This paper discusses an identification input for nominal hydraulic arms. First, we focus on an input-output nonlinearity which exists even in the absence of nonlinear friction and prevents us from observing and measuring the input-output behaviors. Second, we propose a new identification input based on the physical parameters of hydraulic arms via the special nondimensionalization technique. Third, we show the effectiveness of the new identification input experimentally. Finally, we show an application of the proposed new identification input to observe and measure the input-output behaviors. Especially, in the frequency domain, we identify the uncertainty that was impossible for the conventional identification input.
