Ahmad Smaili - Academia.edu (original) (raw)

Papers by Ahmad Smaili

A major hindrance to dynamics and control of flexible robot manipulators is the deficiency of its... more A major hindrance to dynamics and control of flexible robot manipulators is the deficiency of its inherent damping. Damping enhancement, therefore, should result in lower vibration amplitudes, shorter settling times, and improvement of system stability. Since the bulk of robot vibrations is attributed to joint compliance, it is a prudent strategy to design joints with sufficient inherent damping. In this article, a method is proposed to estimate critical damping at each joint and identify the joint that should be targeted for design with sufficient built-in damping. The target joint identification process requires that a n-joint robot system is divided into n-subsystems. Subsystem i includes the compliance of joint i and the inertia of the succeeding links, joint mechanisms, and payload. An equivalent single degree of freedom torsional model is devised and the natural frequency and critical damping is evaluated for each subsystem. The estimated critical damping at the joints are used to determine the elastodynamic response of the entire robot system from a model that includes joint compliance, shear deformation, rotary inertia, and geometric stiffness. The response revealed the following conclusion: The joint of the manipulator that would result in lower amplitudes of vibrations and shorter settling times when designed with sufficient built-in damping is the one that renders a subsystem whose natural frequency is the lowest of all subsystems comprising the robot.

A robomech is a crossbreed of a mechanism and a robot arm. It has a parallel architecture equippe... more A robomech is a crossbreed of a mechanism and a robot arm. It has a parallel architecture equipped with more than one end effector to accomplish tasks that require the coordination of many functions. Robomechs with multi degrees of freedom that are based on the 4R and 5R chains have found their way into the literature. This article presents a new, two-degree of freedom robomech whose architecture is based on the 7R chain. The robomech is capable of performing two-function tasks. The features, kinematic constraints, and synthesis procedure of the robomech are outlined and an application example is given.

ASME 1995 Design Engineering Technical Conferences collocated with the ASME 1995 15th International Computers in Engineering Conference and the ASME 1995 9th Annual Engineering Database Symposium, Sep 17, 1995

Noise Control and Acoustics, 1999

This article presents the results of an experimental investigation into the compressional vibrati... more This article presents the results of an experimental investigation into the compressional vibration in an elastic-viscoelastic-elastic three-layer sandwich beam. The fundamental assumption of most of the current mathematical models is that shear deformation results in the largest energy losses for damping while compressional damping is negligible. In this experiment the relative displacements of the base beam and the constraining layer were measured directly to determine the amount of compression in the viscoelastic core. The experiment showed a maximum difference of 25% between the base beam and constraining layer motions. This suggests that neglecting compressional damping in the mathematical model is an erroneous assumption under most circumstances.

<jats:title>Abstract</jats:title> <jats:p>This paper presents Robomech-III, the... more <jats:title>Abstract</jats:title> <jats:p>This paper presents Robomech-III, the third of a new class of linkage arms called robomechs. A robomech is a parallel architecture arm that combines features of a mechanism and a robot devised to perform coordinated multi-function tasks. In particular, Robomech-III is formed from a stack of three planar four-bar (4R) chain. This robomech requires three independently actuated joints to perform a specific triple-function task. The features of Robomech-III are discussed, a synthesis procedure is outlined and an application example is given.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This paper presents and compares two ... more <jats:title>Abstract</jats:title> <jats:p>This paper presents and compares two optimal synthesis techniques for direct application in creating a robomech-II, the second manipulator presented in a new class of linkage arms called Robomcchs. The first optimal synthesis approach will solve the problem as a nonlinear optimization, with a subset of the device parameters described in a linear system and solved directly in a least squares sense. The second approach will employ a least squares optimization using Lagrange Multipliers to contend with nonlinear constraints. In this paper, each optimal synthesis procedure is developed for the general case and then applied to robomcch-II through an example.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this article, a simple, finite ele... more <jats:title>Abstract</jats:title> <jats:p>In this article, a simple, finite element based model for a constrained layer of viscoelastic damping for beams is developed and implemented. The proposed model uses a series of discrete springs and dampers to model the stiffness and damping, and lumped masses to account for the mass of the viscoelastic material while the base material and constraining layers are modeled with a five-node Timoshenko beam element. The accuracy of the model is verified experimentally by testing damped beams with various damping treatment configurations. The results from the proposed model and the experiments are then compared with the Mead-Markus analytical model. Concerns over the accuracy of the Mead-Markus analytical model are raised and discussed. The results demonstrate that the proposed model can predict the fundamental natural frequency of damped beams to within 3.5% or better of the experimentally determined values and that, with the exception of short and intermediate length constraining layers, the damping ratio can be predicted to within about 8% of the experimental values under most circumstances.</jats:p>

Volume 14: Design, Systems, and Complexity, 2019

Four-bar linkages are commonly used mechanisms in various mechanical systems and components. Seve... more Four-bar linkages are commonly used mechanisms in various mechanical systems and components. Several techniques for optimum synthesis of planar mechanisms have been suggested in literature such as the Genetic, Tabu, Simulated Annealing, Swarm-Based and many other algorithms. This paper covers optimization of four-bar mechanisms with path generation tasks using a Dynamic Ant Search (DAS) algorithm. Unlike the Modified Ant Search (MAS) technique where ants unanimously moved between the exploration and exploitation phases, in the proposed algorithm, each ant is free to travel between the two aforementioned phases independent of other ants and as governed by its own pheromone intensity level. Moreover, sensitivity analysis is conducted on the design parameters to determine their corresponding neighborhood search boundaries and thus improve the search while in the exploitation mode. These implemented changes demonstrated a remarkable impact on the optimum synthesis of mechanisms for path...

14th Biennial Conference on Mechanical Vibration and Noise: Vibrations and Dynamics of Robotic and Multibody Structures, 1993

Accurate determination of the dynamic response of high speed flexible manipulators requires that ... more Accurate determination of the dynamic response of high speed flexible manipulators requires that the dynamic model incorporates the influence of joint compliances, in addition to faithfully representing the physical characteristics of the links. A finite element model is herein presented for this purpose. The model is based on a 4-node isoparametric Timoshenko beam element to model the structural characteristics of the links including the effects of shear deformation and rotary inertia. It also includes the influence of the rigid body motion and the time derivatives of the elastic deformations of the manipulator on the characteristic matrices of the system, and accounts for the inertia of the drive units and payload and the damping of externally applied dampers. Quasistatic analysis, modal analysis, and linear and nonlinear vibrational responses of a 3-R planar manipulator are determined by solving the appropriate equations of equilibrium. The results of the analysis revealed that t...

This paper presents an interval analysis based approach for analysis and optimization of planar m... more This paper presents an interval analysis based approach for analysis and optimization of planar mechanisms including the effect of link lengths tolerances and joint clearances. Mathematical models describing the effect of the mechanical errors on the desired output parameters of the mechanism are derived, followed by the commissioning of an ant-gradient based optimization scheme to find the maximum possible deviations in them. A new optimization approach is also devised to design a four bar mechanism with "minimal" sensitivity to clearances and tolerances. An analysis case study is presented and the results are displayed in the form of fuzzy membership functions and compared with results obtained using a similar approach. An example on optimum synthesis of a four-bar mechanism with joint clearances and link tolerances for hybrid exact/approximate points trajectory is also presented. Insights based on the assessment of the results are introduced. INTRODUCTION The inevitable...

In today's competitive markets, engineers face ongoing challenges to produce complex enginee... more In today's competitive markets, engineers face ongoing challenges to produce complex engineering systems with a high level of performance, reliability, value and price. This requires the integration of a number of technologies, which may be accomplished through mechatronics. This paper presents a model for integrating mechatronics education into the Mechanical Engineering curriculum at the American University of Beirut (AUB). A strong component of the model is collaborative, projectbased, learning-by-doing experience in which students realize mechatronics devices, possibly of their own choosing, using various laboratory tools including microcontroller technologies. The implementation strategy involves minimal lecturing, a seamless lab/lecture interface, and just-intime learning. An example of a typical student's project is presented and course assessment is briefly discussed.

Mechanism synthesis requires the use of optimization methods to obtain approximate solution whene... more Mechanism synthesis requires the use of optimization methods to obtain approximate solution whenever the desired number of positions the mechanism is required to traverse exceeds a few (five in a 4R linkage). Deterministic gradient-based methods are usually impractical when used alone because they move in the direction of local minima. Random search methods on the other hand have a better chance of converging to a global minimum. This paper presents a tabu-gradient search based method for optimum synthesis of planar mechanisms. Using recency-based short-term memory strategy, tabu-search is initially used to find a solution near global minimum, followed by a gradient search to move the solution ever closer to the global minimum. A brief review of tabu search method is presented. Then, tabu-gradient search algorithm is applied to synthesize a four-bar mechanism for a 10-point path generation with prescribed timing task. As expected, Tabu-gradient base search resulted in a better solut...

Presented in this paper is a 2-dof robomech that carries two end effectors to perform two functio... more Presented in this paper is a 2-dof robomech that carries two end effectors to perform two functions simultaneously. The robomech has a 7R architecture consisting of two triad wings connected to form two cells. The over-constrained kinematic chain cannot traverse continuous trajectories but may be synthesized to move the end effectors through a set of desired locations. The article presents the architecture of the proposed robomech, establishes its kinematic relations and constraints, and provides dimensional synthesis scheme based on genetic algorithm and gradient search methods. Two case studies are included to demonstrate the applicability of the proposed robomech.

Scopus, 2005

Al-Habaibeh A, 2003, INT J ENG EDUC, V19, P615; Auslander DM, 1996, IEEE-ASME T MECH, V1, P5, DOI... more Al-Habaibeh A, 2003, INT J ENG EDUC, V19, P615; Auslander DM, 1996, IEEE-ASME T MECH, V1, P5, DOI 10.1109-3516.491404; BERGH CT, P 1999 IEEE ASME INT; CARRYER JE, 1995, MECHATRONICS, V5, P787, DOI 10.1016-0957-4158(95)00046-8; Carryer JE, 2003, INT J ENG EDUC, V19, P581; Djordjevich A, 2003, INT J ENG EDUC, V19, P610; Djordjevich A, 2003, INT J ENG EDUC, V19, P544; DURFEE WK, 1995, MECHATRONICS, V5, P775, DOI 10.1016-0957-4158(95)00044-6; *ENG ACCR COMM ACC, 1997, ENG CRIT 2000 CRIT A; Friedman T., 1999, LEXUS OLIVE TREE; Geddam A, 2003, INT J ENG EDUC, V19, P575; Grimheden M, 2003, INT J ENG EDUC, V19, P569; GUPTA SK, 2003, INT J ENG EDUC, V19, P537; Kyura N, 1996, IEEE-ASME T MECH, V1, P10, DOI 10.1109-3516.491405; LEIFER L, 1997, SUITE 210 MODEL GLOB; Meek S, 2003, MECHATRONICS, V13, P1, DOI 10.1016-S0957-4158(01)00058-7; Murray W. R., 1997, J ENG EDUC, V86, P285; Petric J, 2003, INT J ENG EDUC, V19, P597; Ramasubramanian MK, 2003, INT J ENG EDUC, V19, P519; Ressler K, 2003, INT ...

International Journal of Engineering Education, 1993

Scopus, 2005

CHENG HH, 2004, P ASME DES ENG TECHN; Glover F., 1997, TABU SEARCH; KUNJUR, 1997, J APPL MECH ROB... more CHENG HH, 2004, P ASME DES ENG TECHN; Glover F., 1997, TABU SEARCH; KUNJUR, 1997, J APPL MECH ROBOTICS, V4, P8; Pardalos PM, 2002, HDB APPL OPTIMIZATIO; PEREZ A, 2004, P ASME DES ENG TECHN; Pham D.T., 2000, INTELLIGENT OPTIMIZA; PRESS WH, 1989, NUMERICAL RECIPE ART; SANDOR G, 1984, DESIGN MECH, V2; SMAILI A, 2004, P ASME DETC 2004 96; ULAH I, 1997, ASME, V119, P504; YU N, 2002, P ASME DES ENG TECHN

Volume 1C: 16th Biennial Conference on Mechanical Vibration and Noise

This paper presents an analytical investigation on active control of the elastodynamic response o... more This paper presents an analytical investigation on active control of the elastodynamic response of a four-bar (4R) mechanism system using “smart” materials featuring piezoelectric sensor/actuator (S/A) pairs and multivariable optimal control. The 4R mechanism consists of a flexible coupler link, relatively flexible follower link, and a relatively rigid crank. Two thin plate-type piezoceramic S/A pairs are bonded to the flanks of the coupler link at high strain locations corresponding to the first and second vibration modes. Based on the optimal multivariable control theory, a controller which consists of a linear quadratic regulator (LQR) and a Luenberger observer as a state estimator is designed and implemented. As the mechanism changes configuration, its modal characteristics are recalculated, and the controller is redesigned. The dynamic model used for the controller design includes the second and fourth vibration modes of the mechanism system. These modes are predominated by the...

This paper presents analytical and experimental investigations on the elastodynamic control of a ... more This paper presents analytical and experimental investigations on the elastodynamic control of a four-bar mechanism system with a flexible coupler link retrofitted with a collocated piezo electric sensor actuator pair using P-like fuzzy logic control (FLC). A major advantage of FLC is that the controller can be designed without having a model of the system. The four-bar mechanism will be operated close to its fundamental natural frequency, considered to be the major contributor to the system response. Damping the low frequency vibrations is essential to realize light weight flexible mechanisms for viable industrial applications. The viability of the controller design is assessed by comparing the experimental results with those obtained by simulation.

Robotics and Computer-Integrated Manufacturing, 2005

A PC-based, CAD-driven, 5-axis rapid prototyping (RP) robotic system that uses subtractive techno... more A PC-based, CAD-driven, 5-axis rapid prototyping (RP) robotic system that uses subtractive technology is presented. ModelAngelo, as it is called, consists of six integrated hardware and software subsystems. The system utilizes a virtual 3D CAD model to produce a set of commands used to control a 5-axis robotic setup to move the cutting tool, the tip of which is a

Noise Control and Acoustics, 1999

Volume 14: Design, Systems, and Complexity, 2019

14th Biennial Conference on Mechanical Vibration and Noise: Vibrations and Dynamics of Robotic and Multibody Structures, 1993

Scopus, 2005

International Journal of Engineering Education, 1993

Scopus, 2005

Volume 1C: 16th Biennial Conference on Mechanical Vibration and Noise

Robotics and Computer-Integrated Manufacturing, 2005