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Download SimMechanics User`s Guide
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mech_pdf.book Page 16 Tuesday, February 1, 2005 1:57 PM 8 Case Studies Trimming Mechanical Models Trimming a mechanical system refers to the finding of solutions for inputs, outputs, states, and state derivatives satisfying conditions that you specify beforehand. For example, you can seek steady-state solutions where some or all of the derivatives of a system’s states are zero. To use the Simulink trim command on a system represented by a SimMechanics model, you must select the SimMechanics Trimming mode (see “Analyzing the Motion” on page 5-7). You must also specify the conditions that the solution must satisfy. These examples show you how to trim mechanical models. • “Unconstrained Trimming of a Spring-Loaded Double Pendulum” on page 8-17 • “Constrained Trimming of a Four Bar Machine” on page 8-23 Consult the Using Simulink documentation for more on trimming models. You can also enter help trim at the MATLAB command line. Restrictions on Trimming Mechanical Models You should avoid using certain SimMechanics or Simulink features when trimming a model. • A trimmed SimMechanics mechanism must be assembled. Do not use disassembled joints while trimming. (For more information, see “Modeling with Disassembled Joints” on page 4-30.) • You cannot use Driver blocks while trimming a model. • SimMechanics ignores Joint Initial Condition Actuator blocks in a trimmed model. • Do not incorporate events or motion discontinuities in your trimmed model. In particular, do not use SimMechanics Joint Stiction Actuator blocks. Trimming mechanical models with stiction causes an error. 8-16
