U.S. patent application number 09/938509 was filed with the patent office on 2003-04-03 for method and apparatus for controlling a light signal in electrophotographic recording apparatus.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Kim, Yong-Geun.
Application Number | 20030063184 09/938509 |
Document ID | / |
Family ID | 19356327 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030063184 |
Kind Code |
A1 |
Kim, Yong-Geun |
April 3, 2003 |
Method and apparatus for controlling a light signal in
electrophotographic recording apparatus
Abstract
An optical signal control process and circuit providing an
improved electronic photography method reproduction apparatus. The
reproduction apparatus has a data transmitting unit converting data
to be printed to a series of video data in accordance with a first
clock signal and transmitting the converted video data in response
to a horizontal synchronization signal applied with a predetermined
time interval, and a printing control unit for controlling a
mechanism used to print the video data by sending electrical
signals, providing beam data used to switch the light generation of
a light source element controlled by chopped chopping video data
applied to the light source element, and generating the horizontal
synchronization signal on the basis of a beam detection signal
produced by the light source element. A chopping unit is connected
between the data transmitting unit and the printing control unit,
for chopping the converted video data output from the data
transmitting means in response to a second clock signal and for
providing the chopped data as the chopping video data. Accordingly,
the chopped video data is transmitted as beam data by the printing
control unit and is then used to control the amount of light
exposed on the photosensitive drum. The amount of the light is
controlled optimally by the variable selection of the frequency of
the second clock signal.
Inventors: |
Kim, Yong-Geun; (Suwon-city,
KR) |
Correspondence
Address: |
Robert E. Bushnell, Esq.
Suite 300
1522 "K" Street, N.W.
Washington
DC
20005
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
|
Family ID: |
19356327 |
Appl. No.: |
09/938509 |
Filed: |
April 18, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09938509 |
Apr 18, 2002 |
|
|
|
08250770 |
May 27, 1994 |
|
|
|
Current U.S.
Class: |
347/250 ;
347/235 |
Current CPC
Class: |
G06K 2215/0077 20130101;
G06K 15/1223 20130101; G06K 15/1204 20130101; G06K 2215/0091
20130101 |
Class at
Publication: |
347/250 ;
347/235 |
International
Class: |
B41J 002/435; B41J
002/47 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 1993 |
KR |
9481/1993 |
Claims
What is claimed is:
1. An electrophotographic developing type reproduction apparatus,
comprising: data transmitting means for generating converted data
by converting input data to be printed into video data in
accordance with a first clock signal, and for transmitting the
converted data in response to a horizontal synchronization signal
exhibiting a predetermined time interval; chopping means for
providing chopped data by dividing the converted data from said
data transmitting means in accordance with a second clock signal;
and printing control means for providing beam data in response to
said chopped data, for controlling printing of the video data by
generating electrical signals to control generation of a light beam
by a light source element, and for generating said horizontal
synchronization signal in correspondence with a beam detection
signal derived from the light beam by the light source element.
2. The electrophotographic developing type reproduction apparatus
of claim 1, further comprised of the second clock signal having a
frequency greater than the first clock signal.
3. The electrophotographic developing type reproduction apparatus
of claim 1, further comprised of a frequency of the second clock
signal being an integer multiple of a frequency of the first clock
signal.
4. The electrophotographic developing type reproduction apparatus
of in claim 1, further comprised of said chopping means comprising
an AND gate having a first input port coupled to receive said
converted data and a second input port coupled to received said
second clock signal.
5. The electrophotographic developing type reproduction apparatus
of claim 1, further comprised of mode selecting means enabling a
user to externally change a characteristic of said second clock
signal.
6. The electrophotographic developing type reproduction apparatus
of claim 1, further comprised of a semiconductor laser device
serving as the source element.
7. The electrophotographic developing type reproduction apparatus
of claim 1, comprised of: first means for generating a local clock
signal; and second means for generating said second clock signal by
dividing said local clock signal in dependence upon a dividing
ratio component of said input data.
8. The electrophotographic developing type reproduction apparatus
of claim 1, comprised of: means for generating a local clock
signal; first means for generating said first clock signal by
dividing said local clock signal; and second means for generating
said second clock signal by dividing said local clock signal in
dependence upon a dividing ratio component of said input data.
9. The electrophotographic developing type reproduction apparatus
of claim 1, comprised of said chopping means intermittently
transmitting said serial video data during pulses of said second
clock signal.
10. The electrophotographic developing type reproduction apparatus
of claim 1, comprised of: a component of said input data specifying
a dividing ratio; and means for setting a frequency exhibited by
said second clock signal in dependence upon said component.
11. The electrophotographic developing type reproduction apparatus
of claim 1, comprising: a component of said input data specifying a
dividing ratio; means for setting a frequency exhibited by said
second clock signal in dependence upon said component; and said
chopping means dividing said converted data into a series of pulses
exhibiting a pulse frequency corresponding to said frequency
exhibited by said second clock signal.
12. A method for controlling a light signal in an
electrophotographic developing type reproduction apparatus, said
method comprising the steps of: generating converted data by
converting input data to be printed into video data, in accordance
with a first clock signal, and for transmitting the converted video
data in response to a horizontal synchronization signal exhibiting
a predetermined time interval; generating chopped data by dividing
the converted data in dependence upon a second clock signal;
supplying beam data for controlling generation of said light signal
by a light source element in response to said chopped data; and
generating said horizontal synchronization signal in dependence
upon a beam detection signal obtained from said light signal.
13. The method of claim 12, comprising the second clock signal
having a frequency higher than the first clock signal.
14. The method of claim 12, comprising a frequency of the second
clock signal being an integer multiple of a frequency of the first
clock signal.
15. The method of claim 12, comprised of generating the chopped
data by applying the converted data to a first input port of an AND
gate data and applying the second clock signal to a second input
port of the AND gate.
16. The method of claim 15, comprised of changing a characteristic
of the second clock signal in response to a selection made by a
user of the reproduction apparatus.
18. An apparatus for printing video data, comprising: data bus
means for providing input video data and for providing dividing
ratio data; clock signal generating means for generating a first
clock signal and for generating a second clock signal, said second
clock signal exhibiting a characteristic depending upon said
dividing ratio data; data transmitting means for converting said
input video data into serial video data in response to said first
clock signal, and for transmitting said serial video data in
response to a horizontal synchronization signal; logic means for
providing chopped video data in dependance upon said serial video
data and said second clock signal; printing control means for
generating beam data in response to said chopped video data; and
beam scanning means for providing a laser beam for defining images
corresponding to said beam data and for generating a beam detection
signal derived from scanning of said laser beam; said printing
control means generating said horizontal synchronizing signal in
dependence upon said beam detection signal.
19. The apparatus of claim 18, comprised of generating said first
clock signal with a frequency less than said second clock
signal.
20. The apparatus of claim 18, comprised of generating said first
clock signal with a frequency equal to said second clock
signal.
21. The apparatus of claim 18, comprised of said clock signal
generating means comprising means for changing said characteristic
of said second clock signal in correspondence with changes in said
dividing ratio data.
22. The apparatus of claim 18, comprised of said clock signal
generating means comprising: first means for generating a local
clock signal; and second means for generating said second clock
signal by dividing a frequency of said local clock signal in
dependence upon said dividing ratio data.
23. The apparatus of claim 18, comprised of said clock signal
generating means comprising: means for generating a local clock
signal exhibiting a first plurality of pulses characterized by a
local frequency; first means for generating said first clock signal
by dividing pulses of said local clock signal to provide a second
plurality of pulses characterized by a second frequency; and second
means for generating said second clock signal by dividing said
pulses of said said local clock signal in dependence upon said
dividing ratio data, to provide a third plurality of pulses
characterized by a third frequency established in dependence upon
said dividing ratio data.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application makes reference to, incorporates herein and
claims all benefits accruing under 35 U.S.C. .sctn.119 from our
application earlier filed in the Korean Industrial Property Office
on May 31, 1993 of our application entitled Method and Apparatus
for Controlling a Light Signal in Electrophotographic Developing
Type Printer, which application was duly assigned Ser. No.
9481/1993.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an electrophotographic
recording, and more particularly to an apparatus and method for
selectively controlling the amount of light exposed onto a
photosensitive drum without being controlled by a developing unit
when the apparatus prints printing information.
[0003] Generally, the art of printing using an electrophotographic
developing technique is well known as xerography. The apparatus
whether a laser beam printer, facsimile or photocopier, as its
basic principle, utilizes an adhesive force of static electricity
and an optically conductive semi-conductor with differences in
electricity conducting rates controlled according to exposure to
the light. Among these printers, the laser beam printer is a
printing device that uses a laser diode as its light source instead
of a special fluorescent lamp or a mercury lamp, and prints the
printing data provided as, for example, video data for a source
such as a computer, etc., on a printable medium such as individual
sheets of printing paper, instead of merely reproducing images
reflected from a document. As described above, recently developed
laser printers, in comparison with the conventional impact printers
that print letters by using hammers striking a platen, have a
higher printing speed, lower noise level, and form finer shapes of
printed letters. Also, they are very popular and widely used
because they are easily linked with computers to receive signals
conveying information to be printed such as a text signal of a
video signal.
[0004] The printing process of such laser beam printers includes a
developing stage where a toner used as a developing material is
attracted to a latent image formed on the photosensitive drum by
exposure of the photosensitive drum to light, a transferring stage
where the toner attracted to the drum is transferred to a printable
medium such as a sheet of paper fed by a feed roller, and a fusing
stage where the toner that had been transferred onto the printable
medium is fused is then fused onto the printable medium. These
stages of the process also are generally known in the current
art.
[0005] In the printing process mentioned above, it is the
developing stage that is closely related to a consumption of the
toner, and that directly affects the printing quality. Moreover, in
order for a conventional printer to control the printing density,
the bias voltage of a developer is changed to adjust the amount of
the toner developed. See, by way of further explanation, the IMAGE
FORMING APPARATUS COMPRISING MEANS FOR SETTING A PROPER BUS VOLTAGE
OF LASER EMITTING MEANS AND METHOD THEREFORE by S. Ogino, et al,
U.S. Pat. No. 5,061,949. In one contemporary approach to control
printing density, a print control unit controls printing of video
data with electrical signals and supplies beam data, used during
scanning of an image onto the circumstantial exterior surface of
the drum with a beam of light emitted by the light source element
video data signal. This may be seen in for example, the PICTURE
REPRODUCING APPARATUS of M. Yamamoto, et al., U.S. Pat. No.
3,894,182. Also, the print control unit receives beam detection
signals generated by the light source element and supplies a
horizontal synchronization signal and a bias voltage control signal
to a bias voltage generator that provides the bias voltage to the
developer.
[0006] The amount of toner attached on the drum during the
developing stage is determined by the bias voltage and the
intensity of the bias voltage is controlled by an adjusting
terminal known as a printing density selecting switch, installed on
the control panel in an external stage of the printer. A printer
using this approach to control of printing density is very
inconvenient to use however, because the printing density has to be
adjusted for each use. Moreover, this approach requires intense,
uninterrupted concentration from the user. Also, it is very hard
for unskilled users to accurately and repeatedly adjust the
adjustment terminal. Frequently, the durability of the
photosensitive drum in such laser printer is shortened and the
toner consumption is increased when the user fails to adjust the
bias voltage properly.
SUMMARY OF THE INVENTION
[0007] Accordingly, it is an object of the present invention to
provide an improved printing process and apparatus.
[0008] It is another object to provide a method and apparatus for
selectively controlling the amount of light illuminating the
photosensitive drum without controlling the developing unit when an
image is printed with a laser beam being used as a light
signal.
[0009] It is a further object to provide a laser reproduction
process and printer offering an optimum printing quality by
automatically, internally selecting the amount of light
illuminating the photosensitive drum.
[0010] It is a still further object to provide a laser printing
process and printer having a simple circuit externally adjusting
the sharpness of characters, symbols, and graphs to be printed
during the process.
[0011] It is a yet further object to provide a process and control
circuit for reliably controlling toner consumption in an
electrophotographic developer.
[0012] It is a still yet further object to enable a user of an
electrophotographic developer type printer to transmit to a printer
data controlling print quality while transmitting data defining the
images to be printed by the printer.
[0013] These and other objects mentioned above, may be achieved
according to the principles of the present invention with a process
and an apparatus using a data transmitting unit converting video
data in response to a horizontal synchronization signal applied
with a predetermined time interval by converting data to be printed
into a series of lines of serial video data in accordance with a
first clock signal, and a printing control unit regulating a
mechanism used to print the video data by generating electrical
signals representing the video data, providing beam data used to
switch the generation of light provided by a light source element
that had been obtained from chopped video data applied to the light
source element, and generating a horizontal synchronization signal
by processing a beam detection signal produced by the light source
element. A chopping unit connected between the data transmitting
unit and the printing control unit chops the converted video data
received from the data transmitting unit in response to a second
clock signal, and provides the chopped video data.
[0014] According to the present invention, printing may be
performed by converting data to be printed into a series of lines
of video data in accordance with a first clock signal and
transmitting the converted video data in response to a horizontal
synchronization signal exhibiting a predetermined time interval.
Chopped video data is generated by chopping the converted video
data in response to a second clock signal; and beam data obtained
from the chopped video data is supplied for controlling the light
generation of a light source element. The horizontal
synchronization signal is operated by processing a beam detection
signal resulting from the beam of light produced by the light
source element.
[0015] In the practice of the present invention, the frequency of
the first clock signal is set to be either equal to or lower than
the frequency of the second clock signal. If the frequency ratio
between the first and second clock signals is an integer multiple,
a single divider stage may be used; the first and second clock
signals should then be generated from different output terminals of
the divider stage.
[0016] According to the configuration and method of the present
invention, the chopped video data is generated by the printing
control unit as beam data, and is then used for controlling the
amount of light illuminating the photosensitive drum. The amount of
the light is optimally controlled by selecting the second clock
signal. Therefore, the user can adjust the density of printed
images by designating or selecting the data defining the amount of
light exposed by means of software. By doing so, the sharpness of
the printed images can be easily adjusted without adjusting the
bias voltage of a developing unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] A more complete appreciation of this invention, and many of
the attendant advantages thereof, will be readily apparent as the
same becomes better understood by reference to the following
detailed description when considered in conjunction with the
accompanying drawings in which like reference symbols indicate the
same or similar components, wherein:
[0018] FIG. 1 is a block diagram used to provide an abstract
representation showing a simplification of a typical
electrophotographic developing type printing process.
[0019] FIGS. 2A to 2D are exemplary timing charts illustrating
waveforms to explain an operation of the process represented by
FIG. 1.
[0020] FIG. 3 is a block diagram illustrating an apparatus for
controlling the light signal in an embodiment constructed according
to the principles of the present invention.
[0021] FIGS. 4A to 4G are timing charts illustrating waveforms of
signals occurring at corresponding stages in the circuit shown in
FIG. 3.
[0022] FIG. 5 is a graph illustrating a comparison of voltage
potential on the photosensitive drum for an embodiment of the
present invention and for an exemplary embodiment of prior art.
DETAILED DESCRIPTION OF THE INVENTION
[0023] In contemporary printing processes described earlier herein,
the developing stage that is closely related to consumption of the
toner, and therefore directly affects the printing quality.
Moreover, in order for a conventional reproduction apparatus to
control the printing density, the bias voltage of the developer is
typically changed in contemporary printers in order to adjust the
amount of the toner consumed. Referring now to FIG. 1, a diagram
illustrating an exemplary conventional technique for accomplishing
printing control is shown in an abstract representation to
facilitate an understanding of the principles of the present
invention. As shown in FIG. 1, data transmitting unit 10 receives
printing data supplied from data output device 1 of a source such
as a computer having a RIP (Raster Image Processor), via a bus line
2. Also, transmitting unit 10 converts the print data to a series
of lines of video data in correspondence with a clock signal fed in
via a line 52 and then, outputs the converted video data via line
12 in response to a horizontal synchronization signal exhibiting a
predetermined time interval applied via a line 14. Data
transmitting unit 10 contains a shift register type of memory
element. A printing control unit 20 controls a mechanism required
for printing the video data with electrical signals and supplies
beam data, used to switch the light generation of a light source
element located in a beam scanning unit 30, to the light source
element through a line 22 by obtaining the beam data via a line 12
from the video data received. Also, print control unit 20 receives
beam detection signals generated by the light source element 6B for
processing via a line 24 and then, supplies the horizontal
synchronization signal to the line 14. In addition, the printing
control unit 20 supplies a bias voltage control signal via a line
72 to a bias voltage generator 70. Thus, the bias voltage generator
70 provides a bias voltage to the developer not illustrated.
[0024] The beam scanning unit 30 is switched over according the
beam data provided on the line 22 to generate the laser beam to be
scanned upon the photosensitive, uniformly changed circumferential
surface of the drum. Also, beam scanning unit 30, in response to
the beam generated, sends beam detection signals to a line 24. A
clock signal generator 40 supplies a basic clock signal of system
to a dividing unit 50 via a line 42. The dividing unit 50 divides
the basic clock signal into a certain ratio and then supplies the
divided clock signal to the data transmitting unit 10 via a line 52
as the clock signal.
[0025] The timing relationship of waves output from each stage
mentioned above is illustrated in FIGS. 2A to 2D. Referring to
FIGS. 2A to 2D, if an assumption that FIG. 2A is a waveform of the
line 42, FIG. 2B is a waveform of the line 52, and FIG. 2C is a
waveform of the line 12, is made, FIG. 2D is output from the line
22. As illustrated by the examples given here, one dot is printed
on an interval T1 in the waveform of FIG. 2C as black and another
dot is printed on an interval T2 as white (e.g., as by not applying
toner to the corresponding spot on the photosensitive drum). During
interval T3, two dots are printed as black (i.e., successive dots
of toner are fixed to the printed medium passing through the
reproduction apparatus).
[0026] Referring again to FIG. 1, the light source element in the
beam scanning unit 30 emits light according to the waveform of FIG.
2D that is fed in via the line 22 and the beam scanning unit 30
scans the emitted laser beam onto the photosensitive drum.
Therefore, the developing stage is implemented. Note that the
amount of toner attached on the drum during the developing stage is
determined by the bias voltage of the bias voltage generating unit
70 that generates the bias voltage in response to the bias voltage
control signal on the line 72. The generating unit 70 is has a
circuit element capable of outputting a high-voltage and an
adjusting terminal used for adjusting the voltage externally.
Where, the bias voltage control signal on the line 72 is a signal
to switch a generation of the bias voltage, substantially the
intensity of the bias voltage is controlled by the adjusting
terminal installed in external stage of the printer. The adjusting
terminal is well known as a printing density selecting switch on
the control panel. Thus, such control of the bias voltage in the
developing unit is generally known in the art. For example, where
the surface of the photosensitive drum has a voltage potential of
-600 volts on charging, and has a voltage potential of -50 volts on
exposing, the bias voltage adjusted as -500 volts provides a higher
printing density in comparison with the bias voltage adjusted as
-400 volts.
[0027] This reproduction apparatus is very inconvenient to use
because the printing density has to be adjusted for each use.
Furthermore, doing so requires a great concentration from the
users. Also, it is very hard for the unskilled users to adjust the
adjustment terminal. Frequently, the durability of the
photosensitive drum in such laser printer is shortened and the
toner consumption is increased when failing to adjust bias voltage
properly.
[0028] In the following paragraphs, a light signal controlling
apparatus constructed as preferred embodiments in accordance with
the principles of the present invention will be described. To
provide a more thorough understanding of the present invention, the
detailed description on these circuits is given. Those skilled in
the art however, will clearly recognize that the present invention
can be implemented without unnecessarily detailed descriptions.
Also, well known circuit characteristics and its functions are not
explained in detail so as not to obscure an embodiment of the
present invention. Further, the stages that are the same or similar
to those of the conventional techniques described previously will
be assigned with the same reference numerals.
[0029] Referring now to FIG. 3 where an illustration explaining the
preferred embodiments of the present invention is given, data
transmitting unit 10 receives the video data to be printed via data
bus line 2 and converts the data received into serial of video data
according to the first clock signal provided via a line 52 and, by
responding to the horizontal synchronization signal exhibiting a
predetermined time interval that is fed in on line 14, transmits
the converted video data through line 12. A printing control unit
20 controls the mechanism required for printing the video data by
means of electrical signals and provides the beam data used to
switch the light generation of light source element 68 located in
the beam scanning unit 30 to the light source element via a line 32
to emit light beam 90. The beam data is obtained from the chopped
video data fed in via a line 102. Also the printing control unit 20
receives and processes the beam detection signals generated by the
light source element through a line 34, and provides via line 14
the horizontal synchronization signal generated by processing the
beam detection signals. Note that the printing control unit 20 is
generally called an engine control unit. Also, for the light source
element, a semiconductor laser capable of producing 0.6 milli-Watts
is used.
[0030] A chopping unit 100 is preferably constructed using an logic
stage such as an AND gate having one input port coupled to receive
serial video data via lead 12 from data transmitting unit 10 and a
second input port coupled to receive the second clock signal via
lead 62; the output port of the logic stage such as an AND gate
would be coupled to printing control unit 20. During operation of
the chopping unit 100, the data generated by chopping the converted
video data applied through lead 12 in response to the second clock
signal fed in via a lead 62, is provided to lead 102 as the chopped
video data. Here, the term "chopped" means that the video data is
divided according to the second clock signal. This is carried out
by gating of the AND gate with the second clock signal.
[0031] A clock signal generator 40 generates local, or basic, clock
signals and then, applies these clock signals to a lead 42. A first
divider 50 divides the basic clock signals with a certain dividing
ratio and, then provides the first clock signal to lead 52. A
second divider 60 divides the basic clock signal according to
dividing ratio data component of the video data received via lead
2, separated from the video data through output port 5 and fed in
through a line 3 and then, provides the second clock signal on a
line 62, where, the second divider 60 may have a PWM function. An
output port 5 is connected between the data bus line 2 and the line
3, and stores the dividing ratio data. Here, line 2 is normally
made up of sixteen bits or thirty-two bits, and line 3, eight bits.
That is, the data output device 1 such as a computer connected
through the line 2, provides designated dividing ratio data as a
component of the video data signal transmitted via lead 2, in
accordance with the selection by the user and the printing
data.
[0032] After assuming that the dividing ratio data is designated
via the data output device 1, is referring to FIGS. 4A to 4G with
an illustration describing the chopping operation carried out by
the chopping unit 100, a waveform of FIG. 4E is output on the
output line 102 of the chopping unit 100 if an assumption that
waveforms of FIGS. 4A, 4B, 4C, and 4D are output respectively on
the line 42, the line 52, the line 12, and the line 62 in FIG. 3 is
given. Intervals C1, C2, and C3 in the waveform of FIG. 4C are the
same as those of T1, T2, and T3 in FIG. 2. Note that the number of
high pulses as shown in the intervals E1, E3 in the waveform of
FIG. 4E will be larger than the number of pulses in the waveform of
FIG. 4C. Also, the waveform of FIG. 4E is changed to the waveform
of FIG. 4G in case the waveform of FIG. 4D changes to a waveform of
FIG. 4F. That is, if the frequency of the second clock signal
provided by second divider 60 to line 62 is changed by a user
applying video data via lead 2 containing a dividing ratio
component that is greater by a factor of two than the dividing
ratio that was applied to second divider 60 to produce the second
clock signal with the pulse frequency shown in FIG. 4D, the
frequency of the second clock signal will be correspondingly
changed to provide the waveform illustrated in FIG. 4F exhibiting a
pulse frequency twice that of the second clock signal waveform
illustrated in FIG. 4D; concomitantly, the frequency of the chopped
video data transmitted by chopping unit 102 via line 102 also
changes by a factor of two, as is illustrated by with waveform of
FIG. 4G.
[0033] Accordingly, the printing control unit 20 inputs the chopped
video data through the line 102 and then, printing control unit 20
outputs the beam data for switching the light source element
through line 32. Here, the beam data is almost the same as that on
line 102. In response is to this data, light source element 68 in
beam scanning unit 30 lights up to generate laser beam 90. Laser
beam 90 generated by light source element 68 has a wavelength of
650 to 800 nM, generally.
[0034] Also, the faster the second clock signal operates the
greater the number of chopping operations occur. As a result, the
effective amount of light illuminating the photosensitive drum
decreases. On the contrary, when the user designates a smaller
dividing ratio data by using softwear (e.g., abstractly represented
by mode selector 66) to specify the dividing ratio component of the
video data transmitted via data bus 2 in order to lower the
frequency of the second clock signal (i.e., to set the second
frequency to a lower value), the chopped video data transmitted via
line 102 has a lower pulse frequency and consequently, the amount
of light emitted by source 68 increases. Accordingly, the amount of
light to which each point on the photosensitive surface of the drum
is exposed is increased and thus, the density of the toner is
increased. In this manner, printing quality, that is, the sharpness
of printed images, is determined by changing the amount of toner
attached during the developing process according to the change in
the amount of light emitted by light source 68 of beam scanning
unit 30, and thus, the amount of light illuminating the exterior
circumferential surface of the photosensitive drum.
[0035] It is widely known that the amount of light illuminating the
photosensitive drum is proportional to the light output of laser
source 68 and that an exposure time per one dot of laser beam, and
is inversely proportional to the optical area per one dot of the
laser beam. Here, referring to FIG. 5, the pulse G2 represents the
chopping effect in accordance with the present invention. In pulse
G2, the voltage potential on the photosensitive drum is less than
the voltage potential across the same photosensitive drum with the
prior art of pulse G1 by about 50 volts. In FIG. 5, the intervals
EA and NEA represents the exposed area and the unexposed area on
the photosensitive drum, respectively. Therefore, the amount of
toner attracted to the drum decreases since the voltage potential
is lowered by chopping unit 100.
[0036] So far, the present invention has been explained with the
drawings attached and examples given. It should be clear to those
familiar with this field that several changes and modifications on
the invention are possible if they are implemented within the scope
of the techniques utilized in the present invention.
* * * * *