Human interface design method based on the estimation of muscle effort by a musculoskeletal model

Human's skeletal muscles have sensory systems. Human-machine interfaces that consider muscle effort should improve the usability and manipulability of daily products. This paper presents an interface design method that considers muscle effort and illustrates possible applications. A three-dimensional musculoskeletal model is developed based on the upper extremity model with 29 muscles and 16 joints. Muscle activity is estimated by using the OpenSim. We define the muscle effort as the mean of each muscle activity, and the muscle effort is used to determine the physical design or the physical response of the human interface. We applied the proposed physical design modification method to the design of the key height of a keyboard. The key height is changed proportional to the normalized muscle effort. The estimated muscle effort suggests that users can type every keys of the modified keyboard with a similar muscle effort. We also explore to improve the manipulation feeling of the key touching of mobile devices by changing the feedback response according to the estimated muscle effort when users touch keys. The experimental results indicate that the manipulation feeling can be improved by changing the feedback response according to the muscle effort.