Patent attributes
An autofocus system (222C) for measuring the position of a work piece (200) along an axis includes a slit light source assembly (236), a slit detector assembly (238), and a control system (224). The slit light source assembly (236) directs a first slit of light (342A) at a first slit area (344A) of the work piece (200). The slit detector assembly (238) detects light reflected off of the first slit area (344A) and generates a first slit signal relating to the amount of light reflected off of the first slit area (344A) at the slit detector assembly (238). The control system (224) uses the first slit signal from the slit detector assembly (238), and first reflectance information of the first slit area (344A) to determine the position of the work piece (200) along the axis. With this design, the autofocus system (222C) can compensate for the changes in reflectivity of the work piece (200). As a result thereof, measurements taken with the autofocus system (222C) are more accurate and the work piece (200) can be positioned with improved accuracy.
