Many electronic devices support the use of haptic or other tactile feedback. For example, many portable electronic devices include touch-sensitive screens (referred to as “touch screens”), and touch screens supporting haptic feedback allow users to feel vibrations when the users contact the touch screens. As a particular example, haptic feedback could allow a user to feel vibrations when the user invokes a particular function of an electronic device.
Haptic or other tactile feedback is often created in an electronic device using a simple, open-loop approach. For instance, a voltage can be applied to a motor that rotates an eccentric mass at an appropriate frequency, which makes the entire device vibrate. In more advanced systems, a motor's drive signal can be turned on and off with millisecond granularity, but this is still done in an open-loop fashion. A motor often has significant inductance and significant inertia, preventing an instantaneous response and creating high latency for the tactile feedback (often more than 50 ms), which is easily perceptible.