JPH02125762A - Thermal printer - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a thermal printer, and particularly to improving variations in print density.

(b) Conventional technology It is a well-known fact that thermal printers tend to cause variations in print density, and in order to keep the print density constant, the current value and drive pulse width that drive the heating resistor of the thermal head are adjusted. A method of controlling the temperature according to the temperature of the thermal head has been considered, and a method of controlling the driving pulse width of the heating resistor has been put into practical use. The heating resistor drive pulse width is controlled by digitizing the temperature change of the thermal head using an A/D converter and by using microcomputer software, gate arrays, and microcomputer expansion I10.
The driving pulse width of the thermal head is controlled by a timing generation circuit configured with a boat or the like.

In this thermal printer, as shown in FIG. 11, parallel print data 7 input to the thermal printer is converted into serial print data 1 by a parallel/serial converter 8.
3 and sent to the shift register 6 of the driver C3 in synchronization with the CLOCK signal II output from the microcomputer 10 to which the oscillation circuit 12 is connected.
The driver IC 3 is controlled by the LATCI+ signal included in the driver control signal 9 controlled by the microcomputer 10.
It is configured to be latched by the latch circuit 5 of.

Here, variations in print density may be caused by factors such as the temperature of the thermal head, the printing cycle, the resistance value of the thermal head, and the number of printed dots. 14, it is read into the microcomputer IO as a digital signal, the printing cycle is ranked by the paper size signal 15, and the resistance value of the thermal head is ranked by the average resistance value of the thermal head l measured in advance by the dip switch 16. Set the value and input it to the microcomputer IO, and the number of print dots is the serial print data 1 converted to serial.
The number of printed dots 3 is counted by a printed dot counter 17 and manually inputted to the microcomputer 10 to cope with variations in print density.

The microcomputer IO generates data determined by a certain algorithm from the A/D conversion data, the paper size signal 15, the output of the print dot counter 17, and the dip switch function for setting the average resistance value of the thermal head. Timing generation circuit 1
8 determines the pulse width for driving the heating resistor 2, and from the determined pulse width, the decoder 19 determines the pulse width as shown in FIG.
Strobe signal (5TROBE1) for performing divided drive
~8) 20 was made, and the driver IC 3 was configured to drive the heating resistor 2 by the strobe signal.

In addition to this, as shown in FIG. 12, there is a device that digitizes the output of the thermistor 4 using a D/A converter 22 and a comparator 21 instead of the above A/D converter, but the principle is as described above. Same as Shino.

(c) Problems to be Solved by the Invention However, many of the conventional thermal printers described above are extremely complex in terms of circuitry, and in particular, when fine-grained control is required, temperature monitoring, pulse width determination, and Since control is performed, microcomputer software and associated hardware (for example, an A/D converter and a gate array) are required, and there are also problems in that the cost is high and the processing time becomes long.

This invention was made to solve the above problems, and has a simple circuit, low cost, short processing time,
The objective is to provide a thermal printer that can print uniformly.

(D) Means for Solving the Problems According to the second invention, there is provided a thermal head including a plurality of S1 resistors, a current supply means for supplying current to the heat generating resistors, and a temperature detection means for detecting the temperature of the thermal head. , a conversion means for receiving the output of the temperature detection means and converting it into a corresponding frequency signal, a frequency dividing means for receiving the frequency signal and dividing the signal, and a period of the divided frequency signal. A thermal printer is provided, comprising: control means for determining the energization time of the energization means based on the energization time of the energization means.

The present invention is characterized in that the temperature of the thermal head is detected, the temperature is converted into a voltage value and then into a frequency, and the time period for passing the current through the heating resistor is determined based on the period of the frequency.

The thermal head equipped with a plurality of heat generating resistors is usually suitably formed so that the heat generating resistors weighing 500 to 5000 g are arranged in a straight line on a ceramic substrate so that each of the heat generating resistors can output a pixel one by one. .

The energizing means for energizing the heat generating resistor normally includes a system register that can input serial data in synchronization with a clock signal, a latch circuit that can latch this serial data by a LATCH signal, and a 5TROBE signal based on the latched serial data. A driver IC can be used that can output an energization pattern to the heating resistor for a corresponding time.

The temperature detection means for detecting the temperature of the thermal head includes:
For example, Fe5Oa and MgCrtO+ or MgAlt0
It is constructed using a thermistor etc. made by mixing and sintering a solid solution of No. 4, NiOlMNlol, CotO3, etc., and is arranged near the heating resistor to keep the temperature of the thermal head (usually 0 to 80°C).
℃) can be detected and converted to a voltage value.

The conversion means that receives the output of the temperature detection means and converts it into a corresponding frequency signal, for example, integrates the input terminal,
A V/F converter can be used that uses a method of comparing the output voltage of an integrator and a comparison voltage and integrating the results in an electromagnetic counter, etc., and detects the voltage change outputted from the temperature detection means, usually from 0 to 5V. , it is suitable to convert it into a frequency signal, usually between 0 and 100 KHz.

This V/F converter is, for example, a V/F converter consisting of a variable resistor.
A conversion characteristic adjustment circuit can be combined to change the frequency to voltage conversion ratio.

The frequency dividing means that receives the frequency signal and divides the frequency of the signal can use a normal counter timer circuit, and this counter timer circuit is, for example, a countdown type counter that can output 0 and whose initial value can be arbitrarily set. is suitable, and when the output pulse of the V/P converter is input, O output is made at a frequency division ratio according to the initial value (initial value).
It is possible to perform a countdown for each input pulse from , and to output an l pulse output when the counter content reaches 0.

The control means for determining the energization time of the energization means based on the period of the frequency-divided frequency signal, for example, manually inputs the frequency signal to a microcomputer as an interrupt signal;
Furthermore, the microcomputer outputs a 5TROBE signal corresponding to the width of this frequency signal through a decoder, or the frequency signal is not used as an interrupt signal for the microcomputer, and is output by a circuit composed of, for example, an octal counter, a decoder, etc. It is suitable to output a 5TROBE signal corresponding to the width of the frequency signal.

The outputted 5TROBE signal is input to the energizing means, and the energizing means energizes the output based on the latched serial data for a time corresponding to the 5TROBE signal, thereby outputting a energizing pattern to the heating resistor and energizing it. The heating resistor generates heat at a constant temperature, and as a result, it is possible to output a serial data pattern with uniform print density.

(e) Convert the voltage output from the operating temperature sensor into a frequency, divide this frequency, determine the pulse width to drive the heating resistor based on the cycle of the divided pulses, and determine the time corresponding to this pulse width. The temperature of the heating resistor is controlled at a constant level by passing current through the heating resistor.

(f) Example Embodiments of the invention will be described in detail with reference to the drawings.

As shown in FIG. 1, first, the heating resistor 2 and the driver IC
3 and a thermistor 4, and a V/F converter 26 that converts the output voltage of the thermistor 4 into a frequency.
, a circuit 28 for setting and adjusting this conversion characteristic, and a V/P
A signal is output to a counter timer circuit 27 that divides the frequency of the converter 26, and a decoder 19 that generates a strobe signal 20 by manually inputting an interrupt signal 28 from the counter timer circuit 27, and according to the timing chart shown in FIG. The microcomputer 10, which has functions such as outputting driver control signals to the driver IC 3, and the parallel print data 7 are converted into serial print data! Parallel/serial converter 8 that converts to 3 and a print dot counter that counts the number of print dots from serial data! 7, an oscillation circuit 12 connected to the microcomputer 10, a dip switch 16 for setting the average resistance value rank of the heating resistor 2 in the thermal head 1, and a thermal head power supply 24 for supplying the heating resistor 2. A thermal printer including a switch circuit 25 was manufactured.

Driver IC3 CLOCs serial print data 13
It is input in synchronization with the K signal 2, and when all printed dots have been inputted, the contents of the shift register 6 are latched into the latch circuit 5 by the LATCH double signal as shown in FIG. is an example of 8-part printing.
The BE signal 20' is divided into 5 TROBE 1 to 5 TROBE 8 and manually applied to drive the heating resistor. However, 5TRO
While the BE signal is active, the B, E, and 0 signals must be active (5TROBE signal is negative logic, so it is active Loll).

As described above, energy is applied to the heating resistor by the pulse of the 5TROBE signal, and the amount of heat generated can be controlled by the width of the pulse. Therefore, in this embodiment, temperature change is converted into voltage change, this voltage change is further converted into frequency change, and the pulse width of the 5 TROBE pulse is controlled according to the change in frequency period, thereby controlling the amount of heat generated by the heating element. The purpose of this is to control the print density so that it remains constant regardless of any temperature changes.

Next, how the pulse width of the 5TROBE signal is controlled by temperature will be explained in detail with reference to FIGS. 1 and 4 to 1O.

For example, if the temperature of the entire thermal head l changes over time as shown in FIG. 5, the output voltage of the thermistor 4 changes as shown in FIG. 6 in correlation with FIG. When the output voltage of the thermistor 4 is input to the V/F converter 26, the frequency changes as shown in FIG. 7 based on the V/F conversion characteristics shown in FIG. 4(a).

As shown in FIG. 4(b), the V/F converter can change the slope of the straight line in FIG. 4(a) using the volume in the conversion characteristic adjustment circuit 28, so the frequency of FIG. The rate of change can be adjusted. Next, the output pulse of the V/F converter 26 (
A counter timer circuit (CTC
) 27, outputs 0 at a frequency division ratio corresponding to the initial value 23, that is, inputs from the initial value 23, counts down every pulse, and when the counter content reaches 0, outputs 1 pulse. This counter output pulse is used as an interrupt signal 29 for the microcomputer IO. When the interrupt signal 29 is input manually, the microcomputer IO controls the 5TROBE Hals according to the flowchart shown in FIG. 1θ. FIG. 9 shows the 5TROBE signal controlled by this flowchart.

As a result, the pulse width of the 5TROBII: signal is controlled by the temperature change shown in FIG.

The initial value 23 set by the microcomputer IO in the counter timer circuit 27 is based on the contents of the dip switch 16 for setting the average resistance value of the heating resistor, the print synchronization determined from the paper size signal, and the contents of the print dot number counter 17. further determined by the above V/
Control accuracy can be improved by adjusting the volume in the conversion characteristic adjustment circuit 28 of the F converter 26.

Note that the technical scope of the present invention is not limited by the embodiment of the present invention that describes eight-division drive.

(G) Effects of the Invention According to the present invention, it is possible to reduce the processing amount and processing time of a microcomputer, and to provide a thermal printer that can maintain a constant printing density with high precision at a low cost using a simple circuit. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a thermal head drive circuit of a thermal printer manufactured in an embodiment of the present invention, FIG. 2 is a circuit diagram of a driver IC, and FIG. 3 is a timing chart diagram of driver IC-F and driving. , Fig. 4(a) is a human output characteristic diagram of the V/F converter, Fig. 4(b) is a diagram of the V/F conversion characteristic adjustment circuit, and Figs. 5 to 9 correspond to temperature changes. Te5T
FIG. 10 is a diagram of each signal up to the generation of the ROBE signal, and FIG. 1 is a flowchart of the microcomputer's interrupt processing routine. 1 to 12 are explanatory diagrams of a conventional thermal head drive circuit and signal conversion using a D/A converter and a comparator, respectively. ! ...Thermal head, 2...Heating resistor, 3...Driver IC, 4...
Thermistor, 5... Latch circuit, 6...
・Shift reno star, 7...Parallel print data, 8...Parallel/serial converter, 9...
...Driver control signal, IO...Microcomputer, 11...
...CLOCK signal, 12...Oscillation circuit, 13...Serial print data, 14...
・A/D converter, 15...Paper size signal, 16...Deep switch for setting the average resistance value of the oscillating resistor, 17...Printed dot number counter, 18...
...Timing generation circuit, I9...Decoder,
20...5 TROBE signal! ...Comparator, 2...D/A converter, 3...Initial value, 4...Power supply for thermal head, 5...
Switch circuit, 26...V/F converter, 7...
...Counter (CTC), 8...V/F
Conversion characteristic adjustment circuit. B.EΩ. Fig. Thermistor output hawk E Fig. Time closed cylinder Fig. Whistle time Fig. q■

Claims (1)

[Claims] 1. A thermal head equipped with a plurality of heat generating resistors, an energizing means for supplying current to the heat generating resistors, a temperature detecting means for detecting the temperature of the thermal head, and a frequency signal corresponding to the output of the temperature detecting means. It comprises a conversion means for converting, a frequency division means for receiving the frequency signal and dividing the frequency of the signal, and a control means for determining the energization time of the energization means based on the period of the frequency-divided frequency signal. thermal printer.