Kinoform Optical Element for Laser Window Cutting
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Solution Overview
Problem
Current methods for producing windows in security documents, such as banknotes, are either slow and expensive due to the use of laser cutting or lack the ability to efficiently individualize window shapes, while existing techniques during paper production may not offer sufficient precision and adaptability.
Innovation Solution
Incorporating a kinoform optical element in the laser beam path to focus the laser beam onto the security paper, allowing for precise and efficient cutting of window shapes by concentrating the beam along the contour of the window, enabling faster production and individualization of window areas using a high-power laser with a kinoform optical element designed for optimal intensity distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser cutting with a moving laser beam is used, then manufacturing precision and individualization capability are improved, but productivity deteriorates due to very slow cutting speed
Solution Approach 1:
The invention transitions from a moving laser beam (1D scanning) to a stationary laser beam with a kinoform optical element that projects the window contour directly onto the paper (2D direct imaging). This dimensional change allows the entire window shape to be cut simultaneously rather than sequentially, dramatically increasing productivity while maintaining precision.
Solution Approach 2:
The invention replaces the mechanical scanning system (moving laser beam) with an optical system (kinoform optical element) that uses light diffraction and interference patterns to directly project the window contour. This substitution eliminates the speed limitation of mechanical movement while preserving cutting precision.
2Device complexity
If conventional lens arrangement is used, then device complexity is reduced, but manufacturing precision deteriorates due to intensity drop at edge regions
Solution Approach 1:
The kinoform optical element changes the optical parameters by using diffractive structures with varying surface heights or refractive indices to control the phase and amplitude of light. This allows precise control of energy distribution across the window contour, maintaining uniform intensity without requiring complex multi-lens arrangements.
Solution Approach 2:
The kinoform optical element applies local quality by having different optical properties at different locations on the element. Each region of the kinoform is designed with specific surface characteristics to direct light precisely to corresponding regions of the window contour, ensuring uniform energy density throughout the cutting path.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the time required to cut out windows in security paper, enhances the ability to individualize window shapes, and maintains consistent energy density along the cutting path, improving the efficiency and precision of the window-cutting process.
Implementation Method 1
kinoform optical element is arranged, which projects, in particular focuses, the laser beam onto the surface of the security paper
Implementation Method 2
laser beam is projected, in particular focused, onto an area of the surface of the security paper in such a way that the laser beam is projected onto a linear surface area following the contour of the window
Implementation Method 3
laser for producing a window in security paper... the laser beam onto a linear surface area following the contour of the window... Surface area is concentrated
Data Source
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AI summary
The device (1) has a kinoform optical element (11) e.g. programmable kinoform optical element, arranged in an optical path between a laser (10) e.g. carbon dioxide laser, and a surface of a paper reel (12). The optical element projects laser beam (10s) on the surface of the reel, which is arranged on a plate shaped cutting support (14) e.g. vacuum plate, in a cutting area such that the laser beam is concentrated on a linear surface area following a contour of a window and/or a planar surface area enclosing the contour of the window. An independent claim is also included for a method for creating a window in an antifalsification paper that is provided for producing of a valuable or security document by laser beam provided by laser.