Structural design and kinematics of a new parallel reconﬁgurable robot Nicolae Plitea, Dorin Lese, Doina Pisla n , Calin Vaida Technical University of Cluj-Napoca, Memorandumului 28, RO-400114 Cluj-Napoca, Romania article info Article history: Received 11 September 2011 Received in revised form 26 April 2012 Accepted 6 June 2012 Available online 25 July 2012 Keywords: Parallel robots Reconﬁguration Reconﬁgurable structure Kinematics Workspace Simulation abstract Reconﬁgurable robots can be deﬁned as a group of robots that can have different geometries, thus obtaining different structures derived from the basic one, having different degrees of freedom and workspaces. Thanks to the optimum dexterity they offer, the user can accomplish a large variety of industrial tasks, using a structurally optimized robot leading towards better energy control and efﬁciency especially in case of batch size production lines where the task (for the robot) may vary periodically. Reconﬁgurable systems are a challenge for numerous scientists, due to the advantage of dealing with changes and uncertainties on the ever-changing manufacturing market. One of the main problems of reconﬁgurable robots is the proper structural geometry determination, so that the resulting structure is able to perform a variety of tasks. This paper presents the structural design of an innovative parallel robot with six degrees of freedom and its proposed conﬁgurations with ﬁve, four, three and two degrees of freedom. The kinematic analysis and the workspace representations of all the presented conﬁgurations of the parallel robot, called Recrob, are also presented. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Reconﬁgurable robots have variable geometry, obtained by modifying leg positions, using kinematic links with variable length and joints that can block one or more degrees of freedom (DOF), or by adding/removing different constraint elements from the robotic system. Compared to a conventional industrial robot with ﬁxed geometry, such a system provides higher degree of ﬂexibility enabling the user to accomplish a wider variety of tasks through proper selection and reconﬁguration of a large inventory of func- tional components [1]. Parallel robots are best known for their speed, accelerations, reduced masses in motion and high load/own mass ratio, due to the multiple chains linking the mobile and ﬁxed platforms having the actuators positioned on (or close to) the base [2,3]. The use of multiple chains generates a higher architectural stiffness and accuracy also eliminating the problem of error cumulating pre- sented in serial structures. Another advantage of these robots is higher accuracy compared to their size. Some researches in the ﬁeld of gears provide the speciﬁc conditions of the parallel robotics regarding the transmission of the mechanical power with opti- mized efﬁciency, good accuracy and extended life service as shown in [4,5]. The architecture of parallel robots has also some limita- tions that narrow the application range of these structures. The most important ones refer to the much smaller workspace in comparison with a serial robot, the relatively high-occupied volume and the existence of singular points in their workspace (where the robot can either block or become uncontrollable) [2]. Furthermore, due to the interdependence between the active joints very often the mathematical model is rather more complicated. The balance between serial and parallel structures is often inclined by the application particular requirements thast may impose either one of these architectures. A modular reconﬁgurable parallel robot can be rapidly adapted to a new conﬁguration and its workspace can be varied by changing the leg positions, joint types, and link lengths for a variety of tasks. A reconﬁgurable parallel robot combines the speed, precision, stiffness and reduced mass of parallel robots with the ﬂexibility, rapid changeover of reconﬁgurable robots. For the modular reconﬁgurable parallel robot system to be deployable and effec- tive in performing its assigned tasks, certain issues must be established such as parallel robot conﬁguration structural design, kinematics and workspace analysis. Reconﬁguration is, as mentioned in [6], a change of the characteristics of the robot during operation. Stechert proposes in his paper two types of reconﬁguration:  Static reconﬁguration denotes a manual rebuilding of a struc- ture, for instance the arrangement of drives can be changed. However, rebuilding a complete new structure is possible, too. After rebuilding, a new robot with new kinematic character- istics and a new workspace is available. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/rcim Robotics and Computer-Integrated Manufacturing 0736-5845/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.rcim.2012.06.001 n Corresponding author. E-mail addresses: nicolae.plitea@mep.utcluj.ro (N. Plitea), dorin.lese@mep.utcluj.ro (D. Lese), doina.pisla@mep.utcluj.ro (D. Pisla), calin.vaida@mep.utcluj.ro (C. Vaida). Robotics and Computer-Integrated Manufacturing 29 (2013) 219–235