B. S. Thompson

Automated design of modular fixtures for flexible manufacturing systems

Abstract The absence of adequate flexible fixturing methodologies is a significant impediment to the evolution of truly flexible manufacturing systems. Modular fixturing is one of the principal emerging technologies which addresses this void in computer integrated manufacturing. A methodology is proposed herein for the automated design and robotic assembly of these modular fixturing systems based on the integration of state-of-the-art methodologies from several distinctly different disciplines. The complexity of this challenging frontier problem is discussed and the interdisciplinary nature of the solution philosophy is emphasized.

The computer-aided design of modular fixturing systems

The flexibility of modular fixturing systems can be exploited to significantly enhance the productivity of computer integrated manufacturing facilities. A major impediment to the implementation of this philosophy is the absence of viable methodologies for the automated design and assembly of these fixturing systems. This paper addresses this technological void by proposing a CAD/CAM tool for the automated design and robotic assembly of modular fixturing systems which can form the basis for a fully automated design system. The development of automated flexible fixturing technologies that transcend the traditional time-consuming and expensive practice of manual assembly would significantly contribute to the evolution to the factory-of-the-future.

A new generation of innovative ultra-advanced intelligent composite materials featuring electro-rheological fluids: an experimental investigation

A new generation of revolutionary, intelligent, ultra-advanced composite materials featuring electro-rheological fluids is proposed herein for the active continuum vibrational control of structural and mechanical systems. This paper reports on a pioneer ing proof-of-concept experimental investigation focussed on evaluating the static and elastodynamic transient response characteristics of cantilevered beams fabricated in this new class of materials. The results of this investigation clearly demonstrate for the first time the ability to dramatically change the vibrational characteristics of beam-like speci mens fabricated in ultra-advanced composite materials by changing the electrical field im posed on the fluid. The capability of these materials to interface with modem solid-state electronics can be exploited by extending the fundamental phenomenological work pre sented herein by the successful incorporation of intelligent sensor technologies and modern control strategies in order to significantly accelerate the evolution of this in novative class of multi-functional, dynamically-tunable, ultra-advanced, intelligent com posite materials for military, aerospace, advanced manufacturing applications.

A survey of finite element techniques for mechanism design

Abstract During the creation of a modern machine system, the designer must generally develop a mathematical model to investigate the levels of vibrational activity, dynamic stresses, bearing loads and often the acoustic radiation associated with the system. Since all of these phenomena may be represented by field theories whose governing equations of motion may be stated as either differential, integral or integro-differential equations, they are all amenable to solution by the single most powerful computational tool available to the analyst: the finite element method. Mechanism design methodologies based on this versatile technique are reviewed herein, their different characteristics are highlighted and future trends indicated.

Vibration control of flexible linkage mechanisms using piezoelectric films

Abstract A control methodology for suppressing the elastodynamic responses of high-speed flexible linkage mechanism is presented by adopting the concept of smart structures featuring piezoelectric films. The dynamics of piezoelectric actuators and sensors bonded on the flexible link are developed for a one-dimensional beam model. The linear optimal feedback control law with a Luenberger observer is employed. The instability caused by the combined effect of control and observation spillover is investigated and carefully prevented. Numerical simulation is performed to evaluate the improvement of elastodynamic responses.

Material selection: An important parameter in the design of high-speed linkages

Abstract Numerous studies in the literature have demonstrated that members of high-speed linkages should be designed with high strength-to-weight ratios and high stiffness-to-weight ratios. By satisfying these criteria, the designer is able to minimize the troublesome elastodynamic phenomena associated with demonstrates the advantages of using ultra high strength fiber-reinforced composites in this design field by simulating the dynamic responses of flexible four bar linkages manufactured in three different materials (steel, aluminum and a graphite-epoxy laminate). The mechanisms are analyzed using a displacement finite element model and the equations of motion are solved by numerical integration.

ENVIRONMENTALLY-SENSITIVE DESIGN : LEONARDO WAS RIGHT!

Abstract The design of environmentally-sensitive products and manufacturing facilities is considered by some members of the industrial community to be one of the current frontiers of engineering practice, while others consider it to be another fad. Here today but gone tomorrow. This paper examines this topic from a biological stance by asserting that humankinds activities should emulate natures flora and fauna, and the ecosystems that support them. Leonardo da Vincis profound words of some five centuries ago concerning natures inventive genius provides the motivation. Subsequently these words are buttressed by a set of fundamental biological canons that provide the basis for engineering design rules governing the efficient management of natural resources.

The synthesis of flexible linkages by balancing the tracer point quasi-static deflections using microprocessor and advanced materials technologies

Abstract The contribution of the quasi-static deformation to the total deviation of the tracer point of a flexible path generator linkage from the desired path may be reduced to zero by replacing one of the normally fixed ground link pivots by a sliding joint whose motion is controlled by a microprocessor. If the resulting output characteristics are still unacceptable to the analyst, the remaining high frequency oscillatory component may be attenuated by redesigning the mechanism links in a modern composite material to nominally generate the output associated with a rigid linked system. Illustrative examples are presented for four bar linkages.

Compliant control of a two-link flexible manipulator featuring piezoelectric actuators

This paper presents a control strategy for the position and force control of flexible manipulators exploiting the characteristics of actuators fabricated from smart materials. The governing equations of motion of a planar two-link flexible manipulator which features piezoceramic actuators and piezofilm sensors bonded on each flexible link are derived via Hamiltons principle. A nominal control torque of the motor to command the desired position and force is determined by a sliding mode controller based on the rigid-mode dynamics. In order to take uncertainties into account, the sliding mode controller with perturbation estimation (SMCPE) is adopted. The routine is then incorporated with the fuzzy technique to determine the appropriate control gains while maintaining the stability of the system. A set of fuzzy parameters and control rules is then obtained from the estimated perturbation. During the commanded motion, undesirable oscillations are actively suppressed by applying feedback control voltages to the piezoceramic actuators. These feedback voltages are determined by the SMCPE, and they permit accurate position and force control of the two-link flexible manipulator to be achieved. Computer simulations are undertaken by taking two different surface constraints in order to demonstrate the effectiveness of the proposed control methodology.

Adaptable Fixture Design: An Analytical and Experimental Study of Fluidized-Bed Fixturing

Computer-integrated flexible manufacturing systems are designed to respond quickly and economically to varying production requirements. Since an essential ingredient of all manufacturing operations is fixturing, if these modern manufacturing systems are to be truly flexible, then the fixturing must be adaptable also. Traditional design philosophies focused on dedicated fixtures are clearly inadequate for these applications. This paper reports on an innovative class of adaptable fixtures based on particulate fluidized beds. This mode of fixturing exploits the ability of these devices to change from a solid phase to a liquid phase and vice versa. Design criteria for the holding ability of this novel class of fixtures is established herein, and the proposed design philosophy is validated by an experimental program.