This study evaluated the effects of reading text on an optical see-through head-mounted display during treadmill walking in a virtual environment. Thirty participants were recruited to perform Chinese reading tasks by reading six types of text layouts in two polarity settings. A virtual environment was displayed on a projection screen to simulate a walking situation in which obstacles were encountered. High- and low-density obstacles were applied. Objective measures included reading performance, gait variability, and the error count of obstacles. The subjective measures were the situational awareness rating technique (SART) and NASA-Task Load Index (NASA-TLX) scores. The results indicated that font size and polarity affected the gait variability, reading performance, situational awareness, and mental workload ratings. The obstacle density affects gait variability and situation awareness rating. The layout with 32-point text and positive polarity yielded faster reading speed, better subjective ratings, and less variability in minimum foot clearance.

This study investigates the visual angle threshold value for the recognition of Chinese characters displayed on the optical head-mounted display. As optical head-mounted displays are becoming increasingly popular in various fields, character legibility has become an important topic for research. In this study, a legibility test was conducted by randomly displaying characters on the optical head-mounted display. The characteristics that were tested included the number of strokes, components and usage frequency rankings. The visual angle threshold value of each character was recorded and analysed. The results indicate that Chinese characters with more strokes, more components and lower usage frequency have a larger visual angle threshold value than characters with fewer strokes, fewer components and higher frequency. The number of strokes and usage frequency rankings were inputted into a regression model to predict the visual angle threshold value for character recognition (R² = 0.72; Adj-R² = 0.71). The regression analyses revealed that the foregoing inputs increased the visual angle threshold value. These findings provide a practical reference for the display of Chinese characters on optical head-mounted displays.

A trunk-twisting posture is strongly associated with physical discomfort. Measurement of joint kinematics to assess physical exposure to injuries is important. However, using a single Kinect sensor to track the upper-limb joint angle trajectories during twisting tasks in the workplace is challenging due to sensor view occlusions. This study provides and validates a simple method to optimally select the upper-limb joint angle data from two Kinect sensors at different viewing angles during the twisting task, so the errors of trajectory estimation can be improved. Twelve healthy participants performed a rightward twisting task. The tracking errors of the upper-limb joint angle trajectories of two Kinect sensors during the twisting task were estimated based on concurrent data collected using a conventional motion tracking system. The error values were applied to generate the error trendlines of two Kinect sensors using third-order polynomial regressions. The intersections between two error trendlines were used to define the optimal data selection points for data integration. The finding indicates that integrating the outputs from two Kinect sensor datasets using the proposed method can be more robust than using a single sensor for upper-limb joint angle trajectory estimations during the twisting task.

Powered hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders (UEMSDs). This paper reports an ongoing study to quantify how operators respond to nutrunner reaction forces, with results from twelve male subjects. Three work configurations using pistol grip and angle tools were tested in the laboratory. Handle displacement due to torque reaction was recorded using a cable potentiometer. Grip force was measured on an instrumented handle attached to each tool. A full factorial experiment was designed considering working height, distance, tool, and fastener joint hardness. The results show that working height significantly affected grip force and handle displacement. The mean displacement was 22.75 mm when using pistol grip tools on a horizontal surface on a soft joint, and was 7.15 mm on the hard joint. This study provides information regarding the workstation design and tool selection that could minimize the torque reaction experienced by nutrunner operators.