Design, Mobility Analysis and Gait Planning of a Leech-like Soft Crawling Robot with Stretching and Bending Deformation

Soft climbing/crawling robots have been attracting increasing attention in the soft robotics community, and many prototypes with basic locomotion have been implemented. Most existing soft robots achieve locomotion by planar bending deformation and lack sufficient mobility. Enhancing the mobility of soft climbing/crawling robots is still an open and challenging issue. To this end, we present a novel pneumatic leech-like soft robot, Leechbot, with both bending and stretching deformation for locomotion. With a morphological structure, the robot consists of a three-chambered actuator in the middle for the main motion, two chamber-net actuators that act as ankles, and two suckers at the ends for anchoring on surfaces. The peristaltic motion for locomotion is implemented by body stretching, and direction changing is achieved by body bending. Due to the novel design and two deformation modes, the robot can make turns and transit between different surfaces; the robot, hence, has excellent mobility. The development of the robot prototype is presented in detail in this paper. To control its motion, tests were carried out to determine the relationship between step length and air pressure as well as the relationship between motion speed and periodic delay time. A kinematic model was established, and the kinematic mobility and surface transitionability were analyzed. Gait planning based on the inflating sequence of the actuating chambers is presented for straight crawling, turn making, and transiting between surfaces and was verified by a series of experiments with the prototype. The results show that a high mobility in soft climbing/crawling robots can be achieved by a novel design and by proper gait planning.