Electronics Design and Controller Structure
The drive electronics consist of two function blocks: The commutation electronics for the motor, the interpolation, and the limit switches are located directly in the drive housing. This allows short encoder lines to prevent signal interference. A single cable connects the drive to the second function block and the external electronics, which control the motor, piezo, and encoder. The main controller has three channels. This means that only one controller is required to control all three hybrid drives of a mirror segment. At the same time, it is possible to specify motion commands for each individual drive as well as the desired position of the mirror segment.
The controller then "translates" a command for its three axes. The control principle of the hybrid drive is easy to understand: The motor voltage is derived from the control voltage of the piezo. The greater this voltage, the faster the motor runs. When the piezo expands, the motor drives the spindle in the same direction. In this way, the coarse positioning of the spindle is supplemented by the fine positioning of the piezo. At the same time, the spindle always moves the piezo near to its zero position automatically. This gives it the best chance of correcting the position in both directions. In this way, relatively long travel ranges can be combined with an extremely high positioning accuracy.
The performance of the hybrid drive was confirmed during extensive testing at the ESO. The flexible controller concept is very much appreciated by everyone and this simplifies subsequent enhancement.