Device for a micro-adjustable device and micro-adjustable device equipped with such a device

Description

[0001] The invention relates to the field of devices for microactuators, and in particular for microtechnical grippers.

[0002] Microactuators are mechanical devices capable of producing movements over very small strokes (hereinafter referred to as actuator strokes). In particular, microengineered grippers are microactuators that grip small objects using fingers moving along an actuator stroke. These fingers are usually mounted on finger holders, also called end members.

[0003] Microtechnical tweezers, and more generally microactuators, are most often driven by a piezoelectric actuator capable of expanding and contracting, i.e. deforming, under the action of an electric field. A piezoelectric actuator is generally in the form of a stack, also called « stack », along a stacking direction. This stack deforms longitudinally, controlled by an electric field passing through it along its length. This controlled deformation allows precise gripping over very short strokes.

[0004] The stroke of a piezoelectric stack is approximately one thousandth (1 / 1000th) of its length. The actuator stroke required for industrial applications must be at least 400 µm. In order to achieve a reasonable ratio of actuator stroke to microtechnical gripper compactness, microtechnical grippers include an amplifying structure between the piezoelectric stack and the finger holders. This amplifying structure transforms the deformation of the piezoelectric stack into a movement of the finger holders by multiplying it by an amplification factor.

[0005] However, current amplifier structures for microactuators are not satisfactory.

[0006] For example, CN 105 236 349 discloses a device for a micro actuator according to the prior art.

[0007] The amplification factor of known amplifying structures is low, generally less than 5:1. In fact, microtechnical tweezers have a large footprint, up to 500 mm long. Their integration into an industrial chain is complex, if not impossible.

[0008] These amplifying structures rely on the complex assembly of a large number of fragile elements, such as patent FR 1758847, which describes a microtechnical tweezer with a three-dimensional, membrane-based amplifying structure. Known microtechnical tweezers are not suitable for mass production, and their lifespan is short.

[0009] In some known amplifying structures, the movement of the fingers does not preserve their orientation and is asymmetrical. Microtechnical grippers are known in which only one finger is mobile, or in which the two fingers are animated by different movements. Such microtechnical grippers are difficult to use for the precise manipulations required by industrial applications.

[0010] In particular, the article Wang, Fujun et al. "Design of a Novel Dual Axis Micromanipulator With an Asymmetric Compilant Structure." IEEE / ASME Transactions on Mechatronics 24 (2019): 656-665. describes an amplifier structure with an amplification ratio of up to 11:1 for one finger and 4.6:1 for the other finger. This amplifier structure has a higher amplification factor than other known amplifier structures, but at the cost of strong asymmetry. In addition, its large number of parts makes it complex, fragile, and unusable.

[0011] The invention improves the situation.

[0012] For this purpose, the invention provides a microactuator device according to claim 1.

[0013] The amplification factor of the device of the invention is high. It can exceed 30:1 (or 30 / 1), that is to say that for 1 µm of longitudinal deformation of the actuator, the terminal members move by at least 30 µm, or even 50:1. This device is also easy to manufacture. The robustness of the device is also much greater than that of conventional structures, due to the small number of parts and their simplicity.

[0014] Other characteristics and advantages of the invention will be explained in detail in the following description, made with reference to the appended drawings, in which: [ Fig. 1 ] represents a perspective view of a microactuator equipped with a microtechnical device according to the invention, [ Fig. 2 ] represents a top view of the microactuator of the figure 1 , [ Fig. 3 ] represents a bottom view of the microactuator of the figure 1 , [ Fig. 4 ] represents an exploded view of the microactuator of the figure 1 , [ Fig. 5 ] represents a bottom view of the device of the figure 1 , [ Fig. 6 ] represents a top view of the device of the figure 5 [ Fig. 7 ] represents a variant of the device which is not part of the invention.

[0015] The attached drawings contain, for the most part, elements of a certain character. They may therefore not only serve to better understand the present invention, but also contribute to its definition, where appropriate.

[0016] Reference is now made to the figures 1 à 6 .

[0017] A microactuator 1 comprises a base 10, two end members 20 and 22, and an actuator 30 for actuating said end members 20 and 22.

[0018] In one embodiment, the microactuator 1 is a microtechnical gripper and the end members are gripping members, for example finger holders each capable of receiving a finger. The actuator 30 can actuate the finger holders 20 and 22 in order to carry out gripping by the microactuator 1.

[0019] The finger holders 20, 22 can receive respective fingers to form a microtechnical gripper. In one embodiment, the microactuator 1 comprises a tip 200, mounted on the base 10, comprising a support 202 and two fingers 204 and 206 connected to the support 202 by a respective flexible connecting element 2040, 2060, as described in the Applicant's patent EP2718066. Each finger 204, 206 comprises a respective fixing base 2042, 2062 by which it is fixed to one of the finger holders 20, 22, here by shape cooperation. The support 202 may engage in a notch 2020 provided in the base 10, in order to mount the end piece 200 on the base 10. Alternatively, as described in patent EP2718066, the support could be mounted in a groove provided in the base 10. Alternatively, the fingers could be formed in one piece with the finger holders 20 and 22. The fingers could alternatively be fixed to the base by screwing and / or gluing.

[0020] Here, the actuator 30 is a piezoelectric actuator. The actuator 30 is capable of deforming, i.e. expanding and contracting, along an actuator direction 32, depending on the electric field passing through it. This deformation is bidirectional, i.e. the actuator 30 can expand in both directions along its actuator direction 32. The actuator 30 is here in the form of a parallelepiped piezoelectric stack along the actuator direction 32. The piezoelectric stack may be a stack of the PI brand, for example the parallelepiped model P-883.30 with dimensions 3x3x13.5 mm. Alternatively, the actuator 30 could be an electromagnetic or thermal actuator.

[0021] The microactuator 1 can be mounted on an industrial device, for example attached to the end of a robotic arm. The base 10 of the microactuator 1 is for example provided with two holes 1009 and 1010 via which the microactuator 1 can be attached.

[0022] In the example described here, the base 10 of the microactuator comprises, on one of its sides, a recess 12 used to pass one or more cables for powering and controlling the actuator 30.

[0023] The microactuator 1 further comprises an amplifying structure 100 for transmitting the movement of the actuator 30 to the finger holders 20 and 22. The structure 100 is here generally planar. The structure 100 can be manufactured from a 3.5 mm thick plate. Said plate can for example be made of aluminum, steel or silicon. The structure 100 is fixed to the base 10, here screwed via four screw holes 1001, 1002, 1003 and 1004. The structure 100 houses the actuator 30 and forms the two finger holders 20 and 22.

[0024] The structure 100 here forms the notch 2020 in which the support 202 of the end piece 200 forming the two fingers 204 and 206 can engage. Alternatively, the notch 2020 could be provided in another part of the base 10.

[0025] Reference is now made to the figures 5 And 6 .

[0026] The structure 100 comprises a body 110 by which it can be fixed to the base 10 of the microactuator 1. Here, the body 110 comprises the four screw holes 1001, 1002, 1003 and 1004 via which the structure 100 can be fixed to the base 10. The portion of the structure 100 forming the notch 2020 is not shown in the figure 5 , for readability purposes, but is visible on the figure 6 . The notch 2020 is here formed in the body 110 of the structure 100.

[0027] The structure 100 comprises two walls 120 and 122 which form a housing 124 for the actuator 30 (not shown in the figures 5 And 6 ). The two walls 120 and 122 have a general bowl shape, for example in the shape of a “U” (or, alternatively, a “V”), and face each other. The two walls 120 and 122 together form a first substructure 126 elongated in a first direction 1260.

[0028] Here, the two walls 120 and 122 are symmetrical and of similar general shapes. Alternatively, the two walls 120 and 122 could be asymmetrical and / or of different general shapes.

[0029] The first wall 120 and the second wall 122 in the form of a bowl each have a respective bottom 1200, 1220, a respective first edge 1202, 1222 and a respective second edge 1204, 1224 opposite the respective first edge 1202, 1222. The walls 120 and 122 join on one side by their respective first edges 1202 and 1222 in a fixing portion 1262 and on the other side by their respective second edges 1204 and 1224 in a transmission portion 1264. Here, the two walls (therefore the two bowl shapes facing each other) together form an elongated hexagon whose sides are parallel in pairs.

[0030] The first substructure 126 is fixed to the body 110 by the fixing portion 1262. The fixing portion 1262 and the transmission portion are here thicker than the rest of the walls 120 and 122.

[0031] More generally, the two walls 120 and 122 form an elongated hexagon. Alternatively, the two walls 120 and 122 could form a diamond, an ellipse, an oval or any other shape substantially elongated in the first direction 1260.

[0032] The two walls 120 and 122 longitudinally house the actuator 30 (not shown in the figure 5 ) in the housing 124. The actuator direction 32 of the actuator 30 mounted in the housing 124 coincides with the first direction 1260 of the first substructure 126. The actuator 30 is preferably mounted preloaded in the housing 126, i.e. in continuous support against the bottom 1200, 1220 of each wall 120, 122, including in the rest state. The actuator 30 can optionally be glued to the bottoms 1200 and 1220 of the walls 120 and 122, in order to secure its mounting and improve the service life of the microactuator.

[0033] Here, the bottoms 1200 and 1220 have respective faces 1206 and 1226 parallel and facing each other. The actuator 30 mounted in the housing 126 is in continuous contact with the faces 1206 and 1226.

[0034] The two walls 120 and 122 are deformable. The actuator 30, when it expands (respectively contracts) along the first direction 1260, moves the two bottoms 1200 and 1220 away from each other (respectively brings them together). The two bottoms 1200 and 1220 which move away (respectively towards) each other cause the mutual approaching (respectively moving away) of the fixing portion 1262 and the transmission portion 1264. The fixing portion 1262 being fixed to the body 110, the transmission portion 1264 moves relative to the body 110 and transmits the expansion (respectively the contraction) of the actuator 30. The transmission portion 1264 moves along a second direction 1266 substantially perpendicular to the first direction 1260 by a distance equal to the relative movement of the two bottoms 1200 and 1222 multiplied by a first predetermined amplification factor.

[0035] The first amplification factor depends on the geometry of the first substructure 126. In particular, the first amplification factor depends on the elongation of the general shape of the first substructure 126 and the thickness of the walls 120 and 122. In the embodiment described here, the first amplification factor is between 2:1 and 7:1.

[0036] The structure 100 further comprises a second amplifying substructure 130, opposite the first substructure 126 with respect to the transmission portion 1264. The second amplifying substructure 130 transmits the movement of the transmission portion 1264 to the finger holders 20 and 22.

[0037] The second substructure 130 comprises for each finger holder 20, 22 a respective arm 132, 134. Each arm 132, 134 is fixed at a respective first end 1320, 1340 to the transmission portion 1264. Each arm 132, 134 is fixed to its respective finger holder 20, 22 at a respective second end 1322, 1342 opposite its respective first end 1320, 1340. The arms 132 and 134 are of generally elongated shape, and extend longitudinally close to each other, forming an angle of less than 10 degrees, preferably less than 5 degrees, with the second direction 1266.

[0038] The second substructure 130 further comprises for each finger holder 20, 22 a respective articulation 136, 138. The articulations 136 and 138 make it possible to control the movement of the finger holders 20 and 22 relative to the body 110. The articulations 136, 138 are substantially symmetrical relative to the second direction 1266. Here, the two articulations 136 and 138 are located on either side of the arms 132 and 134.

[0039] In one embodiment, each joint 136, 138 comprises two respective elongated rods 1360 and 1362, 1380 and 1382. The two rods 1360 and 1362 (respectively 1380 and 1382) of the joint 136 (respectively 138) are parallel and of the same length, or, in other words, form two opposite sides of a parallelogram. The other two sides of said parallelogram are expressed in a third direction 1300, which is optionally substantially perpendicular to the second direction 1266. This “parallelogram” arrangement of the two articulations 136 and 138 forces the finger holders 20 and 22 to move parallel and symmetrically with respect to the second direction 1266. The angle between the longitudinal direction of the rods 1360, 1362, 1380 and 1382 and the second direction 1266 is less than 10°, preferably less than 5°.

[0040] When the transmission portion 1264 moves closer to (or away from) the fixing portion 1262, the second substructure 130 drives the finger holders 20, 22 via the arms 132 and 134 in a movement towards (or away from) the third direction 1300. The relative movement of the finger holders 20 and 22 is equal to the relative movement of the transmission portion 1264 relative to the fixing portion 1262 multiplied by a second predetermined amplification factor. In other words, the actuator travel of the finger holders 20 and 22 is linear, and is expressed along the third direction 1300.

[0041] The second amplification factor depends on the geometry of the second substructure 130. In particular, this second amplification factor depends on the angle between the arms 132 and 134 and the second direction 1266, between the rods 1360, 1362, 1380 and 1382 and the second direction 1266, on the length of the rods 1360, 1362, 1380 and 1382, and on the length of the arms 132 and 134. In the embodiment described, the second amplification factor is greater than 2:1, and can be up to 15:1, or even up to 20:1.

[0042] The total amplification factor of the structure 100 is equal to the product of the first amplification factor and the second amplification factor. In the example described here, the total amplification factor of the structure 100 is 50:1, but could reach up to 140:1, which is considerably higher than known amplifier structures. Furthermore, the movements of the finger holders 20 and 22 are symmetrical and parallel to each other. The structure 100 therefore makes it possible to achieve very high amplification factors, without the disadvantages of fragility, complexity or asymmetry of known amplifier structures.

[0043] The relative stiffness of the general shape of the first substructure 126 increases the rigidity of the second substructure 130. Thus, the first substructure 126 provides mechanical stability to the entire structure 100. The shape of the second substructure 130 allows the structure 100 to achieve a very high amplification factor. The second substructure 130 further provides parallelism and symmetry in the movement of the finger holders 20, 22 of the structure 100. The two substructures 126 and 130 thus operate in synergy.

[0044] The structure 100 is here monobloc, and formed of a single profiled plate. Its manufacture is thus very simple, its assembly easy (four screws are enough). The structure 100 can be: machined by electro-erosion (EDM), machined by bar turning, injection molded ("metal injection molding" in English), manufactured by micro-sintering, produced by additive manufacturing (also called "3D printing"), or produced by physico-chemical machining of silicon in a clean room (for example in the case of small-scale manufacturing).

[0045] These manufacturing processes are cited as examples and are not limiting.

[0046] The structure 100 makes it possible to achieve an actuator stroke between 50 µm and 3 mm. In the example described here, the actuator stroke is approximately 800 µm, and the size of the microactuator is 45x23x7.5 mm. An actuator provided with such a structure 100 thus has a size / stroke ratio that is much more advantageous than actuators provided with known amplifier structures.

[0047] In the structure 100, the arms 132 and 134 and the joints 136 and 138 can pivot at their ends relative to the body 110, to their respective finger holders 20, 22 and to the transmission portion 1264, by deformation at their ends. The deformations are elastic, due to the movements of the various parts of the body 110 which are very small, of the order of less than 2° and less than 2 mm.

[0048] The arms 132 and 134 and / or the rods 1360, 1362, 1380 and 1382 may have thinned ends. In the example illustrated in the figure 5 , the ends of the arms 132 and 134 and the rods 1360, 1362, 1380 and 1382 are all thinned. The thinning of said ends improves the ability of the arms 132 and 134 and the rods 1360, 1362, 1380 and 1382 to pivot relative to what they are respectively attached to.

[0049] Optionally, the body may have recesses 1100 and 1102 at the junction between the respective first edges 1202 and 1222 of the walls 120 and 122. This makes it possible to avoid having sharp edges at this junction between the walls 120 and 122 and the body 110, which reduces the local stresses in the material of the structure 100.

[0050] The structure 100 thus described has an amplification factor, a simplicity of design and manufacture which are much more advantageous than the amplifying structures of the state of the art.

[0051] In the embodiment described herein, the structure 100 has plane symmetry with respect to a plane of symmetry perpendicular to the first direction 1260. The plane of symmetry contains the second direction 1266. The plane of symmetry is located between the two arms 132 and 134, between the two cup-shaped walls 120 and 122 and between the finger holders 20 and 22. The plane symmetry of the structure 100 allows the finger holders to move symmetrically with respect to each other.

[0052] Alternatively, the two pairs of rods and the two joints 136 and 138 could be inverted, i.e. the transmission portion 1264 could be connected to the two finger holders 20, 22 by the two pairs of rods 1360, 1362 and 1380, 1382 respectively, and the two finger holders 20, 22 could be connected to the body by the two arms 132 and 134.

[0053] Reference is now made to the figure 7 .

[0054] In this example which is not part of the invention, the structure 100 has a third sub-structure 230 in place of the second sub-structure 130. Here, each articulation of the third sub-structure 230 is formed of a single rod 236, 238. This rod 236, 238 is secured at a first end 2360, 2380 to its respective finger holder 20, 22, and is fixed to the body 110 in a pivoting manner at a second end 2362, 2382.

[0055] The structure 100 is here in one piece and the pivoting at the second ends 2362, 2382 is done by elastic deformation at the junction 2364, 2384 between the body 110 and the second end 2362, 2382. The second ends 2362 and 2382 can be thinned so as to improve this pivoting by elastic deformation.

[0056] The movement of the finger holders 20 and 22 is symmetrical. Since there is only one pivot in the third structure 230, the finger holders 20 and 22 describe an angular movement around the junction 2364, 2368.

[0057] This third structure 230 has an amplification factor even higher than that of the second sub-structure 130, at the cost of losing the parallelism of the movements of the finger holders 20 and 22.

[0058] A globally symmetrical 100-amplifying structure has been described. This symmetry allows the end organs to move symmetrically. However, an asymmetrical 100-amplifying structure could be obtained that would maintain a very high amplification factor and much greater strength than known structures, thanks to the small number of parts and their simplicity.

[0059] An amplifier structure 100 has been described for a microactuator of the microtechnical gripper type. The amplifier structure according to the invention makes it possible to move end members by piezoelectric control over very precise, symmetrical or even parallel strokes. This opens the way to numerous applications in addition to microtechnical grippers.

[0060] In one embodiment, the microactuator 1 is a microtechnical electrical contactor. The two terminal members 20 and 22 each comprise a respective contact member, said two contact members being electrically connected when they are in contact with each other. The actuator 30 then drives the terminal members to switch the contact members between an on state (where the contact members are in contact) and a off state (where the contact members are at a distance from each other and electrically separated).

[0061] Thanks to the amplifying structure, this microtechnical electrical contactor is very compact, active and controllable, especially with very low actuator control currents. In addition, the clamping force that the terminal devices can develop makes it possible to consider the use of such an actuator in situations of high currents or high voltages. The switching of this microtechnical electrical contactor is fast, less than 10 ms, or even less than 1 ms.

[0062] In another embodiment, the microactuator is an optical diaphragm or an optical shutter. Here, the end members each comprise a respective half-diaphragm. The two half-diaphragms have a general right-angled "V" shape, and face each other symmetrically, their respective corners spaced apart. The two general "V" shapes overlap, the two half-diaphragms together forming a square diaphragm. The two half-diaphragms move away and towards each other under the effect of the actuator, which makes it possible to control the dimensions of the square diaphragm they form.

[0063] Here again, the actuation speed of the microactuator is advantageously short (less than 10 ms, or even 1 ms). The size of the diaphragm can be controlled very precisely. The diaphragm also remains centered on an optical axis.

[0064] The invention is not limited to the examples cited above, and is of interest in all fields where the precise movement of two end members over short distances in a symmetrical, or even parallel, manner is required.

Claims

1. A device for a microactuator comprising - a body (110), - two terminal members (20, 22) articulated (136, 138; 236, 238) on the body (110), located on one side of the latter, - two deformable bowl-shaped walls (120, 122) which face one another, arranged to house an actuator (30), two respective first edges (1202, 1222) of said walls (120, 122) located on one side being fastened (1264) on the body (110), whereas two respective second edges (1204, 1224) of said walls (120, 122) located on another side move consecutively to a deformation of the walls (120, 122) under the effect of the actuator (30), - said movement being transmitted by two arms (132, 134) which terminate at the two respective terminal members (20, 22), wherein the bowl-shaped walls (120, 122) each have a respective bottom (1200, 1220) against which the actuator (30) bears, and wherein the two terminal members (20, 22) are articulated on the body (110) by respective rods (1360, 1362, 1380, 1382; 2360, 2380), and wherein the two terminal members (20, 22) are articulated on the body (110) by two respective pairs of rods (1360, 1362; 1380, 1382) substantially parallel and of the same length, and wherein the ends (1322, 1342) of the rods (1360, 1362, 1380, 1382) on the terminal member (20, 22) side are substantially aligned, and wherein the deformation of the actuator (30) is a longitudinal expansion or a longitudinal contraction against the two bottoms (1200, 1220) of the walls (120, 122), wherein an expansion of the actuator (30) against the two bottoms (1200, 1220) drives a coming closer together of the first edges (1202, 1222) and of the second edges (1204, 1224), by which the second edges (1204, 1224) symmetrically drive a relative coming closer together of the terminal members (20, 22) via arms (132, 134), and wherein a contraction of the actuator (30) against the two bottoms (1200, 1220) drives a moving apart of the first edges (1202, 1222) and of the second edges (1204, 1224), by which the second edges (1204, 1224) symmetrically drive a relative moving apart of the terminal members (20, 22) via arms (132, 134).

2. The device according to claim 1, wherein the relative coming closer together and the relative moving apart of the terminal members is generally expressed along a linear travel (1300).

3. The device according to one of the preceding claims, wherein the two bowl-shaped walls (120, 122) generally form a diamond, hexagon or an oval.

4. The device according to one of the preceding claims, wherein the device (100) is made from a single piece.

5. The device according to one of the preceding claims, wherein the device (100) is formed from a profiled plate.

6. The device according to one of the preceding claims, wherein the device has an amplification factor greater than 30:1.

7. The device according to one of claims 2 to 11, wherein the rods (1360, 1362, 1380, 1382; 2360, 2380) and / or the arms (132, 134) are thinned at one or more of their ends (1320, 1322, 1340, 1342; 2362, 2382).

8. The device according to one of the preceding claims, wherein the microactuator is a microtechnology clamp, and the terminal members (20, 22) each comprise a finger carrier and a finger mounted on said finger carrier.

9. The device according to one of the preceding claims, wherein the actuator (30) is a piezoelectric actuator, preferably a piezoelectric stack (34).

10. The device according to one of the preceding claims, wherein the device is symmetrical with respect to a plane of symmetry located between the two walls (120, 122), between the two arms (132, 134) and between the two terminal members (20, 22).