Method and system for controlling tool

A control unit for controlling a tree stem processing tool (30) pivotably mounted to an articulated boom (20) in such a way that orientation of the tool is changed when the tool is controllably rotated about a rotation axis (N) that is oriented substantially vertically， the articulated boom being rotatably connected to a mobile work machine (10)， wherein the control unit (50) is adapted to automatically apply a control mode in the control unit in which control mode a power-driven operation is controlled according to a predetermined dependency in such a way that one or more operating parameters influencing the power-driven operation vary as a function of a prevailing separation or a prevailing distance determined in relation relating to a predetermined hazard direction (S) or predetermined hazard trajectory (V) associated with the tool.