Methods are apparatus for monitoring the diffuse reflectivity of a surface
First Claim
1. A method of monitoring the diffuse reflectivity of a portion of a surface (3), the method comprising:
- exposing the surface portion to a beam of radiation (9);
sensing the intensity of a part of the diffuse radiation, reflected by the surface portion, at two sensing positions situated such that the intensity of the diffusely reflected radiation, sensed at each sensing position, is substantially invariant within a working range of distances (D) between the sensing position and the surface portion, the size and position of the surface portion within the plane of the surface being substantially constant within the working range of distances; and
determining from each sensed intensity a value representative of the diffuse reflectivity of the surface portion;
the method further comprising;
arranging the sensing positions in symmetrical locations to either side of the beam of radiation; and
averaging the intensities sensed at the sensing positions to obtain a diffuse reflectivity value for the surface portion which is substantially invariant to folds and creases in the surface portion.
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Accused Products
Abstract
A method and apparatus for monitoring the diffuse reflectivity of a portion of a surface. The method is particularly applicable to soil detection of banknotes. The method comprises exposing the surface portion (3) to a beam of radiation from a source (2). At least one part of the diffuse radiation reflected by the surface portion (3) is sensed by a sensor (6) located closely behind an aperture (7) such that the aperture (7) defines, in effect, a sensing position situated such that the intensity of the diffusely reflected radiation sensed is substantially invariant within a working range of distances (D) between the aperture (7) and the surface portion (3). A value representative of the diffuse reflectivity of the surface portion (3) is then determined from the sensed intensities.
104 Citations
17 Claims
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1. A method of monitoring the diffuse reflectivity of a portion of a surface (3), the method comprising:
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exposing the surface portion to a beam of radiation (9); sensing the intensity of a part of the diffuse radiation, reflected by the surface portion, at two sensing positions situated such that the intensity of the diffusely reflected radiation, sensed at each sensing position, is substantially invariant within a working range of distances (D) between the sensing position and the surface portion, the size and position of the surface portion within the plane of the surface being substantially constant within the working range of distances; and determining from each sensed intensity a value representative of the diffuse reflectivity of the surface portion; the method further comprising; arranging the sensing positions in symmetrical locations to either side of the beam of radiation; and averaging the intensities sensed at the sensing positions to obtain a diffuse reflectivity value for the surface portion which is substantially invariant to folds and creases in the surface portion. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 11)
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9. Apparatus for monitoring the diffuse reflectivity of a surface, the apparatus comprising:
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a radiation beam source (2); a surface support member (10) mounted such that the radiation impinges, in use, on a surface (3) supported by the support member such that the size and position of a portion of the surface within the plane of the surface and exposed to the radiation beam remains substantially constant with variations within a working range of separations between the surface and the support member; and two radiation sensors (6) for generating respective signals for feeding to processing means (11);
each signal corresponding to the intensity of a part of the diffuse radiation reflected by the surface and passing through a sensing position, and each sensing position being situated such that the intensity of the diffusely reflected radiation sensed thereat is substantially invariant within a working range of distances (D) between the sensing position and the surface portion (3);the sensing positions being arranged in symmetrical locations to either side of the beam of radiation; the apparatus further comprising means for averaging the respective signals sensed at the sensing positions to obtain a diffuse reflectivity value for the surface portion which is substantially invariant to folds and creases in the surface portion. - View Dependent Claims (10, 12, 14, 15, 16, 17)
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13. Apparatus according to claim 90, wherein at least part of the support member (10) is movable relatively to the beam of radiation (9) and each sensing position whereby a series of positions on the surface is scanned.
Specification