JP5631792B2 - Machine tool monitoring device - Google Patents

Machine tool monitoring device Download PDF

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JP5631792B2
JP5631792B2 JP2011070440A JP2011070440A JP5631792B2 JP 5631792 B2 JP5631792 B2 JP 5631792B2 JP 2011070440 A JP2011070440 A JP 2011070440A JP 2011070440 A JP2011070440 A JP 2011070440A JP 5631792 B2 JP5631792 B2 JP 5631792B2
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stability limit
chatter vibration
rotational speed
rotation speed
vibration frequency
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JP2012200848A (en
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浩平 西村
浩平 西村
上野 浩
浩 上野
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オークマ株式会社
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  The present invention relates to a monitor device for monitoring a machining state related to vibration in a machine tool that performs machining while rotating a tool or a workpiece mounted on a rotary shaft.
In a machine tool such as a machining center that performs machining while rotating a tool or a workpiece mounted on a rotary shaft, chatter vibration may occur depending on processing conditions such as the rotational speed and feed rate of the rotary shaft. This chatter vibration generates a periodic pattern generally called a chatter mark on the machined surface, which causes deterioration of the finished surface properties and machining accuracy. Further, since the cutting force fluctuates periodically, there is a possibility that noise is generated and tool wear or chipping is caused.
As a means for avoiding chatter vibration, for example, as disclosed in Patent Document 1, the rotation speed is calculated by calculating the rotational axis rotational speed that is most stable from the vibration frequency and the number of tool blades measured by detecting vibration during machining. An invention of a vibration suppressing device to be changed is known.
JP 2008-290188 A
However, since the vibration suppression device of Patent Document 1 does not display a stability limit diagram indicating the relationship between the rotational speed and the stability of chatter vibration, the stable rotational speed can be obtained even if a specific stable rotational speed can be known. There is a problem that the area is difficult to understand. In particular, when chatter vibration occurs due to a plurality of natural frequencies, the relationship between the rotational speed and the stability limit becomes complicated. Therefore, it is desirable to display a stability limit diagram showing the relationship between the rotation speed and the stability limit so that the operator can easily determine a stable rotation speed region.
However, in order to create a stability limit diagram, modal analysis is performed on the transfer function measured by attaching the tool used for machining to the rotating shaft, and identification is made from the machining result. It is necessary to repeat the procedure of calculating the rotational speed corresponding to the stability limit based on the modal parameter and chatter vibration frequency, which takes time.
  Accordingly, the present invention has been made to solve the above-described problem, and is capable of promptly displaying a stability limit diagram by a simple means and promptly informing a stable rotation speed region. Is intended to provide.
In order to achieve the above object, the invention according to claim 1 is a machine tool that performs machining by rotating a tool or a workpiece mounted on a rotating shaft at a predetermined rotational speed, and includes a display unit to perform machining related to vibration. A monitoring device for monitoring the state,
Based on vibration detection means for detecting vibrations associated with machining, chatter vibration frequency acquisition means for detecting the occurrence of chatter vibrations from the detected vibrations and calculating the frequency of chatter vibrations, and the chatter vibration frequency and the rotation speed The optimum rotation speed calculating means for calculating the optimum rotation speed using the following formulas (1) to (6), the following formulas (1), (2), and (4), and the preset rotation speed becomes unstable. An unstable rotational speed calculation means for calculating an unstable rotational speed based on the phase information obtained, and a stability limit diagram between the optimum rotational speed and the unstable rotational speed are created using an approximate curve, and And a plotting display means for displaying on the display section.
k ′ value = 60 × chatter vibration frequency / (number of tool blades × rotational speed) (1)
k value = integer part of k ′ value (2)
Stable rotation speed = 60 x chatter vibration frequency / (arbitrary integer x number of tool blades) (3)
Phase information = k ′ value−k value (4)
Coefficient = a−b × k value + c × phase information (a, b, c are constants) (5)
Optimum rotation speed = coefficient × stable rotation speed (6)
According to a second aspect of the present invention, in the configuration of the first aspect, the optimum rotational speed calculating means and the unstable rotational speed calculating means are provided for each of the chatter vibration frequencies generated due to a plurality of natural frequencies. The optimum rotation speed and the unstable rotation speed are calculated, and the drawing display means creates individual stability limit diagrams based on the optimum rotation speed and the unstable rotation speed calculated for each chatter vibration frequency. The individual stability limit diagrams are summed to create the stability limit diagram for the chatter vibration caused by all the natural frequencies.
According to a third aspect of the present invention, in the configuration of the second aspect, the drawing display means weights the individual stability limit diagrams in accordance with the magnitude of the chatter vibration frequency, and then the individual stability charts. The sum of the limit diagrams is obtained.
According to a fourth aspect of the present invention, in the configuration of the second aspect, the drawing display means measures the chatter vibration frequency at a plurality of rotational speeds in advance and is set according to the number of detections of the chatter vibration frequency. Further, the sum of the individual stability limit diagrams is obtained by reflecting the weighting of the chatter vibration frequency in the individual stability limit diagrams.
According to the first aspect of the present invention, the stability limit can be calculated by simple means. Therefore, when chatter vibration occurs, a stability limit diagram can be displayed immediately, and a stable rotation speed region can be quickly notified to the operator. An appropriate rotation speed can be changed by the operator.
According to the invention described in claim 2, in addition to the effect of claim 1, chatter vibration is generated due to a plurality of natural frequencies, and the relationship between the rotational speed and the stability limit is complicated. By adding the individual stability limit diagrams calculated for each natural frequency, the operator can easily know the overall stable rotational speed.
According to the third aspect of the invention, in addition to the effect of the second aspect, chatter vibration caused by a natural frequency having a large vibration can be strongly reflected in the finally obtained stability limit diagram. A more accurate stability limit diagram can be obtained.
According to the invention described in claim 4, in addition to the effect of claim 2, the larger the number of rotation speeds at which chatter vibration occurs, the stronger it can be reflected in the finally obtained stability limit diagram, A more accurate stability limit diagram can be obtained.
It is a schematic block diagram of a vertical machining center. It is explanatory drawing of the approximation method of a stability limit. It is an example of a display of a stability limit diagram. It is a display example of a stability limit diagram in consideration of chatter vibration caused by a plurality of natural frequencies.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a vertical machining center which is an example of a machine tool. The vertical machining center 1 is provided with a spindle 3 which is rotatable on a spindle head 2 provided above, and a tool 4 attached to the spindle 3. The NC device 13 provided in the monitor device 10 to be described later has a well-known configuration for machining the workpiece 6 set on the lower machining table 5 and controls the rotation of the spindle 3 in accordance with the NC program, and is not shown in the drawing. The tool 4 can be automatically changed by the tool changer.
The monitor device 10 includes an FFT calculation unit 11, a stability limit diagram calculation unit 12, an NC device 13, an input unit 14 such as the number of tool blades, a storage unit 15 such as the number of tool blades input, and a stable A limit diagram display unit 16 is provided.
The FFT calculation unit 11 is connected to vibration sensors 7a to 7c that are provided on the spindle head 2 and serve as vibration detection means for measuring vibration. The vibration sensors 7a to 7c detect time-domain vibrations (vibrations on the time axis) that occur as the main shaft 3 rotates, and the time-domain vibrations in the X-axis, Y-axis, and Z-axis directions orthogonal to each other. It is attached to the spindle head 2 in a state where vibration information can be detected. The FFT calculation unit 11 performs Fourier analysis based on the vibrations detected by the vibration sensors 7a to 7c, and determines that chatter vibration has occurred when the calculated vibration acceleration in the frequency domain exceeds a predetermined threshold.
When the FFT calculation unit 11 determines that chatter vibration has occurred, the stability limit diagram calculation unit 12 will be described later based on the chatter vibration frequency obtained from the FFT calculation unit 11 and the number of tool blades input from the input unit 14. The stability limit is calculated by the means described above, and the obtained stability limit diagram is output to the NC device 13.
The NC device 13 displays the input stability limit diagram on the display unit 16, and when the operator inputs an instruction to change the rotation speed from the input unit 14, the rotation speed of the main spindle 3 is adjusted so as to be the rotation speed. Also make changes.
Next, a procedure for creating a stability limit diagram in the stability limit diagram calculation unit 12 will be specifically described.
First, the stability limit diagram calculation unit 12 is based on the following equations (1) to (6) from chatter vibration frequencies obtained from the vibration sensors 7a to 7c and the number of tool blades obtained from the input unit 14. To calculate the optimum rotation speed. At the same time, an unstable rotational speed is calculated based on the k value and phase information obtained by the equations (1), (2), and (4). The phase information used here is preliminarily stored in the storage unit 15 as phase information in which the rotational speed becomes unstable. For example, 0.75 is stored. An unstable rotational speed is calculated from this phase information and the above equation.
k ′ value = 60 × chatter vibration frequency / (number of tool blades × rotational speed) (1)
k value = integer part of k ′ value (2)
Stable rotation speed = 60 x chatter vibration frequency / (arbitrary integer x number of tool blades) (3)
Phase information = k ′ value−k value (4)
Coefficient = a−b × k value + c × phase information (5)
Optimum rotation speed = coefficient × stable rotation speed (6)
In the above equation (4), a, b, and c are predetermined constants, and are determined to be a = 0.971, b = 0.003, and c = 0.045, for example.
This constant is created based on conditions such as the relationship between the rotational speed of the main shaft 3 and the chatter vibration frequency, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2008-290188) presented earlier. Determined from the stability limit diagram. That is, test machining is performed at various rotational speeds, and vibrational acceleration detected during the machining is Fourier-analyzed, and phase information, k value, and stable rotational speed at each rotational speed are expressed by the above formulas (1) to (4). The relationship between the phase information and k value and the value (coefficient) obtained by dividing the rotational speed at which the vibration acceleration in the frequency domain is the minimum value by the stable rotational speed is obtained, and the constant is determined from the relation. .
After calculating the optimum rotation speed and the unstable rotation speed in this way, a stability limit diagram between the optimum rotation speed and the unstable rotation speed on the plane having the rotation speed as the first axis and the stability limit as the second axis, Draw using approximate curve. FIG. 2 is an explanatory diagram showing an example of a method for approximating the stability limit between the optimum rotation speed and the unstable rotation speed.
First, the optimum rotational speed S 2 at which two lobes of k value = n and k value = n + 1 intersect, and unstable rotational speeds S 1 and S 3 of the respective lobes are expressed by using equations (6) and (4). To calculate. Next, the stability limit between the unstable rotational speed S 1 and the optimal rotational speed S 2 of the lobe with k value = n + 1 is expressed by the following equation using a trigonometric function cos θ (π ≦ θ ≦ 1.6π), for example. Approximate with a curve like (7). S is the current rotational speed.
Similarly, the stability limit between the optimum rotational speed S 2 and the unstable rotational speed S 3 of the k value = n lobe is approximated by a curve such as the following equation (8).
By expanding or reducing a lobe at a certain k value drawn as described above, a lobe at another k value can be drawn. FIG. 3 shows an example of a stability limit diagram obtained by the above means. In this embodiment, a trigonometric function is used as the approximate curve, but other approximate curves such as a quadratic expression may be used.
Therefore, the operator can easily grasp the stable rotation speed region from the stability limit diagram displayed on the display unit 16, and can also change the rotation speed within the stable rotation speed region. .
  Thus, according to the monitor apparatus 10 of the said form, the vibration detection means (vibration sensor 7a-7c) which detects the vibration accompanying process, generation | occurrence | production of chatter vibration is detected from the detected vibration, and the frequency of chatter vibration is set. Chatter vibration frequency acquisition means (FFT calculation unit 11) to calculate, and optimum rotation speed calculation means (stability limit) for calculating the optimum rotation speed using equations (1) to (6) based on the chatter vibration frequency and the rotation speed An unstable rotational speed calculation means (stable) that calculates an unstable rotational speed based on the diagram calculation unit 12), equations (1), (2), and (4) and preset phase information that makes the rotational speed unstable. The limit diagram calculation unit 12) and a plotting display means (stable limit diagram calculation) for creating a stability limit diagram between the optimum rotation speed and the unstable rotation speed by using an approximate curve and displaying it on the display unit 16. Unit 12 and NC device 14) , By providing the can calculate the stability limit by a simple means. Therefore, when chatter vibration occurs, a stability limit diagram can be displayed immediately, and a stable rotation speed region can be quickly notified to the operator. An appropriate rotation speed can be changed by the operator.
In the above form, it is an example of creating a stability limit diagram when chatter vibration occurs due to one natural frequency, but when chatter vibration occurs due to multiple natural frequencies For each chatter vibration due to each natural frequency, the stability limit is simply calculated as described above, all the stability limit diagrams are added, and the result is the chatter due to all the natural frequencies. You may make it display as a stability limit of vibration.
Thereby, even if chatter vibration occurs due to a plurality of natural frequencies, the operator can easily know a comprehensively stable rotational speed.
In addition, when adding the stability limit diagrams in this way, weighting may be performed by determining a coefficient according to the magnitude of vibration measured by the vibration sensor and applying the coefficient to the stability limit. For example, the coefficient is 1 for chatter vibration having a frequency with the largest vibration displacement, and a positive number less than 1 for the chatter having a smaller vibration displacement, with the coefficient being the ratio of the vibration displacement at the frequency to the largest vibration displacement. And
Thereby, the chatter vibration caused by the natural frequency having a large vibration can be reflected more strongly in the finally obtained stability limit diagram, and a more accurate stability limit diagram can be obtained.
  FIG. 4 shows an example of a comprehensive stability limit diagram for chatter vibration caused by a plurality of natural frequencies obtained by the above means. Here, a chatter vibration stability limit diagram (indicated by a dotted line A) due to a certain natural frequency and a chatter vibration stability limit diagram (indicated by a one-dot chain line B) due to another natural frequency having a smaller vibration than this. By adding together, an overall stability limit diagram (shown by a solid line C) of chatter vibration caused by two natural frequencies is obtained.
Furthermore, in order to improve the accuracy of the stability limit diagram, when test processing is performed at various rotational speeds, weighting may be performed by applying a coefficient in accordance with the number of rotational speeds at which chatter vibration occurs.
For example, the coefficient is set to 1 for chatter vibration with the largest number of detected chatter vibrations over all rotation speeds, and the ratio of the number of detected chatter vibrations with the largest number of chatter vibrations with the least number of detected chatter vibrations. And a positive number less than 1.
As a result, the greater the number of rotation speeds at which chatter vibrations occur, the stronger it can be reflected in the finally obtained stability limit diagram, and a more accurate stability limit diagram can be obtained.
  However, simultaneously with the calculation of such a simple stability limit diagram, the modal parameters are identified, the chatter vibration frequency is assumed, and the cutting force when passing the previous cutting edge is used to calculate the current A known means such as solving the stability limit and the corresponding rotational speed from the critical condition formula of the stability limit where the transfer function to the cutting force is a unit matrix and repeating the above calculation for the chatter vibration frequency and the k value. Thus, a more accurate stability limit diagram can be calculated, and as soon as this calculation is completed, a more accurate stability limit diagram can be displayed instead of a simple stability limit diagram.
In addition, the display of the stability limit diagram itself is not limited to the above-mentioned form, and the specific axis such as the rotation speed axis on the vertical axis, the stability limit on the horizontal axis, and the current rotation speed written with markers or numbers. The layout may be changed as appropriate.
In the above-mentioned form, the operator selects and changes the rotation speed based on the display of the stability limit diagram. However, when chatter vibration occurs, the optimum rotation is automatically performed together with the creation and display of the stability limit diagram. You may make it change into speed. In this case, by displaying the stability limit diagram, it can be confirmed that the machining is being performed in the calculated stable rotational speed region, which leads to an operator's anxiety reduction.
On the other hand, as the vibration detection means, it is also possible to detect vibration using a current of a microphone, a position / rotation detector, and a spindle / feed shaft motor in addition to the vibration sensor.
In the monitor device, the stability limit diagram is displayed on the display unit via the NC device. However, the stability limit diagram may be directly displayed on the display unit from the stability limit diagram calculation unit.
And in the said form, although the monitor apparatus is integrally comprised using the existing function of a machine tool, it is provided outside the machine tool via the network connected to NC apparatus, and is an input means. Or a computer with a monitor, and a stability limit diagram may be created and displayed on an external computer. In this way, a plurality of machine tools can be centrally managed in one place.
In addition, the machine tool is not limited to a vertical machining center, and the present invention can be applied to other machine tools such as an NC lathe that performs machining by rotating a workpiece mounted on a spindle.
  1 .... Vertical machining center, 2 .... Spindle head, 3 .... Spindle, 4 .... Tool, 7a-7c ... Vibration sensor, 10 .... Monitor device, 11 .... FFT operation unit, 12 .... Stability limit line Fig. Calculation unit, 13 ... NC device, 14 ... Input unit, 15 ... Storage unit, 16 ... Display unit.

Claims (4)

  1. In a machine tool that performs processing by rotating a tool or work mounted on a rotating shaft at a predetermined rotation speed, the monitor device includes a display unit and monitors a processing state related to vibration,
    Vibration detecting means for detecting vibrations associated with machining;
    Chatter vibration frequency acquisition means for detecting the occurrence of chatter vibration from the detected vibration and calculating the frequency of chatter vibration;
    Based on the chatter vibration frequency and the rotational speed, an optimal rotational speed calculating means for calculating an optimal rotational speed using the following formulas (1) to (6);
    An unstable rotational speed calculating means for calculating an unstable rotational speed based on the following formulas (1), (2), and (4) and preset phase information in which the rotational speed becomes unstable;
    A plotting display means for creating a stability limit diagram between the optimum rotational speed and the unstable rotational speed using an approximate curve and displaying it on the display unit;
    A machine tool monitoring device comprising:
    k ′ value = 60 × chatter vibration frequency / (number of tool blades × rotational speed) (1)
    k value = integer part of k ′ value (2)
    Stable rotation speed = 60 x chatter vibration frequency / (arbitrary integer x number of tool blades) (3)
    Phase information = k ′ value−k value (4)
    Coefficient = a−b × k value + c × phase information (a, b, c are constants) (5)
    Optimum rotation speed = coefficient × stable rotation speed (6)
  2. The optimum rotation speed calculation means and the unstable rotation speed calculation means calculate the optimum rotation speed and the unstable rotation speed for each chatter vibration frequency generated due to a plurality of natural frequencies,
    The plot display means creates an individual stability limit diagram based on the optimum rotational speed and the unstable rotational speed calculated for each chatter vibration frequency, and sums the individual stability limit diagrams. The machine tool monitoring apparatus according to claim 1, wherein the stability limit diagram for the chatter vibration caused by all the natural frequencies is created.
  3.   The drawing display means obtains the sum of the individual stability limit diagrams after weighting the individual stability limit diagrams according to the magnitude of the chatter vibration frequency. The machine tool monitoring device described.
  4.   The plot display means measures the chatter vibration frequency at a plurality of rotational speeds in advance and sets the weighting of the chatter vibration frequency according to the number of detections of the chatter vibration frequency to the individual stability limit diagram. The machine tool monitoring device according to claim 2, wherein the sum of the individual stability limit diagrams is obtained in response to the above.
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CN111601679A (en) * 2018-07-20 2020-08-28 山崎马扎克公司 Machine tool control device, machine tool, and machine tool control method

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JP5862111B2 (en) * 2011-08-23 2016-02-16 株式会社ジェイテクト Machining data correction method
JP6371335B2 (en) * 2016-05-30 2018-08-08 Dmg森精機株式会社 Processing status display device
JP6802054B2 (en) * 2016-07-04 2020-12-16 Dmg森精機株式会社 Machining status display device
US10386831B2 (en) 2016-07-04 2019-08-20 Dmg Mori Co., Ltd. Machining status display apparatus

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JP2005074568A (en) * 2003-09-01 2005-03-24 Mitsubishi Heavy Ind Ltd Multiple spindle machine and workpiece machining method
JP4433422B2 (en) * 2007-05-24 2010-03-17 オークマ株式会社 Vibration suppression device

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111601679A (en) * 2018-07-20 2020-08-28 山崎马扎克公司 Machine tool control device, machine tool, and machine tool control method
CN111601679B (en) * 2018-07-20 2021-05-25 山崎马扎克公司 Machine tool control device, machine tool, and machine tool control method

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