Some flatbed scanners have scan modules that have a short depth of field, for example a scan module that uses a Contact Image Sensor (CIS). The short depth of field requires close alignment between the scanning module and the scanning glass. One method used to maintain the alignment between the scanning module and the scanning glass is to allow the scanning module to ride on or reference the underside of the scanning glass. Many scanners come equipped with an Automatic Document Feeder (ADF). The most common type of ADF uses a second scan window. Typically a second piece of glass is used for the second scan window. When scanning with the ADF, the scanning module is moved underneath the second piece of glass.
USPTO Backgrounds
USPTO Backgrounds