Spatial Calibration of Humanoid Robot Flexible Tactile Skin for Human-Robot Interaction.

Recent developments in robotics have enabled humanoid robots to be used in tasks where they have to physically interact with humans, including robot-supported caregiving. This interaction-referred to as physical human-robot interaction (pHRI)-requires physical contact between the robot and the human body; one way to improve this is to use efficient sensing methods for the physical contact. In this paper, we use a flexible tactile sensing array and integrate it as a tactile skin for the humanoid robot HRP-4C. As the sensor can take any shape due to its flexible property, a particular focus is given on its spatial calibration, i.e., the determination of the locations of the sensor cells and their normals when attached to the robot. For this purpose, a novel method of spatial calibration using B-spline surfaces has been developed. We demonstrate with two methods that this calibration method gives a good approximation of the sensor position and show that our flexible tactile sensor can be fully integrated on a robot and used as input for robot control tasks. These contributions are a first step toward the use of flexible tactile sensors in pHRI applications.

Electromechanically Active As-Electrospun Polystyrene Fiber Mat: Significantly High Quasistatic/Dynamic Electromechanical Response and Theoretical Modeling.

Flexible and lightweight pressure sensors have attracted tremendous attention as a promising component of wearable biological motion sensors and artificial electronic skins. Here, the electromechanical response of as-electrospun fiber mats composed of a commodity polymer, atactic polystyrene, which can be applied in low-cost/large-area, flexible, and lightweight pressure sensors is demonstrated. The fiber mat demonstrates a significantly high apparent converse piezoelectric constant of >30 000 pm V-1 under static measurement and ≈13 000 pm V-1 even at a high frequency of 1 kHz. The first theoretical model to explain the unique electromechanical response is constructed, which reveals that the softness and moderate charge of the fiber mat are the reasons for the significantly high electromechanical response. Further, apparent piezoelectric constants obtained by direct measurement are lower than those obtained by the converse measurement, which is attributed to the densification and hardening of the fiber mat due to prepressure applied in direct measurement. These findings are likely to serve as a milestone for the development of large-area, flexible, and lightweight pressure sensors at low cost, as well as highly movable actuators like optical modulators without a substantial mechanical load.

Actuation Behavior of Polylactic Acid Fiber Films Prepared by Electrospinning.

A poly-DL-lactide (PLA) fiber film was prepared using the electrospinning method. This film consisted of randomly oriented PLA nanofibers. Consequently, it had sponge-like structure and was quite soft compared to PLA films prepared by spin coating. The average diameter of the fibers and the density of the film were 730 nm and 20%, respectively. By applying a voltage, the PLA film was subjected to electric-field-induced strain: expansion and compression in the thickness direction. When a voltage of -200 V was applied to the film, its thickness shrank from 13.5 µm to 10.0 µm (a 26% reduction). Electric-field-induced strain can occur via two different mechanisms: The first is electrostrictive behavior. That. is, in a highly electric field region, a change of film thickness occurs (compression only) from the electrostatic force between electrodes. The second mechanism is piezoelectric-like behavior that occurs in racemic PLA, wherein a PLA nanofiber is expanded and compressed by applying positive and negative voltage. Such piezoelectric-like behavior was not observed in spin-coated PLA films.