We introduce Rhapso, a 3D printing system designed to embed a diverse range of continuous fiber materials within 3D objects during the printing process. This approach enables integrating properties like tensile strength, force storage and transmission, or aesthetic and tactile characteristics, directly into low-cost thermoplastic 3D prints. These functional objects can have intricate actuation, self-assembly, and sensing capabilities with little to no manual intervention. To achieve this, we modify a low-cost Fused Filament Fabrication (FFF) 3D printer, adding a stepper motor-controlled fiber spool mechanism on a gear ring above the print bed. In addition to hardware, we provide parsing software for precise fiber placement, which generates G-code for printer operation. To illustrate the versatility of our system, we present applications that showcase its extensive design potential. Additionally, we offer comprehensive documentation and open designs, empowering others to replicate our system and explore its possibilities.

Reality Rifts are interfaces between the physical and the virtual reality, where incoherent observations of physical behavior lead users to imagine comprehensive and plausible end-to-end dynamics. Reality Rifts emerge in interactive physical systems that lack one or more components that are central to their operation, yet where the physical end-to-end interaction persists with plausible outcomes. Even in the presence of a Reality Rift, users can still interact with a system—much like they would with the unaltered and complete counterpart—leading them to implicitly infer the existence and imagine the behavior of the lacking components from observable phenomena and outcomes. Therefore, dynamic systems with Reality Rifts trigger doubt, curiosity, and rumination—a sense of wonder that users experience when observing a Reality Rift due to their innate curiosity.

Polarized light mosaics (PLMs) are color-changing structures that alter their appearance based on the orientation of incident polarized light. While a few artists have developed techniques for crafting PLMs by hand, the underlying material properties are difficult to reason about; there exist no tools to bridge the high-level design objectives with the low-level physics knowledge needed to create PLMs. In this paper, we introduce the first system for creating Polagons: machine-made PLMs crafted from cellophane with user-defined color changing behaviors. Our system includes an interface for designing and visualizing Polagons as well as a fabrication process based on laser cutting and welding that requires minimal assembly by the user. We define the design space for Polagons and demonstrate how formalizing the process for creating PLMs can enable new applications in fields such as education, data visualization, and fashion.

We present AirRacket, perceptual modeling and design of ungrounded, directional force feedback for virtual racket sports. Using compressed air propulsion jets to provide directional impact forces, we iteratively designed for three popular sports that span a wide range of force magnitudes: ping-pong, badminton, and tennis. To address the limited force magnitude of ungrounded force feedback technologies, we conducted a perception study which discovered the novel illusion that users perceive larger impact force magnitudes with longer impact duration, by an average factor of 2.57x. Through a series of formative, perceptual, and user experience studies with a combined total of 72 unique participants, we explored several perceptual designs using force magnitude scaling and duration scaling methods to expand the dynamic range of perceived force magnitude. Our user experience evaluation showed that perceptual designs can significantly improve realism and preference vs. physics-based designs for ungrounded force feedback systems.

We present Flaticulation, a method to laser cut joints that clutch two cut-in-place flat boards at designated articulated angles. We discover special T-patterns added on the shared edge of two pieces allowing them to be clutched at a bending angle. We analyze the structure and propose a parametric model regarding the T-pattern under laser cutting to predict the joint articulated angle. We validate our proposed model by measuring real prototypes and conducting stress-strain analysis to understand their structural strength. Finally, we provide a user interface for our example applications, including fast assembling unfolded 3D polygonal models and adding detent mechanisms for functional objects such as a mouse and reconfigurable objects such as a headphone.

We present PneuSeries, a series of modularized inflatables where their inflation and deflation are propagated in-between stage by stage to form various shapes. The key component of PneuSeries is the bidirectional check valve that passively regulates the air flowing in/out from/to adjacent inflatables, allowing each of the inflatables to be inflated/deflated one by one through serial propagation. The form of the inflatable series thus is programmed by the sequential operations of a pump that push/pull the air in/out. In this paper, we explored the design of PneuSeries and implemented working prototypes as a proof of concept. In particular, we built PneuSeries with (1) modularized cubical, cuboidal, tetrahedral, prismatic, and custom inflatables to examine their shape forming, (2) fast assembly connectors to allow quick reconfiguration of the series, and (3) folding mechanism to reduce irregularity of the shrunken inflatables. We also evaluated the inflating and deflating time and the flow rate of the valve for simulating the inflating and deflating process and display the steps and time required to transform in our software. Finally, we demonstrate example objects that show the capability of PneuSeries and its potential applications.

Optical illusions have been brought into recent video games to enhance gaming experiences. However, a large corpus of optical illusions remains unused, while few games incorporate illusions seamlessly. To mitigate the gap, we propose a workflow to guide game designers in applying optical illusions to their video games, i.e., in making more illusion games. In particular, our workflow consists of 5 stages: (1) choosing a game object, (2) searching for a matching illusion, (3) selecting an illusion mechanic, (4) integrating the selected illusion into the game, and (5) optionally revealing the illusion. To facilitate our workflow, we provide a tag database with 163 illusions that are labeled by their in-game visual elements and desired effects. We also provide example editing interfaces of 6 illusions for game designers. We walk through our workflow and showcase 6 resulting illusion games. We implemented these 6 games (with and without illusion) and conducted a 12-participant study to gain a preliminary understanding of how illusions enhance gaming experiences. To evaluate our workflow, we invited 6 game designers and 6 experienced players to follow our workflow and design their own illusion games, where 3 experienced game designers completed 2-week in-depth developments. We report their games, qualitative feedback and discuss reflection on our workflow, database and editing interfaces.

We present Impossible Staircase, a real-walking virtual reality system that allows users to climb an infinite virtual tower. Our set-up consists of an one-level scaffold and a lifter. A user climbs up the scaffold by real walking on a stairway while wearing a head-mounted display, and gets reset to the ground level by a lifter imperceptibly. By repeating this process, the user perceives an illusion of climbing an infinite number of levels. Our system achieves the illusion by (1) controlling the movement of the lifter to generate reverse and imperceptible motion, (2) guiding the user through the scaffold with delay mechanisms to reset the lifter in time, and (3) procedural generating overlapping structures to enlarge perceived height of each level. We built a working system and demonstrated it with a 15-min experience. With the working system, we conducted user studies to gain deeper insights into vertical motion simulation and vertical real walking in virtual reality.

We present Haptic-go-round, a surrounding platform that allows deploying props and devices to provide haptic feedbacks in any direction in virtual reality experiences. The key component of Haptic-go-round is a motorized turntable that rotates the correct haptic device to the right direction at the right time to match what users are about to touch. We implemented a working platform including plug-and-play prop cartridges and a software interface that allow experience designers to agilely add their haptic components and use the platform for their applications. We conducted technical experiments and two user studies on Haptic-go-round to evaluate its performance. We report the results and discuss our insights and limitations.

Strength training improves overall health, well-being, physical appearance, and sports performance, with training programs specifying variables such as sets, repetitions, rest time, weight, and tempo. The repetitive nature of strength training, typically performed at fixed tempo, has made it challenging to develop entertaining exergames for common strength training exercises. We present StrengthGaming, which uses scaling and shuffling technique to provide tempo variations to strength training while preserving the training volume and training goals. It affords game designers more flexibility in designing strength training-based exergames. We developed a prototype game, inspired by FlappyBird, that uses a wearable orientation sensor to track the repetition tempo to control a flying character, using both fixed tempo design and dynamic tempo design. Results from our 24-person user study showed that dynamic tempo was significantly more entertaining than fixed tempo (p<0.01), and was preferred by participants.

Procedural generation in virtual reality (VR) has been used to adapt the virtual world to various indoor environments, fitting different geometries and interiors with virtual environments. However, such applications require that the physical environment be known or pre-scanned prior to use to then generate the corresponding virtual scene, thus restricting the virtual experience to a controlled space. In this paper, we present VRoamer, which enables users to walk unseen physical spaces for which VRoamer procedurally generates a virtual scene on-the-fly. Scaling to the size of office buildings, VRoamer extracts walkable areas and detects physical obstacles in real time, instantiates pre-authored virtual rooms if their sizes fit physically walkable areas or otherwise generates virtual corridors and doors that lead to undiscovered physical areas. The use of these virtual structures allows VRoamer to (1) temporarily block users' passage, thus slowing them down while increasing VRoamer's insight into newly discovered physical areas, (2) prevent users from seeing changes beyond the current virtual scene, and (3) obfuscate the appearance of physical environments. VRoamer animates virtual objects to reflect dynamically discovered changes of the physical environment, such as people walking by or obstacles that become apparent. In our proof-of-concept study, participants were able to walk long distances through a procedurally generated dungeon experience and reported high levels of immersion.

We present a system that complements virtual reality experiences with passive props, yet still allows modifying the virtual world at runtime. The main contribution of our system is that it does not require any actuators; instead, our system employs the user to reconfigure and actuate otherwise passive props. We demonstrate a foldable prop that users reconfigure to represent a suitcase, fuse cabinet, railing, and a seat. A second prop, suspended from a long pendulum, not only stands in for inanimate objects, but also for objects that move and demonstrate proactive behavior, such as a group of flying droids that physically attack the user. Our approach conveys a sense of a living, animate world, when in reality the user is the only animate entity present in the system, complemented with only one or two physical props. In our study, participants rated their experience as more enjoyable and realistic than a corresponding no-haptics condition.

Although virtual reality hardware is now widely available, the uptake of real walking is hindered by the fact that it requires often impractically large amounts of physical space. To address this, we present VirtualSpace, a novel system that allows overloading multiple users immersed in different VR experiences into the same physical space. VirtualSpace accomplishes this by containing each user in a subset of the physical space at all times, which we call tiles; app-invoked maneuvers then shuffle tiles and users across the entire physical space. This allows apps to move their users to where their narrative requires them to be while hiding from users that they are confined to a tile. We show how this enables VirtualSpace to pack four users into 16m2. In our study we found that VirtualSpace allowed participants to use more space and to feel less confined than in a control condition with static, pre-allocated space.

We propose a class of passive haptics that we call Sparse Haptic Proxy: a set of geometric primitives that simulate touch feedback in elaborate virtual reality scenes. Unlike previous passive haptics that replicate the virtual environment in physical space, a Sparse Haptic Proxy simulates a scene's detailed geometry by redirecting the user's hand to a matching primitive of the proxy. To bridge the divergence of the scene from the proxy, we augment an existing Haptic Retargeting technique with an on-the-fly target remapping: We predict users' intentions during interaction in the virtual space by analyzing their gaze and hand motions, and consequently redirect their hand to a matching part of the proxy. We conducted three user studies on haptic retargeting technique and implemented a system from three main results: 1) The maximum angle participants found acceptable for retargeting their hand is 40°, with an average rating of 4.6 out of 5. 2) Tracking participants' eye gaze reliably predicts their touch intentions (97.5%), even while simultaneously manipulating the user's hand-eye coordination for retargeting. 3) Participants preferred minimized retargeting distances over better-matching surfaces of our Sparse Haptic Proxy when receiving haptic feedback for single-finger touch input. We demonstrate our system with two virtual scenes: a flight cockpit and a room quest game. While their scene geometries differ substantially, both use the same sparse haptic proxy to provide haptic feedback to the user during task completion.

We explore how to add haptics to walls and other heavy objects in virtual reality. When a user tries to push such an object, our system actuates the user's shoulder, arm, and wrist muscles by means of electrical muscle stimulation, creating a counter force that pulls the user's arm backwards. Our device accomplishes this in a wearable form factor.

Human actuation is the idea of using people to provide large-scale force feedback to users. The Haptic Turk system, for example, used four human actuators to lift and push a virtual reality user; TurkDeck used ten human actuators to place and animate props for a single user. While the experience of human actuators was decent, it was still inferior to the experience these people could have had, had they participated as a user. In this paper, we address this issue by making everyone a user. We introduce mutual human actuation, a version of human actuation that works without dedicated human actuators. The key idea is to run pairs of users at the same time and have them provide human actuation to each other. Our system, Mutual Turk, achieves this by (1) offering shared props through which users can exchange forces while obscuring the fact that there is a human on the other side, and (2) synchronizing the two users' timelines such that their way of manipulating the shared props is consistent across both virtual worlds. We demonstrate mutual human actuation with an example experience in which users pilot kites though storms, tug fish out of ponds, are pummeled by hail, battle monsters, hop across chasms, push loaded carts, and ride in moving vehicles.

We present "Level-Ups", computer-controlled stilts that allow virtual reality users to experience walking up and down steps. Each Level-Up unit is a self-contained device worn like a boot. Its main functional element is a vertical actuation mechanism mounted to the bottom of the boot that extends vertically. Unlike traditional solutions that are integrated with locomotion devices, Level-Ups allow users to walk around freely ("real-walking"). We present Level-Ups in a demo environment based on a head-mounted display, optical motion capture, and integrated with two different game engines. In a user study, participants rated the realism of stepping onto objects 6.0 out of 7.0 when wearing Level-Ups compared to 3.5 without.

TurkDeck is an immersive virtual reality system that reproduces not only what users see and hear, but also what users feel. TurkDeck produces the haptic sensation using props, i.e., when users touch or manipulate an object in the virtual world, they simultaneously also touch or manipulate a corresponding object in the physical world. Unlike previous work on prop-based virtual reality, however, TurkDeck allows creating arbitrarily large virtual worlds in finite space and using a finite set of physical props. The key idea behind TurkDeck is that it creates these physical representations on the fly by making a group of human workers present and operate the props only when and where the user can actually reach them. TurkDeck manages these so-called "human actuators" by displaying visual instructions that tell the human actuators when and where to place props and how to actuate them. We demonstrate TurkDeck at the example of an immersive 300m2 experience in 25m2 physical space. We show how to simulate a wide range of physical objects and effects, including walls, doors, ledges, steps, beams, switches, stompers, portals, zip lines, and wind. In a user study, participants rated the realism/immersion of TurkDeck higher than a traditional prop-less baseline condition (4.9 vs. 3.6 on 7 item Likert).

Motion platforms are used to increase the realism of virtual interaction. Unfortunately, their size and weight is proportional to the size of what they actuate. We present haptic turk, a different approach to motion platforms that is light and mobile. The key idea is to replace motors and mechanical components with humans. All haptic turk setups consist of a player who is supported by one or more turkers. The player enjoys an interactive experience, such as a flight simulation. The motion in the player's experience is generated by the turkers who manually lift, tilt, and push the player's limbs or torso. To get the timing and force right, timed motion instructions in a format familiar from rhythm games are displayed on turkers' mobile devices, which they attach to the player's body. We demonstrate a range of installations based on mobile phones, projectors, and head-mounted displays. In our user study, participants rated not only the experience as player as enjoyable (6.1/7), but also the experience as a turker (4.4/7). The approach of leveraging humans allows us to deploy our approach anytime anywhere, as we demonstrate by experimentally deploying at an art festival in the Nevada desert.

Multitouch tablets, such as iPad and Android tablets, support virtual keyboards for text entry. Our 64-user study shows that 98% of the users preferred different keyboard layouts and positions depending on how they were holding these devices. However, current tablets either do not allow keyboard adjustment or require users to manually adjust the keyboards. We present iGrasp, which automatically adapts the layout and position of virtual keyboards based on how and where users are grasping the devices without requiring explicit user input. Our prototype uses 46 capacitive sensors positioned along the sides of an iPad to sense users' grasps, and supports two types of grasp-based automatic adaptation: layout switching and continuous positioning. Our two 18-user studies show that participants were able to begin typing 42% earlier using iGrasp's adaptive keyboard compared to the manually adjustable keyboard. Participants also rated iGrasp much easier to use than the manually adjustable keyboard (4.2 vs 2.9 on five-point Likert scale.)

Automatic screen rotation improves viewing experience and usability of mobile devices, but current gravity-based approaches do not support postures such as lying on one side, and manual rotation switches require explicit user input. iRotateGrasp automatically rotates screens of mobile devices to match users' viewing orientations based on how users are grasping the devices. Our insight is that users' grasps are consistent for each orientation, but significantly differ between different orientations. Our prototype used a total of 44 capacitive sensors along the four sides and the back of an iPod Touch, and uses support vector machine (SVM) to recognize grasps at 25Hz. We collected 6-users' usage under 108 different combinations of posture, orienta-tion, touchscreen operation, and left/right/both hands. Our offline analysis showed that our grasp-based approach is promising, with 80.9% accuracy when training and testing on different users, and up to 96.7% if users are willing to train the system. Our user study (N=16) showed that iRo-tateGrasp had an accuracy of 78.8% and was 31.3% more accurate than gravity-based rotation.

We present iRotate, an approach to automatically rotate screens on mobile devices to match users' face orientation. Current approaches to automatic screen rotation are based on gravity and device orientation. Our survey of 513 users shows that 42% currently experience auto-rotation that leads to incorrect viewing orientation several times a week or more, and 24% find the problem to be very serious to extremely serious. iRotate augments gravity-based approach, and uses front cameras on mobile devices to detect users' faces and rotates screens accordingly. It requires no explicit user input and supports different user postures and device orientations. We have implemented a iRotate that works in real-time on iPhone and iPad, and we assess the accuracy and limitations of iRotate through a 20- participant feasibility study.

We present TUIC, a technology that enables tangible interaction on capacitive multi-touch devices, such as iPad, iPhone, and 3M's multi-touch displays, without requiring any hardware modifications. TUIC simulates finger touches on capacitive displays using passive materials and active modulation circuits embedded inside tangible objects, and can be used with multi-touch gestures simultaneously. TUIC consists of three approaches to sense and track objects: spatial, frequency, and hybrid (spatial plus frequency). The spatial approach, also known as 2D markers, uses geometric, multi-point touch patterns to encode object IDs. Spatial tags are straightforward to construct and are easily tracked when moved, but require sufficient spacing between the multiple touch points. The frequency approach uses modulation circuits to generate high-frequency touches to encode object IDs in the time domain. It requires fewer touch points and allows smaller tags to be built. The hybrid approach combines both spatial and frequency tags to construct small tags that can be reliably tracked when moved and rotated. We show three applications demonstrating the above approaches on iPads and 3M's multi-touch displays.