JP4442756B2 - Feed mechanism drive system - Google Patents

Description

  The present invention relates to a driving system for a feed mechanism, and in particular, an electric signal applied to an actuator for suppressing sliding of a sliding portion between a stage such as a precision positioning stage and a contact actuator that directly drives the stage. This relates to a driving mechanism of the feed mechanism which is characterized by

With the further improvement of the degree of integration of semiconductor integrated circuit devices in recent years, there is a demand for an exposure technique that enables drawing of a fine line width even in a photolithography process. For circuit manufacture, an exposure technique using ultraviolet rays, X-rays, or electron beams as a light source is required.
In particular, when the microfabrication dimension reaches 70 nm (= 0.07 μm) or less, the electron beam exposure technique is considered promising as a mass production technique.

  In such an exposure apparatus, a high-precision positioning stage is indispensable for aligning the wafer that is the substrate to be exposed. As a feed mechanism, a combination of a rotary electromagnetic motor and a ball screw, a linear electromagnetic motor is used. Commonly used.

  Under such circumstances, in recent years, as a stage feed mechanism mounted on an electron beam exposure apparatus or an electron beam applied measurement apparatus, a linear ultrasonic motor is used from the viewpoint of accuracy, non-magnetism, vacuum environment, size, etc. A representative contact type actuator is attracting attention.

  In particular, the present inventors have used a non-resonant ultrasonic motor using a laminated piezoelectric actuator polarized in a stretching mode and a shear mode, and brought the tip of the shear mode portion of the laminated piezoelectric actuator into contact with the stage, and at the contact interface. It is proposed to drive the stage using the friction of the above (see, for example, Patent Document 1).

In this case, in linear ultrasonic motors widely used as contact actuators, the drive frequency is uniquely determined depending on the shape, so the voltage amplitude control drive method with a fixed frequency is adopted as the drive method. is doing.
For example, driving is performed at a fixed frequency of 25 kHz and a voltage amplitude of 40V.
JP 2001-293630 A

  However, in the contact actuator, the wear of the sliding material at the sliding part greatly affects the durability, reliability, and position accuracy, so that there is a problem that maintenance-free continuous driving becomes very difficult. is there.

  Accordingly, an object of the present invention is to provide a drive system that suppresses the wear of the sliding material at the sliding portion of the contact actuator.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
Refer to FIG. 1. (1) In order to solve the above-mentioned problem, the present invention is an actuator having a function of individually controlling the displacement amount of the pressed member 1 and the tip 3 with respect to each axis of spatial coordinates by an electric signal. 2, a holding member 4 having a function of holding the actuator 2 and pressing the tip 3 against the pressed member 1, and a control circuit 5 for supplying an electric signal to the actuator 2. and in one drive system of fixed feed mechanism for moving the other the of the holding member 4, the side where the time for varying the positive or negative direction against the feed direction displacement amount of the tip 3 of the actuator 2 to move members thrust acting on, and therefore the maximum static friction force a predetermined rule including a condition that does not exceed between the tip 3 of the pressed member 1 actuator 2, it has a variable in one stroke It is characterized by.

That is, by making the increase time or decrease time of the electric signal for controlling the speed of the contact type actuator 2 variable according to a predetermined rule, it is possible to suppress the occurrence of slipping at the sliding portion, and thereby the feed mechanism. The life of a stage or the like equipped with can be realized. Particularly, since the pressed member 1 is set so as not to exceed the maximum static frictional force between the tip 3 of the actuator 2 and the relative speed between the pressed member 1 and the tip 3 of the actuator 2 is zero. The occurrence of slip can be completely prevented.

  The pressed member 1 in this case is typically a stage mechanism for transporting a wafer or sample used in an exposure apparatus, an electron beam drawing apparatus, a length measuring electron microscope, a laser confocal microscope, or the like. In addition, various conveying members such as a probe terminal holding mechanism for manipulators used for electronic measurement such as a prober and a cantilever holding mechanism in an atomic force microscope are mainly targeted.

  The actuator 2 is typically a stacked piezoelectric actuator 2 that can independently control the displacement of the tip 3 in two XY directions, but the displacement of the tip 3 can be independently voltage controlled in three XYZ directions. An actuator 2 having another structure having a function of individually controlling the amount of displacement of the tip 3 by an electric signal with respect to each axis of the spatial coordinates, such as a cylindrical piezoelectric actuator 2 that can be applied, is also applicable.

  The holding member 4 that holds the actuator 2 is typically a preload mechanism using a leaf spring or a coil spring.

(2) Further, the present invention, the above (1) to Oite, the positive direction or at least a portion of the period of change allowed to time in the negative direction, the displacement amount of the tip 3 of the actuator 2 at a constant acceleration with respect to time It is characterized by changing.

  Thus, the feed mechanism can be driven more efficiently by changing the amount of displacement of the tip 3 of the actuator 2 at a constant acceleration with respect to time.

(3) Further, the present invention is Oite above (1), the positive direction or in at least some period of time for varying the negative direction, sinusoidal function the amount of displacement of the tip 3 of the actuator 2 with respect to time It is characterized by being changed by.

  Further, by changing the displacement amount of the tip 3 of the actuator 2 with a sine wave function with respect to time, the drive voltage may be based on a very general sine wave. The configuration can be simplified.

( 4 ) Further, according to the present invention, in any one of the above (1) to ( 3 ), each of the time required to change the displacement amount in the direction orthogonal to the feed direction of the tip 3 of the actuator 2 in the positive direction or the negative direction. The maximum value in the period is equal to or greater than the maximum height of the surface undulation of each of the pressed member 1 and the tip 3 of the actuator 2 in the pressing portion.

  Thus, the maximum value of the displacement amount in the direction orthogonal to the feeding direction of the tip 3 of the actuator 2 is set to be equal to or greater than the maximum height of the surface undulation of each of the pressed member 1 and the tip 3 of the actuator 2 in the pressing portion. Thus, it is possible to realize a sufficient pressing state in which no slip occurs.

( 5 ) Further, according to the present invention, in any of the above (1) to ( 4 ), a vertical drag measurement sensor is added to the holding member 4 and the maximum static friction force is set using the measurement value of the vertical drag measurement sensor. It is characterized by changing the value.

  Since the maximum static frictional force in the present invention is in a relative stationary state between the pressed member 1 and the tip 3 of the actuator 2, when one of the pressed member 1 and the holding member 4 starts to move. Since the apparent maximum static frictional force is reduced, this apparent maximum static frictional force is measured in real time by the vertical drag measurement sensor, and the displacement amount of the tip 3 of the actuator 2 with respect to the feed direction is determined according to the measurement result. By changing the time for changing in the positive direction or the negative direction, more efficient driving becomes possible.

( 6 ) Further, in the present invention, in any one of the above (1) to ( 5 ), the frequency spectrum of the time change function of the displacement amount of the tip 3 of the actuator 2 individually controlled by the electric signal is It is characterized by being composed mainly of components having a frequency lower than the resonance frequency.

  Since the frequency at which the slip does not occur is lower than the resonance frequency of the actuator 2, the frequency spectrum of the time-varying function of the displacement amount of the tip 3 of the actuator 2 individually controlled by the electrical signal is necessary to perform the drive while suppressing the slip. Need to be configured mainly with components having a frequency lower than the resonance frequency of the actuator 2.

  According to the present invention, the sliding material wear is reduced by suppressing the sliding that occurs in the sliding portion of the contact type actuator. It becomes possible to drive continuously.

  The present invention relates to an actuator based on an electrical signal generated by a control circuit when moving a stage mechanism for transporting a wafer or sample used in an exposure apparatus, an electron beam drawing apparatus, a length measuring electron microscope, a laser confocal microscope, or the like. The time for changing the displacement amount of the tip of the actuator in the positive direction or the negative direction with respect to the feed direction is variably controlled so as to realize the condition for suppressing the slip at the contact portion of the actuator tip.

Here, with reference to FIG. 2 thru | or FIG. 7, the drive system of the feed mechanism of Example 1 of this invention is demonstrated.
See Figure 2
FIG. 2 is a schematic configuration diagram of a main part of a non-resonant ultrasonic motor driving stage to which the driving system according to the first embodiment of the present invention is applied. Here, only a feed mechanism in the x direction is shown.
The stage mechanism is a non-resonant ultrasonic motor including a stage 11 that is configured to be guided in the x-axis direction by a cross roller guide 12, two stacked piezoelectric actuators 21 and 22, and a preload mechanism 13 as a holding mechanism. The stage 11 is driven by the frictional force accompanying the shear deformation of the tip portions of the stacked piezoelectric actuators 21 and 22 pressed against the side surface of the stage by the preload mechanism 13.

  In this case, each of the laminated piezoelectric actuators 21 and 22 has a structure in which the expansion / contraction deformation element 23 and the shear deformation element 24 are laminated, and the top of the shear deformation element 24 is made of a high hardness member such as alumina ceramics. A friction chip 25 is provided.

  Further, an electrode layer (not shown) is inserted between the piezoelectric layers constituting the expansion / contraction deformation element 23 and the shear deformation element 24, and electrodes (not shown) are selectively combined with the electrode layers. And applying a voltage between the electrodes to obtain a predetermined stretch deformation and shear deformation.

Also, the two stacked piezoelectric actuators 21 and 22 are used here by setting the stage 11 by driving closer to the case where one is the A phase and the other is the B phase, and the phase is equivalently reversed 180 degrees. This is because one of the stacked piezoelectric actuators 21 and 22 can always drive the stage 11 when moving the distance more than the maximum displacement of the piezoelectric material.
By adopting such a configuration, the positioning performance of the stage 11 can be made more highly accurate.

Based on the above configuration, A-phase and B-phase drive voltage waveforms when the stage 11 is accelerated and driven without any slip are derived.
As shown in FIG. 2, the coordinate axis 0-xy of the inertial system is taken, the position vector from the origin 0 to an arbitrary point P on the stage 11 is ^v r ₀ = (x ₀ , a), and the stacked piezoelectric actuator from the origin The position vector to the friction tip 25 attached to the tips of 21 and 22 is assumed to be ^v r = (x, b).
In this specification, for the purpose of creating the specification, in the case of vector notation, “ ^v ” is added before the vector.

See Figure 3
FIG. 3 shows only the coordinate system taken out by arranging the coordinate systems as described above. On the point (x, b) at a distance of r from the origin 0, the coordinate axis 0'-x 'of another coordinate system is obtained. Take y '.
At this time, if the position vector from the friction tip 25 fixed to the side surface of the stage 11 to the point P (x ₀ , a) is ^v r ′ = (x ′, c),
^v r ₀ = ^v r + ^v r ′
It is.

Here, since the stage 11 is guided only in the x-axis direction, a, b, and c are constants, and x ₀ , x, and x ′ are variables.
Therefore, since the motion of the stage 11 should be considered only in the x-axis direction, if the thrust acting on the stage 11 is F _T , the equation of motion is that the mass of the stage 11 is m and the time is t.
F _T = m (d ² x ₀ / dt ² ) = m [d ² (x ₀ + x ′) / dt ² ] (1)
It becomes.

In this case, it is possible to sufficiently small values as compared with easily thrust F _T friction force generated by the cross roller guide 12, flip and sliding member 14 by the law of the thrust F _T is action and reaction acting on the stage 11 Determined by the frictional force F acting between the
F _T = −F (2)
Is approximated by Therefore, from equation (1)
F = −m (d ² x / dt ² ) −m (d ² x ′ / dt ² ) (3)
It becomes.

If the frictional force F does not exceed the maximum static frictional force, that is, if no slip occurs between the sliding member 14 and the frictional tip 25 during the feeding operation, the frictional tip 25 is relative to the stage 11. Because it will be in a stationary state,
dx '/ dt = 0
Equation (3) becomes
F = −m (d ² x / dt ² ) (4)
It becomes.

The friction tips 25 at the tips of the multilayer piezoelectric actuators 21 and 22 are pressed against the sliding member 14 by the preload mechanism 13 with a preload N. When the friction coefficient is u, the static friction force is less than the maximum static friction force. To become
| F | ≤uN
Because
uN ≧ m | d ² x / dt ² | (5)
It becomes.

Accordingly, the acceleration of the actuator tip ^{a (= d 2 x / dt} 2), when the maximum value and a _m, the maximum acceleration a _m is from (5),
a _m = uN / m (6)
It becomes.
Therefore, if the stage 11 is accelerated at a _m (= uN / m), no slip occurs at the sliding portion and there is no energy loss, so the stage 11 can be accelerated the fastest.

Usually, in a non-resonant type ultrasonic motor, the laminated piezoelectric actuators 21 and 22 send the stage 11 alternately by the two-phase driving of the A phase and the B phase as described above.
Therefore, first, let us say that the stage 11 is sent from the A phase, and the velocity of the A phase actuator at 0 <t ≦ T ₁ is v _A1 and its position is x _A1 .
v _A1 = a _m t (7)
_{x A1 = (1/2) a m} t 2 ··· (8)
It becomes.

Speed v ₁ = v reached _A1m at time T _1, if displaced to the maximum displacement amount A _{m,
v A1m = a m T 1 ···} (9)
A _m = (1/2) a _m T ₁ ² (10)
By transforming equation (10), T ₁ becomes
T ₁ = (2A _m / a _m ) ^1/2 (11)
It is represented by

Next, the stage 11 is sent by the B-phase actuator, where the speed of the B-phase actuator at T ₁ <t ≦ T ₂ is v _B1 and its position is x _B1 .
v _B1 = a _m t (12)
_{x B1 = (1/2) a m} t 2 -2A m ··· (13)
It becomes.

In time T _2, reaches a speed v ₂ = v _B1m, if displaced to the maximum displacement amount A _{m,
v B1m = a m T 2 ···} (14)
A _m = (1/2) a _m T ₂ ² −2A _m (15)
By transforming equation (15), T ₂ becomes
T ₂ = (6A _m / a _m ) ^1/2 (16)
It is represented by

Next, the stage 11 is again sent by the A-phase actuator, where the speed of the A-phase actuator at T ₂ <t ≦ T ₃ is v _A2 and its position is x _A2 .
v _A2 = a _m t (17)
_{x A2 = (1/2) a m} t 2 -4A m ··· (18)
It becomes.

_Assuming that the speed v ₃ = v _A2m is reached at time T ₃ and the maximum displacement A _{m is} displaced,
v _A2m = a _m T ₃ (19)
_{A m = (1/2) a m} T 3 2 -4A m ··· (20)
By transforming equation (20), T ₃ becomes
T ₃ = (10A _m / a _m ) ^1/2 (21)
It is represented by

Therefore, as a general formula, the time T _n and the speed v _n at the end of the n-th feeding operation are
v _n = a _m T _n (22)
T _n = [2 (n−1) A _m / a _m ] ^1/2 (23)
It is represented by
In v _n , the speed of the A phase is obtained when n is an odd number, and the speed of the B phase is obtained when n is an even number.

As described above, when the laminated piezoelectric actuators 21 and 22 are used as the actuator and alumina ceramics is used as the sliding member 14 and the friction chip 25, under typical use conditions, for example, u = 0.3, N = 40 [N], m = 1.4 [kg], and A _m = 0.42 [μm] are assumed.

See FIG. 4 and FIG.
4 and 5 show the acceleration a (= d ² x / dt ² ), the velocity v (= dx / dt), and the position x of the actuator tip of each phase in the feed direction when the stage 11 is accelerated under this condition. 4 is a time chart, FIG. 4 shows the A phase and FIG. 5 shows the B phase.
That is, substituting the above conditions into equation (6),
a _m = 0.3 × 40 / 1.4≈8.6 [m / s ² ]
Thus, T _n and velocity v _n can be obtained from equations (23) and (22), respectively.

See FIG.
FIG. 6 is a time chart of the actuator tip position in the direction orthogonal to the feed direction, that is, the y direction. In the figure, when the position y is 0.23 μm, the actuator tip of each phase is the sliding member 14. In the state where it is in contact with the film, -0.23 μm represents a non-contact state.

Assuming that the drive voltage applied to the actuator is V (t), x∝V (t). Therefore, the drive voltage is a value obtained by multiplying the displacement time chart in each figure by a proportionality constant.
Here, if it is necessary to drive in a region where the displacement and drive voltage are not linearly proportional due to the saturation characteristics of the piezoelectric material, etc., the function is obtained in advance and the corresponding displacement is made to correspond one-to-one. Needless to say, it is sufficient to determine the drive voltage waveform.

See FIG.
FIG. 7 is a time chart of the acceleration, speed, and position of the stage under the above driving conditions. Wearing due to slip is suppressed by performing an equal acceleration motion at an acceleration at which a slip of a _m = uN / m does not occur. It became possible to improve.

  Similarly, when the stage 11 is decelerated, it goes without saying that the drive voltage waveform of each phase of the actuator may be determined so as not to exceed the maximum static frictional force according to the above example.

  Also, when shifting to constant velocity motion, within a range that does not exceed the maximum static frictional force, for example, the maximum displacement of the actuator tip is repeatedly divided by the speed, and the actuator tip is moved at a constant velocity in both phase A and phase B. Alternatively, the tip of the actuator may be moved at a constant speed in both the A phase and the B phase in a time obtained by dividing a displacement amount smaller than the maximum displacement amount by the speed.

Next, a second embodiment of the present invention will be described with reference to FIGS. 8 to 19 in which the voltage V (t) applied to the piezoelectric actuator is a sine wave AC voltage.
See FIG.
FIG. 8 is an explanatory diagram of the drive voltage waveform and the position, speed, and acceleration of the tip of the actuator at that time in Example 2 of the present invention, and the waveform corresponding to a half cycle of the sinusoidal AC voltage V (t) and its piezoelectric The position x of the actuator tip, speed dx / dt, and acceleration d ² x / dt ² are shown.
Where V is the maximum voltage amplitude, ω is the angular frequency, A is any maximum amplitude (constant) for displacement,
V (t) = Vsin (ωt−π / 2)
Since x∝V (t),
x = Asin (ωt−π / 2)
dx / dt = Aω cos (ωt−π / 2)
d ² x / dt ² = −Aω ² sin (ωt−π / 2)
It becomes.

Therefore,
d ² x / dt ² = −Aω ² sin (ωt−π / 2)
Therefore, in order not to cause any slip from equation (5),
uN ≧ mAω ² (24)
It is necessary to satisfy the conditions.

Therefore, if the drive frequency of the applied voltage V (t) is f (= ω / 2π), the condition for preventing slipping is:
f ≦ (1 / 2π) (uN / mA) ^1/2 (25)
It becomes.

  Therefore, when the drive voltage V (t) is a sinusoidal AC voltage, the stage 11 can be driven in a state where the friction chip 25 and the sliding member 14 do not slide within a range satisfying the condition of the expression (25). .

In this case, when the laminated piezoelectric actuator 21 in which the number of laminated layers is 8 and the piezoelectric constant of the shear deformation element 24 is d _{15 as} the actuator and alumina ceramics is used as the sliding member 14, the maximum voltage amplitude is V. In typical use conditions, for example, u = 0.3, N = 40N, m = 1.2 kg, A = 8 × d ₁₅ × V, d ₁₅ = 580 × 10 ⁻¹² m / V, V = 90V Is assumed.

In this case, by substituting each numerical value into equation (25),
f ≦ 0.77kHz
If so, no slip will occur.
Similarly, when the maximum voltage amplitude V is calculated with V = 45V and 135V, f ≦ 1.10 (at 45V), respectively.
f ≦ 0.63 (at 135V)
Thus, as can be seen from the equation (25), there is a trade-off relationship between the frequency at which no slip occurs and the maximum voltage amplitude V for increasing the displacement.

See FIG.
FIG. 9 is a conceptual system configuration diagram of an experiment set up under the above conditions. The sine wave voltage signal generated by the waveform generator 31 is amplified by the amplifier 32 and applied to the stacked piezoelectric actuators 21 and 22. The frequency f is measured with the oscilloscope 33.
On the other hand, the feed amount of the stage 11 is measured by the laser interferometer 34 using the mirror 15 mounted on the stage 11.

See FIG.
FIG. 10 shows the frequency dependency of the feed amount confirmed experimentally. In the experiment, a sine wave is applied to the stage 11 in a stopped state for one cycle of each drive frequency, and laser interference is performed. Subsequent stage feed amounts were measured by a total of 34.
Note that “Theoretical” in the figure represents the position of the maximum frequency that satisfies Equation (25) for each applied voltage.

From the experimental results, under the condition of V = 90 V (in the figure, the voltage value is doubled at peak-to-peak V _pp ), the stage feed amount is kept constant until the drive frequency is near 0.77 kHz. However, if the frequency exceeds 0.77 kHz, it can be confirmed that the stage feed amount is significantly reduced.
This agrees with the above calculation result, that is, in the case of the above condition, when the driving frequency f exceeds 0.77 kHz, the maximum static frictional force cannot be maintained and slipping occurs. .

However, the theoretical value of the feed amount when the drive frequency f is 0.77 kHz or less is 1.67 μm (= 4 A), whereas the experimental value is 0.97 μm, and the actually moving feed amount is It is 58% of the theoretical value.
This is because the applied voltage with respect to the expansion / contraction direction of the actuator is a sine wave function, and the pressing pressure is not constant throughout the period as in the case of the square wave of the first embodiment. This is presumably because a state in which the tip is not completely in contact with the stage occurs.

From the above experimental results, when driving while suppressing the slip of the stage 11, it is sufficient to drive with a sine wave function having a frequency equal to or lower than the frequency determined by the equation (25).
However, this is a conclusion limited to the case where the initial speed of the stage 11 is zero. When the stage 11 that has been driven to obtain the speed is further accelerated, the stage 11 is driven at a frequency exceeding the value of the equation (25). It is also possible to suppress the amount of slip.
As a result, higher-speed stage movement can be realized.

Here, as a second embodiment, a driving method in which the driving speed is controlled by changing the frequency of the sine wave function for each cycle in order to accelerate to a desired target speed will be described.
In order to derive the change pattern of the driving frequency, the following definition close to the actual driving state was used.
n a positive integer, the period of the n th cycle as T _n, the time t _n, the average velocity velocity ^AV v _n, and, when the acceleration a _n, as t ₀ = 0,
t _n = ΣT _i (i = 1 → n)
^AV v _n = (1 / T _n ) Int [(dx / dt) dt: t = t _n−1 → t _n ]
= (2 / T _n ) Int [A _m ω _n cos (ω _n t−π / 2) dt: t = 0 → T _n / 2]
= 2A _m ω _n / π = 4 A _m f _n (26)
^{_{a n = (AV v n -}} AV v n-1) / (T n / 2) ··· (27)
And
However, here, for convenience of description, an expression for integrating the function F (x) from a to b with respect to x is expressed as Int [F (x) dx: x = a → b], and v The average value is expressed as ^AV v _n .

See FIG.
FIG. 11 shows a comparison of the speed and acceleration of the stage before and after introducing the above definition, and the graph on the left side of FIG. 11 shows the stage speed (dx / dt) and acceleration (d ² x / dt ² ).
Further, the graph on the right side shows the stage speed (dx / dt) and acceleration (d ² x / dt ² ) when the definition close to the actual driving state in Example 2 of the present invention is used.

Therefore, based on equation (5):
_{^{uN ≧ m (AV v n -}} AV v n-1) / (T n / 2) ··· (28)
Can be made.

Here, from equation (26)
uN ≧ m [4A _m (f _n −f _n−1 ) / (T _n / 2)]
= M _{[4A m (f n -f n-} 1) / (1 / 2f n) ] _{= 8A m mf n (f n} -f n-1)
And organizing the formula,
f _n ² −f _n f _n−1 −uN / 8A _m m ≦ 0 (29)
The following quadratic inequality is obtained.

Therefore, by solving the quadratic inequality (29) for f _n ,
f _n ≦ [f _n−1 + (f _n−1 ² +4 uN / 8A _m m) ^1/2 ] / 2 (30)
It becomes. However, when n = 1, the initial speed v ₀ is v ₀ = 0, so f ₀ = 0.
f ₁ ≦ [f ₀ + (f ₀ ² +4 uN / 8A _m m) ^1/2 ] / 2 = (4 uN / 8A _m m) ^1/2 / 2 = (uN / 8A _m m) ^1/2
It becomes.

Therefore, the general formula (30) is obtained when n ≧ 2.
f _n ≦ [f _n-1 + (f _n-1 ² + 4f ₁ ² ) ^1/2 ] / 2 (31)
Can be replaced.

See FIG.
FIG. 12 shows driving under the conditions of u = 0.3, N = 40N, m = 1.2 kg, A = 8 × d ₁₅ × V, d ₁₅ = 580 × 10 ⁻¹² m / V, and V = 90V. The frequency change pattern and the tip speed of the actuator at that time are shown.

See FIG. 13 and FIG.
13 shows a drive voltage waveform of displacement in the feed direction (x direction) in FIG. 12, and FIG. 14 shows a drive voltage waveform of displacement in the direction (y direction) perpendicular to the feed direction, both of which are for the A-phase actuator. Is.
Although illustration is omitted, the positive / negative reversal patterns of FIGS. 13 and 14 may be used to drive the B-phase actuator.

Here, in order to make a comparison with the variable frequency drive of the second embodiment of the present invention, the drive frequency is fixed to f, and the voltage amplitude change pattern is obtained for the drive method in which the stage speed is controlled by the drive voltage amplitude.
From the above equations (26), (28), and A _n = 8 × d ₁₅ × V _n , the voltage amplitude V _n at which no slip occurs with respect to the fixed frequency f is
uN ≧ m [4f (A _n −A _n−1 ) / (T / 2)]
= M [4f × 8 × d ₁₅ (V _n −V _n−1 ) / (1 / 2f)]
= 64 md ₁₅ f ² (V _n −V _n−1 )
And
V _n −V _n−1 ≦ uN / 64 md ₁₅ f ² (32)
Is obtained.

Here, when V _{n−1 in the} equation (32) is shifted and sequentially replaced with a lower voltage amplitude, V _n ≦ uN / 64 md ₁₅ f ² + V _n−1
≦ uN / 64 md ₁₅ f ² + uN / 64 md ₁₅ f ² + V _n−2
≦ n (uN / 64md ₁₅ f ² ) + V ₀
Since the initial speed v ₀ is v ₀ = 0,
V _n ≦ n (uN / 64 md ₁₅ f ² ) (33)
It becomes.

See FIG.
FIG. 15 shows that slip occurs when u = 0.3, N = 40N, m = 1.2 kg, A = 8 × d ₁₅ × V, d ₁₅ = 580 × 10 ⁻¹² m / V, and f = 20 kHz. The change pattern of the driving voltage under the non-operating condition and the tip speed of the actuator at that time are shown.

See FIGS. 16 and 17
16 is a drive voltage waveform of displacement in the feed direction (x direction) of the A phase actuator in FIG. 15, and FIG. 17 is a drive voltage waveform of displacement in the direction (y direction) orthogonal to the feed direction of the A phase actuator. is there.
In this case as well, although not shown, the positive and negative inversion patterns of FIGS. 16 and 17 may be used to drive the B-phase actuator.

See FIG.
FIG. 18 shows the relationship between the time and the stage position when each change pattern is derived by setting the target speed to 20 mm / s and the stage is driven by each driving method.
Assuming that the voltage application time in the fixed voltage-frequency fluctuation driving method of the second embodiment and the fixed frequency-voltage fluctuation driving method for comparison are both 4.7 m, in the case of the two-phase driving of the A phase and the B phase, the second embodiment In this driving method, the stage was sent 60 times, and in the driving method for comparison, the stage was sent 188 times.

  As is clear from FIG. 18, the final value of the driving method of Example 2 is 27.4 μm, while the final value of the driving method for comparison is 15.6 μm, and the driving method of Example 2 is about It was found that the stage was moved 1.8 times, and the high driving force transmission efficiency of the driving system of Example 2 of the present invention could be verified.

See FIG.
FIG. 19 shows the relationship between time and stage speed in FIG. 18. As a result of calculating the average acceleration for 2 ms from the time of startup based on the graph, in the case of the driving system of Example 2 of the present invention, FIG. 2.6 m / s ² , while in the case of the driving method for comparison, 0.89 m / s ² , the driving method of Example 2 of the present invention has an acceleration approximately three times that of the driving method for comparison. I was able to get it.

As mentioned above, although each Example of this invention was described, this invention is not restricted to the structure and conditions described in each Example, A various change is possible.
For example, the stage mechanism is premised on a stage mechanism for transporting wafers and samples used in exposure apparatuses, electron beam drawing apparatuses, length measuring electron microscopes, laser confocal microscopes, etc. The present invention is also applicable to various transport mechanisms that require other super-precision positioning, such as a probe terminal holding mechanism for a manipulator to be used and a cantilever holding mechanism in an atomic force microscope.

  Further, in the above-described embodiment, the explanation is made by using the laminated piezoelectric actuator capable of controlling the displacement of the tip independently in the XY directions, but the technical idea of the present invention depends on the specific structure of the actuator. Since it is self-evident that it is not a thing, functions such as a cylindrical piezoelectric actuator that can independently control the displacement of the tip in three directions of XYZ individually control the displacement of the tip by an electrical signal for each axis of spatial coordinates Needless to say, the present invention is also applicable to actuators of various structures having the above.

  Although not specifically described in the above embodiment, the holding member for holding the actuator includes a preload mechanism using a leaf spring or a coil spring and is designed so that the resonance frequency is higher. It is desirable that

In addition, the preload mechanism is equipped with a vertical drag measurement sensor such as a force gauge that measures the pressing force when the actuator tip is pressed against the pressed member, so that the preload is always measured in real time. desirable.
This makes it possible to more stably implement the driving method of the present invention even when the preload changes with time due to wear around the tip of the actuator or wear of the preload mechanism.

  The actuator is driven by a predetermined electrical signal from the control circuit as described above, but in the case of a stacked piezoelectric actuator, the voltage value is approximately linear with respect to the two directions of expansion / contraction direction displacement and shear direction displacement. The value may be controlled independently.

  Further, in the above embodiment, since the laminated piezoelectric actuator is used, the control circuit generates a voltage signal as an electric signal for controlling the movement of the stage, but has another similar function. When independent control of the tip displacement amount is performed by the current value in the actuator, the driving method of the present invention can be similarly applied by replacing the voltage value in the above description with the corresponding current value.

  In the description of the above embodiment, the preload mechanism is fixed and the stage as the pressed member is moved. However, the present invention is not limited to such a configuration, and the pressed member is fixed and preloaded. Even in a self-propelled mechanism that moves the mechanism as a stage, the driving method of the present invention can be applied in exactly the same manner as a relative operation.

  In the description of the above embodiment, the A-phase and B-phase two-phase driving methods are used. However, the present invention is not limited to the two-phase driving method, and when it is not necessary to increase the accuracy, It is possible to implement the voltage fixed-frequency variation (voltage fixed-voltage application time variation) driving method according to the present invention using a single laminated piezoelectric actuator.

Conversely, multi-phase driving such as three phases with different 120 degree phases and four phases with different 90 degree phases may be performed. In this case, the number of actuators is three, four, etc., respectively. Use only numbers.
However, considering the simplification of the drive circuit, it is desirable to reduce the number of phases as much as possible.

  Furthermore, when driving a heavy stage, it may be driven by using a plurality of actuators for each of the A phase and the B phase. In this case, as compared with the case of using one actuator for each phase, Since a larger vertical drag can be applied between the actuator tip and the stage in total, the maximum thrust, that is, the maximum static friction force applied to the stage can be set larger.

  In the description of the above-described embodiment, the displacement amount in the y direction of the tip portion of the actuator is a numerical value sufficiently exceeding the maximum height of the typical surface undulation in the general use condition of the sliding portion. Although it is 23 μm, it may be set to a smaller value if the shape of the surface undulation is smoother. Conversely, when the shape of the surface undulation is rough, it is necessary to set a larger value.

  When the stage mechanism is stopped, for example, both the A phase and the B phase may be stopped in a state where the tip of the actuator is pressed with the maximum static frictional force, or a separate position detection device is added to the stage and the detected value is set. The difference between the command value is calculated based on the command value, and the closed loop servo control is performed so that the difference becomes small, and the actuator tip is finely moved in both the A phase and B phase within the range not exceeding the maximum static frictional force. It may be repeated.

  Further, the above description does not consider the resonance problem of the mechanical structure such as the preload mechanism or the actuator itself. However, when a certain resonance frequency exists, the resonance frequency is higher than the resonance frequency in the frequency spectrum of the electric signal for exciting the actuator. In order to remove the noise, an electric signal may be supplied after performing signal correction by a low-pass filter.

  In the second embodiment, the calculation is performed based on the definition as described above. The maximum acceleration is obtained from the graph on the left side in FIG. 11, and the frequency is set so as to satisfy the condition of the expression (5) accordingly. Needless to say, it can be decided.

  In the first and second embodiments, the driving voltage waveform of the displacement in the feed direction is generated with a constant voltage amplitude with respect to time as shown in FIGS. 4, 5, and 13. As long as the condition of equation 5) is satisfied, the voltage amplitude may be appropriately changed with respect to time as necessary.

  For example, after accelerating and decelerating the stage, there are cases where the influence of minute vibrations in the installation environment must be corrected by active feedback control, but in that case, the voltage amplitude can be changed to a smaller value. This is suitable for realizing minute precision positioning.

  As a practical example of the present invention, a stage mechanism for transporting a wafer or a sample used in an exposure apparatus, an electron beam drawing apparatus, a length measuring electron microscope, a laser confocal microscope, etc. is typical. The present invention is also applicable to various transport mechanisms that require other ultra-precise positioning, such as a probe terminal holding mechanism for manipulators used for electronic measurements, and a cantilever holding mechanism in an atomic force microscope.

It is a principle block diagram of this invention. 1 is a schematic configuration diagram of a main part of a non-resonant ultrasonic motor driving stage to which a driving system according to a first embodiment of the present invention is applied. It is explanatory drawing of the relationship between each coordinate system and the position vector of a component. It is a time chart of the position, speed, and acceleration of the tip of the A-phase actuator in the feed direction. It is a time chart of the position, speed, and acceleration of the B-phase actuator tip in the feed direction. It is a time chart of the actuator front-end | tip position in the direction orthogonal to a feed direction. It is a time chart of the position of a stage, speed, and acceleration. It is explanatory drawing of the position of the drive voltage waveform in Example 2 of this invention, the position of the front-end | tip of an actuator, speed, and acceleration at that time. It is a conceptual system block diagram of the set up experiment. It is explanatory drawing of the frequency dependence of the feed amount confirmed experimentally. It is comparison explanatory drawing of the speed and acceleration of a stage before and after introducing a definition. It is explanatory drawing of the change pattern of the drive frequency in a predetermined condition, and the tip speed of the actuator at that time. It is explanatory drawing of the drive voltage waveform of the feed direction displacement in the drive system of Example 2 of this invention. It is explanatory drawing of the drive voltage waveform of a feed direction and orthogonal displacement in the drive system of Example 2 of this invention. It is explanatory drawing of the change pattern of the drive voltage on the conditions which a slip does not generate | occur | produce, and the tip speed of the actuator at that time. It is explanatory drawing of the drive voltage waveform of the feed direction displacement in the drive system of a comparative example. It is explanatory drawing of the drive voltage waveform of the displacement orthogonal to the feed direction in the drive system of a comparative example. It is explanatory drawing of the relationship between time when a stage is driven with each drive system, and a stage position. It is explanatory drawing of the relationship between time and speed in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressed member 2 Actuator 3 Tip 4 Holding member 5 Control circuit 11 Stage 12 Cross roller guide 13 Preload mechanism 14 Sliding member 15 Mirror 21 Laminated piezoelectric actuator 22 Laminated piezoelectric actuator 23 Expansion / contraction deformation element 24 Shear deformation element 25 Friction chip 31 Waveform generator 32 Amplifier 33 Oscilloscope 34 Laser interferometer

Claims (6)

A member to be pressed, an actuator having a function of individually controlling the amount of displacement of the tip with respect to each axis of spatial coordinates by an electric signal, and a function of holding the actuator and pressing the tip against the member to be pressed. In the drive system of a feed mechanism configured to include a holding member provided and a control circuit that supplies the electrical signal to the actuator, and fixes one of the pressed member and the holding member and moves the other, the actuator The thrust that acts on the moving member during the time required to change the displacement amount of the tip of the tip in the positive direction or the negative direction relative to the feed direction is the maximum static friction between the pressed member and the tip of the actuator. Thus a predetermined rule including a condition that does not exceed the force, the driving method of feeding mechanism, characterized in that a variable in one stroke. 2. The driving mechanism according to claim 1, wherein the displacement amount of the tip of the actuator is changed at a constant acceleration with respect to time during at least a part of the time for changing to the positive direction or the negative direction. method. 2. The feed mechanism according to claim 1, wherein the displacement amount of the tip of the actuator is changed with a sinusoidal function with respect to time during at least a part of the time for changing in the positive direction or the negative direction. Drive system. The maximum value of the displacement amount in the direction orthogonal to the feed direction of the tip of the actuator in each period of time to change in the positive direction or the negative direction is the respective values of the pressed member and the tip of the actuator in the pressing portion. drive system of the feed mechanism according to any one of claims 1 to 3, wherein the at least the maximum height of the surface relief. Adding normal force measuring sensor in the holding member, to any one of claims 2 to 4, characterized in that to change the set value of the maximum static friction force using the measured value of the normal force measuring sensor The drive mechanism of the described feed mechanism. Frequency spectrum of the time variation function of the displacement amount of the tip of the actuator which is individually controlled by the electrical signal, according to claim 1 to 5, characterized in that it is configured to components below the resonant frequency of the actuator mainly The driving mechanism of the feed mechanism according to any one of the above items.

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