Synchronization system and synchronization method of multisystem control apparatus

A synchronization system for synchronizing period signals generated by a plurality of systems composing a synchronous-multisystem apparatus wherein any particular one of said systems comprises:

• a synchronization-reference selecting means for selecting a period signal generated by one of said systems by referring to a period signal generated by said particular system and period signals generated by said systems other than said particular system and outputting a signal of a period corresponding to said selected period signal as a synchronization-reference signal;
• and
• a control-period correcting means for correcting a period of a period signal generated by said particular system on the basis of a synchronization shift between said period signal generated by said particular system and said synchronization-reference signal;
• wherein:
• if said synchronization-reference signal is output by said synchronization-reference selecting means, said control-period correcting means forms a judgment on said synchronization shift between said period signal generated by said particular system and said synchronization-reference signal and corrects said period of said period signal generated by said particular system on the basis of a result of said judgment;
• and
• if said synchronization-reference signal is not output by said synchronization-reference selecting means, on the other hand, said control-period correcting means does not correct said period of said period signal generated by said particular system.

A synchronization method for synchronizing period signals generated by a plurality of systems composing a synchronous-multisystem apparatus wherein any particular one of said systems executes the steps of:

• selecting a period signal generated by one of said systems by referring to period signals generated by said systems and outputting a signal of a period corresponding to said selected period signal as a synchronization-reference signal provided that a majority of period signals have been generated by said systems during a predetermined synchronization-reference selection period;
• correcting a period of a period signal generated by said particular system on the basis of a synchronization shift between said period signal generated by said particular system and said synchronization-reference signal wherein:
• if said synchronization-reference signal is not output, a period of a period signal generated by said particular system is used as a period of said period signal;
• and
• if said synchronization-reference signal is output, on the other hand, a period of a period signal generated by said particular system is shortened provided that said synchronization-reference signal is output, leading ahead of said period signal generated by said particular system, or said period of said period signal generated by said particular system is lengthened provided that said synchronization-reference signal is output, lagging behind said period signal generated by said particular system.