Method for generating a control output for a position control loop

A method for generating a control output for a position control loop of a movable test object, said method comprising the steps of:

• optically measuring the position of the test object by focussing a measuring beam generated by a light source onto the test object using an optical system, and reflecting the measuring beam from the test object as a focussed spot onto a position-sensitive light detector to obtain measured position information;
• reading the measured position information obtained from the light detector serially into an analog to digital converter to obtain digitized position data;
• transmitting the digitized position data a digital signal processor;
• interpolating the digitized position data in said digital signal processor taking into account a distribution function corresponding to the actual intensity distribution to give a position signal corresponding to the geometric center or the maximum (I0) of the intensity distribution of the focused measuring spot;
• calculating a desired position of the test object with a system control computer;
• supplying the calculated desired position to the signal processor;
• generating a digital control value by comparing the position signal of the focussed measuring spot determined by interpolation with the calculated desired position;
• generating an analog control value from the digital control value in a digital to analog converter, and
• inputting the analog control value into a control loop for regulating the position of the test object.