Robotic system for servicing the heat exchanger tubes of a nuclear steam generator

An improved robotic arm system for servicing the tubesheet located within the channel head of a nuclear steam generator is provided. The system includes a robotic arm whose shoulder and elbow joints are rotatable only in the plane parallel to the tubesheet in order to eliminate the imposition of cantileverly-induced torques on the electric motors driving these joints, as well as to minimize the possibility of mechanical interference between the arm and the walls of the channel head. Each of the motorized joint assemblies of the arm includes resolvers connected not only to the output of the drive train that moves the joint, but also to the drive shaft of the electric motor that drives the drive train, wherein the feedback signal generated by the resolver connected to the drive shaft of the electric motor is the primary signal used to modulate the amount of electric power conducted to the motor of the joint. Such a configuration advantageously results in smoother robotic arm movement. Finally, the control circuit assembly of the robotic arm system includes a control processing unit (CPU) which is capable of simultaneously driving not only the joint assemblies of the robotic arm, but also any computer-operated mechanisms associated with a variety of end effectors which the arm is capable of delivering. The CPU, power supply and other components of the control circuit assembly are installable in the containment area surrounding the steam generator in order to eliminate the number of cable penetrations through the containment walls that are necessary to operate the system.