore, by stopping cutting, it is possible to replace the workpiece 2 with a new multi-blade tool and continue machining without causing much damage to the workpiece 2.

In this embodiment, a rotation speed detector 15 is attached to the main shaft 5 in order to detect the rotation speed of the main shaft 5, and its output is converted by a conversion circuit 16 to be connected to a variable bandpass filter 10 and multipliers 17 to 1.
It is given to 9. However, as shown by the broken line in FIG. 1, when a numerical control device 40 is connected to this machine tool and cutting is performed by it, the rotation speed data of the spindle 5 is transferred from the numerical control device 40 to the variable filter setting circuit 41. give to
Variable filter setting circuit 42 ~ data on rotation speed and number of blades
45 to set the passing frequencies of the variable bandpass filters 10 to 14, respectively.

Further, in this embodiment, the number of teeth detection device 20 is connected to the machine tool, but the number of teeth can also be inputted from an input means and applied to each multiplier. Furthermore, in this embodiment, as the second band-pass filter group, a frequency corresponding to the product of the spindle rotation speed and the number of blades and a harmonic twice that frequency are added and divided. It is also possible to provide only the level of the frequency of the product with the number to the division circuit 29.

Further, in this embodiment, the amplified output of the bandpass filter is full-wave rectified, but it may also be half-wave rectified, and the rectified output is directly A/D converted and its frequency components are analyzed using a microcomputer or the like. It is also possible to arrange for the amplitude level to be compared with a threshold value.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a multi-blade tool damage detection device according to an embodiment of the present invention, Fig. 2 is a frequency spectrum of full-wave rectified output obtained during normal cutting work, and Fig. 3 is a multi-blade tool damage detection device. FIG. 3 is a diagram showing the frequency spectrum of the full-wave rectified output when the is damaged. 2--------Workpiece 4--------1 Multi-blade tool
5--------・Main shaft 6---------A E sensor 7--Band pass filter 9--Full wave rectifier circuit 10-14--Variable band pass filter 15・-・・-Rotation speed detector 16・−・−Conversion circuit 17.18, 19.21−・−・−Multiplier
20・-111--Blade number detection device 22-26---
----- Rectification/smoothing circuit 27, 28---
One adder 29------One division circuit 30------
1 Comparator 31--Threshold value setting circuit

Claims (3)

[Claims] (1) A multi-blade tool damage detection device used in a machine tool having a multi-blade tool, comprising: an AE sensor provided near the tool; a rectifier circuit that rectifies the AE signal obtained from the AE sensor; and the rectifier. a first band-pass filter group including a band-pass filter to which the output of the circuit is applied and whose pass frequency is substantially equal to the product of the rotation speed of the main shaft of the machine tool and the number of teeth of the multi-blade tool; The output of the rectifier circuit is given,
a second band-pass filter group whose pass frequency is different from the pass frequency of the first band-pass filter group and whose pass frequency is substantially equal to the rotational speed of the main shaft of the machine tool and its harmonics; and the first band Damage to the tool is detected by comparing the outputs of the first and second adding circuits with first and second adding circuits that add the output levels of the pass filter group and the second band-pass filter group, respectively. A multi-blade tool damage detection device, comprising: comparison means. (2) The comparison means includes the first addition circuit and the second addition circuit.
Multi-blade tool damage detection according to claim 1, further comprising: a division circuit that divides the output level of the addition circuit; and a comparison circuit that compares the output level of the division circuit with a threshold level. Device. (3) The first and second band-pass filter groups are comprised of frequency-variable band-pass filters whose passing frequencies are changed in accordance with rotational speed data of the main shaft. The described multi-edge tool damage detection device.