Watching the original “Star Wars” movie as a mathematically inclined 11-year-old, Helen Greiner, co-founder of iRobot Corp., dreamed of someday creating a robot like the heroic R2-D2. The Roomba vacuum cleaner may be incapable of fixing an X-wing fighter like Luke Skywalker’s trusty droid, but some 1.2 million of the disc-shaped robotic housekeepers have been sold in 25 countries in the past 2 1/2 years. iRobot is now the world’s largest firm solely devoted to robotics, with more than 200 employees.