Towards the Development of a Model for Nonlinear Elements in Machine Tools

Steven M. Whitican P.E., Charles Van Karsen, Jason Blough
In Press: Society of Experimental Mechanics
Machine tool structures contain a number of joints which provide for rotation or translation of connected structural elements. These joints add significant nonlinearity to the system thus making overall performance difficult to predict. Linear guides have been identified as a particular connection which exhibit significant nonlinearity. Linear guides are thus very difficult to accurately model into a dynamic simulation. Linear guideways have predominantly replaced box ways in industrial machinery to facilitate linear directional motion. As opposed to box ways which are scraped to obtain the most contact area possible, linear guides depend on theoretical contact patches between the guide, rail, and rolling element train. Linear guides exhibit complicated dynamics, the accurate prediction of which is necessary for a high-fidelity model of a machine tool. A fixture was developed to study linear guides. This paper highlights some of the properties of linear guides and begins the process of creating a model by studying the form of the nonlinearity using the Acceleration Surface Method (ASM). Future work will involve the comparison of the derived model against other popular linear guide models and the parameterization of the model found here.

Nonlinear Characterization of a Machine Tool Energy Absorber

Steven M. Whitican P.E., Charles Van Karsen, Jason Blough
In Press: Society of Experimental Mechanics
Energy absorbers are used frequently in industrial machinery. The use of energy absorbers allows for the design of a lighter structure while still maintaining the requisite dynamic stiffness for effective operation. A standard energy absorber used on a CNC machine is investigated in this paper. The absorber is connected to a rigid mass to establish fixed boundary conditions at the joint face. Numerous dynamics tests are performed on the absorber and the Acceleration Surface Method applied to assist in the comprehension of the form of the nonlinearity.

Structural Testbed Design and Testing with Controlled Nonlinearities

Steven M. Whitican P.E. and Timothy Copeland
A structure was developed to provide a realistic test bed for high-channel-count linear and nonlinear modal analysis. The goal was to model and construct a linear structure to serve as a platform to introduce controlled nonlinearities. These nonlinearities are designed to mimic airframe nonlinear structures including ailerons, engine mounts, payload and bomb mounts including wingtip stores. The model was constructed and modeled with several pretest analyses performed to identify a minimum sensor configuration that could correlate the modes of interest. Impact testing validated the sensor configuration prior to testing with 144 input channels and multiple sources. Correlation was accomplished and resulted in an updated FE model. Once this baseline was completed the introduction of controlled nonlinearities allowed application of the existing and emerging nonlinear modal analysis tools. This article is a description of the construction, testing and correlation of the structure with a nonlinearity evaluation.


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