JP4701938B2 - Optical deflector - Google Patents

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. 11 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.

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

  Of the sleeve 111 of the rotating body 110, the inner peripheral surface 111a facing the fixed shaft 101 is finished with a bearing surface, while the outer peripheral surface 101a of the fixed shaft 101 facing the inner peripheral surface 111a of the sleeve 111. Are formed with herringbone-shaped grooves 104 as shown by broken lines in the figure, and the rotating body 110 is radially formed 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 that is supported in the direction is configured.

  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 this optical deflector, the positional relationship between the boundary position between the N pole and the S pole of the drive magnet 115 and the ridge line position where the reflecting surfaces of the polygon mirror 113 are adjacent to each other should be substantially matched for convenience of assembly. (For example, see Patent Document 2).

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

  However, when the boundary position between the N pole and the S pole of the drive magnet 115 and the ridge line position where the reflecting surfaces of the polygon mirror 113 are adjacent to each other substantially coincide, the fluctuation in the drive torque generated by the motor M is caused by the polygon mirror 113. There is a problem that it appears as a variation in the pitch between dots of the beam scanned on the photosensitive member or the like by the rotation of. Such a problem becomes apparent as the image formation becomes more accurate.

  The present invention has been made to solve such a problem, and the angular difference between the beam scanning start position on the reflection surface of the polygon mirror and the boundary position between the N pole and the S pole constituting the magnetic pole of the drive magnet is obtained. The object of the present invention is to minimize the fluctuation amount of the pitch between dots of the beam scanned on the photosensitive member with a simple configuration in which the predetermined angle is set.

The optical deflector according to claim 1 includes a polygon mirror having a plurality of reflecting surfaces each having an effective scanning area in which the beam is scanned in the entire circumferential direction, and a plurality of N poles and S poles alternately arranged. And a drive magnet that is rotationally driven together with the polygon mirror, and an iron core coil that is fixedly disposed on the housing so as to face the drive magnet so that the torque ripple has a sine wave shape. configured Rutotomoni, the position of the peaks and valleys in the sinusoidal ripple of the torque, is configured to match the boundary position or the center position of the N and S poles of N and S poles of the drive magnet Motor, and the number of magnetic poles of the drive magnet is nP (n is a natural number) when the number of reflection surfaces is P (P is an even number of 4 or more), and the effective scanning area Oh A scanning start position of the beam that is obtained by the angular difference between the boundary position of the N and S poles constituting the magnetic pole and 90 ° / nP or 270 ° / nP.

  According to the present invention, it is possible to minimize the fluctuation amount of the pitch between dots of the beam scanned on the photosensitive member.

  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 this embodiment, for simplicity of explanation, the number of reflecting surfaces of the polygon mirror is 4 and the number of magnetic poles of the drive magnet is 4, and the light is emitted from a light source (for example, a laser diode). The case where the effective scanning area where the beam scans the reflection surface of the polygon mirror is the entire reflection surface will be described.

  FIG. 1 is a relationship diagram in which A shows the magnetic pole of the drive magnet, B shows the torque ripple of the three-phase motor, and 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.

2 and 3 are plan views showing the positional relationship between the polygon mirror 11 and the drive magnet 12. The polygon mirror 11 is formed with a reflecting surface 31 (one surface), a reflecting surface 32 (two surfaces), a reflecting surface 33 (three surfaces), and a reflecting surface 34 (four surfaces). The angle between the ridge line position 14 and the boundary position 15 between the N pole and the S pole of the drive magnet 2 is α °.
In this embodiment, since the effective scanning area is the entire reflection surface, the ridge line position 14 is the beam scanning start position in the effective scanning area.

(Comparative Example 1-1)
First, when there is no angle difference between the ridge line position 14 where the plurality of reflecting surfaces of the polygon mirror 11 of the prior art are adjacent to each other and the boundary position 15 between the N pole and S pole constituting the magnetic pole of the drive magnet 12 (FIG. 2). Or, α = 0 ° in FIG. 3 will be described with reference to a in FIG.

  In FIG. 1B showing a torque ripple, the driving magnet 12 receives a force from a coil (not shown) from 1 to 3, 5 to 7, and the torque is increased, so that 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 emitted from the laser diode or the like is scanned by the polygon mirror 11, the dot-to-dot pitch of the beam formed on the photoconductor becomes wider from 1 to 2, and further from 2 to 3. Widens, narrows from 3 to 4, narrows from 4 to 5, narrows from 5 to 6, widens from 6 to 7, narrows from 7 to 8, The phenomenon of wider, wider, narrower, and narrower is repeated periodically as it becomes narrower as it goes from 8 to 9. That is, a portion having a large dot pitch and a narrow portion appear alternately.

(Comparative Example 1-2)
Similarly, the case where the angle difference α between the ridge line position 14 and the boundary position 15 is 45 ° will be described with reference to c in FIG.

  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 11 decelerates. On the other hand, since the torque increases from 5 to 7, the rotation of the polygon mirror 11 is accelerated.

As a result, when the beam of a laser diode or the like is scanned by the polygon mirror 11, 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 becoming narrower as it goes from 9 to 9 occurs.
That is, as in Comparative Example 1-1, a portion having a large dot pitch and a narrow portion appear alternately.

Since the comparative example 1-1 and the comparative example 1-2 described above appear alternately in the dot-to-dot pitch of the image formed on the photosensitive member, this is a great drawback for high-precision printing.
On the other hand, as shown below, when the number of reflection surfaces of the polygon mirror is 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 effective. When the angle difference between the scanning start position of the beam in the scanning area and the boundary position between the N pole and S pole constituting the magnetic pole is approximately 90 ° / nP or approximately 270 ° / nP, that is, in this embodiment, When the angle is approximately 22.5 ° (phase difference ¼) or approximately 67.5 ° (phase difference 3/4), the amount of variation in pitch between dots can be minimized.

(Example 1-1)
First, as shown in FIG. 2, the angle difference α between the ridge line position 14 where the plurality of reflecting surfaces of the polygon mirror 11 are adjacent to each other and the boundary position 15 between the north pole and the south pole constituting the magnetic pole of the drive magnet is approximately 22. The case of .5 ° will be described with reference to b in FIG.

  In FIG. 1B showing the torque ripple, the torque increases from 2 to 3, 5 to 7, and the rotation of the polygon mirror 11 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 11 is decelerated.

As a result, the dot-to-dot pitch of the beam formed on the photosensitive member or the like when a beam of a laser diode or the like is scanned by the polygon mirror 11 becomes wider as it goes from 2 to 3, but becomes narrower as it goes from 3 to 4. At point 4, the fluctuation of the pitch between dots is eliminated. Furthermore, since the inter-dot pitch becomes narrower as it goes from 4 to 5, and becomes wider as it goes from 5 to 6, the fluctuation of the inter-dot pitch is eliminated at time 6. Similarly, the inter-dot pitch becomes wider as it goes from 6 to 7, and becomes narrower as it goes from 7 to 8, so that the fluctuation of the inter-dot pitch is eliminated at the time point 8.
In other words, when the exposure of the beam to the photosensitive member or the like from 2 is started, acceleration / deceleration is repeated evenly in a short cycle. Therefore, the variation in the pitch between dots is eliminated in order to eliminate the variation in the pitch between dots in a short cycle. Can be minimized.

(Example 1-2)
Further, as shown in FIG. 3, the angle difference α between the ridge line position 14 where the plurality of reflecting surfaces of the polygon mirror 11 are adjacent to each other and the boundary position 15 between the N pole and the S pole constituting the magnetic pole of the drive magnet 12 is approximately. The case of 67.5 ° will be described with reference to d in FIG.

  In FIG. 1B showing the torque ripple, the torque decreases from 4 to 5, and from 7 to 8, so that the rotation of the polygon mirror 11 decelerates. On the other hand, since the torque increases from 5 to 7, the rotation of the polygon mirror 11 is accelerated.

As a result, the dot-to-dot pitch of the beam formed on the photosensitive member or the like when a beam of a laser diode or the like is scanned by the polygon mirror 11 becomes narrower as it goes from 4 to 5, but becomes wider as it goes from 5 to 6. At point 6, the dot pitch fluctuation is eliminated. Furthermore, since the pitch between the dots of the beam 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 point of 8.
In other words, when exposure of the beam from 4 to the photosensitive member or the like is started, acceleration / deceleration is repeated evenly in a short cycle. Therefore, the variation in pitch between dots is eliminated in order to eliminate the variation in pitch between dots in a short cycle. Can be minimized.

A second embodiment according to the present invention will be described with reference to FIGS.
In addition, about the same part as Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted, and only the main differences from Example 1 are demonstrated in detail.

The difference from the first embodiment is only that the number of magnetic poles of the drive magnet 12 is set to 8.
FIG. 4 is a relationship diagram in which A shows the magnetic pole of the drive magnet, B shows the torque ripple of the three-phase motor, and C shows the surface of the polygon mirror. In the case of a motor having an iron core coil, since cogging torque is generated, the torque ripple of the three-phase motor can be made substantially sinusoidal as in the case of the first embodiment.
5 and 6 are plan views showing the positional relationship between the polygon mirror 11 and the drive magnet 12.

(Comparative Example 2)
As in the case of the first embodiment, the angle difference α between the ridge line position 14 where the plurality of reflecting surfaces of the polygon mirror 11 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 0 °. In the case of (a of C in FIG. 4) and 22.5 ° (c in C of FIG. 1), a portion having a large dot pitch and a narrow portion appear alternately.

  That is, when α = 0 ° (a in FIG. 4C), the torque increases from 1 to 2, 2 to 3 in FIG. 4B, and the rotation of the polygon mirror 11 accelerates. The dot-to-dot pitch of the beam formed on the photosensitive member or the like when scanned with the polygon mirror 11 increases from 1 to 2, and further increases from 2 to 3. The torque decreases from 3 to 4, 4 to 5, and the rotation of the polygon mirror 11 decelerates. Therefore, when the beam of a laser diode or the like is scanned by the polygon mirror 11, the distance between the dots of the beam formed on the photoconductor The pitch becomes narrower as it goes from 3 to 4, and becomes narrower as it goes from 4 to 5.

  When α = 22.5 ° (c in FIG. 4C), the torque decreases from 3 to 5 in B of FIG. 4 and the rotation of the polygon mirror 11 decelerates. The dot-to-dot pitch of the beam formed on the photosensitive member or the like when scanned by the mirror 11 becomes narrower as it goes from 3 to 4, and further becomes narrower as it goes from 4 to 5. Since the torque increases from 5 to 7 and the rotation of the polygon mirror 11 accelerates, the dot-to-dot pitch of the beam formed on the photosensitive member or the like when the beam such as a laser diode is scanned by the polygon mirror 11 is 5 From 6 to 7, and further from 6 to 7.

  In this manner, the pitch between the dots of the beam is wide, further wider, narrower, and narrower periodically, so that a portion having a wide dot pitch and a narrow portion appear alternately.

  On the other hand, as shown below, 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). In this case, the variation in pitch between dots can be minimized.

(Example 2-1)
First, when the angle difference α between the ridge line position where the plurality of reflecting surfaces of the polygon mirror 11 are adjacent to each other and the boundary position between the N pole and S pole constituting the magnetic pole of the drive magnet 12 is approximately 11.25 ° (FIG. 4). C) b) will be described.

  In FIG. 4B showing the torque ripple, the torque increases from 2 to 3, 5 to 7, and the rotation of the polygon mirror 11 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 11 is decelerated.

  As a result, when the beam of a laser diode or the like is scanned by the polygon mirror 11, the dot-to-dot pitch of the beam formed on the photosensitive member or the like becomes wider as it goes from 2 to 3, but becomes narrower as it goes from 3 to 4. At time 4, dot pitch variation is eliminated. Furthermore, since it becomes narrower as it goes from 4 to 5, and it 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.

  That is, when the exposure of the beam to the photosensitive member or the like is started from the position 2, acceleration / deceleration is repeated evenly in a short cycle, so that the fluctuation of the dot pitch can be minimized.

(Example 2-2)
Next, when the angle difference α between the ridge line position where the plurality of reflecting 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 33.75 ° (FIG. 4). The d) of C will be described.

In FIG. 4B showing the torque ripple, the torque decreases from 4 to 5, and from 7 to 8, so that the rotation of the polygon mirror 11 is decelerated. On the other hand, since the torque increases from 5 to 7, the rotation of the polygon mirror 11 is accelerated.
As a result, when the beam of a laser diode or the like is scanned by the polygon mirror 11, the dot-to-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. , 6, dot pitch fluctuations 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 from 4 to the photosensitive member or the like is started, the acceleration / deceleration is repeated evenly in a short cycle, so that the fluctuation of the dot pitch can be minimized.

Hereinafter, another embodiment according to the present invention will be described with reference to FIGS.
In addition, about the same part as Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted, and only the main differences from Example 1 are demonstrated in detail.

FIG. 7 is a perspective view of the polygon mirror, and FIGS. 8 and 9 are plan views showing the positional relationship between the scanning start position of the effective scanning area in the polygon mirror 11 and the boundary position of the magnetic pole of the drive magnet 12.
FIG. 10 is a relationship diagram in which A shows the magnetic pole of the drive magnet, B shows the torque ripple of the three-phase motor, and C shows the surface of the polygon mirror. In the case of a motor having an iron core coil, since cogging torque is generated, the torque ripple of the three-phase motor can be made substantially sinusoidal as in the case of the first embodiment.

  In the first embodiment and the second embodiment described above, the scanning of the beam on one surface is another ridge line position (for example, the ridge line in FIG. 7) adjacent to the ridge line position (for example, the ridge line position 14 in FIG. 7) of the polygon mirror 11. Those up to position 16) are shown. That is, although the entire effective scanning area where the beam can scan the reflection surface of the polygon mirror 11 is shown, in this embodiment, the case where the effective scanning area on each reflection surface is a part will be described. In other words, the difference from the first embodiment is only that the effective scanning area is a part of the reflecting surface.

As shown in FIG. 7, the reflective surface 31 of the polygon mirror 11 is provided with an effective scanning area 40 in which a beam hits the reflective surface from a scanning start position 41 to a scanning end position 42. As a matter of course, the area 43 other than the effective scanning area 40 is not irradiated with the beam.
Similarly, the effective scanning areas 40 having substantially the same size are provided on the other reflecting surfaces 32, 33, and 34.

  In this case, as shown in FIG. 8 or FIG. 9, the angle difference α between the beam scanning start position 41 in the effective scanning area 40 and the boundary position 15 between the N pole and the S pole constituting the magnetic pole in the drive magnet 12 is approximately. By setting it to 90 ° / nP (FIG. 8) or approximately 270 ° / nP (FIG. 9), the fluctuation amount of the inter-dot pitch of the beam can be minimized.

(Example 3-1)
First, the case of α = 90 ° / nP (b in FIG. 8 and FIG. 10C) will be described.
In FIG. 10B showing the torque ripple, the torque increases from 2 to 3, 5 to 7, and the rotation of the polygon mirror 11 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 11 is decelerated.

As a result, when the beam of a laser diode or the like is scanned by the polygon mirror 11, the dot-to-dot pitch of the beam formed on the photosensitive member or the like becomes wider as it goes from 2 to 3, but becomes narrower as it goes from 3 to 4. At time 4, dot pitch variation is eliminated. Furthermore, since it becomes narrower as it goes from 4 to 5, it becomes wider as it goes from 5 to 6, so that the fluctuation of the dot pitch is eliminated at the time of 6. Note that, from the vicinity of 5 to 6, the beam does not scan the effective scanning area 40 of the reflecting surface 31 (one surface), so the photosensitive member is not exposed.
The inter-dot pitch of the beam becomes wider as it goes from 6 to 7, and becomes narrower as it goes from 7 to 8, so that the fluctuation of the dot pitch is eliminated at time 8.

  That is, when the beam is applied to the reflecting surface of the polygon mirror 11 from the position 2 and exposure to the photosensitive member or the like is started, the acceleration / deceleration of the polygon mirror 11 is repeated evenly in a short cycle as in the case of Example 1-1. Therefore, fluctuations in dot pitch can be minimized.

(Example 3-2)
Next, the case where α = 270 ° / nP (d in FIG. 9 and FIG. 10C) will be described.
In FIG. 10B showing the torque ripple, the torque decreases from 4 to 5, and from 7 to 8, so the rotation of the polygon mirror 11 decelerates. On the other hand, since the torque increases from 5 to 7, the rotation of the polygon mirror 11 is accelerated.

  As a result, the dot-to-dot pitch of the beam formed on the photosensitive member or the like when a beam of a laser diode or the like is scanned by the polygon mirror 11 gradually decreases from 4 to 5, but gradually decreases from 5 to 6. Therefore, the fluctuation of the dot pitch is eliminated at the time point 6. Further, since it gradually becomes wider as it goes from 6 to 7, and gradually becomes narrower as it goes from 7 to 8, the fluctuation of the dot pitch at the time point 8 is eliminated. Note that, from the vicinity of 7 to 8, the beam does not scan the effective scanning area 40 of the reflecting surface 31 (one surface), so that the photosensitive member is not exposed.

  That is, when the exposure of the beam from 4 to the photosensitive member or the like is started, the acceleration / deceleration is repeated evenly in a short cycle, 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.

  For example, in order to simplify the description, the above-described embodiment has been described using a polygon mirror having four reflecting surfaces. However, the present invention is not limited to this, and the number P of reflecting surfaces is 4 or more. It only needs to be an even number. That is, it may be a polygon mirror having reflective surfaces such as 6, 8, 10, and 16.

  Moreover, although the above-mentioned Example demonstrated using the thing of 4 poles and 8 poles as the number of the magnetic poles of a drive magnet (the number which added S pole and N pole), this invention is limited to these. If the number of reflecting surfaces is P, the number of magnetic poles may be nP (n is a natural number).

  Furthermore, in the above-described embodiment, the ridge line position 14 between the reflecting surface 31 (one surface) and the reflecting surface 32 (two surfaces) has been described. However, the present invention is not limited to this, and the reflecting surface 32 (two surfaces). ) And the reflective surface 33 (3 surfaces), or a ridge line between the reflective surface 33 (3 surfaces) and the reflective surface 34 (4 surfaces), and the reflective surface 34 (4 surfaces). And a ridge line between the reflecting surface 31 (one surface).

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

FIG. 6 is a relational diagram showing the relationship between the magnetic pole of the drive magnet (A), the torque ripple of the three-phase motor (B), and the reflection surface of the polygon mirror (scanning start position of the effective scanning area) (C). (Example 1) which is a top view which shows the relationship between the scanning start position of an effective scanning area, and the boundary position of the magnetic pole of a drive magnet. (Example 1) which is a top view which shows the relationship between the scanning start position of an effective scanning area, and the boundary position of the magnetic pole of a drive magnet. (Example 2) which is a relationship figure which shows the magnetic pole (A) of a drive magnet, the ripple (B) of the torque of a three-phase motor, and the reflective surface (scanning start position of an effective scanning area) (C) of a polygon mirror. (Example 2) which is a top view which shows the relationship between the scanning start position of an effective scanning area, and the boundary position of the magnetic pole of a drive magnet. (Example 2) which is a top view which shows the relationship between the scanning start position of an effective scanning area, and the boundary position of the magnetic pole of a drive magnet. (Example 3) which is a perspective view of a polygon mirror (Example 3) which is a top view which shows the relationship between the scanning start position of an effective scanning area, and the boundary position of the magnetic pole of a drive magnet. (Example 3) which is a top view which shows the relationship between the scanning start position of an effective scanning area, and the boundary position of the magnetic pole of a drive magnet. FIG. 10 is a relational diagram showing the relationship between the magnetic pole of the drive magnet (A), the torque ripple of the three-phase motor (B), and the reflection surface of the polygon mirror (scanning start position of the effective scanning area) (C). It is a figure which shows the conventional optical deflector.

Explanation of symbols

11 Polygon mirror 12 Driving magnet 14 Edge line position 15 Boundary position 31 Reflecting surface (one surface)
32 Reflective surfaces (2 surfaces)
33 reflective surfaces (3 surfaces)
34 Reflective surfaces (4 surfaces)
40 Effective scanning area 41 Beam scanning start position

Claims (1)

A polygon mirror formed with a plurality of reflecting surfaces having an effective scanning area in which the beam is scanned over the entire length in the circumferential direction;
A plurality of N poles and S poles are alternately and continuously provided in an annular shape, and have a drive magnet that is rotationally driven together with the polygon mirror, and an iron core coil that is fixedly disposed on the housing so as to face the drive magnet. and are configured to torque ripple is sinusoidal Rutotomoni, the position of the peaks and valleys in the sinusoidal ripple of the torque, a boundary position or the N-pole of the N pole and S pole of the drive magnet A motor configured to coincide with the center position of the S pole ;
With
When the number of the reflecting surfaces 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 deflector characterized in that an angle difference between a scanning start position of a beam in the effective scanning area and a boundary position between an N pole and an S pole constituting the magnetic pole is set to 90 ° / nP or 270 ° / nP.

Images