scholarly journals Development of n-DoF Preloaded Structures for Impact Mitigation in Cobots

2018 ◽  
Vol 10 (5) ◽  
Author(s):  
S. Seriani ◽  
P. Gallina ◽  
L. Scalera ◽  
V. Lughi
Keyword(s):  
Three Dimensional ◽  
Impact Loads ◽  
Single Degree Of Freedom ◽  
Impact Mitigation ◽  
Single Degree ◽  
Future Developments ◽  
Core Issue ◽  
Comprehensive Framework ◽  
Peculiar Behavior ◽  
Good Agreement

A core issue in collaborative robotics is that of impact mitigation, especially when collisions happen with operators. Passively compliant structures can be used as the frame of the cobot, although, usually, they are implemented by means of a single-degree-of-freedom (DoF). However, n-DoF preloaded structures offer a number of advantages in terms of flexibility in designing their behavior. In this work, we propose a comprehensive framework for classifying n-DoF preloaded structures, including one-, two-, and three-dimensional arrays. Furthermore, we investigate the implications of the peculiar behavior of these structures—which present sharp stiff-to-compliant transitions at design-determined load thresholds—on impact mitigation. To this regard, an analytical n-DoF dynamic model was developed and numerically implemented. A prototype of a 10DoF structure was tested under static and impact loads, showing a very good agreement with the model. Future developments will see the application of n-DoF preloaded structures to impact-mitigation on cobots and in the field of mobile robots, as well as to the field of novel architected materials.

scholarly journals Blast Simulator Testing of Structures: Methodology and Validation

2011 ◽  
Vol 18 (4) ◽  
pp. 579-592 ◽  
Author(s):  
T. Rodriguez-Nikl ◽  
G.A. Hegemier ◽  
F. Seible
Keyword(s):  
High Speed ◽  
Field Tests ◽  
Detailed Model ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Explosive Materials ◽  
Blast Effects ◽  
Resistance Function ◽  
The University ◽  
Good Agreement

The blast simulator at the University of California, San Diego is a unique tool for conducting full-scale testing of blast effects on structures without the use of explosive materials. This blast simulator uses high speed hydraulic actuators to launch specially designed modules toward the specimen, thereby imparting impulse in a blast-like manner. This method of testing offers numerous advantages over field tests with actual explosives, including cost, turn-around time, repeatability, and a clear view of the progression of damage in the specimen. The viability of this method is established by comparing results obtained in the blast simulator with results obtained with actual explosives. The process by which the impulse is imparted to the specimen is then described by a detailed model based on the equivalent single degree of freedom method. Impulse calculated by the model is found to be in good agreement with the experimentally recorded values. Calculated impulse is found to be relatively insensitive to assumptions made about the specimen's resistance function (often not well known before a test) implying that the model can be used with confidence in designing an experimental study.

Dynamics of a Free Play Type of Nonlinearity System Under Deterministic and Random Excitations

1995 ◽  
Author(s):  
Ismail I. Orabi
Keyword(s):  
Gaussian White Noise ◽  
Harmonic Excitation ◽  
Free Play ◽  
Nonlinear Structures ◽  
Single Degree Of Freedom ◽  
Linearization Technique ◽  
Single Degree ◽  
Nonlinear Responses ◽  
Digital Simulations ◽  
Good Agreement

Abstract The dynamics of nonlinear structures under harmonic and random excitations is studied. The harmonic excitation is modeled by periodic loadings while the random excitations is modeled by segments of stationary Gaussian white noise processes. Transient responses of a single-degree-of-freedom model is studied to illustrate the characteristic of nonlinear responses. A free play type of nonlinearity is considered. The effects of nonlinearities on the overall dynamics of structure is investigated. The linearization technique is used to calculate the response statistics. To check the accuracy of the linearization technique, the results are compared with Monte-Carlo digital simulations and good agreement are observed.

Phase Space Interpretation and Stability Analysis of a Self Excited, Friction Damped Turbine Airfoil

1997 ◽  
Author(s):  
E. Pesheck ◽  
C. Pierre
Keyword(s):  
Stability Analysis ◽  
Phase Space ◽  
Asymptotic Methods ◽  
Three Dimensional ◽  
Space Representation ◽  
Free Response ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Dimensional Phase Space ◽  
Phase Space Representation

Abstract The free response motion of a self excited, friction damped, single-degree of freedom, turbine airfoil model is determined utilizing both exact and asymptotic methods. A three-dimensional phase space representation is used to examine the system’s global stability, and to further intuitive understanding of the system dynamics. Conclusions are reached regarding the validity and application of stability predictions through comparison of approximate and exact solutions.

FOLDING OF A TYPE OF DEPLOYABLE ORIGAMI STRUCTURES

2012 ◽  
Vol 12 (06) ◽  
pp. 1250054 ◽  
Author(s):  
YAO CHEN ◽  
JIAN FENG
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Jacobian Matrix ◽  
Element Analysis ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Element Simulation ◽  
Rigid Plane ◽  
Configuration Changes ◽  
Good Agreement

Some types of rigid origami possess specific geometric properties. They have a single degree of freedom, and can experience large configuration changes without cut or being stretched. This study presents a numerical analysis and finite element simulation on the folding behavior of deployable origami structures. Equivalent pin-jointed structures were established, and a Jacobian matrix was formed to constrain the internal mechanisms in each rigid plane. A nonlinear iterative algorithm was formulated for predicting the folding behavior. The augmented compatibility matrix was updated at each step for correcting the incompatible strains. Subsequently, finite element simulations on the deployable origami structures were carried out. Specifically, two types of generalized deployable origami structures combined by basic parts were studied, with some key parameters considered. It is concluded that, compared with the theoretical values, both the solutions obtained by the nonlinear algorithm and finite element analysis are in good agreement, the proposed method can well predict the folding behavior of the origami structures, and the error of the numerical results increases with the increase of the primary angle.

A First-Passage Approximation in Random Vibration

1971 ◽  
Vol 38 (1) ◽  
pp. 143-147 ◽  
Author(s):  
Ronald L. Racicot ◽  
Fred Moses
Keyword(s):  
Random Vibration ◽  
Numerical Technique ◽  
Joint Probability ◽  
Poisson Processes ◽  
Joint Probability Distribution ◽  
First Passage ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Average Size ◽  
Good Agreement

A numerical technique is described for computing approximate first-passage probabilities for single-degree-of-freedom systems. It is applicable to cases where the joint probability distribution of response at two times can be found. From these distributions, the average size of a clump of consecutive failure crossings is computed. Results are compared to previously published simulation first-passage probabilities and good agreement is found. Examples illustrate applications to Gaussian and filtered Poisson processes.

Design of Cylindrical and Axisymmetric Origami Structures Based on Generalized Miura-Ori Cell

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Yucai Hu ◽  
Haiyi Liang ◽  
Huiling Duan
Keyword(s):  
Three Dimensional ◽  
Design Methods ◽  
Geometric Design ◽  
Degree Of Freedom ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Flat Sheet ◽  
Folded Structure

Origami has shown its potential in designing a three-dimensional folded structure from a flat sheet of material. In this paper, we present geometric design methods to construct cylindrical and axisymmetric origami structures that can fit between two given surfaces. Due to the symmetry of the structures, a strip of folds based on the generalized Miura-ori cells is first constructed and then replicated longitudinally/circumferentially to form the cylindrical/axisymmetric origami structures. In both designs, algorithms are presented to ensure that all vertexes are either on or strictly within the region between the target surfaces. The conditions of flat-foldability and developability are fulfilled at the inner vertexes and the designs are rigid-foldable with a single degree-of-freedom. The methods for cylindrical and axisymmetric designs are similar in implementation and of potential in designing origami structures for engineering purposes, such as foldcores, foldable shelters, and metamaterials.

A Number Synthesis Survey of Three-Dimensional Mechanisms

1965 ◽  
Vol 87 (2) ◽  
pp. 213-218 ◽  
Author(s):  
L. Harrisberger
Keyword(s):  
Practical Importance ◽  
Three Dimensional ◽  
Intensive Study ◽  
Simple Loop ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Number Synthesis ◽  
Space Mechanisms ◽  
Existence Criteria ◽  
Special Space

The applicability and limitations of the present existence criteria for space mechanisms are discussed. The number synthesis technique is applied to the Kutzbach Criterion to identify all the possible simple loop, single degree of freedom space mechanisms which incorporate the known physically realizable pairs. An examination of the 138 kinds of space four-link mechanisms is made within the boundaries of practical realizability to identify the nine kinds of four-link mechanisms which are worthy of intensive study and application. In addition, the practical importance of the several known “special” space mechanisms which exist outside the Kutzbach Criterion is noted.

Kinematic Design of Deployable Structures With Low Actuation Requirements Based on Pop-Up Folding

2021 ◽  
Author(s):  
Eduardo E. Montano ◽  
Edwin A. Peraza Hernandez
Keyword(s):  
Strain Energy ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Kinematic Modeling ◽  
Deployable Structures ◽  
Design Algorithm ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Area And Volume

Abstract This paper presents the kinematic modeling and design of deployable structures inspired by pop-up books. These pop-up structures can exhibit large changes in area and volume through deployment motion that resembles opening the pages of a book. The pop-up structures have a modular topology and are formed by multiple parallelepiped units, here termed as pop-up units. The analysis of the kinematics of single pop-up units and assemblies of these that form larger structures is presented. An algorithm that integrates multiple pop-up units to form structures that approximate two-dimensional and three-dimensional target shapes when deployed is subsequently devised. The algorithm ensures that the structures formed by the assemblies of multiple pop-up units retain the single degree of freedom of a pop-up unit. The stored strain energy of these structures, which can provide the means to deploy them in practice, is also analyzed. Finally, various examples showing the applicability of the design algorithm in the synthesis of pop-up structures that approximate a diverse set of two-dimensional and three-dimensional target shapes are provided. The pop-up structures can be applied to a large spectrum of applications that need extensive deployment from small volumes while requiring a low number of degrees of freedom. These applications may include aerospace structures and MEMS.

Nonlinear Structural Damping Described by the Masing Model and the Method of Slowly Varying Amplitude and Phase

1995 ◽  
Author(s):  
Ulrich Gutzer ◽  
Wolfgang Seemann ◽  
Peter Hagedorn
Keyword(s):  
Standing Waves ◽  
Free Vibrations ◽  
Dissipated Energy ◽  
Continuous Systems ◽  
Structural Damping ◽  
Single Degree Of Freedom ◽  
One Dimensional ◽  
Single Degree ◽  
Explicit Formulae ◽  
Good Agreement

Abstract In this paper we investigate vibrations of discrete and continuous systems with damping of the MASING type. For free vibrations the method of the slowly varying amplitude and phase shows good agreement with numerical results, especially if the damping is small. The equations resulting from this method allow a faster identification of the parameters of a physical model. First, a single degree of freedom system is studied. Explicit formulae are obtained for the changing amplitude and frequency. The results are useful since damping laws of the type under consideration are well suited to describe the energy dissipation in a variety of real structures. In the second part we consider a one dimensional continuum with a distributed MASING model. An explicit formula is found for the dissipated energy per cycle and wavelength in standing waves.

Low-G Electrostatically Actuated Resonant Switch

2012 ◽  
Author(s):  
Abdallah Ramini ◽  
Mohammad I. Younis ◽  
Quang T. Su
Keyword(s):  
Experimental Data ◽  
Response Curves ◽  
Single Degree Of Freedom ◽  
Electrostatically Actuated ◽  
Single Degree ◽  
Earthquake Detection ◽  
Switching Action ◽  
Simulation Results ◽  
Resonant Switch ◽  
Good Agreement

This work investigates a new concept of an electrostatically actuated resonant switch (EARS) for earthquake detection and low-g seismic applications. The resonator is proposed to operate close to instability bands of frequency-response curves, where it is forced to pull-in if operated within these bands. By careful tuning, the resonator can be made to enter the instability zone upon the detection of the earthquake signal, thereby pulling-in as a switch. Such a switching action can be functionalized for alarming purposes or can be used to activate a network of sensors for seismic activity recording. The EARS is modeled and its dynamic response is simulated using a nonlinear single degree of freedom model. Experimental investigation is conducted demonstrating the EARS capability of being triggered at small levels of acceleration as low as 0.02 g. Experimental data and simulation results are compared showing good agreement.

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