Device for adjusting the heat-generating time of a thermal printer head

There is disclosed a device for flexibly adjusting the strobe pulse width corresponding to the heat-generating resistance grade of a thermal printer head through a DIP switch. The DIP switch generates a number of states of voltages corresponding to the grade number of the heat-generating resistance of the thermal printer head. The DIP switch keeps voltage suited for the heat-generating resistance grade of the thermal printer head to supply it to a CPU.

BACKGROUND OF THE INVENTION 
The present invention relates to a driver for a thermal printer head and 
more particularly, to a device for adjusting heat-generating time of the 
thermal printer head (hereinafter referred to as TPH),for example,to be 
used in facsimile apparatus . 
A thermal printing head used for printing in a facsimile system prints 
according to the duration of strobe pulse applied. Conventionally, a TPH 
driving voltage supplied by a power supply is adjusted to a 
heat-resistance grade of the TPH. Namely, in order to adjust the TPH 
driving voltage to the heat-generating resistance grade of the TPH, the 
power supply level is manually adjusted by using a variable resistor of 
the power supply. By this known art, when the TPH being used in the system 
is replaced with another one, the power supply must be disassembled to 
readjust the variable resistor to the heat-generating resistance grade of 
the substituted TPH, and this causes complication of maintenance and 
repair of the system. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a device for efficiently 
adjusting the heat-generation time for a thermal printer head by adjusting 
the duration of a strobe pulse to a given heat-generating resistance grade 
of the thermal printer head, by means of a dual-in-line package (DIP) 
switch, mainly for use in a facsimile apparatus. 
According to one aspect of the present invention, a device for flexibly 
adjusting the heat-generating time of the thermal printer head of a 
facsimile system includes a voltage-fixing type thermal printer head, a 
memory for storing the information relating to a plurality of 
heat-generating resistances and relating to the strobe pulse width 
corresponding to the values of the heat-generating resistances of the 
thermal printer head, a central processing unit CPU for sending the strobe 
pulse suited to the thermal printer head by dividing the frequency of the 
pulses from a driving clock pulse generator according to the strobe pulse 
width, a DIP switch for generating a plurality of signals corresponding to 
the heat-generating resistance of the thermal printer head, and an 
input/output (I/O) buffer for accumulating the information of the DIP 
switch and sending the information to the CPU.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will now be described more specifically with 
reference to the drawing attached only by way of example. 
Referring to FIG. 1, DIP switch includes switches SW1-SW3 and pull-up 
resistors R1-R3 in order to generate a signal for determining the strobe 
pulse width corresponding to the heat-generating resistance grade of 
thermal printer head 70. The I/O buffer 20 buffers the output of the DIP 
switch 10. Memory 40 stores the system program and the various values of 
the heat-generating resistances for the various thermal printer heads. The 
(CPU) 30 for controlling the system controls the memory 40 to output the 
data relating to the strobe pulse width of the thermal printer head 70 
according to the output of the I/O buffer 20. Head driver 60 generates the 
strobe pulse for driving the thermal printer head 70. Head driver 60 
divides the frequency of the pulses from the driving clock pulse generator 
50 according to the strobe pulse width of the thermal printer head 70. The 
thermal printer head 70 prints the data to be printed according to the 
strobe pulse of the head driver 60. Power supply 80 supplies power to the 
thermal printer head 70. 
When using a voltage-fixing type thermal printer head, the strobe pulse 
needs to have its own pulse width suited to the thermal printer head as 
shown in Table 1 corresponding to the heat-generating resistance grade of 
the thermal printer head. 
TABLE 1 
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heat-generation resistance 
strobe pulse width 
(ohms) (.mu.sec) 
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2380-2459 1.52 
2460-2545 1.57 
2546-2637 1.63 
2638-2736 1.68 
2737-2843 1.75 
2844-2958 1.81 
2959-3083 1.89 
3084-3220 1.96 
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The strobe pulse width of Table 1 is obtained under 25.degree. C., and 
varies with the temperature. 
The voltage fixing type TPH should satisfy one of the heat-generation 
resistance values in Table 1. Hence, in order to adjust the strobe pulse 
width to the heat-generating resistance grades of TPH 70, the CPU 30 
should give the data relating to the strobe pulse width of TPH 70 
corresponding to the heat-generating resistance grade of TPH to the head 
driver 60. The DIP switch 10 is used to present the information relating 
to the heat-generating resistance grade of TPH in I/O buffer 20 as 
described above. Namely, a combination of the switches SW1-SW3 provides 
the eight switching signals with the I/O buffer, which accumulates the 
information of one of the eight switching signals and sends it to the CPU 
30. The CPU 30 compares it with the data stored in the memory 40 which has 
the data relating to the heat-generating resistance values of TPH and the 
strobe pulse widths corresponding thereto. Consequently, the CPU 30 
analyzes the data from the I/O buffer 20 and the data in the memory 40 to 
produce the data for setting the strobe pulse width of TPH 70. 
Meanwhile, the head driver 60 divides the frequency of the clock pulses 
from the driving clock pulse generator 50 according to the data for 
setting the strobe pulse width, so as to produce a strobe pulse whose 
width is suited for TPH 70. Then, the TPH 70 prints the data to be printed 
during the duration of the strobe pulse. When the values of 
heat-generating resistance are as shown in Table 1, every possible 
combination of the DIP switch is as shown in Table 2. 
TABLE 2 
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heat-generating resistance (ohms) 
DIP switch 
2380-2459 
2460-2545 
2546-2637 
2638-2736 
2737-2843 
2959-2958 
2959-3025 
3024-3220 
__________________________________________________________________________ 
SW1 OFF OFF OFF OFF ON ON ON ON 
SW2 OFF OFF ON ON OFF OFF ON ON 
SW3 OFF ON OFF ON OFF ON OFF ON 
__________________________________________________________________________ 
Thus, the DIP switch 10 is set to one of the eight switching values as 
shown in Table 2 corresponding to the heat-generating resistance grade of 
the TPH 70, and the CPU 30 reads the data relating to the strobe pulse 
width corresponding to the heat-generating resistance grade from the 
memory 40, according to the state of the DIP switch 10. The head driver 60 
divides the frequency of the pulses of the clock pulse generator according 
to the strobe pulse width so as to produce a strobe pulse for driving the 
TPH 70 suited to the heat-generation resistance grade. 
As described above, the inventive circuit may easily adjust the strobe 
pulse width to the heat-generating resistance grade of a voltage fixing 
type thermal printer head by means of a DIP switch, thereby flexibly 
adjusting the heat-generating time of the TPH with ease and simplifying 
the maintenance and repair of the system even when the TPH is replaced. 
Although specific constructions and procedures of the invention have been 
illustrated and described herein, it is not intended that the invention be 
limited to the elements and construction disclosed. One skilled in the art 
will easily recognize that the particular elements or subconstructions may 
be used without departing from the scope and spirit of the invention.