Control devices for machine tools

Abstract

Provided is a control device of a machine tool that can maintain a speed clamp command, without impairing a chatter vibration suppression effect. A control device of a machine tool comprises a fluctuation command calculation unit that generates a speed fluctuation command on the basis of a speed command for a spindle motor in the machine tool and a fluctuation condition for periodically fluctuating a rotation speed of the spindle motor. The fluctuation command calculation unit changes a phase of the speed fluctuation command or a speed command of the speed fluctuation command, in accordance with a speed clamp command for the spindle motor.

Description

Technical Field

[0001] The present invention relates to a control device for a machine tool.

Background Art

[0002] During cutting by a machine tool, chatter vibration may continuously occur between a tool and a workpiece. Chatter vibration is classified into forced chatter vibration and self-excited chatter vibration according to the cause of vibration generation. Forced chatter vibration is generated under the influence of a forced vibration source, and self-excited chatter vibration occurs without a specific vibration source when the dynamic characteristics of the machine tool and the cutting process overlap and satisfy predetermined conditions. Among self-excited chatter vibrations, regenerative self-excited chatter vibration is caused by fluctuations in chip thickness.

[0003] Conventionally, a technique for suppressing regenerative self-excited chatter vibration by periodically varying the rotational speed of the spindle in a machine tool is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In such a technique for suppressing chatter vibration, the control device of a machine tool may apply a predetermined speed clamp command and perform machining. In this case, in the machine tool, in the speed fluctuation range exceeding the clamp upper limit value of the speed clamp command, the speed of the spindle becomes a constant speed, and chatter vibration cannot be suppressed. Therefore, there is a need for a control device for a machine tool that can maintain the speed clamp command without impairing the chatter vibration suppression effect.

Means for Solving the Problems

[0006] A control device for a machine tool according to one aspect of the present disclosure includes a variable command calculation unit that generates a speed variation command based on a speed command for a spindle motor in the machine tool and a variation condition for periodically varying the rotational speed of the spindle motor, wherein the variable command calculation unit changes the phase of the speed variation command or the speed command of the speed variation command in accordance with a speed clamp command for the spindle motor. [Effects of the Invention]

[0007] According to the present invention, the speed clamp command can be maintained without impairing the chatter vibration suppression effect. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an overview of the machine tool according to this embodiment. [Figure 2] This figure shows the relationship between the speed clamp command, speed fluctuation command, and spindle speed command according to the first embodiment. [Figure 3A] This shows the speed change command before the change. [Figure 3B] The revised speed change command is shown. [Figure 4] This is a flowchart showing the processing of the motor control device according to the first embodiment. [Figure 5] This figure shows the relationship between the speed clamp command, speed fluctuation command, and spindle speed command according to the second embodiment. [Figure 6A] The spindle speed command before the change is shown. [Figure 6B] The modified spindle speed command is shown. [Figure 7] This is a flowchart showing the processing of the motor control device according to the second embodiment. [Figure 8A] Conventional speed fluctuation commands and speed clamp commands are shown. [Figure 8B] This shows the conventional rate of change in velocity. [Figure 8C] The speed fluctuation command and speed clamp command according to the first embodiment are shown. [Figure 8D]The rate of change of speed according to the second embodiment is shown. [Figure 8E] The speed fluctuation command and speed clamp command according to the second embodiment are shown. [Figure 8F] The rate of change of speed according to the second embodiment is shown. [Modes for carrying out the invention]

[0009] An example of an embodiment of the present invention will be described below. Figure 1 is a diagram showing an overview of the machine tool 1 according to this embodiment.

[0010] Machine tool 1 is a device that performs predetermined machining operations such as cutting by controlling the motor control device 10 based on speed commands from numerical control device 2 to rotate the spindle motor 18. Machine tool 1 suppresses regenerative self-excited chatter vibration by periodically varying the rotational speed of the spindle motor 18, for example by causing the rotational speed of the spindle motor 18 to vibrate sinusoidally.

[0011] The motor control device 10 comprises a fluctuation command calculation unit 11, a speed control unit 12, a current control unit 13, and a current detection unit 14.

[0012] The variable command calculation unit 11 generates a speed variation command based on the speed command for the spindle motor 3 in the machine tool and the variation conditions for periodically varying the rotational speed of the spindle motor 18. Specifically, the variable command calculation unit 11 calculates the amplitude of the periodically fluctuating rotational speed of the spindle motor 3 by multiplying the rotational speed of the spindle motor 3 based on the speed command by the variation amplitude ratio (hereinafter also simply referred to as the amplitude ratio), which is a variation condition. Furthermore, the variable command calculation unit 11 generates a speed variation command by calculating the frequency of the periodically fluctuating rotational speed of the spindle motor 3 by multiplying the rotational speed of the spindle motor 3 based on the speed command by the variation frequency ratio (hereinafter also simply referred to as the frequency ratio), which is a variation condition.

[0013] Furthermore, the variable command calculation unit 11 acquires the spindle speed command 21 and the speed clamp command 22 from the numerical control device 2. Then, the variable command calculation unit 11 changes the phase of the speed variable command or the speed command of the speed variable command according to the speed clamp command of the spindle motor 18. As a result, the motor control device 10 can maintain the speed clamp command without impairing the chatter vibration suppression effect.

[0014] Specifically, the speed fluctuation command calculation unit 11 controls the speed fluctuation command so that it does not exceed the value of the speed clamp command 22 by changing (offsetting) the phase of the speed fluctuation command if the speed fluctuation command exceeds the value of the speed clamp command 22.

[0015] Furthermore, if the maximum amplitude value of the speed fluctuation command exceeds the value of the speed clamp command 22, the fluctuation command calculation unit 11 controls the speed fluctuation command by changing the spindle speed command so that it does not exceed the value of the speed clamp command 22.

[0016] The speed control unit 12 generates commands to control the rotational speed of the spindle motor 18 based on the spindle speed command and speed fluctuation command, and outputs them as signals.

[0017] The value obtained by subtracting the value of the actual current feedback output as a signal from the current detection unit 14 from the command value output from the speed control unit 12 is input as a signal to the current control unit 13.

[0018] The current control unit 13 generates a voltage command to drive the spindle motor 18 based on the input signal and outputs it as a signal.

[0019] The current detection unit 14 detects a signal which is the current value of the main shaft motor 18 and outputs the detection result as a signal for actual current feedback.

[0020] The numerical control device 2 outputs a spindle speed command 21 and a speed clamp command 22 to the motor control device 10. The spindle speed command 21 includes the speed command of the spindle motor 18 and is output as a signal. The speed clamp command 22 includes the upper limit of the spindle speed that can be freely changed by the user according to the machining conditions of the machine tool 1. The speed clamp command 22 is generated according to the machining conditions of the machine tool 1 and is output as a signal.

[0021] The spindle motor 18 rotates under the control of the motor control device 10. The speed detection unit 19 detects the rotational speed of the spindle motor 18 and outputs the detection result as a signal of actual speed feedback. The speed detection unit 19 may be, for example, an encoder or the like.

[0022] <First Embodiment> FIG. 2 is a diagram showing the relationship between the speed clamp command S L (t), the speed fluctuation command S V (t), and the spindle speed command S N (t) according to the first embodiment. As described above, when the fluctuation command calculation unit 11 determines that the speed fluctuation command S V (t) is greater than or equal to the speed clamp command S L (t), the phase of the speed fluctuation command S V (t) is changed (offset).

[0023] In the graph showing the relationship between time t and speed in FIG. 2, the triangular wave composed of broken lines indicates the speed fluctuation command S V (t) before the change, and the triangular wave composed of solid lines indicates the speed fluctuation command S V (t) after the change.

[0024] Also, in the graph showing the relationship between time t and phase Θ in FIG. 2, the broken line portion indicates the phase of the speed fluctuation command S V (t) before the change (before offset), and the solid line portion indicates the phase of the speed fluctuation command S V (t) after the change (after offset).

[0025] As shown in the triangular wave in FIG. 2, the speed fluctuation command S V(t) is the speed clamp command S L There is a portion that exceeds (t). On the other hand, the modified speed fluctuation command S V (t) is the speed fluctuation command S V By offsetting the phase of (t), the speed clamp command S L It is controlled so as not to exceed (t).

[0026] Figure 3A shows the speed fluctuation command S before the change. V (t) is shown, and Figure 3B shows the modified speed fluctuation command S V (t) is shown. As shown in Figure 3A, the speed fluctuation command S before the change V (t) is the speed clamp command S L There are parts where (t) is exceeded. As a result, the spindle motor 18 experiences a period where its speed becomes constant, and the motor control device 10 is unable to suppress the chatter vibration.

[0027] On the other hand, as shown in Figure 3B, the modified speed fluctuation command S V (t) is the speed clamp command S L There is no portion that exceeds (t). Therefore, the spindle motor 18 can avoid having a constant speed, and the motor control device 10 can maintain the speed clamp command without impairing the chatter vibration suppression effect.

[0028] Figure 4 is a flowchart showing the processing of the motor control device 10 according to the first embodiment. In step S1, the variable command calculation unit 11 calculates the current spindle speed command S N (t)[min-1] and speed clamp command S L (t)[min-1] is obtained from the numerical control device 2, where t represents the control period [s]. The fluctuation command calculation unit 11 also obtains the fluctuation conditions from the storage unit (not shown) of the motor control device 10.

[0029] In step S2, the variable command calculation unit 11 calculates the current spindle speed command S N (t) and based on the variable conditions, speed variation command S VWe calculate the amplitude A(t)[min-1], frequency F(t)[Hz], and phase Θ(t)[rad] of (t). Here, the amplitude A(t), frequency F(t), and phase Θ(t) are calculated using the following formulas. A(t)=S N (t) × (a / 100) F(t)=(S N (t) / 60) × (f / 100) Θ(t)=mod({Θ(t-1)+(2π×F(t)×t)},2π) Note that the amplitude factor a(%) and frequency factor f(%) are variation conditions, and modulo is the residue function. The residue function modulo rounds Θ(t) by 2π.

[0030] In step S3, the fluctuation command calculation unit 11 calculates the speed fluctuation command S V Calculate (t)[min-1]. Here, the speed fluctuation command S V (t) is calculated using the following formula. S V (t)=S N (t)+A(t)*triΘ(t) Note that triΘ(t) is a function that generates triangular waves, and for example, it is generated as follows. If (Θ(t)≦(π / 2)) {triΘ(t)=Θ(t) / (π / 2)} Else if (Θ(t) ≤ (3 / 2π)) {triΘ(t)=2-(Θ(t) / (π / 2))} Else {triΘ(t)=(2Θ(t) / π)-4}

[0031] Furthermore, the fluctuation command calculation unit 11 may use a function that generates a sine wave instead of the triΘ(t) function that generates a triangular wave. When using a function that generates a sine wave, the fluctuation command calculation unit 11 replaces triΘ(t) with sinΘ(t) to generate the speed fluctuation command S V (t) can be calculated.

[0032] In step S4, the fluctuation command calculation unit 11 calculates the speed fluctuation command S V (t) is the speed clamp command S L Determine whether the value of (t) is exceeded. Speed ​​fluctuation command S V (t) is the speed clamp command S L If the value of (t) exceeds (YES), the process proceeds to step S5. Meanwhile, the speed fluctuation command S V (t) is the speed clamp command S L If the value is less than or equal to (t) (NO), the process then terminates.

[0033] In step S5, the variable command calculation unit 11 calculates the speed variable command S V The phase Θ(t) of (t) is changed to π-Θ(t), and the velocity fluctuation command S V Recalculate (t). In other words, the fluctuation command calculation unit 11 uses the following formula to calculate the speed fluctuation command S V Recalculate (t). Θ(t) = π - Θ(t) S V (t)=S N (t)+A(t)*triΘ(t) This results in a recalculated speed variation command S V (t) is obtained by offsetting the phase Θ(t) with the velocity clamp command S L It is controlled so as not to exceed (t).

[0034] Thus, in the motor control device 10 according to the first embodiment, the fluctuation command calculation unit 11 calculates the speed fluctuation command S V (t) is the speed clamp command S L If (t) exceeds, speed fluctuation command S V The phase of (t) is changed. As a result, the fluctuation command calculation unit 11 calculates the speed fluctuation command S V By offsetting the phase of (t), the speed clamp command S L The motor control device 10 according to the first embodiment can maintain the speed clamp command without impairing the chatter vibration suppression effect.

[0035] <Second Embodiment> Figure 5 shows the speed clamp command S according to the second embodiment. L (t), speed fluctuation command S V (t) and spindle speed command S N This diagram shows the relationship with (t). As described above, the variable command calculation unit 11 changes (offsets) the spindle speed command of the speed variable command if the maximum amplitude value of the speed variable command exceeds the speed clamp command.

[0036] In the graph of Figure 5 showing the relationship between time t and velocity, the triangular wave represented by the dashed line represents the original spindle speed command S. N (t) is shown, and the triangular wave composed of solid lines represents the modified spindle speed command S N (t) is shown.

[0037] As shown by the triangular wave in Figure 5, the original spindle speed command S N (t) is the speed clamp command S L There is a portion that exceeds (t). On the other hand, the modified spindle speed command S N (t) is the spindle speed command S before the change. N By offsetting (t) by the maximum value of the fluctuation amplitude, the speed clamp command S L It is controlled so as not to exceed (t). Note that the spindle speed command S before the change N (t) is the reference speed command, which may be, for example, the average spindle speed.

[0038] Figure 6A shows the spindle speed command S before modification. N (t) is shown, and Figure 6B shows the modified spindle speed command S N This shows (t) + A(t). As shown in Figure 6A, the spindle speed command S before the change. N (t) is the speed clamp command S L There are parts where (t) is exceeded. As a result, the spindle motor 18 experiences a period where its speed becomes constant, and it is unable to suppress chatter vibrations.

[0039] On the other hand, as shown in Figure 6B, the modified spindle speed command S N(t) + A(t) is the speed clamp command S L There is no portion that exceeds (t). Therefore, the motor control device 10 can avoid the speed of the spindle motor 18 becoming constant, and can maintain the speed clamp command without impairing the chatter vibration suppression effect.

[0040] Figure 7 is a flowchart showing the processing of the motor control device 10 according to the second embodiment. In step S11, the variable command calculation unit 11 calculates the current spindle speed command S N (t)[min-1] and speed clamp command S L (t)[min-1] is obtained from the numerical control device 2, where t represents the control period [s]. The fluctuation command calculation unit 11 also obtains the fluctuation conditions from the storage unit (not shown) of the motor control device 10.

[0041] In step S12, the variable command calculation unit 11 calculates the current spindle speed command S N (t) and based on the variable conditions, speed variation command S V We calculate the amplitude A(t)[min-1], frequency F(t)[Hz], and phase Θ(t)[rad] of (t). Here, the amplitude A(t), frequency F(t), and phase Θ(t) are calculated using the same formulas as in the first embodiment.

[0042] In step S13, the fluctuation command calculation unit 11 calculates the speed fluctuation command S V (t) Maximum amplitude value S N (t) + A(t) is the speed clamp command S L Determine whether (t) exceeds the maximum amplitude value S. N (t) + A(t) is the speed clamp command S L If (t) exceeds (YES), the process proceeds to step S14. Meanwhile, the maximum amplitude value S N (t) + A(t) is the speed clamp command S L (t) If the following is the case (NO), the process proceeds to step S15.

[0043] In step S14, the fluctuation command calculation unit 11 offsets the spindle speed command S N (t) by the maximum value of the fluctuation amplitude, thereby changing the spindle speed command S N (t). That is, the fluctuation command calculation unit 11 changes the spindle speed command S N (t) using the following formula. S N (t)=S L (t)-A(t)

[0044] In step S15, the fluctuation command calculation unit 11 calculates the speed fluctuation command S V (t)[min-1]. Here, the speed fluctuation command S V (t) is calculated using the same formula as in the first embodiment. As a result, the calculated speed fluctuation command S V (t) is controlled so as not to exceed the speed clamp command S L (t).

[0045] Thus, in the motor control device 10 according to the second embodiment, when the maximum amplitude value of the speed fluctuation command S V (t) exceeds the speed clamp command S L (t), the fluctuation command calculation unit 11 changes the spindle speed command S V (t) of the speed fluctuation command S N (t). Thereby, the fluctuation command calculation unit 11 offsets the spindle speed command S N (t) before the change by the maximum value of the fluctuation amplitude, so as not to exceed the speed clamp command S L (t). Therefore, the motor control device 10 according to the second embodiment can maintain the speed clamp command without impairing the chatter vibration suppression effect.

[0046] Figures 8A to 8F illustrate the chatter suppression effect and machining efficiency of the motor control device 10 according to the above-described embodiment. Specifically, Figure 8A shows the conventional speed fluctuation command and speed clamp command, Figure 8C shows the speed fluctuation command and speed clamp command according to the first embodiment, and Figure 8E shows the speed fluctuation command and speed clamp command according to the second embodiment. Furthermore, Figure 8B shows the conventional speed change rate, Figure 8D shows the speed change rate according to the first embodiment, and Figure 8F shows the speed change rate according to the second embodiment. Note that when the spindle rotation angle of the spindle motor 3 is from 0 degrees to 360 degrees, the speed change rate is defined as the ratio of the current speed to the speed difference from one rotation ago at the same spindle rotation angle.

[0047] Note that in Figures 8A to 8F, the spindle speed command S N (t) is 900 rpm, and the speed clamp command S L (t) is 900 rpm, and the change conditions are fluctuation amplitude A(t) = 30% and frequency F(t) = 10%. In regenerative self-excited chatter suppression technology using spindle speed fluctuations, it has been found that the greater the speed difference (rate of speed change) between the previous rotation and the current rotation position, the higher the chatter vibration suppression effect. Therefore, it can be said that the higher the rate of speed change per fluctuation period, the higher the chatter suppression effect.

[0048] From the results in Figures 8A and 8B, the average rate of change per cycle of fluctuation (absolute value) in the conventional method is approximately 6.2%. From the results in Figures 8C and 8D, the average rate of change per cycle of fluctuation (absolute value) in the first embodiment is approximately 11%. From the results in Figures 8E and 8F, the average rate of change per cycle of fluctuation (absolute value) in the second embodiment is approximately 19%. Therefore, it can be seen that the rate of change (i.e., the chatter suppression effect) increases in the order of the conventional method, the first embodiment, and the second embodiment.

[0049] Furthermore, regarding machining efficiency, in the case of point feed (where the feed amount per spindle rotation is specified for cutting), which is commonly used in turning, the feed amount (the time taken for cutting, which is roughly the machining efficiency) changes according to the change in spindle speed. Therefore, it can be said that the higher the average spindle speed per cycle of variation, the higher the machining efficiency.

[0050] From the results in Figure 8A, the average spindle speed per cycle of variation is approximately 832 rpm in the conventional method. From the results in Figure 8C, the average spindle speed per cycle of variation is approximately 765 rpm in the first embodiment method. From the results in Figure 8E, the average spindle speed per cycle of variation is approximately 630 rpm in the first embodiment method. Therefore, the machining efficiency (i.e., average spindle speed) is highest in the second embodiment method, followed by the first embodiment method and then the conventional method. However, the conventional method has a low chatter vibration suppression effect, making machining highly unlikely.

[0051] Although embodiments of the present invention have been described above, the motor control device 10 described above can be implemented by hardware, software, or a combination thereof. Furthermore, the control method performed by the motor control device 10 described above can also be implemented by hardware, software, or a combination thereof. Here, implementation by software means that it is implemented by a computer reading and executing a program.

[0052] Programs can be stored and supplied to a computer using various types of non-transitory computer-readable media. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (e.g., hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memory (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (random access memory)).

[0053] Furthermore, while the embodiments described above are preferred embodiments of the present invention, the scope of the present invention is not limited to these embodiments alone. Various modifications can be made to the present invention without departing from its spirit. [Explanation of Symbols]

[0054] 1 Machine tools 2 Numerical control device 10 Motor control device 11. Variable Command Calculation Unit 12 Speed ​​control unit 13 Current Control Unit 14 Current detection unit 18. Main shaft motor 19 Speed ​​detection unit 21 Spindle speed command 22 Speed ​​clamp command

Claims

1. The machine tool includes a speed command calculation unit that generates a speed fluctuation command based on the speed command of the spindle motor and the fluctuation conditions for periodically varying the rotational speed of the spindle motor. The variable command calculation unit controls the speed so that the speed variable command does not exceed the speed clamp command by offsetting the phase of the speed variable command if the speed variable command exceeds the speed clamp command of the spindle motor. Control device for machine tools.

2. The machine tool includes a speed command calculation unit that generates a speed fluctuation command based on the speed command of the spindle motor and the fluctuation conditions for periodically varying the rotational speed of the spindle motor. The variable command calculation unit controls the variable command so that the maximum amplitude value of the speed variable command does not exceed the speed clamp command of the spindle motor by offsetting the spindle speed command of the speed variable command. Control device for machine tools.

3. The control device for a machine tool according to claim 1 or 2, wherein the speed clamp command is generated according to the machining conditions of the machine tool.

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