System for separate measurement of three-dimensional time-variant hand forces

Status:

completed 12/2004

Aims:

A three-dimensional measuring system was required for separate measurement of the forces arising on each hand during manual tasks such as pushing, pulling, lifting and carrying. The system was to permit measurement of the time-variant hand forces for the purpose of long-term studies. The system was further required to be adaptable to any body, and therefore to be small and flexible in its fitting arrangements. The force signals were to be stored, displayed by means of a suitable software application, and assessed qualitatively. They were to be exportable in the form of a text file for the purpose of further processing. The system was to be suitable both for standalone use in plant or laboratory measurements and for integration into the CUELA-HTR measurement system.

Activities/Methods:

An aluminium housing was designed and fabricated and a plastic handle of ergonomic geometry integrated into it. A mould for the plastic handle was fabricated to enable it to be manufactured in larger quantities. The handle was fitted to the housing by means of three-axis force sensors at both ends. Measuring amplifiers for electrical adjustment of the sensor signals were fitted in each of the two handles. All components serving the measurement function were encapsulated. Sub-D ports were employed for the power supply, measurement system control and measurement signal circuits.

Results:

The hand force measurement system produced, which comprises two separate force measurement handles, is an accurate and versatile system for measuring stress forces upon the body separately for both hands. The hand forces are recorded as three-dimensional force components and as total forces both in the co-ordinate system of the handle, and in the spatial co-ordinate system. The hand forces are recorded continuously during short-term or long-term measurements at a rate of 50 samples per second. The force signals can be recorded and stored by means of a data logger or over a cable link. In logger mode, the forces can be recorded for the duration of a work shift. Autonomous hand force measurements can thus be performed during laboratory measurements or on-site in plant measurements, and complete measurements performed in conjunction with the CUELA-HTR body posture measurement system. Measurement of the hand forces permits both ergonomic and biomechanical stress analyses, the results of which are required for instance as input variables for case assessments of certain formally recognized occupational diseases. A number of BGs intend to purchase the versatile measurement system and integrate it into their CUELA-HTR body posture measurement systems. The measurement system is also of interest to other institutes concerned with ergonomic force measurement. It may therefore be manufactured in small batches under licence by a measuring instrument manufacturer.

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