Thermal changes during diamond turning always present to some degree. For small parts with relatively short cut times, the effects can be minimal with modest thermal management. As parts become large and turning times increase, thermal effects can manifest themselves in a variety of ways. In this paper, we describe three different unique applications where temperature cycling and drift modified the original plan for part fabrication: a roll-to-roll embossed microprism array, a large diameter acrylic lens, and diamond turning a large mandrel.
This paper introduces full bandwidth Coarse Integral Holographic Display architecture with spatial tiling for scalability. The new method uses a large resonant scanner in conjunction with spatial tiling of spatial light modulators (SLMs) to create doubling the hologram’s horizontal size and utilize the full bandwidth of the SLMs.
We aim to produce a wide field-of view large autostereoscopic display for multiple viewers based on a 1D retroreflective screen and overheard microprojectors. The 1D retroreflective screen consists of retroreflector, anisotropic diffuser, and embedded fiber-optic array with optical sensors. Microprojectors modified with wide angle converter lenses are mounted unobtrusively over each viewing location. Each projector’s structured lighting is detected by the screen’s sensor array for calibration. Pin-cushion distortion correction, rectification and cross-talk reduction are implemented for proper stereo fusion. We examine common viewing scenarios of single viewer autostereoscopic projection, multiprojector automultiscopic projection, side by side multiviewer common and independent autostereoscopic projection, and frontback autostereoscopic projection.
KEYWORDS: Holograms, 3D image processing, 3D modeling, Visualization, Holography, 3D image reconstruction, Data modeling, 3D displays, 3D vision, Light sources and illumination
An approach of rapid hologram generation for the realistic three-dimensional (3-D) image reconstruction based on the angular tiling concept is proposed, using a new graphic rendering approach integrated with a previously developed layer-based method for hologram calculation. A 3-D object is simplified as layered cross-sectional images perpendicular to a chosen viewing direction, and our graphics rendering approach allows the incorporation of clear depth cues, occlusion, and shading in the generated holograms for angular tiling. The combination of these techniques together with parallel computing reduces the computation time of a single-view hologram for a 3-D image of extended graphics array resolution to 176 ms using a single consumer graphics processing unit card.
One aim of Spatial Augmented Reality is to visually integrate synthetic objects into real-world spaces amongst physical
objects, viewable by many observers without 3D glasses, head-mounted displays or mobile screens. In common
implementations, using beam-combiners, scrim projection, or transparent self-emissive displays, the synthetic object’s
and real-world scene’s light combine additively. As a result, synthetic objects appear low-contrast and semitransparent
against well-lit backgrounds, and do not cast shadows. These limitations prevent synthetic objects from appearing solid
and visually integrated into the real-world space. We use a transparent LCD panel as a programmable dynamic
mask. The LCD panel displaying the synthetic object’s silhouette mask is colocated with the object’s color image, both
staying aligned for all points-of-view. The mask blocks the background providing occlusion, presents a black level for
high-contrast images, blocks scene illumination thus casting true shadows, and prevents blow-by in projection scrim
arrangements. We have several implementations of SAR with LCD masks: 1) beam-combiner with an LCD mask, 2)
scrim projection with an LCD mask, and 3) transparent OLED display with an LCD mask. Large format (80” diagonal)
and dual layer volumetric variations are also implemented.
A holographic rendering algorithm using a layer-based structure with angular tiling supports view-dependent shading and accommodation cues. This approach also has the advantages of rapid computation speed and visual reduction of layer gap artefacts compared to other approaches. Holograms rendered with this algorithm are displayed using an SLM to demonstrate view-dependent shading and occlusion.
The Switching Dual Layer Display with a Dynamic LCD Mask is a multi-layer three-dimensional display capable of independent layer content and occlusion between layers. The display consists of a spaced stack of transparent LCD panel and LCD monitor synchronously switching between content, mask, and backlight states. In the first state, the back layer displays white and the front layer displays its content. The back layer acts as a backlight for the front layer, making the front layer content visible. In the second state, the back layer displays content and the front layer displays a mask. The back layer content is occluded by the front layer mask. Rapidly alternating between states, the viewer perceives opaque high-contrast foreground content occluding the background. Besides multi-plane imagery, depth-blending using opacity allows for smooth 3D volumetric imagery at the cost of reduced field of view. The addition of a relay mirror and a phantom mask allows solid appearing front layer content to optically float above and occlude the back layer. The floating front layer is non-physical, so both display layers are accessible for interactive applications.
Image-based holographic stereogram rendering methods for holographic video have the attractive properties of moderate
computational cost and correct handling of occlusions and translucent objects. These methods are also subject to the
criticism that (like other stereograms) they do not present accommodation cues consistent with vergence cues and thus
do not make use of one of the significant potential advantages of holographic displays. We present an algorithm for the
Diffraction Specific Coherent Panoramagram -- a multi-view holographic stereogram with correct accommodation cues,
smooth motion parallax, and visually defined centers of parallax. The algorithm is designed to take advantage of parallel
and vector processing in off-the-shelf graphics cards using OpenGL with Cg vertex and fragment shaders. We introduce
wavefront elements - "wafels" - as a progression of picture element "pixels", directional element "direls", and holographic
element "hogels". Wafel apertures emit controllable intensities of light in controllable directions with controllable
centers of curvature, providing accommodation cues in addition to disparity and parallax cues. Based on simultaneously
captured scene depth information, sets of directed variable wavefronts are created using nonlinear chirps, which
allow coherent diffraction of the beam across multiple wafels. We describe an implementation of this algorithm using a
commodity graphics card for interactive display on our Mark II holographic video display.
Horizontal-parallax-only holographic stereograms of nearly SDTV resolution (336 pixels by 440 lines by 96 views) of
textured and normal-mapped models (500 polygons) are rendered at interactive rates (10 frames/second) on a single
dual-head commodity graphics processor for use on MIT's third-generation electro-holographic display. The holographic
fringe pattern is computed by a diffraction specific holographic stereogram algorithm designed for efficient
parallelized vector implementation using OpenGL and Cg vertex/fragment shaders. The algorithm concentrates on lightfield
reconstruction by holographic fringes rather than the computation of the interferometric process of creating the
holographic fringes.
The novel frequency-multiplexed modulator architecture of the MIT Mark III holo-video display poses a significant
challenge in generation of appropriate video signals. Unlike in our previous work, here it is necessary to generate a
group of adjacent single-sideband RF signals; as this display is intended to be manufacturable at consumer-electronics
prices we face the added requirement of compact and inexpensive electronics that are compatible with standard PC
graphics processors. In this paper we review the goals and architecture of Mark III and then describe our experiments
and results in the use of a hardware/software implementation of Weaver's single-sideband modulation method to upconvert
six 200MHz baseband analog video signals to a set of RF signals covering a nearly contiguous 1GHz range. We
show that our method allows efficient generation of non-overlapping signals without aggressive filtering.
We introduce a new holo-video display architecture ("Mark III") developed at the MIT Media Laboratory. The goal of
the Mark III project is to reduce the cost and size of a holo-video display, making it into an inexpensive peripheral to a
standard desktop PC or game machine which can be driven by standard graphics chips. Our new system is based on
lithium niobate guided-wave acousto-optic devices, which give twenty or more times the bandwidth of the tellurium
dioxide bulk-wave acousto-optic modulators of our previous displays. The novel display architecture is particularly designed
to eliminate the high-speed horizontal scanning mechanism that has traditionally limited the scalability of Scophony-
style video displays. We describe the system architecture and the guided-wave device, explain how it is driven
by a graphics chip, and present some early results.
Our goal is to produce a micro-optical scanner at the tip of an ultrathin flexible endoscope with an overall diameter of 1 mm. Using a small diameter piezoelectric tube actuator, a cantilevered optical fiber can be driven in mechanical resonance to scan a beam of light in a space-filling, spiral scan pattern. By knowing and/or controlling the fiber position and acquiring backscattered intensity with a photodetector, an image is acquired. A microfabrication process of computer-controlled acid etching is used to reduce the mass along the fiber scanner shaft to allow for high scan amplitude and frequency. A microlens (<1 mm diameter) is fabricated on the end of the optical fiber to reduce divergence of the scanned optical beam. This added mass of the microlens at the free end of the fiber causes the location of the second vibratory node to shift to near the focal length of the microlens. The result is a microlens undergoing angular rotation along two axes with minimal lateral microlens displacement. Preliminary experimental results indicate that this method of optical beam scanning can deliver laser energy over wide fields of view (>50 degrees full angle), up to video scan rates (>10 KHz), while maintaining a scanner diameter of 1 mm. A comparison can be made to bi-axial mirror scanners being fabricated as a MEMS device (micro-electro-mechanical system). Based on the opto-mechanical performance of these microlensed fiber scanners, flexible catheter scopes are possible for new microendoscopies that combine imaging with laser diagnoses.
KEYWORDS: Light sources and illumination, Sensors, Endoscopes, Light sources, 3D metrology, Scanners, Imaging systems, 3D image processing, Photogrammetry, 3D vision
The Single Fiber Scanning Endoscope (SFSE) is a miniature flexible endoscope with unique features that promises to open new minimally invasive procedures for previously inaccessible diseases. There is a need for enhancement of depth cues and 3D measurement in procedures using monoscopic endoscopes. The SFSE uses scanning acquisition that gives it unique imaging properties which are advantageous for 3D vision algorithms -- simultaneous images can be created from multiple sensors all having common viewpoints but different lighting directions. A radiometric dual exists between array and scanning acquisition systems, so scanning acquisition images appear to have the light source originating from the sensors and the viewpoint at the scanner location. Disparity and photometric stereo techniques are investigated. A novel method for interactive virtual lighting allows the surface to be illuminated from any virtual lighting direction, even those not physically possible with endoscope, for use with either monocular or binocular images. This enhances or provides depth cues from shading and parallax. Using the photometric stereo method a 3D mesh representing the surface shape is obtained. A combination of disparity stereo and photometric stereo techniques creates dense range maps and measurements. The ability to make dense 3D measurements allow accurate volume measurements for dosage, risk estimation, and healing progress evaluations.
Commercial optical endoscopes rely on image transfer and acquisition based on an array of photon detectors, such as a coherent fiberoptic bundle, a video camera, and/or the human retina. An alternative approach uses a resonantly vibrating optical fiber that scans laser illumination. However, the limitation of laser-scanning endoscopic development has been the technological challenge of fabricating a small diameter, opto-mechanical scanner. A proof-of-concept micro-optical scanner has been built using a 2.3 mm diameter piezoelectric actuator and 4 mm diameter lenses. Images are generated using resonant spiral scanning of the fiber, projecting monochromatic laser light to an illumination plane. A single photodetector is used to acquire grayscale images one pixel at a time. In vitro, the acquired images of test targets have 10 to 20 micrometers maximum spatial resolution and a field-of-view that can be electronically varied.
The Single Fiber Scanning Endoscope (SFSE) is a new class of endoscopes being developed at the University of Washington's Human Interface Technology lab which uses combinations of a resonating optical fiber and a single photodetector to produce large field of view, high-resolution images from a small flexible package. Although current prototypes show the validity of the concept, the nonlinear response of the resonant optical fiber under open loop control creates image distortion or limits the frame rate. Due to low damping and nonlinear effects in the fiber, open loop control, phase lock loops, PID control, classical and modern controllers are all unable to produce accurate, reproducible, robust high frequency 2D scans. A nonlinear control scheme, feedback linearization, is capable of accurately producing a scan and is robust to most of the unavoidable manufacturing and environmental variability in the resonant scanner. Through theoretical analysis and simulations, this paper reviews the application of the following variety of open loop and closed loop controllers to the nonlinear scanner of the SFSE: open loop control, modelless closed loop control (phase lock loop and PID control), feedforward plus feedback classical and modern state space tracking control, and nonlinear feedback linearization control.
Flexible endoscopes currently used in medicine have a fundamental tradeoff. Either resolution or field of view (FOV) is sacrificed when the scope diameter is less than 3 mm, since the minimum pixel size is usually greater than 4 microns in a pixel-array such as a camera or fiber bundle. Thus, the number of pixels within the image plane determines the minimum size of a conventional scope. However, an image plane is not required for image acquisition using a scanning single-fiber scope. Both high resolution and wide FOV are possible in a scanning single-fiber scope of 1 to 2 mm in diameter. The technical challenge is to produce a two- dimensional scanned beam of light at the distal tip of the scope. By manipulating a resonant fiberoptic cantilever as the optical scanner, various 2-D scan patterns can be produced. The general design concepts and analyses of the fiberoptic scanner for scaling to small size and high resolution/FOV are reviewed. In our initial experimental tests, the size of the photon detector in a fiberoptic scanning scope is demonstrated to not affect image resolution, unlike existing endoscopes with pixel-based detector systems.
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