Functional mimicry of Ruffini receptors with fibre Bragg gratings and deep neural networks enables a bio-inspired large-area tactile-sensitive skin

Collaborative robots are expected to physically interact with humans in daily living and the workplace, including industrial and healthcare settings. A key related enabling technology is tactile sensing, which currently requires addressing the outstanding scientific challenge to simultaneously detect contact location and intensity by means of soft conformable artificial skins adapting over large areas to the complex curved geometries of robot embodiments. In this work, the development of a large-area sensitive soft skin with a curved geometry is presented, allowing for robot total-body coverage through modular patches. The biomimetic skin consists of a soft polymeric matrix, resembling a human forearm, embedded with photonic fibre Bragg grating transducers, which partially mimics Ruffini mechanoreceptor functionality with diffuse, overlapping receptive fields. A convolutional neural network deep learning algorithm and a multigrid neuron integration process were implemented to decode the fibre Bragg grating sensor outputs for inference of contact force magnitude and localization through the skin surface. Results of 35 mN (interquartile range 56 mN) and 3.2 mm (interquartile range 2.3 mm) median errors were achieved for force and localization predictions, respectively. Demonstrations with an anthropomorphic arm pave the way towards artificial intelligence based integrated skins enabling safe human–robot cooperation via machine intelligence

The effect of stiffness on friction, surface strain and contact area of a sliding finger pad simulant

This study investigates the frictional and surface strain behaviour of silicone hemispherical finger pad simulants with different stiffness during tribological interactions with a smooth glass plate. A novel contact area and strain measurement method employing a digital image correlation technique was employed to give new understanding of the pad behaviour during sliding. The frictional behaviour of the sliding finger pad simulant is dominated by the adhesion mechanism, with a small overall contribution from deformation, as suggested by the high principal strains at the edge of the contact area. The strain behaviour is also influenced by the magnitude of the normal force and the stiffness of the samples

Understanding the effect of skin mechanical properties on the friction of human finger-pads

The aim of this work is to achieve an understanding of the effect of skin mechanical properties on the friction of human finger-pads. This project primarily concentrates on gaining a more fundamental understanding of the frictional properties of skin. To achieve this, various parameters (epidermis thickness, sweat-gland counts, etc.) affecting skin friction were evaluated using an in-vivo technique, Optical Coherence Tomography (OCT) and a friction testing device. This project is also interested in investigating how those parameters alter the friction for different ages, genders, ethnicities and different contact conditions, such as moisture, temperature, loads, etc. Experimental studies were conducted to investigate the skin frictional behaviour. The findings showed that the skin friction obeys a two-term relationship. The skin friction was found to be strongly associated with its Young’s modulus. Tests on the skin structural properties showed the moisture level of the skin, skin thickness and skin morphological properties play important roles in determining the skin friction. The findings gained can be applied to explain how the skin friction varies among different participants. Further tests showed that physico-chemical properties of the skin can have a significant effect on the skin friction. The OCT system was combined with a multi-axis force plate to measure the contact area between fingers and smooth surfaces. Static measurement showed both apparent and real contact area increase with normal load following a power-law relationship. This is associated with the skin mechanical properties. The dynamic contact area was investigated using a Digital Image Correlation (DIC) method. As a finger was sliding along a flat surface, the dynamic apparent contact area was found to decrease with time

Innovative robot hand designs of reduced complexity for dexterous manipulation

This thesis investigates the mechanical design of robot hands to sensibly reduce the system complexity in terms of the number of actuators and sensors, and control needs for performing grasping and in-hand manipulations of unknown objects. Human hands are known to be the most complex, versatile, dexterous manipulators in nature, from being able to operate sophisticated surgery to carry out a wide variety of daily activity tasks (e.g. preparing food, changing cloths, playing instruments, to name some). However, the understanding of why human hands can perform such fascinating tasks still eludes complete comprehension. Since at least the end of the sixteenth century, scientists and engineers have tried to match the sensory and motor functions of the human hand. As a result, many contemporary humanoid and anthropomorphic robot hands have been developed to closely replicate the appearance and dexterity of human hands, in many cases using sophisticated designs that integrate multiple sensors and actuators---which make them prone to error and difficult to operate and control, particularly under uncertainty. In recent years, several simplification approaches and solutions have been proposed to develop more effective and reliable dexterous robot hands. These techniques, which have been based on using underactuated mechanical designs, kinematic synergies, or compliant materials, to name some, have opened up new ways to integrate hardware enhancements to facilitate grasping and dexterous manipulation control and improve reliability and robustness. Following this line of thought, this thesis studies four robot hand hardware aspects for enhancing grasping and manipulation, with a particular focus on dexterous in-hand manipulation. Namely: i) the use of passive soft fingertips; ii) the use of rigid and soft active surfaces in robot fingers; iii) the use of robot hand topologies to create particular in-hand manipulation trajectories; and iv) the decoupling of grasping and in-hand manipulation by introducing a reconfigurable palm. In summary, the findings from this thesis provide important notions for understanding the significance of mechanical and hardware elements in the performance and control of human manipulation. These findings show great potential in developing robust, easily programmable, and economically viable robot hands capable of performing dexterous manipulations under uncertainty, while exhibiting a valuable subset of functions of the human hand.Open Acces

Enabling wearable soft tactile displays with dielectric elastomer actuators

PhDTouch is one of the less exploited sensory channels in human machine interactions. While the introduction of the tactile feedback would improve the user experience in several fields, such as training for medical operators, teleoperation, computer aided design and 3D model exploration, no interfaces able to mimic accurately and realistically the tactile feeling produced by the contact with a real soft object are currently available. Devices able to simulate the contact with soft bodies, such as the human organs, might improve the experience. The existing commercially available tactile displays consist of complex mechanisms that limit their portability. Moreover, no devices are able to provide tactile stimuli via a soft interface that can also modulate the contact area with the finger pad, which is required to realistically mimic the contact with soft bodies, as needed for example in systems aimed at simulating interactions with virtual biological tissues or in robot-assisted minimally invasive surgery. The aim of this thesis is to develop such a wearable tactile display based on the dielectric elastomer actuators (DEAs). DEAs are a class of materials that respond to an electric field producing a deformation. In particular, in this thesis, the tactile element consists of a so-called hydrostatically coupled dielectric elastomer actuator (HC-DEAs). HC-DEAs rely on an incompressible fluid that hydrostatically couples a DEA-based active part to a passive part interfaced to the user. The display was also tested within a closed-loop configuration consisting of a hand tracking system and a custom made virtual environment. This proof of concept system allowed for a validation of the abilities of the display. Mechanical and psychophysical tests were performed in order to assess the ability of the system to provide tactile stimuli that can be distinguished by the users. Also, the miniaturisation of the HC-DEA was investigated for applications in refreshable Braille displays or arrays of tactile elements for tactile maps

Tactile Sensors for Friction Estimation and Incipient Slip Detection - Toward Dexterous Robotic Manipulation:A Review

Humans can handle and manipulate objects with ease; however, human dexterity has yet to be matched by artificial systems. Receptors in our fingers and hands provide essential tactile information to the motor control system during dexterous manipulation such that the grip force is scaled to the tangential forces according to the coefficient of friction. Likewise, tactile sensing will become essential for robotic and prosthetic gripping performance as applications move toward unstructured environments. However, most existing research ignores the need to sense the frictional properties of the sensor-object interface, which (along with contact forces and torques) is essential for finding the minimum grip force required to securely grasp an object. Here, we review this problem by surveying the field of tactile sensing from the perspective that sensors should: 1) detect gross slip (to adjust the grip force); 2) detect incipient slip (dependent on the frictional properties of the sensor-object interface and the geometries and mechanics of the sensor and the object) as an indication of grip security; or 3) measure friction on contact with an object and/or following a gross or incipient slip event while manipulating an object. Recommendations are made to help focus future sensor design efforts toward a generalizable and practical solution to sense, and hence control grip security. Specifically, we propose that the sensor mechanics should encourage incipient slip, by allowing parts of the sensor to slip while other parts remain stuck, and that instrumentation should measure displacement and deformation to complement conventional force, pressure, and vibration tactile sensing

Friction Induced Vibration Based Pattern Detection On An Artificial Skin By Preload Control

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2012Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2012Bu çalışma, kayma hızı, önyükleme kuvveti ve tip çapı gibi farklı tasarım parametreleri altında, yapay olarak yapılan yüzeyin deseninin algılanmasını ve sürtünme özelliklerini ortaya koymaktadır. İsteğe göre yapılmış olan yarı otonom sürtünme deney düzeneğinde, düz şeffaf polimer kullanılarak yapılan sürtünme testlerinin neticesinde, düzenek gerçeklenmiş ve uygun çalışma şartları belirlenmiştir. Desen algılama deneyleri, kayma sırasında yüzeye uygulanan önyükleme kuvveti, kuvvet geribesleme kontrolcüsü tarafından sabit tutulurken, sert cam tipe karşı sürtülen, eşit aralıklarla dağıtılmış tümsekleri olan yapay deri üzerinde gerçekleştirilmiştir. Yüzey taraması esnasında oluşan sürtünmenin yol açtığı titreşimler, yapay derinin desenine ait olan ve taranan yüzeyin tümseklerinin yükseklik ve dalgaboyu gibi bilgisini taşıyan frekansın algılanmasına olanak tanımıştır. Bu arada test sonuçlarına göre önyükleme kuvveti, düşük kayma hızı ve yüksek kuvvet altında minimum hata yüzdesiyle sabit kalmaktadır. Buna ek olarak, önyükleme kuvvet hatasının azaltılmasında ve sinyal harmoniklerinin filtrelenmesinde tip çapının etkisi de gözlemlenmiştir.This study exhibits pattern detection and frictional properties of the artificially made surface under different design parameters such as sliding velocity, preload, and tip diameter. In consequence of frictional tests on the custom built semi-autonomous friction set-up using flat soft polymer, the set-up is validated, and proper working conditions are determined. The pattern detection experiments are realized on an artificial skin with evenly distributed ridges rubbed against a rigid glass tip while the preload applied to the surface is kept constant during sliding by the force-feedback controller. The friction induced vibrations occurred during surface scanning allowed to detect the frequency belonging to the pattern of the artificial skin, and carrying the information of the scanned surface like height and wavelength of ridges. Meanwhile, according to the results of the tests, the preload remains consistent with a minimum percentage of error at low sliding velocity and under high preload value. In addition, tip diameter effect on reducing the preload error, and filtering harmonics of the signal is also observed.Yüksek LisansM.Sc