2: Deuterium-tritium fusion reaction

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... ("Symphony" scenario) and 61% ("Jazz" scenario) by 2050. Beyond 2050, several scenarios diverge. Part of that divergence will depend on technological developments, industrial strategies, policy choices and consumer choices. The more pessimistic scenarios predict an energy production peak around 2100 followed by an overall energy shortfall (see Fig. ...

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... to date. Since charged particles move in circles perpendicular to a magnetic field, it is possible to confine them inside a magnet shaped like a torus whose field lines go around in endless cir- cles. This concept gave birth to the so-called tokamak ("toroidal magnetic chamber" in Russian), in which hot plasma is confined by powerful magnets (see Fig. 1.3 and section 1.1.5). The ITER project is based on the tokamak concept. Other concepts of magnetic confinement devices exist, such as the Stellarator, which is distinct from the tokamak in the sense that it is not azimuthally symmetric but helically twisted in order to improve plasma confinement and stability properties (see Fig. 1.4). ...

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... magnets (see Fig. 1.3 and section 1.1.5). The ITER project is based on the tokamak concept. Other concepts of magnetic confinement devices exist, such as the Stellarator, which is distinct from the tokamak in the sense that it is not azimuthally symmetric but helically twisted in order to improve plasma confinement and stability properties (see Fig. 1.4). • Inertial confinement: the idea behind this alternative approach is to make the fusion reaction occur so quickly that the fuel does not have time to disperse before its energy is released. This concept makes use of large, intense lasers (1.8 million joules) to bombard and heat up a frozen pellet of fusion fuel and cause fusion to ...

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... this alternative approach is to make the fusion reaction occur so quickly that the fuel does not have time to disperse before its energy is released. This concept makes use of large, intense lasers (1.8 million joules) to bombard and heat up a frozen pellet of fusion fuel and cause fusion to occur in less than one-millionth of a second (see Fig. 1.5). Whereas magnetic confinement devices maintain steady-state hot plasmas, devices based on inertial confinement operate in pulses. Typical examples of inertial confinement devices are the National Ignition Facility (NIF) in the United States ( Fig. 1.6) and the Laser Megajoule (LMJ) in France ( Fig. 1.7). This concept is presented ...

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... pellet of fusion fuel and cause fusion to occur in less than one-millionth of a second (see Fig. 1.5). Whereas magnetic confinement devices maintain steady-state hot plasmas, devices based on inertial confinement operate in pulses. Typical examples of inertial confinement devices are the National Ignition Facility (NIF) in the United States ( Fig. 1.6) and the Laser Megajoule (LMJ) in France ( Fig. 1.7). This concept is presented for the sake of completeness and will not be addressed further in this thesis. In both confinement methods, once energy has been released by the fusion reaction, its conversion to electric power could be similar to what takes place in contemporary nuclear ...

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... in less than one-millionth of a second (see Fig. 1.5). Whereas magnetic confinement devices maintain steady-state hot plasmas, devices based on inertial confinement operate in pulses. Typical examples of inertial confinement devices are the National Ignition Facility (NIF) in the United States ( Fig. 1.6) and the Laser Megajoule (LMJ) in France ( Fig. 1.7). This concept is presented for the sake of completeness and will not be addressed further in this thesis. In both confinement methods, once energy has been released by the fusion reaction, its conversion to electric power could be similar to what takes place in contemporary nuclear or conventional power plants: the thermal flux ...

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... fusion. How- ever, no solid container can confine such hot plasma. In a tokamak, this problem is solved by confining the electrically charged plasma particles within a magnetic field so they can- not touch the vessel walls. This magnetic cage is achieved by combining the effects of a toroidal magnetic field and a poloidal magnetic field (see Fig. 1.8). The toroidal magnetic field is generated by electric currents circulating in a series of toroidal field coils evenly positioned around the torus. In basic tokamaks, the poloidal magnetic field is produced by a central solenoid that acts as the primary winding of a transformer. A transient electric current circulating inside this ...

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... the charged plasma particles along closed and therefore infinite magnetic field lines. To provide further insight into the principle of a tokamak fusion reactor, and to introduce some technical terminology that will be used throughout this thesis, the following para- graphs describe the main internal components of the ITER tokamak (see also Fig. 1.9 ...

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... using a mix of deuterium and tritium (D-T) as fusion fuel began in the early 1990s at TFTR and JET (see Fig. 1.11). The world's first controlled release of fusion power was achieved at JET in 1991. While JET and TFTR produced a significant amount of fusion power with a Q close to 1, exceptionally long-duration plasma pulses were achieved in Tore Supra (Cadarache, France). As far as it is concerned, JT-60 lacked tritium-handling facilities and was ...

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... following paragraphs focus on four major tokamak projects (see Fig. 1.12) paving the way for commercial fusion power ...

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... device was constructed in Culham (UK) between 1979 and 1983 (see Fig. 1.13). Its very first plasma was achieved on 25 June 1983, but its first controlled fusion power was not produced until November 1991. The record-setting power of 16 MW was achieved for one second in 1997 using mixed deuterium-tritium fuel with a Q factor of 0.65, quite close to the break-even point (Q = 1). Its main features are summarised ...

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... Supra is a French tokamak situated within the Cadarache nuclear research centre. It began operating in 1988 after the discontinuation of TFR (see Fig. 1.14). With a major radius of 2.25 m and a minor radius of 0.70 m, Tore Supra is still the third largest operating tokamak in the world after JET and JT-60. It has been, for a very long time, the only large tokamak featuring superconducting toroidal magnets, which allows the generation of a permanent toroidal magnetic field. Tore Supra is ...

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... ITER project brings together the world's tokamak research community in a single international collaboration. The current participants in the project are the European Union, Japan, the People's Republic of China, the Republic of India, the Republic of Korea, the Russian Federation and the United States (see Fig. 1.15). Currently under construction in France, ITER will be several times larger than any previous tokamak. Although fusion research has made significant scientific progress thanks to the large fusion experiments constructed in the 1980s (short energetic pulses in JET, long pulses in Tore Supra), it was clear from an early stage that ...

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... clearing and leveling took place in 2007 and 2008, respectively. The building con- struction process began in 2010 (see Fig. 1.16), which should lead to the first plasma between 2021 and 2025. This will be followed by an exploitation phase of about 20 years aimed at testing essential physics and technologies for future fusion power ...

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... for extended periods of time, from an energy input of 50 MW. It will therefore be the first fusion experiment to produce net power. To achieve this, ITER will be twice the size of JET and 16 times as heavy as any previous tokamak (more than 5000 t). It will also be equipped with superconducting magnets in order to sustain long plasma pulses (see Fig. ...

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... previously mentioned, the central solenoid is the key component that will induce a powerful current in the ITER plasma and maintain it during long plasma pulses. In JET, the solenoid generates plasma currents of about 5 MA in plasma pulses lasting up to 60 s (see Fig. 1.11 on p. 10). Because the plasma volume in ITER will be 8 times higher than in JET, the magnetic energy required from the central solenoid will be much higher as well. It will initiate and sustain a plasma current of 15 MA for durations in the range of 300-500 ...

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... vehicle/manipulator systems operated simultaneously and travelling along the rail, each of which incorporates a telescopic manipulator capable of access- ing all in-vessel areas except the divertor area (see Fig. ...

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... blanket handling gripper mounted on the telescopic manipulator that grips a blanket module and temporarily bolts it to the VV wall (see Fig. ...

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... multi-functional movers (CMM), including a tractor and a set of change- able end-effectors, which implement the radial transport of components along the RH ports (see Figs. 1.22 and 1.23); • two cassette toroidal movers (CTM) that implement the toroidal transport of cas- settes from the RH port to their final assembly location inside the VV (see Fig. ...

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... several dexterous manipulator arms, equipping both CMM and CTM, for tool han- dling and general purpose manipulation (see Fig. ...

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... remote transfer of clean/activated/contaminated in-vessel components between the VV and the HC facility (see Fig. ...

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... docking and un-docking onto the VV or HC docking flange, including alignment features (see Fig. ...

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... current reference design of the CPRHS (see Figs. 1.26 and 1.27) includes the following ...

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... cally (e.g. during planned shutdowns) or on request (e.g. after a plasma disruption with suspected damages) the IVVS probes will be deployed from their storage positions into the plasma chamber, between the divertor outer target and the lower blanket module, in order to perform viewing and metrology tasks on the plasma facing-components (see Fig. ...

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... fixed shield blocks located around the resident guide tube at the level of the stowed scanning probe in order to protect the IVVS from scattered neutrons; • an electrical and optical vacuum feed-through; and • a 4.2 m-long removable cartridge (see Fig. 1.31) that can be extracted from the port extension into a dedicated transfer cask allowing the maintenance, replacement and/or upgrade of the system. The IVVS cartridge is composed of the following ...

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... 3.8 m-long mobile assembly consisting of a scanning probe relying on the amplitude modulation of a coherent single-mode laser to perform viewing and ranging tasks (see Fig. 1.32), a longitudinal trolley travelling linearly on the guide tube from the cartridge towards the VV and a hinged section allowing the rotation of the scanning probe once deployed inside the ...

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... a beam source manipulator mounted on a trolley that includes a mast and a boom (see Fig. ...

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... a beam-line transporter and manipulator system (see Fig. 1.36); ...

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... Maintenance of in-vessel or neutral beam injection components will generally be accom- plished by the replacement of spent components with new or refurbished units. The ac- tivated and contaminated components (divertor cassettes, blanket modules, etc.) will be transported to the HC facility for eventual repair, refurbishment or disposal (see Fig. ...

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... cleaning workstations (see Fig. ...

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... a cold RH test facility (cold RHTF), transferred to the Assembly Hall, including the following full-scale mock-ups (see Fig. ...

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... comprises a number of local controllers providing real-time control of individual equipment. The overall control system is estimated to contain approximately 250 control cubicles. The RH Supervisory Control System (RHCS) integrates these individual control systems together to form a uniform control system operating from the RH control room (see Fig. 1.40), with the exception of IVVS, which is operated from the main control ...

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... impossible. This implied the need for a Multi-Purpose Deployer (MPD) which would be deployed in-vessel in order to perform these additional tasks during a remote maintenance period. The MPD concept is based on an anthropomorphic robotic arm pro- viding a series of roll, pitch and yaw rotations for in-vessel tool or component deployment (see Fig. 1.41). This concept provides full in-vessel coverage from four equatorial-level ports and provides a high payload ...

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... water will leak into the VV and that helium will leak into the cryostat. In order to limit the impact of these leaks on the availability of the ITER machine, a fast solution for leak localisation and repair is required. The Fast Deployment Device (FDD) is expected to deploy a still-to-be-defined leak-detection device from five upper ports (see Fig. 1.42). When stowed, each unit is retracted into a contamination containment enclosure attached to the VV port but is isolated from the vessel by vacuum isolation valves. The system will operate in air or nitrogen at atmospheric pressure and in the absence of a magnetic field. To date, the FDD is not considered part of the RH system (it ...

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... with five identical titanium mod- ules 160 mm in diameter. Each module includes pitch (±45 • in the vertical plane) and yaw (±90 • in the horizontal plane) joints linked with a parallelogram structure (four-bar mechanism) that maintains a vertical yaw joint axis. This combination of elevation and rotation motions gives the robot eight DOF (see Fig. 1.43). With a payload up to 10 kg and a total weight of 150 kg, this polyarticulated arm can be introduced through a narrow port 250 mm in diameter. To cope with the high temperature requirements, all AIA artic- ulations are actuated by embedded electromechanical components qualified up to 120 • C in use and 200 • C when switched off. All ...

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... with the high temperature requirements, all AIA artic- ulations are actuated by embedded electromechanical components qualified up to 120 • C in use and 200 • C when switched off. All the camera's inner electronic components (CCD sensor, zoom, LEDs, etc.) are actively cooled by nitrogen gas to keep the operating tem- perature below 60 • C (see Fig. 1.45). Other diagnostic tools are currently developed for tokamak in-vessel inspection, such as a leak-detection system based on helium sniffing or a compact laser system for carbon codeposited layer characterisation or treatment ...

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... 2008, the AIA equipped with a vision process was qualified after it carried out an inspection (see Fig. 1.46) inside the Tore Supra tokamak (see section 1.1.6), which operates under the same vacuum and temperature conditions as ...

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... a robotic arm composed of five identical modules and a prismatic joint at the base (see Fig. 1.44). Each module is a two-DOF mechanism comprised of two electrical rotary joints and a parallelogram structure that keeps the elevation axis vertical to minimise the cantilever. Each module includes on-board temperature-hardened control electronics qualified up to 120 • C when in use and 200 • C when switched ...

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... a video process designed and assembled by ECA/HYTEC comprising a CCD colour sensor, zooming and rotating capabilities and high-intensity LED ring lights. All its components are actively cooled by nitrogen gas (see Fig. ...

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... must be carefully placed to perform effective RH operations and must allow active directional control; on-board cameras should be able to track the end- effector position in order to ensure that the task remains in the field of view. Figure 1.47 illustrates that suitably setting up the camera's position and direction is important for obtaining a view that provides that operator with as much of an understanding of the remote environment as possible. ...

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... thus launching a reprocessing program for recycling spent nuclear fuel for civilian purposes. This effort was broadly supported by other European countries who, together with Japan, signed up for French reprocessing services in the 1970s. A major argument for reprocessing is that it dramatically reduces the volume of radioactive waste (see Fig. 1.51). Between 1976 and2006, approximately 23,000 t of light water reactor (LWR) fuel were reprocessed in the two reprocessing lines of La Hague. Since 2000, the plant has processed approximately 1100 t annually. Until 2004, almost half the LWR spent-fuel processed at La Hague was owned by foreign ...

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... slave-arm is a six-DOF (five rotary joints and a telescopic mechanism) 4 m-long manipulator (see Fig. 1.52). Its payload capacity is up to 20 kg for 40 kg of its own weight (maximum torques of 1540 Nm and 385 Nm, respectively, for the two main joints). Its transmission is based on gears and screws for the upper part and cables and chains for the lower joints, which makes the whole system very flexible and subject to ...

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... degrees Celsius. To reach this extreme temperature, several heating systems will be available. The Ion Cyclotron Resonance Heating (ICRH) antenna [24] is one of these systems. Since JET is the closest machine to ITER in terms of plasma conditions, it was decided in the 2000s that an ITER-like ICRH antenna would be installed and tested in JET (see Fig. ...

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... 300 kg antenna was transported into the vessel on a sub-frame connected to the RH- articulated boom via a specific end-effector (see Fig. 1.54). The 10 m-long JET RH boom (see Fig. 1.55) has 19 degrees of freedom and can be controlled either from a joystick, a keyboard or using pre-taught sequences of motion. For the rough approach, the tip was moved along smooth trajectories using pre-defined moves, or teach files, and a virtual rail, which avoids stimulating the natural ...

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... 300 kg antenna was transported into the vessel on a sub-frame connected to the RH- articulated boom via a specific end-effector (see Fig. 1.54). The 10 m-long JET RH boom (see Fig. 1.55) has 19 degrees of freedom and can be controlled either from a joystick, a keyboard or using pre-taught sequences of motion. For the rough approach, the tip was moved along smooth trajectories using pre-defined moves, or teach files, and a virtual rail, which avoids stimulating the natural modes of the assembly (except in an ...

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... on the amplitude modulation of a coherent single mode laser transmitted to the target via a rotating prism. The intensity and phase of the light backscattered from the target are detected concurrently and compared to the emitted signal. Greyscale 2D images are obtained from the intensity, while range data is generated from the phase shifting (see Fig. 1.56). In terms of viewing capabilities, the IVVS should provide greyscale 2D images with a normal resolution better than 1 mm for targets in the range 0.5-4 m and better than 3 mm for targets situated up to 10 m. With respect to metrology, the IVVS should be capable of providing range data with a standard deviation of approximately 500 ...

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... order to cope with these perturbations, the UTFUS unit of ENEA carried out a series of parametric tests in 2009-2010 to assess how the IVVS viewing performance was affected by a probe vibrating at low frequencies (frequency < 1 Hz, 1 mm amplitude). To do so, they used the IVVS probe proof-of-principle prototype developed in the early 2000s (see Fig. 1.57) and placed it on an adjustable vibrating table (see Fig. ...

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... carried out a series of parametric tests in 2009-2010 to assess how the IVVS viewing performance was affected by a probe vibrating at low frequencies (frequency < 1 Hz, 1 mm amplitude). To do so, they used the IVVS probe proof-of-principle prototype developed in the early 2000s (see Fig. 1.57) and placed it on an adjustable vibrating table (see Fig. ...

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... vehicle manipulator system was adopted as the most suitable RH equipment to handle these heavy modules with high positioning accuracy (±2 mm at about 5.5 m). The IVT consists of a vehicle travelling along a rail deployed inside the vessel. It entails a telescopic manipulator capable of accessing all in-vessel areas except the divertor area (see Fig. ...

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... the load conditions during removal are based on the opposite load conditions encountered during module installation. Figure 1.64 illustrates the difference between the unloaded and loaded end-effector positions (A and B, respectively). The measured deflection was, in Cartesian space, ∆x = 5.3 mm, ∆y = 82.5 mm and ∆z = 69.8 ...

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... proposed methodology allowed a decrease in the amplitude of the dynamic deflection during module installation from 4.66 mm to nearly zero (see Fig. ...

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... 2003, JAERI proposed a new sensor-based control [32], which combines distance sensors for rough positioning and contact sensors for fine positioning (see Fig. 1.63). Indeed, contact sensors have a high potential for fine positioning as well as simplicity and high reliability, whereas the positioning accuracy of distance sensors is generally affected by surface conditions and reflections. Consequently, a combination of laser-type distance sensors and three-axes strain-gauge contact sensors was ...

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... of the shapes to be tracked (two circular gripping holes) made the VS highly inaccurate. To cope with these issues, a stereovision system was adopted. It had the additional advantage of providing depth information. JAERI also identified illumination as a major problem and subsequently mounted a ring light concentrically with the camera (see Fig. ...

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... IVT machine vision system was tested using the full-scale manipulator prototype and a dummy blanket module [33] (see Fig. 1.66). For this specific test, two inexpensive commercial off-the-shelf CCD cameras (Flea2 by Point Grey Research Inc. [34]) with resolutions similar to rad-tolerant tube cameras (640×480) were used. OpenCV was used as the real-time computer vision function library to analyse the pictures. The experiment demonstrated positive results ...

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... (Flea2 by Point Grey Research Inc. [34]) with resolutions similar to rad-tolerant tube cameras (640×480) were used. OpenCV was used as the real-time computer vision function library to analyse the pictures. The experiment demonstrated positive results since positioning and angular accuracies of 1 mm and 0.05 • , respectively, were achieved (see Fig. 1.68). ...

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... first robotic arm used in orbit was the Space Shuttle Remote Manipulator System (SRMS), which was known as Canadarm because it was developed by the Canadian Space Agency (CSA) (see Fig. 1.69). The SRMS is a 15 m-long six-DOF mechanical arm that is deployed from the payload bay of the space shuttle in order to manoeuvre and release a payload [35]. Since its first use in 1981 (space shuttle mission STS-2), it has been used more than 100 times during space shuttle flights for various tasks such as payload deploy- ment, ...

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... Space Station Remote Manipulator System (SSRMS), also known as Canadarm 2, was the next generation of space remote manipulator systems designed for specific use on the ISS (see Fig. 1.71) [37]. Launched in 2001, the SSRMS played a key role in the construction and maintenance of the ISS, both by assisting astronauts during extravehicular activities and by receiving payloads from the space shuttle's SRMS. The 17.6 m-long seven-DOF SSRMS can be equipped with the Special-Purpose Dexterous Manipulator (SPDM) to ...

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... European Space Agency (ESA) will also provide a robotic manipulator system, the European robotic arm (ERA), for the ISS ( In Japan, the Japanese Experiment Module Remote Manipulator System (JEMRMS), shown in Fig. 1.71, has been developed by the Japan Aerospace Exploration Agency (JAXA) [39]. The JEMRMS consists of two components: a 9.9 m-long six-DOF main arm and a shorter 1.9 m-long six-DOF arm for fine tasks; together, the two arms form a serial 12-DOF macro-micro manipulator system. After installation, the arm will be used to handle experiment ...

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... a robot system comprising a relatively short arm for fine manipulation mounted on a larger arm for coarse positioning is called a macro-micro manipulator system. The SSRMS equipped with the SPDM and the JEMRMS are relevant examples. In these systems, the base body is the interface between the macro arm's end- point and the micro arm's root ( Fig. 1.72(a)). When the macro arm is locked after operating, the system is considered to be a flexible-based manipulator ( Fig. ...

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... is called a macro-micro manipulator system. The SSRMS equipped with the SPDM and the JEMRMS are relevant examples. In these systems, the base body is the interface between the macro arm's end- point and the micro arm's root ( Fig. 1.72(a)). When the macro arm is locked after operating, the system is considered to be a flexible-based manipulator ( Fig. ...

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... simple method to estimate the capture delay relies on the exchange of timestamps. During operations, timestamps are exchanged between the real-time high-sampling rate controller and the non-real-time supervisor, whose sampling rate is aligned to the camera framerate. This principle is illustrated by Fig. 3.10. Each controller cycle begins with the current timestamp n c being sent to the supervisor. This timestamp is stored in a buffer and is used only if the application on the supervisor side asks for it. Otherwise, the buffer is overwritten at the next cycle. After the timestamp is sent, a second buffer is read to determine if new visual ...

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... all the more because this signal has been obtained from a non-irradiated sensor. In addition, the signal resulting from the visual tracking is far cleaner. However, note that an important delay (of 1/10 s) exists between these two graphs. That this delay is variable explains why the sinusoidal oscillation seen by the camera is so distorted. Fig. 4.15(c) illustrates the proposed algorithm's ability to properly predict a clean vibration measurement that is synchronised with the physical phenomenon. It is sampled at the controller sampling rate; the crosses indicate only the visual data refreshment ...

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... delay time variability is highlighted in Figs. 4.16 and 4.17, which show how the cross-correlation function between the accelerometer signal and visual data enables an accurate estimation of the capture delay. Note that in the selected period of time the capture delay is comprised between 70 ms and 76 ms. During the whole test, its mean value was ¯ ∆ = 74 ms while its standard deviation was σ ...

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... results could eventually be extended to higher-level tasks. Using suitable algorithms would allow the extraction of not only corner features but also more complex geometric shapes (see Fig. 5.1). It would not only make it possible to reject perturbations but also to follow trajectories defined by the in-vessel components themselves, such as the edges between two blanket modules. That would be vision-based trajectory ...