JP2010098894A - Drive system of linear motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive system of a linear motor, capable of switching a servo gain, without adding a special function to a controller and a driver. <P>SOLUTION: In the drive system of the linear motor, the driver 3 includes a drive part 4 to supply a sinusoidal driving current to the linear motor 2 equipped with a mover having a three-phase coil, and a controller 5 which outputs control signals which constitutes a feedback control system to the drive part. A controller 10 for output of position instructions is connected to the driver. The mover is moved toward a target position by a first servo gain. The mover is stopped by switching to a second servo gain (<the first servo gain), when the mover approaches the target position. A program for switching to the second servo gain immediately before the mover is stopped, is stored in a memory built in the driver 3. The mover is stopped by performing the program, immediately before the mover is stopped. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a linear motor drive system that switches servo gains by executing a program stored in a driver.

  In a semiconductor manufacturing apparatus (for example, a projection exposure apparatus or an inspection apparatus), an exposure process or an inspection process is performed by moving a stage on which a glass substrate or the like is mounted to a predetermined position by a coreless type linear synchronous motor (hereinafter simply referred to as a linear motor). Done. The driver for driving this linear motor has a power unit (current amplifier) that supplies a sinusoidal drive current to the winding (multiphase coil), and an external device to achieve high precision positioning accuracy and stopping accuracy. A control unit that compares the target value output from the controller with the current position and current speed of the linear motor and performs feedback control so as to reduce the error is provided.

  In this semiconductor manufacturing apparatus, after a sine wave current of a predetermined amplitude is passed through the multiphase coil to accelerate the mover, a predetermined process is executed while the mover moves at a constant speed, and when the process ends, The mover is decelerated and stopped at the target position. From acceleration to constant speed running, the control system gain (ratio of output and input amplitude in the frequency response) is set to a large value and the mover is moved to a predetermined position. On the other hand, when stopping, if the gain is large, abnormal noise and vibration are generated due to resonance, and the predetermined positioning accuracy cannot be obtained. Therefore, in order to position the stage with high accuracy (submicron or nanometer order) The gain of the control system is reduced.

  Various configurations have been proposed for adjusting the servo tuning gain of the linear motor. In Patent Document 1, the output of the speed deviation output unit is obtained when the mover of the brushless linear DC servo motor (however, the linear pulse motor) is stopped or at a predetermined speed or less and when the mover is accelerating / decelerating or moving. It is described that the servo gain of the error amplifying unit for amplifying the signal is switched in two stages.

  In Patent Document 2, the difference between the position movement timing target value from the software processing unit and the current position of the counter based on the signal from the encoder that detects the rotation of the motor is amplified by a position loop amplifier and output to create a speed. The speed signal from the circuit is amplified and output by the gain variable speed feedback amplifier, and the difference between the two outputs is amplified by the speed loop amplifier and sent to the driver. It is described that the magnitude of the deviation from the target value is obtained and the gain of the gain variable speed feedback amplifier is switched to a large gain when the deviation is larger than a certain value and to a small gain when the deviation is small.

  Patent Document 3 has a gain storage unit that stores a gain determined by a command value and an output, and a gain reading unit that reads the gain and changes the gain of the controller, so that tuning work can be performed initially. Thus, it is described that a real-time gain change can be realized at a low cost in accordance with a load variation in practical use.

  In Patent Document 4, the first gain table and the second gain table are configured to be switched by a changeover switch, and the first gain table and the second gain table are a position proportional gain, a position integral gain, a speed proportional gain, a speed integral gain, and the like. A plurality of control gain sets are stored, and the control gain sets are associated in stages according to the parameters. When the parameter value is increased, the position proportional gain and speed proportional gain are also increased. It is described that a gain set is set, and the positioning time can be shortened even during auto-tuning by switching the control gain according to the operating state of the servo motor.

  Patent Document 5 discloses a current command that a drive device sends to a drive circuit in a stage drive device that includes a motor that moves the stage, a drive device that includes a drive circuit that drives the motor, and a control device that controls the drive device. The gain of PI is amplified by a high gain at a gain other than the inspection section by the switching signal CC sent from the control device to increase the stage movement at a high speed, and the movement of the stage is reduced by amplifying at a low gain in the inspection section. It is described to switch to speed.

JP 60-134793 A (page 3, FIG. 4) Japanese Patent Laid-Open No. 5-6223 (page 3, FIG. 2) Japanese Patent Laid-Open No. 9-9662 (page 2-3, FIG. 1) Japanese Patent No. 3969903 (page 3-6, FIG. 3 to FIG. 5) JP 2006-85566 A (page 3-4, FIGS. 1 to 3)

  Since the control device of Patent Document 1 switches the servo gain based on the moving speed of the mover, the movement of the mover becomes unstable (due to non-linear friction or the like) in the time zone immediately before the mover stops. It is considered that the accuracy is lowered. In addition, the positioning apparatus described in Patent Document 2 does not describe how to configure the software processing unit in order to position the stage with high accuracy (submicron or nanometer order). Since the motor control device described in Patent Document 3 switches the gain at regular intervals, the control circuit becomes complicated and lacks practicality. The control circuit of Patent Document 4 is complicated and lacks practicality. The stage drive device of Patent Document 5 only describes changing the gain of the current command between the inspection section and other sections, and does not describe switching the gain in the vicinity of the stop position.

  Accordingly, an object of the present invention is to provide a linear motor drive system capable of switching servo gain without adding a special function to a controller and a driver.

  In order to achieve the above object, a drive system for a linear motor according to the present invention includes a drive unit for supplying a sinusoidal drive current to a linear synchronous motor having a mover having a three-phase coil, and a feedback control system for the drive unit. A controller that outputs a position command is connected to a driver that includes a control unit that outputs a control signal, and the mover moves toward the target position with a first servo gain, and the mover approaches the target position. In the linear motor control method for stopping the mover by switching to the second servo gain (<first servo gain) when the second servo gain is reached, the second servo is stopped immediately before the mover is stopped in the storage unit built in the driver. A program for switching to gain is stored, and the program is automatically executed immediately before the mover is stopped, so that the mover is It is characterized in that the stop in serial the second servo gain.

  In the present invention, the first servo gain and the second servo gain include a position gain, a speed gain, and an acceleration gain, and the control circuit is a PID type or P It is preferable to configure a PI type control system.

  According to the present invention, it is possible to stop the linear motor at a position substantially coincident with the target position without vibration, and to execute a program stored in the control unit of the driver (software processing) Thus, the servo gain can be switched automatically, which has extremely high practicality.

  Hereinafter, details of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing the configuration of a control system for implementing a variable speed drive system according to an embodiment of the present invention, FIG. 2 is a velocity diagram of a linear motor, and FIG. 3 is a part of FIG. 4 is a block diagram showing the configuration of the gain switching means, FIG. 5 is a flowchart showing the gain switching operation, FIG. 6 is a schematic sectional view of the linear motor, and FIG. 7 is FIG. FIG.

[Control system configuration]
As shown in FIG. 1, a driver 3 that supplies a drive current to a mover (not shown) is connected to a linear motor 2 that moves the stage 100 to a target position. The driver 3 is connected to the line receiver and the controller 4, and receives a command signal (maximum input frequency is, for example, 4 MHz) of the palace train. A power supply line (current bus) 11 between the driver 3 and the linear motor 2 is provided with a current sensor 7 that detects a drive current. The linear motor 2 is provided with a position sensor (for example, a magnetic or optical linear encoder) 8 that reads a current position from a linear scale (not shown).

[Driver configuration]
The driver 3 includes a drive unit 4 that supplies a drive current to a load (three-phase coil) of the linear motor 2, a command signal (for example, a target position and a target speed), and a drive current (actual current) detected by the current sensor 7. In order to realize the variable speed drive of the linear motor 2 by controlling the drive current using the position signal from the linear encoder, the control unit 5 that forms a multiple servo loop of a fully closed loop, and the servo gain of the control system Gain switching means 6 is provided for switching in two steps in terms of software. The deviation between the target position (command pulse number) and the current position (pulse number output from the position sensor 8) is calculated, and the servo gain (position gain, speed gain and integral gain) corresponding to the position deviation is calculated in the servo loop. Although not shown, the driving unit 4 that supplies the switching power source unit (current amplifier) having a full-wave rectifier circuit and a chopper circuit (DC-DC converter) that converts an AC power source (three-phase 200 V) into a predetermined DC voltage; In order to convert a direct current into an alternating current and output a drive current, an inverter unit having a plurality of semiconductor elements is provided.

[Control unit]
The control unit 5 calculates a deviation between the target position (the number of command pulses) and the current position (the number of pulses output from the position sensor 8), and the current speed (position position) based on the position deviation signal. A speed detection unit 51 that calculates a displacement amount), a position control unit 52 that calculates a speed command by subtracting the current position from the target position, and a speed error amount by subtracting the speed command from the current speed. Thus, the speed control unit 53 for calculating the current command and the current control for subtracting the actual current read by the current sensor 7 from this current command to obtain the current error amount and output the control signal to the drive unit 4 The unit 54 (for example, a PWM amplifier) is included. The PWM amplifier, for example, compares a carrier wave (a triangular wave, a sawtooth wave, etc.) whose amplitude changes linearly with time and a modulated signal wave having a phase difference of 120 ° by the switching operation of the semiconductor switch element. Thus, a sine wave current is supplied to the winding of the linear motor by converting to a pulse width modulation output (pulse width proportional to the amplitude) and averaging.

  In the present invention, in order to realize highly accurate positioning, a PID type control system in which the transfer function of the control loop is given by Expression (1) can be used. This transfer function can be obtained by obtaining a differential equation representing the relationship between input and output, performing Laplace transform, setting all initial conditions to 0, and taking the ratio of Laplace transform between output and input. In Expression (1), the first term (Kp: proportional sensitivity) indicates a proportional operation (follows a change in target value). Since the steady position deviation (offset) remains only with the proportional action, the introduction of the second term integral action (TIS: integration time) reduces the steady deviation but the rise time delay. An operation (TDS: derivative time) can be introduced to improve the delay, and the settling time can be shortened (speed response can be improved).

  In the present invention, when the delay of the rise time is slight, a P-PI type control system in which the transfer function of the control loop is given by Expression (2) can be obtained.

[Gain switching means]
In order to realize the switching of the servo gain, the gain switching means 6 includes a position deviation comparing means 61 for comparing the position deviation calculated by the deviation calculating section 50 (IC) with a reference pulse, as shown in FIG. A first gain table 62 for storing the first servo gain (high gain), a second gain table 63 for storing the second servo gain (low gain), and the first servo gain or the second servo based on the position deviation. A gain switching program 64 that reads out the gain and outputs the gain to the position control unit 52, the speed control unit 53, and the current control unit 54 is provided. The position deviation comparing means 61, the first gain table 62, the second gain table 63, and the gain switching program 64 comprise the control unit 5 with a single chip microcomputer (for example, 32 bits), and a built-in storage unit [memory (for example, EEPROM)].

  The first servo gain includes, for example, a position gain Kp1, a speed gain Kv1, and an acceleration gain KI1, and the second servo gain includes, for example, a position gain Kp2 (<Kp1), a speed gain Kv2 (<Kv1), and an acceleration gain KI2 (<KI1 )including. These servo gains are obtained by obtaining a frequency response from the transfer function of Equation (1), transforming a complex number into a polar coordinate form, obtaining an absolute value, and taking its logarithm (obtaining a Bode diagram), thereby obtaining Equation (3). It is represented by In Equation (3), τe is an electrical time constant, and ω is a frequency.

[Linear motor]
The above linear motor 2 has a sinusoidal velocity electromotive force waveform and has a current control loop for controlling the torque (thrust) to a predetermined value, thereby realizing a high speed response (high accuracy and large acceleration). Configured to be able to. As shown in FIGS. 6 and 7, for example, the linear motor 2 includes an X-axis stage (not shown) that moves in the X-axis direction and includes a Y-axis stage 102 that moves in the Y-axis direction. They are arranged at both ends in the X-axis direction (however, only one linear motor is shown in FIG. 5). In the XY stage 100, the Y-axis stage 102 is supported by a rail portion 103 installed on the base 101 via a linear guide 104. The linear motor 2 includes a U-shaped yoke 211 made of a ferromagnetic material and a plurality of permanent magnets 212 fixed to the U-shaped yoke 211, and a magnet unit portion 21 (stator) installed on the base 100 and a three-phase connection. A coil portion 22 (movable element) is formed by molding a plurality of flat air-core coils 221 (for example, Y-shaped connection) with a resin 220. In the permanent magnet 212, magnetic poles having different polarities in the Z-axis direction are opposed to each other in order to form a magnetic circuit in which a sinusoidal magnetic flux density distribution appears in the magnetic gap along the Y-axis direction (see FIG. 6). In addition, magnetic poles of different polarities are arranged at predetermined intervals along the Y-axis direction. The coil unit 22 is connected to the back surface of the Y-axis stage 102 via a coupling unit 222. A drive current [for example, a sine wave current (maximum rated current) of about 6 to 10 A] is supplied to the coil unit 22 from the driver, and the coil unit 22 is driven in the Y-axis direction (see FIG. 6). In this way, torque fluctuation can be reduced by making the current supplied to each winding (air core coil) of the coil part a sine wave.

[Control system operation]
The operation of this feedback control system will be described. When the power of the driver 3 is turned on and the operation of the linear motor 2 is started, and the target position is output from the controller 4 to the control unit 5, the position control unit 52 calculates a speed command. The speed detection unit 55 calculates a current command (target current) from the speed command and the current speed, and the current control unit 53 subtracts the current current from the current command to obtain a current error amount and calculate a voltage command. To do. By outputting this command to the drive unit 4, the stage can be moved to the target position.

  In the above stage, as shown in FIG. 2, after a current in a predetermined direction is passed through the coil to accelerate the mover, a predetermined process is executed while the mover moves at a constant speed, and the process ends. Then, the drive is controlled so that the mover is decelerated and stopped at the target position. Here, in the acceleration region (0-t1), the constant speed region (t1-t2), and the deceleration region (t2-t3), a large gain (first servo gain) is input to the control loop, and the mover is moved to a predetermined position. To move. In the region near the stop position (t3-t4), abnormal noise and vibration are generated due to resonance at a large gain, and a predetermined positioning accuracy cannot be obtained. Therefore, as shown in FIG. 3, immediately before the stop position (t3) (tc: when the position deviation becomes smaller than the reference pulse), a small gain is input to the control loop (by switching to the second servo gain). The stage can be positioned with high accuracy (submicron or nanometer order).

[Gain switching procedure]
As described above, by setting two types of servo gains in the driver and executing the processing procedure shown in FIG. 5, the servo gain can be automatically switched in software. That is, in the section of acceleration, constant speed travel and deceleration (until just before the stop position) [ta in FIG. 2], the linear motor is driven with the first servo gain (S1), and the position deviation is calculated (S2). The position deviation (Sp) is compared with a reference pulse (for example, 30 pulses when the position command is 1000 pulses) (S3). If the position deviation is smaller than the reference pulse, the second servo gain is set. The change is made (S4) and the linear motor is stopped at the target position (S5). That is, immediately before stopping (immediately before the target position) [tb in FIG. 2], the linear motor is driven at a low gain, so that vibration and abnormal noise of the linear motor can be prevented. When the driving of the linear motor is resumed, the process returns to step S1, and the stage can be moved to the next target position by repeating the same steps (S2 to S5) as described above. Note that the optimum reference pulse varies depending on the operation specifications of the linear motor and the like, and is obtained in advance by experiments.

  According to the above embodiment, in order to control the drive current of the linear motor that drives the XY stage, the position detection signal is received from the high gain to the low gain immediately before the linear motor stops, regardless of the external signal. Since switching is performed automatically, the driving of the linear motor can be stopped without any abnormal noise or vibration.

  In the present invention, the parameter values of the first gain and the second gain can be changed by rewriting the driver memory (for example, EEPROM) from a general-purpose personal computer by means of serial communication or the like. It is expensive.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, the present invention can be applied to a stage including a movable magnet type linear motor.

It is a control block diagram of the drive system concerning an embodiment of the invention. It is a speed diagram of a stage. It is the figure which expanded a part of FIG. It is a block diagram which shows the structure of a gain switching means. It is a flowchart which shows gain switching operation. It is sectional drawing which shows an example of the linear motor applied to this invention. It is the arrow view which looked at FIG. 6 from the A direction.

Explanation of symbols

100: stage, 2: linear motor, 3: driver, 4: drive unit, 5: control unit, 6: gain switching means

Claims (2)

A position command is sent to a driver including a drive unit for supplying a sinusoidal drive current to a linear synchronous motor having a mover having a three-phase coil, and a control circuit unit for outputting a control signal constituting a feedback control system to the drive unit. Is connected to the controller to move the mover toward the target position with the first servo gain, and when the mover approaches the target position, the second servo gain (<first servo gain) is switched. In the linear motor drive system that stops the mover by the above, a program for switching to the second servo gain immediately before the mover stops is stored in the storage unit built in the driver, and the program immediately before the mover stops Is automatically executed to stop the mover at the second servo gain. Data drive system. 2. The first servo gain and the second servo gain include a position gain, a speed gain, and an acceleration gain, and the feedback control system is a PID type or P-PI type control system. Linear motor drive system.

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