Collaborative robots

Safe human - robot cooperation

Collaborative industrial robots are complex machines that work hand in hand with people. In a joint working process, robots support and take the load off workers when for example, a robot lifts and positions a heavy workpiece while a person welds lightweight iron hooks. During this work activity, the person is very close to several robotic elements – for example, robot arm or tool – so the robot and person may touch one another. A similar situation takes place with mobile service surroundings in close proximity to people.

Until now, guards were needed when using robots so the persons that were within the robot’s working range could be safely protected against the mechanical effects of fast-moving robot parts. When the industrial robot standards were revised and updated, the new application field of collaborative robots was added as a supplement.

Background:

When collaborative robots are used, guards are no longer installed in certain working or collaboration rooms, so a robot-human collision risk cannot be entirely ruled out. Thus, technical protective measures other than guards must be taken to continuously determine the collision risk and minimize it as part of the robot control system – but a residual risk still exists.

When a workplace that includes a collaborative robot is being planned, the user must carry out a risk assessment based on a legal framework such as machinery directive and industrial robot standards that should also include an evaluation of injury risks caused by robot-human collisions. In the standards that apply to industrial robots, however, there are not enough occupational safety requirements for evaluating these injury risks.

Acting on an initiative of the Expert Committee for Machine Construction, Production Systems and Steel Construction, the Institute for Occupational Safety and Health o the German Social Accient Insurance(IFA, formerly BGIA) compiled in a development project the technological, medical/biomechanical, ergonomic and work schedule requirements made to such workplaces. They supplement and specify the requirements of the standards and have been summarized in BG/BGIA recommendations.

Since a collaborative work process during intended use carries a collision risk between a robot and a person, the task consisted of limiting the straining effects caused by collisions so only small and tolerable injury severity or injury risk could occur. According to this, tolerable severe injuries are only skin and underlying tissue strains that do not penetrate the skin and tissue deeply and do not cause bleeding wounds. Fractures or other injuries of the musculoskeletal system must be ruled out (see diagrammatic representation, left).

Injury severity can be depicted by limit values of connected injury criteria. Limit values for the injury criteria of “impact force”, “clamping/squeezing force” and “pressure/surface pressing” for all regions of a simple body model were established, based on injury data from external mechanical strains that the IFA compiled from bibliographical references and databases. From them, guiding limit values were obtained for the maximum permissible injury severities according to body model and selectively verified by various laboratory control tests.

The results of the project have been summarized in BG/BGIA recommendations for arranging workplaces with collaborative robots. It contains extensive aids for applying occupational safety measures in practice, as part of risk assessments. A team of experts made of robot manufacturers and users collaborated in working out the contents.

Thanks to the BG/BGIA recommendations, workplaces with collaborative robots can be set up so the mechanical effects acting on persons that may occur as a result of a collision do not exceed a tolerable extent. These workplaces can be designed in a way to ensure the required occupational safety for the person in question. The BG/BGIA recommendations can be downloaded.