JPH09211361A - Light beam scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the light beam scanning device which makes it possible to minimize a lengthwise frictional force while precision is held at the time of expansion due to temperature and humidity as to the both-end support system of a long-sized optical element, stably hold even an optical element of small rigidity, and precisely form a synthetic-resin lens with excellent performance against variation in temperature and humidity by using minimum materials. SOLUTION: The light beam scanning device which uses the long-size optical element has a holding part 29 which holds an optical element 20, etc., and a pressing means 26 which applies a pressing force to the long-sized optical element 20, and a roll 32 in a plane provided to a holding member 29 is arranged in a rolling-enabled state by being attracted by applying a magnetic force, so that the long-size optical element 20 is pressed and fixed through the roll member 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an electrostatic latent image on a photoconductor by a laser beam,
In particular, it relates to the configuration of a light beam scanning device used in an image forming apparatus.

[0002]

2. Description of the Related Art A beam scanning optical system using a laser beam is used as an optical system for a laser printer, a digital copying machine, a plain paper FAX or the like. The element is heavily used.
The reason why such a long optical element is frequently used is that the cost is reduced by using a resin for the lens, and that a resin material having a small refractive power is used and the strip shape is relatively easy to form. There is a tendency that the glass lens becomes longer in the main scanning direction than the glass lens used conventionally. FIG. 3 is a diagram showing an example of a conventionally used optical system. A laser beam 9 generated by a laser unit (LD unit) 1 enters a cylindrical lens 2 and forms an image on a rotary polygon mirror 3. The rotary polygon mirror 3 rotates in a constant direction at a constant angular velocity, the laser beam is deflected in the main scanning direction, and the imaging lens 4 and the imaging lens 5 (in particular, the imaging lens 4) on the scanning line on the photosensitive drum 6. The fθ characteristic is provided so that the scanning is performed at a constant speed, and an image is formed so as to have a predetermined beam spot diameter. The mirror 7 reflects a part of the scanning line and guides it to the synchronization detection sensor 8. The synchronization detection sensor 8 detects that the scanning beam has reached a predetermined position, and generates a synchronization signal of an image writing start position.

[0003] Some of these optical elements are usually fixed to an integrally formed holding member having an optical element positioning portion and a mounting surface, which is called an optical housing, in order to stably maintain a desired positional accuracy. Is. Conventionally, such a holding member is often made of high-strength synthetic resin, for example, PC resin / PPE resin / unsaturated polyester resin containing glass fiber, or aluminum / zinc die casting. The imaging lens 4 is made of a transparent synthetic resin, for example, PC or PM.
Since it is made of MA and the refractive power of the synthetic resin is smaller than that of glass, it is larger than the glass lens having the same performance. On the other hand, the imaging lens 5 is a long lens having an anamorphic aspherical surface having a refractive power in the sub-scanning direction, and it is difficult to manufacture it from glass in terms of processing, and like the imaging lens 4 described above. Made of transparent synthetic resin,
For example, it is composed of PC and PMMA. Therefore, the imaging lenses 4 and 5 are generally fixed as described below in consideration of thermal expansion and deformation of parts due to moisture absorption of synthetic resin.

FIGS. 4 and 5 are views for explaining the fixation of the imaging lens 4. As shown in FIG. 4, the imaging lens 4 is a receiving reference plane in the z direction provided on a part of the holding member 10. 10
a. The receiving reference in the x direction is the holding member 10.
However, since it is possible to perform the bonding while holding the position at the time of bonding in the bonding process using the robot, there is no need to provide the protrusion serving as the receiving reference in the x direction. Further, there is no position regulating portion in the y direction which is the longitudinal direction. Therefore, when thermal expansion occurs, the deformation will be symmetrical with respect to the optical axis, and the state (shape) after deformation can be expected, so it is possible to design considering the deformation of thermal expansion with respect to a given temperature change. become. On the other hand, the imaging lens 5
Can be prevented from being deformed by thermal expansion if the same fixing method as that of the imaging lens 4 is used.
The reference surface 10a is short in comparison with the length of the imaging lens 5, the arrangement accuracy around the optical axis is poor, and it is disadvantageous to external vibration. Therefore, as shown in FIGS. 6 and 7, at the center position of the optical axis, the positioning projection 13 provided on a part of the holding member and the projection 5a provided on the imaging lens 5 are fitted to each other and fixed at both ends. This is performed by applying a pressing force in the x direction and the z direction by the leaf spring 14 while the reference surface 5b is pressed against the positioning portion 12. The leaf spring 14 is fixed to the leaf spring fixing portion 11 with a screw 16. If the pressing force of the leaf spring 14 is appropriate, the imaging lens 5 has an optical axis, that is, the positioning protrusion 13
Although it expands naturally in the longitudinal direction (y direction) around the projection 5a of the imaging lens 5 fitted to the lens, if the pressing force of the leaf spring 14 is large, the expansion at both ends is restricted and the lens deforms, which is unexpected. Causes a change in curvature. Therefore, the imaging lens 5
Is provided with ribs for strength reinforcement in parts other than the lens part,
For example, the elongation force of the member due to thermal expansion exceeds the frictional effect in the y direction due to the pressing force even if a relatively large pressing force that does not cause floating from the reference surface due to external vibration acts. Examples of using such a method of fixing a long lens are disclosed in JP-A-62-75671 and JP-A-6-3.
There is one described in Japanese Patent Publication No. 000952.

[0005]

As described above, when a long lens made of synthetic resin having low rigidity is used in the light beam scanning device, there are two methods for fixing the imaging lenses 4 and 5.
Although various types of fixing methods have been adopted, all of these methods require member strength depending on the length, and therefore, in addition to the shape that satisfies the original optical characteristics, shapes such as ribs that take reinforcement into consideration are used. There is a problem in that it is necessary to add more, more resin material is required, and it is difficult to configure the fθ lens at low cost. In addition, since such a lens requires extremely high surface accuracy and shape error, when a reinforcing structure required for strength is molded, uneven resin flow and cooling imbalance that occur during manufacturing occur. ,
There is a problem that the desired precision of the formed product cannot be obtained. Further, in the technique disclosed in Japanese Patent Laid-Open No. 6-300952 described above, elongated holes are formed in the sliding direction at both ends of the elongated lens, and the elongated holes have a function of guiding the deformation direction, but sliding There is a problem in that the member strength corresponding to the length as described above is required without the effect of reducing the above.

Further, in the reflection mirror type optical system using the concave surface as shown in FIG. 8, the method of fixing the long lens as described above becomes more problematic. That is, in the reflection mirror type optical system shown in the figure, since the reflection mirror 15 takes charge of the fθ characteristic and the image forming characteristic, this curved surface becomes an aspherical surface. Therefore, the reflection mirror 15 is made of synthetic resin, and the reflection surface is made of aluminum. It is common to form a vapor deposition film. However, since it is very difficult to maintain the curvature of the reflecting surface because buckling occurs due to the force in the longitudinal direction, and the central portion of the reflecting mirror 15 becomes thin, supporting it in the central portion is a transmission type optical system. In comparison, it is more difficult to perform fixing that is less likely to be affected by external vibration while considering deformation due to thermal expansion. Similar to the conventional imaging lens described above, it is possible to strengthen the rigidity by providing a box-shaped rib other than the lens portion, but in order to form a vapor deposition film after molding evenly. It is not commonly used because the ribs interfere with it. Therefore, the present invention, in the method of supporting both ends of a long optical element, suppresses the frictional force in the longitudinal direction as much as possible while maintaining accuracy during expansion due to temperature and humidity, and even if the optical element itself has a small rigidity. SUMMARY OF THE INVENTION An object of the present invention is to provide a light beam scanning device capable of stably holding a lens made of a synthetic resin having good performance against changes in temperature and humidity with a minimum amount of material and with high precision.

[0007]

In order to solve this problem, the invention according to claim 1 of a light beam scanning device according to the present invention is a light beam scanning device using a long optical element. And the like, and a pressing means for urging a pressing force to the long optical element, and by applying a magnetic force to the roller member in the plane provided in the holding member to attract the roller member, The roller member is rotatably arranged, and the long optical element is pressed and fixed via the roller member. The invention according to claim 2 of the light beam scanning device according to the present invention is, in a light beam scanning device using a long optical element, a holding portion for holding an optical element and the like, and a pressing force applied to the long optical element. And a pressing means for urging the optical element, and the long optical element is pressed and fixed via a roller member arranged in a plane provided in the holding member.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a diagram showing an example of an embodiment of a light beam scanning device according to the present invention, particularly an example used in a reflection mirror type optical system using a concave surface. In the figure, 20 is a reflection mirror, 20a is a protrusion provided at the center of the optical axis of the reflection mirror 20, and 20b is a reference plane provided at both ends of the reflection mirror (however, provided at one end in the figure). Only the reference surface is shown.), 22 is a positioning protrusion provided on a part of the holding member, 24 is a positioning portion, 26 is a leaf spring as a pressing means,
Reference numeral 28 is a leaf spring fixing portion, 29 is a holding portion of an optical element, 30 is a z-axis reference surface provided on the holding portion 29, and 32 is a roller member provided on the z-axis reference surface 30. is there.
The reflection mirror 20 is fixed by fitting a protrusion 20a provided at the center of the optical axis of the reflection mirror 20 between the positioning protrusions 22 and a reference surface 20b of the reflection mirror 20 extending in the z-axis direction of the positioning portion 24a. The leaf spring 26 fixed to the leaf spring fixing portion 28 with a screw 34.
This is performed by pressing the surface 20c facing the reference surface 20a by the x-axis direction pressing portion 26a. Moreover, the upper surface 20d of the reflection mirror 20 is pressed in the z-axis direction by the z-axis pressing portion 26b of the leaf spring 26. Therefore, the reflection mirror 20 which is a long lens is pressed in the x and z directions by the leaf springs 26, and the leaf springs 26 are provided at both ends of the reflection mirror 20 in the y direction. It is receiving the frictional force of the spring.

A roller member 32 is provided on the reference surface 30 in the z-axis direction so that its rolling axis is orthogonal to the longitudinal direction of the reflecting mirror 20, that is, the y-direction.
The reflection mirror 20 is arranged on the roller member 32.
In this embodiment, two roller members 32 are used, but in principle one roller member may be used. However, in order to stably receive the pressing force of the leaf spring 26, it is desirable to use two or more roller members. As described above, since the reflecting mirror 20 is arranged on the reference surface 30 in the z-axis direction by using the roller member 32 and the reflecting mirror 20 is positioned and fixed by the pressing force of the leaf spring 26, the temperature and humidity change. Even in such a case, the bottom surface of the reflection mirror 20 is in line contact with the roller member 32, and the friction coefficient between the roller member 32 and the reflection mirror 20 is low. Therefore, the reflection mirror 20 naturally moves around the optical axis. It can be expanded and contracted. The roller member 32 is required to be freely rollable in the rolling direction in order to enable smooth rolling. Further, in order to hold the reflection mirror 20 with a desired accuracy, the diameter of the roller member 32 needs to be finished to a predetermined accuracy. That is, when the roller member 32 does not roll smoothly, the friction coefficient between the roller member 32 and the reflection mirror 20 increases, and the reflection mirror 20 may be asymmetrically deformed about the optical axis. Further, if the diameter of the roller member 32 is not finished to a predetermined accuracy, smooth rolling of the roller member 32 as described above is impaired, and as a result, unnecessary stress is generated in the reflection mirror 20.

If the above-mentioned light beam scanning device is set, the positional relationship between the roller member 32 and the reflection mirror 20 may shift, or the holding member forming the roller member 32 and the reference surface 30 may slip. If slippage progresses over time due to vibration, the position of the roller member 32 and the point of action of the leaf spring 26 will eventually shift, and as shown in FIG. 1, the roller member 32 will be placed in the desired concave surface. In this case, there is a possibility that the position of the roller member may be displaced and there is a step, and free rolling may be hindered. Considering that the rolling friction of the roller member is significantly smaller than the sliding friction, the pressing force of the leaf spring is temporarily reduced by some shock or vibration, and the roller member 32 and the reflection mirror 20 are deviated. It is considered that an inertial force acts on the roller member at the moment when the sliding friction almost disappears due to a gap between the roller and the roller. Therefore, in order to prevent such positional displacement of the roller member 32, the following measures may be taken.

FIG. 2 is a view showing another embodiment of the present invention, and shows a part of the AA cross section of FIG. The same parts as those in FIG. 1 are designated by the same reference numerals. As shown in the figure, a magnet 36 is arranged immediately below the concave portion of the holding member 29 in which the roller member 32 is arranged, and the roller member is not captured within a predetermined range by using magnetic force. In this case, it is conceivable that the roller member 32 is made of a mild steel rod which is processed with high precision and plated with rust.
Alternatively, the sintered magnet may be accurately formed into a rod shape. With such a configuration, even if the pressing force of the leaf spring 26 is released due to some shock or vibration and the inertial force acts on the roller member, the properly designed restoring force of the magnetic force is exerted, so that from the predetermined position. It does not come off, and it is always the reflection mirror 2
Zero support can be maintained with low friction, i.e. rolling friction. In particular, using two roller members 32,
Further, when the magnets and 36 are arranged on the back surface, the magnetic lines of force of the magnet are omnipresent in the corners of the magnet 36, so that the two roller members 32 can be prevented from contacting each other, and the slip due to the line contact between the roller members 32. It is effective because it causes ideal friction without causing friction. However, even if the roller members 32 come into line contact with each other, the sliding friction is generally very small, and therefore the configuration is not necessarily limited to the configuration in which the roller members 32 do not contact each other.

[0012]

As described above, since the optical beam scanning device according to the present invention can hold an optical element, for example, a reflecting mirror or an imaging lens stably and with low friction, it is a particularly long optical element. In the both-ends support method, even if the optical element expands or contracts due to changes in temperature and humidity, it does not restrain the contraction, and therefore, it is a significant effect in preventing deterioration of optical performance due to unexpected deformation of the optical element. Exert.
Further, by attracting the roller member for pressing and fixing the optical element by a magnetic force using a magnet, the roller member is always arranged at a desired position, without causing deterioration of optical performance due to unexpected deformation of the optical element, It has an effect in favorably holding the optical element.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a light beam scanning device according to the present invention.

FIG. 2 is a diagram showing another embodiment of the light beam scanning device according to the present invention.

FIG. 3 is a diagram showing an example of an optical system that has been conventionally used.

FIG. 4 is a diagram for explaining fixation of an imaging lens in a light beam scanning device which has been conventionally used.

FIG. 5 is a diagram for explaining fixation of an imaging lens in a light beam scanning device which has been conventionally used.

FIG. 6 is a diagram for explaining fixation of an imaging lens in a conventionally used light beam scanning device.

FIG. 7 is a view for explaining fixing of an imaging lens in a light beam scanning device which has been conventionally used.

FIG. 8 is a view for explaining fixing of an imaging lens in a conventionally used light beam scanning device.

[Explanation of symbols]

20 ... Reflective lens (optical element), 26 ... Leaf spring (pressurizing means), 29 ... Holding portion, 32 ...
Roller member, 36 ... Magnet.

Claims (2)

[Claims] 1. A light beam scanning device using a long optical element, comprising: a holding portion for holding the optical element and the like; and a pressurizing means for applying a pressing force to the long optical element, By attracting a roller member in a plane provided in the holding member by applying a magnetic force, the roller member is rotatably arranged, and the long optical element is pressed and fixed through the roller member. A light beam scanning device characterized in that 2. A light beam scanning device using a long optical element, comprising: a holding portion for holding the optical element and the like; and a pressurizing unit for applying a pressing force to the long optical element, The light beam scanning device, wherein the elongated optical element is pressed and fixed via a roller member arranged in a plane provided in the holding member.