Overview of actuators, modeling, and control methods for soft manipulators

Inspired by the biological organs in nature, many robots have been developed and successfully applied by imitating the characteristics of different animals. The design inspiration of a soft robot comes from the bending movement of an elephant trunk and an octopus arm. They can use their soft structure to effectively adapt to a complex and changeable environment and complete various complex operations. Their excellent flexibility and bending have attracted the interest of researchers. Continuing breakthroughs in materials science, chemistry, control, and other disciplines, and in the observation and modeling of soft organisms such as the octopus, worm, and starfish have led to a new robot research direction—soft robot. Soft manipulators are made of soft materials and can be used to accomplish tasks that rigid manipulators cannot accomplish, such as detecting in an unstructured environment, grasping fragile objects, and safer man-machine cooperation. Many countries are investing in this area; soft manipulators of various shapes and functions have been designed, using different manufacturing materials and driving, modeling, and control methods, exhibiting the uniqueness of each device. The driving ways of the soft manipulator are different according to their task purposes. This paper first studies three main driving ways of the soft manipulator: (1) tendon driving (tendon driving), (2) shape memory alloy driving (SMA driving), and (3) pneumatic driving (pneumatic driving). Modeling and control methods of soft manipulators in different driving modes are then studied. Finally, the development of soft manipulators is summarized and prospected from three aspects: (1) driving way, (2) modeling methods, and (3) control methods.