JPH04229283A - Thermal transfer recording apparatus - Google Patents

Abstract

PURPOSE:To detect the density of an image on the basis of a black solid and to accurately correct density irregularity in a main scanning direction. CONSTITUTION:When recording is carried out in order to detect the density of an image, heating resistors adjacent to each other are divided into a plurality blocks so as not to belong to the same block to change the printing times of the respective blocks and the difference DELTAt of the printing timing between the respective blocks is set to an one-line time or longer in a normal printing state.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image density control method for a thermal transfer recording apparatus using a thermal transfer recording principle. The present invention can be suitably used in printers, copying machines, facsimile machines, etc. that use the thermal transfer recording principle.

0002

2. Description of the Related Art FIG. 10 shows the recording principle of a thermal transfer recording apparatus. In FIG. 10, reference numeral 50 indicates a thermal head, and the thermal head 50 includes a substantially semicircular glaze layer 52 on a thermal head base 51, a heat generating resistor 54, and a heat generating resistor 54 for passing current through the heat generating resistor 54. It is constructed by forming an electrode 56 and a protective layer 58 of the heating resistor 54. The thermal head 50 also has a recording paper 6 on its circumferential surface.
It is provided opposite to a platen 62 that holds 0. An ink sheet 64 is placed between the thermal head 50 and the recording paper 60.
are sandwiched between them, and are configured to transmit the heat of the heating resistor 54 to the ink on the ink sheet 64 via the protective layer 58, and transfer the ink to the recording paper 60. Here, a plurality of heating resistors of the thermal head 50 are arranged in a direction perpendicular to the plane of the paper.

When printing is performed with a thermal transfer device having such a structure, the direction in which the thermal heads are lined up (the main scanning direction) is
Density unevenness occurs in the direction perpendicular to the paper surface. The causes of this include: (1) variations in the resistance value R of the heating resistor 54 from one recording head to another, (2) non-uniformity in the thickness t of the protective layer 58, and (2) non-uniformity in the pressing force P of the thermal head 50. As a means for correcting this density unevenness, Japanese Patent Laid-Open No. 59-201
The method disclosed in No. 876 detects variations in resistance values and controls energy (applied voltage) applied between electrodes in accordance with the variations.

0004

[Problem to be Solved by the Invention] However, this method is effective only for (1) of the above three causes, and does not address the other causes, so density unevenness cannot be completely corrected. Not done. Therefore, in Japanese Patent Application No. 63-80697, in order to correct the above three causes all at once, the applicant performed so-called solid printing, in which all the recording heads print once, and detected the density unevenness. have already proposed a method for controlling the energy applied to each resistor. However, subsequent research revealed that even this method had errors in detection accuracy. The error will be explained below.

FIG. 11 shows the image density when printing is performed using each heating resistor. In FIG. 11, the horizontal axis indicates each head position in the arrangement direction of the heating resistors, and the vertical axis indicates image density. Further, the broken line indicates the density distribution when printing is performed using each heating resistor independently, and the solid line indicates the density distribution when printing is performed using all heating resistors. As can be seen from this figure, when solid printing is performed, due to the influence of heat from the surrounding heating resistor, the density difference (ΔOD) that should originally be corrected changes to the density difference (ΔOD') that includes an error. ). . Furthermore, this tendency is particularly noticeable at the end where there is no heating resistor on one side. In addition, FIG. 12 shows multiple rows of the same heating resistor,
FIG. 3 is a diagram showing the relationship between the distance in the conveying direction and the image density when printing. In this figure, the horizontal axis indicates the sheet recording paper conveyance direction, each scale indicates the number of printed lines, and the vertical axis indicates image density. In this case as well, compared to the normal density distribution shown by the broken line, the printed density tends to become darker due to the influence of heat accumulated in the recording head itself for each number of printed lines, as shown by the solid line, and the printed density is detected. Depending on which line is used, there is a risk that the difference from the concentration to be controlled may be overestimated or underestimated. In this way, to measure the printing density, we need to take into account the influence of heat between the heating resistors in the direction perpendicular to the paper surface in Figure 10, and the influence of heat accumulated in the recording head for each number of lines when printing multiple lines. If this is not taken into account, accurate concentration detection will not be possible.

An object of the present invention is to provide a thermal transfer recording apparatus that can accurately correct density unevenness in the main scanning direction.

[0007]

[Means for Solving the Problems] The present invention provides a recording head in which a plurality of heating resistors are arranged in rows in the horizontal direction, image density detection means for detecting the density of an image recorded by the recording head, and applied energy control means for controlling the energy applied to the heating resistor according to the image density detected, records an image when not printing, detects the image density, and controls each heating element according to the detected density. This is a thermal transfer recording device that controls the energy applied to the resistor. When the control means of the apparatus performs recording for image density detection, the heating resistors are divided into a plurality of blocks so that adjacent heating resistors do not belong to the same block, and each block is The printing time is changed, and the printing timing deviation between each block is controlled to be equal to or longer than one line time in the normal printing state.

[0008]

[Operation] In this invention, the heating resistors are divided into a plurality of blocks so that adjacent heating resistors do not belong to the same block, and the printing time is changed for each block. By eliminating the influence of heat and making the printing timing difference between each block longer than one line time under normal printing conditions, the influence of heat accumulated in the recording head for each number of lines to be printed can be reduced. Exclude. Therefore, accurate image density detection can be performed, and accurate correction can be made for each heating resistor.

[0009]

[Examples] Examples of the present invention will be described below. FIG. 1 is a schematic diagram of an embodiment of a thermal transfer recording apparatus according to the present invention. In the figure, reference numeral 2 indicates a recording head in which a plurality of heating resistors are arranged in the horizontal direction. The recording head 2
are arranged in the cylindrical length direction of the platen drum 4. A light source 6 is provided behind the recording head 2 in the rotational direction of the platen drum 4 for irradiating light onto the recorded image density. The light emitted from the light source 6 is reflected by the recording paper 8 held on the peripheral surface of the platen drum 4, and is configured to be irradiated onto a photodetector (CCD) 12 by a condenser lens 10. The control system of this device includes a CCD drive section 14 that drives the CCD 12, and its CC
a correction unit 16 that calculates energy to be applied to each heating resistor of the recording head based on optical information from the D drive unit 14;
The recording head driving section 18 drives the recording head 2. In this embodiment, a recording paper 8 and an ink sheet 20 are sandwiched between a platen drum 4 and a recording head 2, and a heating resistor is activated by an image signal inputted to a recording head drive unit 18 via a correction unit 16. It is configured to heat and transfer the thermal ink applied to the ink sheet 20 onto the recording paper 8 to print an image. The ink sheet 20 is sent from the supply roll 22 to the take-up roll 24 in synchronization with the feeding of the recording paper 8. Note that recording head 2
The on-off control of the heating resistor is performed by the recording head drive unit 18.
The density of the printed image is detected by the light reflected from the light source 6 on the recording paper 8 on the CCD 12.

When the ink sheet 20 is printed, it exhibits density characteristics as shown in FIG. In FIG. 2, the horizontal axis represents the number of pulses that control the applied energy, and the vertical axis represents the image density. As can be seen from Figure 2, the number of pulses is non-linear in the low and high concentration areas, but linear in the medium concentration area, so this part is used to correct the energy applied to each heating resistor. use In this embodiment, the intermediate density ODm is used in the portion where ODm=ODmax/2. In addition, as shown in FIG. 3, a pulse number margin ΔP is set so that the image density ODm of each heating resistor of the recording head 2 falls within the range, and the pulse number Ph corresponding to a high density image is set to Ph=Pm+ΔP. The number of pulses Pl corresponding to a low density image is determined as Pl=Pm-ΔP. In FIG. 3, the horizontal axis represents the position in the line direction, and the vertical axis represents the image density. Then, as in the printing example shown in FIG. 4, images corresponding to Ph and Pl in FIG. 2 are alternately printed on recording paper, and the respective densities are detected by the CCD 12. The CCD drive unit 14 performs shading correction on the recording paper 8 before measurement. The measurement results are shown in Figure 5. In FIG. 5, the circular points indicate the image density corresponding to Ph, and the triangular points indicate the density corresponding to Pl. The horizontal axis is the arrangement number of the heating resistors, that is, the dot number. In this embodiment, as shown in FIG. 2, since the part where the number of pulses and the image density are linear is used, the number of pulses corresponding to the ODm of each heating resistor is calculated from the relationship between the number of pulses and the image density.

[0011] becomes. However, i indicates the number of the heating resistor.

Next, FIG. 6 shows the configuration of the correction section 16 according to this embodiment. In FIG. 6, reference numeral 26 indicates a 1-line OD memory, which is a memory for recording concentration data for each heating resistor. The arithmetic unit 28 is a circuit that performs the arithmetic operation of the equation (2). The line data memory 30 is a memory that records correction data for each heating resistor calculated by the calculation unit 28. The data converter 32 is a circuit that converts image data from an upper level signal device into a signal corresponding to the recording head drive unit 18. In the configuration of such a correction section, first, FIG.
The Ph part of the printing example for density measurement shown in
12 converts it into a voltage, and the CCD drive unit 14 converts it into a digital value and outputs one line O as concentration data for each heating resistor.
Write to D memory 26. Next, the Pl portion is similarly converted into a digital value, and is input into the calculation unit 28 together with the Ph data in the 1-line OD memory 26, and after performing the calculation of equation (2), it is written into the line data memory 30. Next, when printing an actual image, the data converter 32 corrects the number of pulses corresponding to the applied energy using the element number information of the heating resistor and the read correction data of the heating resistor. As a result, uniform heat generation can be achieved as shown in FIG. In addition, in FIG. 7, the horizontal axis represents the line position, and the vertical axis represents the image density.
0 indicates the image density before correction, and 42 indicates the image density after correction.

Here, as shown in FIG. 4, Ph, Pl
When images corresponding to the number of lines are printed alternately on the recording paper, errors occur due to the effect of heat between the heating resistors described above and the effect of heat accumulated in the recording head for each number of printed lines. Next, a method for removing this error will be explained. FIG. 8 is a diagram showing the relationship between energy applied to each heating resistor and time for density correction. Normally, the arrangement direction of the heating resistors is affected by the arrangement pitch of the heating resistors.
Since it is about twice as large, in this case it is divided into three blocks. Therefore, adjacent heating resistors (for example, resistor 1 and resistor 2, resistor 2 and resistor 3, etc.) belong to different blocks. Furthermore, an interval of Δt is provided between printing blocks. Here, Δt is approximately several to several tens of times (indicated by k) the one-line time t0 during regular printing. Here, Δt=kt0. FIG. 9 shows a printed image when printing is performed by dividing into blocks as shown in FIG. In FIG. 9, the vertical direction indicates the ink sheet recording paper conveyance direction, and the horizontal direction indicates the heating resistor arrangement direction. The first line is printed using the 1st, 4th, 7th,...th heating resistor among the heating resistors, and the second line is printed using the 2nd, 5th, 8th... heating resistor among the heating resistors. The third line is printed using the 3rd, 6th, 9th, . . . heat generating resistors among the heat generating resistors. In this way, when the arrangement pitch of the heating resistors is defined as (kX) is removed, so the influence of heat accumulation is also eliminated. Figure 9
By detecting the density of an image such as , and controlling the energy applied to each heating resistor so that the image density is normal, the variations in each heating resistor are extracted and corrected. becomes possible.

Note that the present invention is not limited to the embodiments described above, and various modifications are possible. For example, in the above embodiment, the heating resistors are divided into three blocks, but the same effect can be obtained even if the blocks are divided into blocks of 4, 5, 6, etc. Also, even if the heating resistors are divided into two blocks, the The accuracy of correction will be higher. Further, in the embodiment described above, the energy applied to each heating resistor is controlled by controlling the number of pulses, but if the applied voltage and the applied density are linear, for example, a similar control using voltage may be performed.

[0015]

Effects of the Invention According to the present invention, the influence of heat between the heat generating resistors in the direction perpendicular to the paper surface and the influence of heat accumulated in the recording head for each printing line are eliminated, and the printing of each heat generating resistor is improved. Since the image density can be detected, density unevenness in the main scanning direction can be corrected with high precision.

[0016]

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a thermal transfer recording apparatus according to an embodiment of the present invention.

FIG. 2 is a density characteristic diagram when an ink sheet is printed.

FIG. 3 is a diagram for explaining how to take a pulse number margin ΔP in this embodiment.

FIG. 4 is a diagram showing an example of printing for density detection according to the present embodiment.

FIG. 5 is a diagram showing measurement results according to this example.

FIG. 6 is a block diagram showing the configuration of a correction section according to the present embodiment.

FIG. 7 is a diagram showing image density states before and after correction.

FIG. 8 is a diagram showing the relationship between time and energy applied to each heating resistor for concentration correction.

9 is an enlarged view showing a printed image when printing is performed by dividing into blocks as shown in FIG. 8; FIG.

FIG. 10 is a diagram showing the recording principle of a thermal transfer recording device.

FIG. 11 is a diagram for explaining errors due to the influence of heat between heating resistors.

FIG. 12 is a diagram for explaining errors caused by the influence of heat accumulated in the recording head for each number of printed lines.

[Explanation of symbols]

2 Recording head 4 Platen drum 6 Light source 8 Recording paper 10　　　　　　　　　　　　　Condensing lens 12 Photodetector (CCD) 14 CCD drive circuit 16 Correction section 18 Recording head drive unit 20 Ink sheet

Claims (1)

[Claims] 1. A recording head in which a plurality of heating resistors are arranged in rows in the horizontal direction; image density detection means for detecting the density of an image recorded by the recording head; applied energy control means for controlling the energy applied to the heating resistors, records an image when not printing, detects the image density, and applies energy to each heating resistor according to the detected density. In the thermal transfer recording device, when recording for image density detection, the heating resistors are divided into a plurality of blocks so that adjacent heating resistors do not belong to the same block. A thermal transfer recording device characterized in that the printing time is changed depending on the block, and the difference in printing timing between each block is equal to or longer than one line time in a normal printing state.