THURSDAY, 25 JULY 2024
SOFT ROBOTSMost robots in use today are present in industry, where they perform the same repeatable automated tasks. Robots operate through two mechanisms. Firstly, they sense the environmental cues and encode these cues into an electronic current. Then, once the robot processes this signal, an actuator converts the response signal into physical motion so the robot can respond to the environmental cue. To expand the scope of robotic applications, a variety of factors like design, adaptability to the environment, and learning capabilities have to be considered. A big part allowing future robots to achieve this functionality is working out how we can replace the same metallic sensor and actuator components with soft materials that function similarly to humans.
FLEXIBLE SENSORS
Flexible sensors, also known as soft sensors, are designed with materials that are more flexible and are often characterised by their high stretchability and their lack of traditional hard metallic materials. There have been a variety of massive strides in the field in recent years. One such recent development has been conductive elastomers. Elastomers are materials that can recover their original shape even after being stretched to multiple times their original length. By loading classic silicone elastomers with conductive particles and then stretching them, this generates a change in the charge distribution of the conductive particles. This in turn leads to a change in the electrical conductivity, creating a signal. Conductive elastomers can be used in conjunction with thermally or magnetically-activated sensors, which allows a variety of different environmental stimuli to be received. An incredible example of the application of conductive elastomers is in recently-developed “smart” materials and wearable electronics, where stretches in sensors integrated into clothing items can be used to sense human locomotion, respiratory rate, and a variety of other vital signs during everyday activities.
Another example are optical fibre-based flexible sensors. These sensors change shape in response to external stimuli such as light, heat, and pressure and this leads to a change in the wavelength of light refracted by the optical fibres. This refracted light is then absorbed by a wavelength modulator, or photodetector (light sensing devices), to be converted into a signal that can be used to sense the type of mechanical deformation done on the sensor. Although not the quickest sensors, with a significant delay in their activation and responsiveness, these sensors are being developed for a variety of applications. They are used in robot exoskeletons to detect user movements, in construction-based robotics to sense ground movement in concrete and soil, and in medical robotics to give doctors feedback on pressure being applied during surgery.
IONIC CONDUCTIVITY
Once the sensor has interpreted the stimuli, the signal is sent to determine a response in a number of ways. Although many electronically-conductive silicones are being used today for this purpose, an incredible new alternative has been developed: ionically-conductive soft materials. In response to the buildup of charges on an electrode, ionic interactions cause changes in charge distributions that can then be used to conduct charge over short ranges. This has been a powerful tool in a variety of fields, including bioelectronics where biological materials and systems are used in conjunction with electronic devices. The issue with traditional electronically-conductive soft materials is their incompatibility with biological systems. However, ionically-conductive soft materials can be used to create robots that directly interface with human body systems to sense chemical charge. Also, these soft materials have been instrumental in the development of robotic artificial muscles that mimic the ionically-driven tensing and stretching of actual muscles that could then be used in prosthetics and humanoid robots.
SOFT ACTUATORS
Once the signal is processed, the last step is to send out a response signal so that the robot can then react to the environmental stimuli. Actuators have the job of converting this signal to a physical response, with one such example being pneumatic actuators. By changing the signal into air or gas pressure to induce movement in soft robots, pneumatics are great for generating movement in any soft, deformable materials.
Therefore, these actuators are widely used in soft medical devices that require accuracy and precision, grippers that need the deformable nature of these materials, and crawling robots where simultaneous pneumatically-driven movements can be used to induce robot locomotion on hard surfaces. Another category is dielectric elastomer actuators. These actuators function by applying an electric field to a soft elastomeric material, causing it to deform and change shape. The actuation mechanism is advantageous because of its high responsiveness and ability to simulate natural muscle movements.
APPLICATIONS
The research scope of soft sensors, actuators, and everything in between has been remarkable, with more and more research being done every day to improve understanding of what we can accomplish with these devices. The transformative potential of soft robotics is evident if we look past the industrial applications. In medicine, these devices are being used to create safe tools through which doctors can perform surgery or easily monitor vital signs while removing the risk of human error or blunt injury. Soft robot parts have also been used to simulate lifelike creatures in aquatic and natural environments. A team of researchers created a turtle-like robot with soft, morphing limbs so that the turtle could travel by both land and water - the first instance of robots that could easily adapt to natural environments. At Harvard, scientists created the “octobot”: a squishy robot that f its in the palm of your hand and is the first robot with no hard electronic components. For those with mobility impairments, soft robotic exoskeletons can play a crucial role in rehabilitating those with paralysis or stroke victims. These examples hold one thing in common: soft materials in robots have completely transformed the environments, locomotive functions, and safety with which future robots can function.
FUTURE OF SOFT ROBOTICS
The integration of soft sensors and actuators into robotics has brought numerous changes to robotic functionality and adaptability. From wearable electronics and medical breakthroughs to human-like robot parts capable of directly interacting with society, soft robots could revolutionise our everyday lives. So maybe, 30 years into the future, you may find your packages being delivered by a soft robotic drone, “smart material” being used in your clothing to sense your vital signs so it can tell you to run faster, and surgery being carried out by soft robotic hands. When that moment comes, you can think back to how soft robots and materials really have transformed the way we live.
Artwork by Charles Micou.
