Figure

Claim 1

IN A DRILLING RIG INCLUDING A FRAME, AN UPPER PULLEY BLOCK SECURED TO SAID FRAME, A LOWER MOVABLE PULLEY BLOCK, UPPER AND LOWER PULLEYS ROTATABLY MOUNTED WITHIN SAID PULLEY BLOCKS, RESPECTIVELY, A DRILL STRING SUPPORTED FROM SAID LOWER BLOCK, A ROTATABLE CABLE DRUM, A CABLE WOUND ON SAID CABLE DRUM PASSING AROUND SAID PULLEYS OF SAID PULLEY BLOCKS AND SECURED AT ONE END TO SAID FRAME WHEREBY THE UNWINDING OF SAID CABLE DRUM WILL CAUSE SAID DRILL STRING TO DESCEND, AND A BRAKE MEANS NORMALLY BEARING AGAINST SAID CABLE DRUM SO AS TO PREVENT ROTATION OF THE SAME, THE IMPROVEMENT WHICH COMPRISES AN AUTOMATIC CONTROL SYSTEM INCLUDING A WEIGHT SENSING DEVICE CONTAINING HYDRAULIC FLUID THEREIN AND HAVING A SENSING ELEMENT BEARING AGAINST SAID CABLE, SAID SENSING ELEMENT BEING MOVABLE IN RESPONSE TO THE CHANGES IN TENSION IN SAID CABLE FOR PRODUCING IN SAID SENSING DEVICE A FLUID PRESSURE IN SAID HYDRAULIC FLUID PROPORTIONAL TO THE TENSION IN SAID CABLE, A FLUID PRESSURE RESPONSIVE ACTUATOR ATTACHED TO SAID BRAKE MEANS AND ADAPTED UPON ENERGIZATION TO RELEASE SAID BRAKE MEANS, A CONTROLLER CONNECTED BETWEEN SAID SENSING DEVICE AND SAID ACTUATOR FOR INCREASING THE FLUID PRESSURE IN SAID ACTUATOR FOR ENERGIZING SAID ACTUATOR IN RESPONSE TO AN INCREASE IN FLUID PRESSURE IN SAID SENSING DEVICE AND SO AS TO RELEASE SAID BRAKE WHEN THE TENSION IN SAID CABLE EXCEEDS A PREDETERMINED VALUE, A QUICK RELEASE VALVE CONNECTED BETWEEN SAID CONTROLLER AND SAID ACTUATOR FOR VENTING THE FLUID PRESSURE IN SAID ACTUATOR TO THE ATMOSPHERE SO AS TO DEENERGIZE SAID ACTUATOR IN RESPONSE TO A DECREASE IN OUTPUT PRESSURE FROM SAID CONTROLLER, A SAFETY VALVE CONNECTED TO SAID ACTUATOR, AND MEANS CONNECTED TO SAID SAFETY VALVE AND RESPONSIVE TO A DECREASE IN PRESSURE IN THE HYDRAULIC FLUID IN SAID SENSING DEVICE FOR OPENING SAID SAFETY VALVE TO VENT THE PRESSURE IN SAID ACTUATOR TO THE ATMOSPHERE TO DEENERGIZE SAID ACTUATOR.