Microgripper Prototype Research Articles

A New Two-Phase Design Process for a Compliant Mechanism Gripper

The structural design of the components with high accuracy and controllable motion is the focus of precision industries. As a result, researchers found that components created via compliant mechanisms were much preferable. Monolithic structures known as compliant mechanisms allow motion to be achieved without the need of traditional joints. The compliant mechanisms make it easier to build microscale devices because they do not have hard junctions. In this study, a novel two-phase design methodology for compliant mechanism forceps is proposed. In order to eliminate high-stress areas, forceps are often constructed as a distributed compliant mechanism. To offer a distributed planar design, topological optimization is introduced with new approach. Design domain introduced with pattern of holes restricts the single point contact formation and large area formation which yield distributed compliant mechanism. The parametrization technique is implemented to convert the conceptual design to working design. The design of compliant forceps is assessed using finite element analysis (FEA) based on structural considerations. Finally, a handle-equipped microgripper prototype has been developed. Experimental verification demonstrates the gripper's performance and variation is less than 3% with numerical results. Integerated force sensor measure the gripping force and compared the reaction force estimated through FEA.

Comparative evaluation of three image analysis methods for angular displacement measurement in a MEMS microgripper prototype: a preliminary study

<p class="Abstract"><span lang="EN-US">The functional characterization of MEMS devices is relevant today since it aims at verifying the behavior of these devices, as well as improving their design. In this regard, this study focused on the functional characterization of a MEMS microgripper prototype suitable in biomedical applications: the measurement of the angular displacement of the microgripper comb-drive is carried out by means of two novel automatic procedures, based on an image analysis method, SURF-based (Angular Displacement Measurement based on Speeded Up Robust Features, ADM<sub>SURF</sub>) and FFT-based (Angular Displacement Measurement based on Fast Fourier Transform, ADM<sub>FFT</sub>) method, respectively. Moreover, the measurement results are compared with a Semi-Automatic Method (SAM), to evaluate which of them is the most suitable for the functional characterization of the device. The curve fitting of the outcomes from SAM and ADM<sub>SURF</sub>, showed a quadratic trend in agreement with the analytical model. Moreover, the ADM<sub>SURF</sub> measurements below 1° are affected by an uncertainty of about 0.08° for voltages less than 14 V, confirming its suitability for microgripper characterization. It was also evaluated that the ADM<sub>FFT</sub> is more suitable for measurement of rotations greater than 1° (up to 30°), with a measurement uncertainty of 0.02°, at 95% of confidence level.</span></p>

An Image Analysis Approach to Microgrippers Displacement Measurement and Testing

The number of studies on microgrippers has increased consistently in the past decade, among them the numeric simulations and material characterization are quite common, while the metrological issues related to their performance testing are not well investigated yet. To add some contribution in this field, an image analysis-based method for microgrippers displacement measurement and testing is proposed here: images of a microgripper prototype supplied with different voltages are acquired by an optical system (i.e., a 3D optical profilometer) and processed through in-house software. With the aim to assess the quality of the results a systematic approach is proposed for determining and quantifying the main error sources and applied to the uncertainty estimation in angular displacement measurements of the microgripper comb-drives. A preliminary uncertainty evaluation of the in-house software is provided by a Monte Carlo Simulation and its contribution added to that of the other error sources, giving an estimation of the relative uncertainty up to 3.6% at 95% confidence level for voltages from 10 V to 28 V. Moreover, the measurements on the prototype device highlighted a stable behavior in the voltage range from 0 V to 28 V with a maximum rotation of 1.3° at 28 V, which is lower than in previous studies, likely due to differences in system configuration, model, and material. Anyway, the proposed approach is suitable also for different optical systems (i.e., trinocular microscopes).

Experimental characterizations of bimorph piezoelectric actuator for robotic assembly

Piezoelectric actuator is one of the most versatile types of smart actuators, extensively used in different industrial applications like robotics, microelectromechanical systems, micro-assembly, biological cell handling, self-assembly, and optical component handling in photonics. By applying potential to a piezoelectric actuator, it can produce micro level deflection with large force generation, very fast response, and long-term actuation as compared to other actuators. The design and analysis of the bimorph piezoelectric cantilever using proportional–integral controller are carried out where the bimorph piezoelectric actuator is used as an active actuator for providing the dexterous behavior during robotic assembly. Characterization of bimorph piezoelectric actuator carried out by controlling voltage signal provides steady-state behavior which is verified by conducting experiments. A prototype of micro gripper is also developed which shows the potential of handling small lightweight objects for robotic assembly.

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.

Principle of a Submerged Freeze Gripper for Microassembly

The development of reliable and repeatable strategies to manipulate and assemble microobjects lies in the efficiency, reliability, and precision of the handling processes. In this paper, we propose a thermal-based microgripper working in an aqueous medium. Manipulating and assembling in liquid surroundings can indeed be more efficient than in dry conditions. A comparative analysis of the impact of dry and liquid media on surface forces, contact forces, and hydrodynamic forces is shown. In addition, ice grippers represent flexible manipulation solutions. Nevertheless, when micromanipulation tasks are performed in air, capillary forces can drastically perturb the release. Our submerged freeze microgripper exploits the liquid surroundings to generate an ice droplet to catch microobjects, and to avoid capillary forces during the release. The thermal principle, the first microgripper prototype, an ice generation simulation, and the first tests are presented. The main objective is to validate the manipulation principle. Further research will be focused on control and optimization of the ice generation and the miniaturization of the system.

A microgripper using piezoelectric actuation for micro-object manipulation

Design, fabrication and tests of a monolithic compliant-flexure-based microgripper were performed. The geometry design and the material stresses were considered through the finite element analysis. The simulation model was used to study in detail profiles of von Mises stresses and deformation. The maximum stress in the microgripper is much smaller than the critical stress values for fatigue. The microgripper prototype was manufactured using micro-wire electrode discharge machining. A displacement amplification of 3.0 and a maximum stroke of 170 μm were achieved. The use of piezoelectric actuation allowed fine positioning. Micromanipulation tests were conducted to confirm potential applications of the microgripper with piezoelectric actuation in handling micro-objects. The simulation and experimental results have proven the good performance of the microgripper.