A Miniature Jumping Robot with Flea-inspired Catapult System: Active Latch and Trigger

Small creatures have inherent mobility problems due to their stride limitation and small body size compared to surroundings. Meanwhile, some of them, such as locusts and fleas, have evolved to acquire better mobility by employing saltatorial (jumping) locomotion. In the similar context, the mobility of small-scale robots can be improved by jumping. To date, several small-scale jumping robots have been developed; the jumping robot Grillo is designed for long and consecutive jumping gait [1]. A steerable miniature jumping robot shows great jumping height and steering ability [2]. The closed elastica robot employs snap-through buckling for jumping [3]. They commonly employ the catapult system with passive latch; each of the mechanism lacks active trigger. This paper presents 1g flea-inspired jumping robot. A flea is well-known for its dramatic jumping ability: 100 times as high as its body length. This outstanding performance is contributed to the special catapult system. Known as active latch and trigger, the system generates excellent catapult motion in the cramped anatomy [4][5]. This inspired us to develop extremely small and light jumping robot without conceding the performances. Shape memory alloy (SMA) spring is employed not only as actuator but also as energy storage element in the robot. In fabrication, smart composite microstructure (SCM) process is used for several advantages in small-scale robots: embedded electrical circuit design, machining efficacy, and light weight of the robot [6][7]. In the following sections, we first introduce the detailed mechanism of active latch and trigger system. Equation of motion and its numerical solution are presented to predict the theoretical jumping performance of the robot. Jumping motion of the prototype is captured by high speed camera and analyzed. In this paper, we reinterpreted the flea's active latch system in the mechanical point of view. The kernel of the mechanism is expeditious reversal of joint torque. When the leg is full-flexed, counter clockwise latching torque is generated as the extensor applies tensile force (Fig.1.a). Due to the structural constraint, the full flexion of the leg, the torque does not generate any motion. However large tensile force the extensor applies, the system does not unlock , rather latches itself more firmly. When the trigger pulls the extensor tendon left (Fig.1.b), the line of tensile force moves slightly but creates a completely different situation; the latching torque is reversed to clockwise actuating torque. At this moment, the triggering requires only small force and stroke. Thus, the torque …