JPH02230211A - Luminous flux scanning optical device - Google Patents

Abstract

PURPOSE:To set an image writing start position constant without increasing the external diameter of a scanning lens nor the total size of a device by forming an optical path different from an optical path for writing for image writing start position detection and detecting the light from a deflector which straddles on the optical path. CONSTITUTION:The laser beam L emitted by a laser beam source 1 is made incident on a polygon mirror 3, deflected, and passes through the scanning lens 4 to make a scan on a photosensitive drum 5 from an image writing start position 8 to an end position 9. Then another light source 6 and a photodetector 7 are provided for the writing start position detection. Namely, the photodetector 7 receives the luminous flux from the light source 6 and the image writing start position is set constant on each main scanning line based on the light receiving signal from the detector 7. Then the scanning lens part at the outside of the part where the laser beam passes through the scanning lens 4 need not be used. Consequently, the external diameter of the scanning lens 4 need not be made unnecessarily large for the image formation of the luminous flux for image writing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a beam scanning optical device used in a laser beam printer, etc., and particularly to a main scanning start position on an irradiated object.
More specifically, it relates to a scanning optical device equipped with a means for detecting the image writing start position. [Prior Art] Conventionally, in a laser scanning optical system, a spot formed on a photoreceptor is controlled by rotating an optical deflector such as a polygon mirror.
It scans in the main scanning direction, and during that time the necessary image information is written onto the photoreceptor. In this case, the image writing start position may vary to some extent due to uneven rotation of the deflector rotation motor, variations in the dividing precision of the reflective mirror surface of the polygon mirror, and the like.

For this reason, in conventional laser scanning optical systems, in order to keep the image writing start position constant in the main scanning direction, a means for detecting laser light is provided on the photoconductor outside of this writing start position, and light is received from there. The writing start position is determined based on the signal. This situation will be explained using Figure 7. Laser light #! 2l
After passing through the collimator lens 22, the emitted light enters the polygon mirror 23, where it is deflected and sent to the scanning lens 24.
The image is formed on the photosensitive drum 25 via the photosensitive drum 25 to form a spot. As the polygon mirror 23 rotates in the direction of the arrow, the spot moves from the image writing start position 28 to the image writing end {fff! ! During this period, the laser light source 21 is modulated and driven in accordance with the image signal, thereby writing necessary image information onto the photosensitive drum 25. Here, 32 is a detection device for detecting the writing start position 28, and when the rotational state of the polygon mirror 23 is just before writing, that is, the spot of the laser beam moves from the start position 28 to a certain set value in the main scanning direction. When the laser beam comes to the outside, the laser beam enters the detection device 32. In this way, the laser light source 21 is modulated and driven by the image signal after a predetermined time from when the laser light is incident on the detection device 32, and image writing is started from a fixed position 28 in each main scanning line. There is. [Problems to be Solved by the Invention] However, in the conventional example described above, the following problems occur because the light emitted from the laser light source and passing through the scanning lens 24 is used for detecting the writing start position. 1) The light flux that passes through the scanning lens before writing the image,
In other words, since the light beam that comes outside the writing start position in the main scanning line is used, image writing is possible! It is necessary to use a scanning lens system with a scanning angle wider than the required angle of view (the angle of view between positions 28 and 29 in Figure 7), and the outer diameter of the scanning lens system must be larger than the size required for image formation. Become. (2) If the outer diameter or lens diameter of the scanning lens system is not increased, the angle of view for image writing will be narrowed and the light flux at the maximum angle of view of the scanning lens system will be the same as the light flux for detecting the writing start position. However, since the angle of view for image formation is narrow, it is necessary to increase the focal length of the scanning lens system to ensure a main scanning line width of a certain length, which increases the overall size of the device. Resulting in. (3) In particular, in a laser scanning optical system where the F number of the scanning lens system is small (the scanning lens system is bright) and the purpose is to form a minute spot, the diameter of the light beam in the scanning lens system is also large. The above-mentioned drawbacks become significant and become a major problem in terms of equipment size, cost, etc. Therefore, an object of the present invention is to solve the above-mentioned problem by making it possible to set the image writing start position constant without using the light flux that comes before or outside the image writing start position in the main scanning line via the scanning lens system. The objective is to provide a beam scanning optical device that solves the problem. [Means for Solving the Problems] According to the present invention that achieves the above object, a separate optical path that is at least partially different from the image forming light beam optical path is established, and the light beam of this separate optical path passes through a deflector. A light detection means is provided at a location, and the image writing start position is set to a constant value based on light detection by this detection means. Specifically, a light source separate from the image forming light source is provided, and a light detection means is provided where the light from the light source is deflected by a deflector. A scanning lens system may or may not be included in the optical path connecting the separate light source, deflector, and light detection means. Further, the above-mentioned another optical path may be formed by dividing the light beam from the image forming light source with a beam splitter, and a light detection means may be disposed at a place where the divided light is deflected by a deflector.
The light beam from the image forming light source is deflected by a deflector and reflected by a mirror etc. when it comes in front of the scanning lens system, thereby establishing another optical path, and the light from the mirror is received by the detection means. Forms are also possible. [Example] Figure 1 shows a first example of the present invention. In the figure, the laser beam L emitted from the laser light source 1 is transmitted through the collimator lens 2.
After being collimated, the light enters a polygon mirror 3, where it is deflected, passes through a scanning lens 4, and is imaged onto a photosensitive drum 5 to form a spot. As the polygon mirror 3 rotates in the direction of the arrow, the spot is scanned from the image writing start position 8 to the image writing end position 9. During this time, the laser light source 1 is modulated and driven according to the image signal to obtain necessary information. Write on the photosensitive drum 5. In addition to the above, in order to detect the writing start position, another light source 6 and a light detection device ii! 7 is provided. The rotational position of the polygon mirror 3, that is, one deflection reflection surface 3a of the polygon mirror 3
When the direction of the laser beam L is just before writing, that is, when the spot of the laser beam L deflected by the reflective surface 3a is located outside the starting position 8 by a certain set value, the light emitted from the separate light source 6 is directed toward the polygon mirror 3. , the separate light source 6 and the detection device 7 are arranged so that the light passes through the scanning lens 4 and enters the detection device 7 .
Figure 2 (a) shows the configuration of Figure 1 in the main scanning plane (the plane formed over time by the deflected scanning beam), and the sub-scanning plane (perpendicular to the main scanning line from position 8 to 9). side)
The situation is shown in Figure 2(b). As shown in FIG. 2(a), the light beam from the separate light source 6 passes through a portion of the scanning lens 4 inside the portion of the scanning lens 4 through which the laser beam L passes when heading toward the starting position 8, and passes through the detection device 7.
It is designed to enter. For this purpose, another light source 6 is placed on the opposite side of the scanning lens 4 with the collimator lens 2 in between. Further, as shown in FIG. 2(b), the separate light source 6 and the detection device 7 are arranged on opposite sides of the main scanning plane, so that the ejection 'AI7 receives the writing laser beam L. I try not to. However, if an optical path bending mirror or the like is included in the optical path between the separate light source 6 and the detection device 7 due to the configuration, these positions may be arbitrary, and the actual position of the separate light source 6 and the detection device 7 may vary depending on the main scanning direction. Sometimes they come on the same side.

The separate light source 6 may be an LED or the like in addition to a semiconductor laser, and the separate light source 6 and the detection device RL17 may include a lens, an aperture, a slit, a fiber, etc. as necessary. In the first embodiment with the above configuration, the detection device 7 receives the light flux from the separate light source 6, and the image writing start position is set constant in each main scanning line based on the light reception signal from the detection device 7. ．． Then, position 8 on the photosensitive drum 5
, 9 through which the laser beam L passes through the scanning lens 4, the outer diameter of the scanning lens 4 is larger than that required for imaging the image writing light beam. It doesn't have to be big.

FIG. 3 shows a second embodiment of the invention. In the second embodiment,
When the light emitted from the separate light source 1O is incident on the detection device 1l, it is configured so that it is reflected by the polygon mirror 3 and then enters the detection device 11 without passing through the scanning lens 4. Of course, even when the light from the separate light source 10 is reflected by the polygon mirror 3 and goes elsewhere, it is set so as not to interfere with image formation by the laser beam L. Other points are substantially the same as the first embodiment. FIG. 4 shows a third embodiment of the invention. In comparison with the second embodiment, in this example, lenses 14 and 15 are inserted between the separate light source 12, the detection device 13, and the polygon mirror 3, respectively, and the mirror surfaces of the separate light source 12 and the polygon mirror 3 are The mirror surface of the polygon mirror 3 and the detection device 13 are both placed in a conjugate relationship. Figure 5, viewed from the sub-scanning plane direction, clearly shows this conjugate relationship. Therefore, in the second embodiment, when the light emitted from the separate light source 12 enters the detection device l3, it passes through the lens 14 and is reflected by the mirror surface of the polygon mirror 3, and then is reflected from the lens 15.
FIG. 6 shows a fourth embodiment of the invention. In this example, the positions of the separate light source 16 and the detection device 17 are reversed compared to the first embodiment.

In this case, when the light emitted from the separate light source l6 enters the detection device 17, it passes near the center of the scanning lens 4, is reflected by the polygon mirror 3, and enters the detection device 17.

Other points are the same as the first embodiment.

In the above embodiments, a separate light source was provided to establish an optical path to the detection device, but the light from the image forming light source is split or bent using a beam splitter or mirror, and guided to the detection device, and from there It is possible to keep the writing start position 8 constant based on the light reception signal.

For example, the laser beam L that is reflected by the polygon mirror 3 and should normally be directed outside a certain set value of the starting position 8 is bent by a mirror placed in front of the scanning lens 4 and guided to the detection device. In this case as well, there is no need to make the outer diameter of the scanning lens 4 larger than necessary.

Also, for example, the laser beam L from the laser light source 1 is split by a beam splitter before the polygon mirror 3, and the split light is made incident on the polygon mirror 3 using a mirror or the like, where it is reflected. Laser light that should originally go outside a certain set value of the starting position 8 is guided to the detection device.
In this case, either the scanning lens 4 is not used or the scanning lens 4 is not used.
If the laser beam is guided to the detection device through a portion near the center of the scanning lens 4, there is no need to make the outer diameter of the scanning lens 4 larger than necessary. [Effects of the Invention] As described above, in order to detect the image writing start position, for example, a light source different from the writing light source is provided to form an optical path that is at least partially different from the writing optical path, By providing a means to detect the light from the deflector that follows this path, it is possible to set the starting position of image writing to a constant value without increasing the outer diameter of the scanning lens or the entire device unnecessarily.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of the first embodiment of the present invention, and FIG. 2(a) is a diagram showing the state of the first embodiment in the main scanning plane. FIG. 12(b) is a diagram showing the state in the sub-scanning plane of the first embodiment,
Fig. 3 is a perspective view of the second embodiment of the present invention, Fig. 4 is a perspective view of the third embodiment of the invention, Fig. 5 is a leapfrog for explaining the third embodiment, and Fig. 6 is a book. FIG. 7 is a perspective view of the fourth embodiment of the invention and is a diagram for explaining a conventional laser scanning optical system. 1... Laser light source, 2... Collemator lens, 3... Polygon mirror, 4... Scanning lens, 5... Photosensitive drum %6, 1O, 12, l6
...Another light source, 7, 11, l3, l7...Detection device, 14, l5...Lens

Claims (1)

[Claims] 1. In a light beam scanning optical device having an image forming light source, a light deflector, and a scanning lens system, a light beam emitted from an image forming light source is exposed to light through a light deflector and a scanning lens system. A separate optical path that is at least partially different from the optical path guided to the main scanning line on the body is formed, and a light detecting means is provided at a location where the light beam following this separate optical path is deflected by an optical deflector, and the light detecting means A beam scanning optical device in which the image writing start position of each main scanning line on the photoconductor is set to a constant value based on a light reception signal from the photoreceptor. 2. The beam scanning optical device according to claim 1, wherein the separate optical path is formed between a light source other than the image forming light source and the light detection means. 3. The beam scanning optical device according to claim 2, wherein the light from said separate light source is deflected by a light deflector and then enters the light detection means via a scanning lens system. 4. The beam scanning optical device according to claim 2, wherein the light from said separate light source passes through a scanning lens system, is deflected by a deflector, and then enters the light detection means. 5. The beam scanning optical device according to claim 2, wherein the light from said separate light source is deflected by a light deflector and then enters the light detection means without passing through a scanning lens system. 6. The beam scanning optical device according to claim 5, wherein the separate light source and the deflection surface of the deflector, and the deflection surface of the deflector and the light detection means are each placed in a conjugate relationship with each other by a lens system. 7. The beam scanning optical device according to claim 1, wherein the image forming light source is a laser light source. 8. The beam scanning optical device according to claim 1, wherein the light detecting means receives the light via a separate optical path before the start of surface image writing in each main scan.