Method for the simultaneous optical storage of a first image, optical retrieval and latent formation of a second image, and development of a latent third image

A method for the formation of images utilizing a plurality of optical image memories into each of which image information is written and from each of which said image information is read out sequentially to obtain image-information light that is used for the formation of images; wherein said image information written into one of said optical image memories is read out therefrom at the time when other image information is being written into another predetermined optical image memory.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
This invention relates to a method for the formation of images that 
utilizes optical image memories on which writing and reading of image 
information is performed by means of light, the image information read out 
therefrom in the form of light being used for an image forming process. 
2. Description of the prior art 
An apparatus for the formation of images in which optical image memories 
(an intermediate storage medium), formed of liquid crystals, PLZT, or the 
like, is used has been proposed by Japanese Laid-Open Patent Publication 
No. 54-140542. In such an apparatus, image information is written into the 
optical image memories and light is directed thereto to extract the stored 
image information in the form of reflected or transmitted light 
(image-information light), the image-information light thus obtained being 
projected onto a photosensitive means for forming a latent image thereon. 
The image information written in the optical image memories is retained 
for a certain duration of time. Therefore, in the case of making multiple 
copies of a plurality of originals, for example, it is possible to write 
the information of the original images into a plurality of optical image 
memories, respectively, and then to read out each image information from 
the corresponding optical image memory for a plurality of image forming 
processes. 
There have previously been two methods for making multiple copies of a 
plurality of originals: one method is to first write the information of 
all the original images to be printed into a plurality of optical image 
memories, and then read out the stored image information sequentially for 
forming respective images for the multiple image forming processes; and 
the other method is to first write the image information of a single 
original image to be printed, and read out the information for forming an 
image for the first copy, only the image reading operation being 
sequentially performed for forming images for the second and subsequent 
copies, and then to repeat this operation for other original images to be 
printed. In these methods, however, loss is caused in apparent time since 
no actual image forming process is performed during the writing of image 
information. 
SUMMARY OF THE INVENTION 
The method for the formation of images of this invention, which overcomes 
the above-discussed and numerous other disadvantages and deficiencies of 
the prior art, utilizing a plurality of optical image memories into each 
of which image information is written and from each of which said image 
information is read out sequentially to obtain image-information light 
that is used for the formation of images; wherein said image information 
written into one of said optical image memories is read out therefrom at 
the time when other image information is being written into another 
predetermined optical image memory. 
In a preferred embodiment, the number of said optical image memories is 
three, into each of which said image information corresponding to one of 
three primary colors of light is respectively written. 
In a preferred embodiment, each of the optical image memories is made of a 
smectic liquid crystal device. 
In a preferred embodiment, the image information is written into said 
optical image memories by means of a semiconductor laser device. 
In a preferred embodiment, the image information light obtained from said 
optical image memories is projected onto a photosensitive and 
pressure-sensitive sheet. 
Thus, the invention described herein makes possible the objective of 
providing a method for the formation of images in which the writing of 
image information into an optical image memory is performed simultaneously 
with the reading of other image information from another optical image 
memory, thus eliminating the loss in the processing time and, as a result, 
shortening the image forming time as a whole.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One embodiment of the present invention will be described below, taking the 
case of an apparatus for the formation of images in which 
image-information light extracted from optical image memories is projected 
onto a full-color compatible photosensitive sheet for forming an image. 
The full-color compatible photosensitive sheet, as disclosed for example in 
Japanese Laid-Open Patent Application No. 59-30537, is formed from a resin 
such as a polyester or the like, and coated with three kinds of uniformly 
dispersed pressure-rupturable capsules, each corresponding to one of three 
primary colors. The three kinds of pressure-rupturable capsules are: (1) C 
capsules comprising a resin capsule which contains a photosensitive 
material that is hardened by light with wavelengths in the red region of 
light and a chromogenic material that gives cyan color by reacting with a 
developing material (coated on an image-receiving sheet later described); 
(2) M capsules comprising a resin capsule which contains a photosensitive 
material that is hardened by light with wavelengths in the green region of 
light and a chromogenic material that gives magenta color by reacting with 
the developing material; and (3) Y capsules comprising a resin capsule 
which contains a photosensitive material that is hardened by light with 
wavelengths in the blue region of light and a chromogenic material that 
gives yellow color by reacting with the developing material. Thus, when 
these capsules receive three kinds of light each with wavelengths in one 
of the red, green, and blue regions of light, the C, M, and Y capsules are 
hardened, respectively, in response to each kind of light. When the 
photosensitive sheet is exposed to three kinds of image forming light 
(i.e., image-information light that contains the information of an image 
to be formed) each having wavelengths of one of the red, green, and blue 
region of light, the C, M, and Y capsules are selectively illuminated with 
their respective light in accordance with the information of the image to 
be formed, so that some of the pressure rupturable capsules receive the 
light and become hardened and others do not receive the light and remain 
unchanged. As a result, a latent image that consists of hardened C, M, and 
Y capsules and unhardened C, M, Y capsules is formed on the photosensitive 
sheet. 
The image-receiving sheet is coated with a thermoplastic material and the 
above-mentioned developing material that is used to color the chromogenic 
material enclosed in the C, M, and Y capsules. The chromogenic material 
and the developing material are, for example, leuco dyes and acids that 
color the dyes (e.g., Japanese Laid-Open Patent Publication No. 58-88739). 
When the photosensitive sheet with a latent image formed thereon is pressed 
against the image-receiving sheet, unhardened pressure-rupturable capsules 
rupture, causing chromogenic materials enclosed therein to flow out and 
give colors through reaction with the developing materials on the 
image-receiving sheet, thus forming a colored image on the image-receiving 
sheet. 
General construction of an apparatus for the formation of images 
FIG. 1 shows an apparatus for the formation of full-color images that is 
used in a method of the invention. 
An optical system is disposed in the upper part of the body of the 
apparatus, the optical system including an image writing device 11 and an 
image reading device 12. The image writing device 11 is provided, as 
described below, with optical image memories and a laser unit for writing 
image information into each of the optical image memories. A laser beam is 
projected onto one side of each optical image memory for writing the image 
information thereinto, and light is projected onto the other side thereof 
for reading out the image information therefrom. The image reading device 
12 comprises a light source 12a, lenses 12b and 12c, mirrors 12d and 12e, 
and a color separation filter 12f. Image information is written into the 
optical image memories by means of the image writing device 11, and the 
image information is read out in the form of reflected light by means of 
the image reading device 12 for illuminating a photosensitive sheet to 
obtain a latent image thereon. The optical system will be described in 
detail later. 
An image forming process section is disposed in the lower part of the body 
of the apparatus. In the center of the lower part of the body is mounted a 
cartridge 21 in such a way as to be removable from the body. The cartridge 
21 includes a sheet-feeding rod 21a and a take up rod 21b, the 
sheet-feeding rod 21a being loaded with a new photosensitive sheet in a 
rolled form thereon. The photosensitive sheet is full-color compatible as 
previously mentioned. The photosensitive sheet is drawn out from the 
sheet-feeding rod 21a, and directed through transport rollers 22a and 22b, 
an exposure plate 23, a pair of transport rollers 22c, a buffer roller 24, 
and a pair of pressure rollers 25, before being wound around the take up 
rod 21b. On the exposure plate 23, the photosensitive sheet is exposed to 
image forming light from the image reading device 12 so as to obtain a 
latent image thereon. An entire surface exposure method being employed, 
the photosensitive sheet is made to stay stationary on the exposure plate 
23 after being delivered in a predetermined length from the cartridge 21. 
At this stage, the light reflected from the entire surface of each optical 
image memory is projected onto the entire image-forming area, thereby 
selectively illuminating the image-forming area. As a result, some of the 
pressure-rupturable capsules receive the light to be hardened and others 
do not receive the light and remain unchanged, resulting in a latent 
image. The entire surface exposure thus performed helps to shorten the 
total exposure time as compared with exposure by scanning. 
The photosensitive sheet with the latent image formed thereon is pressed 
against the image-receiving sheet by means of the pressure rollers 25, 
which causes the unhardened pressure-rupturable capsules to rupture, 
thereby allowing the chromogenic materials therein to flow out onto the 
image-receiving sheet. The image-receiving sheet is delivered from a paper 
cassette 26 mounted on the right side of the body of the apparatus. The 
buffer roller 24 is operated for simultaneously performing the 
light-exposure and pressure-transfer operations; this operation will be 
described later. 
The image-receiving sheet accommodated in the paper cassette 26 is 
delivered by means of a paper feed roller 26a till it temporarily stops at 
a timing roller 26b. The timing roller 26b is then started for rotation at 
a predetermined timing to feed the image-receiving sheet so that the 
image-receiving sheet is placed on the latent image of the photosensitive 
sheet for being pressed together by the pressure rollers 25. This causes 
the unhardened pressure-rupturable capsules of the latent image on the 
photosensitive sheet to rupture, and thus the chromogenic materials 
enclosed therein to flow out onto the image-receiving sheet and react with 
the developing materials, thereby forming a colored image on the 
image-receiving sheet. Thereafter, the photosensitive sheet is taken up on 
the take up rod 21b, while the image-receiving sheet is transported by a 
transport belt 28 and then through a glossing unit 29 before being 
discharged out of the body onto a paper-receiving tray 30. 
The glossing unit 29 includes a glossing belt 29c applied between rollers 
29a and 29b, a pressure roller 29d which is pressed against the roller 29b 
with the glossing belt 29c interposed therebetween, and a fan 29e facing 
the roller 29a. A heat source such as a halogen lamp is provided inside 
the roller 29b, the surface temperature thereof being kept between 100 and 
200 degrees Centigrade. The image-receiving sheet discharged from the 
pressure rollers 25 is transported along the glossing belt 29c. The 
image-receiving sheet is heated while being pressed between the roller 29b 
and the pressure roller 29d, thereby causing the thermoplastic material 
coated on the image-receiving sheet to soften and cover the colored image 
surface, which is smoothened to give glossiness to the colored image 
(Japanese Laid-Open Patent Publication No. 60-259490). Also, the heating 
accelerates the coloring reaction between the chromogenic materials and 
the developing materials (Japanese Laid-Open Patent Publication No. 
61-24495), thus giving clearness to the image. 
Provided on one end of the sheet-feeding rod 21a of the photosensitive 
sheet is a sawtooth-like engaging portion with which an actuator 21d 
engages. The actuator 21d is made to swing by the action of a solenoid 
21e. When the solenoid 21e is de-energized, the actuator 21d swings to be 
engaged with the sheet-feeding rod 21a, so that the sheet-feeding rod 21a 
is locked to prevent the photosensitive sheet from being drawn out from 
the cartridge 21. When the solenoid 21e is energized , the actuator 21d is 
disengaged to unlock the sheet-feeding rod 21a to allow the photosensitive 
sheet to be drawn out from the cartridge 21. 
FIG. 2 is an enlarged view of the exposure plate 23, on the top surface of 
which are disposed discharge brushes 27a and 27c. The discharge brush 27a 
is disposed upright on the upstream end (viewed in terms of the 
transporting direction of the photosensitive sheet) of the exposure plate 
23, and the discharge brush 27c is disposed upright on the downstream end 
thereof. The discharge brushes 27a and 27c are respectively fixed to paper 
guides 27b and 27d disposed above the photosensitive sheet. The discharge 
brushes 27a and 27c eliminate the static electricity generated through 
friction of the photosensitive sheet with the exposure plate 23 during the 
transportation of the photosensitive sheet. The discharge brushes 27a and 
27c also block stray light from entering the center portion of the 
exposure plate 23, thus preventing exposure of the photosensitive sheet to 
the stray light. 
FIG. 3 is a block diagram of the control system of the apparatus for the 
formation of images. The apparatus is provided with two CPUs 41 and 51. 
The CPU 41 controls the image forming process section that includes the 
photosensitive sheet transport system, the image-receiving sheet transport 
system, the glossing unit, etc., as well as the input/output to and from 
an operation section (input section), and thence controls the buffer 
roller 24, the pressure rollers 25, etc., in accordance with the number of 
sheets to be printed, or other image forming conditions that are input to 
the operation section. The CPU 51 is provided to control the optical 
system. Image data is input to the CPU 51 from a scanner, computer, etc., 
which are peripheral devices to the apparatus for the formation of images. 
The image data consists of digital data separated into three primary color 
components, red (R), green (G), and blue (B), which, under the control of 
the CPU 51, are stored as image information in an R area, a G area, and a 
B area of an image memory 52, respectively. Then, in the image writing 
operation, each of the stored image information corresponding to R, G, and 
B is written into the respective optical image memories using the image 
writing device 11 that includes a semiconductor laser unit. 
Construction of the optical system 
FIG. 4 shows the image writing device 11 and its adjacent parts. 
The image writing device 11 includes three optical image memories 31R, 31G, 
and 31B. Each of the optical image memories 31R, 31G, and 31B is formed 
for example from a smectic liquid crystal device. 
(1) Description of the smectic liquid crystal device 
FIG. 5 shows the thermoelectro-optic characteristics of the smectic liquid 
crystal device. 
A smectic liquid crystal device comprises two glass substrates between 
which smectic A-type liquid crystals having positive dielectric anisotropy 
are sandwiched. The electrode surface on the inner side of each substrate 
is appropriately treated so that the liquid crystal molecules are aligned 
perpendicular to the plane of the substrate (state (T) as shown in upper 
left in FIG. 5). In this state, the device is transparent. When the entire 
liquid crystal device is slowly heated, the transparency of the device 
slowly increases and then reaches saturation (as shown in upper right in 
FIG. 5). In this state, the molecular alignment in the liquid crystal is 
completely random. The liquid is now in an isotropic state, and not a 
liquid crystal. Next, when this liquid is slowly cooled, the following two 
stable states are obtained depending on the way it is cooled. 
A) When the device is cooled without applying voltage between the 
electrodes, the molecules in the device align partly in a smectic state 
(focal conic). As a result, the device turns to be opaque (state (F) as 
shown in lower left in the FIG. 5). 
B) On the other hand, when the device is cooled while applying a 
sufficiently great high-frequency voltage between the electrodes, the 
liquid crystal molecules come to be aligned perpendicular to the plane of 
the substrates, thus returning to the original smectic A state. That is, 
the device becomes transparent. This is because the liquid crystal 
molecules have positive dielectric anisotropy and therefore align parallel 
to the applied electric field. 
The above states described in A) and B) are retained as long as required 
even after removal of the voltage applied between the electrodes, provided 
that the ambient temperature of the liquid crystal device is controlled so 
as not to exceed the phase transition temperature T.sub.N1. 
There are two ways to bring the device from the state (F) (opaque state) 
back to the state (T) (transparent state) shown in FIG. 5. 
C) The liquid crystal device is reheated till the liquid crystals turn into 
liquid, and then cooled while applying a sufficiently high voltage between 
the electrodes. 
D) An extremely high voltage is applied between the electrodes to forcibly 
bring the device from the state (F) back to the state (T). In this case, 
the liquid crystal device must be kept at the same temperature as the 
ambient temperature. 
Using the above characteristics, it is possible to write and erase 
optically readable (transparent or opaque) image information in a smectic 
liquid crystal device through selective application of voltage and heat. 
Voltage can be selectively applied to any specified pixels by scanning 
matrix electrodes arranged on the glass substrates, while heat can be 
applied to any specified pixels using a laser beam. 
FIG. 6 is a diagram showing the construction of any of the above smectic 
liquid crystal devices (optical image memories) 31R, 31G, and 31B. The 
liquid crystal device comprises two glass substrates 3a, a smectic liquid 
crystal layer 3b sandwiched therebetween, a transparent electrode 3c 
disposed on the left side of the liquid crystal layer 3b, an aluminum 
reflective film 3d disposed on the right side of the liquid crystal layer 
3b, and a Cr.sub.2 O.sub.3 absorption film 3e, which is a laser beam 
absorption film, disposed on the right side of the aluminum reflective 
film 3d. The transparent electrode 3c and the aluminum reflective film 3d 
constitute matrix electrodes as used in a known liquid crystal display, 
one of which serves as the scanning electrode and the other as the signal 
electrode, the electrodes being scanned by a high-frequency voltage 3f. 
Thus, it is possible to make the portion where the scanning and signal 
electrodes intersect function as a pixel, and to apply an electric field 
to any selected pixel by controlling the signal wave applied to the 
electrodes. Disposed on the right side of the liquid crystal device are a 
semiconductor laser unit and a converging lens for heating a selected 
pixel with a laser beam. It is therefore possible to heat any selected 
pixel by scanning with the laser beam and by turning on and off the laser 
beam. 
When light is projected onto the liquid crystal device from the left side 
(the reading side), the light is not reflected by the portion of the 
device where the liquid crystal layer 3b is in a molecule-diffused state 
(opaque state), but the light is reflected by the portion where it is in a 
liquid or transparent state because the light is transmitted through to 
the aluminum reflective film 3d and is reflected by this reflective film 
3d. 
(2) Description of the image writing unit and its adjacent parts 
Referring to FIG. 4, the image writing device 11 includes a semiconductor 
laser unit 32. The semiconductor laser unit 32 receives image information 
stored in the image memory 52, and emits a laser beam, the on-and-off 
operation of which is controlled according to the image information. The 
laser beam is reflected by a mirror 32b provided on a goniometer 32a, 
passes through a pickup lens (converging lens) 32c having a focusing 
function, and is projected onto one of the optical image memories (liquid 
crystal devices) 31R, 31G, or 31B. The goniometer 32a is used for the 
scanning operation of the laser beam. 
The light source 12a, the lenses 12b and 12c, and the color separation 
filter 12f (a part of the image reading device) are disposed on the right 
side of the optical image memories 31R, 31G, and 31B. The color separation 
filter 12f is a disk-shaped frame having an R filter 12f-R that transmits 
the light with wavelengths in the red region of light, a G filter 12f-G 
that transmits the light with wavelengths in the green region of light, 
and a B filter 12f-B that transmits the light with wavelengths in the blue 
region of light. By rotating the color separation filter 12f, one of the 
three filters is positioned to face the light reflected from one of the 
optical image memories. In practice, the R filter 12f-R faces the optical 
image memory 31R, the G filter 12f-G faces the optical image memory 31G, 
and the B filter 12f-B faces the optical image memory 31B. Therefore, when 
reading the image information stored in the optical image memory 31R, for 
example, only the light with wavelengths in the red region of the light 
reflected therefrom is transmitted through the color separation filter 
12f, for illuminating the photosensitive sheet. 
The optical image memories 31R, 31G, and 31B are fixed to a support block 
31 which is movable along a rail 33. A linear motor 34 is provided for 
moving the support block 31 along the rail 33, and under the control of 
this motor, each of the three optical image memories 31R, 31G, and 31B in 
this order is positioned to face the radiation area of the semiconductor 
laser unit 32 or the light source 12a. It is so constructed that the 
optical image memory which is positioned to face the semiconductor laser 
unit 32 is different from the one that is positioned to face the light 
source 12a. In this embodiment, when the Nth optical image memory is 
positioned to face the semiconductor laser unit 32, the (N-1)th optical 
image memory is positioned to face the light source 12a. In FIG. 4, the 
optical image memory 31R is positioned to face the light source 12a, while 
the optical image memory 31G is positioned to face the semiconductor laser 
unit 32. 
Image information written in the optical image memories 31R, 31G, and 31B 
will be retained for a long period of time. Therefore, the image 
information once written into any optical image memory using the 
semiconductor laser unit 32 can be extracted as many times as desired 
using the light source 12a (of the image reading device). 
(3) Description of the operation of the optical system 
FIGS. 7A to 7D show the procedure of the operation in which image 
information is written into and read out from the optical image memories 
31R, 31G, and 31B. The following describes how the writing and reading 
operations are performed. 
First, the optical image memory 31R is positioned to face the semiconductor 
laser unit 32, and image information stored in the R area of the image 
memory 52 is written into the optical image memory 31R using the 
semiconductor laser unit 32, as shown in FIG. 7A. After the writing 
operation is completed, the support block 31 moves so that the optical 
image memory 31G is positioned to face the semiconductor laser unit 32, 
and the optical image memory 31R to face the light source 12a, thus 
performing the writing of image information (stored in the G area of the 
image memory 52) into the optical image memory 31G simultaneously with the 
reading of the image information just written in the optical image memory 
31R, as shown in FIG. 7B. The next step proceeds in the same manner, in 
which the writing of image information (stored in the B area of the image 
memory 52) into the optical image memory 31B is performed simultaneously 
with the reading of the image information from the optical image memory 
31G, as shown in FIG. 7C. In the final step, the reading of the image 
information from the optical image memory 31B is performed, as shown in 
FIG. 7D, to complete the writing and reading operations. 
With the simultaneous performance of the reading and writing operations as 
described above, it is possible to shorten the total processing time as 
compared with the case in which these operations are performed separately. 
In the case of the above example in which three optical image memories are 
used, the total time can be shortened by the time required for the two 
writing operations shown in FIGS. 7B and 7C. 
The photosensitive sheet transport system and its operation 
(1) The construction of the photosensitive sheet transport system 
FIGS. 8A to 8G show the construction of the photosensitive sheet transport 
system, illustrating the respective steps of the transportation of the 
photosensitive sheet. 
It is assumed here that l denotes the length of the photosensitive sheet to 
be positioned on the exposure plate 23 so as to be subjected to the 
light-exposure process. In the case of a continuous image forming 
operation on the photosensitive sheet, image-forming areas l.sub.1, 
l.sub.2, etc., each having the light-exposure length l, are successively 
allocated on the photosensitive sheet, the first latent image being formed 
on the image-forming area l.sub.1, the second latent image on the 
image-forming area l.sub.2, and so on. Non-image areas b are disposed 
separating the image-forming areas l.sub.1, l.sub.2, etc. from one 
another. The photosensitive sheet transport system is controlled so that 
the transportation of the photosensitive sheet will be suspended in such a 
manner that the non-image areas b are positioned at the transport rollers 
22b, the transport rollers 22c, and the pressure rollers 25, respectively. 
It is also assumed here that a denotes the area on the photosensitive sheet 
that stays between the transport rollers 22c and the pressure rollers 25 
at the beginning of the image forming process. Since no image is usually 
formed on this area, it is desirable to keep the length of a as short as 
possible. A non-image area b is also disposed between the area a and the 
image-forming area l, and the photosensitive sheet transport system is 
controlled so that the transportation of the photosensitive sheet will be 
suspended in such a manner that this non-image area b is also positioned 
either at the transport rollers 22b, the transport rollers 22c, or the 
pressure rollers 25. 
The buffer roller 24 disposed downstream of the exposure plate 23 and 
transport rollers 22c is movable in the directions of arrows A and B shown 
in FIG. 8A. A motor (not shown) is provided for this linear movement of 
the buffer roller 24. The buffer roller 24, usually positioned in the home 
position (hereinafter called the HP), moves to positions 24-1, 24-2, and 
24-3, being driven by the motor. Upper right to the buffer roller 24 is a 
buffer section where the photosensitive sheet is transported by the buffer 
roller 24 moving to the positions 24-1, 24-2, and 24-3. The length of the 
photosensitive sheet transported into the buffer section is determined by 
the position of the buffer roller 24, the length being approximately equal 
to the image-forming area (light-exposure length) l with the buffer roller 
24 being at the position 24-1 as shown in FIG. 8C, and approximately 
double the image-forming area (light-exposure length) l with the buffer 
roller 24 being at the position 24-3 as shown in FIG. 8D. Sensors S1, S2, 
S3, and HPS are provided to detect the position of the buffer roller 24. 
The sensors S1, S2, S3, and HPS are activated when the buffer roller 24 
comes to the positions 24-1, 24-2, 24-3, and HP, respectively. 
(2) The operation of the photosensitive sheet transport system at the time 
of the image forming process 
FIGS. 10A to 10D are flowcharts illustrating the procedure of the image 
forming process. FIGS. 9A and 9B are timing charts for the image forming 
process. 
Single printing operation 
When an image is formed on a single image-receiving sheet with use of the 
apparatus that is used in the method in the invention, the buffer roller 
24 remains at the HP. FIG. 9A is a timing chart illustrating the single 
printing operation, and FIG. 10A shows the procedure thereof. 
Referring to FIG. 10A, when the printing operation switch is turned on 
after the number m of the sheets to be printed and other image forming 
conditions are input in steps n1 and n2, the image forming process is 
started according to the number m of the sheets to be printed. When the 
number m is 1, i.e., a single sheet is to be printed (step n3), the 
process proceeds to step n4 in which the exposure process, paper feeding, 
and a timer T.sub.1 are started. The "paper feeding" means the delivery of 
the image-receiving sheet from the paper cassette 26 by the rotation of 
the paper feed roller 26a, the delivered sheet being temporarily stopped 
at the timing roller 26b. The exposure process is controlled by the CPU 
51. 
When the exposure process is started, image information is written into and 
read out from the optical image memories 31R, 31G, and 31B in accordance 
with the procedure shown in FIGS. 7A to 7D, so that the image-information 
light is projected onto the photosensitive sheet to form a latent image 
thereon corresponding to the original full-color image. The exposure light 
(the image-information light) is projected over the area l.sub.1 shown in 
FIG. 8A. The time needed for the exposure process is approximately t.sub.1 
'. 
After completion of the exposure process (step n5), the pressure-transfer 
process starts; i.e., the image-receiving sheet is pressed against the 
latent image formed on the area l.sub.1, of the photosensitive sheet. The 
procedure of this pressure-transfer process will now be described. First, 
in step n6, the sheet-feeding rod 21c of the photosensitive sheet is 
unlocked (the solenoid 21e is energized), and at the same time, the 
pressure rollers 25 are started for rotation. Then, the photosensitive 
sheet, being pulled by the rotation of the pressure rollers 25, is drawn 
out from the cartridge 21. The photosensitive sheet is delivered out by 
the combined length of the areas a and l.sub.1. During the delivery of the 
photosensitive sheet, the image-receiving sheet, which has been conveyed 
from the paper cassette 26 into the timing rollers 26b in the preceding 
paper feeding operation of the step n4, is transported into the pressure 
rollers 25 to be pressed against the image-forming area l.sub.1 to form a 
colored image on the image-receiving sheet. The feeding of the 
image-receiving sheet is therefore started in step n8 with such timing 
that the image-receiving sheet is fed so as to be accurately placed on the 
image-forming area l.sub.1 for the pressure-transfer process. The above 
timely feeding of the image-receiving sheet is started when the timer 
T.sub.1 that was started at the beginning of the exposure process counts 
up to t.sub.2 (step n7). 
FIG. 10D is a flowchart illustrating the above-mentioned timely feeding of 
the image-receiving sheet, which is carried out by the rotation of the 
timing rollers 26b. In step n71, a timer starts at the same time that the 
timing roller 26b is started for rotation. When the time needed for the 
feeding of the image-receiving sheet of the length l elapses in step n72, 
the timing rollers 26b stop in step n73 to complete the timely feeding of 
the image-receiving sheet. After feeding the image-receiving sheet from 
the timing rollers 26b, if the feeding is not the last one (step n74), the 
paper feed roller 26a is again put into operation for feeding another 
image-receiving sheet from the paper cassette 26 in step n75. In the 
single printing operation, since only a single image forming process is 
performed, another paper feeding operation (step n75) is not performed. 
Referring back to FIG. 10A, after completion of the pressure-transfer 
process (step n9), the sheet-feeding rod 21c of the photosensitive sheet 
is locked, and the pressure rollers 25 are stopped in step n10, so that 
the photosensitive sheet cannot be drawn out or transported any more. This 
is the end of the single printing operation. At this time, the next 
image-forming area is positioned on the exposure plate 23. 
Multiple printing operation 
FIG. 9B is a timing chart for a multiple printing operation, and FIGS. 10A 
to 10D show the procedure thereof. The following description deals with a 
multiple printing operation for printing 6 sheets. In the multiple 
printing operation, the buffer roller 24 is moved in such a way that the 
image-forming area with a latent image formed thereon is first drawn out 
into the buffer section, and then fed to the pressure rollers 25 for the 
pressure-transfer process while the light-exposure process is being 
performed on another image-forming area of the photosensitive sheet. Since 
the light-exposure and pressure-transfer processes are simultaneously 
performed, it helps to speed up the image forming operation as a whole. In 
FIG. 9B, l.sub.1, l.sub.2, etc. indicate the image-forming areas which are 
positioned on the exposure plate 23 to be exposed to light or which pass 
through the pressure rollers to be pressed against an image-receiving 
sheet at the time of the corresponding processes. Also, the numeral 
attached to the upper right corner at the end of each operating period of 
the buffer motor and the pressure rollers indicates the position of the 
buffer roller at the end of that operation (i.e., the numeral 1 denotes 
the position 24-1 of the buffer roller 24 shown in FIG. 8, 2 denotes the 
position 24-2, and 3 denotes the position 24-3). 
Referring to FIG. 10A, the printing operation switch is pressed after the 
image forming conditions are input (steps n1, n2). If the number m of the 
sheets to be printed with an image is more than 1 (in step n3), the 
process proceeds to step n21 of FIG. 10B, in which 1 is added to the 
number r of the light-exposure processes that have been completed, the 
further process being performed according to that value. 
For exposure for the first sheet which corresponds to the image-forming 
area l.sub.1, the process proceeds from step n22 of FIG. 10B to step n41 
of FIG. 10C and then to step n42, in which the light-exposure process, 
paper feeding, and timer T.sub.1 are started. For the first exposure 
process, image information is written into and read out from the optical 
image memories 31R, 31G, and 31B as illustrated in FIGS. 7A to 7D, the 
time required for the exposure process being approximately t.sub.1 '. In 
this first light-exposure process, a latent image corresponding to an 
original full-color image is formed on the image-forming area l.sub.1 
which is positioned on the exposure plate 23 as shown in FIG. 8A. At the 
end of the exposure (step n43), the sheet-feeding rod 21c of the 
photosensitive sheet is unlocked to allow the photosensitive sheet to be 
drawn out from the cartridge 21, while the linear movement of the buffer 
roller 24 is started in step n44. The buffer roller 24 travels in the 
direction of arrow A shown in FIG. 8B by the driving of the buffer motor 
till it reaches the position 24-2, where the sensor S2 is activated (step 
n45). When the sensor S2 is activated, the sheet-feeding rod 21c of the 
photosensitive sheet is locked, and the buffer roller 24 is stopped, to 
stop the transportation of the photosensitive sheet in step n46. At this 
point of time, the portion of the photosensitive sheet holding the area a 
and the image-forming area l.sub.1 with the latent image formed thereon is 
positioned in the buffer section, and the next image-forming area l.sub.2 
is positioned on the exposure plate 23 as shown in FIG. 8B. 
Thereafter, the process proceeds through steps n21, n22, and n41 to step 
n47 for the light-exposure process for the second sheet, which corresponds 
to the image-forming area l.sub.2. For exposure for the second and 
subsequent sheets, since the image information is already written in the 
optical image memories 31R, 31G, and 31B, only the reading process is 
required, and thence the time required for the exposure process with 
reading only is approximately t.sub.1. In the step n47, the timer T.sub.1 
and the light-exposure process for the image-forming area l.sub.2 are 
started, and at the same time, the pressure rollers 25 are driven for 
rotation, pulling the photosensitive sheet stored in the buffer section 
into the pressure rollers 25. This causes the buffer roller 24 to move in 
the direction of arrow B into the position 24-1 as shown in FIG. 8C. Thus, 
at the time of the exposure for the second sheet, the area a of the 
photosensitive sheet is fed to the pressure rollers 25 by the rotation of 
the pressure rollers 25, where neither the feeding of the image-receiving 
sheet nor the pressure-transfer process is performed. 
When the buffer roller 24 is moved in the direction of arrow B into the 
position 24-1 to activate the sensor S1, the rotation of the pressure 
rollers 25 stops (steps n48 and n49). At this point of time, the length of 
the photosensitive sheet equivalent to a single image-forming area (the 
image-forming area l.sub.1) is positioned in the buffer section, as shown 
in FIG. 8C. After the suspension of the rotation of the pressure rollers 
25, when the timer T.sub.1 counts up to t.sub.1 in step n50, the 
sheet-feeding rod 21c is unlocked and the buffer roller 24 is driven in 
step n51 to move in the direction of arrow A to draw out another length of 
the photosensitive sheet. 
For the pressure-transfer process, the timely feeding of the 
image-receiving sheet by the rotation of the timing roller 26b must be 
started earlier than the pressure-transfer process starts by a given time, 
i.e. by the time needed for the image-receiving sheet fed by the timing 
roller 26b to reach the pressure rollers 25. Therefore, while another 
length of the photosensitive sheet is being drawn out by means of the 
buffer roller 24 driven in the step n51, the timely feeding of the 
image-receiving sheet is started for the first pressure-transfer process 
that will be performed in one of the succeeding steps later described. In 
this example, the timer T.sub.1, which is started at the beginning of the 
exposure process for the second sheet, is also used to determine the point 
of time at which the timely feeding of the image-receiving sheet is 
started for the first pressure-transfer process. When the timer T.sub.1 
counts up to t.sub.2 ' in step n52, the timely feeding of the 
image-receiving sheet is started in step n53. 
When the buffer roller 24, which was driven to move in the direction of 
arrow A in the step n51, reaches the position 24-3, the sensor S3 is 
activated in step n54, and the sheet-feeding rod 21c is locked and the 
buffer roller 24 stops in step n55, thus stopping the delivery of the 
photosensitive sheet. As a result, the image-forming area l.sub.2 on which 
a latent image has been formed in the second light-exposure process is 
transported into the buffer section, so that the length of the 
photosensitive sheet equivalent to two image-forming areas (l.sub.1 and 
l.sub.2) is positioned in the buffer section, and the next (third) 
image-forming area l.sub.3 is positioned on the exposure plate 23 for the 
third exposure process, as shown in FIG. 8D. (This sheet-transporting 
operation (steps n51, n54, n55) by which an image-forming area with a 
latent image just formed thereon is transported into the buffer section is 
hereinafter referred to as the "delivery operation".) 
After the completion of the above-mentioned "delivery operation", the 
process proceeds again to the steps n21, n22, and n41, and back to the 
step n47 for the third light-exposure process for exposing the third 
image-forming area l.sub.3. 
At the time of the third light-exposure process for the image-forming area 
l.sub.3, the image-forming area l.sub.1 on which the latent image was 
formed in the first light-exposure process is transported from the buffer 
section into the pressure rollers 25 for the first pressure-transfer 
process (the steps n47-n49), in which the image-receiving sheet is pressed 
on the latent image of the image-forming area l.sub.1, resulting in a 
colored image on the image-receiving sheet. In this way, after the 
light-exposure processes for the first and second image-forming areas 
l.sub.1 and l.sub.2 are completed, the pressure-transfer process for the 
first image-forming area l.sub.1 is performed simultaneously with the 
light-exposure process for the third image-forming area l.sub.3. Since two 
image-forming areas with latent images thereon are stored in the buffer 
section before the simultaneous performance of the light-exposure and 
pressure-transfer processes, the light-exposure process for the Nth 
image-forming area l.sub.N (N is an integer of 3 or more) is performed 
simultaneously with the pressure-transfer process for the (N-2)th 
image-forming area l.sub.(N-2). 
After the simultaneous performance of the third light-exposure process and 
the first pressure-transfer process is completed (step n50), the 
above-mentioned "delivery operation" is performed again so that the 
image-forming areas l.sub.2 and l.sub.3 are positioned in the buffer 
section (steps n51, n54, and n55). In the meantime, the timely feeding of 
the image-receiving sheet for the second pressure-transfer process is 
started in step n53. 
The above-mentioned simultaneous performance of the light-exposure and 
pressure-transfer processes and the "delivery operation" are alternately 
repeated until the sixth (last) image-forming area l.sub.6 is transported 
into the buffer section as shown in FIG. 8E. The time required for the 
simultaneous light-exposure and pressure-transfer operation and the time 
for the "delivery operation" are both kept constant during the whole 
printing process. 
The buffer section is thus provided adjoining the exposure plate, the 
photosensitive sheet that holds latent images being continuously stored in 
the buffer section, thus preventing the wasteful use of the photosensitive 
sheet. Since the light-exposure and pressure-transfer processes are 
simultaneously performed, while performing the delivery of the 
photosensitive sheet at a relatively high speed in the meantime, the above 
construction offers the advantage that the total image forming time is 
shortened. Also, because of the employment of the entire surface exposure 
method, the above construction offers the further advantage that the 
light-exposure time is shortened. 
When the last "delivery operation" is performed after completion of the 
exposure for the specified number of image-forming areas (6 image-forming 
areas) (FIG. 8E), the process proceeds through steps n21 and n22 to step 
n23, where the pressure rollers 25 are driven for rotation, as has been 
done theretofore, to perform the pressure-transfer process for the 
image-forming area l.sub.5. As a result, as shown in FIG. 8F, only the 
image-forming area l.sub.6 holding the last latent image is stored in the 
buffer section. Thereafter, the area a of the photosensitive sheet to be 
positioned between the transport rollers 22c and the pressure rollers 25 
is drawn out into the buffer section, as shown in FIG. 8G (steps n26, n29, 
and n30). In the meantime, the timely feeding of an image-receiving sheet 
is started at the specified timing (steps n27 and n28). The 
image-receiving sheet fed at the specified timing reaches the pressure 
rollers 25 at the time when the pressure rollers 25 are driven (step n31) 
for the pressure-transfer process for the last image-forming area l.sub.6. 
When the buffer roller 24 reaches the HP, the sensor HPS is activated so 
that the rotation of the pressure rollers 25 is suspended (steps n32 and 
n33), to complete the last pressure-transfer process, the photosensitive 
sheet transport system being brought back into the original state shown in 
FIG. 8A. 
As described above, according to the invention, the buffer roller is 
operated to transport the photosensitive sheet for continuous image 
forming processes so that the area a where no image is formed is not 
interposed between the image-forming areas l.sub.1, l.sub.2, . . . , thus 
preventing the wasteful use of the photosensitive sheet. 
In this example, description has been given, dealing with the apparatus in 
which an image forming process is carried out using three optical image 
memories into which image information of red, green, and blue color 
components of an original full-color image is written. Alternatively, the 
image information may be of monochrome, or more than three optical image 
memories may be used. In that case also, if the construction is so made as 
to enable simultaneous writing and reading of image information, the 
processing time can be shortened. Also, in the above-mentioned example, 
during the writing of the Nth image information, the (N-1)th image 
information is read out, but alternatively, it may be so designed as to 
perform the reading of the image information numbered lesser than (N-1), 
for example, the reading of (N-2) or (N-3) image information. 
As described above, according to the present invention, it is possible to 
simultaneously perform the writing and reading of image information in the 
optical image memories, thereby saving the apparent time for writing or 
reading and shortening the image processing time as a whole. 
It is understood that various other modifications will be apparent to and 
can be readily made by those skilled in the art without departing from the 
scope and spirit of this invention. Accordingly, it is not intended that 
the scope of the claims appended hereto be limited to the description as 
set forth herein, but rather that the claims be construed as encompassing 
all the features of patentable novelty that reside in the present 
invention, including all features that would be treated as equivalents 
thereof by those skilled in the art to which this invention pertains.