USB camera
The term "USB camera" implies that an industrial camera is connected to a computer via a USB interface. It transfers the parameters, which are used to set the camera, as well as the image data. Actually, this statement is trivial. We emphasize it, since a lot of people read too much into it. One of the common misconceptions is the association of "USB camera" with "low image quality". But actually, the image quality is determined by the CCD sensor or CMOS sensor. The USB interface simply transfers the images taken by these sensors.
The reason for these misunderstandings is due to the history of the USB interface. The first version provided such low bandwidth that the image data had to be compressed considerably or transfered very slowly. Another reason may be that photo cameras behave like a hard disk when they are connected to a computer via USB. This also conveys the impression of "slow" USB cameras.
USB 2.0 versus HDMI™
But meanwhile USB 2.0 (High Speed) is widespread. Its bandwidth is sufficient for all common consumer video cameras and industrial cameras. Only the new HD video cameras require more bandwidth. Thus, they are fitted with an HDMI™ interface.
However, there are no industrial cameras with an HDMI™ interface. It comprises a copy protection mechanism that makes no sense for machine vision applications or even may be a unnecessary source of trouble. Thus, FireWire cameras and GigE cameras are used instead. The Imaging Source is one of the few worldwide manufacturers that offers industrial cameras with all three interfaces.
USB cameras are not fitted with lenses
Industrial cameras are used for a wide spectrum of applications. Thus, the manufacturers usually ship them without an integrated lens. Instead of this, most industrial cameras are "only" fitted with a C-mount or CS-mount thread. Fortunately, both are international standards and thus there is a wide selection of low-priced lenses.
What are the advantages of USB cameras?
Since USB 2.0 has gone through many teething troubles, more and more USB cameras are used in machine vision systems. The reasons are:
- Low price: Due to their application in the consumer market, USB components are highly integrated and low-priced. Therefore the production of USB cameras is more cost-effective than that of FireWire or GigE cameras.
- Easy handling: Meanwhile almost every computer is fitted with at least one USB 2.0 interface. Thus, the setup of a USB camera does not require the installation of specific interface boards. This is also true for laptops.
- Accessories: Since USB 2.0 interfaces are widespread, there is a wide range of reasonably priced accessories. Most off the shelf USB cables (USB 2.0 High Speed) are suitable for industrial cameras.
What are the disadvantages of USB cameras?
Obviously, a USB camera is not a "Swiss army knife". Especially industrial cameras with a very high resolution and/or frame rate are not fitted with a USB interface. Beyond this special case, there are two typical features of USB interfaces that may interfere with their use for industrial cameras:
- Long cables: The maximum length of cables of the USB 2.0 High Speed standard is 5m. Meanwhile, longer cables are available but they are all fitted with "boosters". How well these cables work together with industrial cameras has to be checked for every individual case.
- Concentration on Windows: The realization of up-to-date commercial application software for industrial USB cameras is only possible under Windows. The reason for this is explained at programming interface.
