Working machine and method for working the ground

A working machine, comprising:

• a mast,
• a hydraulic cylinder,
• a rotary head that is vertically movable by the hydraulic cylinder,
• a telescopic Kelly rod having at least two Kelly bars configured to be guided in a displaceable manner by the rotary head, the at least two Kelly bars comprising:
• an outer Kelly bar designed for being supported on the rotary head, and
• an inner Kelly bar which comprises a rope suspension for a rope, the inner Kelly bar being vertically movable by means of a main rope winch,
• wherein, each of the at least two Kelly bars include, on their external and/or internal surfaces, axially running drive keys and locking recesses on the drive keys or latch elements configured to move into the locking recesses for axially locking the at least two Kelly bars or moved out of the locking recesses to unlock the at least two Kelly bars in order to transmit torque from the rotary head to a ground working tool, and
• a drive system, by which at least the hydraulic cylinder, the rotary head or the main rope winch are driven,
• wherein:
• a controller is provided which is configured for the locking and/or unlocking of the Kelly bars,
• the controller is configured such that:
• a first torque can be applied to one of the at least inner or outer Kelly bars, wherein a latch element is applied with pressure to the axially running drive key of another of the inner and outer Kelly bars, and
• the at least two Kelly bars are moved axially relative to each other until the latch element rotates in the circumferential direction into a locking recess,
• the working machine further comprising a detector arranged in the drive system or in the hydraulic cylinder configured to detect a force, torque or pressure change in the drive system indicating rotation of the Kelly bars, and
• wherein the controller is configured to determine the locking of the Kelly bars depending on the detected force, torque or pressure change in the drive system, and
• wherein the force, torque or pressure change is indicated by a temporary load drop measured by the detector.