Piezoelectric actuator for mobile auto focus camera applications

Recently, various multimedia devices such as MP3 player, camera and even TV are integrated into a mobile phone. Consumer demands image cameras in mobile phone to have similar quality and performance as those of dedicated digital cameras. For a good image quality, increasing of resolution requires optical auto focusing, where a small lens group needs to be moved in a limited volume. Due to the efforts for reducing the size of each component in mobile phone, many types of motors have been investigated to achieve AF or zooming functions. However, a motor should be able to provide high controllability and performance to perform auto-focus (AF) camera function. One of the important features that piezoelectric motors have is the ability to maintain moving element position when the motor is not electrically excited. For mobile device application where power consumption is critical, this feature is fitting very well for lens positioning application in phone cameras. In this paper, we have applied our own development of piezoelectric motor for auto focus phone cameras. During auto focusing, we have measured total motor operating time that is less than one percent of total auto focusing time. Average instantaneous power, which is about 65 mWatts, is consumed only when the motor operates, which make piezoelectric motors to be superior over electromagnetic counterparts in terms of energy efficiency.