Sensor Sense: Finding sheets with vision sensors

April 5, 2011
Vision sensors can be as simple as an inductive proximity device or can include multiple circuit boards connected to a PC. A vision system combines the two technologies

Edited by Robert Repas

Vision sensors can be as simple as an inductive proximity device or can include multiple circuit boards connected to a PC. A vision system combines the two technologies to reduce an intricate decision using mathematical evaluations and complex algorithms to simple pass or fail logic.

In simplest terms, a sheet-verification sensor uses a vision system taught to recognize the contents of a page in a book. The camera takes pictures of every page as the book is assembled and compares those pages to the one it was taught. If the page is the same, the system generates a pass signal; if the pages are different, it sends a fail output, stopping the machine until an operator fixes the problem.

A sheet-verification sensor doesn’t check print quality. It only determines if the right sheet is in the proper sequence in the machine. It records only a small 2-in.2 image of the page holding enough detail to guarantee uniqueness compared to all other sheets in the book. Typically, during the teach-in process, the system takes multiple pictures along a sheet. The system then determines which image is the best one to use for sheet verification. Many times the camera images the same area twice while adjusting illumination between takes for best picture quality.

Inputs and outputs connect directly to the sheet-verification sensor so it can operate as a stand-alone unit. A photoelectric trigger activates the sensor when the sheet is about to pass in front of the camera and turns it off when the sheet leaves. An encoder that connects directly to the sensor gives a pulse-train output as the machine moves the paper forward. These pulses let the sensor determine sheet width and exactly where to photograph the page.

Much of the intelligence that was previously required from PC workstations, custom configuration software, or expensive middleware, has now been transferred to the vision sensor itself. This reduces the installation time, system complexity, and overall cost of machine ownership.

Pepperl+Fuchs supplied information for this column.

© 2011 Penton Media, Inc.

Sponsored Recommendations

7 Reasons Why Air Bearings Outperform Mechanical Bearings

Feb. 7, 2025
Frictionless air bearings and air bearing stages have decisive advantages in precision motion and automation applications.

Hexapod Robot Applications in Automation and Automotive Assembly

Feb. 7, 2025
Hexapod 6-DOF Robots in Automation and Automotive Assembly | 6-Axis Precision Parallel Robot | Cobot for High Precision Applications

What is a Difference between a Gantry Positioning System and a Split-Bridge?

Feb. 7, 2025
The design of a Gantry Positioning System and Split-Bridge Positioning system are related. Learn how they differ and what to use best for your application.

Application Solutions with 6-Axis Hexapod Positioning Systems

Feb. 7, 2025
Explore applications, articles, and background information on 6-Axis Hexapod Positioning Systems and how they can help you improve your alignment system.

Voice your opinion!

To join the conversation, and become an exclusive member of Machine Design, create an account today!