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The bulldozer is a mobile earthmoving machine with a differentially steered mobile base and an onboard manipulator used for soil cutting and transportation. Grading the ground to match a desired contour is an end-effector path-following task, with required joint rates dependent on mobile base motion. The offline planning of travel velocity profiles that respect the available hydraulic flowrate limits is difficult due to uncertainties in the machine–soil interactions. Hence, we propose a flow-bounded velocity controller enabling accurate automatic grading with online velocity scaling. The capacity of hydrostatic transmission and manipulator actuators, as well as the desired velocity, are considered when deciding the commanded velocity reference for the mobile base. Our dynamic simulation results show that, with the proposed controller, a desired ground profile is cut accurately when the machine operates at its performance limits. Comparison to constant velocity driving shows that errors in blade positioning are reduced dramatically. Constant velocity selected to keep the flow within limits results in longer completion times compared to our solution, making it more time optimal. Furthermore, the rpm of the diesel engine can be reduced to save fuel without compromising control performance. [ABSTRACT FROM AUTHOR]

Series elastic actuators (SEAs) have become a common actuation method in torque-controlled electric lightweight arm applications that physically interact with the environment in assembly tasks. Compared to traditional actuators, SEAs can provide high force fidelity, shock tolerance, and force sensing for interaction control. Considering inherent system dynamics and the variable stiffness of the fluid, the control design for hydraulic SEAs (HSEAs) that lead into fifth-order system is a challenging task. As a novelty, a full state feedback controller design for the developed fifth-order HSEA system is presented to serve as an inner-loop controller to handle highly nonlinear dynamics behavior. In addition, as an outer-loop impedance controller for HSEAs in heavy-duty applications, the position-based impedance controller is designed to handle control of the HSEA system during the contact motion. Experimental results with a one-degree-of-freedom real-size experimental setup with a payload of 200 kilos demonstrates the effectiveness of the proposed HSEA control methods both in the free-space motion and in a contact impedance motion. [ABSTRACT FROM AUTHOR]

• An adaptive impedance-VDC is proposed with robustness and prediction capabilities. • Robustness is ensured by designing an ancillary control law. • The proposed method is extended to coordinated dissimilar ULE arms. • Experimental tests on two coordinated ULE arms indicate efficiency and precision. Upper-limb exoskeleton (ULE) arms have emerged as promising wearable robotic devices for assisting humans in accomplishing tasks by distributing heavy loads. However, the complex structures, actuators, and power transmissions inherent in ULE arms introduce challenges in their control system. Additionally, the coordination of dissimilar ULE arm systems, stemming from differences in vendor structures and biomechanical variations among users, further complicates the control approach. In response to these challenges, this paper presents a new distributed framework for adaptive impedance-based Virtual Decomposition Control (VDC) tailored to ULE arms. It attains enhanced performance, robustness, and coordination by integrating prediction capabilities and ancillary control laws, which are significant for dissimilar ULE arms when manipulating a common object. Stability analysis is conducted using the input-to-state stability approach. We validate our approach through simulations with six coordinated ULE arms and extensive experiments with two commercial ULE arms, each with seven degrees of freedom, in four scenarios, including obstacle interaction. Comparative analysis against a state-of-the-art adaptive VDC method demonstrates the superiority of our approach. The proposed method enhances performance, robustness, and coordinated control, enabling safe and efficient manipulation across various scenarios. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper aims to develop a robust decomposed system control (RDSC) strategy under input constraints for an electro‐mechanical linear actuator (EMLA) facing model uncertainty and external disturbances. At first, a state‐space model of a complex multi‐stage gearbox EMLA system, driven by a permanent magnet synchronous motor (PMSM), is developed, and the non‐ideal characteristics of the ball screw are presented through the model. The result is a four‐order nonlinear strict‐feedback form (NSFF) system decomposed into three subsystems. As the paper's main result, a novel RDSC strategy with uniform exponential stability for controlling subsystem states is presented. This developed controller avoids the "explosion of complexity" problem associated with backstepping by treating the time derivative of the virtual control input as an uncertain system term. The proposed method, despite assuming load disturbances and input constraints with arbitrary bounds, offers a straightforward control approach for a broader range of applications. Further, the controller's performance is evaluated by simulating two distinct duty cycles, each representing different levels of demand on the actuator facing load disturbances near the rated motor performance. [ABSTRACT FROM AUTHOR]

A gravity-referenced joint angle estimation, which acts in joint space, is proposed for multiple-degree-of-freedom hydraulic manipulators. As a novelty, the estimation pairs up inertial units across a section of an open kinematic chain. In this way, the three-axis linear accelerometers and the three-axis rate gyros provide a drift-free solution for observing the motion state of a rotary joint connecting two links without relying on the full forward kinematics. For a low-noise, low-delay estimate, the linear accelerations acting on the paired inertial units are modeled and robustly combined with the principles of complementary and Kalman filtering. In pick-and-place experiments with a serial-link manipulator on a multiton, off-road forestry vehicle, joint angle sensing error of less than ±1° was achieved in spite of the dynamic interaction between the vehicle base and the terrain. Furthermore, the kinematic modeling’s ability to compensate for the nonplanar, coupled 3-D linkage motion is studied for one- and two-axis rate measurements along with Cartesian path tracking. This gives new insights from the typical planar kinematic models and heavy-duty control viewpoints. [ABSTRACT FROM PUBLISHER]

This paper proposes, for the first time without using any linearization or order reduction, an adaptive and model-based discharge pressure control design for the variable displacement axial piston pumps (VDAPPs), whose dynamical behaviors are highly nonlinear and can be described by a fourth-order differential equation. The rigorous stability proof, with an asymptotic convergence, is given for the entire system. In the proposed novel controller design method, the specifically designed stabilizing terms constitute an essential core to cancel out all the stability-preventing terms. The experimental results reveal that rapid parameter adaptation significantly improves the feedback signal tracking precision compared to a known-parameter controller design. In the comparative experiments, the adaptive controller design demonstrates the state-of-the-art discharge pressure control performance, enabling a possibility for energy consumption reductions in hydraulic systems driven with VDAPP. [ABSTRACT FROM AUTHOR]

In this paper, an optimization method for a redundant serial robotic manipulator's structure is proposed in order to improve their performance. Optimization was considered in terms of kinematics using the proposed objective function and the non-linear Levenberg-Marquardt algorithm for multi-variate optimization. Range limits of the joints, bounds of the design parameters, and a constrained workspace are enforced in the proposed method. A desired manipulator can be optimized to cover the required task points using dimensional synthesis. This approach effectively optimizes the link lengths of the manipulator and minimizes the position and orientation errors of the tool center point. A commercial heavy-duty hydraulic, underground tunneling manipulator was used to demonstrate the capability of the proposed optimization method. The obtained results encourage the use of the proposed optimization method in automated construction applications, such as underground tunneling, where the confined environment and the required task add challenges in the design of task-based robotic manipulators. [ABSTRACT FROM AUTHOR]

This paper addresses the energy-inefficiency problem of four-degrees-of-freedom (4-DOF) hydraulic manipulators through redundancy resolution in robotic closed-loop controlled applications. Because conventional methods typically are local and have poor performance for resolving redundancy with respect to minimum hydraulic energy consumption, global energy-optimal redundancy resolution is proposed at the valve-controlled actuator and hydraulic power system interaction level. The energy consumption of the widely popular valve-controlled load-sensing (LS) and constant-pressure (CP) systems is effectively minimised through cost functions formulated in a discrete-time dynamic programming (DP) approach with minimum state representation. A prescribed end-effector path and important actuator constraints at the position, velocity and acceleration levels are also satisfied in the solution. Extensive field experiments performed on a forestry hydraulic manipulator demonstrate the performance of the proposed solution. Approximately 15–30% greater hydraulic energy consumption was observed with the conventional methods in the LS and CP systems. These results encourage energy-optimal redundancy resolution in future robotic applications of hydraulic manipulators. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of redundancy resolution in closed-loop controlled hydraulic manipulators. The problem is treated at the hydraulic level using proposed cost functions formulated into a dynamic programming approach of minimum-state representation. Bounds on joint range, actuator velocity and acceleration were enforced. This approach minimises the hydraulic energy consumption of the widely popular load-sensing and constant-supply pressure systems. The presented approach can resolve the redundancy more effectively from the hydraulic side than do actuator velocity or energy optimisation approaches, point-wise optimal approaches or some standard direct optimisation tools that may lead to inferior solutions, as shown in simulation results where up to 15–30% greater energy use is seen with some competing approaches. The results obtained motivate joint trajectory optimisation at the hydraulic level in prospective applications at construction sites where frequently driven work cycles of hydraulic construction cranes are automated. [ABSTRACT FROM AUTHOR]

In this paper, a force-sensorless high-performance contact force/motion control approach is proposed for multiple-degree-of-freedom hydraulic manipulators. A rigorous stability proof for an entire hydraulic manipulator performing contact tasks is provided for the first time. The controller design for the manipulator is based on the recently introduced virtual decomposition control approach. As a significant novelty, the end-effector contact force is directly estimated from the manipulator's cylinder pressure data, which provides a practical solution for heavy-duty contact force control without engaging fragile force/torque sensors. In the experiments, the proposed controller achieved a force control accuracy of 4.1% at a desired contact force of 8000 N while in motion. This can be considered a significant result due to the hydraulic actuators’ highly nonlinear behaviors, the coupled mechanical linkage dynamics, and the complex interaction dynamics between the manipulator and the environment. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel modelling approach for a heavy-duty manipulator with parallel–serial structures connected in series. Each considered parallel–serial structure contains a revolute segment with rigid links connected by a passive revolute joint and actuated by a linear hydraulic actuator, thus forming a closed kinematic loop. In addition, prismatic segments, consisting of prismatic joints driven by hydraulic linear actuators, also are considered. Expressions for actuator forces are derived using the Newton–Euler (N–E) dynamics formulation. The derivation process does not assume massless actuators decoupled from manipulator links, which is common in the Lagrange dynamics formulation. Actuator pressure dynamics are included in the analysis, leading in total to a third-order system of ordinary differential equations (ODEs). With fewer parameters than its predecessors, the proposed model in the N–E framework inspires revision of the virtual decomposition control (VDC) systematic process to formulate a control law based on the new model. The virtual stability of each generic manipulator revolute and prismatic segment is obtained, leading to the Lyapunov stability of the entire robot. • General Newton–Euler dynamics equations for a hydraulic manipulator configuration. • Closed kinematic loops are considered using no approximations. • A straightforward analytic solution for a linear hydraulic actuator force is derived. • The results are compared to the ones obtained using the SimScape Multibody™. • A systematic subsystem-based process to formulate control is presented. [ABSTRACT FROM AUTHOR]

In this paper, a stability-guaranteed Cartesian free-space motion control for the redundant articulated hydraulic construction crane is addressed in order to increase system safety and productivity. To cope with the nonlinearities of coupled mechanical linkage dynamics of articulated systems and the inherently strong nonlinearities of hydraulic actuator dynamics, the proposed controller is designed based on the recently introduced Virtual Decomposition Control (VDC) approach. The VDC approach, which was developed especially for the control of complex robotic systems, allows the conversion of the control problem of the entire system to a control problem of individual subsystems, while rigorously guaranteeing the stability of the entire hydraulic system. In the experiments it is demonstrated that, the proposed controller is able to extensively cope with the highly nonlinear nature of the articulated hydraulic system, and an improved control performance is achieved compared to the current state-of-the-art studies in the category of the hydraulic robot manipulators. [ABSTRACT FROM AUTHOR]

Remote handling (RH) systems are used to inspect, make changes to, and maintain components in the ITER machine and as such are an example of mission-critical system. Failure in a critical system may cause damage, significant financial losses and loss of experiment runtime, making dependability one of their most important properties. However, even if the software for RH control systems has been developed using best practices, the system might still fail due to undetected faults (bugs), hardware failures, etc. Critical systems therefore need capability to tolerate faults and resume operation after their occurrence. However, design of effective fault detection and recovery mechanisms poses a challenge due to timeliness requirements, growth in scale, and complex interactions. In this paper we evaluate effectiveness of service-oriented architectural approach to fault tolerance in mission-critical real-time systems. We use a prototype implementation for service management with an experimental RH control system and industrial manipulator. The fault tolerance is based on using the high level of decoupling between services to recover from transient faults by service restarts. In case the recovery process is not successful, the system can still be used if the fault was not in a critical software module. [ABSTRACT FROM AUTHOR]

Abstract: Software requirements have an important role in achieving reliability for operational systems like remote handling: requirements are the basis for architectural design decisions and also the main cause of defects in high quality software. We analyze related recommendations and requirements given in software safety standards, handbooks etc. and apply them to remote handling control systems, which typically have safety-critical functionality, but are not actual safety-systems⿿for example the safety-systems in ITER will be hardware-based. Based on the analysis, we develop a set of generic recommendations for control system software requirements, including quality attributes, software fault tolerance, and safety and as an example we analyze ITER remote handling system software requirements to identify and present dependability requirements in a useful manner. Based on the analysis, we divide a high-level control system into safety-critical and non-safety-critical subsystems, and give examples of requirements that support building a dependable system. [Copyright &y& Elsevier]

Leakages and valve faults are among the most common faults in hydraulic systems. This paper studies the real-time detection and isolation of certain leakage and valve faults based on the results obtained in part one. In the first part, the mathematical model of a hydraulic test bed was analysed with Global Sensitivity Analysis to facilitate a systematic and verified approach to model-based condition monitoring. In this paper, an Unscented Kalman Filter-based Fault Detection and Isolation scheme for leakage and valve faults of a generic servo valve-controlled hydraulic cylinder is devised. Compared to existing literature, the leakage and valve faults are decoupled from cylinder static and dynamic loading which makes the results generic and applicable to any servo valve-controlled hydraulic cylinder. Moreover, a more comprehensive set of fault patterns for the detection and isolation of leakages and valve faults with experimental and simulation results are presented. We show that detecting an external leakage of as small as 0.17 l/min is possible in some cases, but the accuracy of the method varies considerably. We also report why the isolation of valve faults from leakages is very difficult. [ABSTRACT FROM AUTHOR]

Model-based condition monitoring methods are widely used in condition monitoring. They usually rely on ad hoc approaches to verify the system model and then best practices are reported to detect the given set of faults. This first part of a two-piece paper introduces a generic Global Sensitivity Analysis-based approach that can be applied systematically to verify the model parameter sensitivities used for the model-based fault detection. The case study is a generic servo valve-controlled hydraulic cylinder with unknown loading condition which is then systematically analyzed with Global Sensitivity Analysis. The method shows valuable insight into systematic model verification and resulting fault detection in terms of showing the dominant sensitivity of the nominal flow rate and nominal pressure difference, and the 3 exact sensitivities of 0 - 1 dm³ /min external and internal leakages on cylinder chamber pressures and velocity. In the second paper, an Unscented Kalman Filter-based Fault Detection and Isolation scheme for leakage and valve faults of a generic servo valve-controlled hydraulic cylinder is devised and fault patterns are presented. [ABSTRACT FROM AUTHOR]

Abstract: The Cassette Multi-functional Mover (CMM) is designed for performing safety-critical divertor cassettes movements in ITER. Therefore, special attention should be paid to the design and analysis of its feedback controllers. Firstly, the design of the multivariable tracking controller possesses many challenges. The hydraulic manipulator dynamics are highly nonlinear; moreover, the loaded mass spans a wide range. Secondly, a number of test runs (even a large number) do not necessarily reveal the controller sensitivity to all the system uncertainties. Thus, some theoretical tools are needed to assess the robustness of the controller. H ∞-based approach is a reasonable choice since it provides a set of metrics to evaluate the controller robustness which can be validated in tests. In this paper, the dynamic model of CMM is first derived, characterizing the nominal system model and the model uncertainties. Then, a multivariable H ∞ loop-shaping controller is synthesized which ensures both the robust stability and robust performance. Finally, the designed controller is validated by simulation results. [Copyright &y& Elsevier]

Abstract: To carry out a variety of remote handling operations inside the ITER divertor a Water Hydraulic MANipulator (WHMAN) and its control system have been designed and developed at Tampere University of Technology. The manipulator is installed on top of Cassette Multifunctional Mover (CMM) to assist during the cassette removal and installation operations. While CMM is designed to carry heavy components such as cassettes through the service ducts relying on positioning accuracy and repeatability, WHMAN is designed to execute a mix of remote handling operations using position trajectories and master-slave telemanipulation. WHMAN is composed of eight joints: six rotational and two translational. Since a manipulator requires only six joints to acquire the desired position and orientation in operational-space, the two additional joints of WHMAN provide the redundant degrees of mobility. This paper presents how this redundancy of WHMAN can be an advantage to optimize the execution of remote handling tasks. The paper also discusses an effective way to practically exploit the redundancy. The results show that the additional degrees of freedom can be utilized to improve the dynamic behavior of the manipulator. [Copyright &y& Elsevier]

A double approach method for versatile detection of similar objects from the real environment is introduced. By searching both the shape and textural data from the video image, it is possible to solve a generalized location problem without a loss in overall reliability in near-real time. A forest forwarder is used as a proof-of-concept application for the technique. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes one of the research projects carried out in The Preparation of Remote Handling Engineers for ITER (PREFIT) program within the European Fusion Training Scheme (EFTS). This research project is focusing on the design and optimization of water hydraulic manipulators used to test several remote handling tasks of ITER at Divertor Test Platform 2 (DTP2), Tampere, Finland, and later in ITER. In this project, a water hydraulic manipulator designed and build by Department of Intelligent Hydraulics and Automation in Tampere University of Technology, Finland (TUT/IHA) is further optimized as a case study for a given manipulator requirement specification in order to illustrate and verify developed comprehensive design guidelines and performance metrics. Without meaningful manipulator performance parameters, the evaluation of alternative robot manipulators designs remains ad hoc at best. Therefore, more comprehensive design guidelines and performance metrics are needed for comparing and improving different existing manipulators versus task requirements or for comparing different digital prototypes at early design phase of manipulators. In this paper the description of the project, its background and developments are presented and discussed. [Copyright &y& Elsevier]

Abstract: The divertor test platform 2 (DTP2) is a full scale physical test facility intended for testing, demonstrating and refining the remote handling (RH) equipment designs with prototypes which will define the final specifications for call for tenders of ITER RH devices. The facility will also be used for training future ITER RH operators. Digital mock-ups have been extensively used for providing the reference design and manufacturing support of the cassette multi-functional mover, its assisting manipulator and other tooling. Despite DTP2 not being yet fully operational, digital mock-ups of DTP2 and its equipment, together with real-time dynamic simulation models, have been employed to perform studies and designs which will reduce the time needed for the integration and commissioning of new RH equipment delivered to the site. The use of digital mock-ups is currently being used for planning and verifying (in a 3D environment) task procedures of future RH test trials; developing and testing control software and hardware, and graphical user interfaces; estimating the duration of the different RH tasks and to obtain a realistic range of capable motions and speeds of the devices. During DTP2 operations, digital mock-ups will still be employed for improving, optimizing and validating test procedures; assess the difficulty and fatigue experienced by the operators; gather technical specifications for designs and procurements of new RH equipment. The final goal is to produce a complete digital mock-up of the divertor region and its RH equipment, including operations and tasks procedures. Due to the large amount of devices and operations to be tested at DTP2, a product lifecycle management (PLM) system and a Manufacturing Hub are being put into operation. [Copyright &y& Elsevier]

A vision-based guidance methodology is proposed for precise positioning of the tool center point (TCP) of heavy-duty, long-reach (HDLR) manipulators. HDLR manipulators are non-rigid structures with many nonlinearities. Therefore, conventional rigid-body–based modeling and control methods issue challenges for accurate TCP positioning. To compensate for these errors, we compute the pose error between the TCP and an object of interest (OOI) directly in the camera frame, while using motion-based local calibration to find the extrinsic sensor-to-robot correspondence. The proposed pipeline for local calibration is twofold: first, the detected tool is oriented perpendicularly with respect to the OOI. Second, range adjustment is performed in the local planar plane by exploiting the visual measurements. Two methods for adjusting the range were examined: a line equation–based method and a trajectory matching–based method. Real-time experiments were conducted using a HDLR manipulator with a 5 m reach, and visual fiducial markers were used as detectable objects for the visual sensor. The experimental results demonstrated that the proposed methodology can provide sub-centimeter positioning accuracy, which is very challenging to achieve with HDLR manipulators due to their characteristic uncertainties. [ABSTRACT FROM AUTHOR]

The International Thermonuclear Experimental Reactor (ITER) maintenance is performed by means of remote handling (RH) systems and with aid of user interfaces such as haptic and joystick devices, virtual reality (VR) systems, and camera views. Many RH operations involving RH equipment, such as robotic manipulator arms, require millimeter accuracy, but camera views are often occluded or of poor quality, and might be unavailable during sensitive steps that require accurate, close-up views. Moreover, the VR system may not reflect the current scene accurately, as physical conditions may have changed under the harsh environment. The purpose of this research was to prototype and evaluate a novel software system, called 3D Node, that locates and detects the position and orientation of a piece of RH equipment or reactor element with respect to a stereo camera pair. The detection information is utilized to adjust the motion trajectories of a robotic manipulator arm. The 3D Node features stereo-camera calibration, target depth mapping, target position and orientation detection, and online target tracking. This paper reports on the 3D Node demonstration on the ITER Divertor RH use case and discusses the system applicability to other ITER RH systems. [ABSTRACT FROM AUTHOR]

Abstract In addition to high-precision closed-loop control performance, energy efficiency is another vital characteristic in field-robotic hydraulic systems as energy source(s) must be carried on board in limited space. This study proposes an energy-efficient and high-precision closed-loop controller for the highly nonlinear hydraulic robotic manipulators. The proposed method is twofold: 1) A possibility for energy consumption reduction is realized by using a separate meter-in separate meter-out (SMISMO) control set-up, enabling an independent metering (pressure control) of each chamber in hydraulic actuators. 2) A novel subsystem-dynamics-based and modular controller is designed for the system actuators, and it is integrated to the previously designed state-of-the-art controller for multiple degrees-of-freedom (n -DOF) manipulators. Stability of the overall controller is rigorously proven. The comparative experiments with a three-DOF redundant hydraulic robotic manipulator (with a payload of 475 kg) demonstrate that: 1) It is possible to design the triple objective of high-precision piston position , piston force and chamber pressure trackings for the hydraulic actuators. 2) In relation to the previous SMISMO-control methods, unprecedented motion and chamber pressure tracking performances are reported. 3) In comparison to the state-of-the-art motion tracking controller with a conventional energy-inefficient servovalve control, the actuators' energy consumption is reduced by 45% without noticeable motion control (position-tracking) deterioration. [ABSTRACT FROM AUTHOR]

Variable displacement axial piston pumps (VDAPPs) are wildly used in mobile working machines and they play a key role in machine's energy-saving load sensing (LS) systems. Typically, electric load sensing (ELS) systems utilize traditional linear control methods, which only can realize limited control flexibility and performance. This study proposes and experimentally verifies an adaptive robust pressure control strategy for a VDAPP system. To facilitate the model-based controller design, a modified reduced-order dynamic modeling of VDAPPs is proposed. Furthermore, an adaptive robust backstepping control strategy is designed to deal with the dynamic nonlinearities and parametric uncertainties of the VDAPP system for achieving accurate pressure tracking. The controller design consists of two steps, processing the pump pressure tracking and the axial angle control, respectively. Comparative experiments and simulations with different working conditions were performed to validate the advantages of the proposed control strategy. The proposed controller achieved higher pressure tracking accuracy and it showed great capability in dealing with dynamic nonlinearities, uncertainties, and time-varying disturbances. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the inter-subsystem communication channels in a prototype distributed remote handling control system at Divertor Test Platform 2 (DTP2). The subsystems are responsible for specific tasks and, over the years, their development has been carried out using various platforms and programming languages. The communication channels between subsystems have different priorities, e.g. very high messaging rate and deterministic timing or high reliability in terms of individual messages. Generally, a control system's communication infrastructure should provide interoperability, scalability, performance and maintainability. An attractive approach to accomplish this is to use a standardized and proven middleware implementation. The selection of a middleware can have a major cost impact in future integration efforts. In this paper we present development done at DTP2 using the Object Management Group's (OMG) standard specification for Data Distribution Service (DDS) for ensuring communications interoperability. DDS has gained a stable foothold especially in the military field. It lacks a centralized broker, thereby avoiding a single-point-of-failure. It also includes an extensive set of Quality of Service (QoS) policies. The standard defines a platform- and programming language independent model and an interoperability wire protocol that enables DDS vendor interoperability, allowing software developers to avoid vendor lock-in situations. [Copyright &y& Elsevier]

This paper presents a nonlinear, universal, path-following controller for Wheeled Mobile Robots (WMRs). This approach, unlike previous algorithms, solves the path-following problem for all common categories of holonomic and nonholonomic WMRs, such as omnidirectional, unicycle, car-like, and all steerable wheels. This generality is the consequence of a two-stage solution that tackles separately the platform path-following and wheels' kinematic constraints. In the first stage, for a mobile platform divested of the wheels' constraints, we develop a general paradigm of a path-following controller that plans asymptotic paths from the WMR to the desired path and, accordingly, we derive a realization of the presented paradigm. The second stage accounts for the kinematic constraints imposed by the wheels. In this stage, we demonstrate that the designed controller simplifies the otherwise impenetrable wheels' kinematic and nonholonomic constraints into explicit proportional functions between the velocity of the platform and that of the wheels. This result enables us to derive a closed-form trajectory generation scheme for the asymptotic path that constantly keeps the wheels' steering and driving velocities within their corresponding, pre-specified bounds. Extensive experimental results on several types of WMRs, along with simulation results for the other types, are provided to demonstrate the performance and the efficacy of the method. [ABSTRACT FROM AUTHOR]

Abstract: The divertor area of ITER vacuum vessel consists of 54 modular cassettes which must be exchanged after every 3–4 years of plasma operations. Divertor Cassettes are locked in the vacuum vessel by means of compressing them against the rails mounted in the inner and outer walls of the vacuum vessel. According to ITER reference cassette locking system, a Divertor Cassette has to be preloaded with a compression force of 360kN against the vacuum vessel rails. The preloading of the cassettes is carried out with a hydraulic jack tool which is fitted into the cassette body. The Jack will transmit a hydraulic force by pushing the cassette latches against the outer rails, transmitting therefore the required preloading compression force to the cassette. This paper deals with the validation of Divertor Cassette locking system and it also describes the design and testing of a radiation-hard, water hydraulic jack. The validation of Divertor Cassette locking system has been the first Divertor Maintenance operation tested at Divertor Test Platform 2. [Copyright &y& Elsevier]

• Servo valve endurance test was successfully completed. • A servo valve can operate within water hydraulic systems in high temperatures. • The servo valve parameters remained within allowable limits. ITER Divertor maintenance equipment operates in the vacuum vessel in elevated temperature and under considerable radiation load. The heavy Divertor assemblies are lifted and transported using servo valve systems, such as Cassette Multi-functional Mover (CMM). Systems are powered with water hydraulics, using demineralized water as a pressure medium. Operations have not been tested in ITER-relevant environmental conditions and over projected duty cycles. As the hydraulic medium is rather aggressive and there are no servo valves designed for demineralized water, the greater than 2000-h operational time was considered a potential issue. Hence, a project was undertaken to ascertain the component compatibility with the environment and pressure medium, and their robustness over the required operational period. Irradiation of components was not considered at this phase of technology validation. A heated test chamber was constructed to emulate the projected maximum ambient temperature of 50 °C in the Divertor area. Test routines and measurements were specifically tailored to monitor the operational parameters of the servo valve. After the 2188-h test the servo valve parameters remained within the limits promised by the manufacturer. Pressure gain decreased and hysteresis increased but remained within the allowable limits. These changes did not have significant effect on the joint angle tracking error. [ABSTRACT FROM AUTHOR]

Novel Augmented Reality techniques have the potential to have a large positive impact on the way remote maintenance operations are carried out in hazardous areas, e.g. areas where radiation doses that imply careful planning and optimization of maintenance operations are present. This paper describes an Augmented Reality strategy, system and implementation for aiding the remote collimator exchange in the LHC, currently the world׳s largest and highest-energy particle accelerator. The proposed system relies on marker detection and multi-modal augmentation in real-time. A database system has been used to ensure flexibility. The system has been tested in a mock-up facility, showing real time performance and great potential for future use in the LHC. The technical-scientific difficulties identified during the development of the system and the proposed solutions described in this paper may help the development of future Augmented Reality systems for remote handling in scientific facilities. [ABSTRACT FROM AUTHOR]

Integration of heterogeneous and distributed systems is a challenging task, because they might be running on different platforms and written with different implementation languages by multiple organizations. Data-centricity and event-driven architecture (EDA) are concepts that help to implement versatile and well-scaling distributed systems. This paper focuses on the implementation of inter-subsystem communication in a prototype distributed remote handling control system developed at Divertor Test Platform 2 (DTP2). The control system consists of a variety of heterogeneous subsystems, including a client–server web application and hard real-time controllers. A standardized middleware solution (Data Distribution Services (DDS)) that supports a data-centric EDA approach is used to integrate the system. One of the greatest challenges in integrating a system with a data-centric EDA approach is in defining the global data space model. The selected middleware is currently only used for non-deterministic communication. For future application, we evaluated the performance of point-to-point communication with and without the presence of additional network load to ensure applicability to real-time systems. We found that, under certain limitations, the middleware can be used for soft real-time communication. Hard real-time use will require more validation with a more suitable environment. [ABSTRACT FROM AUTHOR]

The work behind this paper takes place in the EFDA's European Goal Oriented Training programme on Remote Handling (RH) “GOT-RH”. The programme aims to train engineers for activities supporting the ITER project and the long-term fusion programme. One of the projects of this programme focuses on the verification and validation (V&V) of ITER RH system requirements using digital mock-ups (DMU). The purpose of this project is to study and develop efficient approach of using DMUs in the V&V process of ITER RH system design utilizing a System Engineering (SE) framework. Complex engineering systems such as ITER facilities lead to substantial rise of cost while manufacturing the full-scale prototype. In the V&V process for ITER RH equipment, physical tests are a requirement to ensure the compliance of the system according to the required operation. Therefore it is essential to virtually verify the developed system before starting the prototype manufacturing phase. This paper gives an overview of the current trends in using digital mock-up within product design processes. It suggests a simulation-based process design centralized around a simulation lifecycle management system. The purpose of this paper is to describe possible improvements in the formalization of the ITER RH design process and V&V processes, in order to increase their cost efficiency and reliability. [ABSTRACT FROM AUTHOR]

The remote maintenance of the ITER divertor is largely dependent on the usage of haptically teleoperated manipulators and man-in-the-loop operations. These maintenance operations are very demanding for the manipulator operators, yet vital for the success of the whole ITER experiment. Haptic shared control of the maintenance manipulators offers a promising solution for assisting the teleoperators in the maintenance tasks. A shared control system assists the operator by generating artificial guiding force effects and overlaying them on top of the haptic feedback from the teleoperation environment. An experimental haptic shared control system, called the Computer Assisted Teleoperation (CAT) has been developed at the Divertor Test Platform 2 (DTP2). In this paper, we investigate the design of the system and how the system integrates with the ITER compliant DTP2 prototype Remote Handling Control System (RHCS). We also experimentally assess the effect of the guidance to the operator performance in an ITER-relevant maintenance scenario using the Water Hydraulic MANipulator (WHMAN), which is specially designed for the divertor maintenance. The result of the experiment gives suggestive indication that the CAT system improves the performance of the operators of the system. [ABSTRACT FROM AUTHOR]

This paper is part of the EFDAs European goal oriented training program on remote handling (RH) GOT-RH. The program aims to train engineers for activities supporting the ITER project and the long-term fusion program. This paper is written based on the results of a project verification and validation (V&V) of ITER RH system using digital mock-ups (DMUs). The purpose of this project is to study an efficient approach of using DMU for the V&V of the ITER RH system design using a system engineering framework. This paper gives an overview of the current trends in product and simulation lifecycle management (PLM/SLM) in the industry. This paper suggests a design verification process centralized around a collaboration platform. The purpose of this paper aims at improving and formalizing the ITER RH design process together with the V&V process. The objective of the suggested process is to improve the cost efficiency and reliability of ITER RH systems. [ABSTRACT FROM PUBLISHER]

Abstract: A key ITER maintenance activity is the exchange of the divertor cassettes. The current major step in this programme involves the full scale physical test facility, namely divertor test platform 2 (DTP2), in Tampere, Finland. The objective of the DTP2 is the design and proof of concept studies of various remote handling (RH) device prototypes and their RH control systems, but is also important to define principles for standardizing control systems and methods around the ITER maintenance equipment. The development process of divertor cassette locking system (CLS) RH Tool prototypes is presented in this paper. The validation of the developed CLS Tool prototypes is accomplished in RH trials at DTP2. For this RH Trial, a CLS task description (TD) and tool prototypes were developed, manufactured and, finally, tested under remote operations. These tools, designed to be operated by water hydraulic manipulator (WHMAN), are water hydraulic jack (WHJ), pin tool (PT) and wrench tool (WT). [Copyright &y& Elsevier]

Abstract: The purpose of the Divertor Test Platform 2 (DTP2) is to demonstrate the proof-of-concept level remote handling operations with ITER maintenance devices, from a dedicated control room. In order to remotely operate these devices safely, a supervisory system composed of several software sub-systems is needed. For each of the devices, a control system is embodied. In the control room, there is no direct visual contact to the operation area and therefore, a remote viewing system having radiation tolerant cameras is required. Should the camera feeds be unavailable or with limited visibility, a 3D visualization system is utilized for showing a virtual model of the scene. As the maintenance sequences are often complicated and subject to formal approval, having them well designed beforehand is mandatory. In this paper, we present the complete software and hardware solution designed and implemented for the DTP2 remote handling operations, already being used with the Water Hydraulic Manipulator (WHMAN) and Cassette Multifunctional Mover (CMM). We present the modular division of systems, each of them in smaller detail, and go through some of the design choices made during the platform evolution. [Copyright &y& Elsevier]

Abstract: A key ITER maintenance activity is the exchange of the divertor cassettes. One of the major focuses of the EU Remote Handling (RH) programme has been the study and development of the remote handling equipment necessary for divertor exchange. The current major step in this programme involves the construction of a full scale physical test facility, namely DTP2 (Divertor Test Platform 2), in which to demonstrate and refine the RH equipment designs for ITER using prototypes. The major objective of the DTP2 project is the proof of concept studies of various RH devices, but is also important to define principles for standardizing control hardware and methods around the ITER maintenance equipment. This paper focuses on describing the control system hardware design optimization that is taking place at DTP2. Here there will be two RH movers, namely the Cassette Multifuctional Mover (CMM), Cassette Toroidal Mover (CTM) and assisting water hydraulic force feedback manipulators (WHMAN) located aboard each Mover. The idea here is to use common Real Time Operating Systems (RTOS), measurement and control IO-cards etc. for all maintenance devices and to standardize sensors and control components as much as possible. In this paper, new optimized DTP2 control system hardware design and some initial experimentation with the new DTP2 RH control system platform are presented. The proposed new approach is able to fulfil the functional requirements for both Mover and Manipulator control systems. Since the new control system hardware design has reduced architecture there are a number of benefits compared to the old approach. The simplified hardware solution enables the use of a single software development environment and a single communication protocol. This will result in easier maintainability of the software and hardware, less dependence on trained personnel, easier training of operators and hence reduced the development costs of ITER RH. [Copyright &y& Elsevier]

Abstract: Department of Intelligent Hydraulics and Automation (IHA) of Tampere University of Technology has been involved in the European Fusion program since 1994 within the ITER reactor maintenance activities. In this paper we discuss the design and development of a six degrees of freedom water hydraulic manipulator with a force feedback for teleoperation tasks. The manipulator is planned to be delivered to Divertor Test Platform 2 (DTP2) during year 2008. The paper also discusses the possibility to improve the fail safe and redundant operation of the manipulator. During the design of the water hydraulic manipulator, special provisions have been made in order to meet the safety requirements such as servo valve block for redundant operation and safety vane brakes for fail safe operation. [Copyright &y& Elsevier]

Abstract: The advantages of Product Lifecycle Management (PLM) systems are widely understood among the industry and hence a PLM system is already in use by International Thermonuclear Experimental Reactor (ITER) Organization (IO). However, with the increasing involvement of software in the development, the role of Software Configuration Management (SCM) systems have become equally important. The SCM systems can be useful to meet the higher demands on Safety Engineering (SE), Quality Assurance (QA), Validation and Verification (V&V) and Requirements Management (RM) of the developed software tools. In an experimental environment, such as ITER, the new remote handling requirements emerge frequently. This means the development of new tools or the modification of existing tools and the development of new remote handling procedures or the modification of existing remote handling procedures. PLM and SCM systems together can be of great advantage in the development and maintenance of such remote handling system. In this paper, we discuss how PLM and SCM systems can be integrated together and play their role during the development and maintenance of ITER remote handling system. We discuss the possibility to investigate such setup at DTP2 (Divertor Test Platform 2), which is the full scale mock-up facility to verify the ITER divertor remote handling and maintenance concepts. [Copyright &y& Elsevier]

Abstract: The RH devices used for ITER divertor maintenance are movers or manipulators composed of electro-hydraulic and electrical actuators. Such devices are CMM, CTM and WHMAN to assist CMM and CTM. These devices execute complex and safety-critical operations while supporting ITER reactor elements weighting several tons. Despite the differences in the load capacity and functionality, the control system of these devices can be categorized as position servo control or force servo control. In this paper we propose the use of unified software development approach currently developed and demonstrated at the DTP2. This new approach takes into account the ITER RH requirements for all maintenance devices, not only the water-hydraulic maintenance devices. The need for extensive software verification and validation utilizing international standards for safety-critical systems is addressed. This applies both to control software architecture and user interface design. In principle, we propose that all ITER maintenance devices are developed and tested with the common software architecture and user interface. This makes it possible to reuse generic software modules that are well documented and tested, resulting decreased verification and validation period and development cost. Utilising this approach also improves reliability and safety of the maintenance operations. [Copyright &y& Elsevier]