Multi-laser scanning unit

Abstract: A multi-laser scanning unit (LSU) in which scanning lines incident parallel onto a photoreceptor have the same scanning direction. The multi-laser scanning unit includes: a driving source (31) for providing a rotatory force; a deflection disk (35) installed around a rotary shaft of the driving source, having at least two sectors (35a) with a hologram pattern for diffracting and deflecting incident light, for scanning light through rotation; at least two light sources (41,43) installed facing one surface of the deflection disk, for irradiating lights onto predetermined points in the at least two sectors of the deflection disk, the predetermined points being symmetrical about the rotary center of the deflection disk; a light path changing portion (M 1 ', M 22 ', M 41 ') for changing traveling paths of the plurality of scanning lines formed by the rotation of the deflection disk, such that the centers of the scanning lines or extended imaginary lines of the scanning lines pass the rotary axis of the deflection disk; and a scanning direction changing portion (50) for changing the scanning direction of one scanning line scanned by the deflection disk in the opposite scanning direction, such that all the scanning lines scan an image in the same scanning direction.

Description: The present invention relates in general to a multi-laser scanning unit (LSU) capable of diffracting and scanning light incident from at least two light sources, and more particularly to a multi-LSU in which a plurality of scanning lines incident parallel onto a photoreceptor are also directionally the same. In general, a multi-LSU is adopted in a color printer and is used to form a plurality of latent electrostatic images required to develop a color image in combination with a plurality of colors including yellow (Y), magenta (M), cyan (C), black (K) and the like. In this case, a plurality of scanning lines scanned by the multi-LSU and incident onto a photoreceptor such as a photosensitive belt or photosensitive drum must be parallel at predetermined intervals, such that scanning directions of the plurality of scanning lines are parallel each other. Referring to Figures 1 through 3, a conventional multi-LSU capable of generating four scanning lines corresponding to the colors Y, M, C and K includes a driving source 11 for providing a rotatory force, a deflection disk 15 having a plurality of sectors each with a hologram pattern 15a, and a light source unit 20 which is arranged facing one surface of the deflection disk 15 and radiates light onto the deflection disk 15. The light source unit 20 includes four light sources 21, 23, 25 and 27 which irradiate light onto four incident points S 1 ,S 2 , S 3 and S 4 , wherein each pair of points adjacent each other form a right angle at the rotary center of the deflection disk 15. Also, the four incident points S 1 , S 2 , S 3 and S 4 are positioned with equal radii from the rotary center of the deflection disk 15. Thus, the centers of the scanning lines formed by the deflection disk 15 passes the center of the deflection disk 15, thereby reducing off-axis. The incident lights are diffracted by the hologram patterns 15a by rotation of the deflection disk 15 and form scanning lines L 11 , L 21 , L 31 and L 41 in the directions indicated by the arrow ( ). Here, the scanning lines L 11 and L 31 are parallel (to the Y-axis) and are opposite in direction. Also, the scanning line L 21 and L 41 , perpendicular to the scanning lines L 11 and L 31 , are parallel (to the X-axis) and are opposite in direction. Traveling paths of the scanning lines L 11 , L 21 , L 31 and L 41 are changed by a plurality of mirrors such that the centers of the scanning lines travel along the X-axis. That is, the scanning line L 11 is reflected by a mirror M 1 to travel in the X-axis direction, and the scanning line L 21 is reflected by a mirror M 21 toward the rotary center of the deflection disk 15 and then reflected again by a mirror M 22 positioned on the rotary center of the deflection disk 15 to travel in the X-axis direction. Also, the scanning line L 31 is reflected by a mirror M 3 to travel in the X-axis direction, and the scanning line L 41 is reflected by a mirror M 41 toward the rotary center of the deflection disk 15 and then reflected again by a mirror M 42 positioned on the rotary center of the deflection disk 15 to travel in the X-axis direction. Scanning directions of scanning lines L 12 , L 22 , L 32 and L 42 scanning in the X-axis direction after being reflected by the mirrors M 1 , M 21 , M 22 , M 3 , M 41 and M 42 are indicated by the arrow (→) in Figure 2. As shown in Figure 2, the scanning lines L 12 , L 22 and L 42 have the same scanning directions, but the direction of the scanning line L 32 is opposite to that of the scanning lines L 12 , L 22 and L 42 . That is, in the case of using a plurality of mirrors and post holographic optical elements to change the traveling path of the light, after being reflected by the mirrors M 1 , M 22 , M 3 and M 42 , the plurality of scanning lines are parallel in scanning directions for a photoreceptor, but the direction of the scanning line L 32 is still opposite to that of the others. Thus, when forming an image on the photoreceptor, image information must be compensated for in circuitry due to the different scanning directions. That is, the light source 25 providing the scanning line L 32 must transfer the image data in the opposite direction to match image provided by the remaining light sources 21, 23 and 27. That is, there is a disadvantage in that the light sources 21, 23 and 27 provides image information in the direction indicated by ⊗ while the light source 25 provides image information in the direction indicated by ⊙ as shown in Figure 3, so the image data processing is complicated. Document US-A-5295004 discloses an optical scanning unit comprising a motor for providing a rotary force, a deflection disk installed around a rotary shaft of the motor and a deflection disk having sectors with a hologram pattern for diffracting incident light. This document forms the pre-characterising portion of the claims appended hereto. It is an aim of the present invention to provide a multi-laser scanning unit (LSU) in which the centers of a plurality of scanning lines formed by a deflection disk pass the rotary center of the deflection disk, and are parallel in the same scanning direction. According to the present invention there is provided a multi-laser scanning unit as set forth in claim 1 appended hereto. Preferred features of the invention will be apparent from the dependent claims and the description which follows. In a preferred embodiment the multi-laser scanning unit (LSU) comprises: a driving source for providing a rotatory force; a deflection disk installed around a rotary shaft of the driving source, having at least two sectors with a hologram pattern for diffracting and deflecting incident light beams, for scanning the light beams through rotation; at least two light sources installed facing one surface of the deflection disk, for irradiating the light beams onto the at least two sectors of the deflection disk; the multi-laser scanning unit comprising: light beam path changing means for changing the direction of at least two scanning lines, each scanning line being formed by one of the light beams being scanned by the rotation of the deflection disk, such that the axis of each of the scanning lines or extended imaginary line of each of the scanning lines intersects the rotary axis of the deflection disk; and a scanning direction changing means for changing the direction of one scanning line generated by the deflection disk to its opposite direction, such that all scanning lines scan an image in a same scanning direction. Preferably, the scanning direction changing means is a concave mirror arranged on the path of the light beam being scanned in the opposite scanning direction by the rotation of the deflection disk, and the concave mirror is for changing the scanning direction by converging and diverging the incident scanned light beam. Preferably, the light path changing means comprises: a plurality of planar mirrors for reflecting the plurality of light beams scanned and deflected by the deflection disk to serve the light beam paths corresponding to each scan region of the image; a plurality of curved mirrors for condensing and reflecting the lights incident via the planar mirrors; and a plurality of holographic optical elements for diffracting the scanning lines reflected by the curved mirrors. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a schematic perspective view of the main portions of a conventional multi-laser scanning unit (LSU); Figure 2 is a plan view showing the optical arrangement of the conventional multi-LSU for parallel scanning lines; Figure 3 is a side view of Figure 2; Figure 4 is a schematic perspective view of the main portions of a multi-LSU according to a preferred embodiment of the present invention; Figure 5 is a plan view showing the multi-LSU shown in Figure 4; Figure 6 is a schematic perspective view of the cylindrical concave mirror of Figure 5; Figure 7 is a plan view of Figure 6; and Figure 8 is a schematic view showing the optical arrangement of the multi-LSU according to the present invention. Referring to Figures 4 through 8, a multi-laser scanning unit (LSU) according to the preferred embodiment of the present invention includes a driving source 31 for providing a rotatory force, a deflection disk 35 having a plurality of sectors each with a hologram pattern 35a, a light source unit 40 which is arranged facing the bottom of the deflection disk 35 and irradiates beams onto the deflection disk 35, a light path changing means for changing a traveling direction of the light diffracted and scanned by the deflection disk 35, and a scanning direction changing means 50 for changing the scanning direction of one scanning line scanned in the opposite direction. The light source unit 40 includes four light sources 41, 43, 45 and 47 corresponding to four colors, yellow (Y), magenta (M), cyan (C) and black (K) for four scanning lines. The lights irradiated by the four light sources 41, 43, 45 and 47 are incident onto incident points S 1 , S 2 ', S 3 ' and S 4 ' of the deflection disk 35. Here, the incident points S 1 ', S 2 ', S 3 ' and S 4 ' form circles of the same radii R centered around the rotary center of the deflection disk 35, and form a right angle with adjacent incident points at the rotary center of the deflection disk. The lights are diffracted and scanned by the deflection disk 35 in the direction indicated by the arrow ( ) to form the scanning lines L 1 , L 2 , L 3 and L 4 and then the light travelling path is changed by the light path changing means such that the centers of the scanning lines L 11 , L 21 , L 31 and L 41 lie along the X-axis. Here, the light path changing means includes a plurality of planar mirrors M 1 ', M 21 ', M 22 ', M 41 ' and M 42 '. The light corresponding to the scanning line L 11 is reflected by the planar mirror M 1 ' such that at the center of the scanning line it travels in the X-axis direction and the light corresponding to scanning line L 21 is reflected by the mirror M 21 ' toward the rotary center of the deflection disk 35 and then reflected again by the mirror M 22 ' positioned at the rotary center of the deflection disk to travel in the X-axis direction. Also, the light corresponding to scanning line L 41 is reflected again by the mirror M 42 ' positioned at the rotary center of the deflection disk 35 to travel in the X-axis direction. Here, the scanning lines L 11 , L 21 and L 41 are scanned in the direction indicated by ⊗ while the scanning line L 31 is scanned in the direction indicated by ⊙ as shown in Figure 5. Thus, the scanning direction changing means 50 is placed on the optical path of the light corresponding to scanning line L 31 so as to change the scanning direction of the scanning line L 31 to the direction indicated by ⊗ as shown in Figure 5. Preferably, the scanning direction changing means 50 is a cylindrical concave mirror 51, which is concave in the scanning direction. The concave mirror 51 converges the light forming the scanning line L 31 scanned in the -Y-axis direction (direction indicated by the arrow in Figure 7) from the incident point S 3 of the deflection disk 35, and diverges the light forming the scanning line L 32 in the Y-axis direction (direction indicated by the arrow ⇑ in Figure 7). Here, the curvature of the concave mirror 51 is determined in a range where the width of the diverging light is equal to that of the scanning line produced by reflection of the light by the mirror M 3 (see Figure 6). The light forming the scanning line L 41 is reflected by the mirror M 41 ' toward the center of the deflection disk 35 and then reflected again by the mirror M 42 ' positioned at the rotary center of the reflection disk to travel in the X-axis. Here, the mirrors M 21 ', M 22 ', M 41 ' and M 42 ' are substantially the same as those of the mirrors M 21 , M 22 , M 41 and M 42 , thus detailed explanation thereof will be omitted. Thus, scanning lines L 12 , L 22 , L 32 and L 42 obtained after reflection of the lights by the mirrors M 1 ', M 22 ' and M 42 ' and the concave mirror 51, respectively, travel in the same scanning direction indicated by ⊗ for an image formed on a photoreceptor 60. Preferably, the light path changing means further comprises a plurality of planar mirrors M other than the mirrors M 1 ', M 22 ' and M 42 ', curved mirrors CM 1 , CM 2 , CM 3 and CM 4 , and holographic optical elements HOE 1 , HOE 2 , HOE 3 and HOE 4 , so as to scan the lights to form the plurality of scanning lines parallel on the image of the photoreceptor 60. The planar mirrors M reflect the lights corresponding to the four scanning lines L 12 , L 22 , L 32 and L 42 reflected by the mirrors M 1 ', M 22 ' and M 42 ', and the concave mirror 51, respectively, to serve the light travelling paths corresponding to each scanning region in the image. The curved mirrors CM 1 , CM 2 , CM 3 and CM 4 converge and reflect the lights forming scanning lines incident via the plurality of the planar mirrors M such that the scanning lines become parallel, and correct bowing of the scanning lines which is due to diffraction of the incident light by the hologram pattern and rotation of the deflection disk 35. The holographic optical elements HOE 1 , HOE 2 , HOE 3 and HOE 4 diffract and transmit the incident lights at a predetermined angle such that the scanning lines go toward the photoreceptor 60 to be incident at a nearly right angle onto the photoreceptor 60. In the multi-LSU according to the present invention, all the centers of the plurality of scanning lines formed by the deflection disk pass the rotary center of the deflection disk, so the optical arrangement of the mirrors is easy and the plurality of scanning lines have the same scanning direction. Thus, because the main scanning directions of all the scanning lines are the same as the image formation directions, there is an advantage in that compensation for the image information in circuitry is not necessary. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s) but solely by the protection conferred by the claims.

Claims: A multi-laser scanning unit (LSU) comprising: a driving source (31) for providing a rotatory force; a deflection disk (35) installed around a rotary shaft of said driving source, said deflection disk (35) having at least two sectors with a hologram pattern (35a) for diffracting and deflecting incident light beams, for scanning the light beams through rotation; and at least two light sources (41,43) installed facing one surface of said deflection disk, for sending incident light beams onto the at least two sectors of said deflection disk; characterised in that the multi-laser scanning unit comprises: light beam path changing means (M) for changing the direction of at least two scanning lines (L 11 , L 21 , L 31 , L 41 ), each scanning line being formed by one of the light beams being scanned by the rotation of the deflection disk (35), such that the axis of each of the scanning lines or imaginary extended line of each of the scanning lines intersects the rotary shaft axis of the deflection disk; and a scanning direction changing means (50) for changing the direction of one scanning line (L 31 ) generated by the deflection disk to its opposite direction, such that all scanning lines (L 11 , L 21 , L 31 , L 41 ) scan an image in a same scanning direction. The multi-laser scanning unit of claim 1, wherein the scanning direction changing means (50) is a concave mirror (51) arranged on the path of the light beam being scanned in the opposite scanning direction by the rotation of the deflection disk (35), and the concave mirror (51) is for changing the scanning direction by converging and diverging the incident scanned light beam. The multi-laser scanning unit of claim 1 or 2, wherein the light path changing means comprises: a plurality of planar mirrors (M) for reflecting the plurality of light beams scanned and deflected by the deflection disk, to serve the light beam paths corresponding to each scan region of the image; a plurality of curved mirrors (CM) for condensing and reflecting the light beams incident via the planar mirrors; and a plurality of holographic optical elements (HOE) for diffracting the scanning lines reflected by the curved mirrors.

Inventors: CHO SUNG-MIN, CHOI HWAN-YOUNG, EUM JAE-YONG, KIM YOUNG-IL, LEE MOON-GYU, MIN JEE-HONG, CHO, SUNG-MIN, CHOI, HWAN-YOUNG, EUM, JAE-YONG, KIM, YOUNG-IL, LEE, MOON-GYU, MIN, JEE-HONG
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 1999
Main classification: G02B26
IPC codes: B41J2, G02B26, H04N1