Implementation of a force controller based on fuzzy rule emulate networks for soft contact with an object with unknown mechanical properties

In this article, a novel force control system for soft contact with an object of unknown mechanical properties is proposed by using an ultrasonic sensor implemented in a 3 DOF manipulator robotic system. The emphasis is on the development of a control system to allow soft contact with an object of nonlinear elastic contact properties. In this work a Multi-input Fuzzy Rules Emulate Network (MiFREN) scheme controller with adaptation is developed to regulate the contact force. We propose the use of an ultrasonic sensor in conjunction with a signal conditioning for force based on a parallel-distributed-model as well as the Hertzian model, and considering the transmission and reflection of ultrasonic wave properties. The IF-THEN rules for the MiFREN control are defined taking into account the human knowledge of a physical system and a stability analysis is developed by the Lyapunov method. The experimental results demonstrate that the system is able to find a stable first contact force and moreover the proposed controller is capable of controlling the contact force for both regulation and tracking tasks.