JPS63249668A - Thermal head driving method - Google Patents

Abstract

PURPOSE:To obtain good printing output generating no density change by correcting energy to be applied at every printing cycle, by mounting an applied energy correcting table. CONSTITUTION:The data of a time width having to apply voltage to a thermal head 1 is outputted to a thermal head interface 2 from CPU 6. At this time, a CPU 6 determines the time width on reference to the applied energy correcting table on a ROM 7. The number of driving dots counted by a counter 5 are transmitted to the CPU 6 on the basis of the previous printing data. The CPU 6 refers to the correction table in matching relation to the previous applied energy per dot and shortens a voltage applying time width by the quantity of the energy corresponding to the previous generated quantity of heat. A series of these operations are repeated until printing is finished to perform the correction of energy to be applied. By this method, high quality image output imparting uniform image density can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION C. Industrial Application Field The present invention relates to a method for driving a thermal head of a hard copy device or a printer using a thermal recording method or a thermal transfer recording method.

[Summary of the invention]

The present invention is a method for driving a thermal head of a hard copy device/printer using a thermal recording method or a thermal transfer recording method, in which the applied energy is controlled by the applied energy that causes a temperature rise. Since the applied energy is determined by the applied energy per dot of the heating resistor and the number of driving dots, the immediately following applied energy is Determine the applied energy.

By printing while performing this correction one after another in cycles of 0.1 to 10 milliseconds, the energy applied to the thermal head is always at the optimum level, ensuring good print output without changes in print density due to overheating or overcooling. It is made so that it can be obtained.

[Conventional technology]

Due to its characteristics, the temperature of a thermal head installed in a hard copy device or printer using a thermal recording method or a thermal transfer recording method increases as printing continues. At this time, if the same power is continued to be applied to the thermal head, the density of the printed image will also increase.

In order to prevent an increase in image density due to this temperature rise, it is possible to control the power applied to the thermal head.
As a means to achieve this, Japanese Patent Publication No. 61-28516 discloses a method that converts temperature changes into resistance changes using a thermistor, etc., and controls the application time width of the thermal head voltage accordingly by controlling the time constant of a monostable multipipe rake. It's changing.

That is, as the temperature rises, the resistance value of the thermistor decreases, thereby reducing the time constant and shortening the time width to prevent an increase in image density.

C Problems to be Solved by the Invention] As mentioned above, the method of directly utilizing changes in the detection element requires that the resistance value change characteristic of the element itself with respect to temperature change has non-linearity, and that the element itself also has non-linearity. Because there are variations,
There are problems in that it is not possible to set an accurate time width, and in the conventional circuit, the circuit configuration must be adapted to the characteristics of the detection element.

In addition, there is always a lag between the actual temperature change in the thermal head and the temperature change in the temperature detection element, making it difficult to compensate for density changes sufficiently. This was a problem.

[Means for solving problems]

As a means to solve the above-mentioned problems, during pre-printing operation,
It is equipped with an applied energy correction table that can uniquely determine the applied energy required for the current printing operation based on two factors: the applied energy per dot of the heating resistor and the number of drive dots. The applied energy was corrected.

[Effect]

At every printing cycle of 0.1 to 10 milliseconds, the applied energy per dot and the number of driven dots in the previous printing cycle are detected.1 The applied energy correction table value is referenced based on both factors, and the applied energy is increased in the previous print. Print with applied energy that is corrected to match the temperature. This corrected applied energy becomes a factor for referring to the correction table during the next printing cycle. The number of driven dots is determined from the print voltage.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

a) Description of Operation In FIG. 1, print data is output from the graphic memory 3 to the thermal head interface 2 in response to a signal output from the print timing controller 4. At the same time, the CPU 6 (central processing unit) outputs information on the time width for applying voltage to the thermal head 1 to the interface 2. At this time, the CPU 6
The time width is determined by referring to the applied energy correction table on M7 (read-only memory).

At the start of printing, the previous applied energy and the number of driven dots are both 0, so the correction is 0. From the 0th order, the number of driven dots counted by the counter 5 based on the previous printing data. is transmitted to the CPU 6 as information, and it is stored in the ROM again along with the previous energy applied per dot that the CPU 6 has. Correction is performed by referring to the above correction table and shortening the voltage application time width, that is, the pulse width, by an amount of energy corresponding to the previous heat generation amount.

By repeating this series of operations until the end of printing, the applied energy is corrected according to the amount of heat generated.

b) Explanation using formula Let the pulse width of the print voltage be τ1. The correction pulse width (correction amount) is S, the number of driven dots is Z, and the two-dimensional correction table (function table) is F (a).

b), Expressing the number of prints with the subscript at the bottom right, the formula -1τ,
l==τoS.

Formula -23n = S++-10F (SR-1, Zn-
+) Equation −3, °, τ7 − τ. S, l-+ F (
S-+, Z-+) Kokote, τ. constant number, s, = o, zo
= o.

Equation-1 is the basic equation for correction. Initial pulse width τ.

, the energy correction amount s for the heat generation component. Reduce.

In 2-2, the correction amount SR is made up of the previous correction amount RA-3 and the value F (S, l-+, Z□,) of the correction table, and the correction table is composed of the previous correction amount 5R-1 and the previous correction value F (S, l-+, Z□,). Drive dot 1
t (determined by Zn-1.

Equation-3 is an equation expressing the printing operation of the present invention. That is, when printing for the nth time, the previous correction l5M-1 is subtracted from the initial pulse width 0, and the previous heat generation amount F(s
, , -1, zll-I) to maintain good printing.

By feeding the correction amount of the previous printing (n-1), the n-th printing is kept appropriate.

C) Description of applied energy control In FIG. 2, (a) when printing is started, (b) it is determined whether or not printing has ended. If it is not the end, (
c) Using two factors: the previous applied energy per dot and the previous number of driven dots, (d) refers to the applied energy correction table, and (e) determines the applied energy. At the time of first printing, since the previous time does not exist, both the two factors are 0. (b) Printing is performed using the determined applied energy, and the flow of control again becomes (b) a decision as to whether or not to end printing. If it does not end, the applied energy is determined in the same way as last time, and if it ends, the control is terminated at that point, and (g) the printing operation ends.

d) Explanation of the correction table FIG. 3 shows an example of the correction table. This is the case with a line-type thermal head in which one line consists of 1024 dots.

An example of referring to the correction table will be described below.

If the previous correction ms*-1 was 80 μaee + H motion dots was 800 dots, the vertical axis of the table would be 75 to 99 μ1 leel, and the horizontal axis would be 768 to 885.
The column where the dots intersect, 0.8 is the current correction table F (
80,800).

Now, if the initial pulse width τ0 is 500μsec, from equation-6, τ, =500 80 0.8 =419.2 (+
"see".

The correction amount Sll this time is S, =80+0.8 =80
．． Since it is 8 μSec, the next reference value is F (80,
8, Z).

It should be noted that this correction table is one of the embodiments, and it goes without saying that it is changed depending on the type of printer and type Ia.

〔Effect of the invention〕

As mentioned above, in this thermal head driving method, (11-line thermal head allows control for each line of printing, so the image density can be maintained uniformly from the print start position to the print end position. High quality image output can be obtained.

(2) Since temperature is not used as a direct factor in thermal control, printing speed can be increased.

(3) Even if the specifications of the thermal head itself are changed, the applied energy can be easily controlled by simply changing the correction table.

(4) Since the detection of control factors is all digital output,
No deterioration or variation over time.

Various effects can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a flowchart of applied energy control, and FIG. 3 is a diagram showing an example of a correction table. 1...Thermal head interface 3...Graphic memory 4...Print timing controller 5...Counter 6...CPU 7...ROM Applicant Seiko Electronics Co., Ltd. Company E
figure

Claims (1)

[Scope of Claims] A recording device that uses a thermal head to record on recording paper in the form of heat sensitivity or thermal transfer, which includes: (a) storing print data to be transferred to the thermal head in a graphic memory; (b) A counter counts the number of drive dots during the print operation of the thermal head from the print data on the graphic memory; The CPU stores the correction table that defines the correction energy during operation.
(d) transfer print data and applied energy data to the thermal head for recording via the thermal head interface; Muru, thermal head driving method.