The Harmonica digital drive from Elmo Motion Control Inc., Westford, Mass., is compact enough to fit in the camera head on the PrintVision line of inspection machines from Advanced Vision Technology Ltd., Atlanta. This contrasts with older machines where the motor and drive were off in a separate cabinet and positioned the head via a belt.

The combo servodrive/ motor/inspection head weighs from 12 to 15 kg, depending on the model. A 100-W dc servomotor scans the head across the web at speeds hitting 3 m/sec under the control of the Harmonica drive operating in position mode. The optical head assembly moves on a beam spanning the web ranging from 1 to 7 m, depending on the press.

The camera signal from the optical head feeds to a vision system. If the system notices a defect in the web, it freezes the image of the appropriate area on one of the system monitors. An alarm goes off while the system marks and classifies the defect.

The AVT systems get applied to a variety of printing, including labels running on narrow webs. It can detect defects that may not be visible to the human eye, including subtle variations in color, misregistration, streaks, and smears.