JPS6121787B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a tool defect detection method in a machine tool. Conventionally, tool loss detection in machine tools involves detecting the vibration of the tool rest, comparing the vibration level with the reference level during normal operation, and determining that the tool is missing if the level difference reaches a certain value. It is being done. However, this method has a problem in that tool damage may not be detected depending on the combination of the cutter and the workpiece. In view of the problems of the conventional methods described above, the purpose of the present invention is to use the shape of the frequency spectrum of the vibration of the tool post to detect tool breakage, and to limit the conditions of the tool and workpiece. The object of the present invention is to improve the reliability of detecting tool defects without causing damage. In the present invention, each vibration level in multiple frequency bands during normal cutting is detected, and the vibration levels in several bands before and after the band giving the maximum vibration level are each normalized by the maximum vibration level and stored as a reference value. Then, when monitoring tool breakage, the vibration level of each frequency band during cutting is normalized by the vibration level of the band that gives the maximum vibration level during normal operation, and compared with the corresponding reference value, and the difference between them is determined to be a constant value. A tool chipping detection method is provided that determines that a tool chipping has occurred when there is one or more bands having the above values. An embodiment of an apparatus using the tool chipping detection method of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a block circuit diagram of the device.
The lathe 10 is provided with a numerical control section 11 and an acceleration pick-up 12 attached to a tool post.
The output of the acceleration pickup 12 is connected to the charge amplifier 13 as vibration data and amplified, and then
It is applied to a 1/3 octave bandpass filter 14.
The 1/3 band filter 14 has a variable center frequency, and can be switched to provide an all-pass filter.
The output of the 1/3 band filter 14 is sent to the logarithmic compressor 15
The output of the logarithmic compressor 15 is applied to a rectifier circuit 16, the output of the rectifier circuit 16 is applied to a smoothing circuit 17, and the output of the smoothing circuit 17 is applied to an analog-digital converter (AD converter) 18. The AD converted output of the AD converter 18 is sent to the first comparator 2.
The second input of the first comparator 21 receives the signal from the interface section 19 . The first comparator 21 determines the steady cutting state based on the whole band vibration level, and when it is determined that the cutting state is the steady cutting state, sends the output to the vibration frequency spectrum calculation circuit 22 at the next stage. The vibration frequency spectrum calculation circuit 22 calculates a vibration frequency spectrum and outputs it to the buffer circuit 23. The buffer circuit 23 accumulates a set of frequency spectra determined by the vibration frequency spectrum calculation circuit 22. The output of the buffer circuit 23 is applied to a first input of a second comparison circuit 24, the second input of which is connected to the reference data memory device 2.
From 7 onwards, the third input of the second comparator circuit 24 is connected from a setpoint table memory device 28 .
In the second comparison circuit 24, the presence or absence of a defect is determined by comparison with standard data, and if it is determined that the tool is defective, a machining stop signal is sent to the interface section 19 via a machining stop indicator 25. ,
If it is not determined that the tool is missing, the process proceeds to the next cutting stage. The filter frequency switch 29 switches the center frequency of the 1/3 octave band filter 14 through the interface section 19. A processing stop signal is provided between the interface section 19 and the numerical control section 11.
Spindle rotation information and machining start/end information are exchanged. Timer 26 controls vibration frequency spectrum calculation circuit 22 and reference data memory device 27 . Next, an example of a method for storing reference data and detecting tool loss through model cutting will be described. Storage of reference data during model cutting is performed as follows. After starting machining, the timer 26 is reset by the first spindle activation signal, and time is counted thereafter. However, the time counting is stopped by the spindle stop signal, and when the spindle start signal is received again, the time counting is resumed and continued. The vibration level in the entire band is monitored, and if the vibration level exceeds a certain value _A0 , it is determined that cutting has begun. Furthermore, the vibration level is monitored, and if the fluctuation has settled within a certain range, it is determined that a steady cutting state has entered. When the steady cutting state is entered, the band filter 1
4 center frequency from 2kHz to 20kHz
Find the vibration level in each band for each 1/3 octave. It is assumed that the center frequency of the band giving the maximum band component level is _1c and the level is A _1nax . The center frequency of the low frequency side band of _1c is set in order.
_1l1 , _1l2 , _1l3 , the center frequency of the high frequency band
Let _1u1 , _1u2 , _1u3 . For example _1c to 6.3k
Assuming Hz, each frequency of _1l1 is _1l3 : 3.15kHz,
_1l2 : 4kHz, _1l1 : 5kHz, _1c : 6.3kHz, _1u1 :
8kHz, _1u2 : 10kHz, _1u3 : 1.25kHz. The vibration component level of each band is A _1l3 , A _1l2 , A _1l
1 , A _1u1 , A _1u2 , A _1u3 , and the ratios of these and A _1nax are R _1l3 , R _1l2 , R _1l1 , R _1u1 , R _1u , respectively.
₂ , R _1u3 . That is, R _1l3 = A _1l3 /A _1na
x , R _1l2 = A _1l2 /A _1nax , R _1l1 = A _1l1 /A _1nax ,
R _1u1 = A _1u1 /A _1nax , R _1u2 = A _1u2 /A _1nax , R _1u
3 = A _1u3 /A _1nax . The above relationship is shown in the table. Figure 2 also shows 1/3 octave center frequency versus A ₁
An example of the relationship between level ratio R and _nax is shown.

[Table] As reference data for the first cutting stage, the time t ₁ at which the vibration data was sampled, the center frequency _1c of the band giving the maximum band component level, the frequency _1l3 of the band three bands below _1c , and each band A _1nax . Ratio R _1l3 ,
Store R _1l2 , R _1l1 , R _1u1 , R _1u2 , and R _1u3 . That is, t ₁ , _1c , _1l3 , R _1l3 , R _1l2 , R _1l1 , R _1u
1 , R _1u2 and R _1u3 are stored. Here R _1l3 , R _1l
If any of ₂ , R _1l1 , R _1u1 , R _1u2 , and R _1u3 is smaller than the constant value R ₀ , operations such as removing that band and a band faster than that band when viewed from _1c are performed. Similar to the first cutting step described above, reference data is determined and stored at each k cutting step. nth k
The reference data in the cutting stage is generally (t _o , _o
c , _ol3 , R _ol3 , R _ol2 , R _ol1 , R _ou1 , R _ou2 , R _ou
3 ). When the reference data during model cutting is stored as described above, the stored reference data is compared with the data in the cutting state of the workpiece, and tool damage can be monitored. During monitoring, the timer is reset and the time is counted in the same way as when cutting the model. Data is obtained at time t _o in accordance with the standard data in the same manner as when cutting the model. The standard data at time t _o is (t _o , _oc , _ol3 , R _ol3 , R _o
l2 , R _ol1 , R _ou1 , R _ou2 , R _ou3 ), the vibration levels of seven bands are determined from _ol3, and the ratio with the band component level A _oc of _oc is determined. Let the respective ratios be R′ _ol3 ,
Let R′ _ol2 , R′ _ol1 , R′ _ou1 , R′ _ou2 , R′ _ou3 . The difference between the above ratio and the standard data ratio is determined for each band. That is, |R _ol3 −R′ _ol3 |, |R _ol2 −R′ _ol2 |, |R _ol1 −
R′ _ol1 |, |R _ou1 −R′ _ou1 |, |R _ou2 −R′ _ou2 |, |R _ou3 −
Calculate R′ _ou3 | If one or more of the calculation results are larger than the constant value Re, it is determined that the tool is defective. FIG. 3 is a characteristic diagram similar to FIG. 2 in which reference data and cutting data to be compared are shown side by side, and the vertical axis R' indicates the ratio of _{the OC} to the band level. According to the present invention, the reliability of detecting tool damage can be improved without being restricted by the conditions of the cutter and the workpiece. Further, according to the present invention, the vibration level is normalized and stored as a reference value, and the actual value is also normalized and compared with the reference value. Even if the vibration level in each band changes due to some cause other than an abnormality, there will be no false detection, and accurate tool loss detection can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a device used in a tool chipping detection method as an embodiment of the present invention, and FIG.
The figure is a characteristic diagram showing the relationship between frequency and the level ratio of A _1nax , and Figure 3 is a characteristic diagram showing the relationship between frequency and the band level of _OC , with standard data and cutting data to be compared. It is. 10...Lathe, 11...Numerical control section, 12...
Acceleration pickup, 13...Charge amplifier,
14... Bandwidth filter, 15... Logarithmic compressor, 1
6... Rectifier circuit, 17... Smoothing circuit, 18...
AD converter, 19...Interface section, 20...
...processing unit, 21...first comparator, 22...vibration frequency spectrum calculation circuit, 23...buffer circuit, 24...second comparison circuit, 25...processing stop indicator, 26...timer, 27...Reference data memory device, 28...Setting value table memory device,
29...Filter frequency switcher.

Claims (1)

[Claims] 1 Detect each vibration level in multiple frequency bands during normal cutting, normalize the vibration levels in several bands before and after the band giving the maximum vibration level by the maximum vibration level, and store it as a reference value to prevent tool damage. At the time of monitoring, the vibration level of each frequency band during cutting is normalized by the vibration level of the band giving the maximum vibration level during normal operation, and compared with the corresponding reference value, and the band in which the difference between them is equal to or greater than a certain value is determined. A tool chipping detection method that determines that a tool chipping has occurred when one or more of the following occur.