# Design, Simulation, and Comparison of Advanced Control Strategies for a 3-Degree-of-Freedom Robot
###### Abstract
Thus, after comparing the three control methodologies, the FLCs proved to be the most suitable and efficient, both under normal operating conditions and under the influence of variable loads applied to the robot's joints. The authors [13] indicate that the SCARA robot is one of the most established robots in the industry due to its high speed and precision, with the controller being key to ensuring its performance. This study presents three sections dedicated to some advanced controllers, as well as the Internet of Things (IoT) and Artificial Intelligence (AI) applying neural networks, particle swarm optimization, and genetic algorithms. For the controllers, the PID controller is described as a closed-loop control system with gains whose magnitude affects the transient response. Among the characteristics of the PID controller are its stability in a system that behaves linearly or nearly linearly and its difficulty in nonlinear systems; it also has insufficient sensitivity to counteract high-speed and precision operational requirements. To overcome the linear response of the PID controller, many have adopted approaches to actively change the PID gain according to the operating condition; one of these is the use of fuzzy logic and AI algorithms. Another type of control is fuzzy logic, which derives from mathematical logic to manipulate the signal between intervals of 0 and 1. Its operation is based on input, inference engine, and output, which will be used to control the robotic arm according to the PID controller gains. This overcomes the fixed gains that require prior tuning and the lack of adaptability to the nonlinear behavior of the SCARA robot, allowing for the alleviation of the PID controller limitation by adding fuzzy logic to improve the smoothness and stability of the robot. There is sliding mode control, which is a nonlinear dynamic control system; its purpose is to control state variables of the system towards a designated surface known as the sliding surface and to ensure that the trajectory of the state variable remains on this designated surface. It has characteristics that provide high precision, control parametric uncertainties, and external disturbances, but its disadvantage is that it can cause high-frequency oscillations in the control signal in a discontinuous control system. Adaptive control is also one of the advanced controllers that can handle nonlinear dynamic systems. Considering that the plant for the SCARA robot is modeled as a linear time-invariant plant in continuous time, the reference model can be represented using the general state-space model according to the adaptation mechanism, which is the adaptive control law; this will continuously adjust the tunable parameter in the controller according to the operating environment based on the reference model. Robust control is a type of controller designed to improve the controller's performance over a specified range. The idea of robust control was proposed by [PERSON] and [PERSON]. The authors, in their conclusions, indicate that the selection of the controller must align with the robot's application due to its respective advantages and disadvantages. If the application involves linear behavior, PID control and fuzzy control are the correct choice, as both control systems rely on fixed gains; PID and FLC are suitable for fixed-load robots that do not have much uncertainty. On the other hand, sliding mode, adaptive, and robust control are suitable for handling high-uncertainty situations. In relation to AI technology, it is noted that it can help the advanced controller achieve better performance than the SCARA robot; however, such powerful AI requires a computer with high hardware specifications. Moreover, IoT can create a more user-friendly environment, as it allows for controlling the SCARA robot with a smartphone. * Findings: a study of three advanced controllers for application in a 3-DoF robot is provided. * Practical implications: the system utilizes the dynamic model of a Scrobot robot, considering 3-DoF.