Modified restoring force surface method for clearance identification in nonlinear multi-degree-of-freedom systems

Clearance is ubiquity in the mechanical system. The contact nonlinearities which are caused by the clearance can significantly affect the dynamic response, and eventually degrade the dynamic performance. If the parameter of the clearance nonlinearity can be identified by taking advantage of the equipment dynamic information, the system can be adjusted to control the influence of the clearance nonlinearity. Based on the multi-degree-of-freedom (MDOF) system with clearance, a modified method which combines the traditional restoring force surface (RFS) method and the orthogonal projection technology in the matrix row space is proposed to identify the clearance value. For the modified method, the traditional restoring force can be estimated by the excitation force and the acceleration response. The traditional restoring force should be projected on the nonlinearity location. The projection restoring force-displacement curve can be drawn, and the clearance size can be identified by inflection points. The feasibility of the proposed method is verified by the simulation, and the superiority is revealed by the comparison with other methods. The effectiveness of the proposed method is verified by the parameter identification experiments which are conducted on the designed testbed with adjustable clearance.