For robots exceeding a certain minimum size, a risk can exist for persons cooperating with these robots, if no additional protection mechanisms are foreseen. During co-operation within a working range of a free robot arm, persons could be injured or killed due to the speed of moving parts in case of a collision, such as with the free end of the robot arm. Therefore care can be taken care to prevent personnel from entering into the working envelope of the robot if the robot is active. This may be achieved by mechanical or virtual walls which prevent persons from entering the working area. Some robot systems include a turnable table such that an operating person on one side of a fence can load the turnable table with pieces and the robot's working area is provided on the other side of the fence.
Small robots which are inherently safe might not be capable of injuring a person in any state of their robot operation. The concept of an “inherently safe robot” is related to a robot which is inherently or intrinsically safe due to its design whereas the power and/or the force effected onto a person or fixed obstacles in case of a collision is limited by a appropriate design (e.g., useful constructive measures); see ISO 10218, part 1, 2006, par. 5.10.5. According to this concept, the force onto a person in case of a collision shall not exceed 150 N respectively, and the dynamic power onto a person shall not exceed 80 W. These conditions cannot be met or fulfilled over certain mechanical thresholds for masses and/or dimensions of a robot. Therefore heavy industrial robots with a rated power of several 100 W and over are not seen as small robots so that the disclosure may be viewed as less applicable for those robots.
The JP 09 254 079 is related to detection of a collision of a robot arm with a person or object using a speed sensing detector and by controlling brakes of a robot according to those signals. In case of a collision, the robot will be slowed down until a stationary position is reached where the robot stops. Afterwards the brakes will be released with a severity of the collision being of high importance.