Abstract:
An optical scanning apparatus having at least one f-θ lens positioned on a rotary device. A collimated light beam is refracted to produce a linear scan by the rotation of the f-θ lens by the rotary device. By not using a rotary polygonal mirror, the optical scanning apparatus has the advantages of better tolerance, less optical parts, easy assembly, low production cost and compact structure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an optical scanning apparatus. In particular, the invention relates to an optical scanning apparatus, which utilizes a rotary polygonal f-θ lens for deflecting a light beam upon, for example, a scanned object or recording media. 
     2. Description of the Related Art 
     FIG. 1 is a drawing for illustrating an optical scanning system of the related art. As shown in FIG. 1, the optical scanning system generally consists of: a semiconductor light source  1 , a collimator lens  2 , a cylindrical lens  3 , a rotary polygonal mirror  4  and an f-θ lens (or toroidal lens)  5 . The semiconductor light source  1  emits a light beam, and the light beam is transformed into a collimated light beam by the collimator lens  2 . Next, the cylindrical lens  3  adjusts the shape and the focus position of the collimated light beam, and then the light beam impinges upon the rotary polygonal mirror  4 . Next, the rotary polygonal mirror  4  with a constant angular velocity deflects the light beam upon the f-θ lens  5 , and then the f-θ lens  5  focuses the light beam onto a mirror  6  to form a linear scan. Finally, the mirror  6  reflects the scanning light beam onto the object  7  at linear constant speed. The aspheric surface of an f-θ lens can be designed by referring to U.S. Pat. No. 4,930,850 or U.S. Pat. No. 4,934,772 . . . etc. 
     In the related art, a rotary polygonal mirror reflects the incoming light beam to generate a scanning light beam, that is to say, a swimming light source. Although the polygonal mirror rotates at a constant angular velocity, the light beam reflected from it impinges on the scanned object at a varied speed. Therefore, the f-θ lens alters the light beam reflected from the rotary polygonal mirror to impinge on the scanned object at a constant speed. 
     However, if a semiconductor light source is misalignment and emits a light beam with an angle error φ, there will introduce an angle error to 2φ after the light beam is incident on a rotary polygonal mirror. Moreover, if a rotary polygonal mirror tilts an angle error φ′, it will also introduce an angle error to 2φ′ after the light beam is reflected. Therefore, the rotary polygonal mirror of the related art has the property of increasing angle error, and further decreases the machining accuracy. Furthermore, the scanning light beam, which is reflected by the rotary polygonal mirror, causes a shift amount. Moreover, the defect of the rotary polygonal mirror causes increases the manufacturing time because aligning of the rotary polygonal mirror and f-θ lens takes longer. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide an optical scanning apparatus, which comprises a semiconductor light source, a collimator lens, a cylindrical lens, and a rotary f-θ lens. The rotary f-θ lens alters the propagating direction of the light beam to scan linearly at a constant speed. 
     A feature of the invention is the inclusion of an f-θ lens rotating at a constant angular velocity. The rotary f-θ lens refracts the light beam to form a linear scan. Therefore, it doesn&#39;t increase the angle error. 
     By not using a rotary polygonal mirror in the optical scanning apparatus, the number of optical components is reduced. Thereby, the present invention achieves the advantages of easy assembly, low production cost, and compact structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the drawings, in which: 
     FIG. 1 is a drawing for illustrating an optical scanning system of the related art; 
     FIGS. 2A to  2 C are perspective top views illustrating the operation of the first embodiment of the invention; 
     FIG. 3 is a perspective side view of an optical scanning apparatus of the second embodiment of the invention; 
     FIGS. 4A to  4 C are perspective top views illustrating the operation of the second embodiment of the invention; 
     FIGS. 5A to  5 C schematically show geometric diagrams of the polygonal f-θ lenses of the invention; 
     FIGS. 6A and 6B respectively show the structures of the optical path of the light source; and 
     FIGS. 7A and 7B respectively show the applications of an optical scanning apparatus of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     First Embodiment 
     Referring to FIGS. 2A to  2 C, the optical scanning apparatus of the present invention comprises an f-θ lens  50 , a rotating device  20  and a light source  10  emitting a collimated light beam producing a linear scan at a constant speed. The light source  10  can be a semiconductor laser, a light-emitting diode, or any of other light sources. The collimated light beam is emitted from a laser  11 , and then a collimator lens  12  and a cylindrical lens  13  adjust the spot size and shape of the light to propagate toward a predetermined direction. The f-θ lens  50  is made of glass or plastic material, and the material can be molded into a predetermined shape. The f-θ lens  50  is integrated with a rotating device  20 , and, therefore, the rotating device  20  can drive the f-θ lens  50  to rotate at a constant angular speed φ. For keeping the rotation balance during high speed, user can position appropriate weight on the opposite side of the f-θ lens  50 . 
     As shown in FIG. 2A, the collimated light beam is incident on a position A of the f-θ lens  50  rotating at a constant angular speed φ. The f-θ lens  50  refracts the light beam to impinge on a position A′ of a scanned object  100 . Next, as the f-θ lens  50  proceeds to rotate to the position shown in FIG. 2B, the collimated light beam is incident on a position B of the f-θ lens  50 . The f-θ lens  50  refracts the light beam to impinge on a position B′ of a scanned object  100 . Next, as the f-θ lens  50  proceeds to rotate to the position shown in FIG. 2C, the collimated light beam is incident on a position C of the f-θ lens  50 . The f-θ lens  50  refracts the light beam to impinge on a position C′ of the scanned object  100 . 
     Furthermore, the rotating device  20  can drive the f-θ lens  50  to rotate in sequence, the light beam based on the sequencing of A′ to B′ to C′ results in linear scan at a constant speed. In another way, the rotating device  20  also can reverse the rotation of the f-θ lens  50 . The optical scanning apparatus bases on the sequencing of C′ to B′ to A′ to produce a linear scan at a constant speed. Therefore, the optical scanning apparatus produces a linear scan with a period of A′ to B′ to C′ to A′ to B′ to C′ at a constant speed. 
     Second Embodiment 
     FIG. 3 is a perspective side view of an optical scanning apparatus of the second embodiment of the invention. An optical scanning apparatus of the second embodiment comprises a polygonal f-θ lens  60 , a rotating device  20  and a light source  10  emitting a collimated light beam producing a linear scan at a constant speed. The light source  10  can be a semiconductor laser, a light-emitting diode, or any of other light sources. The collimated light beam is emitted from a laser  11 , and then a collimator lens  12  and a cylindrical lens  13  adjust the spot size and shape of the light beam to propagate toward a predetermined direction. The polygonal f-θ lens  60  comprises a plurality of f-θ lenses forming the shape of a polygon. The plurality of f-θ lenses can be disposed in a discrete manner or combined with each to form a single lens. Each f-θ lens is made of glass or plastic material, and the material can be molded into a predetermined shape. The polygonal f-θ lens  60  is integrated with a rotating device  20 , and, therefore, the rotating device  20  can drive the polygonal f-θ lens  50  to rotate at a constant angular speed φ. 
     As shown in FIG. 4A, the collimated light beam is incident on a position A of a first surface  61  of the polygonal f-θ lens  60  rotating at a constant angular speed φ. The f-θ lens  61  refracts the light beam to impinge on a position A′ of a scanned object  100 . Next, as the polygonal f-θ lens  60  proceeds to rotate to the position shown in FIG. 4B, the collimated light beam is incident on a position B of the first surface  61  of the polygonal f-θ lens  60 . The f-θ lens  61  refracts the light beam to impinge on a position B′ of a scanned object  100 . Next, as the polygonal f-θ lens  60  proceeds to rotate to the position shown in FIG. 4C, the collimated light beam is incident on a position B of the polygonal f-θ lens  60 . The f-θ lens  61  refracts the light beam to impinge on a position C′ of the scanned object  100 . 
     Furthermore, the rotating device  20  can drive the polygonal f-θ lens  60  to rotate continuously. The light generated by the sequence A′ to B′ to C′ results in linear scan at a constant speed. Therefore, if the collimated light beam is perpendicular to the middle of the linear scan, a polygonal f-θ lens with symmetric shape can be utilized. 
     As shown in FIG. 5A to  5 C, the f-θ lenses can be combined into a single lens or can be disposed discretely. In either case, the lenses take the shape of a polygon, wherein each f-θ lens consists of one lens or a lens set, such as a doublet lens. 
     Moreover, as shown in FIG. 6A and 6B, the light source  10  emitting collimated light beam can be located outside of the polygonal f-θ lens  60 . The collimated light beam can be guided to impinge on the polygonal f-θ lens  60  by a mirror M or a set of mirrors  30 , wherein the polygonal f-θ lens  60  refracts the collimated light beam to produce a linear scan at a constant speed. 
     FIG. 7A shows an optical printer applying an optical scanning apparatus of the invention. The optical scanning apparatus  200  produces a linear scan on a recording medium  300 , such as a photosensitive film or a photoconductor, such that the image is directly recorded onto a recording medium  300 . FIG. 7B shows a display applying an optical scanning apparatus of the invention. A driving display  500  is connected to a light source  210  that emits a collimated light beam of predetermined colour to a polygonal f-θ lens  200 . Next, rotating the polygonal f-θ lens  200  refracts the collimated light beam to produce a linear scan when the linear scan is reflected onto a screen SC by a mirror M. Moreover, rotating the mirror M forms a two-dimensional image due to the temporary retention of light stimuli by the human eye during vision. 
     In the invention, all the embodiments use at least one rotary f-θ lens, wherein the rotary f-θ lens refracts the incoming collimated light beam to form a linear scan. Applying the refraction theory, if the light source has an angle error, the linear scan of the embodiments won&#39;t increase the angle error. Further, the invention prevents small angle error from increasing. Moreover, the invention eliminates the use of the rotary polygonal mirror, thereby allowing for a more compact optical scanning apparatus and lower production cost. 
     While the preferred embodiment of the present invention has been described, it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims.