Showing papers in "Journal of Mechanical Design in 2003"

Adaptive Response Surface Method Using Inherited Latin Hypercube Design Points

Abstract: This paper addresses the difficulty of the previously developed Adaptive Response Surface Method (ARSM) for high-dimensional design problems. ARSM was developed to search for the global design optimum for computation-intensive design problems. This method utilizes Central Composite Design (CCD), which results in an exponentially increasing number of required design experiments. In addition, ARSM generates a complete new set of CCD points in a gradually reduced design space. These two factors greatly undermine the effciency of ARSM. In this work, Latin Hypercube Design (LHD) is utilized to generate saturated design experiments. Because of the use of LHD, historical design experiments can be inherited in later iterations. As a result, ARSM only requires a limited number of design experiments even for high-dimensional design problems. The improved ARSM is tested using a group of standard test problems and then applied to an engineering design problem. In both testing and design application, significant improvement in the efficiency of ARSM is realized. The improved ARSM demonstrates strong potential to be a practical global optimization tool for computation-intensive design problems. Inheriting LHD points, as a general sampling strategy, can be integrated into other approximation-based design optimization methodologies.

Identifying Modular and Integrative Systems and Their Impact on Design Team Interactions

Abstract: The typical approach to developing complex products is to decompose the product into systems, and these into components. We introduce a new notion of system modularity based upon the way components share design interfaces across systems. Modular systems are those whose design interfaces with other systems are clustered among physically adjacent systems, whereas integrative systems are those whose interfaces are physically distributed or functionally integrative across all or most other systems. Our research method allows us to study how system modularity impacts design team interactions. Our approach is illustrated by analyzing the development of an aircraft engine.

Singularity Analysis of 3-DOF Planar Parallel Mechanisms via Screw Theory

Abstract: This paper presents the results of a detailed study of the singular configurations of 3-DOF planar parallel mechanisms with three identical legs. Only prismatic and revolute joints are considered. From the point of view of singularity analysis, there are ten different architectures. All of them are examined in a compact and systematic manner using planar screw theory. The nature of each possible singular configuration is discussed and the singularity loci for a constant orientation of the mobile platform are obtained. For some architectures, simplified designs with easy to determine singularities are identified.

An Approach to Decision-Based Design With Discrete Choice Analysis for Demand Modeling

Abstract: In this paper, we present the importance of using a single criterion approach to DecisionBased Design (DBD) by examining the limitations of multicriteria approaches. We propose in this paper an approach to DBD as an enhancement to Hazelrigg’s DBD framework that utilizes the economic benefit to the producer as the single criterion in alternative selection. The technique of Discrete Choice Analysis (DCA) is introduced for constructing a product demand model, which is crucial for the evaluation of both profit and production cost. An academic universal motor design problem illustrates the proposed DBD approach. It appears that DBD, when applied correctly, is capable of unambiguously selecting the preferred alternative in a rigorous manner. Open research issues related to implementing the DBD approach are raised. The focus of our study is on demonstrating the approach rather than the design results per se. @DOI: 10.1115/1.1587156#

Optimal kinematic design of spatial parallel manipulators: Application to Linear Delta robot

Abstract: An optimal kinematic design method suited for parallel manipulators is developed. The kinematic optimization process yields a design that delivers the best compromise between manipulability and a new performance index, space utilisation. It is shown that the exhaustive search minimization algorithm is effective for as many as four independent design variables and presents a viable alternative to advanced nonlinear programming methods. The proposed kinematic optimization method is applied to the Linear Delta: a three degree of freedom translational manipulator. The kinematics of the Linear Delta are solved via the polynomial method. The mobility, workspace and manipulability characteristics are examined. It is shown that the Linear Delta's manipulability generally exhibits relatively little variation when compared to space utilization. The tendency exists for the solution to converge on a zero workspace size architecture when manipulability is optimized alone. The inclusion of the space utilization index in the cost function is crucial for obtaining realistic design candidates.

Mesh Phasing Relationships in Planetary and Epicyclic Gears

Abstract: Planetary and epicyclic gears (Figure 1) rely on symmetry to achieve the large torque-weight ratios and compactness that make them widely used in multiple applications. A desirable design objective is to divide the load equally such that the multiple sun-planet tooth meshes carry nearly equal load with the same load equality for the ring-planet tooth meshes. To achieve this, one seeks to have all sun-planet meshes be in-phase, that is, each sun-planet mesh nominally has identical mesh conditions (i.e., number of teeth in contact) at all times with similar conditions for the ring-planet meshes. Past research has shown, however, that differing mesh phasing between the sun-planet (and consequently ring-planet) meshes has powerful impact on the dynamic response and can have significant benefits in reducing vibration and noise [1–4]. In essence, designers have a variety of options and objectives in choosing the mesh phasing for a given application, and a clear understanding of the relations governing the mesh phasing is essential.Copyright © 2003 by ASME

A Study of Early Stage Self-Loosening of Bolted Joints

Abstract: Mechanical Engineering, University of Nevada, Reno, NV 89557 Both experimental investigation and finite element analysis were conducted to explore the mechanisms for the early stage self-loosening of bolted joints under transverse cyclic loading The nuts were glued to the bolts using a strong thread locker in the self-loosening experiments to ensure that no backing-off of the nut occurred Depending on the loading magnitude, the clumping force reduction ranged from 10% to more than 40% of the initial preload after 200 loading cycles Three-dimensional elastic-plastic finite element analysis was conducted with the implementation of an advanced cyclic plasticity model The finite element results revealed that the local cyclic plasticity occurring near the roots of the engaged threads resulted in cyclic strain ratcheting The localized cyclic plastic deformation caused the stresses to redistribute in the bolt, and the result was the gradual loss of clamping force with loading cycles The finite element results agreed with the experimental observations quantitatively When the two clamped plates started to slip and the slip displacement was controlled, both experiments and finite element simulations suggested that the friction between the clamped plates has an insignificant influence on the early stage self-loosening

Multi-Speed Gearbox Design Using Multi-Objective Evolutionary Algorithms

Abstract: Optimal design of a multi-speed gearbox involves different types of decision variables and objectives. Due to lack of efficient classical optimisation techniques, such problems are usually decomposed into tractable subproblems and solved. Moreover, in most cases the explicit mathematical expressions of the problem formulation is exploited to arrive at the optimal solutions. In this paper, we demonstrate the use of a multi-objective evolutionary algorithm, which is capable of solving the original problem involving mixed discrete and real-valued parameters and more than one objectives, and is capable of finding multiple nondominated solutions in a single simulation run. On a number of instantiations of the gearbox design problem having different complexities, the efficacy of NSGA-11 in handling different types of decision variables. constraints, and multiple objectives are demonstrated. A highlight of the suggested procedure is that a post-optimal investigation of the obtained solutions allows a designer to discover important design principles which are otherwise difficult to obtain using other means.

Dual quaternion synthesis of constrained robotic systems

Abstract: Constrained robotics systems are serial or parallel robots with less than six degrees of freedom. Dimensional synthesis is defined as the process of dimensioning a robot, that is, designing the link dimensions for a given task or set of tasks. In finite-position synthesis, we define the task as a series of positions that the robot must reach. Dimensional synthesis of planar mechanisms was first solved using graphic methods, and later those methods were transformed into algebraic equations that described the constraints on the movement of the mechanism. This approach was successfully applied to spherical mechanisms and simple cases of spatial mechanisms. The methodology was not extended to general constrained robots due to the difficulty in stating the geometric constraints for robots with more than three links. A systematic approach for the synthesis of spatial robots was developed based on using the kinematics equations of the robot. The kinematics equations are spatial transformations from a fixed frame to the end-effector of the robot, parameterized by both the dimensions of the links and the joint variables. In this dissertation, a method for the kinematic synthesis of constrained robots is presented. It is based on the use of dual quaternions to construct the kinematics equations of the robot from a reference position and to equate them to a set of task positions. A calculation was devised to compute the maximum number of task positions for each robot topology, and a classification of constrained robots was obtained according to this. The design equations produced using this methodology have been solved numerically for both the link dimensions and the joint variables, and also a scheme has been introduced to eliminate the joint variables in order to obtain algebraic equations. These have been further simplified to closed algebraic expressions in several cases. The dual quaternion synthesis methodology provides with a tool for the systematic design of constrained robots. Some of these results have been implemented in computer-aided design systems.

Application of a System Level Model to Study the Planetary Load Sharing Behavior

Abstract: In planetary transmissions, the input torque is split between a number of parallel sun-pinion-ring gear paths. Under ideal conditions, each parallel path carries the same amount of torque. However, manufacturing errors in the pinion pin-hole location cause unequal load sharing between the parallel paths. The nature of this load sharing behavior depends upon the number of pinions in the planetary system. This load sharing behavior is studied for 4, 5 and 6 pinion variants of a planetary transmission. Critical manufacturing tolerances are identified and loss function curves are generated. The effects of sun gear support stiffness, pinion needle bearing stiffness, and input torque on the load sharing results are also studied. It is shown that as the number of pinions in a planetary transmission increases, the pin-hole position error tolerance has to be tightened in order to reap the full benefits of load sharing between the pinions. Gear System Analysis Modules (GSAM) is an analytical tool that can model entire gear systems and will be used in this paper to quantify the load sharing between pinions. The numerical techniques implemented in GSAM will be briefly reviewed.Copyright © 2003 by ASME

Windage Losses in High Speed Gears: Preliminary Experimental and Theoretical Results

Abstract: Power losses in high-speed gears come from the friction between the teeth (sliding and rolling), the lubrication process (dip or jet lubrication), the pumping of a gas-lubricant mixture during the meshing and the losses associated with windage effects. The objective of this paper is to present a number of preliminary experimental and theoretical findings on the prediction of windage losses. Experiments were conducted on a test bench whose principle consists in driving a gear to a given speed and then measuring its deceleration once it has been disconnected from the motor. The transmission between the motor and the rotor is ensured by a friction wheel which also plays the role of speed multiplier. A pneumatic jack either imposes a sufficient contact pressure between the driving wheel and the rotor (transmission of rotation), or is used for separating the parts when the maximum speed is reached. A disk and 4 different gears were tested in the absence of a lubricant at speeds ranging from 0 to 12 000 rpm. Two different theoretical approaches have been developed: i) a dimensional analysis based upon the dimensionless groups of terms which account for the flow characteristics (Reynolds number), the gear geometry (tooth number, pitch diameter, face width) and the speed, ii) a quasi-analytical model considering in detail the fluid flow on the gear faces and inside the teeth. It is found that both approaches give good results in comparison with the experimental evidence and two analytical formulae aimed at predicting windage losses in high-speed gears are proposed.© 2003 ASME

Kinematic Analysis of the Ball Screw Mechanism Considering Variable Contact Angles and Elastic Deformations

Abstract: The theoretical analyses developed by Lin et al. [6] for the kinematics of the ball screw mechanism have been partly adapted for the present study. In order to better understand the sliding behavior arising at two contact areas, the analyses of a ball bearing, while accounting for elastic deformation, are modified through coordinate transformations prior to their applications to the analyses for the ball screw mechanism. The influence of differing the parameters such as friction coefficient, normal force acting on the ball, and contact angle on a ball-screw's mechanism at two contact areas are evaluated. The results of the ball-screw's mechanical efficiency achieved by the present model are displayed to compare with those evaluated based on the model of Lin et al. Substantial differences exist in the results evaluated by these two models, especially those created at high screw rotational speeds.

Strategies for Modeling Friction in Gear Dynamics

Abstract: Sliding friction between meshing teeth is one of the primary excitations for noise and vibration in geared systems. Yet, there exist very limited studies on this topic. This paper proposes new modeling strategies for incorporating frication in the dynamic analysis of a gear pair First. some tribological issues are discussed for estimation of the friction forces under different operating conditions. Second, modeling procedures and results are compared for linear time-invariant, linear time-varying and non-linear time-varying formulations. Criteria such as energy balance, system complexity and desired solution methodology are discussed. Finally, sample results from the various analyses along with their benefits and limitations are examined.

Freeform Skeletal Shape Optimization of Compliant Mechanisms

Abstract: Compliant mechanisms are elastic continua used to transmit or transform force and motion mechanically. The topology optimization methods developed for compliant mechanisms also give the shape for a chosen parameterization of the design domain with a fixed mesh. However, in these methods, the shapes of the flexible segments in the resulting optimal solutions are restricted either by the type or the resolution of the design parameterization. This limitation is overcome in this paper by focusing on optimizing the skeletal shape of the compliant segments in a given topology. It is accomplished by identifying such segments in the topology and representing them using Bezier curves. The vertices of the Bezier control polygon are used to parameterize the shape-design space. Uniform parameter steps of the Bezier curves naturally enable adaptive finite element discretization of the segments as their shapes change. Practical constraints such as avoiding intersections with other segments, self-intersections, and restrictions on the available space and material, are incorporated into the formulation. A multi-criteria function from our prior work is used as the objective. Analytical sensitivity analysis for the objective and constraints is presented and is used in the numerical optimization. Examples are included to illustrate the shape optimization method.

Kinematic Synthesis of a Spatial 3-RPS Parallel Manipulator

Abstract: This paper presents the design of spatial 3-RPS parallel manipulators from dimensional synthesis point of view. Since a spatial 3-RPS manipulator has only 3 degrees of freedom, its end effector cannot be positioned arbitrarily in space. It is shown that at most six positions and orientations of the moving platform can be prescribed at will and, given six prescribed positions, there are at most ten RPS chains that can be used to construct up to 120 manipulators. Further, solution methods for fewer than six prescribed positions are also described.

Experimental studies assessing the repeatability of a functional modeling derivation method

Abstract: This paper presents the results of research attempts to substantiate repeatability and uniqueness claims of a functional model derivation method following a hypothesis generation and testing procedure outlined in design research literature. Three experiments are constructed and carried out with a participant pool that possesses a range of engineering design skill levels. The experiments test the utility of a functional model derivation method to produce repeatable functional models for a given product among different designers. In addition to this, uniqueness of the functional models produced by the participants is examined. Results indicate the method enhances repeatability and leads designers toward a unique functional model of a product. Shortcomings of the method and opportunities for improvement are also identified.

Design Process Error-Proofing: Failure Modes and Effects Analysis of the Design Process

Abstract: This paper presents a new application of Failure Modes and Effects Analysis (FMEA) on product development processes. Our research develops error-proofing methods for product development processes to prevent serious design errors that compromise project features, time, or cost. Design process FMEA categorizes design errors in six areas: knowledge, analysis, communication, execution, change, and organization errors. The paper explains the method, illustrates it with an example, and discusses its effectiveness. The paper concludes with the proposed work to address the existing lack of a systematic approach to design process error-proofing.Copyright © 2003 by ASME

A Review of Formulas for the Mechanical Efficiency Analysis of Two Degrees-of-Freedom Epicyclic Gear Trains

Abstract: This paper after a rigorous proof of the formulas originally proposed by Rodzimovsky, demonstrates the numerical equivalence of the different approaches available for computing the mechanical efficiency of two degrees-of-freedom (d.o.f.) epicyclic gear trains. The paper includes also a discussion on the redundancy of data required by some formulas.

Investigation of Parallel Manipulators Using Linear Complex Approximation

Abstract: This investigation deals with singularity analysis of parallel manipulators and their instantaneous behavior while in or close to a singular configuration. The method presented utilizes line geometry tools and screw theory to describe a manipulator in a given position. Then, this description is used to obtain the closest linear complex, presented by its screw coordinates, to the set of governing lines of the manipulator. The linear complex axis and pitch provide additional information and a better physical understanding of the type of singularity and the motion the manipulator tends to perform in a singular point and in its neighborhood. Examples of Hunt's, Fichter's and 3-UPU singularities, along with a few selected examples taken from Merlet's work [1], are presented and analyzed using this method.

The Design of a New Metal Forming Press with Controllable Mechanism

Abstract: Metal forming press is one of the most commonly used manufacturing machines. Every day millions of parts are produced by metal forming ranging from battery caps to automotive body panels. Therefore, even a small improvement may add to significant corporative gain. Currently, the metal forming presses can be divided into two categories: mechanical presses and hydraulic presses. The former is fast (high speed presses may reach up to several thousand shots per minute) and energy efficient (the large flywheel eases the impulsive force), but lacks flexibility. On the other hand, the hydraulic presses are flexible (their motions can be programmed) and accurate, but are expensive to build and to operate. Recently, there are mechanical presses driven by seryomotors. They could perform as flexible as hydraulic presses with high speed. Nevertheless, they are even more expensive to build and to operate. This paper introduces a new design of mechanical press whose performances are programmable, including the trajectory and the velocity of the stroke, and yet, it is relatively inexpensive to build and to operate. The key idea of the new design is a 2-degree-of-freedom seven-bar linkage mechanism driven by a large constant speed motor and a small servomotor. First, the kinetics and kinematics of the design are presented including the feasibility conditions, mechanical advantage, as well as the torque and power distribution between the two motors. Next, a number of simulation results are given. The design (parameter) optimization is also carried out using Genetic Algorithm (GA). Based on computer simulation, it is shown that the new design is indeed very attractive.

Design Formulas for Permanent-Magnet Bearings

Abstract: As the energy densities in permanent magnet materials increases, permanent magnet (PM) bearings are becoming increasingly attractive machine elements for applications ranging from turbo machinery to energy storage flywheels. Desirable qualities include high speed, low wear, energy savings, and freedom from lubricants that can degrade or contaminate other system components. In this paper we develop analytical expressions for stiffness and peak load in stacked-structure radial magnetic bearings that extend the seminal work of Backers, and Yonnet and co-workers. In addition to the derivation of simple design rules, the axial peak force and negative axial stiffness are calculated.

Valve-Plate Design for an Axial Piston Pump Operating at Low Displacements

Abstract: The objectives of this research are to investigate the principal advantages of using various valve-plate slot geometries within an axial piston pump. In particular, three types of geometries are considered: a constant area slot geometry, a linearly varying slot geometry, and a quadratically varying slot geometry. By analyzing the pressure transients that are associated with each design at low pump displacements, it is shown that the magnitude of the pressure transition itself and the maximum pressure time rate-of-change may be specified for each design. In conclusion, it is shown that the constant area slot design exhibits the principal advantage of minimizing the required discharge area of the slot, the linearly varying slot design exhibits the principal advantage of utilizing the shortest slot length, while the quadratically varying slot design exhibits no principal advantage over either of the other two designs. The results of this research suggest that the use of quadratically varying slot geometry is not justified since it offers no obvious performance improvement.

Use of the Finite Element Absolute Nodal Coordinate Formulation in Modeling Slope Discontinuity

Abstract: A large rigid body rotation of a finite element can be described by rotating the axes of the element coordinate system or by keeping the axes unchanged and change the slopes or the position vector gradients In the first method, the definition of the local element parameters (spatial coordinates) changes with respect to a body or a global coordinate system The use of this method will always lead to a nonlinear mass matrix and non-zero centrifugal and Coriolis forces The second method, in which the axes of the element coordinate system do not rotate with respect to the body or the global coordinate system, leads to a constant mass matrix and zero centrifugal and Coriolis forces when the absolute nodal coordinate formulation is used This important property remains in effect even in the case of flexible bodies with slope discontinuities The concept employed to accomplish this goal resembles the concept of the intermediate element coordinate system previously adopted in the finite element floating frame of reference formulation It is shown in this paper that the absolute nodal coordinate formulation that leads to exact representation of the rigid body dynamics can be effecitively used in the analysis of complex structures with slope discontinuities The analysis presented in this paper also demonstrates that objectivity is not an issue when the absolute nodal coordinate formulation is used due to the fact that this formulation automatically accounts for the proper coordinate transformations

Dynamics of Hypoid Gear Transmission With Nonlinear Time-Varying Mesh Characteristics

Abstract: The coupled translation-rotation vibratory response of hypoid geared rotor system due to loaded transmission error excitation is studied by employing a generalized 3-dimensional dynamic model. The formulation includes the effects of backlash nonlinearity as well as time-dependent mesh position and line-of-action vectors. Its mesh coupling is derived from a qquasi-static, 3-dimensional, loaded tooth contact analysis model that accounts for the precise gear geometry and profile modifications. The numerical simulations show significant tooth separation and occurrence of multi-jump phenomenon in the predicted response spectra under certain lightly loaded operating conditions. Also, resonant modes contributing to the response spectra are identified, and cases with super-harmonics are illustrated. The computational results are then analyzed to quantify the extent of nonlinear and lime-varying factors.

Dimensional synthesis of Bennett linkages

Abstract: This paper presents a synthesis procedure for a spatial 4R linkage, known as Bennett’s linkage. It is known that the two solutions of the RR chain synthesis equations form a Bennett linkage. While analytical solutions to these equations have been developed previously, this paper uses the cylindroid that is known to exist for a Bennett linkage to simplify the solution process. It is interesting that geometric constraint associated with the spatial 4R chain simplifies the solution of the RR chain design equations. An example design is presented.

Evaluation of the Effect of Misalignment and Profile Modification in Face Gear Drive by a Finite Element Meshing Simulation

Abstract: Face gear drives have many advantages over other cross axis transmissions especially in high performance applications. The lack of published design experience and design standards make their design difficult. This is mainly due to the complex geometries and to the lack of practical experience. For these reasons face gears have not been used for long. This work is aimed at investigating the behavior of a face gear transmission considering contact path under load, load sharing and stresses, for an unmodified gear set including shaft misalignment and modification on pinion profile. The investigation is carried out by integrating a 3D CAD system and a FEA code, and by simulating the meshing of pinion and gear sectors with three teeth, using contact elements and an automated contact algorithm. The procedures followed to create the 3D models of teeth in mesh are described and finite element analysis results discussed showing the differences between unmodified, modified and misaligned teeth. Results show the influence of load on theoretically calculated contact paths, contact areas, contact length and load sharing. The differences with respect to the ideal case are sometimes remarkable. Further developments are discussed.© 2003 ASME

Motor integrated parallel hybrid transmission

Abstract: A motor-integrated transmission mechanism for use in parallel hybrid electric vehicles. The transmission can provide five basic modes of operation that can be further classified into sixteen sub-modes: one electric motor mode, four engine modes, four engine/charge modes, three power modes and four regenerative braking modes. Each of these sub-modes can be grouped into like clutching conditions, providing the functional appearance of a conventional 4-speed automatic transmission, with electric launch, engine-only, engine/charge, power-assist, and regeneration capability. CVT capability is provided with one of the engine/charge modes. The transmission can be incorporated in front-wheel drive and in rear-wheel drive vehicles.

Kinematic Analysis of a Novel Translational Platform

Abstract: A new three-d.o.f. parallel mechanism, with 3-RPC topology, is presented in the paper and its kinematics is studied. The proposed architecture, if proper geometrical conditions are satisfied, has an overconstrained structure which allows motions of pure translation. The simple structure of the mechanism allows finding closed-form solutions for both inverse and direct position kinematics; the differential analysis has been developed as well. by deriving a symbolic expression for the Jacobian matrix. Then, some design considerations are exposed to keep the singular points out of the working space of the mechanism and all the isotropic configurations are eventually identified.

Distributed Object-Based Modeling in Design Simulation Marketplace

Abstract: Predictive integrated system modeling is now a pressing issue in the design of complex products ranging from home air conditioners to automobiles and aircraft. While product development organizations have official top-down development processes, it is generally understood that in practice individual participants perform their work in an informal marketplace, bartering service exchange relationships to get what they need to resolve their part of the problem. The authors envision a distributed simulation service marketplace running in parallel with the activities of design participants. This paper develops an object model representation to enable this vision for a decentralized design simulation marketplace. A prototype implementation, called DOME (Distributed Object-based Modeling Environment), is used to illustrate the concept on a beverage container design problem.

The Synthesis of Elliptical Gears Generated by Shaper-Cutters

Abstract: The synthesis of elliptical gears is formulated using envelope theory by means of a suitable shaper-cutter with involute tooth profile. A general algorithm producing the pitch curves of elliptical gears and their rack with any number of lobes is proposed. Evolutes of pitch curves can be also obtained in order to choose a suitable shaper-cutter, even for pitch curves with concave-convex profiles. The complete synthesis of both meshing elliptical gears and their rack is reported, several graphical results being shown for design and analysis purposes. Computer animations are also available.