Feng-Li Lian

Performance evaluation of control networks: Ethernet, ControlNet, and DeviceNet

Many different network types have been promoted for use in control systems. In this article, we compare three of them: the Ethernet bus, with carrier sense multiple access with collision detection, token-passing bus (e.g., ControlNet), and controller area network bus (e.g., DeviceNet). We consider how each control network can be used as a communication backbone for a networked control system connecting sensors, actuators, and controllers. A detailed discussion of the medium access control sublayer protocol for each network is provided. For each protocol, we study the key parameters of the corresponding network when used in a control situation, including network utilization, magnitude of the expected time delay, and characteristics of time delays. Simulation results are presented for several different scenarios, and the advantages and disadvantages of each network are summarized.

Network design consideration for distributed control systems

This paper discusses the impact of network architecture on control performance in a class of distributed control systems called networked control systems (NCSs) and provides design considerations related to control quality of performance as well as network quality of service. The integrated network-control system changes the characteristics of time delays between application devices. This study first identifies several key components of the time delay through an analysis of network protocols and control dynamics. The analysis of network and control parameters is used to determine an acceptable working range of sampling periods in an NCS. A network-control simulator and an experimental networked a machine tool have been developed to help validate and demonstrate the performance analysis results and identify the special performance characteristics in an NCS. These performance characteristics are useful guidelines for choosing the network and control parameters when designing an NCS.

Modelling and optimal controller design of networked control systems with multiple delays

In this paper we discuss the modelling and control of networked control systems (NCS) where sensors, actuators and controllers are distributed and interconnected by a common communication network. Multiple distributed communication delays as well as multiple inputs and multiple outputs (MIMO) are considered in the modelling algorithm. In addition, the asynchronous sampling mechanisms of distributed sensors are characterized to obtain the actual time delays between sensors and the controller. Due to the characteristics of a network architecture, piecewise constant plant inputs are assumed and discrete-time models of plant and controller dynamics are adopted to analyse the stability and performance of a closed-loop NCS. The analysis result is used to verify the stability and performance of an NCS without considering the impact of multiple time delays in the controller design. In addition, the proposed NCS model is used as a foundation for optimal controller design. The proposed control algorithm utilizes the information of delayed signals and improves the control performance of a control system encountering distributed communication delays. Several simulation studies are provided to verify the control performance of the proposed controller design.

Analysis and modeling of networked control systems: MIMO case with multiple time delays

This paper discusses the modeling and analysis of networked control systems (NCS) where sensors, actuators, and controllers are distributed and interconnected by a common communication medium. Therefore, multiple distributed communication delays as well as multiple inputs and multiple outputs are considered in the modeling algorithm. In addition, the asynchronous sampling mechanisms of distributed sensors axe characterized to obtain the actual time delays between sensors and the controller. Due to the characteristics of a network architecture, piecewise constant plant inputs are assumed and discrete-time models of plant and controller dynamics are adopted to analyze the stability and performance of a closed-loop NCS. The analysis result is used to verify the stability and performance of an NCS if the controller is designed without considering the impact of multiple time delays. Also, the NCS model provided can be used as a foundation for further controller design to compensate for the distributed communication delays.

Nonlinear adaptive control for flexible-link manipulators

As has been realized, the flexible-link manipulators have attracted more and more attention from robot control theorists and/or robot users because of its various potential advantages. But since the control degree-of-freedom is much less than that of the system, many control strategies which succeed in the conventional rigid robot control cannot be directly used in the flexible robot control problems. In this paper, a nonlinear control scheme has been proposed as a solution to these control problems. In particular, to cope with the existing model uncertainty, an adaptive version of this nonlinear control law has been proposed. Stability proof of the overall closed-loop system is then given via Lyapunov analysis. In addition, extensive experimental results are also provided to demonstrate the effectiveness of the proposed controller.

Network architecture and communication modules for guaranteeing acceptable control and communication performance for networked multi-agent systems

When sensory and actuation devices in a control system are exchanging data through one common communication medium, the sharing of communication bandwidth will induce unavoidable data latency and might degrade the control performance. Hence, the utilization of communication resource and the requirement of control specification should be analyzed and properly designed when implementing a control system over a network architecture. In this paper, we analyze the performance of information sharing of multiple cooperative agents over one communication network, and propose design methodologies of guaranteeing acceptable control and communication performance in a networked control system. In particular, we study the relationship between the sampling rates of a control system,and the transmission rates of a communication network, and then utilize an integrated networked control design chart to help select design parameters and visualize overall system performance at different sampling and transmission rates. Based on the design parameters selected, the communication modules by utilizing deadband control and state estimation are presented for guaranteeing both control and communication performance. Simulation studies are conducted in a network-and-control simulation tool that is developed on the Matlab/Simulink platform and is used to demonstrate the proposed design methodologies. Both the analysis and simulation results illustrate the characteristics of designing mechanisms between control and communication performance and show the improvement of implementing the proposed communication modules.

Real-time trajectory generation for the cooperative path planning of multi-vehicle systems

This paper discusses a cooperative path planning (CPP) design methodology for multi-vehicle systems and a nonlinear trajectory generation (NTG) algorithm. Three scenarios of multi-vehicle tasking are proposed at the CPP framework. The NTG algorithm is then used to generate a real time trajectory for desired vehicle activities. Given system dynamics and constraints, the NTG algorithm first finds trajectory curves in a lower dimensional space and then parameterizes the curves by the B-spline basis. The coefficients of the B-splines are further solved by the sequential quadratic programming to satisfy the optimization objectives and constraints. The NTG algorithm has been implemented to generate real-time trajectories for a group of cooperative vehicles in the presence of changing missions and constraints.

WLAN location determination in e-home via support vector classification

Because of the advanced development in computer technology, home automation system could provide a variety of convenient and novel services to people. But only providing many kinds of services is not enough; instead, upgrading the quality of services is also a very important issue. One way to upgrade the service quality is to customize the service according to the inhabitants personal situation, and the user location is the key information for the home automation system to customize the services. Another impact of the advanced computer technology is to make the personal digital device to commonly have the capability to communicate through the wireless networks, and the popularity of wireless networks in home has increased in recent years. As a result, home automation system can bring services to personal digital devices held by people through any wireless network, and customize the services according to the location of personal digital device in home. In this paper, we present a location determination system for the home automation system to provide location aware services. This location determination system uses support vector machine to classify the location of a wireless client from its signal strength measures, and we describe its architecture and discuss its performance.

Optimal controller design and evaluation for a class of networked control systems with distributed constant delays

In this paper we discuss the framework for optimal controller design of networked control systems (NCS) where sensors, actuators, and controllers are distributed and interconnected by a common communication network. Multiple distributed communication delays as well as multiple inputs and multiple outputs are considered in the discrete-time modeling algorithm. The proposed NCS model is used as a foundation for optimal controller design to compensate for the multiple time delays. The proposed control algorithm utilizes the information of delayed signals and improves the control performance of a control system with distributed communication delays. Several simulation studies are provided to evaluate the control performance of the proposed controller design.

Control performance study of a networked machining cell

This paper presents a performance analysis of a networked control system (NCS) applied to a machining cell. The statistical analysis and time-delay characteristics of three control networks are first obtained by simulating the network protocols under expected traffic loads. This time-delay data is used in a simulation of a machining system, and the control system performance is evaluated. The simulation results provide guidelines for determining the optimal sampling rate for an NCS.