Layout of a PC-based machine vision system
An image processing system consists of a large number of individual components. In order to solve the inspection task, each application stringently requires the harmonisation of the individual parts. The weakest link in the chain would otherwise limit the overall performance and efficiency of the system. PC-based machine vision systems give the user maximum freedom in putting together the components, but also require the most profound knowledge of the correct combination.
Layout of a traditional PC-based machine vision system
- The test object is illuminated by a light source to create good contrast and highlight the inspected features. The selection of the lighting strongly depends on the test object.
- Optics image the object on the camera sensor. They must be selected in accordance with the camera (image sensor size), working distance, size and type of the test object, etc.
- An industrial camera captures the image on a sensor and sends its digital image data to the host pc using standard digital interfaces, like USB 3.x or Gigabit Ethernet LAN. Bigger amounts of image data are transfered with the help of an an image acquisition card. Depending on the camera type, these can be different standards.
- The image processing board (frame grabber) digitalises or processes the camera data and could do some additional image preprocessing with the help of FPGAs. Then the data are transferred (preferably without CPU load) to the PC working memory.
- Finally special image processing software on the PC performs the actual image analysis.
- High-end PC systems process complex image data with the help of the host CPU, but also in part on FPGAs of frame grabbers, as well sometimes on high-quality NVIDIA or AMD graphics cards.
The accessories, too, play an important role. Protective camera housings, special cables, multiplexers, I/O cards, etc. ensure a trouble-free interaction of all components.
Advantages of a PC-based machine vision system are the free scalability of the components depending on the application task. The number of individual components available on the market is very large, so that an ideal budget-priced combination can be obtained. The user is not necessarily tied to a particular software package and can access further typical Windows system resources.
New camera transfer protocols (GigEVision, CameraLink Express, CoaXPress) and bus systems like USB2 + USB3 Vision and FireWire complement the classic transmission and acquisition of images using frame grabbers. Maximum flexibility is guaranteed.
A possible disadvantage is the increased space requirement for the industrial PC. Yet recent PC developments also allow for compact solutions, such as embedded PC systems, which hardly require any space. Mobile low-power CPUs (Core-I series, Atom series) allow for energy-efficient, fanless systems with reasonable computing capacity. Due to the wide selection options for all components, the system design as a whole is more difficult for the inexperienced user.