Identification of geometric and nongeometric parameters of robots

A general calibration model is developed to represent both geometric and nongeometric errors in manipulator structure including rotary and/or prismatic joints. The aim of this model is to obtain the accuracy limit of the robot, often defined as repeatability. A new definition of this limit is given which takes into account effects such as the encoder resolution and roundoff error of the robot controller. The geometric model uses the modified Denavit-Hartenberg notation including the modified beta parameter. Nongeometric parameters are defined in the geometric model to take into account joint compliance, backlash, and flexion. Calibration equations are presented. They define a linear differential model of independent parameter errors solved by a least-squares method. The results are applied to a six-degree-of-freedom robot including revolute and prismatic joint. The resulting improvement due to this calibration makes it possible to obtain an accuracy value comparable to the limit of the robot.<
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