JPH0251119A - Scanning optical device - Google Patents

Abstract

PURPOSE:To detect the defocusing of a light beam stably by using a grating which has openings arrayed in a scanning direction at positions optically equivalent to a scanning surface and a detector which detects a light beam modulated by the grating. CONSTITUTION:Laser luminous flux L is imaged on a bar code filter 7 arranged at a position optically equivalent to a photosensitive drum 9 and variation in the quantity of the light is detected. Then the position of a collimator lens system 3 is adjusted through a control part 10 according to the detection signal and an increase in the scale of a laser spot system due to environmental variation in temperature, etc., is prevented. Consequently, a spot of desired size is obtained at all time, and consequently the defocusing of the light beam is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] 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 equipped with a mechanism for detecting and correcting a focal position shift of a light beam imaging spot on a scanning surface.

[Prior Art] In recent years, as a scanning optical device, a laser light source is modulated according to an image signal, the laser light from the modulated laser light source is periodically deflected by a deflector, and a lens system is used to record a photosensitive image. Laser beam printers are widely used, which record images by focusing a spot on a medium and performing exposure scanning.

By the way, in conventional laser beam printer devices, the various members constituting the lens system undergo thermal deformation due to changes in environmental temperature, and the convergence position of the L/- laser beam on the photoreceptor (scanning surface) shifts, resulting in poor image quality. The disadvantage was that it decreased.

As a means to solve this drawback, JP-A-60-1001
No. 13 discloses a laser beam printer equipped with a lens moving device having a focus shift detection means for receiving a portion of the beam scanned onto a photoreceptor and detecting a focus shift, and a correction lens for correcting the focus shift. It is disclosed.

However, in the above-mentioned Japanese Patent Application Laid-open No. 100113/1983, an astigmatism method is used as a defocus detection method. Although this method is effective for stationary light beams, it is inappropriate for detecting defocus of light beams that are scanned at high speed.

[Summary of the Invention] An object of the present invention is to provide a scanning optical device that eliminates the drawbacks of the conventional devices described above and is capable of stably detecting defocus of a light beam.

An object of the present invention is to provide a scanning optical device that scans a light beam from a light source on a scanning surface via a deflector and a lens system, and includes a detection mechanism that detects the convergence state of the light beam on the scanning surface. The detection mechanism for detecting the convergence state of the light beam on the scanning surface includes a grating having apertures arranged in the scanning direction at positions optically equivalent to the scanning surface, and a light beam modulated by the grating. This is accomplished by using a detector that detects.

Embodiment FIG. 1 is a diagram showing a schematic configuration of a first embodiment of a scanning optical device according to the present invention. In the figure, reference numeral 1 denotes a laser driver for generating laser light, and a solid-state laser element 2 as a laser light source connected to the laser driver blinks in response to its light emission signal. Reference numeral 3 denotes a collimator lens system that converts the laser beam emitted from the solid-state laser element 2 into substantially parallel light, and can be moved by a predetermined amount in the direction of arrow A, which is the optical axis direction of the laser beam, by a focus adjustment means 4, which will be described later. ing. A rotating polygon mirror 5 reflects the parallel light emitted from the collimator lens system 3 and scans it in the direction of arrow C by rotating at a constant speed in the direction of arrow B.

Reference numerals 6a, 6b, and 6c are fθ lens groups provided in front of the rotating polygon mirror 6, which form an image of the laser beam deflected by the polygon mirror 6 and make the scanning speed constant on the surface to be scanned. L is a laser beam, and this laser beam is guided through a barcode filter 7 onto a photodetecting element 8 as a detection means, and is scanned onto a photosensitive drum 9 as a surface to be scanned. A developing device, a secondary and transfer charger, a fixing device, a cleaner, etc. (not shown) are provided around the photosensitive drum 9, and the latent image formed on the surface of the photosensitive drum 9 is processed by a known electrophotographic process. The image is visualized and transferred to a transfer material. The barcode filter 7 is arranged at a position optically equivalent to the surface of the photosensitive drum 9. Further, the photodetecting element 8 is connected to a control section 10 that controls the laser driver 1 and the focus adjustment means 4. Reference numeral 11 denotes an image processing section, which is connected to the laser driver 1 and the control section 10.

In the above configuration, when forming a desired image, first input the image output signal P from the image processing section 11 to the control section 10, and input the image signal S to the laser driver, and at a predetermined timing, the fixed laser element 2 blinks. The laser beam emitted from the solid-state laser element 2 is converted into substantially parallel light by the collimator lens system 3, and when further rotated in the direction of arrow B, it is scanned by the rotating polygon mirror 5 in the direction of arrow C, and is scanned by the fθ lens groups 6a and 6b. .

6c forms a spot image on the photosensitive drum 9.

Then, by scanning the laser beam, an exposure distribution corresponding to the image minus the scanning is formed on the surface of the photosensitive drum 9, and furthermore, the photosensitive drum 9 is rotated by a predetermined amount for each scan, and the image signal S is printed on the drum 9. A latent image having an exposure distribution corresponding to the exposure distribution is formed and recorded as a visible image on recording paper by a well-known electrophotographic process. The image output signal P is output from the image processing section 11 before the image signal S, and the output ends after the output of image No. 48 S ends. In addition, the control unit 10
The opening operation to which the image output signal P is input from the image processing section 11 is stopped. Therefore, the pixel size and contrast can be kept constant during the image forming operation.

Next, the operation of the focal position adjustment mechanism of the laser beam will be explained. First, an operating signal is input from the control unit 10 to the laser driver 1, and the laser driver outputs an operating signal for a predetermined period of time.
The fixed laser element 2 is turned on at a constant light intensity for a predetermined time in response to this signal. The laser beam from the solid-state laser element 2 is scanned as described above, and is also projected and scanned onto the barcode filter 7 disposed at a position optically equivalent to the photosensitive drum 9.

The laser beam that has passed through the barcode filter 7 enters the photodetector element 8 .

FIG. 2 is a diagram of the barcode filter 7 viewed from the photodetector element 8 side. S is a scanning spot of laser light, and is moving in the direction of arrow C. 7 is a barcode filter, 7a in the filter is a transparent part such as glass, and 7b is a light shielding part formed by aluminum vapor deposition or the like. Furthermore, the width of the transparent portion and the width of the light shielding portion in the direction of arrow C are equal.

FIGS. 3(a) and 3(b) are diagrams showing the amount of transmitted light depending on the position of the scanning spot on the barcode filter. Fig. 3(a) shows a part (transparent part) 7 where the scanning spot is transparent.
It can be seen that the shaded portion of the scanning spot S is transmitted through the filter, and the other portions are blocked.

At this time, if the imaging state is good and the scanning spot S is small in the scanning direction, the ratio of the transmitted light to the entire spot becomes large, that is, the amount of transmitted light becomes large. On the other hand, if the imaging condition is poor and the scanning spot S is large in the scanning direction,
The ratio of transmitted light to the entire spot becomes smaller, that is, the amount of transmitted light becomes smaller. Similarly, when the scanning spot moves next and is at the position of the light-shielding part (light-shielding part) 7b, if the imaging condition is good and the scanning spot S is small in the scanning direction, the adjacent transparent part (transmissive part) 7a The amount of light leaking to the area will be reduced. On the other hand, if the imaging condition is poor and the scanning spot S is large in the scanning direction, the adjacent transparent part (transmissive part)
The amount of light leaking to 7a becomes large. As shown in FIGS. 4(a) and 4(b), the light quantity distribution on the photodetecting element 8 exhibits a strength distribution shape corresponding to the spot diameter size of the laser beam with time.

Figure 4(a) shows a case where the imaging condition is good and the scanning spot S is small in the scanning direction, and Figure 4(b) shows a case where the imaging condition is poor and the scanning spot S is large in the scanning direction and is blurred. shows. The light detection element 8 sends a signal of the change in light amount to the control unit 1.
Send to 0. In the control unit io, the maximum value of the output of the photodetecting element 8 is set as θ+aAX (maximum amount of transmitted light), and the minimum value is set as θ+s1. ．． (minimum amount of transmitted light), the contrast V is calculated using the formula: θ1.8−θl, lIn 2 = (1) θ, 2 + aln. This calculated value is then stored in a storage device (not shown) within the control unit 10 as the contrast at the current collimator lens system position.

Next, the control unit 10 moves the collimator lens system 3 by a predetermined amount using the focus adjustment means 4, and similarly calculates and stores the contrast V.

After performing the above operation a predetermined number of times, the maximum contrast value is searched among the plurality of stored contrasts V, and the collimator lens system is moved and fixed to the position where the maximum contrast value is achieved.

FIG. 5 shows a collimator lens system 3 equipped with a focus adjustment means 4.
This is an enlarged view of the image. As shown in the figure, a frame 41 includes a solid-state laser element 2 and a stepping motor 42.
, a guide shaft 45 is provided, and the collimator lens system 3 is supported by the screw 43 and the guide shaft 45, which are machined on the shaft of the stepping motor 42. One end of the lead screw 43 is supported by a bearing 44 fixed to the frame 41. Further, the collimator lens system 3 is provided with a female thread that is screwed into the lead screw 43, and a slide bearing that is in sliding contact with the guide shaft 45. Here, the stepping motor 42 is driven when a drive signal is manually input from the control unit 10, and the lead screw 43 is rotated. The rotation of the lead screw 43 causes the collimator lens system 3 to move in the direction of arrow A, which is the optical axis direction of the laser beam.

As described above, the laser beam is focused on the barcode filter 7, which is placed at an optically equivalent position to the photosensitive drum 9, and changes in the amount of transmitted light are detected as laser spots caused by environmental changes such as temperature measurement rings. It can prevent the system from becoming enlarged. As a result, a spot of a desired size can always be obtained, and a high-density and high-quality image can be formed.

The operation of the present invention will be explained in detail based on the flowchart shown in FIG. Here, the focal shift of the optical system is corrected 1. to a movable position of the collimator lens system. It is assumed that there is a position where the spot diameter of the laser beam can be minimized.

First, when a signal for operating the focus adjustment mechanism is input to the control unit 1o, the focus adjustment means 4 is operated to return the lens system 3 to its initial position. Then, the laser element 2 is turned on, and the value of the contrast V is calculated from the output of the photodetector element 8.

Next, the calculated contrast l-V value and the 1/
The position of the lens system is stored in a storage device within the control unit 10.

When moving the lens system using the focus adjustment means, it is first determined whether the lens system can be moved, and if possible, the lens system is moved one step and the value of contrast V at the next lens system position is calculated. ,Remember. Then, the above sequence is repeated until the feeding of the lens system reaches the end.

When the feeding of the lens system reaches the end, search for the maximum contrast value among the contrasts V stored in the control unit, move the lens system to the position where this value is achieved, and fix it L/. The operation of the focus adjustment mechanism is ended.

In the example shown in FIG. 1 above, the collimator lens system was used as a means for moving the convergence position of the light beam on the scanning surface, but other means for moving the convergence position of the light beam could be used. Known techniques may be used.

Examples of means for moving the convergence position of the light beam include a method that moves a convex lens placed between a collimator lens and a rotating polygon mirror, as disclosed in Japanese Patent Application Laid-Open No. 100113/1983;
A device that moves a laser light source or an imaging lens as in JP-A-59-116603, JP-A-60-11
Possible examples include those that vary the optical distance between the scanning lens and the scanning medium as in Japanese Patent Application Laid-Open No. 81-275868, and those that vary the power of the laser as in Japanese Patent Application Laid-Open No. 81-275868.

In addition, the width in the scanning direction of the transparent part and the light-shielding part of the barcode filter shown in Fig. 2 is the width of the transparent part and the light-shielding part when the intensity distribution of the incident light beam (rader light) is Gaussian. It is desirable that the width of the light shielding portion in the scanning direction is approximately 2W. Here, W is a beam radius, a radius at which the intensity is 1/e2 compared to the intensity on the optical axis. If a filter with such width is used, it is possible to detect changes in the amount of light effectively.7 In the embodiment shown in Fig. 1 above, a transmissive barcode filter was used, but even if it were made into a reflective type, the effect would not be as great. The same is true.

FIG. 7 shows an embodiment using a reflective barcode filter, in which the same members as in FIG. 1 are given the same reference numerals and detailed explanations will be omitted. In this embodiment, the laser beam reflected by the barcode filter 12 is configured to be incident on the photodetecting element 8.

FIG. 8 shows the reflective barcode filter 12 and the photodetector element 8.
It is a diagram seen from the side. S is laser beam scanning sub 9)
- and moves in the direction of arrow C at 1 no.

Reference numeral 12 denotes a reflective barcode filter, in which a mask 12b that absorbs scanning laser light is coated as a barcode perpendicular to the scanning direction on a reflective member 12a made of aluminum or the like.

Reference numeral 8 denotes a photodetection element, which detects the reflected type of scanning laser light from the bar code filter and generates an output according to the amount of light.

When the center of the scanning spot S is on the reflecting member 12a, the intensity of the reflected light becomes maximum and the output of the photodetecting element also becomes large. Furthermore, when the center of the scanning spot S is on the absorption member 12b, the intensity of the reflected light is the lowest and the output of the photodetector element is also small. However, over time, the scanning gap [・
As the light moves over the reflective barcode filter, the output of the photodetector changes in the same way as with the transmission barcode filter described above, and the relationship between the contrast V and the scanning spot diameter is also the same.

FIG. 9 is a diagram showing another embodiment of the present invention.
Components that are the same as those in the figures are given the same reference numerals, and detailed explanations will be omitted. In this embodiment, the laser beam transmitted through the barcode filter 7 is condensed by a condensing lens 13 and is incident on the photodetecting element 8. With such a configuration, it becomes possible to detect changes in the amount of light more effectively.

Furthermore, in the above embodiments, contrast, which is the ratio of light intensities, was used to determine the imaging state, but if the amount of laser light is constant, the maximum value of the output of the photodetecting element, or It is also possible to make the determination using the minimum value of the output of the photodetector element while the scanning laser beam is passing through the filter, or the difference between them.

[Effects of the Invention] As explained above, the present invention scans a light beam from a light source on a scanning surface via a deflector and a lens system, and
In a scanning optical device equipped with a detection mechanism for detecting a convergence state of a light beam on the scanning surface, the detection mechanism for detecting a convergence state of a light beam on the scanning surface is located at a position optically equivalent to the scanning surface. By using a grating having apertures arranged in the scanning direction and a detector that detects the light beam modulated by the grating, it is possible to stably detect defocus of the light beam.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the N1 embodiment of the scanning optical device according to the present invention, FIGS. 2 and 8 are enlarged views showing the barcode filter, and FIGS. 3(a) and (b) are the scanning filters. Figures 4 (a) and (b) are diagrams showing the relationship between the scanning spot diameter and the transmitted light amount, and Figure 5 is a diagram showing the amount of transmitted light depending on the position of . Figure 5 is a diagram showing the relationship between the scanning spot diameter and the amount of transmitted light. FIG. 6 is an enlarged view showing the mechanism, FIG. 6 is a flowchart explaining the invention in detail, and FIGS. 7 and 9 are schematic diagrams showing other embodiments of the scanning optical device according to the invention. 1-m-Laser driver 2-m-Solid laser element 3-m-Collimator lens system 4-m-Focus adjustment means 7-m-Barcode filter 8-m-Photodetection element 9-m-Photosensitive drum 10-1 Control unit 11-1 image processing unit

Claims (1)

[Claims] (1) A scanning optical device comprising a detection mechanism that scans a light beam from a light source on a scanning surface via a deflector and a lens system and detects a convergence state of the light beam on the scanning surface, A detection mechanism for detecting the convergence state of the light beam on the scanning surface includes a grating having openings arranged in the scanning direction at positions optically equivalent to the scanning surface, and a detection mechanism for detecting the light beam modulated by the grating. A scanning optical device characterized by using a scanning optical device.