bluuebunny/crossref_metadata_2025_split huggingface dataset:
Joint Torque Control of a Collaborative Robot Based on Active Disturbance Rejection With the Consideration of Actuator Delay
Authors: Ren Tianyu , Dong Yunfei , Wu Dan , Wang Guolei , Chen Ken 
Published: January 2018

The application of a robot manipulator to the task of parts assembling or collaboration with human workers requires compliant control and intrinsic safety. As a result, it is necessary to exert accurate torque on each joint of the robot through torque sensing and implementing closed-loop joint torque control. This torque servo system is required to track reference torque signals while operating under the influence of motor friction, flexibility of the harmonic drive, noise from the sensor, robot dynamics modelling error and other unknown certainties, resulting in large control efforts.
This paper focuses on providing better compliance control for collaborative robots and proposes a joint torque controller design under development with active disturbance rejection concept. The controller is designed through a novel extended state observer to estimate and compensate for the unmodelled dynamics of the system, nonlinearly variable motor friction, and other uncertainties. Then, a simple proportional differential controller is designed to produce control law. In spite of the remarkable performance in dealing with the mechanical dynamics of the joint actuator, the original controller does not work well with the electrical factor of the joint actuator due to the limited current loop bandwidth in the hardware of motor and driver. To eliminate the detrimental effect of the time delay in current servo, a predictive output method based on a nonlinear tracking differentiator (TD) is used to improve the controller within the framework of active disturbance rejection control. Both simulations and experiments are conducted on a prototype one degree of freedom manipulator with a joint torque sensor. The results demonstrate the enhancement of both the system stability and disturbance rejection performances. Based on the proper treatment of actuator delay, the dominant effect of the motor friction and the flexibility of the harmonic drive has been reduced to insignificance. Moreover, the proposed controller is easy to implement because the explicit dynamic model of the system is not required.
Wheelchair.q05 Final Design: An Innovative Stair-Climbing Wheelchair
Authors: Quaglia Giuseppe , Nisi Matteo , Franco Walter 
Published: January 2018

The presence of architectural barriers in public or private buildings represents an important limit for the mobility of wheelchair users. Although norms promote barriers removal, often a complete accessibility cannot be guaranteed due to economic or technical reasons. In such cases, it is necessary to provide disable people with devices able to autonomously climb architectural barriers or obstacles.
Referring to user needs, some requirements for the wheelchair can be defined. Firstly, the user must use it autonomously. Secondly, it should be easy to use, simple in the mechanical and control systems and with limited weight, dimensions, and cost. Finally, also the appearance of the wheelchair must be adequate to guarantee the user acceptability.
In literature, several solutions of stair-climbing wheelchair are proposed. However, none of these completely satisfies the identified requirements.
In this paper, the Wheelchair.q05, an innovative concept for a stair-climbing wheelchair, is presented. This idea has been developed through several years of researches and functional designs. In detail, this work presents the final design for a constructive and real scale prototype.
The proposed wheelchair, thanks to a smart and hybrid locomotion system, is able to move on flat ground and to climb stairs and sidewalks. A triangular shaped frame with a wheel on each corner, connected through an internal epicyclical transmission system, constitutes the locomotion unit. This system provides the traction both for flat ground and stair motion. Moreover, the wheelchair has an idle track that represents the rear contact point during stair-climbing and guarantees only a stable and regular climbing motion. The wheelchair structure is thus constituted by the following functional elements: two locomotion units, the track, the seat and a couple of pivoting wheels connected to floating arms that represents the rear support during flat ground motion and during sidewalks overcoming.
Through a kinematic synthesis, the optimal layout has been defined and the mechanisms that connect the functional elements with the frame have been designed. These mechanisms allow controlling the wheelchair reconfiguration that is necessary to adapt the vehicle to different working conditions.
Moreover, attention has been paid to the user comfort. Thanks to the introduction of a mechanism that controls the seat orientation, the oscillations generated by the motion on stair are compensated and a regular trajectory is guaranteed for the user center of mass.
General Integral Equations and Bounds of the Effective Moduli of Random Structure Composites
Authors: Buryachenko Valeriy A. 
Published: January 2018

One considers a linear elastic random structure composite material (CM) with a homogeneous matrix. The idea of the effective field hypothesis (EFH, H1) dates back to Faraday, Poisson, Mossotti, Clausius, and Maxwell (1830–1870, see for references and details [1], [2]) who pioneered the introduction of the effective field concept as a local homogeneous field acting on the inclusions and differing from the applied macroscopic one. It is proved that a concept of the EFH (even if this term is not mentioned) is a (first) background of all four groups of analytical methods in physics and mechanics of heterogeneous media (model methods, perturbation methods, self-consistent methods, and variational ones, see for refs. [1]). New GIEs essentially define the new (second) background (which does not use the EFH) of multiscale analysis offering the opportunities for a fundamental jump in multiscale research of random heterogeneous media with drastically improved accuracy of local field estimations (with possible change of sign of predicted local fields).
Estimates of the Hashin-Shtrikman (H-S) type are developed by extremizing of the classical variational functional involving either a classical GIE [1] or a new one. In the classical approach by Willis (1977), the H-S functional is extremized in the class of trial functions with a piece-wise constant polarisation tensors while in the current work we consider more general class of trial functions with a piece-wise constant effective fields. One demonstrates a better quality of proposed bounds, that is assessed from the difference between the upper and lower bounds for the concrete numerical examples.
Feasibility Study of Different Pseudopotential Multiphase Lattice Boltzmann Methods for Dendritic Solidification
Authors: Nabavizadeh Seyed Amin , Eshraghi Mohsen , Felicelli Sergio D. 
Published: January 2018

The formation of porosity and bubbles during solidification in manufacturing processes like casting or welding of metals has a negative effect on the mechanical properties of the manufactured components. Numerical simulation of this problem is important since the direct observation of the interaction of bubbles with dendrites is limited by the opacity of metals. Therefore, developing a reliable numerical model is essential to predict the mechanical properties of materials after solidification.
The pseudopotential multiphase model is a popular method for simulating multiphase flow using the lattice Boltzmann method. This model and its variations have been used to simulate a variety of problems successfully. However, the original pseudopotential model has some deficiencies, including large spurious current and restriction to model low density and viscosity ratios. Several schemes have been proposed to improve the pseudopotential multiphase model and overcome the limitations, including using a realistic equation of state, introducing a force with higher order of isotropy, introducing a middle-range repulsion force, and implementing the force similarly to the Exact Difference Method (EDM).
The aim of this article is to investigate these various enhancements available for the pseudopotential multiphase model in order to come up with a reliable scheme to simulate motion and interaction of bubbles during dendritic solidification in binary alloys. The proposed model is validated against published literature.
Model-Based Optimal Control of a Small Remotely Operated Vehicle
Authors: Aldana Afanador Andrés Felipe , Esteban Villegas Helio Sneyder , Roa Prada Sebastián 
Published: January 2018

Remotely Operated Vehicles, ROVs, are useful devices that can greatly assist humans in the development deep-sea exploration and underwater tasks. These unmanned vehicles require human intervention for the realization of its underwater jobs and have the ability to carry multiple instruments, sensors and actuators according to the application. There are numerous commercial ROV platforms, ranging from inexpensive to very advanced and costly systems.
Being an underactuated system, one of the most important factors in the development of a ROV is the design of its control system. Depending on the quality of the implemented control strategy, the functioning of the vehicle may or may not fail, or the accuracy with which its assignments are done may be seriously compromised. Different control strategies can be utilized for the stabilization and maneuvering of a ROV. The design of these strategies often require system parameter identification. Appropriate modeling and knowledge about the dynamic behavior of the system is essential for a successful parameter identification. One of the main parameters that must be identified is the drag coefficient of the ROV as it moves in the fluid. This parameter can be either experimentally measured, or estimated using the finite element method, to quantify the forces due to fluid-structure interaction.
This work seeks the design and comparison of different advanced control techniques as applied to a small ROV. A commercial small ROV system has been chosen as the object of study and finite element simulations were carried out to estimate some of its mechanic parameters, using the commercial software COMSOL Multiphysics®. The nonlinear model of the system is developed and linearized to obtain its state space representation. The state space representation of the system is then used in the design of a LQR control system. The comparisons of the responses of the compensated systems allows assessing the suitability of the optimal control strategy for stabilization of ROVs.
Pool Boiling Heat Transfer of Water on Copper Surfaces With Nanoparticles Coating
Authors: Cao Zhen , Preger Calle , Wu Zan , Abbood Sahar , Messing Maria E. , Deppert Knut , Sunden Bengt 
Published: January 2018

Saturated pool boiling heat transfer is investigated experimentally on a copper substrate with copper nanoparticle coatings at atmospheric pressure, in terms of critical heat flux (CHF) and heat transfer coefficient (HTC). Experiments are carried out on the substrate surface with a diameter of 12 mm using DI water as the working fluid. The coating is formed by stacking copper nanoparticles generated by an aerosol method. The aerosol nanoparticles are generated by a spark discharge generator with nitrogen gas as carrier gas and size-selected prior to electrostatic deposition. The thickness of the coating is quantified by the deposition time. In the present study, copper particles with diameter 35± 5 nm are selected, considering better coverage on the surface, while the deposition time is controlled as 4h and 8h, respectively.
The boiling curves and heat transfer coefficient of MS-1 (4h deposition) and MS-2 (8h deposition) were compared with the BS (bare surface). The results show that CHFs of MS-1 and MS-2 are increased by 24% and 36%, respectively compared with the BS, while heat transfer is enhanced as well. High speed visualization tells that the coating provides more active nucleate sites and the hydrophobicity of the coating helps bubbles departure from the surface at low and moderate heat flux. At high heat flux, a hollow well occurs on MSs to supply liquid effectively to avoid dryout. Therefore, CHF and heat transfer are both improved.
Using Acoustic Waves to Modulate Stem Cell Growth and Differentiation
Authors: Maynard Jacqueline A. , Arabiyat Ahmad S. , Elefante Anna , Shearer Lucas , King Eoin , Kwaczala Andrea 
Published: January 2018

During spaceflight, the loss of mechanical loads due to microgravity leads to rapid bone loss, where bone deteriorates at a rate of 1–2% per month, where some astronauts can lose as much as 20% of their skeletal mass in a single expedition [NASA, 2001]. In order to prevent muscle and bone loss, long-term space flight exercise regimes are strictly implemented [Shackleford, 2004]. Current research has demonstrated that mechanical vibrations can help to maintain or improve bone mass [Chan, 2013] and reduce adiposity [Chen, 2015, Sen, 2011] when signals are applied at the appropriate frequency and amplitude.
We have developed an acoustic sound chamber that can apply sound waves to stem cells grown in vitro. Characterization of the culture conditions inside the vibration chamber showed considerable variance across the culture plates where an applied acceleration of 0.6g varied at different spots in a 12-well tissue culture plate from as low as 0.47g to 0.78g. We believe the variance is caused by differences in the rigidity of the culture plates that makes the waves transmit inconsistently through the plastic. We hypothesized acoustic waves would induce osteogenic differentiation when applied to stem cells. We utilized pre-osteoblastic stem cells (MC3T3-E1-Subclone 4) to observe the effects of acoustic waves when applied at 0.3g and 0.6g, compared to non-vibrated controls. Cells were vibrated for 30 minutes a day for either 6 days (n = 24/group) or 12 days (n = 12/group). Cellular changes were characterized by assessing well-by-well cell number by a manual cell count and mineral content by Alizarin Red S staining. Differences between groups were determined using One-Way ANOVA with a post hoc test: Student’s t-test. To assess the effects of the variance across the culture plates, correlative analysis was conducted for well-by-well variation using Regression Analysis. Acoustically vibrated wells had 10x more cells after 6 days and showed more mineralization than non-vibrated wells at both 6 and 12 days. Acoustic waves have the ability to increase cell proliferation and can drive stem cell differentiation towards an osteoblastic lineage, this could lead to therapies that prevent bone loss during spaceflight.
Development of an Innovative Coupling System for Industrial Vehicles: An AGV Oriented Approach
Authors: Pereira Davide , Machado José , Mendonça João Pedro 
Published: January 2018

In this paper, authors explore the analysis and development of a innovative coupling system for industrial vehicles. After an introduction of the topic and the objectives, the advantages for developing such a system are described in detail. Some previously published studies with similar content or conclusions necessary to the understanding of the system under study are also presented.
In order to develop a system more precise than the currently used, the common systems are study in this paper, focusing on four wheeled trailers, varying the coupling system’s rotation center, which can be on the front or rear vehicles. In the commonly used systems the trailers tend to get too close from the rotation center, this means that both trailers have lower trajectory paths and not ideal precision.
Having studied the systems currently used in shop floor, a new coupling system is developed, with the aim of increasing trailers’ trajectory precision and manoeuver options. Two different systems were under study. The first one is to control the trailers steering mechanism, in order to position the trailer in a more precise position. The other system is simply altering the coupling system length and rotation centers. By analyzing both results, the solution with the rotation of the rear axle in each trailer guarantees better precision, where the trailers perform a trajectory precision of 100%. However, the solution that better fits the industrial reality is the solution with the alteration of the length and the rotation center of the coupling system. This solution allows less precision but its better in price, cost and implementation effort.
An Integrated Parallelizable Algorithm for Computer Motion Simulation of Large-Sized Bio-Molecular Structures
Authors: Duan Shanzhong (Shawn) 
Published: January 2018

In this paper, an integrated parallelizable algorithm is presented for computer simulation of dynamics of multibody molecular structures in polymers and biopolymers. The algorithm is developed according to an integrated O(N) simulation procedure developed by the author for calculating interatomic forces and forming/solving equations of motion for large-sized bio-molecular structures. Specifically, the simulation procedure is created via a proper integration between a parallelizable multibody molecular simulation method (PMMM) produced by the author and a parallelizable fast multipole method (PFMM). PFMM is utilized for calculation of atomic forces such as Van der Waals and Coulomb attractions between the atomics in the molecular structures. The parallelizable multibody molecular method is used for forming/solving equations of motion of large-sized molecular structures in polymers and biopolymers.
Currently, the calculation of interatomic forces and formation/solution of equations of motion are treated separately by various procedures. For instance, Fast Multipole Method (FMM) and Cell Multipole Method (CMM) are applied for calculating interatomic forces only. Cartesian Coordinate Method (CCM) and Internal Coordinate Molecular Dynamics Method (ICMM) have been introduced independently for forming/solving equations of motion. Though formation and solution of equations of motions, and atomic force calculations are needed for same molecular structure, there is no direct conversation between two group methods.
The proposed algorithm integrates multibody molecular method with fast multipole method in a parallel fashion so that both calculating atomic forces and forming/solving equations of motion can be carried out concurrently in a combined procedure. Computational loads associated with these two simulation tasks then can be divided among sub-chains, and each sub-chain is allocated to a processor on a parallel computing system via a proper integration between PFMM and PMMM. The algorithm can be used on both shared-memory and distributed-memory parallel computational systems. Compared with its counterpart of the integrated O(N) procedure developed by the author before, this algorithm has a computational complexity of O(logN) theoretically (N is number of subsets). The algorithm may find its applications for force calculation and motion simulation associated with large-sized molecular structures of polymers and biopolymers.
Distributed Wind Energy Technologies: High Speed Scalable Epicyclic Gear Train Design
Authors: Menon Shruti Mohandas , Goudarzi Navid 
Published: January 2018

Renewable energies are becoming increasingly favorite for grid connected and standalone applications. With recent concerns over climate change and global warming, the US department of Energy has implemented the use of alternative forms of energy with a target of 30 % energy production using renewable energy by 2025. However, there are certain disadvantages associated with the use of alternative forms such as intermittent energy generation, and high initial investment. This makes renewable energy less reliable leading to reluctance in adoption of these new technologies amongst consumers.
In this work, a high-speed scalable epicyclic gear train design is developed and studied analytically and numerically. An earlier developed Wind Tower Technology (WTT) is used as the case study for the gear train input parameters. Epicyclic gears are known to have advantages over parallel shaft drives in terms of weight, number of components, size, and power loss. These make epicyclic gear train a suitable choice for the WTT and similar concepts where an increase in the output shaft power in areas with low annual mean wind speed is required. The gear train configuration is designed based on the desired output speed and torque values, taking into consideration, the materials and the ease and novelty of machining and manufacturing. This work provides the preliminary analysis and results of developing this gearbox system for the WTT.
Study of Devolatilization Rates of Pine Wood and Mass Loss of Wood Pellets
Authors: Fraga Lelis , Silva João , Soares Delfim F. , Ferreira Manuel , Teixeira Senhorinha F. , Teixeira José Carlos 
Published: January 2018

The present work investigates the mass loss of fine wood biomass using a TA INSTRUMENTS SDT 2960 simultaneous DSC-TGA instrument. The samples of sawdust were classified according to the grain size (< 0.063, 0.063–0.125, 0.125–0.25, 0.25–0.5, 0.5–1, and > 1 mm) and the micro samples were tested with air at a constant heating rate of 10 K/min, from the room temperature up to 800°C. From the results the kinetic properties of the biomass fuel were determined using the 1st order Coats-Redfern equation.
A transient thermal model of the fuel was implemented and was coupled with the biomass kinetic data in order to compute the mass loss of individual pellets and the results were compared with experimental data. The remaining mass, as fix carbon and ashes or unburnt substances, is approximately 3%. The kinetic parameters indicate that the biomass reactivity depends upon the particle size. The heating treatment of wood pellets at constant temperature and different time produced less nitrogen and more carbon and hydrogen for the short period of time.
Haptic-Assisted Virtual Osteotomy As a Training Tool
Authors: Govea-Valladares Eder H. , Medellín-Castillo Hugo I. , García-Zugasti Pedro J. , Limon-Leyva Pablo A. 
Published: January 2018

The maxillofacial surgery is a complex surgical procedure to correct facial malformations located in the head of the patient. A precise and reliable surgical planning is necessary for a successful maxillofacial surgical procedure. The experience and clinical practice of surgeons play a very important role during the surgical procedures. Modern Computer Aided Systems (CAS) have been developed in order to speed up the surgical planning process and to increase the accuracy and reliability of the surgical procedure. However, CAS systems have not been focused on their ability to train and to provide experience and clinical practice to novice surgeons or medical student. In this way CAS systems could be a potential tool to improve the skill of surgeons in order to decrease human errors in the maxillofacial treatment and surgical procedures.
This paper presents an investigation to evaluate the use of virtual reality and haptic systems as a training tool for maxillofacial surgeries, in particular osteotomies procedures. The aim is to evaluate the effect of virtual training on surgeon skills. Thus, a virtual osteotomy system has been developed and is presented. The system is based on an open source computer and programming resources, and makes use of haptic technologies to provide the users with the sense of touch. The virtual osteotomy procedures implemented are based on current surgical orthognathic surgery procedures. Free-form 3D manual cutting of bone is available in the system by means of the haptic device and the force feedback provided to the user, which increases the level of realism of the virtual procedure. The evaluation results show that the haptic-enabled virtual training of osteotomies increases the psychomotor skills of the practitioner, leading to an improved accuracy when carrying out the actual bone cut.