A brief discussion from 1D vision system to 3D machine vision system

1D vision system

 1D vision analyzes the digital signal one scan line at a time, rather than looking at the entire image at once, such as evaluating the difference between a newly acquired set of 10 scan lines and a previously acquired set of scan lines. As shown below, this technology is commonly used to detect and classify defects in materials produced during continuous manufacturing processes, such as paper, metal, plastic, and other non-textile sheets or rolls.

▲ As the process continues, the 1D vision system scans one line at a time. In the example above, the 1D vision system detects a defect in the sheet.

2D vision system

Most common inspection cameras perform area array scanning, as shown in the figure below, which requires the collection of 2D snapshots at different resolutions. Another type of 2D machine vision also performs line scanning, as shown in Figure 12 below, which creates a two-dimensional image through line scanning.

▲ 2D vision system can generate images of different resolutions

▲ Line scanning technology refers to creating a 2D image by scanning one line at a time

Area scan and line scan

In some applications, line scan systems offer specific advantages over area scan systems. For example, when inspecting circular or cylindrical components, multiple area scan cameras may be needed to cover the entire surface of the component. But if we put the component in front of a line scan camera and then rotate the component so that the image spreads out, we can capture an image of the entire surface. Line scan cameras are also easier to install into tight application spaces, for example, where the camera must pass through rollers on a conveyor belt to see the bottom of a component. In addition, line scan systems are often able to provide much higher resolution than traditional cameras. Because line scan systems require movement of elements to create images, they are often well suited for inspecting products that are in continuous motion.

▲ Line scan cameras are able to: (a.) unfold cylindrical items for inspection, (b.) fit vision systems into space-constrained applications, (c.) meet high-resolution inspection requirements, and (d.) Detect objects in continuous motion

3D vision system

3D machine vision systems usually consist of multiple cameras or one or more laser displacement sensors. In robot guidance applications, a 3D vision system composed of multiple cameras can provide component orientation information to the robot. This type of system requires multiple cameras to be installed at different locations to form a "triangular" surrounding state of objects at their locations in 3D space.

▲ 3D vision systems usually use multiple cameras

▲ 3D inspection system using only one camera

In contrast, 3D laser displacement sensor applications typically include surface inspection and volume measurement, using only one camera to provide 3D inspection results. A height map is generated from the positional displacement of the laser light reflected on the object. Similar to line scan technology, when using this technology, the item or camera must be moved to scan the entire product. The displacement sensor is equipped with a calibrated displacement laser, which can measure parameters such as surface height and plane, and can achieve 20μm level accuracy. Figure 15 above shows a 3D laser displacement sensor detecting defects on the brake pad surface.