Commonly encountered problems in the manipulation of objects with robotic hands are the contact force control and the setting of approaching motion. Microelectromechanical systems (MEMS) sensors on robots offer several solutions to these problems along with new capabilities. In this review, we analyze tactile, force and/or pressure sensors produced by MEMS technologies including off-the-shelf products such as MEMS barometric sensors. Alone or in conjunction with other sensors, MEMS platforms are considered very promising for robots to detect the contact forces, slippage and the distance to the objects for effective dexterous manipulation. We briefly reviewed several sensing mechanisms and principles, such as capacitive, resistive, piezoresistive and triboelectric, combined with new flexible materials technologies including polymers processing and MEMS-embedded textiles for flexible and snake robots. We demonstrated that without taking up extra space and at the same time remaining lightweight, several MEMS sensors can be integrated into robotic hands to simulate human fingers, gripping, hardness and stiffness sensations. MEMS have high potential of enabling new generation microactuators, microsensors, micro miniature motion-systems (e.g., microrobots) that will be indispensable for health, security, safety and environmental protection.

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MEMS-Based Tactile Sensors: Materials, Processes and Applications in Robotics

High-magnification microgripper with low output displacement loss

The typical technique of hardness testing of pharmaceutical microcapsules uses pressure transducer-based bulky devices by averaging mechanism. This not only produces non-precise results but also causes wastage of costly core material present in the microcapsules. To overcome these issues a miniaturized version of the device using a micro electromechanical system (MEMS)-based microgripper has been proposed, which can mechanically characterize a single microcapsule of sizes ranging from 5 µm to 20 µm with a maximum rupture force of 13.33 mN. The proposed microgripper consists of a hybrid chevron thermal actuator and integrated capacitive force sensor and has been designed using standard silicon-on-insulator multi-user MEMS processes with a device size of 2.5 × 3.2 mm2. The microgripper is efficiently modelled to produce a temperature gradient of about 350 °C from the actuator to the jaws making it able to handle temperature-sensitive samples.

Analytical design and finite element analysis of a microgripper for characterizing a single microcapsule

In this article, a novel two-axis optical nano-electromechanical-system (NEMS) accelerometer based on metamaterials is presented for biomedical applications. This sensor consists of a proof mass with two different patterns of split-ring resonators (SRR) on its fingers to form a tunable metamaterial device. The fingers connected to the proof mass are movable, while the others are anchored to the sensor framework. In fact, in this structure, two separated parts of the metamaterial cells are coated on the movable and the fixed fingers that are coupled by a nanoscale air gap. When the accelerated proof mass is displaced by physical activities in the xy plane, the coupling of meta-arrays changes and the sensing wavelengths are thus varied. Detection of these changes leads to the measurement of body accelerations or position estimation occurred in different situations. The proposed BioNEMS accelerometer is then analyzed by numerical and analytical methods, which result in the functional characteristics of this platform as follows: <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> -direction optical sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\text {ox}} =116$ </tex-math></inline-formula> nm/g, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> -direction optical sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\text {oy}} =88$ </tex-math></inline-formula> nm/g, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${x}$ </tex-math></inline-formula> -direction mechanical sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\text {mx}} =133.3$ </tex-math></inline-formula> nm/g, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${y}$ </tex-math></inline-formula> -direction mechanical sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\text {my}} =133.3$ </tex-math></inline-formula> nm/g, and measurement range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${M}_{r} = \pm 20$ </tex-math></inline-formula> g for both directions and bandwidth of BW = 500 Hz. According to the results, the presented two-axis BioNEMS accelerometer can be a highly sensitive nanoscale platform for measuring accelerations in various medical applications, such as wearable devices (smartwatches or robot gloves), surgery robots, and medical imaging probes. 

A Dual-Axis Metamaterial BioNEMS Accelerometer for Biomedical Applications

Improving the vacuum degree inside the vacuum device is vital to the performance and lifespan of the vacuum device. The influence of the Ti and ZrCoCe barrier layers on the performance of ZrCoCe getter films, including sorption performance, anti-vibration performance, and binding force between the ZrCoCe getter film and the Ge substrate were investigated. In this study, the Ti and ZrCoCe barrier layers were deposited between the ZrCoCe getter films and Ge substrates. The microtopographies of barrier layers and the ZrCoCe getter film were analyzed using scanning electron microscopes. The sorption performance was evaluated using the constant-pressure method. The surface roughness of the barrier layers and the getter films was analyzed via atomic force microscopy. The binding force was measured using a nanoscratch tester. The anti-vibration performance was examined using a vibration test bench. The characterization results revealed that the Ti barrier layer significantly improved the sorption performance of the ZrCoCe getter film. When the barrier material was changed from ZrCoCe to Ti, the initial sorption speed of the ZrCoCe getter film increased from 141 to 176 cm3·s−1·cm−2, and the sorption quantity increased from 223 to 289 Pa·cm3·cm−2 in 2 h. The binding force between the Ge substrate and the ZrCoCe getter film with the Ti barrier layer was 171 mN, whereas that with the ZrCoCe barrier layer was 154 mN. The results showed that the Ti barrier layer significantly enhanced the sorption performance and binding force between the ZrCoCe getter film and the Ge substrate, which improved the internal vacuum level and the stability of the microelectromechanical system vacuum devices.

https://www.mdpi.com/1996-1944/16/7/2916/pdf?version=1680771792

Influence of Barrier Layers on ZrCoCe Getter Film Performance

Lower stiffness can improve the performance of capacitive-based microelectromechanical systems sensors. In this paper, softened beams, achieved by the electrostatic assembly approach, are proposed to lower the stiffness of a capacitive MEMS accelerometer. The experiments show that the stiffness of the accelerometer is reduced by 43% with softened beams and the sensitivity is increased by 72.6%. As a result, the noise of the accelerometer is reduced to 26.2 μg/√Hz with an improvement of 44.5%, and bias instability is reduced to 5.05 μg with an enhancement of 38.7%. The electrostatic assembly-based stiffness softening technique is proven to be effective and can be used in many types of MEMS devices.

https://www.mdpi.com/2072-666X/13/3/459/pdf?version=1647514461

Design of a Capacitive MEMS Accelerometer with Softened Beams

Rotatory microgripper based on a linear electrostatic driving scheme

This paper reports a DC electric field sensor (EFS) based on the mode localization phenomenon. The EFS consists of 3-degrees-of-freedom weakly coupled resonators (WCRs) and two capacitor arrays that are electrostatically coupled with the WCRs. The capacitor arrays sense the electric field and produce a stiffness perturbation that causes an amplitude ratio change of the WCRs. The EFS is fabricated using a silicon-on-insulator process and evaluated in a vacuum chamber. The amplitude ratio of the resonators changes from 2.2 to 7.5 as the electric field strength ranges from 0 to 7 kV/m, with a sensitivity of 0.76 /(kV/m). The noise, resolution, and stability of the mode-localized EFS are 11.5 (V/m)/√Hz, 22.9 V/m, and 9.1 V/m, respectively, which are competitive compared with that of other high-performance micromachined EFS.

Zheng Sun

Papers

Design of a Capacitive MEMS Accelerometer with Softened Beams

Rotatory microgripper based on a linear electrostatic driving scheme

A Mode-localized DC Electric Field Sensor