KR0132366B1 - The laser printing apparatus and method - Google Patents

Abstract

A computer(40) outputs print information to be printed. Then, a interface part(51) outputs the print information to a control part(52). The control part receives the print information and outputs the first data, dot data, calculating deviation distance of the focus to be formed at the standard distance, accesses the third data, correction data of correction table, and outputs. A laser driving part(53) receives the first data that is output from the control part(52), modulating so it is converted to laser beam and outputs after being amplified. A laser source(54) makes an optical conversion, generating laser beam and outputs through optical fiber.

Description

Laser printing apparatus and method

1 is a block diagram of a conventional laser printing apparatus

2 is a block diagram of a laser printing apparatus according to the present invention

FIG. 3 shows the configuration of the printhead and the characteristics of the laser beam in FIG.

4 is a diagram showing the configuration and operation characteristics of the sensor in FIG.

＊ Explanation of symbols on main parts of drawing

40: computer 50: printing device

51 interface unit 52 control unit

53: laser drive unit 54: laser source

55: first optical coupling portion 56: optical fiber

7: second optical coupling portion 58: printhead

1: imaging optics 72: distance sensor

3: actuator 81: detection optics

2: one-dimensional image sensor 61: drum

2: paper 63: photosensitive medium

4: engine frame 65: lead screw

66: guide bar 67: the first step motor

8: second step motor

The present invention relates to a laser printing apparatus and method, and more particularly, to an apparatus and method capable of printing print information transferred onto a photosensitive medium using a laser beam.

In general, a laser printer (LASER printer) currently used to fix the toner on the electrostatic latent image on the drum formed by the laser beam to print the information to be printed.

The laser printer scans the print information on the drum by using a rotary polygon mirror.

However, a laser printing method different from the laser printer using the toner as described above is now emerging.

That is, a photosensitive material is used to expose a laser beam onto the photosensitive material, or the energy generated at the focusing portion may be imaged through energy conversion such as opto-electric conversion and opto-thermal conversion. This method prints (image) or text.

Here, the printing apparatus using the above printing method is called a laser printing apparatus.

Operation of the laser printing apparatus as described above is performed by High Definition Thermal Transfer Printing Using Heating (Mitsuru Irie et al, Journal of Imaging Science Technology, Vol. 37, No. 3, 1993, pp235-234) and Halftone Color Imaging by Laser Dye Transfer. Proc. Of the 9th Int. Congress on Advacces in Non-impact Printing (NIP) Technologies, Yokohama, Japan, Oct. 4-8, 1993, pp 366-369.

In order to achieve a high resolution (high definition: 500 dpi (dot per inch) or more, dot diameter 50 μ or less) in the laser printer, a focused laser spot size formed on a reaction material is determined. It must be precisely controlled.

In order to perform the above control, it is necessary to accurately maintain the distance between the writing head in which the laser beam is generated and the photosensitive medium in which the laser beam is formed. To this end, in the current laser print apparatus, since most of them rely on precise mechanical devices, the mechanical installation process is difficult, and the cost of parts is increased and output quality and reliability are degraded, making it difficult to realize high speed.

In general, the configuration of the laser printing apparatus has the configuration as shown in FIG.

Print data of the laser printing apparatus is output from the computer 10.

At this time, the computer 10 outputs coordinate information of the print data in addition to the print print data.

The print data and the coordinate information output from the computer 10 are applied to the interface unit 21.

The first configuration for converting the print data into a laser beam by converting the optical data into a laser beam comprises: a laser driver 22, a laser diode 23, an optical fiber 24, a beam centering unit 26, and an imaging optics. It may be composed of focusing optics 27. In this case, the print head 25 may be composed of a beam guider 26 and an imaging optical unit 27.

In addition, the second configuration for converting the print data into a laser beam by converting the entire light may be composed of a laser driver 22, a laser diode 23 and an imaging optical unit 27.

In this case, the printhead 25 is composed of a laser diode 23 and an imaging optical unit 27.

Referring to the above-described configuration, the operation of converting the print data into the laser beam will be described. The laser driver 22 receiving the print data outputting the interface unit 21 modulates and amplifies the print data so as to convert the print data into the laser beam. .

The laser diode 23 converts the print information output from the laser driver 22 into a laser beam.

The laser beam output to the laser diode 23 is transmitted through the optical fiber 24, and the beam guider 25 controls the laser beam output from the optical fiber 24 to be positioned at the center of the imaging optical unit 27.

That is, the beam guider 26 allows the optical axis of the optical fiber 24 and the optical axis of the imaging optical unit 27 to be positioned at the center.

The imaging optical unit 27 then forms the laser beam on the drum 29.

In this case, since the photosensitive medium and the printing paper are positioned on the drum 29, the photosensitive medium is transferred to the printing paper by the laser beam to perform a printing function.

That is, when heat is generated by focusing a laser beam, the photosensitive medium is transferred to printing paper due to the heat, and print data is printed.

Such thermal transfer methods include sublimation thermal transfer and melt thermal transfer.

In addition, the X-axis position of the print data is determined by transferring the print head 25 to the left and right, and the Y-axis position is determined by rotating the drum 29.

The configuration for determining the position of the X axis is composed of a first step motor 33, a lead screw 31 and a slide 32, and the position of the Y axis is determined by the second step motor 34.

Since the print head 25 is coupled to the lead screw 31 and the lead screw 31 is connected to the first step motor 33, the print head 25 may be traversed with respect to the rotational direction of the drum 28.

In addition, in order to improve the movement accuracy of the print head 25 which is moved by the lead screw 31 and the first step motor 33, the slide 32 is fastened and supported by the crit head 25 in most cases.

Therefore, the print head 25 may be moved left and right by the X coordinate information and the Y coordinate information output by the interface unit 21 during the printing operation, and the drum 29 may perform a two-dimensional printing operation by performing a rotational movement.

The laser printing apparatus having the configuration as described above may perform a high resolution printing function.

This is because the density of the laser beam and the high definition function can be performed by the characteristics of the laser beam.

At this time, when the imaging unit 27 receiving the laser beam forms the focus of the laser beam on the drum 29, it must be precisely controlled to form an image within the depth of focus.

This is the most important factor in determining the resolution of the radar printing apparatus.

To this end, in the conventional laser printer, in order to accurately control the print head 25, the lead screw 31 and the slide 32 have to be mechanically designed very precisely.

That is, when the print head 25 is moved horizontally, if fine imaging occurs in the imaging optical unit 27 vertically or horizontally, resolution and print quality are deteriorated.

In other words, if the axis of the drum 29 and the moving axis of the print head 25 are not accurately leveled, the quality of the print is degraded because the focal size of the laser beam varies depending on the print position.

Therefore, the lead screw 31 and the slide 32 have to be designed very precisely so that such movement does not occur, which causes a problem that the print speed is lowered because the horizontal moving speed of the print head 25 is lowered.

In addition, when bending occurs in the photosensitive medium and the printing paper positioned on the drum 29, a problem arises in that the focus imaging cannot be adaptively controlled by the horizontal moving means fixed mechanically.

Accordingly, it is an object of the present invention to provide a printhead device and a control method thereof capable of adaptively performing a focus servo function according to a focus imaging state of a laser beam in a laserprint apparatus.

Another object of the present invention is to provide an apparatus and method for automatically correcting a focal length of a laser beam by detecting a focal length and an error of a laser beam after detecting a focal length of a laser beam during printing in a laser printer. .

It is still another object of the present invention to incorporate an imaging optical unit, a distance sensor, and an actuator into a printhead in a laser printing apparatus, and to receive a focus of a laser beam output from the imaging optical unit through a distance sensor to print a focus with a reference focal length. The present invention provides an apparatus and method for automatically controlling a focusing servo of the imaging optical unit by driving the actuator to a value corresponding to the analyzed deviation distance after analyzing the deviation.

In order to achieve the above object of the present invention, the laser printing apparatus of the present invention includes a correction table, and outputs dot data to be printed and analyzes the received deviation distance information to output corresponding correction data in the correction table. Means; Means for generating a laser beam corresponding to said dot data; Optical means for imaging the focus of the laser beam on the drum, a distance sensor for receiving the reflected laser beam formed on the drum and detecting deviation distance information and outputting the deviation laser beam to the control means; And a printhead comprising an actuator for controlling the focus of the optical means by the correction data.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

It should be noted that the same parts in the figures represent the same reference signs wherever possible.

In the following description many specific details such as the width, focal radius, focal diameter, depth of focus and the like of a ray point beam are presented to provide a more general understanding of the invention.

It will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

The term first data used herein denotes dot data to be printed.

The term “second data” refers to deviation distance information of the reflected laser beam detected by the distance sensor.

The term “third data” refers to information for correcting the deviation distance.

The term deviation distance refers to the distance from the reference position where the focus is normally formed to the position where the deviation occurs.

2 is a configuration diagram of a laser printing apparatus according to the present invention, and the computer 40 outputs print information to be printed.

The interface unit 51 outputs the print information output from the computer 40 to the control unit 52.

The control unit 52 includes a correction table for compensating for the focal interval in which the deviation occurs, and receives the print information output from the interface unit 51.

The controller 52 outputs first data, which is dot data to be printed, from the print information, receives the second data, which is deviation distance information, calculates a deviation distance to a focus position formed by falling to a reference focal length, and the deviation distance. The third data, which is the correction data of the correction table, is accessed and output.

In addition, the controller 52 generates first drive data for moving the print head 58 in the X-axis direction and second drive data for rotating the drum 61 from the print information.

The laser driver 53 receives the first data output from the controller 52.

The laser driver 53 modulates and amplifies and outputs the first data so as to convert the first data into a laser beam. A laser source 54 receives the output of the laser driver 53. The laser source 54 converts the first data outputting the laser driver 54 into a laser beam.

A first optical fiber connector 55 is connected between the output of the laser source 54 and the optical fiber 56 and outputs the laser beam to the optical fiber 56.

A second optical fiber connector 57 is connected between the optical fiber 56 and the imaging optical unit 71 of the printhead 58 to output a laser beam totally reflected from the optical fiber 56 to the imaging optical unit 71.

Accordingly, the optical fiber 56 totally reflects the laser beam output from the laser source 54 by the first coupling unit 55 and the second optical coupling unit 57 and outputs the imaging optical unit 71.

A printing head 58 has an input terminal connected to the second optical coupler 57 and includes a focusing optics 71, a distance sensor 72, and an actuator 73. The imaging optical unit 71 forms a focus on the photosensitive medium 63 by imaging the received laser beam.

The distance sensor 72 receives the reflected laser beam of the formed laser beam and converts the converted laser beam into an electrical signal. The distance sensor 72 generates the deviation distance from the focus reference position to the position where the actual focus is formed as second data and outputs the second data to the controller 52. .

The actuator 73 is located close to the imaging optical unit 71, and is driven by the third data output from the control unit 52 to adjust the imaging optical unit 71 up and down.

The print head 58 may include a laser source 54, an imaging optical unit 71, a distance sensor 72, and an actuator 73 when the optical fiber 56 is not commercially available.

The means for driving the print head 58 in the X-axis direction includes a first step motor 67, a lead screw 65, and a guide bar 66.

The first step motor 67 is driven by X coordinate data output from the controller 52.

The lead screw 65 is connected to the print head 58 and controlled according to the output of the first step motor 67.

The lead screw 65 is rotated by the first step motor 67 to move the print head 58 from side to side.

Guide bar 66 supports the printhead 58.

The second step motor 68 is driven by the Y coordinate data output from the controller 52. The second step motor 68 is connected to the drum 61 to rotate the drum 61.

On the drum 61, a reaction layer 63 and a printing paper 62, which react with the focal-formed laser beam, are lightly adhered to each other.

Accordingly, the drum 61 is rotated by the second step motor 68 to transfer the photosensitive medium 63 and the printing paper 62 up and down, and is printed according to the focus of the photosensitive medium 63 formed by the imaging optical unit 71 of the printhead 58. The first data is printed on the paper 62.

The laser printer device connected to the computer 40 receives the print data and the position information output from the computer 40 and prints them on the printing paper 62 by thermal transfer.

The interface unit 51 receives the print data and the position information output from the computer 40 and outputs the same to the controller 52.

Then, the controller 52 receives the print data and the position information to control the overall operation of the laser printing apparatus.

First, the print data is received as coded data. Then, the controller 52 converts the encoded print data into dot data and outputs the converted dot data.

In addition, the controller 52 generates X coordinate data and Y coordinate data to determine a position to print the dot data.

The X coordinate data is output to the first step motor 67.

Then, the first step motor 67 rotates the lead screw 65 according to the coordinate data, and the print head 58 is horizontally moved in the horizontal direction by the rotation of the lead screw 65.

At this time, the guide bar 66 functions to fix the playhead and vibration so that the print head 58 does not occur.

The Y coordinate data is output to the second step motor 68. Then, the second step motor 68

The drum 61 is rotated according to Y coordinate data.

When the drum 61 is rotated, the print paper 62 and the photosensitive medium 63 which are lightly adhered to the drum 61 are rotated together.

Accordingly, the print head 58 is moved left and right by the X coordinate data to determine a horizontal position on the printing paper 62, and the drum 61 is rotated by the Y coordinate data to determine a vertical position of the printing paper 62.

The first data outputting the controller 52 is output to the laser driver 53, and the laser driver 53 modulates and amplifies the first data into a laser beam.

Thereafter, the first data outputting the laser driver 53 is applied to the laser source 54, and the laser source 54 converts the first data into a laser beam and outputs the laser beam.

The laser beam is applied to the imaging optical portion 71 of the printhead 58 via the bee 1 light coupling portion 55, the optical fiber 56, and the second light coupling port 57.

The imaging optical unit 71 forms the focus of the laser beam onto the photosensitive medium 63. Then, the photosensitive medium 63 reacts with the heat of the laser beam to print the first data on the printing paper 63.

That is, the photosensitive medium 62 is to perform a printing operation on the printing paper 62 by the thermal transfer of the laser beam.

At this time, the imaging optical unit 71 should accurately focus the ray point on the photosensitive medium 63.

This is because the first data can be clearly printed on the printing paper 62 only when the depth of focus of the laser beam is accurately formed on the photosensitive medium 63 as described above.

Therefore, when the imaging optical unit 61 does not accurately focus on the photosensitive medium 63, the printed image may not be clear and the resolution may be deteriorated.

Therefore, in the present invention, after receiving the laser beam reflected on the photosensitive medium 63 to detect the focal length actually formed, the deviation between the reference focal length and the actual image focal length between the preset imaging optical unit 61 and the photosensitive medium 63 is detected. Deviation distance is corrected by detecting distance information. The distance sensor 72 detects the deviation distance information.

The distance sensor 72 is a one-dimensional image sensor, and may use a position sensitive detector (PSD) or a linear charge coupled device (CCD).

The distance sensor 72 receives a laser beam scattered from the photosensitive medium 63 to detect a deviation from a reference focal length.

Therefore, the distance sensor 72 detects the focal length and deviation distance actually formed at the preset reference focal length and outputs the second data to the controller 52.

The control unit 52 has correction data for correcting the deviation distance as described above so that the imaging optical unit 71 can maintain the reference focal length.

Each of the correction data of the correction table is set to correspond to the second data, which is the deviation distance information output from the distance sensor 72.

Therefore, when receiving the second data from the distance sensor 72, the controller 52 accesses the correction data corresponding to the second data in the correction table and outputs the third data.

The third data output from the controller 52 is applied to the actuator 73 positioned in proximity to the imaging optical unit 71.

Then, the actuator 73 is driven by the third data to move the imaging optical unit 71 upward or downward to perform a focusing servo function.

Therefore, the imaging optical unit 71 can accurately image the focus of the laser beam generated on the week performing the printing operation on the photosensitive medium 63.

The actuator 73 may use an electromagnetic induction linear actuator or a piezoelectric actuator.

4 is a view for explaining the relationship between the printhead 58 and the photosensitive medium 63. Reference numerals in FIG. 4 are as follows.

Dapt: Aperture Diameter of the imaging optics 71

L: primary plane of the focusing optics,

O: reference nomal point of reaction layer formed on the photosensitive medium 63,

M: normal point of reaction layer at far position,

H: principal plane of the imaging optics,

R: reference center cell of the PSD

N: position of nth cell of sensor 82 when deviation occurs

Zo: reference focal length from imaging optical part 71 to zero of photosensitive medium 63,

α: reference angle ∠LOH,: deviation angle ∠OHM,

d: deviation distance from the reference position

5 is a configuration diagram of the sensor 82 when the distance sensor 72 is implemented as a PSD in FIG. 4, and each reference numeral is as follows.

R: center cell of sensor 82,

BIS: Blurred image of the focusing spot formed on sensor 82 when deviation occurs

n: center cell in the region of the sensor 82 when deviation occurs,

ns: cell at the rightmost position in the sensor 82 area when a deviation occurs,

n1: Cell at the leftmost position in the area of sensor 82 when deviation occurs,

δ: width of each cell of the sensor 82,

n * δ: deviation distance information

Referring to FIGS. 4 and 5, the imaging optical unit 71 focuses an image on the photosensitive medium 63. The laser beam outputted through the imaging optical unit 71 focuses on the surface of the photosensitive medium 63. When a spot is formed, light energy is converted into thermal energy, causing a phase transfer of the photosensitive medium 63 and transferring to the printing paper 62.

At this time, if the photosensitive medium 63 is located at the reference focal length Z0 where the focusing spot diameter is minimum, the image of the focal point is shown through image optics 81 of the distance sensor 72 as shown in FIG. The central reference cell on the optical sensor 82 is formed, and the central optical axis (line segment LO) of the imaging optical unit 71 and the central optical axis (line segment OH) of the sensing optical unit 81 form a reference angle α.

In this case, the laser beam is accurately focused on the photosensitive medium 63 and does not perform a separate correction operation.

However, when the distance between the imaging optical unit 71 and the photosensitive medium 63 is closer or farther than the focal reference distance Z0, the image of the focus formed on the optical sensor 82 is out of the central reference cell R of the optical sensor 82, and the imaging optical The angle formed between the central optical axis of the unit 71 and the central optical axis of the sensing optical unit 81 is also deviated by the deviation angle θ.

3 illustrates a case where the distance between the imaging optical unit 71 and the photosensitive medium 63 is farther than the focal reference distance Z0.

Here, when the distance between the imaging optical unit 71 and the photosensitive medium 63 is farther than the focal reference distance Z0, the image of the focus formed on the optical sensor 82 is the central reference cell R of the optical sensor 82 as shown in FIG. 5. Deviates to the left by n * δ, and the angle formed by the central optical axis of the imaging optical unit 71 (line segment LM) and the central optical axis of the sensing optical unit 81 (line segment MH) is also obtained by subtracting the deviation angle θ from the reference angle α. Becomes

At this time, due to various aberration and diffraction effects of the imaging optical unit 71 and the sensing optical unit 81, the image BIS formed on the optical sensor 82 may not be sharp.

To solve this problem, the center cell number n of the image BIS formed as an average value from the range ns of the rightmost cell to the range n1 of the leftmost cell where the optical sensor 82 starts to be sensitive can be obtained. That is, when the center cell number of the image BIS is found when the deviation occurs, n = (ns + nℓ) / 2 can be obtained.

As shown in FIG. 5, the intensity of the nth sensor cell is the highest from the reference cell R on the optical sensor 82.

The deviation angle θ from the plane reference angle α is given by the following equation.

θ = tan-1 (n * δ / s)

Where n is the nth sensor cell of the optical sensor 82, δ is the width of one cell, and s represents the length of the line segment HR, which is the distance from the plane H of the sensing optical unit 82 to the reference cell R of the optical sensor 82.

Therefore, the gap between the tip L of the imaging optical unit 71 and the photosensitive medium 63 is changed due to various factors.

In this case, the deviation distance d can be obtained as follows from the above equation for obtaining the configuration and the deviation angle θ as shown in FIG.

d = n * δ * z0 / s * sin (α ± θ) `` +: near position,-: far position ''

The deviation distance d determined by the above equation is then used as information for adjusting the imaging optical unit 71 to accurately focus the laser beam on the photosensitive medium 63. The controller 52 receives the cell number formed by the image BIS from the optical sensor 82 as the second data as described above, and calculates the deviation distance d as described above.

The controller 52 outputs, as third data, correction data for driving the actuator 73 to a value corresponding to the deviation distance d.

That is, the controller 52 includes a look up table according to the driving value of the actuator 73 which controls the deviation distance d and the focal length of the imaging optical unit 51.

This can control the actuator 73 to measure the relationship between the deviation distance d and the correction value.

In this case, when the actuator 73 is a linear actuator, the correction data is output as a current value, and in the case of a piezoelectric actuator, the correction data is output as a voltage value.

The correction table of the control unit 52 as described above can be configured as shown in Table 1 and Table 2.

Therefore, when the controller 52 receives the second data related to the deviation distance d from the distance sensor 72, the controller 52 calculates the deviation distance d, calculates the deviation distance d, and then corrects the correction data corresponding to the deviation distance d. Alternatively, the data is output as the third data after accessing the correction table as shown in Table 2.

Then, the actuator 73 is driven to adjust the imaging optical unit 71 to a value corresponding to the third data. Therefore, the focus of the laser beam formed from the imaging optical unit 71 is always located on the photosensitive medium 63.

That is, when the deviation distance d is generated, it is compared with the correction table of the control unit 52, and generates a z-direction displacement of the imaging optical unit 71 by using a linear actuator or a piezo actuator using an electromagnetic induction phenomenon. Keep it at the interval you want.

As an embodiment of the present invention, the collimated laser beam width ω = 0.8 mm (1 / e2 Gaussian Beam width) coming into the focusing optics 71 may be used as a reference for the imaging optics 71. The focal length is f = 26mm (z0), the wavelength λ = 700mm, the aperture diameter Dapt = 1.2mm of the imaging optics, and is caused by various aberrations and diffraction effects such as spherical aberration. Using an optical system with a blurring factor of r = 1.35 (typically 1.3r2), the following results can be obtained.

Width of laser beam in diffraction limitted system (1 / e2 Gaussian beam waist)

Spot radius to 1st minimum of the airy disk due to diffracton

Spot diameter on reference surface due to various aberrations

φ = 2r0 * r = 50μ

Distance at which ω 0 changes ± 5% in the z direction, i.e. depth of focus

In the above example, although the system was configured with considerable margin, a resolution corresponding to 500 dpi was obtained. In fact, using a commercially available optical system, a resolution of 4,000 dpi or more can be easily realized.

On the other hand, when the distance between the imaging optical unit 71 and the reference suface changes, an image of a focal image formed on the optical sensor 82 of the distance sensor 72 as shown in FIGS. 4 and 5. Will move continuously from side to side.

As a result, when the light passes through the vicinity of the edge of the photosensitive medium 63 or the printing paper 62, the movement of the focus image appears discontinuously.

This phenomenon can be used to implement precise edge detection, thus eliminating the need for an additional edge detection sensor.

In addition, even if the photosensitive medium 63 or the printing paper 62 is not completely adhered to the drum 61 and a slight curvature occurs, the spot size is kept constant so that the error is corrected and the curved surface within the range that can be controlled by the depth of focus and the actuator. It is also possible to print on.

In addition, although the conventional precision mechanical method increases the error due to the large error, the concept of the present invention makes it easy to increase the size of the system without employing a precise mechanical device, thereby increasing the output size.

In addition, since the gap between the imaging optical unit 71 and the photosensitive medium 63 can be detected, by using the concept of the present invention, if the spot diameter of the focal image formed on the photosensitive medium 63 is servo controlled to a desired size, it is printed. Advantageous characteristics can be obtained for the multi-gradation implementation of information.

Claims (16)

And a control unit for receiving the focal length information and outputting correction data corresponding to the deviation distance, and printing the photosensitive medium onto the drum by lightly adhering the printing paper and the photosensitive medium onto the drum to focus the laser beam. A printhead comprising: optical means for forming a laser beam, which is print information, as a focal point on the photosensitive medium, and detecting an image reflected from the photosensitive medium to detect a focal length between the optical means and the photosensitive medium to the controller. And means for outputting, and an actuator positioned in proximity to the optical means, for controlling the laser beam to form a focus on the photosensitive medium by adjusting the optical means by correction data received from a control unit. Printhead of the laser printer. 2. The optical sensor according to claim 1, wherein the distance detecting means comprises sensing optical means for forming an image of a focus scattered from the photosensitive medium, and a plurality of cells, the optical signal output from the sensing archeological means. A printhead of a laser printing apparatus, comprising: an optical sensor configured to generate an electrical signal corresponding to a focal length in response to a corresponding cell being received. A laser printing apparatus which transfers a photosensitive medium onto a printing paper by lightly adhering a printing paper and a photosensitive medium on a drum to focus a laser beam, the laser printing apparatus comprising: a correction table for storing data for correcting a deviation distance; A control unit for outputting the first data in a dot form, analyzing the received second data to calculate the deviation distance, and accessing correction data corresponding to the deviation distance from the correction table and outputting the third data as the third data; A laser source for converting data into a laser beam, optical means for forming the laser beam into focus on the photosensitive medium, an image reflected by the photosensitive medium, and detecting a distance between the optical means and the photosensitive medium Detection means generated by the second data and located near the optical means and driven by the third data And a print head comprising an actuator for controlling the optical means, and maintaining a distance between the optical means and the photosensitive medium in a constant state so that the focus of the ray point ratio is accurately formed on the photosensitive medium. Laserprint device. 4. The apparatus of claim 3, wherein the detection means of the printhead comprises sensing optical means for forming an image reflected from the photosensitive medium, and a plurality of cells, and receives an optical signal output from the sensing optical means. The laser print apparatus, characterized in that consisting of an optical sensor for generating an electrical signal corresponding to the focal length in response to the corresponding cell. The laserprint apparatus according to claim 4, wherein the control unit calculates the deviation distance d in the following manner. d = n * δ * z0 / s * sin (α ± θ), θ = tan-1 (n * δ / s) n: cell number of the optical sensor that received the reflected image, δ: width of one cell of the optical sensor, z0: reference focal length between the optical means and the photosensitive medium, s: distance between the sensing optical means and the central cell of the optical sensor, α: the reference angle formed by the optical means, the photosensitive medium and the sensing optical means at the reference focal length, θ: deviation angle, d: deviation distance The laser printing apparatus of claim 5, wherein the optical sensor is a linear position detector (PSD). 7. The laserprinting apparatus according to claim 6, wherein the actuator is a linear actuator. 7. A laser printing apparatus according to claim 6, wherein said actuator is a piezoelectric actuator. The laser printing apparatus of claim 5, wherein the optical sensor is a one-dimensional charge coupled device (Linear CCD). 10. The laserprinting apparatus according to claim 9, wherein the actuator is a linear actuator. 10. The laser printing apparatus according to claim 9, wherein the actuator is a one-dimensional charge coupled device (Linear CCD). A laser printing apparatus for transferring a photosensitive medium to a printing paper as heat generated when a printing paper and a photosensitive medium are lightly adhered onto a drum to focus a laser beam, the laser printing apparatus comprising: a correction table for storing data for correcting a deviation distance; A control unit for outputting the print data as first data in a dot form, analyzing the received second data to calculate the deviation distance, and accessing correction data corresponding to the deviation distance from the correction table to output the third data. And a laser source for converting the first data into a laser beam, a first optical coupling means connected to an output end of the laser source, and an optical fiber connected between the first optical coupling means and the second optical coupling means. Means for forming a passage of a laser beam, and connected to the second light coupling means to form the laser beam as a focal point on the photosensitive medium. Optical means, a sensing means for sensing an image reflected on the photosensitive medium to detect a distance between the optical means and the photosensitive medium, and generating the second data; and being located in proximity to the optical means and driven by the third data. And a print head comprising an actuator for controlling the optical means, the optical head and the photosensitive medium being maintained at a constant state so that the focus of the laser beam is precisely formed on the photosensitive medium. Laser print device. 13. An optical signal according to claim 12, wherein the detection means of the printhead comprises sensing optical means for forming an image of a focus scattered from the photosensitive medium, and a plurality of cells, and an optical signal output from the sensing optical means. Responding to the corresponding cell receiving the laser printer, characterized in that consisting of an optical sensor for generating an electrical signal corresponding to the focal length. The laserprint apparatus according to claim 13, wherein the controller calculates the deviation distance d in the following manner. d = n * δ * z0 / s * sin (α ± θ), θ = tan-1 (n * δ / s) n: cell number of the optical sensor that received the reflected image, δ: width of one cell of the optical sensor, z0: reference focal length between the optical means and the photosensitive medium, s: distance between the sensing optical means and the central cell of the optical sensor, α: the reference angle formed by the optical means, the photosensitive medium and the sensing optical means at the reference focal length, θ: deviation angle, d: deviation distance Optical means for imaging a laser beam on a photosensitive medium as a focal point, sensing optical means and an optical sensor, and means for receiving an image reflected from the photosensitive medium to detect distance information on the optical means and the photosensitive medium; A printhead comprising a printhead comprising an actuator for controlling the focus of an optical means, wherein a printing paper and a photosensitive medium are lightly adhered to a drum to focus the laser beam, thereby transferring the photosensitive medium to a printing paper. Converting the print data into a laser beam to form a focus of the laser beam on the photosensitive medium through the optical means of the printhead, receiving the distance information through the detection means of the printhead, and After receiving the distance information, the reference focal length between the optical means and the photosensitive medium and the actual Calculating a deviation distance representing a difference between focal lengths, and outputting correction data for adjusting the position of the optical means to the actuator to correct the deviation distance, between the optical means and the photosensitive medium. A method of printing a laser printer, characterized in that the distance is always operated to maintain the reference focal length. The method of claim 15, wherein the calculating of the deviation distance comprises: calculating a deviation angle between the optical means, the photosensitive medium, and the detection means by the following equation; θ = tan-1 (n * δ / s) θ: deviation angle, n: cell number of the optical sensor that received the reflected image, δ: width of one cell of the optical sensor, s: distance between the sensing optical means of the detecting means and the central cell of the optical sensor A method of printing a laser printer, characterized in that the process of calculating the deviation distance with respect to the distance between the optical means and the center cell of the optical sensor by the following equation. d = n * δ * z0 / s * sin (α ± θ) n: cell number of the optical sensor that received the reflected image, δ: width of one cell of the optical sensor, z0: focal length between the optical means and the photosensitive medium, s: distance between the sensing optical means and the central cell of the optical sensor, α: reference angle formed by the optical means, the photosensitive medium and the sensing optical means at the reference focal length, θ: deviation angle, d: deviation distance