Scanning optical system

Abstract: A synthetic resin lens (17) for an optical system of a scanning optical system comprises a guide hole (1 ) for an adhesive curing promoting light formed at a mount area thereof.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a scanning optical system comprising the features of the pre-characterizing clause of claim 1. A scanning optical system of this kind is used in an information recording apparats such as a laser beam printer. Related Background Art Fig. 10 shows a plan view of a prior art scanning optical system of an information recording apparatus and Fig. 11 shows a sectional view thereof. A laser oscillator 2, a collimator lens 3 and a cylindrical lens 4 are secured to a side wall of an optical box 1 and a deflector formed by a polygon mirror 5 is mounted therein. A spherical lens 6, a toric lens 7 and a reflection mirror 8 are sequentially arranged in a direction of an outgoing light beam. The laser beam emitted by the laser oscillator 2 passes through the collimator lens 3 and the cylindrical lens 4, is deflected by the polygon mirror 5, and it is f-corrected by the spherical lens 6 and the toric lens 7, and a resulting scanning light beam is reflected by the reflection mirror 8 and directed to a photoconductor drum which is an information recording medium. In the prior art scanning optical system, the spherical lens 6 and the toric lens 7 are made of glass and the glass lenses are secured to a base formed by the optical box 1 by an ultraviolet light ray cured adhesive so that the curing of the adhesive is promoted by irradiating an ultraviolet ray through the lens. Recently, lenses made of synthetic resin are frequently used in order to improve the productivity of the lenses, reduce the weight, reduce the cost and improve the performance by non-spherical planes. A preferable material of the synthetic resin is polycarbonate resin in view of good optical characteristic, small change of dimension by humidity and physical strength. However, polycarbonate resin has a lower ultraviolet ray transmission than that of glass and it has only one fourth or fifth of the glass transmission. When it is to be secured by the ultraviolet ray cured adhesive as it is in the prior art glass lens, the following problem is encountered. The ultraviolet ray irradiation time is long and the workability is low. The adhesive is not uniformly cured due to ununiform irradiation. If the intensity of the ultraviolet ray is too high, the polycarbonate resin is deteriorated by a photo-oxidization reaction. Document JP-A-60-144710 discloses a lens formed of a synthetic resin which is mounted in a lens barrel. For mounting the lens in the barrel, the lens comprises screw threads formed in a radially outer mounting portion which is arranged beyond the effective area of the lens. Furthermore, the lens comprises a circular thin projection which serves to properly position the lens in the barrel. SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-noted disadvantage peculiar to the prior art and to improve the prior art scanning optical system such that it permits short time bonding of a synthetic resin lens. This object is achieved by the scanning optical system according to claim 1. In the scanning optical system of the present invention, the adhesive is applied to a rear surface or a front surface of the projection, and the lens is positioned on the fixed base and the curing promoting light is irradiated normally to the thin planar projection. In this manner, the lens is securely bonded to the fixed base in a short time. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a perspective view of a first embodiment of the scanning optical system of the present invention, Fig. 2 shows a perspective view of a scanning synthetic resin lens of Fig. 1, Fig. 3 shows a sectional view of the scanning synthetic resin lens of Fig. 1, Figs. 4, 5 and 7 illustrate a method for securely bonding the scanning synthetic resin lens, Figs. 6, 8 and 9 show perspective views of further embodiments of the scanning synthetic resin lens, Fig. 10 shows a plan view of a prior art scanning optical system, and Fig. 11 shows a sectional view of the prior art scanning optical system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention are now explained in detail with reference to the drawings. In a first embodiment of the scanning optical system for a laser beam printer of the present invention, as shown in Fig. 1, a light beam emitted from a laser unit 41 which comprises a laser light source and a collimator lens passes through a cylindrical lens 42, is deflected by a deflector formed by a rotary polygon mirror 43 and is focused onto a photoconductor drum 46 by a toric scanning lens 45 secured to a fixed base 44. A scanning synthetic resin lens to be explained later is used in the scanning optical system of the laser beam printer shown in Fig. 1. Fig. 8 shows a perspective view and Fig. 9 shows a sectional view of the scanning lens 45. A mounting portion of the scanning lens 45 comprises tongue shaped projections 45a∼45d which project at the opposite longitudinal ends of the thick scanning lens 45 below an effective area of the scanning lens 45. To securely bond the scanning lens 45 to the fixed base 44, adhesive is applied to adhesive application areas 45a' ∼ 45d' on the rear sides of the projections 45a ∼ 45d as shown in Fig. 4, the lens is positioned to the fixed base 44 and ultraviolet light ray V is irradiated from above to the projections 45a ∼ 45d through an optical fiber F. When the ultraviolet ray cured adhesive is used, a mercury tube having a wavelength of approximately 357 nm, and a light power of approximately 200 W ∼ 1 KW is usually used as an ultraviolet light source. Thus, the transmission of the bonding material is less than 1% for the prior art scanning lens 7 having a thickness of approximately 13 mm and an irradiation time of approximately 1 ∼ 2 minutes is required. In the scanning lens 45 of the present embodiment where the length of the projections 45a ∼ 45d is L1 = 5 mm and the thickness is L2 = 2 ∼ 3 mm, the ultraviolet ray transmission is approximately 20 ∼ 30% and the curing of the adhesive is completed in several seconds. Thus, the irradiation time of the ultraviolet ray is materially shortened and the uneven irradiation of the ultraviolet ray is eliminated. The thickness L2 of the projection of the scanning lens 45 is preferably 1 ∼ 5 mm. The mounting work is facilitated if the length L1 of the projection is longer than 1 mm, and preferably 3 mm or longer in order to improve the workability in the securing operation. The scanning lens 45 may be secured by forming a hole 44a in the fixed base 44 and by applying the adhesive to adhesive application areas 45a' ∼ 45d' on the front surfaces of the projections 45a ∼ 45d to bond the lens to the fixed base 44, as shown in Fig. 11. In this case, the ultraviolet light ray V is irradiated from the rear side of the scanning lens 45 through the optical fiber F, and the same effect as that of the bonding method described above is attained. The position of the optical fiber F has a relatively large degree of freedom and the height of the scanning lens 45 may be reduced. Accordingly, this method is effective when an allowable height of the scanning lens 45 in the scanning optical system is small. Fig. 6 shows a perspective view of a scanning lens 47 according to another embodiment. A thin projection 47a which extends horizontally and then vertically is formed integrally with the scanning lens 47 at the bottom of the scanning lens 47. When the scanning lens 47 is to be securely bonded to the fixed base 44, a step 44b which conforms to the contour of the projection 47a is formed on the fixed base 44 as shown in Fig. 7 and the lens is bonded by using the area of the projection 47a facing the step 44b as an adhesive application area 47a'. The vertical positioning of the scanning lens 47 is attained without the adhesive by the formation of the projection 47a. It is effective when the allowable height of the scanning lens 47 in the optical design is small. The projection 47a may extend longitudinally of the scanning lens 47 as described above, or may partially extend longitudinally so long as a necessary area to securely bond the lens is assured. Fig. 8 shows a perspective view of a scanning lens 48 according to another embodiment. Two thin projections 48a and 48b are formed integrally with the scanning lens 48 beyond the effective area of the lens to project at the longitudinally opposite ends. A thin projection 48c is also integrally formed in a side other than a bottom of the scanning lens 48 to project in a plane normal to the projections 48a and 48b. To securely bond the scanning lens 48 to the fixed base 44, a projection 44c which abuts against the projection 48c is formed in the fixed base 44 and the rear surfaces of the projections 48a ∼ 48c are used as the adhesive application areas 48a' ∼ 48c'. The positioning precision and the reliability of the bonding are improved by forming the projection 48c on the side plane in addition to the bottom of the scanning lens 48. The laser scanning synthetic resin lens of the scanning optical system according to the present invention has the integrally molded thin projections which extend beyond the effective area of the lens. The ultraviolet ray cured adhesive is applied to the rear surface or the front surface of the projection, and the lens is positioned to the fixed base, and the ultraviolet ray is irradiated normally to the plane of the thin projection. In this manner, the bonding is completed in a short time, the number of steps is reduced and the cost is reduced. Since the mounting portion is formed by at least one projection, the adhesive is evenly cured and the bonding distortion after the curing does not affect the lens effective transmissive effective area of the lens. Thus, the deterioration of the optical characteristic is prevented. Fig. 9 shows a perspective view of a scanning lens according to a further embodiment. A bonding plane 52 of a synthetic resin lens 50 is a bottom surface of a thin projection 51 which projects at a center bottom of the synthetic resin lens 50. The synthetic resin lens 50 is positioned in the manner described in the above embodiments and the ultraviolet ray cured adhesive is applied to the bottom surface of the thin projection 51. The projection 51 for bonding is integrally molded to project longitudinally of the lens in the vicinity of the optical axis. In the present embodiment, the synthetic resin lens 50 is secured to the fixed base 44 by the narrow area bonding by the bonding area 52, and no distortion is created. A distortion of the effective lens area is suppressed by increasing the distance between the thin projection 51 and the effective lens area. Because the projection 51 is thin, the transmission of the ultraviolet ray is high and the bonding time can be shortened. In the present embodiment, the thickness of the projection 51 of the synthetic resin lens 50 is preferably 1 mm ∼ 5 mm. The length of the projection is longer than 1 mm to facilitate the mount operation, and it is preferably longer than 3 mm to improve the workability of the securing operation. Since only one thin projection is used, the compact synthetic resin lens is attained. While the toric lens has been explained in the above embodiments, the present invention is also applicable to other synthetic resin lenses.

Claims: A scanning optical system, comprising a light source (41); a deflector (43) for deflecting a light beam from said light source (41); a lens for directing the light beam deflected by said deflector (43) to a predetermined direction, and a base (44) for mounting said lens, wherein said lens comprises an effective area for transmitting said light beam and a mounting portion secured to said base (44) by means of a cured adhesive placed between the mounting portion and a portion of said base (44), characterized in that said lens for directing the deflected light beam to the predetermined direction is a synthetic resin lens (45, 47, 48, 50), and in that said mounting portion comprises a thin projection (45a to 45d, 47a, 48a, 48b, 48c, 51) projecting beyond said effective area of said synthetic resin lens (45, 47, 48, 50) and being adapted to being irradiated by an adhesive curing promoting light. A system according to claim 1, wherein a single projection (47a, 51) is formed in the resin lens (47, 50). A system according to claim 1, wherein a plurality of projections (45a to 45d, 48a, 48b, 48c) are formed in the resin lens (45, 48). A system according to one of claims 1 to 3, wherein the resin lens is a toric lens (45, 47, 48, 50). A system according to one of claims 1 to 4, wherein a thickness of said projection (45a to 45d, 47a, 48a, 48b, 48c, 51) is lmm to 5mm inclusive. A system according to one of claims 1 to 5, wherein a length of said projection (45a to 45d, 47a, 48a, 48b, 48c, 51) is no smaller than lmm. A system according to claim 3, wherein said projections (48a, 48b, 48c) are formed in a bottom and a side of the resin lens (48). A system according to claim 3, wherein said projections (45a to 45d) are provided at both sides in a longitudinal direction of the resin lens (45). A system according to claim 1, wherein said projection (47a) extends in horizontal and vertical directions. A system according to claim 1, wherein said projection (51) is provided in the vicinity of an optical axis in a longitudinal direction of the resin lens (50). A system according to one of claims 1 to 10, wherein said system is used in a laser beam printer.

Inventors: MOGI SHIN, UZUKI KAZUO, MOGI, SHIN, UZUKI, KAZUO, MOGI, SHIN, C/O CANON KABUSHIKI KAISHA, Uzuki, Kazuo, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: G02B7
IPC codes: G02B7