Karl-Friedrich Böhringer

Parallel microassembly with electrostatic force fields

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.

Modeling and Controlling Parallel Tasks in Droplet-Based Microfluidic Systems

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

CMOS integrated ciliary actuator array as a general-purpose micromanipulation tool for small objects

muhboxl

Sensorless manipulation using massively parallel microfabricated actuator arrays

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.

Single-crystal silicon actuator arrays for micro manipulation tasks

The first micromachined bimorph organic ciliary array with on-chip CMOS circuitry is presented. This ciliary array is composed of an 8/spl times/8 array of cells each having four orthogonally oriented actuators in an overall die size of 9.4/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 array was programmed to do simple linear and diagonal translations and squeeze-, centering-, and rotating-field manipulations. All three tasks were demonstrated using silicon pieces of various shapes and either 0.55 mm or 0.10 mm thick.

Modeling of capillary forces and binding sites for fluidic self-assembly

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.<<ETX>>

Algorithms for sensorless manipulation using a vibrating surface

Arrays of electrostatic MEMS actuators have been fabricated using a modified, multi-layer SCREAM (S_ingle-C_rystal R_eactive E_tching and M_etallization) process. The devices consist of released, torsionally suspended grids with high aspect ratio single-crystal silicon (SCS) tips. They can be used to generate a force field for the manipulation of small, flat objects. Calculations and experiments show that the actuator array is strong enough to move macroscopic parts. An individual actuator can generate a force of approximately 10 /spl mu/N and a displacement of 5 /spl mu/m. Monolithic arrays have been built reaching a size of up to 10 cm/sup 2/, with up to 15000 individual single-crystal silicon actuators on one chip. We investigate micro actuators for manipulation tasks, and discuss important issues and trade-offs in design, processing and fabrication. We describe manipulation experiments in which small, flat objects where lifted and moved. We conclude with an outlook on applications of programmable actuator arrays to more elaborate micro manipulation tasks and give an outline on how they can be used for transporting, positioning, sorting, and assembly of small parts.

A theory of manipulation and control for microfabricated actuator arrays

Massively parallel self-assembly is emerging as an efficient, low-cost alternative to conventional pick-and-place assembly of microfabricated components. The fluidic self-assembly technique we have developed exploits hydrophobic-hydrophilic surface patterning and capillary forces of an adhesive liquid between binding sites to drive the assembly process. To achieve high alignment yield, the desired assembly configuration must be a (global) energy minimum, while other (local) energy minima corresponding to undesired configurations should be avoided. Thus, the design of an effective fluidic self-assembly system using this technique requires an understanding of the interfacial phenomena involved in capillary forces; improvement of its performance involves the global optimization of design parameters such as binding site shapes and surface chemistry. This paper presents a model and computational tools for the efficient analysis and simulation of fluidic self-assembly. The strong, close range attractive forces that govern our fluidic self-assembly technique are approximated by a purely geometric model, which allows the application of efficient algorithms to predict system behavior. Various binding site designs are analyzed, and the results are compared with experimental observations. For a given binding site design, the model predicts the outcome of the self assembly process by determining minimum energy configurations and detecting unwanted local minima, thus estimating expected yield. These results can be employed toward the design of more efficient self-assembly systems.

Using constraints to achieve stability in automatic graph layout algorithms

Abstract. We describe a programmable apparatus that uses a vibrating surface for sensorless, nonprehensile manipulation, where parts are systematically positioned and oriented without sensor feedback or force closure. The idea is to generate and change the dynamic modes of a vibrating surface. Depending on the node shapes of the surface, the position and orientation of the parts can be predicted and constrained. The vibrating surface creates a two-dimensional force vector field. By chaining together sequences of force fields, the equilibrium states of a part in the field can be successively reduced to obtain a desired final state. We describe efficient polynomial-time algorithms that generate sequences of force fields for sensorless positioning and orienting of planar parts, and we show that these strategies are complete. Finally we consider parts feeders that can only implement a finite set of force fields. We show how to plan and execute strategies for these devices. We give numerical examples and experiments. and discuss tradeoffs between mechanical complexity and planning complexity.

Distributed Robotic Manipulation: Experiments in Minimalism

This paper investigates manipulation tasks with arrays of microelectromechanical structures (MEMS). We develop a 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 micro-scale contacts between actuator and moving object, which can be used to efficiently predict the motion of the object on an actuator array. We develop a theory of sensorless manipulation with microactuator arrays. It is shown how simple actuator control strategies can be used to uniquely align a part up to symmetry. These manipulation strategies can be computed efficiently and do not require 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 low-temperature SCREAM process. They exhibit high aspect ratios and high vertical stiffness, which is of great advantage for an effective implementation of our theory. Calculations show that arrays of these actuators can generate forces that are strong enough to levitate and move e.g. a piece of paper.