JP5615681B2 - Vibration suppression apparatus and method for machine tool - Google Patents

Description

  The present invention relates to a vibration suppressing apparatus and method for suppressing vibration generated during machining in a machine tool that performs machining while rotating a tool or a workpiece.

  2. Description of the Related Art Conventionally, there are machine tools in which, for example, a tool is supported on a rotatable spindle and moved relative to the tool and the workpiece while moving the workpiece to process the workpiece. In the machine tool, if the depth of cut in the cutting process is excessively increased, “chatter vibration” occurs during the process, and problems such as deterioration of the finishing accuracy of the processed surface, rapid tool wear, and tool breakage occur. In order to suppress this chatter vibration, Patent Document 1 discloses a technique for reducing chatter vibration by reducing the rotational speed and the amount of cutting, and Patent Document 2 discloses a value of 60 times the frequency of the tool. Techniques are disclosed in which a value obtained by dividing the number of blades by a product of a predetermined integer is used as the rotation speed.

JP 2006-150504 A JP 2003-340627 A

  However, in the above-mentioned conventional technology, chatter vibration can be reduced by adjusting the processing conditions such as the rotational speed and the amount of cutting, but the amount of time required to complete the processing is also changed because the amount of cutting that affects the processing time is changed. There is a risk of change. In addition, there are types of chatter vibration such as forced chatter vibration and regenerative chatter vibration, and countermeasures are different for each. Therefore, there is a possibility that the chatter cannot be dealt with only by increasing the rotation speed and decreasing the cutting depth. Furthermore, if the rotational speed is increased excessively or the cutting depth is decreased excessively, there is a risk that chatter will increase.

  Therefore, the present invention provides a machine tool that can appropriately deal with the generated chatter vibration without changing the time required for completion of machining or causing an increase in chatter vibration due to an excessive change in machining conditions. An object of the present invention is to provide a vibration suppressing device and method.

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,
An upper limit rotational speed setting means for setting an upper limit of the rotational speed based on a preset limit cutting speed and cutting edge radius of the tool, and a work-affected layer depth of the material type of the workpiece , and generation of the chatter vibration Vibration detecting means for detecting, vibration discriminating means for discriminating the type of the detected chatter vibration, and storage means for storing the rotational speed and vibration amount at the time when chatter vibration is detected by the vibration detecting means If the chatter vibration discriminated by the vibration discriminating means is a forced chatter vibration, a rotational speed changing means for changing the rotational speed to the upward side, and the forced chatter even if the rotational speed is changed to the upward side. If the amount of vibration increases, or if the next rotational speed to be changed to the upward side exceeds the upper limit rotational speed set by the upper limit rotational speed setting means, Rotational speed selection means for selecting the rotational speed that minimizes the vibration amount from the rotational speed stored in the storage means without changing the rotational speed to the rising side. .
According to a second aspect of the present invention, in the configuration of the first aspect, when the forced chatter vibration is not suppressed even when the rotational speed is changed to the rising side by the rotational speed changing means, the rotational speed by the storage means and The storage of the vibration amount and the change to the increase side of the rotation speed by the rotation speed changing unit are repeated, and the rotation speed selection unit is configured to calculate the vibration amount at the rotation speed before the change and the vibration amount at the rotation speed after the change. When the difference becomes positive for a certain number of times or more, it is determined that the amount of vibration has increased.
According to a third aspect of the present invention, in the configuration of the first or second aspect , the upper limit rotational speed setting means includes a rotational speed n _lim0 which is a preset limit cutting speed of the tool, and the following formula (1) ( Among the two rotation speeds n _lim1 and n _lim2 calculated based on 2), the smallest rotation speed is set as the upper limit rotation speed.
n _lim1 = v _f / (N × f _Z1 ) (1)
n _lim2 = v _f / (N × f _Z2 ) (2)
v _f : spindle feed speed per minute, N: number of tool blades, f _Z1 : R × P (R: tool blade radius, P: adjustment factor), f _Z2 : T × Q (T: material type of workpiece) Deterioration depth of processed layer, Q: adjustment factor)
According to a fourth aspect of the present invention, in the configuration according to any one of the first to third aspects, the vibration discriminating means includes k = 60 f _C / n ₀ N (f _C : chatter vibration frequency, n ₀ : current rotation speed, N: number of tool blades) is calculated, and when k is an integer, it is determined to be forced chatter vibration, and otherwise, it is determined as regenerative chatter vibration.

In order to achieve the above object, according to a fifth aspect of the present invention, in a machine tool having a rotating shaft for rotating a tool or a workpiece, chatter vibration generated with the rotation of the rotating shaft is detected. A vibration suppression method that suppresses by changing speed,
An upper limit rotational speed setting step for setting an upper limit of the rotational speed based on a preset limit cutting speed and cutting edge radius of the tool, and a work-affected layer depth of the material type of the workpiece , and generation of the chatter vibration. A vibration detecting step for detecting, a vibration determining step for determining the type of the detected chatter vibration, and a storage step for storing the rotation speed and the vibration amount when chatter vibration is detected by the vibration detecting step. If the chatter vibration determined in the vibration determination step is forced chatter vibration, the rotation speed changing step for changing the rotation speed to the rising side, and the forced chattering even if the rotation speed is changed to the rising side. When the amount of vibration increases or the next rotational speed to be changed to the rising side is set in the upper limit rotational speed setting step A rotation speed selection step for selecting the rotation speed at which the amount of vibration is minimized from the rotation speed stored in the storage step without changing the rotation speed to an increase side when exceeding the limit rotation speed; Is executed.

According to the first and fifth aspects of the invention, the forced chatter vibration can be appropriately suppressed by changing the rotational speed to the higher side, while the forced chatter vibration is suppressed even if the rotational speed is changed to the higher side. Can not be obtained, it is possible to limit the change to the rotational speed at which the cutting depth does not become extremely small. Therefore, it is possible to appropriately deal with the generated chatter vibration without changing the time required until the machining is completed or causing an increase in chatter vibration due to an excessive change of the machining conditions.
According to the second aspect of the invention, in addition to the effect of the first aspect, it is possible to appropriately determine an increase in the vibration amount.
According to the third aspect of the invention, in addition to the effect of the first or second aspect, the upper limit rotation speed can be set in a region with the most margin.
According to the fourth aspect of the invention, in addition to the effect of any one of the first to third aspects, forced chatter vibration and regenerative chatter vibration can be easily distinguished.

It is a schematic block diagram of a vertical machining center. It is a flowchart of the vibration suppression method. It is explanatory drawing which shows the generation | occurrence | production mechanism of forced chatter vibration. It is explanatory drawing which shows the input by the tool blade passage frequency in the a-a 'cross section of FIG. It is explanatory drawing which shows the transfer function of the mechanical system in the a-a 'cross section of FIG. It is explanatory drawing which shows the vibration amount in the aa 'cross section of FIG. It is explanatory drawing which shows the input in the generation | occurrence | production mechanism of a forced chatter vibration. (A) is explanatory drawing which shows the cutting in normal cutting, (B) is explanatory drawing which shows the dimension effect in minute cutting.

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 from the vibration sensor 7, a calculation value calculated by the calculation device 13, and a rotation of the spindle 3. A storage device 14 serving as storage means for storing the speed, the maximum acceleration of chatter vibration, and the like, and an input device 15 for inputting predetermined parameters to the arithmetic device 13 are provided. Among these, the arithmetic unit 13 functions as an upper limit rotational speed setting unit, a vibration discriminating unit, and a rotational speed selection unit, respectively, as a vibration detecting unit together with the vibration sensor 7, and as a rotational speed changing unit together with the NC unit 12. Function.

Hereinafter, a vibration suppression method during processing in the control device 11 will be described based on the flowchart of FIG. 2.
First, in S1, each parameter used in the arithmetic device 13 is input by the input device 15. As the parameters, the tool edge radius R, the work alteration depth T of the workpiece type, the upper limit rotation speed n _lim0 of the spindle 3, the threshold value of vibration amount (maximum acceleration), and the number of tool edges are set. The In S2, upon receiving the parameter input, the arithmetic unit 13 calculates the upper limit rotational speed n _lim1 based on the following formula (1) and the upper limit rotational speed n _lim2 based on the following formula (2). The three upper limit rotation speeds n _lim0 , n _lim1, and n _lim2 are compared, and the smallest value is set as the upper limit rotation speed n _lim of the spindle 3 in the storage device 14 (upper limit rotation speed setting step).

n _lim1 = v _f / (N × f _Z1 ) (1)
n _lim2 = v _f / (N × f _Z2 ) (2)
v _f : spindle feed speed per minute, N: number of tool blades, f _Z1 : R × P (R: radius of tool edge roundness, P: adjustment factor (for example, a value from 100% to 500%)), f _Z2 : T × Q (T: Deformed layer depth of workpiece grade, Q: Adjustment factor (for example, a value from 100% to 500%))
Therefore, for example, the upper limit rotational speed n _lim0 set from the limit cutting speed of the tool is 10,000 min ⁻¹ , the upper limit rotational speed n _lim1 considering the dimensional effect of the specific cutting resistance is 6,000 min ⁻¹ , and the work-affected layer depth is When the considered upper limit rotation speed n _lim2 is 8,000 min ⁻¹ , the selected upper limit rotation speed n _lim is 6,000 min ⁻¹ .

Next, machining is started in S3. During machining, vibration acceleration during machining obtained from the vibration sensor 7 is detected, converted into acceleration in the frequency domain by the arithmetic unit 13, and the obtained vibration amount (maximum acceleration). ) Is compared with a preset threshold value (S4). If the maximum acceleration exceeds the threshold value, it is determined that chatter vibration has occurred (vibration detection step), and it is determined whether the chatter vibration is a forced chatter vibration or a regenerative chatter vibration from the chatter frequency, the number of tool blades, and the rotational speed (S5). , Vibration discrimination step). In this determination, for example, the k value is calculated by the following expression, and when the k value is an integer, it is determined as forced chatter vibration, and otherwise it is determined as regenerative chatter vibration.
k = 60f _C / n ₀ N
(F _C : chatter vibration frequency, n ₀ : current rotation speed, N: number of tool blades)

  As shown in FIG. 3, the forced chatter vibration is generated in the range of f1, f2, and f3 by the input due to the cutting force fluctuation at the tool blade passing frequency indicated by the oblique dotted line of k = 1, 2, 3,. The k value obtained by the above calculation is an integer because it occurs on the part indicated by the oblique solid line that matches the indicated resonance frequency, that is, on the tool blade passing frequency line where the k value is an integer. This is to distinguish it from forced chatter vibration.

If it is determined NO in S5, that is, if it is regenerative chatter vibration, the optimum rotational speed n is calculated by the following formula in S6, the rotational speed of the spindle 3 is changed to the optimum rotational speed n, and the process returns to S4.
n = 60f _C / {(k1 + 1) N}
(K1: integer part of k value)

On the other hand, if the forced chatter vibration is determined in S5, the rotation speed and the vibration amount are stored in S7 (storage step), and the rotation speed is increased by a predetermined number in S8 (rotation speed changing step). .
As shown in FIG. 3, the rotational speed is increased when focusing on a certain resonance frequency, and when the rotational speed is increased, the interval between the tool blade passing frequencies (interval between dotted lines) becomes wider. This is because the rotation speed range in which the pass frequency and the resonance frequency range do not coincide with each other widens, and therefore there is a high possibility that there is a rotation speed at which no forced chatter vibration occurs.

  Also, as shown in FIGS. 4 to 6, the vibration amount is the product of the input at the tool blade passing frequency at each frequency and the transfer function of the mechanical system, so the input is reduced or the transfer function is reduced. Alternatively, the amount of vibration generated can be reduced by shifting the frequency between the input and the resonance frequency having a large transfer function. Here, it can be seen from FIG. 7 that when the feed of the tool 4 per minute (arrow A) is constant, the length of the cutting section 20 of the workpiece 6 is reduced by increasing the rotational speed at the arrow B. Since the input is proportional to the cut cross-sectional area of the product of the length of the cut cross-section 20 and the depth of cut in the direction perpendicular to the drawing, the input is reduced by reducing the length of the cut cross-section 20. For this reason, when the rotational speed is increased, the input is reduced and the amount of vibration is reduced.

After increasing the rotation speed in S8, the vibration amount is compared with the threshold value again in S9. Again, if the vibration amount is equal to or greater than the threshold value, that is, if the effect of suppressing the forced chatter vibration is not obtained even if the rotational speed is changed to the rising side, the vibration tends to expand from the result up to the current rotational speed in S10. Determine whether or not. For example, if the machining at the current rotational speed is the Nth, the difference between the Nth and N−1th vibration amounts is positive, and the difference between the N−1 and N−2th vibration amounts. If the difference in vibration amount becomes positive continuously for a certain number of times or more as the rotational speed is increased, it is determined that the vibration tends to expand.
If it is determined that the vibration tends to expand, the rotation speed is changed to the rotation speed with the smallest vibration amount in the storage device 14 in S11 (rotation speed selection step), and the rotation speed is processed until the processing ends in S12. Continue processing at.

On the other hand, if it is determined in S10 that the vibration does not tend to expand, it is determined in S13 whether the next rotation speed obtained by adding the rotation speed increase to the current rotation speed exceeds n _lim set in S2. Confirm. If n _lim is not exceeded, the process returns to S4 and continues control. Therefore, when the vibration amount still exceeds the threshold value (YES in S4) and forced chatter vibration (YES in S5), the rotational speed and the vibration amount are stored in S7, and then the rotational speed is again determined in S8. In step S9, the vibration amount is compared with the threshold value. That is, forced chatter vibration is suppressed by increasing the rotation speed stepwise within a range where the rotation speed does not reach n _lim .
If the next rotational speed exceeds n _lim in S13 without the forced chatter vibration being suppressed, the rotational speed is changed to the rotational speed with the smallest vibration amount in the storage device 14 in S11 (rotational speed selection step). The machining is continued at the rotational speed until the machining is finished.

In S10, it is determined whether or not the vibration tends to expand. In S13, it is determined whether or not the next rotational speed exceeds n _lim. The reason for changing to a rotational speed with a small amount of vibration is as follows.
First, as shown in FIG. 8 (A), when the cutting amount 21 is such that the influence of the roundness of the tool cutting edge 4A is negligible, the rounding of the tool cutting edge 4A as shown in FIG. 8 (B). When the cut depth is 22 so that the influence is not negligible, the specific cutting resistance is reduced by reducing the rake angle due to the "dimensional effect of specific cutting resistance" (see "Basic Cutting Machining" (Kyoritsu Publishing Co., Ltd.)). This is because chatter vibration is likely to occur. In addition, since the hardness is generally higher near the surface due to work hardening of the work-affected layer, chatter vibration is likely to occur when chipping is performed near the surface, chipping occurs, This is because wear progresses quickly. That, S10, judgment in S13, by the rotational speed kept up to near n _lim, to avoid the problem of defective tool or vibration is increased chatter conversely depth of cut is too small or generated It is processing of.

  As described above, according to the vibration suppressing device and method of the above aspect, when forced chatter vibration occurs, the rotational speed is changed to the upward side to reduce the vibration, but even if it is changed to the upward side, the vibration is reduced. If it is not connected, or if the next rotation speed to be changed exceeds the upper limit rotation speed, the rotation speed that minimizes the vibration amount is selected. If the effect of suppressing the forced chatter vibration cannot be obtained, the change to the rotation speed at which the cutting depth does not become extremely small can be made. Therefore, it is possible to appropriately deal with the generated chatter vibration without changing the time required until the machining is completed or causing an increase in chatter vibration due to an excessive change of the machining conditions.

  In particular, here, if forced chatter vibration is not suppressed even if the rotation speed is changed to the increase side, the storage of the rotation speed and vibration amount in S7 and the change to the increase side of the rotation speed in S8 are repeated, and the arithmetic unit 13, in S10, the vibration tends to expand, that is, the difference between the vibration amount at the rotation speed before the change and the vibration amount at the rotation speed after the change is calculated, and the difference becomes positive continuously for a certain number of times or more. In this case, since it is determined that the vibration amount has increased, it is possible to appropriately determine the increase in the vibration amount of the forced chatter vibration.

Further, the arithmetic unit 13 sets the lowest rotation speed among the rotation speed n _lim0 which is a preset limit cutting speed of the tool and the two rotation speeds n _lim1 and n _lim2 as the upper limit rotation speed. Therefore, the upper limit rotation speed can be set in the area with the most margin.
Further, the calculation device 13 calculates k = 60 f _C / n ₀ N (f _C : chatter vibration frequency, n ₀ : current rotation speed, N: number of tool blades), and when k is an integer, forced chatter vibration In other cases, since the chatter vibration is discriminated, the type of chatter vibration can be easily discriminated.

  The configuration related to the vibration suppression device of the present invention is not limited to the mode described in the above embodiment, and the configuration of the vibration detection means and the control device, the vibration suppression control, etc. depart from the spirit of the present invention. As long as it is not, it can be changed as needed.

For example, a displacement meter or a microphone can be employed as the vibration detection means, and vibration displacement or vibration sound can be used instead of vibration acceleration.
In the above embodiment, the rotation speed is automatically changed to the finally selected rotation speed, but a display device for displaying the result stored in the storage device is provided, and the operator manually operates based on the displayed result. You may change to the final rotation speed.
Furthermore, in the parameter setting in S1, the limit cutting speed V _lim and the tool diameter D of the tool can be set, and in S2, the upper limit rotational speed n _lim0 is set as n _lim0 = V _lim / (π × D). You may make it set.
In addition, the resonance frequency is measured in advance so that the resonance frequency can be input in S1, and the rotation speed is changed so as to exclude the rotation speed assumed to be unstable in consideration of the oblique solid line shown in FIG. The range may be limited.

Furthermore, in S10, whether or not the vibration tends to expand is calculated, but instead of comparing the measurement results for each time, the measurement results for several times may be averaged and compared. In this way, the influence of measurement errors can be suppressed. However, if the amount of vibration has increased before and after a single change in rotational speed, the rotational speed with the smallest amount of vibration may be selected without further increasing the rotational speed.
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 .... Tool, 5 .... Machining table, 6 .... Workpiece, 7 .... Vibration sensor, 10 .... Vibration suppression device, 11 .... Control device, 12 ·· NC device, 13 ·· Calculation device, 14 ·· Storage device, 15 ·· Input device, 20 ·· Cutting section, 21 ·· Cutting amount, 22 ·· Micro cutting amount.

Claims (5)

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,
Upper limit rotational speed setting means for setting an upper limit of the rotational speed based on a preset limit cutting speed and radius of cutting edge of the tool, and a work-affected layer depth of the material type of the workpiece ;
Vibration detecting means for detecting occurrence of chatter vibration;
Vibration discriminating means for discriminating the type of the detected chatter vibration;
When chatter vibration is detected by the vibration detection means, storage means for storing the rotation speed and vibration amount at that time;
If the chatter vibration discriminated by the vibration discriminating means is a forced chatter vibration, a rotational speed changing means for changing the rotational speed to the rising side;
If the amount of forced chatter vibration increases even when the rotational speed is changed to the upward side, or the next rotational speed to be changed to the upward side is the upper limit rotational speed set by the upper limit rotational speed setting means. A rotation speed selection means for selecting the rotation speed at which the amount of vibration is minimized from the rotation speed stored in the storage means without changing the rotation speed to the rising side. Vibration suppression device for machine tools characterized by   If the forced chatter vibration is not suppressed even if the rotation speed is changed to the increase side by the rotation speed change means, the rotation speed and vibration amount are stored by the storage means and the rotation speed is increased by the rotation speed change means. The rotation speed selection means calculates the difference between the vibration amount at the rotation speed before the change and the vibration amount at the rotation speed after the change, and the difference is corrected continuously for a certain number of times. 2. The vibration suppression device for a machine tool according to claim 1, wherein the vibration amount is determined to have increased in a case of becoming. The upper limit rotational speed setting means includes a rotational speed n _lim0 which is a preset limit cutting speed of the tool, and two rotational speeds n _lim1 and n _lim2 calculated based on the following equations (1) and (2). among them, the vibration suppression device for a machine tool according to the smallest rotational speed to claim 1 or 2, characterized in that the upper limit rotation speed.
n _lim1 = v _f / (N × f _Z1 ) (1)
n _lim2 = v _f / (N × f _Z2 ) (2)
v _f : spindle feed speed per minute, N: number of tool blades, f _Z1 : R × P (R: tool blade radius, P: adjustment factor), f _Z2 : T × Q (T: material type of workpiece) Deterioration depth of processed layer, Q: adjustment factor) The vibration discriminating means calculates k = 60 f _C / n ₀ N (f _C : chatter vibration frequency, n ₀ : current rotation speed, N: number of tool blades), and when k is an integer, forced chatter vibration, the vibration suppression device for a machine tool according to any one of claims 1 to 3 Otherwise, characterized in that to determine the playback chatter vibration. 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,
An upper limit rotation speed setting step for setting an upper limit of the rotation speed based on a preset limit cutting speed and a cutting edge radius of the tool, and a work-affected layer depth of the material type of the workpiece ;
A vibration detecting step for detecting occurrence of the chatter vibration;
A vibration discriminating step for discriminating the type of the detected chatter vibration;
When chatter vibration is detected by the vibration detection step, a storage step for storing the rotation speed and vibration amount at that time;
If the chatter vibration determined in the vibration determination step is a forced chatter vibration, a rotation speed changing step for changing the rotation speed to the rising side;
If the amount of forced chatter vibration increases even when the rotational speed is changed to the upward side, or the next rotational speed to be changed to the upward side is the upper limit rotational speed set in the upper limit rotational speed setting step. If the rotation speed exceeds the rotation speed, the rotation speed selection step of selecting the rotation speed at which the amount of vibration is minimized is executed from the rotation speed stored in the storage step without changing the rotation speed to the rising side. A method for suppressing vibration of a machine tool.

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