JPS60133416A - Cylindrical lens for surface inclination correcting and scanning optical system - Google Patents

Abstract

PURPOSE:To reduce the extent of defocusing and improve image forming performance by decreasing the refracting power of a cylindrical lens gradually from the center of a scanning line to ends. CONSTITUTION:An incident beam 1 is reflected by a rotary polygon mirror 2 and converged and scanned on a photosensitive body surface 4 through a strip- shaped fTHETA lens 3. Then, a cylindrical lens 5 which has refracting power only in a plane perpendicular to a plane containing the scanning line is placed so as to prevent pit irregularity due to the inclination of a reflecting surface of the rotary polygon mirror 2. The focal length fpsi of the cylindrical lens 5 is increased from the center to end as shown by an equation according to the angle psi of incident of the scanning light 6. In this case, (n) is the refracting index of the lens material and f0 is the focal length at the part on an optical axis where psi=0. The effective focal length is f0 and the focusing position of the scanning beam 6 is made coincident to the photosensitive body surface 4.

Description

Detailed Description of the Invention (Field of application in terms of production) This invention is a cylindrical lens used in a set meal original school thread that uses a cylindrical lens to correct surface irregularities, using a rotating polygon mirror, etc. I will serve you.

(Prior art hook) In some cases, such as a laser beam link, a rotating device such as a rotating polygon mirror or a hologram disk is often used as a scanning device. However, in these Q scanning devices, It is known that an angular error of the reflecting surface of a polygon mirror with respect to the rotation axis or an angular error of the hologram with respect to the disk causes bit irregularities in the scanning line.

In order to correct this bit irregularity, a cylindrical lens that increases the refractive power to ■ in a plane perpendicular to the scan line is placed near the scanning plane, and the anti-leopard and bhikkhu planes are geometrically adjusted in this plane. It is common practice to arrange them so that they are optically conjugate.

Although the scanning optical system line using this cylindrical lens and the supplementary iJn beam dry area are widely used, it is clear that problems will occur when trying to reduce the spot size to make it possible to have a single member. .

In other words, near the end of the scanning line, the beam enters the cylindrical lens at a certain point, the effective focal length of the cylindrical lens becomes small, the focal spot becomes larger due to defocusing, and the beam is incident on the cylindrical lens. Since the military service is no longer related to military service, compensation for pinch irregularities in the running iIN will no longer be applied to the principal.

On the other hand, the cylindrical lens for m+ail correction is curved into a concave arc toward the fixed surface so that as the beam size increases, the cylindrical lens approaches the scanning surface. It is suggested that you eat at least one meal. (The method is to make the focusing spot uniform in the 11th National Conference of the Yamatai Electronics Society in 1988. Since the lens is compressed and curved between the lenses, the processing of lenses with curved surfaces increases costs, and the cylindrical lens also has to be bent, and there are restrictions on the thickness of the plastic material H5. , if the cylindrical lens is placed away from the scanning surface, the defocus (h) will increase, the curvature half of the bending will become smaller, and this will cause a problem of deterioration of the 184 performance. (Objective of the Invention) By gradually weakening the refractive power of the cylindrical lens from the center to the end of the cylindrical lens, the aim is to create a cylindrical lens that can produce 1Wb34 optical fibers without meeting the above-mentioned drawbacks.

(Structure of the Invention) The Q invention will be described in detail below.

Figure 1 is a conceptual diagram showing the overall configuration of a scanning optical system using the cylindrical lens of the present invention. f shaped into the shape
The d-lens 3 scans the image onto the photoreceptor surface 4. In order to prevent pitch unevenness due to the reflection curve υ of the rotating ψ-plane mirror 2, 71. : In the plane perpendicular to the plane where the climbing is carried out, a cylindrical lens 5 having a power of 8A is placed, which is the best in this city, and the photoreceptor surface 4v + anterior eclipse line and the reflecting mirror 1m are geometrically optically connected. Maintain military service ties. As a result, even if the reflected light of the incident light 1 is tilted upward or downward in the figure due to an error in the positioning of the reflective surface υ, the position of υ incident on the photoreceptor surface 4 will not be negatively affected.

However, due to the change in the incident angle ψ'v of the light 6υ to the cylindrical lens 5, the effective focal length Ifmf' of the cylindrical lens 5 becomes As f'=f (1-(”gate)2)2 ・・・・・・(1)
Therefore, the focusing position of the scanning beam is point IfM7 in Fig. 1.
The photoreceptor surface is shifted forward by 4v+ as shown in . As previously mentioned, this defocus causes spot enlargement and pitch unevenness caused by running.

In this invention, the focal length r+k of the cylindrical lens 5 is set to become larger from the center to the edge according to the incident angle ψ of the scanning light 6υ. However, the focal length where fJd has an incident angle of 90, f is on the optical axis,
In other words, p is the focal length of the part where ψd0
2)"=fOll It is possible to make the focusing position of the scanning beam 6 coincident with the photoreceptor surface 4.

As shown in the cross-sectional shape of a cylindrical lens with a refractive power distribution similar to that of Kamishiragi, the height from the optical axis ψ = 0 of the lens is R6 to the human angle ψ, and the Q curvature R9. However, R8 only needs to have a curvature of υ on the original axis.

(Effect of origin) This invention has the above-mentioned configuration υ 1. Since there is no necessity to curve the entire cylindrical lens, the cost of the lens frame can be reduced. 〇2. The cylindrical lens is concave inwardly. Since there is no required shell, it is easy to set the lens arrangement to the 6γ value given by Ini Hasikura, and there is no restriction on the lens arrangement τ.

3. It is easy to handle as a cylindrical lens is sufficient.

4. It is easy to prevent the cost of the lens itself from going up by molding the lens into a plastic mold.

etc. 11++ has a remarkable effect.

[Brief explanation of the drawing]

Figure 1? ``This Origin'' is a conceptual diagram of a scanning optical system using a 7-lindrical lens, and Figure 2 is a top view of the cylindrical lens of this invention in one direction and a cross-section of each part. 1 Figure 1: Incident beam 2: Rotating multi-faceted lens 3: ftj lens
4: Photosensitive rhinoceros 4: fij5 Nijilintorical lens 6
: Front beam 7: Beam focusing position comb 9 1 Applicant Ricoh Co., Ltd. - Applicant's agent Patent attorney Fumi Sato (1 other person)

Claims (1)

[Claims] It includes a scanning/rotating device such as a rotating polygon mirror, a focusing lens, and a cylindrical lens having a refractive power in a plane perpendicular to the scanning line, in which the rotating scanning section and the scanning line are at a geometrically optically conjugate position. The above-mentioned cylindrical lens used in the scanning optical system Pc arranged in the lens has a refractive power that changes continuously from the optical axis to the end so that the effective focal length according to the angle of incidence ψ on the lens is constant. IiI cylindrical lens with %