JP2008290188A - Vibration suppressing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vibration suppressing apparatus which can achieve an exact optimum rotational speed, and further can shorten the time necessary for calculating the optimum rotational speed from the beginning of chatter vibration. <P>SOLUTION: The vibration suppressing apparatus 10 comprises vibration sensors 2a to 2c for detecting the acceleration of the vibration of a rotary shaft 3 during rotation in the time domain, and a control unit 5 which calculates the frequency of the chatter vibration and the acceleration of the vibration of the rotary shaft 3 in the frequency domain at the frequency of the chatter vibration based on the acceleration of the vibration in the time-domain detected by the vibration sensors 2a to 2c, and also calculates the optimum rotational speed based on specified parameters and turns the rotary shaft 3 at the calculated optimum rotational speed when the calculated acceleration of the vibration in the frequency domain exceeds a specified threshold value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a vibration suppressing device for suppressing vibration generated during processing, particularly regenerative chatter vibration, in a machine tool that performs processing 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, a particularly problematic problem is “regenerative chatter vibration” which is self-excited vibration. In order to suppress the “regenerative chatter vibration”, as described in Patent Documents 1 and 2, When performing machining, find the natural frequency of the system that generates “chatter vibration” such as tools and workpieces and chatter frequency during machining, multiply the natural frequency or chatter frequency by 60, and the number of tool blades and a predetermined integer. It is known that a value obtained by dividing by the rotation speed may be used as a rotation speed (hereinafter, the rotation speed calculated by the method is referred to as a stable rotation speed).

  Then, in order to obtain the natural frequency of a system in which “chatter vibration” occurs, as described in Patent Document 1, a tool or a work is subjected to impulse vibration to measure the vibration frequency. Is known. Further, in order to obtain the chatter frequency during machining, as described in Patent Document 2, a sound sensor is arranged in the vicinity of a rotating tool or workpiece and detected by the sound sensor during machining. There is a method of obtaining “chatter frequency” based on the vibration frequency.

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

However, when the “natural frequency” is obtained by the method of Patent Document 1, an expensive impulse device is required, which increases the cost. In addition, although the vibration method disclosed in Patent Document 1 requires a high level of technology, the “natural frequency” measured before machining does not necessarily match the “natural frequency” during machining, so that an accurate optimum rotational speed is obtained. There is also a problem that it is inferior in practicality, such as difficult to obtain.
On the other hand, in the method of Patent Document 2 described above, a “chatter frequency” is obtained by analyzing a rotating sound or the like by a sound sensor, but the “chatter frequency” calculated by analyzing the rotating sound or the like and an optimum rotational speed are obtained. Since there is a difference with “chatter frequency”, it is difficult to obtain an accurate optimum rotational speed, as in the method of Patent Document 1. In other words, when calculating the “chatter frequency” from rotating sound, etc., after the vibration frequency corresponding to “chatter vibration” is detected, after further processing and measurement several times, asymptotically “the chatter frequency” Therefore, it takes time until the optimum rotation speed is calculated after the “chatter vibration” is detected, and as a result, there is a problem that marks due to chatter remain on the processed surface.

  Therefore, the present invention has been made in view of the above problems, and is capable of obtaining an accurate optimum rotation speed and suppressing vibrations that can reduce the time from the occurrence of chatter vibration until the optimum rotation speed is calculated. The device is to be provided.

In order to achieve the above object, the invention according to claim 1 of the present invention is a chatter vibration generated when a rotating shaft for rotating a tool or a workpiece is rotated in the machine tool. A vibration suppressor for detecting vibration in a time domain by the rotating shaft during rotation, and a chatter frequency based on the vibration in the time domain detected by the detection means And calculating the vibration in the frequency domain at the chatter frequency, and when the calculated vibration in the frequency domain exceeds a predetermined threshold, based on a predetermined parameter, the optimum rotational speed of the rotating shaft capable of suppressing chatter vibration And a rotation speed control means for rotating the rotating shaft at the optimum rotation speed calculated by the calculation means. To.
According to a second aspect of the present invention, in the first aspect of the present invention, the computing means uses the k value and phase information calculated based on at least equations (1) to (3) described later as the predetermined parameters. And calculating the optimum rotation speed.
k ′ value = 60 × chat vibration frequency / (number of tool blades × rotating shaft rotation speed) (1)
k value = integer part of k ′ value (2)
Phase information = k ′ value−k value (3)
According to a third aspect of the present invention, in the second aspect of the present invention, a plurality of coefficients associated with the k value and the phase information calculated by the above formulas (1) to (3) are provided to the calculation means. The information is stored in advance, and the calculation means selects a specific coefficient based on the calculated k value and phase information, and calculates the optimum rotation speed using the coefficient.
The “vibration” described in claim 1 includes vibration acceleration, displacement due to vibration, sound pressure due to vibration, and the like.

  According to the present invention, the detection means for detecting vibration in the time domain due to the rotating rotating shaft, and the chatter frequency and the frequency at the chatter frequency based on the vibration in the time domain detected by the detection means. Calculating means for calculating vibration acceleration in the region, and calculating means for calculating the optimum rotation speed of the rotating shaft capable of suppressing chatter vibration based on a predetermined parameter when the vibration in the calculated frequency region exceeds a predetermined threshold; And a rotation speed control means for rotating the rotation shaft at the optimum rotation speed calculated by the calculation means, and the optimum rotation speed based on “chatter vibration” generated in the rotation shaft that is actually rotating. Therefore, a more accurate optimum rotation speed can be immediately calculated, and the calculated optimum rotation speed can be immediately used for the rotation of the rotating shaft. Therefore, the “chatter vibration” generated on the rotating shaft can be effectively suppressed, the finishing accuracy of the machined surface can be maintained at a high quality, the tool wear can be suppressed, and the tool can be prevented from being lost. it can.

  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 a time region generated in the rotating rotating shaft 3. Sensor (detection means) 2a to 2c for detecting the vibration acceleration of the motor, and a control device (calculation means and rotation) for controlling the rotational speed of the rotary shaft 3 based on the detection values by the vibration sensors 2a to 2c. Speed control 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.

Here, suppression control of “chatter vibration” in the control device 5 will be described with reference to FIGS. FIG. 4 is an explanatory diagram showing an example of the Fourier analysis result of vibration acceleration in the time domain, and FIG. 5 is an explanatory diagram showing an example of the relationship between the coefficient necessary for calculating the optimum rotational speed, the k value, and the phase. It is. FIG. 6 is a flowchart showing the control for suppressing “chatter vibration”.
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 frequency (chatter) of the rotating shaft 3 as shown in FIG. Frequency) and vibration acceleration in the frequency domain of the rotating shaft 3 at the frequency (meaning vibration acceleration on the frequency axis) are calculated (S2). When Fourier analysis of the vibration acceleration in the time domain is performed, a plurality of waveforms as shown in FIG. 4 showing the relationship between the frequency and the vibration acceleration in the frequency domain are acquired. Therefore, in the present embodiment, the following control is performed using a waveform that maximizes the vibration acceleration value in the frequency domain.
Next, the parameter computing device 7 compares the vibration acceleration in the frequency domain calculated in the FFT computing device 6 with a predetermined threshold value set in advance (S3), and the calculated vibration acceleration in the frequency domain is obtained. When a predetermined threshold value is exceeded (for example, when the vibration acceleration value 4 in the frequency domain in FIG. 4 is detected), it is assumed that “chatter vibration” to be suppressed occurs on the rotating shaft 3 and the following arithmetic expression The optimum rotational speed is calculated according to (1) to (5) (S4). Then, the rotation speed of the rotary shaft 3 is controlled by the NC device 8 so as to obtain the calculated optimum rotation speed (S5), and amplification of “chatter vibration” is prevented, that is, suppressed.
As described above, the suppression control of “chatter vibration” in the control device 5 is performed.

k ′ value = 60 × chat vibration frequency / (number of tool blades × rotating shaft rotation speed) (1)
k value = integer part of k ′ value (2)
Phase information = k ′ value−k value (3)
Coefficient = a−b × k value + c × phase information (4)
Optimal rotation speed = coefficient x stable rotation speed (5)
Here, it is assumed that the “number of tool blades” in the equation (1) is set in the parameter calculation device 7 in advance. Further, the rotation axis rotation speed in the equation (1) is the current rotation speed (before the optimum rotation speed). Further, the stable rotational speed in the equation (5) is a rotational speed calculated by the method described in the background art, and the “chatter frequency” uses a value obtained by Fourier analysis in the calculation. To do.

The determination of the constants a, b, and c in the equation (4) will be described.
The constants a, b, and c are determined from a stability limit diagram created based on various conditions such as the relationship between the rotational speed of the rotary shaft 3 and “chatter frequency”. For example, test machining is performed at various rotational speeds, Fourier analysis of vibration acceleration in the time domain detected during machining is performed, and the frequency of the rotation axis (chatter frequency) and vibration acceleration in the frequency domain at the frequency are determined. Is calculated. Here, the vibration acceleration in the frequency domain during machining is periodically increased or decreased according to the change in the rotation speed, and the rotation speed at which the vibration acceleration in the frequency domain is the minimum value is the optimum rotation speed to be obtained. . Therefore, the phase information, k value, stable rotation speed, etc. at each rotation speed are obtained by the above formula, and each element (phase information and k value) and the rotation speed at which the vibration acceleration in the frequency domain is the minimum value are stabilized. The relationship with the value divided by the rotational speed (that is, the coefficient) is obtained as shown in FIG. Then, from the relationship shown in FIG. 5, the constants a, b, and c of the above-described coefficient arithmetic expression (formula (4)) are determined using various analysis techniques (for example, a = 0.971, b = 0. 003, c = 0.045, etc.).

  According to the vibration control device 10 that performs the control related to vibration suppression as described above, “vibration vibration” generated during the rotation of the rotary shaft 3 by the vibration sensors 2a to 2c, the FFT calculation device 6, and the parameter calculation device 7 is detected in real time. When the occurrence of “chatter vibration” is detected, the optimum rotational speed is immediately calculated by the above arithmetic expressions (1) to (5), and the rotational speed of the rotary shaft 3 is set as the optimum rotational speed. Suppresses “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. Therefore, the “chatter vibration” can be effectively suppressed, the finishing accuracy of the machined surface can be kept high, and effects such as suppression of tool wear and prevention of tool chipping can be achieved.

  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 accuracy of the relationship between the phase information, the k value, and the coefficient as shown in Expression (4) and FIG. 5 is further improved by appropriately investigating and determining according to the type of machine tool. Can do. That is, the calculation of the coefficient is not limited to the equation (4) described in the above embodiment.
In the above-described embodiment, the coefficient is calculated and calculated by Expression (4). However, a plurality of coefficient values are stored in the control device in advance in a state corresponding to the k value and the phase information, and the calculation is performed. It is also possible to adopt a configuration in which a coefficient is selected and determined in accordance with the k value and phase information (the expression (4) is omitted).
Furthermore, when Fourier analysis of the vibration acceleration in the time domain detected by the detection means is performed, in the above embodiment, the waveform having the maximum vibration acceleration in the frequency domain is used to suppress “chatter vibration”. Although such control is performed, the optimum rotational speed is calculated using a plurality of waveforms (for example, three) having higher values of vibration acceleration in the frequency domain, so that the effect of suppressing “chatter vibration” can be reduced. Further improvements may be made.

Furthermore, in the above embodiment, the detection means detects the vibration acceleration of the rotating shaft, and calculates the optimum rotation speed based on the detected vibration acceleration. However, the detection means detects the displacement and sound pressure due to vibration. 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 explanatory drawing which showed an example of the relationship between the coefficient required for the calculation of the optimum rotation speed, the k value, and the phase. It is the flowchart figure shown about 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 (3)

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,
Detection means for detecting vibration in the time domain due to the rotating shaft during rotation, and calculation of vibration frequency and vibration in the frequency domain at the chatter frequency based on the vibration in the time domain detected by the detection means And calculating means for calculating an optimum rotational speed of the rotating shaft capable of suppressing chatter vibration based on a predetermined parameter when the calculated vibration in the frequency domain exceeds a predetermined threshold, and the calculating means And a rotation speed control means for rotating the rotation shaft at the optimum rotation speed calculated by the above. 2. The calculation means according to claim 1, wherein the calculation means calculates the optimum rotational speed using at least a k value and phase information calculated based on equations (1) to (3) described later as the predetermined parameter. The vibration suppression apparatus as described.
k ′ value = 60 × chat vibration frequency / (number of tool blades × rotating shaft rotation speed) (1)
k value = integer part of k ′ value (2)
Phase information = k ′ value−k value (3)   The calculation means stores in advance a plurality of coefficients associated with the k value and phase information calculated by the above equations (1) to (3), and the calculation means calculates the calculated k value and phase. 3. The vibration suppression device according to claim 2, wherein a specific coefficient is selected based on the information, and the optimum rotational speed is calculated using the coefficient.

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