Volunteers in Slovenia are allowing themselves to be repeatedly punched -- by a robot -- in an effort to assess human-robot pain thresholds, a researcher says.

The late science fiction author Isaac Asimov's famous First Law of Robotics -- "A robot may not injure a human being" -- appears to be taking a hammering, but the scientist behind it says it's all in a good cause, NewScientist.com reported Wednesday.

Borut Povse, who has ethical approval for the work from the University of Ljubljana where he's conducting the research, says the experiment is to help future robots adhere to the rule.

"Even robots designed to Asimov's laws can collide with people. We are trying to make sure that when they do, the collision is not too powerful," Povse says.

"We are taking the first steps to defining the limits of the speed and acceleration of robots, and the ideal size and shape of the tools they use, so they can safely interact with humans," he says.

Using a borrowed industrial robot, Povse and his colleagues programmed the robot arm to move towards a volunteer's outstretched forearm.

Each volunteer was punched 18 times at different impact energies by the robot arm fitted with one of two tools, one blunt and round and one sharper.

Volunteers were asked whether each collision was painless, or engendered mild, moderate, horrible or unbearable pain.

Povse, who tried the system before asking for volunteers, says most felt the pain was in the mild to moderate range.

The aim of the research, Povse says, is to limit the speed a robot should move at when it senses a nearby human, to avoid hurting them.