ABSTRACT
A confocal laser displacement sensor using a micro-machined varifocal mirror is reported. The focal length modulation is a key function of the confocal sensor. The mechanism of the focal length modulation determines the measurement speed and range. Here, we propose application of the micro-machined varifocal mirror for the modulation. The varifocal mirror can realize faster modulation, small size, and low energy consumption for the confocal displacement sensor. The electrostatically actuated varifocal mirror made by single crystalline silicon is used. The working distance of the sensor is designed to be 31 mm. The actuating range at 7 kHz is 310 µm. The linearity error in the actuating range is from -1.1% to 1.2%.
ABSTRACT
This paper reports a microelectromechanical systems (MEMS) resonant varifocal mirror integrated with piezoresistive focus sensor. The varifocal mirror is driven electrostatically at a resonant frequency of a mirror plate to obtain the wide scanning range of a focal length. A piezoresistor is used to monitor the focal length of the varifocal mirror. The device is made of a silicon-on-insulator (SOI) wafer and a glass wafer. A mirror plate and a counter electrode are fabricated by a top silicon layer of the SOI wafer and on the glass wafer, respectively. The piezoresistor is fabricated by ion implantation on a supporting beam of the mirror plate. The stress variation of the beam, which is detected by the piezoresistor, correspond the focal length of the varifocal mirror. The focus length varies from -41 to 35 mm at the resonant frequency of 9.5 kHz. The focal length of the varifocal mirror is monitored by the piezoresistor in real time.
