JPH07151986A - Light beam scanner - Google Patents

Abstract

PURPOSE:To reduce the increase of the deflecting angle of an auxiliary deflector as small as possible when the fluctuation of the projecting position of a beam spot in a sub-scanning direction caused by secular change is corrected. CONSTITUTION:A piezoelectric actuator 5 is driven by a standard driving signal and the masks 17 and 21 of both sensors 19 and 23 are scanned with a light beam LB. The. masks 17 and 21 are provided with a step-like light shielding part and a step-like light transmitting part having level difference. Besides, the horizontal boundary part of the step part is in parallel with the sub-scanning direction (y). Based on detection signals V3 and V4 the driving signal V2 required for moving the respective light beams LB reflected on respective surfaces to the nearest horizontal boundary part is decided. By the driving signal V2, the actuator 5 is driven and the incident angle of the light beam LB on a polygon mirror 11 is corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device using a polygon mirror as a main deflecting means, which is used in processes such as photoengraving, copying and printed circuit board production.

[0002]

2. Description of the Related Art In a light beam scanning device using a polygon mirror (rotary polygonal mirror) as a deflector, as is well known, a light beam (image) formed on an exposed surface of a photosensitive material by an fθ lens as a scanning lens. (Which is modulated based on the signal) is scanned by the polygon mirror in the main scanning direction and is relatively transferred in the sub-scanning direction orthogonal to the main scanning direction, thereby exposing the photosensitive material exposed surface, that is, recording an image. It is carried out. However, when the polygon mirror is used, there arises a problem that the position of the beam spot in the sub-scanning direction (hereinafter referred to as the projection position in the sub-scanning direction) changes due to so-called surface tilt. Therefore, it is necessary to correct the surface error, but as the technology for realizing such surface error correction, several technologies described below have been proposed.

One of them is Japanese Patent Publication No. 52-28666.
It is disclosed in Japanese Patent Publication No. In this prior art, two cylindrical lenses are arranged on the incident side and the reflecting side optical paths of the polygon mirror, respectively, and the polygon mirror surface and the photosensitive material exposure surface are within the plane defined by the optical axis and the sub-scanning direction. The surface tilt correction is performed by optically conjugating with.

As another method to the above-mentioned conventional technique, the incident angle of the light beam on the polygon mirror is minutely changed according to the projection position deviation in the sub-scanning direction, and the light beam is minutely deflected in the sub-scanning direction. There are those that perform face-to-face correction. In this case, an auxiliary deflector for changing the incident angle is required on the incident side optical path of the polygon mirror. Regarding this prior art, due to the difference in the method of detecting the projection position deviation or the method of determining the minute deflection amount,
The following three technologies have been proposed.

One of them is JP-A-2-114228.
This is disclosed in the publication (see FIGS. 1A and 4A of the publication). In this conventional technique, as shown in FIG. 17A, a grating sensor having a pattern in which L-shaped (shaded portions in the figure) light-shielding portions are arranged at regular intervals in the main scanning direction is used. There is. Therefore, when the center of the light beam (the center of the beam spot) is scanned along the horizontal boundary portion 70 of the L-shaped light-shielding portion, the detection signal of the grating sensor becomes as shown in FIG.
Then, the grating sensor is arranged at a position optically equivalent to the exposed surface of the photosensitive material, and two light beams, that is, a light beam for exposure and a light beam for the grating sensor are prepared. The beam is deflected and scanned by the same polygon mirror. At this time, since the light beam for the grating sensor scans the grating sensor in synchronization with the light beam for exposure, it is possible to directly detect the actual projection position in the sub-scanning direction. That is, the distance between the horizontal boundary portion 70 of the L-shaped light-shielding portion and the current projection position in the sub-scanning direction is detected by the change in the detection signal shown in FIG. 17B, and from this detection result, the center of the light beam is detected. Is always located on the horizontal boundary 70, and the auxiliary deflector is controlled by this drive signal. Therefore, the control system constitutes a closed loop. This is because the projection position error in the sub-scanning direction is always detected at each position in the main scanning direction, and the minute deflection amount is determined according to the amount.

The second conventional technique is disclosed in Japanese Patent Application Laid-Open No. 58-100111 (Japanese Patent Publication No. 3-81134) and Japanese Patent Application Laid-Open No. 58-100118. This prior art is based on the premise that the projection position deviation in the sub-scanning direction is periodical (the point that this premise does not capture all the truth will be described later), and the projection position deviation for one cycle. Is empirically determined in advance and stored in a memory or the like, and the stored data is read during scanning to drive and control the auxiliary deflector, thereby determining a minute deflection amount. In this sense, it can be said that the control system of this conventional technique is an open loop.

Further, as a third technique, Japanese Patent Laid-Open No.
-2142 publication. This prior art is, outside the effective scanning area (the area where exposure and printing are actually performed) within the scanning range in the main scanning direction, specifically,
Sensors that detect projection position deviations in the sub-scanning direction are arranged at both the start position and the end position, and an appropriate drive signal is determined using the detection signals of both sensors. And
By controlling the auxiliary deflector with this drive signal,
A small amount of deflection is set. At that time, a sensor having a mask having an L-shaped light-shielding portion (see FIG. 17) as described in the above-mentioned conventional technique is used. Therefore, as in the prior art, the drive signal is determined so that the center of the beam spot is always scanned on the horizontal boundary portion 70 of the L-shaped light-shielding portion. here,
It can be said that the control system in this conventional technique constitutes a semi-closed loop. In other words, when the light beam is scanned within the effective scanning area, the control system does not form a closed loop in the above-mentioned sense, but conversely, when the light beam is scanned over both sensors, This is because the control system constitutes a closed loop.

[0008]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In each case, the trouble correction can be realized to some extent. However, as factors of the actual deviation of the projection position in the sub-scanning direction, there are changes due to aging in addition to the surface tilt. Therefore, there is a problem in that the light beam cannot always be scanned in parallel with the scanning line in the main scanning direction unless the influence of the change with time is removed. Here, if the factors due to such changes with time are listed, the following four factors can be considered.

(I) Time-dependent change in tilt angle: Polygon mirrors are usually manufactured by using a metal body such as aluminum. In addition, in order to reduce the load of a motor or the like for rotating the polygon mirror, a groove is usually formed between the central portion and the peripheral portion of the polygon mirror (see, for example, FIG. Equivalent to the shaded area in the figure)). Therefore, when the ambient temperature rises due to heat generated from peripheral devices (electrical circuit system, etc.) or the operating environment temperature fluctuates, the polygon mirror rotates at high speed, and this temperature change causes the outer edge of the polygon mirror to be uneven. As a result of expansion or deformation, the surface tilt angle (angle formed by each surface and the rotation axis) changes for each surface. It is clear that the temporal change of the surface tilt angle affects the variation of the projection position in the sub-scanning direction. Of course, the projection position deviation due to this factor fluctuates periodically.

(Ii) Tilt of the rotating shaft (wobbling):
As is well known, the polygon mirror itself is supported by an air bearing. At the time of rotation, a small air gap is generated between the rotary shaft of the polygon mirror and the air bearing, and the polygon mirror rotates in a non-contact state with the air bearing, that is, in a state where the rotary shaft floats. This means that the rotation axis of the polygon mirror slightly moves each time. Moreover, since the fine movement has no regularity, the factor of this tilting of the rotary shaft involves a problem that it is impossible to predict it. This factor causes an aperiodic projection position deviation in the sub-scanning direction, unlike the surface tilt and the factor (i). Moreover, this factor (ii) contributes to the projection position deviation as a low-frequency component, as compared with the case of the surface tilt and the factor (i).

(Iii) Change in gain of actuator:
This factor (iii) occurs in the related arts. That is, in the above-mentioned related arts, as an auxiliary deflector, a mirror that reflects a light beam and an actuator that changes the inclination of the main mirror (piezo actuator, etc.)
Is used. Therefore, when the ambient temperature changes, the characteristics of the actuator (V-.theta. Characteristic, V: voltage, .theta .: tilt angle of mirror) change, and this characteristic change must also be corrected. Moreover, since the temperature dependence of the V-θ characteristic is not necessarily linear, the correction is not easy. Therefore, the projection position deviation in the sub-scanning direction caused by this factor (iii) is also an aperiodic low frequency component.

(Iv) Actuator Drift: This factor (iv) is also associated with the related arts 1 to 4, and the main scanning line is shifted in the sub-scanning direction by a certain amount as the temperature changes.

As described above, it is necessary to newly correct the four temporal change factors (i) to (iv) simultaneously with the correction of the face tilt. Therefore, if the above prior arts 1 to 3 are reconsidered in view of this viewpoint, the following problems occur.

First, in the prior art, since the plane tilt correction is realized by the optical conjugate relation, the above (i),
The effect of (ii) can be removed for the time being. However, when the effective scanning area in the main scanning direction is large, the optical system such as the scanning lens and the cylindrical lens has to be further enlarged, and naturally, the processing accuracy is also required, which is satisfactory in some cases. There is also a possibility that the processing accuracy that can be achieved is not good.
Therefore, in these respects, the conventional technique is not preferable when the effective scanning area is large.

Next, the conventional technique has an advantage that the system configuration is simplified, but the above factors (i) to
Among the factors (iv), the factors (ii) to (iv) that cause non-periodic components cannot be sufficiently corrected. In other words, such an aperiodic component cannot be accurately predicted in the first place, and therefore proper drive data cannot be stored in the memory itself.
Moreover, in accordance with the temperature characteristics of the gain of the control system (gain of the actuator), within the operating temperature range (for example, 0 to 5).
The correction data must be prepared for each temperature of 0 ° C., and the amount of data to be stored becomes enormous. That is, it is not preferable from the viewpoint of memory capacity. Furthermore, each surface of the actual polygon mirror has distortion within the range of its smoothness, and the effect itself due to this distortion is completely unpredictable. Therefore, it can be said that it is also difficult to accurately predict this point and create correction data. As described above, this conventional technique also has a problem that the factors (ii) to (iv) cannot be solved.

On the other hand, the conventional technique has an advantage that the projection position in the sub-scanning direction can be detected with certainty, but a light beam for a grating sensor is required in addition to the light beam for exposure. Therefore, there is a problem that the optical system becomes complicated.

Further, in the prior art and, correction is made in response to all of the above factors (i) to (iV). At this time, due to factors (ii) and (iV), the projection position in the sub-scanning direction corresponding to each surface of the polygon mirror is a position shifted in the sub-scanning direction from the original ideal main scanning line. Main scanning lines corresponding to the respective surfaces of the polygon mirror are formed at the shift positions. This shift of the main scanning line itself does not essentially need to be corrected. However, in the above-mentioned prior art and the above-mentioned configuration, the shift is also intended to be corrected, so that it is necessary to increase the deflection capability of the auxiliary deflector. When the shift amount of the main scanning line is large, there is a possibility that the auxiliary deflector cannot be used for adjustment.

As described above, it is impossible to correct the variation of the projection position of the light beam in the sub-scanning direction due to the change with time by using any of the conventional techniques. Here, as a method for correcting the fluctuation, a so-called "arbitrary point type" is used.
A method of using an optical sensor referred to as, and moving the optical sensor according to the change over time of the projection position of the light beam in the sub-scanning direction can be considered. The arbitrary point type optical sensor is a sensor that can recognize the position of a light beam regardless of the position on the sensor. As such an arbitrary point type sensor, PSD (photo sensitive devic
e) can be mentioned. However, for PSD, it is 0 ..
Since it is difficult to secure a resolution of 1 μm, PSD cannot be applied to this case. Further, although a method of using a CCD line sensor or a CCD area sensor as an arbitrary point type optical sensor and combining it with a waveform processing technique is conceivable,
In this case, it becomes difficult to secure high-speed response in about 1 μs, which can be said to be against the cost reduction economically.

Alternatively, the above-mentioned JP-A-2-114228.
"Fixed-point type" optical sensor as disclosed in Japanese Patent Publication (sensitivity is high only when a light beam passes near a certain fixed point on the optical sensor, and when passing through other points, only a direction can be discriminated at most. It is also conceivable that the optical sensor is used to detect the optical beam by moving the optical sensor following the fluctuation of the projection position of the light beam in the sub-scanning direction. However, in this case, it may be possible to prevent the expansion of the driving range of the auxiliary deflector, but since an actuator is newly required as a moving source that follows anyway, it is rather necessary to increase the size of the optical sensor unit. The problem of being lost will be revealed anew. Also in terms of cost, it is disadvantageous because it increases the cost. Therefore, this method is also an unrealistic technique.

The present invention has been made against the background of such problems, and even if the displacement (projection position deviation) of the beam spot in the sub-scanning direction occurs due to a change with time, the drive range of the auxiliary deflecting means is increased. The present invention is intended to realize a light beam scanning device that can perform correction without performing the correction.

[0021]

According to a first aspect of the present invention, a light beam modulated on the basis of an image signal is reflected by a polygon mirror as a main deflecting means toward a photosensitive material exposure surface, and the light beam after the reflection is further reflected. In the light beam scanning device for recording an image by scanning the light beam in the main scanning direction on the light-sensitive material exposure surface by forming an image on the light-sensitive material exposure surface through the scanning lens, the light beam is incident on the polygon mirror. Of the auxiliary deflector arranged on the optical path of the light beam for correcting the incident angle of the light beam on the polygon mirror according to the drive signal, and at least one of the start position or the end position of the scanning range in the main scanning direction. At each position, projection position deviation detecting means for detecting a projection position deviation of each light beam in each sub-scanning direction (direction orthogonal to the main scanning direction) on each surface of the polygon mirror, and projection position deviation Drive signal determining means for determining a drive signal based on the detection signal of the detecting means and outputting the drive signal to the auxiliary deflecting means. The projection position deviation detection means has a pattern for a light beam, the pattern including a light-transmitting portion that transmits the light beam and a light-shielding portion that shields the light beam, and any one of the light-transmitting portion and the light-shielding portion. One has a plurality of rectangular areas arranged in the number of N and M (N ≧ 1, M ≧ 1) in the main scanning direction and the sub-scanning direction, respectively. S _ij length respectively, as H _ij, the main scanning direction and the sub scanning direction of the spacing of the two rectangular regions adjacent to each directions S _'ij, H' as _ij, next against further main scanning direction If the step in the sub-scanning direction of both matching rectangular areas is expressed as P _ij (1 ≦ i ≦ N, 1 ≦ j ≦ M), the plurality of rectangular areas are respectively (1) S _ij ≧ (the main part of the light beam). (Beam diameter in scanning direction), (2) H _ij ≧ (beam diameter of light beam in sub-scanning direction) / 2, (3) H ′ _ij ≧ (beam diameter of the light beam in the sub-scanning direction) / 2, (4) H _ij ≧ (amount of change in surface tilt of polygon mirror + amount of change in characteristic of auxiliary deflecting means), (5)
H ′ _ij ≧ (the amount of change in the surface tilt of the polygon mirror + the amount of change in the characteristic of the auxiliary deflecting means), (6) S ′ _ij ≧ 0, (7) P _ij >
In addition to satisfying the relationship of 0, the projection position deviation is information on the distance between the horizontal boundary part which is a boundary line horizontal to the main scanning direction in the boundary line of each rectangular area and the center of each beam spot.

According to a second aspect of the invention, the projection position deviation detecting means relating to the first aspect of the invention is arranged only at the start position.

According to a third aspect of the invention, the projection position deviation detecting means relating to the first aspect of the invention is arranged only at the end position.

The invention according to claim 4 relates to the invention according to claim 1, wherein the projection position deviation detecting means is arranged at each of the start position and the end position.
And the second projection position deviation detecting means, and the drive signal determining means is means for determining the drive signal based on the respective detection signals of the first and second projection position deviation detecting means.

According to a fifth aspect of the present invention, the driving voltage signal determining means according to any one of the first to fourth aspects is configured as follows. That is, the drive signal determining means stores the standard drive signal for each surface of the polygon mirror, and outputs the standard drive signal for each surface to the auxiliary deflecting means on the basis of each detection signal obtained. Is corrected and the corrected standard drive signal is determined as the drive signal.

[0026]

(Invention of Claim 1) The light beam is incident on each surface of the polygon mirror through the auxiliary deflecting means. Then, the light beam is reflected by each surface of the polygon mirror, focused on the photosensitive material exposure surface by the scanning lens, and then scanned in the main scanning direction. At this time, the projection position of the light beam in the sub-scanning direction fluctuates for each surface as a result of not only the surface tilt of the polygon mirror but also the effect of the change of each surface and the characteristic change of the auxiliary deflection means.

At this time, the projection position deviation detecting means detects the projection position deviation in the sub-scanning direction of the light beam reflected by each surface of the polygon mirror. That is, since the projection position deviation detecting means has a light-transmitting portion or a light-shielding portion composed of a plurality of rectangular regions, for example, considering a case where the rectangular region is the light-shielding portion, a part of the beam spot is a rectangle. Each time the light beam passes over the area, an increase or decrease in the light beam amount is detected according to the degree of overlap with the rectangular area. The increase / decrease can be determined based on the light amount detected when the center of the beam spot is on the horizontal boundary portion parallel to the main scanning direction of the rectangular area. Moreover, the N rectangular areas in the main scanning direction are formed so that adjacent areas have a step P _ij . Therefore, the detection signal of the projection position deviation detecting means is "the distance between the center of the beam spot of each light beam and the horizontal boundary, that is, the center of each beam spot is closest to the horizontal boundary of which rectangular area". It contains information.

Based on this detection signal, the drive signal determining means determines a drive signal that minimizes the displacement of the center of each beam spot, and outputs it to the auxiliary deflecting means. As a result, the auxiliary deflecting means changes the incident angle of the light beam on each surface of the polygon mirror according to the level of the drive signal. This eliminates the influence of the amount of change in the surface tilt of the polygon mirror and the amount of change in the characteristics of the auxiliary deflecting means.

(Invention of Claim 2) The drive signal determining means determines the drive signal based only on the detection signal of the projection position deviation detecting means arranged at the start position.

(Invention of Claim 3) The drive signal determining means determines the drive signal based only on the detection signal of the projection position deviation detecting means arranged at the end position.

(Invention of Claim 4) The drive signal determining means determines the drive signal based on both detection signals of the first and second projection position deviation detecting means arranged at both the start position and the end position. .

(Invention of Claim 5) The drive signal determining means outputs the standard drive signal to the auxiliary deflecting means. As a result, the auxiliary deflecting means changes the incident angle of the light beam on each surface of the polygon mirror by an angle corresponding to the standard drive signal. After that, a detection signal regarding the projection position deviation of the light beam in the sub-scanning direction is input to the drive signal determining means for each surface, and the drive signal determining means corrects the standard drive signal based on the detection signal. Then, this time, the auxiliary deflecting means is controlled by the corrected standard drive signal, whereby the influence of the amount of change in the surface tilt of the polygon mirror is removed.

[0033]

1 is a perspective view showing an embodiment of a scanning optical system in a light beam scanning device. In the figure, three flat plates 2, 10 and 12 are fixedly mounted on the base 1.
First, an L-shaped block 3 for supporting and fixing a laser diode 4 as a light source is fixedly mounted on the flat plate 2. That is, one part of the L-shaped block 3 (base 1
A small hole is bored in a portion (not fixed to), and the laser diode 4 is inserted and fixed in the small hole. The modulation signal V ₁ of the laser diode 4 is
The light beam LB that is a signal generated based on an image signal that gives an image to be recorded, and consequently the laser diode 4 oscillates is a light beam that is modulated by the image signal. Then, the correction mirror 6 is placed on the optical path of the light beam LB.
A piezo actuator 5 having a tip coupled to one end of the correction mirror 6 is fixedly mounted on the flat plate 2 so that the mirror surface of the correction mirror 6 is arranged. The piezo actuator 5 receives the drive signal V ₂ and is displaced, and the mirror surface of the correction mirror 6 is tilted by an amount corresponding to this displacement. Therefore, the incident angle of the light beam LB on the correction mirror 6 changes,
Therefore, the reflection angle also changes. As a result, the angle of incidence of the light beam LB on the polygon mirror 11, which will be described later, changes. As described above, the piezo actuator 5 and the correction mirror 6 form the minute deflector 7. Here, if the polygon mirror 11 is regarded as the main deflecting means, it can be said that the minute deflector 7 functions as the auxiliary deflecting means. Further, on the flat plate 2, an L-shaped block 8 for fixing the collimating lens 9 is provided, and the reflected light beam L
It is fixed on the optical path side of B. The collimating lens 9 itself is inserted and supported in the opening of the block 8 as shown in FIG. As a result, the light beam LB is reflected by the correction mirror 6 and then converted into a parallel beam by the collimator lens 9.

A polygon mirror 11 is arranged on the flat plate 10. As described above, the polygon mirror 11 is supported via the air bearing (not shown). Therefore, the light beam LB incident on each surface of the polygon mirror 11
Is reflected by the surface and scanned in the main scanning direction y.

On the flat plate 12, f as a scanning lens is used.
A θ lens 13 is provided. The light beam LB is imaged on the exposure surface of the photosensitive material 14 by the fθ lens 13, and is scanned at a constant speed in the main scanning direction y.

On the other hand, the photosensitive material 14 is moved by the roller 15 every time one scanning in the main scanning direction y is completed.
The sheet is conveyed in the (direction orthogonal to the main scanning direction y). Although the symbol SL indicates a scanning line in the main scanning direction, the position where the light beam LB is projected shifts from the scanning line SL in the sub scanning direction x due to the above-mentioned temporal factors.
And it fluctuates. In addition, the scanning direction of the light beam LB is inclined with respect to the scanning line SL due to the distortion of each surface of the polygon mirror 11.

Outside the effective scanning range of the photosensitive material 14, the mirrors 16 and 2 are provided on the base 1 on the start position side and the end position side.
0 is arranged such that its mirror surface is parallel to the xy plane. At the focal position of the light beam reflected by the mirrors 16 and 20 (position conjugate with the exposure surface of the photosensitive material 14),
The masks 17 and 21 are also arranged so as to be parallel to the xy plane. The masks 17 and 21 have a pattern in which light transmitting portions that transmit the light beam LB and light shielding portions that shield the light beam LB are alternately arranged. It can be said that the shape of this pattern is the most characteristic part in this embodiment. However, since this pattern is formed of a thin film of chrome or the like, infrared light can pass through the light shielding portion. However, in this embodiment, since the light beam LB oscillated by the laser diode 4 is visible light or near red light,
Infrared light detection is only a dark current.

Immediately after the masks 17 and 21, the light amount detector 1 is so arranged that its detection surface covers all the above patterns.
8, 22 (photodiodes, etc.) are arranged. Therefore, the light beam LB scans the patterns of the masks 17 and 21 within a range of passing through the reflection surfaces of the mirrors 16 and 20, and the light amount detectors 18 and 22 detect the light amounts of the light beams LB that have passed through the patterns. To detect. The detection signals V ₃ and V ₄ are output to the electric system described later. The detection signals V ₃ and V ₄ are detection signals of the start position and the end position, and also signals obtained by relatively detecting the projection position of the light beam LB in the sub-scanning direction x within the range of the pattern of the masks 17 and 21. is there. Therefore, the mask 17 and the light amount detector 18
Are collectively referred to as a start sensor 19, and the mask 21 and the light amount detector 22 are collectively referred to as an end sensor 23.
The start sensor 19 and the mirror 16 and the end sensor 23 and the mirror 20 form a projection position deviation detecting means.

As described above, in this embodiment, the sensors (start sensor 19 and end sensor 23) having the same structure and the same function are provided at both the start position and the end position. Polygon mirror 11
This is because each surface has distortion, and in consideration of this, the accuracy and precision of the correction are further improved. Therefore,
In this embodiment, the detection signals V ₃ and V ₃ of both sensors 19 and 23 are detected.
Based on ₄ , the drive signal V ₂ is determined. A detailed method for determining this point will be described later.

Here, first, general features of a pattern shape applicable as a mask pattern will be described, and then the actual shapes of the patterns of the masks 17 and 21, which are application examples thereof, will be described.

FIG. 2 is a view generally showing the pattern shape of the mask 17 on the side of the start position.
It corresponds to the plan view of this pattern viewed from the 6 side. In the figure, a hatched portion 45 and rectangular areas 47 to 5
0 is a light shielding part, and the other part is a light transmitting part. In particular, in the figure, the translucent part located on the leftmost side is referred to as a perfect translucent part 51.
I am calling. Then, the boundary portion 46 between the light shielding portion 45 and the completely transparent portion 51 becomes the main scanning detection position, that is, the start position detection position. Therefore, in order to confirm that the light quantity of the light beam LB changes from 0 value to its maximum value, the width T of the completely transparent portion 51 is set to be larger than the beam diameter of the light beam LB in the main scanning direction. Other light-shielding parts 47 to 50 (hereinafter,
A rectangular area is a pattern for detecting the projection position of the light beam LB in the sub-scanning direction. In addition,
Instead of the light shielding portion 45, the light shielding portion may be formed at the position indicated by the dotted line.

Here, N rectangular areas corresponding to the rectangular areas 47 to 50 (N ≧ 1) in the main scanning direction y and M (M ≧ 1) in the sub scanning direction x are formed. Be present. However, (N × M) ≧ 2 must be satisfied. or,
The main scanning direction y and the sub-scanning direction of the rectangular area (i, j) corresponding to the i-th main scanning direction y (1 ≦ i ≦ N) and the j-th sub-scanning direction x (1 ≦ j ≦ M). The lengths of x are represented as S _ij and H _ij , respectively, and the two rectangular regions (i, j) and (i +) that are adjacent to each other in the main scanning direction y are adjacent to each other.
1 and j) is represented as S ′ _ij , and the sub-scanning direction x
Adjacent rectangular areas (i, j), (i, j +)
1) represents the distance between the H _'ij. Further, a step P _ij is formed between the two rectangular areas (i, j) and (i + 1, j). This step P _ij is a characteristic part of this embodiment. In Figure 2, between the rectangular region 47, 48 has only been stepped P ₁₁ is formed on its upper side, between the rectangular region 49 and 50 with respect thereto, a step P ₁₂ in either its upper side and a lower side Has been formed. This is the length H
_{It is} nothing more than the result of the setting method of ₂₁ and H ₂₂ . When these symbols are defined as described above and their dimensional relationship is shown, they are expressed as in the following mathematical expression 1.

[0043]

[Equation 1]

In the above relational expression, "the amount of change in the surface tilt of the polygon mirror 11" means the above-mentioned change factors (i) and (i
i) the projection position deviation in the sub-scanning direction that occurs based on
Further, the "characteristic change amount of the minute deflector 7" is a projection position deviation in the sub-scanning direction that is generated based on the temporal change factor (iii). Both are empirical parameters obtained by actual measurement. That is, these values are obtained in advance by actual measurement within the operating temperature range, and based on the obtained values, the above conditions
The length H _ij and the interval _H'ij are determined.

Regarding the condition, depending on the shape of the pattern, it may be necessary to set the step P _{ij so} as to satisfy the condition [': 0 <P _ij ≤H _ij ] instead of the condition. There is also. Specifically, the pattern examples adopted in FIGS. 5 to 7 described later correspond to this case.

The pattern of the mask 21 on the end position side is the same as that of FIG. 2 for the rectangular region (i, j) in the light shielding part, but the light shielding part having the boundary portion as the end position detection position. That is, what corresponds to the light-shielding portion 45 in FIG. 2 is not located at the leftmost position in the figure, but is located at the rightmost position (the boundary is 46A) shown by the dotted line. Further, the same pattern as in FIG. 2 may be used for the mask 21.

Here, FIG. 3 is a diagram showing a positional relationship between a horizontal boundary portion (a horizontal boundary line in the main scanning direction y) between the light shielding portion and the light transmitting portion and the beam spot, and FIG. FIG. 4 is a diagram showing the relationship between the position of a beam spot and the amount of light, which is drawn corresponding to FIG. 3. Now, if the beam spot is displaced from the light-shielding portion of the mask to the light-transmitting portion as shown in FIG. 3, the amount of transmitted light at that time changes as shown in FIG. In this case, the displacement amount of the center of the beam spot with respect to the horizontal boundary portion and the light amount change do not have a linear relationship, but with a normal Gaussian beam, the light amount is 0.5, that is, the beam spot is entirely in the light transmitting portion. When the amount of light becomes half, the change in the amount of light per unit displacement of the beam spot becomes maximum.
In this state, the center of the beam spot is exactly on the horizontal boundary part, and the energy is most concentrated in the center, so that a large light amount change is brought about even if the center is slightly displaced. In this case, the sensitivity depends on the beam diameter of the beam spot, and if the beam diameter is determined by 1 / e ² intensity of the central intensity, for example, the beam diameter is 4
When it is 0 μm, the amount of light changes by 0.4% just by changing it by 0.1 μm.

Such a variation in the amount of light is a value that can be detected sufficiently even by a normal photodiode, and therefore in the present embodiment, a photodiode is used as an example of the light amount detector. Therefore, a light intensity of 0.5 means 0.4%
If it is confirmed with the accuracy of 1), it is possible to detect that the beam spot is on the horizontal boundary portion with the accuracy of 0.1 μm. In this embodiment, with this point as a basic matter, the pattern shape of the mask is set in order to always detect how much the center of the beam spot is displaced from the horizontal boundary portion for each surface. There is. Therefore, a pattern having a step P _ij is provided in the sub-scanning direction to create a plurality of horizontal boundary portions. This is the central idea of this embodiment.

The above conditions (or ') are exactly the conditions for realizing this idea. conditions~
Is a condition for ensuring an area where the rectangular area can include the entire beam spot. This is when the central part of the beam spot covers the rectangular area and both end parts of the rectangular area cover the translucent part. In addition, when the light quantity is 0.5, it is set in order to avoid a situation in which it becomes impossible to quantitatively determine which horizontal boundary portion the light beam is close to. Furthermore, the opposite case,
That is, even when the center of the beam spot is in the light-transmitting portion and both ends of the beam spot are in the upper and lower rectangular regions, respectively,
The same problem may occur and is also to avoid it. In other words, always at the center of the beam spot,
The projection position in the sub-scanning direction can be detected.

In addition, the condition is that, even if the beam spot is displaced in the sub-scanning direction x due to a change with time, the positional relationship of the beam spot after displacement with respect to the horizontal boundary portion is always represented by the step P _ij in the main scanning direction y. This is a condition for enabling detection by the horizontal boundary of each rectangular area arranged in.
As a result, the center of the light beam LB can be shifted to the nearest horizontal boundary portion only by driving the minute deflector 7 with a driving amount that corresponds to a distance of about half the step P _ij. It will be possible. Therefore, the corrected light beam always passes through the same horizontal boundary portion. This point will become clearer in the description below.

Hereinafter, the point that the projection position of the light beam LB in the sub-scanning direction x can be obtained from the light amount detection by using the mask patterns shown in FIGS. 5 and 6 will be described. This point can be said to be the principle of detecting the projection position in this embodiment. Both figures 5,
The mask pattern 6 (a) is exactly the same as the mask pattern in FIG. 2 with N = 3, M = 4, and S _ij = 1m.
m, S ′ _ij = 0 mm, P _ij = 30 μm, H _ij = 90 μ
This is an example when m, H ′ _ij = 90 μm is set, and the beam diameter at this time is 40 μm. As a result, a pattern is formed in which four step-shaped light shielding portions are arranged at equal intervals H ′ _ij in the sub scanning direction y. In addition, in this pattern, including the completely transparent portion and the completely light-shielded portion,
Five zones W, P, Q, R and B are formed.

Now, as shown in FIGS. 5 and 6, the light beam LB
Let a to LBh cross this pattern. In this case, each of the light beams LBa to LBh has a polygon mirror (8
It corresponds to each of the faces a to h of the face piece). When the beam spot enters the zone W, sampling is started and, for example, four light quantity data W _{1 to} W ₄ are collected for each light beam. Then, the light amount data W _{1 to} W ₄ are averaged for each light beam to determine the light amount data W _A for the zone W. Since there is no light shield in zone W,
The light amount data W _A indicates the total light amount of the beam spot. Similarly, for the zones P to R, the light amount data P _{A to} R _A for each light beam LB are obtained. The collected light amount data is shown in FIG. 5 (2) for the light beams LBa to LBd.
5 (5), the light beams LBe to LBh are shown in FIG.
(2) to Fig. 6 (5). From these changes in the light amount data, as shown below, the horizontal boundary portion closest to the scanning line of each of the light beams LBa to LBh can be known.

That is, in the case of the light beams LBa, LBb, LBc, the nearest horizontal boundary portion is in the zone Q, and in the light beams LBd, LBe, LBh, the nearest horizontal boundary portion is in the zone R, and the light beams LBg and It can be seen that in LBh, the nearest horizontal boundary is in zone P.

FIG. 7 is a plan view showing the patterns of the masks 17 and 21 applied to this embodiment. In relation to the general shape of FIG. 2, N = 6, S _ij = 500 μm, S ′ _ij
= 0 mm, P _ij = 6 μm, H _ij = 36 μm (= P _ij ×
6) and H ′ _ij = 36 μm (= P _ij × 6). As a result, six rectangular regions of 500 μm × 36 μm are connected in the sub-scanning direction x while shifting by 6 μm each, and the step-shaped light-shielding portions 60 thus formed are equally spaced by 6 μm in the sub-scanning direction. A pattern arranged in x is formed. The beam diameter of the light beam LB applied in this embodiment is 4
It is 0 μm to 45 μm, and the above conditions 1 to 4 are satisfied. Further, the present applicant has measured the amount of change in the tilt of the polygon mirror and the change in the characteristics of the micro-deflector within the temperature range of 0 ° C. to 40 ° C. It was about 5 μm at maximum. Therefore, since H _ij and H ′ _ij are 36 μm, respectively, the conditions and are sufficiently satisfied. In principle, the relationship between the conditions and the size may be good, but in practice, the margin is set by setting as in Equation 2. In addition, the conditions and 'are also satisfied.

[0055]

[Equation 2]

In FIG. 7, assuming that the polygon mirror 11 is a hexahedron, the light beams LB1 to LB reflected on the respective surfaces are shown.
The scan line B6 (before correction) is drawn. As will be described later, these scanning lines are obtained by driving the minute deflector 7 with a preset standard drive signal.

FIG. 8 is a block diagram showing a configuration of an electric system in the light beam scanning device. The electric system includes an output engine 43 configured with the controller 25 as a core.
And the DTP (Desk Top) which is the command tower of the light beam scanning device.
Publishing computer 44. The DTP computer 44 is a part that creates a modulation signal based on the image signal, and also outputs a command signal for operating each part of the light beam scanning device to the host computer 41 of the output engine 43. For example, the modulation signal V ₁ for oscillating the laser diode 4 and the polygon mirror 11
And a command signal for controlling the rotation of the roller 15 and a command signal for issuing the drive signal V ₂ to the piezo actuator 5. These signals are collectively referred to as the command signal V ₁₄ in FIG.

The output engine 43 includes the described start sensor 19 and end sensor 23, controller 25, host computer 41, mechanical system controller 42, piezo actuator 5 (described), piezo actuator driver 5D, laser diode 4 (described). It is roughly divided into. Of these, the controller 25 is the output engine 43
This is a core part of the above, and is a part for determining the optimum drive signal V ₂ for each surface by arithmetic processing based on the detection signals V ₃ , V ₄ of both sensors 19, 23.

The host computer 41 receives the command signal V ₁₄ from the DTP computer 44, and receives the mechanical system controller 42, the laser diode 4 and the controller 25.
The control signal V ₁₂ , the modulation signal V _1, and the operation command signal V ₁₁ are output to the processor 35 of FIG. Here, the mechanical system controller 42 is a generic term for controllers that control each drive mechanism (motor or the like) such as the polygon mirror 11 and the roller 15.

The controller 25 has a processor 35 as a core, and also has voltage conversion circuits 26, 27, and
Adder circuit 28, A / D converter 29, averaging circuit 30, comparators 31, 33, program ROM 36, static RAM 37, standard data ROM 38 for face tilt correction and D
It has an A / A converter 39. Program ROM 36
Sends the drive signal V _{2 to} the processor 35 based on the detection signals V ₃ and V ₄ of the start sensor 19 and the end sensor 23.
It holds a program relating to a correction algorithm for executing the correction process of determining. The surface tilt correction standard data ROM 38 holds the standard drive signal V ₁₅ used in the correction processing for each surface of the polygon mirror 11. Furthermore, static RAM37
Is D for each surface obtained by the correction process by the processor 35.
This is a memory that holds the drive signal V ₁₀ given to the / A converter 39.

The detection signal V ₃ (current signal) of the start sensor 19 is once amplified by the OP amplifier 24 and then converted into a detection signal V ₅ as a voltage value by the voltage conversion circuit 26. Then, the detection signal V ₅ is input to the input terminals of the adder circuit 28 and the comparator 31. Of these, the comparator 31 is a circuit for generating the interrupt signal V ₈ and giving the signal V ₈ to the processor 35, and compares the detection signal V ₅ with the comparison level 32 to generate the interrupt signal V _8.
To generate. The same applies to the detection signal V ₄ of the end sensor 23.

The adder circuit 28 adds the two detection signals V ₅ and V ₆ to generate a detection signal V ₇ . That is, V
₇ = it is a V ₅ + V _6. By the way, when the light beam LB is scanned on the start sensor 19, the end sensor 21 does not detect the light beam LB, and the detection signal V
_{Since 6} is 0 except the offset value, the detection signal V
₇ is substantially the detection signal V ₅ itself. On the contrary, when the light beam LB is scanned on the end sensor 21, the detection signal V ₇ is substantially the detection signal V ₆ itself. The detection signal V ₇ is then averaged. This means that A / A is individually detected for each of the detection signals V ₃ and V _4.
This is equivalent to providing a D conversion circuit and performing A / D conversion. That is, the number of relatively expensive A / D conversion circuits can be reduced by providing the addition circuit 28 and performing the addition processing of both detection signals V ₃ and V ₄ . Of course, without using such a circuit configuration, A /
You may perform D conversion processing.

The processor 35 is the host computer 4
In response to the operation command signal V ₁₁ output from the controller 1, the execution of the correction algorithm is started. Then, it receives the detection signal V _{3 in} response to the interrupt signal V ₈ , and further acquires the detection signal V ₄ according to the interrupt signal V ₉ . Therefore, the details of the correction algorithm will be described below.

Here, the number of faces of the polygon mirror 11 is set to 6, and a correction algorithm for stabilizing the six faces will be described. Of course, this correction algorithm can be applied regardless of the number of faces of the polygon mirror 11. This correction algorithm is summarized as follows.

1) The light beam LB is scanned with the standard drive signal V ₁₅ , and the light amount is measured.

2) From the measured data, the one having the light quantity value closest to 0.5 is obtained from the six scanning lines, and the horizontal boundary portion to be the reference is specified by this.

3) The standard drive signal V ₁₅ is corrected to obtain the drive signal V ₂ so that each scanning line is along the horizontal boundary portion to be the reference. These processes are performed on both detection signals V ₃ and V ₄ .

9 and 10 are flowcharts showing the correction algorithm. Among them, step S1 is a preparation step and a step of determining the standard drive signal V ₁₅ . This is determined using the method disclosed in Japanese Patent Laid-Open No. 2-114228. That is, a grating sensor, which is periodically formed so that the L-shaped pattern covers the entire scanning range, is arranged on the scanning line SL, and the grating sensor is scanned with an exposure light beam. Then, from the obtained light amount detection signal,
Horizontal boundary 70 of L-shaped pattern (horizontal in the main scanning direction)
Piezo actuator 5 so that the light beam scans the top
Determine the drive signal of. This drive signal is exactly the standard drive signal V ₁₅ , and this signal V ₁₅ is stored in the standard data ROM 38 for face tilt correction after the determination. After this, the grating sensor is removed.

In step S2, the micro deflector 7 is controlled by the standard drive signal V ₁₅ , and the light beam LB is actually scanned in the main scanning direction y. However, at this time, the light beam LB is not modulated by the image signal, and the roller 15
The exposed surface of the photosensitive material 14 is not located above.

The DTP computer 44 sends the command signal V ₁₄
The host computer 41 outputs an operation command signal V ₁₁ to the processor 35 in response to the output. In response to this, the processor 35 activates the correction algorithm program in the program ROM 36, and based on the command of this program, the standard data RO for face tilt correction.
From M38, the standard drive signal V ₁₅ is read corresponding to each surface of the polygon mirror 11, and each signal V ₁₅ is read by the D / A converter 39.
And to the piezo actuator 5 via the piezo actuator driver 5D. Thereby, the minute deflector 7 changes the incident angle of the light beam LB to the polygon mirror 11 by a predetermined amount for each surface. In this case, the projection position of the light beam LB in the sub-scanning direction changes for each surface under the influence of the above-described change over time and the distortion of each surface.

In step S3, the start sensor 19
Detects the amount of light at the start position side for each surface (here, for 6 scanning lines), and the detection signal V ₃ is taken into the processor 35. The same applies to the end sensor 23. The averaging circuit 30 is a part for averaging the light quantities described in the description of FIGS. 5 and 6. That is,
The averaging circuit 30 averages detection signals at several positions in one zone for each zone assumed in the mask pattern, and uses the averaged detection signal as a light amount signal in the zone. Output to 35.

Steps S4 to S7 are all arithmetic processes performed in the processor 35. First, in step S4, the processor 35 normalizes the light amount signal of each zone for each surface of the polygon mirror 11. This normalization process is executed for each of the light amount signals on the start position side and the end position side, and is specifically performed by the calculation given by the following mathematical expression 3.

[0073]

[Equation 3]

However, in Equation 3, each surface of the polygon mirror 11 is numbered and the surface number is represented as k (1 ≦ k ≦ 6), and the light beam LB reflected by the k-th surface is represented.
The light amount signals in the completely light-transmitting portion and the light-shielding portion are shown as W (k) and b (k), respectively.

The signal P _zl (k) is the l-th signal in the pattern.
The light quantity signal (averaged) for the k-th surface in the 1st (l-th (1 ≦ l ≦ 6) from the left side in FIG. 7) zone Z _l is represented by the symbol Abs.
It means to take the absolute value of the calculated value in [...].

The pattern of FIG. 7 has a stepped shape.
Since the light-shielding portion 60 is substantially a basic unit, there are _six zones Z _{1 to} Z ₆ excluding the complete light-transmitting portion 61. Therefore, at each of the start position and the end position, the normalized data P _Z1 (k) to P _Z6 (k) of the light amount signals of the _six zones Z _{1 to} Z ₆ are obtained for each of the six surfaces.

In step S5, the processor 35, for each of the start position side and the end position side, for each zone Z _l , determines which light beam LB in the zone Z _l .
The scanning line of the step portion 62 is the horizontal boundary portion 63 (the light shielding portion 6).
It is determined whether the boundary between 0 and the transparent portion 64 is the closest to the boundary parallel to the main scanning direction y). This determination is based on the arithmetic processing (step S51) given by the following equation 4 and the equation 5
The calculation process (step S52) given by

[0078]

[Equation 4]

[0079]

[Equation 5]

Here, the symbols Max and Min are respectively
It means "taking the maximum value" and "determining the horizontal boundary portion taking the minimum value".

In step S5, the six light beams L
A zone Z ₀ having a horizontal boundary portion (light amount: 0.5) that should move all the projected positions of B to that position is obtained. That is, the position of the horizontal boundary portion is predicted, which can reduce the load on the piezoelectric actuator 5 required to move the projection position of each light beam LB as much as possible.

However, at this stage, it is not yet finally specified whether such a horizontal boundary portion is above or below in the sub-scanning direction in the light shielding portion 60. In other words, there are two horizontal boundary portions 63 on the upper side and the lower side in the zone Z ₀ (this means that another zone Z _l
Can also be said. ), It is necessary to determine which of these horizontal boundary portions 63 should be specified to reduce the load on the actuator 5. The calculation process for that is step S6. This is judged as follows.

First, the processor 35 determines the previous step S5.
With respect to the zone Z0 specified by, the standardized light quantity signal P1 _Z0 (k) is calculated for each surface according to equation 6.

[0084]

[Equation 6]

Then, the standard drive signal V ₁₅ is used with the data signal corresponding to the amount of displacement of several μm upward on the image plane as an offset.
In addition to driving, the detection signals V ₃ and V ₄ are taken into the processor 35. Then, the processor 35
For the zone Z ₀ , the light quantity signal p ′ obtained this time
_{Using Z0} (k), the normalized light amount signal _P2Z0 (k) is calculated again ( _Equation 7).

[0086]

[Equation 7]

Further, the processor 35 calculates the sum P1 and P2 of the light amounts given by the equation 8 and compares the sum P1 and P2 of the two light amounts.

[0088]

[Equation 8]

Here, as shown in FIGS. 11A and 11B,
When the relationship of P1 <P2 is obtained, the horizontal boundary 63 to be obtained is the upper horizontal boundary 63 in the zone Z ₀ .
Is. On the contrary, when the relation of P1> P2 is obtained,
It can be seen that it is the lower horizontal boundary 63. In this way, the processor 35 determines the horizontal boundary 6 to be obtained.
Specify 3. Then, in this way, the processor 35
Specifies the horizontal boundary portion 63 to be obtained. Then, all the scanning lines of the six light beams LB are moved to the specified horizontal boundary portion 63.

Exactly in FIG. 7, six light beams LB1 to LB6 corresponding to the respective surfaces traverse one of the stepped light shielding portions 60. In this case, the horizontal boundary 6 to be obtained
3 is a horizontal boundary portion 66 on the lower side of the rectangular area belonging to the zone Z ₃ . Therefore, the standard drive signal V ₁₅ of each surface is corrected so that the six light beams LB1 to LB6 are scanned on the horizontal boundary portion 66.

In step S7, the processor 35 outputs the drive signal V ₂ for scanning each light beam LB on the determined horizontal boundary portion for each surface on the data of the start position side and the end position side. Is calculated in combination. This is the number 9
It is executed by the arithmetic processing given by.

[0092]

[Equation 9]

Here, the symbol k indicates the surface number, and the symbol m indicates the number of the position in the main scanning direction (position within the scanning range). In this embodiment, the scanning range is divided into N _S, so that 1 ≦ m ≦ N _S. Also, the symbol V ₁₅ (k, m)
Is the standard drive signal at the m-th position in the main scanning direction on the k-th surface, and is represented by the symbols α (k) and β (k).
Is the start sensor 1 for the kth surface.
9 and the offset amount of the end sensor 23.
This offset amount is a correction value that must be applied to the piezo actuator 5 in order to scan the light beam LB reflected by the k-th surface to the specified horizontal boundary portion on the start position side or the end position side. Means Here, the processor 35 holds the relationship between the level of the light amount signal p _Zl (k) and the drive correction amount of the piezo actuator 5 as a table value in advance within one step, and the table value and the measured value are calculated and calculated. Light intensity signal p
By comparing with _Z0 (k), the offset amount α
(K) and β (k) can be determined immediately.

FIG. 12 shows the standard drive signal V before correction.
₁₅ (k, m) and the drive signal V ₂ (k, m) that has been corrected by the correction algorithm and is a diagram for illustrating contrasting. However, for convenience, only the first to third surfaces of the six surfaces are shown.

In step S8, the corrected drive signal V ₂
(K, m) drives the piezo actuator 5 and the light beam LB actually modulated by the image signal
To scan. At this time, the drive signal V ₂ (k, m) is set so that the load on the piezo actuator 5 is as close as possible, so that the deflection angle of the micro-deflector 7 necessary for detecting the change factor with time is As shown in FIG. 13 (b), it is significantly reduced. In FIG. 13, the shaded portion is the deflection angle necessary to correct the factor with time, and the non-shaded portion is the face tilt correction amount. Further, FIG. 7A shows the deflection angle required in the conventional technique.

As described above, according to the present embodiment, by displacing the beam spot by P _ij / 2 by the minute deflector 7, the beam spot can be formed on the horizontal boundary portion where the load on the piezo actuator 5 can be minimized. Can be moved,
The deflection angle of the minute deflector 7 can be reduced.

In the previous embodiment, the pattern shape of the mask was S ′ _ij = 0 in all cases, but other than that, for example, those shown in FIGS. 14 and 15 may be used. In the example of FIG. 14, the lengths S _ij and H _ij , the intervals S ′ _ij and H ′ _ij , and the step P _ij are the same for all rectangular regions. Further, in the example of FIG. 15, H ₁₁ = H ₂₁ + P ₁₁ = H
₃₁ + P ₁₁ + P ₂₁ , S ′ ₁₁ = 0, S ₁₁ = S ₂₁ = S ₃₁ , P ₁₁
= P ₂₁ .

Further, in the previous embodiment, in the pattern shape of the mask, each step P _ij is set in the downward direction of the drawing (FIGS. 5 to 7), and a step-shaped light shielding portion is formed. However, the present invention is not limited to such a pattern shape, and the reverse case in which the step P _ij is always formed in the upper direction of the drawing, or in the upper and lower directions. The case where the steps P _ij formed _{facing each other} are mixed can also be adopted as the pattern shape of the present invention. The latter example is a schematic illustration,
It is the pattern shown in FIG. In this example, the step P ₁₁
Are formed in the downward direction and satisfy the relationship of P ₁₁ > H ₁₁ , on the contrary, the step P ₂₁ is formed in the upward direction, and P ₂₁ <H ₁₁ , P ₂₁ < _{H 31, (P 11 -P 21} ) <
Satisfies the relationship of H ₁₁ . That is, in this example, each step P
_{In this example, ij} satisfies the condition and at least one of them satisfies the condition '.

Further, in the previous embodiment, the sensors (19, 23) were set on both sides of the start position and the end position, but this is to correct the distortion in one surface of the polygon mirror 11. It is adopted, and the present invention is not limited to this configuration. That is, the smoothness is realized to such an extent that there is almost no distortion in the plane of the polygon mirror 11, and the influence due to thermal expansion or the like can be neglected, or in the rough image reproduction of a laser printer or the like. When applied, the present sensor (mask + light amount detector) may be provided at either the start position or the end position. However, when the above sensor is provided at the end position, a separate sensor for detecting the start position is required.

In the above-mentioned embodiment, the start sensor 1
Although 9 has both the detection of the start position and the detection of the projection position deviation in the sub-scanning direction, these two functions may be separately realized. That is, the sensor for detecting the start position and the sensor for detecting the projection position deviation may be sequentially arranged. This also applies to the end sensor 23.

In this embodiment, the fθ lens 13 is used as a scanning lens, but instead of this, tan θ is used.
A lens or an arcsine lens may be used as the scanning lens.

Further, in this embodiment, the rectangular area is used as the light-shielding portion,
Although the other portion is used as the light shielding portion, it is also possible to reverse this relationship and use it. That is, it is possible to use a mask pattern in which the rectangular region serves as the light transmitting portion and the other portion serves as the light shielding portion.

Further, as the light quantity detector, a photoelectric element such as a photomultiplier tube, a photoelectric tube, a PIN photodiode or an avalanche diode may be used in addition to the photodiode.

[0104]

According to each of the first to fifth aspects of the present invention, even if the projection position of the beam spot in the sub-scanning direction changes for each surface of the polygon mirror due to a change with time, the drive range of the auxiliary deflecting means increases. It is possible to correct the above-mentioned fluctuation by minimizing the above.

[Brief description of drawings]

FIG. 1 is a perspective view showing a scanning optical system of a light beam scanning device.

FIG. 2 is an explanatory diagram generally showing the shape of a mask pattern.

FIG. 3 is an explanatory diagram showing a positional relationship between a horizontal boundary portion in a mask pattern and the center of a beam spot.

FIG. 4 is an explanatory diagram showing a relationship between a center position of a beam spot and a light amount.

FIG. 5 is an explanatory diagram showing a pattern shape of a mask and a light amount for each light beam.

FIG. 6 is an explanatory diagram showing a pattern shape of a mask and a light amount for each light beam.

FIG. 7 is a plan view showing the shape of a mask pattern as an example.

FIG. 8 is a block diagram showing an electric system of the light beam scanning device.

FIG. 9 is a flowchart showing a correction algorithm.

FIG. 10 is a flowchart showing a correction algorithm.

FIG. 11 is an explanatory diagram illustrating a process of determining a horizontal boundary portion.

FIG. 12 is an explanatory diagram showing an example of a corrected drive signal together with its standard drive signal.

FIG. 13 is an explanatory diagram showing an effect of the present invention.

FIG. 14 is an explanatory diagram showing a modified example of a mask pattern.

FIG. 15 is an explanatory diagram showing a modified example of the mask pattern.

FIG. 16 is an explanatory diagram showing a modified example of the mask pattern.

FIG. 17 is an explanatory diagram showing a conventional technique.

FIG. 18 is an explanatory diagram showing a problem.

[Explanation of symbols]

 4 Laser diode 5 Piezo actuator 6 Correction mirror 11 Polygon mirror 13 fθ lens 14 Sensitive material 16, 20 Mirror 17, 21 Mask 18, 22 Light intensity detector 19 Start sensor 23 End sensor 35 Processor 38 Standard data ROM 40 controller for face tilt correction 41 host computer 46 main scanning detection position 47, 48, 49, 50 rectangular area 60 step light shielding part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Nagata 1 at 1 Tenjin Kitamachi 4-chome Tenjin Kitamachi, Horikawa-dori Teranouchi, Kamigyo-ku, Kyoto (72) Inventor Hiroyuki Shirota Kyoto City 4-chome, Tenjin Kitamachi, 1-chome, Horikawa-dori, Kamigyo-ku 1 Dai Nippon Screen Manufacturing Co., Ltd. (72) Inventor, Takao Matsuda 1-chome, 1-chome, Tenjin-kitamachi, 4-chome, Horikawa-dori, Tenjin, Kyoto, Kyoto Nippon Screen Manufacturing Co., Ltd. (72) Inventor Katsuki Fukuyama 1 at No. 1 Tenjin Kitamachi 4-chome, Horikawa-dori Teranouchi, Kamigyo-ku, Kyoto Dai Nippon Screen Manufacturing Co., Ltd. (72) Inventor Masahiro Tokonami Kyoto Horikawa-dori Teranouchi, Kamigyo-ku, 1-chome, Tenjin Kitamachi 4-chome, Tenjin Dai Nippon Screen Manufacturing Co., Ltd.

Claims (5)

[Claims] 1. A light beam modulated on the basis of an image signal is reflected by a polygon mirror as a main deflecting means toward a light-sensitive material exposure surface, and the light beam after reflection is exposed through a scanning lens to the light-sensitive material exposure. In a light beam scanning device for recording an image by scanning the light beam in the main scanning direction on the light-sensitive material exposure surface by forming an image on a surface, the light beam is incident on the optical path of the light beam entering the polygon mirror. An auxiliary deflecting unit which is disposed and corrects an incident angle of the light beam on the polygon mirror according to a drive signal; and at least one of a start position and an end position of a scanning range in the main scanning direction. Projection position deviation detecting means for detecting a projection position deviation of each light beam in a sub-scanning direction orthogonal to the main scanning direction on each surface of the polygon mirror; Drive signal determining means for determining the drive signal based on the detection signal of the detecting means and outputting the drive signal to the auxiliary deflecting means, the projection position deviation detecting means for the light beam. Has a pattern including a light-transmitting portion that transmits the light beam and a light-shielding portion that shields the light beam, and one of the light-transmitting portion and the light-shielding portion is N in the main scanning direction and the sub-scanning direction, respectively. And a plurality of M (N ≧ 1, M ≧ 1) arranged rectangular regions, and the lengths of the rectangular regions in the main scanning direction and the sub scanning direction are S _ij and H _ij , respectively. The intervals between the two rectangular areas adjacent to each other in the main scanning direction and the sub-scanning direction are S ′ _ij and H ′ _ij , respectively, and the rectangular areas adjacent to each other in the main scanning direction are in the sub-scanning direction. If the level difference to P is expressed as P _ij (1 ≦ i ≦ N, 1 ≤ j ≤ M), and the plurality of rectangular regions are (1) S _ij ≥ (beam diameter of the light beam in the main scanning direction) and (2) H _ij ≥ (sub-scanning direction of the light beam, respectively). Beam diameter) / 2, (3) H ′ _ij ≧ (beam diameter of the light beam in the sub-scanning direction) / 2, (4) H _ij ≧ ( _plane tilt change amount of the polygon mirror + the auxiliary deflection means Characteristic change amount), (5) H ′ _ij ≧ (the amount of change in the surface tilt of the polygon mirror + the amount of change in the characteristic of the auxiliary deflecting means), (6)
The relationship of S ′ _ij ≧ 0 (7) P _ij > 0 is satisfied, and the projection position deviation is a horizontal boundary portion which is a boundary line horizontal to the main scanning direction in the boundary lines of the rectangular regions. An optical beam scanning device, which is information about a distance from the center of each beam spot. 2. The light beam scanning device according to claim 1, wherein the projection position deviation detection means is arranged only at the start position. 3. The light beam scanning device according to claim 1, wherein the projection position deviation detecting means is arranged only at the end position. 4. The projection position deviation detecting means comprises first and second projection position deviation detecting means arranged at the start position and the end position, respectively, and the drive signal determining means includes the first and second projection position deviation detecting means. 2. The light beam scanning device according to claim 1, which is means for determining the drive signal based on each detection signal of the two-projection position deviation detection means. 5. The drive signal determining means stores a standard drive signal for each surface of the polygon mirror and outputs the standard drive signal for each surface to the auxiliary deflecting means. 5. The light beam scanning device according to claim 1, wherein the standard drive signal is corrected based on each detection signal, and the corrected standard drive signal is determined as the drive signal.