Ultrahigh-speed dynamic light projection method and system based on laser array

Abstract

The invention relates to the technical field of structured light projection, in particular to an ultrahigh-speed dynamic light projection method and system based on a laser array, and the method comprises the steps: building a plurality of paths of coherent light sources, carrying out the beam combination of the emergent laser of the plurality of paths of coherent light sources, and forming the combined laser transmitted along the same optical axis in a second direction; applying controllable phase modulation to the combined laser by using a phase modulator to generate modulated laser with different phase states; the modulated laser is incident to a diffractive optical element, and the incident modulated laser is diffracted along a second direction to form periodic structured light stripes; the phase modulator is controlled to be switched between different preset phase states, so that the structured light stripes generate equivalent continuous or stepping phase translation in the second direction; and projecting the structured light stripes subjected to phase translation to the surface of a measured object, and synchronously collecting structured light images modulated by the surface of the object in different phase states.

Description

Technical Field

[0001] This invention relates to the field of structured light projection technology, specifically to an ultra-high-speed dynamic light projection method and system based on a laser array. Background Technology

[0002] Structured light projection technology is widely used in industrial 3D measurement, machine vision, and online inspection due to its high precision and non-contact characteristics. Currently, mainstream structured light projection systems mainly employ digital micromirror devices (DLP) or liquid crystal silicon devices (LCOS). These systems acquire the 3D shape of objects by sequentially loading different grayscale stripe patterns and combining them with phase-shifting algorithms.

[0003] However, existing technologies have the following significant drawbacks: Phase shift speed bottleneck: DLP / LCOS systems rely on the physical flipping or state change of micromirrors or liquid crystal cells to switch patterns, and their refresh rate is limited by the response time of the device itself. In order to generate high-quality sinusoidal fringes, multiple frames of images are usually required to synthesize, which leads to a significant drop in the effective 3D frame rate, making it difficult to meet the real-time measurement requirements of high-speed moving objects.

[0004] Low light energy utilization: In DLP systems, a large amount of light energy is lost due to the deflection of micromirrors to the optical trap; LCOS systems suffer from polarization-dependent absorption and reflection losses, resulting in low overall light efficiency; and in order to obtain a sufficient signal-to-noise ratio, high-power light sources are often required, which leads to heat dissipation, power consumption and lifespan problems.

[0005] System stability and complexity: Microelectromechanical systems (MEMS) based DLP optomechanics suffer from thermal drift and long-term reliability issues during high-speed operation. Furthermore, complex calibration and compensation algorithms are required to correct projection nonlinearity and gamma effects, and the correction parameters are prone to drift with time and environmental changes.

[0006] Multi-period projection is inefficient: To achieve unambiguous phase unwrapping, it is often necessary to project multiple sets of fringes with different periods. In time-series projection schemes, this significantly increases projection and data acquisition time, reducing measurement efficiency.

[0007] Therefore, there is an urgent need for a method that can fundamentally overcome the phase shift velocity limitation, improve light energy utilization, enhance system stability, and efficiently realize multi-period structured light projection. Summary of the Invention

[0008] To address the problems of the prior art, the core idea of ​​this invention is to decouple the spatial morphology generation of structured light stripes from temporal phase modulation: high-quality periodic stripes are generated in a fixed spatial manner using static diffractive optical elements, while the wavefront phase of the incident laser is rapidly and precisely electronically modulated by a high-speed phase modulator, thereby achieving an equivalent spatial translation of the stripes without needing to refresh any spatial pattern.

[0009] This invention provides, in one aspect, a method for ultra-high-speed dynamic optical projection based on a laser array, comprising: A multi-channel coherent light source is constructed, and the multi-channel coherent light source is arranged along a first direction to form a laser array; the emitted lasers from the multi-channel coherent light source are combined to form a combined laser beam propagating along the same optical axis along a second direction, the second direction being perpendicular to the first direction; A phase modulator is used to apply controllable phase modulation to the combined laser beam, generating modulated lasers with different phase states; The modulated laser is incident on a diffractive optical element, and according to the grating structure of the diffractive optical element with a specific phase distribution, the incident modulated laser is diffracted along the second direction to form periodic structured light stripes. By controlling the phase modulator to switch between different preset phase states, the structured light stripes are made to produce an equivalent continuous or step phase shift in the second direction. Phase-shifted structured light stripes are projected onto the surface of the object under test, and structured light images modulated by the object surface are acquired synchronously at different phase states.

[0010] The emitted laser beams from multiple coherent light sources are sequentially combined using a polarizing beam splitter, specifically as follows: The polarization direction of some of the emitted lasers in the laser array is rotated and controlled by a half-wave plate, so that the polarization states of the emitted lasers from adjacent lasers are orthogonal. The first output laser is incident from the side onto the first polarizing beam splitter, and the second output laser is incident from the front onto the first polarizing beam splitter. The first polarizing beam splitter outputs the first-stage combined laser beam. The first-stage combined laser is used as a light source and incident from the side onto the second polarizing beam splitter. The third-stage output laser is incident from the front onto the second polarizing beam splitter, and the second polarizing beam splitter outputs the second-stage combined laser. The beams are combined sequentially at each stage until the final polarization beam splitter outputs a combined laser beam from all coherent light sources.

[0011] The diffractive optical element is designed to simultaneously generate at least two periodic structured light fringe patterns with different spatial frequencies, and the period values ​​corresponding to the different spatial frequencies are coprime.

[0012] The phase modulator is controlled by a preset N-step phase sequence to switch between different preset phase states.

[0013] The ultra-high-speed dynamic light projection method also includes performing image processing calculations to obtain the absolute phase of the object under test by combining structured light images of the surface of the object under test with at least two different periodic stripes.

[0014] The specific operation of calculating the absolute phase of the measured object through image processing is as follows: Each image acquired by the imaging acquisition module contains two sets of stripe information with different periods. The intensity information of the two sets of stripes is separated from a single image by frequency domain filtering or demodulation algorithms. For each group of images acquired from a phase-shift sequence, the wrap-around phase map corresponding to period P1 and period P2 is calculated independently. F 1 and F 2 ; Using a dual-frequency phase expansion algorithm, from F 1 and F 2 Directly calculate the unambiguous absolute phase diagram over a larger synthesis period. F abs .

[0015] Another aspect of the present invention provides a laser array-based ultra-high-speed dynamic light projection system for implementing the laser array-based ultra-high-speed dynamic light projection method as described above, comprising a system controller, and a laser array, a beam combining optical component, a phase modulator, a diffractive optical element, a projection lens group and an imaging acquisition module arranged sequentially along the optical axis, wherein the system controller is electrically connected to the laser array, the phase modulator and the imaging acquisition module respectively. The system controller controls the phase switching sequence of the phase modulator and synchronously triggers the program acquisition module to acquire structured light images of the object under test in different phase states; it acquires structured light images acquired by the imaging acquisition module and performs image processing to calculate the absolute phase of the object under test. Laser arrays are used to generate multiple independent laser beams; Beam combining optical components are used to combine multiple laser beams into a coaxial laser beam; A phase modulator is used to apply phase modulation to the coaxial laser emitted from a beam combining optical assembly. Diffractive optical elements are used to diffract a phase-modulated light beam in a specific direction to form periodic structured light fringes. The projection lens group is positioned behind the optical path of the diffractive optical element and is used to project structured light fringes onto the surface of the object being measured. The imaging acquisition module is used to acquire structured light images of the surface of the object under different phase modulation states, and transmit the acquired structured light images to the system controller for image processing.

[0016] The beam combining optical component adopts a multi-level polarization beam combining structure; the multi-level polarization beam combining structure includes multiple polarization beam splitters.

[0017] The phase modulator is an acousto-optic modulator and / or an electro-optic modulator.

[0018] Beneficial effects: This invention is an ultra-high-speed dynamic light projection method and system based on a laser array. It uses a laser as the light source, which concentrates the light energy. It directly "shapes" the light field to form stripes through diffractive optical elements, avoiding a large amount of ineffective reflection and occlusion loss in DLP. Most of the light energy is effectively projected, which significantly improves the signal-to-noise ratio and the light energy utilization rate on low reflectivity surfaces or under strong ambient light. Since phase shift is achieved solely by changing the drive signal of the phase modulator, without involving any mechanical or electrical refresh of the spatial pattern, its speed is limited only by the response time of the modulator itself and the drive electronics, enabling equivalent phase shift frequencies in the hundreds of kHz or even MHz range, thus improving phase shift speed. The spatial morphology of the fringes is determined by the physically fixed DOE and is unaffected by the drift of electrical driving parameters, thus exhibiting excellent sinusoidal and periodic stability. This system has no high-speed moving macroscopic mechanical parts, resulting in high reliability and good long-term stability. By designing diffractive optical elements, multiple fringe patterns can be generated at once. All patterns share the same high-speed phase shift process, and multi-period information can be acquired simultaneously without adding extra projection time, which greatly improves the efficiency of phase unwrapping and absolute three-dimensional measurement. Attached Figure Description

[0019] The solutions and advantages of this application will become clear to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0020] In the attached diagram: Figure 1 The flowchart shows a method for ultra-high-speed dynamic light projection based on a laser array. Figure 2 This is a schematic diagram of an ultra-high-speed dynamic light projection system based on a laser array. Detailed Implementation

[0021] Exemplary embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings.

[0022] Example 1 like Figure 2As shown, this embodiment provides an ultra-high-speed dynamic optical projection system based on a laser array, including a system controller, and a laser array, a beam combining optical component, a phase modulator, a diffractive optical element, a projection lens group, and an imaging acquisition module arranged sequentially along the optical axis. The system controller is electrically connected to the laser array, the phase modulator, and the imaging acquisition module respectively.

[0023] The laser array is located at the front end of the optical path and can simultaneously output multiple independent laser beams. The beam combining optical component is located at the rear end of the laser array and is used to combine multiple laser beams into a coaxial laser. The phase modulator is located on the output side of the beam combining optical component and is used to apply phase modulation to the coaxial laser emitted by the beam combining optical component. The diffractive optical element is located at the rear end of the phase modulator and can diffract the phase-modulated laser. The projection lens group is located on the output path of the diffractive optical element and can project structured light fringes onto the surface of the object under test. The imaging acquisition module is triggered synchronously with the phase modulator and is used to acquire structured light images of the surface of the object under test under different phase modulation states, and transmit the acquired structured light images to the system controller for image processing.

[0024] In this embodiment, the laser array consists of multiple semiconductor lasers or fiber-coupled lasers arranged linearly in one dimension along a direction perpendicular to the horizontal line (a first direction). The lasers emit light along a second direction, which is perpendicular to the first direction. The arrangement can be equidistant or non-equidistant depending on the requirement for beam uniformity. The emitted laser light from each laser forms a narrow band spot in the first direction or, after homogenization and diffusion, forms a spot of finite width.

[0025] The beam combining optical component adopts a multi-stage polarization beam combining structure; the multi-stage polarization beam combining structure includes multiple polarization beam splitters; adjacent lasers in the laser array are beam combined stage by stage through polarization beam splitters.

[0026] The phase modulator is an acousto-optic modulator, an electro-optic modulator, or a combination thereof. The phase modulator is preferably an acousto-optic modulator, which, based on the acousto-optic effect, achieves rapid modulation of the laser phase by changing the phase, frequency, or timing of the driving signal. Furthermore, the modulation bandwidth of the acousto-optic modulator can reach hundreds of MHz, and the phase switching time is on the order of nanoseconds to microseconds, thus enabling phase shift frequencies from 10 kHz to over 1 MHz.

[0027] A diffractive optical element is used to diffract phase-modulated laser light. The surface of the diffractive optical element is etched with a grating structure of a specific phase distribution, used to diffract the incident laser light along a second direction to form periodic structured light fringes. Simultaneously, the diffractive optical element can be designed to output two or more structured light fringes with different spatial frequencies, such as fringes with periods of 12 pixels and 13 pixels respectively, whose period lengths are coprime, facilitating subsequent phase unwrapping processing.

[0028] Based on the ultra-high-speed dynamic light projection system described above, see [link to relevant documentation]. Figure 1 This embodiment provides an ultra-high-speed dynamic light projection method based on a laser array, and its specific implementation steps are as follows: S1. Construct a multi-channel coherent light source, wherein the multi-channel coherent light source is arranged along a first direction to form a laser array; combine the emitted lasers from the multi-channel coherent light source to form a combined laser beam propagating along the same optical axis along a second direction, wherein the second direction is perpendicular to the first direction.

[0029] The emitted laser beams from multiple coherent light sources are sequentially combined using a polarizing beam splitter, specifically as follows: The polarization direction of some of the emitted lasers in the laser array is rotated and controlled by a half-wave plate, so that the polarization states of the emitted lasers from adjacent lasers are orthogonal. The first emitted laser is incident from the side onto the first polarizing beam splitter, and the second emitted laser is incident from the front onto the first polarizing beam splitter. The first polarizing beam splitter outputs a first-stage combined laser beam, which contains the energy of both the first and second emitted laser beams and is a coaxial beam with completely consistent propagation directions. The first-stage combined laser is used as a light source and incident from the side onto the second polarizing beam splitter. The third-stage output laser is incident from the front onto the second polarizing beam splitter, and the second polarizing beam splitter outputs the second-stage combined laser. The beams are combined sequentially at each stage until the final polarization beam splitter outputs a combined laser beam from all coherent light sources.

[0030] S2. A phase modulator is used to apply controllable phase modulation to the combined laser beam to generate modulated lasers with different phase states. S3. The modulated laser is incident on a diffractive optical element, and according to the grating structure of the specific phase distribution of the diffractive optical element, the incident modulated laser is diffracted along the second direction to form periodic structured light stripes. The diffractive optical element is designed to incorporate two one-dimensional grating structures with different spatial frequencies f1 and f2 on the same element. When illuminated by a collimated laser, it can simultaneously generate two sets of overlapping sinusoidal fringes in the far field, with periods P1=1 / f1 and P2=1 / f2, respectively. The period lengths corresponding to the two different spatial frequencies are coprime.

[0031] When the system controller triggers the phase modulator to work, the phase modulation applied by the phase modulator will affect the two sets of structured light stripes simultaneously and to the same extent, causing them to shift synchronously.

[0032] S4: By controlling the phase modulator to switch between different preset phase states, the structured light stripe produces an equivalent continuous or step phase shift in the second direction. The system controller generates corresponding radio frequency phase control signals according to a preset N-step phase shift sequence (such as four-step phase shift: 0, π / 2, π, 3π / 2), and sends them to the driver of the acousto-optic modulator. The driver controls the acousto-optic modulator to quickly switch the phase state corresponding to each phase shift.

[0033] S5. Project phase-shifted structured light stripes onto the surface of the object being measured, and simultaneously acquire structured light images modulated by the object surface under different phase states.

[0034] While controlling the phase modulator to rapidly switch phase states, the system controller sends a synchronization trigger signal to the imaging acquisition module to ensure that the imaging acquisition module exposes and acquires one image in each stable phase state. After completing a full phase shift sequence, the system controller obtains a set of images that can be used to calculate the wrap phase. Since the phase switching of the phase modulator can be completed in microseconds or even less, the entire phase shift data acquisition can be completed within tens of microseconds, thereby achieving a 3D frame rate far exceeding that of traditional DLP methods.

[0035] Furthermore, the ultra-high-speed dynamic light projection method also includes calculating the absolute phase of the object by combining structured light images of the surface of the object with at least two different periodic fringes, specifically as follows: Each image acquired by the imaging acquisition module contains two sets of stripe information with different periods. Through frequency domain filtering or demodulation algorithms, the intensity information of the two sets of stripes can be separated from a single image. For each group of images acquired from a phase-shift sequence, the wrap-around phase map corresponding to period P1 and period P2 is calculated independently. F 1 and F 2 ; Using a dual-frequency phase expansion algorithm, from F 1 and F 2 Directly calculate the unambiguous absolute phase diagram over a larger synthesis period. F abs This greatly expands the single measurement range of the system, eliminating the need for time-consuming time-series multi-frequency projection.

Claims

1. A method for ultra-high-speed dynamic optical projection based on a laser array, characterized in that, include: A multi-channel coherent light source is constructed, and the multi-channel coherent light source is arranged along a first direction to form a laser array; The emitted lasers from multiple coherent light sources are combined to form a combined laser beam that propagates along the same optical axis in a second direction, which is perpendicular to the first direction. A phase modulator is used to apply controllable phase modulation to the combined laser beam, generating modulated lasers with different phase states; The modulated laser is incident on a diffractive optical element, and according to the grating structure of the diffractive optical element with a specific phase distribution, the incident modulated laser is diffracted along the second direction to form periodic structured light stripes. By controlling the phase modulator to switch between different preset phase states, the structured light stripes are made to produce an equivalent continuous or step phase shift in the second direction. Phase-shifted structured light stripes are projected onto the surface of the object under test, and structured light images modulated by the object surface are acquired synchronously at different phase states.

2. The ultra-high-speed dynamic optical projection method based on a laser array according to claim 1, characterized in that, The emitted laser beams from multiple coherent light sources are sequentially combined using a polarizing beam splitter, specifically as follows: The polarization direction of some of the emitted lasers in the laser array is rotated and controlled by a half-wave plate, so that the polarization states of the emitted lasers from adjacent lasers are orthogonal. The first output laser is incident from the side onto the first polarizing beam splitter, and the second output laser is incident from the front onto the first polarizing beam splitter. The first polarizing beam splitter outputs the first-stage combined laser beam. The first-stage combined laser is used as a light source and incident from the side onto the second polarizing beam splitter. The third-stage output laser is incident from the front onto the second polarizing beam splitter, and the second polarizing beam splitter outputs the second-stage combined laser. The beams are combined sequentially at each stage until the final polarization beam splitter outputs a combined laser beam from all coherent light sources.

3. The ultra-high-speed dynamic optical projection method based on a laser array according to claim 1, characterized in that, The diffractive optical element is designed to simultaneously generate at least two periodic structured light fringe patterns with different spatial frequencies, and the period values ​​corresponding to the different spatial frequencies are coprime.

4. The ultra-high-speed dynamic optical projection method based on a laser array according to claim 1, characterized in that, The phase modulator is controlled by a preset N-step phase sequence to switch between different preset phase states.

5. The ultra-high-speed dynamic optical projection method based on a laser array according to claim 1, characterized in that, It also includes calculating the absolute phase of the object by combining structured light images of the surface of the object with at least two different periodic stripes and performing image processing.

6. The ultra-high-speed dynamic optical projection method based on a laser array according to claim 5, characterized in that, The specific operation of calculating the absolute phase of the measured object through image processing is as follows: Each image acquired by the imaging acquisition module contains two sets of stripe information with different periods. The intensity information of the two sets of stripes is separated from a single image by frequency domain filtering or demodulation algorithms. For each group of images acquired from a phase-shift sequence, the wrap-around phase map corresponding to period P1 and period P2 is calculated independently. Φ 1 and Φ 2 ; Using a dual-frequency phase expansion algorithm, from Φ 1 and Φ 2 Directly calculate the unambiguous absolute phase diagram over a larger synthesis period. Φ abs .

7. A laser array-based ultra-high-speed dynamic light projection system for implementing the laser array-based ultra-high-speed dynamic light projection method of claim 1, characterized in that, It includes a system controller, and a laser array, a beam combining optical component, a phase modulator, a diffractive optical element, a projection lens group and an imaging acquisition module arranged sequentially along the optical axis. The system controller is electrically connected to the laser array, the phase modulator and the imaging acquisition module respectively. The system controller controls the phase switching sequence of the phase modulator and synchronously triggers the program acquisition module to acquire structured light images of the object under test in different phase states; it acquires structured light images acquired by the imaging acquisition module and performs image processing to calculate the absolute phase of the object under test. Laser arrays are used to generate multiple independent laser beams; Beam combining optical components are used to combine multiple laser beams into a coaxial laser beam; A phase modulator is used to apply phase modulation to the coaxial laser emitted from a beam combining optical assembly. Diffractive optical elements are used to diffract a phase-modulated light beam in a specific direction to form periodic structured light fringes. The projection lens group is positioned behind the optical path of the diffractive optical element and is used to project structured light fringes onto the surface of the object being measured. The imaging acquisition module is used to acquire structured light images of the surface of the object under different phase modulation states, and transmit the acquired structured light images to the system controller for image processing.

8. The ultra-high-speed dynamic light projection system based on a laser array according to claim 7, characterized in that, The beam combining optical component adopts a multi-level polarization beam combining structure; the multi-level polarization beam combining structure includes multiple polarization beam splitters.

9. The ultra-high-speed dynamic light projection system based on a laser array according to claim 7, characterized in that, The phase modulator is an acousto-optic modulator and / or an electro-optic modulator.

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