Page 529 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

526 CHAPTER 19 Manipulators
(a)
(b)
FIGURE 19.24
(a) Kraft FFB (force feedback) manipulator and (b) controller.
physical envelopes the same as hydraulic manipulators, then they might be an option through not having to convert electric power to hydraulic power, which would make the system more efficient. But unfortunately, the packaging of electric motors and/or actuators does not match the packaging efficiency of hydraulic actuators. In addition, the larger work-class vehicles used in offshore com- mercial applications all have large hydraulic power units—some as much as 200 horsepower or more.
The choices become more complex when MSROVs are being used. As the vehicles grow in size, they soon morph into hydraulically operated systems. So when in that gray area between the small observation class and the larger work-class vehicles, the operator has a choice to make. If available electrically operated arms do not meet the operational requirements, and the vehicle is still all-electric, then there are a couple of choices. The first is to mount a hydraulic motor, valve package, and compensator system somewhere within the vehicle’s frame. The second is to attach a skid below the vehicle’s frame that can carry the necessary hardware (see Chapter 20). When using a skid, the manipulators could also be attached to the vehicle’s main structure.
Whenever configuring a vehicle with additional equipment, whether electric or hydraulic, the stability of the vehicle must be kept in mind. The deployment of a manipulator can have a signif- icant effect on a small vehicle’s static as well as dynamic stability. This can become even more severe if using a tool or picking up a heavy object. The vehicle, and its thruster system, must maintain a stable enough configuration to allow the vehicle to maneuver properly. It will not do the operator any good if the vehicle is tilted forward at a 45 angle when trying to maneuver, especially if trying to return to the surface. However, if the goal is to grab an object and bring it back to the surface, then the vehicle can essentially turn into a shackle (Figure 19.25) between the umbilical and manipulator/grabber, as long as the strength of the umbilical and its termination with the vehicle is sufficient. Such an option may not exist when using a tether management sys- tem (see Chapter 9). Examples of the various components commercially available for configuring an ROV are provided in later sections.
(Courtesy Kraft Telerobotics.)