柔性机器人协调操作的无内力载荷分配

为解决柔性机器人协调操作系统的逆动力学问题，提出一种无内力载荷分配法。该方法首先在操作空间基于无内力的原则规划载荷分配系数，然后在关节空间以关节输入力矩最小为目标确定机器人各个关节的输入力矩。以2个3R柔性机器人协调操作刚性物体为例，验证了该方法的有效性。     

柔性机器人协调操作的无内力载荷分配

为解决柔性机器人协调操作系统的逆动力学问题,提出一种无内力载荷分配法。该方法首先在操作空间基于无内力的原则规划载荷分配系数,然后在关节空间以关节输入力矩最小为目标确定机器人各个关节的输入力矩。以2个3R柔性机器人协调操作刚性物体为例,验证了该方法的有效性。     

Nonlinear friction compensation in mechatronic servo systems

Friction, especially its nonlinear component, may degrade the tracking performance of robots. Based on Kang’s method, a novel compensation method for nonlinear friction is presented in this paper, which modified Southward’s traditional compensation method for nonlinear friction. The stability of the systems which adopt the novel compensation method is proved with Layapunov’s stability theorem, and is enhanced further. Having estimated the nonlinear friction model using an identification method, the effect caused by its nonlinear component can be compensated, and enhanced tracking performance is verified under the SCARA robot experimental platform using Windows NT and VenturCom’s real-time extension module (RTX) environment.     

Sensorless and modeless estimation of external force using time delay estimation: application to impedance control

This paper proposes an external force estimation algorithm that requires neither dynamical models nor force-torque (F/T) sensors. Considering cost reduction, ‘indirect estimation’ of external force can be preferable to ‘direct sensing’ of the force. However, the explicit use of robot dynamical models, required by most previous studies on ‘indirect estimation’ of external force, can be practically unfavorable due to inevitable modeling errors as well as arduous identification of system parameters. As a remedy for this problem, the Time-Delay Estimation (TDE) scheme has been incorporated in this research. TDE efficiently provides an accurate estimate of nonlinear robot dynamics including external force. Using TDE, the external force has been effectively and efficiently estimated without F/T sensors or robot dynamical models. Through application to impedance control of a robot, the practical advantages of the proposed estimation algorithm are demonstrated.     

An orbital design method for satellite formation flying

An orbital design method of the formation initialization based on the relative orbital element method is presented. It firstly constructed the relative motion equation of the satellite formation flying in terms of the leader and followers’ orbital elements. Then the equation was simplified when the orbit eccentricity of the leader satellite was small. And according to the satellites’ mission, a general design method for the relative trajectory was proposed. The advantage of this method is that one can get a very simple analytical formula of each follower satellite’s orbital elements when the orbital eccentricity of the leader satellite is zero. The simulation results show that the method is effective.     

Adaptive PID formation control of nonholonomic robots without leader's velocity information

This paper proposes an adaptive proportional integral derivative (PID) algorithm to solve a formation control problem in the leader–follower framework where the leader robot's velocities are unknown for the follower robots. The main idea is first to design some proper ideal control law for the formation system to obtain a required performance, and then to propose the adaptive PID methodology to approach the ideal controller. As a result, the formation is achieved with much more enhanced robust formation performance. The stability of the closed-loop system is theoretically proved by Lyapunov method. Both numerical simulations and physical vehicle experiments are presented to verify the effectiveness of the proposed adaptive PID algorithm.     

A switching formation strategy for obstacle avoidance of a multi-robot system based on robot priority model

This paper describes a switching formation strategy for multi-robots with velocity constraints to avoid and cross obstacles. In the strategy, a leader robot plans a safe path using the geometric obstacle avoidance control method (GOACM). By calculating new desired distances and bearing angles with the leader robot, the follower robots switch into a safe formation. With considering collision avoidance, a novel robot priority model, based on the desired distance and bearing angle between the leader and follower robots, is designed during the obstacle avoidance process. The adaptive tracking control algorithm guarantees that the trajectory and velocity tracking errors converge to zero. To demonstrate the validity of the proposed methods, simulation and experiment results present that multi-robots effectively form and switch formation avoiding obstacles without collisions.     

A force/position control for two-arm motion coordination and its stability robustness analysis

This paper presents a motion coordination of two robot manipulators coordinating an object. To coordinate the object, a force/position control scheme in a mode of leader/follower is devised. The dynamics of the object is incorporated into the dynamics of the leader arm, which yields a reduced order model of two arm system. In order to regulate interaction forces between two arms, the dynamics of the follower arm is expressed as force dynamic equations such that a novel direct force control scheme is devised. For the devised control scheme, a numerical simulation is shown. Under the coupling forces between two arms and two different type of bounded input disturbances, boundedness and asymptotic stability results based on a proposed Lyapunov function are shown. Also, a sufficient condition for a stability robustness is derived based on the Lyapunov approach.     

Stable joint torque optimization for multiple cooperating redundant manipulator system

In this paper, joint torque optimization for multiple cooperating redundant manipulators rigidly handling a common object is considered. This work focuses on finding the optimal and stable distribution of the operational forces of a multiple redundant manipulator system to the individual manipulators. Two joint torque optimization schemes (local joint torque minimization and natural joint motion) are formulated and compared. When a redundant manipulator with its joints free is driven by its tip, a naturally inducing joint motion can be called ‘natural joint motion’. From the simulation results of a system of three cooperating redundant manipulators, the natural joint motion scheme is shown to be better than the local joint torque minimization scheme with regard to global torque minimization capability and the resulting stability of motion. However, in order to guarantee the stability, the null space damping method is required for the both schemes. The effectiveness of the null space damping method is demonstrated by simulation. Additionally, the condition for the distribution of the operational forces required to drive the given system along a natural joint motion trajectory is addressed.     

Decentralized control of quadrotors in a leader–follower formation

A problem of control of quadrotors in a leader–follower formation is considered. A method is proposed, which allows control actions for the follower robot to be formed only on the basis of information about the follower motion parameters and the relative positions of the leader and follower.     

CAD of devices for gripping tapered components

The design of gripper jaws for the concentric handling of tapered components is investigated. The jaws have specially shaped profiles made up of a series of curves resembling the Greek character ‘v’, stacked one on top of another. The equations for the profiles are derived. The geometrical parameters affecting their dimensions and shapes are identified. The selection of values for the parameters to yield optimum profiles is discussed.     

Application of Computational Fluid Dynamics and Fluid–Structure Interaction Method to the Lubrication Study of a Rotor–Bearing System

Computational methods were used to analyse the elasto-hydrodynamic lubrication of a complex rotor–bearing system. The methodology employed computational fluid dynamics (CFD), based on the Navier–Stokes equation and a fluid–structure interaction (FSI) technique. A series of models representing the system were built using the CFD–FSI methodology to investigate the interaction between the lubrication of the fluid film, and elastic dynamics of the rotor and journal bearing. All models followed an assumption of isothermal behaviour. The FSI methodology was implemented by setting nodal forces and displacements to equilibrium at the fluid–structure interface, therefore allowing the lubrication of the fluid and the elastic deformation of structures to be solved simultaneously. This is significantly different to the more common techniques—such as the Reynolds equation method—that use an iterative solution to balance the imposed load and the force resulting from the pressure of the fluid film to within a set tolerance. Predictions using the CFD–FSI method were compared with the results of an experimental study and the predictions from an ‘in-house’ lubrication code based on the Reynolds equation. The dynamic response of the system was investigated with both rigid and flexible bodies for a range of different bearing materials and dynamic unbalanced loads. Cavitation within the fluid film was represented in the CFD–FSI method using a simplified phase change boundary condition. This allowed the transition between the liquid and vapour phases to be derived from the lubricant’s properties as a function of pressure. The combination of CFD and FSI was shown to be a useful tool for the investigation of the hydrodynamic and elasto-hydrodynamic lubrications of a rotor–bearing system. The elastic deformation of the bearing and dynamic unbalanced loading of the rotor had significant effects on the position of its locus.     

A new force distribution calculation model for high-quality production processes

Industrial robots have been introduced to the belt grinding of free-form surfaces in order to obtain high-quality products and high-efficiency. One of the critical problems of high-precision belt grinding is to compute the force distribution in the contact area between the workpiece and elastic grinding wheel. The finite element method (FEM) is the traditional way to solve such a contact problem. However, the FEM model is too time-consuming. Normally, a single calculation takes several minutes on a powerful PC, which is unacceptable for real-time simulations and on-line robot control. A new model based on a neural network (NN) technique is developed instead of the FEM model to calculate the force distribution. The new model approximates the old FEM model with an acceptable tolerance but can be executed much faster than FEM model. With this new model, real-time simulation and on-line robot control of grinding processes can be further conducted.     

The Damping Effect on Critical Values of Nonconservative Loads

A systematic study of the effect of energy dissipation on critical nonconservative loads within the stability calculation is carried out. Some classical nonconservative elastic stability problems are considered: the stability of a linear form of equilibrium of a double pendulum under the action of a follower force, the stability of a cantilever beam compressed by a follower force (Beck’s problem), and the stability of a flat panel in a supersonic gas flow. The dependences of critical loads on the damping parameters are built, and the conditions of mechanical system stabilization and destabilization are determined for the cases when damping coefficients vary over a wide range and for various ratios. The external and internal frictions (according to the Voigt model) are considered for the distributed parameter systems. Conclusions about the effect of various types of energy dissipation on the critical values of nonconservative load parameters and about the conditions of nonconservative system destabilization due to the energy dissipation are formulated.     

Distributed ESO based cooperative tracking control for high-order nonlinear multiagent systems with lumped disturbance and application in multi flight simulators systems

Based on extended state observer, a novel and practical design method is developed to solve the distributed cooperative tracking problem of higher-order nonlinear multiagent systems with lumped disturbance in a fixed communication topology directed graph. The proposed method is designed to guarantee all the follower nodes ultimately and uniformly converge to the leader node with bounded residual errors. The leader node, modeled as a higher-order non-autonomous nonlinear system, acts as a command generator giving commands only to a small portion of the networked follower nodes. Extended state observer is used to estimate the local states and lumped disturbance of each follower node. Moreover, each distributed controller can work independently only requiring the relative states and/or the estimated relative states information between itself and its neighbors. Finally an engineering application of multi flight simulators systems is demonstrated to test and verify the effectiveness of the proposed algorithm.     

Novel drive mechanism for in-tube micro robots

The volume of an in-tube micro robot is small and its interior space is very limited. However, conventional transmission methods are unfit to drive in-tube micro robots. A novel micro drive mechanism called the micro-elastic-meshing-wheel is presented in this paper. It can be used for transmitting power and locomotion between two shafts, which are upright and cross in a micro space. The mechanical model of the novel drive mechanism is built, and the maximal transmission force is deduced. Then, sufficient experiments are carried out to test maximal transmission force produced by the novel drive mechanism. The calculation and experiment results show that the novel drive mechanism can transmit sufficient power to in-tube micro robots. __________ Translated from Journal of South China University of Technology (Natural Science Edition), 2006, 34(7): 45–49 [译自: 华南理工大学学报 (自然科学版)]     

Distributed coordinated attitude tracking control for spacecraft formation with communication delays

This paper investigates the distributed coordinated attitude tracking control problem for spacecraft formation with time-varying communication delays under the condition that the dynamic leader spacecraft is a neighbor of only a subset of follower spacecrafts. We consider two cases for the leader spacecraft: i) the attitude derivative is constant, and ii) the attitude derivative is time-varying. In the first case, a distributed estimator is proposed for each follower spacecraft by using its neighbors’ information with communication delays. In the second case, to express the dynamic leader’s attitude, an improved distributed observer is developed to estimate the leader’s information. Based on the estimated values, adaptive coordinated attitude tracking control laws are designed to compensate for parametric uncertainties and unknown disturbances. By employing the Lyapunov–Krasovskii functional approach, the attitude tracking errors and estimation errors are proven to converge to zero asymptotically. Numerical simulations are presented to illustrate the effectiveness of theoretical results.     

The use of displacement threshold for switching frequency strategy for structural vibration mitigation

This paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called ‘smart pin’, mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses of polarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one ‘smart pin’ damper, mounted at each beam-column connection and subjected to two scaled earthquake excitations, namely El-Centro 1940 and Northridge 1994, which respectively represent near- and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for ‘proof-of-concept’ investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required. An erratum to this article is available at .     

多机器人系统的编队路径跟踪控制

介绍了一种多机器人系统的编队路径跟踪控制方法。首先将非完整约束机器人的动态方程转化为跟随者和领航员间相对运动模型,克服了非完整约束机器人结构奇异的缺点。随后将滑模控制方法应用于多机器人系统中,分别设计了领航员跟踪希望路径的滑模控制律和跟随者跟踪领航员的滑模控制律。算例仿真表明了应用本文介绍的编队路径跟踪控制律,各机器人能够较快地形成希望的编队,并按希望队形跟踪希望路径。仿真结果验证了此控制方法的有效性。     

An experimental study on characteristics of two-phase flows in vertical pipe

The characteristics of two-phase flow in a vertical pipe are investigated to provide information for understanding the excitation mechanisms of flow-induced vibration. An analytical model for two-phase flow in a pipe was developed by Sim et al. (2005), based on a power law for the distributions of flow parameters across the pipe diameter, such as gas velocity, liquid velocity and void fraction. An experimental study was undertaken to verify the model. The unsteady momentum flux impinging on a ‘turning tee’ (or a ‘circular plate’) has been measured at the exit of the pipe, using a force sensor. From the measured data, especially for slug flow, the predominant frequency and the RMS value of the unsteady momentum flux have been evaluated. It is found that the analytical method, given by Sim et al. for slug flow, can be used to predict the momentum flux.