WO2018103695A1 - 一种大景深可编程模拟光栅生成方法 - Google Patents

一种大景深可编程模拟光栅生成方法 Download PDF

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WO2018103695A1
WO2018103695A1 PCT/CN2017/115010 CN2017115010W WO2018103695A1 WO 2018103695 A1 WO2018103695 A1 WO 2018103695A1 CN 2017115010 W CN2017115010 W CN 2017115010W WO 2018103695 A1 WO2018103695 A1 WO 2018103695A1
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grating
laser
laser beam
galvanometer
mems scanning
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PCT/CN2017/115010
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English (en)
French (fr)
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周翔
杨涛
金瑞
刘涛
马力
李欢欢
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西安知象光电科技有限公司
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Publication of WO2018103695A1 publication Critical patent/WO2018103695A1/zh
Priority to US16/776,368 priority Critical patent/US11327297B2/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
    • G01B11/2536—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object using several gratings with variable grating pitch, projected on the object with the same angle of incidence
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems
    • G02B26/101—Scanning systems with both horizontal and vertical deflecting means, e.g. raster or XY scanners
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G01B11/25—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures by projecting a pattern, e.g. one or more lines, moiré fringes on the object
    • G01B11/2518—Projection by scanning of the object
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
    • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/0075—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 with means for altering, e.g. increasing, the depth of field or depth of focus
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/30—Collimators

Definitions

  • the invention belongs to the field of optical detection, and relates to a method for generating a grating, in particular to a method for generating a programmable infrared grating with a large depth of field.
  • 3D measurement technology As a bridge between the real world and the virtual digital world, 3D measurement technology has become more and more important. It is widely used in many industries such as industrial testing, medical health, digital entertainment, e-commerce, and cultural relics protection.
  • Optical three-dimensional measurement has become the most important technology in the field of three-dimensional detection due to its advantages of non-contact, high precision and high speed.
  • Optical 3D measurement can be divided into active and passive.
  • the passive measurement method is represented by stereo vision.
  • the stereo vision technology system has a simple structure and low cost.
  • there is a bottleneck of "matching difficulty" and the operation is huge and the robustness is poor.
  • Active three-dimensional measurement techniques include time-of-flight methods, structured light projection methods, and interferometry methods. Among them, the structure light projection method is simple, the cost is relatively low, and the precision is high, so it is the most widely used.
  • the structured light projection method generally projects a specific coded light onto the surface of the object to be measured, and uses a camera to capture a modulated signal of the coded light on the surface of the object, further demodulates the modulated signal related to the depth information, and finally obtains a three-dimensional surface of the object after calibration.
  • Morphology The projected coded light typically includes a sine-cosine raster map, a Gray code, a color code, a random shape code, and the like. Among them, the sine-cosine grating projection measurement method is the most commonly used because of its phase measurement method, high precision and good robustness.
  • a projection pattern such as a Roach grating is mainly produced by etching on a material such as glass in the early stage.
  • digital projection measurement technology including LCD (Liquid Crystal Display) technology, DLP (Digital Light Processing) technology and LCOS (Liquid Crystal On Silicon). )technology.
  • the digital signal projected by the digital light technology onto the surface of the object has the advantage of signal programming. This advantage makes time domain de-wrapping technology possible, and can improve the measurement accuracy by projecting different coded signals onto the surface of the object.
  • the disadvantage of digital light technology is the limitation of resolution. Usually the resolution is 1280x800. The high resolution digital projection chip is very expensive.
  • the physical grating is projected onto the surface of the object as an analog signal, that is, a continuous signal, so the resolution is high (it can be considered as an infinite resolution).
  • the physical grating has the disadvantage that the projection pattern is fixed and the use is not flexible.
  • both the digital light projection technology and the analog pattern of the physical raster projection are images of the negative film, which is an imaging relationship, and therefore there is a limitation of depth of field. The range of 3D measurements is greatly limited.
  • the method uses a laser beam as a light source and is reflected by a two-dimensional MEMS scanning galvanometer to the surface of the object to be measured, and the two-dimensional MEMS scanning galvanometer performs two-dimensional scanning under the driving current excitation in both directions.
  • the intensity of the laser is modulated by sine (or cosine).
  • sine or cosine
  • a large depth of field programmable analog grating generation method according to the following steps: a laser beam emitted by a laser, after being focused and collimated by a collimating lens, obtains a collimated Gaussian laser beam that meets the requirements; the laser beam undergoes a specular reflection and wears
  • the circular aperture aperture is incident on the MEMS galvanometer; the beam is reflected by the MEMS galvanometer to the surface of the object to be measured; the laser sinusoidally modulates the brightness of the laser beam under the control of the sinusoidal current signal generated by the driving plate; the MEMS galvanometer is driving Under the excitation of the driving signal generated by the board, the two-dimensional rotation is performed, thereby driving the laser beam to scan and generating a raster image.
  • the first step is to set the optical parameters of the system: determine the working range of the grating, determine the maximum working distance L 2 and the minimum working distance L 1 according to the working distance of the grating; the maximum spot ⁇ max of ⁇ L in the depth of field; the row of the single frame raster image scanning
  • the numbers M, M are determined by the characteristics of the laser beam;
  • the second step is to generate a MEMS galvanometer driving signal: 1) MEMS scanning galvanometer fast axis driving signal; 2) MEMS scanning galvanometer slow axis driving signal; 3) laser driving signal;
  • the third step is to generate a grating: using the galvanometer driving signal generated in the second step, driving the MEMS galvanometer to perform two-dimensional scanning; using the laser driving signal generated in the second step to drive the laser to generate a laser beam continuously modulated by the light intensity; The beam is irradiated onto the surface of the galvanometer at a certain angle of incidence, and then reflected by the galvanometer to the surface of the object to form an analog grating light field continuously modulated by the intensity of the light; the frequency and phase of the laser driving signal are changed; and gratings of different pitches and phases are obtained.
  • the MEMS galvanometer fast axis driving signal is a current signal of a sinusoidal waveform or a cosine waveform current signal, and its frequency f x is equal to the resonant frequency f of the fast axis direction of the MEMS scanning galvanometer, and its peak-to-peak I x peak is determined by the MEMS The parameters of the galvanometer are determined.
  • the driving signal of the laser is a sinusoidal current signal or a cosine current signal.
  • the frequency of the signal determines the width of the projected sinusoidal current signal or the cosine current signal grating.
  • the highest frequency f LD is determined by the characteristics of the laser beam.
  • the highest frequency f LD is calculated as follows:
  • the grating of the Gaussian beam scanned at different distances is equivalent to the ideal grating image filtered by a linear Gaussian low-pass filter. For simplicity, only one direction is considered, and the Fourier transform of the laser Gaussian spot intensity distribution is expressed as:
  • ⁇ (L 0 ) is the Gaussian beam waist radius at the projection surface L 0
  • e is a natural constant
  • u is a frequency
  • ⁇ is the impact function
  • B is the contrast of the trigonometric function
  • u 0 is the reference frequency corresponding to the trigonometric function
  • spatial filtering is equivalent to frequency domain multiplication, ie:
  • the Gaussian laser beam emitted by the laser passes through the collimating lens, is incident on the MEMS scanning galvanometer, and is reflected to the surface of the object.
  • the focal plane of the Gaussian beam is at L 0 , and the designed depth of field is ⁇ L.
  • the beam is calculated according to the ABCD matrix. after the lens spot size, the spot size of the maximum working distance of the [omega] L 2 2, the minimum spot size at the working distance L 1 is a [omega] 1, constrained by the following formula 1-1, L 1 and L finalized 2;
  • the optical resolution is determined by the spot characteristics and the angle of the galvanometer.
  • the rotation angle of the galvanometer fast and slow axis is ⁇ x and ⁇ y , and the calculation of the number of rows M satisfies the formula 1-2;
  • the following steps are performed: the laser beam emitted by the laser is focused and collimated by the collimating lens, and a collimated Gaussian laser beam satisfying the first design requirement is obtained; in order to reduce the optical path volume, the laser beam passes through a mirror surface.
  • the reflection is incident on the MEMS galvanometer through the aperture of the circular aperture; the effect of the aperture is to remove stray light from the periphery of the beam and improve the shape quality of the spot; the beam is reflected by the MEMS galvanometer to the surface of the object to be measured; the laser is generated on the driver board Under the control of the sinusoidal current signal, the intensity of the laser beam is sinusoidal or cosine modulated; the MEMS galvanometer is excited by the driving signal generated by the driving plate to perform two-dimensional rotation, thereby driving the laser beam to scan and generate a grating.
  • the invention utilizes the scanning of the laser beam to generate the grating.
  • the depth of field of the generated grating is expanded by more than 10 times, and the measurement range is greatly improved; the grating produced by the invention is programmable.
  • the spatially continuous distribution of the analog grating reduces the discretization rounding error compared to the digital light technique.
  • the resulting grating has a small minimum pitch. Can greatly improve the accuracy of 3D measurement.
  • FIG. 1 is a working principle diagram of the present invention
  • FIG. 2 is a timing relationship diagram of a line synchronization signal according to the present invention.
  • FIG. 3 is a structural diagram of the system of the present invention.
  • Figure 4 is a schematic view of the contrast within the working range of the grating of the present invention.
  • the first step is to design system operating parameters.
  • the maximum working distance L 2 and the minimum working distance L 1 are determined according to the working distance of the grating; the maximum spot ⁇ max of ⁇ L in the depth of field; the number of lines M, M of the single-frame raster image is determined by the characteristics of the laser beam.
  • a drive signal is generated.
  • MEMS scanning galvanometer fast axis drive signal which is a sinusoidal (or cosine) waveform current signal whose frequency f x is equal to the resonant frequency f of the MEMS scanning galvanometer fast axis direction, and its peak-to-peak I x peak and peak is determined by MEMS The parameters of the galvanometer are determined.
  • the drive signal of the laser which is a sinusoidal (cosine) current signal. Its highest frequency f LD is determined by the characteristics of its laser beam, and its peak-to-peak and bias current are determined by the characteristics of the laser.
  • the above three driving signals are all analog signals.
  • the third step is to generate a raster.
  • the MEMS galvanometer is driven to perform two-dimensional scanning using the galvanometer drive signal generated in the second step.
  • the laser driving signal generated in the second step is used to drive the laser to generate a laser beam continuously modulated by the intensity of the light.
  • the laser beam is irradiated onto the surface of the galvanometer at a certain angle of incidence, and then reflected by the galvanometer to the surface of the object to form an analog grating light field continuously modulated by the intensity of light.
  • the first step is to design system parameters.
  • the Gaussian laser beam emitted from the laser 11 passes through the collimator lens 12, is incident on the MEMS scanning galvanometer 13, and is reflected to the surface of the object.
  • the focal plane of the Gaussian beam is at L 0 and the design depth of field is ⁇ L.
  • the optical resolution is determined by the spot characteristics and the angle of the galvanometer.
  • the corners of the galvanometer fast and slow axes are ⁇ x and ⁇ y .
  • the calculation of the number of rows M satisfies Equation 1-2.
  • the drive signal is a current signal whose current and voltage characteristics are determined by the electrical characteristics of the MEMS galvanometer used. Its frequency f x is equal to the resonant frequency f of the fast axis direction of the MEMS scanning galvanometer.
  • the drive signal is a sinusoidal (or cosine) current signal. Its current and voltage characteristics are determined by the electrical characteristics of the laser.
  • the frequency of the signal determines the width of the projected sine (or cosine) grating, which affects the measurement accuracy.
  • the highest frequency calculation method is as follows:
  • the grating of the Gaussian beam scanned at different distances corresponds to an ideal raster image filtered by a linear Gaussian low-pass filter.
  • the laser Gaussian spot has a certain size, it will have a blur effect on the raster image. Its function is equivalent to an ideal raster image through a linear Gaussian low-pass filter.
  • the Fourier transform of the laser Gaussian spot intensity distribution can be expressed as:
  • ⁇ (L 0 ) is the Gaussian beam waist radius at the projection plane L 0 .
  • the Fourier transform of the ideal grating is
  • spatial filtering is equivalent to frequency domain multiplication, ie:
  • the third step is to generate a raster.
  • the laser (which can be multiple lasers in different bands) emits a laser beam that is focused and collimated by a collimating lens to obtain a collimated Gaussian laser beam that meets the requirements of the first step.
  • the laser beam is specularly reflected and incident on the MEMS galvanometer through a circular aperture stop.
  • the role of the aperture is to remove stray light from the periphery of the beam and improve the quality of the spot shape.
  • the beam is reflected by the MEMS galvanometer to the surface of the object being measured.
  • the laser sinusoidally (or cosine) modulates the intensity of the laser beam under the control of a sinusoidal current signal generated by the driver board.
  • the MEMS galvanometer rotates under the excitation of the driving signal generated by the driving board to perform two-dimensional rotation, thereby driving the laser beam to scan and generate a grating.
  • the aspherical lens can correct the distortion of the raster image to ensure an undistorted high quality raster image.
  • the program control of the grating pitch and phase can be completed. In this method, since the divergence angle of the laser beam is small, the grating frequency is estimated in the second step, so the obtained grating has a good contrast in the working range, as shown in FIG.

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Abstract

一种大景深可编程模拟光栅生成方法，激光器（2）发出的激光光束（9），经过准直透镜（3）聚焦和准直之后，得到了满足要求的准直高斯激光光束（9）；激光光束（9）经过一次镜面（4）反射，穿过圆孔光阑（8）入射到MEMS振镜（5）；光束经过MEMS振镜（5）反射到被测物体表面；激光器（2）在驱动板（1）生成的正弦电流信号的控制下，对激光光束（9）的亮度进行正弦调制；MEMS振镜（5）在驱动板（1）生成的驱动信号激励下，做二维的转动，从而带动激光光束（9）进行扫描，产生光栅图（7）。改变激光器驱动信号的周期和相位，以得到不同周期和相位的光栅图（7）。该方法产生的光栅兼具数字光栅可编程优势以及物理光栅高分辨率的优势，所产生的光栅的景深扩大10倍以上，测量范围得到了大幅度的提升。

Description

一种大景深可编程模拟光栅生成方法 技术领域：
本发明属于光学检测领域，涉及一种光栅的产生方法，特别是一种大景深可编程模拟光栅的生成方法。
背景技术：
三维测量技术作为沟通现实世界和虚拟的数字世界的桥梁，其重要作用越来越凸显。被广泛的应用于工业检测、医疗健康、数字娱乐、电子商务、文物保护等诸多行业。光学三维测量由于具有非接触、精度高、速度快的优势，已经发展成为三维检测领域最重要的技术。光学三维测量又可分为主动式和被动式两种。被动式测量方法以立体视觉为代表。但立体视觉技术系统结构简单，成本低。但存在着“匹配难”的瓶颈，而且运算量巨大，鲁棒性差的缺点。主动三维测量技术包括飞行时间法、结构光投影法、干涉法等。其中，由于结构光投影法系统简便，成本比较低，而且精度较高，因此应用最为广泛。
结构光投影法，通常向被测物体表面投影特定的编码光，利用相机拍摄编码光在物体表面的调制信号，在进一步解调得到和深度信息有关的调制信号，最后经过标定得到物体表面的三维形貌。投射的编码光通常包括：正余弦光栅图，格雷码，颜色编码，随机形状编码等。其中正余弦光栅图投影测量法由于是相位测量法，精度较高、鲁棒性好，最为常用。在投射方式上，早期主要通过在玻璃等材质上刻蚀来产生投影图案，如罗奇光栅。随着半导体工业的飞速发展，20世纪90年代先后出现了多种数字化投影器件，如数字光投影测量技术包括LCD(Liquid Crystal Display)技术，DLP(Digital Light Processing)技术和LCOS(Liquid Crystal On Silicon)技术。数字光技术向物体表面投射的经过数字化的信号，因此具有信号可编程的优势，这种优势使得时域去包裹技术成为可能，并能通过向物体表面投影不同的编码信号来提高测量精度。数字光技术的缺点在于存在分辨率的限制，通常分辨率在1280x800的水平，高分辨率的数字投影芯片的价格非常的昂贵。通过物理光栅向物体表面投影的则是模拟信号，即连续信号，因此分辨率很高(可认为是无限大的分辨率)。但物理光栅的缺点在于投影图案固定，使用不灵活。此外，无论数字光投影技术还是物理光栅投影的模拟图案，都是对底片的呈像，是一种成像关系，因此都存在着景深的限制。大大限制了三维测量的范围。
发明内容：
本发明的目的在于提供一种大景深可编程的模拟光栅产生方法。该方法以激光光束作为光源，通过二维MEMS扫描振镜反射到被测物体表面，二维MEMS扫描振镜在快慢两个方向的驱动电流激励下进行二维扫描。同时，激光器的光强被正弦(或余弦)调制。从而在被测物的表面形成连续分布的正(或余弦)弦光场。
本发明的目的是通过以下技术方案来解决的：
一种大景深可编程模拟光栅生成方法，按照如下步骤：激光器发出的激光光束，经过准直透镜聚焦和准直之后，得到了满足要求的准直高斯激光光束；激光光束经过一次镜 面反射，穿过圆孔光阑入射到MEMS振镜；光束经过MEMS振镜反射到被测物体表面；激光器在驱动板生成的正弦电流信号的控制下，对激光光束的亮度进行正弦调制；MEMS振镜在驱动板生成的驱动信号激励下，做二维的转动，从而带动激光光束进行扫描，产生光栅图。
具体步骤如下：
第一步，设置系统光学参数：确定光栅的工作范围，根据光栅的工作距离确定最大工作距离L 2、最小工作距离L 1；景深范围内ΔL的最大光斑ω max；单帧光栅图扫描的行数M，M由激光光束特性决定；
第二步，生成MEMS振镜驱动信号：1)MEMS扫描振镜快轴驱动信号；2)MEMS扫描振镜慢轴驱动信号；3)激光器的驱动信号；
第三步，生成光栅：利用第二步中产生的振镜驱动信号，驱动MEMS振镜进行二维扫描；利用第二步中产生的激光器驱动信号驱动激光器产生光强连续调制的激光光束；激光光束以一定的入射角照射到振镜表面，再经过振镜反射到物体表面，形成光强连续调制的模拟光栅光场；通过改变激光器驱动信号频率、相位；得到不同栅距、相位的光栅。
所述MEMS振镜快轴驱动信号，是一种正弦波形的电流信号或余弦波形的电流信号，其频率f x等于MEMS扫描振镜快轴方向谐振频率f，其峰峰值I x峰峰由MEMS振镜的参数确定。
所述MEMS扫描振镜慢轴驱动信号，是一种正弦波形的电流信号、余弦波形的电流信号或者三角波形的电流信号，其频率为f y＝f x/M，其峰峰值I y峰峰由MEMS振镜的参数确定。
所述激光器的驱动信号，是一种正弦电流信号或余弦电流信号，信号的频率决定了投影正弦电流信号或余弦电流信号光栅的宽度，其最高频率f LD由其激光光束的特性决定。
所述最高频率f LD计算方法如下：
高斯光束的在不同距离处扫描得到的光栅，相当于理想光栅图通过一个线性高斯低通滤波器滤波，简单起见，只考虑一个方向，激光高斯光斑光强分布的傅立叶变换表示为：
Figure PCTCN2017115010-appb-000001
其中ω(L 0)为投影面L 0处的高斯光斑束腰半径，e是自然常数，u为频率；
理想光栅的傅立叶变换为：
F(u)＝δ(u)+0.5×B[δ(u+u 0)+δ(u-u 0)]；
其中δ为冲击函数，B为三角函数的对比度，u 0为三角函数对应的基准频率；
根据卷积定理，空域滤波等价于频域相乘，即：
F(u)H(u)＝H(u)+0.5×B[H(u+u 0)+H(u-u 0)]
假设光栅图的对比度下降到原来的1/K，会模糊到严重影响测量精度程度，则H(u)＝H(0)/K时，解出对应的u即为光栅不模糊的最大频率f0；同理计算L1和L2处最大频率f 1和f 2；激光器驱动信号的的最大频率f LD＝max(f 1，f 2)。
设置系统光学参数，按照如下步骤：
1)确定光栅的工作范围：
激光器发出的高斯激光光束经过准直透镜后，入射到MEMS扫描振镜上，再反射到物体表面，高斯光束的聚焦面在L 0处，设计景深为ΔL，根据ABCD矩阵计算得光束在穿过透镜后的光斑大小，最大工作距离L 2处光斑大小ω 2，最小工作距离L 1处光斑大小为ω 1，通过 下式1-1约束，最终确定L 1和L 2；
Figure PCTCN2017115010-appb-000002
2)计算光学分辨率：
光学分辨率由光斑特性和振镜的转角确定。振镜快慢轴的转角为θ x和θ y，行数M的计算满足式1-2；
Figure PCTCN2017115010-appb-000003
生成光栅，按照如下步骤：激光器，发出的激光光束，经过准直透镜聚焦和准直之后，得到了满足第一步设计要求的准直高斯激光光束；为了减小光路体积，激光光束经过一次镜面反射，穿过圆孔光阑入射到MEMS振镜；光阑的作用是去除光束外围的杂散光，并改善光斑形状质量；光束经过MEMS振镜反射到被测物体表面；激光器在驱动板生成的正弦电流信号的控制下，对激光光束的光强进行正弦、或余弦调制；MEMS振镜在驱动板生成的驱动信号激励下，做二维的转动，从而带动激光光束进行扫描，产生光栅。
有益效果：
本发明利用激光光束的扫描产生光栅，相比数字光和物理光栅技术，所产生的光栅的景深扩大了10倍以上，测量范围得到了大幅度的提升；本发明所产生的光栅是可编程的空间连续分布的模拟光栅，相比数字光技术，减小了离散化的舍入误差。此外，所生成的光栅最小栅距很小。能大幅度提高三维测量精度。
附图说明：
图1为本发明的工作原理图；
图2为本发明行同步信号的时序关系图；
图3为本发明的系统结构图；
图4为本发明的光栅工作范围内对比度示意图。
其中：1为驱动板；2为激光器；3为准直透镜；4为镜面；5为MEMS振镜；6为非球面透镜；7为光栅图；8为圆孔光阑；9为激光光束；10为电脑。
具体实施方式：
下面具体结合附图对本发明做详细描述。
技术方案为：
第一步，设计系统工作参数。根据光栅的工作距离确定最大工作距离L 2，最小工作距离L 1；景深范围内ΔL的最大光斑ω max；单帧光栅图扫描的行数M，M由激光光束特性决定。
第二步，生成驱动信号。涉及的驱动信号有三种。1)MEMS扫描振镜快轴驱动信号，这是一种正弦(或余弦)波形的电流信号，其频率f x等于MEMS扫描振镜快轴方向谐振频率f， 其峰峰值I x峰峰由MEMS振镜的参数确定。2)MEMS扫描振镜慢轴驱动信号，这是一种正弦(余弦)或者三角波电流信号。其频率为f y＝f x/M，其峰峰值I y峰峰由MEMS振镜的参数确定。3)激光器的驱动信号，这是一种正弦(余弦)电流信号。其最高频率f LD由其激光光束的特性决定，其峰峰值和偏置电流均由激光器的特性决定。上述三种驱动信号均为模拟信号。
第三步，生成光栅。利用第二步中产生的振镜驱动信号，驱动MEMS振镜进行二维扫描。利用第二步中产生的激光器驱动信号驱动激光器产生光强连续调制的激光光束。激光光束以一定的入射角照射到振镜表面，再经过振镜反射到物体表面，形成光强连续调制的模拟光栅光场。通过改变激光器驱动信号频率、相位，就可以得到不同栅距、相位的光栅。
具体包括以下步骤：
第一步，设计系统参数。
3)确定光栅的工作范围。
如图1，激光器11发出的高斯激光光束经过准直透镜12后，入射到MEMS扫描振镜13上，再反射到物体表面。高斯光束的聚焦面在L 0处，设计景深为ΔL。根据ABCD矩阵计算可得光束在穿过透镜后的光斑大小，最大工作距离L 2处光斑大小ω 2，最小工作距离L 1处光斑大小为ω 1，通过下式1-1约束，最终确定L 1和L 2。
Figure PCTCN2017115010-appb-000004
4)计算光学分辨率。
光学分辨率由光斑特性和振镜的转角确定。振镜快慢轴的转角为θ x和θ y。行数M的计算满足式1-2。
Figure PCTCN2017115010-appb-000005
第二步，生成驱动信号。
1)MEMS扫描振镜快轴驱动信号。
该驱动信号是一种电流信号，信号的电流和电压特性由所使用的MEMS振镜的电学特性决定。其频率f x等于MEMS扫描振镜快轴方向谐振频率f。
2)MEMS扫描振镜慢轴驱动信号。该驱动信号是一种电流信号，一般为正弦或者三角波信号，其电流和电压特性由所使用的MEMS振镜的电学特性决定。其频率为f y＝f x/M。
3)激光器的驱动信号。
该驱动信号是一种正弦(或余弦)电流信号。其电流和电压特性由激光器的电学特性决定。信号的频率决定了投影正弦(或余弦)光栅的宽度，从而影响测量精度。其最高频率计算方法如下：
高斯光束的在不同距离处扫描得到的光栅，相当于理想光栅图通过一个线性高斯低通滤波器滤波。在MEMS振镜扫描过程中，由于激光高斯光斑具有一定的大小，会对光栅图产生模糊效应。其作用相当于理想光栅图通过一个线性高斯低通滤波器。简单起见，只考虑 X方向，激光高斯光斑光强分布的傅立叶变换可表示为：
Figure PCTCN2017115010-appb-000006
其中ω(L 0)为投影面L 0处的高斯光斑束腰半径。理想光栅的傅立叶变换为
F(u)＝δ(u)+0.5×B[δ(u-u 0)+δ(u-u 0)]；
根据卷积定理，空域滤波等价于频域相乘，即：
F(u)H(u)＝H(0)+0.5×B[H(u-u 0)+H(u-u 0)]
假设光栅图的对比度下降到原来的1/e，会模糊到严重影响测量精度程度，则H(u-u 0)＝H(0)/e时，解出对应的u 0＝1/[πω(L 0)]为光栅不模糊的最大频率f 0。同理计算L1和L2处最大频率f 1和f 2。
激光器驱动信号的的最大频率f LD＝max(f 1，f 2)。
信号的时序关系
完成一帧光栅图投影，MEMS振镜快轴、慢轴驱动信号，以及激光器驱动信号，行同步信号的时序关系如图2所示。
第三步，生成光栅。
如图3。激光器(可以是不同波段的多个激光器)，发出的激光光束，经过准直透镜聚焦和准直之后，得到了满足第一步设计要求的准直高斯激光光束。为了减小光路体积，激光光束经过一次镜面反射，穿过圆孔光阑入射到MEMS振镜。光阑的作用是去除光束外围的杂散光，并改善光斑形状质量。光束经过MEMS振镜反射到被测物体表面。激光器在驱动板生成的正弦电流信号的控制下，对激光光束的光强进行正弦(或余弦)调制。MEMS振镜在驱动板生成的驱动信号激励下，做二维的转动，从而带动激光光束进行扫描，产生光栅。非球面透镜的可以对光栅图进行畸变校正，确保得到无畸变的高质量光栅图。通过改变激光器驱动信号的频率和相位，就可以完成对光栅栅距、相位的编程控制。此方法中，由于激光光束的发散角较小，在第二步中对光栅频率进行了估计，所以所得到的光栅在工作范围内均具有很好的对比度，如图4。
以上所述，仅是本发明的较佳实施例而已，并非对本发明作任何形式上的限制，虽然本发明已以较佳实施例揭露如上，然而并非用以限定本发明，任何熟悉本专业的技术人员，在不脱离本发明技术方案范围内，当可利用上述揭示的方法及技术内容作出些许的更动或修饰为等同变化的等效实施例，但凡是未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所作的任何简单修改、等同变化与修饰，仍属于本发明技术方案的范围内。

Claims (8)

  1. 一种大景深可编程模拟光栅生成方法，其特征在于，按照如下步骤：激光器发出的激光光束，经过准直透镜聚焦和准直之后，得到了满足要求的准直高斯激光光束；激光光束穿过光阑入射到MEMS扫描振镜；光束经过MEMS扫描振镜反射到被测物体表面；激光器在驱动板生成的正弦电流信号的控制下，对激光光束的亮度进行正弦调制；MEMS扫描振镜在驱动板生成的驱动信号激励下，做二维的转动，从而带动激光光束进行扫描，产生光栅图；改变激光器驱动信号的周期和相位，以得到不同周期和相位的光栅图。
  2. 如权利要求1所述大景深可编程模拟光栅生成方法，其特征在于：
    第一步，设置系统光学参数：确定光栅的工作范围，根据光栅的工作距离确定最大工作距离L 2，最小工作距离L 1；景深范围内ΔL的最大光斑半径ω max；单帧光栅图扫描的行数M；
    第二步，生成驱动信号：根据第一步确定的系统参数计算MEMS扫描振镜和激光器驱动信号的参数，并生成驱动信号。1)MEMS扫描振镜快轴驱动信号；2)MEMS扫描振镜慢轴驱动信号；3)激光器的驱动信号。
    第三步，生成光栅：利用第二步中产生的振镜驱动信号，驱动MEMS扫描振镜进行二维扫描；利用第二步中产生的激光器驱动信号驱动激光器产生光强连续调制的激光光束；激光光束以一定的入射角照射到振镜表面，再经过振镜反射到物体表面，形成光强连续调制的模拟光栅光场；通过改变激光器驱动信号频率、相位；得到不同栅距、相位的光栅。
  3. 如权利要求2所述大景深可编程模拟光栅生成方法，其特征在于：
    所述MEMS扫描振镜快轴驱动信号，是一种正弦波形的电流信号或余弦波形的电流信号，其频率f x等于MEMS扫描振镜快轴方向谐振频率f，其峰峰值I x峰峰由MEMS扫描振镜的参数确定。
  4. 如权利要求2所述大景深可编程模拟光栅生成方法，其特征在于：
    所述MEMS扫描振镜慢轴驱动信号，是一种正弦波形的电流信号、余弦波形的电流信号或者三角波形的电流信号，其频率为f y＝f x/M，其峰峰值I y峰峰由MEMS扫描振镜的参数确定。
  5. 如权利要求2所述大景深可编程模拟光栅生成方法，其特征在于：
    所述激光器的驱动信号，是一种正弦电流信号或余弦电流信号，信号的频率决定了投影正弦电流信号或余弦电流信号光栅的宽度，其最高频率f LD由其激光光束的特性决定。
  6. 如权利要求5所述大景深可编程模拟光栅生成方法，其特征在于，所述最高频率f LD计算方法如下：
    高斯光束的在不同距离处扫描得到的光栅，相当于理想光栅图通过一个线性高斯低通滤波器滤波，简单起见，只考虑一个方向，激光高斯光斑光强分布的傅立叶变换表示为：
    Figure PCTCN2017115010-appb-100001
    其中ω(L 0)为投影面L 0处的高斯光斑束腰半径，e是自然常数，u为频率；
    理想光栅的傅立叶变换为：
    F(u)＝δ(u)+0.5×B[δ(u+u 0)+δ(u-u 0)]；
    其中δ为冲击函数，B为三角函数的对比度，u 0为三角函数对应的基准频率；
    根据卷积定理，空域滤波等价于频域相乘，即：
    F(u)H(u)＝H(u)+0.5×B[H(u+u 0)+H(u-u 0)]
    假设光栅图的对比度下降到原来的1/K，会模糊到严重影响测量精度程度，则H(u)＝H (0)/K时，解出对应的u即为光栅不模糊的最大频率f0；同理计算L1和L2处最大频率f 1和f 2；激光器驱动信号的的最大频率f LD＝max(f 1，f 2)。
  7. 如权利要求2所述大景深可编程模拟光栅生成方法，其特征在于，设置系统光学参数，按照如下步骤：
    1)确定光栅的工作范围：
    激光器发出的高斯激光光束经过准直透镜后，入射到MEMS扫描振镜上，再反射到物体表面，高斯光束的聚焦面在L 0处，设计景深为ΔL，根据ABCD矩阵计算得光束在穿过透镜后的光斑大小，最大工作距离L 2处光斑大小ω 2，最小工作距离L 1处光斑大小为ω 1，通过下式1-1约束，最终确定L 1和L 2；
    Figure PCTCN2017115010-appb-100002
    2)计算光学分辨率：
    光学分辨率由光斑特性和振镜的转角确定。振镜快慢轴的转角为θ x和θ y，行数M的计算满足式1-2；
    Figure PCTCN2017115010-appb-100003
  8. 如权利要求2所述大景深可编程模拟光栅生成方法，其特征在于，生成光栅，按照如下步骤：激光器，发出的激光光束，经过准直透镜聚焦和准直之后，得到了满足第一步设计要求的准直高斯激光光束；为了减小光路体积，激光光束经过一次镜面反射，穿过圆孔光阑入射到MEMS扫描振镜；光阑的作用是去除光束外围的杂散光，并改善光斑形状质量；光束经过MEMS扫描振镜反射到被测物体表面；激光器在驱动板生成的正弦电流信号的控制下，对激光光束的光强进行正弦、或余弦调制；MEMS扫描振镜在驱动板生成的驱动信号激励下，做二维的转动，从而带动激光光束进行扫描，产生光栅。
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