JPS6350684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an erecting real image mirror lens used in an exposure optical system of a copying machine.

In recent years, several compact imaging lenses have been developed to downsize copying machines. One of these is a focusing light transmitter known as a self-occurring lens. This is an optical fiber whose refractive index changes parabolically from its center in the radial direction, and is used as an array by lining up many fibers of the same length and performance in parallel. This is because the conjugate length, that is, the distance from the object to the image, is currently about 100 mm, which is not very large, and if this is made too large, the imaging performance will deteriorate dramatically. If the conjugate length is short, when used in a copying machine, the degree of freedom in arranging the original and the photoreceptor is reduced, and the space for the illumination light source is also reduced, making it difficult to obtain the target illuminance. On the other hand, the strip lens array
It is a superimposition of three lens arrays with the optical axes of each lens element aligned; for example, the
No. 49-8893. This is because the conjugate length can be larger than the above-mentioned convergent light transmitter array, and since it has a multifaceted configuration to ensure the target imaging performance, multiple plastic lens arrester plates are used. ing. For this reason, high precision is required for each lens array plate, and high precision is also required for the assembly of the lens array plates with each other. Additionally, U.S. Patent No.
The combination of reflective lenses or concave mirror arrays described in 4,141,649 has the same drawbacks as the strip lens array described above.

According to the present invention, there is provided an erecting real image mirror lens whose front surface is a spherical surface and whose rear surface is part of a specific elliptical reflecting surface whose one focal point coincides with the center of the spherical surface, and a plurality of mirror lenses arranged in parallel. An array of individual mirror lenses is provided. The mirror lens according to the present invention has a simple structure and is inexpensive because the entrance and exit surfaces and the reflection surface can be integrally molded, and since field curvature can be substantially eliminated, the conjugate length can also be long. Furthermore, since the mirror lens of the present invention has a recursive property, it has the characteristic that when arranged in an array, a good composite image can be obtained even if the arrangement accuracy of the individual lenses is relatively loose.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an improved erecting real image mirror lens that can be applied to copying machines.

A further object of the present invention is to provide the above-mentioned mirror lens, wherein the front surface is a spherical surface and the rear surface is a specific elliptical reflective surface with one focal point aligned with the spherical center of the spherical surface.

Another object of the present invention is to provide an erect real image type mirror lens array in which a plurality of the above mirror lenses are arranged in parallel.

Other objects and features of the invention will become more apparent from the following description with reference to the drawings.

As described above, in the mirror lens according to the present invention, the front surface is a spherical surface, and the rear surface is a circular reflective surface that meets specific conditions. In order to better understand this invention, we will first explain the imaging effect in the case of a mirror lens whose front and rear surfaces are both spherical.
That is, as shown in FIG.
1, the front surface 12 is composed of a spherical surface having a radius of curvature r, and the rear surface 13 is composed of another spherical surface having a radius of curvature R larger than the radius of curvature r, which has the spherical center 0 of the spherical surface 12 on the front surface as a common spherical center. It consists of some parts. The front surface 12 serves as a light input/output surface, and the rear surface 13
is a reflective surface and an inverted real image focal plane. Reference numeral 14 is an aperture. Such a mirror lens 11
In this case, when the incident light is a parallel light flux, that is, a light flux from an object at an infinite distance, the recurrence property of the light flux near the principal ray strictly holds true, and if the refractive index of the mirror lens 11 is n, then the following A relationship exists.

R=r/n-1 However, for a light beam from an object at a finite distance, as shown in Figure 2, the inverted real image focal plane 1
3 is a rectangular surface 15 having a focal point F ¹ on the spherical center 0 of the entrance/exit surface 12 . Therefore, if the reflective surface 13 is made spherical in this way, when an image is formed on the reflective surface on the optical axis A, as the incident angle increases, the image becomes rear-focused with respect to the reflective surface. As a result, the image plane 16 of the original erect real image after recursion, which coincides with the object plane, becomes a curved surface 17 that is convex toward the lens 11 as shown. From the above, it will be understood that by making the reflective surface 13 coincide with the rectangular surface 15, the field curvature is corrected.

FIG. 3 is a schematic diagram showing the configuration of a mirror lens according to the present invention. For convenience of explanation, the same reference numerals as used in FIGS. 1 and 2 are used. The mirror lens 11 is made of a medium with a refractive index n, and the front surface 12, which serves as the entrance and exit surface for light rays, is a spherical surface with a spherical center of 0 and the radius of curvature r, and the rear surface 13, which serves as a light reflection surface, is a spherical surface 12 Focus F ¹ on sphere center 0
, and is a part of the circular circular surface 15 of rotation about the optical axis A. The principal ray of the light beam emitted from an object point on the object plane 16 located at a finite distance enters the plane of incidence 12 perpendicularly, passes through its spherical center 0, that is, one focal point ^F1 , and is inverted onto the rotating circular circular surface 13. Connect real image points. Since this rotating ellipsoidal surface 13 is a reflective surface, the luminous flux near the chief ray reflected here is transferred to the other focal point F.
The light beam hits the exit surface 12 while heading toward , where it is refracted and forms an erect real image point at the original object point position on the object surface 16 . At this time, the object point on the object plane 16 and the inverted real image point on the reflective surface 13 are in a conjugate relationship, and this inverted real image point and the erected real image point on the image plane 16 after reflection (object plane 16) are also conjugate. Since there is a relationship, the object point and the image point will match. In other words, an imaging system is obtained in which the curvature of field is substantially zero for the light beam near the principal ray.

Next, what kind of radial surface should be used will be explained using a mathematical formula. In FIG. 4, each symbol is as follows.

r: radius of curvature of spherical surface 12 ρ: distance of principal ray from spherical center 0 of spherical surface 12 to object surface 16 ρ ⁰ : distance on optical axis A from spherical center 0 to object surface 16 ρ' ₀ : spherical center 0 Optical axis A from to the circular reflecting surface 13
ρ': Radius in polar coordinates of the circular reflecting surface 13 with the spherical center 0 as the pole θ: Angle in the polar coordinates of the circular reflecting surface 13 with the spherical center 0 as the pole n: Medium forming the mirror lens 11 Here, if the focal length of the mirror lens 11 is f and the refractive index of the medium outside the mirror lens 11 is n', then
On the spherical surface 12 of the mirror lens 11, the laws of reflection and refraction on a spherical surface as defined in geometric optics (for example, "Applied Optics" by Hiroshi Kubota, published by Iwanami Shoten; 1st edition December 19, 1959, May 1976) Month 10th 15th
(See pages 6 to 8 of the print) holds true, so from the Charles equation in geometric optics, the relationship n/ρ-n'/ρ'=-n/f holds true. Here, since the medium outside the mirror lens 11 is usually air, its refractive index is
n'≒1, and the above equation becomes n/ρ-1/ρ'=-n/f.

Also, as is clear from Figure 4, ρ=ρ ₀ /cos θ, so if we rearrange these and expand for ρ', ρ'=f/n/1+f/ρ ₀ cos θ This equation becomes, Eccentricity e= with the right focus F ¹ as the pole
It represents the circle of f/ρ ₀ . Incidentally, when θ=0, the relationship between ρ ₀ and ρ′ ₀ is determined as follows.

ρ′ ₀ =ρ ₀ f/n(ρ ₀ +f) (1) Here, the focal length f is calculated from Atsube's zero invariant equation as follows.

1/r=n(1/r-1/f) ∴f=n/n-1r...(2) Therefore, for r and n used, ρ'=r/n-1/1+nr/ (n-1)ρ ₀ cos θ…
…(3) It is sufficient to use the circular surface as the reflecting surface.

Next, a specific embodiment of the mirror lens according to the present invention will be described with reference to FIG. first,
When the refractive index n is set to 1.5 and the radius of curvature r is set to 10, the focal length f becomes 30 from the above equation (2). Also, if the distance from the sphere center to the object surface is ρ ₀ is 270, then ρ′ ₀ is the above
From equation (1), it becomes 18, and the total lens length L is r + ρ′ ₀ = 28
become. Therefore, the radius circular surface has the right focal point F ¹ as a pole and is expressed as follows from the above equation (3).

ρ′=20/1+e cos θ (however, eccentricity e=1/9
= 0.11...) FIG. 6 is a schematic diagram showing a state in which erect real image mirror lenses according to the present invention are arranged in an array and how images are formed. As is clear from the figure,
On the circular reflective surface of each mirror lens 11,
The object points 17 on the object plane 16 are imaged at different positions 18a, 18b, 18c, 18d, 18e, etc., but they recurse to the same image plane 1 as the object plane.
6, an erect real image point is formed at the same position as the object point 17. Each mirror lens may be arrayed in one row, or may be arrayed in multiple rows as shown in FIG.

FIG. 8 is a schematic front view showing an example in which the erecting real image mirror lens array according to the present invention is applied to an exposure optical system of a transfer type copying machine. The array 18 is arranged so that its optical axis is perpendicular to the document placement glass 19, and each mirror lens making up the array is
They are arranged in parallel in a direction perpendicular to the plane of the paper in which this figure is shown, that is, parallel to the axial direction of the photoreceptor drum 20. The original 21 placed on the original placing glass 19 moving rightward is exposed to the exposure lamp 2.
2 and 23, and the reflected light is incident on the array 18 through the half mirror 24. The light reflected by the circular reflection surface of the array 18 and returned is reflected by the half mirror 24 and then sequentially projected onto the photoconductor drum 20 rotating clockwise. The sexual surface is
Since it is charged in advance by a charger (not shown), the charge in the portion exposed to light is discharged, and an electrostatic latent image corresponding to the original image is formed there. As is well known, this electrostatic latent image is developed with colored fine particles called toner, and the developed image is transferred to transfer paper.

Although this invention has been described above based on the illustrated embodiments, this invention can be modified in various ways within the spirit of the invention as set forth in the claims.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a conventional mirror lens, FIG. 2 is a schematic diagram showing the image forming state of the conventional mirror lens, and FIG. 3 is a schematic diagram showing the configuration and image forming state of the mirror lens according to the present invention. Schematic diagram showing 4th
FIG. 5 is a diagram for explaining an embodiment of the mirror lens according to the present invention. FIG. 6 is a diagram for explaining the rear semicircular reflecting surface of the mirror lens according to the present invention. FIG. FIG. 7 is a schematic partial plan view showing an example of the mirror lens array according to the present invention, and FIG. 8 is a schematic diagram showing the structure and image forming state of the lens array. FIG. It is a schematic partial front view which shows an example. 11... Mirror lens, 12... Front, 13...
...Rear surface, 15...Horizontal surface, 16...Object surface (image surface).

Claims (1)

[Scope of Claims] 1 The front surface is a spherical surface, the rear surface is a part of an elliptical reflecting surface whose one focal point coincides with the spherical center of the spherical surface, and the elliptical reflecting surface substantially comprises the following: An erect real image mirror lens that satisfies the conditions. ρ'=r/n-1/1+nr/(n-1)ρ ₀ cos θ where r: radius of curvature of the spherical surface n: refractive index of the medium constituting the mirror lens ρ ₀ : from the center of the spherical surface to the object surface distance on the optical axis to ρ': Radius in polar coordinates of the circular reflective surface with the spherical center as the pole θ: Angle 2 in polar coordinates of the circular reflective surface with the spherical center as the pole The front surface is a spherical surface, A plurality of erecting real image mirror lenses, each of which has a rear surface that is part of an elongated circular reflecting surface whose one focal point coincides with the spherical center of the spherical surface, and wherein the elongated circular reflecting surface substantially satisfies the following conditions. Erect real image mirror lens array arranged in parallel. ρ'=r/n-1/1+nr/(n-1)ρ ₀ cos θ where r: radius of curvature of the spherical surface n: refractive index of the medium constituting the mirror lens ρ ₀ : from the center of the spherical surface to the object surface distance on the optical axis to