Research on risks of injury at assisting robots

Status:

completed 03/2009

Aims:

This project studied the risk of injury and the permissible biomechanical exposures at workplaces involving collaborative robots. The term "collaborative robot" refers to new forms of workplace in which working areas are shared by human beings and industrial robots. The familiar robot installations, located behind protective guards, are only able to automate work that requires no human intervention whatsoever. Assembly tasks, in particular, often cannot be fully automated. Tasks also exist which can be performed more economically and with lower risk to health by human beings and robots working together. At some of these workplaces, the protective guards are dispensed with, making direct contact possible between human beings and robots.

The existing OSH regulations do not permit persons to enter the close proximity of manufacturing robots; they could be seriously injured by the unpredictable movements of the latter. The objective was therefore to create robots whose movements did not present a hazard. A technical criterion for this are the safe detection of human beings and safe control of the robots. Should it be approached by a person, the robot must respond appropriately. A residual risk of collision nevertheless exists. At what maximum permissible forces and pressures is the residual risk of injury justifiable? How must the robot arm be designed in order to prevent the person from being injured? Based upon existing data from the literature, the project is to serve as a pilot study, providing answers to the essential questions and supporting standardization work. A main study which has already been planned will provide detailed clarification of the issue with tests and measurements of its own.

The result of the pilot study was to be a brief and succinct guidance document for manufacturers and operators of collaborative robots which will enable them to conduct a risk assessment of the mechanical hazards associated with such workplaces. The guidance document was to contain a table of relevant body regions, limit values for a range of stresses, and further necessary requirements for risk assessment. The guidance document also recommends means of testing the specified limit values.

Activities/Methods:

Documented injuries/medical tests and the mechanical stresses causing them were analysed. The focus lay upon: permissible pinch and clamp forces, impact forces, surface pressure, and data on the deformability of body regions subject to a collision risk. Information was obtained from the following sources: BG Rules, national and international studies and rules, accident research data, and orthopaedic databases of critical stresses. Preliminary stress tests conducted specifically for the purpose on a small number of test subjects were used to validate and supplement the data identified in the searches and to adapt it to typical human/robot workplaces.

These modified injury data were compiled and assigned to a simplified body model, such as the head, chest, back, arm regions etc. Together with the expert committee responsible for machine construction, production systems and steel construction work (FA MFS), the BGIA Institute for Occupational Safety and Health defined an acceptable degree of severity of injury for the event of a collision. From these values, corresponding limit values can be derived for force and pressure, and guideline design values for collision areas of the robot. These values detail and supplement the provisions of the current standards governing robots.

Results:

In response to an initiative by the FA MFS, the BGIA 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 provisions of standards.

The maximum acceptable severity of injury was defined such that only stress upon the skin and the underlying tissue may occur, to the exclusion of deeper penetration of skin and tissue, bleeding trauma, and fractures or other damage to the musculoskeletal system.

The severity of an injury can be described in terms of the associated injury criteria. Limit values for the injury 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 BGIA searched the literature and databases for data on injuries caused by external mechanical stresses. Based upon these data, the guideline limit values were determined for degrees of severity of injury based upon the body model. These limit values were validated by various random tests in the laboratory.

The results of the project were summarized in a structured fashion in a guidance document for the design of workplaces involving collaborative robots. This document provides comprehensive support in application of the safety criteria during risk assessments in plant practice. Parallel to the research work, the content of the document was agreed with a team of experts which included robot manufacturers and users.

The guidance document enables workplaces involving collaborative robots to be set up in such a way that stresses upon persons resulting from possible collisions are kept within a tolerable range. These workplaces - robots and the working environment - can be adapted by means of design measures such that the necessary occupational safety of the persons involved is assured.

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