Development of a wheeled inverted pendulum mobile platform with a four-bar parallel mechanism

A wheeled inverted pendulum (WIP) offers benefits such as a small floor occupation area, high dynamic stability, and horizontal force sensitivity. However, the body of a WIP robot inclines at the start of acceleration or deceleration, when an external force is applied, or when the position of a CoG is changed. This incline may result in degraded task performance such as object dropping during delivery or image swaying when taking video. In this paper, a WIP mobile platform adopting a four-bar parallel mechanism which provides robust load position variance and horizontal posture keeping is proposed. The basic structure of this platform connects two front and rear inverted pendulums and two upper and lower bars with free-rotational joints, so as to act as a four-bar parallel link mechanism. Based on the features of the parallel mechanism, the platform can maintain a horizontal posture of the upper bar during balancing motion under various disturbances. The motion equations of the mobile platform showed that a change of the loading condition on the upper bar did not affect the balancing characteristics, as confirmed via balancing simulations. Two possible application tasks, namely object delivery and image taking, were successfully demonstrated to show the utility of the platform in terms of its horizontal posture compensation function and its robustness in terms of load position variance.     

并联六自由度运动平台控制系统研究

本文介绍了并联六自由度平台的机构特点,同时在对平台总体控制系统简要设计的基础上完成了单杆液压控制系统的建模工作.考虑了无干扰和有干扰的情况下,对系统进行了仿真分析,提出了基于神经网络算法的先进PID控制方案,仿真结果表明该方法具有良好的控制效果,证明了电液位置伺服控制系统设计的正确性,为平台进一步控制奠定了基础.     

Control of the angular orientation of the platform of a uniaxial wheeled module moving without slippage over an underlying surface

A method for controlling the angular orientation with respect to the horizon plane of the platform of a uniaxial wheeled module moving without slippage over the underlying surface is considered. For a module involving a one-axis gyroscope, a compensating flywheel, and a stabilizing weight, equations of motion are derived, which describe the module as a nonholonomic system due to the absence of slippage of its wheels over the underlying surface. The conditions for the “force of undisturbability” of the platform by the inertial forces upon its arbitrary translational-rotational motion and the conditions for “informational undisturbability” by the inertial forces of the accelometric sensor of the deviation of the platform from the horizon plane are determined. The analytical relationships determining the conditions for the absence of slippage of the wheels are found. By numerical simulation, rational values of the coefficient in the laws governing the moments of forces developed by the control elements of the structure are obtained. The effectiveness of these laws is confirmed by the results of simulating the control processes over the angular motion of the platform of the module along a typical trajectory of its motion over the underlying surface.     

Suboptimal Control of Rigid Body Motion with a Quadratic Cost

In this paper we consider the problem of controlling the rotational motion of a rigid body using three independent control torques. Given a quadratic cost we seek stabilizing state feedback controllers which guarantee that all motions starting within a specified bounded set have cost less than a given number; i.e., we seek suboptimal stabilizing controllers. For a special class of cost functions, we present explicit expressions for suboptimal stabilizing controllers yielding a cost arbitrarily close to the infimal cost. For the general case, we present sufficient conditions which guarantee the existence of linear, suboptimal, stabilizing controllers.     

Adaptive Motion/Force Tracking Control for a Class of Mobile Manipulators

In this paper, modeling and adaptive motion/force tracking control is considered for a class of mobile manipulators under the holonomic and affine constraints with the presence of uncertainties and disturbances. Based on a suitable reduced dynamic model, adaptive controllers are proposed to ensure that the states of a closed‐loop system asymptotically track desired trajectories while the constraint force remains bounded by tuning design parameters. Detailed simulation results confirm the effectiveness of the control strategy.     

Motion Control of a Two-Wheeled Mobile Vehicle with an Inverted Pendulum

Nested saturation control design techniques are usually applied to derive a control law for a two-wheeled vehicle with an inverted pendulum. In presence of external disturbances, this control law may result in a catastrophic problem of finite escape time in the controlled system. This paper proposes control solutions to overcome the above problem. First, a disturbance observer is designed to estimate the external disturbances exponentially. Several coordinate transformations and partial-feedback linearization techniques are then derived to transform the vehicle’s dynamics into an upper-triangular form. Next, nested p-times differentiable saturation and backstepping techniques are combined to design a control law for the transformed system. Attractive features of our proposed control design include a large domain of attraction and simplicity of tuning control gains and the controller implementation. Numerical simulations illustrate the results.     

基于dSPACE的运动控制仿真平台设计

dSPACE公司所开发的实时控制器因其强大的功能而闻名,其高层次的开放语言-SIMULINK与DSP的实时交互使得引进软件设计方法和测试设计的系统成为可能.由于dSPACE控制器不是为了运动控制领域而特别开发的,所以就需要重点解决运动控制系统中安全逻辑、运动轨迹规划等这些在多数工业级别运动控制卡中常见的功能.本文将介绍一种基于dSAPCE控制器的运动控制平台的设计方法.利用dSPACE的编译平台,使用SIMULINK的S-function模块扩展设计,系统达到设计要求,能满足大多数运动控制系统的前期研发设计工作.     

The VFO-Driven Motion Planning and Feedback Control in Polygonal Worlds for a Unicycle with Bounded Curvature of Motion

Integrated motion planning and control for the purposes of maneuvering mobile robots under state- and input constraints is a problem of vital practical importance in applications of mobile robots such as autonomous transportation. Those constraints arise naturally in practice due to specifics of robot mechanical construction and the presence of obstacles in motion environment. In contrast to approaches focusing on feedback control design under the assumption of given reference motion or motion planning with neglection of subsequent feedback motion execution, we adopt a controller-driven motion planning paradigm, which has recently gained attention of many researchers. It postulates design of motion planning algorithms dedicated to specific feedback control policies, which compute a sequence of feedback control subtasks instead of classically planned open-loop controls or parametric paths. In this spirit, we propose a motion planning algorithm driven by the VFO (Vector Field Orientation) control law for the waypoint-following task. Presented analysis of the VFO control law reveals its beneficial properties, which are subsequently utilized to solve a generally nonlinear and non-convex optimal motion planning problem by formulating it as a mixed-integer linear program (MILP). The solution proposed in this paper yields a waypoint sequence, which is designed for execution by application of the VFO control law to drive a robot to a prescribed final configuration under an input constraint imposed by bounded curvature of robot motion and state constraints resulting from a convex decomposition of task space. Satisfaction of these constraints is guaranteed analytically and exactly, i.e., without utilization of numerical approximations. Moreover, for a given discrete set of possible waypoint orientations, the proposed algorithm computes plans optimal w.r.t. given cost functional, which can be any convex linear combination of quantities such as robot path length, curvature of robot motion, distance to imposed state constraints, etc. Furthermore, the planning algorithm exploits the possibility of both forward or backward movement of the robot to allow maneuvering in demanding environments. Generated waypoint sequences are a compact representation of a motion plan, which can be immediately executed with the VFO controller without any additional post-processing. Validity of the proposed approach has been confirmed by simulation studies and experimental motion execution with a laboratory-scale mobile robot.     

Global uniform asymptotical stability of a class of nonlinear cascaded systems with application to a nonholonomic wheeled mobile robot

In this article, we consider the stability analysis problem for a class of nonlinear cascaded systems by using homogeneous properties. Assume that the driving subsystem and the driven subsystem are both homogeneous and locally uniformly asymptotically stable. If the cascaded term satisfies a given inequality, then the cascaded system is globally uniformly asymptotically stable. Furthermore, in the case that both degrees of homogeneity are negative, the cascaded system is globally uniformly finite-time stable. Compared with the existing methods, the conditions given in this article are much easier to verify. These stability results are applied to the global tracking control problem of a nonholonomic wheeled mobile robot. Simulation results are provided to show the effectiveness of the methods.     

Analyzing the usability of the WYRED Platform with undergraduate students to improve its features

Universal Access in the Information Society - The WYRED ecosystem is a technological ecosystem developed as part of WYRED (netWorked Youth Research for Empowerment in the Digital society), a...     

Chaos-PSO-based Motion Planning and Accurate Tracking for Position-posture Control of a Planar Underactuated Manipulator with Disturbance

Unlike a fully-actuated manipulator, the position-posture control of a planar underactuated manipulator (PUM) is more difficult, but the research on it is significant due to the wide practical applications. The existing control methods consider no external disturbance and are involved in the staged control idea, bringing the problems of nonsmooth control torque and time-consuming. A novel one-stage control approach is proposed in this paper for the position-posture control of a three-link PUM with the first free joint under the external disturbance. By analyzing the coupling relationship between its active joints and free joint, the position-posture control is transformed into the trajectory tracking control. Unlike the general trajectory planning, the trajectories of the active joints are planned to include several parameters. Meanwhile, the parameters are solved using a chaos particle swarm optimization algorithm to guarantee that all joint angles can reach to their desired angles. Then, to obtain the high trajectory tracking accuracy at every moment under the external disturbance, the nonlinear disturbance observer is constructed and a nonlinear fast terminal sliding mode tracking controller is designed. Finally, the feasibility and superiority of this strategy are verified via two simulations.

     

Dynamics and Control of Motion on the Ground and in the Air with Application to Biped Robots

The dynamics of a multi-linkage model of natural or man-made systems with arbitrary holonomic and non-holonomic constraints at the joints are formulated. The formulation is equally applicable to movements on the ground or in the air. Nonlinear control strategies for postural balance and rhythmic motion are presented. A predictive algorithm to compensate for computation or transmission delay is proposed. Digital computer simulations are presented to demonstrate the effectiveness of the control strategy for a five-link three-dimensional biped.     

Control of systems with I/O delay via reduction to a one-block problem

In this paper, the standard (four-block) H/sup /spl infin// control problem for systems with a single delay in the feedback loop is studied. A simple procedure of the reduction of the problem to an equivalent one-block problem having particularly simple structure is proposed. The one-block problem is then solved by the J-spectral factorization approach, resulting in the so-called dead-time compensator (DTC) form of the controller. The advantages of the proposed procedure are its simplicity, intuitively clear derivation of the DTC form of the H/sup /spl infin// controller, and extensibility to the multiple delay case.     

Control of a process with unmeasured disturbances that change its steady-state gain sign

Because the sign of the steady-state gain of an industrial NOx reduction unit changes according to the magnitude of the main external disturbance (hydrogen flow rate), designing an appropriate controller is particularly challenging. To address this issue, theoretical analysis suggested that a simple linear controller can provide adequate control for this process. Interestingly, tuning of this controller deviates from well known guidelines of linear control theory, which dictate that closed-loop stability is maintained by sluggish enough control of a stable linear process. It turns out, that for this nonlinear process, controller tuning must be neither too sluggish nor too aggressive, in an intermediate range suggested by a variant of the small-gain theorem proven here for corresponding nonlinear operators. The operator-based analysis was confirmed via computer simulation on a simple first-principles model, calibrated on real plant data. It is expected that control performance and robustness may improve if a number of ideas suggested in the text are explored further.     

利用VBA及COM+实现多层结构题库系统平台

利用Microsoft Word 2000丰富的多媒体表现能力和XML强大的数据访问功能设计一个基于Internet的题库系统平台。本系统不但实现了Word2000与系统的无缝连接，使之集2000丰富的表现形式和SQL Server2000强大的数据管理能力于一身，而且大大方便了今后本系统的升级和功能扩展。     

Control of a three-link manipulator with inequality constraints on the trajectories of its joints

This work deals with the control of a three-link planar manipulator whose motion is subjected to inequality constraints on the trajectories of its joints, and to other constraints on the trajectory of its end-effector.     

Control of nonlinear systems with output tracking error constraints and its application to magnetic bearings

A constructive method is presented to design controllers that force the output of nonlinear systems in a strict feedback form to track a bounded and sufficiently smooth reference trajectory asymptotically. Under a suitable condition on the initial output tracking error, the proposed controllers guarantee the output tracking error within a symmetric or an asymmetric pre-specified limit range, and boundedness of all signals of the closed-loop system. A transformation is introduced to take care of the output tracking error constraint. Smooth and/or p-times differentiable step functions are proposed and incorporated in the output tracking error transformation to overcome difficulties due to the asymmetric limit range on the output tracking error. As a result, there are no switchings in the proposed controllers despite the asymmetric limit range. The proposed control design is then applied to design a tracking controller for active magnetic bearings as an illustrating application.     

Control of mechanical systems with flexibility via a multi-input VS/backstepping design

The use of a multi-input control design procedure to determine the control law for a class of mechanical systems with uncertainties and flexibilities is described. The proposed procedure is based on the well-known backstepping design technique and relies on the possibility of extending a recently developed second-order sliding mode control approach to multi-input systems with non-matched uncertainties. This keeps the computational load reasonable and increases robustness.     

Control Policies of an M/G/1 Queueing System with a Removable and Non-reliable Server

This paper considers a single non-reliable server in the ordinary M/G/1 queueing system whose arrivals form a Poisson process and service times are generally distributed. We also study a single removable and non-reliable server in the controllable M/G/1 queueing systems operating under the N policy, the T policy and the Min( N , T ) policy. It is assumed that the server breaks down according to a Poisson process and the repair time has a general distribution. In three control policies, we show that the probability that the server is busy in the steady-state is equal to the traffic intensity. It is shown that the optimal N policy and the optimal Min( N , T ) policy are always superior to the optimal T policy. Sensitivity analysis is also investigated.     

Control of spam: a comparative approach with special reference to India

Spam and other related online threats are a real concern to all Internet users as they can lead to online fraud involving counterfeit websites, the theft of personal data such as credit card information, personal information through illicit access to computer systems and false or misleading representations in the market place. These are not imaginary threats but are supported by empirical evidence. This wastes time to users opening spam with misleading subject lines, wastes Internet resources trying to block it, consumes storage and bandwidth, and costs money in fighting it. E-commerce cannot flourish in an uncertain environment where security of personal data is not guaranteed. With the aim of boosting confidence in online commerce and protecting the interests of consumers, governments have introduced anti-spam legislation to protect consumers and businesses. This legislation has introduced different parameters. However, legislation alone cannot prevent spam. It is to be combined with technological measures. There is no separate legislation in India to deal with this problem. This paper analyses technological solutions and legal measures in the light of trans-national developments to provide background for any judicial decision making or legislative policy in India.