Comparison of fractional order sliding mode controllers on robot manipulator

Challenging and time-consuming tasks performed by humans can today be performed faster and more efficiently by robot manipulators with the development of technology. Robotic manipulators are flexible, can fit in small spaces, and are very effective for tasks that require high precision. They are widely used in the production lines of factories (handling, assembly, welding, etc.) and in fields that require manpower, such as medicine and engineering. Since it is used in tasks that require precision, its control is also important. Sliding modal control (SMC), one of the robust control methods, is a control method used in nonlinear systems because it can be applied to unstable systems, is easy to design and, has high accuracy against parameter uncertainties. However, it produces an unstable control signal within a certain range and this discontinuous control signal causes cracking in the system, which causes damage to the system elements. Especially in recent years, one of the most recent and successful methods used to reduce the chattering effect, which is the biggest problem in the SMC approach, is the fractional order design of the sliding surface. In the fractional order SMC (FOSMC) method, the derivative expression in the sliding surface is defined using the system variable’s error to be controlled and the derivative of the error is computed fractionally. In this paper, Caputo FOSMC (CFOSMC), defined with 3 different sliding surfaces using the Caputo fractional operator, is compared with classical SMC for controlling a 2-degree of-freedom (2-DOF) robot manipulator. According to the results obtained from simulation comparisons, it is observed that approach 3 gives better results than the other two approaches and classical SMC in terms of overshoot, settling and error value for some derivative orders.