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Abstract:
This presentation introduces FlexiVol, a novel swept volumetric display system utilizing an elastic diffuser, specifically an array of elastic strips, to enable safe, direct, reach-through interaction with true 3D graphics. The work addresses the limitation of traditional volumetric displays where rigid, fast-moving diffusers pose safety hazards and necessitate indirect interaction methods. The research involves a detailed characterization of potential elastic materials (elastanes, silicone, elastic bands, projection screen fabric) based on mechanical (stiffness, plastic deformation, hysteresis), optical (diffusion, distortion, resolution), and oscillatory (frequency response, resonance) properties, leading to the selection of elastic bands as the optimal diffuser material. A design space for reach-through interaction techniques, combining gestures and actions, is proposed. A user study (N=18) compared FlexiVol's direct interaction (finger tracking) against a traditional 3D mouse for selection, tracing, and docking tasks. Results show direct interaction is significantly faster and perceived as less cognitively demanding (lower NASA-TLX scores), more natural, and intuitive, despite a minor trade-off in accuracy for the docking task. Future work includes integrating haptic feedback (ultrasound, electrotactile), scaling the display, and exploring collaborative applications.
FlexiVol: Enabling Direct Interaction in Volumetric Displays
0:02 Introduction: Elodie Bouzbib introduces FlexiVol, a volumetric display featuring an elastic diffuser to permit direct "reach-through" interaction with 3D content, funded by ERC Intevol and Touchless grants.
0:22 Volumetric Displays Explained: Defines volumetric displays as devices creating true 3D visual representations, offering autostereoscopic views without requiring headsets.
0:47 Swept Volumetric Displays: Details this specific type, which uses a rapidly oscillating diffuser surface synchronized with a projector slicing a 3D object. Persistence of vision creates the perception of a solid 3D volume.
2:00 The Interaction Problem: Highlights that the fast-moving, often rigid, diffusers in traditional swept displays create a safety hazard, preventing direct hand interaction and typically requiring protective domes and indirect methods like 3D mice or hand tracking with avatars.
2:45 Research Goal: Direct Interaction: The core aim is to enable users to safely put their hands directly into the display volume for interaction, aligning input and output space.
3:07 FlexiVol Concept: Proposes using elastic diffusers instead of rigid ones to allow safe reach-through interaction.
3:18 Material Characterization: Investigates necessary properties for elastic diffusers, focusing on mechanical (stiffness, deformation), optical (projection quality), and oscillatory (resonance, shape) characteristics.
3:36 Candidate Materials Tested: Evaluates six materials: three types of elastane, silicone, elastic bands, and a standard projection screen fabric, initially as strips.
3:51 Stiffness & Deformation Testing: Measures force required for displacement using a load cell. Notes that some materials (Elastane C, Projection Screen) exhibit excessive or plastic (permanent) deformation. Elastic bands show high stiffness but remain elastic.
4:45 Hysteresis Testing: Assesses whether materials return to their original state after stretching. Elastic bands showed minimal hysteresis, while others like the projection screen deformed irreversibly or twirled (Elastane C).
5:47 Optical Property Testing: Examines projection quality (RGB stripes, grid, white light) when materials are stretched/unstretched. Silicone reflects too much; some elastanes cause blurring or distortion when stretched; elastic bands show dark lines but maintain overall structure and acceptable RGB intensity.
7:17 Frequency Response Testing: Characterizes how materials oscillate at different frequencies using speakers and stroboscopic light. Resonance frequency is important to avoid conflicts with the display's operating frequency.
7:54 Material Selection Guidelines: Establishes criteria: must remain elastic (no plastic deformation/twirling), maintain optical quality without distortion/blur, and have a resonance frequency different from the system's operating frequency.
8:27 Elastic Bands Selected: Chosen as the best compromise, retaining mechanical/optical properties during elongation, laying flat during oscillation due to anisotropy, and having a suitable resonance frequency.
8:39 Reach-Through Interaction Design Space: Defines possible direct interactions inspired by 2D elastic displays and AR/VR, including actions (swipe, touch, scale, pinch, rotate, push) and gestures (using fingers/hands, interacting with or between strips).
9:55 User Study Overview: A study was conducted to validate FlexiVol by comparing reach-through interaction (using finger tracking) with a traditional 3D mouse across three tasks, measuring time, accuracy, and cognitive load (NASA-TLX).
10:16 User Study Tasks: Included 1) Selection of spheres, 2) Tracing 3D circuits, and 3) Docking small cubes into larger ones.
Selection: Reach-through was significantly faster (avg. 1.0s vs 1.9s for 3D mouse).
Tracing: Reach-through showed significantly better accuracy (smaller position deviation); completion time was similar.
Docking: Reach-through was significantly faster, but the 3D mouse was slightly more accurate (smaller positional error).
Workload: Reach-through had significantly lower cognitive load (NASA-TLX) overall, particularly in mental demand, temporal demand, effort, and frustration.
12:18 User Study Results (Qualitative): Participants largely preferred reach-through, finding it more natural, intuitive, and easier. Initial apprehension about touching the moving strips was overcome, describing the sensation as soft or pleasant. Users expressed interest in more complex gestures (pinching, grabbing) and envisioned various applications (3D modeling, collaboration, medical).
13:09 Future Work Directions: Plans include integrating haptic feedback (focused ultrasound, electrotactile feedback via conductive thread), increasing display size (potentially using helical sweeping), and exploring collaborative use cases.
14:00 Summary of Contributions: Re-iterates the key achievements: the novel elastic diffuser concept, material selection guidelines, interaction design space, and empirical validation of reach-through interaction benefits.