In areas from assembly of machines to surgery, and from deactivation of improvised explosive devices (IEDs) to unmanned flight, robotics is an important and rapidly growing field of science and technology. It is currently dominated by robots having hard body plans—constructions largely of metal structural elements and conventional joints—and actuated by electrical motors, or pneumatic or hydraulic systems. Handling fragile objects—from the ordinary (fruit) to the important (internal organs)—is a frequent task whose importance is often overlooked and is difficult for conventional hard robots; moving across unknown, irregular, and shifting terrain is also. Soft robots may provide solutions to both of these classes of problems, and to others. Methods of designing and fabricating soft robots are, however, much less developed than those for hard robots. We wish to expand the methods and materials of chemistry and soft-materials science into applications in fully soft robots. A robot is an automatically controlled, programmable machine. The limbs of animals or insects—structures typically based on rigid segments connected by joints with constrained ranges of motion—often serve as models for mobile elements of robots. Although mobile hard robots sometimes have limb-like structures similar to those of animals (an example is “Big Dog” by Boston Robotics), more often, robots use structures not found in organisms—for example, wheels and treads. The robotics community defines “soft robots” as: 1) machines made of soft—often elastomeric—materials, or 2) machines composed of multiple hard-robotic actuators that operate in concert, and demonstrate soft-robot-like properties; here, we consider only the former. Soft animals offer new models for manipulation and mobility not found, or generated only with difficulty and expense, using hard robots. Because materials from which this class of devices will be fabricated will usually be polymers (especially elastomers), they fall into the realm of organic materials science. The use of soft materials allows for continuous deformation. This type of deformation, in turn, enables structures with ranges of motion limited only by the properties of the materials. Soft robots have the potential to exploit types of structures found, for example, in marine organisms, and in non-skeletal parts of land animals. The tentacles of squid, trunks of elephants, and tongues of lizards and mammals are such examples; their structures are muscular hydrostats. Squid and starfish 14] are highly adept locomotors; their modes of movement have not been productively used, and permit solutions of problems in manipulation, locomotion, and navigation, that are different from those used in conventional hard robotics. The prototypical soft actuator—muscle—developed through the course of evolution. There is currently no technology that can replicate the balanced performance of muscle: it is simultaneously strong and fast, and enables a remarkable range of movements (such as those of a tongue). Muscle-like contraction and dilation occur in ionic polymeric gels on changes in the acidity or salinity of a surrounding ionic solution, but actuation in macroscopic structures is masstransport limited, and typically slow. Other electroactive polymers (EAPs) include dielectric elastomers, electrolytically active polymers, polyelectrolyte gels, and gel-metal composites. Pneumatically-driven McKibben-type actuators are among the most highly developed soft actuators, and have existed for more than fifty years; they consist of a bladder covered in a shell of braided, strong, inextensible fibers. These actuators can be fast, and have a length-load dependence similar to that of muscle but possess only one actuation mode—contraction and extension when pressurization changes. They are, in a sense, an analogue to a single muscle fibril ; using them for complex movements requires multiple actuators acting in series or parallel. Pneumaticallydriven flexible microactuators (FMAs) have been shown to be capable of bending, gripping, and manipulating objects. Roboticists have explored scalable methods for gripping and manipulating objects at the micro and nano scales. The use of compliant materials allows grippers to manipulate objects such as fruit with varied geometry. The field of robotics has not yet caught the attention of soft-materials scientists and chemists. Developing new materials, techniques for fabrication, and principles of design will create new types of soft robots. The objective of this work is to demonstrate a type of design that provides a range of behaviors, and that offers chemists a test bed for new materials and methods of fabrication for soft robots. Our designs use embedded pneumatic networks (PneuNets) of channels in elastomers [*] Prof. G. M. Whitesides Wyss Institute for Biologically Inspired Engineering Harvard University, 3 Blackfan Circle, Boston, MA 02115 (USA) Fax: (+ 1)617-495-9857 and Kavli Institute for Bionano Science & Technology 29 Oxford Street, Cambridge MA (USA) E-mail: gwhitesides@gmwgroup.harvard.edu Homepage: http://gmwgroup.harvard.edu/

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Soft robotics for chemists

The development of a SU-8-based microgripper that can operate in physiological ionic solutions is presented The electrothermally activated polymer gripper consists of two "hot-and-cold-arm" actuators that are fabricated in a two-mask surface micromachining process The high thermal expansion coefficient of SU-8 (52 ppm//spl deg/C) compared to silicon and metals, allows the actuation of the microgripper with small average temperature elevations (10 - 32/spl deg/C) at low voltages (1-2 V) The polymer microgripper can be used for the manipulation of single cells and other biological species in solution with minimal undesired interactions

Electrothermally activated SU-8 microgripper for single cell manipulation in solution

This paper presents an exercise in comparing the performance of microelectromechanical systems (MEMS) actuators and sensors as a function of operating principle. Data have been obtained from the literature for the mechanical performance characteristics of actuators, force sensors and displacement sensors. On-chip and off-chip actuators and sensors are each sub-grouped into families, classes and members according to their principle of operation. The performance of MEMS sharing common operating principles is compared with each other and with equivalent macroscopic devices. The data are used to construct performance maps showing the capability of existing actuators and sensors in terms of maximum force and displacement capability, resolution and frequency. These can also be used as a preliminary design tool, as shown in a case study on the design of an on-chip tensile test machine for materials in thin-film form.

/pdf/mems-actuators-and-sensors-observations-on-their-performance-1ce9ndvk3j.pdf

MEMS actuators and sensors: observations on their performance and selection for purpose

We report the development of an artificial hair cell (AHC) sensor with design inspired by biological hair cells. The sensor consists of a silicon cantilever beam with a high-aspect-ratio cilium attached at the distal end. Sensing is based on silicon piezoresistive strain gauge at the base of the cantilever. The cilium is made of photodefinable SU-8 epoxy and can be up to 700-mum tall. In this paper, we focus on flow-sensing applications. We have characterized the performance of the AHC sensor both in water and in air. For underwater applications, we have characterized the sensor under two flow conditions: steady-state laminar flow (dc flow) and oscillatory flow (ac flow). The detection limit of the sensor under ac flow in water is experimentally established to be below 1 mm/s. A best case angular resolution of 2.16deg is also achieved for the sensor's yaw response in air.

Design and Characterization of Artificial Haircell Sensor for Flow Sensing With Ultrahigh Velocity and Angular Sensitivity

This paper presents a novel microfabrication technology of three-dimensional (3D) microstructures with inclined/rotated UV lithography using negative thick photoresist, SU-8. In exposure process, a photomask and a SU-8 coated substrate are fixed together, and tilted or tilted and rotated to a UV source. The reflected UV at the interface between the resist and the substrate is also exploited as well as the incident UV. With the 3D microfabrication technology, various 3D microstructures are easily fabricated such as oblique cylinders, embedded channels, bridges, V-grooves, truncated cones, and so on. The angles between fabricated structures and normal lines are 19.5°, when the incident angle of UV in air is 32°. Thus, the refractive index of SU-8 and the maximum refractive angle at the interface between SU-8 and air are expected about 1.6 and 39°, respectively.

3D microfabrication with inclined/rotated UV lithography

In this paper, we present the fabrication process of a shape memory alloy (SMA) thin film in both monolithic and hybrid configurations. This provides an effective actuation part for a gripper made of SU-8 thick photoresist. We also extensively describe and discuss the assembly of the SMA thin film with the SU-8 mechanism. Measurements show that the SU-8 gripper is able to achieve an opening action of 500 μm in amplitude at a frequency of 1 Hz. Finite element model simulations indicate that a force of 50 mN, corresponding to 400 μm of opening amplitude, should be produced by the SMA actuator. Although the assembly of the TiNi SMA thin film with the SU-8 mechanism is demonstrated, the bond reliability needs further development in order to improve the thermal behavior of the interface. In this paper, we show that SU-8 is well suited as a structural material for microelectromechanical systems (MEMS) applications. An attractive feature in the MEMS design is that the SMA generated force is well matched with the elastic properties of SU-8. From the application point of view, a SMA-actuated SU-8 high-aspect-ratio microgripper can serve as a secure means to transport microelectronics device, because it provides good grasping and safe insulation. This is also a preliminary result for the future development of biogrippers.

https://iopscience.iop.org/article/10.1088/0960-1317/13/2/323/pdf

Ph Bidaud

Papers

Fabrication and characterization of an SU-8 gripper actuated by a shape memory alloy thin film