ANALOG ELECTRONIC TIMEPIECE WITH CHARGING FUNCTION

Abstract: An analog electronic timepiece with charging function comprises an electric energy generator (1) such as a solar cell, two capacitors (2,4) for storing electric energy generated by the electric energy generator (1) and a voltage detector circuit (17) for detecting the voltages on the capacitors. A driving pulse generator circuit (18) generates a plurality of drive pulses for a step motor wherein the drive pulses consist of relatively wide interval pulses and relatively narrow interval pulses. A voltage detection timing generator circuit (16) determines a detection timing of the voltage detector circuit (17).

Description: This invention relates to analog electronic timepieces with charging function. One example of a charging circuit of an electronic timepiece with charging function employed heretofore is shown in Figure 2 see also XI e CONGRES INTERNATIONAL DE CHRONOMETRIE, Besançon, 4.-6.10. 1984, Vol.1, p.75-79. In a first state of charging each of a plurality of switches a , b , c which may be MOSFETs are open. Accordingly, a capacitor 2 having a relatively small capacitance is charged with electric energy generated by a solar cell 1. When the voltage VC₂ on the capacitor 2 rises, an integrated circuit 3 begins to operate. This will be referred to as state (1). When the voltage VC₂ on the capacitor 2 exceeds a predetermined value after the integrated circuit 3 begins to operate, the switch a is closed, and a capacitor 4 of relatively large capacitance starts to charge. This will be referred to as stage (2). In the meantime the integrated circuit 3 drives a step motor (not shown) to perform a time keeping operation. In states (1) and (2) the integrated circuit 3 and the step motor are driven by the charge accumulated on the capacitor 2. The capacitance of the capacitor 2 used herein is set to be very small, about 6.8 micro F, for example, for the purpose of reducing the time for starting operation of the integrated circuit 3. It will be assumed that the shift from state (1) to state (2) occurs when the absolute value of the terminal voltage |VC₂| of the capacitor 2 exceeds 2.0V. Further, it will be assumed that the solar cell 1 ceases to be irradiated with light for several seconds at the moment of rise of the terminal voltage |VC₂| above 2.0V brings about the shift to state (2) and thus electric energy ceases to be generated by the solar cell. The terminal voltage |VC₂| of the capacitor 2 falls to approximately 0.9V after having driven the step motor several times. If no measures are taken in this condition the voltage VC₂ falls below the lowest operating voltage of the step motor, which causes operation to cease or failure of rhythmic movement of time indicating hands (not shown) driven by the step motor. Even when the solar cell is again irradiated with light, the terminal voltage |VC₂| of the capacitor 2 rises very slowly since the large capacitance capacitor 4 is connected in parallel across the solar cell 1. Consequently the operation of the step motor ceases for a relatively long time. The capacitance of the capacitor 4 used herein is set to be about 0.3 F, for instance. Accordingly, it takes about 10 minutes for the current of 200 micro A to raise the voltage of the capacitor 4 from, for example, 0.9V to 1.3V which enables operation of the step motor. During this period the electronic timepiece cannot be restarted. In order to prevent this occurrence the voltage VC₂ is detected in state (2) and when VC₂ falls to a predetermined value or below, the switch a is opened to restore state (1). As a result, the capacitor 2 receives all the electric energy generated by the solar cell 1 and therefore the terminal voltage of |VC₂| of the capacitor 2 will be raised in a relatively short time. Accordingly, states (1) and (2) alternate in accordance with a balance between electric energy generated by the solar cell and electric energy consumed by the electronic timepiece in the initial state of charging. The timing of detection of the voltage VC₂, the timing in state (2) in particular, is at issue. Figure 3 shows the prior art voltage detecting timing. This shows the timing of a drive pulse in a compensated driving system in which a compensating drive pulse P₂ is outputted when the step motor is not rotated by a main driving pulse P₁. Such a compensated driving system is a requisite for an electronic timepiece with charging function in order to reduce power requirements. The prior art voltage detection timing is executed after the end of driving of the step motor, as shown by a voltage detection pulse 12 in Figure 3 (the polarity of the pulse 12 means nothing in particular). Diodes 7,8 in Figure 2 are reverse-current check diodes which prevent an ineffective current bypassing the integrated circuit 3. The switch b and the switch c are used in an advanced state of charging. These switches b and c will not be described herein, because they have no direct relation with the description of the present invention. In the case where voltage detection is conducted after a compensating drive pulse P₂ is produced as shown in Figure 3, it sometimes happens that the compensating pulse P₂ cannot rotate the step motor. Assume, for instance, that the condition for a shift from state (2) to state (1) is |VC₂| ≦ 1.3V. If |VC₂| = 1.31V and the pulse width of the main drive pulse P₁ is 4 ms, then the next main drive pulse P₁ drives the step motor but |VC₂| is lowered to approximately 1.05V by the production of the main drive pulse P₁. If the lowest drive voltage for rotating the step motor is 1.2V then the next drive pulse fails to drive the step motor. As the terminal voltage on the small capacitor 2 is so small, the step motor will not be rotated by the compensating drive pulse P₂ as well. Since the condition VC₂ ≦ 1.3V is detected by the voltage detection pulse 12 and the shift is made from state (2) to state (1), thereafter, the potential VC₂ rises rapidly, so that there is sufficient energy to create the next drive pulse. However, the next drive pulse also fails to rotate the step motor due to failure of the preceding drive pulse, thus relating in a delay of 2 seconds. According to the present invention there is provided an analogue electronic timepiece with charging function having an energy generating means for providing the energy to drive a step motor through a step motor driving and detection means and a display; said timepiece comprising: a pulse generator for generating pulses for said step motor driving and detection means and/or display; first and second capacitors each coupled to said energy generating means and said pulse generator, said first capacitor having a relatively small capacitance so as to charge rapidly, said second capacitor having a relatively large capacitance so as to store a large amount of energy; means for detecting the energy stored on said second capacitor and for detecting a terminal voltage VC₂ on said first capacitor; a switch whilst the energy stored in said second capacitor is below a predetermined value, for connecting said first capacitor to said energy generating means when the terminal voltage VC₂ is less than an upper threshold voltage and for connecting said second capacitor to said energy generating means when the first capacitors terminal voltage VC₂ is above a lower threshold voltage; characterised by timing means coupled to said pulse generator and said detecting means for controlling the timing of said detecting means to detect the first capacitors terminal voltage VC₂ after a drive pulse fails to drive said step motor so as to enable said first capacitor to be connected to and thereby charge from said energy generating means for as long as possible before the next pulse is to be generated. Said electric energy generating means may comprise a solar cell or a manually operated generator. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 shows the relationship between drive pulses and timing of voltage detection in an electronic timepiece according to the present invention; Figure 2 is a connection diagram of a conventional charging circuit of an electronic timepiece; Figure 3 shows the timing of voltage detection according to the conventional electronic timepiece; Figure 4 shows the timing of voltage detection of an electronic timepiece according to the present invention; Figure 5 is a block diagram showing schematically the function of an integrated circuit of an electronic timepiece according to the present invention; and Figure 6 shows driving waveforms and timing of voltage detection in the case where cell life display is conducted in an electronic timepiece according to the present invention. In order to solve the above described problem of an analog electronic timepiece with charging function employed heretofore, the present invention is designed to detect voltage between the main driving pulse P₁ and the compensating drive pulse P₂ so as to ensure that the compensating drive pulse P₂ rotates the step motor. The timing of the voltage detection pulse 13 is set, as shown in Figure 4, between the main drive pulse P₁ and the compensating drive pulse P₂. As a result, state (1) is restored owing to voltage detection being executed before the compensating drive pulse P₂, although the potential |VC₂| reduces below the lowest operating voltage of the step motor, under the same condition as described above. On the assumption that the time from voltage detection to the output of the compensating drive pulse P₂ is 10 ms, for example, and the generated current of 200 micro A flows, the terminal voltage |VC₂| can be restored from a 1.05 V to approximately 1.31V until the compensating drive pulse P₂ rises. Therefore the step motor is driven normally by the compensating drive pulse P₂. Figure 5 illustrates schematically an integrated circuit of an electronic timepiece according to the present invention. A reference timing signal produced by an oscillator circuit 14 is frequency divided by a frequency dividing circuit 15. An output signal of the frequency dividing circuit 15 is supplied to a voltage detection timing generator circuit 16 and a driving pulse generator circuit 18. A voltage detector circuit 17 detects voltages VC₂ and VC₁ by a timing outputted from the voltage detection timing generator circuit 16. The driving pulse generator circuit 18 delivers driving pulses to a step motor driving circuit 19. This circuit 19 detects rotation and non-rotation of a step motor, while driving the same, and requests the driving pulse generator circuit 18 for a compensating drive pulse P₂ when non-rotation is detected. The relationship between the timing of an output signal of the voltage detection timing generator circuit 16 and the timing of output of the driving pulse generator circuit 18 is shown in Figure 1. For instance, the timing of a detection pulse 13 of the voltage detector circuit 17, which is the output of the voltage detection timing generating circuit 16, is set at 7.8 ms after the rise of the main drive pulse P₁ while the timing for shifting between states (1) and (2) is set at 0.48 ms after the start of voltage detection. By these settings, a time of 22.97 ms is left until the output of the compensating drive pulse P₂ after the shift between states. Charge stored in the capacitor 2 in the above time period is 4.59 micro C when a charging current is 200 micro A. The charge of 4.59 micro C can raise the terminal voltage VC₂ of the capacitor 2 by about 0.67V when the capacity of the capacitor 2 is 6.8 micro F, for instance. Accordingly, even when the terminal voltage |VC₂| of the capacitor 2 is lowered sharply by generation of the main drive pulse P₁, the voltage VC₂ can be raised by the time the following compensating drive pulse P₂ is generated when the solar cell is irradiated with light. The present invention is effected not only for a compensated drive system of electronic timepiece, but also for a construction in which cell life is displayed by an electronic timepiece. Figure 6 shows a driving waveform in the case where cell life of the electronic timepiece is displayed. In this case also, it sometimes happens that the second drive of those given with a period of 2 seconds cannot be compensated if the detection of voltage is executed during a period of 1.825 second after a first drive pulse P to a following drive pulse A. Therefore, the detection of voltage is designed to be conducted during a period of 125 ms which forms a narrow interval of driving, as shown in Figure 6. As above described, it is necessary for improving the quality or efficiency of electronic timepieces, to set the timing of voltage detection in the period forming a narrow interval of driving in the case of an analog electronic timepiece with charging function based on the compensated driving system or conducting cell life display, which is driven at a relatively wide driving interval and at a relatively narrow driving interval. It is relatively very easy to determine the timing of voltage detection from the output timing of the driving pulse generator circuit 18, by modifying the construction of a logic circuit of the voltage detection tiring generator circuit 16. As above described, in the case where there is a possibility of a step motor being driven at a shorter interval than an ordinary period of operation of time indicating hands as in the compensated driving system, the detection of voltage conducted within said short interval enables the compensation of drive conducted just after detection. As a result, the probability of stoppage of the electronic timepiece or failure of rhythmic movement of time indicating hands in the initial state of charging can be reduced, and thus the efficiency of the electronic timepiece with charging function can be improved.

Claims: An analogue electronic timepiece with charging function having an energy generating means (1) for providing the energy to drive a step motor through a step motor driving and detection means (19) and a display; said timepiece comprising: a pulse generator (18) for generating pulses (P1, P2) for said step motor driving and detection means (19) and/or display; first and second capacitors (2,4) each coupled to said energy generating means (1) and said pulse generator (18), said first capacitor (2) having a relatively small capacitance so as to charge rapidly, said second capacitor (4) having a relatively large capacitance so as to store a large amount of energy; means (17) for detecting the energy stored on said second capacitor (4) and for detecting a terminal voltage VC₂ on said first capacitor (2); a switch (a), whilst the energy stored in said second capacitor (4) is below a predetermined value, for connecting said first capacitor (2) to said energy generating means (1) when the terminal voltage VC₂ is less than an upper threshold voltage and for connecting said second capacitor (4) to said energy generating means (1) when the first capacitors terminal voltage VC₂ is above a lower threshold voltage; characterised by timing means (16) coupled to said pulse generator (18) and said detecting means (17) for controlling the timing of said detecting means (17) to detect the first capacitors terminal voltage VC₂ after a drive pulse fails to drive said step motor so as to enable said first capacitor (2) to be connected to and thereby charge from said energy generating means (1) for as long as possible before the next pulse is to be generated. An analog electronic timepiece as claimed in claim 1 characterised in that said electric energy generating means comprises a solar cell. An analog electronic timepiece as claimed in claim 1 characterised in that said electric energy generating means comprises a manually operated generator.

Inventors: ODAGIRI, HIROYUKI C/O SEIKO INSTRUMENTS INC.
Applicants: SEIKO INSTRUMENTS INC.
Application year: 1987
Main classification: G04C10
IPC codes: G04C10, H02J7, H02J1, G04C3