The printing industry has developed highly sophisticated mechanisms to automate the various print processes. A complementary challenge has been to introduce automatic process and quality controls in order to significantly reduce waste of time and materials when defects are found – usually by the customer, after the printed material has already been delivered. Advanced Vision Technology (AVT) Ltd. is a leader in developing sophisticated machine-vision technologies for inspecting printed substrates for both random and process flaws. The company’s line of PrintVision machines enables printing personnel to automatically detect and analyze defects as part of the printing process, alerting the print operator on-thespot in order to save valuable time and wasted material. The AVT systems can be used with all types of continuous web printing (including labels), and detect certain defects that are not always visible to the human eye, including color variation, misregistration, streaks and mears.
The actual vision mechanism is a high resolution process control camera mounted in the printing press apparatus. The optical head in the inspection unit scans each millimeter of the printed material, back and forth. When a defect is detected, the image of the printed area is frozen on one of the two monitors of the control workstation and an alarm is activated. The defect is marked and classified immediately. At the same time, the inspector/operator is alerted by a special beeper so that the problem can be analyzed and fixed before a large amount of additional material is printed.
The high-resolution optical head operating in the inspection unit must be flexible enough to operate with top accuracy, while the printing press is operating at fast speeds. What is required is a highly responsive drive that controls the position of the head, and yet is small enough – in both weight and size – to be mounted within the head without hindering the actual head motion.
The Harmonica servo drive is compact and flexible enough to be mounted in the moving optical head of the inspection unit
To meet the demanding requirements of the PrintVision system, AVT installed Elmo Motion Control’s compact Harmonica digital servo drive in the optical inspection head of the machine in order to control the position of the camera. In this application the Harmonica operates in position mode with RS-232 serial communication.The drive’s small size and weight, as well as its programmability (for internal scripts and homing)were the critical reasons for devising this solution. Once the Harmonica was installed and operating in the AVT machine,Elmo personnel suggested implementing a CANopen network environment to further enhance the flexibility of the application and extend the drive’s programming capabilities, while at the same time reducing the complexity of the entire machine. This option is currently being investigated.
Compact Drive for Top Accuracy and Flexibility
The Elmo Harmonica digital drive provided the ideal solution required for the high-resolution, moving optical head in the print inspection mechanism. Easily mounted and powerful in terms of its programming capabilities, the Harmonica is managing all required position control of the inspection camera. Furthermore, because the Harmonica could be installed in the moving head, machine size and cabling were greatly streamlined.