Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-05-01
2001-05-22
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S247000, C358S444000
Reexamination Certificate
active
06236425
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image printing apparatus using a plurality of laser beams (multi-laser beam), and more particularly, the invention relates to art edge smoothing circuit for use in an image printing apparatus.
Image printing apparatuses using a laser beam can print with a higher speed and a higher resolution compared to printing apparatuses of other types, and, accordingly, are widely used. In the past, in a image printing apparatus of this type, a semiconductor laser generating a laser beam having a wavelength of 780 nm has been used, and the printing beam spot diameter becomes 50 to 100 &mgr;m when using a general scanning optical system, and, consequently, the resolution of the printing apparatus becomes 300 to 600 dpi. However, as discussed in a paper presented in Applied Physics of Japan, Vol. 16, No. 7 (1996) pp 676-785, the printing beam spot diameter can be decreased to nearly one-half of the conventional printing beam spot diameter by using a GaN semiconductor laser which generates a laser beam having about one-half of the wavelength (420 nm) of the conventional semiconductor laser. Therefore, an image printing apparatus having a higher resolution can be obtained when using such a laser.
However, in this case, the printing speed of the image printing apparatus is decreased, because the scanning beam density has to be increased at the same time. For example, when an image printing apparatus having a scanning beam density of 300 dpi is changed so as to have a scanning beam density of 600 dpi, the printing speed becomes one-half. Although the printing speed can be increased by doubling the rotating angular speed of the rotating polygon mirror for deflecting the laser beam in the image printing apparatus, it is difficult to further increase the rotating speed because the rotating speed is already at the upper limit of the speed range in the high speed printing apparatus. Therefore, Japanese Patent Application Laid-Open No. 8-15623, has proposed an image printing apparatus wherein high speed or high resolution can be attained by increasing the number of laser beams performing the scanning exposure.
On the other hand, in regard to an image printing apparatus using one laser beam, an image quality improving method has been proposed in Japanese Patent Application Laid-Open No. 8-310057, which calls for smoothing a slanting portion in an outline of a character or an image so as not to generate jags by making use of the characteristics that an image printing apparatus using a laser beam can modulate laser intensity continuously in the main scanning direction and can increase or decrease the toner attaching quantity depending on the laser intensity.
FIG. 2
is a block diagram showing a typical system in which a common image printing apparatus is used. A user forms page description data
202
identifying contents of pages to be printed using a data forming apparatus
201
, such as a computer. On starting printing, the page data
202
is transmitted to a controller
203
of the image printing apparatus through a network or the like. The controller
203
expands the page description data
202
for every page on a bit map memory as image data
204
. Therein, it is assumed that the image printing apparatus is a monochromatic binary laser printer, and the image data
204
is binary data corresponding to 1-pixel per 1-bit. When the expansion of the image data
204
is completed, the controller
203
starts an engine
205
of the image printing apparatus, and then transmits the image data
204
to the engine
205
in response to a synchronous signal
206
received from the engine
205
. The engine
205
prints an actual image on a print medium according to the image data
204
.
FIG. 3
is a block diagram of an image printing apparatus using one laser beam. This image printing apparatus has an edge smoothing circuit
301
connected between the controller
203
and the engine
205
, as disclosed in Japanese Patent Application Laid-Open No. 8-310057. The edge smoothing circuit
301
may be installed inside the controller
203
or inside the engine
205
. Therein, among the synchronous signals
206
transmitted from the engine
205
to the controller
203
, a signal for synchronizing a scanning position of the laser beam on the scanning line with the image data
204
is referred to as a line synchronous signal BD. Each of a plurality of laser beam detectors is arranged at a position just before a position starting each line of printing. The line synchronous signal BD is a signal generated when the laser beam being deflected and scanned passes through the laser beam detector. The edge smoothing circuit
301
receives the line synchronous signal BD, a pixel clock signal DCLK in synchronism with the image data
204
, a high frequency pixel clock signal HCLK and an image data signal VD, and outputs a laser modulating image data signal enhanced for edge smoothing.
FIG. 4
shows a timing chart for each of the signals iin the controller
203
. Signal forming with such timing can b,e performed by inputting a clock signal CLK of 50 MHz into an IC (M66235FP: a product of Mitsubishi Electric Corp.) when the printing speed of the image data
204
in the engine
205
is assumed to be 25 M pixels/second (reference: '95 Mitsubishi Semiconductor Data Book, edited by Digital ASSP).
The clock signal CLK of 50 MHz generated by an external quartz oscillator is continuously input to the IC (M66235PF). The line synchronous signal BD is input from the engine
205
out of synchronism with the clock CLK. The IC (M66235PF) generates a clock signal HCLK by synchronizing the phase of the clock CLK with the line synchronous signal BD with a delay represented by a time period of &Dgr;T and a clock signal DCLK having one-half frequency of the clock signal HCLK. Accuracy of the synchronization is ±3 nsec, which is sufficient when taking it into consideration the fact that the frequency of the pixel clock signal DCLK is 25 MHz. The image signal VD is transmitted to the edge smoothing circuit
301
in synchronism with the pixel clock signal DCLK with 1-pixel per 1-bit signal d
0
(d
2
, . . . ).
FIG. 5
shows the construction of an edge smoothing circuit
301
in the conventional apparatus (Japanese Patent Application Laid-Open No. 8-310057). The edge smoothing circuit
301
can be roughly divided into a line memory
501
, a logic circuit
502
and a pulse width modulation circuit (hereinafter, referred to as PWM)
503
. Although the detailed operation is to be described later, an outline thereof is as follows.
The line memory
501
temporarily stores image data signals VD for a plurality of scanning lines, and transfers image data signals VD of pixels to be printed (reference pixels) and several pixels around the reference pixels to the logic circuit
502
as a single unit. The logic circuit
502
judges by template matching what edge the reference pixels compose a part of, and the judged result is transferred to the PWM
503
. The PWM
503
generates enhanced image data (laser modulation) signals Vde for printing the reference pixels by adding appropriate pulse width modulation based on the judged result.
FIG. 6
is a block diagram showing the construction of an image printing apparatus using a plurality of laser beams. This image printing apparatus is composed of a controller
601
and a printer engine
602
. A detailed description will be omitted here, since the details are disclosed in Japanese Patent Application Laid-Open No.815623. The controller
601
supplies the engine
602
with image data signals VD
1
to VD
4
in synchronism with line synchronous signals BD respectively corresponding to plural laser beams.
FIG. 7
is a perspective view showing the construction of an optical system in an engine
701
of an image printing apparatus of the electrophotographic printing type. Here, it is assumed that the image printing apparatus uses four laser beams
701
. The four laser beams
701
must be incident onto a rotating polygon mirror
702
by providing four la
Kikuchi Asahiko
Kobayashi Shin'ya
Sato Kunio
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Le N.
Pham Hai C.
LandOfFree
Image printing apparatus using plurality of laser beams does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image printing apparatus using plurality of laser beams, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image printing apparatus using plurality of laser beams will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2471413