Method of controlling a grinding process in a pocket grinder

A method of controlling a grinding process in a pocket grinder comprising the steps of:

• pressing a batch of wood in at least one pocket against a rotating grindstone by means of a pressure shoe displaceable in the pocket, density of the wood in the batch being other than constant;
• calculating, at predetermined intervals at measuring points of a grinding stroke of the pressure shoe, an amount of pulp produced, said calculating being defined by the relationship:
• M.sub.t =A.multidot.X.sub.t .multidot.D.sub.w
• wherein
• A =cross-sectional area of the pocket,
• X.sub.t =distance of movement of the pressure shoe during the time period t, and
• D.sub.w =average density of the batch in the pocket during the grinding;
• calculating a value of specific energy consumption corresponding to said amount of pulp produced;
• comparing the specific energy consumption to a target figure;
• controlling the grinding of the batch in response to a deviation of said specific energy consumption from said target figure, so that the specific energy consumption remains as constant as possible during an entire grinding stroke of the pressure shoe;
• determining a correction factor for the density of the wood in the batch as a function of position of said pressure shoe;
• and
• calculating a corrected amount of pulp produced by multiplying said amount of pulp produced by said correction factor, whereby the value of said specific energy is corrected to control at least one operating parameter of said pocket grinder.