Time measuring system and related distance measuring system

A spectrum spread type distance measuring apparatus comprising:

• pulse train generating means for generating a pulse train corresponding to a pseudo-random noise code having a predetermined bit length in synchronism with a first reference clock;
• transmitting means for transmitting an electromagnetic wave modulated based on the pulse train generated by said pulse train generating means;
• receiving means for receiving a reflection wave reflected by a measurement object after said electromagnetic wave is transmitted from said transmitting means, and for restoring said pulse train;
• time measuring means for measuring a measurement object time based on the pulse train restored by said receiving means and said pseudo-random noise code, said measurement object time representing a duration from transmission of said electromagnetic wave to reception of said reflection wave;
• and
• means for detecting a distance from the distance measuring apparatus to said measurement object based on the measurement object time measured by said time measuring means,
• wherein said time measuring means comprises:
• coarse measuring means for measuring an approximate measurement object time based on said first reference clock, said approximate measurement object time representing a duration from a measurement start time to an input time of measurement object pulse;
• and
• fine measuring means, cooperating with said coarse measuring means and using a reference time of predetermined periods shorter than those of said first reference clock, for measuring a time difference between a change point of said first reference clock and the input time of measurement object pulse as a correction time of said approximate measurement object time,
• wherein coarse measuring means inputs said pulse train generated in accordance with the pseudo-random noise code in synchronism with the first reference clock, said pulse train serving as said measurement object pulse, and obtains the input time of measurement object pulse based on a correlation value between said pulse train and said pseudo-random noise code, and measures the approximate measurement object time representing a duration from the measurement start time to the input time of measurement object pulse,
• said fine measuring means measures a time difference between a change point of said first reference clock and a change point of at least one pulse signal of said pulse train as said correction time of said approximate measurement object time, and
• a precise measurement object time is obtained based on said approximate measurement object time measured by said coarse measuring means and said correction time measured by said fine measuring means.

A time measuring method, comprising the steps of:

• generating a first reference clock at predetermined periods;
• measuring an approximate measurement object time based on said first reference clock, said approximate measurement object time representing a duration from a measurement start time to an input time of measurement object pulse,
• measuring a time difference between a change point of said first reference clock and the input time of measurement object pulse as a correction time of said approximate measurement object time by using a reference time of predetermined periods shorter than those of said first reference clock, and
• obtaining a precise measurement object time based on said approximate measurement object time and said correction time.

A distance measuring method using a spectrum spread type measuring device, comprising the steps of:

• generating a pulse train corresponding to a pseudo-random noise code having a predetermined bit length in synchronism with a first reference clock;
• transmitting an electromagnetic wave modulated based on said pulse train;
• receiving a reflection wave of transmitted electromagnetic wave which is reflected by a measurement object, and restoring said pulse train;
• measuring a measurement object time based on the restored pulse train and said pseudo-random noise code, said measurement object time representing a duration from transmission of said electromagnetic wave to reception of said reflection wave;
• and
• detecting a distance from the measuring device to said measurement object based on the measurement object time,
• wherein said step of measuring said measurement object time comprises the steps of:
• measuring an approximate measurement object time based on said first reference clock, said approximate measurement object time representing a duration from a measurement start time to an input time of measurement object pulse;
• and
• measuring a time difference between a change point of said first reference clock and the input time of measurement object pulse as a correction time of said approximate measurement object time by using a reference time of predetermined periods shorter than those of said first reference clock,
• wherein said step of measuring said approximate measurement comprises the steps of:
• inputting said pulse train generated in accordance with the pseudo-random noise code in synchronism with the first reference clock, said pulse train serving as said measurement object pulse;
• obtaining the input time of measurement object pulse based on a correlation value between said pulse train and said pseudo-random noise code;
• and
• measuring the approximate measurement object time representing a duration from the measurement start time to the input time of measurement object pulse,
• wherein said step of measuring a time difference is performed to measure a time difference between a change point of said first reference clock and a change point of at least one pulse signal of said pulse train as said correction time of said approximate measurement object time, and
• a precise measurement object time is obtained based on said approximate measurement object time and said correction time.