Multi-rate Control Architectures for Dextrous Haptic Rendering in Cooperative Virtual Environments

This paper presents an analytic design of multirate controllers to guarantee stable haptic interaction and high fidelity. When the reflective force is computed by using slowly simulated virtual model, the control frequency of the conventional controller becomes low. This increases the zero-order-hold effect, and makes the system unstable. We propose a multirate control method to reduce the zero-order-hold effect. The multirate controller is implemented by adding a high frequency controller to the conventional controller. The high-frequency controller is designed to compensate the energy generated by the conventional controller. The stability analysis of the multirate haptic control system shows that the stiffness of the virtual model can be increased while maintaining the stability. A nonlinear virtual coupling is designed using this multirate control scheme. The multirate controller is evaluated by mathematical analysis and experiments.

Internet-based control is the way of monitoring and adjusting plants from a remote site over the Internet. The major challenge of this new kind of control systems is how to deal with Internet time delay. Our recent study illustrated that there is a great potential to overcome Internet time delay from the control system architecture aspect such as by using multi-rate control schemes. In this paper, we formulate a new class of dual-rate control systems with Internet time delay at both feedback and feed-forward channels and investigate their asymptotic stability properties. Some new necessary and sufficient criteria of asymptotic stability for such dual-rate control systems are established. Two examples are given to illustrate the effectiveness of the theoretical results.

This paper deals with multirate tracking control of linear time-invariant systems with two sampling-rates: a slower one for the output and a faster one for the input. It is known that intersample ripples often arise in the outputs of the closed-loop multirate systems although multirate control has interesting advantages. There are some papers which discuss this problem, but only few studies which confirm the validity of the control design methods through experiments. In this paper, a ripple-suppressed multirate control scheme is presented arid applied to a position servo experimental system with an ultrasonic sensor. Experimental results show the effectiveness of the algorithm.

In this paper we present a modular and distributed control architecture in order to achieve natural interaction and mobile manipulation task goals for a humanoid robot. We propose a hierarchically organized architecture with three levels and introduce the mapping of the functional features in this architecture into hardware and software modules. We also describe different functional features which have been realized and integrated into the whole control architecture.

In haptic communication via the network, transmission period is not able to be designed uniquely since it restricted by the line bandwidth, transmission protocol, hardware constraints and so on. To address this problem, downsampling is often employed. Additionally, to enhance the performance of downsampled system, multirate control is proposed. However, the quantitative analysis on downsampling and multirate control are not treated. Therefore, this paper treats downsampling and multirate control system, and performs quantitative analysis by using hybrid parameter. In order to reveal the most effective combination of holder and single or multirate, holders (ZOH, DFOH and PFOH) are considered explicitly, and it is formulated to Laplace domain. The effectiveness of each combination is verified through experiments.

We consider multirate digital control systems which consist of an interconnection of a continuous-time nonlinear plant (described by ordinary differential equations) and a digital lifted controller (described by ordinary difference equations). The input to the digital controller consists of the multirate sampled output of the plant and the input to the continuous-time plant consists of the multirate hold output of the digital controller. We show that when quantizer nonlinearities are neglected, then under reasonable conditions (which exclude the critical cases), the stability properties (in the Lyapunov sense) of the trivial solution of the nonlinear multirate digital control system can be deduced from the stability properties of the trivial solution of its linearization. When quantizer nonlinearities are not neglected, corresponding results can be established for Lagrange stability rather than Lyapunov stability of an equilibrium.

A computationally effective fixed-order multirate digital control scheme is presented for disk drive actuator control. The proposed multirate controller outputs control commands at each control update instant, while the multirate control scheme is evenly computed for every measurement sampling period, thereby eliminating the need for very powerful processors for implementation. Application results demonstrate that the proposed multirate control scheme is useful to smooth control inputs so as not to excite the flexible mode dynamics of the actuator arm and suspensions.

As power systems grow they are incorporating ever-increasing numbers of distributed generation such as renewables but also various other flexible agents e.g. electric vehicles and energy storage, that can act both as loads and generators with the ability to provide a number of ancillary services. This evolution signals a migration of monitoring and control responsibilities often involving embedded intelligence. This work aims to expand on previous investigations considering frequency control and examines distributed communication and control architectures through the medium of Multi-Agent Systems (MAS) focusing on voltage control in a radial microgrid. The investigation assesses control and communication performance across a range of agent architectures against four selected performance criteria, and an increasing agent population. The objective of the paper is to demonstrate that network conditions can be used to determine the most appropriate control and communication architecture. Obtained results demonstrate the effectiveness that a dynamic, self-organising control and communication architecture can have on modern and future distribution grids employing a high number of distributed agents.

Interactions with virtual worlds using the sense of touch, called haptic rendering, have natural applications in many domains such as health or industry. For an accurate and realistic haptic feedback, the haptic device must receive orders at high frequencies, especially to render stiff contacts between rigid bodies. Therefore, it is today still challenging to provide consistent haptic feedback in complex virtual worlds. In this paper, we present a new coupling scheme for haptic display of contacts between rigid bodies, based on the generation of a sub-world around the haptic interaction. This sub-world allows the simulation of physical models at higher frequencies using a reduced quantity of data. We introduce the use of a graph to manage the contacts between the bodies. Our results show that our coupling scheme enables to increase the complexity of the virtual world without having perceptible loss in the haptic display quality.

A frequency analysis procedure for single and multirate sampled-data control systems is presented. The method is taking the inter-sample behaviour into account, and for a sinusoidal input the system power gain is calculated. Also the close correspondence between this method and the principal gain for continuous-time MIMO systems is discussed. Finally our method is illustrated on a sampled-data SISO system.

This paper considers robust control design for large-scale uncertain systems with state, input and output overlapping decompositions. The extension principle, which is a generalized notion of overlapping decomposition, is investigated from a robust control viewpoint. It is shown that if a controller designed for the expanded system achieves robustness in the expanded spaces, then the contracted controller achieves required robustness of the original system. This paper also defines and develops a framework of the extension principle for multirate control systems with hybrid signals. An approach to robust performance design with the overlapping multirate control is proposed.

In this paper a new intelligent control architecture for autonomous multi-robot systems is presented. Furthermore, the paper deals with task description, task distribution, task allocation and coordination of the system components. The main advantage of the new control architecture is the distributed execution of tasks or subtasks by components of the multi-robot system. The components are able to build teams dynamically thereby avoiding the bottle neck problem of the information flow in centralized controlled architectures. The communication and cooperation between components to achieve distributed organized control architectures is studied. The described intelligent control architecture is to replace the former control architecture of the autonomous robot KAMRO. >

This paper presents a newly designed control scheme for haptic interaction with uniform sample rate virtual environment. In most practical application in haptic interaction, we lack the knowledge about the model of the sampling rate. Unfortunately, by using the conventional wave variable method, the impedance parameter should adjust accordingly to guarantee the passivity of the interaction. Considering the inconvenient of the wave variable method, a novel scheme, named multirate wave transformation with energy reusage, is introduced. The proposed control scheme re-harvests the energy leakage caused by sampling rate by an energy observer, and an energy reservoir is formed to accumulate the re-harvested energy. Then, an energy regulator reuses the energy to passify the haptic interaction. Furthermore, we also demonstrated by analysis that the proposed control scheme can achieve a better interactive transparency by comparison with the traditional wave variable method. Finally, the effectiveness and performance of the proposed control scheme are validated with a haptic rendering experimental platform.

Frequency domain robust stability conditions for a Smith Predictor-like control scheme for multi-rate sampled data control schemes are derived using the contraction mapping theorem in l2.

Over the course of this project, we have successfully de-risked our distributed microgrid control architecture by tightly integrating its associated control algorithms into a unified software library, installing the software library on several industrial-grade target hardware platforms, and validating the performance of the resulting microgrid controller in a real-life microgrid. Upon completion of the project, we demonstrated that our distributed control architecture is resilient against (i) failures in control devices, (ii) unreliable communication links, (iii) delays in transmitted data, and (iv) imperfect knowledge of the number of (and state of) generation and load assets in the microgrid. In this final report, we present results from all the milestones that were accomplished over the course of this project.