Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1996-11-13
2001-02-27
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140RC, C235S455000, C330S085000
Reexamination Certificate
active
06194698
ABSTRACT:
DESCRIPTION
The present invention relates to electro-optical sensors and particularly to an electro-optical sensing system which senses the presence or absence of marks on a sheet as the sheet is scanned by the sensor.
The invention is especially suitable for use as an optical detection system for electronic voting apparatus which reads and counts votes corresponding to marks on a paper ballot which are made by a voter at places on the paper corresponding to candidates and issues to be voted upon. Such electronic voting apparatus is sometimes called electronic, computerized vote counting apparatus and may be of the type described in U.S. Pat. No. 4,774,665 issued Sep. 27, 1988 to Kenneth D. Webb. A commercially available vote counting apparatus is available from Global Election Systems, Inc. of Vancouver, British Columbia, Canada and called the “Accu-vote”. The sensor provided by the invention may also be used in scanning answer sheets and other optical information bearing media to derive information from optically discernable marks thereon and is also useful wherever a linear or continuous detector array is required in that it enables such an array to be provided by a plurality of discrete photodetectors, such as photodiodes which are spatially arranged to detect light throughout a pre-defined detection region as may be required by the application to which the detector array is to be put.
Sensing of marks, especially when the marks are on a paper ballot, should sense these marks as they are perceived by the person who makes them on the sheet (the voter on the ballot).
The sensor must not fail to read such marks nor must marks which are out of prescribed locations be read so as to create the danger of counting false marks. Marks are read on the basis of the density of the illumination. This illumination may be deflected from the paper, although it is within the scope of the invention, especially when the paper is thin, to sense the marks from illumination which is transmitted through the paper. Reflected illumination is mentioned hereinafter for purposes of illustrating the presently preferred embodiment of the invention.
In order that marks are sensed by the sensor as perceived in their existence and location by the voter, it is necessary to avoid optical conditions which will interfere with the sensing of the marks as perceived. Thus, the use of non-visible illumination (for example infra-red or IR) may give rise to such conditions. Certain marking materials do not absorb in the infra-red, for example those made by felt tip markers or ink jet printers. Voting on paper ballots in many states is not restricted to specific voting places or precincts. Thus, the use of the marking media is not controllable by the election officials. While IR sensitive detectors have the benefit of less sensitivity to ambient light than do visible light sensitive detectors, it has been found, in accordance with the invention, that the effects of ambient illumination, as well as variation in photo currents and particularly in dark current response and in the characteristics of signal handling and processing amplifiers associated with the detectors, may be compensated without affecting detection thresholds for actual marks.
Another problem related to the marking medium arises out of the use of pencil. The oriented graphite layer of a pencil mark produces specular (mirror-like) reflection rather than diffuse reflection, and effectively reduces the contrast of the reflected illumination so that a pencil mark may not be detected because it produces a signal below the threshold for detection of an actual mark. It is a feature of this invention to use polarized light which is transmitted from the sources of illumination (e.g., LEDs) and is received at the photodetectors (photodiodes for example) via cross-polarizers. Specular reflection is then attenuated thus enhancing contrast of the mark.
In order to detect marks at desired locations which may be in adjacent columns spaced laterally across the sheet, it is desirable to constrain the sensing action to discrete and contiguous zones which are spaced laterally corresponding to the columns in which actual marks are supposed to be made. Leakage of light from regions including other zones which are not being interrogated should be restricted and reduced to a level where such leakage light does not produce signals exceeding the threshold for actual mark detection. The use of apertures or so-called optical hard stops to define the zones in which the paper is illuminated and from which marks may be detected may be undesirable, because apertures tend to vignette illumination which is not directly perpendicular to the zone. Space requirements for the sensor package preclude the use of perpendicular angles (normal) incidence and reflection. In addition, lateral paper meandering, as well as paper motion toward and away from the detector can cause vignetting and effectively modulate the intensity of the detected illumination to an extent where actual marks may produce illumination below the threshold for detection. It is a feature of the invention to provide an electro-optical sensor capable of sensing marks in discrete and adjacent zones on which illumination is focused and from which reflected illumination is focused on photodetectors without the use of apertures or stops to define the zones and without requiring normal incident and reflected illumination to and from the zones.
Paper, especially ballots which are marked, may be folded or even spindled, creased or so mutilated as to have a non-uniform surface. As in the above-referenced patent and in the Accu-vote system the paper ballots are inserted into a slot and then mechanically engaged and driven through the sensor. In this connection it is desirable that both sides of a ballot be read simultaneously during one pass through the sensor. Accordingly, it is desirable to have two sensor boards on opposite sides of the paper. This exacerbates the non-uniformity of the surface presented to the sensors, for example one sensor board may see a peak in the surface while the sensor reading the opposite side of the paper sees a valley. Such peaks and valleys can cause paper motion with respect to apertures, if used in the sensor, which can affect reliable reading of the marks. It is a feature of this invention to provide sensors which use cylindrical rod lenses which extend laterally over the columns of marks and which form the discrete zones of illumination and detection without the need for apertures. The rods also provide a mechanical reference surface which sets the distance between the illumination and detection components of the sensors and the surface of the paper. The reference surface is maintained in contact with the paper by applying a spring pre-load to the sensor assembly in the direction of the paper via flexures on which the sensor assemblies are mounted. The rods thus provide a mechanical means for setting the distance of the sensor assembly to the paper and locating the zones at the paper in locations corresponding to the columns where marks may be placed by the voter. In accordance with another feature of the invention, the unitary sensor assembly includes a board, preferably a printed circuit board which serves as an alignment fixture which locates the illuminating beam (a solid cone of illumination emanating preferably from a source having a lenslet which focuses the light from the LED junction). The beam may then be adjusted in the plane of the board (in x and y) as well as in angular inclination with respect to the rod lens so as to be focused by the lens, which condenses the beam into a generally oblong shape which is narrowest in the longitudinal direction along the columns and of the width of the columns and with a spacing in a lateral direction corresponding to the spacing of the columns. Similarly, the photodetectors may be photodiodes attached, as by soldering, aligned over an opening in the board offset longitudinally from the LED which scans the same zone and on which the reflected light i
Grodevant Scott R.
Zavislan James M.
Lee John R.
Lucid Inc.
Lukacher Kenneth J.
Lukacher Martin
Pyo Kevin
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