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BOOK REVIEWS

RESEARCH PAPERS: Design Automation Papers

J. Mech., Trans., and Automation. 1986;108(3):285-291. doi:10.1115/1.3258727.

Industrial robots in use today lack the total ability to perceive and interact with their environment. This limitation is a major obstacle confronting robotic systems developers. This work outlines an on-line process optimization strategy which allows a robot to work within a time-varying environment. After developing the kinematic model of the robot and its relationship to its environment, the process optimization strategy is simulated. The performance of the system is measured by using an index of performance and comparing the simulation results against a series of non-optimized models. The results indicate that on-line process optimization strategy significantly increases the performance of a robotic system operating in a time-varying environment.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):292-299. doi:10.1115/1.3258728.

Purely mechanical, single-actuator adaptive hard-automation modules can perform highly repetitive simple tasks much more economically, energy-efficiently and accurately than multi-degree-of-freedom, multiple-actuator robotic manipulators. As an example, an RS-SRR-SS adjustable spatial motion generator is synthesized by analytical methods with two exact prescribed positions (including orientations) for each of two different motion tasks, by numerical methods to solve a nonlinear system of equations and by optimization techniques to minimize the motion errors at additional, approximately prescribed positions.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):300-304. doi:10.1115/1.3258730.

An approach is presented for automatically generating a linearized dynamical model which is derived from a nonlinear model in the constrained Lagrangian form. Since the corresponding eigenvalue problem is ill-posed and large, a method for condensing the problem is presented which leads to significant improvements in numerical efficiency.

Topics: Eigenvalues
Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):305-311. doi:10.1115/1.3258731.

The development of high energy-rate forming machines requires the prediction of the vibrational behavior and noise radiation at the design stage. An automatic optimization technique for minimizing the kinetic energy transmitted to the ringing modes of vibration is described. Structural, functional and dynamic constraints are included to ensure the feasibility of the optimum design. The technique is suitable for adaptation to other optimizing criteria and to other types of structure.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):312-314. doi:10.1115/1.3258732.

In searching for an optimum by examining assignments of active constraints, one wishes to avoid assignments with no solution. A simple Maximal Activity Principle is stated to detect situations in which some subset of constraints has too few variables. The principle is illustrated on a well-known weldment design problem.

Topics: Design , Optimization
Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):315-322. doi:10.1115/1.3258733.

A finite-element-based method is developed and applied for geometrically nonlinear dynamic analysis of spatial mechanical systems. Vibration and static correction modes are used to account for linear elastic deformation of components. Boundary conditions for vibration and static correction mode analysis are defined by kinematic constraints between components of a system. Constraint equations between flexible bodies are derived and a Lagrange multiplier formulation is used to generate the coupled large displacement-small deformation equations of motion. A standard, lumped mass finite-element structural analysis code is used to generate deformation modes and deformable body mass and stiffness information. An intermediate-processor is used to calculate time-independent terms in the equations of motion and to generate input data for a large-scale dynamic analysis code that includes coupled effects of geometric nonlinearity and elastic deformation. Two examples are presented and the effects of deformation mode selection on dynamic prediction are analyzed.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):323-329. doi:10.1115/1.3258734.

This paper proposes a method for evaluating forced and self-excited vibrations at the design stage of machine-tool structural systems. Cross modal flexibilities between the forced excited and the displacement pick-up points are analyzed. The relationships between the highest allowable values of receptance and vibrational displacement, and the static compliance and modal flexibility are clarified. Then the algorithms of the evaluative methods which use those analyses are given. Using the proposed method, natural modes which must be disregarded in the evaluation of the characteristics can be determined, (1) even when directional orientations of the excited force at points in regard change greatly as a result of states of operations or cannot be definitely determined, and (2) even if damping properties are not clearly known. Designers can judge whether or not a given structural design has vibrational defects. The procedures of the evaluative method are exemplified with numerical examples.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):330-335. doi:10.1115/1.3258735.

A general procedure is proposed for evolving the form of a density function that is consistent with the concept of subjective probability. The procedure directly applies new data information to the updating of the form of a density function without imposing on it any theoretical distribution that could restrict its shape, and permits the direct use of judgment arising from real world experience. It is based on the simple concept that sample size is a measure of confidence in the shape of a density function. Two possible algorithms are given, and the concept is extended for simple “true” or “false” events. The importance of probability in artificial intelligence is also dicusssed, and its essentially subjective nature is described. Procedures are briefly suggested.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):336-339. doi:10.1115/1.3258736.

An algorithm is presented for the efficient constrained or unconstrained minimization of computationally expensive objective functions. The method proceeds by creating and numerically optimizing a sequence of surrogate functions which are chosen to approximate the behavior of the unknown objective function in parameter-space. The Recursive Surrogate Optimization (RSO) technique is intended for design applications where the computational cost required to evaluate the objective function greatly exceeds both the cost of evaluating any domain constraints present and the cost associated with one iteration of a typical optimization routine. Efficient optimization is achieved by reducing the number of times that the objective function must be evaluated at the expense of additional complexity and computational cost associated with the optimization procedure itself. Comparisons of the RSO performance on eight widely used test problems to published performance data for other efficient techniques demonstrate the utility of the method.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):340-344. doi:10.1115/1.3258737.

The operating speed of a high-speed cam system can be maximized by the proper choice of both kinematic and dynamic parameters of a lumped model. Considering rocker arm ratio as an unconstrained kinematic parameter and Coulomb friction as an unconstrained dynamic parameter, it was found that the camshaft speed at which toss occurred was characterized by several local extrema, all of which were sensitive to the presence of Coulomb friction. For a particular cam system and two separate cam lift curves, design charts have been developed to aid in the choice of optimal rocker arm ratio for maximum operating speed in the presence of Coulomb friction.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):345-350. doi:10.1115/1.3258738.
Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):351-357. doi:10.1115/1.3258739.

The dynamic performance of electromagnetic actuators driving on-off control valves is optimized numerically by combining hybrid lumped-parameter/distributed-parameter actuator models with an efficient constrained optimization technique. Two examples of constrained actuator optimization are presented where up to eight design parameters are optimized. One example problem involves minimizing variations in the response time of a fuel injection control valve caused by manufacturing and assembly tolerances, while the other example deals with minimizing the response time of a high-speed gas sampling valve.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):358-366. doi:10.1115/1.3258740.

In this investigation modal parameters (frequency, damping, and mode shapes) which are determined experimentally using parameter estimation techniques are employed to simulate and predict the dynamic behavior of flexible multibody systems which consist of interconnected rigid and flexible components. The system differential equations of motion and algebraic constraint equations describing mechanical joints in the system are first identified using analytical techniques. Dynamic parameters such as mass, damping, and stiffness coefficients that appear in the system differential equations are then identified using a set of experimentally measured data. Mode shapes which are the result of the experimental identification are used to write the physical elastic coordinates of selected nodal points on the flexible body in terms of a reduced set of modal coordinates. The nonlinear differential and algebraic constraint equations are then written in terms of mixed sets of coupled reference and modal coordinates. These equations are integrated numerically using a direct numerical integration technique coupled with Newton–Raphson type iterations in order to check on constraint violations. The formulation developed is numerically exemplified using a three-dimensional dune buggy vehicle model.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Mechanisms Papers

J. Mech., Trans., and Automation. 1986;108(3):367-372. doi:10.1115/1.3258741.

A cam driving a single lumped mass through a massless, elastic, slider-crank follower linkage is considered. A technique is developed for synthesizing the cam profile to produce a desired output motion at a given design speed. The procedure takes the elasticity and changing geometry of the linkage into account. Analysis equations are also derived to study the output motion at various speeds. The equation of motion for the output link is found to be a Hill equation whose periodicity depends on the changing geometry of the mechanism.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):373-380. doi:10.1115/1.3258742.

This paper presents the analysis and design of a robotic worktable with a structure based on two platforms connected by three four-bar linkages. The worktable has three rotational degrees-of-freedom and is designed for special motion generators, such as gyroscope calibration instruments and flight simulators. Of primary interest is the influence of the characteristics of a single four-bar linkage on the entire-motion characteristics of the worktable. This involves an investigation of the effects of limit positions, rotatability of cranks, transmission-angle characteristics and the variation of design parameters of the four-bar linkages on the characteristics of the compound platform mechanism. Based on the analytical results, some physical insights are interpreted and general guidelines can be drawn on the design of this robotic worktable with prescribed motion characteristics.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):381-386. doi:10.1115/1.3258743.

The article deals with Geneva mechanisms driven with multiple cranks for the generation of multiple indexings with different index ratios during a cycle of motion. Both, Geneva-wheel mechanisms, and Geneva-slider mechanisms for the generation of rotary and linear motions with dwells, respectively, are considered. Design equations for both types of Geneva mechanisms are offered to synthesize the motion and dwell-time distributions, or the index ratio distributions, during a cycle of motion, and synthesize for the dimensions of the system. Partially irregular and completely irregular Geneva mechanisms are considered for both types, where the partially irregular Geneva mechanisms generate the same motion time but different dwell times for different indexings, while the completely irregular Geneva mechanisms generate different motion times as well as different dwell times for different indexings during a sequence of indexings. Sequences of indexings during one cycle of motion (during one rotation of the Geneva wheel, for example) can be repeated several times. The uses of the design equations offered are illustrated with six industrial application examples.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):387-391. doi:10.1115/1.3258744.

The following result for spherical four-bar mechanisms is proved: Let all links of a spherical four-bar linkage be in the range [0, π]. Consider two linkages—one primary (p) and another secondary (s) according to the condition αi p + αf p < αi s + αf s where αs = π − αp . Then the input link is fully rotatable iff αi p + αf p < αc + α0 , |αi p − αf p | > |αc − α0 | and αi p + αf p + αc + α0 < 2π. An alternate form of this result also is developed. Applications of these results in determining full or partial rotatability of grippers in spherical robot wrists are discussed.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):392-398. doi:10.1115/1.3258745.

Through the use of dual graphs, a powerful new representation of the kinematic structure of mechanisms has been developed. This permits the development of a highly efficient completely automatic procedure for the computer-generated enumeration of the kinematic structures of mechanisms. As an example, the kinematic structures of one, two and three-degree-of-freedom plane bar linkages with up to four independent loops have been enumerated on a personal computer.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Power Transmissions and Gearing Papers

J. Mech., Trans., and Automation. 1986;108(3):403-412. doi:10.1115/1.3258748.

The subject paper presents the methods and results of fatigue tests for both torch-cut and machined racks using 40.4 mm module and finite-element elastic stress analyses for these racks. Further, the results of the analysis of fluctuating jack load range distribution over a one-year period for a jack-up rig is presented. The author proposes a fatigue design method of racks for jack-up units based on the foregoing results. The proposed fatigue design method was compared with those of ASME Boiler and Pressure Vessel Code, DNV’s Classification Notes, and the draft proposal of ISO for the strength design of gears, resulting in the conclusion that a single conventional fatigue design method as presented by ASME, ISO and DNV is insufficient for the fatigue design of these racks.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):413-423. doi:10.1115/1.3258749.

The subject of paper discusses an approach taken in evaluating the load acting on racks for jack-up units (the jack load) together with its computed results. The fracture test of a full-scale rack for a jack-up unit and a finite-element elastic stress analysis for this rack were also conducted. These results led to new design criteria for the ultimate strength design method of racks for jack-up units, when exposed to a combination of loads including stormy conditions. Typically, the ultimate strength of the racks was evaluated on the assumption that the cross section of the rack tooth plastically collapses at its root. During this investigation, it was shown, however, that the ultimate strength of the racks needs to be evaluated also on the premise that the rack tooth is subject to shear fracture caused by its mating pinion tooth.

Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):424-432. doi:10.1115/1.3258750.

A spur gear efficiency prediction method previously developed by the authors was extended to include power loss of planetary gearsets. A friction coefficient model was developed for MIL-L-7808 oill based on disk machine data. This, combined with the recent capability of predicting losses in spur gears of nonstandard proportions, allows the calculation of power loss for complete aircraft gearboxes that utilize spur gears. The method was applied to the T56/501 turboprop gearbox and compared with measured test data. Bearing losses were calculated with large-scale computer programs. Breakdowns of the gearbox losses point out areas for possible improvement.

Commentary by Dr. Valentin Fuster

ERRATA

TECHNICAL BRIEFS

J. Mech., Trans., and Automation. 1986;108(3):399-400. doi:10.1115/1.3258746.
Abstract
Topics: Tensors
Commentary by Dr. Valentin Fuster
J. Mech., Trans., and Automation. 1986;108(3):400-402. doi:10.1115/1.3258747.
Abstract
Commentary by Dr. Valentin Fuster

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