Reconfigurable Cable-Driven Parallel Robots

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Cable-driven parallel robots (CDPRs) consist of an end effector, which is suspended by a number of cables. Each cable is wound onto*a servo-actuated spool, which is rigidly attached to a fixed frame. The end effector displacements are controlled by simultaneously winding and unwinding the cables on their respective spools. Our interest in CDPRs stems from five advantages they hold over classical rigid-link robots: (i) They cover a large workspace; (ii) They are inexpensive; (iii) They can generate high speeds and accelerations---Supersonic speeds have been reported!; (iv) They are portable; (v) They are reconfigurable. In our opinion, this last advantage, the ability of CDPRs to quickly reconfigure, has been relatively neglected in previous research. From the perspective of many practical applications, this point is crucial, as the robot can then adapt its geometry and workspace to different workpieces or environments, which most classical robots cannot do.**The objective of the proposed research is thus to improve and demonstrate the ability of cable-driven parallel robots to reconfigure. We have identified three important challenges facing the engineer when reconfiguring a CDPR for a new task: finding the best robot geometry for a given task; changing the end effector or its actuated tool (e.g., gripper, welding torch); and identifying the exact CDPR geometry after it has reconfigured. The proposed research program will address these challenges in a series of five projects numbered from 4.1 to 4.5. **In project 4.1, we will develop a new method of tracing the three-dimensional workspaces of CDPRs. This workspace will take into account the tension limits in the cables, the range of resultant forces and moments they are to generate, and the possible collisions between cables and end effector. In project 4.2, we will develop a new method for the automatic synthesis of CDPRs. This method will take into account all the physical constraints included in project 4.1, which is not possible with currently available approaches. To demonstrate its effectiveness, the synthesis method will be used to design two CDPRs: one for the inspection of large surfaces (project 4.5), and the other, to provide haptic feedback in a virtual environment for physical rehabilitation. **In projects 4.3 and 4.4, we will improve the CDPR tool interchangeability by moving its actuators from the end effector to the ground, thus allowing to use the same motors and controllers for different tools. This will reduce the unit cost of a tool, thus allowing for more different tools to be made. The motion and forces will be transmitted from the fixed actuators to the moving end effector via additional cables parallel to those already forming the CDPR. In project 4.3, we will control a tool with a single degree of freedom by using two motors in differential mode. In project 4.4, we will extend this concept to drive a three-degree-of-freedom robotic arm from the base, thus improving on the idea of the macro-mini manipulator, which is well known in robotics. **In project 4.5, we will apply the analysis and synthesis methods previously developed to design a CDPR for the automatic non-destructive testing (NDT) of large surfaces. A probe will be mounted on the CDPR end effector, and used to scan mockups of objects of various geometries, e.g., an aircraft wing or a reservoir. This project will use the results of projects 4.1 and 4.2, and will require the development of new calibration techniques, so that the CDPR geometry can be precisely identified after it has reconfigured.**Besides providing state-of-the-art training to five students, this research will take the reconfiguration capabilities of CDPRs to a functional level that can be applied to industrial tasks.