Evgueni V. Bordatchev

Performance characterization of in-plane electro-thermally driven linear microactuators

Static and dynamic electro-mechanical performance of a microactuator is a key factor in the functioning of an integrated microsystem composed of moving components such as optical shutters/switches, micropumps, microgrippers, and microvalves. Therefore, the development of such systems primarily focuses on the overall design and parameter optimization of an actuator as the major driving element with respect to the desired performance parameters, e.g., displacement, force, dimensional constraints, material, actuation principle, and method of fabrication. This study presents results on the static and dynamic electro-mechanical performance analysis of an in-plane electro-thermally driven linear microactuator. Each microactuator, having a width of 2220 mm and made of 25 mm thick nickel foil, consisted of a pair of cascaded structures. Connecting several actuation units in a series formed each cascaded structure. Several microactuators with a different number of actuation units were fabricated using the laser micromachining technology. The static performance of these microactuators was evaluated with respect to the maximum linear output displacements, actual resistance, applied current, and consumed electric power. The maximum displacements varied approximately from 3 to 44 mm, respectively, depending on the number of actuation units. The dynamic performance was studied as a response function on constant applied current with respect to the output displacements. In addition, the response time was evaluated for different applied currents and for actuators with 2, 4, and 6 actuation units. The microactuators’ performance results are promising for applications in MEMS/MOEMS, microfluidic, and microrobotic devices.

Microgripper: Design, finite element analysis and laser microfabrication

This research is focused on new and innovative design, finite element analysis, precision laser microfabrication, and performance evaluation of a microgripper. The design of the microgripper with overall dimension of 1.4(W)x2.8(L)mm is based on a pair of cascaded structures oriented in a face-to-face direction, to act as microtweezers. Each cascaded structure is formed by connecting several basic actuation units in series. Each actuation unit consists of a constrainer and two semi-circular-shaped actuation beams. The actuation principle is based on the electrothermal effect. On application of electrical potential, the output displacement and the force are generated from the summation of all basic actuation units in these cascaded structures. Finite element analysis (FEA) is applied to simulate dynamic performance of the microgripper and to choose proper operational voltage parameters. Thin nickel foil of a thickness of 12.5 micrometers was used in the laser microfabrication of these prototypes. Dynamic performance of the prototype device was evaluated within 0-1.9 voltage range. The maximum tweezing displacements of up to 30 micrometers were recorded for nickel microgripper prototype. Larger displacements are feasible through the optimization of design parameters.

An Experimental Study and Statistical Analysis of the Effect of Laser Pulse Energy on the Geometric Quality During Laser Precision Machining

In laser precision machining, process parameters have critical effects on the geometric quality of the machined parts. Due to the nature of the interrelated process parameters involved, an operator has to make a host of complex decisions, based on trial‐and‐error methods, to set the process control parameters related to the laser, workpiece material, and motion system. The objective of this work is to investigate experimentally the effect of laser pulse energy on the geometric quality of the machined parts in terms of accuracy, precision, and surface quality. Experimental study of formation of machined craters on thin copper foil with variation in laser pulse energy, the geometry and the surface topology of craters is presented. The geometrical parameters were measured and statistically analyzed with respect to incident pulse energy. Statistical analysis including pattern recognition was employed to analyze the experimental data systematically and to serve proper selection of the process parameters to achieve the desired geometric quality of the machined parts. Plausible trends in the crater geometry with respect to the laser pulse energy are discussed. The technique has been verified experimentally on simple geometrical features such as circles and grooves, and the geometric quality is evaluated.

Process planning for Floor machining of 2½D pockets based on a morphed spiral tool path pattern

This work proposes a process planning for machining of a Floor which is the most prominent elemental machining feature in a 21/2D pocket. Traditionally, the process planning of 21/2D pocket machining is posed as stand-alone problem involving either tool selection, tool path generation or machining parameter selection, resulting in sub-optimal plans. For this reason, the tool path generation and feed selection is proposed to be integrated with an objective of minimizing machining time under realistic cutting force constraints for given pocket geometry and cutting tool. A morphed spiral tool path consisting of G^1 continuous biarc and arc spline is proposed as a possible tool path generation strategy with the capability of handling islands in pocket geometry. Proposed tool path enables a constant feed rate and consistent cutting force during machining in typical commercial CNC machine tool. The constant feed selection is based on the tool path and cutting tool geometries as well as dynamic characteristics of mechanical structure of the machine tool to ensure optimal machining performance. The proposed tool path strategy is compared with those generated by commercial CAM software. The calculated tool path length and measured dry machining time show considerable advantage of the proposed tool path. For optimal machining parameter selection, the feed per tooth is iteratively optimized with a pre-calibrated cutting force model, under a cutting force constraint to avoid tool rupture. The optimization result shows around 32% and 40% potential improvement in productivity with one and two feed rate strategies respectively.

Topology Optimized Design, Microfabrication and Characterization of Electro-Thermally Driven Microgripper

This article presents a systematic and logical study of the topology optimized design, microfabrication, and static/dynamic performance characterization of an electro-thermo-mechanical microgripper. The microgripper is designed using a topology optimization algorithm based on a spatial filtering technique and considering different penalization coefficients for different material properties during the optimization cycle. The microgripper design has a symmetric monolithic 2D structure which consists of a complex combination of rigid links integrating both the actuating and gripping mechanisms. The numerical simulation is performed by studying the effects of convective heat transfer, thermal boundary conditions at the fixed anchors, and microgripper performance considering temperature-dependent and independent material properties. The microgripper is fabricated from a 25 μm thick nickel foil using laser microfabrication technology and its static/dynamic performance is experimentally evaluated. The static and dynamic electro-mechanical characteristics are analyzed as step response functions with respect to tweezing/actuating displacements, applied current/power, and actual electric resistance. A microgripper prototype having overall dimensions of 1 mm (L) × 2.5mm (W) is able to deliver the maximum tweezing and actuating displacements of 25.5 μm and 33.2 μm along X and Y axes, respectively, under an applied power of 2.32 W. Experimental performance is compared with finite element modeling simulation results.

Femtosecond laser micromachining of polyvinylidene fluoride (PVDF) based piezo films

Piezoelectric polymers have been known to exist for more than 40 years, but in recent years they have been recognized as smart materials for the fabrication of microsensors, microactuators and other micro-electro-mechanical systems (MEMS). In this work, femtosecond laser micromachining of a polyvinylidene fluoride (PVDF) film, coated with NiCu on both sides, has been studied to understand selective patterning mechanisms of NiCu layers and ablation characteristics of PVDF films. A detailed characterization of morphological changes of the laser-irradiated areas has been investigated using scanning electron microscopy. Through morphological analysis, the multiple shot damage thresholds of a 28 µm thick PVDF film and 40 nm thick NiCu layer have been determined. Surface morphology examination indicates that NiCu layers are removed from the PVDF film through a sequence of cracking–peeling off-curling. In addition, the NiCu layer on the rear side was also removed by the partially transmitted laser energy. The PVDF film was removed in forms of bundles of filaments and solid fragments by a combination of pure ablation and explosive removal of material by bursting of bubbles; the role of the explosive removal becomes more dominant with the increase of laser fluence. Optimal process conditions for cutting of the PVDF film and patterning of the NiCu coating without damaging the PVDF polymer have been established and applied to fabricate a vibration microsensor prototype that shows significant potential in using PVDF-based functional microdevices for telecommunications, transportation and biomedical applications.

Design, kinematic modeling and performance testing of an electro-thermally driven microgripper for micromanipulation applications

Microgripping systems incorporate miniature end-effectors used to manipulate micro-sized objects such as tiny mechanical parts, electrical components, biological cells and bacteria. This paper presents a thorough study of the design, kinematics and static/dynamic performances, including electro-thermo performance characteristics, of the new microgripping system. The developed microgripper had a monolithic design which consisted of a combination of an in-plane electro-thermally driven microactuator and a compliant tweezing mechanism. The kinematics of the microgripper was studied as a transformation of input linear actuation motions into output tweezing displacements and compared with microgripper prototypes fabricated from 25 µm thick nickel foil by using laser micromachining technology. The static, dynamic and electro-thermal characteristics of the system performance were analyzed with respect to actual actuation motions, tweezing displacements, voltage, power, electric resistance and overall temperature under constant applied current within a range of {20, 40, ..., 160} mA. Maximum tweezing displacements of 47.5 µm (tweezing gap of 94.9 µm) were achieved under an applied current of 160 mA for a fabricated microgripper having a transform coefficient K = 1.731. The repeatability and reliability of the fabricated microgripper were also tested along with the capability to grip, hold and release a 110 µm diameter glass bead proving that this microgripper can be utilized as a grasping end-effector for micromanipulation, microrobotic and microassembly applications.

Experimental statistical analysis of laser micropolishing process

Laser micropolishing (LµP) is a new advanced m aterial microprocessing technology that attempts to smooth the original surface geometry through laser-material interactions such as melting or material ablation. Despite the significant advantages of LµP micro features, surfaces, parts, moulds and dies with complex 3D geometries from a wide range of materials, LµP is a complicated dynamic process that requires very fine tuning of a number of process parameters related to laser, optics, laser beam motions, and material properties. This paper describes a new approach for statistical analysis of LµP, where LµP is considered as a single-input (original surface) / singleoutput (polished surface) dynamic system. Original and polished cross-sections were obtained experimentally and their statistical characteristics, such as, surface roughness, material ratio function and autospectrums were calculated and analysed. In addition, LµP process was experimentally investigated as a dy namic operator represented by a transfer function and it was analysed using a coherence function. Analysis of these ch aracteristics allowed finding specific characteristics of the LµP process when surface roughness was improved by 21.3 %, lo wering averaged Ra value from 577 nm to 452 nm, and significantly reducing Ra non-uniformity from 132 nm to 44 nm for a Ti6Al4V sample.

Laser micromachining of the miniature functional mechanisms

The actual performance of a miniature mechanism significantly depends on the geometric quality of the machined part and specific features therein. To fabricate functional parts and features with accuracy and precision within +/- 1 μm or less, the laser micromachining system requires the capabilities of following the desired toolpath trajectories with minimum dynamic errors, high positional repeatability, and synchronization of laser firing events at precise time-and-location to ablate the material. The major objectives of this study are to fabricate miniature functional mechanisms using precision laser micromachining method, explore the machining challenges and evaluate the geometrical quality of the machined parts in terms of accuracy, precision and surface quality. Two functional mechanisms based on electro-thermal actuation have been studied. Several machining challenges related to the corner accuracy, the asynchronization of motions and, the laser-on/off events in space and time with respect to the part geometry have been addressed. The source of inaccuracies primarily stems from the geometric complexity of the mechanism that consists of several features, such as, arcs, radii, lines, curvatures, segments and pockets, along with their dimensional aspect ratio. Such a complex design requires a large number of inconsecutive trajectories to avoid thermal deformations. Copper and nickel foils with a thickness of 25 and 12.5 µm respectively were used in the fabrication of the prototypes. The machining challenges were successfully tackled and the geometrical performance of the fabricated prototypes was evaluated. Local feature accuracies within 0.1 - 0.2 µm have been recorded.

Experimental characterization of contaminants in engine lubricants using surface plasmon resonance sensing

Purpose – The purpose of this paper is to develop new knowledge in experimental characterization of contaminants in engine lubricants, using surface plasmon resonance (SPR) sensing that can be applicable for on‐line condition monitoring of lubricant quality and engine component performance.Design/methodology/approach – The effect of change in optical properties (e.g. transparency, absorption, and refractive index) of engine lubricants caused by the introduction of contaminants, such as gasoline, coolant, and water, on the surface plasmon resonance characteristics is analyzed experimentally. In SPR measurement, variations in both the refractive index and absorption cause changes in the SPR curve, which is the dependence of reflectivity vs incidence angle. The SPR characteristics (e.g. refractivity) of engine lubricant contaminated by gasoline, water and coolant at different concentration are measured as a function of resonance angle and analyzed with respect to different concentration (1%‐10%) of contamina...