EP2526468A2

EP2526468A2 - Fluidic actuator and display device having fluidic actuators

Info

Publication number: EP2526468A2
Application number: EP10809018A
Authority: EP
Inventors: Samuel Roselier; Gwénaël CHANGEON; José LOZADA
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2010-01-18
Filing date: 2010-12-14
Publication date: 2012-11-28
Also published as: FR2955404A1; CN102859468A; WO2011086257A2; US20120299905A1; WO2011086257A3; FR2955404B1; US9086728B2

Abstract

The fluidic actuator (12) according to the invention comprises a chamber (32B) filled with a fluid, an element (36) that is movable relative to the chamber (32B) and in contact with the fluid, as well as a passage (44) for circulating the fluid between the inside and the outside of the chamber (32B) so as to vary the quantity of fluid in the chamber and thus cause movement of the movable element (36). The fluid is magneto-rheological and the fluidic actuator (12) comprises magnetic field generation means (26, 28) arranged so as to generate, within the passage (44), a controlled magnetic field.

Description

Fluidic actuator and fluidic actuator display

The present invention relates to a fluid actuator. It also relates to a display device comprising a plurality of fluidic actuators.

More specifically, the invention relates to a fluidic actuator comprising a chamber filled with a fluid, a member movable relative to the chamber and in contact with the fluid, and a fluid circulation passage between the interior and the fluid. outside the chamber to vary the amount of fluid in the chamber and thereby cause the displacement of the movable member.

Such a fluidic actuator is used in particular in two-dimensional display devices with a deformable screen, such as that described in the patent published under the number US 5,222,895. The mechanism implemented in this document is based on the electro-rheological properties of the fluid used. A fluidic valve is formed by the arrangement of electrodes around a fluid circulation passage, closing the passage by increasing the apparent viscosity of the fluid when these electrodes are sufficiently supplied with current. Thus, by opening or closing the passage, the movement of the movable element is allowed or blocked to change or maintain a distortion of the display screen.

This technology requires a significant power of the electrodes when it is desired to close the passage, that is to say when it is desired to maintain a certain distortion of the display screen. It thus becomes essential, for reasons of safety, to provide good electrical insulation between the inside of the actuator and the outer surface of the display device. Finally, it is observed that the energization of the electrodes must be maintained as long as it is desired to block the passage, in other words as long as it is desired to maintain the fluidic valve in the closed position, which implies a certain amount of consumption. 'energy.

A fluidic actuator using the same technology is also described in US Patent No. 5,496,174.

This type of actuator can in particular be used for the design of a display device with a deformable surface, such as for example an information display screen for blind persons in braille or the like, a plurality of actuators then being distributed on the surface of the display screen. Various forms can thus be displayed on the screen in a reconfigurable manner. Achieving this type of screen requires low cost actuators and simple assembly methods to maintain a reasonable manufacturing price. Indeed, a touch interface of size 32 cm x 24 cm having a resolution of 1 mm has 76,800 actuators to operate independently or in groups. In addition, many actuators may have to be activated simultaneously, which poses problems of energy consumption. With the technology proposed in the aforementioned documents, the energy consumption is not optimized.

Other technologies may be envisaged for the manufacture of actuators to be integrated into a deformable surface display device, but they generally do not provide a satisfactory solution in terms of either the complexity of the structure, or the power consumption, or both. Thus, pneumatic actuators are known, but the design of the valves and the connections are complex. Piezoelectric bimetallic actuators are also known, but these are very expensive. They are also very bulky. Solutions based on shape memory alloy wires are also known, but the actuation is done by thermal transfer and the wire must be kept at a predetermined temperature, which consumes a lot of energy. It is the same for the solutions using the thermal expansion of materials to inflate a cavity: it is necessary to maintain a certain temperature in the cavity. Moreover, the response time of each actuator depends on the cooling time of the active elements which considerably limits the dynamic performance of the system.

It may thus be desirable to provide a fluidic actuator that makes it possible to overcome at least some of the aforementioned problems and constraints.

The subject of the invention is therefore a fluidic actuator comprising a chamber filled with a fluid, a member movable with respect to the chamber and in contact with the fluid, a fluid circulation passage between the inside and the outside of the chamber. chamber for varying the amount of fluid in the chamber and thereby causing displacement of the movable member, wherein the fluid is magneto-rheological and wherein the fluidic actuator comprises magnetic field generation means arranged to generate, in the passage, a controlled magnetic field.

A magneto-rheological fluid comprises ferromagnetic particles suspended in a liquid solvent. Under the action of a magnetic field, these particles form chains of resistance to the breakage proportional to the intensity of the field. The apparent viscosity of the magneto-rheological fluid is thus modified. It is then possible to control the flow of the fluid in the passage in which a controlled magnetic field is generated.

The design of such an actuator is very simple and requires few moving mechanical parts, which provides a robust mechanism. In addition, a lower supply voltage than the electro-rheological fluids is sufficient. Finally, the problem of electrical insulation between the inside of the actuator and the outer surface of the device is less sensitive in the presence of a magnetic field than when an electric field is generated.

Optionally, a fluidic actuator according to the invention, in which the magnetic field generation means comprise an electromagnet, may comprise a device for supplying electric current to the electromagnet designed to:

temporarily supplying, to a coil of the electromagnet, an electric current of sufficiently high intensity to generate a magnetic saturation field of magnetizable elements of the actuator, generating a remanent magnetic field remaining after the supply of the electric current and whose intensity is sufficient to maintain the closed passage by action on the viscosity of the magnetorheological fluid located in the passage,

temporarily supplying, to the coil of the electromagnet, a coercive excitation of demagnetization of the magnetizable elements of the actuator by canceling the remanent magnetic field.

In this case, only the moments when it is desired to open and close the passage to cause movement of the movable element require consuming electrical energy, which makes the actuator particularly energy-efficient.

Optionally also, a fluidic actuator according to the invention may further comprise a permanent magnet generator, in the passage, a permanent magnetic field whose intensity is sufficient to maintain the closed passage by action on the viscosity of the magnetoid fluid rheological located in the passage, and the magnetic field generating means can be configured so that the controlled magnetic field at least partially compensates for the effect of the permanent magnetic field, when activated. In this case, only the moments when it is desired to open the passage to cause movement of the movable element require consuming energy, which also makes the actuator energy-hungry.

Optionally also, a fluidic actuator according to the invention may comprise two electromagnets arranged on either side of the permanent magnet so as to channel, between the two electromagnets, the permanent magnetic field generated by the permanent magnet when the two electromagnets are electrically powered.

Optionally also, a fluidic actuator according to the invention may comprise a plate provided with a conduit passing through and forming one of the walls of the chamber, the movable element comprising a piston movable in the conduit.

Optionally also, a fluidic actuator according to the invention may comprise a plate provided with a through conduit and forming one of the walls of the chamber, the movable element comprising a deformable membrane hermetically fixed on a surface of the opposite plate. inside the chamber, the membrane covering the conduit.

The invention also relates to a deformable surface display device comprising a plurality of fluid actuators such as that defined above, the movable elements of which are distributed, in particular regularly matrix, on the deformable surface.

Optionally, a display device according to the invention may comprise a display screen comprising a plate, this plate being provided with a plurality of through ducts vis-à-vis which are arranged chambers filled with magneto fluid rheological fluidic actuators.

Also optionally, a display device according to the invention may comprise a network of common supply lines chambers fluidic actuators magneto-rheological fluid under an adjustable pressure.

Also optionally, a display device according to the invention may comprise an electronic control circuit of each individual magnetic field generation means of each fluidic actuator and common control of the pressure of the magneto-rheological fluid in the pipes of the common network.

The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings in which: FIG. 1 schematically represents a fluidic actuator according to a first embodiment of the invention,

FIGS. 2 to 5 represent the fluidic actuator of FIG. 1 in several operating situations,

FIG. 6 schematically represents a fluidic actuator according to a second embodiment of the invention,

FIG. 7 is a diagrammatic perspective view of a deformable surface display device according to one embodiment of the invention;

FIG. 8 represents a detail of a part of the display device of FIG. 7,

FIG. 9 diagrammatically shows in perspective the display device of FIG. 7 when it is mounted, and

- Figure 10 shows schematically in perspective a portable device provided with a deformable surface display device according to one embodiment of the invention.

The fluidic actuator 12 shown in FIG. 1 comprises an enclosure 14 designed in a material capable of guiding magnetic field lines, for example iron or steel, or more generally a soft ferromagnetic material. This enclosure 14 comprises for example a circular solid base 16, a cylindrical side wall 18 and a circular full upper plate 20 pierced with a through hole 22 centered on the longitudinal axis of symmetry D of the cylindrical side wall 18.

In one embodiment of the invention, within the enclosure 14 a cylindrical permanent magnet 24 is disposed on the base 16, centered around the axis D. Its radius is significantly smaller than the inner radius of the wall cylindrical side 18. On this permanent magnet 24 is disposed a central cylindrical core 26 of the same radius, also centered about the axis D and extending along this axis to a certain height H inside the enclosure 14. This central core 26 is for example also made of iron or steel, more generally of a soft ferromagnetic material, so as to guide field lines in a direction parallel to the axis D.

Around the central core 26, a coil 28 extends between the outer surface of the central core and the inner surface of the side wall 18, without however reach the latter. The coil 28 is made of an electrically conductive yarn wound around the central core 26 to form therewith an electromagnet.

Thus, the permanent magnet 24 generates a first permanent magnetic field B1 whose field lines can be guided by the central core 26, the upper plate 20, the side wall 18 and the base 16, while the electromagnet 26 , 28 is capable of generating, on electrical control, a second controlled magnetic field B2 whose field lines can also be guided by the central core 26, the upper plate 20, the side wall 18 and the base 16.

The height H which extends from the base 16 to the free upper face of the central core 26 inside the enclosure 14 defines a first interior volume 30, in which there is the permanent magnet 24, the core central 26 and the coil 28, filled with a dielectric medium. Beyond this height H, in a reserve 32 whose volume is complementary to the first internal volume 30 in the overall volume of the chamber 14, the latter is filled with a magneto-rheological fluid.

The magneto-rheological fluid is introduced under an adjustable pressure into the reserve 32 by a duct 34 pierced in the side wall 18 beyond the height H. Finally, despite the presence of the through hole 22 in the upper plate 20, the reserve 32 is isolated from the outside of the enclosure 14 by the hermetic disposition of a movable element on the through hole 22, this movable element thus being in contact with the magneto-rheological fluid of the reserve 32.

More specifically, in the embodiment illustrated in Figure 1, the movable member is a deformable membrane 36 hermetically fixed on the outer surface 38 of the upper plate 20 opposite to the inside of the chamber 14. This deformable membrane 36 covers the through hole 22. It is for example a thin elastic membrane, such as a nitrile membrane, both flexible and resistant to corrosion caused by the magneto-rheological fluid.

The dielectric medium filling the first interior volume 30 of the enclosure 14 is for example a resin or glue that drowns the permanent magnet 24, the central core 26 and the coil 28. It can also be simply air but in this case a rigid and hermetic separation 40 must be provided between the first internal volume 30 and the reserve 32. This separation 40 may consist of a plastic or aluminum membrane, more generally of a membrane made of a rigid material and not driving the magnetic field. The dielectric medium filling the first interior volume 30 may also be magneto fluid rheological. In this case there is no separation between the reserve 32 and the first interior volume 30.

As illustrated in FIG. 2, the field lines 42 generated by the field B1 or B2 are guided by the central core 26, the upper plate 20, the side wall 18 and the base 16. In this course of the field lines , an annular air gap 44 is defined between the upper plate 20 and the upper face of the central core 26, the radius of the through hole 22 being smaller than the radius of the central core 26.

This gap 44 constitutes a circulation passage of the magneto-rheological fluid in the reserve 32, between a first fluid supply chamber 32A via the duct 34 and a second chamber 32B for actuating the deformable membrane 36. The second chamber 32B is thus delimited by the upper plate 20, the deformable membrane 36, the gap 44 and the upper face of the central core 26. The magnetorheological fluid it contains is in contact with the deformable membrane 36 and can therefore deform more or less this last according to its volume. As will now be detailed with reference to Figure 2, but also to Figures 3, 4 and 5, the volume of fluid in the second chamber 32B is indeed adjustable under the effect of the fields B1 and / or B2 and the fluid supply pressure in the supply 32 through the duct 34.

In the embodiment illustrated in FIGS. 1 to 5, the presence of the permanent magnet 24 ensures by default the presence of a permanent magnetic field B1 of sufficient intensity to block the flow of magnetorheological fluid in the passage / gap 44.

Thus, as illustrated in FIG. 2, during a first step, the volume of fluid in the second chamber 32B is by default kept constant so that the deformable membrane is maintained in a first position of constant deformation without any consumption of energy. electric energy.

Of course, the permanent magnet 24 is not essential to the embodiment of the invention, the blocking and unblocking of the passage 44 can be completely managed by the electromagnet 26, 28, but thanks to its presence a quantity Substantial electrical energy is saved since it is consumed only during changes in deformation of the deformable membrane 36.

As illustrated in FIG. 3, during a second step, a pressure greater than the pressure in the second chamber 32B is provided at the inlet (ie at the duct 34) of the first chamber 32A and an electric intensity crosses the coil 28 so as to generate a controlled magnetic field B2 whose effect compensates at least partially, preferably completely, the effect of the permanent magnetic field B1 in the passage 44. Thanks to the controlled magnetic field B2 compensating the field B1, the passage 44 opens to the flow of magneto-rheological fluid and thanks to the overpressure provided at the duct 34, the flow is from the first chamber 32A to the second chamber 32B. As a result, the deformable membrane 36 deforms to a second high position. Specifically, the magnetic field B2 causes the channeling of the field lines B1 between the base of the electromagnet 26, 28 and the base 16 of the enclosure 14.

As illustrated in Figure 4, in a third step, the coil 28 is no longer supplied with current so that the passage 44 is closed. The deformable membrane 36 is thus maintained, without electrical consumption, in its second high position.

Finally, as illustrated in FIG. 5, during a fourth step, a pressure lower than the pressure in the second chamber 32B is provided at the inlet (ie at the duct 34) of the first chamber 32A and an electric intensity is supplied. in the coil 28 so as to generate a controlled magnetic field B2 whose effect compensates for the effect of the permanent magnetic field B1 in the passage 44. Thanks to the controlled magnetic field B2 compensating the field B1, the passage 44 opens again at the flow of magneto-rheological fluid and thanks to the depression provided at the duct 34, the flow is from the second chamber 32B to the first chamber 32A. As a result, the deformable membrane 36 deforms to its first position or to a third lower position. Again, the magnetic field B2 causes at this stage the channeling of the field lines B1 between the base of the electromagnet 26, 28 and the base 16 of the enclosure 14.

Sequentially, this fourth step can be executed as follows: the passage 44 is first opened by compensation of the magnetic field B1 by the magnetic field B2; then the input pressure 34 of the first chamber 32A is gradually lowered to reduce deformation of the deformable membrane 36 in a controlled manner.

In the absence of permanent magnet 24, as indicated above, the blocking and unblocking of the passage 44 can be completely managed by the electromagnet 26, 28. In this case, in order not to need to consume electrical energy continuously as long as it is desired to maintain the passage 44 closed, the following protocol, using the remanence properties of a magnetic field, can be implemented to close and open passage 44:

- Temporary supply, to the coil 28, of an electric current of sufficiently high intensity to generate a magnetic field of saturation of the magnetizable elements of the actuator, generating a remanent magnetic field remaining after the supply of electric current and the intensity is sufficient to maintain the passage 44 closed, - temporary supply to the coil 28, a coercive excitation of demagnetization of the magnetizable elements of the actuator by canceling the remanent magnetic field.

The coercive demagnetization excitation may for example consist in the supply of an electric current of direction opposite to that which is provided to close the passage or of a sinusoidal alternating electric current damped logarithmically.

Thus, thanks to this protocol, a substantial amount of electrical energy is saved since it is consumed only during the opening and closing commands of the passage 44. This protocol is implemented by a power device electric current (not shown) electrically connected to the coil 28.

According to another possible embodiment of the invention, the fluidic actuator 12 'shown in FIG. 6 differs from the actuator 12 previously described in two aspects. Note that these two aspects are independent of each other so that they could be the subject of separate embodiments, but only one embodiment including these two aspects will now be described for the sake of brevity.

Firstly, the deformable membrane 36 is replaced by a piston 36 'that is hermetically displaceable in the through hole 22 of the upper plate 20, as a movable element of the actuator 12'.

Then, the actuator 12 'comprises two electromagnets 26A, 28A and 26B, 28B disposed on either side of the permanent magnet 24 so as to channel between these two electromagnets 26A, 28A and 26B, 28B , the permanent magnetic field B1 generated by the permanent magnet 24 when the two electromagnets are electrically powered. Specifically, inside the chamber 14, a central cylindrical core 26A is disposed on the base 16, centered around the axis D. Its radius is significantly smaller than the inner radius of the cylindrical side wall 18. This central core 26A is for example made of iron or steel, more generally of a soft ferromagnetic material, so as to guide field lines in a direction parallel to the axis D. Around this central core 26A, a coil 28A is extends between the outer surface of the central core 26A and the inner surface of the side wall 18, without reaching the latter. The coil 28A consists of an electrically conductive yarn wound around the central core 26A to form therewith a first electromagnet 26A, 28A.

On this first electromagnet 26A, 28A is disposed the cylindrical permanent magnet 24 of the same radius as the central core 26A, also centered around the axis D.

On the permanent magnet 24 is disposed another cylindrical central core 26B of the same radius, also centered around the axis D and extending along this axis to the height H defined previously inside the enclosure 14. This central core 26B is for example, like the central core 26A, made of iron or steel, more generally of a soft ferromagnetic material, so as to guide field lines in a direction parallel to the axis D. Around this central core 26B, a coil 28B extends between the outer surface of the central core 26B and the inner surface of the side wall 18, without reaching the latter. The coil 28B consists of an electrically conductive yarn wound around the central core 26B to form therewith the second electromagnet 26B, 28B.

Thus, the permanent magnet 24 generates the permanent magnetic field B1 whose field lines can be guided by the central cores 26A and 26B, the upper plate 20, the side wall 18 and the base 16, while the electromagnets 26A, 28A and 26B, 28B are capable of generating, on electrical control, controlled magnetic fields B2A and B2B whose field lines can also be guided by the central cores 26A and 26B, the upper plate 20, the side wall 18 and the base 16. In this second embodiment, it can be expected that the field lines are better channeled, between the two electromagnets when they are supplied with current, than in the first embodiment. From an actuator such as one of those described above, it is possible to design a deformable surface display device comprising a plurality of such actuators whose movable elements are distributed over the deformable surface. These mobile elements are for example regularly distributed in a matrix manner on the deformable surface of the display device.

A display device 50 made from actuators such as that of FIG. 1 is for example illustrated in exploded perspective in FIG. 7. It is mounted for example according to a multi-layer design (which is one of the possible methods matrix assembly) by assembling the following elements:

a first rectangular plate 52 made of iron or steel, more generally a soft ferromagnetic material so as to guide magnetic field lines, forming all of the bases 16 of the actuators of the display device 50,

a rectangular frame 54 pierced with through-hole cylindrical holes, made of iron or steel, more generally of a soft ferromagnetic material so as to guide magnetic field lines, forming all of the side walls 18 of the actuators of the device; 50 display,

a second rectangular plate 56, made of iron or steel, more generally of a soft ferromagnetic material so as to guide magnetic field lines, forming all of the upper plates 20 of the actuators of the display device 50,

a rectangular deformable membrane 58 placed on the outer face opposite to the frame 54 of the second rectangular plate 56, and a third rectangular plate 60 whose function is to keep the display device 50 assembled and to hold the membrane hermetically under pressure deformable 58 against the second rectangular plate 56, while allowing this membrane to locally deform through holes regularly arranged in a matrix manner on the third plate 60 vis-à-vis the chambers in the cylindrical holes through the chassis 54 .

More specifically, the third rectangular plate 60 is for example provided with rods regularly disposed on its surface and intended to pass through corresponding holes formed in the plates 52, 56, the frame 54 and the membrane 58 for holding the assembly under pressure. . Holding under pressure can be ensured by screwing when for example at least a portion of the rods is threaded and that the dimensions of the device allow, or by any other conventional technique appropriate to the scope of those skilled in the art.

In this embodiment, the hermetic pressure hold of the membrane 58 between the second and third plates 56 and 60, as well as the possible local deformation of this membrane 58 through each hole of the third plate 60 ensures both the sealing of the actuators and the presence of movable elements in contact with the magneto-rheological fluid of each actuator.

It will be noted that inside each through-hole drilled in the frame 54 are disposed a permanent magnet 24, a central core 26 and a coil 28 to form the corresponding actuator.

Figure 8 shows a detail of the frame 54 in a view from below. It illustrates an embodiment of a network 62 of common supply lines of the actuator chambers magneto-rheological fluid under a predetermined adjustable pressure.

This network 62 of pipes is dug in the bottom of the frame 54 and feeds each actuator chamber arranged in each through-hole drilled in the frame 54 magneto-rheological fluid. It is connected to lateral ducts 64 drilled on the edges of the frame 54 for the supply of magneto-rheological fluid under pressure.

Figure 9 shows the display device 50 of Figure 7 in mounted position. Thanks to the technology used for the actuators, a compact device can be obtained, in particular of thickness less than 5 mm. In addition, due to the low number of moving mechanical parts, the device is reliable.

Note that, although this display device and some elements that compose it have been presented as having a rectangular shape, it can more generally be of any shape.

Finally, FIG. 10 schematically shows a portable device 70 provided with a deformable surface display device such as that (50) of FIG. 9. The portable device 70, which is by extension itself a device of FIG. display, is for example a telecommunication device, a personal digital assistance device or any other portable electronic device. In this case, an electronic control circuit 72 for the display device 50, associated with it, can also be integrated into the portable device 70. More specifically, this electronic circuit 72 is designed to individually control each electromagnet 26, 28 of each fluid actuator 12 and to jointly control the pressure of the magnetorheological fluid in the pipes of the common network 62. An almost infinite number of configurations of the deformable surface and therefore of the shapes on the screen of the portable device 70 can thus be obtained by playing on the differentiated supply of the electromagnets and on the pressure of the magnetorheological fluid used to modify the position of the mobile element ( deformable membrane or piston) of each actuator, between a high position (maximum local deformation of the surface) and a low position (for example, locally flat surface), passing through all the intermediate positions between these two extreme positions.

As is moreover illustrated by way of nonlimiting example, the plan of a geographical area can thus be represented in relief on the deformable surface of the portable device 70, with for example its routes 74, its selected routes 76, its structural elements such as buildings 78, a current position indicator 80 and a destination position indicator 82.

Other applications are obviously conceivable such as the dynamic display of touch buttons according to the evolution of a contextual menu or the display of images, videos in relief. These applications can be considered in public display contexts, disabled accessibility, Braille screen, human-machine interfaces in the automotive sector, etc.

It clearly appears that an actuator such as one of those described above is of simple design and reduced energy consumption. Its integration into a deformable surface display device is therefore advantageous.

Note also that the invention is not limited to the embodiments described above. It will be apparent to those skilled in the art that various modifications can be made to the embodiments described above, in the light of the teaching just disclosed. In particular, the electromagnets described above can be replaced by other equivalent technical means, that is to say capable like them of generating on command a non-permanent magnetic field.

In the following claims, the terms used are not to be construed as limiting the claims to the embodiments set forth in this specification, but should be interpreted to include all the equivalents that the claims are intended to cover because of their formulation and whose forecasting is within the reach of those skilled in the art by applying his general knowledge to the implementation of the teaching that has just been disclosed to him.

Claims

1. Fluidic actuator (12; 12 ') having a chamber (32B) filled with a fluid, a movable member (36; 36') with respect to the chamber (32B) and in contact with the fluid, a passage (44) of fluid circulation between the inside and the outside of the chamber (32B) to vary the amount of fluid in the chamber and thereby cause the displacement of the movable member (36; 36 '), characterized in that the fluid is magneto-rheological and in that the fluidic actuator (12; 12 ') has magnetic field generation means (26, 28; 26A, 26B, 28A, 28B) arranged to generate, in the passageway (44), a controlled magnetic field.

The fluidic actuator (12) according to claim 1, wherein the magnetic field generating means comprises an electromagnet, having an electric power supply device of the electromagnet (26, 28) adapted for:

temporarily supplying, to a coil (28) of the electromagnet, an electric current of sufficiently high intensity to generate a magnetic saturation field of magnetizable elements of the actuator, generating a remanent magnetic field remaining after supplying the electric current and of sufficient intensity to maintain the passage (44) closed by acting on the viscosity of the magnetorheological fluid located in the passage, temporarily supplying the coil (28) of the electromagnet, a coercive excitation of demagnetization of the magnetizable elements of the actuator by canceling the remanent magnetic field.

3. fluid actuator (12; 12 ') according to claim 1, further comprising a permanent magnet (24) generator, in the passage (44), a permanent magnetic field whose intensity is sufficient to maintain the passage ( 44) closed by action on the viscosity of the magneto-rheological fluid located in the passage, and wherein the magnetic field generation means (26, 28; 26A, 26B, 28A, 28B) are configured so that the controlled magnetic field compensates for the less partially the effect of the permanent magnetic field, when activated.

4. fluidic actuator (12 ') according to claim 3, comprising two electromagnets (26A, 26B, 28A, 28B) disposed on either side of the permanent magnet (24) so as to channel between the two. electromagnets (26A, 26B, 28A, 28B), the permanent magnetic field generated by the permanent magnet (24) when the two electromagnets (26A, 26B, 28A, 28B) are electrically powered.

5. fluid actuator (12; 12 ') according to any one of claims 1 to 4, comprising a plate (20) provided with a through conduit (22) and forming one of the walls of the chamber (32B), and wherein the movable member (36 ') has a displaceable piston in the conduit.

6. fluidic actuator (12; 12 ') according to any one of claims 1 to 4, comprising a plate (20) provided with a through conduit (22) and forming one of the walls of the chamber (32B), and wherein the movable member (36) has a deformable membrane sealably attached to a surface of the opposed plate within the chamber, the membrane covering the conduit (22).

7. A display device (50, 70) with a deformable surface comprising a plurality of fluid actuators (12; 12 ') according to any one of claims 1 to 6, the movable elements (36; 36') are distributed , particularly regularly in a matrix manner, on the deformable surface.

A deformable surface display (50, 70) as claimed in claim 7 including a display screen (58, 60) comprising a plate (60), which plate is provided with a plurality of screw-through through ducts. to which the chambers (32B) filled with magneto-rheological fluid of the fluid actuators (12; 12 ') are arranged.

The deformable surface display device (50, 70) according to claim 7 or 8, comprising a network (62) of common chamber supply lines (32B) of the fluidic actuators in magneto-rheological fluid under an adjustable pressure.

The deformable surface display device (50, 70) according to claim 9, comprising an electronic control circuit (72) for individual control of each of the magnetic field generating means (26, 28; 26A, 26B, 28A, 28B). ) of each fluidic actuator (12; 12 ') and common control of the pressure of the magneto-rheological fluid in the pipes of the common network (62).