An imaging system, from US company ImageXpert, has been developed to precisely analyse inkjet printer heads. The system is designed to aid printer and print head manufacturers in producing print heads in which the size, speed and trajectory of ink droplets is perfectly controlled to produce clean, sharp, photo-quality images.
The JetXpert system uses digital cameras from Allied Vision Technologies. An LED is positioned behind the ink droplet so the image of the droplet is in silhouette, which allows for analysis of both transparent and opaque fluids. The LED strobe pulsewidth is, at 250ns, particularly short.
'Once the drops are ejected, they move at a speed of approximately 10 metres per second,' explained Yair Kipman, president of ImageXpert. 'The very short strobe width allows us to capture images with minimal motion blur.' JetXpert uses single strobe events, one strobe per image frame, to capture images of individual droplets in flight. This method of image capture is made possible by the proprietary high-powered LED, and minimises blur caused by droplet aggregation that is common to systems that use multiple strobes per frame.
The camera used is a Stingray F-080b model by Allied Vision Technologies. This monochromatic camera is equipped with an XGA (0.8 Megapixel) image sensor and a high-speed FireWire IEEE1394b interface. The Stingray F-080 delivers 30fps. Kipman commented: 'What was really most valuable for us, however, was the ability to freely set the shutter speed between 48µs and 67s. By being able to change the shutter speed, we can work with very fast ejection systems such as ink jet technology and much slower dispensing systems such as those used in the fabrication of bioarrays.'
The camera is equipped with a Moritex telecentric zoom lens, assuring that small variations in the depth of the ink jet in the image does not lead to a change in scale. Software developed by ImageXpert analyses the images to measure important qualities of the droplets such as: drop volume, trajectory, velocity, ligature length, break off length, etc. The system measures the ink jet's trajectory relative to the print head in either two or three dimensions.
The JetXpert System is already in use by many leading printer and ink manufacturers, and is relevant in markets and research where liquid material is jetted or dispensed, such as printable electronics, adhesives or biotechnology.
