(12) United States Patent
`(10) Patent N0.:
`US 6,525,819 B1
`
`Delawter et al.
`(45) Date of Patent:
`Feb. 25, 2003
`
`US006525819B1
`
`(54) COLORIMETER FOR DENTAL
`APPLICATIONS
`
`(75)
`
`Inventors: S. Brett Delawter, La Canada, CA
`(US); Gregg A. Wagner, Boulder, CO
`(US); Gary Emerson, Golden, CO
`(US); Brian Franklin, Queen Creek,
`AZ (US)
`
`(73) Assignee: PocketSpec Technologies Inc., Denver,
`CO (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/365,438
`
`(22)
`
`Filed:
`
`Aug. 2, 1999
`
`(60)
`
`Related US. Application Data
`Provisional application No. 60/098,855, filed on Sep. 2,
`1998, provisional application No. 60/098,845, filed on Sep.
`2, 1998, provisional application No. 60/098,837, filed on
`Sep. 2, 1998, and provisional application No. 60/098,823,
`filed on Sep. 2, 1998.
`
`Int. Cl.7
`(51)
`........................... G01J 3/50
`
`(52) US. Cl.
`..............
`.. 356/406; 356/425; 433/29
`(58) Field of Search ................................. 356/402, 405,
`356/406, 407, 416, 419, 425, 433/26, 29,
`250/226
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,986,777 A
`4,096,217 A
`
`10/1976 Roll
`6/1978 Roll
`
`........................... 356/176
`............................ 264/20
`
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`
`DE
`EP
`ES
`JP
`
`19534517 A1 *
`367647 A1 *
`2113826—A!
`*
`4—338465
`
`3/1997
`5/1990
`5/1998
`11/1992
`
`JP
`
`5-243541
`
`9/1993
`
`........... H01L/27/14
`
`Primary Examiner—F. L. Evans
`(74) Attorney, Agent, or Firm—LeBoeuf, Lamb, Greene &
`MacRae, L.L.P.; Gayle L. Strong; Elizabeth Stanley
`
`(57)
`
`ABSTRACT
`
`The invention is a colorimeter for dental applications com-
`prising a hand-held probe, similar in size to a dental drill,
`attached by an electrical cable to a small self-contained
`display module. The calorimeter provides the capability for
`measuring the colors of a number points along a line on the
`surface of an object such as a tooth. Ameasurement is made
`while placing the tip of the probe against, or in close
`proximity to, the surface of the object. The display module
`to which probe attaches contains a microprocessor and
`provides a control, display and data interface to the operator.
`The display module can be adapted for fastening to the wrist
`of the operator thereby leaving both hands free to manipu-
`late the probe and other tools. The calorimeter is particularly
`well suited for measuring the color of teeth in a dentist’s
`office in preparation for making dental prostheses which
`accurately match the color of natural teeth. The colorimeter
`generates from a single measurement an array of color data
`points measured along a line on the surface of an object.
`From those data points, the processor can perform statistical
`analysis yielding a single color value, generate and display
`a color profile along a surface, compare measured values
`with a preloaded table of values, or upload color data to a
`remote location for laboratory or manufacturing purposes.
`The colorimeter can also use variations in the color values
`
`measured along a line to identify boundaries of areas on a
`surface. For example,
`the color profile can be used to
`identify the gum line on a tooth. The probe comprises
`multiple light emitting diodes (LEDs) for successively emit-
`ting light of different colors toward a surface, a linear
`photosensor array for receiving light reflected from the
`surface, and a lens for directing light from the target to the
`array, all contained within the probe itself. The calorimeter
`may also comprise a cradle for storing the probe and display
`module when not in use. The cradle may provide a battery
`charger, calibration references, and data links for uploading
`or downloading data from a remote location.
`
`........... A61C/19/04
`
`36 Claims, 8 Drawing Sheets
`
`
`
`0001
`
`Align 2014
`
`3Shape A/S v. Align
`IPR2019-00156
`
`0001
`
`Align 2014
`3Shape A/S v. Align
`IPR2019-00156
`
`

`

`US 6,525,819 B1
`
`Page 2
`
`US. PATENT DOCUMENTS
`
`RE31,290 E
`4,654,794 A
`498369674 A
`5,027,138 A
`5,383,020 A
`5,428,450 A
`5,503,559 A
`5527262 A
`5,690,486 A
`5,691,701 A
`
`.................. 128/6
`6/1983 Moore et a1.
`3/1987 O’Br1en ...................... 364/413
`
`~- 356/319
`6/1989 Leqmme 6t al~ ~
`6/1991 Gagdrud ~~~~~~~~~~~~~~~~~~~~~~ 354/62
`
`1/1995 Vlelllefosse ................ 356/326
`6/1995 Vieillefosse et a1~
`~~~~~ 356/405
`4/1996 Vari
`........................... 433/224
`6/1996 Monroe 6t al~ ~~~~~~~~~~~~~ 600/110
`
`11/1997 Zigelbaum ..........
`433/29
`.......... 340/603
`11/1997 Wohlstein et al.
`
`5,739,915 A
`5,745,229 A
`5,759,030 A
`5,760,929 A
`5,766,006 A
`5,838,451 A
`5,844,680 A
`5,851,113 A
`5,871,351 A
`5,883,708 A
`
`4/1998 Gau et al. ................... 356/406
`4/1998 Jung et a1.
`.................... 356/73
`6/1998 Jung et a1.
`.................... 433/29
`
`6/1998 Ichikawa et a1.
`.
`. 358/518
`6/1998 Murljacic .................... 433/26
`11/1998 McCarthy ................... 356/406
`
`12/1998 Sperling .....
`.. 356/303
`.................... 433/29
`12/1998 Jung et al.
`2/1999 Jung et a1.
`.................... 433/29
`3/1999 Jung et al.
`.................... 356/73
`
`* cited by examiner
`
`0002
`
`0002
`
`

`

`US. Patent
`
`Feb. 25, 2003
`
`Sheet 1 0f 8
`
`US 6,525,819 B1
`
`FIG.1
`
`0003
`
`0003
`
`

`

`US. Patent
`
`Feb. 25, 2003
`
`Sheet 2 0f 8
`
`US 6,525,819 B1
`
`
`
`
`
`on
`
`0004
`
`0004
`
`
`
`
`

`

`US. Patent
`
`Feb. 25, 2003
`
`Sheet 3 0f 8
`
`US 6,525,819 B1
`
`FIG. 3A
`
`38
`
`
`
`
`
`0005
`
`0005
`
`

`

`US. Patent
`
`Feb. 25, 2003
`
`Sheet 4 0f 8
`
`US 6,525,819 B1
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`US. Patent
`
`Feb. 25, 2003
`
`Sheet 6 0f 8
`
`US 6,525,819 B1
`
`Power
`On
`
`Calibrate
`
`to Reference
`
`Start
`Measurement
`
`FIG. 6
`
`
`
`Acquire data
`"MEASURE"
`
`
`
`Yes
`
`No
`
`Power
`orr
`
`
`
`Red LED
` Average
`5 Samples
`Error Message
`ERROR-REMEASURE
`3m Data
`
`Green LED
`Average
`5 Samples
`Store Data
`
`Error Message
`ERROR-REMEASURE
`
`
`
`
`
`
`
`
`
`Display Results m
`
`"COLOR CODE“
`
`Identify Match in
`Look up Table
`
`
`
`
`
`Obtain Closest
`Match for a
`Given Color
`
`
`
`
`
`Blue LED
`
`
`Avera e
`Obtain Closest
`
`5 Samgles
`Match for all
`
`
`Store Data
`Three Colors
`
`
`
`Out of
`
`Range
`
`
`
`
`Error Message
`ERROR-REMEASURE
`
`Yes
`
`Out of
`Range
`
`0008
`
`0008
`
`

`

`US. Patent
`
`Feb. 25, 2003
`
`Sheet 7 0f 8
`
`US 6,525,819 B1
`
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`

`US. Patent
`
`Feb. 25, 2003
`
`Sheet 8 0f 8
`
`US 6,525,819 B1
`
`ColorValue
`
`ColorValue
`
`ColorValue
`
`FIG. 8A
`
`Red
`
`Position
`
`FIG. 88
`
`Green
`
`Position
`
`FIG. 80
`
`Blue
`
`Position
`
`0010
`
`0010
`
`

`

`US 6,525,819 B1
`
`1
`COLORIMETER FOR DENTAL
`APPLICATIONS
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application takes priority under 35 U.S.C. §119 (e) to
`US. provisional applications having Ser. Nos. 60/098,823,
`60/098,837, 60/098,845 and 60/098,855, all filed on Sep. 2,
`1998, and all of which, along with co-pending application,
`Ser. No. 09/365,193 filed simultaneously herewith, are
`incorporated in their entirety by reference herein to the
`extent not inconsistent herewith.
`
`FIELD OF INVENTION
`
`This invention relates generally to devices and methods
`for the measurement of the color and reflectance of a tooth.
`
`The invention also provides for selecting a color and reflec-
`tance for a dental prosthesis which most closely matches that
`of the natural tooth.
`
`BACKGROUND OF THE INVENTION
`
`The conventional method of determining a color to use in
`the manufacture of a dental prosthesis is to use a number of
`comparison samples. The samples are held up to the
`patient’s teeth surrounding the location where the prosthesis
`will be placed and the sample most closely matching the
`color of the teeth is chosen by visual observation. The
`difficulty in obtaining the optimum color match by this
`method is due to several factors which include the color and
`
`intensity of the light illuminating the comparison, the expe-
`rience and visual acuity of the person making the
`comparison, and the use of a limited number of samples.
`A standard, unambiguous system for measuring tooth
`colors is needed. Such a system should provide for accurate
`and repeatable color measurements in different environ-
`ments such as various dentists’ offices and manufacturers’
`
`laboratories. High-resolution color measurement data can
`then be provided to prosthesis manufacturers to ensure an
`optimum color match between a prosthesis and its surround-
`ing natural teeth.
`A number of previous inventions useful for measuring
`tooth colors have been patented. Some describe apparatuses
`for making color measurements and others describe methods
`for making measurements and using the results in the
`manufacture of artificial teeth. Several such inventions are
`
`briefly described in the following paragraphs.
`US. Pat. No. 5,690,486, teaches a device for detecting the
`color of a damaged tooth and determining a color-matched
`restorative material. It describes the use of multiple LEDs
`for successively emitting light of different colors toward a
`target and a light sensor for receiving light reflected from the
`target, all contained within a hand-held, battery powered
`device. The device uses a fiber optic wand to convey light
`between the device and the tooth.
`
`US. Pat. No. 5,739,915 describes as prior art a document-
`scanning system having a set of RGB light sources, a
`self-focus lens array (SLA) comprising a single row of rod
`lenses, and a single-row photosensor array. In operation, the
`light sources of each color are sequentially illuminated and
`light reflected from the document is focused by the lens onto
`the photosensor array. A set of electrical signals correspond-
`ing to each element of the array is produced by the array for
`each of the RGB colors. The RGB signals are then combined
`for subsequent color reproduction.
`US. Pat. No. 5,838,451 discloses an apparatus for the
`measurement of spectral reflectance or spectral absorbance
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`of an object or a material. The reflectance apparatus com-
`prises multiple LEDs surrounding a photosensor, all
`mounted on a common substrate, and a lens for coupling
`light to and from the object.
`US. Pat. No. 5,844,680 also discloses an apparatus for
`measuring and analyzing spectral radiation.
`It discloses
`three embodiments comprising:
`(1) multiple LED light
`sources with a single sensor, (2) a single light source with
`multiple sensors, and (3) multiple sources and sensors.
`US. Pat. No. 5,851,113 discloses a system comprising a
`probe containing a plurality of optical fibers connected to a
`color measurement system. The patent describes various
`means of color measurement, including multicolored light
`sources (red, green, blue=RGB), and various analysis tech-
`niques.
`US. Pat. No. RE 31,290 describes an imaging system
`comprising a rectangular photosensor array and a lens
`contained in a small probe connected to the system by a fiber
`optic bundle. Three light sources produce red, green, and
`blue light in sequence. Light is conducted from the sources
`through the fiber optics to the probe tip and reflected from
`the object of interest back through the lens to the array in the
`probe.
`US. Pat. No. 5,766,006 teaches a system comprising an
`intraoral camera connected to a shade analyzer subsystem.
`The patent discloses a camera comprising either a single or
`a triple charge coupled device (CCD) array for capturing an
`image of the tooth in three (RGB) colors.
`US. Pat. No. 5,760,929 discloses an image processing
`apparatus for discriminating colors and color patterns or
`boundaries in an RGB image signal and for generating
`signals indicating the color boundaries.
`US. Pat. No. 3,986,777 describes a tristimulus colorim-
`eter which measures the red, green and blue light reflected
`from a sample. The sample is illuminated through a probe by
`a light source having a satisfactory uniform distribution of
`light over the visible spectrum. Light reflected from the
`sample through the probe passes through a rotating color
`filter wheel, which is synchronized with a digital voltmeter,
`to a photosensitive diode.
`US. Pat. No. 4,096,217 describes a method of using a
`tristimulus colorimeter in making artificial teeth.
`Each of the preceding examples describes technology,
`apparatuses or methods for making color measurements or
`comparisons. However, none of them describes the inven-
`tion of a small, hand-held and inexpensive colorimeter
`which can permit an operator unskilled in color analysis to
`quickly and objectively make consistent color measure-
`ments and comparisons.
`An object of the present invention is to provide a high-
`resolution colorimeter system, utilizing solid-state opto-
`electronic technology,
`for measuring and characterizing
`tooth and prosthesis colors.
`BRIEF SUMMARY OF THE INVENTION
`
`The invention is a colorimeter especially suited for dental
`applications comprising a hand-held probe, similar in size to
`a dental drill, attached by an electrical cable to a small
`display module.
`The colorimeter provides the capability for measuring the
`colors of a number of points along a line on the surface of
`an object such as a tooth. A measurement is made while
`placing the tip of the probe against, or in close proximity to,
`the surface of the object. The display module to which the
`probe attaches contains a microprocessor and provides a
`
`0011
`
`0011
`
`

`

`US 6,525,819 B1
`
`3
`control, display and data interface to the operator. The
`display module can be adapted for fastening to the wrist of
`the operator thereby leaving both hands free to manipulate
`the probe and other tools. The colorimeter is particularly
`well suited for measuring the color of teeth in a dentist’s
`office in preparation for making dental prostheses which
`accurately match the color of natural teeth. The colorimeter
`generates from a single measurement an array of color data
`points measured along a line on the surface of an object.
`From those data points, the processor can perform statistical
`analysis yielding a single color value, generate and display
`a color profile along a line, compare measured values with
`a preloaded table of values, or upload color data to a remote
`location for laboratory or manufacturing purposes. The
`colorimeter can also use variations in the color values
`
`measured along a line to identify boundaries of areas on a
`surface. For example,
`the color profile can be used to
`identify the gum line on a tooth.
`As used herein, the term “color value” means any repre-
`sentation of a measured color. For example, it can be a single
`number or a symbol, or it can be a group of numbers or
`symbols such as three RGB ratios, a set of tristimulus values,
`or a set of statistical parameters representing a vector. A
`color value can also be represented by the result of a
`comparison of measured color values to stored color values.
`The probe comprises multiple light emitting diodes
`(LEDs) for successively emitting light of different colors
`toward a surface, a linear array of light sensors for receiving
`light reflected from the surface, and a lens for directing light
`from the target to the array, all contained within the probe
`itself.
`
`The LEDs are arranged in a line near the probe tip and
`coupled to the target via a light pipe. The LEDs emit
`preferably three—red, green and blue (RGB)—primary col-
`ors. The three colors are preferably discrete in the sense that
`their wavelengths do not overlap. One or more LEDs of each
`color may be used depending on the efficiency of the LEDs
`of different colors. Additional LED colors may be used for
`greater accuracy if needed.
`The lens is preferably a flat wafer similar in shape to a thin
`cross-section of a conventional lens. The lens focuses an
`
`image of the illuminated surface onto the linear photosensor
`array.
`
`The photosensor array is a relatively broad-spectrum
`integrated circuit device which is sensitive to all the wave-
`lengths emitted by the LEDs. In operation, the LEDs are
`illuminated sequentially by color and the light of each color
`reflected from the target is sensed by the array and repre-
`sented by a vector of electrical signals.
`The probe also contains circuitry for interfacing to the
`optical devices and for coupling the reflected light signals to
`the display module.
`The display module preferably provides a liquid crystal
`display (LCD) and control buttons for operating the colo-
`rimeter. The module contains a microprocessor, memory and
`associated support hardware for processing, storing and
`displaying digital data from the probe, as well as preferably
`rechargeable batteries for providing power to itself and to
`the probe. The microprocessor can run software routines for
`calibrating the color measurement devices and for compar-
`ing measured values with stored values. The stored values
`can be used to compare or match the color of dental
`prostheses to the measured colors of natural
`teeth. The
`processor can be used to detect color boundaries such as a
`gumline by analyzing the spatial profile of data obtained
`from the linear array.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`The colorimeter may also comprise a cradle for storing
`the probe and display module when not in use. The cradle
`may provide a battery charger and the capability of upload-
`ing or downloading data from a remote location via cable,
`infrared (IR) or radio-frequency (RF) links. The cradle may
`also provide references for calibrating the colorimeter.
`The LEDs are strobed, one at a time, and light from each
`is reflected from a tooth and received by a linear photosensor
`array. The photosensor array produces an electrical analog
`signal which is applied to an analog-to-digital converter
`(ADC). The ADC converts the analog signal to digital values
`representing the reflected light intensity. The digital values
`for each color are stored in a storage device. The stored
`values are processed by a microprocessor as necessary to
`specify the color of a prosthesis which will match the color
`of the tooth. When the colors of all areas of interest on a
`
`tooth are measured, the results can be compiled and sent to
`a custom prosthesis manufacturer. Alternatively, the results
`can be compared with a look-up table of standard color
`values stored in the colorimeter’s memory. In the latter case,
`when a match is found this standard color identification
`
`number is displayed on a display panel.
`The colorimeter is calibrated every time that it is turned
`on to insure accurate measurements. Reflectance measure-
`ments of a white calibration reference are made and stored
`
`for use in processing the data when data measurements are
`made.
`
`New reference data on comparison samples can be loaded
`into the colorimeter whenever they are available. The tech-
`nique for the upgrade can either be done via modem, floppy
`disk or hardware.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a drawing showing the components of the
`colorimeter.
`
`FIGS. 2A, 2B, 2C and 2D are top, side, bottom and end
`views of the probe.
`FIG. 3A is a schematic drawing of a first embodiment of
`the optical assembly.
`FIG. 3B is a schematic drawing of a second embodiment
`of the optical assembly.
`FIG. 4 is a plot of light intensity vs. wavelength for the
`illumination system.
`FIG. 5 is a block diagram of the circuits in the colorimeter.
`FIG. 6 is a flow chart of the colorimeter operation.
`FIG. 7 is a state diagram of colorimeter display images.
`FIGS. 8A, 8B and 8C are reflectance vs. position plots for
`three colors.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`like reference numerals indicate like
`In the drawings,
`features; and, a reference numeral appearing in more than
`one figure refers to the same element. The drawings and the
`following detailed descriptions show specific embodiments
`of the invention. Numerous specific details including
`materials, dimensions, and products are provided to illus-
`trate the invention and to provide a more thorough under-
`standing of the invention. However, it will be obvious to one
`skilled in the art that the invention may be practiced without
`these specific details.
`An exterior view of the invention is shown in FIG. 1. The
`
`colorimeter comprises probe 1 and display module 10. Probe
`1 further comprises probe body 2, probe tip 3, cable 4 and
`
`0012
`
`0012
`
`

`

`US 6,525,819 B1
`
`5
`measure button 5. Display module 10 comprises body 11,
`display panel 12, power switch 13, and control switches
`comprising “menu select” button 14, “scroll up” button 15
`and “scroll down” button 16. The colorimeter may also
`comprise an optional cradle (not shown) for storing the
`probe and display module.
`The material of the probe body is preferably an impact-
`resistant polycarbonate. The probe is shaped to facilitate
`one-handed operation and is preferably less than 15 cm in
`length and less than 5 cm2 in cross sectional area.
`The material of display module body is preferably an
`impact-resistant polycarbonate. The module can be clipped
`into a mount or worn on the wrist to allow one hand to
`
`10
`
`operate the colorimeter. The menu and scrolling buttons are
`preferably large and clearly marked to provide a friendly
`user interface.
`
`15
`
`Atop view of the probe is shown in FIG. 2A. Left side and
`bottom cross sectional views of the probe are shown in
`FIGS. 2B and 2C. An distal end view is shown in FIG. 2D.
`
`The probe 1 comprises probe body 2, probe tip 3, cable 4,
`measure button 5, light pipe assembly 30, lens 38, mirror 39,
`linear photosensor array 32, circuit board 23 and optics
`support 24. Measure button 5 is coupled to measure switch
`27.
`
`FIG. 3A is a perspective drawing of the optical assembly.
`In FIG. 3A a light pipe assembly 30 is enclosed within probe
`tip 3 of FIGS. 2A—2D and comprises light pipe 31, LEDs 33,
`illumination surface 34, and baffle 35. The optics assembly
`also comprises optics circuit board 36 and aperture 37. Light
`pipe 31 has the shape of a truncated wedge with the
`illumination surface 34 on its distal end. LEDs 33 are
`
`abutted to, or imbedded in, the proximal end of light pipe 31.
`LEDs 33 are arranged preferably in a row and electrically
`connected to optics circuit board 36. Illumination surface 34
`is preferably a diagonal section through pipe 31 and may be
`tilted inwardly toward the optical axis, with a diffusing
`surface finish, as shown in FIG. 3A or it may be tilted
`outwardly away from the optical axis with a smooth refract-
`ing surface. However, surface 34 may have a diffusing or
`refracting surface of any shape which provides adequate
`illumination of the target. The outer surface of pipe 31 may
`be coated or separated slightly from the interior surface of
`tip 3 to satisfy the index of refraction requirements for light
`pipe operation.
`FIG. 3B is a perspective drawing of an optical assembly
`having two light pipe assemblies 30 and 30' for use when a
`single light pipe assembly provides insufficient illumination.
`Lens 38 is located to focus an image of a line on the target
`(the object plane) onto the light sensitive elements of
`photosensor array 32 (the image plane). Lens 38 may have
`the shape of a conventional lens or the shape of a slice
`through a conventional lens taken parallel to its axis. Mirror
`39 permits mounting the photosensor array off the optical
`axis. The lens and mirror shapes and locations permit
`adjusting the optics for the desired magnification consistent
`with minimum probe size. Mirror 39 may be omitted if array
`32 is located on the optical axis.
`Light emitted from LEDs 33 is contained within light pipe
`31 by total internal reflection (TIR) and guided through
`illumination surface 34 to illuminate the target. If surface 34
`is an inwardly-tilted diffusing surface,
`light
`is scattered
`uniformly over the target. If surface 34 is an outwardly-tilted
`refracting surface, light is refracted onto the target. The
`angle and surface finish of surface 34 can be chosen by one
`of ordinary skill in the art to optimize the uniformity and
`intensity of the illumination of the target. Probe tip 3 shields
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`the target from external ambient light. Light reflected from
`the target passes through aperture 37, lens 38 and is reflected
`off mirror 39 onto array 32. The dimensions of aperture 37
`are chosen to prevent specular reflections from the target
`from reaching array 32. Baffle 35 prevents light from LEDs
`33 from directly reaching array 32. The baffle may be a
`coating on pipe 31 or a separate opaque panel. Coatings may
`be optionally applied to the lens or the mirror to pass only
`light having desired wavelengths and to block light having
`wavelengths outside the spectrum of interest. Optical filters
`may be also be used in the photosensor array light path for
`this purpose. For example, filters or coatings may act as
`bandpass filters which block infrared and ultraviolet light or
`may comprise one or more notch filters to provide separation
`between the wavelengths emitted by the different color
`LEDs. Anotch filter is a filter which blocks light of a narrow
`band of wavelengths.
`Preferably, lens 38 is an achromatic lens which corrects
`on-axis spherical and chromatic aberrations. The preferred
`optical magnification is 0.5. At this magnification, for a
`linear photosensor array providing a resolution of 150 dots
`per inch (DPI), the maximum object size is 16 mm.
`The wafer shape of the lens is chosen to reduce the width
`of the probe. The preferred sensing area is roughly rectan-
`gular (12.5 mm in height by 1.5 mm in width) and the
`preferred width of the lens, looking down along the optical
`path, is 2.0 mm. This reduces the overall width of the probe
`as compared to a circular lens. The lens 38 and mirror 39 are
`mounted to an optics support 24 which provides an integral
`optical assembly.
`The colorimeter uniformly illuminates an oblong region,
`on a target, that is parallel to and in contact with the contact
`plane of the outer sleeve. The LEDs, preferably comprising
`two red (655 nm), two green (565 nm), and two blue (430
`nm) LED’s, are preferably arranged in a linear pattern and
`spaced about 1.25 mm apart from one another. The probe tip
`3 locates the point of contact with the target and shields the
`system from ambient light. The light pipe baffle 35 and
`rectangular aperture 37 prevent direct light from the LED’s
`reaching the photosensor array. The signals generated by the
`array result only from light reflected by the target.
`The aperture preferably prevents light entering at more
`than about 5 degrees from the optical axis from reaching the
`array. The aperture can include an optical filter to attenuate
`light having a wavelength that is more than about 50 nm
`above or below a nominally-measured wavelength.
`The probe tip comprises a sleeve that
`is sufficiently
`flexible and conformable to facilitate fairly tight contact
`with the target surface. Opaque materials are preferred for
`this purpose (e.g., an opaque vinyl or rubber), sufficiently
`flexible and conformable to facilitate fairly tight contact
`with the target surface. Preferably, the sleeve is sufficiently
`flexible to conform to an irregular surface. In medical or
`dental applications, the sleeve should be sanitary and dis-
`posable. A suitably-designed sleeve is preferably stiff
`enough to control the target position relative to the light
`sources and photosensor array. The probe tip can be manu-
`factured so that it is either expendable or can be autoclaved.
`An alternative method of maintaining sterilization is to use
`a thin plastic transparent cover over the tip. The probe tip
`preferably includes a hook or protrusion on its distal edge for
`aligning the edge of the probe tip with the tip of a tooth.
`In operation, probe tip 3 is placed against the target and
`the LEDs of each color are illuminated in sequence. As the
`target is illuminated by each color, a portion of the reflected
`light is captured by the photosensor array which produces a
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`US 6,525,819 B1
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`7
`vector of electrical signals representing the intensity of the
`reflected light along a line on the target. As used herein, a
`vector means an array of values wherein each value corre-
`sponds to one of the photosensor locations in the linear
`photosensor array.
`An exemplary plot of light intensity vs. wavelength for
`three LED colors is shown in FIG. 4. This example shows
`spectral profiles for a red LED 41, a green LED 42 and a blue
`LED 43. In this plot, the three profiles are discrete; that is,
`they do not overlap. However, as known to those skilled in
`the art, LEDs having profiles with different peak wave-
`lengths and different widths may be used. The inherent
`emission profiles of the LEDs can be altered by optical filters
`or coatings on the LED encapsulations. Also, the effective
`profile widths can be altered by the use of optical notch
`filters in the photosensor array light path or by setting a
`detection threshold 44 either within the signal path from the
`photosensor array to the microprocessor or in the digital
`processing routines of the microprocessor. Such a threshold
`can be set to disregard light intensities below the threshold
`and thereby eliminate wavelengths outside the threshold. A
`different threshold can be specified for each color and stored
`in memory. The stored threshold values can be used directly
`by the microprocessor or converted by a digital-to-analog
`converter (DAC) to an analog signal for use by a comparator
`in the analog signal path.
`To compensate for variations in sensitivity of the photo-
`sensor array across the wavelength spectrum and for differ-
`ences in the efficiency of different LEDS, the light output of
`each of the LEDs may be adjusted by varying its current.
`Ablock diagram of the circuits contained in the colorim-
`eter is shown in FIG. 5. Although the circuits are shown as
`separate functional blocks, it will be recognized by those
`with ordinary skill in the art that some or all of the functions
`can be combined in integrated circuits. The term micropro-
`cessor as used herein includes the family of devices known
`as microcontrollers.
`
`Each time the colorimeter is turned on, and prior to its
`operation, a calibration sequence is performed. This consists
`of measuring the known reflectance of a substantially white
`reference surface using all the colors in the probe. In some
`applications, the calibration may also include measuring the
`reflectance of a black reference.
`
`The measurement sequence comprises sending a short
`current pulse to each LED of a color to illuminate the tooth.
`Reflected light from the tooth is focused onto the photosen-
`sor array which converts the light falling on each element of
`the array into an electrical representation of its intensity.
`After the array has been exposed to the reflected light, the
`array generates a vector of electrical signals representing the
`intensity of the light distributed across the array. The signals
`are coupled to an analog-to-digital converter (ADC) that
`converts the analog values into a digital signal comprising a
`vector of digital values which are then stored at a particular
`location in the storage device. This process is then repeated
`for each of the LED colors in the system.
`Current is preferably supplied to the LEDs in short pulses
`to minimize self-heating and the resulting change in effi-
`ciency.
`If necessary to enhance measurement accuracy,
`multiple short pulses can be used for a single measurement
`and the results averaged or otherwise statistically analyzed.
`When all three color measurements are made for an array
`of points,
`the microprocessor computes the ratios of the
`measured values to the calibration values for all the points
`on the line.
`
`As used herein, a color ratio is defined as the ratio of the
`intensity of the light reflected onto each photosensor element
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`from a target, whose color is being measured, to the intensity
`of the light reflected onto each photosensor element from the
`white calibration reference. When a black (or dark) refer-
`ence is used, the color ratio is the ratio of the target intensity
`to the difference in intensity between the white and black (or
`dark) references. A color ratio is preferably generated for
`each photosensor element in the array and for each LED
`color used in the measurement; that is, the number of color
`ratios generated from a single linear measurement is equal to
`the number of LED colors used multiplied by the number of
`photosensor elements in the linear photosensor array.
`After the first line of points is measured, the probe can be
`moved to another location and the sequence repea