JPS62193751A - Multi-blade tool damage detecting device - Google Patents

Abstract

PURPOSE:To detect damage of a multi-blade tool and to enhance the accuracy of detection on a real-time base, by applying the rectified output of an AE sensor to a band-pass filter which allows a frequency corresponding to the rotational speed of a spindle to pass therethrough, to detect the rotational speed of the spindle, and by comparing the output thereof with a predetermined value. CONSTITUTION:During cutting of a workpiece 2, an AE signal detected by an AE sensor 6 is amplified by an amplifier 8, and delivered to a full wave rectifying circuit 9 for delivering frequency signals corresponding to the rotational speed of a spindle and the number of blades of a multi-blade tool 4. If the multi-blade tool 4 is damaged, a signal having a frequency spectrum delivered from the full wave rectifying circuit 9 is added to a variable band-filter 10. Accordingly, the number of frequency components passing through the filter 10 becomes remarkably greater when the tool is damaged, than the during normal machining operation, and the output thereof is delivered to a comparator 14 after being converted into a d.c. level by a rectifying and smoothing circuit 13. Accordingly, by setting threshold levels with the use of a threshold setting circuit 15, it is possible to detect damage such as chipping, defecting of the like in the multi-blade tool, thereby it it possible to enhance the accuracy of detection 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 a multi-blade tool has a frequency component determined by its rotational speed when it is damaged, we calculated the output obtained through a bandpass filter whose pass frequency is a frequency corresponding to the rotational speed. Damage to the multi-blade tool is detected by comparing it with a predetermined level.

[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 damage to the tool is detected based on the signal from the AE sensor. Such a conventional tool damage detection device detects when the AE double signal suddenly rises or the average value exceeds a predetermined dark value level, or when the maximum value of the probability density function of the AE double signal output exceeds a predetermined level. This is used to detect damage to the tool if the tool is damaged.

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-edge tool having a plurality of blades by changing the signal level of the rotational frequency of the spindle 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 bandpass filter is provided with an output and has a passing frequency that is substantially equal to the rotational speed of the main shaft of the machine tool, and a comparison circuit that outputs a damage output when the output of the bandpass filter is equal to or higher than a predetermined level. It is characterized by this.

In a machine tool that has a multi-blade tool, if the multi-blade tool is damaged during operation of the machine tool, a rectified signal from an E-sensor installed near the tool of the machine tool that corresponds to the rotation speed of the spindle will be sent. The level of the frequency component becomes higher. Therefore, in the present invention, the rectified output is applied to a bandpass filter having a pass frequency corresponding to the rotational speed of the spindle to detect the rotational speed component of the spindle, and the output is compared with a predetermined level to detect damage to the multi-blade tool. ing. In this way, damage to multi-edge tools can be detected in real time with high accuracy.

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 frequency IKI (z to IMHz) generated during cutting and converts it into an electrical signal, and its output is given to a bandpass filter.The bandpass filter 7 is For example, frequency 100 KHz =
This is a filter that allows the AE multiplied signal up to I MHz to be processed, and removes noise components associated with mechanical vibrations and the like. The output of the bandpass filter is applied to a full-wave rectifier circuit 9 via an amplifier 8. The full-wave rectifier circuit 9 performs full-wave rectification on the applied signal and provides its output to the variable bandpass filter 1o. Now, a rotation speed detector 11 is attached to the main shaft 5 of the machine tool. The rotation speed detector 11 consists 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. . The output of the rotation speed detector 11 is then converted to the conversion circuit 12.
given to. The conversion circuit 12 converts a pulse signal obtained by the rotational speed of the main shaft into an analog voltage at a level corresponding to the rotational speed, and supplies its output to a variable bandpass filter 0. Variable bandpass filter 1
0 changes its passing frequency in response to the applied analog signal, and is controlled by the conversion circuit 12 so that the passing frequency is substantially the same as the rotational speed of the main shaft 5. The output that has passed through the bandpass filter 10 is then given to a rectifier/smoothing circuit 13. The rectifier/smoothing circuit 13 converts the applied signal to a DC level, and provides its output to the comparator 14. The comparator 14 is supplied with the output of a threshold setting circuit 15 that sets a certain threshold level determined according to the type, number of teeth, rotation, etc. of the multi-blade tool used, and if the input signal is higher than this threshold level. For example, damage to a multi-blade tool is detected and its output is provided to a damage output circuit 16 and a display circuit 17.

Next, the operation of this embodiment will be explained with reference to a frequency spectrum diagram. When the workpiece 2 is being cut with the machine tool described above, 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, the spectrum has a peak at a harmonic component Pct (42,4Hz) that is four times the frequency (10,6Hz) corresponding to the rotational speed of the main shaft 5 and a harmonic that is twice that frequency (84,8Hz). is 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. It was found that the frequency component PH1 (10.6 Hz) and its harmonic components occur simultaneously. The present invention has been made in view of the fact that the frequency component of the rectified signal corresponding to the rotation speed of the spindle has a close relationship with damage to multi-blade tools, and the rotation speed of the spindle 5 is always set to a predetermined value by the conversion circuit 12. Convert to DC level and apply variable bandpass filter 1
The passing frequency of 0 is set to a frequency corresponding to the rotational speed of the main shaft, in this case 10.611z.

Therefore, 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, the band pass filter 7, and the amplifier 8.
Since the full-wave rectified output has a frequency spectrum as shown in FIG. 2, it is cut off by the variable band-pass filter 1o, and the rectifying/smoothing circuit 13 supplies a DC component with a low noise level to the comparator 14. Therefore, the comparator 14 does not output a tool damage output and cutting continues. Now, multi-edged tool 4
If there is damage to the bandpass filter 1o, a signal having a frequency spectrum as shown in FIG. 3 is applied from the full-wave rectifier circuit 9 to the variable bandpass filter 1o.

Therefore, when the work is damaged, the component passing through the variable bandpass filter 10 becomes dramatically larger than when the work is normal as shown in FIG. It will be done. Therefore, by setting the darkness value level according to each tool in the darkness value setting circuit 15, damage such as chipping or chipping of a multi-blade tool can be detected. The output of the comparator 14 is applied to a damage output circuit 16 and a display circuit 17 to provide an output to the outside and to be displayed. Therefore, by immediately 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 11 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 12 and applied to the variable bandpass filter 10. However, as shown by the broken line in FIG. 1, when a numerical control device 2o is connected to this machine tool and cutting is performed by it, the rotation speed data of the spindle 5 is transmitted from the numerical control device 20 to the variable filter setting circuit 20. It is also possible to change the jWi overfrequency of the variable bandpass filter 10 by giving

Further, in this embodiment, the amplified output of the bandpass filter is full-wave rectified, but it may be half-wave rectified and the output may be given to the variable bandpass filter.

Furthermore, in the present invention, the full-wave rectified output is converted to a DC level through a variable bandpass filter and compared with the dark value.
It is also possible to directly A/D convert the full-wave rectified output, analyze its frequency components using a microcomputer, etc., and compare the amplitude level with the dark 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.

Claims (2)

[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 bandpass filter to which the output of the circuit is applied and whose passing frequency is substantially equal to the rotational speed of the main shaft of the machine tool; and a comparison circuit that outputs a damage output when the output of the bandpass filter is equal to or higher than a predetermined level. A multi-blade tool damage detection device characterized by comprising: (2) Multi-edge tool damage detection according to claim 1, wherein the bandpass filter is a variable bandpass filter that is given rotational speed data of the spindle and changes the passing frequency accordingly. Device.