Abstract:
A drive device formed by etching a wafer. The drive device includes a drive element that can sequentially mesh with a driven element and an actuating element that can displace the drive element according to a hysteresis movement thereby driving the driven element. Placement of the drive element on an outer edge of the wafer enables an interfacing of the drive element with a driven element placed opposite therefrom. A clockwork mechanism including a drive device of the aforementioned type and an input gear that can be rotationally driven by the drive device is also provided.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to the area of micro-electromechanical systems (MEMS) or electromechanical microsystems, and more particularly, to the application of these microsystems to clockmaking. 
   2. Discussion of Related Art 
   The movements of electromechanical watches or clocks are normally generated by an electric motor such as a micro-motor with a progressive magnetic gap (called a Lavet motor or stepping motor), which drives a series of gear trains in rotation. These watches or clocks require complex gear mechanisms that are used to adapt the movement of the rotor to the various rotation speeds required of the hands. 
   A concern in the area of clockmaking relates to simplifying the design of the components that constitute the movement generating mechanisms. 
   Another consideration is reducing the number of components used in the mechanisms. Reducing either or both the number of components and the number of assembly operations necessary to create the mechanism allows the efficiency of the mechanisms to be improved, as well as improve the independence of the clock devices and reduce their production costs. 
   SUMMARY OF THE INVENTION 
   In the light of these considerations, a problem that the invention seeks to solve is to limit the number of parts necessary for the creation of the gear mechanisms in watch or clock devices. 
   This problem is solved or addressed by the invention through the use of a drive device which is formed by etching a wafer. The drive device includes a drive element that is capable of meshing sequentially with a driven element, and an actuator element that is capable of moving the drive element with a hysteresis-type motion so that it drives the driven element. The drive element is positioned on an external slice of the wafer in order to allow interfacing of the drive element with a driven element facing it. 
   The invention allows the motors used traditionally in the area of clockmaking, such as Lavet or stepping motors, to be replaced with clock mechanisms that combine a drive device of the MEMS type (micro-electromechanical systems), formed by wafer etching techniques, and a driven element, with no travel limit, created by means of any alternative microtechnology (chemical etching, micro-moulding, etc.). 
   The MEMS type drive device proposed in the context of the invention is capable of generating drive forces that are greater by least one order of magnitude than those generated by existing stepping motors. In particular, this device allows the first gearing stage of the clock movements of previous design to be eliminated, and thus leads to a significant improvement in their efficiency. 
   In the context of the invention, a wafer refers to a substrate onto which the drive device is etched. The wafer is normally formed from a slice of semiconductor material. Several drive devices can thus be manufactured simultaneously from a single wafer. 
   The semiconductor material forming the wafer can be silicon for example. 
   Thus, the proposed drive device can be created by a collective method wherein a large number or plurality of drive devices are simultaneously etched onto a wafer of semiconductor material. 
   Such a collective method can be employed to increase the productivity of drive device production in comparison with the production-line methods employed for the manufacture and assembly of traditional stepping motors. 
   In the drive device of the invention, the drive element is positioned on an external edge of the wafer, meaning that it is located on the periphery of the wafer. 
   The coupling of the drive device to a driven element enables the construction of a modular clock drive mechanism. In fact, the mechanical performance of the clock mechanism is dependent upon the characteristics of the driven element (diameter). 
   The invention also relates to a clock mechanism including a drive device such as that described above and a driven element which can be similar to a sprocket wheel or gear wheel, of any diameter, capable of being driven in rotation by the drive device. 
   The mechanical performance of clock drive mechanisms (motor torque, speed, etc.) is thus modulated according to the radius of the driven element associated with the drive device. 
   According to a first embodiment, the driven element is interfaced with the input sprocket wheel of the clock gear train, with the gear train including several output wheels attached to the hands to be driven, so that the driven element and the input sprocket wheel are mounted on a single shaft by means of a complete and coaxial link. 
   Given the actual forces developed by the MEMS type drive device, this first embodiment is used advantageously to replace the traditional stepping motor as well as the first gearing stage of the clock gear trains of previous design with a simplified clock drive mechanism. 
   According to a second embodiment, the purpose of which is complete elimination of the clock gear trains of previous designs, the driven element or elements are directly attached to the hand or hands to be driven. 
   In this second embodiment, the clock mechanism is simplified in relation to the mechanisms of previous design. The mechanism requires no intermediate gear train, since the movement of the hand is directly generated by the MEMS type drive device. 
   According to a preferred form of this embodiment, the mechanism includes a multiplicity of drive devices of the MEMS type and a multiplicity of driven elements attached respectively to a hand to be driven. 
   The drive devices can be identical to each other. 
   Finally, the invention also relates to a clock drive mechanism, that includes: 
   a first subassembly that includes the MEMS type drive device, a second subassembly that includes a micro-machined driven element, and 
   a base onto which the first and second subassemblies are fixed in order to allow interfacing of the drive element with the driven element facing it, wherein the subassemblies are modular and interchangeable. 
   The coupling of the drive device, formed by etching on a wafer, and an independent driven element, allows the creation of a modular mechanism, meaning a mechanism in kit form. In fact, the mechanical performance of a clock drive mechanism with no travel limit is directly modulated according to the characteristics of the driven element with which it is coupled. This characteristic provides flexibility in the choice of subassemblies, in accordance with the construction constraints of the clock drive mechanism. 
   Other characteristics and advantages of the invention will emerge from the description that follows, which is purely illustrative and non-limiting, and should be read with reference to the appended figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  schematically represents a quartz watch mechanism with a stepping motor according to a previous design. 
       FIG. 2  schematically represents the gearing elements of the mechanism of  FIG. 1 , where the input sprocket wheel of the clock gear train is attached to the rotor of the stepping motor. 
       FIG. 3  schematically represents a quartz watch mechanism according to a first embodiment of the invention, which involves replacing the stepping motor and the first gearing stage with a clock drive mechanism of the MEMS type. 
       FIGS. 4A and 4B  schematically represent subassemblies making up the MEMS type drive mechanism of  FIG. 3 , as well as the mechanical interfacing of the drive mechanism with a conventional gear train (in plane view and in section along the line A-A respectively). 
       FIG. 5  schematically represents, in section, the connection between the drive device and an input sprocket wheel in a quartz watch mechanism according to the first embodiment of the invention. 
       FIG. 6  schematically represents a quartz watch mechanism according to a variant of the first embodiment of the invention. 
       FIG. 7  schematically represents, the actuator element of the drive device, as well as the drive element, as they are created by a monolithic etching technique in a wafer of silicon. 
       FIG. 8  schematically represents the actuator element of  FIG. 7  mounted on a substrate, after executing a cut that separates the addressing electrodes from the elementary actuating modules. 
       FIG. 9  schematically represents, a drive device and a drive element as they are created directly by etching a silicon-on-insulator (SOI) substrate. 
       FIG. 10  is a detailed representation of a structure of an actuator element of the drive device, as well as a drive element. 
       FIG. 11  is a detailed representation of a structure of an engaging actuator, as well as an engaging element. 
       FIG. 12  schematically represents a simplified quartz watch mechanism according to a second embodiment of the invention. 
       FIG. 13  schematically represents, in section, the links between the drive devices and the respective output wheels attached directly to the hands to be driven, in a quartz watch mechanism according to the second embodiment of the invention. 
       FIG. 14  schematically represents a quartz watch mechanism according to a variant of the second embodiment of the invention. 
       FIG. 15  schematically illustrates the creation of an actuator element from a wafer of silicon. 
       FIG. 16  schematically represents a micro-machined driven element that has means for taking up the clearance between the wheel and the axle. 
       FIG. 17  represents the means for taking up the play, which enable spontaneous centering of the driven element on the axle on which it is mounted. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   In  FIG. 1 , a mechanism according to previous designs includes a stepping motor  1  with a rotor  2  and a stator  3 . The rotor  2  is attached to a sprocket wheel  90  which meshes with a driven element in the form of a toothed wheel  100 . The driven element  100  is attached to a multiplicity of input wheels concentric with the driven element  100 . Only one of the input wheels  102  is shown in  FIG. 1 . Each input sprocket wheel meshes with an output wheel attached to a hand to be driven. Only one output wheel  120 , driven by the input sprocket wheel  102  and the associated hand  12 , is shown in  FIG. 1 . The mechanism also includes control electronics  4 , a quartz crystal  5 , a battery  7  and a winding mechanism  8 . 
   According to the mechanism shown in  FIG. 1 , a single motor  1  and a single driven element  100  control a multiplicity of output wheels, each output wheel being associated with a hand to be driven. 
   As can be seen with greater detail in  FIG. 2 , the combination of the sprocket wheel  90  and the toothed wheel  100  form a first gearing stage. In addition, the combination of the input sprocket wheel  102  and the output wheel  120  forms a second gearing stage. The combination of these two gearing stages is used to convert the rotation speed of the rotor  2  into a rotation speed that is suitable to drive the hand  12 . The ratio of the diameters of the wheels of the gear mechanism determines the rotation speed of the hand associated with each output wheel. 
     FIG. 3  represents a quartz watch mechanism according to a first embodiment of the invention. 
   According to this first embodiment, the watch mechanism is identical to the mechanism shown in  FIG. 1 , except that the stepping motor and the sprocket wheel  90  have been replaced by a drive device  10  formed by etching a wafer of semiconductor material. The drive device  10  includes a drive element  250  that is capable of meshing sequentially with the driven element  100 , and an actuator element  20  that is capable of moving the drive element  250  with a hysteresis-type motion so that it drives a driven element  100  formed by a toothed wheel. The drive element  250  is positioned on an edge of the wafer  11  to allow interfacing with the driven element  100  facing it. 
   As can be seen with greater detail in  FIGS. 4A and 4B , in the first embodiment, the first gearing stage has been removed in relation to the mechanism of  FIG. 1 . Through a direct coupling between the drive element  250  and the driven element  100 , the drive mechanism now requires only one gearing stage per hand to be driven, where each gearing stage allows the rotation movement of the driven element  100  to be converted into a rotational movement of one of the hands (seconds, minutes or hours). 
     FIG. 5  represents, in section, the link between the drive device  10  and the driven element  100  in the quartz watch mechanism according to the first embodiment of the invention. The watch mechanism includes a base  18  onto which are fixed the assembly formed by the drive device  10  and a support  6 , as well as an axle  21  extending in a direction generally perpendicular to the base  18 . The support  6  is fixed to the base  18  of the watch mechanism by an insulating layer  56 . The axle  21  supports an input toothed wheel  100  with a rim of triangular teeth and a hub  22  fitted to rotate on the axle  21 . The drive device  10  and the input sprocket wheel  100  are positioned in relation to each other so that at rest, when the drive device  10  is not powered, the drive element  250  is in an engaged position between two teeth of the driven element  100 . 
   In operation, when the drive device  10  is powered, it drives the driven element  100  in rotation. The driven element  100  is associated with one or more input wheels by a complete and coaxial link. The input wheel or wheels  102  mesh with one or more output wheels  120 , with each output wheel being attached to a hand. 
   It will be observed that the driven element  100  formed from a toothed wheel and the hub  22  can be created by a traditional machining technique or by a micro-manufacturing technique, such as, for example, by a deep reactive ion etching (RIE) technique in a monolithic wafer of monocrystalline silicon or in a wafer of the SOI type. The selected technique allows the creation of a tooth pitch that is compatible with the amplitude of movement of the drive element  250 . 
     FIG. 6  illustrates a variant of the first embodiment of the invention. In this variant, the drive device  10  also includes an engaging element  550  that is capable of being inserted sequentially between the teeth of the driven element  100  and an engaging actuator element  50  that is capable of moving the engaging element in an alternating back-and-forth motion so that is inserted between the teeth of the driven element  100 . 
   As can be seen in  FIGS. 3 to 6 , the drive element  250  and the engaging element  550  are positioned on an external edge of the wafer  11 , so that they project out of the wafer  11  and can be coupled to the driven element. 
     FIG. 12  schematically represents a quartz watch mechanism according to a second embodiment of the invention. According to this second embodiment, one or more drive devices each meshes with one or more drive elements. As can be seen in  FIG. 12 , the drive device  10  meshes with the driven element  100  formed by a wheel, with the wheel being directly attached to a hand  12 . 
     FIG. 13  represents, in section, the links between drive devices  10 , and  50  and driven elements  100 ,  104  and  106  formed by toothed wheels in a quartz watch mechanism according to the second embodiment of the invention. 
   In this second embodiment, each drive device  10 ,  30  and  50  is similar to the drive device  10  of the first embodiment illustrated in  FIGS. 3 to 6 . Each drive device  10 ,  30  and  50  includes a drive element, referenced  250 ,  270  and  290  respectively, and an actuator element, referenced  20 ,  40  and  60  respectively. 
   The drive devices  10 ,  30  and  50  can be created by a deep reactive ion etching (RIE) technique in a monolithic wafer of monocrystalline silicon or in a wafer of the SOI type. Each drive device  10 ,  30  and  50  meshes with a driven element  100 ,  104 ,  106 , with each driven element  100 ,  104 ,  106  being attached to a hand  12 ,  14  or  16 . The hands  12 ,  14  and  16  are hands that indicate the seconds, minutes and hours, respectively. Each hand  12 ,  14  and  16  is thus made to rotate individually by a dedicated actuating device  10 ,  30  and  50 . 
   This second embodiment requires no gear mechanism. 
     FIG. 10  represents, in greater detail, the drive device  10  with the actuator element  20  and the drive element  250  in the form of a tooth  250 . The actuator element  20  is composed mainly of a first elementary actuating module  201  that is capable of moving the drive element  250  in a first direction (the radial direction) in relation to the driven element  100 , and of a second elementary actuating module  202  that is capable of moving the drive element  250  in a second direction (the tangential direction) in relation to the driven element  100 . The actuating modules  201  and  202  are capable of being controlled simultaneously in order to generate a combined hysteresis movement of the drive element  250 . 
   The drive element  250  is positioned close to the driven element  100  with the point directed toward the wheel, in a radial direction in relation to the latter. The drive element or tooth  250  is thus able to mesh with the teeth of the input sprocket wheel  100 . 
   In the remainder of this document, the term “radial” refers to any element lying or moving in a radial direction in relation to the driven element  100 , and the term “tangential” refers to any element lying or moving in a tangential direction in relation to the wheel, with the directions radial and tangential being considered at the point of the wheel at which the drive tooth is located. 
   The term “fixed” refers to any element that is fixed in relation to the support of the drive device and the term “mobile” refers to any element that is held at a certain altitude in relation to the support or to the elastic suspension means. 
   The drive tooth  250  is connected by a radial flexible rod  211  to the radial actuating module  201  and by a tangential flexible rod  212  to the tangential actuating module  202 . The radial  201  and tangential  202  actuating modules are electrostatic modules with a comb-like structure, generally known as a comb drive. This type of structure includes interdigital comb pairs. 
   A more precise description will now follow of the radial  201  and tangential  202  actuating modules of the actuator element structure  20 . 
   The radial actuating module  201  is formed from a fixed part  221  and a mobile part  231  to which the radial rod  211  is connected. 
   The fixed part  221  includes a radial electrode  223  from which a set of fixed parallel combs  225  extends in a radial direction. Each comb  225  is formed from a main rod and a series of parallel fingers or cilia connected to the rod and extending perpendicularly in relation to the latter. 
   The mobile part  231  includes a mobile frame  233  in the general shape of a U and located around the fixed part  221 . The mobile frame  233  is connected at each of its ends to the substrate by means of restraining links  237 ,  239  constituting elastic suspensions. Combs  235  extend from the mobile frame  233  in a generally radial direction. These combs  235  are formed from a main rod and a series of parallel fingers or cilia connected to the rod and extending perpendicularly to the latter. 
   The combs  225  of the fixed part  221  and the combs  235  of the mobile part  231  are positioned parallel to each other and interleaved with each other. Moreover, each mobile comb  235  is positioned opposite to a fixed comb  225  so that their fingers interleave with each other, thus forming a pair of so-called “interdigital” combs. 
   The tangential actuating module  202  has a structure similar to that of the radial actuating module  201 , except that it is oriented perpendicularly to the latter. It is formed from a fixed part  222  and a mobile part  232  to which the tangential rod  211  is connected. 
   The fixed part  222  includes a tangential electrode  224  from which a set of fixed parallel combs  226  extends in a radial direction. 
   The mobile part  232  includes a mobile frame  232  connected at each of its ends to the substrate by means of restraining links  238 ,  240  constituting elastic suspensions. Combs  236  extend from the mobile frame  232  in a general tangential direction. 
   The combs  226  of the fixed part  222  and the combs  236  of the mobile part  232  are positioned parallel to each other and interleaved with each other. In addition, each mobile comb  236  is positioned opposite to a fixed comb  226  so that their fingers interleave with each other, thus forming a pair of interdigital combs. 
   A description will now follow of the operation of the radial and tangential modules. 
   The interleaved fingers of the interdigital combs act like flat capacitors in which one of the plates is connected to electrode  223  or  222  and the other plate is grounded or connected to earth via the restraining links  237 ,  239  or  238 ,  240 . 
   When a voltage is applied to the radial electrode  223 , this voltage creates a potential difference between the fixed part  221  and the mobile part  231  of the actuating module  201 . An electric field is established between the plates of the capacitors formed by the fingers of the combs  225  and  235 . This electric field generates a tangential electrostatic force which tends to move the mobile combs  235  in relation to the fixed combs  225  in a direction parallel to the fingers of the combs, and to move the drive element  250  in a corresponding direction. 
   The tangential electrostatic force, acting between the comb fingers, drives the deformation of the frame  233  and, as a result, the movement of the drive tooth  250  by the action of the rod  211  in a radial direction in relation to the driven element  100 . Frame  233  then allows movement of the mobile combs  235  only in the direction of the fingers. 
   Likewise, the same phenomenon occurs when a voltage is applied to electrode  224 . The electrostatic force created drives the deformation of the frame  232  and the movement of the drive tooth  250  by the action of the rod  212  in a tangential direction in relation to the driven element  100 . Frame  232  allows movement of the mobile combs  236  only in the direction of the fingers. 
   The tangential actuating module  202  includes a locating post  260  that is used to limit the amplitude of movement of the mobile frame in order to hold the mobile part  232  at a distance from the fixed part  222  and prevent the mobile combs  236  from coming into contact with the fixed combs  226 . In fact, the bringing into contact of the fixed and mobile combs  226  and  236 , which are at different potentials, would necessarily result in an electrical short-circuit in the device. 
   For its part, the movement of the frame of the radial actuating module  201  is limited by the presence of a stop  270  which limits the movement of the drive tooth  250  in a radial direction. 
   It will be observed that the lateral flexibility of each of the rods allows the deformation of the latter under the action of the other rod. The two flexible radial and tangential rods  211  and  212  bring about a mechanical decoupling of the two actuating modules  201  and  202 . In fact, the flexibility of the rods allows a movement of the drive tooth  250  independently with two elementary degrees of freedom, namely in the two radial and tangential directions of motion. 
   The decoupling of the actuating modules  201  and  202  allows them to take up position in a parallel configuration. The parallel configuration of the two actuating modules  201  and  202  (as distinct from a series configuration) improves access to the electrodes  223  and  224  for the placement of power connections. 
   The electrodes  223  and  224  are controlled by phase-offset alternating voltages V r  and V t  with, for example, a phase offset of a quarter of a period in relation to each other, so that the tooth  250  is moved with a hysteresis-type motion (movement A-B-C-D). The hysteresis movement of the drive tooth  250  alternates between the drive (movement A-B) and disengaged (movement B-C-D-A) phases. This movement allows the drive tooth  250  to mesh with the successive teeth of the driven element  100  and to drive the driven element  100  in a stepped rotation movement in the clockwise direction. The driven element  100  is driven in rotation by low-amplitude excursions of the drive element. 
   To this end, the clock mechanism can advantageously include control means designed to apply periodic addressing voltages V r  and V t  at a frequency of more than 10 Hz. Such a frequency is used in order to achieve rotation movements of the hands that appear to the eye to be continuous. The drive frequency of the hands gives the optical illusion of a continuous movement of the hands. Such an effect is associated with retinal persistence which prevents the stepping movement of the hands from being followed in real time. The quartz watch or clock mechanism can therefore be viewed as a mechanical device. Moreover, the drive device  10  is used to cause the rotation speed of the hands to vary. To this end, the control means are designed so that they are able to vary the frequency of the addressing signals V r  and V t . This characteristic is particularly advantageous since it allows the position of the hands to be changed rapidly, such as when resetting the time or otherwise adjusting the watch or the clock, for example. 
   Furthermore, the drive device  10  is reversible, since it allows the driven element  100  to be moved in the clockwise or counterclockwise direction. To this end, the control means are capable of reversing the phase offset between the addressing signals V r  and V t  in order to reverse the hysteresis movement of the drive element  250  and thus reverse the direction of rotation of the driven element  100 . 
   Finally, the drive device  10  is positioned in relation to the driven element  100  so that at rest, when the drive device is not powered, the drive element  250  meshes with the driven element  100 . The drive element  250  is in the meshed position (position A) when no signal is applied to the electrodes  224  and  223 . This characteristic means that when the device is not supplied with energy, the engaging of the wheel is performed by element  250 . As a consequence, the device has a lower energy consumption. 
     FIG. 11  represents an engaging actuator element  50  which can be used in the embodiment of the clock mechanisms of  FIGS. 6 and 14 . The engaging actuator element  50  is composed of a single radial actuating module  501  and a drive element in the form of a tooth  550 . The radial actuating module  501  is similar to the radial actuating module  201  of the drive actuator element  20 . 
   The radial actuating module  501  is formed from a fixed part  521  and a mobile part  531  to which a radial rod  511  is connected. 
   The fixed part  521  includes a radial electrode  523  from which a set of fixed parallel combs  525  extends in a radial direction. Each comb  525  is formed from a main rod and a series of parallel fingers or cilia connected to the rod and extending perpendicularly in relation to the latter. 
   The mobile part  531  includes a mobile frame  533  in the general shape of a U and located around the fixed part  521 . The mobile frame  533  is connected at each of its ends to the substrate by means of restraining links  537 ,  539  constituting elastic suspensions. Combs  535  extend from the mobile frame  533  in a generally radial direction. These combs  535  are formed from a main rod and a series of parallel fingers or cilia connected to the rod and extending perpendicularly to the latter. 
   The combs  525  of the fixed part  521  and the combs  535  of the mobile part  531  are positioned parallel to each other and interleaved with each other. Moreover, each mobile comb  535  is positioned opposite to a fixed comb  525  so that their fingers interleave with each other, thus forming a pair of so-called “interdigital” combs. 
   The drive tooth  550  is of triangular shape. It is positioned close to the driven element  100  with the point directed toward the driven element, in a radial direction in relation to the latter. The drive tooth  550  is thus able to mesh with the teeth of the driven element  100 . 
   The actuator element  50  also includes a stop  560  that is used to hold the mobile part  531  at a distance from the fixed part  521  in order to prevent the mobile combs  535  from coming into contact with the fixed combs  525 . 
   The engaging module  501  of the engaging actuator element  50  is controlled in synchronisation with the elementary radial  201  and tangential  202  actuating modules of the drive actuator element  20 . The engaging actuator element  50  has the function of keeping the driven element  100  in position when the tooth  250  of the drive device is disengaged. The conjunction of the drive actuator element and the engaging actuator element provides precise control over the positioning of the driven element  100 . The engaging actuator element  50  is controlled so that it moves the tooth  550  in an alternating radial movement in relation to the driven element  100 . 
   The movement of the tooth  550  is synchronized with that of the tooth  250 . When the drive tooth  250  meshes with the driven element  100  and drives the latter in rotation (movement A-B), the engaging tooth  550  is disengaged (in position F). When the drive tooth  250  is disengaged (movement B-C-D-A), the engaging tooth  550  is inserted between the teeth of the driven element  100  (in position E) in order to hold the driven element in its position. 
   As illustrated in  FIG. 15 , the wafer  11  on which the drive device is formed is composed of a portion of a wafer  18 . A large number of elementary drive devices can thus be etched simultaneously on a single wafer using a collective production method. 
     FIGS. 7 and 8  schematically illustrate a first technique for the creation of a drive device. 
   According to this first technique, the actuating modules  201  and  202 , the drive element  250 , and where appropriate the engaging module and the engaging element (not shown), are created by deep plasma etching (Deep Reactive Ion Etching or RIE) in a solid wafer  11 . The wafer  11  can be a single block of monocrystalline silicon for example, whose thickness is between 200 and 300 μm. The wafer is etched through all of its thickness to form the various elements making up the actuating device. As can be seen in  FIG. 7 , all of the elements making up the actuating device (fixed parts  221 ,  222  and mobile parts  231 ,  232 ) are connected to a common dorsal link  270  formed in the wafer. 
   Following the etching operation, the actuating device is of monolithic form. The wafer  11  is hybridized onto a support  6  in  FIG. 8  and the link  270  is eliminated. Removal of the link  270  is effected to electrically isolate the fixed parts  221  and  222  and mobile parts  231  and  232  from each other. The support  6  performs a function of electrical insulation and anchoring for the fixed and mobile parts of the elementary actuating modules  201  and  202 . 
     FIG. 9  schematically illustrates a second technique for the creation of an actuating device. 
   In this second technique, the drive device  10  is created by deep plasma etching (Deep Reactive Ion Etching or RIE) in a wafer  11  of the SOI (Silicon On Insulator) type. Such a wafer  11  includes a silicon substrate layer  15  with a thickness on the order of 380 μm, a sacrificial layer  16  of silicon oxide with a thickness of about 2 μm and a silicon layer  17  with a thickness on the order of 50 to 100 μm. 
   The actuating modules  201  and  202 , the drive element  250 , and where appropriate the engaging module and the engaging element (not shown), are created by deep reactive ion etching (RIE) in the thickness of the silicon layer  15 , up to the silicon oxide layer  16  which constitutes a stop layer. Then the silicon oxide layer  16  is dissolved in zones by wet chemical etching. The dissolved zones liberate the mobile parts of the drive device (mobile combs, rods, drive element, etc.). 
   The parts  16  of the silicon oxide layer that remain after the dissolving action create links between the substrate layer  15  and the actuating modules  201  and  202 . The mobile parts  231 ,  232  of the actuating modules are then raised in relation to the substrate layer  15  to an altitude or height equal to the thickness of the sacrificial silicon oxide layer. The silicon oxide layer performs a function of electrical insulation and anchoring support for the fixed and mobile parts of the elementary actuating modules  201  and  202 . 
   The resulting drive device can then be hybridized onto an insulating support  6 . 
   Other techniques for creation of the actuating device can be employed equally well of course. It is possible, for example, to use an HARPSS etching technique (High Aspect Ratio combined Poly and Single-crystal Silicon) on a wafer of silicon. 
   In comparison with the traditionally motor-driven mechanisms used in the clockmaking field, the drive device that has just been described generally has the following advantages: 
   it allows partial or total removal of the gearing stages in the quartz watch or clock mechanisms, 
   as a result, it improves the efficiency of the clock gear trains, as a result, it provides greater independence to the quartz watch or clock mechanisms, 
   it allows simplification of the mechanical architecture of the clock movements, and 
   it also allows production costs to be reduced. 
     FIG. 16  schematically represents a toothed wheel  100  formed by etching a substrate. The driven element  100  includes a hole  600  formed at its center, this hole being intended to receive an axle  21 , around which the driven element  100  is designed to rotate. The mechanism includes means to take up the play between the driven element  100  and the axle  21 . The means for taking up the play include a multiplicity of flexible elastic leaves  601 ,  602  and  603  positioned between the driven element  100  and the axle  21 . More precisely, as illustrated in  FIG. 16 , the leaves  601 ,  602  and  603  are formed integrally with the driven element  100  during the etching stage. The leaves  601 ,  602  and  603  are formed during the etching of the central hole  600 . Each elastic leaf  601 ,  602  and  603  extends from the driven element  100  and makes contact with the axle  21 . 
   In a more detailed manner,  FIG. 17  represents the position of the hole  600  in the driven element  100  in relation to the axle  21  when the axle  21  is centered in relation to the hole  600 . As can be seen in this figure, the leaves  601 ,  602  and  603  are formed as a single part with the driven element  100  during the etching of the hole  600 . To this end, the hole created in the driven element  100  is not circular, but is cut out to form reliefs making up the means that take up the play between the driven element  100  and the axle  21 . 
   The reliefs in particular include the flexible leaves  601 ,  602  and  603 . The flexible leaves are used to hold the driven element  100  on the rotation axle  21  in spite of any play between the hole  600  of the driven element  100  and the rotation axle  21 . Moreover, the flexible leaves compensate for any offset from center of the axle and/or of the hole in relation to the driven element. 
   The reliefs formed by the hole  600  also include locating posts  611 ,  612  and  613  formed by protuberances, each locating post being positioned between one of the leaves  601 ,  602  and  603  and the driven element  100 . These locating posts  611 ,  612  and  613  are intended to limit the movement of the leaves  611 ,  612  and  613  when the latter are flexed. 
   The reliefs also include locating posts  621 ,  631 ,  622 ,  632 ,  623  and  633  formed by larger protuberances located on either side of the leaves  601 ,  602  and  603 . The locating posts  621 ,  631 ,  622 ,  632 ,  623  and  633  are positioned between the axle  21  and the driven element  100 . The locating posts  621 ,  631 ,  622 ,  632 ,  623  and  633  are intended to limit any offset from center of the axle  21  in relation to the hole  600 . The locating posts  621 ,  631 ,  622 ,  632 ,  623  and  633  thus limit the deformation of the leaves  601 ,  602  and  603  and guarantee continuous contact of the axle  21  with all of the leaves.