Control of Multiple Mobile Agents Via Artificial Potential Functions and Random Motion

This paper investigates the effectiveness of designed random behavior in cooperative formation control of multiple mobile agents. A method based on artificial potential functions provides a framework for decentralized control of their formation. However, it implies heavy communication costs. The communication requirement can be replaced by onboard sensors. The onboard sensors have limited range and provide only local information, and may result in the formation of isolated clusters. This paper proposes to introduce a component representing random motion in the artificial potential function formulation of the formation control problem. The introduction of the random behavior component results in a better chance of global cluster formation. The paper uses an agent model that includes both position and orientation, and formulates the dynamic equations to incorporate that model in artificial potential function approach. The effectiveness of the proposed method is verified via extensive simulations performed on a group of mobile agents and leaders.

Vibrations of Functionally Graded Shells

The behavior of functionally graded structures has received a great deal of attention in recent years. Usually, these structures are made out of a composite material with a modulus of elasticity, a Poisson’s ratio, and a density that vary through the thickness. The non-uniformity through the thickness introduces coupling between the transverse deformations and the deformations of the mid-surface. Previous publications have shown how to account for these added complexities and have presented extensive results in tabular form. In this article, available results are used to show that the behavior of functionally graded shells is similar to that of homogeneous isotropic shells. It is well known that for isotropic shells, results can be presented in non-dimensional form so that, once results are obtained for one material, they can be simply scaled to obtain the corresponding results for shells made out of another material. The same can then be done for functionally graded shells. In addition, if functionally graded shells behave like homogeneous shells, no new method of analysis is required. The second part of the paper examines why this is true.

The Surface Roughness Effect on the Dynamic Stiffness and Damping Characteristics of the Hydrostatic Thrust Spherical Bearings: Part 5 of 5 — Clearance Type of Bearings

This study has theoretically analyzed the surface roughness, centripetal inertia and recess volume fluid compressibility effects on the dynamic behavior of a restrictor compensated hydrostatic thrust spherical clearance type of bearing. The stochastic Reynolds equation, with centripetal inertia effect, and the recess flow continuity equation with recess volume fluid compressibility effect have been derived to take into account the presence of roughness on the bearing surfaces. On the basis of a small perturbations method, the dynamic stiffness and damping coefficients have been evaluated. In addition to the usual bearing design parameters the results for the dynamic stiffness and damping coefficients have been calculated for various frequencies of vibrations or squeeze parameter (frequency parameter) and recess volume fluid compressibility parameter. The study shows that both of the surface roughness and the centripetal inertia have slight effects on the stiffness coefficient and remarkable effects on the damping coefficient while the recess volume fluid compressibility parameter has the major effect on the bearing dynamic characteristics. The cross dynamic stiffness showed the bearing self-aligning property and the ability to oppose whirl movements. The orifice restrictor showed better dynamic performance than that of the capillary tube.

Analysis of the Grasp Planning Method for Manipulation of BH-4 Dextrous Hand

The paper presents method for planning robotic dexterous hand grasping task using example of the Beihang University’s BH-4 dexterous hand. The grasping planning method is devised through modeling and simulation and experimentally verified using physical prototype. The paper presents the method for forward and inverse kinematic solutions of the BH-4 robot 4-DOF finger, including transformation matrix between the palm coordinate system and the finger base coordinate system. In addition, the method of the idiographic manipulation is presented using example of ball grasping. The simulation results and physical experiment verify that the inverse kinematic solution is correct, and kinematic grasping and operating planning is valid and feasible. Finally, the experiment with the complex system integrated robot arm with dexterous hand is carried out. Experimental result shows that the more complicated grasping task can be done by a dexterous hand integrated in the robot arm system.

A New Method for Sensor Degradation Detection, Isolation and Compensation in Linear Systems

The performance of machines and equipment degrades as a result of aging and wear. This decreases performance reliability and increases the potential for faults and failures. To ensure proper functionality of complex systems, advanced technologies for performance diagnosis and control are being incorporated into engineering designs, which requires an ever-increasing number of sensors and measurement devices. Nevertheless, a sensor, just as any other dynamic system, degrades and fails. A faulty sensor may cause process performance degradation, process shut down, or even a fatal accident because it is no longer able to deliver accurate information about the monitored system. Therefore, it is essential to assess sensor performance to ensure system reliability. In this paper, a method is proposed to detect, isolate, and compensate sensor degradation. The numerical algorithm for subspace state space system identification is used to track the changes of the time constants and gains of the sensor and the monitored system. Without imposing requirements for redundant sensors and measurement devices, this method utilizes the fact that sensor readings depict dynamic characteristics of the sensors as well as those of the monitored system. The newly proposed method is verified in angular sensor degradation detection using high-fidelity simulations of an automotive electronic throttle system.

Initial Experiments on the Control of a Mobile Tower Crane

Cranes are used extensively throughout the world in a wide variety of construction and material handling applications. The speed at which these cranes are operated is limited by payload oscillation. Input shaping is one method that reduces this oscillation, allowing higher speeds and improving operational efficiency. Another method to improve the operational capabilities of cranes is to allow base motion. This paper presents initial experimental results from a portable, mobile tower crane. A theoretical model of the crane is presented and experimentally verified. The oscillatory dynamics of the crane are highlighted and controllers to combat these unwanted dynamics are presented.

Decentralized Exergy/Entropy Thermodynamic Control for Collective Robotic Systems

This paper develops a distributed decentralized control law for collective robotic systems. The control laws are developed based on exergy/entropy thermodynamic concepts and information theory. The source field is characterized through second-order accuracy. The proposed feedback control law stability for both the collective and individual robots are demonstrated by selecting a general Hamiltonian based solution developed as Fisher Information Equivalency as the vector Lyapunov function. Stability boundaries and system performance are then determined with Lyapunov’s direct method. A robot collective plume tracing numerical simulation example demonstrates this decentralized exergy/entropy collective control architecture.

Study of Vehicle Dynamic Modeling Fidelity on Haptic Collaboration in Steer-by-Wire Systems

The Steer-By-Wire (SBW) paradigm for vehicle control offers many advantages over traditional use of mechanical steering systems but comes at the cost of loss of proprioception (“road feel”). To this end, haptic interfaces for SBW systems have been proposed to restore the intimacy of interactive control back to the driver. However, the degree of realism for the interaction is dependent on the fidelity of the underlying computational vehicle dynamics model. Hence we focus on quantitative comparative testing of the role of vehicle dynamics modeling fidelity for haptic SBW tasks. Additionally the SBW paradigm can simplify implementation of shared/collaborative control (steering) of the underlying mechanical system (vehicle). Possibilities range from sharing of control between multiple individual users or between user and automation technology. Performance evaluation of 3 modes of shared control vs. individual control of driving was carried out and preliminary analysis of results is presented in the paper.

Hunting Stability Analysis of a New High-Speed Railway Vehicle Model Moving on Curved Tracks

A new dynamic model of railway vehicle moving on curved tracks is proposed. In this new model, the motion of the car body is considered and the motion of the tuck frame is not restricted by a virtual boundary. Based on the heuristic nonlinear creep model, the nonlinear coupled differential equations of the motion of a fourteen degrees of freedom car system, considering the lateral displacement and the yaw angle of the each wheelset, the truck frame and the car body, moving on curved tracks are derived in completeness. To illustrate the accuracy of the analysis, the limiting cases are examined. In addition, the influences of the suspension parameters on the critical hunting speeds evaluated via the linear and the nonlinear creep models respectively are studied. Furthermore, the influences of the suspension parameters on the critical hunting speeds evaluated via the fourteen degrees of freedom car system and the six degrees of freedom truck system, which the motion of the tuck frame is restricted by a virtual boundary, are compared.

Control of Vibration Flow at the Joint of an L-Shaped Frame

There has been an increasing interest in vibration control in recent years. This is due to demands for mechanical structures to be lighter and faster. Lighter and faster structures are more prone to vibrations. Hence, there is an imperative need for practical solutions to vibration problems in complex practical mechanical systems. Regardless of the complexity of a structure, from wave vibration standpoint, it consists of only two basic types of structural components, namely, structural elements and structural joints. In this paper, a control strategy is developed for controlling vibrations flowing from one structural element to another through the structural joint. An L-shaped beam is studied as an example structure. Numerical results are given.