JP3105537B2 - Abnormality prediction device and method for rotary tool - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus and a method for predicting abnormality of a rotary tool used in a machine tool such as a machining center, a lathe, and a milling machine.

(Prior Art) Conventionally, when a workpiece is cut by a rotary tool such as a drill, a tap, an end mill, or the like, an abnormal state such as breakage, breakage, or wear of the rotary tool is detected before the occurrence. For example, a device for predicting abnormality of a rotary tool is disclosed in
No. 48 proposes this. According to this proposed device, a holder equipped with a rotary tool is provided with a detector for detecting a cutting force of the rotary tool, and a first signal for outputting an abnormal signal when the detected cutting force exceeds a predetermined value. Comparing means, a second comparing means for outputting an abnormal signal when a magnification of the cutting force detected by the detector with respect to the cutting force at the start of cutting exceeds a predetermined value, and cutting detected by the detector A third comparing unit that outputs an abnormal signal when the fluctuation component of the force exceeds a predetermined value, and the number of times that the fluctuation component of the cutting force detected by the detector exceeds a predetermined value exceeds a predetermined number of times. And at least one of the fourth comparing means for outputting an abnormal signal when the signal is detected.

This proposed device is shown in FIG. Numeral 1 is a numerical control (NC) device including a spindle for rotating a rotary tool. 2
Is a tool holder type cutting force detecting device. A rotary tool such as a drill is attached to the cutting force detection device 2 to perform cutting. The cutting force (thrust and torque) at this time is output as a cutting force signal from the FM transmitter in the detection device 2,
This signal is input to the amplifier 4 via the external receiving antenna 3. This signal is converted into a digital signal by the A / D converter 5 and various determinations are made by the computer 6. The content of this determination will be described later. If it is determined that the value of the cutting force is abnormal, the computer 6 sends a signal to the alarm device 8 via the D / A converter 7 to activate the device, and the NC device 1 via the remote buffer 9. A signal for avoiding breakage is sent to the machine to stop cutting immediately.

A signal as shown in FIG. (A) and (b) show signals when aluminum material was cut with a 2 mm diameter drill, and (c) and (d) show signals when steel material S50C was cut with a 2 mm diameter drill.
The thresholds of A 'and B' are set, and when the thresholds are exceeded, signals are sent to the alarm device 8 and the NC device 1. Here, the threshold is set according to various cutting conditions, and a threshold obtained by a value obtained by various experiments or a predetermined multiple of an average value after a steady state is obtained after the start of cutting is used as the threshold.

However, when using the thresholds obtained by various experiments when determining the thresholds, countless combinations occur due to the work material, the drill diameter, the cutting conditions, and the like, and it is difficult to obtain the thresholds that match the actual conditions. Due to the large number, automation of cutting control is difficult. On the other hand, a method in which the average value of the cutting force after the start of cutting and in a steady state is obtained and a predetermined multiple of this average value is set as a threshold is a method of roughly determining the threshold, and is suitable for automation. . However, the cutting force differs greatly depending on whether the drill is new or used. In particular, the thrust is remarkable, and there is a problem that there is a large variation in the threshold value setting.

The present invention has been made in view of this point, and an object of the present invention is to provide a rotary machine that can set the same threshold value for drills having different use times, if the same work material and the same cutting conditions are used. An object of the present invention is to provide a tool abnormality prediction device and a method thereof.

(Means for Solving the Problems) In order to achieve such an object, the present invention provides a rotating tool, a holder for holding the rotating tool, and a detection provided in the holder and indicating a cutting force of the rotating tool. An abnormality prediction device for a rotary tool, comprising: a detector for detecting a signal; and a calculation device for outputting an alarm signal when a detection signal value from the detector exceeds a predetermined threshold value. Storage means for capturing and storing a detection signal from the vessel at a constant cycle, first means for detecting the first spike signal among a plurality of spike signals generated each time cutting,
Based on the first spike signal from this first means,
A second means for reading a detection signal stored in the storage means and immediately before the detection of the first spike signal, and setting a threshold value based on the read detection signal value; And a third means for comparing the threshold value set in the above with the detection signal from the detector and outputting an alarm signal. The present invention also provides a method for predicting abnormality of a rotating tool, which detects a detection signal indicating a cutting force of the rotating tool and outputs an alarm signal when the detected signal value exceeds a predetermined threshold. The detected detection signal is captured and stored at a fixed cycle, and the first spike signal is detected among a plurality of spike signals generated for each cutting, and based on the first spike signal, the stored detection signal is used. The detection signal immediately before the detection of the first spike signal is read, a threshold is set based on the read detection signal value, and the set threshold is compared with the detected detection signal to output an alarm signal. It is characterized by doing.

(Operation) In the apparatus and method for predicting abnormality of a rotary tool according to the present invention, a detection signal indicating a cutting force of the rotary tool is captured and stored at a constant cycle, and among a plurality of spike signals generated for each cutting, Detecting a first spike signal, reading the stored detection signal based on the first spike signal, the detection signal immediately before the detection of the first spike signal, and setting a threshold based on the read detection signal value. Is set, and the set threshold value is compared with the detected detection signal to output an alarm signal. As a result, since the detection signal immediately before the first spike signal among the plurality of spike signals generated during cutting is stable, if the same work material and the same cutting conditions are used, the wear state of the rotating tool may be reduced. Regardless, the threshold value for the breakage prediction determination can be the same while the rotary tool is used, and the stable threshold value enables the breakage prediction of the rotary tool and cutting to the cutting limit at which no breakage occurs. In addition, the processing efficiency is improved, and the production efficiency can be increased.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG. In the figure, a cutting force detector 2 is attached to a main shaft of an NC device 1. An amplifier 4 is arranged to receive a torque-thrust signal (cutting force signal) indicating the FM-modulated torque and thrust from the cutting force detector 2 via the antenna 3. The output side of the amplifier 4 has a low-pass filter 10
The A / D converter 5 is connected via the. Reference numeral 11 denotes a CPU serving as an arithmetic unit. The CPU 11 has a RAM 13, a display 14, an external output input / output unit (I / O) 15, and an A / D converter 5 via a common bus 12. An alarm input / output unit (I / O) 16 is connected, and an alarm device 17 is connected to the alarm input / output unit (I / O) 16.

Next, the operation will be described. The cutting force detector 2 FM-modulates the torque / thrust signal indicating the torque / thrust and sends it to the antenna 3 and the amplifier 4. The FM modulation signal is separated and detected by the low-pass filter 10 for a high frequency such as noise, and the torque / thrust signal is obtained. This torque / thrust signal is converted into a digital signal by the A / D converter 5 and the CPU 11
The value is compared with a set threshold value set by the CPU 11, and when the torque / thrust signal value exceeds a predetermined threshold value, an alarm signal is output via the alarm I / O 16 to the alarm device 17.
And the alarm 17 indicates the alarm by display or sound.

Next, examples of the torque / thrust signal detected by the CPU 11 are shown in FIGS. 2 to 4 are steel S45C
A hole of 8 mm was drilled with a 1.5 mm diameter drill in the heat treatment material at a rotation speed of 1800 r.p.
m. and a feed of 0.05 mm / rev. are shown. FIG. 2 is a characteristic diagram in the case of drilling with a new drill. As shown by a and b in FIGS. 2A and 2B, several spike-like signals co-occur with torque and thrust. After the torque signal and the thrust signal have passed a, spike-like signals are generated while increasing smoothly. FIG. 3 (a),
(B) is a characteristic diagram when cutting is repeated several times with the same new drill as in FIG. 2 and the wear of the drill progresses.
The first spike-like signal of the same order as in FIG. 7A occurs at the position indicated by a ', and thereafter the spike signal is generated while increasing smoothly as in b'. The value immediately after the start of cutting is
As can be seen from the value of c 'in FIG. 3, the thrust is about 1.4 times that of c in FIG.

FIG. 4 shows a signal at the time of breakage, and a spike-like signal is generated similarly to FIGS. 2 and 3. The rising signal c ″ is 1.4 times the sliced signal and 1.2 times the torque compared to the new rising signal c in FIG. 2, and c, c ′, c ″.
Is in a steady state, the threshold value also shifts at the same magnification.
However, in each cutting, the torque signal and the thrust signal immediately before a, a ', a ″ at the time of the first spike-like signal were generated, the torque was about 0.96 kgf · cm, the thrust was 20.0 kgf, and the variation was 5%.
It is stable before and after. Since the torque signal and the thrust signal are stable immediately before the first spike-like signal is generated, the values of the torque and the thrust (average value) immediately before a, a ', a "are changed for each cutting. If a predetermined multiple of this is set as a threshold value, the same threshold value can be set for a drill immediately before breakage due to abrasion and a new drill, for example.

Next, a method of setting the predetermined threshold will be described. FIG. 5 is a characteristic diagram showing a relationship between cutting force (torque in this example) and cutting time when cutting is performed with a drill. When cutting is performed, a spike signal (a signal whose level change value per unit time and the absolute value of the level change are abnormally large compared to the cutting force signal) is generated as indicated by SP. Focus on this first spike signal. Then, the cutting force immediately before the generation of the spike signal is used as a reference for setting the threshold. This threshold is used to determine drill breakage prediction, and when the cutting force exceeds the above threshold,
The CPU 11 outputs an alarm signal via the alarm 17 and
The NC unit 1 is operated via the external output input / output unit (I / O) 15 to immediately stop cutting.

The above operation will be described in more detail with reference to FIGS. FIG. 6 shows a model obtained by enlarging the spike signal SP shown in FIG. 5, and the cutting force is sampled by the A / D converter 5 every time Δt and stored in the RAM 13 as data Tr (t _i ). The sampling period should be as short as possible to accurately reproduce the cutting force, but the spike signal actually generated is several hundred Hz or less, so in order to reproduce the waveform, convert it to a sampling frequency of several KHz. Is enough.

Here, attention is paid to the data Tr (t _i ) at the time t _i . The processing flow at this time will be described with reference to FIG. After starting cutting, the cutting force detected by the cutting force detector 2 is stored in RAM1
Read into 3 (step S1). Since the time is t _i , the read data is Tr (t _i ). Next, steps S2 and S3
Then, it is determined whether a spike signal has occurred from the read data. In the embodiment of FIG. 7, step S2
As shown in the figure, the cutting force Tr (t _i ) at the current time (time t _i )
Average of (a-1) cutting forces from time t _(ia) to t _(i-1) The absolute value ΔTr (t _i ) of the deviation from
(T _i ) is compared with a preset value b (step
S3). Note that a is also a preset value. As shown in FIG. 6, if the sampling signal level is simply compared between the current time and the previous time, when the sampling is fast (the sampling period is short), the signal level difference hardly occurs. It is necessary to increase (a-1). When sampling is slow, the number of samples (a-1) may be small. Therefore, a of the sample number a-1 is determined according to the sampling speed. The set value b is determined by an experiment. In order to detect a spike signal, only the spike signal may be extracted by passing the detected cutting force signal through a low-pass filter and a high-pass filter, and the value of the spike signal may be compared with a threshold value such as b.

If it is determined in step S3 that no spike signal has been generated, the process returns to step S1, and the same loop is repeated.
If it is determined in step S3 that a spike signal has occurred, the process proceeds to step S4, and a threshold value C is set. The threshold C is equal to (a−a) immediately before the first spike signal is generated after the start of cutting.
1) Average value of cutting force signal values Multiplied by the given value d Is used. The threshold C, that is, d, may be determined in consideration of parameters such as a drill diameter, a feed, a rotation speed, a drill material, and a work material, or a change in a cutting force signal, for example, a differential value of the cutting force signal. May be used as a parameter,
It may be obtained from an experiment. In step S5, the cutting force Tr is again
(T _i ) is read and compared with the threshold value C in step S6. Tr
If the (t _i ) value exceeds the threshold value C, the process proceeds to step S7, and an alarm signal is output assuming that there is a cutting abnormality. At the same time, the cutting is stopped even during the cutting. Also step
If it is determined in S6 that the Tr (t _i ) value does not exceed the threshold value C, the process proceeds to step S8, and it is determined whether or not the cutting has been completed. If the cutting has been completed, that is, if drilling as planned has been completed, the present program is ended. If not completed, the process returns to step S5 again and repeats the same loop.

In the above embodiment, the value obtained by multiplying the average value of the signal values immediately before the first spike signal generation by the predetermined value d is used as the threshold value C.
However, the present invention is not limited to these. For example, a value obtained by adding a predetermined value corresponding to the magnitude of the signal value immediately before the first spike signal generation to the signal value may be used as the threshold value.

Further, in the description of the above embodiment, the breakage accident of the drill was described as an example. However, it is obvious that the present invention is not limited to the drill and can be applied to a rotary tool such as a tap or an end mill. In addition, it is possible to predict even in the case of a breakage accident or wear. Further, in the description of the above embodiment,
Although an example using a torque signal as the signal has been described, a thrust signal or both signals may be used.

Also, in the description of the above embodiment, only the prediction of an abnormal state has been described. However, even if there is a case where it is not possible to predict for some reason, it is not possible to detect this when an abnormality such as breakage actually occurs. Clearly, at least the working mechanism can be adequately protected. In order to protect the machine tool more completely, an appropriate detection system may be separately used in addition to the prediction device of the present invention.

Further, as the detection device, it is not always necessary to detect both the thrust and the torque, and a device that detects only one of the thrust and the torque may be used according to the comparison means employed. Further, the detection device has been described as an example in which the detection signal is wirelessly transmitted and received, but the detection device may be configured to extract the detection signal by light. Also, an alarm device is not always necessary.

(Effects of the Present Invention) As described above, the present invention provides an apparatus and a method for predicting abnormality of a rotary tool, in which a detection signal indicating a cutting force of the rotary tool is captured and stored at a constant cycle, and is stored for each cutting. Detecting a first spike signal among a plurality of spike signals generated in the memory, and based on the first spike signal, reading out the stored detection signal and a detection signal immediately before the detection of the first spike signal; A threshold value is set based on the read detection signal value, and the set threshold value is compared with the detected detection signal to output an alarm signal. Therefore, the first spike signal among a plurality of spike signals generated during cutting is output. Since the detection signal immediately before the signal is stable, if the same work material and the same cutting conditions, regardless of the wear state of the rotary tool, the threshold for breakage prediction determination Can be the same threshold while using
With the stable threshold value, it is possible to predict the breakage of the rotary tool and perform cutting up to a cutting limit at which no breakage occurs, thereby improving machining efficiency and increasing production efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 to 4 are thrust / torque characteristics diagrams when drilling a steel S45C hole, and FIG.
FIGS. 6, 6 and 7 are characteristic diagrams and flowcharts for explaining a method of setting a predetermined threshold value, FIG. 8 is a block diagram showing a conventional apparatus, and FIGS. 9 (a), (b) and (c). (D) is a thrust torque characteristic diagram when drilling aluminum and steel S50C. 1 ... NC device, 2 ... Cutting force detector, 3 ... Antenna,
4 ... Amplifier, 5 ... A / D converter, 10 ... Low-pass filter, 11 ... CPU, 12 ... Common bus, 13 ... RAM, 14 ...
Display section, 15 I / O for external output, 16 I / O for alarm, 17
... alarm.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B23Q 17/09 B23B 49/00

Claims (2)

(57) [Claims] 1. A rotary tool, a holder for holding the rotary tool, a detector provided on the holder for detecting a detection signal indicating a cutting force of the rotary tool, and a detection signal value from the detector being a predetermined value. An abnormality prediction device for a rotary tool, comprising: a calculation device that outputs an alarm signal when a threshold value is exceeded; wherein the calculation device captures and stores a detection signal from the detector at a constant cycle; First means for detecting a first spike signal among a plurality of spike signals generated each time cutting is performed, and a detection signal stored in the storage means based on the first spike signal from the first means. A second means for reading a detection signal immediately before the detection of the first spike signal and setting a threshold based on the read detection signal value; and a threshold set by the second means and the detector Anomaly device for a rotary tool, characterized in that a detection signal of the third means for outputting an alarm signal by comparing. 2. A method for predicting abnormality of a rotating tool, comprising: detecting a detection signal indicating a cutting force of the rotating tool; and outputting an alarm signal when the detected signal value exceeds a predetermined threshold value. A detection signal is fetched and stored at a fixed cycle, a first spike signal is detected among a plurality of spike signals generated at each cutting, and the stored detection signal is detected based on the first spike signal. A detection signal immediately before the detection of the first spike signal, sets a threshold value based on the read detection signal value, compares the set threshold value with the detected detection signal, and outputs an alarm signal. A method for predicting abnormality of a rotary tool, characterized in that: