Offline Reference Trajectory Shaping for a Cable-Driven Earthquake Simulator Based on a Viscoelastic Cable Model

In an earthquake simulator, which is a device for reproducing seismic waves, it is necessary to accurately reproduce the acceleration. In this letter, the authors propose an offline reference trajectory shaping method for precise acceleration control based on the dynamic model of an earthquake simulator, composed of a planar three-degrees-of-freedom cable-driven parallel mechanism, considering the effect of the viscoelasticity of a synthetic fiber cable. First, Flory’s model representing cable viscoelasticity was introduced into the dynamic model of the system constructed in the authors’ previous study, and a precise dynamic system model including the cable was derived. Next, the viscoelastic behavior of the cable including instantaneous elasticity and tension relaxation was measured experimentally, and the cable model parameters were identified. Based on these, a control method to accurately generate the desired platform acceleration by offline reference trajectory shaping was developed. The effectiveness of the method was confirmed through simulations and experiments.