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Exposure Settings

For XY and brightness profile data, MinLaserOnTime, DefaultLaserOnTime and MaxLaserOnTime control the amount of time the laser will remain on; the camera exposure time will automatically be calculated and managed by the JS-50 device.

Two modes of exposure control are available in the Pinchot API: manual and automatic.

  • Manual mode is active when MinLaserOnTime, DefaultLaserOnTime, MaxLaserOnTime are set to the same number. This will fix the exposure time.
  • In Automatic mode, the ScanHead will determine the optimal exposure time within the range given by the three values. The algorithm will try to find the shortest exposure time that still provides high quality data.

Algorithm

For a detailed description of the Exposure control algorithm, please see Exposure in the System Design Guide.

Here is a brief summary:

Starting from the DefaultLaserOnTime, the algorithm will, over several profiles, increase or decrease the exposure time until the data quality is acceptable. The quality is determined by the SaturationPercentage value. If the percentage of saturated pixels is below the threshold, the exposure time is increased. If the percentage is above the threshold, the exposure time is decreased. This process is repeated until the MinLaserOnTime or MaxLaserOnTime is reached.

Algorithm Considerations

The algorithm will fail if not enough points are captured to make a good decision. This can happen if there is no object in the field of view, or if the object is too dark. In these cases, the algorithm will not be able to find a good exposure time and will default to the DefaultLaserOnTime.

Because of the need for multiple exposures (approx. 10 profiles), scanning light objects against a dark background can lead to an "oscillation" at the beginning of each object, where the algorithm switches between long exposure times (for e.g. a black conveyor belt) and short exposure times (for e.g. a light board). In this case, it is recommended to use manual exposure settings.

In the Exposure Editor, you can test out different settings.

Warning Signs

In automatic mode, you should check if the exposure time the algorithm has chosen is close to the MinLaserOnTime or MaxLaserOnTime. If the algorithm is consistently bumping against either value, it is a sign that the MinLaserOnTime or MaxLaserOnTime are set incorrectly, and can be lowered or raised, respectively.

If the algorithm stays at the DefaultLaserOnTime, it is likely that not enough points are captured to make a good decision.