JP2021146436A - Method and apparatus for measuring change in vibration characteristic of machine tool - Google Patents

Abstract

To provide a technology of measuring a change in a vibration characteristic of a mechanical structure of a machine tool.SOLUTION: A resonance frequency holding unit 10 holds a resonance frequency of a mechanical structure of a machine tool 2. A vibration response acquisition unit 12 acquires a forced vibration response of the mechanical structure when the mechanical structure is vibrated by a plurality of different frequencies in the vicinity of the held resonance frequency, during cutting processing of the machine tool 2. A change amount deriving unit 13 derives at least one of a change amount and a magnitude of attenuation of the resonance frequency from an acquired plurality of forced vibration responses.SELECTED DRAWING: Figure 3

Description

The present disclosure relates to a technique for measuring changes in the vibration characteristics of the mechanical structure of a machine tool.

One of the important performances of a machine tool is its high chatter vibration stability, and the higher the stability limit, the higher the efficiency of machining with a larger depth of cut. At the machining site, a stability limit diagram is created for each machine tool as a countermeasure against regeneration chatter and mode coupling chatter, and before the start of machining, the operator uses the stability limit diagram to set highly efficient machining conditions. do.

FIG. 1 shows a block diagram of a cutting process with chatter vibration. The block diagram shown in FIG. 1 represents a state in which the past vibration displacement is fed back to the current vibration displacement. Non-Patent Document 1 discloses a method for theoretically obtaining a stability limit diagram by solving the closed loop characteristic equation shown in FIG. 1 using the compliance transfer function and the specific cutting resistance of the machine structure of a machine tool.

When a new machine tool is brought to the machining site, the operator measures the compliance transfer function of the machine structure including the tool and work material by a hammering test and the specific cutting resistance using a power meter before the start of operation. taking measurement. The operator starts the software that creates the stability limit diagram on the computer, inputs various parameters including the measured compliance transfer function and specific cutting resistance, and the software creates the stability limit diagram and saves it in the storage device. do. When setting the machining conditions, the operator displays the saved stability limit diagram on the display to find out the spindle rotation speed and depth of cut that realize highly efficient machining.

FIG. 2 shows an example of a stability limit diagram. The horizontal axis of the stability limit diagram represents the spindle rotation speed [rpm], the vertical axis represents the depth of cut [mm] of the tool, and the critical curve indicates the boundary between the stable region and the unstable region of the regenerated chatter vibration. In this stability limit diagram, black circles indicate processing conditions in which chatter vibration is likely to occur, and white circles indicate processing conditions in which chatter vibration is unlikely to occur. The rotation speed region with high chatter vibration stability is called a "stable pocket", and the higher the rotation speed, the wider the stable pocket. For example, in the manufacture of airframe parts for aircraft that cut out a large amount of materials such as aluminum alloys at high speed, a stability limit diagram that correctly shows the position of the stability pocket is necessary for setting highly efficient machining conditions.

"Mechanism and Suppression of Chatter Vibration in Cutting", Eiji Shamoto, Electric Steel, Vol. 82, No. 2 (2011) pp.143-155

As disclosed in Non-Patent Document 1, the rotation speed corresponding to the stable pocket is related to the resonance frequency in the compliance transfer function, and in cutting with a multi-blade tool such as milling, the resonance frequency is used as the tool. It is known that the value is divided by the number of blades and an integer of 1 or more. Therefore, in order for the stable pocket of the stability limit diagram to show the accurate rotation speed, it is necessary that the resonance frequency in the compliance transfer function matches the resonance frequency at the time of spindle rotation.

However, the compliance transfer function measured with the spindle stationary does not always match the compliance transfer function when the spindle is actually rotating. When the spindle rotates (especially at high speed), the preload of the bearing changes due to centrifugal force and thermal deformation, so the resonance frequency shifts between when the spindle is stationary and when it is rotating, and the vibration characteristics change.

Also, when the rotary tool is replaced, the compliance transfer function may change before and after the replacement. For example, when a rotary tool is replaced by an automatic tool changing device, if the contact state changes as compared with that before the replacement, the contact rigidity and the friction damping at the contact portion will be different before and after the replacement. In addition, the resonance frequency of the mechanical structure gradually changes as the moving parts wear due to aging of the mechanical structure.

As mentioned above, the number of revolutions corresponding to the stable pocket is determined by the resonance frequency in the compliance transfer function. Therefore, if the resonance frequency during actual spindle rotation deviates from the resonance frequency in the compliance transfer function, the position of the stability pocket in the stability limit diagram is not accurate, and the operator selects machining conditions that can cause chatter vibration. There is a possibility of doing so. Therefore, it is desired to develop a technique for measuring changes in the vibration characteristics of the mechanical structure of a machine tool.

The present disclosure has been made in view of these circumstances, and an object of the present disclosure is to provide a technique for measuring changes in the vibration characteristics of the mechanical structure of a machine tool.

In order to solve the above problems, one aspect of the present invention relates to a method of measuring a change in vibration characteristics of a machine tool having a rotating mechanism of a spindle to which a cutting tool or a work material is attached. This method includes a step of maintaining the resonance frequency of the mechanical structure, a step of rotating the spindle at a frequency near the resonance frequency held during cutting, and a step of rotating the spindle, and a plurality of different rotations. It has a step of acquiring a forced vibration response of a mechanical structure when the spindle is rotated by a number, and a step of deriving at least one of a change amount of resonance frequency and a magnitude of attenuation from a plurality of acquired forced vibration responses.

Another aspect of the present invention relates to a device for measuring changes in the vibration characteristics of a machine tool having a rotating mechanism of a spindle to which a cutting tool or a work material is attached. This measuring device has a resonance frequency holding unit that holds the resonance frequency of the mechanical structure and a mechanical structure when the mechanical structure is vibrated at a plurality of different frequencies near the holding resonance frequency during cutting of the machine tool. It is provided with a vibration response acquisition unit that acquires the forced vibration response of the above, and a change amount derivation unit that derives at least one of the change amount of the resonance frequency and the magnitude of the attenuation from the acquired plurality of forced vibration responses.

It should be noted that any combination of the above components and the conversion of the expressions of the present disclosure between methods, devices, systems and the like are also effective as aspects of the present disclosure.

According to the present disclosure, it is possible to provide a technique for measuring changes in the vibration characteristics of the mechanical structure of a machine tool.

It is a figure which shows the block diagram of the cutting process. This is an example of a stability limit diagram. It is a figure which shows the functional block of a processing system. It is a figure which shows the example of the compliance transfer function measured by the hammering test. (A) shows the relationship between the cutting force and the angle of rotation generated when machining with a rotary tool, and (b) is a diagram showing the cutting force in the frequency domain obtained by Fourier transforming the periodic waveform of the cutting force. It is a figure which shows the displacement amount derived for each frequency component.

FIG. 3 shows a functional block of the processing system 1 of the embodiment. The machining system 1 includes a machine tool 2 provided with a rotation mechanism for rotating a spindle to which a cutting tool or a work material is attached, a measuring device 3 for measuring changes in vibration characteristics of the machine structure of the machine tool, and a compliance transmission function. It is provided with a stability limit diagram creating device 4 that creates a stability limit diagram using a resonance frequency. In the embodiment, the measuring device 3 and the stable limit diagram creating device 4 are shown as a configuration separated from the machine tool 2, respectively, but at least one of the measuring device 3 and the stable limit diagram creating device 4 has a function of the machine tool 2. It may be incorporated in the machine tool 2.

The vibration sensor 5 outputs vibration data indicating a forced vibration response when the mechanical structure of the machine tool 2 is vibrated to the measuring device 3. The vibration sensor 5 may be a gap sensor that detects vibration displacement, an acceleration sensor that detects the acceleration of vibration, or a speed sensor (for example, a laser Doppler speedometer) that detects the speed of vibration. Further, the vibration sensor 5 may be a sensor that measures physical quantities (force, torque, motor current, strain, sound, etc.) for estimating vibration. The measuring device 3 includes a resonance frequency holding unit 10, a rotation speed output unit 11, a vibration response acquisition unit 12, and a change amount derivation unit 13.

In FIG. 3, each element described as a functional block that performs various processes can be composed of a circuit block, a memory, and other LSIs in terms of hardware, and is loaded into the memory in terms of software. It is realized by a program or the like. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware only, software only, or a combination thereof, and is not limited to any of them.

FIG. 4 shows an example of the compliance transfer function measured by the hammering test. This compliance transfer function is acquired by the operator shaking the machine structure with a hammer while the spindle is stationary before the machine tool starts operation. In the compliance transfer function shown in FIG. 4, the resonance frequency is 1000 Hz. The resonance frequency holding unit 10 holds the value of the resonance frequency in the compliance transfer function. The resonance frequency holding unit 10 may hold the compliance transfer function itself, and in any case, it suffices to hold information that can identify that the resonance frequency is 1000 Hz.

In the embodiment, the measuring device 3 treats the cutting force generated when the machine tool 2 cuts the work material under the actual machining conditions or conditions close to the actual machining conditions as the exciting force for forcibly exciting the machine structure. , Identify changes in the vibrational properties of mechanical structures. The vibration sensor 5 outputs vibration data of the mechanical structure when the machine tool 2 is actually cutting to the measuring device 3, and the measuring device 3 changes the vibration characteristics based on the vibration data, specifically. Measures the amount of change in the resonance frequency. Hereinafter, a method for measuring changes in vibration characteristics when a multi-blade rotary tool such as an end mill tool is used will be described.

FIG. 5A shows an example of the relationship between the cutting force and the angle of rotation generated when machining with a rotary tool. The machine tool 2 of the embodiment has an ability to rotate a spindle at a rotation speed of tens of thousands of rpm, and is used for manufacturing aircraft body parts for cutting a large amount of a material such as an aluminum alloy at high speed. In this example, high-speed machining is performed in which the number of blades of the end mill tool is two, the spindle rotation speed is 30,000 rpm, the spindle rotation frequency is 500 Hz, and the blade passing frequency is 1000 Hz.

FIG. 5B shows the cutting force in the frequency domain obtained by Fourier transforming the periodic waveform of the cutting force shown in FIG. 5A. Since the passing frequency of the blade is 1000 Hz, the cutting force has a frequency component that is an integral multiple of 1000 Hz. Basically, the cutting force of frequency components other than an integral multiple of 1000 Hz is 0. This means that by setting the spindle rotation speed to 30000 rpm, the mechanical structure of the machine tool 2 is vibrated by the fundamental frequency component of 1000 Hz and its harmonic component during cutting.

The vibration sensor 5 detects vibration data when a vibrating force including a fundamental frequency component of 1000 Hz and a harmonic component thereof forcibly vibrates the mechanical structure, and outputs the vibration data to the measuring device 3. The vibration data detected by the vibration sensor 5 may be recorded in a memory (not shown) during the cutting process and supplied to the measuring device 3 after the cutting process is completed.

In the embodiment, the fundamental frequency of the cutting force when the spindle rotation speed is 30000 rpm corresponds to the resonance frequency in the compliance transfer function shown in FIG. Therefore, if the resonance frequency of the compliance transfer function is close to the resonance frequency at the time of spindle rotation, the vibration of the mechanical structure is dominated by the fundamental frequency of the cutting force, and the measurement is easy. To be precise, frequency analysis (generally Fourier transform) may be performed to evaluate the magnitude of vibration of a component close to the resonance frequency of interest.

In cutting, it is known that even if the cutting speed changes a little, the cutting force does not change significantly. Therefore, even if the spindle speed is slightly changed, the cutting force shown in FIG. 5A is obtained unless other machining conditions, that is, the feed amount per blade, the axial depth of cut, and the radial depth of cut are changed. The periodic waveform hardly changes. Therefore, when the spindle speed is changed in the vicinity of 30,000 rpm, the cutting force of an integral multiple component of the passing frequency of the blade shown in FIG. 5B does not change in amplitude but only in frequency.

For example, when the spindle speed is 28500 rpm, the amplitude of the component once the passing frequency of the blade remains at about 106 N, and the frequency becomes 950 Hz. The same applies to the double component of the passing frequency of the blade. When the spindle speed is 28500 rpm, the amplitude of the double component of the passing frequency of the blade remains about 68 N, and the frequency becomes 1900 Hz. That is, the amplitude of the cutting force of the N times component of the passing frequency of the blade does not change, and the frequency becomes (950 × N) Hz. Therefore, when the machine tool 2 rotates the spindle at 28500 rpm, it cuts the work material with the same amplitude cutting force as when it is rotated at 30000 rpm, and with the exciting force including the fundamental frequency component of 950 Hz and its harmonic component. , The mechanical structure can be forced to vibrate.

The same applies when the spindle rotation speed is increased. When the spindle rotation speed is 31500 rpm, the amplitude of the 1x component of the blade passing frequency remains at about 106N, and the frequency becomes 1050Hz, which is twice the blade passing frequency. The frequency remains 2100Hz while the amplitude remains about 68N. That is, the amplitude of the cutting force of the N times component of the passing frequency of the blade does not change, and the frequency becomes (1050 × N) Hz. Therefore, when the machine tool 2 rotates the spindle at 31500 rpm, it cuts the work material with the same amplitude cutting force as when it is rotated at 30000 rpm, and with the exciting force including the fundamental frequency component of 1050 Hz and its harmonic component. , The mechanical structure can be forced to vibrate.

In the embodiment, utilizing the fact that the machine tool 2 can rotate the spindle at high speed, the passing frequencies of a plurality of different blades are set in the vicinity of the resonance frequency of the compliance transfer function, and the machine of the machine tool 2 The structure is vibrated at a frequency near the resonance frequency. The measuring device 3 acquires vibration data from the vibration sensor 5 and measures the resonance frequency in the mechanical structure during operation.

The reasons why the resonance frequency shown in FIG. 4 and the resonance frequency in the mechanical structure during operation do not match are the change in the preload of the bearing when the spindle is stationary and when it is rotated, the secular change in the mechanical structure, and the replacement of the rotating tool. The change of the contact state due to the above can be mentioned. Even if machine tools, holders, and tools of the same model number are used, if any or all of them change, the resonance frequency will change due to individual differences (particularly differences in contact states).

On the other hand, even if it is said that the resonance frequency in the mechanical structure at rest and the resonance frequency in the mechanical structure at operation do not match, it is considered that the difference is small and the shape of the vibration mode hardly changes. The rigidity of the cutting process (a phenomenon in which the cutting process acts as additional rigidity because the cutting force in the direction of pushing back the tool increases as the depth of cut increases) also contributes to the change in resonance frequency (usually increased). The impact will be described later.

Utilizing this fact, in the machining system 1, the machine tool 2 rotates the spindle at a plurality of different rotation speeds that vibrate the machine structure at a frequency near the resonance frequency in the compliance transmission function, and the measuring device 3 has a plurality of measurement devices 3. The forced vibration response when the mechanical structure is vibrated by the excitation force of different frequencies is acquired, and the amount of change in the resonance frequency is derived from the acquired plurality of forced vibration responses. The measuring device 3 may derive the magnitude of attenuation (for example, attenuation ratio) of the vibration mode of interest from the change in compliance near the resonance frequency.

During the cutting process, the vibration sensor 5 acquires vibration data indicating a forced vibration response of the mechanical structure. On the premise that the vibration mode in the mechanical structure is known, it is preferable that the vibration sensor 5 is fixed at a position that is not a node of the vibration mode and does not interfere with actual machining. When the vibration response acquisition unit 12 acquires the vibration data from the vibration sensor 5, the vibration response acquisition unit 12 may estimate the amplitude of each position (including the machining point of the tool tip) of the vibration mode based on the known vibration mode.

When measuring the change in vibration characteristics, the rotation speed output unit 11 outputs the spindle rotation speed set in the machine tool 2. The rotation speed output unit 11 displays the spindle rotation speed to be set on the display, and the operator may set the spindle rotation speed in the machine tool 2 by looking at this display. The rotation speed output unit 11 derives the spindle rotation speed so as to provide an exciting force to the mechanical structure in the vicinity of the resonance frequency held by the resonance frequency holding unit 10. Hereinafter, an example of the relationship between a plurality of different spindle rotation speeds to be derived and the fundamental frequency of the cutting force according to the spindle rotation speed will be shown.
・ 27000rpm-900Hz
・ 27750rpm − 925Hz
・ 28500rpm − 950Hz
・ 29250rpm − 975Hz
・ 30000rpm-1000Hz
・ 30750rpm-1025Hz
・ 31500rpm − 1050Hz
・ 32250rpm-1075Hz
・ 33000rpm-1100Hz

The rotation speed output unit 11 provides the mechanical structure with an excitation force having a frequency within a range of 0.9 times or more and 1.1 times or less of the resonance frequency as an excitation force in the vicinity of the resonance frequency. It is preferable to derive. In this example, the rotation speed output unit 11 derives nine spindle rotation speeds, but a spindle rotation speed of 10 or more may be derived within a predetermined range before and after the resonance frequency.

The operator sets the spindle rotation speed displayed on the display by the rotation speed output unit 11 in the machine tool 2, and the machine tool 2 rotates the spindle at the set rotation speed. In the above example, the operator sets nine spindle speeds in the machine tool 2 in nine cutting steps. If the spindle rotation speed may be changed during one cutting process, the operator can change the spindle rotation speed in the order of 27000 rpm, 27750 rpm, 28500 rpm, 29250 rpm, 30000 rpm, 30750 rpm, 31500 rpm, 32250 rpm, 33000 rpm during one cutting process. The machine tool 2 may be set to change the spindle rotation speed.

The vibration response acquisition unit 12 acquires the forced vibration response of the mechanical structure from the vibration sensor 5 when the mechanical structure is vibrated at a plurality of different frequencies near the resonance frequency during the cutting process of the machine tool 2. When the measurement function by the measuring device 3 is incorporated in the machine tool 2, the machine tool 2 autonomously sets the rotation speed output from the rotation speed output unit 11 as the spindle rotation speed and acquires the vibration response. The forced vibration response of the mechanical structure when the unit 12 rotates the spindle at a plurality of different rotation speeds may be acquired from the vibration sensor 5. The change amount deriving unit 13 has a function of deriving at least one of the change amount of the resonance frequency and the magnitude of attenuation from the acquired forced vibration response at a plurality of rotation speeds.

When monitoring aging in the process of repeating the same machining, set the parts to be machined at multiple different spindle speeds in the machining program during the machining, and measure them according to the machining timing. The device 3 may automatically measure the resonant vibration response of the mechanical structure. In that case, it is desirable that the machining conditions other than the spindle speed are the same in the machining of the portion to be measured.

First, the machine tool 2 rotates the spindle at 27,000 rpm, and vibrates the mechanical structure of the machine tool 2 with a fundamental frequency component of 900 Hz and a harmonic component thereof. The vibration sensor 5 detects vibration data indicating a forced vibration response of the vibrated mechanical structure, and the vibration response acquisition unit 12 acquires the vibration data. The change amount deriving unit 13 derives the displacement amount with respect to the fundamental frequency component of 900 Hz and its harmonic component from the vibration data. This displacement amount is a value that substantially depends on the fundamental frequency component of 900 Hz, which is close to the resonance frequency. To be precise, it is desirable to perform Fourier transform to extract the amount of displacement due to the frequency component of 900 Hz.

Next, the machine tool 2 rotates the spindle at 27750 rpm, and vibrates the mechanical structure of the machine tool 2 with a fundamental frequency component of 925 Hz and a harmonic component thereof. The vibration sensor 5 detects vibration data indicating a forced vibration response of the vibrated mechanical structure, and the vibration response acquisition unit 12 acquires the vibration data. The change amount deriving unit 13 derives the displacement amount with respect to the fundamental frequency component of 925 Hz and its harmonic component from the vibration data. This displacement amount is a value that substantially depends on the fundamental frequency component of 925 Hz, which is close to the resonance frequency. To be precise, it is desirable to perform Fourier transform to extract the amount of displacement due to the frequency component of 925 Hz.

After that, the machine tool 2 rotates the spindle at 28500 rpm, 29250 rpm, 30000 rpm, 30750 rpm, 31500 rpm, 32250 rpm, and 33000 rpm, and the change amount deriving unit 13 derives the displacement amount from the vibration data detected at each rotation speed.

FIG. 6 shows the displacement amount derived for each frequency component. The change amount deriving unit 13 specifies the frequency at which the vibration displacement peaks based on the displacement amount derived from the plurality of forced vibration responses. In this example, the vibration displacement of 975 Hz is the peak, but the rotation speed output unit 11 further outputs the spindle rotation speed near 29250 rpm, the operator sets it in the machine tool 2, and the change amount derivation unit 13 vibrates. A more accurate peak frequency may be derived from the forced vibration response acquired by the acquisition unit 12. This peak frequency is the resonance frequency of the mechanical structure when the spindle rotates, and the change amount derivation unit 13 calculates the change amount of the resonance frequency (1000 Hz) held by the resonance frequency holding unit 10. The amount of change may be calculated as the magnification of change, that is, (specified peak frequency / retained resonance frequency), and in this example, it is derived that the resonance frequency has become 975/1000 times.

変化量導出部１３は、変位量がピーク周波数ｆｐ（975Ｈｚ）の変位量の√２分の１倍になる２つの周波数を特定して、その幅Δｆを導出することで、上記式から減衰比ζを算出してよい。 The change amount deriving unit 13 may derive the magnitude of the damping of the vibration mode. The change amount deriving unit 13 may identify the attenuation ratio as the magnitude of attenuation by, for example, the half-value width method. In the full width at half maximum method, the attenuation ratio ζ is approximately calculated by the following equation from the frequency width Δf at which the magnitude of vibration (displacement amount in this case) is √ 1/2 times the peak value and the peak frequency fp. It is known that it can be calculated.

The change amount deriving unit 13 identifies two frequencies whose displacement amount is √ 1/2 times the displacement amount of the peak frequency fp (975 Hz), and derives the width Δf from the above equation to obtain an attenuation ratio. ζ may be calculated.

The change amount deriving unit 13 may update the resonance frequency held by the resonance frequency holding unit 10 with a specified peak frequency, and supply the derived change amount to the stability limit diagram creating device 4. The stability limit diagram creation device 4 multiplies the created stability limit diagram by the change magnification (975/1000) in the horizontal axis direction to obtain a stability limit diagram in which the position of the stability pocket is accurate. You may recreate it. When the change amount deriving unit 13 also supplies the attenuation ratio ζ to the stable limit diagram creating device 4, the stable limit diagram creating device 4 may recreate the stable limit diagram that also reflects the change in attenuation.

In the embodiment, the processing for measuring the change in the characteristics of the mechanical structure may be performed for the purpose of measuring the change in the compliance transfer function, or may be the processing performed in actual production. In the latter case, processing is performed at the passing frequencies of multiple different blades near the frequency of interest (resonance frequency of the vibration mode for which you want to monitor changes), and the peak value of the forced vibration response is detected with the required frequency resolution. It is preferable to change the passing frequency of the blade. At that time, it is desirable that the machining conditions (cutting amount in the axial direction and the radial direction, the feed amount per blade) are the same. If the machining conditions are different, the cutting force analysis may be used to predict and correct how much the excitation force amplitude value of the n-fold component to be used differs under those different conditions.

The present invention has been described above based on the embodiments. This embodiment is an example, and it will be understood by those skilled in the art that various modifications are possible for each of these components and combinations of each processing process, and that such modifications are also within the scope of the present disclosure. .. In the embodiment, a method for measuring the change in vibration characteristics when a multi-blade rotary tool is used is shown, but the change in vibration characteristics when a single-flute rotary tool is used can also be measured in the same manner.

The vibration sensor 5 may be an acceleration sensor arranged near the fixed side of the bearing near the machining point in the spindle. The detection direction by the accelerometer may be two radial directions of the main axis, one of them, or three directions in which an axial direction is added. Further, the vibration sensor 5 is based on the current value of the motor that drives the feed shaft / spindle of the machine tool 2, the position calculated from the encoder signal of each shaft, the position deviation obtained by subtracting the target position from that position, and the difference between the front and rear positions. It may be a sensor that measures a physical quantity for indirectly estimating vibration, such as a required speed.

In the embodiment, the case where the resonance frequency (1000 Hz) of the target mechanical structure is in the vicinity of one component of the passing frequency of the blade has been described, but the mechanical structure can be forcibly vibrated at a level that can be detected by frequency analysis. If possible, it may be in the vicinity of any N-fold component.

As described in the embodiment, during cutting, the cutting process acts as additional rigidity (the value obtained by multiplying the specific cutting resistance in the cutting thickness direction by the cutting width), so that the resonance frequency of the mechanical structure is slightly increased. Is known to change (usually increase). However, in general, the rigidity of the cutting process is very small compared to the rigidity of the mechanical structure. If they are equivalent, the reduction in cutting thickness (calculated by dividing the cutting force by the stiffness of the machine structure) and the actual cutting thickness (calculated by dividing the cutting force by the stiffness of the cutting process). ) Is equivalent, and only about half of the set cutting thickness can be cut. Cutting is usually the cut thickness because it is the process of transferring the movement of the machine tool to the machined surface to create an accurate shape by removing the material with an actual cut thickness that is approximately equal to the set cut thickness. It is carried out under conditions where the amount of reduction is negligible (specifically, a condition in which a high-rigidity mechanical structure is used and the cutting width is not too large). That is, the rigidity of the cutting process is usually much smaller than the rigidity of the mechanical structure, and the amount of change in the resonance frequency of the mechanical structure due to the addition thereof can be ignored. However, for more accurate identification, the resonance frequency may be estimated in consideration of the influence by measuring or estimating the rigidity of the cutting process.

The outline of the aspects of the present disclosure is as follows. One aspect of the present disclosure relates to a method of measuring changes in the vibration characteristics of the mechanical structure of a machine tool provided with a rotating mechanism of a spindle to which a cutting tool or a work material is attached. The method of measuring the change in vibration characteristics is a step of maintaining the resonance frequency of the mechanical structure and a step of rotating the spindle at a rotation speed for vibrating the mechanical structure at a frequency near the retained resonance frequency during cutting. And, from the step of acquiring the forced vibration response of the mechanical structure when the spindle is rotated at a plurality of different rotation speeds, and from the acquired plurality of forced vibration responses, at least one of the change amount of the resonance frequency and the magnitude of the attenuation is obtained. It has steps to derive.

According to this aspect, by forcibly vibrating the mechanical structure at a frequency near the retained resonance frequency, at least one of the change amount of the resonance frequency and the magnitude of attenuation can be measured relatively easily. The derived amount of change in resonance frequency and / or the magnitude of attenuation may be used to derive the stability limit diagram. This makes it possible to derive a stability limit diagram that matches changes in vibration characteristics.

The step of deriving at least one of the amount of change in the resonance frequency and the magnitude of the attenuation may include a step of identifying at least one of the frequency at which the vibration displacement peaks and the attenuation ratio from the plurality of forced vibration responses. The amount of change may be calculated as (specified frequency / retained resonance frequency).

Another aspect of the present disclosure relates to an apparatus for measuring changes in the vibration characteristics of the mechanical structure of a machine tool provided with a rotating mechanism of a spindle to which a cutting tool or a work material is attached. This measuring device includes a resonance frequency holding unit that holds the resonance frequency of the mechanical structure, and a machine that vibrates the mechanical structure at a plurality of different frequencies near the holding resonance frequency during cutting of the machine tool. It includes a vibration response acquisition unit that acquires the forced vibration response of the structure, and a change amount derivation unit that derives at least one of the change amount of the resonance frequency and the magnitude of attenuation from the acquired plurality of forced vibration responses.

According to this aspect, by forcibly vibrating the mechanical structure at a frequency near the retained resonance frequency, at least one of the change amount of the resonance frequency and the magnitude of attenuation can be measured relatively easily.

1 ... Machining system, 2 ... Machine tool, 3 ... Measuring device, 4 ... Stability limit diagram creation device, 5 ... Vibration sensor, 10 ... Resonance frequency holding unit, 11. .. Rotation speed output unit, 12 ... Vibration response acquisition unit, 13 ... Change amount derivation unit.

Claims (6)

A method of measuring changes in the vibration characteristics of the mechanical structure of a machine tool equipped with a spindle rotation mechanism to which a cutting tool or work material is attached.
Steps to maintain the resonance frequency of the mechanical structure,
At the time of cutting, the step of rotating the spindle at the number of rotations that vibrates the mechanical structure at a frequency near the retained resonance frequency, and
The step of acquiring the forced vibration response of the mechanical structure when the spindle is rotated at a plurality of different rotation speeds, and
A step of deriving at least one of the amount of change in the resonance frequency and the magnitude of attenuation from the acquired multiple forced vibration responses,
A method for measuring a change in vibration characteristics. The step of deriving at least one of the change amount of the resonance frequency and the magnitude of the attenuation includes a step of identifying at least one of the frequency at which the vibration displacement peaks and the attenuation ratio from the plurality of forced vibration responses.
The method for measuring a change in vibration characteristics according to claim 1. The amount of change in the resonance frequency is calculated as (specified frequency / retained resonance frequency).
The method for measuring a change in vibration characteristics according to claim 2. At least one of the derived resonance frequency change amount and attenuation magnitude is used to derive the stability limit diagram.
The method for measuring a change in vibration characteristics according to any one of claims 1 to 3. A device that measures changes in the vibration characteristics of the mechanical structure of a machine tool equipped with a spindle rotation mechanism to which a cutting tool or work material is attached.
Resonance frequency holding part that holds the resonance frequency of the mechanical structure,
A vibration response acquisition unit that acquires a forced vibration response of the machine structure when the machine structure is vibrated at a plurality of different frequencies near the resonance frequency held during cutting of the machine tool.
A change amount derivation unit that derives at least one of the change amount of the resonance frequency and the magnitude of attenuation from the acquired multiple forced vibration responses,
A measuring device characterized by being provided with. For computers that measure changes in the vibration characteristics of the mechanical structure of machine tools equipped with a spindle rotation mechanism to which a cutting tool or work material is attached.
A function to acquire the forced vibration response of the machine structure when the machine structure is vibrated at a plurality of different frequencies near the resonance frequency in the compliance transfer function during cutting of the machine tool.
A function to derive at least one of the amount of change in resonance frequency and the magnitude of attenuation from the acquired multiple forced vibration responses,
A program to realize.

Images