ELECTRONIC TIMEPIECE WITH A SOLAR CELL

Abstract: An electronic timepiece comprises an oscillator (17) for generating a time standard signal; a frequency divider (18) for receiving the time standard signal and producing therefrom time signals; pulse generating circuits (19, 20, 21, 22, 30) receiving the time signals; driving circuits (24, 30) connected to receive pulses from the pulse generating circuits; step motors (25, 31) driven by the driving circuits; energy supplementary source (1) such as a solar cell for generating electric energy; and a capacitor (5) for storing electrical energy. A detecting circuit (6) detects the voltage on the capacitor and generates a signal in order to stop at least one of the motors. A counting circuit (27) counts the time for which said one motor is stopped by the detecting circuit and a control circuit (22) drives the motor that has been stopped to position a hand driven thereby to the present time indication under the control of the counting circuit when the detecting circuit no longer generates the signal to stop that motor.

Description: This invention relates to electronic timepieces having a plurality of motors. Some conventional electronic timepieces in production utilise a "clean" energy source i.e. one in which an electro/chemical reaction is not involved. The "clean" energy source may be an amorphous solar cell which is relatively efficient at converting light energy even at relatively low intensity to electrical energy in combination with a relatively large capacitance capacitor of the electric duplicate layer type. The greatest disadvantage of this type of conventional electronic timepiece is that the length of time it will operate when light is not incident on the solar cell is relatively short compared to the time of operation of a conventional electronic timepiece utilising a silver oxide battery. The reason for this is because energy stored in capacitors is much smaller than that stored in silver oxide batteries, so the stored energy is quickly used up by motors, integrated circuitry, etc. With present technology, it is important that electrical power consumed by a step motor rotating every second is less than that consumed by the integrated circuitry. Thus the present invention seeks to provide an electronic timepiece which drives a plurality of hands with a plurality of motors and which can operate for a relatively long time especially when energy is not supplied from a supplementary means such as a solar battery. According to the present invention there is provided an electronic timepiece comprising: oscillating means for generating a time standard signal; frequency dividing means for receiving said time standard signal and producing therefrom a plurality of signals; a plurality of pulse generating means connected to receive signals from the frequency dividing means; a plurality of driving means connected to receive pulses from the pulse generating means; a plurality of motor means arranged to be driven by said driving means; energy supplementary means for generating electrical energy; and accumulating means for storing said electrical energy characterised by detecting means for detecting the voltage on said accumulating means and generating a signal in order to stop one of said motor means; counting means for counting the time for which said one motor means is stopped by the detecting means; and control means for driving the said one motor means that has been stopped to position a hand driven thereby to the present time indication under the control of said counting means, when the detecting means no longer generates the signal to stop the said one motor means. Said supplementary means may be a solar cell. Said accumulating means may be a capacitor. The electronic timepiece may include pulse generating means for generating a signal of a higher frequency than 1Hz for driving the said one motor means that has been stopped. The electronic timepiece may have a seconds hand. Preferably said one motor means which is stopped by the detecting means is arranged to drive a or the seconds hand. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a block diagram of a motor driving controlling circuit of an electronic timepiece according to the present invention; Figure 2 is a block diagram of an electronic timepiece according to the present invention; Figure 3 is a circuit diagram of part of the circuit shown in Figure 2; Figure 4 is a timing chart of input signals to the circuit of Figure 3; and Figure 5 illustrates the operation of an electronic timepiece according to the present invention and a conventional electronic timepiece. Referring first to Figure 2, there is shown, in block diagram form, an analog electronic timepiece according to the present invention. The electronic timepiece has an amorphous solar battery or solar cell 1, a capacitor 5 and a capacitor 14 which store energy from the solar battery, a main integrated circuit (IC) 7, voltage detecting circuits 3, 4, 6, 15, 16, switches 2, 9, 13, diodes 10, 11 and NOR circuits 8, 12. Initially, energy is not stored in the capacitors 5, 14 when no light is incident on the solar cell 1, and the switches 2, 9, 13 are OFF. When light is incident on the solar cell and when the potential of the capacitor 14 rises, the main IC 7 starts to operate, and a sampling signal for voltage detection is generated. When the sampling signal becomes Hi, the voltage on the capacitor 14 is detected by the voltage detecting circuit 15. When the value of the voltage so detected is a predetermined value, (e.g. 2.2 V), the switch 3 is turned OFF and the switch 2 is turned ON. The capacitor 5 is thus charged from the solar cell 1, while the main IC 7 is powered by the capacitor 14. The capacitor 5 is an electric duplicate layer condenser with a much greater capacitance than the capacitor 14. The voltage detecting circuit 16 turns the switch 13 ON and the switch 9 OFF when the voltage of the capacitor 14 is lower than the predetermined voltage (for example 1.5 V). By repeating the above operation, energy is slowly stored in the relatively large capacitance capacitor 5. When the voltage on the capacitor 5 is detected by the voltage detecting circuit 6 to be greater than a predetermined value (for example 1.5 V), the switch 3 is turned OFF and the switch 9 is turned ON. When the voltage on the capacitor 5 reaches a predetermined value (for example 24 V), the switch 2 is turned ON so that overcharging is prevented. The voltage on the capacitor 5 varies according to the amount of light incident on the solar cell 1. By detecting the voltage on the capacitor with the voltage detecting circuit 6 and by connecting the resultant signal to the main IC 7, the rotation of one of two motors for driving a seconds hand (not shown) is controlled. The diodes 10, 11 are provided for preventing counter or reverse current. Figure 1 is a block diagram of a motor drive controlling circuit of an electronic timepiece according to the present invention. All parts other than the voltage detecting circuit 6, a minutes step motor 25, and a seconds step motor 31, are built in the main IC 7. To the motor driving control circuit are connected a frequency divider circuit (DIV) 18 which divides a standard time signal from an oscillator circuit (OSC) 17, a minutes motor pulse generating circuit 19 having an input derived by waveform synthesising a signal from the divider circuit, a seconds motor revision driving pulse generating circuit 20, a seconds motor driving pulse generating circuit 21, a rotation detecting pulse group generating circuit 22 and a voltage detecting pulse generating circuit 23. For the minutes motor driving pulse generating circuit 19, the signal is sent to a minutes motor driving circuit 24 every 20 seconds, and the minutes motor 25 is driven step-wise every 20 seconds. The seconds motor 31 is driven in a manner to minimise current consumption by the presently practiced "revision drive method". First, the signal from the seconds motor driving pulse generating circuit 21 is fed to a seconds motor drive circuit 30 through a switching circuit 28. The seconds motor 31 is driven by the seconds motor drive circuit 30 which produces general drive pulses. Immediately after the seconds motor is driven, detection of rotation of the motor is indicated by a signal from the rotation detecting pulse group generating circuit 22. When the seconds motor is not rotating, the seconds motor is driven by a revision drive pulse P₂ (Figure 4) from the seconds drive motor revision driving pulse generating circuit 20 within 50 milliseconds of the output of a general drive pulse. The voltage detecting pulse generating circuit 23 outputs sampling pulses to detect the voltage on the capacitor 5. When the voltage on the capacitor 5 is lower than the predetermined value (for example 1.3 V) neither a general pulse P₁ (Figure 4) nor a revision drive pulse P₂ are produced but the seconds motor is stopped. After that, the seconds motor drive pulses are fed to a 60 notation UP/DOWN counter, and the position of a seconds hand driven by the seconds motor is memorised. Then, when the voltage on the capacitor 5 becomes higher than the predetermined value, pulses are produced from the seconds motor revision driving pulse generating circuit, these pulses being of a shorter width than those of the pulses of a non-rotating seconds motor revision driving pulse generating circuit. The revision drive pulses at this point are outputted until the count of a fast forwarding signal of 64Hz becomes 0 at a zero detecting circuit 26. As the pulses are shorter than the pulses at non-rotation, the power consumption by the seconds motor is reduced and thus the draing on the capacitor 5 is reduced. Separately from the seconds motor, the minutes motor 25 is driven through the minutes motor driving pulse generating circuit 19 and through the minutes motor driving circuit 24. Figure 3 shows the seconds motor driving circuit 30 and the motor driving controlling circuit of Figure 2. Figure 4 is a timing chart of signals to the input terminal as shown in Figure 3. The pulses P₁ are outputted from the seconds motor general driving pulse generating circuit 21, their pulse width being relatively shorter, as one pulse each second. The pulses P₂ are outputted from the seconds motor revision driving pulse generating circuit 20 at P₁ and non-rotating condition. The pulses P₁, P₂ are fed from respective terminals 34, 35 to an AND gate 33 through an NAND gate 32. Onto one of the input terminals of the AND gate 33, the output of the voltage detecting circuit 6 is connected, but no output is produced when the voltage on the capacitor 5 is relatively small. The output of the AND gate 33 is connected to a first input terminal of an OR gate 36. The output of the voltage detecting circuit 6 is fed to an AND gate 37 through an OR gate 43. Onto the other input terminal of the OR gate 43, a signal (at a terminal 80) which is generated by operating an external switch is connected. Onto one of the two input terminals of the AND gate 37, a fast forwarding signal P₃ of 64Hz at a terminal 39 is connected, and onto the other input terminal, the output of the zero detecting circuit 26 is connected. The output of the AND gate 37 outputs pulses P₃ until the zero detecting circuit produces an output when the voltage of the voltage detecting circuit 6 becomes high again. This output of the AND gate 37 is connected to the DOWN input of the 60 notation UP/DOWN counter 27, and is also connected to the second input of the OR gate 36. The output of the OR gate 36 is connected to a NAND gate 58 and to the first input of a NAND gate 68 and is also connected to the first inputs of AND gates 49, 59 to an inverter 48. The output of the voltage detecting circuit 6 is connected to an AND gate 45 through an OR gate 38, and is also inputted to an AND gate 41 through the OR gate 43 and through an inverter 40. The other input of the AND gate 45 is a 1Hz signal at a terminal 46. The output from the AND gate 45 is fed as UP data to the 60 notation UP/DOWN counter, and is connected to a second input of an OR gate 44. The other input terminal of the AND gate 41 receives a 64Hz signal. The output of the AND gate 41 is connected to a first input of the OR gate 44. The output of the OR gate 44 is connected to a T-input terminal of a T-flip-flop 47, the Q-output of which is connected to the second input of the AND gate 49, the third input of a NAND gate 58, and to a second input of an OR gate 54. The Q-output of the T-flip-flop 47 is connected to a second input of an AND gate 59, and to the third input of the NAND gate 68. A terminal 77 receives a pulse input causing the seconds motor to move two seconds in a cycle of two seconds, when the voltage on the capacitor 5 is within a certain range (for example 1.5 V to 1.3 V). A terminal 78 receives a sampling pulse to detect an alternating magnetic field. A terminal 79 receives a sampling pulse to detect rotation of the seconds motor. The terminal 77 is connected to NOR gates 50, 60. The terminal 78 is connected to the input terminals of OR gates 54, 64. The terminal 79 is connected to the third input terminals of the NAND gates 58, 68. The output of the NOR gate 50 is connected to a gate terminal of a P-channel MOSFET 53 through inverters 51, 52, and is also connected to an input terminal of a NAND gate 55. The output of the NAND gate 58 is connected to a gate of an N-channel MOSFET 75 through an inverter 76, and is also connected to an input terminal of the NAND gate 55. The output of the NAND gate 55 is connected to the gate input of an N-channel MOSFET 57 through an inverter 56. The output of the NOR gate 60 is connected to a gate of a P-channel MOSFET 63 through inverters 61,62 and is also connected to an input terminal of a NAND gate 65. The output of the NAND gate 68 is connected to a gate of an N-channel MOSFET 74 through an inverter 69, and is also connected to an input terminal of the NAND gate 65. The output of the NAND gate 65 is connected to a gate of an N-channel MOSFET 67 through an inverter 66. The drains of the P-MOSFET 53 and the N-MOSFET 57 are mutually connected to an OUT terminal 72 to the seconds motor, and are connected to a drain of the N-MOSFET 75 through a high resistance resistor 70. By using the terminal 72, detection of motor rotation and detection of alternating magnetic field are conducted. The sources of the P-MOSFETs 53,63 are connected to V DD , and the sources of N-MOSFETS 57, 75, 67, 74 are connected to V SS . The drains of the P-MOSFET 63 and the N-MOSFET 67 are mutually connected to OUT terminal 73 of the seconds motor and are connected to the drain of the N-MOSFET 74 through a high resistance resistor 71. By utilising this terminal 73, detection of motor rotation and detection of alternating magnetic field are conducted. Figure 5 illustrates the operation of an electronic timepiece according to the present invention. The longitudinal axis shows the voltage on the capacitor 5 and the lateral axis shows the time. The dotted line represents the result obtained with a conventional driving method of an electronic timepiece, and solid line represents the result with an electronic timepiece according to the present invention. When light is incident on the solar battery when the voltage on the capacitor 5 is 0 V, the voltage gradually rises, and overcharging is prevented when the voltage rises to 2.4 V, and then is clamped. When light is not incident on the solar battery, the voltage on the capacitor 5 gradually decreases as power is consumed by the IC circuit 7, by the motors and by self-discharge of the capacitor. With the present invention, the seconds motor is stopped when the voltage on the capacitor 5 becomes 1.30 V, operated by the 60 notation UP/DOWN counter, and the position of the seconds hand is memorised. Then, only the minutes motor continues to operate until the voltage on the capacitor 5 is 0.9 V. At this point (until the voltage is 0.9 V), the curve of the voltage on the capacitor is a gentle slope because the power consumption is relatively small. When the voltage ofthe capacitor becomes 0.9 V, the minutes motor also stops and the whole electronic timepiece ceased to operate. With the conventional driving method, the seconds motor could not be stopped so the curve of the voltage on the capacitor is steeper, and, as in the present invention, operation of the seconds motor stops at 0.9 V. The working time, after full charge of the capacitor, of the motor is indicated in Figure 5. With the present invention an electronic timepiece with a greatly increased time of operation when energy is not supplied from a supplementary means is achieved. It will be appreciated that it is possible to stop and drive a seconds motor by operating an external member of the electronic timepiece shown in Figure 3. Therefore, by being operated by the user, it is possible to operate the minutes hand and the hours hand for a relatively long time.

Claims: 1. An electronic timepiece comprising: oscillating means (17) for generating a time standard signal; frequency dividing means (18) for receiving said time standard signal and producing therefrom a plurality of signals; a plurality of pulse generating means (19, 20, 21, 22,30) connected to receive a signal from the frequency dividing means; a plurality of driving means (24, 30) connected to receive pulses from the pulse generating means; a plurality of motor means (25, 31) arranged to be driven by said driving means; energy supplementary means (1) for generating electrical energy; and accumulating means (5) for storing said electrical energy characterised by detecting means (6) for detecting the voltage on said accumulating means and generating a signal in order to stop one of said motor means; counting means (27) for counting the time for which said one motor means is stopped by the detecting means; and control means (22) for driving the said one motor means that has been stopped to position a hand driven thereby to the present time indication under the control of said counting means, when the detecting means no longer generates the signal to stop the said one motor means. 2. An electronic timepiece as claimed in claim 1 characterised in that said supplementary means (1) is a solar cell. 3. An electronic timepiece as claimed in claim 1 or 2 characterised in that said accumulating means (5) is a capacitor. 4. An electronic timepiece as claimed in any preceding claim characterised by a pulse generating means for generating a signal of a higher frequency than 1Hz for driving the said one motor means that has been stopped. 5. An electronic timepiece as claimed in any preceding claim characterised by having a seconds hand. 6. An electronic timepiece as claimed in any preceding claim characterised in that said one motor means which is stopped by the detecting means is arranged to drive a or the seconds hand. 7. An electronic timepiece comprising: oscillating means for generating time standard signal; dividing means inputted said standard signal for generating a plurality of signals; plurality of pulse generating means each inputted said signal for generating a plurality of pulses; plurality of driving means i putted said pulse; plurality of step motors each driven by said driving means; plurality of hands driven by said step motors for indicating time; energy supplementary means for generating electric energy; accumulating means for storing said electric energy; detecting means for detecting voltage of said stored electric energy in accumulating means and generating a signal in order to stop at least one of said motors; counting means for counting the suspension time when the motor is stopped; and control means for revising and driving the suspensed motor to position the hand to the present time indication with said counting means, after the suspension is cancelled.

Inventors: OTAWA SHUJI, OTAWA, SHUJI
Applicants: SEIKO INSTRUMENTS INC.
Application year: 1986
Main classification: G04C10
IPC codes: H02P8, G04C10, G04C3