无人机吊挂飞行系统的减摆控制设计

主要考虑了四旋翼无人机（Unmanned aerial vehicle,UAV）吊挂飞行系统的位置控制及负载摆动抑制的设计问题.在存在欠驱动特性以及未知系统参数的约束下,本文基于能量法设计了一种非线性控制策略,实现了对无人机位置的精确控制和飞行过程中负载摆动的快速抑制.基于Lyapunov方法的稳定性分析证明了闭环系统的稳定性,位置误差的收敛及摆动的抑制.实验结果表明本文提出的控制策略取得了较好的控制效果.     

Disturbance attenuation in precise hexapod pointing using positive force feedback

Negative feedback control improves system performance by high loop gain. However, it is well known that the achievable performance is limited theoretically by right half complex plane (RHP) poles, RHP zeros, time delays, etc. of the plant models, and practically by the input constraints as well as model uncertainties. Though positive feedback has the potential to improve the system performance by direct subtraction of the measured external disturbances from the plant inputs, it is notorious for its sensitivity to measurement errors and lack of robustness. Inappropriate use of positive feedback control could deteriorate the performance, or even result in instability. This paper presents a new combined control strategy for two degrees-of-freedom precise hexapod pointing control, in which positive force feedback (PFF) is used to reject payload disturbances, and extra acceleration feedback loops are added to enhance the PFF loop robustness as well as decrease its sensitivity. Also, a new method for avoiding destructive interference in parallel controller design using a sequential loop closure technique is proposed. Since the payload disturbances cannot be measured directly due to sensor mounting difficulties, an estimate is constructed based on the hexapod model and used for PFF. The algorithm is implemented on one of the University of Wyoming (UW) hexapods, and experimental results demonstrate that pointing errors caused by the payload disturbances are decreased, despite residual coupling and disturbance estimation errors.     

有环境约束时完成一族跟踪任务的力控制

本文为工业机器人提出了一种极点配置控制法，这种控制方法的优点有：一是它的积分作用消除了机器人的微小扰动和稳态误差；二是能任意设置系统的极点，因此能保证闭环系统的稳定性和规定状态变量的暂态响应；三是加入了加速度反馈，抑制了由电枢电感所引起的机械手的振动，最后，给出了ＰＵＭＡ５６２机器人的计算机仿真和实验结果验证了此控制法的有效性。     

An Enhanced Coupling Nonlinear Tracking Controller for Underactuated 3D Overhead Crane Systems

An enhanced coupling nonlinear tracking control method for an underactuated 3D overhead crane systems is set forth in the present paper. The proposed tracking controller guarantees a smooth start for the trolley and solves the problem of the payload swing angle amplitude increasing as the transferring distance gets longer for the regulation control methods. Different from existing tracking control methods, the presented control approach has an improved transient performance. More specifically, by taking the operation experience, mathematical analysis of the overhead crane system, physical constraints, and operational efficiency into consideration, we first select two desired trajectories for the trolley. Then, a new storage function is constructed by the introduction of two new composite signals, which increases the coupling behaviour between the trolley movement and payload swing. Next, a novel tracking control strategy is designed according to the derivation form of the aforementioned storage function. Lyapunov techniques and Barbalat's Lemma are used to demonstrate the stability of the closed‐loop system without any approximation manipulations to the original nonlinear dynamics. Finally, some simulation and experiments are used to demonstrate the superior transient performance and strong robustness with respect to different cable lengths, payload masses, destinations, and external disturbances of the enhanced coupling nonlinear tracking control scheme.     

Enhancement of pointing performance by semi-active variable damping isolator with strategies for attenuating chattering effects

Semi-active control strategy is one of the most attractive approaches for space applications because of it provides better performance than passive systems and higher robustness than active systems. However, conventional semi-active approaches, such as skyhook and bang-bang control, cause the pointing accuracy of the on-board payload to degrade due to chattering effects created by the sudden variation of damping force when a semi-active isolation system is switched on or off. In this paper, we propose a semi-active strategy to minimize performance deterioration due to chattering effects. Numerical simulation result obtained using a simplified on-board payload model demonstrate that the proposed LQ semi-active control logic with variable damping achieves much better isolation performance than the conventional semi-active control laws under single and fly-wheel force excitation environments.     

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.     

Adaptive recurrent neural network control of uncertain constrained nonholonomic mobile manipulators

In this article, motion/force control problem of a class of constrained mobile manipulators with unknown dynamics is considered. The system is subject to both holonomic and nonholonomic constraints. An adaptive recurrent neural network controller is proposed to deal with the unmodelled system dynamics. The proposed control strategy guarantees that the system motion asymptotically converges to the desired manifold while the constraint force remains bounded. In addition, an adaptive method is proposed to identify the contact surface. Simulation studies are carried out to verify the validation of the proposed approach.     

Dynamic optimal payload path planning of mobile manipulators among moving obstacles

This paper is dealt with dynamic analysis of the wheeled mobile manipulators in the presence of moving obstacles considering optimal payload criterion. General dynamic formulation of the system was derived, and the moving obstacle avoidance strategy was proposed in terms of dynamic potential functions. The problem of dynamic motion planning and payload maximization was formulated using open-loop optimal control theory. Then, the indirect solution based on Pontryagin’s minimum principle was employed to solve the problem. Using the proposed method, complete nonlinear states and control constraints were treated without any simplifications such as linearizing the dynamics equations, discretizing the robot’s workspace, or parameterizing the solution. The proposed method will be useful for the system design and in the situation where the trajectories of obstacles are predefined. Finally, capability and applicability of the proposed method were investigated by the number of simulations on a two-link mobile manipulator.     

带有状态约束的双摆效应吊车轨迹规划

对于欠驱动吊车而言,已有方法大都将负载摆动视为单摆进行处理.然而当吊钩质量相比负载质量不可忽略或负载体积较大时,负载会绕吊钩产生第二级摆动,出现双摆效应,使系统的摆动特性更为复杂,欠驱动度更高,其控制更具挑战性;此外,现有方法均无法保证系统的暂态控制性能.针对这些问题,本文提出了一种基于轨迹规划的消摆定位控制方法.具体而言,本方法所规划的台车轨迹具有解析表达式,且充分考虑系统安全性(摆动幅值)及台车运动的物理约束;通过构造新颖的平坦输出信号,将施加在台车运动和两级摆动上的约束/指标转化为对平坦输出的约束,从而将轨迹规划转化为凸优化问题.该方法能够保证整个过程中系统两级摆动的角度、角速度,台车的速度、加速度、加加速度均保持在设定范围内.通过与已有方法进行仿真对比,可见本方法不仅简单易行,且在工作效率与摆动抑制方面均具有更为良好的控制性能.     

Endpoint perfect tracking control of robots — A robust non inversion-based approach

This paper presents a simple and robust non inversion-based perfect tracking control (RNIBPTC) strategy for robot manipulators. The proposed approach is capable to eliminate the environmental problems arising from classic feedforward control design and so guarantees an appropriate level of robustness of control system to uncertainties including external disturbances, unmodeled dynamics, friction force and variation of payload. Extensive simulation results performed using a two degree-of-freedom actuated elbow robot prove the effectiveness of the proposed approach. The results are also compared to those obtained from Internal Model Control approach. Using free model of system in control law design is a considerable point in the field of robot manipulator control.     

Dynamics and flatness-based control of a kinematically undetermined cable suspension manipulator

A kinematically undetermined cable suspension manipulator moves a payload platform in space by several cables with computer-controlled winches, whereby the position of the payload platform is not determined by the lengths of the cables. Trajectory tracking control of the payload platform is achieved by means of the concept of flat systems. A flat system has the property that the state variables and the control inputs can be algebraically expressed in terms of the so-called flat output and a finite number of time derivatives of the flat output. Its application to kinematically undetermined manipulators represents a generalization of computed-torque control. The control forces are algebraically calculated from the desired trajectories of the payload platform and their time derivatives up to the fourth order leading to a feedforward control strategy. Asymptotically stable tracking behavior is achieved by exact linearization of the nonlinear dynamics by means of a so-called quasi-static state feedback. The procedure is described for the trajectory tracking control of the prototype three-cable suspension manipulator CABLEV.     

A switched optimal control approach to reduce transferring time,energy consumption,and residual vibration of payload’s skew rotation in crane systems

In this paper, nonlinear optimal control schemes are proposed to reduce transferring time, energy consumption, and residual vibration for the payload’s skew rotation process of crane systems. The main contribution of this paper is to reduce the energy consumption without trading-off the sub-optimal transferring time. The novel idea is to use an electro-mechanical clutch to intelligently disengage the connection between the motor and the payload during the motion such that the payload can continue rotating only by its own momentum. As a result, a switched optimal control problem must be realized. Two solutions, namely particular and general schemes are proposed in the paper, where physical constraints of the actuator including bounded velocity and bounded acceleration are explicitly taken into account. Both simulation and experimental results are provided to prove the effectiveness of the proposed optimal control systems. The established schemes can be directly applied to transfer the payload to a desirable skew orientation without any residual oscillation, or can be utilized as a sub-optimal-time reference trajectory planner of the skewing control module in either overhead or rotary crane systems. Furthermore, the hybrid rotation process presented in this paper, which is driven by the engaging/disengaging event of the clutch, can be served as a theoretical benchmark for any newly established switched optimal control method.     

Robotic assembly automation using robust compliant control

Industrial robots used to perform assembly applications are still a small portion of total robot sales each year. One of the main reasons is that it is difficult for conventional industrial robots to adapt to any sort of change. This paper proposes a robust control strategy to perform an assembly task of inserting a printed circuit board (PCB) into an edge connector socket using a SCARA robot. The task is very challenging because it involves compliant manipulation in which a substantial force is needed to accomplish the insertion operation and there are some dynamic constraints from the environment. Therefore, a robust control algorithm is developed and used to perform the assembly process. The dynamic model of the robotic system is developed and the dynamic parameters are identified. Experiments were performed to validate the proposed method. Experimental results show that the robust control algorithm can deal with parameter uncertainties in the dynamic model, thus achieve better performance than the model based control method. An abnormal case is also investigated to demonstrate that the robust compliant control method can deal with the abnormal situation without damaging the system and assembly parts, while pure position control method may cause damages. This strategy can also be used in other similar assembly processes with compliant applications.     

Saturated Adaptive Output-Constrained Control of Cooperative Spacecraft Rendezvous and Docking

This paper investigates the robust relative pose control for spacecraft rendezvous and docking with constrained relative pose and saturated control inputs. A barrier Lyapunov function is used to ensure the constraints of states, so that the computational singularity of the inverse matrix in control command can be avoided, while a linear auxiliary system is introduced to handle with the adverse effect of actuator saturation. The tuning rules for designing parameters in control command and auxiliary system are derived based on the stability analysis of the closed-loop system. It is proved that all closed-loop signals always keep bounded, the prescribed constraints of relative pose tracking errors are never violated, and the pose tracking errors ultimately converge to small neighborhoods of zero. Simulation experiments validate the performance of the proposed robust saturated control strategy.      

On the robust control of two manipulators holding a rigid object

In this paper, a control architecture is developed for the closed chain motion of two six-joint manipulators holding a rigid object in a three-dimensional workspace. Dynamic and kinematic constraints are combined with the equations of motion of the manipulators to obtain a dynamical model of the entire system in the joint space. Reduced-order dynamic equations are then developed with regard to the position and force control variables. Robust control laws are then determined such that the force and position control design is decoupled. The control laws that will be discussed are: a robust position tracking controller that yields an exponentially stable position tracking error result, and a robust force tracking controller that yields adjustable bounds on the force tracking error.     

Model predictive control-based longitudinal control for autonomous electric vehicle with changing mass

In this paper, a longitudinal control strategy in terms of model predictive control (MPC) and mass estimator is investigated for an autonomous electric vehicle (AEV). A driving force table (DFT) is established to represent the relationship among throttle opening, speed, and driving force. A mass estimator is designed to obtain the actual mass of AEV. An MPC-based controller with constraints is suggested to get the desired acceleration. Moreover, a feedforward controller is developed to calculate the throttle opening directly. Both the iterative feasibility and stability of the MPC are ensured. The experimental results are given to show the effectiveness of our strategy with mass estimator.     

Distributed model predictive control of constrained weakly coupled nonlinear systems

This paper proposes a distributed model predictive control (MPC) strategy for a large-scale system that consists of several dynamically coupled nonlinear systems with decoupled control constraints and disturbances. In the proposed strategy, all subsystems compute their control signals by solving local optimizations constrained by their nominal decoupled dynamics. The dynamic couplings and the disturbances are accommodated through new robustness constraints in the local optimizations. The paper derives relationships among, and designs procedures for, the parameters involved in the proposed distributed MPC strategy based on the analysis of the recursive feasibility and the robust stability of the overall system. The paper shows that, for a given bound on the disturbances, the recursive feasibility is guaranteed if the sampling interval is properly chosen. Moreover, it establishes sufficient conditions for the overall system state to converge to a robust positively invariant set. The paper illustrates the effectiveness of the proposed distributed MPC strategy by applying it to three coupled cart-(nonlinear) spring–damper subsystems.     

Trajectory Tracking Control for Quadrotor Robot Subject to Payload Variation and Wind Gust Disturbance

This work proposes a hierarchical nonlinear control scheme for quadrotor to track 3D trajectory subject to payload variation and fast time-varying wind gust disturbance. In terms of dynamics model, the 6 DOF dynamics model with parametric and nonparametric uncertainties is built up. Wind gust and propeller momentum drag model are implemented to quantify the wind impact (force and moment disturbances) on quadrotor. In terms of control design, adaptive robust controller is developed for dynamic subsystem to deal with moment disturbance and estimate the system parameters. Global sliding mode controller is implemented for kinematic subsystem to generate adequate desired attitude angles for tracking the planned 3D trajectory. Simulations and experiments under various conditions are carried out for verification, and the results indicate the effectiveness, adaptiveness and robustness of the control strategy.     

A nonregressor nonlinear disturbance observer-based adaptive control scheme for an underwater manipulator

A new nonlinear disturbance observer-based tracking control scheme for an underwater manipulator is presented in this paper. This observer overcomes the disadvantages of existing disturbance observers, which are designed or analyzed by the linear system techniques. It can be applied in underwater manipulator systems for various purposes such as payload compensation, interaction effects compensation, underwater current or external disturbance compensation, and independent system control. The performance of the proposed tracking control scheme is demonstrated numerically by the payload compensation and interaction effects compensation for a two degrees of freedom vertical underwater manipulator.     

A Robust Controller for A 3‐DOF Flexible Robot with a Time Variant Payload

This article describes a new control scheme designed for a three degree of freedom (3‐DOF) flexible robot. The control scheme consists of two multi variable control loops. The inner loop is the motor's position control system, while the outer loop controls the robot tip's position, thus canceling vibrations which are originated by the structural flexibility of the manipulator during movement. As it will be shown, the outer control loop is robust to payload variations. The outer loop performance is based on a perfect cancelation of the inner loop dynamics. The effects of not achieving such perfect cancelation are also studied, and rules for designing a robust controller in this case are developed. Simulations assuming different payloads have been carried out with successful results for trajectory tracking. Trajectory tracking with a variable payload is also achieved.