JPS6118729B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light beam scanning device using a polygonal rotating mirror, and aims to improve its light utilization efficiency and increase its scanning frequency.

Displaying, recording, and reproducing information using laser light;
Examples of reading devices include laser printers, laser facsimiles, laser displays, barcode and character reading devices, and the like. In order to scan the laser beam in these devices, polyhedral rotating mirrors with excellent rotational stability, angular accuracy, and flatness are widely used.

FIG. 1 is a diagram showing a light beam scanning method using a normal polygonal rotating mirror. 1 is a rotating polygon mirror,
When the laser beam 2 is incident on the reflective surface 1a, it is reflected by the reflective surface 1a and is focused onto the scanning surface 4 by the projection lens 3. When the rotary mirror 1 rotates in the direction of the arrow, the angle between the reflective surface 1a and the incident light 2 changes continuously.
The scanning plane 4 is scanned by moving upward in the direction of the arrow. However, since scanning is performed using a polygonal rotating mirror, when the rotating mirror is located at the position shown by the dashed line, for example, the incident light 2 is irradiated across the two surfaces 1a and 1b,
In this case, the shape of the light beam reflected by the reflecting surface 1a becomes a semicircular shape, and the amount of light decreases.
The spot diameter at the top also has an abnormal shape, making it insufficient as a scanning light for reading and writing information. A complete beam spot suitable for reading and writing information is obtained only when the rotating mirror is further rotated from this angle so that all of the incident light 2 is incident on the same reflecting surface 1a, as shown by the solid line. Even when the rotating mirror 1 rotates further and the angle between the reflecting surfaces 1a and 1c comes to the position of the incident light 2, the spot of the scanning light 21 becomes incomplete. Therefore, a beam with a slit 5 is selected so that such a scanning light with an incomplete light spot is blocked and only the complete scanning light with the same entire beam diameter of the incident light reaches the scanning surface 4. A plate 6 is used to cut off the scanning light at both ends in the scanning direction. As a result, the light utilization efficiency becomes extremely poor.

In addition, in order to increase the speed of reading and writing information, that is, the optical scanning frequency, the rotating mirror is supported with high-precision air bearings, etc. to rotate the drive motor at high speed, and the number of surfaces of the rotating mirror is increased. . However, increasing the number of rotations has a limit due to the precision and performance of the rotation axis of the drive motor, and increasing the number of mirror surfaces leads to a decrease in the above-mentioned light utilization efficiency. The problem also appears.

Therefore, the purpose of the present invention is to solve these problems all at once, and to achieve this purpose, the present invention provides a plurality of light beams on the reflective surface of a polygonal rotating mirror in the scanning direction. In the same plane,
Means for making the light incident at different angles is provided, and a slit means is provided at a position in front of the scanning surface to allow only the scanning light to pass through when each light beam is reflected at the center of each reflecting surface of the polygonal rotating mirror. The length A of the slit means is set so that A≦b, where A is the length of the slit means in the scanning direction, and b is the interval between adjacent light spots on the slit means. The structure is as follows.

Next, details of the present invention will be explained based on illustrated embodiments. FIG. 2 is a diagram showing the basic configuration of the present invention, and the polygonal rotating mirror 1, the imaging lens 3, etc. are the same as in the prior art. In the present invention, a plurality of incident lights are made incident on the rotating mirror 1 as indicated by α, β, γ, and each of the incident lights α, β, γ is in-plane in the scanning direction of the scanning light, and the rotating mirror 1 is are arranged so that they are incident at different angles. That is, a plurality of incident lights α,
For example, if the angle between β and γ is +θ in the plane of the scanning direction. In addition to being shifted as shown by -θ, they are also crossed once in the middle.

In this configuration, when the rotary mirror 1 rotates counterclockwise as indicated by the arrow, considering one reflective surface 1a, the incident light γ is first applied to the reflective surface 1a, then β and α are irradiated to the reflective surface 1a in this order. That is, when the reflective surface 1a is located at the position indicated by the chain line as 1a', only the incident light γ enters the area of the reflective surface 1a', and it is rotated by a certain angle from that position. The incident light β enters the reflecting surface 1a' for the first time, and it is not until it rotates further and reaches the position 1a shown by the solid line that the incident light α
irradiates. At this time, the first incident light beam γ is just before leaving the reflecting surface 1a and entering the next reflecting surface 1c. In this way, the incident light enters one reflective surface of the rotating mirror in the order of γ, β, and α, leaves the reflective surface in the same order, and enters the area of the next reflective surface. In this case as well, the beam selection plate 6' is used to block the scanning lights γ' and α' caused by the light incident on the ends of the reflective surface, as shown in the incident lights γ and α in the figure, and to block the scanning lights γ' and Only the light incident near the center of the reflecting surface, as indicated by β, reaches the scanning surface 4 and is used for scanning.

In this way, the reflected light, that is, the scanning light α′, β′, γ′ reflected on the reflecting surface of each incident light α, β, γ
, only the light near the center in the scanning direction that is suitable as the scanning light is selected and used. Each of the scanning lights α', β', and γ' passes through the slit 5 and passes through the scanning surface 4.
By setting the scanning interval as shown in Figure 3, the light can be used 100% effectively. In other words, if the number of reflective surfaces of a reflective mirror is n, then during the rotation angle (2π/n) of one reflective surface, one of the light beams α', β', and γ' always scans the scanning surface. Set to . If the number m of incident lights is three as in the illustrated example, the slits 5 are selected so that the rotation angle (2π/n) of the rotating mirror is divided into three equal parts.

In this way, when there are three incident lights, γ', β',
By sequentially scanning with three scanning beams such as α', γ', β', and α', it is possible to always scan with one of the beams within the rotation angle (2π/n) of one surface. It is easy to increase the light utilization rate to nearly 100%. In addition, within the rotation angle, it is possible to obtain the same number of scanning lights as the number of incident lights (m), and the scanning frequency is m times higher than the conventional rotation mechanism and efforts to improve the number of reflective surfaces. , the scanning frequency is significantly improved.

Next, let us consider the above relationship mathematically. When the focal length of the imaging lens 3 is f and the rotation angle of the rotary mirror 1 is the rotation angle, the scanning distance L on the scanning plane by one scanning light is as follows.

L=f· According to the present invention, when the incident angles of each of the plurality of incident lights are shifted by θ in the scanning direction, the interval b between each light spot on the scanning plane becomes b=f·θ. Therefore, in order to prevent two or more beam spots from forming simultaneously on the scanning plane, the fourth
The size of the slit may be designed so that the length A of the slit 5 shown in the figure satisfies A≦b. This increases the light utilization rate to 100% or 100%.
It will be improved soon. Note that d... is a scanning beam spot.

Next, the angle of incidence θ of each incident light α, β, and γ on the rotating mirror
teeth, becomes. That is, as shown in FIG. 3, in order to scan continuously with a plurality of scanning beams at constant angular intervals, the angles between the incident beams may be shifted by π/nm.

The amount of deviation a of each incident light spot on the reflecting surface shown in FIG. 2 is expressed by the following equation, where r is the radius of the rotating mirror.

a≈2πr/nm By designing the light source system, light beam deflection system, and scanning light selection means to optimal values as described above, the optimal light utilization rate and scanning frequency can be obtained.

In order to perform high-resolution scanning by reducing the scanning beam diameter, the beam diameter of the incident light to the imaging lens must be correspondingly large, and for this purpose an expander lens is placed in the optical path of the incident light. Efforts are being made to expand the beam diameter. However, when the diameter of the incident beam is expanded, the diameter of the incident beam becomes larger relative to the reflecting surface of the rotating mirror, and the effective scanning range becomes correspondingly shorter, further reducing the light utilization efficiency.
Although it is possible to prevent the light utilization efficiency from decreasing to some extent by increasing the diameter of the rotating mirror, it is difficult to manufacture or drive the mirror, and no great effect can be expected. According to the present invention, even if the diameter of the incident beam becomes thicker, the light utilization rate can always be maintained at nearly 100% by simply increasing the number of incident beams accordingly, so when high-resolution and high-speed scanning is desired. It can have a particularly remarkable effect.

As the imaging lens 3, an f-theta lens having an f-theta characteristic is usually used so that the scanning light can always move on the scanning plane at a constant speed regardless of the angle at which the scanning light is incident on the imaging lens. Therefore, according to the present invention, even if the incident angles of the α, β, and γ beams are different, a constant scanning speed can be obtained in any scanning.

In the illustrated example, a slit is used as a means for controlling the range of use of the scanning light, but the method is not limited to this.
For example, various known light control means can be employed, such as placing an optical shutter in the optical path and controlling it, or using an optical modulator.

To obtain multiple incident beams, the laser light sources 7, 7', etc. may be added as shown in Fig. 5, or one laser light source 7 may be added as shown in Fig. 6.
The beam may be divided into multiple beams. In the case of FIG. 6, the half mirror 8 and the reflecting mirror 9 are used to split one beam and obtain the incident angle θ to the rotating mirror, but a similar operation may be performed using a prism. Since the incident light on the rotating mirror is a parallel beam,
There is no problem even if the optical path lengths of the respective incident lights are different in this way. Note that 10 is an expander lens for increasing the beam diameter of incident light, and 11 is a rotating mirror drive motor.

As described above, according to the present invention, a plurality of lights are incident on the rotating mirror, and the angle of incidence on each rotating mirror is made different within the plane of the scanning direction, thereby increasing the light utilization efficiency by 100%. %, and the scanning frequency can be increased by an integral multiple in proportion to the number of incident lights. Moreover, since the structure and control are not particularly complicated, it can be widely used for reading, writing, or recording various types of data, and has excellent versatility.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional laser beam scanning device, FIG. 2 is a side view showing the basic configuration of the laser beam scanning device according to the present invention, FIG. 3 is a time chart showing scanning intervals by multiple scanning beams, and FIG. This figure is a plan view of the scanning beam selection slit, and FIGS. 5 and 6 are diagrams illustrating a method for obtaining a plurality of incident beams. In the figure, 1 is a rotating mirror, 3 is an imaging lens, and 4 is a rotating mirror.
is a scanning surface, 5 is a slit, α, β, and γ are incident lights (laser beams), and α', β', and γ' are scanning lights.

Claims (1)

[Claims] 1. A plurality of light beams are directed onto the reflective surface of a multifaceted rotating mirror,
A means is provided to make the light enter at different angles in the same plane as the scanning direction, and only the scanning light when each light beam is reflected at the center of each reflective surface of the polygonal rotating mirror is placed in front of the scanning plane. Provided is a slit means that allows light to pass through, and if the length of the slit means in the scanning direction is A, and the interval between adjacent light spots on the slit means is b, then the length of the slit means is set so that A≦b. A light beam scanning device characterized in that A is set.