Highspeed Document Sensing and Imaging Optical System

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High-speed Document Sensing and Imaging Optical
System
CANON PIXMA mini320 Compact Photo Printer
Tom Harris, How Laser Printers Work

• Xiao Zhang
• Project advisor Peter B. Catrysse

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Motivation
The system that we will model and analyze in this
project is a new high-speed digital sensing
solution-reflective imaging system for real-time
misprint detection in short-run printing presses.
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Motivation

• Conventional Imaging System
• Low photon capture capability.
• Near Contact System
• Excellent photon capture capability.
• Hard to illuminate the surface.
• Requires the same length of sensor as the web
  width.
• Reflective Imaging System
• Fairly good photon capture capability.
• May have big blurring effects.
• Thus a detailed comparison study is needed for
  evaluation of the possibility to use the
  reflective imaging system.

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Background-f number
An aberration free lens will generate a spherical
wavefront whose radial extent is governed by the
numerical aperture NAn1sina
EE317 Notes
f1/(2NA). For far contact lens, ff/aperture
diameter. For near contact system, f/0.5.
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Background-Refraction at a spherical glass
surface
EE317 Notes
Note that the angle of deflection, (q1- q2), is
proportional to the radius. As q1 increases the
first order approximation becomes more dubious
and aberrations become significant and not all
rays (for different q1) will cross the axis at
the same point this is spherical aberration.
Correcting for spherical, and other, aberrations
can be accomplished by incorporating many
refracting surfaces this is beyond the scope of
this course.
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Background-spherical aberration
W J. Smith Modern Optical Engineering
Spherical aberration is due to nonlinear effect
of Snells law. There are longitudinal and
transverse spherical aberrations. Spherical
aberration is on-axis effect. LA1/(f)2,
TA1/(f)3
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Background- Coma
W J. Smith Modern Optical Engineering
Coma is due to nonlinear effect of Snells
law. There are tangential and sagittal spherical
aberrations. Coma is an off-axis
effect. Tangential/sagittal coma1/(f)2
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Background- Coma
W J. Smith Modern Optical Engineering
Coma is due to nonlinear effect of Snells
law. There are tangential and sagittal
comas. Coma is off-axis effect. Tangential
coma1/(f)2
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Background- Astigmatism
Astigmatism occurs when the tangential and
sagittal (sometimes called radial) images do not
coincide. In the presence of astigmatism, the
image of a point source is not a point, but takes
the form of two separate Lines. Negligible in
this study.
W J. Smith Modern Optical Engineering
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Reflective imaging optics-paraboloidal mirror
Image/stop is at the focus plane
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Reflective imaging optics-spherical mirror
Image is at the focus plane Stop is at R, fR/2,
yR
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Photon Capture
By Peter Catrysse
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Photon Capture
By Peter Catrysse
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Photon Capture
By Peter Catrysse
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Angular Blurring
Not diffraction limited system Spherical
aberration 0 Asigmatism0, because stop is at
the focus plane. Sagittal coma
Up/16(f/)2Up Tangential coma Ffxfy2/4f,
for an f/0.25 paraboloid the marginal zone focus
length is twice that of the paraxial zone and the
magnification is correspondingly large. Optical
view angel 1 Radians (object size20cm,
D10cm), 1/64 of conventional imaging system.
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Angular Blurring
Not diffraction limited system Spherical
aberration 0.0078/(f/)30.5 radians, 512 times
more than conventional imaging system! Asigmatism
0, because stop is at the focus plane. Coma 0,
intrinsic property of spherical mirror. f/0.5
works, blurring0.0625 radians, but photon
reduces to 7.7E-15.
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Conclusion

• Conventional Imaging System
• Low photon capture capability.
• Near Contact System
• Excellent photon capture capability.
• Hard to illuminate the surface.
• Requires the same length of sensor as the web
  width.
• Reflective Imaging System
• Fairly good photon capture capability.
• But strong blurring effects.
• Need a trade-off f/ for reasonable photon
  capture and blurring effects.

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Conclusion

• Spherical mirror
• Fairly good photon capture capability.
• The blurring is limited by a constant spherical
  aberration over field angles.
• Solution Use relatively large f/ (for example,
  0.5).
• Paraboloidal mirror
• Fairly good photon capture capability.
• The blurring is limited by coma proportional to
  field angles.
• Free of chromatic aberration.
• Solution The key is to reduce the object size-
  Use multiple paraboloidal mirrors to image
  different parts of the web. In this case, the
  advantage of photon capture with a small f (for
  example, 0.25), can be retained. But the
  fabrication cost increases.

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Thank you!