JPH06320776A - Thermal head driving device - Google Patents

Abstract

PURPOSE:To obtain a high quality picture having no variety in density by a method wherein the driving of a thermal head, which considers factors such as the temperature of the head, the resistance of a heat generating body element, the speed of transfer of printing medium and the like which contribute to a variety of density, is realized. CONSTITUTION:A thermal head driving device drives a thermal head 104, consisting of a plurality of pieces of heat generating elements, one line by one line in accordance with printing data. The driving device is equipped with a pulse controlling unit A110, satisfying the condition of tA<=1/2t1 when the printing time t1 of one line is divided into a fore half part tA and an aft half part tB and determining a driving pulse during the time tA, a pulse controlling unit B107, determining the driving pulse during the time tB, and a head driving unit 108, driving the thermal head 104 based on the number of pulses which are outputted by the pulse controlling unit 110 and the other pulse controlling unit B107.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head driving device for a color or black and white thermal transfer recording device used as an output device for a computer or the like.
The present invention relates to a thermal head drive device in consideration of factors causing density unevenness such as head temperature, heating element resistance, and print medium conveyance speed.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Laid-Open No. 2-231158.
A "thermal transfer printer" disclosed in Japanese Patent Publication is known. This thermal transfer printer accelerates thermal transfer of the sublimable dye by applying a constant voltage lower than that at the time of printing to a heating element (heating element forming a thermal head) during paper feeding to perform residual heat, It aims to improve printing efficiency and speed up printing.

[0003]

However, in the conventional thermal transfer printer as described above, a constant voltage lower than that at the time of printing is applied to the heating element during the paper feeding time to perform the residual heat. However, normally, the temperature of the thermal head is not constant but changes due to factors such as the temperature condition of the head and variations in resistance of the heating elements. That is, there is a problem in that the residual heat of a constant voltage does not always prevent the occurrence of density unevenness, but rather the density unevenness may increase. Further, when the switching means for the residual heat of the thermal head is provided in the power supply circuit, some noise removing means is required, which is not sufficient in practical use.

The present invention has been made in view of the above, and realizes thermal head driving in consideration of factors that contribute to density unevenness, such as head temperature, heating element resistance, and print medium conveyance speed, to realize density The purpose is to obtain a high quality image without unevenness.

[0005]

In order to achieve the above object, the present invention provides a thermal head driving device for driving a thermal head composed of a plurality of heating elements line by line corresponding to print data. Printing time for one line t _l
Is divided into a first half t _A and a second half t _B , t _A ≤
First pulse control means that satisfies 1 / 2t _l and determines a drive pulse during the t _A time, second pulse control means that determines a drive pulse during the t _B time, and the first pulse The present invention provides a thermal head drive device including a control means and a head drive means for driving the thermal head based on the number of pulses output by the second pulse control means.

Further, it is desirable that the second pulse control means determines the drive pulse based on the print data indicating the gradation.

Further, the first pulse control means has information such as a known resistance value of the thermal head and the end portion of the printing area, ink sheet conveying speed, image receiving sheet conveying speed, ink sheet and image receiving portion. It is desirable to control based on the difference in paper transport speed and the temperature of the thermal head.

[0008]

In the thermal head drive device according to the present invention, the printing time t _l for one line is set to the two _values of the first half t _A and the second half t _B.
The drive pulse during the time t _A is determined by the first pulse control means so as to satisfy t _A ≦ 1 / 2t _l by being divided into two times, and the t _{B is} controlled by the second pulse control means.
The drive pulse during the time is determined and the head drive means drives the thermal head based on the number of pulses output by the first pulse control means and the second pulse control means, so that density unevenness does not occur. Form an image.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of a thermal head driving device according to the present invention. In the figure, the configuration of the print portion is configured as follows. That is,
Reference numeral 101 denotes an ink sheet that is conveyed in a roll shape or a film shape, and includes Y (yellow), M (magenta),
It has a configuration capable of color printing such as C (cyan).
Further, 102 is an image receiving paper onto which the melted ink due to heat generation of the ink sheet 101 is transferred, 103 is a platen roller having a highly smooth surface for supporting the image receiving paper 102 from below, and 104 is a plurality of substrates on the substrate. This is a thermal head in which minute heating elements are arranged in a line and embedded.

The control system of this apparatus is constructed as follows. That is, 105 is a memory unit that stores print data, 106 is a data conversion unit B that executes γ correction processing of print data, 107 is a pulse control unit B that determines the pulse output at time t _B (see FIG. 2), A head drive unit for driving the thermal head 104, 109 is a data conversion unit A, 110 for adding a known resistance value of the thermal head 104, edge information of the print area, and the like, and a pulse for t _A time (see FIG. 2). A pulse control unit A, 111 that determines the output is a head temperature detection unit that detects the heat generation temperature of the thermal head 104, and 112 is the ink sheet 101.
Ink sheet conveyance speed detection unit for detecting the conveyance speed of the
Reference numeral 13 denotes an image receiving paper conveyance speed detection unit that detects the conveyance speed of the image receiving paper 102, and 114 denotes an ink sheet conveyance speed detection unit 112.
And the respective output sides of the image receiving paper conveyance speed detection unit 113 are connected,
Ink sheet that detects the speed difference of each detected transport speed
An image receiving paper speed difference detection unit.

FIG. 2 is a graph showing the relationship between the number of thermal head drive pulses and the print density according to the present invention. In the figure, t _l is the printing time for one line, and is composed of the printing time t _A driven by the residual heat pulse shown in the first half and the printing time t _B driven by the gradation control pulse shown in the latter half. There is. The relationship between the printing time t _A and the printing time t _B is t _A ≤t _B. That is, t _A
+ T _B = t _l , t _A ≦ 1 / 2t _l .

As is apparent from the graph of FIG. 2, the print density at the residual heat pulse during the time t _A remains 0 and t _B
The print density comes out by the gradation control pulse during the time.
In order to obtain a printed image without density unevenness, the characteristics must be stabilized during this t _B time. That is, pulse control is executed so as not to sway in the direction of the arrows (←, →) shown. For that purpose, the heat generation temperature of the thermal head 104, the thermal change of the print medium and the like can be realized by feedback-controlling the drive pulse during the time t _A.

Next, based on the characteristics shown in FIG.
The operation of the thermal head driving device configured as shown in FIG. 1 will be described. First, print data transmitted from a host machine (not shown) such as a personal computer is stored in the memory unit 105. After that, memory unit 1
The print data stored in 05 is sent to the data conversion unit A109 as heat storage information. The print data is sent to the data conversion unit B106 as the original print data. Further, the data conversion unit B106 executes conversion processing (γ correction) for correcting the printing characteristics (the portion of the γ curve) shown in FIG. 2 into a straight line.

In addition, the data conversion unit A109 adds information that the resistance value of the thermal head 104 and the end portion of the printing area are known in advance, and the pulse control unit A110.
Send to. In the pulse control unit A110, the ink sheet 10 detected by the ink sheet transport speed detection unit 112 is used.
1 conveyance speed information, the image reception paper conveyance speed detection unit 113 conveyance speed information of the image receiving paper 102, and the ink sheet / image reception paper speed difference detection unit 114 based on the both conveyance information, the ink sheet 101 and the image reception paper 102. Information about the difference in transport speed of the thermal head 10 from the head temperature detection unit 111.
The temperature information of 4 is transmitted. Then, based on these pieces of information, the final number of residual heat pulses to be driven during the time t _A is determined. The number of drive pulses may be either height or width.

In the pulse control unit B107,
The final pulse number to be driven during the time t _B is determined based on the print data γ-corrected by the data converter B106. That is, the thermal head drive pulse during the time t _B is controlled by the print data indicating the gradation. And
The pulse control unit A110 and the pulse control unit B107
The total number of drive pulses determined by the thermal head 10 is calculated by the head drive unit 108 based on the total value.
Drive 4 As a result, the arrows (←,
Since the factor that touches the (→) direction is corrected, a printed image with stable printing density without uneven density can be obtained.

Further, in the above, the drive pulse control of the thermal head 104 during the time t _{A is performed} in the frame sequential (Y, M,
When performing color printing (C, etc.), since the ink sensitivity varies depending on the type of ink, it is necessary to apply energy for each surface for each color.

Further, in the above description, in consideration of the case where the temperature detection of the thermal head 104 does not follow when high-speed printing is executed, the driving pulse of the thermal head 104 during the time t _A is accumulated. Control based on the printed data. Further, the print data for each heating element is used as heat storage information, and the drive pulse of the thermal head 104 during the time t _A is controlled based on the print data accumulated for each heating element. As a result, the thermal head 1
The heat distribution of No. 04 is made uniform, and uneven density is eliminated.

Further, in order to prevent the occurrence of density unevenness caused by a difference in heat generation energy due to a variation in resistance of the heating element, the drive pulse of the thermal head 104 during the time t _{A is} set to the resistance value of the heating element and the print data. Control based on. Further, at the end of the print area, heat easily escapes and the print density decreases, so the drive pulse of the thermal head 104 during the time t _A is increased in drive energy near the end of the print area.

[0019]

As described above, according to the thermal head driving device of the present invention, the printing time t _{l for} one line is
Is divided into a first half part t _A and a second half part t _B , and t _A ≦ 1 /
2 t _l is satisfied, and the t _{A is} controlled by the first pulse control means.
The drive pulse during the time t _B is determined, and the drive pulse during the time t _B is determined by the second pulse control means.
Since the head drive means drives the thermal head based on the number of pulses output by the pulse control means and the second pulse control means, fine pulse control is realized and high quality without density unevenness is realized. An image is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a thermal head driving device according to the present invention.

FIG. 2 is a graph showing the relationship between the number of thermal head drive pulses and the print density according to the present invention.

[Explanation of symbols]

101 ink sheet 102 image receiving paper 104 thermal head 107 pulse control unit B 108 head drive unit 109 data conversion unit A 110 pulse control unit A 111 head temperature detection unit 112 ink sheet conveyance speed detection unit 113 image reception paper conveyance speed detection unit 114 ink sheet・ Receiving paper speed difference detector

Claims (3)

[Claims] 1. A thermal head driving device for driving a thermal head composed of a plurality of heating elements line by line corresponding to print data, wherein a printing time t _l for one line is a first half t _A and a second half t _B. When divided into t _A ≦ 1
/ 2t _l and first pulse control means for determining a drive pulse during the t _A time, second pulse control means for determining a drive pulse during the t _B time, and the first pulse control Means and a head drive means for driving the thermal head based on the number of pulses output by the second pulse control means. 2. The thermal head drive device according to claim 1, wherein the second pulse control means determines the drive pulse based on print data indicating gradation. 3. The first pulse control means includes information such as a known resistance value of a thermal head and an end portion of a print area, an ink sheet conveying speed, an image receiving sheet conveying speed, an ink sheet and an image receiving portion. 2. The thermal head drive device according to claim 1, wherein the thermal head drive device is controlled based on a difference in paper conveyance speed and a temperature of the thermal head.