Robots acting as household helpers likely will need built-in safety systems to prevent them from harming humans, German researchers said.

In experiments, a robotic arm using bladed tools in some cases managed to inflict wounds that could prove lethal, researchers from the German Institute of Robotics and Mechatronics said at a conference in Alaska.

The researchers equipped a robotic arm with a steak knife, a kitchen knife, scissors and a screwdriver and then programmed the arm to stab and cut a silicone lump, a leg from a dead pig and the arm of a human volunteer.

When the robotic arm's safety system was turned off, the arm stabbed deeply into the silicone and pig leg, the BBC reported Friday.

Injuries were significantly reduced when a collision detection system was turned on. The system used torque sensors to determine when the arm hit a different tissue substance and then limited the force with which the tool hit.

The safety system prevented damage when the arm was tested on humans, the researchers said Thursday at the International Conference on Robotics and Automation in Anchorage, Alaska.