JPH0538839A - Thermal printer - Google Patents

Abstract

PURPOSE:To provide a thermal printer of simple structure which performs printing precisely corresponding to the density of image by changing over the feeding speed of paper corresponding to image density. CONSTITUTION:When it is judged that the image density is thick in comparison with a reference value, a motor 9 is driven at a low speed to lower the feeding speed of paper and when it is judged to be thin, the motor 9 is rotated at a high speed to feed the paper at a high speed so that, when the paper is fed by one pitch for printing the following line, the image density is caused to correspond to heating quantity of a thermal head 8, thereby performing the printing precisely based on image information. And, by changing the feeding speed of paper corresponding to the image density by means of a program, even when a transfer speed is changed over in multiple stages, the structure, required for changing over the transfer speed in multiple stages can be simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer.

[0002]

2. Description of the Related Art Although the image density varies depending on the print data, in the thermal head, the heat energy applied to the thermal head is large when the image density is high and small when the image density is low. Since the rise and fall of heat generation of the thermal head is delayed with respect to the drive pulse to the next line, when the heat density of the thermal head reaches a certain value when the image density changes from a low density to a high density The print density is insufficient because it is sent to. On the contrary, when the image density shifts from the high density state to the light density state, it takes time for the heat energy of the thermal head to drop to a constant value, so that there is a problem that the print density of the next line becomes darker than the image information.

On the other hand, as described in JP-A-58-75958, a changeover switch for changing the transfer speed by a thermal head is provided, and when there are many black images of image information, the changeover switch slows down the transfer speed. However, there is a thermal printer in which the transfer speed is increased when there are few black images.

[0004]

Problems to be Solved by the Invention JP-A-58-7595
In the invention described in Japanese Patent Publication No. 8, since the transfer speed is switched by the changeover switch, the number of changeover switches must be increased when the transfer speed is changed in multiple stages, which complicates the structure and increases the cost. There is a problem.

[0005]

According to the present invention, there is provided a thermal head, a motor for driving a sheet feeding section, a head driving section for changing heat generation energy applied to the thermal head according to an image density based on image information, and at least an image. The storage unit stores a program for changing the rotation speed of the motor according to the image density based on the information, and the motor drive unit that drives the motor under the control of the program of the storage unit.

[0006]

The image density can be determined by the output from the scanner or the dot data called from the character generator corresponding to the print data. However, when it is determined that the image density is higher than the reference value, The motor can be rotated at low speed to feed the paper at low speed, and if it is determined that the image density is low, the motor can be rotated at high speed to feed the paper at high speed. The image density and the heat generation amount of the thermal head can be made to correspond to each other when the paper is fed by one pitch.
Printing can be performed faithfully based on image information. Further, since the paper feed speed corresponding to the image density can be changed by the program, the structure for switching the transfer speed in multiple stages can be simplified even when the transfer speed is switched in multiple stages.

[0007]

An embodiment of the present invention will be described with reference to the drawings. Reference numeral 1 denotes a scanner, and a photoelectric conversion unit 2 such as an image sensor of the scanner is connected to an image memory 4 via an interface 3. The image memory 4 is connected to the controller 5 and the head drive unit 6. The output side of the controller 5 is connected to a head drive unit 6 and a motor drive unit 7, and the head drive unit 6 is connected to a thermal head 8 in which a large number of heating elements are linearly arranged in the main scanning direction. A pulse motor 9 which is a motor for driving a paper feeding unit (not shown) is connected to the motor driving unit 7.

The head drive unit 6 changes the heat generation energy applied to the thermal head 8 according to the image density based on the image information transferred from the image memory 4. The controller 5 has a ROM 10 and a RAM 11 which are storage units in which programs are stored. The ROM 10 includes a program that determines the timing for outputting a drive signal from the head drive unit 6 based on the image information transferred from the image memory 4, and a program that changes the rotation speed of the motor 9 according to the image density. Stores programs that include.

In such a configuration, the image of the original read by the scanner 1 is converted from an optical signal into an electrical signal by the photoelectric conversion unit 2 and stored in the image memory 4 via the interface 3. The head drive unit 6 changes the heat generation energy applied to the thermal head 8 according to the image density based on the image information transferred from the image memory 4.

On the other hand, the controller 5 determines the timing for outputting the drive signal from the head drive section 6 based on the image information transferred from the image memory 4 when the image information exists in the entire area in the main scanning direction. The operation of the motor drive unit 7 is performed to compare the image density of the image information stored in the image memory 5 with a reference value to determine the degree of shading and change the rotation speed of the pulse motor 9 according to the image density. To control.

Therefore, when it is judged that the image density is higher than the reference value, the pulse motor 9 is rotated at a low speed to feed the paper at a low speed, and when it is judged that the image density is low, the motor 9 is driven. It is possible to rotate the paper at a high speed to feed the paper at a high speed, which allows the image density and the heat generation amount of the thermal head 8 to correspond to each other when the paper is fed one pitch for printing the next line. The image information can be printed faithfully. Further, since the sheet feeding speed corresponding to the image density can be changed by the program, even when the transfer speed is switched in multiple stages, the structure for switching the transfer speed in multiple stages can be simplified.

The image density is judged by comparing the dot density in one line with a reference value based on the output of the scanner 1, but the gradation density is compared with the reference value. The image density may be determined by. The present invention is also applied to a thermal printer that does not have the scanner 1. In this case,
The dot density may be determined by calling dot data from the character generator based on the print data from the host computer and comparing the dot density in one line at this time with a reference value.

[0013]

According to the present invention, a thermal head, a motor for driving a paper feeding section, a head driving section for changing heat generation energy applied to the thermal head according to an image density based on image information, and an image based on at least the image information. The storage unit that stores a program that changes the rotation speed of the motor according to the density, and the motor drive unit that drives the motor under the control of the program of the storage unit, output from the scanner, or The image density can be judged by the dot data called from the character generator corresponding to the print data, but if it is judged that the image density is higher than the reference value, the motor is rotated at a low speed and the paper speed is reduced. If it is determined that the image density is low, the motor can be rotated at high speed to feed the paper at high speed. Can, thereby, the heating value of the image density and the thermal head when the sheet for the next line printing sent one pitch can be made to correspond, therefore,
It can be printed faithfully based on image information, and
Since the sheet feeding speed corresponding to the image density can be changed by the program, even when the transfer speed is switched in multiple stages, the structure for switching the transfer speed in multiple stages can be simplified.

[Brief description of drawings]

FIG. 1 is an electronic circuit showing an embodiment of the present invention.

[Explanation of symbols]

 6 Head drive unit 7 Motor drive unit 8 Thermal head 9 Motor

Claims (1)

[Claims] 1. A thermal head, a motor for driving a paper feed unit, a head drive unit that changes heat generation energy applied to the thermal head according to an image density based on image information, and at least according to an image density based on the image information. A thermal printer comprising: a storage unit that stores a program for changing the rotation speed of the motor; and a motor drive unit that drives the motor under the control of the program of the storage unit.