Optical: systems and elements – Deflection using a moving element
Reexamination Certificate
1998-10-09
2001-06-05
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Deflection using a moving element
C359S198100, C359S212100, C359S216100
Reexamination Certificate
active
06243184
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to optical scanners and, more particularly, to methods and apparatus for controlling the airflow produced by a rotating optical component.
Some printers and scanners employ optical sources such as lasers to repeatedly scan an image field. For example, the light beam may sweep out a strip on an object being scanned while the surface of the object moves past the scanning beam. The object may be a document or a surface covered with a photo sensitive medium such as unexposed film or a laser printing drum. To variably expose the photo sensitive medium, the scanning beam may be modulated. To produce the repeated sweep scans, the scanner may employ a rotating mechanical device which sweeps an incoming optical beam along the scan strip at least once during each rotation period.
FIG. 1
schematically illustrates a portion of a light scanner
5
. A light source
10
produces an incoming visible or infrared light beam
15
. A mirror
20
has one or more reflecting facets
50
,
55
that deflect the incoming light beam
15
, towards a focusing lens system
25
, which produces a scan beam
30
. The scan beam
30
sweeps out a scan strip
35
in the image field. To produce the sweeping action of the scan beam
30
, a motor
40
rotates the mirror
20
at a pre-determined angular velocity. During a portion of the rotation period of the mirror
20
, the scan beam
30
sweeps out the strip
35
.
For a high resolution scan, the strip
35
is a very fine, for example, less than about {fraction (1/1000)} of an inch wide. To scan an image field rapidly with such fine scan beams, the motor
40
typically turns the mirror
20
at a high frequency, for example, 20,000 revolutions per minute (RPM).
In high-resolution printing, very small variations in the scan beam
30
can produce image defects detectable by the human eye. Time-varying refractive indices along the incoming and/or deflected light beams
15
,
45
can displace the scan beam
30
by as much as the distance between successive scan strips
35
on the object being scanned (not shown) thereby causing the image defects. Small variations in the local air density can produce a changing refractive index sufficient to cause such image defects in highresolution devices.
The rotating mirror
20
generates pressure waves in the adjacent air. A first source of such waves is a time-changing form, which an axially non-symmetric and rotating mirror presents to adjacent air, in each direction about the rotation axis. For example, the facets
50
,
55
destroy full axial symmetry of the mirror
20
. A second source of pressure waves is viscous drag caused by the rotational velocity of the mirror
20
. Viscous drag can produce pressure waves even if the mirror
20
is replaced by a very symmetric beam deflector (not shown) such as a hologon or holographic deflector. For high-resolution scanners, the high rotational speed of the mirror
20
can produce turbulent and/or vortex airflow in the work space surrounding the mirror
20
. The vortex or turbulent air flow presents a time-dependent air density and refractive index for the incoming and reflected beams
15
,
45
. The turbulent airflow can noticeably degrade the quality of an image scan by introducing image defects known as turbulence banding.
One method of eliminating image defects such as turbulence banding entails evacuating the work space around rotating optical parts such as the mirror
20
of FIG.
1
. Evacuating the work space generally requires a complex and costly vacuum source. The vacuum source may also add significant bulk to the optical scanner. Thus, operating the rotating mirror in a vacuum may not be a convenient or cost-efficient method for eliminating defects such as turbulence banding.
The present invention is directed to overcoming, or at least reducing, one or more of the problems set forth above.
SUMMARY OF THE INVENTION
In a first aspect, the invention provides a light scanner. The light scanner includes a beam deflector supported for rotary motion to deflect an incoming light beam into an image field in response to being rotationally aligned. A motor mechanically couples to rotate the deflector in and out of the rotational alignment. The deflector scans the image field with the deflected incoming light in response to being rotated. The invention features a gas permeable screen structure partially enclosing a region adjacent the rotating deflector. The screen structure reduces gas turbulence in the region of the deflector.
In a second aspect, the invention provides a method of optically scanning an image field. The method features deflecting an incoming light beam off a beam deflector to produce a deflected light beam and rotating the beam deflector to scan an image field with the deflected beam. The beam deflector rotates in a gaseous environment. The method features passing a portion of a gas flow between the rotating beam deflector and the adjacent region through a screen structure.
REFERENCES:
patent: 4583816 (1986-04-01), Kramer
patent: 4973112 (1990-11-01), Kramer
patent: 5726699 (1998-03-01), Itami et al.
patent: 5867296 (1999-02-01), Parl et al.
Cappiello Gregory G.
Weeks Alan L.
ECRM, Inc.
Fish & Richardson P.C.
Schuberg Darren
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