Focus detection method is one of the primary non-contact measurement methods of surface topography. However, the
measuring range of traditional focus detection method is limited because the volume motor is adopted in the focus servo
system. The traditional method has inevitable non-linear error and other measurement error caused by the volume motor.
This paper presents a new non-contact profilometer based on an improved Foucault focus detection method. The
non-contact profilometer is a closed loop control system, which changes the traditional moving volume motor scanning
system into the moving platform scanning system. Without adopting volume motor, the non-contact profilometer has
large measuring range, high resolution and more measurement parameters. When the surface of workpiece is measured,
the undulation of microcosmic surface topography leads to the focusing error signal continuously. According to the
focusing error signal, the computer controls the piezoelectric actuator and the Z direction motor to drive the platform to
move vertically, which ensures that the focus is always on the surface of workpiece and the focusing error signal is zero.
The diffraction grating displacement sensor measures the vertical displacement of the workpiece, then the displacement
signals is processed by the characterization software as the results of the measurement. The non-contact profilometer can
measure roughness, waviness, shape error of different curved surfaces precisely.