Gyouhyung Kyung

Specifying comfortable driving postures for ergonomic design and evaluation of the driver workspace using digital human models.

Specifying comfortable driving postures is essential for ergonomic design and evaluation of a driver workspace. The present study sought to enhance and expand upon several existing recommendations for such postures. Participants (n = 38) were involved in six driving sessions that differed by vehicle class (sedan and SUV), driving venue (laboratory-based and field) or seat (from vehicles ranked high and low by vehicle comfort). Sixteen joint angles were measured in preferred postures to more completely describe driving postures, as were corresponding perceptual responses. Driving postures were found to be bilaterally asymmetric and distinct between vehicle classes, venues, age groups and gender. A subset of preferred postural ranges was identified using a filtering mechanism that ensured desired levels of perceptual responses. Accurate ranges of joint angles for comfortable driving postures, and careful consideration of vehicle and driver factors, will facilitate ergonomic design and evaluation of a driver workspace, particularly when embedded in digital human models.

Grasp and index finger reach zone during one-handed smartphone rear interaction: effects of task type, phone width and hand length

Abstract Recently, some smartphones have introduced index finger interaction functions on the rear surface. The current study investigated the effects of task type, phone width, and hand length on grasp, index finger reach zone, discomfort, and muscle activation during such interaction. We considered five interaction tasks (neutral, comfortable, maximum, vertical, and horizontal strokes), two device widths (60 and 90 mm) and three hand lengths. Horizontal (vertical) strokes deviated from the horizontal axis in the range from −10.8° to −13.5° (81.6–88.4°). Maximum strokes appeared to be excessive as these caused 43.8% greater discomfort than did neutral strokes. The 90-mm width also appeared to be excessive as it resulted in 12.3% increased discomfort relative to the 60-mm width. The small-hand group reported 11.9–18.2% higher discomfort ratings, and the percent maximum voluntary exertion of their flexor digitorum superficialis muscle, pertaining to index finger flexion, was also 6.4% higher. These findings should be considered to make smartphone rear interaction more comfortable. Practitioner Summary: Among neutral, comfortable, maximum, horizontal, and vertical index finger strokes on smartphone rear surfaces, maximum vs. neutral strokes caused 43.8% greater discomfort. Horizontal (vertical) strokes deviated from the horizontal (vertical) axis. Discomfort increased by 12.3% with 90-mm- vs. 60-mm-wide devices. Rear interaction regions of five commercialised smartphones should be lowered 20 to 30 mm for more comfortable rear interaction.

Age-related difference in perceptual responses and interface pressure requirements for driver seat design

Due to typical physiological changes with age, older individuals are likely to have different perceptual responses to and different needs for driver–seat interface design. To assess this, a study was conducted in which a total of 22 younger and older participants completed six short-term driving sessions. Three subjective ratings (comfort, discomfort and overall) were obtained, along with 36 driver–seat interface pressure measures, and were used to assess differences and similarities between the two age groups. For both age groups, localised comfort ratings were more effective at distinguishing between driver seats and workspaces. Older individuals appeared to be less sensitive to discomfort than younger individuals. Across age groups, two distinct processes were used in determining whole-body comfort and discomfort perceptions based on localised comfort/discomfort perceptions. Whole-body discomfort levels were largely affected by lower back discomfort in the younger group versus upper back discomfort in the older group. Four specific pressure measures at several body regions differed between the age groups, suggesting distinct contract pressure requirements and loading patterns among these groups. Practitioner Summary: Driver seats appear to be differentiable only in terms of perceived comfort, but not in terms of perceived discomfort. Different pressure requirements for each age group and for each seat side should be considered comprehensively when designing driver seats and workspaces.

Research on flexible display at ulsan national institute of science and technology

Displays represent information visually, so they have become the fundamental building block to visualize the data of current electronics including smartphones. Recently, electronics have been advanced toward flexible and wearable electronics that can be bent, folded, or stretched while maintaining their performance under various deformations. Here, recent advances in research to demonstrate flexible and wearable displays are reviewed. We introduce these results by dividing them into several categories according to the components of the display: active-matrix backplane, touch screen panel, light sources, integrated circuit for fingerprint touch screen panel, and characterization tests; and we also present mechanical tests in nano-meter scale and visual ergonomics research.

Effects of display curvature and hand length on smartphone usability

The purpose of this study was to examine the effects of display curvature and hand length on smartphone usability, which was assessed in terms of grip comfort, immersive feeling, typing performance, and overall satisfaction. A total of 20 younger individuals with the mean (SD) age of 20.8 (2.4) yrs were divided into three hand-size groups (small: 8, medium: 6, large: 6). Two smartphones of the same size were used – one with a flat display and the other with a side-edge curved display. Three tasks (watching video, calling, and texting) were used to evaluate smartphone usability. The smartphones were used in a landscape mode for the first task, and in a portrait mode for the other two. The flat display smartphone provided higher grip comfort during calling (p = 0.008) and texting (p = 0.006) and higher overall satisfaction (p = 0.0002) than the curved display smartphone. The principal component regression (adjusted R2 = 0.49) of overall satisfaction on three principal components comprised of the remaining measures showed that the first principal component on grip comfort was more important than the other two on watching experience and texting performance. It is thus necessary to carefully consider the effect of display curvature on grip comfort when applying curved displays to hand-held devices such as smartphones.

Effects of Display Curvature and Task Duration on Proofreading Task Performance, Visual Fatigue, Visual Discomfort, and Display Satisfaction:

With more curved display products in the market and more exposure to such products, it is necessary to examine the effects of display curvature and task duration from the ergonomics perspective. The current study examined the effects of these two factors on visual performance, visual fatigue, visual discomfort, and display satisfaction during proofreading tasks. We incorporated five display curvatures (600R, 1140R, 2000R, 4000R, and flat) and five task durations (0, 15, 30, 45, and 60 min). Each of 50 individuals completed a 1-hr proofreading task at one of five display curvature conditions. The horizontal viewing distance was fixed at 600mm. Proofreading performance (speed and error rate), subjective visual fatigue [on ECQ (Eye Complaint Questionnaire)], physiological visual fatigue [CFF (Critical Fusion Frequency), blink duration, and blink frequency], visual discomfort (on VAS), and display satisfaction (on VAS) were measured. The highest mean proofreading speed was at 600R. The mean proofreading speed and error rate increased by 15.5% and 22.3%, respectively, over the 1-h task. The mean ECQ score and visual discomfort increased by 188.6% and 107.2% during 45 and 60 min of the task, respectively. The mean CFF and display satisfaction decreased by 0.49Hz and 11.2% during 15 and 15-45 min of the task. A polynomial regression model for subjective visual fatigue was developed (adjusted R2 = 0.6). These findings can be used when determining ergonomic display curvatures and predicting visual fatigue.

Change propagation analysis for sustainability in product design

Components in complex systems are intricately interconnected with each other. When design changes are needed in terms of sustainability, it is necessary to understand how change propagates and affects other systems. Therefore, the objective of this paper describes how to define the cause of a sustainable design change and the effect of change propagation by utilizing Change Propagation Analysis (CPA) and system dynamics. The interconnections of components in a complex system are investigated by Design Structure Matrix (DSM) and system dynamics. Design changes are subdivided into sustainable classes by the sustainable checklist. The likelihoods of design change are measured by designers in functional DSM and sustainable impact values are calculated by using the sustainable checklist and expressed in sustainable DSM. The system dynamics is used to analyze and visualize patterns and behaviors of sustainable changes based on DSM.

Measuring Drivers’ Dynamic Seating Experience Using Pressure Mats

The objective of this study was to find the relationship between body-seat pressure distribution and driver comfort ratings of dynamic seating experience. A total of 38 participants performed four short-term driving sessions in a commercialized vehicle. These sessions involved two driving environments (lab vs. field-based). Body-seat interface pressure data were recorded continuously during driving, and the comfort ratings of the whole body and local body parts were measured after each session. Several body-seat pressure distribution variables were proposed to improve sitting comfort.

Determining ergonomic forms for rollable display devices

Following commercialization of curved displays, foldable and rollable displays are under development. The rollable display should be unrolled first using a pulling motion to access the screen. The corresponding pulling force acting on the lateral grip (bezel) areas of the device should be higher than the spring force typically used for retracting the screen. The objective of the current study was to examine the effects of hand length and device thickness on the required lateral grip area sizes of the rollable display device and the grip comfort for the screen unrolling motion, and to ultimately determine the ergonomic bezel width and device thickness associated with high grip comfort. Thirty young individuals with the mean (SD) age of 22.1 (2.2) years participated in this study. All participants were recruited from a university population, right-handed, and healthy without any musculoskeletal diseases on their upper limbs. This study was a 3 (Hand length) × 3 (Device thickness) mixed factorial design. Hand length (HandS/M/L; between-subjects factor) consisted of HandS (short hand length; ≤162.5 mm, 10th percentile), HandM (medium hand length; 174.6–177.3 mm, 45th–55th percentile), and HandL (large hand length; ≥189.4 mm, 90th percentile). Device thickness (DeviceThin/Medium/Thick; within-subjects factor) consisted of DeviceThin (2 mm thick), DeviceMedium (6 mm thick), and DeviceThick (10 mm thick). Each of three rollable display device prototypes was comprised of Acrylonitrile Butadiene Styrene plastic panels, a roll of paper screen (to show a default screen), a roller, and a spring (to roll the screen). The thickness of the right side of the device was manipulated, whereas that of the left side was fixed at 10 mm to house the three parts described above (a rollable screen, a roller, and a spring). When fully unrolled, the sizes of each prototype and the screen were 140H × 300W × 2.5R (mm) and 130H × 260W (mm), respectively. The prototype was equally split into two sides, with each grip part (bezel) 20 mm wide. A 1 mm-interval grid image (130H × 20W (mm)) was attached to each bezel to measure the bezel area involved in gripping. The initial pulling force for unrolling the screen was 2.5N. A desk (150 × 60 × 73 cm) and a height-adjustable chair were used. First, participants unrolled and rolled the prototypes freely for five min to familiarize themselves with how to use the prototypes. A randomly assigned prototype was evaluated three times as follows. Each seated participant repeated unrolling and rolling motions with the assigned prototype until they found the most comfortable grip. While the screen was fully unrolled using the most comfortable grip, each grip area was photographed from four different directions. Then, each individual rated the grip comfort of each hand on a 100mm Visual Analogue Scale (0: Very uncomfortable, 100: Very comfortable). A paper-and-pencil method was used for comfort ratings. The entire procedure to evaluate the three prototypes required about 30 min per participant. Regardless of hand length, the width of the grip area from the device side edge was up to 20 mm. The mean (SD) height of the grip areas for HandS/M/L was 108.8 (3.1), 116.8 (2.5), 124.2 (2.3), respectively. Regardless of hand length, the lower end of the grip area reached the bottom of the device, while the upper end moved more upward with hand lengths. The thinner the device was, the smaller the difference in the grip areas was across the three hand-length groups. In addition, grip comfort increased with device thickness. When gripping a thinner object, the grip posture becomes more deviated from a relaxed hand posture to make more flexions of the thumb and fingers. The simple linear regression model for the left-hand grip comfort on the right-hand grip comfort was constructed (R2 = 0.68 and p-values <0.001): Y(left-hand grip comfort)=23.1+0.74×X(right-hand grip comfort) This regression model indicates that the two grip comfort ratings were positively correlated. In addition, the right-hand grip comfort ratings were lower than the left-hand grip comfort ratings. The mean (SD) comfort ratings for the left and right hands were 75.1 (19.2) and 78.6 (17.3), respectively, with p-value for a paired t-test < 0.001. Thus, device thickness appears to be an important design dimension that influences the grip comfort associated with screen unrolling. There are some limitations in the current study. First, the initial pulling force required for screen unrolling was fixed at 2.5N. The screen unrolling motion involves external rotation of the shoulders. To the authors’ knowledge, no study has investigated an ergonomic force range for this motion. Second, some measurement errors may have been involved in manually identifying the grip area based on the photographs. Using touch sensors would provide more accurate and faster measurements. Finally, it is necessary to analyze the grip areas more in detail. The current study investigated the effects of hand length and device thickness on the grip area and the grip comfort of each hand for rollable display devices. The findings suggested that regardless of hand length, the side bezel of a rollable display device should be at least 20 mm wide and the device should be sufficiently thick (preferably 10 mm thick) to ensure high grip comfort. These findings will be useful when designing ergonomic rollable display devices with high grip comfort.

Effects of Display Curvature, Presbyopia, and Task Duration on Visual Fatigue, Task Performance, and User Satisfaction:

Objective: This study examined the effects of display curvature, presbyopia, and task duration on visual fatigue, task performance, and user satisfaction. Background: Although curved displays have been applied to diverse display products, and some studies reported their benefits, it is still unknown whether the effects of display curvature are presbyopia-specific. Method: Each of 64 individuals (eight nonpresbyopes and eight presbyopes per display curvature) performed four 15-min proofreading tasks at one display curvature radius setting (600R, 1140R, 4000R, and flat; mm). Diverse measurements were obtained to assess visual fatigue, task performance, and user satisfaction. Results: The mean pupil diameter was the largest with 1140R, indicating this curvature radius was associated with the least development of visual fatigue; 600R was comparable with 1140R in terms of pupil diameter. The presbyopic group showed a 28.5% slower proofreading speed compared with the nonpresbyopic group, whereas their proofreading accuracy was comparable. For both groups, the mean visual fatigue increased significantly during the first 15 min of proofreading, as indicated by a decrease of 0.11 mm in the mean pupil diameter, an increase of 3.8 in the mean bulbar conjunctival redness, and an increase of 9.13 in the mean eye complaint questionnaire score. Conclusion: The effect of display curvature was not presbyopia-specific. Low visual fatigue was observed with 1140R and 600R. Application: Display curvature radii near or in the range of 600R and 1140R and frequent breaks are recommended for both presbyopic and nonpresbyopic groups to reduce their visual fatigue due to visual display terminal tasks.