Dynamic parameters are crucial for the definition of high-fidelity models of industrial manipulators. However, since they are often partially unknown, a mathematical model able to identify them is ...discussed and validated with the UR3 and the UR5 collaborative robots from Universal Robots. According to the acquired experimental data, this procedure allows for reducing the error on the estimated joint torques of about 90% with respect to the one obtained using only the information provided by the manufacturer. The present research also highlights how changes in the robot operating conditions affect its dynamic behavior. In particular, the identification process has been applied to a data set obtained commanding the same trajectory multiple times to both robots under rising joints temperatures. Average reductions of the viscous friction coefficients of about 20% and 17% for the UR3 and the UR5 robots, respectively, have been observed. Moreover, it is shown how the manipulator mounting configuration affects the number of the base dynamic parameters necessary to properly estimate the robots’ joints torques. The ability of the proposed model to take into account different mounting configurations is then verified by performing the identification procedure on a data set generated through a digital twin of a UR5 robot mounted on the ceiling.
Digital models of industrial and collaborative manipulators are widely used for several applications, such as power-efficient trajectory definition, human–robot cooperation safety improvement, and ...prognostics and health management (PHM) algorithm development. Currently, models with simplified joints present in the literature have been used to evaluate robot macroscopic behavior. However, they are not suitable for the in-depth analyses required by those activities, such as PHM, which demand a punctual description of each subcomponent. This paper aims to fill this gap by presenting a high-fidelity multibody model of a UR5 collaborative robot, containing an accurate description of its full dynamics, electric motors, and gearboxes. Harmonic reducers were described through a translational equivalent lumped parameter model, allowing each constitutive element of the reducer to have its decoupled dynamics and mating forces through non-linear penalty contact models. To conclude, both the mathematical model and the real robot on a test rig were tested with a set of different trajectories. The experimental results highlight the ability of the proposed model to accurately replicate joint angular rotation, speed and torques in a wide range of operational scenarios. This research provides the basis for the development of a model-based PHM-oriented framework to carry out detailed and advanced analyses on the effects of manipulator degradations.
Performance studies of RPC detectors operated with C2H2F4 and CO2 gas mixtures Rigoletti, Gianluca; Guida, Roberto; Mandelli, Beatrice
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
April 2023, 2023-04-00, Letnik:
1049
Journal Article
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Resistive Plate Chambers detectors are largely employed at the CERN LHC experiments thanks to their excellent trigger performances and contained costs. They are operated with a gas mixture made of ...90%–95% of C2H2F4, that provides a high number of ion–electron pairs, about 5% of i-C4H10, that ensures the suppression of photon-feedback effects, and 0.3% of SF6, used as an electron quencher to further operate the detector in streamer-free mode. C2H2F4is known to be a Greenhouse gas, with a global warming potential (GWP) of 1430. CERN has identified several strategies to reduce the consumption of greenhouse gas emissions from particle detectors at LHC experiments. One research line is focused on the study of alternatives to C2H2F4. In this context, a conservative approach for the next years of LHC operation could be to focus on reducing the GWP of the RPC gas mixture by only adding CO2 and not using new gases, whose effects on detector long-term operation have to be studied. The RPC performance with standard gas mixture with the addition of 30%–50% of CO2 (and SF6 concentration between 0.3 and 0.9%) were studied both in laboratory set-up and at the CERN Gamma Irradiation Facility in presence of muon beam and gamma background radiation. Encouraging results were obtained showing that the addition of CO2 to the standard gas mixture can represent a mid-term solution to reduce emissions and lower operational costs by keeping stable detector performance and safe long-term operation.
Resistive Plate Chambers (RPC) are largely employed at CERN LHC experiments thanks to their excellent trigger and timing performances. High Pressure Laminates (HPL) RPCs are operated with a gas ...mixture made of about 95% of C2H2F4, 5% of i-C4H10 and 0.3% of SF6. Both C2H2F4 and SF6 are known to be Greenhouse Gases (GHG), with a global warming potential of 1430 and 22800 respectively. Due to leaks at the detector level, RPCs accounted for about 87% of total GHG emissions from particle detectors at CERN during LHC Run 2. CERN has elaborated several strategies to reduce its GHG emissions and align with the European regulation on fluorinated gases. One strategy consists in the study of alternatives gases for particle detectors, with a particular focus on alternatives to R-134a and SF6. An experimental setup was designed to study RPC performances with eco-friendly gas mixture first with cosmic muons, where several gas mixtures could be tested. Few gas mixtures were then selected and a dedicated setup was installed at the Gamma Irradiation Facility of CERN to characterize detector performance with LHC-like background radiation and muon beam. Results with RPCs operated with lower GWP gas mixtures are presented in this work.
The Resistive Plate Chamber (RPC) detectors are extensively used worldwide and at CERN LHC experiments thanks to their excellent time resolution and low cost. RPCs are often operated with a ...humidified gas mixture made of C2H2F4, SF6 and i-C4H10. Unfortunately, C2H2F4 and SF6 are greenhouse gases (GHGs) with a global warming potential (GWP) of 1430 and 22800 respectively and they are subject to a phase-down policy in Europe (EU F-gas regulation). It is therefore foreseeable that F-gases availability would be uncertain for the future and their price could raise possibly making gas detectors operation very costly. The reduction of GHG emissions is an objective of paramount importance for CERN and four different strategies have been identified to achieve it. One of these strategies is based on the use of gas recirculation systems. This solution is already implemented in all gas systems supplying gaseous mixtures to the CERN LHC detectors. These recirculation systems are complex and sophisticated apparatus for big detector volumes (tens to hundreds of m3) that extend from surface to underground cavern and they are controlled through an industrial Programmable Logic Controller (PLC). Their cost is considerable and therefore they are used for large detector apparatus. In order to cope with the increase of small experiments and detector facilities, the CERN gas team has developed two new portable gas recirculation systems at affordable cost. The first gas recirculation unit can be used for several detectors connected in series or parallel flushed with hundreds of liters per hour. It is controlled though a small PLC and it can regulate detector pressure at the level of the mbar. Some of these gas recirculation systems are already in use since several years at CERN GIF++ facility for CSC, GEM and RPC detectors. A second gas recirculation unit has been developed for laboratory purpose where one or two detectors are flushed with few liters per hour. In this case, the unit has to be very cheap and user-friendly in order to allow an easy operation from the final user. Both portable gas recirculation systems can be easily adapted for the different types of detector systems and set-ups thanks to their low price, flexibility and user-friendly operation. An overview of the LHC, medium and small gas recirculation systems will be given in this contribution.
Resistive Plate Chambers (RPC) are gaseous detectors employed at CERN LHC experiments thanks to their trigger performance, timing capabilities and contained production costs. High Pressure Laminate ...RPCs are operated with a three-component gas mixture, made of 90%–95% of C2H2F4, around 5% of i-C4H10 and 0.3% of SF6. Due to the presence of leaks at detector level and to the greenhouse characteristics of C2H2F4 and SF6, RPCs in ATLAS and CMS were accounting for about 87% of CO2 equivalent emissions during LHC Run 2. The addition of some amount of CO2 into the RPCs gas mixture was explored as a possible short-to-medium term solution to lower the total greenhouse gases emissions and reduce the usage of C2H2F4. A dedicated data taking campaign was performed at the Gamma Irradiation Facility at CERN, where RPCs detectors performance were studied with muon beam and gamma background. The detectors were operated with the addition of 30% and 40% of CO2 to the standard gas mixture, together with an increased fraction of SF6. In addition, the performance with two different amount of i-C4H10 were evaluated in order to assess the compatibility of the gas mixture with the CMS and ATLAS requirements. Results on the muon beam performance of RPCs operated with the aforementioned gas mixtures are reported in this work.
As LP steam turbines are requested to work at strong part-loads, LSB stalled and unstalled flutter may occur. Testing on a downscaled steam turbine in T10MW test plant have been carried out to ...measure LSB aggregated damping at low load. Also numerical analysis to predict aerodynamic damping have been performed and results have been compared to experimental data, allowing software tool validation at low load.
One of the primary elements influencing gaseous detector operation is the purity of the gas mixture. Its quality can be undermined by the presence of impurities, already present in the supply gas ...bottles or that could be created in the gas system or from the detector itself. Gaseous detectors operated with Freon-based gas mixtures are subject to the formation of the products of gas molecules break up, occurring when the gas is exposed to high-rate radiation, and enhanced by the presence of high electric field. The release of highly reactive products could be critical as they could either create polymerized deposits or cause material etching, that could compromise detector performance and accelerate aging processes. Moreover, the operation of gas systems with gas recirculation, nowadays common in many gas systems, could worsen the risk of damage due to possible impurities accumulation. This work focuses on the production of fluorine-based impurities in Triple-GEMs detectors operated with CF4-based gas mixture. Detectors are operated in a LHC-like gas system and exposed to high-rate gamma irradiation thanks to the intense 137Cs source provided by the CERN Gamma Irradiation Facility (GIF++). Impurity production is characterized for different detector operation conditions such as gas mixture, working voltage, input flow rate, and irradiation rates. Furthermore, purifier module operation is validated proving its efficiency in removing Fluoride impurities.
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