In drilling operations, a top drive is used to apply torque to rotate a drill string. The top drive includes a variety of robotic actuators to access and maneuver pipe. These robotic actuators include, for example, elevators, links, grabbers and mud valves. The top drive is attached to the top of the drill string and is suspended in the mast of the drilling platform. The lower portion of the top drive rotates around the axis of the drill string. The upper portion of the top drive is attached to a torque track and does not rotate.
During operation, hydraulic fluid that passes through a high pressure rotary seal located between the upper and lower portions of the top drive is used to control the hydraulic actuators in the lower portion. The rotary seal includes one hydraulic channel for each actuator or feedback signal and an additional common return hydraulic channel. Each channel added to the rotary seal results in an increase in the size and cost of the seal. Additional channels also cause an increase in the drag torque. Consequently, interlocks and feedback signals that could improve operator safety and drilling efficiency are often not implemented. Such feedback could ensure that each actuator has functioned properly before enabling subsequent actuators, and could report the position of each actuator to the control system of the drill operator.
Systems with an electrical control apparatus located below the rotary seal have not been used because the fixed wiring precludes continuous rotation. Electrical slip rings are not practical because the system operates in a harsh environment where components are exposed to shock and vibration. Moreover, because slip rings can spark during operation, they are unsuitable for use in the explosive atmospheres that sometime occur during drilling operations.
Thus, there remains a need for an actuator control system that can control the rotating robotics of a top drive using a simple rotary seal with minimal hydraulic channels, and can transfer control data and power without electrical connections.