JP2000162219A - Tubular actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously obtain both the characteristics of a large dynamic range and good response in a tubular actuator. SOLUTION: A cylindrical piezoelectric element 1 and the respective shaft drive electrodes 11-17, attached to the cylindrical pizoelectric element 1, are provided and at least one shaft drive electrode 12 from among the shaft drive electrodes is divided into a plurality of electrodes 13, 14 and the displacement characteristics of the piezoelectric element by the divided electrodes 13, 14 are differentiated. The displacement characteristics of the piezoelectric element by the split electrodes differentiate displacement quantity and response, and with this constitution, different displacement characteristics are obtained simultaneously with a single actuator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a tube type actuator used for a scanning probe microscope (SPM) and the like.

[0002]

2. Description of the Related Art As a scanning probe microscope (SPM) for two-dimensionally analyzing a fine surface shape, a scanning tunnel microscope (STM) using a tunnel current flowing between a probe and a sample surface, and a scanning probe microscope (STM). 2. Description of the Related Art An atomic force microscope (AFM) for measuring an atomic force acting on a sample surface is known.

In a scanning tunneling microscope (STM), a probe is brought close to the surface of a sample, the probe or the sample can be moved in a three-dimensional direction, and a tunnel current flowing between the probe and the surface of the sample becomes constant. The three-dimensional shape is measured at atomic level resolution by controlling the surface shape, and the surface shape and atomic arrangement of the material surface are observed. An atomic force microscope (AFM) includes a probe, a cantilever that supports the probe, and a displacement measurement system that includes a detecting unit that detects bending of the cantilever, and an atomic force (AFM) between the probe and the sample. (Attraction or repulsion) is detected, and the surface shape of the material surface is observed by controlling the interatomic force to be constant. Thus, it is possible to observe living things, organic molecules, insulators, and the like.

A scanning probe microscope is provided with a scanning means for relatively moving a sample and a probe three-dimensionally in xyz directions in order to scan an observation position. As a scanning unit, a tube-type actuator provided with an integral cylindrical piezoelectric element is known. In the tube-type actuator, three-dimensional fine movement can be performed by bending displacement of the cylindrical piezoelectric element in the xy directions and axial displacement in the z direction.

FIG. 6 is a schematic configuration diagram for explaining the configuration of a conventional tube type actuator. In FIG. 6, a tube-type actuator 100 has a cylindrical piezoelectric element 11, and x-axis electrodes 15, 16 arranged opposite to each other.
And driving in the x and y directions by the y-axis electrode 17 and
Driving in the z direction is performed by the z-axis electrode 40. Note that y
The y-axis electrode facing the axis electrode 17 is not shown.

[0006] The control of the tube type actuator 100 in the z-axis direction is performed by detecting the displacement in the z-axis direction by the displacement measuring unit 2.
The drive current based on the detected amount is supplied from the drive amplifier 32 by the control unit 3 through the impedance element 41 to the z-axis electrode 4.
It can be performed by supplying 0.

[0007]

In order to accurately observe the surface shape of a sample with a scanning probe microscope, a large dynamic range and good responsiveness are required in the axial drive of a tube type actuator.

Since the amount of displacement of the piezoelectric element is proportional to the length of the displaced portion and the applied voltage, in order to increase the dynamic range in the z-axis direction, the length of the z-axis electrode provided on the piezoelectric element must be increased. It is necessary to design or increase the applied voltage. However, when the dynamic range of the piezoelectric element is designed to be large, the electric capacity and the stroke become large, so that the hysteresis becomes large, and the time constant becomes large and the response speed becomes slow.

FIGS. 7 and 8 are diagrams showing displacement characteristics and response characteristics of the piezoelectric element, and show a piezoelectric element A having a short axial electrode length and a piezoelectric element B having a long electrode length. When the magnitudes of the control voltages are the same, the displacement dB of the piezoelectric element B becomes larger than the displacement da of the piezoelectric element A, and the hysteresis also becomes larger. The time constant τB of the piezoelectric element B is larger than the displacement τA of the piezoelectric element A.

For this reason, in a scanning probe microscope, if the axial length of the z-axis electrode of the circular piezoelectric element provided in the tube-type actuator is designed to be long, a large dynamic range can be obtained, but small changes can be satisfactorily performed. There is a problem that it cannot be detected.

FIGS. 9A and 9B are graphs showing detection characteristics of a tube type actuator having a long z-axis electrode in the axial direction. FIG. 9A shows a sample shape, and FIGS. 9B and 9C show an actuator and a sample. Indicates the deviation from the shape and the cumulative deviation,
(D) shows a control signal to the actuator, and (e) shows the displacement of the piezoelectric element. A shows a case where the change is large, and B and C show a case where the change is small.
In the case of A having a large change, it can be dealt with by a large dynamic range. However, in the case of B having a small change, the response delay becomes large due to a large time constant, making it difficult to detect a small change. In the case of C in which small changes are continuous, oscillation occurs in the feedback control loop due to a response delay due to a large time constant, and it is difficult to clearly measure an image.

FIG. 10 is a graph showing detection characteristics of a tube type actuator having a z-axis electrode having a short axial length. (A) to (e) show the sample shape, deviation, cumulative deviation, control signal, and displacement of the piezoelectric element as in FIG. If a large change in the sample shape is detected by an actuator having a short z-axis electrode length in the axial direction, a problem arises in that the displacement of the piezoelectric element is limited or a long time is required for restoration because the dynamic range is small.

Therefore, the conventional tube-type actuator cannot simultaneously obtain both a large dynamic range and good responsiveness characteristics, and sacrifices either a large change or a minute change in the surface shape to the sample. Alternatively, it is necessary to replace the tube type actuator in which the axial length of the z-axis electrode is different.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to solve the above-mentioned conventional problems and to provide a tube type actuator capable of simultaneously obtaining both a large dynamic range and good responsiveness.

[0015]

A tube type actuator according to the present invention includes a cylindrical piezoelectric element and electrodes for driving each axis attached to the cylindrical piezoelectric element, and at least one of the electrodes for driving each axis is provided. The driving electrode of the shaft is divided into a plurality of parts, and the divided electrodes have different displacement characteristics of the piezoelectric element. The displacement characteristics of the piezoelectric element due to each of the divided electrodes differ in displacement amount and response, and this
Different displacement characteristics can be obtained simultaneously with one actuator.

The displacement characteristics can be a dynamic range and a response. The displacement characteristics include an electrode structure such as an electrode shape such as an electrode size and an axial length, an electrode structure such as an installation position on a cylindrical piezoelectric element, and the like. It can be set according to the electrical characteristics of the electrodes. The dynamic range can be set by the electrode structure such as the length in the axial direction. The responsiveness can be set by the electric characteristics of the electrodes, and can be set by changing the time constant determined by the electric capacity of the electrodes, the impedance element connected to the electrodes, and the like.

In the tube type actuator, the divided electrodes having different displacement characteristics can be electrodes in any axial direction. According to predetermined displacement characteristics, the x-axis electrode and the y-axis electrode of the cylindrical piezoelectric element can be used. One of the electrodes for the axis electrode and the z-axis electrode, or any combination thereof.

The electrode may be divided by a structure in which the divided electrodes are individually provided on the piezoelectric element, or a structure in which the divided electrodes are provided on the piezoelectric element.
A plurality of drive voltages can be applied to one electrode, and by applying a drive voltage to each divided electrode, different displacement characteristics corresponding to each electrode can be obtained with one tube-type actuator. it can.

The drive voltage may be inputted to each of the divided electrodes simultaneously, or may be inputted individually by switching. According to the tube-type actuator of the present invention, the drive electrode attached to the piezoelectric element is divided, and a combination of an electrode with a large dynamic range and a slow response and an electrode with a small dynamic range and a fast response, etc. Different types of displacement characteristics such as dynamic range and response can be provided, and a large dynamic range and fast response can be provided simultaneously.

When the tube-type actuator of the present invention is applied to a scanning microscope, a small displacement is detected by an electrode having a fast response, so that an oscillation phenomenon caused by a delay during feedback control can be prevented. By detecting large displacements with a large dynamic range electrode, the limitation of the measured displacement is eliminated,
Measurement errors due to a long restoration time can be prevented.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a tube type actuator of the present invention. In FIG. 1, a tube-type actuator 1 has a cylindrical piezoelectric element 11, and is disposed opposite to the piezoelectric element 11 so that x-axis electrodes 15, 16 and y-axis electrode 17 (y-axis electrode 17). The y-axis electrode (not shown) opposed to 17 is arranged for driving in the x and y directions, and the z-axis electrode 12 is arranged for driving in the z direction. Hereinafter, a configuration example in which the divided driving electrode of the present invention is applied to the z-axis electrode 12 will be described.

The z-axis electrode 12 includes a first z-axis electrode 13 having a different electrode width in the axial direction of the cylindrical piezoelectric element 11 and a second z-axis electrode 13.
and a z-axis electrode 14. In FIG. 1, the electrode width in the axial direction of the first z-axis electrode 13 is formed smaller than the electrode width in the axial direction of the second z-axis electrode 14z. First z-axis electrode 13 and second z
Each of the shaft electrodes 14 has a first impedance element 1
A drive current is supplied through the second impedance element 8 and the second impedance element 19.

In the control of the tube type actuator 100 in the z-axis direction, the displacement measuring unit 2 detects the displacement in the z-axis direction,
This is performed by forming a drive current based on the detected amount by the control unit 3 and driving the z-axis electrode 12 through the impedance element. The displacement measuring unit 2 is an example of an atomic force microscope (AFM), and includes a probe 21, a cantilever 22 supporting the probe 21, and a displacement measuring device 23. The displacement measuring device 23 detects the bending of the cantilever 22 that is displaced according to the surface shape of the sample by using optical means or the like,
The formed displacement is sent to the control unit 3. The control unit 3 calculates and integrates a deviation between the displacement amount and the set value, and forms a control signal in the arithmetic unit 31 such that the deviation becomes zero. The drive amplifier 32 applies a drive current to the z-axis electrode 12 based on the control signal. The z-axis electrode 12 is displaced according to the shape of the sample surface by a feedback system formed by the displacement measurement unit 2, the control unit 3, and the z-axis electrode 12.

The first z-axis electrode 13 and the second z-axis electrode 1
No. 4 can change the displacement stroke by changing the electrode width in the axial direction. For example, the stroke of the first z-axis electrode 13 having a narrow axial electrode width is small, and the stroke of the second z-axis electrode 14 having a wide axial electrode width is large.

The first z-axis electrode 13 and the second z-axis electrode 14 can have different electric capacities by making the axial electrode widths different from each other. For example, if the capacitance of the first z-axis electrode 13 is C1 and the capacitance of the second z-axis electrode 14 is C2, the capacitance C1 is smaller than the capacitance C2.

FIG. 2 is an equivalent circuit example of the first z-axis electrode 13 and the second z-axis electrode 14. According to the equivalent circuit of FIG. 2, when the first z-axis electrode 13 has an impedance value R1 of the first impedance element 18 to be connected, the time constant τ1 can be determined by C1 × R1.
The shaft electrode 14 is connected to the second impedance element 19 to be connected.
, The time constant τ2 is C2
It can be determined by 2 × R2. After the first z-axis electrode 13 and the second z-axis electrode 14 are installed, the time constants τ1 and τ2 are changed by changing the impedance value R1 of the first impedance element 18 and the impedance value R2 of the second impedance element 19. Can be changed.

Therefore, by changing the electrode width in the axial direction, it is possible to obtain a displacement characteristic of a short time constant τ1 with a small stroke by the first z-axis electrode 13,
Further, the displacement characteristic of the long time constant τ2 with a large stroke can be obtained by the second z-axis electrode 14. In addition,
The time constant of the response of the actuator itself is determined by the time constant based on the electrical characteristics of the piezoelectric element and the time constant based on the physical characteristics of the piezoelectric element and the characteristics of the feedback system.

In the above example, the z-axis electrode has been described. However, the 1x-axis electrodes 15 and 16 and the y-axis electrode 17 are also divided in the same manner as the z-axis electrode, and the electrode width and connection are made. The displacement stroke and time constant can be determined by the impedance value of the impedance element. FIG.
10A and 10B are diagrams showing detection characteristics of a tube type actuator having a divided z-axis electrode according to the present invention, wherein FIG. 9A and FIG. 9A show sample shapes, and FIGS. Indicates the deviation from the sample shape and the cumulative deviation,
(D) shows a control signal to the actuator, and (e) shows the displacement of the piezoelectric element.

By using the divided electrode of the present invention as the electrode provided on the piezoelectric element of the tube type actuator, even if a large displacement portion and a minute displacement portion as shown in the sample shape of FIG. In addition, it is possible to cope with each shape characteristic by an electrode portion having different displacement characteristics. For example, the first z-axis electrode 13 having a displacement characteristic of a short time constant τ1 with a small stroke can detect a minute displacement with a fast response, and has a displacement characteristic of a long time constant τ2 with a large stroke. 2nd z
The shaft electrode 14 can detect a large displacement with a large dynamic range.

Next, another configuration example of the electrode division will be described with reference to FIGS. The configuration example of FIG. 4 is an example in which a drive current is switched and supplied to the first z-axis electrode 13 and the second z-axis electrode 14. The switching of the drive current can be performed by a configuration in which a switching device 33 is provided between the first impedance element 18 and the second impedance element 19 and the drive amplifier 32. Switching device 33
Indicates that the drive current from the drive amplifier 32 is supplied to the first z-axis electrode 1
The z-axis electrode 14 can be switched and supplied to the third or second z-axis electrode 14 to drive only one z-axis electrode, and can be selected according to the shape characteristics of the surface of the sample to be measured.

In the configuration example shown in FIG. 5, the z-axis electrode 12 is composed of one electrode, the first impedance element 18 is connected to one end of the electrode, and the second impedance element 18 is connected to the other end. 19, and a ground terminal is connected between both ends of the electrode in the axial direction. Depending on the ground position of the ground terminal
The z-axis electrode 12 can be divided in the axial direction. FIG.
According to the configuration described above, the axial lengths of the first z-axis electrode 13 and the second z-axis electrode 14 can be changed depending on the connection position of the ground terminal on the z-axis electrode 12.

[0032]

As described above, according to the present invention,
It is possible to simultaneously obtain both a large dynamic range and good responsiveness.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a tube-type actuator of the present invention.

FIG. 2 is an equivalent circuit example of a first z-axis electrode and a second z-axis electrode.

FIG. 3 is a diagram illustrating detection characteristics of a tube-type actuator including a divided z-axis electrode according to the present invention.

FIG. 4 is another configuration example of the electrode division of the tube-type actuator of the present invention.

FIG. 5 is another configuration example of the electrode division of the tube-type actuator of the present invention.

FIG. 6 is a schematic configuration diagram for explaining a configuration of a conventional tube-type actuator.

FIG. 7 is a diagram showing displacement characteristics of a piezoelectric element.

FIG. 8 is a diagram showing response characteristics of a piezoelectric element.

FIG. 9 is a diagram showing detection characteristics of a tube type actuator including a z-axis electrode having a long axial length.

FIG. 10 is a diagram illustrating detection characteristics of a tube-type actuator including a z-axis electrode having a short axial length.

[Explanation of symbols]

1,100: tube-type actuator, 2: displacement measuring unit, 3: control unit, 11: cylindrical piezoelectric element, 12, 40 ...
z-axis electrode, 13 ... first z-axis electrode, 14 ... second z-axis electrode, 15, 16 ... x-axis electrode, 17 ... y-axis electrode, 1
8 First impedance element, 19 Second impedance element, 21 Probe, 22 Cantilever, 23 Displacement measuring device, 31 Computing device, 32 Drive amplifier, 33
Switching device.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F063 AA43 BC05 BD11 CA10 CA12 DA01 DA04 DB05 DC08 DD02 EA16 EC00 FA07 GA57 LA11 MA03 2F069 AA60 CC06 DD19 DD20 GG01 GG04 GG62 HH05 HH09 JJ00 LL03 MM32

Claims (1)

[Claims] 1. A cylindrical piezoelectric element, and electrodes for driving each axis attached to the cylindrical piezoelectric element. At least one of the electrodes for driving each axis is divided into a plurality of electrodes. And a tube-type actuator that makes the displacement characteristics of the piezoelectric element differ depending on each divided electrode.