JPH09159963A - Self-amplification deflecting and scanning optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enlarge both the deflection angle and the diameter of a beam deflected for the third time even in the case of the small rotational angle of a rotary polygon mirror by making the beam incident on the rotary polygon mirror three times by using two sets of transmission optical systems. SOLUTION: The beam emitted from the laser 1 is made incident on the reflection surface t1 of the rotary polygon mirror 5 for the first time. The beam reflected by the reflection surface t1 passes through a lens 31, a returning mirror 33 and a lens 32, is guided to the mirror 5 again, and made incident on the reflection surface t2 for the second time. The beam reflected by the relflection surface t2 passes through a lens 41, returning mirrors 43 and 44 and a lens 42, further it is guided to the mirror 5 again, and made incident on the reflection surface t3 for the third time. The beam reflected by the reflection surface t3 passes through an fθ optical system 6 and is made incident on a surface 7 to be scanned. The surface 7 is scanned with the beam deflected by the mirror 5 at constant speed and a beam spot is formed on the surface 7 without causing the curvatute of field by the fθ optical system 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical system used in an image forming apparatus such as a laser printer or a facsimile, and particularly when a beam is deflected by using a rotary polygon mirror, a transmission optical system is used to amplify the deflection angle. The present invention relates to a self-amplifying deflection scanning optical system that enables high-speed scanning.

[0002]

2. Description of the Related Art In a scanning optical system using a rotary polygon mirror, a method of increasing the scanning speed which is the number of scans per unit time includes a method of increasing the rotation speed of the rotary polygon mirror and a method of increasing the rotation speed of the rotary polygon mirror. A method for increasing the number of reflecting surfaces is known.

However, increasing the rotation speed increases the air resistance of the rotary polygon mirror, requires more power for the driving device for the rotary polygon mirror, and causes an increase in the size of the driving device and noise.

On the other hand, in the method of increasing the number of reflecting surfaces of the rotary polygon mirror, when the number of reflecting surfaces increases, the deflection angle of the beam per reflecting surface decreases in inverse proportion to this, and the beam finally scans. In order to obtain a predetermined image height on the surface to be scanned, it is necessary to increase the optical path length. Generally, when the spot diameter of the scanning beam on the surface to be scanned is constant, the beam diameter deflected by the rotating polygon mirror increases in proportion to the optical path length. Also needs to be larger. In order to deflect and scan a beam having a large beam diameter over the entire beam width so as to reduce vignetting on the reflecting surface of the rotating polygon mirror, a rotating polygon mirror having a large outer diameter is required. Therefore, it is usually necessary to increase the outer diameter of the rotary polygon mirror in order to increase the number of reflecting surfaces of the rotary polygon mirror while keeping the beam diameter on the surface to be scanned constant. However, in a rotating polygon mirror with a large outer diameter, air resistance increases, and as in the case of increasing the rotation speed, a large amount of power is required for the driving device of the rotating polygon mirror, which causes an increase in the size of the driving device and noise generation. I will invite you.

In order to solve such a problem, in order to increase the number of reflecting surfaces of the rotary polygon mirror without increasing the outer diameter of the rotary polygon mirror, a beam deflected by the rotary polygon mirror is used by a transmission optical system. A method of again injecting the light into the rotary polygon mirror and deflecting the light is disclosed in Japanese Patent Laid-Open No. 51-52
No. 32340 and JP-A-53-97448. Of these, JP-A-51-3234
In JP-A-0, a beam having a relatively small beam diameter is made incident on the rotating polygon mirror, the beam diameter of the deflected beam is enlarged, and the beam is made incident on the rotating polygon mirror again so as to follow the rotation of the reflecting surface of the rotating polygon mirror. By doing so, it is possible to deflect and scan a beam having a large beam diameter with high scanning efficiency. In JP-A-53-97448, the beam deflected by the deflector is guided to the deflector again by the transmission optical system, and the beam emitted from the transmission optical system is made to the optical axis as the deflector rotates. The transmission optical system is configured so that the angular direction to be turned is opposite to the rotation direction of the deflector, and the deflection angle can be amplified.

[0006]

However, when the number of surfaces of the rotary polygon mirror is increased in order to further increase the scanning speed, the method proposed in the above-mentioned Japanese Patent Laid-Open No. 51-32340 is used. Since it has almost no effect of amplifying the deflection angle, the deflection angle becomes small, and the optical path length becomes long in order to obtain a predetermined image height on the surface to be scanned, resulting in an increase in size of the apparatus.

On the other hand, in the method proposed in Japanese Patent Application Laid-Open No. 53-97448, even if the number of reflecting surfaces of the rotary polygon mirror is increased, the deflection angle can be amplified by the structure of the transmission optical system to obtain a wide deflection angle. it can. However, since the transmission optical system is configured so that the first reflecting surface and the second reflecting surface are substantially conjugate, the transmission optical system should be configured so that the amplification effect of the deflection angle is increased. Then, the optical magnification of the transmission optical system becomes low, and the beam diameter of the beam deflected the second time becomes small.

By the way, in recent years, with the increase in speed and resolution of image forming apparatuses such as laser printers, in the scanning optical system, simultaneously with the increase in speed, the beam spot on the surface to be scanned is changed to correspond to the increase in resolution. It is required to reduce the diameter. For this reason, in the beam deflecting device, it is required to increase the scanning speed and simultaneously deflect and scan a beam having a large beam diameter. However, JP-A-53-974
In the method proposed in Japanese Patent Laid-Open No. 48, it is difficult to achieve both high speed scanning and high resolution by increasing the beam diameter of the deflected beam.

In response to such a demand, in the scanning optical system using the transmission optical system, the amplifying action of the deflection angle is increased in order to increase the scanning speed, and finally the deflection is performed in order to increase the resolution. As a method of increasing the beam diameter of the beam to be reflected, a method of arranging two sets of transmission optics and deflecting the beam by a 3 degree rotating polygon mirror can be considered. However, Japanese Patent Application Laid-Open
In the case of using two sets of transmission optical systems disclosed in Japanese Patent Application Laid-Open No. 3-97448, there is an action of amplifying the deflection angle by the first transmission optical system that guides the beam deflected once to the rotary polygon mirror. The deflection angle of the beam deflected at a certain degree is larger than the deflection angle of the beam deflected at the first degree. Then, the numerical aperture of the second transfer optical system that guides the beam deflected a second time to the rotary polygon mirror becomes larger than the numerical aperture of the first transfer optical system, and spherical aberration in the second transfer optical system and The amount of coma aberration increases, which leads to deterioration of the imaging performance on the surface to be scanned, and the cost increases because the aperture of the second transmission optical system also increases. Further, even if there is no amplification effect of the deflection angle of the first transmission optical system, if the beam diameter of the beam incident on the second transmission optical system is large, the imaging performance is similarly deteriorated.

That is, the object of the present invention is to
Even if a beam with a large beam diameter is deflected and scanned at a wide angle by using a rotating polygon mirror having a large number of reflecting surfaces, two sets of transmission optical systems are arranged to make the beam incident on the rotating polygon mirror. High-speed, with no deterioration in imaging performance and no increase in cost
The present invention provides a high-resolution, high-quality, low-cost self-amplifying deflection scanning optical system.

[0011]

SUMMARY OF THE INVENTION A self-amplifying deflection scanning optical system according to the present invention comprises a rotary polygon mirror having a plurality of reflecting surfaces for deflecting a beam by a rotary motion, and the first reflecting surface of the rotary polygon mirror. For guiding the focused beam to the rotating polygon mirror
And a second transfer optical system for guiding the beam emitted from the first transfer optical system and deflected by the rotating polygon mirror to the second position to the rotating polygon mirror. Rotation of the first transmission optical system so that the deflection angle of the beam emitted from the second transmission optical system and deflected the third time is larger than the deflection angle of the beam deflected the first time. System and the second transmission optical system, which is a self-amplifying deflection scanning optical system, wherein the beam deflected a second time by the rotation of the rotary polygon mirror has a deflection angle of the beam deflected the first time. It is characterized in that it is less than the deflection angle.

Further, the self-amplifying deflection scanning optical system of the present invention comprises a rotating polygon mirror having a plurality of reflecting surfaces for deflecting the beam by a rotational movement, and a beam deflected by the reflecting surface of the rotating polygon mirror for the first time. A first transfer optical system that guides the rotary polygon mirror, and a second transfer optical system that guides a beam emitted from the first transfer optical system and deflected by the rotary polygon mirror a second time to the rotary polygon mirror. And the deflection angle of the beam emitted from the second transfer optical system and deflected for the third degree becomes larger than the deflection angle of the beam deflected for the first time by the rotation of the rotary polygon mirror. In the self-amplifying deflection scanning optical system having the first transmission optical system and the second transmission optical system as described above, the beam deflected by the rotating polygon mirror for the second time is a parallel beam or a focused beam. It is characterized by being.

Further, the beam that passes through the optical axes of the first transmission optical system and the second transmission optical system and scans the scanning center on the surface to be scanned is once moved to the reflection surface of the rotary polygon mirror.
The second and third degrees are characterized in that they are incident at right angles in the main scanning cross section.

Furthermore, the chief ray of a beam other than the beam passing on the optical axis in the first transfer optical system intersects with the optical axis of the first transfer optical system.

Furthermore, the beam which is emitted from the first transfer optical system and is deflected a second time is incident again on the final lens which constitutes the first transfer optical system.

Furthermore, the second transmission optical system is characterized in that it is composed only of a plane mirror provided facing the rotary polygon mirror.

[0017]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a main-scan sectional view of an optical system showing the basic principle of the present invention, in which each optical element is shown in a developed state along the optical axis for easy understanding. In FIG. 1, 1
Denotes a light source such as a semiconductor laser, and 2 denotes a beam shaping optical system for shaping the divergent beam emitted from the light source 1 into a predetermined beam shape. Reference numerals t ₁ , t ₂ and t ₃ respectively denote the same reflecting surface of the rotating polygon mirror (not shown), and 3 is for guiding the beam deflected by the reflecting surface t ₁ to the reflecting surface t ₂ of the rotating polygon mirror again. The first transfer optical system 4 is a second transfer optical system for guiding the beam deflected by the reflecting surface t ₂ to the reflecting surface t ₃ of the rotary polygon mirror again. Beam shaping optical system 2, 1st
The optical axes of the transmission optical system 3 and the second transmission optical system 4 are coincident with each other via the reflecting surfaces t ₁ and t ₂ .

The beam emitted from the light source 1 passes through the beam shaping optical system 2 and is incident on the reflecting surface t ₁ for the first time. The beam reflected by the reflecting surface t ₁ is again guided to the rotary polygon mirror by the first transmission optical system 3 and is incident on the reflecting surface t ₂ for the second time. The beam reflected by the reflecting surface t ₂ is further guided to the rotating polygon mirror by the second transfer optical system 4 and is again reflected by the reflecting surface t _3.
Incident on the third time. The beam reflected by the reflecting surface t ₃ enters an unillustrated surface to be scanned through an unillustrated fθ optical system. The rotating polyhedron when the optical axes of the beam shaping optical system 2, the first transferring optical system 3 and the second transferring optical system 4 coincide with each other via the reflecting surfaces t ₁ , t ₂ and t ₃ of the rotating polygonal mirror. The rotation angle of the mirror is set to 0, and the beam emitted from the light source 1 at this time passes through the respective optical axes of the first transmission optical system 3 and the second transmission optical system 4 to set the scanning center on the surface to be scanned. Each optical element is configured to scan. Dotted lines m _{1 to} m ₅ shown in FIG. 1A are principal rays of the beam deflected when the rotary polygon mirror rotates by the rotation angle φ. When the rotary polygon mirror rotates by the rotation angle φ, the reflecting surface t ₁ is inclined by φ with respect to the optical axis. Beam incident on the reflecting surface t ₁ is deflected by the reflecting surface t _1, the main ray m ₁ is emitted at an angle of 2φ with respect to the optical axis. The angle of the principal ray m ₁ with respect to the optical axis is defined as the _first deflection angle ω ₁ (= 2φ). The beam emitted from the reflecting surface t ₁ is refracted by the first transmission optical system 3, and the principal ray m ₂ forms an angle of ψ ₁ with respect to the optical axis in the same rotation direction as the rotation angle of the reflecting surface t _2. Becomes a beam,
It is incident on the reflecting surface t ₂ at a height h ₁ from the optical axis. The incident beam is reflected by the reflecting surface t ₂ and the principal ray m ₃ emerges as a beam m ₃ forming an angle of 2φ−φ _{1 with} the optical axis. The angle of the principal ray m ₃ of this beam with respect to the optical axis is defined as the _second deflection angle ω ₂ (= 2φ−ψ ₁ ). The beam emitted from the reflecting surface t ₂ is refracted by the second transmission optical system 4, and the principal ray m ₄ makes an angle of ψ ₂ with respect to the optical axis in a rotation direction opposite to the rotation angle of the reflecting surface t _3. It becomes a beam and enters the reflecting surface t ₃ at a height h ₂ from the optical axis. The incident beam is reflected by the reflecting surface t ₃ , and the principal ray m ₅ is 2φ + ψ with respect to the optical axis.
_A beam with _two angles is emitted. The angle of deflection of the principal ray m ₅ of this beam with respect to the optical axis is the third deflection angle ω ₃ (= 2
φ + ψ ₂ ). In this way, the principal ray m ₄ of the beam emitted from the second transmission optical system 4 forms an angle ψ ₂ in the rotation direction opposite to the rotation angle of the reflection surface t ₄ with respect to the optical axis, and the reflection surface t ₃ By injecting the light into the third direction, the third deflection angle ω ₃ is amplified by ψ _{1 with} respect to the _first deflection angle ω ₁ . The principal ray m ₂ of the beam incident on the reflecting surface t ₂ is incident on the reflecting surface t ₂ at a height h ₁ from the optical axis, the beam rotation of the reflecting surfaces t ₂ so as not to protrude from the reflective surface t ₂ This is because the incident light follows the. For this h ₁ , based on the inscribed circle radius of the rotating polygon mirror, the number of reflecting surfaces, the rotation angle, and the beam diameter on the reflecting surface t ₂ ,
The allowable amount is calculated from the condition that the beam does not protrude from the reflecting surface. The first transfer optical system 3 is configured so that h ₁ satisfies the above-mentioned allowable amount. The height h ₂ of the above reflection surface t ₃ of the principal ray m ₄ of the beam incident on the reflecting surface t ₃ are similarly beam allowable amount is calculated from the condition that does not protrude from the reflecting surface t _3, it is calculated The second transfer optical system is configured to satisfy the allowable amount. With such an amplification effect of the deflection angle, a large beam deflection angle can be obtained even with a small rotation angle of the rotary polygon mirror, and the deflection angle can be secured even when the number of surfaces of the rotary polygon mirror is increased. The scanning optical system can be easily increased in speed.

In a self-amplifying deflection scanning optical system using a transmission optical system, the deflection point and the next deflection point guided by the transmission optical system have an almost optical conjugate relationship via the transmission optical system. . For this reason, when only one set of transmission optical system is used, there is a restriction that an attempt to increase the amplification effect of the deflection angle reduces the optical magnification of the transmission optical system and the beam diameter deflected the second time. . It is possible to increase the beam diameter of the beam deflected the second time by increasing the beam diameter of the beam deflected the first time on the reflection surface. Since the length is short, if the beam deflected for the first time does not stick out from the reflecting surface, the scanning efficiency is reduced, and as a result, the deflection angle for the second angle becomes small. The scanning efficiency is 3
The ratio of the rotation angle of the rotary polygon mirror for scanning the scanning area on the surface to be scanned to the angle obtained by dividing 60 ° by the number of faces of the rotary polygon mirror is shown. By increasing the scanning efficiency, the same scanning speed (per unit time) Even when the number of scans is less than 1, the energy of the beam at the light source can be reduced and the data clock for image data modulation in image formation can be lowered. Therefore, a self-amplifying deflection scanning optical system using only one set of transmission optical systems has a limit in achieving both high speed and high resolution. In the present invention, by using two sets of transmission optical systems, the beam is deflected by the three-degree rotating polygonal mirror, so that the scanning optical system can be further speeded up and the resolution can be increased without being restricted by the above-mentioned restrictions.

Further, in the present invention, the principal ray m ₂ of the beam emitted from the first transmission optical system 3 forms an angle ψ ₁ in the same rotation direction as the rotation angle of the reflection surface t ₄ with respect to the optical axis, and the reflection surface is formed. At t ₂ , the second deflection angle ω ₂ is ψ ₁ compared to the _first deflection angle ω _1.
The first transmission optical system 3 is configured so as to be small. Therefore, the numerical aperture of the second transfer optical system 4 can be set to be equal to or smaller than that of the first transfer optical system 3, and the aberration correction in the second transfer optical system 4 can be made good, and Two
Since the diameter of the transfer optical system 4 is also small, the cost of the second transfer optical system 4 can be reduced.

Next, a basic image forming relationship of the beam in the optical system of the present invention will be described. FIG. 1B is a main-scan sectional view showing the image formation relationship of the optical system of the present invention. The injected beam radially from the light source 1 is shaped into a focused beam focused on the point P in the vicinity of the reflecting surface t ₁ by a beam shaping optical system 2 enters the reflecting surface t _1. The beam emitted from the reflecting surface t ₁ forms an image at a point P, then enters the first transfer optical system 3 as a divergent beam, is shaped into a parallel beam or a focused beam by the first transfer optical system 3, and is reflected. It is incident on the surface t ₂ . The beam emitted from the reflecting surface t ₂ enters the second transfer optical system 4 as a parallel beam or a focused beam, is shaped into a substantially parallel beam by the second transfer optical system 4, and is deflected by the reflecting surface t ₃ . The beam from the beam shaping optical system 2 to image in the vicinity of the reflecting surface t ₁ is incident is to increase the scanning efficiency by reducing the beam diameter w ₁ on the reflecting surface t _1. Further, by making the beam deflected a second time by the reflecting surface t ₂ into a parallel beam or a convergent beam, it is possible to prevent the beam diameter incident on the second transfer optical system 4 from increasing, and the second transfer optical system 4 is prevented. Aberration correction in the system 4 can be improved. Further, the intersection point between the principal ray m _{3 of the} beam deflected a second time and the optical axis is point Q, and the intersection point between the principal ray m _{4 of the} beam emitted from the second transmission optical system ₄ and the optical axis is point R. In such a case, since the chief ray m ₃ is incident on the reflecting surface t ₂ at a height h ₁ with respect to the optical axis, the point Q is located in front of the reflecting surface t ₂ , and the points Q and R are the second points. Through the transmission optical system 4 of FIG. Therefore, the beam diameter w _R at the intersection _R becomes a value obtained by multiplying the beam diameter w _Q at the intersection Q by the optical magnification of the second transfer optical system 4. Beam diameter w _R and the beam diameter w ₃ which is deflected Me 3 degrees at the third time point of intersection for beam deflected is substantially collimated beam R is approximately equal, w ₃ and the second transmission almost w _Q It is a value obtained by multiplying the optical magnification of the optical system. As described above, in the self-amplifying deflection scanning optical system using the transmission optical system of the conventional example, if the amplification effect of the deflection angle is increased without changing the deflected beam diameter, the beam diameter incident on the transmission optical system must be increased. However, there is a problem that the scanning efficiency is lowered. According to the present invention, even if the beam diameter w _Q of the intersection Q, which is the beam diameter incident on the second transfer optical system 4, is increased, the beam deflected a second time is made a focused beam, so that the beam is reflected on the reflecting surface t ₂ . It is possible to reduce the beam diameter w ₂ at 1, and to prevent the reduction in scanning efficiency even if the amplification effect of the deflection angle is increased.

(Embodiment 1) Next, an embodiment showing a practical configuration of the present invention will be described.

FIG. 2 is a main-scan sectional view showing the first embodiment of the present invention. In this embodiment, the optical elements are arranged in a plane in the main scanning section, and the optical axes of the optical elements are in the same plane. The first transmission optical system includes two lenses 31,
32 and one folding mirror 33, and the second transmission optical system is composed of two lenses 41 and 42 and two folding mirrors 43 and 44. The beam emitted from the semiconductor laser 1 which is the light source passes through the beam shaping optical system 2 and is incident on the reflecting surface t ₁ of the rotary polygon mirror 5 for the first time. The beam reflected by the reflecting surface t ₁ is a lens 31, a folding mirror 33, and a lens 3 which constitute the first transmission optical system.
After passing through 2, the light is guided again to the rotary polygon mirror 5 and is incident on the reflecting surface t ₂ for the second time. Beam reflected by the reflecting surface t2 the lens 41 constituting the second transmission optics, a folding mirror 43, passes through the lens 42, once again led to the rotary polygonal mirror 5 3 degrees to the reflecting surface t ₃ Incident for The beam reflected by the reflecting surface t ₃ passes through the fθ optical system 6 and enters the surface 7 to be scanned. The fθ optical system 6 is a rotary polygon mirror 5
The beam deflected by is scanned at a constant speed on the surface 7 to be scanned, and a beam spot is formed on the surface 7 to be scanned without causing field curvature. FIG.
The dotted line in the middle shows the chief ray of the beam deflected by the rotary polygon mirror 5 to scan the left and right scanning ends of the scanned surface 7. The first and second transmission optical systems are configured so that these chief rays are incident on the reflecting surfaces t ₂ and t ₃ following the movement of the reflecting surface due to the rotation of the rotary polygon mirror 5. The number of folding mirrors that fold the beam in the main scanning section used in the transmission optical system depends on the condition of following the reflecting surface, and if the number of times the principal ray of the deflected beam intersects the optical axis is an odd number, , If the number of crossing is odd, it must be an even number. Since the deflected beam does not intersect the optical axis in the first transmission optical system in this embodiment, there is only one folding mirror in the main scanning section, and in the second transmission optical system, the deflected beam does not coincide with the optical axis. Since it intersects once, the number of folding mirrors is two.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 3 is a main-scan sectional view showing a second embodiment of the present invention, and FIG. 4 is a sub-scan sectional view of the present embodiment developed from FIG. 3 along the optical axis. In this embodiment, when the rotation angle of the rotary polygon mirror 5 is 0, the optical axes of the beam shaping optical system 2 and the first and second transmission optical systems in the main scanning cross section are the reflecting surfaces t of the rotary polygon mirror 5. It is configured to be at a right angle to ₁ , t ₂ , and t ₃ . The beam that passes through the optical axes of the first transfer optical system 3 and the second transfer optical system 4 and scans the scanning center on the surface to be scanned travels to the reflecting surfaces t ₁ , t ₂ , and t ₃ in the main scanning section. It is incident at a right angle. The beams incident on the respective reflecting surfaces of the rotary polygon mirror 5 are incident on the reflecting surface at an angle in the sub-scanning direction with respect to the reflecting surfaces to prevent interference with the outgoing beams, and the incident beam and the outgoing beam are separated. doing. The first transmission optical system is composed of two lenses 31, 32 and three folding mirrors 33, 34, 35.
The transmission optical system is composed of two lenses 44 and 45 and two folding mirrors 43 and 44. The beam emitted from the semiconductor laser 1 which is the light source is a beam shaping optical system 2
, And enters the reflecting surface t ₁ of the rotary polygon mirror 5 from diagonally below from the first time. The beam reflected by the reflecting surface t ₁ is emitted obliquely upward while avoiding interference with the incident beam, and the lens 31, the folding mirrors 33, 3 constituting the first transmission optical system.
The rotary polygon mirror 5 is passed through the lenses 4 and 35 and the lens 32, and again.
And is incident on the reflecting surface t ₂ from obliquely above for the second time. The beam reflected by the reflecting surface t ₂ is emitted obliquely downward while avoiding interference with the incident beam, and passes through the lens 41, the folding mirror 43, the lens 42, and the folding mirror 44 that constitute the second transmission optical system. Then, it is guided again to the rotary polygon mirror 5 and is incident on the reflecting surface t ₃ obliquely from below at the third angle. The beam reflected by the reflecting surface t ₃ avoids interference with the incident beam, is emitted obliquely upward, passes through the fθ optical system 6, and is incident on the surface 7 to be scanned. Dotted lines in FIG. 3 indicate chief rays of a beam which is deflected by the rotary polygon mirror 5 and scans the left and right scanning ends of the scanned surface 7. These chief rays are directed to the reflecting surfaces t ₂ and t ₃ of the rotary polygon mirror 5. The first and second transmission optical systems are configured so that they are incident following the movement of the reflecting surface due to the rotation.

In the scanning optical system using the rotary polygon mirror as in the first embodiment, in the structure in which the optical axis and the reflecting surface of the rotary polygon mirror do not form a right angle in the main scanning cross section, the reflection is caused by the rotation of the rotary polygon mirror. Due to the displacement of the deflection point, which is the displacement of the surface in the direction of the optical axis, various characteristics of the optical system such as the path of the chief ray and aberration become axially asymmetric with respect to the optical axis. These aberrations cannot be corrected by the commonly used axisymmetric optical system, which hinders the accuracy of the scanning optical system from increasing. It is possible to correct an axially asymmetric aberration by using an axially asymmetric lens or the like in the optical system, but the optical system becomes extremely expensive. In this embodiment, the optical axes of the beam shaping optical system 2 and the first and second transmission optical systems in the main scanning cross section are reflected surfaces t1, t2, t3 when the rotation angle of the rotary polygon mirror 5 is 0. By configuring so as to form a right angle, various characteristics of the optical system can be made axially symmetric with respect to the optical axis, and the accuracy of the scanning optical system can be further improved.

First used in the first and second embodiments
A typical design example of the transmission optical system and the second transmission optical system is shown below. 5A and 5B are main-scan sectional views showing the lens configuration of the present design example, where the dotted line in FIG. 5A shows the chief ray of the beam scanning the scanning end, and FIG. 5B shows the imaging relationship of the beam scanning the scanning center. Show. In the figure, the first and second transmission optical systems are shown expanded along the optical axis for the sake of easy understanding. In this design example, the entrance surface s ₁ and the exit surface s ₂ of the lens 31 forming the first transmission optical system are axisymmetric aspherical surfaces, and all other lens surfaces are spherical surfaces. Table 1 shows the optical specifications of this design example. The symbols in the table are as follows.

S _i : surface number r _i : radius of curvature of surface number i d _i : axial distance from surface number i to surface i + 1 _ni : refractive index of surface number i K _i , A _i , B _i , C _i , D _i : aspherical coefficient of an axisymmetric aspherical surface represented by the following equation when the surface number i is an axisymmetric aspherical surface

[0029]

[Equation 1]

Here, z is the distance from the tangent plane of the aspherical vertex of the aspherical point at the height h from the optical axis. phi: Rotation angle P _r of the rotary polygonal mirror when the beam is scanned from the scanning center to a scanning end: inscribed circle of the rotating polygon mirror radius L: imaging of the beam emerging from the beam shaping optical system from the reflecting surface t ₁ Distance on optical axis to point P ω ₁ : Deflection angle at 1 ° ω ₂ : Deflection angle at _2nd ω ₃ : Deflection angle at _3rd ψ ₁ : Principal ray of beam scanning at scanning end is reflected Tilt angle with respect to the optical axis when incident on the surface t ₂ ψ ₂ : Tilt angle with respect to the optical axis when the principal ray of the beam for scanning the scanning end enters the reflecting surface t ₃ h ₁ : For beam scanning at the scanning end principal ray and the reflection surface height from the optical axis at the intersection of t ₂ h _2: height w from the optical axis at the intersection of the reflective surface t ₃ the principal ray of the beam scanning the scan end _1: scanning the scan center Beam diameter on the reflecting surface t ₁ of the beam w ₂ : Beam diameter on the reflecting surface t ₂ of the beam scanning the scanning center w ₃ : Reflecting surface t of the beam scanning the scanning center Beam diameter on ₃

[0031]

[Table 1]

The beam shaping optical system and the fθ optical system used in the present invention can be easily designed by a generally widely used design method, and a detailed description of their configurations will be omitted here.

(Embodiment 3) Next, a third embodiment of the present invention will be described. FIG. 6 is a main-scan sectional view showing a third embodiment of the present invention, and FIG. 7 is a sub-scan sectional view of the present embodiment in which FIG. 6 is expanded along the optical axis. In this embodiment, as in the case of the second embodiment, when the rotation angle of the rotary polygon mirror 5 is 0, the optical axes of the beam shaping optical system 2, the first and second transmission optical systems in the main scanning cross section. Is the reflecting surface t of the rotary polygon mirror 5.
It is configured to be at a right angle to ₁ , t ₂ , and t ₃ . First
The transmission optical system is composed of two lenses 31, 32 and two folding mirrors 33, 35, and the second transmission optical system is two lenses 41, 42 and two folding mirrors 43,
44. The dotted line in FIG. 6 is the rotary polygon mirror 5.
The principal ray of the beam which is deflected by and scans the left and right scanning ends of the surface to be scanned 7 is shown. In this embodiment, the principal ray of the beam deflected between the lenses 31 and 32 of the first transmission optical system is the optical axis. It is configured to intersect with.

In this embodiment, the lens 3 of the first transmission optical system is used.
By intersecting the principal ray of the beam deflected between 1 and the lens 32 with the optical axis, the number of folding mirrors of the first transmission optical system can be set to 2, and the number of folding mirrors can be reduced.

First and second used in the third embodiment
A typical design example of the transmission optical system is shown below. FIG. 8 is a main-scan sectional view showing the lens configuration of the present design example. The dotted line in (a) shows the chief ray of the beam scanning the scanning end, and (b).
Shows the image formation relationship of the scanning beam at the scanning center. In the figure, the first and second transmission optical systems are shown expanded along the optical axis for the sake of easy understanding. In this design example, only the exit surface s ₂ of the lens 31 constituting the first transmission optical system is an axisymmetric aspherical surface, and all other lens surfaces are spherical surfaces. Table 2 shows the optical specifications of this design example. The symbols in the table conform to those in Table 1.

[0036]

[Table 2]

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. FIG. 9 is a main-scan sectional view showing a fourth embodiment of the present invention, and FIG. 10 is a sub-scan sectional view of the present embodiment in which FIG. 9 is expanded along the optical axis. In the present embodiment, as in the second embodiment, when the rotation angle of the rotary polygon mirror 5 is 0, the beam shaping optical system 2, the first and the second in the main scanning cross section.
Each of the optical axes of the transmission optical system is configured to be perpendicular to the reflecting surfaces t ₁ , t ₂ and t _{3 of the} rotary polygon mirror 5. The first transmission optical system is composed of two lenses 31, 32 and two folding mirrors 33, 35, and the second transmission optical system is three lenses 32, 41, 42 and two folding mirrors 43. , 44. In this embodiment, after the beam emitted from the lens 32 is reflected by the reflecting surface S ₂ ,
It is configured to enter the lens 32 again, and the lens 3
2 is included in both the first and second transfer optics. The beam that has passed through the first transmission optical system and has exited the lens 32 is incident on the reflecting surface t ₂ from an obliquely upper direction, is reflected, and exits obliquely downward to avoid interference with the incident beam, and the lens 3
It is incident on 2 again. The beam emitted from the lens 32 passes through the lens 41, the folding mirror 43, the lens 42, and the folding mirror 44, and is guided to the rotary polygon mirror 5.

In this embodiment, the lens 32 has the first and second lenses.
By including it in both of the transmission optics of
Without increasing the number of lenses in the scanning optical system as a whole,
The number of lenses in the second transfer optical system can be increased, and the aberration correction in the second transfer optical system can be improved.

First and second used in the fourth embodiment
A typical design example of the transmission optical system is shown below. FIG. 11 is a main scanning sectional view showing the lens configuration of this design example (a).
The dotted line indicates the chief ray of the beam scanning the scan end,
(B) shows the imaging relationship of the beam scanning the scanning center.
In the figure, the first and second transmission optical systems are shown expanded along the optical axis for the sake of easy understanding. In this design example, the exit surface s ₂ of the lens 31 forming the first transfer optical system and the entrance surface s of the lens 42 forming the second transfer optical system.
₇ , the exit surface s ₈ is an axisymmetric aspherical lens, and the other lens surfaces are all spherical surfaces. Table 3 shows the optical specifications of this design example. The symbols in the table conform to those in Table 1.

[0040]

[Table 3]

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described. FIG. 12 is a main-scan sectional view showing a fifth embodiment of the present invention, and FIG. 13 is a sub-scan sectional view of the present embodiment developed along the optical axis. This embodiment is the first
In the same manner as in the above embodiment, when the optical axes of the beam shaping optical system and the first and second transmission optical systems are 0 in the main scanning section and the rotation angle of the rotary polygon mirror 5 is 0, the reflecting surfaces t ₁ , t ₂ It is configured to be at a right angle to. The first transmission optical system is composed of two lenses 31, 32 and two folding mirrors 33, 34, and the second transmission optical system is composed of a plane mirror 41 provided facing the rotary polygon mirror 5. ing. FIG. 14 shows the behavior of the beam in the sub-scanning direction on the reflecting surface t ₂ and the plane mirror 41. The beam that has passed through the first transfer optical system and is reflected by the reflecting surface t ₂ is emitted obliquely downward while avoiding interference with the incident beam, as shown in FIG. 14, to form a second transfer optical system. The light is reflected by the plane mirror 41 and is reflected again t
Incident on ₂ from above. The plane mirror 41 is made thin in the sub-scanning direction in order to avoid interference of the beam reflected by the reflecting surface t ₂ . The beam reflected by the reflecting surface t ₂ is emitted obliquely downward so as not to interfere with the incident beam and is emitted from the fθ optical system 6
And then enters the surface 7 to be scanned.

In the present embodiment, the second transmission optical system is composed of only plane mirrors, the second transmission optical system can be extremely simplified, and a low-cost scanning optical system can be constructed.

First and Second Used in Fifth Embodiment
A typical design example of the transmission optical system is shown below. FIG. 15 is a main scanning sectional view showing a lens configuration of this design example (a).
The dotted line indicates the chief ray of the beam scanning the scan end,
(B) shows the imaging relationship of the beam scanning the scanning center.
In the figure, the first and second transmission optical systems are shown expanded along the optical axis for the sake of easy understanding. In this design example, the entrance surface s ₁ and the exit surface s ₂ of the lens 31 forming the first transmission optical system are axisymmetric aspherical surfaces, and all other lens surfaces are spherical surfaces. Table 4 shows the optical specifications of this design example. The symbols in the table conform to those in Table 1.

[0044]

[Table 4]

In any of the embodiments, the lens forming the first or second transmission optical system may be an anamorphic lens such as a cylindrical lens or a toric lens, or the transmission optical system may have a refractive power only in the sub-scanning direction. By adding a lens, each reflecting surface on which the beam is deflected can be made optically conjugate with respect to the sub-scanning direction, and tilting of the reflecting surface can be optically corrected.

[0046]

As described above, according to the configuration of the present invention, the beam is incident on the 3-degree rotating polygon mirror by using two sets of transmission optical systems, so that the rotating angle of the rotating polygon mirror is small. However, both the deflection angle and the beam diameter of the beam deflected for the third time can be increased. In addition, the first transmission optical system is configured so that the deflection angle of the beam deflected to the second degree by the rotating polygon mirror is equal to or less than the deflection angle of the beam deflected to the first degree. (EN) Provided is a self-amplifying deflection scanning optical system which has a small numerical aperture to improve aberration correction in the second transmission optical system and also has a small aperture, which is high-speed, high-resolution, high-precision, and low-priced. You can

Further, by making the beam deflected a second time by the rotating polygonal mirror a parallel beam or a focused beam, it is possible to prevent the beam diameter of the beam incident on the second transmission optical system from increasing. Aberration correction in the second transmission optical system can be improved. Furthermore, the amplification effect of the deflection angle in the second transmission optical system can be increased without changing the beam diameter of the beam deflected the third time and without lowering the scanning efficiency. It is possible to provide a self-amplifying deflection scanning optical system.

Further, the beam that passes through the optical axes of the first transmission optical system and the second transmission optical system and scans the scanning center on the surface to be scanned is directed to the reflecting surface of the rotary polygon mirror once and then to the second. Since the optical system becomes axially symmetric with respect to the optical axis by making the light incident at a right angle in the main scanning cross section at the third time,
The occurrence of axially asymmetric aberration is eliminated, and the accuracy of the optical system can be further improved.

Furthermore, in the first transfer optical system, the first transfer optical system is constructed so that the chief ray of the beam other than the beam passing on the optical axis intersects the optical axis of the first transfer optical system. As a result, the number of folding mirrors that form the first transmission optical system can be reduced, and the cost of the optical system can be further reduced.

Further, the beam deflected a second time by the rotary polygon mirror is made to enter the final lens constituting the first transmission optical system again, thereby increasing the number of lenses in the entire optical system. Instead, the number of lenses forming the second transfer optical system can be increased and the aberration correction in the second transfer optical system can be improved.

Furthermore, by constructing the second transmission optical system only by the plane mirror provided facing the rotary polygonal mirror, the second transmission optical system can be extremely simplified, and the cost of the optical system can be further reduced. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a main-scan sectional view of an optical system showing the basic principle of the present invention.

FIG. 2 is a main-scan sectional view showing the first embodiment of the present invention.

FIG. 3 is a main scanning sectional view showing a second embodiment of the present invention.

FIG. 4 is a sub-scan sectional view showing a second embodiment of the present invention.

FIG. 5 is a main-scan sectional view showing lens configurations of design examples of the first and second examples.

FIG. 6 is a main-scan sectional view showing a third embodiment of the present invention.

FIG. 7 is a sub-scan sectional view showing a third embodiment of the present invention.

FIG. 8 is a main scanning sectional view showing the lens configuration of a design example of the third embodiment of the present invention.

FIG. 9 is a main-scan sectional view showing a fourth embodiment of the present invention.

FIG. 10 is a sub-scan sectional view showing a fourth embodiment of the present invention.

FIG. 11 is a main scanning sectional view showing the lens configuration of a design example of the fourth embodiment of the present invention.

FIG. 12 is a main-scan sectional view showing a fifth embodiment of the present invention.

FIG. 13 is a sub-scan sectional view showing a fifth embodiment of the present invention.

FIG. 14 is a sub-scanning cross-sectional view showing a beam that is incident on a rotating polygon mirror according to a fifth embodiment of the present invention at the second and third times.

FIG. 15 is a main-scan sectional view showing the lens configuration of a design example of the fifth embodiment of the present invention.

[Explanation of symbols]

 1 Light Source 2 Beam Shaping Optical System 3 First Transfer Optical System 4 Second Transfer Optical System 5 Rotating Polygonal Mirror 6 fθ Optical System 7 Scanned Surface

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kyumu Takada 3-3-5 Yamato, Suwa City, Nagano Seiko Epson Corporation

Claims (6)

[Claims] 1. A rotating polygon mirror having a plurality of reflecting surfaces for deflecting a beam by rotational movement, and a first transmission for guiding a beam deflected by the reflecting surface of the rotating polygon mirror to the rotating polygon mirror. An optical system and a second transmission optical system that emits the first transmission optical system and guides the beam deflected by the rotating polygon mirror to the second direction to the rotating polygon mirror are arranged, and rotation of the rotating polygon mirror is provided. By the first transfer optical system so that the deflection angle of the beam emitted from the second transfer optical system and deflected by the third degree becomes larger than the deflection angle of the beam deflected by the first transfer optical system. A self-amplifying deflection scanning optical system that constitutes the second transmission optical system, wherein
A self-amplifying deflection scanning optical system, wherein the deflection angle of the beam deflected at a certain degree is equal to or less than the deflection angle of the beam deflected at the first degree. 2. A rotating polygon mirror having a plurality of reflecting surfaces for deflecting the beam by rotational movement, and a first transmission for guiding the beam deflected to the first by the reflecting surface of the rotating polygon mirror to the rotating polygon mirror. An optical system and a second transmission optical system that emits the first transmission optical system and guides the beam deflected by the rotating polygon mirror to the second direction to the rotating polygon mirror are arranged, and rotation of the rotating polygon mirror is provided. By the first transfer optical system so that the deflection angle of the beam emitted from the second transfer optical system and deflected by the third degree becomes larger than the deflection angle of the beam deflected by the first transfer optical system. A self-amplifying deflection scanning optical system constituting the second transfer optical system, wherein the beam deflected a second time by the rotating polygon mirror is a parallel beam or a focused beam. Optical system. 3. The beam that passes through the optical axes of the first transmission optical system and the second transmission optical system and scans the scanning center on the surface to be scanned is once reflected on the reflection surface of the rotary polygon mirror. The self-amplifying deflection scanning optical system according to claim 1 or 2, wherein the second and third degrees are incident at right angles in the main scanning cross section. 4. The chief ray of a beam other than the beam passing on the optical axis in the first transfer optical system intersects the optical axis of the first transfer optical system. 2. The self-amplifying deflection scanning optical system described in 2. 5. The beam which is emitted from the first transfer optical system and is deflected a second time is incident again on the final lens which constitutes the first transfer optical system. Self-amplifying deflection scanning optical system. 6. The self-amplifying scanning optical system according to claim 3, wherein the second transmission optical system is composed only of a plane mirror provided facing the rotary polygon mirror.