Abstract: In consideration of moving piston in the cylinder, it is hard to measure by sensor to describe its moving state variables: speed, accelerative speed, friction force and unknown resistance directly. Based on the systematical theory method, the position, speed and accelerative speed of the piston are regarded as state vectors. The piston moving can be regarded as evenly the ac-celerative motion in sample interval. The state equations are built to describe moving of the piston with unknown input. An expanded structure of Kalman filter is designed with unknown input when the unmeasured resistance is regarded as colors noise. On the basis of gaseous variety regulation, the position coordinate of piston is obtained by computer at each sampling interval. The minimum square error(MSE) is employed as the measure rule. The estimate recursive algorithm is researched to calculated state variable with color noise as the system input. The algorithm adaptively scents the changes of the unknown input. With the estimate of computed speed and unknown re-sistances of the piston in the stroke, the percussion energy of the nitrogen explosion hydraulic hammer is measured by ex-pand Kalman filter. The result shows that the method has better precision of the survey and agrees with the theoretical design on the whole.

Key words: Hydraulic percussion hammer, Kalman filter, Measurement estimation, State equation