JP2836328B2 - Positioning method and device using piezoelectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning method using a piezoelectric element, and a positioning method capable of significantly shortening the positioning time as compared with the prior art, and a position control actuator comprising a piezoelectric element and a capacitor. The present invention relates to a positioning device using a piezoelectric element capable of changing a driving mode as a coarse movement positioning mode (which is generally fine movement) and a fine movement positioning mode having high positioning accuracy.

[0002]

2. Description of the Related Art A phenomenon in which an electric polarization occurs when a stress is applied to a crystal and a distortion occurs when an electric field is applied is called a piezoelectric effect. A piezoelectric element having this effect is recognized in the world as an actuator having a fine movement resolution that can be easily obtained, and is employed, for example, as a fine movement mechanism in a stepper in a semiconductor manufacturing apparatus. In addition, it is also incorporated in a tool drive mechanism of a machine tool that realizes high-precision machining by controlling a cutting amount in a workpiece. However, while the piezoelectric element has an excellent feature of extremely high positional resolution, it has the following disadvantages.

(1) Hysteresis occurs in response displacement to a voltage applied to a piezoelectric element.

(2) The displacement response to the applied voltage has a time dependency. That is, there is a creep phenomenon.

As a method of eliminating or reducing the above-mentioned disadvantages, it has been known that a capacitor is inserted in series with a piezoelectric element to perform positioning. For example, Japanese Patent Application Laid-Open No. 01-202178, "Method of Linearizing Characteristics of Piezoelectric Actuator", and Japanese Patent Application Laid-Open No. 63-204672, "Piezoelectric Element Control Apparatus" disclose the technical contents in detail. Here, the disclosed contents are shown by experimental results. First, FIG. 3 shows the first effect when a capacitor is inserted in series with the piezoelectric element. In the figure, the horizontal axis is the applied voltage,
The vertical axis indicates the displacement, and FIG. 7A shows the case where the piezoelectric element is used alone, and FIG. 7B shows the static characteristic when the capacitor is inserted in series with the piezoelectric element. Obviously, the hysteresis is reduced by the series insertion of the capacitor.

Next, a second effect is to reduce the creep phenomenon. First, FIG. 4A shows creep known as a drift phenomenon relating to a displacement amount when a constant voltage is applied to a piezoelectric element. As is clear from the comparison between the auxiliary line indicated by the broken line in the figure and the response waveform, creep occurs in which the displacement gradually increases over about one minute. This phenomenon is also improved by inserting a capacitor in series as shown in FIG.

As is clear from the experimental results shown in FIGS. 3 and 4, when the entire device in which a capacitor is inserted in series with the piezoelectric element is driven as an actuator, hysteresis and creep phenomenon are suppressed. Therefore, a high-speed response actuator having extremely high linearity and good stability is obtained as compared with the case of using only the piezoelectric element. That is, if the required positioning accuracy is not relatively high,
It is possible to perform open-loop positioning in which a drive command is given to the entire device in which a capacitor is inserted in series with the piezoelectric element. If the piezoelectric element alone is driven in an open loop as an actuator, it is impossible to perform positioning that satisfies repeated position accuracy due to hysteresis and creep, which are inherent defects of the element. is there.

It should be noted that when a capacitor is inserted in series, there is a disadvantage that the applied voltage required to obtain a desired displacement becomes high, while having the above-mentioned excellent characteristics.

From the above description, it has been found that when a capacitor is inserted in series with the piezoelectric element and this is driven in an open loop, it can be used as an actuator having extremely high linearity. Then, what is the performance when a closed-loop control system related to position is configured? First, FIG. 5 shows a block diagram of a device for positioning a stage (load) in a vertical direction using a piezoelectric element as an actuator. In the figure, a portion 14 surrounded by a broken line is a block to be controlled including the piezoelectric element and the stage. Also, 15
Is a driver for applying a high voltage to the piezoelectric element,
Reference numeral 16 denotes a PI compensator having a role of improving the characteristics of the position control loop. Here, P means proportional operation, I means integration operation, and the symbols shown in the figure are as follows.

B: Voltage displacement conversion coefficient of piezoelectric element [m / V] K: Spring constant of mechanism system [N / m] D: Viscous friction coefficient of mechanism system [Ns / m] M _L : Load mass [Kg] Z _PZT : Displacement of piezoelectric element [m] Z _L : Displacement of load [m] A _d : Driver gain [V / V] T _d : Driver time constant [sec] K _P : PI compensator gain [V] / V] T ₁ : Time constant of PI compensator [sec] T ₂ : Time constant of PI compensator [sec] K ₃ : Gain of position sensor amplifier [V / m] γ: Capacitor C _{cap in} series with piezoelectric element This is a coefficient indicating the effect when inserted, and is expressed by the following equation.

Γ = C _cap / (C _cap + C _PZT ) <1 (1) where C _PZT is the capacitance of the piezoelectric element. Here, based on the control block diagram of FIG. Examine the effect of the condenser.
First, FIG. 6 shows a calculation result of a step response when a capacitor is inserted. However, the target signal is 50 [mV]
And the response is the output of the position sensor amplifier. In the drawing, γ = 1 indicates the case where the piezoelectric element alone is used as the actuator. The other waveforms are response waveforms when γ is changed from 0.5 to 0.1 in increments of 0.1, that is, when the insertion capacity of the capacitor is sequentially reduced. From the step response waveforms shown, it can be understood that the rising portion of the positioning waveform is accelerated by the insertion of the capacitor, but a significant improvement is not achieved.

However, when a capacitor is inserted, the transfer function G _d (s) of the driver 15 is G _d (s) = γA _d / (1 + sγT _d ) (2.a) as shown in FIG. T _d = [output resistance of driver] × [capacitance of piezoelectric element] (2.b), and γ is also applied to the numerator gain term. Since γ is smaller than 1, if a position control loop is formed by simply inserting a capacitor, the loop gain is reduced. That is, the responsiveness of the position deteriorates. Therefore,
In response calculation in FIG. 6, the driver gain .gamma.A _d is corrected by 1 / gamma times. That is, the loop gain of the control device is the same depending on whether or not the capacitor is inserted.
Therefore, in the control block of FIG. 5, the difference in the parameter due to the presence or absence of the insertion capacitor is only the time constant of the driver. That is, in the case of condenser-free insertion is T _d, in the case of the condenser inserted has a [gamma] T _d. Note that the calculation results in FIG. 6 are also confirmed by experimental results using an actual machine.

To illustrate the above fact, that is, why the positioning time is not significantly reduced by the insertion of the capacitor, FIG. 7 shows the open-loop frequency response of the control block (FIG. 5). Here, FIG. 7A shows a case where no capacitor is inserted, and FIG. 7B shows a case where a capacitor is inserted. From the figure, it is understood that the insertion of the capacitor does not cause a change in the crossover frequency. That is, there is almost no difference in the positioning response depending on whether or not the capacitor is inserted.

The conclusions obtained from the above experimental results and analysis will be summarized. (1) The displacement characteristics of the piezoelectric element with respect to the applied voltage include:
Hysteresis and creep occur. Therefore, it is not suitable for use in driving a piezoelectric element in an open loop state. To the last, the piezoelectric element must be used in a closed loop of the position. The reason for this is that when a closed loop of position is provided, the non-linearity of the actuator is compensated. (2) However, in the case where the whole of the actuator in which a capacitor is inserted in series with the piezoelectric element is used as an actuator, the linearity becomes extremely good. Perform the function of
In addition, a high-speed response can be realized when driving in the open loop as compared with driving in the closed loop state. Therefore, it is difficult to abandon the advantage of driving the open loop with the linearity increased. (3) On the other hand, in the case where the closed loop of the position is configured, there is almost no influence of the presence or absence of the insertion capacitor on the positioning time. However, as can be seen in detail from the calculation result of FIG. 6, although the insertion of the capacitor can increase the speed of the rising portion of the waveform, the response is delayed when the capacitor is inserted in a portion where the steady state is entered. . Therefore, when forming a closed loop of the position and performing the minute positioning, it is preferable that the capacitor is not inserted.

[0015]

In a positioning device using a piezoelectric element as an actuator, an ultra-precision fine movement positioning is finally performed, but a coarse movement operation is performed before or after the fine movement positioning. I have to. For example, when a positioning device using a piezoelectric element is mounted on a stepper in a semiconductor manufacturing apparatus, a leveling operation must be performed during the transfer of an IC wafer. That is, coarse movement positioning of a relatively large stroke is also performed. Of course, this operation is not directly related to the exposure performance to the IC wafer, but the handling of the IC wafer, the fine positioning for the exposure, and the re-handling time after the exposure determine the throughput of the entire apparatus. is there. In other words, positioning time in the coarse movement positioning mode and ensuring the accuracy are also important for improving the throughput. Here, it is well known that improving the throughput, which is a productivity index per unit time, is important for reducing the cost of a product.

Conventionally, however, in a positioning device using a piezoelectric element as an actuator, a coarse positioning mode requiring a relatively large stroke and a fine positioning mode are realized by forming the same closed loop. Was. There is a limit to shortening the response time in the closed loop state because the stability of the closed loop must not be destroyed. However, for the purpose of shortening the entire time of the transfer process and the fine positioning operation, the reduction of the time of the transfer process, that is, the time of the coarse movement positioning mode has been left as a major problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a positioning device using a piezoelectric element for shortening the positioning time of the entire coarse movement positioning and fine movement positioning modes. is there.

[0018]

In order to solve the above-mentioned problems, according to the present invention, in a coarse positioning mode, a capacitor is inserted in series with a piezoelectric element, and a driver is inserted into the capacitor.
The through positioning in the applied open loop position command signal is made to remove the inserted capacitor becomes fine positioning mode and an actuator piezoelectric element alone, on this
The difference signal between the output signal of the position sensor and the position command signal is
Provided is an apparatus configuration in which positioning is performed by the action of a closed loop position control system input via a driver .

[0019]

In the positioning device using the piezoelectric element, in the coarse positioning mode, the piezoelectric element and the entire capacitor inserted in series with the piezoelectric element are used as an actuator, and an open-loop drive for directly giving a position command to the actuator is performed.
In this case, the insertion of the capacitor reduces the hysteresis and creep of the piezoelectric element itself, so that the linearity of the actuator is good, and positioning can be performed with sufficient accuracy even in open-loop driving in the case of coarse movement operation. Moreover,
The response is much faster than if a closed loop for position control was implemented. Of course, in the case of the fine movement positioning mode, the difference signal between the output signal of the position sensor and the position command signal is transmitted.
Signal to the actuator to perform closed loop control,
In this case, disconnect the series connection of the piezoelectric element and the capacitor.
And the above signal is
It is entered. This is because, in the closed-loop response when the capacitor is inserted, as shown in FIG. 6, the time to enter the steady state is slightly slower than when the capacitor is not inserted.

As described above, by driving the coarse movement positioning mode and the fine movement positioning mode by open loop control and closed loop control, respectively, the positioning time of the entire operation from coarse movement to fine movement and from fine movement to coarse movement can be reduced.

[0021]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a positioning device using a piezoelectric element according to one embodiment of the present invention. In the figure, 1
Is a piezoelectric element, which functions as an actuator for vertically displacing the stage 2 as a load. As shown in the figure, the displacement of the stage 2 is detected by a non-contact position sensor 4 attached to the holder 3, and is converted into an electric signal by a sensor amplifier 5. Reference numeral 6 denotes a mechanism that compresses the stage 2 in the direction of gravity and applies a preload to the piezoelectric element 1. This is, for example, a coil spring.
The stage 2 is housed in a casing 7, which also serves as a guide mechanism for the stage 2. A capacitor 8 is inserted in series with the piezoelectric element 1, and a switch 9 is connected in parallel to both ends of the capacitor 8. As is clear from FIG. 1, reference numeral 10 denotes a driver for applying a high voltage to the piezoelectric element 1 or a piezoelectric element 1 and a capacitor 8 connected in series.
1 typically uses a compensator to function properly when a closed loop of position is configured. For example, it is common to use a PI compensator.

Now, in the above-described configuration of the positioning device, a target signal for positioning the stage 2 to a predetermined position is applied from the terminal R. First, in the coarse movement positioning mode, the switch 12 is turned on, and the R target signal is applied to the input side of the driver 10. At this time, the switch 13 provided in the compensator 11 is also on, and the output of the compensator is reset to zero. Further, in this state, the switch 9 is turned off. Therefore, the target signal applied from R passes through the driver 10 and is applied to the piezoelectric element 1 and the capacitor 8 connected in series. At this time, since the output of the compensator 11 is zero, no closed loop is formed. Therefore, in the coarse movement positioning mode, the whole of the piezoelectric element 1 and the capacitor 8 connected in series constitutes an actuator, which is driven in an open loop state. Therefore, high-speed coarse movement positioning is realized.

Next, in the fine positioning mode, the switches 12 and 13 are turned off and the switch 9 is turned on. Therefore, a closed loop control of the position is formed, and the minute positioning is performed by the target signal applied from R.

Note that, as shown in FIG.
Opening and closing of 2 and 13 is controlled by a logic input applied from a terminal C. The switching of the coarse / fine positioning mode by the logical input is realized by using the output obtained from the sensor amplifier 5 through the comparison circuit as the input to the terminal C. Alternatively, when there is an IC wafer on the stage 2, a comparison circuit output of an output of a position measuring means using a lens or a CCD element existing above the IC wafer may be used. Further, regardless of which position measuring means is used, the switching between coarse and fine movement is performed by [deviation] = [position setting value] − [current position], [one-step difference of deviation], [two-step difference of deviation] , [Operation amount change to driver 10] as observation data.

[0026]

Other Embodiments In the above embodiment, the piezoelectric element 1 and the capacitor 8 were inserted in series in the coarse movement positioning mode. However, another piezoelectric element 1 ′ may be inserted in series with the piezoelectric element 1 as shown in FIG. That is, the piezoelectric elements 1 and 1 'are mechanically arranged in parallel, and both piezoelectric elements are electrically connected in series. That is, a configuration may be adopted in which the two piezoelectric elements cooperate to roughly position the stage 2 having the same load.

In this case, in order to set to the fine movement positioning mode, one of the piezoelectric elements is considered to be the same as the capacitor of the previous embodiment, and the series connection of the piezoelectric elements is released.
Only one piezoelectric element is used as an actuator.

When a closed-loop position control system is configured, the response is improved by increasing the loop gain. But,
Increasing the loop gain has a limitation because it gradually degrades the stability of the control loop. However, if the whole thing in which a capacitor is inserted in series with the piezoelectric element is used as an actuator to drive an open loop that does not form a closed loop of the position, there is no need to worry about the stability problem. In addition, a high-speed response can be realized as compared with a closed loop. Therefore, there is an effect that high-speed positioning of a large stroke motion can be easily realized without imposing a design burden.

When the apparatus is a fine movement positioning apparatus mounted on a stepper, first, the stage 2 is moved upward in the coarse movement positioning mode to set an IC wafer, and then, after the completion of the setting, the coarse movement is performed again. In the positioning mode, the stage can be moved downward, and finally the mode can be smoothly shifted to the fine movement positioning mode for exposure. Therefore, it is possible to reduce the time for a series of operations such as the transfer of the IC wafer and the fine positioning for exposure. Conventionally, a stage 2 is provided with a mechanism for performing only this operation for handling the IC wafer. However, according to the present apparatus configuration, not only the mechanism around the stage 2 becomes simple, but also the time required for the operation of the handling mechanism is significantly reduced. Further, since the coarse movement positioning mode and the fine movement positioning mode can be switched in a timely manner, the characteristics of each mode can be utilized by selecting one of the modes according to the purpose of positioning.

[0030]

As described above, according to the present invention, the response is improved by increasing the loop gain during the closed loop control, and the piezoelectric element and the capacitor are connected in series during the open loop control. When the actuator is driven as an actuator, stability is improved, and a high-speed response can be realized as compared with closed-loop control. Therefore, high-speed positioning can be easily realized without imposing a design burden. Further, since the positioning device of the present invention can switch between the coarse positioning mode and the fine positioning mode in a timely manner, it is possible to take advantage of the characteristics of each mode by selecting either mode according to the purpose of positioning. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a positioning device using a piezoelectric element according to one embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a positioning device using a piezoelectric element according to another embodiment of the present invention.

FIGS. 3A and 3B are experimental results showing static characteristics of displacement with respect to an applied voltage.

FIGS. 4A and 4B are experimental results showing a drift phenomenon of a displacement amount with respect to an applied voltage.

FIG. 5 is a control block diagram of a positioning device using a piezoelectric element as an actuator.

FIG. 6 is a calculation result of a step response.

FIGS. 7 (a) and (b) are open loop frequency responses of a position controller.

[Explanation of symbols]

 1, 1 'Piezoelectric element 2 Stage 3 Holder 4 Position sensor 5 Sensor amplifier 6 Preload mechanism 7 Casing 8 Capacitor 9 Switch 10 Driver 11 Compensator 12 Switch 13 Switch 14 Control target 15 Driver 16 PI compensator

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G01B 7/34 H02N 2/00 B H02N 2/00 H01L 41/08 K (56) References JP-A-3-73252 (JP, A) JP-A-63-204672 (JP, A) JP-A-1-202178 (JP, A) JP-A-60-146650 (JP, A) JP-A-63-52114 (JP, U) (58) Int.Cl. ⁶ , DB name) B23Q 15/24 B23Q 5/28 B23Q 16/00 H01L 41/09 G01B 7/00 G01B 7/34 H02N 2/00

Claims (2)

(57) [Claims] Using a piezoelectric element as claimed in claim 1] positioning actuator, First, the coarse positioning mode positioning accuracy is not high relative to connect the capacitor in series to the piezoelectric element in this mode, the piezoelectric element and the capacitor
And a position command via a driver
A signal is applied to drive the position control in an open loop, and then, in the fine movement positioning mode in which the positioning accuracy is relatively high, before the series connection of the piezoelectric element and the capacitor is released.
Actuator without capacitor and controlled
An output signal of a position sensor for detecting a position of an object and the position finger
Command signal from the control signal via the driver.
A positioning method using a piezoelectric element , comprising inputting the input to an actuator from which a denser has been removed and performing position control driving in a closed loop. 2. A piezoelectric element for controlling a position of a controlled object;
Connected in series with the piezoelectric element when the open loop control 閉Ru
And a capacitor Ru solved the series connection of the piezoelectric element when the-loop control, in the position control actuator, acting upon the closed loop control to this, a position sensor for detecting the position of the controlled object, the position a differential output unit that outputs a signal of the difference between the output signal and the position command signal of the sensor, the deviation output
From the deviation output device connected between the device and the piezoelectric element.
A voltage applied to the piezoelectric element based on the signal of
A positioning device using a piezoelectric element provided with a bar and capable of performing positioning control by either open-loop control or closed-loop control.