Method for controlling a piston fed wood grinder

A method for controlling a piston fed wood grinder, wherein a plurality of wood charges are fed by pressure media driven pistons against a motor driven grinding stone comprising the steps of driving each of said pistons toward said grinding stone, determining a value for the actual speed of movement between selected positions of each of the pistons by direct digital measurement and comparing the value of the actual speed with a predetermined value indicative of a desired speed, simultaneously comparing the consumption of power by the motor driving grinding stone with a predetermined limit value indicative of the overload of the motor driving said grinding stone, controlling the pressure media driving said piston as a function of the difference between the value of the actual speed of the piston and said desired speed value to maintain said piston at a substantially constant speed so long as the power consumption is below the predetermined overload limit and upon said power consumption reaching the overload limit automatically shifting the control of the pressure media driving said piston as a function of the power consumption to vary the speed of said piston until the power consumption falls below the predetermined overload limit and thereafter returning control of said pressure media driving said piston as a function of the difference between the value of the actual speed of said piston and the predetermined value of the desired speed.