Human skin is a remarkable organ. It consists of an integrated, stretchable network of sensors that relay information about tactile and thermal stimuli to the brain, allowing us to maneuver within our environment safely and effectively. Interest in large-area networks of electronic devices inspired by human skin is motivated by the promise of creating autonomous intelligent robots and biomimetic prosthetics, among other applications. The development of electronic networks comprised of flexible, stretchable, and robust devices that are compatible with large-area implementation and integrated with multiple functionalities is a testament to the progress in developing an electronic skin (e-skin) akin to human skin. E-skins are already capable of providing augmented performance over their organic counterpart, both in superior spatial resolution and thermal sensitivity. They could be further improved through the incorporation of additional functionalities (e.g., chemical and biological sensing) and desired properties (e.g., biodegradability and self-powering). Continued rapid progress in this area is promising for the development of a fully integrated e-skin in the near future.

25th Anniversary Article: The Evolution of Electronic Skin (E-Skin): A Brief History, Design Considerations, and Recent Progress

Starting from human ?sense of touch,? this paper reviews the state of tactile sensing in robotics. The physiology, coding, and transferring tactile data and perceptual importance of the ?sense of touch? in humans are discussed. Following this, a number of design hints derived for robotic tactile sensing are presented. Various technologies and transduction methods used to improve the touch sense capability of robots are presented. Tactile sensing, focused to fingertips and hands until past decade or so, has now been extended to whole body, even though many issues remain open. Trend and methods to develop tactile sensing arrays for various body sites are presented. Finally, various system issues that keep tactile sensing away from widespread utility are discussed.

Tactile Sensing—From Humans to Humanoids

This paper focuses on the mechanical properties of polydimethylsiloxane (PDMS) relevant for microelectromechanical system (MEMS) applications. In view of the limited amount of published data, we analyzed the two products most commonly used in MEMS, namely RTV 615 from Bayer Silicones and Sylgard 184 from Dow Corning. With regard to mechanical properties, we focused on the dependence of the elastic modulus on the thinner concentration, temperature and strain rate. In addition, creep and thermal aging were analyzed. We conclude that the isotropic and constant elastic modulus has strong dependence on the hardening conditions. At high hardening temperatures and long hardening time, RTV 615 displays an elastic modulus of 1.91 MPa and Sylgard 184 of 2.60 MPa in a range up to 40% strain.

https://iopscience.iop.org/article/10.1088/0960-1317/18/6/065008/pdf

Mechanical properties of silicones for MEMS

This article focuses on the rheological, mechanical and optical properties of polydimethylsiloxane (PDMS) relevant for microelectromechanical systems (MEMS). In view of the limited amount of published data, we analyzed the two products most commonly used in MEMS, namely RTV 615 from Bayer Silicones and Sylgard 184 from Dow Corning. As far as rheological parameters are concerned, the viscosity and spin curves were measured. With regard to mechanical properties, we focused on the measurement of the inconstant elastic modulus up to 115% strain. For the optical characterization we concentrate on the optical dispersion and the wavelength-dependent damping coefficient.

Process and material properties of polydimethylsiloxane (PDMS) for Optical MEMS

A wide variety of tactile (touch) sensors exist today for robotics and related applications. They make use of various transduction methods, smart materials and engineered structures, complex electronics, and sophisticated data processing. While highly useful in themselves, effective utilization of tactile sensors in robotics applications has been slow to come and largely remains elusive today. This paper surveys the state of the art and the research issues in this area, with the emphasis on effective utilization of tactile sensors in robotic systems. One specific with the use of tactile sensing in robotics is that the sensors have to be spread along the robot body, the way the human skin is-thus dictating varied 3-D spatio-temporal requirements, decentralized and distributed control, and handling of multiple simultaneous tactile contacts. Satisfying these requirements pose challenges to making tactile sensor modality a reality. Overcoming these challenges requires dealing with issues such as sensors placement, electronic/mechanical hardware, methods to access and acquire signals, automatic calibration techniques, and algorithms to process and interpret sensing data in real time. We survey this field from a system perspective, recognizing the fact that the system performance tends to depend on how its various components are put together. It is hoped that the survey will be of use to practitioners designing tactile sensing hardware (whole-body or large-patch sensor coverage), and to researchers working on cognitive robotics involving tactile sensing.

Directions Toward Effective Utilization of Tactile Skin: A Review

This paper describes two kinds of 3 × 3 force sensor arrays using fiber Bragg gratings (FBG) and transducers for tactile sensation to detect a distributed normal force. One array is developed for a large area tactile sensor that has good sensitivity but low spatial resolution, similar to human body skin. The other is for a small area tactile sensor that has good sensitivity and spatial resolution, similar to human finger skin. The transducer is designed such that it is not affected by chirping and light loss. We also present the fabrication process and experimental verification of the prototype sensors. Experimental tests show that the newly designed sensors have good performance: good sensitivity, repeatability, and no-hysteresis. The load calibration is accomplished by a verified uniaxial load cell. In order to provide a more precise measurement, temperature compensation is applied to all taxels. These force sensor arrays are flexible enough to be attached to a curved surface and they also have simple wiring compared with other types of small force sensors for tactile sensation.

Tactile sensor arrays using fiber Bragg grating sensors

Stimulated Brillouin scattering in optical fibers can be used to measure strain or temperature in a distributed manner. Brillouin optical time domain analysis (BOTDA) is the most common sensor system based on the Brillouin scattering. This paper presents the experimental analysis of the characteristics of Brillouin gain spectrum (BGS) influenced by the width of launched pulse. Brillouin strain coefficient is also examined for the different pulse widths, which is important to apply a Brillouin scattering-based sensor to a structural health monitoring. Experimental results showed that not only the Brillouin linewidth and gain but also the Brillouin frequency were dependent on the pulse widths.

Pulse width dependence of Brillouin frequency in single mode optical fibers.

In this paper, we present a new real-time visual servoing unit for laparoscopic surgery. This unit can automatically control a laparoscope manipulator through visual tracking of the laparoscopic surgical tool. For the tracking, we present a two-stage adaptive CONDENSATION (conditional density propagation) algorithm to detect the accurate position of the surgical tool tip from a surgical image sequence in real-time. This algorithm can be adaptable to abrupt changes of illumination. The experimental results show that the proposed visual tracking algorithm is highly robust.

Visual tracking algorithm for laparoscopic robot surgery

This paper describes a tactile sensor system which can detect distributed temperature and distributed force using a fiber Bragg grating (FBG) sensor. The newly designed temperature sensor using FBG is introduced and the performance of this temperature sensor is evaluated. Combining this temperature sensor array with the force sensor array, a new tactile sensor system capable of measuring a temperature distribution and a force distribution is evaluated. In particular, through the use of the distributed temperature sensor array, the distributed force sensor array can be compensated for a temperature effect that prevents an accurate distributed force measurement.

Jin-Seok Heo

Papers

Tactile sensor arrays using fiber Bragg grating sensors

Pulse width dependence of Brillouin frequency in single mode optical fibers.

Visual tracking algorithm for laparoscopic robot surgery

Temperature Sensor Array for Tactile Sensation Using FBG Sensors