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.

中文翻译：

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设备背面力反馈改善了移动设备的触摸屏交互

触摸屏交互存在遮挡问题，因为手指可以覆盖小目标，这使得与此类目标的交互具有挑战性。为了提高触摸屏交互的准确性，从而选择小的或隐藏的对象，我们为智能手机引入了设备后端力反馈系统。我们推出了一种新的解决方案，结合背面的力反馈来增强正面屏幕上的触摸输入。该接口包括位于智能手机背面的三个驱动引脚。所有三个引脚均由微伺服驱动，可驱动至 50 Hz 的频率和 5 mm 的最大振幅。在第一个心理物理学用户研究中，我们探索了系统的局限性。此后，我们通过性能研究证明所提出的界面可以提高触摸屏交互精度，与最先进的方法相比。特别是小目标的选择在力反馈方面表现得非常好。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，我们讨论了前后反馈设计问题，并通过几个原型概念展示了潜在的应用，以说明设备后部力反馈在哪些方面可能是有益的。