Compact intraoral 3d scanner and method of optimization thereof

Abstract

The present disclosure relates generally to compact intraoral 3D scanners. More specifically, the present disclosure relates to the field of meeting the conditions of compact intraoral 3D scanners, in particular to enable optimal performance of intraoral 3D scanning. The present disclosure also relates to a method of optimizing a compact intraoral 3D scanner.

Description

Technical Field

[0001] This disclosure generally relates to compact intraoral 3D scanners. More specifically, this disclosure relates to the field of satisfying the conditions for compact intraoral 3D scanners—particularly enabling intraoral 3D scanning to be optimally performed. This disclosure also relates to a method for optimizing compact intraoral 3D scanners. Background Technology

[0002] 3D scanning is a mature technology across various industrial sectors, with different 3D scanning techniques having been used for decades. Some 3D scanning techniques are related to triangulation, while others are related to confocal, focusing, or defocusing distance measurement.

[0003] Triangulation is based on observing a scene from one, two, or more different directions that are different from the direction of light projection.

[0004] Confocal scanning can be mechanical or color scanning. In mechanical confocal scanning, optical elements (such as lenses) are mechanically moved back and forth to scan the volume while the projected light is spatially filtered in the detector plane. In color confocal scanning, the volume is scanned by passing the illumination light through a high-chroma material and changing the scanning wavelength, while the projected light is spatially filtered in the detector plane.

[0005] In focus-range scanning, optical elements (such as lenses) are also moved back and forth to scan the volume, and depth is estimated based on focus measurements without spatial filtering. In defocus-range scanning, optical properties such as aperture change between the capture of two images, thereby estimating depth by determining the degree of defocus between the two images.

[0006] Both mechanical confocal scanning and autofocus rangefinding scanning have optical elements that move back and forth to scan a volume. Therefore, in this respect, they remind each other of one another, but autofocus rangefinding has many advantages over mechanical confocal scanning.

[0007] For example, because focusing rangefinders do not spatially filter light like mechanical confocal scanners, the luminous flux in focusing rangefinders is much higher than in mechanical confocal scanners. Therefore, low-power light sources such as light-emitting diodes (LEDs) can be used in focusing rangefinders instead of the high-power lasers typically used in mechanical confocal scanners. This means several additional advantages, including a generally simpler mechanical structure compared to mechanical confocal scanners, and the option to use LEDs to provide the same color images, thus eliminating the need for an additional light source. All of this also means that focusing rangefinders are generally smaller than mechanical confocal scanners. Furthermore, as mentioned above, focusing rangefinders are generally associated with lower manufacturing costs.

[0008] Some of these advantages and facts have been generally described in Zamofing et al.’s article “Applied multifocus 3D microscopy” (SPIE Vol. 5265-19, 2023). This paper compares different scanning techniques: focusing distance measurement (multifocus 3D microscopy), color confocal scanning (chromatic aberration), mechanical confocal scanning (confocal microscopy), and white light interferometry.

[0009] In the dental field, 3D scanning is also well-established, and scanners can be used either as 3D laboratory scanners for impression scanning or as 3D intraoral scanners for intraoral scanning. For at least the past forty years, the various scanning technologies described above have been applied and developed in the field of intraoral scanning.

[0010] 3D intraoral scanners are developed in various sizes, depending on many factors, including the scanning technology employed. The goal is to provide a compact and lightweight intraoral 3D scanner. First, a compact and lightweight scanner allows the operator to easily maneuver the intraoral 3D scanner during the scan. A lightweight and compact design is advantageous because it ensures the scanner can move smoothly throughout the oral cavity while acquiring information, and in some cases, there is no need to adjust the handle on the scanner. Second, a compact scanner provides patient comfort because the intraoral 3D scanner is inserted into the mouth. A compact scanner also ensures access to areas with limited space within the oral cavity. Most intraoral scanners today are relatively large, thus necessitating the provision of a compact intraoral scanner.

[0011] A compact 3D intraoral scanner is described in US2018 / 0192877.

[0012] Although US2018 / 0192877 describes a compact intraoral 3D scanner, it does not disclose how to provide an optimal intraoral 3D scanner.

[0013] Therefore, it is desirable to provide a compact and lightweight intraoral 3D scanner, and also to provide a method for optimizing a compact and lightweight intraoral 3D scanner. Summary of the Invention

[0014] This disclosure provides a compact intraoral 3D scanner.

[0015] This disclosure provides a compact intraoral 3D scanner, comprising:

[0016] - Detector, consisting of a horizontal sensor size H sensor limited,

[0017] Among them, Hsensor Less than 10mm, and

[0018] The detector consists of a pixel array, where each pixel has a width d. pixel limited;

[0019] Limited field of view H FOV One or more optical elements, the field of view being related to the sensor size, with the relationship H. FOV =mH sensor ,

[0020] Where m is the magnification greater than m = 1.5;

[0021] - A light source for emitting light defined at least by a dominant wavelength λ, thereby configuring the scanner to illuminate an object inside the mouth with light;

[0022] - A beam splitter that communicates optically with a light source, one or more optical elements, and a detector;

[0023] The one or more optical elements are optical focusing elements configured to move the focal plane of light at an intraoral object, the focal plane being defined by the object space numerical aperture NA of the one or more lenses. object limited,

[0024] Its features are:

[0025] ο pixel width d pixel Less than 10 micrometers; and

[0026] The intraoral 3D scanner satisfies the condition: 0.20 ≤ ξ ≤ 0.6, where:

[0027] ξ=(λ((1+1 / m)) / (md pixel NA obj ).

[0028] This disclosure also provides a method for optimizing an intraoral 3D scanner.

[0029] The method includes the following steps:

[0030] - Provides an optical system for an intraoral 3D scanner, the intraoral 3D scanner comprising:

[0031] The detector consists of a horizontal sensor of size H. sensor limited,

[0032] Among them, H sensor Less than 10mm, and

[0033] The detector consists of a pixel array, where each pixel has a width d. pixel limited;

[0034] The field of view H was limited. FOV One or more optical elements, field of view H FOV Related to sensor size, the relationship is H FOV =mH sensor Where m is a magnification greater than m = 1.5;

[0035] ο A light source for emitting light defined by at least the dominant wavelength λ, thereby enabling the intraoral 3D scanner to illuminate intraoral objects with light;

[0036] A beam splitter that communicates optically with the light source, the one or more optical elements, and the detector.

[0037] The one or more optical elements are configured such that when the movable lens is translated by a certain focal distance, the focal plane of the light at the object within the aperture is moved, and the focal plane is determined by the object space numerical aperture NA of the one or more lenses. object limited,

[0038] - Select the object space numerical aperture for the intraoral 3D scanner, which is related to the depth of field (DOF). object ), via NA obj 2 =λ / DOF object limited;

[0039] Its features

[0040] - By increasing the pixel width d of the imaging sensor pixel Select the following to optimize the compact intraoral 3D scanner: d pixel =λ(1+1 / m) / (mξNA) obj ), where ξ is 0.20≤ξ≤0.6, thus the pixel width d pixel Less than 10 micrometers.

[0041] To gain a more detailed understanding of the currently disclosed compact intraoral 3D scanner and the methods for optimizing the compact intraoral 3D scanner, the derivation of the equations and the insights of the inventors that led to the present invention are described.

[0042] Theories and insights that led to this invention

[0043] Horizontal magnification is calculated by dividing the image height by the object height.

[0044] m T =h image / h object (1)

[0045] Lateral magnification is also known as lateral magnification, linear magnification, or paraxial magnification.

[0046] In machine vision, the so-called principal magnification M is defined as...

[0047] M = H sensor / H FOV (2)

[0048] Among them, H sensor It refers to the horizontal sensor size, while H... FOV It is the horizontal field of view (FOV).

[0049] This corresponds to the lateral magnification through the following relationship:

[0050] M = |m T |。(3)

[0051] The reciprocal of the principal magnification is simply called the magnification m, therefore:

[0052] m = |1 / M|. (4)

[0053] Axial magnification m Z Also known as vertical magnification, its relationship with horizontal magnification is as follows:

[0054] m Z =n0 / n1 m T 2 (5)

[0055] Where n0 is the refractive index of air, and n1 is the refractive index of the lens. For optical systems, such as scanners, n0 is generally the refractive index of the object-side medium, while n1 is the refractive index of the object-side medium. An approximate value, or in special cases when n0 ≈ n1, is:

[0056] m Z ≈m T 2 (6)

[0057] In addition to lateral and horizontal magnification, there is also a magnification factor called angular magnification, m. A The following relationship exists between angular magnification and lateral magnification:

[0058] m T m A = n0 / n1. (7)

[0059] Furthermore, the following relationship exists between axial magnification and angular magnification:

[0060] m Z =n0 / n11 / m A 2 (8)

[0061] Therefore, we can conclude that:

[0062] m Z =m T / m A (9)

[0063] Therefore, when the axial magnification of an optical system increases, the lateral magnification also increases, and / or the angular magnification decreases.

[0064] Depth of field (DOF) is determined through the following relationship:

[0065] DOF object =n0λ / NA obj 2 (10)

[0066] The numerical aperture of the object space is defined as follows:

[0067] NA object =n0sinθ object (11)

[0068] Where, θ object It is the maximum half-angle of the light cone that can enter or leave the lens.

[0069] The image space values ​​are similarly limited as follows:

[0070] NA image =n0sinθ image ≈1 / (2N W (12)

[0071] Where, θ image The image is the maximum half-angle of the light cone that can enter or exit the lens, N. W It is the working focal ratio (f-number).

[0072] It can be seen that the magnification m can also be obtained with the following relationship:

[0073] m = NA image / NA object =1 / M (13)

[0074] Therefore, based on equations (10), (12) and (13), the depth of field can be approximated as:

[0075] DOF object =n0λ / NA obj 2 ≈4n0λN W 2 1 / m 2 (14)

[0076] As an approximation, the working focal ratio can be approximated as:

[0077] Nw ≈(1-m T )N=(1+1 / m 1 / P)N, (15)

[0078] Where m T The value is negative, and P is the pupil magnification, which is the ratio of the exit pupil diameter to the entrance pupil diameter, i.e., d. Enp / d Enp .

[0079] Therefore, the working focal ratio can be written as:

[0080] N w =β(1+1 / m)N, (16)

[0081] Where β is a constant, it depends on the pupil magnification P and the magnification m. The constant β is written as β = (1 + 1 / m + 1 / P) / (1 + 1 / m). For symmetrical and telecentric lenses, when P = 1, it decreases to β = 1. For asymmetrical and non-telecentric lenses, β ≠ 1. Therefore, β is a constant that depends on the degree of non-telecentricity.

[0082] Depth of field, DOF object Depth of focus (DOF) image (Related by magnification)

[0083] DOF object =1 / m 2 DOF image =M 2 DOF image . (17)

[0085] This stems directly from the limitations imposed by magnification and depth of field. Therefore, for a given depth of field and a large magnification m, the corresponding depth of focus will decrease.

[0086] The depth of focus is known to be related to the so-called acceptable circle of blur (CoC) diameter d. CoC Related, d CoC It is a constant that depends on the application and visual perception or contrast.

[0087] Depth of focus is limited according to CoC as follows:

[0088] DOF image =2d CoC N (18)

[0089] In digital imaging using image sensors, d CoC It is usually set to be equal to the pixel size, i.e., d CoC =d pixel However, this is a rather strict standard, and a more lenient standard is defined as where the tolerable blur circle is set to two pixels, i.e., d.CoC =2d pixel .

[0090] With this in mind, the depth of focus can therefore be written as:

[0091] DOF image =2αd pixel N, (19)

[0092] Where α=d CoC / d pixel α is a constant that depends on the sampling level. In typical vision systems, α is set between 1 and 2. As mentioned above, this depends on the application. Depending on the constraints, α also depends on how the tolerable blur circle is defined; therefore, α is not a well-defined constant.

[0093] According to equations (14) and (16), the depth of field can be approximated as:

[0094] DOF image ≈4n0λ(β(1+1 / m)N) 2 1 / m 2 (20)

[0095] From equations (19) and (20), we can obtain the following equation:

[0096] 2n0λ(β(1+1 / m)N) 2 =αd pixel N (21)

[0097] Therefore, by setting n0 = 1 (in the case of air), the focal ratio can be obtained as follows:

[0098] N=αd pixel / (2λ(β 2 (1+1 / m) 2 ) (twenty two)

[0099] Using equations (19) and (22), the depth of field is found to be:

[0100] DOF image =α 2 d pixel 2 / (2λ(β 2 (1+1 / m) 2 ) (twenty three)

[0101] Therefore, the depth of focus can be found to be:

[0102] DOF object =m 2 α 2 / β 2 d pixel2 / (2λ((1+1 / m) 2 ) = m 2 ξ 2 d pixel 2 / (2λ((1+1 / m) 2 ),(twenty four)

[0103] Where ξ = α / β is a constant, similar to α and β, and is defined in this disclosure. According to the definition, ξ depends on the sampling degree and the degree of non-centroidalization. According to the definition, ξ is:

[0104] ξ=α / β=d CoC (1+1 / m) / ((1+1 / m 1 / P)d pixel (25)

[0105] Since α is between 1 and 2 for typical well-sampled systems, and β = 1 for telecentric systems, ξ is typically between 1 and 2. For intraoral 3D scanners, the optimal value of ξ is not obvious, especially since the acceptable circle of blur is not explicitly defined and also depends on the application. However, from equation (24), we can then derive:

[0106] ξ=DOF object 1 / 2 (λ 1 / 2 ((1+1 / m)) / (md pixel (26)

[0107] Or simply:

[0108] ξ=λ((1+1 / m)) / (md pixel NA obj (27)

[0109] The inventors of this disclosure have discovered that, for several optimized intraoral 3D scanners designed, all 3D scanners include an optical focusing element for moving the focal plane of light at the intraoral object, ξ being approximately ξ = 0.4.

[0110] However, it is found that variations are also acceptable, for example, such that ξ varies from 0.2 to 0.6, more preferably, such that ξ varies from 0.30 to 0.55, even more preferably, such that ξ varies from 0.30 to 0.50, and even more preferably, such that the range of variation of ξ is 0.3 to 0.45.

[0111] As mentioned above, ξ depends on the application and is limited to the degree of sampling and non-telecentricity. In effect, ξ defines the optimal resolution. Therefore, if ξ is too small, the signal-to-noise ratio becomes too small for accurate depth estimation, while if ξ is too large, the resolution becomes too inaccurate to provide a correct depth estimate. The optimal condition for intraoral 3D scanning is not readily apparent.

[0112] As described herein, the inventors of this disclosure have discovered that an optimal intraoral 3D scanner is provided when the optical design is optimized in such a way that it includes an optical focusing element configured to move the focal plane, i.e., such that 0.20≤ξ≤0.6, more preferably such that 0.30≤ξ≤0.55, even more preferably such that 0.30≤ξ≤0.50, and most preferably such that 0.3≤ξ≤0.45.

[0113] Therefore, this specific range defines how various optical parameters must be set to provide an optimal intraoral 3D scanner. Furthermore, this range of ξ reflects how the blur circle is defined for an optimized intraoral 3D scanner. The specific range of ξ defines whether an optical intraoral 3D scanner has been achieved.

[0114] Examples of the present invention

[0115] For example, the inventors designed a compact intraoral 3D scanner with the following sensor parameters:

[0116] -H sensor =7.86mm;

[0117] -d pixel =7.8μm;

[0118] When designing a compact intraoral 3D scanner, it is desirable to have a field of view suitable for intraoral 3D scanning, which means the field of view should be around 15-20 mm. With this FOV, scanning becomes easier and stitching errors are minimized. It is determined that a FOV very close to 20 mm is desirable, which then limits the magnification to:

[0119] -m=2.46

[0120] Furthermore, it is desirable for the intraoral scanner to operate using multicolor light, therefore the dominant wavelength is set as follows:

[0121] -λ=530nm=0.53μm.

[0122] When designing a compact intraoral 3D scanner, the final optimized design is based on NA. obj =0.109 ends, providing a depth of field of 44μm (DOF). image ).

[0123] By inserting these numbers into equation (27), we find that the value of ξ is ξ = 0.35. This verifies that the intraoral 3D scanner designed according to this disclosure is optimally designed for intraoral 3D scanning.

[0124] Using a dominant wavelength below 0.53 μm obviously requires changing ξ to a lower value, and it was found that a lower value less than ξ = 0.35 was optimal for intraoral 3D scanning.

[0125] The example above shows that once the four parameters m, λ, and d are established... pixel NA obj Then it can be verified whether the optical design has been optimized for intraoral 3D scanning, thus being optimized according to the present invention.

[0126] The magnification factor can be determined by measuring the relationship between the sensor size and the field of view. Wavelength, pixel size, and numerical aperture can also be measured. All four parameters can then be found directly from optical design programs such as Zemax, OSLO, or CodeV.

[0127] If only four parameters m, λ, and d are established pixel NA obj Of the three parameters, the fourth parameter can be optimized according to the present invention by requiring ξ to be between 0.2 and 0.6.

[0128] This disclosure provides a method for precisely selecting d by requiring ξ to be between 0.2 and 0.6. pixel Methods to optimize optical design.

[0129] If the design cannot be optimized, then at least one fourth parameter must be optimized for intraoral 3D scanning.

[0130] As an example of the latter, attention can be paid to the design disclosed in US2018 / 0192877. In that disclosure, Figure 4A shows a compact intraoral 3D scanner. The illustration shows a horizontal FOV of 18 mm. The beam splitter is illustrated and shown as 10 mm, from which it can be inferred that the sensor (which is approximately half the size of the beam splitter) has a horizontal dimension of approximately 5 mm. From this, it can be inferred that the magnification m is approximately m ≈ 3.6.

[0131] US2018 / 0192877 does not disclose any optical system NA. object Or pixel size, and therefore, these parameters are not disclosed for the system shown in Figure 4A of US2018 / 0192877.

[0132] However, US2018 / 0192877 discloses that the scanner is a confocal scanner, and that the size of the pinhole can be configured to suit the numerical aperture of the optical system and the wavelength of the light source. No further details are provided.

[0133] In confocal scanning, a pinhole is required, but the optimal pinhole is known to be determined by the following relationship:

[0134] d pinhole =0.5M obj λ / NA object (28)

[0135] Where, M obj It refers to the magnification of the microscope objective lens.

[0136] Magnification M of the microscope objective lens obj This is the reciprocal of the magnification m disclosed in this paper. Furthermore, in confocal scanners, it is well known that the pinhole size needs to be proportional to the pixel size d. pixel A match. Therefore, for confocal scanners, such as those disclosed in US2018 / 0192877, the optimal numerical aperture must be determined to be:

[0137] NA object,confocal =(0.5 1 / 3.6λ) / d pixel =0.139λ / d pixel (29)

[0138] This is also evident from the generally accepted fact that in confocal microscopy, resolution (i.e., the distance between two resolvable points) is given by the following formula:

[0139] r confocal =0.8λ / NA object,confocal。 (30)

[0140] Furthermore, in well-sampled confocal scanners, the optimal pixel size for sampling the image is at least half the spatial resolution; this is known as the Nyquist sampling theorem. Therefore, in confocal scanners:

[0141] d pixel =r confocal / 2=0.4λ / NA object,confocal =0.4λ / NA object,confocal (31)

[0142] Considering the magnification m, the following results can be obtained for a confocal scanner:

[0143] d pixel =0.4λM / NA object,confocal =0.4λ / (m NA) object,confocal (32)

[0144] This allows for the matching of the confocal pinhole, as described in equation (28). Therefore, the numerical aperture of the confocal scanner is:

[0145] NA object,confocal =0.4λm / d pixel (33)

[0146] When m = 0.36, the following relationship is obtained:

[0147] NA object,confocal =0.111λ / d pixel (34)

[0148] It is very close to the optimal numerical aperture given in equation (29).

[0149] It is worth noting that for non-confocal scanners, the known resolution is r non-confocaI =1.22λ / NA object Therefore, it gives:

[0150] NA object,non-confoca =0.66λ / (md) pixel (35)

[0151] The above only shows that, with the same numerical aperture, the resolution of a confocal scanner is √2 times higher than that of a non-confocal scanner. The coefficient √2 is directly derived from the derivation of the resolution of the confocal scanner and clearly demonstrates the advantage of the confocal scanner, namely, its more accurate resolution.

[0152] Based on the above understanding, it can be determined that the numerical aperture of the confocal scanner with m=3.6 disclosed in US2018 / 0192877 is usually set according to equation (29), therefore NA object,confocal =0.139λ / d pixel .

[0153] This numerical aperture can be compared with the optimal numerical aperture defined by the currently disclosed compact intraoral 3D scanner. To compare the numerical apertures of the two different scanners, m is also set to m = 3.6, thus the optimal numerical aperture of the currently disclosed compact intraoral 3D scanner can be determined from equation (27):

[0154] NA object,intraoral 3D-scanner =0.355λ / (d picel ξ). (36)

[0155] According to this disclosure, the optimal and minimum optimal numerical apertures are when ξ = 0.6, therefore, at this time...

[0156] NAobject,intraoral 3D-scanner =0.59λ / d pixel (37)

[0157] By comparing equation (37) with the optimal numerical aperture of a confocal compact scanner as disclosed in US2018 / 0192877 and described relative to Figure 4A, i.e. with the well-known equation (29) when m = 3.6 (where NA is NA), object,confocal =0.139λ / d pixel By comparison, it can be seen that the optimal object space numerical aperture of the confocal scanner is displayed as a coefficient, which is 1 / 4 of the minimum optimal numerical aperture of the currently disclosed compact intraoral 3D scanner.

[0158] Even comparing equation (27) with the optimal numerical aperture for a non-confocal scanner—which is defined by the well-known equation (35) at m = 3.6—is NA. object,non-confocal =0.183λ / d pixel The object space numerical aperture of this typical non-confocal scanner is a coefficient that is greater than 1 / 3 of the numerical aperture of currently disclosed compact intraoral 3D scanners.

[0159] As stated above, for a normal imaging system, as mentioned at the beginning, ξ is typically between 1 and 2, while according to this disclosure, for an intraoral 3D scanner, the optimal ξ is between ξ = 0.2 and ξ = 0.6. Therefore, there exists at least a coefficient of 1 / 0.6 = 1.66 between ξ for a normal imaging system and ξ for an intraoral 3D scanner, and this coefficient can be as high as 2 / 0.2 = 10.

[0160] In summary, the above content demonstrates how to optimize an intraoral 3D scanner and how to verify whether the optical design is optimal.

[0161] The above also shows that the optimal numerical aperture of a compact intraoral 3D scanner is very different from that of both non-confocal and confocal scanners known in the art. Attached Figure Description

[0162] The above and / or additional objects, features, and advantages of this disclosure will be further described in the following illustrative and non-limiting detailed description of embodiments of this disclosure with reference to one or more accompanying drawings, wherein:

[0163] Figure 1 An example of a compact intraoral 3D scanner according to this disclosure is shown. Detailed Implementation

[0164] Preferred embodiment of ξ

[0165] As described in the section “Theory and Insights Leading to the Invention”, a preferred embodiment was obtained for 0.30 ≤ ξ ≤ 0.55. This range was found to be generally optimal for light with dominant wavelengths in the mid-visible domain.

[0166] As mentioned above, a more preferred embodiment is obtained for 0.30 ≤ ξ ≤ 0.50. It was found that this range is optimized primarily by limiting the depth of field, thereby making the depth determination more optimized.

[0167] As mentioned at the end, the optimal embodiment was obtained for 0.30≤ξ≤0.45. It was found that this range was mainly optimized by limiting the depth of field, thereby determining the optimal depth.

[0168] Because the value of ξ is directly related to the depth of field (DOF), it can also provide the corresponding DOF.

[0169] However, in the most preferred embodiment of this disclosure, the depth of field (DOF) is in the range of 10 micrometers to 100 micrometers, more preferably between 20 micrometers and 90 micrometers, and most preferably around 35 micrometers to 55 micrometers.

[0170] Regarding the value of ξ, a small DOF has the advantage of more accurately determining the correct focal plane, which is crucial for accurate point cloud calculations. DOFs smaller than 10 micrometers are typically used for microscopy, but this is unnecessary for intraoral scanning. Furthermore, DOFs smaller than 10 micrometers may be impractical because they may be too small compared to the resolution of devices constructed to move the focal plane of light (e.g., motors with lens encoders for moving or translating optical focusing elements). On the other hand, if the DOF is too large, accuracy is severely compromised. The inventors of this disclosure have found that the aforementioned DOF range is optimal for intraoral scanning of the scanners disclosed herein.

[0171] Magnification factor

[0172] In one embodiment of the invention, the magnification factor is greater than 2.0 and less than 2.9. This provides a relatively small sensor size compared to the field of view.

[0173] In another embodiment of the invention, the magnification factor is greater than 2.3 and less than 2.5. This provides a relatively small sensor size compared to the field of view and is optimal in terms of light collection.

[0174] One or more optical elements and optical focusing elements

[0175] In one embodiment of this disclosure, the intraoral scanner is configured such that the focal plane is shifted by 10-20 mm, preferably 12-18 mm, and more preferably about 15 mm. This focal plane shift is optimal for scanning teeth with a size of about 10 mm.

[0176] In one embodiment of this disclosure, the focal plane is moved by configuring an optical focusing element to translate the focusing distance. For example, the optical focusing element may be an optical lens element that translates the focusing distance on a translation stage.

[0177] In a preferred embodiment, the focusing distance is less than 5mm. For example, the focusing distance could be 4mm, or 3mm, or even 2mm or 1mm.

[0178] In the most preferred embodiment of this disclosure, the intraoral scanner is configured such that the focus-gearing ratio, which is the ratio between the focal plane shift and the focusing distance, is greater than 2, more preferably greater than 3, and most preferably greater than 4, for example, about 5. A high focus-gearing ratio of about 5 provides a very compact scanner. For example, if the focus shift is about 15 mm and the focus-gearing ratio is about 5, the focusing distance is about 3 mm. This means that the optical focusing element only needs to be translated by 3 mm.

[0179] In a more preferred embodiment of the invention, the optical focusing element is an optical lens weighing less than 5 grams. When the optical lens weighs less than 5 grams, the scanner can scan quickly, i.e., move back and forth, and this low weight provides a solution for optimal scanning speed.

[0180] In a more preferred embodiment, the optical lens is a single unit. This provides a simple and easy way to manufacture a compact intraoral scanner.

[0181] In the most preferred embodiment, the optical focusing element is translated back and forth by a translation stage at a scanning frequency, wherein the translation stage is configured to scan at a scanning frequency of approximately 20 or more scans per second, preferably, for example, 22 scans per second, or preferably, for example, 23 scans per second, preferably, for example, 24 scans per second, or more preferably, for example, 25 scans per second. In other words, the translation stage can be configured to scan at a frequency between 10 Hz and 12.5 Hz. One solution to achieve scanning frequencies between 10 and 12.5 Hz is to provide an optical focusing element in the form of an optical lens with a mass of less than 5 grams, and / or to provide a focus lever ratio such that it is approximately 5. By employing both an optical lens with a mass of less than 5 grams and a focus lever ratio of approximately 5, a technical solution is provided in which a short focusing distance and low mass simultaneously contribute to achieving a scanning frequency between 10 Hz and 12.5 Hz.

[0182] In one embodiment of this disclosure, one or more optical elements are at least three lens groups: a first lens group close to the beam splitter, a second lens group away from the beam splitter, and a third lens group located between the first and second lens groups, such that the optical focusing element is part of the first lens group.

[0183] In another embodiment of this disclosure, each lens group comprises only spherical lenses. Such embodiments can provide a low-cost system because spherical lenses are easier to manufacture than, for example, aspherical lenses.

[0184] In yet another embodiment, the lens group comprises only a single lens or a double lens. Such embodiments can also provide a low-cost system because single or double lenses are easier to manufacture than, for example, triple lenses.

[0185] In related embodiments, both the second lens group and the third lens group include a dual-body lens.

[0186] Detector and beam splitter

[0187] According to this disclosure, intraoral 3D scanning using an optical focusing element configured to move the focal plane of light at an intraoral object is typically performed using a handheld intraoral 3D scanner.

[0188] Therefore, in most embodiments, the compact intraoral 3D scanner disclosed herein is handheld.

[0189] In handheld intraoral 3D scanning, short data acquisition time is usually a prerequisite for eliminating relative motion between the teeth and the handheld device.

[0190] Furthermore, during 3D scanning, as mentioned in this disclosure, this means that the optical focusing element moves the focal plane of light at the object within the aperture. During this focal plane movement, the scanner records a so-called sub-scan. As previously stated, the shift of the focal plane can be provided by translating a lens element, such as a focusing lens, by a focusing distance. Therefore, when the focusing lens is translated, for example, by a focusing distance of 15 mm, a complete sub-scan can be recorded.

[0191] In a preferred embodiment, it may be desirable to record sub-scans in less than 1 / 10 of a second, more preferably about 1 / 15 of a second, or most preferably about 1 / 20 of a second. In such a preferred embodiment, the detector or image sensor can be configured to acquire images very rapidly and continuously.

[0192] Focal plane shifting can provide multiple focal planes during intraoral 3D scanning. A complete subscan can, for example, include approximately 200 focal planes, such as no more than 200 focal planes, or fewer than 100 focal planes, such as fewer than 50 focal planes.

[0193] If an embodiment with 200 focal planes is required, a 15mm translation of the focusing lens is used, which corresponds to a depth resolution of 15mm / 200mm = 75 micrometers. Therefore, in such an embodiment, the detector or image sensor can be configured to have a frame rate of 15 × 200fps = 3000fps.

[0194] In other embodiments, the detector is configured to have a frame rate of approximately 3000 fps, while in a preferred embodiment, the detector is configured to have a frame rate greater than 3000 fps, such as 6000 fps or even higher, such as 12000 fps.

[0195] In an alternative embodiment, where lower depth resolution may be feasible, the detector is configured to have a frame rate of less than 3000 fps, for example, about 2000 fps, more preferably about 1000 fps.

[0196] In very specific embodiments, the frame rate may be less than 100 fps, for example, about 30 fps.

[0197] In a preferred embodiment, the detector may be a CCD sensor configured with a frame rate suitable for intraoral 3D scanning purposes. Typically, CCD sensors cannot achieve very high frame rates, such as approximately 3000 fps or higher. Therefore, in the most preferred embodiment, the detector is a CMOS sensor. CMOS sensors are advantageous over CCD sensors because they include a global shutter.

[0198] According to this disclosure, the detector has a horizontal sensor size H of less than 10 mm. sensor Therefore, in some embodiments, the horizontal sensor size H sensor It can be 7.86 mm. In related embodiments, the vertical sensor size can be 6.74 mm. In other words, the effective area of ​​the sensor can be 7.86 mm × 6.74 mm. For example, in one instance, the sensor measures less than 15 mm along the diagonal.

[0199] Furthermore, according to this disclosure, the pixel width d pixel Less than 10 micrometers. Therefore, in some embodiments, the pixel width d pixel It can be 7.8 micrometers.

[0200] In some embodiments, the size H of the horizontal sensor sensor It is 7.86mm, and the pixel width d picel It can reach 7.8 micrometers. This configuration provides a compact scanner.

[0201] As described with respect to this disclosure, a smaller sensor or detector affects the overall optical system compared to a larger sensor. For example, as mentioned above, the lateral magnification of an optical system depends on the field of view and the sensor size. Therefore, if it is desired that the field of view is constant for an optical system with a large sensor and an optical system with a smaller sensor, the smaller sensor will increase the lateral magnification.

[0202] It has a small sensor (i.e., in this example, the horizontal sensor size H) sensor Sensors smaller than 10 mm with high frame rates (e.g., approximately 3000 frames per second or higher) were previously impossible because such sensors only emerged recently. This has only recently become possible with the development of small, high-speed sensors. Therefore, this disclosure provides a solution for designing and optimizing an intraoral scanner that precisely combines a small sensor size with a high frame rate.

[0203] High lateral magnification further alters the image spatial numerical aperture, i.e., if the object numerical aperture remains constant. Therefore, an intraoral scanner with a small sensor according to this disclosure also affects the ray angle on the sensor compared to an intraoral scanner designed with a larger sensor size. For a smaller sensor, the ray angle will only become larger.

[0204] Light with large incident angles may pose a challenge to the quantum efficiency of coatings and sensors.

[0205] In one embodiment, the beam splitter has a high refractive index, for example greater than 1.6, more preferably greater than 1.8, and most preferably about 1.84666, particularly at a wavelength of 587.5618 nm. Due to such a high refractive index, the incident light within the beam splitter (e.g., a beam splitter cube) is reduced. Therefore, this embodiment provides a solution to the aforementioned challenges. In particular, the high refractive index described herein has the effect of reducing the angle of light reaching the sensor. This also results in a smaller scanner, i.e., because the distance from the beam splitter to the sensor becomes smaller. The reduction in the wide range of light angles within the cube, as provided by the described refractive index, may also benefit the effect of the optical coating on the beam splitter, i.e., because the coating will be able to accept more light. In one embodiment, the beam splitter is coated, for example, with a polarizing coating. In a preferred embodiment, the beam splitter has both the high refractive index described above and the coating described above.

[0206] Solutions (one or more) for beam splitters with high refractive indices as described above provide the use of a horizontal sensor size H. sensor Solutions for small sensors (one or more) less than 10mm, which can ensure accurate detection.

[0207] light source

[0208] In one embodiment of the invention, the scanner further includes an illumination pattern located between the light source and the beam splitter, whereby the illumination pattern is projected as an image onto the object.

[0209] In another embodiment of the invention, the intraoral scanner further includes a lens module located between the light source and the beam splitter, wherein the lens module includes two lenses arranged along the optical axis of the intraoral scanner.

[0210] In a preferred embodiment of the present invention, the light source is an LED module.

[0211] Example 1 – Preferred embodiment of a compact intraoral 3D scanner

[0212] Figure 1 A preferred embodiment of the compact intraoral 3D scanner 1 according to the present disclosure is shown.

[0213] In such Figure 1 In the preferred embodiment shown, detector 2 is measured diagonally to be less than 15 mm. The effective area of ​​the detector is specifically measured to be 7.86 mm × 6.74 mm.

[0214] Beam splitter 3 guides light from an object (not shown) into detector 2. Furthermore, beam splitter 3, as a beam splitter cube, also guides light from light source 4 (not shown) onto the object.

[0215] In the preferred embodiment shown here, the object-side numerical aperture is NA. object =0.10.

[0216] Furthermore, in the preferred embodiment shown here, the light emitted from the light source 4 of the scanner 1 is in the visible field, and the center or dominant wavelength is approximately 500 and 550 nm, for example, approximately λ = 530 nanometers = 0.53 micrometers.

[0217] Figure 1 An optical element 5 is also shown, which is an optical focusing element 6 configured to move the focal plane of light at the object inside the mouth.

[0218] The scanner comprises a total of three optical elements 5. In this embodiment, four of the optical elements are lens elements.

[0219] The focal plane consists of the object space numerical aperture NA of three optical elements 5. object limited.

[0220] Therefore, NA can be found from equation (7). object =0.1 corresponding DOF object And thus:

[0221] DOFobject =0.53 / 0.1 2 = 53 micrometers.

[0222] In the embodiment shown here, the optical axis along the optical element is bent by a reflective surface 7, such as a mirror. This allows light to enter the oral cavity and be directed toward objects inside the cavity, such as teeth and gums.

[0223] This ensures that a correct 3D model of an object inside the mouth can be obtained. However, other designs for intraoral scanners, such as those without reflectors, are also feasible.

[0224] In this embodiment, no object (one or more) is shown, but the focal plane 8 provided by this scanner is curved.

[0225] According to currently disclosed scanners, the optical focusing element 6 is configured to direct the focal plane 8 of light at the point where an object within the mouth moves. For example... Figure 1 As shown, the optical focusing element is configured to translate back and forth between two vertical lines 9 and 10. The front glass element 11 is located in front of the reflecting surface 7. Since the focal plane is defined by the object space numerical aperture, this object space numerical aperture varies with the position of the optical focusing element.

[0226] It should be noted that the intraoral 3D scanner satisfies the condition 0.20≤ξ≤0.6, where:

[0227] ξ=(λ((1+1 / m)) / (md pixel NA obj ).

[0228] Therefore, this also means that ξ must satisfy the conditions of all focal planes. Thus, it is difficult to obtain a single value for ξ, and the aforementioned range reflects this variation.

[0229] Further details of this disclosure are provided by the following projects.

[0230] project:

[0231] 1. A compact intraoral 3D scanner, comprising:

[0232] - Detector, consisting of a horizontal sensor size H sensor limited,

[0233] Among them, H sensor Less than 10mm, and

[0234] The detector consists of a pixel array, where each pixel has a width d. pixel limited;

[0235] Limited field of view H FOVOne or more optical elements, the field of view being related to the sensor size, with the relationship H. FOV =mH sensor ,

[0236] Where m is the magnification greater than m = 1.5;

[0237] - A light source for emitting light defined at least by a dominant wavelength λ, thereby configuring the scanner to illuminate an object inside the mouth with light;

[0238] - A beam splitter that communicates optically with a light source, one or more optical elements, and a detector;

[0239] The one or more optical elements are optical focusing elements configured to focus the light at a moving object within the mouth, the focal plane being defined by the object space numerical aperture NA of the one or more optical elements. object limited,

[0240] Its features are:

[0241] ο pixel width d pixel Less than 10 micrometers; and

[0242] The intraoral 3D scanner satisfies the condition 0.20≤ξ≤0.6, where:

[0243] ξ=(λ((1+1 / m)) / (md pixel NA obj ).

[0244] 2. Based on the intraoral 3D scanner of Project 1, where 0.30≤ξ≤0.55.

[0245] 3. Based on the intraoral 3D scanner of Project 1, where 0.30≤ξ≤0.50.

[0246] 4. Based on the intraoral 3D scanner of Project 1, where 0.30 ≤ ξ ≤0.45.

[0247] 5. Based on the intraoral 3D scanner of Project 1, the magnification factor is greater than 2.0 and less than 3.0.

[0248] 6. Based on the intraoral 3D scanner of Project 1, the magnification factor is greater than 2.3 and less than 2.9.

[0249] 7. The intraoral 3D scanner according to Project 1, wherein the intraoral scanner is configured such that the focal plane is shifted by 10-20 mm, preferably by 12-18 mm, and more preferably by about 15 mm.

[0250] 8. The intraoral 3D scanner according to Project 7, wherein the focal plane is moved by configuring the optical focusing element to translate the focusing distance, wherein the focusing distance is less than 5 mm, for example about 4 mm, for example about 3 mm, for example about 2 mm or for example about 1 mm.

[0251] 9. An intraoral 3D scanner according to Projects 7 and 8, wherein the intraoral scanner is configured to have a focusing lever ratio greater than 2, more preferably greater than 3, most preferably greater than 4, for example, about 5, which is the ratio between focal plane displacement and focusing distance.

[0252] 10. An intraoral scanner according to any of the aforementioned projects, wherein the optical focusing element is an optical lens with a mass of less than 5 grams.

[0253] 11. An intraoral scanner based on any of the aforementioned projects, wherein the optical focusing element is a single unit.

[0254] 12. An intraoral scanner according to any of the preceding items, wherein the optical focusing element is configured to translate back and forth via a translation stage at a scanning frequency, wherein the translation stage is configured to scan at a scanning frequency between 10 Hz and 12.5 Hz.

[0255] 13. An intraoral scanner according to any of the foregoing items, wherein the one or more optical elements are at least three lens groups: a first lens group close to the beam splitter, a second lens group away from the beam splitter, and a third lens group located between the first and second lens groups, such that the optical focusing element is part of the first lens group.

[0256] 14. The intraoral scanner according to item 13, wherein each of the lens groups comprises only a spherical lens.

[0257] 15. An intraoral scanner according to any of items 13-14, wherein each of the lens groups comprises only a single or dual lens.

[0258] 16. An intraoral scanner according to any of items 13-15, wherein the second lens group and the third lens group each include a dual body.

[0259] 17. An intraoral scanner according to any of the preceding projects, wherein the scanner further includes an illumination pattern located between a light source and a beam splitter, whereby the illumination pattern is projected as an image onto an object.

[0260] 18. An intraoral scanner according to any of the foregoing projects, wherein the intraoral scanner further includes a lens module located between the light source and the beam splitter, wherein the lens module includes two lenses arranged along the optical axis of the intraoral scanner.

[0261] 19. An intraoral scanner based on any of the aforementioned projects, wherein the light source is an LED module.

[0262] 20. A method for optimizing a compact intraoral 3D scanner, comprising the following steps:

[0263] - Provides an optical system for the intraoral 3D scanner, the intraoral 3D scanner comprising:

[0264] The detector consists of a horizontal sensor of size H. sensor limited,

[0265] Among them, H sensor Less than 10mm, and

[0266] The detector consists of a pixel array, where each pixel has a width d. pixel limited;

[0267] οLimited Field of View H FOV One or more optical elements, field of view H FOV Related to sensor size, the relationship is H FOV =mH sensor , where m is the magnification greater than m = 1.5;

[0268] ο A light source for emitting light defined by at least the dominant wavelength λ, thereby enabling the intraoral 3D scanner to illuminate intraoral objects with light;

[0269] a beam splitter that communicates optically with the light source, one or more optical elements, and the detector.

[0270] The one or more optical elements are configured to be the focal plane of light at the point of moving an object within the mouth, the focal plane being defined by the object space numerical aperture (NA) of the one or more optical elements. object limited,

[0271] - Select the object space numerical aperture for the intraoral 3D scanner, which is related to the depth of field (DOF). object ) via NA obj 2 =λ / DOF object limited;

[0272] Its features

[0273] - By increasing the pixel width d of the imaging sensor pixel Select the following to optimize the compact intraoral 3D scanner: d pixel =λ((1+1 / m)) / (mξNA) obj ), where ξ is 0.20≤ξ≤0.6, thus making the pixel width d pixel Less than 10 micrometers.

[0274] 21. Based on the method in Project 20, where depth of field and DOF are... object It was selected to be around XY.

[0275] 22. According to the method of any item in Projects 20-21, where 0.30≤ξ≤0.55.

[0276] 23. According to the method of any item in Items 20-22, where 0.30≤ξ≤0.50.

[0277] 24. According to the method of any item in items 20-23, where 0.30≤ξ≤0.45.

[0278] 25. According to the method of any of the items in Items 20-24, where the magnification factor is greater than 2.0 and less than 3.0.

[0279] 26. According to the method of any of the items in Items 20-25, where the magnification factor is greater than 2.3 and less than 2.5.

[0280] 27. The method according to any of items 20-26, wherein the intraoral 3D scanner further constructs and / or includes any feature according to any of items 7-16.

Claims

1. A compact intraoral 3D scanner, comprising: - Detector, composed of horizontal sensor size limited, in, Less than 10mm, and The detector includes a pixel array, where each pixel is a pixel width limited; Limited field of view One or more optical elements, field of view Related to the size of the sensor, the relationship is as follows: , Where m is the magnification greater than m=1.5; - A light source for emitting light defined at least by a dominant wavelength λ, thereby configuring the scanner to illuminate an object inside the mouth with light; - A beam splitter that communicates optically with the light source, the one or more optical elements, and the detector; Wherein, the one or more optical elements are optical focusing elements configured to move the focal plane of light at the intraoral object, the focal plane being determined by the object-space numerical aperture of the one or more optical elements. limited, Its features are: ○ The pixel width Less than 10 micrometers; and The compact intraoral 3D scanner meets the condition: 0.20 ≤ ξ ≤ 0.6, where: ξ= (λ(1+1 / m)) / (md pixel NA object )。 2. The compact intraoral 3D scanner according to claim 1, wherein, 0.30≤ξ≤0.

55.

3. The compact intraoral 3D scanner according to claim 1, wherein, 0.30≤ξ≤0.

50.

4. The compact intraoral 3D scanner according to claim 1, wherein, 0.30≤ξ≤0.

45.

5. The compact intraoral 3D scanner according to claim 1, wherein, The amplification factor is greater than 2.0 and less than 3.

0.

6. The compact intraoral 3D scanner according to claim 1, wherein, The amplification factor is greater than 2.3 and less than 2.

5.

7. The compact intraoral 3D scanner according to any one of claims 1-6, wherein, The optical focusing element is an optical lens with a mass of less than 5 grams.

8. The compact intraoral 3D scanner according to any one of claims 1-6, wherein, The optical focusing element is configured to translate back and forth via a translation stage at a scanning frequency, wherein the translation stage is configured to scan at a scanning frequency between 10 Hz and 12.5 Hz.

9. The compact intraoral 3D scanner according to any one of claims 1-6, wherein, The beam splitter has a refractive index greater than 1.8 to reduce the angle at which light hits the sensor, thereby further reducing the size of the compact intraoral 3D scanner.

10. The compact intraoral 3D scanner according to claim 1, wherein, The multiple optical elements are at least three lens groups: a first lens group close to the beam splitter, a second lens group away from the beam splitter, and a third lens group located between the first and second lens groups, such that the optical focusing element is part of the first lens group.

11. The compact intraoral 3D scanner according to claim 10, wherein, Each of the lens groups consists of only spherical lenses.

12. The compact intraoral 3D scanner according to any one of claims 10-11, wherein, Each of the lens groups consists of only a single or double lens.

13. The compact intraoral 3D scanner according to any one of claims 10-11, wherein, The second lens group and the third lens group each include a dual body.

14. A method for optimizing a compact intraoral 3D scanner, comprising the following steps: - Provides an optical system for the compact intraoral 3D scanner, the compact intraoral 3D scanner comprising: ○ Detector, the detector being composed of a horizontal sensor size limited, in, Less than 10mm, and The detector consists of a pixel array, where each pixel has a width d. pixel limited; ○Limited field of view One or more optical elements, the field of view being related to the sensor size, with the following relationship: ,in It is greater than =1.5 magnification; ○ Used for transmitting at least the dominant wavelength A limited light source is used, thereby the compact intraoral 3D scanner is configured to illuminate intraoral objects with light; A beam splitter that communicates optically with the light source, the one or more optical elements, and the detector. The one or more optical elements are configured to move the focal plane of light at the intraoral object, the focal plane being defined by the object space numerical aperture of the one or more optical elements. limited, - Select the object space numerical aperture for the compact intraoral 3D scanner, which has a depth-of-field relationship. pass To limit; characterized in that: - By saying the pixel width The following options were selected to optimize the compact intraoral 3D scanner: d pixel =(λ(1+1 / m)) / (mξNA object ), where ξ is 0.20≤ξ≤0.6, thus the pixel width d pixel Less than 10 micrometers.

15. The method of claim 14, wherein the depth of field They were chosen to be 35 and 55 micrometers.

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