Tribology of Microball Bearing MEMS

This dissertation explores the fundamental tribology of microfabricated rolling bearings for future micro-machines. It is hypothesized that adhesion, rather than elastic hysteresis, dominates the rolling friction and wear for these systems, a feature that is unique to the micro-scale. To test this hypothesis, specific studies in contact area and surface energy have been performed. Silicon microturbines supported on thrust bearings packed with 285 µm and 500 µm diameter stainless steel balls have undergone spin-down friction testing over a load and speed range of 10-100mN and 500-10,000 rpm, respectively. A positive correlation between calculated contact area and measured friction torque was observed, supporting the adhesion-dominated hysteresis hypothesis. Vapor phase lubrication has been integrated within the microturbine testing scheme in a controlled and characterized manner. Vapor-phase molecules allowed for specifically addressing adhesive energy without changing other system properties. A 61% reduction of friction torque was observed with the utilization of 18% relative humidity water vapor lubrication. Additionally, the relationship between friction torque and normal load was shown to follow an adhesion-based trend, highlighting the effect of adhesion and further confirming the adhesion-dominant hypothesis. The wear mechanisms have been studied for a microfabricated ball bearing platform that includes silicon and thin-film coated silicon raceway/steel ball materials systems. Adhesion of ball material, found to be the primary wear mechanism, is universally present in all tested materials systems. Volumetric adhesive wear rates are observed between 4x10^-4 µm^3/mN*rev and 4x10^-5 µm3/mN*rev were determined by surface mapping techniques and suggest a self-limiting process. This work also demonstrates the utilization of an Off-The-Shelf (OTS) MEMS accelerometer to confirm a hypothesized ball bearing instability regime which encouraged the design of new bearing geometries, as well as to perform in situ diagnostics of a high-performance rotary MEMS device. Finally, the development of a 3D fabrication technique with the potential of significantly improving the performance of micro-scale rotary structures is described. The process was used to create uniform, smooth, curved surfaces. Micro-scale ball bearings are then able to be utilized in high-speed regimes where load can be accommodated both axially and radially, allowing for new, high-speed applications. A comprehensive exploration of the fundamental tribology of microball bearing MEMS has been performed, including specific experiments on friction, wear, lubrication, dynamics, and geometrical optimization. Future devices utilizing microball bearings will be engineered and optimized based on the results of this dissertation

Closed-Loop Control of a Micropositioner Using Integrated Photodiode Sensors

A closed-loop control system with photodiode position sensors has been implemented in a microball bearing supported linear electrostatic micromotor to improve accuracy and reliability. The fabrication sequence of the previously developed micromotor was modified to integrate a photodiode-based position sensing mechanism. Proportional control law is used in the control system and device step response is analyzed for several step sizes at various maximum applied voltages by varying the constant of proportionality. Two critical functions for micropositioning applications have been demonstrated; the device can establish a necessary frame of reference for coordinate-based positioning and autonomously respond to arbitrary disturbances. The closed-loop position control system presented in this work illustrates the feasibility and functionality of smart microsystems using integrated feedback sensors

Second International Symposium on Magnetic Suspension Technology, part 2

In order to examine the state of technology of all areas of magnetic suspension and to review related recent developments in sensors and controls approaches, superconducting magnet technology, and design/implementation practices, the 2nd International Symposium on Magnetic Suspension Technology was held at the Westin Hotel in Seattle, WA, on 11-13 Aug. 1993. The symposium included 18 technical sessions in which 44 papers were presented. The technical sessions covered the areas of bearings, bearing modelling, controls, vibration isolation, micromachines, superconductivity, wind tunnel magnetic suspension systems, magnetically levitated trains (MAGLEV), rotating machinery and energy storage, and applications. A list of attendees appears at the end of the document

Design, Fabrication, and Characterization of a Rotary Variable-Capacitance Micromotor Supported on Microball Bearings

The design, fabrication, and characterization of a rotary micromotor supported on microball bearings are reported in this dissertation. This is the first demonstration of a rotary micromachine with a robust mechanical support provided by microball-bearing technology. One key challenge in the realization of a reliable micromachine, which is successfully addressed in this work, is the development of a bearing that would result in high stability, low friction, and high resistance to wear. A six-phase, rotary, bottom-drive, variable-capacitance micromotor is designed and simulated using the finite element method. The geometry of the micromotor is optimized based on the simulation results. The development of the rotary machine is based on studies of fabrication and testing of linear micromotors. The stator and rotor are fabricated separately on silicon substrates and assembled with the stainless steel microballs. Three layers of low-k benzocyclobutene (BCB) polymer, two layers of gold, and a silicon microball housing are fabricated on the stator. The BCB dielectric film, compared to conventional silicon dioxide insulating films, reduces the parasitic capacitance between electrodes and the stator substrate. The microball housing and salient structures (poles) are etched in the rotor and are coated with a silicon carbide film to reduce friction. A characterization methodology is developed to measure and extract the angular displacement, velocity, acceleration, torque, mechanical power, coefficient of friction, and frictional force through non-contact techniques. A top angular velocity of 517 rpm corresponding to the linear tip velocity of 324 mm/s is measured. This is 44 times higher than the velocity achieved for linear micromotors supported on microball bearings. Measurement of the transient response of the rotor indicated that the torque is 5.620.5 micro N-m which is comparable to finite element simulation results predicting 6.75 micro N-m. Such a robust rotary micromotor can be used in developing micropumps which are highly demanded microsystems for fuel delivery, drug delivery, cooling, and vacuum applications. Micromotors can also be employed in micro scale surgery, assembly, propulsion, and actuation

MEMS Gyroscopes for Consumers and Industrial Applications

none2mixedAntonello, Riccardo; Oboe, RobertoAntonello, Riccardo; Oboe, Robert

NASA Tech Briefs, July 1996

Topics covered include: Mechanical Components; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences; Life Sciences; Books and Report

Concept, modeling and experimental characterization of the modulated friction inertial drive (MFID) locomotion principle:application to mobile microrobots

A mobile microrobot is defined as a robot with a size ranging from 1 in3 down to 100 µm3 and a motion range of at least several times the robot's length. Mobile microrobots have a great potential for a wide range of mid-term and long-term applications such as minimally invasive surgery, inspection, surveillance, monitoring and interaction with the microscale world. A systematic study of the state of the art of locomotion for mobile microrobots shows that there is a need for efficient locomotion solutions for mobile microrobots featuring several degrees of freedom (DOF). This thesis proposes and studies a new locomotion concept based on stepping motion considering a decoupling of the two essential functions of a locomotion principle: slip generation and slip variation. The proposed "Modulated Friction Inertial Drive" (MFID) principle is defined as a stepping locomotion principle in which slip is generated by the inertial effect of a symmetric, axial vibration, while the slip variation is obtained from an active modulation of the friction force. The decoupling of slip generation and slip variation also has lead to the introduction of the concept of a combination of on-board and off-board actuation. This concept allows for an optimal trade-off between robot simplicity and power consumption on the one hand and on-board motion control on the other hand. The stepping motion of a MFID actuator is studied in detail by means of simulation of a numeric model and experimental characterization of a linear MFID actuator. The experimental setup is driven by piezoelectric actuators that vibrate in axial direction in order to generate slip and in perpendicular direction in order to vary the contact force. After identification of the friction parameters a good match between simulation and experimental results is achieved. MFID motion velocity has shown to depend sinusoidally on the phase shift between axial and perpendicular vibration. Motion velocity also increases linearly with increasing vibration amplitudes and driving frequency. Two parameters characterizing the MFID stepping behavior have been introduced. The step efficiency ηstep expresses the efficiency with which the actuator is capable of transforming the axial vibration in net motion. The force ratio qF evaluates the ease with which slip is generated by comparing the maximum inertial force in axial direction to the minimum friction force. The suitability of the MFID principle for mobile microrobot locomotion has been demonstrated by the development and characterization of three locomotion modules with between 2 and 3 DOF. The microrobot prototypes are driven by piezoelectric and electrostatic comb drive actuators and feature a characteristic body length between 20 mm and 10 mm. Characterization results include fast locomotion velocities up to 3 mm/s for typical driving voltages of some tens of volts and driving frequencies ranging from some tens of Hz up to some kHz. Moreover, motion resolutions in the nanometer range and very low power consumption of some tens of µW have been demonstrated. The advantage of the concept of a combination of on-board and off-board actuation has been demonstrated by the on-board simplicity of two of the three prototypes. The prototypes have also demonstrated the major advantage of the MFID principle: resonance operation has shown to reduce the power consumption, reduce the driving voltage and allow for simple driving electronics. Finally, with the fabrication of 2 × 2 mm2 locomotion modules with 2 DOF, a first step towards the development of mm-sized mobile microrobots with on-board motion control is made

EUROSENSORS XVII : book of abstracts

Fundação Calouste Gulbenkien (FCG).Fundação para a Ciência e a Tecnologia (FCT)