JP3073801B2 - Optical scanning lens and optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning lens and an optical scanning device.

[0002]

2. Description of the Related Art Optical deflecting devices that converge a light beam deflected at a constant angular velocity as a light spot on a surface to be scanned by an optical scanning lens and optically scan the surface to be scanned at a constant speed have been widely known. Have been. In such an optical scanning device, assuming a “virtual optical path” in which a light beam path from the light source to the surface to be scanned is linearly developed, a direction parallel to the main scanning direction on this virtual optical path is referred to as “a main scanning direction”. A direction parallel to the sub-scanning direction on the virtual optical path is referred to as a “sub-scanning corresponding direction”. In the optical scanning device as described above, in order to align the scanning starting points of the periodically repeated optical scanning, a synchronous detection signal is generated by detecting a deflecting light beam deflected to the optical scanning region by a synchronous detection optical sensor. The optical scanning is started after a predetermined time from the generation of the synchronization detection signal. In this case, it is preferable that the synchronization detection optical sensor be provided in the same plane as the surface to be scanned on which the light spot is formed by the optical scanning lens. This is because the deflected light beam is focused on a spot having a small diameter in the same plane as the surface to be scanned, so that the deflected light beam can be reliably detected even on the small light receiving surface of the synchronization detecting optical sensor.

However, since a photosensitive recording medium such as a photoconductive photosensitive member is generally provided on the surface to be scanned, it is necessary to provide an optical sensor for synchronization detection at a position which does not hinder the arrangement of the photosensitive recording medium. There is. As a method for performing this, there is a method of “setting the arrangement position of the synchronization detection optical sensor away from the optical scanning area in the same plane as the surface to be scanned”. There is a problem in that the lens system in the direction corresponding to the main scanning of the lens becomes large, it is difficult to manufacture the optical scanning lens, and the cost of the optical scanning lens is increased. As another method, “a light beam condensed by the optical scanning lens is turned back by a mirror or the like, and a position equivalent to the surface to be scanned (a position where an image of the surface to be scanned is formed by the mirror)
Although there is a method of “deploying an optical sensor”, extra space is required for the arrangement of a mirror and the like, and from a practical point of view, there are great restrictions on the arrangement of the mirror and the optical sensor for synchronization detection.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a novel optical scanning lens capable of increasing the degree of freedom in the arrangement of a synchronous detection optical sensor, and a novel optical scanning lens. It is an object of the present invention to provide an optical scanning device using a lens.

[0005]

According to a first aspect of the present invention, there is provided an optical scanning lens comprising: a light beam from a light source is deflected at an equal angular velocity by an optical deflector, and the deflected light beam is formed as a light spot on a surface to be scanned by an imaging lens. Optical scanning device that performs optical scanning by focusing light. "
, A lens provided on the optical path between the deflector and the surface to be scanned. The above optical scanning device is based on the premise that correction of so-called "surface tilt" in the optical deflector is not performed.

The optical scanning lens according to the first aspect has a "single structure in which the imaging lens portion and the synchronization detecting lens portion are integrated". The “imaging lens part” has the function of condensing the deflected light beam as a light spot on the surface to be scanned and the linearity correction function, and the “synchronization detection lens part” collects the deflected light beam on the synchronization detection optical sensor. It has the function of light. The imaging lens portion and the synchronization detection lens portion have different imaging characteristics. Here, "different imaging characteristics" means that the respective lens portions have different focal lengths and / or optical axes. The optical scanning lens is entirely molded from plastic. When integrally molded by molding, “the lens portion for synchronization detection is molded on the side of the gate in molding”. The optical scanning lens according to claim 1 may be formed by adjusting the optical axis such that the synchronous detection lens portion moves the synchronous detection deflected light beam away from the optical scanning deflection area. (Claim 2).

An optical scanning device according to a third aspect of the present invention is an optical scanning device using the optical scanning lens as described above, wherein a "light source device" and a light beam from the light source device are deflected at a constant angular velocity. An optical deflector, the optical scanning lens for condensing the light beam deflected by the optical deflector as a light spot on the surface to be scanned, and an optical sensor for synchronization detection for synchronizing optical scanning. Having. The optical scanning device according to the third aspect is based on the premise that correction of surface tilt is not performed as described above. Therefore, as the deflector, it is desirable to use a rotating polygon mirror whose surface tilt is corrected with high accuracy, a pyramidal mirror or a tenon type mirror which has almost no surface tilt in principle. The deflected light beam incident on the optical scanning lens according to claim 1 may be a parallel light beam, a weakly divergent light beam, or a weakly convergent light beam. When the deflected light beam is a parallel light beam, the linearity correction function is a so-called fθ function, and the imaging lens portion is an fθ lens.

According to a fourth aspect of the present invention, there is provided an optical scanning lens which forms a light beam from a light source as a long line image in a main scanning direction,
Optical scanning in which light is deflected at an equal angular velocity by an optical deflector having a deflecting and reflecting surface near the image forming position of a line image, and the deflected light beam is condensed as a light spot on a surface to be scanned by an imaging lens to perform optical scanning. In the "device", it is a lens provided on the optical path between the deflector and the surface to be scanned. The optical scanning device using the optical scanning lens has a function of correcting "surface tilt" as described above. An optical scanning lens according to a fourth aspect is a single-piece structure formed by integrating an imaging lens portion and a synchronization detection lens portion, like the optical scanning lens according to the first aspect. The "imaging lens portion" has a linearity correction function in the main scanning corresponding direction, and has a function of "making the position of the deflecting reflection surface and the position of the scanned surface substantially geometrically optically conjugate" in the sub-scanning corresponding direction. And converges the deflected light beam as a light spot on the surface to be scanned. The "synchronous detection lens portion" focuses the deflected light beam on the synchronous detection optical sensor, and has different imaging characteristics from those of the imaging lens portion and the synchronous detection lens portion. That is, the imaging lens portion and the synchronization detection lens portion are at least in the main scanning corresponding direction.
Different focal lengths and / or optical axes. The optical scanning lens is entirely molded from plastic. When integrally molded by molding, “the lens portion for synchronization detection is molded on the side of the gate in molding”.
The optical scanning lens according to the fourth aspect may be formed by adjusting the optical axis such that the synchronous detection lens portion moves the deflection light flux for synchronization detection away from the light scanning deflection area. (Claim 5).

An optical scanning device according to a sixth aspect is an optical scanning device using the optical scanning lens according to the fourth or fifth aspect.
This optical scanning device includes a “light source device”, a “line image forming optical system” for forming a light beam from the light source device as a long line image in the main scanning direction, and a light source near the image forming position of the line image. "Optical deflector" that has a reflective surface and deflects a light beam at a uniform angular velocity
The "optical scanning lens" for condensing the light beam deflected by the optical deflector as a light spot on the surface to be scanned, and the "optical sensor for synchronization detection" for synchronizing optical scanning. As described above, this optical scanning device has a function of correcting surface tilt, so that an ordinary rotating polygon mirror or the like can be used as an optical deflector. The deflected light beam incident on the optical scanning lens is divergent in the sub-scanning direction, but may be parallel, weakly divergent, or weakly convergent in the main scanning direction. When the light flux is parallel in the direction, the imaging lens portion becomes a well-known anamorphic fθ lens.

In the first or fourth aspect, "condensing the deflected light beam on the synchronization detecting optical sensor" means that the deflected light beam is present in the light receiving surface of the synchronization detecting optical sensor at least in the main scanning corresponding direction. This means that the light beam converges, and it is not always necessary for the deflected light beam to form an image on the light receiving surface.

[0011]

According to the present invention, as described above, the optical scanning lens is formed by integrating the imaging lens portion and the synchronization detection lens portion. However, the imaging lens portion and the synchronization detection lens portion are different from each other. Since it has image characteristics, the focal length and optical axis of the synchronization detection lens are adjusted according to the desired position of the synchronization detection optical sensor, and the deflected light beam is properly adjusted on the light receiving surface of the synchronization detection optical sensor. Can be collected. When molding an elongated lens, such as the optical scanning lens according to claims 1, 2, 4, and 5, the gate at the time of molding is:
It is usually located on one side in the longitudinal direction. In the vicinity of the gate, the precision of molding tends to decrease. For this reason, the accuracy of the lens surface is higher on the side farther from the gate in the lens longitudinal direction, lower on the side closer to the gate, and tends to be asymmetric with respect to the optical axis. When the synchronization detection lens portion is integrally formed at the longitudinal end of the imaging lens portion as in the optical scanning lens of the present invention, the lens surface accuracy of the synchronization detection lens portion is equal to that of the imaging lens portion. Since the gate may be relatively rough as compared with the above, by setting the gate on the side of the lens portion for synchronization detection, it is possible to effectively prevent a decrease in lens surface accuracy in the imaging lens portion. Further, as in the optical scanning lens according to the second and fifth aspects, "the synchronous detection lens portion moves the deflection light beam for synchronization detection away from the deflection region for optical scanning."
As described above, when the optical axis is adjusted and formed, the arrangement position of the optical sensor for synchronization detection can be moved away from the deflection area for optical scanning, and the optical sensor for synchronization detection prevents the scanning light from being "blurred". Therefore, the degree of freedom of the arrangement position of the optical sensor for synchronization detection is increased.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The optical scanning device shown in FIG. 1A is an embodiment of the optical scanning device according to claim 6.

The light source device 1 is composed of a combination of a light source such as a semiconductor laser or a light emitting diode and a collimating lens, and emits a substantially parallel light beam. The emitted parallel light beam is given a converging property only in the sub-scanning corresponding direction by the cylinder lens 2 as a line image forming optical system, and is focused near the deflection reflecting surface of the rotary polygon mirror 3 which is an optical deflector. It forms an image as a long line image in the scanning corresponding direction, and is reflected by the deflecting / reflecting surface. The reflected light flux becomes a deflected light flux deflected at a constant angular velocity by the rotation of the rotary polygon mirror 3, enters the optical scanning lens 4, and converges toward the surface to be scanned. On the scanned surface,
A drum-shaped photoconductive photoconductor 5 is provided with the generatrix aligned with the surface to be scanned. The drum-shaped photoconductive photoconductor 5 rotates in the direction of the arrow in synchronization with the optical scanning, and moves the peripheral surface of the photoconductor to be optically scanned in the sub-scanning direction. send. Prior to each optical scanning, the deflected light beam is detected by the synchronization detecting optical sensor 8, and the optical scanning is synchronized.

As shown in FIG. 1B, the optical scanning lens 4 includes an imaging lens portion 41 and a synchronization detecting lens portion 42.
Is a unitary structure that is integrated. Imaging lens part 41
Is an anamorphic fθ lens, which has an fθ function in the main scanning corresponding direction. Therefore, the light spot formed on the surface to be scanned by the imaging lens portion 41 optically scans the surface of the photoconductor at a constant speed. Synchronous detection lens part 4
Reference numeral 2 focuses the deflected light beam toward the synchronization detection optical sensor 8. The synchronization detecting optical sensor 8 is provided at a desired position between the optical scanning lens 4 and the surface to be scanned on the side of the optical scanning area on the optical scanning start side. The synchronous detection lens portion 42 has its focal length set in accordance with the position where the synchronous detection optical sensor 8 is provided, and deflects a deflecting light beam that deflects toward the optical scanning area toward the light receiving surface of the synchronization detection optical sensor 8. To collect light. The light sensor 8 for synchronization detection is, for example, a PIN photodiode or the like, and its light receiving surface has a diameter of about 1 to 2 mm. It is enough to collect light.

In this embodiment, the imaging lens portion 41
Has a function of correcting the tilt of the rotary polygon mirror 3 as an optical deflector, but the synchronization detection lens portion 42 does not necessarily have to have the tilt correction function. If the synchronization detection lens portion 42 is not provided with the surface tilt correction function, the deflection light beam incident on the synchronization detection optical sensor 8 fluctuates in the sub-scanning corresponding direction, and in some cases, the detection failure of the deflection light beam may occur. It can also happen. In order to avoid this, it is only necessary that the light beam condensed on the light receiving surface of the synchronization detecting optical sensor 8 be long in the sub-scanning corresponding direction. For this purpose, the power of the synchronization detection lens portion 42 may be made different in the main / sub-scanning corresponding directions. However, in the case of the embodiment being described, the deflected light beam incident on the optical scanning lens 8 is a parallel light beam in the main scanning corresponding direction and divergent in the sub scanning corresponding direction. Even if is configured as a spherical lens, there is no problem because the state of the light beam focused on the light receiving surface of the synchronization detection optical sensor 8 is long in the sub-scanning corresponding direction.

The size of the synchronization detecting lens portion 42 may be about 4 to 5 mm in the main scanning corresponding direction. Therefore, even if this portion is integrated with the imaging lens portion 41, the size of the optical scanning lens 4 is It is not so different from conventional lenses. The optical scanning lens 4 is formed by molding a plastic material. As described above, when molding an elongated lens such as the optical scanning lens 4,
It is common to have a gate during molding on one side in the longitudinal direction, and the accuracy of the lens surface is likely to be asymmetric with respect to the optical axis. When the synchronization detection lens portion is integrally formed at the end of the direction, the lens surface accuracy of the synchronization detection lens portion is
Since the gate may be relatively rough as compared with the imaging lens portion, by setting the gate on the side of the synchronization detecting lens portion, it is possible to effectively prevent a decrease in lens surface accuracy in the imaging lens portion.

FIG. 2 shows another embodiment of the invention, in which only the characteristic portions are shown. In this embodiment, the effective deflection angle 2 [Theta] ₁ by the optical deflector 3, the effective optical scanning deflection angle 2 [Theta] ₂ is large, the angular θ
₁ −θ ₂ is relatively small. Therefore, the optical axis of the synchronous detection lens portion 42A of the optical scanning lens 4A is adjusted by the synchronous detection optical sensor 8 so that the scanning light is not "eclipsed", and the direction of the synchronous detection deflection light beam 10 is adjusted. Is located away from the optical scanning deflection area, and the position of the synchronization detecting optical sensor 8 is located away from the optical scanning deflection area (claim 5). The embodiment of the optical scanning lens according to claim 5 and the embodiment of the optical scanning device according to claim 6 have been described above. However, when the cylinder lens 2 is removed from the configuration of FIG. An example. For this device,
Since the tilting of the optical deflector is not corrected, the rotating polygon mirror 3 should have a sufficiently high accuracy of the deflecting reflecting surface and the rotating shaft so as to prevent tilting, or use a pyramidal mirror or a mirror as the optical deflector. A tenon mirror is used. Of course, the imaging lens portion of the optical scanning lens does not need to be anamorphic, but may be a normal fθ lens having a lens surface rotationally symmetric about the optical axis.

[0018]

As described above, according to the present invention, a novel optical scanning lens and optical scanning device can be provided. Since the present invention is configured as described above, the degree of freedom in the arrangement of the optical sensor for synchronization detection for synchronizing optical scanning is increased.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a view showing another embodiment of the invention, showing only the characteristic portions;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source device 2 Cylinder lens as a line image imaging optical system 3 Rotating polygon mirror as an optical deflector 4 Optical scanning lens 5 Photoconductive photoreceptor 8 Synchronous detection optical sensor 41 Imaging lens part 42 Synchronous detection lens part

Claims (6)

(57) [Claims] An optical scanning device for performing optical scanning by deflecting a light beam from a light source at an equal angular velocity by an optical deflector and condensing the deflected light beam as a light spot on a surface to be scanned by an image forming lens. A lens disposed on the optical path between the scanner and the surface to be scanned, which has a linearity correction function and focuses the deflected light beam as a light spot on the surface to be scanned, and synchronously detects the deflected light beam Is a unitary structure that integrates a synchronization detection lens part that condenses light on the optical sensor for use.The imaging lens part and the synchronization detection lens part have different imaging characteristics, and the whole is made of plastic. An optical scanning lens, which is molded, and a lens part for synchronization detection is molded on a side of a gate in the molding. 2. The optical scanning lens according to claim 1, wherein the synchronization detection lens portion is adjusted in optical axis so that the deflection light beam for synchronization detection is separated from the deflection region for optical scanning. Characterized by the optical scanning lens. 3. A light source device, an optical deflector for deflecting a light beam from the light source device at a constant angular velocity, and an optical scanning lens for condensing a light beam deflected by the light deflector as a light spot on a surface to be scanned. And an optical sensor for synchronization detection for synchronizing optical scanning, wherein the optical scanning lens is the optical scanning lens according to claim 1 or 2. 4. A light beam from a light source is formed as a long line image in a direction corresponding to the main scanning, and is deflected at an equal angular velocity by an optical deflector having a deflecting / reflecting surface near an image forming position of the line image. In an optical scanning device for performing optical scanning by condensing a light beam as a light spot on a surface to be scanned by an imaging lens, a lens provided on an optical path between the deflector and the surface to be scanned, comprising: It has a linearity correction function for the corresponding direction,
An imaging lens portion having a function of making the position of the deflecting reflective surface and the position of the scanned surface substantially geometrically conjugate with respect to the sub-scanning corresponding direction, and condensing the deflected light beam as a light spot on the scanned surface. And a synchronous detection lens portion for condensing the deflected light beam on the synchronous detection optical sensor, and has a unitary structure. The imaging lens portion and the synchronous detection lens portion are at least in the main scanning direction. An optical scanning lens, characterized in that it has different imaging characteristics with respect to the above, wherein the whole is molded from plastic, and a lens part for synchronization detection is molded on the side of the gate in the molding. 5. The optical scanning lens according to claim 4, wherein the synchronization detecting lens portion adjusts the optical axis so as to keep the deflection light beam for synchronization detection away from the deflection region for optical scanning. Characterized by the optical scanning lens. 6. A light source device, a line image forming optical system for forming a light beam from the light source device as a long line image in the main scanning direction, and a deflecting / reflecting surface near an image forming position of the line image. An optical deflector for deflecting a light beam at an equal angular velocity, an optical scanning lens for condensing a light beam deflected by the optical deflector as a light spot on a surface to be scanned, and a synchronization detecting light for synchronizing optical scanning. An optical scanning device comprising: a sensor; and the optical scanning lens is the optical scanning lens according to claim 4.