Multi-robot Implicit Control of Massive Herds

This paper solves the problem of herding countless evaders by means of a few robots. The objective is to steer all the evaders towards a desired tracking reference while avoiding escapes. The problem is very challenging due to the highly complex repulsive evaders' dynamics and the underdetermined states to control. We propose a solution that is based on Implicit Control and a novel dynamic assignment strategy to select the evaders to be directly controlled. The former is a general technique that explicitly computes control inputs even in highly complex input-nonaffine dynamics. The latter is built upon a convex-hull dynamic clustering inspired by the Voronoi tessellation problem. The combination of both allows to choose the best evaders to directly control, while the others are indirectly controlled by exploiting the repulsive interactions among them. Simulations show that massive herds can be herd throughout complex patterns by means of a few herders.Comment: E. Sebastian, E. Montijano and C. Sagues,"Multi-robot Implicit Control of Massive Herds'', Fifth Iberian Robotics Conference (ROBOT22), 202

A new run-to-run approach for reducing contact bounce in electromagnetic switches

Contact bounce is probably the most undesirable phenomenon of electromagnetic switches. It reduces the performance of relays and contactors and is directly related to some of the processes that result in the destruction of the device. In this paper, a complete formulation of the problem is provided and a new strategy inspired by Runto-Run control is presented for reducing contact bounce. The method, which makes use of the repetitive functioning of these systems, is highly versatile and may be applied to different switches under diverse operating conditions. In addition, it is able to deal with changes during the service life of the device, such as plastic deformations or the erosion of the contacts. Several experimental results are included to prove the effectiveness of the method

An efficient dynamical model of reluctance actuators with flux fringing and magnetic hysteresis

This paper presents an efficient and accurate dynamical model of reluctance actuators, suitable for prediction and control applications. It is a hybrid lumped-parameter state-space model that takes into account the mechanical and electromagnetic dynamics, including eddy currents, flux fringing, magnetic hysteresis and saturation. Special emphasis is placed on the hysteresis model, which is based on the Jiles–Atherton theory. The novel parts of the model – the gap reluctance expression and the modified Jiles–Atherton hysteresis model – are identified, showing that the simulated results fit very well the experimental data. Furthermore, its potential application for control is exemplified with a feedback strategy, in which the design of the controller and observer are based on the proposed dynamical model

A new model of electromechanical relays for predicting the motion and electromagnetic dynamics

In this paper, a novel multiphysics and nonlinear model for electromechanical relays is presented. The electromagnetic dynamics is analyzed by calculating the total reluctance of the magnetic equivalent circuit (MEC), which is composed of a fixed length iron core and an angular air gap. Magnetic saturation and angular dependency of the reluctance are considered in the analysis. Then, an energy balance over the electromagnetic components of the system is used to obtain the torque which drives the movable armature. A planar mechanism of four rigid bodies, including spring-damping torques that restrict the motion and model the contact bounces that occur in the switchings, is proposed to explain the dynamics of the movable components. Experimental tests show the accuracy of the model in both the electromagnetic and the mechanical parts

Design of a perfect-tracking soft-landing controller for electromagnetic switching devices

Electromagnetic switching devices such as electromechanical relays and solenoid valves suffer from impacts and mechanical wear when they are activated using a constant-voltage policy. This paper presents a new control approach that aims at achieving soft landing in these devices, i.e., a movement without neither impacts nor bouncing. The hybrid nonlinear dynamics of the system is firstly described taking into account the limited range of motion that characterizes this class of devices. Then, the nonlinear expression of the control law is derived and a method to design a soft-landing reference trajectory is proposed. It is shown that, when certain conditions are met, the design methodology presented in the paper results in a controller that achieves perfect tracking of the reference trajectory and, hence, soft landing is accomplished. The theoretical analysis is validated by simulation using a dynamical model of a specific switching device

Precise Dynamic Consensus under Event-Triggered Communication

This work addresses the problem of dynamic consensus, which consists of estimating the dynamic average of a set of time-varying signals distributed across a communication network of multiple agents. This problem has many applications in robotics, with formation control and target tracking being some of the most prominent ones. In this work, we propose a consensus algorithm to estimate the dynamic average in a distributed fashion, where discrete sampling and event-triggered communication are adopted to reduce the communication burden. Compared to other linear methods in the state of the art, our proposal can obtain exact convergence under continuous communication even when the dynamic average signal is persistently varying. Contrary to other sliding-mode approaches, our method reduces chattering in the discrete-time setting. The proposal is based on the discretization of established exact dynamic consensus results that use high-order sliding modes. The convergence of the protocol is verified through formal analysis, based on homogeneity properties, as well as through several numerical experiments. Concretely, we numerically show that an advantageous trade-off exists between the maximum steady-state consensus error and the communication rate. As a result, our proposal can outperform other state-of-the-art approaches, even when event-triggered communication is used in our protocol

Model-free sliding-mode controller for soft landing of reluctance actuators

Some electromagnetic actuators suffer from high velocity impacts during non-controlled switching operations, which cause contact bouncing, mechanical wear, and acoustic noise. Soft-landing control strategies aim at minimizing the impact velocities of these devices to improve their performance. This paper presents a sliding-mode controller for soft landing of single-coil reluctance actuators. It is a switching model-free controller, which results in a very simple implementation. A generalized dynamical hybrid model of an actuator is utilized for deriving the robustness condition, based on the Lyapunov theory. Then, the condition is evaluated for a dynamical model, based on a commercial device, and several reference trajectories. Finally, the controller performance is validated through simulations. The effect of the sampling rate on the resulting impact velocities is also analyzed

Rauch-Tung-Striebel Smoother for Position Estimation of Short-Stroke Reluctance Actuators

This article presents a novel state estimator for short-stroke reluctance actuators, intended for soft-landing control applications in which the position cannot be measured in real time. One of the most important contributions regards the system modeling for the estimator. The discrete state of the hybrid system is treated as an input. Moreover, the model is simplified to facilitate the identification of parameters and the implementation of the estimator. Thus, auxiliary variables are added to the state vector in order to indirectly account for modeling errors. Another important contribution is the state estimation approach. It is based on the Rauch–Tung–Striebel fixed-interval smoother, which allows refining past data from later observations. Numerous simulations are performed to analyze and compare the proposal and several alternatives. In addition, experimental testing is presented to evaluate and validate the estimator. As the simulated and experimental analyses demonstrate, the combined effect of the novel additions results in significantly smaller estimation errors of position and velocity

Probability-Based Optimal Control Design for Soft Landing of Short-Stroke Actuators

The impact forces during switching operations of short-stroke actuators may cause bouncing, audible noise, and mechanical wear. The application of soft-landing control strategies to these devices aims at minimizing the impact velocities of their moving components to ultimately improve their lifetime and performance. In this brief, a novel approach for soft-landing trajectory planning, including probability functions, is proposed for optimal control of the actuators. The main contribution of the proposal is that it considers the uncertainty in the contact position, and hence, the obtained trajectories are more robust against system uncertainties. The problem is formulated as an optimal control problem and transformed into a two-point boundary value problem for its numerical resolution. Simulated and experimental tests have been performed using a dynamic model and a commercial short-stroke solenoid valve. The results show a significant improvement in the expected velocities and accelerations at contact with respect to past solutions in which the contact position is assumed to be perfectly known