JPH05127106A - Laser beam scanning optical device - Google Patents

Abstract

PURPOSE:To divert the laser beam scanning optical device for other kinds of equipment by adjusting the distance between an SOS sensor and a light converging lens and adjusting the scanning speed on the SOS sensor. CONSTITUTION:This laser beam scanning optical device consists of a light source assembly 1 which emits a laser beam, a cylindrical lens 2 for altering the shape of the laser beam, a polygon mirror 3 for changing the laser beam, a toroidal lens 4 which is combined with the cylindrical lens 2 to correct the surface tilt of the polygon mirror 3, an ftheta mirror 5 which guides the laser beam onto a photosensitive body, the SOS sensor 8 which easily moves so as to determine an image write position, and the light converging lens 7 which converges the laser beam on the SOS sensor 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam scanning optical device, and more particularly to a laser beam scanning optical device which deflects a laser beam in a plane by a deflector and forms an image on a photosensitive member.

[0002]

2. Description of the Related Art In recent years, various laser beam scanning optical devices incorporated for image writing in image forming apparatuses such as laser beam printers and facsimiles have been provided.
In these devices, a laser beam emitted from a light source is deflected in one plane by a deflector (polygon mirror) and then f
A θ lens, a reflection mirror, and the like are used to guide the light onto the photoconductor to form an image. Then, a light receiving element (hereinafter referred to as an SOS sensor) is arranged at a position equivalent to the image plane on the photoconductor, and S
In order to focus the laser beam on the center of the light-receiving surface of the OS sensor, a condenser lens is arranged immediately in front of the SOS sensor, and the SOS sensor is irradiated with a part of the laser beam to write an image on each main scanning line. The horizontal sync signal of is obtained.

[0003]

In order to reduce the manufacturing cost, there is a demand to commonly use such a laser beam scanning optical device for image forming apparatuses having different printing densities and scanning speeds.

However, if the print density or the scanning speed is changed, the detection output period of the SOS sensor changes, which causes a shift in synchronization.

Specifically, as shown in FIG. 6 (1), S
When the detection output period of the OS sensor is sufficiently longer than the output period of the clock signal for detecting it (see FIG. 6 (2)), the horizontal synchronization signal can be obtained, but FIG. 6 (3)
As shown in, when the detection output period of the SOS sensor is shorter than the output period of the clock signal, the beam cannot be detected and the horizontal synchronizing signal cannot be obtained.

In order to eliminate such inconvenience, it is conceivable to change the size of the SOS sensor according to the change of the print density or the scanning speed. With this change, the position of the condenser lens is changed and the control is performed. The circuit had to be changed, and it was difficult to commonly use the laser beam scanning optical device.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a laser beam scanning optical device which can be easily commonly used for image forming apparatuses having different printing densities and scanning speeds.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a deflector for deflecting a laser beam modulated according to image information and scanning the surface of a photoconductor, and a part of the laser beam deflected and scanned by the deflector. In the laser beam scanning optical device including a light receiving sensor for detecting an image writing start position for receiving the light, and a condenser lens provided immediately before the light receiving sensor for condensing the laser beam on the light receiving element, It is characterized in that the distance to the condenser lens can be changed.

[0009]

The light receiving time of the SOS sensor can be adjusted by changing the relative position between the condenser lens and the SOS sensor, and the light receiving time of the SOS sensor can be made equal even if the print density or the scanning speed is changed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a laser beam scanning optical device according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a plan view of an optical unit 100 of a laser beam printer according to an embodiment with an upper lid removed. The optical unit 100 incorporates a laser diode light source (hereinafter referred to as an LD light source) and a collimator lens. A light source assembly 1, a cylindrical lens 2,
Polygon mirror 3, toroidal lens 4, fθ mirror 5, and SOS for detecting the image writing start position
The sensor 8 and the SOS mirror 6 for guiding a laser beam to the SOS sensor 8 and the SOS sensor 8 immediately before the SOS sensor 8
The sensor 8 is composed of a condenser lens 7 for condensing the laser beam at the center of the light receiving surface. The above parts are
It is housed in a unit case 11 which is a resin molded product.

The LD light source is modulated (ON / OFF) controlled based on image information input to a control unit (not shown), and a laser beam is emitted from the light source assembly when ON.
This laser beam is converted by the collimator lens into a convergent light beam that is condensed at a finite rear position, and then the cylindrical lens 2
Then, the spot shape is changed to a substantially linear shape whose longitudinal direction is parallel to the main scanning direction and reaches the polygon mirror 3.
The polygon mirror 3 is rotationally driven at a constant speed, and based on this rotation, the laser beam is changed to a constant angular speed within one plane perpendicular to the mirror rotation axis and guided to the toroidal lens 4. The toroidal lens 4 has an incident surface and an exit surface formed concentrically within a scanning cross section, has a constant power in a direction perpendicular to the deflecting surface, and corrects the surface tilt of the polygon mirror 3 in combination with the cylindrical lens 2. .. The laser beam is further reflected by the fθ mirror 5, and the reflected light is imaged on a photosensitive drum (not shown) from a slit formed on the bottom surface of the unit case 11. Image formation on the photosensitive drum is performed by main scanning by rotation of the polygon mirror 3 and sub-scanning by rotation of the photosensitive drum. The fθ mirror 5 has an fθ function (distortion correction) for correcting the main scanning speed of the laser beam and a function for correcting the field curvature on the photosensitive drum.

On the other hand, of the light reflected by the fθ mirror 5, the tip portion in the main scanning direction is reflected by the SOS mirror 6 and enters the SOS sensor 8 via a condenser lens 7 to determine the image writing position. Used as a horizontal sync signal. Here, the condenser lens 7 has a function of condensing the laser beam on the central portion of the light receiving surface of the SOS sensor 8, and is movably installed as described later.

Next, the shape of the condenser lens 7 and its mounting structure will be described.

In FIG. 2, the condenser lens 7 is integrally molded from a plastic of an appropriate material, and a pair of protrusions 7a having small protrusions 12 on both sides of the effective lens portion 13,
7a is formed. On the other hand, as the lens mounting portion 9, an opening 15 is formed in the wall portion 14 of the unit case 11 and grooves 16 and 16 are formed on both sides thereof. In addition, SOS
The condenser lens 7 for the sensor 8 may be formed of glass of an appropriate material instead of plastic.

The condenser lens 7 is fixed by press-fitting the protruding pieces 7a, 7a on both sides into the groove portions 16, 16 from above. Since the groove portions 16 and 16 fix the projecting pieces 7a and 7a,
The width dimension thereof is slightly larger than the thickness of the projecting piece 7a and slightly smaller than the thickness including the small protrusion 12. Since the condenser lens 7 is small and light, it is fixed in such a state that it can endure vibration by such pressure contact of the small protrusions 12. The mounting height of the condenser lens 7 is precisely regulated by the bottom surfaces of the grooves 16 and 16, and is laterally regulated by the side wall surface. Grooves 16, 1
Most of the strain applied during press-fitting into 6 is absorbed by the small projection 12. By providing the small protrusions 12 as far as possible from the effective lens portion 13, the influence of distortion at the time of press fitting can be eliminated.

FIG. 3 is an enlarged view of the mounting portion 9 of the condenser lens 7 and the SOS sensor 8.

The SOS sensor 8 is held at the center of a plate-shaped SOS sensor holding member 17. And the SOS
The sensor holding member 17 is precisely positioned so that the laser beam is incident on the central portion of the light-receiving surface of the SOS sensor 8 via the sensor position adjusting members 10, 10 that are detachably provided and include a pair of washers, and the screw. It is attached to the unit case 11 by 18. And SO
The distance between the S sensor 8 and the condenser lens 7 is adjusted by changing the thickness of the sensor position adjusting member 10.

In this way, the SOS sensor 8 and the condenser lens 7 are
Since the distance between and can be changed, the optical unit 100 can easily be commonly used for laser beam printers having different printing densities and scanning speeds. This is shown in FIG.
Will be described in detail below.

FIG. 5 (A) shows the positional relationship between the SOS sensor 8 and the condenser lens 7 that can obtain a horizontal synchronization signal with no synchronization deviation when the scanning speed is high or the printing density is high. (B) shows the positional relationship between the SOS sensor 8 and the condenser lens 7 that can obtain a horizontal synchronization signal without synchronization deviation when the scanning speed is slow or the print density is low. In any case, the laser beam is condensed by the condenser lens 7 and scans and moves in the direction of arrow a.
Further, the detection output periods of the SOS sensor 8 are set to be the same.

When the scanning speed is slowed or the print density is lowered in the state of FIG. 5A, the detection output period of the SOS sensor 8 becomes short, and the horizontal synchronizing signal is obtained as described above with reference to FIG. I will not be able to.

On the other hand, when the scanning speed is increased or the print density is increased in the state of FIG. 5B, the detection output period of the SOS sensor 8 is shortened and the horizontal synchronizing signal cannot be obtained.

From this, when the scanning speed is changed to a slow speed, for example, the SOS sensor 8 is moved away from the position shown in FIG.
The position is changed to the position (B), and the detection output period of the SOS sensor 8 is made constant. On the other hand, when the scanning speed is changed to a high speed, the SOS sensor 8 is moved from the position of FIG.
The position is changed to the position (A), and the detection output period of the SOS sensor 8 is also fixed.

As described above, the optical unit 100 can be commonly used for image forming apparatuses having different specification values in scanning speed with a simple structure in which the distance between the SOS sensor 8 and the condenser lens 7 is changed. it can. The relative positional relationship between the SOS sensor 8 and the condenser lens 7 is appropriately set according to the specification value of the scanning speed.

Next, a second embodiment of the present invention will be described.

In the first embodiment, the condenser lens 7 is fixed and S
Although the distance between the SOS sensor and the condenser lens 7 was changed by moving the OS sensor 8, in the second embodiment, SO
By fixing the S sensor 8 and moving the condenser lens 7,
The distance between the sensor 8 and the condenser lens 7 is changed. As shown in FIG. 4, the first groove portions 20 and 20 for holding the condenser lens 7 in the groove portions 16 and 16.
And second groove portions 21 and 21 are provided, and the condenser lens 7
By changing the distance between the SOS sensor 8 and the condenser lens 7. Other configurations are similar to those of the first embodiment.

In the above embodiment, either the SOS sensor 8 or the condenser lens 7 is moved to change the distance between the SOS sensor 8 and the condenser lens 7.
The distance may be changed by moving both the S sensor 8 and the condenser lens 7 at the same time.

In the above embodiment, the SOS sensor 8 and the condenser lens 7 are attached to the unit case 11 by providing the mounting portion 9, but the holding member such as a lever holds the SOS sensor 8 and the condenser lens 7. Then, the distance between the SOS sensor 8 and the condenser lens 7 may be changed by moving the holding member.

[0029]

As is apparent from the above description, the laser beam scanning optical device according to the present invention is configured so that the distance between the light receiving sensor for receiving a part of the laser beam and the condenser lens can be changed. Even if you change the scanning speed or print density, just change the distance between the light receiving sensor and the condenser lens,
Since the detection output period of the light receiving sensor can be the same, the laser beam scanning optical device can be easily commonly used for the image forming apparatuses having different scanning speeds and print densities, and the manufacturing cost can be further reduced.

[Brief description of drawings]

FIG. 1 is a plan view showing a state where an upper lid of an optical unit of a laser beam printer according to an embodiment of the present invention is removed.

FIG. 2 is a diagram showing the shape of a condenser lens and its mounting structure.

FIG. 3 is an enlarged view of a mounting portion for a condenser lens and an SOS sensor of the first embodiment.

FIG. 4 is an enlarged view of a mounting portion of a condenser lens and an SOS sensor according to a second embodiment.

FIG. 5 is a diagram for explaining the principle of the present invention.

FIG. 6 is a diagram showing the relationship between the detection output period of the SOS sensor and the output time of a clock signal for detecting the output of the SOS sensor.

[Explanation of symbols]

 3 Polygon mirror 7 Condenser lens 8 SOS sensor 10 Sensor position adjusting member 100 Optical unit

Claims (1)

[Claims] 1. A deflector for deflecting a laser beam modulated according to image information to scan on a surface of a photosensitive member, and an image writing start position detection for receiving a part of the laser beam deflected and scanned by the deflector. In a laser beam scanning optical device provided with a light receiving sensor for light and a condenser lens which is provided immediately before the light receiving sensor and focuses a laser beam on a light receiving element, the distance between the light receiving sensor and the condenser lens is A laser beam scanning optical device characterized in that it can be changed.