Dynamic modeling and end position control of a 5-BAR flexible robot with 6-DOF

In this thesis, a new dynamic model for a six-degree-of-freedom (6-DOF) flexible robot and a new control scheme for a three-degree-of-freedom (3-DOF) flexible robot have been designed and implemented. The dynamic model has been designed on the assumption that the entire mass is concentrated at the center of mass of the set wrist-mass, which is the combined mass of the wrist and the spherical mass attached to it, signifying a compliance matrix can be used to model the oscillations of the structure. This therefore makes the dynamics of the robot very simple: a lumped single mass and an inertia tensor model rather than the usual distributed mass model. A two-nested control-loop scheme has been used to control the position of the base of the wrist by employing encoders and gauge measurements as feed-backs. A stability analysis of the control scheme has been carried out, and the robustness of the proposed control scheme under payload changes is also depicted. Lastly, simulation results that prove the effectiveness of the proposed control scheme are shown

Ecuaciones prácticas para resolver ejercicios de tiro parabólico

There will be an easy solution for solving fundamental problems of free-flight motion of a projectile? This is a basic question from which this paper starts. In this research five equations were obtained, that simply solves Two-Dimensional problems of free-flight motion of a projectile under a constant downward acceleration. Air Viscous Friction is not taken into account. These equations are obtained from the constant acceleration equations. Five problems of free-flight motion of a projectile were solved using those equations vs Classical Theory. Results show that there is a variation between them of 0.237%, which demonstrates the effectiveness of the proposed method.Esta investigación surge de la pregunta si habrá una forma directa de resolver ejercicios de tiro parabólico, el cual es un tema básico, pero, a la vez, complejo en cursos introductorios de física. Por esta razón, es importante conocer, comprender y analizar este tipo de fenómenos físicos. En este trabajo se obtuvo un conjunto de ecuaciones para resolver ejercicios de tiro parabólico en dos dimensiones de forma directa, para casos donde se considera una aceleración gravitacional constante y se desprecia la fuerza de rozamiento del aire. Estas ecuaciones son deducidas algebraicamente a partir de las ecuaciones generales del movimiento rectilíneo uniforme y uniformemente acelerado. Cinco tipos de ejercicios de tiro parabólico fueron resueltos empleando el método presentado en este trabajo y los métodos clásicos. Los resultados obtenidos muestran que la variación de su magnitud en todos los casos es menor a 0.372%, lo que demuestra la aceptable efectividad de la propuesta presentada

Effect of end-clamping constraints on bending crashworthiness of square profiles

The bending crashworthiness performance of thin-walled structures is affected by several factors such as the end-clamping constraints. The end-clamping configuration should be carefully investigated since it is an important part of the real working condition of a structure under bending loading. End-clamping fixtures (pads) can be used intentionally as complementary energy dissipating mechanisms to trigger new plastic deformation. The present article explores the use of pads to improve the crashworthiness of square tubes under lateral loads. For this purpose, internal, external, and combined pads were located at the profile ends which were subjected to a modified three-point bending test using finite element simulations. The effect of assembly force (fN) and pad length (lp) on the energy absorption was investigated. The structures were made of aluminum 6063-T5 and modeled with elasto-plastic properties considering ductile and shear damage criteria with evolution. Additionally, the numerical results were validated by an experimental three-point bending test on a square profile with constrained and free ends. Our results for a structure with end-clamping fixtures show an improvement of crashworthiness performance in a range from 42.38 – 57.89% relative to a structure with free-ends. The best crush force efficiency (CFE) of 0.78 was obtained when external pads were implemented. Moreover, the importance of fN on the end-clamping pads was noticed since CFE is increased by 9.30% when a normalized force of 0.109 is applied. The importance of pad length was also demonstrated. An improvement of 69.38% in CFE was achieved when a normalized length Lp= 0.138 was implemented. Finally, with the findings of our work, a design of end-clamping fixtures for an automobile’s side-door impact beam is presented and analyzed

Bending crashworthiness of elliptical tubes with different aspect ratio and stiffeners

Lateral car collisions are common scenarios that represent one of the top causes of passenger’s fatalities and injuries. For this purpose, the current article investigates the effect of cross-sectional aspect ratio (β) on the crashworthiness performance of elliptical profiles under lateral loads. For this purpose, structures with different aspect ratios (β) were evaluated. Special emphasis was set on modelling progressive damage by the Johnson–Cook (J-C) failure model for aluminum 6063-T5. The accuracy of our numerical results was determined by experimental validation of a first three-point bending model. From the numerical results, an improvement of energy absorption (Ea) and crushing force efficiency (CFE) is achieved as the aspect ratio (β) increases. In this sense, the best CFE performance (0.728) was obtained for a structure with β= 1.50, which means an improvement of 30.59% of Ea and 9.96% of CFE relative to a circular tube. At this point, the limits for sizing of elliptical profiles in terms of (β) were determined by practical equation. To improve even more the crashworthiness capacity of the elliptical profile with β= 1.50, the use of plates in horizontal, vertical, and combined mode was also explored. As a result, the effectiveness of vertical ribs was demonstrated. The highest CFE performance was obtained for a structure vertically reinforced with three ribs, which allowed a further increase of CFE up to 0.805. Then a final improvement in CFE of 21.60% was computed. Finally, an application of our study to a side sill system is also investigated