In this paper, a practical method to design a robust controller for a SCARA robot using quantitative feedback theory (QFT) is proposed. The models used to describe robots contain uncertainties that are the result of insufficient knowledge on the dynamics of the robot, external disturbances, pay load changes, and friction, etc. Thus, the application of robust control methods to create the precise control of robots is of considerable interest. This paper considers a robot arm manipulator, a system whose models contain non-linear coupled transfer functions. In the first step of applying the QFT technique the non-linear plant is converted into a family of linear uncertain plants. This is achieved using a fixed-point theorem and then suitable disturbance rejection bounds are found. A robust controller is designed for the tracking problem. Non-linear simulations on the tracking problem for a three-dimension elliptical path are performed and the results highlight the success of the designed controllers and pre-filters. The presented results indicate that applying the proposed technique successfully overcomes the obstacles to robust control of non-linear SCARA robots.

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