JPH02235769A - Image printer - Google Patents

Abstract

PURPOSE:To obtain desirable quality of an image without density difference by previously grasping an irregularity in the resistance values of resistors for forming dots of a thermal head, and controlling a printing time based on the irregular data at the time of printing. CONSTITUTION:When a power source is, for example, turned ON at the time of image printing, stored data of EEPROM 5 is immediately read. If the resistance value of the resistor of a dot to be printed is larger than an average value based on the data, a shorter strobe pulse than a reference strobe pulse is output to the resistor, and if the resistance value is smaller than the average value, a longer strobe pulse is output to a latch circuit 2 from a CPU 4. Thus, a printing time is controlled to be increased or decreased in response to the resistance value of the resistor to make the density of each dot to be printed substantially uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a thermal transfer printing device using a thermal head, and in particular, to eliminate differences in print density and obtain good image quality.

Conventional technology> Conventionally, a thermal head used in a thermal transfer printing device performs a printing operation based on printing conditions such as head applied voltage and printing time, and the printing conditions at this time are such that each dot of the thermal head is formed. The design is based on the average resistance value of the resistor.

<Problems to be Solved by the Invention> Due to manufacturing reasons, the resistance value of the resistor forming each dot of the thermal head usually varies by about ±15%. For this reason, when the printing conditions of the printing device are set constant, there is a problem in that the printing density varies from dot to dot due to variations in the resistance value of each dot.

The present invention has been made in view of the above problem, and measures and stores data on the variation in resistance of the resistor that forms each dot of the thermal head in advance, and uses the data based on this variation data at the time of printing. The purpose is to obtain good image quality without density differences by controlling the printing time for each dot.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a thermal transfer printing device using a thermal head in which each dot is formed by a resistor. A device such as a dedicated memory that can be electrically read, written, and erased is used to store value variation data, and data on the resistance value variation stored in the element at the time of printing is read out to each thermal head. The present invention provides a printing apparatus characterized by comprising means for controlling the printing time of dots.

For example, an EEPROM (Electrical
lyErasable and Progratata
Able ReadOnIy Memory (electrically erasable and writable read-only memory) is preferably used.

Further, as means for controlling the printing time, a CPU inputs a resistance value variation data signal from the above-mentioned element during printing, and outputs a signal for controlling the application time to each dot of the thermal bed based on the data. is used.

<Function> As mentioned above, by understanding in advance the variation in the resistance value of the resistor that forms each dot of the thermal head, and controlling the printing time during printing based on this variation data, the variation in resistance value can be reduced. When printing with a thermal head that uses certain dots, it is possible to obtain good image quality without any difference in speed.

<Example> Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a printing device based on the present invention,
A is a thermal head for performing a printing operation, and the thermal head A includes a soft renostar 11, a latch circuit 2, and
It is provided with a plurality of resistors 111, n − , R 3 , . . . Rn formed of heating elements constituting each dot. The shift register 1 and latch circuit 2 are connected to the CPU 4, and various data signals are input from the CPU 4.

Resistor R. , R, , R, . A/ to the above ammeter 6
A D converter 3 is connected to the A/D converter 3, and the CPU
4 is connected, and the current value flowing through the head applied voltage terminal detected by the ammeter 6 is converted by the A/D converter 3,
This data is input to the CPU 4.

An electrically readable, writable, and erasable element, such as an EEPROM (dedicated memory) 5, is connected to the CPU 3, and as will be described later, each of the resistors 1N, R! of the thermal head A measured in advance is connected to the CPU 3. The resistance value of ... is memorized.

In the printing apparatus having such a configuration, the shift register 1 shifts head data continuously outputted from the CPU 4 using a shift clock, and converts it into parallel data. The converted parallel data is latched in the latch circuit 2 by a latch signal. The latch circuit 2 has latched data “BI” or “O” based on the head data, but if the strobe signal from the CPU 4 is input in this state, the latched “1” Only the connected resistor generates heat while the strobe pulse is applied, and printing operation is performed.

As described above, each resistor R. , R, . . . due to manufacturing process. Therefore, in the process of assembling the printing device, the variation in the resistance value of the resistor is measured in advance and written (stored) in the EEPROM 5. ). That is, for example, when determining the resistance value of the resistor R1, the CPU is configured such that only the latch circuit 2 to which R1 is connected is latched at "1", and the others are latched at "0".
Head data is output from 4. Then, the ammeter 6 detects the value of the current flowing through the head applied voltage terminal while outputting the strobe signal, and this detected value is transferred to the A/D converter 3.
A/D conversion is performed by the CPU 4, and this data signal is read by the CPU 4. At this time, current flows only through R1 due to the constant voltage applied to the head. Therefore, the resistance value of R1 is the value obtained by dividing the head applied voltage value by the current value read by A/D conversion. In this way, the low antibody R forming each dot sequentially
1. Read the resistance value of R t... and read the resistance value of EEPROM.
5 is remembered. Based on this stored data, CP
In U4, each resistor R. , R, . . . to determine the reference strobe pulse width.

When printing, for example, when the power is turned on, the EEPR
Read the data stored in OM5, and based on this data, if the resistance value of the resistor of the dot to be printed is larger than the average value, a strobe pulse shorter than the reference strobe pulse is applied to the resistor. On the other hand, a longer strobe pulse is output to the latch circuit 2 from the CPLJ 4 for a resistor whose resistance value is smaller than the average value. By controlling the printing time in accordance with the resistance value of the resistor in this way, it is possible to make the shading of each dot to be printed substantially uniform.

<Effects of the Invention> As is clear from the above description, the present invention measures and stores in advance the variation in the resistance value of the resistor that forms each dot of the thermal head used, and eliminates this variation during printing. Since the printing time is controlled according to the data, it is possible to obtain high quality images with no difference in density.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a printing apparatus according to the present invention.

Claims (1)

[Claims] (1) In a thermal transfer printing device that uses a thermal head in which each dot is formed by a resistor, it is possible to electrically read, write, and erase data for storing previously measured resistance variation data of each resistor. The apparatus is characterized by comprising an element such as a dedicated memory, and a means for controlling the printing time of each dot of the thermal head by reading data on the variation in the resistance value stored in the element at the time of printing. Printing device.