Time Domain Passivity Control Research Articles

Adaptive Wave Reconstruction Through Regulated-BMFLC for Transparency-Enhanced Telerobotics Over Delayed Networks

Bilateral telerobotic systems have attracted a great deal of interest during the last two decades. The major challenges in this field are the transparency and stability of remote force rendering, which are affected by network delays causing asynchrony between the actions and the corresponding reactions. In addition, the overactivation of stabilizers further degrades the fidelity of the rendered force field. In this article, a real-time frequency-based delay compensation approach is proposed to maximize transparency while reducing the activation of the stabilization layer. The algorithm uses a regulated bound-limited multiple Fourier linear combiner to extract the dominant frequency of force waves. The estimated weights are used in conjunction with the relatively phase-lead harmonic kernels to reconstruct the signal and generate a compensated wave to reduce the effect of the delay. The reconstructed force will then pass through a modulated time-domain passivity controller to guarantee the stability of the system. We will show that the proposed technique will reduce the force-tracking error by 40% and the activation of the stabilizer by 79%. It is shown, for the first time, that through the utilization of online adaptive frequency-based prediction, the asynchrony between transmitted waves through delayednetworks can be significantly mitigated while stability can be guaranteed with less activation of the stabilization layer.

Teleoperation of wheeled mobile robots subject to longitudinal slipping and lateral sliding by time-domain passivity controller

Wheeled mobile robot (WMR)-based exploration on soft terrains has created new difficulties for its tele-control system. A critical problem is that wheel-terrain contact areas may induce both longitudinal slipping and lateral sliding. In this paper, a new approach for tele-driving a WMR that addresses the difficulties simultaneously induced by both longitudinal slipping and lateral sliding is presented. In the augmented coordination between the master and slave site, the translational and angular velocities of the slave WMR were modified by the wheel sliding angle. Moreover, they were separately coordinated with the positions of the master haptic interface. To improve the command-tracking performance with the augmented coordination, the teleoperator was designed with feedforward of the sliding angle. To compensate for the non-passivity induced by longitudinal slipping and lateral sliding, a time-domain passivity controller also is proposed. The stability and transparency of the proposed approach were analyzed based on the passivity theory. Numerical experiments validate that this proposed approach can effectively improve the teleoperation performance of human operators for the WMR on soft terrains.

Dual-Master/Single-Slave Haptic Teleoperation System for Semiautonomous Bilateral Control of Hexapod Robot Subject to Deformable Rough Terrain

The increasing application requirements of multilegged walking robots in outdoor environments pose new challenges regarding the design of their teleoperation systems. Some of these challenges arise from the multiple degrees of freedom of the telerobotic system and nonpassive exogenous disturbance. Herein, a novel control system based on a dual-master/single-slave bilateral haptic teleoperation framework using a semiautonomous strategy for hexapod robots walking on deformable rough terrains is proposed. In this teleoperation system, the body velocities and postures of the hexapod robot are determined according to the positions of two haptic master robots. The proposed teleoperator includes a time-domain passivity control approach to compensate for the system’s potential nonpassivity induced by the contact slippage between the foot and the ground. Furthermore, a posture-level bilateral controller is designed to overcome the unpredictable posture vibration. Information about the velocity loss and posture error is displayed to the human operator in the form of haptic force. In the underlying controller of the slave robot, a foot-force optimization algorithm is developed to improve the local autonomy of the teleoperation system. Furthermore, the stability of the system is demonstrated by its passivity. Experimental results indicate that the proposed controllers can provide a stable and transparent bilateral haptic teleoperation system for a hexapod robot under environmental perturbations.

A Time Domain Passivity Control Scheme for Bilateral Teleoperation

Conventional time domain passivity control inevitably embodies division. Zero division can occur under a tiny force or velocity, which may be inevitable, and will be the cause of control crash. To avoid the zero division problem and control crash, we propose a switching dissipation controller for guaranteed stability. The parametric design of the proposed approach is discussed. The switching time domain passivity control is then applied to teleoperation and safe operation is achieved. Simulation and experimental results are demonstrated to validate the effectiveness of the proposed control scheme.

Automerlin mobile robot's bilateral telecontrol with random delay

The main focus of this work is to design a bilateral telecontrol of a mobile robot AutoMerlin through the Internet. The Internet has an inherent delay, packet drop, out of order data transmission, duplication, and other impediments as a communication channel. These factors cause the system to become unstable and difficult to control through the Internet. The velocity tracking becomes really hard and the force feedback also rises to an unacceptable level due to delay and other impediments. In order to address these issues, a power based TDPC (Time Domain Passivity Control) has been utilized in this work for the development of stable telecontrol. This approach is based on energy. The energy has been classified as positive and negative energy to make passivity analysis independent of monitoring of net system energy in real time. Thus, monitoring the net energy output at each port enables the extension of TDPC for delayed systems called TDPN (Time Delay Power Network). TDPN helps in velocity/force tracking. It transmits velocity/force unaltered by rejecting the active energy. PO (Passivity Observers) indicate the active behavior and the PC (Passivity Controllers) dissipate extra surplus energy to keep the system stable and passive all times. The performance has been tested and plotted to show the effectiveness of the bilateral controller under random delay and other limitations.

Bilateral Tele-Rehabilitation System using Electrical Stimulation applying Modulated Time-Domain Passivity Control

This paper considers a bilateral tele-rehabilitation system by using an electrical stimulation based on a scattering matrix method by applying a modulated time-domain passivity control for a human lower limb. The scattering matrix method includes a scattering transformation, a phase control filter, and a wave filter. In our previous works, a non-passive approach based on a scattering matrix method has been applied to the bilateral tele-rehabilitation system. However, variable long time delay affects the control performance in the experiment through the Internet. Because the feedforward control with the phase-lead filter is used in the patient side, the feedforward controller may provide the large control input force for the tired patient’s lower limb. The main contribution of this paper is to apply the modulated time-domain passivity control to improve the control performance of the bilateral tele-rehabilitation system. In the previous bilateral tele-rehabilitation with the modulated time-domain passivity control, the velocity and the force are communicated between the therapist and the patient. In this paper, the position and the force are communicated in the proposed bilateral tele-rehabilitation system, and the improvement of the tracking performance is expected. The proposed bilateral tele-rehabilitation system is verified in the experiment with the variable time delay. It can be confirmed that the control performance is improved by using the modulated time-domain passivity control.

A Time Domain Passivity Approach for Asymmetric Multilateral Teleoperation System

Time-domain passivity control (TDPC) is a widely used reliable approach to ensure the stability of the teleoperation systems. Although TDPC almost guarantees the stability of the system, there can be a possibility of instability as TDPC inherits the zero division problem in its conventional control laws. Low value force or velocity signals can lead to zero division in control laws and can be a reason of control failure. A multilateral teleoperation system is much more complex as compared to a bilateral teleoperation system. A multilateral teleoperation system comprises of multiple humans and multiple master and slave robots which results in increased transmission of signals over a communication network. So, it is substantially invaluable for multilateral teleoperation system to have a control scheme which ensures a safe and stable operation. This paper, an extension of our previous work, presents a novel design of TDPC laws for multilateral teleoperation, which not only maintains the passivity of the system for stability but also avoids zero division, thus guaranteeing a stable operation. A new architecture of communication channel is introduced to assign different weights to the masters and slaves depending upon the task requirements. The control strategy proposed in this paper is valid for different numbers of masters and slaves. Simulation and experimental results are presented to demonstrate the efficacy of the control design.

Soft landing control strategy for biped robot

PurposeThe purpose of this paper was to present a soft landing control strategy for a biped robot to avoid and absorb the impulsive reaction forces (which weakens walking stability) caused by the landing impact between the swing foot and the ground.Design/methodology/approachFirst, a suitable trajectory of the swing foot is preplanned to avoid the impulsive reaction forces in the walking direction. Second, the impulsive reaction forces of the landing impact are suppressed by the on-line trajectory modification based on the extended time-domain passivity control with admittance causality that has the reaction forces as inputs and the decomposed swing foot’s positions to trim off the forces as the outputs.FindingsThe experiment data and results are described and analyzed, showing that the proposed soft landing control strategy can suppress the impulsive forces and improve walking stability.Originality/valueThe main contribution is that a soft landing control strategy for a biped robot was proposed to deal with the impulsive reaction forces generated by the landing impact, which enhances walking stability.

A Passivity-Based Approach for Stable Patient–Robot Interaction in Haptics-Enabled Rehabilitation Systems: Modulated Time-Domain Passivity Control

In this paper, a novel passivity-based technique is proposed to 1) analyze and 2) guarantee the stability of haptics-enabled robotic/telerobotic systems when there is a possibility of having a source of nonpassivity (namely, a nonpassive environment) in addition to the conventional nonpassive component in teleoperation systems (namely, a delayed communication channel). The need for the proposed technique is motivated by safe and optimal implementation of the haptics-enabled robotic, cloud-based, and remote rehabilitation systems. The objective of the controller proposed in this paper is to perform minimum alteration to the system transparency, in a dynamic and patient-specific manner, by utilizing quantifiable biomechanical capability of the user’s limb (i.e., excess of passivity) in dissipating interactive energies to guaranteeing human–robot interaction safety, in the context of the strong passivity theorem. The proposed controller is named modulated time-domain passivity control (M-TDPC) approach and is a new member of the family of the state-of-the-art TDPC techniques. Simulations and experimental results are presented in support of the proposed technique and the developed theory.

A novel multilateral teleoperation scheme with power-based time-domain passivity control

Multilateral teleoperation systems, which are extended from the traditional bilateral teleoperation, have become subject to increasing attention in current years, with increasing industrial requirements, such as the remote operation of larger objects and more complex tasks. In this paper, a general multilateral teleoperation control problem is discussed, in which n masters remotely control n slaves through delayed communication channels. A novel communication structure is proposed to satisfy the multiple master–slave communication requirement, in which weighting coefficients are chosen freely to perform the weighted effects of different masters or slaves. Power-based time-domain passivity control is subsequently developed for the complex multiple master–slave communication channel, to achieve the passivity of multilateral teleoperation systems under time delay. Experiments on a teleoperation system with two masters and two slaves are described; the results verify the effectiveness of the proposed control scheme.

Time domain passivity control of time-delayed bilateral telerobotics with prescribed performance

A novel approach applying the extended prescribed performance control (PPC) and the wavebased time domain passivity approach (wave-based TDPA) to teleoperation systems is proposed. With the extende ...

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.

Bilateral teleoperation with delayed force feedback using time domain passivity controller

Time delay is a long standing impediment of bilateral control and can destabilize the system evidently. This paper presents a mode-based approach to alleviate some of the problems associated with time delays in a master-slave robot system. The originality of the approach proposed mainly lies in its capacity to take into account explicitly the slave force feedback modified according to the output of Passivity Observer (PO). This method consists of a virtual slave environment model together with a PO to calculate the system energy on the master side. The local environment model is built by the parameters that are identified online at the slave side. Simulation results show the superior performance of the proposed control scheme in the presence of time delays. Experimental results, using a 1-DOF master-slave teleoperation system, support this conclusion. Parameters of remote slave environment can be accurately identified by the RLS method.Passivity observer (PO) together with a virtual environment model is built on the local master side and the system passivity can be judged by the PO.Stable force tracking is achieved by the proposed method with time delay.The proposed method is robust to random communication time delay.

Time domain passivity controller for 4-channel time-delay bilateral teleoperation.

This paper presents an extension of the time-domain passivity control approach to a four-channel bilateral controller under the effects of time delays. Time-domain passivity control has been used successfully to stabilize teleoperation systems with position-force and position-position controllers; however, the performance with such control architectures is sub-optimal both with and without time delays. This work extends the network representation of the time-domain passivity controller to the four-channel architecture, which provides perfect transparency to the user without time delay. The proposed architecture is based on modelling the controllers as dependent voltage sources and using only series passivity controllers. The obtained results are shown on a one degree-of-freedom setup and illustrate the stabilization behaviour of the proposed controller when time delay is present in the communication channel.

Model-based passive bilateral teleoperation with time delay

Noisy behaviour of time domain passivity control (TDPC) at low velocity is a well known problem for delayed teleoperation systems. This paper presents a novel adaptive model-based passive controller to alleviate some of the noise problems associated with delayed teleoperation system using the TDPC approach. By composing an online estimation of phantom human tissue model and passivity observer on the master side, a high transparency of teleoperation can be achieved while the system passivity is maintained by modifying the damping of the master. The performance of the developed approach was validated using one-degree-of-freedom master–slave robot system with constant time delay. Results show that the phantom tissue parameters can be accurately estimated. In addition, the passivity of the system is observed by the passivity observer using the output of the identified tissue model. Results demonstrate that stable teleoperation with time delay can be achieved and the environment force can be accurately reflected to the operator without chattering.

Bilateral Teleoperation With Time-Varying Delay: A Communication Channel Passification Approach

In this paper, the activeness of bilateral communication with time-varying delay is analyzed. Based on the power-based time-domain passivity control previously proposed, a time-domain passivity control approach is derived for bilateral communication. Teleoperation experimental results verify the effectiveness.

A Power-Based Time Domain Passivity Control for Haptic Interfaces

In this paper, a power based time domain passivity control is presented. Compared to the energy based time domain passivity control, integration is not needed in the calculation and the energy estimation error is avoided. The new passivity observer (PO) distributes the activation of the passivity controller (PC) along the time index and helps to smooth the output of the PC. Applications of the approach to haptic interfaces are simulated. Comparisons with the two existing energy based approaches are made. Simulation results show the computational simplicity and effectiveness of the approach.

Realisation of a bilaterally teleoperated robotic vehicle platform with passivity control

In this study, a new bilateral teleoperated vehicle testing platform is proposed. In the platform, the authors apply a new power-based time domain passivity control (PTDPC) method in an effort to improve the transparency. A new bilateral teleoperation platform is realised where steering angle commands were transmitted from a steering wheel interface to a remote vehicle, and road surface forces are sent back from the vehicle to the steering wheel interface. The communication channel between the steering wheel (master side) and the remote vehicle (slave side) introduces time-varying delays in the transmitted signals. To ensure the stability of the whole system, PTDPCs are applied to each side of the communication channel, which further improve the tracking performance as well as reduce the overall effort required of the human operator. The alternative advantage of the passivity control is the simplicity: the dynamic models of both master and slave side systems are not required to be known. The algorithms, hardware and software realisations are described thoroughly in the study. Finally, experimental results are demonstrated to show the effectiveness of the proposed approach as well as the functionality of the new testing platform.

Passivity control of a haptic device for the simulation of knobs

Knobs are one of the details from which household appliances are commonly judged by the customers. Although very subjective, the customers’ requirements reflect real needs, such as robustness and easy use; therefore the design of knobs and buttons, that are the most widely used end-user interfaces, is of utmost importance from the commercial point of view and requires careful investigation. A mechatronic device has been designed to simulate the knobs’ behaviour for supporting an extensive campaign of end-users tests. The impedance control approach is applied exploiting a model of the actuator. However, as the acceleration information is extracted through double differentiation of position measurements, the inertia cannot be compensated; this can sometimes compromise the stability. The stability problem is therefore addressed through the time-domain passivity control approach, which guarantees stability and is easy to implement, but produces a slight decrease in performance, namely a mismatch between desired and real torque.

Time Domain Passivity Control for Position-Position Teleoperation Architectures

This article presents a method for passivating the communication channel of a symmetric position-position teleoperation architecture on the time domain. The time domain passivity control approach has recently gained appeal in the context of timedelayed teleoperation because passivity is not established as a design constraint, which often forces conservative rules, but rather as a property which the system must preserve during operation. Since passivity is a network property, the first design rule within this framework is to represent consistent and comprehensible circuit (i.e., network) representations of the mechanical teleoperation system. In particular, the energetic behavior of these networks is interesting because it allows straightforward conclusions about system stability. By means of so-called passivity observers (PO) and passivity controllers (PC) (Hannaford & Ryu, 2001), the energetic response of a delayed communication channel is captured and modulated over time so that the network in question never becomes nonpassive. The case analyzed in this paper tackles a communication channel that conveys position data back and forth. This type of channel does not offer intuitive network representation since only flows are actually being transmitted. Although energy clearly travels from one side to the other, port power identification, as defined by the correlated pair flow and effort, is not evident. This work first investigates how this kind of channel can be represented by means of circuit networks even with the lack of physical effort being transmitted through the channel, and identifies which networks are susceptible to become nonpassive due to the channel characteristics (i.e., time delay, discretization or package loss). Once achieved, a distributed control structure is presented based on a PC series that keeps the system at the verge of passivity (and therefore stability) independent from the channel properties. The results obtained by the simulation and by experiment sustain the presented approach.