Developing control and integration software for flexible manufacturing systems

The slow growth of computer-integrated manufacturing is attributed to the complexity of designing and implementing their control and integration software. This article expands on a methodology for designing and implementing this software that was introduced in [16]. The goal of this methodology is to build flexible and resuable control and integration software for computer-integrated manufacturing systems. It hinges upon the concepts of software/hardware components, their assemblages, a distributed common language environment, formal models, and generic controllers. Major sources of flexibility are obtained by decoupling process plan models from the model of the factory floor and by using a generic controller. Reusability is achieved by building selfcontained software/hardware components with general, possibly parametrized, interfaces. The interplay between simulated and actual hardware internals of software/hardware components is used as the basis of a testing strategy that performs off-line simulation followed by on-line testing.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43095/1/10952_2005_Article_BF02265064.pd

Centralized and distributed algorithms for on-line synthesis of maximal control policies under partial observation

This paper deals with the on-line control of partially observed discrete event systems (DES). The goal is to restrict the behavior of the system within a prefix-closed legal language while accounting for the presence of uncontrollable and unobservable events. In the spirit of recent work on the on-line control of partially observed DES (Heymann and Lin 1994) and on variable lookahead control of fully observed DES (Ben Hadj-Alouane et al. 1994c), we propose an approach where, following each observable event, a control action is computed on-line using an algorithm of linear worst-case complexity. This algorithm, called VLP-PO , has the following additional properties: (i) the resulting behavior is guaranteed to be a maximal controllable and observable sublanguage of the legal language; (ii) different maximals may be generated by varying the priorities assigned to the controllable events, a parameter of VLP-PO ; (iii) a maximal containing the supremal controllable and normal sublanguage of the legal language can be generated by a proper selection of controllable event priorities; and (iv) no off-line calculations are necessary. We also present a parallel/distributed version of the VLP-PO algorithm called DI-VLP-PO . This version uses several communicating agents that simultaneously run (on-line) identical versions of the algorithm but on possibly different parts of the system model and the legal language, according to the structural properties of the system and the specifications. While achieving the same behavior as VLO-PO, DI-VLP-PO runs at a total complexity (for computation and communication) that is significantly lower than its sequential counterpart.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45126/1/10626_2005_Article_BF01797138.pd

PSPACE-completeness of Modular Supervisory Control Problems*

In this paper we investigate computational issues associated with the supervision of concurrent processes modeled as modular discrete-event systems. Here, modular discrete-event systems are sets of deterministic finite-state automata whose interaction is modeled by the parallel composition operation. Even with such a simple model process model, we show that in general many problems related to the supervision of these systems are PSPACE-complete. This shows that although there may be space-efficient methods for avoiding the state-explosion problem inherent to concurrent processes, there are most likely no time-efficient solutions that would aid in the study of such “large-scale” systems. We show our results using a reduction from a special class of automata intersection problem introduced here where behavior is assumed to be prefix-closed. We find that deciding if there exists a supervisor for a modular system to achieve a global specification is PSPACE-complete. We also show many verification problems for system supervision are PSPACE-complete, even for prefix-closed cases. Supervisor admissibility and online supervision operations are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45090/1/10626_2004_Article_6210.pd

Secure two-user AF relaying networks using cooperative jamming

In this paper, we investigate secure two-user AF relaying networks based on a destination assisted cooperative jamming (DACJ). We consider two sources, one destination, one eavesdropper and multiple amplify-and-forwards (AF) relays. In the first time slot, each source broadcasts the information signal to the relays. In order to protect the source message from being eavesdropped, the destination simultaneously transmits a jamming signal to each relay. The selected relay amplifies and forwards the combined signal to the destination and eavesdropper. We introduce reactive relay selection and power allocation to decrease the power consumption. Closed-form expressions for lower bound of ergodic secrecy capacity (ESC) are provided. Numerical results are presented to verify the exactness of the proposed mathematical analysis. ? 2018 IEEE.This publication was made possible by NPRP grant # 8-1781-2-735 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors

Hybrid FES-Exoskeleton Controller to Assist Sit-To-Stand movement

International audienceSit-To-Stand (STS) movement is an important daily living activity and usually a difficult task to achieve, particularly, by post-stroke patients. In this study, a hybrid control approach that combines the use of an impedance-based exoskeleton controller and an event-based Functional Electrical Stimulation (FES) of the knee extensor muscle is proposed to assist the STS transfer movement within an assistance as needed strategy. Actuation of the active lower limb exoskeleton is done using a Serial Elastic Actuator (SEA) that uses a torsion spring to guarantee the measurement of the human exoskeleton interaction torque. The measured torque is fed to a linear desired impedance model to generate a desired trajectory, which will be tracked by the exoskeleton's actuators. Experiments were conducted with one healthy subject to evaluate the feasibility and effectiveness of the proposed approach. The obtained performances show the synergy between the assistance provided through FES of the quadriceps muscle during the extension sub-phase of the STS movement and the one delivered by the knee joint actuator of the lower limb exoskeleton

Assistive Control Strategies For a Lower-Limb Exoskeleton (E-ROWA)

International audienc

Impedance modulation control of a lower limb exoskeleton to assist sit-to-stand movements

As an important movement of the daily living activities, sit-to-stand (STS) movement is usually a difficult task facing elderly and dependent people. In this article, a novel impedance modulation strategy of a lower limb exoskeleton is proposed to provide appropriate power and balance assistance during STS movements while preserving the wearer’s control priority. The impedance modulation control strategy ensures adaptation of the mechanical impedance of the human-exoskeleton system towards a desired one requiring less wearer’s effect while reinforcing the wearer’s balance control ability during STS movements. A human joint torque observer is designed to estimate the joint torques developed by the wearer using joint position kinematics instead of electromyography (EMG) or force sensors; a time-varying desired impedance model is proposed according to the wearer’s lower limb motion ability. A virtual environmental force is designed for the balance reinforcement control. Stability and robustness of the proposed method are theoretically analyzed. Simulations were implemented to illustrate the characteristics and performance of the proposed approach. Experiments with four healthy subjects were carried out to evaluate the effectiveness of the proposed method and show satisfactory results in terms of appropriate power assist and balance reinforcement