Speed-accuracy tradeoff of controlling absolute magnitude of fingertip force

Controlling absolute magnitudes of fingertip force is an important skill in many haptic interactions such as surgical operations and mechanical assemblies. A fundamental question in the force control is how quickly human can output a target force with expected accuracy. In this paper, human´s capability to control absolute magnitudes of fingertip force under audio or visual feedback was observed through experiments. Twelve participants applied a target force by pressing a force sensor with their fingers and maintained the force within a specified tolerance for a specific period of time (500ms). The magnitudes of target force and tolerance were manipulated systematically to yield varied levels of task difficulty. The experimental data showed that the applied fingertip force obeyed Fitts´ law under both visual and auditory feedback modes when the index of difficulty (ID) was smaller than a threshold. The results may be used as guidelines for the applications that rely on accurate and quick changing force control over a target region such as multiple tapping tasks.