Optics: measuring and testing – Shape or surface configuration – By focus detection
Reexamination Certificate
2001-02-01
2004-02-24
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
By focus detection
C356S601000
Reexamination Certificate
active
06697164
ABSTRACT:
FIELD OF THE INVENTION
This invention in the field of imaging techniques and relates to a method and an apparatus for non-contact imaging of three-dimensional structures, particularly useful for direct surveying of teeth.
BACKGROUND OF THE INVENTION
A great variety of methods and systems have been developed for direct optical measurement of teeth and the subsequent automatic manufacture of dentures. The term “direct optical measurement” signifies surveying of teeth in the oral cavity of a patient. This facilitates the obtainment of digital constructional data necessary for the computer-assisted design (CAD) or computer-assisted manufacture (CAM) of tooth replacements without having to make any cast impressions of the teeth. Such systems typically includes an optical probe coupled to an optical pick-up or receiver such as charge coupled device (CCD) and a processor implementing a suitable image processing technique to design and fabricate virtually the desired product.
One conventional technique of the kind specified is based on a laser-triangulation method for measurement of the distance between the surface of the tooth and the optical distance probe, which is inserted into the oral cavity of the patient. The main drawback of this technique consists of the following. It is assumed that the surface of the tooth reflects optimally, e.g. Lambert's reflection. Unfortunately, this is not the case in practice and often the data that is obtained is not accurate.
Other techniques, which are embodied in CEREC-l and CEREC-2 systems commercially available from Siemens GmbH or Sirona Dental Systems, utilize the light-section method and phase-shift method, respectively. Both systems employ a specially designed hand-held probe to measure the three-dimensional coordinates of a prepared tooth. However, the methods require a specific coating (i.e. measurement powder and white-pigments suspension, respectively) to be deposited to the tooth. The thickness of the coating layer should meet specific, difficult to control requirements, which leads to inaccuracies in the measurement data.
By yet another technique, mapping of teeth surface is based on physical scanning of the surface by a probe and by determining the probe's position, e.g. by optical or other remote sensing means, the surface may be imaged.
U.S. Pat. No. 5,372,502 discloses an optical probe for three-dimensional surveying. The operation of the probe is based on the following. Various patterns are projected onto the tooth or teeth to be measured and corresponding plurality of distorted patterns are captured by the probe. Each interaction provides refinement of the topography.
SUMMARY OF THE INVENTION
The present invention is directed to a method and apparatus for imaging three-dimensional structures. A preferred, non-limiting embodiment, is concerned with the imaging of a three-dimensional topology of a teeth segment, particularly such where one or more teeth are missing. This may allow the generation of data for subsequent use in design and manufacture of, for example, prosthesis of one or more teeth for incorporation into said teeth segment. Particular examples are the manufacture of crowns or bridges.
The present invention provides, by a first of its aspects, a method for determining surface topology of a portion of a three-dimensional structure, comprising:
(a) providing an array of incident light beams propagating in an optical path leading through a focusing optics and a probing face; the focusing optics defining one or more focal planes forward said probing face in a position changeable by said optics, each light beam having its focus on one of said one or more focal plane; the beams generating a plurality of illuminated spots on the structure;
(b) detecting intensity of returned light beams propagating from each of these spots along an optical path opposite to that of the incident light;
(c) repeating steps (a) and (b) a plurality of times, each time changing position of the focal plane relative to the structure; and
(d) for each of the illuminated spots, determining a spot-specific position, being the position of the respective focal plane, yielding a maximum measured intensity of a respective returned light beam; and
(e) based on the determined spot-specific positions, generating data representative of the topology of said portion.
By a further of its aspects, the present invention provides an apparatus for determining surface topology of a portion of a three-dimensional structure, comprising:
a probing member with a sensing face;
an illumination unit for providing an array of incident light beams transmitted towards the structure along an optical path through said probing unit to generate illuminated spots on said portion;
a light focusing optics defining a one or more focal planes forward said probing face at a position changeable by said optics, each light beam having its focus on one of said one or more focal plane;
a translation mechanism coupled to said focusing optics for displacing said focal plane relative to the structure along an axis defined by the propagation of the incident light beams;
a detector having an array of sensing elements for measuring intensity of each of a plurality of light beams returning from said spots propagating through an optical path opposite to that of the incident light beams;
a processor coupled to said detector for determining for each light beam a spot-specific position, being the position of the respective focal plane of said one or more focal planes yielding maximum measured intensity of the returned light beam, and based on the determined spot-specific positions, generating data representative of the topology of said portion.
The probing member, the illumination unit and the focusing optics and the translation mechanism are preferably included together in one device, typically a hand-held device. The device preferably includes also the detector.
The determination of the spot-specific positions in fact amounts to determination of the in-focus distance. The determination of the spot-specific position may be by measuring the intensity per se, or typically is performed by measuring the displacement (S) derivative of the intensity (I) curve (dI/dS) and determining the relative position in which this derivative function indicates a maximum maximum intensity. The term “spot-specific position (SSP)” will be used to denote the relative in-focus position regardless of the manner in which it is determined. It should be understood that the SSP is always a relative position as the absolute position depends on the position of the sensing face. However the generation of the surface topology does not require knowledge of the absolute position, as all dimensions in the cubic field of view are absolute.
The SSP for each illuminated spot will be different for different spots. The position of each spot in an X-Y frame of reference is known and by knowing the relative positions of the focal plane needed in order to obtain maximum intensity (namely by determining the SSP), the Z or depth coordinate can be associated with each spot and thus by knowing the X-Y-Z coordinates of each spot the surface topology can be generated.
In accordance with one embodiment, in order to determine the Z coordinate (namely the SSP) of each illuminated spot the position of the focal plane is scanned over the entire range of depth or Z component possible for the measured surface portion. In accordance with another embodiment the beams have components which each has a different focal plane. Thus, in accordance with this latter embodiment by independent determination of SSP for the different light components, e.g. 2 or 3 with respective corresponding 2 or 3 focal planes, the position of the focal planes may be changed by the focusing optics to scan only part of the possible depth range, with all focal planes together covering the expected depth range. In accordance with yet another embodiment, the determination of the SSP involves a focal plane scan of only part of the potential depth range and for illuminated spots w
Babayoff Noam
Glaser-Inbari Isaia
Cadent Ltd.
Fitch Even Tabin & Flannery
Font Frank G.
Punnoose Roy M.
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