Printing apparatus

A printing apparatus for serial printing by displacement of a printing head, in which a discriminating circuit identifies the typefont of the printing head mounted on the carriage, and a coincidence circuit compares the result of typefont identification with the typefont to be printed and provides alarm if the two are different.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a printing apparatus, and more 
particularly to a printing apparatus with several interchangeable printing 
heads for obtaining desired typefont. 
2. Description of the Prior Art 
In the printing apparatus, for example serial thermal printers, the 
displacement of the carriage having a thermal printing head has generally 
been achieved by a stepping motor because of simplicity in drive circuit 
and ease in control for performing reciprocating motion. However such a 
drive system has been associated with a drawback that the moving pitch of 
the carriage has to be constant because of the constant rotating angle of 
the stepping motor, eliminating the possibility of employing plural 
typefonts different in size and shape for the characters. 
In order to avoid said drawback, the present applicant has disclosed, in 
its Japanese patent application No. 116845/1980, a printing apparatus 
capable of automatically regulating the printing pitch according to the 
typefont of the printing head. In said printing apparatus, however, the 
user has not necessarily been assuring whether the printing is achieved 
with the desired typefont. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a printing apparatus 
capable of assuring the printing with the characters of a desired 
typefont. 
Another object of the present invention is to provide a printing apparatus 
capable of prohibiting the printing operation with a typefont other than 
the character information stored in a memory.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a schematic block diagram showing an embodiment of the present 
invention, wherein a servo motor drive circuit 1 drives a servo motor 3 
through an amplifier 2. Said servo motor 3 is provided with position 
detectors 4, 5 of which output signals are amplified by amplifiers 6, 7. 
Thus, along with the rotation of the servo motor 3, two position detectors 
4, 5 composed of slits or optical elements generate pulse signals of 
different timings. 
Said servo motor 3 is mechanically linked, through unrepresented gears or 
wires, to a carriage 8 having a thermal printing head 9 composed of a 
column of plural heat-generating elements, which performs reciprocating 
motion in the printing direction along with the rotation of the servo 
motor 3. 
On the carriage 8 there is provided a connector 10 as shown in FIG. 2 for 
supporting and electrically connecting the thermal head 9 in 
interchangeable manner. Facing the heat-generating elements of the thermal 
head 9 there are provided a recording paper 11 and a platen 12, to which 
the thermal head 9 is continuously maintained in contact during the 
printing operation. 
Again referring to FIG. 1, a head discriminating circuit 13 is connected to 
said connector 10 for identifying the thermal head 9 mounted thereon. 
Also a head coincidence circuit 14 identifies if the head identified by the 
head discriminating circuit 13 coincides with the printing head of the 
typefont designated by the printing instruction. The printing instruction 
includes the print start information for instructing the start of a series 
of printing operation and the typefont information instructing the 
typefont of the characters to be printed, and the head coincidence circuit 
14 utilizes said typefont information. A loudspeaker 15 is provided for 
giving alarm. 
A selection circuit 16 selects the timing pulses either from the position 
detector 4 or 5 according to the output signal from said head coincidence 
circuit 14, and the timing pulses thus selected are supplied to the motor 
drive circuit 1 controlled by the print instruction thereby compensating 
the motor speed to a designated speed. 
The motor drive circuit 1 is instructed of the start timing of motor drive 
by the print start information of the print instruction, and of the motor 
rotating speed by the typefont information. 
The timing pulse selected by the selection circuit 16 is further supplied 
to a head drive circuit 17 to instruct the timing of energization of the 
thermal head. Thus, in response to the entry of a timing pulse, the head 
drive circuit 17 is activated from the stand-by state realized by the 
print start information of the print instruction thereby driving the 
thermal head 9 through an amplifier 18 during a period and at a voltage 
determined by the typefont information of the print instruction. 
FIG. 2 shows the arrangement of a device for discriminating the thermal 
head 9, which is composed of a graze portion 91, a printed circuit board 
93 for supplying current to heating elements 19a and a head sink 92 to 
which said graze portion 91 and circuit board 93 are fixed with screws. 
The circuit patterns on said circuit board 93 include U-shaped patterns 
93a, 93b which are independent from the circuits leading to the heating 
elements and which may be partially cut in the part of 93b to represent 
different resistances according to the typefonts of the thermal heads. 
There printed circuit board 93 of the thermal head 9 is connected through 
the connector 10 to a flexible cable 10a, of which a lead 10b connected to 
said pattern 93b is grounded while a lead 10c connected to said pattern 
93a is connected to an input terminal a of the head discriminating circuit 
13. Said circuit 13 is composed of a latch circuit having a same level at 
the input terminal a and at the output terminal b, and also functions to 
prevent erroneous operation of the printer resulting from the noise 
generated at the mounting of the thermal head 9. 
The above-explained embodiment functions in the following manner. 
Upon insertion of a thermal head 9 into the connector 10 on the carriage 8, 
the input terminal a of the head discriminating circuit 13 connected to 
the power supply through a resistor R changes the voltage level according 
to the specification of the thermal head. As explained in the foregoing, 
the pattern 93a of the printed circuit board 93 of the thermal head 9 is 
connected to said input terminal a of the head discriminating circuit 13 
through the connector 10, while the lead 10b is grounded. Thus upon 
insertion of the thermal head corresponding for example to a character 
size of 12 points in which the pattern 93b is cut, the head discriminating 
circuit 13 receives a high-level input voltage at the terminal a to 
provide likewise a high-level output voltage at the terminal b. 
Similarly upon insertion of a thermal head corresponding to a character 
size of 10 points in which the pattern 93b is not cut, the head 
discriminating circuit 13 receives a low-level input at the terminal a to 
provide a low-level output at the terminal b. In response to such 
automatic identification of the thermal head 9 at the head discriminating 
circuit 13, the head coincidence circuit 14 compares the result of said 
identification with the typefont information of the print instruction and 
activates an alarm, i.e. loudspeaker 15 in case a different thermal head 9 
is mounted, thus advising the operator to exchange the thermal head. The 
motor 3 is stopped in this state. On the other hand, in case a correct 
thermal head is mounted, the selection circuit 16, in response to the 
output signal from the head coincidence circuit 14, selects the position 
detector 4 or 5 for position detection for energizing the thermal head 9. 
Also the servo motor 3 is rotated by the motor drive circuit through the 
amplifier 2 according to a speed designated by the typefont information of 
the print instruction. 
The carriage 8 is set into motion in this manner, and, in response to the 
position detection timing transmitted from the selection circuit 16, the 
head drive circuit 17 which has been in stand-by state by the print start 
information of the print instruction, energizes the heating elements 91a 
at determined positions of the printing paper 11 through the amplifier 18, 
connector 10 and printed circut board 93 for a period determined by the 
typefont information of the print instruction, thereby achieving thermal 
printing. 
In this manner it is rendered possible to modify the displacing speed of 
the carriage 8, the energizing timing and period to the recording paper 11 
according to the species of the thermal head 9, thus ensuring appropriate 
printing. 
Now FIGS. 3 to 5 illustrate a second embodiment of the present invention, 
in which the result of identification by the head discriminating circuit 
is compared with a memory content storing the character to be printed, 
and, if the two are different, an instruction for head change is issued 
and the printing pitch is regulated according to the changed head. 
In FIGS. 3 and 4, a central processing unit (CPU) 19 releases an 
instruction to a character generator (CG) 20 to form a typefont of 
characters and symbols, and said character generator 20 releases character 
signals of one line to a random access memory (RAM) 21 for storage 
therein. The output signal from said RAM 21 and that from a head 
discriminating circuit 13 are compared in a head coincidence circuit 14, 
and, if the typefont to be printed is different from the data stored in 
the RAM 21, an alarm means such as a loudspeaker 15 is activated and the 
printing head to be mounted is displayed on a display unit 22. On the 
other hand, in case the head coincidence circuit 14 provides a coincidence 
output signal, a selection circuit 16 selects a position detector of which 
timing signal is supplied to a motor drive circuit 1 and a head drive 
circuit 17. The energizing period and voltage of said head drive circuit 
to the thermal head 9 are designated by typefont information stored in the 
RAM 21. Also the rotating speed of the motor 3, controlled by the motor 
drive circuit 1, is determined by the typefont information stored in the 
RAM 21 supplied to said circuit 1 through the CPU 19. 
FIG. 5 shows the content of memory in the RAM 11, in which each address 
contains a character obtained by the character generator 20 (for example a 
"Kanji" or phonetic character at the address "0001") and information 
indicating the species of character (for example a character of 10 points 
at the address "0001"). Upon completion of printing of one line, the RAM 
is reset and stores the information for the next line. 
The above-explained second embodiment functions in the following manner. 
Upon receipt of a print instruction, the CPU 19 rotates the servo motor 3 
through the motor drive circuit 1 and the amplifier 2, thereby displacing 
the mechanically linked carriage 8 and thermal head 9 in the printing 
direction. At the same time, the thermal head 9 for 10-point characters is 
identified by the head discriminating circuit 13 and compared with the 
typefont information stored in the RAM 21 by the head coincidence circuit 
14, which releases a coincidence output signal if the two coincide with 
each other. As explained in the foregoing, the thermal head for 10-point 
characters has the intact pattern 93b, whereby the head discriminating 
circuit 13 provides a low-level output signal. In response to said 
coincidence signal, the selection circuit 16 selects the position detector 
4 for 10-point characters, of which output pulses are supplied to the 
motor drive circuit 1 and the head drive circuit 17 to serially print 
characters "ESTIMATED AMOUNT" in 10-point characters corresponding to the 
addresses 0001 to 0005. In this state, the rotating speed of the motor 3 
controlled by the motor drive circuit 1 and the energizing period and 
voltage of thermal head 9 controlled by the head drive circuit 17 are 
designated by the typefont information stored in the RAM 21. 
After serial printing with 10-point characters in this manner, the carriage 
8 and the thermal head 9 reaches a position for character printing 
corresponding to the address 0006 with 12-point character. However, as the 
connector 10 currently holds a thermal head for 10-point characters, the 
head coincidence circuit identifies the difference and releases an alarm 
through the loudspeaker 15, simultaneously with a display "Change head to 
12 points" on the display unit 22. At the same time the non-coincidence 
output signal from the head coincidence circuit 14 cuts off the motor 
drive circuit 1 to stop the servo motor 3. 
In this manner the printing with 10-point characters is interrupted and the 
head replacement is requested to the operator. Upon replacement of the 
10-point head by the 12-point head according to said request, the head 
discriminating circuit 13 changes the output level at the terminal b. The 
12-point thermal head 9 has a cut pattern 93b on the printed circuit board 
93 to provide a high-level voltage at the input terminal a thereby giving 
a high-level output at the terminal b. 
In this manner the 12-point thermal head 9 is identified by the head 
discriminating circuit 13 and compared with the data stored in the RAM 21 
by the head coincidence circuit 14, which thus terminates the alarm 
through the loudspeaker 15 and the display on the display unit 22 and 
restarts the rotation of the servo motor 3 at a speed corresponding to the 
12-point character printing, thus initiating the printing with 12-point 
characters from the address 0006 of RAM 21 by the displacement of the 
carriage 8 and thermal head 9. In this state, in response to the output 
signal from the head coincidence circuit 14, the selection circuit 16 
selects the timing pulses from the position detector 5 for 12-point 
characters. Also the rotating speed of the motor 3 controlled by the motor 
drive circuit 1 and the energizing period and voltage to the thermal head 
controlled by the head drive circuit 17 are newly designated by the 
typefont information for 12-point characters stored in the RAM 21. In this 
manner the printing with 12-point characters is continued from the address 
0006 to 0011. 
At the address 0012 from which the characters are again changed to 10 
points, the carriage 8 stops in the aforementioned manner, and a request 
is given for head replacement. The printing thereafter proceeds in a 
similar manner with intermediate head replacements. 
In the foregoing embodiment, the carriage is stopped at each position of 
typefont change, but it is also possible to return the carriage to the 
start position at each typefont change, to displace the carriage to the 
interrupted printing position after replacement of the thermal head and to 
continue the printing. It is furthermore possible to print all the 
10-point characters in a line at first, then to replace the thermal head 
without paper advancement and to conduct carriage scanning again for 
printing 12-point characters. As explained in the foregoing, the second 
embodiment ensures printing with desired typefonts without error even when 
different fonts are mixed in a line, owing to the comparison of the output 
signal from the head discriminating circuit 13 with the data stored in the 
RAM 21. 
Although the foregoing description has been limited to a one-column type 
thermal head, the present invention is by no means limited to such 
embodiment but covers other printing heads such as a 5.times.7 dot-matrix 
thermal head, a wire-dot printing head or a printing head with 
conventional typefont. In addition the present invention is not limited to 
interchanging of two different printing heads but also covers 
interchanging of three or more printing heads, and the discriminating 
method for heads can also be modified in various manners.