SD is not a pure mechanical watch. It has an IC to control the watch heart beat as oppose to using a spring. I know there are arguments about this and each has their own merits. I not going to discuss that over this here. With the IC control, it gives superb accuracy and smooth second hand sweep motion but it is "cheating" in a way. One of the things I love in the SD is the tick-less second hand motion. I was mesmerized by it.
From the patent description below, SpringDrive is a mechanical timepiece. It is just without the escapement that most mechanical watches have. An analogy of this will be saying that that current versions of VW Beetle are not Beetle because it has a liquid cooled engine instead of air cooled engine!
Patent RE38110
Electronically controlled mechanical timepiece and control method therefor
Inventor: Shinkawa, et al.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an electronically controlled mechanical timepiece that is free from phase excursions and has rapid control system response, and to a control method therefor.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an electronically controlled mechanical timepiece including: a mechanical energy source; a generator driven by the mechanical energy source connected to the generator via a wheel train.[.bridge.]. , which generates induced electric power for supplying electric energy; a brake circuit for braking the generator; pointers joined to the wheel train .[.bridge.]. ; and a rotation control circuit for controlling the rotation cycle of thegenerator by controlling the brake circuit; wherein the rotation control circuit includes: a rotation detection circuit for generating a rotation signal of the generator; a target-signal generating circuit for generating a target signal corresponding toa target number of revolutions; and a phase-difference compensating circuit for detecting the phase difference of the target signal output from the rotation detection circuit, and the target signal output from the target-signal generating circuit, andoutputting a phase-difference compensation signal which is used as a braking control signal in the brake circuit.
An electronically controlled mechanical timepiece of the present invention uses a mechanical energy source such as a spring to drive pointers and a generator, and controls the number of rotations of a rotor, i.e., the pointers by braking thegenerator. At this time, the electronically controlled mechanical timepiece compares the phases of a rotation signal of the generator and a target signal such as a timepiece's standard signal, and inputs based on the phase difference a brake controlsignal to a brake circuit for the generator, whereby a so-called phase-synchronization circuit or phase-locked-loop control (PLL control) is realized in an electronically controlled mechanical timepiece. Accordingly, since a braking level can be set bycomparing the waveforms of generated power in each cycle, the activation of a locked range realizes a stable, rapidly responsive system and enables the elimination of phase excursions unless the waveforms of generated power remarkably change suddenly.
Under these circumstances, it is preferable that the generator and the brake circuit constitute a voltage-controlled oscillator, and that the phase-difference compensating circuit include: a phase-comparison circuit for comparing the phases ofthe rotation signal and the target signal; and a brake control circuit for inputting to the voltage-controlled oscillator the phase-difference compensation signal for controlling the brake circuit based on an output from the phase-comparison circuit.
Under these circumstances, it is preferable that the rotation control circuit include a waveform shaping circuit for converting the output waveform of the voltage-controlled oscillator into rectangular-wave pulses, and outputting as the rotationsignal to the phase-comparison circuit.
The output waveform of the voltage-controlled oscillator changes in accordance with a control method therefor. However, by providing the waveform shaping circuit, the different part of the output waveform can be absorbed, and rectangular-wavepulses capable of being compared with a time standard signal can be output to the phase-comparison circuit, irrespective of the output waveform from the voltage-controlled oscillator. Thus, the phase-comparison circuit, etc., can be used in common toenable a reduction in a component cost.
In addition, it is preferable that the rotation control circuit include a frequency-to-velocity converter for converting the frequency of an output signal from the voltage-controlled oscillator into velocity, and that the brake control circuit becapable of outputting a signal which controls the brake circuit, based on an output from the phase-comparison circuit and an output from the frequency-to-velocity converter.
By providing the frequency-to-velocity converter, the time constant of a control circuit can be reduced, and responsiveness can be further improved.
Moreover, it is preferable that the phase-difference compensating circuit include a phase-difference detection circuit and a compensation-signal generating means for receiving an output from the phase-difference detection circuit that therotation signal and the target signal be repetitive pulses, that the phase-difference detection circuit include counters for counting the numbers of rises or falls of the respective signals, and that one counter be incremented or decremented when thetarget signal rises or falls, or is incremented or decremented when the rotation signal rises or falls, and outputs an output of the counter as a phase-difference signal to the compensation-signal generating circuit.
By using a counter to constitute the phase-difference detection means, circuit arrangement can be simplified, and a cost can be also reduced. In addition, a counter capable of holding a plurality of counts can be used. Thus, a phase differencein a broad range can be detected, and even if phase differences are totaled, the total can be held. Accordingly, control in accordance with a total of phase differences can be performed, and more accurate velocity-controlled control can be performed.
Under these circumstances, it is preferable that the phase-difference detection circuit include: an integral counter for measuring a total of the phase excursion periods of the rotation signal and the target signal; a proportional counter formeasuring phase excursion periods; and an adder for increasing or reducing the value of each counter in accordance with a lead or lag of the phase excursion of the rotation signal with respect to the target signal.
According to the present invention, there is provided a control method for an electronically controlled mechanical timepiece including a mechanical energy source; a generator driven by the mechanical energy source connected to the generator via awheel train .[.bridge.]. , which generates induced electric power for supplying electric energy, a brake circuit for braking the generator, pointers joined to the wheel train .[.bridge.]. , and a rotation control circuit for controlling the rotationcycle of the generator by controlling the brake circuit, wherein a rotation signal of the generator and a target signal generated in accordance with a target number of revolutions are compared to detect the phase difference therebetween, and aphase-difference compensation signal in accordance with the phase difference is used to control the brake circuit.
In the present invention, phase excursions can be eliminated, and stable, rapidly responsive control system is realized because an electronically controlled mechanical timepiece can be controlled by phase-synchronization circuit control (PLLcontrol).
Under these circumstances, it is preferable that the control method comprise: using an integral counter to measure a total of the phase excursion periods of the rotation signal and the target signal, and using a proportional counter to measurephase excursion periods; determining a lead or lag of the phase excursion of the rotation signal with respect to the target signal; computing a phase-difference compensation signal for setting a braking time by increasing or reducing the value of eachcounter in accordance with the determined result; and using the phase-difference compensation signal to control the brake circuit. The setting of the braking time includes not only the case where a braking time is directly set, but also the case whereindirect braking is performed by setting a braking release time in which braking is not performed in a predetermined cycle.
