3D scanner system with dynamic calibration

Abstract

The present disclosure relates to a 3D scanner system comprising an intraoral scanner comprising: a housing and a transparent window located in the distal end of said housing, wherein the transparent window comprises a pattern of fiducial markers arranged in a predefined arrangement. The intraoral scanner further comprising two or more scan units located in the housing, each scan unit comprising one or more camera units configured for acquiring a set of images, wherein at least a part of the pattern of fiducial markers is imaged by the camera unit(s); and one or more processors configured for comparing the imaged pattern of fiducial markers to the predefined arrangement, whereby a difference may be determined; determining whether a geometric relationship between the scan units and / or the camera units has changed based on the difference; and correcting the geometric relationship in a geometric model of the intraoral scanner based on the difference, whereby the scanner is calibrated.

Description

[0001] 3D scanner system with dynamic calibration

[0002] Technical field

[0003] The present disclosure relates to a 3D scanner system comprising an intraoral scanner. In particular, the present disclosure relates to a system and method of recalibrating an intraoral scanner.

[0004] 3D intraoral scanners are widely used in dentistry for creating a digital impression of teeth. This technology enables dentists to obtain a detailed and accurate representation of the teeth in a digital format, which can then be used for a variety of applications, including the design and fabrication of dental restorations, orthodontic appliances, and other dental prostheses.

[0005] One significant challenge associated with intraoral scanning technology is the need for accurate calibration. Calibration ensures that the intraoral scanner produces reliable and consistent measurements, which are crucial for accurate digital impressions, diagnosis, treatment planning, and the fabrication of dental restorations. Oftentimes, intraoral scanners are calibrated at the factory and sometimes rely on subsequent recalibration. Existing calibration methods often rely on manual adjustments and are time-consuming, labor- intensive, and prone to human error.

[0006] Typically, a recalibration of the scanner is intended to take into account changes on the timescale of hours or even days. However, there is a need for a system and method that is able to take into account changes happening on a much shorter timescale, e.g., over the course of a single scan. Such a system should be capable of providing accurate measurements, thereby enhancing the overall reliability and usability of intraoral scanning technology in dental practices.

[0007] Typically, an intraoral scanner needs to be calibrated at least one time, e.g. at a manufacturing facility. However, a challenge with intraoral scanners is that this calibration does not always provide an accurate calibration of the scanner that corresponds to the usage of the scanner. Intraoral scanners often feature a number of optical and electronic components that generate heat during use. A problem associated herewith is that said components may change their relative geometric relationship, e.g. due to thermal drift. If the true geometric relationship deviates from the predefined relationship as defined in a geometric model of the scanner in the calibration, then the 3D scans generated by the scanner become inaccurate and the scanner needs recalibration. The presently disclosed 3D scanner addresses these challenges by providing a 3D scanner system that is capable of dynamic calibration, i.e. such that the intraoral scanner is calibrated during use of the scanner. This is achieved by utilizing a pattern of fiducial markers placed in an optical transparent window of the scanner, through which light is being projected during use. The pattern of fiducial markers is placed at a predefined location in the optical window. Hence, the exact location of the fiducial markers is known a priori. If, during use, the position of said markers move, or become distorted, in the acquired images by the scanner, e.g. due to thermal drift of one or more components of the scanner, then that movement or new position of the markers can be detected by the 3D scanner system. It can also be the case that the pattern of fiducial markers is distorted, i.e. such that the shape of the markers changes and / or such that the spacing between the markers changes.

[0008] The 3D scanner system is preferably configured for detecting any of such changes in the pattern of fiducial markers in order to facilitate dynamic calibration of the intraoral scanner. This has the advantage of improving the accuracy of the scanner, whereby a more accurate 3D model can be generated of the scanned object. In particular, in case the scanner comprises two or more scan units, it is important to know the geometric relationship between said scan units, such that 3D scan data obtained by the units can be accurately stitched together.

[0009] Accordingly, the present disclosure solves the above-mentioned challenges by providing a 3D scanner system comprising:

[0010] - an intraoral scanner comprising:

[0011] - a housing having a distal end for being inserted into an oral cavity;

[0012] - a transparent window located in the distal end of said housing, wherein the transparent window comprises a pattern of fiducial markers arranged in a predefined arrangement; the intraoral scanner further comprising one or more scan units, such as two or more scan units, located in the housing, each scan unit comprising;

[0013] - one or more camera units configured for acquiring a set of images comprising at least one image from each camera unit, wherein at least a part of the pattern of fiducial markers is imaged by the camera unit(s);

[0014] - one or more processors configured for:

[0015] - comparing the imaged pattern of fiducial markers to the predefined arrangement, whereby a difference may be determined;

[0016] - determining whether the geometric relationship between the scan units and / or the camera units has changed based on the difference; and correcting the geometric relationship in a geometric model of the intraoral scanner based on the difference, whereby the scanner is calibrated.

[0017] The present disclosure further relates to a method of calibrating an intraoral scanner, the method comprising the steps of:

[0018] - acquiring two or more sets of images, wherein the sets of images are acquired by separate scan units of the intraoral scanner, each scan unit comprising one or more camera units, wherein a pattern of fiducial markers is present each set of images;

[0019] - determining a difference between the imaged pattern of fiducial markers and a predefined arrangement of said fiducial markers;

[0020] - determining whether a geometric relationship between the scan units and / or the camera units has changed based on the determined difference; and

[0021] - correcting the geometric relationship in a geometric model of the intraoral scanner based on the determined difference, whereby the scanner is calibrated.

[0022] Any of the embodied methods disclosed herein may be performed, either fully or partly, by the 3D scanner system disclosed herein. The method may be implemented as a computer- implemented method. Thus, the present disclosure further relates to a data processing system, such as a 3D scanner system, comprising one or more processors configured for performing the steps of the disclosed method of calibrating an intraoral scanner. The present disclosure further relates to a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the disclosed recalibration method. The computer may form part of the 3D scanner system. The present disclosure further relates to a computer-readable data carrier having stored thereon said computer program product.

[0023] Accordingly, the presently disclosed system and method enables dynamic calibration of an intraoral scanner, whereby a more accurate 3D model can be generated of a scanned object.

[0024] Brief description of the drawings

[0025] Fig. 1 shows an embodiment of an intraoral scanner according to the present disclosure.

[0026] Fig. 2 shows an exploded view of some components of an intraoral scanner according to an embodiment of the present disclosure.

[0027] Fig. 3 shows another embodiment of an intraoral scanner according to the present disclosure.

[0028] Fig. 4 shows another embodiment of an intraoral scanner according to the present disclosure, wherein the housing of the scanner comprises a removable part. Fig. 5 shows another embodiment of an intraoral scanner according to the present disclosure.

[0029] Fig. 6 shows an embodiment of a scan unit according to the present disclosure.

[0030] Fig. 7 shows an embodiment of a 3D scanner system according to the present disclosure.

[0031] Fig. 8 shows another embodiment of a 3D scanner system according to the present disclosure.

[0032] Fig. 9 shows an embodiment of a pattern to be projected along with a pattern of fiducial markers.

[0033] Fig. 10 shows an embodiment of a transparent window for an intraoral scanner as disclosed herein.

[0034] Fig. 11 shows another embodiment of a transparent window for an intraoral scanner as disclosed herein, wherein the projected pattern is shown.

[0035] Detailed description

[0036] Scanner

[0037] The scanner disclosed herein may be an intraoral scanner for acquiring images within an intraoral cavity of a subject. The scanner may be a handheld scanner, i.e. a device configured for being held with a human hand. The scanner may employ any suitable scanning principle such as triangulation-based scanning, stereo vision, structure from motion, confocal scanning, or other scanning principles. In preferred embodiments, the scanner employs a triangulationbased scanning principle.

[0038] Scan unit

[0039] The scanner may comprise one or more scan units, such as two or more scan units. A scan unit may be understood as a unit or device comprising at least one projector unit and one or more camera units. In some embodiments, each scan unit comprises at least two camera units having at least partly overlapping fields of view along different camera optical axes. Preferably, each scan unit comprises at least four camera units having at least partly overlapping fields of view along different camera optical axes. An advantage of having overlapping fields of view of the camera units is an improved triangulation of 3D points, and consequently an improved accuracy of the generated 3D representation.

[0040] In preferred embodiments, the scanner employs a triangulation-based scanning principle. As an example, the scanner may comprise a projector unit and one or more camera units for determining points in 3D space based on triangulation. As another example, the scanner comprises a projector unit and two or more camera units, wherein the camera units are configured to image the scanned object from separate views, i.e. from different directions. In particular, the camera units may be configured to acquire a set of images, wherein a correspondence problem is solved within said set of images based on triangulation. The images within the set of images may be acquired by separate camera units of the scanner.

[0041] A camera unit may be understood herein as a device for capturing an image of an object. Each camera unit may comprise an image sensor for generating an image based on received light recorded on the image sensor. The image sensor(s) may comprise an array of pixels, wherein each pixel is associated with a corresponding camera ray. The array of pixels may be a two- dimensional (2D) array. Each pixel may be covered by a micro lens. In some embodiments, the image area, i.e. the 2D array of pixels, is rectangular or quadratic. Each camera unit may further comprise one or more focus lenses for focusing light onto the image sensor of the given camera unit. In some embodiments, each camera unit comprises two or more lenses, or lens elements, assembled in a camera lens stack. Thus, each camera unit may comprise a camera lens stack comprising a plurality of lens elements. The purpose of the focus lens(es) or camera lens stack may be to define or ensure a predetermined focus distance, or working distance, of the camera unit.

[0042] The images within the set of images are preferably acquired simultaneously by the camera units, i.e. at the same moment in time, wherein each camera contributes at least one image to the set of images. The images within the set of images preferably captures substantially the same region of the dental object. The images may comprise a plurality of image features corresponding to pattern features in a pattern of light projected on the surface of the dental object. The correspondence problem may generally refer to the problem of ascertaining which parts, or image features, of one image correspond to which parts of another image within the set of images. Specifically, in this context, the correspondence problem may refer to the task of associating each image feature with a projector ray emanating from the projector unit. In other words, the problem can also be stated as the task of associating points in the images with points in the projector plane of the projector unit. A system and method for solving the correspondence problem is further described in PCT / EP2022 / 086763 and PA 2023 70115 by the same applicant, which are herein incorporated by reference in their entirety.

[0043] The scanner may comprise one or more scan units, wherein each scan unit comprises a projector unit and one or more camera units. As an example, the scanner may comprise one scan unit comprising one projector unit and at least two camera units. As another example, the scanner may comprise one scan unit comprising one projector unit and four camera units. In yet another example, the scanner may comprise at least two scan units, wherein each scan unit comprises a projector unit and two or more camera units. In yet another example, the scanner may comprise at least two scan units, wherein each scan unit comprises a projector unit and four camera units. The projector unit and camera units of each scan unit may be provided as modular units for being inserted into a fixation unit of the scan unit. This has the benefit of providing a more easy and intuitive assembly method of the scan unit. It further has the benefit of fixing the projector unit and the camera unit(s) in a rigid structure, such that the geometric relationship between said units is ideally fixed and maintained. In some embodiments, the scanner has a field of view of at least 18 x 18 mm2, such as at least 20 x 20 mm2, at a given working distance, such as at a working distance between 15 mm and 50 mm.

[0044] In some embodiments, the scanner comprises two or more scan units, such that the field of view of the scanner may be extended or enlarged. An example of such an embodiment is shown in figure 1 , which shows a scanner comprising two scan units placed in series in a distal end of the scanner. In this embodiment, each scan unit is arranged in combination with a mirror to redirect the projected light toward an object, such as a person’s dentition. A scanner having an extended field of view is further described in PCT / EP2023 / 058980 by the same applicant, which is herein incorporated by reference in its entirety.

[0045] Projector unit

[0046] A projector unit may be understood herein as a device configured for projecting light onto a surface, such as the surface of a three-dimensional object. In preferred embodiments, the projector unit is configured to project a pattern of light onto the surface of a dental object. Preferably, the projector unit is configured to project a pattern of light such that the pattern of light is in focus at a predefined focus distance, or focus range, measured along a projector optical axis. The projected pattern may be in focus in a predefined depth of field of the scanner. The projector unit may be configured to project unpolarized light.

[0047] The projector unit may comprise Digital Light Processing (DLP) projectors using a micro mirror array for generating a time varying pattern, or a diffractive optical element (DOE), or front-lit reflective mask projectors, or micro-LED projectors, or Liquid crystal on silicon (LCoS) projectors or back-lit mask projectors, wherein a light source is placed behind a mask having a spatial pattern, whereby the light projected on the surface of the dental object is patterned. The pattern may be dynamic, i.e. such that the pattern changes over time, or the pattern may be static in time, i.e. such that the pattern remains the same over time. An advantage of projecting a static pattern is that it allows the capture of all the image data simultaneously, thus preventing warping due to movement between the scanner and the object.

[0048] The projector unit may comprise one or more collimation lenses for collimating the light from the light source. The collimation lens(es) may be placed between the light source and the mask. In some embodiments, the one or more collimation lenses are Fresnel lenses. The projector unit may further comprise one or more focus lenses, or lens elements, configured for focusing the light at a predefined working distance or focus range such as defined by the depth of field of the scanner. In some embodiments, the projector unit comprises a projector lens stack comprising a plurality of lens elements. The projector lens stack may define the projector optical axis. In some embodiments, the lens elements of the projector lens stack are attached together to form a single unit.

[0049] In preferred embodiments, the projector unit of the scanner comprises at least one light source and a pattern generating element for defining a pattern of light. The pattern generating element is preferably configured for generating a light pattern to be projected on the surface of one or more objects, such as the dentition of a patient. As an example, the pattern generating element may be a mask having a spatial pattern. Hence, the projector unit may comprise a mask configured to define a pattern of light. The mask may be placed between the light source of the projector unit and the one or more focus lenses, such that light transmitted through the mask is patterned into a light pattern. As an example, the mask may define a polygonal pattern comprising a plurality of polygons, such as a checkerboard pattern. The projector unit may further comprise one or more lenses such as collimation lenses or projection lenses. In other embodiments, the pattern generating element is based on diffraction and / or refraction to generate the light pattern, such as a pattern comprising an array of discrete unconnected dots.

[0050] Preferably, the projector unit is configured to generate a predefined static pattern, which may be projected onto a surface. Alternatively, the projector unit may be configured to generate a dynamic pattern, which changes in time. The projector unit may be associated with its own projector plane, which is determined by the projector optics. As an example, if the projector unit is a back-lit mask projector, the projector plane may be understood as the plane wherein the mask is contained. The projector plane may comprise a plurality of pattern features of the projected pattern. Preferably, the camera units and projector unit are arranged such that the image sensors and the projector plane, e.g. defined by the mask, are in the same plane.

[0051] The projector unit may be configured to project a plurality of projector rays, which are projected onto the surface of an object to be scanned. Solving the correspondence problem may include the steps of determining image features in the images within a set of images, and further associate said image features with a specific projector ray. In preferred embodiments, the correspondence problem is solved jointly for groups of projector rays, as opposed to e.g. solving the correspondence problem projector ray by projector ray. The inventors have found that by solving the correspondence problem jointly for groups or collections of projector rays, a particularly reliable and robust solution can be obtained, consequently leading to a more accurate 3D representation. Subsequently, the depth of each projector ray may be computed, whereby a 3D representation of the scanned object may be generated. The projector unit may comprise one or more light sources. The projector unit may be configured to project a pattern of light defined by a plurality of projector rays when the light source(s) are on / active. The projector unit may be configured for sequentially turning the light source on and off at a predetermined frequency, wherein the light source is on for a predetermined time period. The light source(s) may be configured to generate light of a single wavelength or a combination of wavelengths (mono- or polychromatic). The combination of wavelengths may be produced by a light source configured to produce light comprising different wavelengths, or a range of wavelengths (such as white light). The light source may be configured to generate unpolarized light, such as unpolarized white light.

[0052] In some embodiments, each projector unit comprises a light source for generating white light. An advantage hereof is that white light enables the scanner to acquire data or information relating to the surface geometry and to the surface color simultaneously. Consequently, the same set of images can be used to provide both geometry of the object, e.g. in terms of 3D data / a 3D representation, and color of the object. Hence, there is no need for an alignment of data relating to the recorded surface geometry and data relating to the recorded surface color in order to generate a digital 3D representation of the object expressing both color and geometry of the object. Alternatively, the projector unit may comprise multiple light sources such as LEDs individually producing light of different wavelengths (such as red, green, and blue) that may be combined to form light comprising different wavelengths. Thus, the light produced by the light source(s) may be defined by a wavelength defining a specific color, or a range of different wavelengths defining a combination of colors such as white light. In some embodiments, the light source is a diode, such as a white light diode, or a laser diode. In some embodiments, the projector unit comprises a laser, such as a blue or green laser diode for generating blue or green light, respectively. An advantage hereof is that a more efficient projector unit can be realized, which enables a faster exposure compared to utilizing e.g. a white light diode.

[0053] Projected pattern

[0054] The projector unit may be configured to project a pattern of light defined by a plurality of projector rays when a light source of the projector unit is turned on. The terms ‘illumination pattern’, ‘pattern of light’, and ‘projected pattern’ are used herein interchangeably. The projected pattern may be generated using a pattern generating element, e.g. located in the projector unit. The pattern generating element may be a mask, such as a transparency or transmission mask, having a spatial pattern. The mask may be a chrome photomask. In other embodiments, the pattern generating element comprises one or more diffractive optical elements (DOEs) configured to utilize diffraction and / or refraction to generate a light pattern. The use of a pattern of light may lead to a correspondence problem, where a correspondence between points in the light pattern and points seen by the camera unit(s) viewing the pattern needs to be determined. In some embodiments, the correspondence problem is solved jointly for groups of projector rays emanating from the projector unit.

[0055] The projected pattern may be a polygonal pattern comprising a plurality of polygons. The polygons may be selected from the group of: triangles, rectangles, squares, pentagons, hexagons, and / or combinations thereof. Other polygons can also be envisioned. In general, the polygons are composed of edges and corners. In preferred embodiments, the polygons are repeated in the pattern in a predefined manner. As an example, the pattern may comprise a plurality of repeating units, wherein each repeating unit comprises a predefined number of polygons, wherein the repeating units are repeated throughout the pattern. Alternatively, the pattern may comprise a predefined arrangement comprising one or more stripes, squares, dots, triangles, rectangles, and / or combinations thereof. In some embodiments, the pattern is non-coded, such that no part of the pattern is unique.

[0056] In some embodiments, the generated pattern of light is a polygonal pattern, such as a checkerboard pattern comprising a plurality of checkers. Similar to a common checkerboard, the checkers in the pattern may have alternating dark and bright areas corresponding to areas of low light intensity (dark) and areas of high(er) light intensity (bright). In some embodiments the pattern of light is a checkerboard pattern comprising alternating squares of dark and bright light, i.e. of different intensity in light. In other embodiments, the light pattern comprises a distribution of discrete unconnected spots of light.

[0057] The pattern preferably comprises a plurality of pattern features. The pattern features may be arranged in a regular grid. In some embodiments of the presently disclosed scanner, the total number of pattern features in the pattern is at least 1000, preferably at least 3000, more preferably at least 10000, even more preferably at least 15000. When projecting a pattern comprising such pattern features onto a surface of the 3D object, the acquired images of the object will similarly comprise a plurality of image features corresponding to the pattern features. A pattern / image feature may be understood as an individual well-defined location in the pattern / image. Examples of image / pattern features include corners, edges, vertices, points, transitions, dots, stripes, etc. In some embodiments, the image / pattern features constitute corners in a polygon pattern such as corners of checkers in a checkerboard pattern.

[0058] Mirror

[0059] The scanner may further comprise a mirror, arranged in combination with a given scan unit. The mirror is preferably configured to reflect light from the projector unit of the scan unit and / or from the surface of the dental object and onto the image sensor(s) of each camera unit of the scan unit associated with the mirror. In preferred embodiments, the scanner comprises or constitutes an elongated probe, which defines a longitudinal axis of the scanner. In some embodiments, the height of the mirror as seen along the projector optical axis is between about 13 mm to about 20 mm. An advantage hereof is that the tip height of the scanner is kept at a minimum, in particular for working distances above 15 mm. Thus, the mirror allows for part of the optical path to be folded or redirected inside the scanner, such that the scanner may accommodate an optical system, e.g. a scan unit, having a working distance longer than the intended height of the probe or tip of the scanner. Consequently, the tip or probe can be made smaller, in particular the height of the probe, such that it may easily enter e.g. an oral cavity of a patient. A smaller probe also more easily captures data in the back of the mouth of the patient.

[0060] Fiducial markers

[0061] The intraoral scanner may comprise a pattern of fiducial markers arranged in a predefined arrangement, such as a two-dimensional arrangement. The pattern of fiducial markers may be placed in the optical path of the scanner, such as in or on the surface of a transparent window of the scanner. A fiducial marker may be understood as an object placed in the field of view of an imaging system that appears in the image produced, for use as a point of reference or a measure. The fiducial markers utilized may preferably be substantially two- dimensional objects, e.g. located on the surface of a transparent window of the intraoral scanner. Advantageously, the fiducial markers are provided on said transparent window or inside the window. The fiducial markers may resemble any geometrical shape such as squares, rectangles, circles, dots, triangles, hexagons, crosses, and / or combinations thereof. In particular, the fiducial markers may have a predefined geometric shape selected from the group of: polygonal shape, rectangular shape, triangular shape, cross-shape, diamond shape, circular shape, line shape, and / or combinations thereof.

[0062] The markers can be manufactured by a variety of techniques suitable for creating a predefined pattern inside or on the surface of a material, such as by etching, engraving, abrasive blasting, printing, coating, electroplating, micro-machining, micro milling, and / or combinations thereof.

[0063] As an example of how to produce the pattern of fiducial markers in the transparent window, a laser engraving machine or a chemical etching process may be used to selectively remove material from the transparent window to create the desired pattern of fiducial markers. As another example, a mask can be placed on the transparent window to cover areas where the pattern should not appear, and then sandblasting, chemical etching, or abrasive blasting can be used to remove material from the exposed areas, leaving the pattern behind. As yet another example, screen printing, inkjet printing, or other printing methods can be used, or specialized inks or coatings that adhere to the transparent surface may be used to form the predefined pattern. As yet another example, the pattern may be etched using ultraviolet (UV) lithography and a suitable etchant. As yet another example, one can use precision machining tools or micro-milling machines to remove material from the transparent window and create the desired pattern with micron-level accuracy.

[0064] In some embodiments, the fiducial markers are illuminated by the intraoral scanner during use of the scanner, such as illuminated by one or more projector units of the scanner. An advantage hereof is that the fiducial markers are illuminated with a known illumination. Consequently, the fiducial markers appear more similar in the images across sets of images acquired at different times. Accordingly, the reproducibility of the markers in the images is enhanced by illuminating the fiducial markers with an internal light source of the scanner, such as provided by the projector unit(s) of the scanner. In case the imaged fiducial markers change over time, i.e. across the acquired sets of images, this may indicate that the geometric relationship between one or more scanner components has changed. In response hereto, the scanner is preferably configured for automatically recalibrating the scanner by adjusting one or more parameters of the geometric model of the scanner as outlined elsewhere herein.

[0065] Housing

[0066] The intraoral scanner may comprise a housing, such as an elongated housing, wherein the distal end of the housing is suitable for being inserted in an oral cavity of a subject. In particular, the housing may resemble an elongated probe, wherein the distal end of the probe is configured for being inserted in an oral cavity, e.g. the mouth of a person, in order to acquire images and / or 3D data of the person’s teeth. The housing may be made in one or more pieces. In some embodiments, the housing is made in one piece. The housing is preferably made of one or more polymers, such as selected from the group of: Acrylonitrile Butadiene Styrene (ABS), Polycarbonate (PC), Polyethylene (PE): High-density polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS), or Polymethyl Methacrylate (PMMA). Other materials can be envisioned without departing from the scope of the present disclosure.

[0067] Transparent window

[0068] The intraoral scanner disclosed herein may comprise a transparent window. In preferred embodiments, the pattern of fiducial markers is arranged in the window or on the surface of the window. The transparent window may be located in the distal end of the scanner, such as in the housing of said scanner. In some embodiments, the window is substantially flush with the surface of the housing.

[0069] The transparent window may be made of a variety of materials that are suitable for creating a transparent region such that light can be transmitted through the window material. As an example, the transparent window may be made of a glass material, such as Sapphire. As another example, the window may be made of a polymer, such as poly(methyl methacrylate) (PMMA). Preferably, the window is made in a rigid material, such as the aforementioned examples. The window is preferably made substantially planar and fixedly mounted in the housing of the intraoral scanner disclosed herein.

[0070] Figure 10 shows an outline of a transparent window, wherein a predefined arrangement of fiducial markers are placed in the window. The markers may be placed near the edge of the window in order to allow for one or more regions where a projected pattern of light can be transmitted through the window, ideally without hindrance with the pattern of fiducial markers. Thus, in some embodiments, the pattern of fiducial markers is located outside the projected pattern, such that it does not overlap with the projected pattern.

[0071] Processor(s)

[0072] In accordance with some embodiments, the scanner comprises one or more processors, such as selected from the group of: central processing units (CPU), accelerators (offload engines), general-purpose microprocessors, graphics processing units (GPU), neural processing units (NPU), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), Advanced RISC Machines (ARM), dedicated logic circuitry, dedicated artificial intelligence processor units, and / or combinations thereof.

[0073] The one or more processors may be configured for at least partly carrying out any of the methods disclosed herein, such as the method of recalibrating the intraoral scanner. As, an example, the processor(s) may be configured for performing the steps of: determining a difference between the imaged pattern of fiducial markers and a predefined arrangement of said fiducial markers; determining whether a geometric relationship between the scan units and / or the camera units has changed based on the determined difference; and correcting the geometric relationship in a geometric model of the intraoral scanner based on the determined difference, whereby the scanner is recalibrated.

[0074] The scanner may further comprise computer memory for storing instructions, which when executed, causes the processor(s) to carry out the step of determining a difference between the imaged pattern of fiducial markers and a predefined arrangement of said fiducial markers. The computer memory may further store instructions, which when executed, causes the processor(s) to carry out the step of determining whether a geometric relationship between the scan units and / or the camera units has changed based on the determined difference and correcting the geometric relationship in a geometric model of the intraoral scanner based on the determined difference, whereby the scanner is recalibrated.

[0075] The processor(s) may be located on the scanner or they may be part of an external computer system forming part of the disclosed 3D scanner system. The processors may be operatively connected such that a first processor provides input to a second processor. Some of the processing, e.g. some steps of the disclosed calibration method, may be performed on the scanner and other steps of the method may be performed by a computer system.

[0076] Module for transmitting data

[0077] The scanner preferably comprises a module for transmitting data to one or more external devices, such as a computer system. The module may be a wireless module configured to wirelessly transfer data from the scanner to the computer system. The wireless module may be configured to perform various functions required for the scanner to wirelessly communicate with a computer network. The wireless module may utilize one or more of the I EEE 802.11 WiFi protocols / integrated TCP / IP protocol stack that allows the scanner to access the computer network. The wireless module may include a system-on-chip having different types of inbuilt network connectivity technologies. These may include commonly used wireless protocols such as Bluetooth, ZigBee, Wi-Fi, WiGig (also known as 60 GHz Wi-Fi), etc. The scanner may further, or alternatively, be configured to transmit data using a wired connection, such as via an ethernet cable or a USB cable. The scanner may be configured to continuously transfer the data during a scanning session. It may further be configured to transfer said data in realtime.

[0078] Computer system

[0079] A computer system may be understood as an electronic processing device for carrying out sequences of arithmetic or logical operations. In the present context, a computer system refers to one or more devices comprising at least one processor, such as a central processing unit (CPU), along with some type of computer memory. Examples of computer systems falling within this definition include desktop computers, laptop computers, computer clusters, servers, cloud computers, quantum computers, mobile devices such as smartphones and tablet computers, and / or combinations thereof.

[0080] The computer system may comprise hardware such as one or more central processing units (CPU), graphics processing units (GPU), and computer memory such as random-access memory (RAM) or read-only memory (ROM). The computer system may comprise a CPU, which is configured to read and execute instructions stored in the computer memory e.g. in the form of random-access memory. The computer memory may be configured to store instructions for execution by the CPU and data used by those instructions. As an example, the memory may store instructions, which when executed by the CPU, cause the computer system to perform, wholly or partly, any of the computer-implemented methods disclosed herein. The computer system may further comprise a graphics processing unit (GPU). The GPU may be configured to perform a variety of tasks such as video decoding and encoding, rendering of the 3D representation, and other image processing tasks.

[0081] The computer system may further comprise non-volatile storage in the form of a hard disc drive. The computer system preferably further comprises an I / O interface configured to connect peripheral devices used in connection with the computer system. More particularly, a display may be connected and configured to display output from the computer system. The display may for example display a 2D rendering of the generated digital 3D representation. Input devices may also be connected to the I / O interface. Examples of such input devices include a keyboard and a mouse, which allow user interaction with the computer system. A network interface may further be part of the computer system in order to allow it to be connected to an appropriate computer network so as to receive and transmit data (such as scan data and / or images) from and to other computing devices. The scan data may comprise or constitute 3D data, such as depth maps or point clouds, or it may comprise 2D data, such as images. The CPU, volatile memory, hard disc drive, I / O interface, and network interface, may be connected together by a bus.

[0082] The computer system is preferably configured for receiving data from the scanner, either directly from the scanner or via a computer network such as a wireless network. The data may comprise images, processed images, point clouds, sets of data points, or other types of data. The data may be transmitted / received using a wireless connection, a wired connection, and / or combinations thereof. In some embodiments, the computer system is configured for generating a digital 3D representation of a three-dimensional (3D) object as described herein. In some embodiments, the computer system is configured for receiving data, such as point clouds, from the scanner and then subsequently performing the steps of reconstruction and rendering a digital 3D representation of a three-dimensional (3D) object. Rendering may be understood as the process of generating one or more images from three-dimensional data. The computer system may comprise computer memory for storing a computer program, said computer program comprising computer-executable instructions, which when executed, causes the computer system to carry out any of the methods disclosed herein.

[0083] Method outlined

[0084] A first step of the method may be to acquire two or more sets of images using an intraoral scanner. The sets of images may be acquired by separate scan units of the intraoral scanner, wherein each scan unit comprises one or more camera units. Each set of images may comprise a plurality of two-dimensional images, such as at least one image for each camera unit of a given scan unit. As an example, in case a scan unit comprises four camera units, a set of images may comprise four images. In the case of two scan units, then two of such sets of images may be acquired, preferably simultaneously. The camera units may have at least partially overlapping fields of view, such that the acquired images may similarly have overlapping fields of view. Thus, the projected pattern being reflected of the scanned object may ideally be visible in all the images within a set of images. Furthermore, at least a part of the pattern of fiducial markers should be present in the images. Ideally, the entirety of the pattern of fiducial markers is collectively imaged by the camera units, but the entire pattern does not need to appear in each of the images in a set of images. This is illustrated in figure 10, which shows an outline of a transparent window along with overlapping fields of views of camera units and a pattern of fiducial markers placed in the window. Accordingly, the pattern of fiducial markers may appear in the sets of images, whereby an imaged pattern of fiducial markers is generated.

[0085] Another step of the method may be to determine a difference between the imaged pattern of fiducial markers and a predefined arrangement of said fiducial markers. As an example, the determined difference may be selected from the group of: position of the fiducial markers, size of the fiducial markers, orientation of the fiducial markers, and / or combinations thereof. For a perfectly calibrated intraoral scanner, there will ideally be no difference between the imaged pattern of fiducial markers and the predefined arrangement of said fiducial markers in the transparent window. Thus, both the geometric shape, the size, and the position of the markers are all predefined and known a priori. Any difference in one or more of said parameters in a subset of the markers would indicate some deviation from a perfect calibration of the scanner. Such a deviation can arise e.g. from thermal drift or thermal expansion in one or more of the components (optical, electrical, etc.) of the scanner. Thus, the scanner is preferably configured to automatically, during use, detect and determine said difference between the imaged pattern of fiducial markers and the predefined arrangement.

[0086] In the same step, or in a subsequent step, the scanner may be configured to determine whether a geometric relationship between the scan units, and / or between the camera units, of the scanner has changed based on the determined difference. As previously mentioned, the scanner may comprise two or more scan units, each scan unit comprising one or more camera units, wherein the scan units are positioned in a predefined known geometric relationship. Figure 1 shows an embodiment of such a scanner, wherein two scan units are positioned in series next to each other. Thus, the position and orientation of each scan unit is predefined. The position and orientation may collectively be referred to as the pose of a given scan unit. An example of how the pose can be defined is shown in figure 6.

[0087] Another step of the method may be to correct the geometric relationship in a geometric model of the intraoral scanner based on the determined difference, whereby the scanner is calibrated. The geometric model of the intraoral scanner may define a variety of parameters of the imaging system I optical system of the scanner in order to capture accurate 3D data and reconstruct the scanned object. As an example, the geometric model may include one or more calibration parameters related to the camera units, such as intrinsic parameters (focal length, principal point, etc.) and extrinsic parameters (camera position and orientation). The geometric model may further include parameters related to the optics of the imaging system, such as focal length, depth of field, field of view, aperture, image sensor size, pixel size, lens distortion, lighting model, etc.

[0088] In particular, the geometric model may describe the pose of each scan unit and / or the relative pose between the scan units. The pose of a given scan unit may comprise the position and orientation of the scan unit. The orientation of a given scan unit may be defined by the optical axis of the projector unit forming part of the scan unit. In some embodiments, the geometric relationship between the scan units and / or the camera units is corrected based on a Euclidean transformation of the pose (position and / or orientation) of at least one scan unit. The Euclidean transformation may have at least three degrees of freedom, or in some cases at least six degrees of freedom. The Euclidean transformation may include one or more rotations, translations, reflections, or any sequence of these.

[0089] Thus, the geometric model may be updated by adjusting the value of one or more of said parameters, such as the position and / or orientation of the scan units, in response to the determined difference. It may also be the position and / or orientation of one or more camera units of a given scan unit, which is adjusted, whereby the geometric relationship is corrected. Some of the parameters of the geometric model may be fixed, and others may be free to vary within some predefined range. The adjustment of the parameters may be performed continuously during scanning, such that the presently disclosed system and method enable real-time and dynamic calibration of the intraoral scanner.

[0090] Detailed description of the drawings

[0091] Fig. 1 shows an embodiment of an intraoral scanner 1 according to the present disclosure. In this embodiment, the scanner 1 comprises a housing 2 having a distal end for being inserted into an oral cavity, and a transparent window 3 located in the distal end of said housing, wherein the transparent window comprises a pattern of fiducial markers (not shown) arranged in a predefined arrangement. The intraoral scanner 1 further comprises two or more scan units 5 located in the housing 2, each scan unit 5 comprising one or more camera units, here embodied as four, configured for acquiring a set of images comprising at least one image from each camera unit, wherein at least a part of the pattern of fiducial markers is imaged by the camera units. The intraoral scanner further comprises a mirror 8 for each scan unit arranged in front of each scan unit 5, such that light projected by the scan unit(s) is guided out the transparent window 3 and onto an object to be scanned. Similarly, light reflected from the surface of the scanned object can be reflected by the mirrors 8 and redirected into the camera units of each scan unit 5. The pattern of fiducial markers in the transparent window 3 may look as shown in figures 9-10.

[0092] Fig. 2 shows an exploded view of some components of an intraoral scanner 1 according to an embodiment of the present disclosure. In this embodiment, the scanner comprises two scan units 5, each scan unit comprising a plurality of camera units 6 and a plurality of flexible printed circuit boards (PCB) 12 connected between the camera units 6 and a main PCB (not shown). The scanner further comprises a rigid frame 9 for receiving the scan units 5, such that they can be mounted in said frame 9. The frame may be manufactured in one piece. The frame may further be configured for receiving and housing the mirrors 8, wherein each mirror is arranged in combination with a scan unit 5 as explained in relation to figure 1.

[0093] Fig. 3 shows an embodiment of an intraoral scanner 1 according to the present disclosure. In this embodiment, the scanner 1 comprises a housing 2 having a distal end for being inserted into an oral cavity, and a transparent window 3 located in the distal end of said housing, wherein the transparent window comprises a pattern of fiducial markers (not shown) arranged in a predefined arrangement. In this embodiment, the scanner further comprises a battery (not shown) and a port 14 for charging the battery and / or for transmitting data via a cable connected to the port.

[0094] Fig. 4 shows an embodiment of an intraoral scanner 1 according to the present disclosure. In this embodiment, the scanner 1 comprises a housing 2 having a distal end for being inserted into an oral cavity, and a transparent window 3 located in the distal end of said housing, wherein the transparent window comprises a pattern of fiducial markers (not shown) arranged in a predefined arrangement. In this embodiment, the scanner further comprises a battery 13 and a port 14 for charging the battery and / or for transmitting data via a cable connected to the port. In this embodiment, the housing 2 can be dissembled in at least two parts, i.e. such that the housing 2 comprises a removable part, wherein the transparent window 3 is located in said removable part. This is advantageous in case the window 3 needs to be replaced or serviced. Furthermore, the removable part of the housing may enable easy access to a battery compartment for housing the battery 13.

[0095] Fig. 5 shows an embodiment of an intraoral scanner 1 according to the present disclosure. In this embodiment, the scanner 1 comprises a housing 2 having a distal end for being inserted into an oral cavity, and a transparent window 3 located in the distal end of said housing, wherein the transparent window 3 comprises a pattern of fiducial markers (not shown) arranged in a predefined arrangement. The pattern of fiducial markers in the transparent window 3 may look as shown in figures 9-10. In this figure, the housing 2 is made transparent for illustrative purposes. The intraoral scanner 1 further comprises two scan units 5 located in the housing 2, each scan unit 5 comprising one or more camera units configured for acquiring a set of images comprising at least one image from each camera unit, wherein at least a part of the pattern of fiducial markers is imaged by the camera units. The intraoral scanner further comprises a mirror 8 for each scan unit arranged in front of each scan unit 5, such that light projected by the scan unit(s) is guided out the transparent window 3 and onto an object to be scanned. Similarly, light reflected from the surface of the scanned object can be reflected by the mirrors 8 and redirected into the camera units of each scan unit 5. The scanner 1 further comprises a battery 13 and a port 14 for charging the battery and / or for transmitting data via a cable connected to the port.

[0096] Fig. 6 shows an embodiment of a scan unit 5 according to the present disclosure. In this embodiment, the scan unit comprises a projector unit 10 for projecting a predefined pattern and a plurality of camera units 6 (here exemplified as four camera units). The projector unit 10 has an optical axis 11 corresponding to the line of sight of a central ray projected by the projector unit and / or corresponding to an axis of radial symmetry of the projector unit. The figure further shows a pose of the scan unit, said pose comprising a position and an orientation. The pose is indicated by a cartesian coordinate system (x, y, z), wherein the optical axis 11 coincides with one of the axes, here exemplified as the z-axis. Thus, the position and orientation of the scan unit may be defined by the indicated coordinate system. However, other origins of the coordinate system may be chosen as well as other orientations, as long as the pose (position / orientation) is predefined. Then, any deviations from said predefined pose and / or any deviations of the relative pose between two scan units can be used to infer that their relative geometric relationship has changed, e.g. due to thermal drift / expansion. The two scan units may also be defined in a common coordinate system.

[0097] Fig. 7 shows an embodiment of a 3D scanner system according to the present disclosure. In this embodiment, the scanner system comprises an intraoral scanner 1 having a distal end for being inserted into an oral cavity, whereby one or more dental objects 15 can be scanned. The scanner comprises a transparent window 3 at the distal end of the scanner. The system further comprises a computer system 16 for generating a 3D representation of the dental object(s), such as a patient’s dentition, and / or for visualizing said 3D representation in a display. The scanner 1 may be configured to transmit data 17 to the computer system.

[0098] Fig. 8 shows an embodiment of a 3D scanner system according to the present disclosure. In this embodiment, the scanner system comprises an intraoral scanner 1 comprising two scan units 5, a mirror 8 arranged in combination with each scan unit. The scanner further comprises a transparent window 3 located in the distal end of the scanner, wherein the transparent window comprises a pattern of fiducial markers (not shown) arranged in a predefined arrangement. The scanner system further comprises one or more processors 7 configured for comparing the imaged pattern of fiducial markers to the predefined arrangement, whereby a difference may be determined; and / or for determining whether a geometric relationship between the scan units and / or the camera units has changed based on the difference; and / or for correcting the geometric relationship in a geometric model of the intraoral scanner based on the difference, whereby the scanner is calibrated. The processors 7 may be located on the intraoral scanner 1 or form part of an external computer system 16. The scanner system may further comprise a power supply 18 for powering the scanner 1 and / or for charging a battery located in the scanner. In this embodiment, the scanner comprises a port 14 for charging and / or powering the scanner. The port 14 may additionally or alternatively be configured for data transfer 17 to a computer system 16. The scanner may comprise a transfer unit, such as a wireless module, for wirelessly transferring data 17 to a computer system, e.g. via a wireless network (Wi-Fi).

[0099] Fig. 9 shows an embodiment of a pattern to be projected 19 along with a pattern of fiducial markers 4. In this embodiment, the projected pattern 19 resembles a checkerboard pattern, but other patterns (line stripes, dots, triangles, hexagons, etc.) can be envisioned. Each fiducial marker is exemplified as a cross; however, other shapes may be utilized. Each scan unit of the scanner may comprise a projector unit (not shown) for projecting the pattern 19. The scanner may further comprise a transparent window (not shown), wherein the pattern of fiducial markers 4 is located. Figure 6 shows an example of a scan unit with a projector unit and a plurality of camera units. The scanner system may be configured to calibrate the intraoral scanner based on the pattern of fiducial markers 4 located in the transparent window.

[0100] Fig. 10 shows an embodiment of a transparent window 3 for an intraoral scanner as disclosed herein. In this embodiment, the transparent window comprises a pattern of fiducial markers 4. Thus, the pattern of fiducial markers 4 is physically located in or on the window, and thereby not forming part of the projected pattern (not shown in the figure). As an example, the pattern 4 may be coated on the window 3 or form an integrated part of the window. Furthermore, in this embodiment, the scanner comprises two scan units, each scan unit comprising a plurality of camera units (not shown), wherein at least a part of the pattern of fiducial markers 4 is imaged by the camera unit(s). The field of view 20 of each camera unit is outlined in the figure. Thus, the scanner may comprise two or more camera units, such as four camera units, having at least partially overlapping field of views 20 as indicated in the figure. The overlap between the field of views is indicated in the figure by the shaded area 21 , which corresponds to a common field of view of the camera units. In this embodiment, only a part of the fiducial marker pattern 4 is visible in the field of view of a given camera unit. However, collectively, the camera units view / image all fiducial markers 4 in the pattern. The figure shows two sets of camera units having overlapping fields of view, where each set of four camera units belongs to a given scan unit. Furthermore, there is a pattern of fiducial markers 4 associated with each scan unit, such that said pattern 4 can be used to infer any deviations in the geometric relationship between the two scan units. The scanner system may further comprise one or more processors 7 (not shown) configured for comparing the imaged pattern of fiducial markers to the predefined arrangement 4, whereby a difference may be determined; and / or for determining whether a geometric relationship between the scan units has changed based on the difference; and / or for correcting the geometric relationship in a geometric model of the intraoral scanner based on the difference, whereby the scanner is calibrated. The projected pattern may be similar to the one shown in figure 9. It is noted that the figure illustrates the predefined arrangement of the fiducial markers. For a perfectly calibrated scanner, the imaged pattern of fiducial markers will be exactly similar to the predefined arrangement.

[0101] Fig. 11 shows an embodiment of a transparent window 3 for an intraoral scanner as disclosed herein. In this embodiment, the transparent window comprises a pattern of fiducial markers 4. The pattern of fiducial markers 4 is physically located in or on the window, and thereby not forming part of the projected pattern 19. Similar to figure 10, this embodiment shows overlapping camera fields of view 20, such that the camera units collectively image the pattern of fiducial markers 4 and the reflected projected pattern 19. In this embodiment, the two scan units are arranged in succession, i.e. they are placed next to each other, such that they each project a pattern 19 on the same side of the scanner and preferably such that said patterns line up closely next to each other without overlapping. This is illustrated in the figure. In this embodiment, a total of six fiducial markers are placed in or on the window 3; however, other numbers of fiducial markers can be envisaged without departing from the scope of the disclosure. It is noted that even though the projected pattern 19 is shown on the figure, it does not form part of the transparent window 3. Rather, it is projected through the transparent window 3 during use of the intraoral scanner. Here, the projected pattern 19 is exemplified as a checkerboard pattern. However, other patterns, such as polygonal-, stripe- or dot patterns, can be envisaged without departing from the scope of the disclosure.

[0102] Further details of the invention

[0103] 1. A 3D scanner system comprising:

[0104] - an intraoral scanner (1) comprising: - a housing (2) having a distal end for being inserted into an oral cavity;

[0105] - a transparent window (3) located in the distal end of said housing, wherein the transparent window comprises a pattern of fiducial markers (4) arranged in a predefined arrangement; the intraoral scanner further comprising one or more scan units (5) located in the housing, each scan unit comprising:

[0106] - one or more camera units (6) configured for acquiring a set of images comprising at least one image from each camera unit, wherein at least a part of the pattern of fiducial markers is imaged by the camera unit(s);

[0107] - one or more processors (7) configured for:

[0108] - comparing the imaged pattern of fiducial markers to the predefined arrangement, whereby a difference may be determined;

[0109] - determining whether a geometric relationship between the scan units and / or the camera units has changed based on the difference; and

[0110] - correcting the geometric relationship in a geometric model of the intraoral scanner based on the difference, whereby the scanner is calibrated. The scanner system according to item 1, wherein the intraoral scanner comprises two or more scan units. The scanner system according to any of the preceding items, wherein the geometric relationship comprises the pose of each scan unit and / or the relative pose between the scan units. The scanner system according to item 3, wherein a given pose of a scan unit comprises the position and orientation of the scan unit. The scanner system according to item 4, wherein the orientation of a given scan unit is defined by the optical axis of a projector unit forming part of the scan unit. 6. The scanner system according to any of the preceding items, wherein the geometric relationship between the scan units and / or camera units is corrected based on a Euclidean transformation of the pose of at least one scan unit or camera unit.

[0111] 7. The scanner system according to item 6, wherein the Euclidean transformation has at least three degrees of freedom.

[0112] 8. The scanner system according to item 6, wherein the Euclidean transformation has at least six degrees of freedom.

[0113] 9. The scanner system according to any of the preceding items, wherein the determined difference is selected from the group of: position of the fiducial markers, size of the fiducial markers, orientation of the fiducial markers, and / or combinations thereof.

[0114] 10. The scanner system according to any of the preceding items, wherein each scan unit of the intraoral scanner comprises two or more camera units.

[0115] 11. The scanner system according to any of the preceding items, wherein each scan unit of the intraoral scanner comprises four or more camera units.

[0116] 12. The scanner system according to any of the items 10-11 , wherein the camera units are configured for acquiring a set of images, the set of images comprising at least one image from each camera unit.

[0117] 13. The scanner system according to any of the items 10-12, wherein the camera units are configured for simultaneously acquiring the images forming part of the set of images.

[0118] 14. The scanner system according to any of the preceding items, wherein each camera unit comprises an image sensor and one or more focus lenses for focusing light onto the image sensor.

[0119] 15. The scanner system according to any of the preceding items, wherein the intraoral scanner further comprises one or more projector units configured for projecting a pattern through the transparent window. 16. The scanner system according to item 15, wherein the projector unit(s) comprises a mask for defining the pattern.

[0120] 17. The scanner system according to any of the items 15-16, wherein the projected pattern is a checkerboard pattern.

[0121] 18. The scanner system according to any of the items 15-17, wherein the pattern of fiducial markers is aligned to the pattern projected through the transparent window.

[0122] 19. The scanner system according to any of the items 15-18, wherein the pattern of fiducial markers is located outside the projected pattern, such that it does not overlap with the projected pattern.

[0123] 20. The scanner system according to any of the items 15-19, wherein the projected pattern comprises a plurality of empty spaces for encompassing the fiducial markers.

[0124] 21. The scanner system according to any of the items 15-20, wherein the pattern of fiducial markers is fully enclosed in the projected pattern.

[0125] 22. The scanner system according to any of the items 15-21, wherein the projector unit is configured for illuminating the fiducial markers.

[0126] 23. The scanner system according to any of the items 15-22, wherein the geometric relationship is corrected by adjusting the position and / or orientation of one or more camera units relative to each other and / or relative to the projector unit.

[0127] 24. The scanner system according to any of the preceding items, wherein the fiducial markers have a predefined geometric shape selected from the group of: polygonal shape, rectangular shape, triangular shape, cross-shape, diamond shape, circular shape, line shape, and / or combinations thereof.

[0128] 25. The scanner system according to any of the preceding items, wherein the transparent window is made of a glass, such as Sapphire.

[0129] 26. The scanner system according to any of the preceding items, wherein the transparent window is made of a polymer, such as poly(methyl methacrylate) (PM MA). The scanner system according to any of the preceding items, wherein the processor(s) are configured for continuously calibrating the intraoral scanner during use based on continuously correcting the geometric relationship. The scanner system according to any of the preceding items, wherein the processor(s) are configured for calibrating the intraoral scanner in real-time during use of the scanner. A method of recalibrating an intraoral scanner, the method comprising the steps of:

[0130] - acquiring two or more sets of images, wherein the sets of images are acquired by separate scan units of the intraoral scanner, each scan unit comprising one or more camera units, wherein a pattern of fiducial markers is present each set of images;

[0131] - determining a difference between the imaged pattern of fiducial markers and a predefined arrangement of said fiducial markers;

[0132] - determining whether a geometric relationship between the scan units and / or the camera units has changed based on the determined difference; and

[0133] - correcting the geometric relationship in a geometric model of the intraoral scanner based on the determined difference, whereby the scanner is recalibrated. The method according to item 29, wherein the geometric relationship is corrected continuously and in real-time. The method according to any of the items 29-30, wherein the steps of the method is performed continuously and in real-time. The method according to any of the items 29-31 , wherein the pattern of fiducial markers is located in a window of the intraoral scanner. The method according to any of the items 29-32, wherein the geometric relationship comprises the pose of each scan unit and / or the relative pose between the scan units. 34. The method according to item 33, wherein a given pose of a scan unit comprises the position and orientation of the scan unit.

[0134] 35. The method according to any of the items 29-34, wherein the geometric relationship comprises the pose of each camera unit and / or the relative pose between the camera units.

[0135] 36. The method according to item 35, wherein a given pose of a camera unit comprises the position and orientation of the scan unit.

[0136] 37. The method according to item 34, wherein the orientation of a given scan unit is defined by the optical axis of a projector unit forming part of the scan unit.

[0137] 38. The method according to any of the items 29-37, wherein the geometric relationship between the scan units and / or the camera units is corrected based on a Euclidean transformation of the pose of at least one scan unit.

[0138] 39. The method according to any of the items 29-38, wherein the geometric relationship between the camera units is corrected based on a Euclidean transformation of the pose of at least one camera unit.

[0139] 40. The scanner system according to item 39, wherein the Euclidean transformation has at least three degrees of freedom.

[0140] 41. The scanner system according to item 39, wherein the Euclidean transformation has at least six degrees of freedom.

[0141] 42. The method according to any of the items 29-41, wherein the determined difference is selected from the group of: position of the fiducial markers, size of the fiducial markers, orientation of the fiducial markers, and / or combinations thereof.

[0142] Although some embodiments have been described and shown in detail, the disclosure is not restricted to such details, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilized, and structural and functional modifications may be made without departing from the scope of the present disclosure. Furthermore, the skilled person would find it apparent that unless an embodiment is specifically presented only as an alternative, different disclosed embodiments may be combined to achieve a specific implementation and such specific implementation is within the scope of the disclosure.

[0143] Reference numerals

[0144] 1. Intraoral scanner

[0145] 2. Housing

[0146] 3. Transparent window

[0147] 4. Pattern of fiducial markers

[0148] 5. Scan unit(s)

[0149] 6. Camera unit(s)

[0150] 7. Processor(s)

[0151] 8. Mirror(s)

[0152] 9. Frame

[0153] 10. Projector unit

[0154] 11. Optical axis of projector unit

[0155] 12. Flexible PCB(s)

[0156] 13. Battery

[0157] 14. Port for charging and / or data transfer

[0158] 15. Dental object(s)

[0159] 16. Computer system

[0160] 17. Data transfer

[0161] 18. Power supply

[0162] 19. Projected pattern

[0163] 20. Field of view of a camera unit

[0164] 21. Common field of view of camera units

Claims

Claims1. A 3D scanner system comprising:- an intraoral scanner (1) comprising:- a housing (2) having a distal end for being inserted into an oral cavity;- a transparent window (3) located in the distal end of said housing, wherein the transparent window comprises a pattern of fiducial markers (4) arranged in a predefined arrangement; the intraoral scanner further comprising one or more scan units (5) located in the housing, each scan unit comprising:- one or more camera units (6) configured for acquiring a set of images comprising at least one image from each camera unit, wherein at least a part of the pattern of fiducial markers is imaged by the camera unit(s);- one or more processors (7) configured for: i. comparing the imaged pattern of fiducial markers to the predefined arrangement, whereby a difference may be determined; ii. determining whether a geometric relationship between the scan units and / or the camera units has changed based on the difference; and iii. correcting the geometric relationship in a geometric model of the intraoral scanner based on the difference, whereby the scanner is calibrated.

2. The scanner system according to claim 1 , wherein the intraoral scanner comprises two or more scan units.

3. The scanner system according to any of the preceding claims, wherein the geometric relationship comprises the pose of each scan unit and / or the relative pose between the scan units.

4. The scanner system according to claim 3, wherein a given pose of a scan unit comprises the position and orientation of the scan unit.

5. The scanner system according to claim 4, wherein the orientation of a given scan unit is defined by the optical axis of a projector unit forming part of the scan unit.

6. The scanner system according to any of the preceding claims, wherein the geometric relationship between the scan units and / or camera units is corrected based on a Euclidean transformation of the pose of at least one scan unit or camera unit.

7. The scanner system according to claim 6, wherein the Euclidean transformation has at least three degrees of freedom.

8. The scanner system according to claim 6, wherein the Euclidean transformation has at least six degrees of freedom.

9. The scanner system according to any of the preceding claims, wherein the determined difference is selected from the group of: position of the fiducial markers, size of the fiducial markers, orientation of the fiducial markers, and / or combinations thereof.

10. The scanner system according to any of the preceding claims, wherein each scan unit of the intraoral scanner comprises two or more camera units.

11. The scanner system according to any of the preceding claims, wherein each scan unit of the intraoral scanner comprises four or more camera units.

12. The scanner system according to any of the claims 10-11 , wherein the camera units are configured for acquiring a set of images, the set of images comprising at least one image from each camera unit.

13. The scanner system according to any of the claims 10-12, wherein the camera units are configured for simultaneously acquiring the images forming part of the set of images.

14. The scanner system according to any of the preceding claims, wherein each camera unit comprises an image sensor and one or more focus lenses for focusing light onto the image sensor.

15. The scanner system according to any of the preceding claims, wherein the intraoral scanner further comprises one or more projector units configured for projecting a pattern through the transparent window.

16. The scanner system according to claim 15, wherein the projector unit(s) comprises a mask for defining the pattern.

17. The scanner system according to any of the claims 15-16, wherein the projected pattern is a checkerboard pattern.

18. The scanner system according to any of the claims 15-17, wherein the pattern of fiducial markers is aligned to the pattern projected through the transparent window.

19. The scanner system according to any of the claims 15-18, wherein the pattern of fiducial markers is located outside the projected pattern, such that it does not overlap with the projected pattern.

20. The scanner system according to any of the claims 15-19, wherein the projected pattern comprises a plurality of empty spaces for encompassing the fiducial markers.

21. The scanner system according to any of the claims 15-20, wherein the pattern of fiducial markers is fully enclosed in the projected pattern.

22. The scanner system according to any of the claims 15-21, wherein the projector unit is configured for illuminating the fiducial markers.

23. The scanner system according to any of the claims 15-22, wherein the geometric relationship is corrected by adjusting the position and / or orientation of one or more camera units relative to each other and / or relative to the projector unit.

24. The scanner system according to any of the preceding claims, wherein the fiducial markers have a predefined geometric shape selected from the group of: polygonal shape, rectangular shape, triangular shape, cross-shape, diamond shape, circular shape, line shape, and / or combinations thereof.

25. The scanner system according to any of the preceding claims, wherein the transparent window is made of a glass, such as Sapphire.

26. The scanner system according to any of the preceding claims, wherein the transparent window is made of a polymer, such as poly(methyl methacrylate) (PM MA).

27. The scanner system according to any of the preceding claims, wherein the processor(s) are configured for continuously calibrating the intraoral scanner during use based on continuously correcting the geometric relationship.

28. The scanner system according to any of the preceding claims, wherein the processor(s) are configured for calibrating the intraoral scanner in real-time during use of the scanner.

29. A method of recalibrating an intraoral scanner, the method comprising the steps of: a. acquiring two or more sets of images, wherein the sets of images are acquired by separate scan units of the intraoral scanner, each scan unit comprising one or more camera units, wherein a pattern of fiducial markers is present each set of images; b. determining a difference between the imaged pattern of fiducial markers and a predefined arrangement of said fiducial markers; c. determining whether a geometric relationship between the scan units and / or the camera units has changed based on the determined difference; and d. correcting the geometric relationship in a geometric model of the intraoral scanner based on the determined difference, whereby the scanner is recalibrated.

30. The method according to claim 29, wherein the geometric relationship is corrected continuously and in real-time.

31. The method according to any of the claims 29-30, wherein the steps of the method is performed continuously and in real-time.

32. The method according to any of the claims 29-31 , wherein the pattern of fiducial markers is located in a window of the intraoral scanner.

33. The method according to any of the claims 29-32, wherein the geometric relationship comprises the pose of each scan unit and / or the relative pose between the scan units.

34. The method according to claim 33, wherein a given pose of a scan unit comprises the position and orientation of the scan unit.

35. The method according to any of the claims 29-34, wherein the geometric relationship comprises the pose of each camera unit and / or the relative pose between the camera units.

36. The method according to claim 35, wherein a given pose of a camera unit comprises the position and orientation of the scan unit.

37. The method according to claim 34, wherein the orientation of a given scan unit is defined by the optical axis of a projector unit forming part of the scan unit.

38. The method according to any of the claims 29-37, wherein the geometric relationship between the scan units and / or the camera units is corrected based on a Euclidean transformation of the pose of at least one scan unit.

39. The method according to any of the claims 29-38, wherein the geometric relationship between the camera units is corrected based on a Euclidean transformation of the pose of at least one camera unit.

40. The scanner system according to claim 39, wherein the Euclidean transformation has at least three degrees of freedom.

41. The scanner system according to claim 39, wherein the Euclidean transformation has at least six degrees of freedom.

42. The method according to any of the claims 29-41 , wherein the determined difference is selected from the group of: position of the fiducial markers, size of the fiducial markers, orientation of the fiducial markers, and / or combinations thereof.

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