bluuebunny/crossref_metadata_2025 huggingface dataset:
Instability and Failure of Fiber Composites in Compression
Authors: Kyriakides S. , Perry E. J. , Liechti K. M.
Published: April 2009

This paper addresses the uniaxial compressive failure of unidirectional, fiber-reinforced polymer matrix composites. The material that was used in this combined experimental/numerical effort was APC-2/AS4. Failure was found to result in kink bands of distinct widths oriented at an angle to the line of loading. Kink bands were preserved by conducting a series of experiments where failure was confined. Fiber misalignments in the prepreg and from the lamination process were identified as the imperfections that, in conjunction with the nonlinear shear response of the matrix material, essentially govern the formation of zones of localized bending. This, in turn, causes fibers to break and into distinct kink bands. The process was modeled by considering a micro-section of material with wavy fibers under compression. The formulation accounted for material and geometric nonlinearities and various distributions of waviness. It was illustrated that failure is associated with a limit load instability, followed by localized fiber bending which leads to kinking.
Nonlinear Viscoelastic Constitutive Equations for Composites Based on Work Potentials
Authors: Schapery R. A.
Published: April 2009

Constitutive equations for nonlinear viscoelastic composites are discussed. The effects of time-independent inelastic behavior, microcracking and time-dependent residual strains are considered along with the viscoelastic effects that are traditionally associated with the behavior of monolithic and reinforced polymeric materials. Time-independent behavior is discussed first, in which the experimentally observed insensitivity of mechanical work to deformation or load paths is used as the basis for a simplified constitutive model. This representation is then modified to account for time- or rate-effects due to microcrack-like evolution laws. Effects due to broad spectrum nonlinear, viscoelastic behavior of the polymer matrix are reviewed and then used in a generalized constitutive equation with both time-independent and time-dependent effects. Emphasis of this paper is on a thermodynamically-based phenomenological description of deformation response and the use of simplifications based on experimental observations. However, there is a limited discussion of physical mechanisms for nonlinear time-dependent behavior.
Flows of Electrolytes Through Charged Hydrated Biological Tissue
Authors: Lai W. M. , Gu W. , Mow V. C.
Published: April 2009

In this paper, analyses of the flows of water and electrolytes through charged hydrated biologic tissues (e.g., articular cartilage) are presented. These analyses are based on the triphasic mechano-electrochemical theory developed by Lai and coworkers (1991). The problems analyzed are 1-D steady permeation flows generated by a hydraulic pressure difference and/or by an osmotic pressure difference across a finite thickness layer of the tissue. The theory allows for the complete determination of the ion concentration field, the matrix strain field as well as the ion and water velocity field inside the tissue during the steady permeation. For flows generated by a hydraulic pressure difference, the frictional drag induces a compaction of the solid matrix causing the fixed charge density (FCD) to increase and the neutral salt concentration to decrease in the downstream direction. Further, while both ions move downstream, but relative to the solvent (water), the anions (Cl−) move with the flow while the cations (Na+) move against the flow. The theory also predicts a well-known experimental finding that the apparent permeability decreases nonlinearly with FCD. For flows generated by an osmotic pressure difference, first, fluid flow varies with the FCD in a nonlinear and non-monotonic manner. Second, there exists a critical FCD below which negative osmosis takes place.
Viscoelastic Models for Ligaments and Tendons
Authors: Woo S. L.-Y. , Johnson G. A. , Levine R. E. , Rajagopal K. R.
Published: April 2009

Ligaments and tendons serve a variety of important functions in the human body. Many experimental studies have focused on understanding their mechanical behavior, mathematical modeling has also contributed important information. This paper presents a brief review of viscoelastic models that have been proposed to describe the nonlinear and time-dependent behavior of ligaments and tendons. Specific attention is devoted to quasi-linear viscoelasticity (QLV) and to our most recent approach, the single integral finite strain model (SIFS) which incorporates constitutive modeling of microstructural change. An example is given in which the SIFS model is used to describe the viscoelastic behavior of a human patellar tendon.
Influence of Blood Rheology and Vessel Wall Motion on Arterial Fluid Mechanics
Authors: Tarbell John M.
Published: April 2009

Most model studies of arterial fluid mechanics have assumed that blood is a Newtonian fluid and that vessel wall motion driven by the pressure pulse has a small influence on the local velocity and pressure distributions. This paper provides a brief historical review of arterial flow modeling which emphasizes recent developments in non-Newtonian blood analog fluids and studies of the influence of vessel wall motion on local flow fields. It is pointed out that vessel wall motion can have a dominant effect on mean pressure gradient and a significant effect on mean wall shear stress in the aorta.
Lomer Dislocations in Al: Deformation Field Analysis
Authors: Phillips Rob
Published: April 2009

We examine two issues that arise in connection with the description of dislocations in metals. First, the experiments of Mills and Stadelmann on Lomer dislocations in Al are considered in light of atomistic simulations of their core structures. It is shown that the results of such a microscopic analysis are consistent with those obtained earlier on the basis of image simulation. Secondly, we examine these Lomer dislocations using the recently developed technique of Computational Fourier Transform Moire` (CFTM) analysis. This technique allows for a determination of the strain fields near a defect directly from a high-resolution image without the necessity of obtaining a trial structure for the defect, complementing traditional approaches to the interpretation of high-resolution data.
Nanofracture Mechanics Approach to Dislocation Generation and Fracturing
Authors: Cherepanov G. P.
Published: April 2009

As applied to the problem of dislocation nucleation, nanofracture mechanics suggested earlier by the author advances a simpler and more powerful alternative to the Rice-Thomson approach. This alternative is briefly described in the present paper. It is shown that the predictions of nanofracture mechanics differ many times from those of the Rice-Thomson approach. Nanofracture mechanics allows one to approach to the problems with many dislocations (which cannot be solved by the Rice-Thomson approach). Some results on the screw and tear mode crack growth with the generation of many dislocations are brought in the paper. The known ideal plasticity and brittle fracture mechanics solutions are found to follow from the nanofracture mechanics as some limiting cases.
Feedback Control of Turbulence
Authors: Moin Parviz , Bewley Thomas
Published: April 2009

A brief review of current approaches to active feedback control of the fluctuations arising in turbulent flows is presented, emphasizing the mathematical techniques involved. Active feedback control schemes are categorized and compared by examining the extent to which they are based on the governing flow equations. These schemes are broken down into the following categories: adaptive schemes, schemes based on heuristic physical arguments, schemes based on a dynamical systems approach, and schemes based on optimal control theory applied directly to the Navier-Stokes equations. Recent advances in methods of implementing small scale flow control ideas are also reviewed.
Experiments and Simulations on Turbulence Modification by Dispersed Particles
Authors: Eaton John K.
Published: April 2009

Experiments and direct numerical simulations on simple flows have been performed to examine the attenuation of gas-phase turbulence by fine particles. The experiments were performed in a developing boundary layer and in a fully developed channel flow. Both showed significant turbulence attenuation for mass loading ratios greater than 10%. Numerical simulations on homogeneous/isotropic turbulence show similar levels of turbulence attenuation. Both experiments and simulations have demonstrated the importance of preferential concentration in which particles are collected in highly strained regions of the flow. Two-equation models for turbulence attenuation have been found to be inadequate when preferential concentration occurs.
Modelling Dispersed Two-Phase Flows: Closure, Validation and Software Development
Authors: Viollet P. L. , Simonin O.
Published: April 2009

Closure for the Eulerian modelling of two-phase flows have been developed, based upon extensions of the theory of Tchen of the dispersion of particles in homogeneous turbulence. This model has been validated using large-eddy simulation of homogeneous turbulence, jets loaded with particles, and bubbly flows. In addition with k-epsilon model for the continuous phase, and closures for the Reynolds stresses of the dispersed phase, this theory has been implemented in 2D and 3D software solving the Eulerian two-phase equations (Me´lodif in 2D, as a research code, and ESTET-ASTRID in 3D). These softwares have been applied to complex situations of industrial interest.
Constitutive Equations With Internal State Variables for the Inelastic Behavior of Soft Rocks
Authors: Aubertin M. , Gill D. E. , Ladanyi B.
Published: April 2009

The mechanical behavior of soft rocks is quite complex as it may involve a variety of deformation mechanisms. When loaded under compressive stresses at intermediate temperature, such rocks often show a semi-brittle response controlled by dislocations motion and microcracking. Because these two types of physical processes are acting simultaneously, the constitutive equations should involve a coupled approach. In this paper, the authors extend an existing unified model with internal state variables, developed for the ductile regime, to accommodate semi-brittle behavior of low porosity rocks. To do so, a damage variable Dv is introduced into the model. This requires a modification of the kinetic law and the addition of an evolution law for Dv. After presenting some of the main features of soft rocks behavior, the main equations are introduced together with a few attributes of this new model.
A Graphical Technique to Locate the Center of Curvature of a Coupler Point Trajectory
Authors: Pennock Gordon R. , Kinzel Edward C.
Published: April 2009

This paper presents an original technique to locate the center of curvature of the path traced by an arbitrary point fixed in the coupler link of a planar four-bar linkage. The method is purely graphical and the center of curvature; i.e., the center of the osculating circle, can be located in a direct manner with few geometric constructions. The advantage of this technique, compared to the classical approach using the Euler-Savary equation, is that measurements of angles and distances between points are not required. Also, it is not necessary to locate inflection points or draw the inflection circle for the instantaneous motion of the coupler link. The technique is based on the novel concept of a virtual link, which is valid up to, and including, the second-order properties of motion of the coupler link. The virtual link is coincident with the path normal to the coupler curve; i.e., the line connecting the coupler point to the velocity pole of the coupler link. The absolute instant center of the virtual link defines the ground pivot for the link and is, therefore, coincident with the center of the osculating circle. The authors believe that the graphical technique presented in this paper represents an important contribution to the kinematics literature on the curvature of a point trajectory.
Necessary and Sufficient Conditions for Localization of Multiple Robot Platforms
Authors: Zhang Fan , Kumar Vijay , Pereira Guilherme A. S.
Published: April 2009

In this paper, we consider the problem of cooperatively localizing a formation of networked robots/vehicles in SE(2). First, we propose necessary and sufficient conditions to establish when a team of robots with heterogeneous sensors can be localized. We then show how these conditions are analogous to well-known results in the literature on kinematics of planar mechanisms. We show how localization is equivalent to solving a system of nonlinear closure equations. Depending on what sensors are available for each robot, the multirobot formation can be modeled as a sensing graph consisting of vertices representing robots and edges corresponding to sensory information. We establish conditions that must be satisfied by this graph and show how this graph influences estimates of positions and orientations of the robots in a team through experiments and simulations.
Variable Structure Control of a Three-Link SMA-Actuated Robot
Authors: Ashrafiuon Hashem , Eshraghi Mojtaba , Elahinia Mohammad H.
Published: April 2009

A fast, accurate and robust position controller is proposed for a planar three degree of freedom robot arm actuated by rotary Shape Memory Alloy actuators and servomotors. Servomotors are used to actuate the first link and the gripper, while the remaining two links are actuated by a combination of shape memory alloy wires and pulleys. Initially, a model of the robot arm is developed for theoretical controller development. The model combines robot kinematics and dynamics with the SMA wire heat convection, constitutive law, and phase transformation equations. The model is then used to develop several nonlinear position controllers based on the Variable Structure Control, also called sliding mode control. The controller development is of an evolutionary nature starting from a simple switching control based only on position feedback and then adding velocity and integral feedbacks, respectively. Several simulations of the proposed controllers are presented. Several experiments have been performed with a desktop prototype of the robot arm. The experimental results verify the effective and accurate performance of the controllers despite significant modeling inaccuracies and parameter uncertainties.
Force Relationships for an XYZ Micromanipulator With Three Translational Degrees of Freedom
Authors: Jensen Kimberly A. , Lusk Craig P. , Howell Larry L.
Published: April 2009

This paper introduces the force analysis of the XYZ Micromanipulator (XYZM). The XYZM has three independent linear inputs and a positioning platform. The positioning platform remains horizontal throughout its motion and has translation in the x, y, and z directions. The design and displacement analysis for the XYZM was reported previously. This paper concentrates on the input-output force relationships and the derivation of the XYZM kinematic coefficients. Equations for the three versions of the XYZM are reported and sample results provided. Slider displacements of 45 micrometers result in a predicted out-of-plane displacement of 188 micrometers for the rigid-body XYZM and 262 micrometers for the compliant XYZM. This correlates to output force of 286 micronewtons with an input force of 150 micronewtons for the rigid-body XYZM and 261 micronewton output force with an input force of 150 micronewtons for the compliant XYZM.
Nanorobotics Control Design: A Practical Approach Tutorial
Authors: Cavalcanti Adriano , Freitas Robert A. , Kretly Luiz C.
Published: April 2009

The authors present a new approach using genetic algorithms, neural networks and nanorobotics concepts applied to the problem of control design for nanoassembly automation and its application in medicine. As a practical approach to validate the proposed design, we have elaborated and simulated a virtual environment focused on control automation for nanorobotics teams that exhibit collective behavior. This collective behavior is a suitable way to perform a large range of tasks and positional assembly manipulation in a complex 3D workspace. We emphasize the application of such techniques as a feasible approach for the investigation of nanorobotics system design in nanomedicine. Theoretical and practical analyses of control modelling is one important aspect that will enable rapid development in the emerging field of nanotechnology.
Analytic Form Solution of the Direct Position Analysis of the SP-2RS Architectures
Authors: Di Gregorio Raffaele
Published: April 2009

When the actuators are locked, parallel manipulators (PMs) become parallel structures, that are structures constituted by two rigid bodies (platform and base) connected by a number of kinematic chains (limbs) with only passive kinematic pairs. A set of PMs is the one collecting the manipulators (SP-2RS architectures) which become structures with one limb of type SP and two limbs of type RS (P, R and S stand for prismatic pair, revolute pair and spherical pair respectively). The analytic determination of the assembly modes of the SP-2RS structures (i.e. the solution in analytic form of the direct position analysis of the SP-2RS architectures) has not been presented in the literature yet. This paper presents the solution in analytic form of the DPA of the SP-2RS architectures. In particular, the closure equation system of a generic SP-2RS structure is written in the form of three non-linear equations in three unknowns. The solution of the non-linear system is reduced to the determination of the roots of a sixteenth-degree univariate polynomial equation plus a simple back substitution procedure. The proposed solution algorithm is applied to a real case. The result of this study is that the solutions of the direct position analysis of all the SP-2RS architectures are at most sixteen and can be analytically determined through the proposed algorithm.
Dualities in the Analysis of Mechanisms With Multiple Loops and Parallel Mechanisms With Loops in Their Connecting Chains
Authors: Sugimoto Koichi
Published: April 2009

There exists a duality relationship between a twist and a wrench in the dynamics of a mechanism or a multi-body system. Using this relationship, the coordinate-free expressions for the dynamic analysis of multi-loop mechanisms is derived. In the analysis, a Jacobian matrix expressing the relationship among loops is defined, and it is clarified, by using this matrix, that both twists and wrenches can be easily analyzed based on the duality relationship among them. A parallel mechanism having connecting chains with loops is also analyzed, and it is shown that the same procedure can be applied to a parallel mechanism with connecting chains, each loop of which has a motion space that is different from that of the mechanism.
An MRI-Compatible Probe Exchanger for Early Diagnosis and Treatment of Breast Cancer
Authors: Larson Blake T. , Erdman Arthur G. , Tsekos Nikolaos V.
Published: April 2009

The objective of this project is to develop a device to exchange interventional probes such as biopsy needles, local anesthesia, ablation tools, and lesion removal devices to perform multiple procedures for breast cancer diagnosis and treatment during single session in the MR scanner. Used as a supplement to an existing five degree-of-freedom (DOF) interventional probe positioning device, the apparatus is fitted with two additional DOF for the selection and exchange of interventional probes to be used in an automated probe positioning device. The entire system is constructed of MR compatible materials, i.e. non-magnetic and non-conductive, to eliminate artifacts and distortion of the MR images. The apparatus is remotely controlled by means of ultrasonic piezoelectric motors and a graphical user interface, providing MRI-guided planning and monitoring of the procedure while it is in progress. Based on a timing analysis, the device can quickly exchange a probe (48 seconds), thereby reducing the complexity and cost of the overall procedure.
Topological Synthesis of a Parallel Wrist Mechanism
Authors: Hess-Coelho Tarcisio A.
Published: April 2009

To determine a suitable kinematic structure for a specific application is a complex task. Some available methods may provide a list of possible architectures for a robot wrist. However, a systematic method for selecting one among others is still an open problem. The paper presents a qualitative procedure for topological synthesis based on criteria that consider wrist design requirements and parallel mechanism peculiarities. The performance of chosen topology is evaluated according to described requirements.
Studies on Isotropy of Planar 5-Bar Linkages
Authors: Amarnath C. , Umesh K. N.
Published: April 2009

The ability to move at reasonable ease in all directions is an important requirement in the design of manipulators. The degree of ease of mobility varies from point to point in the workspace of the manipulator’s end effector. Maximum ease of mobility is obtained at an isotropic point, and the minimum occurs at singularities. An attempt has been made here to use a geometric approach for determining the isotropic points in the workspace of planar 5-bar linkages. The geometrical approach leads to interesting observations on the location of isotropic points in the workspace. The procedure also yields a technique for the synthesis of 5-bar linkages and associated coupler points exhibiting isotropic behaviour. Additionally it has been shown that coupler points exhibiting isotropic mobility occur in pairs.
Design and Analysis of a Cable Actuated Hand Prosthesis
Authors: Yang Jingzhou , Abdel-Malek Karim , Pen˜a Pitarch Esteban
Published: April 2009

Design and analysis of a cable actuated hand prosthesis is presented. The hand has multi-actuated fingers, four with two joints, and the thumb with three joints. Each joint is designed using a novel flexible mechanism based on the loading of a compression spring in both transverse and axial directions and using cable-conduit systems. The rotational motion is transformed to tendon-like behavior, which enables the location of the actuators to be far from the arm (e.g., on a belt around the waist). It is shown that the solution of the transverse deflection of each finger segment is obtained in a general form through a Haringx model followed by an element stiffness model. Also, we use a FEM model (ANSYS) to visualize the deflection of one finger. A prototypic finger is experimentally tested, results are verified, and the hand prosthesis is built.
Teeth-Number Synthesis of an Automatic Planetary Transmission Using Evolutionary Computation
Authors: Simionescu P. A. , Beale D. G. , Dozier G. V.
Published: April 2009

The gear-teeth number synthesis of an automatic planetary transmission used in automobiles is formulated as a constrained optimization problem that is solved with the aid of an Estimation of Distribution Algorithm. The design parameters are the teeth number of each gear, the number of multiple planets and gear module, while the objective function is defined based on the departure between the imposed and the actual gear ratios, constrained by teeth-undercut avoidance, limiting the maximum overall diameter of the transmission and ensuring proper planet spacing.
Graphical Methods to Locate the Secondary Instant Centers of Single-Degree-of-Freedom Indeterminate Linkages
Authors: Foster David E. , Pennock Gordon R.
Published: April 2009

This paper presents graphical techniques to locate the unknown instantaneous centers of zero velocity of planar, single-degree-of-freedom, linkages with kinematic indeterminacy. The approach is to convert a single-degree-of-freedom indeterminate linkage into a two-degree-of-freedom linkage. Two methods are presented to perform this conversion. The first method is to remove a binary link and the second method is to replace a single link with a pair of links connected by a revolute joint. First, the paper shows that a secondary instantaneous center of a two-degree-of-freedom linkage must lie on a unique straight line. Then this property is used to locate a secondary instant center of the single-degree-of-freedom linkage at the intersection of two lines. The two lines are obtained from a purely graphical procedure. The graphical techniques presented in this paper are illustrated by three examples of single-degree-of-freedom linkages with kinematic indeterminacy. The examples are a ten-bar linkage with only revolute joints, the single flier eight-bar linkage, and a ten-bar linkage with revolute and prismatic joints.
Seven-DOF Cable-Suspended Robot With Independent Metrology
Authors: Williams Robert L. , Snyder Ben , Albus James S. , Bostelman Roger V.
Published: April 2009

This paper presents a new cable-suspended robot. It is a 7-cable spatial design with a closed-form forward pose kinematics solution. Applications include automated machining, construction, and sculpting. This paper presents two new ideas. First, an independent, passive, six-string-pot-based Cartesian metrology system was built and tested since length measurements through the active drive system may be inaccurate for large-scale systems. Second, we introduce a new active cable tensioning approach wherein we control the displacement of a physical spring in-line with one of the active drive cables in attempt to ensure only positive cable tensions in all active cables. This is compared with an existing particular/homogeneous tensioning solution approach. Simulation examples are presented in this paper; we are currently building the proposed system for future evaluation work.
Adaptive Nonlinear PD Learning Control for Robot Manipulators
Authors: Ouyang P. R. , Zhang W. J. , Gupta M. M.
Published: April 2009

A new control method, called adaptive nonlinear PD learning control (NPD-LC), is proposed for robot manipulator applications in this paper. The proposed control structure is a combination of a nonlinear PD control structure and a directly learning structure. Consequently, this new control method possesses both adaptive and on-line learning properties. One of the unique features of the NPD-LC algorithm is that the learning is based on the previous torque profile of the repetitive task. It is proved that the NPD-LC enjoys the asymptotic convergence for both tracking positions and tracking velocities. Simulation studies were conducted by comparing the proposed method with many other existing methods. As a result, it was demonstrated that the NPD-LC method can achieve a faster convergence speed. The proposed NPD-LC is robust and can be implemented for the control of robot manipulators.
Analytic Form of the Six-Dimensional Singularity Locus of the General Gough-Stewart Platform
Authors: Li Haidong , Gosselin Cle´ment M. , Richard Marc J. , Mayer-St-Onge Boris
Published: April 2009

The determination of the 6-D singularity locus of the general Gough-Stewart platform is discussed in this article. The derivation of the velocity equation and the corresponding Jacobian matrices is first presented. Then a new procedure is introduced to obtain the analytical expression of the singularity locus, which is a function of six variables (x, y, z, φ, θ, ψ), using the velocity equation. Examples are also given to illustrate the results obtained. Gough-Stewart platforms can be used in several robotic applications as well as in flight simulators. The determination of the singularity locus is a very important design and application issue.
Mechanical Manipulator for Intuitive Control of Endoscopic Instruments With Seven Degrees of Freedom
Authors: Jaspers J. E. N. , Shehata M. , Wijkhuizen F. , Herder J. L. , Grimbergen C. A.
Published: April 2009

Performing complex tasks in Minimally Invasive Surgery (MIS) is demanding due to a disturbed hand-eye co-ordination, the use of non-ergonomic instruments with limited degrees of freedom (DOFs) and a lack of force feedback. Robotic telemanipulatory systems enhance surgical dexterity by providing up to 7 DOFs. They allow the surgeon to operate in an ergonomically favorable position with more intuitive manipulation of the instruments. Commercially available robotic systems, however, are very bulky, expensive and do not provide any force feedback. The aim of our study was to develop a simple mechanical manipulator for MIS. When manipulating the handle of the device, the surgeon’s wrist and grasping movements are directly transmitted to the deflectable instrument tip in 7 DOFs. The manipulator consists of a parallelogram mechanism with steel wires. First phantom experience indicated that the system functions properly. The MIM provides some force feedback improving safety. A set of MIMs seems to be an economical and compact alternative for robotic systems.
Spatial Static Gravity Balancing With Ideal Springs
Authors: te Riele Freek L. S. , Herder Just L. , Hekman Edsko E. G.
Published: April 2009

This paper discusses mechanisms that allow for perfect static balancing of rotations about a fixed spherical joint by means of ideal springs. Using a potential energy consideration, balancing conditions of a spatial three-spring balancer will be derived. It will be shown that not satisfying these conditions causes non-constant terms in the potential energy expression of the spring-mechanism, which can be eliminated by coupling the spring-mechanism to an inverted pendulum.
A Testbed for Human-Robot Interactions
Authors: Ong Kai Wei , Seet Gerald , Sim Siang Kok , Teoh William , Lim Kean Hee , Yow Ai Nee , Low Soon Chiang
Published: April 2009

This paper describes the design and implementation of a testbed for facilitating the study of human-robot interactions (HRI). HRI has long been a part of robotics research, where humans were typically required to guide the robot task in progress and to ensure safe operation. The current state of human interaction with robots, versus simple “machines” (e.g. in manufacturing automation) is quite different. This called for the need to look into different interaction roles between humans and robots. Robots differ from simple machines in that they are mobile, some may be autonomous and hence not as predictable in their actions. To facilitate the research in this domain, the aim is to develop an easy to use and safe front-end human-robot system for human users to interact with physical mobile robots. This testbed provides different types of system configurations (i.e. one human to one robot, one human to multiple robots, etc.) and interfaces for conducting experiments under different HRI scenarios.
Modeling of Tolerances and Clearances in Mechanisms Using Interval Analysis
Authors: Wu Weidong , Rao S. S.
Published: April 2009

It is important to conduct error analysis of assemblies in order to ensure that the manufactured parts satisfy the design specifications. Traditionally, mechanical tolerances and clearances are modeled as random variables and the analysis is conducted using probabilistic methods. In this work, a new approach, based on interval analysis, is presented for the modeling and analysis of tolerances and clearances. The basic procedure of interval analysis involving solution of simultaneous nonlinear equations is described. The application of the approach in the fuzzy error analysis of planar mechanisms is outlined. The treatment of the tolerances and clearances of the mechanism as interval numbers leads to a better and a more realistic estimation of the analysis results. Numerical results are presented to illustrate the computational procedure. The results of the interval analysis, although philosophically different, are compared with those given by the probabilistic method for comparable input data; the differences found in the two sets of results are explained in terms of the basic characteristics of the two methods. This work denotes the first application of interval methods for the modeling of tolerances and clearances and the fuzzy error analysis of mechanisms.
Locating N Points of a Rigid Body on N Given Planes
Authors: Wampler Charles W.
Published: April 2009

This paper describes a method for finding the location of a rigid body such that N specified points of the body lie on N given planes in space. Of special interest is the case N = 6, which is the minimum number to fully constrain the body. This geometric problem arises in two seemingly disparate contexts: metrology, as a generalization of so-called “3-2-1” locating schemes; and robotics, as the forward kinematics problem for 6ES or 6SE parallel-link platform robots. For N = 6, the geometric problem can be formulated algebraically as 3 quadratic equations having, in general, eight possible solutions. We give a method for finding all eight solutions via an 8 × 8 eigenvalue problem. We also show that for N ≥ 7, the solution can be found uniquely as a linear least squares problem.
On Dynamically Equivalent Force Systems and Their Application to the Balancing of a Broom or the Stability of a Shoe Box
Authors: Herder Just L. , Schwab Arend L.
Published: April 2009

The stability of a rigid body on which two forces are in equilibrium can be assessed intuitively. In more complex cases this is no longer true. This paper presents a general method to assess the stability of complex force systems, based on the notion of dynamic equivalence. A resultant force is considered dynamically equivalent to a given system of forces acting on a rigid body if the contributions to the stability of the body of both force systems are equal. It is shown that the dynamically equivalent resultant force of two given constant forces applies at the intersection of its line of action and the circle put up by the application points of the given forces and the intersection of their lines of action. The determination of the combined center of mass can be considered as a special case of this theorem. Two examples are provided that illustrate the significance of the proposed method. The first example considers the suspension of a body, by springs only, that is statically balanced for rotation about a virtual stationary point. The second example treats the roll stability of a ship, where the metacentric height is determined in a natural way.
Optimal Design and Fabrication of “CEDRA” Rescue Robot Using Genetic Algorithm
Authors: Meghdari A. , Pishkenari H. N. , Gaskarimahalle A. L. , Mahboobi S. H. , Karimi R.
Published: April 2009

This article presents an overview of the mechanical design features, fabrication and control of a Rescue Robot (CEDRA) for operation in unstructured environments. As a preliminary step, the essential characteristics of a robot in damaged and unstable situations have been established. According to these features and kinematical equations of the robot, design parameters are optimized by means of Genetic Algorithm. Optimum parameters are then utilized in construction. Upon fabrication, this unit has been tested in clean laboratory environment, as well as, ill-conditioned arenas similar to earthquake zones. The obtained results have been satisfactory in all aspects, and improvements are currently underway to enhance capabilities of the rescue robot unit for various applications.
Kinematics of a 3-DOF Translational Parallel Mechanism With 3-PRPaR Topology
Authors: Lee Chung-Ching , Chou Jeng-Hong
Published: April 2009

From the standpoint of kinematics, we present a type of three-dof pure spatial translational parallel mechanism with 3-PRPaR topology as an alternative to design automation devices and a regional structure of a six-dof hybrid parallel platform. First, we describe the structural properties of mechanism and analyze its kinematic mobility. It is verified that a pure translational motion does exist through the coordinate transformation technique and the well-known D-H parametric notations. Then, we proceed with the forward and inverse kinematic analysis and derive their analytical closed-form solutions by the matrix algebra method. For the confirmation of the derived equations, some numerical examples are also taken. Furthermore, with the help of the forward kinematics, we derive the workspace in the analytical form. Finally, taking account of the overall Jacobian matrix provides the condition number and the identification of singular configuration is explored based on direct and inverse kinematics Jacobian matrix.
A Robotic Device for Three-Dimensional Manipulation Over the Internet
Authors: Madden Christopher P. , Stein Matthew R.
Published: April 2009

The PumaPaint site has been allowing users to create paintings remotely over the Internet since 1998. Although this site allows for some artistic creativity, the task is inherently two-dimensional and lacks any real manipulation capability by the remote user. On a similar theme but with much higher complexity, we are creating a robotic device that will allow true, three-dimensional manipulation by the remote user with an added capacity for force control and kinesthetic feedback. The robotic device will be a roughly anthropomorphic pair of limited degree-of-freedom mechanical hands arranged in mutual opposition. We are designing these hands by building parametric models using AutoDesk Inventor® and then fabricating the components in our sparsely equipped machine shop. This paper will preset the design concept and details of the modeling process, plus how this process is informed by our fabrication capacity. The paper will also present the partially completed robotic device and discuss remaining obstacles to completion.
Feasibility Study of a Fully Compliant Statically Balanced Laparoscopic Grasper
Authors: Stapel Aa¨ron , Herder Just L.
Published: April 2009

Compliant mechanisms have many advantages over their rigid-body counterparts. One disadvantage however is the fact that motion of the mechanism is associated with elastic energy storage in the compliant parts. This is a problem especially in cases where accurate force transmission is of primary concern, such as in medical graspers. A solution to this problem is to statically balance the elastic forces by the addition of a spring force compensation mechanism, such that the effect of the compliance is neutralized. The complete resulting mechanisms resulting from this concept are called statically balanced compliant mechanisms (SBCMs). This paper presents a feasibility study into the design of a grasper for medical purposes and demonstrates that the concept is possible and practically viable. It is shown that the compliant gripper of a laparoscopic forceps can be statically balanced with a single-piece compliant compensation mechanism, with a balancing error of only 0.03N while dimensions are such that the compensation part of the mechanism can be stored inside the hand grip of the instrument.
Algorithms for Involute and Octoidal Bevel-Gear Generation
Authors: Figliolini Giorgio , Angeles Jorge
Published: April 2009

A suitable formulation and the implementing algorithms for involute and octoidal bevel-gear generation are proposed in this paper. In particular, the exact spherical involute tooth profile of bevel gears and their crown-rack is obtained through the pure-rolling motion of a great circle of the fundamental sphere on the base cone. Moreover, the tooth flank surface of octoidal bevel gears is obtained as the envelope of the tooth flat flank of the octoidal crown-rack during the pure-rolling motion of its flat pitch curve on the pitch cone. The proposed algorithms have been implemented in Matlab; several examples are included to illustrate their applicability.
Jacobian Derivation of 5-DOF 3R2T Parallel Mechanisms
Authors: Li Qinchuan , Hu Xudong , Huang Zhen
Published: April 2009

This paper presents a method for the Jacobian derivation of 5-DOF 3R2T PMs (parallel mechanisms), where 3R denotes three rotational DOFs (degrees of freedom) and 2T denotes two translational DOFs. First the mobility analysis of such kind of parallel mechanisms is reviewed briefly. The Jacobian matrix of the single limb kinematic chain is obtained via screw theory, which is a 6 × 5 matrix. Then it is shown that the mobility analysis of such kind of PM is important when simplifying the 6 × 5 matrix into a 5 × 5 Jacobian matrix. After obtaining the 5 × 5 Jacobian matrix for each limb, a 5 × 5 Jacobian matrix for the whole mechanism can be established.
Geometric Synthesis and Enumeration of the Family of 3-DOF Translational Parallel Manipulators via the Screw Theory
Authors: Yu Jingjun , Bi Shusheng , Zong Guanghua , Fang Yuefa
Published: April 2009

In this paper, a systematic method based on the screw theory is proposed for the geometric synthesis of a family of 3-DoF translational parallel manipulators (TPMs). The theory of screws and reciprocal screws is employed for the analysis of the geometric conditions undergoing the different types of constraints for the TPMs. In terms of these established geometric conditions, limb structures that can be used for constructing TPMs are enumerated, and a number of novel TPMs including both symmetrical structure and asymmetrical structure are synthesized accordingly. On the other hand, some composite kinematic pairs are proposed. The involvement of these composite kinematic pairs into the limbs of a TPM greatly enlarges the family of the TPMs.
Characterization of Instantaneous Point-Line Motions
Authors: Zhang Yi , Ting Kwun-Lon
Published: April 2009

This article discusses systematically the characterization of instantaneous point-line motions, and the higher-order relationship between a point-line motion and the associated rigid body motions. The transformation of a point-line between two positions is depicted as a pure translation along the point-line followed by a screw displacement about their common normal and expressed with a unit dual quaternion referred to as the point-line displacement operator. The derivatives of the point-line displacement operator characterize the point-line motion to various orders with a set of characteristic numbers. Such a treatment leads to a consistent expression or unified treatment for the transformation of lines, point-lines, and rigid bodies. The relationships between point-line motions and rigid body motions are addressed in detail up to the third order.
A Dynamic Simulation of Cam Actuated Robotized Gearbox
Authors: Pennestri` E. , Stefanelli R. , Valentini P. P. , Vita L.
Published: April 2009

In this paper a simulation of the cam actuator of a robotized gearbox is presented. The actuator is a barrel cam which moves a pin according to a prescribed motion law. The model of contact, between cam and follower, is based on a finite elements approach of the theory of beam on continuous elastic foundation, modified by the authors to include the effect of shear on the deformation and dynamic effects. The foundation modulus is computed using Hertz theory taking also into account the change of principal curvature values during the relative motion between cam and follower. This model has been embodied in a complete gear shifting simulation in order to compare the effects on contact forces, wear actions and shifting time of different cam profiles.
A Dual Number Approach to the Kinematic Analysis of Spatial Linkages With Dimensional and Geometric Tolerances
Authors: Cecchini Emanuele , Pennestri` Ettore , Stefanelli Roberto , Vita Leonardo
Published: April 2009

Design robustness is somewhat connected to tolerances. In fact, the lower is the sensitivity of the kinematic function to the deviations of manufacturing process, the higher is the robustness of the design. In this investigation is described a tolerance analysis method based on dual vectors kinematic modeling of spatial linkages and on Monte Carlo simulation of the random variables. In the present analysis the hypothesis of rigid bodies is valid and only kinematic variables are considered in output. The method is applied to a Cardan joint modelled as an RCCC linkage with main dimensions considered as stochastic variables with Gaussian distribution. Dual vectors are well known in kinematic analysis and synthesis of spatial mechanisms. When compared with traditional vectorial methods, dual vectors show an enhanced capability to model misalignments among kinematic pairs axes. Although this is not the first time that dual vectors are used for the kinematic and dynamic analysis of spatial mechanisms with manufacturing errors, the present use of dual vectors to model joint clearances seems somewhat novel.
Special Cases of Input Speed Doubling Linkage Mechanisms and Their Dynamics Advantage
Authors: Rastegar J. , Zhang J.
Published: April 2009

In a recent study, Rastegar, et al. (2003), presented a special class of planar and spatial linkage mechanisms in which for a continuous full rotation or continuous rocking motion of the input link, the output link undergoes two continuous rocking motions. In a special case of such mechanisms, for periodic motions of the input link, the output motion is periodic with a doubled fundamental frequency. The above class of linkage mechanisms were referred to as “speed-doubling” linkage mechanisms. Such mechanisms can be cascaded to further double the fundamental frequency (rocking motion) of the output motion. They can also be cascaded with other linkage mechanisms to obtain crank-rocker or crank-crank type of mechanisms. The conditions for the existence of “speed-doubling” linkage mechanisms were also provided. In this paper, a study of the dynamics of a “speed-doubling” linkage mechanism is presented. It is shown that such mechanisms have dynamic advantage over regular mechanisms designed to achieve similar output motions. The main advantage of such mechanisms is shown to be their lower peak input torque requirement, and that the required torque generally has lower amplitude high-frequency components. The speed-doubling mechanisms have practical applications, particularly when higher output speeds are desired, since higher output motions can be achieved with lower input speeds and smaller motors.
Mobility of Stephenson Six-Bar Chains: Part II — The Motion Order
Authors: Guo Xiao-Ning , Chu Jin-Kui
Published: April 2009

Based on the model for circuit analysis of a Stephenson six-bar chain, this paper presents a feature point loop method to identify the motion order defect of a Stephenson six-bar chain. The proposed method can determine whether a linkage synthesized by precision point synthesis can pass through all positions in the prescribed order and yet not have to carry through the detailed kinematic analysis of the linkage. In addition, this method is applicable to any type Stephenson six-bar linkage and regardless of whichever link is used as the input. The result resolves one fundamental and troublesome problem encountered in a Stephenson six-bar linkage synthesis.
Synthesis of the Pitch Cones of N-Lobed Elliptical Bevel Gears
Authors: Figliolini Giorgio , Migliozzi Paolo
Published: April 2009

A general formulation for the synthesis of the pitch cones of N-lobed elliptical bevel gears and the pitch surface of their conjugate crown-rack is proposed. In particular, both pitch cones and the pitch surface of their crown-rack can be obtained for any number and combination of lobes and in any configuration during their pure-rolling motion. This formulation has been implemented in a suitable Matlab program and several significant examples are shown, where circular bevel gears become a particular case. Computer animations are also available at URL: http://webuser.unicas.it/weblarm/larmindex.htm.