JPH02217815A - Light beam scanning device - Google Patents

Abstract

PURPOSE:To eliminate the influence of the wind of a rotary polygon mirror upon scanning, to reduce the irregularity of the scanning, and to improve the quantity of an obtained image and reduce the manufacture cost by thinning out and using reflecting surfaces of the rotary polygon mirrors at specific intervals of the number of reflecting surfaces. CONSTITUTION:The rotary polygon mirror 5 has n1 reflecting surfaces 5a-5f (n1: natural number except prime number) and a scanned surface is scanned only with a light beam 1 which is made incident on every n2th specific reflecting surfaces (n2: natural number containing n2+1 as a divisor of n1 except n1). For example, a signal generating means 10 outputs a timing signal every time reflecting surfaces where the light beam 1 is made incident are switched in synchronism with the rotation of the rotary polygon mirror 5 and an image signal output circuit 9 outputs an image signal with the signal from a signal generating means 10 only while the reflecting surfaces 5a, 5c, and 5e are positioned on the optical path of the light beam 1, but stops outputting the image signal while the reflecting surfaces 5b, 5d, and 5f are positioned. Consequently, the influence of the irregularity of the scanning upon the picture quality is reducible without increasing the manufacture cost of the rotary polygon mirror.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a light beam scanning device that scans a surface to be scanned by deflecting a light beam with a rotating polygon mirror, and in particular, the present invention relates to a light beam scanning device that scans a surface to be scanned by deflecting a light beam with a rotating polygon mirror, and in particular, the present invention corresponds to the reflecting surface of the above-mentioned rotating polygon mirror. The present invention relates to a light beam scanning device that can reduce the effects of scanning unevenness.

(Prior Art) In recent years, various light beam scanning devices have been developed that read and/or record images using light beams. In such devices, a light beam emitted from a light source is reflected and deflected by a deflector such as a rotating polygon mirror, and is sent at a constant speed in a direction relatively perpendicular to the direction of deflection (sub-scanning). Main scanning is performed on the surface to be scanned, and the surface to be scanned is two-dimensionally scanned. However, with the rotating polygon mirror used in conventional scanning devices, it is technically difficult to make each reflecting surface on which the light beam enters completely parallel to the rotation axis of the rotating polygon mirror, resulting in so-called surface tilt. There are many cases where this happens. When such a surface tilt occurs, the reflection direction of the light beam reflected by each reflecting surface will be different in the sub-scanning direction, resulting in unevenness in the interval (pitch) of the main scanning lines formed on the scanned surface. This has the disadvantage of causing a problem.

Various methods have been proposed in the past to eliminate the above-mentioned pitch irregularities, and among them, many scanning devices have been proposed that eliminate pitch irregularities by optical means such as anamorphic optical systems. $2-86210 etc.). In other words, a light beam scanning device equipped with an anamorphic optical system is equipped with an incident optical system such as a cylindrical lens between a beam source and a rotating polygon mirror, and directs the light beam to the rotating polygon mirror. is incident as a line image perpendicular to , and between the rotating polygon mirror and the scanned surface, the rotating polygon mirror and the scanned surface are placed in a conjugate relationship in the sub-scanning direction.
An anamorphic optical system is installed to form a point image of the light beam incident on the rotating polygon mirror as a line image on the surface to be scanned. The image is formed at a predetermined position.

However, in order to correct pitch unevenness with high precision using such an optical method, it is necessary to improve the performance of each optical element of the anamorphic optical system, and such optical elements are expensive and expensive. Even with such a method, it is difficult to completely eliminate the pitch unevenness due to the curvature of field of the correction optical system and the movement of the reflection position of the light beam within the same reflection plane due to the rotation of the rotating polygon mirror. There is a problem in that some periodic pitch unevenness remains.

Furthermore, in the rotating polygon mirror, it is technically difficult to make the reflectances of the reflecting surfaces completely equal between the reflecting surfaces, and variations in reflectance often occur. When the reflectance varies from reflection surface to reflection surface, intensity unevenness occurs in the light beam scanning the surface to be scanned, and density unevenness appears in the final image. Therefore, has a device been proposed that adjusts the intensity of the light beam in response to the variation in the reflectance determined in advance (Japanese Patent Application Laid-Open No. 178920/1983)? It is difficult to remove such particles, and the correction accuracy may be insufficient in devices that require highly accurate scanning of a light beam, such as an image recording device that records so-called continuous-tone images.

(Problem to be Solved by the Invention) Therefore, in order to eliminate the scanning unevenness inherent to each reflecting surface of the rotating polygon mirror, such as the above-mentioned pitch unevenness of the main scanning line and intensity unevenness of the light beam, it is necessary to Dimensional accuracy and reflectance accuracy must be extremely high, resulting in the disadvantage that the manufacturing cost of the rotating polygon mirror increases significantly.

The present invention has been made in view of the above-mentioned problems, and
without significantly increasing the manufacturing cost of rotating polygon mirrors.
It is an object of the present invention to provide a light beam scanning device that can reduce the influence of the above-mentioned scanning unevenness on image quality.

(Means and effects for solving the problem) Even if the above-mentioned scanning unevenness occurs in the light beam scanning device, as long as the scanning unevenness is to the extent that it cannot be visually recognized, it can be considered that the scanning unevenness does not pose a problem in practice. can. Human visual sensitivity to visually recognize scanning unevenness depends on the spatial frequency of the main scanning line. For example, the visibility limit value of the density difference in the main scanning line due to the reflectance variation of the reflective surface of a rotating polygon mirror is As shown in Figure 2, the visual sensitivity becomes the lowest and the highest when the spatial frequency is 1/dragon. Moreover, when the spatial frequency becomes larger than this, visual sensitivity rapidly decreases. In addition, the visibility limit value of the pitch unevenness of the main scanning line due to the surface tilt of the rotating polygon mirror is
Similarly, visual sensitivity becomes the smallest near one spatial frequency ZIIIl, and as the spatial frequency increases, visual sensitivity rapidly decreases. The pitch of main scanning lines in a scanning device using a rotating polygon mirror is usually 80 to 100 μm, and the number of surfaces of a rotating polygon mirror is 6 to 1
Since it is an O-plane, the spatial frequency of the main scanning line is at most 2/
am, and the minimum is about 1 line/l1111. Therefore, it can be considered that in such an apparatus, as the spatial frequency becomes smaller, scanning irregularities such as density irregularities and pitch irregularities become more noticeable.

The present invention was derived based on the above-mentioned findings, and includes a rotating polygon mirror having 01 reflective surfaces (where nl is a natural number excluding a prime number), and includes a rotating polygon mirror having 01 reflective surfaces (nl is a natural number excluding a prime number), and every 02 reflective surfaces among the reflective surfaces (nl is a natural number excluding a prime number). , n2 is a natural number such that n2+1 is a divisor of n1 excluding nl).

That is, the scanning device of the present invention increases the spatial frequency of the above-mentioned main scanning line by 02+1 times by thinning out the reflecting surface of the rotating polygon mirror, thereby making the above-mentioned scanning unevenness difficult to see. be. Note that in order to increase the spatial frequency by reducing the number of reflecting surfaces used, it is possible to use a rotating polygon mirror with the number of surfaces such as n1/2 surface or nl/3 surface in advance; -6
In this case, the number of reflective surfaces of the rotating polygon mirror is 3 and 2.
This makes it difficult to use in reality. Also, if the number of reflective surfaces in the shell decreases, the light beam will be affected by the wind generated by the rotation of the rotating polygon mirror, making stable scanning more likely to be hindered. Regardless, it is desirable to have a large number of rotating polygon mirrors. Therefore, the apparatus of the present invention can increase the spatial frequency of the main scanning line without increasing the influence of the wind, thereby reducing the influence of scanning unevenness.

In this device, in order to prevent the light beam from entering the scanned surface due to a reflective surface other than the reflective surface used, such a reflective surface must prevent the emission of the open beam on the optical path of the light beam. It may be possible to interrupt the
The structure of such a reflecting surface may be changed so that the light beam cannot be incident on the surface to be scanned.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic perspective view of a light beam scanning recording device which is an embodiment of the present invention.

In this device, a semiconductor laser 2 is used as a light source that emits a light beam 1 that is recording light.
After being shaped into a beam with a predetermined cross-sectional shape by the cylindrical lens 4, the beam is made incident on the reflecting surface of the rotating polygon m5 as a line image perpendicular to the rotation axis of the rotating polygon mirror.

The rotating polygon mirror 5 has six reflecting surfaces 5a and 5b.

5c, 5d, 5e, and 5f, and reflect and deflect the light beam 1 by rotating at high speed in the direction indicated by the arrow. On the optical path of the deflected light beam, there is a lens group that forms a point image on the recording surface 7, which is the surface to be scanned, from the light beam 1 that has entered the reflective surface as a line image as described above. An imaging lens 6 is provided, and the light beam 1 that has passed through the imaging lens 6 repeatedly scans the recording surface 7 in the direction of arrow B. The recording surface 7 is conveyed at a constant speed in the direction of arrow C, which is substantially perpendicular to the main scanning direction, and is sub-scanned, and the recording surface 7 is two-dimensionally scanned by the light beam 1. Moreover, since this device is equipped with the above-mentioned cylindrical lens 4 and imaging lens 6, the rotating polygon #1'! The pitch unevenness of the main scanning line due to the surface tilt of the reflecting surface of No. 5 can be corrected to a certain extent.

The semiconductor laser 2 is capable of so-called analog direct modulation in which the output is changed by changing the drive current, and the semiconductor laser drive circuit 8 drives the semiconductor laser 2 according to the output signal of the image signal output circuit 9. A light beam 1 having an intensity corresponding to the output signal (image signal) is emitted. Therefore, image information based on the image signal is recorded on the recording surface 7.

By the way, in this scanning device, the pitch of the main scanning lines formed on the recording surface 7 is, for example, 100 μm, and when all six reflective surfaces 58 to 5f of the above-mentioned rotating polygon ff15 are used, the trouble of each reflective surface is Scanning unevenness due to deviation and reflectance variation is 100μ771x5-800μm
Even if the period is , the spatial frequency of scanning unevenness is about 1.7 lines/ll11. On the other hand, in this example,
The above six reflective surfaces are used every other side, and the reflective surface 5g,
Only 5c and 5e reflect the light beam. That is, this scanning device includes a signal generating means lO that outputs a timing signal every time the reflecting surface on which the light beam 1 is incident is switched in synchronization with the rotation of the rotating polygon mirror 5, and the image signal output circuit 9 outputs an image signal according to the signal emitted from the signal generating means 10 only while the reflecting surfaces 5a, 5c, and 5e are located on the optical path of the light beam 1, and reflects the image signal on the optical path of the light beam 1. Surfaces 5b, 5d, 5f
The output of the image signal is stopped while the is located. When the output of the image signal is stopped, the light beam 1 is no longer emitted from the semiconductor laser 2 and the recording surface 7
A main scanning line is formed above by only the light beams reflected by the reflecting surfaces 5a, 5c, and 5e. Note that the signal generating means IO may store the timing of movement of each reflecting surface in advance, or may obtain information indicating the rotation of the rotating polygon mirror from a drive means for the rotating polygon mirror, etc. The above-mentioned timing signal may be generated.

If every other reflective surface of the rotating polygon mirror is used in this way, the above-mentioned scanning unevenness can be reduced to 100 μm x 3-30 μm.
The spatial frequency of scanning unevenness is approximately 3 μm.
．． 3 / become concerned. Therefore, the spatial frequency increases significantly compared to the case where all six reflecting surfaces are used, and scanning irregularities such as pitch irregularities of scanning lines and density irregularities become less visible. Therefore, according to the present device, even if a rotating polygon mirror with the same accuracy as the conventional one is used, scanning unevenness becomes less noticeable, so it is possible to improve the quality of reproduced images without increasing manufacturing costs. Furthermore, if the conventional level of image quality is sufficient, the finishing precision of the rotating polygon mirror can be relaxed, and the manufacturing cost thereof can be reduced. For example, when all six reflecting surfaces are used as in the conventional case, the variation in the reflection rate of each reflecting surface is 0.
It was desired that the variation in reflectance be within 0.4%, and that the surface inclination of each reflective surface be within 10'. ′
It became possible to expand each within the same period.

Note that in order to thin out the reflective surfaces and use them without changing the recording speed for the recording surface 7, it is necessary to increase the rotational speed of the rotating polygon mirror 5 by twice as much as when using all the reflective surfaces. If it is difficult to increase the rotation speed of the rotating polygon mirror 5 compared to the conventional one, the conveyance speed of the recording surface 7 may be slowed down so that main scanning lines are formed at a predetermined pitch.

Furthermore, the number of reflective surfaces of the rotating polygon mirror used in the device of the present invention is not limited to six, but four, eight,
If a certain number of reflective surfaces are always used (i.e., the number of surfaces is not a prime number) when the reflective surfaces are thinned out by a predetermined number of surfaces, such as 9 or 10, then after any number of surfaces, It's good. Further, the reflective surfaces used are not limited to every other surface as in the above embodiment, but may be every second or third surface, or the like. Further, as a light source for emitting a light beam, in addition to a semiconductor laser, a gas laser, a solid laser, or the like can be used. In that case, since these lasers cannot be directly modulated, an acousto-optic modulator (
AOM) etc. may be used.

Furthermore, in order to prevent the light beam from scanning the recording surface by the thinned out reflective surfaces, in addition to stopping the light beam emission as in the above embodiment, the inclination of the thinned out reflective surfaces is changed and these The light beam reflected by the reflective surface may be prevented from entering the recording surface. Even in that case, while the light beam is incident on the reflecting surface to be thinned out,
It is necessary to avoid modulation based on the image signal.

In addition, if the device is equipped with an optical system for correcting tilting as in the embodiment described above, the light beam that is tilted and reflected in the vertical direction is also guided to a predetermined scanning position by the optical system. Therefore, it is necessary to increase the inclination of the reflecting surface to such an extent that the light beam does not enter the elements of these optical systems.

Further, the light beam scanning device of the present invention may be a recording device that records a continuous tone image, or a recording device that records a binary image, or an image that is accumulated and recorded on a stimulable phosphor sheet. It may be a reading device such as a radiation image information reading device that scans information with excitation light and reads image information photoelectrically.

(Effects of the Invention) As explained above, according to the light beam scanning device of the present invention, since the reflecting surfaces of the rotating polygon mirror are thinned out at predetermined intervals, scanning by the wind of the rotating polygon mirror is It is possible to reduce the spatial frequency of scanning irregularities such as pitch irregularities of main scanning lines and density irregularities, without increasing the influence of the scanning irregularities, thereby making the scanning irregularities less noticeable. Therefore, it is possible to improve the image quality of the finally obtained image, or to reduce the manufacturing cost by loosening the finishing precision of the rotating polygon mirror.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view of a light beam scanning recording apparatus according to an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the visibility limit value of the density difference of the main scanning line and the spatial frequency. 1... Light beam 5... Rotating polygon mirror 5a,
5b, 5c, 5d, 5e, 5f--Reflection surface 7...Recording surface 8...Semiconductor laser drive circuit 9...Image signal output circuit 10...Signal generation means Cm18 bulge

Claims (1)

[Claims] A scanned surface that deflects a light beam in the main scanning direction by a rotating polygon mirror having n_1 reflective surfaces (n_1 is a natural number excluding a prime number) and moves it in the sub-scanning direction relative to the light beam. In the light beam scanning device for scanning two-dimensionally, among the reflective surfaces of the rotating polygon mirror, n
A light beam characterized in that the surface to be scanned is scanned only by the light beam incident on a predetermined reflective surface every two surfaces (n_2 is a natural number such that n_2+1 is a divisor of the n_1 excluding the n_1). scanning device.