Workspace Analysis of 6–6 Cable-Suspended Parallel Robots

N, Cable Driven Parallel Robots (CDPRs), the moving platform is connected to the base platform by a number of cables. CDPRs have several advantages compared to traditional serial or parallel robots. They have high ratio of payload to robot weight and a much larger workspace which make them appropriate for high speed applications [1], lifting heavy loads [2], camera positioning in sports stadiums [3], service robot [4] and many others. Based on the number of cables (m) and the number of degrees of freedom (n), there are three categories for the CDPRs [5], [6], i.e. the incompletely restrained cable robots (mn+1). There have been some works in implementation of the incompletely restrained six cable robot such as NIST Robocrane [2] and the large scale FAST system [7]. The static equilibrium workspace of the cable robot is defined by the set of points where the mass center of the moving platform (MP) can be positioned while all the cables are in tension [8]. To this end, at each point within a search volume, the equation describing the force in each cable is used to check if tension is obtainable or not. Some authors attempted to tackle some aspects of the optimal design of incompletely restrained six cable robots by presenting the accuracy and workspace volume of the robot for several geometric configurations, various sizes and orientations of the base and the MPs [8]-[12]. In 2004, Pusey et al. [8] concluded that for any geometry of the base and MPs, the largest workspace volume occurs when the MP is the same size as the base platform (BP). In other words, for a fixed size of the BP, as the ratio of MP/BP increases, the workspace volume increases as shown in their Fig. 5.