Abstarct: In this thesis, an adaptive observer-baxsed fault detection system is designed. This system detects a fault in the event of failure in the robot actuators and activates the system fault alarms. The fault detection system for a rigid and flexible robot arm with a DC motor drive is designed to withstand the disturbance signal, such as a change in load of the arm of the robot, or modeling uncertainties, has the lowest sensitivity, and has a maximum sensitivity to the actuator faults. In order to simplify the nonlinear and complex equations of the robot, the idea of voltage control strategy is used. The adaptive observer performance has been studied in terms of speed and accuracy in detecting the actuator faults. Simulation results show the effectiveness of this method.