Pain threshold map of the human body for the specification of limit values for machine guarding

Status:

completed 07/2011

Aims:

A pain threshold map is to be produced for the purpose of evaluating strain levels in the event of mechanical stress upon the human body at the human-machine interface. The pain threshold map constitutes an important instrument by which the force-pressure limit values of the BG/BGIA Recommendations on the design of workplaces with collaborative robots are to be adapted and validated if required. This is required as part of future standardization work concerning industrial robots. Owing to the necessary occupational medical component of the work, the project was conducted in co-operation with the University Medical Center at the Johannes Gutenberg University in Mainz (JGU Mainz). The pain threshold is defined as the transition from the perception of stress to the feeling of pain, and varies according to the specific mechanical stress type. Pain thresholds generally lie close to the onset of injury, and are therefore an important indicator for the evaluation of low degrees of injury. Pilot studies were conducted in this project, for example by way of literature surveys, and the foundations created for the future DGUV research project for creation of a pain threshold map.

Activities/Methods:

In the first phases, literature surveys were conducted of studies into pain thresholds, critical anatomical structures and particular anatomical aspects. The influence was also examined of diseases of the locomotor apparatus and inner organs and of active pharmaceutical ingredients upon the body's ability to resist strain in collisions at the human-machine interface. In the IFA 5113 development project, "Development of an algometer test facility for research projects in the area of the human-machine interface", a fully automated algometer was developed and fabricated for the measured of pain thresholds. A biomechanical strain model was defined, measurement variables and measurement parameters set out, and the complete laboratory study design developed. A test cohort of approximately 100 persons was considered in the studies. The test apparatus was developed such as to permit flexible and extremely variable positioning of the test subject with complete immobilization of individual body points to be subjected to strain. The mechanical stress is applied to the body point to be studied by means of the algometer. A comprehensive study design was developed for the test procedure, for recording of the measurement variables, and for all necessary studies and informing of the test subjects. Adequate attention was paid to the necessary care for ensuring acceptable strain and for the test subjects' recovery. The study design was presented to the ethics commission of the University of Mainz.

Results:

Within a framework agreement governing ten discrete project tasks, the JGU Mainz conducted comprehensive literature surveys on the subject of the human body's resistance to mechanical strain at low levels of stress such as those which may be permissible during collisions with collaborative robots.The results were summarized by the JGU Mainz in seven reports and interpreted further by the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) and the German Social Accident Insurance Institution for the woodworking and metalworking industries (BGHM). They contain structured collections of known pain threshold measurements, searches concerning mechanically critical structures on the head, neck, torso and extremities, a collection of clinical characteristics exerting an influence and of critical drugs, and an estimation in the light of the existing literature of the systematic relationship between pain thresholds and the onset of tissue damage. These results were submitted to the national standards committee and to international standardization projects concerning collaborative robots. Based upon the test apparatus developed in Project 5113 for the measurement of pain thresholds, the IFA developed a reproducible, software-controlled test procedure for use of the algometer in such measurements. This also included the provision of basic support equipment, including vacuum mattresses, by which the body measurement points can be immobilized during measurements. The algometer was set up in a laboratory at the JGU Mainz, where it is being used to determine a pain threshold map based upon a cohort of approximately 100 test subjects. The entire test design thus includes all mechanical, safety-related, control, instrumentation and software components required for the systematic measurement of pain thresholds in a test cohort. The control software that has been developed and a custom test management programme for the team of testers at the JGU Mainz enables all measurements to be conducted, saved and archived simply and reliably together with all boundary data. All relevant data from a pain threshold measurement are stored in text files suitable for further processing. The entire test design was approved by the ethics commission of the JGU Mainz for creation of the pain threshold map.

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