Moulding machines shall be understood here to be injection moulding machines, transfer moulding presses, presses and in particular vertical presses and the like. For the sake of simplicity reference will frequently be made to an injection moulding machine, but without this being understood to be restrictive, since equivalent statements also apply to other moulding machines.
Generic power supply devices serve to supply electrical energy to most electrical drive systems of the injection moulding machine—for example clamping drives and injection drives. They have an intermediate circuit to which a supply module is connected. The supply module is connected to a power supply network and ensures that the correct voltage is fed into the intermediate circuit from the power supply network.
The drives of the injection moulding machine are then connected to the intermediate circuit and receive their electrical power from this.
Since power supply networks generally deliver AC voltage and since in the intermediate circuit a DC voltage should usually prevail, the supply module in most cases comprises a rectifier. If the power supply network already delivers the desired type of current (direct current or alternating current, desired voltages), then in its simplest form the supply module would merely comprise connecting leads between the power supply network and the intermediate circuit.
The most common type of intermediate circuit for injection moulding machines is, as mentioned, a DC voltage intermediate circuit. In the state of the art this essentially comprises a capacitor connected in parallel. In generic power supply devices however other intermediate circuit designs can indeed also be used.
It is known, in addition to the drives of the injection moulding machine, to connect an energy storage device to the intermediate circuit (see U.S. Pat. No. 6,333,611 B1). From WO 2005/110711 A1, for example, it is also known to execute this energy storage device as a flywheel with a drive, wherein the energy is stored as kinetic energy of the rotating flywheel.
This allows energy returned from electrical drives to be stored in the energy storage device and later reused. If a component is for example slowed down, an electrical drive can work as a generator delivering the energy to the energy storage unit and this energy can be used to accelerate this or any other drive.
The disadvantage with generic energy supplies is that in the intermediate circuit quite high fluctuations and peaks occur for example in the intermediate circuit voltage or a current strength in the intermediate circuit. The reason for this is that with injection moulding machines both very high and very small amounts of energy are transferred. As a rule, over short periods very high amounts of energy are discharged from the intermediate circuit, and these are followed by periods in which this happens only to a very small extent.
Introducing closed loop control of the intermediate circuit on its own does not provide a remedy, for it is difficult to closed loop control the drives of the injection moulding machine in such a way that the peaks and fluctuations are significantly suppressed. The drives that are normally used in injection moulding machines respond too slowly for this or are unable to utilise the available energy at the respective point in time.
The fluctuations and peaks in the intermediate circuit mean that comprehensive overload protection devices have to be provided, which is of course detrimental to the cost efficiency.