JP2006035477A - Optical deflector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem as a variation in driving torque being generated from a motor consisting of a driving magnet and a core coil appears as a variation in inter-dot pitch of a beam for scanning a photosensitive body through rotation of a polygon mirror. <P>SOLUTION: In the optical deflector comprising a polygon mirror in which a plurality of mirror faces are formed, and a motor consisting of a driving magnet for rotary driving the polygon mirror and a core coil, number of magnetic poles of the driving magnet is nP (n is a natural number) assuming the number of mirror faces of the polygon mirror is P (P is an even number of 4 or more). When the angular difference between the ridge position where the plurality of mirror faces adjoin mutually and the boundary position of N and S poles constituting the magnetic poles is set at about 90°/nP or 270°/nP, variation in inter-dot pitch of a beam for scanning a photosensitive body can be minimized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical deflector used in an image forming apparatus such as a laser printer or a digital copying machine.

  Conventionally, as an optical deflector used in an image forming apparatus such as a laser printer or a digital copying machine, one shown in FIG. 6 is known (for example, see Patent Document 1).

The optical deflector includes a columnar fixed shaft 101 fixedly disposed on the housing 100 and a rotating body 110 that is rotatably supported by the fixed shaft 101.
The rotating body 110 includes a sleeve 111 disposed with a slight gap between the rotating shaft 110, a ring-shaped magnet 112 fixedly disposed on the upper inner side of the sleeve 111, and an outer central portion of the sleeve 111. A polygon mirror 113 fixedly disposed on the lower surface of the sleeve 111 and a ring-shaped drive magnet 115 fixedly disposed on the outside of the lower portion of the sleeve 111 via a flange 114.
Reference numeral 116 denotes a groove in which a balance weight (not shown) for correcting the eccentricity of the weight of the rotating body 110 is attached.

  A ring-shaped magnet 102 is fixedly disposed on the outer side of the upper portion of the fixed shaft 101 so as to face a ring-shaped magnet 112 provided on the rotating body 110. The rotating body 110 is supported by the ring-shaped magnets 102 and 112. A thrust magnetic bearing S for bearing in the thrust direction is configured.

  Further, an iron core coil 103 is fixedly disposed in the housing 100 so as to face a ring-shaped magnet 115 provided on the rotating body 110, and the rotating body 110 is rotated by the ring-shaped magnet 115 and the iron core coil 103. A motor M is configured.

  Of the sleeve 111 of the rotating body 110, the inner peripheral surface 111a facing the fixed shaft 101 is mirror-finished, while the outer peripheral surface 101a of the fixed shaft 101 facing the inner peripheral surface 111a of the sleeve 111 is mirror-finished. Is formed with herringbone-shaped grooves 104 as shown by broken lines in the figure, and the rotating body 110 is moved in the radial direction by the grooves 104 provided on the inner peripheral surface 111a of the sleeve 111 and the outer peripheral surface 101a of the fixed shaft 101. A radial dynamic pressure bearing R is supported.

  In this optical deflector, when the rotating body 110 is rotated by the motor M, the rotating body 110 is supported in a non-contact manner with respect to the fixed shaft 101 by the radial dynamic pressure bearing R, and at the same time by the thrust magnetic bearing S. The fixed shaft 101 is supported at a constant height. Accordingly, there is an advantage that the height of the optical deflector can be made lower than that of a type using a dynamic pressure bearing as a bearing in the thrust direction.

  In such an optical deflector, the positional relationship between the boundary position between the N pole and the S pole of the drive magnet and the ridge line position where the mirror surfaces of the polygon mirror are adjacent to each other is made to substantially coincide with each other for convenience of assembly. (For example, refer to Patent Document 2).

JP-A-5-71532 JP 2000-94747 A

  However, in such a case, there is a problem that the fluctuation of the driving torque generated by the motor M appears as the fluctuation of the inter-dot pitch of the beam scanned on the photosensitive member or the like by the rotation of the polygon mirror. Such a problem becomes conspicuous as the image formation is highly accurate.

  The present invention has been made to solve such a problem, and an angular difference between a ridge line position where a plurality of mirror surfaces of a polygon mirror are adjacent to each other and a boundary position between an N pole and an S pole constituting a magnetic pole of a drive magnet. An optical deflector is provided that minimizes the amount of fluctuation in the pitch between dots of a beam scanned on a photoconductor or the like with a simple configuration in which the angle is set to a predetermined angle.

  The optical deflector according to claim 1 is an optical deflector having a polygon mirror formed with a plurality of mirror surfaces, a drive magnet for rotationally driving the polygon mirror, and a motor composed of an iron core coil. When P (P is an even number equal to or greater than 4), the number of magnetic poles of the drive magnet is nP (n is a natural number), and a plurality of mirror surfaces are adjacent to each other in the ridge line position, and the N pole and S constituting the magnetic pole The angle difference from the pole boundary position is approximately 90 ° / nP or approximately 270 ° / nP.

  According to the present invention, it is possible to supply an optical deflector that minimizes the amount of fluctuation in the dot-to-dot pitch of a beam scanned on a photoreceptor or the like.

  Hereinafter, the present invention will be described in detail using examples.

A first embodiment of the present invention will be described with reference to FIGS.
In order to simplify the explanation, the number of mirror surfaces of the polygon mirror is 4 and the number of magnetic poles of the drive magnet is 4. FIG. 1 shows a magnetic pole of the drive magnet in A, a torque ripple of the three-phase motor in B, C Shows the surface of the polygon mirror.
In the case of a motor having an iron core coil, cogging torque is generated, so that the torque ripple of the three-phase motor can be made into a substantially sine waveform.

(Comparative Example 1)
First, when there is no angle difference between the ridge line position where a plurality of mirror surfaces of the polygon mirror according to the prior art are adjacent to each other and the boundary position between the N pole and S pole constituting the magnetic pole of the drive magnet (a in FIG. 1C) Will be explained.

In FIG. 1B showing the torque ripple, the torque increases from 1 to 3, 5 to 7, and the rotation of the polygon mirror is accelerated. On the other hand, since the torque decreases from 3 to 5, and from 7 to 9, the rotation of the polygon mirror is decelerated.
As a result, when the beam of a laser diode or the like is scanned by a polygon mirror, the dot-to-dot pitch of the beam formed on the photosensitive member becomes wider as it goes from 1 to 3, and becomes narrower as it goes from 3 to 5. A phenomenon occurs that the width becomes wider toward 7 and becomes narrower toward 7 to 9 as well.
That is, a portion having a large dot pitch and a narrow portion appear alternately.

(Comparative Example 2)
Similarly, a case where the angle difference between the ridge line position and the boundary position is 45 ° (c in FIG. 1C) will be described.

In FIG. 1B showing the torque ripple, the torque decreases from 3 to 5, and from 7 to 9, so the rotation of the polygon mirror decelerates. On the other hand, since the torque increases from 5 to 7, the rotation of the polygon mirror is accelerated.
As a result, when the beam of a laser diode or the like is scanned with a polygon mirror, the inter-dot pitch of the beam formed on the photoconductor becomes narrower as it goes from 3 to 5, and becomes wider as it goes from 5 to 7. The phenomenon of narrowing toward 9 occurs.
That is, a portion having a large dot pitch and a narrow portion appear alternately.

Comparative Example 1 and Comparative Example 2 described above are serious drawbacks for high-precision printing.
On the other hand, as shown below, when the angle difference between the ridge line position and the boundary position is approximately 22.5 ° (phase difference 1/4) or approximately 67.5 ° (phase difference 3/4) Can minimize the variation in pitch between dots.

(Example 1-1)
As shown in FIG. 2, when the angle difference α between the ridge line position where the mirror surfaces of the polygon mirror are adjacent to each other and the boundary position between the N pole and S pole constituting the magnetic pole of the drive magnet is approximately 22.5 ° ( FIG. 1C b) will be described.

In FIG. 1B showing the torque ripple, the torque increases from 2 to 3, 5 to 7, and the rotation of the polygon mirror is accelerated. On the other hand, since the torque decreases from 3 to 5, and from 7 to 8, the rotation of the polygon mirror is decelerated.
As a result, when the beam of a laser diode or the like is scanned with a polygon mirror, the inter-dot pitch of the beam formed on the photoconductor becomes wider as it goes from 2 to 3, but becomes narrower as it goes from 3 to 4. At that time, fluctuations in dot pitch are eliminated. Furthermore, since it becomes narrower as it goes from 4 to 5, and becomes wider as it goes from 5 to 6, the fluctuation of the dot pitch is eliminated at the time of 6. Further, since it becomes wider as it goes from 6 to 7, and becomes narrower as it goes from 7 to 8, the fluctuation of the dot pitch is eliminated at the time of 8.
In other words, when the exposure of the beam to the photosensitive member or the like is started from 2, acceleration / deceleration is repeated uniformly, so that the fluctuation of the dot pitch can be minimized.

(Example 1-2)
Further, as shown in FIG. 3, the angle difference α between the ridge line position where the mirror surfaces of the polygon mirror are adjacent to each other and the boundary position between the N pole and S pole constituting the magnetic pole of the drive magnet is approximately 67.5 °. The case (d in FIG. 1C) will be described.

  In FIG. 1B showing the torque ripple, the torque decreases from 4 to 5, and from 7 to 8, so the rotation of the polygon mirror decelerates. On the other hand, since the torque increases from 5 to 7, the rotation of the polygon mirror is accelerated.

As a result, when the beam of a laser diode or the like is scanned with a polygon mirror, the inter-dot pitch of the beam formed on the photoconductor becomes narrower as it goes from 4 to 5, but becomes wider as it goes from 5 to 6. At that time, fluctuations in dot pitch are eliminated. Further, since it becomes wider as it goes from 6 to 7, and becomes narrower as it goes from 7 to 8, the fluctuation of the dot pitch is eliminated at the time of 8.
That is, when the exposure of the beam to the photosensitive member or the like is started from 4, acceleration / deceleration is repeated evenly, so that the fluctuation of the dot pitch can be minimized.

A second embodiment according to the present invention will be described with reference to FIG.
In this embodiment, the number of mirror surfaces of the polygon mirror is 4 and the number of magnetic poles of the drive magnet is 8. FIG. 4 shows a magnetic pole of the drive magnet, A is a ripple of torque of a three-phase motor, and C is a polygon. It shows the surface of the mirror.

(Comparative example)
As in the case of the first embodiment, the angle difference α between the ridgeline position where a plurality of mirror surfaces of the polygon mirror are adjacent to each other and the boundary position between the N pole and S pole constituting the magnetic pole of the drive magnet is approximately 0 ° (FIG. 4). In the case of C of a) and 22.5 ° (c of FIG. 1C), a portion having a large dot pitch and a narrow portion appear alternately.

(Example 2-1)
On the other hand, as shown below, when the angle difference between the ridge line position and the boundary position is approximately 11.25 ° (phase difference ¼) or approximately 33.75 ° (phase difference 3/4). Can minimize the variation in pitch between dots.

  When the angle difference α between the ridge line position where a plurality of mirror surfaces of the polygon mirror are adjacent to each other and the boundary position between the N pole and the S pole constituting the magnetic pole of the drive magnet is approximately 11.25 ° (b in FIG. 4C) Will be explained.

In FIG. 4B showing the torque ripple, since the torque increases from 2 to 3, 5 to 7, the rotation of the polygon mirror is accelerated. On the other hand, since the torque decreases from 3 to 5, and from 7 to 8, the rotation of the polygon mirror is decelerated.
As a result, when the beam of a laser diode or the like is scanned with a polygon mirror, the inter-dot pitch of the beam formed on the photoconductor becomes wider as it goes from 2 to 3, but becomes narrower as it goes from 3 to 4. At that time, fluctuations in dot pitch are eliminated. Furthermore, since it becomes narrower as it goes from 4 to 5, and becomes wider as it goes from 5 to 6, the fluctuation of the dot pitch is eliminated at the time of 6. Further, since it becomes wider as it goes from 6 to 7, and becomes narrower as it goes from 7 to 8, the fluctuation of the dot pitch is eliminated at the time of 8.
In other words, when the exposure of the beam to the photosensitive member or the like is started from 2, acceleration / deceleration is repeated uniformly, so that the fluctuation of the dot pitch can be minimized.

(Example 2-2)
Further, when the angle difference α between the ridge line position where the mirror surfaces of the polygon mirror are adjacent to each other and the boundary position between the N pole and the S pole constituting the magnetic pole of the drive magnet is approximately 33.75 ° (in FIG. d) will be described.

In FIG. 4B showing the torque ripple, the torque decreases from 4 to 5, and from 7 to 8, so the rotation of the polygon mirror decelerates. On the other hand, since the torque increases from 5 to 7, the rotation of the polygon mirror is accelerated.
As a result, when the beam of a laser diode or the like is scanned with a polygon mirror, the inter-dot pitch of the beam formed on the photoconductor becomes narrower as it goes from 4 to 5, but becomes wider as it goes from 5 to 6. At that time, fluctuations in dot pitch are eliminated. Further, since it becomes wider as it goes from 6 to 7, and becomes narrower as it goes from 7 to 8, the fluctuation of the dot pitch is eliminated at the time of 8.
That is, when the exposure of the beam to the photosensitive member or the like is started from 4, acceleration / deceleration is repeated evenly, so that the fluctuation of the dot pitch can be minimized.

  The above-described embodiments are illustrated for explanation, and the present invention is not limited thereto, and those skilled in the art will recognize from the claims, the detailed description of the invention, and the description of the drawings. Modifications and additions are possible without departing from the technical idea of the present invention.

  The effects shown in the first and second embodiments are as follows. When the number of mirror surfaces of the polygon mirror is P (P is an even number of 4 or more), the number of magnetic poles of the drive magnet is nP (n is a natural number). It can be obtained when the angle difference between the ridge line position where a plurality of mirror surfaces are adjacent to each other and the boundary position between the N pole and S pole constituting the magnetic pole is approximately 90 ° / nP or approximately 270 ° / nP.

  The present invention is applied to an optical deflector used in an image forming apparatus or the like.

(Example 1) which is a figure which shows the relationship between the ridgeline position of the polygon mirror which concerns on this invention, and the boundary position of the magnetic pole of a drive magnet (Example 1) which is a figure which shows the relationship between the ridgeline position of the polygon mirror which concerns on this invention, and the boundary position of the magnetic pole of a drive magnet (Example 1) which is a figure which shows the relationship between the ridgeline position of the polygon mirror which concerns on this invention, and the boundary position of the magnetic pole of a drive magnet (Example 2) which is a figure which shows the relationship between the ridgeline position of the polygon mirror which concerns on this invention, and the boundary position of the magnetic pole of a drive magnet It is a figure which shows the conventional optical deflector.

Claims (1)

A polygon mirror formed with a plurality of mirror surfaces;
In an optical deflector having a motor composed of a drive magnet and an iron core coil for rotationally driving the polygon mirror,
When the number of mirror surfaces of the polygon mirror is P (P is an even number of 4 or more),
The number of magnetic poles of the drive magnet is nP (n is a natural number),
An optical deflection characterized in that an angle difference between a ridge line position where the plurality of mirror surfaces are adjacent to each other and a boundary position between the N pole and the S pole constituting the magnetic pole is approximately 90 ° / nP or approximately 270 ° / nP. vessel

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