Despite widespread industrial applicatzon of harmonic drives, the source of some elastokinetic phenomena and their impact on overall system behavior has not been fully addressed thus far. Some of these phenomena severely influence the behavior of robot arms, both in free and constrained motions, when the end effector is in contact with an environment. The primary goal of this study is to derive an effective, control-oriented model of a harmonic-drive-based robot joint. Systematic observations of an experimental robot with harmonic drives has revealed that the harmonic drive could not entirely transmit the input torque to the output shaft, due to a nonlinear meshing process between the flexible and circular spline teeth. The torque transmitted to the output shaft might saturate at a much lower value than expected (e.g., motor torque multiplied by the gear ratio). This phenomenon may severely influence the system behavior, par ticularly in force/impedance control tasks when full joint-torque capacity and wide bandwidth are needed. To understand the harmonic-drive behavior, as well as to derive a convenient form of its model, we have shown restrained motion experi ments to be much more useful than free-motion experiments. In this article, we also introduce mathematical models and describe experiments related to other physical phenomena, such as nonlinear stiffness, hysteresis, and soft windup. The goal of our modeling strategy was not to develop a precise and possi bly complicated model, but to generate an appropriate model that could be easily used by control engineers to improve joint behavior To visualize the developed model, equivalent mechan ical and electrical schemes of the joint are introduced. Finally, a simple and reliable estimation procedure has been established for obtaining joint parameters, to ascertain the integrity of the proposed model.

A B S T R A C TThe IRIS Facility is a modular, reconfigurable and expandable robot system to be used for experiments in grasping, manipulation and force control. The baseline layout of the Facility will have two manipulators with four rotary joints each. Each manipulator can be easily disassembled and reassembled to assume a multitude of configurations. Each joint is driven by d.c. brushless motors coupled with harmonic cup drives and instrumented with position, and torque sensors. A six d.0.J forcdtorque sensor is mounted at the tip link. Additional manipulators with different joint layouts will be added in the future.The real-time controller of the IRIS Faciliry has also been designed to be modular and expandable. It is based on a nodal architecture with a PC-486 host and an AMD29050 co-processor as the CPU of each secondary node. Each node is capable of controlling 8 joints at I kHz while executing over lo00 FP (Floating Point) operations per joint in each sampling interval. This paper describes the design of the IRIS Facility and its functional capabilities. I n addition, the rationale behind the major design decisions is given.

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SUMMARYThis paper presents a new program package for the generation of efficient manipulator kinematic and dynamic equations in symbolic form.The basic algorithm belongs to the class of customized algorithms that reduce the computational burden by taking into account the specific characteristics of the manipulator to be modelled. The output of the package is high-level computer program code for evaluation of various kinematic and dynamic variables: the homogeneous transformation matrix between the hand and base coordinate frame, Jacobian matrices, driving torques and the elements of dynamic model matrices. The dynamic model is based on the recursive Newton-Euler equations. The application of recursive symbolic relations yields nearly minimal numerical complexity. Further improvement of computational efficiency is achieved by introducing different computational rates for the terms depending on joint angles, velocities and accelerations. A comparative study of numerical complexity for several typical industrial robots is presented.

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