Human Posture Estimation: A Systematic Review on Force-Based Methods-Analyzing the Differences in Required Expertise and Result Benefits for Their Utilization.

Force-based human posture estimation (FPE) provides a valuable alternative when camera-based human motion capturing is impractical. It offers new opportunities for sensor integration in smart products for patient monitoring, ergonomic optimization and sports science. Due to the interdisciplinary research on the topic, an overview of existing methods and the required expertise for their utilization is lacking. This paper presents a systematic review by the PRISMA 2020 review process. In total, 82 studies are selected (59 machine learning (ML)-based and 23 digital human model (DHM)-based posture estimation methods). The ML-based methods use input data from hardware sensors-mostly pressure mapping sensors-and trained ML models for estimating human posture. The ML-based human posture estimation algorithms mostly reach an accuracy above 90%. DHMs, which represent the structure and kinematics of the human body, adjust posture to minimize physical stress. The required expert knowledge for the utilization of these methods and their resulting benefits are analyzed and discussed. DHM-based methods have shown their general applicability without the need for application-specific training but require expertise in human physiology. ML-based methods can be used with less domain-specific expertise, but an application-specific training of these models is necessary.

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.

Prediction of Tool Forces in Manual Grinding Using Consumer-Grade Sensors and Machine Learning.

Tool forces are a decisive parameter for manual grinding with hand-held power tools, which can be used to determine the productivity, quality of the work result, vibration exposition, and tool lifetime. One approach to tool force determination is the prediction of tool forces via measured operating parameters of a hand-held power tool. The problem is that the accuracy of tool force prediction with consumer-grade sensors remains unclear in manual grinding. Therefore, the accuracy of tool force prediction using Gaussian process regression is examined in a study for two hand-held angle grinders in four different applications in three directions using measurement data from an inertial measurement unit, a current sensor, and a voltage sensor. The prediction of the grinding normal force (rMAE = 11.44% and r = 0.84) and the grinding tangential force (rMAE = 18.21% and r = 0.82) for three tested applications, as well as the radial force for the application cutting with a cut-off wheel (rMAE = 19.67% and r = 0.80) is shown to be feasible. The prediction of the guiding force (rMAE = 87.02% and r = 0.37) for three tested applications is only possible to a limited extent. This study supports data acquisition and evaluation of hand-held power tools using consumer-grade sensors, such as an inertial measurement unit, in real-world applications, resulting in new potentials for product use and product development.

Analysis of factors influencing the productivity of hammer drilling - user forces, human fatigue, drilling direction, and drill bit.

In order to be able to develop a hammer drill with which the user can work as ergonomically and productively as possible, the relevant influencing factors must be known. In addition to the unknown influence of the drilling direction, there is a lack of understanding of the relations between user forces, human fatigue, and productivity. To analyze these relations, an experiment was carried out with 15 professional users. First, the influence of feed force, drilling direction, and drill bit on the rate of penetration was examined. Taking into account the rate of penetration and human fatigue, it was then investigated which of the three feed forces produces the highest productivity. Furthermore, the lateral forces applied by the participants during the drilling process were analyzed. Based on the study, it was found that the drilling direction (p < .001, r = -0.198) and the drill bit type (p < .041, r = -0.16) have a significant influence on the rate of penetration. Moreover, it was found that the rate of penetration tends to increase with higher feed forces, however, the theoretical cumulative drilling meters decrease when taking user fatigue into account. Finally, the experiment showed that the participating professionals applied lateral forces (Mdn = 16.7 N) of 13% to the feed force when working with a hammer drill. On the basis of this knowledge, investigations can be done to analyze the influences of lateral forces on the drilling process. The findings help drill and hammer drill manufacturers in testing and development processes. For craftsmen, on the other hand, the knowledge helps to perform the task as ergonomically and time-efficiently as possible.

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.