Velocity measurement using phase orthogonal spatial filters

An optical pattern on an object's surface is converted into a component of a specific spatial frequency through a spatial filter, and the movement or the velocity of the object can be estimated from the spatial frequency. An error of the velocity measurement based on the conventional spatial filter method is large in case of low-speed measurement. The authors develop a velocity measurement system based on a new spatial filter method that can compensate the error. This paper presents the system configuration and the compensating method.