JPH0396359A - Thermal head driver - Google Patents

Abstract

PURPOSE:To rewrite table data corresponding to condition change during printing by using a RAM as a memory for holding a gradation table, and rewriting the gradation table. CONSTITUTION:An optimum gradation table immediately before printing is written in a RAM 2 by a CPU 1, a thermal head driving circuit 6 is operated based on the table data and quantized image data, the resistor of a thermal head 7 is controlled ON, OFF, and conduction time is controlled to obtain a desired density printing image. A state change to be deviated from an optimum state is detected by condition change such as temperature of the thermal head, etc., to rewrite the gradation table for the RAM 2 based on a command from the CPU 1 thereby to always hold the optimum gradation data in the conditions such as temperature, etc., and to print an image of a desired density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head driving device n, which is equipped with a thermal head and configured to print a multivalued image, such as a video printer device. It is something. [Prior Art] Figure i2 is a block diagram showing the configuration of a conventional thermal head driving device. In the same figure, (5) corrects the time between energization of the resistor of the thermal head for each multi-value gradation. ROM that holds a data table (hereinafter referred to as gradation table) that is a table of data; (7) is a thermal head; (7) is a thermal head;
8) is a thermal head drive circuit that selects the data of the gradation table from the image data and the temperature of the thermal head (7), and controls the energization time to the resistor (not shown) of the thermal head (7). It is. Next, the operation of the above configuration will be explained. When using the thermal head (7) to obtain a printed image with multilevel gradations, the shorter the time when electricity is applied to the resistor of the thermal head (7), the lighter the color will be, and the longer the time, the darker the color will be. In other words, it is possible to obtain a print image of any density by controlling the time when the resistor of the thermal head (7) is energized;
) The time when electricity is applied to the resistor and the color density are not proportional.
Needs to be corrected.

A table of this correction data for each gradation, that is, a gradation table, is written in R OM (5). Since the coloring characteristics of this gradation table change depending on the temperature of the thermal head (7), a large number of tables are used.
It is written in O M (5).

Thermal head drive circuit (6) is the thermal head (7)
Select one data from the gradation table written in R O M (5) based on the temperature of
), thereby obtaining a printed image with a desired density.

[Problems to be Solved by the Invention] Since the conventional thermal head driving device is configured as described above, it is necessary to write gradation data in the ROM in advance, and furthermore, color development due to temperature changes of the thermal head. In order to eliminate changes in characteristics, it is necessary to store a large number of gradation tables in a ROM, which poses problems such as an increase in memory capacity.

This invention was made in order to solve the above-mentioned problems.It uses a memory with a low capacity sufficient to hold one optimal gradation table immediately before printing, while also adjusting the temperature and other conditions during printing. It is an object of the present invention to provide a thermal head driving device that can rewrite table data in response to changes.

[Means for Solving the Problems] The thermal head driving device according to the present invention uses a RAM as a memory for holding a gradation table, and is configured so that the gradation table can be rewritten in this RAM. It is characterized by what it did.

[Function] According to the present invention, by using a RAM as a memory that holds a gradation table, it is only necessary to have this RAM hold only one optimum gradation table immediately before printing.
This makes it possible to reduce the capacity of the memory and to freely rewrite the gradation table in response to temperature changes in the thermal head during printing.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of a thermal head driving device according to an embodiment of the present invention.
1) is the CPU that transfers the gradation table, and (2) is the RAM that holds the gradation table.The other configurations are the same as the conventional example shown in Fig. 2, so the corresponding parts are given the same reference numerals. The detailed explanation thereof will be omitted.

Next, the operation of the above configuration will be explained.

The optimum gradation table immediately before printing is written from c p u (l) into R A M (2), and the thermal head drive circuit (6) is operated based on the table data and the quantized image data. and thermal head (7
) By controlling the on/off of the resistor and controlling the energization time, a printed image with the desired density can be obtained.

In addition, the gradation table may deviate from the optimal state due to changes in conditions such as the temperature of the thermal head during printing. By rewriting the gradation table for A M (2), you can always maintain the optimal gradation data for conditions such as temperature, and output this to print images with the desired density regardless of changes in conditions. It becomes possible to print.

[Effects of the Invention] As described above, according to the present invention, by using RAM as the memory that holds the gradation table, it is possible to respond to changes in temperature of the thermal head, etc., without reducing the reading speed of table data. The gradation table can be freely rewritten, and the memory capacity can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a thermal head driving device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional thermal head driving device. (1)...CPU, (2)...RAM, (6)...
- Thermal head drive circuit, (7)...Thermal head. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) A thermal head, a memory that holds a data table containing correction data for the energization time to the resistor of the thermal head for each multi-value gradation, and a table based on the table data output from this memory. The thermal head drive device includes a thermal head drive circuit that controls the energization time of the thermal head, wherein the memory is composed of a RAM, and the RAM is provided with means for rewriting the data table. A thermal head drive device featuring: