Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C9/00—Impression cups, i.e. impression trays; Impression methods
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61C—DENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
  • A61C9/00—Impression cups, i.e. impression trays; Impression methods
  • A61C9/004—Means or methods for taking digitized impressions
  • A61C9/0046—Data acquisition means or methods
  • A61C9/0053—Optical means or methods, e.g. scanning the teeth by a laser or light beam
  • A61C9/006—Optical means or methods, e.g. scanning the teeth by a laser or light beam projecting one or more stripes or patterns on the teeth

Definitions

• the present invention relates to a method for contactless measuring of the three- dimensional shape of different types of objects.
• the invention also relates to a device for performing this method.
• objects of which the shape can be measured according to the invention are teeth, auditory meatuses, etc.
• restoration material which is shaped directly in the mouth, such as amalgams or plastic. Instead there is used, for example, ceramic material which is produced mechanically based on measured shape information. Consequently, there is an increasing requirement for determining the shape of dental objects.
• a determination of a shape can take place directly in the mouth, on castings or on models.
• the measuring is made difficult because the teeth are formed of a material which is semi-transparent to light, wherefore, for example, measurement of the contact position for laser light cannot take place with sufficiently high measuring accuracy.
• Saliva can also impair the measuring result.
• the patent DE 4034007 describes an example of such equipment. In order to improve the optical quality of the surface of the tooth, it is sometimes prepared with, for example, a fine chalk powder.
• Stereo and photogrammetry are methods which are often used for measuring three- dimensional shapes.
• the methods require that the object being examined has an outer structure, the angular position of which can be compared from different observation positions.
• Dental objects and the human skin contain no, or indistinct, surface structures, which leads to problems for stereo methods.
• a possible way of solving the problem is to pattern the surface in order to facilitate later measuring of the shape.
• PCT/SE96/01329 a way of patterning the object with a fluorescent pattern is shown. By illuminating the patterned object with light of a wavelength which excites the fluorescent pattern, and then registering this pattern with a camera unit which is sensitive to the fluorescent light, an extremely good picture of this fluorescent pattern is obtained.
• This invention is a further development of that method.
• An object of the invention is to provide a method and a device for improving measuring compared with the above method.
• Another object is to provide an accurate measuring of limits where the surface normal of the surface of the object changes direction, such as by so-called preparation interfaces.
• preparation interfaces the interfaces between unprepared surface and prepared surface
• Yet another object of the invention is to provide a method and a device which, compared with the prior art technique, more accurately and in a more cost-effective way measures the three-dimensional shape of, for example, dental objects.
• a further object is to effect the production of customer-adapted hearing aids which have a perfect fit to the auditory meatus, and where the transition between the auditory meatus and the ear drum is clearly discernable.
• the electronic camera unit partly reproduces the object to be measured with an illumination adapted to the pattern provided on its surface. Then a picture is registered with illumination from one side. Thereafter a further picture is taken with illu- mination from the opposite side. Further registrations occur after the angles between the camera unit and the object have been changed.
• the position for the gradient changes in the shape of the surface such as preparation interfaces are calculated.
• the pictures are electronically subtracted from each other, whereby a difference picture is obtained. Further difference pictures are generated, where the remaining pairs of illumination are used.
• the angle for the surface normal for the different x,y-positions of the object being measured are calculated.
• the computer software has special algorithms for processing and possibly filtering away measurement date which, during unfavourable angular conditions, have been collected near to preparation interfaces and edges, have been collected from positions where the object being measured has shadowed parts of the transmitter or receiver beam path, or have been collected in combinations of the above cases.
• Fig. 1 shows a view from above of a bored tooth in order to illustrate the principle of the invention.
• Fig. 2 shows a lateral view of a tooth bored for attachment of a crown.
• Fig. 3 illustrates schematically an embodiment of a device according to the invention.
• Figure 4 shows an embodiment of a constructed unit with light and camera.
• Fig. 1 shows from above a tooth 1 provided with a bore hole 3 which is coated with a fluorescent pattern of dots 2.
• the tooth 1 is illuminated from the side with a light source 5 with a first type of light.
• the light is incident so that the bore 3 is illuminated and the tooth itself is in shadow.
• a sharp edge 4 marks the transition between the bore 3 and the remaining part of the tooth.
• the position in space in three dimensions for this transition 4 must be determined accurately to obtain a completely even transition between the remaining tooth and the filling. This is especially required when a filling of porcelain is to be manufactured and placed in the bored hole 3.
• the object being measured 1 or 6 which will be described as being a tooth, is bored and cleaned.
• the measuring can take place on any other object needing a filling such as, for example, a model of a tooth or a casting of a dental object, a part of a hearing aid which is well fitting to an auditory meatus, a repair in a desktop or in a wall or the like.
• a model of a tooth or a casting of a dental object a part of a hearing aid which is well fitting to an auditory meatus, a repair in a desktop or in a wall or the like.
• a pattern of paint which preferably is fluorescent.
• a pattern of e.g. black or coloured dots can, for example, be carried out by controlled spraying of the surface with the paint.
• the pattern can be of another type, but a pattern of dots is easy to produce and is therefore illustrated.
• Fig. 3 shows very schematically an embodiment for measuring the three-dimensional shape of an object to be measured 10, which is shown here provided with a central bore hole 11 with edges 11a.
• the object to be measured has a spray ed-on pattern of dots 12 of substances which preferably are fluorescent.
• a first illumination unit comprising at least one light source 13a and 13b, emits light with a wavelength, e.g. blue, which excites the sprayed-on fluorescent substances 3 in the pattern of dots applied on the object to be measured (the tooth) 1.
• the light source should suitably offer an illumination of the area being investigated around, and in, the bored hole 11, which is as even and without shadows as possible.
• a camera unit 14 movable between two or more positions A and B, or alternatively several camera units
• a second illumination unit comprising several illumination units 15a, 15b, 15c, 15d thereafter emits sequentially from two or more positions light with a wavelength to which the camera unit 14 is also sensitive, e.g. red.
• the illumination from the light elements 15a-15d in this registration is obliquely incident light.
• Each illumination unit 15a-15d can, for example, be provided with a light diode or an end of an illuminating light conductor.
• the light should have a relatively well delimited lobe.
• the registrations are made sequentially, e.g. pairwise from opposite sides after each other and with peripheral changes between each registration in opposing pairs, so that in Fig. 1 the light sources are illuminated in the following sequence 15a, 15b, 15c, 15d.
• the position of the measuring unit can thereafter be displaced relative to the object being measured, whereby further camera registrations according to the above are performed.
• the measuring is finished when all interesting partial surfaces have been registered from a sufficient number of advantageous angles.
• the registrations of the object to be measured taken with obliquely instant light from different angular positions are used primarily for calculating the preparation interfaces but data can also be used in order to improve the accuracy of the shape measuring.
• the registrations of the dotted pattern are used in the main for electronic and/or computer-aided calculations of the shape of the object to be measured, preferably with so-called CAD-techniques.
• the filling or crown can thereafter be manufactured in so-called CAM-equipment which is supplied with the result of the CAD-proces- sing. This result can be transferred to some computer media, e.g. a computer dis- cette, and sent to a laboratory with CAM-equipment.
• the camera unit 14 can, for example, be of a type of stereo camera wherein two simultaneous registrations are made from two angular positions.
• the camera 14 can, for example, have a lens with two or more picturing optical elements, which either can each take a picture simultaneously or be provided with a shutter, which means that one picture at a time can be taken.
• Each picture of the object being measured is reproduced on at least one picture sensor which, for example, can be formed of a two-dimensional matrix of sensor elements.
• the camera can be designed so that the object being measured 10 is reproduced on a coherent bundle of fibres, wherein a picture sensor is arranged at the second end of the bundle of fibres.
• Each light source can also be connected to at least one light fibre which carries the light to the vicinity of the object being measured.
• the measuring heads which are placed near to the object being measured can in this way be made small and easily positioned.
• the embodiment shown in Fig. 4 of a measuring instrument is especially usable for flexible placement near to an object being measured, which can be relatively difficult to access, for measuring of this, such as a tooth inside the mouth of a patient and especially for measuring of a hole bored in a tooth.
• a measuring head 20 with "camera”-equipment can be placed at the end of a guide means 21.
• the guide means 21 is shown as a handle which is easily manoeuvrable by an operator and the outer end 20 of which with the "camera”-equipment is slightly bent to give good access in tight spaces.
• the guide means 21 can instead be controllably bendable and/or a possibly guidable arm can be connected with the outer end 20 itself in order to guide it, and the light fibre bundle 11 in this case can come directly from the end 20.
• the picture collecting end is placed inside the outer end 20 in Fig. 4.
• a fibre bundle 11 is bendable outside the rod 21 and coherently arranged between the end of the measuring head and an electronically readable picture sensor 22, such as a second position of impact detector unit, placed at a distance from the measuring head 20.
• the electronically readable picture sensor 22 is connected to evaluation circuits 23.
• the teeth are coated before the measuring with a coating of fluorescent particles which can be brushed off.
• a spray painting equipment connected to the measuring head 20 and which comprises a controllable paint unit 24 connected by a hose 25 to at least one nozzle (not shown) on the measuring head 20.
• a controllable paint unit 24 connected by a hose 25 to at least one nozzle (not shown) on the measuring head 20.
• the appropriate pictures are taken and signal-processed, whereafter the coating is brushed and rinsed away.
• the light units 13a, 13b are placed beside the measuring head 20.
• the light units 15a-15d, which are to provide incident light obliquely from the side, are, in the embodiment shown in Fig. 4, placed in a ring 26 which is held by a support on the measuring head 20, possibly rotatable for oblique positioning in relation thereto, as required.
• the evaluation circuit 23 is preferably a computer provided with software, which performs the illuminations of the different light units 13a,13b,15a-15d, the camera adjustments with the application of filters, and opening and shutting of suitable shutters for the different registrations.
• the registrations are processed in the evaluation circuit 23, which thereby calculates the three-dimensional position in space and the shape of the tooth which is of interest for the reproduction.
• the evaluation circuit 23 can perform the required CAD-calculation with the special calculation of the positions of edges between different parts of the object, for example, with photogrammetry or correlation between several registrations of the same points in several different registration angles.
• a small plate 27, provided with another type of pattern in e.g. fluorescent paint, in connection with either the measuring head 20 or the ring 26 is so placed that it is inserted into the field of view of the camera unit and comes into the registered picture at the side of the measuring region.
• the plate 27 can thereby be placed directly against the object to be measured.
• the pattern on the plate 27 can, for example, comprise a scale as a calibration pattern.
• the importance of the calibration pattern is that it should be able to give a standardization and therefore should have a known geometry with known dimensions.
• the calibration pattern can instead of being placed on a place 27 be directly applied onto the object being measured at the side of the measuring region before measuring.
• the angle for the surface normal for the different partial surfaces of the object being measured 1, 6, is calculated.
• the calculation of the position and shape of the pattern parts is made from the pattern registrations.
• the position for gradient changes in the surface shape of the object is calculated from the registrations of the appearance of the surface.
• a three- dimensional shape with borders connected to the object being measured at the gradient changes is calculated for the filling or crown or some other type of supplementary object.
• the information concerning gradient changes is used for correction of shape data calculated from earlier calculations, e.g. from registra- tions of dotted pattern.
• the computer software has special algorithms for processing and possibly filtering away measurement data, which have been collected during unfavourable angular conditions, have been collected close to the preparation interfaces 4, 8 and edges, have been collected from positions where the object being measured 1, 6 has shaded parts of the sender or receiver beam path, or have been collected in combinations of the above cases.
• the type of algorithms and calculations of CAD-type can be of different suitable conventional types and are not part of the invention itself and are therefore not described more closely.
• the calculations of the three-dimensional position in space of the position of the pattern parts are performed by triangulation between parts in picture registrations, taken from different angles, and occur by geometric calculations.

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• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Dentistry (AREA)
• Epidemiology (AREA)
• Physics & Mathematics (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Length Measuring Devices By Optical Means (AREA)

Applications Claiming Priority (3)

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• 1997
  • 1997-04-18 SE SE9701481A patent/SE510203C2/sv not_active IP Right Cessation
• 1998
  • 1998-04-14 WO PCT/SE1998/000675 patent/WO1998048242A1/en not_active Application Discontinuation
  • 1998-04-14 EP EP98917889A patent/EP0975935A1/en not_active Withdrawn
  • 1998-04-14 AU AU70932/98A patent/AU7093298A/en not_active Abandoned

Non-Patent Citations (1)

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