Thermal printer with printing plate making mode

A thermal printer has a plurality of head elements which are selectively energized for periods of time corresponding to tone levels of image densities. The thermal printer has a mode for recording necessary printing plate making information data such as print positioning marks and color information data or the like outside an effective image area to facilitate preparing block copies.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a thermal printer and, more particularly, 
to an improvement in a thermal printer suitably used for preparing a block 
copy. 
2. Description of the Prior Art 
A typical conventional thermal printer is shown in FIG. 1. A thermal ink 
ribbon 3 overlays recording paper 2 wound around a platen 1. The thermal 
ink ribbon 3 and the recording paper 2 are selectively heated by a thermal 
head 4 to transfer ink from the ink ribbon 3 to the recording paper 2. In 
order to print a halftone image in a thermal printer, an image 5, divided 
into 1024.times.512 picture elements, is formed by scanning with the 
thermal head 4 having 512 heating elements 6 in the direction V indicated 
by the arrow shown in FIG. 2. In this case, the thermal head 4 is 
intermittently moved relative to the paper 1024 times for completing an 
image. The heating elements 6 are seleotively energized and heated for 
periods of time corresponding to the image densities of the picture 
elements. The elements 6 are intermittently stopped to print a line 
extended in the V direction (which is here-in-after referred to as a V 
line). It should be noted the head 4 in the printer of FIG. 1 is fixed, 
and that the platen 1 is intermittently rotated to perform the required 
scanning. 
In order to reproduce a full-color image, four ink ribbon sheets such as Y 
(yellow), M (magenta), C (cyan), and B (black) color ink ribbon sheets are 
used, and scanning is performed one color at a time. In some case, B 
(Black) color printing may be omitted. 
The above conventional printer is disclosed in U.S. Pat. No. 4,496,955. 
In the field of full-color printing, when four block copies, i.e., Y, M, C, 
and B copies are prepared from a single full-color image, the full-color 
image is separated by a color scanner to obtain four monochromatic images 
whose densities respectively correspond to levels of Y, M, C, and B color 
components. These monochromatic images are converted into dot pictures to 
prepare the corresponding block copies. 
The above method requires an expensive color scanner, and color separation 
is also cumbersome and time-consuming. 
SUMMARY OF THE INVENTION 
It is a first object of the present invention to provide a thermal printer 
capable of easily preparing block copies for the respective colors by 
adding a simple printing plate making mode to a conventional printer 
without using an expensive color scanner. 
It is a second object of the present invention to provide a thermal printer 
wherein alignment mark data and color identification mark data (gray scale 
data or color bar data) are stored in a memory and can be selectively read 
out during printing. 
It is a third object of the present invention to provide a thermal printer, 
wherein the alignment marks are automatically printed outside an effective 
image area at predetermined positions with high precision.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In this embodiment, Y, M, C, and B block copies are prepared by the thermal 
printer. The thermal printer has a printing plate making mode. In the 
printing plate making mode, Y, M, C, and B ink ribbon sheets are not used, 
but only B (black) ink ribbon is used. The same ink ribbon is used for 
each one of the four colors, and thus four monochromatic images 
corresponding to the densities of these colors are obtained. The four 
monochromatic images are converted into four dot pictures to prepare four 
block copies. 
In this embodiment, print positioning marks 8.sub.1 to 8.sub.4 and color 
information data 9.sub.1 and 9.sub.2 are also recorded at predetermined 
positions of an image area 7, as shown in FIG. 4. Since the marks 8.sub.1 
to 8.sub.4 and information data 9.sub.1 and 9.sub.2 are recorded outside 
the effective image area, the four block copies can be easily positioned 
at the time of full-color image printing, and the color of each block copy 
can be easily identified. 
Referring to FIG. 4, the image area 7 includes an effective image area 10 
used for actually recording an image. Left, right, upper, and lower blank 
portions 11.sub.1 to 11.sub.4 each having a predetermined width are formed 
to define the effective image area 10 in the image area 7. The number of 
picture elements along the H direction of the effective image area 10 is, 
e.g., 784, and the number of picture elements along the V direction is, 
e.g., 466. 
The print positioning marks 8.sub.1 to 8.sub.4 are recorded as crosses at 
upper and lower predetermined positions of the left and right blank 
portions 11.sub.1 and 11.sub.2. The color information data 9.sub.1 and 
9.sub.2 of "Y" representing yellow are formed substantially at the centers 
between the upper and lower marks. It should be noted that the color 
information data 9.sub.1 and 9.sub.2 represent "Y", "M", "C", or "B" 
according to a given color. The marks 8.sub.1 to 8.sub.4 and information 
data 9.sub.1 and 9.sub.2 are formed within the area where 466 picture 
elements are present along the V direction of the effective image area 10. 
Therefore, the marks 8.sub.1 to 8.sub.4 and information data 9.sub.1 and 
9.sub.2 can be recorded by the 466 heating elements 6 (of the thermal head 
4) used for recording an image of the effective image area. These marks 
may be recorded in the upper and lower blank portions 11.sub.3 and 
11.sub.4, as shown in FIG. 5. In this case, the marks 8.sub.1 to 8.sub.4 
and information data 9.sub.1 and 9.sub.2 can be recorded by the heating 
elements 6 outside those (a total number of heating elements 6 along the V 
direction is 512) used for recording an image within the effective image 
area. Referring to FIGS. 4 or 5, the pair of print positioning marks 
8.sub.1 and 8.sub.2 and the pair of print positioning marks 8.sub.3 and 
8.sub.4 are respectively recorded in the left and right blank portions 
11.sub.1 and 11.sub.2, or the pair of print positioning marks 8.sub.1 and 
8.sub.3 and the pair of print positioning marks 8.sub.2 and 8.sub.4 are 
respectively recorded in the upper and lower blank portions 11.sub.3 and 
11.sub.4. However, one print positioning mark may be recorded in each of 
the left and right blank portions 11.sub.1 and 11.sub.2 or each of the 
upper and lower blank portions 11.sub.3 and 11.sub.4. Similarly only one 
of the color information data 9.sub.1 and 9.sub.2 may be used in the 
pattern shown in FIGS. 4 or 5. The pattern of the print positioning marks 
8.sub.1 to 8.sub.4 and the symbols of the color information data 9.sub.1 
and 9.sub.2 may be modified by use of other shapes and symbols. 
FIG. 3 shows an embodiment of the thermal printer having the printing plate 
making mode. In this case, an image obtained from a video signal is 
recorded. 
Referring to FIG. 3, the gain of a video signal Sv is controlled by a white 
peak AGC (Automatic Gain Control) circuit 12, and a one-frame 
AGC-controlIed video signal is written in a frame memory 13 in the form of 
digital data signals. A signal read out from the memory 13 is converted 
into an analog signal. An A/D converter (not shown) is connected to the 
input terminal of the memory 13, and a D/A converter (not shown) is 
connected to the output terminal of the memory 13. The video signal read 
out from the memory 13 is converted by a Y, M, C converter 14 from R, G 
and B signal components to Y, M, and C signal components. The converted 
signal is suppIied to a white pedestal addition circuit 15. A white 
pedestal level pulse is added to the converted signal during the blanking 
period. The gain of the signal with the pedestal level is controlled by a 
black peak AGC circuit 16. The AGC-controlled signal from the black peak 
AGC circuit 16 is supplied to a color masking circuit 17 and a signal 
processor 18. A switch 19a is operated to sequentially select the Y, M, 
and C components. In the normal printing mode, a switch 19b is set in the 
position of a contact a. However, in the print plate making mode, the 
switch 19b is set in the position of a contact b. In the normal printing 
mode, undercolor removal of the Y M, and C signal components is performed 
in the color masking circuit 17, and the resultant signal oomponents are 
supplied to a correction circuit 20 through the switches 19a and 19b. In 
the print plate making mode, signal processing (e.g., density conversion 
in addition to undercolor removal) for print plate making is performed, 
and the resultant color components are supplied to the correction circuit 
20 through the signal processor 18 and the switch 19b. 
Necessary correction such as edge correction is performed in the correction 
circuit 20. The corrected signal is converted into a digital signal by an 
A/D converter 21. The digital signal from the A/D converter 21 is applied 
to a printing control circuit 22. The print positioning marks 8.sub.1 to 
8.sub.4 and the color information data 9.sub.1 and 9.sub.2 are added to 
the digital signal by the control circuit 22. At the same time, the 
control circuit 22 also performs predetermined correction operations. An 
output from the printing control circuit 22 is supplied to a head unit 23 
which includes a head driver and the thermal head 4. Information is then 
recorded by the head unit 23 on recording paper (not shown). 
In the normal printing mode, Y, M, and C, components in an order of Y, M, 
and C are sequentially recorded on single recording paper, to obtain a 
single full-color image along the V direction. In the print plate making 
mode, only black ink is used, and the paper is scanned in the order of Y, 
M, C, and B. Recording progresses in the V line direction, thereby 
obtaining four monochromatic images which respectively correspond to Y, M, 
C, and B images. 
FIG. 6 shows a detailed arrangement of the printing control circuit 22. 
In this embodiment, the energization time of each heating element 6 of the 
thermal head 4 is controlled according to the required density of the 
image. For this purpose, a control signal comprises a PWM (Pulse-Width 
Modulated) signal having a pulse width corresponding to the density of 
each picture element. 
Referring to FIG. 6, image data from the A/D converter 21 (FIG. 3) is 
supplied to a data buffer 24 associated with a CPU 25 in the printing 
control circuit 22. The CPU 25 is operated in response to a mode change 
signal, a color change signal, and other timing signals, all of which are 
applied to a control timing interface 26. The CPU 25 generates address 
data signals for a ROM 27 and a correction data ROM 28, in response to the 
image data, the color change signal, and so on. The ROM 27 stores data 
representing the marks outside the effective image area. The address data 
signals are supplied to the ROMs 27 and 28. The ROM 27 stores marking data 
for displaying the print positioning marks 8.sub.1 to 8.sub.4 and the 
color information data 9.sub.1 and 9.sub.2, as shown in FIGS. 4 and 5. The 
marking data is read out at predetermined times in response to the address 
data signals supplied from the CPU 25. The readout marking data is sent to 
the data buffer 24. The ROM 28 stores correction data such as gamma 
correction data. The correction data is read out at predetermined times in 
response to the address data signals supplied from the CPU 25. The readout 
data is sent to the data buffer 24. 
The data buffer 24 receives the image data, the marking data, and the 
correction data in units of V lines. The V line data is written from the 
buffer into a one-line RAM 29, in response to address data supplied from 
an address counter 31. 
An oscillator 30 generates clock pulses (or a clock) CK having a 
predetermined pulse repetition rate or frequency. The clock CK is supplied 
to the CPU 25, the address counter 31, and a frequency dividing counter 
32. The address counter 31 addresses the data in the RAM 29 for writing 
and reading out the single line of data stored therein, in series. 
A reference tone level generator 33 generates density reference level data 
representing one of several tone levels every time a carry pulse P1 is 
sent from the frequency dividing counter 32 thereto. In this embodiment, 
the density is represented by one of 32 tone levels D1 to D32, for 
example. The reference levels D1 to D32 are sequentially generated and 
supplied to a comparator 34. If the reference level D1 is generated, 466 
data signals of the first V line are sequentially read out from the RAM 29 
and are sequentially compared with the level D1. If the readout data has a 
level higher than the level D1, the comparator 34 generates a logic "1" 
(i.e., high level). Otherwise, the comparator 34 generates a logic "0" 
(i.e., low level). The output from the comparator 34 is stored at the 
corresponding address of a latch 35. When comparison associated with the 
level D1 is completed, the contents stored in the latch 35 are supplied to 
the corresponding heating elements 6 in the thermal head 4 through a head 
driver 36. The heating eIements 6 which receive the logic "1" are 
energized to perform printing. During printing associated with the 
reference level D1, the next 466 data signals are sequentially compared 
with the reference level D2, and the sequential outputs of the comparator 
34 are latched by the latch 35 and are applied to the thermal head 4 
through the head driver 36, thereby energizing the heating elements 6 
which receive the logic "1". Similarly, the heating elements 6 are 
energized when the result of the comparison, respectively, with the 
reference levels D2 to D32 represents a logic "1". However, when the 
comparison result represents a logic "0", the corresponding heating 
elements 6 is deenergized. In this case, the energization pulse for each 
of the heating elements 6 comprises a PWM pulse having a pulse width 
corresponding to the density of the picture element pixel corresponding to 
the heating element 6. 
When the printing of one V line is completed, the tone level generator 33 
is reset in response to a carry pulse P2 from a counter 37 which receives 
the pulse P1 and effects a 1/32 frequency-dividing. 
When the first V line is completely printed, the drum 1 in FIG. 1 is 
rotated by one pitch of the picture element and is stopped. Data of the 
second V line is converted into the PWM signals, and information 
represented by the PWM signals is printed in the same manner as described 
above. When printing is completed, the drum 1 is rotated by one pitch of 
the picture elements. The above operation is repeated to complete scanning 
along the H direction, thereby printing the entire image. 
The print positioning marks 8.sub.1 to 8.sub.4 and the color information 
data 9.sub.1 and 9.sub.2 are recorded as data representing the marks 
outside the effective image area. However, the data representing the marks 
outside the effective image area may include other necessary print plate 
making data, such as gray scale data and color bar data. The gray scale 
data and the color bar data may be stored in the ROM 27 and can be 
selectively read out and printed in the blank portions 11.sub.1 to 
11.sub.4. 
FIGS. 7A and 7B constitute a flow chart for executing printing by using the 
recording pattern of FIG. 4 in the block-making mode. 
Printing is started in step (1), and data representing the marks outside 
the effective area is checked in step (2). In particular, the CPU 25 
checks in step (2) that the color information data 9.sub.1 and 9.sub.2 are 
properly received. In step (3), the data representing the marks outside 
the effective image area is set into the RAM 29, to print the 
predetermined marks or the like. In step (4), the data is read out from 
the RAM 29 and is transferred to the head unit 23 to print the data. The 
CPU 25 checks in step (5) that the predetermined marks have been properly 
printed. The CPU 25 determines in step (6) whether printing of the 
predetermined marks is completed. If not, the flow returns to step (2) and 
printing continues. If YES in step (6), the flow advances to step (7). In 
step (7), the currently printed marks are checked to be located on the 
printing start or end side, i.e., in the blank portion 11.sub.1 or 
11.sub.2 in FIG. 4. The CPU 25 determines in step (8) whether the marks 
are printed on the printing start side, i.e., in the blanking portion 
11.sub.1. If YES in step (8), i.e., the marks 8.sub.1, 8.sub.2 and 
information data 9.sub.1 are printed in the blank portion 11.sub.1, the 
flow advances to step (9) to print the effective image 10. 
In step (9), the video signal SV is A/D converted. In step (10), correction 
data is read out from the ROM 28 and added to the digital video signal to 
obtain printing data. The printing data is set into the RAM 29 in step 
(11). In step (12), the data is read out from the RAM 29 and is 
transferred to the head unit 23, thereby printing the image data. 
The CPU 25 checks printing of the video signal in step (13) and determines 
in step (14) whether printing is completed. If NO in step (14), the flow 
returns to step (9). However, if YES in step (14), the flow returns to 
step (2). 
In step (2) and the subsequent steps (3), (4), . . . (7), printing of the 
marks 8.sub.3, 8.sub.4 and information 9.sub.2 in the blank portion 
11.sub.2 is performed. If NO in step (8), the CPU 25 determines that the 
marks are printed on the printing end side (i.e., the blank portion 
11.sub.2). In this case, the flow advances to step (15), and printing is 
ended. 
Referring to FIGS. 7A-7B, in the normal printing mode, the flow jumps from 
step (1) to step (9), and the operations in steps (9) to (14) are 
performed. If YES in step (14), printing is ended. 
When printing is performed according to the recording pattern in FIG. 5 in 
the block-making mode, data representing the marks (i.e., the marks 
8.sub.1 to 8.sub.4 and information data 9.sub.1 and 9.sub.2) outside the 
effective image area is equivalently dealt as the image data. In this 
case, the operations in steps (9) to (14), i.e., the operations in the 
normal printing mode, are performed. However, it should be noted that the 
data set into the RAM 29 includes image data and also the data 
representing the marks outside the effective image area. 
According to the preferred embodiment of the present invention as described 
above, Y, C, M, and B block copies can be easily prepared. In addition, 
the print positioning marks 8.sub.1 to 8.sub.4, the color information data 
9.sub.1 and 9.sub.2, or the like of each block copy can be automatically 
printed at predetermined positions of the image area with high precision. 
It is apparent that various modifications and additions can be made in the 
apparatus of the present invention without departing from the essential 
feature of novelty thereof, which are intended to be secured by the 
appending claims.