Kinematic modeling and singularity of wheeled mobile robots

This paper presents a global singularity analysis for wheeled mobile robots (WMRs). First, a kinematic model of a generic wheel is obtained using a recursive kinematics formulation. This novel and efficient approach is valid for all the common types of wheels: fixed, centered orientable, off-centered orientable (caster or castor) and Swedish or Mecanum. Then, a procedure for generating robot kinematic models is presented based on the set of wheel equations and the null space concept. Next, the singularity of kinematic models is discussed: first, the kinematic singularity condition in forward models is obtained, and then the singularity condition in inverse, or even mixed, models. A generic and practical geometric approach is established to characterize the singularity of any kinematic model of any WMR with the mentioned wheels. To illustrate the applications of the proposed approach, the singular configurations for many types of WMRs are depicted. Finally, the singularity characterization is extended to include other specialized wheels: dual-wheel, dual-wheel castor, ball-type and orthogonal.     

Three-Dimensional Path Planning of a Climbing Robot Using Mixed Integer Linear Programming

The City-Climber robot is a novel wall-climbing robot developed at The City College of New York that has the capability to move on floors, climb walls, walk on ceilings and transit between them. In this paper, we first develop the dynamic model of the City-Climber robot when it travel on different surfaces, i.e., floors, walls and ceilings, respectively. Then, we present a path planning method for the City-Climber robot using mixed integer linear programming (MILP) in three-dimensional (3-D) building environments that consist of objects with primitive geometrical shapes. MILP provides an optimization framework that can directly incorporate dynamic constraints with logical constraints such as obstacle avoidance and waypoint selection. In order to use MILP to solve the obstacle avoidance problem, we simplify and decouple the robot dynamic model into a linear system by introducing a restricting admissible controller. The decoupled model and obstacle can be rewritten as a linear program with mixed-integer linear constraints that account for the collision avoidance. A key benefit of this approach is that the path optimization can be readily solved using the AMPL and CPLEX optimization software with a MATLAB interface. Simulation results show that the framework of MILP is well suited for path planning and obstacle avoidance problems for the wall-climbing robot in 3-D environments.     

Effect of layer compliance on frictional behavior of soft robotic fingers

In this paper, the modeling and design for frictional loads applied by robotic fingertips through a soft contact interface are investigated. The dependence of the sustainable friction forces and moments due to the normal force applied on the contact area is studied. A model that considers the dependence of both the contact area and the coefficient of friction on the application of normal force is proposed. Specimens of simplified fingertips, made with different materials and shaped with different thickness of the covering soft layer, were tested in order to validate the proposed model via designed experiments. The results obtained have very important relevance to the design of robotic hands and fingers equipped with soft pads or skins, and can help in the choice of suitable features for the different layers of contact pads or skins.     

Modified shear lag model for fibers and fillers with irregular cross-sectional shapes

For fibers with irregular cross sections such as ultrahigh modulus polyethylene (UHMPE) fibers and ribbon-like carbon fibers, the original shear lag model would not provide accurate calculations for interfacial shear stress because it assumes a circular fiber cross section. In this study, a modified shear lag model is proposed to calculate the interfacial shear stress that reflects the change of fiber cross-sectional shape. Microbond test on a UHMPE fiber/epoxy system was used for verification of the model. The difference between the interfacial shear strength (IFSS) calculated using the modified model and that using the original model assuming an equivalent fiber diameter was found to be as high as 15% and it linearly increased as the irregularity of the cross-sectional shape increased. When the irregularity constant exceeds 1.12, the error in IFSS involved in using the original shear lag model and an equivalent fiber diameter is greater than 10%.     

Statistical Modeling at 18 GHz Using of Broadband Wireless LAN Channels Directive Antennas

Measurements of indoor radio channels in thefrequency domain were carried out in acommunicationslaboratoryat 18-19 GHz using directiveantennas of beamwidths equal to 25 V × 53 H.Statistical modeling of the channel parameters wasderived from 800 data profiles. The main resultsobtained are: (1) The arrival times of the multipathcomponents have a clustering property, with itsstatistical distribution fitting very well to themodified Poisson process; (2) the amplitudes of themultipath components and the mid-scale power attenuationobey the log-normal distribution; (3) the power decreasewith the antenna separation exponentially, with theexponent around 1.9 for Line-of-Sight (LOS) locations,2.7 for non-line-of-sight (NLOS) locations, and 2.2 forboth LOS and NLOS locations; (4) the RMS Dels are generally quite small, with a global meanvalue of 4.8 ns, and standard deviation value of 5.3 ns.Its statistical distribution was found to follow thenormal distribution for the same antenna separation aswell as for all the measurement data with differentantenna separations; (5) the RMS delay spread isinversely proportional to the channel coherencebandwidth, with the proportional coefficient greater forLOS data than for NLOS data, and also decaying with theincrement of antenna separations.     

CONCEPTUAL MODELING BASED ON LOGICAL EXPRESSION AND EVOLVEMENT

Aiming at the problem of abstract and polytype information modeling in product conceptual design, a method of conceptual modeling based on logical expression and evolvement is presented. Based on the logic expressions of the product conceptual design information, a function/logic/structure mapping model is set up. First, the function semantics is transformed into logical expressions through function/logic mapping. Second, the methods of logical evolvement are utilized to describe the function analysis, function/structure mapping and structure combination. Last, the logical structure scheme is transformed into geometrical sketch through logic/structure mapping. The conceptual design information and modeling process are described uniformly with logical methods in the model, and an effective method for computer aided conceptual design based on the model is implemented.     

Ionic Polymer–Metal Composite of Thermo-Responsive Selemion AMV Coated with Gold Foils

Highly dehydrated gold foil-coated Selemion AMV exhibited large bending under electrical stimulation. It bore a relatively well-controllable bending characteristic by the control of electrical stimulation. Conventional ionic polymer–metal composite bending mechanisms could not explain its bending behavior. We speculated that Joule heat played a central role in the bending induction. Employing the classical lamination theory, the influence of Joule heat on its bending behavior was theoretically investigated. The results calculated roughly agreed with the experimental results. Hence, we concluded that the Joule heat was the primary cause of bending induction.     

System modeling based measurement error analysis of digital sun sensors

Stringent attitude determination accuracy is required for the development of the advanced space technologies and thus the accuracy improvement of digital sun sensors is necessary.In this paper,we presented a proposal for measurement error analysis of a digital sun sensor.A system modeling including three different error sources was built and employed for system error analysis.Numerical simulations were also conducted to study the measurement error introduced by different sources of error.Based on our model and study,the system errors from different error sources are coupled and the system calibration should be elaborately designed to realize a digital sun sensor with extra-high accuracy.     

Pilot control of an auto-balancing two-wheeled cart

The control system of an auto-balancing two-wheeled cart (ABTWC) is inherently unstable, displays a non-minimum phase and can be piloted by a joystick that has 2 d.o.f. This paper employs a state feedback technique to design the stabilizing controller for an ABTWC and develops a pilot algorithm, i.e., differential steering, which converts two joysticks' commands into two torque directives for transportation. This allows the user to operate this cart linearly for both motion and orientation control via a joystick. Control examples are given to illustrate the feasibility and the effectiveness of the proposed controller and pilot algorithm.     

Adhesion evaluation for a stratified system in JKR geometry

The JKR test, which consists of investigating the contact between an elastic lens and a rigid substrate, is a local and precise adhesion test. However, in the classical JKR mechanical analysis, the dimensions of the system must be large compared to the size of the contact area; we consider here a rigid substrate coated with a thin layer of a softer material. We show that this case cannot be analysed using the JKR theory. We propose a simple mechanical approach, modeling the layer as an elastic mattress, which accounts for the experimentally observed phenomena.