Method of producing a microstructured product

A two-sided microstructured product comprising:

• primary product features provided at a first surface;
• secondary product features provided at an opposed surface in alignment with the primary product features;
• a registration-array of focusing elements at the first surface;
• and
• a registration-array of reference objects at the opposed surface,
• wherein the registration-array of focusing elements is aligned with primary product features at the first surface and the registration-array of reference objects is aligned with secondary product features at the opposed surface, wherein the first and second registration features are provided so that each focusing element is arranged to magnify a small section of an associated reference object so that the registration-array of focusing elements and the registration-array of reference objects are arranged to provide a synthetic integral three dimensional image perceivable as a magnified representation of the reference objects and so that relative misalignments between the arrays are magnified in the synthetic integral three dimensional image, and wherein the registration-array of reference objects comprises one or more pairs of adjacent complementary sub arrays of reference objects that have different periods of repetition in at least one direction so that the one or more pairs of complementary sub arrays gives rise to deviating synthetic integral three dimensional image representation effects in response to a misalignment.

An apparatus for producing a two-sided microstructured product in a continuous process along an elongated substrate sheet comprising:

• means for providing primary product features at a first surface of the substrate sheet;
• means for providing secondary product features at the opposed surface of the substrate sheet;
• means for providing primary registration features comprising a registration array of focusing elements on the first side of the substrate sheet, which primary registration features are aligned with the primary product features at the first surface of the substrate sheet;
• means for providing secondary registration features comprising a registration array of reference objects on the opposed side of the substrate sheet, which secondary registration features are aligned with the secondary product features at the opposed surface of the substrate sheet, wherein the registration-array of focusing elements and the registration-array of reference objects are arranged to provide a synthetic image perceivable as a representation of the reference objects, wherein the registration-array of reference objects comprises one or more pairs of adjacent complementary sub arrays of reference objects that have different periods of repetition in at least one direction, so that the pair of complementary sub arrays gives rise to deviating synthetic integral three dimensional image representation effects in response to a misalignment;
• a registration detection system arranged to register the mutual alignment of the primary and secondary product features and to estimate alignment parameters, involving identification of the relative positions of the primary and the secondary registration features of the registration structure, wherein the synthetic integral three dimensional image is used to improve the accuracy of the registration features, and
• an alignment control system arranged to align the provision of primary and secondary product features by controlling at least one of the means for providing product features by feedback of alignment parameters.