The active interferometer has been approved as an effective architecture to increase the precision of surface profile
measurement by detecting the environmental vibration and then stabilized by a piezoelectric transducer. The
performance of such system can improve the accuracy within nano-meters. Most of the active interferometers have being
implemented on the PC based platform because it is easy to be setup and modulized, However, the latency of image
grabbing processing, mathematic algorithm and I/O trigger delay is around 10~15ms. Moreover, the latency is varying if
different PCs are used.
In this study, an embedded real-time controller based on the ADI Blackfin BF561 DSP microprocessor was developed to
improve the performance of a vibration-resistance system using white-light interferometer. The purpose of this
embedded control system is to detect the vibration and compensate it for White Light Interferometer when processing
stepping photograph grabbing for surface profile measurement.
A customized embedded control system with a 600 MHz high performance microprocessor, Camera Link interface,
DAC circuit and UART command port has been developed. A complete command set has also been defined to
communicate with PC based interferometer user interface for close-loop control. The latency has been reduced from tens
of millimeters to 250 μs as tested for all the procedures from CCD trigger, image processing, to PZT control signal
output. It has been proved to be useful of fixing the latency between phase detecting and compensation output. With this
advantage, the response of the interferometer can accelerated so that the vibration-resistance is improved and the overall
accuracy can be in the range of a few nano-meters.