EP1128239B1 - Portable object, in particular time piece, incorporating a piezo-electric transducer for manually introducing data - Google Patents

Abstract

The button free watch (1) has a piezoelectric transducer (32) fixed to the rear of the case (2) which creates command and data control impulses.

Description

The present invention relates to a portable object such as, in particular, a timepiece, comprising a piezoelectric transducer for the manual introduction of data. More particularly, the present invention aims to use the piezoelectric transducer operating as a sound generator in an alarm wristwatch to perform the function of a push switch.

We know by the patent US 5,742,564 in the name of Junghans Uhren GmbH a timepiece such as a wristwatch comprising a flat box or a slightly sealed case closed by an ice-cream. A circular plate serving as a dial carries index hours. This plate, placed under the ice, is forced into the box. It is delimited at its periphery by a support flange which extends along the inner cylindrical surface of the box and which defines a space between the ice and said plate in which the needles of the watch move. Piezoelectric sensors, preferably four in number, are arranged at regular intervals on the flange of the flange, between this flange and the flange facing the ice. These sensors act as control switches for the watchmaking functions of the watch. They are manually operated by axial pressure on the edge of the ice. To be able to respond to requests from the user, the ice must be slightly mobile. For this purpose, the ice is elastically mounted relative to the box by means of a rigid rubber ring. The piezoelectric sensors are connected to an electrical circuit arranged under the dial and which detects the pressures exerted on these sensors.

The invention described in the Junghans patent provides a wristwatch that is devoid of rod or push button and is therefore less expensive to manufacture and a more attractive aesthetic appearance. The watch functions of this watch are controlled by simple mechanical pressure on piezoelectric sensors which, in response to this solicitation, produce a voltage that acts on the desired watch function via an appropriate electronic circuit.

The Junghans watch has unfortunately some drawbacks among which we can mention the fact that the ice must be mounted slightly movable, which poses significant problems of adjustment of this ice compared to the watch case. These problems of course have a negative impact on manufacturing costs and are only partially solved by the use of a rigid ring. rubber disposed between said ice and the middle of said box. Indeed, because of its rigidity, the rubber ring can hardly compensate for the games between the ice and the watch case, so that a good seal can not be guaranteed. The risks of moisture entering the watch are therefore important which, it will be easily understood, is not acceptable. Similarly, solid particles can be housed between the rubber ring and the ice and seize the operation of the mechanism. Finally, as described above, the Junghans system is activated by a succession of mechanical pressures exerted on the ice of the watch. Under these pressures, the piezoelectric sensors deform and generate a voltage that is applied to the input of an electronic circuit of interpretation. In response to this signal, the electronic circuit will act on the desired horological function. However, the repetition of these pressures may, after a while, damage or even put the sensors out of use. Above all, it is not easy for the user to exert sufficient pressure to actuate the sensors without being excessive and risk damaging these sensors.

The document US 4,769,797 discloses a timepiece, comprising means for displaying at least one piece of information and a case formed of an upper part comprising an ice covering the display means and a bottom part delimited by a bottom located underneath. said display means, said object comprising a piezoelectric transducer producing an electrical voltage when a mechanical pressure is exerted on said upper part, the voltage produced by the piezoelectric transducer being applied to a first electronic circuit which will generate a logic signal in response to the pressure exerted, this electronic circuit being arranged inside said housing, said piezoelectric transducer being arranged in the lower part of said housing and is rigidly connected to this housing.

Thanks to these characteristics, the mechanical pressure that accompanies the manual introduction of data can be exerted anywhere on the surface of the ice. Under the effect of this pressure, the wrist of the wearer of the watch exerts a reaction force on the housing. The latter then deforms very slightly, whether plastic, metal or other. Since the piezoelectric transducer is rigidly connected to this housing, it is deformed by the deformations of the housing and typically generates an electrical voltage in response to this deformation. This is no more likely to damage the transducer under the effect of too high mechanical pressure. Similarly, the transducer, which is no longer wedged between a fixed part and a moving part, can withstand a very large number of successive pressures without its physical characteristics being degraded over time.

Another advantage of such a watch lies in the fact that the portable object has no moving part. Thus, the watch crystal is fixedly mounted relative to the case of said watch, for example by gluing or ultrasonic welding or by driving with interposition of a seal between the ice and the box. The waterproofness of the watch is thus not impaired and the construction of such a watch is very simple and therefore inexpensive.

Such a device is a watch whose watch functions can be controlled by simple mechanical pressure on the ice. Thus, the watch may be devoid of rod or push button, which further reduces its manufacturing costs. There are, of course, other tactile pressure data entry systems which use, for example, capacitive, inductive, ultrasonic or infrared keys. The disadvantage of such systems however lies in the fact that before they can be used, they must be placed in an active mode of receiving commands in which they consume electric current.

The portable object described in US 4,769,797 further comprises a second electronic circuit that operates the piezoelectric transducer as a source of vibration for a sound generator.

Thanks to this characteristic, the same piezoelectric transducer can be used both as a sound generator for an alarm device, for example in an electronic wristwatch, and as a means for introducing data by mechanical pressure on the ice of this watch. Such an embodiment is, it will be easily understood, particularly advantageous. It reduces the number of components used, and therefore the volume that these components occupy in the box, and limit manufacturing costs.

The present invention relates to a portable object of the type indicated in the preamble of claim 1 (described in US 47 69 797 and characterized by the features of the characterizing portion of claim 1. Optional features are described in the dependent claims.

• la figure 1 est une vue générale en coupe dans une pièce d'horlogerie selon l'invention;
• la figure 2 représente un schéma électrique d'un circuit permettant d'utiliser le transducteur piézo-électrique fonctionnant comme générateur de son pour réaliser la fonction d'un commutateur à poussoir, et
• la figure 3 est un diagramme des niveaux de tension en fonction du temps en deux endroits du circuit de la figure 2.

Other characteristics and advantages of the present invention will appear more clearly on reading the following detailed description of an exemplary embodiment of the portable object according to the invention, this example being given purely by way of illustration and not limitation, in conjunction with the accompanying drawings in which:

• the figure 1 is a general sectional view in a timepiece according to the invention;
• the figure 2 represents a circuit diagram of a circuit for using the piezoelectric transducer operating as a sound generator to perform the function of a push switch, and
• the figure 3 is a diagram of voltage levels versus time in two places in the circuit of the figure 2 .

It will be noted from now on that, although the following description concerns a timepiece and, in particular, a wristwatch, the present invention is not limited to such a timepiece and can easily be applied any other portable object in which is arranged a piezoelectric transducer for the manual introduction of data.

We will first refer to the figure 1 on which is represented a timepiece according to the invention, designated as a whole by the general reference numeral 1.

The timepiece 1 conventionally comprises a housing 2 provided with a middle part 4 and a bottom 6 which delimits the housing 2 in its lower part. In the example shown, the bottom 6 is made in one piece with the middle part 4. However, it goes without saying that the present invention applies in the same way to a box that would not be monohull and which would include a bottom distinct from the middle part. The housing 2 can be made, for example, of a plastic material according to well-known injection techniques. The present invention is not limited to the choice of such a material and the housing 2 can be made of any type of material adapted to the needs of the watch industry such as, in particular, steel.

The timepiece 1 also comprises a horometric movement 8 mounted in a casing ring 10. This movement 8 is supplied with current by an electric battery 12 which can, if necessary, be recharged after exhaustion. The battery 12, shown schematically on the figure 1 typically has the shape of a pellet. It can be housed in the bottom 6 of the watch 1. The lower face of the battery 12 which constitutes one of its poles is electrically connected to the mass of the watch 1, for example by means of a contact with spring 13 fixed on the bottom 6 of said watch 1. The other pole of the battery 12 which is constituted by its upper face is, in the usual way, electrically connected to the horometric movement 8.

In its upper part, the housing 2 is delimited by an ice 14 covering display means 16 of a time information. In the example shown in figure 1 these display means 16 consist of a dial 18 above which move an hour hand 20, a minute hand 22 and a second hand 24. It is therefore analog means of displaying the time. It could also be digital display means constituted by a liquid crystal cell.

Finally, the housing 2 comprises at its upper periphery a notch 26 in which is engaged a telescope 28 which ensures the attachment of the lens 14 to the housing 2. The bezel 28 is fixedly mounted on the housing 2, for example by gluing or by ultrasonic welding or else by driving. The window 14 is sealed against the housing 2 by the use of a seal 30 wedged between the window and the housing.

A piezoelectric transducer 32 is arranged in the lower part of the case 2 of the watch 1 and is rigidly connected to this case 2. This transducer 32 can be used for the sole purpose of introducing data into the watch 1. The transducer 32 is used both as a sound generator for the alarm device of watch 1, and as a means for introducing data by successive mechanical pressure on the glass 14 of this watch 1. For this purpose, the piezoelectric transducer 32 consists of an element made, for example, of a piezoelectric ceramic. This element may have, without limitation, a circular shape, its diameter typically being between ten and fifteen millimeters, and its thickness being of the order of a few tenths of millimeters. As is apparent from the figure 1 this element is bonded between two upper metal electrodes 34 and lower 36. The lower electrode 36 is rigidly connected to the bottom 6 of the housing 2 by any appropriate means such as, for example, by gluing. The electrodes 34, 36 are connected via an electronic circuit 38 for training and interpretation which will be described in detail with reference to FIG. figure 2 at the terminals of the electric battery 12 by means of contact strips respectively 34a and 36a.

The electrical circuit 38 whose diagram is shown in FIG. figure 2 comprises, connected to the output of switching means comprising a transistor T _R0 alternately passing and blocked, a coil L ₁ . The piezoelectric transducer 32 is connected in parallel to the coil L ₁ . This electrical circuit 38 receives, on an input connection "a", a pulsed pulse control signal corresponding to that shown in curve A of FIG. figure 3 whose abscissa represents the time "t" and the ordinate the voltage "v". From the input terminal "a", this signal is applied to the base of the transistor T _R0 via a resistor R ₀ . When the transistor T _R0 , which is a bipolar transistor npn, is held through the pulse of the control signal, an electric current flows through the coil L ₁ from a DC voltage source + E, while the connection "b" of the piezoelectric transducer 32 is connected by the transistor T _R0 to the ground of the electrical circuit 38 as shown by the curve B of the figure 3 (which has the time "t" on the abscissa and the voltage "v" on the ordinate).

At the moment when the transistor T _R0 goes to the off state during the falling edge of each pulse of the waveform A, all the energy accumulated in the coil L ₁ is transmitted to the terminals of the piezoelectric transducer 32, charging it has a voltage well above the supply voltage + E. This high amplitude pulse provides the piezoelectric transducer 32 with the efficient electrical energy it needs to function as a sound generator. According to a variant, to obtain a higher sound pressure, it is possible to mount a diode (not shown) in series with the coil L ₁ . For more details, refer to the patent No. 641,625 in the name of Seiko.

At this stage of the description, it is essential to understand that the circuit elements which have just been described serve only to drive the piezoelectric transducer 32 to operate as a sound generator in an alarm device equipping, for example, the above-mentioned wristwatch 1. Consequently, these various components are not necessary for the implementation of the present invention. They simply show that, thanks to the particular features of the invention, a single piezoelectric transducer can be advantageously used both as a sound generator and as a means for introducing data into a watch. In what follows, we will now be interested in the part of the electrical circuit 38 for training and interpretation that converts a succession of mechanical pressures data that can be understood by a microprocessor equipping the watch 1 according to the invention and to control the watch functions of the latter.

The successive mechanical pressures that are exerted by the user on the mirror 14 of the watch 1 result, at the terminals of the piezoelectric transducer 32, by a low frequency electrical signal, typically of the order of 1 Hz, whose level must be increased. For this purpose, the electrical circuit 38 for training and interpretation shown in FIG. figure 2 comprises, firstly, a capacitor C ₁ mounted between the coil L ₁ and the transducer 32. At low frequency, the impedance of the coil L ₁ is low, so that it plays practically the role of a short circuit. Therefore, the variation of the voltage at the connection point "b" of the transducer 32 is also small. To remedy this problem, the capacitor C ₁ is added. Indeed, the variation of the voltage at the connection point "b" will be significant only if one has a high impedance at this connection point "b". Gold, at low frequency, the capacitor C ₁ has a high impedance, so that the voltage at said connection point "b" reaches a high threshold. On the other hand, when the piezoelectric transducer 32 is driven at high frequency, typically of the order of 1 kHz, to function as a sound generator, the capacitor C ₁ has a low impedance and thus acts substantially in the manner of a simple electrical connection between the coil L ₁ and the transducer 32. The capacitor C ₁ does not interfere with the operation of the transducer 32 as a sound generator.

Comme on le comprendra aisément, le filtre 40 sert à filtrer le signal haute fréquence présent aux bornes du transducteur 32 lorsque celui-ci fonctionne comme générateur de son à une fréquence de l'ordre de 1 kHz, et à éviter que ce signal ne se propage vers les étages d'amplification et de conversion qui seront décrits ci-après. Par contre, à basse fréquence, lorsqu'on agit mécaniquement sur le transducteur piézo-électrique 32, le signal électrique peut passer.The electrical circuit 38 for driving and evaluation is completed by a passive filter 40 connected in parallel across the piezoelectric transducer 32. This filter 40 is conventionally composed of a resistor R ₁ and a capacitor C ₂ . The cutoff frequency beyond which the filter 40 no longer lets a signal pass is determined by the relation $\mathrm{f}\mathrm{=}\frac{\mathrm{1}}{\mathrm{2}{\mathrm{\pi R}}_{\mathrm{1}}{\mathrm{<figure-callout\; id="2"\; label="VS"\; filenames="imgf0001.png"\; state="\{\{state\}\}">VS</figure-callout>}}_{\mathrm{2}}}\mathrm{.}$

As will be readily understood, the filter 40 serves to filter the high frequency signal present across the transducer 32 when it operates as a sound generator at a frequency of the order of 1 kHz, and to prevent this signal from occurring. propagation to the amplification and conversion stages which will be described below. On the other hand, at low frequency, when one acts mechanically on the piezoelectric transducer 32, the electric signal can pass.

The electrical circuit 38 finally comprises, connected in parallel with each other across the terminals of the passive filter 40, a polarization resistor R ₂ , an amplification stage 42 and a conversion stage 44. The amplification stage 42 comprises a pMOS transistor T _R1 whose source is connected to the DC voltage source + E and whose drain is connected to a resistor R ₃ . The gate of transistor T _R1 is connected to one of the ends "c" of resistor R ₂ whose other end is connected to DC voltage source + E.

For the conversion stage 44, it is possible to envisage all the inverters available in current technologies. By way of nonlimiting example only, the conversion stage 44 comprises a CMOS inverter which consists of a pMOS transistor T _R2 connected to a nMOS transistor T _R3 . The gates of these two transistors T _R2 and T _R3 are connected to the connection point "d" between the drain of the transistor T _R1 and the resistor R ₃ . This connection point "d" constitutes the input of the inverter 44. The source of the pMOS transistor T _R2 is connected to the DC voltage source + E, and its drain is connected to the drain of the transistor T _R3 . The point of connection "f" between the drains of transistors T _R2 and T _R3 constitutes the output of inverter 44. As for the source of transistor T _R3 , it is connected to the ground of circuit 38.

When the piezoelectric transducer 32 is at rest, that is to say when no pressure is exerted on the ice 14 of the watch 1, the resistance R ₂ , which is of considerable value, serves to maintain the gate-source voltage of the transistor T _R1 to zero in order to prevent this transistor T _R1 from conducting. It will also be noted that between two successive pressures exerted on the transducer 32, the latter can be discharged through the resistor R ₂ , so that the voltage at its terminals gradually regains its resting value.

As we have just seen in the above paragraph, when the piezoelectric transducer 32 is at rest, the transistor T _R1 does not conduct. The connection point "d" between the drain of the transistor T _R1 and the resistor R ₃ is therefore connected to the ground of the circuit 38. However, the connection point "d" constitutes the input of the conversion stage 40. Therefore, the gate-source voltage of the pMOS transistor T _R2 is equal to -E. This voltage is lower than the threshold voltage of transistor T _R2 which is of the order of -0.6 V, so that transistor T _R2 conducts. At the same time, the gate-source voltage of the nMOS transistor T _R3 is zero, that is to say less than the tripping voltage of this transistor T _R3 . Therefore, the transistor T _R3 is blocked. Thus, the voltage at the connection point "f" which constitutes the output of the conversion stage 44 is equal to + E, while the voltage at the connection point "d" which constitutes the input of the conversion stage 40 is zero. The conversion stage 44 functions well as an inverter.

We now examine the case where it exerts a mechanical pressure on the piezoelectric transducer 32. Under the effect of this pressure, the transducer 32 is polarized and the voltage at its connection point "b" decreases. Similarly, the gate voltage of the pMOS transistor T _R1 decreases. The gate-source potential difference of transistor T _R1 will become smaller than the trigger voltage, so that transistor T _R1 will start driving. Under the effect of the conduction of the transistor T _R1 , the potential at the connection point "d" which constitutes the input of the conversion stage 44 will increase and tend towards + E. At this time, the gate-source voltage of the pMOS transistor T _R2 becomes greater than the threshold voltage of this transistor T _R2 , so that said transistor T _R2 will go to the off state. At the same time, the gate-source voltage of the nMOS transistor T _R3 becomes greater than the tripping voltage of this transistor T _R3 , so that the latter will start driving. The voltage at the connection point "f" which constitutes the output of the conversion stage 44 will go to zero. Thus, the voltage at the input of the conversion stage 44 is at + E, while the output of the conversion stage 40 is at zero. The conversion stage 44 functions well as an inverter.

The voltage at the output point "f" of the conversion stage 44 therefore alternately passes the value + E when the piezoelectric transducer 32 is at rest at a zero voltage value when the transducer 32 is activated. This logic signal is applied to the input of a microprocessor (not shown) which will control the watch functions of watch 1.

It should be noted that it is advantageous to introduce data by pressing on the ice 14 of the watch 1 while the transducer 32 functions as a sound generator. Indeed, the passive filter 40 prevents the high frequency signals generated by the transducer 28 from reaching the amplification stages 42 and conversion 44. Therefore, the data input system according to the invention is permanently available. . The filter can also be digital, switched capacitor or realized with an active filter.

It will be understood, on the other hand, that the polarity of the supply voltage of the electrical circuit 38 for driving and evaluation can be reversed. In this case, the bipolar transistor npn T _R0 will be replaced by a pnp transistor, and the pMOS transistors will be replaced by nMOS transistors and vice versa.

It goes without saying that various variants and simple modifications are within the scope of the present invention as defined in the claims.

Claims (15)

1. Portable object such as, in particular, a timepiece (1), including means (16) for displaying at least one data item and a case (2) formed of a top portion including a crystal (14) covering the display means (16) and a bottom portion delimited by a back cover (6) located below said display means (16), this object further including a piezoelectric transducer (32) generating an electric voltage when mechanical pressure is exerted on said top portion, the voltage generated by the piezoelectric transducer (32) being applied to a first electronic circuit which is arranged to generate a logic signal in response to the pressure exerted, this object also comprising a second electronic circuit arranged to cause the piezoelectric transducer (32) to operate as a vibration source for an acoustic generator, these first and second electronic circuits being arranged inside said case (2), said piezoelectric transducer (32) being arranged in the bottom portion of said case (2) and being rigidly connected to said case (2), characterised in that the first electronic circuit includes a capacitor (C₁) arranged to raise the threshold of the voltage produced by the piezoelectric transducer (32) when the latter operates at the frequency at which the mechanical pressure is exerted, said capacitor (C₁) exhibiting a low impedance and being thus arranged to behave substantially like a simple electric connection when the piezoelectric transducer (32) is driven to operate like a sound generator at a frequency higher than the frequency at which the mechanical pressure is exerted.
2. Portable object according to claim 1, characterised in that the piezoelectric transducer (32) is bonded between two upper (34) and lower (36) electrodes.
3. Portable object according to claims 1 or 2, characterised in that the piezoelectric transducer (32) is bonded to the back cover (6) of the case (2).
4. Portable object according to any of claims 1 to 3, characterised in that the first electronic circuit, connected in parallel across the piezoelectric transducer (32), includes amplification (42) and conversion (44) means in a logic signal of the voltage generated by said piezoelectric transducer (32) under the effect of mechanical pressure.
5. Portable object according to claim 4, characterised in that the first electronic circuit further includes means (40) for filtering the acoustic pulses generated by the piezoelectric transducer (32) when the latter operates as a sound generator.
6. Portable object according to claim 5, characterised in that the filtering means (40) include a resistor (R₁) and a capacitor (C₂).
7. Portable object according to claim 5, characterised in that the filter is a digital filter, a filter with switched capacitors or made with an active filter.
8. Portable object according to any of claims 4 to 7, characterised in that the amplification (42) and conversion (44) means respectively include a circuit branch in which a transistor (T_R1) and a resistor (R₂) are mounted in series and an inverter connected in parallel across said circuit branch.
9. Portable object according to claim 8, characterised in that the inverter is of the CMOS type.
10. Portable object according to claims 8 or 9, characterised in that a polarisation resistor (R₂) is mounted in parallel between the piezoelectric transducer (32) and the circuit branch including the transistor (T_R1).
11. Portable object according to any of claims 1 to 10, characterised in that the second electronic circuit includes:

    - switching means arranged to be activated upon reception of a pulsed control signal, these means supplying acoustic frequency pulses to the piezoelectric transducer (32);

    - means for supplying a voltage so as to cause an electrical current to flow in said switching means, and

    - a coil (L₁) connected between the means supplying a voltage and said switching means, said piezoelectric transducer (32) being connected in parallel across the coil (L₁).
12. Portable object according to claim 11, characterised in that a capacitor (C₁) is mounted between the coil (L₁) and the piezoelectric transducer (28).
13. Portable object according to claims 11 or 12, characterised in that the second electronic circuit further includes a diode connected in series with the coil (L₁).
14. Portable object according to any of claims 11 to 13, characterised in that the switching means are formed by a transistor operating in switching mode.
15. Portable object according to claim 14, characterised in that the transistor (T_R0) is a bipolar transistor.

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