JPS63206718A - Optical scanner - Google Patents

Abstract

PURPOSE:To effectively prevent attraction of a rotor to a yoke or axial run-out by forming the pole ends of a yoke to apply electromagnetic driving force to the rotor as a pair of pole pieces which sandwich the turning locus of the rotor from above and below along the axial direction of a torsion bar. CONSTITUTION:The torsion bar 16 is fixed and held to supporting arms 12, 14 provided at both ends of a base plate 10 and the rotor 22 is fixed to nearly the central part thereof. The yoke 25 having an approximately U-shaped plane section is disposed to the position corresponding to the rotor 22. The pole ends 26, 27 formed to a pair of the pole pieces sandwiching the turning locus of the rotor 22 from above and below along the axial direction of the torsion bar 16 are provided to the yoke 25. Electromagnetic driving power is applied from the ends 26, 27 to the rotor 22 by the electric current flowing in an excitation coil 28 and a light beam 100 projected to a reflecting mirror 24 according to the rotating angle of the rotor 22 is reflected as scanning light 200. Generation of a trouble such as the axial run-out of the rotor 22 or the attraction of the rotor to the yoke 25 is obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a yoke that provides electromagnetic drive to a rotor in an optical scanning device, particularly a galvanometer type optical scanning device.

[Prior Art] Optical scanning devices that deflect and scan laser beams or other light beams are widely used in object recognition devices that read two-dimensional or three-dimensional objects, image display devices, laser printers, and the like.

There are various types of optical scanning devices, such as electro-optic, acousto-optic, hologram, and one-sided rotating mirror systems. The method is known.

The galvanometer type optical scanning device is manufactured by the Japanese Patent Publication Publication No. 50-14
02) JP-A-51-87708 or JP-A-53-1
43910, a rotor that is fixed to a torsion bar and has a reflection mirror on a part thereof is electromagnetically driven, and a light beam is irradiated onto the mirror, and when the rotor rotates, a desired scanning beam is generated by the reflected beam. It is characterized by obtaining.

According to this type of galvanometer type optical scanning device, high-speed optical scanning is possible due to the high natural frequency of the vibration system including the torsion bar, and for example, in recent laser printers, etc., a latent image is written on the photosensitive drum surface. This is extremely useful for obtaining high-resolution scanning beams.

[Problems to be Solved by the Invention] However, as is well known, conventional optical scanning devices generate driving magnetic flux opposite the extreme outer circumference of the rotor in order to apply electromagnetic driving force to the rotor. A static neutral position of the rotor is set at a position where the rotor and the yoke face each other.

Therefore, according to such a facing drive mechanism, an electromagnetic driving force is applied when the rotor is in a static neutral position, and this driving force causes the rotor to be attracted to the yoke.

That is, the rotor is suspended by torsion bars, and only rotational movement of the rotor is necessary for optical scanning, but because of the suspension structure by the relatively long torsion bars, the rotor shaft itself is extremely susceptible to bending. As a result, when an electromagnetic driving force acts between the rotor and the yoke at a position where they face each other or at a position close to this, this electromagnetic driving force is applied not only in the direction of rotation of the rotor but also in the direction of rotation of the rotor. This causes a problem in that when the torsion bar is deflected, the rotor comes to a halt while being attracted to the yoke.

Furthermore, even if the rotor is not attracted to the rotor, if an electromagnetic driving force is applied when the rotor and yoke are close to each other, this will cause axial wobbling in the rotor axis, making it difficult to obtain stable scanning light at the bottom of the rotor. The problem was that I couldn't do it.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide an improved optical scanning device that can effectively prevent adhesion of the rotor to the yoke or axial wobbling in a galvanometer type optical scanning device. Our goal is to provide the following.

[Means for Solving the Point of Connection] In order to achieve the above object, the present invention provides a means for resolving the rotation of the rotor by connecting the extreme end of the yoke that applies electromagnetic driving force to the rotor suspended by torsion bars fixed at both ends. The track is formed as a pair of pole pieces sandwiched at the top and bottom along the axial direction of the torsion bar,
It is characterized in that an electromagnetic attractive force for rotationally driving the rotor is applied from this pair of pole pieces.

[Operation] Therefore, according to the present invention, the electromagnetic driving force for rotationally driving the rotor is applied from the pair of pole pieces that are the ends of the yoke. That is, the electromagnetic attractive force generated between the rotor and the yoke end is applied equally to the rotor from two downward directions along the axial direction of the torsion bar.

In this way, the rotor is rotationally driven by the electromagnetic attraction force generated in the vertical direction, so the electromagnetic attraction force applied from the direction perpendicular to the axis of the torsion bar is weakened, and the axial force generated by the rotor being pulled in the lateral direction is weakened. There is no risk of problems such as blur or adhesion to the yoke.

[Example] Preferred embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the main parts of an optical scanning device according to the present invention, which is suitable as an optical scanning device for forming a desired latent image on a photosensitive drum surface in, for example, a laser printer.

In the figure, support arms 1 provided at both ends of the base 10
At 2.14, a torsion bar 16 is firmly fixed at both ends. That is, both the support arms 1
A tightening piece 18.20 is attached to the tip of the torsion bar 12.20 so that it can be tightened with a bolt, and the large diameter portions 16a and 16b at both ends of the torsion bar 16 fit into the V groove provided on the end face of each support arm 12.14. It is firmly tightened and fixed in the state where it is positioned at 12a and 14a.

A rotor 22 is predetermined in the torsion portion of the torsion bar 16, approximately at the center of the torsion bar 16 in the embodiment, and the torsion bar 16 and rotor 22 form an armature 23 of a galvanometer.

Therefore, it is understood that the armature 23 forms a resonant vibration system of a predetermined frequency by the torsional vibration of the torsion bar 16.

The rotor 22 is provided with a reflective mirror, and in the embodiment, the reflective mirror of the rotor 22 is formed from a portion whose side surface is polished to a mirror surface, and is designated by reference numeral 24 in the figure.

The rotor 22 receives an electromagnetic driving force from an electromagnetic driving device as described later, and is therefore made of a high magnetic permeability material such as permalloy, and the reflecting mirror 24 is made of permalloy which is mirror-polished and further plated with nickel and vapor-deposited with aluminum. The surface is finished with a high reflectance and reflects the light beam 100 irradiated from a laser light source (not shown) as a scanning light 200, and the direction of reflection of the scanning light 200 is determined according to the rotation angle of the rotor 22. can be arbitrarily selected or moved.

At a position corresponding to the rotor 22, a yoke 25 having a substantially U-shaped planar shape is arranged.

This yoke 25 is provided with extreme ends 26, 27 around the rotation area of the rotor 22, which apply an electromagnetic attraction force to the rotor 22.

A feature of the present invention is that the extreme ends 26 and 27 are formed into a pair of pole pieces that sandwich the rotary orbit of the rotor 22 at the upper and lower ends along the axial direction of the torsion bar.

Figures 2 (A) and (B) show the extremes 26.27 of this example.
FIG. 2(A) is a perspective view of the yoke 25, and FIG. 2(B) is a front view of the yoke 25.

In this embodiment, the extreme ends 26 and 27 are formed into a U-shaped cross section as shown in the figure, and both legs 26a and 26b of the U-shape are formed.
and 27a and 27b are used as a pair of pole pieces.

That is, the legs 26a and 26b face each other so as to sandwich the rotational trajectory of one end of the rotor 22 from above and below, and the legs 27
a and 27b face each other so as to sandwich the rotational path of the other end of the rotor 22 from above and below.

In the embodiment, the yoke 25 has a substantially U-shape, and is fixed to a projecting portion 10a provided at a substantially central portion of the base 10 with screws.

An excitation coil 28 is wound around the leg of the yoke 25, and in the embodiment, this excitation coil 28 is connected to the yoke 26.
The current flowing through the excitation coil 28 generates a predetermined magnetic flux in the yoke 25, thereby applying an electromagnetic driving force to the rotor 22 from the extremes 26° 27.

In the embodiment, the excitation coil 28 is wound around both legs of the yoke 25, but it is also possible to use a single excitation coil.

In this embodiment, in order to cause the excitation coil 28 to generate magnetic flux at a predetermined timing, the rotational phase of the rotor 22 is constantly monitored, and for this purpose a phase detector is provided.

In FIG. 1, this phase detector consists of an optical sensor 29 in which a light emitting part and a light receiving part are integrally provided, and the rotor 22 outputs a substantially sinusoidal output depending on the size of the reflection of the test light from the optical sensor 29. The timing of the drive signal supplied to the excitation coil 28 is controlled by electrically shaping and delaying the drive signal based on the detector output waveform.

As described above, according to the optical scanning device shown in FIG.
Reflection scanning is performed as shown by 0, and this scanning speed is determined by the torsional natural frequency of the torsion bar 16, so that scanning light with an extremely stable scanning speed can be obtained.

In the embodiment, the static neutral position of the rotor 22 described above is set to a position initially biased by a predetermined angle from the position where the rotor 22 and the yoke 25 face each other.

FIG. 3 shows the initial bias position of the rotor 22, in which the rotor 22 is at rest position A when the torsion bars have stopped vibrating and the excitation coil 28 is in the de-energized state.
is positioned.

Therefore, in this static neutral position A, the rotor 22 is offset by 00 from the position facing the extremes 26, 27 of the yoke 25, and this initial bias angle θ. can be arbitrarily set according to the characteristics of the optical scanning device.

FIGS. 4 and 5 show a half-cycle rotation state of the rotor 22 in this embodiment, and in this embodiment, the rotor 22 is moved from its initial bias position A by the supply of excitation current. It rotates to the maximum rotation position B shown in FIG. 4, which is opposite to the extreme ends 26 and 27 of the yoke 25, and then twists due to natural vibration due to cutting off of the excitation current and passes through the initial bias position, that is, the neutral position A. They move simultaneously to the maximum rotational position C, which is deviated by θ1 from the opposing position shown in FIG. 5, and then reverse. That is, it vibrates back around the initial bias position A between the maximum rotation position B and the maximum rotation position C.

According to this embodiment, since the torsional rotation of the rotor 22 is used for optical scanning, it is possible to obtain an extremely stable optical scanning effect.

FIG. 6 shows an example of a drive circuit for supplying excitation current to the excitation coil 28, in which the drive transistor 32 is controlled to be on-off in response to a drive pulse supplied to the input terminal 30, and Current supply to the excitation coil 28 connected to the emitter side of the transistor 32 is controlled in accordance with the drive pulse.

The rotational operation of the rotor 22 explained above is based on the excitation coil 28
This is done by applying an electromagnetic attraction to the rotor 22 from the extreme 26° 27 of the yoke by supplying a current O (supply);
27a and leg portion 26b.

27b applies electromagnetic attractive force from above and below the rotor 22, respectively.

Therefore, the rotor 22 is rotated not only by horizontal electromagnetic attraction from the extreme ends 26 and 27, but also by applying electromagnetic attraction evenly from above and below through the legs 26a1, 27M, 26b, and 27b. be able to.

As a result, the electromagnetic attraction force applied directly to the rotor 22 from the horizontal direction is reduced, so that the rotor is pulled and the torsion bar 16 bends, causing axial vibration of the rotor 22 or adhesion between the rotor and the extreme ends. The occurrence of military soldiers can be effectively prevented.

Further, according to this embodiment, the reflection mirror 24 of the rotor 22
Optical scanning by reflection of the light beam at
Optical scanning is performed during free oscillations.

Therefore, optical scanning can be performed at a stable speed determined by the vibration frequency of the entire armature 23 without being affected by external force.

[Effects of the Invention] As described above, according to the present invention, the electromagnetic attraction force for rotating the rotor can be applied from above and below the rotor by the pole pieces forming the extreme ends of the yoke.

Therefore, it is possible to ensure stable rotor rotation without causing problems such as rotor axial wobbling or adhesion to the yoke when the rotor rotates, so it is possible to always perform good optical scanning. becomes.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of essential parts showing a preferred embodiment of an optical scanning device according to the present invention, FIG. 2(A) is a perspective view of a yoke used in the embodiment, and FIG. 2(B) is a front view of the yoke. 3, 4, and 5 are explanatory views showing the rotor driving action of the optical scanning device shown in FIG. 1, and FIG. 6 is a driving circuit diagram in this embodiment. 16... Torsion bar 22... Rotor 23... Armature 24... Reflection mirror 25... Yoke 26.27... Extreme 100... Front beam 200... Scanning light

Claims (2)

[Claims] (1) An armature having a torsion bar fixed at both ends and torsionally vibrating, and a rotor fixed to the torsion portion of the torsion bar and having a reflecting mirror in a part thereof, and rotating the rotor by electromagnetic attraction force. a yoke having an extreme end provided around the rotating region of the rotor to cause the rotor to rotate; and an excitation coil that generates a magnetic flux in the yoke at a predetermined timing; In an optical scanning device that performs reflection scanning by rotation of a rotor, the yoke extremes are formed as a pair of pole pieces that sandwich the rotating orbit of the rotor at the upper and lower sides along the axial direction of the torsion bar, and An optical scanning device characterized in that the attractive force is applied evenly from above and below along the axial direction of the torsion bar by the pair of pole pieces. (2) An optical scanning device according to claim 1, wherein the pair of pole pieces are formed by both legs of an end of a yoke having a U-shaped cross section.