JP4891150B2 - Vibration suppressor for machine tools - Google Patents

Description

  The present invention relates to a vibration suppressing device for suppressing vibration generated during machining in a machine tool that performs machining while rotating a tool or a workpiece.

  2. Description of the Related Art Conventionally, for example, there is a machine tool that supports a workpiece on a rotatable main shaft and processes the workpiece while feeding a tool to the workpiece. In the machine tool, if the depth of cut in the cutting process is increased more than necessary, there is a problem that so-called “chatter vibration” occurs during the process, and the finished accuracy of the processed surface is deteriorated. Particularly problematic at this time are “regenerative chatter vibration” that is self-excited vibration generated between the tool and the workpiece, and “forced chatter vibration” in which the machine tool including the tool is a vibration source. Of these, with regard to regenerative chatter vibration, as described in Patent Documents 1 and 2, when processing, the natural frequency of the system in which chatter vibration of tools and workpieces occurs and the chatter frequency during machining are obtained. It is known that a value obtained by multiplying the natural frequency or chatter frequency by 60 and dividing by the number of tool blades and a predetermined integer may be used as the rotation speed. On the other hand, in the case of forced chatter vibration, it has been found that countermeasures such as shifting the rotation speed, lowering the feed speed, and reducing the cut into the workpiece are effective.

JP 2003-340627 A JP-T-2001-517557

  However, although the chatter frequency ranges from several tens of Hz to 10 kHz, the chatter frequency is obtained by performing Fourier analysis with a single sampling frequency, etc., so there is a limit to the measurement resolution. The chatter frequency cannot be detected for a short time and with high accuracy in the range of. Accordingly, there has been a problem that the change of the rotation speed is not always accurate and does not lead to effective suppression of chatter vibration.

  Therefore, the present invention has been made in view of the above problems, and can determine chatter frequency over a wide range in a short time and with high accuracy, and can accurately suppress chatter vibration by calculating an accurate optimum rotation speed. An object of the present invention is to provide a vibration suppressing device for a machine tool that can be used.

In order to achieve the above object, the invention according to claim 1 is a machine tool having a rotating shaft for rotating a tool or a workpiece, in order to suppress chatter vibration generated when the rotating shaft is rotated. of a vibration suppressing device, a detecting means for detecting the vibration acceleration in the time domain of the rotary shaft during rotation, the vibration acceleration of the detected time domain preset respectively at different sampling frequencies by the detection means A plurality of signal analyzing means for analyzing and obtaining chatter frequency and its acceleration, and when the acceleration of chatter frequency calculated by any of the signal analyzing means exceeds a predetermined reference value, the chatter frequency is determined based on a predetermined parameter. Calculation means for calculating the optimum rotation speed of the rotation shaft capable of suppressing vibration, and rotation speed control means for rotating the rotation shaft at the optimum rotation speed calculated by the calculation means; Wherein the calculating means, the plurality of the plurality of chatter frequencies obtained by the signal analyzing means to a predetermined threshold value and each comparison, if the plurality of chatter frequency is lower than the predetermined threshold, The chatter frequency obtained by analysis by the signal analysis means having a low sampling frequency among the plurality of signal analysis means, and when the plurality of chatter frequencies are higher than the predetermined threshold, the plurality of signals Among the analysis means, the signal analysis means having a high sampling frequency selects the chatter frequency obtained by analysis and calculates the optimum rotational speed.

According to a second aspect of the present invention, in the first aspect of the present invention, the calculation means calculates the optimum rotational speed based on the following calculation formulas (1) to (3) which are predetermined parameters. It is a thing.
k ′ value = 60 × chat vibration frequency / (number of tool blades × rotational axis rotation speed) (1)
k value = integer part of k ′ value (2)
Optimal rotation speed = 60 x chatter frequency / (number of tool blades x k value) (3)

According to the present invention, since the optimum rotation speed is calculated based on chatter vibration generated in the rotating shaft that is actually rotating, it is possible to immediately calculate a more accurate optimum rotation speed and to calculate the calculated optimum rotation speed. Immediately, it can be used to rotate the rotating shaft. In particular, here, a plurality of signal analysis means having different sampling frequencies are provided, and the calculation means selects the chatter frequency having the optimum accuracy from the analysis result obtained by each signal analysis means and calculates the optimum rotation speed. Therefore, the chatter frequency can be obtained in a wide range in a short time and with high accuracy, and an accurate optimum rotational speed can be calculated to effectively suppress chatter vibration. Therefore, the finishing accuracy of the machined surface can be maintained at a high quality, and it can be expected to suppress the tool wear and prevent the tool from being lost.

  Hereinafter, a vibration suppression device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing a block configuration of the vibration suppressing device 10. FIG. 2 is an explanatory view showing the rotary shaft housing 1 to be subjected to vibration suppression from the side, and FIG. 3 is an explanatory view showing the rotary shaft housing 1 from the axial direction.
The vibration suppressing device 10 is for suppressing chatter vibration generated in the rotating shaft 3 provided in the rotating shaft housing 1 so as to be rotatable around the C axis, and is vibration in the time domain generated in the rotating rotating shaft 3. Vibration sensors (detecting means) 2a to 2c for detecting acceleration and a control device 5 for controlling the rotation speed of the rotary shaft 3 based on the detection values by the vibration sensors 2a to 2c are provided.

  The vibration sensors 2a to 2c are attached to the rotary shaft housing 1 as shown in FIGS. 2 and 3, and one vibration sensor is a time domain vibration acceleration (on the time axis) in a direction perpendicular to the other vibration sensors. (For example, the vibration sensors 2a to 2c detect vibration accelerations in the time domain in the X-axis, Y-axis, and Z-axis directions orthogonal to each other, respectively). To do).

  On the other hand, the control device 5 includes a plurality of FFT operation devices 6, 6... As signal analysis means for performing analysis based on vibration acceleration in the time domain detected from the vibration sensors 2 a to 2 c at different sampling frequencies. A parameter calculation device 7 as calculation means for calculating the optimum rotation speed based on a value calculated by any one of the FFT calculation devices 6, and a rotation speed control means for controlling machining in the rotary shaft housing 1. And an analysis as described later in the FFT arithmetic unit 6 and monitoring of the rotational speed of the rotary shaft 3.

Hereinafter, the chatter vibration suppression control in the control device 5 will be described based on the flowchart of FIG. 5.
First, the vibration acceleration signals in the time domain of the vibration sensors 2a to 2c that are constantly detected during rotation are distributed to each FFT arithmetic unit 6, and Fourier analysis is performed with the sampling frequency set in each FFT arithmetic unit 6. (S1) and the maximum acceleration as shown by 4 in FIG. 4 and its vibration frequency (chatter frequency) are calculated (S2).
Next, the parameter calculation device 7 compares each maximum acceleration calculated in S2 with a predetermined reference value set in advance (S3), and when any one of the maximum accelerations exceeds the reference value, Assuming that chatter vibration to be suppressed occurs on the rotary shaft 3, in S4, the calculated chatter frequency value is compared with a preset frequency threshold value and obtained at the optimum sampling frequency. Select chatter frequency.

For example, suppose that there are two FFT arithmetic units with sampling frequencies of 1 kHz and 10 kHz. When the number of analysis points is 1024, the minimum resolution is about 1 kHz for the former and about 10 kHz for the latter, and the time required for sampling is about 1 second and 0.1 second, respectively.
When the chatter frequency detected here is in the low range of about 50 Hz, the calculation error is about 20% in the latter device when the optimum rotation speed is obtained, but the accuracy is as high as about 2% in the former device. . On the other hand, when the detected chatter frequency is as high as about 400 Hz, when the optimum rotational speed is obtained, the measurement accuracy of the maximum acceleration is greatly reduced in the former device, whereas the latter device has sufficient resolution. Will have. Further, in the latter device, the calculation error of chatter frequency is as high as 2.5%.

Therefore, in this case, the threshold value is set to 100 Hz, and if it is lower than this, the chatter frequency analyzed by the FFT arithmetic unit related to the former sampling frequency is selected, and if it is higher, the latter relates to the latter sampling frequency. If the chatter frequency analyzed by the FFT arithmetic unit is selected, the target chatter frequency can be acquired without impairing the magnitude of the acceleration and the accuracy of the frequency.
When there are a plurality of FFT operation devices on the low frequency side and the high frequency side with the threshold as a boundary, an FFT operation device with a lower sampling frequency is set on the low frequency side, and an FFT with a higher sampling frequency is set on the high frequency side. What is necessary is just to select an arithmetic unit.

  Next, in S5, the optimum rotational speed is calculated from the chatter vibration frequency, the number of tool blades, and the rotational speed of the rotary shaft 3 acquired in S4 by the following arithmetic expressions (1) to (3).

k ′ value = 60 × chat vibration frequency / (number of tool blades × rotational axis rotation speed) (1)
k value = integer part of k ′ value (2)
Optimal rotation speed = 60 x chatter frequency / (number of tool blades x k value) (3)

Here, it is assumed that the “number of tool blades” in the calculation formula (1) is set in the parameter calculation device 7 in advance together with the previous threshold value and the like. Further, the rotation shaft rotation speed in the calculation formula (1) is the current rotation speed (before the optimum rotation speed).
In S6, the NC device 8 changes the rotation speed of the rotary shaft 3 so as to obtain the calculated optimum rotation speed, thereby preventing chatter vibration from being amplified, that is, suppressing it.
As described above, chatter vibration suppression control in the control device 5 is performed.

  Thus, according to the vibration control device 10 of the above embodiment, chatter vibration generated during the rotation of the rotary shaft 3 is monitored in real time by the vibration sensors 2a to 2c, the FFT calculation device 6, and the parameter calculation device 7. When occurrence of chatter vibration is detected, the optimum rotational speed is immediately calculated by the above-described arithmetic expressions (1) to (3), and amplification of chatter vibration is suppressed with the rotational speed of the rotating shaft 3 as the optimum rotational speed. That is, since the optimum rotation speed is calculated based on chatter vibration generated in the rotating shaft 3 that is actually rotating, a more accurate optimum rotation speed can be immediately calculated. In particular, here, a plurality of FFT operation devices 6 having different sampling frequencies are provided, and the parameter operation device 7 selects a chatter frequency having the optimum accuracy from the analysis result obtained by each FFT operation device 6 and performs the optimum rotation. Since the speed is calculated, the chatter frequency can be obtained in a wide range in a short time and with high accuracy, and an accurate optimum rotational speed can be calculated to effectively suppress chatter vibration. Therefore, the finishing accuracy of the machined surface can be maintained at a high quality, and it can be expected to suppress the tool wear and prevent the tool from being lost.

  The configuration related to the vibration suppression device of the present invention is not limited to the mode described in the above embodiment, and the configuration related to vibration suppression control in the detection means, the control device, and the control device, The present invention can be changed as appropriate without departing from the spirit of the present invention.

For example, in the above embodiment, the signal from the acceleration sensor is divided into a plurality of signals and analyzed at different sampling frequencies. However, a plurality of acceleration pickups for measuring a predetermined direction are installed and each signal is transmitted. The present invention can be adopted even with the analysis method.
In addition, the arithmetic expressions (1) to (3) and the k value used here may be appropriately changed.
Furthermore, in the above embodiment, when Fourier analysis of the vibration acceleration in the time domain detected by the detection means is performed, the control related to suppression of chatter vibration is performed using a waveform in which the vibration acceleration in the frequency domain shows the maximum value. However, the optimal rotational speed is calculated using a plurality of (for example, three) waveforms with the highest vibration acceleration value in the frequency domain, and the chatter vibration suppression effect is further improved. You may plan.

In addition, in the above-described embodiment, the vibration is detected in the rotating shaft of a machine tool such as a so-called machining center that rotates the tool. May be. Furthermore, it can also be applied to a machine tool that rotates a workpiece such as a lathe. In that case, it detects vibrations on the spindle side that holds the workpiece that is the rotation axis, or detects vibrations on the tool that is on the fixed side. can do. Needless to say, the installation position, the number of installations, and the like of the detection means may be appropriately changed according to the type and size of the machine tool.

It is explanatory drawing which showed the block structure of the vibration suppression apparatus. It is explanatory drawing which showed the rotating shaft housing used as the object of vibration suppression from the side surface. It is explanatory drawing which showed the rotating shaft housing from the axial direction. It is explanatory drawing which showed an example of the Fourier-analysis result of the vibration acceleration of a time domain. It is a flowchart which concerns on suppression control of chatter vibration.

Explanation of symbols

  1 ··· Rotating shaft housing, 2a, 2b, 2c ·· Vibration sensor, 3 ··· Rotating shaft, 5 ·· Control device, 6 ·· FFT computing device, 7 ·· Parameter computing device, 8 ·· NC device, 10 ..Vibration suppression devices

Claims (2)

In a machine tool provided with a rotating shaft for rotating a tool or a workpiece, a vibration suppressing device for suppressing chatter vibration generated when the rotating shaft is rotated,
Detecting means for detecting the vibration acceleration in the time domain of the rotary shaft during rotation, frequency chatter by analyzing a preset respectively different sampling frequencies of vibration acceleration of the detected time domain by the detecting means and its A plurality of signal analysis means for obtaining acceleration, and the rotation shaft capable of suppressing chatter vibration based on a predetermined parameter when the acceleration of chatter frequency calculated by any of the signal analysis means exceeds a predetermined reference value Calculation means for calculating the optimum rotation speed of the rotation speed control means for rotating the rotation shaft at the optimum rotation speed calculated by the calculation means,
The arithmetic means compares the plurality of chatter frequencies obtained by the plurality of signal analysis means with a predetermined threshold value, respectively, and when the plurality of chatter frequencies are lower than the predetermined threshold value, Of the signal analysis means, the chatter frequency obtained by the analysis by the signal analysis means having a low sampling frequency, and when the plurality of chatter frequencies are higher than the predetermined threshold, the plurality of signal analysis means Among them, the vibration suppression device for a machine tool is characterized in that the optimum rotational speed is calculated by selecting each chatter frequency obtained by analysis by the signal analysis means having a high sampling frequency . The vibration suppression device for a machine tool according to claim 1, wherein the calculation means calculates the optimum rotation speed based on the following calculation formulas (1) to (3) serving as predetermined parameters.
k ′ value = 60 × chat vibration frequency / (number of tool blades × rotational axis rotation speed) (1)
k value = integer part of k ′ value (2)
Optimal rotation speed = 60 x chatter frequency / (number of tool blades x k value) (3)

Images