Autofocus measurement system

Autofocus Principle: A laser beam from the sensor is focussed onto the surface to be measured. The reflected
light is gathered by the sensor lens, decoupled and divided in two orthogonal focal lines.

If the surface to be measured is exactly in the focus so that the laser beam is correctly focussed, a detector
which is positioned in the middle of the focal lines forms a circle. Every deviation from the focus results in an
ellipse. From the direction and eccentricity of the ellipse the software derives the height changes of the surface.

The deviation of the ellipse form from the circle form will be evaluated by means of the different current distribution
in the four quadrants of a photo diode. A control circuit controls the adjustment and tracking of the lens until the
surface is in the focus again. That tracking of the lens is determined by a glass scale and results in the measurement
value.


          

Technical Data Autofocus:

Measurement range:                     [µm]            1500
Resolution vertical:                        [nm]            > 10
Reproducibility:                             [nm]            < 10
Working distance:                         [mm]           2
Laser wave length:                        [nm]            780
Laser class:                                                   1
Laser spot diameter:                     [µm]            approx. 2
Tilt angle max.:                             [°]               ± 25
Scanning rate, max.:                     [kHz]          10


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