A new rate-type gradient-dependent viscoplastic approach for stop-and-go strain band propagation. Numercial vs. physical experiments

1998 ◽  
Vol 08 (PR8) ◽  
pp. Pr8-143-Pr8-150 ◽  
Author(s):  
C. Faciu ◽  
A. Molinari ◽  
M. Dablij ◽  
A. Zeghloul
Keyword(s):  
Physical Experiments ◽  
Stop And Go ◽  
Rate Type

scholarly journals Task space adaptation via the learning of gait controllers of magnetic soft millirobots

2021 ◽  
pp. 027836492110218
Author(s):  
Sinan O. Demir ◽  
Utku Culha ◽  
Alp C. Karacakol ◽  
Abdon Pena-Francesch ◽  
Sebastian Trimpe ◽  
...  
Keyword(s):  
Human Body ◽  
Degrees Of Freedom ◽  
Bayesian Optimization ◽  
Small Scale ◽  
Soft Robots ◽  
Modeling And Control ◽  
Walking Gait ◽  
Physical Experiments ◽  
Efficient Learning ◽  
Task Environments

Untethered small-scale soft robots have promising applications in minimally invasive surgery, targeted drug delivery, and bioengineering applications as they can directly and non-invasively access confined and hard-to-reach spaces in the human body. For such potential biomedical applications, the adaptivity of the robot control is essential to ensure the continuity of the operations, as task environment conditions show dynamic variations that can alter the robot’s motion and task performance. The applicability of the conventional modeling and control methods is further limited for soft robots at the small-scale owing to their kinematics with virtually infinite degrees of freedom, inherent stochastic variability during fabrication, and changing dynamics during real-world interactions. To address the controller adaptation challenge to dynamically changing task environments, we propose using a probabilistic learning approach for a millimeter-scale magnetic walking soft robot using Bayesian optimization (BO) and Gaussian processes (GPs). Our approach provides a data-efficient learning scheme by finding the gait controller parameters while optimizing the stride length of the walking soft millirobot using a small number of physical experiments. To demonstrate the controller adaptation, we test the walking gait of the robot in task environments with different surface adhesion and roughness, and medium viscosity, which aims to represent the possible conditions for future robotic tasks inside the human body. We further utilize the transfer of the learned GP parameters among different task spaces and robots and compare their efficacy on the improvement of data-efficient controller learning.

scholarly journals An extended state observer-based full-order sliding mode control for robotic joint actuated by antagonistic pneumatic artificial muscles

2021 ◽  
Vol 18 (1) ◽  
pp. 172988142098603
Author(s):  
Daoxiong Gong ◽  
Mengyao Pei ◽  
Rui He ◽  
Jianjun Yu
Keyword(s):  
Sliding Mode Control ◽  
Sliding Mode ◽  
State Observer ◽  
Extended State Observer ◽  
Artificial Muscles ◽  
Extended State ◽  
Robot System ◽  
Mode Control ◽  
Physical Experiments ◽  
Pneumatic Artificial Muscles

Pneumatic artificial muscles (PAMs) are expected to play an important role in endowing the advanced robot with the compliant manipulation, which is very important for a robot to coexist and cooperate with humans. However, the strong nonlinear characteristics of PAMs hinder its wide application in robots, and therefore, advanced control algorithms are urgently needed for making the best use of the advantages and bypassing the disadvantages of PAMs. In this article, we propose a full-order sliding mode control extended state observer (fSMC-ESO) algorithm that combines the ESO and the fSMC for a robotic joint actuated by a pair of antagonistic PAMs. The fSMC is employed to eliminate the chattering and to guarantee the finite-time convergence, and the ESO is adopted to observe both the total disturbance and the states of the robot system, so that we can inhibit the disturbance and compensate the nonlinearity efficiently. Both simulations and physical experiments are conducted to validate the proposed method. We suggest that the proposed method can be applied to the robotic systems actuated by PAMs and remarkably improve the performance of the robot system.

scholarly journals Constraint and Mobility Change Analysis of Rubik’s Cube-inspired Reconfigurable Joints and Corresponding Parallel Mechanisms

2020 ◽  
Vol 33 (1) ◽  
Author(s):  
Duanling Li ◽  
Pu Jia ◽  
Jiazhou Li ◽  
Dan Zhang ◽  
Xianwen Kong
Keyword(s):  
Parallel Mechanism ◽  
Unique Feature ◽  
Theoretical Method ◽  
Geometric Constraint ◽  
Parallel Mechanisms ◽  
Change Analysis ◽  
Application Range ◽  
And Topology ◽  
Physical Experiments ◽  
Underlying Principle

Abstract The current research of reconfigurable parallel mechanism mainly focuses on the construction of reconfigurable joints. Compared with the method of changing the mobility by physical locking joints, the geometric constraint has good controllability, and the constructed parallel mechanism has more configurations and wider application range. This paper presents a reconfigurable axis (rA) joint inspired and evolved from Rubik's Cubes, which have a unique feature of geometric and physical constraint of axes of joint. The effectiveness of the rA joint in the construction of the limb is analyzed, resulting in a change in mobility and topology of the parallel mechanism. The rA joint makes the angle among the three axes inside the groove changed arbitrarily. This change in mobility is completed by the case illustrated by a 3(rA)P(rA) reconfigurable parallel mechanism having variable mobility from 1 to 6 and having various special configurations including pure translations, pure rotations. The underlying principle of the metamorphosis of this rA joint is shown by investigating the dependence of the corresponding screw system comprising of line vectors, leading to evolution of the rA joint from two types of spherical joints to three types of variable Hooke joints and one revolute joint. The reconfigurable parallel mechanism alters its topology by rotating or locking the axis of rA joint to turn all limbs into different phases. The prototype of reconfigurable parallel mechanism is manufactured and all configurations are enumerated to verify the validity of the theoretical method by physical experiments.

scholarly journals A thermodynamic approach to rate-type models in deformable ferroelectrics

2020 ◽  
Author(s):  
Claudio Giorgi ◽  
Angelo Morro
Keyword(s):  
Free Energy ◽  
Electric Field ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Energy Models ◽  
Polarization Electric Field ◽  
Field Plane ◽  
Vector Valued ◽  
Rate Type ◽  
Hysteretic Properties

AbstractThe purpose of the paper is to establish vector-valued rate-type models for the hysteretic properties in deformable ferroelectrics within the framework of continuum thermodynamics. Unlike electroelasticity and piezoelectricity, in ferroelectricity both the polarization and the electric field are simultaneously independent variables so that the constitutive functions depend on both. This viewpoint is naturally related to the fact that an hysteresis loop is a closed curve in the polarization–electric field plane. For the sake of generality, the deformation of the material and the dependence on the temperature are allowed to occur. The constitutive functions are required to be consistent with the principle of objectivity and the second law of thermodynamics. Objectivity implies that the constitutive equations are form invariant within the set of Euclidean frames. Among other results, the second law requires a general property on the relation between the polarization and the electric field via a differential equation. This equation shows a dependence fully characterized by two quantities: the free energy and a function which is related to the dissipative character of the hysteresis. As a consequence, different hysteresis models may have the same free energy. Models compatible with thermodynamics are then determined by appropriate selections of the free energy and of the dissipative part. Correspondingly, major and minor hysteretic loops are plotted.

scholarly journals Acoustic Emission Characteristics and Joint Nonlinear Mechanical Response of Rock Masses under Uniaxial Compression

Energies ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 200
Author(s):  
Zhongliang Feng ◽  
Xin Chen ◽  
Yu Fu ◽  
Shaoshuai Qing ◽  
Tongguan Xie
Keyword(s):  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Inclination Angle ◽  
Failure Modes ◽  
Strain Curve ◽  
Particle Flow Code ◽  
Rock Masses ◽  
Physical Experiments ◽  
Inclination Angles ◽  
Joint Inclination

The joint arrangement in rock masses is the critical factor controlling the stability of rock structures in underground geotechnical engineering. In this study, the influence of the joint inclination angle on the mechanical behavior of jointed rock masses under uniaxial compression was investigated. Physical model laboratory experiments were conducted on jointed specimens with a single pre-existing flaw inclined at 0°, 30°, 45°, 60°, and 90° and on intact specimens. The acoustic emission (AE) signals were monitored during the loading process, which revealed that there is a correlation between the AE characteristics and the failure modes of the jointed specimens with different inclination angles. In addition, particle flow code (PFC) modeling was carried out to reproduce the phenomena observed in the physical experiments. According to the numerical results, the AE phenomenon was basically the same as that observed in the physical experiments. The response of the pre-existing joint mainly involved three stages: (I) the closing of the joint; (II) the strength mobilization of the joint; and (III) the reopening of the joint. Moreover, the response of the pre-existing joint was closely related to the joint’s inclination. As the joint inclination angle increased, the strength mobilization stage of the joint gradually shifted from the pre-peak stage of the stress–strain curve to the post-peak stage. In addition, the instantaneous drop in the average joint system aperture (aave) in the specimens with medium and high inclination angles corresponded to a rapid increase in the form of the pulse of the AE activity during the strength mobilization stage.

scholarly journals Development of a Smartphone-Based University Library Navigation and Information Service Employing Wi-Fi Location Fingerprinting

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 432
Author(s):  
Guenther Retscher ◽  
Alexander Leb
Keyword(s):  
Performance Improvement ◽  
Low Cost ◽  
Information Service ◽  
Raspberry Pi ◽  
University Library ◽  
Stop And Go ◽  
Promising Solution ◽  
Localization Performance ◽  
The University ◽  
Suitable Location

A guidance and information service for a University library based on Wi-Fi signals using fingerprinting as chosen localization method is under development at TU Wien. After a thorough survey of suitable location technologies for the application it was decided to employ mainly Wi-Fi for localization. For that purpose, the availability, performance, and usability of Wi-Fi in selected areas of the library are analyzed in a first step. These tasks include the measurement of Wi-Fi received signal strengths (RSS) of the visible access points (APs) in different areas. The measurements were carried out in different modes, such as static, kinematic and in stop-and-go mode, with six different smartphones. A dependence on the positioning and tracking modes is seen in the tests. Kinematic measurements pose much greater challenges and depend significantly on the duration of a single Wi-Fi scan. For the smartphones, the scan durations differed in the range of 2.4 to 4.1 s resulting in different accuracies for kinematic positioning, as fewer measurements along the trajectories are available for a device with longer scan duration. The investigations indicated also that the achievable localization performance is only on the few meter level due to the small number of APs of the University own Wi-Fi network deployed in the library. A promising solution for performance improvement is the foreseen usage of low-cost Raspberry Pi units serving as Wi-Fi transmitter and receiver.

scholarly journals Autonomes Fahren statt Stop and Go: Vorschläge zur effektiven Gestaltung der deutschen Kurzarbeit

2019 ◽  
Vol 68 (3) ◽  
pp. 252-260
Author(s):  
Almut Balleer ◽  
Britta Gehrke ◽  
Brigitte Hochmuth ◽  
Christian Merkl
Keyword(s):  
Labor Market ◽  
Business Cycle ◽  
Great Recession ◽  
Timely Manner ◽  
Rule Based ◽  
The Great Recession ◽  
Stop And Go ◽  
Time Work ◽  
The Business Cycle ◽  
Short Time

Abstract This article argues that short-time work stabilized employment in Germany substantially during the Great Recession in 2008/09. The labor market instrument acted in timely manner, as it was used in a rule-based fashion. In addition, discretionary extensions were effective due to their interaction with the business cycle. To ensure that short-time work will be effective in the future, this article proposes an automatic facilitation of the access to short-time work in severe recessions. This reduces the likelihood of a too extensive use at the wrong point in time as well as structural instead of cyclical interventions.

A Convex Complementarity Approach for Simulating Large Granular Flows

2010 ◽  
Vol 5 (3) ◽  
Author(s):  
Alessandro Tasora ◽  
Mihai Anitescu
Keyword(s):  
Granular Flow ◽  
Complementarity Problems ◽  
Particle Interaction ◽  
Granular Flows ◽  
Rigid Bodies ◽  
Integration Time ◽  
Frictional Contacts ◽  
Physical Experiments ◽  
Dense Granular Flow ◽  
Number Of Particles

Aiming at the simulation of dense granular flows, we propose and test a numerical method based on successive convex complementarity problems. This approach originates from a multibody description of the granular flow: all the particles are simulated as rigid bodies with arbitrary shapes and frictional contacts. Unlike the discrete element method (DEM), the proposed approach does not require small integration time steps typical of stiff particle interaction; this fact, together with the development of optimized algorithms that can run also on parallel computing architectures, allows an efficient application of the proposed methodology to granular flows with a large number of particles. We present an application to the analysis of the refueling flow in pebble-bed nuclear reactors. Extensive validation of our method against both DEM and physical experiments results indicates that essential collective characteristics of dense granular flow are accurately predicted.

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