JPH06135039A - Applying energy correcting method for thermal transfer multicolor printer - Google Patents

Abstract

PURPOSE:To allow effective enhancement of print quality at low cost by measuring the temperature of a thermal head before and after execution of test print, comparing the temperature difference with an expected value, and controlling the applying power. CONSTITUTION:A print control block starts test print operation (S2) and converts the resistance of a temperature-sensitive element into a digital value at an A/D converter block upon finish of print operation thus detecting the temperature T2 of a thermal head (S32). Difference between temperature T1 before test print and temperature T2 after test print is then determined (S4) and compared with a reference temperature rise of a standard thermal head (S52). When a detected temperature value or T1-T2 is higher than a reference temperature value or a reference temperature rise value, applying power is lowered (S6) otherwise the applying power is increased (S7). This method makes uniform the amount of energy contributable to printing when the width of applying pulse is constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting applied energy in a thermal transfer type multicolor printing apparatus.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed and realized as a method of driving a thermal head in a thermal transfer type multicolor printing apparatus. In the case of the thin film type, the current thermal head is configured by forming a heating resistor and an electrode on a ceramic substrate and mounting a drive IC on it.
The resistance value specifications of the heating resistor differ depending on the individual specifications, but in general, the variation within the thermal head is about ± 15% and the variation between the thermal heads is about ± with respect to the average resistance value.
There is a manufacturing variation of about 10%.

Energy E applied to the thermal head
Is obtained by the following formula. E = P * T = (V 2 / R) * T where, P is the amount of power applied to the thermal head, T is the pulse width to be applied, V is the voltage applied, R represents is the average resistance of the thermal head .

Therefore, when the average resistance value of the thermal head increases or decreases compared to the average value, the voltage applied to the thermal head or the pulse width applied to the thermal head in order to obtain a uniform density is varied to obtain the amount of applied energy. Have changed. When the amount of applied energy is changed by the applied pulse width in the equal power drive, the applied voltage value is changed according to the average resistance value of the thermal head in order to keep the applied power constant.

V = SQRT (P * R) From the above, the voltage value to be applied with respect to the average resistance value of each thermal head can be obtained by calculation. Variable to set the required voltage value.

[0006]

However, not all of the energy applied to the thermal head contributes to printing, but about 60% of the energy is radiated through the heat sink. Therefore, even if the average resistance value of the thermal head is the same, if the thermal resistance on the heat radiating side increases or decreases, the amount of energy that contributes to printing differs, so the density value changes and density unevenness occurs.

[0007]

In order to solve the above-mentioned problems, the present invention contributes to printing by printing a test pattern, detecting the temperatures before and after printing, and finding the temperature difference. The estimated energy amount is estimated and the applied energy amount is corrected.

[0008]

[Function] By comparing the estimated amount of energy contributing to printing with the originally required applied energy, the applied energy amount is corrected to be small when the energy amount is large and large when the energy amount is small. It is possible to obtain high-quality printing with the same density.

[0009]

1 is a flow chart showing an embodiment of the present invention, FIG. 2 is a block diagram of a thermal transfer type multicolor printing apparatus to which the method of the present invention is applied, and FIG. 3 is a diagram showing the experimental results thereof. Is. The present invention will be described below with reference to the drawings.

In FIG. 2, a memory 1 is a memory for temporarily storing image data input from a user interface circuit (not shown). TP
The HI / F 2 reads the image data from the memory 1 in synchronization with a transfer target feeding mechanism (not shown), and
Transfer the print data to 3. TPH3 is the TPHI
The heating resistor is selectively energized by the print data and the control signal input from / F2.

The temperature sensitive element 4 is fixed to the heat radiation portion of the TPH 3, and when the TPH 3 is energized and the temperature changes, the resistance value increases or decreases according to the temperature change. The A / D converter block 5 detects the resistance value of the temperature sensitive element 4 output as the analog signal a, converts it into a digital value, and transmits it to a print control block (not shown).
The D / A converter block 6 converts a digital value instructed from a print control block (not shown) into an analog signal b and transmits it to the PSU block 7.

The PSU block 7 is a power supply unit for supplying the driving power of the thermal head, and the analog signal b input from the D / A converter block 6 is used as a quasi voltage, and the voltage value of the output power signal c to the TPH 3 is set. To control. For example, if the analog signal b is 20V, TP
The voltage value is controlled by applying internal feedback so that the output voltage signal c to H3 becomes 20V.

From the above, the print control block (not shown) can control the voltage value of the output voltage signal c of the PSU block 7 via the D / A converter block 6. As a printing condition, a sublimation type thermal transfer is applied with a thermal head applied power of 0.1 W / dot, a line cycle of 15 ms and 2560 dots / line, and a single-color solid print pattern is printed as a test pattern of 3072 lines. It will be described based on.

First, before the printing operation is started, the resistance value indicated by the temperature sensitive element 4 is converted into a digital value by the A / D converter block 5 to obtain the initial temperature value (T
1) is detected (S1 in FIG. 1). Since the thermal resistance of the environment changes depending on the environmental temperature and the heat dissipation characteristic of the thermal head differs, the initial temperature value of the thermal head is used for the correction count. Here, the initial temperature value is 25 ° C.

Next, assuming that the amount of electric power applied to TPH3 is P and the average resistance value is R, the PSU block 7 outputs TPH3.
The voltage V applied to is calculated by the following formula. In order to simplify the calculation formula, VCE loss, common impedance, and wiring impedance loss of the drive IC in TPH3 are ignored.

V = SQRT (P * R) When the average resistance value of the thermal head is 3500Ω, the applied voltage value is calculated to be about 18.7V. Then, the print control block (not shown) controls the output analog signal b of the D / A converter block 6 to be 18.7V. In the PSU block 7, the analog signal b is 1
Since it is 8.7V, the output power signal c to TPH3 is 1
It operates so that it becomes 8.7V.

Next, a print control block (not shown) starts a test printing operation (S2 in FIG. 1), and after the printing operation is completed, the resistance value of the temperature sensitive element 4 is digitally converted by the A / D converter block 5. And the temperature (T2) of the thermal head is detected (S3 in FIG. 1).

FIG. 3 is a plot of the temperature change state of the temperature sensitive element 4 during printing. In the case of a standard thermal head, the TPH temperature changes as indicated by the circles in the figure.
Here, it can be seen that at the time when 3072 lines are printed, the Δ mark in the figure has a temperature of about 1 ° C. higher than that of the O mark, and conversely, the □ mark has a temperature of about 0.8 ° C. lower. The thermal head marked with Δ has high printing density at the same time as the temperature is high, while the thermal head marked with □ has a lower printing density than the thermal head marked with ○. That is, when comparing the detected temperature value of the thermal head with the reference temperature value using the standard thermal head temperature rise value as the reference value, if the detected temperature is higher than the reference temperature value, the amount of heat that contributes to printing Means that the thermal head has a large amount of heat and a small amount of heat to be radiated.

On the other hand, when the detected temperature is lower than the reference temperature value, it means that the thermal head has a large amount of heat radiation and a small amount of heat contributing to printing. Generally, the temperature T1 before test printing is not necessarily the same as the initial temperature value when the temperature rise value of the standard thermal head is calculated, so the temperature T1 before test printing and the test printing The difference in the subsequent temperature T2 is obtained (S4 in FIG. 1). Then, the reference temperature rise value in the standard thermal head is compared with the temperature difference | T ₁ -T ₂ | (S in FIG. 1).
5).

Then, the detected temperature value or temperature difference | T ₁
When −T ₂ | is higher than the reference temperature value or the reference temperature rise value, the applied power amount is decreased (S6 in FIG. 1), and conversely, when it is low, the applied power amount is increased (S7 in FIG. 1). This makes it possible to make the amount of energy that contributes to printing uniform when the applied pulse width is the same. Here, the energy amount is changed by changing the applied power amount, but the same thing can be changed by the applied pulse width, the line period, the number of multi-pulses, or the like.

As described above, when the thermal characteristics of the thermal head are indicated by Δ in FIG. 3 by executing the test printing and correcting the applied power, the temperature difference at the initial temperature of the thermal head of 25 ° C. is 1 ° C. Focusing on this point, it is possible to realize thermal characteristics equivalent to those of the thermal head marked with a circle by selecting an interpolation value from the correction table, calculating the applied power P, and reducing the applied power P. is there.

[0022]

As described above, the present invention measures the temperature of the thermal head before and after the test printing in order to correct the amount of electric power applied to the thermal head, and compares the temperature difference with an expected value. Since the applied power is controlled by the method, the printing quality can be effectively improved at low cost.

[Brief description of drawings]

FIG. 1 is a flowchart showing an embodiment of an applied energy correction method for a thermal transfer multicolor printing apparatus of the present invention.

FIG. 2 is a block diagram of a thermal transfer type multicolor printing apparatus to which the applied energy correction method of the present invention is applied.

FIG. 3 is a diagram showing an experimental result of the applied energy correction method of the present invention.

[Explanation of symbols]

 1 Memory 2 TPHI / F 3 TPH 4 Temperature Sensitive Element 5 A / D Converter Block 6 D / A Converter Block 7 PSU Block

Claims (1)

[Claims] 1. A thermal transfer multicolor printing apparatus comprising: a means for detecting the temperature of the thermal head; a means for executing test printing for raising the temperature of the thermal head; and a means for varying the amount of energy applied to the thermal head. , Correct the amount of energy that contributes to printing by the following procedure,
A method for correcting an applied energy amount, which is characterized by improving print quality. (A) Detecting the temperature of the thermal head before starting the printing operation, (b) executing test printing, (c) detecting the temperature of the thermal head after executing test printing, and (d) (ii) ) And (C) the temperature difference is calculated, (E) The calculation result of (D) is compared with the expected value, and (F) The amount of energy applied to the thermal head so that the difference from the expected value is reduced. Be variable.