Use of data-driven design for the development of knob-shaped handles in the context of impedance measurements.

It can be inferred from hand-arm impedance analyses that the grip forces of users have a great influence on the transmitted vibrations. To determine this influence on test benches, the state of research suggests a cylindrical measuring handle. Since this shape is not suitable for all power tool handles, we develop a design for a knob-shaped measuring handle. The grip force applied to an orbital sander was measured in a test person study. The recorded data was combined with a 3D scan and evaluated by an algorithm which determined the separation plane of the measuring handle to integrate the force sensors. This plane is perpendicular to the vector of the subjects' grip forces. Furthermore, it divides the knob-shaped handle of the sander primarily vertically. The determination of the separation plane enables the design of a knob-shaped measuring handle for grip force measurement to analyze the hand-arm impedance of an overlying hand position.

The contact length parameter as a geometric factor for user-centered design of pistol grip geometries of power tools.

In this study the geometric parameter of the contact length is introduced, which intends to combine force exertion and perceived handle comfort in an anthropometric length in order to determine an optimal handle circumference. To prove suitability of the approach, 31 subjects were determined and correlations to handle circumferences with the highest finger forces and highest rated comfort were investigated. For all fingers, medium correlations were found among the contact lengths and the circumferences determined with maximum force (p < 0.001, rindex = 0.348, rmiddle = 0.419, rring = 0.374 and rlittle = 0.337) with high accordance of median values. Weak to moderate correlations were found between circumferences with maximum comfort and the contact lengths (p < 0.001, rindex = 0.150, rmiddle = 0.265, rring = 0.174). Using finger-specific proportionality factors, the contact lengths can be determined directly from the hand lengths, which enables great benefits for user-centered design.

Objective usability evaluation of drywall screwdriver under consideration of the user experience.

During validation of power tools, one objective is to determine the usability of the device for several applications. A common way to gain this user knowledge is to carry out tests under laboratory conditions with non-professional craftsmen, whereby a non-professional user does not work and evaluate a power tool similarly to a professional. Therefore an experimental study was conducted to investigate the possibility of training non-professionals in the professional working methods and evaluation of relevant key criteria for drywall screwdrivers. 39 subjects were divided into three groups and trained in the professional use of a drywall screwdriver. Results indicate that targeted training significantly improves the professional way of working (professional hand position p = 0.000, ß = -0.764) and evaluation (testing of mass distribution p = 0.000, ß = -0.731) of a drywall screwdriver. The gained knowledge can be used for the implementation of objective usability test-environments to derive specific and differentiated user-centered development potentials under laboratory conditions.