“…To overcome the shortcomings of the trajectory planning method to solve the problem of "FOV constraints," researchers at home and abroad put forward a series of nontrajectory planning methods. By combining different visual servo structures or designing a new VS structure, the object is always in the camera FOV, such as combining IBVS and PBVS approach, 21 switching approach, 22 zooming VS approach, 23 direct VS approach, 24 and IBVS with a Kalman-neural-network filtering approach. 25 Besides, some advanced control laws are designed to deal with the FOV constraint problem, such as sliding mode control, 26,27 model predictive control, [28][29][30] prescribed performance control, 31,32 switched controller, 6,33 and so on.…”