Projector Array Research Articles

Non-coaxial optical screen based projection 3D display with extended viewing distance range

A non-coaxial optical screen based projection 3D display with extended viewing distance range is proposed. The proposed 3D display is composed of a projector array and a non-coaxial optical screen constructed with a series of one-dimensional retro-reflective components (1DRRCs). The projector array projects parallax images onto the screen, then the non-coaxial optical screen converges light to linearly shaped region which pass through the position of the projector and forms a view area by one-dimensional retro-reflection. At each view area, different parallax images corresponding to the projectors can be observed respectively, therefore 3D display is formed. In the proposed 3D display, the optical axis of each 1DRRC shares a common direction and isn't parallel to the normal of the non-coaxial optical screen plane. Consequently, reflected light converges into a linearly shaped region. This linearly shaped region isn't parallel to the non-coaxial optical screen, so that it can cover a extended range from back to front and lead to larger viewing distance range. A prototype is developed to verify the principle. In the prototype, the viewing distance range covers a range of 959–2083 mm, then demonstrating the proposed 3D display agree well with the theory.

High-Resolution, Wide-Field-of-View, and Real-Time 3D Imaging Based on Spatial-Temporal Speckle Projection Profilometry with a VCSEL Projector Array

High-Resolution, Wide-Field-of-View, and Real-Time 3D Imaging Based on Spatial-Temporal Speckle Projection Profilometry with a VCSEL Projector Array

Design of large-angle distortion-free and spot adjustable LED spot array projector based on microlens array and eyepiece

The spot array projector has long been a challenging and intriguing research focus in the fields of projection and lighting applications. In the current literature, there is a lack of a comprehensive and detailed presentation on the design and analysis method for a spot array generator based on the structure of imaging eyepiece and MLA. We present a novel design and optimization method for a large-angle, distortion-free and spot adjustable LED spot array projector that is composed of an eyepiece, two microlens arrays (MLAs), and a micro-LED array (MLEDA). The eyepiece system is optimized using imaging optical methods to project sub-beams to the target plane with a large angle. The sub-lens of condenser MLA is also optimized using imaging optical methods to refocus the collimating beam and match the numerical aperture (NA) with the eyepiece, and the sub-lens of the collimating MLA is acquired by using simulated annealing (SA) global illumination optics optimization method to achieve collimation and far-field homogenization. The predistortion MLEDA and the MLAs are proposed and implemented by the radial basis function (RBF) interpolation method, which correct the large-angle distortion introduced by the eyepiece. Both near-field and far-field applications can be realized by the proposed system. In the near-field applications, different spot geometries at the near-field target plane can be achieved. In the far-field applications, the power matching of the MLEDA is used to improve far-field uniformity of spot array. Moreover, the predefined-geometry arrangement spot array can be realized in both near and far fields. Two design examples with full field of view (FOV) projection of 80° and 100° are provided to validate the proposed method. Overall, the proposed system offers a promising solution for various applications requiring target identification or 3D calibration.

In-Lab Demonstration of an Underwater Acoustic Spiral Source.

Underwater acoustic spiral sources can generate spiral acoustic fields where the phase depends on the bearing angle. This allows estimating the bearing angle of a single hydrophone relative to a single source and implementing localization equipment, e.g., for target detection or unmanned underwater vehicle navigation, without requiring an array of hydrophones and/or projectors. A spiral acoustic source prototype made out of a single standard piezoceramic cylinder, which is able to generate both spiral and circular fields, is presented. This paper reports the prototyping process and the multi-frequency acoustic tests performed in a water tank where the spiral source was characterized in terms of the transmitting voltage response, phase, and horizontal and vertical directivity patterns. A receiving calibration method for the spiral source is proposed and showed a maximum angle error of 3° when the calibration and the operation were carried out in the same conditions and a mean angle error of up to 6° for frequencies above 25 kHz when the same conditions were not fulfilled.

The Flipping-Free Full-Parallax Tabletop Integral Imaging with Enhanced Viewing Angle Based on Space-Multiplexed Voxel Screen and Compound Lens Array

Tabletop integral imaging display with a more realistic and immersive experience has always been a hot spot in three-dimensional imaging technology, widely used in biomedical imaging and visualization to enhance medical diagnosis. However, the traditional structural characteristics of integral imaging display inevitably introduce the flipping effect outside the effective viewing angle. Here, a full-parallax tabletop integral imaging display without the flipping effect based on space-multiplexed voxel screen and compound lens array is demonstrated, and two holographic functional screens with different parameters are optically designed and fabricated. To eliminate the flipping effect in the reconstruction process, the space-multiplexed voxel screen consisting of a projector array and the holographic functional screen is presented to constrain light beams passing through the corresponding lens. To greatly promote imaging quality within the viewing area, the aspherical structure of the compound lens is optimized to balance the aberrations. It cooperates with the holographic functional screen to modulate the light field spatial distribution. Compared with the simulation results, the distortion rate of the imaging display is reduced to less than 9% from more than 30%. In the experiment, the floating high-quality reconstructed three-dimensional image without the flipping effect can be observed with the correct 3D perception at 96° × 96° viewing angle, where 44,100 viewpoints are employed.

Implementation of continuously steerable beam patterns for a uniform circular projector array.

A continuously steerable super-cardioid beam pattern (SCBP) has advantages such as controllable direction, narrower beam width, and higher gain. It is generally implemented with a uniform circular array (UCA). Here, an implementation method of continuously steerable SCBPs is proposed for a projector array. The synthesis and the implementation of the continuously steerable SCBP are studied and analyzed based on a UCA model composed of omnidirectional sources. An improved version of the common method is proposed. It requires fewer array elements and the massive power amplifiers matched to each array element, which reduces the cost and the installation space. Subsequently, a continuously steerable SCBP is implemented with a uniform circular projector array (UCPA). This system is composed of single-sided radiation flextensional transducers and is studied and analyzed with a finite element method, which verified that the proposed method is suitable for the underwater acoustic projector array. Finally, UCPA prototypes were fabricated. The tests demonstrated that the proposed implementation method is a flexible way for the application of the continuously steerable SCBP in the low-frequency emission field.

Development of a Dual-Layer Structure for Cymbal Transducer Arrays to Achieve a Wider Bandwidth.

Cymbal transducers are typically grouped and arranged in planar arrays. For projector arrays, a wide bandwidth on the transmitting voltage response (TVR) spectrum is required for better underwater communication and data transmission within a short time. The purpose of this study is to develop a wideband cymbal array by controlling the center-to-center (CTC) spacing between the cymbal transducers in the array. In the practical design of the array, due to the arrangement of elements in one layer, the minimum CTC spacing between the cymbals is constrained to the diameter of the cymbals in use. To overcome this limitation, we propose a new dual-layer array structure. Finite element analysis of the cymbal array showed that the bandwidth was generally inversely proportional to the CTC spacing. We explained the mechanism of this relationship using a theoretical analysis of the mutual radiation impedance between the cymbals in the array. Subsequently, we identified the optimum CTC spacing to achieve the widest possible bandwidth for the cymbal array. The validity of the wideband array design was verified through the fabrication and characterization of prototype arrays. We confirmed that the two-layered arrangement could significantly widen the bandwidth of the cymbal array while maintaining the TVR above a specified level.

The Effects of Manufacturing Inaccuracies in an Underwater Acoustic Projector Array on the Acoustic Interactions

We report on the importance of considering manufacturing inaccuracies in underwater acoustic projectors by elucidating how small variations affect the response characteristics of a projector array in the presence of mutual-loading effects. A wave-based distributed mechanical model accurately calculates the changes arising from small variations, so rapid changes occurring in the vicinity of the transducer resonance can be simulated. The results showed the effects of mutual loading between projector units and confirmed that the changes can be drastically intensified in the presence of manufacturing inaccuracies. A voltage adjustment method to compensate for these changes is also demonstrated as a solution. This framework could guide the design of projector arrays in sound navigation and ranging (SONAR) systems for a variety of applications and, in particular, may contribute significantly to determining manufacturing tolerances.

View-synthesized ‘re-calibration’ of an array projector for 3D measurement from an arbitrary monocular view

We previously presented a method on how to calibrate a high-speed Multi-Aperture Array Projector (MAAP) in order to obtain three-dimensional (3D) surface measurements using only a single camera instead of a stereo-camera configuration. The MAAP calibration procedure however can be time-consuming as it requires the camera to encode each aperture's illumination frustum by imaging the pattern incident on a depth-wise scanned test plane. This is as if recording discretized depth slices of the illumination frustums. This can be detrimental as the calibration is coupled to a single specific camera view. It would be laborious and time-consuming to repeat the entire MAAP calibration process for an alternate camera view. This study demonstrates a so-called MAAP ‘re-calibration’ solution that artificially synthesizes MAAP calibration images from an arbitrary camera view without direct imaging. This presents the opportunity to decouple the MAAP calibration from a single camera view and obtain 3D measurements from alternate camera placement setups without having to perform the entire MAAP calibration process again. This study shows that the synthesized MAAP calibration images resemble well the ground truth images. As a result, the proposed method has similar 3D measurement performance compared to when calibrating the MAAP with true images.

Modeling and Design of a Rear-Mounted Underwater Projector Using Equivalent Circuits.

Tonpilz is a popular transducer for underwater projector arrays for sonar systems. For low-frequency transmission, a larger axial dimension of the conventional Tonpilz transducer is required. However, a bulky and heavy Tonpilz element is not suitable due to limitations in terms of the space and payload of the array platform. To address this problem, we developed a rear-mounted Tonpilz transducer to generate a sub-fundamental resonance in addition to the common longitudinal resonance. For this purpose, we developed a new equivalent circuit model that can reflect all the effects of the key design parameters of the transducer, such as suspension thickness (stiffness), tail mass thickness, and head mass thickness. The impedance and transmitting voltage response were evaluated as performance factors at both resonance frequencies. The validity of the circuit was verified by comparing the analysis results with those from the finite element analysis of the same transducer. Based on the results, the transducer structure was designed to have comparable transmitting performance at both resonance frequencies by employing relatively high suspension stiffness, light tail mass, and heavy head mass. The novel design can permit the dual-band operation of the transducer so that the transducer can operate as a wideband projector.

Virtual multiplication of light sources for a 360°-viewable tabletop 3D display

A method to construct a virtual annular projector array that acts as numerous light sources to produce 360°-viewable 3D images on a round table is proposed. The conventional method requires multiple projectors and a conical screen for its 3D imaging principle but is limited physically by the projector arrangement. The proposed approach significantly increases the number of projectors virtually by inserting cylindrical mirrors into the optical paths used in the conventional method. This paper describes the multiplication principle and a prototype 3D display produces 3D images that are approximately 10 times denser than those produced by the conventional method.

Retro-reflection based projection 3D display with low crosstalk

Retro-reflection based projection 3D display with low crosstalk is proposed. The 3D display consists of a retro-reflective sheet, an image projector array, a vertical scattering layer, and two optical noise sources projectors. The image projector array is used to provide parallax images. The retro-reflective sheet is used to reflect parallax images to different horizontal viewpoints to form 3D images. The vertical scattering layer is used to scatter the reflected light in the vertical directions, and form viewing areas in the vertical projection area of each corresponding projector. The optical noise source projector provides salt and pepper noise to reduce crosstalk. A prototype of the proposed 3D display is developed, and the experiment results agree well with the theory.

33‐2: Improving Image Quality of 360‐degree Tabletop 3D Screen System

For improving the image quality of a 360‐degree tabletop 3D screen system, we propose a method that uses 60 4K projectors to improve the resolution. We adopt a double‐stack projector array and show that linear blending is established. We also developed a screen that reduces stray light and achieves higher image quality.

Light field display using wavelength division multiplexing

We propose a large screen 3D display which enables multiple viewers to see simultaneously without special glasses. In prior researches, methods of using a projector array or a swinging screen were proposed. However, the former has difficulty in installing and adjusting a large number of projectors and the latter cases occurrence of vibration and noise because of the mechanical motion of the screen. Our proposed display consists of a wavelength modulation projector and a spectroscopic screen. The screen shows images of which color depends on viewing points. The projector projects binary images to the screen in time-division according to wavelength of projection light. The wavelength of the light changes at high-speed with time. Therefore, the system can show 3D images to multiple viewers simultaneously by projecting proper images according to each viewing points. The installation of the display is easy and vibration or noise are not occurred because only one projector is used and the screen has no mechanical motion. We conducted simulation and confirmed that the proposed display can show 3D images to multiple viewers simultaneously.

Seamless ultrathin rear projection display

AbstractA new architecture for a thin (2‐cm depth) rear projection display is described. In order to achieve this small depth, a very high density of rear projectors is used. Three prototype displays using rear projectors on both 5‐ and 2‐cm pitch arrays are described. The displays can achieve an effective screen pixel pitch of as small as 0.5 mm, which makes this technology competitive in terms of resolution with fine pitch LED displays; however, orders of magnitude fewer LEDs are required: Each rear projector requires only one white LED and a color liquid crystal light modulator. In the three prototypes, the projector light modulators utilize 101‐cm (40 in.), 80‐cm (31.5 in.), and 60‐cm (24 in.) diagonal liquid crystal display glass. To minimize cost, no lenses are utilized for the rear projectors. An RGB LED array may augment the projector array, which provides a low resolution component of the image onto which the high resolution component is superimposed by the projector array. Edge gaps between active areas on adjacent LCD glass units are completely eliminated by the rear projection approach enabling low profile wall‐size seamless displays. Display contrast depends on rear projection screen design.

Optimization-based extrinsic calibration of a three-dimensional sensor composed of an array projector and a single camera

We previously presented a technique calibrating a multiaperture array projector (MAAP) for performing high-speed three-dimensional (3-D) surface topology measurements with aperiodic sinusoidal fringe structured illumination. Although a stereo-camera setup used to be required for triangulation, the presented MAAP calibration technique re-enables photogrammetric 3-D measurements to be made using a single CCD or CMOS camera. For such a monocular-view photogrammetric system, intrinsic camera calibration, intrinsic projector calibration, and extrinsic system calibration are vital to obtain high-measurement performance. However, there is currently no such technique that can comprehensively perform the required extrinsic system calibration when using an MAAP and a single-camera setup. A comprehensive optimization-based method is proposed and the resulting measurement performance is evaluated. With the new calibration technique, we are able to achieve a surface standard deviation of ∼50 μm.

Scalable visible light communications with a micro-LED array projector and high-speed smartphone camera.

Solid-state camera systems are now widely available in portable consumer electronics, providing potential receivers for visible light communications in every device. Typically, data rates with camera receivers are limited by the 60 fps frame rate of both the image sensor and projector systems. Recent developments in high-frame rate microdisplays and slow-motion cameras for smartphones now permit high-speed, spatially structured signals to be transmitted and captured. Here, we present a method for transmitting data to a smartphone using a CMOS-controlled micro-LED projector system. Spatial patterns are projected onto a wall at a refresh rate of 480 Hz, which can be captured by the smartphone's 960 fps camera. Data transfer is performed over meter scale distances, and the use of an alignment frame gives the system a level of tolerance to motion and misalignment. The current system allows data transmission at a peak rate of 122.88 kb/s using a 16 × 16 micro-LED array, which can be readily scaled to Mb/s rates with a higher resolution transmitter.

Iterative solutions of the array equations for rapid design and analysis of large projector arrays.

A fast computational method for modeling and simulation of large projector arrays is presented. The method is based on the array equations that account for the acoustic interaction among the projector elements as well as the individual characteristics of each projector. Unlike the existing solution method in which the acoustic interaction must be known a priori in the form of interaction impedance matrix Z, the present method seeks the solution of modified array equations through iterations without explicitly evaluating the Z matrix. This significantly speeds up the analysis of complex arrays with surrounding structures, where the evaluation of the Z matrix may require a large number of time-consuming finite element computations. The method is compared with the traditional Z-matrix method for the case of a cylindrical array of 72 × 8 Tonpilz transducers. For the same level of accuracy, the iterative method is shown to be up to 2 orders-of-magnitude faster than the Z-matrix method. The method can be used for rapid design and analysis of active sonar arrays and medical ultrasonic transducers, often made of hundreds and even thousands of elements.

Calibration of an array projector used for high-speed three-dimensional shape measurements using a single camera.

Geometric calibration of digital light processing projectors in single-camera, fringe-projecting 3D measurement systems have been studied assuming the projector is inverse pinhole modeled. Conversely, a high-speed multi-aperture array projector (MAAP) projecting aperiodic fringes is not dependent on a digital mirror device and cannot be pinhole modeled. With MAAP projection, a stereo camera setup is required. This paper presents a model-less method to calibrate a MAAP by direct measurement of its illumination field and re-enables 3D measurements with a single camera even with surface discontinuities present. Experimental proof of principle and preliminary measurement performance are shown.

Time-multiplexed multi-view three-dimensional display with projector array and steering screen.

A novel time-multiplexed multi-view three-dimensional (3D) display has been implemented using a projector array to provide the image source and an angular steering-screen module to generate multiple high density horizontal views. The liquid crystal (LC)-based steering screen was specially developed to deflect light beams over a small range and operate in synchronism with the projector array with the use of a customized FPGA driver. The prototype produces vivid color 3D scenes with smooth parallax to multiple viewers. The experimental results verify the proposed multi-projection time-multiplexed multi-view 3D display method that uses a steering screen to produce dense views. Displaying both static and dynamic 3D contents is achieved in our implemented 36-view 3D display prototype. The results of crosstalk measurements are given and analyzed to evaluate the display performance.