Motor simulation and parameter identification in a reciprocating mechanism

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Virginia Tech

In this study, a slider-crank mechanism driven by an induction motor was studied for the purpose of deriving simulation data for the identification of the important operating parameters in the machine. First, a modification of a motor simulation program emphasizing losses is presented. The program is used to generate dynamic motor data for an analysis of a reciprocating mechanism. By analyzing the dynamic motor data, the operating parameters in the mechanism can be identified.

The purpose of the reciprocating mechanism analysis was to define an algorithm for the identification of the parameters of mass, damping, spring stiffness, and preload force of the mechanism. The time domain data (e.g. the motor net input torque, the mechanism load torque, the angular velocity, and angular acceleration, etc.) of the mechanism from a simulation can be related through the use of Newton’s dynamic motion equation. By transforming the time domain data into frequency domain spectra and using a least squares algorithm, the mechanism parameters can be estimated.

The results show that the calculated mass and stiffness can be accurately solved to within 1%. While the damping and preload force may be solved within 2% and 4% respectively. The results also confirm that the separation of the load torque signal can be used in the solution technique. That is, the load torque signal of the mechanism is an arithmetic sum of the contribution of mass, damping, spring stiffness, and preload force.

The identification method of the above parameters could lead to an advancement in machine diagnosis in the future, since the operating parameters in a reciprocating machine are greatly related to an impending machine failure.