In this paper, we developed a detailed mathematical model of dual action pneumatic actuators controlled with proportional spool valves. Effects of nonlinear flow through the valve, air compressibility in cylinder chambers, leakage between chambers, end of stroke inactive volume, and time delay and attenuation in the pneumatic lines were carefully considered. We performed system identification, numerical simulation, and model validation experiments for two types of air cylinders and different connecting tubes length. The mathematical model of the present article is used in a sequel article to develop high performance nonlinear pneumatic force controllers. [S0022-0434(00)00503-7]

This article deals with the rigid body collisions of planar kine matic chains with an external surface while in contact with other surfaces. Two solution procedures that cast the impact equations in differential and algebraic forms are developed to solve the general problem. The differential formulation can be used to obtain three sets of solutions based on the kinematic, kinetic, and energetic definitions of the coefficient of restitution, whereas the algebraic formulation can be used to obtain solu tions based on the approaches presented in Whittaker (1904) and Brach (1991). A specific example of a planar three-link chain with two contact points is studied to compare the out comes predicted by each approach. A particular emphasis is placed on the energy loss that results from the application of each solution scheme. The circumstances in which various methods lead to identical or distinct outcomes are investigated. Most importantly, the study elaborates on the rebounds at the noncolliding ends, a phenomenon that is observed only in multicontact collisions. The interaction of the chain with the contact surfaces at the noncolliding contact points is examined, and the differences in the prediction of rebounds that arise from using various methods are investigated.

The main focus of the present investigation is the development of quantitative measures to assess the dynamic stability of human locomotion. The analytical methodology is based on Floquet theory, which was developed to investigate the stability of nonlinear oscillators. Here the basic approach is modified such that it accommodates the study of the complex dynamics of human locomotion and differences among various individuals. A quantitative stability index has been developed to characterize the ability of humans to maintain steady gait patterns. Floquet multipliers of twenty normal subjects were computed from the kinematic data at Poincaré sections taken at four instants of the gait cycle, namely heel strike, foot flat, heel off, and toe off. Then, an averaged stability index was computed for each subject. Statistical analysis was performed to demonstrate the utility of the stability indices as quantitative measures of dynamic stability of gait for the subject population tested during the present study.

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This article deals with the collision of steel bars with external surfaces. The central issue of the article is the investigation of the fundamental concepts that are used to solve collision problems by using rigid body theory. We particularly focus on low velocity impacts of relatively rigid steel bars to test the applicability of these concepts.An experimental analysis was conducted to study the rebound velocities of freely dropped bars on a large external surface. A high speed video system was used to capture the kinematic data. The number of contacts and the contact time were determined by using an electrical circuit and an oscilloscope. Tests were performed by using six bar lengths and varying the pre impact inclinations and the velocities of the bars. The experimental results were used to verify the applicability of Coulomb's law of friction and the invariance of the coefficient of restitution in the class of impacts considered in this study.Then, given the unusual variation the coefficient of restitution as a result of changing pre impact inclinations, a theoretical model was developed to explain this variation. A discrete model of the bar was