A simple technique that has proven effective is to use laser light strips in conjunction with a 2D camera. An overhead 2D camera provides a rough location of parts in a bin. This camera also identifies the next part to be selected. A second camera mounted to the robot works in conjunction with a laser. The robot moves the laser and camera over the next part and then the laser places a cross hair over a target on the part. This target could be an edge, circle or other distinct feature on the part. Through simple triangulation, the camera can locate the position and orientation of the part in 3D.
The ultimate application is to use a 3D vision system to locate randomly oriented parts in a bin. There are many challenges to this application including the possibility of parts being tangled up with one another, and avoiding the bin walls.
Tactile Feedback
Although vision systems are the most common form of intelligent sensors for robots, they are not the only alternative. Six degrees of freedom force sensors are commonly used to give robots tactile feedback. For high precision assembly, force sensors are used to guide tight fit insertions such as for inserting shafts, with or without keys, into holes. Robots with force sensors can also be used for more complex assembly tasks such as inserting gears into housings such as transmissions. Gears being inserted into clutches will often need to engage and then pass through multiple stages. The robot can be programmed just like a person and move a gear back and forth until it engages with each stage.
Another example of using force sensors to give robots tactile feedback is for polishing or grinding a complex contour. Traditionally this is handled with compliant devises, but these devises may not meet the tolerances required for precise applications. Adding a 6D force sensor to a robot and then attaching a grinding disk gives the robot the ability to maintain a constant force as the orientation varies, compensating for gravitational effects.
Beyond Today's Solutions
Intelligent sensor technology has played a critical part in the successful use of robots in a variety of applications. As intelligent sensor technologies continue to advance, robots will have even greater capabilities in the future. Nothing will ever replace the super computer in each person's brain that can make very complex distinctions, but applications once thought to be impractical are now common tasks for intelligent robots.
Mark Handelsman is an industry marketing manager at FANUC Robotics America Inc.
