Pablo Falcón

Basic Send-on-Delta Sampling for Signal Tracking-Error Reduction

This paper investigates the dynamic selection of an appropriate threshold for basic Send-on-Delta (SoD) sampling strategies, given an available transmission rate to reduce the signal tracking-error. The paper formulates the error-reduction principle and proposes an algorithm that calculates, in real time, the amplitude threshold value (also called delta value) for a desired mean transmission rate. The algorithm is implemented to be computed in a Send-on-Delta driver and is tested with three signals that match the step response of a second order control system. Comparison results with a conformant periodic transmission strategy reveals that it improves deeply the tracking-error while maintaining the desired average throughput.

Modeling of Parrot Ardrone and passivity-based reset control

This paper is motivated by the teleoperation of a quadcopter (Parrot ARDrone). This problem is addressed within the framework of passivity and by the reset control. First, the quadcopter model is identified from input-output experimental data. Second, the plant model is passified by nonlinear gain compensation and pole/zero cancelation. Finally, the passified plant model is controlled by a reset controller. The very-strict passivity (VSP) of the reset controller has been proven and discussed. Final simulations show the validity of the approach.

Four-Channel Teleoperation with Time-Varying Delays and Disturbance Observers

This paper addresses the robust stability of teleoperated systems under the four-channel architecture, affected by time-varying communication delays and using disturbance observers. It is based on our previous work which provides a framework for robust stability against delays with bounded variation and a bounded time-derivative, using structured singular values (SSV). The main new feature here is the inclusion of disturbance observers (DOBs). The DOB concept is well-documented and relevant to many applications, since only position (but not force) measurements are usually available. In this paper, we adapt two DOBs (master and slave) to our generic framework, by representing them as stable, fast filters affected by the uncertainty in the plant modelling. Our main result is an SSV test to verify robust stability. The simulation results confirm the usefulness of this approach.

Stability Analysis of Bilateral Teleoperation With Bounded and Monotone Environments via Zames–Falb Multipliers

This paper provides less conservative stability conditions for bilateral teleoperation by exploiting the advantages of the integral quadratic constraint (IQC) framework, where the environment can be defined as a memoryless, bounded, and monotonic nonlinear operator. Recent advances in multiplier theory for appropriate classes of uncertainties/nonlinearities are applied. Since the classes of multipliers have infinite dimension, parametrization of these multipliers is used to obtain convex searches over a finite number of parameters. The stability of the system is analyzed as a Lurye system containing time delay and monotone nonlinearity. As a result, less conservative delay-dependent conditions can be developed. These results are then applied to bilateral teleoperation. Stability results are tested with different experiments, in particular, bilateral teleoperation experiments over the Internet between Manchester, U.K., and Vigo, Spain, have been carried out. The advantage of the proposed approach is demonstrated by reaching higher transparency index for two-channel position–force teleoperation while ensuring absolute stability.

IoT integration on industrial environments

Internet of Things (IoT) devices in industrial environments can be a significant increase in the network load of the local IP backbone, involving the network performance. To deal with the important amount of network traffic generated by the IoT devices, this paper proposes the use of IoT gateways in industrial environments (but not limited to) that unifies the data structures improving the size efficiency, and filters the data to be send across the shared IP backbone. To implement this solution some data structures and a multidimensional deadband scheme are presented. Simulations are performed using Networked Control Systems as IoT devices to show the feasibility of the proposed solution.

Wheel slip reset controller in automotive brake systems

The use of new technologies in brake systems, allows to generate independent brake forces at each wheel by slip controllers. The aim of these controllers is to provide certain degree of slip on each wheel independently, maximizing the friction between the tire and road, avoiding simultaneously its lock. This paper investigates the application of reset control to the slip control in automotive brake systems. A reset controller is a standard linear controller that, at some instants, resets to zero its internal states (or part of the states). The reset instants are triggered by the event of zero crossing of the tracking error. It has been proven in many other applications (process control, teleoperation, motor drives etc.) that reset control is able to overcome linear limitations, that is, achieves time responses with good speed and damping properties, combined in a way that no other linear controller is able to produce. We investigate the addition of a reset integrator (Clegg integrator CI) to a PI used as slip controller. We have found by simulations that the PI+CI has superior performance and gives a better solution to the trade-off between speed and damping. The controller design is based on a simplified vehicle model, taking into account the interaction tireroad, actuator saturation and time-delay in the communications between local and central units. We check through simulations that the application of reset controllers instead of the conventional ones will allow an improvement on the robustness and performance of the system.

Passive teleoperation of mobile robot with input-output linearization and dynamic extension

This paper describes a proposal for architecture of teleoperation of a mobile robot Quanser Qbot. The robot is telemanipulated by a haptic device Sensable Phantom Omni. For this task, a basic model of the mobile robot is input-output linearized with dynamic extension and it is controlled safely in a teleoperation task in passivity framework. The advantages of the proposal are: (i) the I/O linearization changes the Qbot kinematics from polar to cartesian, facilitating the matching with the omni workspace and (ii) the stability of the system is ensured from the passivity framework adopted.

Robust stability in γ-4C based teleoperation

This paper investigates the possibility of deriving frequency-domain conditions for robust stability in presence of time-varying communication delays and parametric uncertainties in the four-channel control scheme. This teleoperation setup can be modeled as a negative single feedback loop containing a linear time invariant LTI block and an uncertain time-varying delay for applying the analysis tool based on mu-plots. With this model we can also justify the proposed γ-4C scheme, which introduces a tuning factor γ to increase in practical conditions the stable region fixing the desired bounds on time-varying delay, with the particularity of maintaining the tracking properties provided by the 4C transparent control scheme. Simulation results justify the proposed controllers and confirm the stability robustness.

Sensor/actuator system for internet delays and packet losses

Network delays and packet losses are two critical parameters for the performance of networked control systems (NCS) in non-deterministic packet networks, such as the Internet. To avoid the need of a remote location, the laboratory experiences in teleoperation or telerobotics uses network simulators to reproduce the delays and packet losses. This paper presents an Internet emulation system that performs as a sensor of Internet delays and packet losses and as an actuator that reproduces these parameters into a local data flow. The paper presents some comparative results and makes a performance analysis of the whole system.

Reset Controller Design Based on Error Minimization for a Lane Change Maneuver

An intelligent vehicle must face a wide variety of situations ranging from safe and comfortable to more aggressive ones. Smooth maneuvers are adequately addressed by means of linear control, whereas more aggressive maneuvers are tackled by nonlinear techniques. Likewise, there exist intermediate scenarios where the required responses are smooth but constrained in some way (rise time, settling time, overshoot). Due to the existence of the fundamental linear limitations, which impose restrictions on the attainable time-domain and frequency-domain performance, linear systems cannot provide smoothness while operating in compliance with the previous restrictions. For this reason, this article aims to explore the effects of reset control on the alleviation of these limitations for a lane change maneuver under a set of demanding design conditions to guarantee a suitable ride quality and a swift response. To this end, several reset strategies are considered, determining the best reset condition to apply as well as the magnitude thereto. Concerning the reset condition that triggers the reset action, three strategies are considered: zero crossing of the controller input, fixed reset band and variable reset band. As far as the magnitude of the reset action is concerned, a full-reset technique is compared to a Lyapunov-based error minimization method to calculate the optimal reset percentage. The base linear controller subject to the reset action is searched via genetic algorithms. The proposed controllers are validated by means of CarSim.