Mohsin Rizwan

Three dimensional waveguide fabrication in PMMA using femtosecond laser micromachining system

Femtosecond lasers have been widely used for the micro structuring of transparent materials for a wide range of applications. The local change in refractive index by the irradiation of laser pulse has been exploited for optical applications ranging from optical data storage to the fabrication of waveguides and couplers. In this work, a Ti:Sapphire femtosecond laser (800nm, ~150 fs and 1 kHz) is used for the fabrication of three dimensional (3D) waveguides in thick PMMA substrates. The femtosecond laser microfabrication (FLM) system consists of the laser and three translational (X, Y and Z) stages and one rotational controlled motorized stages. The coordinated motion of these four stages can be used to generate desired three dimensional pattern inside the transparent material due to refractive index modification. This work will present the design of 3D waveguide using commercially available solid modeler, the generation of motion control codes using a customized post processor and the writing of the developed pattern. Also, control of the laser process parameters to obtain desired feature quality by minimizing self-focusing and self-trapping in PMMA is discussed. This FLM system along with the 4-axis machining capability can be effectively used for the fabrication of complex 3D waveguide circuits in a single step process.

On the Design of a Biodegradable POC-HA Polymeric Cardiovascular Stent

The current state of the art in coronary stent technology, tubular structures used to keep the lumen open, is mainly populated by metallic stents coated with certain drugs to increase biocompatibility, even though experimental biodegradable stents have appeared in the horizon. Biodegradable polymeric stent design necessitates accurate characterization of time dependent polymer material properties and mechanical behavior for analysis and optimization. This manuscript presents the process for evaluating material properties for biodegradable biocompatible polymeric composite poly(diol citrate) hydroxyapatite (POC-HA), approaches for identifying material models and three dimensional solid models for finite element analysis and fabrication of a stent. The developed material models were utilized in a nonlinear finite element analysis to evaluate the suitability of the POC-HA material for coronary stent application. In addition, the advantages of using femtosecond laser machining to fabricate the POC-HA stent are discussed showing a machined stent. The methodology presented with additional steps can be applied in the development of a biocompatible and biodegradable polymeric stents.© 2012 ASME

Analysis and design of a two-wheeled robot with multiple user interface inputs and vision feedback control

Environments for robotics research and education are usually based on open source code or use proprietary software tools. Open source usually requires a user to know a low level programming language and proprietary software does not provide the environment needed for research and educational activities. In addition to the software, the hardware must be inexpensively and easily fabricated and assembled for teaching and experimentation purposes. In this manuscript, we will present the design and fabrication of a small size two-wheel mobile robotic platform developed for research and education purposes. Subsequently, the software environment for controlling the robot which is based on LabVIEW will be presented. LabVIEW was chosen because it provides many built-in toolboxes, and it is characterized by expandability and ease of interface with external devices. The software allows experienced as well as novice users to develop control code with ease. The robot communicates with control software in LabVIEW through a Bluetooth device. The developed environment is used to control the robot through multiple interfaces, to implement obstacle avoidance algorithms with ease, to implement open and closed loop control algorithms, to easily incorporate and use an inexpensive web camera for vision calibration, and is currently used to implement image processing and voice processing algorithms for robot localization and control both for research and education in both undergraduate and graduate courses.Copyright

On the optimum synthesis of a microconveyor platform for micropart translocation using differential evolution

Abstract Micromanipulation is an active research topic in the development of MEMS devices. At the microscale the microforces encountered are highly nonlinear and behave differently than their macroscale equivalent ones. Thus, if an inverse problem were to be posed in the MEMS world, the problem could be investigated and the parameters identified using non-traditional evolutionary based approaches. In this manuscript, the notion of a microconveyor platform along with the highly nonlinear microscale forces of the interaction between the microconveyor and a micropart is introduced. The proposed microconveyor platform for micromanipulation based on the active surface concept is investigated for the controlled translocation of a micropart to a predefined destination in minimum time and within a predefined distance tolerance. The current work poses the microconveyor concept as an inverse problem that aims to identify the optimum values of system control parameters for controlled micropart motion. Differential evolution is employed for solving this inverse problem because of the discontinuity and nonlinearity of the system dynamics which do not render conventional direct line search techniques suitable for control parameter estimation. The design variables based on physical conditions, the boundary constraints on design variables along with other constraints and the objective function are introduced. The convergence of the proposed objective function, design variables and evaluation of system output at the identified optimized set of control parameters are discussed. The optimization results reinforce the feasibility of the concept of active surface based microconveyor comprising of a series of actuators for controlled micropart translocation.

Towards the Realization of a Conveyor Platform for Microparts Employing a Deformable Surface

Various approaches ranging from micro-sized air-nozzles to direct manipulation through bimetallic actuators have been proposed to displace/orient sub-millimeter sized parts for automatic assembly of homogeneous and/or heterogeneous microdevices Keeping in view the micromanipulation requirements, based on the concept of active surface, a new approach for micromanipulation has been proposed by the authors which comprises of controlled deformation of a flexible continuous surface [1]. A single actuator system has limited micropart translocation capability and multiple sequential actuators need to be used if the required translocation distance is more than the capability of an actuator. For a single actuator system, the parameters of the system and their influence on the system output (translocation distance or travel distance) have already been discussed as function of the input frequency, actuator stroke, surface roughness and deformation wavelength [2]. In a multiactuator system, the subsequent actuators engage the micropart with a finite initial velocity and at some position relative to the actuator. Therefore, a sequential array of actuators exhibits a different set of overall operational characteristics. This manuscript describes the operational characteristics of sequential actuators towards a microconveyor system over a range of actuator frequencies and other system parameters and estimates the system output i.e. the micropart distance travelled or translocation. The discussion is based on a two actuator system with the conclusions generalized for a multi-actuator system.© 2012 ASME

Sensitivity Analysis of Micropart Motion on a Controlled Deformable Continuous Surface

Various approaches have been investigated for micropart (∼250 μm in size) manipulation especially for their controlled positioning for automated assembly of MEMS devices. The motion dynamics of a micropart in a dry-friction environment due to controlled deformation of a continuous flexible surface have been developed and are used to study the sensitivity of micropart motion and micropositioning as function of micropart and surface material properties and input actuator properties. The dynamics consider Van der Waal’s forces, effects of surface deformation profile, relative surface roughness, the dynamic compression of asperities and their effect on the dynamic friction coefficient based on extending Kogut-Etsion friction model through a quasi-dynamic coefficient of friction estimation. The motion of the micropart is affected by these parameters, and it is found that for some combinations of parameters a range exists that could cause motion while outside this range either there is no motion or the micropart detaches from the surface. The understanding of the effects of these parameters on micropart motion could pave the way towards controlled micropart translocation and manipulation employing a continuous flexible surface for microassembly, processes requiring controlled micropart handling for homogeneous or heterogeneous microdevice mass production, or for the development of microconveyor systems.Copyright

Finite Element Analysis of Weld Area in Spot Bonding Process to Predict Bond Strength in Transparent Materials Using Ultrafast Lasers

Laser spot bonding is an approach to weld transparent materials at micro level or bonding in/for MEMs devices. This manuscript intends to investigate the dynamics of welding procedure in transparent materials with ultrafast lasers acting as the heat source. Spot bonding takes place when a laser beam creates a molten pool of the two materials to be bonded and subsequently the molten materials interact, gel with each other and solidify to create a bond. Thus, predicting the correct amount of molten matter is highly important for a reliable bond. Proper understanding of ultrafast laser matter interaction will provide the means to define ultrafast laser parameters for controlled molten volume leading to controlled bonding strength. This study will utilize the non linear breakdown caused by ultrafast lasers in borosilicate glass to determine the temperature profile and estimate the radial weld area. A finite element (FE) model of the system is presented and solved in ANSYS to estimate the weld area in borosilicate glass strips under action of a single ultrafast laser pulse. The effects of the focusing location of the laser beam, laser process parameters (energy level, focusing lens, pulse width) and material properties (optical and thermal absorptivity) will be discussed.Copyright