JPH0132024B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chatter monitoring device for a machine tool, and particularly to a chatter monitoring device suitable for a machine tool such as a machining center that cuts a workpiece using various tools.

An object of the present invention is to enable accurate determination of the presence or absence of chatter in cutting conditions by various tools with a simple configuration.

Generally, vibrations associated with cutting of a machine tool are detected, this detection signal is input to a bandpass filter to extract only signals in a predetermined frequency range, and the value of the detection signal in this predetermined frequency range is compared with a reference value. It is known to detect the presence or absence of chatter and to control a machine tool.

However, in machine tools such as machining centers that cut workpieces by sequentially mounting various tools on the spindle according to a predetermined program, the self-excited chatter vibration frequency and the magnitude of chatter vibration differ for each tool. Therefore, it is not possible to accurately grasp the chatter condition of each tool by simply comparing the detection signal with a certain reference value as in the above-mentioned known method, and the method of determining the reference value for each tool makes it difficult for the equipment to There are problems that can be extremely complex and expensive.

In order to solve this problem, the inventors conducted various experiments and found that the acceleration value at which chatter occurs during cutting with various tools has a correlation with the self-excited chatter vibration frequency, and the presence or absence of chatter is determined by the tool. A method has been found that allows discrimination based on the relationship between vibration frequency and acceleration, regardless of the type of vibration. In other words, Figure 2 shows the state of occurrence of chatter when cutting a workpiece using various tools, depending on the self-excited chatter vibration frequency f.
It is shown in the relationship between and acceleration g, and in the figure ○
The mark indicates the presence of chatter, and the mark x indicates the absence of chatter. What is clear from Fig. 2 is that the acceleration values at which chatter occurs are different in lower and higher frequency regions with a certain chatter vibration frequency as a boundary, and that the acceleration values at which chatter occurs in each frequency range are different. It was found that the value was almost constant.

Therefore, in a machine tool that performs cutting using various tools, the present invention separates the acceleration signal of an acceleration converter using at least two bandpass filters, and sets the outputs of each of these bandpass filters to different set values. It is an object of the present invention to provide a chatter monitoring device that can accurately determine the presence or absence of chatter regardless of the type of tool.

Embodiments of the present invention will be described below based on the drawings.
In FIG. 1, numeral 10 indicates a spindle head of a numerically controlled machine tool equipped with an automatic tool changer, for example, and a spindle 11 supported by this spindle head 10 has various tools 12 in accordance with a predetermined machining program. They are being inserted in sequence. An acceleration converter 13 is attached to the spindle head 10, and this acceleration converter 13 detects the acceleration of mechanical vibrations generated during cutting and inputs the detection signal to an amplifier 14.
First and second bandpass filters 15 and 16 are connected to the amplifier 14, and the first bandpass filter 15 extracts only signals in a predetermined frequency range of the acceleration signal, and the second bandpass filter 16 Accordingly, only signals in a predetermined frequency range higher than the above frequency range are extracted.

A first comparator 17 is connected to the first bandpass filter 15, and the comparator 17 compares the acceleration signal taken out from the bandpass filter 15 with the set value A set by the first setting device 18. are compared, and if the acceleration signal is smaller than the set value A, an OK signal is output, and if it is larger, an NG signal is output. Similarly, a second comparator 19 is connected to the second band pass filter 16, and this comparator 19 uses the acceleration signal taken out from the band pass filter 16 and the setting value set by the second setting device 20. B is compared, and if the acceleration signal is smaller than the set value B, an OK signal is output, and if it is larger, an NG signal is output.
Therefore, the first and second comparators 17, 19
If an OK signal is output from both of the
If an NG signal is output from one or both of the second comparators 17 and 19, an abnormal signal is sent through the OR circuit 22. such first and second comparators 17,
19, first and second setters 18 and 20, an AND circuit 21, and an OR circuit 22 constitute a determining device 25 that determines the presence or absence of chatter.

Based on the experimental results shown in FIG. 2, the first bandpass filter 15 passes the frequency range of 300Hz to 700Hz, and the second bandpass filter 16 passes the frequency range of 700Hz to 3000Hz. Furthermore, the first setting device 18 has an acceleration value of 0.1g as a setting value A, and the second setting device 20 has an acceleration value of 0.04g as a setting value B.
The acceleration value of is set. However, it is clear that these values vary depending on the machine tool, especially the rigidity of its spindle system, etc.
This is merely an example.

Next, the operation of the above configuration will be explained.
When the tool 12 is attached to the spindle 11 of the spindle head 10, the workpiece is machined under predetermined cutting conditions, and the self-excited chatter vibration generated by the cutting process is converted into the acceleration of the spindle head 10. Vessel 13
detected by. The acceleration signal detected by the acceleration converter 13 is amplified by the amplifier 14, and then separated into two frequency components by two bandpass filters 15 and 16 having different frequency domains. The acceleration signal in one frequency range (300Hz to 700Hz) is compared by the first comparator 17 to see if it is larger or smaller than the set value A, and if it is larger, it is assumed that vibration has occurred and an NG signal is output. If the value is smaller, an OK signal is output.
The acceleration signal in the other frequency range (700Hz to 3000Hz) is compared by the second comparator 19 to see if it is larger or smaller than the set value B, and if it is larger, it is assumed that vibration has occurred and an NG signal is output. output, and if it is small, outputs an OK signal.
When OK signals are output from both comparators 17 and 19, a normal signal is sent from the AND circuit 21, and also when one of the comparators 17 and 19 outputs a normal signal.
When an NG signal is output, an abnormal signal is sent from the OR circuit 22, and based on this abnormal signal, the cutting process is stopped, an alarm signal is issued, or the cutting conditions are changed again to prevent chatter. Prevent occurrence.

In this way, the present invention has discovered the fact that, regardless of the type of tool, it is possible to determine the presence or absence of chatter based on constant acceleration values that differ from each other at a certain vibration frequency in cutting processes using various tools. The output of the acceleration converter that detects the vibration caused by the vibration is separated by two bandpass filters that pass signals in different frequency regions, and the outputs of each of these bandpass filters are compared with different set values. It is designed to be able to determine the state of chatter.

Therefore, according to the present invention, even in a machine tool such as a machining center that performs cutting using various tools, there is no need for complex control such as setting a reference value for each tool and comparing and determining it, and moreover, it is possible to eliminate chatter. This has the effect of providing a chatter monitoring device that can highly accurately determine the presence or absence of.

In the above embodiment, the chatter vibration frequency is set to 2.
Although we have described an example in which the chatter vibration frequency is divided into two regions, three or more bandpass filters may be used to divide the chatter vibration frequency into three or more regions, and the determination may be made by comparing with a predetermined set value in each region. .

[Brief explanation of drawings]

The drawings show an embodiment of the present invention. Fig. 1 is a block diagram schematically showing a chatter monitoring device for machine tools, and Fig. 2 is a diagram showing the acceleration at which chatter occurs in various tools compared to the vibration frequency. This is experimental data. 10...Spindle head, 11...Spindle, 12...Tool, 13...Acceleration converter, 15, 16...Band pass filter, 17, 19...Comparator, 18,
20... Setting device, 25... Discrimination device.

Claims (1)

[Claims] 1 An acceleration converter that detects vibrations generated by cutting using various tools attached to the main spindle;
at least two bandpass filters that extract only signals in different frequency regions from the output of the acceleration converter; at least two setting devices that set different setting values; a first comparator that compares whether it is larger or smaller than the set value set by the setter and outputs an OK signal if it is smaller than the set value, and an NG signal if it is larger; A second comparison that compares whether the output of the pass filter is larger or smaller than the setting value set by the other setting device, and outputs an OK signal if it is smaller than the setting value, and outputs an NG signal if it is larger. and a logic circuit that sends out an abnormal signal when an NG signal is output from at least one of the first and second comparators.