JP2008290194A - Vibration suppressing apparatus of machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively suppress chatter vibration in a short time. <P>SOLUTION: The Fourier analysis for the acceleration of the chatter vibration is carried out in S1, and the maximum acceleration and its frequency are calculated in S2. Next, the maximum acceleration is compared with a preset specified threshold value in S3. When the maximum acceleration exceeds the threshold value, a k value and the information about a phase are calculated in S4 from the chatter frequency, the number of the cutting edges of a tool, and the rotational speed of a rotary shaft. Next, the information about the phase is compared with a preset constant in S5. When the information about the phase is larger than the set constant, a k1 value is calculated in S6 based on a changing expression (1). On the other hand, when the information about the phase is smaller than the set constant, the k1 value is calculated in S7 based on a changing expression (2). Then, the optimum rotational speed for minimizing the change of the rotational speed is calculated in S8 from the chatter frequency, the number of the cutting edges of the tool, and the k1 value. <P>COPYRIGHT: (C)2009,JPO&INPIT

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. At this time, the “regenerative chatter vibration” which is a self-excited vibration generated between the tool and the workpiece is particularly problematic. With respect to this regenerative chatter vibration (hereinafter simply referred to as “chatter vibration”), as described in Patent Documents 1 and 2, the natural frequency of a system in which chatter vibration of a tool or a workpiece occurs when machining is performed. Further, it is known that the chatter frequency during machining is obtained, and the value obtained by dividing the natural frequency or chatter frequency by 60 times and dividing by the number of tool blades and a predetermined integer is used.

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

  However, since the above countermeasure is in the direction of decreasing the rotational speed, it takes time to suppress chatter vibration when the amount of change in the rotational speed is large, and there is a problem that chatter marks remain on the processed surface.

  Therefore, the present invention has been made in view of the above problem, and when chatter vibration occurs, the optimum rotation speed that minimizes the time required for suppressing the vibration can be obtained instantaneously. It is an object of the present invention to provide a machine tool vibration suppressing device that can be effectively suppressed by the above.

  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. A vibration detecting device for detecting vibration in a time domain of a rotating rotating shaft, a chatter frequency and a frequency at the chatter frequency based on the vibration in the time domain detected by the detection unit. Calculation means for calculating the vibration of the region and, when the calculated vibration of the frequency region exceeds a predetermined threshold, calculating the optimum rotation speed of the rotating shaft capable of suppressing chatter vibration based on a predetermined parameter, and the calculation Rotation speed control means for rotating the rotary shaft at the optimum rotation speed calculated by the means, and the calculation means is predetermined based on a predetermined condition when calculating the optimum rotation speed. It is characterized in that the variation amount of the rotation speed by changing the parameters for calculating an optimum rotation speed to minimize.

According to a second aspect of the present invention, in the first aspect of the present invention, the calculating means calculates the optimum rotational speed based on the following calculation formulas (1) to (4) that are predetermined parameters. Yes, the phase information calculated based on the arithmetic expression (3) is compared with a predetermined set constant, and the k value of the arithmetic expression (4) is changed based on the comparison result.
k ′ value = 60 × chat vibration frequency / (number of tool blades × rotational axis rotation speed) (1)
k value = integer part of k ′ value (2)
Phase information = k ′ value−k value (3)
Optimal rotation speed = 60 x chatter frequency / (number of tool blades x k value) (4)

According to a third aspect of the present invention, in the second aspect of the present invention, when the phase information is 0.5 or more, which is a predetermined setting constant, the calculation means sets the k value of the calculation formula (4) to 1 Is added to calculate the optimum rotational speed.
According to a fourth aspect of the present invention, in the second aspect of the present invention, when the phase information is equal to or greater than 0.75 which is a predetermined setting constant, the calculation means sets the k value of the calculation formula (4) to 1 Is added to calculate the optimum rotational speed.
According to a fifth aspect of the present invention, in the second aspect of the present invention, the computing means has two optimum rotational speeds for k and k + 1, respectively, for the k value of the arithmetic expression (4). By calculating and selecting the rotation speed with the smaller difference between the two optimum rotation speeds and the current rotation speed, the optimum rotation speed that minimizes the amount of change in the rotation speed is calculated. .
The term “vibration” as used in claim 1 refers to a physical that can be detected on a rotating shaft indirectly due to vibration, as well as vibration itself, such as vibration acceleration, displacement due to vibration, and sound pressure due to vibration. Change.

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, since the calculation means calculates the optimum rotation speed by changing a predetermined parameter so that the amount of change in the rotation speed is minimized, chatter vibration can be suppressed in a short time. 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 (detection means) 2a to 2c for detecting acceleration, and a control device (calculation means and rotation speed control) for controlling the rotation speed of the rotary shaft 3 based on the detection values by the vibration sensors 2a to 2c. Means) 5.

  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 is optimal based on the FFT calculation device 6 that performs analysis based on vibration acceleration in the time domain detected from the vibration sensors 2a to 2c, and the value calculated by the FFT calculation device 6. A parameter calculation device 7 for calculating the rotation speed and the like and an NC device 8 for controlling machining in the rotary shaft housing 1 are provided. Analysis as described later in the FFT calculation device 6 and monitoring of the rotation speed of the rotary shaft 3 are provided. It is carried out.

Hereinafter, the chatter vibration suppression control in the control device 5 will be described based on the flowchart of FIG. 5.
First, the FFT processing unit 6 performs Fourier analysis of vibration acceleration in the time domain in the vibration sensors 2a to 2c that are constantly detected during rotation (S1), and the maximum acceleration and its frequency (chatter) as shown in 4 of FIG. Frequency) is calculated (S2).
Next, the parameter calculation device 7 compares the maximum acceleration calculated in S2 and a predetermined threshold value set in advance (S3). If the threshold value is exceeded, chatter vibration to be suppressed on the rotating shaft 3 is detected. In S4, the k value and the phase information are calculated from the chatter frequency, the number of tool blades, and the rotational speed of the rotary shaft 3 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)
Phase information = k ′ value−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. Further, the rotation shaft rotation speed in the calculation formula (1) is the current rotation speed (before the optimum rotation speed).

Next, in S5, the phase information obtained by the arithmetic expression (3) is compared with the set constant. If the phase information is greater than or equal to the set constant, the k1 value is calculated based on the change equation (1) in S6. On the other hand, if the phase information is less than the set constant, the k1 value is calculated based on the change equation (2) in S7.
k1 value = k value + 1... change formula (1)
k1 value = k value... change formula (2)
Note that the amount of change in the rotational speed is minimized if the set constant is normally set to 0.5. However, when the change rate of the rotation speed is small, depending on the direction of changing the rotation speed, it may fall below the lower cutting limit in the stability limit diagram and cause regenerative chatter. Compare with information. In that case, it is desirable to select 0.75 as the setting constant.

Next, in S8, the optimum rotational speed is calculated from the chatter frequency, the number of tool blades, and the k1 value obtained in S6 and 7, based on the following calculation formula (4).
Optimal rotation speed = 60 x chatter frequency / (number of tool blades x k1 value) (4)
In S9, the rotation speed of the rotary shaft 3 is changed by the NC device 8 so as to obtain the calculated optimum rotation speed, and chatter vibration amplification is prevented, that is, suppressed.
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 the occurrence of chatter vibration is detected, the optimum rotational speed is immediately calculated by the arithmetic expressions (1) to (4) and the modified expressions (1) and (2), and the rotational speed of the rotary shaft 3 is determined as the optimum rotational speed. As a suppression of chatter vibration amplification. 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, the parameter calculation device 7 compares the phase information with the set constant and calculates the optimum rotation speed with the parameter changed according to the comparison result, so that chatter vibration can be suppressed in a short time. 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.

FIG. 6 is a graph showing the effect of suppressing each chatter frequency (chatter frequency) when the conventional vibration suppression device not employing the present invention is employed, and FIG. is there. In the case of FIG. 6, since the rotational speed changes greatly from 6800 min ⁻¹ to 6250 min ^−1, it takes time to suppress chatter, whereas in the case of FIG. 7, the rotational speed quickly increases from 6800 min ⁻¹ to 7000 min ⁻¹ . It turns out that the optimum rotational speed is reached, the maximum acceleration G decreases earlier than the timing of FIG. 6, and chatter vibration can be suppressed in a short time.

  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, the phase information, the k value, the setting constant, etc. as shown in the arithmetic expressions (1) to (4) and the changing expressions (1) and (2) and the relationship thereof are appropriately investigated according to the type of the machine tool. By making the determination, the accuracy can be further improved.
Further, regarding the optimum rotation speed calculated from the k1 value, instead of the processing from S5 to S8, two optimum rotation speeds are calculated from the k value and the k value + 1 in the arithmetic expression (4), respectively. The optimum rotational speed with the smaller rate of change in rotational speed is selected from the difference between the two optimal rotational speeds and the current rotational speed, and the rotational speed of the rotary shaft 3 is changed by the NC device 8 to suppress chatter vibration. May be performed.
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.

Furthermore, in the above-described embodiment, the configuration is such that the vibration acceleration of the rotating shaft is detected by the detection means, and the optimum rotation speed is calculated based on the detected vibration acceleration. It may be configured to detect and calculate the optimum rotational speed based on the detected displacement and sound pressure.
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. However, the vibration on the non-rotating side (fixed side) or the vicinity thereof is detected. Anyway. 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. It is a graph which shows the conventional suppression effect of chatter vibration. It is a graph which shows the inhibitory effect of the chatter vibration of this invention.

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 (5)

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,
Based on the detection means for detecting the vibration in the time domain of the rotating shaft during rotation and the vibration in the time domain detected by the detection means, the vibration frequency and the vibration in the frequency domain at the chatter frequency are calculated. When the calculated vibration in the frequency domain exceeds a predetermined threshold, based on a predetermined parameter, calculating means for calculating the optimum rotational speed of the rotating shaft capable of suppressing chatter vibration, and the calculating means Rotation speed control means for rotating the rotation shaft at an optimum rotation speed, and
The calculating means calculates the optimum rotation speed so as to minimize the amount of change in rotation speed by changing the predetermined parameter based on a predetermined condition when calculating the optimum rotation speed. Vibration suppression device for machine tools. The calculation means calculates the optimum rotation speed based on the following calculation formulas (1) to (4) serving as predetermined parameters, and sets the phase information calculated based on the calculation formula (3) to a predetermined setting. The vibration suppression device for a machine tool according to claim 1, wherein the vibration suppression device for machine tool according to claim 1, wherein the k value of the arithmetic expression (4) is changed based on a comparison result with a constant.
k ′ value = 60 × chat vibration frequency / (number of tool blades × rotational axis rotation speed) (1)
k value = integer part of k ′ value (2)
Phase information = k ′ value−k value (3)
Optimal rotation speed = 60 x chatter frequency / (number of tool blades x k value) (4)   3. The calculating means according to claim 2, wherein when the phase information is 0.5 or more, which is a predetermined setting constant, the optimal rotation speed is calculated by adding 1 to the k value of the calculation formula (4). Vibration suppressor for machine tools.   3. The calculating means according to claim 2, wherein when the phase information is not less than 0.75 which is a predetermined setting constant, the calculating means calculates the optimum rotation speed by adding 1 to the k value of the calculation formula (4). Vibration suppressor for machine tools.   The calculation means calculates two optimum rotation speeds for k and k + 1 for the k value in the equation (4), and the difference between the two optimum rotation speeds and the current rotation speed is calculated. 3. The vibration suppression device for a machine tool according to claim 2, wherein an optimum rotational speed at which a change amount of the rotational speed is minimized is calculated by selecting a smaller rotational speed.

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