Designing robots that interact naturally with people requires the integration of technologies and algorithms for communication modalities such as gestures, movement, facial expressions and user interfaces. To understand interdependence among these modalities, evaluating the integrated design in feasibility studies provides insights about key considerations regarding the robot and potential interaction scenarios, allowing the design to be iteratively refined before larger-scale experiments are planned and conducted. This paper presents three feasibility studies with IRL-1, a new humanoid robot integrating compliant actuators for motion and manipulation along with artificial audition, vision, and facial expressions. These studies explore distinctive capabilities of IRL-1, including the ability to be physically guided by perceiving forces through elastic actuators used for active steering of the omnidirectional platform; the integration of vision, motion and audition for an augmented telepresence interface; and the influence of delays in responding to sounds. In addition to demonstrating how these capabilities can be exploited in human-robot interaction, this paper illustrates intrinsic interrelations between design and evaluation of IRL-1, such as the influence of the contact point in physically guiding the platform, the synchronization between sensory and robot representations in the graphical display, and facial gestures for responsiveness when computationally expensive processes are used. It also outlines ideas regarding more advanced experiments that could be conducted with the platform.

Redundantly actuated mobile robots using conventional wheels need a precise coordination of their actuators in order to guarantee a safe and precise motion without generating high internal forces and slippage. Using the instantaneous centre of rotation (ICR) of the chassis to describe this motion is a well established method. But the ICR is a mathematical concept which is hardly achieved on a real robot. This paper addresses the problem of ICR estimation of a non-holonomic omnidirectional mobile robot using conventional wheels. Instead of estimating the ICR in the working space, our approach estimates it in the actuators' space. The algorithm is presented in its general form and then adapted for a particular robot. The use of the algorithm with other omnidirectional robots is also discussed. Results from extensive testing done in simulation as well as with a real robot are presented, demonstrating the effectiveness of the proposed method.

Humans use direct physical interactions to move objects and guide people, and the same should be done with robots. However, most of today's mobile robots use non-backdrivable motors for locomotion, making them potentially dangerous in case of collision. This paper presents a robot, named AZIMUT-3, equipped with differential elastic actuators that are backdrivable and torque controlled, capable of being force-guided. Real world results demonstrate that AZIMUT-3 can move efficiently in response to physical commands given by a human pushing the robot in the intended direction.

Omnidirectional mobile robots, i.e., robots that can move in any direction without changing their orientation, offer better manoeuvrability in natural environments. Modeling the kinematics of such robots is a challenging problem and different approaches have been investigated. One of the best approaches for a nonholonomic robot is to model the robot's velocity state as the motion around its instantaneous center of rotation (ICR). In this paper, we present a motion planner designed to compute efficient trajectories for such a robot in an environment with obstacles. The action space is modeled in terms of changes of the ICR and the motion around it. Our motion planner is based on a Rapidly-Exploring Random Trees (RRT) algorithm to sample the action space and find a feasible trajectory from an initial configuration to a goal configuration. To generate fluid paths, we introduce an adaptive sampling technique taking into account constraints related to the ICR-based action space.

AZIMUT-3 is an omnidirectional non-holonomic (or pseudo-omnidirectional) robotic platform intended for safe human-robot interaction. In its wheeled configuration, shown in Fig. 1, AZIMUT-3 uses eight actuators for locomotion: four for propulsion and four for steering the wheels, which can rotate 180 degrees around their steering axis. Propulsion is done using standard DC brushless motors (Bayside K064050-3Y) with optical encoders (US Digital E4-300-157-HUB, 0.3 deg of resolution), capable of reaching 1.47 m/s. The platform uses steerable wheels motorized using differential elastic actuators (DEA), which provide compliance, safety and torque control capabilities. AZIMUT-3's hardware architecture consists of distributed modules for sensing and low-level control, communicating with each other through a 1 Mbps CAN bus. A Mini-ITX computer equipped with a 2.0 GHz Core 2 duo processor running Linux with real-time patches (RT-PREEMPT) is used on-board for high-level control modules. Nickel-metal hydride batteries provide power to the platform for up to 3 hours of autonomy. A passive vertical suspension mechanism (Rosta springs) is used to connect the wheels to AZIMUT-3's chassis, allowing them to keep contact with the ground on uneven surfaces. The platform has a 34 kg payload capacity and weights 35 kg.

Robots are usually built using stiff actuators that can provide impressive motion performances. However, they struggle to control the force, they do not handle collisions graciously and are generally bad at interacting significantly with partially unknown or kinematically constrained environments. One solution is to add a force sensor in the closed-loop control of backdrivable actuators [1], but this is limited in terms of stability, safety and robustness [2] [3]. One of the foremost initiatives using this method was undertaken by the German Aerospace Center (DLR) and resulted in three generations of extensively optimized lightweight robotic arms [4] that can physically interact with people. Performances are impressive but robustness is still an issue.

Most modern robotic systems are fast and repeatable position controlled machines. However, because of their inability to interact safely, robustly and in a versatile manner, they mostly remain confined to controlled areas where they execute specific preprogrammed actions. Providing high performance motion simultaneously with the ability to physically interact significantly remains a challenge.

Today's robotic systems are mostly rigid and position-controlled machines designed to operate in structured environments. To extend their application domains to partially unknown, dynamic, or anthropic environments, improved physical-interaction capabilities are required. In this new context, to blend the requirements for safety, robustness, and versatility is often a challenge, in part, because commonly available actuator technologies are inadequate. This paper presents our solution with the introduction of the dual-differential rheological actuator (DDRA) concept, which is based on the synergistic combination of an electromagnetic (EM) motor and two differentially coupled magnetorheological (MR) brakes. This paper describes the approach and the prototype design. It then discusses performances in force, motion, and interaction control.

For complex robotic tasks (e.g., manipulation, locomotion), the lack of knowledge of precise interaction models, the difficulties to precisely measure the task associated physical quantities (e.g., position of contact points, interaction forces) in real-time, the finite sampling time of digital control loops and the non-collocation of sensors and transducers have negative effects on performance and stability of robots when using simple force or simple movement controllers. To cope with these issues, a new compact design for high performance actuators specifically adapted for integration in robotic mechanisms is presented. This design makes use of a mechanical differential as its central element. Results shown that differential coupling between an intrinsically high impedance transducer and an intrinsically low impedance mechanical spring provides the same benefits as serial coupling, but in a more compact and simple design. This new actuator, named Differential Elastic Actuator (DEA), provides interesting design implementations, especially for rotational actuators used for mobile robot locomotion.

The most common ground locomotion method to make a mobile robot move is to use two-wheel drive with differential steering and a rear balancing caster. Controlling the two motors independently makes the robot non-holonomic in its motion. Such robots can work well indoor on flat surfaces and in environments adapted for wheelchairs. But the benefit of providing mobility to a robot directly relies on its locomotion capability, for handling different types of terrains (indoors or outdoors) and situations such as moving slowly or rapidly, with or without the presence of moving objects (living or not), climbing over objects and potentially having to deal with hazardous conditions. It is with this objective in mind that we designed AZIMUT. AZIMUT is a legged tracked wheeled robot capable of changing the orientation of its four articulations. Each articulation has three degrees of freedom (DOF): it can rotate 360deg around its point of attachment to the chassis, can change its orientation over 180deg, and rotate to propulse the robot.

This video shows the functionalities of a 3 serial DOF robotic arm. Each DOF is actuated with a patent pending differential elastic actuator (DEA) [1,2]. Compared to the abundantly studied series elastic actuator [3,4], DEA uses a differential coupling between a high impedance mechanical speed source and a low impedance mechanical spring. Possible implementations of a mechanical differential include the use of a standard gearbox, harmonic drive, cycloidal gearbox, bar mechanism, cable mechanism and all other mechanism that implement a differential function between three mechanical ports. For the implementation reported in this video, we used a harmonic drive for a very compact design. A passive torsion spring (thus the name elastic), with a known impedance characteristic corresponding to the spring stiffness, is used, with an electrical DC brushless motor. A non-turning sensor connected in series with the spring measures the torque output of the actuator.

Navigating in rough terrain is a complex task that requires the robot to be considered as a holistic system. Algorithms, which don't consider the physical dimensions and capabilities of the mobile robot lead to inefficient motion and suffer from a lack of robustness. A physical model of the robot is necessary for trajectory control. In this paper, quasi-static modeling of a six-wheeled robot with a passive suspension mechanism is presented together with a method for selecting the optimal torques considering the system constraints: maximal and minimal torques, positive normal forces. The aim of this method is to limit wheel slip and to improve climbing capabilities. The modeling and the optimization are applied to the shrimp rover.

This paper presents a new robotic concept, called SWARM-BOT, based on a swarm of autonomous mobile robots with self-assembling capabilities. SWARM-BOT takes advantage from collective and distributed approaches to ensure robustness to failures and to hard environment conditions in tasks such as navigation, search and transportation in rough terrain. One SWARM-BOT is composed of a number of simpler robots, called s-bots, physically interconnected. The SWARM-BOT is provided with self-assembling and self-reconfiguring capabilities whereby s-bots can connect and disconnect forming large flexible structures. This paper introduces the SWARM-BOT concept and describes its implementation from a mechatronic perspective.