It is known in some industrial, medical, and consumer applications to scan objects. For example, U.S. Pat. No. 5,321,501 to Swanson et al. entitled Method and Apparatus for Optical Imaging with Means for Controlling the Longitudinal Range of the Sample, describes an assembly that scans angularly and transversely as shown in FIGS. 4A and 4B therein. As discussed in Swanson, the mechanism (107) that provides the scanning motion can be a piezoelectric crystal, a stepper motor, an electromagnetic actuator, or an electrostatic actuator. Some of these scanning mechanism may have control problems. For example, the oscillatory response of a piezoelectric crystal may suffer from hysteresis. Stepper motors can be large and consume significant power. Electromagnetic actuators may not be easily made in small sizes.
Scanners may also be utilized in biomedical areas. Some applications in the biomedical area include corneal resurfacing, optical imaging, and hair and tattoo removal. It is known to use galvanometers and other resonant scanners to steer optical beams in these types of biomedical applications. While galvanometers may offer a range of scan speeds and scan angles, galvanometers may require large magnetic bases and mirrors having relatively large masses to achieve desirable performance characteristics.
It is also known to fabricate scanners on silicon wafers using polysilicon as a substrate. It is also known to use electrostatic forces (amplified using comb drives), magnetic fields, thermal bending of bimorph cantilevers, and piezoelectric actuation to move mirrors in such scanners. These scanners can produce optical scan angles of about 7 to 180 degrees at frequencies from 40 Hz to 34 kHz using voltages in a range from 20 volts to 171 volts.