JPH03265817A - Optical scanner - Google Patents

Abstract

PURPOSE:To align the beam waist position of a deflected laser beam to be converged and imaged with the surface of a medium to be scanned for environmental temperature variation at all times by controlling a voltage applied to an electrooptic lens according to the output signal of a temperature sensor, and varying the focal length of the electrooptic lens. CONSTITUTION:A temperature sensor 5 fitted to a support member 15 in an optical housing 9 detects the temperature in an equipment and the output signal of the sensor 5 is amplified by an amplifier 10 and converted by an A/D converter 11 into a digital signal, which is inputted to a conversion table 12. The conversion table 12 contains data on the relation between temperature and the output voltage of the temperature sensor in advance. Then a bit code outputted by the conversion table 12 is converted by a D/A converter 13 into an analog signal, and the DC voltage applied to the electrooptic lens 3 is controlled to vary the focal length of the lens 3. Consequently, the beam waist position is aligned with the surface of the medium 15 to be scanned at all times.

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to an optical scanning device, and more particularly, to an optical scanning device. Convergent spot position 1 using electro-optic lens (variable focal length lens) in laser printer

[Related to an optical scanning device that corrects variations in t (bim waist position). For example, this applies to digital copiers, digital color laser fanoxes, and the like. Prior art Publicly known documents describing the prior art related to the present invention include "Laser unit 1 ~" published in Equity=yx 1-2838 F-, and 1-light scanning method J published in Japanese Patent Application Laid-Open No. 58-57108. . The above-mentioned Japanese Patent Publication No. 3-28381 discloses that the distance between the laser light source and the optical system is maintained so that the distance between the laser light source and the optical system does not change due to temperature changes within the device, and the convergence position of the laser beam is kept constant. It is disclosed that the wavelength shift due to temperature changes in the semiconductor laser is cooled using a Peltier element to prevent temperature rise. However, as the temperature inside the device rises, the semiconductor laser element moves toward the collimator lens due to thermal expansion of the laser holding member, and the collimator lens moves toward the semiconductor laser element side due to thermal expansion of the collimator lens holding member. The distance between the collimating lens and the semiconductor laser element is reduced. In order to compensate for this reduction, the distance between the semiconductor laser element and the collimator lens is expanded due to thermal expansion of the connecting member, which makes the structure complicated.
Even if the coefficient of thermal expansion and the like are considered, it is difficult to compensate accurately. In addition, there are drawbacks such as the use of a Peltier element in order to prevent heat generation in the semiconductor laser, resulting in a Goss level of 1 to high. In addition, Japanese Patent Application Laid-open No. 58-57108 discloses that in a light beam scanning optical system, each lens system can be moved without identifying the positional relationship, and the imaging characteristics of the optical system can be changed to make the optical system complicated and expensive. An optical scanning method that can be improved without any problems is disclosed.
Specifically, the movement of collimator lenses, condensing lenses, etc. is controlled by actuators to improve imaging characteristics in plane scanning. However, deviations from plane scanning that occur within one scanning period of the laser beam are corrected by controlling the movement of collimator lenses, condensing lenses, etc. in the optical axis direction, and such methods require precise settings. This has the disadvantage that the optical system has moving parts, which significantly reduces reliability. Purpose The present invention was made in view of the above-mentioned circumstances.
In order to prevent the imaging optical system from shifting due to temperature changes within the equipment and the beam waist position of the convergent beam deviating from the surface of the scanned medium,
By using an electro-optical lens with a focal distance variable function and controlling the voltage U applied to the electro-optic lens according to temperature changes, the beam waist position is always constant, and one scan of the laser beam 11 is The deviation from plane scanning that occurs during the period is corrected by a high-frequency voltage applied to the electro-optic lens without moving the optical system part, and a DC bias voltage applied to the electro-optic lens is used to compensate for temperature changes inside the device. The object of the present invention is to provide an optical scanning device that is capable of performing good plane scanning by correcting the above. In order to achieve the above object, the present invention provides (1) a laser light source, an electro-optic lens into which the laser light from the laser light source enters, and a laser light emitted from the electro-optic lens. an optical deflector for deflecting and scanning the optical beam; an imaging optical system for converging and imaging the laser beam deflected by the optical deflector;
a power source for applying a DC voltage to the electro-optical nonce; an optical housing that houses the laser light source, the electro-optical lens, the optical deflector, and the imaging optical system; and a temperature sensor installed in the optical housing. and a scanned medium scanned by the deflected laser beam, by controlling the voltage applied to the electro-optic lens according to the output signal from the temperature sensor and changing the focal length of the electro-optic lens. , the beam waist position of the deflected laser beam that has been focused and imaged is always aligned with the surface of the scanned medium despite changes in environmental temperature; and (2)
It has a power source that applies a DC bias voltage to the electro-optical lens and a power source that applies a high frequency driving voltage, and the beam waist position is kept constant by changing the DC bias voltage in response to changes in environmental temperature. For the changes in the position of the beam waste 1 that occur within one line scanning of the deflected laser beam. The present invention is characterized in that the correction is performed using the high frequency driving power source. An explanation will be given below based on one embodiment of the present invention. Generally, in a laser beam printer, a laser beam emitted from a laser passes through an optical modulator, enters a rotating polygon mirror, and is horizontally scanned in a one-dimensional direction. When a semiconductor laser is used as a light source, a modulator is not necessary because of direct modulation. The laser beam reflected by the rotating polygon mirror enters the fO lens. The fO lens is a lens designed so that light reflected in the direction O with respect to the optical axis is focused at a position f-0 when the focal length of the lens is f. An electrophotographic photosensitive tram, such as those used in copying machines, is placed at the light condensing point, and is uniformly charged just before writing. Thereafter, the area irradiated with the laser light is removed from the electric potential, and carbon toner is applied thereto. The laser beam is scanned horizontally, and the force-sensitive light 1 ~ ram moves in a direction perpendicular to it, so when modulation is applied to the laser beam, it is formed as an image, character pattern, or potential pattern, similar to the scanning of a television screen. . The toner attached to the photosensitive drum is transferred to printing paper and then fixed using heat, pressure, or the like. FIGS. 1(a) and 1(b) are configuration diagrams for explaining an embodiment of the optical scanning device according to the present invention, and FIG. 1(c'l) is a sectional view of the scanning optical system, and FIG. is a perspective view. In the figure, soil is a semiconductor laser, 2 is a collimating lens, 3 is an electro-optical lens, 4 is a cylinder lens, 5 is a temperature sensor, 6 is a polycon mirror, 7 is an fO lens, 8 is a drive motor, 9 is a housing, and 10 is a amplifier, Ll is an A/D converter, 12 is a conversion table, 13 is a D/A converter, 1-4
1 is a DC power supply, 1-5 is a support member, and A is a scanned medium. A diverging beam from a semiconductor laser 1 is made into a parallel beam by a collimator lens 2, and is made incident on an electro-optic lens 3. The electro-optical lens 3 has a focal length variable function, and the focal length can be varied by changing the applied voltage. Further, the output beam subjected to a lens action by the electro-optic lens 3 passes through the cylinder lens 4, is deflected and reflected by the polycon mirror 6, and is converged into an image on the scanning surface by the fO train 7. The number of sheets of the fo-relen increases as high-quality printing is desired. The polycon mirror 6 is rotated by a motor 8. The temperature inside the device is detected by the temperature sensor 5 attached to the support member 15 in the optical housing 9, the output signal from the temperature sensor 5 is amplified by the amplifier 10, and converted into a digital signal by the A/D converter 11. , is input into the conversion table 12. Data regarding the relationship between the predetermined temperature and the output voltage of the temperature sensor is incorporated into the conversion table J2. The bit code output from the conversion table j2 is converted into an analog signal by the D/A converter J3, and the DC voltage applied to the electro-optic lens 3 is controlled so that the beam waist position always matches the surface of the scanned medium 15. do. Figures 2 (a) to (c) are configuration diagrams of electro-optic lenses.
Figure (a) is a perspective view, figure (b) is a side view seen from the individual beam direction of figure (a), figure (c) is a side view seen from the opposite side of figure (b), and in the figure, 16,]7,''9.2Q,21.2
2 is an electrode film, and 18 is a power source. The electro-optic lens 3 forms electrode films 16, 7 on opposite surfaces of an electro-optic medium (electro-optic crystal without electrodes), and the electrode films 16, 17
A power supply 18 is provided to apply a voltage to the power supply. As an electro-optic medium, P L Z T (lead (Plomb
)], anthanum zirconate tit
anate) electro-optic crystal is used, and its composition is 9/
65/35 (65% PbZrO3, PbTi
0. is a 35% d product with La 9z Dorf. (to provide transparency) is suitable, but other compositions may be used. The surfaces on which laser light enters and exits the PLZT electro-optic crystal are optically polished, and Au is formed as an electrode film along the optical path on a surface perpendicular to these surfaces by vacuum evaporation.
Other conductive materials may also be used. Screen printing may be used as a forming method using a conductive paste. Explain the principle of electro-optic lenses. When no voltage is applied to the electro-optic lens, the incident laser beam exits without any change. At this time, it has no lens effect. When a voltage is applied, an electric field distribution as shown in FIG. 1(b) and the dotted line in FIG. 1(c) is generated, being strong near the electrodes and weak near the center. As a result, a refractive index distribution occurs within the crystal due to the electro-optic effect. Assuming that the direction of the electric field is Z, the direction of the incident laser beam 11 is Y, the incident laser beam is polarized in the X direction, and the refractive index Z/& when a voltage is applied is nZ, then . n is the refractive index of the L Z T electro-optic crystal; Said (
According to the equation (2), the change in refractive index due to the electric field E2 Δ(2)2 is proportional to the square of the electric field strength. The refractive index is small in regions where the electric field is strong, and the refractive index is large in regions where the electric field is weak. As a result, lens action occurs in the X direction and towards the center in the X direction. The longer the optical path length of an electro-optic lens, the greater the lens effect. Furthermore, when the laser beam linearly polarized in the X direction enters the electro-optic lens as a parallel beam, electrode films are formed on the top and bottom of the optical path] 6.17.
``1J undergoes a lens action, and the focal length becomes 1°, which is A.
converge to a point. Next, when the laser beam enters the area shown in Figure (c), it receives a lens action in the X direction due to the voltage applied to the electrode film 19, 20, 21, 22, and the focal length becomes f.
'o and converges to point A. At point A, a spot converged in both the X and Z directions is obtained. In this way X and 2
In order to converge to the same point A in both directions, the length of the electrode film, Ω', may be set according to the convergence performance in each direction. FIG. 3 shows actually measured values of the focal length f versus the applied voltage of the electro-optic lens of the present invention. The focal length lf in this case is the distance from the center of the electro-optic lens to the convergence position. FIG. 4 shows the variation in the position of the beam waste 1 in the optical scanning device when no electro-optic lens is used, with respect to changes in the environmental temperature. A factor contributing to this variation is that the oscillation wavelength of the semiconductor laser shifts to longer wavelengths as the temperature rises (for example, approximately 0,3
nm/'C) and changes in the distance between the lenses and the distance between the semiconductor laser and the lens due to thermal expansion of the optical system and the supporting member of the semiconductor laser]2. In particular, the wavelength shift of a semiconductor laser greatly contributes to the beam wear position fluctuation. Therefore, in the embodiment shown in FIG. 1, the voltage applied to the beam waste 1 is controlled so that the fluctuation due to environmental temperature changes in the position of the beam waste 1 is kept constant at 1; The operation will be explained below. In Fig. 3, when a DC voltage of vb is applied to the electro-optic lens, the focal length becomes f. Vb is set so that the beam width 1~position of the beam is on the surface of the scanned medium (Vb=300 V/mm). FIG. 5 shows the relationship between the environmental temperature and the applied voltage such that the position of the beam waste 1 is always constant. This temperature change includes the temperature stability of the electro-optic lens and is corrected. Therefore, if a conversion table is created in advance so as to output the voltage shown in FIG. 5, the beam waist position can be made constant using the electro-optic lens. FIG. 6 is a block diagram showing another embodiment of the present invention, in which reference numeral 23 denotes a high frequency power source, and parts having the same functions as those in FIG. 1 are given the same reference numerals. The difference from the embodiment of the present invention shown in FIG. 1 is that a high frequency power source 23 is provided. This high frequency power source 23 is designed to correct the curvature of field that occurs within one scanning period of the laser beam at the same time as temperature correction. In this case, the high frequency voltage applied to the electro-optic lens is the electrode film of the electro-optic lens], 6.17 and ]-
You can apply the same voltage to 9, 20, 2, and 22, and make the correction amount of 1JiJ the same for main scanning and sub-scanning, or prepare two high-frequency power supplies and apply different high-frequency voltages to each. It is also possible to change the amount of correction in the main scanning and sub-scanning directions by applying a temperature sensor. As is clear from the above explanation, the present invention has the following effects: (1) The temperature sensor The environmental temperature inside the device is measured, and the output from the sensor (No.゛1'
It is possible to prevent changes in the beam waist position caused by shifts in the oscillation wavelength of the conductor laser, deviations in spacing due to thermal expansion of the support of the semiconductor laser and optical system, and changes in the focal length of the electro-optic lens itself. The position of the tape 11 and waste 1 is always on the surface of the scanned medium regardless of temperature changes, and a stable optical scanning device is realized. (2) In addition to preventing fluctuations in the position of the beam waste 1 due to environmental temperature changes, it is also possible to control the electro-optical lens using a high-frequency power source to correct field curvature that is limited within the laser beam's scanning period. It is possible to maintain '-' regardless of temperature changes.
A stable optical scanning device in which the beam waste 1 is located on the surface of the scanned medium and has no field curvature is realized.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an optical scanning device according to the present invention, FIG. 2 is a configuration diagram of an electro-optical lens,
Figure 3 is a diagram showing actual measured values of the focal length of the electro-optic lens with respect to the applied voltage, Figure 4 is a diagram showing the beam waste position fluctuation of the optical scanning device when the electro-optic lens is not used, and Figure 5 The figure shows the relationship between the environmental temperature and the applied voltage such that the beam waist position is constant, and FIG. 6 is a configuration diagram showing another embodiment of the present invention. 1 Semiconductor Laser, 2 Corinot 1~lens, 3 Electro-optical lens, 4 Cylinder lens, 5 ・Temperature sensor, 6
Polygon mirror, 7...fO lens, 8 motor,
9.Housing, 11-Amplifier, 11-4/D converter, 12.Conversion chifur, 3D/A converter, 14 DC power supply, 15 Support member. (b) Figure (Q) (C) Figure Applied voltage (X ro2V/mm) Figure Environmental temperature Bim waist position fluctuation

Claims (1)

[Claims] 1. A laser light source, an electro-optic lens into which the laser light from the laser light source enters, an optical deflector for deflecting and scanning the light beam emitted from the electro-optic lens, and the optical deflector. an imaging optical system for converging and imaging a laser beam deflected by a device, a power source for applying a DC voltage to the electro-optic lens, the laser light source, the electro-optic lens, an optical deflector, and an imaging optical system. An electro-optic lens is configured to include an optical housing housing the system, a temperature sensor installed in the optical housing, and a scanned medium scanned by the deflected laser beam. By controlling the voltage applied to the electro-optic lens and changing the focal length of the electro-optic lens, the beam waist position of the converged and imaged deflected laser beam is always aligned with the surface of the scanned medium despite changes in environmental temperature. An optical scanning device characterized by: 2. It has a power source that applies a DC bias voltage to the electro-optical lens and a power source that applies a high frequency drive voltage, and the beam waist position is kept constant by changing the DC bias voltage in response to changes in environmental temperature. 2. The optical scanning device according to claim 1, wherein a change in beam waist position occurring within one line scanning of the deflected laser beam is corrected by the high frequency drive power source.