Punching device, image forming apparatus, and punching method

A punching device comprising:

• a punching unit configured to punch at least three holes in a transported sheet sequentially along a transport direction of the sheet;
• a driving unit configured to move the punching unit in an orthogonal direction which is orthogonal to the transport direction;
• an edge detecting unit configured to detect, in at least two locations separated from each other in the transport direction, an edge position of an edge of the sheet on one side edge in the orthogonal direction;
• a punching position setting unit configured to set a punching position corresponding to a hole to be punched by the punching unit in the orthogonal direction, on the basis of an amount of change in the orthogonal direction between the at least two edge positions detected by the edge detecting unit;
• and
• a punching controlling unit configured to cause the punching unit to move to the punching position set by the punching position setting unit and punch a hole in the sheet, wherein
• the edge detecting unit detects a first edge position corresponding to a first hole which is punched first in the sheet and a second edge position corresponding to a second hole which is punched downstream of the first hole in the transport direction,
• the punching position setting unit sets the punching position corresponding to a third hole which is punched by the punching unit downstream of the second hole in the transport direction in the orthogonal direction, on the basis of an amount of change between the first edge position and the second edge position detected by the edge detecting unit,
• the punching controlling unit causes the punching unit to move in the orthogonal direction on the basis of the first edge position and punch the first hole, move in the orthogonal direction on the basis of the second edge position and punch the second hole, and move to the punching position corresponding to the third hole set by the punching position setting unit and punch the third hole, and
• the punching position setting unit calculates a first separation distance in the sheet transport direction between the first hole and the second hole and a second separation distance in the sheet transport direction between the second hole and the third hole, calculates a position that is separated in the orthogonal direction from the punching position corresponding to the second hole by an amount of movement obtained by multiplying the amount of change between the first edge position and the second edge position by a ratio of the second separation distance to the first separation distance, and sets the calculated position as the punching position of the punching unit for the third hole.