External-pipe-climbing piezoelectric actuator with high climbing/towing capability and untethered movement

To accomplish high climbing/towing capability and untethered movement, a miniature external-pipe-climbing piezoelectric actuator (MEPCPA) is developed by integrating a pair of wing-shaped transducers driven by piezoelectric stack plates and an onboard circuit. Here, the transducers provide the climbing and clamping functions with the driving feet and the spring, respectively; these interestingly imitate the propelling and hugging functions of the sloth’s lower and upper limbs. The micro controller, boost module, and transistors arranged in the H-bridge shape form the minimum system of a lightweight onboard circuit. To verify our proposal, first, by constructing a vibration model, the transducer was designed to enhance the driving force without excessively increasing the weight. Meanwhile, the friction coefficient was modified by considering the surface roughness to predict the climbing/towing performance. Then, a prototype whose mechanical part had the size of 52 × 35 × 72 mm³ and the weight of 20.5 g was fabricated for performance assessment. In a tethered manner, the MEPCPA climbed up the glass tube vertically, towed the maximal weight of 120 g (equal to 5.9 times the mechanical part’s weight), and yielded the maximal speed of 103.8 mm/s. Installed with a 12-V 300-mAh battery, the MEPCPA successfully climbed up the tube having the tilting angle of 45° with the ground and it produced the maximal towing weight, the maximal climbing speed, and the minimal stepwise displacement of 20 g, 18 mm/s, and 0.36 μm, respectively, at the tilting angle of 30° To the best of our knowledge, this study is an initial report regarding piezoelectric actuators climbable in an untethered manner, and provides fundamental technique for designing miniature piezoelectric actuators potentially applicable to narrow environments particularly lacking external power source.