JPH0725052A - Thermal head drive - Google Patents

Abstract

(57) [Abstract] [Purpose] The purpose is to simplify the circuit configuration and improve the power supply efficiency by heating and energizing the heating element of the head only with chopping pulses, which in turn facilitates head temperature control. . According to the thermal head printing apparatus of the present invention, the duty ratio of the heating chopping pulse is changed according to the printing rate of black dots printed in the past, and is maintained according to the environmental temperature where the thermal head is placed. By increasing or decreasing the number of thermal chopping pulses, the temperature of the thermal head is controlled to the optimum temperature for printing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head driving device, and more particularly to head temperature control.

[0002]

2. Description of the Related Art Conventionally, a method of driving a thermal head using a pulse, as disclosed in Japanese Patent Application Laid-Open No. 63-1559, uses a pulse signal () to sufficiently raise the temperature of the thermal head to a printable threshold temperature. (Hereinafter, referred to as a heating pulse block) and a pulse signal (hereinafter, referred to as a heating pulse block) that maintains the temperature of the thermal head at the threshold temperature and regulates the print density.
It is called a heat retention pulse block. ) And two kinds of pulse signals.

The heating pulse block of the former is a pulse having a long pulse width composed of a single pulse or multiple pulses, and the heating pulse block of the latter is a pulse train composed of a predetermined number of chopping pulses. The drive pulse signal by the pulse block is supplied to the thermal head according to the print information.

[0004] In the past, regardless of the state of the head, the printing operation was continued by giving the driving pulse signal of the same time width and the same value to the thermal head. Then, when high-duty printing continues, pulses are supplied one after another before the heating element of the head is sufficiently cooled, so that the temperature of the head gradually rises. If printing is performed in a state in which the head temperature is abnormally high, dot crushing and print unevenness may occur, and eventually the thermal head itself may be damaged.

Therefore, as disclosed in Japanese Unexamined Patent Publication No. 63-21156, a printer using a thermal head of this type is provided with a temperature sensing element such as a thermistor in the thermal head or stores a printing history. It had a memory. Then, based on the print rate calculated from the head temperature and print history detected by the temperature sensing element,
The width of the pulse signal supplied to the thermal head is increased or decreased, or the number of pulses of the pulse signal is increased or decreased to control the head temperature so as not to become an abnormally high temperature.

[0006]

However, in the above-mentioned prior art, since the heating pulse and the heat retention pulse are composed of different pulses and controlled independently, a pulse having a long pulse width is generated. A circuit, a circuit for generating a chopping pulse having a short cycle, a circuit for synthesizing the two pulses, and a means for controlling each circuit are required. Therefore, the circuit to compose becomes complicated,
Naturally, their control was also complicated.

Further, the control by a pulse having a long pulse width is
It was apt to cause a sharp temperature rise of the thermal head and was not suitable for fine temperature control.

The present invention has been made in order to solve the above-mentioned problems, does not require a special mechanism, can generate a heating current with a simple structure, and can further control fine temperature and power consumption. It is an object of the present invention to provide a driving device for a thermal head capable of saving energy.

[0009]

In order to achieve this object, a method of driving a thermal head according to the present invention uses a thermal head composed of a plurality of heating resistors to set the thermal head to a printable temperature based on print information. A heating pulse consisting of a heating pulse for heating up to a printable temperature and a heating pulse for holding the thermal head at a printable temperature is supplied, and the heating current is changed according to the printing environment. A pulse generating means for generating a heating pulse and a heat retaining pulse by using a chopping pulse, a detecting means for detecting a printing environment, and a heating pulse generated by the pulse generating means corresponding to the printing environment detected by the detecting means. And a duty ratio changing means for changing the duty ratio per cycle.

The detecting means is composed of a memory for storing print information up to the past n dots and a calculating means for calculating a ratio of the print dots in the memory, and the duty ratio changing means is for the pulse ratio. The duty ratio of the heating pulse generated by the generating means may be changed to a duty ratio inversely proportional to the ratio obtained by the calculating means.

The detecting means further has a temperature detecting means for detecting the ambient temperature at which the thermal head is operating, and the number of chopping pulses of one heat-retaining pulse generated by the pulse generating means is calculated as follows. It may be provided with a pulse number varying means for varying the number in inverse proportion to the environmental temperature detected by the temperature detecting means.

[0012]

In the thermal head driving device of the present invention having the above structure, the printing environment is first detected by the detecting means. The duty ratio varying means determines the duty ratio per cycle of the heating pulse according to the printing environment detected by the detecting means. Then, the pulse generating means generates a heating pulse having the duty ratio, and the heating pulse is supplied to each heating element of the thermal head based on the print information.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram for realizing a thermal head control device. The control device of the thermal head includes 128 heating elements TH1 to TH128 for printing.
Thermal heads T that are arranged in a row
H, a gate unit G composed of 128 NAND gates G1 to G128, and 128 shift registers R1
Register unit R, 128 composed of
It has a latch section L composed of individual latches L1 to L128, and a print control section 1 for controlling the operation of the thermal head.

Then, each heating element TH1 of the thermal head
Each of ~ TH128 is connected to a + V drive power source, and the other end is connected to the output terminals of the NAND gates G1 to G128 of the gate section G. Also, NAND gate G1
One end of each input terminal of G128 is a latch L of the latch section.
1 to L128 are respectively connected to the output terminals, the other ends of the input terminals are respectively connected to the print control unit 1, and the heat generation current is input from the print control unit 1. The output terminals of the shift register R1 of the register unit R are connected to the input terminals of the latches L1 to L128, and the print data is latched from the register unit R by the latch signal from the print control unit 1. Input terminals of the shift registers R1 to R128 are connected to the print control unit 1, and print data is written from the print control unit 1 at a predetermined timing.

As shown in FIG. 2, the print control unit 1 includes a CPU 11 which is a central control unit, a ROM 12 which stores a print control program and the like, and an R which stores print data.
The CPU 11 includes an AM 13, and the CPU 11 controls print data according to a program previously recorded in the ROM 12.
Performs pulse signal control and information processing calculations.

Further, the print control unit 1 has a chopping pulse generation unit 14 for generating a chopping pulse having a constant period.
A duty ratio changing unit 15 that determines the duty ratio of the chopping pulse generated from the chopping pulse generation unit 14; and a temperature detection unit 16 that includes a thermistor that detects the environmental temperature around the thermal head TH.
And a pulse number varying unit 17 that determines the number of pulses generated from the chopping pulse generating unit 14. still,
The chopping pulse generator 14 corresponds to the pulse generator of the present invention, the duty ratio variable unit 15 corresponds to the duty ratio variable unit of the present invention, and the pulse number variable unit 17 corresponds to the pulse number variable unit of the present invention.

The chopping pulse generator 14 is a CPU that sends a pulse transmission command via the duty ratio variable unit 15.
11 and is also connected to the CPU 11 via the pulse number varying unit 17, receives signals from each and operates to output a + V chopping pulse to each NAND gate G1 to G128 of the gate unit G. .

Here, the configuration of the chopping pulse generator 14 will be described. Chopping pulse generator 14
As shown in FIG. 3, a clock CLK, three counters CT, and ON / O according to the outputs of the respective counters CT.
It is composed of a switch SW that performs an FF operation. A predetermined pulse length of one cycle is set in the counter CT1, and a length of ON time in one cycle is set in the counter CT2 from the duty ratio changing unit 15.
In 3, the number of ON / OFF operations is set by the pulse number varying unit 17.

The counter CT1 counts the number of signals from the clock CLK, and outputs a predetermined signal when the value reaches the above-mentioned set value. Then, the counting is restarted from the beginning, and the signal is similarly output. The counter CT2 counts clock signals by using the signal output from the counter CT1 as a signal. Then, when the set value is reached, a predetermined signal is output. After that, similarly, the counter CT
The output of 1 is used as a signal to start counting and output a signal. Counter CT3 is counter CT1 and counter CT2
The number of signals is counted, and similarly, when the set value is reached, a predetermined signal is output.

Each output of the counter CT is a switch SW.
Connected to. The switch SW receives the signal from the counter CT1 and turns on. Conversely, the switch SW is
When it receives a signal from the counter CT2, it turns off. When receiving the signal from the counter CT3, the switch SW stops.

Next, the operation of the thermal head driving device of this embodiment will be described with reference to the flow chart. FIG. 8 shows a flowchart of an embodiment of the present invention.

When the print data C is to be printed,
First, the CPU 11 receives the detection signal output from the environment temperature detection unit 16, A / D-converts the detection signal, and calculates the environment temperature t (S1). Then, the environmental temperature t is sent to the pulse number varying unit 17. In the above operation, the environmental temperature detection unit 16 and the CPU 11 correspond to the temperature detection unit of the detection unit of the present invention.

Then, the pulse number varying unit 17 determines the number of chopping pulses having an interruption time inversely proportional to the environmental temperature t and stores it (S2).

Further, the CPU 11 determines from the RAM 13 to the past 2
The print information up to (= n) dots is read, and the calculation is performed based on the read print information to calculate the print ratio. The printing rate calculated here is obtained as follows. First, CPU 11 is RAM
The previous two times of the print data read from 13 and the previous print data are A (A1, A2, ... A128), B (B
1, B2, ... B128), and print data to be printed at present is C (C1, C2, ... C128). Then, weighting set in advance in the ROM 12 is performed according to the combination (AB) of A and B for each bit. That is, the combination 00, 01, 10, 11
The numerical values 3, 2, 1, 0 are given as the print ratio in accordance with After that, the first bit to the 128th bit are added, and the calculated value is output to the duty ratio varying unit 15. In the above operation, the RAM 13 corresponds to the memory of the detecting means of the present invention, and the CPU 11 corresponds to the calculating means of the detecting means of the present invention.

The duty ratio varying unit 15 receives the calculated value, determines the duty ratio inversely proportional to the calculated value (S3), and generates the chopping pulse having the duty ratio. The duty ratio is set in the counter CT2 of (S4).

Further, the CPU 11 reads out the predetermined number of heating chopping pulses from the ROM 12,
This value is set in the counter CT3 of the chopping pulse generator 14 (S5). Then, a command is sent to the chopping pulse generator 14 to generate a chopping pulse (S6).

The chopping pulse generator 14 is a CPU
When receiving the command from 11, each counter CT starts operating. While the counter CT2 is counting, the switch SW is in the ON state and outputs + V pulse,
Otherwise, the switch SW is turned off and the output is 0.
become. Then, when the counter CT3 counts to the set value, the chopping pulse generator 14 stops its operation. Then, the chopping pulse train shown in FIG. 4 is generated. This pulse is sent to the inputs of the NAND gates G1 to G128, and in this embodiment, the chopping pulse corresponding to this portion is called a heating chopping pulse.

In this case, when the heating chopping pulse is output to the NAND gates G1 to G128, the print data C is set in the corresponding bits R1 to R128 of the shift register R, respectively. This data C is stored in the CPU 11
It is written in the latch L by the latch signal from and is output to each of the NAND gates G1 to G128. The NAND gates G1 to G128 logically operate the NAND of the data C and the data C based on the heating chopping pulse signal,
It is determined whether or not to energize the heating elements TH1 to TH128.

That is, the first bit (C1) of the data C
Is a logic "1", the output of the NAND gate G1 that prints the dots in the first row is at a logic low level, the heating element TH1 is energized by the + V driving power source, and the heating element TH1 generates heat. On the contrary, when C1 is a logic "0", the heating element TH1 does not generate heat. Heat generation control based on the heating chopping pulse is performed on each of the heating elements TH1 to TH128.

As a result, as shown in FIG. 5, when the printing rate of the past two dots of a certain heating element is low (the calculated value is 0
To 127), a heating chopping pulse having a high duty T1 as shown in FIG. 5A is output. Further, in the case of printing in which the calculated values of the past two dots are 128 to 255, the heating chopping pulse with the duty T2 as shown in FIG. 5B is output.

Similarly, as shown in FIGS. 5 (3) and 5 (4), the duty ratio of the heating chopping pulse changes depending on the printing state of the past two dots. That is, as a result, the shorter the elapsed time since the heat was generated in the past, the more heat is stored in the corresponding heating element, and the temperature gradient for heating is made gentler.

As a result, the duty of the heating chopping pulse changes even if a difference in heat storage occurs in the heating elements in the past two-dot printing shown in FIGS. The exothermic temperature is adjusted and made uniform. In this control, the past two dots are checked each time the print dot advances.

After the heating chopping pulse is generated, CP
The U11 reads out a predetermined duty ratio of the heat retention chopping pulse from the ROM 12, and sets this value in the counter CT2 of the chopping pulse generator 14 (S7). Further, the number of pulses determined by the pulse number varying unit 17 is set in the counter CT3 of the chopping pulse generating unit 14 (S8), and a command is sent to the chopping pulse generating unit 14 to generate the heat retaining chopping pulse (S).
9).

As a result, specifically, when the environmental temperature t is low, the number of heat-retaining chopping pulses is increased as shown in FIG. 7A, and when the environmental temperature t is high, FIG.
As shown in (2), on the contrary, it is decided to reduce the number of pulses.

This heat retaining chopping pulse is also output to the NAND gates G1 to G128 in the same manner as the heat chopping pulse. At this time, the print data C is set in the shift register R as described above. Therefore, the print data C is latched by the latch L, and each NAND gate G1
.. to G128, the print data C is chopped at each output. As a result, the current flowing through each of the heating elements TH1 to TH128 is also interrupted, and the heat generation temperature repeatedly rises and falls and becomes a constant state.

After the heat-retaining chopping pulse is generated, it is determined whether or not the next print data exists. If there is print data (S10: NO), the process returns to S1 to set a new print pulse and print. continue.

In the above, the duty ratio of the heating chopping pulse is updated for each printing according to the past black dot printing rate. Therefore, a change in print density due to heat storage of the thermal head in a row is corrected every moment, and a more uniform print density is obtained. Here, the number of heating chopping pulses is not limited to four in this embodiment, and may be any appropriate number.

On the other hand, the environmental temperature t is also constantly monitored.
Therefore, if the environmental temperature changes during printing according to the procedure described above, the length of the chopping pulse is adjusted at any time as described above. As a result, the print density can be kept constant even if the environmental temperature such as the room temperature changes. Here, the detection element of the temperature detection unit 16 may be provided at a position where the temperature can be detected in the printer main body, and the environmental temperature may be considered in consideration of the temperature rise due to continuous operation of the printer. As a result, the print density can be made more uniform.

Further, in the above operation, by setting the drive voltage of + V to a high value, the rise of heat generation by the heat history chopping pulse can be made steep.

In this embodiment, since the drive pulse supplied to the thermal head is generated by one pulse generator, the circuit structure is much simpler than the conventional one.
In addition, since the chopping pulse is used, for printing that contains a lot of pixels such as Chinese characters, the heating chopping pulse prevents abnormal heating of the heating element of the thermal head, and the heat retention chopping pulse keeps the entire thermal head. The effect of preventing the heat accumulation of is to prevent print deterioration such as print crushing. In other words, the heat generation temperature of the heating element is corrected both from a temporary viewpoint by the heating chopping pulse considering the temperature change of each heating element and from a comprehensive viewpoint by the heat retaining chopping pulse considering the environmental temperature. There is.

In addition, when the electric power applied to the heating element is set high and printing is performed with a single pulse for high-speed printing, the temperature of the heating element rises too much and burns out, thus shortening the life of the heating element. I was invited. However, in this embodiment, since the chopping pulse is provided, there is an advantage that the burnout of the heating element can be prevented and the life can be extended.

Further, since all the pulses are composed of chopping pulses, the power source efficiency is relatively good.

[0043]

As is apparent from the above description, according to the thermal head driving device of the present invention, the heating current can be supplied to each heating element with a simple structure. The control for keeping the printing temperature constant can be simplified. Further, by using the chopping pulse, the power supply efficiency is improved and the excessive temperature rise of the heating element can be prevented, so that a constant print density can be secured.

[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 print control unit.

FIG. 3 is a configuration diagram of a chopping pulse generator.

FIG. 4 is an explanatory diagram showing a configuration of a chopping pulse input to a gate.

5 (1) to 5 (4) are explanatory diagrams of heating chopping pulses corresponding to respective printing rates.

6 (1) and 6 (2) are explanatory views showing the relationship between each heating chopping pulse and the temperature rise of the heating element.

FIGS. 7 (1) and 7 (2) are explanatory views showing the relationship of the temperature rise of the heating element with the change of each heat retention chopping pulse.

FIG. 8 is a flowchart of an embodiment of the present invention.

[Explanation of symbols]

 1 Print Control Section TH1 to TH128 Heating Element 11 CPU 12 ROM 13 RAM 14 Chopping Pulse Generation Section 15 Duty Ratio Variable Section 16 Temperature Detection Section 17 Pulse Number Variable Section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B41J 3/20 116

Claims (3)

[Claims] 1. A heating pulse that heats the thermal head to a printable temperature and a heat retention pulse that heats the thermal head to a printable temperature based on print information in a thermal head composed of a plurality of heating resistors. In a thermal head driving device that changes the heating current according to the printing environment while supplying the heating current, a pulse generation unit that generates a heating pulse and a heat retention pulse by using a chopping pulse with a constant cycle, And a duty ratio varying means for varying the duty ratio per cycle of the heating pulse generated by the pulse generating means in response to the printing environment detected by the detecting means. Characteristic thermal head drive device. 2. The detecting means comprises a memory for storing print information up to the past n dots, and a calculating means for calculating a ratio of the print dots in the memory, wherein the duty ratio varying means comprises the pulse 2. The thermal head driving device according to claim 1, wherein the duty ratio of the heating pulse generated by the generating means is changed to a duty ratio inversely proportional to the ratio obtained by the calculating means. 3. The detection means further has a temperature detection means for detecting an environmental temperature in which the thermal head is operating, and the number of chopping pulses of one heat-retention pulse generated by the pulse generation means is calculated as follows. 3. The thermal head driving device according to claim 2, further comprising pulse number varying means for varying the number in inverse proportion to the environmental temperature detected by the temperature detecting means.