Described below are an electrical drive system for a door and to a method for operating an electrically driven door.
Door systems driven by electric motor are sufficiently well-known from the related art. Door systems of the type are usually driven by a rotationally operating electric motor which is supplied with current by a control device in such a way that the door is moved into its desired position (OPEN/SHUT). In order to supply such a drive system with electric power, a power supply unit is provided by which the grid-side supply voltage is converted into a voltage suitable for the door control device.
It is furthermore known to make the drive system aware of the end positions of the door, i.e. fully open or fully closed, with the aid of suitably positioned end switches. Alternatively, however, it is also possible and known to equip the electric motor with an encoder for determining the rotor position and the rotational speed. Taking the transmission ratio realized in the drive system in to account, it is possible to deduce the position of the door by suitable evaluation of the rotor position. Magnetic or optical encoder systems can be used for this purpose.
A distinction is made in principle between absolute and incremental encoders. So-called sine-cosine encoders are often used for determining the angular position of the rotor of the electrical machine or of the rotor shaft. These have the capability to determine the absolute position of the rotor in the range between 0° and 360° with the aid of two sinusoidal oscillations phase-shifted by 90°. With so-called single-turn encoders, the absolute position determination is possible for precisely one revolution. A suitable incrementation is therefore necessary in order to be able to track a change in the position of a door performed by an electric motor, since normally this requires numerous revolutions of the rotor shaft.
In order to be able to determine the absolute position of the door with the aid of such incremental encoder systems, it is first necessary to perform an initialization. For this purpose the door is initially driven into a known position, for example into one of the end positions. Starting from the position, each further position of the door can then be determined based on determination of the angular position of the rotor and the complete rotor revolutions that have already been performed.
However, if the drive system is disconnected from the electricity supply grid, such information about the absolute position of the door determined in the way described is lost. In order to be able to perform a further position determination with the aid of the rotary encoder system after the grid voltage is reapplied, the door must first be driven back into the initialization position.