Patent ID: 7628556

Claim:
An image forming apparatus comprising: a guide rod extending in a main scanning direction; a linear scale provided above said guide rod; a carriage unit held by said guide rod and configured to slide in the main scanning direction along the guide rod, said carriage unit comprising: a main body including an attachment part formed in an upper part of the main body and having an opening therein; a sensor holding member detachably attached to the main body and including a holding part and a base plate part attached to the holding part; and an encoder sensor attached to the sensor holding part, wherein the encoder sensor includes a groove part having a space through which a linear scale passes, and the groove part is open in a downward direction so that when the sensor holding member is moved in an upward direction, the linear scale no longer occupies the space inside of the groove part, wherein the opening is configured for inserting and extracting the sensor holding member therethrough, the holding part is configured to pass through the opening, and the base plate part is configured such that when the holding part is inserted through the opening, the base plate part remains above the attachment part of the main body and is prevented from passing through the opening, wherein when said sensor holding member is attached to the main body of the carriage unit, the sensor holding member is positioned above the guide rod with the linear encoder being in said space of said groove part.