JPS6098418A - Optical scanner - Google Patents

Abstract

PURPOSE:To reduce a shift of a light spot position by using a polyhedral rotary mirror of a multiple structure consttituted of plural polyhedral mirrors. CONSTITUTION:A polyhedral rotary mirror 7 is formed by sticking two polyhedral mirrors 12, 13 with a difference of a phase angle alpha, and two beams 21, 22 are scanned with a time difference DELTAt. DELTAt=alpha/omega, provided that omega is an angular velocity of the polyhedral rotary mirror 7. In this state, if a variation occurs in a revolving speed of the polyhedral rotary mirror 7, when a set value or a design value of the time difference DELTAt and the angular velocity omega are deonted as DELTAtd and omegad, respectively, and those which are caused by a variation of the rotation are denoted as DELTAtc and omegac, respectively, a shift DELTAx of a light spot position after T seconds from the scanning start point is shown by DELTAx=(vd-vc)T=2FalphaT(1/DELTAtd-1/DELTAtc). Provided that vd and vc denote a set value or a design value of an optical scanning speed, and that which is caused by a variation of the rotation, respectively, and F denotes a focal distance of an Ftheta lens. When a design value of a time T extending from a scanning start point to a recording point, and that of a time of a variation of the rotation are denoted as Td and Tc, respectively, DELTAx=vdTd-vcTc=2Falpha(Td/DELTAtd-Tc/DELTAtc) is obtained, and the time T can be varied by changing a picture signal click, and the sift DELTAx can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device, and more particularly to an optical scanning device used in a laser printer or an optical reader.

Conventionally, when realizing recording or reading by scanning a light beam on a surface such as a laser printer or an optical reading device, a light source such as a laser and a light beam emitted from the light source are directed onto the surface to be scanned. An optical scanning device is used that includes a polygonal rotating mirror for scanning and a scanning start detector for detecting rare fish light for determining a scanning reference point for the optical scanning. In this device, it is possible to perform light scanning to some extent by using only a light source and a polygonal rotating mirror, but it is impossible to recognize the position of the light spot, and synchronization with an external circuit is difficult, so a scanning start detector is required. A scanning reference signal is generated so that an external circuit can, in principle, accurately recognize the position of the light spot.

If the scanning start detector performs optical scanning at a constant angular velocity, the position of the light spot can be accurately determined, but if the rotational speed of the polygonal rotating mirror fluctuates or the mirror surface is uneven, Light scanning no longer has a constant angular velocity. Therefore, a deviation occurs between the position of the light spot estimated by the external circuit based on the scan reference signal generated from the scan start detector and the position of the light spot that is actually being scanned. If an optical scanning device with such a misalignment is used for laser printing, it will appear as jitter on the recording surface, and if it is used for optical reading, it will appear as jitter on the read signal, both of which will have a serious negative impact on image quality. This will affect the

In order to compensate for such jitter, efforts have been made to improve the rotation accuracy and surface processing accuracy of multifaceted rotating mirrors, but this has the problem of limitations in terms of cost and yield p.几.

An object of the present invention is to provide an optical scanning device that can reduce the deviation of the light spot position in the optical scanning device, achieve accurate synchronization with an external circuit, and further reduce the rotational accuracy and surface processing accuracy of a polygonal rotating mirror. The goal is to provide equipment.

According to the present invention, in an optical scanning device having a light source, a polygonal rotating mirror, and a scanning start detector, the polygonal rotating mirror is of a multi-NW structure made up of a plurality of polygonal mirrors. An optical scanning device is obtained.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an optical system of a laser printer showing an embodiment of the optical scanning device of the present invention, FIG. 2 is a plan view showing an example of the polygonal rotating mirror in FIG.
FIG. In the figure, a laser beam emitted from a laser l is split by a beam splitter 2 into two beams 21, 22 and fx9, a beam 21 is incident on an optical switch 3, and a beam 22 is reflected by a reflecting mirror 5. After that, the light enters the optical switch 6. Here, the main switch 3 is operated by the recording image signal of the beam 21 shown by the one-dot chain line, and the optical switch 6 starts scanning when the laser beam (beam 22) shown by the two-dot chain line is scanned. This is so that the beam is irradiated only in the vicinity of the detector 10 and is closed off in other areas, so that the beam does not affect the recording medium 11 in the recording range. Double beam 21.2
2 are reflected by reflecting mirrors 4 and 8, respectively, and then rotated by a polygonal rotating mirror 7.
The light is incident on the recording medium 11, is p-scanned by the polygon mirrors 12 and 13 shown in FIG. 2, is focused by the Fθ lens 9, and is irradiated onto the recording medium 11. The polygonal rotating mirror 7 is shown in Fig. 2 fa),
As shown in (b), two polygon mirrors 12 and 13 have a phase angle α
It is constructed by pasting them together with a difference of .

Therefore, the time difference Δt between the two beams 21 and 22 is expressed by the following equation:
scanned.

Δt=α/ω (1) However, ω is the angular velocity of the polygonal rotating mirror 7.

These two polygon mirrors 12 and 13 are cut and polished at the same time and are bonded together so that the corresponding surfaces have a phase and α, thereby making it possible to create a structure that is free from the influence of the 5-division error. The two beams 21 and 22 that are also scanned
can be adjusted to scan on the same line on the surface of the recording medium 11 and the detection surface of the scan start detector 10 by adjusting the inclination angles of the reflecting mirrors 4 and 8. Therefore, the scan start detector 10
Then, after the recording beam scanned by the polygon mirror 12 is detected, the scanning light by the polygon mirror 13 is detected after a time Δ has elapsed.

Here, if a change occurs in the rotation speed of the polygonal rotating mirror 70.

The angular velocity ω changes and the time difference Δt becomes different from the initially set value. By detecting and recognizing this time difference Δt, it is possible to reduce the shift in the position of the light spot. In other words, the set values or design values of time difference Δt and angular velocity ω are respectively Δtd and ω4, and the difference due to rotational fluctuation is Δ
te, ω8, the deviation ΔX of the light spot position after T seconds from the scanning start point is expressed by the following equation.

Δx = (vd-Ve)T = 2pαT (1/Δt<
1/Δte)...[21 However, v4 and v8 are values based on the set value or design value of the optical scanning speed and rotational fluctuation, respectively, and F is the focal length of the Fθ lens.

Here, assuming that the time T from the scanning start point to the recording point can be changed due to rotational fluctuations, the design value of 5 hours T is T41.
Let Ta be the value at the time of rotational fluctuation.

Δx=v4TlI−vcT,=2Fα(T4/Δt4T
c/Δ is obtained as follows: 2 hours T8 can be changed by changing the clock that manages the image signal. That is, by making it possible to switch the light beam of the image signal clock or the frequency division ratio of the frequency division stage depending on the value of the time difference Δ1c, the shift ΔX can be reduced. Actually, F.

α, T□Δt are quantities that can be determined at the time of design, and the maximum or minimum value of Δ1c can be suppressed from the specifications of the rotation accuracy of the polygonal rotating mirror.

A design value for the time T6 can be obtained from a general conditional expression that suppresses ΔX below the jitter standard value.

In this embodiment, a method that requires some kind of calculation is shown, but a simpler method is to set α=36 (1/2N (where N is the number of polygonal mirrors) and detect the scanning light by the polygonal mirror 12 in the first half of scanning. By using the signal as the scanning reference signal and using the signal from the polygon mirror 13 as the scanning reference signal in the second half of scanning, it is possible to reduce the deviation.In this case, by increasing the number N of polygon mirrors, the deviation can be reduced even more precisely. be able to.

As is clear from the above description, according to the optical scanning device of the present invention, the polygonal rotating mirror is made into a multiplexed structure consisting of a plurality of polygonal mirrors to increase the chances of recognizing the scanning reference point. This not only has the technical effect of reducing noise and achieving accurate synchronization with an external circuit, but also has the economical effect of reducing the rotation accuracy and surface processing accuracy of the multifaceted rotating mirror.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical system of a laser printer showing an embodiment of the optical scanning device of the present invention, and FIGS. 2 fa) and [b) are plan views showing an example of the polygonal rotating mirror in FIG. FIG. In the figure, ■... Laser, 2... Beam splitter, 316... Optical switch, 4.
5. (3...Reflector, 7...Polygonal rotating mirror, 9...Fθ lens lO...Scan start detector b11...Record Body, 12°13・
...Polygon mirror% 21.22 ...Beam procedure amendment (voluntary) Commissioner of the Japan Patent Office 1, Indication of case 1982 Patent application No. 207029
No. 2, Title of the invention: Optical scanning device 3, Relationship to the amended case: Applicant: Shiba 1i, I', Minato-ku, Tokyo 33-1 (423)
NEC Corporation Representative: Tadahiro Sekimoto 4, Agent: 108 Shiba-go-cho, Minato-ku, Tokyo +1:17 Yama) 1shi: I
l', + 1llln (Contact information: Japan As shown by the dashed dotted line, "Im 21" is deleted.

Claims (1)

[Claims] 1. An optical scanning device comprising a light source, a polygonal rotating mirror, and a scanning start detector, wherein the polygonal rotating mirror has a multiplexed structure composed of a plurality of polygonal mirrors.