(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2012/0075425A1
`(43) Pub. Date:
`Mar. 29, 2012
`Thiel
`
`US 20120075425A1
`
`(54) HAND HELD IDENTAL CAMERA AND
`METHOD FOR CARRYING OUT OPTICAL 3D
`MEASUREMENT
`
`(75) Inventor:
`
`Frank Thiel, Ober-Ramstadt (DE)
`
`(73) Assignee:
`
`Sirona Dental Systems GmbH,
`Bensheim (DE)
`
`(21) Appl. No.:
`
`13/213,893
`
`(22) Filed:
`
`Aug. 19, 2011
`
`Related U.S. Application Data
`(63) Continuation of application No. PCT/EP2010/
`052241, filed on Feb. 23, 2010.
`
`(30)
`
`Foreign Application Priority Data
`
`Feb. 23, 2009 (DE) ...................... 10 2009 OO1 O86.6
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`H04N I3/02
`(52) U.S. Cl. ................................... 348/46; 348/E13.074
`(57)
`ABSTRACT
`A handheld dental camera performs three-dimensional, opti
`cal measurements. The camera includes a light Source that
`emits an illuminating beam, a scanning unit, a color sensor,
`and a deflector. The scanning unit focuses the illuminating
`beam onto a surface of an object to be measured. The surface
`of the object reflects the illuminating beam and forms a moni
`toring beam, which is detected by the color sensor. Focal
`points of wavelengths of the illuminating beam form chro
`matic depth measurement ranges. The scanning unit stepwise
`displaces the chromatic depth measurement ranges by a step
`width Smaller than or equal to a length of each chromatic
`depth measurement range, so that a first chromatic depth
`measurement range in a first end position of the scanning unit
`and a second chromatic depth measurement range in a second
`end position are precisely adjoined in a direction of a mea
`Surement depth, or are partially overlapped.
`
`
`
`8
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`Align Ex. 1012
`U.S. Patent No. 9,962,244
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`Patent Application Publication
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`Patent Application Publication
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`Mar. 29, 2012 Sheet 2 of 2
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`Ms. M
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`Pig
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`US 2012/0075425 A1
`
`Mar. 29, 2012
`
`HAND HELD IDENTAL CAMERA AND
`METHOD FOR CARRYING OUT OPTICAL 3D
`MEASUREMENT
`
`RELATED APPLICATIONS
`0001. This application is a continuation of International
`Application PCT/EP2010/052241, filed Feb. 23, 2010,
`claims benefit of the filing date of that application under 35
`U.S.C. S 120, and claims benefit under S 119 of German Appli
`cation No. 10 2009 001086.6, filed Feb. 23, 2009. The entire
`contents of those two applications are incorporated herein by
`reference.
`
`TECHNICAL FIELD
`0002. The invention relates to a handheld dental camera
`for carrying out optical 3D measurement using a confocal
`measuring method, which handheld dental camera comprises
`a chromatic objective, a polychromatic light Source, and a
`color sensor, and also to a method for using the dental camera
`of the invention.
`
`PRIOR ART
`0003 Confocal microscopy is well-known in the prior art
`and is disclosed, interalia, in the patent specification U.S. Pat.
`No. 3,013,467.
`0004. The chromatic confocal measuring method pro
`vides the possibility of effecting focusing without the need for
`mechanically moving components, and as a result usually
`reduce measuring time significantly, as was proposed by G.
`Molesini in 1983 in conjunction with a spectrometer (GB
`2144537 and DE 3428593 C2). An example of successful
`application of the chromatic confocal measuring method is
`described by H.J. Tiziani and H.-M.Uhde in the professional
`article "Three-dimensional image sensing by chromatic con
`focal microscopy' in Applied Optics, Vol. 33, No. 1, April
`1994, pp. 1838 to 1843. In this case, the spectral analysis is
`performed by means of three color filters. Thus the depth
`measurement range and the depth resolution achievable in
`this application are limited.
`0005. The patent specification DE 10321885 AI discloses
`a chromatic confocal system comprising a component having
`variable refractive power, for example, a diffractive compo
`nent. In the optical arrangement shown in FIG. 2 of said
`patent specification, a series of micro-lenses is provided for
`illumination in order to obtain the confocal signals via the
`wavelength, and, for analysis, a spectrometer comprising an
`area Scan camera is disposed downstream so that line profiles
`can be obtained from a single planar camera image by means
`of a line spectrometer. In the publication “Chromatic confocal
`detection for speed micro-topography measurements' by A.
`K. Ruprecht, K. Koerner, T. F. Wiesendanger, H.J. Tiziani, W.
`Osten in Proceedings of SPIE, Vol. 5302-6, pp. 53-60, 2004,
`FIG. 4 shows a chromatic confocal line sensor for topo
`graphic measurement. In this case, in order to obtain the
`confocal signals via the wavelength, a line spectrometer is
`disposed downstream of the chromatic confocal system so
`that line profiles of the surface of an object can be ascertained
`from a single camera image using a single area Scan camera
`and a line spectrometer. The use of a spectrometer basically
`allows for higher spectral resolution compared with an
`arrangement comprising three color filters or an RGB color
`camera or even a four channel color camera and is thus more
`advantageous.
`
`0006. On pages 12 and 13 of the dissertation entitled "3D
`Spektrofotometrie extragalaktischer Emissionslinien' (3D
`Spectrophotometry of extragalactic emission lines by J.
`Schmoll, submitted to the University of Potsdam in June
`2001, lenticular direct coupling is described, which was first
`applied in the TIGER spectrograph by Courtes et al. in 1988.
`In said citation, the lenticular raster is rotated through an
`angle counter to the direction of dispersion. Because of the
`shift of adjacent spectra, this technique has the reputation of
`being complicated for evaluation purposes, and the area of the
`area sensor is not utilized economically, because the filling
`factor is low. In Scientific papers, terms such as 3D-spectro
`photometry and imaging spectroscopy and integral-field
`spectrophotometry are also used in this connection.
`0007. The chromatic confocal measuring method has the
`advantage that the camera can, in principle, be one not having
`any mechanically moving components, and that the data rate
`is low, since only a single color spectrum needs to be recorded
`for any one measuring point.
`0008. However, the disadvantage of the chromatic confo
`cal measuring method is that a spectral broadband light
`Source must be used that has a wavelength spectrum that is as
`broad and continuous as possible. Therefore, primarily halo
`gen lamps and Xenongas-discharge lamps are suitable for use
`as the light source. These light sources are comparatively
`unwieldy and large, due to their design. A compact light
`Source Such as a laser diode or a Super-luminescent diode is
`less Suitable for the chromatic confocal measuring method,
`since it typically has a rather narrow wavelength spectrum.
`The depth measurement range is therefore greatly restricted
`and not suitable for measuring relatively large objects such as
`teeth.
`0009. In a classical scanning confocal measuring method
`with mechanical depth measurement, the position of a single
`focal point is moved by mechanically moving individual lens
`elements of the optical system or by moving the entire optical
`system relatively to the object. The light source used is one
`that has the narrowest possible wave spectrum in order to
`keep the area of the focal point Small. For scanning a single
`measuring point, the optical system must thus be mechani
`cally moved, in steps, over the entire measurement depth, a
`data set being acquired for each position of the optical system
`and an elevation value then determined from all of the data
`sets acquired. The resolution of the elevation values depends
`on the width of the individual mechanical steps carried out for
`moving the optical system. Therefore, the classical scanning
`confocal measuring method suffers from the shortcoming
`that very large amounts of data accumulate that have to be
`processed for the purpose of carrying out good resolution.
`0010. The classical scanning confocal measuring method
`has the advantage that compact light sources Such as LEDs
`and LDS can be used that have a narrow-band wavelength
`spectrum.
`0011. The object of this invention is to provide a confocal
`apparatus and a confocal method that makes it possible to
`carry out rapid optical 3D measurement of the object to be
`measured, in which confocal method it is possible to use a
`compact light source and the data rates are low.
`
`SUMMARY OF THE INVENTION
`
`0012. This object is achieved by means of the handheld
`dental camera of the invention and the method of the inven
`tion.
`
`0004
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`US 2012/0075425 A1
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`Mar. 29, 2012
`
`0013 The handheld dental camera of the invention for
`carrying out optical 3D measurement comprises a chromatic
`objective, a polychromatic light source, and a color sensor, in
`which handheld dental camera the polychromatic light Source
`emits an illuminating beam (8) that can be focused, at least in
`terms of one wavelength thereof, onto the surface of an object
`of interest by means of the chromatic objective. The illumi
`nating beam is reflected by the Surface to form a monitoring
`beam, which is capable of being detected by means of the
`color sensor. The focal points of the various wavelengths of
`the illuminating beam form a chromatic depth measurement
`range.
`0014. The handheld dental camera further comprises an
`movable Scanning unit comprising at least the chromatic
`objective. The chromatic depth measurement range can be
`moved in steps by means of the scanning unit so that at least
`a second chromatic depth measurement range in a second
`position of the scanning unit adjoins a first chromatic depth
`measurement range in a first position of the Scanning unit or
`at least partly overlaps the first chromatic depth measurement
`range. In this manner, an enlarged overall depth measurement
`range is formed from the at least two different depth measure
`ment ranges.
`0015 The handheld dental camera for carrying out optical
`3D measurement can be a handheld camera that is particu
`larly Suitable for producing dental intraoral images of teeth
`and that combines the principles of chromatic confocal depth
`measurement and scanning confocal depth measurement.
`0016. In the chromatic confocal measuring method, the
`measurement is carried out without mechanically moving the
`optical system in that the focal points of different wavelengths
`are distributed over the entire measurement depth and use is
`made of spectral analysis to ascertain the wavelength of
`which the focal point is located on the surface. The focal
`position, that is, the Z coordinate of the object surface can be
`ascertained from this wavelength. The resolution of the z
`coordinate depends primarily on the continuous distribution
`of wavelengths in the spectrum of the illuminating beam used,
`and on the precision of the spectral analysis used.
`0017 For this purpose, a polychromatic light source is
`used, of which the spectral range emitted in the form of the
`illuminating beam has a plurality of wavelengths. This illu
`minating beam is focused by means of a chromatic objective
`onto the object to be measured. Since a chromatic objective
`intensifies the effect of chromatic aberrations, the focal points
`for the different wavelengths of the illuminating beam are
`kept well apart. The focal points of the shortest and longest
`wavelengths of the spectral range of the illuminating beam
`can be spaced from each other by up to 5 mm, and they form
`the chromatic depth measurement range of the handheld den
`tal camera. An elevation value can be assigned to each wave
`length within this chromatic depth measurement range.
`0018. As a result of this separation of the focal points, only
`the focal point of a single wavelength or at least a very narrow
`wavelength range of the spectral range of the illuminating
`beam is located exactly on the surface of the object of interest,
`and this wavelength dominates the spectral intensity profile of
`the monitoring beam.
`0019. The monitoring beam is detected by means of a
`color sensor capable of detecting abroad spectral range and of
`differentiating the individual wavelengths. A spectrometer or
`a CCD sensor is suitable for this purpose.
`0020. Thus that wavelength of the monitoring beam that
`has the maximum intensity can be ascertained, and an eleva
`
`tion value corresponding to this wavelength can be assigned
`to the measuring point on the Surface as long as the measuring
`point is located within the chromatic depth measurement
`range.
`0021. In the present invention, use is made of compact
`polychromatic light sources such as LEDs, laser diodes
`(LDs), and super-luminescent diodes (SLDs), of which the
`wavelength spectrum is narrow compared with halogen
`lamps or Xenon gas-discharge lamps. In order to still make it
`possible to measure a sufficiently large depth measurement
`range, the chromatic confocal measuring method is combined
`with the classical scanning confocal measuring method.
`0022. In the Scanning confocal measuring method, a
`single focal point is moved along the measurement depth by
`mechanically moving the optical system stepwise, and the
`detected intensities of the monitoring beam are used to iden
`tify that step of the mechanical movement of the optical
`system in which the focal point is located exactly on the
`surface of the object to be measured. The focal position can
`then be ascertained from the step in which a maximum inten
`sity of the illuminating beam is detected. The resolution of the
`Z coordinate, i.e. the elevation value, is ascertained in this
`method by means of the step width of the mechanical move
`ment of the optical system.
`0023. By means of the scanning unit in the handheld den
`tal camera, which scanning unit comprises at least the chro
`matic objective, the plurality of focal points that are kept apart
`by the use of the polychromatic light source and the chromatic
`objective can be moved at the same time over the depth
`measurement range. The step width can be such that it is
`equal, as precisely as possible, to the length of the chromatic
`depth measurement ranges. Thus it is possible for several
`chromatic depth measurement ranges that adjoin or overlap
`each other along the Z axis to be measured Successively and a
`3D data set to be acquired for an enlarged overall depth
`measurement range from the data sets thus acquired. This
`enlarged depth measurement range is given by the Sum of the
`chromatic depth measurement ranges that adjoin or overlap
`each other. For example, a chromatic depth measurement
`range that can beachieved by means of a compact light Source
`such as an LED, L.D. or SLD can have a length of 0.5 mm. If
`an overall depth measurement range of 20 mm is to be mea
`Sured, this measurement can be carried out in 40 steps having
`a step width of 0.5 mm.
`0024. It is thus possible, in spite of a narrow chromatic
`depth measurement range, to achieve a measurement depth
`that makes it possible to Scan an object such as a tooth.
`0025. One advantage of the handheld dental camera of the
`invention over the purely chromatic confocal method is the
`ability to use more compact light sources such as LEDs, LDS,
`and SLDs, since a narrower spectral range Aw is Sufficient. It
`is therefore possible to dispense with the unwieldy and large
`light sources Such as halogen lamps and Xenon gas-discharge
`lamps that are used typically in the chromatic confocal mea
`Suring method.
`0026. A further advantage of the handheld dental camera
`of the invention is that the number of mechanical steps
`required for moving the scanning unit is significantly smaller
`than in the purely scanning confocal method and thus the
`amount of data to be processed is also significantly reduced.
`0027 Advantageously, the scanning unit can be moved to
`exactly two positions, namely, from one end position directly
`to another end position.
`
`0005
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`US 2012/0075425 A1
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`Mar. 29, 2012
`
`0028. As a result, it is possible to measure a depth mea
`Surement range that is twice as large as that possible using a
`purely chromatic confocal method, and the mechanical
`movement of the scanning unit is simpler than in the classical
`scanning confocal method since the Scanning unit moves to
`only two positions that can each be defined by means of end
`stops.
`0029 Advantageously, the handheld dental camera com
`prises a deflector, which is disposed between the chromatic
`objective and the object to be measured, the illuminating
`beam being deflectable by the deflector in a direction extend
`ing at right angles to the longitudinal axis of the handheld
`dental camera toward the object to be measured.
`0030 The deflector can be a prism or a mirror that is
`disposed at a fixed angle of 45° relative to the illuminating
`beam so that the illuminating beam is deflected at an angle of
`90° toward the object of interest. Thus the handheld dental
`camera of the invention can be of a very compact design and
`it can enable intraoral images to be collected from an awk
`ward position in the oral cavity of the patient.
`0031 Advantageously, the light source can be a halogen
`lamp or a Xenon gas-discharge lamp having a wavelength
`spectrum ranging from 500 nm to 2000 nm.
`0032. Thus a broad wavelength spectrum is provided so
`that the chromatic depth measurement range will be larger
`and the required overall depth measurement range will be
`covered in only a few steps. Since halogen lamps and Xenon
`gas-discharge lamps are too large to be integrated in a com
`pact handheld dental camera, they can be connected to the
`handheld dental camera by, say, a fiber-optic light guide.
`0033 Advantageously, the light source can be a super
`luminescent diode (SLD).
`0034. A super-luminescent diode (SLD) is a diode that has
`a relatively broad wavelength spectrum and output power
`comparable to that of laser diodes and showing extremely low
`spectral noise.
`0035. The use of an SLD has the advantage that it can be
`integrated in a handheld dental camera due to its compact
`design, while a relatively broad wavelength spectrum is pro
`vided in spite of its compactness.
`0036 Advantageously, the super-luminescent diode
`(SLD) can have a spectrum having a wavelength ranging from
`900 nm to 1000 nm.
`0037. There are different types of Super-luminescent
`diodes having different wavelength ranges. The SLD having
`a wavelength range of from 900 nm to 1000 nm has a rela
`tively constant intensity at all wavelengths. The color sensor
`used must be chosen according to the wavelength-dependent
`intensity profile Such that the wavelength-dependent detec
`tion efficiency is not reduced to zero.
`0038 Advantageously, the super-luminescent diode
`(SLD) can have a spectrum having a wavelength ranging from
`1500 nm to 1650 nm.
`0039 Thus abroader wavelength spectrum is provided, as
`a result of which the number of mechanical scanning steps
`can be reduced.
`0040 Advantageously, the light source can be a white
`light LED.
`0041. On account of its compactness, a white-light LED
`can be integrated in a handheld dental camera, and the broader
`spectrum of a white-light LED makes it possible to reduce the
`number of mechanical scanning steps.
`0042 Advantageously, the chromatic depth measurement
`range can have a length of from 0.5 mm to 5 mm.
`
`0043. Thus the handheld dental camera of the invention is
`particularly suitable for scanning teeth. Therefore, for
`example, an overall depth measurement range of 30 mm can
`be measured in only six steps of 5 mm each.
`0044 Advantageously, the handheld dental camera com
`prises a data processing unit or a connector to which a data
`processing unit can be connected. By means of the data pro
`cessing unit, it is possible to acquire data and produce a data
`set for each chromatic depth measurement range. These dif
`ferent data sets can then be combined to form an overall 3D
`data set for the total depth measurement range.
`0045 Thus the handheld dental camera can be of compact
`design and capable of covering a depth measurement range
`that makes it possible to measure an entire tooth.
`0046 Advantageously, the scanning unit can be moved
`mechanically at a frequency ranging from 1 Hz to 1000 Hz.
`0047 Thus the surface of the object of interest can be
`scanned in a relatively short period of time. When use is made
`of a handheld camera, it is particularly important that the
`intervals between exposures be as short as possible, since a
`user cannot hold the camera steadily for more than very short
`periods of time.
`0048 Advantageously, a pivotal mirror is disposed
`between the light source and the surface of the object so that
`the illuminating beam can be moved, in steps, in the lateral
`direction over the entire surface of the object of interest by
`stepwise tilting of the pivotal mirror.
`0049. Depending on the embodiment, there is provided
`eitherapattern that entirely covers the surface of the object to
`be measured, or a line, or a single dot in the Xy plane to serve
`as the illuminating beam. In the case of a line, this must be
`moved stepwise across the object in a direction at rightangles
`to the line, and an image must be produced at each step so that
`the individual data sets can then be combined to form a data
`set for the entire object of interest. Similarly, an illuminating
`beam in the form of a dot must be moved stepwise across the
`object in the X and y directions, and the individual data sets
`can then be combined to forman overall data set of the object
`of interest.
`0050. It is a further object of the invention to provide a
`method for carrying out optical 3D measurement, in which
`method an illuminating beam emitted by a polychromatic
`light source is focused, at least in terms of one wavelength
`thereof, by a chromatic objective onto the surface of an object
`to be measured, and the illuminating beam reflected by the
`Surface to form a monitoring beam is detected by a color
`sensor. The focal points of the different wavelengths of the
`illuminating beam form a chromatic depth measurement
`range. A scanning unit comprising at least the chromatic
`objective is moved stepwise Such that at least a second chro
`matic depth measurement range in a second position of the
`scanning unit adjoins or partly overlaps a first chromatic
`depth measurement range in a first position of the scanning
`unit. In this way, an enlarged overall depth measurement
`range is formed from the at least two depth measurement
`ranges.
`0051 One advantage of the method of the invention is that
`scanning is carried out more rapidly than in the classical
`scanning method, since the scanning unit is mechanically
`moved, not continuously but only between a few, at least two,
`predetermined positions.
`0.052 A further advantage of the method of the invention is
`that lower data rates occur which can be analyzed using
`existing methods in a relatively short period of time.
`
`0006
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`US 2012/0075425 A1
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`Mar. 29, 2012
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`0053 Advantageously, the scanning unit is moved just
`once from one end position directly to another end position.
`0054 As a result, a depth measurement range can be mea
`Sured that is larger than that possible in a purely chromatic
`confocal method, and the movement of the scanning unit can
`be carried out more simply than is possible in the classical
`scanning confocal method, since the scanning unit moves
`only to two positions that can each be defined by with end
`stops.
`0055 Advantageously, the illuminating beam is deflected
`by a deflector toward the object of interest.
`0056. Thus the direction of the illuminating beam is
`adjusted in a simple manner, for example by means of a
`deflection mirror.
`0057 Advantageously, a light source having a spectral
`range of from 300 nm to 2000 nm is used.
`0058. Thus a relatively large chromatic depth measure
`ment range can be scanned in a single step so that only a few
`steps are required for measuring the entire object.
`0059 Advantageously, a light source having a spectral
`range of from 900 nm to 1000 nm or from 1500 nm to 1650
`nm is used.
`0060. In this case, it would be necessary to carry out more
`steps for measuring the entire object, but compact light
`sources such as LEDs, LDs and SLDs can be used.
`0061 Advantageously, focal points for the different wave
`lengths are enlarged so that a chromatic depth measurement
`range having a length of from 0.5 mm to 5 mm may be
`achieved.
`0062. Thus fewer steps need to be carried out for move
`ment of the scanning unit, which makes it possible to scan the
`object of interest more rapidly.
`0063 Advantageously, a data set is ascertained for each
`chromatic depth measurement range, the data sets being
`saved in the handheld dental camera and then combined to
`form a 3D data set of the object of interest or transmitted to a
`data processing unit.
`0064. If only small quantities of data are to be processed,
`it is possible to reduce the data-transmission time by process
`ing these data within the camera. In the case of larger quan
`tities of data, it may be advantageous to carry out the data
`processing externally of the camera.
`0065 Advantageously, the scanning unit can be moved at
`a frequency ranging from 1 Hz to 1000 Hz.
`0066. Thus the surface of the object to be measured can be
`measured in a relatively short period of time, and an appro
`priate handheld dental camera can therefore be held in the
`hand in order to carry out a measuring process.
`0067. Advantageously, the illuminating beam is moved in
`the lateral direction across the entire surface of the object of
`interest by stepwise tilting of a pivotal mirror.
`0068. As a result, the entire object of interest can be
`scanned even when the illuminating beam is incident upon the
`object only in the form of a dot or a line.
`0069 Advantageously, the movement of the scanning unit
`for the purpose of measuring the individual chromatic mea
`Suring regions giving the total measuring region is carried out
`in a number of steps. Then the Scanning unit is moved back to
`its first position in an additional step, and this scanning cycle
`of the scanning unit is repeated until the measuring procedure
`is complete.
`0070 Thus the illuminating beam is moved, in steps, from
`a top end of the total depth measurement range to a bottom
`end of the total depth measurement range and back to its
`
`original position at the top end of the total depth measurement
`range for the purpose of measuring the next adjacent measur
`ing point. This scanning cycle provides more rapid measure
`ment of the entire surface.
`0071 Advantageously, the movement of the scanning unit
`for the purpose of measuring the individual chromatic mea
`Suring regions giving the total measuring region is carried out
`in a number of steps. Then the Scanning unit is moved back, in
`steps, to its first position, and this scanning cycle of the
`scanning unit is repeated until the measuring procedure is
`complete.
`0072 This scanning cycle omits the step in which the
`illuminating beam is moved back to its original position, so
`that the duration of the scanning procedure is shortened.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0073 Exemplary embodiments of the invention are shown
`in the drawings, in which:
`0074 FIG. 1 shows a handheld dental camera:
`0075 FIG. 2 is a first diagram of a measuring sequence
`0076 FIG.3 is a second diagram of a measuring sequence.
`
`EXEMPLARY EMBODIMENTS
`0077 FIG. 1 shows an exemplary embodiment of a hand
`held dental camera 1 of the invention for carrying out 3D
`measurements. The handheld dental camera 1 comprises a
`scanning unit which, in this exemplary embodiment, com
`prises a chromatic objective 2, a polychromatic light source 3.
`a pivotal mirror 5, and a beam splitter 6, and which is capable
`of being moved along the longitudinal axis A within the
`handheld dental camera 1. The handheld dental camera 1
`further comprises a color sensor 4, a deflector 7, for example
`a deflection mirror, and a connector 11 to which a data pro
`cessing unit 12 can be connected.
`0078. The polychromatic light source 3 emits an illumi
`nating beam 8 that passes through the beam splitter 6, for
`example, a semi-transparent mirror or a beam splitter prism,
`with as little obstruction as possible, and is deflected by the
`pivotal mirror 5 toward the chromatic objective 2. The illu
`minating beam 8 is focused by the chromatic objective and
`deflected by the deflector 7 toward the object 9 of interest,
`such as a tooth. The surface 10 of the object 9 of interest
`reflects a portion of the illuminating beam 8 back into the
`handheld dental camera 1 in the form of a monitoring beam 8'.
`The monitoring beam 8 is deflected by the deflector 7 toward
`the chromatic objective 2, and it passes through the chromatic
`objective 2, and is deflected by the pivotal mirror 5 toward the
`beam splitter 6, and is deflected to a maximum extent by the
`beam splitter 6 toward the color sensor 4, such as a CCD
`sensor. The image data recorded by the CCD sensor are trans
`ferred by way of the connector 11 to a data processing unit 12
`in the form of a PC.
`007.9 The method for carrying out optical 3D measure
`ment of the invention comprises both elements of a chromatic
`confocal measuring method and elements of a scanning con
`focal measuring method.
`0080. The polychromatic light source 3 has a spectral
`range of two or more wavelengths. The illuminating beam
`emitted by the light source 3 thus has at least two wavelengths
`differing from each other. Primarily, a compact polychro
`matic light source Such as an LED, a laser diode (LD) or a
`super-luminescent diode (SLD) can be used as the polychro
`matic light source for the handheld dental camera 1 of the
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`0007
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`US 2012/0075425 A1
`
`Mar. 29, 2012
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`invention. Halogen lamps or Xenon gas-discharge lamps can
`also be used as the light Source. However, these lamps, due to
`their size, are only suitable for the handheld dental camera 1
`of the invention when they are not disposed inside the camera
`1 itself but are instead connected thereto by means of a fiber
`optic light guide.
`0081. The beam splitter 6 is a semi-transparent optical
`element that allows the illuminating beam to pass through, at
`least partially, without any obstruction and deflects the moni
`toring beam, at least partially, toward the color sensor for the
`purpose of detection.
`0082. The pivotal mirror 5 is a mirror that is mounted for
`rotation about at least one axis and is angularly adjusted by
`means of an electric motor in a computer-controlled manner.
`The illuminating beam 8 can be moved over the entire object
`9 of interest by tilting the mirror into different positions 5.1,
`5.2 in order to make it possible to determine an elevation
`value, i.e. a Z value, for all points 17, 17" in the xy plane of the
`object 9 of interest, and to combine the same to forma3D data
`set of the object 9 of interest.
`0083. The chromatic objective 2 is an optical element that
`intensifies the effect of chromatic aberrations such that the
`focal points for the different wavelengths of the illuminating
`beam 8 are kept clearly apart. This results in a chromatic
`depth measurement range 15.1 that extends from the position
`of a first focal point 13 located closest to the chromatic objec
`tive 2 to the position of a second focal point 14 located
`farthermost from the chromatic objective 2. Within this chro
`matic depth measurement range 15.1, it is possible to acquire
`an elevation value. The measuring accuracy depends on the
`distance between the intermediate focal points of the addi
`tional wavelengths present in the illuminating beam 8.
`0084. The scanning unit 20 is a unit that is moved in the
`direction of the arrow 21 within the handheld dental camera1
`along the longitudinal axis A of the handheld dental camera 1,
`for example, by means of an electronically controlled electric
`motor, so that the focal points 13, 14 of the illuminating beam
`8 are moved along the Z axis, i.e. along the depth measure
`ment range 15.1 at right angles to the longitudinal axis A of
`the handheld dental camera 1. Thus, after a first depth mea
`Surement range 15.1 has been acquired by the scanning unit in
`a first position, the latter is moved to a second position 20', as
`a result of which the focal points 13, 14 are moved to such an
`extent that the position of the focal point 13 in the second
`position of the scanning unit corresponds to that of the focal
`point 14 in the first pos