JP2019107751A - Machine tool, processing method, and processing program - Google Patents

Abstract

To provide a machine tool in which a vibration strength of forced chattering vibration can be further suppressed compared to a conventional one.SOLUTION: A machine tool comprises: a spindle for rotating a work-piece or a tool; a sensor for detecting a vibration frequency of the spindle or the tool; a calculation part which calculates a vibration strength of forced chattering vibration, which occurs in the spindle or the tool, based on the vibration frequency; and an adjustment part which adjusts a set value for controlling a rotation number of the spindle. The adjustment part decides a variation range of a rotation number of the spindle based on such a fact that chattering vibration occurs, changes the rotation number of the spindle in the variation range and acquires a vibration strength concerning each of plural rotation numbers, and uses a rotation number of the plural rotation numbers, such that the vibration strength becomes relatively smaller compared to the case before changing the rotation number of the spindle, as a set value.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a technique for suppressing forced chatter vibration generated in a machine tool.

  When machining a workpiece with a machine tool, the cutting edge of the tool may minutely vibrate. Such vibration is called chatter vibration. If chatter vibration occurs, the processing accuracy of the workpiece is reduced.

  Chatter vibration includes forced chatter vibration and regenerative chatter vibration. Forced chatter vibration is vibration generated by intermittent cutting and occurs when the vibration frequency of the tool becomes equal to the natural frequency of the tool. Regeneration chatter vibration is vibration that occurs when the relationship between the vibration frequency of the tool and the depth of cut of the workpiece by the tool satisfies a predetermined condition.

  There exists Unexamined-Japanese-Patent No. 2012-115963 (patent document 1) as a technique for suppressing forced chatter vibration. The machine tool disclosed in Japanese Patent Application Laid-Open No. 2012-115963 raises the spindle rotational speed when forced chatter vibration occurs, and stores the vibration intensity at each spindle rotational speed. The machine tool stops the increase of the spindle rotational speed when the vibration intensity increases more than before the change of the spindle rotational speed. The machine tool selects a spindle rotation number at which the vibration intensity is minimum among the stored spindle rotation numbers.

JP, 2012-115963, A

  Conventionally, it has been considered that once the vibration intensity increases in the process of increasing the spindle rotational speed, the vibration intensity does not decrease even if the spindle rotational speed is subsequently increased. However, the inventors newly discovered that if the spindle rotational speed is further increased after the vibration intensity once increases, the vibration intensity may further decrease. Therefore, like the machine tool shown in Patent Document 1, if the search for the spindle rotational speed is stopped when the vibration intensity once increases, the possibility that the spindle rotational speed at which the vibration intensity becomes minimum can not be searched. There is.

  The present disclosure has been made to solve the problems as described above, and it is an object of an aspect of the present invention to provide a machine tool capable of suppressing the vibration intensity of forced chatter vibration as compared to the prior art. . The purpose in another aspect is to provide a processing method that can suppress the vibration intensity of forced chatter vibration more than before. The purpose in another aspect is to provide a processing program that can suppress the vibration intensity of forced chatter vibration more than before.

  According to an aspect, a machine tool is generated on the spindle or the tool based on the spindle for rotating the workpiece or the tool, a sensor for detecting the vibration frequency of the spindle or the tool, and the vibration frequency. A calculation unit for calculating the vibration intensity of chatter vibration, and an adjustment unit for adjusting a set value for controlling the rotation speed of the spindle. The adjusting unit determines a fluctuation range of the rotation speed of the spindle based on the occurrence of the chatter vibration, changes the rotation speed of the spindle within the fluctuation range, and determines each of the plurality of rotation speeds. The vibration intensity is acquired, and among the plurality of rotation numbers, the rotation number which is relatively smaller than that before changing the rotation number of the spindle is used as the setting value.

  Preferably, the adjustment unit uses, as the set value, a rotation number at which the vibration intensity is minimized among the plurality of rotation numbers changed within the fluctuation range.

  Preferably, the adjustment unit changes the number of rotations of the main spindle by a predetermined value within the variation range and sequentially acquires the vibration intensity for each number of rotations, and the value of the vibration intensity acquired for adjacent numbers of rotations When the degree of increase exceeds a predetermined threshold, changing the number of revolutions of the spindle is stopped.

  Preferably, the calculation unit performs Fourier transform on the vibration frequency to calculate the vibration intensity for each frequency, and calculates the maximum vibration intensity among the calculated plurality of vibration intensities as the vibration intensity.

  Preferably, when the range of cutting conditions in which chatter vibration does not occur in the relationship between the cutting depth of the work by the tool and the number of rotations of the spindle is set as the stable region, the machine tool is in the stable region Among the cutting conditions, it further includes a specifying unit for specifying a plurality of rotation speeds that can make the cutting depth relatively deeper than the other rotation speeds. The variation range is included between a first rotation number of the plurality of rotations identified above and a second rotation number adjacent to the first rotation among the plurality of rotations.

  Preferably, the fluctuation range is included between the first rotation number and an average value of the first rotation number and the second rotation number.

  Preferably, the frequency of the chatter vibration is fc, the number of blades of the tool is z, the current number of revolutions of the spindle is N, and the integer part of 60 × fc / (z × N) is k. The above-mentioned fluctuation range corresponds to the range of N shown in the following formula (1).

  According to another aspect, a machining method by a machine tool is provided. The machine tool includes a spindle for rotating a workpiece or a tool, and a sensor for detecting the vibration frequency of the spindle or the tool. The processing method comprises the steps of: calculating the vibration intensity of chatter vibration occurring in the spindle or the tool based on the vibration frequency; and adjusting a set value for controlling the number of rotations of the spindle. Prepare. The adjusting step determines a fluctuation range of the rotation speed of the spindle based on the occurrence of the chatter vibration, changes the rotation speed of the spindle within the fluctuation range, and changes each of the plurality of rotation speeds. And acquiring, among the plurality of rotational speeds, using the rotational speed that is relatively smaller than that before changing the rotational speed of the main spindle as the setting value. .

  According to another aspect, there is provided a machining program to be executed on a machine tool. The machine tool includes a spindle for rotating a workpiece or a tool, and a sensor for detecting the vibration frequency of the spindle or the tool. The machining program comprises the steps of: calculating, on the machine tool, the vibration intensity of chatter vibration occurring in the spindle or the tool based on the vibration frequency; and setting values for controlling the number of rotations of the spindle. And adjusting. The adjusting step determines a fluctuation range of the rotation speed of the spindle based on the occurrence of the chatter vibration, changes the rotation speed of the spindle within the fluctuation range, and changes each of the plurality of rotation speeds. And acquiring, among the plurality of rotational speeds, using the rotational speed that is relatively smaller than that before changing the rotational speed of the main spindle as the setting value. .

In one aspect, it is possible to suppress the vibration intensity of forced chatter vibration more than before.
The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention taken in conjunction with the accompanying drawings.

It is a figure showing an example of the machine tool according to an embodiment. It is a figure for demonstrating the suppression method of forced chatter vibration. It is a figure showing an example of functional composition of a machine tool according to an embodiment. It is a figure which shows roughly the calculation process of the vibration strength by a calculation part. It is the figure which expanded fluctuation range (DELTA) R vicinity in the graph G2 shown by FIG. It is a figure which shows an example of the cutting aspect of the workpiece | work W. FIG. It is a figure showing the cutting aspect shown by FIG. 6 from a Z direction. It is a flowchart showing adjustment processing of a spindle rotational speed. It is a block diagram showing the main hardware constitutions of the machine tool according to an embodiment.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description of these will not be repeated. In addition, each embodiment and each modification which are explained below may be combined suitably suitably.

[A. Configuration of machine tool 100]
The configuration of the machine tool 100 will be described with reference to FIG. FIG. 1 is a view showing an example of a machine tool 100. As shown in FIG.

  A machine tool 100 as a machining center is shown in FIG. Although the machine tool 100 as a machining center will be described below, the machine tool 100 is not limited to the machining center. For example, the machine tool 100 may be a lathe or any other cutting machine or grinding machine. The machine tool 100 may be a vertical machining center to which a tool is attached in the vertical direction, or may be a horizontal machining center to which a tool is attached in the horizontal direction.

  As shown in FIG. 1, the machine tool 100 has a bed 12, a saddle 18, a column 21, a spindle head 41, and a table 26 as main components.

  The bed 12 is a base member for mounting the saddle 18, the column 21 and the like, and is installed on a mounting surface of a factory or the like.

  A column 21 is attached to the bed 12. The column 21 is fixed to the bed 12. The column 21 generally has a gate-like shape standing on the upper surface of the bed 12.

  More specifically, the column 21 has side portions 22 (22s, 22t) and a top 23 as its component parts. The side portion 22 is provided to rise vertically upward from the upper surface of the bed 12. The side 22s and the side 22t are spaced apart in the X axis direction parallel to the horizontal direction. The top 23 extends from the side 22s to the side 22t along the X-axis direction.

  The machine configuration of the machine tool 100 basically has a left-right symmetric structure with respect to the center in the X-axis direction. In the present embodiment, the configurations in which “s” and “t” are attached to reference numbers are a pair of parts corresponding to the left-right symmetry.

  A saddle 18 is attached to the bed 12. The saddle 18 is provided slidably in the X axis direction with respect to the bed 12. A spindle head 41 is attached to the saddle 18. The spindle head 41 extends toward the table 26 through the space surrounded by the side 22s, the top 23, the side 22t and the bed 12. The spindle head 41 is parallel to the horizontal direction, and is provided slidably in the Z-axis direction orthogonal to the X-axis direction.

  The spindle head 41 has a spindle 42 and a housing 43. The main shaft 42 is disposed inside the housing 43, and rotatably provided by motor drive around a central axis AX1 parallel to the Z-axis direction. At this time, the housing 43 does not rotate. On the spindle 42, a tool for processing a workpiece to be processed is mounted. As the main shaft 42 rotates, a tool mounted on the main shaft 42 rotates about the central axis AX1. When the machine tool 100 is a lathe, a work is mounted on the spindle. In this case, as the main shaft 42 rotates, the work mounted on the main shaft 42 rotates.

  The housing 43 is provided with an acceleration sensor 110 for detecting the vibration frequency of the tool 32 or the spindle 42. Preferably, a plurality of acceleration sensors 110 are provided in the housing 43, and each acceleration sensor 110 detects vibrations of the tool 32 or the spindle 42 in different directions (for example, X, Y, Z directions). The sensor for detecting the vibration frequency of the tool 32 or the main shaft 42 is not limited to the acceleration sensor 110, and any sensor capable of detecting the vibration frequency of the tool 32 or the main shaft 42 may be used.

  The bed 12, the saddle 18, and the spindle head 41 are used as a feed mechanism, a guiding mechanism, and a drive source to enable sliding movement of the saddle 18 in the X axis direction and sliding movement of the spindle head 41 in the Z axis direction. A servomotor etc. are suitably provided.

  A table 26 is attached to the column 21. The table 26 is provided parallel to the column 21 so as to be slidable in the Y-axis direction orthogonal to the X-axis direction and the Z-axis direction with respect to the column 21.

  The table 26 is a device for fixing a work, and has a pallet 27 and rotation mechanisms 29 (29s, 29t).

  The pallet 27 is a metal base and works are attached using various clamp mechanisms. The pallet 27 is provided so as to be pivotable about a central axis AX2 parallel to the X-axis by the rotation mechanism unit 29 (a-axis pivoting). The rotation mechanism portion 29s and the rotation mechanism portion 29t are disposed at an interval in the X-axis direction. The pallet 27 is mounted between the rotation mechanism 29s and the rotation mechanism 29t. The pallet 27 may be further provided so as to be pivotable about a central axis orthogonal to the main surface of the pallet 27 (b-axis pivoting).

  The column 21 and the table 26 are appropriately provided with a feed mechanism and a guide mechanism for enabling the slide movement of the table 26 in the Y-axis direction, a servomotor as a drive source, and the like.

  The slide movement of the saddle 18 in the X-axis direction, the slide movement of the spindle head 41 in the Z-axis direction, and the slide movement of the table 26 in the Y-axis direction combine to form the machining position of the workpiece by the tool mounted on the spindle 42 Move in three dimensions.

  The machine tool 100 further includes a magazine 30 and an automatic tool changer (ATC: Automatic Tool Changer) 36. The magazine 30 is a device for accommodating the replacement tool 32 mounted on the main shaft 42. The automatic tool changer 36 is a device for changing tools between the main shaft 42 and the magazine 30.

  The magazine 30 has a magazine body 31, column members 14 and 16, and a base member 33.

  The magazine body 31 has a plurality of tool holders 34 and sprockets 35. The tool holder 34 is configured to be able to hold the tool 32. The plurality of tool holders 34 are annularly arranged around the sprocket 35. The sprocket 35 is rotatably provided about a central axis AX3 parallel to the Y axis by motor drive. Along with the rotation of the sprocket 35, the plurality of tool holding portions 34 rotate about the central axis AX3.

  The magazine body portion 31 is supported by the column members 14 and 16 and the base member 33 at a position where the distance from the bed 12 in the vertically upward direction is provided.

  As the sprocket 35 rotates, a tool holder 34 for holding a specific tool 32 is indexed to a predetermined position in front of the machine. The specific tool 32 is transported in the Z-axis direction by a tool transport device (not shown) and moved to the tool replacement position. By pivoting the double arm 37 of the automatic tool changer 36, the specific tool 32 transported to the tool change position and the tool mounted on the spindle 42 are exchanged. The tool 32 that can be mounted on the spindle 42 includes, for example, a milling cutter such as an end mill.

[B. Adjustment processing of spindle speed]
When the machine tool 100 processes a workpiece, chatter vibration may occur in which the cutting edge of the tool 32 slightly vibrates. Chatter vibration includes forced chatter vibration and regenerative chatter vibration. Forced chatter vibration is vibration generated by the machine tool 100 as a vibration source and occurs when the vibration frequency of parts such as the tool 32 and the spindle 42 becomes equal to the natural frequency of the part. Regeneration chatter vibration is vibration that occurs when the relationship between the vibration frequency of the tool 32 and the depth of cut of the workpiece by the tool 32 satisfies a predetermined condition.

  Below, with reference to FIG. 2, the suppression method of forced chatter vibration is demonstrated. FIG. 2 is a diagram for explaining a method of suppressing forced chatter vibration.

  In FIG. 2A, the relationship between the number of revolutions of the spindle 42 and the depth of cut of the workpiece W by the tool 32 is shown as a graph G1. The graph G1 is also referred to as a stable lobe (stable limit diagram). Hereinafter, the number of revolutions of the main spindle 42 is also simply referred to as “spindle number of revolutions”. In addition, since the spindle 42 interlocks with the tool 32, the spindle rotational speed is synonymous with the rotational speed of the tool 32.

  The horizontal axis of the graph G1 represents the spindle rotational speed. The unit of the spindle rotational speed is represented, for example, by "rpm (Rotation Per Minute)". That is, the spindle rotational speed represents the rotational speed per unit time. The vertical axis of the graph G1 represents the cutting depth of the work W by the tool 32. The cutting depth referred to here is the length of the contact portion between the tool 32 and the work W in the axial direction of the main spindle 42.

  A boundary line 50 is shown in the graph G1. The range in which the cutting depth of the workpiece is smaller than the boundary line 50 represents cutting conditions in which regenerative chatter vibration is less likely to occur. The range is shown as stable region A. The stable area A represents the range of cutting conditions in which the regenerative chatter vibration does not occur with respect to the relationship between the cutting depth of the workpiece W by the tool 32 and the spindle rotational speed. The range in which the cutting depth of the workpiece is larger than the boundary line 50 represents cutting conditions in which regenerative chatter vibration is likely to occur. The range is shown as unstable region B. The unstable region B represents the range of cutting conditions in which the regenerative chatter vibration occurs in the relation between the cutting depth of the workpiece W by the tool 32 and the spindle rotational speed.

  In FIG. 2B, the relationship between the spindle rotational speed and the vibration intensity of the forced chatter vibration is shown as a graph G2. The graph G2 shows the relationship between the spindle rotational speed and the vibration intensity of the forced chatter vibration when the spindle rotational speed is set to the depth of cut "h" which is always within the stable range. The horizontal axis of the graph G2 represents the spindle rotational speed. The unit of the spindle rotational speed is expressed, for example, in rpm. The vertical axis of the graph G2 represents the vibration intensity of chatter vibration. Details of a method of calculating the vibration intensity of chatter vibration will be described later.

  If the cutting conditions of the cutting depth of the workpiece W and the spindle rotational speed exist in the stable region A, the regenerative chatter vibration does not occur. However, even if the cutting conditions of the cutting depth of the workpiece W and the spindle rotational speed exist in the stable region A, forced chatter vibration may occur. The forced chatter vibration can be suppressed by changing the spindle rotational speed, but if the cutting conditions of the cutting depth of the workpiece W and the spindle rotational speed enter the unstable region B, then the regenerative chatter vibration occurs. Therefore, the machine tool 100 needs to change the cutting conditions so as to suppress both forced chatter vibration and regeneration chatter vibration. Whether or not the forced chatter vibration is occurring, and whether or not the regenerative chatter vibration is produced can be determined by the magnitude of the vibration strength. Therefore, the machine tool 100 can suppress chatter vibration regardless of the types of forced chatter vibration and regenerative chatter vibration by setting the cutting conditions so as to reduce the vibration strength as much as possible.

  Conventionally, the vibration intensity of forced chatter vibration is maximized at the peak portions M1 and M2 of the boundary 50 at which the integral multiple of the cutting edge passing frequency coincides with the natural frequency, and the boundary 50 between the peak portions M1 and M2 It was considered to be the smallest in the valley portion V1. That is, it is considered that the vibration intensity decreases as the spindle rotational speed increases from "r1" to "r10", and the vibration intensity increases again as the spindle rotational speed increases from the rotational speed "r10" to the rotational speed "r20" It was being done.

  However, as shown by the graph G2, the inventors do not uniformly reduce the vibration intensity in the process of the spindle rotational speed rising from the rotational speed "r1" to the rotational speed "r10", and the spindle rotational speed rotates. It was discovered that the vibration intensity did not increase uniformly in the process of rising from the number "r10" to the rotational speed "r20". Such a discovery itself is novel and can be said to be the achievements of the inventors.

  One of the reasons why the vibration intensity does not change uniformly with respect to the spindle rotational speed is that a plurality of parts such as the tool 32 and the spindle 42 are involved in the processing of the work in a combined manner. Since the natural frequencies of these parts are different, the natural frequencies are different at each point. Therefore, it is considered that the vibration intensity does not change uniformly with respect to the spindle rotational speed.

  The machine tool 100 according to the present embodiment adjusts the spindle rotational speed so that the vibration intensity of forced chatter vibration can be suppressed even when the vibration intensity does not change uniformly with respect to the spindle rotational speed. More specifically, machine tool 100 determines variation range ΔR of the spindle rotational speed based on the occurrence of forced chatter vibration. Thereafter, the machine tool 100 changes the spindle rotational speed within the fluctuation range ΔR and acquires vibration intensity for each spindle rotational speed.

  Hereinafter, the spindle rotational speed selected from the fluctuation range ΔR is also referred to as “spindle rotational speed of setting candidate”. In FIG. 2, spindle rotational speeds “r1” to “r10” are shown as spindle rotational speeds of setting candidates.

  When the spindle rotational speeds "r1" to "r10" are respectively set, the vibration intensities are "a1" to "a10", respectively. The machine tool 100 uses, as the setting value, the spindle rotation number which is relatively smaller in vibration intensity than before changing the spindle rotation number among the spindle rotation numbers “r1” to “r10” of the setting candidates. Thereby, the machine tool 100 can suppress the vibration intensity more reliably even if the vibration intensity does not change uniformly with respect to the spindle rotational speed.

  Preferably, the machine tool 100 uses, as the setting value, the spindle rotational speed “r8” at which the vibration intensity is minimum among the spindle rotational speeds “r1” to “r10” of the setting candidates. Thereby, the machine tool 100 can minimize the vibration intensity of chatter vibration.

  In addition, if the machine tool 100 has a spindle rotation number at which the vibration intensity is smaller than before the change of the spindle rotation number, any spindle rotation number among the spindle rotation numbers "r1" to "r10" of the setting candidate is set. It can be used as a value. That is, the machine tool 100 does not necessarily have to use the spindle rotational speed "r8" at which the vibration intensity is minimum as the setting value. For example, the machine tool 100 may use, as the setting value, the spindle rotational speed “r9” having the second smallest vibration intensity among the spindle rotational speeds “r1” to “r10” of the setting candidates. Alternatively, the machine tool 100 specifies a predetermined number of spindle rotational speeds in which the vibration intensity is relatively smaller than the spindle rotational speed before change among the spindle rotation speeds “r1” to “r10” of the setting candidate An average value or median value of a predetermined number of spindles may be used as the setting value.

[C. Method of determining fluctuation range ΔR]
The variation range ΔR of the spindle rotational speed can be determined by various methods. In the following, specific examples 1 to 3 of the method of determining the fluctuation range ΔR will be described with reference to FIG.

(C1: Specific example 1 of the method of determining the fluctuation range ΔR)
First, a specific example 1 of the method of determining the fluctuation range ΔR will be described.

  In this specific example, the machine tool 100 determines the fluctuation range ΔR of the spindle rotational speed based on the spindle rotational speeds “r1” and “r20” in the mountain portions M1 and M2 of the stable area A. The spindle rotational speeds “r1” and “r20” at the mountain portions M1 and M2 are spindle rotations capable of making the cutting depth relatively deeper than other spindle rotational speeds among the cutting conditions in the stable region A. It corresponds to the number. That is, the spindle rotational speeds “r1” and “r20” correspond to the spindle rotational speeds that can make the cutting depth maximum or substantially maximum among the spindle rotational speeds within the predetermined range. The machine tool 100 determines the variation range ΔR of the spindle rotational speed based on the spindle rotational speeds “r1” and “r20” in the mountain portions M1 and M2.

  As an example, the spindle rotational speed in the mountain portion is calculated according to the following equation (2).

  “N” shown in the equation (2) corresponds to the main spindle rotational speed in the mountain portion in the stable area A. "Fc" represents the frequency of chatter vibration. "Z" represents the number of cutting tools. "K" is referred to as the order of chatter vibration. The order represents the wave number of the processing surface generated by the vibration of the tool 32 from the time when the first blade of the tool 32 contacts the work to the time when the second blade contacts the work. The above equation (2) is a modified example of the Tobias equation. Assuming that “fc” in the above equation (2) is a natural frequency of the tool and “k” is a natural number, the above equation (2) is a Tobias equation. "K" shown by the said Formula (2) is represented by following formula (3).

“N ₀ ” shown in the equation (3) represents the present spindle rotational speed (spindle rotational speed before change). “[]” Shown in equation (3) is a Gaussian symbol, and extracts the integer part in parentheses. That is, in the equation (3), the integer part of “60 × fc / (n ₀ × z)” is extracted.

  The machine tool 100 substitutes the current spindle rotational speed into the above-mentioned equation (3), and calculates the order “k” corresponding to the current spindle rotational speed. Thereafter, the machine tool 100 substitutes the calculated order "k" into the above equation (2) to calculate the spindle rotational speed "N". The main spindle rotational speed “N” corresponds to the main spindle rotational speed “r1” in the mountain portion M1.

  Next, the machine tool 100 calculates the spindle rotational speed “N” after replacing “k” in the above equation (2) with “k−1”. The main spindle rotational speed “N” corresponds to the main spindle rotational speed “r20” in the mountain portion M20. At this time, by setting “k” in the above equation (2) to “k + n” (n: integer), it is possible to calculate more spindle rotational speeds in the mountain portion.

  The machine tool 100 has a fluctuation range ΔR so as to be included between the spindle rotational speed “r1” (first rotational speed) calculated based on the above equations (2) and (3) and the spindle rotational speed “r20”. Decide. That is, in the present specific example, any fluctuation range ΔR can be adopted as long as it is between the spindle rotational speeds “r1” and “r20”. The machine tool 100 can reliably detect the spindle rotational speed at which the vibration intensity can be minimized by fluctuating the spindle rotational speed within the wide fluctuation range ΔR.

(C2: Specific example 2 of the method of determining the fluctuation range ΔR)
Next, specific example 2 of the method of determining the fluctuation range ΔR will be described.

  In this specific example, the machine tool 100 calculates the spindle rotational speed based on the spindle rotational speed "r1" in the peak portion M1 of the stable area A and the spindle rotational speed "r10" in the valley portion V1 of the stable area A. The fluctuation range ΔR is determined.

  The spindle rotational speed “r1” in the mountain portion M1 corresponds to the spindle rotational speed capable of making the cutting depth relatively deeper than the other spindle rotational speeds among the cutting conditions in the stable region A. That is, the spindle rotational speed "r1" corresponds to the spindle rotational speed capable of maximizing or substantially maximizing the cutting depth within the spindle rotational speed within the predetermined range.

  The spindle rotational speed “r10” in the valley portion V1 corresponds to the spindle rotational speed at which the cutting depth is relatively shallower than the other spindle rotational speeds among the cutting conditions in the stable region A. That is, the spindle rotational speed "r10" corresponds to the spindle rotational speed at which the cutting depth is minimized or substantially minimized among the spindle rotational speeds within the predetermined range.

  The machine tool 100 determines the variation range ΔR of the spindle rotational speed based on the spindle rotational speed “r1” in the peak portion M1 and the spindle rotational speed “r20” in the valley portion V1.

  The spindle rotational speed “r1” in the mountain portion M1 is calculated based on the above equations (2) and (3). The method of calculating the spindle rotational speed "r1" is as described above, and therefore the description thereof will not be repeated.

  The spindle rotational speed "V1" in the valley portion V1 is calculated based on, for example, the spindle rotational speeds "r1" and "r20" in the adjacent mountain portion. As an example, the machine tool 100 calculates the average value of the spindle rotational speeds "r1" and "r20" as the spindle rotational speed "r10" in the valley portion V1.

  The machine tool 100 determines the fluctuation range ΔR so as to be included between the spindle rotational speed “r1” in the mountain portion M1 and the spindle rotational speed “r10” in the valley portion V1. That is, the machine tool 100 determines the variation range ΔR so as to be between the main spindle rotation number in the peak portion closest to the current main spindle rotation number and the main spindle rotation number in the valley portion adjacent to the peak portion.

  It is highly possible that the fluctuation range ΔR determined in this manner includes the main spindle rotational speed at which the vibration intensity is minimized. Further, the search range of the spindle rotational speed is further limited, whereby the search time of the spindle rotational speed is shortened. The machine tool 100 can detect the spindle rotational speed that can minimize the vibration intensity reliably and at an early stage by fluctuating the spindle rotational speed within the fluctuation range ΔR thus determined.

(C3: Specific example 3 of the method of determining the fluctuation range ΔR)
Next, a specific example 3 of the method of determining the fluctuation range ΔR will be described.

  In this specific example, the machine tool 100 determines the fluctuation range ΔR of the spindle rotational speed so as to be between the spindle rotational speeds of the valley portions located on both sides of the peak portion M1 of the stable area A. In the above-mentioned “second specific example of the method of determining the variation range ΔR”, the main spindle rotational speed in the valley portion is calculated to be an average value of the main spindle rotational speeds “r1” and “r20” in the peak portions M1 and M2. In the present specific example, the spindle rotational speed in the valley portion is calculated based on the above equations (2) and (3).

  More specifically, the machine tool 100 sets the spindle rotational speed calculated by replacing “k” in the above equation (2) with “k + 0.5” as the lower limit value, and makes “k” in the above equation (2) The fluctuation range ΔR is determined with the spindle rotational speed calculated by replacing “k−0.5” as the upper limit value. That is, the range of “N” shown in the following equation (4) corresponds to the variation range ΔR.

  The “N”, “fc”, “z” and “k” shown in the above equation (4) are as described in the above equation (2), and therefore the description thereof will not be repeated.

  The machine tool 100 can easily calculate the spindle rotational speed at the valley portion by using the above-mentioned equation (4). It is highly possible that the fluctuation range ΔR determined in this manner includes the main spindle rotational speed at which the vibration intensity is minimized. The machine tool 100 can reliably discover the spindle rotational speed at which the vibration intensity can be minimized by fluctuating the spindle rotational speed within the fluctuation range ΔR determined in this manner.

[D. Functional configuration of machine tool 100]
The functions of the machine tool 100 will be described with reference to FIGS. 3 to 7. FIG. 3 is a diagram showing an example of a functional configuration of the machine tool 100. As shown in FIG.

  The machine tool 100 includes a control device 101 and a storage device 120 as main hardware configurations. The control device 101 is, for example, an NC control device for executing a numerical control (NC) program. The NC controller is configured by at least one integrated circuit. The integrated circuit is configured by, for example, at least one central processing unit (CPU), at least one application specific integrated circuit (ASIC), at least one field programmable gate array (FPGA), or a combination thereof.

  As shown in FIG. 3, the control device 101 calculates a vibration intensity of chatter vibration occurring in the machine tool 100, an adjustment unit 150 for adjusting the spindle rotational speed, and the spindle 42. And an output unit 160 for outputting a control command value to a motor for driving the motor.

  Hereinafter, details of the functions of the calculation unit 140, the adjustment unit 150, and the output unit 160 will be described in order.

(D1. Calculation unit 140)
First, the function of the calculation unit 140 will be described with reference to FIG. FIG. 4 is a diagram schematically showing the calculation process of the vibration intensity by the calculation unit 140. As shown in FIG.

  The calculation unit 140 includes an FFT (Fast Fourier Transform) unit 142 and an extraction unit 144. The FFT unit 142 samples the acceleration detected by the acceleration sensor 110 (see FIG. 1) during processing of the workpiece at a predetermined sampling rate, and Fourier-transforms the sampling result. Typically, the FFT unit 142 samples the acceleration while the tool 32 is in contact with the workpiece W. FIG. 4 shows a vibration frequency 70A as an example of the sampling result.

  The FFT unit 142 performs fast Fourier transform on the vibration frequency 70A to perform frequency decomposition of the vibration frequency 70A, and calculates the vibration intensity for each frequency. A spectrum 70B is shown in FIG. 4 as an example of the result of the Fourier transform. The horizontal axis of spectrum 70B represents frequency. The vertical axis of the spectrum 70B represents the vibration intensity. The said vibration intensity shows the magnitude | size of an amplitude.

  The extraction unit 144 extracts the maximum vibration intensity as the vibration intensity of the tool 32 or the spindle 42 among the vibration intensities at each frequency shown in the spectrum 70B. In the example of FIG. 4, the vibration intensity at the frequency “f” is extracted as the vibration intensity of the tool 32 or the spindle 42. The calculated vibration intensity is sequentially output to the adjustment unit 150.

  In the above, an example in which the vibration intensity is calculated from the detection result of acceleration in one direction has been described, but the vibration intensity from the detection result of acceleration in a plurality of directions (for example, X to Z directions shown in FIG. 1) May be calculated. In this case, the maximum value of the vibration intensity detected in each direction is adopted as the vibration intensity. Alternatively, the average value of the vibration intensity detected in each direction is calculated as the vibration intensity.

(D2. Adjustment unit 150)
Next, the function of the adjustment unit 150 will be described with reference to FIG. FIG. 5 is an enlarged view of the vicinity of the fluctuation range ΔR in the graph G2 shown in FIG.

  Adjustment unit 150 includes a change unit 152 and a setting unit 154. The changing unit 152 determines the fluctuation range ΔR of the spindle rotational speed based on the occurrence of the forced chatter vibration. The method of determining the fluctuation range ΔR is as described above, and therefore the description thereof will not be repeated. The changing unit 152 raises the setting value 124 of the spindle rotational speed by a predetermined value within the determined fluctuation range ΔR. In the example of FIG. 5, the changing unit 152 changes the setting value 124 in order from the spindle rotational speed “r1” to the spindle rotational speed “r10”. As a result, it is assumed that the vibration intensity of the main shaft 42 changes in the order of “a1” to “a10”.

  At this time, the adjustment unit 150 may sequentially change the cutting depth of the work W so as to be within the stable region A, or may maintain the currently set cutting depth. When maintaining the currently set depth of cut, the adjustment unit 150 sequentially changes the spindle rotational speed within the range that falls within the stable region A. In other words, the adjustment unit 150 sequentially changes the spindle rotational speed so as not to adopt the cutting condition in the unstable region B.

  The changing unit 152 stops changing the spindle rotational speed when the degree of increase in vibration intensity acquired for the spindle rotational speeds adjacent to each other exceeds a predetermined threshold. If the vibration intensity of the spindle 42 becomes larger than a predetermined threshold, the vibration intensity will be further increased even if the spindle rotational speed is changed thereafter, and there is a risk that the damage to the tool, the machine tool, and the work will increase. It is for. In addition, when the vibration intensity of the main shaft 42 becomes larger than a predetermined threshold value, the possibility that the vibration intensity decreases is low even if the spindle rotational speed is changed thereafter. In the example of FIG. 5, when the spindle rotational speed is changed from "r9" to "r10", the vibration intensity is increased from "a9" to "a10". When the increase degree of the vibration strengths “a9” and “a10” acquired for the spindle rotational speeds “r9” and “r10” adjacent to each other exceeds the predetermined threshold, the change unit 152 changes the spindle rotational speed Stop making changes. The change unit 152 can shorten the time required for the adjustment processing of the spindle rotational speed by stopping the change of the spindle rotational speed midway, and can prevent the increase of the vibration intensity in advance.

  The setting unit 154 sets, as the setting value 124, the spindle rotational speed whose vibration intensity is relatively smaller than that before the change of the spindle rotational speed among the spindle rotational speeds “r1” to “r10” changed in the fluctuation range ΔR. Use. At this time, the setting unit 154 can adopt any spindle rotation number from among the spindle rotation numbers “r1” to “r10” as long as the vibration intensity is smaller than that before the change of the spindle rotation number. . In one aspect, as illustrated in FIG. 5, the setting unit 154 uses, as the setting value 124, the spindle rotational speed “r8” that minimizes the vibration intensity among the spindle rotational speeds “r1” to “r10”. Thereby, the machine tool 100 can minimize the vibration intensity of forced chatter vibration.

(D3. Output unit 160)
The output unit 160 generates a control command value for a servo driver 106 (see FIG. 9) described later, in accordance with the current setting value 124. The control command value includes, for example, a rotational speed and a target position. The servo driver 106 controls the servomotor 107 (see FIG. 9) that drives the main shaft 42 based on the reception of the control command value from the output unit 160. A workpiece is processed by sequentially outputting control command values from the output unit 160.

  FIG. 6 is a view showing an example of a cutting mode of the work W. As shown in FIG. FIG. 7 is a view showing the cutting mode shown in FIG. 6 from the Z direction.

  6 and 7 show a tool 32 as an end mill. The tool 32 has a plurality of blades on its side and cuts the workpiece W by contacting the workpiece W while rotating. In the example of FIG. 6 and FIG. 7, the tool 32 repeatedly cuts the work W along the processing path L determined in advance according to the control command value from the output unit 160.

  More specifically, the tool 32 successively cuts the first cut portion of the cutting width Ap for each cutting width Ae. Next, the tool 32 sequentially cuts the second-stage cut portion of the cutting width Ap for each cutting width Ae. Next, the third-step cut portion of the cutting width Ap is sequentially cut for each cutting width Ae. Next, the fourth cut portion of the cutting width Ap is sequentially cut for each cutting width Ae. As described above, the tool 32 processes the work W into an arbitrary shape by sequentially cutting the work W with the cutting widths Ae and Ap equally divided along the predetermined processing path L.

[E. Control structure of machine tool 100]
The control structure of the machine tool 100 will be described with reference to FIG. FIG. 8 is a flowchart showing adjustment processing of the spindle rotational speed. The process of FIG. 8 is realized by the control device 101 of the machine tool 100 executing a program. In other aspects, some or all of the processing may be performed by circuit elements or other hardware.

  In step S110, the control device 101, as the calculation unit 140 (see FIG. 3) described above, determines whether or not forced chatter vibration occurs in the machine tool 100. More specifically, the control device 101 calculates the present vibration intensity based on the output value from the acceleration sensor 110 (see FIG. 1). The method of calculating the vibration intensity is as described above with reference to FIG. The control device 101 determines that forced chatter vibration occurs when the current vibration intensity exceeds a predetermined threshold. When it is determined that the forced chatter vibration is occurring (YES in step S110), the control device 101 switches the control to step S112. If not (NO in step S110), control device 101 ends the process shown in FIG.

  In step S112, the control device 101 determines the variation range ΔR (see FIG. 2) of the spindle rotational speed as the adjustment unit 150 (see FIG. 3) described above. The method of determining the fluctuation range ΔR is as described above, and therefore the description thereof will not be repeated.

  In step S120, the control device 101 causes the spindle rotation number to increase by a predetermined value above the current value, as the adjustment unit 150 described above. The increase amount of the spindle rotational speed may be set in advance or may be arbitrarily set by the user.

  In step S122, the control device 101 samples the output signal from the acceleration sensor 110 (see FIG. 1) at a predetermined sampling rate at the main spindle rotational speed after the change in step S120 as the calculation unit 140 described above. The sampling result is acquired as a vibration frequency.

  In step S124, the control device 101, as the calculation unit 140 described above, calculates the vibration intensity based on the vibration frequency acquired in step S122. The method of calculating the vibration intensity is as described above with reference to FIG.

  In step S126, the control device 101 causes the main spindle rotational speed after change in step S120 to correspond to the vibration intensity calculated in step S124 as the calculation unit 140 described above, and then the correspondence relationship between them is described later. The detection information 123 (see FIG. 9) is written.

  In step S130, the control device 101, as the adjusting unit 150 described above, determines whether or not the change of the spindle rotational speed is to be ended. As an example, next, when the spindle rotational speed is increased by a predetermined value in step S120, when the spindle rotational speed after the increase exceeds the fluctuation range ΔR, it is determined that the change of the spindle rotational speed is ended. . Further, when the degree of increase to the vibration intensity calculated at this time from step S124 exceeds the predetermined threshold from the vibration intensity calculated at step S124, the control device 101 changes the spindle rotational speed. Judge to finish. When it is determined that the change of the spindle rotational speed is finished (YES in step S130), the control device 101 switches the control to step S132. If not (NO in step S130), control device 101 returns the control to step S120.

  In step S132, as the adjustment unit 150 described above, the control device 101 causes the spindle rotation number to relatively decrease the vibration intensity from among the combination of the spindle rotation number and the vibration intensity stored in the detection information 123 in step S126. Is used as a setting value. Preferably, from among the spindle rotational speeds indicated by the detection information 123, the control device 101 uses the spindle rotational speed at which the vibration intensity is minimized as the setting value.

[F. Hardware configuration of machine tool 100]
An example of the hardware configuration of the machine tool 100 will be described with reference to FIG. FIG. 9 is a block diagram showing the main hardware configuration of the machine tool 100. As shown in FIG.

  The machine tool 100 includes a main shaft 42, a control device 101, a ROM 102, a RAM 103, a communication interface 104, a display interface 105, a servo driver 106, a servo motor 107, an input interface 109, and an acceleration sensor 110. And a storage device 120.

  The control device 101 controls various operations of the machine tool 100 by executing various programs such as a machining program 122 (NC program) of the machine tool 100. The control device 101 reads the machining program 122 from the storage device 120 or the ROM 102 to the RAM 103 based on the acceptance of the execution command of the machining program 122. The RAM 103 functions as a working memory, and temporarily stores various data necessary for the execution of the machining program 122.

  A LAN, an antenna, and the like are connected to the communication interface 104. The machine tool 100 exchanges data with an external communication device via the communication interface 104. The external communication device includes, for example, a server and other communication terminals. The machine tool 100 may be configured to be able to download the processing program 122 from the communication terminal.

  The display interface 105 is connected to the display 130, and sends an image signal for displaying an image to the display 130 in accordance with an instruction from the control device 101 or the like. The display 130 is, for example, a liquid crystal display, an organic EL display, or another display device.

  The servo driver 106 receives an input of the target rotational speed from the control device 101, and controls the servomotor 107 so that the main spindle 42 rotates at the target rotational speed. More specifically, the servo driver 106 calculates the number of revolutions of the main shaft 42 from the output signal of the encoder (not shown) of the servomotor 107, and when the number of revolutions is smaller than the target number of revolutions, The rotational speed is increased, and when the rotational speed is larger than the target rotational speed, the rotational speed of the servomotor 107 is decreased. Thus, the servo driver 106 brings the rotation speed of the main shaft 42 close to the target rotation speed while sequentially receiving feedback of the rotation speed of the main shaft 42.

  Input interface 109 may be connected to input device 131. The input device 131 is, for example, a mouse, a keyboard, a touch panel, or any other device capable of accepting user operations.

  The storage device 120 is, for example, a storage medium such as a hard disk or a flash memory. Storage device 120 includes a processing program 122 according to the present embodiment, detection information 123 for storing a detection result of vibration intensity with respect to the spindle rotational speed, a set value 124 (for example, spindle rotational speed) referred to by processing program 122, etc. Store The storage location of the processing program 122, the detection information 123, and the setting value 124 is not limited to the storage device 120, and a storage area of the control device 101 (for example, cache memory etc.), ROM 102, RAM 103, external equipment (for example, server) And the like may be stored.

  The processing program 122 may be provided as part of any program, not as a single program. In this case, control processing according to the present embodiment is realized in cooperation with an arbitrary program. Even a program that does not include such a part of modules does not deviate from the spirit of the processing program 122 according to the present embodiment. Furthermore, some or all of the functions provided by the processing program 122 may be realized by dedicated hardware. Furthermore, the machine tool 100 may be configured as a so-called cloud service in which at least one server executes a part of the processing of the processing program 122.

[G. Summary]
As described above, when forced chatter vibration occurs, machine tool 100 determines fluctuation range ΔR of the spindle rotational speed, and increases the spindle rotational speed by a predetermined value within fluctuation range ΔR, and also rotates each spindle. Calculate the vibration intensity in numbers. At this time, the machine tool 100 stores the vibration intensity at each spindle rotational speed in association with each spindle rotational speed. Thereafter, the machine tool 100 uses, from among the stored spindle rotational speeds, the spindle rotational speed at which the vibration intensity is minimum as the setting value. Thereby, the machine tool 100 can suppress the vibration intensity more reliably even if the vibration intensity does not change uniformly with respect to the spindle rotational speed.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

  12 bed, 14, 16 pillar member, 18 saddle, 21 column, 22, 22s, 22t side, 23 top, 26 table, 27 pallet, 29, 29s, 29t rotating mechanism part, 30 magazine, 31 magazine body part, 32 Tools, 33 base members, 34 tool holders, 35 sprockets, 36 automatic tool changers, 37 double arms, 41 spindle heads, 42 spindles, 43 housings, 50 boundaries, 70 A vibration frequency, 70 B spectrum, 100 machine tools, 101 Control unit, 102 ROM, 103 RAM, 104 communication interface, 105 display interface, 106 servo driver, 107 servo motor, 109 input interface, 110 acceleration sensor, 120 storage device, 122 processing program, 123 inspection Information 124 set value, 130 display, 131 input device, 140 calculation unit, 142 FFT unit, 144 extraction unit 150 adjusting section 152 changing unit 154 setting unit, 160 output unit.

Claims (9)

A spindle for rotating the workpiece or tool,
A sensor for detecting the vibration frequency of the spindle or the tool;
A calculation unit for calculating the vibration intensity of chatter vibration occurring in the spindle or the tool based on the vibration frequency;
An adjusting unit for adjusting a set value for controlling the number of revolutions of the spindle;
The adjustment unit determines a fluctuation range of the rotation speed of the spindle based on the occurrence of the chatter vibration, changes the rotation speed of the spindle within the fluctuation range, and determines each of the plurality of rotation speeds. A machine tool which acquires the vibration intensity and uses, as the set value, a rotation number which is relatively smaller than the rotation number of the spindle among the plurality of rotation numbers as compared to before changing the rotation number of the spindle.   The machine tool according to claim 1, wherein the adjustment unit uses, as the set value, a rotation speed at which the vibration intensity is minimum among the plurality of rotation speeds changed within the fluctuation range.   The adjustment unit changes the number of rotations of the main spindle by a predetermined value in the variation range and sequentially acquires the vibration intensity for each number of rotations, and the increase degree of the vibration intensity acquired for the number of rotations adjacent to each other is The machine tool according to claim 1 or 2, which stops changing the number of rotations of the spindle when a predetermined threshold is exceeded.   The calculation unit calculates the vibration intensity for each frequency by Fourier transforming the vibration frequency, and calculates the maximum vibration intensity among the plurality of calculated vibration intensities as the vibration intensity. The machine tool according to any one of 3. In the relationship between the cutting depth of the work by the tool and the number of rotations of the spindle, if the cutting condition range in which chatter vibration does not occur is set as the stable region, the machine tool is the cutting condition within the stable region. And a specific unit for specifying a plurality of rotation speeds that can make the cutting depth relatively deeper than the other rotation speeds,
The variation range is included between a first number of rotations among the plurality of specified rotation numbers and a second number of rotations adjacent to the first rotation number among the plurality of rotations. The machine tool according to any one of Items 1 to 4.   The machine tool according to claim 5, wherein the fluctuation range is included between the first rotation number and an average value of the first rotation number and the second rotation number. Assuming that the frequency of the chatter vibration is fc, the number of blades of the tool is z, the current number of revolutions of the spindle is N, and the integer part of 60 × fc / (z × N) is k, the fluctuation range Corresponds to the range of N shown in the following formula (1),

The machine tool according to any one of claims 1 to 6. The machining method by a machine tool
The machine tool is
A spindle for rotating the workpiece or tool,
A sensor for detecting a vibration frequency of the spindle or the tool;
The processing method is
Calculating the vibration intensity of chatter vibration occurring in the spindle or the tool based on the vibration frequency;
Adjusting a set value for controlling the number of revolutions of the spindle.
The adjusting step determines a fluctuation range of the rotation speed of the spindle based on the occurrence of the chatter vibration, changes the rotation speed of the spindle within the fluctuation range, and changes each of the plurality of rotation speeds. And acquiring, among the plurality of rotational speeds, using the rotational speed that is relatively smaller than that before changing the rotational speed of the main spindle as the setting value. , Processing method. A machining program to be executed on a machine tool
The machine tool is
A spindle for rotating the workpiece or tool,
A sensor for detecting a vibration frequency of the spindle or the tool;
The processing program is for the machine tool
Calculating the vibration intensity of chatter vibration occurring in the spindle or the tool based on the vibration frequency;
Adjusting the set value for controlling the number of revolutions of the spindle;
The adjusting step determines a fluctuation range of the rotation speed of the spindle based on the occurrence of the chatter vibration, changes the rotation speed of the spindle within the fluctuation range, and changes each of the plurality of rotation speeds. And acquiring, among the plurality of rotational speeds, using the rotational speed that is relatively smaller than that before changing the rotational speed of the main spindle as the setting value. , Machining program.

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