Patent ID: 8776650

Claim:
A method of punching sheets by using a punch unit having a punching section configured to punch a sheet transported, comprising: a step of calculating a transverse-direction skew of a sheet at an upstream side of the punching section of the punch unit which punches the sheet transported as a function of times at which the sheet passes through first and second sensors which are spaced apart in a line intersecting at right angles with a direction in which the sheet is transported, prior to transport of the sheet to the punch unit; a step of rotating the punching section back and forth in the direction in which the sheet is transported, comprising: rotating a lever shaft in accordance with the transverse-direction skew via rotation of a longitudinal-registering motor, connected to the lever shaft, thereby punch blades of the punching section are parallel to the transverse-direction of the sheet, and rotating a tongue strip via the lever shaft, wherein the tongue strip intersects at a right angle with the direction in which the sheet is transported and rotates in a longitudinal direction; and a step of punching the sheet after adjusting the position of the punching section.