WO2011135254A1

WO2011135254A1 - Microactuator and microclamp

Info

Publication number: WO2011135254A1
Application number: PCT/FR2011/050954
Authority: WO
Inventors: Ioan Alexandru Ivan; Micky Manitrarivo Rakotondrabe
Original assignee: Centre National De La Recherche Scientifique - Cnrs -; Universite De Franche Comte
Priority date: 2010-04-30
Filing date: 2011-04-27
Publication date: 2011-11-03
Also published as: FR2959437A1; FR2959437B1

Abstract

The invention relates to a microactuator which includes an actuator arm (4) including at least one first layer (8) having a first thermal expansion coefficient and a second layer (10) having a second thermal expansion coefficient, the second thermal expansion coefficient being different from the first thermal expansion coefficient; and to a drive device (6) for moving the actuator arm (4) including a heat device (26, 28, 30) suitable for exchanging heat with at least one portion of said actuator arm (4) in order to cause the actuator arm (4) to move by flexing said actuator arm (4); said microactuator being characterised in that the first layer (8) is made of a piezoelectric material. The invention also relates to an associated microclamp.

Description

Micro-actuator and micro-clip

The present invention relates to a micro-actuator and an associated micro-gripper.

In micro-assembly, micro-manipulation and micro-gripping applications, so-called transfer arm tasks consist of taking, transporting and positioning small objects from one location to another.

In these applications, the objects to be moved have a size less than one millimeter, tasks by transfer arm thus require the use of actuators having a resolution of the order of a micrometer or less than the micrometer.

As a result, intelligent materials of the piezoelectric type, shape memory alloys, electrostrictive materials, thermal materials, etc. are generally preferred to DC motors or hinges for the development of micro-actuators, micro-robots or micro-systems. Indeed, these smart materials are more compact and offer more mechanical deflections and greater resolution. One of the best known systems for transfer arm tasks is the micro-gripper.

A micro-gripper is generally composed of two actuating arms of which one or both are driven by intelligent material.

Some micro-clips are made from the principle of bimetallic bimetals. The arms of these micro-clamps are able to move over a large path often greater than 100 microns. However, these micro-clips have a low resolution.

Some micro-clips are made from piezoelectric materials. These have a high resolution but a lower travel distance.

The present invention is intended to overcome these disadvantages and to provide a micro-actuator and a micro-gripper having a large displacement stroke and high resolution.

For this purpose, the subject of the invention is a micro-actuator comprising:

an actuating arm comprising at least a first layer having a first coefficient of thermal expansion and a second layer having a second coefficient of thermal expansion, the second coefficient of thermal expansion being different from the first coefficient of thermal expansion; and

a drive device for moving the actuating arm comprising a heating device capable of exchanging heat with at least a part of said arm actuating means for causing the movement of the actuating arm by bending of said actuating arm. The micro-actuator is remarkable in that the first layer is made of a piezoelectric material.

According to particular embodiments, the micro-actuator may comprise one or more of the following characteristics, taken separately or in combination:

the second layer is a passive layer;

the second layer comprises a material chosen from a metal and a polymer;

the second layer comprises one of nickel, copper and silicon;

the difference in absolute value between the second coefficient of thermal expansion and the first coefficient of thermal expansion is greater than 2 μιη-m ^l -K ^l , and preferably greater than 7 μτη-τη ^ι -Κ ^ι ;

the second layer has a thickness of between 20 and 500 μιη, and preferably between 50 and 200 μιη;

the actuating arm has a maximum dimension of between 0.5 and 50 mm, and preferably between 3 and 17 mm;

the heat device comprises a thermoelectric module able to provide heat by the Peltier effect;

the heat device comprises an electrical resistance capable of supplying Joule heat;

the micro-actuator comprises a heat absorber in contact with at least one face of the heating device for absorbing heat from said heating device;

the absorber comprises a block of a material with a high thermal conductivity, preferably one block from an aluminum block and a copper block;

- The drive comprises a voltage generator adapted to apply a voltage to each main face of the first layer to cause a displacement of the actuating arm proportional to the applied voltage;

the actuating arm is mounted cantilevered on said heating device; the second layer is in contact with the heating device.

The invention also relates to a micro-gripper which comprises:

two micro-actuators according to the invention, as defined above; and a device for assembling the micro-actuators suitable for assembling the two micro-actuators so as to provide a space between the actuating arms.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the drawings, in which:

FIG. 1 is an exploded schematic view of a micro-actuator according to one embodiment of the invention; and

FIG. 2 is a perspective view of a micro-gripper comprising two micro-actuators such as that of FIG. 1.

With reference to FIG. 1, the micro-actuator 2 according to the invention comprises an actuating arm 4 and a driving device 6 adapted to move said actuating arm 4.

The actuating arm 4 is formed from a flat beam or blade which may in particular comprise a first layer 8 and a second superimposed layer 10.

The first layer 8 is made, for example, from a piezoelectric ceramic containing lead, zirconium and titanium. Other types of piezoelectric materials can also be used. This piezoelectric ceramic has a first coefficient of thermal expansion T1.

The first layer 8 may have, for example, a thickness of between 10 and 1000 microns and preferably between 40 and 500 microns.

One of the main faces of the first layer 8 is bonded, for example, using a thermal glue of the Epoxy H22 type, to the second layer 10. Other methods of bonding / reporting are also possible, by means of thermocompression, plating, etc.

The second layer 10 is made of a material that is able to expand or contract during heat input, or under the influence of a variation in temperature. It is usually called passive material. Such a passive material is, for example, described in Ivan et al. COMSOL 2009 (Ioan Alexandru Ivan, Micky Rakotondrabe and Nicolas Chaillet, 'High Coupling Factor Materials for Bending Actuators: Analytical and Finite Elements Modeling Results', COMSOL Conference, Milan Italy, October 2009). The second layer 10 is generally called the passive layer.

The passive material used to make the second layer 10 is for example a metal or a polymer. Preferably, this material is nickel, copper or silicon. The second layer 10 has, for example, a thickness between 20 and 500 μιη and, preferably, between 50 and 200 μιη.

The second layer 10 has a second coefficient of thermal expansion T2 different from the first coefficient of thermal expansion T1.

Advantageously, the difference in absolute value between the second coefficient of thermal expansion T2 and the first coefficient of thermal expansion Tl is greater than 2 μιη-η ^ ΚΓ ¹ and, preferably, greater than 7 μτη-τη ^ι -Κ ^ι .

When a temperature variation is applied to the actuator arm 4, the first 8 and the second 10 layers contract or expand with different amplitudes due to the fact that they have different coefficients of thermal expansion. This results in a deflection of the actuating arm 4. This deflection is used in the micro-actuator 2 according to the invention to take, hold and place a small object.

The actuating arm 4 has a maximum dimension D of between 0.5 and 50 mm and preferably between 3 and 30 mm. Advantageously, this actuating arm 4 has a maximum dimension of 17 mm.

The maximum dimension D is defined in this patent application as the largest dimension of the actuating arm. When the actuating arm 4 has the shape of a blade as illustrated in FIGS. 1 and 2, this dimension D is the length of the diagonal of a main face 12 of the actuating arm 4.

Alternatively, the actuating arm 4 may have a triangular shape, circular or otherwise.

To facilitate the gripping of microscopic objects or the support on such an object, an end 22 of the actuating arm 4 may be provided with a rigid or compiling member such as a claw or deflector 24.

The driving device 6 in displacement of the actuating arm 4 comprises a voltage generator 18 suitable for applying a voltage to the two opposite main faces of the first layer 8, and a heating device 26 capable of exchanging heat (FIG. that is to say bring heat or absorb heat) with at least a portion of the actuating arm 4 to cause its displacement by bending.

The voltage generator 18 is connected, via the electric wires 20 to the main face 14 of the first layer 8 and to its opposite main face which is thermally bonded to the second layer 10. These two main faces thus form electrodes. The voltage generator 18 further comprises a voltage variation unit 19 adapted to vary the voltage applied between the two main faces of the first layer 8.

When a voltage is applied to the first layer 8 by the generator 18, the latter contracts and expands to cause a flexion or a deflection of the entire actuating arm 4. The unit 19 of variation of the voltage is used to control small displacements with a high resolution of the actuating arm 4, that is to say displacements of the order of 30 microns and resolutions up to a few hundred nanometers.

According to a first embodiment of the invention illustrated in FIGS. 1 and 2, the heating device 26 comprises a thermoelectric module 28 capable of providing or absorbing heat by the Peltier effect. It is usually called Peltier module or Seebeck module. This module is particularly advantageous since it is able to provide heat or cold depending on the direction of the current flowing through it.

The thermoelectric module 28 consists of a set of pairs of elements electrically connected to each other. Each pair consists of an element in a p-type semiconductor material and an element in an n-type semiconductor material. These two elements are joined by a conductive material whose thermoelectric power is assumed to be zero. The two elements p and n of the pair and all the other couples constituting the thermoelectric module 28 are connected in series electrically and in parallel thermally. The set of couples is connected to a current generator 30 by the electrical wires 32.

The current generator 30 comprises a current variation unit 36 adapted to vary the intensity of the generated current as well as a unit 38 for modifying the direction of the current applied to the thermoelectric module 28.

In known manner, during the application to the thermoelectric module 28 of an electric current in a given direction, a face 38 of the thermoelectric module 28 generates heat while its opposite face 40 absorbs heat. When applying a current in the opposite direction to the thermoelectric module 28, the face 38 absorbs heat while the face 40 generates heat.

According to a variant of the invention not shown, the heat device 26 may comprise an electrical resistance capable of providing heat by Joule effect. This resistance may, for example, be micro-machined on the main face 16 of the second layer 10; said main face 16 being opposed to the main face bonded to the first layer 8.

According to another variant of the invention not shown, the heat device 26 may be constituted by a light source emitting radiation in the visible or infrared.

The micro-actuator 2 according to the invention further comprises a heat absorber 42 in contact with the face 40 of the thermoelectric module 28. It should be noted that the thermoelectric module 28 has been shown in FIG. 1 away from the absorber 42 only to facilitate the understanding of the invention.

The absorber 42 is able to absorb heat from the heat device 26, it comprises a block of a material with high thermal conductivity. It may be, for example, constituted by an aluminum block or a copper block.

According to one embodiment of the invention not shown, the absorber 42 may be replaced by a heat sink consisting, for example, by cooling fins.

According to the embodiment described, the second layer 10 is in contact with the heat device 26. However, the micro-actuator 2 according to the invention could also be made according to an embodiment in which the first layer 8 would be in contact with one side of the heat device 26.

The micro-actuator 2 as shown in Figure 1 can be used to press or push on a small object.

Advantageously, it is compact, capable of a stroke greater than 120 microns with a resolution less than one micrometer, or better than a tenth of a micron.

For example, the absorber 42 has a height of between 25 and 12 mm, a length of between 38 and 20 mm and a width of between 20 and 10 mm. The main faces of the heat device 26 have an area of between 40 and 20 mm. The active length of the actuating arm 4, that is to say the length of said arm not in contact with the thermoelectric module, is between 15 and 7 mm, the width of the actuating arm is between 1 and 2 mm. The first and second layers have a thickness of between 0.1 and 0.2 mm.

Consequently, this micro-actuator 2 makes it possible to move the actuating arm 4 over a large displacement stroke with a very precise positioning thereof. AT this effect, the current generator 30 is able to generate a current to induce a displacement of the actuating arm 4 over a large stroke. Then, the voltage generator 18 provides a voltage to the main faces of the first layer 8 to drive the actuating arm 4 on a short stroke with a high resolution.

With reference to FIG. 2, the micro-clamp 44 according to the invention is constituted by two micro-actuators 2 as described above assembled to each other as well as to a clip 46 by a device of FIG. assembly.

This assembly device comprises, for example, a bolt 48 comprising a screw mounted in two through holes of the absorber 42 and the attachment 46, and a nut screwed to the free end of the screw.

This assembly device further comprises a circuit board 50 arranged between the two micro-actuators 2 to provide a space for movement between the two deflectors 24 mounted at the ends of the actuating arms 4.

Connectors 52 have also been fixed to the printed circuit 50. These connectors 52 make it possible to electrically connect the electrical wires 20 and 32 to the voltage generator 18 and respectively to the current generator 30.

Claims

1. Micro-actuator (2) comprising:

an actuating arm (4) comprising at least a first layer (8) having a first coefficient of thermal expansion (Tl) and a second layer (10) having a second coefficient of thermal expansion (T2), the second coefficient of thermal expansion (T2) being different from the first coefficient of thermal expansion (Tl); and

- a driving device (6) in displacement of the actuating arm (4) comprising a heating device (26, 28, 30) able to exchange heat with at least a part of said actuating arm (4) to cause moving the actuating arm (4) by bending said actuating arm (4);

characterized in that the first layer (8) is made of a piezoelectric material.

2. Micro-actuator (2) according to claim 1, wherein the second layer

(10) is a passive layer.

3. - micro-actuator (2) according to any one of claims 1 and 2, wherein the second layer (10) comprises a material selected from a metal and a polymer.

4. - micro-actuator (2) according to any one of claims 1 to 3, wherein the second layer (10) comprises a material from nickel, copper and silicon.

5. - micro-actuator (2) according to any one of claims 1 to 4, wherein the difference in absolute value between the second coefficient of thermal expansion (T2) and the first coefficient of thermal expansion (Tl) is greater than 2 μΐϊΐ-π ^ Κ ^-1 , and preferably greater than 7 μΐϊΐ-πΓ ^ Κ ^-1 .

6. - micro-actuator (2) according to any one of claims 1 to 5, wherein the second layer (10) has a thickness between 20 and 500 μιη, and preferably between 50 and 200 μιη.

7. - micro-actuator (2) according to any one of claims 1 to 6, wherein the actuating arm (4) has a maximum dimension of between 0.5 and 50 mm, and preferably between 3 and 17 mm.

8. - micro-actuator (2) according to any one of claims 1 to 7, wherein the heating device (26, 28, 30) comprises a thermoelectric module (28) adapted to provide heat Peltier effect.

9. Micro-actuator (2) according to any one of claims 1 to 7, wherein the heating device (26, 28,30) comprises an electrical resistance to provide heat Joule effect.

10. - micro-actuator (2) according to any one of claims 1 to 9, which further comprises a heat absorber (42) in contact with at least one face (40) of the heating device (26, 28, 30). ) to absorb heat from said heat device (26, 28, 30).

11. - micro-actuator (2) according to claim 10, wherein the heat absorber (42) comprises a block of a high thermal conductivity material, preferably a block from an aluminum block and a block of copper.

12. - micro-actuator (2) according to any one of claims 1 to 11, wherein the drive device (6) comprises a voltage generator (18) adapted to apply a voltage to each main face of the first layer (8) for causing a displacement of the actuating arm (4) proportional to the applied voltage.

13. - micro-actuator (2) according to any one of claims 1 to 12, wherein the actuating arm (4) is mounted cantilever on said heating device (26, 28, 30).

14. Micro-actuator (2) according to any one of claims 1 to 13, wherein the second layer (10) is in contact with the heating device (26, 28, 30).

15.- micro-clamp (44) characterized in that it comprises:

- two micro actuators (2) according to any one of claims 1 to 14; and

- an assembly device (46, 48, 50) of said micro-actuators (2) adapted to assemble the two micro-actuators (46, 48, 50) so as to arrange a space between said actuating arms (4) .