Functional thinking in cost estimation through the tools and concepts of axiomatic design

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (leaf 27).There has been an increasing demand for cost estimation tools which aid in the reduction of system cost or the active consideration of cost as a design constraint. The existing tools are currently incapable of anticipating the unseen or latent effects of design changes made in an effort to cut cost. This paper presents an example of how the tools and concepts of axiomatic design theory can be integrated with the parametric cost estimation process, and then presents a series of arguments for why tools such as these which examine the functional architecture of a system are useful for optimizing cost at the preliminary design level.by Lael Ulam Odhner.S.B

Stochastic recruitment strategies for controlling artificial muscles

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 171-176).This thesis presents a new architecture for controlling active material actuators inspired by biological motor recruitment. An active material is broken down into many small fibers and grouped together to form one large actuator. Each of these fibers is held in a binary state, either relaxed or contracted, using a small local controller which responds to a broadcast input signal from a central controller. The output force and displacement of the actuator is a function of the number of contracted fibers at any point in time. This architecture enables the creation of large-scale, controllable actuators from highly non-linear active materials. The key innovation enabling the central controller to coordinate the behavior of very many small identical units is to randomize the behavior of each unit. This thesis explains how a collection of active material motor units responding in a random, uncorrelated fashion to broadcast commands will exhibit a predictable response that can be stabilized with feedback control and observed using a Kalman filter. Various control strategies will be presented and discussed, including open-loop plant behavior, linear feedback, optimal control, and model-based look-ahead control. Performance metrics such as accuracy and convergence time will be analyzed using dynamic programming and other control techniques. Parallels will also be discussed between this control problem and similar control problems in the field of swarm robotics.(cont.) The stochastic, recruitment-like actuator architecture is demonstrated in shape memory alloy actuators, each composed of 60 individual elements, having a displacement of over 20 mm and a peak force of over 100 N. Control of displacement, isometric force and stiffness are demonstrated using the observer-controller framework. Two actuators are used in an antagonistic fashion to control the stiffness and position of a 1-DOF arm joint.by Lael Ulam Odhner.Sc.D

Sensorless temperature estimation and control of Peltier devices

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaf 26).Peltier devices, also known as thermoelectric devices (TEDs), are solid state junctions of two dissimilar materials in which heat transfer and electrical conduction are coupled. A current running through a TED causes heat to flow; likewise, the presence of an external temperature gradient will induce an electrical potential across the TED. The former effect is known as the Peltier effect; the latter is known as the Seebeck effect. While TEDs are used primarily as heat pumps, they can also serve as temperature sensors. This thesis presents the design for a controller which uses a TED to simultaneously sense and control the temperature of a shape memory alloy (SMA) wire. The pulse width-modulating driving circuitry in the controller is capable of measuring the undriven voltage across the TED at a rate of 200 Hz between pulses. A low order ARX model is then used to estimate the SMA temperature. The SMA temperature can be controlled using this estimate. This method will enable the production of large arrays of TED-driven SMA tendon actuators, particularly for large DOF robotic systems.by Lael Ulam Odhner.S.M