Patent Description:
Intraoral scanners are generally used to capture direct digital impression of a patient's teeth directly from patient's oral cavity. The scanner projects light onto dental area to be scanned. <NUM> dimensional images captured by imaging sensors in response to the projected light are processed such as by a scanning software to generate a 3D digital representation of the scanned dental area.

In both prosthodontic and orthodontic procedures, obtaining surficial 3D digital representation of a dental object in the oral cavity may be a first step in performing a diagnosis or treatment. The more complete and accurate the scans of the dental object are, the higher the quality of the surficial 3D digital representation, and thus the greater the ability to design an optimal prosthesis or orthodontic treatment appliance. However, in the existing intraoral scanners, it is difficult to change a focal plane to capture images of the dental object at different focal planes, which limits the quality and completeness of 3D digital representation of the dental object. <CIT> discloses an intra-oral handheld 3D optical scanner.

It is desired to have a scanner comprising a mechanical system such as a drive mechanism configured to linearly move at least one lens to change the focal plane of a lens system to capture images of dental object.

An intraoral scanner may include an optical probe (i.e. scanner tip) configured to be moved within an oral cavity of a patient during scanning of dental object(s) within the oral cavity, an illumination module comprising at least one light source configured to generate illumination signal (e.g. incident light) for illuminating the dental object within the oral cavity, and focusing optics configured to focus the illumination signal to a focal plane external to the optical probe. The focal plane may be orthogonal or non-orthogonal to a direction of propagation of the incident light. The scanner may further include an image sensor configured to obtain data in response to the illumination of the dental object. The obtained data includes a 2D image that correspond to characteristic(s) of a dental object being scanned. The characteristics includes at least one of surface topology or texture data such as color data of the dental object. A processor, either comprised in the scanner or at least partly remote from the scanner, is configured to determine the surface topography and/ or texture data of the patient's teeth based on the obtained data. The focusing optics typically includes a lens assembly and for a specific position of the lens assembly, the focal plane may be fixed relative to the optical probe during scanning of the dental object.

One aspect of the disclosure is to provide an intraoral scanner that is configured to change a focal plane to allow obtaining two dimensional images of a dental object at various focal planes.

One aspect of the disclosure is to provide an intraoral scanner having a mechanical system that is configured to move a lens assembly to change the focal plane of the intraoral scanner. For a specific position of the lens assembly comprising a lens during scanning of the dental object, the focal plane may be fixed relative to the optical probe.

One aspect of the disclosure is to provide a drive assembly having a drive (e.g., electric motor) and a guide that is configured to be rotated by the drive. The rotation of the drive allows for back-and-forth movement of the lens assembly about a translation axis, preferably without changing a direction of rotation of the drive. The motion of the lens assembly positions the lens assembly at different positions along the translation axis, thus allowing changing the position of the focal plane and obtaining two dimensional images corresponding to different positions of the focal plane.

One aspect of the disclosure is to provide an intraoral scanner having reduced friction during back-and-forth movement of the lens assembly. This may be achieved, for example by providing lubrication between components that interface during movement such as between one or more rails and the lens housing or between coupling element and guide. This provides a smooth motion of the lens assembly, thereby allowing to change the focal plane.

One aspect of the disclosure is to provide a coupling element for engaging the guide with the lens housing. The coupling element, especially when operationally coupled with a biasing member such as a spring, reduces vibration during transfer of motion from the drive assembly to the lens assembly.

At least some of the above recited aspects are provided by an intra-oral handheld 3D optical scanner. The scanner includes an illumination module configured to generate an illumination signal to illuminate a dental object, and an image sensor configured to obtain data in response to the illumination of the dental object. The data is configured to be used to generate a 3D dental model of the dental object. The scanner also includes a lens housing comprising an optical lens that is configured to direct the illuminating signal towards the dental object. The scanner further includes a drive comprising a shaft that is configured to rotate around a rotation axis, a guide extending continuously along at least a part of a length of the shaft, and a spring arranged intermediate between the lens housing and the guide. The spring is configured to exert a spring force towards the guide.

The optical lens may further be configured to direct the reflected illuminating signal from the illuminated dental object towards an image sensor.

In some aspect, the drive assembly is supported/mounted on the frame/ housing130 of the scanner by using suitable brackets.

In some embodiments, the illumination signal is a light or a structured light. The light may include a white light or a plurality of colored light sources. The plurality of colored light sources (e.g. RGB) may typically be switched on sequentially during scanning of the dental object.

In some embodiments, the structured light includes a pattern corresponding to at least one of a physical structure introduced in light path between at least a light source of the illumination module and dental object, a digitally generated light pattern, or relative arrangement of more than one light source of the illumination module. The pattern may include different patterns such as periodic pattern of parallel lines or dots extending in a plane perpendicular to the optical axis such as checkerboard pattern with alternating relatively brighter and relatively darker regions.

The structured light facilitates in determining/obtaining surface geometry information and surface color information of the dental object. Use of the structured light in context of intraoral optical scanner is disclosed in <CIT> assigned to 3Shape AS.

In some embodiments, a length of the shaft is along the rotation axis.

In some embodiments, a longitudinal axis of the shaft is parallel to an optical axis of the optical lens.

In some embodiments, the guide extends continuously around the circumferential surface of the shaft.

In some embodiments, the guide is defined by a closed path.

In some embodiments, the guide is defined by the closed path that is non-parallel to the rotation axis of the shaft. The closed path is generally understood as a path having a start point and end point that are same. The start point and end point of the guide correspond to one back and forth linear movement of the lens assembly along the translation axis, i.e. the lens assembly moves from one extreme point to another extreme point and back from the another extreme point to one extreme point along the translation axis.

In some embodiments, the guide is defined by the closed path such that a 2D projection of the closed path is non-parallel to the rotation axis. The 2D projection is in a direction perpendicular to the rotation axis.

The closed path of the guide that is non-parallel to the rotation axis of the shaft enables back and forth (i.e., reciprocating motion of the lens housing) between two extreme positions without changing a direction of rotation of the drive. Accordingly, reducing the vibrations of the lens assembly during scanning of the dental object.

In some embodiments, the guide extends sinusoidally around the circumferential surface.

In some embodiments, the shaft comprises an end part connected coaxially with rest of the shaft and the guide is arranged on the end part. The end part may include a part that is detachably connected to the rest of the shaft. Alternatively, the end part may be an integral portion of the shaft, and the guide is defined along an outer circumferential surface of the shaft. The end part is adapted to rotate along the shaft around the rotational axis. The end part and the rest of the shaft are typically made up of different materials.

In some embodiments, the guide extends continuously to form a closed sinusoidal curve around the circumferential surface of the shaft.

In some embodiments, the shaft is configured to rotate around the rotation axis for producing a linear movement of the lens housing along a translation axis.

In some embodiment, linear movement of the lens housing is based on cylindrical cam-follower mechanism. The shaft comprising the guide may represent the cylindrical cam and the spring loaded coupling may represent the follower.

In some embodiments, the linear movement comprises back and forth movement between a first extreme position and a second extreme position.

In some embodiments, a distance of the linear movement of the lens housing corresponds to the length of the guide around the circumferential surface of the shaft.

In some embodiments, the spring is arranged such that the longitudinal axis of the spring is orthogonal to the optical axis of the optical lens.

In some embodiments, the spring is arranged such that the longitudinal axis of the spring is spatially separated relative to the optical axis of the optical lens.

In some embodiments, the spring is arranged such that the longitudinal axis of the spring is normal to the rotation axis.

In some embodiments, the lens housing comprises an attachment part where the spring fixedly attaches with the lens housing.

In some embodiments, the attachment part comprises a gap comprising at least a part of the spring arranged therein.

In some embodiments, the attachment part comprises a plurality of protrusions, the plurality of protrusions at least partly encircles a free space. The spring is arranged in the free space and the spring being at least partly encircled by the protrusion.

In some embodiments, the lens housing comprises at least one pin extending from the lens housing, the spring being arranged such that the at least one pin extends along the longitudinal axis of the spring and supports the spring.

In some embodiments, the spring is configured to transfer a spring force towards the guide and the lens housing.

In some embodiments, the scanner includes a coupling element operationally connecting the guide with the spring.

In some embodiments, the spring applies a force configured to maintain a connection between the coupling element and the lens housing.

In some embodiments, the shaft is configured to rotate around the rotation axis. The coupling element is configured to move along the guide in response to the rotation of the shaft, and the lens housing is configured to linearly move between a first extreme position and a second extreme position along a translation axis in response to the movement of the coupling element along the guide.

In some embodiments, the spring applied force is configured to maintain a connection between the coupling element and guide.

In some embodiments, the spring applies a force configured to maintain a connection between the coupling element and lens housing during the movement of lens housing along the translation axis.

In some embodiments, the spring applies force configured to maintain a connection between the coupling element and the guide during the movement of lens housing along the translation axis.

In some embodiments, the spring is configured to transfer a spring force between the coupling element and the lens housing.

In some embodiments, the spring is configured to transfer a lateral force between the coupling element and the lens housing.

In some embodiments, the spring is configured to transfer an axial force component to maintain a physical contact between the coupling element and the guide in response to the rotation of the drive.

In some embodiments, the spring comprises a stiffness that allows transferring an axial force component to maintain a physical contact between the coupling element and the guide during the rotation of the drive to the lens housing.

In some embodiments, at least a part of the coupling element is arranged in the attachment part.

In some embodiments, at least a part of the spring and at least a part of the coupling element is at least partly encircled by the plurality of protrusions.

In some embodiments, the guide is one of a male part or a female part and the coupling element is another of the female part or male part.

In some embodiments, a female guide part is a groove.

In some embodiments, the groove comprises a V-groove.

In some embodiments, the male coupling element part is a ball element configured to operationally interact with the female guide part.

In some embodiments, the male guide part is a protruded structure.

In some embodiments, the female coupling element part comprises a slot configured to operationally interact with the male guide part.

In some embodiments, lubrication is provided at an interface between the coupling element and the guide.

In some embodiments, the lens housing is configured to move along one or more rails.

In some embodiments, the lens housing includes a structure to house and support the focus lens that is configured to create focal planes.

In some embodiments, the lens housing includes at least one bracket attached to the ring structure and slidably supported on one or more rails. The at least one bracket is configured to slide along the one or more rails, thus allowing linear movement of the lens along the one or more rails to allow creating focus planes.

In some embodiments, the spring is arranged such that the longitudinal axis of the spring is normal to one of the one or more rails.

In some embodiments, the spring comprises a stiffness such that the spring allows for a backlash free connection between the coupling element and the guide.

In some embodiments, one or more rails is ferromagnetic.

In some embodiments, one or more magnets are arranged adjacent to the one or more rails.

In some embodiments, one or more magnets are arranged in or on the lens housing.

In some embodiments, the one or more magnets are configured to mitigate vibration of the lens housing during movement of the lens housing along the one or more rails.

In some embodiments, the magnetic flux density of the one or more magnets is at least <NUM> Tesla, such as between <NUM> - <NUM> Tesla.

In some embodiments, lubrication is provided between the one or more rails and the lens housing.

In some embodiments, the lens housing is configured to slide along at least two rails, and the lens housing interfaces at two contact surfaces with at least one rail of the at least two rails.

In some embodiments, the lens housing is configured to slide along at least two rails, and the lens housing interfaces at one contact surface with at least one rail of the at least two rails.

Having thus described example embodiments of the present disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:.

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that the present disclosure can be practiced without these specific details. In other instances, apparatus and methods are shown in block diagram form only in order to avoid obscuring the present disclosure.

Reference in this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. The appearance of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Some of these embodiments may appropriately be combined with one another. Further, the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Similarly, various requirements are described which may be requirements for some embodiments but not for other embodiments.

Some embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the disclosure are shown.

The embodiments are described herein for illustrative purposes and are subject to many variations. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient but are intended to cover the application or implementation without departing from the scope of the present invention as defined by the appended claims. Further, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting. Any heading utilized within this description is for convenience only and has no legal or limiting effect.

Referring to <FIG>, a schematic view of an intra-oral handheld 3d scanner <NUM> (hereinafter referred to as scanner <NUM>) according to an embodiment of the disclosure is shown. As shown, the scanner <NUM> includes an illumination module <NUM> configured to generate an illumination signal to illuminate a dental object <NUM> within an oral cavity, i.e. mouth, of a patient, an image sensor <NUM> to capture images of the dental object <NUM>, and a lens system <NUM> to focus/direct the illumination signal from the illumination module <NUM> towards the dental object <NUM> and images the dental object <NUM> on the image sensor <NUM>. In an embodiment, the image sensor <NUM> obtains data in response to the illumination of the dental object <NUM> via the lens system <NUM> and the data is used to generate a 3D dental model of the dental object <NUM>. In some embodiments, the data is in the form of 2D images of the dental object <NUM>.

The illumination signal may be a light or a structured light. In some embodiments, the structured light may include a pattern corresponding to at least one of a physical structure introduced in light path between at least a light source <NUM> of the illumination module <NUM> and the dental object <NUM>, a digitally generated light pattern, or relative arrangement of more than one light source of the illumination module <NUM>. To provide a structured light, in an embodiment, the illumination module <NUM> may include a pattern generating element <NUM> to incorporate a spatial pattern of light into a light beam generated by the at least one light source <NUM>. As shown, the pattern generating element <NUM> may be arranged between the light source <NUM> and the lens system <NUM> to introduce a spatial pattern inside the light beam. As shown, the structured light may be provided by introducing/placing a suitable physical structure <NUM> in the path of the illumination signal provided by the at least one light source <NUM>. In some embodiments, the structured light may be generated by arranging multiple light sources <NUM> in a suitable spatial arrangement.

In some embodiments, the scanner <NUM> may include a beam splitter <NUM> arranged between the pattern generating element <NUM> and the lens system <NUM>. The beam splitter <NUM> facilitates in directing the reflected light received from the dental object <NUM> through the lens system <NUM> to the image sensor <NUM>.

In an embodiment, the image sensor <NUM> includes a color filter array <NUM>. Although drawn as a separate entity, the color filter <NUM> array is typically integrated with the image sensor <NUM>, with a single-color filter for every pixel. Moreover, the scanner may include polarization optics <NUM>. Having the color filter array (e.g. Bayer filter) allows for simultaneously capturing data that may be used for both determining topology and color of the dental object, thereby allowing generation of 3D digital representation with color information of the dental object. Alternatively, instead of using a color filter array, the scanner may include multi-colored light sources (e.g. RGB) that are switched sequentially so that data corresponding to different colored light source may be captured. Any of the color data obtained by illuminating the dental object, using one of the multi-colored light sources, may be used to determine surface topology. Color data may be obtained by illuminating the dental object using each of the multi-colored light sources may be used to use specific color data. The specific color data and surface topology may be mapped to generate 3D digital representation with color information of the dental object.

Polarization optics <NUM> may be used to selectively image specular reflections and block out undesired diffuse signal from sub-surface scattering inside the scanned object <NUM>. The scanner <NUM> may include folding optics, e.g. a mirror <NUM>, which directs the light out in a direction different to the optical path of the lens system <NUM>, e.g., in a direction perpendicular to the optical path of the lens system <NUM>.

In an embodiment, the lens system <NUM> includes a lens assembly <NUM> having at least one optical lens <NUM>. The lens system is adapted to move along an optical axis <NUM> of the lens system <NUM> to shift a focal plane of the lens system <NUM>. The optical lens <NUM> (i.e., lens <NUM>) is configured to direct the illumination signal towards the dental object <NUM>. In an embodiment, the lens <NUM> may be a single lens, a doublet lens, or even a triplet lens.

Referring now to <FIG>, which illustrates a part of the intraoral scanner <NUM> with some of the components of the intra-oral scanner removed and depicting a lens assembly <NUM> and a drive assembly <NUM> operatively engaged with the lens assembly arranged inside a housing of the intra-oral scanner according to an embodiment. The lens assembly <NUM> is arranged inside a frame <NUM> of the scanner <NUM> and operatively coupled to a drive assembly <NUM> of the scanner <NUM> is shown. The drive assembly <NUM> is supported/mounted on the frame <NUM> by using suitable brackets. As shown in <FIG>, the lens assembly <NUM> is mounted on at least one rail such as a pair of rails <NUM>, <NUM> arranged inside the frame <NUM> and is adapted to move linearly back and forth between a first extreme position and a second extreme position along at least a part of respective lengths of the rails <NUM>, <NUM>. It may be appreciated that a translation axis (<NUM>, <FIG>) of the lens assembly <NUM> is substantially parallel to the optical axis <NUM>. The rails, for example, a first rail <NUM> and a second rail <NUM>, are arranged spaced apart from each other and are supported by a supporting mechanism within the frame <NUM>.

As best shown in <FIG>, the lens assembly <NUM> includes a lens housing <NUM> adapted to house and support the lens <NUM> and is movably arranged on the rails <NUM>, <NUM>. In an embodiment, the lens <NUM> is attached, e.g. adhesively coupled, to the lens housing <NUM> and is arranged such that the lens <NUM> is aligned to optical axis (<NUM>, <FIG>). The lens assembly <NUM> may include a magnetic encoder to determine a position of the lens assembly <NUM> relative to rails <NUM>, <NUM>, the determined position may be associated with a focal plane and used to generate 3D digital representation of dental object from the oral cavity. As shown, the lens housing <NUM> may include a ring structure <NUM> to house and support the lens <NUM>, and a pair of brackets, for example, a first bracket <NUM> and a second bracket <NUM>, attached to the ring structure <NUM> and slidably supported on the rails <NUM>, <NUM>. The first bracket <NUM> and the second bracket <NUM> are supported on the first rail <NUM> and the second rail <NUM> respectively, and extend from the ring structure <NUM> in a direction, such as radial direction. The brackets <NUM>, <NUM> may also be substantially parallel to a central longitudinal axis of the ring structure <NUM>. Moreover, a length of the two brackets may be equal or different with one bracket longer than the other, such as the first bracket <NUM> being greater than a length of the second bracket <NUM>. Each of the brackets <NUM>, <NUM> may include substantially semicircular cross-section when looking from a front of the lens housing <NUM>. The first bracket <NUM> includes a first longitudinal end (<NUM>, <FIG>) attached to the ring structure <NUM> and a second longitudinal end (<NUM>, <FIG>) arranged away from the ring structure <NUM> and defines a free end of the first bracket <NUM>. The second longitudinal end <NUM> is arranged proximate to the drive assembly <NUM> and may be operatively coupled to the drive assembly <NUM>. In an embodiment, the first bracket <NUM>, the second bracket <NUM>, and the ring structure <NUM>, may be constructed as one part.

Referring to <FIG>, the drive assembly <NUM> includes a drive <NUM>, for example, an electric motor, having a drive shaft <NUM> (i.e., shaft <NUM>) operatively engaged with the first bracket <NUM> (i.e., the lens housing <NUM>). The first bracket <NUM> is engaged with the drive <NUM> such that a rotation of the shaft <NUM> around its rotation axis <NUM> causes a translation movement of the lens housing <NUM> along the translation axis <NUM> disposed parallel to the optical axis <NUM> of the lens system <NUM>. In the illustrated embodiment, the rotation of the shaft <NUM> about the rotation axis <NUM> causes a back-and-forth movement of the lens housing <NUM> (i.e., the lens assembly <NUM>) between the first extreme position and the second extreme position.

As shown in <FIG>, a length of the shaft (<NUM>, <FIG>) is along the rotation axis <NUM> and coincides with a central longitudinal axis <NUM> of the shaft <NUM>. Further, the longitudinal axis (<NUM>, <FIG>) of the shaft <NUM> is parallel to the optical axis <NUM>. To operatively engage the lens housing <NUM> (i.e., the first bracket <NUM>) with the shaft <NUM>, the drive assembly <NUM> includes a guide <NUM> arranged or defined continuously along an outer circumferential surface of an end part <NUM> of the shaft <NUM>. In the illustrated embodiment, the end part <NUM> is a separate component and is removably attached, as attached for example by a pin-locking mechanism, at an end of the shaft <NUM> and is arranged coaxially to the shaft <NUM>. However, it may be appreciated that the end part <NUM> may be an integral portion of the shaft <NUM>, and the guide <NUM> is defined along an outer circumferential surface of the shaft <NUM>. The end part <NUM> is adapted to rotate along the shaft <NUM> around the rotational axis <NUM>.

As shown, the guide <NUM> is a groove <NUM> extending continuously along the outer circumferential surface of the end part <NUM>. As shown, the guide <NUM> is a female guide and defines a closed path on the outer circumferential surface of the end part <NUM>. As shown in <FIG>, <FIG>, and <FIG>, the groove <NUM> is defined along the outer circumference surface such that the closed path of the groove <NUM> is arranged at an angle that is greater than <NUM> degrees and less than <NUM> degrees relative to the rotation axis <NUM>. Accordingly, the closed path of the groove <NUM>, and hence the guide <NUM>, is non-parallel to a central longitudinal axis <NUM> of the end part <NUM>, and hence is non-parallel to the rotation axis <NUM>. Accordingly, the guide <NUM> is defined by the closed path such that a 2D projection of the closed path is non-parallel to the rotation axis <NUM>. In some embodiments, the groove <NUM> extends in an elliptical manner along the outer circumferential surface of the end part <NUM> such that a plane of the ellipse having both major axis and minor axis are at an angle relative to the rotation axis <NUM> and the central axis <NUM> of the end part <NUM>. Also, in some embodiments, the guide <NUM>, and hence the groove <NUM>, follows a path of a sinusoidal curve around the outer circumferential surface of the end part <NUM>. Accordingly, the guide <NUM>, and hence the groove <NUM>, extends continuously to form a closed sinusoidal curve around the circumferential surface of the shaft <NUM> or the end part <NUM> of the shaft <NUM>. In an embodiment, the groove <NUM> is V-shaped groove (as best shown in <FIG>).

It may be appreciated that distance of the linear movement of the lens housing <NUM> (i.e., lens assembly <NUM>) between the first extreme position and second extreme position corresponds to a length of the closed path of the guide <NUM> around the circumferential surface of the shaft (e.g. end part <NUM>) along which the coupling member travels from a start point to end point of the closed path. The distance of the linear movement of the lens housing <NUM> is lesser than half the length of the closed path guide <NUM> around the circumferential surface of the shaft (e.g. end part <NUM>). The distance of the linear movement of the lens housing <NUM> in one direction during the back-and-forth movement equals to an axial distance between the two most distant points on the guide that is located at the circumferential surface of the shaft. The axial distance may be defined along the rotational axis of the shaft.

Although the guide <NUM> is described as the closed path, it may be envisioned that guide may include an open path. In such a case, the lens housing <NUM> (i.e., the lens assembly <NUM>) is moved back and forth by rotating the shaft <NUM>, and hence the end part <NUM>, in both directions. For open path guide, this may be performed by configuring the motor to change rotational direction of the shaft to allow back and forth movement of the lens housing. Alternatively, for open path guide, this may be performed by having two motors, one motor configured to rotate the shaft in a first rotational direction and another motor configured to rotate the shaft in a second rotational direction opposite to the first rotational direction to allow back and forth movement of the lens housing.

Additionally, as shown in <FIG>, the scanner <NUM> includes a coupling element <NUM> as a male part for operatively engaging the end part <NUM> with the first bracket <NUM> (i.e., lens housing <NUM>). The coupling element <NUM> is adapted/arranged to move along the guide <NUM> in response to the rotation of the guide <NUM>, and hence the end part <NUM>, to enable the translation movement of the lens housing <NUM> along the translation axis <NUM>. As shown, the coupling element <NUM> is a spherical ball <NUM> arranged partially inside the guide <NUM> and partially inside a gap <NUM> defined by an attachment part <NUM> extending from the first bracket <NUM>, as best shown in <FIG>. As best shown in <FIG>, the attachment part <NUM> is arranged proximate to the second longitudinal end <NUM> of the first bracket <NUM> and extends radially outwardly/inwardly from an outer surface of the first bracket <NUM>. As best shown in <FIG>, the attachment part <NUM> is in the form a hollow portion extending inwardly from an outer surface of the first bracket <NUM> and defining a free space (i.e., the gap <NUM>) therebetween to receive a part of the coupling element <NUM>, thereby supporting the coupling element <NUM>. In some embodiments, the attachment part <NUM> may include a plurality of protrusions arrayed circularly and encircling a free space to define the gap <NUM> therebetween for receiving a part of the coupling element <NUM>. In such a case, the protrusions are arranged spaced apart from each other and extend outwardly from the outer surface of the first bracket <NUM>.

Also, the coupling element <NUM> exerts a force on the attachment part <NUM> as the coupling element <NUM> travels along the guide <NUM> to enable the translational movement of the lens assembly <NUM> (i.e., the lens housing <NUM>) along the translation axis <NUM> between the first extreme position and the second extreme position. Although the coupling element <NUM> is contemplated as the spherical ball <NUM>, it may be envisioned that that the coupling element <NUM> may be a cylindrical pin, or having any other geometrical shape that is designed to slidably engage with the guide. It may be appreciated that a height of the attachment part <NUM> and a width of the gap <NUM> are selected such that a portion of the coupling element <NUM> is arranged inside the gap <NUM>. Although the guide <NUM> is shown and contemplated as a female part and the coupling element <NUM> is shown and contemplated as a male part, it may be appreciated that the guide <NUM> may be a male part, for example a protruded structure, and a coupling element <NUM> may be a female part, for example, a slot in which the protruded structure extends. To enable smooth movement of the coupling element <NUM> along the path of the guide <NUM>, lubrication is provided at an interface between the coupling element <NUM> and the guide <NUM>.

To keep the coupling element <NUM> engaged with the guide <NUM> and to facilitate a smooth movement of the coupling element <NUM> along the path of the guide <NUM>, the lens assembly <NUM> includes a biasing member <NUM>, for example, a spring <NUM> (best shown in <FIG> and <FIG>). Referring to <FIG>, the spring <NUM> is configured to apply spring force to keep a part of the coupling element <NUM> engaged with the guide <NUM> (i.e., inside the groove <NUM>). Accordingly, the spring <NUM> facilitates in maintaining the engagement of the coupling element <NUM> with the guide <NUM> as coupling element <NUM> moves along the path defined by the guide <NUM>. As shown, the spring <NUM> is arranged inside the gap <NUM> defined by the attachment part <NUM> such that spring <NUM> is arranged between the outer surface of the first bracket <NUM> (i.e., the lens housing <NUM>) and the coupling element <NUM>, and exerts a biasing force towards the end part <NUM> (i.e., guide <NUM>) of the shaft <NUM> to retain the coupling element <NUM> engaged with the guide <NUM>. In an embodiment, an end of the spring <NUM> is fixedly attached with the first bracket <NUM>, and hence the lens housing <NUM>, and other end of the spring <NUM> is engaged with the coupling element <NUM>.

As shown, the coupling element <NUM> rests on the spring <NUM> and compresses the spring <NUM>. Accordingly, spring <NUM> exerts a force towards the guide <NUM> and the lens housing <NUM> (i.e., first bracket <NUM>) in an axial direction. Also, the spring <NUM> is configured to transfer a lateral force between the coupling element <NUM> and the lens housing <NUM> to enable the linear movement of lens housing <NUM> between the first extreme position and the second extreme position. Further, the spring <NUM> and the attachment part <NUM> are disposed such that a longitudinal axis <NUM> of the spring <NUM> and the optical axis <NUM> are arranged in different plane, and therefore, the longitudinal axis <NUM> and optical axis <NUM> are arranged separated from each other. Also, the spring <NUM> is arranged such that the longitudinal axis <NUM> of the spring is arranged orthogonal (i.e., normal) to the optical axis <NUM>. Also, the longitudinal axis <NUM> is substantially perpendicular to the rotation axis <NUM>. Also, the longitudinal axis <NUM> is substantially normal to the first rail <NUM>. It may be appreciated that a stiffness of the spring <NUM> is selected such that the connection between the coupling element <NUM> (i.e., ball <NUM>) and the guide <NUM> (i.e., groove <NUM>) is a backlash free connection.

Additionally, to mitigate vibrations, magnets are provided in the lens housing <NUM> in the immediate vicinity of the first and second rails <NUM>, <NUM>, which in an embodiment, are made of ferromagnetic material. For example, as best shown in <FIG>, a first magnet <NUM> is removably or permanently arranged inside the lens housing <NUM> and is disposed proximate to the first end <NUM> of the first bracket <NUM> and the first rail <NUM>, while a second magnet <NUM> is removably or permanently arranged inside the lens housing <NUM> and extends inside the second bracket <NUM> and proximate to the second rail <NUM>. Further, both the rails <NUM>, <NUM> are made of ferromagnetic material to enable a magnetic coupling of the magnets <NUM>, <NUM> with respective rails <NUM>, <NUM>. In some embodiments, to mitigate vibrations and to magnetically couple and support the lens housing <NUM> on the rails <NUM>, <NUM>, the magnetic flux density of the one or more of the magnets <NUM>, <NUM> is between <NUM> Tesla and <NUM> Tesla depending on the size and the weight of the lens assembly <NUM>.

In an embodiment, the first and second brackets <NUM>, <NUM> are arranged relative to the rails <NUM>, <NUM> so as to reduce contact area between the first and second brackets <NUM>, <NUM> and the associated rails <NUM>, <NUM>. In an embodiment, the first and second brackets <NUM>, <NUM> and the rails <NUM>, <NUM> are arranged relative to each other such that line contacts or point contacts exist between the first and second brackets <NUM>, <NUM> and the rails <NUM>, <NUM>. As shown in <FIG>, the lens housing <NUM> (i.e., the first bracket <NUM>) interfaces at two contact surfaces with the first rail <NUM>, while the lens housing <NUM> (i.e., the second bracket <NUM>) interfaces at one contact surface with the second rail <NUM>). Further, to reduce the friction between the lens housing <NUM> and the rails <NUM>, <NUM>, suitable lubrication is provided between the rails <NUM>, <NUM> and the brackets <NUM>, <NUM>.

A working of the scanner <NUM> to change a focal plane of the lens system <NUM> is now described. For moving focal plane of the lens <NUM> along the optical axis <NUM>, the lens assembly <NUM> is moved linearly and back and forth between the first extreme position and the second extreme position along the translation axis. In the first extreme position, the lens <NUM> is arranged proximate to the illumination module <NUM> relative to the second extreme position. For moving the lens assembly <NUM> (i.e., lens housing <NUM> along with the lens <NUM>), the drive <NUM> is powered, causing the rotation of the drive shaft <NUM> about its rotation axis. <NUM> In response to the rotation of the drive shaft <NUM>, the end part <NUM> also rotates about the rotation axis <NUM>. As the ball <NUM> (i.e., coupling element <NUM>) is arranged inside the groove <NUM> (i.e., the guide <NUM>), the ball <NUM> moves along the closed path defined by the groove <NUM> in response to the rotation of the end part <NUM>.

As the groove path is inclined relative to the rotation axis <NUM> and the path being a closed path, the ball <NUM> moves/translates in a first direction (i.e., forward direction) towards the drive <NUM> during one half of each rotation of the end part <NUM> about the rotation axis <NUM>, and moves/translates in a second direction (i.e., a rearward direction) away from the drive <NUM> during remaining half of the rotation of the end part <NUM>, or vice versa, where the first direction is away from the drive, and the second direction is towards the drive. Due to the back-and-forth motion of the ball <NUM> along the guide <NUM>, the ball <NUM> exerts a force on the attachment part <NUM>, and hence the lens housing <NUM>, causing the back-and-forth movement of the lens assembly <NUM> relative to the rails <NUM>, <NUM> along the translation axis <NUM>. Accordingly, the lens assembly <NUM> moves towards the one extreme position when the ball <NUM> moves in the first direction, and the lens assembly <NUM> moves towards another extreme position opposite to the one extreme position when the ball <NUM> moves in the second direction. In this manner, by moving the lens assembly <NUM> back and forth along the translation axis <NUM>, the focal plane of the lens system <NUM>, and hence the scanner <NUM> can be changed. This allows for acquiring a plurality of two-dimensional images of the dental object at different focal planes. It may be appreciated that the scanner <NUM> may be orientated at various orientation and the focal plane of the scanner <NUM> is changed by moving the lens assembly <NUM> at each orientation to take a stack of 2D images for each orientation. These 2D images are stitched together by applying known techniques such as Iterative Closest Point (ICP) to obtain three-dimensional digital representation of the dental object <NUM>.

Claim 1:
An intra-oral handheld 3D optical scanner (<NUM>) comprising:
an illumination module (<NUM>) configured to generate an illumination signal to illuminate a dental object (<NUM>);
an image sensor (<NUM>) configured to obtain data in response to the illumination of the dental object, the data being configured to be used to generate a 3D dental model of the dental object;
a lens housing (<NUM>) comprising an optical lens (<NUM>) that is configured to direct the illuminating signal towards the dental object;
a drive (<NUM>) comprising a shaft (<NUM>) that is configured to rotate around a rotation axis (<NUM>);
a guide (<NUM>) extending continuously along at least a part of a length of the shaft; characterised by
a spring (<NUM>), arranged intermediate between the lens housing and the guide, configured to exert a spring force towards the guide.