Drive device, particularly for a clockwork mechanism

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.

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.

DESCRIPTION OF PREFERRED EMBODIMENTS

InFIG. 1, a mechanism according to previous designs includes a stepping motor1with a rotor2and a stator3. The rotor2is attached to a sprocket wheel90which meshes with a driven element in the form of a toothed wheel100. The driven element100is attached to a multiplicity of input wheels concentric with the driven element100. Only one of the input wheels102is shown inFIG. 1. Each input sprocket wheel meshes with an output wheel attached to a hand to be driven. Only one output wheel120, driven by the input sprocket wheel102and the associated hand12, is shown inFIG. 1. The mechanism also includes control electronics4, a quartz crystal5, a battery7and a winding mechanism8.

According to the mechanism shown inFIG. 1, a single motor1and a single driven element100control a multiplicity of output wheels, each output wheel being associated with a hand to be driven.

As can be seen with greater detail inFIG. 2, the combination of the sprocket wheel90and the toothed wheel100form a first gearing stage. In addition, the combination of the input sprocket wheel102and the output wheel120forms a second gearing stage. The combination of these two gearing stages is used to convert the rotation speed of the rotor2into a rotation speed that is suitable to drive the hand12. 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. 3represents 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 inFIG. 1, except that the stepping motor and the sprocket wheel90have been replaced by a drive device10formed by etching a wafer of semiconductor material. The drive device10includes a drive element250that is capable of meshing sequentially with the driven element100, and an actuator element20that is capable of moving the drive element250with a hysteresis-type motion so that it drives a driven element100formed by a toothed wheel. The drive element250is positioned on an edge of the wafer11to allow interfacing with the driven element100facing it.

As can be seen with greater detail inFIGS. 4A and 4B, in the first embodiment, the first gearing stage has been removed in relation to the mechanism ofFIG. 1. Through a direct coupling between the drive element250and the driven element100, 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 element100to be converted into a rotational movement of one of the hands (seconds, minutes or hours).

FIG. 5represents, in section, the link between the drive device10and the driven element100in the quartz watch mechanism according to the first embodiment of the invention. The watch mechanism includes a base18onto which are fixed the assembly formed by the drive device10and a support6, as well as an axle21extending in a direction generally perpendicular to the base18. The support6is fixed to the base18of the watch mechanism by an insulating layer56. The axle21supports an input toothed wheel100with a rim of triangular teeth and a hub22fitted to rotate on the axle21. The drive device10and the input sprocket wheel100are positioned in relation to each other so that at rest, when the drive device10is not powered, the drive element250is in an engaged position between two teeth of the driven element100.

In operation, when the drive device10is powered, it drives the driven element100in rotation. The driven element100is associated with one or more input wheels by a complete and coaxial link. The input wheel or wheels102mesh with one or more output wheels120, with each output wheel being attached to a hand.

It will be observed that the driven element100formed from a toothed wheel and the hub22can 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 element250.

FIG. 6illustrates a variant of the first embodiment of the invention. In this variant, the drive device10also includes an engaging element550that is capable of being inserted sequentially between the teeth of the driven element100and an engaging actuator element50that is capable of moving the engaging element in an alternating back-and-forth motion so that is inserted between the teeth of the driven element100.

As can be seen inFIGS. 3 to 6, the drive element250and the engaging element550are positioned on an external edge of the wafer11, so that they project out of the wafer11and can be coupled to the driven element.

FIG. 12schematically 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 inFIG. 12, the drive device10meshes with the driven element100formed by a wheel, with the wheel being directly attached to a hand12.

FIG. 13represents, in section, the links between drive devices10, and50and driven elements100,104and106formed by toothed wheels in a quartz watch mechanism according to the second embodiment of the invention.

In this second embodiment, each drive device10,30and50is similar to the drive device10of the first embodiment illustrated inFIGS. 3 to 6. Each drive device10,30and50includes a drive element, referenced250,270and290respectively, and an actuator element, referenced20,40and60respectively.

The drive devices10,30and50can 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 device10,30and50meshes with a driven element100,104,106, with each driven element100,104,106being attached to a hand12,14or16. The hands12,14and16are hands that indicate the seconds, minutes and hours, respectively. Each hand12,14and16is thus made to rotate individually by a dedicated actuating device10,30and50.

This second embodiment requires no gear mechanism.

FIG. 10represents, in greater detail, the drive device10with the actuator element20and the drive element250in the form of a tooth250. The actuator element20is composed mainly of a first elementary actuating module201that is capable of moving the drive element250in a first direction (the radial direction) in relation to the driven element100, and of a second elementary actuating module202that is capable of moving the drive element250in a second direction (the tangential direction) in relation to the driven element100. The actuating modules201and202are capable of being controlled simultaneously in order to generate a combined hysteresis movement of the drive element250.

The drive element250is positioned close to the driven element100with the point directed toward the wheel, in a radial direction in relation to the latter. The drive element or tooth250is thus able to mesh with the teeth of the input sprocket wheel100.

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 element100, 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 tooth250is connected by a radial flexible rod211to the radial actuating module201and by a tangential flexible rod212to the tangential actuating module202. The radial201and tangential202actuating 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 radial201and tangential202actuating modules of the actuator element structure20.

The radial actuating module201is formed from a fixed part221and a mobile part231to which the radial rod211is connected.

The fixed part221includes a radial electrode223from which a set of fixed parallel combs225extends in a radial direction. Each comb225is 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 part231includes a mobile frame233in the general shape of a U and located around the fixed part221. The mobile frame233is connected at each of its ends to the substrate by means of restraining links237,239constituting elastic suspensions. Combs235extend from the mobile frame233in a generally radial direction. These combs235are formed from a main rod and a series of parallel fingers or cilia connected to the rod and extending perpendicularly to the latter.

The combs225of the fixed part221and the combs235of the mobile part231are positioned parallel to each other and interleaved with each other. Moreover, each mobile comb235is positioned opposite to a fixed comb225so that their fingers interleave with each other, thus forming a pair of so-called “interdigital” combs.

The tangential actuating module202has a structure similar to that of the radial actuating module201, except that it is oriented perpendicularly to the latter. It is formed from a fixed part222and a mobile part232to which the tangential rod211is connected.

The fixed part222includes a tangential electrode224from which a set of fixed parallel combs226extends in a radial direction.

The mobile part232includes a mobile frame232connected at each of its ends to the substrate by means of restraining links238,240constituting elastic suspensions. Combs236extend from the mobile frame232in a general tangential direction.

The combs226of the fixed part222and the combs236of the mobile part232are positioned parallel to each other and interleaved with each other. In addition, each mobile comb236is positioned opposite to a fixed comb226so 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 electrode223or222and the other plate is grounded or connected to earth via the restraining links237,239or238,240.

When a voltage is applied to the radial electrode223, this voltage creates a potential difference between the fixed part221and the mobile part231of the actuating module201. An electric field is established between the plates of the capacitors formed by the fingers of the combs225and235. This electric field generates a tangential electrostatic force which tends to move the mobile combs235in relation to the fixed combs225in a direction parallel to the fingers of the combs, and to move the drive element250in a corresponding direction.

The tangential electrostatic force, acting between the comb fingers, drives the deformation of the frame233and, as a result, the movement of the drive tooth250by the action of the rod211in a radial direction in relation to the driven element100. Frame233then allows movement of the mobile combs235only in the direction of the fingers.

Likewise, the same phenomenon occurs when a voltage is applied to electrode224. The electrostatic force created drives the deformation of the frame232and the movement of the drive tooth250by the action of the rod212in a tangential direction in relation to the driven element100. Frame232allows movement of the mobile combs236only in the direction of the fingers.

The tangential actuating module202includes a locating post260that is used to limit the amplitude of movement of the mobile frame in order to hold the mobile part232at a distance from the fixed part222and prevent the mobile combs236from coming into contact with the fixed combs226. In fact, the bringing into contact of the fixed and mobile combs226and236, 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 module201is limited by the presence of a stop270which limits the movement of the drive tooth250in 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 rods211and212bring about a mechanical decoupling of the two actuating modules201and202. In fact, the flexibility of the rods allows a movement of the drive tooth250independently with two elementary degrees of freedom, namely in the two radial and tangential directions of motion.

The decoupling of the actuating modules201and202allows them to take up position in a parallel configuration. The parallel configuration of the two actuating modules201and202(as distinct from a series configuration) improves access to the electrodes223and224for the placement of power connections.

The electrodes223and224are controlled by phase-offset alternating voltages Vrand Vtwith, for example, a phase offset of a quarter of a period in relation to each other, so that the tooth250is moved with a hysteresis-type motion (movement A-B-C-D). The hysteresis movement of the drive tooth250alternates between the drive (movement A-B) and disengaged (movement B-C-D-A) phases. This movement allows the drive tooth250to mesh with the successive teeth of the driven element100and to drive the driven element100in a stepped rotation movement in the clockwise direction. The driven element100is 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 Vrand Vtat 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 device10is 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 Vrand 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 device10is reversible, since it allows the driven element100to 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 Vrand Vtin order to reverse the hysteresis movement of the drive element250and thus reverse the direction of rotation of the driven element100.

Finally, the drive device10is positioned in relation to the driven element100so that at rest, when the drive device is not powered, the drive element250meshes with the driven element100. The drive element250is in the meshed position (position A) when no signal is applied to the electrodes224and223. This characteristic means that when the device is not supplied with energy, the engaging of the wheel is performed by element250. As a consequence, the device has a lower energy consumption.

FIG. 11represents an engaging actuator element50which can be used in the embodiment of the clock mechanisms ofFIGS. 6 and 14. The engaging actuator element50is composed of a single radial actuating module501and a drive element in the form of a tooth550. The radial actuating module501is similar to the radial actuating module201of the drive actuator element20.

The radial actuating module501is formed from a fixed part521and a mobile part531to which a radial rod511is connected.

The fixed part521includes a radial electrode523from which a set of fixed parallel combs525extends in a radial direction. Each comb525is 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 part531includes a mobile frame533in the general shape of a U and located around the fixed part521. The mobile frame533is connected at each of its ends to the substrate by means of restraining links537,539constituting elastic suspensions. Combs535extend from the mobile frame533in a generally radial direction. These combs535are formed from a main rod and a series of parallel fingers or cilia connected to the rod and extending perpendicularly to the latter.

The combs525of the fixed part521and the combs535of the mobile part531are positioned parallel to each other and interleaved with each other. Moreover, each mobile comb535is positioned opposite to a fixed comb525so that their fingers interleave with each other, thus forming a pair of so-called “interdigital” combs.

The drive tooth550is of triangular shape. It is positioned close to the driven element100with the point directed toward the driven element, in a radial direction in relation to the latter. The drive tooth550is thus able to mesh with the teeth of the driven element100.

The actuator element50also includes a stop560that is used to hold the mobile part531at a distance from the fixed part521in order to prevent the mobile combs535from coming into contact with the fixed combs525.

The engaging module501of the engaging actuator element50is controlled in synchronisation with the elementary radial201and tangential202actuating modules of the drive actuator element20. The engaging actuator element50has the function of keeping the driven element100in position when the tooth250of 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 element100. The engaging actuator element50is controlled so that it moves the tooth550in an alternating radial movement in relation to the driven element100.

The movement of the tooth550is synchronized with that of the tooth250. When the drive tooth250meshes with the driven element100and drives the latter in rotation (movement A-B), the engaging tooth550is disengaged (in position F). When the drive tooth250is disengaged (movement B-C-D-A), the engaging tooth550is inserted between the teeth of the driven element100(in position E) in order to hold the driven element in its position.

As illustrated inFIG. 15, the wafer11on which the drive device is formed is composed of a portion of a wafer18. A large number of elementary drive devices can thus be etched simultaneously on a single wafer using a collective production method.

FIGS. 7 and 8schematically illustrate a first technique for the creation of a drive device.

According to this first technique, the actuating modules201and202, the drive element250, 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 wafer11. The wafer11can 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 inFIG. 7, all of the elements making up the actuating device (fixed parts221,222and mobile parts231,232) are connected to a common dorsal link270formed in the wafer.

Following the etching operation, the actuating device is of monolithic form. The wafer11is hybridized onto a support6inFIG. 8and the link270is eliminated. Removal of the link270is effected to electrically isolate the fixed parts221and222and mobile parts231and232from each other. The support6performs a function of electrical insulation and anchoring for the fixed and mobile parts of the elementary actuating modules201and202.

FIG. 9schematically illustrates a second technique for the creation of an actuating device.

In this second technique, the drive device10is created by deep plasma etching (Deep Reactive Ion Etching or RIE) in a wafer11of the SOI (Silicon On Insulator) type. Such a wafer11includes a silicon substrate layer15with a thickness on the order of 380 μm, a sacrificial layer16of silicon oxide with a thickness of about 2 μm and a silicon layer17with a thickness on the order of 50 to 100 μm.

The actuating modules201and202, the drive element250, 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 layer15, up to the silicon oxide layer16which constitutes a stop layer. Then the silicon oxide layer16is 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 parts16of the silicon oxide layer that remain after the dissolving action create links between the substrate layer15and the actuating modules201and202. The mobile parts231,232of the actuating modules are then raised in relation to the substrate layer15to 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 modules201and202.

The resulting drive device can then be hybridized onto an insulating support6.

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. 16schematically represents a toothed wheel100formed by etching a substrate. The driven element100includes a hole600formed at its center, this hole being intended to receive an axle21, around which the driven element100is designed to rotate. The mechanism includes means to take up the play between the driven element100and the axle21. The means for taking up the play include a multiplicity of flexible elastic leaves601,602and603positioned between the driven element100and the axle21. More precisely, as illustrated inFIG. 16, the leaves601,602and603are formed integrally with the driven element100during the etching stage. The leaves601,602and603are formed during the etching of the central hole600. Each elastic leaf601,602and603extends from the driven element100and makes contact with the axle21.

In a more detailed manner,FIG. 17represents the position of the hole600in the driven element100in relation to the axle21when the axle21is centered in relation to the hole600. As can be seen in this figure, the leaves601,602and603are formed as a single part with the driven element100during the etching of the hole600. To this end, the hole created in the driven element100is not circular, but is cut out to form reliefs making up the means that take up the play between the driven element100and the axle21.

The reliefs in particular include the flexible leaves601,602and603. The flexible leaves are used to hold the driven element100on the rotation axle21in spite of any play between the hole600of the driven element100and the rotation axle21. 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 hole600also include locating posts611,612and613formed by protuberances, each locating post being positioned between one of the leaves601,602and603and the driven element100. These locating posts611,612and613are intended to limit the movement of the leaves611,612and613when the latter are flexed.

The reliefs also include locating posts621,631,622,632,623and633formed by larger protuberances located on either side of the leaves601,602and603. The locating posts621,631,622,632,623and633are positioned between the axle21and the driven element100. The locating posts621,631,622,632,623and633are intended to limit any offset from center of the axle21in relation to the hole600. The locating posts621,631,622,632,623and633thus limit the deformation of the leaves601,602and603and guarantee continuous contact of the axle21with all of the leaves.