Method and device for detecting defects during sealing of a package comprising a film

A method for detecting defects during sealing of a package comprising film, comprising:

• positioning the film and another part of the package comprising film between two parallel sealing bars, wherein the sealing bars extend in a longitudinal direction;
• moving one or both of the sealing bars towards each other along a trajectory A, wherein a connection is formed between the film and the part of the package comprising film;
• moving one or both of the sealing bars along the trajectory A, wherein the sealing bars are removed from each other;
• and removing the sealed package;
• characterized in that at least during the moving of one or both of the sealing bars towards each other, distances between both of the sealing bars or distances between one of the sealing bars and a sealing bar holder are measured by means of several distance sensors, and in that the method comprises calculating a unitless measure of deviation at a point in time T and comparing the unitless measure of deviation to a predetermined threshold value, wherein the point in time T is in a time interval in which the measured distances change or have changed by moving the one or both of the sealing bars towards each other and before the one or both of the sealing bars are removed from each other, wherein the unitless measure of deviation is calculated from a relative measure for a distance between both of the sealing bars or between one of the sealing bars and the sealing bar holder;
• and
• characterized in that the unitless measure of deviation is the square root of a weighted square sum of at least a first term and a second term, where the first term is a relative measure for a distance between both of the sealing bars or between one of the sealing bars and the sealing bar holder and where the second term is a relative measure of a rotation of one of the sealing bars about an axis E, and where the axis E intersects the sealing bar and is transverse to the trajectory A and transverse to the longitudinal direction of the sealing bars.