JPH0772767B2 - Polygon mirror - Google Patents

Description

The present invention relates to a polygon mirror used in an optical deflector.

(Prior Art) An optical deflector employing a polygon mirror will be described with reference to FIGS. 2 and 3 of the accompanying drawings.

An armature coil group 9 is provided on the upper surface of the iron-based printed circuit board 10.
To arrange. A fixed shaft bush 12 is fixed to the central portion of the printed board 10. The fixed shaft 3 is fixed to the fixed shaft bush 12. A pair of ball bearings 11, which are bearing means rotatable with the hub 4, are mounted on the outer periphery of the fixed shaft 3. A back yoke 7 is fixed to the lower surface of the hub 4,
An electric motor driving magnet 8 is adhered and fixed to the inside of the back yoke 7. Also, on the upper outer surface of the hub 4,
A U-shaped annular groove 14 is provided by cutting or the like, and on the other hand, the pressing cap 15 can engage with the U-shaped annular groove 14 provided on the upper outer surface of the hub 4 to play a role of retaining. The half-folded protruding portion 13 that is a plurality of engaging members is provided. After mounting the polygon mirror 1 on the step portion of the hub 4, the pressing cap 15 is pushed down while pressing the elastic body O-ring 6 located on the upper surface of the polygon mirror 1, and the half-folded protruding portion 13 of the pressing cap 15 is attached to the hub 4. By engaging with the U-shaped annular groove 14, the polygon mirror 1 is sandwiched and fixed by the hub 4 and the O-ring 6. Reference numeral 3b is a preload means for the bearing means provided at the upper end of the fixed shaft 3.

When the polygon mirror 1 is supported by the hub 4 and rotates on the outer periphery of the fixed shaft 3, various measures have been taken to maintain the horizontal balance during the rotation of the polygon mirror 1 and improve its accuracy.

One of them is the configuration shown in FIG. In FIG. 2, on the upper surface of an octahedral polygon mirror 1 having mirror surfaces A1, A2, A3, A4, A5, A6, A7, A8, the reference center hole H of this mirror 1 is a concentric cross-section. A circular groove D is engraved. The polygon mirror 1 is incorporated in an optical deflector and mounted on a motor, and in order to adjust the balance during rotation due to the rotation of the motor, a weight W is embedded at a predetermined position in the U-shaped circular groove D in cross section, This is a plan for smooth rotation of the polygon mirror 1. Also, a circular groove with a U-shaped cross section is provided on the lower surface of the polygon mirror.
There is also a conventional example in which a weight is embedded in a predetermined portion of these.

(Problems to be Solved by the Invention) However, even if the weight W is embedded in the U-shaped circular groove D having the U-shaped cross section formed on the upper surface F of the polygon mirror 1 or the surface opposite to the upper surface as described above, the rotation of the optical deflector is prevented. The weight W moves in the circular groove D due to the centrifugal force generated by or due to the centrifugal force, the weight W protrudes from the upper opening of the circular groove and falls off, so that the purpose of maintaining the smooth rotation of the polygon mirror may not be achieved. Especially when rotating at high speed or when using a polygon mirror with a large thickness for the hub that supports it, it is difficult to maintain balance during rotation because the weight moves and falls. was there.

The invention of this application aims to solve the above problems.

(Means for Solving the Problem) In an optical deflector incorporating a polygon mirror 2 forming a plurality of mirror surfaces A1 to A8 on the outer periphery, an upper surface F of the polygon mirror 2 and a reference on the outer periphery of a reference center hole H of the polygon mirror 2. A circular groove B having an L-shaped cross section with a bottom surface extending in the outer peripheral direction with the reference center hole H as a core on the inner side surface I of the center hole H, and a cross section on the inner side surface of the reference center hole H. The U-shaped circular groove C and the circular groove B formed on the upper surface are located above the reference center hole H, and the circular groove C formed on the inner surface is located inside the reference center hole H. Polygon mirror 2 which is opened and has weights W1 and W2 embedded in predetermined positions in these circular grooves B and C.
I will provide a.

(Operation) An optical deflector is formed by forming a circular groove with an L-shaped cross section whose bottom extends concentrically in the outer peripheral direction of the reference center hole and a circular groove on the inner side surface of the center hole, and embedding a weight in each of these grooves. The balance can be easily maintained and the weight can be prevented from moving or falling off due to centrifugal force during rotation of the optical deflector. Particularly, when the optical deflector is rotating at a high speed and a polygon mirror having a large thickness is adopted, the balance of the polygon mirror can be easily adjusted and good balance can be maintained.

(Embodiment) An embodiment of the invention of this application will be described below with reference to the accompanying drawings.

The polygon mirror 2 of the present invention used for the optical deflector is an octagonal polygon mirror formed with a plurality of outer peripheral mirror surfaces A1, A2, A3, A4, A5, A6, A7, A8. On the upper surface F of the polygon mirror 2, a circular groove B is formed in the outer periphery of the reference center hole H concentrically therewith, and in the outer peripheral direction, the bottom surface thereof has an L-shaped cross section. Further, a circular groove C having a U-shaped cross section is also formed on the inner surface I of the reference center hole H concentrically with the reference center hole H. The circular groove B is opened above the polygon mirror 2, and the circular groove C is opened inside the reference center hole H. In order to maintain the balance when the polygon mirror 2 is supported by the hub 4 and rotates around the fixed shaft 3 with high accuracy, the weights W1 and W2 are embedded at appropriate places in the circular grooves B and C. . That is,
In the circular groove B whose bottom surface has an L-shaped cross section, the weight is arranged so as to be deeply inserted into the L-shaped portion of the bottom surface, so that the weight cannot be removed. Further, in the U-shaped circular groove C, the weight is embedded in a portion opened to the inner side surface of the reference center hole. As described above, in the polygon mirror 2, since the weights W1 and W2 are embedded as balance weights at a plurality of positions in the plurality of circular grooves B and C in the shape of the circular groove, During rotation,
Since the weights W1 and W2 are pressed into the groove in the direction of centrifugal force by the centrifugal force during rotation, they can be prevented from falling out of the groove or moving, so that it is possible to maintain a highly accurate balance of the polygon mirror. The structure with multiple concentric circular grooves, and the weights embedded in these grooves according to the shape of the grooves, maintains a highly accurate balance especially when the polygon mirror is thick or when the polygon mirror rotates at high speed. It is useful.

In the present embodiment, the polygon mirror forming the octahedron has been described, but it goes without saying that the same principle can be applied to polygon mirrors having other surface numbers, and the number of circular grooves is not limited to two. A single or multiple items may be set.

(Effect) In the present invention, since a plurality of concentric circular grooves are formed with the reference center hole of the polygon mirror as the core and the balance weights are arranged in these circular grooves, respectively, they are incorporated in the optical deflector. The polygon mirror helps maintain a highly accurate balance during rotation. That is, when the weight is embedded in a circular groove having an L-shaped cross section, the bottom surface of which extends in the outer peripheral direction on the upper surface of the reference center hole of the polygon mirror, the end portion of the weight has a bottom surface section L due to the centrifugal force during rotation of the polygon mirror. When the weight is inserted deeply into the letter-shaped part or is embedded in the circular groove opened on the inner surface of the reference center hole, the weight is inside the circular groove opened in the direction opposite to the centrifugal force due to the centrifugal force during rotation of the polygon mirror. When the polygon mirror rotates, it is prevented from falling out of the circular grooves due to centrifugal force during rotation of the polygon mirror, and from being displaced due to protrusion from the opening of the weight. In particular, when the polygon mirror is rotated at a high speed or when a polygon mirror having a large thickness is adopted, it is possible to maintain a highly accurate balance. Therefore, the vibration when the optical deflector rotates can be minimized. Therefore, the optical beam scanning stability of the optical deflector is improved, and when the optical deflector is used in a laser beam printer or the like, the printing quality is improved.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a polygon mirror according to the present invention. FIG. 2 is a partially cutaway perspective view of a conventional polygon mirror. FIG. 3 is a sectional view of an optical deflector that employs a polygon mirror. 1,2 …… Polygon mirror, 3 …… Fixed axis, 4 …… Hubs A1 to A
8 …… Mirror surface, B, C, D …… circular groove, F …… top surface, H …… reference center hole, I …… inside surface, W, W1, W2 …… weight.

Claims (1)

[Claims] 1. An optical deflector incorporating a polygon mirror for forming a plurality of mirror surfaces on the outer circumference, wherein the bottom surface of the polygon mirror has an L-shaped cross section with the bottom surface extending in the outer circumferential direction on the upper surface of the reference center hole. A circular groove that is concentric with the hole is formed, and a circular groove having a U-shaped cross section is formed concentrically with the reference center hole on the inner surface of the reference center hole, and the circular groove opening is formed on the upper surface. The polygon mirror is characterized in that the portion is opened upward, the circular groove formed on the inner side surface is opened toward the center of the reference center hole, and the weight is embedded in a predetermined position in these circular grooves.