Patent ID: 7938272

Claim:
A method for controlling a screening machine comprising a vibrating screen having at least one screen surface, said vibrating screen conveying material from a first end towards a second end, feeding means comprising a conveyor that feeds material to be screened towards the screen surface and at a fixed location in the first end onto the screen surface where the material is separated into a first fraction remaining on the screen surface and into a second fraction passed through the screen surface while the material is moving along the screen surface towards the second end, the method comprising: determining the amount of material on the screen surface by automatic measurement; and controlling the amount of material on the screen surface by adjusting the conveying speed of the conveyor on the basis of the measurement by automatic control in such a manner that the conveying speed, which is above zero, is changed to a different conveying speed, which is above zero, in both of the following ways: a) providing upper and lower preset values (val max , val min ) for the measurement value (val m ) of a variable dependent on the amount of material on the screen surface, lowering the conveying speed of the conveyor without stopping the conveyor when the measurement value (val m ) passes one of the preset values, and increasing the conveying speed of the conveyor when the measurement value (val m ) passes the other preset value, and b) providing a preset value ((Δval m /Δt) max ) for a speed of change of the measurement value (val m ) of the variable dependent on the amount of material on the screen surface, and changing the conveying speed of the conveyor without stopping the conveyor when the speed of change of the measurement value (val m ) of the variable exceeds the preset value ((Δval m /Δt) max ).