A tight path following algorithm of an UAS based on PID control

When an unmanned aerial system(UAS) performs missions along the sophisticated pre-determined path in the complicated terrains or highly dangerous regions with anti-air threats, disturbances like wind cause the UAS to deviate from the original path. This means that a tight path following method for the UAS is needed for successful completion of missions. In this paper, we suggest a PID controller with feed-forward for tight path following. Since the PID control technique is very accustomed to ordinary engineers, they can easily exploit the proposed method for the path following of an UAS without any heavy mathematical background. As the reference input to the PID controller, the information of the pre-determined path such as the feed-forward term is required to compensate the curvature of the pre-determined path. Since the pre-determined path is typically given by a set of data points, not only the curvature and the derivative of the pre-determined path are not available but also it requires a large size of onboard memory. Hence, we adopt the cubic spline method to convert the original path given by points to a continuously differentiable function based on several waypoints on the original path. Also, in this way, we can efficiently upload the complex path information to the flight control computer of an UAS.