Image forming apparatus with conveying portions having a loop detector with contact portion for contacting the sheet

An image forming apparatus comprising:

• an upstream conveying portion which conveys a sheet;
• a downstream conveying portion which is disposed downstream of the upstream conveying portion and which conveys the sheet conveyed by the upstream conveying portion;
• wherein a loop is formed in the sheet between the upstream conveying portion and the downstream conveying portion by a difference of a sheet conveying velocity of the upstream conveying portion and a sheet conveying velocity of the downstream conveying portion while conveying the sheet with the upstream conveying portion and the downstream conveying portion;
• and
• a loop detector which brings a contact portion into contact with the sheet which is conveyed on a sheet conveying path between the upstream conveying portion and the downstream conveying portion,
• wherein at least one of the sheet conveying velocity of the upstream conveying portion and the sheet conveying velocity of the downstream conveying portion is controlled based on a detection signal of the loop detector, and the sheet is conveyed while maintaining a loop amount of the loop within a predetermined range, and
• a driving portion which moves the contact portion to a projecting position where the contact portion is in contact with a conveyed sheet and to a retracted position where the contact portion is not in contact with the conveyed sheet on the sheet conveying path;
• and
• a controlling portion which controls the driving portion such that the contact portion is moved from the projecting position to the retracted position before a leading edge of a sheet in a sheet conveying direction which enters the sheet conveying path reaches a position on the sheet conveying path that corresponds to the contact portion and the contact portion is moved to the projecting position from the retracted position before the leading edge of the sheet which has passed through the position corresponding to the contact portion reaches the downstream conveying portion.