Rolling Shutter Artifacts on a Moving Inspection Line
Rolling shutter inspection lines require pulsed strobe lighting within global overlap windows or native global shutter sensors to eliminate motion shear errors.
Line Scan Frequency
Scan Rate
Rate at which a linear sensor array captures single rows of pixels to build a two dimensional image of a moving object. High speed imaging systems depend on line scan frequency to synchronize the acquisition with the velocity of the material being inspected. It determines the vertical resolution of the resulting image and the maximum throughput of the inspection station.
Velocity Matching
Synchronization between the conveyor speed and the camera trigger is necessary to prevent the image from appearing stretched or compressed. Adjusting the line scan frequency allows the system to maintain a constant aspect ratio regardless of fluctuations in the production line speed. An encoder mounted on the drive shaft typically provides the timing signal for each new line.
Exposure Timing
Shorter intervals between lines limit the amount of time available for the sensor to collect light for each row. A high line scan frequency requires intense illumination to ensure the image has a sufficient signal to noise ratio. Increasing the gain of the sensor can compensate for low light but also introduces electronic noise that may obscure fine details.
This balance is critical when inspecting dark or non-reflective surfaces at high speeds.
Bandwidth Constraint
Data transmission rates from the camera to the processing unit are limited by the interface standard used. If the line scan frequency exceeds the capacity of the cable, the system will drop frames and lose information. Choosing the correct interface ensures that the full resolution of the sensor is available for analysis.