KANBrief 4/10
When human beings and robots work in close proximity at the same workplace, a risk of collision cannot be fully ruled out. It is important for employees not to be exposed to a serious risk of injury. Since the standards governing industrial robots do not currently contain adequate provisions in this area, the IFA (Institute for Occupational Safety and Health of the German Social Accident Insurance) and the FA MFS (Expert committee for machine construction, production systems and steel construction work) have drawn up a guide formulating comprehensive requirements. The contents of this guide are also being submitted within standardization activity.
In the area of industrial robots, Parts 1 and 2 of ISO 10218 (Robots and robotic devices – Safety requirements) have been revised and restructured in recent years, and in the process, the new application of collaborative robots has been created. Collaborative robots are complex machines which work hand in hand with human operatives, supporting and relieving them in a common work process. During this task, the close physical proximity between the robot and the worker can result in direct contact between the two. An essential element of such a workplace is a safe robot control system, which monitors all movements. Excessive robot speed or force results in immediate stoppage.
When a workplace involving a collaborative robot is to be set up, the user of the standard is required to conduct a risk assessment in accordance with the statutory requirements, such as the Machinery Directive, standards governing industrial robots, etc. Such risk assessments must now also include the risk of injury caused by collisions in collaborative applications. The standards, however, do not yet contain adequate safety requirements and test methods for assessment of these risks.
In response to an initiative by the expert committee responsible for machine construction, production systems and steel construction work (FA MFS), the IFA conducted a development project in which technical, medical/biomechanical, ergonomic and work organization criteria were formulated. The purpose of these criteria, which have been compiled in a guidance document, was to supplement and detail the standards. The medical/biomechanical requirements in particular must limit the strain effects resulting from a collision such that only a minor, tolerable physical strain is able to occur. This physical strain was defined by the responsible accident insurance institution for the metalworking industry in North and South Germany as follows: collision must not lead to deeper penetration of the skin and of the underlying tissue with bleeding trauma, nor to fractures or other damage to the musculoskeletal system.
The severity of physical strain can be described in terms of various associated criteria. Limit values for the strain criteria of „impact force“, „clamp/pinch force“ and „pressure/surface pressure“ were defined for all regions of a simple body model. For this purpose, the IFA conducted searches in the literature for data on strain and injuries caused by external mechanical stress. Based upon these data, the medical/ biomechanical limit values were determined for the permissible severity of strain for all body regions, and validated by various random tests in the laboratory.
The results of the project were summarized in a guide (BG/BGIA recommendations for risk assessment in accordance with the Machinery Directive – design of workplaces involving collaborative robots). The guide includes advice on its application in the field. These recommendations enable workplaces involving collaborative robots to be set up in such a way that the potential strain upon persons resulting from a collision remains within a tolerable range.
Further research has the aim of validating the limit values and developing suitable methods for verifying the values to be met. A further important step is the determining of pressure pain thresholds which can be used to define the limit values more effectively. To date, the project partners of the IFA and the DGUV have been the University Medical Center of the Johannes Gutenberg University Mainz and the Fraunhofer IFF in Magdeburg. The targets and results of the studies and developments are being continually re-evaluated in consideration of the situation in the field. The limit values determined are being submitted to the work of ISO/TS 15066 (Robots and robotic devices – Industrial collaborative workspace). The content of this document is to be adopted within the next three years in Part 2 of ISO 10218.
Hans Jürgen Ottersbach
hans-juergen.ottersbach@dguv.de
Dr. Michael Huelke
michael.huelke@dguv.de