JP2875353B2 - Optical scanning device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used for a laser printer, a digital copying machine, and the like.

2. Description of the Related Art In recent years, an electrophotographic method has been developed as a simple and high-quality printing method, and an optical scanning device exists as a device for realizing the electrophotographic method. This optical scanning device is such that a scanning mirror having at least one reflection surface is mounted on a rotation axis of a driving device and arranged on an emission optical path of a laser light source, and a scanning surface is provided on a reflection optical path of the reflection surface of the scanning mirror. There is a post-objective or pre-objective type optical scanning device (both not shown) due to differences in the optical path and the arrangement of the optical components. I have. Such an optical scanning device forms a main scanning light by deflecting and scanning the output light of a laser light source with an optical deflector such as a rotating scanning mirror, and forms a main scanning light by moving the main scanning light relatively in a sub-scanning direction. The electrostatic latent image is formed by irradiating the surface to be scanned. Then, for example, the electrostatic latent image on the photosensitive member is developed with a charged toner and transferred to a printing paper to form an image by electrophotography.

Here, in the above-described optical scanning device, a laser diode is generally used as a laser light source, which has a characteristic that a wavelength changes according to a temperature change. In this case, when the wavelength of the laser beam changes, the refractive index of the imaging optical system also changes, and the beam waist position changes. A means for correcting is required.

To solve such problems, Japanese Patent Publication No. 1-28
There is an optical scanning device disclosed in Japanese Patent Publication No. 381. This corrects that the holding member of the optical component expands due to a temperature change and the imaging position is displaced, and the thermal expansion of the holding member of the laser diode or the collimator lens, and the thermal expansion of the connecting member of these holding members. Are formed so that the beam waist position is kept constant, and the heat generated by the laser diode is compensated by the cooling action of the Peltier element.

In general, in an optical scanning device, a scanning line on a surface to be scanned is linear, but a laser beam deflected and scanned by an optical deflector converged on such a straight line by an imaging optical system. It is difficult to locate the beam waist.

To solve such a problem, there is an optical scanning device disclosed in Japanese Patent Application Laid-Open No. 58-57108.
This is to control the position by supporting the laser diode and the optical components of the imaging optical system so as to be movable in the optical axis direction. By controlling and driving such a mechanism, the scanning target surface is scanned. The displacement of the beam waist position is corrected.

Problems to be Solved by the Invention In the optical scanning device disclosed in Japanese Patent Publication No. 1-28381, the displacement of the beam waist position is corrected by using the thermal expansion of each part connected to the optical component. But,
In practice, it is extremely difficult to produce a member that expands thermally as designed. Furthermore, in the optical scanning device disclosed in Japanese Patent Publication No. 1-28381, the temperature of the laser diode is made uniform by the cooling action of the Peltier element. However, this reduces the productivity of the device due to its complicated structure. Become.

On the other hand, in the optical scanning device disclosed in JP-A-58-57108, the beam waist is positioned on the main scanning line by controlling the position of each optical component in the optical axis direction. Moving the optical components undesirably reduces the optical accuracy and the reliability of the device, which is not desirable. In addition, since the speed of optical scanning is restricted by the speed of position control of the optical components, the speed of the device increases. Is also inhibited.

Means for Solving the Problems According to the invention of claim 1, an image forming optical system including an electro-optical lens and an optical deflector are arranged on an optical path from a laser light source to a surface to be scanned. Imaging position detection means for detecting a beam waist position of the laser light converged by the imaging optical system, and applying a DC voltage corresponding to a detection value of the imaging position detection means to the electro-optical lens to thereby form an optical path in the optical path; An image forming position equalizing means for correcting the beam waist position of the image is provided.

According to a second aspect of the present invention, there is provided a scanning image forming position for detecting a change position of a beam waist position during scanning of a laser beam emitted from a laser light source, converged by an image forming optical system, and deflected and scanned by an optical deflector. And a scanning position equalizing means for correcting a displacement of a beam waist position during scanning by applying a high-frequency voltage corresponding to a detection value of the scanning image forming position detecting means to the electro-optical lens.

According to the first aspect of the present invention, the beam waist position of the laser light emitted from the laser light source and converged by the image forming optical system including the electro-optical lens is detected by the image position detecting means, and the detected value corresponds to the detected value. The DC voltage is applied to the electro-optical lens by the imaging position equalizing means to correct the beam waist position in the optical path, so that the beam waist position of the laser beam is adjusted once by the electro-optical lens that is feedback-controlled according to the displacement. Can be corrected for each scan.

According to a second aspect of the present invention, the amount of displacement of the beam waist position during scanning of the laser beam is detected by the scanning image position detecting means,
The scanning position equalizing means applies a high-frequency voltage corresponding to the detected value to the electro-optical lens to correct the displacement of the beam waist position during scanning, thereby changing the beam waist position of the deflected and scanned laser light by the displacement. Can be corrected during scanning by an electro-optical lens that is feedback-controlled according to the following formula, so that aberrations such as curvature of field during scanning that have been inevitably generated in the conventional optical scanning device can be corrected.

Embodiment An embodiment of the present invention will be described with reference to FIGS. First, in the optical scanning device 1 of the present embodiment, as illustrated in FIG. 2, a collimator lens 3 which is a part of an image forming optical system is electrically connected to an optical axis of a laser diode 2 which is a laser light source. A reflection surface 7 of a polygon mirror 6 serving as an optical deflector is located via an optical lens 4 and a cylindrical lens 5.
Gθ lens 8 which is a part of the imaging optical system
The surface to be scanned 11 is arranged via. Here, a beam waist detecting device 13 which is an image forming position detecting unit is disposed on a reflection optical path of the polygon mirror 6 and outside a scanning region of the surface to be scanned 11 via a reflecting mirror 12, As illustrated in FIG. 1, the beam waist detection device 13 has a structure in which a knife edge 14 and two-part photodiodes 15, 16 are sequentially arranged on an optical path. Then, the photodiodes 15 and 16 of the beam waist detecting device 13 are connected to a DC power supply 18 serving as an image forming position equalizing means via a subtracter 17, and the DC power supply 18 is connected to each surface of the electro-optical lens 4. Feedback connection is made to the formed electrodes 19 and 20.

In such a configuration, like the conventional optical scanning device, the laser beam emitted from the laser diode 2 is converged by the optical components 3 to 5, 8 to 10, and the polygon mirror 6 The light beam is scanned by the beam waist on the surface 11 to be scanned.

Here, as described above, when the ambient temperature changes, the wavelength of the laser beam emitted from the laser diode 2 changes or the position of each optical component is displaced when the ambient temperature changes, so that the position of the beam waist on the optical path is changed. Changes. For example, when the present applicant actually manufactured a device having the above structure and measured the fluctuation of the beam waist position due to the temperature change, as shown in FIG. It was found that the beam waist position was about 0.3 (mm).

Therefore, in the optical scanning device 1 of the present embodiment, when the position of the beam waist changes, the refractive index of the electro-optical lens 4 is changed to correct the beam waist position on the surface 11 to be scanned.

Here, the operation of the electro-optical lens 4 will be described in detail below with reference to FIGS. First, as illustrated in FIG. 4, the electro-optical lens 4 of the optical scanning device 1 has a composition of 9/65/35 PLZT (Lead Zirco-Titanate Dope
d With Lanthanum) The light-incident surface and the light-exit surface are formed in a rectangular parallelepiped shape polished by electro-optic crystal or the like, and the center and both sides of the upper and lower surfaces are electroded by vacuum evaporation of Au or screen printing. , 20 are formed. In the electro-optical lens 4, the direction of deflection of the laser beam by the electro-optical lens 4 is z, the refractive index of the electro-optical lens 4 when no voltage is applied is N _O , and the matrix component of the secondary electro-optical constant is
R ₃₃ , the electro-optic lens 4 according to the voltage applied from the electrodes 19 and 20
Assuming that the electric field generated in Ez is Ez, the z-direction component Nz of the refractive index when a voltage is applied is When the refractive index change ΔNz due to the electric field Ez is obtained from the above equation, Becomes That is, as shown in FIG. 6, the electro-optic lens 4 has a characteristic in which the refractive index decreases as the electric field increases, and the amount of change in the refractive index is proportional to the square of the electric field strength. Therefore, the optical axis direction y of the laser beam
On the other hand, assuming that the voltage application direction is z and the direction orthogonal to y and z is x, the electrode 19 formed at the center of the upper and lower surfaces of the electro-optic lens 4 as illustrated in FIG. When a voltage is applied to the laser beam, the laser beam converges in the z direction and converges to a point A at a focal length f ₀ , and further, as illustrated in FIG. When a voltage is applied to the electrode 20 formed in the portion, the laser beam converges in the x direction and converges on the point A at the focal length f ₀ ′. That is, by applying a voltage to the electrodes 19 and 20 arranged as described above, the laser beam deflected by the electro-optical lens 4 can be converged to one point to form a beam waist. In the electro-optic lens 4 having such a shape, when no voltage is applied to the electrodes 19 and 20, the incident laser light is transmitted without being refracted.

The operation of the optical scanning device 1 for correcting the beam waist position using the electro-optical lens 4 having the above-described characteristics will be described below in detail with reference to FIGS. 7 and 8. First,
In the optical scanning device 1, in a normal state, the beam waist of the laser beam is located on the surface to be scanned 11 and converges between the two-part photodiodes 15 and 16 of the beam waist detecting device 13. Here, these two-division photodiodes 15 and 16 receive a laser beam whose half of the beam is shielded by the knife edge 14, and as illustrated in FIGS. 7 and 8 (a). When the beam waist position of the laser light is shifted back and forth, the amount of light received by one of the photodiodes 15 and 16 increases. Then, when the difference signal between the detection values of the two-division photodiodes 15 and 16 is calculated by the subtractor 17 to detect the focusing signal, FIG.
The relationship between the focusing signal and the amount of displacement of the beam waist position is represented as an S-shaped curve passing through the origin.

Then, when the DC power supply 18 applies a DC voltage to the electro-optical lens 4 according to the focusing signal thus obtained, the electro-optical lens 4 is feedback-controlled according to the displacement of the beam waist of the laser light. Accordingly, the optical scanning device 1 can optically scan the surface 11 to be scanned with the beam waist of the laser light whose position is corrected each time scanning is performed, so that the print quality of the laser printer is not affected by a temperature change or the like. It can contribute to implementation and the like.

Next, an embodiment of the present invention will be described with reference to FIG. In this optical scanning device 21, a plurality of scanning image forming position detecting means (not shown) having the same structure as that of the beam waist detecting device 13 are covered by the polygon mirror 6 via a half mirror (not shown). A high-frequency power supply 22, which is arranged on a scanning optical path to the scanning surface 11 and is a scanning position equalizing means for outputting a high-frequency voltage corresponding to a detection value of the scanning image forming position detecting means, is electrically connected via a capacitor 23. The optical lens 4 is connected in parallel with a DC power supply 18 to which a resistor 24 is connected.

In such a configuration, the optical scanning device 21 corrects the displacement of the beam waist position of the laser light due to a temperature change or the like, similarly to the optical scanning device 1 described above. Further, in the optical scanning device 21, when the displacement of the beam waist position during scanning is detected by the scanning image forming position detecting means, a high-frequency voltage corresponding to the detected value is applied to the electro-optical lens 4 to cause the scanning during the scanning. The beam waist position of the laser light is feedback-controlled, and the scanned surface 11 is optically scanned by the beam waist with the laser light corrected to pass on a straight line, for example. In other words, the optical scanning device 21 can correct aberrations such as curvature of field during scanning which have been inevitable in the conventional optical scanning device, so that it contributes to the improvement of print quality of a laser printer. Can be.

In the optical scanning device 21 of the present embodiment, one high-frequency power supply 22 is commonly connected to the power supplies 19 and 20 of the electro-optical lens 4 to perform the same aberration correction in the main scanning direction and the sub-scanning direction. However, the present invention is not limited to the above structure.For example, a light source for connecting a dedicated high-frequency power source to each of the electrodes 19 and 20 to perform different aberration correction in the main scanning direction and the sub-scanning direction. A scanning device (not shown) or the like can be implemented.

According to the first aspect of the present invention, an image forming optical system including an electro-optical lens and an optical deflector are arranged on an optical path from a laser light source to a surface to be scanned, and the image forming optical system is emitted from the laser light source. Image position detecting means for detecting the position of the beam waist of the laser beam converged in step 2, and applying a DC voltage corresponding to the detected value of the image position detecting means to the electro-optical lens to thereby obtain a beam waist position in the optical path. Is provided, the beam waist position of the laser beam can be corrected for each scanning by an electro-optical lens that is feedback-controlled in accordance with the displacement, so that the beam waist converges. This has such an effect that the scanned surface can be optically scanned with a laser beam whose position is always uniform.

According to a second aspect of the present invention, there is provided a scanning image forming position for detecting a change position of a beam waist position during scanning of a laser beam emitted from a laser light source, converged by an image forming optical system, and deflected and scanned by an optical deflector. By providing a detecting means, applying a high-frequency voltage corresponding to the detection value of the scanning image position detecting means to the electro-optical lens, by providing a scanning position uniforming means for correcting the displacement of the beam waist position during scanning, The beam waist position of the laser beam that has been deflected and scanned can be corrected during scanning by an electro-optical lens that is feedback-controlled in accordance with the displacement, so that the image plane during scanning that is inevitably generated in the conventional optical scanning device Aberrations such as curvature can be corrected, and the convergence position of the beam waist is always located on the surface to be scanned, so that the surface to be scanned can be optically scanned with laser light having good optical characteristics. It is those having the effect.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention. FIG. 1 is a structural explanatory view of an embodiment of the invention according to claim 1, FIG. 2 is a perspective view, FIG. 3 is a characteristic diagram, and FIG. FIG. 5 is an operation explanatory diagram, FIG. 6 is a characteristic diagram, FIG. 7 is a side view of a main part, FIG. 8 is a characteristic diagram, and FIG. 9 is an embodiment of the present invention. It is a structural explanatory view showing an example. Reference numerals 1, 21: optical scanning device, 2: laser light source, 3-5, 8-10: imaging optical system, 4: electro-optic lens, 6: optical deflector, 13: imaging position detecting means, 18: imaging Position uniformizing means, 22 ... Scanning position uniformizing means

Claims (2)

(57) [Claims] An image forming optical system including an electro-optical lens and an optical deflector are arranged on an optical path from a laser light source to a surface to be scanned.
Imaging position detection means for detecting the position of the beam waist of the laser light emitted from the laser light source and converged by the imaging optical system, and the DC voltage corresponding to the detection value of the imaging position detection means An optical scanning device comprising: an imaging position equalizing unit that corrects a beam waist position in an optical path by applying to an electro-optic lens. 2. A scanning image position detecting means for detecting a change position of a beam waist position during scanning of laser light emitted from a laser light source and converged by an image forming optical system and deflected by an optical deflector. Scanning position equalizing means for correcting a displacement of a beam waist position during scanning by applying a high-frequency voltage corresponding to a detection value of the scanning image position detecting means to the electro-optical lens. The optical scanning device according to claim 1.