Abstract:
An apparatus to detect a laser beam at a predetermined location within a light scanning unit of an image forming apparatus in order to synchronize a start position at which an electrostatic latent image is formed on a surface of a photosensitive body is disclosed. The apparatus includes laser beam detection optics, which may be formed of either a single unit lens or a cluster of one or more lenses that are placed in close proximity of each other. The laser beam detection optics receives the laser beam directed in the direction of the photosensitive body at a predetermined location relative to the start position on the photosensitive body, redirects the received laser beam towards a sensor, and focuses the laser beam on the sensing area of the sensor. The close proximity of, or the fact that the laser beam detection optics, minimizes the possibility of misalignment during the assembly that may result in the improper focusing of the laser beam on the sensor sensing area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 2002-79034, filed Dec. 12, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a light scanning apparatus for use in an image forming apparatus such as a printer, a facsimile machine, a copier, etc., and more particularly, to an apparatus to detect a laser beam, and to produce a laser beam detect signal that may be used to synchronize scanning operation of the image forming apparatus, which is capable of minimizing the dimension of the components and reducing performance degradation caused by the assembly deviations introduced in the fabricating and assembling processes, thereby enhancing the printing quality. 
     2. Description of the Related Art 
     Generally, a light scanning apparatus of an image forming apparatus such as a printer, a facsimile machine or a copier uses a light source that generates a beam of light, such as a laser beam, in order to form an electrostatic latent image on a photosensitive body, such as a photosensitive drum or a photosensitive belt. 
     The light scanning apparatus forms the electrostatic latent image on the photosensitive body by converting the laser beam from the light source, such as a semiconductor laser, into a parallel ray of light of a predetermined size through a collimator lens, leading the laser beam to a light deflector that rotates at a high speed, deflecting the direction of the laser beam at the light deflector and emitting the laser beam along a scanning line on the photosensitive body through a scanning lens such as an f-θ (f-theta) lens. 
     In order to precisely locate the starting location where the electrostatic latent image is to be first formed on the photosensitive body, i.e., the starting location of the laser beam scanning line, an apparatus to detect the laser beam at a certain predetermined location relative to the intended starting point of the scanning line is employed. The apparatus to detect the laser beam, generates a beam detect signal, which is used by the image forming apparatus to synchronize the timing of the laser beam firing, or the like, so that the scanning is started at the intended starting point. 
     FIG. 1 schematically shows a conventional light scanning apparatus  10  to form an electrostatic latent image on a photosensitive body. 
     Referring to FIG. 1, the light scanning apparatus  10  includes a semiconductor laser  1  emitting a laser beam  14 , a collimator lens  2  arranged in correspondence with the semiconductor laser  1  to form the laser beam  14  into a parallel ray of light, a slit  3  through which the laser beam  14  which has passed through the collimator lens  2  is converted into a predetermined form, a cylindrical lens  4  through which the laser beam which has passed through the slit  3  is transformed into a linear light, and a light deflector  5  to deflect the laser beam  14 . The light deflector  5  includes a rotary polygon mirror  5   a  supported on a spindle motor (not shown) to be rotatably driven at a given speed. 
     The light scanning apparatus  10  also includes an f-θ lens  6  that compensates for the error included in the laser beam  14  deflected from the rotary polygon mirror  5   a , thereby emitting the laser beam  14  to a photosensitive drum  20 . The beam detect signal generating part  30  generates a signal used by the image forming apparatus to correctly synchronize the formation location of the electrostatic latent image along a laser beam scanning line  20   a , shown across the photosensitive drum  20 . 
     The beam detect signal generating part  30  includes a reflective mirror  8  secured on a spring  7  on a portion of the optical path of the laser beam  14  that would not interfere with the scanning of the laser beam  14  along the length of the laser beam scanning line  20   a . The reflective mirror  8  deflects the laser beam  14  in the direction of a laser beam detecting lens  9 . The laser beam detecting lens  9  has an incident face and an emissive face which are spherical, cylindrical or plane surfaces to converge the laser beam  14  from the reflective mirror  8  onto a laser beam detecting sensor  11 . The laser beam detecting sensor  11  may be a photo diode sensor, and upon detection of the laser beam  14 , generates a beam detect signal. The laser beam detecting sensor  11  may be assembled either in a printed circuit board  12  (PCB), which also supports the semiconductor laser  1 , or in a separate printed circuit board (not shown). 
     The operation of the conventional light scanning apparatus  10  will now be described. 
     In accordance with the input image signals, the laser beam  14  is emitted from the semiconductor laser  1 , and converted into a parallel ray of light by the collimator lens  2 . Then, after passing through the slit  3  that shapes the laser beam  14  in a predetermined form, the laser beam  14  is passed through the cylindrical lens  4 , and then deflected by the deflecting faces of the polygon mirror  5   a  that is rotated at relatively high speed by the spindle motor. 
     Next, the laser beam  14  is made to selectively pass through the f-θ lens  6  to be converged on the photosensitive drum  20  in the form of a light spot, thereby scanning the scanning line  20   a  of a predetermined, effective scanning width along a main scanning direction as shown in FIG.  1 . At this time, the photosensitive drum  20  is driven to rotate in a sub-scanning direction by a driving motor (not shown). Accordingly, as a result of the scanning movements of the light spots in the main scanning direction and the rotation of the photosensitive drum  20  in the sub-scanning direction, a predetermined electrostatic latent image is formed on the photosensitive drum  20 . 
     In order to start each of the scanning lines  20   a  at the correct starting point, the laser beam  14  deflected from the rotary polygon mirror  5   a  is detected at a predetermined location either prior to the start of or past the end of the effective scanning width of the laser beam scanning line  20   a . In the embodiment shown in FIG. 1, the beam detection is shown to be made at a location prior to the start of the scanning line  20   a . The laser beam  14 , which have passed through the f-θ lens  6 , is deflected by the reflective mirror  8  placed at the predetermined location in the main scanning direction towards the laser beam detecting lens  9 . When the laser beam  14  deflected by the reflective mirror  14  is received by the laser beam detecting sensor  11 , the laser beam sensor  11  in response thereto produces a beam sensed signal. The beam sensed signal itself may be taken as the beam detect signal, or, in the alternative, is converted into suitable voltage and/or current, by a beam detect signal generation circuit (not shown), which may be disposed on the same PCB  12 , to generate the beam detect signal . 
     The beam detect signal so generated is input to a controller unit (not shown), which controls the timings of both the scanning start and image formation of the light spots on the photosensitive drum  20 . The controller uses the beam detect signal in order to determine the proper location for the scanning start. 
     However, the conventional light scanning apparatus  10  operated as above has a rather complex structure in which the reflective mirror  8  and the laser beam detecting lens  9  are separated by a relatively large distance in a narrow space in the light scanning apparatus  10 . In addition, dimension and assembly deviations or errors are frequently generated during the process of fabricating and assembling the parts such as the reflective mirror  8 , the laser beam detecting lens  9 , and the laser beam detecting sensor  11 . 
     When the errors occur during the fabrication and assembly, the center of the optical axis of the laser beam detecting lens  9  may not properly align with the reflective mirror  8 , resulting in the laser beam  14  being irregularly incident on the laser beam detecting sensor  11 . Accordingly, the detection location of the laser beam varies, and as a result, a constant printing quality is not guaranteed. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an aspect of the present invention to provide an apparatus to detect a laser beam detect signal in which without using a separate reflective mirror, a laser beam detecting lens such as a focusing lens has a function of a reflective mirror to minimize the dimension of the components and to reduce performance degradation caused by the assembly deviations introduced in the fabricating and assembly processes, thus enhancing the printing quality. 
     It is another aspect of the present invention to provide an apparatus to detect a laser beam detect signal that can reduce the number of parts to allow the fabrication process to become simpler, thereby decreasing the fabrication costs. 
     Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     The foregoing and/or other aspects are achieved by providing an apparatus for generating a laser beam detection signal in a light scanning unit that causes a laser beam to be scanned across a surface of a photosensitive body of an image forming device to form an electrostatic latent image on the photosensitive body, the laser beam being scanned across the surface of the photosensitive body in at least one scanning line that has a beginning point and an end point, the laser beam detection signal being used by the image forming apparatus to control the light scanning unit so that the beginning point occurs at a desired location, the laser scanning unit including at least a laser source and means for directing the laser beam emanating from the laser source towards a range of locations, the apparatus comprising: a laser beam detecting sensor disposed at a sensor location that falls outside the range of locations; and a single integrated optical element disposed at a predetermined location that falls within the range of locations, the single integrated optical element being arranged to receive the laser beam from the directing means, to deflect the received laser beam towards the laser beam detecting sensor, and to focus the deflected laser beam on the laser beam detecting sensor, the laser beam detecting sensor in response to the laser beam being focused thereon producing a signal indicative of the laser beam being detected at the predetermined location. 
     The single integrated optical component may comprise a first face having a reflective surface formed thereon; and a second face having an incident surface and an emissive surface formed thereon, the incident surface having a first shape to direct laser beam received from the directing means to the reflective surface at an incident angle, and the emissive surface having a second shape to focus the laser beam reflected from the reflective surface on a sensing area of the laser beam detecting sensor. 
     The reflective surface may have at least one of a planar shape and a cylindrical shape, and the first shape and the second shape may be at least one of a spherical shape and a cylindrical shape. 
     The predetermined location may be located at an upstream of the beginning point of the at least one scanning line along the range of locations such that the laser beam received from the directing means is received by the single integrated optical element prior to the laser beam being incident on the beginning point of the at least one scanning line. 
     The sensor location may be located at an opposite side of the at least one scanning line from the predetermined location. 
     The foregoing and/or other aspects may also be achieved by providing an apparatus for generating a laser beam detection signal in a light scanning unit that causes a laser beam to be scanned across a surface of a photosensitive body of an image forming device to form an electrostatic latent image on said photosensitive body, the laser beam being scanned across the surface of the photosensitive body in at least one scanning line that has a beginning point and an end point, the laser beam detection signal being used by the image forming apparatus to control the light scanning unit so that the beginning point occurs at a desired location, the laser scanning unit including at least a laser source and means for directing the laser beam emanating from the laser source towards the photosensitive body, the apparatus comprising: a laser beam detecting sensor; and one or more closely arranged optical element clustered together at a predetermined location that is at least one of a first predetermined location and a second predetermined location, the first predetermined location being upstream of the beginning point of the at least one scanning line such that the laser beam received from the directing means is received by at least one member of the one or more closely arranged optical element prior to the laser beam being incident on the beginning point of the at least one scanning line, the second predetermined location being downstream of the end point of said at least one scanning line such that the laser beam received from the directing means is received by at least one member of the one or more closely arranged optical element after to the laser beam being incident on the end point of said at least one scanning line, the one or more closely arranged optical element being configured to receive the laser beam from the directing means, to deflect the received laser beam towards the laser beam detecting sensor, and to focus the deflected laser beam on the laser beam detecting sensor, the laser beam detecting sensor in response to the laser beam being focused thereon producing a signal indicative of the laser beam being detected at the predetermined location. 
     The one or more closely arranged optical element may comprise a single integrated optical element having a first face having a reflective surface formed thereon and a second face having an incident surface and an emissive surface formed thereon, the incident surface having a first shape to direct laser beam received from the directing means to the reflective surface at an incident angle, and the emissive surface having a second shape to focus the laser beam reflected from the reflective surface on a sensing area of the laser beam detecting sensor. 
     The reflective surface may have at least one of a planar shape and a cylindrical shape, and the incident surface and the emissive surface may have at least one of a spherical shape and a cylindrical shape. 
     The foregoing and/or other aspects may also be achieved by providing a light scanning unit for scanning a laser beam across a surface of a photosensitive body of an image forming device to form an electrostatic latent image on the photosensitive body, comprising: a laser source for generating the laser beam; means for directing the laser beam emanating from the laser source towards a range of locations, at least a portion of the range of locations being at least one scanning line across the surface of the photosensitive body, the at least one scanning line having a beginning point and an end point; a laser beam detecting sensor mounted in the light scanning unit at a sensor location that falls outside the range of locations; and one or more closely arranged optical element clustered together at a predetermined location that falls within the range locations, the predetermined location being at least one of a first predetermined location and a second predetermined location, the first predetermined location being upstream of the beginning point of the at least one scanning line such that the laser beam received from the directing means is received by at least one member of the one or more closely arranged optical element prior to the laser beam being incident on the beginning point of the at least one scanning line, the second predetermined location being downstream of the end point of the at least one scanning line such that the laser beam received from the directing means is received by at least one member of the one or more closely arranged optical element after to the laser beam being incident on the end point of the at least one scanning line, the one or more closely arranged optical element being configured to receive the laser beam from the directing means, to deflect the received laser beam towards the laser beam detecting sensor, and to focus the deflected laser beam on the laser beam detecting sensor, the laser beam detecting sensor in response to the laser beam being focused thereon producing a signal indicative of the laser beam being detected at the predetermined location. 
     The one or more closely arranged optical element may comprise a single integrated optical element having a first face having a reflective surface formed thereon and a second face having an incident surface and an emissive surface formed thereon, the incident surface having a first shape to direct laser beam received from the directing means to the reflective surface at an incident angle, and the emissive surface having a second shape to focus the laser beam reflected from the reflective surface on a sensing area of the laser beam detecting sensor. 
     The sensor location may be near the first predetermined location if said one ore more closely arranged optical element is positioned at the second predetermined location, and be near the second predetermined location if the one or more closely arranged optical component is positioned at the first predetermined location. 
     The reflective surface may have at least one of a planar and a cylindrical shape, and the incident surface and the emissive surface may have at least one of a spherical and a cylindrical shape. The reflective surface may be formed of a reflective film formed on the first face, or a mirror member attached to the first face. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which: 
     FIG. 1 is a schematic top plan view of a conventional light scanning apparatus; 
     FIG. 2 is a schematic top plan view of an illustrative exemplary embodiment of a light scanning apparatus having an apparatus to generate a beam detect signal according to the principles of the present invention; 
     FIG. 3 is a top plan view of an illustrative exemplary embodiment of a focusing lens that may be employed in an apparatus to generate a beam detect signal according to the principles of the present invention; and 
     FIG. 4 is a schematic top plan view of another illustrative exemplary embodiment of a light scanning apparatus according to the principles of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
     FIG. 2 shows a light scanning apparatus  100  having an apparatus  130  for generating a beam detect signal according to an embodiment of the present invention. 
     The light scanning apparatus  100  includes a semiconductor laser  101  emitting a light beam, such as a laser beam  114 , a collimator lens  102  forming a parallel ray of light, a slit  103  converting the laser beam  114  into a predetermined form, a cylindrical lens  104  transforming the laser beam  114  into a linear light, a light deflector  105  deflecting the direction of the laser beam  114 , and a scanning lens  106  such as an f-θ lens compensating for errors included in the laser beam  114  and to emit the laser beam to the photosensitive drum  120 . 
     A description of the construction of the above elements will be omitted here, since these elements are similar to those of the conventional apparatus previously described above. 
     An apparatus  130  to generate a beam detect signal according to an embodiment of the present invention includes a focusing lens  108  disposed along a path of the laser beam  114  at a predetermined location relative to the photosensitive body  120 . The focusing lens  108  forms a laser beam detecting path, deflects the laser beam  114  received from the light deflector  105  towards, and focuses the same on, a laser beam detecting sensor  111 . The laser beam detecting sensor  111  upon detecting the laser beam  114  reflected from the focusing lens  108  causes a beam detect signal to be generated. A controller (not shown) uses the beam detect signal to synchronize the start position of the laser beam scanning line  120   a . The laser beam detecting sensor  111  may be supported on a PCB  112 . 
     In the embodiment shown in FIG. 2, the focusing lens  108  is arranged between the scanning lens  106  and the photosensitive drum  120 . Accordingly, the semiconductor laser  101 , the collimator lens  102 , the slit  103 , the cylindrical lens  104 , the light deflector  105 , the scanning lens  106 , and the laser beam detecting sensor  111  form the laser beam detecting path together with the focusing lens  108 . 
     As shown in FIG. 3, the focusing lens  108  has a first face  109  having a reflective surface  109   a  formed thereon to reflect the laser beam  114 , and a second face  110  having an incident surface  110   a  and an emissive surface  110   b  formed thereon. The incident surface  110   a  leads a portion of the laser beam  114 , to the reflective surface  109   a , whereas the emissive surface  110   b  emits the laser beam  114  reflected from the reflective surface  109   a  toward a sensing area of the laser beam detecting sensor  111 . 
     The incident surface  110   a  and the emissive surface  110   b  may be formed of a spherical shape or a cylindrical shape, and the reflective surface  109   a  may be formed of a plane shape or a cylindrical shape. 
     Accordingly, the shape of the incident surface  110   a /reflective surface  109   a /emissive surface  110   b  of the focusing lens  108  is formed of a combination of spherical shape/cylindrical shape/spherical shape, spherical shape/plane shape/spherical shape, cylindrical shape/cylindrical shape/cylindrical shape, or cylindrical shape/plane shape/cylindrical shape. 
     The reflective surface  109   a  can be formed on the first face  109  of the focusing lens  108  by depositing or attaching a reflective film in the form of a membrane, or attaching a separate mirror member, after machining the first face  109  of the focusing lens  108  into an appropriate shape. 
     According to a preferred embodiment, in the focusing lens  108  of the apparatus  130 , the first face  109  and the second face  110  of the focusing lens  108  are shown as an integrally formed single unit. However, in an alternative embodiment, the focusing lens  108  may comprise two or more optical elements placed in close proximity to one another such that the distances between the two respective adjacent elements is not susceptible to the level of alignment deviation that were possible in the conventional light scanning apparatus earlier discussed. 
     For example, according to an alternative embodiment of the present invention, the focusing lens  108  may comprise two optical components, first one of which including the first face  109 , and the other including the second face  110 . The two optical components may be arranged to abut each other. In other words, in this embodiment, the focusing lens  108  shown in FIG. 3, may be divided or split into two components along a line perpendicular to the optical axis of the focusing lens  108 , and is the optical components can be arranged to abut each other while their optical axis is aligned. 
     In another alternative embodiment, the focusing lens  108  shown in FIG. 3, may be divided or split into two or more components, and all of the optical elements are arranged in close proximity of one another so that the group of optical elements that together make up the focusing lens  108  are disposed on the same side of the laser beam scanning line  120   a , i.e., all of the optical elements in the group are placed either prior to the start of the laser beam scanning line  120   a  or after the end of the laser beam scanning line  120   a  in close proximity to one another. Due to the closeness of the reflective surface  109   a  to the second face  110 , deviations in the assembling process can be minimized, thereby preventing degraded printing quality. 
     Moreover, while the preferred embodiment shown in FIG. 3 illustrates three surfaces, namely, the reflective surface  109   a , incident surface  110   a , and the emissive surface  110   b , to perform the functions of receiving, reflectively deflecting towards the laser beam detecting sensor  111 , and focusing the laser beam  114  onto the sensing area of the laser beam detecting sensor  111 , respectively, the three functions may be accomplished by a single concave surface having an appropriate reflective quality and curvature of radius R, which allows the laser beam  114  to be incident on the concave surface, and be deflected towards, and focused onto, the sensing area of the laser beam detecting sensor  111 . 
     In addition, the preferred embodiment of FIG. 2 shows the focusing lens  108  being located before the starting point of the laser beam scanning line  120   a , however, the focusing lens may placed anywhere along the scanning path of the laser beam  114  so long as such placement does not interfere with the laser beam  114  being scanned across the laser beam scanning line  120   a.    
     The laser beam detecting sensor  111 , which may be a photo diode sensor, is fixed on the PCB  112  on which the semiconductor laser  101  generating the laser beam  114  may be disposed as the light source. 
     Alternatively, the laser beam detecting sensor  111  can be supported on a separate holder (not shown) or a separate PCB (not shown), instead of the PCB  112 . 
     The operation of the apparatus  130  according to the preferred embodiment will now be explained below with reference to FIGS. 2 and 3. 
     First, when the laser beam  114  is emitted from the semiconductor laser  101  and then deflected by the deflecting faces of a polygon mirror  105   a  via the collimator lens  102 , the slit  103 , and the cylindrical lens  104 , the laser beam  114  from the polygon mirror  105   a  becomes incident with a predetermined incident angle on the incident surface  110   a  of the focusing lens  108  via the scanning lens  106 . 
     Next, the laser beam  114  incident on the incident surface  110   a  is refracted in a predetermined refraction index according to the shape of the incident surface  110   a , and guided to the reflective surface  109   a.    
     At the reflective surface  109   a , the laser beam  114  is reflected at an angle symmetrical to the incident angle of the laser beam  114  to the reflective surface  109   a , and is refracted by a predetermined refraction index corresponding to the shape of the emissive surface  110   b  through the emissive surface  110   b  to be converged in the direction of the laser beam detecting sensor  111 . It should be apparent to, and readily understood by, one skilled in the art that the respective curvatures of the incident surface  110   a  and the emissive surface  110   b  may be identical, or may vary significantly from one to the other depending on the relative location of the focusing lens  108  with respect to the polygon mirror  105  and to the laser beam detecting sensor  111 . 
     Thereafter, the laser beam  114  is focused onto the sensing area of the laser beam detecting sensor  111  supported on the PCB  112 . 
     The laser beam detecting sensor  111 , upon receiving the laser beam  114 , either by itself or in conjunction with additional circuitry, sends a beam detect signal, which is sent to a controller (not shown) that controls the timing of both the scanning start and image formation of the light spots on the photosensitive drum  120 . 
     FIG. 4 shows yet another embodiment of the light scanning apparatus  100 ′ having the apparatus  130  to generate the beam detect signal. 
     The light scanning apparatus  100 ′ is identical to that of the light scanning apparatus  100  shown in FIG. 2 except that the focusing lens  108  has a modified scanning lens  106 ′ to directly reflect the laser beam  114  from the light deflector  105  to the focusing lens  108 , rather than through the scanning lens  106  as shown in FIG.  2 . 
     In the light scanning apparatus  100 ′, the semiconductor laser  101 , the collimator lens  102 , the slit  103 , the cylindrical lens  104 , the light deflector  105 , and the laser beam detecting sensor  111  form a laser beam detecting path together with the focusing lens  108 . 
     As is apparent from the forgoing description, according to the embodiments of the present invention, the focusing lens according to the principles of the present invention does not require the reflective optical component to be at a great distance from another optical element in order to focus the laser beam onto the sensing area of the laser beam detect sensor, thus minimizing the possible assembly deviations in the assembling process, and thereby guaranteeing printing quality. In the preferred embodiment, in which a single unit optical element is used as the focusing lens, since the number of parts is reduced, the fabrication process becomes simpler and the fabrication costs may decrease. 
     Although an embodiment of the present invention has been shown and described, it will be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.