Patent GB-1425840-A (GB)
Title: Electronic timepiece
IPC: H02P8/02
Filed: 1973-12-20
Abstract: 1425840 Electronic timepieces SUWA SEIKOSHA KK 20 Dec 1973 [22 Dec 1972] 59151/73 Heading G3T [Also in Division H2]  In an electronic timepiece wherein a stepper motor drives secs, mins and hours hands via a gear train and also a day and date display, the drive current pulse width or amplitude is increased when a greater load is imposed or is about to be imposed on the motor due to actuation of the calendar mechanism.  The time taken for a predetermined angular rotation of the motor rotor is said to depend upon the load on the motor and the motor load is considered to be substantially zero (e.g. 0À5ÁA) when driving the secs, mins and hours hands only, and comparatively high when the calendar mechanism is actuated. Thus the time taken to perform a predetermined angular rotation is detected as a function of the load and is used to control the drive pulse width as in Figs. 6, 7 embodiment and in Figs. 10, 11 (not shown), or the drive pulse amplitude, Figs. 12, 13, accordingly. In Figs. 6, 7 a voltage is induced in a detector coil 41 of stepper motor 33 during a predetermined angular step by permanent magnet rotor 37, which voltage will terminate at the end of the step. The detector voltage is applied to a drive current control circuit Fig. 7 together with timing signal pulses(A, B) Fig. 9 (not shown) applied at terminals 47, 48 respectively. The rotor commences rotation in response to a timing signal. The rectified output of the detector is applied to an inverter amplifier 43 which has normally a relatively low output but produces a relatively high output immediately after the rotor has completed a predetermined angular rotation - and drives a monostable multi-vibrator 44. The output of 44 is fed to an inverter 45 which has normally a high output but goes low when the output of 43 is high. Thus, in the latter instance, the two outputs of a NAND gate 46 go high with the result that a driving current pulse to the motor drive coil 40 from an inverter 49, waveforms (D, E) Fig. 9 (not shown) will be terminated immediately after the rotor completes said angular rotation. Thereby the drive pulse width is made to vary according to the time taken for an angular step which is dependent upon the load on the motor. In another embodiment Fig. 10 (not shown) the angular rotation is detected by an electrostrictive (strain gauge) device (of barium titanate) fixed to a strip having a pawl at its free end engaging a gear-wheel driven by the motor whereby the strip is caused to vibrate and the device produces a signal accordingly. In a further embodiment Figs. 12, 13, an insulating ring 64 on a date advancing wheel 62 defines a time zone during which the date is not being advanced and load is considered to be negligible. A sliding contact 65 rides on the ring 64 until at the end of said time zone it engages the wheel 62 which is electrically conductive and constitutes with the contact 65, a switch 70, Fig. 13. When the switch is open a resistance 74 is effectively in series with the motor drive coil 76, whereas when the switch is closed a transistor 73 is rendered conducting and shunts the resistance 74 increasing the amplitude of the motor drive current pulses. The drive pulse width remains fixed, timing signals of a predetermined pulse width and period being supplied at terminals 80, 81 from a time standard generator (not shown). Alternatively the angular rotation of the motor may be determined without a sensor by detecting when the driving current i L  reaches a peak saturation value indicating that the rotor has completed a predetermined angle of rotation, and the current is terminated at that point, the current being first converted to a voltage and amplified to facilitate detection. The current consumption of the timepieces may be further reduced by using C.M.O.S. components. The timing signals may be derived from a quartz crystal.