SCANNING CARRIAGE MOTION CONTROL IN AN IMAGE INPUT DEVICE
Original Publication Date: 1990-Aug-31
Included in the Prior Art Database: 2004-Apr-05
Xerox Disclosure Journal
In an image input device, there is provided an arrangement for producing a control signal for controlling the motion of a scanning carriage by the imaging device used for image acquisition. With reference to Figures 1 and 2, a fine resolution target, indicated by lines 198, is provided along the path of the scanning carriage, at a position for detection by array 64 positioned outside the area of image acquisition or outside the area of platen 112. In this area of photosensitive element array 64, there are typically several unused elements, from which acquired data is ignored. Typically the lines will be about 8-10 pixels long (although Figure 1 shows fewer photosites for detection of the line for the purpose of illustrating the invention, only) extending in a direction parallel to the length of the array, at a relatively high frequency. The frequency required is based on the speed of the scanning device, as will be further described. The image of the line target will be available for several photosensitive elements to assure that the line is detected by a working element that accurately detects the line. An average value over several elements may be used. In an alternative embodiment of the invention two targets arranged side by side, and out of phase by 90" may be used, to provide incremental quadrature encoding of the carriage position to determine direction of travel. Alternatively, the lines may have a non-uniform width or frequency, if for some reason variations in the control signal produced by detection of the lines is desired, such as for controlling acceleration.