JPH0682171B2 - Beam position detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laser beam printer or the like that scans an image forming surface with a laser beam that is repeatedly deflected by a deflecting means within a constant angle range and modulated according to a recording signal. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam position detecting device for detecting a scanning laser beam at a predetermined scanning position in order to obtain the timing of modulation for laser beam scanning, that is, horizontal synchronization in an image forming apparatus.

[Prior Art] Recently, a charged laser beam (photosensitive drum) is exposed and scanned by a laser beam modulated based on image information such as figures and characters to form an electrostatic latent image, which is developed (developed). Image), transfer, fixing and other copying processes (copying process by so-called electrophotography) to obtain a hard copy of image information on recording paper, or a laser beam scans the surface of the photosensitive material to print. Image forming apparatuses such as laser photoplotters for drawing original plates such as substrates are becoming widespread.

An image forming apparatus for repeatedly deflecting and scanning such a laser beam repeats the laser beam from the semiconductor laser 2 by a polygon mirror 4 which is a deflecting means, as shown in FIGS. 6 to 7 as an example of a laser beam printer. The image forming surface (photosensitive drum 1) is deflected to perform main scanning in the rotation axis direction. The photosensitive drum 1 is rotated (sub-scanned) in synchronization with the main scanning by the laser beam.

In this case, in order to accurately form a latent image of image information on the surface of the photosensitive drum 1, it is indispensable to modulate the laser beam in synchronism with the scanning, and therefore, the end of the scanning range that does not contribute to image formation. The scanning laser beam is detected by the light receiving element 7, and the laser beam detection signal from the light receiving element 7 is used as the horizontal synchronizing signal. That is, the writing start position is synchronized by starting the laser beam modulation after a predetermined time when the light receiving element 7 detects the laser beam.

The laser beam repeatedly deflected by the polygon mirror 4 is corrected by the fθ lens 5 so as to scan the surface of the photosensitive drum 1 at a constant velocity proportional to the deflection angle, and is converged on the surface of the photosensitive drum 1. Therefore, the light receiving element 7
Is normally arranged at a position where the distance from the fθ lens 5 is equal to the distance from the fθ lens 5 to the surface of the photosensitive drum 1. For example, as shown in FIG. 6, a mirror 8 which is a position detecting laser beam reflecting member for reflecting and bending the scanning laser beam is arranged at the end of the scanning range of the laser beam, and on the optical path of the scanning laser beam reflected by the mirror 8. The light receiving element 7 is arranged at a predetermined position of the
And the optical path lengths to the photosensitive drum 1 are set to be equal. Reference numeral 6 in the drawing denotes a cylindrical lens for focusing the laser beam toward the light receiving element 7 even when the laser beam is deviated in the direction orthogonal to the scanning movement direction. By arranging the cylindrical lens in this way, it is possible to allow a certain amount of laser beam deviation in a direction orthogonal to the laser beam position while maintaining the laser beam scanning position detection accuracy, and it is possible to relax the accuracy of components and the assembly accuracy. It is a thing.

By the way, recently, there is a demand for downsizing of the entire apparatus, and there is a demand for making the entire apparatus compact by shortening the optical path length of the scanning laser beam as much as possible, but for that purpose, the lens system must have a high refractive index. Therefore, there is a problem that the aberration increases and the cost increases. In other words, there is a conflicting requirement that the optical path length of the scanning laser beam should be made as short as possible in order to make the entire apparatus compact, while the optical path length should be made as long as possible in terms of cost and performance.

Therefore, the optical path of the laser beam is bent by a mirror,
It ensures both the required optical path length and the downsizing of the device. That is, as shown in FIGS. 6 to 7, the fθ lens 5
To the photosensitive drum 1 with mirrors 10 and 20 in the optical path,
The optical path of the scanning laser beam is bent by the mirrors 10 and 20 to secure a required optical path length, and the overall size of the apparatus is reduced.

[Problems to be Solved by the Invention] However, in the case where the scanning laser beam is configured to be reflected and bent through the mirrors 10 and 20 in the optical path from the fθ lens 5 to the photosensitive drum as described above, The mirrors 10 and 20 that guide the scanning laser beam to the photosensitive drum 1 and the mirror 8 that guides the scanning laser beam at the end of the scanning range to the light receiving element to obtain the horizontal synchronizing signal interfere with each other to hinder the free arrangement structure. This has been an obstacle to miniaturization.

[Object of the Invention] The present invention has been made in view of the background as described above, and the mirror that bends the optical path of the scanning laser beam and guides it to the photosensitive drum can be arranged freely, and the optical path length is secured. It is also an object of the present invention to provide a beam position detection device that can be configured in a small size as a whole.

[Means for Solving the Problems] Therefore, in the beam position detecting device according to the present invention, the mirror member is formed with the surface of the light-transmitting base material as a reflecting surface, and a predetermined side before the image writing is formed on the side of the mirror member. A position detecting laser beam reflecting member for reflecting and bending the scanning laser beam at the scanning position in the direction of incidence from the side end face is provided in the mirror member, and the laser beam reflected and bent by the position detecting laser beam reflecting member is The light receiving element is arranged to face the end of the mirror member that transmits through the mirror member and exits.

Further, the mirror member is formed by using the surface of the light transmitting base material as a reflecting surface, and a side end portion of the mirror member irradiated with a scanning laser beam at a predetermined scanning position before image writing,
A transmissive surface portion through which a laser beam can be transmitted and incident into the mirror member, and an inner reflection surface that is bent and reflected in a direction in which the scanning laser beam incident into the mirror member through the transmissive surface portion is transmitted through the mirror member. And a light receiving element is arranged opposite to the end of the mirror member through which the laser beam reflected and bent by the inner reflecting surface passes through the mirror member and is emitted.

Furthermore, the laser beam emitting surface of the mirror member is formed in a cylindrical lens shape.

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

FIG. 1 is a schematic configuration diagram of a scanning optical system in a laser beam printer to which an embodiment of a beam position detecting device according to the present invention is applied.

The laser beam printer is used as an external output device such as a computer, and the information decomposed into dots is irradiated by the laser beam X from the semiconductor laser 2 to the photosensitive drum 1.
The surface is scanned in the axial direction of the photosensitive drum 1 (main scanning), the photosensitive drum 1 is rotated (sub scanning), and the toner is transferred (printed) to a recording sheet (not shown) by an electrophotographic method and output. .

The scanning optical system shown in the figure scans the photosensitive drum 1 with a laser beam X from a semiconductor laser 2 by a rotating polygon mirror 4, and includes a semiconductor laser 2, a cylinder lens 3, a polygon mirror 4, an fθ lens 5, and a cylindrical lens. 6, a light receiving element 7, a mirror 8 as a position detecting laser beam reflecting member, a first mirror 10 and a second mirror 20 are arranged in a predetermined positional relationship.

That is, the semiconductor laser 2 is arranged so as to emit a laser beam toward the polygon mirror 4 at a predetermined angle, and the polygon mirror 4 is placed between the semiconductor laser 2 and the polygon mirror 4.
The cylinder lens 3 is arranged with the direction orthogonal to the rotation axis of the above as the cylinder axis direction. An fθ lens 5, a first mirror 10 and a second mirror 20 are installed between the polygon mirror 4 and the photosensitive drum 1, and the polygon mirror in which the laser beam from the semiconductor laser 2 of the first mirror 10 rotates. Four
The mirror 8 is arranged on the side of the end face 13 which is the scanning start side of the laser beam reflected and scanned by, and the light receiving element 7 is arranged on the side end on the opposite side.

The first mirror 10 is formed on the one surface of the substrate 11 formed of glass, which is a light transmissive member, in an elongated rectangular shape with a predetermined thickness,
The reflective surface 12 is formed by vacuum deposition of aluminum or the like. The reflecting surface 12 faces the polygon mirror 4 and is arranged at a predetermined position in the optical path of the scanning laser beam at a predetermined angle so as to reflect the scanning laser beam toward the second mirror 20. The length is equal to or longer than the scanning range of the scanning laser beam at the installation position of the first mirror 10.

As described above, the mirror 8 is arranged on the side of the end surface 13 on the scanning start side, and the scanning laser beam at the predetermined scanning position before image writing is reflected in the first mirror 10 from the side end thereof. It is arranged at a predetermined angle so as to be bent.

The cylindrical lens 6 and the light receiving element 7 are arranged in series facing the end surface 14 of the first mirror 10 opposite to the side end surface 13 side on which the mirror 8 is arranged.

Like the first mirror 10, the second mirror 20 has one surface as a reflecting surface, and the reflecting surface causes the scanning laser beam reflected by the reflecting surface 12 of the first mirror 10 to be reflected and bent to form a photosensitive drum. It is arranged at a predetermined position and at a predetermined angle so as to be guided to one surface.

Thus, in the scanning optical system in the laser beam printer device configured as described above, the scanning laser beam is detected by the light receiving element 7 by operating as follows, and the horizontal synchronizing signal is obtained.

That is, the laser beam X from the semiconductor laser 2 is repeatedly deflected by a rotating polygon mirror 4 within a certain angle range,
The scanning laser beams X ', X "are obtained.

Of these, the scanning laser beam X ′ at a predetermined position on the scanning start side end portion that does not contribute to image formation is reflected and bent by the mirror 8 as shown in FIG. The light enters the base material 11 from the end surface 13 of the mirror 10, passes through the first mirror 10 in the longitudinal direction, exits from the opposite end surface 14, and enters the light receiving element 7 via the cylindrical lens 6. Then, the scanning position of the laser beam is detected by the light receiving element 7 detecting the scanning laser beam X '.

As described above, since the scanning laser beam X ′ that obtains the horizontal synchronizing signal when detected by the light receiving element 7 is configured to pass through the first mirror 10, the mirror 8 and the mirror that guides the scanning laser beam to the photosensitive drum 1 are provided. Since interference with (10, 20) can be prevented and the mirrors can be freely arranged, the entire device can be made smaller while ensuring the optical path length.

In the above embodiment, the mirror 8 and the light receiving element 7 are arranged on the side of the first mirror 10 so that the scanning laser beam X'is transmitted through the first mirror 10, but the second mirror 20 is transmitted. It may be configured as follows.

Next, a second embodiment of the present invention shown in FIGS. 3 to 4 will be described. The basic configuration of this embodiment is substantially the same as that of the first embodiment described above, and the portions having the same functions are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the first mirror 10, which is a mirror member for guiding the scanning laser beam onto the photosensitive drum 1, has a function as a position detecting laser beam reflecting member.

That is, the first mirror 10 is, as in the first embodiment, a reflecting surface 12 formed by vacuum-depositing aluminum or the like on one surface of a base material 11 formed of glass, which is a light-transmitting member, in an elongated rectangular shape with a predetermined thickness. Is formed on the end face 13 side of the scanning start side, a transmissive portion 11A as a transmissive surface portion in which a reflective coating such as aluminum is not formed is formed, and the transmissive portion 11A formation side The end surface 13 of the is formed obliquely at a predetermined angle in the thickness direction to form an inner reflecting surface 11B. When the transmitting portion 11A is irradiated with the scanning laser beam X ', as shown in FIG. X'is incident on the base material 11 of the first mirror 10 without being reflected, and the internal reflection surface
At 11B, the first mirror 10 is reflected and bent in a direction of being transmitted in the longitudinal direction.

The cylindrical lens 6 and the light receiving element 7 are arranged in series so as to face the end surface 14 on the side opposite to the end surface on which the transmissive portion 11A and the inner reflection surface 11B are formed.

Thus, in the laser beam printer device configured as described above, the laser beam X from the semiconductor laser 2 is repeatedly deflected by a polygon mirror 4 which is rotated, and becomes a scanning laser beam X ′, X ″.

Of these, the scanning laser beam X ′ at the end portion on the scanning start side, which does not contribute to image formation, is transmitted through the transmissive portion 11A of the first mirror 10, enters the base material 11, and is reflected and bent by the inner reflection surface 11B. . The laser beam at the predetermined scanning position, which is reflected and bent by the inner reflection surface 11B, passes through the inside of the first mirror 10 in the longitudinal direction and is emitted from the opposite end surface 14, and the cylindrical lens 6
The light beam is incident on the light receiving element 7 through the light receiving element 7, and the light receiving element 7 detects the scanning laser beam X ′, whereby the scanning position of the laser beam is detected.

With the above configuration, a mirror (corresponding to the mirror 8 in the prior art and the first embodiment) for guiding the scanning laser beam to the light receiving element is unnecessary, and therefore, the mirror and the scanning laser beam are provided to the photosensitive drum. Mirror leading to 1 (10,2
(0) does not interfere with each other, and the mirrors can be freely arranged. Therefore, the entire apparatus can be made smaller while ensuring the optical path length.

FIG. 5 shows the light receiving element 7 in the first and second embodiments described above.
FIG. 6 is a perspective view of an embodiment in which the cylindrical lens 6 arranged in front of is formed integrally with a mirror (a first mirror 10 in the embodiment) through which a laser beam passes.

In this, the end face 14 of the first mirror 10 on the laser beam emitting side (on the side where the light receiving element 7 is arranged) is formed in a cylindrical lens shape. With this configuration, a cylindrical lens and a component for fixing the cylindrical lens, which are separate components, are not required, and the component cost and the assembly cost for installing and fixing the cylindrical lens can be reduced. That is, the number of parts can be reduced and the assembling cost can be reduced, which can contribute to the cost reduction of the entire apparatus.

[Advantages of the Invention] As described above, according to the beam position detecting apparatus of the present invention, it is possible to freely arrange the mirror that bends the optical path of the scanning laser beam and guides it to the photosensitive drum, and to secure the optical path length. In addition, the entire device can be made compact.
Further, the cost can be reduced by forming the end surface of the mirror member into a cylindrical lens shape.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a scanning optical system of a laser printer to which an embodiment of a beam position detecting device according to the present invention is applied, FIG. 2 is its II arrow view, and FIG. 3 is a second embodiment. FIG. 4 is a schematic perspective view of a scanning optical system of a laser printer, FIG. 4 is a view taken along arrow IV, FIG. 5 is a partially enlarged perspective view of an embodiment in which a cylindrical lens is integrally formed with a mirror, and FIG. 6 is a conventional example. FIG. 7 is a schematic perspective view of a scanning optical system of the laser printer, and FIG. 7 is a side view thereof. 1 ... Photosensitive drum (image forming surface) 4 ... Polygon mirror (deflecting means) 7 ... Light receiving element 10 ... First mirror (mirror member) 11 ... Base material 11A ... Transmissive portion (transmissive surface portion) 11B ...... Internal reflecting surface 12 ...... Reflecting surface 13 ...... Side end surface 14 ...... Laser beam emitting side end surface (laser beam emitting surface) X ...... Laser beam X '…… Scanning laser at a predetermined scanning position before image writing Beam X ″ ... Scanning laser beam

Claims (3)

[Claims] 1. A laser beam, which is repeatedly deflected by a deflecting means within a certain angle range, is modulated in accordance with a recording signal, and the laser beam is reflected and bent by a mirror member to be guided to an image forming surface for main scanning. In the image forming device
The mirror member is formed by using the surface of the light-transmitting substrate as a reflecting surface, and a scanning laser beam at a predetermined scanning position before image writing is made incident on the side of the mirror member into the mirror member from its side end surface. A position detecting laser beam reflecting member for reflecting and bending in a direction to be made is provided, and the laser beam reflected and bent by the position detecting laser beam reflecting member is transmitted through the mirror member and emitted, and the light receiving element is provided at an end portion of the mirror member. The beam position detecting device is characterized in that the two are arranged to face each other. 2. A laser beam, which is repeatedly deflected by a deflecting means within a certain angle range, is modulated in accordance with a recording signal, and the laser beam is reflected and bent by a mirror member to be guided to an image forming surface for main scanning. In the image forming device
The mirror member is formed with the surface of the light transmitting base material as a reflecting surface, and a side end portion of the mirror member irradiated with a scanning laser beam at a predetermined scanning position before image writing,
A transparent surface portion through which a laser beam can be transmitted and incident into the mirror member, and an internal reflection that reflects and bends the scanning laser beam incident into the mirror member through the transparent surface portion in a direction of transmitting through the mirror member. A laser beam forming a surface, wherein a laser beam reflected and bent by the inner reflection surface is configured by disposing a light receiving element at an end of the mirror member that is transmitted through the mirror member and emitted. Position detection device. 3. A laser beam emitting surface of the mirror member,
The beam position detection device according to claim 1, wherein the beam position detection device is formed in a cylindrical lens shape.