Conveyance device and image forming apparatus

An image forming apparatus, comprising:

• a conveyed object that includes a recording head that forms an image onto a sheet;
• a guide element that guides the conveyed object in a predetermined conveying direction while supporting the conveyed object;
• a conveyance unit that conveys the conveyed object in the conveying direction along the guide element;
• a linear encoder that outputs an encoder signal corresponding to displacement of the conveyed object;
• the image forming apparatus being configured to form a sequence of line images along the conveying direction onto the sheet placed opposite the recording head by causing the recording head to perform an image forming operation onto the sheet while moving the conveyed object in the conveying direction through the conveyance unit,
• wherein the linear encoder comprises:
• an encoder fence, which is elongated in the conveying direction, provided on an intersecting plane that intersects a reference plane orthogonal to a direction in which the guide element supports the conveyed object, and having a plurality of light-transmitting portions that transmit light and a plurality of light-shielding portions that shield light arranged alternately in the conveying direction on a side along the intersecting plane;
• and
• an encoder sensor fixed on the conveyed object, that includes a light-emitting element and a light-receiving element provided in such a manner as to sandwich therebetween a portion of the encoder fence having the light-transmitting portions and the light-shielding portions formed thereon, and outputs the encoder signal in accordance with a light-receiving state of the light-receiving element that receives light outputted from the light-emitting element;
• wherein the encoder fence is configured to have the light-transmitting portions and the light-shielding portions formed thereon so that a first point on each boundary between each of the light-transmitting portions and each of the light-shielding portions adjacent to each other and a second point on the each boundary, which is positioned separately from the first point with respect to a direction along the side of the encoder fence and perpendicular to the conveying direction, are separately positioned with respect to the conveying direction;
• a controller configured to:
• measure a time interval between edges of the encoder signal of rectangle-like shape outputted from the linear encoder;
• and
• determine whether or not the encoder sensor moving in synchronization with the conveyed object is displaced in a direction perpendicular to the reference plane based on a change in a measured value.