Simulated Industrial Task Research Articles

A portable inflatable soft wearable robot to assist the shoulder during industrial work.

Repetitive overhead tasks during factory work can cause shoulder injuries resulting in impaired health and productivity loss. Soft wearable upper extremity robots have the potential to be effective injury prevention tools with minimal restrictions using soft materials and active controls. We present the design and evaluation of a portable inflatable shoulder wearable robot for assisting industrial workers during shoulder-elevated tasks. The robot is worn like a shirt with integrated textile pneumatic actuators, inertial measurement units, and a portable actuation unit. It can provide up to 6.6 newton-meters of torque to support the shoulder and cycle assistance on and off at six times per minute. From human participant evaluations during simulated industrial tasks, the robot reduced agonist muscle activities (anterior, middle, and posterior deltoids and biceps brachii) by up to 40% with slight changes in joint angles of less than 7% range of motion while not increasing antagonistic muscle activity (latissimus dorsi) in current sample size. Comparison of controller parameters further highlighted that higher assistance magnitude and earlier assistance timing resulted in statistically significant muscle activity reductions. During a task circuit with dynamic transitions among the tasks, the kinematics-based controller of the robot showed robustness to misinflations (96% true negative rate and 91% true positive rate), indicating minimal disturbances to the user when assistance was not required. A preliminary evaluation of a pressure modulation profile also highlighted a trade-off between user perception and hardware demands. Finally, five automotive factory workers used the robot in a pilot manufacturing area and provided feedback.

Sensemaking, adaptation and agency in human-exoskeleton synchrony.

Introduction: Wearable I robots such as exoskeletons combine the strength and precision of intelligent machines with the adaptability and creativity of human beings. Exoskeletons are unique in that humans interact with the technologies on both a physical and cognitive level, and as such, involve a complex, interdependent relationship between humans and robots. The aim of this paper was to explore the concepts of agency and adaptation as they relate to human-machine synchrony, as human users learned to operate a complex whole-body powered exoskeleton. Methods: Qualitative interviews were conducted with participants over multiple sessions in which they performed a range of basic functional tasks and simulated industrial tasks using a powered exoskeleton prototype, to understand their expectations of the human-technology partnership, any challenges that arose in their interaction with the device, and what strategies they used to resolve such challenges. Results: Analysis of the data revealed two overarching themes: 1) Participants faced physical, cognitive, and affective challenges to synchronizing with the exoskeleton; and 2) they engaged in sensemaking strategies such as drawing analogies with known prior experiences and anthropomorphized the exoskeleton as a partner entity in order to adapt and address challenges. Discussion: This research is an important first step to understanding how humans make sense of and adapt to a powerful and complex wearable robot with which they must synchronize in order to perform tasks. Implications for our understanding of human and machine agency as well as bidirectional coadaptation principles are discussed.

An Occupational Shoulder Exoskeleton Reduces Muscle Activity and Fatigue During Overhead Work.

This paper assesses the effect of a passive shoulder exoskeleton prototype, Exo4Work, on muscle activity, muscle fatigue and subjective experience during simulated occupational overhead and non-overhead work. Twenty-two healthy males performed six simulated industrial tasks with and without Exo4Work exoskeleton in a randomized counterbalanced cross-over design. During these tasks electromyography, heart rate, metabolic cost, subjective parameters and performance parameters were acquired. The effect of the exoskeleton and the body side on these parameters was investigated. Anterior deltoid activity and fatigue reduced up to 16% and 41%, respectively, during isometric overhead work, and minimized hindrance of the device during non-overhead tasks. Wearing the exoskeleton increased feelings of frustration and increased discomfort in the areas where the exoskeleton and the body interfaced. The assistive effect of the exoskeleton was less prominent during dynamic tasks. This exoskeleton may reduce muscle activity and delay development of muscle fatigue in an overhead working scenario. For dynamic applications, the exoskeleton's assistive profile, which mimics the gravitational torque of the arm, is potentially sub-optimal. This evaluation paper is the first to report reduced muscle fatigue and activity when working with an occupational shoulder exoskeleton providing one third of the gravitational torque of the arm during overhead work. These results stress the potential of occupational shoulder exoskeletons in overhead working situations and may direct towards longitudinal field experiments. Additionally, this experiment may stimulate future work to further investigate the effect of different assistive profiles.

Impacts of Enhanced Physical Abilities via Exoskeletons on Attentional Performance and Workload

Exoskeletons have great potential for reducing physical fatigue and work-related musculoskeletal disorders. Prior research investigating the effects of wearing an exoskeleton on the wearers’ cognitive performance suggested both potentially positive and negative impacts. However, the precise effects of wearing different types of exoskeletons on the individual’s various aspects of cognitive functions are under-studied. This study investigated the effects of wearing upper and lower-body unpowered exoskeletons on visual attentional performance while performing simulated industrial tasks, using an innovative augmented reality (AR)-based attentional visual field task. This study also compared physical task performance and self-reported mental workload while wearing an exoskeleton vs. not wearing an exoskeleton. While no universal change in cognitive performance with exoskeleton use was observed, the current study demonstrated large individual differences, which may have significant practical and theoretical implications.

Effect of attention demand on upper trapezius muscle activity – A moderated mediation model

Manufacturing continues to become more automated. Consequently, production operators are monitoring automated processes for prolonged durations. The sustained attention required for monitoring work has been was found to be stressful for humans. This study hypothesises that sustained attention is a psychosocial stressor that increases upper trapezius muscle activity via a psychophysiological pathway in a series of simulated industrial tasks. A moderated mediation model was tested and accepted with the parasympathetic nervous system acting as a mediator contingent on certain levels of end-tidal CO2. The study outcomes confirmed that sustained attention acts as a psychosocial stressor which increases upper trapezius muscle activity by inhibiting the action of the parasympathetic system and increasing hyperventilation.

Physiological and perceptual effects of a cooling garment during simulated industrial work in the heat

ObjectiveEvaluate physiological and perceptual responses using a phase change cooling (PCC) garment during simulated work in the heat. MethodsTwenty males wearing compression undergarments, coverall suit, gloves, and hard-hat, completed two randomly assigned trials (with PCC inserts or control, CON) of simulated industrial tasks in the heat (34.2 ± 0.05 °C, 54.7 ± 0.3%RH). Trials consisted of two 20 min work bouts, a maximum performance bout, and 10 min of recovery. ResultsPhysiological strain index (PSI) was lower during PCC after the second work bout and during recovery (all P < 0.05). PCC reduced heat storage (27.0 ± 7.6 W m−2) compared to CON (42.7 ± 9.9 W m−2, P < 0.001). Perceptual strain index (PeSI) was reduced with PCC compared to CON (P < 0.001), however performance outcomes were not different between trials (P = 0.10). ConclusionsPCC during work in the heat attenuated thermal, physiological, and perceptual strain. This PCC garment could increase safety and reduce occupational heat illness risk.

The impact of an increase in work rate on task demands for a simulated industrial hand tool assembly task

Global competition in the manufacturing sector has created an environment for continuous improvement resulting in methods to increase capacity while lowering cost. Speed Fastening (SF) is one manufacturing assembly method currently being modified to improve its production capacity. This semi-automated riveting process is limited by a lack of continuous feed of fasteners supplied to the tool. One path to productivity improvement that has been identified for improving productivity in SF is the development of a continuous feed tool, which would eliminate non-value added time currently scheduled for reloading. In preparation for the design of a new tool, a proactive investigation was conducted to characterize the influence of work rate (i.e. frequency of fastener insertion) on task demands (e.g. muscular effort, posture, etc.) for manual SF work. Twelve healthy female subjects participated in simulated SF work over four test sessions. The first test session was used to familiarize subjects with the task, as well as the data collection protocol. Subsequent test days were block randomized to one of three work rates (7, 14 and 21 fasteners per minute) with subjects required to complete 120 min of simulated SF work at waist and shoulder height. Overall, an increase in work rate imposed a significant increase ( p < 0.0001, 7 %MVIC) in the muscle activity recorded from the wrist extensors, despite the fact that no significant changes were observed in the 50th percentile upper extremity joint posture. As expected, the location of work (i.e. waist vs. shoulder height) imposed significant differences in muscle activity and joint posture. On average, participants assumed significantly greater magnitudes of wrist flexion ( p = 0.0025) and ulnar deviation ( p < 0.001) for shoulder height trials. Based on these findings it is expected that an increased work rate may expose SF operators to an elevated risk of MSI, particularly for work completed at shoulder height. Relevance to industry Repetitive work performed with a powered hand tool is considered a risk factor for the development upper extremity musculoskeletal injury. This investigation contributes to an improved understanding of the impact that an increased pace of work has on the physical demands of operators during a simulated industrial task.

Analysis of visual acuity and motion resolvability as measures for optimal visual perception of the workspace

For working tasks with high visual demand, ergonomic design of the working stations requires defining criteria for comparative evaluation and analysis of the visual perceptibility in different regions of the workspace. This paper provides kinematic models of visual acuity and motion resolvability as adopted measures of visual perceptibility of the workspace. The proposed models have been examined through two sets of experiments. The first experiment is designed to compare the models outputs with those from experiments. Time measurements of the participants’ response to visual events are employed for calculation of the perceptibility measures. The overall comparison results show similar patterns and moderate statistical errors of the measured and kinematically modeled values of the parameters. In the second experiment, the proposed set of visual perceptibility measures are examined for a simulated industrial task of inserting electronic chips into slots of a working table, resembling a fine assembly line of transponders manufacturing. The results from ANOVA tests for the visual acuity and the motion resolvability justify the postures adopted by the participants using visual perceptibility measures for completing the insertion tasks.

Postural stability during task performance on elevated and/or inclined surfaces

The purpose of this study was to subjectively and objectively evaluate the postural stability of forty industrial workers while performing simulated industrial tasks on inclined and elevated surfaces under various combinations of environmental lighting and noise distraction conditions. The results suggest the following ordering for the effects of risk factors on objective measure of postural balance: (1) environmental lighting, (2) elevation of standing surface, (3) gender, (4) inclination of standing surface, (5) age. The task performed would be ranked highest had the data been analyzed across the three tasks. The postural sway length significantly increased with increasing elevations and inclination angles for the stationary and bending tasks implying body's perceived risk of fall deployed increase in postural muscle contraction. This compensatory mechanism indicated by increased sway length actually did reduce postural sway amplitudes with increasing elevation but for increasing inclination the postural sway amplitudes increased. While the objective measure of postural sway increased with the increasing combination of elevation and inclination, the subjective measure of stability did not show a significant two way interaction, implying that the participants were not able to perceive the combined risk to postural imbalance, causing potential inability to deploy appropriate postural muscle corrective actions.

An Analysis of Shoulder Loading Differences for Simulated Industrial Task Performance between Injured and Non-Injured Subject Populations

Detailed characterization of differences in motions between injured and non-injured populations has not been widely studied. These motion differences may have an impact on physical loading of injured populations performing work tasks. This study included analysis of tasks performed by three populations: control, spinal cord injured, and low back pain. Shoulder loading was examined for goal-directed simulated sagittal and lateral plane work tasks through calculation of maximum external dynamic shoulder moments. The significant main effects in determining shoulder moments included: type of task performed (one or two-handed load movement), horizontal distance to target, vertical height of target, and population membership. There was also a significant interaction effect between population and task type. This study establishes that both task requirements and injury status quantitatively effect shoulder loading, particularly for lateral motions, and suggests that ergonomists should consider factors beyond task-defined characteristics when designing job interfaces for injured populations.

Psychophysical and physiological study of one-handed and two-handed combined tasks

Most studies in manual material handling (MMH) have paid attention to single MMH activities – lifting, lowering, carrying, holding, pushing or pulling and have ignored combined activities. Also, most studies have involved two-handed (symmetric) MMH activities rather than one-handed MMH activities. Very few studies have reported information on workers' capacities for combinations of one-handed MMH activities (e.g. lifting a box, then carrying the box, and lowering the box). These kinds of combined activities are common in industry and in our daily lives. The objective of this study was to utilize the psychophysical approach to examine the combinations of lifting, carrying and lowering activities from a simulated industrial task involving one-handed and two-handed combined tasks, and to develop mathematical models for combined tasks. Ten male students served as subjects for the study. Maximum acceptable weight workload capacities for 1 h work periods for one-handed and two-handed combined tasks (lifting a box from floor-to-knuckle height, carrying the box for 4.3 m, and lowering the box from knuckle-to-floor height) were determined psychophysically under three frequencies: six handlings per minute, one handling per minute, and one handling per 5 min. In addition to maximum acceptable weight, heart rate, ratings of perceived exertion (RPE) values and tasking time were also measured as response variables. Combined MMH capacity models for one-hand and two-handed tasks were developed. The advantages and disadvantages of different models are discussed. Relevance to industry The combinations of lifting, carrying and lowering activities in sequence are an integral and common part of material handling tasks in industry. Adequate scientific information is presently not available for assessing combined manual material handling tasks. Developing a model to predict the capacity of a combined task would make it easier to predict the maximum acceptable weight of both one and two-handed combined MMH tasks.

A single metric for quantifying biomechanical stress in repetitive motions and exertions

The relative effects of repetition, force and posture were studied in order to investigate how continuous biomechanical measurements can be combined into a single metric corresponding to subjective discomfort. A full factorial experiment was conducted involving repetitive wrist flexion from a neutral posture to a given angle against a controlled force. Seven subjects performed the task using two paces (20 and 4 motions/min), two force levels (15 and 45 N) and two angles (15 and 45°) for 1 h each. Discomfort was reported on a 10 cm visual analogue scale anchored between ‘no discomfort’ and ‘very high discomfort’. Repeated measures analysis of variance showed that all main effects were statistically significant (p< 0.05) and no significant interactions were observed. A linear regression model was fitted to the data and used for generating frequency weighted digital filters that shape continuous recordings of repetitive motions and exertions into an output proportional to relative discomfort. The resulting high-pass digital filter had a 22 dB/decade attenuation slope. A simulated industrial task used for validating the model involved repetitively transferring pegs across a horizontal bar and inserting them into holes against a controlled resistance. Angular wrist data were recorded using an electrogoniometer and filtered. Six subjects performed the task of the three conditions consisting of (1) 15° wrist flexion, 15 N resistance and 6 motions/min, (2) 15° wrist flexion, 45 N resistance and 12 motions/min, and (3) 45° wrist flexion, 45 N resistance and 15 motions/min. Subjective discomfort was reported after performing the task for 1 h. Pearson correlations between subjective discomfort ratings and the integrated filtered biomechanical data for individual subjects ranged from 0·90 to 1·00. The pooled correlation across subjects was 0·67. This approach may be useful for physical stress exposure assessment and for design of tasks involving repetitive motions and exertions.

Validation of a Frequency Weighted Filter for Repetitive Wrist Flexion Tasks against a Load

This experiment validates an instrument that implements a force and frequency weighted filter for biomechanical stress exposure assessment. This filter network was developed based on a previously established discomfort model that associated physical stress of force, posture and repetition with subjective discomfort. A simulated industrial task was used in the current study to test the instrument involving repetitively transferring a peg and inserting it into a hole against a controlled resistance. Ten subject performed the task for six conditions. Continuous wrist angular data were recorded using an electrogoniometer and processed through the filter. Subjective discomfort was reported after performing the task for one hour using a 10 cm visual analog scale. The discomfort model was shown to estimate relative discomfort for the experimental conditions tested ( r2 = 0.98, p &lt; .05). Linear regression analysis showed that the instrument aptly predicted subjective discomfort ( r2 = 0.87, p &lt; .05). Applications and limitations of this instrument are explored.

Evaluation of Grip Force Exertions in Dynamic Manual Work

An obstacle to the development of guidelines for reducing forceful hand movements is that manual force is not easily measured or estimated at the worksite, especially during highly dynamic activities. Grip force requirements during manual work are dependent not only on object weight, but also on the surface characteristics of the object and the task dynamics. In theory, it is possible to predict grip force requirements for manual tasks using Newtonian laws of physics; however few researchers have attempted to measure grip force during dynamic work, much less to compare actual grip force values to predicted levels. Therefore, a laboratory experiment was conducted to examine grip force exertions during two simulated industrial tasks. In each task, participants repetitively grasped and moved aluminum handles against varying levels of weight or resistance. Grip force was measured using a strain gauge mounted inside the handles. Results indicate that grip force varied continuously throughout each work cycle in response to changes in the motion of the hand/handle. The pattern of variation was consistent between subjects and could be approximated by a sinusoidal model. Greater interindividual variation in grip force exertion was observed when the task allowed greater flexibility in selecting a movement strategy. The results also indicate that subjects are more likely to “overshoot” the necessary grip force (i.e., apply more force than needed) at the initiation of movement, especially at lower weight levels. This study demonstrates that it is possible to predict variations in grip force during dynamic work, although further refinements in the procedure are needed. Use of modelling techniques will enable industrial designers to better estimate grip force requirements and to identify design strategies that will reduce the risk of musculoskeletal injury to the worker.

An analysis of handle designs for reducing manual effort: The influence of grip diameter

Biomechanical principles indicate that the risk of upper extremity cumulative trauma disorders (CTDs) can be mitigated by designing tools to reduce manual effort. Specifically, research suggests that handle design should be based on anthropometric considerations. A laboratory study was designed to evaluate the effects of handle diameter on manual effort during a simulated industrial task. Three handle diameters were studied: (1) a handle matched to inside grip diameter, (2) a handle 1.0 cm smaller than inside grip diameter, and (3) a handle 1.0 cm larger than inside grip diameter. The task was performed against three levels of resistance. Applied grip force and surface electromyography (EMG) of select forearm muscles were recorded. The results indicate that grip strength was maximized by the smaller handle. Grip strength was also greater with the matched handle than with the larger handle. There were no differences in grip force exerted with different handles during the experiment. However, because the smaller handle provided the greatest capacity for exerting grip force, effort was reduced when the smaller handle was used. Forearm muscle activity was also reduced when the smaller handle was used. The study indicates handles 1.0 cm smaller than the user's inside grip diameter may reduce effort and the potential for injury.

Managerial Implications of Extended Breaks on Predicting Performance Times for Industrial Tasks

Production Managers and Industrial Engineers have relied upon learning (progress) curves for over fifty years. However, until recently only the impacts of extended breaks on performance time predictions were considered. This study examined the effect of breaks on two typical simulated industrial tasks. Fifty-eight subjects performed either the traditional peg-board, a low cognitive task, or a spreadsheet graphic, a moderately-high cognitive task, for 28 iterations. Upon completion of the assigned task, a break period that ranged from 2 to 83 days was randomly assigned to each subject. After the break, subjects replicated their assigned task. Regression analysis was used to select the best model to predict the performance time for the first iteration after a break. An exponential model was selected for the low cognitive task and a multiple linear model for the moderately-high cognitive task. Both models selected were no-intercept models and had multiple correlation coefficients of 0.729 and 0.897 respectively. The ability to accurately predict the first iteration time after a break is a key element in calculating time lost to forgetting and determining the forgetting function. These models may be useful in assisting production managers and industrial engineers in establishing more realistic progress curves and accurate standard times, thus reducing excessive idle time.

Prediction of leadership in a simulated industrial task.

Prediction of leadership in a simulated industrial task.