The optimization process of the laws of motion described in the previous paragraph was assisted by the results of the multibody models developed in RecurDyn.
The cut and weld unit was initially represented using a multibody model made of rigid bodies only. This model was suitable for use during the optimization process because the time required for the calculation was less than 20 seconds. This model was then used to optimize the laws of motion for the two electric motors, and also to verify their synchronization. (The synchronization of the motors is very important to perform a precise cut of the film and to avoid collision with the other components). Once the optimization process was complete, several components of the cut and weld unit were transformed from rigid to flexible bodies (Fig. 8). The simulation was repeated to calculate the stress acting on the components under dynamic conditions. No structural problems were found demonstrating that the optimization of the laws of motion was able to increase the performance of the machine as required, minimizing the variation of internal loads. At the same time, this result proved the robustness of the machines designed by OPEM.
The model for the film feeder was not developed starting from rigid bodies alone: the flexibility of the film was taken into account from the outset to ensure that the modification of the law of motion did not affect its dynamics and final position. The film was modelled using RecurDyn’s proprietary Full Flex approach to correctly represent the film’s large displacements during lateral movement. (Full Flex technology transfers the full stiffness matrix of an object to the RecurDyn solver, i.e. all the degrees of freedom (d.o.f) of the flexible bodies are taken into account during the solution, which allows the correct representation of nonlinearities such as: large deflections, nonlinear materials and contacts over flexible surfaces). Once the optimization process was completed, the side plates of the unit were transformed from rigid to flexible (Fig. 9) to calculate both the stress acting on these components, and to assess whether their flexibility could cause unwanted lateral oscillations of the film at the end of the movement.
Once again, the optimization process led to a law of motion able to meet the requirements without introducing structural problems. In addition, the interaction between EnginSoft and OPEM’s engineers highlighted some areas where the weight of the unit could be further reduced to achieve even better performance in the future.
The multibody model developed to study the conveyor included more than 300 contact points since all the chain links are supported without the use of joints. Their interaction with the sprockets and guides relies only on the contacts. This model was used to calculate the motor torque, to simulate the chain dynamics and to calculate the chain tension resulting from the preload and the conveyor’s movement.
The loads obtained from the multibody models were subsequently used for the structural verification of the frame. A finite element model was constructed using ANSYS Workbench to calculate both the deformation and the stress acting on the structure (Fig. 10 and Fig. 11).
Fig. 10 - Magnified view of the frame’s deformation
Fig. 11 - von-Mises stress contour