JP2012111020A - Vibration suppressing device for machining tool and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suitably suppress chattering vibration without decreasing the machining efficiency.SOLUTION: A controller 11 of a vibration suppressing device 10 includes: an NC unit 12; an arithmetic unit 13 for performing Fourier analysis based on vibration acceleration in a time domain detected by a vibration sensor 7; a storage unit 14 for storing a calculated value calculated by the arithmetic unit 13, chatter vibration suppression history, etc.; a display unit 15 for displaying a result calculated by the arithmetic unit 13, or a result of calculation based on the calculated result; and an operating device 16 for an operator to perform an input operation to the NC unit 12. When occurrence of chattering vibration is detected, the arithmetic unit 13 calculates a k' value by dividing a numerical value sixty times as many as a chatter vibration frequency by the product of the number of cutting edges of a tool and a rotation speed of a rotary shaft, and determines whether the calculated k' value is less than one. If the calculated k' value is less than one, the rotation speed is changed to a rising side to suppress the chatter vibration.

Description

  The present invention relates to a vibration suppressing device and a method for suppressing chatter vibration generated with rotation of a rotating shaft in a machine tool including a rotating shaft that rotates a tool or a workpiece.

  2. Description of the Related Art Conventionally, a machine tool is known in which a tool or a work is supported on a main shaft that is a rotating shaft, and the work is processed by moving the tool or the work while moving the tool or the work. In such a machine tool, if the depth of cut in the cutting process is too large, chatter vibration will occur during machining, resulting in problems such as deterioration of the finishing accuracy of the machined surface, rapid tool wear, and tool chipping. Occurs. As a countermeasure against the chatter vibration suppression, as described in Patent Documents 1 and 2, the chatter vibration frequency is specified. For example, in Patent Document 2, the following formulas (1) and (2) are used. A technique has been devised that guides the optimum rotational speed and performs vibration suppression treatment.

n = 60fc / {(k + 1) N} (1)
k ′ = 60fc / (n ₀ N) (2)
n is the optimum rotational speed obtained by calculation, n ₀ is the current rotational speed, N is the number of blades of the tool, fc is the detected vibration frequency, k is k ′ (one blade of vibration transferred onto the work surface The integer part of the number in the pitch).

JP-T-2001-517557 JP 2007-44852 A

However, since the vibration suppression processing according to Patent Documents 1 and 2 automatically calculates the optimum rotation speed based on the above (1) and (2), when k ′ <1, the rotation speed is simply increased. in spite of the vibration suppression effect is obtained, there is the optimum rotational speed n is smaller than the current rotational speed n _0. Thus, the reduction in the rotational speed leads to a reduction in processing efficiency.

  Accordingly, an object of the present invention is to provide a vibration suppression device and method for a machine tool that can suitably suppress chatter vibration without reducing machining efficiency.

In order to achieve the above object, according to a first aspect of the present invention, there is provided a machine tool including a rotary shaft for rotating a tool or a workpiece, wherein chatter vibration generated with the rotation of the rotary shaft is subjected to rotation of the rotary shaft. A vibration suppression device that suppresses by changing speed,
Vibration detection means for detecting the occurrence of chatter vibration, and when the occurrence of chatter vibration is detected, a value 60 times the chatter vibration frequency is divided by the product of the number of tool blades and the rotation speed of the rotary shaft. k ′ value calculating means for calculating a k ′ value, and determining means for determining whether or not the calculated k ′ value is less than 1, wherein the k ′ value is less than 1 as determined by the determining means. If there is, the chatter vibration is suppressed by changing the rotational speed to the rising side.
According to a second aspect of the present invention, in the configuration of the first aspect of the present invention, the display unit displays a determination result of the determination unit.
In order to achieve the above object, according to a third aspect of the present invention, there is provided a machine tool including a rotary shaft for rotating a tool or a workpiece, wherein chatter vibration generated with the rotation of the rotary shaft is subjected to rotation of the rotary shaft. A vibration suppression method that suppresses by changing speed,
A vibration detection step for detecting occurrence of chatter vibration, and when occurrence of chatter vibration is detected, a value 60 times the chatter vibration frequency is divided by the product of the number of tool blades and the rotation speed of the rotary shaft. a k ′ value calculating step for calculating a k ′ value, a determining step for determining whether or not the calculated k ′ value is less than 1, and if the k ′ value is less than 1 in the determination by the determining step, And a rotation speed changing step for changing the rotation speed to the rising side.
According to a fourth aspect of the present invention, in the configuration of the third aspect, a display step for displaying a determination result in the determination step is executed between the determination step and the rotation speed changing step. It is.

According to the first and third aspects of the present invention, if k ′ <1, the rotational speed is changed to the higher side to suppress the vibration, and thus the chatter vibration can be suitably suppressed without reducing the processing efficiency. It becomes.
According to the second and fourth aspects of the invention, in addition to the above effect, whether or not k ′ <1 can be reliably determined, and the rotation speed can be easily changed by the operator.

It is explanatory drawing which showed the block structure of the vibration suppression apparatus of a machine tool. It is a flowchart which concerns on suppression control of chatter vibration. It is explanatory drawing of a stability limit diagram. It is a flowchart which concerns on the example of a change of suppression control of chatter vibration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram schematically showing a vertical machining center as an example of a machine tool and a vibration suppressing device provided in the vertical machining center.
First, the vertical machining center 1 is provided with a spindle 3 as a rotary shaft that is rotatable around a C axis on a spindle head 2 provided above, and is set on a machining table 5 below by a tool 4 attached to the spindle 3. The NC device 12 controls the rotation of the spindle 3 in accordance with the NC program, and the tool 4 can be automatically changed by an automatic tool changer (not shown).

The vibration suppressing device 10 is for controlling “chatter vibration” generated on the main shaft 3, and includes a vibration sensor 7 for detecting vibration acceleration in the time domain generated on the rotating main shaft 3, and the vibration sensor 7. And a control device 11 for controlling the rotational speed of the main shaft 3 based on the detected value obtained by the above.
The control device 11 includes an NC device 12, a calculation device 13 that performs Fourier analysis based on vibration acceleration in the time domain detected by the vibration sensor 7, and suppression of calculation values and chatter vibrations calculated by the calculation device 13. An operator performs an input operation on the storage device 14 for storing the history, the display device 15 as a display means for displaying the result calculated by the arithmetic device 13 or the calculation result based on the result, and the NC device 12. And an operating device 16. The arithmetic device 13 constitutes a vibration detection means together with the vibration sensor 7 and also functions as a k ′ value calculation means and a discrimination means.

Hereinafter, suppression control of “chatter vibration” in the control device 11 will be described based on the flowchart of FIG. 2.
First, an arbitrary initial rotation speed is set in S1, and machining is started in S2. During machining, vibration acceleration during machining obtained from the vibration sensor 7 is detected and converted into acceleration in the frequency domain by the arithmetic unit 13 (S3), and occurrence of chatter vibration is determined at S4 (vibration detection step). . This determination is performed by comparing the maximum acceleration value obtained in S3 with a preset threshold value. If the maximum acceleration exceeds the threshold value, it is determined that chatter vibration has occurred, and then in S5, Are stored in the storage device 14.

Next, in S6, the computing device 13 computes the result of associating the rotational speed stored in S5 with the vibration state, and the relation between the rotational speed and machining stability limit as shown in FIG. Is created and displayed on the display device 15 (S7). At the same time, the arithmetic device 13 calculates the k ′ value using the equation (2) shown in the background art above (k ′ value calculation step), and determines whether or not the calculated k ′ value is less than 1. (Determination step) is displayed on the display device 15 (display step).
The stability limit diagram shows that the horizontal axis is the rotational speed, the vertical axis is the limit cut amount, the lower side of the curve is the stable region, and the upper side is the unstable region. The dotted line A is a rotational speed at which k ′ = 1, and the right side of the dotted line A is an area where k ′ <1 and the left side is k ′> 1. Further, the dotted line B is the initial rotational speed, and the dotted line C is the tool limit rotational speed.

Therefore, the operator checks whether or not k ′ <1 in S8, and if k ′ <1 (YES in S8), the limit of the tool in the right region in S9 is input by the operation device 16. The rotational speed is increased to a stable rotational speed (dotted line D) considering the peripheral speed (rotational speed changing step). At this stable rotational speed, the rotational speed shifts to the rising side and the limit cutting amount increases, so that the machining efficiency can be improved.
On the other hand, if k ′ ≧ 1 (NO in S8), the operator selects the rotational speed in the left region while referring to the stability limit diagram, inputs it to the operating device 16, and changes the rotational speed (S10). .

  Then, after changing the rotation speed in S9 and S10, if the processing is not finished in the determination of S11, the process returns to S3 again to detect the vibration acceleration. If chatter does not occur in the subsequent determination of S4, the machining is performed at the changed rotation speed until the machining is finished in S11. If chattering is confirmed in S4, the processing of S5 to S10 is repeated to change the rotation speed.

As described above, according to the vibration suppression device 10 and the vibration suppression method of the above embodiment, when occurrence of chatter vibration is detected, the k ′ value is calculated to determine whether this is less than 1 or not. For example, since the chatter vibration is suppressed by changing the rotation speed to the increasing side, the chatter vibration can be suitably suppressed without reducing the machining efficiency.
In particular, here, since the determination result of whether k ′ <1 is displayed on the display device 15, it is possible to reliably determine whether the k ′ value is less than 1, and the operator can easily change the rotation speed. Can be done.

In the above embodiment, after confirming whether k ′ <1 or not, the operator arbitrarily changes the rotation speed in response to the display result. However, as shown in the flowchart of FIG. If k ′ <1 in S8, the calculation device 13 calculates the rotational speed on the ascending side in consideration of the limit peripheral speed of the tool and displays the rotational speed (S9). If k ′ ≧ 1 in S8, Then, the rotational speed may be calculated using the equation (1) shown in the background art and the rotational speed is displayed (S10), and the operator may change the rotational speed in S11 according to each display. .
Further, the rotation speed is not limited to the change by the operator's input command, and the calculation device 13 may automatically calculate the rotation speed to be changed based on the determination result of S8, and the NC device 12 may change the rotation speed. .

On the other hand, in addition to the vibration sensor, the current of the microphone, position / rotation detector, spindle / feed shaft motor can be used to detect vibration from the machine tool, and the result of associating the rotational speed with the vibration state is displayed. However, the graph is not limited to the stability limit diagram, and may be a graph showing the relationship between the rotational speed and the vibration acceleration, or may be displayed using the vibration frequency, the cutting speed, the feed speed, the rotation shaft torque, or the like. Of course, it is possible to omit the display of such figures and graphs and display only whether k ′ <1 or not, and the arithmetic unit automatically changes the rotation speed based on the determination result as described above. In this case, the display of k ′ <1 can be omitted.
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 rotary shaft.

  1 .. Vertical machining center 2... Spindle head 3.. Spindle 4. NC device, 13 ... arithmetic device, 14 ... storage device, 15 ... display device, 16 ... operation device.

Claims (4)

In a machine tool provided with a rotating shaft for rotating a tool or a workpiece, a vibration suppressing device that suppresses chatter vibration generated with rotation of the rotating shaft by changing the rotation speed of the rotating shaft,
Vibration detecting means for detecting occurrence of chatter vibration;
When the occurrence of chatter vibration is detected, k ′ value calculating means for calculating a k ′ value by dividing a numerical value 60 times the chatter vibration frequency by the product of the number of tool blades and the rotational speed of the rotary shaft;
Discriminating means for discriminating whether or not the calculated k ′ value is less than 1;
If the k ′ value is less than 1 as determined by the determination means, the rotation speed is changed to an increase side to suppress the chatter vibration, and a vibration suppression device for a machine tool.   2. The machine tool vibration suppression device according to claim 1, further comprising display means for displaying a discrimination result of the discrimination means. In a machine tool provided with a rotating shaft for rotating a tool or a workpiece, a vibration suppressing method for suppressing chatter vibration generated with rotation of the rotating shaft by changing the rotation speed of the rotating shaft,
A vibration detecting step for detecting occurrence of the chatter vibration;
When the occurrence of chatter vibration is detected, a k ′ value calculating step of calculating a k ′ value by dividing a numerical value 60 times the chatter vibration frequency by the product of the number of tool blades and the rotation speed of the rotary shaft;
A determination step of determining whether or not the calculated k ′ value is less than 1;
If the k ′ value is less than 1 in the determination in the determination step, a rotation speed changing step for changing the rotation speed to the rising side;
A vibration suppression method for machine tools, characterized in that   4. The vibration suppression method for a machine tool according to claim 3, wherein a display step for displaying a determination result in the determination step is executed between the determination step and the rotation speed changing step.

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