Printing-while-moving: a new paradigm for large-scale robotic 3D Printing

Building and Construction have recently become an exciting application ground for robotics. In particular, rapid progress in materials formulation and in robotics technology has made robotic 3D Printing of concrete a promising technique for in-situ construction. Yet, scalability remains an important hurdle to widespread adoption: the printing systems (gantry- based or arm-based) are often much larger than the structure to be printed, hence cumbersome. Recently, a mobile printing system - a manipulator mounted on a mobile base - was proposed to alleviate this issue: such a system, by moving its base, can potentially print a structure larger than itself. However, the proposed system could only print while being stationary, imposing thereby a limit on the size of structures that can be printed in a single take. Here, we develop a system that implements the printing-while-moving paradigm, which enables printing single-piece structures of arbitrary sizes with a single robot. This development requires solving motion planning, localization, and motion control problems that are specific to mobile 3D Printing. We report our framework to address those problems, and demonstrate, for the first time, a printing-while-moving experiment, wherein a 210 cm x 45 cm x 10 cm concrete structure is printed by a robot arm that has a reach of 87 cm.Comment: 6 pages, 7 figur

Search full text options here 3 of 3 Heat-Mitigated Design and Lorentz Force-Based Steering of an MRI-Driven Microcatheter toward Minimally Invasive Surgery

Catheters integrated with microcoils for electromagnetic steering under the high, uniform magnetic field within magnetic resonance (MR) scanners (3-7 Tesla) have enabled an alternative approach for active catheter operations. Achieving larger ranges of tip motion for Lorentz force-based steering have previously been dependent on using high power coupled with active cooling, bulkier catheter designs, or introducing additional microcoil sets along the catheter. This work proposes an alternative approach using a heat-mitigated design and actuation strategy for a magnetic resonance imaging (MRI)-driven microcatheter. A quad-configuration microcoil (QCM) design is introduced, allowing miniaturization of existing MRI-driven, Lorentz force-based catheters down to 1-mm diameters with minimal power consumption (0.44 W). Heating concerns are experimentally validated using noninvasive MRI thermometry. The Cosserat model is implemented within an MR scanner and results demonstrate a desired tip range up to 110 degrees with 4 degrees error. The QCM is used to validate the proposed model and power-optimized steering algorithm using an MRI-compatible neurovascular phantom and ex vivo kidney tissue. The power-optimized tip orientation controller conserves as much as 25% power regardless of the catheter\u27s initial orientation. These results demonstrate the implementation of an MRI-driven, electromagnetic catheter steering platform for minimally invasive surgical applications without the need for camera feedback or manual advancement via guidewires. The incorporation of such system in clinics using the proposed design and actuation strategy can further improve the safety and reliability of future MRI-driven active catheter operations

MRI-powered Magnetic Microrobotics

Minimally invasive surgeries have replaced many open surgical operations in clinics today, and their success created a high demand for less and less invasive methods. Recently, magnetic microrobotic approaches have been proposed to address the miniaturization challenges of minimally invasive methods. Since magnetically actuated microrobots do not require tethered force transmissions systems, such as tendons and hydraulics, they could be miniaturized down to submillimeter-size scales and even operate wirelessly to access hard-to-reach regions in the patient body. However, the localization of these microrobots in the patient’s body during operations is still a major challenge for medical microrobotic applications. Since the small scale of microrobots prohibits on-board localization systems, an external localization system is needed. Therefore, medical imaging platforms bringing magnetic actuation and image-based localization have been proposed for microrobots. Among many medical imaging modalities, magnetic resonance imaging (MRI) attracts the most attention with superior image contrast, unlimited imaging depth, and ionizing radiation-free nature. MRI is considered the gold standard in many diagnostic applications, such as brain tumor and stroke diagnosis, and has already proven itself in guiding medical tools, such as biopsy needles and focus ultra- sound. Besides its high-quality medical imaging, MRI scanners are human-sized electromagnetic systems that could be used for magnetic actuation purposes, which makes them a perfect candidate for a combined imaging and actuation platform for magnetic microrobots. However, transforming MRI scanners to a microrobotic platform is a major scientific and engineering challenge and requires an in-depth investigation of magnetic actuation concepts in high magnetic fields, MR imaging, and tracking principles for magnetic microrobots. This dissertation elucidates MRI-powered magnetic actuation and MR imaging principles for magnetic microrobots to transform MRI scanners into microrobotic platforms for future minimally invasive medical applications. First, we introduced an MRI-powered magnetic micro-capsule robot design actuated by MRI gradient coils and developed one-dimensional and two-dimensional MRI-based tracking methods using template matching and deep learning algorithms. Then, combining MRI-based position feedback and magnetic actuation, we demonstrated closed-loop control and precise navigation methods for wireless magnetic microrobots. Later, we showed on-demand microrobotic drug delivery as a potential biomedical operation using acoustic triggering. In the second part, we proposed magnetic actuation methods using the ultrahigh magnetic field of MRI scanners. First, elucidating the uniaxial magnetization characteristics of permanent magnets in ultrahigh magnetic fields, we developed ultrahigh field (UHF) magnetic actuation principles. Later, we proposed magnetic guidewire steering methods using MRI scanners’ UHF. Finally, we developed a magnetic guidewire prototype that could be steered in the vasculature system. Overall, we provided the fundamental scientific background for magnetic microrobot actuation and tracking methods in MRI scanners and developed microrobotic tools for future minimally invasive medical operations.Minimalinvasive Eingriffe haben heute viele offene chirurgische Eingriffe in Kliniken ersetzt, und ihr Erfolg hat eine große Nachfrage nach weniger invasiven Methoden ausgelöst. Kürzlich wurden magnetische mikrorobotische Ansätze vorgeschlagen, um die Herausforderungen der Miniaturisierung minimalinvasiver Methoden zu bewältigen. Da magnetisch betätigte Mikroroboter keine gebundenen Kraftübertragungssysteme wie Sehnen und Hydraulik benötigen, könnten sie bis auf Submillimeter-Größe miniaturisiert werden und sogar drahtlos arbeiten, um schwer zugängliche Regionen im Körper des Patienten zu erreichen. Die Loka- lisierung dieser Mikroroboter im Körper des Patienten während der Operation ist jedoch immer noch eine große Herausforderung für medizinische Mikroroboteranwendungen. Da die geringe Größe von Mikrorobotern ein bordeigenes Lokalisierungssystem nicht zulässt, ist ein externes Lokalisierungssystem erforderlich. Daher wurden medizinische Bildgebungsplattformen mit magnetischer Betätigung und bildbasierter Lokalisierung für Mikroroboter vorgeschlagen. Unter den vielen medizinischen Bildgebungsmodalitäten zieht die Magnetresonanztomographie (MRT) die meiste Aufmerksamkeit auf sich, da sie einen hervorragenden Bildkontrast, eine unbegrenzte Bildtiefe und keine ionisierende Strahlung bietet. Die MRT gilt als Goldstandard für viele diagnostische Anwendungen, z. B. für die Diagnose von Hirntumoren und Schlaganfällen, und hat sich bereits bei der Führung medizinischer Instrumente wie Biopsienadeln und Fokussierungs Ultraschall bewährt. Abgesehen von der hohen Qualität der medizinischen Bildgebung sind MRT-Scanner elektromagnetische Systeme in menschlicher Größe, die für magnetische Antriebszwecke verwendet werden können, was sie zu einem per- fekten Kandidaten für eine kombinierte Bildgebungs- und Antriebsplattform für magnetische Mikroroboter macht. Die Umwandlung von MRT-Scannern in eine mikrorobotische Plattform stellt jedoch eine große wissenschaftliche und technische Herausforderung dar und erfordert eine eingehende Untersuchung von magnetischen Antriebskonzepten in hohen Magnetfeldern, MR-Bildgebung und Verfolgungsprinzipien für magnetische Mikroroboter. In dieser Dissertation werden die Prinzipien der magnetischen Betätigung und der MR-Bildgebung für magnetische Mikroroboter untersucht, um MRT-Scanner in mikrorobotische Plattformen für zukünftige minimal-invasive medizinische Anwendungen zu verwandeln. Zunächst stellten wir ein MRI-getriebenes magnetisches Mikrokapsel-Roboterdesign vor, das durch MRI-Gradientenspulen angetrieben wird, und entwickelten ein- und zweidimensionale MRI-basierte Verfolgungsmethoden unter Verwendung von Template-Matching- und Deep-Learning Algorithmen. Durch die Kombination von MRI-basierter Positionsrückmeldung und magnetischer Betätigung demonstrierten wir eine geschlossene Regelschleife und präzise Navigationsmethoden für drahtlose magnetische Mikroroboter. Später zeigten wir die bedarfsgerechte mikrorobotische Verabreichung von Medikamenten als potenzielle biomedizinische Operation mit akustischer Auslösung. Im zweiten Teil schlugen wir magnetische Betätigungsmethoden vor, die das ultra-hohe Magnetfeld von MRT-Scannern nutzen. Zunächst haben wir die einachsigen Magnetisierungseigenschaften von Dauermagneten in ultrahohen Magnetfeldern untersucht und Prinzipien für die magnetische Betätigung in ultrahohen Feldern (UHF) entwickelt. Später schlugen wir Methoden zur Steuerung von magnetischen Führungsdrähten vor, die das UHF-Feld von MRI-Scannern nutzen. Schließlich haben wir einen Prototyp eines magnetischen Führungsdrahtes entwickelt, der im Gefäßsystem gesteuert werden kann. Insgesamt lieferten wir den grundlegenden wissenschaftlichen Hintergrund für magnetische Mikroroboter-Antriebs- und Verfolgungsmethoden in MRT-Scannern und entwickelten mikrorobotische Werkzeuge für zukünftige minimalinvasive medizinische Eingriffe

Magnetic Resonance Imaging-Based Tracking and Navigation of Submillimeter-Scale Wireless Magnetic Robots

Magnetic resonance imaging (MRI) scanners have recently been used for magnetic actuation of robots for minimally invasive medical operations. Due to MRI's high soft-tissue selectivity, it is possible to obtain 3D images of hard-to-reach cavities in the human body, where the wireless miniature magnetic robots powered by MRI could be employed for high-precision targeted operations, such as drug delivery, stem cell therapy, and hyperthermia. However, the state-of-the-art fast magnetic robot-tracking methods in MRI are limited above millimeter-size scale, which restricts the potential target regions inside the human body. Herein, a fast 1D projection-based MRI approach that can track magnetic particles down to 300 mu m diameter (1.17 x 10(-2) emu) is reported. The technique reduces the trackable magnetic particle size in MRI-powered navigation fivefold compared with the previous fast-tracking methods. A closed-loop MRI-powered navigation with 0.78 +/- 0.03 mm trajectory-following accuracy in millimeter-sized in vitro 2D channels and a 3D cavity setup using the tracking method is demonstrated. Furthermore, the feasibility of submillimeter magnetic robot tracking in ex vivo pig kidneys (N = 2) with a 3.6 +/- 1.1 mm accuracy is demonstrated. Such a fast submillimeter-scale mobile robot-tracking approach can unlock new opportunities in minimally invasive medical operations.ISSN:2640-456

Radio Frequency Sensing-Based In Situ Temperature Measurements during Magnetic Resonance Imaging Interventional Procedures

Magnetic resonance imaging (MRI)-tuned radio-frequency (RF) sensors are used as a radiation-free alternative for tracking minimally invasive medical tool positions. However, in situ temperature sensing capabilities of the MRI-tuned RF sensors have not been thoroughly investigated yet. A self-resonating RF sensor capable of remote in situ temperature sensing during real-time interventional MRI is presented. The proposed RF sensor design relies on the temperature-dependent permittivity to tune or detune the resonant frequency. The sensor is tuned to match the resonant frequency of a 7 Tesla MRI (298 MHz) at body temperature, enabling a hyperintense signal in MR images. As temperature increases, the sensor detunes due to the change in the relative permittivity, and the hyperintense signal disappears in the MR image, serving as a direct visual indicator of the temperature change in real-time. In addition, the localized signal can be used for 3D position tracking of interventional medical devices. Using a 7 Tesla preclinical MRI, in vitro characterization and ex vivo feasibility of the proposed temperature sensing method are demonstrated in the clinically relevant temperature range of 36–42 °C with an accuracy of ±0.6 °C. Such RF sensors can provide safer operations in future MRI interventional procedures.ISSN:2365-709XISSN:2365-709

Magnetic guidewire steering at ultrahigh magnetic fields

With remote magnetic steering capabilities, magnetically actuated guidewires have proven their potential in minimally invasive medical procedures. Existing magnetic steering strategies, however, have been limited to low magnetic fields, which prevents the integration into medical systems operating at ultrahigh fields (UHF), such as magnetic resonance imaging (MRI) scanners. Here, we present magnetic guidewire design and steering strategies by elucidating the magnetic actuation principles of permanent magnets at UHF. By modeling the uniaxial magnetization behavior of permanent magnets, we outline the magnetic torque and force and demonstrate unique magnetic actuation opportunities at UHF, such as in situ remagnetization. Last, we illustrate the proposed steering principles using a magnetic guidewire composed of neodymium magnets and a fiber optic rod in a 7-Tesla preclinical MRI scanner. The developed UHF magnetic actuation framework would enable nextgeneration magnetic robots to operate inside MRI scanners.ISSN:2375-254

Heat-Mitigated Design and Lorentz Force-Based Steering of an MRI-Driven Microcatheter toward Minimally Invasive Surgery

Catheters integrated with microcoils for electromagnetic steering under the high, uniform magnetic field within magnetic resonance (MR) scanners (3-7 Tesla) have enabled an alternative approach for active catheter operations. Achieving larger ranges of tip motion for Lorentz force-based steering have previously been dependent on using high power coupled with active cooling, bulkier catheter designs, or introducing additional microcoil sets along the catheter. This work proposes an alternative approach using a heat-mitigated design and actuation strategy for a magnetic resonance imaging (MRI)-driven microcatheter. A quad-configuration microcoil (QCM) design is introduced, allowing miniaturization of existing MRI-driven, Lorentz force-based catheters down to 1-mm diameters with minimal power consumption (0.44 W). Heating concerns are experimentally validated using noninvasive MRI thermometry. The Cosserat model is implemented within an MR scanner and results demonstrate a desired tip range up to 110° with 4° error. The QCM is used to validate the proposed model and power-optimized steering algorithm using an MRI-compatible neurovascular phantom and ex vivo kidney tissue. The power-optimized tip orientation controller conserves as much as 25% power regardless of the catheter's initial orientation. These results demonstrate the implementation of an MRI-driven, electromagnetic catheter steering platform for minimally invasive surgical applications without the need for camera feedback or manual advancement via guidewires. The incorporation of such system in clinics using the proposed design and actuation strategy can further improve the safety and reliability of future MRI-driven active catheter operations.ISSN:2198-384

Comparison of Central Corneal Thickness Measurements by Ultrasonic Pachymetry and Orbscan II Corneal Topography and Evaluation of Ultrasonic Pachymetry Repeatability

Objectives: Comparison of central corneal thickness (CCT) measurements by ultrasonic pachymetry and Orbscan II corneal topography and evaluation of ultrasonic pachymetry repeatability for same observer. Materials and Methods: The study included 132, 82, and 80 eyes of 66 patients with primary open-angle glaucoma (POAG), 41 patients with ocular hypertension (OHT), and 40 controls, respectively. All subjects were subjected to routine ophthalmic examination. Orbscan II (Bausch&Lomb) corneal topography and ultrasonic pachymetry (Nidek Ultrasonic Pachymetry UP-1000) were used for measurement of CCT. ANOVA (Turkey test) was used for variable distribution, paired sample t-test was used for repeated measurements, and the analyses were done by SPSS 20.0. Results: Mean CCT was 558.9±37.2 µm by ultrasonic pachymetry and 553.4±37 µm by corneal topography. There was a significant difference between the two measurements (p<0.0001). CCT was mean 5.55±8.28 µm thicker by ultrasonic pachymetry compared to corneal topography. There was no significant difference between the two genders (p>0.05). CCT was 555±39.2 µm, 564.3±28.4 µm, and 559.7±41.5 µm by ultrasonic pachymetry in POAG, OHT, and control subjects, respectively; CCT was 550.3±38.3 µm, 558.5±28 µm, and 553.2±42.5 µm by Orbscan II corneal topography in POAG, OHT, and control subjects, respectively. There was a significant linear correlation between Orbscan II corneal topography and ultrasonic pachymetry in CCT measurements (r=0.975, p<0.0001). Repeatability of ultrasonic pachymetry for same observer was (ICC value) 0.990. Conclusion: There is a significant correlation between Orbscan II corneal topography and ultrasonic pachymetry in CCT measurements. These two methods of measurements should not be substituted for each other, since ultrasonic pachymetry measures CCT greater than Orbscan II corneal topography. Repeatability of ultrasonic pachymetry for same observer is very high. (Turk J Ophthalmol 2014; 44: 263-7