Printer

A color image recording apparatus operates in a color print mode and in a monochrome printing mode. A set of color print heads are driven in accordance with corresponding color image data. A monochrome print head is driven in accordance with black image data. A controller transmits in parallel or in serial the color image data and the black image data to the corresponding print heads in a color printing mode. The controller transmits the black image data faster in the monochrome printing mode than in the color printing mode, thereby increasing printing speed. The controller may include signal processing circuits such as compressing circuits and expanding circuit for the respective color image data and black image data. In the monochrome printing mode, the controller divides the black image data into a plurality of segments and supplies the segments in parallel to the signal processing circuits. The signal processing circuits process the segments and supply the processed data to the monochrome print head in a predetermined sequence, thereby increasing printing speed.

BACKGROUND OF THE INVENTION 
The present invention relates to a printer which is capable of performing a 
multi-color printing and a monochrome printing. The present invention also 
relate to a color image recording apparatus where image forming section 
are aligned in tandem and images of different colors are recorded in 
registration with one another on a print medium to form a color image. 
Various documents are produced using computers, word processors, and other 
business machines and the documents are printed by printers connected 
thereto. Such printers include electrophotographic printer, thermal 
printer, wire-dot printer, and ink jet printer. These printers receive 
print data from their host apparatuses, and store the print data therein, 
reform the print data, and provide the reformed print data at 
predetermined timings to print engines. With color printers, the print 
data is edited according to color such as yellow, magenta, cyan, and 
black. 
Color printers are often required to print documents whose print data is 
mostly characters in the form of a black-and-white image. Thus, many color 
image-recording apparatuses have a black-and-white printing function as 
well as a color printing function. 
The aforementioned conventional art suffers from the following drawbacks. 
Print data includes four items of data for four colors and the respective 
items of data are subjected to compression and expansion before being fed 
to print engines. For this purpose, color printers are capable of 
processing about four times as large an amount of data as monochrome 
printers. 
Thus, when the conventional color printer prints black-and-white images, 
only a part of its high data-processing capability is used. This is not 
economical. One solution to increased printing speed in the monochrome 
printing may be to transferring the data at a speed four times as high as 
in the color printing. However, increasing data transfer speed by a factor 
of four needs a higher system clock frequency. Higher clock frequencies 
impose a noise problem. 
A conventional color image recording apparatus has image forming sections 
for yellow, magenta, cyan, and black images. A print medium is fed one 
page at a time from a paper cassette. A carrier belt attracts the print 
medium with the aid of Coulomb force and transports the print medium from 
section to section. Each image forming section has a corresponding 
recording head with recording elements aligned in line in a traverse 
direction perpendicular to an advance direction in which the print medium 
is transported. As the print medium passes the image forming sections, the 
print heads record images of corresponding colors on the print medium on a 
line-by-line basis. 
The image forming section for black image is usually located most 
downstream of the transport path of the print medium. In the monochrome 
printing, the print medium is transported through the yellow, magenta, 
cyan image forming sections to the black image forming section. 
Accordingly, the print medium is transported in the monochrome printing at 
the same speed as in the color printing even though only the black image 
forming section operates to print images. This is inefficient. 
SUMMARY OF THE INVENTION 
The present invention was made in view of the aforementioned drawbacks of 
the prior art image forming apparatus. 
A color image recording apparatus includes a set of color print heads, 
monochrome print head, and controller. The set of color print heads are 
driven in accordance with corresponding color image data. The monochrome 
print head is driven in accordance with black image data. The controller 
transmits the color image data to corresponding color print heads and the 
black image data to the monochrome print head. The controller transmits in 
parallel or in serial the color image data and the black image data to the 
corresponding print heads in a color printing mode. The controller 
transmits the color image data and black image data at a first transfer 
speed in the color printing mode and the black image data at a second 
transfer speed in the monochrome printing mode. 
The controller may include signal processing circuits such as compressing 
circuits and expanding circuit that processes the color image data and 
black image data before transmitting the color image data and black image 
data to the corresponding color print heads and the monochrome print head. 
In a color printing mode, the signal processing circuits process the color 
image data and black image data and then transmit processed color image 
data and black image data to the corresponding print heads. In a 
monochrome printing mode, the controller divides the black image data into 
a plurality of segments and supplies the segments in parallel to the 
signal processing circuits. The signal processing circuits process the 
segments and supply the processed data to the monochrome print head in a 
predetermined sequence. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
The preferred embodiments of the invention will be described with reference 
to the accompanying drawings. 
First Embodiment 
&lt;General Construction of Recording Apparatus&gt; 
FIG. 1 illustrates a color image recording apparatus 1 according to the 
present invention. 
FIG. 2 is a perspective view of a color image forming section of FIG. 1. 
Referring to FIG. 1, there are provided two printing mechanisms P1 and P2 
in the form of an electrophotographic LED printing mechanism. The printing 
mechanism P1 and P2 are aligned from a medium insertion side to a medium 
discharging side. The first printing mechanism P1 is for yellow, magenta, 
and cyan images and the second printing mechanism P2 is for black images. 
The first printing mechanism P1 includes a color image forming unit A, 
which is constructed of image forming sections 2Y, 2M, and 2C, 
photoconductive drum 6Y, 6M, and 6C, charging rollers 7Y, 7M, and 7C, LED 
heads 3Y, 3M, and 3C, and developing sections 8Y, 8M, and 8C. These 
structural elements are supported on a frame 13. The photoconductive drums 
6Y, 6M, and 6C rotate about their rotational shafts 5Y, 5M, and 5C. The 
charging rollers 7Y, 7M, and 7C rotate in contact with the corresponding 
photoconductive drums and charges the photoconductive drums. The LED heads 
illuminate the corresponding photoconductive drums to form electrostatic 
latent images in accordance with the image data. The developing sections 
8Y, 8M, and 8C develop the electrostatic latent images into toner images, 
which in turn are transferred to a print medium. 
The developing sections 8Y, 8M, and 8C include developing rollers 9Y, 9M, 
and 9C, developing blades 10Y, 10M, and 10C, sponge rollers 11Y, 11M, and 
11C, and toner tanks 12Y, 12M, and 12C. 
The second printing mechanism P2 has a black image forming section 2K. The 
black image forming section 2K includes a photoconductive drum 6K, 
charging roller 7K, LED head 3K, developing section 8K, and transfer 
roller 4K. The developing section 8K includes a developing roller 9K, 
developing blade 10K, sponge roller 11K, and toner tank 12K. The 
structural elements are supported on a frame 14 and operate the same way 
as those in the first printing mechanism P1. 
The image forming sections 2Y, 2M, 2C, and 2K are of the same construction 
and therefore the image forming section 2Y will be described by way of 
example. 
Non-magnetic, one component toner supplied from the toner tank 12Y is 
directed via the sponge roller 11Y to the developing blade 10Y, which 
forms a thin layer of toner to the developing roller 9Y formed of a 
semiconductive rubber material. The toner is then brought into contact 
with the surface of the photoconductive drum 6Y as the photoconductive 
drum and the developing roller 9Y rotate. The toner undergoes friction 
between the developing roller 9Y and developing blade 10Y so that the 
toner is triboelectrically charged. In the present invention, the tone is 
negatively charged. The sponge roller 11Y supplies an appropriate amount 
of toner to the developing blade 10Y. When the toner has been exhausted, 
the toner tank 12Y is replaced for new, unused toner. 
The LED head 3Y includes a selfoc lens array 16Y and a circuit board 15Y on 
which an LED array and drive ICs for driving the LED array are mounted. 
The LED array are driven in accordance with the image data received 
through a later described interface, thereby illuminating the negatively 
charged surface of the photoconductive drum 6Y to form an electrostatic 
latent image. The developing roller 9Y applies toner to the electrostatic 
latent image to from a toner image. The LED head 3Y is urged downwardly by 
a spring 17Y in FIG. 1. Movably mounted between the photoconductive drum 
6Y and transfer roller 4Y is a later described carrier belt 20. 
The developing unit 8Y, 8M, and 8C hold yellow, magenta, and cyan toners 
therein. The developing unit 8K holds black toner therein. The color image 
signal is separated into yellow, magenta, cyan, and black image signals, 
which are received by LED heads 3Y, 3M, 3C, and 3K, respectively. 
Referring to FIGS. 1-2, there are two cam shafts 21a and 21b, rotatably 
supported on the frame 13 of the color image-forming unit A. The cam 
shafts 21a and 21b have eccentric cams 32 attached to opposite 
longitudinal ends thereof. The frame 13 is formed with cutouts 13a at four 
lower ends thereof in which the cam shafts 21a and 21b are rotatably 
received. 
The frame 13 is urged downward by the LED heads 3Y, 3M, and 3C, which are 
urged by springs 17Y, 17M, and 17C, respectively. When the cam shafts 21a 
and 21b are rotated, the eccentric cams 22 abut and push the frame 13 
upward in a direction shown by arrow B, causing the frame 13 to move 
upward. The cam shaft 21a has a gear 23 firmly attached to one end 
thereof. The gear 23 is in mesh with a motor gear 24, which in turn is 
securely connected to the rotational shaft of a cam motor 25. The cam 
shaft 21b is coupled to the cam shaft 21a through gears and belts, not 
shown, so that they rotate through the same angle in the same direction. 
The cam shaft 21a has a disc 26 attached to one end thereof. The disc 26 
is formed with a slit 26a therein which is detected by a photosensor 27 as 
the cam shaft 21a rotates, thereby detecting the rotational position of 
the eccentric cam 22. 
Referring to FIG. 2, the frame 13 is formed with windows 13c and guide pin 
holes 13d and 13e. The corresponding LED heads 3Y, 3M, and 3C are received 
in the windows 13c and positioned by the pin holes 13d and 13e with 
respect to corresponding photoconductive drums 6Y, 6M, and 6C. 
Referring to FIG. 1, the carrier belt 20 is formed of a film of a high 
resistance semiconductive plastics material. The belt 20 is of an endless 
type and is mounted about a drive roller 30, driven roller 31, and tension 
roller 32. The resistance of the carrier belt 20 is in a range such that 
the carrier belt 20 sufficiently attracts the print medium S by Coulomb 
force and the residual static electricity stored on the carrier belt 20 is 
neutralized after the print medium S has been released from the carrier 
belt 20. The drive roller 30 is coupled to a motor, not shown, which 
drives the drive roller 30 in rotation in a direction shown by arrow C. 
The tension roller 32 is urged by a spring, not shown, in a direction 
shown by arrow D so as to apply a proper tension to the carrier belt 20. 
The upper half of the carrier belt 20 runs in contact with the 
photoconductive drums 6Y, 6M, 6C, and 6K and transfer rollers 4Y, 4M, 4C, 
and 4K of the printing mechanism P1 and P2. 
The carrier belt 20 is sandwiched between the drive roller 30 and a 
cleaning blade 33. The cleaning blade 33 is formed of a flexible rubber 
material or plastics. The cleaning blade 33 is positioned with a tip 
thereof pressed against the carrier belt 20. When the carrier belt 20 
runs, the cleaning blade 33 scrapes the residual toner deposited on the 
carrier belt 20 into a toner tank 34. 
A paper feeding mechanism 40 is disposed on the lower right-hand side of 
the color image recording apparatus 1. The paper feeding mechanism 40 
includes a paper cassette, paper feeding mechanism, and registry rollers 
45. The paper cassette includes a recording medium tray 41, push-up plate 
42, and push-up means. The paper feeding mechanism includes a separator 
44, spring 45, and paper pick-up roller 46. The spring 45 urges the paper 
separator 44 against the paper pick-up roller 46 so that the paper 
separator 44 is in pressure contact with the paper pick-up roller 46. 
The spring 45 pushes up the recording medium S in the recording medium tray 
41 so that the leading end of recording medium S is in pressure contact 
with the paper pick-up roller 46. When the paper pick-up roller 46 rotates 
in a direction shown by arrow F, the separator 44 separates the top page 
of the recording medium S from the rest so as to feed the recording medium 
S one page at a time from the recording medium tray 41. Each page is 
guided between guides and 49 and pulled in between the transport roller 50 
and a first registry roller 51 and then between the transport roller 50 
and a second registry roller 52. The transport roller 50 and second 
registry roller 52 feed the recording medium S to the attraction roller 
54. 
The attraction roller 54 is urged against the driven roller 31 with the 
carrier belt 20 sandwiched therebetween so as to charge and attract the 
recording medium S delivered from the paper feeding mechanism. For this 
purpose, the attraction roller 47 is made of a semiconductive rubber 
material having a high electrical resistance. Provided between the first 
printing mechanism P1 and the attraction roller 54 is a photosensor 55 
that detects the leading end of the recording medium S. 
The recording apparatus also has a manual insertion tray 56 and a guide 57 
through which the user manually feeds the recording medium S. The manually 
inserted recording medium S is detected by a sensor 58 and is pulled in 
between the second registry roller 52 and the transport roller 50. 
A neutralizing unit 60 is disposed over the carrier belt 20 near the drive 
roller 30. The neutralizing unit neutralizes the charges on the recording 
medium S transported by the carrier belt 20 after transferring a toner 
image, so that the recording medium 21 is separated smoothly from the 
carrier belt 20. A photosensor 61 is disposed downstream of the 
neutralizing unit 60 with respect to the transport path of the recording 
medium 21 and detects the trailing end of the recording medium 21. 
A guide 62 and a fixing unit 63 are disposed downstream of the neutralizing 
unit 60. The fixing unit 63 fixes the toner image of the respective 
colors, which have been transferred onto the recording medium S. The 
fixing unit 48 includes a heat roller 64 for heating the toners on the 
recording medium 21, and a pressure roller 65 for pressing the recording 
medium S against the heat roller 64. A paper exit 66 is located downstream 
of the fixing unit 63 and a paper stacker 67 is disposed outside of the 
paper exit 66. The printed recording medium S is discharged to the paper 
stacker 67 through the paper exit 66. 
FIG. 3 is a block diagram illustrating a controller of the first 
embodiment. References Y, M, C, and K represents yellow, magenta, cyan, 
and black image forming sections. The controller 81 takes the form of, for 
example, a microprocessor, and controls the overall operation of the color 
image recording apparatus 1. The controller 81 is connected to an SP bias 
power supply 82 that supplies power to the sponge rollers 11 of the 
respective developing units, a DB bias power supply 83 that supplies power 
to the developing rollers, a charging power supply 84 that supplies power 
to the charging rollers 7, and a transfer power supply 85 that supplies 
power to the respective transfer rollers 4. 
The controller 81 is also connected to a charging power supply 86 that 
supplies power to the attraction roller 54, and a neutralizing power 
supply 87 that supplies high voltage power to the neutralizing unit 60. 
The driven roller 31 is grounded so that a potential difference between 
the attraction roller 54 and the driven roller 31 creates a Coulomb force 
that attracts the recording medium to the carrier belt 20. The controller 
81 controls the aforementioned power supplies to turn on and off. 
The controller 81 is also connected to a print controlling circuit 88, 
which controls the respective image forming sections. The print 
controlling circuit 88 receives the image data from the image memory 89 
and sends the image data of the respective colors to the LED heads 3Y, 3M, 
3C, and 3K, respectively, which in turn illuminate the surfaces of 
corresponding photoconductive drums to form electrostatic latent images of 
the respective colors. 
The interface 90 receives image data from an external device, for example, 
host computer, and separates the received image data into yellow, magenta, 
and cyan image data. These items of data are stored in a corresponding 
storage area of the image memory 89. 
A fixing unit controlling circuit 91 controllably drives a heater, not 
shown, in a heat roller 64 so as to maintain a constant temperature of the 
heat roller 64 of the fixing unit 63. 
A motor drive circuit 92 is connected to motors 100-106 and cam motor 25, 
and controls these motors. The motors 100-103 drives in rotation the 
rotating components of the image forming sections 2Y, 2M, 2C, and 2K and 
transfer rollers 4Y, 4M, 4C, and 4K. The motor 105 drives the carrier belt 
20 in rotation. The motor 104 drives the pick-up roller 46 and transport 
roller 50 in rotation. The motor 106 drives the fixing unit 63. The cam 
motor 25 drives the cam shafts 21a and 21b in order to bring the 
photoconductive drums of the color image forming sections into and out of 
contact with the carrier belt 20. The sensor receiver/driver 96 drives the 
photosensors 55, 58, 61, and 27 and receives output waveforms therefrom 
and sends them to the controller 81. 
FIG. 4 is an equivalent electrical circuit of the transfer power supply 85 
for the yellow image forming section. The transfer power supply 85 is 
provided with a high voltage source 20Y and a transfer current detector 
121Y that detects a current flowing through the transfer roller and 
photoconductive drum. There are also provided high voltage sources and 
transfer current detectors, not shown, for magenta, cyan, and black image 
forming sections. 
&lt;General Operation&gt; 
The operation of the aforementioned color image recording apparatus 1 
according to the first embodiment will now be described. 
FIG. 5 illustrates the color image-forming unit A when it is at a 
non-operative position where the photoconductive drums are out of contact 
engagement with the transfer rollers. 
Upon power-up, the controller 81 of the color image recording apparatus 1 
causes the motor drive circuit 92 to drive the cam motor 25 into rotation. 
When the photosensor 27 detects the slit 26a in the disc 26, the 
controller 81 causes the cam motor 25 to stop. This is the position shown 
in FIG. 5 where the color image forming unit A of FIG. 2 is at the 
non-operative position. 
Thereafter, the controller 81 performs initialization of the recording 
apparatus and then causes the motor 106 to drive the heat roller 64 in 
rotation, thereby cleaning the surface of the heat roller 64 with a 
cleaning pad 70. At the same time, the controller 81 causes the fixing 
unit controlling circuit 91 to preheat the heat roller 64 to a 
predetermined temperature. This preheat operation is also performed when 
the image recording apparatus 1 returns from a sleep mode where electric 
power to the heat roller 64 is temporarily shut off to save electric power 
when no printing is performed for a period longer than a predetermined 
length of time. The fixing unit controlling circuit 91 controls the heat 
roller 64 at a constant temperature. 
When the heat roller 64 reaches the predetermined temperature, the 
controller 81 causes the motor drive circuit 92 to drive the motor 105, 
thereby driving the drive roller 30 in rotation so that the carrier belt 
20 runs in a direction shown by arrow E and the cleaning blade 33 scrapes 
residual toner and dirt deposited on the carrier belt 20 into toner tank 
34. When the carrier belt 20 has run a little longer than one complete 
rotation, the motor 105 is stopped so that the carrier belt 20 stops. 
During the cleaning operation, the motors 100-103 are also driven in 
rotation, and the controller 81 turns on the SP bias power supply 82, DB 
bias power supply 83, and charging power supply 84, thereby applying 
predetermined high voltages to the charging rollers 7, developing rollers 
9, and sponge rollers After completion of the initialization, the 
controller 81 waits for image data which will be received through the 
interface 80 from an external device. The aforementioned initialization is 
also performed shortly after the cover of the color image recording 
apparatus 1 is opened for replacement of the image forming sections or 
removal of jammed print paper, and subsequently closed. 
Upon receiving the image data through the interface 90 from the host 
computer, the controller 81 provides instructions to the interface 90 and 
the image memory 89. In response to the instruction, the interface 90 
separates the received image data for one page of the recording medium S 
into the images data for the respective colors and stores the separated 
image data into the corresponding areas in the image memory 89. 
Upon determining that the received image data is color image data, the 
controller 81 causes the motor drive circuit 92 to drive the cam motor 25, 
thereby moving the color image forming unit A to the operative position 
shown in FIG. 1. In other words, the color image forming unit A is moved 
to the position where the photoconductive drums 6Y, 6M, and 6C are brought 
into contact with the carrier belt 20, and then causes the cam motor 25 to 
stop. The movement of the color image forming unit A from the position 
shown in FIG. 5 to the position shown in FIG. 1 is controlled in terms of 
the number of steps of rotation of the cam motor 25. 
With the color image-forming unit A at the position shown in FIG. 5, the 
printing operation starts. 
The controller 81 causes the motor drive circuit 92 to drive the motor 104 
to rotate the pick-up roller 46. The pick-up roller 46 rotates to feed one 
page of the recording medium S from the recording medium tray 41 into the 
guides 48 and 49. The controller 81 causes the motor drive circuit 92 to 
rotate the pick-up roller 46 so that the leading end of the recording 
medium S travels over a distance little longer than the distance between 
the first registry roller 51 and the recording medium tray 41. This allows 
the leading end of the recording medium S to abut the contact area between 
the first registry roller 51 and the recording medium tray 41 so that the 
recording medium S has some slack, thereby eliminating the skew of the 
recording medium S. 
The controller 81 causes the motor drive circuit 92 to drive the motors 
100-103 and 105-106, thereby driving in rotation the photoconductive drums 
6Y, 6M, 6C, and 6K, charging roller 7Y, 7M, 7C, and 7K, developing rollers 
9Y, 9M, 9C, and 9K, sponge rollers 11Y, 11M, 11C, and 11K, transfer 
rollers 4Y, 4M, 4C, and 4K, drive roller 30, transfer roller 50, and heat 
roller 64. At the same time, the controller 81 turns on the charging power 
supply 84, DB bias power supply 83, and SP bias power supply 82, thereby 
applying voltages to the charging rollers 7Y, 7M, 7C, and 7K, developing 
rollers 9Y, 9M, 9C, and 9K, and sponge rollers 11Y, 11M, 11C, 11K. In this 
manner, the surfaces of the photoconductive drums 6Y, 6M, 6C, and 6K are 
uniformly charged and the developing rollers 9Y, 9M, 9C, and 9K and sponge 
rollers 44Y, 11M, 11C, and 11K receive predetermined high voltages. 
The transport roller 50 rotates in a direction shown by arrow G, so that 
the recording medium S is transported by the first and second registry 
rollers 51 and 52 through a medium guide 53 until the leading end of the 
recording medium S reaches between the attraction roller 54 and carrier 
belt 20. At this point of time, the controller 81 turns on the attraction 
power supply 86 to apply a high voltage to the attraction rollers 54. The 
leading end of the recording medium S is attracted by the Coulomb force 
developed by an electric field between the attraction roller 54 and driven 
roller 31. A further rotation of the transport roller 50 in the direction 
shown by arrow F allows the recording medium S to travel in the direction 
shown by arrow E, the recording medium S being attracted to the carrier 
belt 20. The sensor/receiver driver 96 informs the controller 81 that the 
photosensor 55 has detected the leading end of the recording medium S. 
When the trailing end of the recording medium S leaves the separator 44, 
the controller 81 causes the motor drive circuit 92 to stop the motor 104. 
&lt;Recording Operation&gt; 
The recording operation will be described. 
A predetermined length of time after the transport roller 50 starts 
rotating, the controller 81 causes the image memory 89 to provide yellow 
image data for one line to the print controlling circuit 88. In accordance 
with an instruction from the controller 81, the print controlling circuit 
88 reforms the image data from the image memory 89 into a form suitable 
for driving the LED head 3Y for yellow and transmits the reformed image 
data to the LED head 3Y. The LED head 3Y energizes LEDs therein in 
accordance with the image data, thereby forming a yellow electrostatic 
latent image for one page of recording medium. As the photoconductive drum 
6Y rotates, the yellow electrostatic latent image is carried to the 
developing unit where the yellow electrostatic latent image is developed 
into a yellow toner image. 
When the leading end of the recording medium S reaches between the 
photoconductive drum 6Y and transfer roller 4Y, the controller 81 turns on 
the transfer power supply 85 in order to apply the high voltage to the 
transfer roller 4Y, so that the yellow toner image on the photoconductive 
drum 6Y is transferred to the recording medium S. As the photoconductive 
drum 6Y rotates, the toner images are transferred line after line so that 
yellow image for one page is transferred to the recording medium S. A 
predetermined length of time after the trailing end of the recording 
medium S has passed between the photoconductive drum 6Y and transfer 
roller 4Y, the controller 81 shuts off the high voltage to the transfer 
roller 4Y. 
The carrier belt 20 continues to run, carrying the recording medium S from 
the image forming section 2Y to the image forming section 2M where a 
magenta toner image is printed on the recording medium S. 
The controller 81 sends an instruction to the image memory 89 in which 
magenta image data is stored, so that the memory provides the magenta 
image data for one line to the print controlling circuit 88. In accordance 
with the instruction from the controller 81, the print controlling circuit 
88 reforms the magenta image data from the image memory 89 into a form 
suitable for driving the LED head 3M, and transmits the reformed image 
data to the LED head 3M. The LED head 3M energizes LEDs therein in 
accordance with the magenta image data, thereby forming a magenta 
electrostatic latent image for one page of recording medium. As the 
photoconductive drum 6M rotates, the electrostatic latent image is carried 
to the developing unit where the magenta electrostatic latent image is 
developed into a magenta toner image. Subsequent operation is the same as 
in the yellow image and the description thereof is omitted. 
The recording medium S further travels from the image forming section 2M to 
the image forming section 2C where image for cyan is printed on the 
recording medium S. After the transfer of the toner image of cyan, the 
recording medium S advances to the second printing mechanism P2 where a 
black toner image is transferred to the recording medium S. 
As described above, the toner images of the respective colors are 
transferred to the recording medium S in registration with one another. 
Thereafter, the recording medium S is carried on the carrier belt 20 to 
the neutralizing unit 60. The controller 81 turns the neutralizing power 
supply 87, thereby neutralizing the recording medium S so that the 
recording medium S leaves the carrier belt 20 without difficulty. 
When the recording medium S passes over the drive roller 30, the recording 
medium S leaves the carrier belt 20 and is then guided by the guide 62 to 
the fixing unit 63. When the recording medium S leaves the neutralizing 
unit 63, the controller 81 turns off the neutralizing power supply 87. 
Then, the recording medium S passes through the fixing unit 63 where the 
colored toner images are fused on the recording medium S into a full color 
image. Thereafter, the recording medium S is delivered to the paper 
stacker 67. When the photo interrupter 61 detects the trailing end of the 
recording medium S, the controller 81 determines that the recording medium 
S has been discharged. 
Upon discharging the recording medium S, the controller 81 causes the motor 
drive circuit 92 to stop the motors 105 and 106. The controller 81 also 
turns off the charging power supply 84, SP bias power supply 82, DB bias 
power supply 83, and transfer power supply 85. As mentioned above, a color 
image is recorded on the recording medium S. 
Likewise, a color image can be recorded on a recording medium that is 
manually inserted through the manual insertion tray 56. That is, a user 
sets the recording medium S into the manual insertion tray 56. The 
photosensor 58 detects the recording medium S and provides a detection 
signal to the sensor receiver/driver 96, which in turn informs the 
controller 81 of the insertion of the recording medium S. Then, the 
controller 81 causes the motor drive circuit 92 to drive the cam motor 25, 
thereby bringing the color image forming unit A to the position shown in 
FIG. 1. Then, the controller 81 drives in rotation the photoconductive 
drums 6Y, 6M, 6C, and 6K, charging roller 7Y, 7M, 7C, and 7K, developing 
roller 9Y, 9M, 9C, and 9K, sponge roller 11Y, 11M, 11C, 11K, transfer 
roller 4Y, 4M, 4C, and 4K, drive roller 30, and heat roller 64. At the 
same time, the controller 81 turns on the attraction power supply 86 to 
apply a voltage to the attraction roller 54. 
The rotation of the transport roller 50 in the direction shown by arrow G 
allows the recording medium S, sandwiched between the transport roller 50 
and second registry roller 52 to further advance to the attraction roller 
54 through the medium guide 53. The rest of the operation is the same as 
the case in which the recording medium S is automatically fed from the 
medium tray 41 and the description thereof is omitted. 
&lt;Transferring image data in parallel&gt; 
&lt;&lt;Color Printing&gt;&gt; 
The print data is checked on a page-by-page basis to determine whether the 
image data is for the monochrome printing or the color printing. 
The first embodiment is characterized in that the controller 81 transmits 
yellow, magenta, cyan, and black image data in parallel to the LED heads 
3Y, 3M, 3C, and 3K, respectively. 
FIG. 6 is a timing chart illustrating the operation of the LED heads. The 
controller 81 causes the print control circuit 88 to transmit image data 
to the LED heads 3Y, 3M, 3C, and 3K on a line-by-line basis, each line 
extending in the traverse direction perpendicular to the advance direction 
in which the recording medium S travels. The image data for one line 
(e.g., 2560 bits or dots for 300 dpi) is transmitted to each of the LED 
heads upon a sync signal LSYNC over the respective data lines, each bit of 
the image data being attended by a clock CLK. The signal LSYNC is a print 
timing signal at which image data for one line is transferred to a 
corresponding LED head. 
When the image data for one line has been transferred to the LED heads 3Y, 
3M, 3C, and 3K, the controller 81 provides load signals LOAD to the LED 
heads 3Y, 3M, 3C, and 3K, so that the LED heads 3Y, 3M, 3C, and 3K hold 
the corresponding image data for one line. Upon the next LSYNC, LEDs of 
the each LED head are driven in accordance with the image data for one 
line held in the LED head. The LEDs of each LED head are grouped into four 
groups, each group including 2560/4=640 dots. The four groups of LEDs are 
energized during strobe signals STROBE 1 to STROBE 4. The four LED heads 
operate in response to the same LSYNC and therefore the four LED heads are 
driven simultaneously. This implies that a power supply should have a 
current capacity four times larger than that required for driving LEDs 
(i.e., 640 dots) during each of the strobe signals STROBE1 to STROBE4. 
If all the LEDs of the image forming sections 2Y, 2M, 2C, and 2K are to be 
energized simultaneously, the power supply must have a current capacity 
still four times that described above, i.e., 8 times the current required 
for driving LEDs during each strobe signal. This increases the size of the 
recording apparatus. For this reason, the LEDs for each line are driven in 
a time-division method using the strobe signals STROBE1 to STROBE4. 
&lt;&lt;Monochrome Printing&gt;&gt; 
Prior to the transmission of the image data, the host computer outputs a 
command indicating whether the transmitted image data is for the 
monochrome printing or for the color printing. Upon receiving the image 
data for the monochrome printing from the host computer via the interface 
90, the controller 81 instructs the interface 90 to store the received 
monochrome image data into the image memory 89. The controller 81 causes 
the motor drive circuit 92 to drive the cam motor 25 in rotation, thereby 
bringing the color image forming unit A to the non-operative position 
shown in FIG. 5. Thus, the photoconductive drums 6Y, 6M, and 6C are in out 
of contact engagement with the carrier belt 20. 
The drums and rollers of the color image-forming unit A are not driven in 
rotation during the monochrome printing. The voltages for these rollers 
are not applied. Then, the recording medium S is fed from the paper 
feeding mechanism 40. 
The recording medium S is then attracted to the carrier belt 20 which 
transports the recording medium S to the black image forming section 2K 
where a black toner image is transferred to the recording medium S. This 
operation is much the same as in the color printing except that the image 
forming sections 2K is operated at a faster speed(e.g. , four times) than 
the image forming sections 2Y, 2M, and 2C. 
The controller 81 causes the motor drive circuit 92 to select either the 
monochrome printing speed or the color printing speed depending on the 
kind of printing. 
In the present invention, only the LED head 3K is operated in the 
monochrome printing. If the monochrome printing is to be performed at the 
same speed as the color printing, the required drive current capacity of 
the power supply can be 1/4 of that required for the color printing. This 
implies that the exposing cycle in the monochrome can be four times as 
fast as that in the monochrome printing if the power supply operates to 
its full capacity. 
FIG. 7 is a timing chart illustrating the operation of the LED heads. 
It is to be noted that LSYNC is four times faster in the monochrome 
printing than in the color printing. The image data DATA, clock CLK, and 
load LOAD are the same as in the color printing. Each bit of the image 
data DATA is attended by the clock CLK which is four times faster in the 
monochrome printing than in the color printing. 
The strobe signals STROBE1 TO STROBE4 are simultaneously outputted so that 
all the LEDs in one line are energized simultaneously. Simultaneously 
energizing all the LEDs allows exposure of one line in a time of 1/4 of 
that required in the color printing. It is to be noted that the current 
capacity required in the monochrome printing is substantially the same as 
that required in the color printing. 
As described above, in the monochrome printing, the color image forming 
unit A is brought to the non-operative position (FIG. 5), and the 
recording medium S is fed at high speed, and the black image forming 
section 2K is operated at high speed. Thus, a high-speed monochrome 
printing can be achieved without increasing the current capacity of the 
power supply. A check is made on a page-by-page basis to determine whether 
the image data is for the monochrome printing or the color printing. Thus, 
the monochrome printing can be performed at high speed even if the print 
data includes monochrome pages mixed with color pages, thereby shortening 
the overall printing time. 
&lt;Modification of transferring image data in parallel&gt; 
This is a modification of the first embodiment and characterized in that 
the LED head for black image is of a high intensity type. 
The LED head 3K uses LEDs having light emission about four times that of 
the LED heads 3Y, 3M, and 3C. The rest of the construction is the same as 
the first embodiment. 
In the first embodiment, STROBE1 to STROBE 4 are simultaneously issued in 
the high-speed monochrome printing. Thus, current drawn by the LED head 3K 
in the monochrome printing can be up to four times that drawn by the 
respective LED heads in the color printing, depending on the number of 
dots to be printed in the line. This large current causes some voltage 
drops due to resistance in wires in the LED head 3K, resulting in 
variations in light spot size. The variation in light spot size causes 
detectable variation in dot size with increasing number of printed dots. 
Such variation in dot size is not a problem in character-only prints but 
somewhat degrades the print quality in relatively dark prints such as gray 
scale images. 
FIGS. 8 and 9 are timing charts illustrating the operation for driving the 
LED heads, FIG. 8 showing the color printing and FIG. 9 showing the 
monochrome printing. 
For the color printing, since the LED head 3K uses LEDs having an intensity 
four times as high as those for the LED heads for other colors. Thus, the 
time required for driving the LED head 3K during each of STROBE 1 to 
STROBE4 is 1/4 of that required for the driving the LED heads for the 
other colors. 
As shown in FIG. 9, the time required for driving the LED head 3K in the 
monochrome printing is the same as in the color printing. Thus, no 
detectable voltage drops develop in the LED head 3K, not causing dot 
variations and offering good print quality. 
Modification of First Embodiment 
&lt;Construction&gt; 
This modification is characterized in that a controller 110 transfers 
yellow, magenta, cyan, and black image data in serial to the LED heads 3Y, 
3M, 3C, and 3K. 
FIG. 10 illustrates an interface between the controller 110 and the print 
engine 120 of the image recording apparatus 1. The expression "-N" at the 
end of the name of each signal indicates that the signal becomes active 
when it goes low. For example, LSYNC-k-N represents that LSYNC for a black 
becomes active or valid when it goes low. 
FIG. 11 is a block diagram showing an overall construction of the image 
recording apparatus 1. 
Referring to FIG. 11, the image recording apparatus 1 includes a controller 
110 that controls the printing operation and a print engine 120. The 
controller 110 includes an interface 112 connected to a host apparatus 
111, processor 114, program memory 115, working memory 116, font memory 
117, image memory 118, and print engine interface 119, which are connected 
to the interface 112 via a system bus 113. 
The processor 114 performs the overall operations of the controller 110 
under the control of an operation program stored in the program memory. 
The working memory 116 temporarily stores parameters for the printing 
operation and other data. The font memory 117 stores, for example, font 
data for printing. The image memory 118 store the print data received from 
the host apparatus 111 through the interface 112, and holds the print data 
until the printing operation completes. 
The print engine 120 has a mechanical controller 120a (PU) and a printing 
mechanism 120b. The controller 110 provides the print data 119a to the 
print engine 120 through the print engine interface 119, and receives 
print controls signal 119b from the print engine 120 through the print 
interface 119. 
The host apparatus 111 is, for example, a computer, word processor, or 
image reader and produces the print data and provides the print data to 
the controller 110. The interface 112 takes the form of, for example, 
RS232C interface or parallel interface. The print engine interface 119 
reads the print data from the image memory 118 in response to the 
instruction issued from the processor 114 and transfers the print data to 
the print engine 20. The print engine interface 119 also receives print 
control signal 119b output from the print engine 120 and transmits the 
interface control signal 119b to, for example, the processor 114. 
The image recording apparatus of the aforementioned construction receives 
the print data from the host apparatus 1 through the interface 112. The 
image recording apparatus also control commands, characters, graphic 
commands, bit image data and so on and temporarily stores them into the 
working memory 116 appropriately. The processor 114 in the controller 10 
reforms the print data and stores in the image memory 118, and 
subsequently transfers the print data from the image memory 118 to the 
print engine. The printing mechanism 120b of the print engine 120 is of 
the same construction as in the first embodiment. 
Referring to FIG. 10, the controller 110 communicates signals shown in FIG. 
10 with the mechanical controller 120a. The print engine interface 119 
includes a video interface 119A and a command interface 119B. The video 
interface 119A provides a print initiating signal PRINT-N to the print 
engine 120. The print engine 120 provides to the video interface 119A a 
print ready signal PRDY-N, feed initiating signal FSYNC-N indicating that 
a recording medium is being fed to a corresponding printing mechanism, and 
a line sync signal LSYNC-N indicative of a beginning of a line of image 
data. 
The command interface 119B is an interface that transmits and receives 
various commands including a command that specifies a print color. 
&lt;Transferring image data in serial&gt; 
&lt;&lt;Color Printing&gt;&gt; 
FIGS. 12A-12C are timing charts illustrating the transfer operation of 
print data. 
The operation of the print engine interface 9 shown in FIG. 10 will be 
described with reference to FIGS. 12A-12C. 
The controller 10 provides the print initiating signal PRINT-N to the print 
engine 20 prior to the printing operation of one page of recording medium. 
In response to PRINT-N, the print engine 20 transmits PRDY-N to the 
controller 10. When a sensor located immediately in front of the printing 
mechanism detects the leading end of the recording medium being 
transported, the sensor outputs FSYNC-N and continues to output FSYNC-N 
until the recording medium has passed the printing mechanism. Waveform (d) 
is an expanded view of waveform (c). 
When the LED head has received serial data WDATA for one line, the print 
engine 20 provides LSYNC (logic "0") to the controller 10, prompting the 
controller 10 to transmit WDATA for the next one line. Waveform (h) is an 
expanded view of LSYNC shown at (e) in FIG. 12A. When a gate signal 
LGATE-N becomes valid, WDATA for one line is transferred to the exposing 
unit. 
Waveform (j) is an expanded view of WDATA and waveform (k) is an expanded 
view of WCLK. As shown by waveforms (k) and (1), each pulse of WCLK 
attends each bit of WDATA. 
FIG. 13 is a timing chart illustrating the operation of the video interface 
9A. Arrows show directions in which the respective waveforms are 
transmitted and received between the controller (CU) 10 and the print 
engine (PU) 20. 
When the controller 10 transmits PRINT to the print engine 20 and receives 
PRDY from the print engine, the controller waits for FSYNC. 
When the sensors detect the leading end of the recording medium, the 
sensors located immediately in front of the image recording sections for 
yellow, magenta, cyan, and black images provide FSYNC-Y-N, FSYNC-M-N, 
FSYNC-C-N, and FSYNC-K-N, respectively. Since the recording medium travels 
through the respective image forming sections in the order of yellow, 
magenta, cyan, and black, FSYNC-Y-N, FSYNC-M-N, FSYNC-C-N, and FSYNC-K-N 
are outputted in this order in such a way that a following FSYNC is 
outputted a predetermined time after a preceding FSYNC is outputted. This 
predetermined time is a time required for the recording medium to travel 
from a preceding sensor to the following sensor. During the periods of 
FSYNC-Y-N, FSYNC-M-N, FSYNC-C-N, and FSYNC-K-N, the LED heads 3Y, 3M, 3C, 
3K receive WDATA for corresponding colors. 
FIG. 14 illustrates the operation where WDATA for corresponding colors is 
selected by the color selecting signals CSEL1 and CSEL2. 
Referring to FIG. 14, time duration T1 of FIG. 13 is expanded to show the 
relationship among the LSYNC-N, WDATA, CSEL1, and CSEL2. Upon each 
LSYNC-N, WDATA is transmitted to the exposing unit of the print engine 20 
in the order of yellow, magenta, cyan, and black. When both CSEL1 and 
CSEL2 are of a logic "1", the yellow image data Y is transmitted. When 
CSEL1 and CSEL2 are of logic "0" and logic "1", respectively, the magenta 
image data M is transmitted. When CSEL1 and CSEL2 are of logic "1" and 
logic "0", respectively, the cyan image data C is transmitted. When both 
CSEL1 and CSEL2 are of a logic "0", the black image data K is transmitted. 
FIG. 15 illustrates the operation before and after FSYNC-K-N is issued. 
Referring to FIG. 6, time duration T2 of FIG. 13 is expanded to show the 
relationship among the LSYNC-N, FSYNC-K-N, WDATA, CSEL1, and CSEL2. 
FSYNC-K becomes valid at time t1. Before time t1, the black image data K 
is not transmitted to the print engine 20. After time t1, the black image 
data K is transmitted when both CSEL1 and CSEL2 are of a logic "0". From 
time t1 onward, the image data Y, M, C, and K are transmitted until the 
entire image data Y for the page has been transmitted. 
FIG. 16 illustrates the operation before and after FSYNC-Y-N becomes 
invalid. Referring to FIG. 15, time duration T3 of FIG. 13 is expanded to 
show the relationship among the LSYNC-N, FSYNC-Y-N, WDATA, CSEL1, and 
CSEL2. FSYNC-Y becomes invalid at time t2 since the trailing end of the 
recording medium has passed the sensor at the yellow image forming 
section. Before time t2, the yellow image data for final one line of the 
page is transmitted to the print engine 20. After time t2, since FSYNC-Y 
is invalid. Thus, the yellow image data is not transmitted even when both 
CSEL1 and CSEL2 are of a logic "1". From time t2 onward, the image data M, 
C, and K are transmitted until all the image data M for the page has been 
transmitted. 
FIG. 17 illustrates the operation during time duration T4 of FIG. 13 to 
show how each bit of the image data is transmitted upon clock CLK. 
A command transmit signal CBSY-N (FIG. 17) becomes valid when the 
controller 10 transmits a command to the print engine 20. Commands SC-N 
are transmitted serially from the controller 10 to the print engine 20 and 
vice versa. The clock SCLK is a clock that attends each bits of a command 
when the command is transferred. 
For example, the final bit M2560 of one line of the magenta image data is 
transmitted upon the trailing end of a clock WCLK. CSEL1 goes to "1" and 
CSEL2 goes to "0" at time t3. After time t3, each bit in one line of cyan 
image data is transmitted to the exposing unit of the print engine 20 upon 
the trailing end of the clock WCLK. 
&lt;&lt;Monochrome Printing&gt;&gt; 
Slow speed mode 
FIG. 18A illustrates the monochrome printing, which uses the aforementioned 
interface, at the same speed as in the color printing mode. 
The controller 10 issues LSYNC-N at intervals of T which is the same as 
that of LSYNC shown in FIGS. 14-16. Here, by way of example, the 
monochrome printing of a black image will be described. The same operation 
can be equally performed for other colors. 
Shortly after the LSYNC-N, WDATA for one line of a black image is 
transferred from the controller 10 to the print engine 20. CSEL1 and CSEL2 
are both of a logic level "0" during the transfer of WDATA for the black 
image. 
A black-and-white image and a color image have the same number of bits in 
one line of WDATA. Thus, if one line of a black-and-white image is to be 
transmitted during the time required for transmitting each line of yellow, 
magenta, cyan, and black image in the color printing, the clock frequency 
for transmitting one line of the black-and-white image can be 1/4 of that 
required in the color printing. Thus, WDATA in the slow speed monochrome 
printing is transmitted at a speed of 1/4 of that in the color printing. 
Using a slow clock frequency allows reduction of noise level to a 
sufficient level. 
High speed mode 
Next, a high-speed monochrome printing will be described. 
FIG. 18B illustrates the monochrome printing performed at a speed four 
times higher than the monochrome printing shown in FIG. 18A. 
Both CSEL0 and CSEL2 are of logic "0", thereby specifying black image data. 
The line sync signal LSYNC-N is outputted at time intervals of T/4. The 
rest of the operation is the same as in the monochrome printing described 
with reference to FIG. 18A. 
Since the clock frequency in the high-speed monochrome printing is the same 
as that in the color printing, there is no chance of noise increasing from 
a level in the color printing. Moreover, using the timings for the color 
printing at which one line of each of yellow, magenta, cyan, and black 
image data is transmitted can transmit four lines of black image data. 
Therefore, the effective speed of the data transfer in the high-speed 
monochrome printing is four times that of the color printing. As a result, 
the recording unit for black image can operate at a speed four times that 
of the color printing. 
&lt;Specifying Color through Command Interface&gt; 
The operation of the command interface 9B in the controller 10 will be 
described. 
Although the monochrome printing is specified by the color selecting 
signals CSEL0 and CSEL2 in the examples described with reference to FIGS. 
18A and 18B, the image forming sections of the respective colors may also 
be specified by using the command interface 9B. 
FIG. 19 is a timing chart illustration the operation of the command 
interface 9B. 
The controller 10 shown in FIG. 1 provides a command SC-N to the print 
engine 20 when CBSY-N is valid before time t4. The command SC-N is an 
8-bit signal and each bit is transmitted from the controller 10 to the 
print engine 20 upon the clock SCLK. 
Upon recognizing the command SC-N, the print engine 20 sends a command 
response to the controller 10 when a signal SBSY-N is valid (after time 
t4). Each bit of the command response or command SC-N is transmitted upon 
a pulse of clock SCLK. Then, the print engine 20 causes only the black 
image forming section to operate. 
In this manner, the command can be used to specify the monochrome printing, 
thereby overriding the color-selecting signal CSEL-N. This command SC-N is 
a command to specify a single color such as black, magenta, and so on. The 
period T of the line sync LSYNC-N described with reference to FIG. 18A can 
also be specified. In other words, a command can be issued to set printing 
conditions such as high speed printing and low speed printing. 
FIG. 20 is a flowchart illustrating the specific operation of the command 
interface 9B. 
At step S1, the controller 10 checks the print data for one frame to 
determine whether the print data includes only a single color. A frame is 
a unit of data size that corresponds to one page of recording medium. If 
it is determined that the print data describes a black-and-white image, 
the program proceeds to step S2 where a monochrome command is issued to 
print the black-and-white image. Upon receiving the monochrome command, 
the print engine 20 is set to print only the black image. 
At step S3, the controller 10 issues a high-speed command specifying a 
print mode shown in FIG. 18B. Then, at step S4, the monochrome printing is 
performed. 
If it is determined that the print data describes a color image, the 
program proceeds to step S5 where commands for the respective colors are 
issued for the color printing. At step S6, a normal speed command is 
issued which specifies the printing at a normal speed (color print speed). 
At step S4, the monochrome printing is performed for the respective 
colors. 
As described above, the print data can be transmitted at a high clock rate 
or at a low clock rate, thereby performing the monochrome printing at high 
speed or low speed. The aforementioned control may be implemented for not 
only electrophotographic printers, but also for thermal printers and ink 
jet printers. 
Second Embodiment 
A second embodiment is characterized in that in order to increase printing 
speed in the monochrome printing, black image data is processed not only 
by the circuits for black image but also by the circuits for yellow, 
magenta, and cyan images. 
A color printer prints print data for four colors. Therefore, the image 
memory must have a larger capacity in the color printing than in the 
monochrome printing. For this reason, bit mad data received from a host 
apparatus is compressed before being stored in the image memory. The 
compressed image data is read from the image memory and outputted to the 
print engine, the compressed image data being expanded immediately before 
printing. The present embodiment is directed to an effective use of the 
compressing and expanding circuits in the monochrome printing. 
FIG. 21 is a block diagram illustrating the data processing in the present 
embodiment. 
Referring to FIG. 21, compressed data memories 40Y, 40M, 40C, and 40K store 
compressed image data for yellow, magenta, cyan, and black images. The 
image data is compressed by using a well-known conventional method. 
The expanding circuits 242Y, 242M, 242C, and 242K expand the image data for 
corresponding colors. Buffers 243Y, 243M, 243C, and 243K temporarily store 
the corresponding expanded image data. The expanded image data is 
converted into video signals 245Y, 245M, 245C, and 245K in the form of 
serial data and outputted to the print engine. The video circuit 244 is a 
timing controlling circuit, which reads the expanded image data from the 
buffers 243Y, 243M, 243C, and 243K and transfers the expanded data to the 
corresponding print engines. 
An address generator 241 is disposed between the data memories 243Y, 243M, 
243C, and 243K and the expanding circuits 242Y, 242M, 242C, and 242K. The 
address generator 241 includes, for example, a circuit that controls 
addresses so that the compressed data read from the memory 240Y is 
transferred to the expanding circuit 242Y. In the color printing, the 
video signals in the form of serial data are simultaneously and 
continuously transferred, and therefore the expanding circuits 242Y, 242M, 
242C, and 242K operate simultaneously. 
Conventionally, only an expanding circuit and a buffer that stores the 
expanded image data are operated in the monochrome printing. In the 
present embodiment, circuits provided for other colors are effectively 
used in the monochrome printing, thereby increasing the printing speed. 
Specifically, the address generator 241 divides the compressed image data 
for a black-and-white image stored in the memory 240K into four items of 
data, and outputs the divided data to the corresponding expanding circuits 
242Y, 242M, 242C, and 242K. The respective expanding circuits 242Y, 242M, 
242C, and 242K expand the compressed data and store the expanded data into 
the buffers 243Y, 243M, 243C, and 243K, respectively. Then, the video 
circuit 244 rearrange the expanded data outputted from the buffers 243Y, 
243M, 243C, and 243K into the original order before transferring the data 
as the video signal 245K to the print engine for black image. 
Generally speaking, than the time required for expanding the compressed 
data is much longer time required for reading the compressed data from the 
memory 240K. Thus, use of a plurality of expanding circuits can increase 
processing speed. Using two expanding circuits increases the speed by a 
factor of two and using four expanding circuits increases the speed by a 
factor of four. In order to provide for such a control, the memory 240K 
stores the image data on a block basis. 
FIG. 22 illustrates the contents of the memory that stores the compressed 
data. 
The compressed data is divided into a plurality of blocks such as CDATA1, 
CDATA2 . . . , CDATAn-1 and so on. Each block has a header that describes 
the data size of a corresponding block and expanding circuit specifying 
data BS1, BS2 . . . , BSn-1 and so on. 
Thus, every time the address generator 241 reads a block of compressed data 
from the memory 240K, the address generator 241 checks the expanding 
circuit specifying data BSn of the block. Then, the address generator 241 
generates an address of a corresponding expanding circuit and transfers 
the block to the expanding circuit. In the monochrome printing, by 
performing the processing repeatedly, the compressed data is distributed 
evenly to a plurality of expanding circuits for effectively processing the 
compressed data. The video circuit 244 reads image data corresponding to 
the blocks from the respective buffers 243Y, 243M, 243C, and 243K and 
outputs the image data in the order in which the image data is read from 
the buffers. 
As mentioned above, when the color image recording apparatus performs the 
monochrome printing, circuits for other colors than black can be 
effectively used to increase the printing speed. 
If the print engine is to perform the monochrome printing at a speed four 
times that in the color printing, the print data must also be processed 
four times faster. The expanding circuits process the largest amount of 
data of all the circuits in the recording apparatus and therefore are 
required to operate at the highest speed. The use of expanding circuits 
for other colors than black may achieve a high-speed monochrome printing 
while maintaining the same signal processing speed of the respective 
expanding circuits. This way of signal processing will not increase noise 
in the high-speed printing. 
Modification of Second Embodiment 
The aforementioned signal processing can be applied to various stages from 
reception of print data from a host apparatus till the print data is 
outputted to the print engine. 
FIG. 23 is a block diagram illustrating the data processing in the present 
embodiment. 
FIG. 23 illustrates the flow of data from reception of print data from a 
host apparatus till the outputting of the print data to the print engine. 
The print data 250 received from an external apparatus is first stored in 
a buffer 251. This data is RGB data used for displaying on a computer 
display. A data converter 252 converts the RGB data into YMCK data that 
can be printed. The YMCK data is stored into a buffer 253. 
A compressing circuit 254 compresses the YMCK data and the compressed data 
is stored into a raster buffer 255. The data stored in the raster buffer 
255 is sequentially expanded and transferred to a video buffer 257. In 
this manner, the YMCK data is provided to printing mechanisms 258Y, 258M, 
258C, and 258K on a line-by-line basis. 
FIG. 24 is a block diagram illustrating the data processing in the present 
embodiment. 
Each of yellow, magenta, cyan, and black image data is processed by buffers 
253Y, 253M, 253C, and 253K, compressing circuit 254Y, 254M, 254C, and 
254K, raster buffer 255Y, 255M, 255C, and 255K, expanding circuits 256Y, 
256M, 256C, and 256K, video buffers 257Y, 257M, 257C, and 257K, 
respectively, aligned in this order. 
A signal selector 61 is provided between the buffers 253Y, 253M, 253C, and 
253K and the compressing circuits 254Y, 254M, 254C, 254K. The outputs of 
video buffers 257Y, 257M, 257C, and 257K are transferred through a head 
signal controlling circuit 62 to printing mechanisms 258Y, 258M, 258C, and 
258K. The head signal controlling circuit 262 controls the transferring of 
video signals so that the video signals are transferred from the video 
buffers 257Y, 257M, 257C, and 257K to corresponding printing mechanisms 
258Y, 258M, 258C, and 258K, respectively, on a line-by-line basis. 
Just as described with reference to FIGS. 21-23, the present embodiment 
also uses circuits for other colors than black when performing the 
monochrome printing. 
Specifically, the signal selector 261 divides the data for black-and-white 
image, stored in the buffer 253K, into four items of data and distributes 
the four items of data to the compressing circuits 254Y, 254M, 254C, and 
254K, respectively. The data may be distributed on a block-by-block basis, 
each block including a predetermined amount of data just as in the second 
embodiment. Alternatively, the data may be distributed byte by byte or 
line-by-line. In any case, the compressing circuits 254Y, 254M, 254C, and 
254K and expanding circuits 256Y, 256M, 256C, and 256K process portions of 
the data, so that the printing speed is increased. 
The head signal controlling circuit 262 receives the data from the 
respective video buffers 257Y, 257M, 257C, and 257K in order and transfers 
the data to the printing mechanism 258K. In this manner, printing speed in 
the monochrome printing can be increased by a factor of four while 
maintaining the same data processing speed. 
FIG. 25 is a block diagram illustrating another data processing. The 
structure of the block diagram is much the same as that shown in FIG. 24 
except that a signal selector 263 is located after the compressing 
circuits 254Y, 254M, 254C, and 254K. In other words, the signal selector 
263 distributes the compressed data for black-and-white image to the 
raster buffers 255Y, 255M, 255C, and 255K when performing the monochrome 
printing of a black-and-white image. 
As described earlier, the time required for expanding the compressed data 
outputted from the memory 40K is longer than other signal processing 
operations. Thus, use of all of the expanding circuits 256Y, 256M, 256C, 
and 256K can increase the signal processing speed. Moreover, using the 
raster buffers 255Y, 255M, 255C, and 255K both in the color printing and 
in the monochrome printing allows more effective use of memory resources 
than using the raster buffers only in the color printing. 
FIG. 26 is a block diagram illustrating still another data processing. 
The structure of the block diagram is much the same as those shown in FIGS. 
24 and 25 except that a signal selector 264 is located between the 
expanding circuits 256Y, 256M, 256C, and 256K and the video buffers 257Y, 
257M, 257C, and 257K. The video buffers 257Y, 257M, 257C, and 257K are 
effectively used in the printing operation. 
Conventionally, only a video buffer for a specific color is operated in the 
monochrome printing. Video buffers have only a limited capacity and often 
dictates the printing speed and other controls. According to the data 
processing shown in FIG. 26, video buffers for other colors than black may 
be effectively used in the monochrome printing, thereby increasing 
printing speed. The signal processing shown in FIG. 26 is particularly 
useful in a case where the signal processing takes a long time. 
The configurations shown in FIGS. 24-26 can be applied not only to a 
black-and-white image but also to the monochrome printings of other 
colors. Although, the embodiment has been described with respect to a case 
where the circuits for all the colors are used, the printing speed may be 
increased by using circuits for only a limited number colors. 
&lt;Using four wires for increased printing speed&gt; 
This modification uses a 4-wire LED head that has four wires for receiving 
image data DATA. 
FIG. 27 is a block diagram illustrating the relevant portion of the 
embodiment. 
Referring to FIG. 27, a print controlling circuit 288 is connected to 
buffers 211-213 having output enabling terminals 211a-213a and to a 4-bit 
shift register 214. The outputs of the buffers 211-213 are connected to 
yellow LED head 203Y, magenta LED head 203M, and cyan LED head 203C, 
respectively. The buffers 211-213 are controlled to be "valid" or 
"invalid" in accordance with a selector signal 215 issued from the print 
controlling circuit 288. 
The shift register 214 is connected to a 4-bit input type selector 216, 
which is connected to the black LED head 203K. The shift register 214 
holds four bits of the black image data and outputs the four bit data to 
an A-input of the selector 216. The data lines of the respective colors 
are connected to a B-input of the selector 216. The black data output from 
the print controlling circuit 288 is also connected to the B-input. The 
selector 216 selects either the input or B input in accordance with the 
selector signal 215, and outputs the selected data. 
In the first embodiment, the frequency of the clock CLK is increased in the 
monochrome printing, thereby transferring the data for a black image at an 
increased speed. If the data is transferred at a higher speed, then the 
LED head must operate at a higher speed accordingly. The embodiment 
addresses such a problem. 
The operation of the second embodiment will be described. 
FIGS. 28 and 29 are timing charts illustrating the signals when the LED is 
driven. FIG. 28 illustrates signals in the color printing and FIG. 29 
illustrates signals in the monochrome printing. 
In the color printing, the buffers 211-213 direct the yellow, magenta, and 
cyan image data outputted from the print controlling circuit 288, to the 
LED heads 203Y, 203M, and 203C, respectively. 
The selector 216 selects the A-input when the selector signal 215 is of a 
low level. Thus, the four bits of black image data held on the 4-bit shift 
register 214 are transferred through the selector 216 to the LED head 
203K. The black image data is transferred from the print controlling 
circuit 288 to the 4-bit shift register 214 at a speed four times that of 
image data for the other colors and the four bit parallel data is 
transferred from the selector 216 to the LED head 203K at the same speed 
as the image data for the other colors. 
The print controlling circuit 288 is connected to the shift register 214 
through short wires in the circuit board. Thus, transferring the image 
data at high speed will not cause significant noise. After the image data 
has been transferred to the LED head 203K, the operation of the LED head 
203K is the same as in the first embodiment. 
The monochrome printing will now be described. 
The print controlling circuit 288 sets the selector signal 215 to a high 
level, which in turn disables the buffers 211-213. The selector signal 215 
causes the selector 216 to select the B-input so that black image data is 
transferred over the yellow, magenta, cyan, and black data lines and 
through the B-input to the LED head 203K. The strobe signals STROBE1 to 
STROBE4 are simultaneously outputted so that LEDs of the LED head 203K are 
all driven simultaneously. 
As described above, the monochrome printing is performed by using not only 
a black image data area of the image memory 289 but also image data areas 
for other colors, and by operating all the circuits in the print 
controlling circuit 288 just as in the color printing, thereby effecting 
parallel processing of image data just as in the color printing. In this 
manner, the signal processing speed in the monochrome printing can easily 
be increased. 
As shown in FIG. 29, the use of a 4-wire LED head for black shortens the 
time required for transferring image data while still maintaining the same 
clock frequency for the clock CLK. 
The aforementioned second embodiment and the modification thereof offer the 
same advantages as the first embodiment. Since the clock frequency is not 
increased, there is no need for using an LED head that is capable of 
operating at higher clock signals, and there is no chance of interfering 
radio waves radiating. 
Third Embodiment 
&lt;Printing gradation data&gt; 
FIG. 30 is a block diagram illustrating a third embodiment. The third 
embodiment is characterized in that a black LED head 303K is of an 
adjustable gradation type where light emission is adjusted in accordance 
with multi value data. 
Referring to FIG. 30, the print controlling circuit 388 provides the 
selector signal 315 to a selector 321. The print controlling circuit 388 
is connected to the buffers 311-313 and selector 321 via data lines 
LINE-Y, LINE-M, LINE-C, and LINE-K for yellow, magenta, cyan, and black 
image data, respectively. The buffers 311-313 have output enabling 
terminals 311a-313a. The data lines LINE-Y, LINE-M, and LINE-C for yellow, 
magenta, and cyan image data respectively, are connected to corresponding 
terminals of the B-input of the selector 321 while the data line LINE-K 
for black image data is connected to four terminals of the input A. The 
outputs of the buffers 311-313 are connected to yellow LED head 303Y, 
magenta LED head 303M, cyan LED head 303C, respectively. The buffers 
311-313 are controlled to be "valid" or "invalid" in accordance with the 
selector signal 315 issued from the print controlling circuit 388. When 
the selector 321 is shifted to the B input, the selector 321 transmits 
4-bit gradation data D0-D3 to black LED head 303K. 
The operation of the third embodiment will be described. 
In the color printing, the print controlling circuit 388 sets the selector 
signal 315 to a logic "0" which causes the buffers 311-313 to output 
yellow, magenta, and cyan image data to the LED head 303Y, LED head 303M, 
and LED head 303C, respectively. 
The print controlling circuit 388 outputs one bit of image data for each 
black dot and the one bit of image data is input into the four terminals 
of the A-input. Thus, the 4-bit data input into the A-input is "0" or "15" 
in value. Since the selector signal 315 selects the A-input, the 4-bit 
gradation data of "0" or "15" is outputted to the LED head 303K. In other 
words, the value of black image data inputted to the LED head 303K is "0" 
or "15" in the color printing. 
In the monochrome printing, the print controlling circuit 388 sets the 
selector signal 315 to a logic "1" which causes the outputs of the buffers 
311-313 to be shut off and causes the selector 321 to select the B-input. 
The print controlling circuit 388 provides 4-bit gradation data over the 
data lines LINE-Y, LINE-M, LINE-C, and LINE-K for yellow, magenta, cyan, 
and black image data to the selector 321. The least significant bit b0 is 
output to LINE-Y, and the most significant bit b3 is output to LINE-K. 
In the monochrome printing, storage areas in the image memory 389 for other 
colors than black are used so that each storage area stores one bit of 
information of 4-bit gradation data. The image data is processed in 
parallel in the print controlling circuit 388 just as in the color 
printing, so that the image data is processed at a higher speed in the 
monochrome printing than in the color printing. 
The data transferring operation is the same as the timing chart illustrated 
in FIG. 7 except that the black image data is 4-bit parallel data. The 
strobe signals STROBE1 to STROBE4 are simultaneously outputted. 
Fourth Embodiment 
&lt;Printing black image with lowered resolution&gt; 
In general, a decrease in resolution causes a prominent decrease in image 
quality in color print. For this reason, a high resolution such as 600 dpi 
is required in the color printing. In the monochrome printing, images 
often include only characters. A relatively low resolution still maintains 
print quality in character-only images. 
For example, for character-only images, resolutions in the range from 150 
dpi to 300 dpi are sufficient in many cases. Thus, in the fourth 
embodiment, resolution is decreased in order to increase printing speed in 
the monochrome printing. 
Hardware for signal processing in such a low-resolution printing may be 
those shown FIGS. 24-26. The compressing circuits and expanding circuits 
perform the following operations so as to reduce the amount of data to be 
processed in the monochrome printing and increase printing speed. 
FIG. 31 illustrates an image having a resolution of 600 dpi. 
FIG. 31 shows an arrangement of pixels to print a character "A" at a 
resolution of 600 dpi. In other words, there are 600 dots per inch. For 
example, the compressing circuit 254K shown in FIG. 30 compresses the data 
(FIG. 31) stored in the buffer 253K by a factor of 2 both in the traverse 
direction and in the advance direction. In other words, logical sums of 
two adjacent dots are taken in the traverse direction, and every other 
line is deleted in the advance direction. Then, the data whose resolution 
is decreased is subjected to the ordinary compression and subsequently 
stored into the raster buffer 252K. 
FIG. 32 illustrates an image of a resolution of 300 dpi obtained by the 
aforementioned operation. The number of pixels of the image shown in FIG. 
32 is 1/4 of that of the image of 600 dpi. Thus, the compression and 
expansion can be carried out at a speed four times that of the image of 
600 dpi. The printing mechanism 258K is designed for 600 dpi, and 
therefore, the expanding circuit 256K expands the data, stored in the 
raster buffer 255K, in the usual method, thereby restoring a resolution of 
600 dpi. The image data with restored resolution is stored into the video 
buffer 257K. 
FIG. 33 illustrates the restored image with 600 dpi. As shown in FIG. 33, 
the same bit of the data of 300 dpi is outputted twice in the traverse 
direction and the same line of the data is outputted twice in the advance 
direction. As is clear from FIGS. 31 and 33, images such as characters can 
be restored with a sufficient print quality in the monochrome printing. 
By carrying out the aforementioned signal processing, signal-processing 
speed can be increased when the image is reduced in resolution and then 
restored in resolution, thereby achieving a high-speed printing. Such a 
restoration of data can be effected immediately before the printing 
mechanism operates to print. Thus, the print engine may have a 
data-restoring function. This decreases the amount of data to be 
processed, thereby allowing the data to be transferred from the controller 
to the print engine. 
Fifth Embodiment 
&lt;High speed conversion from RGB data to YMCK data&gt; 
This embodiment is directed to the process processing for converting the 
RGB signal into YMCK signals. 
FIG. 34 is a block diagram showing the structure of a data converting 
section where optical color data is converted into print color data. 
Received data 350 is optical color data including red, green, and blue 
data, which are received into buffers 351R, 351G, and 351B, respectively. 
A data converter 352 converts the optical color data into print color data 
by. Buffers 353Y, 353M, 353C, and 353K store print data, i.e., yellow (Y), 
magenta (M), cyan (C), and black (K) image data, respectively. 
The data converter 352 takes the form of software and performs 
sophisticated data conversion of the red, green, and blue data. The data 
conversion is time consuming and is an obstacle to high-speed printing. In 
the embodiment, this data conversion is simplified to achieve high-speed 
monochrome printing. 
FIG. 35A lists the values of the optical color data R, G, and B in the 
monochrome printing. 
FIG. 35B lists the values of the print colors Y,M,C, and K corresponding to 
the optical color data RGB of FIG. 35A. 
The data is expressed in hexadecimal. Thus, the data can have 256 different 
values, from "00" to "FF." The value "00" indicates a density of 0% and 
the value "FF" represents a density of 100%. 
The red (R), green (G), and blue (G) are three primary colors of light 
while yellow, magenta, cyan ,and black are three print colors. The former 
is additive and the latter is subtractive. Thus, if all of R, G, and B 
have a density of 100%, then the resultant printed color is white, i.e., 
all of Y, M, C, and K have a density of 0%. If all of R, G, and B have a 
density of 0%, then the resultant printed color is black, i.e., all of Y, 
M, and C have a density of 0% and black has a value of "FF." Using this 
characteristic, data conversion can be simplified in the monochrome 
printing. 
FIG. 36 is a flowchart illustrating the data conversion. Prior to the 
monochrome printing, a host apparatus transmits a black-image command 
indicative of a black image. 
At step S1, a check is made to determine whether the image recording 
apparatus has received print data together with the black-image command. 
If the answer at step S1 is NO, then the program proceeds to step S8 where 
a normal data conversion is performed for the color printing. If the 
answer is YES at step S1, then the data converter 352 performs steps 
S2-S6. 
At step S2, a color component R is checked. If R is "00", then color 
component K is set to "FF" at step S3. Since the monochrome printing has 
been specified, any data in the monochrome printing should describe either 
black or white. Thus, if the component R is found to be "00", then green 
and blue need not be checked. 
If the component R is found to be "FF", the print color will be white. 
Thus, the program proceeds to step S4 and then to S5 where the color 
component K is set to "00." Since the monochrome printing has been 
specified, the data should describe either black or white. Thus, if the 
component R is found to be "FF", then green and blue need not be checked. 
The values for Y, M, C, and K are all assigned "00" at step S6. Although 
step S6 is carried out on a data-by-data basis, the step S6 may be carried 
out at a time on the entire print data of a document to be printed. 
A check is made at step S7 to determine whether all the RGB data has been 
converted into YMCK data. If the answer is NO, the program jumps back to 
step S2 where data conversion begins for the next data. 
As mentioned above, if the image recording apparatus is informed that the 
data is only for monochrome printing only, printing, then data conversion 
is very much simplified, increasing overall printing speed in the 
monochrome printing. 
As shown in FIG. 34, the data for three colors received from a host 
apparatus is stored into the buffers 351R, 351G, and 351B, respectively. 
In the monochrome printing, only the component R is checked. Thus, the 
data for green and blue need not be stored. The present embodiment is 
directed to an effective use of the buffers 351R, 351G, and 351B. 
FIG. 37 is a block diagram showing the structure of a data converting 
section where optical color data is converted into print color data. The 
data converting section of FIG. 37 differs from that of FIG. 34 in that a 
signal selector 360 that receives data 350 from the host apparatus prior 
to the printing operation. The signal selector 360 receives only color 
component R from the data received from the host apparatus. The received 
component R is divided and stored into buffers 351R, 351G, and 351B in 
this order. 
The data converter 352 reads the data for R from the buffers 351R, 351G, 
and 351B in this order and performs data conversion of the data read out 
of these buffers. 
As described above, the buffers 351R, 351G, and 351B are effectively used 
in the monochrome printing. The apparent capacity of buffers as a whole 
becomes large, achieving high-speed reception of print data and therefore 
increasing overall printing speed in the monochrome printing. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art intended to be included within 
the scope of the following claims.