JPH11348329A - Thermal transfer recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal transfer recording apparatus capable of obtaining a good image by preventing the generation of image irregularity in a recording paper feed direction even when a thermal head is shaken because a printing ratio is different at every line. SOLUTION: In a thermal transfer recording apparatus feeding an ink film along recording paper by using a thermal head having a plurality of heat sources for printing a plurality of dots corresponding to one line at once to control a plurality of the heat sources according to image data to perform printing on the recording paper at every one line, the printing ratio of existing printing lines (n-1) already printing on the recording paper and that of present printing lines (n) to be printed are compared to alter the feed pitch of the recording paper on the basis of the comparison result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal transfer recording apparatus, and more particularly, to a thermal transfer recording apparatus capable of preventing unevenness of an image caused by a difference in printing rate for each line.

[0002]

2. Description of the Related Art As an embodiment of a thermal transfer recording apparatus, a thermal head having a plurality of heat sources for printing a plurality of dots for one line at a time is used, and an ink film is conveyed along a recording sheet to form an image. In some cases, printing is performed on recording paper line by line by controlling the plurality of heat sources in accordance with data.

Conventionally, in such a thermal transfer recording apparatus, the transport pitch in the recording paper transport direction has always been fixed regardless of the content of the image data. Therefore, FIG.
As shown in FIG. 12B, when the difference in the printing rate between the printing lines is small, the dot pitch in the recording paper transport direction on the output image is constant, but as shown in FIG. When the difference in the printing ratio is large, there is a problem that the dot pitch on the output image is not constant, and the image becomes uneven.

[0004] Such a deviation of the dot pitch in the recording paper conveyance direction is caused by a difference in the printing rate of each line, and the amount of heat generated by the thermal head differs for each line. Since the coefficient of friction between the ink film and the thermal head changes and the conveyance load of the recording paper changes, as shown in FIG.
This occurs because the thermal head (T / H) slightly swings in the recording paper transport direction, and the printing position is slightly changed with respect to the recording paper fed at a constant transport pitch.

The cause of such a slight swing of the thermal head is considered as follows. Since the thermal head is in contact with the ink film at a constant pressure, a force (or a force depending on the device configuration, hereinafter the same) acting on the ink film and the recording paper in the transport direction is applied as the ink film and the recording paper are transported. Further, since the thermal head is supported by the support member, a force for maintaining a fixed position acts on the pulling force in the transport direction due to the rigidity of the support member. Such a force is constant when the printing rate of each line is the same, that is, when the heat generation amount of the thermal head does not change significantly for each line and the coefficient of friction between the thermal head and the ink film does not change. Since the balance is maintained as the force acting in the direction, the thermal head does not swing. However, when the difference in printing rate between the lines is large and the amount of heat generated by the thermal head changes, the coefficient of friction between the ink film and the thermal head changes, and the pulling force in the transport direction changes rapidly. For this reason, a sudden difference is generated between the force for pulling the thermal head, which has been balanced so far, and the force for keeping the thermal head at a fixed position, and the thermal head swings.

[0006]

The simplest method for preventing the printing unevenness due to the swinging of the thermal head is to increase the rigidity of the member for supporting the thermal head and to increase the rigidity of the member when the ink film is transported. The purpose is to always keep the thermal head at a fixed position so as not to swing even if the force acting on the thermal head changes.

However, the use of such a rigid support member requires the support member itself to be large or heavy, or to use a high-rigidity and expensive component. It is not preferable because it causes a rise in the price of a product as an apparatus.
Further, depending on the device configuration, there is a device that changes the position of the thermal head between when printing and when only the recording paper is conveyed without printing, and in such a device configuration, the thermal head is changed. Not only the support member but also the position change mechanism of the thermal head must be a mechanism that does not cause the thermal head to swing even if the force applied to the thermal head changes, so that the mechanical configuration itself is complicated and expensive. It is not preferable because it is used.

Accordingly, an object of the present invention is to prevent the occurrence of image unevenness in the recording paper conveyance direction and obtain a good image even when the thermal head swings because the printing rate differs for each line. It is an object of the present invention to provide a thermal transfer recording device that can perform the above.

[0009]

The object of the present invention is achieved by the following means.

(1) Using a thermal head having a plurality of heat sources for printing a plurality of dots for one line at a time, transporting an ink film along a recording paper, and applying the plurality of heat sources in accordance with image data. By controlling
In a thermal transfer recording apparatus for performing printing on recording paper line by line, means for determining a printing ratio of a printed line already printed on the recording paper, and determining a printing ratio of a current printing line to be printed on the recording paper from now on Means, a printing rate comparison means for comparing the printing rate of the already printed line with the printing rate of the current printing line, and changing the recording paper conveyance pitch in the recording paper conveyance direction based on a comparison result by the printing rate comparison means. A transfer pitch changing means for performing the transfer.

(2) The means for determining the printing rate of the already printed line calculates the printing rate of the already printed line from the image data for which printing has already been completed on the recording paper, and calculates the printing rate of the current printing line. The thermal transfer recording apparatus is characterized in that the means for calculating calculates a print ratio of a current print line from image data to be printed on the recording paper.

(3) The printing rate of the already-printed line is obtained by averaging the cumulative value of the printing rates of each of a plurality of already-printed lines from the current printing line to a predetermined number of lines before. A thermal transfer recording apparatus having an average printing rate.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

Embodiment 1 FIG. 1 is a schematic sectional view showing the structure of a thermal transfer recording apparatus to which the present invention is applied, FIG. 2 is a sectional view schematically showing an operation state of the thermal transfer recording apparatus, and FIG. FIG. 2 is a block diagram for explaining a configuration of a control system of the device.

For convenience of explanation, the edge of the recording paper which is the leading edge when the recording paper is discharged is referred to as the leading edge of the recording paper.

The thermal transfer recording apparatus 10 is used, for example, in a developing station for printing a photograph, and outputs a so-called index print for reproducing information recorded on a plurality of frames of a negative film on a single recording sheet. Used to The thermal transfer recording device 10 includes a host computer (not shown) for performing various image processing on information recorded on the negative film.
(See FIG. 3), and an image signal and a control signal from the host computer are input to the control system via the interface 8. The configuration of the control system of the thermal transfer control device 10 will be described later. Also,
Such a thermal transfer recording apparatus 10 is connected to a computer or the like and used for printing an image created by a computer, in addition to printing a photograph or the like.

In the thermal transfer recording apparatus 10, a lid member 12 is mounted on an upper surface of a housing 11 forming a main body so as to be openable and closable about a swing shaft 12a. It is designed to be loaded at a predetermined position in the inside. The left hand side in the figure is the front surface of the apparatus 10, a paper discharge unit is provided on the front side, and a paper supply unit 21 is provided on the back side. The paper feed unit 21 is provided with a paper feed tray 14 that stores a plurality of recording papers in an inclined manner.

The thermal transfer recording apparatus 10 is provided with a recording paper cutting section for cutting unnecessary portions (the leading end and / or the trailing end of the recording paper) of the recording paper after reproducing the image. A duster section 24 for storing the cut recording paper pieces is provided on the front side of the apparatus so as to be freely inserted and removed. The recording paper from which unnecessary portions have been cut passes through the recording paper discharge port 16 and is discharged in a vertical direction onto a discharge tray 17 provided integrally on the front surface of the duster 24. Since the recording paper is discharged in the vertical direction in this manner, the discharge tray 1
The dimension in which the 7 protrudes from the front surface of the housing 11 is relatively small. Further, the paper feed tray 14 is provided at an angle. Therefore, the installation space of the entire thermal transfer recording apparatus 10 is small, and the recording apparatus is suitable for being installed in a place where the working space is narrow.

Further, in the thermal transfer recording apparatus 10 of the present embodiment, an ink film coated with a heat sublimable ink is used, and the recording paper as an image receiving paper for trapping the sublimated ink is such as photographic paper. Thick and strong (150
２５０250 μm).

The outline of the internal structure of the thermal transfer recording apparatus 10 can be summarized as follows: a printing section 20 which is located at a substantially central portion and in which the recording paper 18 is transported in a parallel transport mode; A paper supply unit 21 provided at an angle of about 45 degrees above the paper supply unit 21;
Paper discharge unit 22 provided on the opposite side of paper supply unit 21
And The printing quality of the thick and stiff recording paper 18 is improved by using the printing unit 20 in the parallel transport system. By inclining the paper feed unit 21,
As described above, the installation space is reduced. Further, by providing the paper discharge unit 22 on the opposite side of the paper supply unit 21 with the print unit 20 interposed therebetween, usability such as using a facsimile can be obtained, and the apparatus form is easily accepted by the user. Also, the paper discharge unit 22 includes
A recording paper cutting portion 23 for cutting unnecessary portions of the recording paper 18 after reproducing an image is provided, and the duster portion 24 is disposed below the recording paper cutting portion 23.

The internal structure of the thermal transfer recording apparatus 10 will be described in detail. A platen roller 25 is rotatably supported in the housing 11, and a thermal coupling member (not shown) A head base 27 to which the head 26 is fixed is attached to the platen roller 25 so as to be movable forward and backward. When the head base 27 moves forward with respect to the platen roller 25, the thermal head 26 moves to a position where it comes into pressure contact with the platen roller 25. On the other hand, when the head base 27 moves backward with respect to the platen roller 25, the thermal head 26 makes pressure contact. Move to the position to release. The head base 27 is attached to the thermal head 2 by a resilient means such as a spring (not shown).
6 is urged in the direction shown by the arrow R in FIG.

The thermal head 26 has a plurality of heat sources for printing one line of dots at a time, and the plurality of heat sources are controlled so as to generate heat in accordance with image data. Print each time.

A drive shaft 28 rotatably attached to the cover member 12 is brought into contact with a head base 27 to move the head base 27 forward, thereby pressing the thermal head 26 against the platen roller 25. 29 are fixed. By rotating the drive shaft 28, the eccentric cam 2
A thermal head drive motor M <b> 1 composed of a pulse motor is connected to the drive shaft 28 in order to rotate the drive 9.

Thermal head 26 and platen roller 25
As described later (see FIG. 2), a belt-shaped ink film 32 which is fed from the supply reel 30 and wound on the take-up reel 31 is conveyed. The ink film 32 is formed by applying three color ink layers of yellow, magenta and cyan and an overcoat layer to the base film in this order. The reels 30 and 31 on the supply side and the winding side are housed in an ink film cassette 33.

The ink film cassette 33 is detachable from the housing 11, and is set at a predetermined position by being set on a holding plate 34 mounted in the housing 11. The take-up reel 31 has a gear (not shown) for rotating the take-up reel 31.
A part of the gear faces an opening formed in the ink film cassette 33. When the cassette is mounted, a driving gear 36 provided on the apparatus side meshes with the gear. The driving gear 36 is connected to the motor M2.
The ink film 32 is rotated and driven by the
On the take-up reel 31.

An ink film take-up roller 37 is provided near the platen roller 25 so as to form a transport path for the ink film 32 when the cassette is mounted. The ink film take-up roller 37 is normally free of rotation, but is driven by the ink film take-up motor M3 by engaging a clutch (not shown) only when it is desired to move the ink film 32 during non-printing. On the other hand, at the time of printing, the ink film 32 is sent out as the recording paper 18 is conveyed, and is sent to the ink film guide plate 38 provided at the tip of the thermal head 26 and the ink film take-up roller 37 in a free rotation state. It is guided and wound on the take-up reel 31.

The recording paper 18 is held on the paper feed tray 14 in an inclined state. The recording paper 1 is placed in the paper feed tray 14.
A width regulating plate 40 is provided to regulate the width direction of 8. The width regulating plate 40 is slidable in the width direction according to the size of the recording paper 18.

The recording paper 18 on the paper feed tray 14 is fed one by one by a paper feed roller 45 and a separating roller 46 disposed with a small gap from the paper feed roller 45. The sheet is conveyed while being guided by the guide member 47. The paper feed roller 45 is driven to rotate by a paper feed motor M4 composed of a pulse motor, but the separating roller 46 is not rotated. The separating roller 46 has a hardness of 70 degrees, and its surface is coded. The gap is set to about 0.3 mm obtained by adding a predetermined dimension to the paper thickness. With this configuration, the thick recording paper 18 can be fed smoothly, and the surface of the recording paper 18 is not scratched.

On the upstream side of the platen roller 25, adjacent to the platen roller 25, a grip roller 50 and a pinch roller 5 which comes into contact with the grip roller 50 are arranged.
1 and the fed recording paper 18 is fed between the rollers 50 and 51. Grip roller 5
0 is a grip roller drive motor M composed of a pulse motor
5, the pinch roller 51 is driven to rotate as the recording paper is conveyed.

On the downstream side of the platen roller 25, a first discharge roller pair 53 positioned on the recording paper discharge port 16 side and a position positioned on the platen roller 25 side for discharging the recording paper 18 onto the discharge tray 17. The second discharge roller pair 54 is attached at a predetermined distance. These discharge roller pairs 53 and 54 are driven to rotate by a transport motor M6 composed of a pulse motor.

Between the platen roller 25 and the discharge roller pair 54, there is provided a guide member 55 for guiding the conveyance of the recording paper 18 during the discharge processing. This guide member 55
A storage space 56 for storing the recording paper 18 when a printing operation is performed is formed below the space.

Under the guide member 55, the recording paper 18 conveyed by the grip roller 50 and the pinch roller 51 is transferred to the paper discharge section 22 provided with discharge roller pairs 53 and 54 or the storage space 56. A swing guide 58 is provided so as to be swingable about the support shaft 57 in order to selectively guide the swing guide 58 to one of them. The swing guide 58 is formed of a flexible material. When the swing guide 58 is swung to the upper position, the recording paper 18 conveyed by the grip roller 50 or the like is stored in the storage space 56. On the other hand, when the swing guide 58 swings clockwise about the support shaft 57 from the upper position to the lower position, the recording paper 18 is conveyed toward the paper discharge unit 22.

In order to improve the print quality, it is necessary to prevent the recording paper 18 from being caught by the pair of discharge rollers 53 and 54 during printing. If the storage space 56 is formed at a position below the transport path to the paper section 22, the platen roller 25
And the distance between the discharge roller pair 53 and 54 can be reduced, and the floor area of the apparatus 10 can be reduced.

Further, the recording apparatus 10 is provided with a sensor S1 adjacent to the grip roller 50 for detecting the leading edge of the recording paper at the time of paper feeding or the trailing edge of the recording paper at the time of printing. The sensor S1 issues an ON signal when detecting the leading or trailing edge of the recording paper 18. In addition,
Since the sensor S1 detects the trailing edge of the recording paper during printing, in the following description, for the sake of convenience, the trailing edge detection sensor S1 will be described.
Called.

In the vicinity of the paper discharge section, a cutter unit 23,
A leading edge detection sensor S2 for detecting the leading edge of the recording paper is provided. A cutter 60 for cutting the recording paper 18 is provided in the cutter unit 23. The leading edge detection sensor S2 issues an ON signal when detecting the leading edge of the recording paper 18. The pulse for driving the transport motor M6 is managed based on the time when the leading edge detection sensor S2 detects the leading edge of the recording paper 18, and the recording paper 1 is moved by a predetermined length from the leading edge of the recording paper.
8 and a rear end cut for cutting the recording paper 18 by a predetermined length from the rear end of the recording paper.

The basic operation of reproducing a color image on the recording paper 18 by the illustrated thermal transfer recording apparatus 10 is as follows. First, as shown in FIG.
And transported in the direction indicated by arrow P. At this time, the pressing eccentric cam 29 is set so that the thermal head 26 is at the pressing release position with respect to the platen roller 25. Then, as shown in FIG. 2B, the recording paper 18 is stored in the storage space 56. In this state, the pressure contact eccentric cam 29 is rotated so that the thermal head 26 comes to a position where the thermal head 26 is pressed against the platen roller 25. Next, from this state, an image is formed as shown in FIG. 2C while returning and transporting the recording paper 18 in the direction indicated by the arrow Q.
That is, the return printing method is used. When the printing is completed, the platen roller 2 of the thermal head 26
The pressure contact with 5 is released. That is, the thermal head 2
The thermal head 26 is in contact with the platen roller 25 only during the return conveyance. When the recording paper 18 is conveyed forward, the thermal head 26 is separated from the platen roller 25.

To reproduce the color image, the yellow image is transferred while the recording paper 18 is returned and conveyed, and then the recording paper 18 is conveyed forward in preparation for reproducing the next magenta image. In this way, a color image is formed on the recording paper 18 by transferring, for example, three color images in an overlapping manner by the frame sequential method. When the return conveyance and the forward conveyance are repeated during the printing operation, the grip roller 50 and the pinch roller 51 always hold the recording paper 18 therebetween.

A control unit 19 is disposed below the inside of the thermal transfer recording apparatus 10. As shown in FIG. 3, the control unit 19 controls the operation of the entire printer and also temporarily stores the CPU 1 for correcting the transport pitch described later and the image data of the already printed line as described later. RAM 2, ROM 3 storing table data including a printing rate difference and a recording paper transport pitch, which will be described later, and a control circuit for converting gradation data into an output value of thermal head 26 and controlling a voltage applied to thermal head 26 And a grip roller drive motor M for driving the grip roller 50 of the recording paper transport system from the CPU 1
An input / output (I / O) port 6 for transmitting a signal for controlling the motor 5 to the motor M5, receiving image data from a host computer or the like (not shown), and transmitting the status of the recording apparatus 10 to the host. Interface (I / F) 8 for sending to computer
Consisting of Here, the print voltage control circuit 4 includes a buffer 4 for temporarily storing therein gradation data of one line.
a, and a conversion circuit 4 b for converting the gradation data into an output value of the thermal head 26.

The operation of the control unit 19 is briefly described below. First, image data to be printed is received from the host computer via the I / F 8 and stored in the buffer 4a. When the data received at this time is a color image, image data of three colors, yellow, cyan, and magenta,
One line is sequentially received for each color. As a form of the control device, in addition to the buffer 4a for temporarily storing one line of data, a large capacity capable of storing several lines, or one or several pages of print lines at a time. In some cases, a buffer is provided.

Thereafter, the CPU 1 gives a rotation instruction to the grip roller drive motor M5, and conveys the recording paper 18.
Then, when a signal that detects the rear end of the recording paper 18 is received from the rear end detection sensor S <b> 1, the thermal head 26 is moved to a position where the thermal head 26 is pressed against the platen roller 25. When the preparation for the return printing is completed in this way, the CPU 1 executes the conversion circuit 4b.
To start printing.

The conversion circuit 4b converts the thermal head 2 from the image data for one line stored in the buffer 4a such that the gradation for each dot is reproduced on the recording paper 18.
The output voltage to the thermal head 26 is calculated.

In the CPU 1, the motor M5 is driven simultaneously with the output of the electric power to the thermal head 26 by the conversion circuit 4b to convey the recording paper 18 in the return direction. At this time, C
The PU1 calculates the printing rate for each printing line as described later, and based on the result, the recording paper conveyance pitch (conveyance amount).
Change and control. Thereby, the thermal head 2
6 is pressed at a constant pressure toward the platen roller 25 while sandwiching the recording paper 18 and the ink film thereon, so that the ink film is transported together with the recording paper 18 in the return direction. Then, at the time of conveyance in the return direction, an image for one line is printed by heat from the thermal head 26.

By continuously performing such operations, all lines are printed, and an image for one screen is printed. In the case of a color image, the same processing is performed for each of yellow, cyan, and magenta.

During the printing operation, the thermal head 26 is pulled in the recording paper transport direction by friction between the ink film 32 and the recording paper 18 as the ink film 32 and the recording paper 18 are transported. (Pressed down) force is applied. With such a force,
The position of the thermal head 26 is slightly, but slightly, shifted in the recording paper transport direction as compared with the state where the recording paper 18 is not transported.

At this time, if the coefficient of friction between the thermal head 26 and the ink film 32 in contact with the thermal head 26 is always constant, the slight displacement of the thermal head 26 is always constant, so that it is given to the image being printed. Has little effect. However, the thermal head 26 and the ink film 3
2 changes with the change in the amount of heat generated by the thermal head 26. The change in the coefficient of friction changes as the change in the amount of heat generated by the thermal head 26 increases. Therefore, if there is a large difference between the printing rate of a certain line and the printing rate of the line to be printed next to that line, the heat value of the thermal head changes rapidly, and the coefficient of friction with the ink film changes. As a result, the thermal head 26 oscillates, which results in an adverse effect on an image to be printed.

For example, as shown in FIG. 4, the thermal head 26 has a total print dot number of one line K, which is composed of 1848 dots, and each dot has a gradation width of 8 bits, that is, 0 to 0. If the amount of heat generated for each dot of the thermal head 26 can be controlled by the gradation data up to 255, all the dots of the already printed line (n-1) before the current printing line n to be printed are toned. Assuming that data 255 is printed (the darkest value) and the gradation data of the current print line n is 10, the print ratio of the already printed line (n-1) and the print ratio of the current print line n are significantly different. 5, the heat value of the thermal head up to the already printed line (n-1) and the heat value of the current print line n change, and as shown in FIG. The thermal head 26 is swung force on the heads or others 26 is changed, previously printed lines (n-1)
The apparent transport pitch on the output image increases between the current print line n and the current print line n, resulting in a shift in the print position of the current print line n. In the case of the drawing, the apparent increase in the apparent transport pitch is that the prescribed paper transport pitch is 4 step / l.
At the time of ine, when the recording paper is actually conveyed, it appears to be 7step / line due to the swing of the thermal head,
That is, it has increased by 3 steps / line. Here, step means
In the present embodiment, since a stepping motor is used as the grip roller drive motor M5, which is a motor for conveying the recording paper, the rotation angle is one excitation of the stepping motor. Therefore, for example, 4step / l
Ine means that the stepping motor is rotated by four steps to feed the recording paper for one line. In the case other than the stepping motor, this step may be considered as the minimum rotation angle of the used motor.

In the first embodiment, the deviation of the apparent transport pitch due to such a difference in the print ratio is determined by calculating the print ratio of the already-printed line and the current print line. The increase (or decrease) is corrected. Therefore, in the above example, the apparent transport pitch is increased by 3 steps / line, and thus, by changing the actual transport pitch to 1 step / line as shown in FIG. The pitch deviation is corrected so that printing is performed at an accurate position.

In the first embodiment, the sum of the gradation data of each dot in one line is used as the printing rate of each line, as described later. This is because, when the gradation is different for each dot and the density is different for each dot, the difference in the density and the dots printed in one line (gray level 1 or more) and the dots not printed (gray level This is because the value is suitable for expressing the printing rate in one line, including the case where 0) exists. Therefore, the printing ratio referred to here represents not only the ratio of a printed portion to a non-printed portion but also a ratio including the density of each dot.

FIG. 7 is a flowchart showing an operation procedure for changing and controlling the conveying pitch of the recording paper and the ink film based on the difference in the printing ratio and printing according to the first embodiment.

First, a variable n indicating the number of print lines required for processing prior to printing is cleared to 0 (S1). Subsequently, when the image data to be printed is transmitted from the host computer, the image data for one line is transferred to the buffer 4a (S2).

Next, from the gradation data of each dot of the image data for one line transferred to the buffer 4a, the total of gradations in the line (current printing line n) is calculated (S3). The sum of the obtained gradation data is the printing rate of the current printing line n to be printed.

Next, as will be described later, from the image data of the printed line (n-1) stored in the RAM 2, the sum of the gradation data of each dot of the printed line (n-1) is calculated ( S4). The sum of the tone data obtained here is the printing rate of the already printed line (n-1).

Next, the difference between the printing rate of the current printing line n and the printing rate of the already-printed line (n-1) is calculated (S5).

Next, with reference to the table data for setting the transport pitch, a transport pitch corresponding to the difference between the print rate of the already printed line (n-1) and the print rate of the current print line n is set. (S6). Here, the table data is shown in FIG.
As shown in FIG. 7, the transport pitch corresponding to the difference ΔS from the printing rate of the current printing line n is stored. Such table data is stored in advance in an actual apparatus by the difference in printing rate and the amount of heat generated by the thermal head. The difference is obtained as to how much the apparent transport pitch changes, and the transport pitch for correcting this is stored. In the case shown in the figure, the number of dots per line is 18 as in the above-described example.
The thermal head has 48 dots and the gradation width of each dot is 8 bits.

Next, the output value of each dot of the thermal head is calculated according to the image data for one line stored in the buffer 4a (S7), and a voltage is applied to each dot of the thermal head according to this output value. (S8). At the same time, the grip roller is driven to convey the recording paper and the ink film at the conveyance pitch set in the step S6 (S9).

As a result, the printing of one line is completed, so that the image data of the current printing line stored in the buffer 4a is transferred to the RAM 2 and the already-printed line (n-1)
(S10). The gradation data of each dot in the stored image data is used for calculating the total sum of the gradation data of the already-printed line in step S4 when printing the next line.

Then, it is determined whether or not all the lines have been printed (S11). If the printing has not been completed, n is incremented by 1 (S12), and step S2 is performed for printing the next line.
Return to Here, if printing of all lines has been completed, it is next determined whether printing of all colors has been completed (S13). If not completed, the process returns to S1 and returns to S1. Print a color image. On the other hand, if the printing of the images of all colors has been completed, the printing operation is completed.

The correction of the transport pitch performed according to the above-described processing will be described with reference to a specific example. Here, as in the example described above, the number of dots in one line is 1848 dots, and the already printed lines (n-
The case where the gradation data of 1) is 255 for all dots and the gradation data of the current print line n is 10 for all dots will be described.

First, the total sum of the gradation data of the current print line n calculated in the step S2 is the gradation data of all the dots 10. Therefore, the total sum _Saf is expressed by the following (1).
As shown in the equation (where (1), T _{i, n} is the gradation value of the i-th dot on the n-th line, K is the total number of dots on one line (see FIG. 4)), and becomes 18480, which is the current printing. This is the printing rate of line n.

[0060]

(Equation 1)

[0061] On the other hand, the gradation data sum S _BE already printed line being calculated in the step S3 (n-1), since the tone data is all the dots 255, the following (2)
As shown in the equation _(where T _{i, (n−1)} is the gradation value of the i-th dot on the (n−1) th line and K is the total number of dots in one line), 471240 This is the already printed line (n
-1) is the printing rate.

[0062]

(Equation 2)

The difference ΔS between the printing ratio (total sum S _{be of} gradation data) of the already printed line (n−1) and the printing ratio (total sum S _{af of} gradation data) of the current printing line n is obtained in step S5. 452760 according to the following equation (3).

[0064]

(Equation 3)

Referring to the table shown in FIG. 8 based on the value of ΔS, the corrected transport pitch of one line is 1
step / line.

Therefore, in this example, by setting the transport pitch when printing the current print line n after printing the already-printed line (n-1) to 1 step / line, as shown in FIG. The apparent transport pitch caused by the swing of the thermal head due to the difference in the printing rate is corrected, and printing is performed at an accurate position.

As a result, even when there is a large difference in the printing rate for each printing line, the image is not displaced and a good image can be reproduced.

In the first embodiment, in order to calculate the printing rate of the already-printed line, the gradation data is stored in the RAM 2 at the time when the printing of the current printing line is completed (the processing of S8 described above). ), Used as gradation data for calculating an already printed line when printing the next line. However, the present invention is not limited to such a calculation method. After the printing of the current print line is completed, the data may be stored in the RAM 2 as it is, and this may be used as the print ratio of the already printed line when printing the next line. By doing so, the processing in step S4 in the above-described flowchart can be omitted.

Embodiment 2 In Embodiment 1 described above, a print line (n-
The conveyance pitch is corrected by comparing only 1).
Therefore, for example, as shown in FIG. 9A, an image in which dark lines and light lines are printed alternately, and as shown in FIG. 9B, an image in which dark lines continue and then light lines are printed. In the case where the gradations of the current print line n and the previous print line (n-1) are the same, in the first embodiment, the print line (n-1) and the current print line n
And the corrected conveyance pitch between them becomes the same.

However, depending on the configuration of the thermal transfer recording apparatus, particularly the rigidity of the member supporting the thermal head, as shown in FIGS. 9A and 9B, the immediately preceding printed line (n
Lines (n-2) and (n-3) even before -1)
If the printing rate is different, the swing amount of the thermal head between the current printing line n and the immediately preceding printing line (n-1) may not be the same.

Thus, in the second embodiment, printing on the printed lines (n-2) and (n-3), etc., which is further preceding the printed line (n-1) immediately before the current printed line n, as described above. By correcting the transport pitch in consideration of the rate, printing deviation for each line is prevented.

Since the mechanical configuration of the thermal transfer recording apparatus and the configuration of the control unit in the second embodiment are the same as those in the first embodiment, only the printing operation in the second embodiment will be described here. . As in the first embodiment, the sum of the gradation data of each line is used for the printing rate.

First, the operation of correcting the transport pitch in the second embodiment will be outlined. In the second embodiment, FIG.
As shown in A, the printing rate of a predetermined fixed number of lines L among the printing lines that have been printed so far is determined, and the average value of the cumulative printing rates of these printing lines is calculated. FIG. 10B shows a value obtained by dividing the accumulated printing rate by the number of lines L, which is referred to as an average accumulated printing rate.
As shown in (1), the printing rate in the already printed line is set, the difference between the average cumulative printing rate and the current printing line n is obtained, and the transport pitch is set based on the difference.

The following is a more detailed description with reference to the flowchart shown in FIG.

First, variables n and Ln used in the processing are cleared to 0 (S21). Here, n is the number of lines of the current printing line, Ln is the number of lines of the already-printed lines to be stored, and the value of Ln is the number of lines printed so far by the processing of steps S31 and S32 described later. Until the number exceeds the predetermined number L of lines, the number of lines printed so far is reached, and after exceeding L, Ln = L. The value of the number of lines L depends on the rigidity of the member supporting the thermal head. Specifically, it is necessary to determine how much accumulation can be performed using an actual machine to make it possible to correct the optimum transport pitch. Is preferred. Note that empirically, about 10 lines are sufficient (of course, the present invention is not limited to this).

Subsequently, when image data to be printed is transmitted from the host computer, one line of image data is transferred to the buffer 4a (S22).

Then, the total of the current print line is calculated from the gradation data of each dot of the image data for one line transferred to the buffer 4a (S23). This is the printing rate of the current printing line n.

Next, the already-printed line (n-1) Ln lines before the already-printed line (n-1) immediately before the current print line n
The average value of the values obtained by accumulating the total sum of the gradation data for all the lines up to Ln) is calculated (S24). This is the average cumulative printing rate of the already printed lines. It should be noted that the gradation data of the already-printed line is stored in the R
A predetermined number of lines L are held as image data of the already printed lines in AM2.

Next, the difference between the print rate of the current print line and the average cumulative print rate of the already printed lines is determined (S25).

Then, with reference to the table data for setting the obtained transport pitch, a transport pitch corresponding to the difference between the print rate of the current print line n and the average cumulative print rate of the already-printed lines is set (S26). ). Here, the table data stores the transport pitch corresponding to the difference from the printing rate of the current printing line n as shown in FIG. The degree to which the apparent transport pitch changes depending on the difference in the amount of heat generated by the head is determined.

Next, the output value of each dot of the thermal head is calculated in accordance with the image data for one line stored in the buffer 4a (S27), and a voltage is applied to each dot of the thermal head according to this output value. (S28). At the same time, the grip roller is driven to convey the recording paper and the ink film at the conveyance pitch set in the step S26 (S29).

As a result, printing for one line is completed, and the image data for one line stored in the buffer 4a is transferred to the RAM 2 (S30). The RAM 2 stores this as the image data of the already-printed line for a predetermined number of lines L, and when the number of lines exceeds L, erases the image data of the line stored first and deletes the newly transferred image data. Is stored.

Next, it is determined whether or not the variable Ln is equal to L (S31). If not, Ln is incremented by 1 (S31).
32) If they are the same, the process directly proceeds to step S33.

Next, it is determined whether or not all the lines have been printed (S33). If the printing has not been completed, the variable n is incremented by 1, and the process returns to step S22. Here, when printing of all lines is completed, it is determined whether or not printing of all colors is completed (S34).
Return to 1 and print the next color image. On the other hand, if the printing of the images of all colors has been completed, the printing operation is completed.

Here, the operation of setting the transport pitch in the second embodiment will be described with a more specific example.

As a specific example, it is assumed that one line consists of 1848 dots, and the current print line n
When the gradation data of all the dots 10 are printed, the already printed line (n-1) immediately before the current printing line n is 25 as the gradation data of the already printed line printed before that.
5, the previous (n−2) is 10, and the previous (n−2)
Assuming that the current print line n is printed after the already-printed line is printed alternately with the high density line and the low density line, as in the case of -3) = 255.

First, the printing rate of the current print line is calculated as the total sum S _af of the gradation data of the current print line by the following equation (4) in step S23, and here, S _af = 18480.

[0088]

(Equation 4)

Next, the average cumulative printing rate of the already printed lines is
In the above step S24, the following equation (5) ((5)
In the formula, T _{i, j} is the gradation value of the i-th dot on the j-th line, and K is the total number of dots in one line), so that each line from the already printed lines (n−1) to (n−Ln) It is calculated as an average value S _beave of the sum of the sum S _af of the gradation data for each, and here, S _beave = 244860. It is assumed that the number of already printed lines Ln has already been printed equal to or more than the predetermined number L of lines. Therefore, Ln = L.

[0090]

(Equation 5)

Subsequently, the difference ΔS between the calculated print rate of the current print line n and the average cumulative print rate of the already-printed lines is determined in the above-mentioned step S25 as shown in the following equation (6). Here, ΔS = 226380.

[0092]

(Equation 6)

Then, based on the difference ΔS between the obtained print rate of the current print line n and the average cumulative print rate of the already-printed lines, FIG.
Referring to the data table shown in FIG.
Determined by step / line.

As described above, in the second embodiment, the thermal history of the thermal head by the previous printing is determined by calculating the difference in the printing ratio from the current printing line based on the printing ratios of a plurality of printed lines. It becomes possible to set the transport pitch with consideration.

Although the two embodiments have been described above, the present invention is not limited to these embodiments, and can be applied to various thermal transfer recording devices within the technical idea of the present invention. It goes without saying that this can be applied not only to a thermal transfer recording apparatus for printing a color image but also to a thermal transfer recording apparatus for monochrome or monochromatic printing.

[0096]

According to the present invention described above, the following effects can be obtained for each claim.

According to the first aspect of the present invention, the printing ratio of the already printed line and the printing ratio of the current printing line to be printed from now on are compared, and based on the comparison result, the recording paper conveyance is performed. Since the pitch is changed, if there is a difference between the printing rate of the already printed line and the printing rate of the current printing line, the coefficient of friction between the recording paper or ink film and the thermal head due to the amount of heat generated by the thermal head The change in the apparent recording paper conveyance pitch caused by the change can be corrected, the dot pitch for each line on the output image can be kept constant, and a good image without a pitch shift in the recording paper conveyance direction can be formed. .

According to the second aspect of the present invention, the print ratio of the already-printed line and the print ratio of the current print line are calculated based on the respective image data. A printing rate that accurately reflects the amount can be obtained.

According to the third aspect of the present invention, the printing rate of each printed line per line is calculated from a plurality of printed lines printed before the current printing line as the printing rate of the already printed lines. Therefore, according to the state of the image data printed before the current print line,
The transport pitch can be changed, and even when the thermal history of the thermal head differs depending on the image data, the dot pitch in the recording paper transport direction on the output image can always be kept constant, and A good image without a dot pitch shift can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of a thermal transfer recording apparatus to which the present invention is applied.

FIG. 2 is a schematic cross-sectional view for explaining an operation state of the thermal transfer recording apparatus.

FIG. 3 is a block diagram for explaining a configuration of a control system of the thermal transfer recording apparatus.

FIG. 4 is a drawing showing a dot configuration of a thermal head used in the thermal transfer recording apparatus.

FIG. 5 is a diagram for explaining an apparent transport pitch when the recording paper transport pitch is not corrected.

FIG. 6 is a diagram for explaining an apparent transport pitch when the recording paper transport pitch is corrected.

FIG. 7 is a flowchart illustrating a procedure for correcting a conveyance pitch in the first embodiment.

FIG. 8 is a diagram illustrating an example of a data table used for setting a transport pitch.

9A and 9B are diagrams for explaining a case where the density is different among a plurality of printed lines, and FIG. 9A shows a case where a line with a high density and a line with a low density are printed alternately;
Indicates a case where a line with a low density is printed after a line with a high density continues.

FIG. 10 is a drawing for explaining an outline of a correction operation of a transport pitch in the second embodiment.

FIG. 11 is a flowchart for explaining a transport pitch correction processing procedure according to the second embodiment.

FIG. 12 is a diagram for explaining that an apparent transport pitch changes due to a difference in printing ratio in a conventional thermal transfer recording apparatus.

FIG. 13 is a schematic view showing a state in which a thermal head slightly swings due to a difference in printing rate in a conventional thermal transfer recording apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... CPU, 2 ... RAM, 3 ... ROM, 4 ... Voltage application control circuit, 18 ... Recording paper, 26 ... Thermal head, 32 ... Ink film.

Claims (3)

[Claims] 1. A thermal head having a plurality of heat sources for printing a plurality of dots for one line at a time,
In a thermal transfer recording apparatus, which conveys an ink film along a recording sheet and controls the plurality of heat sources according to image data to perform printing on the recording sheet line by line, an already printed line already printed on the recording sheet Means for determining the printing rate of the current printing line to be printed on the recording paper, and printing rate comparison for comparing the printing rate of the existing printing line with the printing rate of the current printing line. And a conveyance pitch changing means for changing a recording paper conveyance pitch in a recording paper conveyance direction based on a comparison result by the printing ratio comparison means. 2. The printing rate of the already printed line is calculated by calculating the printing rate of the already printed line from the image data for which printing has already been completed on the recording paper, and obtaining the printing rate of the current printing line. 2. A thermal transfer recording apparatus according to claim 1, wherein said means calculates a printing ratio of a current printing line from image data to be printed on said recording paper. 3. The printing rate of the already printed line is obtained by averaging the cumulative value of the printing rates of each of a plurality of printed lines from the current printing line to a plurality of lines before the predetermined printing line. 3. The thermal transfer recording apparatus according to claim 1, wherein the thermal transfer recording apparatus has an average printing rate.