The term “soft robots” designs a broad class of robotic systems whose architecture includes soft elements, with much higher elasticity than traditional rigid robots. Articulated Soft Robots are robots with both soft and rigid parts, inspired to the muscloloskeletal system of vertebrate animals – from reptiles to birds to mammalians to humans. Compliance is typically concentrated in actuators, transmission and joints (corresponding to muscles, tendons and articulations) while structural stability is provided by rigid or semi-rigid links (corresponding to bones in vertebrates).
The other subgroup in the broad family of soft robots includes continuum soft robots, i.e. robots whose body is a deformable continuum, including its structural, actuating and sensing elements, and take inspiration from invertebrate animals such as octopuses or slugs, or parts of animals, such as an elephant trunk.
Soft robots are often designed to exhibit natural behaviours, robustness and adaptivity, and sometimes mimick the mechanical characteristics of biological systems.
Articulated Soft Robots are built taking inspiration from the intrinsic properties of muscle-skeletal system of vertebrates, whose compliant nature enables humans and animals to effectively and safely perform a large variety of tasks, ranging from walking on uneven terrains, running, and climbing, to grasping and manipulating. It also makes them resilient to highly dynamic, unexpected events such as impacts with the environment. The interplay of the physical properties of vertebrates with the neural sensory-motor control makes motion very energy–efficient, safe and effective.
Robots able to co-exist and co-operate with people and reach or even surpass their performance require a technology of actuators, responsible for moving and controlling the robot, which can reach the functional performance of the biological muscle and its neuro-mechanical control.
The most promising class of actuators for soft robots is the class of Variable Impedance Actuators (VIA) and the subclass of Variable Stiffness Actuators (VSA), complex mechatronic devices that are developed to build passively compliant, robust, and dexterous robots. [1] VSAs can vary their impedance directly at the physical level, thus without the need of an active control capable to simulate different stiffness values. The idea of varying the mechanical impedance of actuation comes directly from natural musculo-skeletal systems, which often exhibit this feature. [2] [3] [4]
A class of Variable Stiffness Actuators achieve simultaneous control of the robot by using two motors antagonistically to manipulate a non-linear spring which acts as an elastic transmission between each of the motors and the moving part, so as to control both the equilibrium point of the robot, and its rigidity or compliance. [5] [6]
Such control model is very similar in philosophy to Equilibrium-Point hypothesis of human motor control. This similitude makes soft robotics an interesting field of research capable to exchange ideas and insights with the research community in motor neuroscience. [7]
Variable Impedance Actuators increase the performance of the soft robotics systems in comparison with the traditional rigid robots in three key aspects: Safety, Resilience and Energy-Efficiency.
One of the most revolutionary and challenging features of the class of articulated soft robots is Physical Human-Robot Interaction. Soft robots designed to physically interact with people are designed to coexist and cooperate with humans in applications such as assisted industrial manipulation, collaborative assembly, domestic work, entertainment, rehabilitation or medical applications. Clearly, such robots must fulfill different requirements from those typically met in conventional industrial applications: while it might be possible to relax requirements on velocity of execution and absolute accuracy, concerns such as safety and dependability become of great importance when robots have to interact with humans. [8]
Safety can be increased in different ways. The classical methods include control and sensorization, e.g. proximity-sensitive skins, or the addition of external soft elements (soft and compliant coverings or airbags placed around the arm for increasing the energy-absorbing properties of protective layers).
Advanced sensing and control can realize a “soft” behavior via software. [9] Articulated Soft Robotics realizes a different approach at increasing the safety level of robots interacting with humans by introducing mechanical compliance and damping directly at the mechanical design level., [10] [11]
“By this approach, researchers tend to replace the sensor-based computation of a behavior and its error-prone realization using active actuator control, by its direct physical embodiment, as in the natural example. Having compliance and damping in the robot structure is by no means sufficient to ensure its safety, as it might indeed be even couterproductive for the elastic energy potentially stored: just like a human arm, a soft robot arm will need intelligent control to make it behave softly as when caressing a baby, or strongly as when punching”. [12]
Physical interaction of a robot with its environment can also be dangerous to the robot itself. Indeed, the number of times a robot is damaged because of impacts or force overexertion is rather large.
Resilience to shocks is not only instrumental to achieve viable applications of robots in everyday life, but would also be very useful in industrial environments, substantially enlarging the scope of applicability of robot technology.
Soft robotics technologies can provide solutions that are effective in absorbing shocks and reducing accelerations: soft materials can be used as coverings or even as structural elements in robot limbs, but the main technological challenge remains with soft actuators and transmissions. [13]
The dynamic behavior of the actuators with controllable compliance guarantees high-performance, lifelike motion and higher energy efficiency than rigid robots. [14]
The natural dynamics of the robot can adapt to the environment, and thus the intrinsic physical behavior of the resulting system is close to the desired motion. In these circumstances, actuators would only have to inject and extract energy into and out of the system for small corrective actions, thus reducing energy consumption. [15]
The idea of embodying desirable dynamics in the physical properties of soft robots finds its natural application in humanoid robots, having to resemble the movements of humans, or in robotic systems realized for prosthetic uses, e.g. anthropomorphic artificial hands. A relevant example of use is in and walking/running robots: [16] indeed, the fact that natural systems change the compliance of their muscular system depending on the gait and environmental conditions, and even during the different phases of the gait, seem to indicate the potential usefulness of Variable Impedance Actuators (VIA) for locomotion. [17] An emerging trend of use of VIA technologies is connected to the growing of a novel category of industrial robots connected to Industry4.0, the Co-Bots.
Exploration of soft robots’ full potential is leading to more and more applications in which the robots overcome conventional- robot performance, and it is widely believed that more applications are yet to come [18]
Dario Floreano is a Swiss-Italian roboticist and engineer. He is Director of the Laboratory of Intelligent System (LIS) at the École Polytechnique Fédérale de Lausanne in Switzerland and was the founding director of the Swiss National Centre of Competence in Research (NCCR) Robotics.
A virtual fixture is an overlay of augmented sensory information upon a user's perception of a real environment in order to improve human performance in both direct and remotely manipulated tasks. Developed in the early 1990s by Louis Rosenberg at the U.S. Air Force Research Laboratory (AFRL), Virtual Fixtures was a pioneering platform in virtual reality and augmented reality technologies.
Adaptable Robotics refers to a field of robotics with a focus on creating robotic systems capable of adjusting their hardware and software components to perform a wide range of tasks while adapting to varying environments. The 1960s introduced robotics into the industrial field. Since then, the need to make robots with new forms of actuation, adaptability, sensing and perception, and even the ability to learn stemmed the field of adaptable robotics. Significant developments such as the PUMA robot, manipulation research, soft robotics, swarm robotics, AI, cobots, bio-inspired approaches, and more ongoing research have advanced the adaptable robotics field tremendously. Adaptable robots are usually associated with their development kit, typically used to create autonomous mobile robots. In some cases, an adaptable kit will still be functional even when certain components break.
RHex is an autonomous robot design, based on hexapod with compliant legs and one actuator per leg. A number of US universities have participated, with funding grants also coming from DARPA.
Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots. Robotics is related to the sciences of electronics, engineering, mechanics, and software.
Robotics is the interdisciplinary study and practice of the design, construction, operation, and use of robots.
William Ward Armstrong is a Canadian mathematician and computer scientist. He earned his Ph.D. from the University of British Columbia in 1966 and is most known as the originator Armstrong's axioms of dependency in a Relational database.
A mobile manipulator is a robot system built from a robotic manipulator arm mounted on a mobile platform.
The impedance analogy is a method of representing a mechanical system by an analogous electrical system. The advantage of doing this is that there is a large body of theory and analysis techniques concerning complex electrical systems, especially in the field of filters. By converting to an electrical representation, these tools in the electrical domain can be directly applied to a mechanical system without modification. A further advantage occurs in electromechanical systems: Converting the mechanical part of such a system into the electrical domain allows the entire system to be analysed as a unified whole.
Impedance control is an approach to dynamic control relating force and position. It is often used in applications where a manipulator interacts with its environment and the force position relation is of concern. Examples of such applications include humans interacting with robots, where the force produced by the human relates to how fast the robot should move/stop. Simpler control methods, such as position control or torque control, perform poorly when the manipulator experiences contacts. Thus impedance control is commonly used in these settings.
Tendon-driven robots (TDR) are robots whose limbs mimic biological musculoskeletal systems. They use plastic straps to mimic muscles and tendons. Such robots are claimed to move in a "more natural" way than traditional robots that use rigid metal or plastic limbs controlled by geared actuators. TDRs can also help understand how biomechanics relates to embodied intelligence and cognition.
As humans move through their environment, they must change the stiffness of their joints in order to effectively interact with their surroundings. Stiffness is the degree to a which an object resists deformation when subjected to a known force. This idea is also referred to as impedance, however, sometimes the idea of deformation under a given load is discussed under the term "compliance" which is the opposite of stiffness . In order to effectively interact with their environment, humans must adjust the stiffness of their limbs. This is accomplished via the co-contraction of antagonistic muscle groups.
Mechanical–electrical analogies are the representation of mechanical systems as electrical networks. At first, such analogies were used in reverse to help explain electrical phenomena in familiar mechanical terms. James Clerk Maxwell introduced analogies of this sort in the 19th century. However, as electrical network analysis matured it was found that certain mechanical problems could more easily be solved through an electrical analogy. Theoretical developments in the electrical domain that were particularly useful were the representation of an electrical network as an abstract topological diagram using the lumped element model and the ability of network analysis to synthesise a network to meet a prescribed frequency function.
Robotic prosthesis control is a method for controlling a prosthesis in such a way that the controlled robotic prosthesis restores a biologically accurate gait to a person with a loss of limb. This is a special branch of control that has an emphasis on the interaction between humans and robotics.
Soft robotics is a subfield of robotics that concerns the design, control, and fabrication of robots composed of compliant materials, instead of rigid links. In contrast to rigid-bodied robots built from metals, ceramics and hard plastics, the compliance of soft robots can improve their safety when working in close contact with humans.
Antonio Bicchi is an Italian scientist interested in robotics and intelligent machines. He is professor at the University of Pisa and senior researcher at Istituto Italiano di Tecnologia in Genoa. He is an adjunct professor at the School of Biological and Health Systems Engineering of Arizona State University in Tempe, Arizona, US.
A continuum robot is a type of robot that is characterised by infinite degrees of freedom and number of joints. These characteristics allow continuum manipulators to adjust and modify their shape at any point along their length, granting them the possibility to work in confined spaces and complex environments where standard rigid-link robots cannot operate. In particular, we can define a continuum robot as an actuatable structure whose constitutive material forms curves with continuous tangent vectors. This is a fundamental definition that allows to distinguish between continuum robots and snake-arm robots or hyper-redundant manipulators: the presence of rigid links and joints allows them to only approximately perform curves with continuous tangent vectors.
Sami Haddadin is an electrical engineer, computer scientist, and university professor in the field of robotics and artificial intelligence (AI). Since April 2018, he has been the executive director of the Munich Institute of Robotics and Machine Intelligence (MIRMI) at the Technical University of Munich and holds the Chair of Robotics and Systems Intelligence.
A peristaltic robot, also known as a worm-bot, is a robot that uses peristaltic locomotion to move, mimicking the movement of earthworms. Peristaltic locomotion relies on compressions and expansions of the metameres, or body segments, of earthworms. This method of movement is especially effective in navigating through narrow and intricate surfaces, making it particularly suitable for small millimeter-scale robots. Peristaltic robots have a wide range of applications, including endoscopy, mining operations, and pipe inspections.
Force control is the control of the force with which a machine or the manipulator of a robot acts on an object or its environment. By controlling the contact force, damage to the machine as well as to the objects to be processed and injuries when handling people can be prevented. In manufacturing tasks, it can compensate for errors and reduce wear by maintaining a uniform contact force. Force control achieves more consistent results than position control, which is also used in machine control. Force control can be used as an alternative to the usual motion control, but is usually used in a complementary way, in the form of hybrid control concepts. The acting force for control is usually measured via force transducers or estimated via the motor current.