Page 520 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

FIGURE 19.15
RigMaster WCROV grabber.
19.2.2 Dexterous arms
(Courtesy Schilling Robotics.)
19.2 Manipulator types 517
The dexterity of the arm, that is, more DoF, essentially increases its capability from that of a grab- ber to the more sophisticated status, that of a “manipulator.” Dexterous manipulators generally have at least six DoF plus the end effector, which could be a tool or gripper. Today’s manipulators, such as Schilling’s 7-function, position-controlled Titan 4 manipulator (Figure 19.16) are efficiently designed. Their hydraulic and electrical lines are located within the arm, which protects them from getting damaged when working on or in an object or structure. The wrist and hand area is also a clean design, which not only prevents snagging on an object but also does not block the view of the operator. It does no good for an operator to have the arm or tool block his vision so that he can- not see the target object. This brings up another consideration, that of the viewing system—always ensure that, whatever the tasks for which the manipulator is designed, adequate viewing options exist for the operator. Multiple perspectives are always an asset.
Most work tasks are on the seafloor or on a vertical plane in front of the ROV. Therefore, the industry standard manipulator design is the backhoe or elbow-up configuration. This design is far from anthropomorphic, or human-like, while it maximizes the work volume and minimizes the stor- age requirements on the ROV (Figure 19.17).
The more dexterous manipulators usually have a wrist rotate function that allows continuous gripper rotation (with use of the “gerotor” actuator). This feature is valuable for tasks like valve actuation, shackle makeup, or screw clamping. Continuous rotation allows the operator to make multiple turns of the gripper or tool without letting go of, and re-grasping, the object.
With increased dexterity comes the ability to use more sophisticated control functions. Such functions allow the operator to perform complex motions of the manipulator/tool, such as the abil- ity to move in a straight line or to move along paths that require all arm functions to be actuated