JPS63121009A - Rotary deflecting mirror for optical scan of optical printer - Google Patents

Abstract

PURPOSE:To make an expensive correcting mean unnecessary, by using a mirror having a spiral affine circular cone surface as a rotating deflecting mirror and forming the affine circular cone surface to such a curved surface that one circumference whose center is on the axis of a cylindrical member is contained in the surface as a base circle and the vertical angle of the generator continuously changes in accordance with the rotational angle. CONSTITUTION:A mirror 5 has a spiral affine circular cone surface and one circumference 6 whose center is on the axis of a cylindrical member 4 and radius is (r) is contained in the surface. The mirror surface has such a curved surface that the circumference 6 is the base circle and the vertical angle of the generator of the circular cone continuously changes in accordance with the angular position theta of the generator in the rotating direction. Since the vertical angle of the generator, namely, inclined angle to the axis 3 at each rotating position theta of the mirror surface 5 continuously changes in accordance with the rotating angle theta, direction of reflecting laser light varies in a plane and is deflected in the space between the direction of an angle theta0 and another angle theta1 around a reflecting point, when the cylindrical member 4 is rotated at a fixed angular velocity. As a result, a photosensitive body 1 is linearly scanned by the laser light 12. Therefore, a change in the position of the reflecting point of the laser light can be prevented.

Description

TECHNICAL FIELD The present invention relates to a rotating deflection mirror for optical scanning of an optical printer that deflects laser light over a predetermined range using a rotating mirror to write image information on a photoreceptor.

Prior Art Conventionally, optical writing optical systems such as optical printers and digital copying machines scan a photoreceptor with a laser beam modulated by an image information signal to expose the photoreceptor and create an image using an electrophotographic process. As a deflection means for scanning, a rotating polygon mirror 32 that rotates at a constant speed around a certain axis 31 is widely used as shown in FIG. When this rotating polygon mirror rotates in the direction shown by the arrow in the figure, the reflection direction 34 of the laser beam 33 coming from a certain direction is deflected within a certain angular range.
Thereby, the photoreceptor surface 35 arranged parallel to the axis 31 of the mirror can be optically scanned in a direction perpendicular to the axis 31.

However, when this rotating polygon @ is used as a means for deflecting laser light, the position of the reflection point changes as shown by Δt in the figure depending on the rotation angle of the mirror, and the imaging position changes. requires a complex lens. Moreover, when the rotating polygon mirror 32 rotates at a constant angular velocity, the reflected light ray 34
is also deflected at a constant angular velocity, so when the photoreceptor 35 is scanned in a straight line, the scanning speed becomes higher toward both ends of the scanning width than at the center, so the scanning speed is equal across the entire scanning width. Moreover, it is necessary to insert an f-theta lens between the rotating polygon mirror 32 and the photoreceptor 35 so as to form an image on a straight line, which has the disadvantage of increasing costs.

Purpose: In view of the above-mentioned drawbacks of the rotating polygon mirror widely used as a deflection means for optical scanning in conventional laser printers, etc., the present invention provides a rotating deflection mirror in which the position of the reflection point of the laser beam does not change, and furthermore, , a rotating deflection mirror such that the laser beam moves at a constant velocity on the writing surface? The purpose is to provide.

Configuration The rotating deflection mirror of the present invention for achieving the above object includes a spiral pseudo-conical surface formed on one end surface of a cylindrical member rotatable around an axis parallel to the scanning direction of the image writing surface. The quasi-conical surface includes one circumference centered on the axis of the cylindrical member on its surface, the circumference is the base circle, and the apex angle of the generatrix corresponds to the rotation angle. It is characterized by a curved surface that changes continuously.

In the above configuration, if the apex angle of the mirror's generatrix is changed equiangularly with respect to the rotation angle, when the mirror is rotated around the axis at a constant angular velocity, the incident light will be reflected by the mirror at a fixed point. The reflected light moves at a constant angular velocity. Furthermore, if the change in the apex angle of the generatrix of the mirror is set so that the laser beam is reflected by the rotation of the mirror at a constant angular velocity and moves linearly at a constant velocity on the image writing surface, fCf-θ, which is conventionally required, can be changed.
The lens can be omitted.

Embodiments of the present invention will be described in detail below with reference to the drawings.

As illustrated in FIG. 1, the rotating deflection mirror of the present invention is a cylindrical member rotatable at a constant angular velocity around an axis 3 parallel to the scanning direction 2 of a photoreceptor 1 on which an image is to be written by a laser beam. It is formed on one end surface of 4. As seen in the figure, the shape of this mirror 5 is a spiral pseudo-conical surface, and a circumference 6 having a radius r centered on the axis of the cylindrical member 4 is included on the surface. ing. The mirror surface has a circumference 6 as a base circle, and is a curved surface such that the apex angle of the generatrix of the cone changes continuously according to the rotational angular position θ (FIG. 2) of the generatrix.

The laser beam 8 emitted from the laser diode 7 parallel to the axis 3 of the cylindrical member 4 is made into a parallel beam by the collimator lens 9, passes through the first cylindrical lens 10 and the aperture lli, and is directed to the above-mentioned circumference of the rotating deflection mirror 5. 6
is incident on the top at a predetermined spatial position. The reflected light 12 travels within a plane determined by the axis 3 of the cylindrical member 4 and the axis of the optical path of the incident laser beam 8 and forms an image on the photoreceptor l.

Since the apex angle of the generatrix of the mirror surface 5 at each rotational position θ, in other words, the inclination angle with respect to the axis 3, changes continuously according to the rotational angle θ, the cylindrical member 4 When rotated at a constant angular velocity, the direction of the reflected laser beam 12 changes within the above plane, and the reflected laser beam 12 is deflected between the direction of the angle and the direction of θ1 around the reflection point, and 1 in a straight line.

Now, in FIGS. 1 and 2, when the cylindrical member 4 is rotated by θ from the reference position, the inclination angle with respect to the horizontal of the generatrix of the spiral conical surface 6 passing through the laser beam reflection point is 1ce>
Then, the condition for the cylindrical member 4 to rotate at a constant angular velocity and the reflected laser beam to be deflected at a constant angular velocity is 01 = Cg "°°°°°°° (1) - earth throw fC so, 'Cg = constant, gl(-dθ, °, where = 3θ + b
・・・・・・・・・(1'), where a and b are constants, the inclination angle of the mirror surface at the position of θ=0 `` ''(0), θ=
If the inclination angle rough is 2π, then (2π] crosspiece.) = Σ[θ. -1〕 ・・・・・・・・・
...(2) is the sum of minute and horse.

θ Pa・ = (Da [2π] − Sai D))・50 g O・
・・・・・・・・・(4) (2) , (3) and (4
) From the formula, = (!L knee) θ
−Σ ]4π 2 That is, (a and b in Equation 15 are each −[”, b=θ.−100) a−4π.

The light beam reflected by this mirror is deflected at a constant angular velocity, so when scanning a photoreceptor with this light beam, the scanning speed increases from the center of the scanning width to both ends, and the image formation point is strictly It will move off the top of your body. However, this is different from the f-
This problem can be solved by inserting the θ lens 13 into the optical path of the reflected polarized light. Furthermore, by inserting the second cylindrical lens 14i near the photoreceptor in the writing optical path,
Even if the direction of the tangent perpendicular to the incident light at the laser beam incident position on the surface of the mirror 5 is slightly tilted from the direction perpendicular to the radius passing through the incident point, it is possible to scan on a predetermined scanning line. Become.

As shown in FIG. 3, a mirror 5''i consisting of a part of a twisted conical surface of the same shape is attached to one end of one cylindrical member 4 in series on the circumference for one rotation. By providing them at equal intervals, the photoreceptor can be scanned multiple times per rotation of the cylindrical member 4.

Furthermore, as another example, by determining the shape of the mirror so that the reflected light reflected by a rotating deflection mirror that rotates at a constant angular velocity moves linearly at a constant velocity on the image writing surface, It becomes possible to omit the lens. In that case, the inclination of the generatrix at each rotational position of the spiral pseudo-conical surface of the rotating deflection mirror can be determined as follows. Figure 4 is a side view of this embodiment, and Figure 5 is a side view of the mirror. FIG.

In the figure, the laser beam 8 emitted parallel to the axis of the cylindrical member 24 is transmitted to the axis 23 of the cylindrical member 24 included on a rotating mirror surface 25 forming a spiral pseudo-conical surface.
It is incident on the circumference 26 of the radius [゛ with ゛ as the center and 1. The reflected light beam is deflected in a plane determined by the axis 23 of the cylindrical member 24 and the optical axis of the incident laser beam 8 according to the inclination angle of each part, and is deflected at a distance t from the optical axis of the incident laser beam. A certain image writing surface l is optically scanned over a length W centered on the position where the laser beam is perpendicularly incident on the writing surface. , height from the center of the writing width of the laser beam′
J&: If we assume ■, the condition for the laser beam to move linearly at a constant velocity on the writing surface is the mouse = Ch...
・(5) Assuming that Ch is a constant 0, the height of the laser beam on the writing surface when θ=0 is he)
, If the height of the laser beam when θ=2π is i h (2π), then It<03 ” -2 (6) 11 (
2π) = i°°°°°°°°° (7) (6) , (7
) from lol ・・・・・・・・・(
8) h(@ = −θ−Σ 2π gift ・・・・・・・・・(9
)g('s: is the drawing force, and the inclination angle of the mirror surface at each rotation position is 0() is 1(
o) = Ctsn (fluent) - figure] ・・・・・・
...It is represented by (lO).

In the case of this embodiment as well, by providing a plurality of mirrors of the same shape in a series at equal intervals in the circumferential direction, it is possible to perform scanning a plurality of times for one rotation of the cylindrical member.

Effects As described above, according to the present invention, the writing surface can be scanned by keeping the position of the reflection point of the laser beam constant and deflecting it.
Furthermore, since uniform speed scanning becomes possible, expensive correction means is not required, contributing to cost reduction.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a plan view of the rotating deflection mirror surface, FIG. 3 is a perspective view showing a rotating deflection mirror of another embodiment of the present invention, and FIG. 4 5 is a side view of still another embodiment of the present invention, FIG. 5 is a plan view of the rotating deflection mirror surface thereof, and FIG. 6 is a schematic diagram showing an example of a conventional rotating mirror for optical scanning. l... Photoreceptor (image writing surface) 2... Scanning direction 3.
...Rotating deflection mirror center line 4...Cylindrical member 5...
・Rotating deflection mirror 6... Circumference 8... Laser beam 12... Reflected beam Figure 1

Claims (4)

[Claims] (1) Laser light emitted from a laser light source in a certain direction is deflected and reflected within a predetermined angle range by a rotating mirror, and this reflected light is focused on an image writing surface to illuminate the image writing surface. In the rotating deflection mirror of the scanning optical printer optical scanning device, the rotating deflection mirror has a spiral shape formed on one end surface of a cylindrical member rotatable around an axis parallel to the scanning direction of the image writing surface. a mirror with a conical surface shape, the pseudo-conical surface includes a circumference centered on the axis of the cylindrical member on its surface, and the circumference is a base circle;
A rotating deflection mirror characterized by having a curved surface such that the apex angle of the generatrix continuously changes according to its rotation angle. (2) The rotating deflection mirror according to claim 1, wherein the apex angle of the generatrix of the mirror changes equiangularly with respect to the rotation angle. (3) The change in the apex angle of the generatrix of the mirror described above is set so that the laser beam reflected by the constant angular velocity rotation of the mirror moves in a uniform linear motion on the image writing surface. A rotating deflection mirror according to claim 1. (4) Rotational deflection according to claim 1, characterized in that the mirrors are formed in a series of a plurality of mirrors in the same shape at equal intervals in the circumferential direction around the axis of the cylindrical member. mirror.