JPH07228004A - Mechanism for detecting writing start-off position of optical scanning apparatus - Google Patents

Abstract

PURPOSE:To miniaturize the optical scanning apparatus by improving the degree of freedom for arranging optical members such as a photo acceptance unit. CONSTITUTION:A curved mirror 28 is arranged close to the position corresponding to the start-off position for writing data on a photosensitive drum in a surface scanned by a light beam B3. A photo acceptance unit 29 is placed on the upstream side of the scanning by the light beam B3 opposite to the curved mirror 28. A light beam B4 which is reflected by a polygon mirror 22 and outgoing from a ftheta lens is collected by the curved mirror 28 to be focused on the photo acceptance face of the photo acceptance unit 29.

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 for scanning a light beam in order to write print data on a photosensitive drum in a laser printer or the like, and more particularly, to detect a writing start position on the photosensitive drum. Related to the mechanism.

[0002]

2. Description of the Related Art A conventional optical scanning device of this type is shown in FIG. The light information generated by the light source unit 11, that is, the light beam B1 passes through the correction cylinder lens 12 and enters the reflecting surface of the polygon mirror 13 that rotates at a constant speed. With the rotation of the polygon mirror 13, the light beam B1 scans in the direction of arrow A, and the scanning speeds of the fθ lenses 14 and 15 are corrected to constant values.

Before the writing of optical information on the photosensitive drum D is started, the light beam B2 emitted from the fθ lens 15 is reflected by the beam detection mirror 16 and is incident on the light receiving element 18 via the correction cylinder lens 17. Is irradiated. When the amount of light received by the light receiving element 18 exceeds a predetermined value, the beam detection circuit 19 outputs a horizontal synchronizing signal. When the horizontal synchronization signal is input to the control unit (not shown) of the light source unit 11, the light source unit 11 is driven after a predetermined time elapses with reference to this input time point, and the scanning light beam B3 transmits optical information to the photosensitive drum D. Is started to be written.

[0004]

However, when it is necessary to bring the light receiving element 18 and the beam detection circuit 19 closer to the beam detection mirror 16 side, such as when the optical scanning device is downsized, the correction cylinder lens 17 is provided. Light beam B3
However, such an arrangement cannot be adopted because the light beam B3 interferes with the light beam B3. That is, according to the conventional configuration, the mounting position of the optical member such as the light receiving element is limited, and there is a certain limit to miniaturization of the optical scanning device.

It is an object of the present invention to provide a writing start position detecting mechanism which can increase the degree of freedom of arrangement of optical members such as light receiving elements and further downsize the optical scanning device.

[0006]

A writing start position detecting mechanism according to the present invention writes predetermined information on a photosensitive member by deflecting a light beam emitted from a light source by an optical deflector to perform main scanning. An optical scanning device comprising: a light receiving element capable of detecting a light beam; and a single optical member for reflecting and condensing the light beam and irradiating the light receiving element with the light receiving element. It is characterized in that it is arranged at a position upstream of the information writing start position in the light beam main scanning direction.

[0007]

The present invention will be described below with reference to illustrated embodiments. FIG. 2 is a plan view showing the configuration of an optical scanning device having a write start position detecting mechanism according to an embodiment of the present invention.

A polygon mirror (optical deflector) 22 is provided in the housing 21, and the polygon mirror 22 is provided.
Is driven by a motor (not shown) and rotates counterclockwise in the figure at a constant speed. A light source 23 for generating optical information is provided on the wall of the housing 21. A correction cylinder lens 26 that corrects optical characteristics such as astigmatism due to a processing error of the fθ lenses 24 and 25 is disposed between the light source unit 23 and the polygon mirror 22, and is generated by the light source unit 23. The light information, that is, the light beam B1 passes through the correction cylinder lens 26 and enters the reflecting surface of the polygon mirror 22.

The fθ lenses 24 and 25 are provided on the exit 27 side of the housing 21 with respect to the polygon mirror 22. The rotation of the polygon mirror 22 causes the light beam B1 to perform main scanning in the direction of the arrow A, and the scanning speed is corrected to a constant value by passing through the fθ lenses 24 and 25. Light beam B3 emitted from the fθ lenses 24 and 25
Passes through the ejection port 27 and is irradiated onto the photosensitive drum (photosensitive member) D, whereby a charge signal corresponding to optical information is formed on the photosensitive drum D.

The photosensitive drum D rotates about the major axis, that is, in the sub-scanning direction. The light beam B3 is a laser beam that is on-off modulated and is irradiated onto the photosensitive drum D to form a latent image in a dot sequence. By rotating the photosensitive drum D, these dot arrays form a latent image together with other dot arrays, and this latent image is printed on a predetermined surface by a known method.

A curved mirror 28 is arranged in the vicinity of a position on the exit 27 side of the f.theta. Lens 25 and corresponding to a position where information writing onto the photosensitive drum D is started. That is, the curved mirror 28 is provided in the plane scanned by the light beam B3.

The reflecting surface 28a of the curved mirror 28 is the light source section 2
A light receiving element 29 that faces the third side and is capable of detecting the light beam B4 reflected by the curved mirror 28 is provided between the curved mirror 28 and the light source unit 23. That is, the light receiving element 29 causes the light beam B3 to pass through the curved mirror 28.
Is arranged on the side opposite to the scanning direction, that is, on the upstream side in the scanning direction. The curved mirror 28 focuses the light beam B4 in the sub-scanning direction perpendicular to the main scanning direction, whereby the light beam B4 irradiates the light receiving element 29 with sufficient energy, and the surface of the reflecting surface of the polygon mirror 22 is tilted. The effect of is compensated.

A beam detecting circuit 30 is connected to the light receiving element 29. The beam detecting circuit 30 sends a horizontal synchronizing signal to the control section 31 of the light source section 23 when the light receiving element 29 receives the light beam B4. Output. The control unit 31 receives the horizontal synchronization signal, and after a predetermined time has passed, the light source 23
And the light source 23 turns on the laser light. That is, the curved mirror 28 is provided at a position where the light beam B4 is applied to the light receiving element 29 and the measurement of the predetermined time is started prior to the start of writing the optical information on the photosensitive drum D.

FIG. 3 is a perspective view showing the curved mirror 28. As can be understood from FIGS. 2 and 3, the reflecting surface 28a of the curved mirror 28 is a concave surface having a curvature in the sub-scanning direction, and the light beam B4 emitted from this reflecting surface 28a is condensed and received by the light receiving element 29. Is configured to focus on the light receiving surface of the.

The operation of this embodiment will be described. The light beam B1 output from the light source unit 23 is corrected by the correction cylinder lens 26.
Is reflected by the reflecting surface of the polygon mirror 22, and enters the fθ lenses 24 and 25. As the polygon mirror 22 rotates, the light beam B1 is reflected by the curved mirror 28 and enters the light receiving element 29. Light receiving element 29
When the light beam B4 is detected, the horizontal synchronizing signal is output from the beam detecting circuit 30 and input to the control unit 31 of the light source unit 23. As a result, the light source unit 23 is driven after a predetermined time elapses with respect to this input time point, and the scanning light beam B3
Thus, writing of optical information on the photosensitive drum D is started.

As described above, in this embodiment, the light receiving element 29
Is arranged upstream of the curved mirror 28 in the scanning direction of the light beam B3. In other words, the light receiving element 29 and the curved mirror 28 cause the light beam B3 to write optical information on the photosensitive drum D. Therefore, the area R to be scanned is provided in front of the scanning direction. Therefore, according to the present embodiment, even if the light receiving element 29 and the beam detecting circuit 30 are provided in the portion close to the curved mirror 28, the light receiving element 29 and the beam detecting circuit 3 do not interfere with the light beam B3.
Since the degree of freedom of the arrangement of 0 is improved, it is easy to downsize the optical scanning device.

Further, according to this embodiment, the light beam B4 is focused on the light receiving surface of the light receiving element 29 only by the curved mirror 28 as an optical member, and a correction is made between the curved mirror 28 and the light receiving element 29. No cylinder lens is provided. Therefore, compared with the conventional device, the number of parts is reduced, the configuration is simplified, and the cost can be reduced.

FIG. 4 shows a prism 42 for irradiating the light receiving element 29 with the light beam B4.
Has an emission surface 42a which is curved in a cylindrical shape. The light beam B4 emitted from the fθ lens 25 (FIG. 2) is condensed and emitted on the convex emission surface 42a having a curvature in the sub-scanning direction, and is incident on the light receiving element 29 (FIG. 2).

The prism 42 is made of plastic and can focus the light beam B4 on the light receiving element 29 without providing a correction cylinder lens. Therefore, even if the prism 42 is used, the same effect as that obtained by using the curved mirror 28 can be obtained.

The position where the light receiving element 29 is provided is
The position is not limited to between the curved mirror 29 and the light source unit 23 as shown in FIG. 2, and may be, for example, closer to the emission port 27 side than the curved mirror 28.

[0021]

As described above, according to the present invention, the degree of freedom in arranging the optical members such as the light receiving element is increased, and the optical scanning device can be further downsized.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of a conventional optical scanning device.

FIG. 2 is a plan view showing the configuration of an optical scanning device including a write start position detection mechanism that is an embodiment of the present invention.

FIG. 3 is a perspective view showing a curved mirror.

FIG. 4 is a perspective view showing a prism for irradiating a light beam on a light receiving element.

[Explanation of symbols]

 22 polygon mirror (optical deflector) 23 light source section 28 curved mirror 29 light receiving element 42 prism D photosensitive drum

Claims (6)

[Claims] 1. An optical scanning device for writing predetermined information on a photosensitive member by deflecting a light beam emitted from a light source by an optical deflector to perform main scanning, and a light receiving device capable of detecting the light beam. An element and a single optical member that reflects and collects the light beam and irradiates the light-receiving element, and the optical member is configured to emit the light beam from a position where the writing of information on the photosensitive member is started. A write start position detection mechanism of an optical scanning device, which is arranged at a position on the upstream side in the main scanning direction. 2. The write start position detection mechanism of the optical scanning device according to claim 1, wherein the optical member focuses a light beam. 3. The write start position detection mechanism of the optical scanning device according to claim 1, wherein the optical member focuses the light beam in a sub-scanning direction perpendicular to the main scanning direction. 4. The write start position detection mechanism of the optical scanning device according to claim 3, wherein the optical member focuses the light beam in the main scanning direction. 5. The write start position detecting mechanism of the optical scanning device according to claim 1, wherein the optical member is a mirror having a curved reflecting surface. 6. The write start position detecting mechanism of the optical scanning device according to claim 1, wherein the optical member is a prism having a curved exit surface.