Origami-inspired soft pneumatic robots for safe human-robot interaction

Abstract

Fast-growing interests in safe and effective robot-environment/human interactions have stimulated wide investigations on soft robotics. Soft robotics is a quickly emerging field showing great potentials in wearable, service, and biomimetic robot applications. Such applications emphasize substantially on robot compliance and safety, together with low system complexity and cost. This feature list led to investigations on novel soft robotic actuators fundamentally distinctive from the electric motors widely adopted today. However, further development of soft robots towards more effective and controllable performance is constrained due to the high nonlinearity of soft robots with their hyper-elastic soft materials and complex motions which drastically reduce their force capability and increase the difficulties in precise system modeling and control. Significant improvements on the fundamental design principals, modeling, fabrication and control approaches of soft robots for human-robot interactive applications are emphasized in this thesis to address those limitations. These efforts will provide insightful references for the soft-robotic approach to safe interaction and pave the way of soft robots to wider applications. In this thesis, an origami-inspired design approach with automation fabrication method is proposed for achieving significant improvements on soft actuators performance and facilitating fully-customizable actuator design and fabrication toward the desired performance. Based on the developed approach, three types of origami-inspired pneumatic soft actuators: fiber-reinforced origamic robotic actuator (FORA), bidirectional linear soft actuator (BLSA) and soft origami rotary actuator (SoRA), are proposed with customizable superior performance. In addition to a high degree of customization, high performance linearity of actuator is brought by the novel origami design, which further efficiently simplifies the modeling process. The unique working mechanism of origami structures, taking advantages of the origami structure rearrangements to generate desired motion instead of materials inflation and stretch, makes the energy loss in materials inflation could be ignored in the modeling of actuators. Hence, the developed analytical models of three origami-inspired pneumatic soft actuators could precisely describe the actuator performance, including motion range, force capability and stiffness. These efforts could be further used to guide the actuator control towards safe human-robot interaction. Based on the derived analytical models, a hybrid controller is developed with actuator-position servo and stiffness/compliance tuning, achieving the balance of fast trajectory-following capability and safe robot-environments/humans interactions in a behavioral level. This distinctive controller, characterized by the pneumatic system with inner-loop pressure and outer-loop position feedback, could effectively ensure the precise and safe pressure regulation for the system, and provide external position and compliance setting for the desired performance. A comprehensive guideline is formulated from modeling, design, fabrication and control, to the customization of soft robotic actuation systems. Following this guideline, the developed three types of origami-inspired pneumatic soft actuators, showing high performance linearity, large force/torque output, fast trajectory-following capability and compliant robot-environment interactions, significantly facilitate effective human-robot interactive applications. Applications in wearable robotic devices are explored, with two soft robotic gloves developed from soft linear actuators and a soft elbow device from soft rotary actuator, demonstrating the great potentials and promising perspectives of origami-inspired pneumatic soft actuators for human-robot interaction.