JP2692944B2 - Scanning optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a scanning optical device that scans a light beam from a light source on a scanning surface via a deflector and a lens system. The present invention relates to a scanning optical device capable of correcting a focus shift of an image forming spot of a laser beam.

[Conventional technology]

In recent years, a scanning optical device such as a laser beam printer which scans a laser beam and forms a latent image on a photoconductor by flickering the laser beam to record a desired image has been widely known.

FIG. 5 shows a schematic configuration of a laser scanning unit 100 for scanning a laser beam in this type of apparatus. When a laser beam is scanned by the laser scanning unit 100, first, a light emission signal generator is generated based on an input image signal.
101 causes the solid-state laser element 102 to blink at a predetermined timing. The laser light emitted from the solid-state laser element 102 is converted into a substantially parallel light beam by a collimator lens system 103, and furthermore, a rotating polygon mirror that rotates in the direction of arrow b.
104 f [theta] lens group 1 while being scanned in the arrow c ₀ direction by
Images 05a, 105b, and 105c form spots on the surface to be scanned 106 such as the photosensitive drum.

An image-scanning exposure distribution is formed on the scanned surface 106 by the scanning of the laser light, and the scanned surface 106 is scrolled by a predetermined amount perpendicular to the scanning direction for each scan. Thus, an exposure distribution according to the image signal is obtained on the scanned surface 106. Then, by printing this latent image on recording paper by a well-known electrophotographic process, a high-density image can be obtained.

By the way, in such a conventional example, in order to perform high density recording by the latent image formed on the photoconductor, the surface to be scanned 10
It is necessary to reduce the size of the spot irradiated to 6 according to the density to be recorded. For example, when a Gauss spot that blinks every pixel is scanned, the exposure distribution on the scanned surface 106 changes as shown in FIG. 6 depending on the spot diameter on the scanned surface 106. That is, when the spot diameter in the main scanning direction is small, the exposure distribution by the laser light is close to the rectangular wave that matches the blinking timing and the contrast is high, but as the spot diameter increases, the laser light penetrates into the adjacent pixels and the exposure is performed. Since the amplitude of the distribution is small and the contrast is low, the quality of the output image is deteriorated. Therefore, for example, when configuring a printer with a high resolution of 800 dpi (32 dots / mm), the contrast is set to 80.
%, The size of the spot imaged on the photosensitive member must be suppressed to about 40 μm (Gauss distribution spot, 1 / e ² diameter) or less.

On the other hand, in order to obtain a laser spot with such a small diameter, an imaging optical system with a large F / N is generally required, but when this F / N value increases, the depth of focus of the imaging optical system increases. Is known to be very shallow. For example, in an apparatus capable of scanning an imaging spot having a diameter of 40 μm in the main scanning direction, the focus position of the imaging optical system is set to the surface to be scanned 106.
It must be kept within a very small range of ± 0.8mm before and after.

However, when a scanning optical device like the above-mentioned conventional example is actually constructed, each member constituting the optical system undergoes thermal deformation due to environmental changes, particularly temperature changes, and the focal plane moves beyond the depth of focus. As a result, the spot diameter may become larger than the desired value. In such a case, in the above-described conventional example, since the positions of the respective members are fixed, the contrast on the scanned surface 106 is reduced, and the image quality when forming an image is deteriorated. Had problems.

[Summary of the Invention]

The present invention has been made to solve the above conventional problems, and an object of the present invention is to provide a scanning optical system capable of accurately scanning a laser beam while preventing a shift of an imaging position due to a change in environmental temperature. To provide a device.

[Means (and action) for solving the problem]

To achieve the above object, in the present invention, in a scanning optical device for scanning a laser beam output from a laser light source on a scanned surface via a deflector and a lens system, the laser beam on the scanned surface is Detection means for detecting the image formation state of the scanning optical device and temperature detection means for detecting the temperature of a specific portion of the scanning optical device, and detection for detecting the image formation state when a temperature change is detected by the temperature detection means. The image forming position of the laser beam is adjusted based on the signal obtained by the means.

〔Example〕

 The present invention will be described below based on the illustrated embodiments.

FIG. 1 shows a schematic configuration of a first embodiment of a scanning optical device according to the present invention. In FIG. 1, reference numeral 1 denotes a light emission signal generator for generating laser light, and a solid-state laser element 2 as a laser light source connected to the light emission signal generator blinks according to the light emission signal. Reference numeral 3 denotes a collimator lens system for making the laser light flux emitted from the solid-state laser element 2 into substantially parallel light. The correction lens in the collimator lens system is an arrow A which is the optical axis direction of the laser light by a focus adjusting means 4 described later. It can be moved in any direction.
Reference numeral 5 denotes a rotary polygon mirror which, when rotated at a constant speed in the direction of arrow B, reflects parallel light emitted from the collimator lens system 3 and scans in the direction of arrow C. Reference numerals 6a, 6b and 6c denote fθ lens groups provided in front of the rotary polygon mirror.
The laser beam whose angle is deviated by is imaged and its scanning speed is made constant on the surface to be scanned.

Further, L is a laser beam, which is scanned on the photosensitive drum 9 as the surface to be scanned, and when the image formation state of the laser light on the surface to be scanned is detected, CC is passed through the movable mirror 7.
It is led onto the detection means 8 consisting of D. When forming an image on the surface to be scanned, the movable mirror 7 is moved outside the optical path.

The detection means 8 is arranged in a position optically equivalent to the surface of the photosensitive drum 9, that is, at a position equivalent to the surface to be scanned, and is arranged in a control section 10 for controlling the light emission signal generator 1 and the focus adjustment means 4. It is connected.

Further, the temperature detecting means 11 is arranged in contact with or close to the collimator lens system 3, and is connected to the control section 10.

Around the photosensitive drum 9, there are provided a developing device, a primary and transfer charging device, a fixing device, a cleaner, etc., which are not shown,
The latent image formed on the surface of the photosensitive drum 9 is visualized by a known electrophotographic process and transferred to a transfer material.

In the above-described configuration, when a desired image is formed, first, the image signal S is input to the light emission signal generator 1, and the solid-state laser element 2 blinks at a predetermined timing. The laser light emitted from the solid-state laser element 2 is converted into substantially parallel light by the collimator lens system 3, and then is scanned in the direction of arrow C by the rotary polygon mirror 5 which rotates in the direction of arrow B, and at the same time, the fθ lens groups 6a and 6b. , 6c form a spot-shaped image on the photosensitive drum 9.

Then, an exposure distribution for image-scanning is formed on the surface of the photosensitive drum 9 by such scanning of the laser beam L,
Further, the photosensitive drum 9 is rotated by a predetermined amount for each scan to form a latent image having an exposure distribution according to the image signal S on the drum 9 and is recorded as a visible image on a recording sheet by a well-known electrophotographic process.

By the way, when the laser beam L is imaged on a minute spot on the photosensitive drum 9 by the optical system as shown in FIG. 1 to form a high density image, the depth of focus becomes very shallow as described above. Is well known. Accordingly, the members constituting the optical system are thermally deformed due to environmental temperature changes such as heat generation during laser light emission, and the solid-state laser element 2
When the distance between the photosensitive drum 9 and the surface of the photosensitive drum changes, the image point of the laser light flux L deviates from the depth of focus, the spot diameter of the beam increases, and the contrast decreases as shown in FIG. May deteriorate.

Therefore, in the present invention, the position of the image forming point of the laser light flux L is adjusted when the temperature of each member constituting the optical system changes.

That is, first, the presence or absence of a temperature change in the optical system is detected by the temperature detecting means 11 shown in FIG. At this time, which member of the optical system is brought into contact with or in proximity to the temperature detecting means 11 depends on which member is dominant as a factor for varying the position of the image forming point with respect to the temperature change. In the present embodiment, the collimator lens system, which is expected to easily affect the image forming point position due to the thermal deformation of the members constituting the optical system, is brought into contact with or in the vicinity thereof. Of course, any other member may be used as long as it can finally detect the temperature change of the optical system.

If the temperature change is detected and it is determined that the amount of change affects the position of the image forming point of the laser beam L, the movable mirror 7 is moved to detect the image forming state of the laser beam L using the detecting means 8. To detect. Since the movable mirror 7 is outside the optical path of the laser beam L during a normal image forming operation, it is difficult to always detect the image formation state, and it is important when the detection system is activated. In the present embodiment, since the temperature detecting means is operated only when the movement of the image forming point is expected, it is possible to detect and adjust the image forming state only when necessary.

Of course, it is possible to detect the laser light flux L outside the image area, but at that time, it is necessary that the laser spot diameter is optically equivalent to the inside of the image area even outside the image area. Here, the inside of the image area refers to an area of the surface to be scanned where the image information is actually formed by the laser light flux L.

However, it is not only difficult to stably obtain a laser spot having a minute diameter as used in the present invention even outside the image area, and even if it is obtained, it is possible to form an image of the minute laser spot for design reasons. The position may deviate from the actual position on the surface to be scanned.

FIG. 2 shows an example showing the deviation of the image forming position of the spots for forming the minute laser spots from the surface to be scanned, and shows the state in the scanning cross section. Even if the deviation amount is included in the depth of focus of the optical system within the image area, it is not limited to the outside of the image area, and there is a high possibility that the difference between the spot image forming position and the surface to be scanned is greatly opened. . It has been confirmed that the amount of deviation of the image forming position outside the image area greatly changes depending on the lens accuracy and assembly accuracy of the optical system. Therefore, it may be difficult to control the actual image formation state within the image area by detecting the image formation state outside the image area.

In this embodiment, since the laser light flux L in the image area is directly measured, there is an advantage that the control of the image formation state in the image area becomes more reliable.

 Next, a method of detecting and adjusting the image formation state will be described.

First, a rectangular wave which is turned on and off at a constant interval as shown in FIG. 3 (a) is generated from the generated signal generator 1 for a predetermined period, and the solid-state laser element 2 is blinked in response to this signal. The laser light from the solid-state laser element 2 is scanned as described above, reflected by the reflecting mirror 7, and projected and scanned on the CCD 8 arranged at a position optically equivalent to the photosensitive drum 9.

Before the laser beam L scans on the CCD 8, the control unit 10
The accumulated charge in each pixel of the CCD8 is reset, and after the charge is accumulated in each pixel of the CCD8 by spot scanning of one line, this charge is read out as an electric signal.

When the solid-state laser element 2 blinks the laser light and scans once, the CCD 8 is at the position optically equivalent to the photosensitive drum 9. Therefore, the exposure distribution on the CCD 8 surface is as shown in FIG. The distribution shape of strength and weakness according to the spot diameter is shown. Therefore, the output of each pixel of the CCD8 has a distribution as shown in FIG. 3 (b), and the signal is sent to the control unit 10.
In the controller 10, the maximum value of the output of the CCD 8 is θ _max and the minimum value is θ _min , and the contrast V is Calculate and measure according to the formula.

In this case, the smaller the spot diameter in the scanning direction is, the larger the contrast V is.
When V is smaller than a predetermined value by comparing with V calculated by the equation, a drive signal is sent from the control unit 10 to the focus adjusting means 4 to drive the collimator lens system 3 as shown in FIG. The correction lens 3-2 therein is moved in the direction of arrow A by a predetermined amount. Then, the contrast V is measured at each position where the correction lens 3-2 is moved, and if the correction lens 3-2 is fixed at the position where this value is maximum, the defocus of the optical system is corrected and the laser light flux L is corrected. The spot diameter in the scanning direction can be minimized.

The temperature detecting means is not limited to the collimator lens portion, but may be arranged in another member of the scanning optical system, the f-θ lens system, or a polygon scanner motor portion that can also be a heat generation source. Also, even outside the scanning optical system, the temperature of a portion where the temperature change of the optical system can be predicted, for example, the temperature of the main body member in the vicinity or the air in the vicinity may be detected.

Further, the image forming state detecting means is not limited to the CCD, and is a method of calculating the contrast by scanning the light detecting element provided with the optical slit corresponding to ON / OFF of the laser of the present embodiment while the laser is being emitted. It doesn't matter.

Further, a means for moving the entire collimator lens system or a means for moving the position of the laser light source may be used as the image forming position correcting means.

〔The invention's effect〕

As described above, in the present invention having the above-described configuration, by detecting the temperature change of the specific member of the scanning optical device by the temperature detection means, the focus position of the member that constitutes the optical system is deformed due to thermal deformation. The occurrence of spot diameter change due to movement can be predicted.

As a result, it is possible to detect the image formation state only when the temperature change is detected and adjust the image formation position of the laser beam based on the signal, so that the image formation state of the laser beam on the scanned surface is always maintained. Since it is possible to provide a detecting means for detecting the image formation state in the image area, it is possible to reliably adjust the spot diameter change in the image area due to the temperature change to a desired size. It will be possible. Therefore, there is an effect that a high-density and high-quality image can be formed on the surface to be scanned.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a scanning optical device according to the present invention, FIG. 2 is a diagram showing a deviation of an image forming position of a spot from a surface to be scanned, and FIGS. 3 (a), (a). b) shows a signal during an adjusting operation in the embodiment, FIG. 7A is a graph showing a signal from a light emission signal generator, FIG. 8B is a graph showing an output signal from a CCD, FIG. 4 is an enlarged vertical sectional view showing a mechanism for moving the correction lens for adjusting the image forming position, FIG. 5 is a schematic configuration view showing a conventional scanning optical device, and FIG. 6 is a spot diameter of a laser beam and an exposure distribution. It is a graph which shows the relationship of. 2 ... Solid-state laser element (laser light source) 3 ... Collimator lens system 4 ... Focus adjustment means 7 ... Movable mirror 8 ... CCD (detection means) 9 ... Photosensitive drum (scanned surface) 10 ... Control unit

Claims (2)

(57) [Claims] 1. A scanning optical device for scanning a laser beam output from a laser light source on a surface to be scanned through a deflector and a lens system, and detecting means for detecting an image formation state of the laser beam on the surface to be scanned. And a temperature detecting means for detecting a temperature change of a specific portion of the scanning optical device, and a signal obtained by the detecting means for detecting the image formation state when the temperature change is detected by the temperature detecting means. A scanning optical device which adjusts the image forming position of the laser light based on the above. 2. The scanning optical system according to claim 1, wherein the detecting means for detecting the image formation state is provided at a position corresponding to an image area on the surface to be scanned. apparatus.