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