Emmanuel Nuño

Position Tracking for Non-linear Teleoperators with Variable Time Delay

In this paper the problem of position tracking in the presence of variable time delay is studied. It is proved that simple P-like and PD-like controllers can stabilize the teleoperator under variable time delays and, moreover, they provide position tracking. Then, a controller based on the scattering transformation that also provides position tracking is proposed. In this paper we present the conditions under which the velocities and position error of the non-linear teleoperator, for the three controllers, are bounded, and if the human does not move the local manipulator and the remote manipulator does not interact with the environment, then it is proved that velocities and position error converge to zero. Simulations and real experiments, using the Internet from Urbana-Champaign (USA) to Barcelona (Spain), validate the proposed schemes.

Nonlinear Bilateral Teleoperation: Stability Analysis

This paper aims to take a first step towards the unification of the stability analysis for teleoperators with time-delays. It proposes a general Lyapunov-like function that, upon slight modification, allows to analyze the stability of different control schemes, ranging from constant to variable time delays, with or without the scattering transformation and with or without position tracking. It also presents design examples of the corresponding Lyapunov-like function for some schemes based on PD controllers and on the scattering transformation for variable time-delays.

Passive Bilateral Teleoperation Framework for Assisted Robotic Tasks

This paper addresses the problem of stable bilateral teleoperation, through a time-delayed communication channel, for a n-DOF system without position drift. The classical wave variables-based scheme encodes velocity and force whilst the proposed scheme encodes position and integral of force. The resulting passive communication scheme is used in an extended teleoperation framework, in which the human operator can define geometrical motion restrictions in order to increase his awareness and his feeling of immersion, hence improving his ability to perform complex tasks. The framework also provides the operator with video feedback and 3D rendering of the remote scene.

A New Proportional Controller for Nonlinear Bilateral Teleoperators

Abstract One of the major breakthroughs in the problem of control of bilateral teleoperators with guaranteed stability properties has been the use of scattering signals to transform the transmission delays into a passive transmission line. Under the reasonable assumption that the human operator and the contact environment define passive (force to velocity) maps, stability of the overall system is then ensured. This robust and physically appealing scheme, first proposed by Anderson and Spong, has ever since dominated the field. In this paper we propose two novel teleoperation schemes, based on a simple P-Like controller. These schemes do not make use of the scattering or wave variables. Moreover, under the classical assumption of passivity of the terminal operators plus a gravity compensation term, we can ensure position coordination of the master and the slave.

Asymptotic stability of teleoperators with variable time-delays

This paper extends the previous results on position tracking for bilateral teleoperators with constant time-delays, reported in Nuño et al. IEEE Trans. Robot., vol. 24, no. 3, pp. 753–758, June 2008, to the case of variable time-delays in the teleoperators communications. The key part is the extension of a previous Lemma that is used to prove that P+d or PD+d controllers can stabilize the teleoperator under variable timedelays, and moreover, they provide position tracking. The paper outlines the conditions under which velocities and position errors, of the nonlinear teleoperator, are bounded, and using Barbălats Lemma, it is proved asymptotic converge to zero if the local manipulator stands still and the remote manipulator does not interact with the environment. Simulations and real experiments validate the proposed schemes. The experiments have been performed using the Internet as communication channel between Urbana-Champaign, USA and Barcelona, Spain.

Bilateral Teleoperation Experiments: Scattering Transformation and Passive Output Synchronization Revisited

Abstract It is well known that the scattering variables transform the transmission delays into a passive virtual transmission line, hence, its interconnection with passive subsystems preserves passivity of the overall system. However, wave reflections may occur. Using a symmetric velocity controller, on the master and the slave, and by matching the impedances, the scattering transformation reduces to a passive output synchronization scheme. In this paper we revisit this relation and perform some experiments on this line.

Force Reflecting Teleoperation Via IPv6 Protocol with Geometric Constraints Haptic Guidance

When dealing with teleoperated systems, several important aspects have to be considered: unstructured environment, communication delay, human operator uncertainty, and safety at the remote site, amongst others. The main contribution of this work, that tackles some of the aforementioned issues, is a system that combines a force feedback teleoperation scheme with geometric constraints and haptic guidance. The allowed motion space of a robot can be reduced by specifying a set of geometric relations between the robot tool and the workcell’s fixed objects. These relations are processed by a geometric reasoning module that generates a compatible motion subspace. Restriction forces are then fed to the operator via a haptic interface in order to guide its movements inside this subspace. The communication channel between the local center and the remote cell is implemented using high speed networks with the novel IPv6 protocol. The slave robot control is based on position or velocity. Experimental results validate the proposed approach.

Nonlinear control and geometric constraint enforcement for teleoperated task execution

This work presents a multimodal teleoperation framework that makes use of novel tools and techniques, such as: nonlinear teleoperators control, for ensuring position tracking in the presence of variable time-delays; relational positioning, for increasing operator performance on precise movement execution by visually and haptically displaying geometric constraints; and augmented reality, for visually combining real and virtual information in a compelling way. Experimental evidence is presented that validates the aptitude of the different components of the proposed framework.

On the equivalence of z-domain and s-domain: The inverse of convolution integral and its application to systems identification

In this work we present an equation that obtains the Laplace transform of a time function from its z-transform. This equation is the integral representation of the inversion of the well know convolution integral, which obtains the z-transform using the Laplace transform. The paper also presents the application of the presented method to obtain the estimation of continuous systems through their discrete time samples.

Control of bilateral teleoperators in the operational space without velocity measurements

This paper proposes a proportional plus damping injection (P + d) controller for bilateral teleoperators in the operational space. Unit quaternions are used to describe the end-effectors orientation since they exhibit the well known property of being a singularity-free representation. The proposed controller does not need the measurement of the velocities, instead a passivity-based filter is used. Under the reasonable assumptions that the human operator and the environment define passive maps from force to velocity, it is proved that velocities and pose (position and orientation) errors between the local and the remote manipulators are bounded. Moreover, in the case that the human and the environment forces are zero, the velocities and pose errors converge asymptotically to zero. Finally, experimental validation using two robots of 6-Degrees-of-Freedom (DoF) shows the effectiveness of the proposed control scheme.