Statistical Process Control Guardbanding Methods for Inline Optical Screening Systems
Inline optical screening guardbanding absorbs measurement uncertainty into narrowed specification limits to guarantee target consumer risk levels.
Line-Scan Sensors
Meaning
Optical imaging hardware captures images by reading a single row of pixels at a time rather than a full two-dimensional grid. The use of line-scan sensors is common in web production environments where materials like paper, metal or fabric move continuously past the camera. A complete image is built by stitching these individual lines together as the object moves in the direction of travel.
This architecture allows for high resolution in the axis of motion without the need for large area sensors.
Temporal Resolution
The rate at which the camera captures lines must be synchronized with the speed of the production line. If the line-scan sensors trigger too slowly, the resulting image will appear compressed, while triggering too fast causes elongation. Encoders are typically used to provide a hardware pulse that ensures each line corresponds to a fixed distance on the material.
Throughput Velocity
These devices excel at inspecting large surface areas for tiny defects such as scratches or pinholes. Because line-scan sensors can operate at tens of thousands of lines per second, they can monitor wide webs moving at hundreds of metres per minute. This capability makes them the standard choice for high-volume roll-to-roll manufacturing.
Illumination Profile
Continuous illumination is required because the sensor is always active during the scan. While traditional cameras use strobes to freeze motion, systems using line-scan sensors rely on high-intensity line lights that focus energy on the narrow strip being captured. This concentration of light allows for very short exposure times and high throughput speeds.
The illumination must remain constant across the entire width of the sensor to prevent false gradients in the data.