Designing a Wearable User Interface for Hands-free Interaction in Maintenance Applications Hendrik Witt, Tom Nicolai and Holger Kenn University of Bremen, Germany TZI Wearable Computing Group {hwitt, nicolai, kenn}@tzi.de Abstract— One challenge in wearable computing is the design of proper user interfaces and interaction concepts for applica- tions. This paper discusses the design of hands-free wearable user interfaces and shows an example interface for an aircraft maintenance application. The user interface we present used a wireless data glove for interaction. I. I NTRODUCTION In order to achieve user acceptance, the user interface of a computer system and its method of interaction are important parts. However, designing interactive user interfaces that are intuitive and even fun to use is a challenging task. For stationary computers, there exists a wealth of research results and software frameworks and a number of well-established interface classes such as desktop and touch-screen interfaces. For general-purpose mobile systems such as PDAs, desktop- based systems have been adapted and the desktop metaphor is mostly kept up. However, these interfaces are based on the implicit assumption that the user fully concentrates on the user interface, uses visual feedback to control the pointer, and most of the time has two hands available for controlling the user interface. In the desktop situation, he might use one hand for the mouse and the other to push and hold modifier keys on the keyboard. In the mobile situation, he usually uses one hand to hold the device and the second one to control it with a stylus, a keypad, a scroll wheel, or a joystick. These implicit assumptions have important effects. For example, the use of a mobile phone while steering a car is forbidden in many countries with the exception of using both headset and voice-activated speed dialing, thus removing both implicit assumptions of full user concentration and two-handed use. In wearable computing, these implicit assumptions also do not hold. As one of the goals of wearable computing is its situated use, e.g., in a work environment, we neither can assume that the user concentrates fully on the user interface nor that both hands are free. Additionally, limitations of wearable computers, e.g., used head-mounted displays (HMD) or low computation power make user interface development even more challenging [1]. This paper focuses on the question of how to design hands- free wearable user interfaces, i.e. user interfaces that do not force users to hold a device in hand while interacting with the system. The user interface we present will be used in aircraft maintenance. Aircraft technicians will be equipped with a wea- rable computer, HMD, and a wireless data glove interaction device that offers hands-free operation. The applications focus is on aircraft cabin inspection and repair tasks by utilizing the existing electronic cabin logbook infrastructure. The logbook is used by flight attendants to report defects and system failures in the cabin. More details about the use case are given in [2]. The three main requirements that constrained the user interface (UI) design for the application along with their implications are as follows: 1) Small and lightweight hardware: The UI has to be resource saving as small and lightweight wearable com- puters often offer only limited computation capabilities like e.g. the QBIC belt-worn computer [3]. 2) Hands-free operation: The UI has to be operated without the need of holding an interaction device either in one or both hands. Therefore, gyroscopic mice or track-balls are not appropriate. 3) No full attention demand: The UI cannot use binocular or even large monocular HMDs that would significantly effect or restrict the view field of the technicians. The primary attention of the technician is on the maintenance task and therefore the interaction with the wearable computer must only be a secondary activity. A. Outline The remainder of this paper is structured as follows: Section II reviews related work in the field. Section III discusses the advantages and drawbacks of different interaction styles for wearable computing. In section IV we describe the developed hands-free user interface for the aircraft maintenance applica- tion. Section V concludes the paper. Finally, section VI points out some future work. II. RELATED WORK There are different interaction devices for wearable compu- ting. Beside text-input devices for wearable computing such as Twiddler2 [4] or FrogPad [5] more complex devices for wearable computer interaction were developed. Those devices usually use a set of sensors to recognize the user’s input, e.g., by gestures. The GestureWrist [6] is a wrist-watch type input device. It recognizes hand gestures that can be mapped to a set of application control commands. The Fingermouse [7] is a wearable mouse input device that is controlled by finger