Horology: time measuring systems or devices – Chronological – With manually actuated display
Reexamination Certificate
1999-11-01
2001-06-26
Roskoski, Bernard (Department: 2859)
Horology: time measuring systems or devices
Chronological
With manually actuated display
C368S185000, C368S187000
Reexamination Certificate
active
06252825
ABSTRACT:
The present invention concerns a timepiece, in particular a watch, including a rotating member and an electric capacitive detection device for detecting positions and/or movements of said wheel, wherein the detection device includes at least one capacitive sensor, having a fixed portion provided with one or more fixed electrodes and a mobile portion provided with an electrically conductive rotor driven by said rotating member, and electronic detection means which are sensitive to variations in said sensor's capacitance.
The invention applies particularly, but not exclusively, to the control of functions such as the manual correction of the time or date in an electronic watch by means of the conventional control stem fitted with an external crown. Detection of said stem's movements of rotation and translation are usually essentially based on electromechanical switches actuated by an arrangement of cams attached to the stem, such cams acting on flexible contact strips which touch fixed contacts generally provided on a printed circuit which includes other timepiece components.
The main difficulty in manufacturing and assembling such switches lies in the reliability of the electric contact closure, which requires very precise positioning of each contact strip with respect to the corresponding cam and wit respect to the corresponding fixed contact. It is thus necessary to perform operating tests and perhaps adjustments during assembly of each timepiece. These operations are expensive and considerably inconvenience automation of the assembly of the watches.
Similar problems arise with electric contacts arranged to detect particular positions of a rotating member, for example the “zero” position of a chronograph hand or a date indicator.
It would thus be desirable to replace the aforementioned switches with contactless devices, able to be used in watches.
German Patent Application 3934158 A1 discloses a pulse generator able to be used for controlling an electronic watch in a domestic appliance, such generator approximately corresponding to a capacitive sensor of the type indicated in the preamble hereinbefore. A disc-shaped rotor, which rotates about an axis perpendicular to the disc, carries a flat electrode having two diametrically opposite sectors, opposite a flat stator provided with several fixed electrodes arranged in a particular manner and connected to electronic detection circuits. A thin dielectric is placed between the stator and the rotor. When the rotor rotates, pulses are generated from variations in the capacitive coupling generated by the rotor's electrode between different electrodes of the stator, as a result of variations in the overlapping surface between the rotor and each fixed electrode, while the thickness of the dielectric between the electrodes remains constant.
Such a construction requires far too much space for applications in the horological industry, in particular for watches. Moreover, the rotor must be assembled with sufficient accuracy and stability for the distance between the electrodes, i.e. the thickness of the dielectric, to remain constant.
An object of the present invention is to avoid the drawbacks of the prior art by providing a reliable contactless detection device, able to be used in a timepiece, such as a watch, able to be made and assembled inexpensively and able to be advantageously applied to correction of the time or date or detection of a particular position of a rotating member.
The invention thus concerns a timepiece as defined in the preamble, characterized in that each fixed electrode is arranged facing a peripheral surface of the rotor, said surface including teeth arranged to pass close to each fixed electrode during rotation of the rotor.
Thus, the detection device essentially acts via capacitance variation as a result of the variation in distance between the toothed peripheral surface of the rotor and each fixed electrode. By its very nature, such a device can be made in a compact, low electric energy consuming form, making it well suited to use in a watch. Moreover, capacitive sensors which allow a fairly high number of successive angular positions, for example eight or twelve positions per revolution, can be made without excessive complication.
In a particular embodiment, the fixed portion of the capacitive sensor includes a pair of fixed electrodes and the rotor is arranged to influence the electric field between the fixed electrodes by its position of rotation. The rotor may be held at a fixed potential, its teeth being arranged to form a shield in the electric field between the fixed electrodes.
These two fixed electrodes are preferably coplanar on a substrate and are separated from each other by a gap, the axis of the rotor being arranged facing said gap and parallel to the fixed electrodes. The substrate may advantageously form part of a printed circuit element of the timepiece, i.e. using an element which already exists in an electronic or electromechanical clockwork movement.
In the aforementioned embodiment, in order to maintain a constant gap between the rotor and the fixed electrodes, the rotor may be attached to the rotating member, which includes a support cylinder which abuts by sliding against a dielectric layer disposed on the substrate and/or on the fixed electrodes. This allows any adjustment of the sensor to be avoided during assembly of the rotating member.
In another arrangement with two fixed electrodes, the fixed electrodes form two respective opposite spaced plates and the rotor is disposed between them, its axis of rotation being parallel thereto. As a result of the toothed shape of the peripheral surface of the rotor, the variation in capacitance between the electrodes is due in this case to the dielectric thickness modulation. In this arrangement also, the fixed electrodes can be situated on a same printed circuit substrate, for example on two opposite edges of an opening in the substrate. The rotor may be insulated and act as transmitter of an electric signal between the two fixed electrodes. The rotor is then at a floating potential.
Another advantageous embodiment of the sensor including a pair of fixed electrodes is characterized in that the rotor is a mobile electrode which is connected to the detection means and whose teeth, during rotation thereof, pass alternately opposite one or other of the fixed electrodes. The rotor thus forms a third electrode for injecting a signal into the two capacitors which it forms respectively with the two fixed electrodes.
Another embodiment is characterized in that the fixed portion of the capacitive sensor includes an annular stator provided with inner teeth forming a fixed electrode and in that the rotor is disposed within the stator, its teeth forming a mobile electrode facing the stator teeth. One thereby obtains, in a construction of relatively small volume, electrodes having a relatively large surface and a small distance between such surfaces, thus quite a high capacitance. The higher the number of teeth, the higher the angular resolution of the sensor. The stator may be coated inside with a thin dielectric layer against which the rotor is capable of sliding, which assures the centering of the rotor within the stator.
In order for the contactless detection device to be able also to indicate the direction of rotation of the rotating member, the detection device also preferably includes two of said capacitive sensors, which are offset angularly so as to provide respective output signals which are in quadrature during rotation of the rotating member.
Other features and advantages of the present invention will appear in the following description of different embodiment examples, with reference to the annexed drawings, in which:
FIG. 1
shows schematically a first embodiment of the invention, more particularly a contactless device for detecting the positions of a rotating member, such device including a capacitive sensor,
FIG. 2
is a similar view to
FIG. 1
, illustrating another position of the rotating member,
FIG. 3
is a schematic transve
ETA SA Fabriques d'Ebauches
Griffin & Szipl, P.C.
Roskoski Bernard
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