JP5622070B2 - Linear motor drive device - Google Patents

Description

  The present invention relates to a linear motor driving apparatus for feedback control of the speed of a linear motor used in a semiconductor manufacturing apparatus or the like by a PWM method.

  In a manufacturing apparatus (exposure apparatus, inspection apparatus, etc.) such as a semiconductor element or a liquid crystal panel, for example, a linear synchronous motor having a coil unit and a magnet unit on a stage on which a member to be exposed (wafer) or a mask (rectile) is mounted Driving is performed (hereinafter simply referred to as a linear motor) (see Patent Document 1). In particular, scanning reduction projection exposure equipment transfers while moving the wafer stage and the reticle stage at a constant speed. To ensure nano-order scanning accuracy, synchronous constant-speed feed, high-precision positioning, and thrust ripple improvement are important. is there.

  In order to move a movable member (for example, a coil unit) with a thrust according to the current value, the linear motor described above has a sinusoidal shape on a load (a three-phase coil including a U-phase coil, a V-phase coil, and a W-phase coil) It is driven by supplying a driving current (for example, several A to 10 A). This drive current is supplied from a voltage source inverter having a converter unit that converts a commercial power supply into a DC voltage by full-wave rectification and an inverter unit that converts a DC voltage smoothed by a capacitor into an AC of an arbitrary frequency. . This inverter unit compares a carrier wave (for example, a triangular wave) and a signal wave, and switches each phase of the switching element by shifting the control phase by 120 ° (UV-UW-VW-VU-WU-WV) on / off. By doing so, it is controlled by the PWM system that modulates to a sinusoidal drive current. A normal linear motor includes a position sensor that detects the position of the mover in order to switch the moving direction of the mover (change the direction of the current supplied to the coil) (see Patent Document 2).

  If a ripple component is included in the thrust of the linear motor described above, precise speed control and positioning control become difficult. Therefore, the drive current supplied to the load (three-phase coil) is detected and based on the current value. The inverter unit controls the speed of the motor by changing the frequency of the voltage. That is, in the inverter unit, the output voltage is stabilized by feeding back the output current to generate the PWM signal.

  In the PWM method, since a pulse width modulation output is obtained by comparing the carrier wave and the signal wave, the carrier frequency is increased (for example, 100 KHz), and unnecessary carrier frequencies other than the modulation signal are moved to a high frequency region as a sideband. To improve the waveform. That is, a noise filter (hereinafter referred to as a low-pass filter) is inserted between the midpoint of the switching element and GND, and high frequency is cut using the insertion loss, thereby reducing noise radiated to the outside. Is generally (see, for example, Patent Document 2). This low-pass filter consists of an inductance connected in series with the circuit to cut the high frequency (impedance increases as the frequency increases) and a capacitor connected in parallel to the circuit to cut the low frequency. (Impedance decreases as frequency increases).

  In addition, the noise generated in the inverter section is generated between the normal mode component superimposed on the DC voltage between the output terminals (plus and minus) and between the ground and the output terminal, and the common in common between the output terminals It consists of mode components. Common mode noise changes to normal mode when there is an imbalance in the circuit. Generally, when common mode noise increases, noise radiated to the outside also increases. However, as described above, the voltage source (inverter unit) and the load It can be removed by inserting a low-pass filter (LC filter) between them.

  In the PWM current control system (feedback control) described above, if the control loop gain is increased in order to improve the transient response characteristics of the output voltage against a sudden change in the load current or the input voltage, the phase delay is caused by the low-pass filter. As a result, the feedback loop that should be negative feedback becomes positive feedback, and the output voltage is likely to oscillate. On the other hand, if the control loop gain is decreased in order to suppress oscillation, the output voltage response decreases, and if the load current increases, the output voltage decreases. Therefore, in order to achieve both output response and system stability, a switch circuit that switches the input power according to the PWM signal to form a pulse waveform, and converts the pulse waveform to direct current and outputs it. In the switching power supply controller including the smoothing circuit, the time ratio adjusting unit that changes the time ratio of the PWM signal so as to suppress the fluctuation of the output voltage according to the output voltage of the smoothing circuit, and the PWM signal The correction feedback loop provided to correct the pulse width of the PWM signal by calculating the time ratio and the average value of the output from the detection element that detects the current flowing through the smoothing circuit is obtained, and the inside of the time ratio adjustment unit When the average value is added to the time ratio adjustment unit via a subtractor, the subtraction process is performed, but the phase of the output voltage advances. It has been proposed to be added (see Patent Document 3).

JP 2003-47285 A (second page) JP 2003-88170 A (page 3-4, FIGS. 1 and 2) Japanese Patent No. 3740133 (page 3-4, FIG. 1, FIG. 2, FIG. 3)

  Since noise is generated by the intermittent current flowing in the line, normal mode noise reciprocating between the lines is large, but since the radiation to the space is small and the degree of failure is small, no special countermeasure has been proposed. However, the linear motor current control system requires high-accuracy speed control, that is, reduction of thrust ripple, so normal mode noise generated in the drive unit cannot be ignored. There is a problem that is not done.

  Accordingly, an object of the present invention is to provide a linear motor driving device that can broaden the cut-off frequency band of a noise filter than before and reduce normal mode noise.

  In order to achieve the above object, the linear motor driving device of the present invention corrects the pulse width of the error amplifier that amplifies the difference between the external input signal and the negative feedback signal from the output side, and the signal output from the error amplifier. A phase compensation amplifier that advances the phase of the output voltage, a PWM amplifier that performs pulse width modulation of the output voltage, and a coil input type low-pass filter including an LC circuit provided between the PWM amplifier and the load coil. In the linear motor driving device, the low-pass filter includes a resistor connected in series with a capacitor constituting the LC circuit, and the circuit constant including the resistor smoothes the frequency characteristic in the vicinity of the cutoff frequency. It is characterized by being set to.

  In the present invention, the low-pass filter can connect a capacitor in parallel with the capacitor and the resistor, or can connect a capacitor in parallel with the resistor.

  In the linear motor driving device of the present invention, a common mode choke coil can be connected between the low pass filter and the load coil.

  According to the present invention, a resistor connected in series with a capacitor is included between the PWM amplifier and the load coil, and a circuit constant including the resistor is set so that the frequency characteristic near the cutoff frequency is smoothed. Since the coil input type low-pass filter is provided, the cut-off frequency band of the noise filter is wider than before and normal mode noise can be reduced.

It is a block diagram which shows the electric current control system of the linear motor provided with the drive device of this invention. It is a circuit diagram which shows the principal part of the drive device of this invention. FIG. 3 is a circuit diagram showing an equivalent circuit of FIG. 2. It is a figure which shows the gain-frequency characteristic of a feedback control system, (a) is a Bode diagram of a closed loop which has a low-pass filter of this invention, (b) is a Bode diagram of a closed loop which has a low-pass filter of a comparative example. It is. It is a figure which shows the gain-frequency characteristic of a feedback control system, (a) is the Bode diagram of an open loop which has the low-pass filter of this invention, (b) is the Bode diagram of the open loop which has a low-pass filter of a comparative example. It is. It is a figure which shows the relationship between the resistance of a low-pass filter, voltage ripple, and resistance loss. It is a circuit diagram which shows the other example of this invention. It is a circuit diagram which shows the other example of this invention. It is a Bode diagram of a closed loop in a feedback control system having a low pass filter of the present invention. It is a Bode diagram of an open loop in a feedback control system having a low pass filter of the present invention. It is a Bode diagram of a closed loop in a feedback control system having a low-pass filter of a comparative example. It is a Bode diagram of an open loop in a feedback control system having a low-pass filter of a comparative example.

(Feedback control system)
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. As shown in FIG. 1, the linear motor driving device of the present invention is a PWM driver having a specific noise filter to supply a driving current with less unnecessary harmonic components to the load (three-phase winding) 2 of the linear motor. 3 is provided. The linear motor drives a mover (coil or magnet unit) by supplying a driving current to a load (three-phase winding: a three-phase coil including a U-phase coil, a V-phase coil, and a W-phase coil). The PWM driver 3 that controls the drive current supplied to the load has an error amplifier 31 that calculates and amplifies the deviation between the current command (analog input) from the controller 1 and the detected current fed back from the load 2 side. The phase compensation amplifier 32 that compensates for the phase difference between the deviation and the thrust command, and the current command from the controller and the output current are compared to control the on-time of the switching element, and the pulse width is modulated at a predetermined duty ratio. A PWM amplifier 33 that outputs a drive current and a low-pass filter 34 that removes noise from the drive current are provided. This detected current is detected as a voltage drop across both ends of the shunt resistor 35 connected between the load 2 and the PWM driver 3, and is supplied to the error amplifier 31 via the insulation amplifier 36. Since both ends are insulated, it is difficult for noise to be superimposed, and highly accurate current detection is possible.

(PWM amplifier)
The PWM amplifier 33 has three sets of switching elements (only one set is shown in FIG. 1) that are bridge-connected. For example, when a MOSFET is used as the switching element, the built-in diode (parasitic diode) serves as a feedback diode in antiparallel with the switching element, so that the return current from the load can flow. The PWM amplifier 33 compares the voltage of a carrier wave (for example, a triangular wave) and a sine wave (modulated wave) (chops a pulse having a constant height to change the duty ratio), and sets the control phase of each switching element to 120. A circuit structure of a sine wave PWM system is obtained in which a waveform with few low-order harmonics is obtained by turning on and off by shifting by [deg.] (UV-UW-VW-VU-WU-WV).

(Low-pass filter)
As shown in FIG. 2, a low-pass filter 34 is inserted between a PWM amplifier 33 having switching elements M1 and M2 that are turned on and off by driving means (not shown) and a coil L13 (load), and the low-pass filter 34 A shunt resistor Rs for detecting a drive current is connected between the coil L13 (winding of the linear motor). Since the output voltage of the PWM amplifier 33 is supplied to the coil L13 via the low-pass filter 34, noise generated when the switching element is turned on / off is removed. The low-pass filter 34 includes a coil L1 connected in series with the load (coil L13), a capacitor C1 connected in parallel with the load, and a resistor R1 connected in series with the capacitor C1 (a capacitor C1 connected in series). This is a coil input type noise filter having a resistor R1 (referred to as a connection body) . Although an actual linear motor has three-phase coils (U-phase coil, V-phase coil, and W-phase coil) that are Y-connected or Δ-connected, FIG. 2 shows only one phase.

  Since this low-pass filter 34 has at least a second order consisting of an inductor and a capacitor, a phase rotation of 180 ° or more occurs in the analog signal (sine wave current) that has passed through the filter, so that stable negative feedback operation is achieved. In order to do this, it is necessary to reduce the loop gain and perform phase advance compensation. Therefore, a resistor R1 is connected in series with the capacitor C1. By adding a resistor to the LC circuit in this way, the loop gain near the cutoff frequency is lowered, so that a stable negative feedback operation can be performed.

  However, simply reducing the loop gain reduces the response, so the frequency characteristics change by lowering the Q value, which is an index indicating the sharpness of the change in the frequency response of the low-pass filter (single unit), that is, the filter. (It is necessary to reduce the Q value so that a sharp series resonance circuit is not formed by the connection circuit and the filter). Therefore, by appropriately selecting the circuit constant of the low-pass filter, particularly the resistance value of the additional resistor, it is possible to widen the frequency band, thereby achieving both the effect of reducing the radiation noise and the responsiveness.

(Equivalent circuit of low-pass filter)
In actual feedback control, the drive current is affected by the resistance of the coil constituting the filter, the resistance of the load coil, and the like, so the results of investigation with the equivalent circuit shown in FIG. 3 will be described. The low-pass filter 34 includes a coil L1, a capacitor C1, and an additional resistor R1 (C1 forms a series circuit with R1), and includes a resistance included in the coil, that is, a copper loss R5 and an iron loss R6. The load side is a series circuit of a coil inductance L11 and its resistance R11, and includes a shunt resistor Rs for detecting current. From this equivalent circuit, the sum (ESR + R1) of the equivalent series resistance (ESR) and the additional resistance R1 of the capacitor C1 is sufficiently smaller than the impedance (Z _c ) of the capacitor, and the impedance Z _{c of the} capacitor is the impedance (Z _{L of the} coil). ) Is sufficiently smaller than (), the current Ic flowing through the filter does not depend on the load resistance R1, and the effect of the noise filter can be maintained.

Therefore, in FIG. 3, each element constant is set as follows to calculate the Q value of the filter. For example, the low-pass filter has an inductance Z _c = 0.4 mH, a copper loss R5 = 0.5Ω, an iron loss R6 = 1500Ω, and a capacitance of the capacitor C1 in order to set the cutoff frequency to approximately 20 kHz (for example, 17 kHz). 220 nF, additional resistance R1 = 3Ω, winding of the linear motor (coil), inductance L11 = 8 mH, resistance R11 = 5Ω [impedance (+ j) = 4.8 kΩ], shunt resistance Rs = 0.02Ω, PWM The switching frequency of the amplifier was 100 kHz, and the input voltage was ± 175V. In the equivalent circuit of FIG. 3, the Q value of the filter is the impedance Z _L (+ j = 240Ω) of the coil L1, the impedance (−j = 7Ω) of the capacitor C1, the additional resistor R1, and the on-resistance (when the switching element is turned on / off). Loss) and copper loss (240Ω / ESR + external resistance (R1) + on-resistance (switching loss) + copper loss (R6)). It is clear that the phase margin increases. In this filter circuit, the filter constant (C / L) is determined so that the cut-off frequency is set to the upper limit of the frequency of the signal to be passed (insertion loss starts increasing at the cut-off frequency). When the frequency is lowered, the element constant may be increased. Further, similarly to a normal noise filter, in the present invention, it is preferable to use a coil L1 having a high series resonance frequency and a large high frequency loss.

(Gain-frequency characteristics of low-pass filter)
In the equivalent circuit of FIG. 3, the results of calculating the frequency characteristics of the filter circuit by simulation with the constants of each element set in the same manner as shown above are shown in FIG. 4A. For comparison, the external resistance is shown in FIG. FIG. 4B shows the simulation result in the case where there is not.

  As shown in FIG. 4B, the gain of the closed loop including the low-pass filter of the comparative example has a sharp peak of about 30 dB near 20 kHz (cut-off frequency), whereas it is shown in FIG. Thus, it can be seen that the gain of the closed loop provided with the low-pass filter of the present invention has a peak in the vicinity of 20 kHz, but its value decreases to 20 dB and becomes a gentle gain fluctuation before and after the peak. Further, comparing the attenuation characteristics of the gain, it can be seen that the gain of 100 kHz (switching frequency) is substantially the same value (about −30 dB) in FIG. 4A and FIG. That is, by adding a resistor having an impedance sufficiently smaller than the impedance of the coil L and the capacitor C to the low-pass filter (LC circuit), the cutoff frequency does not vary, but the filter Q value is significantly reduced. Accordingly, it can be seen that the loop gain of the feedback control system can be increased, that is, a highly responsive negative feedback operation can be realized without deteriorating the noise removal function of the low-pass filter.

  The frequency characteristics shown in FIG. 4 are the results calculated by simulation, but the results of actually measuring the gain-frequency characteristics by the operation check circuit are almost the same as the simulation results, but the gain peak values are different. It was confirmed that the peak value of gain at the cutoff frequency (20 kHz) was lowered by about 10 dB.

(Gain-frequency characteristics of feedback control system)
Next, FIG. 5A shows the result of calculating the gain-frequency characteristics of the feedback control system (see FIG. 1) provided with the low-pass filter of the present invention by simulation (circuit constants are the same as those in FIG. 4). For comparison, FIG. 5B shows the result of simulation under the same conditions as in FIG. 5A except that a low-pass filter without the resistor R1 in FIG. 2 is provided. As shown in FIG. 5 (a), the peak of the open loop gain of the feedback control system including the low-pass filter of the present invention is present near the cutoff frequency, and its value is equivalent to the gain at the frequency near 4 kHz. The peak of the open loop gain of the feedback control system provided with the conventional low-pass filter shown in FIG. 5B is substantially equal to the gain at a frequency near 2 kHz, that is, the motor driving frequency bandwidth is doubled. I understand that I can do it. Therefore, in the feedback control system provided with the low-pass filter of the present invention, negative feedback is applied from the output terminal of the circuit for detecting the drive current (actual current), so that the gain of the feedback control system is changed by the fluctuation of the power supply voltage of the PWM amplifier. Even in such a case, when considering the gain margin (in the Bode diagram, the value obtained by inverting the sign of the gain at the phase intersection), stability can be ensured without impairing responsiveness. it can.

  Further, the frequency characteristic shown in FIG. 5 is also a result calculated by the simulation. When the result of actually measuring the rise time of the drive current when the input command is given by the step-like voltage in the operation check circuit described above, It was confirmed that there was a margin for gain changes due to voltage (input command) fluctuations, and that stable operation was possible.

(Element constant setting)
In the low-pass filter shown in FIG. 2, when the value of the resistor R1 added to the LC circuit is changed, the loss (Ploss) at the resistor R1, the voltage (VR1pp) applied to the resistor R1, and the switching element on / off FIG. 6 shows the result of calculating the voltage ripple (Vout1pp) generated at both ends of the resistor by simulation. From the figure, when the resistance R1 increases, the voltage applied to the resistance R1 also increases, so the loss increases. It can also be seen that the ripple component (the voltage is the sum of the impedance of the capacitor and the resistance) increases slowly until the resistance R1 is 5Ω, and rapidly increases when the resistance R1 is 7Ω or more. From this simulation result, it can be seen that the ripple voltage can be reduced up to a resistance R1 of 5Ω. However, if the resistance R1 is too low, the effect of lowering the loop gain in the vicinity of the cutoff frequency is reduced, and it becomes difficult to perform a stable negative feedback operation. It is preferable to set the range. This resistance value may be set in consideration of the operation specifications (thrust, drive current, stroke, etc.) of the linear motor, the configuration of the control device, and the usage environment (wiring, grounding method, etc.). For example, in the case of a linear motor used in a reduction projection exposure apparatus for manufacturing a semiconductor, the resistor R1 added to the low-pass filter may be set within the above range (2 to 5Ω).

(Common mode choke coil)
Further, in the present invention, not only the circuit configuration shown in FIG. 2 but also a low-pass filter and a load coil are used to further reduce radiation noise (to remove common mode noise) as shown in FIGS. A circuit configuration in which a common mode choke coil formed by winding three coils in the direction in which the voltages generated in the respective windings cancel each other out can be formed. 7 shows a three-phase three-wire system that supplies a drive current to each phase of a Y-connected three-phase coil, and FIG. 8 supplies a drive current to the neutral point of the Y-connected three-phase coil. It is a three-phase four-wire system. 7 and 8, the load coil may be Δ-connected.

  In the circuit of FIG. 7, the drive currents output from each set of switching elements (M1 and M2, M3 and M4, M5 and M6) are low-pass filters 34a (L1, R1, C1) and 34b (L2, R2, C2), 34C (L3, R3, C3) and common mode choke coils (L14, L15, L16) are supplied to the coils L13, L12, and L11 of each phase.

  In the circuit of FIG. 8, the driving currents output from the respective switching elements (M1 and M2, M3 and M4, M5 and M6) are respectively low-pass filters (34a, 34b, 34C) and common mode as in FIG. The choke coils (L14, L15, L16) are supplied to the coils L13, L12, and L11 of each phase. The drive current output from the remaining switching elements (M7 and M8) is supplied to the neutral point of the load coil via the low-pass filter 34d (L18, R4, C4).

(Operational stability and responsiveness)
FIG. 9 and FIG. 10 show the results of measuring the gain-frequency characteristics of the current control circuit shown in FIG. 8 in order to confirm the stability of the operation of the current control system including the low-pass filter of the present invention and the response to the current command. Shown in The constants of the elements constituting the low-pass filter are the same as in FIG. For comparison, FIG. 11 and FIG. 12 show the results of measuring the gain-frequency characteristics of the same current control circuit except that the low-pass filter excluding the additional resistor in FIG. 8 is provided. 9 and 11 are closed-loop Bode diagrams, and FIGS. 10 and 12 are open-loop Bode diagrams. 9 and 11, according to the present invention, the gain peak is reduced by 2.3 dB in the vicinity of the cutoff frequency (20 kHz) as compared with the comparative example, but the characteristics other than the peak are hardly changed. That is, it can be seen that stable operation can be performed even if the power supply voltage increases by about 30% and the gain increases accordingly. 10 and 12, it can be seen that the open loop gain is 2.3 dB higher as a whole, and the responsiveness is improved by about 20%.

(Modification of low-pass filter)
The low-pass filter of the present invention is not limited to the circuit configuration described above, and can be modified as follows (not shown), for example. That is, in the filter circuit shown in FIG. 2, a capacitor can be connected in parallel with the resistor R1. A capacitor can be added in parallel to the series circuit of the capacitor and the resistor. Since the Q value of the filter can be adjusted by adding a bypass capacitor to the low-pass filter in this way, it is estimated that the cutoff frequency of the filter can be finely adjusted. If these circuit configurations are adopted, the element constant should be set so that the effect of reducing the filter characteristics (Q value) at the switching frequency can be maintained by making the impedance of the capacitor at the switching frequency sufficiently larger than the resistance. Good.

(Normal mode noise)
When two or more wires connecting two circuits are affected by the same noise at the same time (common mode noise), currents of the same magnitude and direction are generated in each wire. Can be removed. However, when multiple wirings are affected by different noises (normal mode noise), this noise cannot be removed in principle. Therefore, in the present invention, multiple connection lines should be wired in the same environment. Is preferred.

1: controller, 2: load, 3: PWM driver, 31: error amplifier, 32: phase compensation amplifier, 33: PWM amplifier, 34: low-pass filter, 35: shunt resistor, 36: insulation amplifier

Claims (3)

An error amplifier that amplifies the deviation between the external input signal and the negative feedback signal from the load coil side, a phase compensation amplifier that corrects the pulse width of the signal output from the error amplifier and advances the phase of the output voltage, In a linear motor driving apparatus having a PWM amplifier that performs pulse width modulation on a phase-compensated signal, and a low-pass filter including an LC circuit provided between the PWM amplifier and the load coil, the low-pass filter includes the load A normal mode choke coil connected in series with the coil, a capacitor connected in parallel with the load coil, and an additional resistor connected in series with the capacitor, the connection body formed of the capacitor and the additional resistance the opposite end of the connection end of the normal mode choke coil is connected to the ground side of the PWM amplifier, the Pressurizing element constants of the resistor is driven by a linear motor device characterized by Q value of the filter circuit without substantial variation in the cut-off frequency is set so as to reduce.

  The linear motor driving apparatus according to claim 1, wherein the low-pass filter includes at least a bypass capacitor connected in parallel with a resistor.   The linear motor driving apparatus according to claim 1, wherein a common mode choke coil is connected between the low-pass filter and the load coil.

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