The design of high performance motion controls for industrial robots is based on accurate models for the robot arm and drive systems. This paper presents analytical models and experimental data to show that interactions between electromechanical drives coupled with compliant linkages to arm link drive points are of fundamental importance to robot control system design. Flexibility in harmonic drives produces resonances in the 5 Hz to 8 Hz range. Flexibility in the robot linkages and joints connecting essentially rigid arm members produces higher frequency modes at 14 Hz and 40 Hz. The nonlinear characteristics of the drive system are modeled, and compared to experimental data. The models presented have been validated over the frequency range 0 to 50 Hz. The paper concludes with a brief discussion of the influence of model characteristics on motion control design. IntroductionThe successful design of any high-performance control system is based on accurate knowledge of the dynamics of the physical plant. This knowledge is particularly important when the "unmodeled dynamics", physical effects not included in the model, produce poles near the imaginary axis. If the control design does not account for these lightly-damped poles, there is great risk that the closed-loop system will become unstable or exhibit very poor robustness to variations in plant parameters.The design of multivariable controllers for industrial robots is a subject of great current interest. Nearly all papers in the literature on the subject of robot motion control are based on models for the arm that, based on the results of research presented in this paper, are inadequate for a large class of contemporary arm mechanical designs. Since there are major differences in the dynamic behavior of real robot arms from the idealized models found in the literature, it is difficult to assess the benefits to be obtained through implementation of advanced control schemes.The principal limitation of published models for industrial robots is the assumption that their dynamic behavior is represented adequately by interconnected rigid bodies driven by actuators modeled as pure torque sources or as first-order lags. It is noteworthy that there is very limited published experimental evidence to substantiate this assumption. In contrast, in this paper the importance of dynamic interactions between the multiple link arm and its electromechanical drive systems is demonstrated through analysis and experimentation. Specifically, this paper addresses the following aspects of model development for the purposes of control system design for real industrial robots:

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AIBSTRACTThe design and implementation of a microprocessor based control system to control the interaction forces between a five axis articulated robot and a workpiece is described. The control system w o r b in parallel with a robot controller by calculating position corrections that allow force to be controlled in the desired manner. The Corrections were successfully interfaced to the position control loop on an individual axis level.limitations imposed by flexibility in the robot drive train. InStable force control algorithms were designed in spite of the multi-degree of freedom control case it is shown that each axis can be considered autonomous, obviating the need for a multivariable approach. Control was implemented in edge following experiments. Across levels of commanded normal force ranging from 0 to 15 N, the RMS force errors remain constant. Errors increased from 0.5 N to 1.5 N RMS as tangential speed was increaxd from 0 to 9 cm/sec. The performance of the force control system during deburrin operations is characterized a c m s the full force and apeelf range of the cutting tools used. Smoothness of cut is shown to be consistent with standard deburring operations in terms of optimal feed and metal removal rates.