Tendon-Driven Manipulators: Analysis, Synthesis, and Control

As the development of light-weight, small volume and versatile manipulators has grown in the field of robotics, the need for more efficient and relevant power transmission systems in the manipulators has become increasingly apparent. It is clear that the advent of efficient, low friction, and backlash-free actuation systems promises to provide significant gains in manipulator performance. Tendon transmission has been widely used to actuate small volume and light-weight articulated manipulators, such as dextrous mechanical hands, for it permits actuators to be installed remotely from the end-effector, thus reducing the bulk and inertia of the manipulator system. Current research on such actuation systems is accomplished on the basis of specialized designs. The lack of systematic approaches has limited our scope in realizing our scope in realizing performance of such transmission systems. Therefore, when associated with systematic methodologies, the study of tendon-driven manipulators promises to be of major importance in the field of robotics.This dissertation is concerned with four issues to enhance our use and understanding of tendon-driven manipulators. First, a systematic approach for the kinematic analysis of tendon-driven manipulators is established. Graph is used to represent the kinematic structure of tendon-driven manipulators. It is shown that the kinematic structure of tendon-driven manipulators is in every way similar to that of epicyclic gear trains. The fundamental circuit equation developed for the kinematic analysis of epicyclic gear trains can thus be applied to this type of mechanism. The displacement equation governing joint angle space and tendon space can be easily obtained.Secondly, the concept of structural isomorphism and the structural characteristics of tendon-driven manipulators are investigated. Based on the explored properties, a methodology for the enumeration of tendon-driven manipulators is developed. By applying the methodology, a class of kinematic structures having pseudo-triangular structure matrix is enumerated.Thirdly, a method for assessing the kinematic/static performance of tendon- driven manipulators is developed. Transmission ellipsoids of the manipulators are investigated. A criterion for differentiating force transmission characteristics and a procedure for identifying least maximum- tendon-force are established. Based on the rationale developed, it is shown that optimal kinematic structure can be achieved fir certain types of tendon routings.Finally, the dynamic characteristics of tendon-driven manipulators are examined in detail. When integrating with a control algorithm in the manipulator, the dynamic performance of tendon-driven manipulators is realized and identified with more fidelity

Kinematic Analysis of Tendon-Driven Robotic Mechanisms Using Graph Theory.

The kinematic structure of tendon-driven robotic mechanisms has been investigated with the aid of graph theory. The correspondence between the graph representation of the kinematic structure and the mechanism has been established We have shown that the kinematic structure of tendon-driven kinematic chains is similar to that of epicyclic gear trains. We have also shown that, using the concept of fundamental circuit, displacement equations of tendon driven robotic mechanism can be systematically derived from the kinematic structure. The theory has been demonstrated by the kinematic analysis of three articulated robotic devices

Topological Analysis of Tendon-Driven Manipulators

This paper investigates the effect of tendon routing on kinematic and static force transmission associated with tendon-driven manipulators. The transmission characteristics can be described by the velocity and/or force ellipsoid. We have shown that the effect of tendon routing can be characterized by a condition number and the direction of a homogeneous solution. The condition number is defined as the ratio of the maximum to the minimum singular value of the structure matrix and the homogeneous solution is the set of tendon forces that results in no net joint torques. A methodology for calculating maximum tensions in a tendon-driven manipulator has been developed. We have also shown that among the various tendon routings in three- DOF manipulators, the one with an isotropic transmission ellipsoid possesses minimal maximum tendon force

Dynamic Simulation of Tendon-Driven Manipulators

This paper investigates some dynamic characteristics of tendon- driven manipulators. The dynamic equations including the effect of rotor inertia for a class of n x (n +1) tendon-driven manipulators are formulated. A control algorithm based on the computed torqued method is developed. Then, the implementation of such control algorithm is demonstrated in the simulation of a three-DOF tendon-driven manipulator. Through the simulation, several dynamic characteristics of the system are identified. In particular, it is shown that rotor inertia can have significant effect on the system dynamics and that pretension can play an important role on the stability of the system. It is also shown that among the five non-isomorphic kinematic structures of three- DOF manipulators, the one which satisfies the isotropic transmission and least maximum tendon force conditions also requires smallest tendon force in the dynamic simulations

On the Structural Synthesis of Tendon-Drive Manipulators Having Pseudo-Triangular Structure Matrix.

Tendons have been widely used for power transmission in the field of anthropomorphic manipulating systems. This paper deals with the identification and enumeration of the kinematic structure of tendon-driven robotic mechanisms. The structural isomorphism of tendon-driven manipulators is defined and the structural characteristics of such mechanical systems are described. Applying these structural characteristics, a methodology for the enumeration of tendon-driven robotic mechanisms has been developed. Mechanism structures with up to six degrees of freedom have been enumerated

Torque Resolver Design for Tendon-Driven Manipulators

Given desired joint torques in an n-DOF tendon-driven manipulator with n +1 control tendons, the determination of tendon forces is an indeterminate problem. Usually, the pseudo-inverse technique can be used to solve for such a problem. In this paper, rather than using the pseudo-inverse technique, an efficient methodology for transforming joint torques (n elements) to motor torques (n + 1 elements) has developed. This technique, called "torque resolver", utilizes two circuit-like operators to transform torques between two different vector spaces. It can be easily programmed on a digital computer or implemented into an analog- circuit system. It is hoped that this technique will make real- time control using computed torque method feasible. The technique has been demonstrated through the dynamic simulation of a three- DOF manipulator