Chevron Actuator Research Articles

Design and analysis of novel microelectromechanical system based microgripper for manipulating microbiological species and micro objects

Design and analysis of a pair of novel microelectromechanical system (MEMS) microgrippers having single and multiple sets of jaws respectively, incorporated with displacement amplification mechanism and electrostatic force sensor is presented in this research work. The novelty of the proposed microgrippers is their unique and efficient designs, having the versatility of gripping ranges. The size of the microgripper is 3.2 × 3.7 mm2 in both cases and has one and three sets of jaws with gripping ranges of 30–64 µm, 175–200 µm, and 350–380 µm respectively. The three jaw sets are application-specific to the multicellular small organism, eukaryotic cells, and microcells, respectively. The microgrippers are being actuated by an optimized V-shaped thermal chevron actuator whose input is amplified by using a pantograph displacement amplification mechanism with an amplification factor of 54. The force applied to the gripping object is sensed by a rotary comb electrostatic force sensor. Special attention has been paid to the structural design, and detailed stress analysis has been discussed. This research work includes static, electrostatic, parametric, and electrothermal analysis carried out using Finite Element Method (FEM) techniques and analytical modeling. The results show that the operating voltage range of the devices is from 4 to 9.25 V, having a maximum operational temperature of 380 °C with a factor of safety of 1.026. The maximum capacitance change with the full operational range of microgrippers is 0.63 µf, having a capacitive sensitivity of 19.6 nf/µm. The microgrippers can be used as an instrument to grip not only the microbiological species but also can be beneficial to carry out manipulations at the micro-level like micro-assembly. The proposed microgripper has a substantial structural stability, has a high amplification factor and accommodates manipulation of a wide range of microorganism.

Design and analysis of four-jaws microgripper with integrated thermal actuator and force sensor for biomedical applications.

This research paper presents design and analysis of the multi-jaw microgripper that can manipulate microbiological organisms and species, cell probing and measurement, biomedical sample sorting, and preparation. Four jaws, actuated with a single thermal chevron actuator, can grip microbiological species ranging from 300 to 700 μm, 1 to 340 μm, 100 μm pool, and 1 to 120 μm spongy cells, respectively. Jaws are designed in such a way that they can grip regular, irregular, and spongy shaped biological species and their organelles. Parametric analysis of the microgripper exhibited that at 10V, the efficiency of the thermal actuator is at maximum with respect to displacement, force, and temperature. To enhance displacement to voltage ratio and increase the energy efficiency, a class 3 lever mechanism has been incorporated. The amplification factors at four jaws are 17.21, 13.82, 4.02, and 4.93, respectively. For controlled application of the force to microspecies, two electrostatic force sensors have been amalgamated with jaws having capacitive sensitivities of 1.59 nf/μm, 1.91 nf/μm, 17 nf/μm, and 14.5 nf/μm, respectively. Electrothermal, static, and electrostatic analyses have been carried out with the finite element methods based software IntelliSuite®. Stress magnitudes are within the limits of structural integrity of silicon having a factor of safety 2.5. Thermal analysis revealed that at a differential voltage of 10V, the maximum temperature goes up to 425 °C. Buckling analysis results depicted that the critical load for the thermal actuator is 241 μN with the buckling load factor greater than unity. This paper focuses on microbiological applications only; however, the designed microgripper can be used to manipulate micro-objects, microstructures, microelectronics parts, and micro assembly.

Design and characterization of a polymer electrothermal microgripper with a polynomial flexure for efficient operation and studies of moisture effect on negative deflection

Microgrippers are important devices for micro-manipulation in various applications in automation, microrobotics, material science, and biological studies. There has been a significant interest in improving the performance and reliability of microgrippers by developing efficient designs and actuation methods, and in reducing the cost of fabrication by utilizing polymer materials. This paper presents the design and characterization of an SU-8 based electrothermal microgripper with embedded Au thin film heaters. The design combines a Z-shape chevron actuator and a polynomial-shape flexure to convert the driving force into rotational movement of the microgripper arm. The results of electro-thermo-mechanical simulation using COMSOL Multiphysics software tool have shown that the optimized polynomial design is 5–10% more efficient in operation as compared to the straight beam design due to better stress distribution. The microgripper was capable of producing a gripping stroke of ~ 80 µm at 0.4 V driving voltage, the corresponding heater temperature was 120 °C. The characteristic behavior of negative deflection in SU-8 based microgrippers was observed at low actuation temperatures, resulting in several microns of displacement in the direction opposite to the expected movement. This effect was found to be associated with moisture absorption from the ambient environment by the polymer structure. Further tests under controlled humidity conditions were carried out and showed that the negative deflection is due to the moisture absorption effect in the SU-8 structures. It is shown that the microgripper is capable of performing pick-and-place of micro-objects using spherical glass micro-beads, therefore demonstrating the potential for applications in microassembly.

Modeling and Thermal Metrology of Thermally Isolated MEMS Electrothermal Actuators for Strain Engineering of 2D Materials in Air

We present electrothermal microelectromechanical (MEMS) actuators as a practical platform for straining 2-D materials. The advantages of the electrothermal actuator are its high output force and displacement for low input voltage, but its drawback is that it is actuated by generating high amounts of heat. It is crucial to mitigate the high temperatures generated during actuation for reliable 2-D material strain device implementation. Here, we implement a chevron actuator design that incorporates a thermal isolation stage in order to avoid heating the 2-D material from the high temperatures generated during the actuation. By comparing the experiment and simulation, we ensure our design does not compromise output displacement while keeping the 2-D material strain device stage cool. We also provide a simple analytical model useful for quickly evaluating different thermal isolation stage designs.

Reconfigurable MEMS latching-type capacitors for high power applications

This paper reports the design and characterization of two reconfigurable MEMS discrete capacitor banks for high power and low frequency applications. The first design is a 3-bit capacitor bank built using three parallel-connected series-switched comb-drive capacitors with appropriately scaled values. The second design is a compact discretized comb-drive varactor that can be operated as 2-bit or 3-bit capacitor bank depending on the number of latched states. Both devices are demonstrated using the METALMUMP process where 20 µm-thick plated nickel is the only structural and metal layer. The MEMS switches use thermal actuation with chevron actuator design. This allows for large displacements at relatively low actuation voltages. Using mechanical latching for both designs, the switch reconfiguration energy is minimized. The relatively very high mechanical stiffness inherent to both thermal actuator designs provides an excellent immunity to self-actuation at high RF power levels. The proposed MEMS switches are capable of operating under low-pressure conditions (e.g. in a package), without degradation of their thermo-mechanical performance.

Modelling of Chevron electrothermal actuator and its performance analysis

In this work, a Chevron electrothermal actuator is designed and its analytical model is developed. Chevron actuator works on the principle of Joules heating effect and thermal expansion. Aluminum is chosen as a material for actuator because of its good electrical and thermal properties and also it produces large displacement of about 10.94 µm with lower operating temperature of 448 °C for single beam. The Chevron based electrothermal actuator holds good when compared to the other conversion based conventional microactuators in terms of applied voltage vs displacement achieved. The analytical model is validated by comparing with 3D finite element model. The mathematical modeling is derived and the analytical calculations were performed over the mathematical model. The displacement and temperature results obtained from simulation and analytical models are in good agreement. The comparative results provides the proof for having a better performance in simulation which is again validated by the 0.3% of error with the analytical modeling of the Chevron based electrothermal microactuator.

Direct integration of MEMS, dielectric pumping and cell manipulation with reversibly bonded gecko adhesive microfluidics

We present an approach to form a microfluidic environment on top of MEMS dies using reversibly bonded microfluidics. The reversible polymeric microfluidics moulds bond to the MEMS die using a gecko-inspired gasket architecture. In this study the formed microchannels are demonstrated in conjunction with a MEMS mechanical single cell testing environment for BioMEMS applications. A reversible microfluidics placement technique with an x-y and rotational accuracy of ±2 µm and 1° respectively on a MEMS die was developed. No leaks were observed during pneumatic pumping of common cell media (PBS, sorbitol, water, seawater) through the fluidic channels. Thermal chevron actuators were successful operated inside this fluidic environment and a performance deviation of ~15% was measured compared to an open MEMS configuration. Latex micro-spheres were pumped using traveling wave di-electrophoresis and compared to an open (no-microfluidics) configuration with velocities of 24 µm s−1 and 20 µm s−1.

Design and simulation of an optimized electrothermal microactuator with Z-shaped beams

The displacement of the central shuttle of a Z-shape chevron actuator can be calculated using a developed approach from other authors. Who demonstrated that the actuators with this geometry offer a larger displacement compared with V-shape actuators. Z-shape offers a larger stiffness and output force for the case of only one arm. This paper is focused on the optimization of the Z-shaped beams of a chevron actuator of eight beams, which seeks to increase the previously described response. The structure is designed in parametric solid modeling 3D software Autodesk Inventor, and simulated by finite element method in Ansys 15.0. These simulations were implemented considering several modifications on the length of the Z-shaped beams in order to choose the most appropriate length. The electric potential applied in all cases was from 0.2 V up to 5 V. The Z-shape length of the arms for the case of the optimized Z-shape actuator increases the shuttle’s displacement in approximately 50% compared to V-shape actuator, and 38% compare to the original Z-shape. Analytical adjusted approach is extremely matched with the simulations results. Length of the Z-shape beam is the determinant factor of the displacement. The low stiffness of the optimized Z-shape actuator (89% lower than the original V-shape and 58% compared to Z-shape) can allow its use as load sensor.

Design and simulation of a novel metallic microgripper using vibration to release nano objects actively

In this study, we investigate a novel metallic microgripper which is able to grasp and transport nano particles (nano tubes/wires) and release them on desirable substrate by vibrating the gripper arms. This microgripper consists of a chevron actuator to grip nano object electrothermally and interdigited comb drive systems to generate vibration at the gripper arms electrostatically. Metallic (nickel) properties enable the chevron actuator to close the gap and pick the nano particle at low voltage and temperature. In order to reduce the out of plane bending during operation and also increase the gripping force, thickness of the nickel layer must be increased, hence electroplating process is proposed for deposition of nickel layer. To generate vibration at the end effectors, comb drive systems are stimulated by applying two voltage signals at desired resonant frequency to the stators. Practically, by sweeping the frequency of these signals around the resonant frequency the end effectors start vibrating. The vibration results in overcoming the adhesion forces due to inertial effects.

Characterization of Kink Actuators as Compared to Traditional Chevron Shaped Bent-Beam Electrothermal Actuators

This paper compares the design and performance of kink actuators, a modified version of the bent-beam thermal actuator, to the standard chevron-shaped designs. A variety of kink and chevron actuator designs were fabricated from polysilicon. While the actuators were electrically probed, these designs were tested using a probe station connected to a National Instruments (NI) controller that uses LabVIEW to extract the displacement results via image processing. The displacement results were then used to validate the thermal-electric-structural simulations produced by COMSOL. These results, in turn, were used to extract the stiffness for both actuator types. The data extracted show that chevron actuators can have larger stiffness values with increasing offsets, but at the cost of lower amplification factors. In contrast, kink actuators showed a constant stiffness value equivalent to the chevron actuator with the highest amplification factor. The kink actuator also had larger amplification factors than chevrons at all designs tested. Therefore, kink actuators are capable of longer throws at lower power levels than the standard chevron designs.

A thermal-driven silicon micro xy-stage integrated with piezoresistive sensors for nano-positioning

This paper describes a novel micro xy-stage, driven by double-hot arm horizontal thermal micro-actuators integrated with a piezoresistive sensor (PS) for low-voltage operation and precise control. This micro xy-stage structure is linked with chevron beams and optimized to amplify the displacement generated by the micro-actuators that provide a pull force to the movable platform. The PS employed for in situ displacement detection and feedback control is fabricated at the base of a cold arm, which minimizes the influence of temperature change induced by electro-thermal heating. The micro xy-stage structure is defined through the use of a simple micromachining process, released by backside wet etching with a special tool. For an input power of approximately 44 mW, each chevron actuator provides about 16 µm and the total displacement of the platform is close to 32 µm. The sensitivity of the PS is better than 1 mV µm−1, obtained from the amplified voltage output of the Wheatstone bridge circuit. The potential applications of the proposed micro xy-stage lie in micro- or nano-manipulation, as well as the positioning of ultra-small objects in nanotechnology.

Development and Testing of a Multilevel Chevron Actuator-Based Positioning System

We present the design, fabrication, and testing of a microscale positioning system. The system was designed in the SUMMiT V process to produce in-plane, bidirectional, micrometer-scale linear motion of a shuttle using a ratcheting mechanism and multilayered chevron actuators. A single latching system with oppositely faced ratchet teeth on either side of the shuttle is used for achieving the bidirectional actuation. The device has a smaller footprint and fewer electrical connections compared to similar devices, without compromising performance. Moreover, this device is capable of generating more force compared to previous devices. A LabVIEW-based optical characterization setup was developed for automated testing of the device. The device produced a maximum displacement of ~180 μm with a step size of 9 μm.

Force, deflection and power measurements of toggled microthermal actuators

Force and power characteristics are experimentally measured for three types of toggling microthermal actuators: (i) standard two-arm thermal actuators, (ii) chevron or ‘V’ type actuators and (iii) chevron actuators with a toggle amplifier. Micro-Newton scale forces and micron scale displacements are experimentally measured using an off-chip probe. For each type of actuator, force versus deflection curves are measured to determine mechanical advantage and maximum ranges. For each type of actuator, work output versus input power curves are measured to determine actuator effectiveness. Different actuator designs are compared in terms of force, displacement, power and effectiveness.