JP7125746B2 - Chatter vibration suppression method and chatter vibration suppression system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a chatter vibration suppression method and a chatter vibration suppression system.

A method for suppressing chatter vibration is known, for example, as described in Patent Document 1 proposed by the inventor of the present application. The chatter vibration suppressing method described in Patent Document 1 is a method of suppressing chatter vibration based on information on vertical and horizontal intervals of chatter pattern stripes remaining on the machined surface, and has achieved certain results.

JP 2017-202555 A

However, the method described in Patent Literature 1 has a problem that it is difficult to read the intervals of the chatter pattern stripes remaining on the machined surface, and its application range is limited.

The present invention has been made in view of the above circumstances, and its object is to provide a chatter vibration suppression method and a chatter vibration suppression system that can easily read the intervals of the chatter pattern stripes remaining on the machined surface. to provide.

In order to solve the above problems, a method for suppressing chatter vibration according to the present invention includes:
A chatter vibration suppression method for suppressing chatter vibration generated during cutting in a machine tool for cutting a workpiece by rotating a tool, comprising:
a step of photographing the machined surface of the workpiece to generate image data of the chatter pattern;
performing a two-dimensional discrete Fourier transform on the image data;
a step of selecting a peak of the power spectrum obtained by the two-dimensional discrete Fourier transform and calculating a vertical interval of the chatter pattern fringes from the frequency of the selected peak;
calculating a chatter frequency and a phase difference of the chatter vibration from the longitudinal interval;
A two-dimensional discrete Fourier transform analysis method comprising:

In the chatter vibration suppression method,
The two-dimensional discrete Fourier transform analysis method includes:
When the feed speed of the tool with respect to the workpiece is constant, the step of comparing the phase difference calculated from the horizontal spacing of the fringes of the chatter pattern with the phase difference calculated from the vertical spacing can be included.

In the chatter vibration suppression method,
a step of rotating the tool at a rotation speed S _C0 and calculating the chatter frequency f _C0 and the phase difference ε _C0 by the two-dimensional discrete Fourier transform analysis method;
calculating a distance ΔS from the rotational speed S _C0 to the rotational speed S _S0 within the stability pocket based on the chatter frequency f _C0 ;
setting the number of revolutions _SC1 based on the number of revolutions _SC0 and the distance ΔS;
a step of rotating the tool at the rotational speed S _C1 and calculating a phase difference ε _C1 by the two-dimensional discrete Fourier transform analysis method;
calculating the rotational speed _SS0 based on the phase difference ε _C0 and the phase difference ε _C1 when the phase difference ε _C1 satisfies 0≦ε _C1 <2π;
A method for estimating stable cutting conditions comprising:

In the chatter vibration suppression method,
a step of rotating the tool at the rotational speed S _S0 calculated by the stable cutting condition estimation method and calculating the phase difference ε _S0 by the two-dimensional discrete Fourier transform analysis method;
The tool is rotated at the corrected rotational speed _SSj obtained by performing the j-th correction (where j≧1) with respect to the rotational speed _SS0 , and the phase difference ε _Sj is calculated by the two-dimensional discrete Fourier transform analysis method. a calculating step;
Using a threshold ε _e whose initial value is ε _C0 ,
R _S =(ε _C1 −ε _C0 )(ε _Sj −ε _e )>0 and 0≦ε _Sj <2π
determining whether or not the same stable lobe discriminant R _S is satisfied;
When the same stable lobe discriminant R _S is satisfied, the threshold ε _e is updated to ε _Sj , and the corrected rotational speed S _Sj is set to S _Sj +ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ). a correcting step;
a step of correcting the corrected rotational speed S _Sj to S _Sj −ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ) when the same stable lobe discriminant R _S is not satisfied;
A stable cutting condition correction method comprising:

Further, in order to solve the above problems, the chatter vibration suppression system according to the present invention includes:
A chatter vibration suppression system for suppressing chatter vibration generated during cutting in a machine tool for cutting a workpiece by rotating a tool, comprising:
a photographing device for photographing the machined surface of the workpiece and generating image data of the chattering pattern;
and a control device that controls the rotation speed of the tool,
The control device is
a process of performing a two-dimensional discrete Fourier transform on the image data;
A process of selecting the peak of the power spectrum obtained by the two-dimensional discrete Fourier transform and calculating the vertical interval of the chatter pattern fringes from the frequency of the selected peak;
a process of calculating the chatter vibration frequency and the phase difference of the chatter vibration from the longitudinal interval;
It is characterized by executing a two-dimensional discrete Fourier transform analysis process consisting of:

In the above chatter vibration suppression system,
The control device is
As the two-dimensional discrete Fourier transform analysis process,
When the feed speed of the tool with respect to the workpiece is constant, a process of comparing the phase difference calculated from the horizontal spacing of the stripes of the chatter pattern with the phase difference calculated from the vertical spacing can be executed.

In the above chatter vibration suppression system,
The control device is
A process of rotating the tool at a rotation speed S _C0 and calculating the chatter frequency f _C0 and the phase difference ε _C0 by the two-dimensional discrete Fourier transform analysis process;
a process of calculating a distance ΔS from the rotational speed _SC0 to the rotational speed _SSO within the stability pocket based on the chatter frequency _fCO ;
a process of setting the number of revolutions _SC1 based on the number of revolutions _SC0 and the distance ΔS;
A process of rotating the tool at the number of revolutions S _C1 and calculating a phase difference ε _C1 by the two-dimensional discrete Fourier transform analysis process;
a process of calculating the number of rotations _SS0 based on the phase difference ε _C0 and the phase difference ε _C1 when the phase difference ε _C1 satisfies 0≦ε _C1 <2π;
It can be configured to execute a stable cutting condition estimation process consisting of.

In the above chatter vibration suppression system,
The control device is
A process of rotating the tool at the rotational speed S _S0 calculated by the stable cutting condition estimation process and calculating a phase difference ε _S0 by the two-dimensional discrete Fourier transform analysis process;
The tool is rotated at the corrected rotational speed S _Sj obtained by performing the j-th correction (where j≧1) with respect to the rotational speed S _S0 , and the phase difference ε _Sj is calculated by the two-dimensional discrete Fourier transform analysis process. a process of calculating;
Using a threshold ε _e whose initial value is ε _C0 ,
R _S =(ε _C1 −ε _C0 )(ε _Sj −ε _e )>0 and 0≦ε _Sj <2π
A process of determining whether or not the same stable lobe discriminant _RS represented by is satisfied;
When the same stable lobe discriminant R _S is satisfied, the threshold ε _e is updated to ε _Sj , and the corrected rotational speed S _Sj is set to S _Sj +ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ). a correction process;
A process of correcting the corrected rotational speed S _Sj to S _Sj −ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ) when the same stable lobe discriminant R _S is not satisfied;
It can be configured to execute a stable cutting condition correction process consisting of:

ADVANTAGE OF THE INVENTION According to this invention, the chatter vibration suppression method and chatter vibration suppression system which can read the space|interval of the fringe of chatter pattern left on a machined surface easily can be provided.

1 is a block diagram of a chatter vibration suppression system according to an embodiment of the present invention; FIG. FIG. 4 is a diagram showing a model of chatter patterns caused by a single chatter frequency; 4 is a flow chart of a two-dimensional discrete Fourier transform analysis method according to an embodiment of the present invention; Stability limit diagram, (A) is a diagram showing the relationship between the rotation speed and the cutting amount, (B) is a diagram showing the relationship between the rotation speed and the chatter frequency, (C) is the rotation speed and the phase difference It is a figure which shows the relationship with. 4 is a flow chart of a method for estimating stable cutting conditions according to an embodiment of the present invention; 4 is a flow chart of a method for correcting stable cutting conditions according to an embodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a chatter vibration suppression method and a chatter vibration suppression system according to the present invention will be described with reference to the accompanying drawings.

[Chatter vibration suppression system]
FIG. 1 shows a chatter vibration suppression system 1 according to one embodiment of the present invention. The chatter vibration suppression system 1 includes a machine tool 10 for cutting a workpiece W, an imaging device 20 for imaging a machined surface of the workpiece W, and a control device 30 .

The machine tool 10 rotates the end mill 11 (corresponding to the "tool" of the present invention) at a predetermined number of revolutions and moves the end mill 11 in the horizontal direction (the Y direction in FIG. 1) at a predetermined feed rate. A tool holder 12 and a work holder 13 for holding a work W are provided. Instead of the tool holder 12 moving the end mill 11 in the Y direction at a predetermined feed speed, the work holder 13 may move the workpiece W in the Y direction at a predetermined feed speed.

When chatter vibration occurs during cutting (here, it is assumed that the end mill 11 makes a simple vibration in the X direction), a periodic striped pattern called a chatter pattern is produced on the side surface of the workpiece W to be machined.

FIG. 2 shows a model of chatter patterns caused by a single chatter frequency. In this embodiment, g [mm] is the vertical interval (interval in the direction perpendicular to the feeding direction) of the stripes of the chatter pattern, e [mm] is the horizontal interval (interval in the feeding direction), and β [deg. ].

A WEB camera or a digital camera, for example, can be used as the imaging device 20 . The photographing device 20 photographs the machined surface of the work W and generates image data of the chatter pattern. The chatter pattern image data is sent to the control device 30 .

A personal computer, for example, can be used as the control device 30 . The control device 30 includes an arithmetic unit 31 , a storage unit 32 and a control unit 33 .

The computing unit 31 executes at least two-dimensional discrete Fourier transform analysis processing, and preferably further executes stable cutting condition estimation processing and stable cutting condition correction processing. The storage unit 32 stores information (data) necessary for executing the above processing, processing results of the calculation unit 31, and the like. The controller 33 controls the rotation speed of the end mill 11 based on the processing result of the calculator 31 .

The two-dimensional discrete Fourier transform analysis process, the stable cutting condition estimation process, and the stable cutting condition correction process are the two-dimensional discrete Fourier transform analysis method, the stable cutting condition estimation method, and the stable cutting condition correction method of the chatter vibration suppression method, respectively. , is the processing executed by the control device 30 .

[Chattering vibration suppression method]
A chatter vibration suppression method according to an embodiment of the present invention is executed by the chatter vibration suppression system 1 . The chatter vibration suppression method of this embodiment includes at least a two-dimensional discrete Fourier transform analysis method, and preferably further includes a stable cutting condition estimation method and a stable cutting condition correction method.

(2D Discrete Fourier Transform Analysis Method)
FIG. 3 shows a flowchart of the two-dimensional discrete Fourier transform analysis method according to this embodiment.

In this embodiment, when chatter vibration occurs in the machine tool 10 during cutting (S101), the imaging device 20 takes an image of the machined surface of the workpiece W and generates image data of the chatter pattern (S102). The chatter pattern image data is sent to the control device 30 as grayscale image data.

（１）式において、ｗ［ｘ，ｙ］は窓関数である。窓関数は、例えば、矩形窓を用いることができる。また、Ｎ_ｘ，Ｎ_ｙはそれぞれｘ，ｙ方向のデータ長を示し、ｕ，ｖはそれぞれｘ，ｙ方向の有限データ中に含まれる正弦波の数（周波数）を示す。 The control device 30 performs a two-dimensional discrete Fourier transform on the image data (S103). The two-dimensional discrete Fourier transform is a transform for expressing two-dimensional discrete data f[x, y] in the frequency domain F[u, v], and is calculated by the following equation (1).

In equation (1), w[x, y] is a window function. A rectangular window, for example, can be used as the window function. Also, N _x and N _y indicate data lengths in the x and y directions, respectively, and u and v indicate the number (frequency) of sine waves included in the finite data in the x and y directions, respectively.

Since a grayscale image has one pixel value (intensity) at each coordinate, it can be thought of as two-dimensional discrete data f[x,y]. However, since the pixel value takes an integer value from 0 to 255, when the two-dimensional discrete Fourier transform is performed using the formula (1), the peak of the DC component (peak at the origin) becomes large and the other peaks become inconspicuous. .

（２）式において、μ_ｆは画素値の平均値である。このように、平均値μ_ｆからの偏差を扱うことで直流成分を小さくすることができる。 Therefore, in this embodiment, the control device 30 performs a two-dimensional discrete Fourier transform based on the following equation (2).

In equation (2), _μf is the average value of pixel values. In this way, the DC component can be reduced by handling the deviation from the average value _μf .

The controller 30 preferably applies zero padding to the two-dimensional discrete data f[x,y] when performing the two-dimensional discrete Fourier transform. With zero padding, since the extended part is 0, the frequency resolution can be increased without affecting the original data.

Next, the control device 30 selects a peak that satisfies a predetermined condition in the power spectrum of the frequency domain F[u,v] (S104). A power spectrum can be represented by the square of the absolute value of F[u,v]. Further, since chatter vibration may be caused by a plurality of chatter frequencies, a predetermined condition may be set so that the control device 30 can select a plurality of peaks.

（３）式および（４）式において、α［ｍｍ／ｐｘ］は画像データの縮尺が１ピクセルあたり何ｍｍかを表す係数である。 Next, the control device 30 specifies the selected peak frequencies u _peak and v _peak (S105), and from the frequencies u _peak and v _peak , the vertical interval g [mm] and the horizontal interval e [mm] of the chatter pattern stripes are determined. Calculate (S106). Specifically, the control device 30 calculates the longitudinal interval g based on the following equation (3), and calculates the lateral interval e based on the following equation (4).

In equations (3) and (4), α [mm/px] is a coefficient representing how many mm per pixel the scale of the image data is.

As described above, in this embodiment, the chatter pattern image data is subjected to a two-dimensional discrete Fourier transform, and the information is visualized in the frequency domain, thereby reading the vertical interval g and the horizontal interval e of the stripes of the chatter pattern. Automated.

The control device 30, which has calculated the vertical spacing g and the horizontal spacing e of the chatter pattern stripes, acquires information on the feed rate _ft [mm/tooth] per tooth of the end mill 11 from the machine tool 10, and determines the feed rate _ft is constant (S107).

The control device 30, having determined that the feed rate f _t is constant, calculates the first phase difference ε [rad] of chatter vibration based on the following equation (5) (S108). That is, the control device 30 calculates the first phase difference ε from the lateral distance e.

（６）式において、Ｄはエンドミル１１の直径［ｍｍ］、Ｓはエンドミル１１の回転数［ｍｉｎ^－１］、θはエンドミル１１のねじれ角［ｒａｄ］である。 After calculating the first phase difference ε, the control device 30 calculates the chatter frequency f _C [Hz] based on the following equation (6) (S109). That is, the control device 30 calculates the chatter frequency f _C from the longitudinal interval g.

In the formula (6), D is the diameter [mm] of the end mill 11, S is the number of revolutions [min ⁻¹ ] of the end mill 11, and θ is the twist angle [rad] of the end mill 11 .

（７）式において、Ｚはエンドミル１１の刃数である。 After calculating the chatter frequency f _C , the control device 30 calculates the integer part q of the chatter frequency f _C and the second phase difference ε based on the following equation (7) (S110).

(7), Z is the number of teeth of the end mill 11 .

Next, the control device 30 compares the first phase difference ε calculated from the horizontal interval e and the second phase difference ε calculated from the vertical interval g (S111). This allows you to check each other's validity.

When the difference between the first phase difference ε and the second phase difference ε is within a predetermined range, the control device 30 selects either the first phase difference ε or the second phase difference ε, Alternatively, the average value of both is used as the phase difference ε of the chatter frequency _fC . As a result, the integer part q of the chatter frequency f _C and the phase difference ε are determined (S112).

On the other hand, the control device 30, having determined in step S107 that the feed rate f _t is not constant, first calculates the chatter frequency f _C [Hz] based on the equation (6) (S113). That is, the control device 30 calculates the chatter frequency f _C from the longitudinal interval g.

After calculating the chatter frequency f _C , the control device 30 calculates the integer part q of the chatter frequency f _C and the phase difference ε based on the equation (7) (S114). As a result, the integer part q of the chatter frequency f _C and the phase difference ε are determined (S112).

As the phase difference ε approaches 2πk (k=0, 1), cutting becomes more stable and chatter vibration decreases. 11 rotation speed is controlled.

Incidentally, in the two-dimensional discrete Fourier transform analysis method according to this embodiment, steps S107 to S111 may be omitted. In this case, after step S106, the process proceeds to step S113.

(Method for estimating stable cutting conditions)
Next, a method for estimating stable cutting conditions according to this embodiment will be described.

The depth of cut in the axial direction and the rotational speed S of the end mill 11 have a relationship such as the stability limit diagram shown in FIG. 4A, which is known as a stability lobe. A place where the depth of cut in the axial direction is locally large is called a stability pocket. In the stable pocket, even with a relatively large axial depth of cut, stable cutting can be performed and chatter vibration can be suppressed.

The chatter frequency f _C and the phase difference ε change discontinuously in the stability pocket, as shown in FIGS. 4(B) and 4(C). In other words, it changes continuously within the same stable lobe. The method for estimating stable cutting conditions according to the present embodiment utilizes this property to adjust the rotation speed _S of the end mill 11 to the rotation speed SS0 within the stable pocket.

FIG. 5 shows a flowchart of the stable cutting condition estimation method according to this embodiment.

In this embodiment, it is assumed that chatter vibration occurs when cutting is performed by rotating the end mill 11 at the rotation speed _SC0 (S201).

The chatter vibration suppression system 1 executes a two-dimensional discrete Fourier transform analysis method to calculate various parameters of chatter vibration (chatter frequency f _C0 , phase difference ε _C0 , integer part q _C0 ) (S202).

Next, the control device 30 sets the number of samples including cutting at the number of revolutions _SC0 (S203). In this embodiment, since linear approximation is performed in step S204 below, the number of sample points is set to two. Note that the number of samples may be set before step S202.

Next, the control device 30 assumes that the chatter frequency hardly changes within the same stable lobe (specifically, the relationship between the spindle rotation speed and the chatter frequency is approximated by a straight line or a curve (in this embodiment, , approximating with a straight line and setting the slope α of the approximation line to ₀ )), and calculating the distance ΔS from the rotation speed _SCO to the rotation speed SSO in the stability pocket based on the following equation (8) ( S204).

（９）式において、ηは補正係数であり、安定ポケット内の回転数Ｓ_Ｓ０を超えないように、０．５以下に設定されていることが好ましい。 After calculating the distance ΔS, the controller 30 sets the rotation speed _SC1 at a sample point different from the rotation speed _SC0 based on the following equation (9) (S205).

In equation (9), η is a correction coefficient, and is preferably set to 0.5 or less so as not to exceed the rotational speed _SSO within the stability pocket.

The chatter vibration suppression system 1 performs cutting by rotating the end mill 11 at the rotation speed S _C1 , executes the two-dimensional discrete Fourier transform analysis method, and calculates the chatter vibration frequency f _C1 (S206).

同安定ローブ内では整数部は一定なので、ｑ_Ｃ０を用いることができる。 Next, the control device 30 calculates the phase difference ε _C1 based on the following equation (10) (S207).

Since the integer part is constant within the same stable lobe, q _C0 can be used.

Next, the control device 30 determines whether or not the phase difference ε _C1 satisfies the following expression (11) (S208).

If the phase difference ε _C1 does not satisfy the expression (11) (NO in S208), it is considered that the rotation speed S _C1 and the rotation speed S _C0 are not within the same stable lobe. Therefore, in this case, the control device 30 newly sets the rotational speed _SC1 (S209). For example, the control device 30 changes the correction coefficient η in equation (9) to set a new rotational speed _SC1 . After that, the process proceeds to step S206.

On the other hand, if the phase difference _{ε C1} satisfies the expression (11) ( _YES in _S208 ), the control device 30 _calculates the stability lobe (approximate expression of the relationship between the spindle speed and the phase difference in the same stable lobe) is calculated (S210). In this embodiment, since the approximation formula of the stability lobe is represented by a linear function, the slope α and the intercept β of the linear function are calculated. In order to improve the accuracy of the stability lobe approximation formula, the number of sample points should be increased to increase the order of the approximation line.

（１２）式および（１３）式において、αは上記近似式（一次関数）の傾き、βは切片である。 After calculating the approximation formula of the stability lobe, the control device 30 calculates the rotational speed _SS0 within the stability pocket based on the following formula (12) or (13) (S211).

In equations (12) and (13), α is the slope of the approximate expression (linear function), and β is the intercept.

The chatter vibration suppression system 1 can suppress chatter vibration by performing cutting by rotating the end mill 11 at the rotational speed S _S0 calculated based on the formula (12) or (13).

(Method for correcting stable cutting conditions)
Next, a method for correcting stable cutting conditions according to this embodiment will be described. This method of correcting stable cutting conditions is a method for correcting the rotational speed _SSO calculated by the method of estimating stable cutting conditions.

In the present embodiment, it is assumed that the rotation speed of the end mill 11 is set to the rotation speed _SS0 calculated by the stable cutting condition estimation method, and chatter vibration occurs during cutting. Various parameters of the chatter vibration are set to chatter frequency f _S0 , phase difference ε _S0 , and integer part q _S0 . These parameters can be calculated by a two-dimensional discrete Fourier transform analysis method.

FIG. 6 shows a flowchart of the stable cutting condition correction method according to this embodiment.

（１４）式において、ΔＳは、（１２）式または（１３）式によって求めた回転数Ｓ_Ｓ０と最初の回転数Ｓ_Ｃ０との差によって算出（補正）される。すなわち、ΔＳ＝Ｓ_Ｓ０－Ｓ_Ｃ０である。なお、以下の式においても、同様にΔＳ＝Ｓ_Ｓ０－Ｓ_Ｃ０とする。 The control device 30 sets the number of times of correction (number of times of cutting) j of the number of revolutions S _S0 to 0 (S301), and based on the following equation (14), the corrected number of revolutions S _Sj obtained by correcting the number of revolutions S _S0 once. (j=1) is calculated (S302).

In the equation (14), ΔS is calculated (corrected) by the difference between the rotation speed _SS0 obtained by the equation (12) or (13) and the initial rotation speed _SCO . That is, ΔS=S _S0 −S _C0 . It should be noted that ΔS=S _S0 −S _C0 also in the following equations.

The chatter vibration suppression system 1 performs cutting by rotating the end mill 11 at the corrected rotational speed S _Sj (j=1 since it has been corrected once; the same shall apply hereinafter) (S303), and checks whether or not chatter vibration has occurred. Determine (S304). Whether or not chatter vibration has occurred can be determined using, for example, the machined surface roughness.

If chatter vibration occurs (YES in S304), the chatter vibration suppression system 1 executes a two-dimensional discrete Fourier transform analysis method to calculate the chatter frequency f _Sj (S305).

Next, the control device 30 calculates the phase difference ε _Sj based on the following equation (15) (S306).

（１６）式において、ε_ｅは閾値であり、その初期値はε_Ｃ０である。 After calculating the phase difference ε _Sj , the controller 30 determines whether or not the same-stable lobe discriminant R _S expressed by the following equation (16) is satisfied (S307).

In equation (16), ε _e is a threshold, and its initial value is ε _C0 .

If the same stable lobe discriminant R _S is not satisfied (NO in S307), the control device 30 corrects the corrected rotational speed S _Sj to the corrected rotational speed S _Sj+1 based on the following equation (17) (S308).

On the other hand, if the same-stable lobe discriminant R _S is satisfied (YES in S307), the control device 30 updates the threshold ε _e of the same-stable lobe discriminant R _S to ε _Sj (S309).

Next, the control device 30 corrects the corrected rotational speed S _Sj to the corrected rotational speed S _Sj+1 based on the following equation (18) (S310).

The chatter vibration suppression system 1 performs cutting by rotating the end mill 11 at the corrected rotational speed S _Sj+1 (j=1), in other words, at the second corrected rotational speed S _Sj (j=2) (S311). It is determined whether or not vibration has occurred (S304).

If chatter vibration does not occur (NO in S304), the method for correcting stable cutting conditions is terminated (S312).

As a result, according to the chatter vibration suppression method according to the present embodiment, the longitudinal interval g of the chatter pattern stripes can be automatically read by the two-dimensional discrete Fourier transform analysis method, so that the work can be greatly shortened. can be done. Further, in the two-dimensional discrete Fourier transform analysis method according to the present embodiment, even a chatter pattern in which a plurality of stripes are mixed or a chatter pattern in which stripes appear fragmentarily can be analyzed.

The method for suppressing chatter vibration according to this embodiment supports not only a single chatter model but also multiple chatter models as a model of the chatter vibration phenomenon. It can be carried out. In the case of many chatter vibrations, since a plurality of chatter vibrations can be simultaneously suppressed in the stability pocket, it is possible to make a comprehensive judgment without contradiction.

In the chatter vibration suppressing method according to the present embodiment, since the phase difference is calculated from the chatter vibration frequency, the restriction that the feed rate _ft must be constant during cutting can be eliminated.

Although the embodiments of the chatter vibration suppression method and the chatter vibration suppression system according to the present invention have been described above, the present invention is not limited to the above embodiments.

For example, the two-dimensional discrete Fourier transform analysis method of the present invention is
(1) Step of photographing the machined surface of the workpiece and generating image data of the chatter pattern (2) Step of performing a two-dimensional discrete Fourier transform on the image data (3) Step of power spectrum obtained by the two-dimensional discrete Fourier transform and calculating the vertical interval of the chatter pattern fringes from the frequency of the selected peak (4) calculating the chatter frequency and phase difference from the vertical interval. .

The method for estimating stable cutting conditions of the present invention includes:
(5) Rotate the tool at the number of revolutions S _C0 and calculate the chatter frequency f _C0 and the phase difference ε _C0 by a two-dimensional discrete Fourier transform analysis method. (6) Based on the chatter frequency f _C0 , the number of revolutions Step (7) Calculate the distance ΔS from _SC0 to the rotation speed SS0 in the stable pocket (7) Set the rotation speed SC1 based on the rotation speed _SC0 and the distance _ΔS (8) Set the tool rotation speed _{S C1} and calculating the phase difference ε _C1 by a two-dimensional discrete Fourier transform analysis method (9) When the phase difference ε _C1 satisfies 0≦ε _C1 <2π, the phase difference _{ε C0} If a step of calculating the number of revolutions _SS0 based on the above is included, the configuration can be changed as appropriate.

The stable cutting condition correction method of the present invention comprises:
(10) Rotate the tool at the rotation speed S _S0 calculated by the stable cutting condition estimation method, and calculate the phase difference ε _S0 by the two-dimensional discrete Fourier transform analysis method (11) Step j for the rotation speed S _S0 Step (12) of calculating the phase difference ε _Sj by the two-dimensional discrete Fourier transform analysis method by rotating the tool at the corrected rotational speed S _Sj corrected to (j≧1), the threshold ε whose initial value is ε _C0 using _e
R _S =(ε _C1 −ε _C0 )(ε _Sj −ε _e )>0 and 0≦ε _Sj <2π
(13) If the same-stable lobe discriminant _{R S is} satisfied, the threshold ε _e is updated to ε _Sj , and the corrected rotational speed S Step (14) for correcting _Sj to _{S Sj} +ΔS/2 ^j+1 (where ΔS=S _S0 −S _{C0 ) .} 2 ^j+1 (where ΔS=S _S0 −S _C0 ), the configuration can be changed as appropriate.

The chatter vibration suppression system of the present invention includes an imaging device and a control device, and can be modified as appropriate so long as it executes at least the two-dimensional discrete Fourier transform analysis method (two-dimensional discrete Fourier transform analysis processing) of the present invention.

1 Chatter Vibration Suppression System 10 Machine Tool 11 End Mill 12 Tool Holder 13 Work Holder 20 Imaging Device 30 Control Device 31 Calculation Unit 32 Storage Unit 33 Control Unit

Claims (8)

A chatter vibration suppression method for suppressing chatter vibration generated during cutting in a machine tool for cutting a workpiece by rotating a tool, comprising:
a step of photographing the machined surface of the workpiece to generate image data of the chatter pattern;
performing a two-dimensional discrete Fourier transform on the image data;
a step of selecting a peak of the power spectrum obtained by the two-dimensional discrete Fourier transform and calculating a vertical interval of the chatter pattern fringes from the frequency of the selected peak;
calculating a chatter frequency and a phase difference of the chatter vibration from the longitudinal interval;
a two-dimensional discrete Fourier transform analysis method consisting of
calculating the number of rotations in the stable pocket from the chatter frequency calculated by the two-dimensional discrete Fourier transform analysis method and the phase difference of the chatter vibration, and performing cutting by rotating the tool at the calculated number of rotations. include
A chatter vibration suppression method characterized by: The two-dimensional discrete Fourier transform analysis method includes:
The step of comparing the phase difference calculated from the horizontal spacing of the fringes of the chatter pattern with the phase difference calculated from the vertical spacing when the feed rate of the tool with respect to the workpiece is constant. 2. The method for suppressing chatter vibration according to 1. a step of rotating the tool at a rotation speed S _C0 and calculating the chatter frequency f _C0 and the phase difference ε _C0 by the two-dimensional discrete Fourier transform analysis method;
Based on the chatter frequency _fC0 , a provisional rotation speed, which is a provisional value of the rotation speed _SSO in the stable pocket, is obtained from the rotation speed _SC0 , and the relationship between the rotation speed of the tool and the chatter frequency has a slope of zero. a step of calculating a distance ΔS to the provisional rotation speed calculated by approximating with a straight line ;
setting the number of revolutions _SC1 based on the number of revolutions _SC0 and the distance ΔS;
a step of rotating the tool at the rotational speed S _C1 and calculating a phase difference ε _C1 by the two-dimensional discrete Fourier transform analysis method;
calculating the rotational speed _SS0 based on the phase difference ε _C0 and the phase difference ε _C1 when the phase difference ε _C1 satisfies 0≦ε _C1 <2π;
3. The method for suppressing chatter vibration according to claim 1 or 2, comprising a stable cutting condition estimation method comprising: a step of rotating the tool at the rotational speed S _S0 calculated by the stable cutting condition estimation method and calculating the phase difference ε _S0 by the two-dimensional discrete Fourier transform analysis method;
The tool is rotated at the corrected rotational speed _SSj obtained by performing the j-th correction (where j≧1) with respect to the rotational speed _SS0 , and the phase difference ε _Sj is calculated by the two-dimensional discrete Fourier transform analysis method. a calculating step;
Using a threshold ε _e whose initial value is ε _C0 ,
R _S =(ε _C1 −ε _C0 )(ε _Sj −ε _e )>0 and 0≦ε _Sj <2π
determining whether or not the same stable lobe discriminant R _S is satisfied;
When the same stable lobe discriminant R _S is satisfied, the threshold ε _e is updated to ε _Sj , and the corrected rotational speed S _Sj is set to S _Sj +ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ). a correcting step;
a step of correcting the corrected rotational speed S _Sj to S _Sj −ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ) when the same stable lobe discriminant R _S is not satisfied;
4. The method for suppressing chatter vibration according to claim 3, comprising a method for correcting stable cutting conditions comprising: A chatter vibration suppression system for suppressing chatter vibration generated during cutting in a machine tool for cutting a workpiece by rotating a tool, comprising:
a photographing device for photographing the machined surface of the workpiece and generating image data of the chattering pattern;
and a control device that controls the rotation speed of the tool,
The control device is
a process of performing a two-dimensional discrete Fourier transform on the image data;
A process of selecting the peak of the power spectrum obtained by the two-dimensional discrete Fourier transform and calculating the vertical interval of the chatter pattern fringes from the frequency of the selected peak;
a process of calculating the chatter vibration frequency and the phase difference of the chatter vibration from the longitudinal interval;
Execute a two-dimensional discrete Fourier transform analysis process consisting of
The number of revolutions in the stable pocket is obtained from the chatter vibration frequency calculated by the two-dimensional discrete Fourier transform analysis process and the phase difference of the chatter vibration, and the tool is rotated at the calculated number of revolutions to perform cutting. Run
A chatter vibration suppression system characterized by: The control device is
As the two-dimensional discrete Fourier transform analysis process,
A process of comparing the phase difference calculated from the horizontal spacing of the stripes of the chatter pattern with the phase difference calculated from the vertical spacing when the feed speed of the tool with respect to the workpiece is constant. Item 6. A chatter vibration suppression system according to Item 5. The control device is
A process of rotating the tool at a rotation speed S _C0 and calculating the chatter frequency f _C0 and the phase difference ε _C0 by the two-dimensional discrete Fourier transform analysis process;
Based on the chatter frequency _fC0 , a provisional rotation speed, which is a provisional value of the rotation speed _SSO in the stable pocket, is obtained from the rotation speed _SC0 , and the relationship between the rotation speed of the tool and the chatter frequency has a slope of zero. A process of calculating the distance ΔS to the provisional rotation speed calculated by approximating with a straight line ;
a process of setting the number of revolutions _SC1 based on the number of revolutions _SC0 and the distance ΔS;
A process of rotating the tool at the number of revolutions S _C1 and calculating a phase difference ε _C1 by the two-dimensional discrete Fourier transform analysis process;
a process of calculating the number of rotations _SS0 based on the phase difference ε _C0 and the phase difference ε _C1 when the phase difference ε _C1 satisfies 0≦ε _C1 <2π;
7. The chatter vibration suppression system according to claim 5 or 6, wherein a stable cutting condition estimation process comprising: The control device is
A process of rotating the tool at the rotational speed S _S0 calculated by the stable cutting condition estimation process and calculating a phase difference ε _S0 by the two-dimensional discrete Fourier transform analysis process;
The tool is rotated at the corrected rotational speed S _Sj obtained by performing the j-th correction (where j≧1) with respect to the rotational speed S _S0 , and the phase difference ε _Sj is calculated by the two-dimensional discrete Fourier transform analysis process. a process of calculating;
Using a threshold ε _e whose initial value is ε _C0 ,
R _S =(ε _C1 −ε _C0 )(ε _Sj −ε _e )>0 and 0≦ε _Sj <2π
A process of determining whether or not the same stable lobe discriminant _RS represented by is satisfied;
When the same stable lobe discriminant R _S is satisfied, the threshold ε _e is updated to ε _Sj , and the corrected rotational speed S _Sj is set to S _Sj +ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ). a correction process;
A process of correcting the corrected rotational speed S _Sj to S _Sj −ΔS/2 ^j+1 (where ΔS=S _S0 −S _C0 ) when the same stable lobe discriminant R _S is not satisfied;
8. The chatter vibration suppression system according to claim 7, wherein a stable cutting condition correction process comprising:

Images