JP2020080015A - Monitoring apparatus and monitoring method - Google Patents

Abstract

To provide a monitoring apparatus and so on which can easily estimate vibration characteristics and a cutting force of a mechanical structure, based on a result of vibration measured upon actual cutting, without using a force sensor and but only with a vibration sensor.SOLUTION: A monitoring apparatus 1 according to the present invention has a control device 4 connected to an acceleration sensor 2 for monitoring at least one of vibration characteristics and cutting force of an NC milling machine having a main shaft P with the acceleration sensor 2. The acceleration sensor 2 measures vibration when the main shaft P is rotated at a plurality of rotation speeds for cutting to obtain vibration measurement results for each rotation speed. A cutting force component for a plurality of dimensions is temporarily determined and each frequency component in vibration fluctuation is removed by the cutting force component. Thus, a compliance transmission function for the vibration characteristics is calculated by the frequency component, and an error as an evaluation value for the error is calculated from a calculated estimation value of the function. Thus, the cutting force component is repeatedly temporarily determined until the error becomes a predetermined value or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a monitoring device that monitors vibration characteristics and cutting force of machines such as machine tools, and a monitoring method that can be executed by the monitoring device.

In order to perform highly efficient and highly accurate cutting with a machine tool, it is necessary to select appropriate cutting conditions in consideration of the vibration characteristics and cutting force of the machine structure. If the rigidity, which is one of the vibration characteristics, is insufficient, chatter vibration occurs, which deteriorates the finished surface property and the tool life, and the tool or the work (work) bends to deteriorate the dimensional accuracy. On the other hand, the cutting force not only affects the cutting power, but also causes vibration and bending as in the case of the vibration characteristics, or causes tool loss when the cutting force is excessive.
The vibration characteristics of the machine tool can be obtained by using an actually measured value by an impulse response method or a simulation, as described in [0012] of Patent Document 1 (JP-A-2014-221510). , It is specified by selecting a vibration characteristic that is considered to be close to the vibration characteristic of the target machine tool from the existing vibration characteristics. The cutting force is measured by a dynamometer.

JP, 2014-221510, A

Whether the vibration characteristics are actually measured or simulated, or similar ones are selected from existing vibration characteristics, specialized techniques and knowledge are required, which is troublesome. ..
On the other hand, a dynamometer for measuring cutting force is very expensive, and if it is attached to a machine tool as a production facility, interference with the dynamometer and wiring will occur and the rigidity of the machine tool will decrease. To relax. Therefore, the dynamometer is currently rarely used in production sites.
Therefore, the present disclosure can use a measurement result of vibration during actual cutting, and can easily estimate a vibration characteristic and a cutting force of a mechanical structure without using a force sensor only by a vibration sensor or a monitoring device. The purpose is to provide a method.

In order to achieve the above object, the present disclosure is a monitoring device for monitoring at least one of a vibration characteristic and a cutting force in a machine having a rotating part, the rotating speed controlling a rotating speed of the rotating part. The control unit includes a control unit, a sensor attached to the machine, and a control unit connected to the sensor. The rotation speed control unit changes the rotation speed of the rotating unit within a predetermined range to perform the control. The means, by the sensor, to measure the vibration at the time of cutting by rotating the rotating portion at a plurality of the rotation speed, to obtain a vibration measurement result for each of the rotation speed, the cutting force according to a plurality of orders. A component is provisionally determined, and each frequency component of the vibration measurement result is divided by the provisionally determined cutting force component to calculate each frequency component of the transfer function related to the vibration characteristic, and the estimated transfer function is calculated. The evaluation value for the error from the value is calculated, the cutting force component is tentatively re-determined until the evaluation value becomes a predetermined value or less, and the cutting force when the evaluation value becomes the predetermined value or less At least one of the ratio of the components and the ratio of each frequency component of the transfer function is preferably used for identifying at least one of the cutting force and the vibration characteristic of the machine.
Further, the present disclosure is a monitoring method for monitoring at least one of a vibration characteristic and a cutting force in a machine having a rotating part by a computer, wherein a plurality of the rotating parts are detected by a sensor attached to the machine. The vibration at the time of cutting by rotating at the rotation speed is measured, and the vibration measurement step of acquiring the vibration measurement result for each of the rotation speeds and the cutting force component relating to a plurality of orders are provisionally determined, and the vibration measurement result. By dividing each frequency component of the above by the tentatively determined cutting force component, a transfer function frequency component calculating step of calculating each frequency component of the transfer function related to the vibration characteristic, and calculating an estimated value of the calculated transfer function. A transfer function estimation value calculation step, an evaluation value calculation step of calculating an evaluation value for an error from the calculated estimation value, and the cutting force component is tentatively calculated until the calculated evaluation value becomes a predetermined value or less. Redetermining, at least one of the ratio of the cutting force component and the ratio of each frequency component of the transfer function when the evaluation value becomes a predetermined value or less, the cutting force and the vibration characteristics of the machine It is desirable to have an error evaluation step used for at least one identification.

  According to the present disclosure, it is possible to use a measurement result of vibration during actual cutting, and it is possible to easily estimate a vibration characteristic and a cutting force of a mechanical structure without using a force sensor only by a vibration sensor or monitoring. A method is provided.

It is a schematic diagram of a machine tool (a vertical NC milling machine capable of end milling) equipped with a monitoring device according to the present invention. It is a block diagram showing the relationship between excitation force and vibration. 6 is a flowchart according to an operation example (monitoring method) of the monitoring device in FIG. 1. It is a graph which concerns on the frequency analysis result over the harmonic components from the 1st order to the 10th order of the vibration displacement in the range of the rotation speed of the main shaft. It is a graph relating to the compliance transfer function calculated from the tentatively determined cutting force and the measured vibration displacement, and the evaluation value of the error from the estimated value is not less than a predetermined value and the variation of the compliance transfer function is large. Is a graph for the case where the upper part is the real part and the lower part is the imaginary part. It is a partially expanded view of FIG. 5 (real part). It is a graph of the compliance transfer function on a complex plane at a certain frequency (750 Hz). It is a graph of the ratio of the cutting force component for each order when it is determined that the variation of the compliance transfer function is small. 6 is a graph in which the vertical axis represents the ratio of compliance transfer function components when it is determined that the variation in the compliance transfer function is small, and the horizontal axis represents frequency. It is a graph which concerns on the example of the estimated cutting force. 9 is a graph relating to a ratio of a compliance transfer function component identified by a modified example and represented by a real part imaginary part. 7 is a graph relating to a ratio of a compliance transfer function component identified by a modification, which is represented by an amplitude phase. It is a graph which concerns on the ratio of the cutting force component for every order identified by the modification. It is a graph which concerns on the cutting force waveform with respect to the tool rotation angle estimated using the inverse Fourier transform from each order component of the cutting force identified by the modification.

  Hereinafter, embodiments and operation examples according to the present invention will be described with reference to the drawings as appropriate. The present invention is not limited to the following embodiments and operation examples.

<<Overall structure>>
FIG. 1 is a schematic view of a machine tool (a vertical NC milling machine J capable of end milling) as an example of a machine equipped with a monitoring device 1 according to the present invention.
The NC milling machine J is capable of mounting a spindle P (rotating portion) on which an end mill V is mounted, a spindle head H that rotatably supports the spindle P, a column C that supports the spindle head H, and a work W. A work table Q and a table T are provided.
The end mill V is mounted so that its central axis is along the vertical direction (Z-axis direction).
The work table T includes a work feeding mechanism D that feeds the work W in the X-axis direction and the Y-axis direction that are orthogonal to the Z-axis direction and are orthogonal to each other.
In order to make the description easy to understand, it is assumed that the work table Q easily vibrates in one direction (Y-axis direction).
Further, although not necessary for the configuration of the monitoring device 1, for convenience of explanation, it is assumed that the dynamometer O is installed between the work table Q and the table T.

The monitoring device 1 is electrically connected to the acceleration sensor 2 attached to the work table Q (adjacent to the processing point, the work side) and the acceleration sensor 2 and is capable of performing various calculations and commands. Control means, computer).
The acceleration sensor 2 is capable of measuring the acceleration of the work table Q, and here, it is assumed that at least the vibration in the Y-axis direction can be measured. In place of or together with the acceleration sensor 2, a microphone for measuring sound pressure, a displacement sensor, a speed sensor, a motor (not shown) for rotating the main shaft P, or a motor (not shown) for driving each feed mechanism. At least one of a current value (torque), a rotational position (a speed may be used, or a deviation from a command value may be used) or the like may be used.
The control device 4 also serves as rotation speed control means for controlling the rotation speed of the spindle P. The control device 4 also serves as a feed control unit that controls the feed amount of the work W in the work feed mechanism D. At least one of the rotation speed control means, the feed control means, and the control device 4 may be separately configured in a state of being electrically connected to each other.

<<Monitoring of vibration characteristics and cutting force>>
FIG. 2 is a block diagram showing the relationship between the excitation force and the vibration.
In a general end milling process, the fluctuation of the cutting force due to intermittent cutting becomes the exciting force F, and the product with the vibration characteristic G of the mechanical structure becomes the vibration X (displacement, speed, acceleration, etc.) generated during the cutting process. The exciting force F, the vibration characteristic G, and the vibration X may represent the amplitude and phase as a complex number, or may represent only the amplitude as a real number. In addition, the "cutting force" may include the cutting torque, and the "vibration" may include the fluctuation of the current value and the fluctuation of the rotational position.

In other words, each frequency component of the vibration generated during cutting is the frequency component of the input cutting force and the frequency component of the transfer function (compliance, mobility, inertance, etc.) that is one of the vibration characteristics. Product. The transfer function may be input with the cutting torque instead of the cutting force, or may be output with changes in the motor current value, rotational position, etc., instead of the displacement, speed, and acceleration.
Based on this, the monitoring device 1 estimates the vibration characteristic (compliance) and the cutting force from the measurement result of the vibration during cutting measured by the acceleration sensor 2 as follows.
First, the monitoring device 1 drives the spindle P under a plurality of rotation speed conditions via the control device 4 to perform machining (for example, end mill machining) of a work. The rotation speed condition may be changed every time the machining is started and finished, or may be changed from one machining start to one end or a part thereof. Here, in order to prevent the feed amount and cutting thickness of each blade from changing, for example, when the number of rotations is doubled, the feed speed is also doubled. In such processing, the vibration amplitude of the fundamental wave at each rotation speed of the spindle P is extracted and plotted by frequency analysis (for example, Fourier transform) of the time change of vibration measured by the acceleration sensor 2. The plot is made to understand the characteristics of vibration of the NC milling machine J, and is unnecessary in actual monitoring.
Here, although the magnitude of the cutting force depends on the cutting thickness, it is considered that the influence of the rotation speed of the tool is small.Therefore, the plot result of the vibration amplitude with respect to the rotation speed is It is approximately equal to the output and has a shape similar to the plot shape of compliance against frequency. Further, by using the vibration amplitude of the higher harmonic in addition to the vibration amplitude of the fundamental wave, it is possible to densely estimate and plot the compliance characteristic with respect to the frequency under the condition that the rotation speed of the spindle P is smaller.

However, when the vibration amplitude of the harmonic is used, since the magnitude of the cutting force input differs for each order, the compliance characteristic cannot be directly plotted as it is.
Therefore, the monitoring device 1 separately estimates the ratio for each order related to the harmonic of the cutting force from the vibration measurement result.
That is, the monitoring device 1 selects two or more kinds of rotational speed conditions of the spindle P so that harmonics having different orders have the same frequency with respect to a certain frequency. The ratio of the magnitudes of vibrations obtained at these same frequencies is the ratio itself for each order related to the harmonics of the input cutting force. This is based on the fact that even if the orders are different, the frequencies are the same, and therefore the magnitudes of the compliances for amplifying the inputs are the same. The magnitude of the vibration may be estimated by interpolation or the like from the one obtained at a close frequency, instead of the one obtained at the frequency.
For example, by using a two-blade end mill V, the spindle P is rotated through the control device 4 under two conditions of 3750 min ⁻¹ (revolutions/minute) and 5000 min ⁻¹ , and vibration is obtained from the acceleration sensor 2 during machining. Then, the third harmonic of the frequency of the fourth harmonic and 5000 min ^-1 of 3750Min ^-1 is equal 500 Hz (hertz).
It is known that the effect of the cutting speed on the cutting force is small, and even if the rotation speed of the spindle P changes, if the feed speed changes at the same ratio, the cutting force change with respect to the rotation position is the same. You can consider that. That is, it may be approximately considered that the cutting force component that is an integral multiple of the rotation frequency is unchanged.

Therefore, the monitoring device 1 can obtain the ratio of the third harmonic wave to the fourth harmonic wave of the cutting force in the above-mentioned example by comparing the vibration amplitudes under the two kinds of rotation speed conditions, and in other cases as well. Similarly, the ratio of cutting force can be obtained. Further, the control device 4 can obtain the ratio of each order related to the harmonics of the cutting force by performing the same steps under the rotational speed conditions of the plurality of spindles P, and using the vibration amplitude of the higher harmonics. With a smaller change in the rotational speed condition of the spindle P, it is possible to closely estimate and plot the compliance characteristic with respect to frequency, and monitor the vibration characteristic.
Furthermore, as shown in FIG. 2, since there is a fixed relationship between the input cutting force, the vibration characteristic, and the output vibration, the monitoring device 1 is different in processing after the vibration characteristic is identified. It is also possible to estimate and monitor the cutting force without changing the rotation speed under different conditions, different work materials (workpieces), conditions in which chatter vibration occurs, and the like. Until the vibration characteristics are identified, only the rotation speed is changed under the same machining conditions, that is, the feed speed is changed along with the rotation speed, and the axial and radial cuts, the feed amount for each blade, and the cut thickness are Is kept constant. Further, since the acceleration sensor 2 is provided on the work side, the vibration characteristics change when the size or material of the work is changed. It is desirable that the vibration characteristics be re-identified.
That is, by using the vibration measurement results of a plurality of orders under a plurality of types of rotational speed conditions, the ratio of the components of each order of the cutting force and the ratio of each frequency component of the compliance transfer function are identified, and the vibration characteristics and the cutting force are identified. Can be monitored.
In general, in a machine tool, a tool is smaller than a work, closer to a cutting point, and a shape change due to cutting of the work is relatively large. Therefore, the acceleration sensor 2 includes a non-rotating portion (spindle head H Alternatively, it is desirable to be attached to the column C). In this case, it is desirable that the vibration characteristics be re-identified when the tool changes.

≪Specific examples or verification of monitoring≫
A specific example of monitoring of vibration and cutting force in the Y-axis direction in the NC milling machine J and its verification will be described with reference to FIG. In the following description, the processing step is abbreviated as S as appropriate.

Here, a case where a brass work W is made of cobalt high speed steel and is cut by an end mill V having a diameter of 20 mm (millimeter), a helix angle of 30° (deg), and a groove number of 2 will be described as an example.
The cutting conditions are as follows. The rotation speed (rotation speed) of the spindle P is 500 min ⁻¹ or more and 7500 min ⁻¹ or less, the cutting speed is 31 m/min (meter/minute) or more and 471 m/min or less, and the feed amount of the work feeding mechanism D is 0.1 mm for each blade. , The axial (Z-axis) direction incision is 1 mm, the radius (Y-axis) direction incision is 5 mm, the cutting method is down-cut, and no cutting oil is used.
Further, the cutting depth in the radial direction is set to be relatively small with respect to the diameter of the end mill V so that the cutting force is input to the higher harmonics as much as possible. Further, in order to avoid chatter vibration as much as possible, the cut in the axial direction is set to be relatively small.

  First, the monitoring device 1 rotates the spindle P under a plurality of rotation speed conditions through the control device 4, cuts the work W, and measures the vibrations of a plurality of orders by the acceleration sensor 2 (S1, vibration). Measurement step). Here, displacements (vibrations) of orders from the 1st to the 10th are measured. For reference, FIG. 4 shows a frequency analysis result of the displacement (Displacement, μm, micrometer) in the range of the rotational speed of the above-described main axis P over the first to tenth harmonic components. In FIG. 4, plots of the same order are given with the same combination of shape and filling, such as "●" and "●" or "○" and "○". That is, in FIG. 4, “●” and “◯” are the results of measurement with different orders even if the frequencies are the same. In FIG. 4, it can be confirmed that the displacement of the work table Q changes stepwise for each harmonic order. Note that the upper limit of the order to be measured is not limited to the tenth order, and may be appropriately changed to the ninth order or less or the eleventh order or more. Similarly, the lower limit is not limited to the first order.

Next, the monitoring device 1 tentatively determines the ratio of the cutting force for each order based on the vibration measurement results of the plurality of orders for the plurality of rotation speed conditions, and obtains the cutting force component for each frequency. Further, the displacement (vibration) component of each frequency component is divided by those cutting force components to calculate each frequency component of the compliance transfer function (S2, transfer function frequency component calculation step).
Specifically, the cutting force component for each order calculated from the provisionally determined ratio of the cutting force for each order is F _k , the displacement (vibration) component for each order is X _j,k , and the compliance transmission calculated from these When each order component of the function is G _j,k (μm/N, micrometer per Newton), these have the following relationship of [Equation 1]. Note that all these values are complex numbers.
In addition, j is a number added in ascending order to a plurality of rotation speed conditions, and k represents an order.

Here, the monitoring device 1 grasps the distribution according to the frequency in G _j,k as shown in FIG. 5 (the upper part is a real part and the lower part is an imaginary part (Imag. part)). By appropriately adding interpolation points, the compliance transfer function G _l,k including the interpolation points is _obtained . It should be noted that l is a number assigned to the frequency in ascending order, and G _l,k represents each frequency component of the compliance transfer function.
FIG. 6 is an enlarged view of a part of the real part of G _1,k in FIG. In FIG. 6, a black-filled plot represents G _j,k, and a difference in plot shape (hexagram, left-pointing triangle, rhombus, right-pointing triangle, pentagram) represents a difference in order k. For these black-painted plots, the monitoring device 1 connects the same shapes (same orders) with, for example, a straight line (indicated by a broken line in FIG. 6), and positions of frequencies at which other-order black-painted plots exist on the line. , Add interpolation points. In FIG. 6, the interpolation points are shown by outline plots having a shape corresponding to the order. In this way, the monitoring device 1 grasps the compliance transfer function G _l,k including the calculated interpolation point. Incidentally, some or all of the addition of the interpolation points may be omitted. In addition, the interpolation point may be determined by a method other than linear interpolation between adjacent plots.

Subsequently, the monitoring device 1 evaluates whether or not the calculated compliance transfer function G _l,k is a function whose variation is smaller than a predetermined threshold value, in the following manner, and thereby the cutting force and the vibration of the NC milling machine J are evaluated. Identify the value for the property.
First, the estimated value G _l,est of each frequency of the compliance transfer function is calculated (S3, transfer function estimated value calculation step). Here, as the estimated value G _l,est , an average value at each frequency of the compliance transfer function as shown in the following [Equation 2] is calculated.

Here, s _l and e _l represent the lower and upper limits of the order in which the compliance transfer function G _l,k exists at the l-th frequency.

Next, the monitoring device 1 calculates the evaluation value E of the error from the estimated value of the compliance transfer function G _l,k as shown in [Equation 4] using the evaluation function E _l,k of [Equation 3]. (S4, evaluation value calculation step).
Here, b indicates the number of frequency components of the compliance transfer function (upper limit of 1).
It should be noted that G _1,k to G _1,est are all complex numbers, and when the value of a certain frequency (750 Hz in FIG. 6) is considered on the complex plane as shown in FIG. 7, the evaluation function of [Equation 3] is obtained. E _{l, k} denotes the distance between the respective frequency components _{G l} compliance transfer _{function, k} the estimated value _{G l,} and _est.

The monitoring device 1 determines whether the evaluation value E of the error from the estimated value is equal to or less than a predetermined value (S5, error evaluation step), and the evaluation value E of the error from the estimated value is outside the predetermined range. When the evaluation value E of the error from the estimated value exceeds the predetermined value (FIGS. 4 and 5), it is determined that the variation of the compliance transfer function G _l,k is large (NO in S5). In this case, the ratio of the cutting force for each order is tentatively determined again based on the magnitude of the evaluation value E of the error from the estimated value, and it is determined that the variation in the compliance transfer function G _l,k is smaller than the predetermined threshold value. The steps of S2, S3, and S4 are repeated until it is reached.

If the cutting force component of each order is corrected so that the evaluation value E of the error from the estimated value becomes small, the monitoring device 1 identifies the correct ratio of the cutting force component and the ratio of the compliance transfer function component. be able to.
When the evaluation value E of the error from the estimated value becomes equal to or less than the predetermined value and it is determined that the variation of the compliance transfer function G _l,k is small (YES in S5), the absolute value (Ratio) of the ratio of the cutting force component for each order of cutting force harmonics, |F _n /F ₁ |) are identified as shown in FIG. 8, and FIG. 9 is obtained as the absolute value (Magnification, |G/G ₁ |) of the ratio of the compliance transfer function for each frequency. Here, G ₁ is displayed as G _l,k when l=1 and k=1. The shapes of the points plotted in these figures are the same as in FIG.

Further, the monitoring device 1 uses the current value information of the motor that rotates the spindle P and the motor that drives each feed mechanism, for example, to quantitatively identify the cutting force component and the compliance transfer function component (S6, quantification). Identification step). Incidentally, S6 may be omitted.
Since the cutting force component in the Y-axis direction, which is the same as the vibration to be measured, is quantified, it is possible to estimate the thrust force relatively easily, for example, from the motor current that drives the Y-axis feed mechanism, and start the processing of the estimated thrust force. The cutting force can be estimated as the difference between the front and back. However, the estimation of the thrust force by the motor current generally has poor frequency characteristics, and tends to allow more accurate estimation of low-frequency components.
Therefore, the monitoring device 1 preferably uses only low-order components to quantify the cutting force.
In the examples of FIGS. 4, 8 and 9, a value obtained by converting the measurement result of the acceleration sensor 2 into a displacement is used, and information related to the DC component (integral constant) is missing. When the displacement sensor is used instead of the acceleration sensor 2, the information of the DC component can be used, so the monitoring device 1 uses the average value of the thrust (DC component) to quantify the order component of the cutting force in the Y direction. Then, the compliance transfer function can also be obtained from the result as a vibration value (displacement [μm] in the figure) with respect to the unit cutting force.
In addition, the monitoring device 1 uses the inverse Fourier transform to calculate the cutting force (Cutting force, N) with respect to the rotation angle (Rotation angle, deg) of the main axis P from each order component of the identified cutting force, as shown in FIG. 10. Can also be estimated. In addition, the monitoring device 1 can also express the cutting force with respect to time by dividing the rotation angle (Rotation angle, deg) corresponding to the horizontal axis of FIG. 10 by the rotation angular velocity.

In addition, the monitoring device 1 acquires the information from the operator or the CAM about the detailed machining conditions such as the shape of the end mill V, the cutting in the radial direction, and the cutting in the axial direction, and combines it with the cutting force simulation. The above identification can be performed more accurately.
For example, even if the information on the DC component is missing in the vibration measurement, this can be supplemented. Alternatively, the rotational torque of the spindle P is estimated from, for example, the motor current, and the force in the X and Y directions at the cutting point is estimated from the average value of the torque (DC component) to obtain each of the X and Y direction cutting forces. It is possible to quantitatively obtain the order component and each frequency component of the compliance transfer function.
In FIG. 10, “Estimated” is the average of the rotational torque of the spindle P estimated from the motor current by combining the detailed machining conditions and the cutting force simulation as described above, supplementing the information of the DC component missing in the vibration measurement. The estimated cutting force is shown by quantifying the Y-direction cutting force component from the value (DC component). The estimated cutting force is in good agreement with the cutting force measured by the dynamometer O indicated by "Measured".

The monitoring apparatus 1 may use the following [Equation 5] instead of [Equation 3] in which all the compliance transfer functions G _l,k are equally used in S4.
In [Equation 3], since the compliance transfer function G _l,k near the resonance frequency of the mechanical system is likely to have a relatively large error, in [Equation 5] the compliance transfer function G _l,k near the resonance frequency _. Weighting is applied to _{k so} that its influence is small. That is, by dividing the evaluation function E _l,k by the absolute value of the estimated value of the compliance transfer function that increases near the resonance frequency, the influence of the error near the resonance frequency is reduced.
In addition, it is also possible to predict the resonance frequency from the tendency of the absolute value of the compliance transfer function or the phase and to weight using the predicted resonance frequency.

The monitoring apparatus 1 may use the following [Equation 6] instead of [ _Equation 2] for calculating the estimated value G _l,est at each frequency of the compliance transfer function in S3.
In [Equation 6], one or more vibration modes are assumed, and those modal parameters are assumed, whereby the estimated value G _l,est of the compliance transfer function is determined by the modal parameters.
In [Equation 6], m is a number assigned to the vibration mode, c is the number of assumed vibration modes, M _m is an equivalent mass, C _m is an equivalent damping coefficient, and K _m is an equivalent spring constant. In addition, in [Equation 6], the residue (residual) may be considered.
When the vibration mode is assumed as described above, the monitoring device 1 reduces the evaluation value of the error from the estimated value of the compliance transfer function by correcting the modal parameter as well as the cutting force component of each order. May be.

FIG. 11 is a diagram in which the ratio of the compliance transfer function at each frequency identified by the monitoring device 1 using [Equation 2], [Equation 5], and [Equation 4] is divided into a real part and an imaginary part and expressed. , FIG. 12 is a diagram expressed separately for the amplitude (Amplitude) and the phase (Phase). Further, FIG. 13 is a diagram showing the ratio of the cutting force component for each order (Harmonic order) identified by the monitoring device 1. Furthermore, FIG. 14 is a diagram showing the cutting force waveform with respect to the tool rotation angle estimated by the monitoring device 1 from the respective order components of the identified cutting force using the inverse Fourier transform.
The result identified here is the ratio to G _1,k when 1=1, k=1, and the value on the vertical axis in each figure is relative. Of course, S6 may be further executed to quantitatively identify the cutting force component and the compliance transfer function component.

<<Effects>>
As described above, the monitoring device 1 monitors at least one of the vibration characteristics and the cutting force in the NC milling machine J having the spindle P, and the rotation speed control means (control device 4) for controlling the rotation speed of the spindle P. , An NC milling machine J, and an acceleration sensor 2 attached to the NC milling machine J, and a control device 4 connected to the acceleration sensor 2. The rotation speed control means changes the rotation speed of the spindle P within a predetermined range to monitor the rotation speed. The acceleration sensor 2 measures the vibration when the spindle P is rotated under a plurality of rotational speed conditions for cutting to obtain a vibration measurement result for each rotational speed and a cutting force component related to a plurality of orders. Is calculated and each frequency component of the vibration displacement, which is the vibration measurement result, is divided by the temporarily determined cutting force component to calculate each frequency component of the compliance transfer function G _l,k related to the vibration characteristic. The error E, which is an evaluation value for the error from the estimated value of the compliance transfer function G _l,k , is calculated, and the cutting force component is tentatively re-determined until the error E becomes equal to or less than a predetermined value, and the error E is predetermined. At least _one of the ratio F _n /F ₁ of the cutting force component and the ratio G/G ₁ of each frequency component of the compliance transfer function G _l,k when the value is less than or equal to the value, the cutting force and vibration characteristics in the NC milling machine J Is used for identifying at least one of the above.
Therefore, the monitoring device 1 can easily estimate the vibration characteristics and the cutting force of the NC milling machine J. Further, if the estimated vibration characteristic is used, vibration such as chatter can be more appropriately reduced or avoided, and more efficient machining can be performed.
For example, when a chatter vibration is generated, the monitoring device 1 is further provided with a display means such as a monitor, and the frequency of the chatter vibration is compared with the resonance frequency to determine the cause of the chatter vibration and its countermeasure. It can be estimated and displayed on the display means. Further, the monitoring device 1 can automatically take vibration suppression measures such as changing the rotation speed condition of the spindle P via the control device 4 instead of or together with the display.
Further, the monitoring device 1 can monitor the cutting force only by introducing the acceleration sensor 2 into the NC milling machine J, and can indirectly monitor the wear state of the tool, eccentricity, chipping, and the like.
Furthermore, the monitoring device 1 can visualize the vibration suppression of the mechanical structure of the work W, the tool (end mill V), the jig, etc. to the operator when the display means is used, and If the data is stored in the storage means, it can be utilized for processing diagnosis and various improvements.

On the other hand, the monitoring method is a method of monitoring at least one of the vibration characteristic and the cutting force in the NC milling machine J having the spindle P by a computer. A vibration measurement step S1 of measuring the vibration when rotating and cutting under a speed condition and acquiring a vibration measurement result for each rotation speed, and a cutting force component relating to a plurality of orders are provisionally determined, and the vibration measurement result is obtained. A transfer function frequency component calculation step S2 for calculating each frequency component of the compliance transfer function G _1,k related to the vibration characteristic by dividing each frequency component of the vibration displacement by the temporarily determined cutting force component, and the calculated compliance transfer Transfer function estimated value calculation step S3 for calculating an estimated value of the function G _1,k , evaluation value calculation step S4 for calculating an error E which is an evaluation value of an error from the calculated estimated value, and calculated error The cutting force components are tentatively re-determined until E becomes equal to or less than a predetermined value, and when the error E becomes equal to or less than the predetermined value, the cutting force component ratios F _n /F ₁ and the compliance transfer functions G _l,k An error evaluation step S5 in which at least one of the frequency component ratios G/G ₁ is used for identifying at least one of the cutting force and the vibration characteristics in the NC milling machine J is included.
Therefore, in the monitoring method, similarly to the monitoring device 1, it is possible to easily estimate the vibration characteristics and the cutting force of the NC milling machine J. Further, if the estimated vibration characteristic is used, vibration such as chatter can be more appropriately reduced or avoided, and more efficient machining can be performed.
In the monitoring device 1 and the monitoring method according to the present invention, “machine” and “machine tool” include at least one of a tool, a tool holder, a workpiece (work), and a jig as appropriate. .

In addition, the monitoring device 1 includes the average value of the current values of the motor that rotates the main shaft P and the motor that drives each feed shaft, the ratio F _n /F _{1 of} the cutting force component, and the ratio G of each frequency component of the compliance transfer function. At least one of the cutting force and the vibration characteristic in the NC milling machine J is quantitatively identified by using at least _one of /G ₁ and the quantitative identification step S6 is executed. Therefore, the cutting force and the vibration characteristic are quantified by the monitoring device 1 or the monitoring method.
Further, the monitoring device 1 calculates each frequency component of the compliance transfer function at each frequency for a plurality of orders as an estimated value, and adopts the average value thereof. Alternatively, the monitoring device 1 adopts each frequency component of the compliance transfer function at each frequency determined by the modal parameters by assuming one or more vibration modes as the estimated value and assuming those modal parameters. Therefore, in the monitoring device 1 or the monitoring method, the error from the estimated value of the compliance transfer function G _1,k is accurately and easily determined.

<<Examples of changes>>
The monitoring device 1 and the monitoring method have modifications as described below, in addition to the modifications described above.
The machine tool may be not only an NC milling machine, but also a milling machine, a lathe or an NC lathe as long as the cutting force (cutting thickness or cutting width) changes in synchronization with rotation. In the case of a lathe system, the rotating part rotates the work, not the tool, and the work shape is appropriately considered as the processing condition. The type of processing by the machine tool is not limited to the cutting by the end mill, and may be the cutting by using another cutting tool. Alternatively, in the lathe, the work may have a key groove.
Display means capable of displaying various information, operation panel with or without the display means is added, control means is separate from machine tool, control means is individually provided for spindle, sensor, etc. The components, order, shape, arrangement, number, presence/absence, material, form, etc. of various processes or members or portions may be appropriately changed, such as being provided in a distributed manner.
Further, the vibration characteristic to be identified is not limited to the compliance transfer function, and the measured vibration is not limited to the displacement. The speed, the acceleration, etc. can be changed as appropriate, and the transfer function indicating the vibration characteristic can also be changed. Further, the evaluation value E of the error from the estimated value evaluated by using [Equation 3] to [Equation 5] is an arithmetic expression in which the smaller the value is, the smaller the variation is. Alternatively, by inverting the sign, it is possible to appropriately change the arithmetic expression so that the larger the value, the smaller the variation.
In addition, the vibration characteristic may follow a rotating coordinate system. For example, information on vibration measured by a sensor such as an encoder attached to a portion rotated by the main shaft is used to identify the vibration characteristic of the rotating portion. As a more specific example, when the motor current (torque) is used as the vibration and the cutting torque is identified as the cutting force, the cutting torque applied to the tool edge is input as the vibration characteristic, and the current generated in the spindle motor is output. The transfer function (torsional vibration characteristic of the main shaft rotating part) is simultaneously identified.

  1... Monitoring device, 2... Acceleration sensor (sensor), 4... Control device (control means, rotation speed control means), C... Column, D... Work feed mechanism, H... Spindle head, J...・NC milling machine (machine tool), O・・dynamometer, P・・spindle (rotating part), Q・・work table, S1・・vibration measurement step, S2・・transfer function frequency component calculation step, S3・・transmission Function estimation value calculation step, S4... Evaluation value calculation step, S5... Error evaluation step, S6... Quantitative identification step, T... table, V... end mill, W... work.

Claims (8)

A monitoring device for monitoring at least one of vibration characteristics and cutting force in a machine having a rotating part,
Rotation speed control means for controlling the rotation speed of the rotating portion,
A sensor attached to the machine,
Control means connected to the sensor,
Is equipped with
The rotation speed control means changes the rotation speed of the rotating portion within a predetermined range,
The control means is
By the sensor, by measuring the vibration at the time of cutting by rotating the rotating portion at a plurality of the rotation speed, while obtaining the vibration measurement result for each rotation speed,
Tentatively determining a cutting force component related to a plurality of orders, by dividing each frequency component of the vibration measurement result by the tentatively determined cutting force component, to calculate each frequency component of the transfer function related to the vibration characteristics,
By calculating an evaluation value for an error from the estimated value of the calculated transfer function, re-determining the cutting force component until the evaluation value becomes a predetermined value or less,
When the evaluation value is equal to or less than a predetermined value, at least one of the ratio of the cutting force component and the ratio of each frequency component of the transfer function is used to identify at least one of the cutting force and the vibration characteristic of the machine. A monitoring device characterized by being used. Further, the control means, at least one of the low frequency component of the torque in the rotating portion and the low frequency component of the thrust of the feed shaft, and at least one of the ratio of the cutting force component and the ratio of each frequency component of the transfer function. 2. The monitoring device according to claim 1, wherein at least one of the cutting force and the vibration characteristic in the machine is quantitatively identified by using. The monitoring device according to claim 1, wherein, as the estimated value, each frequency component of the transfer function at each frequency is calculated for a plurality of orders, and an average value thereof is adopted. As the estimated value, assuming one or more vibration modes and assuming those modal parameters, each frequency component of the transfer function at each frequency determined by the modal parameters is adopted. The monitoring device according to claim 1 or 2. A monitoring method for monitoring at least one of vibration characteristics and cutting force in a machine having a rotating part by a computer,
With a sensor attached to the machine, a vibration measurement step of measuring the vibration when the rotary unit is rotated at a plurality of the rotation speeds and cutting and acquiring a vibration measurement result for each of the rotation speeds,
Transfer for calculating each frequency component of the transfer function related to the vibration characteristic by temporarily determining the cutting force components related to a plurality of orders and dividing each frequency component of the vibration measurement result by the provisionally determined cutting force component A function frequency component calculation step,
A transfer function estimated value calculating step of calculating an estimated value of the calculated transfer function;
An evaluation value calculation step of calculating an evaluation value for an error from the calculated estimated value,
Temporarily redetermining the cutting force component until the calculated evaluation value becomes equal to or less than a predetermined value, and when the evaluation value becomes equal to or less than a predetermined value, the ratio of the cutting force component and each frequency of the transfer function. At least one of the component ratios, an error evaluation step used to identify at least one of the cutting force and the vibration characteristics in the machine,
A monitoring method comprising: Furthermore, using at least one of the low frequency component of the torque of the rotating portion and the low frequency component of the thrust of the feed shaft, and at least one of the ratio of the cutting force component and the ratio of each frequency component of the transfer function, The monitoring method according to claim 5, further comprising a quantitative identification step of quantitatively identifying at least one of the cutting force and the vibration characteristic in the machine. 7. The monitoring method according to claim 5, wherein, as the estimated value, each frequency component of the transfer function at each frequency is calculated for a plurality of orders, and an average value thereof is adopted. As the estimated value, assuming one or more vibration modes and assuming those modal parameters, each frequency component of the transfer function at each frequency determined by the modal parameters is adopted. The monitoring method according to claim 5 or claim 6.

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