Soft robotics

Soft Robotics is the specific subfield of robotics dealing with constructing robots from highly compliant materials, similar to those found in living organisms.

Soft robotics draws heavily from the way in which living organisms move and adapt to their surroundings. In contrast to robots built from rigid materials, soft robots allow for increased flexibility and adaptability for accomplishing tasks, as well as improved safety when working around humans. These characteristics allow for its potential use in the fields of medicine and manufacturing.

Types and designs
The bulk of the field of soft robotics is based upon the design and construction of robots made completely from compliant materials, with the end result being similar to invertebrates like worms and octopuses. The motion of these robots is difficult to model, as continuum mechanics apply to them, and they are sometimes referred to as continuum robots. Soft Robotics is the specific sub-field of robotics dealing with constructing robots from highly compliant materials, similar to those found in living organisms. Similarly, soft robotics also draws heavily from the way in which these living organisms move and adapt to their surroundings. This allows scientists to use soft robots to understand biological phenomena using experiments that cannot be easily performed on the original biological counterparts. In contrast to robots built from rigid materials, soft robots allow for increased flexibility and adaptability for accomplishing tasks, as well as improved safety when working around humans. These characteristics allow for its potential use in the fields of medicine and manufacturing. However, there exist rigid robots that are also capable of continuum deformations, most notably the snake-arm robot.

Also, certain soft robotic mechanics may be used as a piece in a larger, potentially rigid robot. Soft robotic end effectors exist for grabbing and manipulating objects, and they have the advantage of producing a low force that is good for holding delicate objects without breaking them.

In addition, hybrid soft-rigid robots may be built using an internal rigid framework with soft exteriors for safety. The soft exterior may be multifunctional, as it can act as both the actuators for the robot, similar to muscles in vertebrates, and as padding in case of a collision with a person.

Biomimicry
Plant cells can inherently produce hydrostatic pressure due to a solute concentration gradient between the cytoplasm and external surroundings (osmotic potential). Further, plants can adjust this concentration through the movement of ions across the cell membrane. This then changes the shape and volume of the plant as it responds to this change in hydrostatic pressure. This pressure derived shape evolution is desirable for soft robotics and can be emulated to create pressure adaptive materials through the use of fluid flow. The following equation models the cell volume change rate:


is the rate of volume change.
is the cell membrane.
is the hydraulic conductivity of the material.
is the change in hydrostatic pressure.
 is the change in osmotic potential.

This principle has been leveraged in the creation of pressure systems for soft robotics. These systems are composed of soft resins and contain multiple fluid sacs with semi-permeable membranes. The semi-permeability allows for fluid transport that then leads to pressure generation. This combination of fluid transport and pressure generation then leads to shape and volume change.

Another biologically inherent shape changing mechanism is that of hygroscopic shape change. In this mechanism, plant cells react to changes in humidity. When the surrounding atmosphere has a high humidity, the plant cells swell, but when the surrounding atmosphere has a low humidity, the plant cells shrink. This volume change has been observed in pollen grains and pine cone scales.

Scientific challenges
According to the IEEE.org group, these challenges are interdisciplinary and some still consider prospective; they concern in particular:

the contributions of biomimetics A large part of living beings is made up of soft beings, and the internal organs are almost always so.
methods and tools (software) for modeling and simulation of " soft robotic organs " (possibly complex and printed "monoblock" in 3D); Many robots have a form reminiscent of invertebrates, but the soft robotics can also contribute to creating complex humanoid robots.
studies of unconventional flexible materials (still in exploratory phase);
the hierarchical inventory of flexible materials available and useful or desirable for all or part of robotic applications (conventional and future);
the best tools and methods of manufacturing and / or assembling this type of robot;
the integration of sensors that should evolve towards "flexible and extensible" sensors 7 (including for a possible photovoltaic skin) in a more or less elastic and deformable structure;
an actuation revised to be adapted to the soft robot, possibly "modular" and / or enhancing the systems of "passive adaptations" (energy saving);
internal self-organization and distributed control capabilities
completely revised control systems (cobotics);
the prototyping, testing (including aging);
reinforcement and a better sharing of knowledge and technological know-how in flexible robotics;
opportunities for "self-redress", in relation to resilience issues;
the self-replication;
applications for a "soft robotics".

Robotic specificities
A flexible robot interacts differently with its environment, since it can generate or undergo elastic deformations more or less constrained by its morphology, its size, the degree of elasticity and coherence of its structure.

It is often - but not necessarily - biomimetic (or bio-inspired) and always characterized by the use of specific materials.

His actuators are partly different or adapted.

They have disadvantages and advantages over rigid robots.

Disadvantages
The field of soft robotics is still very emerging. It has proved itself only by a few prototypes. There are no or few spare parts or soft robots marketed, and R & D funding is still preferentially oriented towards classical robotics;

the behavior of soft materials (and flexible structures especially when they are complex) is far more difficult to model than hard materials, and therefore more difficult to control and operate;
Some of the soft materials that constitute them are vulnerable to certain external aggressions (although in some cases the "soft" character also allows to absorb the energy of shocks or effects of "punching" and to protect the robot.

Advantages
the deformable structures allow a soft robot to better adapt to certain dynamic circumstances or tasks, including in an uncertain environment (eg displacement in a fluid with high turbulence, locomotion in uneven ground and unknown, action of gripping object of form, weight and fragility unknown).. or when in contact with a living being or an organ (in the case of a surgical or industrial robot);

the rapid progress of elastomer injection, then of the 3D printing of certain elastomers makes it possible to mold (and today to print) elastic polymer blends, of different elasticity, opening up new possibilities; It seems even possible in the near future to associate synthetic polymers with biopolymers, or with living cells;

Some soft and elastic materials have an energetic interest: for example phase change materials, deformable structures (eg springs) or shape memory or integrating a compressed gas can also theoretically store and release a certain amount of energy. This energy can be used for the movements and changes of shape of the robot and / or be mobilized for other tasks;

After having been torn, pierced or slightly damaged, certain elastomers made up of thermoreversible covalent networks (so-called "Diels-Alder Polymers" or "Diels-Alder Polymers" for English speakers) can (simply by being slightly warmed and then cooled) reassemble; Robust envelopes or organs capable of self-healing thus become possible; Tests published in 2017 by Science Robotics show that materials can then repair itself after cuts, then moves back despite some scars almost complete performance even after two cycles repair / healing. This has been successfully tested for three pneumatic actuators flexible robotics (flexible forceps, hand and artificial muscles) self-healing after injuries by piercing, tearing or blows on the polymer in question;

Soft robotics are often much less expensive than the hard parts of "classic" robots.

Manufacturing
Conventional manufacturing techniques, such as subtractive techniques like drilling and milling, are unhelpful when it comes to constructing soft robots as these robots have complex shapes with deformable bodies. Therefore, more advanced manufacturing techniques have been developed. Those include Shape Deposition Manufacturing (SDM), the Smart Composite Microstructure (SCM) process, and 3D multimaterial printing..

SDM is a type of rapid prototyping whereby deposition and machining occur cyclically. Essentially, one deposits a material, machines it, embeds a desired structure, deposits a support for said structure, and then further machines the product to a final shape that includes the deposited material and the embedded part. Embedded hardware includes circuits, sensors, and actuators, and scientists have successfully embedded controls inside of polymeric materials to create soft robots, such as the Stickybot and the iSprawl.

SCM is a process whereby one combines rigid bodies of carbon fiber reinforced polymer (CFRP) with flexible polymer ligaments. The flexible polymer act as joints for the skeleton. With this process, an integrated structure of the CFRP and polymer ligaments is created through the use of laser machining followed by lamination. This SCM process is utilized in the production of mesoscale robots as the polymer connectors serve as low friction alternatives to pin joints.

3D printing can now be used to print a wide range of silicone inks using Robocasting also known as direct ink writing (DIW). This manufacturing route allows for a seamless production of fluidic elastomer actuators with locally defined mechanical properties. It further enables a digital fabrication of pneumatic silicone actuators exhibiting programmable bioinspired architectures and motions. A wide range of fully functional softrobots have been printed using this method including bending, twisting, grabbing and contracting motion. This technique avoids some of the drawbacks of conventional manufacturing routes such as delamination between glued parts. Another additive manufacturing method that produces shape morphing materials whose shape is photosensitive, thermally activated, or water responsive. Essentially, these polymers can automatically change shape upon interaction with water, light, or heat. One such example of a shape morphing material was created through the use of light reactive ink-jet printing onto a polystyrene target. Additionally, shape memory polymers have been rapid prototyped that comprise two different components: a skeleton and a hinge material. Upon printing, the material is heated to a temperature higher than the glass transition temperature of the hinge material. This allows for deformation of the hinge material, while not affecting the skeleton material. Further, this polymer can be continually reformed through heating.

Control
All soft robots require some system to generate reaction forces, to allow the robot to move in and interact with its environment. Due to the compliant nature of these robots, this system must be able to move the robot without the use of rigid materials to act as the bones in organisms, or the metal frame in rigid robots. However, several solutions to this engineering problem exist and have found use, each possessing advantages and disadvantages.

One of these systems uses Dielectric Elastomeric Actuators (DEAs), materials that change shape through the application of a high-voltage electric field. These materials can produce high forces, and have high specific power (W/kg). However, these materials are best suited for applications in rigids robots, as they become inefficient when they do not act upon a rigid skeleton. Additionally, the high-voltages required can become a limiting factor in the potential practical applications for these robots.

Another system uses springs made of shape-memory alloy. Although made of metal, a traditionally rigid material, the springs are made from very thin wires and are just as compliant as other soft materials. These springs have a very high force-to-mass ratio, but stretch through the application of heat, which is inefficient energy-wise.

Pneumatic artificial muscles are yet another method used for controlling soft robots. By changing the pressure inside a flexible tube, it will act as a muscle, contracting and extending, and applying force to what it’s attached to. Through the use of valves, the robot may maintain a given shape using these muscles with no additional energy input. However, this method generally requires an external source of compressed air to function.

History
Of clocks, of automata and mechanical toys use for several decades various forms of springs and sometimes leather, fabric forming flexible connections, or twisted elastic or compressed air in a flask as an energy reservoir. But the polymers needed to make real, strong, durable robots have only been available for a few decades.

For about half a century, industrial robots have been rigid and rather adapted to fast and repetitive tasks. More or less flexible or soft materials were sometimes used in their construction, but were often of secondary importance; they were reserved for moving cables, fluid lines, joint jackets, vacuum systems (for gripping fragile objects, for example) or shock damping, etc. The science fiction in comics, novels and movies have popularized robots often have metallic armor (or sometimes very humanoid, including with a synthetic skin).

From 2009 to 2012, the appearance of technical silicones, various other moldable polymers, shape memory materials made it possible to explore new avenues. The use of electroactive polymers and the prospect of being able to produce artificial muscle systems (including those based on electroactive hydrogel), coupled with the regular improvement of the performance of 3D printers could, in particular in connection with the development of biomimeticsboost the development of a soft robotics allowing new abilities such as compression, stretching, torsion, swelling, morphing, etc. in ways that would be impossible with rigid elements of classical robotics.

In 2013, at an international conference devoted to artificial intelligence and in an article summarizing their point of view, Rolf Pfeifer and his colleagues at the University of Zurich present soft robots and biomimetics as the next generation of "intelligent machines".

Recent discoveries and demonstrations have also (and for example) focused on:

"gas robotics" (which focuses on robots lighter than air)
the interest of soft and prehensile appendages, like the elephant horn or tentacles, possibly miniaturized; in this case, muscular hydrostats often made almost entirely of muscular and connective tissue may change their shape if they are pressurized by osmosis, as well as in certain plant or fungal organs.
a self-winding yarn and made highly stretchable (imitating the principle of the drops that coat the cobwebs)
the use of simple materials such as grains of sand that can be "shaped" via the principle of "jamming transition" to give the equivalent of a robotic forceps first soft and enveloping, that it can then be hardened at will
Materials with shape memory
ionic polymer metal composites
dielectric elastomers (or DEs for Dielectric elastomers.
the use of 3D printing for example to produce a cordless or battery-free soft-body robot where a small reservoir of hydrogen peroxide serves as a source of gas (which can be activated by putting the peroxide in contact with a catalyst (platinum) capable of inflating a network of 3D-printed pneumatic chambers (eg Octobot presented in 2016).
The forecasters expect robots capable of self-repair, grow, recycle or biodegrade, and can configure their morphology for different tasks and / or environment.
Soft micro- robots (possibly microscopic) are also expected by some (as a logical consequence of the crossing of soft robotics and miniaturization) but others like (Jay) Kim wonder why; are there compelling or motivating reasons to invent them?

Uses and applications
Soft robots can be implemented in the medical profession, specifically for invasive surgery. Soft robots can be made to assist surgeries due to their shape changing properties. Shape change is important as a soft robot could navigate around different structures in the human body by adjusting its form. This could be accomplished through the use of fluidic actuation.

Soft robots may also be used for the creation of flexible exosuits, for rehabilitation of patients, assisting the elderly, or simply enhancing the user’s strength. A team from Harvard created an exosuit using these materials in order to give the advantages of the additional strength provided by an exosuit, without the disadvantages that come with how rigid materials restrict a person’s natural movement.

Traditionally, manufacturing robots have been isolated from human workers due to safety concerns, as a rigid robot colliding with a human could easily lead to injury due to the fast-paced motion of the robot. However, soft robots could work alongside humans safely, as in a collision the compliant nature of the robot would prevent or minimize any potential injury.

International journals
Soft Robotics (SoRo)
Soft Robotics section of Frontiers in Robotics and AI
International events
2018 Robosoft, first IEEE International Conference on Soft Robotics, April 24–28, 2018, Livorno, Italy
2017 IROS 2017 Workshop on Soft Morphological Design for Haptic Sensation, Interaction and Display, 24 September 2017, Vancouver, BC, Canada
2016 First Soft Robotics Challenge, April 29–30, Livorno, Italy
2016 Soft Robotics week, April 25–30, Livorno, Italy
2015 "Soft Robotics: Actuation, Integration, and Applications – Blending research perspectives for a leap forward in soft robotics technology" at ICRA2015, Seattle WA
2014 Workshop on Advances on Soft Robotics, 2014 Robotics Science an Systems (RSS) Conference, Berkeley, CA, July 13, 2014
2013 International Workshop on Soft Robotics and Morphological Computation, Monte Verità, July 14–19, 2013
2012 Summer School on Soft Robotics, Zurich, June 18–22, 2012

In popular culture
The 2014 Disney film Big Hero 6 revolved around a soft robot, Baymax, originally designed for use in the healthcare industry. In the film, Baymax is portrayed as a large yet unintimidating robot with an inflated vinyl exterior surrounding a mechanical skeleton. The basis of Baymax concept comes from real life research on applications of soft robotics in the healthcare field, such as roboticist Chris Atkeson's work at Carnegie Mellon's Robotics Institute.

Scientific Community
Some elements of "classic" robots (industrial, military, etc.) have long been made of soft and sometimes elastic materials, but the idea of robots almost entirely "soft" is recent. It associates with classical robotics new types of modeling, and disciplines that were only slightly (polymer chemistry in particular). The principles of design and construction are largely to be reviewed.

At the beginning of 2010, an international scientific and technical community gathered around the idea of exploring the tracks opened by soft robotics, with:

since October 2012, an IEEE RAS technical committee dedicated to soft robotics (IEEE RAS Technical Committee on Soft Robotics) whose mission is to coordinate the research community;
since 2014, a newspaper dedicated to the deformable robotic is published every three months.
in France, a research team from INRIA has made it its specialty.

Innovation
One of the challenges to be met (including the repair of flexible robots) is to have flexible and elastic and waterproof glue. This seems to be about to happen: mid- 2017, academic physicists have succeeded in producing in the laboratory a highly elastic cyanoacrylate glue that can stick hard and / or soft substances (including electronic components) to hydrogels (materials like "Gels" used in certain medical devices and flexible robots). This opens the way for the creation of batteries and electrical circuits truly elastic and stretchable. The cyanoacrylate is associated with an organic component (which, without being a solvent, diffuses rapidly in the melt so as to prevent it becoming brittle). At the time of pressing the setting of the adhesive takes a few seconds 29. The elasticity can reach 2000%.

In 2017, the researchers succeeded in developing the first soft robot able to move without a motor or mechanical system, an innovation that, using memory alloys, opens the way to many possibilities in both aerospace and in nanoscopic research.

Source from Wikipedia