The present invention relates to a very low cost portable compact scanner employing a single scanning carriage incorporating a reading head and a printing head to permit essentially simultaneous reading and writing of an original document and a copy. More particularly it is directed to document and copy sheet registration for such a scanner.
Historically, copies of original documents have been produced by a xerographic process wherein the original document to be copied is placed on a transparent platen, either by hand or automatically through the use of a document handler, and the original document illuminated by a relatively high intensity light. Image rays reflected from the illuminated document are focused by a suitable optical system onto a previously charged photoconductor, the image light rays functioning to discharge the photoconductor in accordance with the image content of the original to produce an electrostatic latent image of the original on the photoconductor. The electrostatic latent image so produced is thereafter developed by a suitable developer material commonly referred to as toner, and the developed image transferred to a sheet of copy paper brought forward by a suitable feeder. The transferred image is thereafter fixed to the copy paper by fusing to provide a permanent copy while the photoconductor is cleaned of residual developer preparatory to recharging. More recently, interest has arisen in electronic imaging where, in contrast to the aforedescribed xerographic system, the image of the document original is converted to electrical signals or pixels and these signals, which may be processed, transmitted over long distances, and/or stored, are used to produce one or more copies. In such an electronic imaging system, rather than focusing the light image onto a photoreceptor for purposes of discharging a charged surface prior to xerographic development, the optical system focuses the image rays reflected from the document original onto the image reading array which serves to convert the image rays to electrical signals. These signals are used to create an image by some means such as operating a laser beam to discharge a xerographic photoreceptor, or by operating some direct marking system such as an ink jet or thermal transfer printing system.
It is generally advantageous if the normally separate document reading and copy printing operations could be combined. If some of these reading/writing functions could be combined, system operation and synchronization could be simplified and system cost reduced through the use of fewer parts.
There are systems in the prior art that address the above identified concerns. For example:
U.S. Pat. No. 4,496,984 to Stoffel and U.S. Pat. No. 4,583,126, a division of the above-identified reference, disclose an input/output scanner for simultaneously reading a document and writing a copy. The document and copy sheet are fed in back to back relation to the read/write station. A monolithic full width reading array reads each line in two steps, to improve resolution. The writing array consists of rows of ink jet nozzles, of which the number and disposition is in direct correspondence to the sensors of the read bar.
U.S. Pat. No. 4,424,524 to Daniele discloses a full width read/write LED array for scanning a document in the read mode or exposing the photoreceptor in the write mode. A Selfoc optical fiber lens array is used for focusing the full width LED array on the document or photoreceptor.
A difficulty with these prior art systems is the complexity and cost of separate components such as the complex optics, photoreceptor and developer in a typical xerographic process such as the Daniele system. In other systems such as the Stoffel system, it is necessary for an operator to manually combine a document and copy sheet into a single unit for manual insertion to the machine feed rolls. Such a system also has a significant cost penalty associated with components such as the monolithic full width reading array.
In the above cross reference application entitled "Compact Multimode Input and Output Scanner" Ser. No. 547,887 an input output scanner concept is described wherein a single pair of paper path rolls drive both the document at the 12 o'clock position and the copy paper at the 6 o'clock position and the circumference of the roll was equal to the width of the input and the output chips. The scanning carriage has secured thereto a reading head and a printing head which carriage system scans across a document scanning a band of information across the document and printing a band of information across a copy sheet. The carriage system has a separate indexing mechanism to index the scanning carriage to a second position to scan another band of information across the document.
Between imaging scans both the paper and the document are advanced exactly the same amount by one complete revolution of the drive rolls thus eliminating the need for tight control of the run out tolerances on the rolls thereby insuring lower costs for the parts. The advantages of such an architecture could be lost if the copy sheet and document have to be driven by larger diameter rolls or by separate rolls which may be required where either or both the input and output chip are vertically oriented and have a dimension greater than the width of the scanning path. The present invention is directed to an alternate architecture directed to minimizing such difficulties as well as providing a copy sheet and document registration system to enable such a system.