The accuracy and quality of the imaging data achieved in industrial OEM cameras partly depends on the accuracy of the sensor mounting and alignment processes. Despite this, it may not be a consideration in the machine vision camera selection process.
With industrial cameras there is often a shallow depth of field (DOF) in order to get the most amount of light matched with the image sensor's sensitivity. The DOF in the scene is translated by the lens from an image towards the image sensor with a DOF at sensor side in the magnitude of 50- 100um. If there is any tilt in the mounting and positioning of the sensor, one edge of the image could be sharp while the other edge is blurry. If the alignment is not precisely centered, part of the image could be unusable.
Not only is attention to detail in the initial alignment process necessary, but also measures need to be taken to maintain the alignment during operation such as careful material selection. The sensor is in a ceramic package and needs to remain aligned despite heating up during camera operation. Even though the package will expand the sensor needs to stay exactly at the optical center. In many outdoor applications this is further challenged by a combination of extreme environmental temperatures, shock, and vibration.
Accurate sensor alignment needs done in all 6 degrees of freedom (DoFs; translations x, y, z and rotations around x, y, z axis). As a note, it is the sensor, and not the sensor package, that is positioned for optimal performance.
Often this is done with a combination of measurement equipment and an experienced operator. With the release of the Quartz Q-12A65 into production, Adimec also developed a fully automated alignment tool to make sure each sensor is put into our cameras exactly the same way. Sharpness is measured until the fastening is stable requiring no user intervention while completing the process very quickly. This guarantees that all specification points on the alignment will be accurate, regardless the operator controlling the tool.
The result of this attention to precision placement and alignment is extremely consistent cameras. This allows for improved tool matching, minimal set-up time, exchangeability, and simplified system alignment, and many other benefits depending on the application.
For instance, in traffic applications the camera can be 10 to 20 meters above the highway. As the system heats up and the lens mounts expands, the image can get out of focus and blurry without accurate sensor mounting and proper heat resistant materials. The other options to compensate for this are to get a bigger depth of focus, which means less sensitivity in dark, or use a special (expensive) lens.
This is a detail that may be overlooked in the evaluation process. The camera provided for evaluation may not represent the typical camera or without evaluating a few cameras, the camera-to-camera consistency cannot be measured. When finalizing your camera selection, we recommend evaluating the sensor alignment after long periods of operation (in typical system conditions) as well as that of at least 3 cameras of the same model.
See also: How to select the best industrial camera