JP2001030528A - Image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of white streaks without using a special head and form high-quality images by arranging a plurality of image form elements via a predetermined distance in a horizontal scanning direction and setting an image form head so that an arrangement direction of the image form elements tilts to a vertical scanning direction. SOLUTION: A light source 36 for fixing is set to the side of a transfer roller 32 of a thermal head 28 at a position spaced by a predetermined distance from a guide plate 38 to be opposite to the guide plate 38. The thermal head 28 has a plurality of rectangular heating elements R1-Rn arranged at predetermined intervals, preferably at equal intervals in a horizontal scanning direction of the thermal head 28. The heating elements adjacent to a platen roller 30 are connected to a power source via respective drivers. The thermal head 28 is set so that an arrangement direction of the heating elements R1-Rn tilts to a vertical scanning direction. In this case, an angle ϕ of not smaller than tan-1 (D/L) is preferred wherein D is the interval of the heating elements and L is a length of a part of the heating element in contact with the recording sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus having an image forming head in which a plurality of image forming elements are arranged at regular intervals in a main scanning direction.

[0002]

2. Description of the Related Art In a conventional thermal printer, a thermal head in which a plurality of heating elements as image forming elements are arranged in a line is arranged at right angles to a conveying direction of a multicolor heat-sensitive recording sheet. There is a portion of the color thermosensitive recording sheet that does not contact any of the heating elements. For this reason, when an image is formed by the thermal head, a gap is generated between pixels adjacent in the main scanning direction, and there is a problem that, for example, a white streak occurs when a solid image is formed.

[0003] In order to solve this problem, there has been proposed a technique of reducing the interval between the heating elements or changing the shape of the heating elements. When the interval between the heating elements is narrowed, the gap between adjacent pixels is also narrowed and white streaks are not conspicuous, but the manufacturing of the thermal head becomes difficult, and the manufacturing yield is reduced, which causes an increase in cost. In addition, there is a limit to the interval that can be narrowed, and there is also a limit to the effect of making white streaks inconspicuous.
Further, by changing the shape of the heating element from a rectangle to a different shape such as a parallelogram, the gap between adjacent pixels can be narrowed, but it is difficult to align a mask at the time of manufacturing a head, and it is also difficult to manufacture a thermal head. Therefore, it has hardly been put to practical use due to the problem of manufacturing yield.

[0004]

As described above, various proposals have been made for the structure of a thermal head in order to improve the defects of a printed image. However, precise work of a heating element causes an increase in manufacturing cost. It is not realistic.

Accordingly, an object of the present invention is to provide an image capable of preventing white streaks and obtaining a high-quality image without using a head having a small gap between adjacent image forming elements or a specially shaped head. An object of the present invention is to provide a forming apparatus.

[0006]

In order to achieve the above object, an image forming apparatus according to the present invention comprises a plurality of image forming elements arranged at predetermined intervals in a main scanning direction, and the arrangement direction of the image forming elements is changed. An image forming head is provided so as to be inclined with respect to the sub-scanning direction.

According to the present invention, since the arrangement direction of the image forming elements is inclined with respect to the sub-scanning direction, the pixel interval formed by the image forming elements becomes smaller due to the interval between the image forming elements. White streaks can be prevented from occurring.

In the present invention, in order to more effectively prevent the generation of white streaks, the gap between the image forming elements in a state where the main scanning direction and the sub scanning direction are orthogonal to each other is D, When the length in the scanning direction is L, the image forming head is moved to tan ^-1 (D /
L) It is preferable to incline at an angle of not less than By inclining at such an angle, adjacent pixels come into contact with each other or overlap with each other, so that generation of white streaks can be prevented.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment in which the present invention is applied to a multicolor thermal printer for recording an image on a multicolor thermal recording sheet will be described below in detail with reference to the drawings.

As shown in FIG. 1, a printer 10 is a device for thermally recording a color image on a substantially rectangular multicolor thermal recording sheet 12 and fixing the recorded image with light to form an image. It is stored in the casing 14.

On one side of the casing 14, an insertion opening 18 for the multicolor thermal recording sheet 12 to which the mounting table 16 is mounted is provided. On the other side of the casing 14, a mounting table 20 is mounted. Multicolor thermal recording sheet 1
A second outlet 22 is provided. And the insertion port 18
A transport device that transports the multicolor thermosensitive recording sheet 12 from the insertion port 18 to the discharge port 22 is disposed between the discharge port 22 and the discharge port 22.

The transport device includes a pair of transport rollers 24 provided near the insertion port 18 and a pair of transport rollers 32 provided near the discharge port 22.
A guide plate 26 is provided downstream of the transport roller 24 in the transport direction, and a guide plate 38 is provided upstream of the transport roller 32 in the transport direction.

A thermal head 28 as a thermal recording means and a platen roller 30 are provided between the guide plates 26 and 38 so as to face each other. A sensor 27 and a light source 34 are disposed on the side of the thermal roller 28 on the transport roller 24 side. The light source 34 is 300 to 450 nm, preferably 425, with respect to the conveyed multicolor thermosensitive recording sheet 12.
A light source that emits light having wavelengths of nm and 365 nm can be used, and this light source is also used as a fixing light source for fixing each color-forming layer.

A fixing light source 36 is arranged on the side of the transport roller 32 of the thermal head 28 at a position separated from the guide plate 38 by a predetermined distance in a state facing the guide plate 38. As shown in FIG. 2, the thermal head 28 has a plurality of rectangular heating elements R1 to Rn that are connected to a power source 83 via respective drivers in the vicinity of the platen roller 30.
Are separated by a predetermined distance in the main scanning direction of the thermal head 28,
Preferably, they are arranged at equal intervals. The thermal head 28 is arranged such that the arrangement direction of the heating elements R1 to Rn is inclined with respect to the sub-scanning direction.

As shown in FIG. 3, azimuth formed by the direction in which the heating elements R1 to Rn of the thermal head 28 are arranged (main scanning direction) and the direction perpendicular to the direction in which the multicolor thermosensitive recording sheet 12 is conveyed (sub-scanning direction). When the angle φ is D, the gap between the heating elements when the main scanning direction and the sub-scanning direction are orthogonal to each other is the length of the heating element in the sub-scanning direction (the length of the portion where the heating element contacts the multicolor thermal recording sheet). Tan ⁻¹ (D /
L) The thermal head 28 is inclined so as to have an angle equal to or greater than the angle. For example, if the heating element has a long side of 150 μm and an element interval of 13 μm, the azimuth angle φ is tan ⁻¹ (3
/ 150) (about 5 °) or more.

A control circuit 50 shown in FIG. 4 is housed in the casing 14. The control circuit 50 is configured to include a microcomputer, and the signal processing unit 5
4 is provided with a main controller 52 connected thereto.
The signal processing unit 54 includes an A / D converter 58 that converts input image data 56 into a digital electric signal by reading a document by a scanner or the like, based on an electric signal from the A / D converter 58. A conversion controller 60 for obtaining image signals corresponding to RGB (red, green, blue) colors and a RAM 62 for temporarily storing image data output from the conversion controller 60 are provided. At this time, the image data is stored at an address represented by rectangular coordinates (x, y).

Note that image data taken by a digital camera and input from an external interface (not shown) or a memory slot (not shown) can be directly stored in the RAM 65.

The RGB color signals stored in the RAM 62 are
It is input to the main controller 52. The main controller 52 sends Y (yellow), M
A ROM 64 storing a program for calculating each color data of (magenta) and C (cyan), a program for calculating converted coordinates described later, an image frame memory 66, and a device for manually inputting data and the like. Actuator 9
0 is connected.

On the output side of the main controller 52, based on signals from the main controller, Y,
A switch 68 for selecting any one of the data of each of the colors M and C, a driver 72 for driving the thermal head 28 via a line buffer 70 are connected, and reflection of light emitted from the light source 34 is performed. A driver 76 that is connected to the sensor 27 that receives light and that drives a rotation drive source 74 for rotating the platen roller 30
And a driver 78 for driving the light source 34 and the fixing light source 36 are connected.

The printing on the multicolor heat-sensitive recording sheet is performed as follows. When the multicolor thermosensitive recording sheet 12 is taken out of the packaging package and the multicolor thermosensitive recording sheet 12 is inserted from the insertion port 18, the inserted multicolor thermosensitive recording sheet is inserted into the casing 14 by the conveying roller 24, and then the multicolor thermosensitive recording sheet 12 is moved to the initial position. When printing is completed and printing preparation is completed, printing processing is started.

The main controller 52 has the following (1):
The inclination coordinates (x ', y') are calculated from the rectangular coordinates (x, y) of the original image according to the equation (2), and the image data at the address of the inclination coordinates (x ', y') is obtained from the RAM 62 as follows. Read out.

X ′ = xy × tan φ (1) y ′ = y (2)

First, one line of Y-color image data corresponding to the heating elements R1 to Rn is read, and
Drives the thermal head 28 based on the read image data and heats the color-forming layer corresponding to the Y color by one line while conveying the multicolor heat-sensitive recording sheet 12 so that the color is formed and fixed. The light is fixed by the light source 38. This is repeated by the number of lines in the sub-scanning direction, and printing of one side is completed. Next, the multicolor heat-sensitive recording sheet 12 is conveyed in the reverse direction.
The coloring and fixing of the color-forming layer corresponding to the color are performed, and the C-color image data is read out, and the color of the color-forming layer corresponding to the color C is formed.

In the printer 10, the thermal head 2
Numeral 8 is inclined with respect to the direction perpendicular to the direction of transport of the multicolor heat-sensitive recording sheet 12 so as to form an azimuth angle φ satisfying the condition of tan φ ≧ D / L. For this reason, as shown in FIG. 3, the locus drawn by the corner A of the heating element Ri overlaps with the locus drawn by the corner B of the heating element Ri + 1 adjacent to Ri. No gap is generated in the space. Thereby, generation of white streaks can be prevented.

Next, a second embodiment in which the present invention is applied to a circular multicolor thermal recording sheet or a multicolor thermal printer for recording an image on a disk provided with the multicolor thermal recording sheet will be described in detail. In the present embodiment, instead of the transport device for linearly transporting the multicolor heat-sensitive recording sheet, a rotating device provided with a rotating plate for mounting and rotating the disk is provided, and the image is formed while rotating the disk. Except for the formation and the like, the configuration is the same as that of the first embodiment, and the description is omitted.

As shown in FIG. 5, the thermal head 28 forms the above-described azimuth angle φ with a direction perpendicular to the rotation direction (the tangential direction of the disk and the sub-scanning direction) of the multicolor thermal recording disk 12a. Are located.

When the disk 12a provided with the multicolor heat-sensitive recording sheet rotates, the rectangular coordinates (x, y) of the original image are converted to the polar coordinates (r, r) according to the following equations (3) and (4).
θ), and calculates the inclined polar coordinates (r ′, θ ′) from the polar coordinates (r, θ) according to the following equations (5) and (6).

R ² = x ² + y ² (3) θ = tan ⁻¹ (y / x) (4) r ′ = r (5) θ ′ = θ−sin ⁻¹ (d / r1) + φ (6)

The above conversion equation (6) can be derived by the following procedure. As shown in FIG. 6, r is the radius of the disk, and d is the heating elements R1 to R of the thermal head 28.
This is the distance between the center O and the foot of the perpendicular when a perpendicular is drawn from the center O of the disc on the main scanning line indicating the direction in which n are arranged. The value of θ1 at a point where the distance from the center O of the main scanning straight line is r1 can be represented by the following equation.

R1 × sin θ1 = d θ1 = sin ⁻¹ (d / r1) Here, since θoff = θ1−φ, the above equation (6) is obtained.

In this embodiment, the thermal head 2
Numeral 8 is inclined so as to form an azimuth angle φ satisfying a condition of tan φ ≧ D / L with a direction perpendicular to the rotation direction of the multicolor thermal recording disk 12a. For this reason, as shown in FIG. 3, the locus drawn by the corner A of the heating element Ri overlaps with the locus drawn by the corner B of the heating element Ri + 1 adjacent to Ri. No gap is generated in the space. Thereby, generation of white streaks can be prevented.

In the first and second embodiments, only one thermal head 28 is provided for the multicolor thermal recording sheet 12 or the disk 12a having the multicolor thermal recording sheet. As shown in FIGS. 7, 8, and 9, two or more may be arranged.

As shown in FIG. 7, the thermal head 28A
Thermal head 28 at a position corresponding to the gap between the heating elements
B so that the heating element of B is located.
And the thermal head 28B can be arranged in parallel. With this arrangement, the thermal head 28A
Between adjacent pixels formed by the thermal head 28B
The pixel formed by is located, and the generation of white streaks can be further prevented. Further, the thermal head tilted as described in the second embodiment is used in FIG.
, Two may be arranged, and as shown in FIG. 9, three may be arranged. In these cases, fixing lamps 31A and 31A are provided between the thermal heads.
1B, 29A and 29B are arranged. When three thermal heads are arranged, for example, the thermal head 28A
Can be used for Y color development, the thermal head 28B can be used for M color development, and the thermal head 28C can be used for C color development, so that it is not necessary to switch each color, and the thermal head 28A is used for color development. The Y-color forming layer is fixed by the lamp 29A, and then the thermal head 2
The M color layer formed by 8B is fixed by the lamp 29B, and then the C color layer is formed by the thermal head 28C. Therefore, a color image can be formed by at least 1/3 rotation.

The two or more thermal heads need not necessarily be arranged so as to form a predetermined angle φ with a direction perpendicular to the sub-scanning direction. As shown in FIGS. It may be arranged along the direction.

In the above, an example in which the present invention is applied to a multi-color thermal printer has been described. However, the present invention can be applied to various printers such as an ink jet printer, a thermal transfer printer, and an electrophotographic printer.

Further, when printing a portion such as a window frame or a grid where the density of a picture suddenly changes, the coefficient of friction between the thermal head and the multicolor heat-sensitive recording sheet suddenly changes, which may cause uneven feeding. However, in the present invention, since the thermal head prints diagonally on the multicolor thermal recording sheet,
Even in the case of a pattern whose density changes suddenly, it is possible to prevent uneven feeding.

[0037]

According to the image forming apparatus of the present invention, white streaks can be prevented and a high-quality image can be obtained without using a head having a small gap between adjacent image forming elements or a specially shaped head. This has the effect.

[Brief description of the drawings]

FIG. 1 is a schematic view of a multicolor thermal printer according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating an arrangement state of a thermal head according to the first embodiment.

FIG. 3 is an explanatory diagram illustrating a preferred arrangement state of the thermal head according to the first embodiment.

FIG. 4 is a block diagram of a control circuit according to the embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating an arrangement state of a thermal head according to a second embodiment.

FIG. 6 is an explanatory diagram for explaining a procedure of coordinate conversion according to the second embodiment;

FIG. 7 is a schematic diagram showing an example of the arrangement of two or more thermal heads.

FIG. 8 is a schematic diagram showing an example of the arrangement of two or more thermal heads.

FIG. 9 is a schematic diagram showing an example of the arrangement of two or more thermal heads.

FIG. 10 is a schematic diagram showing an example of the arrangement of two or more thermal heads.

FIG. 11 is a schematic diagram showing an example of the arrangement of two or more thermal heads.

[Description of Signs] 12 Multicolor thermal recording sheet 28 Thermal head 30 Platen roller 50 Control circuit

Claims (2)

[Claims] 1. An image comprising an image forming head in which a plurality of image forming elements are arranged at predetermined intervals in a main scanning direction, and wherein the arrangement direction of the image forming elements is inclined with respect to a sub-scanning direction. Forming equipment. 2. When the gap between image forming elements in a state where the main scanning direction and the sub scanning direction are orthogonal to each other is D, and the length of the image forming elements in the sub scanning direction is L, the image forming head is 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is inclined at an angle of tan ^-1 (D / L) or more with respect to a direction orthogonal to the scanning direction.