说明：  通过非线性扩张观测器可实现被控对象的位置、速度和未知部分观测。在实际控制工程中，可采用本观测器实现无需速度测量的控制，并实现对未知不确定性和外加干扰补偿
(Through the expansion of nonlinear observer can realize the location of the controlled object, speed and unknown part of the observation. Can be used in actual control engineering, the observer is to realize the control without speed measurement, and implement the unknown uncertainties and external disturbance compensation)