WCA September 2016

❍ ❍ Figure 6 : Speed and torque on each back-twist shaft As active parts of the machine, the electric motors, are modelled taking into account the real inertia of the rotating parts and using the real constructive curves (torque and speed) of modern induction motors. Starting from the MFL 3D CAD geometry of the machine, the dynamic model is defined in the RecurDyn ® environment.The result is an accurate model with more than 100 bodies. Most of the inertial proprieties are derived automatically from CAD, but several bodies are parametrised inside the multi-body software. Obviously, the connection between the different bodies perfectly simulates the real kinematic link (gear, shafts, and so on) in order to obtain a model which is the closest as possible to the real machine in terms of degrees of freedom. Gear elements are special features of the RecurDyn ® library, designed to simulate both kinematics (transmission ratio) and dynamics (reciprocal loading) occurring at any gear couple. Figure 4 shows the gears back-twist system. It is easy to see that the “gear feature” of RecurDyn ® has been massively used due to the conformation of the transmission chain. When each simulation runs, all loads are automatically combined together along the transmission chains, leading to a precise estimation of the power demand at all motor shafts.

❍ ❍ Figure 4 : Planetary back-twist

Power (kW)

Speed (rpm)

Torque (Nm)

❍ ❍ Figure 7 : Torque curve on a gear

Speed (rpm)

❍ ❍ Figure 5 : Induction motor power and torque curves

In other words, this activity is the scientific and precise application of the design of experiment (DOE). Rigid body dynamics model A rigid body dynamic analysis is performed; internal loads and motor power torques mainly depend on accele- ration and inertias of moving parts, so that there is not a clear need of introducing flexibilities into the model (which would significantly increase the computational effort).

Back twister 1 – wheel 2 – torque mag (Nm)

Time (s)

106

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Wire & Cable ASIA –September/October 2016