WO1998024594A2

WO1998024594A2 - Prehensile device in shape memory material and construction process

Info

Publication number: WO1998024594A2
Application number: PCT/EP1997/006966
Authority: WO
Inventors: Yves Bellouard; Jacques-Eric Bidaux; Thomas Sidler
Original assignee: Andromis S.A.
Priority date: 1996-12-06
Filing date: 1997-12-04
Publication date: 1998-06-11
Also published as: WO1998024594A3; EP0946334A2; JP2001506546A; FR2756767A1; AU5662698A

Abstract

The invention concerns a prehensile and/or fastening device (2) containing a first (4) and a second (6) prehensile element capable of motion with respect to one another, these first and second elements being entirely constructed of a single block of shape memory material. The invention also relates to a construction process for a shape memory material.

Description

GRIP MEMORY MATERIAL GRIPPING DEVICE

AND IMPLEMENTATION METHOD

DESCRIPTION

Technical area

The invention relates to the field of grippers and / or fixing devices for objects of small sizes, substantially between a few tens of micrometers and a few millimeters.

The invention also relates to the field of forceps for foreign bodies, biopsy forceps and surgical micro-scissors.

The invention also relates to the field of shape memory materials, and the manufacture of devices, in particular grippers, from these materials.

The invention finds an application in the field of manufacturing endoscopes, in particular for gripping and / or handling lenses and / or microlenses and / or multi-core fibers.

The invention also finds applications in the following fields:

- gripping of micro-systems in general, that is to say of objects smaller than one millimeter,

- assembly of small optical components (of smaller dimensions or of the order of a few millimeters). Example: Selfoc lens in the case of automated assembly of flexible micro-endoscopes,

- production of active minimally invasive surgery tools, such as biopsy forceps, foreign body forceps or micro-scissors, - manipulation of living tissue or to be maintained in a biological environment. This is for example the case in the study of the biomechanical behavior of arterioles.

Prior art

Grippers using shape memory materials are known from the article by K. Escher et al. entitled "Robots grippers: An application of two way shape memory" published in Progrès in Shape memory Alloys, S. Oucken Editor, DG Informationsgesellschaft Verlag, 1992, pages 301-316. Such devices are also known from the article by D. Grant published in IEEE International Conference on Robotics and automation, 1995, entitled "Design of Shape Memory Alloy with High Strain and Variable Structure Control", pages 2305-2312. Finally, other grippers are known from the article by K. Ikuta entitled "Microminiature Shape Memory Alloy Actuator", published in IEEE, Int. Conf. On Robotics and Automation, Cincinatti, 1990, pages 2156-2161.

All these articles describe grippers of fairly complex shapes, and the manufacturing technique of which is cumbersome and difficult to implement. In particular, the device described in the article by D. Grant is an example of a gripper using wires made of a shape memory material as actuators. The device described in the article by K. Ikuta is also of the type in which return springs made of a shape memory material are used, the branches of the gripper being moreover made of a conventional material. In these devices, in which the "activation" parts are made of memory material in form, there is the problem of reducing friction or friction in the articulated parts: in the case of microgroppers, this is an important problem, because of the small size of the components. In addition, these devices require a delicate assembly phase.

The article by K. Escher describes grippers of which only one of the activation elements is made of a shape memory material, or else a grip in which arms are made of a shape memory material, these arms having an aspect of twisted wire mounted on a support. Such a device is very difficult to implement in the context of an industrial application, because it is very imprecise. In addition, such a system is difficult to miniaturize: it indeed requires a delicate assembly.

It is therefore necessary to find a new gripping or fixing device, in particular suitable for gripping small objects, of structure and assembly simpler than known devices.

There is also the problem of finding gripping and / or fixing devices which make it possible to avoid these friction problems.

Statement of the invention

The invention relates to a gripping or fixing device whose structure is much simpler than known devices, and in which the friction problems do not arise. More specifically, the invention relates to a gripping or fixing device comprising a first and a second gripping element which can undergo a relative movement with respect to each other, all of the first and second elements being made of a one-piece material with shape memory.

All of the first and second elements being made of a one-piece material, with shape memory, no friction problem arises. Furthermore, the structure produced is simple.

In order to produce a gripping device suitable for small objects, the amplitude of the relative movement of the two elements is provided as being at most equal to a few millimeters (for example 10 mm) or at most equal to 1 mm, or to no more than 500 μm, or no more than 100 μm.

Preferably, the gripping device is obtained by cutting in the plane of a blade of shape memory material, the relative movement taking place in this plane.

One can also provide a geometric structure adapted to better dissipation of heat energy or better heat transfer: thus, the first and second elements may for example be provided with fins.

The device may also include means for handling or fixing or positioning the assembly of the first and second elements, with which they may constitute a monobloc assembly, made of the same shape memory material.

Again, one can provide a geometry suitable for efficient heat transfer (fins, growths, holes, etc.). We can also provide a geometry, or cut out a particular shape, which serve as a visual reference symbol for a particular production.

These handling means can be connected to means for controlling the temperature of the first and second elements of the gripping device: this makes it possible to control the opening, or closing, of this device.

These control means can for example be of the Peltier effect type, by Joule effect heating (electric current), by induction heating or by laser heating.

The invention also relates to a handling device comprising a gripping device as described above, as well as means for controlling the means for controlling the temperature of the first and second elements, and means for visual control of the relative position. first and second elements of the gripping device.

The invention also relates to a gripping or fixing device comprising at least three gripping elements, each of which can undergo a bending movement in a plane, all of the gripping elements being produced in a single piece, from a memory material. of form. Here again there is a gripping device of simpler structure than the known devices and in which the friction problems do not arise.

A support element for the gripping elements can be provided. The gripping elements can each have the shape, for example of a finger, which can be provided with one or more bending recess (s). According to another aspect, the device is obtained by cutting in the plane of a blade of shape memory material, then by constraint of the cut shape obtained, for example around a cylinder or a tube.

Means for controlling the temperature may be provided: for example, a Peltier element, or a laser or means for inducing a current in the shape memory material or means for circulating a current in the memory material of form.

The invention also relates to a handling device comprising a gripping device as above, as well as means for controlling the temperature control means and means for visual control of the relative position of the gripping elements.

The known methods for preparing shape memory elements are incompatible with the production of microsystems. Furthermore, the processes for manufacturing thin layers do not allow layers greater than 100 μm to be produced.

In addition, all these methods involve an operation of annealing small samples which is a delicate operation, expensive and sometimes long. Furthermore, the production of a large quantity of parts is difficult and the forms which can be produced are limited. In order to solve these problems, the invention also proposes a method for preparing an element made of a shape memory material, adapted in particular to the production of the gripping device according to the invention.

The subject of the invention is therefore a method of preparing an element made of a shape memory material comprising the following steps: a) annealing a substrate of the shape memory material, then b) cutting the element in the substrate.

This process makes it possible to obtain any form of element. It also makes it possible to produce a very large quantity of parts for a single annealing operation. Therefore, this process guarantees excellent reproducibility of the material properties of each of the parts produced (transformation temperature, dislocation rate, etc.). Finally, for microsystems, it is the only process which makes it possible to obtain objects with shape memory of significant thickness, in particular greater than 100 μm.

The cutting step can be carried out by laser or by electroerosion or else by water jet, or by laser and coupled water jet or by any other method making it possible not to disturb the microscopic structure of the material of the substrate obtained after annealing. : for example, it is produced so as not to disturb the structure of the substrate over more than 10 μm or more than 5 μm beyond the cut.

The invention also relates to a method of handling an object comprising the seizure and transport of the object using a device according to the invention. This object can be for example a lens or a microlens. This process is particularly advantageous in the case of the production of a multi-core (or multi-fiber) fiber-lens assembly, this assembly then being produced by displacement and positioning of the lens, facing one end of the fiber, in accordance with the handling process. according to the invention, then by fixing, for example by gluing, the lens on the end of the fiber. This avoids any contact between the lens and the hand of an operator, which can lead to chipping of the lens or the deposit of dust on its surface.

Brief description of the figures. In any case, the characteristics and advantages of the invention will appear better in the light of the description which follows. This description relates to the exemplary embodiments, given by way of explanation and without limitation, with reference to the appended drawings in which:

FIGS. 1 to 3B represent grippers according to the invention, in the form of a ring,

FIG. 4 is a device for controlling a gripper, FIG. 5 schematically represents an endoscope,

FIG. 6 represents another example of a gripper,

FIGS. 7A to 7C represent various stages of a manufacturing process according to the prior art,

FIGS. 8A to 8D represent steps of a method according to the invention, FIG. 9 is a diagram of a laser cutting device,

FIGS. 10A and 10B represent devices for machining by electroerosion, FIGS. 11 to 12B represent another type of gripper according to the invention, with several gripping elements,

FIGS. 13a to 13C represent the application of a gripper according to the invention to a spring system allowing the obstruction of an artery,

FIG. 14 represents the application of the invention to a biopsy forceps,

FIG. 15 represents the application of the invention to a dilator,

- Figure 16 shows the embodiment of a connection device according to the invention.

Detailed description of embodiments of the invention

A first example of a gripper according to the invention will be described in connection with FIG. 1. In this figure, the gripping system consists of a single block of a shape memory material. It is in the form of an open ring 2 comprising a first and a second branch 4, 6. This form has the advantage of distributing the stresses uniformly in the ring, and moreover makes it possible to grasp objects with wide tolerances as to their diameter (± 50 μm for lenses of 250 μm in diameter). The radius R of the ring depends on the temperature range in which the system is located. Thus, for a temperature T ₂ , the system opens and allows the insertion or the taking of an object. For a temperature Tj_, the system closes on the object, thus ensuring the fixing or gripping function as the case may be. The material chosen can, for example, be a NiTi shape memory alloy. This alloy has the characteristic of being biocompatible.

The ring of FIG. 1 is shown in perspective in FIG. 2, mounted on a handling and / or fixing support 8. Typically, the thickness e of the branches of the ring is for example between 70 and 80 μm , or between 45 and 50 μm. The diameter D of the ring is for example less than or equal to 3 mm; a ring was made, with a diameter of 200 μm. The dimensions of the support can be for example the following: 50 μm <h <500 μm, 500 μm <L <lmm, 100 μm <l <lmm

Thus, according to an exemplary embodiment: L = 500 μm, h = 180 μm, 250 μm <D <300 μm, e≡70 μm. According to another exemplary embodiment, the dimensions are the same except for e which is of the order of 50 μm.

The average theoretical clamping force of such a device is of the order of 0.2 N.

Preferably the support 8 is itself made of the same shape memory material as that used for the production of the gripper 2.

Another example of embodiment of a gripper, mounted on its fixing and / or handling means, is illustrated in FIG. 3A. The fixing means are designated by the reference 10 and comprise a first part 12, of approximately parallelepiped shape, and a second part 14 which tapers in the direction of the ring 2, from the first part 12. In this second part 14, a hole, or opening, 16 makes it possible to limit the accumulation of stresses due to the embedding of the ring. In addition, the hole allows better compliance of the arm system 4, 6.

As illustrated in FIG. 3A, the fixing means can be connected to means for controlling the temperature of the ring. In FIG. 3A, these temperature control means successively comprise a copper finger 18 and an element, or microelement, Peltier 20. The latter may for example have a size of 7 mm × 5 mm.

The use of a Peltier effect micromodule is particularly advantageous for the following reasons. First of all, such a micromodule makes it possible to heat or cool the shape memory material, therefore to open or close the ring or the gripper as required. In addition, Peltier elements allow a wide range of temperatures to be reached; typically, a range between -100 ° C and +200 ^C can be covered, compatible with the use of many shape memory materials. Finally, this type of device constitutes, from the point of view of its control, a first-order system, simple and very robust.

Another simple gripper structure, based on the same principle, is illustrated in Figure 3B. As in FIG. 1, the gripper is in the form of an open ring 2 comprising first and second branches 4, 6. This assembly is made of a shape memory material, and in one piece * It further comprises two legs 15, 17. A zone 7 located between the ring and the legs 15, 17 is of small width and the effect of heating the current (Joule effect) is the most significant there. Zone 7 is therefore the warmest during the passage of an electric current i. To make the electrical interface with a control circuit, the "bonding" technique traditionally used for microchip connections can be used. The contact zones are then for example located at the end of the tabs 15, 17. This control technique makes it possible to control the ring or the gripper during either the opening or its closing.

According to another embodiment, a control of the temperature of the ring, for example that of FIG. 2, can be carried out by heating the support 8, for example using a laser beam. According to other embodiments, it is possible to carry out induction heating, or else mount a resistor, either directly on the ring, or on a support on which the ring rests, such as the support 8 in FIG. 2. In the latter case, the circulation of a current in the resistor causes the latter to heat up by the Joule effect, part of the heat thus produced being transferred to the ring or to its support.

FIG. 4 schematically represents a device for controlling a gripper according to the invention. The gripper is designated by the reference 22, and can be a gripper as described above in conjunction with FIGS. 1 to 3A. This gripper is in contact with a Peltier 20 element, itself supported by a positioning arm 26 for carrying out various movements, for example displacements along three axes X, Y, Z. This arm makes it possible to bring this gripper 22 into contact with an object 24 to be grasped and moved. A control system 28 makes it possible, by means of a measurement of the temperature of the Peltier element (and therefore, of the gripper), to control the opening and closing of the latter. A video camera 30 is connected to a video acquisition device 32 and allows the opening or closing state of the gripper 22 to be displayed on a screen 36. Depending on this state, a command can be transmitted to the device 28 to vary the temperature of the Peltier element 20, and therefore the opening and closing of the gripper 22.

The video camera can also be replaced by a multicore fiber fitted with a SELFOC lens and coupled to a video acquisition system.

According to a variant, the opening or closing of the ring is controlled by a current flowing in the material of the ring or by heating by laser or by induction or by a resistance applied to the gripper. A control device like that of FIG. 4 can therefore also be implemented, the control system 28 no longer acting on a Peltier element but on a laser or an induction system or a current flowing in a resistor mounted on the 'ring or flowing in the ring itself.

Such a gripping device, with its control means, can be advantageously used in the context of a method of manufacturing objects for which parts of small sizes must be transported, for example from one assembly station to another.

This is the case in particular, for mounting cylindrical microlenses (GRIN microlenses), used in endoscopy.

Endoscopy is a human body investigation technique that allows practitioners to acquire information, or images, from parts of the body, such as the stomach, lungs, or heart. A device for implementing such a technique is shown diagrammatically in FIG. 5, where the reference 40 designates a light source which is focused by a lens 42 at the input of a light guide 46. The latter is in fact most often connected to a plurality of optical fibers 48, 50 arranged at the periphery of a multi-core fiber 52. An illumination beam 54 can thus be directed onto an area 56 of an object or an organ to be observed, which reflects radiation 58 at the input 60 of the multi-core fiber 52. The latter comprising a coherent beam of individual hearts, these therefore transmit the light in an orderly manner between them, and the image obtained at output 62 multicore fiber corresponds to the image formed at the input 60. Means 64, 66 for storing, analyzing and / or representing the image can also be provided in combination with this device.

This imaging technique is described for example in the articles by A. Katzir: "Optimal Fibers in Medicine", Scientific American, vol. 260 (5), p. 120-125, 1989 and "Optimal Fiber Techniques (Medicine)", Encyclopedia of Physical Science and Technology, vol. 9, p. 630-646, 1987. In practice, a multi-core fiber such as fiber 12 can comprise approximately 700 to 10,000 cores, for applications in microendoscopy.

The concept of multi-core fiber is to be distinguished from that of multi-fiber, which is an assembly or bundle of independent fibers placed together and possibly glued at the end.

Both multi-core fibers and multi-fibers can be used in endoscopy. In both cases, a lens 60 (see figure

5), generally of the GRIN type, is mounted on an entry face of the fiber, on the side which goes into the human being. Currently, the mounting of such a lens on the multifiber or on the multicore fiber is done manually. This manipulation can lead to chipping of the lens, or to the addition of dust to its surface. It is therefore necessary to find a technique allowing, in general, the manipulation of the lenses, but also the positioning of a lens, in front of a fiber, without manual intervention.

The device which has been described above, in connection with FIG. 4, is suitable for this manipulation and makes it possible to transport the microlenses, for example from a storage area, to an area where they are aligned with the fibers, so as to be glued to them. The gripper being of the shape memory type, its opening is controlled by a temperature variation, which makes it possible to avoid any contact between an operator and the lenses. This greatly reduces the risk of chipping lenses or depositing dust on their surface. The invention has been described in the case of a gripper having a substantially annular shape

(Figures 1-3). One can also consider grippers having a different shape, for example in which the two arms of the gripper constitute a

"V", monobloc and in shape memory material.

FIG. 6 represents another type of gripper, made of a shape memory material. This gripper comprises a zone 100 for fixing the gripper, and a flexible arm 102 which is articulated on the zone 100 for fixing. The zone 100 in fact defines a second arm 104, rigid, with respect to which the flexible arm can be moved. The end of the arms defines a gripping area 106. These ends can have shapes adapted to such or such type of objects to be grasped by the gripper. Thus, in Figure 6, the fixed arm 104 has a recess 108, of triangular section. This recess allows, in combination with the movement of the arm 102, to pick up objects, in particular of the cylindrical type, for example GRIN lenses, and to position them precisely in the gripper.

The device described in FIG. 6 can be controlled by a Peltier microelement, with the same advantages as those already described above.

The gripping devices according to the invention are made of a shape memory material. Shape memory alloys are materials that have two solid phases, for two characteristic temperature ranges. The phase change is accompanied by a change in the physical properties and the atomic organization of the material, which can generate significant macroscopic deformations (up to 8% elongation for NiTi). It is possible to "memorize", for each of the two phases, a given form, by a process called "education", and by an appropriate heat treatment. Educational methods are described for example in the document by J. Perkins et al. Entitled "the Two-Way Shape Memory Effect" published in Engineering Aspect of Shape Memory Alloys, Butterworth Heinemann, London, 1990, pages 195-206. We then obtain a device with a two-way memory effect, well suited to the realization of a gripper.

Generally, the expression "austenite" is used to designate the high temperature solid phase of a shape memory alloy. The expression "martensite" designates the low temperature solid phase. The characteristic temperatures at the start and end of the austenite-martensite transformation are designated by M _s and M _f . The characteristic temperatures at the start and end of the martensite-austenite transformation are designated by A _s and A _f .

As regards the alloy to be chosen, the NiTi alloy has the advantage of being biocompatible, which is of interest in the case of medical applications of the endoscopy type. A NiTi alloy having a composition close to the equiatomic composition also offers the advantage of having, at high temperature, a centered cubic structure of type B ₂ . This alloy presents a martensitic phase transformation towards monoclinic, orthorhombic, or rhombohedral structures, after quenching. The same alloy can present several successive transitions. The transition temperatures can be adjusted as desired by changing the composition and, to a lesser extent, the heat treatments. Thus, an alloy rich in Ti will have a high transition temperature M _s , while an alloy rich in Ni will have a low temperature M _s . The alloy is preferably quenched, or at least cooled rapidly, in order to avoid risks of decomposition, in particular by precipitation. In some cases, a controlled precipitation is produced in order to promote the two-way memory effect. Preferably, an alloy is used for this, the Ni concentration of which is greater than 50.6 atomic%. In the case where it is sought to use the memory effect of the alloy in order to produce a gripper, the transition temperatures M _s and A _s are preferably higher than ambient temperature.

Other shape memory materials such as CuZnAl or NiTiCu can be used. The materials described by CM can also be used. Wayman et al. in "Introduction to martensite and Shape Memory", published in Engineering Aspect of Shape Memory Alloys, Butterworth Heinemann, London, 1990.

The traditional method of manufacturing elements having shape memory properties is shown diagrammatically in FIGS. 7A to 7C. A selected material 110, with shape memory (FIG. 7A) is first shaped according to the structure that one wishes to memorize (FIG. 7B). Thus, in the case of a ring, the selected material 110 is constrained around a cylindrical shape, before any operation annealing. It is only afterwards, during a second step (FIG. 7C) that the material is annealed, generally around 500 ° C., in order to freeze it in the desired shape. It is often necessary to constrain the material to achieve such a result: we then use a template or a mold. This method has drawbacks:

- For microsystems, due to their small size, shaping is a difficult operation. This problem arises in particular in the case of the production of micro-grippers (whose amplitude of the relative displacement of its gripping elements is less than 1 mm), for example for grasping micro-lenses. - In addition, annealing small samples is a delicate and time-consuming operation.

- In addition, the production of a large quantity of parts is difficult, due inter alia to the delicacy of the shaping operations, and especially of annealing. In addition, each annealing operation is costly in production time.

- Finally, the shape that we can achieve is limited: we can only make simple pieces. Thus, a gripper of the type illustrated in FIG. 3 or in FIG. 6 is impossible to produce with such a method.

In order to solve these problems, the inventors propose another technique for preparing shape memory materials, which will be described in conjunction with FIGS. 8A to 8D.

In a first step, a base material 120 is selected (FIG. 8A). During a second step (FIG. 8B) this material 120 is annealed in an oven 122. Then (FIG. 8C) the desired shape is cut directly from the annealed blade: this cutting is carried out using a technique which, preferably, only disturbs the material very locally. Such a technique can be a laser cutting technique or an electroerosion or jet cutting technique, which are minimally destructive methods. Thus, the desired shapes 125, 127, 129 are obtained (FIG. 8D), the imprints 124, 126, 128 of which, after cutting, are left in the material plate 120. This process has the following advantages:

- It is possible to obtain any form of material. - In microsystems, this is the only technology which makes it possible to obtain shape memory objects of significant thickness, for example of the order of 500 μm in the case of laser cutting.

- From the base material, a very large quantity of parts can be produced for a single annealing operation.

- The properties of the material depend on the quality of the annealing. Annealing is therefore a critical operation if the annealing is carried out element after element. In the present case, a single annealing is carried out for the entire blade. In addition, the advantage of being able to produce a large number of parts of the same annealing guarantees reproducibility of the physical properties from one part to another. The method according to the invention makes it possible to produce parts of any shape, in particular of the type of those already described above, in conjunction with FIGS. 3 or 6. With regard to cutting after annealing, the use of the EDM technique makes it possible to cut thicker parts than if the laser cutting technique is used: the latter is well suited for blades of thickness less than about 1 mm, but is less well suited for blades of greater thickness.

The properties of the material can be characterized by means of differential scanning calorimetry: for a given temperature variation ΔT, the quantities of heat supplied are compared, on the one hand to a reference sample holder, and on the other to a sample holder containing the material to be studied, both of which are in the form of small mass samples of the order of a few micrograms. In fact, the emission and / or absorption of heat linked to the phase transformation are measured on these samples. This technique allows precise measurement of the transition temperatures (M _s , M _f , A _s , A _f ).

The method described above also offers the advantage of avoiding a step of memorizing the high temperature shape. Conventionally, the shape is memorized during high temperature annealing, the material being forced, beforehand, to take a certain shape by means of a template. Thereafter, whatever the deformation that the material will undergo in the martensitic state, it will find the memorized form by a simple heating above the martensite-austenite transformation temperature. A big advantage of the technique described above is that it avoids this memorization step preliminary: machining is carried out after annealing, and the memorized shape is directly that machined.

As at the end of the conventional process, the product obtained by the process according to the invention has only the one-way memory effect: if it is deformed in the martensitic state (temperature T <M _S ), it regains its formed by heating above the martensite-austenite transformation temperature (T> A _f ). However, if it is again cooled below M _s , no change in shape occurs. Such a material is suitable for producing a fixing device according to the invention.

So that the memory effect occurs in both directions (for a gripper) one can use a spring, or a weight, which restores the deformation on cooling; it is also possible, according to another technique, to create a particular microstructure of the alloy which makes it possible to select certain variants during transformation. The latter technique is called the "education" technique. The first method is not easy to apply for microscopic devices, since it requires the assembly of several components, and therefore the second method is preferred. Several educational methods can be applied. One of them is pseudoelastic cycling in the austenitic state.

A device will be described, in conjunction with FIG. 9, for carrying out the laser cutting of the material, after annealing. This device essentially comprises an NdrYAG 130 laser, operating in pulse mode. A resonant cavity in "Z" is formed by four mirrors Mi, M ₂ , M ₃ , M ₄ . The beam generated by the laser passes successively a quarter-wave plate 132 and a telescope 133, the latter making it possible to enlarge the beam. With this device, it is possible to obtain light spots of 15 μm in diameter, at the outlet of a cutting head 134. The system is furthermore equipped with a table 136, digitally controlled, with a resolution of the order of μm . This table enables efficient laser cutting (at a speed typically between 30 and 60 mm per minute), and with a light spot of diameter approximately 24 μm, for a material with a thickness of 0.3 mm or less. The area affected by heat, along the cut, is less than 2 to 3 μm in size. The absolute precision and reproducibility, on a surface of 10x10 mm ² , is of the order of 2 μm. The table is controlled by control means 138 and a microcomputer 140. A binocular microscope 142 also makes it possible to control the focusing position of the beam on the table 136.

Devices will now be described, which allow cutting by electroerosion. A first device is illustrated in FIG. 10A and makes it possible to remove material by erosion, by sinking. An electrode 142 having a shape complementary to the desired shape (here: the shape of the gripper to be produced) is inserted into the part 144 to be machined (here: the shape memory material).

So that this electrode can penetrate the part, sparks will locally melt the material: during the bursting of the spark, the electrical energy transformed into heat by the Joule effect, will release enough thermal energy to allow local vaporization of the material. A second device is illustrated in FIG. 10B and relates to wire cutting.

If the principle of material removal is identical to that of sinking, the use of the EDM process in the case of wire is different.

Instead of an electrode which is printed in the part 144, it is a wire 146 (an electrode) which cuts this one. Due to the wear of the electrode, the wire is constantly renewed, using means 148, 150 allowing it to run.

This difference (supply and recovery of the wire) leads to quite different mechanical solutions from the sparking machines. The characteristics of the spark are also specific to the process of wire EDM.

A numerical control makes it possible to control the various axes of the machine (x, Y, U, V) as well as the speed of travel of the wire and the distance between the guides of the wire.

The axes U and V make it possible to identify the inclination of the wire and allow the cutting of non-cylindrical parts. Thanks to this draft angle it is possible to machine adjusted surfaces and therefore very complex parts.

The water jet technique can be carried out with a pure water jet or mixed with an abrasive, focused in a small diameter jet of 0.08 to 0.8 mm at pressures of the order of 3500 to 4000 bars. The jet speed is for example around 600 m / s, thus delivering a large pfd of the order of 120 kW / mm ² . In comparison, that of a 4 kW laser is around 1 kW / mm ² . The addition of abrasive particles by Venturi effect makes it possible to cut very hard and compact materials without thermally modifying the physico-chemical structure of the material. It is also possible to use a combined laser-water jet technique, such as for example described in Industry and Technology, n ° 780, MARCH 1997, pages 9-10.

The methods set out above are suitable for cutting a shape memory material; preferably the chosen method does not disturb the microscopic structure of the material, in any case not beyond a few μm (for example 5 μm or 10 μm) relative to the zone or to the trace of the cut. One means of controlling the structure of the material is electron microscopy, which makes it possible to observe on the μm scale, therefore which makes it possible to observe whether the material is disturbed or not.

EXAMPLE

An example of a gripper embodiment relates to a NiTiCu alloy. The presence of Cu gives a smaller hysteresis, and better stability during thermal cycling. In this alloy, precipitation of Ni does not occur. The alloy is in the form of a blade having a thickness of approximately 300 μm.

The alloy was first annealed for 10 minutes at 450 ° C in an argon controlled oven, and quenched in water at 20 ° C. After quenching, the alloy is in the martensitic state. Processing temperatures as measured by Differential calorimetry are as follows: M _S = 47 ° C, M _f = 31 ° C, A _S = 51 ° C, A _f = 70 ° C.

By cutting the NiTiCu sheet by laser machining, it is then possible to obtain a gripper having the desired shape, for example the ring shape of FIG. 1. The cut shape is the memorized shape. The gripper can then be deformed by means of a conical needle, which is introduced for example into the ring. The increase in the diameter of the ring is such that the deformation is of the order of 1 to 5%. The deformation should preferably not exceed 8%, to avoid irreversible deformation of the alloy. By heating the latter by means of a Peltier effect element, the martensite-austenite transformation occurs, and the alloy recovers the shape it had before deformation, that is to say the shape after laser cutting. If an object is inserted in the ring, the shape memory effect only partially occurs, until the moment when the grip ring comes into contact with the object. Then, the ring generates a force depending on the state of transformation of the material during the austenite-martensite passage. In cooling, the ring does not open in principle: the lens remains stuck in the gripper. In order for the ring to open, we give it a two-way memory effect: one of the ways to obtain this two-way effect is to educate the material. This can be done by opening and closing the ring at a temperature higher than the temperature A _s , repeatedly, for example about ten times. This makes it possible subsequently to obtain spontaneous opening of the ring during cooling. Another type of gripper, or fixing device, is illustrated in FIG. 11. The devices illustrated in the preceding figures include gripping elements working essentially in a single plane. The device of FIGS. 11 et seq. Comprises several gripping elements, each of which can perform a movement in a plane. For example, the device in FIG. 11 comprises three gripping elements 162, 164, 166, each working in a plane Pi, P ₂ , P, the planes making angles of 2π / 3 between them. The assembly is made of a shape memory material, and is in one piece. A support 160 supports the three fingers 162, 164, 166. On each of these fingers, or gripping elements, two grooves or circular necks 162-1, 162-2, 164-1, 164-2, 166 are produced. 1, 166-2 which facilitate the inclination or the bending of each finger in the corresponding plane.

A hole, or an opening, 168 can be made in the base 160, this hole or this opening allowing the passage of a light beam, or of a sensor, or of means making it possible to control the opening and / or closing the gripping or fixing device. Such means can be, as already described above, a Peltier element, or a laser beam, or the circulation of a current (either directly, in the shape memory material, or in one or more resistors mounted or glued on the gripping or fixing device). Furthermore, such a device can be used in conjunction with a control device of the type already described above in conjunction with FIG. 4. The diameter of the base 160 of the gripper of FIG. 11 can be of the order of a few millimeters (for example: 2 mm) or of the order of a millimeter or less than 1 mm (for example: 500 μm). The thickness 1 ₂ of each gripping element can be, in the region of the groove 162-1, between for example 10 μm and 100 μm.

The machining of such a device can be done by electro-erosion technique, in several passes. This technique has already been described above. We start, for example, from a rod made of a shape memory material, which is cut to the desired length, then in which we release, by successive passes, the different fingers or gripping elements 162, 164, 166. Then , in successive stages, the grooves 162-1, .... 166-2 are produced.

The presence of two grooves 162-1, 162-2 allows each finger to be bent or to flex in two places. It is also possible to make three or more grooves, or a single groove, or no groove at all, depending on the degree of flexibility required.

Another embodiment is illustrated in Figures 12A and 12B. It is a gripper carrying three fingers 182, 184, 186, produced in a plane, also in a shape memory material. A cutting device, for example by laser, makes it possible to release three fingers 182, 184, 186 and an area 180 which serves as a support. It is also possible, as illustrated in FIG. 12A, to make recesses 182-1, 182-2, ... 186-2, 187. Zones 188, 190 make it possible to establish electrical contact with a device for food. An electric current, circulating in the different fingers, allows them to be heated by the Joule effect and to obtain the appropriate bending of the elements 182, 184, 186 in shape memory material. The openings 182-1, 182-2, .... 187 make it possible to limit the passage of the current. However, the device can also operate without these openings. Furthermore, when the openings are made, the lateral thicknesses ei, e ₂ of each of the fingers of the gripper can be equal or different: the production of different thicknesses results in a different transformation of the right and left parts of the element of corresponding grip when the current flows. Heating can also be carried out by other methods, for example by laser or induction or by Peltier element.

Once produced in a planar form, the gripper can be constrained, for example around a tube or a cylinder 192 of diameter d (FIG. 12B): in this case, we choose to produce the initial system, in its form plane, with a length Li (FIG. 12A) such that Lι <π.d. Each finger 182, 184, 186 can then work in bending in a plane. In the embodiments illustrated in FIG. 12B, each of the three bending planes P'i, P ' ₂ , P' ₃ forms with the other two an angle of 2π / 3. Such a system can advantageously be used on an endoscope or a catheter.

A gripping or fixing device as just described can be used for the implementation of a method of handling an object. In the medical field, the shape memory grippers according to the invention make it possible either to fix an implant (of orthopedic, cardiac, neurosurgical type or relating to other parts of the human body), or to release an implant at a precise location of the body ("coil", "stent" or others), or finally to make surgical micro-instruments (scissors, conventional forceps or foreign body or biopsy). It is also possible, using the fixing device, to make surgical staples (for sutures) or "clips" (forceps or hemostatic forceps). We can use a clip for example to block blood in an artery by pinching it.

The grippers are reproducible, and also very small (less than 0.5 mm or 0.7 mm). It is therefore possible to produce medical or surgical instruments having the same characteristics, in particular of size, which is impossible to obtain by the conventional micromechanical technique (using micro-hinges).

A first example of application in the medical field is illustrated in FIGS. 13A and 13C. In FIG. 13A, a micro-gripper 202, of the type of shape memory grippers according to the invention, already described above, is introduced into a catheter 200. The micro-gripper 202 can grasp and hold a spring 204. The assembly can for example be placed inside an artery. The micro-gripper 202 is fixed to a metal guide 203.

Once the system is in place, and the spring 204 positioned at the desired location in the artery, this the latter is released by the opening of the micro-gripper 202.

Figure 14 shows another application, to biopsy forceps, which allow to take tissue in order to analyze it. These clamps are composed of two cups 206 which move at the end of a tube 207. According to the invention, a clamp can be produced using a shape memory gripping device. It is thus possible to carry out a small biopsy forceps.

FIG. 15 illustrates another application of the invention, in the medical field. A micro-gripper 212, according to the invention, makes it possible to bring a dilator, or "stent" 214 (or a "coil", FIGS. 13A, 13B, 13C) to a desired location, for example inside a 'an artery or ureter. The dilator 214 makes it possible to exert a mechanical force opposing the contraction of the wall 210 of the duct of the artery or of the ureter. Once the dilator is in place, the gripper 212 is actuated to open, and is extracted from the conduit into which it is introduced. This technique can be used for example after dilation of a stenosated artery by an atheroma plaque. Thus, a micro-gripper according to the invention makes it possible to produce "stents" of very small dimensions.

In the examples given above, the gripper can be controlled by laser heating (via an optical fiber) or by the circulation of a current. Another example of application of a device according to the invention relates to the field of making connections or connectors, for example electrical or optical. An exemplary embodiment of a connector is illustrated in FIG. 16. The connector has a male part 216, which can for example be an optical fiber or the metallic male part of an electrical connector. The female part 218 comprises two lips 220, 222, which are in fact the gripping elements of a gripping or fixing device according to the invention, as already described above. The female part is controlled to open and / or close by one of the means already described above. The male part 216 is introduced into the female part 218, the gripping elements 220, 222 are actuated on closing and therefore provide contact between the male part and the female part. The gripper or the fixing device forming the female part can itself be connected to other metallic or optical elements.

Claims

1. Gripping or fixing device (2, 22) comprising first and second gripping elements (4, 6, 102, 104) capable of undergoing a relative movement relative to each other, all of the first and second elements being made of a one-piece material with shape memory.

2. Gripping or fixing device according to claim 1, the amplitude of the relative movement of the two elements being at most equal to 10 mm.

3. Gripping or fixing device according to one of claims 1 or 2, obtained by cutting in the plane of a blade (120) of shape memory material, the relative movement taking place in this plane. . Gripping or fixing device according to one of claims 1 to 3, further comprising means (8, 10) for handling all of the first and second elements. 5. Gripping or fixing device according to claim 4, the means for handling the assembly of the first and second elements constituting with them a one-piece assembly.

6. gripping or fixing device according to claim 4 or 5, the handling means being connected to means (15, 17, 20) for controlling the temperature of the first and second elements of the gripping device.

7. Device according to claim 6, the means (15, 17, 20) for controlling the temperature comprising a Peltier element, or a laser or means for inducing a current in the shape memory material or means ( 15, 17) to do flow a current through the shape memory material.

8. Device according to claim 6 or 7 further comprising control means (26) control means (15, 17, 20) of the temperature of the first and second elements and control means (30, 32, 36) visual of the relative position of the first and second elements of the gripping device.

9. Gripping or fixing device according to one of the preceding claims, the amplitude of the relative movement of the first and second elements relative to each other being less than 500 microns.

10. Gripping or fixing device according to one of the preceding claims, the amplitude of the relative movement of the first and second elements relative to each other being less than 100 microns.

11. Device according to one of claims 1 to 11, the material being with a double sense memory effect or having undergone an education process making it possible to obtain the double sense memory effect.

12. Gripping or fixing device (158, 178) comprising at least three gripping elements (162, 164, 166, 182, 184, 186) each capable of undergoing a movement of bending in a plane, all the elements of gripping being made in a single piece, in a shape memory material.

13. Device according to claim 12, further comprising an element (160, 180) for supporting the gripping elements. 14. Device according to claim 12 or 13, the gripping elements having the shape of a finger.

15. Device according to claim 14, one or more finger (s) being provided (s) with one or more recess (s) of bending (162-1, ..., 166-2).

16. Device according to one of claims 12 to 14, obtained by cutting in the plane of a blade of shape memory material, then by stressing the plane.

17. Device according to one of claims 12 to 14, further comprising means for controlling the temperature of the gripping elements.

18. Device according to claim 17, the temperature control means comprising a Peltier element, or a laser or means for inducing a current in the shape memory material or means (188, 190) for circulating a current in the shape memory material.

19. Device according to claim 18, further comprising means for controlling the temperature of the gripping elements. 20. Device according to claim 19, further comprising means for visual control of the gripping elements.

21. A handling device comprising a gripping or fixing device (202) according to one of claims 1 to 20 and a catheter (200) into which it can be inserted.

22. Biopsy forceps device (206) comprising a gripping device according to one of claims 1 to 20. 23. Clip or clamp, in particular surgical, comprising a device according to one of claims 1 to 20.

24. Connection device (218) comprising a male part (216) and a female part (218), the latter comprising a device according to one of claims 1 to 20. 25. Method for preparing an element made of a material shape memory comprising the following steps: a) annealing a shape memory material from a substrate (120), then b) cutting the element (125, 127, 129) in the substrate.

26. The method of claim 25, the cutting being carried out so as not to disturb the microscopic structure of the material of the substrate obtained after annealing.

27. The method of claim 25 or 26, the cutting being carried out so as not to disturb the microscopic structure of the substrate material on more than 5 microns beyond the cutting. 28. Method according to one of claims 25 to

27, the cutting of the element in the substrate being carried out by laser.

29. Method according to one of claims 23 to 27, the cutting of the element in the substrate being carried out by electroerosion.

30. Method according to one of claims 23 to 27, the cutting of the element in the substrate being carried out by water jet.

31. A method of handling an object comprising gripping and transporting the object using a device according to one of claims 1 to 20.

32. The method of claim 31, the object being a (24, 60) microlens or an optical fiber.

33. Method for producing an assembly of a multicore fiber (52), or of a multifiber, with a lens (60), comprising:

the displacement and positioning of the lens facing an end of the fiber, in accordance with the method according to claim 32,

- the fixing of the lens on the end of the fiber.

34. The method of claim 31, the object being a device for obstructing an artery.

35. The method of claim 34, the device being a coil spring (204). 36. Process for removing tissue comprising:

- a step of introducing a gripping device according to one of claims 1 to 20, at the place where this tissue is to be removed, - a step of removing the tissue using this gripping device.

37. A method of expanding a conduit (210) comprising:

a step of introducing and positioning a dilator (214) at the place where the duct is to be expanded, using a gripping device according to one of claims 1 to 20,

- A step of opening the gripping device after positioning the dilator (214).