Input force estimation using an inverse structural filter

A new method for the estimation of structural input forces is presented. The time domain technique uses a non-causal inverse structural filter (ISF) which takes as input, the structural response data, and returns, as output, an estimate the input forces. This technique allows pseudo-real-time estimation of input forces for non-collocated sensor/actuator pairs for multi-input/multi-output (MIMO) systems. The formulation allows the estimation of input forces for systems that possess unstable transmission zeros and hence are non-minimum phase. Input force estimation for such systems is difficult due to the unstable nature of the non-collocated inverse system. The theory for the development of the ISF is discussed and the applicability of the formulation is derived from linear system theory. Two examples are discussed. The first is a single-input/single-output (SISO) one-dimensional spring/mass chain in which a remote accelerometer is used to estimate an input force at one end. In the second example, the technique is used to estimate six docking forces and moments between the Space Shuttle and the Russian MIR Space Station during a docking simulation.