JP6803248B2 - Machine tool vibration suppression method and equipment - Google Patents

Description

The present invention relates to a method and an apparatus for suppressing chatter vibration generated during machining in a machine tool for machining a work by rotating a tool or a work.

In end mill machining, chatter vibration may occur and the machined surface may deteriorate depending on the machining conditions such as the depth of cut and the rotation speed of the rotating shaft. In addition, the tool is damaged by chatter vibration, which leads to a deterioration in tool life.
Non-Patent Document 1 is known as a technique for suppressing this chatter vibration, and Patent Document 1 is known as a vibration suppression method using this technique. In this vibration suppression method, in order to suppress the regenerative chatter vibration as self-excited vibration that causes deterioration of the finishing accuracy of the machined surface, the natural frequency of the chatter vibration generation system of the tool or work is set to the tool or work. It is obtained by impulse vibration, multiplied by 60, and the value obtained by dividing by the number of tool blades and a predetermined integer is set as the optimum rotation speed, and machining is performed at the optimum rotation speed.
On the other hand, Patent Document 2 is known as a calculation method using the chatter frequency at the time of chatter generation instead of the natural frequency of the machine. In Patent Document 2, the chatter frequency is measured by a vibration sensor arranged in the machine, and the optimum rotation speed is obtained by using the parameter calculated from the chatter frequency.
The above-mentioned Patent Documents 1 and 2 are considered to be effective for chattering in a single mode, but for example, in the case of machining conditions in which chattering occurs in a plurality of modes as shown in FIG. 4, the stable speed with respect to one mode. The region may overlap with the unstable region of another mode, and in such a case, the optimum rotation speed cannot be correctly obtained.
The method of Patent Document 3 has been proposed as an effective control method when such a plurality of vibration modes appear in an overlapping manner. In Patent Document 3, the optimum rotation speed in consideration of the overlap of a plurality of vibration modes is obtained by using the distance between the optimum speeds for each vibration mode as an index.
However, since the above method depends on the calculation accuracy of the optimum speed for each vibration mode, sufficient accuracy may not be obtained depending on the calculation method and the vibration state.

In addition to the method of obtaining the optimum speed by a calculation formula as in Patent Documents 1 to 3, a method of sequentially changing the spindle speed and comparing the vibration states at each spindle speed as in Patent Document 4 to find a better processing speed. Has also been proposed. Since it is generally difficult to place the vibration sensor near the machining point, the absolute value of the vibration acceleration is affected by the transfer function of the mechanical system, so it is accurate to search for the optimum speed based on the magnitude of the acceleration. There is a problem above. Therefore, in Patent Document 4, the optimum speed is searched for using the vibration frequency and a parameter called a phase difference obtained by the following equation as an index.
Phase difference = {60 x chatter vibration frequency / (number of tool blades x rotation speed)} In addition, in Patent Document 5, the autocorrelation coefficient is calculated from the time-series vibration data and obtained from the autocorrelation waveform. An invention in which a phase difference is calculated based on the period Tx and the period T1 in which the cutting edge contacts the work, and the spindle rotation speed is increased or decreased based on the calculated phase difference to detect and avoid chatter vibration. It is disclosed.

Japanese Patent No. 4177028 Japanese Patent No. 4433422 Japanese Unexamined Patent Publication No. 2012-183596 JP-A-2010-17783 Japanese Unexamined Patent Publication No. 2012-56051

March 6, 2015, Japan Society of Mechanical Engineers No.15-16 Workshop-Basic production processing course-Let's learn in practice "Basic knowledge of cutting and chatter vibration" Workshop text p1-12

In the method of Patent Document 4, a threshold value is set separately, and when the amount of change in the phase difference exceeds this threshold value, it is regarded as the optimum speed. However, since the distribution of the phase difference with respect to the spindle speed depends on various parameters such as the characteristics of the tool and the workpiece and the machining conditions, it is very difficult to uniquely set the threshold value. In particular, when a plurality of vibration modes appear to overlap each other as shown in FIG. 4, the amount of change in the phase difference near the stable speed becomes small, which makes it more difficult to set the threshold value.
Further, in the method of Patent Document 5, the phase difference is merely used as an index for increasing or decreasing the rotation speed, and even here, it is not possible to deal with the case where there are a plurality of vibration modes.

Therefore, the present invention is a vibration suppression method for a machine tool that can obtain the optimum rotation speed for chatter vibration with high accuracy without being affected by the calculation accuracy by approximate calculation even under machining conditions in which chatter vibration due to a plurality of modes is mixed. And the purpose is to provide the device.

In order to achieve the above object, the invention according to claim 1 is a vibration suppressing method for suppressing chatter vibration generated when the work is machined in a machine tool provided with a rotating shaft for rotating a tool or a work. And
The vibration detection step for detecting the chatter vibration and
An optimum speed range estimation step for estimating a range including the rotation speed of the rotation shaft, which is optimal for suppressing the detected chatter vibration, and
In the upper limit speed and the lower limit speed in the above range, the phase difference calculation step of obtaining the phase difference by the following equations 1 and 2, respectively, and
A phase difference gradient maximum value saving step of calculating the phase difference gradient with respect to the rotation speed and saving the obtained phase difference gradient as a provisional maximum value, and
A rotation speed change step of changing the rotation speed to decrease or increase within a predetermined change range within the range, and
A phase difference gradient comparison step of calculating the phase difference gradient with respect to the changed rotation speed and comparing the obtained phase difference gradient with the provisional maximum value.
When the phase difference gradient does not exceed the provisional maximum value in the comparison, the rotation speed is changed by setting the change direction of the rotation speed to the same direction as the previous change, while the phase difference gradient is changed in the comparison. When the provisional maximum value is exceeded, the change direction of the rotation speed is set in the direction opposite to the previous change, the change width is set smaller than the previous time, and the phase difference gradient is updated to the provisional maximum value. The second rotation speed change step for changing the rotation speed and
It is characterized by executing.
Equation 1: k = {60 x chatter vibration frequency / (number of tool blades x rotation speed)}
Equation 2: Phase difference = k- [k-α] However, 0 ≦ α ≦ 1 and [k-α] are floor functions. The invention according to claim 2 is the second rotational speed in the configuration of claim 1. The change step and the phase difference gradient comparison step based on the rotation speed changed here are repeatedly executed, and when the change width in the second rotation speed change step reaches a predetermined threshold value, the rotation speed is reached. It is characterized by further performing a judgment step for determining that is optimized.
In order to achieve the above object, the invention according to claim 3 is a vibration suppression device for suppressing chatter vibration generated when the work is machined in a machine tool provided with a rotating shaft for rotating a tool or a work. And
The vibration detecting means for detecting the chattering vibration and
Optimal speed range estimating means for estimating the range including the rotational speed of the rotating shaft, which is optimal for suppressing the detected chatter vibration,
A phase difference calculating means for obtaining the phase difference by the following equations 1 and 2 at the upper limit speed and the lower limit speed in the above range, respectively.
A phase difference gradient maximum value storage means that calculates the phase difference gradient with respect to the rotation speed and stores the obtained phase difference gradient as a provisional maximum value.
A rotation speed changing means for changing the rotation speed to decrease or increase by a predetermined width within the range.
A phase difference gradient comparing means for calculating the phase difference gradient with respect to the changed rotation speed and comparing the obtained phase difference gradient with the provisional maximum value.
When the phase difference gradient does not exceed the provisional maximum value in the comparison, the rotation speed is changed by setting the change direction of the rotation speed to the same direction as the previous change, while the phase difference gradient is changed in the comparison. When the provisional maximum value is exceeded, the change direction of the rotation speed is set in the direction opposite to the previous change, the change width is set smaller than the previous time, and the phase difference gradient is updated to the provisional maximum value. The second rotation speed changing means for changing the rotation speed and
It is characterized by having.
Equation 1: k = {60 x chatter vibration frequency / (number of tool blades x rotation speed)}
Equation 2: Phase difference = k- [k-α] However, 0 ≦ α ≦ 1 and [k-α] are floor functions. The invention according to claim 4 has the second rotational speed in the configuration of claim 3. The changing means and the phase difference gradient comparing means based on the rotation speed changed here are repeatedly executed, and when the change width in the second rotation speed changing means reaches a predetermined threshold value, the rotation speed is reached. It is characterized in that it is provided with a judgment means for determining that the is optimized.

According to the present invention, since the optimum rotation speed for suppressing chatter vibration is searched for by using the phase difference gradient with respect to the rotation speed, it is optimal even for complicated chatter vibration in which a plurality of vibration modes coexist. The rotation speed can be obtained with high accuracy.

It is a block block diagram of the vibration suppression device of a machine tool. It is a flowchart of vibration suppression control. It is explanatory drawing of this control for chatter vibration which a plurality of vibration modes are mixed. It is a stability limit diagram when a plurality of vibration modes are mixed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block configuration diagram showing an example of a vibration suppression device. In the machine tool 1, a vibration sensor 3 for detecting vibration during machining is installed on the spindle 2, and a vibration frequency is calculated on the NC device 4 based on the vibration signal detected from the vibration sensor 3. The frequency analysis unit 5 that performs the above, the phase difference calculation unit 6 that calculates the phase difference based on the obtained vibration frequency, and the phase difference gradient based on the amount of change in the spindle rotation speed and the amount of phase difference change at that time. A phase difference gradient calculation unit 7 for calculation and an optimum speed range estimation unit 8 for estimating an expected range of the optimum rotation speed based on the vibration frequency obtained by the frequency analysis unit 5 are provided.

The phase difference gradient calculated by the phase difference gradient calculation unit 7 is sent to the phase difference gradient maximum value storage unit 9. The phase difference gradient maximum value storage unit 9 compares the phase difference gradient maximum value stored in itself with the phase difference gradient obtained from the phase difference gradient calculation unit 7, and sets the larger value as the new maximum. Store as a value. Further, when the maximum value of the phase difference gradient is updated here, the rotation speed command value calculation unit 10 is notified.
In the rotation speed command value calculation unit 10, the next rotation speed command is based on the calculation result in the optimum speed range estimation unit 8 and the phase difference provisional maximum value update information notified from the phase difference gradient maximum value storage unit 9. Calculate the value. The calculated rotation speed command value is sent to the spindle control device 12, and the spindle speed of the machine tool 1 is changed. Further, the calculated rotation speed command value is also sent to the optimum speed storage unit 11, and the calculation result is stored as the optimum speed.

Here, the vibration sensor 3 and the frequency analysis unit 5 are vibration detecting means, the optimum speed range estimation unit 8 is the optimum speed range estimation means, the phase difference calculation unit 6 is the phase difference calculation means, the phase difference gradient calculation unit 7 and the phase difference gradient maximum. The value storage unit 9 functions as a phase difference gradient maximum value storage means, a phase difference gradient comparison means, and a determination means. Further, the rotation speed command value calculation unit 10 and the spindle control device 12 serve as the rotation speed changing means, the phase difference gradient maximum value storage unit 9, the rotation speed command value calculation unit 10, and the spindle control device 12 serve as the second rotation speed changing means. Each works.

Hereinafter, the details of the vibration suppression method (vibration suppression control) by the vibration suppression device will be described with reference to the flowchart of FIG. 2 and the vibration data example of FIG.
First, in S1, the occurrence of chatter vibration during machining is detected (vibration detection step). The frequency analysis unit 5 analyzes the vibration in the time domain obtained by the vibration sensor 3 into the vibration in the frequency domain, and determines that chatter vibration occurs when the analyzed vibration exceeds a predetermined threshold value.

Next, in S2, the optimum speed range estimation unit 8 provisionally calculates the optimum rotation speed for the chatter vibration analyzed by the frequency analysis unit 5, and in S3, the rotation speed command value calculation unit 10 and the spindle control device 12 The rotation speed of the spindle 2 is changed via. In the calculation of the optimum rotation speed here, for example, as disclosed in Patent Document 2, the chatter frequency is multiplied by 60 to obtain the stable rotation speed divided by the number of tool blades and a predetermined integer, and a predetermined rotation speed is obtained. A known method such as determining a coefficient based on the k value and phase information calculated from the equation and calculating the optimum rotation speed from the coefficient and the stable rotation speed can be used.
However, as described above, since an approximate calculation is generally used for calculating the optimum rotation speed for chatter vibration, it is not always possible to change to the optimum conditions at one time. For example, as shown in (1) → (2) in FIG. 3, the transition to different vibration modes is made, and the stable region remains narrow.

Therefore, in this control, in S4, the optimum speed range estimation unit 8 determines whether or not the optimum rotation speed has been passed by changing the rotation speed in S3. As this determination method, for example, a method disclosed in Patent Document 3 (determining whether or not there is a region having a large stability margin between the current rotation speed and the rotation speed before the change, and a region having a large stability margin). If there is, it is determined that the optimum rotation speed has been passed).
When it is determined in S4 that the optimum rotation speed has been passed by changing the rotation speed, the optimum rotation speed is within the range before and after the change. If it is determined that the optimum rotation speed has not been passed, the process returns to S2 and the optimum rotation speed is calculated again.

Therefore, in S5, the rotation speed before and after the change is estimated as the range including the optimum rotation speed, and the phase difference calculation unit 6 sets the upper limit speed and the lower limit speed of the estimated optimum speed range by the following equations 1 and 2. Calculate the phase difference respectively (optimal speed range estimation step and phase difference calculation step).
Equation 1: k = {60 x chatter vibration frequency / (number of tool blades x rotation speed)}
Equation 2: Phase difference = k- [k-α] However, 0≤α≤1 and [k-α] are floor functions. Next, in S6, the phase difference gradient calculation unit 7 provisions the phase difference gradient with respect to the rotation speed. The maximum value is calculated (Vε in FIG. 3) and stored in the phase difference gradient maximum value storage unit 9 (phase difference gradient maximum value preservation step).

Subsequently, the optimum rotation speed is specified by searching in detail within the optimum speed range estimated in S5. Hereinafter, this search process will be described in detail with reference to S7 to S11.
First, since it is known that the optimum rotation speed was crossed in the previous change in rotation speed (Fig. 3 (1) → (2)), the change width of the rotation speed was changed in Fig. 3 (1) → (2) in S7. The rotation speed is slightly changed in the opposite direction (rotation speed change step).
Next, in the determination of S8, the phase difference gradient is calculated by the phase difference gradient calculation unit 7 based on the changed rotation speed, and the calculated phase difference gradient is stored first in the phase difference gradient maximum value storage unit 9. Compare with the provisional maximum value (phase difference gradient comparison step).

At this time, since the change in the phase difference is shown in FIGS. 3 (2) to (3), the calculated phase difference gradient exceeds the provisional maximum value Vε. Therefore, since it can be determined that the optimum rotation speed is crossed, the change width of the rotation speed is further halved in S9, the search direction (change direction) is reversed, and the provisional maximum value of the phase difference gradient is updated in S10.
Next, in S11, it is determined whether or not the change width in S9 is equal to or greater than a predetermined threshold value. Here, if it is equal to or more than a predetermined threshold value, the process returns to S7 and the rotation speed is slightly changed based on the change width and the search direction set in S9 (second rotation speed change step).

Therefore, the rotation speed transitions from FIG. 3 (3) to (4), but since there is a discontinuity in the phase difference between (3) and (4), the vibration mode changes due to this transition. You can see that there is. If the optimum rotation speed is searched by simply using only the change in the vibration mode, it will be mistaken that there is an optimum rotation speed during this period, but from the limit depth of cut in FIG. 3, the optimum rotation speed is actually during this period. It turns out that does not exist.
Therefore, in the next determination of S8, the phase difference gradient becomes smaller in the transition from FIG. 3 (3) to (4) than in the case of (2) to (3), and the provisional maximum value is not updated. It can be judged that the speed is not crossed.

Then, the process returns to S7 again, and the rotation speed is slightly changed based on the same change width and search direction set in S9 (second rotation speed change step). Therefore, the changes shown in FIGS. 3 (4) to (5) are made.
Here, since the phase difference gradient becomes larger than the provisional maximum value (YES in S8), it can be seen that the optimum rotation speed is straddled. Therefore, the change width is reduced and the search direction is reversed in S9, and the provisional maximum value of the phase difference gradient is updated in S10. Then, if the change width in S9 is above the threshold value in the determination of S11, the process returns to S7, and the rotation speed is slightly changed based on the change width and the search direction set in S9 (second rotation speed change step). ). That is, the search proceeds in more detail as shown in FIGS. 3 (5) → (6).
By continuing the processing from S7 to S11 in this way, the optimum rotation speed can be asymptotically approached.

Then, when the change width of the rotation speed is less than a predetermined threshold value in the determination in S11, the search step is ended and the final rotation speed is determined to be the optimum rotation speed (determination step). The threshold value of this change width can be set to 10 rotations, for example, when the optimum rotation speed is to be obtained with an accuracy of ± 10 rotations.

As described above, according to the vibration suppression device and the vibration suppression method of the above-described embodiment, the range including the vibration detection step (S1) for detecting chatter vibration and the rotation speed of the spindle 2 which is optimal for detecting chatter vibration is included. The optimum speed range estimation step (S5) to be estimated, the phase difference calculation step (S5) for obtaining the phase difference by the above equations 1 and 2 at the upper limit speed and the lower limit speed of the range, and the gradient of the phase difference with respect to the rotation speed are obtained. A phase difference gradient maximum value saving step (S6) that calculates and saves the obtained phase difference gradient as a provisional maximum value, and a rotation speed changing step that changes the rotation speed to decrease or increase by a predetermined change range within the range. (S7), the phase difference gradient comparison step (S8) in which the phase difference gradient for the changed rotation speed is calculated and the obtained phase difference gradient is compared with the provisional maximum value, and the phase difference gradient is the provisional maximum value in the comparison. If it does not exceed, the rotation speed is changed by setting the rotation speed change direction to the same direction as the previous change, while if the phase difference gradient exceeds the provisional maximum value in the comparison, the rotation speed change direction is changed to the previous change. The second rotation speed change step (S7 to S11) in which the change width is set smaller than the previous time, the phase difference gradient is updated to the provisional maximum value, and the rotation speed is changed while setting in the opposite direction to the change. To execute. That is, since the optimum rotation speed for suppressing chatter vibration is searched for by using the phase difference gradient with respect to the rotation speed, the optimum rotation speed can be increased even for complicated chatter vibration in which multiple vibration modes coexist. It can be calculated with accuracy.

The configuration of the vibration suppression device is not limited to the above embodiment, for example, the phase difference calculation unit and the phase difference gradient calculation unit may be integrated, or the phase difference gradient maximum value storage unit and the optimum rotation speed storage unit may be integrated. It can be changed as appropriate.
Further, also in the vibration suppression method, in the above embodiment, if the phase difference gradient does not exceed the provisional maximum value in the comparison of S8, the rotation speed is slightly changed in S7 with the same change width as the previous time. Even in this case, it is possible to gradually reduce the change width.
Further, it is conceivable to change the threshold value of S11 to terminate the search to other than 10 rotations, or to terminate the search by setting an upper limit on the number of changes in the rotation speed instead of the threshold value.
In addition, the present invention is applicable not only to a machine tool for machining by attaching a tool to a rotating shaft, but also to a machine tool for machining by gripping a work on a rotating shaft.

1 ... Machine tool, 2 ... Spindle, 3 ... Vibration sensor, 4 ... NC device, 5 ... Frequency analysis unit, 6 ... Phase difference calculation unit, 7 ... Phase difference gradient calculation unit, 8 ... Optimal speed range estimation unit, 9 ... Phase difference gradient maximum value storage unit, 10 ... Rotation speed command value calculation unit, 11 ... Optimal speed storage unit, 12 ... Spindle control device.

Claims (4)

A vibration suppression method for suppressing chatter vibration generated when machining the work in a machine tool provided with a rotating shaft for rotating a tool or a work.
The vibration detection step for detecting the chatter vibration and
An optimum speed range estimation step for estimating a range including the rotation speed of the rotation shaft, which is optimal for suppressing the detected chatter vibration, and
In the upper limit speed and the lower limit speed in the above range, the phase difference calculation step of obtaining the phase difference by the following equations 1 and 2, respectively,
A phase difference gradient maximum value saving step of calculating the phase difference gradient with respect to the rotation speed and saving the obtained phase difference gradient as a provisional maximum value, and
A rotation speed change step of changing the rotation speed to decrease or increase within a predetermined change range within the range, and
A phase difference gradient comparison step of calculating the phase difference gradient with respect to the changed rotation speed and comparing the obtained phase difference gradient with the provisional maximum value.
When the phase difference gradient does not exceed the provisional maximum value in the comparison, the rotation speed is changed by setting the change direction of the rotation speed to the same direction as the previous change, while the phase difference gradient is changed in the comparison. When the provisional maximum value is exceeded, the change direction of the rotation speed is set in the direction opposite to the previous change, the change width is set smaller than the previous time, and the phase difference gradient is updated to the provisional maximum value. The second rotation speed change step for changing the rotation speed and
A method of suppressing vibration of a machine tool, which is characterized by performing.
Equation 1: k = {60 x chatter vibration frequency / (number of tool blades x rotation speed)}
Equation 2: Phase difference = k- [k-α] where 0≤α≤1 and [k-α] are floor functions The second rotation speed change step and the phase difference gradient comparison step based on the rotation speed changed here are repeatedly executed, and the change width in the second rotation speed change step becomes a predetermined threshold value. The method for suppressing vibration of a machine tool according to claim 1, wherein when the speed is reached, the determination step for determining that the rotation speed has been optimized is further executed. A vibration suppression device for suppressing chatter vibration generated when machining the work in a machine tool provided with a rotating shaft for rotating a tool or a work.
The vibration detecting means for detecting the chattering vibration and
Optimal speed range estimating means for estimating the range including the rotational speed of the rotating shaft, which is optimal for suppressing the detected chatter vibration,
A phase difference calculating means for obtaining the phase difference by the following equations 1 and 2 at the upper limit speed and the lower limit speed in the above range, respectively.
A phase difference gradient maximum value storage means that calculates the phase difference gradient with respect to the rotation speed and stores the obtained phase difference gradient as a provisional maximum value.
A rotation speed changing means for changing the rotation speed to decrease or increase by a predetermined width within the range.
A phase difference gradient comparing means for calculating the phase difference gradient with respect to the changed rotation speed and comparing the obtained phase difference gradient with the provisional maximum value.
When the phase difference gradient does not exceed the provisional maximum value in the comparison, the rotation speed is changed by setting the change direction of the rotation speed to the same direction as the previous change, while the phase difference gradient is changed in the comparison. When the provisional maximum value is exceeded, the change direction of the rotation speed is set in the direction opposite to the previous change, the change width is set smaller than the previous time, and the phase difference gradient is updated to the provisional maximum value. The second rotation speed changing means for changing the rotation speed and
A vibration suppression device for a machine tool, which is characterized by being provided with.
Equation 1: k = {60 x chatter vibration frequency / (number of tool blades x rotation speed)}
Equation 2: Phase difference = k- [k-α] where 0≤α≤1 and [k-α] are floor functions The second rotation speed changing means and the phase difference gradient comparing means based on the rotation speed changed here are repeatedly executed, and the change width in the second rotation speed changing means reaches a predetermined threshold value. The vibration suppression device for a machine tool according to claim 3, further comprising a determination means for determining that the rotation speed has been optimized when the rotation speed is reached.

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