Flatness based control of an injection moulding machine
Sprache des Vortragstitels:
Fourteenth International Conference on Computer Aided Systems Theory, EUROCAST 2013
Sprache des Tagungstitel:
In injection moulding especially the appearance of a work piece depends much on the exact compliance with certain trajectories of temperature or pressure in the mould. Since the parameters of the process depend on the actual form of the work piece and the several pieces which are manufactured on one machine differ from each other an automatic identification of the interesting parameters is compulsory.
This is entirely done with open source software released under GNU General Public License which is an interesting alternative to save development costs.
It turns out that during the holding phase the work piece can be sufficiently modelled by a nonlinear spring. Its characteristic line is identified automatically using least squares cubic spline fitting.
If the screw is positioned by hydraulic actuators, the elastic behaviour of the oil in the hydraulics can not be neglected due to the high pressure during the holding phase. This yields another nonlinear differential equation for the pressure of the oil.
The overall system is flat with the flat out put being the position of the screw. So the trajectories are planned and ensured with an input-state-linearising controller. For a stainless piece the sign of the velocity of the screw must not change. So the trajectories have to be monitored closely and re-planned if necessary leading to a model predictive algorithm.
Since the entire state is not measurable a reduced observer is implemented whose error dynamics are linear despite of the nonlinear system.