Lukas Merker

This paper presents a tensegrity structure used as a force sensing platform for the precision measurement of small forces. It was experimentally evaluated for forces up to 0.12 N. The design includes two rigid bodies, which are connected by a tension spring and three sections of optical fibers in a pre-stressed state. These smart optical fibers serve a dual role by providing sensing capabilities based on the fiber segment interferometry technique, while simultaneously acting as load-bearing structural components. We demonstrate that the cumulative strain over the three fibers is directly proportional to the load applied to the platform. Furthermore, based on evaluation of strain distribution between the individual fibers, the point of load application can be determined to enable force localization. The design of the structure is very scalable with customizable mechanical properties, making it adaptable for a wide range of sensing applications.

Scanning and reconstructing the environment using tactile sensors alongside optical sensors is a promising approach in mobile robotics. Within the present paper, we take advantage of a recently presented vibrissa‐inspired tactile sensor concept for 3D object scanning and reconstruction, broadening our previous studies. The sensor consists of a slender, cylindrical, highly flexible probe, one‐sided clamped to some force‐torque measuring device. The probe is shifted relatively to an object of interest by displacing its clamping position quasi‐statically. Consequently, the probe gets bent, sweeps over the object and transmits mechanical signals (observables) to its support. The focus of the present investigation is on how the probe sweeps over a new type of object (paraboloid), verifying a necessary condition for optional contact points. Finally, this condition allows to find multiple equilibrium states for a single clamping position.

Just as the sense of touch complements vision in various species, several robots could benefit from advanced tactile sensors, in particular when operating under poor visibility. A prominent tactile sense organ, frequently serving as a natural paragon for developing tactile sensors, is the vibrissae of, e.g., rats. Within this study, we present a vibrissa-inspired sensor concept for 3D object scanning and reconstruction to be exemplarily used in mobile robots. The setup consists of a highly flexible rod attached to a 3D force-torque transducer (measuring device). The scanning process is realized by translationally shifting the base of the rod relative to the object. Consequently, the rod sweeps over the object’s surface, undergoing large bending deflections. Then, the support reactions at the base of the rod are evaluated for contact localization. Presenting a method of theoretically generating these support reactions, we provide an important basis for future parameter studies. During scanning, lateral slip of the rod is not actively prevented, in contrast to literature. In this way, we demonstrate the suitability of the sensor for passively dragging it on a mobile robot. Experimental scanning sweeps using an artificial vibrissa (steel wire) of length 50 mm and a glass sphere as a test object with a diameter of 60 mm verify the theoretical results and serve as a proof of concept.

Vibrissae are an important tactile sense organ of many mammals, in particular rodents like rats and mice. For instance, these animals use them in order to detect different object features, e.g., object-distances and -shapes. In engineering, vibrissae have long been established as a natural paragon for developing tactile sensors. So far, having object shape scanning and reconstruction in mind, almost all mechanical vibrissa models are restricted to contact scenarios with a single discrete contact force. Here, we deal with the effect of multi-point contacts in a specific scanning scenario, where an artificial vibrissa is swept along partly concave object contours. The vibrissa is modeled as a cylindrical, one-sided clamped Euler-Bernoulli bending rod undergoing large deflections. The elasticae and the support reactions during scanning are theoretically calculated and measured in experiments, using a spring steel wire, attached to a force/torque-sensor. The experiments validate the simulation results and show that the assumption of a quasi-static scanning displacement is a satisfying approach. Beyond single- and two-point contacts, a distinction is made between tip and tangential contacts. It is shown that, in theory, these contact phases can be identified solely based on the support reactions, what is new in literature. In this way, multipoint contacts are reliably detected and filtered in order to discard incorrectly reconstructed contact points.

Rats and mice use some special tactile hairs in their snout region for a non‐visual exploration of their environment. These hairs, known as mystacial macro‐vibrissae, are each embedded in their own elastic support, called follicle‐sinus complex. This consists of several mechanoreceptors converting tactile information into neural impulses for the central nervous system (CNS). Using their vibrissae, rats and mice are capable of detecting distances to objects, object contours and surface textures. Due to this outstanding ability vibrissae frequently serve as a paradigm for technical tactile sensors. In this paper, we present a model for object shape scanning and contour reconstruction. Here, we especially focus on the important property “elasticity” of the follicle‐sinus complex, which has rarely been taken into account for object scanning in literature. We set up models for three different elastic supports. Based on solutions of the arising boundary‐ and initial‐value problems, we simulate the scanning process, investigate the related support reactions during a single rotational quasi‐static sweep of a straight vibrissa along a strictly convex object contour and reconstruct its shape. In doing this, we investigate the influence of the different elasticities of the model on the scanning and reconstruction procedure.

Many mammals use some special tactile hairs, the so-called mystacial macrovibrissae, to acquire information about their environment. In doing so, rats and mice, e.g., are able to detect object distances, shapes, and surface textures. Inspired by the biological paradigm, we present a mechanical model for object contour scanning and shape reconstruction, considering a single vibrissa as a cylindrically shaped Euler-Bernoulli-bending rod, which is pivoted by a bearing. In doing so, we adapt our model for a rotational scanning movement, which is in contrast to many previous modeling approaches. Describing a single rotational quasi-static sweep of the vibrissa along a strict convex contour function using nonlinear Euler-Bernoulli theory, we end up in a boundary-value problem with some unknown parameters. In a first step, we use shooting methods in an algorithm to repeatedly solve this boundary-value problem (changing the vibrissa base angle) and generate the support reactions during a sweep along an object contour. Afterwards, we use these support reactions to reconstruct the object contour solving an initial-value problem. Finally, we extend the scanning process adding a second sweep of the vibrissa in opposite direction in order to enlarge the reconstructable area of the profile.