Sensor Sense: Giving Robots Laser-Guided Vision

Jan. 14, 2011
Tracking gaps in a laser-drawn line of light measures the position errors between two separate parts. Robots can then mount the two parts flush with equal spacing all around

Robots used in assembly and testing applications typically give high degrees of operational reliability and repeatability. But fitting a car door precisely into an automotive body has not been one of those applications. It usually takes skilled personnel to solve the “gap-and-flush” problem between the body and door. Using experience and a good amount of patience, car doors are set using plastic fitting tools such that the doors mount flush with an even gap all around.

This mounting process not only takes time, but the tools used typically touch painted body parts — something no automotive process engineer likes to see on a regular basis because of possible scratches or nicks in the painted surface. Even worse, the quality of the fit depends on the installer and is thus subject to human inconsistencies and errors. Fortunately, though, the creation of a new laser-based camera sensor, called a line runner, now gives robots the ability to perform this work automatically.

The line-runner sensor mounts to the robot that guides it over the door gap to be evaluated. Let’s call this the X direction just for reference. A laser line projects across the gap while the camera takes real-time images of the projected laser line. Any discontinuity in the laser line determines the position of the contour edges, transmitting their real-world Y and Z coordinates to the robot-control system.

As the robot guides the sensor along the door gap, it determines not just the width of the gap but also the relative height of the door panel and body panel along the entire path. After this measurement run, the data is analyzed and used to calculate offset values of X, Y, and Z translation, as well as yaw, pitch, and roll. With these offset values known, the mounting robot repositions the door to mount flush with the body with an even gap between it and the door frame.

The initial position of the door prior to final mounting may have large gap and height variations. Consequently, the laser-line projection width must be relatively wide with a camera imaging array large enough to measure the offset. Fortunately, this is no problem with line-runner sensors as they typically cover 30-to-40-mm gaps at mounting distances on the order of 100 mm.

Pepperl+Fuchs ( supplied information for this column.

Edited by Robert Repas, Associate Editor

© 2011 Penton Media, Inc.

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