Patent ID: 8028980

Claim:
A sheet folding device comprising: a sheet guide for transferring a sheet to a predetermined position, said sheet guide including a linear sheet carry-in path having a sheet inlet and a sheet outlet; a first switchback path situated under the linear sheet carry-in path and communicating with an outside of the sheet outlet; a second switchback path extending downwardly from the linear sheet carry-in path between the sheet inlet and the sheet outlet to pass around the first switchback path, said second switchback path being curved to project toward the sheet inlet; a third path extending downwardly from an outlet of the second switchback path and being curved to project toward the sheet outlet; and a fourth path located at an upstream side of the third path and extending beyond the outlet of the second switchback path; a sheet end regulating device formed at the third path for supporting a sheet bunch, a folding roll device having a first folding roll and a second folding roll arranged at a fold position in pressure contact with each other, the folding roll device being arranged at a side offset and away from the third path; a folding blade inserting the sheet bunch supported on the sheet end regulating device in the third path of the sheet guide to a nip position between the first and second folding rolls; a roll driving device for rotationally driving the first and second folding rolls; and a blade driving device for moving the folding blade from a standby position to the nip position on the folding rolls; wherein the third path of the sheet guide has a curved guide section and an outlet guide section connected to the curved guide section to guide the sheet bunch to the folding roll device, the curved guide section comprises a curved guide plate so that the sheet bunch curved toward the sheet inlet in the second switchback path rolls back toward the folding roll device in the third path, and the outlet guide section comprises a pair of opposite guide plates inclined so as to fold the sheet bunch inserted to the nip position on the folding rolls by the folding blade.