Abstract:
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.

Description:
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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which FIG. 1 is a schematic diagram of the inventive circuit. 
    
    
     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______________________________________heat-generation resistance             strobe pulse width(ohms)            (μsec)______________________________________2380-2459         1.522460-2545         1.572546-2637         1.632638-2736         1.682737-2843         1.752844-2958         1.812959-3083         1.893084-3220         1.96______________________________________ 
    
     The strobe pulse width of Table 1 is obtained under 25° 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__________________________________________________________________________ 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    ONSW2   OFF   OFF   ON    ON    OFF   OFF   ON    ONSW3   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.