JPS6220526B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a scanning device using a deflector that rotates or vibrates at high speed, and particularly to a scanning device suitable for scanning a surface to be scanned in the form of a slit. Conventionally, when scanning a flat surface to be scanned using a rotating or rotationally vibrating deflector, there is a problem in that the optical path length between the deflector and the surface to be scanned changes as the deflector rotates. Therefore, in an apparatus incorporating such a scanning system, it is necessary to correct the change in the optical path length by some means. FIG. 1 is a schematic diagram showing an example of a copying optical system incorporating the above scanning device.
The surface to be scanned 1 forms a cylindrical surface centered on the rotation axis 2 of the rotary reflecting mirror 3. Therefore, when the light beam from the surface to be scanned 1 is deflected by the rotating reflector 3 and reaches the recording drum 5 via the imaging lens system 4, it is always reflected regardless of the rotation angle of the rotating reflector 3. The optical path length between the scanning surface and the recording drum 5 is kept constant.
However, using a cylindrical surface to be scanned in this way not only makes it difficult to manufacture a large cylindrical surface, but also makes it impossible to scan a flat object. The present invention aims to improve the above-mentioned drawbacks, and it is possible to correct the optical path length even when the surface to be scanned is flat when the surface to be scanned is scanned with a rotating or rotationally vibrating deflector. A scanning device is provided. A further object of the present invention is to provide a scanning device having the above-mentioned structure, which can scan a surface to be scanned at a constant speed. In the scanning device according to the present invention, the above object is achieved by providing a rotationally asymmetrical imaging optical system between a rotating or rotationally vibrating deflector and a flat surface to be scanned. In the rotationally asymmetric imaging optical system, when forming an image of a flat scanned surface, the normal line of the deflection surface of the deflector is within a plane that is formed over time as the deflector rotates. In the plane (referred to as a deflection scanning plane), an image is formed as if the position of the image were at approximately the same distance from the deflection plane of the deflector. In other words, if a perpendicular line is drawn at each point of the image of the scanned surface formed by the asymmetric imaging optical system in the deflection scanning plane, each of the above points between the image of the scanned surface and the deflection surface will be The distances along the perpendicular lines are approximately equal. In the scanning device according to the present invention, within the deflection scanning plane, the rotationally asymmetric optical system satisfies the following in a third-order aberration region: =0, P=1/g'. Here, P is the astigmatism, P is the Petzvaar sum, and g' is the deflection surface of the deflector within the deflection scanning plane, within a line passing through the center of the image of the scanned plane and perpendicular to the scanned plane. It represents the distance from
g' represents a negative quantity, and if it is a real image, g' represents a positive quantity. Furthermore, in the scanning device of the present invention, in order to scan the scanned plane at a constant speed when the deflection surface of the deflector is rotated at a constant angular speed, the value of the third-order distortion aberration V of the rotationally asymmetric imaging optical system is is set to -2/3 in the deflection scanning plane. The scanning device according to the present invention includes a scanning method in which a slit scans the surface to be scanned on the deflection scanning plane with a certain slit width, or a scanning method in which a slit is scanned in the longitudinal direction of the slit,
In other words, the beam is scanned at high speed on the scanned surface in a direction perpendicular to the deflection scanning plane, and in this state, the beam is also scanned within the deflection scanning plane. There are several scanning methods. Further, scanning of the surface to be scanned can be performed by reading information on the surface to be scanned or writing information on the surface to be scanned. Therefore, the scanning device of the present invention makes it possible to scan a flat surface to be scanned at high speed and without distortion. Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 2 is a diagram showing an embodiment of a recording device using an example of a scanning device for explaining the principle of the scanning device according to the present invention. In FIG. 2, a virtual image 12 of the scanned plane 11 is formed by a rotationally asymmetric imaging optical system 13 disposed between the scanned plane 11 and a rotating reflection mirror 15 rotating about a rotation axis 14. . This rotationally asymmetric imaging optical system 13 has a surface that is formed over time by the surface normal of the rotational reflection mirror 15 as it rotates (in FIG. In the same case), the image 12 of the scanned plane is formed into a cylindrical surface. In the deflection scanning plane, a line 18 passing through the center of the image 12 of the cylindrical scanned plane and perpendicular to the scanned plane 11 passes through the rotation axis 14 of the rotary reflection mirror 15 in this case. When viewed from the position where this line 18 intersects the deflection plane of the rotating reflection mirror (which can be considered as the rotational axis 14 in FIG. 2), the image 12 is located at approximately the same distance as the cylinder. The image is formed into a shape. Therefore, the light beam emitted from the point P ₁ on the scanned surface 11 enters the rotationally asymmetric optical system 13, and then enters the rotational reflection mirror 15 as if it were emitted from the point P ₂ on the conjugate image 12 thereof. The rotating reflection mirror 15 rotates so as to always form a mirror image of the image point P ₂ at a constant position P ₃ . and point P ₃
The mirror image formed is focused by the imaging lens system 16 onto a fixed position P ₄ on the recording drum 17 . As described above, as the rotary reflection mirror 15 rotates, the scanned point _P1 on the scanned surface 11 moves on the scanned surface 11 within the deflection scanning plane (in the plane of the paper), and ₁
The point is always imaged onto a point P ₄ on the recording drum 17 via the rotationally asymmetric imaging optical system 13 , the rotary reflection mirror 15 and the imaging lens system 16 . Therefore, if the recording drum 17 is rotated in synchronization with the angular velocity of the rotating reflective mirror 15, the information on the scanned surface 11 will be transferred to the recording drum 1.
recorded on 7. As shown in FIG. 2, in the present invention, the flat scanned surface 11 is replaced by the cylindrical scanned surface 1 shown in FIG.
A rotationally asymmetric imaging optical system 13 is used to make the surface equivalent to
The image 12 of the scanned surface 11 is formed by
It is possible to scan a flat surface to be scanned. The rotationally asymmetric imaging optical system forms the image of the scanned surface 11 into the cylindrical image 12 as described above in the deflection scanning plane. The aberration coefficient and Betsuvial sum P satisfy the following: =O, P=1/g' (i). However, g' indicates the distance from the point where the above-mentioned line 18 (which actually coincides with the optical axis of the asymmetrical rotating imaging optical system) intersects with the rotating reflection mirror to the image 12 along the above-mentioned line 18, and the imaging optical system If the image 12 of the scanned surface 11 by 13 is a virtual image as shown in FIG. 2, the physical quantity g' is negative;
When the image of the surface to be scanned 11 obtained by 3 is a real image, the physical quantity g' is positive. Furthermore, in order to scan the surface to be scanned at a constant speed when the rotating reflection mirror 15 is rotated at a constant speed, the rotationally asymmetric imaging optical system 1 is installed in the deflection scanning plane.
The value of the distortion aberration coefficient V of No. 3 is set to V=-2/3 (ii). However, as a condition for determining the above aberration coefficient, in the deflection scanning plane including the optical axis 18 of the rotationally asymmetric imaging optical system 13, the height from the optical axis at the center position (i.e., exit pupil position) of the rotational reflection mirror 15. We will use the exit pupil radius normalized so that is 1.0. Next, the above conditions (i) and (ii) that are satisfied by the rotationally asymmetric imaging optical system will be described. FIG. 3 is an explanatory diagram for this purpose, and first, the conditions for uniform velocity will be described. Second
The rotating reflection mirror 15 shown in the figure is located at the exit pupil of the rotationally asymmetric imaging optical system 13 and rotates at a constant angular velocity. Radius g (In Figure 3, the coordinate system is right-handed, and in this case g is a positive quantity by definition, but the second
This is the negative amount shown in the figure. ) is a minute portion of the image plane on the circular arc of △θ.
Then, △l=g′・△θ ...(1). Now, since the rotating reflecting mirror rotates at a constant angular velocity, △θ=ωdt ...(2) ω: angular velocity of the mirror (constant) △l=g'ωdt ...(3). Also, if the minute part on the scanned surface is △Y ₁ ,
In order to scan the surface to be scanned at a constant speed, △l=g′ωdt=β△Y ₁ ...(4) (β: magnification) must be satisfied. From equation (4), integrate both sides of ωdt=β/g′△Y ₁ to obtain ωt=β/g′Y ₁ +C ₁ ...(5) (C ₁ : integral constant). Since t=0 when Y ₁ =0, C ₁ =0 ωt=β/g'Y ₁ ...(6). From Fig. 3, ωt = θ, and if the ideal height of the curved image plane is up to the intersection of the perpendicular from the optical axis and the circular arc, and this is Yc', then θ=sin ^-1 (Y'c/g')... …(7) becomes. Substituting equation (7) into equation (6), sin ^-1 (Yc′/g′)=β/g′Y ₁ Yc′=g′sin(β/g′Y ₁ ) ……(8) That is, In order to keep the scanning speed on the surface to be scanned constant, the ideal image height Yc' must be determined by equation (8). Expanding equation (8) to the cubic term, Yc′=g′[(βY ₁ /g′)−1/6(βY ₁ /g
') ³ ]...(9) Also, aberration theory (written by Matsui: Applied Physics Vol. 28, No. 12, 5)
According to the practical application of the theory of second-order aberrations, However, N' is the refractive index of the image space α; the inclination angle α′ of the object paraxial ray is converted to the incidence; the inclination angle converted the output of the object paraxial ray ′ is the inclination angle converted the output of the pupil paraxial ray; Substituting into equation 9) and rearranging, we get Yc′=-1/2α′ [-2(αY ₁ )+1/3(α′/N′) ² (αY ₁ ) ³
]...(11) Since (α ₁ Y ₁ ) ³ , the second term on the right side of equation (11), is a field angle term regardless of the aperture, from the aberration theory mentioned above, it is a third-order distortion where the image plane is curved. The aberration coefficient Vc is Vc=1/3(α'/N') ² (12). Vc is a condition that requires a third-order distortion aberration coefficient when the image plane is curved, but this is converted into a distortion aberration coefficient V specific to the optical system. From Figure 5, X'c〓1/2D ₃ Y'c ² +1/8D ³ ₄ Y'
c ⁴ ...(13) D ₃ and D ₄ in equation (13) are the curvature coefficients of the field surface. Since the image plane is now on a circular arc with radius g', D ₃ = D ₄ = -1/g' According to aberration theory, Vc = V + α'/α' D ₃ /N' ...(14) V=Vc−α′/α′ D ₃ /N′ Substituting D ₃ =−1/g′ and equation (12) into this, V=−2/3(α′/N′) ² ……(15 ) becomes. ' is considered normalization based on the exit pupil, so '=-1, and N' is the refractive index of the image space, so N' = 1. Therefore, uniform speed scanning is possible if the third-order distortion V of the rotationally asymmetric imaging optical system is -2/3. Next, the above condition (i) will be described. The astigmatism coefficient c and the spherical field curvature coefficient IVc when the image plane is curved are expressed by the aberration coefficient specific to the optical system and IV. From the above aberration theory, c= IVc=IV+D ₃ /N, respectively. ′...(16). Therefore, in order for the image plane to be on a circular arc with radius g, it must be c==0 IVc=0 (17). From the equation below equation (17), IVc=IV+D ₃ /N'=0 Substituting IV++P and D ₃ =-1/g', +P-1/N'g'=0 From equation (17), = 0. Therefore, in order for IVc = 0, P = 1/N'g'...(18). Since N′=1 now,
In the end, P becomes P=1/g'. FIG. 5 shows an embodiment of the rotationally asymmetric optical system 13 of FIG. The rotationally asymmetrical imaging optical system 23 consists of three cylindrical lenses whose generatrix is perpendicular to the plane of the paper in FIG. Rotationally asymmetric optical system 23
creates a conjugate image of the scanned plane (□170×□170) on the cylindrical surface 22. Since the central axis of the cylindrical surface and the rotational central axis of the deflection mirror 24 are made to coincide with each other, the light beam emitted from a point on the scanned surface 21 enters the rotationally asymmetric optical system 23, and its conjugate image point, that is, the cylindrical surface. The light beam enters the deflection mirror 24 as if it were emitted from a point on the deflection mirror 22. FIG. 7 is an optical path diagram at that time. Next, the configuration of the rotationally asymmetric optical system 23 will be shown below. As mentioned above, the optical system 23 is composed of a cylindrical lens that has no power in the plane perpendicular to the plane of the paper, so the curvature r in the plane parallel to the plane of the paper is
Aspheric coefficients B, C and surface spacing D shown in equation (19)
and the refractive index N. However, as shown in Figure 7, the shape of the aspheric surface is as follows: r is the paraxial radius of curvature at the apex of the aspheric surface, r is the paraxial radius of curvature at the apex of the aspheric surface; When taking the Y axis that passes through the vertex, the amount of deviation when the Y coordinate is h is x.

[Table] However, S ₁ is the axial distance from the r ₁ surface of the lens system 23 to the scanned plane 21, tk is the axial distance from the r ₆ surface of the lens system 23 to the deflection mirror 24, and then the above optical system shows the aberration coefficient in the plane parallel to the paper surface. = 0.00000020451 = 0.000006828 = -0.0000021 P = -0.0019621 V = -0.62445 f = 39441.108 Furthermore, Fig. 8 is a diagram showing the aberration in the plane parallel to the plane of the paper of the rotationally asymmetric imaging optical system 23 shown in Fig. 5;
FIG. 9 shows the rotationally asymmetric imaging optical system 23 shown in FIG.
10 is a diagram showing aberrations in a plane perpendicular to the plane of the paper, and FIG. 10 is a diagram showing aberrations in a plane rotated by 45 degrees from a plane parallel to the plane of the paper of the rotationally asymmetric imaging optical system 23 shown in FIG. FIG. 3 is a diagram showing angular aberrations. FIG. 11 is a diagram showing an embodiment of a copying machine to which a scanning device according to the present invention is applied, mainly showing the periphery of the optical system. In FIG. 11, 31 is a document, 32 is a conjugate image of the document 31 by a rotationally asymmetric lens 34, 33 is an illumination device, 35 is a deflection mirror, 36 is an imaging lens, 37 is a slit,
38 is a cylindrical drum. The light beam emitted from the original 31 is incident on the rotationally asymmetric lens 34, and is incident on the deflection mirror 35 as if the light beam were emitted from its conjugate image point, that is, a point on the cylindrical surface 32. The deflection mirror 35 rotates and oscillates a mirror image of a line that includes the conjugate image point and is parallel to the rotation axis of the deflection mirror so that it is always on a line that includes the optical axis of the imaging lens 36 and is parallel to the rotation axis of the deflection mirror. . The mirror image is formed on a fixed line 39 of the cylindrical drum 38 by the imaging lens 36. Therefore, when the deflection mirror 35 rotates, the image of the slit 37 formed by the imaging lens 36 and the rotationally asymmetric lens 34 scans the scanned surface 31 from one end to the other along the scanning direction. That is, the scanned surface 31 is slit-scanned with the width of the image of the slit 37. A photosensitive medium is provided on the cylindrical drum 38, and since the cylindrical drum 38 rotates in synchronization with the deflection mirror 35, the original 31
is recorded on a photosensitive medium on a cylindrical drum 38.
As a photoreceptor suitable for high-speed copying using a rotary vibration method, for example, one has a three-layer structure, which has a photoconductive layer on a support and an insulating layer on top of the photoconductive layer. good. This support may be electrically conductive or insulating. Further, as an example of forming a latent image on the photoreceptor, a latent image can be formed by primary charging, followed by neutralization or reverse polarity charging, and then whole surface exposure. In this optical system, the deflection mirror 35 can rotate at high speed. Therefore, in this apparatus, a high-speed copying apparatus with a flat original surface can be achieved. At this time, since only the rotation of the deflection mirror 35 is required, the rotation input structure can be extremely simplified. Although the above-mentioned deflector is of a rotary vibration type, it is also possible to use something like a polygon mirror. As described above, in the scanning device according to the present invention, by providing a rotationally asymmetric imaging optical system between the rotating or rotationally vibrating deflector and the scanning plane, the scanning plane can be scanned at high speed without distortion. and
It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a copying optical system using a conventional scanning device, FIG. 2 is a diagram for explaining the principle of a scanning device according to the present invention, and FIGS. 3 and 4 are diagrams showing an example of a copying optical system using a conventional scanning device. A diagram for explaining the rotationally asymmetrical imaging optical system used in the device, FIG. 5 is a diagram showing an example of the rotationally asymmetrical imaging lens used in the device according to the present invention, and FIG. 6 is the lens shown in FIG. 7. Figure 7 is a diagram for explaining the definition of an aspherical surface, Figures 8, 9, and 10 are aberration diagrams showing the aberrations of the lens shown in Figure 6, and Figure 11. 1 is a diagram showing an embodiment in which a scanning device according to the present invention is applied to a copying machine. 11... Surface to be scanned, 12... Image of surface to be scanned, 13...
Rotationally asymmetric imaging optical system, 15...rotating reflection mirror.

Claims (1)

[Claims] 1. In an apparatus that scans a flat surface to be scanned in a slit shape using a rotating or rotationally vibrating deflector, an image of the surface to be scanned is disposed between the surface to be scanned and the deflector. A rotationally asymmetrical imaging optical system formed in a cylindrical shape is provided, and the normal line of the deflection surface of the deflector forms a tertiary axis of the rotationally asymmetrical imaging optical system within a deflection scanning plane formed over time as the deflector rotates. The astigmatism coefficient and the Petzval sum P are: =0, P=1/g', where g'; A scanning device characterized in that the distance from a deflector to an image of a scanned surface as measured along a line approximately satisfied.