Sheet length measuring device and image forming apparatus

A sheet length measuring device comprising:

• a rotating body configured to rotate with a movement of a sheet in a conveying direction;
• a position detecting unit configured to detect a leading end and a trailing end of the sheet passing through a position of the rotating body;
• a rotation amount measuring unit configured to measure a rotation amount of the rotating body;
• an origin signal generating unit configured to generate and output a pulse signal as an origin signal per one revolution of the rotating body from variable components in one revolution of the rotating body measured by the rotation amount measuring unit;
• a storage unit configured to store changes of a sheet conveying amount with respect to respective rotation angles in one revolution of the rotating body, the rotation angles being measured by the rotation amount measuring unit with respect to an output of the origin signal from the origin signal generating unit;
• and
• a calculating unit configured to calculate a corrected length of the sheet from a value obtained from a rotation angle of the rotating body with respect to an output of the origin signal when the leading end of the sheet is detected by the position detecting unit and a value obtained from a rotation angle of the rotating body with respect to an output of the origin signal when the trailing end of the sheet is detected by the position detecting unit.

An image forming apparatus comprising:

• a rotating body configured to rotate with a movement of a sheet in a conveying direction;
• a position detecting unit configured to detect a leading end and a trailing end of the sheet passing through a position of the rotating body;
• a rotation amount measuring unit configured to measure a rotation amount of the rotating body and output a pulse signal as an origin signal per one revolution of the rotating body;
• a storage unit configured to store changes of a sheet conveying amount with respect to respective rotation angles in one revolution of the rotating body, the rotation angles being measured by the rotation amount measuring unit with respect to an output of the origin signal;
• and
• a calculating unit configured to calculate a corrected length of the sheet from a value obtained from a rotation angle of the rotating body with respect to an output of the origin signal when the leading end of the sheet is detected by the position detecting unit and a value obtained from a rotation angle of the rotating body with respect to an output of the origin signal when the trailing end of the sheet is detected by the position detecting unit.