P Robuffo Giordano

CyberWalk: Enabling unconstrained omnidirectional walking through virtual environments

Despite many recent developments in virtual reality, an effective locomotion interface which allows for normal walking through large virtual environments was until recently still lacking. Here, we describe the new CyberWalk omnidirectional treadmill system, which makes it possible for users to walk endlessly in any direction, while never leaving the confines of the limited walking surface. The treadmill system improves on previous designs, both in its mechanical features and in the control system employed to keep users close to the center of the treadmill. As a result, users are able to start walking, vary their walking speed and direction, and stop walking as they would on a normal, stationary surface. The treadmill system was validated in two experiments, in which both the walking behavior and the performance in a basic spatial updating task were compared to that during normal overground walking. The results suggest that walking on the CyberWalk treadmill is very close to normal walking, especially after some initial familiarization. Moreover, we did not find a detrimental effect of treadmill walking in the spatial updating task. The CyberWalk system constitutes a significant step forward to bringing the real world into the laboratory or workplace.

On the kinematic modeling and control of a mobile platform equipped with steering wheels and movable legs

Mobile platforms equipped with several steering wheels are known to be omnidirectional, i.e., able to independently translate and rotate on the plane. As an improvement to this design, the Justin mobile platform also possesses the ability to vary its footprint over time by extending/retracting the wheel legs during motion. In this paper, we discuss the kinematic modeling and control issues for such a platform. The goal is to obtain a tracking controller which is able to realize an arbitrary linear/angular platform motion while, at the same time, independently expanding/retracting each leg. Experimental results support the proposed approach.

A novel framework for closed-loop robotic motion simulation - part I: Inverse kinematics design

This paper considers the problem of realizing a 6-DOF closed-loop motion simulator by exploiting an anthropomorphic serial manipulator as motion platform. Contrary to standard Stewart platforms, an industrial anthropomorphic manipulator offers a considerably larger motion envelope and higher dexterity that let envisage it as a viable and superior alternative. Our work is divided in two papers. In this Part I, we discuss the main challenges in adopting a serial manipulator as motion platform, and thoroughly analyze one key issue: the design of a suitable inverse kinematics scheme for online motion reproduction. Experimental results are proposed to analyze the effectiveness of our approach. Part II [1] will address the design of a motion cueing algorithm tailored to the robot kinematics, and will provide an experimental evaluation on the chosen scenario: closed-loop simulation of a Formula 1 racing car.

A novel framework for closed-loop robotic motion simulation - part II: Motion cueing design and experimental validation

This paper, divided in two Parts, considers the problem of realizing a 6-DOF closed-loop motion simulator by exploiting an anthropomorphic serial manipulator as motion platform. After having proposed a suitable inverse kinematics scheme in Part I [1], we address here the other key issue, i.e., devising a motion cueing algorithm tailored to the specific robot motion envelope. An extension of the well-known classical washout filter designed in cylindrical coordinates will provide an effective solution to this problem. The paper will then present a thorough experimental evaluation of the overall architecture (inverse kinematics + motion cueing) on the chosen scenario: closed-loop simulation of a Formula 1 racing car. This will prove the feasibility of our approach in fully exploiting the robot motion capabilities as a motion simulator.

Feedback/Feedforward Schemes for Motion Control of the CyberCarpet

Abstract The CyberCarpet is an actuated platform that allows unconstrained locomotion possibilities to a walking user for VR exploration. The platform has two actuating devices (linear and angular) and the motion control problem is dual to that of nonholonomic wheeled mobile robots. The main control objective is to keep the walker close to the platform center. Simple but global kinematic control schemes are presented, addressing in particular the handling of singularity issues. The feedback stabilizing part, which is based only on the users pose information, is complemented by a feedforward term derived from a walkers velocity observer. Numerical and graphical simulation results are presented.

Does jerk have to be considered in linear motion simulation

Perceptual thresholds for the detection of the direction of linear motion are important for motion simulation. There are situations in which a subject should not perceive the motion direction as, e.g., during repositioning of a simulator, but also opposite cases where a certain motion percept must intentionally be induced in the subject. The exact dependency of the perceptual thresholds on the time evolution of the presented motion profile is still an open question. Previous studies have found evidence for a sensitivity of the thresholds on the rate of change of acceleration, called jerk. In this study we investigate three motion profiles which differ in their jerk characteristics. We want to evaluate which profile can move people furthest in the horizontal plane in a given time without them noticing the direction. Our results suggest that a profile with a minimum peak jerk value should be chosen.

Temporal processing of self-motion: Translations are processed slower than rotations

Reaction times (RTs) to purely inertial self-motion stimuli have only infrequently been studied, and comparisons of RTs for translations and rotations, to our knowledge, are nonexistent. We recently proposed a model (Soyka et al., 2011) which describes direction discrimination thresholds for rotational and translational motions based on the dynamics of the vestibular sensory organs (otoliths and semi-circular canals). This model also predicts differences in RTs for different motion profiles (e.g., trapezoidal versus triangular acceleration profiles or varying profile durations). In order to assess these predictions we measured RTs in 20 participants for 8 supra-threshold motion profiles (4 translations, 4 rotations). A two-alternative forced-choice task, discriminating leftward from rightward motions, was used and 30 correct responses per condition were evaluated. The results agree with predictions for RT differences between motion profiles as derived from previously identified model parameters from threshold measurements. To describe absolute RT, a constant is added to the predictions representing both the discrimination process, and the time needed to press the response button. This constant is approximately 160 ms shorter for rotations, thus indicating that additional processing time is required for translational motion. As this additional latency cannot be explained by our model based on the dynamics of the sensory organs, we speculate that it originates at a later stage, e.g., during tilt-translation disambiguation. Varying processing latencies for different self-motion stimuli (either translations or rotations) which our model can account for must be considered when assessing the perceived timing of vestibular stimulation in comparison with other senses (Barnett-Cowan and Harris, 2009; Sanders et al., 2011).