TETROBOT: A NOVEL MECHANISM FOR RECONFIGURABLE PARALLEL ROBOTICS. Student, Machine Building Faculty, Technical University of Cluj-Napoca

Size: px

Start display at page:

Download "TETROBOT: A NOVEL MECHANISM FOR RECONFIGURABLE PARALLEL ROBOTICS. Student, Machine Building Faculty, Technical University of Cluj-Napoca"

Nancy Newman
5 years ago
Views:

UNIVERSITATEA TRANSILVANIA DIN BRA0OV Catedra Desin de Produs 1i Robotic2 Simpozionul na8ional cu participare interna8ional9 PRoiectarea ASIstat9 de Calculator P R A S I C ' 02 Vol.

1 UNIVERSITATEA TRANSILVANIA DIN BRA0OV Catedra Desin de Produs 1i Robotic2 Simpozionul na8ional cu participare interna8ional9 PRoiectarea ASIstat9 de Calculator P R A S I C ' 02 Vol. I Mecanisme 1i Triboloie 7-8 Noiembrie Bra>ov, România ISBN TETROBOT: A NOVEL MECHANISM OR RECONIGURABLE PARALLEL ROBOTICS Emil TEUAN*, Olimpiu TTAR*, Seriu STAN** * Department of Mechanisms, ine Mechanics and Mechatronics, Technical University of Cluj-Napoca ** Student, Machine Buildin aculty, Technical University of Cluj-Napoca Abstract: Tetrobot is defined to be a complex mechanism which belons to a particular class of parallel robotics. The Tetrobot desin provides a systematic approach of modular robotic systems which has the advantae that can be confiured in many and different forms for a wide variety of applications. Accordin to the latest development in Tetrobot system desin, the new enerations of these reconfiurable robots will provide the infrastructure for a wide rane of applications where traditional robots often do not meet the demands of strenth, riidity, kinematic structure, reconfiurability, robustness and flexibility [1]. Tetrobots are easily reconfiurable havin as an important benefit the ability to adapt to chanin requirements in a task. Usin easy-to-replace components the repair of any mechanism for Tetrobot is reatly simplified. In this modular approach, the dynamic model of the tetrahedron Tetrobot was obtained usin Newton s method. Keywords: Tetrobot, Reconfiurable Parallel Robotics, Redundant parallel manipulators 1. Introduction- What is a Tetrobot? The hihly redundant robotic mechanism called Tetrobot, was oriinally proposed by Hamlin and Sanders [2],[3],[4]. Redundancy is described in McKerrow s Introduction to robotics [1] as follows: When a manipulator can reach a specified position with more than one confiuration of the linkaes, the manipulator is said to be redundant. Acordin to this definition, redundancy means more than one solution to inverse kinematic transform. Two adjectives are often coupled with the idea of a redundant manipluator. Hihly or hyper redundant manipulator [2], [3], [4] are often used in conjunction with the term snake robots. The intent is clear, such devices either bein planar or fully spatial should have a joint space dimension that is much reater than the dimension of the end-effector space, i.e. n>>m. Since the maximum m can reach is 6 any value of n reater than 10 fulfills this criterion. Tetrobot is a complex mechanism which belons to a class of modular reconfiurable parallel robotic systems. Because Tetrobot uses a novel joint mechanism desin, it can be used for creatin various types of parallel or hybrid series-parallel robots. Since Tetrobots are easily reconfiurable, they can be used in different applications for performin different tasks. A very important feature of Tetrobot is modularity. The Tetrobot system is modular at a number of levels, and while the entire mechanism may be composed from a lare number of components, the number of different types of components is still very small. The Tetrobot structure presents a certain feature. It is composed of tetrahedral and octahedral cells which contains one or more actuated links. The links are either riid or are linear actuators whose lenth can be controlled. In a Tetrobot system it can be

used almost any kind of linear actuator. The linear actuators can be electric, pneumatic, hydraulic actuators or even shape memory alloy or piezoelectric.

Such variable eometry manipulators like Tetrobot are often hihly redundant by usin many unit cells.

2 used almost any kind of linear actuator. The linear actuators can be electric, pneumatic, hydraulic actuators or even shape memory alloy or piezoelectric. or the Tetrobot systems it is recommended electric actuators because they are simpler to use since they do not require compressors and tubin as the hydraulic and pneumatic do. Such variable eometry manipulators like Tetrobot are often hihly redundant by usin many unit cells. This redundancy increases the flexibility and workspace over the Stewart platform type parallel manipulator [1]. The simplest form of a Stewart platform is based on the octahedron. This type of platform consists of trianular top and bottom plates joined by six linear actuators connectin the vertices of the trianles. Stewart proposed in 19 this class of mechanisms for use as aircraft fliht simulators. The oal of the control problem for Stewart platforms is the same as for serial manipulators, except that most Stewart platforms do not have an end-effector as such. Instead, the movin top platform is the element whose position and orientation is to be controlled. Various applications of the Stewart platform have been investiated such as a compliance device for assembly [2], a force/torque sensor [3], an active vibration isolator [4], and a master controller mechanism for some disadvantaes that forward kinematics is too complex to solve in real-time and the prediction of the motion of each joint is not intuitive. D. Stewart Platform with six derees of freedom. Proceedins of the Institute of Mechanical Enineerin, The elements within the structure of a Tetrobot are connected toether usin mechanisms of the type presented in fiure 1. i.1. The modular concept is applied to formulate the kinematic and the dynamic solutions are obtained by propaation throuh the structure [1], and the basic alorithm remains the same for any confiuration in the modular family. The link in the Tetrobot structure are connected to one another at spherical joints. The spherical joints used in the Tetrobot have a number of properties which are of benefit to the Tetrobot system, a) is easy to manufacture, b) allows a number of bars to be connected to a common center of rotation c) is quick to assemble and disassemble. So, the Tetrobot system is not a particular robot but rather a system of hardware components, alorithms and software which are used to assemble an arbitrary number of different robot confiurations. i.2. In fiure 2. is presented the way in which several elements (three elements for the presented case) are connected to a common rotation centre. The presented models have been achieved usin SolidWorks software, which allows the obtainin of some functional models on the scale. In this way it can be studied the problems referrin to the correct operatin conditions of these Tetrobot type structure. The manipulator of this type structure, with a variable eometry is statistically determined assembled from identic unit cells. Each cell has one or more driven elements, which chane the eometry of the cell and thus, move the whole mechanism. The Tetrobot could have tetrahedrical, octohedronal or other simple eometrical form. Startin from these mechanisms placed at the top of the octohedronal, tetrahedrical, etc., type cells, different structures of Tetrobots can be obtained.

Such a structure is presented in fiure 3. The tetrobot is built by linkin a number of octohedronal or tetrahedrical cells. The cells are attached so that they share a sinle common trianular face.

3 Such a structure is presented in fiure 3. The tetrobot is built by linkin a number of octohedronal or tetrahedrical cells. The cells are attached so that they share a sinle common trianular face. When a tetrahedron is attached to an existent Tetrobot only one new node and three elements are connected from it to other three nodes on one of the faces. or n 5 : n& ) (3) ( = = 75 or n 4 : n& ) (4) ( = = = 74 i Dynamic Model of Tetrobot In this section, the dynamic model of the Tetrobot is obtained usin Newton s method [5]. iure 4 shows the free body diaram of a Tetrobot composed of 4 tetrahedral modules. To this dynamic analysis are applied the followin assumptions: 1) the masses of links are concentrated on the node points 2) links are riid 3) friction forces at the joints are nelected. Applyin Newton s equation of motion, I=ma, ives the followin equations: or n 7 : n& ) (1) ( 7 i. 4 Expressin e. above in the matrix forms: 74 7 x y (5) 76 7 z [ ] or n 6 : n& ) (2) 67 6 ( 6 = x ]. 6 6 y z (6)

4 5x ]. 5 5 y (7) 5z 4x y n4z && (8) ] =, 4 where : [ ] [ ] 5 [ ] 6 =, (9) =, [ ] =, (10) are the matrices which contain unit vectors alon the struts of each module. The matrices denoted by [ ] node represent the confiuration of each module and do not have relation to the adjacent modules. The actuantin forces are obtained by multiplyin the inverse of [ ] node.the actuatin forces of each node point can be expressed in eneral form as, node = 1 [ ] { M noden& node M node ij ij} & (11) where ij ij are the interactin forces between the adjacent modules. All of the terms in e(?? ) can be obtained from the information of each module except the interactin forces. The actuatin forces can be calculated by propaatin from the end-effector to the base. This principle of propaation may be applied to any tetrahedronbased Tetrobot. 3. Concluzions The paper has presented the basic mechanism used at Tetrobots. This mechanism behavies as a sferical joint of the 3 rd class and, it is formed from rotation joint of the 5 th classes. At the same time, some aspects concernin the dynamics of the reconfiurable modular robots have been mentioned. The dynamic problems are solved by the matricial method. The analysis allows the pointi out of the followin advantaes: 1. the modularity offers the flexibility to the robots (allowin these to be reconfiurable), 2. it ensures an execellent achievement for the new developin tehnoloies, 3. it encouraes the development and interation of the new technoloies, 4. robustness is due to the identical modules which can replace each other. References: 1 Hamlin,G., Sanderson, A.C,. Tetrobot a modular approach to Reconfiurable Parallel Robotics, Kluwer Academic Publishers,Boston, Hamlin,G., Sanderson, A.C, A Novel Concentric Multilink Sferical Joint with Parallel Robotics Applications, IEEE International Conf. on Robotics and Automation, pp ,may, Hamlin,G., Sanderson, A.C, Tetrobot:A modular System for Hyper-Redundant Parallel Robotics, IEEE International Conf. on Robotics and Automation, pp.8-870, May, Hamlin,G., Sanderson, A.C, Tetrobot:A Modular Approach to Parallel Robotics, IEEE Robotics and Automation Maazine, March, Lee,W.H., Sanderson, A.C., Dynamic Simulation of Tetrahedron- Based Tetrobot, IEEE International Conf. on Intellient Robots and Systems, Oct., Handra-Luca, V., Mecanisme, Lito.UTC-N, Cluj-Napoca, * * * SolidWorks 2000, Massachusetts, 2000

Geometric Approach For Inverse Kinematics Solution: 3-PSU Parallel Kinematic Manipulator

Geometric Approach For Inverse Kinematics Solution: 3-PSU Parallel Kinematic Manipulator Mr. Arya B Changela P.G. Student, School of Engineering RK University, Rajkot. Prof. Keyur P Hirpara Assistant Professor,