A Crawling Based Locomotive Mechanism Using a Tiny Ultrasonic Linear Actuator

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39th International Symposium on Robotics 2008 Seoul, Korea / October 15~17, 2008

Proceedings of the 39nd ISR(International Symposium on Robotics), 15~17 October 2008

A Crawling Based Locomotive Mechanism Using a Tiny Ultrasonic Linear Actuator (TULA) Hyunjun Park, Byungkyu Kim School of Aerospace and Mechanical Engineering Korea Aerospace University 100, Hanggongdae gil, Gyeonggido, Korea E-mail : bkim@kau.ac.kr Jong-Oh Park School of Mechanical System Engineering Chonnam National University Korea Seok-Jin Yoon Thin Film material Research Center KIST Korea

Abstract A crawling based locomotive mechanism for inspection of small sized pipes is developed by using a tiny ultrasonic linear actuator. In case of piezo material based actuators, it is known that they have small displacement with high voltage supply. In order to overcome the limitation of common piezo actuators, the impact based piezo actuator(TULA) has been developed to realize long stroke up to 11 mm. By using TULA, we develop a crawling locomotive mechanism. Previously reported locomotive mechanisms such as earthworm-like and inchworm-like mechanism can not realize continuous motion but move with step-wise motion since they have clamping and elongation sequence for movement. Therefore, long time loss for movement of one stroke is inevitable. In this crawling mechanism, nearly continuous motion is achieved by using both directions of actuating forces. Owing to the light weight and the simple structure of the actuator, the crawling based locomotive mechanism has simple design with 9mm diameter, 40mm length and 1.1g weight. It shows 9.2mm/s in 18.5mm inside diameter of a pipe regardless of the pipe’s tilting angle. 1. Instruction The development of modern industries brought about the complexity of machines and devices and they require smallsized in-pipe locomotive mechanisms for inspection and repair. Since large-sized in-pipe locomotive mechanisms [1] using conventional motors are not suitable for the inspection of complex devices, the researches on micro in-pipe moving mechanisms using micro motors [2,3], micro pneumatic actuators [4,5] and smart material based actuators such as piezo actuators [6,7] and SMA (shape memory alloy) actuators [8,9] are carried out. The micro motor is tiny, but it requires additional devices to convert rotating motion into linear motion for actuating of locomotive mechanism. The micro pneumatic actuator has flexibility, compactness and high generative force. But, it always has to connect to pneumatic power source and the pneumatic line causes high friction force between pipe wall and body of locomotive mechanism. On the other hand, SMA has such slow

actuating speed since it actuates based on joule heating. In case of the piezo actuator, it generates small displacement although it produces rapid actuating speed and high generative force. Therefore, the novel impact based ultrasonic PZT linear actuator (Tiny Ultrasonic Linear Actuator, TULA) has been developed, which generates larger amounts of displacement compared to conventional piezo actuators. It enables to embody locomotive mechanism with long stroke [10]. The typical locomotive mechanism using the linear actuator is earthworm-like and inchworm-like mechanism [8, 9]. Such locomotive mechanisms cannot move continuously due to working principal consisted of clamping and moving sequences. Therefore, the crawling based locomotive mechanism utilizing both directions of actuating forces of the linear actuator is developed. In order to investigate locomotion efficiency of the proposed locomotive mechanism, it is tested under various diameters and tilting angles of pipe.

Figure 1. Fabricated TULA(Tiny ultrasonic linear actuator)

2. An impact based piezo actuator The developed piezo linear actuator is shown in figure 1, TULA is composed of piezoelectric ceramics, elastic material, a housing element to fix piezoelectric ceramics and a shaft to guide a moving...
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