Practical Risk Assessment Guide for Workplaces with Cobots: Conversion of Biomechanical Limit Values

The DGUV has funded several research projects (FP317, FP411, FP430) in which the IFA, together with other research institutions, has identified certain biomechanical limit values that can now be used in the assessment of mechanical hazards arising from so-called collaborative robots (cobots). Different locations of the body with different tissue constellations (skin, muscle, fat, bone) can tolerate characteristic deformations depending on the force and pressure, resulting in specific stiffnesses. In day-to-day practice, the impact of cobots must be measured with suitable measuring devices in order to ensure compliance with the limit values. Since the stiffnesses determined for different body regions sometimes differ from the spring rates used in measuring devices, the measured force must be converted in a way that matches the actual constellation. This is where the IFA’s practical solution comes in: The Conversion Table determines energetically optimised values that take account of the actual stiffnesses of the individual measuring devices, thus allowing a risk assessment of dynamic impact loads with only a few measurements.

The Conversion Table was commissioned by the Social Accident Insurance Institution for Wood and Metal (BGHM) as part of project IFA 5160. The conversion is based on the biomechanical corridors determined in the final project report by IFA and Fraunhofer IFF . Another element that is taken into account is the detection threshold of the cobot, as it allows the determination of the energy fraction that needs to be used for the conversion. In addition to smoothed peak pressure values, the table also provides a value for surface pressing (average pressure). Stiffnesses are set as defaults in five clusters; however, the table also allows assessments involving fewer measuring devices, and it is therefore also possible to enter a known measuring device stiffness manually.

The Conversion Table provided here by the IFA significantly simplifies the risk assessment for a workplace involving collaborative robots. The Application Guideline (PDF, 375 kB, non-accessible) contains an overview of how exactly the critical test points can be identified with the help of the Conversion Table.