The present invention relates to synchronized vibration devices that can provide haptic feedback to a user. A wide variety of actuator types may be employed to provide synchronized vibration, including linear actuators, rotary actuators, rotating eccentric mass actuators, and rocking mass actuators....http://www.google.co.uk/patents/US20060290662?utm_source=gb-gplus-sharePatent US20060290662 - Synchronized vibration device for haptic feedback
