Validation of an instrumented dummy to assess mechanical aspects of discomfort during load carriage

Abstract

Due to the increasing load in backpacks and other load carriage systems over the last decades, load carriage system designs have to be adapted accordingly to minimize discomfort and to reduce the risk of injury. As subject studies are labor-intensive and include further challenges such as intra-subject and inter-subject variability, we aimed to validate an instrumented dummy as an objective laboratory tool to assess the mechanical aspects of discomfort. The validation of the instrumented dummy was conducted by comparison with a recent subject study. The mechanical parameters that characterize the static and dynamic interaction between backpack and body during different backpack settings were compared. The second aim was to investigate whether high predictive power (coefficient of determination R2>0.5) in assessing the discomfort of load carriage systems could be reached using the instrumented dummy. Measurements were conducted under static conditions, simulating upright standing, and dynamic conditions, simulating level walking. Twelve different configurations of a typical load carriage system, a commercially available backpack with a hip belt, were assessed. The mechanical parameters were measured in the shoulder and the hip region of the dummy and consisted of average pressure, peak pressure, strap force and relative motion between the system and the body. The twelve configurations consisted of three different weights (15kg, 20kg, and 25kg), combined with four different hip belt tensions (30N, 60N, 90N, and 120N). Through the significant (p<0.05) correlation of the mechanical parameters measured on the dummy with the corresponding values of the subject study, the dummy was validated for all static measurements and for dynamic measurements in the hip region to accurately simulate the interaction between the human body and the load carriage system. Multiple linear regressions with the mechanical parameters measured on the dummy as independent variables and the corresponding subjective discomfort scores from the subject study as the dependent variable revealed a high predictive power of the instrumented dummy. The dummy can explain 75% or more of the variance in discomfort using average pressures as predictors and even 79% or more of the variance in discomfort using strap forces as predictors. Use of the dummy enables objective, fast, and iterative assessments of load carriage systems and therefore reduces the need for labor-intensive subject studies in order to decrease the mechanical aspects of discomfort during load carriage.

Safety Assessment of Rehabilitation Robots: A Review Identifying Safety Skills and Current Knowledge Gaps

“…Pressure mats have been used for analyzing contact surfaces in e.g., backpacks (Wettenschwiler et al, 2017), wheelchairs (Apatsidis et al, 2002;Tam et al, 2003;Pipkin, 2008), beds (Defloor, 2000;Moysidis et al, 2011;Hemmes et al, 2017) and prosthetics (Rajtukova et al, 2014;Al-Fakih et al, 2016), and also in previous experiments to measure interface pressures in exoskeletons (Levesque et al, 2017;Huysamen et al, 2018) or soft exosuits (Xiloyannis et al, 2019). For this purpose, pressure mats must be flexible and compliant as the contact surface of a rehabilitation robot is usually curved and a stiff sensor would change the physical human-robot interaction.…”

Soft manikin as tool to evaluate bra features and pressure

“…In considering the uncontrollable and unavoidable noise from the evaluation of comfort with human subjects, human manikins and 3D biomechanical mathematical models have been developed to predict and investigate pressure performances of bra features (Nayak & Padhye, 2017;Fan & Chan, 2005;Wettenschwiler et al, 2017;Chang, Gao, & Yan, 2009;Haake & Scurr, 2010;Page & Steele, 1999;Starr et al, 2005;Yanmei, Weiwei, Fan, & Qingyun, 2014;Ying, Wang, Liu, & Zhang, 2011). Due to the lack of information on the human soft tissues, traditional manikins and mathematic modelling approach in previous biomechanical analyses of bra-breast contact pressure were generally assumed to be rigid and incompressible, which adversely affects the accuracy and reliability of the garment pressure results.…”

Safety first in rehabilitation robots! Investigating how safety-related physical human-robot interaction ca be assessed

“…Pressure mats have been used for analyzing contact surfaces in e.g. backpacks [148], wheelchairs [149]- [151], beds [152]- [154] and prosthetics [155], [156], and also in previous experiments to measure interface pressures in exoskeletons [157], [158] or soft exosuits [159]. For this purpose, pressure mats must be flexible and compliant as the contact surface of a rehabilitation robot is usually curved and a stiff sensor would change the physical human-robot interaction.…”

“…A method that can be considered as gold standard for measuring normal and tangential forces is the load cell, frequently using piezoresistors. However, these sensors are rather bulky and cost-intensive, which are possible reasons why many studies implement force sensitive resistors (FSRs) to assess the interaction between a human and a robotic, orthotic or load-carrying device [38], [40], [42], [148], [199].…”