The Bielefeld anthropomorphic robot head "Flobi"

A robot’s head is important both for directional sensors and, in human-directed robotics, as the single most visible interaction interface. However, designing a robot’s head faces contradicting requirements when integrating powerful sensing with social expression. Furher, reactions of the general public show that current head designs often cause negative user reactions and distract from the functional capabilities. Therefore, this contribution presents a novel anthropomorphic robot head called “Flobi”, which combines state-of-the-art sensing functionality with an exterior that elicits a sympathetic emotional response. It can display primary and secondary emotions in a human-like way, to enable intuitive human-robotinteraction. To facilitate further research on facial appearance, the exterior is fully modular and replaceable. While current state-of-the-art still requires trade-offs when integrating sensing and social expression, Flobi has been designed to enable service robotic applications, with highresolution, wide-angle stereo vision, gyroscope motion compensation and stereo audio. For ease of integration, the head is selfcontained, including 18 actuators, sensors and control boards, all in a human-head sized package. I. THE CHALLENGE OF SENSING VS. EXPRESSION Building robots that are well suited for interaction with humans is a challenging task that needs to be addressed by a range of disciplines. One of the most challenging issues in this vein at the moment, and for the foreseeable future, is the design of a robot’s head. This is because a head has to realize multiple functions with partially contradicting requirements. Most important among these are active sensing and social expression for intuitive human-robot interaction. Corresponding to the first function, many robotic heads have been reported on in the literature that exhibit powerful, active sensing capabilities: Here, many, often large, sensors are packed together and combined with few, powerful actuators for rapid, accurate motion. Examples include POPEYE [1], Cog [2] and the Karlsruhe Humanoid Head [3]. A recognizably distinct line of research has given us robotic heads with social expressiveness that is intuitively understandable to humans. These usually need many, small actuators that are capable of smooth motion with varying This work was partially supported by the German Federal Ministry of Education and Research (BMBF) under grant no. 01IME01N and the German Research Society (DFG) within the Collaborative Research Centre 673 “Alignment in Communication”. Ingo Lütkebohle, Frank Hegel, Britta Wrede and Gerhard Sagerer are with the Applied Informatics Group, Bielefeld University, Germany. {iluetkeb,fhegel,bwrede}@techfak.uni-bielefeld.de Matthias Hacke is with Mabotics GmbH, Germany. [email protected] Simon Schulz and Sven Wachsmuth are with the Central Lab Facilities, Cognitive Interaction Technology Excellence Cluster, Bielefeld University, Germany. {sschulz,swachsmu}@techfak.uni-bielefeld.de dynamics. The exterior of such robots tends to be nonfrightening and generally signals the robot’s capabilities to the non-technical eye. Examples of this approach include Kismet [4], iCub [5], Infanoid [6] and iCat [7]. Obviously, both of these lines always exhibit features of the other: Social robot heads also need sensors and sensor heads also have an exterior. However, their requirements partially contradict each other and therefore it is no surprise that most projects so far have chosen a trade-off that favors either sensing or social communication. We have summarized the relevant state-of-the-art briefly in section II. However, we believe that the state of the art has advanced to a level where significant progress can only be made if both aspects are implemented, and evaluated, in conjunction. It has long been recognized that the motion of directed sensors, such as cameras, is interpreted socially by humans, even if not intended to do so [8]. This has two consequences: Firstly, any kind of robotic head, when directed at humans, has a social impact and adverse reactions can result if the effect of its exterior and motion are not adequately considered. The consequences of failing to address this fact can readily be discerned from popular reporting about robotics research, which abounds with negative remarks about appearance. Secondly, the social impact of a robot cannot be divided from its function and studies of social behavior therefore benefit from the use of a head whose function is comparable to a functional system. Fig. 1. Flobi male-neutral (left) and female-smiling (right) configurations. The “Flobi” head is our contribution towards addressing both the requirements for a sensor head and the requirements for social interaction. On the sensor side, the head combines a wide-angle, high resolution stereo camera setup with gyroscopes for motion compensation and stereo microphones for speaker localization and speech recognition. The cameras 2010 IEEE International Conference on Robotics and Automation Anchorage Convention District May 3-8, 2010, Anchorage, Alaska, USA 978-1-4244-5040-4/10/$26.00 ©2010 IEEE 3384 are actuated on two tiers (“eyes” and “neck”) to provide both high rotational speed as well as large pan and tilt range. The mechanical construction has been optimized to reduce noise, to improve auditory perception. To facilitate social interaction, we have designed the head to, firstly, feature a standard exterior that prevents the uncanny valley [9] effect and affects the user in a positive way. Secondly, it facilitates experimentation with very different exteriors through swappable plastic masks. We have already produced a number of such masks and can swap the full set in less than five minutes. To the best of our knowledge, this is the first robotic head to allow this level of experimentation. Furthermore, we will present a novel, patent-pending magnetic actuation system for the robot’s mouth. It is both closer to the human motion range than previous constructions and at the same time hides the mechanism from view. Last, but not least, heads intended for human-robotinteraction are expected to be employed in a variety of areas, from service robotics to psychological studies. This puts constraints on both the physical packaging as well as the level of control expertise (and hardware) available. Therefore, we have designed the head to be a self-contained package, including actuators and motor controllers (excluding only the power supply). The motor controllers are a custom design to fit the space requirements and they provide all real-time sensitive control aspects, thus reducing the burden on the end-user’s side. II. STATE OF THE ART A large number of anthropomorphic robotic heads have been reported on in the literature and a good overview is available in [10]. Naturally, they all have different strenghts and weaknesses and we have attemped to present a representative sample, containing the respectively best heads in several categories. The WE-4RII head [11], has a particular wide range of emotional expressions available. Nexi, a robotic head which suceeds the seminal works in social robotics by Cynthia Breazeal, has been chosen as the newest development in that line[12]. The iCub head [5] is one of the smallest, fastest and best-documented heads. A widely available commercial social platform is the iCat [7]. The predecessor to the current head was the android head BARTHOC [13]. An example of a typical sensor head for service robotics is the Karlsruhe Humanoid Head (KHH) [3]. Table I compares the mentioned heads in terms of the offered degrees of freedom (DoF) for the moving parts, their basic sensor equipment, motion range and speeds for sensorrelated motions and the size of the heads. Additionally, we have specified whether technology is clearly visible to the casual observer, i.e. because of holes, exposed motors or unnatural sensors. Where the tables is empty, the information was not available from the published literature, ”n/a” means that the joint was not present. 1estimated from size of contained SwissRanger SR3 series camera WE-4RII iCub Nexi ICAT BARTHOC KHH Breadth (cm) 18.6 15.2 ̃241 18 14