JP2002055299A - Light beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a line neatly aligned to a straight form by eliminating the offsetting, bending, etc., in the sub-scanning direction of a scanning line after joining together. SOLUTION: The light beam scanner, which forms an image by scanning a photoreceptor with light beams from its prescribed position to its end by two writing optical systems by using one deflecting means, is provided with a stepping motor 17 as a means for regulating the beam positions in the sub- scanning direction at one of respective final mirrors 9-1 and 9-2 for introducing the beams of the two writing systems onto a surface to be scanned and an eccentric cam 18 as a means for regulating the inclination of the beam at the other thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device used as an optical writing device for an image forming apparatus such as a digital copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art While digitalization of copiers is progressing, digitalization of wide-width machines is also progressing, and higher image quality is required. At present, LED arrays are mainly used for wide-width digital devices such as A1 and A0, but the cost is higher and the image quality is inferior to the laser system. However, considering the laser writing of A0 width, the size of the unit and the cost are high due to the length of the optical path, the size of the lens, the size of the polygon motor, the size of the mirror, and the length of the reflection mirror. Become. As a means for solving this problem, various methods have been conventionally proposed for connecting two writing systems in the main scanning direction to obtain a wide scanning width. According to this method, the unit can be made compact and the cost can be reduced. However, it is difficult to achieve a technique for accurately aligning the joints (a technique for synchronizing the rotation of the two polygons and correcting the deviation of the scanning line). There are various issues for practical use.

FIG. 13 is a schematic perspective view of a light beam scanning device showing an example of this kind of technology. 8, the left half optical system in FIG. 8 is referred to as a first optical system 100, and the right half is referred to as a second optical system 200. In the first optical system 100, a laser diode (hereinafter, referred to as “LD”) 1-1 as a light emitting unit is controlled by a driving device (not shown) to emit a laser beam modulated according to an image signal. The beam converted into parallel light by the collimating lens 2-1 passes through the cylindrical lens 3-1 and enters the polygon mirror 4. The laser light reflected and scanned by the polygon mirror 4 is divided into first and second laser beams.
Are changed from constant angular velocity deflection to constant velocity deflection by the Fθ lenses 5-1 and 6-1 respectively, and reflected by the first, second and third folding mirrors 7-1, 8-1 and 9-1,
It is guided in the direction of the photosensitive drum 10 and is scanned from a predetermined position substantially at the center of the scanning position toward the end.

[0004] The second optical system 200 is connected to the first optical system 10.
The laser beam emitted from LD 1-2 of 1-2 is arranged at a position rotated by 180 degrees about the polygon mirror, and travels through a similar path to reach the photosensitive drum 10 to be substantially at the center of the scanning position. Scanning is performed from a predetermined position toward an end in a direction opposite to the first optical system 100.

[0005] 11-1, 11-2 and 16-1, 16-
Reference numeral 2 denotes a synchronization detection unit and a synchronization detection mirror of the first and second optical systems 100 and 200, respectively.
1-1 and 11-2 are provided outside the image area of the laser beam and detect the scanning timing of the laser beam for each scanning of the laser beam. A writing control circuit (not shown) synchronizes the scanning timing of the laser beam with the writing start position in accordance with the detected timing.

[0006] Fig. 14 is a schematic diagram of this as viewed from above. The thick two-dot chain line indicates the position where the scanning light is reflected by the reflecting mirror.
A thick dashed line indicates the center line of the photosensitive drum 10, and a thin dashed line indicates the optical axis of the scanning beam. Arrow 1
Numeral 3 indicates the direction of rotation of the polygon mirror, and arrow 14 indicates the direction in which scanning lines are scanned on the photosensitive drum 10.

FIG. 15 shows the optical system shown in FIG.
The trajectory of the beam after being turned back at 8-2, the synchronization detection mirrors 16-1, 16-2 and the synchronization detection unit 11-
FIG. 16 and FIG.
7 shows a view of the optical path viewed from the side, FIG. 16 shows a positional relationship including only the first optical system, and FIG. 17 shows a positional relationship including the second optical system. FIG. 18 is a view of FIG. 10 viewed from the side in the longitudinal direction. Note that FIGS. 15B and 18B are enlarged views of central portions of FIGS. 15A and 18A, respectively.

The synchronous light of each optical system is transmitted to third mirrors 9-1 and 2-1.
And then the third mirrors 9-1 and 9-1 and the photosensitive drum 1
The light is turned back by the synchronization detection mirrors 16-1 and 16-2 provided between 0, respectively, and enters the synchronization detection units 11-1 and 11 provided at positions corresponding to the photosensitive drums. The synchronization detection mirrors 16-1 and 16-2 are tilted in the sub-scanning direction, and guide synchronization light to the respective synchronization detection units 11-1 and 11-2. These optical writing devices are usually hermetically sealed inside an optical box (not shown), and fixed and arranged with high precision in order to prevent adhesion of dust and the like. However, since the laser emission port needs to be opened, twelve dustproof glasses are arranged to prevent dust from entering.

In the light beam scanning apparatus described above, two beams are made incident on and deflected on different deflecting surfaces of one deflecting means, and one scanning area on the surface to be scanned is changed by two different imaging optical systems. Light scanning is performed in a divided manner. Since two scanning lines are simultaneously scanned by one deflecting unit, a shift of the scanning lines in the sub-scanning direction hardly occurs. Furthermore, since each scanning line is scanned from substantially the center to both ends of the scanning area, synchronization detection can be provided substantially at the center, and the scanning lines can be accurately joined in the main scanning direction. Can be.

Next, a method of detecting the scanning beam position by the synchronization detecting units 11-1 and 11-2 will be described.

The synchronization detecting plate 16 shown in FIG. 19 has a triangular light receiving section 161 and the exit side 162 of the beam is the hypotenuse of the inclination θ. Assuming that the beam passing position without initial beam scanning position deviation is A, the synchronization detection signal detection time is t
Suppose A. It is assumed that the beam passing position when the position shift occurs due to the temperature fluctuation is B and the synchronization signal detection time has changed to tB. The beam position fluctuation amount pv at this time
Is V for the beam scanning speed and θ for the angle of the hypotenuse of the sensor.
Then, pv = V · (tA−tB) / tan θ = V · Δt / tan θ

Further, as shown in FIG. 20, the synchronous detection plate 1 is composed of two sensors, and the sensor on the exit side is inclined by 45 °.
6, the deviation of the beam scanning position can be obtained from the difference in beam passage time between the two sensors 163 and 164 by the following equation: pv = V ＝ Δt / tanθ (where tanθ = 1) = V ・ Δt.

The two signals detected by the first and second synchronization detections
By summing the amounts of change of the two beams and correcting the beam position by the beam scanning position correcting means by an amount equal to this amount, a high-quality image in which the two beams are not displaced due to temperature fluctuation or the like can be obtained. As a synchronization signal for determining a write start position in the main scanning direction, a detection signal 1 that does not change with the beam scanning position is used.

[0014]

In the above-mentioned invention, it is assumed that the two optical systems are arranged at positions 180 ° rotationally symmetric about the polygon so that the beam positions in the sub-scanning direction become equal. . However, in an actual apparatus, deviations from an ideal beam layout occur due to component tolerances.

That is, there is a problem that a deviation occurs in the sub-scanning direction at a beam joining portion or that the respective scanning lines do not have parallelism, so that the beam is bent at the center. In addition, due to the structure, the deflecting means is located at the center of the beam scanning device, and has a structure in which the synchronization detecting mirror and the final turning mirror are held directly below the deflecting means. It was easy.

The present invention has been made in view of such a background, and an object of the present invention is to eliminate a shift or a bend in a sub-scanning direction of a scanning line after joining, and to provide a line that is neatly aligned in a straight line. An object of the present invention is to provide a light beam scanning device that can be obtained.

Another object of the present invention is to obtain a good image having no inclination (skew) of an image formed by scanning lines after joining.

Another object is to obtain a good image by equalizing the beam diameters of the two writing systems.

Still another object is to generate heat by the deflection means,
An object of the present invention is to provide a good image by reducing adverse effects such as vibration.

[0020]

To achieve the above object, the present invention provides a light source for emitting a light beam, a deflecting means having a plurality of deflecting surfaces for deflecting the light beam, and a light source for deflecting the deflected light beam. A writing system having imaging means for forming an image on a surface to be scanned, and a housing for holding these components, wherein the deflection means is a single deflection means shared by the two writing systems; After guiding the light beams emitted from the two light sources to different deflecting surfaces of a single deflecting device having a plurality of deflecting surfaces, the light beams are deflected in different directions, The two systems of light beams are guided on the same surface to be scanned, and the scanning region on the surface to be scanned is optically scanned by dividing it into two parts. Configured to be scanned In the light beam scanning device, one of the two final mirrors for guiding the beams of the two writing systems onto the surface to be scanned is provided with a beam position adjusting means in the sub-scanning direction, and the other is provided with a beam tilt adjusting means. It is characterized by having.

In this case, it is preferable to provide a means for adjusting the attitude of the light beam scanning device itself with respect to the surface to be scanned. Also,
The two final mirrors may be mounted on one positioning member, and the positioning member may be provided with a mechanism for adjusting the relative position with respect to the surface to be scanned.

The position where the positioning member holding the two final mirrors is fixed to the housing is set far enough to reduce the influence of the heat and vibration of the deflecting means.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, the same parts as those in the above-described conventional example are denoted by the same reference numerals, and overlapping description will be omitted.

FIG. 1 shows the trajectory of the beam after being turned back by the mirrors 8-1 and 8-2 of the light beam scanning apparatus according to the embodiment of the present invention, and the synchronization detection mirrors 16-1 and 16-2 and the synchronization detection. The positional relationship with the units 11-1 and 11-2 is shown. As can be seen from the figure, this embodiment corresponds to FIG. 10 in the above-described conventional example, and the synchronization detection mirror 16-which is conventionally provided in each of the first optical system 100 and the second optical system 200. One and two are one, and two synchronous detection plates 11-
Reference numerals 1 and 11-2 are disposed adjacent to the single synchronization detection mirror 16. The other components are the same as those of the above-described conventional example.

Since the synchronization detecting plates 11-1 and 11-2 are located at positions corresponding to the photosensitive members, the photosensitive drum 10 and the synchronization detecting plates 1
1-1 and 1-2 have a symmetrical positional relationship with respect to the synchronization detection mirror 16, and the synchronization beams that scan the synchronization detection plates 11-1 and 11-2 are also aligned.

In this arrangement, when the attitude of the synchronization detection mirror 16 changes due to thermal expansion or the like, the synchronization detection plate 1
Although the synchronous beam scanning position for scanning on 1-1 and 1-2 also changes, since the synchronous detection mirror 16 is common to the two optical systems,
The change amounts are equal, and the relative positions of the two beams do not change.

The problem that is noticeable on the image is a relative displacement (degree of discontinuity of the line) at the joint portion of the two beams, and a slight displacement of the scanning line position on the image is a human. This is not a problem, since it cannot be distinguished from it. However, when actually arranging the components as in the layout of this embodiment, the polygon scanner, the synchronization detecting plates 11-1 and 11-2, the third folding mirror 9
-1 and 2, the synchronization detection mirrors 16 are all concentrated in the central part, and there is no room in space, and it is difficult to mount them. In addition, since the synchronization detection plates 11-1 and 11-2 are disposed immediately below the polygon scanner 4 that can be a heat source, it can be said that a problem is likely to occur.

Therefore, this point is improved in the embodiment shown in FIGS.

In this embodiment, the synchronous detection mirror 16a is inclined at approximately 45 ° in the sub-scanning direction, and synchronous light is extracted in the horizontal direction. For this reason, the synchronization detecting plates 11-1 and 11-2 can be arranged at a sufficient distance from other constituent members, and the arrangement of each constituent member is facilitated.

FIG. 3 is a right side view of the light beam scanning device according to this embodiment, FIG. 4 is a perspective view showing a positional relationship between a third mirror, a synchronization detection mirror, and a synchronization detection plate, and FIG.
FIG. The thick arrow in FIG. 5 indicates the scanning direction of the beam, and the two synchronization beams cross at the position of the synchronization detection mirror 16b and cross the same position on the synchronization detection mirror 16b in the opposite direction. Further, the synchronization detection plate 11
-1 and 11-2 are also arranged in a straight line at positions opposite to the respective optical systems, and the synchronous light scans toward the center from the opposite direction. With such an arrangement, the size of the synchronous mirror can be reduced, and the entire apparatus can be made simpler.

In this embodiment, if the incident angle θ of the scanning beam on the photosensitive member is equal to the incident angle θ ′ of the synchronous beam on the synchronous detecting plate, the beam movement amounts on the photosensitive member and the synchronous detecting plate are equalized. As a result, the detection accuracy of the beam movement amount increases.

In the embodiments described above, the method of easily joining the two beams, the method of detecting and correcting the occurrence of the deviation, and the like have been described. However, in an actual apparatus, deviation from an ideal beam layout occurs due to component tolerances as described above. In other words, there has been a problem in that a deviation occurs in the sub-scanning direction at the beam joining portion, and that the respective scanning lines do not have parallelism, so that the beam is bent at the center.

FIG. 6 shows an embodiment in which an adjusting means for correcting such an initial shift is provided.

FIG. 6 is an external perspective view of the light beam writing device using one synchronization detection mirror 16b described with reference to FIGS. In FIG.
The final folding mirror 9-2 of the optical system 200 is configured such that the end on the center side of the device is located on the positioning member 2 installed in the housing 20.
The other end is pressurized by a spring 19 and held by a shaft 18 a of an eccentric cam 18.

FIGS. 7A to 7C show the movement of the mirror end when the eccentric cam 18 is turned. The mirror end moves following the movement of the axis 18a. Since the center end is held at two points, the angle of the mirror does not change. Therefore, the inclination of the scanning line turned back by the third (final) turning mirror 9-2 of the second optical system 200 can be adjusted.

On the other hand, the third (final) folding mirror 9-1 of the first optical system 100 has an end on the center side of the apparatus held at one point of the positioning member 22, and the other end has an angle of the axis. Stepper motor-17 that can be changed subtly
Is held by As described above, by adjusting the mirror angle of the third folding mirror 9-1 with a small angle by the stepping motor, the position of the scanning line guided to the surface to be scanned can be adjusted in the sub-scanning direction. In order to make fine adjustment possible, a fine adjustment mechanism using a ball and an arrowhead may be provided between the stepping motor and the mirror. Since the parallelism and the position in the sub-scanning direction of the two scanning lines can be adjusted by these two adjusting mechanisms, the two scanning lines can be aligned in a straight line.

However, the two scanning lines aligned in a straight line are not necessarily parallel to the axis of the surface to be scanned. An embodiment provided with a means for adjusting this is shown in FIGS.

FIG. 8 is an external view of the optical writing apparatus as viewed obliquely from above. The optical writing device is
Although they are positioned in the height direction at points, they are fixed by stepped screws 23 via springs 24, respectively, so that they are movable in the horizontal direction. further,
Although one of the four points of the optical writing device is positioned by the positioning pin 25, the other point is positioned by the eccentric cam 26. Therefore, as shown in FIGS. Can be fine-tuned.

FIG. 10 is a detailed view of the eccentric cam 26. The eccentric shafts 26a and 26b are structured to be inserted into the elongated hole 28 of the housing and the hole 29 of the stay. By performing the tilt adjustment of the optical writing device itself by this adjustment mechanism, the skew can be adjusted and a good image can be obtained.

FIG. 11 is an external perspective view of an optical writing device according to still another embodiment as viewed obliquely from below. this is,
This is an improvement of the optical writing device shown in FIG. 6, in which final folding mirrors 9-1 and 9-2 and an adjusting mechanism 1 for the posture thereof are provided.
7, 18, 19, 21, 22 and the synchronization detection unit 16,
11-1 and 11-2 parts are installed on the stay member 30 extending in the longitudinal direction of the housing. The stay member 30 is slidable in three directions, and has a structure in which the positions of both ends of the stay member can be finely adjusted by a spring 32 and an eccentric cam 31.

With this configuration, by adjusting one of the eccentric cams, the stay member rotates around the other eccentric cam, so that the eccentric cam 26 shown in FIG.
The same effect as described above can be obtained. Further, in this device, it is possible to move the stay member 30 in parallel by adjusting two more eccentric cams from the state where the skew adjustment has been adjusted.

Usually, the first optical system 100 and the second optical system 20
Reference numeral 0 indicates that the beam waist position is deviated or the beam is thickened at the waist position due to the tolerance of the component parts, the mounting position, and the tolerance of the posture, thereby causing a difference in the beam diameter on the surface to be scanned. Therefore, if the stay member 30 is moved to the left in parallel as shown in FIGS. 12A and 12B, the optical path length from the polygon mirror 4 to the surface to be scanned becomes shorter in the second optical system 200, and the beam waist position is reduced. Moves to the far side of the scanned surface of the photosensitive drum 10. At this time, in the second optical system 200, the optical path length from the polygon mirror 4 to the surface to be scanned becomes longer by the same amount, and the beam waist position moves to the near side of the surface to be scanned. If the stay member 30 is translated in the right direction, the opposite effect can be obtained.

Therefore, it is possible to adjust the beam waist position of the two optical systems and to adjust the beam diameter at the joining portion so that the beam diameter becomes equal. Image can be obtained.

In the optical writing device of the present embodiment, the polygon motor 4 is located at the center of the device due to its configuration, and the holding portions 21 of the final folding mirrors 9-1 and 9-2 are located immediately below the polygon motor 4.
Since the synchronization detectors 11-1 and 11-2 are located, the vibration and heat of the polygon motor 4 have had an adverse effect. The adverse effects include, for example, occurrence of jitter on the image and vertical line fluctuation due to the vibration of the final mirrors 9-1 and 9-2, deterioration of the synchronization detection due to the vibration of the synchronization detection mirror 16, and the detection accuracy of the scanning line position shift, or temperature. This is a change in the detection accuracy of the synchronization detection plate due to the rise.

Therefore, as shown in FIG.
0 sets the positions 30a and 30b that abut on the housing 20 at positions farthest from the polygon motor at both ends of the stay so that the vibration and heat are not easily transmitted. As a result, it has become possible to improve the quality of the image, which is free from the influence of the vibration and heat of the polygon motor, as well as the accuracy of the synchronization and the detection of the scanning line displacement.

[0046]

As described above, according to the first aspect of the present invention, the beam position adjusting means in the sub-scanning direction is provided on one of the final mirrors for guiding the beams of the two writing systems onto the surface to be scanned. Is equipped with beam tilt adjustment means,
It is possible to eliminate a shift or a bend in the sub-scanning direction of the scanning lines after joining, and to form a clean straight line, so that a good image can be obtained.

According to the second aspect of the present invention, since the means for adjusting the attitude of the light beam scanning device itself with respect to the surface to be scanned is provided, the inclination (skew) of an image formed by the joined scanning lines is reduced. No good images can be obtained.

According to the third aspect of the invention, one point is positioned on the stay by the positioning pin, the other point is positioned by the eccentric cam, and the attitude of the light beam scanning device itself is adjusted by rotating the eccentric cam. Therefore, the posture of the light beam device itself can be adjusted with a simple configuration.

According to the fourth aspect of the present invention, the two final mirrors are mounted on one positioning member, and the positioning member is provided with a mechanism for adjusting the relative position with respect to the surface to be scanned. It is possible to make the diameter equal,
Thereby, a good image can be obtained.

According to the fifth aspect of the present invention, the fixing position of the positioning member holding the two final mirrors to the housing is set at the position where the positioning member is farthest from the deflecting means. If the distance to the side portion is small enough to reduce the influence of vibration, adverse effects such as heat generation and vibration by the deflecting means are reduced, and a good image can be obtained.

According to the sixth aspect of the present invention, the positioning member and the eccentric cam are used to urge the positioning member in one direction and the eccentric cam which contacts the positioning member and moves the positioning member against the urging force of the spring. Since the relative position with respect to the scanning surface can be adjusted, adjustment can be easily performed only by turning the eccentric cam.

[Brief description of the drawings]

FIG. 1 is a diagram showing a trajectory of a beam after being turned back by a mirror of a light beam scanning device according to an embodiment of the present invention and a positional relationship between a synchronization detection mirror and a synchronization detection unit.

FIG. 2 is a side view of the relationship shown in FIG. 1;

FIG. 3 is a side view showing an arrangement of each part of the embodiment together with an optical path for suppressing occurrence of a beam position shift in a sub-scanning direction.

FIG. 4 is a perspective view illustrating a relationship among a synchronization detection mirror, a synchronization detection unit, and a third folding mirror in FIG. 3;

FIG. 5 is a view of FIG. 4 as viewed from above.

FIG. 6 is an external perspective view of the light beam writing apparatus using one synchronization detection mirror described with reference to FIGS.

FIG. 7 is a view for explaining the movement of the mirror end when the eccentric cam is turned.

FIG. 8 is an external view of the optical writing apparatus having a mechanism for adjusting a scanning line, as viewed obliquely from above.

FIG. 9 is a view for explaining a mechanism for finely adjusting the inclination around the positioning pin in FIG. 8;

FIG. 10 is a perspective view showing details of the eccentric cam shown in FIG. 8;

FIG. 11 is an external perspective view of an optical writing device according to still another embodiment as viewed obliquely from below.

FIG. 12 is a view for explaining the adjustment mechanism of FIG. 11;

FIG. 13 is a schematic perspective view showing one configuration of a light beam scanning device that has been conventionally implemented.

FIG. 14 is a view of FIG. 13 as viewed from above.

FIG. 15 is a diagram showing a trajectory of a beam after being turned back by a mirror in the optical system of FIG. 14 and a positional relationship between a synchronization detection mirror and a synchronization detection unit.

FIG. 16 is a side view of the optical path in FIG. 15, showing only the first optical system.

FIG. 17 is a side view of the optical path of FIG. 15, showing first and second optical systems.

FIG. 18 is a view of FIG. 15 as viewed from a longitudinal side surface.

FIG. 19 is a diagram showing an example of a synchronization detection plate together with a timing chart.

FIG. 20 is a diagram showing another example of the synchronization detection plate together with a timing chart.

[Explanation of symbols]

1-1, 1-2 LD 2-1, 2-2 Collimating lens 3-1, 3-2 Cylindrical lens 4 Polygon mirror 5-1, 5-2, 6-1, 6-2 Fθ lens 7-1, 7-2, 8-1, 8-2, 9-1, 9-2 Folding mirror 10 Photoconductor drum 11-1, 11-2 Synchronous detection unit (synchronous detection plate) 16, 16a, 16b Synchronous detection mirror 17 Stepping Motor 18 Eccentric cam 18a Shaft 19 Spring 20 Housing 23 Step screw 24 Spring 25 Positioning pin 26 Eccentric cam 27 Stay 28 Long hole of housing 29 Stay hole 30 Stay member 30a, 30b Location where stay member abuts on housing 31 Eccentric cam 32 spring

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H04N 1/113 H04N 1/04 104A F-term (Reference) 2C362 AA28 AA47 AA48 BA49 BA53 BA61 BA67 BA71 BA87 DA02 DA03 2H043 BC00 2H045 AA01 BA02 BA22 BA36 CA00 DA02 DA04 DA41 5C051 AA02 CA07 DB24 DC04 DE23 DE24 5C072 AA03 BA04 DA04 DA21 DA23 HA02 HA06 HA08 HA13 HB08 HB10 XA05

Claims (6)

[Claims] 1. A light beam scanning apparatus for forming an image by scanning a light beam from a predetermined position to an end of a photoconductor by two writing optical systems using one deflection means. A light beam scanning device, wherein one of the final mirrors for guiding the light beam on the surface to be scanned is provided with a beam position adjusting means in the sub-scanning direction and a beam tilt adjusting means is provided on the other. 2. The light beam scanning device according to claim 1, further comprising means for adjusting the attitude of the light beam scanning device itself with respect to the surface to be scanned. 3. The adjusting means includes: positioning one point on a stay by a positioning pin; positioning another point by an eccentric cam; and rotating the eccentric cam to adjust the attitude of the light beam scanning device itself. 3. The light beam scanning device according to claim 2, wherein: 4. The light beam scanning apparatus according to claim 1, wherein the two final mirrors are mounted on one positioning member, and the positioning member is provided with a mechanism for adjusting a relative position with respect to the surface to be scanned. 5. The light beam scanning device according to claim 4, wherein a fixing position of the positioning member holding the two final mirrors to the housing is set to a position where the positioning member is farthest from the deflecting means. . 6. The positioning of the positioning member is performed by a spring that biases the positioning member in one direction and an eccentric cam that contacts the positioning member and moves the positioning member against the biasing force of the spring. 5. The light beam scanning device according to claim 4, wherein: