WO2023277972A1

WO2023277972A1 - Laser scanning unit for processing multiple beams

Info

Publication number: WO2023277972A1
Application number: PCT/US2022/017703
Authority: WO
Inventors: SuWhan KIM
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2021-06-30
Filing date: 2022-02-24
Publication date: 2023-01-05
Also published as: KR20230004094A

Abstract

An image forming device includes a first light source and a second light source to emit first light and second light, respectively, toward a direction perpendicular to a first straight line between the first light source and the second light source, a single synchronization detecting sensor to receive the first light and the second light, and a lens to change light paths of the first light and the second light to cause the first light and the second light to reach the single synchronization detecting sensor.

Description

LASER SCANNING UNIT FOR PROCESSING MULTIPLE BEAMS

BACKGROUND

[0001] An image forming device, such as a laser printer, forms an image by scanning a light beam onto a photosensitive drum by using a light scanning device to form an electrostatic latent image, developing the electrostatic latent image into a toner image by using toner, and transferring the developed toner image onto a printing medium.

[0002] A light scanning unit uses a polygonal rotating mirror to scan a light beam onto a photosensitive drum. In a color image forming device for producing a color image, a light scanning unit scans four light beams corresponding to the respective colors of black (K), cyan (C), magenta (M), and yellow (Y) by using one or more polygonal rotating mirrors.

[0003] For a light scanning unit to scan a light beam onto a photosensitive drum with correct timing, a synchronization signal detecting unit to detect a horizontal synchronization signal of a scanned light beam may be used. To produce a color image, a light scanning unit scans a plurality of light beams by using a polygonal rotating mirror, wherein light sources are arranged so that light beams are incident symmetrically with respect to the center of the polygonal rotating mirror,

[0004] A synchronization signal detecting unit detects a horizontal synchronization signal by using a beam detecting sensor. The detected horizontal synchronization signal is then transferred to a printer video controller (PVC). The PVC transmits video data to a laser diode driver (LDD) in a light scanning unit according to the received horizontal synchronization signal, and the LDD controls on/off operation of a light source according to the video data so as to emit a light beam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The present disclosure may be easily understood by the combination of the following detailed descriptions and accompanying drawings, in which reference numerals refer to structural elements,

[0008] FIG. 1 illustrates an example of a light scanning unit and a printer controller of an image forming device.

[0007] FIG. 2 illustrates a configuration example of light sources, a lens and a synchronization detecting sensor of an image forming device.

[0008] FIG. 3 is a block diagram of a signal processor of an image forming device, according to an example.

[0009] FIG. 4 illustrates an example of processing a horizontal synchronization signal.

[0010] FIG. 5 illustrates another example of processing a horizontal synchronization signal.

[0011] FIG. 6 illustrates a configuration example of light sources of an image forming device.

[0012] FIG. 7 illustrates another example of a light scanning unit and a printer controller of an image forming device.

[0013] FIG. 8 is a flowchart of a method of detecting a synchronization signal. [0014] FIG. 9 illustrates an example of an image forming device.

DETAILED DESCRIPTION

[0015] Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings, in which examples of the present disclosure are shown such that those skilled in the art may easily work the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the examples described herein. [0018] An "image forming device" may be any kind of device capable of performing an image forming operation, such as a printer, a scanner, a fax machine, a multi-function printer (MFP) or a display device, etc. The image forming device may also be a two dimensional (2D) image forming device or a 3D image forming device. An "image forming operation performed by the image forming device" may be an operation related to printing, copying, scanning, faxing, storage, transmission, coating, etc., or a combination of two or more of the operations described above.

[0017] A "main scanning direction" refers to a direction in which scanning lines are drawn on a scanned surface 180 in FIG. 1. That is, the main scanning direction is a direction in which a spot of light beams L1 and L2 deflected by a polygonal rotating mirror 150, and formed on the scanned surface 180 propagates on the scanned surface 180. Because a light path of light beams L1 and L2 may be changed by a light path changing member such as a reflective mirror, the main scanning direction may be changed as the light path is changed. Without considering the presence of the light path changing member, the main scanning direction is equal to the direction of scanning lines on the scanned surface because the main scanning direction on the light path of the light beams L1 and L2 corresponds to the main scanning direction on the scanned surface. A "sub scanning direction" refers to a direction that is perpendicular to both the main scanning direction and a proceeding direction (i.e,, light path) of light beams L1 and L2 deflected by the polygonal rotating mirror 150. Because a light path of light beams L1 and L2 may be changed by a light path changing member such as a reflective mirror, the sub scanning direction may be changed as the light path is changed. Without considering the presence of the light path changing member, the sub scanning direction is the same as a direction of a rotational axis of the polygonal rotating mirror 150. !n addition, a main scanning plane is defined as a plane on which both a proceeding direction of iight beams L1 and L2, and a main scanning direction, i.e., a plane across which Iight beams L1 and L2 are deflected and scanned by the polygonal rotating mirror 150. A sub scanning plane refers to a plane perpendicular to the main scanning plane. [0018] FIG. 1 illustrates an example of a light scanning unit and a printer controller of an image forming device.

[0019] FIG. 1 shows an optical arrangement of a light scanning unit 100 with respect to a main scanning plane, in which an optical path of an image forming optical system 170 is not folded for convenience of illustration.

[0020] Referring to FIG. 1. an image forming device may include a light scanning unit 100, and a printer controller 200 to control the light scanning unit 100. The light scanning unit 100 may be referred to as a laser scanner unit (LSU).

[0021] The light scanning unit 100 may include light sources 110a and 110b, synchronization detecting sensor 180, and a lens 185, but is not limited thereto, and may include more or fewer components. For example, the light scanning unit 100 may further include a polygonal rotating mirror 150. The polygonal rotating mirror 150 may deflect and scan light beams L1 and 12 to a scanned surface 180 in a main scanning direction. Referring to FIG. 1 , the polygonal rotating mirror 150 may include six reflective surfaces (i.e., a hexagon mirror) and rotate at a constant speed using a driver such as a spindle motor. The polygonal rotating mirror 150 may rotate clockwise as illustrated in FIG. 1 , but is not limited thereto, and may rotate counterclockwise. The polygonal rotating mirror 150 may include six reflective surfaces, but is not limited thereto, and may include 4, 5, 6, 7, or more reflective surfaces.

[0022] A configuration of a synchronization detecting sensor 160 and a lens 165 will be explained by further referring to FIG. 2.

[0023] FIG. 2 illustrates a configuration example of light sources 110a and 110b, a synchronization detecting sensor 160, and a lens 165 of an image forming device.

[0024] Referring to FIG, 1 , light sources 110a and 110b may emit light beams 11 and L2, respectively. The light sources 110a and 110b may be semiconductor laser diodes to emit laser beams. A laser diode driver (LDD) 190 may be mounted on a circuit board 130 on which light sources 110a and 110b are disposed. Circuit elements to control the power of lights, such as variable resistance may be mounted on the circuit board 130. The LDD 190 drives an on/off operation of the light sources 110a and 110b, light beams L1 and L2 emitted from the light sources 110a and 110b based on input video data may form an electrostatic latent image on the scanned surface 180. The above operations may be repeated until scanning is terminated.

[0025] The light sources 110a and 110b may be referred to as a first light source 110a and a second light source 110b. The first light source 110a and the second light source 110b may be vertically arranged to scan a first light beam 11 and a second light beam L2 toward one surface of the polygonal rotating mirror 150. The first light source 110a and the second light source 110b may be arranged in parallel to the sub scanning direction. Therefore, as shown in FIG. 1 , the first light source 110a and the second light source 110b may overlap each other on the main scanning plane. Furthermore, the light beams L1 and L2, which are emitted from the first light source 110a and the second light source 110b respectively and incident on the polygonal rotating mirror 150 may be incident obliquely at different angles on one reflective surface of the polygonal rotating mirror 150 in the sub scanning direction. The light beams 11 and L2 may be incident in parallel to each other on the reflective surface of the polygonal rotating mirror 150.

[0026] Referring to FIG. 1 , an incidence optical system may be disposed on light paths of the light beams L1 and L2 between the light sources 110a and 110b and the polygonal rotating mirror 150. The incidence optical system may include a collimating lens 120 and a cylindrical lens 140, but is not limited thereto. For example, the incidence optica! system may further include a slit located between the collimating lens 120 and the cylindrical lens 140. Some of the collimating lens 120, the slit, and the cylindrical lens 140 may be omitted or formed integrally with other optical components. The collimating lens 120 is a condenser lens to convert the light beams L1 and L2 emitted from the light sources 110a and 110b into parallel light or convergent light. The collimating lens 120 may include a plurality of collimating lenses 120a and 120b respectively corresponding to the light sources 110a and 110b as shown in FIG. 2. The slit is an aperture to adjust a diameter and a shape of the light beams L1 and L2. The cylindrical lens 140 is an anamorphic lens to linearly form an image on a reflective surface of the polygonal rotating mirror 150 by focusing the light beams L1 and L2 in a direction corresponding to the main scanning direction and/or the sub scanning direction. The light beams L1 and L2 may be incident on the polygonal rotating mirror 150 while being adjacent to each other and spaced a predetermined interval apart from each other in the sub scanning direction, and thus, the single cylindrical lens 140 may be shared by the light beams 11 and L2. The cylindrical lens 140 may be implemented as a plurality of lenses individually disposed on the light paths of the light beams L1 and 12.

[0027] The synchronization detecting sensor 160 may be, for example, a photodetector, a photo diode or a photo sensor integrated circuit (IC), but is not limited thereto. The synchronization detecting sensor 160 may be disposed on a portion of the circuit board 130 towards which a synchronization detecting light beams LT and L2‘ are directed to detect a start point of one scanning period of the light beams L1 and L2 scanned by the polygonal rotating mirror 150. The synchronization detecting light beam LT and L2' correspond to a point just before the start point of one effective scanning period of the light beams L1 and L2 reflected off the reflective surface of the polygonal rotating mirror 150. The synchronization detecting light beam LT and L2’ detected by the synchronization detecting sensor 160 may be converted into a horizontal synchronization signal (Hsync) indicating a beginning of scanning of the light beams L1 and L2. The synchronization signals detected by the synchronization detecting sensor 160 may be transferred to the printer controller 200. The synchronization signal may be used to control light emitting timing of the light sources 110a and 110b to improve the image quality.

[0028] As shown in FIG. 1 , a circuit board on which the synchronization detecting sensor 160 is installed and a circuit board on which the light sources 110a and 110b are installed may be separate from each other, but are not limited thereto. For example, the synchronization detecting sensor 160 and the light sources 110a and 110b may be disposed together on a single circuit board.

[0029] As shown in FIGS. 1 and 2, to use the single (or one) synchronization detecting sensor 160 for the light sources 110a and 110b, a lens 165 to focus the synchronization detecting light beams LT and L2' on the synchronization detecting sensor 160 may be interposed between the synchronization detecting sensor 160 and the polygonal rotating mirror 150. The lens 165 may focus the light beams L1 ' and L2' emitted from light sources 110a and 110b arranged vertically. For example, the lens 185 may be a convex lens. For example, the lens 185 may be a lens in which a convex lens and a concave lens are combined. [0030] As shown FIG. 2, the synchronization detecting sensor 180 may be located on a point on which the light beams L1' and L2' passing through the lens 165 are focused, but is not limited thereto. For example, the synchronization detecting sensor 180 may be located in the light paths of the light beams L1' and L2\ For example, the synchronization detecting sensor 180 may be located between the light paths of the light beams L1 ’ and L2'. For example, the synchronization detecting sensor 180 may be located closer to the lens 185 than shown in FIG. 2 as long as the synchronization detecting lens 160 can cover both the light beams Lt and L2\

[0031] As shown in FIG. 2, a center between the light sources 110a and 110b, a center of the synchronization detecting sensor 160, a center of the lens may be located on the same plane. The synchronization detecting sensor 160 may be located between two straight lines extended from the light sources 110a and 110b with respect to the circuit board 130. A part of the lens 185 overlapping with a straight line extended from the center between the light sources 110a and 110b with respect to the circuit board 130 may have be thicker than other parts of the lens 185 respectively overlapping with two straight lines extended from the light sources 110a and 110b with respect to the circuit board 130. The other parts of the lens 185 respectively overlapping with two straight lines extended from the light sources 110a and 110b with respect to the circuit board 130 may have the same lens thickness,

[0032] As shown in FIGS. 1 and 2, the single synchronization detecting sensor 160 may be used to detect the light sources 110a and 110b. In order to use the single synchronization detecting sensor 160 to detect the light sources 110a and 110b, light emitting timing of the light sources 110a and 110b may be adjusted, which will be explained by referring to FIGS. 3, 4, and 5.

[0033] Two synchronization detecting sensors may be used for the light sources 110a and 110b, which increases production cost of the image forming device. In case where the two synchronization detecting sensors respectively corresponding to light sources 110a and 110b are used, two lenses to focus synchronization detecting light beams L1 ' and L2' on the two synchronization detecting sensors are introduced, which increases the production cost of the image forming device. Therefore, the production cost of the image forming device may be reduced by using one synchronization detecting sensor 180 for the light sources 110a and 110b,

[0034] By way of another example, a synchronization detecting sensor may be used for either one of light sources 110a and 110b. For example, one synchronization detecting sensor may be used for the one light source 110a. However, reflective surfaces of the polygonal rotating mirror 150 are not ideal, and a processing deviation (error) of the reflective surfaces may result in synchronization error of another light source 110b, which may cause more or the like due to an x-direction shift to deteriorate an output image. Although light beams LT and L2‘ emitted from the light sources 110a and 110b vertically arranged are scanned on the same reflective surface of the polygonal rotating mirror 150, the emission direction of the light sources 110a and 110b or the polygonal rotating mirror 150 may have deviation across its reflective surface. When the one synchronization detecting sensor is used for one light source 110a, a user may not be able to recognize a problem of another light source 110b due to the absence of synchronization detecting sensor for the other light source 110b. [0035] The light scanning unit 100 of the present disclosure uses the single synchronization detecting sensor 160 for the light sources 110a and 110b, thereby, reducing the production cost and image deterioration. In order to use the single synchronization detecting sensor 160 for the light sources 110a and 110b, light emitting timing of the light sources 110a and 110b may be adjusted, which will be explained by referring to FIGS. 3, 4, and 5.

[0036] Referring to FIG. 1 , an image forming optical system 170 may be disposed between the polygonal rotating mirror 150 and the scanned surface 180. The image forming optical system 170 may include first and second image forming lenses 171 and 172 to image the light beams L1 and L2, deflected by the polygonal rotating mirror 150, on the scanned surface 180. As described above, the light beams L1 and L2 are adjacent to each other in the vicinity of the polygonal rotating mirror 150, and the first and second image forming lenses 171 and 172 may be shared for the light beams L1 and L2 reflected by the polygonal rotating mirror 150, but are not limited thereto. For example, the first image forming lens 171 and the second image forming lens 172 may be a plurality of first image forming lenses and a plurality of second image forming lenses, respectively. The first image forming lens 171 and the second image forming lens 172 may be disposed individually on light paths of the light beams L1 and L2 emitted from the light sources 110a and 110b.

[0037] The first and second image forming lenses 171 and 172 may be f-theia (ίq) lenses to have condensing function and f0 characteristics. The first image forming lens 171 , which is relatively closes to the polygonal rotating mirror 150, may be designed to have approximately zero refractive power in the sub scanning direction. The second image forming lens 172, which is disposed relatively farther away from the polygonal rotating mirror 150 may be designed to have a positive refractive power in the sub scanning direction. FIG. 1 illustrates that the Image forming optical system 170 includes two lenses, an optical configuration of the image forming optical system 170 may be changed in various ways. For example, the image forming optical system 170 may be implemented by disposing one or more lens. In order to reduce the size of the light scanning unit 100 and image the light beams L1 and L2 scanned by the light scanning unit 100 in a predetermined direction, reflective members (not shown) may be disposed within the image forming optical system 170.

[0038] FIG. 3 is a block diagram of a signal processor of an image forming device according to an example.

[0039] Referring to FIG. 3, a printer controller 200 may include a processor 210 a memory 220. The printer controller 200 may receive, from an image processor, input data, such as bitmap data, and form an image on a paper based on the input data. The printer controller 200 may control the light scanning unit 100. The processor 210 of the printer controller 200 may execute a program stored on the memory 220 to control the light scanning unit 100. The processor 210 may be a central processing unit (CPU) or a hyper print video controller (HPVC) in a main board of the image forming device. [0040] The processor 210 may compare synchronization signals Hsynd and Hsync2 transmitted from the synchronization detecting sensor 160. The synchronization signals Hsynd and Hsync2 may be generated by the synchronization detecting sensor 160 based on the light beams IT and L2' respectively emitted from the light sources 110a and 110b of FIG. 1. The synchronization detecting sensor 160 may detect the synchronization signals Hsynd and Hsync2 based on the light beams LT and L2' respectively emitted from the light sources 110a and 110b of FIG. 1. Comparison of synchronization signals Hsynd and Hsync2 will be explained by further referring to FIGS. 4 and 5.

[0041] The light sources 110a and 110b may emit light beams alternately so that effective synchronization signals Hsynd and Hsync2 can be generate based on the light beams LT and L2' respectively emitted from the light sources 110a and 110b of FIG. 1. By alternating the emission of the light sources 110a and 110b, the accuracy of the synchronization signals Hsynd and Hsync2 generated by the one synchronization detecting sensor 160 may be improved. The synchronization detection may be conducted while an image signal of processor 210 is not outputted, because the light sources 110a and 110b alternately emit light beams. For example, the synchronization signal Hsynd and Hsync2 may be not detected while the image signal is not output, for example, during an initialization period when the image forming device is turned on or waken up, a pre-printing period, an after-printing period, or a pausing period between printing jobs. The image forming device uses the one synchronization detecting sensor 160 to detect the synchronization signals Hsynd and Hsync2 based on the light beams LT and L2' respectively emitted from the light sources 110a and 110b so a problem caused by either one of the light sources 110a and 110b may be recognized instantly. For example, the image forming device may notify a user that a problem has occurred in a light source in response to determining that either one of the light sources 110a and 110b is not detected. For example, a notification indicating that a problem has occurred in a light source may be displayed on a display of the image forming device. For example, the image forming device may transmit to a user or a manager of the image forming device a message indicating that a problem has occurred in a light source. A way to process an image based on a comparison result of synchronization signals Hsynd and Hsync2 will be explained by referring to FIGS. 4 and 5.

[0042] FIG. 4 illustrates an example of processing a horizontal synchronization signal.

[0043] FIG. 5 illustrates another example of processing a horizontal synchronization signal.

[0044] Light sources 110a and 110b may alternately emit lights based on a predetermined cycle. For example, the light sources 110a and 110b may alternately emit lights based on a rotation cycle of the polygonal rotating mirror 150. For example, while the light source 110a is turned on to emit light for a predetermined number of rotation periods of the polygonal rotating mirror 150, the other light source 110b may be turned off. For example, while the light source 110a is turned on to emit light during one rotation period T of the polygonal rotating mirror 150, the other light source 110b may be turned off. Alternate emission of the light sources 110a and 110b may be repeated a predetermined number of times. For example, the alternate emission of the light sources 110a and 110b may be repeated while the polygonal rotating mirror 150 rotate ten times, that is, 10T. The other light source 110b may be turned on after a predetermined time elapses after the light source 110a is turned on and off. For example, the light sources 110a and 110b may be turned off during the predetermined time, and the predetermined time may be identical to the number of rotation periods of the polygonal rotating mirror 150, but is not limited thereto. For example, the predetermined time may be identical to one rotation cycle of the polygonal rotating mirror 150, that is, 1T.

[0045] FIG. 4 illustrates an example where an offset value between the synchronization signals of the light sources 110a and 110b are the same on reflective surfaces of the polygonal rotating mirror 150.

[0048] The processor, for example processor 210 of FIG. 3, may determine an offset value by comparing the synchronization signals of the light sources 110a and 110b. Referring to FIG. 4, a synchronization signal of a light source 110b has an offset value delayed by "a" from another synchronization signal of another light source 110a. in case where a synchronization signal of a light source 110b has an offset value delayed by "a" than another synchronization signal of another light source 110a for all reflective surfaces of the polygonal rotating mirror 150, the processor 210 may control a laser diode driver 190 to delay light emitting timing of the light source 110a by "a'¹ or to advance light emitting timing of the light source 110b by "a" to compensate for the offset value. Therefore, light beams from the light sources 110a and 110b may be simultaneously imaged on the scanned surface.

[0047] The comparison result may be stored on the memory 220 and used for subsequent printing jobs.

[0048] FIG. 5 illustrates an example where an offset value between the synchronization signals of the light sources 110a and 110b are different according to reflective surfaces of the polygonal rotating mirror 150.

[0049] The processor, for example processor 210 of FIG. 3, may determine an offset value by comparing the synchronization signals of the light sources 110a and 110b. Referring to FIG. 5, a synchronization signal of a light source 110b has an offset value delayed by "a” than another synchronization signal of another light source 110a at 3/6 T period of a rotation cycle (T) of the polygonal rotating mirror 150, and the synchronization signal of the light source 110b has an offset value delayed by "b" than the other synchronization signal of the other light source 110a at 5/6 T period of the rotation cycle (T) of the polygonal rotating mirror 150. The printer controller 200 may control the laser diode driver 190 to delay light emitting timing of the light source 110a by "a" or to advance light emitting timing of the light source 110b by "a" at 3/6 T period of the rotation cycle (T) of the polygonal rotating mirror 150 to compensate for the offset value. The printer controller 200 may control the laser diode driver 190 to delay light emitting timing of the light source 110a by "b" or to advance light emitting timing of the light source 110b by "b" at 5/6 T period of the rotation cycle (T) of the polygonal rotating mirror 150 to compensate for the offset value. Therefore, light beams from the light sources 110a and 110b may be simultaneously imaged on the scanned surface when reflective surfaces of the polygonal rotating mirror 150, or light sources have deviation with each other. [0050] When offset values between the synchronization signals of the light sources 110a and 110b are different according to reflective surfaces of the polygonal rotating mirror 150, detecting and comparing of synchronization signals and storing a comparison result are conducted based on a unit of printing job or a motor-ready-on signal of LSU motor of the printer controller 200 [0051] FIG. 6 illustrates a configuration example of light sources of an image forming device.

[0052] FIG. 7 illustrates another example of a light scanning unit and a printer controller of an image forming device.

[0053] Referring to FIG. 7, the light scanning unit 100' may further include other light sources 110c and 110d in addition to the light sources 110a and 110b. Referring again to FIG. 7, the light sources 110a and 110b may be disposed to emit light 11 and light L2 toward the polygonal rotating mirror, respectively, and the light sources 110c and 110d may be disposed to emit light L3 and light L4 toward the polygonal rotating mirror. The first light L1 originating from the light source 110a continues to be referred to as the first light L1 even after its light path is changed. The second, third and fourth lights L2, L3 and L4 also continue to be referred as the second, third and fourth lights L2, L3 and L4 even after their light paths are changed.

[0054] Referring to FIG. 6, the light sources 110a and 110b may be arranged vertically on a circuit board 130', and the light sources 110c and 110d may be arranged vertically on a circuit board 130'. Referring again to FIG. 8, a pair of the light sources 110a and 110b, and another pair of the light sources 110c and 110d may be arranged laterally on the circuit board 130'.

[0055] As shown in FIGS. 8 and 7, a center between the light sources 110a and 110b, a center of the synchronization detecting sensor 160a, a center of the lens 185a may be located on the same plane. Furthermore, a center between the other light sources 110c and 110d, a center of the synchronization detecting sensor 160b, a center of the lens 185b may be located on the same plane. As shown in FIG. 6, a straight line on which the light sources 110a and 110b are disposed are parallel with a straight line on which the light sources 110c and 110d are disposed. [0058] FIG. 7 illustrates that the synchronization detecting sensors 180a and 160b are located on different planes, but are not limited thereto. For example, the synchronization detecting sensor 180a and 180b may be located on the same plane by using a mirror to change a light path. For example, the synchronization detecting sensor 180a and 180b may be located on the same circuit board. For example, the synchronization detecting sensor 160a and 160b may be located on the same circuit board on which the light sources 110a, 110b, 110c and 110d are located. For example, the mirror to change the light path may be formed integrally with the lens 165b or 165a.

[0057] FIG. 8 is a flowchart of a method of detecting a synchronization signal. [0058] In operation 810, an image forming device may alternately emit lights. For example, the image forming device may control two light sources 110a and 110b vertically arranged to alternately emit first light and second light toward a surface of the polygonal rotating mirror 150.

[0059] For example, the image forming device may control two light sources 110a and 110b vertically arranged to alternately emit first light and second light toward the polygonal rotating mirror 150 and control other two light sources 110c and 110d vertically arranged to alternately emit third light and fourth light toward the polygonal rotating mirror 150.

[0060] As shown in FIG. 8, first light source 110a and third light source 110c to emit first light L1 and third light L3 are arranged laterally, and second light source 110b and fourth light source 110d to emit second light L2 and fourth light L4 are arranged laterally. While the first light L1 and the third light L3 is turned on, the second light 12 and the fourth light 14 may be turned off. While the second light L2 and the fourth light L4 is turned on, the first light L1 and the third light L3 may be turned off. The first light 11 and second light L2, and the third light 13 and fourth light L4 may be alternately emitted according to a rotation cycle of the polygonal rotating mirror. For example, the first light L1 and the third light L3 are emitted during a rotation cycle of the polygonal rotating mirror, and the second light L2 and the fourth light L4 are emitted during another rotation cycle of the polygonal rotating mirror, but are not limited thereto. For example, the first light L1 and the fourth light L4 may be emitted together, second light L2 and the third light L3 may be emitted together, or the first light L1 may be emitted during a period overlapping with a period when the third light L3 or the fourth light L4 is emitted.

[0061] In operation 820, the image forming device may receive lights emitted alternately. For example, the image forming device may receive the lights L1 and L2 through the synchronization detecting sensor 160 as shown in FIG. 1 , The first and second lights L1 and L2 alternately emitted from two light sources 110a and 110b arranged vertically may be detected by one synchronization detecting sensor 160. A lens 165 may be disposed on light paths of the first and second lights L1 and L2 so that the first and second lights L1 and L2 are received by the one synchronization defecting sensor 160.

[0062] For example, the image forming device may receive through one synchronization detecting sensor 160a, the first and second lights 11 and 12 alternately emitted from the two light sources 110a and 110b vertically arranged, and may receive through another synchronization detecting sensor 160b, the third and fourth lights L3 and L4 alternately emitted from the two light sources 110c and 110d vertically arranged.

[0063] The first light L1 and the third light L3 are received during a rotation cycle of the polygonal rotating mirror, and the second light L2 and the fourth light L4 are received during another rotation cycle of the polygonal rotating mirror, but are not limited thereto. A receiving period of the first, second, third and fourth light L1 , L2, L3 and L4 may correspond to an emitting period of the first, second, third and fourth light L1 , L2, L3 and L4.

[0064] In operation 830, the image forming device may detect synchronization signals based on the received lights. For example, the image forming device may detect first and second synchronization signals through one synchronization detecting sensor 160 based on the lights received from the two light sources 110a and 110b arranged vertically, as shown in FIG. 1 .

[0065] For example, the image forming device may detect first and second synchronization signals through one synchronization detecting sensor 160a based on the lights received from the two light sources 110a and 110b arranged vertically, and detect third and fourth synchronization signals through another synchronization detecting sensor 160b based on the lights received from the two light sources 110c and 110d arranged vertically.

[0068] Calculation of offset values of the synchronization signals are explained above by referring to FIGS. 3. 4 and 5, and a redundant description thereof will be omitted.

[0087] In operation 840, the image forming device may control emission of light based on the detected synchronization signals. For example, the image forming device may control at least one light emitting timing of two light sources 110a and 110b based on the detected first and second synchronization signals, as shown in FIG. 1.

[0088] For example, the image forming device may control at least one light emitting timing of two light sources 110a and 110b based on the detected first and second synchronization signals, control at least one light emitting timing of other two light sources 110c and 110d based on the detected third and fourth synchronization signals, as shown in FIG. 7.

[0069] An element described as performing a certain function includes any means to perform the certain function, such element may include a combination of circuit elements to perform the certain function, or any type of software including firmware, micro-codes, etc., combined with a circuit to execute software to perform the certain function. For example, operations to alternately emit lights, detect synchronization signals based on the lights received at a synchronization detecting sensor, calculate offset values between the lights based on the detected synchronization signals, and output a printer image signal based on compensating for the calculated offset values may be implemented by a combination of circuit elements to perform the certain function, or any type of software including firmware, micro-codes, etc., combined with a circuit to execute software to perform the certain function.

[0070] A hardware module may be implemented mechanically or electronically. For example, the hardware module may include a specially-designed permanent circuit or logic component (such as a dedicated processor, e.g., an FPGA or ASIC) to perform a specific operation. The hardware module may also include a programmable logic component or circuit temporarily configured by software (for example, including a general-purpose processor or another programmable processor) for performing a specific operation, and may be implemented in a computer readable storage medium to store instructions or data executable by a computer or a processor

[0071] FIG. 9 illustrates an example of an image forming device. For example, the image forming device may be various types of equipment such as printers, facsimile machines, copiers, or duplicators, but is not limited thereto.

[0072] Referring to FIG. 9, the image forming device includes four light scanning units 100, a printer controller 200, develop devices 300, a transfer device 400, and a fixing device 500.

[0073] To print color images, the light scanning unit 100 includes four light scanning units to respectively scan four light beams corresponding to the respective colors of black (K), cyan (C), magenta (M), and yellow (Y).

[0074] As shown in FIG. 9, the develop devices 300 may be provided for the respective colors of black (K), cyan (C), magenta (M), and yellow (Y), Each of the develop devices 300 includes a photosensitive drum 31 as an image receptor on which an electrostatic latent image is formed, and a develop roller 32 to develop the electrostatic latent image.

[0075] The photosensitive drum 31 is an example of a photosensitive medium, and is formed by forming a photosensitive layer on an outer circumference surface of a cylindrical metal pipe to a predetermined thickness. Outer circumference surfaces of the photosensitive drums 31 correspond to the scanned surface (180 in FIG. 1). A charging roller 33 is positioned near a region upstream from a portion of the outer circumference surface of each photosensitive drum 31 exposed by the corresponding light scanning unit 100. The charging roller 33 is an example of a charger for charging a surface of the photosensitive drum 31 while contacting the photosensitive drum 31 and rotating against the photosensitive drum 31 . A charging bias is applied to the charging roller 33. A corona charger (not shown) may be used instead of the charging roller 33.

[0078] The develop roller 32 supplies toner attached to an outer circumference surface thereof to the photosensitive drum 31 . A developing bias for supplying the toner to the photosensitive drum 31 is applied to the develop roller 32. Although not shown, each of the develop devices 300 may further include a supply roller for attaching toner accommodated therein to the develop roller 32, a regulator for regulating an amount of the toner attached to the develop roller 32, a supply roller for supplying the toner, and/or a stirrer for moving the toner towards the develop roller 32.

[0077] The transfer device 400 may include an intermediate transfer belt 41 and four transfer rollers 42. The Intermediate transfer belt 41 is disposed on opposite portions of the outer circumference surfaces of the photosensitive drums 31 , which are exposed out of the develop devices 300. The intermediate transfer belt 41 is supported by a plurality of support rollers 43, 44, 45, and 46, and is circulated. The four transfer rollers 42 face the photosensitive drums 31 of the develop devices 300, with the intermediate transfer belt 41 interposed there between, A transfer bias is applied to the transfer rollers 42.

[0078] The photosensitive drums 31 of the develop devices 300 are charged with a uniform potential by a charging bias applied to the charging rollers 33. The light scanning units 100 scan four light beams corresponding to image information of black (K), cyan (C), magenta (M), and yellow (Y) to the photosensitive drums 31 of the develop devices 300 to form electrostatic latent images. A develop bias is applied to the develop rollers 32. Then, the toner attached to the outer circumference surfaces of the develop rollers 32 is attached to the electrostatic latent images to thereby form toner images of black (K), cyan (C), magenta (M), and yellow (Y) on the respective photosensitive drums 31 of the develop devices 300.

[0079] A medium for finally receiving the toner, e.g., a sheet of printing paper P, is drawn out of a cassette 60 by a pickup roller 61 . The printing paper P is placed on the intermediate transfer belt 41 by a transport roller 62. The sheet of printing paper P is attached to a surface of the intermediate transfer belt 41 by an electrostatic force, and is transported at the same speed as a linear speed of the intermediate transfer belt 41 ,

[0080] For example, when a front end of the toner image of cyan (C) formed on the outer circumference surface of the corresponding photosensitive drum 31 of the develop device 300 reaches a transfer nip facing the transfer roller 42 corresponding to the photosensitive drum 31 , a front end of the sheet of printing paper P reaches the transfer nip. When a transfer bias is applied to the transfer roller 42, the toner image formed on the photosensitive drum 31 is transferred onto the sheet of printing paper P. As the printing paper P is transported, the toner images of black (K), cyan (C), magenta (M), and yellow (Y) formed on the photosensitive drums 31 of the develop devices 300 are sequentially transferred onto the sheet of printing paper P so as to overlap with each other, thereby creating a color toner image on the sheet of printing paper P.

[0031] The color toner image transferred onto the sheet of printing paper P is maintained on a surface of the sheet of printing paper P by an electrostatic force. The fixing device 500 fixes the color toner image on the sheet of printing paper P by using heat and pressure. The sheet of printing paper P is ejected out of the image forming device by an ejection roller 63.

The above-described operation method may be implemented in the form of a computer-readable storage medium to store instructions or data executable by a computer or a processor. The above-described operation method of the image forming device may be written in a program executable by a computer, and may be implemented in a general-purpose digital computer that operates such a program using a computer-readable storage medium. Examples of such a computer-readable storage medium may include read-only memory (ROM), random-access memory (RAM), flash memory, compact disc (CD)-ROMs, CD- recordables (Rs), CD+Rs, CD- rewritables (RWs), CD+RWs, and digital versatile disc (DVD)-ROMs, DVD-Rs, DVD+Rs, DVD-RWs, DVD+RWs, DVD-RAMs, blu- ray disc (BD)-ROMs, BD-Rs, BD-recordable low to highs (R LTHs), BD-REs, magnetic tapes, floppy disks, magneto-optical data storage devices, optical data storage devices, hard disks, solid-state disks (SSDs). and any device capable of storing instructions or software, associated data, data files, and data structures, and providing a processor or computer with instructions or software, associated data, data files, and data structures such that the processor or computer may execute the instructions. [0082] It should be understood that examples described herein should be considered in a descriptive sense and not for purposes of limitation. Descriptions of features or aspects within each example should typically be considered as available for other similar features or aspects in other examples. While one or more examples have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. An image forming device comprising: a first light source and a second light source to emit first light and second light, respectively, toward a direction perpendicular to a first straight line between the first light source and the second light source; a single synchronization detecting sensor to receive the first light and the second light; and a lens to change light paths of the first light and the second light to cause the first light and the second light to reach the single synchronization detecting sensor.

2. The image forming device of claim 1 , further comprising: at least one processor to detect a synchronization signal based on the received first light and the received second light, and to control light emitting timing of the first light source and the second light source based on the detected synchronization signal.

3. The image forming device of claim 1 , further comprising: at least one processor to: detect a synchronization signal based on the received first light and the received second light; calculate an offset value between the first light source and the second light source based on the detected synchronization signal; and output a printing image signal by compensating for the offset value.

4. The image forming device of claim 1 , further comprising: at least one processor to control the first light source and the second light source to alternately emit the first light and the second light.

5. The image forming device of claim 4, wherein the at least one processor does not to output a printer image signal while the first light and the second light are alternately emitted.

6. The image forming device of claim 1 , wherein the lens focuses the first light and the second light on the single synchronization detecting sensor.

7. The image forming device of claim 1 , wherein the lens focuses the first light and the second light on one point.

8. The image forming device of claim 1 , wherein a center between the first light source and the second light source, a center of the single synchronization detecting sensor, and a center of the lens are located on a same plane.

9. The image forming device of claim 1 , wherein a center of the single synchronization detecting sensor is located between two lines extended from the first light source and the second light source toward a direction perpendicular to the first straight line.

10. The image forming device of claim 9, wherein the lens is located across one straight line extended from a center between the first light source and the second light source to a direction perpendicular to the first straight line, and the two straight lines.

11 . The image form ing device of claim 10, wherein a first lens thickness of the lens overlapping with the one straight line is thicker than a second lens thickness and a third lens thickness of the lens respectively overlapping with the two straight lines.

12 The image forming device of claim 1 , further comprising: polygonal rotating mirror to deflect the first light and the second light respectively emitted from the first light source and the second light source; and at least one processor to control the first light source and the second light source to alternately emit the first light and the second light according to a rotation cycle of the polygonal rotating mirror.

13. The image forming device of claim 1 , further comprising: a third light source and a fourth light source, arranged on a second straight line, to respectively emit a third light and a fourth light toward a direction perpendicular to the second straight line; another synchronization detecting sensor to receive the third light and the fourth light; and another lens to change light paths of the third light and the fourth light to cause the third light and the fourth light to reach the other synchronization detecting sensor, wherein a center between the first light source and the second light source, a center of the single synchronization detecting sensor, and a center of the lens are located on a same plane, and wherein a center between the third light source and the fourth light source, a center of the other synchronization detecting sensor, and a center of the other lens are located on the same plane.

14. A method comprising: alternately emitting first light and second light from a first light source and a second light source arranged on a first straight line, the first light and the second light being emitted toward a direction perpendicular to the first straight line; receiving the first light and the second light; detecting a first synchronization signal and a second synchronization signal based on the received first light and the received second light; and controlling emission of the first light and the second light based on the detected first synchronization signal and the detected second synchronization signal.

15. A non-transitory computer-readable storage medium storing instructions executable by a processor to execute operations comprising: alternately emitting first light and second light from a first light source and a second light source arranged on a first straight line, the first light and the second light being emitted toward a direction perpendicular to the first straight line; receiving the first light and the second light; instructions to detect a first synchronization signal and a second synchronization signal based on the received first light and the received second light; and controlling emission of the first light and the second light based on the detected first synchronization signal and the detected second synchronization signal.