How to choose a suitable camera for a novice who is making a vision system?

In addition to a wide range of models, the vision system is also a sensor with multiple elements such as light source and control. Conversely, as long as the key items are understood in advance, it is also a sensor that can achieve stable detection and find out the advantages of the introduction. Here, the steps and key points that need to be understood from the introduction, installation, and use of the vision system are explained in a simple and understandable manner.

Do you have the trouble of “visual system is difficult” or “troublesome to import”?

In addition to a wide range of models, the vision system is also a sensor with multiple elements such as light source and control. Conversely, as long as the key items are understood in advance, it is also a sensor that can achieve stable detection and find out the advantages of the introduction. Here, the steps and key points that need to be understood from the introduction, installation, and use of the vision system are explained in a simple and understandable manner.

This topic mainly explains the equipment required for inspection and how to choose a vision camera.

How to choose a suitable camera for a novice who is making a vision system?

Main items to be confirmed before importing the vision system

The types of cameras used in vision systems can be roughly divided into the following categories. According to the application, select the camera that can obtain the best image.

How to choose a suitable camera for a novice who is making a vision system?

①High pixel type
②High-speed type
③Standard type
④Small
*Each includes color and black and white cameras
The following are the specific principles and methods of camera selection:

Principle 1: Choose by the number of pixels (high pixel type or standard type)

The CCD imaging element used in the vision system is a collection of smaller pixels arranged in a grid. Among the 310,000-pixel CCDs that are frequently used as standard types, there are 2 to 21-megapixel CCDs called high-pixel types.

But how to distinguish the difference in the number of pixels used?

Generally, the camera is selected from the two points of “view size” and “pixel resolution”.

The “field of view size” is within the range of shooting and detecting objects and can be changed by the lens to be used. In addition, “pixel resolution” refers to “how many mm is equivalent to 1 pixel of a CCD”, and the relationship between each is expressed by the following formula.

Pixel resolution = Y-direction field of view size (mm) ÷ CCD Y-direction pixels

Then, try to consider the pixel resolution when the field of view size is 30mm in the Y direction. Even if the CCD is included in the standard type 310,000 pixels (Y=480 pixels) and the high pixel type, the general-purpose 2 million pixels (Y=1200 pixels) can still be used.

That is[pixel resolution when using a 310,000-pixel camera]= 30mm÷480 pixels = 0.063mm/pixel

[Pixel resolution when using a 2 million pixel camera]= 30mm÷1200 pixels = 0.025mm/pixel
As long as the pixel resolution is known, the reference size of the field of view at this time can be calculated.

The representative application cases of the vision system are “appearance inspection” and “size inspection”. In the “appearance inspection”, the “minimum inspection size” is used to judge the quality; in the “size inspection”, the “dimension tolerance” is used.

The respective benchmarks are generally calculated on the basis of “minimum detection size” = 4 pixels square; “size tolerance” = ±5 pixels.

According to the pixel resolution calculated before, the “minimum detection size” for “appearance detection” can be obtained.

That is[the minimum detection size when using a 310,000-pixel camera]= 0.063mm/pixel×4 pixels square = 0.25mm square

[Minimum detection size when using a 2 million pixel camera]= 0.025mm/pixel×4 pixels square = 0.1mm square

If you want to detect foreign objects with a maximum of ø0.1mm within a field of view of 30mm, you need to select a camera with 2 million pixels or more.

How to choose a suitable camera for a novice who is making a vision system?

*Camera recommendation Tips: From the point of “pixel resolution” to add the basis of good or bad judgment, you can choose the camera with the best number of pixels!

Principle 2: Choose according to the type of CCD (color type or black and white type)

A color camera or a black and white camera, which one should I choose? “We often hear such questions.

Generally, if the points you want to detect are different due to “tone changes”, using a color camera will have advantages.

The following is an example of using color processing to detect yellow stains on a white background that are difficult to detect with a black-and-white camera.

How to choose a suitable camera for a novice who is making a vision system?

However, there is an advantage in choosing a black and white camera.

As shown in the following “Size measurement using backlight”, it is not a “color change”, but a black-and-white camera can be selected when there is a large difference in “brightness change”.

How to choose a suitable camera for a novice who is making a vision system?

*Camera recommendation Tips: By distinguishing whether the point you want to detect is “color change” or “brightness change”, you can distinguish between color cameras and black and white cameras!

Principle 3: Choose according to the transmission speed (high-speed type or standard type)

Even if the number of pixels of the camera of the vision system is the same, the transmission speed still has a high-speed type.

Taking the 310,000 pixel type as an example, for the standard transmission speed of 16.0ms, the high-speed type can achieve a transmission speed of 4.7ms. Some shooting functions can also achieve further speedups.

In addition to high-speed production lines, in normal-speed production line inspections, if you want to perform inspections that further improve stability such as “additional pre-processing”, “additional inspection tool double inspection”, the high-speed type will be very effective.

How to choose a suitable camera for a novice who is making a vision system?

*Camera recommended Tips: The advantage of choosing a high-speed camera is not only “speeding up the detection efficiency”, but also “stabilizing processing”!

Principle 4: Choose according to the size of the camera (small or standard)
The specifications of the compact camera remain unchanged, and it is a product that greatly reduces the size of the camera. There are small models for high-resolution, standard color, and monochrome cameras, and they are basically used to effectively utilize the limited installation space.

Especially when there is no space for retrofitting to existing equipment, there is no need to remodel the equipment significantly, so it has the advantage of choosing a small camera.

[Viewpoint of requiring installation space]

As shown in the figure below, a total of A: WD (working distance = distance from the tip of the lens to the workpiece), B: lens size, C: camera size, D: cable space (including bending) is the installation space required for the camera part.

How to choose a suitable camera for a novice who is making a vision system?

*Camera recommendation Tips: By selecting a small camera after confirming the installation space in advance, unnecessary equipment modification steps can be eliminated!

Summarize:

Choosing a camera suitable for image processing is the most basic and most important option for stable detection.

This time I have prepared a “camera model comparison table” for everyone, which can be checked and confirmed with the following selection steps to help you choose the best camera more easily.

How to choose a suitable camera for a novice who is making a vision system?