Publikationen von Maximilian Schrapel

Iterative design cycles for tangible user interfaces and wearable devices require efficient prototyping techniques to optimize development and to elevate the overall design efficacy. A key challenge for rapid prototyping techniques such as cardboard prototyping, 3D printing, or laser cutting is the integration of conductive surfaces. Additional wiring, conductive paint, or special materials like conductive filament often lack the necessary high conductivity and sufficient durability for designing on-skin wearables to measure muscle activity or to electrically stimulate the skin and muscles. To solve this problem we propose to combine spraying and electroplating to create surfaces that exhibit high conductivity, are solderable, corrosion-resistant and skin-friendly, and embody both practical functionality and aesthetic value. In this paper, we describe an effective spraying and electroplating process for rapid prototyping and demonstrate its applicability using several examples of tangible user interfaces. Further, we discuss advantages and disadvantages and describe limitations of the approach.

Urban environments are often characterized by loud and annoying sounds. Noise-cancelling headphones can suppress negative influences and superimpose the acoustic environment with audio-augmented realities (AAR). So far, AAR exhibited limited interactivity, e. g., being influenced by the location of the listener. In this paper we explore the superimposition of synchronized, augmented footstep sounds in urban AAR environments with noise-cancelling headphones. In an online survey, participants rated different soundscapes and sound augmentations. This served as a basis for selecting and designing soundscapes and augmentations for a subsequent in-situ field study in an urban environment with 16 participants. We found that the synchronous footstep feedback of our application EnvironZen contributes to creating a relaxing and immersive soundscape. Furthermore, we found that slightly delaying footstep feedback can be used to slow down walking and that particular footstep sounds can serve as intuitive navigation cues.

Although in many cases contracts can be made or ended digitally, laws require handwritten signatures in certain cases. Forgeries are a major challenge with digital contracts, as their validity is not always immediately apparent without forensic methods. Illiteracy or disabilities may result in a person being unable to write their full name. In this case x-mark signatures are used, which require a witness for validity. In cases of suspected fraud, the relationship of the witnesses must be questioned, which involves a great amount of effort. In this paper we use audio and motion data from a digital pen to identify users via handwritten symbols. We evaluated the performance our approach for 19 symbols in a study with 30 participants. We found that x-marks offer fewer individual features than other symbols like arrows or circles. By training on three samples and averaging three predictions we reach a mean F1-score of F1 = 0.87, using statistical and spectral features fed into SVMs.

Creating tactile patterns on the body via a spatial arrangement of many tactile actuators offers many opportunities and presents a challenge, as the design space is enormous. This paper presents a VR interface that enables designers to rapidly prototype complex tactile interfaces. It allows for painting strokes on a modeled body part and translates these strokes into continuous tactile patterns using an interpolation algorithm. The presented VR approach avoids several problems of traditional 2D editors. It realizes spatial 3D input using VR controllers with natural mapping and intuitive spatial movements. To evaluate this approach in detail, we conducted a user study and iteratively improved the system. The study participants gave predominantly positive feedback on the presented VR interface (SUS score 79.7, AttrakDiff “desirable”). The final system is released alongside this paper as an open-source Unity project for various tactile hardware.

We present SpectroPhone, a surface material sensing approach based on the rear camera of a smartphone and external white LED light sources. Warm and cool white LEDs, as used for dual or quad flashlights in smartphones, differ in their spectral distribution in the red and blue range. Warm and cool white LEDs in combination can produce a characteristic spectral response curve, when their light is reflected from a surface. We show that with warm and cool white LEDs and the rear-camera of a smartphone 30 different materials can be distinguished with an accuracy of 99 \%. Based on a dataset consisting of 13500 images of material surfaces taken at different LED light intensities, we report recognition rates of support vector machines with different parameters.

Smartwatches can be used independently from smartphones, but input tasks like messaging are cumbersome due to the small display size. Parts of the display are hidden during interaction, which can lead to incorrect input. For simplicity, instead of general text input a small set of answer options are often provided, but these are limited and impersonal. In contrast, free-form drawings can answer messages in a very personal way, but are difficult to produce on small displays. To enable precise drawing input on smartwatches we present a magnetic stylus that is tracked on the back of the hand. In an evaluation of several algorithms we show that 3D position estimation with a 7.5x20mm magnet reaches a worst-case 6% relative position error on the back of the hand. Furthermore, the results of a user study are presented, which show that in the case of drawing applications the presented technique is faster and more precise than direct finger input.

Public bookcases offer the opportunity to serendipitously discover books and to anonymously share books with others. The set of available books as well as the sharing patterns are highly dynamic, as anybody can freely take or donate books. This makes it difficult for users to see what is available or of interest to them. To support book sharing via public bookcases we developed a mobile AR application that highlights relevant books in the camera viewfinder and that facilitates searching for specific books. The application recognizes books via text and color features on the spine. In a lab study with 15 participants we evaluated our book recognition algorithm and found that it outperforms unaided visual search. We interviewed users of public bookcases and analyzed the bookcases’ setup and rate of change. A subsequent field evaluation of the AR application on nine public bookcases found a recognition accuracy of 80 % for 450 books under different conditions. The proposed approach provides the basis for effectively sharing books via public bookcases.

Winter sports like skiing are becoming increasingly popular for both competitive and recreational activities. To minimize the risk of injury, new innovations in skiing equipment have been developed in recent years. However, unexpected slope conditions can still increase risks during skiing. The static categorisation of ski slopes in winter sports resorts does not take into account dynamic changes of difficulty due to high traffic volumes or sudden weather changes. Up to now, efforts have been made to measure the current conditions via satellite imaging or installations on the slope. However, this requires intervention in nature and causes high maintenance costs. To solve these issues we present our preliminary design of a wearable system to let skiers implicitly measure current slope conditions during their skiing experience. Audio and motion data are recorded from a prototype mounted on a ski boot. We show that the data generated by the prototype can be successfully classified with a neural network. We collected data from a skiing activity to demonstrate our concept and discuss the identified challenges in fitting the proposed approach to winter sports equipment.

Complex software-based systems involve several stakeholders, their activities and interactions with the system. Vision videos are used during the early phases of a project to complement textual representations. They visualize previously abstract visions of the product and its use. By creating, elaborating, and discussing vision videos, stakeholders and developers gain an improved shared understanding of how those abstract visions could translate into concrete scenarios and requirements to which individuals can relate. [Question/problem] In this paper, we investigate two aspects of refining vision videos: (1) Refining the vision by providing alternative answers to previously open issues about the system to be built. (2) A refined understanding of the camera perspective in vision videos. The impact of using a subjective (or “ego”) perspective is compared to the usual third-person perspective. [Methodology] We use shopping in rural areas as a real-world application domain for refining vision videos. Both aspects of refining vision videos were investigated in an experiment with 20 participants. [Contribution] Subjects made a significant number of additional contributions when they had received not only video or text but also both – even with very short text and short video clips. Subjective video elements were rated as positive. However, there was no significant preference for either subjective or non-subjective videos in general.

Digital pens emit ink on paper and digitize handwriting. The range of the pen is typically limited to a special writing surface on which the pen's tip is tracked. We present Pentelligence, a pen for handwritten digit recognition that operates on regular paper and does not require a separate tracking device. It senses the pen tip's motions and sound emissions when stroking. Pen motions and writing sounds exhibit complementary properties. Combining both types of sensor data substantially improves the recognition rate. Hilbert envelopes of the writing sounds and mean-filtered motion data are fed to neural networks for majority voting. The results on a dataset of 9408 handwritten digits taken from 26 individuals show that motion+sound outperforms single-sensor approaches at an accuracy of 78.4% for 10 test users. Retraining the networks for a single writer on a dataset of 2120 samples increased the precision to 100% for single handwritten digits at an overall accuracy of 98.3%.

Everyday mobility encompasses different forms of public and private transportation and different forms of physical activity. However, in general everyday mobility does not involve substantial levels of physical activity. There are sometimes structural reasons or a lack of motivation and time to realize an active lifestyle in the context of mobility. The goal of this workshop is to investigate ways to integrate physical activity into everyday mobility in accordance with widely accepted health recommendations. We aim to explore wearable and ambient systems that sense and support active navigation as well as conceptual aspects from a variety of perspectives, such as persuasive technologies, and thus invite researchers from different disciplines to contribute their point of view by means of position papers, posters, and demonstrations. One planned outcome of this workshop is a set of design guidelines for navigation systems that explicitly consider health aspects. For the full-day workshop we aim to explore requirements and design challenges in a creative setting.

Nowadays, wearables can easily monitor and display physical activities throughout the day. Health recommendations are often used to set daily goals, but these barely take individual requirements into account. In addition, due to limited individual adaptability, there are various life situations in which these goals are not achieved due to missing motivation or time. In this position paper we discuss in particular how health recommendations can be integrated into everyday life and what challenges arise. We also address spatial requirements that are necessary for an active lifestyle.

Bewegungsmangel ist laut WHO zu einem der führenden Risikofaktoren für gesundheitliche Probleme geworden (WHO 2007: 8) und resultiert aus unserer veränderten Lebens- und Arbeitswelt mit langen körperlichen Ruhezeiten. Neben diesen Phasen, die beispielsweise sitzend am Büroarbeitsplatz verbracht werden, spielt hierbei auch unser Mobilitätsverhalten eine zentrale Rolle. Knapp die Hälfte der Wege, die mit dem Automobil zurückgelegt werden, sind fünf Kilometer lang oder kürzer (infas & DLR 2010, 41). Diese Streckenlängen können auch durch Fuß- und Radverkehr als Bestandteile der aktiven Mobilität geleistet werden. An dieser Stelle setzt das Forschungsprojekt „Aktive Navigation“ der Forschungsinitiative „Mobiler Mensch: Intelligente Mobilität in der Balance von Autonomie, Vernetzung und Security“ der Leibniz Universität Hannover an. Aufbauend auf der Nutzung von Wearables und Smartphones wird eine App entwickelt, die basierend auf der Vorhersage der täglichen Aktivität der Nutzenden eine Route zum Ziel auswählt. Die Routenwahl schließt andere Verkehrsmittel mit ein, soll insgesamt aber dazu dienen, die tägliche Schrittzahl und damit die körperliche Aktivität zu erhöhen.

Most common forms of haptic feedback use vibration, which immediately captures the user's attention, yet is limited in the range of strengths it can achieve. Vibration feedback over extended periods also tends to be annoying. We present compression feedback, a form of haptic feedback that scales from very subtle to very strong and is able to provide sustained stimuli and pressure patterns. The demonstration may serve as an inspiration for further work in this area, applying compression feedback to generate subtle, intimate, as well as intense feedback.