JPH0345363A - Printing control method and device thereof in thermal head - Google Patents

Abstract

PURPOSE:To eliminate a dispersion in printing density in a high-speed printing by a method wherein a simple preheating circuit is added to a printing controller to conduct an initial preheating before printing and/or apply a preheating to resistors which have not between used for printing in a printing process. CONSTITUTION:With an output of a control signal CONT from a printing control circuit 1, initial preheating data indicating all bits ON is sent to a thermal head drive circuit 10 under the control of a preheating control circuit 8. After an initial preheating just before the start of printing is applied to resistors R, a first printing is conducted based on printing data, a clock signal, a latch signal, and a strobe signal, which are directly transmitted from the printing control circuit 1. After that, the reverse data of the printing data formed by a preheating data circuit 6 is transmitted to the thermal head drive circuit as a preheating signal, whereby a preheating is applied only to the resistors R which have not between used in the first printing cycle. Therefore, a printing without a dispersion in density can be realized. The small quantity of the preheating data does not require a long operating time for processing the data, thus satisfactorily responding to a high-speed printing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printing control method and apparatus for eliminating variations in printing density in printing using a thermal head.

[Prior Art] In recent years, thermal printers have been used in a wide variety of applications due to their advantages such as instantaneous printing, low noise, and ease of handling, and their printing speeds have become increasingly faster. The printing mechanism of the thermal head used in this thermal printer is to supply electric power (pulse voltage) to a resistive element installed on the surface of an electrically insulating substrate, and the heat generated is used to apply dye to the surface of the thermal paper. Printing is done by developing color, or by melting and sublimating ink applied to a thermal transfer film and transferring it to plain paper.

Here, a print control operation in a conventional thermal head will be explained.

FIG. 8 shows an example of a conventional thermal head printing control device, and FIG. 9 shows a timing chart of each control signal sent from the printing control circuit l in the figure to the thermal head drive circuit lO. There is. In these figures, n
Printing control circuit containing printing/non-printing data for pits
The data (2) for one print of the serial signal Sr is sent to the n-bit shift register 2 by the clock, and is held as a parallel signal in the n-bit latch register 3 by the latch signal. The print data for each bit latched in the latch register 3 is processed by AND gate AND, ~A
The AND with the strobe signal is calculated at NDn, and these ANDs are applied to the resistance element R (R, ~R) of the thermal head.
n) driving transistor T r (T rl to T rn
) is sent as a control signal.

FIG. 10 shows the voltage VIID applied to the resistance element R and the temperature T of the resistance element R in the drive circuit. Note that temperature TI) in the figure indicates the minimum temperature of the resistance element R required for printing. Immediately before printing starts, the hot water temperature T of the resistance element R is at room temperature RT, but as the printing voltage VIID is repeatedly applied, the temperature of the resistance element R at the start of printing gradually rises, and the temperature at the cycle time of the third printing increases. The temperature is from RT to T. Therefore, when the printing pulse voltage is applied, the temperature reached by the resistive element R also shifts to a higher temperature side, and the printing density gradually becomes higher.

The reason for this is that the heat generated in the resistive element R acts on the thermal paper, etc., and some of it is also dissipated to the outside via the insulating substrate. This is because a large amount of power is supplied in a short period of time, so heat dissipation through the insulating substrate becomes insufficient, heat is accumulated in the insulating substrate, and the temperature of the resistance element itself increases. In addition, if there is a non-printing cycle in the middle and the cooling time from the application of a printing pulse voltage to the resistive element to the application of the next printing pulse voltage varies, the amount of heat dissipated during this period also changes and printing The temperature of the resistance element immediately before starting also varies, causing variations in print density.

In this way, in the conventional printing control circuit, the printing density changes at the beginning of printing and for each printing/non-printing resistor element, degrading printing quality.

As a measure to prevent heat accumulation in the substrate, which causes such variations in print density, there is a method of controlling the applied power by taking into account the thermal history of each resistance element. That is, the power supplied to each resistive element during printing is controlled according to the state of supply of printing power from several printing cycles ago. Furthermore, the power applied to the resistive element has been controlled by taking into consideration the thermal history of not only the resistive element but also adjacent resistive elements. The size of the thermal history that should be taken into consideration here depends on the size of the thermal time constant determined by law based on the components that make up the thermal head and their mechanical dimensions, so the amount of heat stored during printing will be calculated from the time of printing. It is necessary to decide based on time rather than the number of print cycles.

Therefore, the number of printing cycles for each print within a certain past time is <l! when the printing speed is high. , and the amount of data that must be taken into account for heat storage correction also increases. Furthermore, as printing becomes faster, it is necessary to take into account the thermal history of each resistive element and shorten the processing time so as to reflect this in the power supplied to the resistive element during printing. In other words, in order to correct heat accumulation in the thermal head during high-speed printing using the conventional technology,
It became necessary to process a large amount of data in a short period of time, and the scale of the hardware and software for heat accumulation correction increased.

On the other hand, one way to control the heat accumulation generated in the substrate is to reduce the amount of heat accumulation by increasing the heat dissipation to the substrate by reducing the thickness of the glaze applied to the ceramic or metal plate that makes up the substrate. There is. However, when the glaze layer is made thinner, the temperature rise of the resistor element is suppressed, so the power applied to the resistor element increases accordingly, resulting in deterioration of the resistor element and loss of reliability. There was also the problem of increasing the size.

The present invention was devised to solve these problems, and by adding a part of the circuit to control the heat storage screen without changing the conventional thermal head drive circuit, it can also be used for high-speed printing. The present invention provides a printing control method and apparatus that eliminates variations in printing density.

[Means for Solving the Problems] The thermal head printing control method of the present invention preheats all the resistance elements and/or the non-printing resistance elements to a predetermined temperature immediately before starting printing. A printing control device that is characterized by preventing variations in density and to which the method of the present invention is applied includes a circuit that preheats all of the above-mentioned resistance elements to a predetermined temperature based on a control signal output at the start of printing, and an inversion of printing data. A circuit that preheats a non-printed resistance element using data, and one or both of the following circuits are provided.

[Function] By preheating all resistance elements at the start of printing,
The first printing will not be thin, and by preheating the non-printing resistance element during the printing process, the temperature of the resistance element during the next printing will be almost constant regardless of printing or non-printing. This eliminates variations in print density. The predetermined temperature for preheating is set below the minimum temperature necessary for printing and higher than room temperature so that printing does not occur due to preheating. In addition, because preheating always keeps the resistive element at a temperature higher than room temperature, the power that must be supplied to the resistive element during printing can be reduced compared to when no preheating is used, and therefore the resistive element can be used with high reliability over a long period of time. can be maintained.

[Embodiment] An embodiment of a printing control device to which the thermal head printing method of the present invention is applied is shown in Fig. 8, and the same parts as in the conventional example shown in Fig. 8 are given the same reference numerals. There is. Strobe signals, latch signals, and serial print data S1. between the print control circuit 1 and the thermal head drive circuit 10. OR gates OR+~OR, are inserted in each signal path of the clock, and the other input parts of these OR gates OIL, ~OR, receive a strobe signal, a latch signal, serial print data Sl, and a clock as input signals, respectively. , preheating strobe circuit 4. Preheat latch circuit 5, preheat data circuit 6. Each output signal of the preheating clock circuit 7 is input manually. Further, a preheating control circuit 8 for controlling these circuits 4 to 7 is provided, and this preheating control circuit 8 includes:
The input signal is a control signal C0NT from the print control circuit 1, which is a motor drive signal for paper feeding or thermal head movement, which is output just before the start of printing. The operation of each of these circuits 4 to 8 will be described in detail when the control operation is explained below. Furthermore, the printing control circuit l
Strobe signal output from.

The latch signal, serial data ST and clock are sent to the thermal head drive circuit IO via OR gates OR and -0R4, respectively, and the normal printing operation is the same as in the conventional example.

FIG. 2 is a time chart showing the operation of the apparatus shown in FIG. 1, and its control operation will be explained along this time chart.

The control signal C0NT from the print control circuit l is “L”
” to “H” level, the preheating control data from the preheating control circuit 8 is set to the “H” level for a period of t as a trigger for the preheating data circuit 6. This preheating data circuit 6 It generates data for preheating (■) and preheating data for non-printing resistance elements (■, ■).
During the "H" level, on-signals for n pits are output based on the upstream clock of the preheating clock circuit 7, which will be described later.

On the other hand, when outputting preheating data (2) and (2) after printing, it is necessary to identify printing/non-printing in each printing cycle using resistive elements for n pits. This is the point that the present invention has focused on, and in this embodiment, data ■, ■ of the serial print data S■ for n pits from the print control circuit l are received by an inverter, and the serial inverted data (print resistor element is an off signal, and an on signal is obtained for non-printed resistive elements. After holding this serial inversion data in a shift register for n pits provided in the preheating data circuit 6, the ON signal is sent to the shift register 2 of the thermal head drive circuit 10 as preheating data based on the upstream clock of the preheating clock circuit 7, which will be described later. Forward.

The preheating clock circuit 7 receives the initial preheating data (■) and the post-printing preheating data (■) from the preheating data circuit 6.

It outputs a preheating clock for transferring (1) to the shift register 2, and the preheating clock for initial preheating is a pulse falling of the preheating control clock output from the preheating control circuit 8 at the rising edge of the preheating control data. The preheating clock output as a trigger and for preheating after printing uses the print clock output from the print control circuit 1 as a trigger, and is output 11 hours after this print clock.

The preheating latch circuit 5 outputs a latch signal for causing the latch register 3 to hold in parallel the initial preheating data and post-printing preheating data stored in the shift register 2 in a norial manner. The latch signal for data is triggered by the falling edge of the preheating control latch pulse output from the preheating control circuit 8 at the falling edge of the preheating control data signal, and the launch signal for preheating data after printing. is triggered by the print latch pulse output from the print control circuit 1, and is output 12 hours after the fall of this print latch signal.

The preheating strobe circuit 4 outputs a preheating strobe signal for applying the initial preheating data latched in the latch register 3 and the post-printing preheating data to the resistance element R. The strobe signal is triggered by the falling edge of the preheating control latch signal output from the preheating control circuit 1 at the falling edge of the preheating control latch signal, and the strobe signal for preheating after printing is output by the printing control circuit. The print strobe signal output from 1 is used as a trigger, and the print strobe signal is output 43 hours after the fall of this print strobe signal. As shown in the figure, the preheating strobe signal is a plurality of rectangular pulses with a narrow time width so that the temperature of the resistance element R preheated by this strobe signal is below the minimum temperature required for printing and higher than the room temperature. It is said that

As can be seen from the explanation in section 2 below, when the print control circuit 1 outputs the recontrol signal C0NT, the initial preheating data (with all bits on) is sent to the thermal head drive circuit IO under the control of the preheating control circuit 8. After initial preheating is applied to the resistive element R immediately before printing starts, the first printing is performed based on the conventional printing data (print data), clock, latch signal, and strobe signal directly sent from the printing control circuit 1. will be carried out. Thereafter, the inverted data (2) of the above (2) formed by the preheating data circuit 6 is sent to the thermal head drive circuit as a preheating signal, so that the resistor element which was not printed in the first printing cycle is Only preheating is applied. Thereafter, printing using the normal printing data ■ and preheating using the inverted data ■ of this printing data ■ are repeated, and by preheating the non-printing resistance element R, the density varies regardless of the printing/non-printing state. Printing without any blemishes is achieved.

3 and 4 show the resistance element R in the above drive circuit.
The applied voltage VD and the temperature T of the resistance element R are shown. FIG. 3 shows the case where printing is performed in each printing cycle after initial preheating, and the temperature of the resistance element R at the start of each printing is T. is a constant value. Also, Figure 4 shows
Indicates when preheating is performed for non-printing in the first cycle and the second cycle, and printing is performed in the third cycle,
In this case as well, the temperature of the resistance element R at the start of printing is the temperature T at the start of printing when printing is performed continuously. is maintained.

If the preheating of the resistor elements is adjusted in consideration of printing/non-printing in the resistor elements adjacent on both sides of each resistor element, more precise heat accumulation correction can be performed. In this case, the printing/non-printing state to be considered may be the dot pattern in cases (A) to H) shown in FIG. When all three consecutive resistance elements are printed (ON) as shown in (A), the temperature of the center resistance element Rc is the highest, so there is no need to preheat the center resistance element Rc. However, when all three resistance elements are not printing (OFF) as in (H), the center resistance element RC requires the maximum preheating. From this,
The amount of preheating may be controlled by increasing or decreasing the number of pulses of the preheating strobe signal in accordance with each dot pattern of (A) to (I()). An example of each strobe signal in this case is shown in FIG. Also, a time chart is shown in FIG.

Here, after normal print data ■ is sent to the thermal head drive circuit 10 and printed, inverted data ■ of this print data ■ is sent out using (n-1) clocks and latched into the latch register 3. , the resistance element R is preheated by two preheating strobe signals. By this preheating, the presence or absence of preheating of the resistor element R is determined by the printing/non-printing state of the resistance wire r (H) on the right side of the resistor element R.Next, one clock signal converts the inverted data Let it proceed (
After shifting to the right) and latching, the resistance element is preheated by six preheating strobe signals. In this case, whether or not the resistance element R is preheated is determined depending on its printing/non-printing state. Furthermore, after advancing the inverted data ■ by l bits and latching it by one clock signal,
Preheating of the resistance element is performed using two strobe signals. In this case, whether or not to preheat the resistance element R is determined by the printing/non-printing state of the resistance element RL on the left side. By executing the above as one printing cycle, the preheating strobe signal shown in FIG. 6 is obtained. The newly required signals in this case are the clock and latch signals shown in FIG. 7, and can be easily handled by the preheating circuit shown in FIG. 1.

Further, the preheating circuit shown in FIG. 1 shows a means for realizing the present invention without making any changes to conventional hardware and software, and these circuits can be incorporated into the print control circuit l or It goes without saying that the effects of the present invention can be obtained even when software measures are used to generate the signals shown in FIG.

[Effects of the Invention] As explained above, the present invention adds a simple preheating circuit to a conventional printing control device, performs initial preheating before printing, and/or controls resistance elements that are not printing during the printing process. However, since preheating is performed, variations in print density can be eliminated. Further, in the present invention, since there is little data for preheating, the calculation time for processing the data is short, and therefore, it is fully applicable to thermal printers that perform high-speed printing. Furthermore, in the present invention, since the resistive element is always kept at a temperature higher than room temperature, the power that must be supplied to the resistive element during printing can be reduced compared to when there is no preheating, so the resistive element can maintain high reliability over a long period of time. It is possible to avoid increasing the size of the power supply due to faster printing.

[Brief explanation of drawings]

FIG. 1 is a control block diagram showing one embodiment of the thermal head printing control device of the present invention, FIG. 2 is a time chart showing control operations in the device of FIG. 1, and FIGS. 3 and 4 5 is a time chart showing the voltage applied to the resistance element and the temperature of the resistance element in the apparatus of FIG.
The figure shows the classification of printing/non-printing dot patterns when performing more accurate correction using the apparatus of the present invention. And the time chart of each signal, Fig. 8,
A block diagram of a conventional thermal head printing control device, FIG. 9 is a time chart showing each signal in the device of FIG. 8, and FIG. It is a time chart showing. l...print control circuit, 2...shift register, 3.
...Latch register, 4...Preheating strobe circuit, 5
・・・Preheating latch circuit, 6 Preheating data circuit, 7...
Preheating clock circuit, 8... Preheating control circuit, R... Resistance element, Tr... Transistor, AND... AND gate, OR... OR gate, 10... Thermal head drive circuit.

Claims (1)

[Scope of Claims] 1) In a thermal head printing control method in which a pulse voltage is applied to a plurality of resistance elements and printing is performed by heat generation, immediately before the start of printing, all the resistance elements and/or the non-printing A method for controlling printing of a thermal head, characterized in that variations in printing density are prevented by preheating a resistance element to a predetermined temperature. 2) In a thermal head printing control device that applies pulse voltage to multiple resistance elements and prints by generating heat, a circuit that preheats all of the above resistance elements to a predetermined temperature based on a control signal output at the start of printing, and printing. 1. A printing control device for a thermal head, comprising one or both of the following circuits: a circuit for preheating a non-printing resistor element using inverted data.