Robust PID control of fully-constrained cable driven parallel robots

In this paper dynamic analysis and robust PID control of fully-constrained cable driven parallel manipulators are studied in detail. Since in this class of manipulators cables should remain in tension for all maneuvers in their workspace, feedback control of such robots becomes more challenging than that of conventional parallel robots. In this paper, structured and unstructured uncertainties in dynamics of the robot are considered and a robust PID controller is proposed for the cable robot. To ensure that all cables remain in tension internal force concept is used in the proposed PID control algorithm. Then, robust stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov direct method and it is shown that by suitable selection of the PID controller gains, the closed-loop system would be robustly stable. Finally, the effectiveness of the proposed PID algorithm is examined through experiments on a planar cable driven robot and it is shown that the proposed control structure is able to provide suitable performance in practice.     

Position regulation in Cartesian space of a class of inextensible soft continuum manipulators with pneumatic actuation

This work investigates the position regulation in Cartesian space of a class of inextensible soft continuum manipulators with pneumatic actuation subject to model uncertainties and to unknown external disturbances that act on the tip. Soft continuum manipulators are characterised by high structural compliance which results in a large number of degrees-of-freedom, only a subset of which can be actuated independently or instrumented with sensors. External disturbances, which are common in many applications, result in uncertain dynamics and in uncertain kinematics thus making the control problem particularly challenging. We have investigated the use of integral action to model the uncertain kinematics of the manipulators, and we have designed a new control law to achieve position regulation in Cartesian space by employing a port-Hamiltonian formulation and a passivity-based approach. In addition, we have compared two adaptive laws that compensate the effects of the external disturbances on the system dynamics. Local stability conditions are discussed with a Lyapunov approach and are related to the controller parameters. The performance of the controller is demonstrated by means of simulations and experiments with two different prototypes.     

An adaptive controller for a direct-drive SCARA robot

A direct adaptive controller for trajectory tracking of high-speed robots such as a direct-drive SCARA robot is presented. In this robot, nonlinear effects due to centrifugal, Coriolis, and inertial forces are more important than friction and gravity forces, unlike most industrial robots. The control law of the adaptive scheme consists of a PD regulator plus feedforward compensation of full dynamics. The feedforward terms are adjusted by an adaptation law so that the steady-state position errors are zero. With this adaptive controller, the joint acceleration measurement is not required and no inversion of the estimated mass matrix is involved. The tracking performances of the controller applied to a two-degree-of-freedom SCARA is illustrated by a real-time implementation based on a single-chip digital signal processor (DSP)     

Full-state tracking and internal dynamics of nonholonomic wheeled mobile robots

In the paper, the stable full-state tracking problem is investigated for nonholonomic wheeled mobile robots under output-tracking control laws. Dynamics of such wheeled mobile robots are nonholonomic and pose challenging problems for control design and stability analysis. The dynamics formulated in terms of full-state tracking errors offer some properties that allow better understanding of the internal and zero dynamics of the tracking-error system and more insights to the trajectory tracking stability. Output functions are chosen as virtual reference points for various types of wheeled mobile robots in aid of output controller designs. Sufficient conditions are derived to ensure the stable full-state trajectory tracking under output-tracking control laws. A type (1,1) mobile robot of car-like configuration is studied in detail and further numerical analysis provides more results which are beyond the reach of analytical means. An example and simulation results are presented to confirm the theory and observations.     

Backing control problem of a mobile robot with multiple trailers:fuzzy modeling and LMI-based design

The paper presents backing control of computer simulated mobile robots with multiple trailers by fuzzy modeling and control. We deal with two kinds of mobile robots: a mobile robot with five trailers and a mobile robot with ten trailers. To design fuzzy controllers, nonlinear models of the mobile robots with multiple trailers are represented by Takagi-Sugeno fuzzy models (TS fuzzy model). Before making TS fuzzy models, we simplify the nonlinear dynamics of the mobile robots. Under an assumption, TS fuzzy models are made from the simplified nonlinear models. The so-called parallel distributed compensation (PDC) is employed to design fuzzy controllers from the TS fuzzy models. Next, we derive a stability condition based on the Lyapunov approach. The stability condition of the designed fuzzy control system is cast in terms of linear matrix inequalities (LMI's) since it is reduced to a problem of finding a common Lyapunov function for a set of Lyapunov inequalities. Convex optimization techniques based on LMI's are utilized to solve the problem of finding stable feedback gains and a common Lyapunov function for the designed fuzzy control system. The simulation results show the effects of the fuzzy modeling, the controller design via the PDC, and the stability analysis based on LMIs     

Autonomous decentralized control for formation of multiple mobile robots considering ability of robot

The purpose of this study is to control multiple mobile robots in formation considering the ability of a robot using the "Leader-Following" strategy. There are three features of this study. First, a performance index that shows mobile robot ability is quantified. Specifically, maximum acceleration and maximum velocity of a robot are defined by maximum admissible rotation and maximum continuous torque of a motor. The performance index is quantified from arrival time on the destination using these parameters. Second, a new controller is proposed based on the performance index, so that robots can be controlled according to robot ability. Third, a compliance controller using a virtual repulsion is suggested in this paper, so that each robot can avoid collision. Finally, simulation and experiments are done in a real-time system using RT-Messenger. RT-Messenger allows robots to transmit information regarding their positions to each other in real time. These results shows the validity of the proposed method.     

Leader‐Following Formation Control of Multiple Robots with Uncertainties through Sliding Mode and Nonlinear Disturbance Observer

This paper presents a control scheme for the leader‐following formation of multiple robots. The control scheme combines the sliding mode control (SMC) method with the nonlinear disturbance observer (NDOB) technique. The formation dynamics suffer from uncertainties because the individual robots are uncertain. Concerning such formation uncertainties, the leader‐following formation dynamics are modeled. Assuming that the formation uncertainties have an unknown boundary, an NDOB‐based observer was designed to estimate the formation uncertainties. A sliding surface containing the observer outputs has been defined. Regarding the sliding surface, an SMC‐based controller was investigated to form uncertain robots. A sufficient condition in the sense of the Lyapunov theory was proven such that the formation system is asymptotically stable. Herein, some comparison results between the sole SMC method and the second‐order SMC method are presented to demonstrate the effectiveness and feasibility of the control scheme for multiple robots in the presence of uncertainties.     

基于Backstepping和神经动力学的非完整移动机器人点镇定

以非完整移动机器人为控制对象,围绕机器人运动控制中重要的点镇定问题进行深入研究.本文在考虑移动机器人模型和极坐标系下的位姿误差模型基础上,提出一种Backstepping与神经动力学相结合方法,设计具有渐近稳定的点镇定控制器.该控制方法能有效解决因初始误差存在而引起的速度和力矩突变问题,使机器人从静止状态快速收敛到任意...     

Adaptive Control of Harmonic Drives Based on Virtual Decomposition

Harmonic drives are interesting for robotic applications due to their attractive properties such as high reduction ratio, compact size, low mass, and coaxial assembly. However, the high friction and the dynamics of the flexspline are the main issues that significantly challenge the control systems. In this paper, an adaptive controller capable of adaptively compensating the friction, while incorporating the dynamics of the flexspline, is developed in both joint torque and joint-position control modes. The virtual decomposition control approach allows the dynamics of harmonic drives to be controlled separately from the conventional dynamics of the robots. Adaptive friction compensation and flexspline dynamics based control are the two main contributions of this paper. The$L_2/L_infty$stability and the$L_2$-gain-induced$H_infty$stability are guaranteed. Experimental results demonstrated in both time and frequency domains confirm the feasibility of the proposed approach.     

Kinematic and dynamic description of non-standard snake-like locomotion systems

The paper deals with terrestrial locomotion systems. Worms and snakes are living paragons for the development of biological inspired crawling robots. We set up certain models of worm- and snake-like locomotion systems and present purely analytical investigations in this paper. We try to follow an analytical framework, i.e., analyzing kinematics at first. Later on, we switch to dynamics and control of these models, to get hints for a technical development. The systems are modeled as chains of mass points. The mass points are interconnected via massless links with time-varying link-length. In contrast to the literature, the snake systems exhibit passive joints, but active links and rotatable skids. The combination of shape variation (via active links) together with the ground contact (via ideal spikes guaranteeing a one-sided velocity restriction) results in a global movement of the systems — undulatory locomotion. In dynamics, these link functions should be adjusted via, e.g., a force actuator between each mass point. Because it is impossible to determine a-priori these force outputs generating a desired gait, we apply an adaptive controller which adjusts these force outputs on-line on its own and λ-tracks a certain gait to achieve a movement of the whole system.     

A systematic design procedure of force controllers for industrialrobots

In this paper, the problem of designing a force controller for industrial robots with a positional interface is addressed. A systematic design procedure to compute structures and parameters of the controller is devised, to provide a useful tool for rapid and robust setup of force control at the industrial level. The proposed method for synthesis of the force controller simply requires technology parameters provided by the robot manufacturer and desired performance expressed in non-technical terms by the user. The automated design algorithm is described in detail and its effectiveness was proved by experiments on two different industrial robots. On the first robotic setup, the performance of the designed controllers was evaluated by analyzing the experimental results of responses to canonical reference signals; on the second setup, the controller reliability and applicability at the industrial level were demonstrated through the results of a mechanical parts mating task     

Managing the Dynamics of a Harmonic Potential Field-Guided Robot in a Cluttered Environment

This paper demonstrates the ability of the harmonic potential field (HPF) planning method to generate a well-behaved constrained path for a robot with second order dynamics in a cluttered environment. It is shown that HPF-based controllers may be developed for holonomic, as well as nonholonomic, robots to effectively suppress the effect of inertial forces on the robot's trajectory while maintaining all the attractive features of a purely kinematic HPF planner. The capabilities of the suggested navigation controller are demonstrated using simulation results for the holonomic and nonholonomic cases.      

Using role-based control to produce locomotion in chain-type self-reconfigurable robots

This paper presents a role-based approach to the problem of controlling locomotion of chain-type self-reconfigurable robots. In role-based control, all modules are controlled by identical controllers. Each controller consists of several playable roles and a role-selection mechanism. A role represents the motion of a module and how it synchronizes with connected modules. A controller selects which role to play depending on the local configuration of the module and the roles being played by connected modules. We use role-based control to implement a sidewinder and a caterpillar gait in the CONRO self-reconfigurable robot. The robot is made from up to nine modules connected in a chain. We show that the locomotion speed of the caterpillar gait is constant even with loss of 75% of the communication signals. Furthermore, we show that the speed of the caterpillar gait decreases gracefully with a decreased number of modules. We also implement a quadruped gait and show that without changing the controller the robot can be extended with an extra pair of legs and produce a hexapod gait. Based on these experiments, we conclude that role-based control is robust to signal loss, scales with an increased number of modules, and is a simple approach to the control of locomotion of chain-type self-reconfigurable robots.     

Nonlinear bilateral teleoperators with non-collocated remote controller over delayed network

Remote robots in bilateral teleoperation systems are utilized to accomplish various missions in different locations, which are generally far away from local robots collocated with a human operator. In order to enhance flexibility of teleoperators with extensive applicability, this paper proposed a novel control framework, where the remote controller is non-collocated with the robot in the environment. In contrast to traditional teleoperation systems, the remote robot only needs to send out sensory information and receive control commands from the local side. Stability and transparency of the proposed teleoperators are studied for PD-like controller with fixed time delays, and P-like controller with time-varying delays. If the control gains are contingent to upper bounds of time delays, then the system is stable with guaranteed position tracking and force reflection. Numerical simulations and experiments were conducted to demonstrate the effectiveness of the proposed control algorithms in bilateral teleoperation.     

Therapeutic Robotics: A Technology Push

In this paper, we present a retrospective and chronological review of our efforts to revolutionize the way physical medicine is practiced by developing and deploying therapeutic robots. We present a sample of our clinical results with well over 300 stroke patients, both inpatients and outpatients, proving that movement therapy has a measurable and significant impact on recovery following brain injury. Bolstered by this result, we embarked on a two-pronged approach: 1) to determine what constitutes best therapy practice and 2) to develop additional therapeutic robots. We review our robots developed over the past 15 years and their unique characteristics. All are configured both to deliver reproducible therapy but also to measure outcomes with minimal encumbrance, thus providing critical measurement tools to help unravel the key question posed under the first prong: what constitutes "best practice"? We believe that a "gym" of robots like these will become a central feature of physical medicine and the rehabilitation clinic within the next ten years     

An exoskeletal robot for human shoulder joint motion assist

We develop exoskeletal robots to assist the motion of physically weak persons such as elderly persons or handicapped persons. In our previous research (2001), a prototype of a two degree of freedom exoskeletal robots for shoulder joint motion assist have been developed. In this paper, we propose an effective fuzzy-neuro controller, a moving mechanism of the center of rotation (CR) of the shoulder joint of the exoskeletal robot, and an intelligent interface in order to realize a practical and effective exoskeletal robot for shoulder joint motion assist. The fuzzy-neuro controller enables the robot to assist a person's shoulder motion. The moving mechanism of the CR of the robot shoulder joint is used to fit the CR of the robot shoulder joint to that of the physiological human shoulder joint during the shoulder motion. The intelligent interface is realized by applying a neural network and used to cancel out the effect the human subject's arm posture change. The effectiveness of the proposed method was evaluated by experiment.     

Emulation of robots interacting with environment

In this paper, we present a methodology for emulation of a target robot operating in a complex environment by using an actual robot. The emulation scheme aims to replicate the dynamical behavior of the target robot interacting with an environment, without dealing with a complex calculation of the contact dynamics. This method forms a basis for the task verification of a flexible space robot. The actual emulating robot is structurally rigid, while the target robot can represent any class of robots, e.g., flexible, redundant, or space robots. Although the emulating robot is not dynamically equivalent to the target robot, the dynamical similarity can be achieved by using a control law developed herein. The effect of disturbances and actuator dynamics on the fidelity and the contact stability of the robot emulation is thoroughly analyzed. The concept of robot emulation is demonstrated by performing a number of preliminary experiments for emulation of flexible-joint robots.     

Stable kinematic teleoperation of wheeled mobile robots with slippage using time-domain passivity control

Wheel slippage creates control challenges for wheeled mobile robots (WMR). This paper proposes a new method for haptic teleoperation control of a WMR with longitudinal slippage by using the time-domain passivity control (TDPC) approach. We show the potential non-passivity for the environment termination caused by the slippage dynamics. The utilized TDPC approach maintains the passivity of teleoperation system terminations through a passivity observer and a passivity controller at the environment termination. The teleoperation controllers are then simply constrained by Llewellyn's absolute stability criterion for closed-loop stability purposes. Experiments with the proposed controller demonstrate that it can result in stable bilateral teleoperation with a satisfactory tracking performance with TDPC.     

Adaptive sliding mode fuzzy control for unknown robots with arbitrarily-switched constraints

This article addresses the control problem of robots with unknown dynamics and arbitrarily-switched unknown constraints. Such kind of robots will be shown to be unknown hybrid systems with arbitrary switching and an Adaptive Sliding Mode Fuzzy Control (ASMFC) strategy is proposed that handles the unknown dynamics of the robot along with the unknown constraints arbitrary switching. The ASMFC is a synergy of finding a Common Lyapunov Function (CLF) between the resulted switched subsystems of the considered robots, employing the Fuzzy Logic Systems (FLS), and the use of the Sliding Mode Control (SMC). The CLF accommodates the constraints arbitrary switching, the SMC adds robustness against possible parameters drift, and the FLS approximates the unknown robot dynamics. All unknown parameters are adapted online and all closed loop signals are guaranteed to be bounded. The proposed strategy is validated by conducting an experiment on a KUKA Lightweight Robot (LWR) doing a typical force-guided peg-in-hole assembly task that falls in the category of robot systems under consideration. Excellent tracking performance is obtained when using the ASMFC strategy. Comparison is conducted with the performance of a PD controller that is widely used in commanding industrial robots and the superiority of the proposed strategy is shown.     

Adaptive control of uncertain nonlinear teleoperation systems

Kinematic parameters of a robotic manipulator are hard to measure precisely and the varying size and shape of tools held by the robot end-effector introduce further kinematic uncertainties. Moreover, the exact knowledge of the robot nonlinear dynamics may be unavailable due to model uncertainties. While adaptive master–slave teleoperation control strategies in the literature consider the dynamic uncertainties in the master and the slave robots, they stop short of accounting for the robots’ kinematic uncertainties, which can undermine the transparency of the teleoperation system. In this paper, for a teleoperation system that is both dynamically and kinematically uncertain, we propose novel nonlinear adaptive controllers that require neither the exact knowledge of the kinematics of the master and the slave nor the dynamics of the master, the slave, the human operator, and the environment. Therefore, the proposed controllers can provide the master and slave robots with a high degree of flexibility in dealing with unforeseen changes and uncertainties in their kinematics and dynamics. A Lyapunov function analysis is conducted to mathematically prove the stability and master–slave asymptotic position tracking. The validity of the theoretical results is verified through simulations as well as experiments on a bilateral teleoperation test-bed of rehabilitation robots.