Ricardo Pizá

A Delay-Dependent Dual-Rate PID Controller Over an Ethernet Network

In this paper, a methodology to design controllers able to cope with different load conditions on an Ethernet network is introduced. Load conditions induce time-varying delays between measurements and control. To face these variations an interpolated, delay-dependent gain scheduling law is used. The lack of synchronization is solved by adopting an event-based control approach. The dual-rate control action computation is carried out at a remote controller, whereas control actions and measurements are taken out locally at the controlled process site. Stability is proved in terms of probabilistic linear matrix inequalities. TrueTime simulations in an Ethernet case show the benefit of the proposal, which is later validated on an experimental test-bed Ethernet environment.

Multirate LQG controller applied to self-location and path-tracking in mobile robots

Presents an approach to solving the linear quadratic Gaussian problem for controlling MIMO multirate sampled-data systems. The problem is split into three parts: first a generalized discrete multirate model is computed, second the solution of the linear quadratic regulator problem is computed and then a multirate Kalman filter is obtained. The model is composed by a time invariant single rate part, involving the basic process dynamics and a periodic one determined by the external sampling strategy. This allows an easy analysis of the effects of the multirate sampling on the plant. The approach has been applied to solve problems of self-location and path tracking in mobile robots. As is common in many auto-guided vehicles the sensory system is very complex, so some kind of sensor data fusion has been implemented.

Hierarchical Triple-Maglev Dual-Rate Control Over a Profibus-DP Network

This paper addresses a networked control system application on an unstable triple-magnetic-levitation setup. A hierarchical dual-rate control using a Profibus-decentralized peripherals network has been used to stabilize a triangular platform composed of three maglevs. The difficulty in control is increased by time-varying network-induced delays. To solve this issue, a local decentralized H∞ control action is complemented by means of a lower rate output feedback controller on the remote side. Experimental results show good stabilization and reference position accuracy under disturbances.

Control of the rotary inverted pendulum through threshold-based communication

This paper deals with the real implementation of an event-based control structure for the classical rotary inverted pendulum. The communication between controller and plant is performed through Ethernet (TCP/IP) which leads to a Networked Control System. The bandwidth used by the control loop is reduced, compared with the one that needs a conventional control, by using a threshold-based communication. The values of the thresholds have been determined by means of simulation techniques. The results over the real plant show how this technique can reach a significant reduction of the bandwidth consumed with a negligible worsening of the performance.

Multirate Obstacle Tracking and Path Planning for Intelligent Vehicles

This paper introduces a new approach for tracking and path planning for intelligent vehicles. The tracking application takes into account the trajectories followed by the obstacles, making a prediction of their future positions and corresponding uncertainties. This idea introduces a stochastic model for obstacle and vehicle kinematics. A multi-rate Kalman filter is considered in the tracking process in order to manage the uncertainty. Potential Field approach for path planning is redefined according to the new stochastic models. In particular, the repulsive potential field is modified to consider these models projected into a prediction horizon. The use of future information minimizes the risk of collisions and generates smoother trajectories.

Networked Control Systems: control structures with bandwidth limitations

The aim of this paper is to propose a control to be used in Networked Control Systems. A periodic model of the plant, as it is seen by the controller, is proposed. It can be converted into a multivariable model and used to design a multivariable controller. A second structure becomes a periodic control that uses the plant to supply the lost information. Non linear behaviour, periodicity and any other irregularities can be included in the model. The control is tested on the control of X and Y axis from a model crane, using Profibus-DP to close the loop.

Multirate control with incomplete information over Profibus-DP network

When a process field bus-decentralized peripherals (Profibus-DP) network is used in an industrial environment, a deterministic behaviour is usually claimed. However, due to some concerns such as bandwidth limitations, lack of synchronisation among different clocks and existence of time-varying delays, a more complex problem must be faced. This problem implies the transmission of irregular and, even, random sequences of incomplete information. The main consequence of this issue is the appearance of different sampling periods at different network devices. In this paper, this aspect is checked by means of a detailed Profibus-DP timescale study. In addition, in order to deal with the different periods, a delay-dependent dual-rate proportional-integral-derivative control is introduced. Stability for the proposed control system is analysed in terms of linear matrix inequalities.

Maglev platform networked control: A Profibus DP application

This paper addresses a practical networked based control application. A Profibus DP is considered in order to coordinate a triangular maglev platform. The control of this magnetic levitation process is a complicated system from an control engineering point of view due to its unstable, non-minimum phase and non-linear nature; the difficulty is growing up because the bandwidth limitation and some other problems introduced by the network which consideration is neccesary in order to prepare control, supervision and coordination of local loops tasks. A rude local classical control and a refinated based LMI solution in remote side allow to solve this problem where the packets have a variable time delays compromising performance or even stability. The results shows a good stabilization and reference position accuracy even when the operating point is changing with an external load.

A packet-based dual-rate PID control strategy for a slow-rate sensing Networked Control System

This paper introduces a packet-based dual-rate control strategy to face time-varying network-induced delays, packet dropouts and packet disorder in a Networked Control System. Slow-rate sensing enables to achieve energy saving and to avoid packet disorder. Fast-rate actuation makes reaching the desired control performance possible. The dual-rate PID controller is split into two parts: a slow-rate PI controller located at the remote side (with no permanent communication to the plant) and a fast-rate PD controller located at the local side. The remote side also includes a prediction stage in order to generate the packet of future, estimated slow-rate control actions. These actions are sent to the local side and converted to fast-rate ones to be used when a packet does not arrive at this side due to the network-induced delay or due to occurring dropouts. The proposed control solution is able to approximately reach the nominal (no-delay, no-dropout) performance despite the existence of time-varying delays and packet dropouts. Control system stability is ensured in terms of probabilistic Linear Matrix Inequalities (LMIs). Via real-time control for a Cartesian robot, results clearly reveal the superiority of the control solution compared to a previous proposal by authors.

NETWORKED CONTROL SYSTEMS WITH INFORMATION RECOVERY OVER PROFIBUS-DP

Abstract The aim of this paper is to propose a control structure suitable to be used in Networked Control Systems in which the shared communication medium imposes a limitation in the amount of information that can be transmitted. In this kind of systems, the link to perform the communication between controller and plant is used to close several control loops. The bandwidth must be shared between all the sender devices and the available bandwidth for each loop is reduced as much as the number of devices using the link is increased. With conventional techniques the control frequency must be decreased to fit the available bandwidth. If the number of devices sharing the link is large, the control frequency may be not enough to reach the desired specifications. When frequency decreasing, imposed by the shared link, is present in the loop it can be modeled as a periodic system. The paper proposes control structure based on the periodic behavior of the plant, as it is seen from the point of view of the controller through the shared medium. The control is easy to be implemented and it has been designed to make the most advantage of the available bandwidth. This periodic control uses the model of the plant to supply the information that could not be sent due to the bandwidth limitations. Once the information is recovered, a conventional control designed without considering the limitations imposed by the shared medium, can be used. One of the main advantages of the proposed control is that the model of the plant, in which is based the information recovery, does not need to be linear and time-invariant. Non linear behavior, periodicity and any kind of irregularities can be included for a better recovery of the information loss. The proposed control is tested on the control of X and Y axis from a model crane, using Profibus-DP as the shared medium to close the loop. Copyright