Abstract
Many people, when interacting with personal data entry devices, e.g., remote control, mobile phone or PDA, use single hand to manipulate them for the convenience and mobility. However, it is possible that the poor-designed mobile device interfaces may cause not only discomfort but also repetitive strain injury (RSI) on thumb and fingers when continuously entering data for a long enough period of time. This study intends to redesign the user interface of mobile devices to ease the heavy workload on the thumb as well as to better fit our hand with the devices when grasping. Based on the motion characteristics of thumb and index finger and the one-handed operated interface requirements, a new design idea was emerged. The design principles were taken into consideration for the new interface design in order to increasing comfort and reducing muscle workload of the thumb. The method of this study is divided into two stages: new device innovation and evaluation. In the first stage, representative subjects were recruited for observing the texting behavior and collecting hand anthropometric data including the lengths of thumb, angles of neutral hand posture, and the handle shape of the finger-palm enclosure. Based on first study, a mockup of new mobile phone user interface was developed. In order to comparing the operational performance between the new interface and that of a redesigning general mobile phone, twelve subjects were recruited for the second stage experiment and evaluation will be carried out. The joint angle changes, operation time, muscle workload, and subjective feeling scale were measured. After experimental analysis, this study suggests: 1. Designing for the grasping region by curve contour and fillet and considering average anthropometric data for the mobile devices are suggesting. 2. Considering the anthropometric data of operating digit in distributing the location of keypad region could not only lower the joint angle changes of operating digit but enhance the accessibility when reaching each key. 3. The effort of adding index finger keys for reducing fatigue level is not seem to be obvious. Finally, the thesis suggests that consider the situation of using mobile device would be helpful in designing one-handed mobile device.