Patent Grant
7636277
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.
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.
In
According to the mechanism shown in
As can be seen with greater detail in
According to this first embodiment, the watch mechanism is identical to the mechanism shown in
As can be seen with greater detail in
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.
As can be seen in
In this second embodiment, each drive device 10, 30 and 50 is similar to the drive device 10 of the first embodiment illustrated in
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.
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 Vr and Vt 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 Vr and Vt 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 Vr and Vt. 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 Vr and Vt 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.
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
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
Following the etching operation, the actuating device is of monolithic form. The wafer 11 is hybridized onto a support 6 in
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.
In a more detailed manner,
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04 09333 | Sep 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/054298 | 9/1/2005 | WO | 00 | 3/5/2007 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/024651 | 3/9/2006 | WO | A |
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