Preface. 1. Introduction. 2. Rigid Motions and Homogeneous Transformations. 3. Forward and Inverse Kinematics. 4. Velocity Kinematics-The Jacobian. 5. Path and Trajectory Planning. 6. Independent Joint Control. 7. Dynamics. 8. Multivariable Control. 9. Force Control. 10. Geometric Nonlinear Control. 11. Computer Vision. 12. Vision-Based Control. Appendix A: Trigonometry. Appendix B: Linear Algebra. Appendix C: Dynamical Systems. Appendix D: Lyapunov Stability. Index.

/pdf/robot-modeling-and-control-2n3memrp6g.pdf

Robot Modeling and Control

Electrical actuators were made from films of dielectric elastomers (such as silicones) coated on both sides with compliant electrode material. When voltage was applied, the resulting electrostatic forces compressed the film in thickness and expanded it in area, producing strains up to 30 to 40%. It is now shown that prestraining the film further improves the performance of these devices. Actuated strains up to 117% were demonstrated with silicone elastomers, and up to 215% with acrylic elastomers using biaxially and uniaxially prestrained films. The strain, pressure, and response time of silicone exceeded those of natural muscle; specific energy densities greatly exceeded those of other field-actuated materials. Because the actuation mechanism is faster than in other high-strain electroactive polymers, this technology may be suitable for diverse applications.

http://science.sciencemag.org/content/sci/287/5454/836.full.pdf

High-Speed Electrically Actuated Elastomers with Strain Greater Than 100%

The widespread use of controlled molecular-level motion in key natural processes suggests that great rewards could come from bridging the gap between the present generation of synthetic molecular systems, which by and large rely upon electronic and chemical effects to carry out their functions, and the machines of the macroscopic world, which utilize the synchronized movements of smaller parts to perform specific tasks. This is a scientific area of great contemporary interest and extraordinary recent growth, yet the notion of molecular-level machines dates back to a time when the ideas surrounding the statistical nature of matter and the laws of thermodynamics were first being formulated. Here we outline the exciting successes in taming molecular-level movement thus far, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion. We also highlight some of the issues and challenges that still need to be overcome.

Synthetic molecular motors and mechanical machines.

This tutorial/survey paper: (1) provides a concise point of departure for researchers and practitioners alike wishing to assess the current state of the art in the control and monitoring of civil engineering structures; and (2) provides a link between structural control and other fields of control theory, pointing out both differences and similarities, and points out where future research and application efforts are likely to prove fruitful. The paper consists of the following sections: section 1 is an introduction; section 2 deals with passive energy dissipation; section 3 deals with active control; section 4 deals with hybrid and semiactive control systems; section 5 discusses sensors for structural control; section 6 deals with smart material systems; section 7 deals with health monitoring and damage detection; and section 8 deals with research needs. An extensive list of references is provided in the references section.

Structural control: past, present, and future

The widespread use of molecular machines in biology has long suggested that great rewards could come from bridging the gap between synthetic molecular systems and the machines of the macroscopic world. In the last two decades, it has proved possible to design synthetic molecular systems with architectures where triggered large amplitude positional changes of submolecular components occur. Perhaps the best way to appreciate the technological potential of controlled molecular-level motion is to recognize that nanomotors and molecular-level machines lie at the heart of every significant biological process. Over billions of years of evolution, nature has not repeatedly chosen this solution for performing complex tasks without good reason. When mankind learns how to build artificial structures that can control and exploit molecular level motion and interface their effects directly with other molecular-level substructures and the outside world, it will potentially impact on every aspect of functional molecule and materials design. An improved understanding of physics and biology will surely follow.

The first steps on the long path to the invention of artificial molecular machines were arguably taken in 1827 when the Scottish botanist Robert Brown observed the haphazard motion of tiny particles under his microscope.1,2 The explanation for Brownian motion, that it is caused by bombardment of the particles by molecules as a consequence of the kinetic theory of matter, was later provided by Einstein, followed by experimental verification by Perrin.3,4 The random thermal motion of molecules and its implications for the laws of thermodynamics in turn inspired Gedankenexperiments (“thought experiments”) that explored the interplay (and apparent paradoxes) of Brownian motion and the Second Law of Thermodynamics. Richard Feynman’s famous 1959 lecture “There’s plenty of room at the bottom” outlined some of the promise that manmade molecular machines might hold.5,6 However, Feynman’s talk came at a time before chemists had the necessary synthetic and analytical tools to make molecular machines. While interest among synthetic chemists began to grow in the 1970s and 1980s, progress accelerated in the 1990s, particularly with the invention of methods to make mechanically interlocked molecular systems (catenanes and rotaxanes) and control and switch the relative positions of their components.7−24

Here, we review triggered large-amplitude motions in molecular structures and the changes in properties these can produce. We concentrate on conformational and configurational changes in wholly covalently bonded molecules and on catenanes and rotaxanes in which switching is brought about by various stimuli (light, electrochemistry, pH, heat, solvent polarity, cation or anion binding, allosteric effects, temperature, reversible covalent bond formation, etc.). Finally, we discuss the latest generations of sophisticated synthetic molecular machine systems in which the controlled motion of subcomponents is used to perform complex tasks, paving the way to applications and the realization of a new era of “molecular nanotechnology”.

1.1. The Language Used To Describe Molecular Machines
Terminology needs to be properly and appropriately defined and these meanings used consistently to effectively convey scientific concepts. Nowhere is the need for accurate scientific language more apparent than in the field of molecular machines. Much of the terminology used to describe molecular-level machines has its origins in observations made by biologists and physicists, and their findings and descriptions have often been misinterpreted and misunderstood by chemists. In 2007 we formalized definitions of some common terms used in the field (e.g., “machine”, “switch”, “motor”, “ratchet”, etc.) so that chemists could use them in a manner consistent with the meanings understood by biologists and physicists who study molecular-level machines.14

The word “machine” implies a mechanical movement that accomplishes a useful task. This Review concentrates on systems where a stimulus triggers the controlled, relatively large amplitude (or directional) motion of one molecular or submolecular component relative to another that can potentially result in a net task being performed. Molecular machines can be further categorized into various classes such as “motors” and “switches” whose behavior differs significantly.14 For example, in a rotaxane-based “switch”, the change in position of a macrocycle on the thread of the rotaxane influences the system only as a function of state. Returning the components of a molecular switch to their original position undoes any work done, and so a switch cannot be used repetitively and progressively to do work. A “motor”, on the other hand, influences a system as a function of trajectory, meaning that when the components of a molecular motor return to their original positions, for example, after a 360° directional rotation, any work that has been done is not undone unless the motor is subsequently rotated by 360° in the reverse direction. This difference in behavior is significant; no “switch-based” molecular machine can be used to progressively perform work in the way that biological motors can, such as those from the kinesin, myosin, and dynein superfamilies, unless the switch is part of a larger ratchet mechanism.14

Artificial Molecular Machines

An analysis is presented in this paper for the equilibrium of a class of parallel manipulators resembling the Stewart platform in a general form. General coordinates and 4 x 4 homogeneous transformations are employed to arrive at exact expressions for the force distribution in all six legs given the general 6-dimensional wrench (generalized force) at the upper platform of a parallel manipulator. Numerical examples are carried out to examine the validity of the approach and the accuracy of the numerical technique employed.

Analysis of static equilibrium of a parallel manipulator

This paper discusses the conceptual design of a family of specially-designed temperature surety sensors made with shape-memory alloys (SMA). These sensors are capable of detecting a one time temperature excursion or variance form a predetermined temperature range. The propose designs can also be used to detect a one-time temperature rise and persistence above a certain pre-selected critical temperature. In that respect, these sensors relate to a family of one-time thaw sensors detecting whether or not frozen food items or other frozen products or objects experience a thawing-refreezing process in their journey from point A to point B. The proposed sensor can also detect a one time temperature excursion into non-allowable temperatures for non-frozen food, as well as pharmaceutical or other medical products. The essential design of these smart sensor is a lever arm attached to an SMA wire whose temperature is initially below Austenite start temperature or well into the Martensite region. As a given product experiences an undesirable temperature range which pushes the SMA material into the Austenite region the wire contracts and moves the lever arm outside a display window area and exposes either a red working indicator or a graduated scale calibrated to the range of temperature excursion experienced by the product. The sensor is designed such that if the temperature returns to normal the excursion indication will not disappear, but will permanently shown the amount of excursion above the temperature surety region for that product. Several possible design variations are presented and discussed. The proposed embodiments include a rupture type thaw sensor made with short SMA springs or bellows, SMA foil roll-up type sensors, SMA wire-loaded shutter type thaw sensors, SMA torsion strut-loaded shutter type thaw sensors, multiple shutter SMA wire-loaded thaw sensors, multiple shutter, SMA torsion-rod-loaded thaw sensors, and rupture-Type SMA spring-loaded thaw sensors.

Smart temperature sensors

Presented in this paper is a new design approach for a bias force type of shape memory alloy (SMA) rotatory joint actuator, which uses an SMA contractile wire as an actuating element. A quasi-static analysis is assumed and a coefficient of variation of bias stress, fi, is introduced to give a quantitative expression of a variation of bias stress in terms of a working stress range of the SMA wire. The effects of this coefficient on the load efficiency and the bias spring's parameters of a bias force SMA rotatory joint actuator are described. The use of this coefficient,B leads to a simple design procedure. An example design case is carried out by using this design procedure to demonstrate its usefulness. This paper does not cover an analysis of thermal response history of a designed actuator. The design approach described in this paper will provide a practical and convenient method for use in design of bias force SMA rotatory joint actuators for design requirements of maximum loads and maximum displacements.

A New Design for a Rotatory Joint Actuator Made with a Shape Memory Alloy Contractile Wire

Presented are a number of novel designs for large-motion shape-memory alloy (SMA) actuators that may minimize the performance constraints associated with such actuators. Shape-memory alloy (SMA) actuators suffer from two performance constraints, namely small strains (epsilon) , such that (epsilon) <EQ 6%, and heat transfer problems in computer- controlled ohmic heating of contractile SMA fiber bundles to induce contraction and/or expansion type linear actuators. Intelligent material systems and structures have become important in recent years due to some potential engineering applications. Accordingly, based on such materials, structures and their integration with appropriate sensors and actuators, novel applications, useful for a large number of engineering applications have emerged. In the present paper a number of conceptual designs and their respective mathematical models are presented for large motion SMA actuators. The dynamic modeling is preceded by a model of a small motion SMA linear actuator. This model considers the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs or hyperelastic springs such as rubber-like materials. The proposed theory presents a description of such processes for resilient shape-memory alloy fiber bundles. We consider the fiber bundle of SMA to be either in a serial configuration with a linear tension spring or a parallel configuration circumscribed inside a helical compression spring with flat heads or in parallel with a number of helical compression spring, end-capped by two parallel circular plates with embedded electrodes to which the ends of the SMA fibers are secured. Thus, the fibers can be electrically heated and subsequently contracted to either expand the tension spring or compress the helical compression spring back and forth. Design details are first described. In essence the dynamic behavior of the actuator depends on the frictional interference effects as well as the interaction between the current supplied to the wires and the heat transfer from the wires. Further, a mathematical model is presented to simulate the electro-thermomechanics of motion of such actuators. The proposed model takes into account all pertinent variables such as the strain (epsilon) , the temperature of the fibers T(t) as a function of time t, the ambient temperature T0, the martensite fraction (xi) , the helical compression spring constant k, the frictional effect and the coefficient of friction (mu) and the overall heat transfer coefficient h. Numerical simulations are then carried out and the results are compared with experimental observations of a number of fabricated systems.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design, Modeling and Performance Evaluation of A Novel Large Motion SMA Actuator

In this paper, the authors present the contraction/elongation behavior of cation-modified Polyacrylonitrile (PAN) fibers, which identifies the fibers to be effectively used as biomimetic actuators and artificial muscles. The research was initiated by realizing that the contraction/elongation behavior of PAN is governed by the diffusional processes of ions/solvents interaction. The PAN fibers were suitably annealed, cross-linked and hydrolyzed to become active. The cation-modification process was performed using KOH, NaOH, and LiOH, respectively, for the boiling and alkaline-soaking mediums. It was found that the PAN fibers, regardless of whether being activated in KOH, NaOH, or LiOH, increased from their initial length after being activated and soaked in distilled water. Lengths then decreased after the fibers were soaked in the bases. Fibers treated with LiOH had the largest increase in length following immersion in distilled water. Fibers soaked in any of the three mediums generally had the same decrease in length following immersion in the alkaline solutions, as also occurred following immersion in HCl. Especially noticeable with the fibers treated with LiOH was that greater displacement in the lengths occurred using the 2 N solutions. It is our general notion that the Osmotic pressure of free ions plays an import role on the properties of PAN. However, the observation that Li + treated PAN fibers exhibit the largest contraction/expansion capability compared to Na + or K + treated PANs, can raise another important issue, i.e. hydration. Realizing that the Osmotic pressure of electrolyte systems is weakly dependent upon the types of ions, it is highly likely that the hydration phenomena of free ions within the PAN network plays a key role on its deformation properties. It should be noted that PAN fibers have the capability of changing their effective longitudinal strain more than 100% and have comparable strength to human muscle.

Contraction/elongation behavior of cation-modified polyacrylonitrile fibers

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