Magnification error correction method for image forming apparatus

A magnification error correction method for an image forming apparatus including:

• a printer unit which includes:
• a photosensitive drum motor which rotates a photosensitive drum having scanned surface and which is capable of correcting its rotational speed;
• and a polygonal motor which rotates a polygonal mirror scanning on the scanned surface of the photosensitive drum along a main scanning direction by a light beam, and which forms an image corresponding to an input image data;
• a scanner unit which provides an image data corresponding to a document image and which includes:
• a line sensor scanning a document along a main scanning direction;
• and a carriage motor which drives a carriage that scans the document along a feed direction and which is capable of correcting its speed;
• a control unit for inputting a motor correction value and displaying the motor correction value;
• a reference pattern generating unit for generating a reference pattern data;
• and
• a memory for storing a correction value input by the control unit, comprising the steps of:
• a first correction step of providing a first polygonal motor correction value and a first drum motor correction value to the polygonal motor and the photosensitive drum motor so that an image formed by the printer unit has a desired magnification, on the basis of the reference pattern data provided from the reference pattern generating unit, and storing these correction values in the memory;
• a second correction step of scanning a document, on which a predetermined pattern is printed, by the scanner unit, providing a second polygonal motor correction value and a carriage motor correction value to the polygonal motor and the carriage motor so that an image printed using the printer unit has a desired magnification, storing these correction values in the memory, and providing the first drum motor correction value to the photosensitive drum motor;
• and
• a step of forming an image using the first polygonal motor correction value, the carriage motor correction value and a second drum motor correction value calculated from the first and second polygonal motor correction values and the first drum motor correction value in the case of scanning a document by the scanner unit, and forming an image by the printer unit in a state that a main scanning/feed direction of the image is inverted.