CN1186671C - Production method and device of projection structural light - Google Patents

Abstract

The invention discloses a method and a device for generating projection structured light. For the beam of coherent light source, through beam splitting, diffraction, direction fine-tuning, spatial filtering, beam spacing transformation, focusing and amplification process, the method projects static fringe structured light with sinusoidal distribution of interference fringe intensity on the scene. It is characterized in that the two beams of parallel light after beam splitting respectively enter the two input ports of the two AOMs at the Bragg angle, and at the same time adopt the radio frequency signal dual AOMs with the same frequency and an adjustable phase difference of 0-2π and Change the frequency of the RF signal in real time. The device is composed of a coherent light source, a beam splitter, an acousto-optic modulator, a radio frequency drive circuit, an optical wedge, a filter, a pitch converter, a focusing lens, and a microscopic objective lens. The advantages of the present invention are that the device does not have any mechanical moving parts, can generate spatially variable frequency and phase shifted projected structured light in real time, has strong anti-interference ability, good stability, good controllability and universal applicability.

Description

Method and device for generating projected structured light

Technical field

The present invention relates to a method and device for generating projected structured light, more specifically to a technology for real-time generating projected structured light with spatial frequency conversion and phase shifting.

Background technique

The 3D sensing technology based on fringe structured light projection and phase measurement has the characteristics of full-field, non-contact, and fast information acquisition. This method does not require any mechanical or optical scanning mechanism and has high measurement accuracy, so it has been extensively researched and developed. The method and device for generating fringe structured light and known spatial phase shift are the key links of fringe structured light projection and phase measurement technology. At present, the main two types of methods for generating fringe structured light projection are laser interference projection and white light grating projection; the main method for generating phase shift is to adjust the optical path or projection grating position by controlling the mechanical deformation of piezoelectric crystals. The main difficulties in the practical application of the above methods are: the methods and devices based on laser interference projection (such as Mach-Zehnder structure) are poor in stability, extremely sensitive to mechanical vibration and other various disturbances, and difficult to generate real-time spatial Frequency-converted projected structured light and phase shift make it difficult to apply to on-site and dynamic environments; although the projection based on white light gratings has a stable structure, it is generally difficult to generate sinusoidal structured light with Ronchi gratings, and it is also difficult to change the structure of structured light dynamically and in real time. spatial frequency. Due to the presence of mechanical motion in the above two types of methods and devices, the speed and reliability of phase shifting are greatly limited. There are four comparable technical literatures:

[1] K.Creath, Y.Y.Cheng, and J.Wyant, "Contouring aspheric surface using two wavelengthphase-shifting interferometry," Opt. Acta 32(12), 1455-1464(1985).

[2] Y.B.Choi and S.W.Kim, "Phase-shifting grating projection Moire topography," Opt.Eng.37(3), 1005-1010(1998).

[3] M.S.Mermelstein, D.L.Feldkhun and L.G.Shirley, "Video-rate surface profiling withacousto-optic accordion fringe interferometry," Opt.Eng.39(1):106-113(2000).

[4] Invention of projection on the scene to obtain the interference fringe intensity as sinusoidal points patent: application number 98111691.

Contents of Invention

The object of the present invention is to provide a method and device for generating projected structured light. The device does not have any mechanical moving parts, and the method can rapidly generate projected structured light with high stability and strong universality.

In order to achieve the above object, the present invention is achieved through the following technical solutions. The method for generating projected structured light is characterized in that it comprises the following steps: the beam of a coherent light source is split by a beam splitter, and the two beams of parallel light after beam splitting respectively enter the two input ends of two acousto-optic modulators at Bragg angles, and at the same time Use RF signals with the same frequency and adjustable phase difference of 0-2π to drive the two AOMs and change the frequency of the RF signals in real time, so that the output deflection angle and relative phase can be controlled at the two output ends of the two AOMs The two beams of first-order diffracted light are then fine-tuned in direction, space filtered, beam spacing changed, and focused and enlarged to project static fringe structured light with sinusoidal intensity of interference fringes on the scene.

According to the method described above, a device for projecting structured light is produced. The device mainly includes a coherent light source, a beam splitter, an acousto-optic modulator, a signal generator and a radio frequency drive circuit, an optical wedge, a spatial filter, a parallel beam spacing converter, a focusing lens, and a microscopic objective lens. It is characterized in that when the coherent light source is a visible light laser, the beam splitter is composed of two prisms glued on the semi-transparent and semi-reflective film; the acousto-optic modulator is a lead molybdate crystal, the working frequency is 40-80MHz, and the driving power is 0.8-1.2 W, the dynamic response time is less than 1ms; the wedge angle of each wedge is 1-1.5 degrees; the focusing lens is a plano-convex lens with a focal length of 10mm. The magnification of the microscope objective lens is 10-40x; the signal generator is a phase-locked frequency synthesizer, and the dynamic response time to frequency and phase changes is less than 1ms.

The advantages of the present invention are that the device does not have any mechanical moving parts, can generate space-converted and phase-shifted projected structured light in real time, has strong anti-interference ability, good stability, and has good controllability and universality.

Description of drawings

Fig. 1 is a structural block diagram of the device of the present invention.

FIG. 2 is a schematic structural diagram of the integrated beam splitter in FIG. 1 .

In the figure, 101 is a laser, 102 is an integrated beam splitter, 103 and 104 are acousto-optic modulators, 105 and 106 are optical wedges, 107 is a dual hole spatial filter, 108 is a beam combiner, 109 is a focusing lens, and 110 is a display Micro-objective lens, 111 is a scene, 112 and 113 are radio frequency power amplifiers, 114 is a signal generator of radio frequency power amplifiers, 201 is a semi-transparent and semi-reflective film, 202 and 203 are prisms.

Detailed ways

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in FIG. 1 , the continuous laser beam generated by the laser 101 is divided into two parallel beams with equal or nearly equal intensity after passing through the beam splitter 102 . They respectively enter the acousto-optic modulators 103 and 104 to generate first-order diffracted light. They will leave the AOM at a small angle proportional to the frequency of the AOM drive signal. An optical wedge as a beam direction fine tuner is used to adjust the angle between two beams. After passing through the optical wedges 105 and 106, two beams of parallel light are respectively obtained, and after passing through the spatial filter 107 and entering the beam combiner 108, two beams of light are obtained. The beam combiner 108 has the same structure as the beam splitter 102, but used in reverse. The two beams of light generated after they are focused by the focusing lens 109 are then projected into space by the microscope objective lens 110 to form two beams of expanded beams, which overlap each other in space to generate interference. AOMs 103 and 104 are driven by signals generated by RF amplifiers 112 and 113, respectively. The input signals of the amplifiers 112 and 113 are generated by a signal generator 114 . The two signals are sine waves with the same frequency, and the phase difference between them is a preset value. Changing the frequency of the two signals can control the spacing of the generated interference fringes, and changing the phase difference between the two signals can control the spatial phase of the generated interference fringes. The frequency of the two signals and the phase difference between them can be controlled manually or by computer programming.

The laser 101 in FIG. 1 can be any single-frequency laser, typically helium-neon laser and single-mode semiconductor laser. The beam splitter 102 and the beam combiner 108 can be any combination of reflective mirrors or prisms, but the use of integrated combined prisms as shown in FIG. 2 will make the structure of the entire fringe projection device compact and stable. If the laser is a visible light laser, the acousto-optic modulator can use aluminum molybdate crystal, its typical operating frequency is 40-80MHz, the driving power is 0.8-1.2W, and the dynamic response time is less than 1ms. The wedge angles of the optical wedges 105 and 106 are determined by the operating frequencies of the AOMs 103 and 104, and the typical value is 1-1.5 degrees. The focusing lens 109 is a plano-convex lens with a typical focal length of 10 mm. The magnification of the microscope objective lens 110 is preferably 10-40x.

The signal generator 114 can be a phase-locked frequency synthesizer, and the dynamic response time to frequency and phase changes is less than 1 ms.

In Fig. 2, the incident light beam is incident on the semi-transparent and semi-reflective film 201 and is divided into two beams of equal light intensity, and then totally reflected by the glued prisms 202 and 203 to obtain two beams of parallel light.

Claims (2)

1, a kind of production method of projecting structural optical, this method feature may further comprise the steps, to the light beam of coherent source through the beam splitter beam splitting, after the beam splitting two bundle directional light enters two input ends of two acousto-optic modulators respectively with Bragg angle, adopt frequency identical and have radio frequency signals drive two acousto-optic modulators of 0～2 π adjustable phase difference and a frequency of real time altering radiofrequency signal simultaneously, thereby two output terminals at two acousto-optic modulators, the two bundle first-order diffraction light that output deflection angle and relative phase are controlled, this two-beam is finely tuned through direction again, spatial filtering, the beam separation conversion, focus on amplification process, penetrate at the scene upslide and obtain the static striated structure light that fringe intensity is a Sine distribution.

2, a kind of device that produces projecting structural optical, this device comprises that mainly coherent source, beam splitter, acousto-optic modulator, signal generator and radio-frequency (RF) driver circuit, wedge, spatial filter, parallel beam spacing transducer, condenser lens, microcobjective constitute, it is characterized in that: coherent source is a visible laser, and beam splitter constitutes by being glued at two prisms of semi-transparent semi-reflecting film; Acousto-optic modulator is the lead molybdate crystal, and frequency of operation is 40～80MHz, driving power 0.8～1.2W, and dynamic response time is less than 1ms; The angle of wedge of each wedge is the 1-1.5 degree; Condenser lens is a planoconvex lens, and focal length value is 10mm; The enlargement factor of microcobjective is at 10-40x; Signal generator is a frequency synthesizer of phase locking, to the dynamic response time of frequency and phase change all less than 1ms.

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