Patent ID: 8262189

Claim:
A conveyance device comprising: a conveyed object; 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; 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; an encoder sensor fixed on the conveyed object, which 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, and 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.