Abstract:
The electromechanical escapement device is associated with an electronic circuit having a quartz oscillator and calculation means suitable for calculating the difference between the period of the quartz oscillator and the period of a mechanical oscillator and releasing an escape wheel, normally controlled by said mechanical oscillator, when the difference between said periods is greater than a threshold value.

Description:
The content of application No PCT/CH2007/00346, filed Jul. 18, 2007 in Switzerland is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The object of the present invention is an electromechanical escapement device and a timepiece part utilizing such a device. 
     For a mechanical timepiece part, the escapement device is used for sustaining the oscillation movement of the mechanical oscillator comprising the balance and the balance spring on the one hand and for transmitting the frequency of this oscillator to the gear-train driving the time display. 
     Entirely mechanical escapement devices are therefore well-known in the prior art. The manuals “Echappements et moteurs pas à pas” (Escapements and step motors) of Charles Huguenin edited by the Fédération des Ecoles Techniques de Suisse (Swiss Federation of Technical Colleges) and “Théorie d&#39;horlogerie” (Watch-making theory), ISBN 2-940025-10-X, also edited by the Fédération des Ecoles Techniques de Suisse, describe several mechanical escapement devices called &lt;&lt;anchor&gt;&gt;, &lt;&lt;detent&gt;&gt;, &lt;&lt;Graham&gt;&gt; escapements, etc. 
     As mentioned earlier, traditional mechanical escapement devices directly transmit the frequency of the mechanical oscillator to the gear-train driving the time display. The frequency of the mechanical oscillator, generally comprised between 2 and 4 Hz, is unfortunately not very accurate and further highly dependent on the position of the watch. The accuracy of a mechanical watch is consequently less than that of an electronic quartz watch. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to propose an electromechanical escapement device with which the accuracy of a mechanical watch may be markedly improved. 
     Another object of the invention is to propose a mechano-electronic timepiece part equipped with such an escapement device. 
     These objects are achieved by an electromechanical escapement device as described in claim  1 , as well as by a timepiece part as described in claim  9 . Alternative embodiments are described in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be understood by means of the following description which describes a particular embodiment of the invention, as well as with the appended drawing including the figures, wherein: 
         FIG. 1  illustrates a block diagram of a traditional mechanical watch, 
         FIG. 2  illustrates a block diagram of a mechano-electronic watch utilizing an electromechanical escapement device according to the invention, 
         FIG. 3  illustrates an embodiment of an electromechanical escapement according to the invention, 
         FIG. 4  illustrates details of an escapement wheel, 
         FIG. 5  illustrates details of mobile parts rotating around the centre O 2  of  FIG. 3 , 
         FIG. 6  illustrates details of mobile parts rotating around the centre O 3  of  FIG. 3 , 
         FIG. 7  illustrates details of mobile parts rotating around the centre O 4  of  FIG. 3  as well as a mechanical converter, 
         FIG. 8  illustrates the blocking position, 
         FIG. 9  illustrates the mechanical release phase, 
         FIG. 10  illustrates the energy transmission phase, 
         FIG. 11  illustrates the repositioning phase, 
         FIG. 12  illustrates the electromagnetic release phase, and 
         FIG. 13  illustrates a block diagram of an associated electronic device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a block diagram of a traditional mechanical watch in which the mechanical energy from a manual or automatic winding-up device is stored in a barrel spring  1  in order to be distributed through a wheel assembly  2  to an escapement device  3  and to a display  4 . 
     The escapement device  3  is used for sustaining the movement of the mechanical oscillator  5  comprising a balance and a balance spring on the one hand and for transmitting the frequency of this oscillator to the gear-train  2  driving the time display  4  on the other hand. At each oscillation period of the mechanical oscillator  5 , the gear-train  2  linked to the display  4 , advances by a set angle and consequently the velocity of rotation of the gear-train  2  is proportional to the frequency of the mechanical oscillator  5 , so that the accuracy of the display  4  is directly dependent on this frequency. 
     The frequency of a mechanical oscillator, generally comprised between 2 and 4 Hz, is unfortunately not very accurate and further very dependent on the position of the watch. The accuracy of a traditional mechanical watch is consequently lower than that of an electronic quartz watch. 
       FIG. 2  illustrates a block diagram of a mechano-electronic watch utilizing an electromechanical escapement device according to the invention. The mechanical energy stored in a barrel spring  6  is distributed through an assembly of wheels  7  to an electromechanical escapement device  9  and to a display  8 . The electromechanical escapement device  9  according to the invention has multiple functions:
         the first one is to sustain the oscillatory movement of the mechanical oscillator  11 ,   the second is to transmit the frequency of the oscillator  11  to the gear-train  7  driving the time display  8 ,   the third is to transform a portion of the received mechanical energy into electrical energy for powering the electronic device  10  which has a quartz time base,   finally, the last function of the electromechanical escapement device  9  is to cause the gear-train  7  to advance when it receives electric correction pulses from the electronic device  10 .       

     It may be noted that on this diagram, the barrel spring  6 , the gear-train  7 , the display  8 , as well as the mechanical oscillator  11 , are components identical with those of the same names in  FIG. 1 . 
     At each oscillation period of the mechanical oscillator  11 , the gear-train  7  linked to the display  8  as well as the electromechanical escapement device  9  advance by a set angle and transmit the electric energy and the oscillation period of the mechanical oscillator  11  to the electronic device  10 , through an electromechanical converter of the device  9 , described later on. This electronic device  10  has an electric energy accumulator and a quartz time base taken as a reference time base; it compares the mechanical oscillation period with a reference period. When the sum of the differences between these periods exceeds a certain limit, the electronic device  10  sends electric correction pulses through an electromechanical converter in order to cause the electromechanical escapement device  9  as well as the gear-train  7  and the display  8  to advance. 
     It is seen that unlike a traditional mechanical escapement, the movement of which is synchronous with that of the mechanical oscillator, the electromechanical escapement  9  according to the invention advances at each period of the mechanical oscillator  11  and also, independently of the mechanical oscillator  11 , when it receives pulses from the electronic circuit  10 . 
     In order to obtain proper operation of the timepiece part according to  FIG. 2 , it is sufficient to adjust the period of the mechanical oscillator  11  so as to be slightly longer than that of the reference time base of the quartz time base. The electronic circuit  10  measures the difference between these periods and sends a set of correction pulses in order to make up for lost time. In practice, the adjustment of the period of a mechanical oscillator with an accuracy of one per thousand may easily be achieved. 
       FIG. 3  illustrates an embodiment of an electromechanical escapement device according to the invention. This device comprises several mobile parts rotating around 4 centres O 1 , O 2 , O 3  and O 4 . 
     The escapement wheel  12 , illustrated in details in  FIG. 4 , rotates around the centre O 1  and is provided with pins  121 . In this example, the number of pins is equal to 8, but selection of another number of pins is also possible. 
     Two superposed mobile parts simultaneously rotate around the centre O 2 : a blocking means  14  and a cogwheel  13 , both of these mobile parts being illustrated in details in  FIG. 5 . The mechanical oscillator  11 , comprising the balance and the balance spring, rotates around the centre O 3 . In  FIG. 3  as well as in the detailed drawing of  FIG. 6 , only the disc  15 , integral with the balance and including the pulse lever  151  as well as the release pin  152  is illustrated. 
     Three superposed mobile parts simultaneously rotate around the centre O 4 : a mechanical clearing means  16 , a cogwheel  17  meshed with the cogwheel  13  and a rotor  182  of the electromechanical converter made as a permanent magnet.  FIG. 7  illustrates the details of these mobile parts as well as the electromechanical converter  18  including, in addition to the rotor  182 , a stator  181  in a soft magnetic material provided with recesses  184 , as well as a coil  183 . 
     The electromechanical converter  18  has several distinct functions:
         by means of the recesses  184 , the rotor  182  has two stable positions of equilibrium aligned on the axis S 1 -S 2  in the absence of current in the coil  183 ,   when current is provided to the coil  183  with the suitable polarity, the rotor  182  rotates in an anticlockwise direction as indicated by the arrow F,   finally, when the rotor  182  of the converter  18  is driven by the escapement wheel  12  via the cogwheels  13  and  17 , this converter  18  operates as a generator and provides a voltage on the terminals B 1  and B 2  of the coil  183 .       

     The operation of the electromechanical escapement device according to the invention is described below, comprising several main phases:
         blocking phase: most of the time, when the disc  15  of the mechanical oscillator  11  is not in mechanical contact with the escapement wheel  12  via the pulse lever  151 , or with the release means  16  via the release pin  152 , the escapement wheel  12  is found in the blocking position.  FIG. 8  illustrates this blocking position. In this figure, the escapement wheel  12  is subject to a torque from the barrel  6  in the direction indicated by the arrow F 2 . By means of the shape of the blocking means  14  and of the magnetic positioning torque from the rotor  182  via the wheels  17  and  13 , the escapement wheel  12  is blocked in this position while the disc  15  of the mechanical oscillator  11  continues with its movement.   Mechanical release phase:  FIG. 9  illustrates the mechanical release phase. In this figure, the pin  152  of the disc  15 , rotating in the direction of the arrow F 3 , actuates the release means  16  and via the wheels  17  and  13 , releases the pin  121  from the blocking means  14 . The escapement wheel  12  may rotate, under the effect of the torque transmitted by the barrel  6  in the direction of the arrow F 2 .   Energy transmission phase: in this phase, the escapement wheel  12  transmits the energy to the mechanical oscillator  11  as well as to the electromechanical converter  18 .  FIG. 10  illustrates this energy transmission phase. After the mechanical release phase, the escapement wheel  12  rotates in the direction of the arrow F 2 , one of the pins  121  of this wheel actuating the pulse lever  151  of the disc  15 , in order to provide the energy intended for sustaining the movement of the oscillator  11 . The pin  121  preceding the one mentioned above in the direction of rotation, actuates the blocking means  14 , which transmits the mechanical energy via the wheels  13  and  17  to the electromechanical converter  18  which transforms it into electric energy on the terminals of the coil  183 .   Repositioning phase: this phase is illustrated by  FIG. 11 . After the energy transmission phase, the blocking means  14  and wheel  13  continue to rotate in the same direction as indicated by the arrow F 4  and, under the effect of the magnetic positioning torque, again find a new blocking position at 180 degrees relatively to the preceding blocking position. In this phase, the escapement wheel  12  continues to provide energy to the mechanical oscillator  11  via the pulse lever  151  of the disc  15 .   Electromagnetic release phase: this phase is illustrated by  FIG. 12 . One of the particularities of the electromechanical escapement device according to the invention is that it is able to release the escapement wheel  12  from the blocking position, independently of the frequency of the mechanical oscillator  11 . To do this, it is sufficient to send a set of electric pulses to the coil  183  of the electromechanical converter  18 . The interaction between the magnetic field generated by the current in the coil  183  and the magnetic field of the magnet of the rotor  182  generates an electromagnetic torque in the direction of the arrow F 5 , larger than the positioning torque which actuates the blocking means  14  in the opposite direction via the wheels  13  and  17 . The electromagnetic release phase is generally carried out outside the mechanical release, energy transmission and repositioning phases. During this phase, the angular velocity of the mechanical oscillator  11  is practically zero. In this phase of electromagnetic release, the escapement wheel  12  does not transmit any energy to the mechanical oscillator  11 .       

       FIG. 13  illustrates the block diagram of the electronic device  10  of  FIG. 2 . This device comprises:
         charging means  100 ,   energy storage means  101 ,   means  102  for shaping the voltage from the coil  183 ,   means  103  for measuring the period of the mechanical oscillator  11  based on a reference time base from a quartz oscillator  104 ,   means  105  for calculating and providing a set of electric correction pulses.       

     The electrical signal from the coil  183  during the energy transmission phase is sent to the charging means  100  which store the energy in a condenser or another energy accumulator  101 . This signal is also sent to the shaping means  102  which transmit the information to the means  103  for measuring the period of the mechanical oscillator  11 , based on a reference time base from a quartz oscillator  104 . The means  105  calculate the sum of the errors of the mechanical period and send a set of electric correction pulses from the coil  183  when this sum exceeds a certain limit. 
     A particular embodiment of the electromechanical escapement device was described above; it is quite obvious that alternative designs may be contemplated. In particular, the mechanical link between the mechanical blocking means, the mechanical release means as well as the rotor, described here in the form a two cogwheels, may be different from those described, subject to providing the same function. Other design alternatives, which may be contemplated by one skilled in the art, should also be considered. 
     Thus, a timepiece part equipped with an electromechanical escapement device as described above has its operative accuracy notably improved since the latter then depends on the accuracy of the quartz oscillator.