Vision of soft robots

In the realm of robotics, a new and exciting paradigm has emerged – the world of soft robots. These pliable and adaptable machines, inspired by nature itself, are revolutionizing the field with their unique capabilities. With their inherent flexibility, adaptability, and safety, soft robots are poised to revolutionize how we interact with machines and navigate our world. In the future, soft robots could seamlessly integrate into our daily lives, transforming industries and enhancing human experiences.

Here is a compilation of areas where soft robots hold the potential to make positive contributions:

1. In the healthcare sector, soft robots with their gentle touch and flexibility could support surgical procedures, deliver targeted therapies, and aid in rehabilitation. These robots could provide personalized and adaptive care, improving patient comfort and treatment outcomes.
2. In industries, soft robots revolutionize automation by effortlessly adapting to various product shapes and sizes. For example, soft grippers can increase efficiency, productivity, and customization in industrial processes, as they can conform to different surfaces and manipulate delicate objects.
3. Soft robots have the potential to thrive in exploration and search-and-rescue missions, adeptly navigating unstructured and challenging terrains like uneven surfaces, high radiation, or underwater environments. Equipped with sensing and feed-back control capabilities, they could autonomously adapt to changing conditions, providing critical assistance in disaster response scenarios.
4. Soft robots will also find their place in the realm of human-robot interaction. Their compliant and non-threatening nature will enable closer collaboration and cooperation between humans and robots. They will assist in physical tasks, support individuals with disabilities, and serve as interactive companions, or even offer emotional support and interactive companionship.

 Challenges in soft robotics: sensing, control, and integration

Despite the vast potential and rapid evolution of soft robotics, we took close attention to several challenges that need to be addressed to fully harness the capabilities of soft robots.

Challenge 1: dependence on rigid components for sensing and control

Soft robots require sensing and control systems to manipulate their compliant structures effectively. In the past, sensing and control systems in pneumatic robotics, for example, predominantly depended on rigid solenoid valves and bulky electronic components. However, this approach is still being employed in soft robots, despite their inherent incompatibility with the compliant and flexible characteristics of such robotic systems.

Specifically, whereas traditional rigid robots required interconnection of sensors, controllers, and regulators through intricate wiring and coding, attempting to incorporate these into the flexible bodies of soft robots undermines the primary advantages of mechanical compliance and adaptability that soft robots offer. Also, tethering soft robots to spatially isolated electronics restricts their operational range. Furthermore, these limitations severely constrain the potential applications of soft robots and environments where conventional electronic devices are impractical, such as in vivo settings, underwater environments, or in the presence of sparks or high radiation.

Challenge 2: seamless integration of components and miniaturization

Integrating components and achieving miniaturization are significant hurdles in the field of soft robotics. The successful development of functional and practical soft robots relies on seamlessly combining sensing and control components into a unified system, with all elements designed in soft forms. Although there have been advancements in creating soft counterparts to individual rigid components, effectively integrating these components into a compact, compatible, and lightweight form factor remains highly complex. This is particularly crucial in applications that demand agility, portability, and human-robot interaction, such as medical robotics and wearable devices.

 Our work and behind the story

We developed a soft self-sensing tensile valve (STV) capable of sensing and controlling of a soft pneumatic robot. This valve, constructed solely from flexible materials, detects its extension length, and accordingly adjusts its internal structure to output continuously controllable pressure states. The STV, with its cost-effective materials priced under $0.6, features a compact and lightweight tubular design measuring 5 mm in diameter. This 1D linear form factor, similar to that of widely used soft actuators (e.g., artificial muscles) and soft sensors, offers a substantial advantage for seamless integration across a wide range of applications. By integrating the sensing and control functions into this single soft valve, we hope to open up new exciting research opportunities and present a promising alternative to traditional electronic devices in the field of soft robotics. Now, here are some behind the story during developing the STV.

We first embarked on a mission to create a soft valve that could self-sense and continuously control a soft pneumatic actuator using only flexible materials. To achieve this, we conceived the idea of utilizing the continuous deformation of a soft material to regulate the inflow and outflow of air. After exploring various approaches, we discovered that by helically wrapping a yarn around a rubber tube, the structure would consistently deform under tension. This phenomenon. which we call “helical pinching”, occurred because the yarn naturally tightened under tension and deformed the internal structure of the rubber tube.

Nevertheless, we came to realize that simply wrapping a yarn around a single rubber tube would solely decrease the cross-sectional area of the chamber when subjected to tension, resulting in an increase in air flow resistance. In order to accomplish continuous control, it became evident that both the inflow and outflow chambers needed to undergo reciprocal and simultaneous transformations under the same tension. Hence, our subsequent objective revolved around developing a counter mechanism to address this challenge and achieve the desired reciprocal transformation of the inflow and outflow chambers.

To solve this, our approach involved utilizing two soft tubes with different diameters arranged along a central axis. This approach allowed the valve to have two separate air flow chambers (one from the inner tube and one from the space between inner and outer tube). Then we leveraged the helical pinching phenomenon by helically wrapping a yarn around the inner tube. Consequently, the whole inflow and outflow chamber structure underwent a natural and counter deformation. This ingenious design allowed the soft valve to regulate the inflow and outflow of air, thereby continuously controlling the pressure states and soft actuator's movement.

Importantly, this design presented a remarkable advantage in terms of its compactness, lightweight nature, contributing to the overall practicality of the STV. Additionally, through rigorous analytical analysis and numerical simulations, we were able to further program and customize the desired output behavior of the STV directly onto its structure, paving the way for adaptable performance and versatility in a range of applications. As an example of the STV usage, we developed a soft assistive exosuit that can detect the movement of a desired body part and accordingly control the exosuit's actuator in a programmable manner. Through continued research, we anticipate that in the future, soft robots will be able to achieve various control functions using valve logic or memory, enabling them to intelligently adapt to continuously changing and unfamiliar environments.

 Conclusion

As soft robotics continues to advance, breakthroughs in materials, sensors, and control systems will push the boundaries of what is possible. By leveraging the unique helical pinching mechanism, we have paved the way for exciting developments in soft robotics. By further fostering interdisciplinary collaboration and merging knowledge in robotics, materials science, biology, and artificial intelligence, we can unleash the complete capabilities of soft robots and seamlessly incorporate them into our everyday lives. We are thrilled to contribute and be part of this exciting future.