Laser Line Triangulation Profilometry Principles on Continuous Paperboard Substrates
Inline blue laser triangulation measures paperboard surface topography at high speeds by overcoming fiber light penetration and isolating mechanical flutter.
Center of Gravity Shift
Radial Displacement
Dynamic eccentricity in a winding roll of paper or board occurs when the geometric center of the roll departs from its rotational axis. This eccentricity creates a continuous center of gravity shift as the material unwinds at high speeds on converting lines. The movement arises from non-uniform caliper profiles across the web, which accumulate unevenly with each wrap on the core.
When the heavier side of the roll rotates, it produces a cyclical force that increases quadratically with rotational speed.
Mechanical Tension
Vibration and tension variations on the unwind stand directly depend on the magnitude of the displacement. As the center of gravity shift grows, it introduces a variable pull on the paper web that destabilizes the tension control system. Converting lines must adjust brakes and motors dynamically to compensate for these pulses, or risk web breaks.
The mechanical strain on the chucks and bearings also increases, which shortens the operating life of the machinery.
Rotational Boundary
Operating limits for web speed are governed by the maximum allowable force from the unbalanced mass. Converters typically run high-caliper board rolls at lower rotational speeds to prevent the center of gravity shift from reaching critical limits. When a roll exceeds the safety threshold, the resulting vibration causes sheet flutter and misregistration in printing and die-cutting steps.
Control of this effect relies on profiling the thickness of the paperboard during manufacturing to maintain cross-direction uniformity.