JP2012187685A - Method and device for controlling rotational shaft of machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce chatter vibration by acquiring information from an actual machining state and performing highly accurate analysis to discriminate a type of the chatter vibration and thereby to properly cope with the generated chatter vibration.SOLUTION: An initial rotation speed of a main shaft and a change pattern from the initial rotation speed are set in S1, and machining is performed at the initial rotation speed in S2. The vibration generated during the machining is detected in S3, and determination whether or not the detected vibration is forced chatter vibration in S4. If the vibration is the forced chatter vibration, the rotation speed is changed from the initial rotation speed based on the change pattern in S6-S9. If the forced chatter vibration is still generated even after the change of the rotation speed, a vibration frequency in the maximum vibration quantity of the forced chatter vibration is calculated in S10, a resonance frequency is specified based on the vibration frequency in S14, a rotation speed evading the specified resonance frequency is calculated in S15, and the rotational speed is changed to the calculated rotation speed in S16.

Description

  The present invention relates to a method and an apparatus for controlling the rotation of a rotary shaft in order to suppress chatter vibration generated during machining in a machine tool that performs machining by rotating a tool or a workpiece mounted on the rotary shaft.

2. Description of the Related Art Conventionally, there are machine tools in which, for example, a tool is supported on a rotatable spindle and moved relative to the tool and the workpiece while moving the workpiece to process the workpiece. In the machine tool, if the depth of cut in the cutting process is excessively increased, “chatter vibration” occurs during the process, and problems such as deterioration of the finishing accuracy of the processed surface, rapid tool wear, and tool breakage occur.
For this reason, there is a method for predicting chatter vibration occurring in advance and taking a countermeasure. Specifically, as described in Patent Document 1, a technique has been devised that predicts machining conditions in which chatter vibrations are generated by simulation and measurement before machining, and performs machining under machining conditions in which chatter vibrations are less likely to occur. ing. There is also a method of detecting and analyzing vibration during processing and taking countermeasures. As described in Patent Documents 2 and 3, the type of chatter vibration is discriminated using the analysis result, and the chatter vibration generated during machining is adjusted to an appropriate rotation speed for each chatter vibration. It has become a technology for reducing measures.

JP 2009-274179 A JP 2008-290186 A JP 2009-0783350 A

  However, in the method of Patent Document 1, if the simulation accuracy is low, the error of the natural frequency with the real object becomes large, and depending on the processing, there may be different characteristics in the stationary state and the processed state. There is also a risk of proposing incorrect machining conditions even if performed. In addition, in the methods of Patent Documents 2 and 3, if the calculation accuracy is low, accurate analysis cannot be performed, and the type of chatter vibration cannot be correctly determined, and there is a risk of performing an erroneous treatment, while high calculation accuracy is obtained. If it tries to do so, processing time will become long and calculation load will become large, and there exists a possibility that sufficient reduction effect of chatter vibration may not be acquired.

  Therefore, the present invention has been made in view of the above problems, and performs analysis with high accuracy by obtaining information from an actual machining state, and even when some analysis error is included, the type of chatter vibration is determined. It is an object of the present invention to provide a rotating shaft control method and apparatus that can be discriminated, appropriately dealt with chatter vibrations generated, and expected to reduce chatter vibrations.

In order to achieve the above object, the invention according to claim 1 is a rotating shaft control method for controlling rotation of the rotating shaft in a machine tool that performs machining by rotating a tool or a workpiece mounted on the rotating shaft. Because
A parameter setting step for setting an initial rotation speed of the rotation shaft and a change pattern from the initial rotation speed, and processing by rotating the rotation shaft at the initial rotation speed, and detecting vibrations generated during the processing. A vibration detecting step; a vibration determining step for analyzing the detected vibration to determine whether the vibration is a forced chatter vibration; and if the vibration is a forced chatter vibration, the initial rotation speed is used to determine the vibration based on the change pattern. A rotation speed changing step for changing the rotation speed, and detecting and analyzing the vibration after the change of the rotation speed. If the vibration is a forced chatter vibration, the vibration amount of the forced chatter vibration is maximized. A resonance frequency specifying step for specifying a resonance frequency based on a vibration frequency, and calculating the rotation speed to avoid the specified resonance frequency It is characterized in performing a rotational speed calculation / changing step of changing to the rotational speed.
According to a second aspect of the present invention, in the configuration of the first aspect, the upper and lower limits of the rotational speed are respectively set in the parameter setting step, and the upper and lower limits of the rotational speed are different in the resonance frequency specifying step. Calculate whether there is the rotation speed at which the amount of vibration is the maximum vibration frequency on the harmonics line, and if there is the rotation speed, specify the resonance frequency based on the vibration frequency on the harmonics line, In the rotation speed calculation / change step, the rotation speed that avoids the plurality of resonance frequencies specified on each harmonic line is calculated and changed to the rotation speed.

In order to achieve the above object, a third aspect of the present invention provides a rotary shaft control device for controlling the rotation of the rotary shaft in a machine tool that performs machining by rotating a tool or a workpiece mounted on the rotary shaft. Because
Parameter setting means for setting an initial rotation speed of the rotation shaft and a change pattern from the initial rotation speed, vibration detection means for detecting vibration generated when the rotation shaft is rotated, and detection A vibration discriminating means for analyzing whether the vibration is a forced chatter vibration and a rotation for changing the rotation speed from the initial rotation speed based on the change pattern if the vibration is a forced chatter vibration. If the vibration detected and analyzed after the rotation speed is changed is the forced chatter vibration, the resonance frequency is specified based on the vibration frequency when the vibration amount of the forced chatter vibration becomes maximum. Resonance frequency specifying means; and rotation speed calculation / change means for calculating the rotation speed that avoids the specified resonance frequency and changing the rotation speed to the rotation speed. And it is characterized in and.
According to a fourth aspect of the present invention, in the configuration of the third aspect, the parameter setting means sets upper and lower limits of the rotational speed, and the resonance frequency specifying means differs within the upper and lower limits of the rotational speed. Calculate whether there is the rotation speed at which the amount of vibration is the maximum vibration frequency on the harmonics line, and if there is the rotation speed, specify the resonance frequency based on the vibration frequency on the harmonics line, The rotation speed calculation / change means calculates the rotation speed that avoids the plurality of resonance frequencies specified on each harmonic line, and changes the rotation speed to the rotation speed.

According to the first and third aspects of the present invention, in order to efficiently obtain a plurality of information from an actual machining state, even when an error is included in measurement or analysis, the type of chatter vibration can be quickly and accurately determined. And take appropriate action. Therefore, reduction of machining vibration can be expected.
According to the second and fourth aspects of the invention, in addition to the above-described effects, it is possible to reliably avoid a resonance frequency that is highly likely to cause forced chatter vibration and to select an optimum rotation speed.

It is a schematic block diagram of a vertical machining center. It is a flowchart of spindle control. It is a Campbell diagram. It is a Campbell diagram of a specific example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a vertical machining center which is an example of a machine tool. The vertical machining center 1 is provided with a spindle 3 as a rotating shaft on a spindle head 2 provided above, and a tool 4 attached to the spindle 3. Thus, the tool 4 can be automatically changed by an automatic tool changer (not shown) with a well-known configuration for machining the workpiece 6 set on the lower machining table 5.

Further, the vertical machining center 1 includes a spindle control device 10 as a rotary shaft control device. The spindle control device 10 controls the rotation of the spindle 3 based on a vibration sensor (here, an acceleration pickup) 7 provided on the spindle head 2 as vibration detecting means for detecting vibration and a detection value by the vibration sensor 7. And a control device 11.
First, the vibration sensor 7 detects vibration in the time domain (vibration on the time axis) that occurs as the main shaft 3 rotates, and vibration information in the time domain in the X axis, Y axis, and Z axis directions orthogonal to each other. Is attached to the spindle head 2 in such a state that can be detected.

The control device 11 is input as parameter setting means for inputting the upper and lower limits of the rotational speed of the spindle 3 and the rotational speed change pattern (here, the rotational speed change range and the number of changes), the threshold value related to the spindle control, and the number of tool blades. An arithmetic unit 13 that performs Fourier analysis based on the vibration acceleration detected by the device 12 and the vibration sensor 7, determines whether chatter vibration is occurring, determines the type of chatter vibration, calculates the rotation speed, and the like; A storage device 14 that stores the rotation speed of the main shaft 3 in association with the measurement result transmitted from the vibration sensor 7 and the calculation result in the arithmetic device 13, and an NC that controls the rotation of the main shaft 3 in response to a command from the arithmetic device 13. Device 15.
Here, the arithmetic unit 13 functions as a vibration discriminating unit and a resonance frequency specifying unit, and the arithmetic unit 13 and the NC unit 15 function as a rotational speed changing unit and a rotational speed calculating / changing unit.

  The spindle control device 10 configured as described above, when chatter vibration occurs during machining, when it is determined that there is a possibility of forced chatter vibration, the amount of vibration falls below a threshold value or a plurality of rotational speeds. While monitoring whether or not a behavior considered to be forced chatter vibration is observed, a stable rotation speed is calculated from the obtained measurement result, and the vibration speed generated during machining is reduced by changing to the rotation speed. Hereinafter, the control of the spindle 3 will be described based on the flowchart of FIG.

First, in S1, before starting machining, the input device 12 uses the input device 12 to determine the vibration amount threshold value, the number of tool blades, the upper and lower limits of the rotational speed, and the rotational speed change range (for example, the initial rotational speed ± number Within a range of%, the speed is changed in a stepwise manner from the small side to the large side) and the number of times of change is set (parameter setting step).
Machining is started in S2, and during machining, the vibration acceleration measured by the vibration sensor 7 by the arithmetic device 13 is Fourier-analyzed to calculate a vibration amount (here, maximum acceleration), and the vibration amount is compared with a threshold ( S3, vibration detection step). If the vibration amount is smaller than the threshold value, the control is terminated. On the other hand, if the amount of vibration is greater than or equal to the threshold value in the determination in S3, it is determined that chatter vibration has occurred, and in S4, the arithmetic unit 13 determines whether the generated chatter vibration is forced chatter vibration or regenerative chatter vibration. (Vibration discrimination step). If it is determined that the chatter vibration is a regenerative chatter vibration, the optimum rotational speed is changed in S5 and the process returns to S3.

  On the other hand, if it is determined in S4 that the forced chatter vibration has occurred, the calculation device 13 stores the rotational speed, vibration amount, and vibration frequency at that time in the storage device 14 in S6, and in S7, the NC device 15 according to the set change pattern. The rotational speed is changed via, and the vibration amount is compared with the threshold value again in S8. If the vibration amount is smaller than the threshold value, the control is terminated. If the vibration amount is equal to or larger than the threshold value, it is determined in S9 whether or not the number of rotation speed changes has reached the set number. If the set number of times has not been reached, the process returns to S6 to store the rotation speed again, the rotation speed is changed in S7, and the vibration amount is compared with the threshold value in S8. If the amount of vibration does not fall below the threshold value, the processes of S6 to S8 are repeated until the number of changes reaches the set number in S9 (rotation speed changing step).

When the rotational speed change reaches the set number of times without the vibration amount falling below the threshold (YES in S9), the arithmetic unit 13 determines in S10 that the vibration amount is the largest among the data stored in S6. Is calculated as f _max , and in S11, it is determined whether or not there is a rotational speed that can be f _max on different harmonic lines within the upper and lower limits of the set rotational speed. Here, if the rotation speed exists on other harmonic lines, the process returns to S3 and the vibration amount is compared with the threshold value while changing the rotation speed also on the harmonic lines to calculate _fmax .

When it is confirmed in S11 that there is no rotation speed that can be f _max on different harmonic lines, the arithmetic device 13 performs the same processing as S4 on the measurement data stored in the previous processing in S12. Next, it is determined whether the chatter vibration generated at each rotation speed on each harmonic line is forced chatter vibration or regenerative chatter vibration. Here, when it is determined that the forced chatter vibration and the regenerative chatter vibration are mixed, the rotation speed is changed to the smallest vibration amount in the stored measurement data in S13, and the control is terminated. On the other hand, when only the forced chatter vibration is determined to have occurred in the determination of S12, in S14, by comparing the values of the f _max calculated in each harmonics line, the f _max within a certain frequency difference The resonance modes are classified as the same resonance mode, and the average value of f _max is specified as the resonance frequencies f _C1 , f _C2 ... In each of the divided resonance modes (resonance frequency specifying step). Next, in S15, to calculate the rotational speed S _a to be such as to avoid their resonant frequency input, the rotational speed is changed to S _a ends the control (rotation speed calculation / change step) in S16.

  Here, in the above procedure, in the determination of whether or not the forced chatter vibration is in S4 and S12, for example, using the phase information of the following formulas (1) to (4) included in Patent Document 2, the same as in the same Patent Document It can be determined by the method. Specifically, if the phase information obtained by the expression (3) is a value close to 0, for example, larger than the constant 1 set to 0 and smaller than the constant 2 set to 0.1, forced chatter vibration has occurred. In other cases, it can be determined that regenerative chatter vibration has occurred. In this case, in the change to the optimum rotation speed in S5, for example, the rotation speed calculated using the calculation formula (4) can be used. The k1 value used here may be calculated by, for example, k1 value = k value + 1. By changing to this rotational speed, regenerative chatter vibration can be most suppressed.

k ′ value = 60 × chatter frequency / (number of tool blades × spindle rotation speed) (1)
k value = integer part of k ′ value (2)
Phase information = k ′ value−k value (3)
Optimal rotation speed = 60 x chatter frequency / (number of tool blades x k1 value) (4)

Next, the determination of S11 will be described based on the Campbell diagram of FIG. First, each input harmonic line f _k (S) can be calculated as a linear function of S expressed by the following equation (5).
f _k (S) = S × Z × k / 60 (k: integer value) (5)
Here, S is the rotational speed and Z is the number of tool blades. If this value matches the resonance frequency band f1, as in S31 of FIG. 3, forced chatter vibration occurs. Here, when the upper limit rotational speed _Smax and the lower limit rotational speed _Smin are set as shown in FIG. 3, within the range, as shown in S32 of FIG. 3, the resonance frequency band f1 also on the harmonic line of k = 3. Therefore, it is determined that forced chatter vibration occurs, and therefore it is determined that there is a rotation speed that can be f _max on different harmonic lines.

  If the amount of vibration at f2 is large at the rotational speed tried on a different harmonic line, the same operation as f1 is performed at a rotational speed that matches the resonance frequency band of f2. The same applies when the amount of vibration is large in different resonance frequency bands.

The calculation of the rotational speed in S15 and the change in S16 will be described based on the Campbell diagram of FIG. It is assumed that, for example, the resonance frequency bands of f1 and f2 are confirmed based on the operations up to S14. At this time, from equation (5), the rotation speed that does not match either the resonance frequency band (e.g., the rotational speed S _a in FIG. ₃₎ is calculated, occurrence of forced chatter vibration by changing to the rotational speed S _a Stable processing can be performed.

Hereinafter, a control example is shown based on FIG.
First, in S1, the tool number of blades Z is four tools, when the initial rotational speed 1400Min ^-1, set upper limit rotation speed 2500min ^-1, at the lower limit rotation speed 1000min ^-1 each parameter respectively, started working in S2 In S3, the vibration amount exceeded the threshold at 187 Hz and became the largest. In S4, since it is determined that the forced chatter vibration using equation (3), the processing to change the stepwise rotational speed 1540Min ^-1 from 1260Min ^-1 to be 10% ± from 1400Min ^-1 in S6~S9 As a result, the vibration was largest at 200 Hz at 1500 min- ¹ o'clock (S10).
.
Therefore, it can be determined that a resonance frequency exists at 200 Hz, and a region of ± 10% is calculated as a region where forced chatter vibration occurs in the resonance frequency band, that is, 180 Hz to 220 Hz.

Next, in S11, determination is performed according to the following procedure.
First, by substituting each value into Expression (5), the following Expression (6) is obtained.
S = f _k (S) × 15 / k (6)
Here, when the above 180 Hz to 220 Hz is substituted for f _k (S), the following expression (7) is obtained, and it is predicted that forced chatter vibration will occur at the rotational speed S.
S = 2700 / k-3300 / k (7)
In Expression (6), S = 1000 at 200 Hz, k = 3, and the range included in the lower limit rotational speed 1000 min ⁻¹ . Therefore, the determination in S11 is YES.
Therefore, the S6~S9 followed back to S3, for machining by changing the rotational speed 1000min ^-1 ~1100min ^-1.

Here, in the example 1000min ^-1 ~1100min ^-1, generated vibration of 600Hz～660Hz, the most vibration is increased at 1000min ^-1 at 600Hz in S10. Therefore, it can be determined that a resonance frequency exists at 600 Hz, and a region of ± 10% is calculated as a region where forced chatter vibration occurs in the resonance frequency band, that is, 540 Hz to 660 Hz.
Therefore, when calculation is performed in the same manner as in the above procedure, the following equation (8) is obtained, and forced chatter vibration occurs at the rotational speed S.
S = 8100 / k-9900 / k (8)
In the formula (6), 600Hz, the k = 4 to 9, because it has a range included in the upper limit rotation speed 2500min ^-1, the lower limit rotational speed 1000min ^-1, discrimination of S11 is YES. Therefore, returning to S3, the same processing is performed at these rotational speeds.

Then, when processing is performed with each rotational speed changed on each harmonic line in this manner, if forced chatter vibration still occurs on each harmonic line in S12, a resonance frequency band of 200 Hz and a resonance of 600 Hz are obtained in S14. frequency band identified respectively, in S15, it is possible to avoid the forced chatter vibration by calculating the rotational speed S _a the other to calculate the rotational speed of the input matches the respective resonance frequency band. In this case, for example, 2000min ⁻¹ corresponds to this, and therefore, in S16, forced chatter vibration can be avoided by changing to the rotation speed.
When the threshold is cut during the rotation speed change, the control is terminated at the rotation speed.

As described above, according to the spindle control device 10 of the above embodiment, in order to efficiently obtain a plurality of information from the actual machining state, even when measurement or analysis includes an error, the type of chatter vibration can be performed quickly and with high accuracy. Can be determined and appropriate measures can be taken. Therefore, reduction of machining vibration can be expected.
In particular, here, if there is a rotation speed at which the vibration amount is the maximum vibration frequency even on different harmonic lines, the resonance frequency is specified also on the harmonic line, and the rotation speed that avoids multiple resonance frequencies specified on each harmonic line. Therefore, it is possible to select an optimal rotation speed while reliably avoiding a resonance frequency that is highly likely to cause forced chatter vibration.

In addition, the structure which concerns on the rotating shaft control apparatus of this invention is not limited at all to the aspect described in the said embodiment, It can change suitably as needed in the range which does not deviate from the meaning of this invention. .
For example, it is possible to employ a displacement meter or a microphone instead of an acceleration pickup for vibration detection, and use vibration displacement or vibration sound instead of vibration acceleration.
In the above control example, the resonance frequency band is ± 10% of the resonance frequency. However, it can be changed to a different ratio, can be changed, or can be in the range of the absolute value of the rotation speed.
Furthermore, in the above control example, processing at a plurality of rotational speeds is attempted even on different harmonic lines, but it is also possible to perform processing only at the rotational speeds having the specified resonance frequency in order to shorten the control time.

On the other hand, in the above embodiment, the control of the rotation speed is automatically executed, but it goes without saying that each operation may be performed manually and interactively instead of the automatic control.
In addition, the machine tool is not limited to a vertical machining center, and the present invention can be applied to other machine tools such as an NC lathe that performs machining by rotating a workpiece mounted on a spindle.

  1 .... Vertical machining center 2 .... Spindle head 3 .... Spindle 4 .... Tool 6 ... Workpiece 7 ... Vibration sensor 10 .... Spindle control device 11 .... Control device 12, ... Input device, 13 ... arithmetic device, 14 ... storage device, 15 ... NC device.

Claims (4)

In a machine tool that performs processing by rotating a tool or a workpiece mounted on a rotating shaft, a rotating shaft control method for controlling the rotation of the rotating shaft,
A parameter setting step for setting an initial rotation speed of the rotating shaft and a change pattern from the initial rotation speed;
A vibration detecting step for performing processing by rotating the rotating shaft at the initial rotational speed, and detecting vibration generated during the processing;
A vibration discriminating step for analyzing the detected vibration and discriminating whether it is forced chatter vibration;
If the vibration is forced chatter vibration, a rotation speed changing step for changing the rotation speed based on the change pattern from the initial rotation speed;
The resonance is detected and analyzed after the rotation speed is changed, and if the vibration is forced chatter vibration, the resonance frequency is specified based on the vibration frequency when the vibration amount of the forced chatter vibration becomes maximum. A frequency identification step;
A rotation speed calculation / change step for calculating and changing the rotation speed to avoid the identified resonance frequency and changing the rotation speed to the rotation speed is executed. In the parameter setting step, upper and lower limits of the rotational speed are respectively set,
In the resonance frequency specifying step, it is calculated whether or not there is the rotation speed at which the vibration amount becomes the maximum vibration frequency on different harmonic lines within the upper and lower limits of the rotation speed. Identify the resonance frequency based on the vibration frequency on the harmonics line,
2. The machine tool according to claim 1, wherein in the rotation speed calculation / change step, the rotation speed that avoids the plurality of resonance frequencies specified on each harmonic line is calculated and changed to the rotation speed. Rotation axis control method. In a machine tool that performs processing by rotating a tool or a workpiece mounted on a rotating shaft, a rotating shaft control device for controlling the rotation of the rotating shaft,
Parameter setting means for setting an initial rotation speed of the rotating shaft and a change pattern from the initial rotation speed, and
Vibration detecting means for detecting vibrations generated when processing is performed by rotating the rotating shaft;
Vibration discriminating means for analyzing the detected vibration and discriminating whether it is forced chatter vibration;
If the vibration is forced chatter vibration, rotation speed changing means for changing the rotation speed based on the change pattern from the initial rotation speed;
Resonance frequency specifying means for specifying a resonance frequency based on a vibration frequency when the vibration amount of the forced chatter vibration is maximum if the vibration detected and analyzed after the rotation speed is changed is a forced chatter vibration; ,
A rotation axis control device for a machine tool, comprising: a rotation speed calculation / change means for calculating the rotation speed that avoids the specified resonance frequency and changing the rotation speed to the rotation speed. The parameter setting means sets upper and lower limits of the rotation speed,
The resonance frequency specifying means calculates whether or not there is the rotation speed at which the vibration amount becomes a maximum vibration frequency on different harmonic lines within the upper and lower limits of the rotation speed. Identify the resonance frequency based on the vibration frequency on the harmonics line,
The machine tool according to claim 3, wherein the rotation speed calculation / change means calculates the rotation speed that avoids a plurality of resonance frequencies specified on each harmonic line and changes the rotation speed to the rotation speed. Rotation axis control device.

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