Development of hybrid hydraulic–electric power units for field and service robots

Energetic autonomy of a hydraulic-based mobile robot requires a power source capable of both hydraulic and electrical power generation. The hydraulic power is used for locomotion, and the electric power is used for the control computer, sensors and other peripherals. In addition, the power source must be lightweight and quiet. This study presents several designs of internal combustion engine-based power units. Each power unit is evaluated with a Ragone plot which shows its performance over a wide range of operation times. Several hydraulic–electric power units (HEPUs) were built and successfully demonstrated on the Berkeley lower extremity exoskeleton (BLEEX). The best-performing design of the HEPUs, based upon the Ragone plot analysis, is described in detail. This HEPU produces constant pressure hydraulic power and constant voltage electric power. The pressure and voltage are controlled on board the power unit by a computer. A novel characteristic of this power unit is its cooling system in which hydraulic fluid is used to cool the engine cylinders. The prototype power unit weighs 27 kg and produces 2.3 kW (3.0 hp) hydraulic power at 6.9 MPa (1000 p.s.i.) and 220 W of electric power at 15 V DC.     

Mobile Agent-Based Management in the INSERT Project

This paper describes work carried out atUniversity College London to evaluate the use of MobileAgents (MA), written in Java, in network and systemmanagement. The work draws on experience fromconventional management systems based on ISO CommonManagement Information Protocol (CMIP) andInternet Simple Network ManagementProtocol (SNMP). These systems make use of theconcept of a Managed Object (MO). The paper describes the way in which the MOconcept has been translated into a form suitable forMA-based management and how the features of the Javalanguage may be used to express management information and to implement MOs. A platform has beenimplemented which allows MOs to be instantiated,controlled and stored. The platform also allows the easyproduction of MAs, their launching into the system and their subsequent management. Details of theplatform implementation are given and an initialassessment of performance is presented.     

Management Issues of a Mobile Agent-Based Service Environment

This paper introduces the concepts of a servicemanagement system for mobile agent-based services. Incontrast to several other approaches in whichagent-based applications are used to handletraditional network or service managementaspects, this paper describes a way to manage thedistributed agent environment itself. The proposedapproach was designed and developed by using OSI SystemsManagement concepts as a starting point, which are modified andadjusted in order to fulfill the new requirementsassociated with the mobile agent paradigm. However, thispaper does not cover integration or co-existence of the introduced agent management system (AMS)and traditional OSI management systems. Instead, theentire AMS environment is based on mobile agenttechnology. At present, this approach is validated inthe context of the European research project MobileAgent Environments in Intelligent Networks(MARINE).     

Fracture mechanics approach to forecast delamination lifetime

Interlaminar fracture (delamination) is one of the major concerns in the design of laminated composite structures, adhesive joints, coatings, sealants and other multilayered material systems. Service lifetime of a laminated structure is limited by the time an interlaminar flaw propagates to a size perceived critical to the stiffness and/or the strength of the structure. The time required to cause certain magnitude of delamination, under stresses below the initiation stress, could be forecasted if the constitutive equation for the rate of delamination is known. This paper describes an approach to develop the constitutive equation for delamination under mode I conditions. The approach rests on principles of linear elastic fracture mechanics (LEFM) and uses elevated temperature to accelerate interlaminar fracture at constant loads. The experiments used double cantilever beam test specimens fabricated as a model system from poly(methyl methacrylate) (PMMA) beams and epoxy adhesive whose stiffness was equivalent to that of a typical carbon/epoxy laminated composite. Mechanistic observations indicated that the fracture front displayed similar mechanism at all test conditions. A modified form of Paris power law is suggested to forecast service lifetime in terms of temperature, service load and the initial flaw size.     

Access Protocols for Cellular High-Speed Data Services

In this contribution, novel access techniquesfor the future cellular information networks areproposed. To facilitate a fast deployment, the suggestedaccess techniques have been implemented over well-known technological platforms, namely DECT (DigitalEnhanced Cordless Telecommunications) containing aFDM/TDMA (Frequency Division Multiplex/Time DivisionMultiple Access) structure. Two situations areconsidered: i) no limits in the use of the all carriers atterminal (ideal case) and ii) maximum number ofcontiguous/simultaneous carriers at terminal (realisticcase). First, to grant a quick access channel, a random access mechanism with reservation is proposed.It is called contention-TDMA (C-TDMA). Next, in order tostudy the feasibility of better collision resolutionalgorithms for C-TDMA, a centralized approach called Centralized C-TDMA Demand Assignment(CC-TDMA-DA) has also been studied. For the ideal case,numerical results indicate that C-TDMA and CC-TDMA-DAyield similar throughput values in typical cellular scenarios. Also, CC-TDMA-DA tends to bepreferable for traffic sources with long messages andweak delay constraints, while C-TDMA performs better forbursty traffic sources with hard time requirements. Additional numerical results for the realisticcase have demonstrated that system performancedeteriorates little with respect to the ideal case interms of collisions, delays and throughputfigures.     

A Generic Architecture Multimedia Service and Management

A multimedia service architecture is constructedby using a generic component model. In order to derivespecific components, a generic service agent and genericservice component architectures are developed. Using generic agent and the service components,a TINA-C conformant object-oriented hierarchical genericservice component is developed and presented. As anexample, a multimedia QoS service and management architecture is presented.     

Optimization and Adaptation of Error Control Algorithms for Wireless ATM

A common problem of all wireless digital datatransmission systems is the bit error rates of the radiosubsystem, which can be several orders of magnitudehigher than for a wire- or fiber-based technology. Forward error correction (FEC), automaticrepeat request (ARQ), and interleaving are used as meansto improve throughput and bandwidth efficiency. Thispaper presents some considerations on the optimization and adaptation of these algorithms with focuson recent wireless ATM developments. The optimization,with respect to the target bit error rate and themapping of the wireless connection quality to the ATM quality of service (QoS) concept, is discussedin detail. In addition to the theoretical evaluation,which is verified by extensive simulations, we presentcomprehensive architecture and implementation considerations on the design of an adaptiveerror control system for a wireless ATMnetwork.     

GSM Point-to-Point Short Message Service

GSM short message service provides aconnectionless transfer of messages with low-capacityand low-time performance. This article provides atutorial on GSM point-to-point short messaging. Theshort message protocol hierarchy is introduced and the mobileoriginated/terminated messaging procedures aredescribed.     

A Model ATM Network and APIs for Service Management on an ATM Network

The architectural reference point for our workis a reference model which associates functionality withoperational planes along three orthogonalabstractedmodels. Within the context of this reference model a service management model is proposed. Themodel makes use of APIs for communicating managementinformation between a management application and serviceentities distributed in an ATM network. The APIs are based upon native ATM APIs that are similarto those that have recently been adopted by the ATMForum. The viability of the model is demonstrated bybuilding ATM multimedia services with service management capabilities. The model and the APIs have beenapplied to services executing in a national ATM network.Although the work is motivated by an ATM network, theservice management model is general, and may be applied to other networks as well. Some openissues in service management are brought out.