We present an analytical model of air spring suspensions that is based on an experimental characterization. The suspension consists of three principal parts: the air spring, an auxiliary tank, and a pipe connecting the two. An analytical nonlinear fluid dynamics model is first analyzed, modeling the suspension stiffness, damping factor, and transmissibility. The model is then linearized and this linear version is studied in depth, finding that the behaviour of the suspension as reflected in the aforementioned three characteristics is strongly dependent on the size of the three suspension parts. The analysis allows us to propose a practical strategy for the operation of the suspension. NOMENCLATUREA s Spring effective area [m 2 ] C r The pipe restriction coefficient [N 5 /m/s] D p The pipe's cross section diameter [m] F Force exerted at the air spring [N] g Acceleration due to gravity [m/s 2 ] k Pneumatic suspension total stiffness [N/m] k as Air spring effective area stiffness [N/m] k s Air spring stiffness [N/m] k vs Air spring volume stiffness [N/m] k vsr Pneumatic suspension volume stiffness [N/m] l p The pipe length [m] M Sprung mass [kg] n Polytropic coefficient P r Relative pressure at the reservoir [bar] P s Relative pressure at the air spring [bar] R Gas constant for air [J/kg/K] T Air suspension temperature [K] V r Reservoir volume [m 3 ] V s Air spring volume [m 3 ] V sr Reservoir plus spring volume [m 3 ] x Absolute response [m] y Excitation [m] z Suspension height [m] z 0 Initial height for the air spring [m] γ Specific heat ratio ε Dimensionless parameter θ Dimensionless parameter µ Dynamic viscosity of air [Pa·s] ρ Density of air [kg/m 3 ] ω tr Transition frequency [rad/s] m Mass flow rate [kg/s]

This paper describes the mechanical devices, the movements and the associated kinematic models of a novel wheelchair prototype capable of climbing staircases. The key feature of the mechanical design is the use of two decoupled mechanisms in each axle, one used to negotiate steps, and the other to position the axle with respect to the chair to accommodate the overall slope. This decoupling makes possible many different climbing strategies, the overall mechanism being extraordinarily versatile from a control point of view. Kinematic models have been developed for the different mechanical configurations that appear during all the ascend/descend processes. These models are required to control the actuators of the wheelchair in such a way that its centre of mass is able to follow arbitrary spatial trajectories. This is very important as one has to design very smooth spatial trajectories, keeping a near null inclination of the seat all the time in order to guarantee the comfort of the passenger, usually a handicapped or injured person. A real prototype is presented, and experimental results are reported that show the efficiency of the mechanism and the accuracy of the kinematic models developed.

This paper describes the mechanical devices conforming a novel wheelchair prototype capable of climbing staircases. The key feature of the mechanical design is the use of two decoupled mechanisms in each axle, one to negotiate steps, and the other to position the axle with respect to the chair to accommodate the overall slope. This design simplifies the control task substantially. Kinematic models are necessary to describe the behavior of the system and to control the actuated degrees of freedom of the wheelchair to ensure the passenger's comfort. The choice of a good climbing strategy simplifies the control and decreases the power consumption of the wheelchair. In particular, we demonstrate that if the movement of the wheelchair has the same slope as the racks or the same slope as the terrain that supports the wheel axles (depending on the configuration mechanism), control is easier and power consumption is less. Experimental results are reported which show the behavior of the prototype as it moves over different situations: (a) ascending a single step of different heights using different climbing strategies; and (b) climbing a staircase using an appropriate climbing strategy that simplifies the control and reduces the power consumption of the wheelchair.

Estimation of human emotions plays an important role in the development of modern brain-computer interface devices like the Emotiv EPOC+ headset. In this paper, we present an experiment to assess the classification accuracy of the emotional states provided by the headset’s application programming interface (API). In this experiment, several sets of images selected from the International Affective Picture System (IAPS) dataset are shown to sixteen participants wearing the headset. Firstly, the participants’ responses in form of a self-assessment manikin questionnaire to the emotions elicited are compared with the validated IAPS predefined valence, arousal and dominance values. After statistically demonstrating that the responses are highly correlated with the IAPS values, several artificial neural networks (ANNs) based on the multilayer perceptron architecture are tested to calculate the classification accuracy of the Emotiv EPOC+ API emotional outcomes. The best result is obtained for an ANN configuration with three hidden layers, and 30, 8 and 3 neurons for layers 1, 2 and 3, respectively. This configuration offers 85% classification accuracy, which means that the emotional estimation provided by the headset can be used with high confidence in real-time applications that are based on users’ emotional states. Thus the emotional states given by the headset’s API may be used with no further processing of the electroencephalogram signals acquired from the scalp, which would add a level of difficulty.