Concept, modeling and experimental characterization of the modulated friction inertial drive (MFID) locomotion principle:application to mobile microrobots

A mobile microrobot is defined as a robot with a size ranging from 1 in3 down to 100 µm3 and a motion range of at least several times the robot's length. Mobile microrobots have a great potential for a wide range of mid-term and long-term applications such as minimally invasive surgery, inspection, surveillance, monitoring and interaction with the microscale world. A systematic study of the state of the art of locomotion for mobile microrobots shows that there is a need for efficient locomotion solutions for mobile microrobots featuring several degrees of freedom (DOF). This thesis proposes and studies a new locomotion concept based on stepping motion considering a decoupling of the two essential functions of a locomotion principle: slip generation and slip variation. The proposed "Modulated Friction Inertial Drive" (MFID) principle is defined as a stepping locomotion principle in which slip is generated by the inertial effect of a symmetric, axial vibration, while the slip variation is obtained from an active modulation of the friction force. The decoupling of slip generation and slip variation also has lead to the introduction of the concept of a combination of on-board and off-board actuation. This concept allows for an optimal trade-off between robot simplicity and power consumption on the one hand and on-board motion control on the other hand. The stepping motion of a MFID actuator is studied in detail by means of simulation of a numeric model and experimental characterization of a linear MFID actuator. The experimental setup is driven by piezoelectric actuators that vibrate in axial direction in order to generate slip and in perpendicular direction in order to vary the contact force. After identification of the friction parameters a good match between simulation and experimental results is achieved. MFID motion velocity has shown to depend sinusoidally on the phase shift between axial and perpendicular vibration. Motion velocity also increases linearly with increasing vibration amplitudes and driving frequency. Two parameters characterizing the MFID stepping behavior have been introduced. The step efficiency ηstep expresses the efficiency with which the actuator is capable of transforming the axial vibration in net motion. The force ratio qF evaluates the ease with which slip is generated by comparing the maximum inertial force in axial direction to the minimum friction force. The suitability of the MFID principle for mobile microrobot locomotion has been demonstrated by the development and characterization of three locomotion modules with between 2 and 3 DOF. The microrobot prototypes are driven by piezoelectric and electrostatic comb drive actuators and feature a characteristic body length between 20 mm and 10 mm. Characterization results include fast locomotion velocities up to 3 mm/s for typical driving voltages of some tens of volts and driving frequencies ranging from some tens of Hz up to some kHz. Moreover, motion resolutions in the nanometer range and very low power consumption of some tens of µW have been demonstrated. The advantage of the concept of a combination of on-board and off-board actuation has been demonstrated by the on-board simplicity of two of the three prototypes. The prototypes have also demonstrated the major advantage of the MFID principle: resonance operation has shown to reduce the power consumption, reduce the driving voltage and allow for simple driving electronics. Finally, with the fabrication of 2 × 2 mm2 locomotion modules with 2 DOF, a first step towards the development of mm-sized mobile microrobots with on-board motion control is made

Dispositif de plusieurs micros robots mobiles contrôlés par un projecteur

Le but de ce projet est de tester le principe du « friction drive » sur des micro-robots avec un minimum de composants « on board ». Le « friction drive » est une utilisation d’une vibration horizontale et d’un changement, par différents moyens, de la force de contact entre le robot et sa surface de guidage. Le but de ce projet est de développer un dispositif capable de tester ce principe en utilisant une table vibrante en XY pour la vibration horizontale et une force électrostatique pour varier la force de contact. La table réalise des translations dans le plan XY selon des cercles de 0,1 à 4 mm de rayon avec une fréquence de 15 Hz. Elle est montée sur des lames pour la maintenir dans un plan horizontal. La commande des robots est faite au travers d’un projecteur vidéo. Les robots sont munis d’électrodes pour le serrage électrostatique sur le dessous et de cellules solaires pour la mise sous tension de ces électrodes sur le dessus. Les tests ont montré que le principe fonctionne dans des conditions très précises. L’excentricité de la table, la propreté du support, l’humidité doit être très bien maîtrisé. La vitesse du robot est de l’ordre de 5 mm/s

Actionneur linéaire basé sur le principe du « Inchworm » inertiel

Le but de ce projet était de développer un actionneur linéaire haute résolution basé sur le principe du « Inchworm », dans lequel le blocage des pieds sera effectué par la force inertielle d’une vibration verticale. Les vibrations des pieds sont réalisées par des céramiques piézoélectriques. La vitesse maximum de l’actionneur réalisé est 1,2 mm/s, la force maximum est de 19 grammes, le mouvement a une très bonne linéarité et la résolution est meilleure que 25 nm

A review on actuation principls for few cubic millimeter sized mobile micro-robots

Actuation systems for few cubic millimeter sized mobile autonomous robots are subject to severe constraints in terms of e.g. size, fabrication or power consumption. Also the onboard electronics has limited performance due to both size and power restrictions, so actuation voltages, currents and frequency should be minimized. Various principles of electrical to mechanical energy conversion will be presented (piezoelectric, polymer, electrostatic) and their performances compared considering the above mentioned constraints. For propulsion, a further mechanical to mechanical conversion is necessary to allow long strokes. We will compare four principles for this conversion: inertial drives, walking, inch-worm and propulsion based on asymmetrical friction forces. Solutions where the energy is not onboard but rather scavenged in the environment are also reviewed. These solutions try to circumvent the energy limitations but present some inconveniences, especially when several micro-robots have to be simultaneously steered and/or propelled

Significant under expression of the DosR regulon in M. tuberculosis complex lineage 6 in sputum

YesMycobacterium africanum lineage (L) 6 is an important pathogen in West Africa, causing up to 40% of pulmonary tuberculosis (TB). The biology underlying the clinical differences between M. africanum and M. tuberculosis sensu stricto remains poorly understood. We performed ex vivo expression of 2179 genes of the most geographically dispersed cause of human TB, M. tuberculosis L4 and the geographically restricted, M. africanum L6 directly from sputa of 11 HIV-negative TB patients from The Gambia who had not started treatment. The DosR regulon was the most significantly decreased category in L6 relative to L4. Further, we identified nonsynonymous mutations in major DosR regulon genes of 44 L6 genomes of TB patients from The Gambia and Ghana. Using Lebek's test, we assessed differences in oxygen requirements for growth. L4 grew only at the aerobic surface while L6 grew throughout the medium. In the host, the DosR regulon is critical for M. tuberculosis in adaptation to oxygen limitation. However, M. africanum L6 appears to have adapted to growth under hypoxic conditions or to different biological niches. The observed under expression of DosR in L6 fits with the genomic changes in DosR genes, microaerobic growth and the association with extrapulmonary disease.European Research Council-INTERRUPTB starting grant nr.311725 (to BdJ, BO, FG, MA, CM)

Magnetic Springs - Fast Energy Storage for Reciprocating Industrial Drivetrains

Industrial machines with reciprocating (oscillating) motion such as weaving looms tackle primarily high inertial loads, conventionally operating within frequency ranges of 5-15 Hz with relatively large strokes. Recent trends of individual electrification of parts of weaving loom drivetrains for reasons of increased flexibility of use make this problem even worse, as the inertial loads are less averaged out. Adding springs to such oscillating drivetrains can allow to improve the energy efficiency and downsize the actuators. To get an estimation of energy sinks and peak power consumption in a reciprocating drivetrain of a weaving loom, a spring assisted demonstrator available at Flanders Make has been modelled using a 1D multiphysical dynamic model. Next to energy requirements, industrial machines have strict lifetime demands. Target lifetime of 50 000 hours results in over 1E9 spring cycles. Mechanical spring design and fatigue modelling for this number of cycles is a difficult design problem with high levels of uncertainty. Therefore, magnetic springs are proposed instead of mechanical springs as a technological novelty with benefits of no material fatigue and additional flexibility in design. In the developed drivetrain model the mechanical spring is replaced by an off-the-shelf magnetic spring in order to perform a first estimation of the impact on the dynamic behavior.Poster presented at EMVeM First Industrial Workshopstatus: publishe

Magnetic Springs: Fast Energy Storage for Reciprocating Industrial Drivetrains

Industrial machines with reciprocating (oscillating) motion such as weaving looms tackle primarily high inertial loads, conventionally operating within frequency ranges of 5-15 Hz with relatively large strokes. Recent trends of individual electrification of parts of weaving loom drivetrains for reasons of increased flexibility of use make this problem even worse, as the inertial loads are less averaged out. Adding springs to such oscillating drivetrains can allow to improve the energy efficiency and downsize the actuators. To get an estimation of energy sinks and peak power consumption in a reciprocating drivetrain of a weaving loom, a spring assisted demonstrator available at Flanders Make has been modelled using a 1D multiphysical dynamic model. Next to energy requirements, industrial machines have strict lifetime demands. Target lifetime of 50 000 hours results in over 1E9 spring cycles. Mechanical spring design and fatigue modelling for this number of cycles is a difficult design problem with high levels of uncertainty. Therefore, magnetic springs are proposed instead of mechanical springs as a technological novelty with benefits of no material fatigue and additional flexibility in design. In the developed drivetrain model the mechanical spring is replaced by an off-the-shelf magnetic spring in order to perform a first estimation of the impact on the dynamic behavior.status: publishe

Energy oriented design of highly dynamic industrial drivetrains

edition: 1status: publishe

Optimal Magnetic Spring for Compliant Actuation-Validated Torque Density Benchmark

© 2019 by the authors. Magnetic springs are a fatigue-free alternative to mechanical springs that could enable compliant actuation concepts in highly dynamic industrial applications. The goals of this article are: (1) to develop and validate a methodology for the optimal design of a magnetic spring and (2) to benchmark the magnetic springs at the component level against conventional solutions, namely, mechanical springs and highly dynamic servo motors. We present an extensive exploration of the magnetic spring design space both with respect to topology and geometry sizing, using a 2D finite element magnetostatics software combined with a multi-objective genetic algorithm, as a part of a MagOpt design environment. The resulting Pareto-optima are used for benchmarking rotational magnetic springs back-to-back with classical industrial solutions. The design methodology has been extensively validated using a combination of one physical prototype and multiple virtual designs. The findings show that magnetic springs possess an energy density 50% higher than that of state-of-the-art reported mechanical springs for the gigacycle regime and accordingly a torque density significantly higher than that of state-of-the-practice permanently magnetic synchronous motors.status: publishe