With two orthogonal spatial filters all directions of two-dimensional motion can be measured. A modification of the
aperture function of the lattice allows an innovative measuring real time system for particle sizing and position
Every plane motion can be described with two velocity components. If two planar local filters are formed, then the
directional characteristic can be changed, so that for all directions of object motion an evaluable output signal is
generated. It is preferable to use orthogonal speed components because these produce minimal resultant error in the
velocity vector. In our approach two-dimensional structured photo detector arrays are used as a spatial filter [1-3].
A modification of the aperture function of the lattice allows the realization of an innovative measuring system for
particle sizing. The output signal is comprised of equidistant signal effacements, whose distances are dependent on the
particle size [4-6].
What makes this method very interesting, particularly with regard to real time systems, is the possibility of pixel
linking inside the sensor.
Conventional humanitarian mine detectors based on magnetic and magneto-inductive procedures are able to detect very small metal pieces in the ground. These evaluation methods however result in a high rate of false alarm; the presence of metallic parts detected which are not to be assigned as mines. If you want to classify the metal piece in the ground (e.g. the shape) you have to measure the electro-magnetic field at different positions. Therefore the actual position must be known for each measuring point. By use of the optical spatial filtering method we are able to measure the velocity vector. With the sample time we get the required x-y-position. In our approach we use structured photo detectors as a filter grating and as a detector too. This technique for position determination possesses some interesting advantages such as the use of incoherent light and simplicity of the optical and mechanical set up. New two-dimensional CMOS sensor arrays with direct pixel access allow a fast read out of sub frames. A disadvantage is the slow signal to noise ratio and the price of industrial CMOS cameras that facilitate frame grabbing. The use of simple CCD web cameras limit the maximum measurable velocity, having a read out time of 60 Hz (max), but the price decrease extreme.
Early tests using structured photo detectors and spatial filtering methods for position determination show very good results for velocities from 0 to 250 mm/s. A local resolution of 1 mm can be achieved. Tests have also been performed using an ordinary optical mouse as the position determination system.
A modified opto-electronic method for the determination of velocity, direction of motion and particle size is presented. This method is based on the use of two-dimensional structured photo detector arrays like CMOS-sensors. The principle of measurement utilised is the optical spatial filtering method, which is in widespread use in industrial speed indicators. This technique possesses some interesting advantages such as the use of incoherent light and simplicity of the optical and mechanical set up. In comparison to CCD sensors, new two-dimensional CMOS sensor arrays with direct pixel access allow a faster read out of sub frames. Another advantage of these sensor types is the possibility to realise several spatial filters simultaneously. New more effective measuring procedures can be realised. For instance with two velocity components you are able to describe every plane motion of an object. Thus the determination of direction is made possible. Furthermore, a novel method to determine the particle size by application of a spatial filter can be realised. The possibility of linking pixels inside the sensor (hardware design) makes these spatial filtering methods very interesting particularly with regard to real time systems.