3D imaging is a very popular topic today but where and when to use 3D imaging techniques is not always understood. Multipix Imaging, 3D machine vision component specialists, tell us more about when 3D is most applicable and what 3D imaging technology is available in the market place today.
Julie Busby, Director at Multipix Imaging, tells us “In virtually every industry, 3D sensors/cameras are being used to optimise production processes, improve quality control and reduce manufacturing costs. As 3D technology becomes more accessible we are finding more and more customers seek advice on which technology they should use. Affordable hardware and powerful 3D imaging software are having a significant impact on today’s vision solutions.
Selecting the correct 3D Imaging method
There are a variety of hardware technologies available, each have their benefits depending on your inspection task. You may need to consider…
|What type of inspection is required?||Shape, position, orientation, alignment, presence…|
|Which degree of accuracy is required?||Micrometer, millimeter, centimeters…|
|What are the features of the objects?||Size, reflectivity, transparency…|
|What are the general conditions?||Illumination, in motion, processing time, budget…|
3D Camera Technology Explained…
A minimum of two different camera views of an object are required to create a stereo 3D image (Fig1a). Where extended coverage or more detailed information is required, multiple cameras can be used and is commonly known as multi-view stereo (Fig1b).
Typically the cameras are calibrated using machine software such as MVTec’s HALCON. Images are then captured and result in a disparity image or 3D point cloud which can be used for real-world measurements, 3D object recognition, robot control and so on.
A good example of the ‘projected texture stereo vision’ principle are the fully calibrated Ensenso 3D cameras . With two integrated CMOS sensors and a projector that casts a random point pattern onto the object to be captured, allowing structures that are not visible or only faintly visible on the surface to be enhanced or highlighted.
Laser Triangulation (Sheet of light)
With this method of 3D imaging, there is one camera which has a known physical relationship with a laser line projector (Fig3a).
The laser line is projected across the surface of an object which creates a profile.
Many profiles are taken as the object moves under the camera-laser combo and these are used to recreate the surface of the object.
SmartRay, manufacturers of the ECCO Series of 3D laser triangulation cameras are ideal for applications that benefit from using pre-calibrated all-in-one laser camera units which can provide high resolution results.
Time of Flight (ToF)
3D ToF cameras use either a pulsed or continuous wave Near Infra-Red light to illuminate the object/scene. When using pulsed light, the time it takes for the light to be reflected back is measured and used to calculate distance. Whereas with continuous wave, it is the phase shift between emitted and reflected light that is measured to determine distance.
The Basler ToF camera, uses pulsed NIR and is delivered as a fully calibrated unit with a GigE Vision interface for ease of connectivity. It provides both a 2D image as well as per-pixel depth information.
The importance of selecting the correct 3D imaging method
Aside from accuracy, object surface/material is also important as it can influence how the light is reflected and captured, or not, by the sensor. If your object moving or stationary is another important factor to consider.
|3D Technology||Hardware Requirements||Object Size||Accuracy|
|Binocular Stereo||Two Cameras|
|50mm – 2.5M||mm’s|
|Multi-View Stereo||Multiple Cameras|
|50mm – 2.5M||mm’s|
|Sheet of Light /|
3D Laser Triangulation
Laser Line Projector
Unit to move the object,
|Object must fit onto the moving unit||Single microns|
|Photometric Stereo||Telecentric Camera|
At least three Telecentric light sources
|Restricted by view of telecentric lens||0.3mm to 5mm|
Depth from focus
|i.e Calibrated ToF|
Hardware to vary the focus position
|50cm – 13m approx. <2cm||+/-1cm Single microns|
Julie Busby concludes, “Multipix Imaging is uniquely placed, offering a variety of 3D hardware technology all of which have a direct interface to MVTec’s HALCON which includes industry leading 3D software tools.
By providing a sample evaluation service, advice and training, Multipix is demystifying 3D vision and helping customers create successful solutions previously unattainable with 2D imaging”