Electromechanical microsystem for moving a mechanical part in two opposite directions

Description

DOMAINE DE L'INVENTION

[0001] The invention relates to the field of microelectromechanical systems. ETAT DE LA TECHNIQUE

[0002] Microelectromechanical systems (or MEMS) are miniature mechanical systems manufactured by etching from a semiconductor material. These microsystems include mechanical parts with micrometric dimensions and use electricity as a power source to operate.

[0003] Document FR 2 874 907 describes, for example, a drive device formed by etching in a wafer of semiconductor material, such as, for example, silicon. The drive device comprises a drive tooth capable of sequentially meshing with a toothed wheel, and an actuator composed of a first elementary module capable of moving the drive tooth in a first direction (radial direction) and a second elementary module capable of moving the tooth in a second direction (tangential direction) relative to the toothed wheel. The first elementary module and the second elementary module are electrostatic modules having an interdigitated comb structure.

[0004] The first elementary module and the second elementary module are controlled by means of phase-shifted alternating addressing signals, so as to move the drive tooth in a cyclical movement with a hysteresis trajectory. During this cyclical movement, the drive tooth alternates between drive phases and disengagement phases. In each cycle, the drive tooth meshes with a tooth of the wheel and rotates the toothed wheel by one step. The cycles are repeated so that the drive tooth meshes with successive teeth of the toothed wheel, and consequently drives the toothed wheel in a step-by-step rotational movement.

[0005] During the drive phase, the drive tooth is moved under the effect of electrostatic forces generated by the interdigitated combs. On the other hand, during the disengagement phase, the drive tooth is moved in the opposite direction under the effect of elastic restoring forces generated by suspensions of the interdigitated combs.

[0006] Such a drive device has the advantage that it can be used to drive a toothed wheel of a watch mechanism, replacing traditional watch motors, and generally allows the number of mechanical parts required to drive the toothed wheel into rotation to be reduced.

[0007] However, in such a device, the intensity of the electrostatic forces generated by the interdigitated combs is inversely proportional to the spacing between the fingers of the fixed combs and the fingers of the movable combs.

[0008] However, the spacing between the fingers of the fixed combs and the fingers of the moving combs depends on the engraving technique used to manufacture the device.

[0009] Indeed, for a given engraving depth, the spacing between the mechanical parts of the device must be greater than a predefined minimum spacing. Otherwise, it is not possible to guarantee good separation of the parts.

[0010] Document US 5998906 A describes a microactuator having a fixed comb and a movable comb for driving a mirror, the combs comprising fingers and a locking mechanism such that for an initial unlocked configuration the fingers of the movable comb are not engaged between the fingers of the fixed comb and when the mechanism is locked, the fingers of the movable comb and the fixed comb are engaged. RESUME DE L'INVENTION

[0011] One aim of the invention is to propose an electromechanical microsystem making it possible to increase the driving power generated by the interdigitated combs, while overcoming the spacing constraints imposed by the etching technique used.

[0012] This aim is achieved within the framework of the present invention, thanks to an electromechanical microsystem according to claim 1.

[0013] It is thus possible to design a microelectromechanical system in which, during the manufacturing process of the microelectromechanical system, the fingers of the interdigitated combs are not engaged with each other (i.e. the fingers of the movable comb and the fingers of the fixed comb do not interpenetrate) and can therefore be etched with an initial spacing greater than or equal to the minimum spacing predefined by the etching technique.

[0014] However, once the engraving is complete, the locking mechanism can be locked, in order to engage the fingers of the movable comb between the fingers of the fixed comb (i.e., the fingers of the movable comb and the fingers of the fixed comb interpenetrate), so as to reduce the spacing between the fingers of the interdigitated combs. The final spacing obtained may be less than the predefined minimum spacing.

[0015] The locking mechanism lock is definitive, in that it allows the comb fingers to be held at this close spacing throughout subsequent operation of the actuator.

[0016] In this way, the driving power generated by the interdigitated combs is greater than the driving power that would normally be generated with an actuator whose interdigitated comb fingers have a spacing greater than or equal to the predefined minimum spacing.

[0017] The microelectromechanical system may also have the following characteristics: when the locking mechanism is in the initial unlocked configuration, the fingers of the movable comb are spaced from the fingers of the fixed comb with a first spacing, and when the locking mechanism is in the final locked configuration, the fingers of the movable comb are spaced from the fingers of the fixed comb with a second spacing, less than the first spacing; the second spacing is between 0.1 and 5 µm, preferably between 1 and 3 µm; a ratio between a height of the fingers and the second spacing between the fingers of the fixed comb and the fingers of the movable comb is between 50 and 400, preferably between 70 and 150; the actuator comprises a stop which, once the locking mechanism is in the final locked configuration, prevents a movement of the first movable part tending to disengage the fingers of the movable comb from between the fingers of the fixed comb;the locking mechanism comprises at least a first latching lug connected to the stop and a second latching lug connected to the support, the first latching lug being able to be engaged with the second latching lug when the locking mechanism is in the final locked configuration; once the first latching lug is engaged with the second latching lug, the first latching lug and the second latching lug prevent the locking mechanism from returning to the initial unlocked configuration;the microsystem comprises a suspension connecting the movable drive part to the support, and the movable drive part is capable of being displaced relative to the fixed drive part in a first direction, under the effect of an electrostatic force generated by the application of a non-zero voltage between the fixed drive part and the movable drive part, the displacement of the movable drive part relative to the fixed drive part causing elastic deformation of the suspension, and the movable drive part is capable of being displaced relative to the fixed drive part in a second direction, opposite to the first direction, when the applied voltage decreases, under the effect of an elastic restoring force generated by the suspension having been elastically deformed, the elastic restoring force being opposed to the electrostatic force;the locking mechanism comprises a pusher, the pusher being arranged such that when the movable drive portion is first moved relative to the fixed drive portion in the first direction, the movable drive portion pushes the pusher in the first direction, thereby causing the locking mechanism to move from the initial unlocked configuration to the final locked configuration; the locking mechanism comprises a flexible beam connecting the pusher to the support, the flexible beam being deformed by the movement of the pusher in the first direction. ; PRESENTATION DES DESSINS

[0018] Other characteristics and advantages will emerge from the following description, which is purely illustrative and not limiting, and must be read in conjunction with the appended figures, among which: there figure 1 schematically represents, in side view, a microelectromechanical system in accordance with a possible embodiment of the invention, the figure 2 schematically represents, in top view, the microelectromechanical system, the figure 3 is a detailed view of the microelectromechanical system of the figure 2 , showing part of a drive module, a stop and a locking mechanism for positioning the stop, the figure 4 is a detailed view of the microelectromechanical system of the figure 2 , showing part of a clutch release module, the figure 5 is a detailed view of the microelectromechanical system of the figure 2 , showing part of an indexing module, the figure 6 is a detailed view of the microelectromechanical system of the figure 2 , showing a drive tooth and an indexing tooth, the figure 7 , there figure 8 , there figure 9 and the figure 10 schematically represent the initialization steps of the locking mechanism, the figure 11 schematically represents the drive module, before initialization of the locking mechanism, the figure 12 schematically represents the drive module, after initialization of the locking mechanism, the figure 13 is a diagram schematically representing the intensities of the different forces which act on the drive tooth, when the movable drive part is moved relative to the fixed drive part in the first direction, for a first width of flexible beam, the figure 14 is a diagram schematically representing the intensity of the elastic return force which acts on the drive tooth, when the movable drive part is moved relative to the fixed drive part in the second direction, opposite to the first direction, for a first width of flexible beam, the figure 15 is a diagram schematically representing the intensities of the different forces which act on the drive tooth, when the movable drive part is moved relative to the fixed drive part in the first direction, for a second width of flexible beam, the figure 16 is a diagram schematically representing the intensity of the elastic return force which acts on the drive tooth, when the movable drive part is moved relative to the fixed drive part in the second direction, opposite to the first direction, for a second width of flexible beam, the figure 17 is a detail view of the shape of the fingers of the interdigital combs, the figure 18 schematically represents a first cyclical movement of the drive tooth allowing a toothed wheel to be driven in a first direction of rotation, the figure 19 schematically represents a second cyclical movement of the drive tooth allowing a toothed wheel to be driven in a second direction of rotation, opposite to the first direction of rotation, the figure 20 and the figure 21 schematically represent a microelectromechanical system according to a possible embodiment of the invention, respectively before the initialization of the locking mechanism, and after the initialization of the locking mechanism, the figure 22 is a diagram schematically representing an electrical control signal of the drive module, an electrical control signal of the clutch module, and an electrical control signal of the indexing module, each electrical control signal having a square wave shape, the figure 23 is a diagram showing in more detail the electrical control signal of the drive module, the electrical control signal of the clutch module, and the electrical control signal of the indexing module, over a period, the figure 24 is a diagram schematically representing the movements of the drive module, the clutch module and the indexing module obtained when the actuator is controlled with the electrical control signals of the figures 22 And 23 , there figure 25 is a diagram schematically representing the movement of the drive module as a function of the value of the voltage of the electrical control signal of the drive module, the figure 26 is a diagram schematically representing the displacement of the clutch module as a function of the voltage value of the electrical signal controlling the clutch module, the figure 27 is a diagram schematically representing the displacement of the indexing module as a function of the value of the voltage of the electrical control signal of the indexing module, the figure 28 is a diagram schematically representing an electrical control signal of the drive module, an electrical control signal of the clutch module, and an electrical control signal of the indexing module, in accordance with a possible embodiment of the invention, the figure 29 is a diagram schematically representing the movement of the drive module obtained when the actuator is controlled with the electrical control signals of the figure 14 , there figure 30 is a diagram schematically representing the displacement of the clutch module obtained when the actuator is controlled with the electrical control signals of the figure 14 , there figure 31 is a diagram schematically representing an electrical control signal of the drive module and an electrical control signal of the clutch module, in accordance with another possible embodiment of the invention, the figure 32 schematically represents a control circuit for controlling the microelectromechanical system, the figure 33 schematically represents a damping circuit forming part of the control circuit of the figure 32 . DESCRIPTION DETAILLEE D'UN MODE DE REALISATION

[0019] On the figures 1 à 6 , the electromechanical microsystem 10 shown was obtained by an etching process in a substrate 1 made of semiconductor material, such as silicon for example.

[0020] The substrate 1 used is for example of the “Silicon On Insulator” (SOI) type. This substrate 1 comprises a thick lower silicon layer (first layer 2), an intermediate silicon oxide layer (second layer 3), and an upper silicon layer (third layer 4) of thickness less than that of the lower layer. The upper layer 4 of the substrate 1 has been etched to form a set of mechanical parts 5 while the lower layer 2 of the substrate 1 has not been etched, so as to constitute a support 6 for the mechanical parts 5. A portion of the intermediate silicon oxide layer 3 has served as a sacrificial layer and has been removed to allow the movable mechanical parts to be detached from the support 6, while another portion of the sacrificial layer remains and allows the mechanical parts to be fixed to the support 6.In addition, the remaining part of the sacrificial layer serves as an electrical insulator between the mechanical parts 5 and the support 6, and consequently, between the different mechanical parts 5.

[0021] The microelectromechanical system 10 illustrated on the figures 1 à 6 thus comprises a support 6 and mechanical parts 5 having micrometric dimensions. The mechanical parts 5 are arranged above a surface of the support 6.

[0022] More specifically, in the example illustrated on the figures 1 à 6 , the microelectromechanical system 10 comprises an actuator 11 and a wheel 12. The actuator 11 has been formed in the upper layer 4 of the substrate 1. The wheel 12 may also have been formed in the upper layer 4 of the substrate 1 or may be an added part, having been formed independently.

[0023] The actuator 11 is configured to drive the wheel 12 in rotation relative to the support 6, around an axis of rotation.

[0024] The actuator 11 illustrated in the figures 2 à 4 includes a 100 frame and three elementary modules 200, 300 and 400.

[0025] The frame 100 is fixed relative to the support 6.

[0026] The three basic modules include a 200 drive module, a 300 clutch module and a 400 indexing module.

[0027] The wheel 12 is a toothed wheel. That is to say, it has, at its periphery, a series of teeth. Each tooth extends in a radial direction relative to the axis of rotation of the wheel. The toothed wheel 12 may have a diameter of between 2000 and 10000 µm. The toothed wheel 12 may, for example, have between 200 and 1000 teeth.

[0028] The drive module 200 comprises a fixed drive part 210 and a movable drive part 220.

[0029] The fixed drive part 210 is fixedly mounted on the support 6. The fixed drive part 210 comprises a first carrier 214 and a plurality of fixed combs 211 extending perpendicularly from the first carrier 214. Each fixed comb 211 comprises a rod 212 and fingers 213 extending perpendicularly from the rod 212.

[0030] The movable drive portion 220 comprises a second carrier 224 and a plurality of movable combs 221 extending perpendicularly from the second carrier 224. Each movable comb 221 comprises a rod 222 and fingers 223 extending perpendicularly from the rod 222.

[0031] The actuator 11 further comprises a first suspension 230 connecting the movable drive part 220 to the frame 100. The first suspension 230 comprises two flexible beams 231 extending parallel to the rods 222 of the movable combs 221. The flexible beams 231 connect the second support 224 to the frame 100.

[0032] The movable combs 221 are arranged interposed between the fixed combs 211. That is, the movable combs 221 are arranged alternately with the fixed combs 211. In addition, the movable combs 221 and the fixed combs 211 are arranged in pairs, each pair comprising a fixed comb 211 and an associated movable comb 221. More specifically, the fingers 213 of each fixed comb 211 of a pair extend with their free ends directed toward the fingers 223 of the associated movable comb 221 of the same pair. Similarly, the fingers 223 of the movable comb 221 of a pair extend with their free ends directed toward the fingers 213 of the fixed comb 211 of the same pair. In addition, the fingers 213 of the fixed combs 211 and the fingers 223 of the movable combs 221 extend parallel to a tangential direction.

[0033] By "tangential direction" is meant a direction perpendicular to a radius of the wheel 12 passing at the location where the actuator 11 interacts with the wheel 12.

[0034] The drive module 200 further comprises a contact pad 215 formed on the fixed drive part 210. The contact pad 215 is capable of being connected to a control circuit for applying an electrical control signal to the fixed drive part 210. The contact pad 215 may be formed by depositing a metal layer on the fixed drive part 210.

[0035] The actuator 11 further comprises one or more contact pads 115 formed on the frame 100. The contact pad(s) 115 is (are) suitable for being connected to ground. The contact pad(s) 115 may be formed by depositing one or more metal layer(s) on the frame 100.

[0036] The actuator 11 further comprises a drive tooth 116 and a drive beam 117 connecting the drive tooth 116 to the movable drive part 220 of the drive module 200.

[0037] The drive tooth 116 is adapted to mesh with the teeth 121 of the toothed wheel 12 to drive the toothed wheel 12 in rotation. The drive beam 117 extends in a tangential direction relative to the toothed wheel 12.

[0038] The application of a non-zero electrical voltage between the fixed drive part 210 and the movable drive part 220 via the electrical contact pads 115, 215, generates an electrostatic force which attracts the movable combs 221 towards the fixed combs 211. More precisely, each movable comb 221 of a pair is attracted towards the fixed comb 211 of the same pair. Under the effect of the electrostatic force generated between the combs 211, 221, the movable drive part 220 moves relative to the fixed drive part 210 in a first direction (arrow A), parallel to the tangential direction.

[0039] The movement of the movable drive part 220 relative to the fixed drive part 210 in the first direction causes an elastic deformation of the first suspension 230. The elastic deformation of the suspension 230 includes a bending of the flexible beams 231 which connect the movable drive part 220 to the frame 100. Due to this elastic deformation, the first suspension 230 generates an elastic restoring force, tending to oppose the electrostatic force. This elastic restoring force increases with the amplitude of the elastic deformation undergone by the first suspension 230.

[0040] When the voltage applied between the fixed drive part 210 and the movable drive part 220 decreases or becomes zero, the electrostatic force becomes less than the elastic return force or becomes zero. Under the effect of the elastic return force generated by the first suspension 230, the movable drive part 220 moves relative to the fixed drive part 210 in a second direction (arrow B), opposite to the first direction, parallel to the tangential direction. More precisely, each movable comb 221 of a pair moves away from the fixed comb 211 of the same pair.

[0041] Since the drive tooth 116 is connected via the drive beam 117 to the movable drive part 220, the drive tooth 116 can thus be moved, parallel to a tangential direction, successively in the first direction (arrow A) then in the second direction (arrow B) by the drive module 200.

[0042] The clutch module 300 comprises a fixed clutch portion 310 and a movable clutch portion 320.

[0043] The fixed clutch portion 310 is fixedly mounted on the support 6. The fixed clutch portion 310 comprises a third bearing 314 and a plurality of fixed combs 311 extending perpendicularly from the third bearing 314. Each fixed comb 311 comprises a rod 312 and fingers 313 extending perpendicularly from the rod 312.

[0044] The clutch movable portion 320 comprises a fourth bearing 324 and a plurality of movable combs 321 extending perpendicularly from the fourth bearing 324. Each movable comb 321 comprises a rod 322 and fingers 323 extending perpendicularly from the rod 322.

[0045] The fixed combs 311 and the movable combs 321 of the clutch module 300 are oriented perpendicularly to the fixed combs 211 and the movable combs 221 of the drive module 200.

[0046] The actuator 11 further comprises a second suspension 330 connecting the movable clutch part 320 to the frame 100. The second suspension 330 comprises two flexible beams 331 extending parallel to the rods 322 of the movable combs 321. The flexible beams 331 connect the fourth bearing 324 to the frame 100.

[0047] The movable combs 321 are arranged interposed between the fixed combs 311. In addition, the movable combs 321 and the fixed combs 311 are arranged in pairs, each pair comprising a fixed comb 311 and an associated movable comb 321. More specifically, the fingers 313 of each fixed comb 311 of a pair extend with their free ends directed toward the fingers 323 of the associated movable comb 321. Similarly, the fingers 323 of the movable comb 321 extend with their free ends directed toward the fingers 313 of the fixed comb 311. In addition, the fingers 313 of the fixed combs 311 and the fingers 323 of the movable combs 321 extend parallel to a radial direction.

[0048] By "radial direction" is meant a direction parallel to the radius of the wheel 12 passing through the location where the actuator 11 interacts with the wheel 12.

[0049] The clutch module 300 further comprises a contact pad 315 formed on the fixed clutch part 310. The contact pad 315 is capable of being connected to a source of electrical potential for applying an electrical control signal to the fixed clutch part 310.

[0050] The actuator 11 further comprises a clutch beam 118 connecting the drive tooth 116 to the movable clutch part 320 of the clutch module 300.

[0051] The clutch beam 118 extends in a radial direction relative to the toothed wheel 12.

[0052] Applying a non-zero voltage between the fixed clutch portion 310 and the movable clutch portion 320 via the electrical contact pads 115, 315 generates an electrostatic force that attracts the movable combs 321 toward the fixed combs 311. More specifically, each movable comb 321 of a pair is attracted toward the fixed comb 311 of the same pair. Under the effect of the generated electrostatic force, the movable clutch portion 320 moves relative to the fixed clutch portion 310 in a third direction (arrow C), parallel to the radial direction.

[0053] The movement of the movable clutch part 320 relative to the fixed clutch part 310 in the third direction causes an elastic deformation of the second suspension 330. The elastic deformation of the suspension 330 includes a bending of the flexible beams 331 which connect the movable clutch part 320 to the frame 100. Due to this elastic deformation, the second suspension 330 generates an elastic restoring force, tending to oppose the electrostatic force. This elastic restoring force increases with the amplitude of the elastic deformation.

[0054] When the voltage applied between the fixed clutch portion 310 and the movable clutch portion 320 decreases or becomes zero, the electrostatic force becomes less than the elastic return force or becomes zero. Under the effect of the elastic return force generated by the second suspension 330, the movable clutch portion 320 moves relative to the fixed clutch portion 310 in a fourth direction (arrow D), opposite to the third direction, parallel to the radial direction.

[0055] Since the drive tooth 116 is connected via the clutch beam 118 to the movable clutch part 320, the drive tooth 116 can thus be moved, parallel to a radial direction, successively in the third direction (arrow C) and in the fourth direction (arrow D) by the clutch module 300.

[0056] The drive beam 117 and the clutch beam 118 are each sufficiently flexible to transmit the tangential movement generated by the drive module 200 and the radial movement generated by the clutch module 300 to the drive tooth 116, respectively, while allowing decoupling of the two movements. In this way, the two movements (tangential movement and radial movement) can be controlled independently of each other.

[0057] The indexing module 400 comprises a fixed indexing part 410 and a movable indexing part 420.

[0058] The fixed indexing portion 410 is fixedly mounted on the support. The fixed indexing portion 410 comprises a fifth bearing 414 and a plurality of fixed combs 411 extending perpendicularly from the fifth bearing 414. Each fixed comb 411 comprises a rod 412 and fingers 413 extending perpendicularly from the rod 412.

[0059] The movable indexing portion 420 comprises a sixth bearing 424 and a plurality of movable combs 421 extending perpendicularly from the sixth bearing 424. Each movable comb 421 comprises a rod 422 and fingers 423 extending perpendicularly from the rod 422.

[0060] The actuator 11 further comprises a third suspension 430 connecting the movable indexing part 420 to the frame 100. The third suspension 430 comprises two flexible beams 431 extending parallel to the rods 422 of the combs 421. The flexible beams 431 connect the transverse beam 424 to the frame 100.

[0061] The movable combs 421 are arranged interposed between the fixed combs 411. In addition, the movable combs 421 and the fixed combs 411 are arranged in pairs, each pair comprising a fixed comb 411 and an associated movable comb 421. More specifically, the fingers 413 of each fixed comb 411 of a pair extend with their free ends directed toward the fingers 423 of the associated movable comb 421. Similarly, the fingers 423 of the movable comb 421 extend with their free ends directed toward the fingers 413 of the fixed comb 411. In addition, the fingers 413 of the fixed combs 411 and the fingers 423 of the movable combs 421 extend parallel to a radial direction.

[0062] The actuator 11 further comprises an indexing tooth 120. In the example illustrated in the figure 3 , the indexing tooth 120 comprises two protrusions 126 and a recess 127 formed between the two protrusions 126. When the indexing tooth 120 is engaged with the teeth 121 of the toothed wheel 12, the recess 127 receives a tooth 121 of the toothed wheel 12 in the recess 127, which has the effect of blocking the wheel 12 in rotation.

[0063] The actuator 11 further comprises an indexing beam 128 connecting the indexing tooth 120 to the movable indexing part 420 of the indexing module 400.

[0064] The indexing beam 128 extends in a radial direction relative to the toothed wheel 12.

[0065] The application of a non-zero voltage between the fixed indexing part 410 and the movable indexing part 420 via the electrical contact pads 415 and 115 generates an electrostatic force which attracts the movable combs 421 towards the fixed combs 411. More precisely, each movable comb 421 of a pair is attracted towards the fixed comb 411 of the same pair. Under the effect of the generated electrostatic force, the movable indexing part 420 moves relative to the fixed indexing part 410 in the third direction (arrow C), parallel to the radial direction.

[0066] The movement of the movable indexing part 420 relative to the fixed indexing part 410 in the third direction causes an elastic deformation of the third suspension 430. The elastic deformation of the suspension 430 includes a bending of the flexible beams 431 which connect the movable indexing part 420 to the frame 100. Due to this elastic deformation, the third suspension 430 generates an elastic restoring force, tending to oppose the electrostatic force. This elastic restoring force increases with the amplitude of the elastic deformation.

[0067] When the voltage applied between the fixed indexing part 410 and the movable indexing part 420 decreases or becomes zero, the electrostatic force becomes less than the elastic restoring force or becomes zero. Under the effect of the elastic restoring force generated by the third suspension, the movable indexing part 420 moves away from the fixed indexing part 410 in the fourth direction (arrow D), opposite to the third direction, parallel to the radial direction.

[0068] Since the indexing tooth 120 is connected via the indexing beam 128 to the movable indexing part 420, the indexing tooth 120 is thus moved, parallel to a radial direction, successively in the third direction and in the fourth direction by the indexing module.

[0069] It is thus possible to move the indexing tooth 120 in an alternating radial movement, relative to the wheel 12.

[0070] By appropriately controlling the drive module 200 and the clutch module 300 by means of phase-shifted periodic electrical control signals, it is possible to move the drive tooth 116 according to a first cyclic movement in hysteresis (movement illustrated in the figure 18 ) or according to a second cyclic movement in hysteresis (movement illustrated on the figure 19 ), reversed with respect to the first cyclic movement in hysteresis.

[0071] When the drive tooth 116 is moved according to the first cyclic movement in hysteresis, the drive tooth 116 meshes with successive teeth 121 of the toothed wheel 12, so as to drive the toothed wheel 12 in a step-by-step rotational movement, according to a first direction of rotation.

[0072] When the tooth is moved according to the second cyclic movement in hysteresis, the drive tooth 116 meshes with successive teeth 121 of the toothed wheel 12, so as to drive the toothed wheel 12 in a step-by-step rotational movement, in a second direction of rotation, opposite to the first direction of rotation.

[0073] In parallel, the indexing module 400 is controlled by means of an electrical control signal, in phase opposition with the electrical control signal applied to the clutch module 300.

[0074] In this way, the indexing tooth 120 is engaged with the teeth 121 of the wheel 12 when the driving tooth 116 is disengaged from the teeth 121 of the wheel 12. Conversely, the indexing tooth 120 is disengaged from the teeth 121 of the wheel 12 when the driving tooth 116 is engaged with the teeth 121 of the wheel 12.

[0075] The indexing tooth 120 thus prevents untimely rotation of the wheel 12, while the drive tooth 116 is disengaged from the teeth 121 of the wheel 12 (during the disengagement phases). On the other hand, the indexing tooth 120 does not prevent the rotation of the wheel 121 caused by the drive tooth 116 (during the drive phases).

[0076] The actuator 11 further comprises a stop 240 making it possible to limit a movement of the movable drive part 220 of the drive module 200 in the second direction (arrow B).

[0077] The actuator 11 also includes a locking mechanism 500 for positioning the stop 240 relative to the support in a predefined position.

[0078] On the figure 3 , the stop 240 and the locking mechanism 500 are shown as they are obtained immediately after the manufacture of the microelectromechanical system 10, that is to say before the locking of the locking mechanism 500 which precedes the operation of the microelectromechanical system.

[0079] In this figure, the locking mechanism 500 is in the unlocked configuration.

[0080] Furthermore, as can be seen in this figure, in this configuration, the fingers 223 of the movable combs 221 of the drive module 200 are not engaged between the fingers 213 of the fixed combs 211 of the drive module 200.

[0081] The locking mechanism 500 comprises a pusher 510 and elastic tabs 511 extending from the pusher 510 in a tangential direction. In the example illustrated in the figure 3 , the locking mechanism comprises two elastic tabs 511.

[0082] Each elastic tab 511 has a free end and comprises a first snap-in lug 512 arranged at its free end.

[0083] The locking mechanism 500 further comprises flexible beams 520 connecting the pusher 510 to the frame 100. In the example illustrated in the figure 2 , the locking mechanism 500 comprises two flexible beams 520. The flexible beams 520, parallel to each other, extend in a radial direction.

[0084] The stop 240 is integral with the pusher 510. In other words, the stop 240 is fixed relative to the pusher 510. More precisely, in the example illustrated in the figure 3 , the stopper 240 and the pusher 510 are formed from a single piece of material.

[0085] Furthermore, the frame 100 comprises second snap-in lugs 112. In the example illustrated in the figure 3 , the frame 100 comprises two second snap-in lugs 112.

[0086] THE figures 7 à 10 schematically represent locking steps of the locking mechanism 500, allowing the locking mechanism 500 to be switched from the unlocked configuration (configuration illustrated in the figure 7 ) to a locked configuration (configuration shown in the figure 10 ).

[0087] As illustrated in the figure 7 , a non-zero electrical voltage is applied between the fixed drive part 210 and the mobile drive part 220 of the drive module 200 via the electrical contact pads 115, 215.

[0088] The applied electrical voltage generates an electrostatic force which has the effect of moving the movable drive part 220 of the drive module 200 relative to the fixed drive part 210 in the first direction (arrow A), parallel to the tangential direction.

[0089] As illustrated in the figure 8 , during its movement, the movable drive part 220 pushes the pusher 510, which has the effect of moving the pusher 510 and also moving the stop 240 in the first direction (arrow A).

[0090] This also has the effect of pushing the first detent lugs 512 against the second detent lugs 112.

[0091] Due to their shapes, the first snap-on lugs 512 slide on the second snap-on lugs 112, causing the elastic tabs 511 to bend. In the example illustrated in the figure 8 , the elastic legs 511 flex as they move closer to each other.

[0092] As illustrated in the figure 9 , thanks to the bending of the elastic tabs 511, the first snap-in lugs 512 are pushed beyond the second snap-in lugs 112.

[0093] Once the first snap-in lugs 512 have passed the second snap-in lugs 112, the elastic tabs 511 tend to return to their initial shape. In the example illustrated in the figure 9 , the elastic tabs 511 move apart from each other. The separation of the elastic tabs 511 has the effect of engaging the first latching lugs 512 with the second latching lugs 112.

[0094] As illustrated in the figure 10 , the electrical voltage applied between the fixed drive part 210 and the movable drive part 220 of the drive module 200 is then removed. The electrostatic force disappears.

[0095] Under the effect of the elastic return force exerted by the first suspension 230, the movable drive part 220 of the drive module 200 is moved relative to the fixed drive part 210 of the drive module 200 in the second direction (arrow B), parallel to the tangential direction. The movable drive part 220 of the drive module 200 is moved relative to the fixed drive part 210 in the second direction until the movable drive part 220 of the drive module 200 comes to bear against the stop 240.

[0096] However, the stop 240 is retained by the first snap-in lugs 512 and the second snap-in lugs 112, which prevent the pusher 510 from returning to its initial position.

[0097] Once the locking mechanism 500 is in the locked configuration, the stop 240 is in a position in which the stop 240 prevents movement of the first movable drive part 220 in the second direction to a rest position in which the elastic force generated by the first suspension would be zero.

[0098] In other words, the stop 240 is positioned so as to maintain the first suspension 230 in a state of permanent elastic deformation. The position of the stop 240 determines a minimum value of the elastic return force exerted by the first suspension 230.

[0099] Due to the presence of the stop 240, the elastic return force exerted by the first suspension 230 cannot be less than this minimum value.

[0100] There figure 11 schematically represents the drive module 200, before locking the locking mechanism 500.

[0101] As illustrated in this figure, the fingers 223 of the movable combs 221 are not engaged between the fingers 213 of the fixed combs 211.

[0102] In addition, the first suspension 230 is in a rest position. That is to say, the flexible beams 231 of the first suspension 230 are not deformed. The elastic return force exerted by the first suspension 230 is therefore zero.

[0103] There figure 12 schematically represents the drive module 200, after locking the locking mechanism 500.

[0104] As illustrated in this figure, the fingers 223 of the movable combs 221 are partially engaged in the spaces provided between the fingers 213 of the fixed combs 211.

[0105] Since the stop 240 prevents the movable drive part 220 from returning to the rest position, the flexible beams 231 are maintained in a state of elastic deformation. In this way, the elastic return force exerted by the first suspension 230 is not zero.

[0106] There figure 13 is a diagram schematically representing the intensities of the different forces which act on the drive tooth 116, when the movable drive part 220 is moved relative to the fixed drive part 210 in the first direction (direction of arrow A).

[0107] The forces acting on the drive tooth 116 are the electrostatic force generated by the electrical voltage applied between the fixed drive part 210 and the movable drive part 220, and the elastic return force due to the deformation of the first suspension 230.

[0108] The elastic restoring force opposes the electrostatic force. Thus, the intensity of the driving force exerted on the driving tooth 116 is the difference between the intensity of the electrostatic force and the intensity of the elastic restoring force.

[0109] The gray area of ​​the diagram of the figure 13 illustrates the driving force exerted on the driving tooth 116 for a first stiffness value of the first suspension 230 (beam width: 33µm) in the first direction of rotation (direction of arrow A).

[0110] As can be seen in this diagram, the intensity of the electrostatic force remains relatively constant during the movement of the movable drive part 220 relative to the fixed drive part 210.

[0111] On the other hand, the intensity of the elastic restoring force increases as the movable drive part 220 is moved in the first direction.

[0112] The increase in the intensity of the elastic restoring force depends on the stiffness of the first suspension 230. For comparison, the diagram shows a variation in the intensity of the elastic restoring force for a first stiffness value of the first suspension 230 (beam width = 33 µm) and a variation in the intensity of the elastic restoring force for a second stiffness value of the first suspension 230 (beam width = 15 µm).

[0113] Furthermore, when the displacement of the movable drive part 220 is zero, the intensity of the elastic return force is not zero. Indeed, in this position, the first suspension 230 is deformed due to the presence of the stop 240.

[0114] There figure 14 is a diagram schematically representing the intensity of the elastic return force which acts on the drive tooth 116, when the movable drive part 220 is moved relative to the fixed drive part 210 in the second direction (direction of arrow B), opposite to the first direction.

[0115] As can be seen in this diagram, no electrostatic force acts on the moving part.

[0116] The movable drive part 220 is moved relative to the fixed drive part 210, in the second direction, solely under the action of the elastic return force.

[0117] The intensity of the elastic return force decreases as the movable drive part 220 is moved in the second direction. However, thanks to the presence of the stop 240, the intensity of the elastic return force does not become zero. The intensity of the elastic return force remains greater than a minimum, non-zero value.

[0118] As illustrated in this diagram, the decrease in the intensity of the elastic restoring force depends on the stiffness of the first suspension 230. Thus, the diagram shows a variation in the intensity of the elastic restoring force for the first stiffness value of the first suspension (beam width = 33 µm).

[0119] The gray area of ​​the diagram figure 14 illustrates the driving force exerted on the driving tooth 116 for a first stiffness value of the first suspension 230 (beam width: 33µm) in the second direction of rotation (direction of arrow B).

[0120] There figure 15 is a diagram schematically representing the intensities of the different forces which act on the drive tooth 116, when the movable drive part 220 is moved relative to the fixed drive part 210 in the first direction.

[0121] The forces acting on the drive tooth 116 are the electrostatic force generated by the voltage applied between the fixed drive part 210 and the movable drive part 220, and the elastic return force due to the deformation of the first suspension 230. The elastic return force opposes the electrostatic force.

[0122] The diagram shows a variation in the intensity of the elastic restoring force for the second stiffness value of the first suspension 230 (beam width = 15 µm).

[0123] The gray area of ​​the diagram of the figure 15 shows the variation in the intensity of the driving force exerted on the driving tooth 116 in the first direction (direction of arrow A) for the second stiffness value of the first suspension 230 (beam width: 15 µm). This second stiffness value, lower than the first stiffness value, leads to a larger gray area (comparison of the areas of the gray areas of the figures 13 And 15 ) and therefore to a greater intensity of the driving force in the first direction as well.

[0124] There figure 16 is a diagram schematically representing the intensity of the elastic return force which acts on the drive tooth 116, when the movable drive part 220 is moved relative to the fixed drive part 210 in the second direction, opposite to the first direction, for the second stiffness value of the first suspension 230.

[0125] As can be seen from this diagram, no electrostatic force acts on the movable drive part 220.

[0126] The movable drive part 220 is moved relative to the fixed drive part 210, in the second direction, solely under the action of the elastic return force.

[0127] The intensity of the elastic restoring force decreases as the movable drive part 220 is moved in the second direction.

[0128] However, due to the presence of the stop 240, the intensity of the elastic return force does not become zero. The intensity of the elastic return force remains greater than a minimum, non-zero value.

[0129] The diagram shows a variation in the intensity of the elastic restoring force for the second stiffness value of the first suspension 240 (beam width = 15 µm).

[0130] The gray area of ​​the diagram of the figure 16 illustrates the driving force exerted on the driving tooth 116 for the second stiffness value of the first suspension 230 (beam width: 15 µm) in the second direction of rotation (direction of arrow B). For comparison, the driving force in the second direction for the first stiffness value is also plotted on this same diagram.

[0131] THE figures 13 à 16 show that the higher the stiffness of the first suspension 230, the more quickly the driving force used to drive the toothed wheel 12 in the first direction of rotation decreases.

[0132] Thus, depending on the intended applications, the stiffness of the first suspension 230 can be adjusted in order to favor better efficiency of the rotational drive of the toothed wheel 12 in the first direction of rotation or better efficiency of the rotational drive of the toothed wheel 12 in the second direction of rotation.

[0133] There figure 17 is a detailed view of the shape of the fingers 213 of a fixed comb 211 and that of the fingers 223 of a mobile comb 221 of the drive module 200.

[0134] The etching techniques used for the etching of serial microelectromechanical systems require a minimum spacing between the fixed and moving parts of each microsystem.

[0135] For example, in the case of a microelectromechanical system, such as that illustrated in the figures 1 à 6 , it is necessary to provide a minimum spacing between the fingers of the fixed and moving combs.

[0136] The minimum Gu spacing depends on the etch depth. For example, for an etch performed by a deep reactive ion etching (DRIE) technique at a depth of 200 µm, the minimum Gu spacing can be approximately 4 to 6 µm.

[0137] Before locking the locking mechanism 500, the fingers 223 of the movable comb 221 are not engaged between the fingers 213 of the fixed comb 211. The fingers 223 of the movable comb 221 are spaced from the nearest fingers 213 of the fixed comb 211 with a first spacing G1.

[0138] The spacing G1 between the fingers 213 of the fixed comb 211 and the fingers 223 of the movable comb 221 is greater than the minimum spacing Gu. The “spacing” between two fingers is defined as the shortest distance separating the two fingers.

[0139] After locking the locking mechanism 500, the fingers 223 of the movable comb 221 are engaged between the fingers 213 of the fixed comb 211.

[0140] In this way, the fingers 223 of the movable comb 221 are spaced from the nearest fingers 213 of the fixed comb 211 with a second spacing G2 and with a third spacing G3, less than the first spacing G1. More precisely, the finger 223 of the movable comb 221 is spaced from a finger 213 of the fixed comb 211 located on one side of the finger 223 of the movable comb 221 with the second spacing G2, and is spaced from another finger 213 of the fixed comb 211 located on the other side of the finger 223 of the movable comb 221 with the third spacing G3. The spacings G2 and G3 between the fingers 213 and 223 of the fixed combs 211 and the fingers 223 of the movable combs 221 may be less than the minimum spacing Gu. The G2 spacing and / or the G3 spacing may be between 0.1 and 5 µm, preferably between 1 and 3 µm. For example, the G2 spacing may be 3 µm and the G3 spacing may be 4 µm.

[0141] In particular, the ratio between the thickness of the fingers 213, 223 (i.e. the etching depth of the upper silicon layer) and the spacing between the fingers 213 of the fixed comb 211 and the fingers 223 of the mobile comb 221 may be between 50 and 400, preferably between 70 and 150.

[0142] Since the electrostatic force generated by the drive module 200 is inversely proportional to the spacing between the fingers 213 of the fixed combs 211 and the fingers 223 of the movable combs 221, this has the effect of increasing the driving power generated by the drive module 200, by overcoming the spacing constraints imposed by the etching technique used.

[0143] The second spacing G2 may be different from the third spacing G3, in order to take into account the fact that during the movement of the movable drive part 220 relative to the fixed drive part 210, the movement of the fingers 223 of the movable combs 221 is not perfectly rectilinear, nor perfectly parallel to the fingers 213 of the fixed combs 211.

[0144] THE figures 20 et 21 schematically represent a microelectromechanical system 10 according to another possible embodiment of the invention.

[0145] This alternative embodiment differs from the embodiment illustrated in the figures 1 à 6 , in that the drive module 200 is symmetrical with respect to an axis of symmetry parallel to the tangential direction.

[0146] As in the embodiment of the figures 1 à 6 , the drive module 200 comprises a fixed drive part 210 and a movable drive part 220.

[0147] The fixed drive part 210 is fixedly mounted on the support 6.

[0148] In this embodiment, the fixed drive portion 210 comprises two first carriers 214, a first series of fixed combs 211 extending perpendicularly from one of the first carriers 214 and a second series of fixed combs 211 extending perpendicularly from the other of the first carriers 214.

[0149] The movable drive portion 220 comprises a second carrier 224 and a plurality of movable combs 221 extending perpendicularly from the second carrier 224.

[0150] In this embodiment, the movable combs 221 comprise a first series of movable combs extending from a first side of the second carrier 224 and a second series of movable combs extending from a second side of the second carrier 224, opposite the first side. In this way, the movable combs 221 extend symmetrically on either side of the second carrier 224.

[0151] Similarly, the fixed combs 211 of the first series of fixed combs extend on the first side of the second carrier 224 and the fixed combs 211 of the second series of fixed combs extend on the second side of the second carrier 224, opposite the first side. In this way, the fixed combs 211 extend symmetrically on either side of the second carrier 224.

[0152] The actuator 11 further comprises a first suspension 230 connecting the movable drive part 220 to the frame 100. The first suspension 230 comprises four flexible beams 231 extending parallel to the rods 222 of the movable combs 221. The flexible beams 231 connect the second carrier 224 to the frame 100. The four flexible beams 231 include two flexible beams extending on the first side of the second carrier 224 and two other flexible beams extending on the second side of the second carrier 224. In this way, the first suspension 230 is symmetrical with respect to the axis of symmetry parallel to the tangential direction

[0153] The movable combs 221 are arranged interposed between the fixed combs 211. That is, the movable combs 221 are arranged alternately with the fixed combs 211. In addition, the movable combs 221 and the fixed combs 211 are arranged in pairs, each pair comprising a fixed comb 211 and an associated movable comb 221. More specifically, the fingers 213 of each fixed comb 211 of a pair extend with their free ends directed toward the fingers 223 of the associated movable comb 221 of the same pair. Similarly, the fingers 223 of the movable comb 221 of a pair extend with their free ends directed toward the fingers 213 of the fixed comb 211 of the same pair. In addition, the fingers 213 of the fixed combs 211 and the fingers 223 of the movable combs 221 extend parallel to a tangential direction.

[0154] There figure 20 schematically represents the drive module 200, before locking the locking mechanism 500.

[0155] As illustrated in this figure, the fingers 223 of the movable combs 221 are not engaged between the fingers 213 of the fixed combs 211.

[0156] In addition, the first suspension 230 is in a rest position. That is to say, the flexible beams 231 of the first suspension 230 are not deformed. The elastic return force exerted by the first suspension 230 is therefore zero.

[0157] There figure 21 schematically represents the drive module 200, after locking the locking mechanism 500.

[0158] As illustrated in this figure, the fingers 223 of the movable combs 221 are partially engaged in the spaces provided between the fingers 213 of the fixed combs 211.

[0159] Since the stop 240 prevents the movable drive part 220 from returning to the rest position, the flexible beams 231 are maintained in a state of elastic deformation. In this way, the elastic return force exerted by the first suspension 230 is not zero.

[0160] An advantage of this embodiment is that, due to the symmetrical configuration of the first suspension 230, the movement of the fingers 223 of the movable combs 221 is perfectly rectilinear and parallel to the fingers 213 of the fixed combs 211, during the movement of the movable drive part 220 relative to the fixed drive part 210.

[0161] In other words, the second bearing 224 is constrained to move in a tangential direction and cannot move in a radial direction.

[0162] It is thus possible to further reduce the spacing G2 or G3 between the fingers 213 and 223 of the fixed combs 211 and the movable combs 221. In addition, the second spacing G2 and the third spacing G3 can be equal. The spacings G2 and G3 (illustrated on the figure 17 ) may be less than 1 µm.

[0163] This allows the electrostatic force generated by the drive module 200 to be further increased.

[0164] There figure 22 schematically represents an example of an electrical signal for controlling the drive module, an example of an electrical signal for controlling the clutch module, and an example of an electrical signal for controlling the indexing module.

[0165] On the figure 22 , each electrical control signal is a voltage electrical control signal. The diagram of the figure 22 therefore represents the variation of the voltage of each electrical control signal as a function of time. Each electrical control signal is periodic and has a substantially square wave shape.

[0166] For example, the electrical control signal of the drive module alternately takes a minimum voltage value (for example Vmin = 0) and a maximum voltage value (for example Vmax = 110 Volts).

[0167] The diagram of the figure 23 more precisely represents the variation of the voltage of each electrical control signal as a function of time, over a period.

[0168] There figure 24 schematically represents the movement over time of the mobile drive part 220 of the drive module 200, the movement over time of the mobile clutch part 320 of the clutch module 300 and the movement over time of the mobile part 420 of the indexing module 400.

[0169] These movements were obtained when the actuator 11 is controlled with electrical control signals identical to those illustrated in the figures 22 And 23 .

[0170] There figure 24 shows that the movable drive part 220 of the drive module 200 undergoes rebounds. These rebounds occur essentially when the movable drive part 220 reaches the end of its travel. More precisely, these rebounds are visible when the movable drive part 220 comes into contact with the stop 240 during an elementary movement in the second direction (arrow B), that is to say when the movable drive part 220 returns to its initial position under the effect of the elastic return force generated by the first suspension 230 having been elastically deformed.

[0171] There figure 24 also shows that the clutch moving part 320 of the clutch module 300 and the indexing moving part 420 of the indexing module 400 also undergo residual oscillations.

[0172] These residual bounces or oscillations are detrimental to the proper functioning of the actuator 11.

[0173] On the one hand, it is necessary to wait until these bounces or oscillations are sufficiently attenuated, before ordering a movement of the moving part in the opposite direction, which limits the frequency at which the actuator can be controlled.

[0174] On the other hand, rebounds generate repeated shocks between mechanical parts, which cause premature wear of the contact surfaces, and reduce the lifespan of the microelectromechanical system.

[0175] There figure 25 is a diagram schematically representing the movement of the mobile drive part 220 of the drive module 200 as a function of the value of the voltage of the electrical control signal applied between the mobile drive part 220 and the fixed drive part 210.

[0176] This diagram shows more particularly the amplitude of the displacement of the mobile drive part 220 relative to the fixed drive part 210 when the value of the voltage of the electrical control signal applied to the drive module 200 increases progressively, linearly, over time.

[0177] As can be seen on the figure 25 , when the value of the voltage of the electrical control signal is lower than a threshold voltage value Vstart, the movable drive part 220 does not move relative to the fixed drive part 210. Indeed, the electrostatic force generated between the movable drive part 220 and the fixed drive part 210 is insufficient to overcome the elastic return force generated by the first suspension 230 and is therefore insufficient to cause a movement of the movable drive part 220 relative to the fixed drive part 210. In other words, the first suspension 230 is subjected to an elastic prestress, which the electrostatic force must overcome in order to be able to move the movable drive part 220 relative to the fixed drive part 210.

[0178] When the voltage value of the electrical control signal is between the voltage threshold value Vstart and a voltage threshold value Vend, the movable drive part 220 moves relative to the fixed drive part 210. Indeed, the electrostatic force generated between the movable drive part 220 and the fixed drive part 210 causes a movement of the movable drive part 220 relative to the fixed drive part 210. The amplitude of the movement of the movable drive part 220 relative to the fixed drive part 210 increases continuously with the voltage value of the electrical control signal.

[0179] When the value of the voltage of the control signal is greater than the voltage Vfin, the movable drive part 220 no longer moves relative to the fixed drive part 210. In fact, the movable drive part 220 is in abutment against the frame 100. Thus, an increase in the electrostatic force does not cause additional movement of the movable drive part 220 relative to the fixed drive part 210.

[0180] There figure 26 is a diagram schematically representing the movement of the movable clutch part 320 of the clutch module 300 as a function of the value of the voltage of the electrical control signal applied to the clutch module 300.

[0181] As for the drive module 200, it is possible to determine a voltage threshold value Vstart below which the electrostatic force generated between the movable clutch part 320 and the fixed clutch part 310 is insufficient to cause a movement of the movable clutch part 320 relative to the fixed clutch part 310.

[0182] In the case of the clutch module 300, when the voltage value of the electrical control signal is lower than the voltage threshold value Vstart, the movable clutch part 320 does not move relative to the fixed clutch part 310. Indeed, since the fingers 323 of the movable combs 321 are not engaged with the fingers 313 of the fixed combs 311, the electrostatic force generated between the fixed combs 311 and the movable combs 321 is very weak.

[0183] It is also possible to determine a voltage threshold value Vfin above which the moving clutch part 320 is in abutment against the frame 100.

[0184] When the voltage of the control signal is between the voltage threshold value Vstart and the voltage threshold value Vend, the movable clutch part 320 moves relative to the fixed clutch part 310. The amplitude of the movement of the movable clutch part 320 relative to the fixed clutch part 310 increases continuously with the value of the voltage of the electrical control signal.

[0185] There figure 27 is a diagram schematically representing the movement of the movable indexing part 420 of the indexing module 400 as a function of the value of the voltage of the electrical control signal applied to the indexing module 400.

[0186] As for the clutch module 300, it is possible to determine a voltage threshold value Vstart below which the electrostatic force generated between the movable indexing part 420 and the fixed indexing part 410 is insufficient to cause a movement of the movable indexing part 420 relative to the fixed indexing part 410.

[0187] It is also possible to determine a voltage threshold value Vfin above which the movable indexing part 420 is in abutment against the frame 100.

[0188] When the voltage of the control signal is between the voltage threshold value Vstart and the voltage threshold value Vend, the movable indexing part 420 moves relative to the fixed indexing part 410. The amplitude of the movement of the movable indexing part 420 relative to the fixed indexing part 410 increases continuously with the value of the voltage of the electrical control signal.

[0189] There figure 28 is a diagram schematically representing an electrical control signal of the drive module 200, an electrical control signal of the clutch module 300, and an electrical control signal of the indexing module 400, in accordance with a possible embodiment of the invention.

[0190] As illustrated in this figure, the electrical control signal of the drive module 200 alternately takes a minimum voltage value (for example Vmin = 0) and a maximum voltage value (for example Vmax = 110 volts).

[0191] During the transition from the maximum voltage value Vmax to the minimum voltage value Vmin, the voltage value of the electrical control signal decreases monotonically from the maximum voltage value Vmax to the minimum voltage value Vmin.

[0192] In addition, during this decrease, the electrical control signal successively presents: a first average slope between the maximum voltage value Vmax and the voltage threshold value Vfin defined for the drive module (in this example Vfin ≈ 0.83 x Vmax), a second average slope, lower in absolute value than the first average slope, between the voltage threshold value Vfin and the voltage threshold value Vstart (in this example, Vstart ≈ ​​0.41 x Vmax), and a third average slope, higher in absolute value than the second average slope, between the voltage threshold value Vstart defined for the drive module and the minimum voltage value Vmin (in this example Vmin = 0).

[0193] The first average slope is defined as an average of the instantaneous slope of the electrical control signal over the time interval [Tmax, Tfin] during which the value of the electrical control signal changes from the value Vmax to the value Vfin. In other words, the first average slope is equal to: (Vfin - Vmax) / (Tfin - Tmax), where (Tfin - Tmax) is the time taken by the electrical control signal to change from the value Vmax to the value Vfin.

[0194] The second average slope is defined as an average of the instantaneous slope of the electrical control signal over the time interval [Tfin, Tstart] during which the value of the electrical control signal changes from the value Vfin to the value Vstart. In other words, the second average slope is equal to: (Vstart - Vfin) / (Tstart - Tfin), where (Tstart - Tfin) is the time taken by the electrical control signal to change from the value Vfin to the value Vstart.

[0195] The third average slope is defined as an average of the instantaneous slope of the electrical control signal over the time interval [Tstart, Tmin] during which the value of the electrical control signal changes from the value Vstart to the value Vmin. In other words, the third average slope is equal to: (Vmin - Vstart) / (Tmin - Tstart), where (Tmin - Tstart) is the time taken by the electrical control signal to change from the value Vstart to the value Vmin.

[0196] In the example illustrated on the figure 28 , the electrical control signal is linear over each time interval [Tmax, Tfin], [Tfin, Tstart] and [Tstart, Tmin]. In this case, the first average slope is equal to the instantaneous slope of the signal which is constant over the time interval [Tmax, Tfin], the second average slope is equal to the instantaneous slope of the signal which is constant over the time interval [Tfin, Tstart] and the third average slope is equal to the instantaneous slope of the signal which is constant over the time interval [Tstart, Tmin].

[0197] However, other forms of the electrical control signal are of course possible, for example forms where the electrical control signal is not linear over each interval.

[0198] On the figure 28 , several possible values ​​for the second average slope have been illustrated.

[0199] As illustrated in the figure 28 , the electrical control signal of the clutch module 300, and the electrical control signal of the indexing module 400, have a form similar to that of the electrical control signal of the drive module 200.

[0200] As illustrated in this figure, the electrical control signal of the clutch module 300 (respectively of the indexing module 400) alternately takes a minimum voltage value (for example Vmin = 0) and a maximum voltage value (for example Vmax = 110 volts).

[0201] During the transition from the maximum voltage value to the minimum voltage value, the voltage value of the electrical control signal decreases monotonically from the maximum voltage value Vmax to the minimum voltage value Vmin.

[0202] In addition, during this decrease, the electrical control signal successively presents: a first average slope between the maximum voltage value and the voltage threshold value Vfin defined for the clutch module 300 (respectively of the indexing module 400) (in this example Vfin ≈ 0.91 x Vmax), a second average slope, lower in absolute value than the first average slope, between the voltage threshold value Vfin and the voltage threshold value Vstart (in this example, Vstart ≈ ​​0.27 Vmax), and a third average slope, higher in absolute value than the second average slope, between the voltage threshold value Vstart defined for the clutch module 300 (respectively of the indexing module 400) and the minimum voltage value Vmin (in this example Vmin = 0).

[0203] On the figure 28 , several possible values ​​for the second average slope have been illustrated.

[0204] There figure 29 is a diagram schematically representing the amplitude of the displacement of the movable drive part 220 relative to the fixed drive part 210, over time, obtained when the drive module 200 is controlled with the electrical control signals of the figure 28 .

[0205] Depending on the second average slope chosen for the electrical control signal applied to the drive module 200 (i.e. depending on the time taken by the control signal to go from the voltage value Vfin to the voltage value Vstart), the rebounds of the moving part 220 are more or less attenuated.

[0206] It is possible to determine an optimal value for the second average slope (or an optimal value for the time taken by the control signal to go from the voltage value Vfin to the voltage value Vstart), that is to say a value of the second average slope which allows to obtain the best attenuation of these rebounds.

[0207] In the example illustrated on the figure 29 , the time taken by the control signal to go from the voltage value Vfin to the voltage value Vstart which allows the best attenuation of the rebounds is 0.42 ms. This time is substantially equal to a natural period of free oscillation of the mobile drive part 220 relative to the fixed drive part 210. For example, this time is within a range of 0.7 to 1.3 times the natural period of free oscillation of the mobile drive part 220 relative to the fixed drive part 210.

[0208] Likewise, the figure 30 is a diagram schematically representing the amplitude of the displacement of the movable clutch part 320 relative to the fixed clutch part 310 of the clutch module 300, over time, obtained when the clutch module 300 is controlled with the electrical control signals of the figure 28 .

[0209] In this example, the time taken by the control signal to go from the voltage value Vfin to the voltage value Vstart which allows the best attenuation of the oscillations is 0.56 ms. This time is substantially equal to a natural period of free oscillation of the moving clutch part 320 relative to the fixed clutch part 310.

[0210] There figure 31 is a diagram schematically representing electrical control signals of the drive module and electrical control signals of the clutch module, in accordance with another possible embodiment of the invention.

[0211] In this embodiment, as in the previous embodiment, the control signal alternately takes a minimum voltage value Vmin and a maximum voltage value Vmax.

[0212] However, in this embodiment, during the transition from the minimum voltage value to the maximum voltage value, the voltage value of the electrical control signal increases monotonically from the minimum voltage value to the maximum voltage value.

[0213] In addition, the voltage value of the electrical control signal successively presents: a fourth average slope between the minimum voltage value Vmin and the voltage threshold value Vstart, a fifth average slope, lower in absolute value than the fourth average slope, between the voltage threshold value Vstart and the voltage threshold value Vfin, and a sixth average slope, higher in absolute value than the fifth average slope, between the voltage threshold value Vfin and the maximum voltage value Vmax.

[0214] The fourth average slope is defined as an average of the instantaneous slope of the electrical control signal over the time interval [Tmin, Tstart] during which the value of the electrical control signal changes from the value Vmin to the value Vstart. In other words, the fourth average slope is equal to: (Vstart - Vmin) / (Tstart - Tmin), where (Tstart - Tmin) is the time taken for the electrical control signal to change from the value Vmin to the value Vstart.

[0215] The fifth average slope is defined as an average of the instantaneous slope of the electrical control signal over the time interval [start, Tend] during which the value of the electrical control signal changes from the value Vstart to the value Vend. In other words, the fifth average slope is equal to: (Vend - Vstart) / (Tend - Tstart), where (Tend - Tstart) is the time taken by the electrical control signal to change from the value Vstart to the value Vend.

[0216] The sixth average slope is defined as an average of the instantaneous slope of the electrical control signal over the time interval [Tfin, Tmax] during which the value of the electrical control signal changes from the value Vfin to the value Vmax. In other words, the sixth average slope is equal to: (Vmax - Vfin) / (Tmax - Tfin), where (Tmax - Tfin) is the time taken for the electrical control signal to change from the value Vfin to the value Vmax.

[0217] In the example illustrated on the figure 31 , the electrical control signal is linear over each time interval [Tmin, Tstart], [Tstart, Tend] and [Tend, Tmax]. In this case, the fourth average slope is equal to the instantaneous slope of the signal which is constant over the time interval [Tmin, Tstart], the fifth average slope is equal to the instantaneous slope of the signal which is constant over the time interval [Tstart, Tend] and the sixth average slope is equal to the instantaneous slope of the signal which is constant over the time interval [Tend, Tmax].

[0218] However, other forms of the electrical control signal are of course possible, for example forms where the electrical control signal is not linear over each interval.

[0219] There figure 32 schematically represents a control circuit 13 adapted to control the actuator 11 of the microelectromechanical system 10.

[0220] In this example, the control circuit 13 comprises: a damping circuit 131, a power supply circuit 132 comprising a charge pump converter and a voltage regulator, the power supply circuit 132 being configured to generate a high voltage power supply signal, a switching circuit 133 comprising high voltage switches, the switching circuit being configured to connect the actuator 11 selectively to the output of the power supply circuit 132 and to the damping circuit 131, a bootstrap circuit 134 configured to drive the damping circuit, a voltage level shift circuit 135, a low voltage digital microprocessor 136.

[0221] The snubber circuit 131, the power supply circuit 132, the switching circuit 133, the bootstrap circuit 134 and the voltage level shifting circuit 135 may be components of the same ASIC circuit.

[0222] The digital processor 136 (also called "Low voltage digital core") is a programmable low voltage digital processor which is configured to drive the various components of the ASIC circuit.

[0223] The power supply circuit 132 is for example configured to generate a high voltage power supply signal characterized by a maximum voltage of 125 Volts, possibly regulated between two values ​​lower than the maximum voltage and a variable rise time of less than 1 ms depending on the operating frequency of the charge pump.

[0224] The charge pump is an analog circuit comprising capacitors for amplifying the voltage of the electrical control signal applied to the input of the switching circuit 133 (the charge pump is also called a "voltage multiplier"). This analog circuit makes it possible, for example, to go from an input voltage of 1.5 to 3 Volts of a conventional battery (button cell) to an output voltage greater than 100 Volts required for powering the modules 200, 300 and 400 of the actuator 11.

[0225] The switches of the switching circuit 133 are configured to allow switching between the high voltage terminal (110 Volts) required for the voltage rise of the electrical control signal applied to the actuator 11 and the damping circuit 131. These switches comprise for example one or more power MOSFET transistor(s) capable of withstanding high voltages.

[0226] The bootstrap circuit 134 (also called “VDD Bootstrap”) is configured to control the MOSFET transistors of the snubber circuit 131. The bootstrap circuit 134 is an analog circuit for adapting, converting and injecting a low voltage digital control signal generated by the digital processor 136 to the gate of the MOSFET transistor of the snubber circuit 131.

[0227] The voltage level shifter circuit 135 (also called a “High Voltage Level Shifter”) is an analog circuit configured to convert the low voltage digital control signal generated by the digital processor 136 into a high voltage control signal applied to the gate of the MOSFET transistor of the switching circuit 133.

[0228] There figure 33 schematically represents the damping circuit 131 forming part of the control circuit 13 of the figure 18 .

[0229] In this figure, the actuator 11 has been likened to a capacitor. Indeed, the drive module 200, the clutch module 300 and the indexing module each comprise a moving part and a fixed part. The moving part and the fixed part can be likened to armatures of a capacitor.

[0230] On the figure 33 , only the drive module 200 has been shown. However, the diagram of the damping circuit 131 is identical for all three modules.

[0231] The snubber circuit 131 comprises a diode D1, a resistor R1 and a MOSFET transistor Q1. The diode D1, the resistor R1 and the MOSFET transistor Q1 are electrically connected in parallel between the switching circuit 133 and ground.

[0232] MOSFET transistor Q1 is driven by bootstrap circuit 134. Bootstrap circuit 134 is connected to the gate of the transistor and is configured to drive the transistor so as to selectively turn the transistor off or turn the transistor on.

[0233] When MOSFET transistor Q1 is off, no electrical current flows through the transistor (between drain and source).

[0234] When MOSFET transistor Q1 is turned on, an electric current can flow through the transistor.

[0235] The operation of the control circuit 13 is as follows.

[0236] MOSFET transistor Q1 is initially off.

[0237] When the voltage of the high voltage supply signal changes from the minimum voltage value (Vmin) to the maximum voltage value (Vmax), the switching module 133 is in a first configuration in which the switching module 133 connects the actuator 11 to the output of the supply circuit 132. The actuator 11 is therefore supplied by the high voltage supply signal generated by the supply circuit 132.

[0238] When the voltage of the high voltage supply signal changes from the maximum voltage value (Vmax) to the minimum voltage value (Vmin), the switching circuit 133 switches to a second configuration in which the switching module 133 connects the actuator 11 to the damping circuit 131.

[0239] Thus, when the switching circuit 133 is in the second configuration, the drive module 200 discharges through the damping circuit 131.

[0240] The discharge of the drive module 200 takes place in three successive phases.

[0241] Initially, the voltage between the fixed drive part 210 and the movable drive part 220 is equal to the maximum voltage value Vmax. During the discharge of the drive module 200, the voltage between the fixed drive part 210 and the movable drive part 220 decreases.

[0242] As long as the voltage between the fixed drive part 210 and the mobile drive part 220 is greater than the voltage threshold value Vfin (first phase), the discharge current of the actuator 11 passes through the diode D1. The voltage across the drive module 200 decreases sharply from the maximum voltage value Vmax to the voltage threshold value Vfin. The variation in the voltage across the drive module 200 from the maximum voltage value Vmax to the voltage threshold value Vfin has a first slope. In this example, the first average slope is almost vertical. In other words, the first average slope is less than -1V / µs. The time taken by the electrical control signal to go from the maximum voltage value Vmax to the voltage threshold value Vfin (Tfin - Tmax) is less than 50 µs, or even less than 10 µs.

[0243] When the voltage between the fixed drive part 210 and the mobile drive part 220 becomes lower than the voltage threshold value Vfin (second phase), the diode D1 is no longer conductive. The discharge current of the actuator 11 passes through the resistor R1. The voltage between the fixed drive part 210 and the mobile drive part 220 decreases from the voltage threshold value Vfin to the voltage threshold value Vstart. The variation in the voltage across the drive module 200 has a second average slope which depends on the value of the resistor R1. The second average slope is lower in absolute value than the first average slope. In other words, the decrease in the voltage between the fixed drive part 210 and the mobile drive part 220 is less rapid than during the first phase. The resistor R1 serves to dampen the movement of the movable drive part 220 relative to the fixed drive part 210.

[0244] When the voltage between the fixed drive part 210 and the mobile drive part 220 becomes lower than the voltage threshold value Vstart (third phase), the MOSFET transistor Q1 is activated. Thus, the discharge current of the actuator 11 passes through the MOSFET transistor Q1. The voltage across the drive module 200 decreases sharply from the voltage threshold value Vstart to the minimum voltage value Vmin. The variation in the voltage across the drive module 200 has a third average slope. In this example, the third slope is almost vertical. In other words, the third average slope is less than -1V / µs. The time taken by the electrical control signal to go from the maximum voltage value Vstart to the voltage threshold value Vmin (Tmin - Tstart) is less than 50 µs, or even less than 10 µs. The third slope is greater in absolute value than the second slope.

[0245] In practice, the priming circuit 134 drives the MOSFET transistor Q1 so that during the first phase and during the second phase, the transistor is blocked, and during the third phase, the MOSFET transistor Q1 is activated. For this purpose, the priming circuit 134 generates an electrical driving signal which has a period adapted to block and activate the MOSFET transistor Q1 alternately, in a synchronized manner with the high-voltage supply signal generated by the supply circuit 132. The synchronization of the two signals is obtained by the fact that the supply circuit 132 and the priming circuit 134 are controlled by the digital processor 136.

Claims

1. A microelectromechanical system (10), comprising a support (6) and an actuator (11), the actuator (11) comprising a drive module (200) comprising: - a fixed drive portion (210), mounted fixedly on the support (6), and comprising a fixed comb (211) with fingers (213), and - a movable drive portion (220) mounted movably relative to the support (6), and comprising a movable comb (221) with fingers (223), - a latching mechanism (500) that is movable between an initial unlatched configuration and a final latched configuration, wherein the movable comb (221) is arranged facing the fixed comb (211) so that when the latching mechanism (500) is in the initial unlatched configuration, the fingers (223) of the movable comb (221) are not engaged between the fingers (213) of the fixed comb (211), and once the latching mechanism (500) is in the final latched configuration, the fingers (223) of the movable comb (221) are engaged between the fingers (213) of the fixed comb (211) and the latching mechanism (500) prevents disengagement of the fingers (223) of the movable comb (221) from between the fingers (213) of the fixed comb (211), characterised in that in the final locked configuration, the locking mechanism allows a movement of the movable drive portion (220) relative to the fixed drive portion (210) throughout the subsequent operation of the actuator (11).

2. The microsystem according to claim 1, wherein when the latching mechanism (500) is in the initial unlatched configuration, the fingers (223) of the movable comb (221) are spaced from the fingers (213) of the fixed comb (211) by a first spacing (G1), and when the latching mechanism (500) is in the final latched configuration, the fingers (223) of the movable comb (221) are spaced from the fingers (213) of the fixed comb (211) by a second spacing (G2, G3) less than the first spacing (G1).

3. The microsystem according to one of claims 1 and 2, wherein the second spacing (G2, G3) is comprised between 0.1 and 5 µm, preferably comprised between 1 and 3 µm.

4. The microsystem according to one of claims 1 to 3, wherein a ratio between a height of the fingers (213, 223) and the second spacing (G2, G3) between the fingers (213) of the fixed comb (211) and the fingers (223) of the movable comb (221) is comprised between 50 and 400, preferably comprised between 70 and 150.

5. The microsystem according to one of claims 1 to 4, wherein the actuator (11) comprises a stop (240) which, once the latching mechanism (500) is in the final latched configuration, prevents movement of the first movable portion (220) tending to disengage the fingers (223) of the movable comb (221) from between the fingers (213) of the fixed comb (211).

6. The microsystem according to claim 5, wherein the latching mechanism (500) comprises at least one first locking lug (512) connected to the stop (240) and a second locking lug (112) connected to the support (6), the first locking lug (512) being able to be engaged with the second locking lug (112) when the latching mechanism (500) is in the final latched configuration.

7. The microsystem according to claim 6, wherein once the first locking lug (512) is engaged with the second locking lug (112), the first locking lug (512) and the second locking lug (112) prevent a return of the latching mechanism to the initial unlatched configuration.

8. The microsystem according to one of claims 1 to 7, comprising a suspension (230) connecting the movable drive portion (220) to the support (6), and wherein the movable drive portion (220) is able to be moved relative to the fixed drive portion (210) in a first direction (A), as a result of an electrostatic force generated by the application of a nonzero voltage between the fixed drive portion (210) and the movable drive portion (220), the movement of the movable drive portion (220) relative to the fixed drive portion (210) causing an elastic deformation of the suspension (230), and the movable drive portion (220) is able to be moved relative to the fixed drive portion (210) in a second direction (B), opposite to the first direction (A), when the applied voltage decreases, as a result of an elastic return force generated by the suspension (230) having been deformed elastically, the elastic return force being opposed to the electrostatic force.

9. The microsystem according to claim 8, wherein the latching mechanism (500) comprises a tappet (510), the tappet (510) being arranged so that when the movable drive portion (220) is moved for the first time relative to the fixed drive portion (210) in the first direction (A), the movable drive portion (220) pushes the tappet (510) in the first direction, which has the effect of making the latching mechanism (500) pass from the initial unlatched configuration to the final latched configuration.

10. The microsystem according to claim 9, wherein the latching mechanism (500) comprises a flexible beam (520) connecting the tappet (510) to the support, the flexible beam (520) being deformed as a result of the movement of the tappet (510) in the first direction (A).