Piezoelectric Sensor Frequency Response Calibration for Folding Boxboard Converting
Piezoelectric sensor frequency response calibration prevents amplitude distortion during high speed creasing by matching amplifier cutoff to rule strike transients.
Nyquist Frequency
Sampling Limit
Theoretical thresholds in digital signal processing define the maximum frequency that a scanning system can accurately capture without distortion. The nyquist frequency represents half of the sampling rate of the optical sensor or digital camera used in paper inspection. When scanning printed paperboard, any surface details or halftone patterns that exceed this limit cannot be reconstructed correctly.
This limitation requires prepress software to adjust image resolution before plate making to ensure high-fidelity reproduction.
Moire Control
Halftone printing uses regular patterns of tiny dots to create the illusion of continuous tone images. When the spatial frequency of these halftone dots approaches or exceeds the nyquist frequency of the plate scanner or plate setter, severe optical interference occurs. This mismatch generates visible, wavy moiré lines across the printed surface, spoiling the appearance of the packaging graphics.
To avoid this distortion, prepress operators must use stochastic screening or adjust the angle of the halftone grids. Such steps ensure the printed frequencies remain safely below the capture limit of the digital reproduction equipment.
Inspection Resolution
Automated inline cameras used to detect defects on moving paperboard webs rely on high-resolution sensors. These cameras must have a nyquist frequency that is higher than the finest print details on the board.