Electrophotography – Document handling – Copy
Reexamination Certificate
2001-12-14
2003-08-05
Beatty, Robert (Department: 2852)
Electrophotography
Document handling
Copy
C271S227000, C324S701000
Reexamination Certificate
active
06603953
ABSTRACT:
RELATED APPLICATIONS
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet media position sensing device for an image producing apparatus, such as a laser printer. It is more specifically directed to a sheet media position sensor for registering the printed image with the sheet media.
2. Discussion of the Background
In an image forming apparatus, such as a laser printer, a sheet media feeder is provided for transporting the individual sheets into substantial alignment with a xerographic printing device.
In most printing apparatus of this type a sheet media storage tray is mechanically positioned to register the sheet media as it is fed into the mechanism in proper alignment with a transport path to the image producing device. Thus, mechanically the sheet media is properly aligned by the storage tray with respect to both the transport path and the print producing apparatus. A suitable mechanism, such as a sheet feeder roller, is employed in relation to the storage tray to feed a single sheet of the media from the tray into nipped rollers provided along the transport path of the sheet. The feed roller and nipped rollers move the sheet media as accurately as possible, but in many cases the sheet becomes skewed or shifted with respect to the center line of the transport path, which places the sheet media out of proper position with respect to the image producing portion of the printing apparatus.
Up to now, the primary way of attempting to correct this condition is to provide some kind of mechanical apparatus along the transport path to reposition the sheet media into an accurate position required for the image transfer. In the past, individual rollers set laterally with respect to the transport path or individual positioning rollers along the path which can be arranged perpendicular to the longitudinal axis of the path or skewed at an angle with respect to the path have been provided. Various types of sensors, such as photoelectric detectors have been provided in the transport path to determine the position of the sheet media. It is necessary to not only measure the position of the sheet media laterally with respect to the center line of the transport path but also with respect to whether it is skewed with respect to that axis. Once this measurement has been taken and the position calculated the mechanical correction systems, such as the lateral rollers or individual rollers, are rotated at different velocities in an attempt to return the sheet media to the proper position prior to being fed into the image producing device.
Thus, this method produces a sheet alignment mechanism for correcting the positional shift in the sheet media during transportation which is usually caused by rollers which are misapplied or worn within the sheet transporting mechanism. These types of correction devices usually include one of two different types of registration systems. One system is a “lead” registration reference in which the posture or position of the sheet media is realigned with respect to the leading edge of the sheet, and the second registration system is a “side” registration reference in which the position of the sheet is realigned with respect to the side edge of the sheet media. With the first system, a lateral gate is usually positioned across the transport path so that the sheet media as it moves along the transport path will be stopped momentarily by the lateral gate to reposition the sheet properly with respect to the image producing device. The second registration system causes the sheet to move laterally so as to register the side of the sheet against a fixed elongated member which aligns the sheet with respect to the proper transport path and the image producing device.
The problems with these systems are that with the leading edge registration the sheet is caused to abut and temporarily stop to finalize the correct position of the sheet media. The side registration does not always function properly in that the side of the sheet may buckle preventing the sheet from becoming properly aligned with the respect to the imaging device. This is especially true when the thickness of the sheet media is quite thin and provides little strength or rigidity for the alignment process.
In other prior art, small individual rollers are used at various locations along the transport path and once the position of the sheet is determined, various mechanisms, such as stepper motors or motor driven belts, are used to rotate the rollers at various speeds in order to move the sheet into proper alignment with the transport path. Various slippage between the sheet media and the rollers and the inevitable wear of the mechanical devices driving the rollers as well as the rollers themselves cause variations in the rotational speed of the placement rollers which, in turn, affect the actual correction or realignment of the sheet media with respect to the image producing device.
One of the most critical elements of this type of position alignment and correction is a system for measuring the actual location of the sheet media with respect to the transport path. In one configuration, an LED light bar is used in conjunction with a photosensitive bar. These two elements are placed one above and one below the transport path for the sheet media so that the sheet will pass between. Thus, the LED light bar and photosensitive bar are set perpendicular to the transport path. At predetermined time intervals, readings of the position of the sheet media are recorded which Identifies the actual position of the sheet media and whether it is skewed in relation to the center line of the transport path. This arrangement is quite expensive due to the costs of producing the LED light bar as well as the sensing bar. In fact, it is so expensive that the use of this type of position sensor has been substantially ignored.
The present invention addresses the limitations and problems which exist with the present type of sheet media alignment registration and de-skewing devices. The arrangement provided in the present invention and disclosed in this application is considerably cheaper and more reliable than those prior art devices. No attempt is made to actually move the sheet media, thus, eliminating the considerable number of electrical and mechanical devices which have been utilized in the past. As a result, the reliability and the accuracy of the present invention will considerably improve any printing process using the present correcting arrangement.
INFORMATION DISCLOSURE STATEMENT
The following statement is provided to comply with the applicant's acknowledged duty to inform the Patent and Trademark Office of any pertinent information of which he is aware. The following information refers to the most pertinent patents of which the applicant has knowledge with respect to the subject matter of the present invention. There is no intent to show that a comprehensive patent ability search has been performed on this subject.
In the Castelli, et al. patent (U.S. Pat. No. 5,887,996) a de-skewing and registering device for an electro-photographic printing machine is provided. A single sensor determines the actual position and the skew of a sheet in a paper path and generates a signal indicative of this position. A pair of independently driven nip rollers forwards the sheet to a registration position at a proper time based on signals from a controller which generates the motor control signals for applying the necessary corrections to reposition the sheet. An additional single photoelectric sensor can be used to provide feedback for updating the control signals for positioning the sheet.
The Uedo, et al. patent (U.S. Pat. No. 5,857,130) shows an image forming apparatus which has the capabilities of correcting a slant of the image which is recorded after the scanning of a document. The image signal is electrically processed so as to correct the slant of the image to be printed in a xerographic printing process.
The Fujikura, et al. patent (U.S. Pat. No. 6,273,418) discloses a sheet registration
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