JPH08110488A - Optical scanning device - Google Patents

Abstract

PURPOSE: To improve the performance of a detecting system for scanning starting signal. CONSTITUTION: A laser beam generated from a laser unit 1 is deflected/scanned by means of a rotating polygon 2, its end part Lp is returned to the rotating polygon 2 by a detecting mirror 5, introduced to a photosensor 8 through a condenser lens 6 and converted to a scanning starting signal. Most of the remained laser beams Lm forms the image on the photosensitive body of a rotating drum 4. Since the end part Lp of the laser beam returned by the rotating polygon 2 becomes a scanning beam for scanning with twice angular velocity, the rise of the output of the photosensor 8 is sharp and a detecting system for scanning starting signal of high performance is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in an image forming apparatus such as a laser beam printer, a laser facsimile or a digital copying machine.

[0002]

2. Description of the Related Art A conventional example of an optical scanning device used in an image forming apparatus such as a laser beam printer, a laser facsimile or a digital copying machine will be described with reference to FIG.
This has a rotary polygon mirror R for deflecting and scanning a laser beam generated from a laser unit E, and the laser beam deflected and scanned by the rotary polygon mirror R passes through an imaging lens system F and is a photoconductor on a rotary drum M. Image on.

The laser light imaged on the photosensitive member forms an electrostatic latent image by main scanning by rotation of the rotary polygon mirror R and sub-scanning by rotation of the rotary drum M.

A part of the laser beam deflected and scanned by the rotary polygon mirror R is introduced into the light receiving surface of the optical sensor D by the detection mirror B through the imaging lens system F, and the laser unit E is output by the output signal. Start write modulation.

When the laser light reflected by the rotary polygon mirror R reaches the end in the main scanning direction (Y-axis direction), the detection mirror B reflects it to the lower side of the main scanning surface (XY plane), It is introduced into the optical sensor D located on the opposite side of the main scanning surface. The output of the optical sensor D is converted into a scanning start signal through an amplifier and a light intensity detector (not shown) and transmitted to the drive circuit of the semiconductor laser E ₁ of the laser unit E.

The driving circuit of the semiconductor laser E ₁ is a memory for storing image signals sent from an external computer,
It has a timer that starts driving by a scan start signal, and after a predetermined time after receiving the scan start signal, write modulation based on the output of the memory is started.

The position of the light receiving surface of the optical sensor D is determined by the length of the optical path of the laser light that reaches the optical sensor D from the imaging lens system F through the detection mirror B and from the imaging lens system F to the rotary drum M. It is desirable that the positions are such that the lengths of the optical paths of the arriving laser beams are substantially equal to each other, that is, the imaging positions of the laser beams introduced into the light receiving surface of the optical sensor D. The reason is as follows.

If the light receiving surface of the optical sensor D is at the image forming position of the laser light introduced thereto, the light intensity distribution of the laser light on the light receiving surface of the optical sensor D will be close to a Gaussian distribution. When the light receiving surface of the sensor D deviates from the image forming position of the laser light, its light intensity distribution becomes a gentle curve having a rising edge more than that of the Gaussian distribution. Even if the light intensity of the light changes even slightly, the timing at which the scanning start signal is generated remarkably shifts, resulting in a large deterioration in the image quality of the image forming apparatus.

The laser unit E has a collimator lens E ₂ for collimating the laser light emitted from the semiconductor laser E ₁ and a slit E ₃ for narrowing the emitted light to a predetermined beam diameter. The parallel beam shaped to have a predetermined beam diameter is linearly focused on the reflecting surface of the rotary polygon mirror R by the cylindrical lens C.

FIG. 7 shows another conventional example.
A part Lpo of the reflected light of the rotary polygon mirror 102 is separated by a detection mirror 105 arranged between the rotary polygon mirror 102 and the imaging lens 103, and introduced into an optical sensor 108 arranged on the opposite side of the main scanning surface. To do. In this case, the optical path of the image forming laser beam Lmo and the scanning start signal laser beam Lp.
Since it is difficult to make the optical path lengths of o the same, it is common to use a concave mirror as the detection mirror 105.

A slit 107 is provided at the image forming position of the laser beam Lpo for the scanning start signal, and the laser beam Lpo which is a part of the reflected light of the rotary polygon mirror 102 is emitted from the rotary polygon mirror 102. The rotation causes scanning in the direction crossing the slit 107 as indicated by arrow A.

As described above, the laser beam for the scanning start signal is compared with the length of the optical path of the laser beam Lmo for image formation which reaches the photoconductor of the rotary drum 104 from the rotary polygon mirror 102 through the imaging lens 103. When the length of the optical path of Lpo is short, the scanning speed V at which the laser beam Lpo for scanning start signal crosses the slit 107 becomes slow in proportion to the ratio of the length of the optical path. Similarly, a laser beam L for a scanning start signal
The diameter d of the point image formed by forming po on the surface of the slit 107 is also small.

That is, as shown in FIG. 4A, the length of the optical path of the laser beam Lmo for image formation from the rotary polygon mirror 102 to the photosensitive member of the rotary drum 104 and the optical sensor 10.
When the optical paths of the laser light Lpo for scanning start signal introduced into the optical path 8 are equal in length, the scanning speed of the point image on the surface of the slit 107 is the laser light L for image formation on the photoconductor.
It is the same as the scanning speed V _{1 of} mo, and thus has a light intensity distribution similar to a Gaussian distribution. Slit 10 at this time
If 7 the diameter of the point image on the surface of was d _1, the scanning speed when the length of the optical path of the laser beam Lpo for the scanning start signal is reduced to 1/2 V _1/2, the slits 107 on The point image diameter is theoretically d as shown in Fig. 4 (b).
_1/2.

On the other hand, in order to manage the timing of generating the scanning start signal with high accuracy and obtain a high quality image, the optical sensor 1
It is desired that the output of 08 is sharply risen, but the rise of the optical sensor 108 is sharper as the diameter of the point image formed on the slit 107 is smaller and the scanning speed thereof is faster.

In the case of FIG. 4B, the length of the optical path of the laser beam Lpo for the scanning start signal is shortened and the scanning speed is halved, but the diameter of the point image formed is also halved. The rising curve of the output of the optical sensor 108 is almost the same as the rising curve of the optical sensor 108 in the case of (a) of FIG. 4, and is, for example, the one shown by the curve U ₁ of FIG. 5, and thus theoretically. It is assumed that the accuracy of the timing of generating the scan start signal does not change.

[0016]

However, according to the above-mentioned conventional technique, in reality, the optical path of the laser beam for the scanning start signal is shortened, so that the depth of focus of the point image introduced into the optical sensor becomes shallow. Therefore, an error due to variations in the finished state of the reflecting surface of the detection mirror and a slight positional deviation at the time of assembly cause a remarkable focus deviation. As a result, what theoretically has a sharp rising light intensity distribution as shown in FIG. 4B actually becomes a gentle curve shown in FIG. 4C, and therefore the diameter of the point image is When the scanning speed decreases, the rising of the output of the optical sensor becomes slower as shown by the curve U ₂ in FIG. 5, and the scanning is caused by contamination of the reflecting surface of the rotating polygon mirror or slight disturbance. There is an unsolved problem that the timing of generating the start signal is remarkably deviated to cause a trouble such as so-called writing jitter and the image quality of the image forming apparatus is significantly deteriorated.

The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and provides an optical scanning device in which a scanning start signal detection system for detecting a scanning start signal has extremely high performance. It is intended to be provided.

[0018]

In order to achieve the above object, an optical scanning device of the present invention comprises a rotary polygonal mirror and a photosensitive member with the remainder except a part of the scanning light deflected and scanned by the rotary polygonal mirror. A first optical system for forming an image and a second optical system for introducing the part of the scanning light into a scanning start signal detector, the second optical system including the second part of the scanning light. It is characterized in that a part thereof is reflected by the rotary polygon mirror at least once and then introduced into the scanning start signal detector.

The second optical system may include a detection mirror for reflecting a part of the scanning light toward the rotary polygonal mirror, and a condenser lens provided in the optical path of the part of the scanning light.

Further, it is preferable that the second optical system includes a concave detection mirror for reflecting and condensing a part of the scanning light toward the rotary polygon mirror.

Further, it is preferable that the scanning start signal detector is arranged close to the light source of the scanning light.

Further, the light source of the scanning light imaged on the photosensitive member and the light source of the scanning light introduced into the scanning start signal detector may be different.

[0023]

A part of the scanning light deflected and scanned by the rotary polygon mirror is separated from the remaining part by the second optical system, and is reflected at least once by the rotary polygon mirror before being introduced into the scanning start signal detector. It At this time, since scanning is performed again by the rotary polygon mirror, the scanning speed of the scanning light introduced into the scanning start signal detector is doubled, which makes the output of the scanning start signal detector sharply rise,
The accuracy of the timing of generating the scan start signal can be significantly improved.

Even when the optical path of the second optical system from the rotary polygon mirror to the scanning start signal detector is short and compact as compared with the optical path of the first optical system from the rotary polygon mirror to the photosensitive member. By doubling the scanning speed of the scanning light introduced into the scanning start signal detector as described above, it is possible to prevent the rising of the output of the scanning start signal detector from becoming blunt and to generate the scanning start signal. It is possible to realize an optical scanning device in which there is no risk of being disturbed by contamination of the reflecting surface of the rotating polygon mirror or slight disturbance.

When the number of times the scanning light is reflected by the rotary polygon mirror increases by one, the scanning speed of the scanning light introduced into the scanning start signal detector doubles each time, and the scanning start signal detector The output rise can be made even sharper.

[0026]

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

FIG. 1 is an explanatory view for explaining an optical scanning device according to an embodiment, which is a rotary polygon mirror 2 for deflecting and scanning a laser beam generated from a laser unit 1 which is a light source.
Most of the laser light, which is the scanning light deflected and scanned by the rotary polygon mirror 2, Lm forms an image on the photoconductor on the rotary drum 4 via the imaging lens 3 which is the first optical system.

The laser light Lm imaged on the photosensitive member forms an electrostatic latent image by main scanning by rotation of the rotary polygon mirror 2 and sub-scanning by rotation of the rotary drum 4.

The imaging lens 3 has a so-called fθ function for scanning the reflected light of the rotary polygon mirror 2 on the rotary drum 4 at a constant speed, and a function of correcting a point image distortion due to the surface tilt of the rotary polygon mirror 2. Is an anamorphic aspherical lens having

The end portion Lp of the laser light, which is the scanning light deflected and scanned by the rotary polygon mirror 2, is reflected back to the reflecting surface 2a of the rotary polygon mirror 2 by the detection mirror 5, and then, together with the detection mirror 5. An image is formed on the surface of the slit 7 by the condenser lens 6 which constitutes the second optical system, and is detected by the optical sensor 8 which is a scanning start signal detector.

The laser unit 1 has a semiconductor laser 1a, a collimator lens 1b, a light source slit 1c, and the like. The laser light generated from the semiconductor laser 1a is collimated by the collimator lens 1b, and the light source slit 1c is formed.
The beam is shaped into a predetermined beam diameter by the cylindrical lens 9 and is linearly focused on the reflecting surface 2a of the rotary polygon mirror 2 by the cylindrical lens 9.

The optical sensor 8 is generally called a BD sensor which is composed of a pin photodiode or the like. The output of the optical sensor 8 passes through an amplifier and a light intensity detector (not shown) as a scanning start signal and the semiconductor laser 1 of the laser unit 1.
a to the drive circuit.

The drive circuit of the semiconductor laser 1a is a memory for storing image signals sent from an external computer,
It has a timer that starts driving by a scan start signal, and after a predetermined time after receiving the scan start signal, write modulation based on the output of the memory is started.

The laser beam Lp for the scanning start signal incident on the detection mirror 5 is scanned at the same angular velocity as the laser beam Lm for image formation, is reflected back to the rotary polygon mirror 2 by the detection mirror 5, and is doubled as described above. The light is introduced into the optical sensor 8 as scanning light that scans at an angular velocity. As described above, the laser beam Lp for the scanning start signal is reflected twice by the rotary polygon mirror 2 to double its scanning speed, and as a result, the rise time of the output of the optical sensor 8 is shortened to 1/2. The accuracy of the timing of generating the scan start signal can be greatly improved.

That is, even if the length of the optical path of the laser beam Lp for the scanning start signal is greatly shortened by using the condenser lens, the focal depth of the point image introduced into the optical sensor 8 becomes shallow by this. The drawback can be compensated by increasing the scanning speed of the laser beam Lp for the scanning start signal.

Therefore, restrictions on the arrangement position and installation space of the detection mirror, the optical sensor, etc. can be greatly reduced, and an extremely high-performance scanning start signal detection system can be realized even if it is compact. For example, by arranging the optical sensor 8 in a position close to the semiconductor laser 1a, it is possible to mount both on a single flexible substrate.

As a result, a compact and high-performance optical scanning device can be realized.

FIG. 2 shows a first modified example in which a concave mirror is used as the detection mirror 15 and the condenser lens is omitted. By omitting the condenser lens, the number of parts to be assembled can be reduced and the manufacturing cost of the optical scanning device can be reduced.

FIG. 3 shows a second modification, which is a laser unit 21 having a semiconductor laser 21a for generating a laser beam for image formation, a collimator lens 21b and the like.
Separately, a semiconductor laser 22a, which is a light source for generating a laser beam for a scanning start signal, and a collimator lens 22b are provided. When the photosensitive member on the rotating drum has high sensitivity, the output of the semiconductor laser 21a that generates the laser light for image formation is small, and therefore a part of the laser light generated from this is used as a laser for a scanning start signal. When used as light, the photosensor 8 needs to have extremely high sensitivity.

In this modification, a semiconductor laser for generating a laser beam for a scanning start signal and a semiconductor laser for generating a laser beam for image formation are separately provided, so as to make up for the above-mentioned drawback. Therefore, it has an advantage that an inexpensive optical sensor can be used.

In this embodiment, the laser beam separated for the scanning start signal is reflected only once by the rotating polygon mirror and then introduced into the optical sensor. The reflection may be repeated more than once.

[0042]

Since the present invention is configured as described above, it has the following effects.

It is possible to realize an optical scanning device in which the scanning start signal detection system for detecting the scanning start signal has extremely high performance. The use of such an optical scanning device can greatly contribute to downsizing and high performance of the image forming apparatus.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating an optical scanning device according to an embodiment.

FIG. 2 is an explanatory diagram illustrating an optical scanning device according to a first modification.

FIG. 3 is an explanatory diagram illustrating an optical scanning device according to a second modification.

FIG. 4 is a graph showing the relationship between the scanning speed and the diameter of a point image.

FIG. 5 is a graph showing a rising curve of the output of the optical sensor.

FIG. 6 is an explanatory diagram illustrating an optical scanning device according to a conventional example.

FIG. 7 is an explanatory diagram illustrating an optical scanning device according to another conventional example.

[Explanation of symbols]

 1, 21 Laser unit 1a, 21a, 22a Semiconductor laser 2 Rotating polygonal mirror 3 Imaging lens 4 Rotating drum 5,15 Detection mirror 6 Condensing lens 7 Slit 8 Optical sensor

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display area H04N 1/113

Claims (5)

[Claims] 1. A rotary polygonal mirror, a first optical system for forming an image on a photosensitive member with the exception of a part of the scanning light deflected and scanned by the rotary polygonal mirror, and scanning the part of the scanning light. A second optical system for introducing into a start signal detector, wherein the second optical system reflects the part of the scanning light at least once by the rotary polygon mirror, and then the scanning start signal; An optical scanning device configured to be introduced into a detector. 2. The second optical system comprises a detection mirror for reflecting a part of the scanning light toward the rotary polygonal mirror, and a condenser lens provided in the optical path of the part of the scanning light. The optical scanning device according to claim 1, which is characterized in that. 3. The second optical system comprises a concave detection mirror for reflecting and condensing a part of the scanning light toward the rotary polygon mirror. Optical scanning device. 4. The optical scanning device according to claim 1, wherein the scanning start signal detector is arranged in the vicinity of the light source of the scanning light. 5. The light source of the scanning light imaged on the photoconductor and the light source of the scanning light introduced into the scanning start signal detector are different from each other, according to any one of claims 1 to 4. Optical scanning device.