28 Mar 2017
2:30 pm – 4:30 pm
Talks: By Professor Fumiya Iida & By Professor Robert J. Full
EPFL, Lausanne Suisse
|Talks: Model-free design optimization of soft robots: Any hope? By Professor Fumiya Iida (Cambridge Univ.), (14:30 – 15:30). BioMotion Science: Leapin’ Lizards, Compressed Cockroaches and Smart Squirrels Inspire Robots By...|
30 Sep – 7 Jan 2016
|The origami robot Tribot from Paik lab is currently at the exhibition in +Ultra Knowledge & Gestaltung in Berlin|
Looking for publications? You might want to consider searching on the EPFL Infoscience site which provides advanced publication search capabilities.
Dielectric elastomer actuators (DEAs), a soft actuator technology, hold great promise for biomimetic underwater robots. The high-voltages required to drive DEAs can however make them challenging to use in water. This paper demonstrates a method to create DEA-based biomimetic swimming robots that operate reliably even in conductive liquids. We ensure the insulation of the high-voltage DEA electrodes without degrading actuation performance by laminating silicone layers. A fish and a jellyfish were fabricated and tested in water. The fish robot has a length of 120 mm and a mass of 3.8 g. The jellyfish robot has a 61 mm diameter for a mass of 2.6 g. The measured swimming speeds for a periodic 3 kV drive voltage were 8 mm/s for the fish robot, and 1.5 mm/s for the jellyfish robot.
Typical deflection sensors like strain gauges or devices based on optical fibers require physical contact with the deflected substrate during the measurement process. Such contact, however, impacts on the softness of the substrate and may falsify the measurements. In order to overcome this drawback, a novel method of contactless deflection sensing was proposed in a recent work. It was verified that the deflection angle between two planes can be extracted using only a photosensor and a light source bearing a bell-shape angular emission profile. Yet, the range of operation was limited to concave shapes. In this paper, we introduce an alternative configuration of this light-based deflection sensing method to extend its functionality to convex surfaces. Here, a spheroidal mirror bearing a customized profile is introduced above the light source. This mirror redirects part of the emitted light towards the photosensor hindered by the bending surface during convex deflections.We make use of a ray tracing simulation method to design the mirror profiles, which are accurately reproduced in the manufactured prototypes by tuning the fabrication variables of the manufacturing process. Using a shape-sensing prototype, it is verified that the use of the mirror extends the range of detectable deflections by 55deg. to convex bendings, yielding a deviation of only 8.3% from simulated results. Our deflection sensing solution is a promising method to be used as a shape sensor in numerous applications, such as soft robotics platforms or prosthetic devices.
In the emerging field of soft robotics, there is an interest in developing new kinds of sensors whose characteristics do not affect the intrinsic compliance of soft robot components. Additionally, non-invasive shape and deflection sensors may provoke improved solutions to assist in the control of mechanical parts in these robots. Herein, we introduce a novel method for deflection sensing where an LED element and a photodiode are placed on to two substrates connected physically or virtually at a deflection point. The deflection angle between the two planes can be extracted from the LED light intensity detected at the photodiode due to the bell-shaped angular intensity profile of the emitted light. The main advantage of this system is that the components are not in physical contact with the deflection region as in the case of strain gauges and similar sensing methods. The sensor is characterized in a range of deflections of 105-180 degrees, showing a near 1 degree resolution. The experimental data are compared to simulations, modeled by ray tracing. The light intensity vs. deflection angle measurements in our setup display a maximum difference of 9% and an average difference of approximately 5% with respect to the model. Finally, a shape monitoring system has been developed using the proposed concept for a flexible PCB. The system is composed of 12 deflection sensors that operate at frame rate of 33 Hz. This device could be applied to monitor the body shape of a soft robot.
We demonstrate here a configuration of soft actuator which has several features such as, being completely soft, simple, thin, foldable, and stretchable while having uni/bidirectional bending actuation. Theoretically the actuation can be extended to multidirectional. We used Dielectric Elastomer Actuators (DEA) as a base actuation mechanism, and molded PDMS was used as a substrate of the device.
Soft robotics may provide many advantages compared to traditional robotics approaches based on rigid materials, such as intrinsically safe physical human-robot interaction, efficient/stable locomotion, adaptive morphology, etc. The objective of this study is to develop a compliant structural actuator for soft a soft robot using dielectric elastomer minimum energy structures (DEMES). DEMES consist of a pre-stretched dielectric elastomer actuator (DEA) bonded to an initially planar flexible frame, which deforms into an out-of-plane shape which allows for large actuation stroke. Our initial goal is a one-dimensional bending actuator with 90 degree stroke. Along with frame shape, the actuation performance of DEMES depends on mechanical parameters such as thickness of the materials and pre-stretch of the elastomer membrane. We report here the characterization results on the effect of mechanical parameters on the actuator performance. The tested devices use a cm-size flexible-PCB (polyimide, 50 μm thickness) as the frame-material. For the DEA, PDMS (approximately 50 μm thickness) and carbon black mixed with silicone were used as membrane and electrode, respectively. The actuators were characterized by measuring the tip angle and the blocking force as functions of applied voltage. Different pre-stretch methods (uniaxial, biaxial and their ratio), and frame geometries (rectangular with different width, triangular and circular) were used. In order to compare actuators with different geometries, the same electrode area was used in all the devices. The results showed that the initial tip angle scales inversely with the frame width, the actuation stroke and the blocking force are inversely related (leading to an interesting design trade-off), using anisotropic pre-stretch increased the actuation stroke and the initial bending angle, and the circular frame shape exhibited the highest actuation performance.
Current drones are developed with a fixed morphology that can limit their versatility and mission capabilities. There is biological evidence that adaptive morphological changes can not only extend dynamic performances, but also provide new functionalities. In this paper, we present different drones from our recent developments where folding is used as a mean of morphological adaptation. First, we show how foldable wings can enable the transition between aerial and ground locomotion or to fly in different aerodynamic conditions, advancing the development of multi-modal drones with an extended mission envelope. Secondly, we show how foldable structures allow to transport drones easily without sacrificing payload or flight endurance. Thirdly, we present a foldable frame that makes drones to withstand collisions. However, the real potential of foldable drones is often limited by the use of conventional design strategies and rigid materials, which motivates to use smart, functional materials. Lastly, we describe a dielectric elastomer based foldable actuator, and a variable stiffness fiber using low melting point alloy for drones. The foldable actuator acts as an active compliant joint with folding functionality and mechanical robustness in drones, thanks to the compliance of dielectric elastomer, a class of smart materials. We also show re-configuration of a drone enabled by the variable stiffness fiber that can transition between rigid and soft states.
Here we describe a sensor capable of perceiving complex one-dimensional (1-D) shape of an underlying substrate in a static and dynamic manner. The sensor consists of seven, serially connected, hyper-flexible strain gauges, manufactured using stretchable-gold-conductordeposited-on-PDMS technology. The custom designed read-out scheme allows decoupling strain-sensitive resistances of the strain-gauges from the parasitic pressure- and temperature-sensitive resistances of the connectors. The developed prototype device confirms full operation within the tested deflections ranging from 0 o to 35 o, showing an average sensitivity of 36 !/o and an average resolution of 0.22 o. The read-out frequency of 100 Hz allows quick scanning of the whole sensor array.
The ease of use and versatility of drones has contributed to their deployment in several fields, from entertainment to search and rescue. However, drones remain vulnerable to collisions due to pilot mistakes or various system failures. This paper presents a bioinspired strategy for the design of quadcopters resilient to collisions. Abstracting the biomechanical strategy of collision resilient insects’ wings, the quadcopter has a dual-stiffness frame that rigidly withstands aerodynamic loads within the flight envelope, but can soften and fold during a collision to avoid damage. The dual-stiffness frame works in synergy with specific energy absorbing materials that protect the sensitive components of the drone hosted in the central case. The proposed approach is compared to other state-of- the art collision-tolerance strategies and is validated in a 50g quadcopter that can withstand high speed collisions.
A method for fabricating an imaging system, the method comprising providing a flexible substrate (200), a first layer (220) comprising a plurality of microlenses (232) and a second layer (240) comprising a plurality of image sensors (242). The method further comprises stacking the first and the second layer (220; 240) onto the flexible substrate (200) by attaching the plurality of image sensors (242) to the flexible substrate, such that each of the plurality of microlenses (232) and image sensors (242) are aligned to form a plurality of optical channels (300) , each optical channel comprising at least one microlens and at least one associated image sensor, and mechanically separating the optical channels (300) such that the separated optical channels remain attached to the flexible substrate (200) to form a mechanically flexible imaging system.