GB2059103A - Projecting device comprising an array of single bar lenses - Google Patents

Abstract

A projecting device is composed of an array of axial element lens systems, wherein each element lens system is composed of a single bar lens bearing a light absorbing layer 18 and having an axial length larger than the effective aperture and adapted for forming an intermediate image 20 of a pixel of the object plane and further projecting an erect image of a magnification of unity not inverted vertically nor laterally in such a manner that the light intensity on the image plane corresponding to said pixel is defined in the form of Gaussian distribution by the eclipse of the aperture, said element lens systems being arranged in a plane perpendicular to the optical axis so as to cause the light intensity distributions of said systems to mutually overlap in the peripheral areas thereof on the image plane, wherein each row of the systems in the array is preferably displaced by a half pitch with respect to the neighboring row to constitute a staggered arrangement thereby achieving a uniform exposure distribution integrated in time in the scanning direction. <IMAGE>

Description

SPECIFICATION Projecting devices BACKGROUND OF THE INVENTION Field of the invention This invention relates to a projecting device.

Description of the prior art There is already known the use of a so-called compound lens system, composed of plural optical system each capable of projecting a partial area or pixel (picture element) of the object onto a determined partial area of the image plane (such system being hereinafter referred to as element lens system) arranged in a plane perpendicular to the optical axis and along a determined direction for example along the slit employed in a copier utilizing the slit-exposure process for the purpose of reducing the conjugate distance from the object plane to the image plane and thus compactizing the entire apparatus of the copier.

Such element lens system is already disclosed for example in the U.S. Patent No. 3,592,421 as a system composed of axially arranged three lenses, or in the U.S. Patent No.3,584,952 as a system composed of axially arranged three lenses (in these systems in the central lens functioning as a field lens), or in the Japanese Patent Laid-Open Sho 53-122426 corresponding to the U.S. Patent Application Ser. No. 889,404 as a system composed of two bar lenses having axial lengths larger than the effective aperture (in which the central air layer functions as an air field lens).Although these known lenses are advantageous in effectively transmitting the light to the image plane by the function of said field lens, they are still defective in requiring delicate optical adjustment for the eventual eccentricity of two or three lenses arranged in the axial direction and in that the dust present in the vicinity of the field lens is projected on the final image plane to form a noise in the obtained image.

In the U.S. Patent No. 3,580,675 there is disclosed an element lens system composed of a single oblong lens which does not form an intermediate image in the scanning direction in a plane perpendicular to the optical axis but in the array direction orthogonal to said scanning direction, thus forming a final image erect only in one direction. The element lens system of the present invention is however different in that it forms an intermediate image both in the scanning direction and in the array direction in a plane perpendicular to the optical axis, thus forming a final image erect in both directions.

The element lens system of the present invention is also different from that obtainable from the combination of the U.S. Patents Nos. 3,580,675 and 3,592,542 in the manner explained in the following.

The element lens system disclosed in the U.S. Patent No. 3,592,542 shows, as represented in Figure 6 thereof, a substantially rectangular light intensity distribution practically without the effect of the eclipse of aperture, except for the effect of cosine 4th-power rule, because of the presence of a complete field lens.

Stated differently the obtained light intensity distribution is substantially represented by a determined bias amount overlapped with the effect of the cosine 4th-power rule etc. In case of arranging a plural number of such element lens systems in a row with a given pitch and further arranging a plural number of such rows in a staggered fashion mutually displaced by a half pitch, there will be required a very accurate pitch of arrangement, with very difficult adjustment, in order to obtain a uniform exposure integrated in time in the scanning direction.

In addition to the aforementioned transmission-type optical systems, there is also known a reflection-type element lens system composed of a single bar lens as disclosed in the Japanese Patent Laid-Open Sho 54-54057 corresponding to the U.S. Patent Application Ser. No. 949047. Such element lens system however requires a difficult optical adjustment between the bar lens and the associated mirror.

Summary of the invention The object of the present invention is to provide a projecting device which is compact in size and provides a uniform exposure distribution with a simple optical adjustment.

- One aspect of the invention therefore provides a projecting device comprising element lens system each composed of a single bar lens having an axial length larger than the effective aperture thereof and adapted for forming an intermediate inverted image in said lens and then projecting an erect image of a magnification of unity on the image plane corresponding to a pixel of the object plane with a Gaussian distribution of light intensity thereon and arranging such element lens systems in rows with a determined pitch in a plane perpendicular to the optical axis, wherein said rows are mutually displaced by a half pitch to constitute a so-called staggered arrangement.

Brief description of the drawings Figures 1 to 3 are schematic views of conventional element lens systems; Figure 4 is an optical explanatory view of the element lens system of the present invention; Figure 5 is a view showing the light intensity distribution of the element lens system of the present invention; Figure 6 is a schematic view of the projecting device composed of a staggered arrangement of the element lens systems of the present invention; Figure 7 is a schematic view showing the peripheral absorbing layer of the bar lens of the present invention; Figure 8 is a schematic view showing a process for forming a spherical surface in the bar lens of the present invention; Figures 9, IOA, lOB and 11 are views of various embodiments of supporting the plural element lens systems of the present invention in support members; and Figure 12 is a schematic view of a copier in which the projecting device of the present invention is applied.

Description of the preferred embodiments Figures 1 to 3 illustrate conventional element lens systems. In Figure 1 an object 4 is projected as an erect image 5 of a magnification of unity by means of lenses 1,2 and 3, in which the lens 2 functions as a field lens where an inverted intermediate image is formed. In the lens system shown in Figure 2, an object 8 is at first focused as an inverted intermediate image 9 and further projected as an erect image 10 of a magnification of unity by means of bar lenses 6,7 of an axial length larger than the effective aperture. A ray 12 exceeding said effective aperture is absorbed by an absorbing layer 11 extended in the axial direction and is therefore not transmitted to the image plane. The light intensity distribution on the image plane is thus defined by the eclipse of the aperture.

In the lens system shown in Figure 3, an object 14 is projected as an image 17 through bar lenses 13, a mirror 16 and a bear splitter 15. The bar lens 13 and the mirror 16 are so arranged as to constitute a system equivalent to the system of lenses 6 and 7 shown in Figure 2.

Figure 4 schematically illustrates the element lens system of the present invention, wherein the effective aperture of the bar lens 18 substantially coincides with the internal diameter of an absorbing layer 18. In the following explanation it is assumed that said effective aperture is equal to the external diameter of the lens, but a comparable performance is obtainable even if the external diameter of the lens is larger than the effective aperture as long as the two can be considered substantially identical. The bar lens 18 has an axial length of the order of the combined length of the lenses 6,7 in Figure 2 and thus larger than the effective aperture. An object 19 is at first focused as an inverted intermediate image 20 at the axial center of said bar lens 18 and finally projected on the image plane as an erect image 21 of a magnification of unity.The light beam from the object 19 is refracted by the first face of the bar lens 18 to converge on the intermediate image plane, then diverges therefrom and is again refracted by the second face of said bar lens 18 to converge on the image plane. The solid angle of the light beam converging to the image plane is largest on the optical axis, gradually decreases as the beam is diverted from the optical axis as represented by Q in Figure 5 and finally becomes equal to zero at the end of the effective view angle. In this manner the eclipse of the aperture increases with the increase of the imaging angle and reaches 100% at the boundary of the effective view field where the light beam contributing to the imaging becomes zero. Figure 5 shows the light intensity distribution on the image plane.In case the object has a uniform brightness distribution, the light intensity on the image plane assumes a Gaussian distribution because of the above-mentioned eclipse of the aperture. In Figure 5 the ordinate represents the light intensity while the abscissa represents the image angle, or the image height corresponding to the vertical distance frpm the optical axis.

In case the lens is symmetrical to the left and to the right, a ray bisecting the angle of the light beam contributing to the imaging, said ray being defined as the principal ray, passes through the bar lens parallel to the optical axis. Consequently the light beam contributing to the imaging on the image field side becomes symmetrical to that on the object field side.

In order to obtain a desired light intensity distribution on the image plane by means of the ideal eclipse of the aperture, it becomes necessary to prevent the transmission of the light beam present outside the effective aperture area of the lens to the image plane. For this purpose, outside the effective aperture of the bar lens 18, there is provided an absorbing layer 22 for dissipating the light beam exceeding the effective aperture area. Said light absorbing layer 22 may be of a type effecting light absorption on the surface thereof or effecting light absorption during the course of light transmission therein.The light absorption of the former type is achievable for example with a black paint or a lens tube provided around the lens, while the light absorption of the latter type is achievable for example by means of a combination of a plastic lens and an absorbing layer of a black acrylic resin of a substantially same refractive index for reducing the internal reflection at the boundary. Also a light diffusing face can substantially serve as such absorbing layer.

Now there will be explained the parameters of the bar lens 18, which should preferably satisfy the conditions represented by the following equations (4) to (7). It is now assumed that the radius of curvature of the first face at the object field side of the bar lens 18 is r1; the radius of the curvature of the second face thereof at the image field side is r2 (negative in the illustrated case); the axial lens thickness or the distance between the first and second faces along the optical axis is d; the refractive index is n; the effective aperture of the lens is cpl; the maximum diameter of the effective object field is 4)o; the distance from the first face of said bar lens 18 to the object 19 is S1 (negative in the illustrated case); and the effective F-number at the object field side is Fe. Fe, S1, n and q)O are parameters determinable in advance, from which there can be determined other parameters r1, r2, d and (P1 according to the ideal imaging theory.

In the first place, from the definition of the F-numberthere can be obtained the following equation:

Also the paraxial imaging theory in an erect imaging system of a magnification of unity leads to the following equation: a1e' + f1e' = 2 (2) In consideration of the case of the lens manufacture it is assumed that the first and second faces have a same refractive power. In the foregoing equation (2) al is the converted inclination angle at the object field side, 9 is the refractive power of the first face, and e' din.

Further there is obtained the following equation from the condition that the effective aperture becomes zero at the maximum image angle:

wherein (Po > 0 and 1 < 0.

The foregoing equations (1), (2) and (3) are solved in combination to obtain 1, r1, r2 and d in the following manner:

Furthermore the present inventors have verified that the desired optical performance is obtainable even when the above-mentioned parameters are deviated from the foregoing definitions by +10%, namely as long as the following relations are satisfied:

where in K1 = 0.9, and K2 = 1.1.

In the following there will be given certain numerical examples of said parameters, which are represented in millimeters except for the refractive index: Numerical Examples Mate (Po 1 S1 n rial r1 r2 d P 1 5.43 1.68 28.2 1.720000 LaK8 4.798 -4.798 30 1.68 II 5.04 1.68 29.1 1.51633 BK7 3.756 -3.756 29.4 1.68 The object fields of the element lens systems, each having a Gaussian distribution of the light intensity, can be overlapped by arranging a plurality of such element lens systems along a determined direction with a determined pitch in a plane perpendicular to the optical axis and further making plural rows of such arrangement.Such rows of element lens systems may be arranged simply parallel but are preferably in so-called staggered arrangement in which each row is displaced by a half pitch with respect to the neighboring row thereby improving the uniformity, over the slit length, of the exposure integrated in time in the scanning direction.

The above-mentioned pitch P of the arrangement has a tolerance defined below: M1 x p < P < M2 X (Pi wherein M1 = 0.9 and M2 = 1.5, though M2 may be selected even larger, if desirable.

In case the bar lens 18' is provided with a minutely coarse surface on the external periphery thereof and thereon with an absorbing layer 22' of a refractive index substantially equal to that of the lens as shown in Figure 7, it is rendered possible to obtain the desired light intensity of Gaussian distribution because the unnecessary beam entering the boundary between the bar lens 18' and the absorbing layer 22' is almost transmitted therethrough, due to the absence of difference in the refractive index, and attenuated in said absorbing layer 22', and a minor component reflected at said boundary is also attenuated by diffusion.

Figure 8 shows a process for forming the spherical faces of the bar lens, in which a glass fiber rod 23 of which outer diameter is ground in advance to a precision of +5yam is fitted in a collette chuck 25 supported by a high precision bearing 24. Said glass fiber rod 23 may be provided with an external light-shielding treatment for example with a black paint. The holding with said chuck is easily achievable since the bar lens to be finally obtained has a relatively large axial length. Opposed to said glass fiber rod 23 there is provided a working grindstone 26 supported by a high precision bearing 27. 28 and 29 are motors. Said grindstone 26 is of a cylindrical shape for effecting the grinding function with the internal surface thereof and is provided with a rotating axis diagonally crossing the central axis of said glass fiber rod 23.

The glass fiber rod 23 is rotated without vibration by the motor 28 at a low speed, while the grindstone 26 is rotated at a high speed by the motor 29.

Said grindstone 26 is advanced, together with the bearing 27 and the motor 29, along the direction of arrow and is returned to the illustrated position after completing the work to a determined position. In this manner the spherical face at an end is completed. The spherical face at the other end can be obtained in the similar manner. In this process one spherical face is completed as short as Ca. 3 seconds, and the centering step can be dispensed with as the eccentricity is determined by the precision of the working machine.

A spherical surface of a large radius of curvature, i.e. requiring a small amount of grinding, may be satisfactorily obtained with a fine grindstone, but it is preferable, for achieving a higher face precision, to employ a coarse grindstone (&num;400 to &num;600) and a fine grindstone (&num;2000 to &num;3000) in combination.

Now reference is made to Figures 9 to 11 for explaining the method of supporting the aforementioned element lens systems. In an embodiment shown in Figure 9, plural element lens systems are arranged in an array and fixed, by means of an adhesive elastomer material, in a grooved block30a having U-sectioned grooved of a regular pitch, then another grooved block 30b is likewise provided with plural element lens systems, and said grooved blocks 30a and 30b are combined together after an opaque elastomer material 31 is filled as a corking material in the spaces between said element lens systems. The grooves on said block 30a are so positioned as to be displaced by a half pitch from those in said block 30b, whereby said plural element lens systems are arranged in a staggered fashion when seen from the entrance side.Said grooves of the blocks 30a, 30b may also be V-sectioned instead of U-sectioned.

Figures 10A and 10B show another embodiment, in which plural bar lenses 18 positioned at a regular pitch on a grooved block 32 provided with V-sectioned grooves and, after coated with an adhesive elastomer material, transferred and fixed on a flat plate 33. After the first row orthe array is completed in this manner, a second row similar fixed on a plate 33' are combined in such a mannerthatthe bar lenses 18 mutually contact at the outer periphery thereof and constitute a staggered arrangement. The bar lenses in the same row can also be arranged in substantially mutually contacting positions by the appropriate selection of the pitch of grooves.

Figure 11 shows still another embodiment wherein an integral block 34 is provided with through holes which are arranged in a staggered fashion when seen from the entrance end and which accommodate the bar lenses 18. In this embodiment said block 34 serves as a light-shielding member.

Now reference is made to Figure 12 showing an application of the present invention in a copier, wherein a drum 35 is rotated by an unrepresented motor at a constant speed in the direction of arrow and is provided on the periphery thereof with a photosensitive member 36 composed in succession of a conductive substrate, a photoconductive layer and a surfacial transparent insulating layer. Said photosensitive member 36 is at first uniformly charged, by means of a corona discharger 37, either positively or negatively respectively when said photoconductive material is composed of a N-type or P-type semiconductor.

Subsequently the photosensitive member 36 is subjected to an imagewise exposure of an original 39 placed on a transparent original carriage 38 which is displaced in the direction of arrow in synchronization with the rotation of said drum 35 and at a speed equal to the peripheral speed of said drum 35 multiplied by the reciprocal of the imaging magnification (same speed in case of a magnification of unity), said image being focused onto said photosensitive member 36 by means of a projecting lens array 40. An area of said original 39 opposed to said lens array 40, i.e. an area to be imaged on said photosensitive member 36, is illuminated by an illuminating unit composed of a lamp and a reflector. The amount of exposure to said photosensitive member 36 can be adjusted for example by regulating the amount of illumination.

Simultaneous with said imagewise exposure by said lens array 40, the photosensitive member 36 is subjected to a charge elimination by means of a corona discharger 42 of a polarity opposite to that of the aforementioned corona discharger 37, thereby forming a charge pattern on said photosensitive member 36 corresponding to the image on said original 39. Said photosensitive member 36 is further subjected to a uniform exposure by a lamp 43 to form thereon an electrostatic latent image of an elevated contrast. The latent image thus formed is rendered visible as a toner image in a developing station 44 for example utilizing cascade development or magnet brush development.Subsequently said toner image is transferred onto a transfer sheet 47 which is supplied from unrepresented supply means and is maintained on contact with the photosensitive member 36 by means of rollers 45, 46 and advanced at a same speed as that of said photosensitive member 36. In order to improve the transfer efficiency, said transfer sheet 47 is given, on the back side thereof at the transfer position, a charge of a polarity opposite to that of the developing toner by means of a corona discharger 48. The transfer sheet is advanced to unrepresented storage means after said toner image thereon is fixed in a suitable fixing station for example a heat fixer provided with paired rollers 49, 50 maintained in pressure contact with the transfer sheet 47.

The photosensitive member after the image transfer is subjected to a cleaning step with an elastic blade 51 maintained in pressure contact with said photosensitive member for removing the eventually remaining toner particles, and is again used for the succeeding image cycle. In the foregoing explanation the discharger 42 is so positioned as to effect the charge elimination of the surface of the photosensitive member 36 simultaneously with the imagewise exposure, but it may also be positioned between the discharger 37 and the imaging system to effect the charge elimination prior to the imagewise exposure. In such case it is possible to dispense with the lamp 43. Also the photosensitive member 36 may be of a type not provided with the surfacial insulating layer. In such case the discharger 42 and the lamp 43 are no longer necessary.

As explained in the foregoing, the present invention a projecting device featured in stable optical performance, easy optical adjustment and a short conjugate distance adapted for use in a compact copier or the like.

Claims (10)

1. A projecting device, comprising: Dlural element lens systems, each composed of a single bar lens having an axial length larger than the effective aperture thereof and adapted for projecting, after forming an inverted intermediate image in the intermediate portion of said lens, a pixel of an object plane as an erect image of a magnification of unity on a determined area of an image plane; and an absorbing layer provided on the external periphery of each of said bar lens for defining the light intensity on the final image plane into a Gaussian distribution.

2. A projecting device according to the claim 1, wherein said element lens systems are arranged in a staggered fashion in which each row of element lens systems is displaced by a half pitch with respect to the neighboring row when seen from the light entrance end.

3. A projecting device according to the claim 2, wherein each element lens system satisfies the following relations:

wherein: r, and r2: radii of curvature of the first and second faces, respectively, of the lens; d: axial thickness of the lens; n: refractive index of the lens; ,: effective aperture ofthe lens; ;p0 maximum diameter of the effective object field; Si: distance from the first face of the lens to the object plane; and K1 = 0.9 and K2 = 1.1.

4. A projecting device, comprising: first element lens systems each composed of a single bar lens having an axial length larger than the effective aperture thereof and adapted for projecting, after forming an inverted intermediate image in the intermediate portion of said lens, a pixel of an object plane as an erect image of a magnification of unity on a determined area of an image plane thereby creating a Gaussian distribution of light intensity thereon; a first grooved block for arranging, by means of grooves of a regular pitch provided thereon, a plurality of said first element lens systems in an array arranged in a perpendicular direction to the optical axis; a second grooved block for arranging a plurality of second element lens systems by means of grooves displaced by a half pitch from the grooves on said first grooved block when seen from the light entrance end; and a light-shielding member for intercepting the light entering the spaces between said element lens systems.

5. A projecting device according to the claim 4, wherein said light-shielding member is composed of an elastomer material.

6. A projecting device according to the claim 4, wherein the refracting faces of said bar lenses are formed solely by grinding.

7. A projecting device, comprising: first element lens systems each composed of a single bar lens having an axial length larger than the effective aperture thereof and adapted for projection, after forming an inverted intermediate image in the intermediate portion of said lens, a pixel of an object plane as an erect image of a magnification of unity on a determined area of an image plane thereby creating a Gaussian distribution of light intensity thereon; a first support member for supporting a plurality of said first element lens systems thereon at a regular pitch; a second support member for supporting a plurality of second element lens systems in such a manner that they are in tangential contact with said first element lens systems; and a light-shielding member for intercepting the light entering the spaces between said element lens systems.

8. A projecting device according to the claim 6, wherein said light-shielding member is composed of an elastomer material.

9. A projecting device according to the claim 6, wherein the refracting faces of said bar lenses are formed solely by grinding.

10. A projecting device substantially as hereinbefore described with reference to Figures 4 to 12 of the accompanying drawings.