阅读说明：本技术 一种多频相移牙齿三维重建方法 (Multi-frequency phase-shift tooth three-dimensional reconstruction method ) 是由 钟波 于 2020-10-15 设计创作，主要内容包括：本发明公开一种多频相移牙齿三维重建方法,该方法包括如下步骤：步骤A：将多帧有一定相移的条纹光栅图像,通过投影仪投射到待测物体上；步骤B：由相机采集带有光栅的物体图像,并传递到PC主机；步骤C：采用多频外差相移算法计算出物体图像连续的相对相位值；步骤D：将所得到的相对相位值展开以进行三维重构,得出光栅的绝对相位值；步骤E：再依据相机的标定参数来计算牙齿真实数据,采用多幅多角度点云数据图像拼合以后,由软件合并数据并封装,获取牙模的曲面。本发明采用结构光的方式,通过多频相移的方式对牙齿进行三维重建,该方式能够有效的降低成本,达到在低成本的基础上,快速并有效实现牙齿模型的数据成型的目的。(The invention discloses a multi-frequency phase-shift tooth three-dimensional reconstruction method, which comprises the following steps: step A: projecting a plurality of frames of fringe grating images with certain phase shift onto an object to be measured through a projector; and B: collecting an object image with a grating by a camera and transmitting the object image to a PC host; and C: calculating a continuous relative phase value of the object image by adopting a multi-frequency heterodyne phase shift algorithm; step D: the obtained relative phase value is expanded to carry out three-dimensional reconstruction, and an absolute phase value of the grating is obtained; step E: and calculating tooth real data according to calibration parameters of the camera, combining and packaging data by software after splicing a plurality of multi-angle point cloud data images, and acquiring the curved surface of the dental cast. The invention adopts a structured light mode, and carries out three-dimensional reconstruction on teeth in a multi-frequency phase shift mode, and the mode can effectively reduce the cost and achieve the aim of quickly and effectively realizing the data forming of the tooth model on the basis of low cost.)

1. A multi-frequency phase-shift tooth three-dimensional reconstruction method is characterized by comprising the following steps:

step A: projecting a plurality of frames of fringe grating images with certain phase shift onto an object to be measured through a projector;

and B: collecting an object image with a grating by a camera and transmitting the object image to a PC host;

and C: calculating a continuous relative phase value of the object image by adopting a multi-frequency heterodyne phase shift algorithm;

step D: the obtained relative phase value is expanded to carry out three-dimensional reconstruction, and an absolute phase value of the grating is obtained;

step E: and calculating tooth real data according to calibration parameters of the camera, combining and packaging data by software after splicing a plurality of multi-angle point cloud data images, and acquiring the curved surface of the dental cast.

2. The multi-frequency phase-shift tooth three-dimensional reconstruction method according to claim 1, wherein in step a, a DLP projector is used for fast projection.

3. The method of claim 1, wherein in step B, the camera captures at least three object images.

4. The method of claim 3, wherein the calculation formula of the relative phase values in step C is as follows:

I_i(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+δ_i]

wherein, I_i(x, y) is the average intensity of the image, I' ((x, y))x, y) is the amplitude of the light intensity, delta_iRespectively, the phase shift of the image, phi (x, y) being the relative phase value of each point to be calculated.

5. The multi-frequency phase-shift tooth three-dimensional reconstruction method as claimed in claim 4, wherein in the step C, the multi-frequency heterodyne phase-shift algorithm comprises the following specific steps: phase function of three different frequenciesThe corresponding relative phase values are respectively phi₁、φ₂、φ₃Using heterodyne principle to superimpose phi separately₁、φ₂And phi₂、φ₃To obtain a frequency of lambda₁₂、λ₂₃Phase phi of₁₂And phi₂₃Then the frequency is set to be lambda₁₂、λ₂₃The phase of the phase-shift-compensation-unit is superposed to obtain the phase phi with only one period in the whole field range₁₂₃。

6. A multi-frequency phase-shifted dental three-dimensional reconstruction method as claimed in claim 5, wherein said frequency is λ₁₂、λ₂₃The phase function adopts three steps of phase shift, and the formula is respectively as follows:

I₁(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)]

I₂(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+2π/3]

I₃(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+4π/3]

the formula for deriving the relative phase values of the object image is as follows:

7. the multi-frequency phase-shifting tooth three-dimensional reconstruction method as claimed in claim 1, wherein in step D, the heterodyne principle is adopted to expand the relative phase values of the spatial points.

8. A multi-frequency phase-shifting tooth three-dimensional reconstruction method as claimed in claim 1, wherein in step E, the data is merged and encapsulated by using Geomagic software.

Technical Field

The invention relates to an oral cavity measuring technology, in particular to a multi-frequency phase-shift tooth three-dimensional reconstruction method.

Background

The traditional oral prosthesis manufacturing process specifically comprises the following steps: preparing a restoration according to the pathological condition of a patient → occluding materials such as silica gel or resin, copying the shape of oral teeth, pouring gypsum, copying an oral tissue shape model → combining the oral condition of the patient on the model, making a specific design → finishing cutting and substitution, coating a gap agent, carving a wax pattern and other complex procedures by a professional technician in the center of the technician → finally embedding and casting into a metal restoration, uniformly baking a ceramic layer on a porcelain oven, penetrating color and beautifying, finishing the manufacture of the restoration → after fine processing meets the requirement, trying, positioning and adjusting in the mouth of the patient to recover the lost shape and function → regularly rechecking, correcting and maintaining to ensure that the normal physiological function is carried out, and thus finishing the traditional oral cavity restoration treatment process.

The traditional restoration process is almost manually operated in each step, the flow is complex, the defects of low efficiency, long treatment period, low restoration precision, great pain of a patient, incapability of realizing simulation of a restoration result and the like exist, and the requirement of the patient on quickly restoring the function of the tooth body cannot be met. This repair is becoming increasingly unable to meet market demands. Therefore, a new method for quickly manufacturing the dental prosthesis is needed, the traditional treatment period measured in weeks and months is changed into the treatment period measured in hours and minutes, and the treatment period is greatly shortened; the traditional manual operation is changed into computer automatic processing, so that the working efficiency is improved, the traditional method that patients frequently try on, adjust and interact is changed into digital analog simulation, and the pain of the patients is relieved; the traditional visual inspection by experience is changed into high-precision quantitative measurement, so that the manufacturing precision and quality of the restoration are ensured, and the digital oral restoration technology is provided.

The existing oral cavity measuring methods comprise:

one, indirect measurement mode

The indirect measurement is to copy the teeth in the mouth of the patient through plaster, and the three-dimensional data of the teeth is indirectly obtained by measuring the plaster working model by using a three-dimensional measuring system. The measurement mode avoids the limitation of various complex environments of intraoral measurement, has low requirement on measurement speed, can obtain a three-dimensional digital model of the tooth body of a patient with high precision and stability, but needs impression reproduction, costs extra time, increases the period and cost of diagnosis and treatment, introduces an error of impression taking, and increases the pain of impression taking of the patient. The measurement comprises a contact type and a non-contact type, wherein the contact type mainly refers to a three-coordinate measurement method, and the non-contact type mainly comprises laser line structured light measurement, grating surface structured light measurement, binocular stereoscopic vision measurement, tomography measurement and the like. Indirect measurement is the mainstream of research and application at present.

(1) Contact three-coordinate measurement

Contact type three-coordinate measurement is a traditional reverse data acquisition method, is already applied in industry, and related technologies are mature. The method has strong universality and high precision, can be connected with a flexible manufacturing system, and obtains three-dimensional data by repeatedly contacting the surface of a model on a planned measuring path by using a probe arranged at the tail end of a measuring arm. Higher measurement accuracy can be achieved by programmatically compensating for the probe radius, but the mechanical means to control the movement of the probe is very time consuming. The method is difficult to measure for tooth models with complex shapes, such as undercut in tooth shapes, inlays and the like. Currently, the use of this method in oral measurements is diminishing. The typical oral cavity commercial measuring system is a Minnesota system, which is developed by Rekow ED et al, Minnesota university in America, and a micro remote control detecting arm (a machine touch device) controls a mechanical probe to collect shape data at the dental crown, facial fossa, tip, ridge and other parts in the oral cavity or on the surface of a dental model of a patient, and has the advantages that the accurate data of the edge of a preparation body can be obtained without retracting gingiva and being influenced by the outside, and the precision can be controlled within the range of 40-60 mu m; titan system, also known as DCS, was developed by Israel and manufactured by DCS (digital Computer System) production AG of Basel, Switzerland with a measurement accuracy of 50 μm. The point-by-point measurement method has limited measurement data, and the data which cannot be measured is subjected to curve fitting interpolation, so that the precision is damaged, and the time is consumed; also included are the Denti CAD systems developed by Rekow ED and manufactured by BEGO, Germany, the Celay system manufactured by Mikroma, Zurich, odontology, Eidenbin, and Renisshaw, England and DEA, Italy, which are essentially the earliest measurement systems.

(2) Line laser measurement

The line laser measuring method belongs to the field of structural light vision measurement, and its basic principle is trigonometry, the light projected by laser is formed into a light plane in the space, the laser line projected on the surface of object is modulated and deformed by object height, the point on the deformation curve is mapped into camera, and between said point and light plane a geometric trigonometric relation is formed, and the calibrated system parameters are used to implement three-dimensional measurement of measured object. Rieux and Bird realized the measurement of object morphology based on this principle in 1993, and later used a single stripe projector instead of the traditional laser; the time domain peak value of each pixel is considered to be the most accurate laser strip position by Curles and Levoy, and the accuracy of measurement is directly determined by the extraction accuracy of the light strip; the Goesele, Fuchs and Seidel also carry out deep research on the measurement precision, and the proposed bevel edge modulation technology improves the measurement precision; subsequently, many precision improvement algorithms have emerged. The main disadvantage of the laser-based method is the slow measuring speed, which only allows one line of data to be measured at a time. A typical oral measurement system includes: the Duret system, also known as the Sopha Bioconcent system, was developed and manufactured jointly by Sopha Bioconcept and a research group led by professor Francois Duret of the university of Ranon, France; the 3Shape Dental 3D Scanner device, which is released by 3Shape company of Denmark in 2007, adopts laser scanning measurement, the system consists of two CCD cameras and a laser, and the slow speed of measurement is the main disadvantage; the Cicero system, which is an abbreviation of Computer-integrated crown recovery, is a product of Elephan corporation of the Netherlands, a laser scanning detector emits 640mm helium-neon laser beams which linearly irradiate on a plaster model, the light irradiation direction is a Z axis, and the reflected light is a surface array CCD (600 multiplied by 625 pixels)

The camera receives the data and realizes the measurement of the three-dimensional surface shape data of the model by a triangulation method; the PRECISCAN laser three-dimensional measuring instrument of the German DCS fractional AG company can complete the measurement of a steeper preparation body, the scanning height reaches 35mm, and 300000 data points can be acquired within 1 minute.

(3) Surface structure light measuring method

The method based on the surface structured light mode is similar to the line laser structured light method in principle, and is different in that the projector can measure the whole surface data each time when projecting the surface structured light. According to different coding and decoding implementation modes, the coding and decoding method can be divided into space dimension coding and time dimension coding. The spatial dimension coding is used for realizing correct decoding of the whole image according to coding information of adjacent pixels in one image so as to further realize three-dimensional shape measurement of a measured object, and the vertical strip coding with four kinds of color information is provided by Boyer and Kak, and the mode types are many; the grid pattern proposed by Ito; chen et al define a vertical stripe code consisting of color information; later, a De Bruijn sequences series spatial coding mode with higher robustness appears; m-arrays coding mode with window matching fast property, etc. The method can realize the recovery of the three-dimensional shape of the measured object by only one image, has the application prospect of dynamic measurement, but has limited measurement precision. Structured light coding based on time dimension is a method which is widely researched, a Gray code method proposed by Besl in 1989 is early time dimension coding, the coding is considered as deformed binary coding, and the accuracy and stability of code words are higher than those of binary coding; a similar approach was later proposed in Zongker and Werner, except that the display was placed behind the object, enabling a larger angle measurement by refractive properties; phase shift is also a more studied coding method, and Oppenheim and Lim were studied as early as 1981, and the research is mainly focused on the aspects of phase unwrapping correctness and stability. Bone was the first scholarer who studied phase-quality oriented-based phase unwrapping algorithms, and a number of phase unwrapping algorithms were subsequently developed. Non-positive linear errors in phase solution are a ubiquitous problem, and Schwider has conducted intensive studies on the higher harmonic influence of phase. In addition, there are many surface structured light coding methods such as binary coding, N-bit coding, pseudo-random coding, gray code-line shift, phase shift coding, etc. The method has stable coding and small error. The Cerec system is a typical commercial system based on grating surface structured light measurement, is a product launched by Sirona company in Germany in 2007, is the most successful system for commercial development, and the newly launched third-generation product Bluecam scanning accuracy can reach 19 mu m at most under laboratory conditions; the Jolmoumar oral CAD/CAM (Kavo Everst System) system produced by Germany Kavo company is also introduced in 2007, Gray code-phase shift coding patterns are projected on the surface of a tooth to be measured, accurate measurement of dental model data is realized, the method is simple in structure, high in precision and stable in measurement, the measurement system can complete measurement of a tooth model within 3 minutes, and the measurement precision can reach below 20 mu m; the Pro 50TM scanning system developed by the cynoavad company of canada is based on a structured light measurement method of a grating, and uses color grating stripes instead of time-domain gray-scale grating stripes, so that the measurement speed is improved, but the system is sensitive to the influence of the background.

(4) Binocular stereo vision measuring method

The binocular stereo vision measuring method is another kind of method in vision measuring technology, and the method simulates human eyes to realize the measurement of the measured object in principle, matches and corresponds two-dimensional images of the same object collected in two cameras, and realizes three-dimensional measurement by utilizing the difference of image coordinates, which is also called as a parallax method. The traditional stereo vision measuring method is to realize the three-dimensional measurement of a space object by only using two cameras and realize the matching correspondence of two images by using a matching technology, and the realization method is not restricted by conditions such as environment, object texture, illumination, view field and the like, but the matching only depending on the gray level information of images with different view angles is difficult. At present, the research on a wider stereoscopic vision measurement technology refers to an improved visual measurement method, a light source projection device is added on the basis of two cameras to project some coded pattern information, the matching of images of the two cameras is realized by coding, analyzing and identifying the collected images, and the projected patterns are similar to those in the structured light measurement method, but are different: in the stereo vision measuring method, the projected pattern is only a match of two images as long as it satisfies uniqueness in the image space or uniqueness in one-dimensional direction of the image, and the code pattern thereof includes the structured light pattern in structured light measurement. The method needs more complex hardware, and has no advantages in the aspects of miniaturization of the measuring system and cost of the system compared with a structured light measuring system which needs one more camera hardware. The German Hi Scan scanning System was developed by Fraunhofer applied optics and precision engineering institute in Germany in combination with the company Hint-Els,the Dental CAD system adopts binocular stereo vision technology and uses faciesAnd calculating the projected grating structure light mode by using a correlation method to realize the matching of binocular images.

Two, direct measurement mode

The direct measurement mode is to directly acquire three-dimensional data of teeth by using a measuring device, and comprises two types of intraoral tooth surface three-dimensional topography measurement and tooth internal tomography measurement, wherein one type of intraoral tooth surface three-dimensional topography measurement is acquired, and the other type of intraoral tooth tissue data is acquired. The three-dimensional topography of the surface of the intraoral tooth is measured without copying a plaster model, the measurement is convenient, the measurement speed is high, the pain of a patient is small, but the requirements on measurement equipment, measurement conditions and technology are high. The measuring method is a development trend of oral cavity measurement application, and has the advantages of small size in appearance, high measuring speed in the measuring technology, real-time performance, automatic positioning and splicing functions of space free visual angle measurement, portability in operation, simple structure, easiness in use and the like. At present, the research of the related technology is still in an exploration phase, and the measurement methods are different.

(1) Surface structure light measuring method

The intraoral measurement mainly meets the requirements of measurement rapidity, realizes data measurement within the relative rest time limit tolerated by people, and meets the measurement precision requirement, so that the measurement method based on the surface structured light is a good method for balancing the measurement speed and precision. The intraoral three-dimensional camera developed by Sirona, Germany, was based on this measurement method and was first developed by Drifnu Mormannu and Drifsonii, university of Zurich, Switzerland, in 1983, and was later manufactured by Siemens, Germany. The initial structured light is generated by interference light projection, a light source is infrared invisible light, based on a piezoelectric precision positioning device and CCD chip image acquisition in principle, through development for 30 years, a Bluecam system with higher precision and resolution is successfully provided at present, and the Bluecam system is also the only commercially successful intraoral measurement system at present.

(2) Confocal measurement method

The basic principle of confocal measurement is that probe light emitted from a point source is focused through a lens onto the object to be measured, and if the object is exactly in focus, the reflected light should be focused back to the source through the original lens. When the method is used for three-dimensional measurement, the illumination and detection plane is set to be conjugate relative to the focal plane of the objective lens, points on the focal plane are focused on the illumination and detection plane at the same time, points outside the focal plane cannot be imaged on the detection plane, then a measured space is calibrated, the functional relation between the distance of a measured object and the focusing is obtained, and the focusing images of the surfaces of all measured objects are obtained by changing the distance between the measured object and a measurement system, so that the three-dimensional shape measurement of the measured object is realized. The method has wide expansion space in the aspect of physical optical application, and is mainly used for microscopic measurement in the microscopic field such as cell three-dimensional measurement, nano measurement, molecular biology and the like. At present, there is also a report of the related art that the technology is used for oral cavity three-dimensional measurement, and the three-dimensional measurement of teeth is realized by acquiring optical cross section confocal images of multi-layer teeth.

Denmark 3Shape

The TRIOS intraoral scanning system developed by the company based on the principle adopts a super-high-speed camera for measurement, and can realize the acquisition of more than 3000 per second

The scanning system has the remarkable characteristic of freedom in movement and positioning, and is convenient for realizing splicing measurement of multiple visual angle data.

(3) Laser-based vision measurement method

Based on the trigonometry vision measurement principle, three-dimensional measurement can be realized by adopting different coding modes under the condition of meeting the requirement of quick matching reconstruction. Based on the principle, the Lava Chairside Oral Scanner system is provided by American 3M ESPE company, the system realizes three-dimensional image measurement of about 20 frames per second through stroboscopic blue laser projection and high-speed camera image acquisition, basically realizes real-time modeling, and has already provided a system prototype product; an Itero intraoral three-dimensional measuring system in the United states realizes the acquisition of tooth surface contour data based on a laser spot mode, can acquire up to 10 ten thousand laser spot area data each time, can realize 360-degree data measurement of a whole circle on a tooth preparation body, and the whole scanning process takes about 3-5 minutes. Laser projection components and parts in the two types of measuring systems are complex, and the technical difficulty is high.

(4) Stereo vision measuring method

The stereo vision measuring method based on the sine grating matching is the principle of a Direct Scan intraoral scanning system of Hint-Els company in Germany, the system adopts a stereo vision measuring technology, data measurement is realized on a projected grating image by utilizing gray level correlation, and the currently developed intraoral measuring system is still in a research and development stage and has the difficulty that the matching speed is slow, and the requirement on rapidity of oral measurement is difficult to realize.

(5) Tomography method

The tomography method is also a three-dimensional measurement method, and mainly utilizes substances with penetrating properties, such as X rays, magnetic fields and the like to project on a measured object, and the three-dimensional measurement of the measured object is realized by acquiring information of shielded reflection through a camera. The method can be used for measuring three-dimensional data in an object, solves the problem of obtaining internal data under the condition of not damaging external tissues of the organism, and is gradually applied to the field of oral cavity repair measurement. In order to understand the oral cavity more clearly and accurately, the three-dimensional shape of the internal teeth is acquired without damaging the soft tissue of the gum, and the measurement method is needed: such as the type of implant in dental prosthetics, requires a clear reconstruction of the subgingival teeth and dental nerve locations. At present, the research and application of the method in the field of oral repair have a gradually increasing trend, the method provides tooth root data under soft tissue of gum, but the measurement precision of the method is limited at present, and the method is also a main difficulty of future research. The oral cavity X-ray imaging system HELIODEN proposed by Sirona in Germany is provided with a high-frequency generator of high-energy radiation, so that the imaging is detailed, tiny details can be recognized, and the precise acquisition of the data of the inner part of the tooth surface and the tooth root can be realized by combining a three-dimensional shape measuring device.

In general, the current foreign related technology development has the following two characteristics: firstly, the research of the extraoral three-dimensional measurement technology is mature, a plurality of methods are adopted, the commercial verification is mainly focused on the structured light measurement method based on the grating and the laser, the two methods have good comprehensive performance in the aspects of measurement precision, stability, speed and the like, and commercial products are launched in the last 3-4 years; the grating-based surface structured light measurement method can meet the measurement requirements of the inside and the outside of the mouth at the same time, can achieve better balance in the aspects of measurement precision and measurement speed, and is the main direction of research on oral cavity measurement technology.

The existing oral cavity measuring method has the problems of high cost and high charge, the hardware cost of foreign products is high due to different use schemes, and certain cost is charged every year when software is used, so that the whole price is high.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a multi-frequency phase-shift tooth three-dimensional reconstruction method, which adopts a structured light mode and carries out three-dimensional reconstruction on teeth in a multi-frequency phase-shift mode, and the method can effectively reduce the cost, so that the overall price is reduced to a certain range and is easy to accept in markets.

The technical scheme of the invention is as follows:

a multi-frequency phase-shifted tooth three-dimensional reconstruction method, comprising the steps of:

step A: projecting a plurality of frames of fringe grating images with certain phase shift onto an object to be measured through a projector;

and B: collecting an object image with a grating by a camera and transmitting the object image to a PC host;

and C: calculating a continuous relative phase value of the object image by adopting a multi-frequency heterodyne phase shift algorithm;

step D: the obtained relative phase value is expanded to carry out three-dimensional reconstruction, and an absolute phase value of the grating is obtained;

step E: and calculating tooth real data according to calibration parameters of the camera, combining and packaging data by software after splicing a plurality of multi-angle point cloud data images, and acquiring the curved surface of the dental cast.

And in the step A, a DLP projector is adopted for carrying out rapid projection.

In step B, the camera at least acquires three groups of object images.

In step C, the calculation formula of the relative phase value is as follows:

I_i(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+δ_i]

wherein, I_i(x, y) is the average intensity of the image, I' (x, y) is the amplitude of the intensity, δ_iRespectively, the phase shift of the image, phi (x, y) being the relative phase value of each point to be calculated.

In step C, the specific steps of the multi-frequency heterodyne phase shift algorithm are as follows: phase function of three different frequenciesThe corresponding relative phase values are respectively phi₁、φ₂、φ₃Using heterodyne principle to superimpose phi separately₁、φ₂And phi₂、φ₃To obtain a frequency of lambda₁₂、λ₂₃Phase phi of₁₂And phi₂₃Then the frequency is set to be lambda₁₂、λ₂₃The phase of the phase-shift-compensation-unit is superposed to obtain the phase phi with only one period in the whole field range₁₂₃。

Said frequency is λ₁₂、λ₂₃The phase function adopts three steps of phase shift, and the formula is respectively as follows:

I₁(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)]

I₂(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+2π/3]

I₃(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+4π/3]

the formula for deriving the relative phase values of the object image is as follows:

and D, expanding the relative phase value of the space point by adopting a heterodyne principle.

And step E, adopting Geomagic software to merge data and package.

Compared with the prior art, the invention has the beneficial effects that:

the invention can quickly and effectively realize the data forming of the tooth model on the basis of low cost, and lays a solid foundation for the oral cleaning equipment.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a schematic diagram of the relationship of modules of the present invention;

FIG. 2 is a heterodyne schematic of the present invention;

FIG. 3 is a schematic phase unwrapping diagram in accordance with the present invention;

FIG. 4 is a schematic diagram of the multi-frequency heterodyne principle of the present invention;

FIG. 5 is a schematic diagram of scan data and real data according to the present invention;

FIG. 6 is a diagram illustrating a comparison between Geomagic scan data and real data according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to explain the technical means of the present invention, the following description will be given by way of specific examples.

Examples

The invention provides a multi-frequency phase-shift tooth three-dimensional reconstruction method, and referring to fig. 1, the method comprises the following steps:

step A: projecting a plurality of frames of fringe grating images with certain phase shift onto an object to be measured through a projector;

and B: collecting an object image with a grating by a camera and transmitting the object image to a PC host;

and C: calculating a continuous relative phase value of the object image by adopting a multi-frequency heterodyne phase shift algorithm;

step D: and unfolding the obtained relative phase value to carry out three-dimensional reconstruction to obtain an absolute phase value of the grating, and establishing a relation between the surface information of the object and the phase value of the grating so as to obtain the real surface topography of the object.

Assuming that the light intensity of the fringe image is a standard sine distribution, the light intensity of any point in the fringe image is approximately expressed by a following cosine distribution function:

I_i(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+δ_i]

wherein, I_i(x, y) is the average intensity of the image, I' (x, y) is the amplitude of the intensity, δ_iRespectively, the phase shift of the image, phi (x, y) being the relative phase value of each point to be calculated.

Due to I_i(x, y), I' (x, y), φ (x, y) are three unknowns, so at least three sets of object images need to be acquired to calculate φ (x, y).

In the prior art, various phase shift algorithms exist, and the stability and error response of the phase shift algorithm affect the phase calculation and the subsequent three-dimensional reconstruction precision, so that the selection of a proper phase shift algorithm is particularly important. In the step A, a DLP projector is adopted for fast projection, and the influence of factors such as DLP projection setting is limited, so that a 4+3+3 phase shift projection mode is selected, a group of 4-step phase shifts is used for calculating the relative phase value of the object image, and the advantage can be that the influence of a background item of a detector is eliminated. Taking 4 grating images with phase shifts of 0, pi/2, pi and 3 pi/2 respectively, thereby obtaining

I₁(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)]

I₂(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+π/2]

I₃(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+π]

I₄(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+3π/2]

The relative phase value of the object image can be calculated according to the four formulas

The phase diagram calculated by the four-step phase shift method is discontinuous, and if the one-to-one correspondence relation of the surface topography of the object to be measured is to be established, continuous phase values must be obtained. The phase reconstruction technique can expand the phase diagram obtained by the phase shift method to carry out three-dimensional reconstruction.

The method adopts the principle of multi-frequency heterodyne, and combines phase functions of three different frequencies The corresponding relative phase values are respectively phi₁、φ₂、φ₃Using heterodyne principle to superimpose phi separately₁、φ₂And phi₂、φ₃To obtain a frequency of lambda₁₂、λ₂₃Phase phi of₁₂And phi₂₃Then the frequency is set to be lambda₁₂、λ₂₃The phase of the phase-shift-compensation-unit is superposed to obtain the phase phi with only one period in the whole field range₁₂₃. Said frequency is λ₁₂、λ₂₃The phase function adopts three steps of phase shift, and the formula is respectively as follows:

I₁(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)]

I₂(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+2π/3]

I₃(x,y)＝I'(x,y)+I”(x,y)cos[φ(x,y)+4π/3]

the phase principal value of the grating image can be calculated according to the three formulas

The heterodyne principle refers to a function of the phase of two different frequenciesAndsuperimposed on a lower frequency phase function phi_b(x) As shown in FIG. 2, where λ₁、λ₂、λ_bAre respectively a phase functionAnd phi_b(x) The corresponding frequency.

φ_b(x) Frequency λ of_bThe calculation can be expressed as:

the heterodyne principle can be used to spread the relative phase values of spatial points, and in order to perform phase spreading unambiguously over the full field, a suitable λ must be chosen₁、λ₂Value of so that_b1. As shown in FIG. 3, tan α is the entire field of the image₁、tanα₂Is equal to the ratio of the periods of the projected image (set to R)₁Is a constant), the following pair can be adoptedUnfolding:

wherein:

the multifrequency heterodyne principle is shown in fig. 4.

Step E: and calculating tooth real data according to calibration parameters of a camera, combining and packaging the data by using Geomagic software after splicing a plurality of multi-angle point cloud data images to obtain the curved surface of the dental model. As shown in fig. 5 and 6.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.