Method and arrangement of controlling of percussive drilling based on the stress level determined from the measured feed rate

An arrangement in connection with a rock drill apparatus, which rock drill apparatus comprises a rock drill machine provided with a percussion device, a feed device and a tool, the tool end comprising a bit for breaking rock, and the tool being arranged to transmit impact energy generated by the percussion device as a compression stress wave to the bit and the feed device being arranged to thrust the tool and the bit against the rock to be drilled, whereby on drilling at least part of the compression stress wave generated by the percussion device to the tool reflects from the rock to be drilled back to the tool as tensile stress, the arrangement comprising

• a measuring means for determining drilling penetration rate and
• a control unit that is arranged to determine the level of tensile stress reflecting from the rock to be drilled to the tool on the basis of interdependence of the penetration rate of the drilling and the level of tensile stress and in which arrangement the impact energy of the percussion device is arranged to be adjusted on the basis of the level of tensile stress reflecting from the rock to be drilled to the tool.