An autofocusing measurement system with a piezoelectric translator

An autofocusing system that consists of a compact disc (CD) optical head and a piezoelectric translator (PZT) is developed for measuring the displacement or profile of a tested surface. The displacement or the profile of the tested surface can be obtained with varying accuracy by measuring the curve of the driving voltage to the expansion distance of the PZT or by using a secondary sensing device of displacement. The resolution of the system can reach 10 nm and the accuracy is 0.05 μm. Some design considerations, such as the control algorithm of the focus servo and error analysis of the system, are addressed in this paper.