Redundant-Drive Backlash-Free Robotic Mechanisms: Mechanisms Creation, Analysis, and Control
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In this dissertation, the concept of transmission lines for topological synthesis of articulated gear mechanisms is introduced. It is shown that the structure matrix, which related input displacements to the joint angles of a multi-degree-of- freedom articulated gear mechanisms, can be derived using the concept of transmission lines. Applying the characteristics of the structure matrix, a new methodology for the topological synthesis of articulated gear mechanisms has been established. All the basic admissible structure matrices of conventional, three-DOF (degree-of-freedom), geared robotic mechanisms have been enumerated.<P>Furthermore, an innovative concept for the control of gear backlash in robotic mechanisms has been conceived. The concept utilizes redundant unidirectional drives to assure positive coupling of gear meshes at all time. It is shown that, through proper arrangement of gear trains, backlash of an N-DOF robotic mechanism can be completely eliminated by a minimum of (N + 1) unidirectional drives. A methodology for the enumeration of admissible RBR (Redundant-drive Backlash-free Robotic) mechanisms has been established. This class of mechanisms also has the fail-safe advantage in that, unless there is loss of backlash control, the mechanisms can continue to function whenever any one of its actuators fails.<P>The actuator sizing has been studied for a general class of N-DOF RBR mechanisms. The actuator torques are given in term of either the joint torques or the end-effector dynamical performance requirement. The methodology for the determination of actuator size can also be applied to tendon-driven robotic mechanisms.<P>Frictional forces in gear-coupled robotic mechanisms can have significant effect on the manipulator dynamics and control and are therefore also included in this study. Gearing efficiency for various gear drives, e.g., two mating gears, N mating gears with a common carrier, and gear trains, has been investigated. As an example, the frictional effect has been demonstrated where it involves the dynamics of a two-DOF RBR arm.<P>In order to demonstrate this concept, a two- DOF experimental RBR arm has been constructed. A computed torque with PD control scheme is implemented in the experimental RBR robot. An experiment using a laser tracking system to verify the improvement of repeatability was conducted. In order to compare the performance difference, two control algorithms, one with redundant drives and the other without, were used in this experiment. The result of this experiment has shown that use of redundant drives greatly improves the repeatability.