You may have heard about line scan cameras but are not sure exactly what they are and why they are so useful?
Here is a brief overview of all the basic information about line scan cameras to help understand these ingenious image capturing devices better.
What exactly is a line scan camera
As its name suggests, a line scan camera capture images line by line. The result is a high precision and very detailed image of the object being scanned. These types of cameras are irreplaceable when it comes to capturing images of fast-moving objects.
They are usually used for capturing all details and for detecting any defects or other detailed on continuous high-speed processes, such as a continuous product on a conveyor production line, free falling objects or rotating ones.
Line scan cameras are also used for those precise finish line images (photo finish) which you have probably seen if you have ever watched sprints and other athletic disciplines where every millisecond and millimeter counts when it comes to establishing who the winner of the race is.
Why are line scan cameras so useful for quality control and production monitoring?
Imaging a huge production, where continuous rolls and sheets of different materials are moving on conveyor lines through all production phases. While before human quality control was utilized for ensuring the production doesn’t have any defects, today more manufacturers are installing machine vision systems for control and defect detection. Line scan cameras are essential parts of these systems for production control.
With their help, the production can go on without the need to be stopped periodically for quality control. Needless to say, this saves immense amounts of time, manpower, and money for the manufacturers.
Also, the resulting images from a line scan camera allow for much more detailed inspections and finding defects which the naked eye can miss.
How exactly does a line scan camera work?
This type of camera has a single row of pixels which are light sensitive and capture single-pixel slices of the object either as the object passes by the light scan camera or by moving the camera on top of it.
The cameras are programmed to take a specific number of images for a certainly predetermined time frame. All of the slices captured within that time are called a “frame”.
The line scan camera is connected to the other elements of the line scanning system or machine vision system. The slices in each frame are precisely lined up along one another in a consecutive succession with the help of a special motion encoder. This encoder calculates the speed of the moving object and the camera line rate and synchronizes them perfectly in order to stitch all of the image slices in correct order. The result is a very clear, detailed and not blurred image of the entire object.
The process is not as simple as it may sound though due to the fact that conveyor lines, falling objects or other moving objects being monitored can move at different speed at different times.
This is why for separate objects, trigger pulses are used for detecting the exact moment when the start and the end of an object occur as it passes in front of the camera.
For rolling objects, rotary motion encoders with toggle switches are used to determine the exact moment when an object begins rolling and fully rotates so that the line scan camera can capture slices of each and every part of the rolling object.
Another essential aspect of the proper functioning of such line scan systems is the synchronization of the sensors of the line scan camera with the lighting. This is why frame grabber cards are used as part of these machine vision inspection systems.
A well set up and synchronized system for automatic control and detection by line scanning needs to be properly connected with reliable input lines.
It should enable the increase of the line scan camera acquisition rate if a faster speed of the objects is detected, and likewise to decrease the rate if the speed of the conveyor or other mobbing object or action decreases.
What are the most common uses of line scan cameras?
These types of cameras are highly effective for the production and quality control of various types of production and sorting processes. Line scan cameras and the machine vision inspection systems can provide real-time detailed monitoring for defects or other problems of continuous production processes without disrupting or stopping it.
These cameras are particularly useful for the inspection of continuous long sheets of metal, paper, textile, telecommunication fibers, glass, wafers, and others. They are also used for the control of the production of various electronic components, print, raw material inspection, barcode scanning and reading in all kinds of industries.
Line scan cameras can help automate and speed up precise sorting of postal packages, foodstuffs, waste management, pharmaceuticals and others.
They are also commonly used to monitor free falling objects such as molten metal, glass and other types of production which cannot be stopped for manual inspection.
As mentioned in the beginning of the article, line scan cameras are also still very much used for capturing various sports events, such as photo finish images and other critical parts of a sports event or race, which cannot be captured by a normal camera, and which are important for determining the winner or other essential elements of a sports event.
Types of line scan cameras
Apart from the traditional one-pixel line scan camera, nowadays there are others which capture 2-pixel lines of the same slice simultaneously allowing for a much brighter and clearer image.
There are also modern TDI line scan cameras with multiple pixel lines, which capture the same slice of the image multiple times while collecting more incidental light in the process. These are used when the lighting is low or inconsistent, as well as for cases when very high precision imaging is needed.
Hopefully, this brief overview of the basics of line scan cameras has given you an idea of what they are, what they are used for and just how useful these types of cameras really are!