JPS6033606B2 - Self-excited chatter vibration detection device for boring machine tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling self-excited chatter vibration in a boring machine tool. The purpose is to provide a device that automatically sets values.

Chatter vibration occurs in all cutting machines, and is basically vibration in the direction of escape of the cutting edge caused by the cutting edge escaping from the workpiece during cutting.

When this chatter vibration becomes large, the cutting trajectory and depth of the object to be cut fluctuate, making it impossible to obtain the desired surface processing accuracy. In the present invention, self-excited chatter vibration refers to the vibration in the direction of relief of the cutting edge that occurs during reprocessing cutting, as will be explained in detail later, and is especially generated in boring machine tools with low rigidity from the base to the cutting edge. It's easy.

- To explain the configuration of a boring machine tool using a horizontal boring machine tool as an example, it has a table that can fix the workpiece and position it in the horizontal direction, can move perpendicular to the direction of the cutting edge, and a table that stands upright from the base. A cutting blade is attached to the tip of the cutting rotation axis extending parallel to the base via a spindle head that can be fixed to the column so as to be movable up and down.

The distance from the base to the cutting edge is longer than that of other machine tools, and the cutting rotation axis must be quite long to raise the cutting hole, and its diameter must be smaller than the cutting hole, making it thin and long. becomes. Therefore, the rigidity from the tool base to the cutting edge is small compared to other machine tools, and the thin and long rotating shaft in particular is easily bent. This is a major cause of chatter.For reference, when looking at other cutting machine tools, when machining with a lathe, the workpiece rotates and the surface of the workpiece is cut with a fixed cutting blade, so the cutting edge is lower than the fixed end. It can be short up to, and therefore has high rigidity.

In addition, in the case of planing with a planing machine, ``the distance from the base to the cutting edge is longer to some extent as with horizontal boring machine tools, but ``the cutting edge does not rotate and cuts the surface of the workpiece, so it is difficult to cut. The supporting material for the blade can be made thicker, increasing the rigidity from the base to the cutting edge.In milling with a milling machine, both ends of the rotating blade are supported, and the distance from the base to the cutting edge is small. Because it is short, it has high rigidity and is less likely to cause vibrations at the cutting edge.As mentioned above, boring machine tools have the fateful disadvantage that vibrations at the cutting edge are more likely to occur due to a small amount of force applied to the cutting edge than other machine tools.

Generally, when implementing automatic control of machine tools, machine rigidity,
Because there are various parameters such as tool shape, weight, and cutting conditions, ``realization involves considerable technical difficulties.

For example, ``In the cutting process, adaptive control systems that control cutting conditions according to the conditions have been attempted for several years.
Since these are mainly intended to improve cutting efficiency, there are problems with machining accuracy and appearance, and the current situation is that a product that is worth the price has not yet been realized.With this background, recently, various Chatter control devices have been developed, but the main one is a method that detects the presence or absence of chatter based on comparison with a preset darkness value.However,
This function value needs to be changed depending on the cutting conditions, and therefore it has to be determined empirically by conducting cutting experiments at several dozen points for each model or tool, and is then set manually, which requires a great deal of effort. However, if the cutting conditions change even slightly, the accuracy cannot be guaranteed, which is extremely imperfect, inconvenient, and has a major drawback. Boring with a boring machine tool involves drilling a hole in the workpiece by rotating the cutting blade and moving the workpiece forward. So-called regenerative cutting is performed in which the speed is adjusted so that the cutting blade passes again a portion of the cutting marks from one rotation ago.

As described above, the blade of a boring machine tool is held at the tip of the spindle, one end of which is semi-fixed, but the tip of the cutting blade vibrates during cutting. This vibration mainly occurs in the direction perpendicular to the center line (the direction of relief of the cutting blade), and a slight wavy trajectory is generated on the cut surface of the workpiece.
When re-cutting is performed, the cutting blade re-cuts a part of the slight wavy locus on the cut surface from one revolution before, so the vibration of the cutting blade increases due to the influence of the wavy surface. From Kasumoko's point of view, ``The vibration becomes larger, and the resulting cutting marks become so uneven that the unevenness of the surface is clearly visible even when observed with the naked eye.'' In the present invention, this is referred to as self-excited chatter vibration.

According to the detailed observation and analysis of chatter vibration by the inventors, the vibration of the cutting edge does not increase very much from the start of cutting the workpiece until the cutting blade rotates 5 to 6 times. The roughness is stable and relatively close to the so-called theoretical roughness in which the workpiece is cut without any vibration of the cutting edge. Also 5-6
It was found that the time required for rotation varies depending on the material to be cut, the cutting blade, the cutting diameter, etc., but it is about 0.2 to 5 seconds.The present invention utilizes this phenomenon and is relatively stable. By using the period of chatter vibration vibration as a reference value, t
This makes it possible to predict and detect the occurrence of eye jerking in advance. In other words, the self-excited chatter phenomenon caused by regenerative cutting is first detected and determined as an electrical signal, and an adaptive control device that controls the cutting speed and feed rate uses an intensifier with a filter that passes through the self-excited chatter frequency range, a detection rectifier, and a smoothing circuit. , an integral intensifier, and a long-term maximum value holding circuit are installed in the vertical gun, and the vibration signal at the start of cutting is held for a long time to automatically set the chatter value. This invention relates to a self-excited chatter vibration detection device in a machine.In other words, the present invention is applicable to a period when cutting is relatively stable at the start of cutting (for example, about 0.2 to 5 seconds in boring). The feature is that the vibration signal is sampled at the same time, and a constant multiple of the integral value is entered as a function value in a circuit that holds the highest value for a long time.According to this method, the function value corresponding to the actual cutting conditions is determined by the machine. This method has the effect of reducing labor and increasing the stability of self-excited chatter detection compared to the conventional method in which the determination is made through experiments for each tool. The case where the present invention is applied to a boring machine will be explained in detail with reference to the attached block diagram and its signal waveform diagram. Figure 3 shows the signal waveform of the cutting blade for 1 to 1.5 rotation periods when idling (column 1) , No chatter observed by naked eye (Column D) Chatter observed by naked eye (Column m) Since it is modulated by rotation, the signal waveform during idling before cutting is D-1, then D-Ro during a relatively stable period, and D-m when chatter occurs. These signals are transmitted through a filtered multiplier 1 that passes only the self-excited chatter frequency range.
The modulation caused by the spindle rotation is removed, and the waveforms are E-1, E-D, and E-m only during chatter vibration, respectively.

This is converted into an instantaneously fluctuating DC voltage F through a detection rectifier 2, and further converted into an oscillating oscillating G by a smoothing circuit 3 to obtain G-1, G-ro, and G-m, respectively. FIG. 2 shows the change in signal waveform over time. When the cutting start signal A is input from the outside while the vibration waveform during cutting is being shaped, the gate control circuit 7 causes the cut object to start cutting. The sampling time setting signal and the reset signal C are output after a short time (impact time) of about 0 to 3 seconds (T,) to eliminate the impact vibration between the cutting blade and the integral multiplier 5.
It is integrated for about 0.2 to 5 seconds (T2) and multiplied by a constant.

The value multiplied by a constant by the integral multiplier 5 is held as a threshold value in the maximum value holding circuit for a long time. Since this function value is an integral increase of the vibration during a certain period of time immediately after the start of cutting, it corresponds to several times the average value during a relatively stable vibration. Normally, the vibration vibration during vibration during vibration is several times to several tens of times higher than during the relatively stable several seconds of vibration immediately after the start of cutting without vibration chatter, so the above threshold value should be set. By setting the value below the value during vibration when chatter occurs, the occurrence of vibration vibration can be detected regardless of the workpiece or cutting conditions. According to experiments conducted by the present inventors, by setting T2 to 1.9 seconds and setting the constant to 2, the darkness value can be set to a value equivalent to three times the stable shaking value at the start of cutting, and most Can accommodate various cutting conditions.

``In order to achieve the best machining accuracy and cutting efficiency, we conducted two cutting experiments with and without self-excited chatter in advance.''
The optimum L and constant can be found and set by repeating the process ~3 times.

After the threshold value is held in the holding circuit 6, the
Self-excited chatter comparison detector 8 similar to the one disclosed in No.
The vibration during cutting G and the threshold value J are compared. The detector 8 detects a no-jitter signal when G<J;
When J, a chatter signal is sent to a cutting control device (not shown). If the cutting control device receives a no-chatter signal,
Increase the cutting speed and/or feed rate and control the amount of cutting to increase to increase cutting efficiency, and if a chatter signal is received, control to decrease the amount of cutting to prevent chatter. suppress. As described above, the device of the present invention can detect the vibration of a boring machine where chatter is likely to occur, and can set threshold values based on the vibration during a relatively stable period. It does not require many cutting experiments and can sufficiently follow changes in cutting conditions.

Note that even when machining accuracy and cutting efficiency are maximized, threshold values can be set by several cutting experiments.

If this detection device is used, the number of cutting experiments can be extremely reduced, so the work efficiency of the boring machine can be greatly improved.

[Brief explanation of drawings]

The attached drawings show an example of the implementation of the present invention, and FIG. 1 is a block diagram showing the configuration of the eye vibration chatter detection device, and FIG.
The figure shows the change in the signal waveform over time, and FIG. 3 shows the signal waveforms during idling, when there is no chatter, and when there is chatter. 1... Multiplier with filter, 2... Detection rectifier, 3...
... Smoothing circuit, 4... Gate, 5... Integral intensifier,
6... Long-term maximum value holding circuit, 7... Gate control device, 8... Eye vibration vibration comparison detector, A... Sampling start signal, B... Sampling time setting signal, C
...Reset signal, D...Input signal from vibration detector, E...Waveform after passing through D's filtered intensifier, F.
...E instantaneous fluctuation DC voltage, G...F smoothed waveform, day...G integral waveform, 1... day's highest value, T. ...
Delay time, T2...sampling time. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 Attach a vibration detector that continuously extracts the vibration waves transmitted to that part as an electrical signal to a predetermined part of the machine tool where cutting vibrations are transmitted, and detect only the self-excited chatter frequency range of the output signal from the vibration detector. An amplifier with a filter that allows the power to flow through the amplifier, a detection rectifier that converts the output of the amplifier with a filter into a DC voltage, and a smoothing circuit that smoothes the output of the detection rectifier are installed. The self-excited chatter vibration wave transmitted to the part is converted into an instantaneously fluctuating DC voltage and input to the self-excited chatter amplitude comparison detector as a smoothed waveform, while the output of the smoothing circuit is integrated and the integrated value is multiplied by a constant. An integral amplifier, a gate control circuit that connects the output of the smoothing circuit to the integral amplifier for a certain period of time, and a long-term maximum value holding circuit that holds the output of the integral amplifier for a long time, A constant multiplication value of the integral value of the output of the smoothing circuit is held within a certain period of time after the impact time has elapsed immediately after the start of cutting, and the constant multiplication value is input to the self-excited chatter amplitude comparison detector, and the self-excited chatter amplitude comparison detector is In the excited chatter amplitude comparison detector, a smoothed value obtained by converting the self-excited chatter vibration wave transmitted to a predetermined part of the machine tool during cutting into an instantaneously fluctuating DC voltage and the constant held by the long-term maximum value holding circuit are used. A self-excited chatter vibration detection device for a boring machine tool, which detects the presence or absence of chatter by successively comparing the double value with the double value.