U.S. patent application number 11/119931 was filed with the patent office on 2005-09-29 for image forming apparatus and image forming method.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Kawana, Takashi.
Application Number | 20050213161 11/119931 |
Document ID | / |
Family ID | 26553840 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050213161 |
Kind Code |
A1 |
Kawana, Takashi |
September 29, 2005 |
Image forming apparatus and image forming method
Abstract
An image forming apparatus for forming an image of multilevel
image data includes a driving unit for driving an image forming
element for image formation, an additional data generating unit for
generating a digital signal string based on predetermined
additional data, and an input unit for superposing a digital signal
string related to the multilevel image data and the digital signal
string based on the additional data and inputting the superposed
digital signal string to the driving unit.
Inventors: |
Kawana, Takashi; (Tokyo,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
26553840 |
Appl. No.: |
11/119931 |
Filed: |
May 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11119931 |
May 3, 2005 |
|
|
|
09675141 |
Sep 29, 2000 |
|
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Current U.S.
Class: |
358/3.28 ;
340/5.86; 347/232; 358/530; 399/366 |
Current CPC
Class: |
H04N 1/3871 20130101;
H04N 1/00838 20130101 |
Class at
Publication: |
358/003.28 ;
399/366; 347/232; 358/530; 340/005.86 |
International
Class: |
H04N 001/50; B41J
002/435; G08B 029/00; G06K 015/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 1999 |
JP |
11-280596 |
Sep 30, 1999 |
JP |
11-280600 |
Claims
1-16. (canceled)
17. An image forming apparatus for forming an image of multilevel
image data, comprising: driving means for receiving a digital
signal string related to the multilevel image data and driving an
image forming element for image formation; and additional data
generating means for generating a digital signal string based on
predetermined additional data, wherein said driving means has an
input terminal for forcedly controlling light emission of said
image forming element, and a digital signal string based on the
additional data is input to said input terminal of said additional
data generating means, wherein said input terminal forcedly turns
on or off light emission of said image forming elements.
18. (canceled)
19. The apparatus according to claim 17, wherein said digital
signal string related to the multilevel image data and said digital
signal string based on predetermined additional data are generated
by different clock generation means.
20-22. (canceled)
23. The apparatus according to claim 17, wherein the additional
data is based on information for specifying said image forming
apparatus.
24. (canceled)
25. The apparatus according to claim 17, further comprising means
for generating horizontal scan position information and vertical
scan position information in printing scan by said image forming
element, wherein said additional data generating means generates a
digital signal string based on the additional data on the basis of
the horizontal scan position information and the vertical scan
position information.
26. (canceled)
27. The apparatus according to claim 17, wherein said additional
data generating means comprises means for inputting information of
a position on the image to which the additional data is to be
added.
28. (canceled)
29. The apparatus according to claim 17, wherein the multilevel
data includes data of at least yellow, cyan, and magenta, and said
additional data generating means generates a digital signal string
based on the additional data only for a digital signal string of
the multilevel image data pertaining to yellow.
30. (canceled)
31. The apparatus according to claim 17, wherein said image forming
element is a light-emitting element.
32. (canceled)
33. An image forming method of forming an image of multilevel image
data by using an image forming element for image formation and
driving means for driving said image forming element, said driving
means having an input terminal for forcedly controlling light
emission of said image forming element, comprising the steps of:
inputting a digital signal string related to the multilevel image
data to said driving means; and generating a digital signal string
based on predetermined additional data and inputting the digital
signal string to said input terminal, wherein said input terminal
forcedly turns on or off light emission of said image forming
element.
34. (canceled)
35. The method according to claim 33, wherein said digital signal
string related to the multilevel image data and said digital signal
string based on predetermined additional data are generated by
different clock generation means.
36-38. (canceled)
39. The method according to claim 33, wherein the additional data
is based on information for specifying an apparatus for executing
said image forming method.
40. (canceled)
41. The method according to claim 33, wherein horizontal scan
position information and vertical scan position information in
printing scan by said image forming element are generated and, on
the basis of the generated horizontal scan position information and
vertical scan position information, a digital signal string based
on the additional data is input to said input terminal.
42. (canceled)
43. The method according to claim 33, wherein information of a
position on the image to which the additional data is to be added
is generated and, on the basis of the generated position
information, a digital signal string based on the additional data
is generated.
44. (canceled)
45. The method according to claim 33, wherein the multilevel data
includes data of at least yellow, cyan, and magenta, and a digital
signal string based on the additional data is generated only for a
digital signal string of the multilevel image data pertaining to
yellow.
46. (canceled)
47. The method according to claim 33, wherein said image forming
element is a light-emitting element.
48. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an image forming apparatus
and image forming method and, more particularly, to an image
forming apparatus and image forming method capable of contributing
to prevention of, e.g., copying of securities.
BACKGROUND OF THE INVENTION
[0002] Recently, image forming apparatuses such as printers have
been given color capability and used as various expressing means by
users. In particular, color page printers are attracting attention
because they are silent and capable of high-quality, high-speed
printing.
[0003] A multicolor beam printer as one color page printer is
characterized by printing a multicolor image by performing first
development by scanning a light beam on a photosensitive body in a
main scan direction, and then transferring the image onto a
printing medium such as a printing paper sheet on a transfer
carrier to perform predetermined processing.
[0004] A method of printing a multicolor image by this multicolor
beam printer will be described below with reference to FIGS. 18 and
19.
[0005] FIG. 18 is a schematic view of a conventional multicolor
beam printer. FIG. 19 is a block diagram of signal processing.
[0006] Referring to FIG. 18, a photosensitive drum 201 which
rotates in the direction of an arrow at a predetermined constant
velocity is charged to a predetermined polarity and a predetermined
voltage by a charger 204.
[0007] Printing sheets P are fed one by one at a predetermined
timing from a paper feed cassette 215 by a paper feed roller 214.
When a sensor 202 senses the leading edge of the printing sheet, a
laser beam L modulated by an image signal VDO is emitted from a
semiconductor laser 205 toward a polygonal mirror 207.
[0008] This laser beam L is scanned by the polygonal mirror 207 and
guided onto the photosensitive drum 201 via a lens 208 and a mirror
209.
[0009] A signal (to be referred to as TOPSNS hereinafter) from the
sensor 202 placed at one end of light scan is output as a vertical
sync signal to an image processor 250 (FIG. 19).
[0010] The image signal VDO is sequentially supplied to the
semiconductor laser 205 in synchronism with a BD signal (to be
described later) which follows the TOPSNS signal. When the laser
beam L enters a detector 217, a beam detection signal (to be
referred to as a BD signal hereinafter) serving as a horizontal
sync signal is output.
[0011] The polygonal mirror 207 is driven by a scanner motor 206.
This scanner motor 206 is controlled by a motor control circuit 225
so as to rotate at a predetermined constant velocity in accordance
with a signal S2 from a frequency divider 221 which divides the
frequency of a signal S1 from a reference oscillator 220 shown in
FIG. 19.
[0012] The photosensitive drum 201 is exposed by scan in
synchronism with the BD signal, and a developing device 203Y
develops a first electrostatic latent image. After that, a first
toner image of yellow is formed on the photosensitive drum 201.
[0013] Immediately before the leading edge of the printing sheet P
fed at a predetermined timing reaches a transfer start position, a
predetermined transfer bias voltage having a polarity opposite to
that of toner is applied to a transfer drum 216. Consequently, the
first toner image is transferred onto the printing sheet P, and at
the same time this printing sheet P is electrostatically attracted
to the surface of the transfer drum 216.
[0014] Subsequently, a second electrostatic latent image is formed
on the photosensitive drum 201 by manipulating the laser beam L. A
developing device 203M develops this second electrostatic latent
image to form a second toner image of magenta on the photosensitive
drum 201. This second toner image is transferred onto the printing
sheet P so as to be aligned with the position of the first toner
image previously transferred onto the printing sheet P. Note that
the end of the image of each color is defined by the TOPSNS
signal.
[0015] Analogously, a third electrostatic latent image is formed
and developed by a developing device 203C, and a cyan toner image
formed is aligned with and transferred onto the printing sheet P. A
fourth electrostatic latent image is then formed and developed by a
developing device 203K, and a black toner image formed is aligned
with and transferred onto the printing sheet P.
[0016] As described above, a VDO signal of one page is output to
the semiconductor laser 205 in each step. Also, whenever the
transfer step is performed, a cleaner 210 scrapes off any
untransferred toner image.
[0017] After that, when the leading edge of the printing sheet P on
which the toner images of four colors are transferred approaches
the position of a separation pawl 212, this separation pawl 212
comes in contact with the surface of the transfer drum 216 to
separate the printing sheet P from the transfer drum 216. The end
portion of this separation pawl 212 keeps contacting the transfer
drum 216 until the trailing edge of the printing sheet P is
separated from the transfer drum 216. After that, the separation
pawl 212 moves away and returns to the original position. A charger
211 removes stored charge on the printing sheet P to facilitate
separation of the printing sheet P by the separation pawl 212, and
reduces air discharge during separation.
[0018] FIG. 20 is a timing chart showing the relationship between
the TOPSNS signal and the VDO signal described above. Referring to
FIG. 20, reference symbol A1 denotes a printing operation of the
first color; A2, a printing operation of the second color; A3, a
printing operation of the third color; and A4, a printing operation
of the fourth color. These sections A1 to A4 form a color printing
operation of one page.
[0019] FIG. 21 is a block diagram showing the system configuration
of a conventional printer.
[0020] Referring to FIG. 21, a printer 302 receives a control
signal and an image signal 307 from an external apparatus, e.g., a
host computer 301. A printer controller 303 transfers the control
signal to a printer control unit 304. The image signal is supplied
to a laser driver 310 of a printer engine via an image processor
305 in the printer controller 303 and drives a semiconductor laser
306.
[0021] FIG. 22 is a block diagram showing the internal arrangement
of the image processor 305 shown in FIG. 21. The image processor
shown in FIG. 22 receives an image signal of 8 bits for each of R,
G, and B, i.e., a total of 24 bits from the printer controller (not
shown). A color processor 351 converts each of Y, M, C, and K
signals into the 8-bit VDO signal described above at respective
timings (FIG. 23 is a corresponding timing chart).
[0022] A .gamma. correction unit 325 converts these Y, M, C, and K
VDO signals into .gamma.-corrected, 8-bit signals and inputs these
signals to a pulse width modulation unit 353 (to be referred to as
a PWM unit hereinafter) in the next stage. In this PWM unit 353, a
latch 345 synchronizes the 8-bit image signal with the leading edge
of an image clock iVClK. A D/A converter 355 converts the signal
into an analog voltage and inputs the voltage to an analog
comparator 356.
[0023] The image clock iVCLK is converted into a triangular wave by
a triangular wave generator 358 and input to the analog comparator
356. This analog comparator 356 compares the two signals and
outputs an image signal 309 subjected to PWM. An inverter 357
inverts the output signal to obtain a desired PWM signal.
[0024] FIG. 24 shows a timing chart when the PWM unit 353 generates
a PWM signal. As shown in FIG. 24, when the input 8-bit image data
to the PWM unit 353 is FF[H] (H indicates hexadecimal notation),
the widest PWM signal is output. When the image data is 00[H], the
narrowest PWM signal is output.
[0025] Unfortunately, the improved printing performance and
high-quality printing capability of a conventional image forming
apparatus as described above lead to frequent occurrence of forgery
of securities such as paper money.
[0026] As the image formation technology improves in the future,
the image quality improves accordingly, so this sort of crimes are
expected to increase in number.
SUMMARY OF THE INVENTION
[0027] It is, therefore, an object of the present invention to
provide an image forming apparatus and image forming method capable
of adding predetermined information on an image in order to track
down perpetrators in the event of such crimes.
[0028] According to the present invention, there is provided an
image forming apparatus for forming an image of multilevel image
data, comprising driving means for driving an image forming element
for image formation, additional data generating means for
generating a digital signal string based on predetermined
additional data, and input means for superposing a digital signal
string related to the multilevel image data and the digital signal
string based on the additional data and inputting the superposed
digital signal string to the driving means.
[0029] According to the present invention, there is provided an
image forming method of forming an image of multilevel image data
by using an image forming element for image formation and driving
means for driving the image forming element, comprising the steps
of generating a digital signal string based on predetermined
additional data, and superposing a digital signal string related to
the multilevel image data and the digital signal string based on
the additional data and inputting the superposed digital signal
string to the driving means.
[0030] According to the present invention, there is provided an
image forming apparatus for forming an image of multilevel image
data, comprising driving means for receiving a digital signal
string related to the multilevel image data and driving an image
forming element for image formation, and additional data generating
means for generating a digital signal string based on predetermined
additional data, wherein the driving means has an input terminal
for forcedly controlling light emission of the image forming
element, and a digital signal string based on the additional data
is input to the input terminal of the additional data generating
means.
[0031] According to the present invention, there is provided an
image forming apparatus for forming an image of multilevel data,
comprising at least two image forming means, each of the image
forming means comprising driving means for driving an image forming
element for image formation, additional data generating means for
generating a digital signal string based on predetermined
additional data, and input means for superposing a digital signal
string related to the multilevel image data and the digital signal
string based on the additional data and inputting the superposed
digital signal string to the driving means.
[0032] According to the present invention, there is provided an
image forming method of forming an image of multilevel image data
by using an image forming element for image formation and driving
means for driving the image forming means, the driving means having
an input terminal for forcedly controlling light emission of the
image forming element, comprising the steps of inputting a digital
signal string related to the multilevel image data to the driving
means, and generating a digital signal string based on
predetermined additional data and inputting the digital signal
string to the input terminal.
[0033] According to the present invention, there is provided an
image forming method of forming an image of multilevel data by
using at least two image forming elements for image formation and
at least two driving means for driving the image forming elements,
comprising the steps of generating a digital signal string based on
predetermined additional data for each of the driving means, and
superposing a digital signal string related to the multilevel image
data and the digital signal string based on the additional data and
inputting the superposed digital signal string to each of the
driving means.
[0034] Other features and advantages of the present invention will
be apparent from the following description taken in conjunction
with the accompanying drawings, in which like reference characters
designate the same or similar parts throughout the figures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
[0036] FIG. 1 is a sectional view showing the structure of an image
forming apparatus A according to one embodiment of the present
invention;
[0037] FIG. 2 is a block diagram showing an outline of the
arrangement of a printing system using the image forming apparatus
A;
[0038] FIG. 3 is an internal block diagram of a printer controller
3;
[0039] FIG. 4 is a timing chart showing a VDO signal 6, a BD signal
423 as a horizontal sync signal, and a PSYNC signal 424 as a
vertical sync signal;
[0040] FIG. 5 is an internal block diagram of a signal processor
402 of an engine;
[0041] FIG. 6 is an internal block diagram of a tracking pattern
generator 410;
[0042] FIG. 7 is a timing chart showing PCLK signal generation in
the tracking pattern generator 410;
[0043] FIG. 8 is a schematic view showing a unit region
representing a number unique to the machine by a tracking
pattern;
[0044] FIG. 9 is a view showing examples of MKON[7:0] 443 and
MKOFF[7:0] 444 as multilevel signals of tracking pattern dots
generated by the tracking pattern generator 410;
[0045] FIG. 10 is a view showing an image printed by mixing the
tracking pattern shown in FIG. 9 into the VDO image signal 6;
[0046] FIG. 11 is a view showing a case in which the output VDO
data 6 from the printer controller is not in synchronism with the
tracking pattern;
[0047] FIG. 12 is an internal block diagram of another signal
processor 402 of the engine;
[0048] FIG. 13 is an internal block diagram of a tracking pattern
generator 502;
[0049] FIG. 14 is an internal block diagram of still another signal
processor 402 of the engine;
[0050] FIG. 15 is an internal block diagram of tracking pattern
generators 503 and 504;
[0051] FIG. 16 is an internal block diagram of still another signal
processor 402 of the engine;
[0052] FIG. 17 is an internal block diagram of another tracking
pattern generator 410;
[0053] FIG. 18 is a schematic view of a conventional multicolor
beam printer;
[0054] FIG. 19 is a block diagram of signal processing;
[0055] FIG. 20 is a timing chart showing the relationship between a
TOPSNS signal and a VDO signal;
[0056] FIG. 21 is a block diagram showing the system configuration
of a conventional printer;
[0057] FIG. 22 is a block diagram showing the internal arrangement
of an image processor 305;
[0058] FIG. 23 is a timing chart showing individual signals;
and
[0059] FIG. 24 is a timing chart when a PWM unit 353 generates a
PWM signal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0060] Preferred embodiments of the present invention will now be
described in detail in accordance with the accompanying
drawings.
[0061] FIG. 1 is a sectional view showing the structure of an image
forming apparatus A according to one embodiment of the present
invention.
[0062] In this image printing apparatus A, a gripper 103f grips the
leading edge of a paper sheet 102 fed from a paper feeder 101,
holding the paper sheet 102 on the circumferential surface of a
transfer drum 103.
[0063] Latent images formed by different colors on an image carrier
100 by an optical unit 107 are developed by developing devices (Dy,
Dc, Dm, and Db) of the corresponding colors and transferred a
plurality of times onto the paper sheet held on the circumferential
surface of the transfer drum 103, thereby forming a multicolor
image.
[0064] After that, the paper sheet 102 is separated from the
transfer drum 103, fixed by a fixing unit 104, and delivered to a
paper delivery tray 106 by a paper delivery unit 105.
[0065] Each developing device (Dy, Dc, Dm, or Db) has rotating
shafts at its two ends and is held by a developing device selection
mechanism 108 so as to be rotatable around the shafts.
[0066] Also, each developing device (Dy, Dc, Dm, and Db) is rotated
to be selected with its posture maintained constant. After the
selected developing device has moved to a development position, a
selection mechanism holding frame 109 moves around a supporting
point 109b by a solenoid 109a to position the developing device
selection mechanism 108 and the developing device in the direction
of the image carrier 100.
[0067] The operation of the image forming apparatus A constructed
as above will be described below.
[0068] First, a charger 111 shown in FIG. 1 evenly charges the
image carrier (photosensitive drum) 100 to a predetermined
polarity. A first latent image of magenta is formed on this
photosensitive drum 100 by exposure to a laser beam L.
[0069] In this case, a predetermined developing bias voltage is
applied only to the magenta developing device Dm to develop the
magenta latent image, forming a first toner image of magenta M on
the photosensitive drum 100.
[0070] Meanwhile, a transfer paper sheet P is fed at a
predetermined timing. Immediately before the leading edge of this
transfer paper sheet P reaches the transfer start position
described above, a transfer bias voltage (+1.8 KV) having a
polarity (e.g., positive polarity) opposite to that of the toner is
applied to the transfer drum 103. Consequently, the first toner
image on the photosensitive drum 100 is transferred onto the
transfer paper sheet P. At the same time, the transfer paper sheet
P is electrostatically attracted to the surface of the transfer
drum 103. After that, a cleaner 112 removes the residual magenta
toner from the photosensitive drum 100 to prepare for the formation
and development of a latent image of the next color.
[0071] Subsequently, the laser beam L forms a second latent image
of cyan on the photosensitive drum 100. The cyan developing device
Dc develops this second latent image on the photosensitive drum 100
to form a second toner image of cyan C.
[0072] This second toner image of cyan C is transferred onto the
transfer paper sheet P so as to be aligned with the position of the
first toner image of magenta M previously transferred onto the
transfer paper sheet P. In the transfer of this toner image of the
second color, a bias voltage of +2.1 KV is applied to the transfer
drum 103 immediately before the transfer paper sheet reaches the
transfer unit.
[0073] Similarly, third and fourth latent images of yellow and
black are sequentially formed on the photosensitive drum 100 and
sequentially developed by the developing devices Dy and Db,
respectively. Third and fourth toner images of yellow and black
thus formed are sequentially transferred so as to be aligned with
the toner images previously transferred onto the transfer sheet P.
As a consequence, the toner images of the four colors are formed to
overlap each other on the transfer paper sheet P.
[0074] In the transfer of the toner images of the third and fourth
colors, bias voltages of +2.5 and +3.0 KV, respectively, are
applied to the transfer drum 103 immediately before the transfer
paper sheet reaches the transfer unit. The transfer bias voltage is
raised whenever a toner image of each color is transferred in order
to prevent a lowering of the transfer efficiency.
[0075] A primary cause of a lowering of this transfer efficiency is
that when the transfer paper sheet separates from the
photosensitive drum 100 after transfer, air discharge charges the
surface of the sheet to a polarity opposite to that of the transfer
bias voltage (because air discharge slightly charges the surface of
the transfer drum carrying the transfer paper sheet), and this
electric charge builds up each time an image is transferred. If the
transfer bias voltage is held constant, the transfer electric field
lowers whenever transfer is performed.
[0076] Also, during the transfer of the fourth color described
above, when (or immediately before or immediately after) the
leading edge of the transfer paper sheet reaches the transfer start
position, a DC bias voltage of +3.0 KV having the same polarity and
same potential as the transfer bias voltage applied when the fourth
toner image is transferred is superposed on an AC voltage of 5.5 KV
(an effective value, the frequency is 500 Hz), and the resulting
voltage is applied to the charger 111.
[0077] The charger 111 is thus operated when the leading edge of
the transfer paper sheet reaches the transfer start position during
the transfer of the fourth color in order to prevent uneven
transfer. Especially in transfer of a full-color image, even slight
transfer unevenness is conspicuous as a color difference.
Therefore, it is necessary to apply a predetermined-bias voltage to
the charger 111 to perform discharge as described above.
[0078] After that, as the leading edge of the transfer paper sheet
P on which the toner images of the four colors are transferred by
superposition moves close to a separation position, a separation
pawl 113 approaches, and its end portion comes in contact with the
surface of the transfer drum 103 to separate the transfer paper
sheet P from the transfer drum 103. The end portion of this
separation pawl 113 keeps contacting the transfer drum surface
until the trailing edge of the transfer paper sheet P separates.
After that, the separation pawl 103 moves away from the transfer
drum 103 and returns to the original position.
[0079] As described above, the charger 111 operates from the time
the leading edge of the transfer paper sheet P reaches the transfer
start position of the last color to the time the trailing edge of
the transfer paper sheet P separates from the transfer drum 103. In
this manner, the charger 111 removes stored charge (having a
polarity opposite to that of the toner) on the transfer paper sheet
to facilitate the separation of the transfer paper sheet by the
separation pawl 113. Also, the charger 111 reduces air discharge
during the separation of the transfer paper sheet.
[0080] Note that when the trailing edge of the transfer paper sheet
reaches the transfer end position (the exit of a nip formed by the
photosensitive drum 100 and the transfer drum 103), the transfer
bias voltage (ground potential) to be applied to the transfer drum
103 is turned off. Simultaneously, the bias voltage applied to the
charger 111 is turned off.
[0081] The transfer paper sheet P thus separated is conveyed to a
fixing device 104 where the toner images on the transfer paper
sheet are fixed. After that, the transfer paper sheet P is
delivered onto the paper delivery tray 115.
[0082] The operation of laser beam scanning in the image forming
apparatus A will be described below.
[0083] The optical unit 107 as a driving means comprises a
semiconductor laser 120 as an image forming device (light-emitting
device), a polygonal mirror 121, a scanner motor 122, a lens 123,
and a mirror 125. When the printing sheet P is fed and its leading
edge is detected, an image signal VDO of one page is output to the
semiconductor laser 120 in synchronism with the detection.
[0084] The light beam L is modulated by the image signal VDO and
emitted toward the polygonal mirror 125 which is rotated by the
scanner motor 122. In this way the light beam L is guided to the
photosensitive drum 100 by the lens 123 and the mirror 125. Also,
when the light beam L is emitted, a detector (not shown) placed on
the scanning axis detects this light beam L and outputs a beam
detection signal BD as a horizontal sync signal. Consequently, the
light beam L exposes the photosensitive drum 100 by scanning in
synchronism with the BD signal to form an electrostatic latent
image.
[0085] FIG. 2 is a block diagram showing an outline of the
arrangement of a printing system using the image forming apparatus
A. As shown in FIG. 2, a printer 2 (image forming apparatus A)
comprises a printer controller 3 for rasterizing image information
in a predetermined descriptive language supplied from a host
computer 1, and a printer engine including a printer control unit
404 and a signal processor 402.
[0086] The host computer 1 also supplies bit data of, e.g., RGB
read by an image reader or the like.
[0087] An image processor 401 in the printer controller 3 converts
an RGB image into a YMCK image and performs pulse width modulation
and dither processing for data by using the multilevel image,
thereby generating a VDO signal 6 as a 1-bit image data string.
[0088] FIG. 3 is an internal block diagram of the printer
controller 3. As shown in FIG. 3, this printer controller 3
comprises an image rasterizer 406, a page memory 407, and the image
processor 401. The image rasterizer 406 converts information of a
printer language supplied from the host computer 1 into bit map
data. The page memory 407 stores the data of one page. The image
processor 401 converts RGB information supplied from the page
memory into YMCK information and generates the VDO signal 6
converted to have a pulse width corresponding to the multilevel
density. This VDO signal 6 is one hard signal. The image processor
401 can be controlled by a clock signal corresponding to one dot of
600 Dpi as printing dots.
[0089] FIG. 4 is a timing chart showing the VDO signal 6 supplied
from the printer controller 3, a BD signal 423 as a horizontal sync
signal supplied from the engine to the printer controller, and a
PSYNC signal 424 as a vertical sync signal. As shown in FIG. 4,
magenta data, cyan data, yellow data, and black data are output in
this order in synchronism with the PSYN signal 424.
[0090] FIGS. 5, 12, and 14 are internal block diagrams showing
examples of the signal processor 402 of the engine. The example
shown in FIG. 5 will be described first.
[0091] The VDO signal 6 supplied from the printer controller 3 is
transferred to a laser driving circuit 500 via an OR gate 414 and
an AND gate 415.
[0092] An image mask signal generator 411 is a block for generating
a MASK signal 419 as a control signal for forcedly turning off a
laser outside a printing region.
[0093] This MASK signal is "1" outside a printing region and "0" in
a printing region. The MASK signal is generated on the basis of the
BD signal and PSYNC signal by receiving desired information from a
CPU 412.
[0094] A tracking pattern generator 410 as an additional data
generating means is a block for generating a signal by which dots
representing a number unique to the machine are printed on printed
matter by yellow toner difficult to see. A code is expressed by the
arrangement of this tracking pattern on printed matter.
[0095] The tracking pattern generator 410 receives an output clock
signal CCLK from a quartz oscillator 413 installed in the engine,
the BD signal 423, and the PSYNC signal 424, and generates a signal
MKON for forcedly turning on the laser and a signal MKOFF for
forcedly turning off the laser. These signals MKON and MKOFF can be
asynchronous to the VDO signal 6 from the printer controller 3.
[0096] Note that the tracking pattern generator 410 is given
arrangement information 421 of the tracking pattern by the CPU 412.
The CPU 412 reads out a number unique to the machine from a memory
420 and encodes the number to generate the arrangement information
421 of the tracking pattern.
[0097] Note also that this tracking pattern is added to the VDO
signal 6 when a yellow plane is printed; the tracking pattern is
desirably not added in a plane of another color.
[0098] FIG. 6 is an internal block diagram of the tracking pattern
generator 410 shown in FIG. 5.
[0099] The frequency of the clock CCLK of the quartz oscillator 413
is the same as or close to the image transfer rate of the printer
controller 3.
[0100] The frequency of this CCLK signal is multiplied by 8 by a
frequency multiplier 434. A clock signal 445 having this eightfold
frequency is output to shift registers 432 and 433 and a frequency
divider 435. In synchronism with the leading edge of the BD signal
423, the frequency divider 435 generates a clock PCLK, which
synchronizes with the BD signal, at the same frequency as the
quartz oscillator 413. FIG. 7 is a timing chart showing these
signals.
[0101] A counter 426 is a 4-bit counter for counting the image
clocks PCLK in a main scan direction. This counter 426 is reset by
the BD signal 423 to start counting from 0h to Bh repeatedly.
[0102] A counter 427 is a 5-bit counter for counting the BD signal
423 in a sub-scan direction. This counter 427 is reset by the PSYNC
signal 424 to start counting from 0h to 1Fh repeatedly.
[0103] An output signal 426 from these counters is information
representing the coordinates of a printed dot. If coincidence
circuits 428 and 429 in the subsequent stage determine that the
information is a desired coordinate position, coincidence signals
447 and 448 are "1". Selectors 430 and 431 select A inputs if the
coincidence signals 447 and 448 are "1", select B inputs if the
coincidence signals 447 and 448 are "0", and output the A or B
inputs from Y.
[0104] As shown in FIG. 10, the basic pixels of the tracking
pattern are such that forced OFF dots are arranged on the two sides
of a forced ON dot. The selector 430 in FIG. 6 outputs multilevel
information 443 which indicates a forced ON dot, i.e., outputs FCh
at a timing at which a forced ON dot is printed and outputs 00h in
other cases. The selector 431 outputs multilevel information 444
which indicates a forced OFF dot, i.e., outputs F8h at a timing at
which a forced OFF dot is printed and outputs 00h in other cases.
The output 8-bit signals from these selectors are converted into
serial data output by parallel-serial converters 432 and 433.
[0105] Coordinate data (437 and 438) for printing tracking patterns
to be set in the coincidence circuits are previously set by a CPU
(not shown).
[0106] Note that the circuit for mixing the tracking pattern in the
VDO signal can also be an EX-OR gate, rather than an AND gate or an
OR gate. When this is the case, tracking dots are not constituted
by forced ON and OFF dots; they form an inverted print of an
original image.
[0107] Another example of the signal processor 402 shown in FIG. 12
will be described below.
[0108] The difference from FIG. 5 is that the tracking pattern is
neither ANDed nor ORed in the input stage of a laser driving
circuit 501 but superposed on an image signal by using terminals (a
forced ON port ON and a forced OFF port OFF) which the laser
driving circuit 501 has to forcedly control a laser.
[0109] In the example shown in FIG. 12, the image signals 6
supplied from the printer controller 3 are operation signals/VDO
and VDO.
[0110] FIG. 13 is an internal block diagram of a tracking pattern
generator 502 shown in FIG. 12. Referring to FIG. 13, a tracking
pattern is generated by a clock from a quartz oscillator 413, so
the tracking pattern has jitter of one clock. Also, since dots
forming the tracking pattern are controlled in units of dots, no
P-S converter is necessary. As described above, the circuit shown
in FIG. 12 is simple and hence can be realized at low cost.
[0111] Still another example of the signal processor 402 shown in
FIG. 14 will be described below.
[0112] This example is an embodiment of a laser beam printer which
performs laser scan in a main scan direction by using two or more
lasers (in this example, two).
[0113] As shown in FIG. 14, exclusive OR (EX-OR) gates 507 and 508
for superposing tracking patterns are placed before laser driving
circuits 505 and 506 for driving the lasers.
[0114] FIG. 15 is an internal block diagram of tracking pattern
generators 503 and 504. In this example, tracking patterns are
expressed by inverting image data VDO 513 and 514. So, output
signals are only MKOT 511 and 512.
[0115] FIG. 8 is a view schematically showing a unit region
representing a number unique to the machine by using tracking
patterns. As shown in FIG. 8, a predetermined code is expressed by
nine patterns in a region indicated by the broken lines. Of these
nine patterns, two patterns are reference patterns. The positions
of the seven remaining patterns represent codes "0" to "3" (two
bits), so these seven patterns express a total of 14 bits; in
decimal notation, 0 to 16383. FIG. 8 expresses 11384. This pattern
is repeated in the main scan and sub-scan directions.
[0116] FIG. 9 shows examples of the MKON[7:0] 443 and MKOFF[7:0]
444 as multilevel signals of tracking pattern dots generated by the
tracking pattern generator 410.
[0117] In FIG. 9, if MKON[7:0] is FCh, 11111100B is converted into
serial data and output as MKON to the OR gate 414 (not shown). That
is, a 6/8 dot of one dot is forcedly printed. If MKOFF[7:0] is F8h,
11111000B is converted into serial data and output as MKOFF to the
AND gate 415 (not shown).
[0118] That is, a 5/8 dot of one dot is forcedly printed. If the
signal is 00h, the VDO signal 6 is directly output to a laser
driver. Also, this tracking pattern is printed every four
lines.
[0119] FIG. 10 is a view showing an image printed by mixing the
tracking pattern shown in FIG. 9 into the image signal VDO 6. In
FIG. 10, the VDO data 6 output from the printer controller is in
phase with the tracking pattern. That is, the frequency of the
control clock of the image processor 401 in the printer controller
3 perfectly matches the frequency of the control clock CCLK of the
tracking pattern generator 410. Assume that the VDO signal is
printing an even intermediate density.
[0120] FIG. 11 is a view when the output VDO data 6 from the
printer controller is not in synchronism with the tracking pattern.
That is, the frequency of the control clock of the image processor
401 in the printer controller does not perfectly match the
frequency of the control clock CCLK of the tracking pattern
generator 410.
[0121] This can happen because, as described earlier, both of the
printer controller 3 and the tracking pattern generator 410 of the
engine have a circuit for generating a clock signal synchronized
with the horizontal sync signal BD. Referring to FIG. 11, the
frequency of the control clock CCLK of the tracking pattern
generator 410 is 1/1.5 the frequency of the control clock of the
image processor 401.
[0122] As a modification of this embodiment, the frequency of the
quartz oscillator of the engine can be made different from the
image transfer rate of the controller. If a quartz oscillator
having a frequency several times as high as the image transfer rate
is used, the frequency multiplier 434 is unnecessary. Also, a
frequency lower than the image transfer rate can be multiplied by
the frequency multiplier 434 to obtain a clock having a desired
frequency.
[0123] FIG. 16 is an internal block diagram of the signal processor
402 in this case. The difference from the above case is that
instead of a quartz oscillator being included in the engine, an
image transfer clock signal VCLK 449 of the printer controller is
output from the engine and used in the tracking pattern
generator.
[0124] Analogously, FIG. 17 is an internal block diagram of the
tracking pattern generator 410 in a case like this. This circuit
obviates the need for a frequency divider for dividing the
frequency of a block in synchronism with the BD signal, which is
necessary in the above example.
[0125] A tracking pattern mixed in this example is in synchronism
with the VDO signal 6 as an image signal. So, the printed state is
as shown in FIG. 10.
[0126] Although a preferred embodiment of the present invention has
been described above, the present invention naturally includes
arbitrary combinations of some of the abovementioned
arrangements.
[0127] Also, both the forced ON dot and the forced OFF dot are
smaller than one dot in the above embodiment. However, these dots
can be larger than one dot, e.g., can be 11/8 dots or 5/4 dots.
[0128] Furthermore, PCLK output from the frequency divider 435 can
be entirely different from the image transfer rate. If this is the
case, the size and interval of tracking pattern dots are not
integral multiples of an image dot. This is established because not
absolute dimensions but a printing interval ratio is used to
extract codes from the positions of tracking pattern dots. The use
of a clock signal of a quartz oscillator by another circuit makes
any additional quartz oscillator unnecessary. This can realize an
inexpensive arrangement.
[0129] In the above embodiment, after the frequency of the output
clock from the quartz oscillator 413 is raised by the frequency
multiplier 434, the clock is synchronized with the horizontal sync
signal to set the phase jitter of a tracking pattern to be several
times as small as one dot. However, the phase jitter can also be
set to be equal to one dot without using the frequency multiplier
434. Since the frequency multiplier and the like are unnecessary,
an inexpensive arrangement can be realized.
[0130] Furthermore, although a P-S converter is used to divide one
tracking dot into eight portions, PWM (Pulse Width Modulation) is
also usable.
[0131] In FIG. 6, the counters 426 and 427, the coincidence
circuits 428 and 429, the selectors 430 and 431, the P-S circuits
432 and 433, the frequency multiplier 434, the frequency divider
435, the OR gate 415 (not shown), and the AND gate 416 (not shown)
can be contained in an ASIC. Additionally, although the OR gate and
AND gate are used to mix tracking dots in the VDO signal 6, a
selector circuit can also be used.
[0132] As many apparently widely different embodiments of the
present invention can be made without departing from the spirit and
scope thereof, it is to be understood that the invention is not
limited to the specific embodiments thereof except as defined in
the appended claims.
* * * * *