Dalsa ML-FM-16K07A Manual page 85

Randomly Compressed Images
It is possible that when the scan speed nears the maximum allowed, based on the exposure time
used, the image will be randomly compressed and possibly smeared for short periods in the scan
direction.
This is indicative of the inspection systems transport mechanism dynamics causing momentary
over-speed conditions. The camera can tolerate very short durations of over-speed, but if it lasts
too long, then the camera can only maintain its maximum line rate, and some EXSYNC pulses will
be ignored, resulting in the occasional compressed image.
The loss EXSYNC due to over-speed may also cause horizontal image artifacts.
Over-speeding may be due to inertia and / or backlash in the mechanical drive mechanism, causing
variations around the target speed.
The greater the speed variation, the lower the target speed needs to be to avoid over-speed
conditions. If the speed variation can be reduced by eliminating the backlash in the transport
mechanism and / or optimizing the motor controller characteristics, then a higher target speed will
be achievable.
Distorted Image when Slowing Down Changing Direction
The camera must align the rows in a fashion that accurately follows the object motion.
When the scan direction changes, then the process must reverse to match the reversed image
motion across the sensor.
Only when all rows being accumulated have received the same image will the output be correct.
Prior to this some lines have been exposed to one direction and other lines exposed to the opposite
direction in the accumulated output.
Appendix B: Troubleshooting Guide • 85