Designing Robots with Movement in Mind
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! ! ! ! ! Designing Robots with Movement in Mind ! ! Guy Hoffman Media Innovation Lab, IDC Herzliya and Wendy Ju Center for Design Research, Stanford University ! This paper makes the case for designing interactive robots with their expressive movement in mind. As people are highly sensitive to physical movement and spatiotemporal affordances, well-designed robot motion can communicate, engage, and offer dynamic possibilities beyond the machines’ surface appearance or pragmatic motion paths. We present techniques for movement centric design, including character animation sketches, video prototyping, interactive movement explorations, Wizard of Oz studies, and skeletal prototypes. To illustrate our design approach, we discuss four case studies: a social head for a robotic musician, a robotic speaker dock listening companion, a desktop telepresence robot, and a service robot performing assistive and communicative tasks. We then relate our approach to the design of non-anthropomorphic robots and robotic objects, a design strategy that could facilitate the feasibility of real- world human-robot interaction. Keywords: human-robot interaction, design, non-humanoid, non-anthropomorphic, gestures, movement, case studies, expressive movement ! 1. Introduction As robots enter applications where they operate around, before, and with humans, it is important for robot designers to consider the way the robot’s physical actions are interpreted by people around them. In the past, robots’ actions were mainly observed by trained operators. However, if we are to deploy robots in more lay contexts—in homes and offices, in schools, on streets, or on stages—the quality of these robots’ motion is crucial. It is therefore time to consider more seriously the expressive power of a robot’s movement, beyond the crude, choppy, and awkward mannerisms they are famous for. Instead we want to design robots with movements accurately expressing the robot’s purpose, intent, state, mood, personality, attention, responsiveness, intelligence, and capabilities. Any robot inherently displays in an interplay between its surface appearance and its physical motion. The way a robot looks sets the context for the interaction, framing expectations, triggering emotional responses, and evoking interaction affordances; however, movement is critical to conveying more dynamic information about the robot. The robot’s movement in space can support ! Authors retain copyright and grant the Journal of Human-Robot Interaction right of first publication with the work simultaneously licensed under a Creative Commons Attribution License that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal. Journal of Human-Robot Interaction, Vol. 3, No. 1, 2014, Pages 89-122, DOI 10.5898/JHRI.3.1.Hoffman ! Hoffman & Ju, Designing Robots with Movement in Mind action coordination, communicate internal states, and also has its own emotional impact. While recent years have seen an increasing respect for the importance and influence of robot appearance, far less attention has been paid to date on the design and effects of accurate expressive motion. Designing robots with expressive movement in mind presents a number of interesting challenges for HRI designers and researchers. Significant iteration is required to understand how the robot’s physical motion relates to its surface appearance. People’s understanding of non-verbal factors is often tacit and intuitive, and new methods for evaluating designs and eliciting guidelines are needed. Finally, prioritizing movement and expressivity will create new engineering challenges that will likely require technological innovations to solve. In this paper, we outline an expressive movement centric design approach for interactive robots. We delve more deeply into the rationale for well-designed expressive robot motion and discuss the implications of prioritizing the communicative aspects of movement in the design of robotic systems. We list specific techniques we employ to design robots with expressive movement in mind. To illustrate these points, we present case studies illustrating different methods used to design interactive robots. We conclude with key challenges of our approach, and why we believe that this approach can lead to simple non-anthropomorphic robot designs that might lower the barrier of entry for real-world human-robot interaction. ! 1.1 Contrast to Other Robot Design Approaches Our approach differs from common design approaches in the robotics and HRI community, in particular, two differences that we denote are the pragmatic and the visual approach. We use the word pragmatic after Kirsh and Maglio (1994), who distinguish between pragmatic and epistemic actions in human behavior and define pragmatic actions as “actions performed to bring one physically closer to a goal.” Similarly, we will distinguish between the pragmatic movements of a robot, those that are aimed at achieving a physical goal, and its expressive movements, those aimed at communicating the robot’s traits, states, and intents to human interaction partners. A pragmatic design approach sets out from specifications required of the robot’s spatial activity towards physical goals, as defined by users of the system. Mechanical engineers design the robot’s parts and relationships to fulfill these requirements as efficiently as possible, both in terms of energy and of cost. The resulting design is usually an assembly of limbs with more or less exposed links, actuators, and cables. For reasons of mechanical optimization, these limbs are often structured as chains of cantilevers from a rotation point, and follow principles of symmetry, orthogonality, and concentric relations. In some cases, a shell is designed post-hoc to cover internal parts and achieve a certain “look” for the robot. The shape and structure of the shell is highly constrained by the existing core of the robot, and usually follows its lines and proportions closely. A visual approach is to design robots with appearance in mind. This is common for robots intended specifically for expressive interaction, as well as for entertainment robots. Industrial design practices are used to develop the look of the robot through a variety of sketching and modeling techniques. The robot’s parts are specified by the robot’s users to support the intended interaction, which often includes gaze, smiles, pointing gestures, etc. Visual designers of robots then need to decide how far along the humanoid spectrum to place their design (Fink, 2012). This can affect the choice of shape, materials (e.g., metal or silicone), body and facial parts (DiSalvo, Gemperle, Forlizzi, & Kiesler, 2002), as well as the amount of detail sculpted into the robot’s form. In both cases, the robot’s expressive quality of movement is developed later in the process, if at all. Once the robot is completed, a 3D model of the robot is usually generated. This model is then used to programmatically develop the way it moves. In some cases, the robot is modeled in a 3D animation program and a pipeline is created to translate the animation from the 3D model to the physical robot (e.g., Gray, Hoffman, Adalgeirsson, Berlin, & Breazeal, 2010). In contrast, designing interactive robots from their expressive movement up takes the communicative power of movement into consideration early on in the design process. This is not to say that visually aesthetic and pragmatic considerations are not taken into account. Using an ! 92! ! Hoffman & Ju, Designing Robots with Movement in Mind iterative design methodology, these are factored in throughout the design process, as demonstrated in the case studies below. However, the expressive nature of the robot’s movement is not added on after the robot is designed, or—more commonly—completely built. Instead, it is factored in from the onset and converses with both the visual and the pragmatic requirements of the robot. In addition to its outcomes in terms of expressivity, we have found that this design approach can lead to a different kind of robot than that usually found in research labs: One that displays formal simplicity and abstract geometric shapes, while exhibiting its complexity and sophistication primarily through carefully designed movement qualities. ! 2. Why Movement Matters Regardless of the appearance of an object or organism, its movement is a powerful interaction and expression medium. Humans, like most animals, are highly sensitive to perceived motion, which is a fact utilized by conspecifics, other animals, and designers of artifacts. In interaction, humans use kinesics—the generation and interpretation of nonverbal behavior expressed as movement of the body—to communicate information, reason about mental states, accompany speech, denote real and imaginary objects in the world, express emotions and attitudes, self-present, accomplish rituals, and more (Argyle, 1988; Ekman & Friesen, 1969). People also use proxemics—spatial distance—to define themselves in relation to their environment and to people around them, to set up expectations and communication channels, establish boundaries, claim territory, and signal context (Hall, 1969). Movement and gestures are important to the coordination and performance of joint activities, where they serve to communicate intentions and refer to objects of common ground (Clark, 2005). A significant body of work concerning the analysis of nonverbal acts and resulting perceptions exists, e.g., Knapp and Hall (2002); Moore, Hickson,