3D time of flight cameras
Pulses of IR light are sent from the cameras inbuilt illuminator with the sensor measuring the time for the reflection of the light to return. Currently TOF cameras are common with less than VGA spatial resolutions with early products featuring megapixel resolutions. The Z resolution is also relatively low with repeatability in the centimetre range over a metre or so. This lends itself to 3D object detection rather than accurate measurement. A growing application area is
3D stereo cameras
Stereo 3D imaging has been around for many years, however, in recent years it is becoming more common in robotic and bin picking applications. In simple terms stereo uses the same principle as the human eye namely spatial offset. While just two cameras are required, stereo relies on identifying the same feature by both cameras. As an object may not have features, often random pattern projection is used.
The distortion and offset of the pattern between the two cameras allow a costeffective solution with an accuracy between fringe projection and TOF. Like fringe projection, using a random pattern, a single camera can be used to keep costs down with reduced accuracy. A similar technique is seen in the gaming industry with the Microsoft Kinect.
In addition to the techniques described previously such as binning, ROI and partial scan, specialist cameras are available that provide highspeed image capture while maintaining resolution. These cameras generally use highend CMOS sensors and can capture more than 1000 frames per second at megapixel resolutions. Due to the large amount of data being recorded and the limited bandwidth common to most digital interfaces, these products often record onto local memory and the images are then transferred at a slower rate for later analysis in an off-line mode.
The high speeds of these cameras leave little time for light collection on the sensor, so it is necessary to use high-powered lighting in order to illuminate an event. High-speed cameras are often used in applications where a minor mechanical error in a production line can cause a huge amount of waste. Although these products are expensive when compared to most standard industrial cameras, they can sometimes pay for themselves after recording just one system failure. Solutions utilising this kind of camera technology can be found also in the vision systems section of the handbook.
Ultra high-fidelity cameras
Ultra high-fidelity cameras are used in highly demanding industrial and scientific applications and can be found with sensor resolutions of up to 57 megapixels for area scan cameras and line scan cameras with up to 16K line resolution. Where higher resolutions are still demanded, the use of pixel shifting sensors is possible. By shifting the sensor by 1/4 or 1/8 pixel over subsequent images resolutions of up to 260 million pixels can be achieved.
Camera systems for X-ray applications
Camera technology can be used in X-ray systems by imaging a phosphor screen where the X-rays are converted into photons visible to the camera. The phosphor is either mounted on a fibre optic layer, or on a scintillator plate that is imaged on to the sensor via an image intensifier or lens system.