JPS62139525A - Photoscanning device - Google Patents

Abstract

PURPOSE:To obtain a small-sized, low-cost, and high-performance scanning lens by using a single lens which is so constituted rotationally symmetrically so that both surfaces are made aspherical and also has a surface inclination correcting function. CONSTITUTION:Projection light from a light source is converged only in the sagittal direction through both a collimator and a cylindrical lens which are not shown in a figure and forms its image linearly nearby a mirror surface SM. The luminous flux is deflected at an equal angular speed in a tangential plane by the rotation of a polygon mirror 5 and reflected at an angle theta of deflection corresponding to the rotation of the mirror 5. Then, the luminous flux after passing through a scanning lens 1 forms its image on a scanned plane 7 at a point T1 whose coordinate value Y is proportional to the angle theta of deflection. The lens 1 has such distortion characteristics that the luminous flux moves on the plane at the equal speed and is the single lens which has both surfaces S1 and S2 made asymmetrical and one or both surfaces made rotationally asymmetrical so that the curvature of field of the luminous flux on the plane 7 is zero or almost zero, so an excellent image formation spot is obtained without any aberration. Further, the scanning lens is constituted which provides wide-angle deflection and is short in optical axis length, so plastic can be used as a lens medium. Thus, the small-sized, low-cost, and high-performance scanning lens is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical scanning device used in a laser beam printer or the like. More particularly, the present invention relates to a scanning lens system.

[Technical background of the invention]

Laser beam printers, which record image information by deflecting and scanning laser beams at high speed, have nine outstanding features: high speed, high resolution, and low noise, and are becoming smaller and cheaper. The demand for it is increasing rapidly. Therefore, as an optical head, which is an important improvement point, Yasugi's ability to reduce the size and cost of the optical scanning device is large.The optical scanning device can be broadly divided into a light source, a deflector, and a scanning lens. In particular, simplifying the scanning lens system is effective in reducing the size and cost. The scanning lens system is distorted so that the original spot moves at a constant speed on the scanning surface in accordance with the rotation #wa of the deflector, for example, when the deflector is a rotating polygon mirror and the light beam is deflected at a constant angular velocity. It has a distortion such that the deflection angle θ is proportional to the image height Y, and uniformly forms a light spot to a desired diameter everywhere on the tanshi surface. S! must have the ability.

Furthermore, in the case of a rotating polygonal mirror deflector, a surface tilt correction function is also required to compensate for variations in the tilt of each surface of the mirror (surface tilt error) t-. Conventionally, a high-performance scanning lens with a high resolution ability that combines these functions has inevitably been large, complicated, and expensive.

[Conventional technology]

Therefore, JP-A-54-98627. Japanese Patent Publication No. 55-772'
l,'? Kaisho 58-5706. Attempts have been made to develop a scanning lens as disclosed in et al. However, in Japanese Patent Application Laid-Open No. 54-98627, aberrations can be corrected widely and well for various values of parameters such as shape by using custom rotation for a deflector with sinusoidal vibration characteristics, but it is not possible to correct aberrations at high speed. For these reasons, the rotating polygonal mirror deflector, which is currently most widely used, has an aspherical surface to accommodate the constant angular velocity rotation characteristics, but it can only be used under extremely limited conditions as a special case. First, it is not possible to flexibly respond to various requirements such as the dimensions of the optical system, the light source, and the diameter of the dots that can be used safely.

However, in Japanese Patent Application Laid-Open No. 55-7727, the fo lens is constructed with a mo-convex lens, but it cannot be said that it has good focusing performance in terms of field curvature, etc.

Furthermore, in Japanese Patent Application Laid-Open No. 58-5706, a meniscus lens with positive power is used as a fo lens t[[It], but there is a problem in terms of curvature of the spherical truncated surface.1. To solve this problem, it is necessary to add a cylindrical lens that also serves as a surface tilt correction optical system.Furthermore, in order to provide all three rows mentioned above with a surface tilt correction function, a new lens must be added to the Ic. However, it is possible to keep the aberrations within the allowable range by increasing the optical axis length and narrowing the deflection angle. , which is difficult because the entire optical system becomes larger.

Incidentally, the material of the lens is also an important issue when considering miniaturization and cost reduction. Conventionally, glass has been used as the material for scanning lenses, but since the optical system requires diffraction-limited performance and the required precision is high, manufacturing costs such as polishing are high. methacrylate) (P
If plastics such as MMA), polycarbonate, and polystyrene are used as the lens medium, large-scale production by injection modification becomes possible, and thus inexpensive VcW manufacturing can be achieved. However, there are only a few types of optical plastic materials, and none of them have a higher refractive index than glass, so it is more difficult to reduce the number of lenses and downsize the optical system than with glass.

Taking all of these points into account, we have developed a system that can effectively correct aberrations regardless of the refractive index of the material and even with short optical axis lengths.
It can be seen that a lens shape with a large degree of freedom is desired.

(Problems to be solved by the invention) The present invention has been made in view of the above-mentioned problems.
The purpose is to provide a compact, low-cost, and high-performance optical scanning device, especially a scanning lens.

For the above purpose, the optical scanning device t of the present invention includes a light source that emits a narrow light beam, a rotating polygon mirror deflector that deflects and scans the light beam t at a collar angular velocity, and a rotating polygon mirror deflector that deflects and scans the light beam at a mirror surface of the rotating polygon mirror. a linear imaging optical system that forms a linear image parallel to the deflection plane in the vicinity;
a scanning lens for forming an image of the light beam deflected by the deflector on the surface to be scanned;
The distance Y from the optical axis to the focal length mm on the surface is almost completely proportional to the deflection angle θ. It is a single lens that has aspherical surfaces on both sides and has a rotationally asymmetrical surface tilt correction function on one or both surfaces so that both meridional field curvature aberrations are zero or almost zero.
-Special feature.

A companion means for solving the problem C] The optical scanning device of the present invention includes a light source that emits a narrow light beam, a rotating polygon mirror deflector that deflects and scans the light beam at a constant angular velocity, and a rotating polygon mirror deflector that deflects and scans the light beam at a constant angular velocity. It is equipped with a linear imaging optical system that forms a linear image parallel to the deflection surface near the mirror surface of the mirror, and a scanning lens that forms an image of the light beam deflected by the deflector onto the scanning surface. , the scanning lens is such that the distance Y from the optical axis to the position on the scanning plane is completely or almost perfectly proportional to the deflection angle θ, and the scanning lens can be used at any position on the scanning plane. Both surfaces are aspherical and one or both surfaces are configured rotationally asymmetrically so that both the spherical field curvature aberration and the meridional rectangular curvature aberration of the light beam are zero or almost VR2. ′′ to be a jade lens? ! j.

cPrinciple of the present invention] The principle of the present invention will be explained below using Figure 1, Figure 2, Figure @3, and Figure 4.

As mentioned above, the running lens is a light beam deflected at a constant angular velocity by a rotating polygonal mirror deflector.
It forms an image without curvature of the iron surface, and has the ability to give distortion so that the acid spot is scanned at a high speed on the scanned plane.

That is, as shown in FIG. 1, the light beam emitted from the light source is reflected by the mirror surface 8M at a deflection angle U corresponding to the rotation of the polygon mirror 5. The scanning lens 1 directs this light flux to a point TIl'l on the wave travel plane where the coordinate axis Y is proportional to the deflection angle θ.
: Set to end.

The scanning lens of the present invention is based on the Bem principle described below and is a single-lens lens that highly utilizes the aspherical features on both sides of T Sl n S2 shown in Figure 1, and is capable of wide-angle deflection with little aberration. It is.

The principle of #1 diagram of the lens surface shape according to the present invention is based on the assumption that the scanned light beam is very thin, expresses the light beam only by the parameters of the position and direction of the principal ray, and the imaging distance, and A certain point on the top has a direction i with respect to only the chief ray passing through it, vh, and its inclination and curvature are determined so as to change the imaging distance. So, if we think about this in terms of aberration correction, we can ignore spherical aberration and coma aberration, and calculate field curvature aberration and distortion aberration. This means that it is completely corrected, including even higher-order terms. The above assumption generally holds true in scanning optical systems such as laser beam printers.

Furthermore, in a scanning lens system, the chief ray of a light beam deflected at any deflection angle is always on the same plane (this is called the meridian plane), so in addition to the fact that the light beam is very narrow,
It can be seen that the points where the inclination and curvature are specified above are only on the curve where the meridian plane intersects the lens surface. Therefore, the second Fs modification principle of the present invention is to create a curve on the meridian plane, and at any point on the curve, the inclination and curvature in the meridian plane achieve the purpose of the scanning lens described above. Furthermore, it is assumed that a surface can be formed if the chief ray is given the curvature of a cross section perpendicular to the Kurami meridian (called a spherical cross section) at any point on the curve.

However, since the inclination and curvature in the meridian direction are connected continuously and the position of the lens surface in the meridian plane is shaped like Therefore, it is obvious that the scope of the present invention also includes an optical system to which the above-mentioned construction principles of 1. and 2. are applied only to the lens surface shape in the meridian plane.

Hereinafter, the Tonari principle of the lens according to the present invention will be specifically explained using the perspective view of FIG.

In Figure 1, the luminous flux (II-j-tl is converted to a luminous flux (Lm) by the surface 8iVC. The imaging distance measured from T< of the luminous flux (Lj) is gmj for the meridional luminous flux and gs for the spherical luminous flux.
Let it be i. In general, gmi and gsi are equal, and as mentioned above, the luminous flux is very narrow, so when dealing with the luminous flux (Ljl,
The imaging distance Q of the chief ray Lci and the meridian zero sphere? 7H
Now, the direction of the chief ray Lci after passing through lTi1Si1 can be controlled by the normal direction a4 of the surface SZ where τ<K. In addition, the imaging distance gmi and gs4 after passing through the surface s7 are the radius of curvature Rmi of the meridian section at T6 and the radius of curvature Rsi of the spherical section of the surface s6.
can be controlled with. Therefore, the function of focusing a single beam of light deflected at a certain angle to a position on the scanning plane where uniform speed scanning can be realized is determined by the position of a point on the lens surface and its differential amount (
Therefore, by making it continuous and providing the above function at each point with the lens surface corresponding to the light beam deflected at an arbitrary angle, it can be used for the purpose of scanning. This determines the lens shape. This is the first
There is a principle of Fs construction.

Now, as mentioned above, since the chief ray Lci etc. do not leave the meridian plane, the surface 81 ■ normal direction vector Gi is also within the meridian plane, and the optical axis and normal direction vector Gi shown in FIG. It is twisted with one degree of freedom of the angle αi formed by the line vector, and the surface 8
The calf cross-sectional curvature of i is the differential amount of the straight line αi, and the differential amount of the position on the 4th surface of the 1st plane αiFi plane a4, so in the end it specifies the inclination and curvature of the plane in the meridian direction. It can be seen that this has the same meaning as creating a two-dimensional curve on the meridian plane by solving the differential equations t, t-. Furthermore, since the curvature of the spherical section is determined without affecting the curve, it is determined for each point on the curve after one curve is created. This is the Harunari principle of Joy 2.

A scanning lens can be realized based on the above-mentioned principle, and the fact that it can be realized with an olfactory lens having both aspherical surfaces will be explained using the principle diagram in Fig. t-1!3. Happy 3rd map - and the paper is meridian o! Irk is displayed.

First, think about being in the meridian plane. The ray we just constrained is the chief ray, and the coordinates of the intersection TI of the non-transparent plane aX are the two degrees of freedom, where I and TI' are the imaging points. In order to constrain the travel position Y of the light beam i, we specify the face angle α of the surface at all positions with 11
For example, if you specify the coordinate 1 of the intersection point P1 with the optical axis (X s and the slope there is 0), VC is determined in one way like Sl, and you can specify the radius of curvature Rm l on that surface. The point 'l' where the luminous flux is not on the target plane x
The image will be formed at I. Conversely, if you specify the medium radius of curvature Rm l of the surface at all positions on the surface in order to constrain the imaging point, you cannot similarly specify α-o. , like this V
In order to constrain one degree of freedom among the parameters of the CC edge line to an arbitrary value of the deflection angle θ, Ktil surfaces are required, so in order to constrain the two degrees of freedom mentioned above, I &
Two low lens surfaces are required.

Next, considering the spherical beam, the constrained ^ is the spherical direction imaging distance (one degree of freedom of 181), which is the constrained state ``f'' in the meridian plane, that is, the shape of the curve is preserved. Since it can be controlled by adding curvature to the curve on the meridian plane in a direction perpendicular to it, there is no need to add a new surface to the two surfaces mentioned above.

Therefore, it can be seen that a single lens with only two lens surfaces is sufficient. Furthermore, since both surfaces are inclined at all positions of the lens surface and have specified curvature, a single lens must have both aspherical surfaces.

Now, here is the above 1! Let's consider the direct symmetry of E's nest and aspherical lenses. If two curves created in the meridian plane are rotated around some axis such as the optical axis, the degree of freedom of the radius of curvature in the direction of the sphere will be lost. Therefore, if rotational symmetry is given, the connection of the beam of the sphere will be reduced. Regarding zero-plane symmetry, which causes spherical field curvature aberration when controlling the image, since the light beam is always on the meridian plane, it is clearly symmetrical about the meridian,
Furthermore, assuming that the light flux passing through the optical axis has a deflection angle of 0, the light flux with a deflection angle of θ and the light flux with a deflection angle of 10 are under the same conditions, so they are perfectly symmetrical about a plane that includes the original axis and is perpendicular to the meridian plane.

In this way, the scanning lens of the present invention has symmetry except that there are two planes of symmetry, and as a result, spherical curvature aberration,
It is possible to completely correct meridional field curvature aberration and % distortion aberration.

Hereinafter, a specific method for realizing the shape of the scanning electric double aspherical lens of the present invention will be described using the principle diagram shown in Fig. @4. First, how to create and collect two curves on the meridian plane tN5? , reveal. As shown in Fig. 4, the lens surfaces 81 and 82 are respectively 9 distances 5laBN along the curve from the intersection point Pl*Pt with the optical axis, and the angle of inclination α1 from the perpendicular direction to the optical axis at that point. αt
It is defined in relation to Reexpressing this in orthogonal coordinates, if we take the plane 81m''2 and take the light @tx axis as the origin and the lens height direction as the y axis, then the coordinate value of point PR6P1 (Zt.us) e (zt
e yz)tl.

r; 1 = (,”” 5inaldsly1=door c
osα1d8N, 2=l・5ind2dB “1t*=
I” cosa2da@.

As shown in Figure 4, the deflection angle is 0.5 from the exit point on the yt axis. Nine bundles Lj (j=
0.1.2) intersects the surface 81m5M at 16Tl and the image plane S and TI, and the emission position and emission direction of the luminous flux are expressed as follows, that is, CO8θ PMTI = i0 Cs1ntl) cosθI T1T proverb = , -shio (,)
(2) aznθC08#I Tx"=JsC-)IItBe@, and further, let the radius of curvature of the meridian section at T1+Tl of the surface S1S! be I(ffil, R7FLl, respectively,
In addition, the meridional imaging distance 't fjWNa of the luminous flux L1aL2
(It is assumed to be 1ms.

According to the above description method, the purchasing principle of the nine lens shapes described above can be formulated. Formulation t - Below 1c shows 6
I will explain each item separately.

■The direction of the light beam is controlled by the inclination of the surface at the intersection of the surface 'le Sm and the light beam.

■Mother's Day 1#S! The imaging distance of the beam is controlled by the curvature of the surface at the intersection of the beam and the beam.

The coordinates of the intersection of the zero plane and the light beam are the same.

■Each point on the surface is smoothly continuous.

(2) The light beam forms an image on the scanning plane.

(2) The imaging point is scanned at a constant speed with the scanning plane.

The relationship between the inclination of the refractive surface and the direction of the light beam in (■) is based on the well-known law of refraction: ``1a'' z plane and IIl+L
s:in (a'1-θ) = nain(as-θ1
) = 81 sides (3) n8in (ffl-θ1) = ai
It can be expressed as n (as-as): 8a plane (4). This is the refractive index of the lens medium.

The relationship between the curvature of the surface and the imaging distance of the light beam in (2) can be determined by applying the relational expression of the meridional imaging distance when a thin light beam obliquely enters a surface with a certain curvature to the 81st surface and the E38th surface. 5) 8′“(6) is obtained.

Regarding (2), if the orthogonal coordinates of the surface position calculated using the above ω formula and the orthogonal coordinates of the refraction point of the ray calculated based on the above C) formula are equal, then JoCO8θ−f” si
nαsds* +Xt (7)υ J6sinθ= , /51coaalds1
(8)-1/ICO8θ1+J6cosθ=
/” 5ina2ds goose+Xs (9)
Am s inθ1+Ik6sitrθ= f”cox
αzdll* There is a relationship of 10. The angle x1 is the two coordinates ffi of the intersection of the plane H 凰 and the optical axis, xI t and the plane S! The X coordinate of the intersection of the original axis and the original axis is one perpendicular.

■The conditions for continuous surfaces are (7) to ((1
This means that the integration in the equation is possible. Further, the condition for the surface to be smooth is that the value C1,α of the surface is differentiable, and there is a relationship dJ Rml.

The condition for the image point to run at a constant speed on the tansashi plane in (①) is that the intersection of the image plane and the light beam (XX, 1) is XI = 71608θx + A1 cos θs + It6c
osθ α3Y = As 5inOt+Jt 5
inlj t +Ao sid (There is a relationship of 14, and scanning point C[YItli% deflector rotation ￥f
Note θ=lF/τ)a! 3 using Y == K, F” (θ)
It becomes αO. The curve F″″1 is the inverse function of F, τ
is a time parameter and K is a suitable proportionality constant. now,
Since the rotation characteristic is constant angular velocity deflection, F(τ) = ωτ ω: angular velocity α, YI =, - ω = ffj f = 5: constant (L8ω). Also, xI in ■2 is the scanning plane 2 coordinates 'r: represents the optical axis length.

The conditions for uniting on the scanning plane of (2) are that the meridional beam joining distance gm 2 in equation (6) is 4:3, and C2 expressed by equation 14.
is satisfied if it is equal to . That is, gm 2 = A z
(g As above, the principle of groove cutting of the lens shape according to the VC of the present invention is (3) (4) (5) (6) (η(8) <9
) Similar) 1ll) C2t:3 The formula 14 of 41609 was rejected, but by calculating these, the lens surface shape can actually be expressed directly by some kind of cedar. Of which, the deflection angle θ,
The initial meridional image formation gm6 is given at the time of emission and is known.

Also, the optical axis length
1+Xm The constant of constant speed running is a constant value that does not depend on the deflection angle θ. Therefore, the unknowns remain ``Isθ2゜C1,C2
,81,82,gml,gLrrL! , A6, 41.7
! , Hm 1, R'In! , Y-ko 14
Since the above-mentioned 14 equations are all independent, the simultaneous equations can be solved and the above-mentioned 14 variables can be expressed as a function of the deflection angle θ by enclosing them. Therefore, for example, when expressing the surface S1, the relationship between the inclination C1 and the distance S1 along the surface from the optical axis may be made to correspond to the deflection angle θ as a parameter.

By the way, since the above-mentioned 14-element simultaneous equations are non-linear and include differential terms and integral terms, they cannot be solved directly and must be solved using the direct solution method. One solution method can be considered, and the present invention is not limited thereto, but here, as a real matrix, this equation is actually numerically calculated using a method of numerical integration in a differential vector field, and the solution is that the lens shape is What can you decide? Let me show you.

Solving using differential vector equations means expressing all equations in differential form, assuming that all of the current variables are known, and calculating the increment (number of differential molecules) of each variable to find the next variable. It is something. If we rearrange Equation 14 and express it in differential form, Equations (3) and (4) become (dam − da) cos (
a! −ri= Qdtxl−da1 )cos(ds−
01) eOn(daz-dtl 1)cos(dx-
ds ) = (dam − dtl 2) cos(C2−
da) 8tJ(ω(6) formula and (lj (12 formulas together, (α-ri)dB-
Ne-m6os (C2-θri) blood,
Neri f L Qm t is (
C) (C) Eliminate simultaneous expressions.

Also, equations (7) to 10 are dB6 cosθ-＠sinθ411 = 8itw
r t dB t e4M6sind+
, -1 shi (1cogθdθ= cosαtcl!St
(15d
llcosθr −At 5intj 1 dtJ 1
+MocostJ-A65inedθ=5ina
2 dB 2till 5inlJ 1+L1 cas
tj 1411 t+ di(, 5intj -1-,
#g cosθdtJ = C08(1! dB 2e
'7J tJ 14 t, is 0=dltz cos(J 2-1p2 sid s
+ #1 cos θ bi right sin θ ldl' t + u
.

COBθ-! 65itLtJdtJ
e) JdY engineering == dJl2 si
nθ2+A2 cost, da2→temu-8tn”
t+A1 cosθ1 dθl ten dim 5itd
j +Ao cosθdl)
gxJCOX is dYI: K(F-'(θ))'dθ
Equation 119, which becomes (to), can be simply substituted into the unknown fine molecule e! 1
try da1 e d' 2 # αd 1 sda
2 @ d day t # d” 1 # di O # di
1 e dJl 2 @ dYI, upper (a)
~ Equation (a) can be easily solved because it is linear except that it is a quadratic equation by combining equations (2) and (to) into one equation, and can be easily solved using the known differential variable dθ. For example, dtJl−Fθt(Otaθ, C1, α2a S1m
52aI10+A1*Am)・da
Kfi can be expressed like θ force. If this goes up, θ1 is.

θ1-7"Fθ1dθ+θ?
By integrating with $2, the deflection angle θ can be expressed as a parameter. The angle θ1 is the initial stage. The actual calculation is based on the initial value of θ1. θ2. α1. α! + '1g i about 81
to a Jo * At * J2 VC'Dvste'd c1X1. X.

, using the directivity of XI, zo = X 1 i1 = X2 - XI θj!
2=X knee

can be calculated by numerical integration.

Now, as described above, the curve on the meridian plane of the lens shape of the present invention is materialized, and in the process of materialization, f
c constant? L * xl e x a Xxm fmOs
K is the degree of freedom that the lens shape of the present invention can take. That is, some suitable set of constants (X↑.

There is one lens shape for each of X*, xZ), and the present invention naturally includes all of these.

In addition, if the meridional initial connection distance gJ is set to infinity, that is, if the meridional light flux is closed to the golden flux before entering the scanning lens, the beam diameter etc. can be easily controlled and the optical system becomes easy to handle. As mentioned above, the scanning lens can of course be applied to parallel light beams.

Now, next, a method for determining the spherical breakage (fold distance t-controlled spherical breakage cross-sectional curvature ef-Re 1 , Ra z will be described).

<s> The relational expression of the meridional convergence distance when a narrow beam of light is obliquely incident is shown in the formula <6), but regarding the sphere defective imaging distance, The condition that there is an imaging point between gaz=lk2 130
It is. (b) θ! The radius of curvature Rs of the spherical section is determined by formula 380.

Rm is determined, and in the formula p6. il,j
! , α1. α1. θ, θ! , θ2 are known because the meridional curve has already been determined by the method described above, and g
Since 85 is given, the unknowns Vigsl, gs words
There are four Rj l a RII 2. Therefore, there are three redundant degrees of freedom in the three equations, and one of the unknowns can be determined appropriately.

Since the surface shape is simple f, if 88 ri is always set to infinity and the second term on the right side of equation (b) is OK, the surface becomes a surface that has no curvature in the μ sphere direction.

Note that the initial sphere missing distance g8o may be given arbitrarily, but if the deflector is a rotating polygon mirror, if gs6 = 0, the reflection point and the scanning point of the heald surface become a conjugate consideration point, which improves the surface tilt correction FR function. ? You can have it.

〔Example〕

Practical columns in which the lens straight shape was calculated based on the principle of construction of the lens shape according to the present invention are shown in Tables 1 to 9 and Figures 5 to 12.

As mentioned above, the lens shape of the present invention is determined by the refractive index n of the lens medium, the initial imaging separation go, and the position where the first and second surfaces of the lens intersect with the optical axis (plane center position) xl a xZ s
Six parameters t, including the optical axis length XX and Tanshi rate constant, can each be changed independently IC, and one lens shape exists for one set of one parameter. Therefore, there are a large number of ritual sequences that at first glance seem to have completely different shapes, and since it is impossible to list them all, I will only show the successive Yi-tM sequences here.

The calculation conditions common to the examples shown below are: refractive index of the proboscis lens medium s = 1.486 ◆ f'1 jll length from the deflection point to the runned beard surface x 2 depth 200u - The single deflector is a rotating polygonal mirror deflector The constant angular velocity deflection/initial meridian connection has an infinite distance gm6'ri, that is, the light beam before entering the scanning lens is a parallel light beam.

・The spherical cross-sectional curvature is only given to the 2nd surface.

- The initial spherical missing edge distance QBQ is O1. Therefore, the reflection point and the scanning point of the rotating polygon mirror become conjugate image points, and a surface tilt correction function is provided.

It is.

Note that the lens shape according to the present invention is not expressed by a simple number or formula, but the result is determined as a sequence of numbers, for example. For convenience, the shape of the curve on the meridian plane is expressed using the well-known aspherical coefficients: Coordinate value.

The curvature of the spherical cross section of the second surface R82VC')Vs is expressed as Rs 1= R'j *+Ay ''+Ey '+Cy
'10Dy'+Ey'' (represented by 38, the error from the true shape when approximated in this way is 0.0
It is about 0.01% to 0.01 inch.

In Table 1, Table 2, and Table 3, there are coefficients that indicate the shape of the curve on the meridian plane of @1 surface S1.
l IIi k, 4th table, @5fi, 6th fiK @2f
fiS, O coefficient indicating the curve shape on the meridian plane Rmz, B
@,C! aD2+Bst, 7th fi, wXg table, @9 table shows the coefficient Ram A that shows the change in the radius of curvature in the direction of the spherical cut section.
8・C8・D8. Is it? , parameter θe a x
th The effective deflection angle θe is a parameter used in place of the scanning speed coefficient in Equation 18 above, and the effective scanning width 'k
If it is set as 200 m, then θ-=ya (rαd)@
This is the position of the point where the plane 82 intersects with the original axis. Note that under the above-mentioned common calculation conditions, the parameter set θe a xt
Lenses with the same r Xx Off & are the same lenses.

Furthermore, the outline of the curve shape on the meridian plane for β in the row shown in Fig. 5 is shown in Figs. 5 to 12 along with the original schematic diagram. Since the transferred music 111i1 is symmetrical about the optical axis, the side opposite to the original axis is omitted.

In all the implementations listed here, in accordance with the wt formation principle of the present invention, spherical iron surface curvature aberration and meridional 1-plane curvature aberration are completely eliminated, and the distortion characteristics are such that the short point moves at a constant speed. completely defined.

However, perfection is an ideal state, and the lens shape at the east end has slope curvature aberration and distortion due to calculation errors when calculating the shape, manufacturing errors, etc. occurs to some extent. Of course, these aberrations have a certain tolerance range, and within that range, the lens is effective as a scanning lens, so the present invention does not exclude them.

1st Table 40, 40. 60. 289.26-. 1292E
-05,1O12E-09,42QOE-12-,31
59E-15 Table 2 45.40. 80. 227.44-. 6081E
-06,3567E-09-,8526E-13,15
40E-16 3rd x, m, l;ju, 8[1,25-,200
3E-0' rye ooooooooooo 066
C; 6C; 6C;
o 66c; 666 66t666 66o'cic
c; Table 5 45.40.80. -80.12-. 1658E-06
,3407E-09-,1[144E-12,4259
E-16 Table 6 50.25+130. -92.22.12511E-L
lcl, co%ZI+;-1u-, Au//W-AJ4t
lu:111-A/Table 7 40, 40. 60. 18. [12,2292C
-02-, 3520E-05, 7349E-011-,
6105E-11, 1782E-14 Table 8 45.40. 80. 20.91. 3000E
-03,2579E-05-,2011E-08,58
93E-12-, 5341E-16 Table 9 Figure 13 shows the entire optical system of a laser beam printer using an embodiment of the lens shape based on the VC of the present invention.
The light beam emitted from the semiconductor laser 2, shown in the I+ view, becomes a consonant light beam by the collimator lens 3, and is converged only in the spherical direction by the cylindrical lens 4, forming a linear image near the mirror surface of the rotating polygon mirror deflector 6. do. The light beam is deflected at a constant angular velocity within the meridian plane by the rotation of the polygon mirror 5, and after passing through the set meal lens 1 according to the present invention, the light beam is formed on the photosensitive drum 7 in the one-sphere direction, where the mirror surface and the photosensitive drum surface are It is a conjugate connection point and forms a surface tilt correction system. The image point is fixed at a constant velocity in the axial direction of the photosensitive drum 7 by the set food lens IVc of the present invention, and is focused on a straight line without field curvature. The photosensitive drum rotates by one pitch for each scan, and as this is repeated, a hidden spot is formed on the photosensitive drum.

〔effect〕

As described above, in the optical scanning device of the present invention, the lens for set meals has a distortion such that the light beam moves at a constant speed on the surface to be scanned, and Because it is a single lens with aspherical surfaces on both sides and rotationally asymmetric on one or both sides so that the field curvature aberration of the light beam at is zero or almost zero, even with a single lens there is almost no aberration and an extremely good imaging spot. In addition, a scanning lens with a wide angle deflection and a short optical axis length can be obtained. Furthermore, for the same reason, even if the lens medium has a low refractive index, there is no problem with the design, and therefore the lens medium can be made of plastic. Therefore, it is possible to provide a compact, low-cost, and high-performance optical scanning device. It has the effect fc.

Furthermore, by purchasing a lens that forms an image at β angle in the direction of the spherical defect near the reflection point of the polygon mirror, it is possible to provide the FM function for correcting the surface tilt of the polygon mirror without adding a new lens. It is also advantageous to be able to provide a high-performance optical set meal device at a lower price.

Drawing Library 11i Explanation 41 Figure 1''!: A principle diagram showing the outline of the fixed meal device of the present invention, the second figure is a principle for explaining the principle of forming the lens shape of the present invention. Figure 3 is a principle diagram for explaining that the lens for set meals of the present invention can be realized with a bi-aspherical lens of the olfactory bulb, and Figure 4 shows the method for calculating the shape of the lens for set meals of the present invention. 5 to 12 are diagrams showing the implementation sequence of the lens shape of the present invention, and Figure 13 is a diagram showing the implementation sequence of the entire light traveling device of the present invention. It is a diagram.

In the figure: 1. Lens for spotting 2. Half-length laser 5. Polygonal mirror 6. E-rotating polygonal deflector 7. Photosensitive drum and Applicant Seiko Epson Ajishiki Company Agent Patent Attorney Mogami WIftl1 person''・1・・
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· "of' Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 S! Arrow-40 χriX+ χ=X2 18WI χ−×1 χ1×2 Figure 9.

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1×1 χ×2 Figure 10.

S〉×1　　　χ　×2 Figure 1I jIIz diagram

Claims (1)

[Claims] (1) A light source that emits a narrow light beam, a rotating polygon mirror deflector that deflects and scans the light beam at a constant angular velocity, and a line that images the light beam into a line parallel to the deflection surface near the mirror surface of the rotating polygon mirror. a scanning lens that forms an image of the light beam deflected by the deflector on a scanned plane; The distance Y and the deflection angle θ are completely or almost completely proportional, and both the spherical field curvature aberration and the meridional field curvature aberration of the light beam at any position on the scanned plane are zero or almost zero. An optical scanning device characterized in that it is a single lens having an aspherical surface on both sides, one or both of which has a rotationally asymmetrical structure and has a surface tilt correction function.