JP2015027236A - Servo control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a servo control system capable of suppressing amplification of switching noise even in controlling a multi-shaft motor.SOLUTION: The servo control system includes a plurality of drive sections for operating a drive mechanism and a plurality of servo control sections which are provided to meet each of the plurality of drive sections and switch supplied currents to the drive sections at carrier frequencies different from each other.

Description

  Embodiments according to the present invention relate to a servo control system.

  In the servo control system, the inverter has a function of switching a direct current to flow an alternating current to the motor, thereby driving the motor. Such an inverter generates noise (hereinafter also referred to as switching noise) during current switching. A technique is known in which the switching frequency is periodically changed in order to spread the adverse effects of switching noise over time (Patent Document 1).

JP-A-7-099795

  When the servo control system controls a multi-axis motor, a plurality of inverters switch the current supplied to the corresponding motor. In this case, even if the switching frequency is periodically changed, the switching timing may be superimposed on a plurality of inverters. When the switching timing is superimposed, switching noises of a plurality of inverters are superimposed and amplified. Since the switching noise affects the communication line between the servo amplifiers, if the switching noise is amplified, it may cause a communication abnormality. Therefore, when the servo control system controls a multi-axis motor, it is necessary to suppress amplification of switching noise.

  Accordingly, the present invention has been made to solve the above-described problems, and is to provide a servo control system capable of suppressing amplification of switching noise even when a multi-axis motor is controlled. .

  The servo control system according to the present embodiment is provided with a plurality of driving units that operate the driving mechanism and a plurality of servos that switch the supply currents to the driving units at different carrier frequencies. And a control unit.

  The plurality of servo control units may control the plurality of driving units by a PWM control method.

  The carrier frequencies of the plurality of servo control units may be shifted by a certain frequency.

  The frequency of the clock that becomes the carrier frequency of the plurality of servo control units may be the same in all of the plurality of servo control units.

The number of the plurality of drive units and the number of the plurality of servo control units are each N, the variable range of the carrier frequency of the plurality of servo control units is Fr, and the carrier frequency of the plurality of servo control units is constant. If the frequency is shifted by Δf,
If N does not exceed Fr / Δf,
Fk = Fref + (k−1) × Δf (Formula 1)
K is 1 to N.
When N exceeds Fr / Δf,
Fk = Fref + (k−1) × Δf
K is 1 to Fr / Δf.
Fk = Fref + (k-1- (Fr / Δf)) × Δf
K is (Fr / Δf) +1 to N) (Formula 2)
Formula 1 or Formula 2 may be satisfied.

The block diagram which shows an example of a structure of the servo control system 1, numerical controller NC, and drive mechanism DM1-DM3 by this embodiment. The block diagram which shows an example of a structure of servo amplifier AMP1. The table | surface which shows an example of the correspondence of an axis number and a carrier frequency. The figure which shows the communication signal on which the some switching noise was superimposed at the same timing, and the figure which shows the communication signal on which the some switching noise from which timing shifted mutually was superimposed.

  Embodiments according to the present invention will be described below with reference to the drawings. This embodiment does not limit the present invention.

  FIG. 1 is a block diagram showing an example of the configuration of a servo control system 1, a numerical controller NC, and drive mechanisms DM1 to DM3 according to the present embodiment.

  The servo control system 1 includes servo amplifiers AMP1 to AMP3 as servo control units and motors M1 to M3 as drive units. The servo amplifiers AMP1 to AMP3 are provided corresponding to the motors M1 to M3, respectively. The servo amplifiers AMP1 to AMP3 receive a position command from the numerical controller NC, generate a speed command and a current command according to the position command, and drive the motors M1 to M3 based on the speed command and the current command. The servo amplifiers AMP1 to AMP3 switch the current supplied to the motors M1 to M3 by PWM (Pulse Width Modulation) control, thereby driving the motors M1 to M3. The motors M1 to M3 receive power supply from the servo amplifiers AMP1 to AMP3, respectively, and operate the drive mechanisms DM1 to DM3. The number of servo amplifiers AMP1 to AMP3, motors M1 to M3, and drive mechanisms DM1 to DM3 is not limited to three, but may be two or four or more.

  The motors M1 to M3 are provided with rotary encoders RE1 to RE3, respectively. The rotary encoders RE1 to RE3 detect the rotation of the shafts of the motors M1 to M3, respectively, and measure the position shift. The rotary encoders RE1 to RE3 feed back the shaft position shifts of the motors M1 to M3 to the servo amplifiers AMP1 to AMP3.

  The drive mechanisms DM1 to DM3 are provided with linear encoders LE1 to LE3, respectively. The linear encoders LE1 to LE3 measure the displacement of the positions of the drive mechanisms DM1 to DM3. The linear encoders LE1 to LE3 feed back position shifts of the drive mechanisms DM1 to DM3 to the servo amplifiers AMP1 to AMP3.

  Servo amplifiers AMP1 to AMP3 receive feedback from the rotary encoders RE1 to RE3 and the linear encoders LE1 to LE3, and then correct the position measurement values to correct the positions of the drive mechanisms DM1 to DM3 or the motors M1 to M3. Generate a speed command. Further, the servo amplifiers AMP1 to AMP3 drive the motors M1 to M3 based on the speed command. Thus, the servo control system 1 functions to move the drive mechanisms DM1 to DM3 to a desired position in accordance with the position command from the numerical controller NC.

  Further, the servo amplifiers AMP1 to AMP3 are communicably connected to each other via a communication line CL.

  FIG. 2 is a block diagram illustrating an example of the configuration of the servo amplifier AMP1. Note that the configuration of the servo amplifiers AMP2 and AMP3 may be the same as the configuration of the servo amplifier AMP1, and therefore detailed description thereof is omitted.

  The servo amplifier AMP1 includes an inverter 2, a power supply 3, a buffer 4, a CPU 5, and an oscillator 11. The inverter 2 is provided between the power source 3 and the motor M1, and switches power from the power source 3. The inverter 2 receives a pulse signal from the CPU 5 via the buffer 4 and performs a switching operation according to the pulse signal (pulse width). That is, the switching of the inverter 2 is controlled by the PWM method.

  The CPU 5 includes a control unit 6, a sequencer 8, and a storage unit 10. The control unit 6 outputs a current command to the sequencer 8 from the position command and the measured value fed back. The sequencer 8 generates a pulse signal based on a predetermined carrier frequency stored in the storage unit 10. The pulse signal is sent to the inverter 2 for switching control of the inverter 2.

  The storage unit 10 stores the axis number and the carrier frequency. The axis number is a number unique to the motor M1 corresponding to the servo amplifier AMP1, and is set to be distinguished from the other motors M2 and M3. Here, the carrier frequency is set according to the axis number. The correspondence between the axis number and the carrier frequency will be described later.

  The oscillator 11 generates a clock signal that is a source of the carrier frequency of the servo amplifier AMP1. The frequency of the clock signal is the same in all of the plurality of servo amplifiers AMP1 to AMP3.

  Next, the operation of the servo control system 1 according to the present embodiment will be described.

  First, upon receiving a position command from the numerical controller NC, the control unit 6 calculates a speed command and a current command according to the position command, and inputs the current command to the sequencer 8.

  The sequencer 8 outputs a control signal so as to switch the inverter 2 at a duty ratio corresponding to the current command. At this time, the sequencer 8 generates a PWM carrier having a carrier frequency stored in the storage unit 10 based on the clock of the oscillator 11. The sequencer 8 generates a pulse signal based on the PWM carrier.

  Then, the inverter 2 performs on / off switching based on this pulse signal, and supplies power from the power source to the motor M1.

  Here, when the plurality of servo amplifiers AMP1 to AMP3 control the plurality of motors M1 to M3 at the same carrier frequency, switching noises of the plurality of servo amplifiers AMP1 to AMP3 may be superimposed. For example, the switching noise of the servo amplifiers AMP1 to AMP3 may be superimposed on a signal propagating through the communication line CL. In this case, since the switching noises of the three servo amplifiers AMP1 to AMP3 are superimposed, the switching noise is greatly amplified. If the switching noise is large, the servo amplifiers AMP1 to AMP3 are more likely to erroneously detect a signal propagating through the communication line CL, resulting in a communication abnormality.

  Therefore, the plurality of servo amplifiers AMP1 to AMP3 of the servo control system 1 according to the present embodiment are configured to switch supply currents to the motors M1 to M3 at different carrier frequencies.

  FIGS. 3A and 3B are tables showing an example of the correspondence between axis numbers and carrier frequencies. With reference to FIG. 3 (A) and FIG. 3 (B), the setting of the carrier frequency by this embodiment is demonstrated. 3A and 3B, 16 motors M1 to M16 are provided, and the carrier frequency Fc (kHz) for each motor M1 to M16 is displayed. These tables are preset and stored in the storage unit 10. The servo amplifiers corresponding to the motors M1 to M16 are AMP1 to AMP16, respectively.

  In the table shown in FIG. 3A, the reference carrier frequency Fref generated based on the clock frequency is 5 kHz. The clock frequency is common to all axes (motors M1 to M16, servo amplifiers AMP1 to AMP16), and therefore the reference carrier frequency Fref is equally common to all axes. The variable range (range) Fr of the carrier frequency Fc is 5.0 kHz to 6.0 kHz. The variable width Δf of the carrier frequency Fc is 0.1 kHz. That is, the carrier frequencies Fc of the motors M1 to M16 are set so as to shift by a variable width Δf between the variable ranges Fr. For example, in FIG. 3A, the carrier frequencies Fc of the motors M1 to M10 are 5.0 kHz, 5.1 kHz, 5.2 kHz... 5.9 kHz, and the carrier frequencies Fc of the motors M11 to M16 are 5. It is set to 0.0 kHz, 5.1 kHz, 5.2 kHz... 5.5 kHz.

  By setting the carrier frequency Fc in this way, the carrier frequencies Fc of the motors M1 to M10 are shifted by a variable width Δf (0.1 kHz), so that the switching noises of the motors M1 to M10 are not superimposed. Further, since the carrier frequencies Fc of the motors M11 to M16 are also shifted by the variable width Δf (0.1 kHz), the switching noise of the motors M11 to M16 is not superimposed.

  Since the carrier frequencies of the motors M1 to M6 are equal to the carrier frequencies of the motors M11 to M16, the switching noises of the motors M1 to M6 may overlap with the switching noises of the motors M11 to M16, respectively. However, in order to allocate the carrier frequencies of a large number of axes (M1 to M16 and AMP1 to AMP16) within the limited variable range Fr, it may be necessary to allow the switching noises of the two axes to overlap. is there. If the two switching noises overlap, the influence (amplification factor) exerted on each other is small, and no communication abnormality occurs between the servo amplifiers AMP1 to AMP16.

  Further, when the motors M1 to M16 are arranged in the order of M1 to M16, nine motors M2 to M10 are arranged between the motor M1 and the motor M11 having the same carrier frequency. Therefore, it can be said that the switching noise between the motor M1 and the motor M11 has a small influence (amplification factor) on each other. The relationship between the motors M2 and M12, the relationship between the motors M3 and M13, the relationship between the motors M4 and M14, the relationship between the motors M5 and M15, and the relationship between the motors M6 and M16 are the relationship between the motor M1 and the motor M11. It is the same.

  In the table shown in FIG. 3B, the reference carrier frequency Fref generated based on the clock frequency is 10 kHz. The clock frequency is common to all axes (motors M1 to M16, servo amplifiers AMP1 to AMP16), and therefore the reference carrier frequency Fref is equally common to all axes. The variable range (range) Fr of the carrier frequency Fc is 9.0 kHz to 10.0 kHz. The variable width Δf of the carrier frequency Fc is 0.1 kHz. That is, the carrier frequencies Fc of the motors M1 to M16 are set so as to shift by a variable width Δf between the variable ranges Fr. For example, in FIG. 3B, the carrier frequencies Fc of the motors M1 to M10 are 9.0 kHz, 9.1 kHz, 9.2 kHz, 9.9 kHz, and the carrier frequencies Fc of the motors M11 to M16 are 9 These are set to 0.0 kHz, 9.1 kHz, 9.2 kHz, and 9.5 kHz.

  By setting the carrier frequency Fc in this way, the carrier frequencies Fc of the motors M1 to M10 are shifted by a variable width Δf (0.1 kHz), so that the switching noises of the motors M1 to M10 are not superimposed. Further, since the carrier frequencies Fc of the motors M11 to M16 are also shifted by the variable width Δf (0.1 kHz), the switching noise of the motors M11 to M16 is not superimposed.

  In the example shown in FIG. 3B, the switching noises of the motors M1 to M6 may overlap with the switching noises of the motors M11 to M16, respectively. However, as described above, if the two switching noises overlap, no communication abnormality occurs between the servo amplifiers AMP1 to AMP16, and the influence on each other from the arrangement of the axes can be suppressed.

  This embodiment can be generalized as follows.

  The number of axes (the number of motors and the number of servo amplifiers) is N (N is a natural number), the variable range of the carrier frequency is Fr (Fref to Fref + Fr), and the carrier frequency of the servo amplifier is shifted by a certain frequency Δf. It shall be.

If N does not exceed Fr / Δf, the carrier frequencies F ₁ to F _N of the motors M ₁ to _MN are Fref, Fref + Δf, Fref + 2 × Δf... Fref + (N−1) × Δf, respectively. Good. That is, Formula 1 is established.
Fk (k = 1 to N) = Fref + (k−1) × Δf (Formula 1)
In addition,

If N is greater than Fr / Delta] f, the motor _M 1 ~M each carrier frequencies _F 1 of the _N to F _N are each Fref, Fref + Δf, Fref + 2 × Δf ··· Fref + Fr- (Fr / Δf), Fref, Fref + Δf , Fref + 2 × Δf... That is, Formula 2 is established.
Fk (k = 1 to Fr / Δf) = Fref + (k−1) × Δf
Fk (k = (Fr / Δf) +1 to N) = Fref + (k−1− (Fr / Δf)) × Δf (Formula 2)

When N exceeds 2 × Fr / Δf, the carrier frequencies F ₁ to F _N of the motors M ₁ to _MN are Fref, Fref + Δf, Fref + 2 × Δf... Fref + Fr− (Fr / Δf), Fref, respectively. Fref + Δf, Fref + 2 × Δf... Fref + Fr− (Fr / Δf), Fref, Fref + Δf, Fref + 2 × Δf.

By setting the carrier frequencies F _{1 to} F _N for each axis in this way, it is possible to suppress as much as possible a plurality of switching noises from overlapping. When the carrier frequency is high, heat generation in the servo amplifier increases. Therefore, it is preferable to avoid as much as possible the frequency near the upper limit value of the variable range Fr as the carrier frequency.

  As described above, the plurality of servo amplifiers of the servo control system 1 according to the present embodiment switches the supply current to the plurality of motors at different carrier frequencies. Thereby, the timings of the switching noises of the plurality of servo amplifiers are shifted from each other, and the overlapping of the plurality of switching noises can be suppressed as much as possible. That is, the servo control system 1 can suppress amplification of switching noise even when controlling a multi-axis motor. As a result, switching noise superimposed on a signal propagating through the communication line CL is reduced, and accurate communication can be ensured.

  For example, FIG. 4A is a diagram illustrating a communication signal in which a plurality of switching noises are superimposed at the same timing. FIG. 4B is a diagram illustrating a communication signal on which a plurality of switching noises having different timings are superimposed. In FIG. 4A, noise is amplified by a plurality of switching noises. For this reason, a large noise is generated in the communication signal. Therefore, there is a high possibility that the communication signal is erroneously detected. In contrast, in FIG. 4B, the switching timings of the inverters 2 of a plurality of axes are shifted from each other as in the servo control system 1 according to the present embodiment. For this reason, switching noise is dispersed and switching noise is not amplified. Therefore, the switching noise superimposed on the communication signal is small, and the communication signal can be transmitted relatively accurately.

DESCRIPTION OF SYMBOLS 1 ... Servo control system, NC ... Numerical control device, DM1-DM3 ... Drive mechanism, AMP1-AMP3 ... Servo amplifier, M1-M3 ... Motor, RE1-RE3 ... Rotary encoder, LE1-LE3 ... Linear encoder, 2 ... Inverter, 3 ... power supply, 4 ... buffer, 5 ... CPU, 11 ... oscillator

Claims (5)

A plurality of drive units for operating the drive mechanism;
A servo control system comprising a plurality of servo control units provided corresponding to each of the plurality of drive units and switching supply currents to the drive units at different carrier frequencies.   The servo control system according to claim 1, wherein the plurality of servo control units control the plurality of drive units by a PWM control method.   The servo control system according to claim 1, wherein carrier frequencies of the plurality of servo control units are shifted by a certain frequency.   4. The servo according to claim 1, wherein a frequency of a clock that is a base of a carrier frequency of the plurality of servo control units is the same in all of the plurality of servo control units. 5. Control system. The number of the plurality of drive units and the number of the plurality of servo control units are each N, the variable range of the carrier frequency of the plurality of servo control units is Fr, and the carrier frequency of the plurality of servo control units is constant. If the frequency is shifted by Δf,
If N does not exceed Fr / Δf,
Fk = Fref + (k−1) × Δf (Formula 1)
K is 1 to N.
When N exceeds Fr / Δf,
Fk = Fref + (k−1) × Δf
K is 1 to Fr / Δf.
Fk = Fref + (k-1- (Fr / Δf)) × Δf
K is (Fr / Δf) +1 to N) (Formula 2)
The servo control system according to any one of claims 1 to 4, wherein Formula 1 or Formula 2 is established.

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