WO2014064953A1

WO2014064953A1 - Method for suppressing chatter of operating machine

Info

Publication number: WO2014064953A1
Application number: PCT/JP2013/060569
Authority: WO
Inventors: 保宏駒井; 洋光盛田
Original assignee: エヌティーエンジニアリング株式会社
Priority date: 2012-10-23
Filing date: 2013-04-01
Publication date: 2014-05-01
Also published as: JP5288318B1; JP2014083674A

Abstract

A chatter suppression method for an operating machine detects vibration generated when rotation of a turning tool (22) or a work piece (W) starts, and when the vibration detected from the rotation start time is determined to exceed a vibration threshold value during idling of the machine main shaft, the vibration is analyzed using Fourier series expansion and the frequency due to regenerative chatter is calculated, and an estimated damping ratio is further added to the frequency due to the regenerative chatter to obtain a regenerative chatter avoidance frequency in order to adjust the speed of the main shaft (18).

Description

Chatter control method for work machines

The present invention relates to a chatter suppressing method for a working machine for suppressing occurrence of chatter when a workpiece is processed through a processing tool.

Generally, various machine tools are used to process a workpiece through a processing tool. For example, in the boring process, a boring tool provided with a boring tool (cutting edge) is attached to a rotating spindle (spindle) of a machine tool, and the boring tool is sequentially fed along a pilot hole while rotating at a high speed. A highly accurate hole is processed at a predetermined position with the cutting edge diameter.

¡In this type of work machine, bending due to cutting resistance is likely to occur in the spindle, processing tool and workpiece. Then, due to this bending, vibration is induced in the machining tool or workpiece, and this vibration may become chatter (including so-called regenerative chatter) and appear in machining. In order to suppress the above chatter, for example, a chatter suppressing method and apparatus for a work machine disclosed in JP 2010-247316 A is known.

This chatter suppressing method is detected when a machining tool or workpiece starts to rotate, a step of setting a vibration during idling of the machine spindle as a threshold, and a machining spindle is detected during machining. Determining whether or not the machining vibration exceeds the threshold, and when it is determined that the machining vibration exceeds the threshold, the machining vibration is analyzed by Fourier series expansion, and frequency × 60 ÷ number of blades ( Or a step of adjusting the number of rotations of the mechanical spindle from an arithmetic expression.

Generally, it is recognized that the vibration frequency (frequency) of chatter is the same value as the natural frequency of a processing tool or a workpiece that is a rotating body. However, it has been found that there is a slight difference between the frequency of chatter when chatter occurs and the frequency data of the natural frequency.

The present invention can correct a difference between a chatter frequency and a natural frequency by a simple process, prevent chattering as much as possible, and perform a highly accurate machining operation efficiently. An object is to provide a chatter suppressing method.

The present invention relates to a chatter suppressing method for a working machine for suppressing chatter from occurring when a workpiece is processed through a processing tool.

This chatter suppressing method is detected when a machining tool or workpiece starts to rotate, a step of setting a vibration during idling of the machine spindle as a threshold, and a machining spindle is detected during machining. Determining whether or not the machining vibration exceeds the threshold, and when it is determined that the machining vibration exceeds the threshold, the machining vibration is analyzed by Fourier series expansion to calculate a frequency due to regenerative chatter. From the step, a step of obtaining a regenerative chatter avoidance frequency by adding an estimated damping ratio to the calculated frequency due to the regenerative chatter, and a regenerative chatter avoidance frequency × 60 ÷ the number of blades (or its multiplication) Adjusting the rotational speed of the machine spindle.

Further, in this chatter suppressing method, it is preferable that the estimated damping ratio is estimated based on the natural frequency of the machining tool or the workpiece.

Furthermore, in this chatter suppressing method, the estimated attenuation ratio is preferably set within a range of 0.01 to 0.05.

In the chatter suppressing method for a work machine according to the present invention, vibration is detected from the start of rotation, and the vibration is analyzed by Fourier series expansion to calculate a frequency due to regenerative chatter. Then, a playback chatter avoidance frequency is obtained by adding an estimated attenuation ratio to the calculated playback chatter frequency.

For this reason, a feedback chatter avoidance frequency with high accuracy can be obtained by feeding back the estimated damping ratio. As a result, it is possible to adjust the rotational speed of the machine spindle and to suppress the occurrence of regenerative chatter as much as possible before the effect of chatter actually occurs.

1 is a schematic explanatory diagram of a chatter suppressing device for a work machine according to an embodiment of the present invention. It is explanatory drawing of the chatter suppression controller which comprises the said chatter suppression apparatus. It is a front | former stage of the flowchart explaining the chatter control method by the said chatter suppression apparatus. It is the latter part of the flowchart. It is explanatory drawing of the vibration at the time of idling, and the vibration at the time of cutting. It is explanatory drawing when a main shaft rotation speed exists in a stable area | region. It is explanatory drawing at the time of stable processing. It is explanatory drawing of the state from which the harmonic at the time of stable processing was removed. It is explanatory drawing of various waveforms in the natural frequency and chatter frequency which were acquired with the FFT analyzer. It is explanatory drawing of a damping ratio.

As shown in FIG. 1, a chatter suppressing device 10 that performs a chatter suppressing method according to an embodiment of the present invention is applied to a machine tool (work machine) 12.

The machine tool 12 includes a spindle (machine spindle) 18 that is rotatably provided in a housing 14 via a bearing 16, and a boring bar (processing tool) 20 that is detachable from the spindle 18. A boring tool 22 for boring is attached to the tip. A work W is placed on the work table 24.

The chatter suppressing device 10 includes an acceleration sensor (vibration detection mechanism) 26 attached to a side portion of the housing 14 in order to detect vibration generated when rotation of the boring bar 20 is started, and rotation of the boring bar 20. The vibration detection controller 30 analyzes the vibration detected from the start by Fourier series expansion, adjusts the rotation speed of the main shaft 18, and outputs an updated value to the machine control device 28. The machine control device 28 controls the machine tool 12 and is connected to the control operation panel 32.

As the vibration detection mechanism, in addition to the acceleration sensor 26, a microphone 34 that acquires vibration sound using sound waves is used. The acceleration sensor 26 may be attached to the work W side, for example, the work table 24 instead of the housing 14.

As shown in FIG. 2, the chatter suppression controller 30 includes a chatter suppression arithmetic unit (arithmetic mechanism) 38 that amplifies and captures mechanical vibration (machining vibration) detected by the acceleration sensor 26 and the like by an amplifier and filter circuit 36. .

The chatter suppression calculation unit 38 has processing conditions such as an instruction unit 40 for instructing a threshold value (to be described later) for starting calculation processing from the vibration monitoring state, the number of rotations of the spindle 18 and the number of blades of the cutting tool 22. Processing condition input unit 42 for inputting, estimated attenuation ratio input unit 43 for inputting an estimated attenuation ratio for complementation (described later), a display unit 44 for displaying the machining state and the like, and arithmetic processing described later Is connected to an update value output unit 46 for outputting the spindle rotational speed adjusted by the above. The updated value output unit 46 automatically outputs the updated spindle rotational speed to the machine tool control device 28 of the machine tool 12.

The chatter suppressing method by the chatter suppressing apparatus 10 configured as described above will be described below with reference to flowcharts shown in FIG.

As shown in FIG. 1, in the machine tool 12, the spindle 18 to which the boring bar 20 is attached is driven to rotate along the prepared hole Wa of the workpiece W. Then, the boring bar 20 moves relatively to the prepared hole Wa side of the workpiece W. For this reason, the boring bar 20 rotates, and boring is performed on the inner wall surface constituting the prepared hole Wa via the cutting tool 22 attached to the boring bar 20.

The chatter suppressing device 10 starts monitoring the machining vibration by the acceleration sensor 26 (and / or the microphone 34) at the same time as the spindle 18 starts to rotate (step S1) (step S2). In the chatter suppression arithmetic unit 38, it is determined whether or not the machining vibration taken in via the amplifier and filter circuit 36 exceeds a preset threshold value, for example, a vibration during idling of the spindle 18 (step S3). .

Here, before starting machining, the vibration at the time of idling of the spindle 18 and the vibration at the time of cutting actually change as shown in FIG. Then, the vibration analysis threshold value is calculated with the vibration at the time of idling of the spindle 18 as an allowable value.

Next, when it is determined that the machining vibration has exceeded the threshold value (YES in step S3), the process proceeds to step S4, and the operational analysis is performed by Fourier transformation (Fourier series expansion) of the machining vibration. Specifically, the temporal vibration f (t) is represented by f (t) = Σ (a _j cos 2πJt + b _j sin2πJt). Here, a _j is the cosine harmonic component Fourier coefficient of frequency J, and b _j is the sine harmonic component Fourier coefficient of frequency J.

And the Fourier coefficient for frequency J is Fourier series expansion based on a _j = 1 / 2T∫f (t) cos (2πJt) dt and b _j = 1 / 2T∫f (t) sin (2πJt) dt. I do. The integration interval is 0 to T, and the integration interval T is an integer multiple of the period 1 / J.

Here, in order to improve the real-time property (immediateness) by the Fourier series expansion, the number of data for analysis is minimized by limiting to the vibration frequency that actually causes chatter, for example, 20 Hz to 4000 Hz.

In step S5, the power spectrum P (J) (maximum vibration amplitude) is calculated from P (J) = a _j ² + b _j ² based on the obtained Fourier coefficient.

Next, the process proceeds to step S6, where a rough search for frequency peaks is performed. Coarse search refers to roughly scanning a power spectrum peak of a vibration signal subjected to Fourier series expansion processing and searching for a peak value in the peak. Specifically, a frequency range between 20 Hz and 4000 Hz is scanned every 10 Hz (first frequency).

If there is no peak value (NO in step S7), the process returns to step S2 and the vibration monitoring process is performed. On the other hand, if it is determined that there is a peak value (YES in step S7), the process proceeds to step S8, and a rough search of the peak value roughly searched is performed. In the fine search, scanning is performed every 1 Hz (second frequency) for the number + Hz before and after the roughly searched peak value.

And it progresses to step S9, and when there is no peak value (in step S9, NO), it returns to step S2 and a vibration monitoring process is performed. On the other hand, if it is determined that there is a peak value (YES in step S9), the process proceeds to step S10, and the frequency peak (fundamental wave) with the maximum power is searched.

Here, when the mechanical vibration is expanded by Fourier series, a fundamental frequency component and its harmonic component (second harmonic, third harmonic, etc.) are calculated. The harmonic component is a frequency that is an integral multiple of the fundamental frequency, and is an unnecessary signal that is not linked to the physical cause of the vibration having the original fundamental frequency. For this reason, when it is determined in step S11 that a harmonic component is present (YES in step S11), the process proceeds to step S12 to delete this harmonic. Thereby, only the fundamental wave connected with the cause of vibration is obtained.

Usually, when stable machining is performed by the machine tool 12, as shown in FIGS. 6 and 7, the rotational speed of the spindle 18 is in a stable region. FIG. 6 shows a change in the limit cut at which chattering occurs with respect to the rotational speed of the main shaft 18, and there is a so-called stability pocket in which the stability limit is partially increased.

On the other hand, as shown in FIG. 7, the calculated frequency components include, for example, a fundamental frequency component (the number of rotations of the spindle 18 when idling) A, a vibration component B before chatter growth, a second harmonic component C, and A third harmonic component D is included. The fundamental frequency component A is a numerical value input in advance to the machining condition input unit 42 and does not instruct to change the numerical value.

Therefore, in the harmonic elimination process, first, the acquired vibration frequency is expanded into a Fourier series and then converted into a power spectrum, and the frequency with the highest power peak is selected from the data. Next, using this as a fundamental wave, a frequency that is an integral multiple of that is used as a harmonic, and the harmonic is calculated and compared with the peak value of the power spectrum.

The comparison is performed in order from the lowest frequency peak, and if there is a match, it is deleted. As a result, only the fundamental frequency component from which the harmonics (second-order harmonic component C and third-order harmonic component D) are deleted remains, and this is a vibration frequency that is not directly corrected and is associated with the physical cause of vibration. Only this is detected (see FIG. 8).

Similarly, the next frequency peak (fundamental wave) with the maximum power is searched (step S13), and if it is determined that there is no next peak (YES in step S14), the process proceeds to step S15 to determine whether chatter vibration is present. Judgment is made.

In the present embodiment, since it is performed within a practical vibration range (for example, 20 Hz to 4000 Hz), the vibration frequency is the rotation frequency of the main shaft 18 (including harmonics), and the number of teeth of the cutting tool 22 used for the rotation. Includes the multiplied frequency (including harmonics) and the chatter frequency associated with machining.

Therefore, the number of rotations of the spindle 18 and the number of blades of the cutting tool 22 are input to the chatter suppressing operation unit 38 in advance. Accordingly, vibrations that do not correspond to the vibration frequency obtained by multiplying the rotation frequency of the main shaft 18 and the number of blades of the cutting tool 22 are chatter vibration frequencies or signs thereof. For this reason, if these series of processes are always performed from the start of machining, a sign of chatter vibration is automatically calculated from the mechanical vibration.

Specifically, the peak value of the calculation frequency from which the harmonic component has been deleted is the frequency of the rotation speed of the spindle 18 (rotation speed ÷ 60) input in advance as a machining condition, or the vibration frequency (rotation speed of the cutting tool 22). The number is compared with the number of blades / 60) (step S16 and step S17).

Here, when the peak value of the calculation frequency coincides with these pre-input information values (YES in steps S16 and S17), this is a change in machining force generated as the main shaft 18 rotates, or a bite 22 Is determined to be forced vibration due to intermittent cutting of the cutting edge (step S18), and the process returns to vibration monitoring (step S19).

On the other hand, if an arithmetic frequency peak that does not meet this condition is detected (NO in steps S16 and S17), it is determined as the vibration frequency of playback chatter (step S20). Then, the process proceeds to step S21, and a process of obtaining a playback chatter avoidance frequency by adding an estimated attenuation ratio to the frequency due to playback chatter is performed.

The applicant of the present invention has found through a demonstration experiment that a slight difference occurs between the frequency due to the chatter and the frequency data of the natural frequency of the measurement object (spindle 18 and bite 22). Specifically, in the machine tool 12, the tip of the boring bar 20 attached to the spindle 18 was vibrated with an impact hammer, and the vibration state of the measurement object was obtained as a signal by the acceleration sensor.

Next, while inputting the excitation force of the impact hammer, the vibration signal from the acceleration sensor was output, and these were taken into an FFT analyzer for Fourier analysis and calculation. Furthermore, the natural frequency and damping ratio were obtained using the output / input as a transfer function.

The data of the FFT analyzer obtained by the measurement of the natural frequency is shown, for example, on the upper side of FIG. In FIG. 9, the upper part on the upper side represents the state of vibration input by the impact hammer, the middle part on the upper side represents the degree of vibration of the measurement object as the output of the acceleration sensor 26, and the lower part on the upper side transmits the output / input. Expressed as a function. (Fn) indicated by a vertical line represents the natural frequency (Hz) of the measurement object.

A machining experiment was performed using the same machine tool 12 as described above, and vibration data such as a regenerative chatter generation state was acquired. The machining vibration (including chatter vibration) was acquired by the acceleration sensor 26, and the machining experiment was performed while observing the vibration amplitude and the power spectrum by taking this into the FFT analyzer and analyzing it.

Here, the lower side of FIG. 9 shows a state in which regenerative chatter occurs during processing. In FIG. 9, the lower part on the lower side represents the power spectrum when regenerative chatter occurs at the chatter frequency (fc), and the upper part on the lower side represents the vibration waveform at that time.

Therefore, there is a slight frequency difference Δf1 between the chatter frequency (fc) when regenerative chatter occurs and the natural frequency (fn) acquired in advance. That is, it has been found that the chatter frequency (fc) is a numerical value (for example, 0.03) higher than the natural frequency (fn).

In this case, in this embodiment, the playback chatter avoidance frequency is calculated by feeding back the frequency due to playback chatter in consideration of the frequency difference Δf1. At that time, it has been found that the frequency difference Δf1 is the same as the half width (Δf2) of the natural frequency measurement (see FIG. 10). The half width at half maximum (Δf2) is calculated by the product of the damping ratio ζ and the natural frequency (fn). Accordingly, the damping ratio ζ = Δf2 / (2 × fn).

Therefore, as the frequency to be changed, the value of the attenuation ratio ζ of the measurement data of the natural frequency (fn) that is the same value as the frequency difference Δf1 is substituted into the feedback value as the estimated attenuation ratio. Specifically, regenerative chatter avoidance frequency (Hz) = regenerative chatter frequency / (1 + estimated damping ratio), and regenerative chatter avoidance rotation speed (RPM) = reproduced chatter frequency / (1 + estimated damping ratio) × 60. It is calculated from the relational expression.

On the other hand, when the natural frequency (fn) is not measured in advance and the value of the damping ratio ζ is unknown, the estimated damping ratio is set to 0.01 to 0.05. The value of the damping ratio of the natural vibration characteristics (fn) of the spindle system and jig work system is in the range of 0.01 to 0.05 in a general use example, and this value is reflected as a feedback value (complementation) This is because chatter avoidance processing with high accuracy is performed.

Next, in step S21, after being converted to the regenerative chatter avoidance frequency, the process proceeds to an instruction to change the mechanical rotational speed for adjusting the rotational speed of the spindle 18 (step S22). In step S22, in order to suppress chatter vibration, the machining state is monitored in real time, and when a predictive vibration of chatter occurs, the regenerative chatter avoidance frequency based on the stable pocket method with the supplemented frequency × 60 ÷. The number of teeth (or its multiplication) is calculated. As a result, the updated rotational speed of the main shaft 18 is calculated, which automatically represents the central rotational speed of the stable pocket method.

Next, the chatter suppressing arithmetic unit 38 displays the calculated updated rotation speed of the main spindle 18 on the display unit 44, and as a machine rotation speed change signal (for example, an override instruction from the outside of the rotation speed of the main spindle 18). Automatic feedback output from the update value output unit 46 to the machine tool controller 28 is performed. For this reason, the machine tool 12 is immediately changed to the instructed number of rotations of the main shaft 18, and cutting without harmful chatter becomes possible.

In this case, in this embodiment, vibration is detected from the start of rotation, and the vibration is analyzed by Fourier series expansion to calculate the frequency due to regenerative chatter. Then, a playback chatter avoidance frequency is obtained by adding an estimated attenuation ratio to the calculated playback chatter frequency.

For this reason, a feedback chatter avoidance frequency with high accuracy can be obtained by feeding back the estimated damping ratio. Thereby, before the influence by chatter actually occurs, the rotational speed of the machine spindle can be adjusted and the occurrence of regenerative chatter can be suppressed as much as possible.

Claims

A chatter suppressing method for the work machine (12) for suppressing chatter from occurring when processing the workpiece (W) via the processing tool (20),
Detecting vibration generated when rotation of the machining tool (20) or the workpiece (W) is started;
Setting the vibration during idling of the machine spindle (18) as a threshold;
Determining whether machining vibration detected during machining of the machine spindle (18) exceeds the threshold;
Analyzing the machining vibration by Fourier series expansion when it is determined that the machining vibration exceeds the threshold, and calculating a frequency due to regenerative chatter;
A step of obtaining a playback chatter avoidance frequency by adding an estimated attenuation ratio to the calculated frequency due to the playback chatter;
Adjusting the rotational speed of the mechanical spindle (18) from the calculation formula of the regenerative chatter avoidance frequency × 60 ÷ the number of blades (or its multiplication);
A chatter suppressing method for a work machine, comprising:
The chatter suppressing method according to claim 1, wherein the estimated damping ratio is estimated based on a natural frequency of the machining tool (20) or the workpiece (W).
The chatter suppressing method according to claim 1, wherein the estimated damping ratio is set within a range of 0.01 to 0.05.
3. The chatter suppressing method according to claim 2, wherein the estimated damping ratio is set within a range of 0.01 to 0.05.