Control of compliant robotic systems with muscle-like actuators and saturated feedback

This paper is devoted to the problem in controlling a compliant robotic system by means of actuators with musclelike properties, which underlie prescribed bounds due to the natural muscle behavior. A typical example to demonstrate the effectiveness of developed control schemes is the choice of a (inverted) pendulum with higher degree of freedom. Due to the force restriction of the driving muscle forces, we have to sought (saturated) feedback strategies to control the system behavior (e.g. tracking of paths) which have to be limited a-priori. A suitable control variable can be generated by adaptive controllers, e.g., a PID-λ-stabilization. But, the classical torque control variable has to be converted to the muscle force at the joints, and the joint angle velocity has to be converted to the contraction velocity. The effective force at every joint is the difference of the antagonistic muscles pairs with the muscle characteristic curve of HILL (force-velocity-relation). The aim is now, to hold the control variable inside the area restricted by the muscle pairs. Several simulations show the effectiveness of the designed controllers

Multi-segmented artificial locomotion systems with adaptively controlled gait transitions

This paper is devoted to the analysis and simulation of multi-segmented artificial locomotion systems. The biological paradigm is the earthworm. Here, we restrict our investigation to a crawling system which is moving along a straight line, more precisely, the system is firstly moving unidirectionally. Recent results from the examined literature present investigations of short worms (n < 4). In contrast to this, the developed mechanical model in this paper consists of a chain of 10 discrete mass points. Let us point out, that the presented investigations are not restricted to a fixed number of mass points. To achieve a movement of the system, the distances between neighboring mass points are controlled by viscoelastic force actuators. Due to a prescribed reference gait, an adaptive controller determines the necessary forces to adjust the prescribed values. Then, due shortening and lengthening of these distances together with a spiky ground contact at the mass point (preventing velocities from being negative), we achieve a global movement of the whole system – called undulatory locomotion. Specific prescribed gaits are required to guarantee a controlled movement that differ especially in the number of resting mass points and the load of actuators and spikes. To determine the most advantageous gaits, numerical investigations are performed and a weighting function offers a decision of best possible gaits. Finally, a gait transition algorithm for an autonomously change of the locomotion velocity and number of resting mass points in dependence on the spike and actuator force load is presented and tested in numerical simulations

A vibrissa-inspired highly flexible tactile sensor: scanning 3D object surfaces providing tactile images

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

Validation of the FluoroType MTBDR Assay for Detection of Rifampin and Isoniazid Resistance in Mycobacterium tuberculosis Complex Isolates.

For Mycobacterium tuberculosis complex (MTBC), the rapid and accurate diagnosis of drug resistance is crucial to ensure early initiation of appropriate therapy. Recently, a new molecular diagnostic test, the FluoroType MTBDR, aimed at detecting rifampin and isoniazid resistance has become available. This study aimed to evaluate the FluoroType MTBDR in comparison to phenotypic drug susceptibility testing (DST) using M. tuberculosis complex isolates. MTBC isolates underwent phenotypic DST and were tested using the FluoroType MTBDR and Genotype MTBDRplus. Sanger sequencing of the key regions of rpoB, katG, inhA, and aphC was performed for isolates with discordant phenotypic and molecular results. Furthermore, isolates with specific wild-type bands missing in the Genotype MTBDRplus, indicating the presence of a mutation, were investigated by Sanger sequencing. Specificity and sensitivity, defined as the proportions of isolates correctly determined as susceptible and resistant by the FluoroType MTBDR compared to phenotypic DST, were calculated. A total of 180 culture isolates were included; phenotypic DST showed 85 isolates susceptible to isoniazid and rifampin, 7 with isoniazid monoresistance, 7 with rifampin monoresistance, and 81 with multidrug resistance. The specificity of the FluoroType MTBDR was 100% (95% confidence interval [CI], 96.0 to 100%) for both rifampin and isoniazid. The sensitivity was 91.7% (95% CI, 83.6 to 96.6%) for isoniazid and 98.9% (95% CI, 93.8 to 100.0%) for rifampin. The FluoroType MTBDR has a high sensitivity and specificity for the detection of rifampin and isoniazid resistance when using culture isolates

Obstacle scanning by technical vibrissae with compliant support

Rodents, like mice and rats, use tactile hairs in the snout region (mystacial vibrissae) to acquire information about their environment, e.g. the shape or contour of obstacles. For this, the vibrissa is used for the perception of stimuli due to an object contact. Mechanoreceptors are processing units of this stimuli measured in the compliant support (follicle sinus complex). We use this behavior from biology as an inspiration to set up a mechanical model for object contour scanning. An elastic bending rod interacts with a rigid obstacle in the plane. Analyzing only one quasi-static sweep of the rod along the obstacle (in contrast to literature), we determine a) the support reactions (the only observables of the problem), and then b) the (discrete) obstacle contour in form of a set of contact points. In doing this, we first assume a stiff support (clamping) of the vibrissa, but in a next step we increase the elasticity of the support in focussing on a bearing with a rotational spring (also to control or delimitate the bending moment at the support). Thereby, we present a fully analytical treatment of the non-linear differential equations emerging from Bernoulli’s rod theory and a representation by Standard Elliptic Integrals