JP2000258716A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical scanner constituted so that scanning speed is made higher and an image area is extended by preventing the malfunction of a laser beam source by returning light and simultaneously improving the lighting time of the laser beam source restricted by the returning light. SOLUTION: In this optical scanner 10, divergent luminous flux Lbo emitted from the light emitting part 104 of the laser beam source 12 is deflected to scan by a rotary polygon mirror and partially returns to the laser beam source 12, so that the returning light beam is generated. A pedestal 102 supporting the light emitting part 104 is arranged to a direction where the returning light beam is made incident on the laser beam source 12 are the returning light beams Bm1 and Bm2 made incident on a light receiving part 106 to measure the luminous energy of the light emitting part 104 are intercepted, whereby the malfunction of the laser beam source 12 is prevented.

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,
In particular, the present invention relates to an optical scanning device for forming an electrostatic latent image by guiding a laser beam used for an image forming apparatus such as a digital copying machine and a laser printer onto a photosensitive member.

[0002]

2. Description of the Related Art Generally, an optical scanning device used in an image forming apparatus such as a laser printer emits a divergent light beam modulated according to an image signal from a laser light source, and the divergent light beam is scanned in a scanning direction by a first optical system. Into a long linear light flux,
Further, the linear light beam is deflected and scanned by a rotary polygon mirror, and the deflected and scanned light beam is formed into a spot on a photoreceptor by a second optical system, thereby forming an electrostatic latent image.

[0003] In this type of optical scanning device, there is a state in which a laser beam returns from a rotary polygon mirror in the direction of the laser light source, that is, a so-called "return light" is generated. The incidence causes a problem that the operation of the laser light source becomes unstable.

Various proposals have conventionally been made to prevent the laser light source from malfunctioning due to such return light.

For example, in Japanese Patent Application Laid-Open No. 63-67074, the semiconductor laser is prevented from emitting light when the return light from the light deflecting means (rotating polygon mirror) returns to the laser light source. That is, the timings of the synchronization detection and the light quantity control, which need to turn on the laser light source, are set so as not to overlap with the timing at which the return light enters the laser light source.

In Japanese Patent Application Laid-Open No. Hei 6-118319, at least one of the optical members, which are provided in the optical path from the light source to the photosensitive member and allow the light beam to pass therethrough, are arranged at an angle to the optical axis of the light beam. The direction of the return light is changed so as not to return to the laser light source, thereby preventing a malfunction or the like of the laser light source.

On the other hand, in recent image forming apparatuses, high-speed scanning is required for higher-speed or higher-definition image formation, and there is also a need to support printing on various paper sizes.

On the other hand, in synchronous detection and light quantity control in image formation, a certain time interval is required for performing these operations. Therefore, in the high-speed scanning, the rotating polygon mirror is rotated at a high speed, so that the scanning length on the surface to be scanned with respect to these fixed time intervals (hereinafter, referred to as “equivalent scanning length”).
Is required longer than usual. For example, in the case where the lighting time of the laser light source in synchronization detection or light quantity control is limited, it is necessary to reduce the time limit and to secure a long equivalent scanning length in order to speed up the scanning. Condition.

When printing is performed in a free size slightly larger than the standard size, it is necessary to increase the main scanning length of image formation in order to obtain an image area larger than the standard size. Here, instead of increasing the equivalent scanning length as described above, for example, the scanning area (timing) for synchronization detection and light quantity control performed outside the image forming area is changed for each scanning line, and the main scanning length is set to be longer. It can be handled by changing to an area that can be lengthened.

However, even in this case, if the lighting time of the laser light source is limited, the time limit limits the scanning area for synchronous detection and light quantity control.
It is required to reduce this time limit.

That is, when the lighting time of the laser light source is limited in increasing the scanning speed or expanding the image area, the point is to make the lighting time longer.

[0012]

However, according to the above prior art, there are the following problems. In Japanese Patent Application Laid-Open No. 63-67074, since the laser light is turned off at the timing of the return light, it is difficult to secure a sufficient time for performing the synchronization detection and the light amount control by reducing the lighting time. Therefore, it cannot cope with high-speed scanning and expansion of an image area.

On the other hand, according to JP-A-6-118319,
There is no restriction on the laser light-on time, but the configuration of the optical system is complicated, so high-precision parts or high-precision adjustments are required with the realization of products, resulting in cost problems. Come.

In view of the above facts, the present invention prevents malfunction of the laser light source due to the return light, and at the same time, improves the lighting time of the laser light source limited by the return light, so that the scanning is performed at a higher speed. Secondly, it is an object to provide an optical scanning device in which an image area is expanded.

[0015]

An optical scanning device according to claim 1, further comprising: a light source unit having a light emitting unit for emitting a divergent light beam, and a light receiving unit for measuring a light amount of the light emitting unit; An optical system that converts the divergent light beam from the unit into a substantially parallel light beam that is long in the main scanning direction; An optical scanning device comprising: a rotating polygon mirror; and a light shielding unit configured to shield the light receiving unit from light reflected by the rotating polygon mirror and returned from the optical system to the light source unit.

That is, in the present invention, the divergent light beam emitted from the light emitting unit provided in the light source unit is converted into a substantially parallel light beam long in the main scanning direction by the optical system, enters the rotary polygon mirror, and rotates about the axis. It is deflected by a plurality of reflecting surfaces of a rotating polygon mirror.

The light quantity of the light emitting section is measured by the light receiving section, and based on this measurement information, for example, light quantity control for stabilizing the output characteristics of the light emitting section is performed. The light receiving unit is configured to shield the light flux deflected by the plurality of reflection surfaces of the rotary polygon mirror from external light that is reflected in a direction other than the scanning direction for image formation and returns from the optical system to the light source unit. Is shielded from light.

Therefore, the measurement of the light amount of the light emitting unit by the light receiving unit is not affected by the external light, and the malfunction of the light source unit is prevented.

[0019] Thus, the light source unit can be turned on even when the light returns from the optical system to the light source unit, and the lighting time of the laser light source limited by the returned light is improved. This means that, for example, an operation of turning off the light emitting unit when external light is incident is not required. As described above, by increasing the lighting time of the light source unit, the scanning can be further speeded up and the image area can be expanded.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the light shielding unit is a base supporting the light emitting unit.

That is, according to the second aspect of the present invention, since the light shielding means is a base supporting the light emitting portion of the light source, it is not necessary to newly provide a light shielding means, and the structure can be simplified.

[0022]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall configuration of an optical scanning device according to an embodiment of the present invention. The optical scanning device 10
A laser light source 12 that emits a divergent light beam, a collimator lens 14 that converts the divergent light beam into a substantially parallel light beam, an aperture stop 16 that regulates the light beam width, and a light beam that converges in the sub-scanning direction and becomes a long linear light beam in the main scanning direction. Cylinder lens 18 to be guided onto rotating polygon mirror 22, linear polygonal beam of the cylinder lens 18 is rotated at a constant speed about rotation axis 23, and rotating polygonal mirror 22 is deflectively scanned. And the scanned surface L
A scanning lens 24 for scanning the upper image area A at a constant speed is provided.

The optical system 13 is formed by the collimator lens 14, the aperture stop 16, and the cylinder lens 18 here.
In the optical scanning device 10 of the present embodiment, the cylinder lens 18 is used to reduce the size of the optical scanning device.
A folding mirror 20 is disposed between the rotating polygon mirror 22 and the rotating polygon mirror 22.

Further, a synchronization detector 26 for determining a scanning start timing is arranged in the preceding image area S located on the scanning surface L and on the upstream side of the image area A.

FIG. 2 is an enlarged sectional view of the laser light source 12 in the optical scanning device 10. The arrow FR in the figure indicates the forward direction, and the arrow RR indicates the rear direction.

The laser light source 12 is provided on the front surface 1 of the base 100.
The base 102 is erected on the 00a side. Base 102
Is formed in a substantially L-shaped cross-section by a base 102a and an extension 102b bent at a substantially right angle from the base 102a, and a light-shielding surface 102c (front) formed by the extension 102b directed forward. The outer side surface is substantially parallel to the base 100. Furthermore, the extension part 1
02b, the divergent light beam Lbo
A light emitting unit 104 for emitting (laser light) is attached.

On the front surface 100a of the base 100, a position for substantially monitoring the laser light amount of the light emitting unit 104 is provided at a position substantially opposed to the inner side surface 102e behind the light shielding surface 102c of the base 102, that is, behind the light emitting unit 104. A light receiving unit 106 is provided.

Light receiving section 1 provided on base 100
06 and the base 102 to which the light emitting unit 104 is attached are housed in a substantially cylindrical housing 108 attached to the front surface 100 a of the base 100. Further, a transparent protective glass 110 is fitted into the inner surface of the opening 108a provided on the front side (in the direction from which the laser light is emitted) of the housing 108, and contaminates the light emitting unit 104 and the light receiving unit 106. Prevents dust and other intrusions. Thus, the laser light source 12 has an axially asymmetric structure with respect to the optical axis Z of the divergent light beam Lbo emitted from the light emitting unit 104.

The laser light source 12 having these structures
Is connected to a laser light output circuit board 114 by a pin 112 provided on the rear side of the base 100, and a drive current is supplied from the laser light output circuit board 114.

Further, the light emitting section 104 will be described in detail with reference to FIG. The light emitting section 104 is a substantially rectangular parallelepiped in which an active layer 116 for performing laser emission is sandwiched between a P-type semiconductor 118 and an N-type semiconductor 120 and joined in a stacked state.
The base 20 is fixed substantially at the center in the width direction (the direction of the arrow W in the figure) of the base 102 in the laminating direction (the direction of the arrow H in the figure) with the reference numeral 20 as a mounting portion to the front end surface 102d.

The divergent light beam Lbo emitted from the light emitting section 104 of the laser light source 12 is an elliptical divergent light beam having a short width direction (S-axis direction in the drawing) and a long lamination direction (T-axis direction in the drawing). The light quantity distribution as viewed in each axial direction section centered on the optical axis Z has a substantially normal distribution shape as shown in FIGS.

In general, the output characteristics of this type of laser light source tend to fluctuate under the influence of a change in the ambient temperature. Therefore, in order to keep this output characteristic constant, the laser beam emitted backward when the light emitting unit 104 is turned on is monitored by the light receiving unit 106, and the supply of the drive current to the light emitting unit 104 is controlled according to the monitor output. Is performed.

In the image forming apparatus according to the present embodiment, the output characteristics are required to be substantially constant for uniformity of the image density. Light amount control of the light emitting unit 104 is performed.

The synchronization detection for controlling the timing of the start of scanning and the scanning for image formation are performed as follows.
First, the light emitting unit 104 of the laser light source 12 is temporarily turned on on the upstream side of the previous image area S, and the light beam Lba deflected by the rotating polygon mirror 22 rotating in the counterclockwise direction (P direction in the figure).
Scans the previous image area S in the arrow Y direction.

When the light beam Lba enters the synchronous detector 26 and is detected, the laser light source 12 is temporarily turned off, and at the same time, the scanning start timing is determined based on that time.
Starting from the scanning start timing, the laser light source 12 controlled to turn on and off in accordance with the image information
The image area A is scanned by the light beam from the
An electrostatic latent image is formed thereon.

On the other hand, as shown in FIG. 6, in this embodiment, a rotating polygon mirror 22 having a dodecagonal prism shape is used. Here, a linear light beam Lb wider than each reflection surface width of the rotary polygon mirror 22 by the optical system 13 is used to form a reflection surface 22a for forming an image on the surface L to be scanned and a reflection surface 22 adjacent thereto.
This is a so-called “over-filled” optical scanning device that is guided on the rotating polygon mirror 22 across the b and 22c and deflects and scans a part of the linear light beam Lb by the reflection surface 22a.

In this overfilled type, since the total number of reflecting surfaces of the rotary polygon mirror can be increased without increasing the radius of the inscribed circle of the rotary polygon mirror, the load on the drive motor by the rotary polygon mirror 22 is reduced, and at the same time the rotational speed is reduced. This has the advantage that it can be kept low.

In the deflection of the light beam by the rotating polygon mirror 22, the light beam Lb guided to the rotating polygon mirror 22 is changed to the scanning surface L
Reflective surface 22a for deflecting and scanning the upper surface, and adjacent reflective surface 2
When the light beams 2b and 22c are straddled as shown in FIG. 2, unnecessary reflected light beams Lbb and Lbc which do not contribute to the image formation on the scanning surface L are generated from the reflection surfaces 22b and 22c.

The light beam Lba that scans the surface L to be scanned
And the relationship between the unnecessary reflected light beams Lbb and Lbc from the adjacent reflecting surfaces 22b and 22c will be described with reference to FIGS. 1, 6, and 7. FIG.

A light beam Lba that deflects and scans the surface L to be scanned.
Α1 and α between the unnecessary reflected light beams Lbb and Lbc
2, when the reflection angle of the light beam Lba on the reflection surface 22a is a reference (0 °) and the number of surfaces of the rotary polygon mirror 22 is N,
Α1 = + (360 ° N × 2) °, α2 = −
(360 ° N × 2) °. Here, reference numerals are given assuming that the rotation direction of the rotary polygon mirror is the positive direction.

Therefore, in the present embodiment using the twelve rotating polygon mirror, the angle α1 of the unnecessary reflected light beam Lbb with respect to the light beam Lba is α1 = + 60 °, and the unnecessary reflected light beam Lbc
Is α-2 = −60 °, and each light beam is deflected and scanned with this angle difference.

FIG. 7 shows the relationship between the deflection directions of the light beam Lba and the unnecessary reflected light beams Lbb and Lbc. FIG. 7- (1) shows that the light beam Lba is in the vicinity of the synchronization detector 26 in the preceding image area S. 7- (2) shows the light flux Lb
a is a case where scanning is performed near the scanning end end.

The unnecessary reflected light beam Lbc is shown in FIG.
As can be seen from (1) and (2), in any state, the light does not enter the image area A or return to the vicinity of the laser light source 12. Therefore, this unnecessary reflected light flux L
As long as bc is not reflected again by a secondary high-reflection structural wall or the like to enter the image area A or return to the vicinity of the laser light source 12, the operation of the optical scanning device is not adversely affected. In order to prevent the secondary reflection, a structural member having a low reflectance may be provided in the direction of the unnecessary reflected light beam Lbc.

However, the unnecessary reflected light beam Lbb is shown in FIG.
When the light beam Lba scans the vicinity of the synchronization detector 26 in the previous image area S as in (1), the light beam Lba with respect to the incident light beam Lb
The deflection angle α of ba becomes α = −60 °, and the angle α1 between the light beam Lba and the unnecessary reflected light beam Lbb becomes α.
Since 1 = + 60 °, a state occurs in which the incident light beam Lb and the unnecessary reflected light beam Lbb overlap.

Therefore, in this case, the unnecessary reflected light beam Lbb
Are reflected mirrors 20 after being reflected by the reflecting surface 22b,
Like the cylinder lens 18 and the aperture stop 16,
The light goes backward with respect to the incident light beam Lb and is refracted by the collimator lens 14, so that the light returns to the laser light source 12.

This return light is received by the light receiving section 1 in the laser light source 12.
When the light enters the light source 06, the monitor output of the light receiving unit 106 changes due to the influence, and a malfunction such as a change in the laser output characteristic of the light emitting unit 104 occurs. When the light beam Lba in such a state reaches the image area A, the image is disturbed.

In this embodiment, at the timing when the light beam Lba scans upstream of the synchronization detector 26, the reflection surface 22
A state occurs in which b faces the incident light beam Lb. Through this state, the unnecessary reflected light beam Lbb that has returned as light is scanned in the direction of the arrow Ya in front of the laser light source 12. The return light is incident on the laser light source 12 until the light beam Lba scans immediately before the synchronous detector 26.

However, if the unnecessary reflected light beam Lbb deviates from the laser light source 12, there is no problem in its operation. Finally, the light beam Lba scans near the scanning end of the image area A. The scanning is performed to the direction shown in 7- (2).

As described above, the unnecessary reflected light beam Lbb in the direction of the laser light source 12 is scanned in the direction of the arrow Ya, and FIG.
As shown in (2), when the return light Bm1 → Bm2 → Bm3 enters the laser light source 12 in this order, the return light Bm1, Bm3
2 does not enter the light receiving unit 106 because it is blocked by the light blocking surface 102c of the base 102.

As described above, in the present invention, the divergent light beam Lbo emitted from the light emitting portion 104 provided in the laser light source 12 is provided.
Are substantially parallel light beams L long in the main scanning direction by the optical system 13.
b, the light enters the rotary polygon mirror 22 and is deflected by the reflecting surfaces 6a, 6b, and 6c of the rotary polygon mirror 22 that rotates about the rotation axis 23.

The light receiving section 106 is a part of the light beam deflected by the reflecting surfaces 6a, 6b, 6c of the rotary polygon mirror 22.
The optical system 13 is reflected in a direction other than the scanning direction for forming an image.
From the laser light source 12, and is blocked by the base 12 from the return lights Bm1 and Bm2. Thereby, the return light B
In the scanning range from the vicinity of m1 to the arrow Ya, the light receiving unit 106
Therefore, the measurement of the light amount of the light emitting unit 104 is not affected by the return light, so that malfunction of the laser light source 12 is prevented.

Therefore, the laser light source 12 can be turned on even when the return light to the laser light source 12 is generated.
2 can improve the lighting time. Therefore, the equivalent scanning length for synchronization detection and light amount control can be increased, and high-speed scanning and an image area can be expanded.

Furthermore, since a laser lightable area can be secured in front of the synchronous detector 26, such an area can be provided with a degree of freedom in the layout arrangement of the synchronous detector 26 or for controlling the light amount. In this manner, the optical scanning device can be used for expanding the degree of design freedom.

In the optical scanning device according to the present embodiment, there is a case where it is desired to scan the surface L to be scanned in the direction opposite to the direction of the arrow A depending on the method of use. At this time, the rotating polygon mirror 2
2 rotates in the direction opposite to the direction of arrow P, and the synchronous detector 26
Are arranged on the opposite side (upper side in the figure) of the image area A. In this case, as the light beam Lba approaches the scanning downstream end (lower side in the figure) of the image area A, return light to the laser light source 12 is generated, and the scanning downstream area of the image area A poses a problem. Become.

However, in the case of the laser light source 12 of the present embodiment, the same light shielding is performed also in the scanning downstream area, so that the area where the return light enters the light receiving unit 106 is kept away from the image area A. Become.

Therefore, even when the rotary polygon mirror 22 rotates in the opposite direction, the scannable area secured downstream of the image area can be extended to an image area for printing in a free size slightly larger than the standard size. Can be used.

Since the light shielding means of the light receiving unit 106 is the base 102 supporting the light emitting unit 104 of the laser light source 12, the light shielding means can be realized with a simple structure.

In the present embodiment, the description has been given of the mode in which the light beam guided to the rotary polygon mirror straddles the deflection scanning surface and both adjacent surfaces. However, even in the case of a rotating polygonal mirror that enters only one of the adjacent surfaces, the effect on the return light can be similarly obtained.

The means for blocking the return light is not limited to the base of the light emitting section as in the present embodiment.
Various forms are applicable, such as providing a light shielding member separately in the housing.

[0061]

According to the optical scanning device of the present invention, the laser light source does not malfunction due to the return light.
Improving the turn-on time of the laser light source, which is limited by the return light, makes scanning faster and expands the image area.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a main part of a laser light source according to the present invention.

FIG. 3 is an explanatory diagram of a light emitting unit of the laser light source according to the present invention.

FIG. 4 is a graph showing a light amount distribution of a divergent light beam emitted from a light emitting unit of the laser light source according to the present invention, centered on an optical axis in a light emitting unit width direction.

FIG. 5 is a graph showing a light amount distribution of a divergent light beam emitted from a light emitting portion of the laser light source according to the present invention, centered on an optical axis in a light emitting portion stacking direction.

FIG. 6 is an explanatory diagram showing a deflection state of a light beam in the vicinity of a rotary polygon mirror according to the present invention.

FIG. 7 is an explanatory diagram showing a relationship between each deflection direction of a light beam and an unnecessary reflected light beam by the optical scanning device of the present invention;
(1) is the case where the light beam scans near the synchronization detector in the previous image area, and (2) is the case where the light beam scans near the scan end end.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Optical scanning apparatus 12 Laser light source (light source part) 13 Optical system 14 Collimator lens 16 Aperture stop 18 Cylinder lens 22 Rotating polygon mirror 22a, 22b, 22c Reflection surface 23 Rotation axis (axis) 102 Base (light shielding means) 104 Light emitting part 106 Light receiving unit 108a Light shielding unit (light shielding unit) Bm1, Bm2, Bm3 Return light (light returning to the light source unit) Lbo Divergent light beam Lb Light beam

Claims (2)

[Claims] A light source unit having a light emitting unit that emits a divergent light beam and a light receiving unit that measures a light amount of the light emitting unit; and a substantially parallel light beam that emits the divergent light beam from the light source unit in a main scanning direction. An optical system, and a rotary polygon mirror that rotates a substantially parallel light beam incident from the optical system in the main scanning direction and rotates about an axis to deflect by a plurality of reflecting surfaces. An optical scanning device, comprising: a light shielding unit that shields the light receiving unit from light that is reflected by a polygon mirror and returns from the optical system to the light source unit. 2. The optical scanning device according to claim 1, wherein the light shielding unit is a base supporting the light emitting unit.