Boundary feedback stabilization of a rotating body-beam system

This paper deals with boundary feedback stabilization of a flexible beam clamped to a rigid body and free at the other end. The system is governed by the beam equation nonlinearly coupled with the dynamical equation of the rigid body. The authors propose a stabilizing boundary feedback law which suppresses the beam vibrations so that the whole structure rotates about a fixed axis with any given small constant angular velocity. The stabilizing feedback law is composed of control torque applied on the rigid body and either boundary control moment or boundary control force (or both of them) at the free end of the beam. It is shown that in any case the beam vibrations are forced to decay exponentially to zero     

带有弹性联轴器的齿轮传动系统随机非线性分析

带有弹性联轴器的齿轮传动系统中,弹性联轴器的非线性恢复力函数和阻尼力函数均是频率和振幅的函数,在受到随机激励作用下形成了一类非线性随机系统.文中应用基于高斯勒让德积分的路径积分法计算此传动系统的位移-速度概率密度,并给出一些特定时刻的概率密度分布.最后,分析边界外概率丢失的问题,提出相应的解决方案.     

Control of a planar arm by nonlinear feedback gains

The control of a three-link planar robot, whose parameters roughly match a small commercially available arm, is considered. The end effector of the arm moves along a specified trajectory on a surface with dry friction while maintaining a prespecified constant pressure against the surface both with and without force sensors at the tip. A control strategy is presented with nonlinear position and velocity error feedback gains which are state dependent. Digital computer simulations of the motion are provided for comparison purposes and for demonstrating the effectiveness of this strategy.     

Mathematical modeling of a robot collision with its environment

In this article the collision of a robot with its environment is studied. In normal applications of a robot arm, a collision takes place because of the velocity of the end effector relative to the object at the time of contract. The collision has effects on the velocities and internal forces of the robotic system. Firstly, the generalized velocities representing joint rates have abrupt changes at the moment of collison with the environment. The mathematical model is derived to establish the quantitative relationship between this abrupt change and the severity of the collision. The latter is represented by either an external impulsive force or the instantaneous change of the linear velocity of the contact point. Secondly, internal to the system, large impulsive forces and torques of constraint may develop at each joint because of the collision. These impulses cause possible damages to the system. The mathematical model is also derived to establish a quantitative relation between the impulsive forces and torquest of constraint and the collision. These two models are applied to a Stanford Arm designed to pick up an object by its end effector, and the consequences of the collision are analyzed.     

Vibration damping in manipulation of deformable linear objects using sliding mode control

In this paper, we proposed a position-based control strategy for eliminating the vibration at the end of deformable linear objects (DLOs) during its manipulation. Using Schur decomposition of matrices and linear transform of variables, actuated and underactuated parts of the DLO dynamic model are separated. Based on the decoupled dynamic model of a DLO system, a sliding mode control with exponential approach law is designed to force the state variables to converge to an equilibrium and to allow vibration at the end of the DLO to be damped quickly. The DLO system, subjected to control input saturation, is further studied to solve the input saturation problem. An adaptive sliding mode control law is designed to suppress the damping at the end of the DLO. Proposed control strategies are verified by numerical simulations. The simulation results show that proposed methods can effectively damp the vibration at the end of the DLO.     

Spectral determination for a cantilever beam

The eigenvalue specification problem is discussed for a beam with one end clamped and the other end free, which is allowed to have some structural damping, and has a moment force at the free end acting as a control. The spectrum and eigenvectors of the uncontrolled system are first analyzed and are then used to construct the feedback element which solves the problem. It is shown how this feedback element can be numerically approximated, and a spillover result is proved for the approximation. In the case where there is no damping, this method yields a bounded feedback law which exponentially stabilizes the beam     

Global set stabilization of the spacecraft attitude control problem based on quaternion

In this paper, we develop a global set stabilization method for the attitude control problem of spacecraft system based on quaternion. The control law that uses both optimal control and finite‐time control techniques can globally stabilize the attitude of spacecraft system to a set of equilibria. First, for the kinematic subsystem, we design a virtual optimal angular velocity. To obtain the global minimum of the performance index, this optimal angular velocity is only discontinuous in initial values. It can be regarded as a combination of open loop control and closed loop control. Then for the dynamic subsystem, we design a finite‐time control law that can force the angular velocity to track the virtual optimal angular velocity. It is proved that the closed loop system satisfies global set stability in the absence of disturbances. In the presence of disturbances, the system trajectory will converge to a neighborhood of the equilibrium set. Rigorous analysis shows that by introducing finite‐time control techniques, the closed loop system possesses a better disturbance rejection property. The control method is more natural and energy‐efficient. The effectiveness of the proposed method is demonstrated by simulation results. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy-based control of a haptic device using brakes.

This paper proposes an energy-based control method of a haptic device with electric brakes. Unsmooth motion is frequently observed in a haptic system using brakes during a wall-following task. Since it is generally known that a haptic system using brakes is passive due to brake's characteristics, its energy behavior has seldom been investigated. However, force distribution at the end effector reveals that the unsmooth motion of a haptic system using brakes represents active behavior of the system in the specific direction. A force control scheme is proposed that computes the gain for smooth motion by considering the energy behavior of a system. Experiments show that smooth wall following is possible with a proposed force control scheme.     

Dynamic boundary control of a Euler-Bernoulli beam

A flexible beam, clamped to a rigid base at one end and free at the other end is considered. To stabilize the beam vibrations, a dynamic boundary force control and a dynamic boundary torque control applied at the free end of the beam are proposed. It is proved that with the proposed controls, the beam vibrations decay exponentially. The proof uses a Lyapunov functional, based on the energy functional of the system     

Cycle‐by‐Cycle Adaptive Force Compensation for the Soft‐Landing Control of an Electro‐Mechanical Engine Valve Actuator

Electro‐mechanical valve actuators (EMVA) are a solution for implementing variable valve actuation in internal combustion engines. Their use can increase engine power, reduce fuel consumption and pollutant emissions, while significantly improving engine efficiency. The control of this actuator is a complex task since non‐smooth nonlinearities, parameter variations and external forces strongly affect plant dynamics. In addition, the impact of the valve at its end‐strokes translates into mechanical wear and unacceptable noise, and in the worst case the electromagnet may also fail to catch the valve, causing system failure. The design of effective control strategies to ensure valve capture with low impact velocities is therefore essential for the correct functioning of such a mechatronic device. In this paper, the control problem of reducing the impact velocity at “landing” known in the literature as soft landing control, is tackled via novel cycle‐by‐cycle adaptive force compensation control algorithms. Two schemes are presented: a discrete adaptive proportional integral controller to regulate landing velocity to a preassigned set‐point, and a gradient descent method based controller to automatically achieve the minimum admissible impact velocity. The effectiveness of both methods in limiting landing velocities is shown numerically using a high predictive simulator of the EMVA system, when considering unknown varying environmental conditions, such as internal friction and external gas pressure forces.     

Robust Sliding Control of Robotic Manipulators Based on a Heuristic Modification of the Sliding Gain

A task space robust trajectory tracking control is developed for robotic manipulators. A second order linear model, which defines the desired impedance for the robot, is used to generate the reference position, velocity and acceleration trajectories under the influence of an external force. The control objective is to make the robotic manipulator’s end effector track the reference trajectories in the task space. A sliding mode based robust control is used to deal with system uncertainties and external perturbations. Thus, a sliding manifold is defined by a linear combination of the tracking errors of the system in the task space built from the difference between the real and the desired position, velocity and acceleration trajectories in comparison with previous works where the sliding manifold was defined by the desired impedance and the external force. Moreover, the ideal relay has been substituted by a relay with a dead-zone in order to fit in with the actual way in which a real computational device implements the typical sign function in sliding mode control. Furthermore, a higher level supervision algorithm is proposed in order to reduce the amplitude of the high frequency components of the output associated to an overestimation of the system uncertainty bounds. Then, the robust control law is applied to the case of a robot with parametric uncertainty and unmodeled dynamics. The closed-loop system is proved to be robustly stable with all signals bounded for all time while the control objective is fulfilled in practice. Finally, a simulation example which shows the usefulness of the proposed scheme is presented.     

Triplex-pumping CD-like microfluidic platform with parabolic microchannels

In this research, we propose a triplex-pumping CD-like multi-channel electrophoresis-based biomedical separation system that is driven by the interactions of the centrifugal force, the electric field force, and the Coriolis force. In this novel platform,the heat-conduction theory is implemented to formulate the relations between the sample velocity and the dimensions of the microchannel. The parabola microchannel that has the least friction force under triplex-pumping forces is determined by computer simulations. The centrifugal force control of this system is realized by the angular velocity of a DC servo motor, while the electric field is governed through multi-stage potential circuits, which are suitably designed and fabricated by sputtering using the metal mask method, and can be adjusted to provide multi-stage voltages. Experimental results demonstrated that the proposed parabola microchannels can effectively eliminate the effects of friction force.     

PUMA760切割作业力与位置混合控制

本文介绍在 PUMA760 上实现了的切割作业控制系统。我们在 PUMA760 控制系统中引进了力传感器信号,加入了力控制算法,通过调整机器人手部位置,控制机器人与环境物体间的相互作用力。在 VAL 系统中加入了根据传感器信号动作的指令,实现了一种机器人力与位置的混合控制。用扩充后的 VAL 系统编程,成功地使 PUMA760完成了多种材料的切割作业。     

Triplex-pumping CD-like microfluidic platform with parabolic microchannels

In this research, we propose a triplex-pumping CD-like multi-channel electrophoresis-based biomedical separation system that is driven by the interactions of the centrifugal force, the electric field force, and the Coriolis force. In this novel platform,the heat-conduction theory is implemented to formulate the relations between the sample velocity and the dimensions of the microchannel. The parabola microchannel that has the least friction force under triplex-pumping forces is determined by computer simulations. The centrifugal force control of this system is realized by the angular velocity of a DC servo motor, while the electric field is governed through multi-stage potential circuits, which are suitably designed and fabricated by sputtering using the metal mask method, and can be adjusted to provide multi-stage voltages. Experimental results demonstrated that the proposed parabola microchannels can effectively eliminate the effects of friction force.

     

Guidance control of a wheeled mobile robot with human interaction based on force control

This paper presents a mobile robot carrier designed to carry a person using two modes: a mechanism with full support and another with partial support. The carrier is driven through guided control from an operator. Applied force is sensed by a force sensor mounted on the bottom of the handle. The measured force is filtered by the impedance function that generates the desired velocity to drive the motors. The inner loop PID controller is then required to follow the desired velocity, which is the reference input to the system. The impedance function is designed to make the driving condition comfortable for the driver by smoothing out abrupt starts and stops. Feasibility tests on the application of the impedance force control method to the carrier robot have been performed through experimental case studies aimed at evaluating the comfort level of prospective users: one is on a full support case when a user is riding on the carrier and another on a partial support case where the user is pushing the carrier.     

Variable admittance force feedback device and its human-robot interaction stability

In teleoperation, a force feedback device is a medium to build a transparent interaction environment between a human and a remote robotic arm. Using force feedback devices, the users can operate the remote robotic arm intuitively and perceive remote interaction through the force channel, just as if they are in the remote environment. Compared with impedance devices, admittance devices have the advantages of large feedback output, high stiffness, high reverse driving performance, and flexible structure, which are more suitable for the teleoperation of heavy-duty and large-size robotic arms. However, the control of admittance devices is relatively complex and has some inherent limitations such as response delay, instability from high-frequency oscillation, difficulty in achieving constant speed control, etc. Errors in admittance model parameters and human physiological characteristics, such as force application fluctuations, are the root causes of these problems. In this study, we proposed a fuzzy variable damping admittance algorithm, which allows the device to identify the user's movement intention and give respond quickly and accurately. We also established a human-robot interaction (HRI) system model of an admittance master controller device and summarized the principles of the admittance parameter configuration of a stable system. For the device's high-frequency oscillation instability caused by human arm stiffness, we propose an oscillation observation and reduction algorithm. By observing the force signal change characteristics, the algorithm can quickly detect the unstable behavior caused by human hands and perform oscillation reduction. To reduce the influence on upper limb uniform motion caused by fluctuating force application, we proposed a constant velocity intention inference algorithm based on a velocity spherical cone to smooth out the device operating velocity to achieve smooth control. The method proposed in this study achieved stable control in a 6 DOF force feedback device as a master controller, and the effect has been verified by experiments.     

Design and field testing of a rover with an actively articulated suspension system in a Mars analog terrain

This study presents the electromechanical design, the control approach, and the results of a field test campaign with the hybrid wheeled‐leg rover SherpaTT. The rover ranges in the 150 kg class and features an actively articulated suspension system comprising four legs with actively driven and steered wheels at each leg’s end. Five active degrees of freedom are present in each of the legs, resulting in 20 active degrees of freedom for the complete locomotion system. The control approach is based on force measurements at each wheel mounting point and roll–pitch measurements of the rover’s main body, allowing active adaption to sloping terrain, active shifting of the center of gravity within the rover’s support polygon, active roll–pitch influencing, and body‐ground clearance control. Exteroceptive sensors such as camera or laser range finder are not required for ground adaption. A purely reactive approach is used, rendering a planning algorithm for stability control or force distribution unnecessary and thus simplifying the control efforts. The control approach was tested within a 4‐week field deployment in the desert of Utah. The results presented in this paper substantiate the feasibility of the chosen approach: The main power requirement for locomotion is from the drive system, active adaption only plays a minor role in power consumption. Active force distribution between the wheels is successful in different footprints and terrain types and is not influenced by controlling the body’s roll–pitch angle in parallel to the force control. Slope‐climbing capabilities of the system were successfully tested in slopes of up to 28° inclination, covered with loose soil and duricrust. The main contribution of this study is the experimental validation of the actively articulated suspension of SherpaTT in conjunction with a reactive control approach. Consequently, hardware and software design as well as experimentation are part of this study.     

基于高增益观测器的船舶动力定位系统的输出反馈控制

针对动力定位船舶的速度向量不可测的问题, 考虑外部环境扰动, 将高增益观测器、动态面控制技术和矢量backstepping方法相结合, 设计仅依赖于船舶位置和艏摇角测量值的船舶动力定位系统输出反馈控制律. 动态面控制技术的引入, 使控制律结构简单, 易于工程实现. 应用Lyapunov函数证明了所设计的控制律能迫使船舶的位置和艏摇角收敛于期望值, 并保证船舶动力定位输出反馈闭环系统所有信号均一致最终有界. 基于一艘供给船的仿真研究验证了所设计的基于高增益观测器的船舶动力定位输出反馈控制律的有效性.     

Torque distribution using a weighted pseudoinverse in a redundantly actuated mechanism

When mobility, the number of independent variables to describe system motion exactly, is greater than the degree-of-freedom of task space, the system is called a kinematically redundant system. On the other hand, redundant actuation indicates a situation when there are more actuators than a system's mobility. Redundant actuation yields many advantages. First, actuation redundancy can increase the force, velocity and acceleration of an end-effector. Second, if some actuators are out of order, the system can still work well. This fault-tolerant capability is useful for remote control robots in space or nuclear plants. Impulsive force can decrease when modulating arbitrary stiffness without feedback control. The performance of a system can be improved by optimizing redundancy. However, there are some issues of economic efficiency and minimization of a system, because redundant actuation may involve more actuators than non-redundant actuation. In addition, there are infinite torque sets of motors for the same task. We used a weighted pseudoinverse matrix for torque distribution. To reduce the maximum torque, we suggested the use of the minimum norm torque as the weighting values. This method allows for smaller motor capacity, and can contribute to economic efficiency and minimization of a system.     

A method for grinding removal control of a robot belt grinding system

As a kind of manufacturing system with a flexible grinder, the material removal of a robot belt grinding system is related to a variety of factors, such as workpiece shape, contact force, robot velocity, and belt wear. Some factors of the grinding process are time-variant. Therefore, it is a challenge to control grinding removal precisely for free-formed surfaces. To develop a high-quality robot grinding system, an off-line planning method for the control parameters of the grinding robot based on an adaptive modeling method is proposed in this paper. First, we built an adaptive model based on statistic machine learning. By transferring the old samples into the new samples space formed by the in-situ measurement data, the adaptive model can track the dynamic working conditions more rapidly. Based on the adaptive model the robot control parameters are calculated using the cooperative particle swarm optimization in this paper. The optimization method aims to smoothen the trajectories of the control parameters of the robot and shorten the response time in the transition process. The results of the blade grinding experiments demonstrate that this approach can control the material removal of the grinding system effectively.