JPH06286196A - Thermal line printer - Google Patents

Abstract

PURPOSE:To prevent a variation in current supply to a heat generator as much as possible and to make a printing density uniform by providing correcting means for so correcting a conducting time of the generator in a division as to be shorter when a printing rate decreases more with respect to a reference conducting time. CONSTITUTION:A thermal line printer comprises a CPU 1 of a control body, a ROM 2 for storing control program data, a RAM 3 for storing a status, etc., for controlling, an interface (I/F) 4 for fetching print data from an external unit, an ink ribbon drive motor 5, a dot counter and strobe controller 10, etc. Number of black print dots of dot data is counted by the counter for constituting the controller 10 to calculate a printing rate. A conducting time of a heat generator in a division is so corrected based on the rate by a strobe counter as to be shorter as the rate is decreased more with respect to a reference conducting time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal line printer.

[0002]

2. Description of the Related Art A thermal line printer controls the energization time of each heating element of a thermal head having a large number of heating elements arranged in a line by a strobe signal and selectively controls the heating of each heating element. It is designed to print.

In such a thermal line printer, the temperature of the head changes depending on the ratio of the number of black print dots to be actually printed in the heating elements to be printed, that is, the print ratio.

For this reason, conventionally, as shown in FIG. 7, a thermistor is provided, the temperature of the thermal head is detected by this thermistor, the print rate is detected by the detection output, and the strobe signal STB1 ,. The STB2 is controlled to control the energization time t for the heating element. That is, when the printing rate is low and the thermistor detection temperature is low, the energization time is set to t1, and when the printing rate is high and the thermistor detection temperature is high, the energization time is set to t2 (<t1).

[0005]

However, in the case where the print ratio is indirectly detected by the thermistor and the strobe signal is controlled on the basis of the print ratio, the current capacity of the common pattern for supplying the current to each heating element is taken into consideration. Then, the energization amount to the heating element is limited especially when the printing rate is high, and thus the energization amount to the heating element changes depending on the printing rate. As a result, for example, deviation of the printing rate in one line occurs. When it occurs, there is a problem that the printing density changes due to the change of the printing rate, and uniform printing cannot be performed.

In view of the above, according to the present invention, an appropriate energization time control is performed with respect to a change in the print rate to prevent a change in the energization amount to the heat generating element due to the print rate as much as possible, so that a print with a uniform density is always produced regardless of the print rate. It is intended to provide a thermal line printer capable of performing the above.

[0007]

According to the present invention, each heating element of a thermal head having a large number of heating elements arranged in a line is divided into n (n ≧ 1) by a strobe signal, and each division is performed by the strobe signal. In a thermal line printer that controls the energization time of the heating elements inside and prints by selectively controlling the heating elements for each division and printing, counting the number of black print dots in each division from the print dot data and printing Based on the printing rate calculation means for calculating the rate, and the printing rate calculated by the printing rate calculation means, the energization time of the heating element in the division controlled by the strobe signal is kept constant with the energization amount to the heating element. As described above, a correction unit for correcting the reference energization time set in advance as the print ratio becomes lower is provided.

[0008]

In the present invention having such a configuration, the print ratio is calculated by counting the number of black print dots in each division from the print dot data. Then, based on the calculated print rate, the print rate is lower than the reference turn-on time, which is set in advance so that the amount of power to the heat generating element is constant. Correct so that it becomes shorter.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a thermal line printer. 1 is a CPU (central processing unit) which constitutes the main body of a control unit, and 2 is a ROM (read only) which stores program data for the CPU 1 to control each unit.・ Memory), 3 is a RAM that stores status for control, etc.
(Random access memory), 4 is an interface (I / F) that is connected to an external device and receives print data from the external device, and 5 is various motors 7 such as a motor for driving the ink ribbon and a platen. , An I / O port to which various sensor switches 8 such as a paper sensor are connected.

Reference numeral 9 is a thermal head controller for driving and controlling the thermal head 6, and 10 is a dot counter &
Strobe controller, 11 is each of the parts 2, 3, 4,
This is a decoder for selecting 5, 9, and 10.

As shown in FIG. 2, the dot counter & strobe controller 10 comprises a dot counter 101 which constitutes a print ratio calculating means and a strobe controller 102 which constitutes a correcting means. , The strobe controller 102 supplies the strobe signal STRB (1) to the thermal head 6 from the count value counted by the dot counter 101.
(2) is controlled.

Data buses D0 to D7 are connected to the dot counter 101 and the strobe controller 102.

The dot counter 101 has serial data IN transferred to the thermal head 6, its synchronous clock CK, a read signal RD for reading the number of black print dots in the strobe, and a signal CL for clearing the counter 101.
RC and the like are input.

The strobe controller 102 includes:
From the thermal head controller 9, strobe signals STROBE (1), (2), a write signal WR for setting the energization time calculated from the printing rate, a reference clock signal CLKS for the energization time, etc. are input. The strobe controller 102 generates strobe signals STRB (1) and (2) according to the print ratio by these signals and supplies them to the thermal head 6.

FIG. 3 shows a control circuit for the strobe of the dot counter 101. In this embodiment, the one with two strobes is taken as an example.

This control circuit comprises three counters 21,2.
2, 23, a selector 24 and two bus buffers 25,
It is composed of 26.

In this control circuit, the counter 21 counts only the number of black print dots by the serial data IN input to the thermal head 6 and its synchronous clock CK,
The count value is output from the counter 21 to the counters 22 and 23 every 16 dots. In HEX (hexadecimal digital code), it becomes 00H, 01H, 02H, 03H, ....

Assuming that the total number of dots printed by the thermal head 6 (corresponding to the number of heating elements) is 2,560, the CLRC signal from the CPU 1 is obtained when the synchronization clock CK corresponding to half 1,280 dots is counted. It is input and shifts to the count of the number of black print dots of the next strobe. At that time, the count value of the first strobe signal by the CLRC signal is stored in the bus buffers 25 and 26. That is, the bus buffers 25 and 26 store the count value as a HEX code.

The synchronous clock C for 2,560 dots
When K is counted, the number of black print dots in the strobe is read from the bus buffers 25 and 26 by the read signal RD and the chip select signals CS1 and CS2.

The selector 24 is switched and controlled by a select (SEL) signal from the CPU 1, and the counter 2
The count values of 2 and 23 are selectively output to the bus buffers 25 and 26.

FIG. 4 shows the strobe controller 102.
1 shows a control circuit for one strobe.

This control circuit has two counters 31, 3
It is composed of a few D-type flip-flops 33, 34 and 35 and one JK-type flip-flop 36.

This control circuit uses a strobe signal STRO.
The falling edge of BE (1) is used as a trigger to sample the CLKS signal from the CPU 1 and increment the count value corresponding to the number of black print dots latched in advance by the chip select signal CS3 and the write signal WR in the counters 31, 32. It has become. And the counter 31,
When 32 counts up, the carry signal is supplied to the D-type flip-flop 35, and the strobe signal ST is sent from the JK-type flip-flop 36 to the thermal head 6.
RB (1) is output.

In this embodiment having such a structure, C
When the CLRC signal shown in (a) of FIG. 5 is input from the PU1 to the dot counter 101, the counters 21 to 23 are cleared, and then the counters 21 to 23 have the clock CK shown in (b) of FIG. The serial data IN shown in (c) is input from the interface 4, and the number of black print dots in the serial data IN in one strobe is counted. That is, the number of black print dots in 1,280 dots is counted.

Since one line has two strobes, the number of black print dots among the 1,280 dots in the other strobe is counted at the next timing.

When the counting of 2,560 dots is completed, the chip select CS1 shown in FIG. 5E, the select SEL shown in FIG. 5D, the chip select CS2 shown in FIG. Read signal RD shown in (g) of FIG.
As a result, data is read from the bus buffers 25 and 26 to the data bus in the form of an HEX code of 410 (HEX) as shown in FIG. 5H, and the chip select CS3 shown in FIG. Write signal W shown in (j) of FIG.
Counter 3 of strobe controller 102 by R
1 and 32 are stored.

In this state, the counters 31 and 32 are shown in FIG.
After the strobe signal (1) from the thermal head controller 9 falls as shown in (l), the CLKS signal which is the clock from the CPU 1 shown in (k) of FIG. 5 is counted, and the counters 31 and 32 count up. Then, the carry signal is supplied to the D-type flip-flop 35, and J
The K-type flip-flop 36 outputs the strobe signal STRB1 corrected by the printing rate as shown in FIG. 5 (m) and supplies it to the thermal head 6.

FIG. 6 is an example showing the relationship between the counted number of black printed dots and the energization time correction value at that time. In the case of this graph, for example, the counted number of black printed dots is HE.
If the X code is 410 (HEX), the energization time correction value at that time is FE (HEX) of 0.65 μsec.
Also, the counted black print dot number is 25 in HEX code.
If 0 (HEX), the energization time correction value at that time is 18
(HEX) is 74.9 μsec. If the counted black print dot number is 50 (HEX) in HEX code, the energization time correction value at that time is 01 (HEX) and 8
3 μsec.

That is, the energization time correction value is a value that is subtractively corrected from the preset reference energization time, and thus the number of black print dots is large, that is, the number of black print dots is smaller than that when the printing rate is high, that is, the printing is performed. When the rate is low, the energization time is controlled to be short. That is, the lower the print rate, the less energy is used to form the print dots.

As a result, even if the current flowing through the heating element is limited due to the limit of the current capacity of the common pattern when the printing rate is high and the printing energy is reduced, the printing energy is also reduced when the printing rate is low. Even if there is a deviation of the printing rate on one line, uniform printing can be performed as a whole. That is, by appropriately controlling the energization time with respect to the change in the print rate, it is possible to always print with a uniform density regardless of the print rate.

Although the above embodiment has described the case where one line is divided into two strobes, the present invention is not limited to this. One line is controlled by one strobe, and one line is controlled by three or more strobes. May be

[0033]

As described above in detail, according to the present invention, the energization time control is appropriately performed with respect to the change of the print rate to prevent the change of the energization amount to the heating element due to the print rate as much as possible, and to improve the print rate. It is possible to provide a thermal line printer that can always print a uniform density regardless of the situation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a dot counter & strobe controller of the same embodiment.

FIG. 3 is a block diagram showing the configuration of the dot counter shown in FIG.

4 is a block diagram showing a configuration of a strobe controller shown in FIG.

FIG. 5 is a diagram showing an operation timing of the dot counter & strobe controller of the embodiment.

FIG. 6 is a graph showing the relationship between the number of black printed dots and the energization time correction value at that time in the same embodiment.

FIG. 7 is a timing chart for explaining energization time control of a conventional thermal head.

[Explanation of symbols]

 1 ... CPU (Central Processing Unit) 2 ... ROM (Read Only Memory) 6 ... Thermal Head 9 ... Thermal Head Controller 101 ... Dot Counter 102 ... Strobe Controller

Claims (1)

[Claims] 1. A thermal head having a large number of heating elements arranged in a line, each heating element is divided into n (n ≧ 1) by a strobe signal, and the strobe signal indicates the energization time of the heating element in each division. In a thermal line printer that controls and selectively controls heat generation of heating elements for each division to perform printing, a printing rate calculation unit that counts the number of black print dots in each division from print dot data to calculate a printing rate. Based on the printing rate calculated by the printing rate calculation means, the energization time of the heating element in the division controlled by the strobe signal is set to a reference energization value set in advance so that the energization amount to the heating element is constant. A thermal line printer, characterized in that it is provided with a correction means for correcting the shorter the printing rate with time.