JPH11309649A - Device and method for detecting defect of cutting tool, and recording medium capable of reading computer storing defect detecting program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a fracture of a cutting tool even in case where a change of the cutting torque value with the fracture of a cutting tool is small by providing a fracture detecting means for judging the generation of fracture on the basis of a power spectrum of the frequency synchronized with the number of revolution of a spindle. SOLUTION: A peal value detecting part 8 detects a peal value Pp of a powder spectrum, the thereafter, outputs the data of the peak value Pp to a comparing part 10. The comparing part 10 compares the peak value Pp with a fracture judging power spectrum threshold value Pk, and judges whether the peal value Pp exceeds the fracture judging power spectrum threshold value Pk or not. In case where the peak value Pp exceeds the fracture judging power spectrum threshold value Pk, the comparing part 10 judges YES, and outputs the signal S1 to a signal generating part 11. The signal generating part 11 outputs the fracture detecting signal Sk for showing that the fracture of a cutting tool is detected to a control part 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for detecting a defect of a cutting tool used for detecting a defect such as a drill, and a computer-readable recording medium on which a defect detection program is recorded.

[0002]

2. Description of the Related Art Japanese Patent Laying-Open No. 6-198547 discloses a method of predicting the loss of a rotary cutting tool, which predicts the loss of a cutting tool such as a drill, by focusing on the cutting torque when cutting a workpiece. According to this method, the cutting torque and the cutting feed power threshold before the blade is damaged are determined from the patterns of the cutting torque and the cutting feed power when the test work is experimentally cut with a new cutting tool. The value is set. The cutting torque and the cutting feed power are measured by a magnetostrictive torque sensor and a load cell, respectively. Then, in the case of performing the loss prediction, the cutting torque and the cutting feed power at each cutting when a large number of workpieces are actually cut by the cutting tool are respectively detected, and the cutting torque and the cutting feed power are determined as the cutting tool missing risk torque. When the threshold value of the cutting feed power is exceeded, the loss of the cutting tool is predicted.

[0003]

However, according to the conventional method for predicting the loss of a cutting tool, the cutting torque (or cutting force) of a new cutting tool is required when cutting using a certain kind of cutting tool or cutting under certain cutting conditions. In some cases, there is almost no difference between the feed power) and the cutting torque of the missing cutting tool. Here, FIG. 6A is a diagram illustrating the behavior of the cutting torque from 0 to 6 seconds when the first hole is machined in the work. Here, the cutting tool used for the processing of the first hole is a new tool and has no defect. FIG. 6B is a diagram showing the behavior of the cutting torque from 0 to 6 seconds when the workpiece is machined into the 1080th hole. Here, the cutting tool used for the 1080-th machining has a defect. The cutting torque shown in FIGS. 6A and 6B is detected by a magnetostrictive torque sensor attached to a main shaft of a machine tool. FIG.
As can be seen from (a) and (b), when viewed roughly, the behavior of the cutting torque (see FIG. 6 (a)) in the first hole where no defect occurs and the cutting in the 1080th hole where the defect occurs. There is almost no difference from the behavior of the torque (see FIG. 6B).

FIG. 7 is a diagram showing the relationship between the number of holes to be machined and the average torque of the workpiece. The average torque is determined by cutting in three seconds from one second to four seconds after the start of processing. This is the average value of the torque. Here, the cutting tool has a defect at the 841th hole, but as shown in this figure, the average torque includes:
At a high level, there is almost no change regardless of the number of machined holes and the presence or absence of cutting tools. Therefore, in the conventional method of predicting the loss of the cutting tool, a rough prediction method of simply predicting the loss of the cutting tool when the cutting torque exceeds the dangerous torque (threshold value) of the cutting tool is adopted. 6 (a) and 6 (b), it is impossible to capture a slight change in cutting torque. From this, it is presumed that it is actually difficult to accurately predict the loss of the cutting tool in the conventional method for predicting the loss of the cutting tool. The present invention has been made under such a background, and it is an object of the present invention to provide a device and a method for detecting a loss of a blade capable of accurately detecting a loss of a blade and a computer-readable recording medium on which a loss detection program is recorded. With the goal.

[0005]

According to a first aspect of the present invention, there is provided a cutting tool for machining a workpiece, a main shaft for driving the cutting tool to rotate, and a rotation speed detecting means for detecting a rotation speed of the main shaft. A cutting torque detecting unit that detects a cutting torque of the cutting tool; a power spectrum calculating unit that obtains a power spectrum for each frequency in the cutting torque based on a detection result of the cutting torque detecting unit; A frequency range of a predetermined range including a frequency synchronized with the detection result is set, and a peak value calculating means for obtaining a peak value of the power spectrum in the frequency range; and determining whether the peak value and the cutting tool are missing. And comparing the peak value with the power spectrum threshold value for the defect determination, when the peak value exceeds the threshold value for the power spectrum loss determination. There characterized by comprising a defect detection means for detecting that lacking. According to a second aspect of the present invention, there is provided the device for detecting loss of a cutting tool according to the first aspect, further comprising a notifying unit for notifying a detection result of the loss detecting unit. Claim 3
The driving device for stopping the driving of the blade when the defect of the blade is detected based on the detection result of the defect detecting means in the device for detecting the loss of the blade according to the first or second aspect. It is characterized by comprising control means. Further, the invention according to claim 4 includes a first step of detecting the number of revolutions of a main shaft that rotationally drives a cutting tool for processing a workpiece, a second step of detecting a cutting torque of the cutting tool, A third step of obtaining a power spectrum for each frequency in the cutting torque based on the detection result in the second step, and a predetermined frequency range including a frequency synchronized with the detection result in the first step is set. And
A fourth step of obtaining a peak value of the power spectrum in the frequency range; comparing the peak value with a loss determination power spectrum threshold value for determining whether the blade is defective; And a fifth step of detecting that the cutting tool is defective when the power exceeds the threshold value of the loss determination power spectrum. According to a fifth aspect of the present invention, there is provided a cutting tool for processing a workpiece, a main shaft for rotating the cutting tool, a rotation speed detecting unit for detecting a rotation speed of the main shaft, and a cutting torque of the cutting tool. Cutting torque detecting means for detecting,
Based on the detection result of the cutting torque detection unit, a power spectrum calculation unit that obtains a power spectrum for each frequency in the cutting torque, and a predetermined frequency range including a frequency synchronized with the detection result of the rotation speed detection unit is set. And a peak value calculating means for calculating a peak value of the power spectrum in the frequency range, comparing the peak value with a loss determination power spectrum threshold value for determining whether the cutting tool is defective, When the peak value exceeds the loss determination power spectrum threshold, a computer-readable recording medium that records a loss detection program for causing a computer to function as loss detection means for detecting that the cutting tool is defective. is there.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. First, the viewpoint of the inventor of the present invention will be described with reference to FIGS.
FIGS. 1 (a) and 1 (b) show that the cutting tool 84 has a defect.
It is a figure which shows the behavior of the cutting torque in processing of the 840th hole before and after the 1st hole (refer to FIG. 7) and the processing of the 842th hole. That is, FIG. 1 (a) is a diagram showing the cutting torque of a cutting tool having no chipping, while FIG.
(B) is a figure which shows the cutting torque in the cutting tool in which the loss occurred.

Here, when the cutting torque shown in FIG. 1A and the cutting torque shown in FIG. 1B are compared, FIG.
It can be seen that the cutting torque shown in FIG. 1 contains more fluctuation components than the cutting torque shown in FIG. In other words, the inventor has found from the comparison result between FIG. 1A and FIG. 1B that the fluctuation of the cutting torque increases when the cutting tool is chipped. Here, FIGS. 1 (a) and 1 (b)
Was detected by a magnetostrictive torque sensor attached to a main shaft for driving the cutting tool, and the rotation speed of the main shaft at the time of detecting the cutting torque was 1300 rpm.

Further, the inventor of the present invention has shown FIG.
The cutting torque shown in (b) is analyzed by FFT (fast Fourier transform), and the power spectrum for each frequency is shown in FIG.
It was determined as shown in (a) and (b). FIG. 2 (a)
Is the cutting torque in machining the 840th hole (FIG. 1 (a)
FIG. 2B is a diagram showing a power spectrum of FIG.
Is the cutting torque in the machining of the 842 hole (FIG. 1 (b)
FIG. 4 is a diagram showing a power spectrum of the present invention. Here, comparing the power spectrum shown in FIG. 2A with the power spectrum shown in FIG. 2B, the power spectrum shown in FIG.
It can be seen that only the peak value of the power spectrum around 1.7 Hz takes a particularly large value. In addition, since the rotation speed of the main shaft is 1300 rpm, the fluctuation component of the cutting torque around 21.7 Hz is calculated based on the rotation speed of the main shaft (．21.7).
rps).

FIG. 3 is a graph in which the power spectrum (peak value) of the fluctuation component of the cutting torque around the frequency of 21.7 Hz in the machining from the 830th hole to the 860th hole is plotted for each machining hole number. is there. As can be seen from this figure, the peak value of the power spectrum in the machining from the 841th hole onward is larger than the peak value of the power spectrum in the machining from the 830th hole to the 840th hole.

That is, based on the above-mentioned fact, the inventor pays attention to the tendency that the peak value of the power spectrum of the fluctuation component of the cutting torque, which is synchronized with the rotation speed of the spindle, rapidly increases when a defect occurs. The focus was on the fact that the loss of the cutting tool could be detected. Hereinafter, specific examples will be described in detail.

FIG. 4 is a block diagram showing the configuration of a device for detecting the loss of a cutting tool according to one embodiment of the present invention. In this figure, reference numeral 1 denotes a machine tool that performs drilling on a workpiece using a cutting tool (for example, a drill), and includes a torque detection sensor 2 and a control unit 3. The torque detection sensor 2 detects a cutting torque of a cutting tool (drill) not shown, and outputs a detection result as a cutting torque detection signal ST. The control unit 3 controls each unit of the machine tool 1 (drive control of a cutting tool, and the like).

Reference numeral 4 denotes a sensor amplifier for amplifying the cutting torque detection signal ST. Reference numeral 5 denotes an A / D (analog / digital) converter, which converts the cutting torque detection signal ST amplified by the sensor amplifier 4 into digital cutting torque data DT. Reference numeral 6 denotes an FFT calculation unit that obtains a power spectrum (see FIGS. 2A and 2B) for each frequency of the cutting torque by performing FFT (Fast Fourier Transform) on the cutting torque data DT. This FFT
The operation unit 6 outputs the operation result as power spectrum data Dp.

Reference numeral 7 denotes a spindle speed detector for detecting the speed of the spindle (not shown) and outputting the detection result as spindle speed data Dn. The main shaft rotates a cutting tool (not shown). Reference numeral 8 denotes a peak value detection unit that detects a peak value Pp of the power spectrum in the frequency range F1 to F2 from the power spectrum data Dp, and outputs data of the peak value Pp. Here, the frequency range F1
The frequencies F1 and F2 (> F1) that determine F2 are set before and after the frequency synchronized with the spindle speed obtained from the spindle speed data Dn. For example, the frequencies F1 and F2 are set to values around the frequency 21.7 Hz shown in FIG.

Reference numeral 9 denotes a storage unit for storing data of the loss determination power spectrum threshold value Pk. The loss determination power spectrum threshold value Pk is a value to be compared with the peak value Pp, and is a threshold value for determining whether or not the blade has a loss. Reference numeral 10 denotes a comparison unit that compares the peak value Pp with the loss determination power spectrum threshold value Pk. When the peak value Pp exceeds the loss determination power spectrum threshold value Pk, it indicates that the loss of the cutting tool has been detected. The signal S1 is output. 11 is a loss detection signal S indicating that the loss of the cutting tool is detected when the signal S1 is input.
k is generated and output to the control unit 3.

Next, the operation of the device for detecting the loss of a cutting tool according to the above-described embodiment will be described with reference to the flowchart shown in FIG. In step S1 shown in FIG. 5, a setting unit (not shown) sets a loss determination power spectrum threshold value Pk (see FIG. 2B) in the storage unit 9.

Then, when the processing of the workpiece by the cutting tool is started under the drive control of the control section 3, the main spindle is driven and the cutting tool is driven to rotate, thereby starting the detection of a defect (step S2). As a result, the spindle rotation speed is detected by the spindle rotation speed detection unit 7, and the spindle rotation speed detection unit 7 outputs the rotation speed (for example, 1300 rpm ≒ 2).
Spindle speed data Dn (1.7 rps) is output. In step S3, the peak value detection unit 8 takes in the spindle speed data Dn, and then proceeds to step S4.

In step S4, the peak value detecting section 8
Spindle speed obtained from the spindle speed data Dn (= 2
21.7 Hz synchronized with 1.7 rps (see FIG. 2)
(See (b)). Next, the peak value detection unit 8
Sets the frequencies F1 and F2 (see FIG. 2B) before and after the frequency 21.7 Hz.

Further, the cutting torque of the cutting tool is detected by a torque detection sensor 2, and the torque detection sensor 2 outputs a cutting torque detection signal ST corresponding to the cutting torque. Then, after the cutting torque detection signal ST is amplified by the sensor amplifier 4, it is further converted by the A / D converter 5 into cutting torque data DT. Then, in step S5, the FFT calculation unit 6 fetches the cutting torque data DT, and then proceeds to step S6. Step S
In 6, the FFT calculation unit 6 performs a FFT calculation on the cutting torque data DT to obtain a power spectrum of the cutting torque. In this case, assuming that the number of holes to be machined is 840 or less and that the cutting tool has no defect, a power spectrum similar to that shown in FIG. 2A is obtained. Then, the FFT operation unit 6 outputs the power spectrum data Dp corresponding to the power spectrum similar to that shown in FIG.

As a result, in step S7, the peak value detector 8 detects the peak value Pp of the power spectrum in the frequency range F1 to F2 shown in FIG. Output to In step S8, the comparison unit 10 sets the peak value P shown in FIG.
By comparing p with the loss determination power spectrum threshold value Pk, it is determined whether or not the peak value Pp exceeds the loss determination power spectrum threshold value Pk. In this case, since the peak value Pp is equal to or smaller than the loss determination power spectrum threshold value Pk, the peak value detection unit 8 sets the determination result to "NO", returns to step S5, and repeats the above-described operation.

Now, assuming that the machining of the 842 hole has been performed and the cutting tool has a defect, in step S6, the FFT calculation unit 6 calculates the cutting torque data D T of the 842 hole. By performing the FFT operation,
Find the power spectrum of the cutting torque. In this case, a power spectrum similar to that shown in FIG. 2B is obtained. Then, the FFT operation unit 6 outputs power spectrum data Dp corresponding to a power spectrum similar to that shown in FIG.

As a result, in step S7, the peak value detector 8 detects the peak value Pp of the power spectrum in the frequency range F1 to F2 shown in FIG. Output to In step S8, the comparing unit 10 sets the peak value P shown in FIG.
By comparing p with the loss determination power spectrum threshold value Pk, it is determined whether or not the peak value Pp exceeds the loss determination power spectrum threshold value Pk. In this case, since the peak value Pp exceeds the loss determination power spectrum threshold value Pk, the comparison unit 10 outputs the signal S1 to the signal generation unit 11 with the determination result being "YES". Accordingly, in step S9, the signal generation unit 11 outputs a loss detection signal Sk indicating that the loss of the cutting tool has been detected to the control unit 3.

Thus, the control section 3 notifies the buzzer, the display, and the like that the cutting tool is defective, and stops the rotation of the main spindle (cutting tool) and the feed of the main spindle to avoid danger. Control, and in some cases, retreat the spindle.

As described above, according to the device for detecting the loss of the cutting tool according to the above-described embodiment, even if the value of the cutting torque is slightly changed due to the loss of the cutting tool, based on the fluctuation component of the cutting torque. Since the loss determination is performed, the loss of the cutting tool can be accurately detected. Also,
According to the cutting tool defect detection device according to the above-described embodiment, since the vibration frequency of the chatter vibration is different from the rotation speed of the main shaft, the defect of the cutting tool can be accurately detected without being affected by the chatter vibration. .

Although the embodiment of the present invention has been described in detail, the specific configuration is not limited to this embodiment, and the present invention is not limited to a design change without departing from the gist of the present invention. included. For example, in the device for detecting the loss of a cutting tool according to the above-described embodiment, a program for realizing the above-described functions is stored on a flexible disk,
CD-ROM, magneto-optical disk, IC card, DVD-
The loss of the cutting tool may be detected by recording the program on a computer-readable recording medium such as a ROM, and causing the computer system to read and execute the program recorded on the recording medium. Further, the above program is entirely or partially recorded or stored in a portable medium such as a floppy disk, a CD-ROM, or a storage device such as a hard disk. The program is read by a computer, and all or a part of the operation is executed. The recording medium referred to here is not limited to a medium in which a program is statically recorded, such as a magneto-optical disk, but may be a communication line for transmitting a program through a communication line such as a dedicated line of the Internet or a telephone line. In this case, a program that dynamically holds a program for a short time, and a program that holds a program for a certain period of time, such as a server or a memory in a computer in that case, are included.

Further, in the cutting tool defect detecting apparatus according to the above-described embodiment, an example has been described in which the fluctuation component (power spectrum) of the cutting torque is obtained by the FFT operation by the FFT operation unit 6 shown in FIG.
The variation component of the cutting torque may be obtained by using a wavelet transform instead of the calculation.

[0026]

As described above, according to the present invention,
Since the power spectrum of the frequency synchronized with the rotation speed of the spindle, that is, the loss determination is performed based on the fluctuation component of the cutting torque, even if the change in the value of the cutting torque due to the loss of the cutting tool is slight, The effect is obtained that the defect of the cutting tool can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a diagram showing a time-cutting torque characteristic for explaining a principle of detecting a defect in a defect detection device for a cutting tool according to an embodiment of the present invention.

FIG. 2 is a diagram showing a time-power spectrum characteristic for explaining a principle of detecting a loss in the loss detection device for a cutting tool according to the same embodiment.

FIG. 3 is a diagram showing the number of machined holes versus power spectrum characteristic for explaining the principle of detecting a loss in the blade loss detecting device according to the same embodiment.

FIG. 4 is a block diagram showing a configuration of a blade tool loss detecting device according to the same embodiment.

FIG. 5 is a flowchart illustrating an operation of the blade tool loss detection device according to the same embodiment.

FIG. 6 is a diagram showing time-cutting torque characteristics for explaining a problem of a conventional method for predicting loss of a cutting tool.

FIG. 7 is a diagram showing a relationship between the number of machined holes and an average torque characteristic for explaining a problem of a conventional method for predicting loss of a cutting tool.

[Description of Signs] 2 Torque detection sensor 3 Control unit 5 A / D conversion unit 6 FFT calculation unit 7 Spindle speed detection unit 8 Peak value detection unit 9 Storage unit 10 Comparison unit 11 Signal generation unit

Claims (5)

[Claims] 1. A cutting tool for processing a workpiece, a spindle for driving the cutting tool to rotate, a rotation speed detecting means for detecting a rotation speed of the spindle, and a cutting torque detecting means for detecting a cutting torque of the cutting tool. A power spectrum calculating means for obtaining a power spectrum for each frequency in the cutting torque based on a detection result of the cutting torque detecting means; and a frequency range of a predetermined range including a frequency synchronized with the detection result of the rotation speed detecting means. A peak value calculating means for obtaining a peak value of the power spectrum in the frequency range, and comparing the peak value with a loss determination power spectrum threshold value for determining whether the cutting tool is defective. ,
When the peak value exceeds the threshold value of the loss determination power spectrum, a loss detecting unit that detects that the blade is defective is provided. 2. The device for detecting a loss of a cutting tool according to claim 1, further comprising a notifying device for notifying a detection result of the defect detecting device. 3. The apparatus according to claim 1, further comprising: a drive control unit that stops driving the blade when a defect of the blade is detected based on a detection result of the loss detection unit. An apparatus for detecting loss of a cutting tool according to the above. 4. A first step of detecting the number of revolutions of a spindle that rotationally drives a cutting tool for machining a workpiece, a second step of detecting a cutting torque of the cutting tool, and a second step of detecting a cutting torque of the cutting tool. A third step of obtaining a power spectrum for each frequency in the cutting torque based on the detection result, and setting a predetermined frequency range including a frequency synchronized with the detection result in the first step, A fourth step of obtaining a peak value of the power spectrum, and comparing the peak value with a loss determination power spectrum threshold value for determining whether the cutting tool is defective,
And a fifth step of detecting that the cutting tool is defective when the peak value exceeds the threshold value of the loss determination power spectrum. 5. A cutting tool for processing a workpiece, a spindle for driving the cutting tool to rotate, a rotation speed detecting means for detecting a rotation speed of the spindle, and a cutting torque detecting means for detecting a cutting torque of the cutting tool. A power spectrum calculating means for obtaining a power spectrum for each frequency in the cutting torque based on a detection result of the cutting torque detecting means; and a frequency range of a predetermined range including a frequency synchronized with the detection result of the rotation speed detecting means. A peak value calculating means for obtaining a peak value of the power spectrum in the frequency range, and comparing the peak value with a loss determination power spectrum threshold value for determining whether the cutting tool is defective. ,
A computer-readable recording medium recording a loss detection program for causing a computer to function as loss detection means for detecting that the cutting tool is defective when the peak value exceeds the threshold value of the loss determination power spectrum. .