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Communications in Control Science and Engineering (CCSE) Volume 2, 2014
Small Scale Parallel Manipulator Kinematics for Flexible Snake Robot Application Raisuddin Khan*1, Md. Masum Billah2, Mitsuru Watenabe3, Amir Akramin Shafie4 Depart ment of Mechatronics Engineering, International Islamic University Malaysia, 53100 Kuala Lumpur, Malaysia *1
2
3
4
raisuddin@iium.edu.my; mdmasum.b@live.iium.edu.my; nabe@yahoo.com; aashafie@iium.edu.my
Abstract A small-scale parallel manipulator is designed in this paper. The kinematic analysis of the manipulator is also elucidated for the development of multilinked snake robot. A compliant central colum is used to connect two parallel platforms of Incompletely Restrained Positioning Mechanism (IRPM). The compliant column allows the configuration to achieve 3 DOFs with 3 tendons of active materials connected between the upper and loer platform of the mechanism. In particular, this investigation f ocuses on the angular deflection of the upper platform with respect to the lower platform. The application here is a imed at developing an active linkable module that can be connected to one another so as to f orm a “snake robot” of sorts. For an arbitrary angular displacement of the platforms, the corresponding length of each tendon can be determined through inverse kinematics. From the experimental result, the extreme bending of the central column plane of 30° angular displacement with the of the horizontal axis. Keywords 3 DOF; Stewart Platform; Tendon
Introduction During the last two decades research continued on parallel robots, and today many, especially the planar parallel manipulators have found their way into practical applications such as positioning devices, motion generators, an d [1] ultra-fast pick and place robots . P erhaps the most well-known and widely used parallel robot is the Stewart platform, which gained prominence due to its use in flight simul ators. The traditional Stewart platform has given rise to other variations due to modification either of the act uators or joints. Of these variants the ones of interest here are firstly those using compliant members, an d secondl y pl atforms using tendon, or cabl e actuation. In Korea Choi et al proposed a passi ve compliant Stewart platform to accurately measure both position and force on [2] each member of the platform . Though the compliant members were not used as active actuators, their use in [3] Stewart platform open s up new grounds. Moon and Kota , took this concept and applied it to active members. They added compliant joints to piston-like linear actuators and incorporated a central constraining leg when fewer than 6 DOFs were required. The idea of the constraining central leg, introduces another method of configuring the Stewart platform. In the area of tendon-driven or cable-suspended platforms, a few configurations have been proposed. The best known cable[4, 5] , where the end-effector sits on a platform suspen ded plan ar parallel robot is the RoboCranes developed at NIST suspen ded from a fi xed frame using 6 cables to achieve 6 DOF. Issues regarding the workspace an d design of general [6] cable-based planar robots were addressed by Fattah and Agrawal , where the pl atform was not only suspended but also constrained by cables from above and below. As only tension force coul d be tolerated by a ten don, analysi s needs be performed to keep the tendon under tension. Sometimes the end-effector is suspen ded by ten dons and use of the [7] gravity force or any other passive force en sure operation of the platform . Another more applicable sol ution for high acceleration applications is to use redun dant act uators, and to resolve the redundancy to ensure positive tension in [8] all the tendon s. This can be performed in a fully–constrained or over–constrained moving platform . However, [9] [10, 11] . analysis of the geometry or possible workspace is very difficult From the advantages of the compliant members and of the tendon-act uated pl anar parallel mechanisms, a design is suggested h ere where both the compliant aspect as well as tendon act uation could be used to develop simpl e miniature Stewart platforms that could be used as linkable modules for the locomotion of flexible robots. Proposed Model [12]
One of the more comprehensive treatments given to tendon-driven Stewart platforms is that of Verhoeven et al. . In their formul ation, they divi ded such platforms into two major types; the first being the “Compl etely Restrained Positioning Mechanism” (CRPM), where t endons are attach ed both above and below the pl atform. This makes
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