Archive for November, 2011

Compliance: trending topic at the Humanoids 2011

// November 7th, 2011 // No Comments » // Artificial Intelligence, Research, Work

Compliant robot: a robot with the ability to tolerate and compensate for misaligned parts. Or otherwise stated, the ability of the robot to gracefully absorve an external force that tries to modify its position.

At the last Humanoids conference ( everybody was talking about how to control a compliant arm, how to build compliant legs and how to move a compliant humanoid.
We introduced our latest Reem robot to the scientific community and, besides the typical question about how much the robot costs, the top number one of the questions was: is your robot compliant?. Some people even crashed their bodies against the robot in order to check if the robot had compliant arms!.
No, our robot is not compliant… yet.

Of course, compliance is a very important feature for a service robot because we must be sure that a robot that works with humans will not harm a person. Hence, if someone crashes against the robot (or viceversa), we, as builders of the robots, must ensure that nobody gets hurt.

Some other robots in the world have already shown very nice compliant characteristics. This is the case of the Meka robots. You can watch a nice video here, where the robot shows its compliance.

Another case is the omnipresent PR2, where in this video shows how compliance can be useful for cooperation.

However, at present, compliance has its dark side. Due to the fact that a compliant robot must be able to absorb forces, a compliant joint cannot distinguish between situation of crash or a situation of carrying a heavy load. A compliant joint will react in the same way to both situations, that is, letting the joint move on the opposite direction of the force. If the robot were carrying a weight, it would fall off.

This reminds me the training of Chi Sao while doing Wing chun kung fu. In this training, two opponents try to feel the force one of them is doing against the arms of the other, and use it to generate a better attack. The basics of this trainning is to learn to differentiate when you have to push and when you have to diminish.

We suffered the same kind of training when we were babies in order to understand the differences between carrying or being pushed.

The compliant robot is still far from encoding that knowledge. The point is more delicated that just using a flag that indicates when the robot is in carrying mode or when in free mode to absorb collisions (that would be the GOFAI solution). It is necessary to embed into robots a more complex ability that makes them know when they are in one situation or the other.

And that ability is understanding. The robot needs to understand when a force in its body is due to a crash or when is due to an object been carried.

Understanding is the most important feature for a robot, and not only for compliance but for everything. At present, no robot in the world understands a … eemm… anything…

Though work in front of us!