With the Gemstar- and BeltCompact belt sorter models the flow of loose mineral material is transported to the detection area after classification and separation. The individual material components are separated optimally thanks to the constant high speed of the conveyor belt and leave the conveyor belt in a flat parabola trajectory in the direction of the detection area. In some applications the spectral properties of the bulk materials being investigated can also already be recognised on the belt.

By sensibly arranging and selecting the sources of illumination each individual part of the arriving particles can be registered and classified with the assistance of one or more high performance line scan cameras in the various spectral ranges in reflected light and/or transmitted light. This takes place with the assistance of special image processing software in a multi-processor data system. The position in the trajectory and the size of the particles control the corresponding high performance pneumatic valves needed to throw the material, which is to be sorted, from the trajectory or change its trajectory in real time in a precise position and accurately determined quantity of air.

The separation of the material takes place on the basis of differentiation criteria, which are based both on the spectral properties of the material as well as on its non-optical features. The important thing is that the material which is wanted is differentiated from the waste material. It is assumed that the spectral properties of the materials involved are already known. By changing the lighting and by using multi-sensor recognition systems it is also possible to successfully sort bulk materials which cannot be differentiated outwardly or only with difficulty.

Areas of use for the Gemstar- and BeltCompact sorters with single or dual recognition are for example the sorting of primary (kimberlite) and secondary (alluvial) diamonds and other precious stones with grading from 1 mm to 10 mm with throughputs of 2 t / h to 10 t / h.