Method and device for determining the position of an optical boundary surface along a first direction

A device for determining the position of an optical boundary surface along a first direction, comprising:

• an illuminating module for imaging a pattern in a plane transverse to the first direction;
• an imaging module for recording the image of the pattern imaged in the plane;
• and
• a controller which is configured to perform at least the following steps:
• a) imaging the pattern in the plane transverse to the first direction, wherein the pattern varies periodically in the plane in a second direction;
• b) recording a two-dimensional image of the pattern imaged in the plane transverse to the first direction;
• c) repeating step b) for a plurality of different positions in the first direction, wherein the plurality of different positions cover an area in the first direction in which the optical boundary surface lies;
• d) averaging each image from step c) along a direction transverse to the second direction such that in each case a one-dimensional data set is produced;
• e) transforming each data set from step d) into a frequency domain;
• f) determining the frequency of the greatest amplitude of all data sets transformed in step e);
• and
• g) determining the position of the optical boundary surface along the first direction by evaluating the data sets transformed in step e) at the frequency determined in step f).

A device for determining the position of an optical boundary surface along a first direction, comprising:

• an optics that images a pattern in a plane transverse to the first direction;
• a camera to record the image of the pattern imaged in the plane;
• and
• a controller that is configured to perform the following steps:
• a) imaging the pattern in the plane transverse to the first direction, wherein the pattern varies periodically in the plane in a second direction;
• b) recording a two-dimensional image of the pattern imaged in the plane transverse to the first direction;
• c) repeating step b) for a plurality of different positions in the first direction, wherein the plurality of different positions cover an area in the first direction in which the optical boundary surface lies;
• d) averaging each image from step c) along a direction transverse to the second direction such that in each case a one-dimensional data set is produced;
• e) transforming each data set from step d) into a frequency domain;
• f) determining the frequency of the greatest amplitude of all data sets transformed in step e);
• and
• g) determining the position of the optical boundary surface along the first direction by evaluating the data sets transformed in step e) at the frequency determined in step f).