Touchscreen device layout based on thumb comfort and precision

Thumb workspace analysis on touch-sensitive screen is used to assist designers in laying control buttons out on screen devices which are thought to be one-handed operated, e.g. mobile phones. Using inertial motion tracking system, kinematic variables as position and orientation for thumb link are obtained. Based on Euler angles, the motion angle for each thumb joint relative to its comfort position is calculated for a determined number of touch points on the screen. Additionally, touch points are associated to distal phalange link inclination which correspond to a tip thumb contact area that affect the touch precision. The collected data is used to calculate discomfort index and the contact area over the total thumb workspace and map them on the screen. Through calculations it is possible to conclude that some movements are performed easily (comforting) and/or precisely than others, e.g. finger vertical sliding is easier than horizontal one. Finally, in order to improve user comfort and precision, on the screen area, where control buttons should be shown. This analysis is applied, as a practical example, on a personal magazine smartphone application, in order to suggest a suitable design for the control buttons.