IEEE Trans Haptics. 2019 Oct-Dec;12(4):483-496. doi: 10.1109/TOH.2019.2911519. Epub 2019 Apr 15.
Touchscreen interaction suffers from occlusion problems as fingers can cover small targets, which makes interacting with such targets challenging. To improve touchscreen interaction accuracy and consequently the selection of small or hidden objects, we introduce a back-of-device force feedback system for smartphones. We introduce a new solution that combines force feedback on the back to enhance touch input on the front screen. The interface includes three actuated pins at the back of a smartphone. All three pins are driven by microservos and can be actuated up to a frequency of 50 Hz and a maximum amplitude of 5 mm. In a first psychophysical user study, we explored the limits of the system. Thereafter, we demonstrate through a performance study that the proposed interface can enhance touchscreen interaction precision, compared to state-of-the-art methods. In particular, the selection of small targets performed remarkably well with force feedback. The study additionally shows that users subjectively felt significantly more accurate with force feedback. Based on the results, we discuss back-to-front feedback design issues and demonstrate potential applications through several prototypical concepts to illustrate where the back-of-device force feedback could be beneficial.
触屏交互存在遮挡问题，因为手指可能会遮挡小目标，从而使得与这些目标交互变得具有挑战性。为了提高触屏交互的准确性，并因此提高选择小目标或隐藏对象的能力，我们为智能手机引入了一种设备背面力反馈系统。我们引入了一种新的解决方案，将背面的力反馈与正面屏幕上的触摸输入相结合。该界面包括智能手机背面的三个驱动销，所有三个销都由微伺服驱动，可以以 50Hz 的频率和 5mm 的最大振幅驱动。在第一项心理学用户研究中，我们探索了该系统的极限。此后，我们通过一项性能研究表明，与最先进的方法相比，所提出的接口可以提高触屏交互的精度。特别是，使用力反馈可以显著提高小目标的选择精度。该研究还表明，用户主观上感觉力反馈更准确。基于这些结果，我们讨论了背向正向反馈的设计问题，并通过几个原型概念展示了潜在的应用，以说明设备背面力反馈可能带来的好处。
