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Nathan F. Lepora

Publications and source records attributed to Nathan F. Lepora.

At least 73 records · Page 4Linked to original sources
arXiv2020

NeuroTac: A Neuromorphic Optical Tactile Sensor applied to Texture Recognition

Developing artificial tactile sensing capabilities that rival human touch is a long-term goal in robotics and prosthetics. Gradually more elaborate biomimetic tactile sensors are being developed and applied to grasping and manipulation tasks to help achieve this goal. Here we present the neuroTac, a novel neuromorphic optical tactile sensor. The neuroTac combines the biomimetic hardware design from the TacTip sensor which mimicks the layered papillae structure of human glabrous skin, with an event-based camera (DAVIS240, iniVation) and algorithms which transduce contact information in the form of spike trains. The performance of the sensor is evaluated on a texture classification task, with four spike coding methods being implemented and compared: Intensive, Spatial, Temporal and Spatiotemporal. We found timing-based coding methods performed with the highest accuracy over both artificial and natural textures. The spike-based output of the neuroTac could enable the development of biomimetic tactile perception algorithms in robotics as well as non-invasive and invasive haptic feedback methods in prosthetics.

cs.RO↗
arXiv2019

Shear-invariant Sliding Contact Perception with a Soft Tactile Sensor

Manipulation tasks often require robots to be continuously in contact with an object. Therefore tactile perception systems need to handle continuous contact data. Shear deformation causes the tactile sensor to output path-dependent readings in contrast to discrete contact readings. As such, in some continuous-contact tasks, sliding can be regarded as a disturbance over the sensor signal. Here we present a shear-invariant perception method based on principal component analysis (PCA) which outputs the required information about the environment despite sliding motion. A compliant tactile sensor (the TacTip) is used to investigate continuous tactile contact. First, we evaluate the method offline using test data collected whilst the sensor slides over an edge. Then, the method is used within a contour-following task applied to 6 objects with varying curvatures; all contours are successfully traced. The method demonstrates generalisation capabilities and could underlie a more sophisticated controller for challenging manipulation or exploration tasks in unstructured environments. A video showing the work described in the paper can be found at https://youtu.be/wrTM61-pieU

cs.RO↗
arXiv2019

From pixels to percepts: Highly robust edge perception and contour following using deep learning and an optical biomimetic tactile sensor

Deep learning has the potential to have the impact on robot touch that it has had on robot vision. Optical tactile sensors act as a bridge between the subjects by allowing techniques from vision to be applied to touch. In this paper, we apply deep learning to an optical biomimetic tactile sensor, the TacTip, which images an array of papillae (pins) inside its sensing surface analogous to structures within human skin. Our main result is that the application of a deep CNN can give reliable edge perception and thus a robust policy for planning contact points to move around object contours. Robustness is demonstrated over several irregular and compliant objects with both tapping and continuous sliding, using a model trained only by tapping onto a disk. These results relied on using techniques to encourage generalization to tasks beyond which the model was trained. We expect this is a generic problem in practical applications of tactile sensing that deep learning will solve. A video demonstrating the approach can be found at https://www.youtube.com/watch?v=QHrGsG9AHts

cs.RO↗
arXiv2018

TacWhiskers: Biomimetic optical tactile whiskered robots

Here we propose and investigate a novel vibrissal tactile sensor - the TacWhisker array - based on modifying a 3D-printed optical cutaneous (fingertip) tactile sensor - the TacTip. Two versions are considered: a static TacWhisker array analogous to immotile tactile vibrissae (e.g. rodent microvibrissae) and a dynamic TacWhisker array analogous to motile tactile vibrissae (e.g. rodent macrovibrissae). Performance is assessed on an active object localization task. The whisking motion of the dynamic TacWhisker leads to millimetre-scale location perception, whereas perception with the static TacWhisker array is relatively poor when making dabbing contacts. The dynamic sensor output is dominated by a self-generated motion signal, which can be compensated by comparing to a reference signal. Overall, the TacWhisker arrays give a new class of tactile whiskered robots that benefit from being relatively inexpensive and customizable. Furthermore, the biomimetic basis for the TacWhiskers fits well with building an embodied model of the rodent sensory system for investigating animal perception. A video demonstrating this robot can be seen at https://www.youtube.com/watch?v=ksS177ep6yY

cs.RO↗
arXiv2018

Principal Components of Touch

Our human sense of touch enables us to manipulate our surroundings; therefore, complex robotic manipulation will require artificial tactile sensing. Typically tactile sensor arrays are used in robotics, implying that a straightforward way of interpreting multidimensional data is required. In this paper we present a simple visualisation approach based on applying principal component analysis (PCA) to systematically collected sets of tactile data. We apply the visualisation approach to 4 different types of tactile sensor, encompassing fingertips and vibrissal arrays. The results show that PCA can reveal structure and regularities in the tactile data, which also permits the use of simple classifiers such as $k$-NN to achieve good inference. Additionally, the Euclidean distance in principal component space gives a measure of sensitivity, which can aid visualisation and also be used to find regions in the tactile input space where the sensor is able to perceive with higher accuracy. We expect that these observations will generalise, and thus offer the potential for novel control methods based on touch.

cs.RO↗
arXiv2018

Voronoi Features for Tactile Sensing: Direct Inference of Pressure, Shear, and Contact Locations

There are a wide range of features that tactile contact provides, each with different aspects of information that can be used for object grasping, manipulation, and perception. In this paper inference of some key tactile features, tip displacement, contact location, shear direction and magnitude, is demonstrated by introducing a novel method of transducing a third dimension to the sensor data via Voronoi tessellation. The inferred features are displayed throughout the work in a new visualisation mode derived from the Voronoi tessellation; these visualisations create easier interpretation of data from an optical tactile sensor that measures local shear from displacement of internal pins (the TacTip). The output values of tip displacement and shear magnitude are calibrated to appropriate mechanical units and validate the direction of shear inferred from the sensor. We show that these methods can infer the direction of shear to $\sim$2.3$^{\circ}$ without the need for training a classifier or regressor. The approach demonstrated here will increase the versatility and generality of the sensors and thus allow sensor to be used in more unstructured and unknown environments, as well as improve the use of these tactile sensors in more complex systems such as robot hands.

cs.RO↗
arXiv2002

Asymptotically embedded defects

For many cases, the conditions to fully embed a classical solution of one field theory within a larger theory cannot be met. Instead, we find it useful to embed only the solution's asymptotic fields as this relaxes the embedding constraints. Such asymptotically embedded defects have a simple classification that can be used to construct classical solutions in general field theories.

hep-th↗
arXiv2002

Some Simpler Analogues of the Dual Standard Model and their Relation to Bais' Generalisation of the Montenon-Olive Conjecture

We show that the correspondence between SU(5) monopoles and the elementary particles, which underlies the construction of a dual standard model, has some simpler analogues associated with the strong, weak and hypercharge interactions. We then discuss how these analogues relate to Bais' generalization of the Montenon-Olive conjecture and find the representations of the monopoles under the dual gauge group; these representations agree with those of the elementary particles.

hep-th↗
arXiv2002

Embedded Monopoles

Using the embedded defect method, we classify the possible embeddings of a 't Hooft-Polyakov monopole in a general gauge theory. We then discuss some similarities with embedded vortices and relate our results to fundamental monopoles.

hep-th↗
arXiv2002

Some problems when calculating the quantum corrections to the classical 't Hooft-Polyakov monopole

We examine whether the analysis of quantum corrections for the kink soliton carries over to the 't Hooft-Polyakov monopole. For the kink, it is central that the quantum fluctuations are eigenmodes of a Hermitian operator. For the monopole, we show the analogous operator is not Hermitian. This property raises some questions about the quantization procedure for a 't Hooft-Polyakov monopole.

hep-ph↗
arXiv2001

Dual Unification

This manuscript has been withdrawn by the author. Some of the material has been included in the manuscript 'Dualizing the Dual Standard Model' hep-ph/0102084.

hep-ph↗