Fractional Control of a Humanoid Robot Reduced Model with Model Disturbances

Abstract

There is an open discussion between those who defend mass distributed models for humanoid robots and those in favor of simple concentrated models. Even though each of them has its advantages and disadvantages, little research has been conducted analyzing the control performance due to the mismatch between the model and the real robot, and how the simplifications affect the controller's output. In this paper we address this problem by combining a reduced model of the humanoid robot, which has an easier mathematical formulation and implementation, with a fractional order controller, which is robust to changes in the model parameters. This controller is a generalization of the well-known PID structure obtained from the application of Fractional Calculus to control, as will be discussed in the paper. This control strategy guarantees the robustness of the system, minimizing the effects from the assumption that the robot has a simple mass distribution. The humanoid robot is modeled and identified as a triple inverted pendulum and, using a gain scheduling strategy, the performances of a classical PID controller and a fractional order PID controller are compared, tuning the controller parameters with a genetic algorithm.

Experimental Robot Model Adjustments Based on Force–Torque Sensor Information

“…Many improvements and new models have been developed in order to add more information about the robot body or to address the lack of information, such as in [ 9 , 10 ]. In addition, these new models can represent special behaviors or model special tasks [ 11 , 12 ]. This paper presents one of those improvements for dealing with robot inaccuracies such as material flexibility or component tolerances that are very difficult to model.…”

“…These include ankle, hip, and step strategies. For low-intensity disturbances, the body can be considered as a nearly single stiff pendulum, where balance adjustments are mainly made in the ankle joints of the robot [ 12 ]. The hip strategy is applied when the external disturbance increases and the ankle strategy is not sufficient for keeping balance.…”