CN112525104A - Digital holographic three-dimensional shape measuring device and method - Google Patents
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Abstract
The invention relates to a digital holographic three-dimensional shape measuring device and a method, wherein the device comprises: the device comprises a laser, a light splitting component, an object light path for irradiating an object to be detected, a reference light path for reference, a light path synthesis component and an acquisition system comprising a plurality of sensors; the light splitting component splits the light emitted by the laser into two beams, the first beam of light irradiates an object to be measured through an object light path, and the object to be measured reflects the irradiated first beam of light; the second beam of light is transmitted by a reference light optical path as reference light, and the reference light transmitted by the reference light optical path and the reflected light of the object to be detected are converged in the optical path synthesis assembly and enter the detection surfaces of the plurality of sensors; the detection surfaces of a plurality of sensors in the acquisition system record holographic information of the reference light and the reflected light which interfere in the light path synthesis assembly, and the three-dimensional shape of the object to be detected is obtained according to the holographic information. The structure of the invention can measure the surface appearance of the three-dimensional object in high precision, fast and real time.
Description
Technical Field
The invention relates to a holographic imaging measurement technology, in particular to a digital holographic three-dimensional shape measurement device and a method.
Background
The rapid development of precision machining has stimulated the need for precise measurement of the geometric characteristics of objects for which non-destructive and non-contact topographical measurements of three-dimensional objects are important for their design, testing and characterization. Because the digital holography technology has the characteristics of rapidness, real-time performance, full visual field, non-contact, no damage, high-resolution imaging, convenient and flexible hologram storage, reconstruction and transmission and the like, the optical detection by the digital holography is an important research trend in recent years, and the digital holography technology is widely applied to the measurement of three-dimensional morphology and three-dimensional deformation. In digital holography, the intensity and phase of an object light field can be conveniently obtained by computer numerical simulation of diffraction of a digital hologram, the intensity of a reconstructed image represents the gray level distribution of the surface of a three-dimensional object, and the reconstructed phase contains the shape information of the three-dimensional object, which is also the theoretical basis for digital holography to measure the shape of the surface of the object.
In digital holography, the morphology measurement mainly comprises a multi-wavelength method, a birefringence method and a multi-angle illumination method. The method comprises the steps of recording a plurality of holograms with different states, wherein the different states can be caused by the wavelength change or the irradiation angle of irradiation light or the refractive index change of a medium where an object is positioned, reconstructing corresponding phases from the holograms with the different states, obtaining a phase diagram related to the surface topography of the object by differentiating the reconstructed phases with the different states, and finally demodulating the three-dimensional topography of the object.
Most of the existing morphology measurement methods adopt single sensor for collection, and holograms in different states need to be recorded in sequence, so that the measurement environment has high stability, and rapid and real-time morphology measurement cannot be realized.
Disclosure of Invention
Technical problem to be solved
In view of the above disadvantages and shortcomings of the prior art, the present invention provides a digital holographic three-dimensional shape measurement apparatus and method.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
in a first aspect, an embodiment of the present invention provides a digital holographic three-dimensional topography measurement apparatus, including: the device comprises a laser, a light splitting component, an object light path for irradiating an object to be detected, a reference light path for reference, a light path synthesis component and an acquisition system comprising a plurality of sensors;
the light splitting component splits the light emitted by the laser into two beams, the first beam of light irradiates an object to be measured through an object light path, and the object to be measured reflects the irradiated first beam of light; the second beam of light is transmitted by a reference light optical path as reference light, and the reference light transmitted by the reference light optical path and the reflected light of the object to be detected are converged in the optical path synthesis assembly and enter the detection surfaces of the plurality of sensors;
the detection surfaces of a plurality of sensors in the acquisition system record holographic information of the reference light and the reflected light which interfere in the light path synthesis assembly, and the three-dimensional shape of the object to be detected is obtained according to the holographic information.
Optionally, the light splitting assembly comprises: a beam splitter prism;
the object light path includes: the first microscope objective, the first collimating lens and the first plane reflector are arranged in sequence;
after a first beam of light split by the beam splitting prism passes through the first microscope objective and the first collimating lens, the collimated light irradiates an object to be measured through the first plane reflector;
the reference light path includes: the reflecting mirror, the second microscope objective, the second collimating lens and the second plane reflecting mirror;
the second beam of light split by the beam splitting prism passes through a second microscope objective and a second collimating lens after being reflected by the reflecting mirror, and the collimated light is reflected to the light path synthesis assembly by a second plane reflecting mirror;
the optical path synthesizing assembly includes: a beam combining mirror.
Optionally, the acquisition system comprises: the device comprises a computing device and a plurality of sensors connected with the computing device, wherein each sensor is provided with a detection surface; the plurality of sensors includes a central sensor;
the object to be measured, the beam combiner and the central sensor are located on the same axis, more than two sensors are placed around the central sensor, the detection surfaces of all the sensors are not coplanar with each other, and the normals of the detection surfaces of all the sensors face the object to be measured.
Optionally, the acquisition system further comprises: an electrically controlled rotary table and a translation table for supporting each sensor;
the electric control rotating platform is used for adjusting an included angle between a detection surface of the sensor and a detection surface of the central sensor, and the translation platform is used for adjusting the translation amount of the detection surface of the sensor;
the electric control rotating table and the translation table are respectively connected with the computing equipment by respective driving systems.
Optionally, the sensor comprises: a CCD or a CMOS.
In a second aspect, an embodiment of the present invention further provides a measurement method based on any one of the digital holographic three-dimensional topography measurement apparatuses in the first aspect, including:
s1, adjusting the detection surfaces of the sensors in the acquisition system, and recording the angle information of the detection surface of each adjusted sensor relative to the central sensor;
s2, starting the laser to acquire holographic information of the interfered reference light and the reflected light;
and S3, reconstructing the holographic information to obtain the three-dimensional shape of the object to be measured.
Optionally, the S3 includes:
s31, reconstructing holographic information based on conjugate light of reference light collected in a collection system to obtain object light field information in a complex amplitude form for extracting phase information;
s32, preprocessing the object light field information based on the predetermined parameter information and the angle information to offset the inclined phase factor in the angle information introduced when part of the sensors rotate, and obtaining the preprocessed phase of each sensor;
s33, subtracting the preprocessed phases of each sensor to obtain phase difference results of a plurality of groups of sensors;
and S34, unwrapping the phase difference result, and fitting the unwrapped phase by adopting a least square fitting method to obtain the surface appearance of the three-dimensional object of the object to be measured.
Optionally, the S32 includes:
s321, acquiring a tilt phase factor of any sensor of the non-central sensors based on predetermined parameter information;
specifically, let the i (i ═ 1,2.. n) th sensor rotate by an angle θ around the x axis as compared with the center sensor (i ═ 0)ixRotation angle about y-axis of thetaiyThe amount of tilt T causedi(x0,y0) Expressed as:
Ti(x0,y0)＝x0sinθix+y0sinθiy；
at this time, the constructed tilt phase factor is:
s322, preprocessing the object light field information, including:
subtracting the phase in the reconstructed object optical field information from the tilted phase factor,
alternatively, the first and second electrodes may be,
the constructed tilt phase factor is written in complex amplitude form, and then the reconstructed object optical field complex amplitude is divided by the complex amplitude tilt phase factor to extract the phase information.
Optionally, the S33 includes:
the phase obtained after the pretreatment in S33 is
Then, the phase difference between two pairs is expressed as:
wherein the content of the first and second substances,
in order to be the vector of the illumination,
respectively, the observation vectors of different sensors, the phase difference including the height h of the surfacez(x0,y0) Term proportional to hx(x0,y0)，hy(x0,y0) A proportional tilt component.
Optionally, S34 includes:
the phase difference result obtained in S33 is written in vectorized form:
wherein:
fitting the unwrapped phases by a least square fitting method:
obtained hx(x0,y0)，hy(x0,y0)，hz(x0,y0) Wherein the component hx，hyTilt in x and y directions, h, respectively, caused by acquisition from different angleszThe components are projections in the Z-direction, i.e. surface topography information of the three-dimensional object.
(III) advantageous effects
The invention has the beneficial effects that: the device has compact structure, avoids the influence of lens aberration on measurement without using an imaging lens, can take a single shot for collection, reduces the measurement time, and can meet the requirements of high-precision, quick and real-time detection of the surface topography of the three-dimensional object.
The method recovers the phase of the object light field through a digital holographic reconstruction algorithm, utilizes the interference phases of the object light field under different acquisition angles, and fits the three-dimensional shape of the surface of the object to be measured through a least square method. By the mode, the high-precision non-contact rapid real-time morphology measurement method can realize high-precision non-contact rapid real-time morphology measurement on the diffuse reflection object, and can avoid the phase unwrapping process by setting a reasonable acquisition angle for the sensor.
It can be understood that the translation table and the rotation table are controlled by the computer and the controller to move and rotate for calibration, so that the detection surface of the sensor changes the angle, the normal line of the detection surface of the sensor faces to the object through translation, holograms recorded by the sensor under different acquisition angles are reconstructed, phase difference images under different acquisition angle differences are obtained, and the three-dimensional morphology of the surface of the object to be detected is fitted by using a least square method. The acquisition angle of the detection surface of the sensor is reasonably set, so that the surface appearance of the three-dimensional object can be measured quickly and in real time with high precision.
Drawings
Fig. 1A is a schematic structural diagram of a digital holographic three-dimensional topography measuring apparatus according to an embodiment of the present invention;
FIG. 1B is a schematic illustration of a position of a sensing surface of the plurality of sensors of FIG. 1;
FIG. 1C is a schematic diagram of light combining of the beam combiner in FIG. 1;
FIG. 2 is a schematic diagram of the process of the three sensors of FIG. 1;
FIG. 3 is a schematic diagram of the simulation of phase difference results at different collection angle differences based on the device in FIG. 1;
fig. 4 is a schematic surface topography of the object to be measured obtained by performing least square fitting using the method of the embodiment of the present invention.
Description of reference numerals:
1 is a laser; 2 is a beam splitter prism; 3 is a first microscope objective; 4 is a first collimating lens; 5 is a first plane mirror; 6 is a reflector; 7 is a second microscope objective; 8 is a second collimating lens; 9 is a second plane mirror; 10 is a beam combining mirror; 11 is an object to be detected; 12 is the detection surface of a plurality of sensors; 14 is a computing device.
Detailed Description
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
In order to better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
Example one
The embodiment of the invention provides a digital holographic three-dimensional shape measuring device, which comprises: the device comprises a laser, a light splitting component, an object light path for irradiating an object to be detected, a reference light path for reference, a light path synthesis component and an acquisition system comprising a plurality of sensors;
the light splitting component splits the light emitted by the laser into two beams, the first beam of light irradiates an object to be measured through an object light path, and the object to be measured reflects the irradiated first beam of light; the second beam of light is transmitted by a reference light optical path as reference light, and the reference light transmitted by the reference light optical path and the reflected light of the object to be detected are converged in the optical path synthesis assembly and enter the detection surfaces of the plurality of sensors;
the detection surfaces of a plurality of sensors in the acquisition system record holographic information of the reference light and the reflected light which interfere in the light path synthesis assembly, and the three-dimensional shape of the object to be detected is obtained according to the holographic information.
Referring to fig. 1A, in the present embodiment, laser light emitted from a laser 1 passes through a beam splitter prism 2 and is split into two beams; after a first beam of light split by the beam splitter prism 2 passes through the first microscope objective 3 and the first collimating lens 4 for beam expanding and collimating, the collimated light irradiates the object to be measured 11 through the first plane reflector 5, and the light reflected by the object to be measured 11 reaches the beam combiner 10;
the second beam of light split by the beam splitter prism 2 passes through a second microscope objective 7 and a second collimating lens 8 for beam expanding and collimation after being reflected by a reflecting mirror 6, and the collimated light is reflected to a beam combiner 10 by a second plane reflecting mirror 9;
as shown in fig. 1C, the beam combiner 10 combines the object light reflected by the object to be measured and the reference light reflected by the second plane mirror 9 to generate interference, and the interference is sensed and transmitted to the computing device 14 by the detection surfaces of the plurality of sensors 12, so as to obtain the three-dimensional shape of the object to be measured through the processing of the computing device 14. In practical applications, the sensor may record the interfering holographic information, i.e., the hologram, and store it in a digitized form in the computing device.
In this embodiment, the acquisition system includes: the device comprises a computing device and a plurality of sensors connected with the computing device, wherein each sensor is provided with a detection surface; the plurality of sensors includes a central sensor; the plurality of sensors are not limited to three sensors, in this embodiment, in fig. 1A, the object to be detected, the beam combiner and the central sensor are located on the same axis, two or more sensors are disposed around the central sensor, detection surfaces of all the sensors are not coplanar with each other, and normals of the detection surfaces of all the sensors face the object to be detected, as shown in fig. 1B, fig. 1B is only a schematic diagram.
In addition, the acquisition system further comprises: an electrically controlled rotary table and translation table (neither shown) for supporting each sensor; the electric control rotating platform is used for adjusting an included angle between a detection surface of the sensor and a detection surface of the central sensor, and the translation platform is used for adjusting the translation amount of the detection surface of the sensor;
the electric control rotating table and the translation table are respectively connected with the computing equipment by respective driving systems. The normal lines of all the sensor detection surfaces face to the object, and the included angle and the translation amount between the sensors can be completed through the combination of the electric control rotating table and the translation table.
In practical applications, the plurality of sensors shown in FIG. 1A may each include: a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor).
In this embodiment, the laser instrument passes through beam splitting component and splits two bundles of light, a bundle is as object light, another bundle is as the reference light, the reference light shines into the beam combining mirror after the beam expanding collimation, object light shines the object that awaits measuring after the beam expanding collimation, the reflected light and the reference light of object that awaits measuring take place to interfere and shine into a plurality of sensors of different collection angles in the beam combining mirror, the information of interference is gathered to the detection face of the sensor of different collection angles, every sensor notes the hologram promptly, and store in the computing equipment with digital form.
The device has a compact structure, avoids the influence of lens aberration on measurement without using an imaging lens, can take a single shot for collection, reduces the measurement time, and can meet the requirements of high precision, rapidness and real-time detection of the surface morphology of the three-dimensional object.
Example two
The embodiment of the invention also provides a measuring method based on the digital holographic three-dimensional shape measuring device, which comprises the following steps:
and S1, adjusting the detection surface of the sensor in the acquisition system, and recording the angle information of the detection surface of each adjusted sensor relative to the central sensor.
In this embodiment, the angle information of the detection surface of each sensor can be adjusted by the electrically controlled rotary table and the translation table.
The angular information may be angular information relative to a central sensor axis.
And S2, starting the laser to acquire the holographic information of the interfered reference light and the reflected light.
The calibration is carried out by controlling the movement and rotation of the translation and rotation stages by a computing device such as a computer, so that the detection surface of the sensor changes angle, the normal of the detection surface of the sensor faces to the object by translation, the sensors of different acquisition angles record interference fields, and the interference fields are stored in the computer in a digitized form, so as to form a hologram, namely holographic information.
Since the normals of the detection surfaces of the plurality of sensors are all towards the object, compared with the central sensor, the other sensors introduce a phase tilt factor during recording, but since the rotation amount of the sensors is known, when the rotation is performed by using conjugate light of reference light, the tilt factor can be constructed according to the known amount (namely, predetermined parameter information) to offset the tilt factor introduced during rotation, and the pre-processing and the post-reconstruction processing can be performed.
And S3, reconstructing the holographic information to obtain the three-dimensional shape of the object to be measured.
For example, in step S3, the method of the present embodiment may include the following sub-steps:
s31, reconstructing the holographic information by the conjugate light of the reference light to obtain the object light field information in complex amplitude form for extracting the phase information,
that is, the holographic information may be recorded by a plurality of sensors, and the reconstruction process may be diffraction calculation of the hologram, and the reconstruction yields object optical field information in the form of complex amplitudes. The object optical field contains intensity and phase information, and the phase information corresponding to the object to be measured can be extracted based on the object optical field.
And S32, preprocessing the object light field information based on the predetermined parameter information and the angle information.
In this embodiment, the predetermined parameter information may include: laser wavelength, laser irradiation angle, rotation angle of the sensor, object plane size, etc.
When the conjugate light of the reference light is acquired (that is, when the conjugate light of the reference light is reproduced), a tilt factor may be constructed based on the predetermined parameter information to cancel a tilt phase factor introduced during rotation, thereby implementing preprocessing.
The conjugate light of the reference light can be understood as a light ray in the opposite direction to the reference light used at the time of recording. The conjugate light of the reference light is reproduced, i.e. no additional phase distortion factor occurs. The tilt phase may be based on the center sensor, and the other sensors may introduce a tilt amount related to the rotation angle after rotation.
Referring to fig. 2 and 3, fig. 2 shows a schematic diagram of three sensors; in fig. 2, an arrangement is shown in which the rotation about the y-axis is followed by a movement to the position in which the normal of the detection surface is directed towards the center of the object, the object plane parallel to the detection surface being x for the center sensor0y0When the observation vector of the sensor changes, the object plane at the same distance changes into x01y01And x02y02With the object plane x0y0Compared with one more tilted plane, a tilted phase factor is introduced in the reconstruction phase. Let a certain sensor rotate around the x-axis by an angle theta1xRotation angle about y-axis of theta1yInduced slope T1(x0,y0) The following equation.
Obtaining a tilt phase factor of any sensor of the non-central sensors, specifically:
let i (i ═ 1,2.. n) th sensor rotate around x axis by an angle θ with respect to the center sensor (i ═ 0)ixRotation angle about y-axis of thetaiyThe amount of tilt T causedi(x0,y0) Expressed as:
Ti(x0,y0)＝x0sinθix+y0sinθiy；
at this time, the constructed tilt phase factor is:
at this time, the pretreatment may include:
subtracting the extracted phase after reconstruction from the tilted phase factor,
alternatively, the first and second electrodes may be,
the constructed tilt phase factor is written in complex amplitude form, the reconstructed complex amplitude is then divided by the complex amplitude form of the constructed tilt phase factor, and the phase information is extracted.
If the object optical field information obtained in the substep S31 is in the form of complex amplitude, U is seti，
AiIn order to be the intensity information,
is the phase;
the extraction phase is:
at a construction tilt phase factor of
Constructing complex amplitudes of the tilted phase factors by taking the intensity information as a mean value
In this way,
the phase may be extracted from the complex amplitude and subtracted, or the phase may be extracted after being written as the complex amplitude and subtracted, and the results are the same.
One sensor can reconstruct a phase information with the center sensor as a reference, the other sensors can reconstruct phase information with a tilt phase factor, the tilt phase factor is constructed according to the rotation amount, the constructed tilt phase factor is subtracted from the reconstructed phase, and thus the influence caused by the rotation is cancelled, namely the preprocessing in the substep S32.
S33, subtracting the preprocessed phases of the multiple sensor reconstructions pairwise to obtain phase difference results of multiple groups of sensors, namely phase difference results (or wrapping phase difference diagrams) of the multiple groups of sensors at different acquisition angles;
the phase difference results at different acquisition angles (rotation angles of the sensors) can be obtained by subtracting the mutual phase difference (subtraction) obtained by subtracting the tilt phase factor from the phase reconstructed by each sensor.
One sensor can reconstruct phase information, and the phase information of all the sensors is subtracted in pairs to obtain phase difference results of multiple groups of sensors.
Fig. 3 shows the numerical simulation results of the phase difference results at different acquisition angles after the reconstruction preprocessing for different acquisition angles of an elliptical hemisphere with the maximum height of 17.3mm by using 3 sensor acquisition systems.
Let the angle of illumination of object light S be 45 DEG, except that the detection plane of the central sensor is parallel to the object plane, where one sensor is rotated around the x-axis by theta1x0.15 deg. rotation about y-axis1yAt 0.15 °, the other sensor is rotated by θ about the x-axis2xAt-0.2 deg., rotation theta about y-axis2yAnd the distance between the object and the sensor surface (the distance between the object and each sensor surface is the same) d is 1200mm, and after the three sensors are arranged, the interference fields of the object light and the reference light are simultaneously collected by the three sensors, and the information is stored in the computing device. When reproduced with conjugate light of reference light and preprocessed, the resulting phase is
I.e. the phase extracted after reconstruction of the hologram recorded by each sensor is preprocessedThe phase obtained after the process. The serial numbers 0,1,2, … … i are the serial numbers of the sensors, and each sensor can obtain a preprocessed phase.
The phase difference between every two is expressed as:
wherein the content of the first and second substances,
in order to be the vector of the illumination,
respectively, the observation vectors of different sensors, the phase difference including the height h of the surfacez(x0,y0) Term proportional to hx(x0,y0)，hy(x0,y0) A proportional tilt component.
Since each sensor is directly opposite the object, the observation vector may be
Subscripts O of x and y correspond to objects, subscript B corresponds to sensors, and x, y and z are space coordinates. One for each observation vector.
And S34, unwrapping the wrapped phase difference diagram, and obtaining the surface topography of the three-dimensional object by applying a least square fitting method to unwrapped phases under different acquisition angle differences (sensor rotation angle differences corresponding to different wrapped phase difference diagrams) (as shown in FIG. 4).
Generally, the phase extraction is performed by using an arctangent function, which has a main value range of [ - π π ], a phase limited to- π to π, and a "truncated" phase, which is called "wrapped" or "wrapped".
The extracted phase is truncated, and the phase difference result obtained after subtraction is a discontinuous phase, so that the discontinuous phases need to be connected, and the process is called phase unwrapping.
The resulting phase difference is written in vectorized form (i.e. in the form of a system of equations at different rotation angle differences):
wherein:
solving according to a linear least square basic formula to obtain:
obtained hx(x0,y0)，hy(x0,y0)，hz(x0,y0) Wherein the component hx，hyTilt in x and y directions, h, respectively, caused by acquisition from different angleszThe components are projections in the Z-direction, i.e. surface topography information of the three-dimensional object.
Compared with the prior art, the method in the embodiment performs calibration by controlling the translation and rotation of the translation table and the rotation table through the computing equipment/controller, so that the detection surface of the sensor changes the angle, the normal of the detection surface of the sensor faces to the object through translation, the holograms recorded by the sensor under different acquisition angles are reconstructed, phase difference maps under different acquisition angle differences are obtained, and the three-dimensional morphology of the surface of the object to be detected is fitted by using a least square method. The acquisition angle of the sensor is reasonably set, so that the surface appearance of the three-dimensional object can be measured quickly and in real time with high precision.
EXAMPLE III
The embodiment of the invention also provides a processing method of the hologram, which comprises the following steps:
a1, the computing device acquires holographic information of the reference light and the reflected light which interfere.
In this embodiment, the holographic information includes phase information detected by a plurality of sensors, and the plurality of sensors have a certain rotation angle with respect to a central sensor, so that a tilted phase factor exists in the phase information.
And A2, reconstructing the holographic information to obtain the three-dimensional appearance of the object to be measured.
Specifically, the method can comprise the following steps:
a21, reconstructing holographic information based on conjugate light of reference light collected in the collection system to obtain complex amplitude object light field information for extracting phase information,
a22, preprocessing the object light field information based on predetermined parameter information and the angle information to offset a tilt phase factor in the angle information introduced when part of the sensors rotate, and obtaining a preprocessed phase of each sensor;
a23, subtracting the preprocessed phases of each sensor to obtain phase difference results of a plurality of groups of the sensors under the rotation angle;
and A24, unwrapping the phase difference result, and fitting the unwrapped phase by adopting a least square fitting method to obtain the surface appearance of the three-dimensional object of the object to be measured.
For a better understanding of the above, the following formula may be used for illustration.
According to the diffraction theoryIt is assumed that the object light field is O (x) when the laser is irradiated on the object to be measured0,y0) The distribution of the optical field of the object transmitted to the central sensor is U0(x, y), the optical field distribution of the reference light propagating to the sensor is R (x, y), the two beams interfere and are recorded on the sensor surface, and a digital hologram, namely holographic information, is formed. The light intensity distribution of the hologram can be expressed as:
in the formula, the light intensity of the hologram is divided into three parts, the first two terms are zero-order diffraction terms, the third term is an image of a grade "-1", and the fourth term is an image of a grade "+ 1".
In step A2, the numerical reconstruction process is to multiply the hologram H (x, y) by the conjugate light R of the reference light*(x, y) and then letting its wavefield H (x, y) R follow the law of diffraction*(x, y) is obtained by propagating in free space.
When the reconstruction distance is equal to the recording distance d, the reconstructed complex amplitude is, according to the fresnel diffraction integral formula:
in the formula (I), the compound is shown in the specification,
λ is the wavelength of light, k 2 π/λ is the wavenumber, and the intensity and phase can be given by:
I(x0,y0)＝|U(x0,y0)2
in step A22, the detecting surface is parallel to the object plane for the central sensor, and when the sensors at other positions have different viewing angles from the central sensor, their detecting surfaces are parallel to the object planeThe planes are no longer parallel to each other, which introduces a skew phase factor. Let the i (i ═ 0,1,2.. n) th sensor rotate around the x axis by an angle θ with respect to the center sensor (i ═ 0)ixRotation angle about y-axis of thetaiyThe amount of tilt T causedi(x0,y0) Expressed as:
Ti(x0,y0)＝x0sinθix+y0sinθiy；
at this time, the constructed tilt phase factor is:
during preprocessing, only the reconstructed phase is subtracted from the constructed tilt phase factor, or a complex amplitude division form is utilized, so that the influence caused by rotation is removed after the preprocessing;
in step A23, it is assumed that, after reproduction with conjugate light of reference light and preprocessing, the obtained phase is
The phase difference between two pairs can be expressed as:
the same principle is as follows:
wherein the content of the first and second substances,
respectively the view of different sensorsLooking at the vector, the phase difference including the height h from the surfacez(x0,y0) Term proportional to hx(x0,y0)，hy(x0,y0) Proportional inclination components, thereby obtaining a plurality of groups of phase difference maps under different acquisition angles.
In a24, the resulting phase difference is written in vectorized form:
wherein:
solving according to a linear least squares basic formula:
namely:
thus, h can be obtainedx(x0,y0)，hy(x0,y0)，hz(x0,y0) Wherein the component hx，hyTilt in x and y directions, h, respectively, caused by acquisition from different angleszThe components are projections in the Z-direction, i.e. surface topography information of the three-dimensional object.
Compared with the prior art, the method in the embodiment can realize high-precision, quick and real-time measurement of the surface topography of the three-dimensional object.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions.
It should be noted that in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The use of the terms first, second, third and the like are for convenience only and do not denote any order. These words are to be understood as part of the name of the component.
Furthermore, it should be noted that in the description of the present specification, the description of the term "one embodiment", "some embodiments", "examples", "specific examples" or "some examples", etc., means that a specific feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, the claims should be construed to include preferred embodiments and all changes and modifications that fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention should also include such modifications and variations.
Claims (10)
1. A digital holographic three-dimensional topography measurement device, comprising:
the device comprises a laser (1), a light splitting component, an object light path for irradiating an object to be detected, a reference light path for reference, a light path synthesis component and an acquisition system comprising a plurality of sensors;
the light splitting component splits the light emitted by the laser into two beams, the first beam of light irradiates an object to be measured through an object light path, and the object to be measured reflects the irradiated first beam of light; the second beam of light is transmitted by a reference light optical path as reference light, and the reference light transmitted by the reference light optical path and the reflected light of the object to be detected are converged in the optical path synthesis assembly and enter the detection surfaces of the plurality of sensors;
the detection surfaces of a plurality of sensors in the acquisition system record holographic information of reference light and reflected light which interfere in the light path synthesis assembly, and the acquisition system acquires the three-dimensional shape of the object to be detected according to the holographic information.
2. The digital holographic three-dimensional topography measuring device according to claim 1, wherein said light splitting assembly comprises: a beam splitter prism (2);
the object light path includes: the device comprises a first microscope objective (3), a first collimating lens (4) and a first plane reflector (5) which are arranged in sequence;
after a first beam of light split by the beam splitter prism (2) passes through the first microscope objective (3) and the first collimating lens (4), the collimated light irradiates an object to be measured through the first plane reflector (5);
the reference light path includes: a reflector (6), a second microscope objective (7), a second collimating lens (8) and a second plane reflector (9);
the second beam of light split by the beam splitting prism (2) passes through a second microscope objective (7) and a second collimating lens (8) after being reflected by a reflecting mirror (6), and the collimated light is reflected to a light path synthesis assembly through a second plane reflecting mirror (9);
the optical path synthesizing assembly includes: a beam combining mirror (10).
3. The digital holographic three-dimensional topography measuring device according to claim 2, characterized in that the acquisition system comprises: the device comprises a computing device and a plurality of sensors connected with the computing device, wherein each sensor is provided with a detection surface; the plurality of sensors includes a central sensor;
the object to be measured, the beam combiner and the central sensor are located on the same axis, more than two sensors are placed around the central sensor, the detection surfaces of all the sensors are not coplanar with each other, and the normals of the detection surfaces of all the sensors face the object to be measured.
4. The digital holographic three-dimensional topography measurement device according to claim 3, wherein said acquisition system further comprises: an electrically controlled rotary table and a translation table for supporting each sensor;
the electric control rotating platform is used for adjusting an included angle between a detection surface of the sensor and a detection surface of the central sensor, and the translation platform is used for adjusting the translation amount of the detection surface of the sensor;
the electric control rotating table and the translation table are respectively connected with the computing equipment by respective driving systems.
5. The digital holographic three-dimensional topography measurement device according to claim 4, wherein said sensor comprises: a CCD or a CMOS.
6. A measuring method based on the digital holographic three-dimensional shape measuring device of any one of claims 1 to 5, characterized by comprising the following steps:
s1, adjusting the detection surfaces of the sensors in the acquisition system, and recording the angle information of the detection surface of each adjusted sensor relative to the central sensor;
s2, starting the laser to acquire holographic information of the interfered reference light and the reflected light;
and S3, reconstructing the holographic information to obtain the three-dimensional shape of the object to be measured.
7. The measurement method according to claim 6, wherein the S3 includes:
s31, reconstructing holographic information based on conjugate light of reference light collected in a collection system to obtain object light field information in a complex amplitude form for extracting phase information;
s32, preprocessing the object light field information based on the predetermined parameter information and the angle information to offset the inclined phase factor in the angle information introduced when part of the sensors rotate, and obtaining the preprocessed phase of each sensor;
s33, subtracting the preprocessed phases of each sensor to obtain phase difference results of a plurality of groups of sensors;
and S34, unwrapping the phase difference result, and fitting the unwrapped phase by adopting a least square fitting method to obtain the surface appearance of the three-dimensional object of the object to be measured.
8. The measurement method according to claim 7, wherein the S32 includes:
s321, acquiring a tilt phase factor of any sensor of the non-central sensors based on predetermined parameter information;
specifically, let the i (i ═ 1,2.. n) th sensor rotate by an angle θ around the x axis as compared with the center sensor (i ═ 0)ixRotation angle about y-axis of thetaiyThe amount of tilt T causedi(x0,y0) Expressed as:
Ti(x0,y0)＝x0sinθix+y0sinθiy；
at this time, the constructed tilt phase factor is:
s322, preprocessing the object light field information, including:
subtracting the phase in the reconstructed object optical field information from the tilted phase factor,
alternatively, the first and second electrodes may be,
the constructed tilt phase factor is written in complex amplitude form, and then the reconstructed object optical field complex amplitude is divided by the complex amplitude tilt phase factor to extract the phase information.
9. The measurement method according to claim 7, wherein the S33 includes:
the phase obtained after the pretreatment in S33 is
Then, the phase difference between two pairs is expressed as:
wherein the content of the first and second substances,
in order to be the vector of the illumination,
respectively, the observation vectors of different sensors, the phase difference including the height h of the surfacez(x0,y0) Term proportional to hx(x0,y0)，hy(x0,y0) A proportional tilt component.
10. The measurement method according to claim 7, wherein S34 includes:
the phase difference result obtained in S33 is written in vectorized form:
wherein:
fitting the unwrapped phases by a least square fitting method:
obtained hx(x0,y0)，hy(x0,y0)，hz(x0,y0) Wherein the component hx，hyTilt in x and y directions, h, respectively, caused by acquisition from different angleszThe components are projections in the Z-direction, i.e. surface topography information of the three-dimensional object.
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