Roboticists know that some things are still hard for humanoid robots to do. Like walk, or run, or... open doors.
So presentations with titles like "Whole-Body Motion of a Humanoid Robot for Passing Through a Door," given at the IEEE/RSJ International Conference on Intelligent Robots and Systems last month, should perhaps not raise any eyebrows. But as a non-roboticist, I scratched my head. Can it really be that hard to open a door?
I showed up at Hitoshi Arisumi's talk to find out. Arisumi is a researcher at Japan's National Institute of Advanced Industrial Science and Technology (AIST), one of the world's top centers for humanoid research. And as it turns out, opening a door -- in this case, a swinging door -- is actually pretty darn hard, though we humans don't even have to think about it.
First, what do you need? Swinging doors are heavy, and to open them, you need a large force at the beginning of the motion, then you have to follow through with a continuous force to keep the door open as you walk through it. (If you're picturing a robot in hat, chaps, and holster strutting into an Old West saloon, like I was, Arisumi’s doors are more like the kitchen doors you might find in restaurants.)
One way a humanoid robot could open a swinging door would be to punch it, Arisumi said. But that doesn't give the door enough momentum to stay open as the robot passes through. What about a kick? That would leave the bot off balance -- not to mention the door swinging back in its face.
What you need, argued Arisumi, is to open the door to a desired angle and support the door through the entire opening action. It’s not as easy as it sounds.
The factors to consider are numerous: the robot's upper body position and foot position, the opening angle of the door, the angular velocity of the door just after opening, and the impact velocity of the robot, among other things. And keep in mind that when the robot is handling another object like a shopping bag or a tray of food, it's hard to open the door with just one arm. (By now I was impressed that we do it so well, after all.)
Arisumi went through equations and diagrams and graphs to demonstrate the proposed technique of using the robot's whole body to impact with the door, just like you would open it with your hip and side. Their experiments with an HRP-2 humanoid robot produced successful, stable opening of a swinging door with a mass of more than 80 percent of the robot's mass.
Now we just need a gun-slinging robot to complete the Old West picture.