Search

Hierarchical surfaces that aid in the droplet nucleation, growth, and removal is highly desirable for fog and moisture harvesting applications. Taking inspiration from the unique architecture of leaf skeletons, we present a multiscale surface capable of rapidly nucleating, growing, and directional transport of the water droplets. Copper oxide microtufts were fabricated onto the Ficus religiosa leaf skeletons via electroplating and chemical oxidation techniques. The fabricated surfaces with microtufts had high wettability and very good fog harvesting ability. CuO surfaces tend to become hydrophobic over time because of the adsorption of the airborne species. The surfaces were efficient in fog harvesting even when the hydrophobic coating is present. The overall water collection efficiencies were determined, and the role of the microtufts, fractal structures, and the orientation of leaf veins was investigated. Compared to the planar control surfaces, the noncoated and hydrophobic layer-coated copper oxide microtufts on the leaf skeletons displayed a significant increase in the fog harvesting efficiency. For superhydrophilic skeleton surfaces, the water collection rate was also observed to slightly vary with the vein orientation. The CuO microtufts along with high surface area fractals allowed an effective and sustainable way to capture and transport water. The study is expected to provide valuable insights into the design and fabrication of sustainable and efficient fog harvesting systems. publishedVersion

In soft robotics, actuators, logic and power systems can be entirely fluidic and electronics-free. However, sensors still typically rely on electric or optical principles. This adds complexity to fluidic soft robots because transducers are needed, and electrical materials have to be incorporated. Herein, we show a highly-stretchable pneumatic strain gauge based on a meandering microchannel in a soft elastomer material thus eliminating the need for an electrical signal in soft robots. Using such pneumatic sensors, we demonstrate an all-pneumatic gripper with integrated pneumatic strain gauges that is capable of autonomous closure and object recognition. The gauges can measure at least up to 300% engineering strains. The sensor exhibits a very stable signal over a 12-hour measurement period with no hysteresis. Using pneumatic sensors, all four major components of robots—actuators, logic, power, and sensors—can be pneumatic, enabling all-fluidic soft robots with proprioception and exteroception.

Elämämme modernissa yhteiskunnassa on monin tavoin helpompaa kuin ennen, ja yksi suuri syy tälle on robottien nopea yleistyminen. Ne ovat täyttäneet tehtaat ja valmistuslinjat ja työskentelevät siellä taukoamatta tehden työstämme fyysisesti kevyempää. Jotta robotit voisivat toistaa pikkutarkkoja ja raskaita liikkeitä miljoonia kertoja, täytyy robottien sekä niiden toimielinten, antureiden, ohjausyksiköiden ja voimalähteiden olla kovia ja kestäviä. Tällaisia kovia robotteja tarvitaan tehtaissa, mutta toisaalta kovuus rajoittaa niiden turvallista ja miellyttävää käyttöä ihmisten lähellä. Pehmeiden materiaalien tutkimus on avannut uusia mahdollisuuksia robotiikan alalle luoden uuden alan: pehmorobotiikan. Kovista materiaaleista pehmeisiin siirtymällä 1) roboteista tulee turvallisempia: ne eivät vahingoita, vaikka törmäisivät ihmiseen, 2) robotit mukautuvat pinnan muotoihin ja 3) ne tuntuvat mukavammilta ihoa vasten. Monet pehmorobottien valmistusmenetelmistä on otettu mikrofluidistiikan alalta, jossa on käytetty silikonivaluja pienien ja yksityiskohtaisten mikrofluidististen testausalustojen valmistukseen. Tämä tekniikka mahdollistaa erittäin pienien rakenteiden tarkan kopioimisen muotista lopputuotteeseen, mutta monimutkaiset rakenteet, kuten ulokkeet ja upotetut kanavat, ovat haasteellisia valmistaa, koska muotti pitää saada irrotettua pehmeän rakenteen ympäriltä. Pehmoroboteissa tällaisia monimutkaisia rakenteita kuitenkin tarvitaan liikkuvien toimielinten ja tarttujien aikaansaamiseksi, ja siksi tarvitaan valmistustapa, jolla voidaan tehdä tehokkaasti aidosti kolmiulotteisia rakenteita. Pehmeistä materiaaleista tehdyt tarttujat mukautuvat kohteen muotoihin, mikä mahdollistaa hauraiden asioiden poimimisen vahingoittamatta niitä. Pehmeys voi kuitenkin rajoittaa sitä, kuinka suuria voimia tarttujat pystyvät käsittelemään. Tarttujan kovuus tai jäykkyys voi kasvattaa sen kykyä käsitellä suuria voimia kappaleen kuljetuksen aikana. Materiaalit ja mekanismit, joiden jäykkyyttä voi kontrolloida, voisivat mahdollistaa tällaisen säädettävän tarttumisen ja jäykkyyden. Pehmeiden runkojen lisäksi roboteissa käytettävien antureiden tulee olla venyviä ja pehmeitä. Yksi tärkeimmistä pehmoroboteissa käytetyistä anturityypeistä on venymäanturi, jonka eri kokoonpanoilla voi mitata robotin ulkoista ja sisäistä informaatiota. Venymäantureiden valmistamiseen on ehdotettu monia erilaisia menetelmiä, kuten nestemäiset metallit ja ionijohteet. Monissa menetelmissä tarvitaan kuitenkin useita valmistusvaiheita tai niissä käytettyjä materiaaleja on vaikea käsitellä, joten ne eivät sovellu massavalmistukseen. Tämän lisäksi ehdotetut anturit ovat usein sähköisiä toisin kuin toimielimet, jotka ovat usein pneumaattisia. Siirtymällä pneumaattisiin antureihin voitaisiin robotin kokonaisrakennetta yksinkertaistaa. Tässä väitöskirjassa tutkimme eri menetelmiä pehmorobottien tarttujien ja antureiden valmistamiseksi. Ensiksi tutkimme, voiko uhri-3D-tulostuksella valmistaa pehmeille materiaaleille valumuotteja, joissa on ulkonevia rakenteita. Näytimme, että tapa oli vaivaton ja että sillä pystyttiin valmistamaan upotettuja kanavia pehmeisiin silikonirakenteisiin. Toiseksi me kehitimme pehmotarttujia. Valmistimme kaksi erilaista 3D-tulostettua imukuppitarttujaa: pneumaattisen sekä magneettisesti ohjattavan hydraulisen tarttujan. Totesimme 3D-tulostuksen sopivaksi tavaksi valmistaa pehmotarttujia. Huomasimme myös valmistettujen tarttujien suoriutuvan haasteellisten kohteiden, kuten pienien kappaleiden, epätasaisten kuormien ja hauraiden esineiden, poimimisesta paremmin kuin kaupallisten imukuppitarttujien. Ehdotamme myös, että magnetoreologisen nesteen käytöllä tarttujan jäykkyyttä voidaan säädellä. Viimeiseksi valmistimme ja integroimme antureita pehmorobotteihin. Ehdotimme kahta erityyppistä ratkaisua venymän ja käyryyden mittaamiseen: silkkipainettuja resistiivisiä venyviä antureita sekä pneumaattisia venymäliuskoja. Esitämme, että silkkipainotekniikka on edullinen ja massavalmistukseen soveltuva valmistustapa sähköisten venymäantureiden valmistukseen, kun taas pneumaattiset venymäliuskat ovat askel lähemmäs kokonaan pneumaattisia pehmorobotteja. Kaiken kaikkiaan tämä väitöskirja käsittelee uusia pehmorobottien tarttujien ja antureiden valmistusmenetelmiä. Tavoitteena on löytää yksinkertaisempia tapoja valmistaa älykkäämpiä pehmorobotteja. Our lives in modern society are easier in many ways due to the ongoing revolution of robotics. Robots perform endless tasks in assembly lines and in factories making our work lighter and decreasing the need for human labour. To repeat these precise and heavy tasks millions of times, the robots—including actuators, sensors, and control and power units—are made of hard and tough materials. The hard robots are needed in factories but at the same time the hardness of the robots limits the safety and the comfort while working near humans. The research in soft materials has opened new possibilities in robotics, creating a new field called soft robotics. By shifting from the hard robot materials to soft ones, the robots can be 1) made safer: they cause less damage, even in collision; 2) made to conform to objects; and 3) made to feel comfortable against the skin. Many of the manufacturing methods of soft robots have been adapted from the field of microfluidics. Silicone casting has been widely used to fabricate chips with detailed small structures. The method is efficient for replicating small features. However, complex structures, such as overhangs and buried channels, are particularly difficult to fabricate since the elastomer piece must be removed from the mould. In soft robotics, these kinds of structures are often desired for creating moving actuators and grippers. An efficient and fast way to fabricate fully three-dimensional soft structures is still needed. Grippers made of soft materials can conform to objects, which can enable the picking of fragile objects without damaging them. However, it can limit the holding forces while carrying the object. During the object transport it can be beneficial if the gripper material is stiff or even rigid. Materials and mechanisms with controllable stiffness could be used to achieve this effect. In addition to the soft body of the robot, the sensors need to also be stretchable and soft. One of the most important types of sensors used in soft robots is the strain sensor which in different configurations can measure exteroceptive and proprioceptive information. Many methods for fabricating soft strain sensors have been proposed, such as liquid metals and ionic conductors. However, many of these methods involve multiple fabrication steps or materials which are difficult to handle, so they are not suitable for mass manufacturing. Additionally, these sensors are usually electrical, unlike soft actuators which are often pneumatic. Using pneumatics also for the sensing would simplify the overall structure of the robot. This thesis explores different methods of designing and fabricating soft robots and sensors for them. First, we studied whether sacrificial 3D printing was a suitable method of fabricating soft devices moulds with overhanging structures. We were able to demonstrate that the proposed method is straightforward and can be used to fabricate buried channels in soft silicone elastomer structures. Second, we developed soft robotic grippers. We fabricated two different 3D printed suction-based grippers: a pneumatic one and a magnetically switchable hydraulic one. 3D printing was found to be a suitable method for soft gripper fabrication. We also found that the grippers outperformed commercial suction grippers with small, unevenly loaded and fragile objects. We propose using magnetorheological fluid, embedded inside a soft robotic gripper, to control the stiffness of the gripper. Last, the sensors were fabricated and integrated into soft robots. Two different approaches were proposed for strain and curvature sensing: screen-printed stretchable sensors and soft pneumatic strain sensors. We propose that screen-printing is a low-cost method suitable for mass manufacturing electric strain sensors, whereas soft pneumatic strain sensors are a step towards fully pneumatic soft robots. To conclude, this dissertation describes new methods of fabricating soft robots and sensors for them, aiming at simpler ways to fabricate smarter soft robots with perception.

Capacitive sensors have many applications in tactile sensing, human-machine interfaces, on-body sensors, and patient monitoring. Particularly in biomedical applications, it would be beneficial if the sensor is disposable and readily degradable for efficient recycling. In this study, we report a biodegradable capacitive tactile pressure sensor based on sustainable and bio resourced materials. Silver-nanowire-coated rubber tree leaf skeletons are used as transparent and flexible electrodes while a biodegradable clear tape is used as the dielectric layer. The fabricated sensor is sensitive and can respond to low pressures (7.9 mN when pressed with a probe with a surface area of 79 mm2 / 0.1 kPa) ranging to relatively high pressures (37 kPa), with a sensitivity up to ≈ 4.5×10-3 kPa-1. Owing to all bio resourced constituents, the sensor is biodegradable and does not create electronic waste. publishedVersion

A 3D‐printed pneumatically actuated soft suction gripper with an elastomer film is proposed. Suction in such gripper is actively controlled by applying a negative pressure behind the film. The elastomeric gripper body is 3D‐printed, making it easy to customize and integrate into future robotic gripping systems. The gripper can pick a wide variety of objects, such as delicate fruits, small parts, and parts with uneven loads, with high pull‐off forces (over 7.4 N with ∅ 20 mm/55 kPa). The achieved pull‐off forces are significantly higher than the previously reported suction cup grippers with films and more comparable with commercial vacuum grippers. The pull‐off forces show no significant differences with surfaces of varying roughness (up to root‐mean‐square roughness of 5.66 μm) and the gripper is able to pick and release target objects repeatedly. The gripper is also compared with a commercial vacuum gripper with comparable dimensions. It outperforms the commercial gripper in the case of fragile objects, objects smaller than the gripper diameter, and objects with uneven loads. It can apply high pull‐off forces while having controllable release, and is suitable for gripping a wide variety of real‐world objects, including heavy, rough, small, thin, and fragile ones.

The development of soft electronics is critical to the realization of artificial intelligence that comes into direct contact with humans, such as wearable devices, and robotics. Furthermore, rapid prototyping and inexpensive processes are essential for the development of these applications. We demonstrate here an additive, low-cost method for fabricating polydimethylsiloxane based soft electronics by inkjet printing. Herein, a novel approach using a water-soluble polyvinyl alcohol layer as the substrate, inexpensive, fully digital fabrication of capacitive pressure sensors is enabled by sandwiching mesh-like conductive layers and microstructured dielectric in a straightforward, convenient manner. These sensors exhibit improved sensitivity (4 MPa-1) at low pressures (< 1 kPa) in contrast to sensors with a flat elastomer dielectric and can still detect large pressures around 50 kPa, having excellent long-term repeatability over 2000 cycles, without significant hysteresis (≤ 8.5 %). The tactile sensing ability of the fabricated devices was demonstrated in a practical application. Moreover, sensor characteristics are easily adjustable, simply by changing printing parameters or tuning the ink solution. The proposed approach provides scalable solution for fabricating high-sensitivity printed sensors for e-skin and human-machine interfaces. publishedVersion

While suction cups prevail as common gripping tools for a wide range of real-world parts and surfaces, they often fail to seal the contact interface when engaging with irregular shapes and textured surfaces. In this work, the authors propose a suction-based soft robotic gripper where suction is created inside a self-sealing, highly conformable and thin flat elastic membrane contacting a given part surface. Such soft gripper can self-adapt the size of its effective suction area with respect to the applied load. The elastomeric membrane covering edge of the soft gripper can develop an air-tight self-sealing with parts even smaller than the gripper diameter. Such gripper shows 4 times higher adhesion than the one without the membrane on various textured surfaces. The two major advantages, underactuated self-adaptability and enhanced suction performance, allow the membrane-based suction mechanism to grip various three-dimensional (3D) geometries and delicate parts, such as egg, lime, apple, and even hydrogels without noticeable damage, which can have not been gripped with the previous adhesive microstructures-based and active suction-based soft grippers. The structural and material simplicity of the proposed soft gripper design can have a broad use in diverse fields, such as digital manufacturing, robotic manipulation, transfer printing, and medical gripping., Advanced Science, 8 (17), ISSN:2198-3844

Bioinspired, highly flexible, fast, and biodegradable heaters are fabricated based on Ag nanowires and leaf skeletons of different plant species. The leaf skeletons act as transparent substrates with a high surface-area-to-volume ratio and allow a uniform dispersion of the Ag nanowires through the surface. Ag nanowires adhered to the leaf skeletons display very good transmittance (up to ≈87%) and mechanical (flexibility) properties (curvature values >800 m−1) without any post-treatment. The flexible leaf skeleton-based heaters reach high temperatures very quickly, with very low voltages (

Tactile electronic skin (e-skin) has multitude of potential applications, such as a prosthetic artificial skin, wearable sensors and health monitoring. However, current fabrication methods tend to involve complex processing or materials that are not widely available. In this paper, we show that high quality capacitive tactile sensors for an e-skin can be fabricated by sandwiching a microstructured dielectric elastomer layer between two conductive fabric electrodes. The fabric can be easily cut to quickly prototype different sensor configuration and can be bent into three dimensional shapes. The fabricated sensors display excellent linearity and very little long-term drift. We demonstrate the integration of these sensors in an anthropomorphic robotic hand, which is entirely fabricated using rapid prototyping techniques.

In biomedical sciences, there is demand for electronic skins with highly sensitive tactile sensors, having applications in patient monitoring, human–machine interfaces, and on-body sensors. In clinical applications, it would be especially beneficial if the sensors would be disposable. Here, an all plant-material-based biodegradable capacitive tactile pressure sensor for disposable electronic skins is reported. Silver-nanowire-coated leaf skeletons are used as breathable and flexible electrodes while freeze-dried rose petals are used as the dielectric layer. The leaf skeleton electrodes have a rough fractal-like architecture, which provides good adhesion to the silver nanowires and maintains interconnections between the silver nanowires when the electrodes are bent. The electrodes display low constant resistance up to curvature of 800 m−1. The rose petal dielectric layer has a multiscale 3D cell wall microstructure, which compresses elastically when subjected to pressure. The fabricated sensor can respond to pressures ranging from 0.007 to at least 60 kPa, with a maximum sensitivity of ≈0.08 kPa−1. The signal is stable for at least 5000 pressure cycles, after an initial break-in period. Owing to the all biomaterial constituents, the sensor is biodegradable under aqueous conditions. The sensor is successfully applied as an e-skin in touch sensing and gesture monitoring. publishedVersion

Castable elastomers have been used to fabricate soft fluidic actuators and the technique scales well from prototyping to mass manufacturing. However, similarly scalable techniques for integrating strain or curvature sensors into such devices are still lacking. In this paper, screen-printed silver conductors are shown to serve as curvature sensors for soft fluidic actuators. The sensors are realized in a single printing step onto elastomer substrates. Resistance measurement allows estimating the curvature of soft actuators, limited by the hysteresis of the sensors. These sensors can detect if the motion of an actuator has been blocked, clearing the path towards simple-to-fabricate soft robots that react to their surroundings.

Castable elastomers have been used to fabricate soft robotic devices and it has been shown that the technique scales well from prototyping to mass manufacturing. However, similarly scalable techniques for integrating strain or curvature sensors into such devices are still lacking. In this paper, we show that screenprinted silver conductors serve well as curvature sensors for soft robotic devices. The sensors are produced onto elastomer substrates in a single printing step and integrated into soft pneumatic actuators. We characterized the resistance-curvature relationship of the sensors, which allows the curvature of the actuators to be estimated from the sensor measurements. Hysteresis was observed, which does limit the absolute accuracy of the sensors. However, temperature characterizations showed that the sensor measurements are not significantly affected by temperature fluctuations during normal operation. Dynamic experiments showed that the bandwidth of the sensors is larger than the bandwidth of the actuators. We experimentally validated that these sensors can be used to detect whether the motion of an actuator has been blocked, clearing the way towards simple-tofabricate soft robots that react to their surroundings. Finally, we demonstrate a three-fingered soft robotic gripper with integrated sensors. We conclude that screen-printing is a promising way to integrate curvature sensors into soft robots. acceptedVersion