When you think about a line scan camera, probably the first thing that comes to mind are those strange looking photo finish images we have all seen when watching the Olympics or other important races where the photo finish often is the determining factor for selecting the winner of a sprint or other fast race.
Yes, line scan cameras have been used for capturing significant moments in sports where no other camera or person can see exactly who has crossed the finish line first especially when the difference between the runners or other athletes can be measured only in milliseconds or millimeters.
But there are other very important uses for these small and yet highly efficient cameras as well.
Line scan cameras and machine vision systems for quality and process control
Machine vision systems for inspection and control featuring line scan cameras allow for highly efficient process control, automatic inspection and robot guidance in various industries.
Line scan cameras are often used for machine vision systems for the inspection and control of industries and processes which involve fast moving actions, processes, and objects.
Some of the most common uses of machine vision inspection and control systems featuring line scan cameras include the production of continuous webs or sheets of textile, glass, metal, wood, paper, and others. These productions usually consist of fast-moving conveyor lines and the quality control of the product is very difficult to be performed without the aid of this modern technology often because detects are not visible to the naked eye, and more importantly, they cannot be seen without the production process being stopped.
With the help of a line scan camera which is properly synchronized with the other elements of the machine vision system, this control can be performed automatically and continuously without the need of stopping the conveyor line.
Another very useful implementation of line scan cameras is for the sorting of fast moving or free-falling objects in the postal service, or in the food or pharmaceutical industry.
Line scan cameras are indispensable for document scanning and print inspection of fast-moving conveyor lines too.
They can be used for the control of the processes in industries where there is molten glass or metal which cannot be inspected in any other way because the process cannot be stopped without the product being damaged.
How do line scan cameras actually work
A line scan camera typically has just one single line of light-sensitive pixels which captures just one line of an image at a time. But it is a very high-speed camera, so it is able to capture multiple consecutive lines or slices of the fast-moving object so that the software of the machine vision system can stitch them together to create a whole and very detailed image of the object being monitored.
This may sound quite simple, but in actuality, such a machine vision system is quite complex and consists of various essential elements interconnected with reliable connections and working in perfect synchronization with one another to produce such non-distorted and very precise images.
Linear motion encoders are used to measure the speed of the conveyor line in order to determine the frame rate and the number of lines which the camera needs to capture per second or minute. They also detect when the line speeds up or slows down in order to adjust the acquisition rate of the line scan camera with the speed.
In the cases when rotating objects such as pill bottles or other objects are being inspected, a rotary motion encoder is used to determine the exact start and finish of a full rotation of each object and thus determine the acquisition rate of the line scan camera.
When the conveyor line is carrying separate products, trigger impulses are used for determining the frame rate of the camera in accordance to the exact moment and place where the object begins and when and where it ends.
Frame grabber cards are also crucial parts of a machine vision system. They synchronize the sensors of the cameras with the light sensitivity. This is very important due to the fluctuating light of most fast moving productions.
In the end, special software is used for the automatic “stitching together” of the separate slices of each frame and for creating the full image of the product or other object being monitored.
Why are line scan cameras so useful for fast object monitoring and inspection systems
Typically, line scan cameras are very small, so they can be placed in very compact or tight spaces, where no other form of monitoring and control and be implemented.
They are also less expensive and are much more efficient than human quality control.
Plus, with a well-synchronized machine vision system, there is no need to stop the production process in order to perform detailed quality control of the products, which is a huge plus for many industries where the production cannot be stopped, or where each stopping of the production line causes big losses.
Line scan cameras provide much more detailed control of the quality of the products and can capture images of defects which are often impossible to spot by the naked eye.
Overall, these systems for automatic quality control and process control are saving huge amounts of time and money for different industries, and line scan cameras are often the centerpieces of these systems.
For some specific needs, production owners install line scan cameras with two or more pixel lines (TDI line scan cameras). These capture multiple images of a single line, and then these images are put together for a more precise and brighter image of the moving object.
There are also color line scan cameras, and line scan cameras systems which can take 3D images of the moving objects.
In other words, line scan cameras are truly indispensable for the automatized control and monitoring of a number of productions and industries.