JPS6317581B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an RMS (root meam square) processing device in a cutting edge defect detection device for a face milling cutter.

The cutting edge of a tool often suddenly develops chipping defects during cutting, and it is very difficult to predict this. For this reason, research has been actively conducted on methods to continuously monitor tool cutting edges and detect chipping and chipping, and the present inventors have also previously published patent application No. 57-24794 to detect changes in tool vibration. detection,
We have proposed a method that can detect even relatively small occurrences of chipping through analysis.

To explain more specifically, this proposed detection method involves attaching a vibration pickup to the tool system of a cutting machine to detect vibrations during cutting, and transmitting the output signal in advance to the unique vibration that occurs during cutting in the tool system. After measuring the vibration frequency and passing it through multiple bandpass filters with frequency bands set around them, RMS processing is performed, and cutting edge defects are detected based on the fluctuation of the RMS value obtained. This is a characteristic feature.

However, when applying this detection method to interrupted cutting such as face milling, that is, generally, intermittent cutting of around 100 ms or less is repeated and the interval between cutting is relatively long. , there are some problems with the RMS processing method. For example, when a thermal integration method (offline) is used, there is a significant time delay and high-speed signal processing is not possible. Also, although a method using an A/D converter and a microcomputer is effective, such a computer is insufficient for signal processing during high-speed cutting. Particularly when performing RMS processing on intermittent signals obtained by intermittent cutting, if such processing with a large time delay is performed, appropriate effective values cannot be obtained.

The present invention aims to solve such problems regarding signal processing speed and to provide an RMS processing device in a cutting edge defect detection device that makes it possible to perform accurate detection.

In order to achieve such an object, the present invention detects vibrations accompanying cutting of a cross section milling cutter using a vibration pickup, and converts the output signal of the vibration pickup to the unique vibration frequency generated during cutting in the tool system. In a cutting edge defect detection device that detects cutting edge defects based on fluctuations in the RMS value obtained by performing RMS processing after passing through a plurality of bandpass filters with frequency bands set in the vicinity of The RMS processing device that performs the processing consists of a multiplication circuit that squares the input acceleration signal, a CR integration circuit that integrates the output over time, and a gate pulse that is generated in synchronization with the intermittent cutting cycle of the tool. The invention is characterized in that it is comprised of a gate control circuit that performs the above-mentioned integration only during a certain cutting period and controls the gate so as to clear the integration circuit after that period, and a root circuit that performs the square root of the output. It is something.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an example of a face milling cutter for which cutting edge damage is to be detected. An acceleration pickup 2 is attached to the back side of the tool 1 to collect acceleration signals. The pick-up can optionally be attached to a cutting machine or a workpiece.

In experiments conducted by the present inventors, we investigated the power spectrum of the vibrations detected by such pickups, and found that multiple frequency components unique to the tool system appeared prominently. By dividing the acceleration signal into multiple frequency bands using a bandpass filter and detecting changes in the respective acceleration levels, it can be seen that chipping has occurred in the portion of the cutting edge that corresponds to the frequency band.

Therefore, the acceleration signal output from the acceleration pickup 2 is either a slip ring or an FM
It is taken out via a transmitter/receiver, etc., and recorded on a data recorder as necessary. Thus, the acceleration signal is passed through a plurality of band pass filters 11, 12, 1.
3, the frequency bands around each vibration frequency specific to the tool system, or the frequency bands around the main vibration frequencies, are divided by 3, and the output of each bandpass filter is processed by the RMS processing device 2.
1, 22, and 23 to form a signal with an effective value corresponding to the acceleration level.

The frequency band of the above bandpass filter is determined by measuring the vibration frequency that occurs during cutting in the tool system in advance, and for example, the vibration frequency is 0.65, 2, 4, 7k.
If it is around Hz, then 1.4 ~
2.2kHz, 3.5~4.5kHz, 5.8~7.5kHz (ignore the frequency of 0.65kHz as it has little correlation with chipping).

Further, the RMS processing devices 21, 22, 23 are
Equalizes the output of the bandpass filter and eliminates noise (for example, spike noise N as shown in Figure 3)
, and converts it into a signal with an effective value corresponding to the vibration level. In particular, by switching with a pulse signal synchronized with the rotation of the main shaft 3, discontinuous input signals can be eliminated.
It is characterized by performing RMS processing to enable online processing, and is configured as shown in FIG. 2. That is, the waveform of the acceleration signal x from the bandpass filter is squared in the multiplication circuit 24, and then integrated intermittently for a certain period of time in the CR integration circuit 25. A gate control circuit 26 that controls the time integration in the integration circuit 25 controls the integration by using a gate pulse synchronized with the intermittent cutting cycle of the tool, which is output from the rotating system of the main shaft 3 of the tool 1 by appropriate means. It performs switching control of gates 27 and 28 in the circuit, and by opening and closing these gates 27 and 28, the above integration is performed only during a certain intermittent cutting period, and the next integration is performed at an appropriate time after that period. In preparation for this, the integral value held in the integrating circuit is cleared. The output of the integrating circuit 25 is then subjected to square rooting in the root circuit 29 at the next stage, thereby outputting an RMS value which is the effective value of the acceleration signal x.

Figure 3 shows the gate pulse from the tool rotation system mentioned above, the acceleration signal from the pick-up, and the RMS.
It shows an example of an RMS value output from a processing device.

Since the RMS value corresponding to the level of vibration obtained in this way increases in accordance with chipping and defects, it is displayed on the record display meter 30,
Alternatively, chipping or loss can be detected by comparing it with an appropriate threshold value in a chipping determination device comprising a comparator.

As is clear from the detailed description above, the RMS processing device of the present invention can process intermittent signals from a pickup at high speed by analog processing and switching integral processing.
Therefore, the averaging time constant (CR product in Figure 2)
Even if it is designed to be sufficiently large, processing can be performed with fast response and high average accuracy, making it possible to accurately detect chipping and chipping of tool cutting edges in-process.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the cutting edge defect detection device of the present invention;
FIG. 2 is a block diagram of the RMS processing device, and FIG. 3 is an explanatory diagram of signal waveforms. 11, 12, 13...Band pass filter, 2
1, 22, 23... RMS processing device, 24... Multiplication circuit, 25... CR integration circuit, 26... Gate control circuit, 27, 28... Gate, 29... Route circuit, 30... Recording display meter.

Claims (1)

[Claims] 1. Vibration caused by cutting with a face milling cutter is detected by a vibration pickup, and the output signal of the vibration pickup is passed through a plurality of band-pass filters whose frequency band is set near the unique vibration frequency that occurs during cutting in the above tool system. After passing through
In a cutting edge defect detection device that performs RMS processing and detects cutting edge defects based on fluctuations in the RMS value obtained by the RMS processing, the RMS processing device that performs the RMS processing is replaced by a multiplier circuit that squares the input acceleration signal. and a CR integration circuit that time-integrates the output.
a gate control circuit that performs the above integration only during a certain cutting period using a gate pulse generated in synchronization with the intermittent cutting cycle of the tool, and controls the gate so that the integration circuit is cleared after that period; 1. An RMS processing device for a cutting edge defect detection device for a face milling cutter, comprising a root circuit for square rooting the output.