JPH04240816A - Light beam scanner - Google Patents

Abstract

PURPOSE:To detect the focal point of light beam over the entire area in the main scanning direction of the light beam and to bring the focal point position onto a scanning surface. CONSTITUTION:A sensor part 15 is installed along the main scanning direction in the end position of a movable table 2 existing on the same plane as the plane of the scanning surface. The sensor part 15 is provided with grating glass 16 having plural pieces of light transparent parts of approximately the same width as the beam diameter in the focal point position of the light beam and a photodiode existing behind this glass. The out-of-focus quantity at the respective points in the main scanning direction is led out in accordance with the detection of the quantity of the light beam over the entire area in the main scanning direction and an ftheta lens 13 is moved in a sub-scanning direction in accordance therewith and is turned around the axial center perpendicular to the sub-scanning direction, by which the light beam is focused.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a light beam scanning device that records or reads images by scanning a light beam emitted from a light source, and particularly relates to a light beam scanning device that records or reads an image by scanning a light beam emitted from a light source. The present invention relates to a light beam scanning device that can detect and adjust the light beam.

0002

2. Description of the Related Art When a light beam scanning device is applied to image recording or reading, an important requirement from the viewpoint of resolution is that the light beam be focused on the scanning plane. Therefore, in a normal light beam scanning device, before starting the actual scanning recording, a photosensitive film is set on the scanning surface and is scanned and printed with a light beam, and from the line width of the printing result, the light beam It was observed whether the light beam was focused on the scanning plane, and if there was a focus shift, the position of the scanning plane and the focused position of the light beam were aligned. According to this method, in order to detect the focused point of the light beam, it is necessary to develop the film and rely on experts to observe the development results, leading to increased costs due to the multiplication of steps. Not only that, but it's also inefficient. Therefore, a light beam scanning device equipped with a mechanism for detecting the focal point of a light beam is disclosed in Japanese Patent Publication No. 60-29087 and Japanese Patent Publication No. 60-60.
It is described in the No.-9243 publication. These devices will be cited as conventional examples and will be described below.

(A) First, the Special Public Interest Publication No. 60-29087
The device disclosed in the publication will be explained with reference to FIG. This device converts a light beam emitted from a laser light source 60 into a parallel beam by guiding it through a reflecting mirror 61 to a beam expanding lens 62 and a parallel lens 63, and converting it into a parallel beam through a scanning mirror 64 to a scanning lens 65 (fθ lens). The beam is focused and irradiated onto the scanning surface 67. Then, by rotating the scanning mirror 64, the scanning surface 67 is scanned with the light beam. In order to detect the diameter of the light beam at the scanning surface 67, a half mirror 66 is installed between the scanning lens 65 and the scanning surface 67 to branch a part of the light beam, and the branched light beam is focused. A lattice plate 69 is installed on a virtual scanning plane 68 connecting the . The grating plate 69 has a grating pattern in which transparent parts and light blocking parts are alternately formed at approximately the same intervals as the beam diameter at the focused position of the light beam, and as shown in the figure, It is installed tilted at a predetermined angle.

When the light transmitted through the grating plate 69 is detected by the photodetector 70, the amount of light from the transparent portion corresponding to the focal position of the light beam becomes maximum, and the detected signal value also reaches its peak. That is,
When the detection signal from the center point A of the grating plate 69 reaches the maximum value, it means that the focus of the light beam is located on the virtual scanning plane 68, which means that the focus of the light beam is on the actual scanning plane 67. It also means that it is located. If the focus of the light beam is at a position shifted from the scanning plane 67, the peak of the detection signal of the light transmitted through the grating plate 69 will appear at a position shifted from the center point A. From the peak position of such a detection signal, the scanning plane 67
Detection of the focal position of the light beam in the scanning plane 6
The amount of deviation between the position 7 and the focal position of the light beam is detected.

(B) Next, the apparatus disclosed in Japanese Patent Publication No. 60-9243 will be explained with reference to FIG. 11. This device transmits a light beam emitted from a laser light source 71 to an optical modulator 72 and a beam expander 73.
The light is guided through a rotating polygon mirror 74 (also called a polygon mirror), and then focused by a scanning lens 75 (fθ lens) and irradiated onto a scanning surface 76. Then, by rotating the rotating polygon mirror 74, the scanning plane 76 is scanned with the light beam. To detect the light beam diameter on this scanning surface 76,
A photodetector 77 is placed on the extension line of the scanning line of the scanning surface 76.
A linear knife edge 78 is arranged in front of the detection surface of the photodetector 77.

When the amount of light beam that crosses the knife edge 78 and enters the photodetector 77 is detected, it becomes a signal corresponding to the diameter of the light beam. That is, when the diameter of the light beam is large, the amount of light that enters the photodetector 77 via the knife edge 78 gradually increases. Also,
If the diameter of the light beam is small, the photodetector 77
The amount of light entering the area increases rapidly. In this way, the focus of the light beam is detected from the degree of change in the detection signal of the photodetector 77 depending on the diameter of the light beam, and the focal position of the light beam and the scanning plane position are adjusted.

[0007]

However, the conventional device having such a configuration has the following problems.

That is, in the apparatus described in (A), the amount of transmitted light from the inclined grating plate 12 is detected, and the focused position of the light beam is detected from the peak position of the detection signal, and the scanning of the light beam is performed. The in-focus point is not detected over the entire width. This also applies to the device described in (B), in which the focused point of the light beam can only be detected at one point on the extension of the scanning line.

However, the diameter of the light beam at each point on the same scanning line may differ due to distortion or misalignment of the optical system components such as the scanning lens (fθ lens) or rotating polygon mirror (polygon mirror). There is. Therefore, it is insufficient to detect the focal point of the light beam at just one point, as in the conventional device. Therefore, if the light beam is not focused on the scanning line other than the detection point, it cannot be detected, and the resolution when recording and reading the image decreases, causing "blur" in the image. invite

The present invention has been made in view of the above circumstances, and includes detecting the focus of a light beam over the entire main scanning direction and aligning the focused point position with the light beam scanning surface position. The object of the present invention is to provide a light beam scanning device that can perform the following steps.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration. That is, the light beam scanning device according to the present invention includes a plurality of transparent portions arranged in the main scanning direction on the same plane as the light beam scanning surface and having a width substantially equal to the beam diameter at the focused position of the light beam. a grating plate having a grating plate, a light quantity detecting means for detecting the light quantity of the light beam that has passed through the transparent part of the grating plate, and a focus shift of the light beam at each point in the main scanning direction based on a detection signal value of the light quantity detecting means. A focus shift deriving means for deriving the amount of focus shift, an output means for outputting the derived focus shift amount, and an optical system lens for focusing the light beam on the scanning surface are displaced in the sub-scanning direction. It is characterized by comprising a focus adjustment mechanism that rotates around an axis perpendicular to the scanning direction.

0012

[Function] The function of the structure of the present invention is as follows. First, a grating plate is scanned with a light beam in order to derive the amount of defocus of the light beam. The light amount detection means detects the amount of light beam that has passed through the transparent portion of the grating plate, and outputs a detection signal according to the diameter of the light beam. In other words, if the light beam is focused at the grating plate position, the entire amount of light beam passes through the transparent part of the grating plate, and the detection signal value becomes the maximum value; if it is not focused (the light beam diameter is larger than the beam diameter at the focal point position), a portion of the light beam is blocked by the light shielding portion of the grating plate, and the detected signal value becomes smaller than the maximum value. As described above, since there is a correlation between the output value of the light amount detection means and the amount of focus deviation of the light beam, the focus deviation derivation means calculates each of the main scanning directions based on the detection signal value of the light amount detection means. Derive the amount of defocus of the light beam at the point. The output means outputs the derived defocus amount to the outside to present it to the operator. Next, in order to correct the amount of focus deviation, the operator operates the focus adjustment mechanism while observing the amount of focus deviation output from the output means, and adjusts the optical system lens so that the amount of focus deviation is minimized. It is displaced in the scanning direction and/or rotated around an axis perpendicular to the main scanning direction and the sub-scanning direction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a schematic configuration of a light beam scanning device according to this embodiment. This figure shows an example in which a light beam scanning device is used for image recording. Note that the present invention can also be applied to a light beam scanning device for image reading.

Movable table 2 on which photosensitive sheet 1 is placed
is movably supported by a pair of guide rails 3a and 3b. At the bottom of the movable table 2 is a threaded rod 4.
A gear 5 fixed to the tip of the threaded rod 4 is engaged with an output gear 7 of a motor 6. As the motor 6 rotates, the threaded rod 4 rotates, and the movable table 2 is guided by the guide rails 3a and 3b and moves in the X-axis direction. This X-axis direction is photosensitive sheet 1
This is the sub-scanning direction of the light beam irradiated to the area.

The irradiation light beam is emitted from a laser light source 8, converted into a wide parallel beam by a beam expander 10, and rotated by a motor 12 to rotate a polygon mirror 11 around the Z axis. After being scanned in the Y-axis direction by the scanning lens 13 (fθ lens 13)
is focused on. This Y-axis direction is the main scanning direction of the light beam. In the present invention, the fθ lens 13 corresponds to an optical system lens that focuses a light beam on a scanning surface.

The light beam focused by the fθ lens 13 is
The optical path of the light is changed at right angles by the total reflection mirror 14, and the light is irradiated onto the photosensitive sheet 1 (on the scanning surface). A sensor section 15 is mounted on an extension of the scanning surface, that is, along the edge of the movable table 2 that is flush with the scanning surface (that is, in the main scanning direction).

FIG. 2 is an enlarged perspective view of the sensor section 15. As shown in FIG. The sensor section 15 is an integrated structure that includes a grating glass 16 formed by alternately forming slit-shaped light-transmitting sections 19 and light-shielding sections 20, and a sensor stand 18 on which a large number of photodiodes 17 are mounted horizontally. . The width of the transparent portion 19 is determined by the beam diameter (
The photodiode 17 is formed to have a size substantially equal to the focal diameter (hereinafter referred to as the focal diameter), and the photodiode 17 is provided over the entire area of the grating glass 16. grating glass 1
6 corresponds to the grid plate in the present invention, and the photodiode 1
7 corresponds to a light amount detection means. When recording an image with a light beam scanning device having such a configuration, (1) move the movable table 2, place the sensor section 15 attached to the end of the movable table 2 on the optical path position, and scan it with the light beam; . Then, the amount of defocus of the light beam is derived based on the output voltage value of the photodiode 17, and this is displayed on a monitor display, which will be described later. (2) The operator observes the amount of defocus displayed on the monitor display.
The fθ lens 13 is set at a position where the amount of defocus is minimized by operating a focus adjustment mechanism, which will be described later, that displaces the fθ lens 13.

(1) First, the derivation of the amount of defocus of a light beam will be explained with reference to FIGS. 3 and 4. Figure 3
and FIG. 4 respectively show the relationship between the diameter of the light beam incident on the sensor section 15 and the output voltage value of the photodiode 17. As illustrated in FIG.
1>d), and the output voltage value of the photodiode 17 is assumed to be V1. On the other hand, as shown in FIG. 4, when the diameter φd2 of the light beam B2 substantially matches the width d of the transparent portion 19 (φd2≒d), the output voltage value of the photodiode 17 is higher than V1. V2 (V2>V1). That is, when the diameter of the light beam is larger than the width d of the light-transmitting part 19, part of the light quantity is blocked by the light-shielding part 20, and the output voltage value of the photodiode 17 becomes lower than the maximum value. The size is approximately equal to the width of the transparent portion 19 (
(the size of the minimum focal point), the entire light amount of the light beam enters the photodiode 17, and the output voltage value of the photodiode 17 becomes the maximum value. In this way, the output voltage value of the photodiode 17 changes depending on the light beam diameter.

How to determine the amount of defocus of the light beam from the output voltage value of the photodiode 17 will be explained with reference to the logic circuit diagram shown in FIG.

The output voltage value VPD proportional to the output current of the photodiode 17 reverse-biased with the reference voltage +V is amplified to the output voltage value VOP by the operational amplifier OP, and is applied to the comparator C and the A/D converter 22. Given. Comparator C compares the output voltage value VOP from the operational amplifier OP with the reference voltage Vsh from the reference voltage generator 21, and
>Vsh, a signal of "H-level" is output. As a result, while the light beam is incident on the transparent portion 19, a pulse-like signal that is at "H-level" is output. Hereinafter, this pulse signal will be referred to as a grating clock (a clock pulse that is output for each pitch of the transparent portions 19 formed on the grating glass 16).

The A/D converter 22 samples the inputted output voltage waveform of the photodiode 17 in synchronization with the pulse timing of the grating clock, converts it into a digital signal, and outputs it to the memory M. Address counter AC counts the number of grating clocks and outputs it to memory M as address data. As a result, the light amount data for one scanning line is stored in the memory M for each pitch of the transparent portions 19 of the grating glass 16.

The CPU 23, which corresponds to the focus deviation deriving means, reads out the light amount data from the memory M, supplies the light amount data as read address data to the lookup table 24, and reads out the corresponding data. The contents registered in the lookup table 24 are shown in graph form in FIG. As shown in this figure, the lookup table 24 shows the amount of light detected by the photodiode 17,
This is a two-dimensional table that stores the relationship with the amount of defocus, and has been determined experimentally in advance. As is clear from the figure, the larger the amount of light, the smaller the amount of defocus. C.P.
U23 creates a graph having the read out focus shift amount on the vertical axis and the address value on the horizontal axis. The address value is the number of pulses of the grating clock (the number of pitches of the transparent part 19)
Since the value corresponds to , this is information indicating the main scanning position of the light beam. Therefore, by creating a graph with the address value on the horizontal axis and the amount of defocus on the vertical axis, it is possible to know at which position on the scanning plane and by how much the focus has deviated. Figure 7 shows an example of the created graph.
Shown below. This graph is stored in the display memory 25 and then displayed on the monitor display 26. Note that a printer may be provided in place of the monitor display 26 to output the graph as a printed matter.

(2) In this way, when the amount of focus shift is displayed on the graph, the focus adjustment mechanism is operated to adjust the position of the fθ lens 13 so that the amount of focus shift is minimized while looking at this graph. It will be done. Below, the perspective view of Fig. 8 and Fig. 9
The focus adjustment mechanism will be explained with reference to the plan view of FIG. The fθ lens 13 is fitted into a lens frame 30 and attached to the upper surface of a rotary table 31. A cylindrical member 32 (Fig. 9
) is integrally provided, and the cylindrical member 32 is rotatably inserted into a cylindrical member 34 erected on the upper surface of the movable table 33. As a result, the fθ lens 13 rotates around an axis P perpendicular to the main scanning direction and the sub-scanning direction. Attached to the outer peripheral surface of the cylindrical member 34 are bases of a pair of arms 35a, 35b extending in the horizontal direction. A support member 37 is provided at the tip of one arm 35a, which is urged inward by a spring 36, and a support member 37 is provided at the tip of the other arm 35b, which is also inwardly biased by the driving force of a built-in motor (not shown). An electric micrometer 39a is provided with a movable rod 38 that moves forward and backward toward the electric micrometer 39a. These supporting members 3
7 and the movable rod 38 of the electric micrometer 39a, a protrusion 40 that protrudes from the rotary table 31 between the arms 35a and 35b is held. That is, when the movable rod 38 of the electric micrometer 39a moves back and forth, the support member 37 follows it due to the elastic force of the spring 36, and the protrusion 40 remains held between them as the electric micrometer 39a moves back and forth. Moving. Due to the moving force, the rotary table 31 is rotationally displaced (oscillating motion) around the axis P.

The movable table 33 is installed on a fixed table 42 via a guide rail 41 extending in the sub-scanning direction, and an electric micrometer 39b similar to that described above is installed on the longitudinal end surface of the guide rail 41. Movable rod 43
are connected. The main body of this electric micrometer 39b is fixedly attached to a fixed table 42. That is, when the movable rod 43 of the micrometer 39b moves back and forth, the moving table 42 is guided by the guide rail 41 and displaced in the sub-scanning direction. Each motor built into these electric micrometers 39a, 39b is driven by a respective motor drive circuit 44, 45, and each motor drive circuit 44, 45 is configured to be controlled by a controller 46. The controller 46 is provided with two switches S1 and S2 for the operator to operate the forward and backward movement of each micrometer.

The operator controls the controller 4 while observing the amount of defocus displayed on the monitor display 26.
6, the fθ lens 13 is adjusted so that the amount of defocus at each point in the main scanning direction is minimized.
Adjust the position. Note that the grating plate is not limited to the grating glass as in the embodiment, but may be one in which a transparent portion is arranged only at the focal shift detection position of the light beam. Further, instead of directly displaying the amount of focus shift as described above, the amount of focus shift may be displayed indirectly by displaying the beam diameter at each position in the main scanning direction. Since there is a correlation between the amount of defocus and the beam diameter, the derivation of the amount of defocus in the present invention includes such derivation of the beam diameter. Furthermore, as described above, instead of the operator operating the switches S1 and S2 to adjust the position of the fθ lens 13, the data on the derived focus shift amount is output to the controller 46, and the data is adjusted according to the focus shift amount. It may also be configured to control the electric micrometers 39a, 39b.

[0026]

As is clear from the above description, the light beam scanning device of the present invention detects the amount of light beam that scans the grating plate and determines the amount of defocus of the light beam at each point in the main scanning direction. By deriving and outputting this to the outside, it is possible to detect the defocus of the light beam over the entire main scanning direction, rather than just one point like conventional equipment, and present this to the operator. Can be done. Also,
The operator operates a focus adjustment mechanism attached to the optical system lens while observing the amount of focus deviation, and sets the optical system lens at a position where the amount of focus deviation is minimized. Thereby, the light beam can be focused at each point in the main scanning direction, and the resolution when recording or reading an image can be improved.

[Brief explanation of the drawing]

FIG. 1 is an external perspective view of a light beam scanning device according to an embodiment of the present invention.

FIG. 2 is an enlarged perspective view of the sensor section.

FIG. 3 is a diagram showing the relationship between the light beam diameter and the output voltage of a photodiode.

FIG. 4 is a diagram showing the relationship between the focal diameter of a light beam and the output voltage of a photodiode.

FIG. 5 is a logic circuit diagram for deriving the amount of focus shift.

FIG. 6 is a diagram schematically showing the contents of a lookup table.

FIG. 7 is a diagram showing an example of displaying the amount of focus shift in the main scanning direction.

FIG. 8 is a perspective view showing a focus adjustment mechanism attached to an fθ lens.

FIG. 9 is a plan view showing a focus adjustment mechanism attached to an fθ lens.

FIG. 10 is a diagram showing a schematic configuration of a conventional device.

FIG. 11 is a diagram showing a schematic configuration of another conventional device.

[Explanation of symbols]

13 fθ lens 15 Sensor section 16 Grating glass 17 Photodiode 19 Translucent part 20 Light shielding part 23 CPU 24 Lookup table 31 Rotating table 33. Moving table

Claims (1)

[Claims] 1. A grating plate disposed in the main scanning direction on the same plane as the scanning plane of the light beam and having a plurality of transparent parts having a width substantially equal to the beam diameter at the focused position of the light beam; a light amount detection means for detecting the amount of the light beam that has passed through the transparent portion of the plate; and a focus shift derivation that derives the amount of focus shift of the light beam at each point in the main scanning direction based on the detection signal value of the light amount detection means. means, an output means for outputting the derived defocus amount, and an optical system lens for converging the light beam on the scanning surface, which is displaced in the sub-scanning direction, and perpendicular to the main-scanning direction and the sub-scanning direction. A light beam scanning device comprising: a focus adjustment mechanism that rotates around an axis.