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Title:
A METHOD FOR NANOPOSITIONING OBJECT AND DEVICE THEREOF
Document Type and Number:
WIPO Patent Application WO/2008/015700
Kind Code:
A3
Abstract:
A couple of actuators are attached with each other. One of the actuators has shear displacement where as the next one has linear displacement. The shearing actuator (3) is placed in such a way that the moving stage (2) is in contact with the actuator. The linear actuator (4) is placed below the shearing actuator (3). This set up is mounted over the stationary region of the monolithic stage. The stiffness of the holder (1 ) is less than the stiffness of the solid state actuators (3, 4). This combination works well when the continuous pulse is sent to the actuator to its frequency.

Inventors:
ALAM HILAAL (IN)
Application Number:
PCT/IN2007/000230
Publication Date:
September 24, 2009
Filing Date:
June 08, 2007
Export Citation:
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Assignee:
ALAM HILAAL (IN)
International Classes:
B25J7/00; G05D3/10; G12B1/00; H01J37/20; H01L41/09
Domestic Patent References:
WO2005108004A12005-11-17
Foreign References:
US20050269915A12005-12-08
US5237238A1993-08-17
EP0457317A11991-11-21
Attorney, Agent or Firm:
BHOLA, Ravi (# 134 First Floor,60 Ft Domlur Road,Doopanahalli, Indiranaga, Bangalore 0 Karnataka, IN)
Download PDF:
Claims:

I claim:

1. A method for nanopositioning of objects wherein said method comprises steps of: a) placing the object onto a moving stage(2), b) lifting shear actuator(3) vertically by expanding linear actuator(4) placed below the shear actuator(3) to bring it in contact with the moving stage(2), c) moving the stage horizontally in a single axis forward direction by expanding the shear actuator(3), d) making the shear actuator(3) to lose contact with the moving stage(2) by contracting the linear actuator(4), e) maintaining the moving stage in single axis reverse direction due to holder(l ) stiffness and thereby nanopositioning the object.

2. The method for nanopositioning as claimed in step (b) of claim 1, wherein the shear actuator(3) attains zero expansion before it touches the moving stage(2).

3. The method for nanopositioning as claimed in claim 1 , wherein the linear actuator " s(4) contracting and expanding time is equal to that of the shear actuator's (3) time for contracting to zero expansion.

4. The method for nanopositioning as claimed in claim 1, wherein bringing the moving stage(2) to its initial position by the holder (1).

5. The method for nanopositioning as claimed in claims 1 and 4, wherein resultant displacement of the moving stage(2) is difference in displacement due to the shear actuator(3) and displacement due to the holder (1 ).

6. The method for nanopositioning) as claimed in claims 1 and 4, wherein the holder (1) stiffness is less than that of shear actuator (3).

7. The method for nanopositioning as claimed in claims 1 , wherein displacing the moving stagc(2) to long range with small range actuators.

8. A device for nanopositioning of objects comprising: a) moving stage(2) to hold the objects, b) shear actuator(3) to move the moving stage(2), c) linear actuator(4) to lift the shear actuator(3) to come in contact with the moving stage(2) and d) holder (1 ) to maintain the moving stage(2) in single axis direction.

9. The device for nanopositioning as claimed in claim 8, wherein the shear actuator (2) is stacked above the linear actuator (4).

10. The device for nanopositioning as claimed in claim 8, wherein the holder (or spring) (1 ) moves the moving stage (2) in one axis preventing sway and crosstalk motion.

1 1. The device for nanopositioning as claimed in claim 8, wherein the actuators are solid state actuator(s) preferable piezo crystals.

12. The device for nanopositioning as claimed in claim 8, wherein the holder (1) is spring.

13. The device for nanopositioning as claimed in claim 8, wherein the linear actuator ' s contracting and expanding time is equal to that of the shear actuator time for contracting to zero expansion/unactuated state.

14. The device for nanopositioning as claimed in claim 8, wherein the device is a monolithic structure.

15. A system for nanopositioning of objects comprising the device of claim 8 and a circuit to drive the actuators.

Description:

A METHOD FOR NANOPOSITIONING OF OBJECT AND

DEVICE THEREOF FIELD OF INVENTION

The field of invention is related to the nanopositioning technology with nanometer resolution. Moving an object in nanometer resolution for longer range in desired direction with just two actuators, whose expansion range, even with amplification lever is much smaller than the desired positioning range, is the crux of the invention. For example, moving the nanopositioning stage for 1000 micron just with 2 micron actuators is an example of the work.

BACKGROUND OF THE INVENTION

This invention is related to positioning objects such as lenses, fibers, tools, sensors and other objects; with respect to nanometer resolution is a challenging one. With the advent of the technology in various fields such as photonics, optics, semiconductor, microscopy etc., the requirement for precise positioning with nanometer resolution is inevitable. Nano-tribology is another upcoming field which requires nanopositioning technology very much.

Displacement of long range positioning with nanometer resolution is an expensive process even though the applications are numerous. The inchworm or the long range solid state actuators are still expensive solutions. Coupling the Nanopositioners with micropositioners is not a good idea as this will introduce coupling errors and require expensive feedback systems. Qtech Nanosystems has patented another approach called FlexCAR which acts as an engine to drive with short range actuators for long range operation. In FlexCAR approach, the displacement is not continuous. Though the step by step displacement is not bothered in many of the applications, there are some applications such as scanning requires smooth continuous precise displacement with nanometer resolution.

Prior Art

The invention made by M/S Omicron (US 5,237,238, GB 2 246 236, DE 40 23 31 1 C2,

J 2 089 171) is the closest prior art of the invention. However, their methodology introduces friction is not at all desired in Nanopositioning and the invention is based on

the inertia of the objects and stick and slip method. Though Differential Stiffness

Method also is based on inertial property of the stage and the object, the controlling parameters are the systems' stiffness and its natural frequency.

Advantages: The speed of the Nanopositioner can be controlled by adjusting the stiffness of actuator and the mechanical trajectory guide. Larger displacement is possible with just a low range solid state actuators. The disadvantages are loss of motion during the r motion of actuators.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

Figure 1: shows a nanopositioner assembly with various parts of the assembly and their direction of movement.

Figure Ia: shows moving stage(l ) at its initial stage.

Figure Ib: shows a nanopositioner assembly with Linear Actuator(4) fully expanded, Shear Actuators(3) at full expansion (sheared).

Figure Ic: shows a nanopositioner assembly with Linear Actuator (4) zero expanded,

Shear Actuator (3) at zero expansion after moving the moving stage.

Figure Id: shows a nanopositioner assembly with Linear Actuator(4) fully expanded,

Shear Actuator(3) at zero expansion and Nanopositioner at (x - y) displacement. Figure Ie: shows a nanopositioner assembly with Linear Actuator (4) fully expanded,

Shear Actuator (3) at full expansion (sheared) with 'x' " displacement.

Figure 2: shows the actual fabrication of the Nanopositioner.

OBJECT OF THE INVENTION

The primary objective of the invention is to develop a method for nanopositioning of objects.

Another objective of the invention is to place the object onto a moving stage(2) and lifting shear actuator(3) vertically by expanding linear actuator(4) placed below the shear actuator(3) to bring it in contact with the moving stage(2),

Still another objective of the invention is moving the stage horizontally in a single axis forward direction by expanding the shear actuator(3),

Still another objective of the invention is making the shear actuator(3) to lose contact with the moving stage(2) by contracting the linear actuator(4) and maintaining the moving stage in single axis reverse direction due to holder(l) stiffness and thereby nanopositioning the object. Yet another main objective of the present invention is to achieve long range displacement with small range actuators in addition with or without amplification lever in nanopositioners.

Another objective of the invention is to develop a device for nanopositioning of objects.

Yet another objective of the invention is to develop moving stage(2) to hold the objects and shear actuator(3) to move the moving stage(2).

Still another objective of the invention is to develop linear actuator(4) to lift the shear actuator(3) to come in contact with the moving stage(2).

Yet another objective of the invention is to develop holder (1) to maintain the moving stage(2) in single axis direction. Another objective of the invention is to develop a system for nanopositioning of objects comprising the device

STATEMENT OF INVENTION

The present invention is related to a method for nanopositioning of objects wherein said method comprises steps of: placing the object onto a moving stage(2), lifting shear actuator(3) vertically by expanding linear actuator(4) placed below the shear actuator(3) to bring it in contact with the moving stage(2), moving the stage horizontally in a single axis forward direction by expanding the shear actuator(3), making the shear actuator(3) to lose contact with the moving stage(2) by contracting the " linear actuator(4), maintaining the moving stage in single axis reverse direction due to holder(l ) stiffness and thereby nanopositioning the object; and a device for nanopositioning of objects comprising: moving stage(2) to hold the objects, shear actuator(3) to move the moving stage(2), linear actuator(4) to lift the shear actuator(3) to come in contact with the moving stage(2) and holder (1) to maintain the moving stage(2) in single axis direction; and a system for nanopositioning of objects comprising above device and a circuit to drive the actuators.

DETAILED DESCRIPTION OF THE INVENTION

The primary embodiment of the invention is a method for nanopositioning of objects wherein said method comprises steps of: placing the object onto a moving stage(2), lifting shear actuator(3) vertically by expanding linear actuator(4) placed below the shear actuator(3) to bring it in contact with the moving stage(2), moving the stage horizontally in a single axis forward direction by expanding the shear actuator(3), making the shear actuator(3) to lose contact with the moving stage(2) by contracting the linear actuator(4). maintaining the moving stage in single axis reverse direction due to holder(l) stiffness and thereby nanopositioning the object.

In yet another embodiment of the present invention, the shear actuator(3) attains zero expansion before it touches the moving stage(2).

In still another embodiment of the present invention, the linear actuator's(4) contracting and expanding time is equal to that of the shear actuator's (3) time for contracting to zero expansion.

In still another embodiment of the present invention, bringing the moving stage(2) to its initial position by the holder (1).

In still another embodiment of the present invention, resultant displacement of the moving stage(2) is difference in displacement due to the shear actuator(3) and displacement due to the holder (1).

In still another embodiment of the present invention, the holder (1) stiffness is less than that of shear actuator (3).

In still another embodiment of the present invention, displacing the moving stage(2) to long range with small range actuators.

Another main embodiment of the present invention a device for nanopositioning of objects comprising: moving stage(2) to hold the objects, shear actuator(3) to move the moving stage(2), linear actuator(4) to lift the shear actuator(3) to come in contact with the moving stage(2) and holder (1 ) to maintain the moving stage(2) in single axis direction.

In still another embodiment of the present invention the shear actuator (2) is stacked above the linear actuator (4). In still another embodiment of the present invention the holder (or spring) (1 ) moves the moving stage (2) in one axis preventing sway and crosstalk motion.

In still another embodiment of the present invention the actuators are solid state actuator(s) preferable piezo crystals.

In still another embodiment of the present invention the holder (1) is spring.

In still another embodiment of the present invention the linear actuator's contracting and expanding time is equal to that of the shear actuator time for contracting to zero expansion/unactuated state. In still another embodiment of the present invention the device is a monolithic structure.

Another main embodiment of the present invention is a system for nanopositioning of objects comprising above device and a circuit to drive the actuators. The present invention shall now be fully described with reference to the accompanying drawings in which, Figure 1 is a nanopositioner assembly showing the various parts of the assembly and their direction of movement.

The shear and linear actuators (3 and 4) are put together so that they work as a single system. During the forward motion, the shear actuator (3) is provided with the saw tooth triangle electronics signal pulse in such a way that, the shear actuator shears to push the moving stage (2) forward. As the linear actuator (4) is fully expanded, it always holds the shear actuator (3) against the moving stage (2) firmly. Due to the shear in the shear actuator (3), the moving stage (2) goes along with the shear actuator (3). After this first step, there is a sudden drop in voltage supplied to the actuators. Now the shear actuator (3) suddenly contracts and moves to the original location. By the time the shear actuator (3) returns to its original location, the linear actuator (4) contacts and expands to hold the shear actuator (3) against the moving stage (2) for the next action. In order to achieve the sudden contract and expansion for linear actuator (4), the linear actuator (4) is given a step pulse. In this case the speed of the linear actuator (4) should be twice that of the shear actuator (3). The reverse displacement is achieved just by controlling the linear actuator (4) against the flexure force. The stiffness of actuator is higher than the moving stage (2) results in the slow return of the moving stage (2) by which the actuator returns to its initial position and holds the moving stage (2) for the next action. The inertia caused by the mass also can keep the moving stage (2) forward while the actuator returns to its initial point (i.e. zero- actuation). Step by Step Description

Step 1 (see figure Ia): the figure shows moving stage(l ) at its initial stage wherein the holder/spring(l) is not under any stress. The object to be nanopositioned is placed on the moving stage. In the figure the Linear Actuator(4) is fully expanded, Shear Actuators(3) is at zero expansion (i.e.unactuated state) and Nanopositioner at zero displacement. The linear actuator(4) actually lifts the shear actuator(3) vertically there by making the shear actuator to contact the moving stage(2).

The holders( l ) are flexible springs which deforms on application of force, holder (1) maintain the moving stage(2) in single axis direction thereby preventing sway and crosstalk motion of the moving stage..

Step 2 (see figure Ib): Linear Actuator(4) fully expanded, Shear Actuators(3) at full expansion (sheared) with "x" displacement and Nanopositioner at "x" displacement as well.

As shear actuator shears, it takes the moving stage (2) along with it to "x" displacement (i.e. full range expansion of the solid state actuators). Doted lines show the previous state. Now the moving stage (2) has moved 'x' distance horizontally forward.

Step 3 (see figure Ie): Linear Actuator (4) zero expanded, Shear Actuator (3) at zero expansion and Nanopositioner at zero displacement (reversal displacement - y) Linear actuator (4) contracts and shear actuator is released to its original state i.e. non- expansion or unactuated state. During this action of reversal motion, the actuators are not in touch with moving stage (2). So due to spring action of the holder/ spring (1), the moving stage will also tend to go in reverse direction. The speed of reversal motion of actuators is faster than that of the moving stage (2) due to the difference in the stiffness of holder/spring (1) and actuators. Let us say, the reversal displacement of the moving stage(2) due to the stiffness of the holder (1) as "y". Now the resultant displacement of the moving stage (2) is

x = ( χ - y)

As soon as the shear actuator (3) comes to the original state, the linear actuator (4) immediately expands and holds against the moving stage (2) from preventing further reversal movement of the moving stage (2).

Step 4 (see figure Id): Linear Actuator(4) fully expanded, Shear Actuator(3) at zero expansion and Nanopositioner at (x - y) displacement

• Linear actuator (4) expands and shear actuator (3) is still at zero expansion. The moving stage (2) also is stationary. Here the linear actuator's (4) contracting and expanding time is equal to that of the shear actuator's (3) time for contracting to zero expansion.

Step 5 (see figure Ie): Linear Actuator (4) fully expanded, Shear Actuator (3) at full expansion (sheared) with "x" displacement. The Nanopositioner moves from (x - y) by "x'" distance. As shear actuator (3) shears, it takes the moving stage (2) along with it to "X s" displacement (i.e. full range expansion of the solid state actuators). The moving stage (2) moves from (x - y) to x Thus the resultant displacement

X = ((x - y) + x)

X = 2x - y

I f step 1 to step 4 is considered as one cycle, the total displacement that can be produced with the actuator that expands for "x" distance, is

x = ( χ - y)

' For "k" of cycles,

X = k(x - y) Where k = 1 , 2, 3...

Thus with the actuator whose full expansion is small, a large displacement can be achieved.

An apparatus of the invention may comprise the following blocks.

1. Solid state actuator like Piezo crystal/crystals in housing (collectively called a piezo actuator): Piezo actuator acts like a motor to displace the moving stage. The piezo has a characteristic to expand in size when applied with voltage. 2. Mechanical stage: This is mechanical moving stage shown in the figure

3. Power supply to provide power to the piezo actuator: The power supply is required to apply voltage into the piezo such that piezo expands.

The piezo housing has to be designed keeping the piezo material characteristics, housing material, insulation material and preload requirement in mind. The fabrication is done using standard machining techniques like milling, shaping and drilling. The assembly is then undertaken manually. Thereafter, it is tested and calibrated using high-end interferometer equipments or capacitance sensors.

The power supply drives the piezo actuator. These supplies are standard off-the shelf components. The important issues while selecting the right power supply is stability of output, noise, resolution and output current.

Design and Construction details Let

Stiffness of spring / Moving Stage = λg, Stiffness of shear actuator = λs Stiffness of the linear actuator = λl.

The speed of the linear actuator is twice that of the speed of the shear actuator.

I.e. Sl = 2Ss.

The stiffness of the mechanical spring systems is designed to be less than that of the shear actuator. The condition of working model is

λs = ( n λg)

where n is a - non - zero integer = 1 ,2,3.4...

Stage Design:

If the stage is monolithic flexural linear spring, stiffness can be calculated as λs = (8BEtVt) / 9 πL 2 r 1/2 .

Where

B = width

E = Young's Modulus t = Thickness

L = Column Length r = Radius of Flexure

If the stage is monolithic flexible compliance linear spring, stiffness can be calculated as λs = (12EI) / L 3

Where

I = Second Moment of Inertia E = Young's Modulus L = Column Length

The picture in figure 2 shows the actual fabrication of the Nanopositioner. The material is stainless steel with the following specifications:

15 shows the steel made monolithic nanopositioner, 14 is linear actuator " and 13 indicates the shear actuator.

The maximum displacement of the flexible compliance stage can be calculated as

y = F * L 3 / 12EI

With the above specifications, the nanopositioner can produce displacement up to 1000 mircon (1 mm) and the stiffness is 9.5157E-07 kN/micron. The dynamic analysis shows that the natural frequency of the stage is 0.21991612 Hz. Actuator Design The actuator stiffness should be more than that of the stiffness of the stage.

The stiffness of the actuator is 0.003070446 kN / micron which is more than the value of stage.

Advantages of the Invention

The expensive feedback systems, complex algorithm can be avoided.

Long range displacement is possible

No friction is present as in case of Omicron

Entire systems forms a monolithic structure and hence manufacturing process is relatively simple.

Applications of the invention