JP2682666B2 - Optical scanning device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical scanning device.

[Prior Art] A substantially parallel light flux from a light source device is imaged by a first optical system into a line image parallel to a main scanning direction, and a rotation having a deflection reflection surface in the vicinity of the image formation position of this line image. An optical scanning device is well known in which the light flux is deflected by a polygon mirror and the deflected light flux is imaged in a spot shape on the scanning surface by the second optical system to optically scan the scanning surface.

FIG. 4 schematically shows only a main part of a typical example of this type of optical scanning device.

In FIG. 4, reference numeral 1 is a light source device, and a substantially parallel light flux is emitted from the light source device 1. This parallel light flux subsequently enters the cylindrical lens 2 which is the first optical system, becomes a unidirectional focused light flux, and forms a line image LI.

The rotary polygonal mirror 3 has a deflection reflection surface 4 in the vicinity of the line image LI, and the deflection reflection surface 4 reflects the light beam. The reflected light beam is deflected when the rotary polygon mirror 3 rotates around the rotation axis 3A, and this deflection is repeated every time the deflecting / reflecting surface is switched with the rotation of the rotary polygon mirror 3. The light beam deflected by the rotary polygon mirror 3 is transmitted through the lenses 5 and 6 forming the image forming lens which is the second optical system, and is imaged in a spot shape on the scanning surface to optically scan the scanning surface in the main scanning direction. .

The imaging lens composed of the lenses 5 and 6 is an anamorphic lens system having different powers in the main scanning direction and the sub-scanning direction, and in the main scanning direction, the infinity on the incident side and the scanning plane position are in a conjugate relationship. With respect to the sub-scanning direction, the vicinity of the starting point of deflection by the deflecting / reflecting surface and the scanning surface position are in a substantially conjugate relationship.

[Problems to be Solved by the Invention] The problems to be solved by the present invention are as follows.

The rotary polygon mirror 3 is formed of, for example, a light metal such as aluminum. When the optical scanning device is continuously driven, the temperature of the rotary polygon mirror 3 rises due to friction with air and heat transfer from a drive motor. This temperature rise causes the rotary polygon mirror 3 to deform due to thermal expansion.

In FIG. 5, the solid line shape shows the normal size of the rotary polygon mirror 3, and the broken line shape shows a state in which it is similarly expanded and deformed by thermal expansion. That is, the radius of the inscribed circle of the rotary polygon mirror 3 increases from the normal size R by Δ due to thermal expansion. In accordance with this deformation, the position of the reflection start point of the reflected light changes, and for example, a light beam reflected by a normal rotating polygon mirror as indicated by reference numeral 9 is reflected as shown by reference numeral 9'in the enlarged and deformed state. To be done.

FIG. 6 shows a state in which the optical scanning device of FIG. 4 is developed along the optical path of a light beam as viewed from the main scanning corresponding direction. FIG. 6A shows a case where the rotary polygon mirror 3 has a normal size, and the position of the deflecting reflection surface 4 (which coincides with the position of the line image) and the position of the scanning surface 7 are the lenses 5, 6 has a conjugate relationship. In this state, the deflected light beam forms an image of the light beam shape at the position of the deflective reflection surface on the scanning surface in the sub-scanning direction. FIG. 6B shows a state in which the rotary polygon mirror 3 is expanded and deformed, and the position of the deflecting / reflecting surface 4 is deviated from the normal position (the position indicated by the broken line) to the position indicated by reference numeral 4 '. At this time, if the deviation between the line image and the deflective reflecting surface 4'is Δx as shown in the figure, this deviation is deviated by Δx '= β ² · Δx at the position of the scanning surface with the lateral magnification of the imaging lens being β.

Here, for the specificity of the description, the specifications of the lenses 5 and 6 constituting the imaging lens (the second optical system) are specifically given as follows.

The radius of curvature of the i-th lens surface counted from the side of the rotary polygon mirror 3 is rxi in the main scanning direction and r in the sub scanning direction.
yi (i = 1 to 4), i-th surface spacing is di (i = 1 to 1)
3), the refractive index of the j-th lens for light having a wavelength of 780 nm is nj (j = 1 to 2).

i rxi ryi di j nj 1 −107.774 ∞ 5.672 1 1.71221 2 ∞ ∞ 10.966 3 ∞ −52.565 6.807 2 1.675 4 −45.569 −12.052 In addition, the focal length of this imaging lens is fm = 100 in the main scanning direction, and the sub-lens. In the scanning direction, fs = 22.698, the brightness is F / No = 54.7 in the main scanning direction, and the lateral magnification β = −4.12 described above. Further, the deflection angle by the rotary polygon mirror 3 is 67.8 °, the angle formed by the central ray of the incident light beam on the rotary polygon mirror 3 and the optical axis of the imaging lens is 60 °, and the radius of the inscribed circle of the rotary polygon mirror 3 is 60 °. The ratio R / fm is R / fm = 0.132.

FIG. 7 shows the field curvature due to this imaging lens. The field curvature indicated by reference numeral 10 is in the main scanning direction. This field curvature in the main scanning direction is hardly affected by the thermal deformation of the rotary polygon mirror 3. The aberration curve of the solid line is the field curvature in the sub-scanning direction, which is strongly affected by the deformation of the rotary polygon mirror 3. That is, the curve indicated by reference numeral 11 is R /
The curvature of field in the sub-scanning direction at the center value of fm = 0.132, but when the radius of the inscribed circle increases by Δ (R / fm) = + 0.0002, the curvature of field becomes like curve 12, and Δ (R / fm)
When the radius of the inscribed circle is reduced by = -0.0002, the field curvature becomes as shown by the curve 13.

As is well known, the intensity distribution of the laser light flux is a Gaussian type distribution. Therefore, when a laser light source is used as the light source of the light source device 1, when the laser light source is imaged in a spot shape on the scanning surface, the intensity of the scanning spot is increased. The distribution is also Gaussian.

FIG. 8 shows the light intensity distribution of this scanning spot. FIG. 10A shows a state where R / fm = 0.132, that is, a state where the radius R of the inscribed circle of the rotary polygon mirror has a regular value. When the image forming level, that is, the threshold value of the photosensitive energy in the photosensitive medium scanned as the scanning surface is as shown in the figure, the scanning spot diameter is 2ω in the figure. However, when the radius of the inscribed circle of the rotating polygonal mirror 3 changes due to temperature change, the light intensity distribution in the scanning spot sub-scanning direction widens as shown in FIG. Is constant, the diameter of the scanning spot in the sub-scanning direction at this time is 2ω 'in the figure.

Since the scanning spot diameter is an important factor that determines the resolving power of an image recorded by optical scanning, the above-mentioned fluctuation of the scanning spot diameter is a problem that directly affects the quality of optical scanning. It must be suppressed as much as possible. Conventionally, the problem of the scanning spot diameter change due to the deformation of the rotary polygon mirror due to the temperature change has not been considered at all.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a novel optical scanning capable of effectively reducing the fluctuation of the scanning spot diameter due to the deformation of the rotating polygon mirror due to the temperature change. The equipment is provided.

[Means for Solving the Problems] Hereinafter, the present invention will be described.

The optical scanning device according to the present invention forms an image of a substantially parallel light beam from the light source device into a line image parallel to the main scanning corresponding direction by the first optical system, and deflects and reflects the line image in the vicinity of the image forming position of the line image. A device for deflecting the light beam by a rotating polygon mirror having a surface, and for forming an image of the deflected light beam on the scanning surface in a spot shape by the second optical system to optically scan the scanning surface. A laser light source is used.

The optical scanning device includes a scanning light intensity adjusting means,
It has a temperature detection means and an adjustment signal generation means.

The scanning light intensity adjusting means is means for adjusting the intensity of the laser light.

The temperature detecting means is means for detecting the temperature of the rotary polygon mirror.

The adjustment signal generating means is means for generating an adjustment signal to the scanning light intensity adjusting means according to the detection result of the temperature detecting means.

Then, the scanning light intensity adjusting means has a function of controlling the scanning light intensity so that the scanning spot diameter becomes substantially constant irrespective of the temperature of the rotary polygon mirror, according to the adjustment signal.

[Operation] Hereinafter, the operation of the present invention will be described. As described with reference to FIG. 8, when performing optical scanning with the same light intensity, if the rotary polygon mirror is deformed due to temperature change, the size of the scanning spot is deformed by defocusing. The subsequent scanning spot diameter 2ω ′ is larger than the regular scanning spot diameter 2ω before the deformation.

Curves 3-4 and 3-5 in FIG. 3 (b) show the light intensity distributions of the scanning spots formed at the same position on the scanning surface. The difference between the two distributions is the difference in the intensity of the laser light incident on the scanning surface. That is, the distribution when the laser light of weak intensity is imaged on the scanning surface is the curve 3-4, and the curve 3-5 gives the distribution when only the intensity of the laser light is increased.

Since the image forming level is constant, when changing the intensity of the laser light in this way, the distribution 3
If the scanning spot diameter for -4 is 2ω1, it is 2ω1 'when the intensity is increased, and 2ω1'>
It is 2ω1.

 The present invention takes advantage of this fact.

Referring to FIG. 3 (a), reference numeral 3-
The curve indicated by 1 shows the light intensity distribution of the regular scanning spot in the sub-scanning direction when the rotary polygon mirror is not deformed.
Therefore, 2ω2 shown in this figure gives a regular scanning spot diameter.

On the other hand, a curve 3-2 shows the light intensity distribution of the scanning spot defocused by the deformation of the rotary polygon mirror. The scanning spot diameter at this time is 2ω3.

At this time, if the light intensity of the laser light is reduced and the light intensity step of the scanning spot can be made as shown by the curve 3-3, the scanning spot diameter can be corrected to the regular size 2ω2.

Regarding the similar deformation due to the temperature change of the rotating polygon mirror,
If the material of the rotary polygon mirror is known, Δ
(R / fm) can be known.

That is, a proportional relationship of Δ (R / fm) ∝ΔT is established between the temperature change ΔT of the rotating polygon mirror and Δ (R / fm).

Therefore, by detecting the temperature change ΔT and controlling the light intensity of the scanning light accordingly, the fluctuation of the scanning spot diameter due to the deformation of the rotary polygon mirror is corrected, and the scanning spot is irrespective of the deformation of the rotary polygon mirror. The diameter can be made almost constant. That is, in principle, the control may be performed so that the scanning light intensity decreases as the temperature rises.

[Example] Hereinafter, a description will be given according to a specific example.

The embodiment described below is an example in which the present invention is applied to the optical scanning device described above with reference to FIG.

In FIG. 1, reference numeral 3 indicates a rotary polygon mirror as in FIG. Further, reference numeral 20 is a drive motor, reference numeral 22 is a temperature sensor, reference numeral 24 is an analog / digital converter (hereinafter simply referred to as A / D converter 24), reference numeral 26.
Represents a read only memory (hereinafter, simply referred to as ROM 26), and reference numeral 28 represents a digital / analog converter (hereinafter, simply referred to as D / A converter 28).

In this figure, the temperature sensor 22 constitutes a temperature detecting means, and the A / D converter 24, the ROM 24 and the D / A converter 28 constitute an adjusting signal generating means.

Next, referring to FIG. 2, this figure shows the light source of the light source device and the scanning light intensity adjusting means.

That is, the light source of the light source device is the semiconductor laser 32 in this embodiment, and thus the light source device is composed of the semiconductor laser 32 as a light source and a collimator lens (not shown).

A photodiode 34 for receiving and photoelectrically converting laser light emitted backward from the semiconductor laser 32, an amplifier 36 for amplifying an output signal thereof, a comparator 38 to which an output of the amplifier 36 is input, and a control circuit 40 are It constitutes a scanning light intensity adjusting means.

The scanning light intensity adjustment will be briefly described with reference to FIG. In this embodiment, the scanning light intensity is adjusted by adjusting the light emission intensity of the semiconductor laser 32 as a light source.

The emission intensity of the semiconductor laser 32 is determined by the drive voltage of the semiconductor laser drive circuit 30, and by modulating this drive voltage with a modulation signal, laser light whose intensity changes according to the modulation signal can be obtained.

The adjustment of the light emission intensity of the semiconductor laser 32 is to adjust the reference light emission intensity, and is, therefore, nothing but the adjustment of the drive voltage that gives the reference light emission intensity. In this embodiment, the light emission intensity from the semiconductor laser 32 is photoelectrically converted by the photosensor 34, and the photoelectrically converted signal is amplified by the amplifier 36.
Amplify with and take into the comparator. Then, the comparator 38 compares the received signal with the reference voltage Vref and sends a signal corresponding to the difference to the control circuit. The control circuit 40 outputs a signal for changing the drive voltage in response to the signal from the comparator 38 to change the drive voltage, and eventually the signal voltage taken from the amplifier 36 into the comparator 38 becomes equal to the reference voltage Vref. To do so. In this way, the emission intensity of the semiconductor laser 32 is adjusted. By changing the reference voltage Vref, the light emission intensity of the semiconductor laser 32 can be arbitrarily adjusted.

Incidentally, the scanning light intensity adjusting means as shown in FIG. 2 has already been disclosed in JP-A-61-175656, JP-A-61-175655 and JP-A-61-10.
It is well known from Japanese Patent Publication No. 9371, etc., and when carrying out the present invention, the scanning light intensity adjusting means in FIG.

Now, returning to FIG. 1, the temperature of the rotary polygon mirror 3 is detected by the temperature sensor 22, and the detection result is the A / D converter 24.
Is converted into a digital signal by and is sent to the ROM 26.

In the ROM 26, the temperature of the rotary polygon mirror 3 that is detected by the temperature sensor 22 in advance (a temperature that is 1: 1 linked to the temperature of the rotary polygon mirror 3 may be used, and as shown in the figure, it is very close to the rotary polygon mirror 3. The output value corresponding to the ambient temperature may be stored in advance, and the output value corresponding to the input temperature value is output. This output is input to the D / A converter 28.

A constant voltage Vrefo is applied to the D / A converter 28,
The above voltage is modulated according to the input value and the output voltage Vref
Is output. Therefore, the output voltage Vref changes according to the temperature of the rotary polygon mirror 3. This output voltage Vref is the second
It is input to the comparator as the reference voltage Vref shown in the figure. Therefore, the voltage signal Vref output from the D / A converter 28 is nothing but an adjustment signal, and the scanning light intensity adjusting means automatically adjusts the emission intensity of the semiconductor laser 32 thereafter.

The relationship that correlates the input and the output stored in the ROM 26 is to make the relationship between the temperature of the rotary polygon mirror 3 and the scanning light intensity approximately the same regardless of the temperature of the rotary polygon mirror. This can be experimentally determined according to the design conditions of the optical scanning device.

[Effects of the Invention] As described above, according to the present invention, a novel optical scanning device can be provided. Since this device has the above-mentioned configuration, the diameter of the scanning spot can be kept substantially the same regardless of the temperature of the rotary polygon mirror, and good optical scanning can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature detecting means and an adjusting signal generating means of an embodiment of the present invention, FIG. 2 is a diagram for explaining the scanning light intensity adjusting means of the above embodiment, and FIG. FIG. 4 is a diagram for explaining the operation of the present invention, FIG. 4 is a diagram for explaining an optical scanning device, and FIGS. 5 to 8 are diagrams for explaining a problem to be solved by the present invention. 3 ... Rotating polygon mirror, 32 ... Semiconductor laser, 34 ... Photodiode

Claims (1)

(57) [Claims] 1. A rotation in which a substantially parallel light beam from a light source device is imaged by a first optical system into a line image parallel to a main scanning corresponding direction, and a deflection reflection surface is provided in the vicinity of an image forming position of this line image. A device for deflecting the light flux by a polygon mirror and for forming an image of the deflected light flux on the scanning surface by a second optical system to optically scan the scanning surface, wherein the light source of the light source device is a laser light source, Scanning light intensity adjusting means for adjusting the intensity of laser light, temperature detecting means for detecting the temperature of the rotating polygon mirror, and adjustment for generating an adjusting signal to the scanning light intensity adjusting means according to the detection result by the temperature detecting means. The scanning light intensity adjusting means has a function of controlling the scanning light intensity so that the scanning spot diameter becomes substantially constant irrespective of the temperature of the rotary polygon mirror in accordance with the adjustment signal. Optical scanning device characterized in that