An Optical Measurement Device for Evaluating Dust Deposition on Flexible Filter Surfaces

In this paper an optical system for measuring the amount of dust deposition on commercial bag filters is presented. Dust laden gas is blown onto the filter, the dust remains on the surface and forms a compact layer called filter cake. For academic simulations as well as practical filter design it is desirable to know the thickness of this cake over the filter surface during operation, when the cake is building up and after automatic cleaning of the bag. It is shown that the principle of calibrated shape from stereo with pattern projection gives a robust 3D reconstruction of the filter surface, even under industrial conditions. Rigid registration of surface patches using landmark points, combined with an Iterative Closest Point Algorithm as a refinement procedure gives a continuous 3Dmodel of the entire visible filter surface. Cake thickness is calculated by taking the height difference of the two surface models, acquired before and after dust deposition. The challenging problem is to take care of the nonrigid deformation of the filter cloth. A global deformation model is presented using Thin Plate Spline Interpolation based on landmark points on the filter surface.