Abstract:
An electronic device including: a calculation unit configured to generate a signal representative of a physical magnitude, for a motor driving a display device, the motor including two terminals, one positive and one negative, via which the calculation unit controls the motor; at least one shock detection circuit connected between the calculation unit and one terminal of the motor for detection of an external shock applied to the motor. The shock detection circuit includes a comparison part comparing an induced voltage generated in the motor following a shock to a predetermined reference voltage to identify a shock, and a selection part.

Description:
[0001]    The present invention concerns an electronic device comprising a calculation unit capable of generating a signal representative of a physical magnitude, for a motor driving a display device, said motor comprising two terminals, one positive and one negative, via which the calculation unit controls the motor, the electronic device further comprising at least one shock detector circuit connected between the calculation unit and one motor terminal for the detection of an external shock applied to the motor. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are known timepieces comprising a case inside which an electromechanical timepiece movement is arranged. Such a movement is clocked by a quartz oscillator system. For the display of time indications, such as the hour and second, hands are mounted on motors to be driven in rotation. The motors used are Lavet type motors, also called stepping motors. In these motors, a magnetically charged rotor of cylindrical shape creates a radial magnetic field in the air gap of a magnetic circuit, on which is wound a coil whose terminals are connected to a control circuit, generally an integrated circuit, supplying current pulses, each pulse causing the rotor to advance one step. The coil is formed by a very fine wire, wound on a hollow, insulating tube containing therein one part of the magnetic circuit. 
         [0003]    These motors, located inside the watch, are subjected to shocks which may be caused by the watch being dropped or by violent movements of the user. These shocks are then likely to disrupt the operation of the motors. These disruptions consist of an uncontrolled movement of the rotor or rotors whereby their inertia causes the skipping of at least one step. 
         [0004]    Consequently, the time indications provided by the hands are likely to no longer be accurate. 
         [0005]    To overcome this, there exist shock detector systems. An electronic device is therefore responsible for measuring the tension induced by the motor during a shock. Indeed, an induced voltage is generated under the effect of the inertia of the rotor. This induced voltage is detected by a detector circuit which compares the induced voltage to a predetermined threshold. If the voltage is higher than said threshold, the detector circuit deduces that a shock has occurred and transmits the information to a control unit. 
         [0006]    In response to the shock, the control unit sends the motor a blocking pulse used to block any rotation of the rotor caused by the shock. 
         [0007]    However, a regulated voltage inverter is used to measure the induced voltage. To increase sensitivity, the motor coil is short-circuited for a short instant thereby increasing the voltage at the motor coil terminals as a result of the self-induction effect of the motor delta(U)=L*(di/dt) and the current automatically increases. This increase may cause damage to appear. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an object of the invention to overcome the drawbacks of the prior art by proposing to provide a shock detector device for a motor allowing the detection of a shock in a faster and more accurate manner. 
         [0009]    To this end, the present invention concerns an electronic device comprising a calculation unit capable of generating a signal representative of a physical magnitude, for a motor driving a display device, said motor comprising two terminals, one positive and one negative, via which the calculation unit controls the motor, the electronic device further comprising at least one shock detector circuit connected between the calculation unit and one motor terminal for the detection of an external shock applied to the motor, characterized in that the shock detection circuit includes a comparison part for comparing an induced voltage generated in the motor following a shock to a predetermined reference voltage in order to identify a shock, the detection circuit further comprising a selection part for varying the induced voltage to improve the sensitivity of said shock detector circuit. 
         [0010]    One advantage of this invention is that it allows the detection of positive or negative levels. 
         [0011]    In a first advantageous embodiment, the electronic device comprises two shock detection circuits each connected between the calculation unit and a terminal of the motor for detection of an external shock applied to the motor, one shock detection circuit being connected to the positive terminal whereas the other is connected to the negative terminal. 
         [0012]    In a second advantageous embodiment, the comparison part comprises a comparator provided with a positive input and a negative input, the selection part comprising a series of series connected resistors Ri, the first of these resistors being connected to the motor connection terminal whereas the last resistor of the series is connected to earth, the selection part further comprising a selector including an output connected to the positive input of the comparison part and a plurality of selection points pi, each connected to one resistor Ri. 
         [0013]    In a third advantageous embodiment, the selection part further comprises an activation transistor in series with the series of resistors (Ri) for activating or deactivating said shock detection circuit. 
         [0014]    In another advantageous embodiment, the predetermined reference voltage is connected to the negative terminal of the comparison part. 
         [0015]    In another advantageous embodiment, the predetermined reference voltage is negative or positive. 
         [0016]    In another advantageous embodiment, the comparison part comprises a first pair and a second pair of series connected transistors, each pair comprising one p-type transistor and one n-type transistor, the gates of transistors of the same type being connected together, the gates of the p-type transistors being connected to a current source, the gate of the n-type transistor of the first pair being connected to its drain, the drains of the p-type transistors being connected to a supply voltage (Vdd), the source of the n-type transistor of the first pair being connected to the output of the selection part, whereas the drain of the n-type transistor of the second pair is connected to earth. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The objects, advantages and features of the invention will appear more clearly in the following detailed description of at least one embodiment of the invention, given solely by way of non-limiting example and illustrated by the annexed drawings, in which: 
           [0018]      FIG. 1  shows a diagram of the electronic device according to the invention. 
           [0019]      FIGS. 2 and 6  show a schematic view of the electronic device according to the invention. 
           [0020]      FIGS. 3 and 5  show a detailed view of a shock detector circuit according to the invention and one of its variants. 
           [0021]      FIG. 4  represents operating diagrams for the electronic device according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The present invention proceeds from the general idea of providing a shock detector device for a motor allowing the detection of a shock in a faster and more accurate manner. 
         [0023]      FIG. 1  represents a schematic view of an electronic movement. This movement or electronic device  1  comprises a control module  2  clocked by a quartz oscillator system  3 . For the display of time indications, such as the hour and second, hands are mounted on motors  4  to be driven in rotation. The motors used are Lavet motors, also called stepping motors, and comprise two connection terminals Mot 1  and Mot 2 . In these motors, a magnetically charged rotor  4   a  of cylindrical shape creates a radial magnetic field in the air gap of a magnetic circuit  4   b , on which is wound a coil whose terminals are connected to the control module, generally an integrated circuit, supplying current pulses, each pulse causing the rotor to advance one step. The coil is formed by a very fine wire, wound on a hollow, insulating tube containing therein one part of the magnetic circuit. Control module  2  generally comprises a calculation unit  5 . The assembly is powered by a power unit  8 , such as a cell or battery. The power unit supplies a supply voltage Vdd. There is also an earth terminal Vss. 
         [0024]    Advantageously according to the invention, control module  2 , seen in  FIG. 2 , further comprises a detection unit  6  comprising at least one shock detector circuit  7 . Shock detector circuit  7  is used to determine whether a shock has occurred. Thus, if a shock is detected, control module  2  can act accordingly and send a blocking pulse to prevent the rotor from starting to rotate. The shock detector circuit is placed at the output of at least one of the motor terminals. The following description will take the example of a shock detector circuit  7  connected to the negative terminal Mot 2  of the motor. At each motor terminal Mot 1 , Mot 2 , a voltage Vmot is measured. At each terminal Mot 1 , Mot 2 , a motor buffer is arranged, these motor buffers comprise a flip-flop B 1 , B 2  and two different types of series connected transistors, the gates of the transistors being connected to the flip-flop as seen in  FIG. 6 . The buffers are used to pass either a positive or a negative current through the motor coil in order to make it rotate. 
         [0025]    In  FIG. 2 , it is noted that shock detector circuit  7  comprises a selection part  71  directly connected to terminal Mot 2  of motor  4 . This selection part  71  has an output connected to a comparison part  72 . Comparison part  72  is connected to calculation unit  5  so as to provide the signal indicating whether or not a shock is detected. 
         [0026]      FIG. 3  shows a detailed diagram of the detection unit. 
         [0027]    The selection part comprises a series of series connected resistors Ri. The first of these resistors Ri is connected to the connection terminal of motor  4 , whereas the last resistor Ri of the series is connected to a terminal of a transistor T, more particularly to the drain thereof. The resistor series Ri will preferably include four resistors R 1 , R 2 , R 3  and R 4 . 
         [0028]    The source of this transistor T is connected to earth Vss and its gate is connected to calculation unit  5  of control module  2 . Transistor T is used to activate or deactivate shock detection circuit  7 . Indeed, depending on the voltage of a signal applied to the gate of this transistor, the latter will be open or closed. In the case where it is open, transistor T prevents shock detection circuit  7  from operating since the electrical circuit is open and vice versa. For the detection circuit connected to motor terminal Mot 1 , signal Sh 1 _EN will allow shock detection circuit  7  to be activated or deactivated. For the detection circuit connected to motor terminal Mot 2 , signal Sh 2 _EN will allow shock detection circuit  7  to be activated or deactivated. 
         [0029]    Selection part  71  further comprises a selector  71   a  in the form of a multi-position switch. Selector  71   a  comprises an output and a plurality of selection points pi, each connected to a resistor Ri. The first selection point p 1  is connected to resistor R 1  at the terminal of resistor R 1  connected to the motor. The second selection point P 2  is connected to resistor R 2  at the terminal of resistor R 2  connected to resistor R 1  and so on. 
         [0030]    Selector  71   a  further comprises a flip-flop  71   b  for connecting the output of the selector to one of selection points pi. The output of selector  71   a  is voltage V 1  which is connected to comparison part  72 . Comparison part  72  comprises a comparator whose positive input is connected to the output of selector  71   a  and whose negative input is connected to the gate of transistor T for activating or deactivating shock detection circuit  7 . It will thus be understood that the signal applied to the gate of said transistor T is a digital signal whose voltage will be supply voltage Vdd or earth Vss and which starts the comparator. 
         [0031]    Comparator  72   b  of comparison part  72  is composed of a first T 1  and a second T 2  n-type transistor whose gates are connected together. The source of first transistor T 1  is connected to the output of selector  71   a , whereas the gate of first transistor T 1  is connected to its drain. The source of the second n-type transistor T 2  is connected to earth and to the source of transistor T of selection part  71   a.    
         [0032]    The drains of first transistor T 1  and of second transistor T 2  are respectively connected to the drain of third transistor T 3  and to the drain of fourth transistor T 4 , third transistor T 3  and fourth transistor T 4  being p-type transistors. The gates of transistors T 3  and T 4  are connected together and their drains are connected to supply voltage Vdd. Transistor T 3  supplies a current I 1  and transistor T 4  supplies a current I 2 . 
         [0033]    The comparator of the comparison part further includes a current source C 1  connected in series with a fifth p-type transistor T 5 . The drain of fifth transistor T 5  is connected to supply voltage Vdd, whereas the gate of transistor T 5  is connected to its source and to the gates of transistors T 3  and T 4 . 
         [0034]    Transistors T 3  and T 4  are arranged to be identical so that current I 1  is identical to current I 2 . 
         [0035]    Transistors T 1  and T 2  are of the same dimensions and are arranged to operate in a weak inversion mode. However, transistor T 2  is arranged to be placed in parallel N number of times. Transistor T 2  is thus composed of a number N of parallel connected transistors. 
         [0036]    This comparison part further comprises an AND logic gate AND 1  having two inputs: a first input connected to the drain of transistor T 2 , whereas the second input is connected to the gate of the selection part transistor T. 
         [0037]    In weak inversion mode, the equation for a transistor is: 
         [0000]    
       
         
           
             I 
             = 
             
               
                 Is 
                 × 
                 
                   e 
                   
                     ( 
                     
                       Vgs 
                       / 
                       
                         ( 
                         
                           n 
                           × 
                           Ut 
                         
                         ) 
                       
                     
                     ) 
                   
                 
                  
                 
                     
                 
                  
                 
                   = 
                 
                  
                 
                   &gt; 
                 
                  
                 
                     
                 
                  
                 Vgs 
               
               = 
               
                 n 
                 × 
                 Ut 
                 × 
                 
                   ln 
                    
                   
                     ( 
                     
                       I 
                       Is 
                     
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    Consequently, it is deduced that: 
         [0000]    
       
         
           
             
               Vgs 
                
               
                   
               
                
               1 
             
             = 
             
               n 
               × 
               Ut 
               × 
               
                 ln 
                  
                 
                   ( 
                   
                     
                       I 
                        
                       
                           
                       
                        
                       1 
                     
                     
                       Is 
                        
                       
                           
                       
                        
                       1 
                     
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    (where n=1 or 2 depending on the technology.) 
         [0000]    
       
         
           
             
               Vgs 
                
               
                   
               
                
               2 
             
             = 
             
               n 
               × 
               Ut 
               × 
               
                 
                   ln 
                   ( 
                   
                     
                       
                         I 
                          
                         
                             
                         
                          
                         2 
                       
                       N 
                     
                     
                       Is 
                        
                       
                           
                       
                        
                       2 
                     
                   
                   ) 
                 
                 . 
               
             
           
         
       
     
         [0000]    We thus obtain: 
         [0000]    
       
         
           
             
               V 
                
               
                   
               
                
               1 
             
             = 
             
               
                 
                   Vgs 
                    
                   
                       
                   
                    
                   2 
                 
                 - 
                 
                   Vgs 
                    
                   
                       
                   
                    
                   1 
                 
               
               = 
               
                 
                   n 
                   × 
                   Ut 
                   × 
                   
                     ( 
                     
                       
                         ln 
                         ( 
                         
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               2 
                             
                             N 
                           
                           
                             Is 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         ) 
                       
                       - 
                       
                         ln 
                          
                         
                           ( 
                           
                             
                               I 
                                
                               
                                   
                               
                                
                               1 
                             
                             
                               Is 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                           ) 
                         
                       
                     
                     ) 
                   
                 
                 = 
                 
                   n 
                   × 
                   Ut 
                   × 
                   
                     ln 
                      
                     
                       ( 
                       
                         
                           
                             ( 
                             
                               I 
                                
                               
                                   
                               
                                
                               
                                 2 
                                 / 
                                 N 
                               
                             
                             ) 
                           
                           / 
                           Is 
                         
                          
                         
                             
                         
                          
                         2 
                       
                       ) 
                     
                   
                   × 
                   
                     ( 
                     
                       ( 
                       
                         
                           Is 
                           / 
                           I 
                         
                          
                         
                             
                         
                          
                         1 
                       
                       ) 
                     
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    Knowing that at the switching point I 1 =I 2  et Is 1 =Is 2 , we then obtain: 
         [0000]      Vref= V 1= n×Ut ×ln(1/ N ) with  Ut =( k×T )/ q  
 
         [0038]    Now, if N is greater than 1, 1/N is less than 1. Consequently, ln(1/N) is equal to −ln(N). Hence, it is understood that voltage V 1  whose value is Vref is negative and shock detection circuit  7  is thus able to measure a voltage below 0V. 
         [0039]    Depending on the position of the selector, the value Vcomp of voltage Vmot is modified by calculation unit  5 , as seen in  FIG. 6 . The compared voltage Vcomp is calculated, at the switching point, as follows: 
         [0000]    If the selector is in position p 1 , voltage Vcomp is equal to voltage V 1 .
 
If the selector is in position p 2 , voltage Vcomp is equal to:
 
         [0000]    
       
         
           
             Vcomp 
             = 
             
               Vref 
               × 
               
                 ( 
                 
                   
                     
                       R 
                        
                       
                           
                       
                        
                       1 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       2 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       4 
                     
                   
                   
                     
                       R 
                        
                       
                           
                       
                        
                       2 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       4 
                     
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    If the selector is in position p 3 , voltage Vcomp is equal to: 
         [0000]    
       
         
           
             Vcomp 
             = 
             
               Vref 
               × 
               
                 ( 
                 
                   
                     
                       R 
                        
                       
                           
                       
                        
                       1 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       2 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       4 
                     
                   
                   
                     
                       R 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       4 
                     
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    If the selector is in position p 4 , voltage Vcomp is equal to: 
         [0000]    
       
         
           
             Vcomp 
             = 
             
               Vref 
               × 
               
                 ( 
                 
                   
                     
                       R 
                        
                       
                           
                       
                        
                       1 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       2 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       R 
                        
                       
                           
                       
                        
                       4 
                     
                   
                   
                     R 
                      
                     
                         
                     
                      
                     4 
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    Consequently, the voltage at selection point P 4  is higher than the voltage at selection point P 1 . 
         [0040]    By way of example, the resistors could have the following values: R1=5000 Ohms, R2=3000 Ohms, R3=2000 Ohms and R4=1000 Ohms. We thus obtain Vcomp varying from V 1  to 11×V 1 . 
         [0041]    These values of Vref and Vcomp are then considered to be reference values. 
         [0042]    The value of the induced voltage depends on the type of motor, on the intensity and the length of the shock. The object of this system is to measure induced voltages between 50 mV peak-peak and ˜500 mV peak-peak. 
         [0043]    In a variant visible in  FIGS. 2 and 6 , each motor terminal Mot 1 , Mot 2  has a shock detection circuit  7 . This variant thus allows the detection of clockwise or anticlockwise shocks. 
         [0044]    Hence the example of  FIG. 4 , in which each terminal Mot 1 , Mot 2  of the motor has one shock detection circuit, each detector being configured with a negative reference voltage. 
         [0045]    When a shock Sh 1  is applied to the motor, an induced voltage is generated by the movement of the rotor of motor  4 , the value of voltage Vmot thus increases. 
         [0046]    In  FIG. 4 , it is noted that shock Sh 1  causes the appearance of a positive induced voltage at terminal Mot 1  and the appearance of a negative induced voltage at terminal Mot 2 . It is deduced therefrom that the shock is clockwise. 
         [0047]    The induced voltage detected at terminal Mot 1  and the voltage detected at terminal Mot 2  are compared to the negative reference voltage. It is noted, in the case of  FIG. 4 , that the induced voltage detected at terminal Mot 2  exceeds the reference threshold, i.e. it is higher than the negative reference voltage. It is thus understood here that the value of voltage V 1  becomes more negative than value Vref of voltage V 1  and that the value of voltage Vmot becomes more negative than value Vmot. In such case, the digital output of comparator Sh_out 1  changes to 1 indicating the presence of a shock. This information is sent to calculation unit  5  which will act accordingly, for example by sending a blocking pulse to halt the rotation of the rotor. Conversely, if the value of voltage V 1  does not become more negative than value Vref of voltage V 1 , the value of voltage Vmot does not become more negative than value Vmot, and the comparator output remains at 0. 
         [0048]    It will be understood that the reference threshold, i.e. the reference voltage, could also be positive. In this manner, a clockwise shock will be detected via terminal Mot 1 , whereas an anticlockwise shock will be detected via terminal Mot 2 . 
         [0049]    In that case, the comparator visible in  FIG. 5  is digitally inverted so that if the value of voltage V 1  becomes more positive than value Vref of voltage V 1 , the value of voltage Vmot becomes more positive than value Vmot allowing the comparator output Sh_out 2  to change to 1. 
         [0050]    It is thus noted in  FIG. 5  that comparison part  72  further includes a inverter INV 1  placed between transistor T 2  and AND gate AND 1 . Further, this detection circuit  7  with a positive reference threshold is distinguished by having transistor T 1  composed of a multitude of parallel connected transistors whereas transistor T 2  is a single transistor. 
         [0051]    The present invention thus allows the detection of positive or negative levels. 
         [0052]    It will be clear that various modifications and/or improvements evident to those skilled in the art may be made to the various embodiments of the invention described in the present description without departing from the scope of the invention.