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Optical Character Reader with Extended Effective Depth of Field

IP.com Disclosure Number: IPCOM000115412D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 106K

Publishing Venue

IBM

Related People

Mallory, DA: AUTHOR [+2]

Abstract

Described is an optical character reader providing sufficient depth of field to be used as a hand-held device while having sufficient light developed using LEDs (Light Emitting Diodes) to image a CCD (Charge Coupled Device) array. An extended depth of field is provided by changing the optical path length within the device during the scanning process. Data returned while the target is in focus is returned to a data processing system, while invalid data generated while the object is out of focus is discarded.

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Optical Character Reader with Extended Effective Depth of Field

      Described is an optical character reader providing sufficient
depth of field to be used as a hand-held device while having
sufficient light developed using LEDs (Light Emitting Diodes) to
image a CCD (Charge Coupled Device) array.  An extended depth of
field is provided by changing the optical path length within the
device during the scanning process.  Data returned while the target
is in focus is returned to a data processing system, while invalid
data generated while the object is out of focus is discarded.

      Fig. 1 is an isometric view of apparatus for illuminating the
target, together with an entry window for receiving light reflected
from the target.  The target 1, or object to be scanned, is
illuminated by a pair of LEDs 2 in light pipes 3.  Each light pipe 3
includes a rear surface 4 obliquely aligned to reflect light from an
associated LED 2 through a curved front surface 5 toward the target
1.  Since the wave length of light generated by LEDs 2 is in the
visible range, the illuminated pattern produced on the target assists
the user in guiding the device.  Light reflected from the target 1 is
transmitted through an entry window 6 having optical bandpass
properties enhancing the reading ability of the device.

      Fig. 2 is a plan view of the major optical and mechanical
elements of the optical character reader as they are held in a
quiescent, non-operating state.  During operation of the device,
light transmitted through entry window 6 is reflected by a folding
mirror 7, to be focused through a lens 8 on the active surface 9 of a
CCD array 10.  Mirror 7 reduces the overall size of the reading
device by folding the light path.  Lens 8 and CCD array 10 are
mounted on a slide 11 to be moved from the position in which they are
shown in the direction of arrow 12.  Slide 11 includes a rack 13,
which engages a first gear 14 turning with a second gear 15.  An
actuating slide 16, which is also mounted to slide in and opposite to
the direction of arrow 12, includes a rack 17 engaging second gear
15.  Thus, when actuating slide is moved in the direction opposite
arrow 12, slide 11 is moved in the direction of arrow 12.  Slide 11
is shown in its rearmost position, as far as it can be moved in the
direction opposite arrow 12.  Movement from this position is detected
by means of a photodetector 18, which is illuminated by an LED 19 as
end tab 20 of slide 11 moves in the direction of arrow 12.

      When an optical system of this kind is held stationary, a sharp
image of the target is focussed on the active surface 9 of CCD array
10 only when the ta...