Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-01-13
2002-06-04
Lee, Susan S. Y. (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S261000
Reexamination Certificate
active
06400384
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image forming apparatuses, such as copying machines, facsimile machines and printers, that have a printer engine to form an image by scanning a laser beam light using a rotating polygonal deflector deflecting the laser beam light and a motor rotating the polygonal deflector. More particularly, the present invention relates to an image forming apparatus and method to shorten the printing time for a first print sheet by shortening the time a motor rotating a polygonal deflector takes to revolve at a predetermined rate from a rest state.
2. Discussion of the Background
A laser beam printer is a known image forming apparatus having a printer engine for forming an image by scanning a laser beam light using a rotating polygonal deflector deflecting the laser beam light and a motor rotating the polygonal deflector (hereinafter polygon motor). The laser beam printer writes an image on a photoconductor by scanning the laser beam in the main scanning direction with rotation of the polygonal deflector while changing the scanning start position in the sub-scanning direction each time one scanning in the main scanning direction is completed. The laser beam printer is superior in the fast printing speed and high resolution of the printed image compared to other types of printers such as dot matrix impact printers. With recent increasing demand for higher resolution of images printed on print sheets, the demand for better resolution of picture elements (expressed by DPI (dot per inch)) of image forming apparatuses has also increased. Some laser printers offer a capability of selecting a desired picture element resolution from among a plurality of picture element resolutions according to the intended use of the output prints.
When the resolution of picture elements is increased, the number of revolutions of a polygon motor driving a polygonal deflector to be rotated has to be proportionally increased. For example, if the number of revolutions of the polygon motor when the picture element resolution is 200 dpi is 6000 rpm (revolutions per minute), for increasing the picture element resolution to 400 dpi, the number of revolutions of the polygon motor is required to be increased to 12000 rpm. In addition, unless the polygon motor reaches a state of revolving at a predetermined number of revolutions in a relatively short time after starting to revolve, such high speed feature of a laser beam printer is impaired. Therefore, the polygon motor is required to have a relatively short starting time to reach a state of revolving at a predetermined number of revolutions after starting to revolve, in addition to such features as stable revolutions at a relatively high speed, a long life time of bearings used in the motor such that the motor is suitable for use for a long time, and low electric consumption so that the heat emission is suppressed.
For shortening the starting time of a polygon motor, for example, the motor can be kept revolving at a high speed revolution even during a waiting period of an image forming apparatus in which the motor is used. However this causes the life time of the bearings of the motor to be decreased by a factor of several inverse squares of the number of revolutions of the polygon motor. Therefore, the polygon motor generally is stopped during the waiting period of the apparatus and is revolved when a printing operation starts.
Further, an operation of feeding a print sheet is generally started after a lock signal is detected indicating that the polygon motor has reached a state of revolving at a predetermined number of revolutions. However, for shortening the printing time, some image forming apparatuses are configured such that a print sheet is fed to reach an interim point of an image forming portion of the apparatus during the starting time of the polygon motor in order to reach a locked state at a predetermined number of revolutions. That is, the time the polygon motor takes to reach the locked state is estimated in advance with a controller of the image forming apparatus and the printing time is shortened by interleaving (1) the time required for feeding a first print sheet for a first printing job to the interim point of the image forming portion of the apparatus and (2) the time required for the polygon motor to reach the locked state.
However, the time required for a polygon motor to reach the locked state varies depending upon the apparatus in which the motor is used and depending upon the change of the apparatus according to the elapse of time. Therefore, the time to start feeding a first print sheet (i.e., the time. the first print sheet waits to be started to be fed after the revolution of a polygon motor is started) needs to be set such that the first sheet will not reach an image forming portion of the apparatus before the polygon motor reaches the locked state at a predetermined high speed. Accordingly, the timing generally is set such that a first printing operation, such as transferring a toner image to a print sheet from a photoconductor, is performed sufficiently after the polygon motor has been locked.
Also, a method has been proposed in which a polygon motor is revolved at a rate lower than a predetermined rate during a waiting period of the image forming apparatus and the time required for the polygon motor to reach a locked state for printing an image on a first print sheet is shortened. In this case also, the number of revolutions of the polygon motor in the waiting period generally is set higher than an optimum number of revolutions that enables the polygon motor to be locked, after a printing instruction has been received, at a timing closest to the timing when feeding of the first print sheet to the image forming portion is completed (i.e., when the time to feed the sheet to the image forming portion ends). Further, in image forming apparatuses, for coping with a variation in the time a polygon motor takes to reach a locked state resulting from variations in different types of apparatuses or from a change in the apparatus after the elapse of time, the operation of feeding a sheet is started well after the polygon motor has started to revolve.
However, in controlling the timing of starting the operation of feeding a sheet, the difference in the number of revolutions of the polygon motor according to the difference in the picture element resolution is not generally considered, and the timing is controlled simply based upon the longest time the polygon motor takes to reach the locked state, irrespective of the picture element resolution. Therefore, it occurs that the printing time for a first sheet is not shortened, depending upon the picture element resolution. Further, generally, the difference between (1) the time a sheet contained in one of a plurality of sheet cassettes takes to reach an image forming portion after having been started to be fed and (2) the time another sheet in another one of the plurality of sheets cassettes takes, generally is not considered in controlling the timing of feeding the respective sheets. Also, the timing is uniformly set based upon the longest time a sheet takes to reach the image forming portion after the sheet has started to be fed. Therefore, it occurs that the high speed revolution of the polygon motor is uselessly continued while waiting for a print sheet to reach the image forming portion, and thereby, the life time of bearings of the motor is decreased.
FIG. 14
is a timing chart illustrating an example of the operating timings of an image forming apparatus, starting from receipt of a printing instruction from a host computer to an exposure (image writing) of a photoconductor drum. The time when the signal is made high in an operation of receiving a printing instruction from a host computer indicates a time when the printing instruction from the host computer is received by a controller of the image forming apparatus. The time when the signal is made high in an operation of outputting a printing request from the contro
Lee Susan S. Y.
Ricoh & Company, Ltd.
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