Hand-arm vibrations and coupling forces: measurement methods

Status:

completed 12/2007

Aims:

Evaluation of the incidence of occupational disease in the metal industry shows that the recognized occupational diseases BK 2103 and BK 2104, which are caused by vibration, are due principally to work involving impact wrenches, percussion drills and paving breakers, pneumatic rammers, and grinding machines. The weighted acceleration parameter currently specified in standards and regulations for the vibration exposure does not express the vibration exposure adequately for the purpose of assessment of an increased risk of damage to the bones and joints of the hand-arm system or to reduced blood flow in the hands. Further parameters must be identified for quantification of the hazard, in particular for recognition of the working conditions defined by the corresponding procedure as being associated with the occupational diseases (BK 2103 and BK 2104). The essential influencing factors are primarily the "coupling forces", which describe the interaction between the machine and the hand, and the "frequency spectrum", which describes the relationship between the vibration intensity and its distribution over the frequency and thus provides an indication of possible resonance phenomena in the hand-arm system. Virtually no measured data for these influencing factors exists to date. The objective of the project was to develop the methods for in-plant measurements further, and to improve the analysis of sources of hazards in the interests of effective prevention activity.

Activities/Methods:

The existing methods, which are suitable for laboratory use, were developed further for the performance of in-plant measurements of the coupling forces under field conditions. The measurement techniques and methods were first to be tested in this pilot study in general measurements, under real-life conditions, under typical application conditions and in the laboratory, for example on impact wrenches and grinding machines. The measurements are to be performed with reference to guidelines and norms VDI 2057 "Effect of mechanical vibrations on human beings", ISO 5349 "Mechanical vibration - Measurement and evaluation of human hand-transmitted vibration" and DIN V 45 679 "Mechanical vibration - Measurement and evaluation of the grip and feed forces for assessing the exposure of the hand-arm system to vibration". In order for the wealth of experience gained in the EU "VIBTOOL" project to be exploited, the in-plant measurements were conducted in conjunction with the Institut National de Recherche et de Sécurité (INRS). In the interests of improved measurement accuracy, a method for measurement of the handle geometry was developed in a degree project in conjunction with the Koblenz university of applied sciences.

Results:

A measurement chain and a measurement method were available for in-plant measurements which permitted the performance of measurements to DIN 45679 and ISO 15230. Major deviations in the measured values were noted particularly on handles with ergonomic geometry. In order for the accuracy to be improved, a method was developed based upon a three-dimensional photographic reconstruction of the handle and a deviation from the cylindrical geometry. Observations were also made and principles identified for improvements to the sensor mats which measure the contact pressure distribution, from which conclusions can be drawn regarding the force distribution. Further measurements must be performed in order for the knowledge obtained to date to be validated and extended.

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