Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
2011 IEEE International Conference on Robotics and Automation Shanghai International Conference Center May 9-13, 2011, Shanghai, China Endoskeletons using Composite Flexure Joint for BioMimetic Meso-scale Robot Je-Sung Koh, Kyu-Jin Cho, Member, IEEE Abstract— In this video, composites and a polymer flexure joint are used to design mechanical elements. This composite structure can be applied to endoskeleton structures of biomimetic meso-scale robot. The basic active unit of the structure is a revolute joint with an SMA spring actuator that imitates a joint and muscle formation. The conventional mechanical element is replaced by composite structures design on 2D pattern. Using these elements, prototypes of a robot are fabricated to verify feasibility of application of the robot. A I. INTRODUCTION LL THINGS LIVING in nature have their own skeletons to maintain their shape and produce locomotion. Mammals and birds have bones that form an endoskeleton. Insects and some sea animals have a cuticle shell that form an exoskeleton. And mollusks and an annelid, like an earthworm, have an integument that form a hydraulic skeleton. The type of skeleton determines how an animal moves as a whole structure. Similarly, a robot has a main frame that produces motion and forms its body shape. In the design of a robot, first the main skeleton structure and its model are established. Although there are several kinds of skeletons, a model is created using rigid links and joints to simplify the skeleton structure. The rigid link and joint modeling is widely used because of simplicity and ease of control and fabrication. Basically, the rigid link and joint modeling is an endoskeleton, which becomes the frame of the robot. In a small scale below the millimeter range, a novel fabrication method based on composites and polymer films, Fig. 1 Replacement of revolute joint in meso-scale the so called ‘Smart Composite Microstructures (SCM)’, is introduced [1]. The SMA spring actuator is implemented as an artificial muscle on the composite structures, and becomes a basic active joint unit, as shown in Fig. 1. This unit replaces the conventional small-scale mechanical elements. The robot frame is composed of many mechanical components such as a revolute joint, universal joint, rigid link etc. The design area of the meso-scale robot would be expanded by development of these components with composites and flexure joints in small scale. II. MESO-SCALE MECHANICAL ELEMENTS Many mechanical elements are used to make a robot. Composite flexures are used to make these mechanical elements. In order to produce mechanical elements with composite flexure, it needs different design based on 2D pattern. A. Revolute Joint Unit An R-joint element performs a simple flexure. As shown in Fig. 2, the revolute joint is just a composite folding joint at the flexure. The joint’s stiffness and strength are determined by Fig. 2 Concept design of basic active unit Authors are with the School of Mechanical and Aerospace Engineering, Seoul National University (e-mail:kjs15, [email protected]). This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF); the program was funded by the Ministry of Education, Science, and Technology (Grant No. 2010-0001201, 2010-0015500) 978-1-61284-385-8/11/$26.00 ©2011 IEEE 2966 Fig. 3 Replacement of multi DOF joint in meso-scale[2][3] Fig. 4 Foldable joint using SMA torsional spring actuator Fig. 5 Prototype of foldable structure the length and thickness of the flexure. B. Spherical 6-bar Linkage We employed a special pattern design on a 2D plane, namely, the spherical 6-bar linkage folding pattern (Fig. 3). It makes a motion of bending and steering of linkage. The maximum angle of bending and steering is designed according to the angle of the flexure joint axis. The spherical 6-bar linkage has 3 degrees of freedom. The stiffness of the flexure makes it possible to be passive stable joint. The linkage with this passive joint is controlled by two actuators. It generates 2DOF motions. C. Active Foldable Unit A composite flexure structure is foldable. However, previous active joint element with linear spring actuator had difficulty in bending 180 degrees because the artificial muscle actuator was an obstacle. With the torsional SMA spring actuator, the link can fold 180 degrees as shown in Fig. 4. III. MESO-SCALE ROBOTIC APPLICATION With the mechanical element described in previous chapter, a small crawling robot inspired by the inchworm and foldable structures are developed to verify the application feasibility (a) of design robot. The rigid links are made of glass fiber composite and flexure joints are made from a copper laminated Kapton(Poly-imide) film. The copper laminated Kapton can be made into a flexible electric circuit after an etching process. SMA soldered on copper is activated by an electric current of 0.5~0.2A according to the wire diameter and material properties. A. Crawling Robot Inspired by Inchworm: Omegabot The crawling robot inspired by the inchworm is developed with a single flexure joint and spherical 6-bar linkage structures (Fig. 5 (a)). Inchworm crawls with an omega (Ω) shape bending motion and steering motion. The robot structures need joints of multi degree of freedom to generate the inchworm’s motion. The combination of single flexure and spherical 6-bar linkage enables three or higher DOF. B. Meso-scale Gripper inspired by prolegs With a series connection of small scale revolute joints, the soft tissue of the caterpillar’s prolegs can be replaced. Closed loop of 6 links can make the gripping motion with the spine? as shown in Fig. 5 (b). The gripper inspired by prolegs has 1.5cm length and about 5mm thickness. It makes a mechanical gripping force with spines on a rough surface such as those of trees, fabric cloth etc. C. Meso-scale Foldable Structure The foldable structure converts its body frame from a compact folded state to a larger functional state. Foldable structures consist of composite links, flexure joints and SMA torsional spring actuators. Fig. 6 shows the folding sequence of the prototype of foldable structures. Four links are folded by SMA torsional spring actuators. REFERENCES [1] [2] (b) Fig. 6 (a) Crawling robot inspired by Inchworm (b) Meso-scale gripper [2][3] [3] 2967 R.J. Wood, S. Avadhanula, R. Sahai, E. Steltz, and R.S. Fearing, “Microrobot design using fiber reinforced composites,” Journal of Mechanical Design, vol. 130, 2008, p. 052304. J. Koh and K. Cho, "Omegabot: Biomimetic Inchworm Robot using SMA coil actuator and Smart Composite Microstructures(SCM)", Proceedings of the 2009 IEEE International Conference on Robotics and Biomimetics(RoBio 2009), 2009, pp.1154-1159. J. Koh and K. Cho, “Omegabot: Crawling Robot Inspired by Ascotis Selenaria”, Proceedings of the 2010 IEEE International Conference on Robotics and Automation, 2010, pp.109-114.