Printing system

A printing system is provided which allows selected characters or symbols to be emphasized without increasing the density thereof. A video signal containing printing data for a character to be emphasized is delayed and logically added to an undelayed video signal to expand the "black" portion of the signal on the time axis.

BACKGROUND OF THE INVENTION 
This invention relates to printing systems, and more particularly to a 
printing system in which some characters or symbols are printed with 
additional emphasis. 
In printing sentences, sometimes it is necessary to print particular 
characters, phrases or symbols with additional emphasis. In order to meet 
this requirement, in an impact type printer, such characters, phrases or 
symbols are printed plural times so that they become higher in density. 
However, in most non-impact type printers, even if the same position is 
printed plural times as described above, the density is not increased as 
expected; that is, it is practically difficult to increase the visual 
effect of the printed characters, etc. For instance, in a printer 
employing a thermal transfer system, a recording medium coated with 
thermally soluble or thermally sublimating ink is used in a manner such 
that the ink at the portion where printing is effected is heated so as to 
be transferred onto the recording sheet. Under normal recording 
conditions, the ink thus heated is substantially completely transferred 
onto the recording sheet. Accordingly, even if the same part of the 
recording medium is again heated, the amount of transferred ink is 
scarcely increased. In other words, the same position is printed plural 
times as described above, but the density of the position is not increased 
to the extent that it is clearly distinguishable from that of other 
printed positions. Furthermore, it should be noted that in the thermal 
transfer type printer, the recording medium is placed in surface contact 
with the recording sheet, so that the ink is transferred from the former 
to the latter. Therefore, it is impossible to employ a method in which, 
after the recording medium used for recording is peeled off the recording 
sheet, an unused portion of the recording medium is brought into contact 
with the recording sheet, to increase the amount of ink transferred. 
SUMMARY OF THE INVENTION 
In view of the foregoing, an object of this invention is to provide a 
printing system for a printer in which printing is carried out using an 
electrical video (pattern) signal; in which printing can be carried out 
with emphasis, without increasing the density of printed characters, etc. 
In the invention, a delay circuit 1 and a logical summation circuit (or an 
OR circuit) 2 are provided in the printer. When an emphasized printing 
instruction signal 3 for performing printing with extra emphasis is 
produced, a video signal 4 and a delayed video signal obtained by delaying 
the video signal 4 for a predetermined period of time are subjected to 
logical summation (or ORed) to obtain an emphasized video signal 6, the 
emphasized video signal 6 being applied to the printing section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 shows an emphasized video signal production section of a printer. In 
this embodiment, a D latch 1A (which is for instance a bipolar TTL IC 7474 
made by Texas Instrument Co.) is employed as the delay circuit, and a 
two-input OR gate 2A (which is for instance a bipolar TTL IC 7432 made by 
Texas Instrument Co.) is employed as the logical sum circuit. 
A character generator (not shown) in the printer outputs a video signal 
which is sampled by sampling clock signal shown in FIG. 3(a), whereby a 
video signal 4 (FIG. 3(b)) representing particular lines of a character to 
be printed with emphasis is applied to an input terminal D of the D latch 
1A. A clock signal 8 (FIG. 3(c)) obtained by frequency-dividing the 
aforementioned sampling clock signal is supplied to the clock input 
terminal C of the D latch 1A at all times. On the other hand, an 
emphasized printing instruction signal 3 is supplied to the clear terminal 
CLR of the D latch 1A for the period during which a character is to be 
printed with emphasis, so that clearing the D latch 1A is inhibited. 
Therefore, the video signal 4 of (for example) the character "B" is 
supplied to the D latch 1A, and a delayed video signal 5 in which the 
"black" image signal is delayed is provided at the output terminal Q of 
the D latch 1A in synchronization with the rise of the clock signal 8. The 
video signal 4 and the delayed video signal 5 are applied to the two-input 
OR gates 2A. As a result, an emphasized video signal 6 is obtained in 
which the range of the "black" image signal on the time axis is increased, 
as shown in FIG. 3(e). 
The character generator outputs the video signal 4 for every line as 
described above. When these video signals 4 thus outputted are replaced by 
the emphasized video signals for the portions where printing should be 
effected with emphasis, the printing section (not shown) performs printing 
with a pattern corresponding to the time-expanded video signals. 
FIG. 4(a) illustrates the character "B" as printed directly by the video 
signals 4, while FIG. 4(b) shows the character "B" as shifted along the 
time axis by the aforementioned delayed video signals 5. With the 
emphasized vide signals 6, an emphasized printed character "B" is obtained 
by overlapping these characters on the same time axis, as shown in FIG. 
4(c). 
In the invention, emphasized printing is carried out by changing the 
pattern of the characters. Therefore, in the invention, unlike a printing 
system in which a character must be printed plural times, the recording 
speed is not decreased even if emphasized printing is carried out. 
In the above-described embodiment, emphasized printing is carried out by 
expanding the character pattern in the line direction (or in the main 
scanning direction); however, emphasized printing may be carried out by 
expanding the character pattern in the column direction (or in the 
auxiliary scanning direction as well). In the simplest system for 
practicing the former, a delay memory for one line is provided in the 
printer, and the output of the delay memory and a video signal bypassing 
the delay memory are subjected to logical summation (or ORed) only when 
emphasized printing is to be carried out. The emphasized printing method 
of the invention is not limited to only the above-described processes; 
that is, a method in which the character pattern is expanded in both the 
line and column directions may be effectively employed. 
In the above-described embodiment, the video signal was described as being 
supplied by the character generator of the printer; however, the video 
signal may be supplied, for instance, from a host system.