Rotating polygon mirror

A rotating polygon mirror includes a polygon cylinder having a reflection mirror surface formed on at least one of the sides thereof, and mount portions formed on an upper surface and a lower surface thereof, which are to be held by mount members of a laser scan type optical system. At least one of the mount portions on the upper and lower surfaces has such a shape that, when two rotating polygon mirrors are stacked with their non-corresponding mount portions abutting each other, a reference surface formed in at least one of the mount portions of one rotating polygon mirror does not contact the mount portion of the other rotating polygon mirror.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a rotating polygon mirror used in a laser 
scan type optical system, and more particularly to a rotating polygon 
mirror which prevents contact of mount portions of the rotating polygon 
mirrors when a plurality of rotating polygon mirrors are stacked with the 
mounting portions abutting each other, and prevents damages of the 
mounting portions due to the contact from occurring. 
2. Description of the Prior Art 
The rotating polygon mirror is mounted on a laser scan type optical system 
to change a light path of a laser beam so that the laser beam scans a 
photosensing surface. Typically, it is formed by polishing or precisely 
grinding sides of polygon bar made of optical glass or metal such as 
aluminum to form reflection mirror surfaces. 
Such a rotating polygon mirror has continuous upper and lower planes 1 and 
2 as shown in FIG. 1A or offset upper and lower surfaces 3 and 4 as shown 
in FIG. 1B. 
However, when a number of such rotating polygon mirrors are stacked with 
their upper and lower surfaces abutting each other during manufacture, 
storage or transportation, dust may be held between the surfaces of the 
stacked mirrors and the stacked surfaces are damaged, or the stacked 
surfaces are rubbed by each other and the stacked surfaces are damaged. As 
shown in FIG. 2, when the rotating polygon mirror 10 is mounted to a 
rotating device shaft 12 of a scan motor 11 of a scan device by a screw 13 
with the upper surface 1 or the lower surface 2 of the rotating polygon 
mirror 10 being set as a reference plane, if mount portions of the 
rotating polygon mirror 10, that is, the portions to be held by mounting 
members 14 and 15, particularly a reference surface which should be 
precisely normal to the reflection mirror plane has the damage, a scan 
plane angle precision is lowered. Accordingly, it is necessary to prevent 
such damage. 
In the rotating polygon mirror of the above construction, when a coating is 
applied to the mirror surface by vapor-depositing Al, Cu, Au, Ag, 
SiO.sub.2, MgF.sub.2, or Al.sub.2 O.sub.3 in order to protect the mirror 
surface and/or enhance a reflection function of the surface, a plurality 
of rotating polygon mirrors 18 are set on a vapor deposition jig shaft as 
shown in FIG. 3. In order to prevent damage of the rotating polygon 
mirrors and excess deposition of evaporated materials on the upper and 
lower surfaces of the rotating polygon mirrors, spacers 20 must be 
arranged between the respective rotating polygon mirrors. As a result, the 
number of mirrors set in one vapor deposition process is limited because 
of a limited space in the evaporation bath. That is, the space in the 
evaporation bath is partially occupied by the spacers. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a rotating polygon 
mirror which prevents contact of mounting portions, particularly reference 
surfaces of the rotating polygon mirrors when a number of polygon mirrors 
are stacked with the mounting portions abutting each other, and prevents 
damages due to the contact from occurring in the mounting portions and 
allows elimination of spacers in the vapor deposition process. 
In order to achieve the above object, the rotating polygon mirror of the 
present invention comprises a polygon cylinder having a reflection mirror 
surface on at least one side thereof and mount portions on upper and lower 
surfaces thereof, which are to be held by mount members of a laser scan 
type optical system. At least one of the mount portions on the upper and 
lower surfaces has a shape to prevent a reference surface formed on at 
least one of the mount portions from being contacted by other portions 
when two rotating polygon mirrors are placed with noncorresponding 
mounting portions thereof facing each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 4 shows a first embodiment of the rotating polygon mirror of the 
present invention, FIG. 4A is a plan view, FIG. 4B is a sectional view 
taken along a line A-B in FIG. 4A, and FIG. 5 shows the rotating polygon 
mirrors of the first embodiment mounted on an evaporation jig. 
Numeral 22 denotes reflection planes formed on sides of a regular hexagonal 
cylinder, numeral 23 denotes a recess formed in an upper surface 25, 
numeral 24 denotes a projection formed in a lower surface 26, numeral 27 
denotes holes for screws, numeral 28 denotes a through-hole into which a 
rotary drive shaft of a scan device is to be inserted, and numeral 29 
denotes a range or reference surface which is to be contacted to a mount 
member of the scan device. 
The recess 23 is of circular shape which is coaxial with the hexagonal 
cylinder, and a bottom surface 23a thereof has a shape and size 
corresponding to those of the mount member 14 shown in FIG. 6 so that it 
is precisely formed to fit the mount member 14. 
The projection 24 is of a circular shape which is coaxial with the 
hexagonal cylinder and has a larger diameter than the recess 23. 
In the first embodiment, at least the bottom surface 23a of the recess 23 
has the shape and the size corresponding to those of the mount member 14 
of the scan device, and the projection 24 has such shape, size and depth 
that, when a plurality of rotating polygon mirrors are stacked with the 
upper surface and the lower surface abutting each other, the bottom 
surface 23a of the recess 23 formed in the upper surface of one rotating 
polygon mirror does not contact the top surface of the projection 24 
formed in the lower surface of adjacent rotating polygon mirror. 
The recess and the projection of the present embodiment of the rotating 
polygon mirror may be of any shape and size so long as they meet the above 
requirement, but from a standpoint of balance during the rotation of the 
rotating polygon mirror and for ease in machining, a symmetric shape with 
respect to the center axis of the regular polygon cylinder such as a 
circle or regular polygon is preferable. 
As shown in FIG. 7, the recess 33 may have a plurality of steps so that, 
when the recess 33 of one rotating polygon mirror abutts the projection 34 
of another rotating polygon mirror, the top surface of the projection does 
not contact the bottom surface of the projection; alternatively as shown 
in FIG. 8, a plurality of recesses 36 of the same depth and/or a plurality 
of projections 37 of the same height may be formed. In the latter case, 
the shape of the mounting member is also changed to fit the plurality of 
recesses 36 and/or projections 37. 
Other embodiments are explained with reference to FIGS. 9 to 12. 
In the embodiment of FIG. 9, the recess 39 is formed only in the upper 
surface but the lower surface has a flat surface 40. In the present 
embodiment, when the rotating polygon mirrors are stacked, the bottom 
surface of the recess 39 and the mount portion of the lower surface do not 
make contact. 
In the embodiment of FIG. 10, a recess 42 formed in the upper surface is 
larger than a projection 43 formed on the lower surface but a depth D of 
the recess 42 is larger than a height H of the projection 43. Accordingly, 
when the rotating polygon mirrors are stacked, the mount portions do not 
make contact. 
In the embodiment of FIG. 11, recesses 45 and 46 are formed in both the 
upper and lower surfaces respectively to form the mount portions. 
In the embodiment of FIG. 12, a plurality of projections 47 are formed on 
the upper surface in a ring shape and the lower surface has a flat surface 
48. 
In the embodiment shown in FIG. 4, the rotating polygon mirror is a regular 
hexagonal cylinder although it is not restrictive alternative shapes may 
be used. 
In the rotating polygon mirror of the present invention, when a plurality 
of rotating polygon mirrors are stacked with their upper surfaces and 
lower surfaces abutting to each other, the portions on those surfaces, 
which are to be held by the mount members of the scan device, particularly 
the reference surfaces, do not contact each other so that the occurrence 
of damage in those portions is prevented and precise mounting to the scan 
device is permitted. 
Since the rotating polygon mirrors can be stacked one on the other and the 
mount surfaces of the rotating polygon mirrors thus stacked do not make 
contact to each other, they need not be set on the evaporation jig with 
spacers being interposed when the reflection mirror surfaces are to be 
vapor deposited with Al, Cu, Ag, Au, SiO.sub.2, MgF.sub.2 or Al.sub.2 
O.sub.3 for the purpose of protection and enhancement of reflection 
property of the surface. Accordingly, a plurality of rotating polygon 
mirrors 30 can be set side by side on the evaporation jig shaft 19 shown 
in FIG. 5. Thus, the number of rotating polygon mirrors accommodated in 
the evaporation bath increases and manufacturing efficiency is improved. 
Since the rotating polygon mirrors of the present invention can be stacked 
without damaging them, they may be processed in the stacked position in a 
precise grinding or polishing process to form mirror surfaces. 
Accordingly, the manufacturing efficiency is further improved.