Brewster Angle Polarization Inspection for Relief Print Alignment
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Solution Overview
Problem
In the production of relief prints, such as imitation wood, the texture and transparent plastic layer often fail to align perfectly, leading to optically unattractive effects when the displacement exceeds a certain threshold, making it difficult to detect faulty prints during the manufacturing process.
Innovation Solution
A method involving illumination with unpolarized light at the Brewster angle, combined with a recording unit that captures images with polarization perpendicular and parallel to the plane of incidence, allows for the determination of offset between the texture and plastic layer by cross-correlation analysis, enabling precise detection of register accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional illumination and recording methods are used, then the production process can proceed quickly, but the detection of offset between texture and plastic layer is difficult and imprecise
Solution Approach 1:
The patent applies parameter changes by utilizing Brewster's angle illumination and polarization filtering to transform the optical properties of the reflected light. By illuminating at the specific Brewster angle and using polarization filters oriented perpendicular and parallel to the plane of incidence, the system creates distinct image contrast patterns that reveal offset between texture and plastic layer. This physical parameter change enables precise offset detection without requiring mechanically complex equipment.
2Manufacturing precision
If the texture and plastic layer are manufactured with high precision alignment, then optically unattractive effects are eliminated, but manufacturing complexity and cost increase
Solution Approach 1:
The patent implements self-service by using the optical properties of the relief print structure itself to perform the alignment verification function. The Brewster angle illumination and polarization filtering cause light to reflect differently from areas where texture and plastic layer are aligned versus areas where they are offset. This self-indicating optical mechanism allows the product structure to reveal its own alignment status without requiring external complex measurement equipment or additional manufacturing steps.
3Reliability
If offset between texture and plastic layer is detected early, then faulty prints can be eliminated from production, but inspection time is required
Solution Approach 1:
The patent enables continuous quality verification by implementing an optical inspection method that can be performed rapidly during or immediately after the printing process. The Brewster angle illumination and polarization-based imaging allow for quick capture of offset information without requiring stopping the production line or performing time-consuming manual measurements. The method provides continuous feedback on alignment quality, enabling real-time quality control.
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 allows for simple and efficient detection of register accuracy in relief prints, ensuring that the texture and plastic layer align correctly, thereby preventing optically unattractive effects and improving the quality of the prints.
Implementation Method 1
The term Brewster's angle is used in connection with the invention. This corresponds to an angle at which unpolarized light incident on the boundary surface of two dielectric media is only reflected that which is polarized perpendicularly to the plane of incidence. The reflected light is then linearly polarized.
Implementation Method 2
c) with the recording unit taking a first image of the object is created, only light with a polarization perpendicular to the plane of incidence being used for the recording, d) a second image of the object being created with the recording unit, with only light with a polarization parallel to the plane of incidence being used for the recording
Data Source
Figure 1~2
Figure 3~4
Figure 5~5b
AI summary
The invention relates to a method for inspecting an object (1), in particular a flat object, comprising: - a texture (10) with a printed predetermined color gradient, and - a transparent plastic layer (11) with a relief-like gradient corresponding to the color gradient, arranged over the texture (10), to determine whether the texture (10) and the plastic layer (11) are precisely aligned, a) wherein the object (1) is illuminated with unpolarized light, which is directed onto the object (1) at the Brewster angle (ΘB), with a maximum deviation of 10°, b) wherein the object (1) is recorded from the opposite side by means of a recording unit, the optical axis of which is at the Brewster angle (ΘB), with a maximum deviation of +/- 10°, to the surface of the object (1), and wherein the optical axis of the recording unit and the direction of incidence of the incident light lie in the same plane.c) wherein a first image (B1) of the object (1) is created with the recording unit, using only light with a polarization perpendicular to the plane of incidence for recording, d) wherein a second image of the object (1) is created with the recording unit (3), using only light with a polarization parallel to the plane of incidence for recording, e) wherein the two images (B1, B2) are compared with each other by correlation and an offset between the two images (B1, B2) is determined based on the result of the correlation, and f) that the offset thus determined is compared with a predetermined threshold value and, if the threshold value is exceeded by the offset, it is determined that the texture (10) and the plastic layer (11) are not precisely aligned.