JPH0112623B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining the suppression of abnormal vibrations that occur due to various causes such as overload during operation of equipment.

Machine tools such as lathes, drills, and milling cutters, generator rotors, valves in chemical plants, and other equipment that generate abnormal vibrations due to overload, self-excitation, wear and tear of mechanical parts, etc. This abnormal vibration causes product deterioration and, in extreme cases, equipment damage. On the other hand, it is clear that low-load operation without the possibility of abnormal vibrations will lead to a decrease in productivity.

The present inventor utilized the phenomenon that when abnormal vibration occurs, a certain specific frequency component strongly appears in the vibration waveform (for example, noise) corresponding to that vibration, and the peaks of the vibration waveform appear at almost the same period. We have developed a control method for equipment that determines that abnormal vibration has occurred and reduces the load or stops operation. (Precision Machinery Vol. 45, No. 11) In the above method, for example, when a noise signal is taken as a vibration waveform, the occurrence of abnormal vibration is determined as follows.

The signal for judgment is detected as a noise level, and a bandpass filter removes the DC component and high frequency noise, and a half-wave rectifier circuit uses only the positive portion as shown in FIG. 1 for judgment. 1st
The peak point of the signal shown in the figure is detected as the point where the signal changes from an increasing trend to a decreasing trend. and,
The time interval between the appearance of peak points is measured. peak point
The interval between P _o-1 and P _o is D _o-1 , the interval between peak points P _o and P _o+1 is D _o , and the condition is expressed by a certain allowable ratio Q% 1-Q/100≦D _o When /D _o-1 ≦1+Q/100 is satisfied, the waves are assumed to have the same period. When a peak having the same period as defined above appears N times in succession, it is determined that chatter vibration has occurred.

Among the above, the optimum values of the allowable ratio Q and the number of times N are determined experimentally. For example, when cutting with a lathe, chatter marks are left on the cutting surface due to chatter vibration. Figure 2 plots the elapsed time from the start of cutting on the vertical axis, and shows how the time when chatter occurs when Q and N are changed, compared to the true chatter occurrence time determined from the chatter mark above. This shows an example of how it changes. In the case shown in the figure, it is found that it is preferable to set the allowable ratio Q to 10≦Q≦20% and the number of times N of peak intervals to match to 4 or 5. It goes without saying that the optimum values of Q and N must be determined for each object to which this method is applied.

When the occurrence of abnormal vibration is detected in this manner, the load is reduced, for example, by reducing the depth of cut in a lathe or by reducing the feed per tooth in a milling cutter.

In the above paper, the operation of the equipment was stopped due to the occurrence of chatter vibration. However, in order to put the control of such equipment into practical use, it is essential to develop a control method that can reduce the load to the point where abnormal vibrations are suppressed and continue operation.

The present invention aims to establish a method for determining whether to suppress abnormal vibrations in such cases.

That is, signal detection is performed by detecting the noise level emitted by the equipment, and determining whether the periodicity of the appearance of the peak has disappeared. However, when suppressing abnormal vibrations, the periodicity of the peak noise level due to abnormal vibrations does not clearly disappear at a certain point due to load reduction, but the periodicity appears and disappears for a while. The following phenomenon can be seen. Therefore, in order to confirm that the periodicity of the peaks that have appeared has been lost, it is necessary to detect that a sufficient number of peaks do not have periodicity.

A detailed description will be given below with reference to the drawings.

FIG. 3 shows a block diagram when the present invention is applied to cutting using a lathe.

A noise signal from the lathe L is detected by a microphone MC. This signal may be detected from the equipment itself, such as the acceleration signal of the cutting tool T, but for example, the detection signal from the cutting tool includes a strong periodic component even before the occurrence of abnormal vibration, and at the time when abnormal vibration (chatter vibration) occurs. There may be cases where the judgment lacks accuracy. However, this signal extraction portion is appropriately selected depending on the application.

The detected signal is amplified, the DC component and high frequency noise are removed by a bandpass filter, the negative part is cut off by a half-wave rectifier circuit, and the first
Only the positive portion shown in the figure is sent to the AD converter. The AD converter digitizes the signal according to the sampling rate specified by the oscillation circuit and inputs it to the interface, and the CPU determines whether or not the peak of the signal has periodicity, as described above.

When the periodicity is detected N times, 4 to 5 times in the above example, the CPU outputs a load reduction signal to the lathe control section, and the lathe control section thereby reduces the depth of cut.

Whether or not chatter vibration has been suppressed due to this load reduction is determined as follows.

As mentioned above, the interval between two consecutive peak values D _o ,
The periodicity defined by the above equation is not observed during D _o+1 , and when such a relationship occurs N times in a row, it is determined that chatter vibration has been suppressed. In the above example, M=8 is experimentally set. When chatter vibration is suppressed, the vibration appears and disappears for a while. For this reason, it is generally required that the periodic component is not repeated a considerable number of times, such as M=8.

By suppressing this chatter vibration, the CPU issues a stop signal for the load reduction operation to the lathe control unit, maintains this state, and continues subsequent cutting.

In the above operation, if the load must be reduced until cutting becomes impossible, it is determined that an abnormal situation such as tool breakage has occurred, and the operation of the equipment is stopped.

As described above, according to the present invention, the suppression of abnormal vibration can be detected using the same device that detects the occurrence of abnormal vibration, so it can be incorporated into various types of equipment and automatically operate at the maximum load without causing abnormal vibration. It is possible to configure a control device that can be used.

Since signal detection is performed using a microphone, it is easy to apply to various devices, and the control device can be made at low cost.

It is possible to achieve remarkable effects such as:

[Brief explanation of drawings]

Figure 1 shows the signal waveform used in the method of the present invention. Figure 2 shows the allowable ratio Q and the number of peaks to be sampled N.
FIG. 3 is a block diagram when the present invention is applied to a lathe.

Claims (1)

[Claims] 1. Detection of a signal corresponding to vibrations such as noise generated by the operation of equipment, detection of a peak of a specific period in the signal waveform, and the periodicity of the peak being lost a certain number of times in succession. A method for detecting abnormal vibration suppression for equipment that detects.