JPH1048554A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a compact optical scanning device which is easily attached to a housing without needs for a large diameter to a second optical system focusing polarized light flux on a scanned surface. SOLUTION: Optical scanning is performed by coupling luminous fluxes from a light source part 10 through a first optical system 11a, 11b to guide the flux to a light deflection part and focusing the deflected luminous fluxes through an optical deflector on the surface to be scanned 14 in a second optical system 13 as a light spot. The reflected luminous flux to go to an optical scanning start position A is detected by a third optical detector 17 through an optical system 15, and a synchronizing signal for starting the optical scanning is generated. Conditions have been provided, under which the first through third optical systems are not mechanically interfered with each other and are able to be arranged compactly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical scanning device.

[0002]

2. Description of the Related Art In an optical scanning apparatus which is well known in connection with a digital copying apparatus or an optical printer, a light beam which is deflected toward an optical scanning start position is detected by a photodetector, and a synchronizing signal for starting the optical scanning is used. Is occurring. In order to perform detection by a photodetector, a method is known in which a deflected light beam is guided to a photodetector through a portion outside the effective angle of view of an fθ lens (Japanese Patent Application Laid-Open No. 3-221913). In addition to the effective angle of view required for optical scanning, a part for guiding the deflected light beam to the photodetector is required, so that the angle of view of the fθ lens needs to be larger than the angle of view required for optical writing.
This results in an increase in the diameter of the fθ lens. In addition, since the photodetector is necessarily located on the image plane of the fθ lens, the degree of freedom in layout of other optical systems is likely to be limited in order to provide the photodetector.

[0003] Also, JP-A-5-19186 discloses that
An optical system in which a scanning lens unit corresponding to an fθ lens and a BD imaging lens unit that guides a deflected light beam to a photodetector is disclosed, is disclosed in Japanese Patent Application Laid-Open No. 7-281113. There is disclosed an optical system in which a cylinder lens for forming a light beam from the side into a linear image at the position of a deflecting reflection surface of an optical deflector and an anamorphic lens for guiding the deflecting light beam to a photodetector are integrated.

[0004] When the two lenses are integrally formed as described above, the shape of the integrated lens is generally complicated. Therefore, when the integrated lens is formed of plastic, the processing of the gold piece is complicated, and each lens is separately formed. This can be more costly than forming into a body. In addition, since the two integrated lenses have different imaging performances, the mounting accuracy tends to be stricter than when the two lenses are separately mounted. Even if there is a slight mounting error, one or both of the two lenses may be mounted. There is a possibility that the imaging performance is deteriorated.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention can easily be mounted on a housing and can increase the diameter of a second optical system for condensing a deflected light beam on a surface to be scanned. It is another object of the present invention to realize an optical scanning device capable of providing a compact optical system.

[0006]

An optical scanning device according to the present invention includes a light source unit, first to third optical systems, an optical deflector and a photodetector. The “light source section” emits a light beam for optical scanning, and a light source using a semiconductor laser, a light emitting diode, or the like as a light source can be suitably used.
The “first optical system” is an optical system for coupling a light beam from the light source unit and guiding the light beam to the light deflection unit. The light beam coupled by the first optical system becomes a “parallel light beam”, a “weakly converging light beam”, or a “weakly divergent light beam”.

The "optical deflector" has a deflecting / reflecting surface near the light deflecting unit, and reflects the light beam from the first optical system by this deflecting / reflecting surface to deflect the reflected light beam. Therefore, the deflected light beam is deflected by using the light deflector as the “start point of deflection”.

A surface orthogonal to the deflected light beam ideally deflected by the optical deflector is arbitrarily assumed. On this surface, the direction in which the deflected light beam is displaced is referred to as a “scanning direction”, and the light deflected from the light source unit is deflected. On the optical path to the section, a direction corresponding to the scanning direction is called a “scanning direction”, a direction orthogonal to the scanning direction in the plane is a “scanning orthogonal direction”, and the light source section reaches the light deflection section. The direction corresponding to the scanning orthogonal direction on the optical path is referred to as “scanning orthogonal corresponding direction”. It will be easily understood that “the scanning direction is the main scanning direction” and “the scanning orthogonal direction is the sub-scanning direction” on the surface to be scanned. As the optical deflector, a known “polygon mirror, rotating two-sided mirror, rotating single-sided mirror, or the like” can be used.

The "second optical system" is an optical system for condensing the light beam deflected by the optical deflector as a light spot on the surface to be scanned. The light beam from the first optical system is a parallel light beam in the scanning corresponding direction. If so, a so-called “fθ lens” can be used. As the second optical system, a lens system having the above function (a single lens or a sub lens may be used) or a concave mirror having the above function can be used.

[0010] The "photodetector" detects a deflected light beam heading for the optical scanning start position and emits an output. Based on this output, a synchronizing signal for starting the optical scanning is generated. The "third optical system" guides the deflected light beam toward the optical scanning start position to the photodetector. The first, second and third optical systems are separate from each other,
The third optical system is disposed between the first optical system and the second optical system. That is, the deflected light beam deflected by the optical deflector is deflected in a direction away from the optical axis of the first optical system using the optical deflector as a starting point of the deflection, and is deflected in the third optical system before entering the second optical system. Inject into the system.

The optical scanning device according to the first aspect has the following features in such a “basic optical system configuration”. That is, the angle formed by the first optical system optical axis and the third optical system optical axis is θ ₁₃ , and the third optical system optical axis and the main beam of the deflected light beam directed to the second optical system to converge to the optical scanning start position. The angle made with the “light beam” is θ ₃₂ . Further, among the imaging elements constituting the first optical system, with respect to the imaging element closest to the light deflection unit, the element width from the optical axis in the scanning corresponding direction to the third optical system side is S ₁₃ ,
The distance from the surface of the optical deflector side and the light deflection unit and L _11.
Further, among the image forming elements constituting the third optical system, the image forming element closest to the light deflecting section has an element width S ₃₁ from the optical axis in the scanning corresponding direction to the first optical system side. The element width on the second optical system side from the axis is S ₃₂ , and the distance from the surface on the optical deflector side to the optical deflector is L ₃₁ .

At this time, the angles: θ ₁₃ and θ ₃₂ , and the distance: L
₁₁ , L ₃₁ , element widths: S ₁₃ , S ₃₂ satisfy the following conditions: (1) θ ₁₃ > max {S ₁₃ / L ₁₁ , S ₃₁ / L ₃₁ ｝ (2) θ ₃₂ > S ₃₂ / L ₃₁ I do. In condition (1), max ｛S ₁₃ /
L ₁₁ , S ₃₁ / L ₃₁ } means the larger one of S ₁₃ / L ₁₁ and S ₃₁ / L ₃₁ . The condition (1) is a condition for preventing the first optical system and the second optical system from interfering with each other, and the condition (2)
Is a condition for preventing the second optical system and the third optical system from interfering with each other.

An optical scanning device according to a second aspect of the present invention has the following features in the basic optical system configuration. That is, the distance on the optical axis (of the second optical system) from the light deflector to the surface of the second optical system closest to the optical deflector is L ₂₁ , and the distance from the light deflector to the second optical system (along the optical axis). T) The distance to the surface to be scanned is L ₂₂
The distance on the optical axis from the light deflecting unit to the surface closest to the light deflecting unit of the third optical system is L ₃₁ , and the light detector receives light from the light deflecting unit (along the third optical system optical axis). Assuming that the distance to the surface is L ₃₂ , these satisfy the condition: (3) √2 · L ₂₁ <L ₃₁ <L ₂₂ (4) √2 · L ₂₁ <L ₃₂ <L ₂₂ These conditions (3) and (4) are conditions for disposing the third optical system and the photodetector at an appropriate position to obtain a stable synchronization signal.

According to a third aspect of the present invention, in the above-mentioned basic optical system configuration, the above conditions (1), (2),
(3) and (4) are satisfied.

In the optical scanning device according to any one of claims 1 to 3, the light beam coupled by the first optical system may be a parallel light beam or a light beam having a weak divergence or a weak converging light as described above. However, the light beam thus coupled is further focused in the scanning orthogonal direction,
The light deflector may be formed as a long line image in the scanning corresponding direction.

That is, in this case, the first optical system includes a “coupling lens and a line image forming unit that forms the light beam coupled by the coupling lens into a long line image in the scanning corresponding direction on the light deflection unit. Image optical system ". In this case, the deflected light beam is “divergent in the scanning orthogonal direction” and “parallel light beam or weakly divergent or weakly converging light beam in the scanning direction”. The system is an anamorphic lens having a stronger positive power in the scanning orthogonal direction, and in particular, these can be an anamorphic single lens.

According to a fifth aspect of the present invention, in the optical scanning device according to the first or second or third or fourth aspect, the distance from the light source unit to the light deflecting unit via the first optical system is L _12. , when the distance extending from the light deflection unit via the third optical system on the light receiving surface of the photodetector and L _32, these conditions: a _{(5) 4/5 <L 32 /} L 12 <6/5 It is characterized by satisfaction.

When the condition (5) is satisfied, the light source unit and the photodetector can be brought close to each other, so that “the light source unit, the light source driving circuit for driving the light source unit, the photodetector,
It is possible to arrange a detector driving circuit for controlling the photodetector on the same substrate (claim 6).

[0019]

FIG. 1 shows a "semiconductor laser".
The divergent light beam emitted from the light source unit 10 using the light source as a light source is coupled by a coupling lens 11a and converted into a parallel light beam or a weakly convergent or weakly divergent light beam. `` Polygon mirror ''
Then, an image is formed as a "line image long in the scanning corresponding direction" on the "light deflecting unit" near the deflecting reflection surface 12a of the optical deflector 12 (claim 4). The coupling lens 11a and the cylinder lens 11b constitute a "first optical system". However, the first optical system is not limited to this mode, and may have "another lens configuration".

The light beam reflected by the deflecting / reflecting surface 12a becomes a deflecting light beam that deflects clockwise at a constant angular velocity as the light deflector 12 rotates at a constant speed in the direction of the arrow. The deflected light beam is condensed as a light spot on the surface 14 to be scanned by the second optical system 13 and optically scans the surface 14 to be scanned. The second optical system 13 has a function of equalizing the scanning speed of the light spot. The line image is formed on the light deflecting unit near the deflecting / reflecting surface 12a, and the second optical system 13 forms a light spot on the surface to be scanned with the line image as an object point in the sub-scanning corresponding direction. The optical scanning device shown in FIG. 1 has a function of correcting "surface tilt" of the deflecting / reflecting surface 12a.

Although the second optical system 13 has a single lens configuration in the embodiment of FIG. 1, it may be composed of two or more lenses, and is composed of a concave mirror having an image forming action similar to these lenses. You can also. Needless to say, there is a cost advantage to forming the second optical system in a single lens configuration.

The deflected light beam is transmitted to the scanning surface 1 by the second optical system.
Prior to optical scanning of 4, the light enters the photodetector 17 via the third optical system 15. Photodetector 1 as "light receiving element"
7 emits an output upon receiving the deflected light beam in this way,
Based on this output, a synchronization signal for starting optical scanning is generated. On the basis of this synchronization signal, optical scanning with the deflected light beam is started from the optical scanning start position A on the surface 14 to be scanned.

In the embodiment shown in FIG. 1, the second optical system 13,
Both the third optical system 15 has a single lens configuration (claim 4), and both are lenses molded from plastic.

In order to keep the optical scanning start position A constant, the synchronizing signal must be stable. For this reason, the third optical system must form the deflected light beam toward the optical scanning start position A as a light spot having a spot diameter that is somewhat small on the light receiving surface of the photodetector. In order to generate a stable synchronizing signal, it is better that the output of the photodetector is steep in time. However, if the diameter of the light spot formed on the light receiving surface of the photodetector 17 is large, the photodetector 17 This is because the temporal steepness of the output becomes worse and the synchronization signal becomes unstable.

For this reason, the light receiving surface of the photodetector 17 is positioned “near the image forming position of the deflected light beam” by the third optical system 15. If necessary, a knife edge or a slit may be provided between the light receiving surface and the third optical system 15 to restrict the deflecting light flux incident on the light receiving surface, thereby reducing the time sharpness of the output of the photodetector. These slits and knife edges may be provided integrally with the housing of the optical scanning device.

The deflected light beam is a parallel light beam or a weakly convergent or divergent light beam in the scanning direction, and is divergent in the scanning orthogonal direction. Therefore, a light spot having an appropriate spot diameter on the light receiving surface of the photodetector. In order to form an image of a deflected light beam, the second optical system and the third optical system need to be “anamorphic lenses having stronger positive power in the scanning orthogonal direction”.

As shown in FIG. 1, the first optical system 11a, 11a
The angle formed by the optical axis of 1b and the optical axis of the third optical system 15 is θ ₁₃ ,
The angle between the optical axis of the third optical system 15 and the principal ray of the deflected light beam directed to the second optical system 13 for focusing on the optical scanning start position A is θ ₃₂ , and the angle of the imaging element forming the first optical system is Of the imaging element 11b closest to the light deflecting unit side, the element width on the third optical system side from the optical axis in the scanning corresponding direction is S ₁₃ , and the distance from the surface on the light deflector side to the light deflecting unit is L ₁₁ , third optical system 1
Regarding 5, the element width on the first optical system side from the optical axis is S ₃₁ , the element width on the second optical system side from the optical axis is S ₃₂ , and the distance from the surface on the optical deflector side to the optical deflector is L. ₃₁ . These satisfy the conditions (1) and (2) described above.

If the condition (1) is not satisfied, the cylinder lens 11b blocks the optical axis of the third optical system 15, or the third optical system 15 blocks the optical axis of the first optical system. If the condition (2) is not satisfied, the second optical system 13 and the third optical system 15 interfere with each other, and the deflected light beam incident on the third optical system 15 is vignetted by the second optical system 13 or the optical scanning start position. The deflected light beam toward A is vignetted by the third optical system 15.

In FIG. 2, the same reference numerals as those in FIG. 1 indicate the same as those in FIG. As shown in FIG. 2, the distance on the optical axis from the light deflector to the surface of the second optical system 13 on the side of the light deflector 12 is L ₂₁ , and the distance from the light deflector to the surface to be scanned (the light The distance on the optical axis from the light deflecting unit to the light deflecting unit side surface of the third optical system 15 is L ₃₁ , and the distance from the light deflecting unit to the light receiving surface of the photodetector 17 is L ₂₂ . (Third
When the) distance along the optical axis of the optical system 15 and L _32, these are the above conditions (3), thereby satisfying the expression (4) (Claim 2).

In an optical scanning device, the deflection angle of the deflected light beam incident on the third optical system is generally limited to about ± 90 degrees. Therefore, √2 · L ₂₁ indicates the distance between the “substantial end on the optical scanning start side” of the third optical system and the light deflecting unit.
Exceeding the lower limits of the conditions (3) and (4) means that both the third optical system and the photodetector are disposed between the light deflecting unit and the second optical system. The degree of freedom will be significantly impaired.

Exceeding the upper limits of the conditions (3) and (4) means that both the third optical system and the photodetector are arranged farther from the surface to be scanned, which means that the optical scanning optical system is provided. Causes an increase in the size of the housing in which the optical scanning device is provided, and consequently leads to an increase in the size of the optical scanning device.

Further, when the deflected light beam scans the photodetector 17, the scanning position may fluctuate in the scanning orthogonal direction, and "a part of the deflected light beam in the scanning orthogonal direction may not enter the light receiving surface". However, the signal of the photodetector is not proper and an error occurs in the synchronization signal, which causes jitter. To avoid this, it is preferable to reduce the lateral magnification of the third optical system 15, and for this purpose, it is desirable to bring the third optical system 15 closer to the photodetector.

In order to generate a stable synchronization signal,
The sharper the output of the photodetector is, the better the time is. Therefore, the focal length of the third optical system 15 in the scanning direction is increased, and the scanning speed of the light spot focused on the light receiving surface of the photodetector 17 is increased. And for this purpose a third
It is desirable to bring the optical system 15 as close to the optical deflector 12 as possible. By satisfying the above conditions (3) and (4), a preferable arrangement of the third optical system 15 and the optical deflector 17 is possible.

Of course, also in the embodiment of FIG. 2, the aforementioned conditions (1) and (2) are satisfied (claim 3).

As shown in FIG. 2, the distance from the light source unit 10 to the light deflection unit via the first optical systems 11a and 11b is represented by L _12.
When a, which the above-mentioned distance: L ₃₂ satisfies the above conditions (5) (claim 5).

When the condition (5) is satisfied, as shown in FIG. 2, the distance from the light deflector, which is the starting point of deflection by the light deflector 12, to the light source unit 10 and the photodetector 17 is short. Therefore, the light source unit 10 and the photodetector 17 are
8 can be deployed. Out of the range of the condition (5),
It is difficult to dispose the light source unit 10 and the photodetector 17 on the same substrate, and a harness or the like is required. As shown in FIG. 3, the substrate 18 includes a light source unit 10, a light source driving circuit 19 for driving the light source unit 10, a photodetector 17, and a photodetector 17.
And a detector drive circuit 20 for controlling the power supply (claim 6).

[0037]

As described above, according to the present invention, a novel optical scanning device can be realized. In the optical scanning device according to the present invention, the third optical system that guides the deflected light beam to the photodetector for generating the synchronization signal is separate from the second optical system that focuses the deflected light beam on the surface to be scanned. As compared with the case where the deflected light beam is guided to the photodetector via the second optical system, the aperture of the second optical system can be reduced, and each of the first to third optical systems is separately mounted on the housing. The mounting position of the system can be adjusted easily and accurately independently (claims 1 to 6).

According to the first aspect of the present invention, when the conditions (1) and (2) are satisfied, the first to third optical systems are brought close to each other so as not to interfere with each other, and the According to the second aspect of the present invention, since the conditions (3) and (4) are satisfied, the third aspect can be realized.
The optical system and the photodetector can be arranged at appropriate positions, and the reliability of the synchronization signal can be increased. According to the third aspect of the present invention, when the conditions (1) to (4) are satisfied, the optical scanning device can be made compact and the reliability of the synchronization signal can be increased.

According to the fourth aspect of the present invention, the optical scanning device can be made compact and low-cost by using a single lens for the second and third optical systems while correcting surface tilt in the optical deflector. is there. According to the fifth and sixth aspects of the present invention, the electrical system of the optical scanning device can be mounted on the same substrate, thereby making the optical scanning device compact.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining one embodiment of an optical scanning device of the present invention.

FIG. 2 is a diagram for explaining a characteristic portion of the embodiment of the invention described in claim 4;

FIG. 3 is a diagram for explaining a characteristic portion of the embodiment of the invention described in claim 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light source part 11a, 11b 1st optical system 12 Optical deflector 12a Deflection / reflection surface 13 2nd optical system 14 Scanning surface A Optical scanning start position 15 3rd optical system 17 Photodetector

Claims (6)

[Claims] A light source section; a first optical system for coupling a light beam from the light source section to guide the light beam to a light deflecting section; and a deflecting / reflecting surface near the light deflecting section. A light deflector for deflecting the light beam, a second optical system for condensing the deflected light beam as a light spot on the surface to be scanned, and detecting the deflected light beam heading for the optical scanning start position to start optical scanning. And a third optical system for guiding the deflected light beam toward the optical scanning start position to the photodetector, the first, second, and third optical systems. Are separate from each other, the third optical system is disposed between the first optical system and the second optical system, and the angle between the optical axis of the first optical system and the optical axis of the third optical system is θ ₁₃ , 3 optical system optical axis and 2nd to focus on optical scanning start position
The angle formed by the principal ray of the deflected light beam toward the optical system is θ ₃₂ , and among the imaging elements constituting the first optical system, the imaging element closest to the light deflecting unit is located from the optical axis in the scanning corresponding direction. The element width on the third optical system side is S ₁₃ , the distance from the surface on the optical deflector side to the optical deflecting unit is L _11, and the image forming element on the optical deflecting unit side is the most image forming element of the third optical system. Regarding the image element, the element width on the first optical system side from the optical axis in the scanning direction is S ₃₁ , the element width on the second optical system side from the optical axis is S ₃₂ , and the light is deflected from the surface on the optical deflector side. when the distance to the part and L _31, these _{conditions: (1) θ 13> max} {S 13 / L 11, S 31 / L 31} (2) θ 32> satisfies the S ₃₂ / L ₃₁ An optical scanning device characterized by the above-mentioned. 2. A light source, a first optical system for coupling a light beam from the light source and guiding the light to a light deflecting unit, and a deflecting / reflecting surface near the light deflecting unit; A light deflector for deflecting the light beam, a second optical system for condensing the deflected light beam as a light spot on the surface to be scanned, and detecting the deflected light beam heading for the optical scanning start position to start optical scanning. And a third optical system for guiding the deflected light beam toward the optical scanning start position to the photodetector, the first, second, and third optical systems. Are separate from each other, the third optical system is disposed between the first optical system and the second optical system, and on the optical axis extending from the light deflecting unit to the surface of the second optical system closest to the optical deflector. the distance L _21, the distance reaching the surface to be scanned from the light deflecting section L _22, most light deflecting unit of the third optical system from the light deflection unit L ₃₁ a distance on the optical axis leading to the surface of, when the distance reaches the light receiving surface of the photodetector from the light deflection unit and the L _32, these _{conditions: (3) √2 · L 21} < An optical scanning device characterized by satisfying L ₃₁ <L ₂₂ (4) √2 · L ₂₁ <L ₃₂ <L ₂₂ . 3. The optical scanning device according to claim 1, wherein a distance on the optical axis from the light deflecting unit to the surface of the second optical system closest to the light deflector is L ₂₁ , and scanning is performed from the light deflecting unit. L ₂₂ is the distance to the surface, L ₃₁ is the distance on the optical axis from the light deflecting unit to the surface closest to the light deflecting unit of the third optical system, and L is the light receiving surface of the photodetector from the light deflecting unit. When the reaching distance is defined as L ₃₂ , these satisfy the condition: (3) √2 · L ₂₁ <L ₃₁ <L ₂₂ (4) √2 · L ₂₁ <L ₃₂ <L ₂₂ Optical scanning device. 4. The optical scanning device according to claim 1, wherein the first optical system uses a coupling lens and a light beam coupled by the coupling lens as a linear image long in a scanning corresponding direction. A linear image forming optical system for forming an image on the deflecting unit, wherein the second optical system and the third optical system are anamorphic single lenses each having a stronger positive power in the scanning orthogonal direction. Optical scanning device. 5. The optical scanning device according to claim 1, wherein the distance from the light source to the light deflection unit via the first optical system is L.
_12, when the distance extending from the light deflection unit via the third optical system on the light receiving surface of the photodetector and L _32, these are _{conditions: (5) 4/5 <L 32} / L 12 <6/5 An optical scanning device characterized by satisfying the following. 6. The optical scanning device according to claim 5, wherein the light source unit, a light source driving circuit for driving the light source unit, a photodetector, and a detector driving circuit for controlling the photodetector, An optical scanning device which is arranged on the same substrate.