PROJECTS

Non-Operative Correction for Long-Gap Esophageal Atresia

Investigators: Minkyun Noh
Sponsor: Boston Children's Hospital

About 1000 infants a year in the states are born with their esophagus disconnected, which is called Esophageal Atresia (EA). The standard operation for esophageal atresia is Foker process, which requires several thoracotomies for placing traction sutures on esophageal ends, followed by primary anastomosis. There have been attempts to develop non-operative method for correcting esophageal atresia, especially by using magnetic force. Hendren et al. explored electromagnetic bougienage method to correct long gap esophageal atresia. Zaritzky et al. presented a method of magnetic compression anastomosis, which took advantage of large attracting force between two rare-earth permanent magnets.

In our research, a non-operative correction method for long-gap esophageal atresia is proposed. A magnetic-tipped catheter was designed for bougienage and compression anastomosis. The magnetic tip comprise syringe mechanism with an outer barrel, which functions as a fluidic stand-off. The pressure of the fluid could be measured externally so as to estimate the tip force. The catheter moves back and forth by friction drive (long stroke), and the syringe mechanism at the tip also generates more displacement (short stroke).

A pair of the magnetic catheter is put into proximal and distal esophageal pouches respectively. They apply cycling stretching force on esophagus to stimulate it to grow. Once the esophagus grows in sufficient amount, the fluid in the magnetic syringe could be drawn off for magnetic compression anastomosis; the large force between two magnets squeezes the esophageal tissue, necrosis and regeneration of the sandwiched tissue leading to the compression anastomosis. [More Info]

Magnetically Suspended Reaction Sphere

Investigators: Lei Zhou
Sponsor: MIT Lincoln Laboratory

Goal of the Project: Small satellite angular attitude control with a suspended sphere of uniform hard steel instead of 3 reaction wheels; Novel hysteresis drive can generate torque, and stabilize translation in three axes without mechanical bearing.

Introduction: Typical attitude control for small satellites are using 3 reaction wheels in 3 axis, which has the limit of pointing stability due to wheel imbalance, friction disturbances and bearing vibration. In this project we are considering to replace 3 reaction wheels with 1 reaction sphere. In the control scheme, the sphere is magnetically suspended therefore there will be no friction drag; and the sphere is driven with hysteresis motor for moment storage. Currently we are taking the initial steps to demonstrate 1-D prototype, which is a solid spherical rotor being levitated in 3 DOFs and rotating about 1 axis. [More Info]

Modeling and Compensation of Spatial Disturbances on Reluctance Actuators

Investigators: Roberto Meléndez
Sponsor:

A limitation of reluctance actuators that prevent their use in precision positioning is their stiffness. Reluctance actuators are sensitive to both linear and angular disturbances. It is very important for the control system to compensate for the actuator stiffness in order to meet positioning standards. This project involves building a set up that can inject positioning disturbances in three degrees of freedom (z, pitch and roll) and a control system that can be robust to the disturbances.

Portable Control System Laboratories

Investigators: Roberto Meléndez, Mohammad Imani Nejad, Jim Zhen Sun
Sponsor: National Instruments, MIT Department of Mechanical Engineering

Hands-on laboratory components are crucial for students to grasp the concepts of control systems effectively. However students might not have the opportunity to take part in such labs because of time scheduling and/or equipment constraints. Using the National Instrument MyDAQ as a fundamental building block, the Precision Motion Control Laboratory has developed portable control systems labs. Students can now take the lab hardware home and complete experiments in their dorm room, thus avoiding the normal time constraints of a 2 or 3 hour weekly lab period. The MyDAQ allows the students to utilize a function generator, oscilloscope and even a dynamic signal analyzer in the comfort of their dorm room. Current labs include analog integrator plants, a thermal lab, a mechanical second order system and also a mini magnetic levitator. [More Info]

Design and Control Methods for High-Accuracy Variable Reluctance Actuators

Investigators: Ross Ian MacKenzie
Sponsor:

Reluctance actuators can generate high force densities at small operating gaps, making them an attractive actuator technology for high-acceleration applications where low moving mass is critical, such as in photolithography scanners. However, their inherent nonlinearities present challenges for accurate control. These nonlinearities include nonlinear stiffness, magnetic hysteresis and saturation, and eddy currents. In this project, we focus on the modeling and control of these nonlinearities. We have designed a 1-DoF air bearing stage for testing a reluctance actuator prototype design and accompanying control algorithms. A particular focus has been placed on the modeling and control of magnetic hysteresis, and on force-linearizing the actuator through a high-bandwidth local feedback loop from a sense coil.

Design and Testing of a High Accuracy Robotic Single-cell Manipulator

Investigators: Jun Young Yoon
Sponsor:

We have designed, built and tested a high accuracy robotic single-cell manipulator, which is able to pick individual cells from array of microwells, each 30 μm or 50 μm cubed. Design efforts have been made for higher accuracy, higher throughput, and compactness. The proposed system is designed to have a T-drive mechanism with two linear stages for XY-plane positioning to have higher stiffness and less structurally inherent error. Precision is especially required in Z-axis movement for successful cell retrieval procedure and so a rotational mechanism with a voice coil actuator, among many options, is selected for the Z-axis motion because this results in relatively smaller reaction on the system and has advantages of direct drive. The prototype of the robotic single-cell picker integrates the Z-axis and XY stage motion, real-time microscopy imaging, and cell manipulation with a NI PXI-controller centered as a main real-time controller. This prototype is built to test performances of the proposed system in terms of single-cell retrieval. We conducted experiment for the cell-retrieval process with microbeads of the equivalent size to mammalian cells, and it has shown promising results.

This proposed system will be used to help select and isolate an individual hybridoma from polyclonal mixture of cells producing various types of antibodies. It is important to be able to do this cell-retrieval task since a single isolated hybridoma cell produces monoclonal antibody that only recognizes specific antigens, and this monoclonal antibody can be used to develop cures and treatments for many diseases. Our research's development of accurate and dedicated mechatronics solution will contribute to more rapid and reliable investigation of cell properties. Such analysis techniques will act as catalyst for quicker discovery of treatments and vaccines on a wide range of diseases including HIV infection, tuberculosis, hepatitis C, and malaria with potential impact on the society. [More Info]

Self-Bearing Motor Design and Control

Investigators: Mohammad Imani Nejad
Sponsor:

This thesis presents the design, implementation and control of a new class of self-bearing motors. The primary thesis contributions include the design and experimental demonstration of hysteresis self-bearing motors, novel segmented stator structures, MIMO loop shaping control algorithm for levitation and commutation, hysteresis motor analysis including frequency dependency, nonlinear hysteresis model including loop widening, and a novel single-axis self-bearing motor, as well as a zero power configuration for this type of motor. [More Info]

High-Accuracy Atomic Force Microscope for Dimensional Metrology

Investigators: Darya Amin-Shahidi, Dean Ljubicic
Sponsor: National Science Foundation
Grant number: DMI-0506898

Ultra-High Performance Fast Tool Servos for Diamond Turning

Investigators: Xiaodong Lu, Augusto Barton
Sponsor: National Science Foundation
Grant number: DMI-0322590

We have designed, implemented, and tested an electromagnetically driven fast tool servo for diamond turning precision contoured surfaces with nanometer resolution. Our device is based on a novel ultrafast motor utilizing permanent magnets for flux bias in conjunction with steering coils used to control the actuator force. Experimental results demonstrate that our ultrafast tool servo has a stroke of 30 micrometers, achieves 23kHz closed-loop bandwidth, as low as 1.7nm RMS tracking error, 500G peak acceleration at 10kHz open-loop operation, and 2.1nm (0.04%) error in tracking a 3kHz sinusoid of 16mm p-v. To drive and control this ultrafast tool servo, a 1kW linear power amplifier and a high-speed real-time computer with 1MHz sampling rate have been designed and implemented. [More Info]

Rotary Fast-Tool Servo for Diamond Turning of Asymmetric Optics

Investigators: Marten Byl, Joseph Calzaretta, Stephen Ludwick
Sponsors: National Science Foundation
Grant number: DMI-9908325

We have built a prototype turning machine specialized for the production of plastic spectacle lenses. This machine features a novel rotary fast-tool servo, which can track trajectories at frequencies up to 500 Hz, and accelerations of 500 m/s^2. Thus the machine can turn 100 mm diameter toric lenses having surface asymmetries of up to 3 cm in depth. The control system consists of a conventional inner position loop, feedforward filtering, and repetitive control. This high-bandwidth, high-accuracy system allows us to turn a toric surface with tracking errors of less than 2 microns. [More Info]

Atomic Force Microscope Probe with Metrology, for Subatomic Measuring Machine (SAMM)

Investigator: Andrew Stein
Sponsor: National Science Foundation
Grant number: DMI-9821003

Together with UNC Charlotte, we have built a magnetically-suspended stage designed to achieve 0.1-nm resolution, 1-nm repeatability, and 10-nm accuracy over a macroscopic range of 25 mm in X,Y and 100 microns in Z. To complete the project, we are currently developing an atomic force microscope head to allow accurate characterization of the performance of the LORS stage. This probe senses tip-sample separation using a miniature piezoelectric quartz tuning fork. When driven with an AC voltage at its resonant frequency and with a sharp tip mounted to one end, this sensor can resolve topographic features on the atomic scale. Development of integrated metrology with the inherent accuracy of the system remains one of the key design challenges. Scanned probe microscopy typically relies on open-loop control of PZT actuators, which may introduce errors due to hysteresis. Our design will incorporate closed-loop positioning of a PZT tube, thereby improving the probe's accuracy. [More Info]

Noncontact Processing of Fibers, Beams, Webs and Plates

Investigators: Ming-Chih Weng, Xiaodong Lu, Robin Ritter
Sponsor: National Science Foundation
Grant number: DMI-9700973

In some industrial operations, it may be advantageous to handle the material without directly touching it, such as plastic film production, coating, and painting. This project explores the magnetic and electrostatic suspensions of flexible structures such as fibers, beams, webs, and plates. The research involves design of noncontact sensors and actuators, and study of suspension and vibration control. [More Info]

Magnetically Levitated Wafer Stepper for Photolithography

Investigators: Mark Williams, Pradeep Subrahmanyan
Sponsors: Integrated Solutions Inc. (Tewksbury, MA)

Wafer steppers are used in photolithography to position the uncut silicon wafer underneath a lens assembly in order to expose each of the future microchips. As such, the machine is required to have long travel, sub-micron resolution, and a settling time that is as fast as possible. The faster the machine settles, the more microchips can be produced. Typically, steppers are approached by stacking a short-travel, high resolution stage on top of a long-travel, low resolution design. This can lead to difficulties in achieving fast settling times. Our design uses magnetic bearings in combination with a six phase linear motor to combine the actions of the coarse and fine stages into a single moving element, thus allowing the long travel, high resolution, and fast settling times required. [More Info]

Control Techniques for a Single Degree-of-Freedom Magnetic Suspension

Investigator: Pradeep Subrahmanyan
Sponsor: Integrated Solutions Inc. (Tewksbury, MA)

This project involves the design and implementation of various linear and nonlinear control schemes for a single DOF magnetic suspension. Plant uncertainty is introduced on purpose and countered using Robust and Adaptive techniques. Robust adaptive control is found to give the best results. [More Info]

High-Precision Planar Magnetic Levitation

Investigator: Won-jong Kim
Sponsor: Sandia National Laboratories (Albuquerque, NM)

A magnetically-levitated stage for photolithography in the semiconductor manufacturing industry is under development. A single moving part generates all six-degree-of-freedom motions required for focusing, and large planar motions for positioning. The stage includes four linear permanent-magnet motors as key actuators to produce the levitation force, to cancel the weight of the moving part, as well as the driving force. The position stability of the stage is aimed at tens of nanometers so that the stage can be applicable as a high-precision planar positioner, such as a wafer stepper in the current deep-submicron technology. [More Info]

Integrated Capacitance Sensors

Investigator: Sai-Bun Wong
Sponsor: ADE Corporation (Newton, MA)

Capacitance sensors can be used for noncontact measuring of an airgap. Typically, the probe and drive electronics are separated by a length of cable, and disturbances to this cable lead to noise in the position reading. This project involves integrating the capacitance probe electronics into the probe head itself, transforming the displacement measurement directly into a digital signal.

Magnetically Suspended Artificial Heart Pump Impeller

Investigator: Michael Liebman
Sponsor: Charles E. Reed Faculty Initiatives Fund

We have designed a compact, simple magnet suspension for use in an artificial heart pump. Our design unifies the magnetic bearings and motor. Our motor spins the impeller and also can regulate the other five degrees of freedom. This results in a simpler, more compact design. Since each segment of the motor can provide drive and suspension forces, it is easier to design for redundancy and robustness which are essential in this application. [More Info]

Thermally Efficient Linear Motor

Investigators: Michael Liebman
Sponsor: Anorad Corporation

We analyze and design a high force per unit volume linear motor for use in machine tools. The motor is the first to incorporate coils wound with separated end-turns so that each layer of the coil can be directly cooled. Oil flows through the gaps in the end-turns on both sides of a coil to remove heat. A current of 1.6 A causes a 100°C temperature rise in a free convection-cooled coil; it takes a current of 9.0 A to cause the same temperature rise with our cooling technique. Thus our design allows nearly 6 times higher force in steady state and dissipates 32 times as much heat. We also investigate a second cooling scheme where we insert a comb-shaped piece of copper into the separated end-turn coil. Thermal analyses corroborated by experimental results are presented for both techniques.

Electromagnetic Actuator for a Scanning Mirror

Investigator: Don Nohavec
Sponsor: MIT Lincoln Laboratory

Design of a 6 D.O.F. actuator to position a scanning mirror in a Fourier Transform Infrared (FTIR) interferometer. The scanning mirror is used on NASA's Geosynchronous Operational Environmental Satellites (GEOS) used for severe weather observation and anomalous atmospheric behavior.

Six Degree-of-Freedom Oil Floated Magnetic Suspension

Investigators: Stephen Ludwick, Michael Holmes (UNC - Charlotte)
Sponsor: The National Science Foundation, ADE Corporation (Newton, MA)

This device uses active magnetic bearings in combination with squeeze film dampers to form a very stable, vibration resistant motion control stage. Total travel is within a cube of 100 microns, and resolution in the linear axes is better than 0.5 nm. One possible application involves providing the sample motions required in scanned probe microscopy. [More Info]

Actuator Calibration Fixture

Investigators: Yuka Miyake, Tony Poovey (formerly at UNC - Charlotte)

A common problem associated with controlling magnetic suspensions is the lack of an accurate model for the nonlinear relationship between the actuator force, coil current, and gap. We use this calibration fixture to cycle the current to an actuator while capacitance probes and load cells measure the gap and force. In this way, each actuator's behavior (including saturation and hysteresis) can be documented for use in later control system design.

Rotary-Linear Hybrid Axes for Meso-scale Machining

Investigators: Michael Liebman, Marsette Vona, Vijay Shilpiekandula
Sponsor: National Science Foundation
Grant number: DMI-0084981

We are designing and building a prototype hybrid machine tool axis as a key component of new manufacturing machines for meso-scale parts. By hybrid we mean that the two axes of motion are compounded in a single moving component. We define meso-scale parts as having a size on the order of centimeters and thus falling between the domains of microfabrication and standard machining. Such parts include dental restorations, molds, dies, and turbine blades. We currently have built a prototype rotary-linear axis. It consists of a central shaft which is driven in both rotation and translation. This hybridization minimizes machine inertias and thereby maximizes accelerations allowing for the production of complex parts rapidly and accurately. The minimization of inertias also increases the frequency of structural resonances allowing for control at higher bandwidths.