Lyapunov stable displacement-mode haptic manipulation of hydraulic actuators: theory and experiment

In this article, a stable control scheme is designed and experimentally evaluated for haptic-enabled teleoperated control of hydraulic actuators. At the actuator (slave) side, the controller allows the hydraulic actuator to have a stable position tracking. At the master side, the haptic device provides a kind of ‘feel’ of telepresence to the operator by creating a force that acts like a virtual spring, coupling the displacement of the haptic device to the displacement of the hydraulic actuator. In free motion, this virtual spring restricts the operator's hand to move fast when the slave manipulator is behind/ahead in terms of tracking the master manipulator's displacement. On the other hand, when interacting with the environment, the constrained force imposed on the hydraulic actuator is indirectly reflected through this virtual spring force. Extension of Lyapunov's stability theory to non-smooth systems is first employed to prove the stability of the resulting control system. Effectiveness of the controller is then validated via experimental studies. It is shown that the control scheme performs well in terms of both positioning the hydraulic actuator and providing a haptic feel to the operator. The control scheme is easy to implement since very little knowledge about system parameters is needed and the required on-line measurements are actuator's supply and line pressures and displacement.     

Master-slave intelligent robot telepresence system

In this paper, the analysis and design of master-slave intelligent robot telepresence system are discussed. When the operator acts on the master manipulator, the position and attitude information of the master manipulator are gathered by the computer. After calculating and coordinate transforming, the data are send to the computer of the slave manipulator. Then the slave manipulator-PUMA562 robot follows the master manipulator's movement precisely. Six-dimension force/toque sensor(lord cell) is mounted on the slave manipulator. As the master manipulator and the toque on the slave manipulator are different in structure, the force and the slave manipulator should be send to the master manipulator computer and dissociated by the master manipulator computer. Proper ratio of the force on the master manipulator and the force on the slave manipulator is selected, and distribute to the master manipulator joints. So that the operator could feel the force from the master manipulator, which is obtained by the motors of the joints. The proposed control scheme is introduced to a prototype master-slave system and the experimental results show the validity of the proposed scheme.     

Teleoperation Control of a Position‐Based Impedance Force Controlled Mobile Robot by Neural Network Learning: Experimental Studies

Effective haptic performance in teleoperation control systems can be achieved by solving two major problems: the time‐delay in communication channels and the transparency of force control. The time‐delay in communication channels causes poor performance and even instability in a system. The transparency of force feedback is important for an operator to improve the performance of a given task. This article suggests a possible solution for these two problems through the implementation of a teleoperation control system between the master haptic device and the slave mobile robot. Regulation of the contact force in the slave mobile robot is achieved by introducing a position‐based impedance force control scheme in the slave robot. The time‐delay problem is addressed by forming a Smith predictor configuration in the teleoperation control environment. The configuration of the Smith predictor structure takes the time‐delay term out of the characteristic equation in order to make the system stable when the system model is given a priori. Since the Smith predictor is formulated from exact linear modeling, a neural network is employed to identify and model the slave robot system as a nonlinear model estimator. Simulation studies of several control schemes are performed. Experimental studies are conducted to verify the performance of the proposed control scheme by regulating the contact force of a mobile robot through the master haptic device.     

A delayed force-reflecting haptic controller for master–slave neurosurgical robots

This paper presents a new force-reflecting control system for master–slave haptic devices. This controller has been implemented and tested on the robotic systems for minimally invasive neurosurgery developed by our Research Group. Robot-assisted surgery is a very valuable treatment, since it allows benefits of high precision, accuracy, and repeatability of robotic devices. The proposed controller is meant to be used for master–slave haptic robotic surgery, but it can be used for any device that provides haptic feedback. The new controller merges the paradigms of force reflection (FR) control and delayed reference control. Unlike the FR control, the proposed solution enhances the safety since it does not allow an unwanted motion of the slave device once the operator releases the haptic controller. Experimental tests are provided to show the capabilities and the performance of the controller. Closed-loop stability is investigated both theoretically and experimentally. The analytic results on stability impose a limit on the ratio between the measured contact force and the sampling frequency of the closed-loop controller.     

Accurate force reflection method for a multi-d.o.f. haptic interface using instantaneous restriction space without a force sensor in an unstructured environment

This paper proposes an accurate force reflection method for a multi-d.o.f. haptic interface without a force sensor. Sensorless force reflection is possible using position–position (p–p) architecture. However, the conventional p–p architecture in the literature has limitations representing constraint space when it is applied to a multi-d.o.f. haptic interface in that it gives an inaccurate force direction. This paper demonstrates the limitation of the conventional p–p architecture through an example and proposes a novel force reflection method using the instantaneous restriction space (IRS) concept. The IRS can be calculated using the Jacobian and joint angle error of a slave manipulator. Since the proposed method has the form of an impedance two-port architecture in the sense of data flow, it can be easily combined with previous well-known results of two-port haptic display frameworks. The proposed method is especially useful when the slave manipulator collides with unexpected obstacles during motion, even though the slave does not have a force sensor. The performance of the proposed method is evaluated through experiments.     

Bilateral teleoperation of a group of mobile robots for cooperative tasks

A visual and force feedback-based teleoperation scheme is proposed for cooperative tasks. The bilateral teleoperation system includes a haptic device, an overhead camera and a group of wheeled robots. The commands of formation and average velocities of the multiple robots are generated by the operator through the haptic device. The state of the multiple robots and the working environment is sent to the human operator. The received information contains the feedback force through the haptic device and visual information returned by a depth camera. The feedback force based on the difference between the desired and actual average velocities is presented. The wave variable method is employed in the bilateral teleoperation of multiple mobile robots with time delays. The effectiveness of the bilateral teleoperation system is demonstrated by experiments. The robots in the slave side are able to follow the commands from the master side to interact with the environments, including moving in different formations and pushing a box. The results show that the scheme enables the operator to manipulate a group of robots to complete cooperative tasks freely.     

Scaled teleoperation system for nano-scale interaction and manipulation

In this paper, a visual and haptic human–machine interface is proposed for teleoperated nano-scale object interaction and manipulation. Design specifications for a bilateral scaled tele-operation system with slave and master robots, sensors, actuators and control are discussed. The Phantom? haptic device is utilized as the master manipulator, and a piezoresistive atomic force microscope probe is selected as the slave manipulator and as topography and force sensors. Using the teleoperation control system, initial experiments are realized for interacting with nano-scale surfaces. It is shown that fine structures can be felt on the operator's finger successfully, and improved nano-scale interaction and manipulation using visual and haptic feedback can be achieved.     

Nonlinear adaptive control of master–slave system in teleoperation

This paper is devoted to the nonlinear control design problem to achieve stability of master–slave manipulators in teleoperation system and its transparency in the sense of motion/force tracking. Nonlinear adaptive controllers are bilaterally designed for both master and slave sites to guarantee the stability of whole system and motion tracking performance. Global boundedness of the overall adaptive system and asymptotic motion (velocity/position) tracking are established. Especially, the concept of “virtual master manipulator” is introduced to increase degree of freedom of control design for force tracking performance. The resulting force tracking error depends only on the acceleration of the designed virtual master manipulator. Accurate dynamic parameters of manipulators, their acceleration information as well as models of human operator and environment are not required in the control design. Another important feature of our approach is the relaxation for the trade-off between motion and force tracking performances.     

基于STM32的力觉反馈装置及用于主从遥操作实现

在遥操作系统中为了增强现实及实现本地力觉信号再现功能以提高精细化操作的目的 ,设计了用于人机交互功能的力反馈装置;该装置为单自由度结构,基于步进电机驱动;利用STM32微控制器采集触觉力信号以及关节位移信号,通过设计基于力误差的控制律调整位置变量实现输出力信号与标准力信号的匹配;为了验证该力反馈装置进行了标准力信号再现实验;并且利用该力反馈装置作为主机械手与单自由度从机械手搭建遥操作装置,进行了力、位置双边跟踪实验验证,实现了主、从机械手力、位置协同一致的目的.     

Stability guaranteed teleoperation: an adaptive motion/force control approach

An adaptive motion/force controller is developed for unilateral or bilateral teleoperation systems. The method can be applied in both position and rate control modes, with arbitrary motion or force scaling. No acceleration measurements are required. Nonlinear rigid-body dynamics of the master and the slave robots are considered. A model of the flexible or rigid environment is incorporated into the dynamics of the slave, while a model of the human operator is incorporated into the dynamics of the master. The master and the slave are subject to independent adaptive motion/force controllers that assume parameter uncertainty bounds. Each parameter is independently updated within its known lower and upper bounds. The states of the master (slave) are sent to the slave (master) as motion/force tracking commands instead of control actions (efforts and/or flows). Under the modeling assumptions for the human operator and the environment, the proposed teleoperation control scheme is L/sub 2/ and L/sub /spl infin// stable in both free motion and flexible or rigid contact motion and is robust against time delays. The controlled master-slave system behaves essentially as a linearly damped free-floating mass. If the parameter estimates converge, the environment impedance and the impedance transmitted to the master differ only by a control-parameter dependent mass/damper term. Asymptotic motion (velocity/position) tracking and force tracking with zero steady-state error are achieved. Experimental results are presented in support of the analysis.     

Proposal of an Index for the Operator’s Haptic Sensation in a Master-Slave System with Force-Feedback Function

This article proposes an index to estimate the operator’s haptic sensation of the contact between the slave device and the environment in operating master–slave systems with force feedback function. The index value is derived from the velocity information of the master device before and after contact, which is hypothesized to represent the intensity of haptic sensation stimuli presented to the operator. Two characteristics of this index are discussed by means of psychophysics experiment, which are the statistical characteristics of the index value for different operators, and how the change in the operator’s haptic sensation is reflected on the index value. The index is validated by another psychophysics experiment. The experimental results show that the performance of operator’s haptic sensation can be predicted correctly based on the proposed index value. This index is expected to be applied in the parameter design of bilateral-control systems with force feedback function.     

基于伪逆的导轨机械臂关节速度纠偏运动规划方案

针对导轨机械臂在任务执行过程中出现的关节速度偏离期望值的问题,提出了一种基于伪逆算法的导轨机械臂关节速度纠偏运动规划方案。首先,根据机械臂的关节角状态和末端执行器的运动状态,运用伪逆算法对导轨机械臂在速度层上进行冗余度解析。然后,设计时变函数对关节速度进行约束调整,使偏离后的关节速度收敛于期望值。接着,针对末端执行器出现的位置误差设计了误差修正方法以保证轨迹跟踪任务的顺利执行。最后,将运动规划方案在Matlab软件上以基座直线移动和弧形移动的四连杆冗余度机械臂为例进行了仿真实验。仿真结果表明了该方案能纠正导轨机械臂在任务执行过程中偏离期望值的关节速度,且能使末端执行器的轨迹跟踪达到较高的精度。     

自由飞行空间机器人系统的协调运动控制

考虑由载体和机械臂组成的空间机器人系统的协调控制问题,提出了一种新的协调 控制策略.该策略首先利用简单的变结构控制器粗略控制载体的运动,进而设计机械臂控制 器以保证手端精确跟踪其期望的运动轨迹.应用该策略分别对手端自由运动和受限运动设计 了相应的控制器,并对两杆平面空间机器人系统进行了仿真,证实了控制策略的有效性.     

基于伪逆的导轨机械臂关节速度纠偏运动规划方案

针对导轨机械臂在任务执行过程中出现的关节速度偏离期望值的问题，提出了一种基于伪逆算法的导轨机械臂关节速度纠偏运动规划方案。首先，根据机械臂的关节角状态和末端执行器的运动状态，运用伪逆算法对导轨机械臂在速度层上进行冗余度解析。然后，设计时变函数对关节速度进行约束调整，使偏离后的关节速度收敛于期望值。接着，针对末端执行器出现的位置误差设计了误差修正方法以保证轨迹跟踪任务的顺利执行。最后，将运动规划方案在Matlab软件上以基座直线移动和弧形移动的四连杆冗余度机械臂为例进行了仿真实验。仿真结果表明了该方案能纠正导轨机械臂在任务执行过程中偏离期望值的关节速度，且能使末端执行器的轨迹跟踪达到较高的精度。     

Transparent bilateral teleoperation interacting with unknown remote surfaces with a force/velocity observer design

A master–slave teleoperation system is considered, in which the slave manipulator is interacting with a rigid surface with unknown geometry. It is assumed that neither force nor velocity measurements at the slave side are available. To deal with this problem, an extended-state high-gain observer is proposed to estimate in an arbitrary close manner the velocity and force signals. At the same time, the gradient vector for the remote surface is online estimated and employed into an hybrid position/force controller based on the orthogonal decomposition of the task space. A formal proof is presented, which guarantees ultimate boundedness of the state of the system, with arbitrarily small ultimate bound. Furthermore, it is established the transparency of the teleoperation system that, roughly speaking, gives the human operator the sensation of being interacting directly with the remote surface. The proposed scheme is validated through numerical simulations and experiments.     

Neural Network Force Control for Industrial Robots

In this paper, we present a hierarchical force control framework consisting of a high level control system based on neural network and the existing motion control system of a manipulator in the low level. Inputs of the neural network are the contact force error and estimated stiffness of the contacted environment. The output of the neural network is the position command for the position controller of industrial robots. A MITSUBISHI MELFA RV-M1 industrial robot equipped with a BL Force/Torque sensor is utilized for implementing the hierarchical neural network force control system. Successful experiments for various contact motions are carried out. Additionally, the proposed neural network force controller together with the master/slave control method are used in dual-industrial robot systems. Successful experiments are carried out for the dual-robot system handling an object.     

A Composite State Convergence Scheme for Bilateral Teleoperation Systems

State convergence is a novel control algorithm for bilateral teleoperation of robotic systems. First, it models the teleoperation system on state space and considers all the possible interactions between the master and slave systems. Second, it presents an elegant design procedure which requires a set of equations to be solved in order to compute the control gains of the bilateral loop. These design conditions are obtained by turning the master-slave error into an autonomous system and imposing the desired dynamic behavior of the teleoperation system. Resultantly, the convergence of master and slave states is achieved in a well-defined manner. The present study aims at achieving a similar convergence behavior offered by state convergence controller while reducing the number of variables sent across the communication channel. The proposal suggests transmitting composite master and slave variables instead of full master and slave states while keeping the operator’s force channel intact. We show that, with these composite and force variables; it is indeed possible to achieve the convergence of states in a desired way by strictly following the method of state convergence. The proposal leads to a reduced complexity state convergence algorithm which is termed as composite state convergence controller. In order to validate the proposed scheme in the absence and presence of communication time delays, MATLAB simulations and semi-real time experiments are performed on a single degree-of-freedom teleoperation system.      

State and Impedance Reflection Based Control Interface for Bilateral Telerobotic System with Asymmetric Delay

In this paper, we investigate state and imped-ance reflection based robust control strategy for bilateral shared telerobotic system under unsymmetrical time varying delay. Shared input for both master and slave robot is designed by combining delayed position and position-velocity signals with impedance reflection properties of the interaction between slave and environment and between human and master robot manipulator. Adaptive control algorithm is proposed to estimate the interaction properties between human and master manipulator and between slave and remote environment. Then, the delayed estimated interaction properties are reflected back to the master and slave robot manipulator to match with the estimated impedance properties of the interaction between human and remote environment. We combine robust term with adaptive control term to deal with the uncertainty associated with gravity loading vector, unmodeled dynamic and external disturbance. The stability conditions with time varying delays are derived by using Lyapunov-Krasovskii functional. Experimental results are given to demonstrate the validity of the proposed design for real-time applications.     

Neural network learning of robot arm impedance in operational space

Impedance control is one of the most effective control methods for the manipulators in contact with their environments. The characteristics of force and motion control, however, is determined by a desired impedance parameter of a manipulator's end-effector that should be carefully designed according to a given task and an environment. The present paper proposes a new method to regulate the impedance parameter of the end-effector through learning of neural networks. Three kinds of the feed-forward networks are prepared corresponding to position, velocity and force control loops of the end-effector before learning. First, the neural networks for position and velocity control are trained using iterative learning of the manipulator during free movements. Then, the neural network for force control is trained for contact movements. During learning of contact movements, a virtual trajectory is also modified to reduce control error. The method can regulate not only stiffness and viscosity but also inertia and virtual trajectory of the end-effector. Computer simulations show that a smooth transition from free to contact movements can be realized by regulating impedance parameters before a contact.     

Direct adaptive impedance control of robot manipulators

This article presents an adaptive scheme for controlling the end-effector impedance of robot manipulators. The proposed control system consists of three subsystems: a simple “filter” that characterizes the desired dynamic relationship between the end-effector position error and the end-effector/environment contact force, an adaptive controller that produces the Cartesian-space control input required to provide this desired dynamic relationship, and an algorithm for mapping the Cartesian-space control input to a physically realizable joint-space control torque. The controller does not require knowledge of either the structure or the parameter values of the robot dynamics and is implemented without calculation of the robot inverse kinematic transformation. As a result, the scheme represents a general and computationally efficient approach to controlling the impedance of both nonredundant and redundant manipulators. Furthermore, the method can be applied directly to trajectory tracking in free-space motion by removing the impedance filter. Computer simulation results are given for a planar four degree-of-freedom redundant robot under adaptive impedance control. These results demonstrate that accurate end-effector impedance control and effective redundancy utilization can be achieved simultaneously by using the proposed controller.