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Using Line Scanning For Large or Cylindrical Parts

Products and the myriad of parts they are comprised of come in all different shapes, sizes, materials and colors. Inspecting these components is a task often automated by their manufacturers, but is never as easy as it sounds and there are many factors to consider. Using machine vision to automate that process makes sense, but what do you do when the part is either large or cylindrical, such as a can or bottle? One option to consider is using a line scan camera to capture a detailed image for analysis.

Line scan imaging assembles an image from multiple "snaps", with a typical snap covering the entire X or Y axis but is only a single pixel wide. The frames are continuously fed to a computer that joins them to each other and generates an image. This makes sharp pictures of objects that have passed in front of the camera at high speed.

 

When capturing a detailed image of either a cylindrical or large part using line scanning, motion is an essential consideration. Line scan systems are best employed in high-speed processing or fast-moving conveyor line applications. In the case of a cylindrical part, such as a can (image above), the ideal solution would include rotating the part in front of the camera. In the situation involving a large part (image below), the part would be moving on a conveyor. The coordination of motion and image acquisition timing are critical for line scanning, but only simple illumination is required.

 

Line scanning can be an advantage over other methods, such as multiple cameras positioned around a stationary, cylindrical part, in the following situations:

  1. If you are performing surface or dimensional inspections. With a cylindrical part and mulitple area scan cameras evenly arranged around the stationary part, the depth of focus may be negatively affected around the edges. Line scanning better captures any curvatures for precise and accurate inspections. Using multiple cameras and associated lenses can also be costly.
  2. Line scanning produces a continuous image, which prevents missing any aspects of what you are trying to inspect, especially if they happen to occur where the part curves. Additionally, the image can be saved for reference and better quality control.

There are drawbacks to line scanning. The primary one being the larger output file size created when multiple line scans are combined to produce a single image. A secondary consideration when using line scanning to capture images of smaller parts would be any additional optics necessary to achieve the required resolution.

The bottom line is that every situation is unique, and experienced engineers will consider all options when designing the best possible automated inspection solution.