bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of the Integrated Flexpin Bearing for Improving the Performance of Epicyclical Gear Systems
Authors: Fox Gerald P. , Jallat Eric
Published: June 2008

Epicyclical gear systems have typically been equipped with straddle-mounted planetary idlers having pins supported on the input and output sides of the carrier. Torsional wind-up of the carrier, position accuracy of the pins, machining tolerances of the planetary gear system components and bearings clearances can all contribute to a poor load sharing among the planetary idlers as well as misaligned gear contacts in the deflected state. Use of the double-cantilevered flexible pin concept to achieve better load sharing and gear contact patterns among a multiplicity of planetary idlers, has been used to improve reliability in advanced gear drives for many years. The consequence of this practice is to build a compliant epicyclical system that improves power density in the gear length direction because the probability of achieving a properly centered gear contact is increased. The Integrated Flexpin Bearing, the subject of this paper, is capable of achieving additional power density in the gear diameter direction through integration of bearing components, gearing and shafting. This paper presents one designer’s approach to optimizing an Integrated Flexpin Bearing to improve the reliability of an epicyclical gearbox.
An Analysis of a Frictional Coupling Mechanism in Rolling Variators
Authors: Lukowski S. A. , Momot M. E. , Medeksza L. A.
Published: June 2008

This paper presents an analysis of the frictional coupling mechanism in rolling variators. Rolling variators are continuously variable transmissions where the power is transmitted by frictional contact between non-flexible rotating elements. The essential feature of this type of transmission is that the adjoining surfaces rotate when the rolling elements roll against each other resulting in drilling-type friction due to drilling-type motion. The performance characteristics of rolling variators are thus evaluated on the basis of both the drillingtype friction and tangential forces, which transmit the power. Relationships between the characteristic parameters of frictional coupling elements are derived and expressed in the form of integrals, which can be readily evaluated numerically for the tangential force utilization coefficient, power loss coefficient, and geometric efficiency. The analysis of the frictional coupling mechanism in rolling variators constitutes a tangible contribution to the theory dealing with the design of this type of continuously variable transmissions.
The Influence of Additive Chemistry on Gear Micropitting
Authors: O’Connor B. M.
Published: June 2008

Gear micropitting has been a highly visible issue in selected applications in recent years, most notably in large wind turbine transmissions. Various industry groups have addressed the problem from their own area of expertise. This has included evaluation of the gear design characteristics, surface finishing, the use of special coatings, and lubrication. A common approach to improve the lubrication has been first to increase the viscosity and create thicker films, which, in turn, reduce the amount of surface asperity interaction. Another approach from the lubricant side has been to alter the additive chemistry to effect a change in the wear properties of the system. This paper discusses the potential effects observed for different antiwear and EP chemistry on the micropitting of cylindrical gears. Tests were conducted in an FZG test rig which has been used by the industry as a guide to general gear performance. Fluids were examined in a series of experimental designs which served as the iterative process leading toward an optimized additive system. The results show that the EP, or antiscuff agent, was the most effective component at reducing the level of micropitting.
TriLab: A Tool for Simulating Tribological Systems
Authors: Stro¨mberg Niclas
Published: June 2008

In this paper TriLab is presented. TriLab is a user-friendly finite element tool for simulating tribological systems. TriLab is based on a method for structural dynamic contact problems with friction and wear. The method is reviewed in the paper as well as the quasi-static formulation of frictional contact, the energy-momentum conserving approach of Simo and Tarnow, and Moreau’s nonsmooth contact dynamics formulation. TriLab is easy to use and can be utilized for solving both small displacement contact, rolling contact as well as impact problems. This is demonstrated by solving a number of examples.
Radio Telemeter for Gear Bulk Temperature Measurement
Authors: Jia Yi , Romero Edwar
Published: June 2008

A radio telemeter was designed and fabricated for gear bulk temperature measurement. The temperature telemeter developed in the paper is based on the principle of an inductor-capacitor (L-C) tuned electronic oscillator. A temperature sensitive capacitor has been integrated into an electronic circuit of an L-C oscillator as a frequency-controlling element. The change in the value of the capacitor due to temperature variation is translated into modulation in the oscillator frequency. This change in frequency, with proper calibration, permits accurate bulk temperature measurements of the gear. The Surface Mount Component and Photolithography technology were employed to fabricate the miniature temperature radio telemeter. Various test results will be presented. These results have proven that the telemeter is a useful device in measuring gear bulk temperature.
Determination of Efficiency (Torque Related Losses) in Planetary Gearsets: Generalized Theory for Simple and Compound Gearsets
Authors: Haka Raymond J.
Published: June 2008

This paper presents the mathematics governing the torque related losses in a planetary gear set. The losses as a function of the Ring to Sun ratio, which element is grounded (Sun, Ring, or Carrier), and whether the system is “Simple” or “Compound” are developed. The paper also develops the mathematics governing the losses in planetary gear sets that are connected together.
Fault Tolerant Motion Planning With Avoidance of the Sudden Change of Joint Velocity for Two Coordinating Redundant Manipulators
Authors: Zhao Jing , Zhang Kailiang , Yao Xuebin
Published: June 2008

The sudden change of joint velocity in fault tolerant operation of two coordinating manipulators for joint-locking failures is studied. First, the difference between the joint velocity of original manipulator and that of reduced manipulator is defined as the sudden change in joint velocity. Then, a corresponding fault tolerant planning algorithm based on this criterion is proposed. At last, a simulation example of fault tolerant operations is implemented with two planar 3R manipulators. Simulation results show that this algorithm can effectively avoid the sudden change of joint velocity occurring in fault tolerant operation of two coordinating manipulators, strengthen their motion stability and so improve their kinematical and dynamic properties in fault tolerant operations.
Kinematics of a New High Precision Three Degree-of-Freedom Parallel Manipulator
Authors: Tahmasebi Farhad
Published: June 2008

Closed-form direct and inverse kinematics of a new three degree-of-freedom (DOF) parallel manipulator with inextensible limbs and base-mounted actuators are presented. The manipulator has higher resolution and precision than the existing three DOF mechanisms with extensible limbs. Since all of the manipulator actuators are base-mounted; higher payload capacity, smaller actuator sizes, and lower power dissipation can be obtained. The manipulator is suitable for alignment applications where only tip, tilt, and piston motions are significant. The direct kinematics of the manipulator is reduced to solving an eighth-degree polynomial in the square of tangent of half-angle between one of the limbs and the base plane. Hence, there are at most sixteen assembly configurations for the manipulator. In addition, it is shown that the sixteen solutions are eight pairs of reflected configurations with respect to the base plane. Numerical examples for the direct and inverse kinematics of the manipulator are also presented.
Compliant Rolling-Contact Element Mechanisms
Authors: Cannon Jesse R. , Lusk Craig P. , Howell Larry L.
Published: June 2008

This paper presents three planar mechanisms capable of performing the functions of a bearing and a spring: the compliant rolling-contact element (CORE), the CORE bearing, and the elliptical CORE bearing. The designs use compliant rolling-contact joints to achieve low friction rotation and to bear high in-plane lateral loads. A model for predicting the behavior of the designs is presented, and manufacturing considerations are discussed for the macro, meso, and micro scales. A case study is presented, and the designs are shown to be capable of meeting the demanding design constraints of the study.
Forward/Reverse Velocity and Acceleration Analyses for a Class of Lower-Mobility Parallel Mechanisms
Authors: Zhu Si J. , Huang Zhen , Guo Xi J.
Published: June 2008

In the family of lower-mobility (degrees of freedom Nf<6) parallel mechanisms, there is a class of mechanisms whose degrees of freedom equal the number of single-degree-of-freedom pairs in each limb. This paper proposes a novel forward/reverse kinematic analyses method for this class of mechanisms, which can build Nf×Nf square Jacobian matrix and Nf×Nf×Nf cubic Hessian matrix. Thus both forward/reverse velocity and acceleration analyses for this class of mechanisms are derivable. In this method, the formulas for different parallel mechanisms have unified forms and consequently the method is convenient for programming. The more complicated the mechanism is (for instance, the mechanism has more kinematic pairs), the more effective the method is. In the rear part of the paper, a 5-DOF mechanism 3-RCRR is analyzed as an example.
Instantaneous Kinematic Characteristics of a Special 3-UPU Parallel Manipulator
Authors: Li Shihua , Huang Zhen
Published: June 2008

The instantaneous kinematics of a special 3-UPU parallel platform manipulator is discussed in this paper. First, the instantaneous motions of the 3-UPU manipulator in four position and a special manipulator are studied by reciprocal screw theory. Then, the principal screws in one of four position are obtained. It is shown that the moving platform has five DOF (degrees of freedom) in the initial position or after a translation along the Z-axis; in the generic position, the mechanism only has three DOF, moreover the three DOF characteristics are difference in different position. The instantaneous kinematic characteristics of alike 3-UPU mechanisms are very different in different position and special structure. The results presented in this paper are important to the use of alike 3-UPU parallel manipulator and contribute to the mechanism theory.
Robotic Material Handling of Flexible Fuel Cell Membranes
Authors: Derby Stephen J. , Lippiatt John
Published: June 2008

One of the biggest challenges in the manufacturing of high temperature fuel cells is the creation of the Membrane Exchange Assembly (MEA). This is the heart of the fuel cell, where the 4–5 components must be assembled with very high tolerances to perform successfully. One of the key components, the membrane, is similar to plastic food wrap. Handling plastic wrap alone in a wrinkle free mode, with precision cut edges is difficult enough. But it also must be saturated in acid, creating a very slippery product. And the membrane will grow or shrink in a matter of 5 minutes when exposed to moisture in the air. So this material handling effort is orders of magnitude more difficult than the established methods for “simple” items like paper. This paper will document the research conducted into the robotic material handling of the fuel cell membranes. It requires a mix of traditional robotic techniques, some techniques from the fabric handling arena, and some new approaches. The issues from lifting a wet film from a PET backer sheet consistently and the sensing requirements for accurate placement have made this a challenging effort.
Application of Taguchi Method on the Tolerance Design of a Four-Bar Function Generation Mechanism
Authors: Chen Fu-Chen , Huang Hsing-Hui
Published: June 2008

The purpose of this paper is to use the Taguchi method on the tolerance design of a four-bar function generator in order to obtain the structural error that is insensitive to variations in manufacturing tolerance and joint clearance. The contribution of each control factor to the variations was also examined to further determine if the tolerance of the factor should be tightened to improve the precision of the mechanism. From the study of the four-bar function generator, it was revealed that the control factor B had the most significant effect on the variation of the structural errors. These were closely followed by factors E, C and D. On the whole, experimental errors contributed only 2.69% to the structural errors, much smaller than the contribution by individual factors, indicating that the design of the experiments was appropriate and the results were highly reliable. By tightening the tolerance, it is apparent that the mean of structural errors is reduced by 0.227 and the change in variance is 69.81% of the initial value, i.e. a reduction of 30.19%.
CMAC Neural Network Control for High Precision Motion of Hybrid Actuator
Authors: Ke Zhang , Shengze Wang
Published: June 2008

Hybrid actuator is a new type of planar parallel robot, and requires precise control of the position of the mechanism. In order to achieve the desired accuracies, nonlinear factors as friction must be accurately compensated in the real-time servo control algorithm. According to the characteristics of the hybrid actuator, a hybrid intelligent control algorithm based on PID control and cerebellar model articulation control (CMAC) techniques was presented and used to perform control of hybrid actuator for the first time. Simulation results show that this method can improve the control effect remarkably compared with the traditional control strategy.
Dynamics Analysis of a Controllable Mechanism
Authors: Ke Zhang , Shengze Wang
Published: June 2008

Hybrid mechanism is a kind of controllable mechanism. It may be composed of one or multiple coupled kinematic loops forming a mechanism network, and is highly nonlinear devices. The bond graph approach provides a compact and versatile representation for kinematics and dynamics of hybrid mechanism, and is more suitable for automatic derivation and computation on a computer. Here, an analysis procedure that can be used to produce the dynamics equations of hybrid mechanism is presented. According to bond graph model, dynamics equations can be derived. The unified formula of dynamics equations derived here is a regularized one. The driving powers of hybrid mechanism can be obtained in terms of physical parameters of mechanism and kinematic states, and no need to analyze acceleration of mechanism. Finally, a numerical example is presented illustrating its validity. The results show that efficiency and reliability of dynamics analysis for hybrid mechanism are enhanced obviously.
Modeling and Alleviating Instability in a MEMS Vertical Comb Drive Using a Progressive Linkage
Authors: Bronson Jessica R. , Wiens Gloria J. , Allen James J.
Published: June 2008

Micro mirrors have emerged as key components for optical microelectromechanical system (MEMS) applications. Electrostatic vertical comb drives are attractive because they can be fabricated underneath the mirror, allowing for arrays with a high fill factor. Also, vertical comb drives are more easily controlled than parallel plate actuators, making them the better choice for analog scanning devices. The device presented in this paper is a one-degree of freedom vertical comb drive fabricated using Sandia National Laboratories SUMMiT™ five-level surface micromachining process. The electrostatic performance of the device is investigated using finite element analysis to determine the capacitance for a unit cell of the comb drive as the position of the device is varied. This information is then used to design a progressive linkage that will seek to alleviate or eliminate the effects of instability. The goal of this research is to develop an electrostatic model for the behavior of the vertical comb drive mirror and then use this to design a progressive-linkage that can delay or eliminate the pull-in instability.
Actuating Input Selection of 5-UPS/PRPU Parallel Machine Tool
Authors: Gao Jian-She , Zheng Ren-Cheng , Zhao Yong-Sheng
Published: June 2008

The actuating input selection is an important basic problem for the parallel mechanism. Based on the screw theory, the constraint screw can be got after locking a kinematic pair in any limb, which can be taken as actuating wrench acted on the moving platform of the parallel mechanism. The constraint screw matrix is composed of the structure constraint screws and the constraint screws of the actuating pairs. The reasonableness of input selection can be judged by the rank of the constraint matrix. The performance of the combinations of actuating inputs is evaluated by the condition numbers of the force constraint matrix and the torque constraint matrix respectively. The theory presented is validated by the simulation and the maching test.
Motion Synthesis of a Chopstick-Type Gripping Mechanism
Authors: Lee Jyh-Jone , Hu Sheng-Lun
Published: June 2008

In this paper, the kinematic synthesis of a chopstick-type gripping mechanism containing rolling pairs is studied. The design equations of the mechanism used as a rigid-body, guidance are established. The number of free choices in design variables in the kinematic synthesis is also discussed. The optimization-based numerical technique is applied to solve the design equations. The synthesized solutions are illustrated to discuss the kinematic states of the mechanism. It is also shown that the optimization-based method is effective in finding the admissible synthesis solution of the mechanism.
The Systemic Research on Loop Characteristics of Planar Kinematic Chains and Its Applications
Authors: Ding H. F. , Huang Z. , Cao Y.
Published: June 2008

Based on the array representation of loop in topological graph of kinematic chains, this paper proposes two basic loop operations. Their existent conditions and properties of the two operations are also researched. In further loop analysis we discuss the important concepts including the independent loop, canonical degree-sequence and perimeter topological graph. Two Theorems deal with the relationship of loops. Based on above basic theory some important applications are given, such as the isomorphism identification based on the loop set concept, the detection of the rigid sub-chains in a kinematic chain and the type analysis of freedom of kinematic chains.
A Generalized Transmission Index for Spatial Linkages
Authors: Chen Chao , Angeles Jorge
Published: June 2008

This paper proposes a generalized transmission index for spatial mechanisms, based on the transmission index introduced by Sutherland and Roth. This index is more general and welldefined in all the cases; it matches the virtual coefficient between the transmission wrench screw and the output twist screw exactly. A method is developed to compute the transmission wrench screw in spatial single-loop linkages. We illustrate the application of this index in a RSCR linkage.
Fully-Isotropic T1R2-Type Parallel Robots With Three Degrees of Freedom
Authors: Gogu Grigore
Published: June 2008

The paper presents singularity-free fully-isotropic T1R2-type parallel manipulators (PMs) with three degrees of freedom. The mobile platform has one independent translation (T1) and two rotations (R2). A method is proposed for structural synthesis of fully-isotropic T1R2-type PMs based on the theory of linear transformations. A one-to-one correspondence exists between the actuated joint velocity space and the external velocity space of the moving platform. The Jacobian matrix mapping the two vector spaces of fully-isotropic T1R2-type PMs presented in this paper is the 3x3 identity matrix throughout the entire workspace. The condition number and the determinant of the Jacobian matrix being equal to one, the manipulator performs very well with regard to force and motion transmission capabilities. As far as we are aware, this paper presents for the first time in the literature solutions of singularity-free T1R2-type PMs with decoupled an uncoupled motions, along with the fully-isotropic solutions.
A Concept for Rapidly-Deployable Cable Robot Search and Rescue Systems
Authors: Bosscher Paul , Williams Robert L. , Tummino Melissa
Published: June 2008

This paper introduces a new concept for robotic search and rescue systems. This system uses a rapidly deployable cable robot to augment existing search and rescue mobile robots. This system can greatly increase the range of mobile robots as well as provide overhead views of the disaster site, allowing rescue workers to reach survivors as quickly as possible while minimizing the danger posed to rescue workers. In addition to the system concept, this paper presents a novel kinematic structure for the cable robot, allowing simple translation-only motion (with moment-resisting capability) and easy forward and inverse kinematics for a 3-DOF spatial manipulator. Also, a deployment sequence is described, a rapid calibration algorithm is presented and the workspace of the manipulator is investigated.
Consistent Kinetostatic Indices for Planar 3-DOF Parallel Manipulators, Application to the Optimal Kinematic Inversion
Authors: Alba-Gomez Ofelia , Wenger Philippe , Pamanes Alfonso
Published: June 2008

This paper investigates the problem of defining a consistent kinetostatic performance index for symmetric planar 3-DOF parallel manipulators. The condition number of the Jacobian matrix is known to be an interesting index. But since the Jacobian matrix is dimensionally inhomogeneous, a normalizing length must be used. This paper proposes two distinct kinetostatic indices. The first one is defined as the reciprocal of the condition number of the Jacobian matrix normalized with a convenient characteristic length. The second index is defined by a geometric interpretation of the “distance” to singularity. The two indices are compared and applied to the kinematic inversion in the presence of redundancy.
Hybrid Target Tracking Manipulation Theories for Combined Force and Position Control in Open and Closed Loop Manipulators
Authors: Giblin David J. , Mu Zongliang , Gan ZhongXue , Kazerounian Kazem
Published: June 2008

This paper presents a new manipulation theory for controlling compliant motions of a robotic manipulator. In previous closed loop control methods, both direct kinematics and inverse kinematics of a manipulator must be resolved to convert feedback force and position data from Cartesian space to joint space. However, in many cases, the solution of direct kinematics in a parallel manipulator or the solution of inverse kinematics in a serial manipulator is not easily available. In this study, the force and position data are packed into one set of “motion feedback,” by replacing the force errors with virtual motion quantities, or one set of “force feedback,” by replacing motion errors with virtual force quantities. The joint torques are adjusted based on this combined feed back package. Since only Jacobian of direct kinematics or Jacobian of inverse kinematics is used in the control scheme, the computational complexity is reduced significantly. The applications of this theory are demonstrated in simulation experiments with both serial and parallel manipulators.
Design of a New Compliant Mechanical Amplifier
Authors: Ouyang P. R. , Zhang W. J. , Gupta M. M.
Published: June 2008

In this paper, a new topology that is a symmetric five bar profile for displacement amplification is proposed, and a compliant mechanical amplifier (CMA) based on the new topology is designed to amplify the stroke of a piezoelectric actuator. The new CMA can convert the motion generated by a PZT actuator with a large amplification ratio (24.4) in a very compact size, and it has a high natural frequency (573 Hz) and no lateral displacement. First, three existing topologies of CMA are analyzed and evaluated, which results in the new topology of CMA. After that, the new CMA is designed with different flexure hinges. The finite element analysis for the CMA shows that the double-beam symmetric five bar structure using the corner-filleted hinges can provide the best performance in terms of the displacement amplification and natural frequencies. The designed CMA is clearly better than the CMA based on the topology of a double symmetric four bar profile. Finally, the design is fine-tuned by examining critical parameters for the proposed CMA in light of a large displacement amplification ratio.
Kinematic Analysis of a Novel Rimless Wheel With Independently Actuated Spokes
Authors: Laney Doug , Hong Dennis
Published: June 2008

One of the major limitations of mobile robots for unstructured environments is their lack of general mobility. Wheeled, treaded, and legged robots each have their advantages and disadvantages, but they all lack the flexibility to be able to cope with a wide range of terrain. The actuated spoke wheel concept is presented in this paper as an alternative locomotive method that allows multiple modes of motion, which give it the ability to stride quickly using one contact point per wheel, walk with static stability with two contact points per wheel, or assume a stable stance using three contact points per wheel. This paper presents the preliminary kinematic analyses of the actuated spoke wheel with no-slip constraints at the ground contacts for a robot using a two actuated spoke wheel configuration. Straight-line motion and considerations for turning are discussed for the one- and two-point contact schemes followed by recommendations for future study.
Spanning Tree Based Topological Optimization of Compliant Mechanisms
Authors: Zhou Hong , Ting Kwun-Lon
Published: June 2008

In graph theory, spanning trees connect all the vertices together using minimum number of edges. A topological optimization method of compliant mechanisms is presented based on spanning tree theory. A valid topology is regarded as a network connecting input, output, support and intermediate nodes, which contains at least one spanning tree among the introduced nodes. Invalid disconnected topologies can be weeded out if no spanning tree is included. No further deformation analysis and performance evaluation is needed for invalid disconnected topologies. Problem-dependent objectives are optimized for topological optimization of compliant mechanisms. Constraints about maximum input displacement and input force, maximum stress and overlapping connections are directly imposed during the optimization process. The discrete optimization problem is solved by genetic algorithm with penalty function handling constraints. An example is presented to verify the effectiveness of the proposed optimization procedure.
Point-Line Distance Under Riemannian Metrics
Authors: Zhang Yi , Ting Kwun-Lon
Published: June 2008

A point-line is the combination of a directed line and an endpoint on the line. A pair of point-line positions corresponds to a point-line displacement, which is known to be associated with a set of rigid body displacements whose screw axes are distributed on a cylindroid. Different associated rigid body displacements generally correspond to different distances under Riemannian metrics on the manifold of SE(3). A unique measure of distance between a pair of point-line positions is desirable in engineering applications. In this paper, the distance between two point-line positions is investigated based on the left-invariant Riemannian metrics on the manifold of SE(3). The displacements are elaborated from the perspective of the soma space. The set of rigid body displacements associated to the point-line displacement is mapped to a one-dimensional great circle on the unit sphere in the space of four dual dimensions, on which the point with the minimum distance to the identity is indicated. It is shown that the minimum distance is achieved when an associated rigid body displacement has no rotational component about the point-line axis. The minimum distance, which has the inherited property of independence of inertial reference frames, is referred to as the point-line distance. A numerical example shows the application of point-line distance to a point-line path generation problem in mechanism synthesis.
Components, Building Blocks, and Demonstrations of Spherical Mechanisms in Microelectromechanical Systems
Authors: Lusk Craig P. , Howell Larry L.
Published: June 2008

Microelectromechanical systems (MEMS) are usually fabricated using planar processing methods which complicates the design of devices capable of complex motions. For applications that need a micro mechanism that rotates out of the plane of fabrication with an in-plane rotational input, or that rotates spatially about a point, spherical kinematics may represent an appropriate solution. This paper describes the design of spherical mechanisms for MEMS including the design of joints and links, and what may be the first demonstration of two spherical micro mechanism building blocks: the spherical four-bar micromechanism and the spherical slider-crank micromechanism. Two other micromechanisms are demonstrated to illustrate how the building block devices may be used to create more complex devices.
Projection Metrics for Rigid-Body Displacements
Authors: Larochelle Pierre M. , Murray Andrew P.
Published: June 2008

An open research question is how to define a useful metric on SE(n) with respect to (1) the choice of coordinate frames and (2) the units used to measure linear and angular distances. We present two techniques for approximating elements of the special Euclidean group SE(n) with elements of the special orthogonal group SO(n+1). These techniques are based on the singular value and polar decompositions (denoted as SVD and PD respectively) of the homogeneous transform representation of the elements of SE(n). The projection of the elements of SE(n) onto SO(n+1) yields hyperdimensional rotations that approximate the rigid-body displacements (hence the term projection metric. A bi-invariant metric on SO(n+1) may then be used to measure the distance between any two spatial displacements. The results are PD and SVD based projection metrics on SE(n). These metrics have applications in motion synthesis, robot calibration. motion interpolation, and hybrid robot control.
Characteristics Analysis of Hydraulic Servo-Valve Torque Motor Using Magnetic Fluid
Authors: Li Songjing , Jiang Dan , Bao Wen
Published: June 2008

Magnetic fluids are added to a torque motor of hydraulic servo-valve, to improve the performance of the torque motor and the servo-valve. The construction and principle of the torque motor are introduced. Using finite element analysis method, the magnetic field distribution of the torque motor is analyzed. The static and dynamic performance of the torque motor with or without magnetic fluids is studied and compared. The simulation results are shown.
Micro-Macro or Link-Integrated Micro-Actuator Manipulation: A Kinematics and Dynamics Perspective
Authors: Zhang J. , Rastegar J.
Published: June 2008

Smart (active) material based actuators, hereinafter called micro-actuators, have been shown to be well suited for the elimination of high harmonics in joint and/or end-effector motions of the robot manipulators and reduce actuator dynamic response requirements. Low harmonic joint and end-effector motions as well as low actuator dynamic response requirements are essential for a robot manipulator to be capable of operating at high speeds with greater precision and with less vibration and control problems. Micro-actuators may be positioned at the end-effector to obtain a micro and macro robot manipulation. Alternatively, micro-actuators may be integrated into the links to vary a link parameter such as the link length. In this paper, the kinematics and dynamics consequences of each alternative are studies for manipulators with serial and closed-loop chains. It is shown that for the robot manipulator constructed with closed-loop chains, the high harmonic components of all joint motions can be eliminated only when micro-actuators are integrated into the structure of the closed-loop chain links. The latter configuration is also shown to have dynamics advantage over micro and macro configuration. thereby reducing the potential vibration and control problems at higher operating speeds. The conclusions also apply to closed-loop chains of parallel and cooperating robot manipulators.
On the Design of a Novel Controllable Mechanical Metal Forming Press Based on 2-DOF Planar Mechanism
Authors: Jin Zhenlin , He Kai , Du R.
Published: June 2008

It is known that the punch motion has a significant effect on sheet metal stamping operations. For example, for deep drawing operations long dwelling is desirable. For blanking operations, on the other hand, the two-step motion can reduce the noise [1]. However, the controlled punch motion cannot be realized using conventional mechanical presses, which has the advantage of being energy efficient, fast and easier to make / maintain. Servo mechanical presses solved some of the problems, but are not energy efficient (because they cannot use flywheels as the conventional mechanical presses). Following our previous research [2–4], this paper presents a new type of controllable mechanical press. It is a 2-DOF planar mechanism driven by a large constant speed motor (which takes 75% of the load) and a small servomotor (which takes 25% of the load). Though, unlike the first design, the new design uses the servomotor to drive a ball screw instead of a crank, which makes building the press simpler and controlling the press easier. The paper describes various issues in designing and controlling the press including (a) Kinematics and inverse kinematics; (b) Static force distribution analysis and parameter design; and (c) Punch motion programming and control. A 250 KN prototype has been built and the experimental testing results confirm that the press is working properly. Comparing to the existing technology, the new press is controllable and energy efficient. It is expected that it will have a significant value to the metal forming industry.
A New and Efficient Algorithm for the Inverse Kinematics of a General Serial 6R
Authors: Husty Manfred L. , Pfurner Martin , Schro¨cker Hans-Peter
Published: June 2008

In this paper a new and very efficient algorithm to compute the inverse kinematics of a general 6R serial kinematic chain is presented. The main idea is to make use of classical multidimensional geometry to structure the problem and to use the geometric information before starting the elimination process. For the geometric preprocessing we use the Study model of Euclidean displacements, sometimes called kinematic image, which identifies a displacement with a point on a six dimensional quadric S62 in seven dimensional projective space P7. The 6R chain is broken up in the middle to form two open 3R chains. The kinematic image of a 3R chain turns out to be a Segre-manifold consisting of a one parameter set of 3-spaces. The intersection of two Segre-manifolds and S62 yields 16 points which are the kinematic images representing the 16 solutions of the inverse kinematics. Algebraically this procedure means that we have to solve a system of seven linear equations and one resultant to arrive at the univariate 16 degree polynomial. From this step in the algorithm we get two out of the six joint angles and the remaining 4 angles are obtained straight forward by solving the inverse kinematics of two 2R chains.
Research of Valve-Less Pumps With Changeable Cone Angle Nozzle/Diffuser Elements
Authors: Kou Jie , Zhang Jianhui , Lai Dehua , Yang Yuhao
Published: June 2008

When it comes to the researches of valve-less pumps with nozzle/diffuser elements of different cone angles, they were usually achieved by manufacturing plural pumps, and the number of the pumps is determined by the accuracy of experiments required. However, the traditional way in which finite pumps of different cone angles were used to simulate the changeable cone angle and it would probably conceal some properties of the nozzle/diffuser elements. Meanwhile, many parameters of the nozzle/diffuser elements other than cone angle can not be kept in consistency. In the research, a new kind of 2-Dimensional nozzle/diffuser elements whose cone angles are changeable is created, and the cone angle of the new nozzle/diffuser elements can be adjusted through adjusting the position of the changeable flow passage. Furthermore, when liquid flow through nozzle/diffuser element, the nozzle/diffuser elements could make consecutive loss coefficient, which makes the changes of flux and flow direction. And the kind of pump with the new structure was developed in the research; the effectiveness and usefulness are also demonstrated and proved in the experiments.
Method for Optimization of a Nonlinear Static Balance Mechanism With Application to Ophthalmic Surgical Forceps
Authors: Powell Katherine M. , Frecker Mary I.
Published: June 2008

A new method for optimizing the dimensions of a nonlinear static balance mechanism has been created. A rigid link slider-crank mechanism with a nonlinear spring is designed to balance a compliant mechanism. This is accomplished by determining the potential energy of the compliant mechanism using finite element analysis and then optimizing the dimensions of the static balance mechanism to balance the potential energy stored in the compliant forceps. The optimization is performed using a sequential quadratic programming algorithm in Matlab’s optimization toolbox. It is seen that using higher order nonlinear springs results in a system that is better statically balanced. The mechanism that is statically balanced is a compliant forceps that has previously been designed for use in ophthalmic surgery. The compliant forceps stores energy when it creates motion, which then creates neutral positions of the mechanism with minimum potential energy. This situation is often unwanted in surgical situations. This paper uses the compliant forceps as an example of how to optimize the dimensions of a nonlinear static balance mechanism.
Dimension Synthesis for Higher-Order Kinematic Parameters and Self-Adjustability Design of Planar Linkage Mechanisms
Authors: Lin Jun , Huang Maolin
Published: June 2008

Dimension synthesis for higher-order kinematic parameters is a method to realize higher motion accuracy and to control the motion characteristics of planar linkage mechanisms. In this paper, taking a two-output impulse generator as an example, the construction of dimension synthesis equations for higher-order kinematic parameters and their solutions were carried out in four steps. In addition, to realize the self-adjustability of planar linkage mechanisms, a novel non-overconstraint basic bar group method was established to eliminate the overconstraint present in the mechanisms, which forms obstacles to planar motions. A prototype of a two-output impulse generator was produced based on the synthesis and self-adjustability design. Experimental results showed that fluctuation range of the output velocity of the two-output impulse generator was reduced by 10.3 % in comparison with a conventional impulse generator and a more steady motion was achieved, indicating the reliable motion accuracy and self-adjustability.
Model-Based Sliding Mode Control for a Robot With SMA Actuators
Authors: Ashrafiuon Hashem , Reddy Jala Vijay
Published: June 2008

This paper presents a model-based sliding mode control law for a planar three-degree-of-freedom robot arm actuated by two rotary Shape Memory Alloy (SMA) actuators and a servomotor. The SMA actuators use a combination of SMA wires and pulleys to produce rotational motion. A model of the robot is developed which combines robot equations of motion with the SMA wire heat convection, constitutive law, and phase transformation equations. Two second-order sliding surfaces are defined leading to derivation of asymptotically stable control laws within the actuation region of the SMA wires. Outside the actuation region, constant inputs are used based on the one-way nature of the SMA actuators. The control law is shown to be effective in several simulations for both set point and trajectory tracking of the robot.
On the Mobility of Single Loop N-Bar Linkage With One Prismatic Joint
Authors: Guo W. Z. , Du R. , Wang J. X.
Published: June 2008

Single loop N-bar linkages that contain one prismatic joint are common in engineering. This paper presents a systematical study on the mobility of this type of mechanism. It is found that this type of mechanisms can be divided into three categories: Class I, Class II and Class III. For each category, the slide reachable range is cut into different regions: Grashofian region, non-Grashofian region and change-point region. At each region, the rotation range of the revolute joint or rotatability of the linkage is able to determine based on Ting’s criteria. The characteristics charts are given to describe the rotatability condition. For active prismatic joint, the input revolute joint(s) is/are dependent in non-Grashofian region but independent in other regions. For passive prismatic joint, the revolvability of input revolute joints is dependent on the offset distance of the prismatic joint. Two special cases are illustrated with four and five bars. Examples are given to demonstrate the presented method able to cover all the cases of N-bar linkages with one or a set of adjoined prismatic joints and N-bar open-loop robotic mechanisms.
Dynamic Modeling and Coupling of Underactuated Flexible Robots
Authors: Chen Wei , Yu Yue-Qing , Zhang Xu-Ping
Published: June 2008

Underactuated robots have fewer control inputs than the degrees of freedom of the system. Dynamic model of an underactuated robot considering link flexibility is firstly proposed based on finite element method. Several dynamic coupling indices for underactuated flexible manipulators are analyzed and discussed including acceleration coupling between active and passive joints, dynamic coupling between passive joints and drive torques, and the coupling effect of elastic deformations and joints. The simulation results illustrate that these coupling effects are very important in structure design, configuration design, actuator placement and the control to underactuated robots system, and show that the elastic deformations of links have influence on dynamic coupling indices.
A Matrix Based Mobility Criterion for Parallel Platforms
Authors: Rico Jose´ M. , Aguilera Luis D. , Gallardo Jaime , Rodriguez Ramo´n , Orozco Horacio , Barrera Juan Manuel
Published: June 2008

This contribution presents a mobility criterion applicable to parallel platforms based on an analysis of the Jacobian matrices associated with the platform legs. It is important to note that this criterion is based on an analysis of the subalgebras of the Lie algebra, se(3), also known as screw algebra, of the Euclidean group, SE(3). The mathematical foundations of the method have been already presented in [1]. In this contribution it is shown that, employing a basic knowledge of linear algebra, it is possible to compute the correct mobility of a wider class of parallel manipulators, including the mobility of kinematically deficient parallel platforms and platforms with inactive pairs. Moreover, the criterion computes the passive degrees of freedom in parallel platforms. Finally, it should be emphasized that, unlike other attempts to develop a mobility criterion, the criterion developed in this contribution does not require any consideration of reciprocal screws.
Systematic Sensitivity Analysis of Spatial One-DOF Models of Diarthrodial Joints
Authors: Di Gregorio R. , Parenti-Castelli V.
Published: June 2008

The identification of an equivalent mechanism which may reproduce at best the relative passive motion of the main anatomical structures of a human articulation is a target of great importance in the study of diarthrodial joints. Passive motion, that is the motion of the joint under virtually unloaded condition, is of basic importance for understanding the role of elements like bones, ligaments, etc. The identification is based on measurements performed during in vitro experiments. Passive motion of a number of human diarthrodial joints may be reproduced by equivalent mechanisms. However, the most critical points when devising the equivalent mechanism are represented by the changes of the subject articulation geometry due to age, sex, body constitution, etc. Thus, the equivalent mechanism sensitivity to the variations of the geometric parameters needs a careful investigation. The passive motion of many diarthrodial joints can be modeled by an equivalent mechanism with one degree of freedom (dof). This paper shows how the sensitivity of a one-dof equivalent mechanism with a finite number of geometric parameters can be studied in a systematic way. A sensitivity index together with some coefficients, called influence coefficients, are proposed which enable measuring the sensitivity of a mechanism, thus allowing the comparison of different equivalent mechanisms from the sensitivity viewpoint. Finally, a case study shows the application of the proposed methodology.
Identifying and Counting the Number of Mechanisms From Kinematic Chains Subject to Design Constraints
Authors: Yan Hong-Sen , Hung Chih-Ching
Published: June 2008

A methodology is presented, based on combinatorial theory, for the enumeration of non-isomorphic mechanisms precisely from kinematic chains. According to the defined permutation groups, an algorithm for generating all non-isomorphic identified mechanisms by assigning various types of links and joints to kinematic chains is proposed. Based on the concepts of Polya’s theory and generating function, mathematical expressions are derived for counting the number of the identified mechanisms subject to the design constraints of adjacent/incident relationship between links and joints. Examples are provided to illustrate the proposed approach.
A Recursive Approach for Analysis of Snake Robots Using Kane’s Equations
Authors: Tavakoli Nia Hadi , Pishkenari Hossein Nejat , Meghdari Ali
Published: June 2008

This paper presents a recursive approach for solving kinematic and dynamic problem in snake-like robots using Kane’s equations. An n-link model with n-nonholonomic constraints is used as the snake robot model in our analysis. The proposed algorithm which is used to derive kinematic and dynamic equations recursively enhances the computational efficiency of our analysis. Using this method we can determine the number of additions and multiplications as a function of n. The proposed method is compared with the Lagrange and Newton-Euler’s method in three different aspects: Number of operations, CPU time and error in the computational procedures.
Path Planning for Manipulator Robots in Cluttered Environments
Authors: Lahouar Samir , Zeghloul Said , Romdhane Lotfi
Published: June 2008

In this paper we propose a new path planning method for robot manipulators in cluttered environments, based on lazy grid sampling. Grid cells are built while searching for the path to the goal configuration. The proposed planner acts in two modes. A depth mode, while the robot is far from obstacles, makes it evolve toward its goal. While a width search mode becomes active when the robot gets close to an obstacle. This method provides the shortest path to go around the obstacle. It also reduces the gap between pre-computed grid methods and lazy grid methods. No heuristic function is needed to guide the search process. An example dealing with a robot in a cluttered environment is presented to show the efficiency of the method.