In this paper, we modeled and analyzed the shape-memory-alloy (SMA) heat engine in steady state. The heat engine is composed of two pulleys, three gears, and an SMA coil spring. We formulated an expression that optimizes the relationship among the parameters for the maximum power and the torque of the heat engine. This article is the first to present the basic procedure to solve the optimal solution for the pulley-gear-type heat engines that are driven by an SMA coil spring. We also discuss the miniaturization of the heat engine to actuate the Bio MEMS and the micro TAS devices as fluidic MEMS actuators.

This Special Section presents recent and original advances in microassembly methods and technologies. An overview of the technical articles and features is provided.

This paper presents general hardware-independent models and algorithms to automate the operation of droplet-based microfluidic systems. In these systems, discrete liquid volumes of typically less than 1$muhboxl$are transported across a planar array by dielectrophoretic or electrowetting effects for biochemical analysis. Unlike in systems based on continuous flow through channels, valves, and pumps, the droplet paths can be reconfigured on demand and even in real time. Algorithms that generate efficient sequences of control signals for moving one or many droplets from start to goal positions, subject to constraints such as specific features and obstacles on the array surface or limitations in the control circuitry, are developed. In addition, an approach toward automatic mapping of a biochemical analysis task onto a DMFS is investigated. Achieving optimality in these algorithms can be prohibitive for large-scale configurations because of the high asymptotic complexity of coordinating multiple moving droplets. Instead, these algorithms achieve a compromise between high runtime efficiency and a more limited nonglobal optimality in the generated control sequences.

In digital microfluidic systems, analyte droplets (volume typically less than 1 /spl mu/l) are transported across a planar electrode array by dielectrophoretic or electrowetting effects. This paper outlines a high-level approach to optimally control digital microfluidic systems, i.e., to develop efficient algorithms that generate a sequence of control signals for moving one or many droplets from start to goal positions in the shortest number of steps, subject to constraints such as minimum required separation between droplets, obstacles on the array surface, and limitations in the control circuitry. However, optimality may be prohibitive for large-scale configurations because of the high asymptotic complexity. Alternative solutions include (1) an investigation of still useful but more limited system configurations; and (2) approximation algorithms that trade off optimality of the control sequences with higher efficiency of the algorithms that generate these control sequences.

Surface-tension driven self-assembly techniques have been successfully employed to assemble and align micro parts on hydrophobic binding sites on a substrate. The driving force for assembly is provided by a liquid lubricant meniscus confined between two hydrophobic surfaces in an aqueous environment. Therefore, the hydrophobic pattern design becomes a critical issue for the self-assembly process. With an ideal design, the part can assemble in a unique position and orientation. In this paper, we study a series of geometric designs based on a first-order approximation energy model. An optimization method is developed to evaluate them, and a class of optimal designs is found consisting of asymmetric rings with additional geometric constraints.

Advances in silicon processing and microelectro-mechanical systems (MEMS) have made possible the production of very large numbers of very small components at very low cost in massively parallel batches. Assembly, in contrast, remains a mostly serial (i.e., non-batch) technique. We argue that massively parallel self-assembly of microparts will be a crucial enabling technology for future complex microsystems. As a specific approach, we present a technique for assembly of multiple batches of microparts based on capillary forces and controlled modulation of surface hydrophobicity. We derive a simplified model that gives rise to geometric algorithms for predicting assembly forces and for guiding the design optimization of self-assembling microparts. Promising initial results from theory and experiments and challenging open problems are presented to lay a foundation for general models and algorithms for self-assembly.

The first micromachined bimorph organic ciliary array with on-chip CMOS circuitry is presented. This device is composed of an 8/spl times/8 array of cells each having four orthogonally oriented actuators in on overall die-size of 9.4 mm/spl times/9.4 mm. The polyimide based actuators were fabricated directly above the selection and drive circuitry. Selection and activation of actuators in this array shows that integration was successful. The integration of CMOS electronics and MEMS micromechanisms allows the implementation of new task-level micromanipulation strategies. New low-level control algorithms (actuator gaits) were also demonstrated. The array was programmed to perform several kinds of manipulation tasks, including linear translation, diagonal motion, as well as vector field operations such as squeeze field and radial field orienting and centering. Preliminary experiments were also performed using thin silicon dice of about 3 mm/spl times/3 mm/spl times/0.5 mm size as the object being moved.

Programmable force fields are a representation of a class of devices for distributed, nonprehensile manipulation for applications in parts feeding, sorting, positioning, and assembly. They generate force vector fields in which the parts move until they reach a stable equilibrium pose. Research has yielded open-loop strategies to uniquely position, orient, and sort parts. These strategies typically consist of several fields employed in sequence to achieve a desired final pose. The length of the sequence depends on the complexity of the part. We show that unique part poses can be achieved with just one field. First, we exhibit a single field that positions and orients any part (except certain symmetric parts) into two stable equilibrium poses. Then, we show that for any part there exists a field in which the part reaches a unique stable equilibrium pose (again, except for symmetric parts). Besides giving an optimal upper bound for unique parts positioning and orientation, our work gives further evidence that programmable force fields are a powerful tool for parts manipulation. Our second result also leads to the design of "universal parts feeders", proving an earlier conjecture about their existence. We argue that universal parts feeders are relatively easy to build, and we report on extensive simulation results which indicate that these devices may work very well in practice. We believe that the results in this paper could be the basis for a new generation of efficient, open-loop, parallel parts feeders.

We propose a new model for gripping parts with an industrial parallel-jaw gripper. In contrast to many previous models, we use two grip points and define candidate grips that are resistant to slipping and torque about the part's center of mass. These grips must also be accessible and robust to perturbations in part position. We give an O(n/sup 3/) algorithm for computing and ranking O(n/sup 2/) such grips on an n-sided polygonal slice through the part. The algorithm will be part of a design and simulation system that can rapidly provide feedback to designers; thus it must run quickly and reliably. We have also implemented the algorithm in a Java applet with a graphical user interface that allows Internet users to define a part; the applet computes, ranks, and displays the set of computed grips.

Microscopic (submillimeter) parts are often fabricated in parallel at high density but must then be assembled into patterns with lower spatial density. We propose a new approach to microassembly using: 1) ultrasonic vibration to eliminate friction and adhesion; and 2) electrostatic forces to position and align parts in parallel. We describe experiments on the dynamic and frictional properties of collections of microscopic parts under these conditions. We first demonstrate that ultrasonic vibration can be used to overcome adhesive forces; we also compare part behavior in air and vacuum. Next, we demonstrate that parts can be positioned and aligned using a combination of vibration and electrostatic forces. Finally, we demonstrate part sorting by size. Our goal is a systematic method for designing implementable planar force fields for microassembly based on part geometry.

We consider the family of area bisectors of a polygon (possibly with holes) in the plane, We say that two bisectors of a polygon P are combinatorially distinct if they induce different partitionings of the vertices of P. We show that there are simple polygons with n vertices that have fl(nz ) combinatorially distinct area bisectors (matching the obvious upper bound), and we present an output-sensitive algorithm for computing an explicit representation of all the bisectors of a given polygon.Our study is motivated by the development of novel, flexible feeding devices for parts positioning and orienting.The question of determining all the bisectors of polygonal parts arises in connection with the development of efficient part positioning strategies when using these devices.

Distributed manipulation experiments were performed using a massively-parallel, microfabricated actuator array. An organic ciliary array of thin-film polyimide bimorph microactuators exploiting combined thermal and electrostatic control was employed to implement task-level, sensorless manipulation strategies for macroscopic objects. The tasks of parts-translation, -rotation, -orientation, and -centering were demonstrated using small integrated circuit (IC) dice. Strategies were programmed in a fine-grained SIMD (single instruction, multiple data) fashion by specifying planar force vector fields. When a part is placed on the array, the programmed vector field induces a force and moment upon it. The part's equilibrium states may be predicted and cascaded (using a sequence of fields) to bring the part to a desired final state. Vector fields with and without potential were tested in experiments, and the behavior of parts in the fields was compared with the theory of programmable vector fields. These fields were implemented by actuating the organic cilia in a cyclic, gait-like fashion. Motion in non-principal (e.g. diagonal) directions was effected by a pairwise coupling of the cilia to implement virtual cilia. These experiments suggest that MEMS actuator arrays are useful for parts-orientation, -posing, -transfer, -singulation, and -sorting.

Programmable vector fields can be used to control a variety of flexible planar parts feeders. When a part is placed on our devices, the programmed vector field induces a force and moment upon it. Over time, the part may come to rest in a dynamic equilibrium state. We demonstrate lower bounds on what the devices cannot do, and results on a classification of control strategies. We suggest sufficient conditions for programmable fields to induce well-behaved equilibria on every part placed on our devices. We define composition operators to build complex strategies from simple ones, and show the resulting fields are also well-behaved. We discuss whether fields outside this class can be useful and free of pathology. Using these tools, we describe new manipulation algorithms, and improve existing planning algorithms by a quadratic factor, and the plan-length by a linear factor. We relax earlier dynamic and mechanical assumptions to obtain more robust and flexible strategies. Finally, we consider parts feeders that can only implement a very limited "vocabulary" of vector fields. We discuss the trade-off between mechanical complexity and planning complexity.

The existing industrial parts feeders move the parts through a sequence of mechanical filters that reject parts in unwanted orientations. In this paper we develop a new setup that uses a different vibratory mechanism to systematically manipulate parts, by actively orienting and localizing them. The idea is to generate and change dynamic modes for a plate by varying the applied frequency of oscillation. Depending on the node shapes of the plate for these frequencies, the position and orientation of the parts can be controlled. We develop an analysis of the underlying dynamics, and show that it can be used to predict the behavior of objects placed on the vibrating plate. Using this analysis, we propose that the applied frequencies can be automatically sequenced to obtain a "sensorless" strategy for manipulating a given object.

This paper investigates manipulation tasks with arrays of microelectromechanical structures (MEMS). We develop a geometric model for the mechanics of microactuators and a theory of sensorless, parallel manipulation, and we describe efficient algorithms for their evaluation. The theory of limit surfaces offers a purely geometric characterization of microscale contacts between actuator and moving object, which can be used to efficiently predict the motion of the object on an actuator array. It is shown how simple actuator control strategies can be used to uniquely align a part up to symmetry without sensor feedback. This theory is applicable to a wide range of microactuator arrays. Our actuators are oscillating structures of single-crystal silicon fabricated in a IC-compatible process. Calculations show that these actuators are strong enough to levitate and move, for example, a piece of paper.>

Automatic layout algorithms are commonly used when displaying graphs on the screen because they provide a “nice” drawing of the graph without user intervention. There are, however, a couple of disadvantages to automatic layout. Without user intervention, an automatic layout algorithm is only capable of producing an aesthetically pleasing drawing of the graph. User- or application-specified layout constraints (often concerning the semantics of a graph) are difficult or impossible to specify. A second problem is that automatic layout algorithms seldom make use of information in the current layout when calculating the new layout. This can also be frustrating to the user because whenever a new layout is done, the user's orientation in the graph is lost.