Dynamic Performance Measurement Research Articles

EVALUATION OF THE DYNAMIC PERFORMANCE OF ARTICULATED VEHICLES (CASE STUDY)

Recently the evaluation of articulated vehicles dynamic performance has been the focus of a significant research effort, where most of the tractors and semitrailers are manufactured separately each in a different place. However, the suitable combinations between them represent a major problem, especially in the military field where the payloads are characterized by unconventional weights and dimensions. The objective of this paper is to investigate the scientific basis for evaluation of the controllability and stability limits of such combinations. In order to achieve this goal, a theoretical analysis, computer simulation and field measurements have been carried out. In the theoretical analysis, the dynamic performance measures of articulated vehicles have been discussed and analyzed. In the computer simulation, the validated models developed by UMTRI (University of Michigan Transportation Research Institute) have been used to evaluate these dynamic performance measures. In order to show the applicability of using these computer tools, a practical case is considered for an existing tractor-semitrailer combination used in the Egyptian army. The possible field measurements are done to obtain the needed input data. Other data are considered either from the manufacturer manuals, or by estimation using the published empirical methods. The practical case study shows the applicability of using this technology in the national scale.

An integrated dynamic performance measurement system for improving manufacturing competitiveness

Until the 1980s manufacturing companies relied solely on performance measurement systems based on traditional cost accounting systems to control, monitor, and improve their operations. However, it has been shown that these systems do not capture the relevant performance issues for today's manufacturing environment. Rather, they focus on monitoring and controlling versus supporting process improvement, promoting overall system optimization, and addressing the dynamics of changing systems. In order to overcome the limitations of the traditional performance measurement systems a variety of integrated systems have been proposed. However, these systems have not yet fully addressed the requirements of a performance measurement system for today's manufacturing environment. This paper presents an integrated dynamic performance measurement system (IDPMS) developed in conjunction with the Missouri Plant of Square D Company. The IDPMS integrates three main areas of the company: management, process improvement team, and factory shop floor. To achieve an integrated system, the three areas are linked through the specification, reporting and dynamic updating of the defined areas of success, performance measures, and performance standards. Three tools are incorporated to support and enhance the integration within the IDPMS. An example is given that illustrates how the IDPMS addresses the current requirements of a performance measurement system.

An alternative approach for analysis of performance of one-sided cusum charts with variable sampling intervals

An alternative approach for analyzing performance of one-sided Cusum charts with variable sampling intervals (VSI) is proposed. In this approach, a Markov chain with some dummy states is used. By this approach some dynamic performance measures of the VSI Cusum charts, such as the distribution of time to signal and the average time to signal against a change-point, can be determined. Some numerical results are shown, and from these results the dynamic performance of VSI Cusum charts is discussed.

Poor correlations between isometric tests and dynamic performance: relationship to muscle activation.

The purpose of this research was to perform isometric tests at two joint angles and examine their relationship to dynamic performance. In addition, electromyograph data were collected from the triceps brachii and pectoralis major muscles to compare underlying neural characteristics between the isometric tests and dynamic movement. A group of 24 healthy male subjects performed two isometric tests in a bench press position, at elbow angles of 90 and 120 degrees. From these data, the maximal force and rate of force development were determined. In addition, each subject performed a seated medicine ball throw as a measure of dynamic upper body performance. Correlations showed that isometric measurements of force (r = 0.47-0.55) and rate of force development (r = 0.08-0.31) were poor predictors of dynamic performance. The angle of isometric assessment had little effect on the relationship between the tests and measurements of performance. The myo-electric data was processed in terms of the integrated electromyogram and the Fourier transformed frequency spectrum. These data demonstrated differences in the neural activation patterns of the musculature, between the isometric 90 degrees test and the medicine ball throw. The poor relationship between isometric tests and medicine ball performance was consequently, at least partially, attributed to differing motor unit activation patterns between isometric and dynamic movement. The results of this research strongly suggest that isometric tests have limited value when assessing dynamic upper body performance.

Reliability studies on assembly robots using the finite element method

The concept of manipulator reliability is useful in obtaining a statistical measure of the manipulator dynamic performance based on the deflections of the end-effector. Considerations of link flexibility and inertial effects are important for estimating end-effector errors due to self-weight and payload. Three-dimensional (3D) beam elements, direct stiffness formulation of the finite element method, kinematic pair modelling, effects of friction at the joints, and inertial effects have been considered for analysis to compute the dynamic deflections of the end-effector. Reliability estimation of a manipulator with 5 R and I P pairs performing an assembly task is given as an example based on the elastic deflections of the end-effector.

Optimal determination of feedback controller parameters conditioned on probabilistic dynamic loadings

A chance constrained optimization model is presented for determining dynamic control parameters for active members within structural designs. To begin, a dynamic model of a structure with linear displacement and velocity control at every member is developed. The optimal feedback control parameters are determined by minimizing the levels of each control parameter conditioned on the probability that displacements at any time do not exceed pre-specified maxima. The actual displacements at any point are calculated by solving the governing equations of motion subject to a given excitation which is expressed in terms of random variables. Structural response constraints, originally expressed as probability statements, are transformed into deterministic equivalent constraints using the cumulative distribution of the random force variables. The optimization model is solved using a Monte-Carlo simulation in which the objective is to minimize the control feedback parameters for each member. An example is presented using a single mode model of a one-bay, one-story frame subject to a probabilistic point force to illustrate the performance of the optimization model. The technique presented here may be used to aid engineers in locating active members within structural designs and provide a measure of the probable dynamic performance of the structure.

Singular value decomposition for dynamic system design sensitivity analysis

A computer-based method for automatic generation and efficient numerical solution of mixed differential-algebraic equations for dynamic and design sensitivity analysis of dynamic systems is developed. The equations are written in terms of a maximal set of Cartesian coordinates to facilitate general formulation of kinematic and design constraints and forcing functions. Singular value decomposition of the system Jacobian matrix generates a set of composite generalized coordinates that are best suited to represent the system. The coordinates naturally partition into optimal independent and dependent sets, and integration of only the independent coordinates generates all of the system information. An adjoint variable method is used to compute design sensitivities of dynamic performance measures of the system. A general-purpose computer program incorporating these capabilities has been developed. A numerical example is presented to illustrate accuracy and properties of the method.

Effective Bits: Is That All There Is?

The number of effective bits is becoming accepted as an overall measure of dynamic performance for analog-to-digital converters and waveform recorders. However, units with the same number of effective bits can respond very differently to waveforms of identical input data.