The Design of Tendon-Driven Manipulators with Isotropic Transmission Characteristics

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This dissertation deals with the synthesis of the mechanical power transmission structure in tendon-driven manipulators. The force transmission characteristics from the end-effector space to the actuator space has been investigated. It is shown that tendon forces required to generate an output force at the end- effector are functions of the transmission structure matrix and the manipulator Jacobian matrix. The sufficient and necessary conditions for a transmission structure to be admissible are summarized and an efficient algorithm to check admissible structures is derived.

Based on the analysis of static force transmission, a general theory is developed for the synthesis of tendon-driven manipulators with isotropic transmission characteristics. It is shown that an n-dof (degree of freedom) manipulator can possess these characteristics if it is made up of n + 1 of 2n tendons and if its link lengths and pulley sizes are designed according to two equations of constraint. Design equations for synthesizing a manipulator to posses isotropic transmission characteristics are derived.

To demonstrate the theory, two examples are used: (1) a two-dof planar manipulator and (2) a three-dof spatial manipulator. The tendon forces in each manipulator with different transmission structures are compared. It is shown that manipulators with an isotropic transmission structure have more uniform forces distribution among their tendons.

To further understand the isotropic transmission characteristics, the properties of a manipulator with an isotropic transmission structure are then discussed from many different perspectives. The discussion includes the tension control algorithm, maximum tensions, kinematic performance, antagonistic forces among tendons, and survivability of a transmission structure with 2n tendons.

Finally, a new design methodology is developed to determine tendon routings and pulley sizes of a special three-dof tendon-driven manipulator. This design methodology ensures that each tendon will subject equal maximum tension when an external force is applied to the end- effector in all possible directions. The design is further enhanced when the criteria of isotropic transmission are imposed. A design example is presented to demonstrate the features and to compare with the Salisbury finger.