A method for understanding and digitizing manipulation activities using programming by demonstration in robotic applications

Robots are flexible machines, where the flexibility is achieved, mainly, by the re-programming of the robotic system. To fully exploit the potential of robotic systems, an easy, fast, and intuitive programming methodology is desired. By applying such methodology, robots will be open to a wider audience of potential users (i.e. SMEs, etc.) since the need for a robotic expert in charge of programming the robot will not be needed anymore. This paper presents a Programming by Demonstration approach dealing with high-level tasks taking advantage of the ROS standard. The system identifies the different processes associated to a single-arm human manipulation activity and generates an action plan for future interpretation by the robot. The system is composed of five modules, all of them containerized and interconnected by ROS. Three of these modules are in charge of processing the manipulation data gathered by the sensors system, and converting it from the lowest level to the highest manipulation processes. In order to do this transformation, a module is used to train the system. This module generates, for each operation, an Optimized Multiorder Multivariate Markov Model, that later will be used for the operations recognition and process segmentation. Finally, the fifth module is used to interface and calibrate the system. The system was implemented and tested using a dataglove and a hand position tracker to capture the operator’s data during the manipulation. Four users and five different object types were used to train and test the system both for operations recognition and process segmentation and classification, including also the detection of the locations where the operations are performed.Peer reviewe

Extending the motion planning framework—MoveIt with advanced manipulation functions for industrial applications

MoveIt is the primary software library for motion planning and mobile manipulation in ROS, and it incorporates the latest advances in motion planning, control and perception. However, it is still quite recent, and some important functions to build more advanced manipulation applications, required to robotize many manufacturing processes, have not been developed yet. MoveIt is an open source software, and it relies on the contributions from its community to keep improving and adding new features. Therefore, in this paper, its current state is analyzed to find out which are its main necessities and provide a solution to them. In particular, three gaps of MoveIt are addressed: the automatic tool changing at runtime, the generation of trajectories with full control over the end effector path and speed, and the generation of dual-arm trajectories using different synchronization policies. These functions have been tested with a Motoman SDA10F dual-arm robot, demonstrating their validity in different scenarios. All the developed solutions are generic and robot-agnostic, and they are openly available to be used to extend the capabilities of MoveIt.publishedVersionPeer reviewe

Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA

Second asymptomatic carotid surgery trial (ACST-2): a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86–1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91–1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable. Funding: UK Medical Research Council and Health Technology Assessment Programme

Effect of H 2_{2} /H 2_{2} O ratio on thermally grown chromia scales formed on Ni25Cr alloy in Ar–H 2_{2} –H 2_{2} O atmospheres at 1000°C

The oxidation behaviour of a NiCr-base model alloy with a 25% chromium content is investigated at 1000°C in different low p(O2) environments (Ar –H2–H2O) with the emphasis of how hydrogen andyor water vapour affects the oxidation behaviour of chromia forming alloys \in low p(O2) environments containing H2 and H2O. After equilibrium conditions are achieved, chromia growth on Ni25Cr in low p(O2) type test gases containing H2 and H2O is ruled by the concentration of Cr interstitials available for Cr outward transport. The chromia microstructure, therefore, consists largely of columnar shaped oxide grains. The chromia scales are growing predominantly from oxygen coming from the water vapour in the test gas. H-species may facilitate oxide growth in pores at the metal – oxide interface. H-defects affect the transport properties of chromia scales formed on Ni25Cr. At low p(O2) the H-defects in the chromia scale are compensated by a lower concentration of Cr interstitials. Depending on the nature of the test gas, i.e. p(O2), p(H2) and p(H2O), as well as on the Cr activity in the metal substrate, the growth of chromia scales on NiCr alloys may be featured and shaped differently

Influence of Alloying Elements on the Behavior of Different Ferritic Steels and Candidate Materials for SOFC Interconnect

The efficiency of a solid oxide fuel cell (SOFC) can be improved by using a Ni-mesh between the ferritic steel interconnect and the Ni/YSZ anode. However, interdiffusion processes can lead to internal oxidation within the Ni-mesh and some microstructural changes, i.e., formation of an austenite zone and accelerated formation of σ-phase at the ferrite/austenite interface. These changes may adversely affect the performance of the cell during long-term operation. The present work focused on the influence of certain alloying elements on the overall behavior of the ferritic steel under simulated SOFC operating conditions to define conditions to minimize σ-phase formation without degrading the oxidation resistance and mechanical properties of the steel. The experimental results indicate that decreasing the amount of Cr and adjusting the amount of Nb, Si and W of the steel is a possible way to achieve that goal

Sigma-Phase Formation in High Chromium Ferritic Steels at 650°C

A binary Fe–30 wt.%Cr alloy and corresponding ternary alloys containing manganese, molybdenum or tungsten were studied with respect to σ-phase formation at 650 °C. Although even after 3000 h exposure complete equilibration was not attained, the presence of tungsten and especially molybdenum was found to promote σ-phase formation. More extensive σ-phase formation was observed in the tungsten and especially in the molybdenum-containing alloys than in the binary and manganese-containing alloy. Apparently the bulk free energy decrease driving the nucleation of σ-phase is substantially larger when tungsten or molybdenum are present in the alloy.The presence of a nickel layer, to simulate the contact between ferritic steel interconnects and nickel mesh in a Solid Oxide Fuel Cell (SOFC) results in the formation of an austenitic zone and in accelerated formation of a σ-phase rich layer at the ferrite/austenite interface, due to interdiffusion processes. This interface acts as a highly efficient heterogeneity for the nucleation of σ-phase. The nucleation is enhanced by an increased Cr/Fe-ratio at that interface. Several possible modes for the growth of the σ layer were identified but the available experimental data were not sufficient to distinguish among these. The σ-rich layer, which appears to act as an interdiffusion barrier, is thicker in the case of the binary Fe–Cr and the Fe–Cr–Mn alloy than for the molybdenum- or tungsten-rich alloys.The results show that the stability range of σ-phase is larger than indicated by the presently used thermodynamic data bases