Mechanical timepiece

1 . A mechanical timepiece comprising:

a spring;

a balance configured to be driven by power from the spring;

an oscillation circuit configured to output a clock signal;

a speed governing mechanism including a permanent magnet and a coil, one of the permanent magnet and the coil being held by the balance;

an external magnetic field detection mechanism configured to detect an external magnetic field by the coil;

a vibration detection mechanism configured to detect vibration of the balance and output a vibration detection signal;

a speed governing control mechanism configured to output a drive pulse in accordance with a result of comparison between the clock signal and the vibration detection signal, output a current to the coil by the drive pulse to generate an electromagnetic force, and cause the generated electromagnetic force to act on the permanent magnet to perform processing for governing the balance;

a power storage mechanism configured to store electric energy to be supplied to the speed governing control mechanism; and

a generator configured to generate the electric energy,

wherein the speed governing control mechanism is configured to change a processing content of the speed governing of the balance in accordance with a result of the detection of the external magnetic field.

2 . The mechanical timepiece according to claim 1 , wherein

a first power supply line and a second power supply line configured to supply the electric energy to the speed governing control mechanism from the power storage mechanism are provided,

the speed governing control mechanism includes:

a first switch coupled between a first terminal of the coil and the first power supply line;

a second switch coupled between a second terminal of the coil and the first power supply line;

a third switch coupled between the first terminal of the coil and the second power supply line; and

a fourth switch coupled between the second terminal of the coil and the second power supply line,

the first switch, the second switch, the third switch, and the fourth switch are transistors, and

the speed governing control mechanism is configured to execute the processing for governing the balance by controlling the first switch, the second switch, the third switch, and the fourth switch.

3 . The mechanical timepiece according to claim 2 , wherein

the external magnetic field detection mechanism includes a fifth switch and a first resistance element that are coupled in series between the first terminal and the first power supply line, and is configured to execute processing for performing control of turning on the fifth switch, to detect the external magnetic field.

4 . The mechanical timepiece according to claim 3 , wherein

the external magnetic field detection mechanism includes a sixth switch and a second resistance element that are coupled in series between the second terminal and the first power supply line, and is configured to execute processing for performing control of alternately turning on the fifth switch and the sixth switch, to detect the external magnetic field.

5 . The mechanical timepiece according to claim 3 , wherein

the vibration detection mechanism includes

the fifth switch and the first resistance element that are coupled in series between the first terminal and the first power supply line.

6 . The mechanical timepiece according to claim 5 , wherein

the speed governing control mechanism is configured to perform control of turning off the first switch, the second switch, the third switch, and the fourth switch during a period other than a detection period of the external magnetic field, a vibration detection period, and an output period of the drive pulse.

7 . The mechanical timepiece according to claim 1 , wherein

when the external magnetic field detection mechanism detects the external magnetic field,

the speed governing control mechanism stops the processing for governing the balance during a first period.

8 . The mechanical timepiece according to claim 7 , wherein

the external magnetic field detection mechanism is configured to execute processing for detecting the external magnetic field after elapse of the first period, and

the speed governing control mechanism

further stops the processing for governing the balance during the first period when the external magnetic field detection mechanism detects the external magnetic field, and

restarts the processing for governing the balance when the external magnetic field detection mechanism does not detect the external magnetic field.

9 . The mechanical timepiece according to claim 8 , further comprising:

a storage unit configured to store a period during which the processing for governing the balance is stopped,

wherein the speed governing control mechanism reduces an interval of output of the drive pulse in accordance with the period stored in the storage unit, when the processing for governing the balance is restarted.

10 . The mechanical timepiece according to claim 1 , wherein

the generator is an electromagnetic generator including a power generation rotor configured to rotate through a train wheel with power from the spring, and a power generation coil configured to generate power by rotation of the power generation rotor.

11 . The mechanical timepiece according to claim 1 , wherein

the generator is an electromagnetic generator including the permanent magnet and the coil and configured to generate power through a relative movement of the permanent magnet and the coil by vibration of the balance.