Planning the trajectory of manipulator gripper with a parallel structure and flexible links

Abstract

Abstract. Traditionally, the tasks of the objects transportation in working space are solved using manipulation robots with a sequential kinematic structure. However, the increasing requirements for the mechanical rigidity, load-carrying capacity, mass-size and speed parameters caused the need to develop a new classes of manipulation robots with a parallel connecting circuit. The closed kinematic scheme of such manipulators provides a more higher rigidity of the entire structure. The reduced mass of moving parts reduces the load on electric drives and thus provides an increase in manipulator gripper dynamics and the accuracy of positioning. Finally, the energy efficiency of the process increases. The problems of planning the trajectory of manipulator gripper with a parallel structure and flexible links are considered within the paper. Parallel structure manipulatorAs the name implies, a cable-driven parallel manipulator, or cable robot, is a type of parallel manipulator in which the platform is driven by a set of cables in place of traditional rigid links. These cables are sometimes referred to as tendons, or wires. A winch, consisting of a tensioning motor and spool, is used to adjust the length or tension in each cable. Coordinated retraction and extension of the cables allows for the position and orientation of the platform to be controlled. Cable-driven systems offer many advantages over traditional parallel manipulators. Replacement of the heavy prismatic actuators with relatively light cables facilitates performance at higher accelerations and allows for potentially vast workspaces. Mounting of the winches to the fixed base further reduces the system's moving inertia. Compared to the moving platform, the cables have relatively low mass and inertial properties and thus, their effects are oftentimes considered negligible -an assumption which greatly simplifies the modeling and analysis. The simple design of cable-driven robots also gives rise to a system that is reconfigurable, less expensive to construct and maintain, and easily transported, disassembled, and re-assembled.The limitations in parallel robot mechanism paved a path for the cable robots. The research was directed towards developing a mechanism that would keep the characteristics of parallel robot intact and reduce the drawbacks, especially small workspaces. The abilities of parallel robots to move with high speed and accelerations, stiff structure, high force carrying capacity were important to be kept intact.Workspace computation is an important aspect of robot design, as it gives an idea of reachability of the robot.The kind of workspace required depends largely on the application of the system. As discussed in [6] of the paper, there are many ways to analyse the workspace of a robot. The force feasible workspace approach is adopted for this study as it is based primarily on the force values. A feasible workspace is considered as a set of positions and orientations of a robot in which the EEs are controllable, tensions in cables are positive, ...