# Reconfiguration for the Maximum Dynamic Wrench Capability of a Parallel Robot
## 1 Introduction  
A parallel robot actually is a machine with a closed kinematic structure having more than 1 degree of freedom, and has therefore been used in a wide variety of applications due to its many advantages such as high stiffness, low inertia, precise positioning capability, and large force/torque capacity over their serial counterparts. Recently, in the demand for flexibility, rapid changeover, or a specific task within the operational constraints, the reconfigurability of the parallel robot has proved to be important. Moreover, a parallel robot possessing an adjustable architecture can achieve a relatively larger workspace, and avoid singularities and interference among the system components along a prescribed trajectory. For now, two main approaches have been proposed for the reconfiguration of the parallel robot, one is based on a modular design, and the other is via a variable geometry methodology [1]. A modular reconfigurable parallel robot can be made through the integration of a set of adjustable joint modules and link modules, such that the parallel robot can generate various configurations by changing the number and types of the modules [2]. For example, [PERSON] _et al._[3] presented a reconfigurable parallel robot constructed by two base tripods, in which the first tripod is fixed to the moving platform, and branches of the second tripod are designed to be detachable from the moving platform such that this parallel robot can be reconfigured from six DOFs to three, four or five DOFs, respectively. [PERSON] and [PERSON] [4] designed a reconfigurable 6-DOF Gough-Stewart platform whose reconfiguration is achieved through a modular design, such that any of the leg modules can be replaced by another with a different range of motion, and can be placed on the mobile platform as well as the base at any desired location and orientation. Even when these modules are assembled, the topologies of a parallel robot can be further changed for a task-specific architecture, thus its adaptability for changes can be maximized. The variable geometry methodology is based on the rearrangement of the leg attachments on the base or on the moving platform so that the parallel robot geometry can be modified to adapt it to particular tasks. [PERSON] _et al._[PERSON] _et al._ (2016) presented a 5-SPU platform whose base leg attachments can be easily reconfigured, statically or dynamically, without altering its singularity locus. [PERSON] _et al._[PERSON] _et al._ (2016) made an effort to characterize the parameters for developing a reconfigurable Stewart platform for a contour generation through the variable geometry approach. The trajectory with maximum stiffness for complex contours was then obtained by the generic approach along with the stiffness model. Research also showed that the placements of the legs and the moving ranges of the respective legs have a great effect on the shape and size of the workspace, accommodation of different task requirements, or even improving the stiffness of the parallel robots ([PERSON] _et al._, 2016; 2017). Although there are many designs to date for reconfigurable robots, most of these proposed systems are lower mobility mechanisms, _i.e._, three to five DOFs. As a result, it is not sufficiently flexible and reconfigurable for a manufacturing facility. In this paper, a six DOF Stewart-platform robot with sliding lockable base joints is proposed. The advantages of designing such a manipulator allow for added reconfiguration so that the mechanical properties can be changed passively and will improve its various applications. However, multiple configurations of a reconfigurable parallel robot also increase the difficulty of determining the optimum task-based geometry. The current state-of-the-art as related to the research of the proposed Stewart-platform robot with sliding lockable base joints can be found in ([PERSON] _et al._, 2016; 2017; 2018; 2019).