In the past few years, soft robotics has rapidly become an emerging research topic, opening new possibilities for addressing real-world tasks Perception can enable robots to effectively explore the unknown world, and interact safely with humans and the environment Among all extero- and proprioception modalities, the detection of mechanical cues is vital, as with living beings A variety of soft sensing technologies are available today, but there is still a gap to effectively utilize them in soft robots for practical applications Here, the developments in soft robots with mechanical sensing are summarized to provide a comprehensive understanding of the state of the art in this field Promising sensing technologies for mechanically perceptive soft robots are described, categorized, and their pros and cons are discussed Strategies for designing soft sensors and criteria to evaluate their performance are outlined from the perspective of soft robotic applications Challenges and trends in developing multimodal sensors, stretchable conductive materials and electronic interfaces, modeling techniques, and data interpretation for soft robotic sensing are highlighted The knowledge gap and promising solutions toward perceptive soft robots are discussed and analyzed to provide a perspective in this field

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201800541

Toward Perceptive Soft Robots: Progress and Challenges

During the last decades, smart tactile sensing systems based on different sensing techniques have been developed due to their high potential in industry and biomedical engineering. However, smart tactile sensing technologies and systems are still in their infancy, as many technological and system issues remain unresolved and require strong interdisciplinary efforts to address them. This paper provides an overview of smart tactile sensing systems, with a focus on signal processing technologies used to interpret the measured information from tactile sensors and/or sensors for other sensory modalities. The tactile sensing transduction and principles, fabrication and structures are also discussed with their merits and demerits. Finally, the challenges that tactile sensing technology needs to overcome are highlighted.

https://www.mdpi.com/1424-8220/17/11/2653/pdf

Novel Tactile Sensor Technology and Smart Tactile Sensing Systems: A Review.

Over the last two decades, considerable scientific and technological efforts have been devoted to developing tactile sensing based on a variety of transducing mechanisms, with prospective applications in many fields such as human–machine interaction, intelligent robot tactile control and feedback, and tactile sensorized minimally invasive surgery. This paper starts with an introduction of human tactile systems, followed by a presentation of the basic demands of tactile sensors. State-of-the-art tactile sensors are reviewed in terms of their diverse sensing mechanisms, design consideration, and material selection. Subsequently, typical performances of the sensors, along with their advantages and disadvantages, are compared and analyzed. Two major potential applications of tactile sensing systems are discussed in detail. Lastly, we propose prospective research directions and market trends of tactile sensing systems.

Recent Progress in Technologies for Tactile Sensors

We propose a new type of tactile sensor that can detect both the contact force and hardness of an object. It consists of a diaphragm with a mesa structure, a piezo-resistive displacement sensor on the diaphragm, and a chamber for pneumatic actuation. An array of these sensors can detect the two-dimensional contact force-distribution and hardness-distribution information and the surface texture of the contacted object. We theoretically analyzed the operation of the tactile sensor, and designed its specifications for a device for detecting the touch of a human finger. We fabricated devices of several different sizes by micromachining technologies to prove the principle. The sensor element is 6.0 mm x 6.0 mm x 0.4 mm, and it has a displacement sensor element of piezo-resistance at the periphery of the diaphragm structure. We experimentally confirmed the characteristics of the device by using pneumatic actuation.

Active tactile sensor for detecting contact force and hardness of an object

Tactile Internet (TI) is envisioned to create a paradigm shift from the content-oriented communications to steer/control-based communications by enabling real-time transmission of haptic information (i.e., touch, actuation, motion, vibration, surface texture) over Internet in addition to the conventional audiovisual and data traffics. This emerging TI technology, also considered as the next evolution phase of Internet of Things (IoT), is expected to create numerous opportunities for technology markets in a wide variety of applications ranging from teleoperation systems and Augmented/Virtual Reality (AR/VR) to automotive safety and eHealthcare towards addressing the complex problems of human society. However, the realization of TI over wireless media in the upcoming Fifth Generation (5G) and beyond networks creates various non-conventional communication challenges and stringent requirements in terms of ultra-low latency, ultra-high reliability, high data-rate connectivity, resource allocation, multiple access and quality-latency-rate tradeoff. To this end, this paper aims to provide a holistic view on wireless TI along with a thorough review of the existing state-of-the-art, to identify and analyze the involved technical issues, to highlight potential solutions and to propose future research directions. First, starting with the vision of TI and recent advances and a review of related survey/overview articles, we present a generalized framework for wireless TI in the Beyond 5G Era including a TI architecture, the main technical requirements, the key application areas and potential enabling technologies. Subsequently, we provide a comprehensive review of the existing TI works by broadly categorizing them into three main paradigms; namely, haptic communications, wireless AR/VR, and autonomous, intelligent and cooperative mobility systems. Next, potential enabling technologies across physical/Medium Access Control (MAC) and network layers are identified and discussed in detail. Also, security and privacy issues of TI applications are discussed along with some promising enablers. Finally, we present some open research challenges and recommend promising future research directions.

/pdf/toward-tactile-internet-in-beyond-5g-era-recent-advances-3w8qex819e.pdf

Toward Tactile Internet in Beyond 5G Era: Recent Advances, Current Issues, and Future Directions

We report novel low-cost and rapid fabrication technologies for the fabrication of movable polymer-based MEMS structures, electrically actuated. Using SU-8 photoresist as structural material, both ordinary and functionalized by conductive fillers (nano-Ag particles and carbon nanotubes), the novel fabrication methods provide simple processes, without the use of any sacrificial layer, for achieving suspended structures (beams and membranes) through either binary or gray-scale photolithography. Experimental validation has demonstrated high yields (over 99% for one of the process flows) in achieving electrostatically actuated microstructures with resonant frequencies in the 0.5–0.8 MHz range, with a stable dynamic behavior tested for a period longer than three months. The technology also confirms that 'doping' SU-8 with conductive fillers can preserve its photo-patterning capabilities, while modifying other physical properties (electrical conductivity). As the patterning of SU-8 films can take place on either rigid or flexible substrates, this low-cost technology promises a wide range of applications.

http://iopscience.iop.org/article/10.1088/1361-6439/aa5dfb/pdf

MEMS transducers low-cost fabrication using SU-8 in a sacrificial layer-free process

The authors report the fabrication of polymer MEMS transducers, without using any sacrificial layers, on flexible substrates. The elimination of sacrificial layers and the process overhead associated with them is achieved through maskless grayscale UV lithography of SU-8 photoresist, and results in a simplification of the overall fabrication process. Six batches, with a total of 60 cantilevers and 60 double- clamped beams, and three batches, with a total of 1500 circular membranes, have been fabricated on commercially available, 45 um Kapton® polyimide sheets coated with a 35um copper layer. The validation of the fabrication process has been done through functional characterization of the bi-directional electro-mechanical interface and robustness to mechanical bending. The test and measurement results of the fabricated microstructures validate a good design predictability (geometry error:

A sacrificial-layer-free fabrication technology for MEMS transducer on flexible substrate

The authors report, for the first time, a simple one-step manufacturing process, without the use of any sacrificial layers, applied for the fabrication of SU-8 ultrasound transducers. Based on grayscale lithography, the method has a high degree of simplicity compared to traditional microfabrication flows. The fabrication of SU-8 CMUT arrays is a case study that validates the application potential of the developed process, its robustness, reproducibility and design predictability. To demonstrate the predictability of the fabrication process, a custom calibration of the SU-8 grayscale lithography has been performed, and the mechanical performance of the CMUT cells has been simulated through FEA tools based on calibration measurement. The dynamical properties of the manufactured SU-8 CMUTs have been experimentally assessed and compared with the simulation results. The CMUT cells have a fundamental resonant frequency at 1.75 MHz, suitable for biomedical imaging; their statistical characterization shows a good match with design simulations with small deviations, indicating acceptable reproducibility, predictability, and robustness. Both mechanical and electrical characterizations show that the proposed grayscale manufacturing technology led to functional CMUT arrays with robust performances. This low-cost, rapid micromanufacturing technique is suitable for any out-of-plane SU-8 based MEMS devices, from pressure sensors to inertial devices and ultrasonic transducer arrays.

Design and fabrication of SU-8 CMUT arrays through grayscale lithography

Resonating MEMS mass sensors are microdevices with broad applications in fields such as bioscience and biochemistry. Their advantageous surface-to-volume ratio makes their resonant frequency highly sensitive to variations in their mass induced by surface depositions. Recent global challenges, such as water quality monitoring or pandemic containment, have increased the need for low-cost (even disposable), rapidly fabricated microdevices as suitable detectors. Resonant MEMS mass sensors are among the best candidates. This paper introduces a simple and robust fabrication of polymeric piezoelectric resonating MEMS mass sensors. The microfabrication technology replaces the traditional layer-by-layer micromachining techniques with laser micromachining to gain extra simplicity. Membrane-based resonant sensors have been fabricated to test the technology. Their characterization results have proven that the technology is robust with good reproducibility (around 2% batch level variations in the resonant frequency). Initial tests for the MEMS mass sensors’ sensitivity have indicated a sensitivity of 340 Hz/ng. The concept could be a starting point for developing low-cost MEMS sensing solutions for pandemic control, health examination, and pollution monitoring.

https://www.mdpi.com/1424-8220/22/8/2994/pdf?version=1649855480

Chang Ge

Papers

Novel Tactile Sensor Technology and Smart Tactile Sensing Systems: A Review.

MEMS transducers low-cost fabrication using SU-8 in a sacrificial layer-free process

A sacrificial-layer-free fabrication technology for MEMS transducer on flexible substrate

Design and fabrication of SU-8 CMUT arrays through grayscale lithography

Simple and Robust Microfabrication of Polymeric Piezoelectric Resonating MEMS Mass Sensors