Mohammad Mayyas

An active micro joining mechanism for 3D assembly

An active joining mechanism for the construction of microstructures, comprising detethered microparts and locking actuators fabricated on a wafer, has been implemented. An active locking mechanism is a system on chip (SOC) type of actuator which is designed to control the sockets opening to allow insertion of a micropart with zero force. This allows the delicate micropart to be secured without the need of substantial forces that could cause damage to the micropart or the socket. Moreover, it enhances the assembly throughput, tolerance and yield due to the frictionless self-alignment of the micropart. The design concept, assembly and extensive characterization have been illustrated for 100 µm thick microstructures made of SOI wafers and patterned by deep reactive ion etching. Single-sided and double-sided electrothermal bent beam actuators are utilized for the socket to actively open during assembly and close to lock the micropart against the locking mechanism. Finally, the mechanical and electrical characteristics of the joints can be further enhanced by reflow of the deposited layers of the 80Au–20Sn solder alloy at the contact areas.

Design Tradeoffs for Electrothermal Microgrippers

Microgrippers based on electrothermal actuation were designed and fabricated using the deep reactive ion etching (DRIE) process with 100mum thick silicon on insulator (SOI) wafer. The design requirements are restricted to basic manipulation tasks such as pick and place, and nonprehensile manipulation. This paper explores several electrothermal end-effectors which have been fabricated for serial and parallel microassembly. The end-effectors include three main building blocks: 1) Integrated and symmetrical actuators of V and U shapes. The symmetrical expansions on Chevron and hot arms allow combination of forward translations that amplify angular motion at the tips of a gripper. 2) A joule heating element based on a resistive V-shape electrothermal actuator. In 3D microassembly, the joining of a micropart is essentially performed by providing an integrated microheater device. 3) A force or position feedback sensing block based on self-straining or electrostatic principle. The integrated sensor can be calibrated for both position and force measurements. Serial heterogeneous assembly of meso and micro-scale objects is demonstrated using a 3D microassembly station. Black-box dynamical models for microgrippers are derived using experimentally obtained data, and performance variations due to the way the microgrippers are mounted onto the robot are discussed.

A Study on the Thermal Behavior of Electrothermal Microactuators Due to Various Voltage Inputs.

The steady state temperature profiles of U- and I-shaped electrothermal microactuators are analytically derived. The temperature profiles could be used to evaluate the performance sensitivity of the microactuator due to various parameter changes. In this work, the analysis assumes an unpackaged silicon microactuator with an air gap between the actuator and substrate and the profiles are evaluated for various input voltage amplitudes. It was found that at low voltage inputs the temperature profile is exponential in nature with the failure being due to thermo-structural stresses and/or structure melting. At voltages larger than a critical value, a combined sinusoidal and exponential temperature profile is observed with the failure being strongly due to structural melting as well. However, higher voltage excitation causes a fully distributed sinusoidal temperature profile. In this mode, failures occur at different locations and due to high localized thermal stresses causing the temperature to exceed the material melting point. The behavior of U- and I-shaped microactuators based on silicon on insulator (SOI) fabrication and femtosecond laser micromachining was experimentally examined with the results corroborating the conclusions drawn from the analysis.© 2006 ASME

Methodologies for the Assembly of a Fiber-Coupled MEMS Fourier Transform Spectrometer

This manuscript presents methodologies followed in the construction and packaging of a 3-D microelectromechanical system (MEMS) Fourier transform (FT) spectrometer based on integrated heterogeneous microassembly and packaging systems. We develop procedures, assembly, and packaging work-cells configured for sequential active alignment of miniaturized optical components. Component-to-system-level tolerance analysis is introduced to compensate for the misalignments associated. Furthermore, an inverse methodology based on the self-alignment of fibers is presented to counter the shifts resulting from the fiber packaging process.

Static and dynamic modeling of thermal microgripper

The performance of any micro-component affects the overall performance of the system especially in the micro-level. In this research work, the thermal and structural performances of microgripper based on silicon are studied. The present study is part of a larger effort in developing, modeling and characterization procedures toward understanding the behavior of microgripper. This is essential to develop better control algorithms and to facilitate the study of robot arms dynamic on gripping performance. The structural stiffness and failure of microgripper in static loading are characterized for two actuation modes: in-plane and off-plane. Moreover, building block attempts are introduced for dynamical modeling of microgripper/sensor and environment. The electromechanical system model of sensor is experimentally identified and utilized in identifying the performance of hypothesized lumped models of microgripper

An active locking mechanism for assembling 3D micro structures

Microassembly is an enabling technology to build 3D microsystems consisting of microparts made of different materials and processes. Multiple microparts can be connected together to construct complicated in-plane and out-of-plane microsystems by using compliant mechanical structures such as micro hinges and snap fasteners. This paper presents design, fabrication, and assembly of an active locking mechanism that provides mechanical and electrical interconnections between mating microparts. The active locking mechanism is composed of thermally actuated Chevron beams and sockets. Assembly by means of an active locking mechanism offers more flexibility in designing microgrippers as it reduces or minimizes mating force, which is one of the main reasons causing fractures in a microgripper during microassembly operation. Microgrippers, microparts, and active locking mechanisms were fabricated on a silicon substrate using the deep reactive ion etching (DRIE) processes with 100-um thick silicon on insulator (SOI) wafers. A precision robotic assembly platform with a dual microscope vision system was used to automate the manipulation and assembly processes of microparts. The assembly sequence includes (1) tether breaking and picking up of a micropart by using an electrothermally actuated microgripper, (2) opening of a socket area for zero-force insertion, (3) a series of translation and rotation of a mating micropart to align it onto the socket, (4) insertion of a micropart into the socket, and (5) deactivation and releasing of locking fingers. As a result, the micropart was held vertically to the substrate and locked by the compliance of Chevron beams. Microparts were successfully assembled using the active locking mechanism and the measured normal angle was 89.2°. This active locking mechanism provides mechanical and electrical interconnections, and it can potentially be used to implement a reconfigurable microrobot that requires complex assembly of multiple links and joints.

Application of Thin Plate Splines for Surface Reverse Engineering and Compensation for Femtosecond Laser Micromachining

The femtosecond laser micromachining (FLM) systems could potentially be used for the rapid prototyping of microstructures on the surface of a workpiece. However, surface scale characteristics or workpiece holding fixtures could introduce position and orientation errors of the workpiece surface. These errors must be accounted and compensated for during FLM such that the focused laser spot position is known in the coordinates of the measured and not of an ideal surface thus assuring the desired machining results. In this manuscript, an algorithm for offline surface topography reconstruction from measured scattered control points is introduced. The target machining points are interpolated by thin-plate splines (TPS), an approach based on minimizing a roughness cost function. The reverse engineered surface could then be interfaced and used with a CAD/CAM system such that the focal spot is fully compensated for based on the measured wafer surface

Bioinspired legged-robot based on large deformation of flexible skeleton.

In this article we present STARbot, a bioinspired legged robot capable of multiple locomotion modalities by using large deformation of its skeleton. We construct STARbot by using origami-style folding of flexible laminates. The long-term goal is to provide a robotic platform with maximum mobility on multiple surfaces. This paper particularly studies the quasistatic model of STARbots leg under different conditions. We describe the large elastic deformation of a leg under external force, payload, and friction by using a set of non-dimensional, nonlinear approximate equations. We developed a test mechanism that models the motion of a leg in STARbot. We augmented several foot shapes and then tested them on soft to rough grounds. Both simulation and experimental findings were in good agreement. We utilized the model to develop several scales of tri and quad STARbot. We demonstrated the capability of these robots to locomote by combining their leg deformations with their foot motions. The combination provided a design platform for an active suspension STARbot with controlled foot locomotion. This included the ability of STARbot to change size, run over obstacles, walk and slide. Furthermore, in this paper we discuss a cost effective manufacturing and production method for manufacturing STARbot.

Microsurface Reverse Engineering and Compensation for Laser Micromachining

Microsurface scale characteristics (roughness, waviness and form) and the workpiece mounting fixture effects must be accounted and compensated for during laser micromachining such that the focused laser spot position is known in the coordinates of the measured surfaces. Thus, allowing rapid and accurate micromachining on the true workpiece engineering surface. The thin-plate splines (TPSs), a mathematically simple theory, is modified and employed in the reconstruction of 2 1/2 D unfolded continuous and differentiable microtopographical surfaces from a limited set of sampled digital elevation data. The TPS theory aids in restoring bad samples and in enhancing the visualization of the reconstructed surface and the characterization of microelectromechanical systems (MEMS) structures. The reverse engineered surface could also be interfaced and used with a CAD/CAM system to compensate for the focal spot location of a laser beam based on the actual reversed engineered workpiece surface. The practical examples of the real microsurfaces presented in this work, combine comprehensive identification with the ultimate goal of utilizing the algorithms in the compensation of the laser focused spot for a femtosecond laser micromachining (FLM) system currently under development in our laboratory.

Micro-surface construction and characterization from digital elevation model using thin plate splines in MATLAB environment

The Thin Plate Splines (TPS) theory is modified and employed in the reconstruction of 2D 1/2 unfolded micro-topographical surfaces. The modified TPS allows the reconstruction of MEMS structures based on sampled digital elevation model (DEM). The developed algorithms are implemented in MATLAB and applied to restore bad samples, enhance surface reconstruction, and compensate for surface irregularities for micromachining purposes. In addition, the restored surface reveals the scale components of the real surface (roughness, waviness and form). The irregularity of meso, micro and nano surfaces is then characterized into slope, curvature, strike, dip, azimuth and energy surfaces. It is concluded that the simplicity, differentiability of TPS and roughness components relaxation make the proposed theory advantageous on reconstruction and characterization of micro surfaces for a variety of applications.© 2006 ASME