(Georgia Institute of Technology, 2011-03)
Heather C. Humphreys; Book, Wayne J.; Huggins, James D.
In some operator-controlled machines, motion of the controlled machine excites motion of the human operator, which is fed back into the control device, causing unwanted input and sometimes instability; this phenomenon is termed biodynamic feedthrough. In operation of backhoes and excavators, biodynamic feedthrough causes control performance degradation. This work utilizes a previously developed advanced backhoe user interface which uses coordinated position control with haptic feedback, using a SensAble Omni six degree-of-freedom haptic display device. Backhoe user interface designers and our own experiments indicate that biodynamic feedthrough produces undesirable oscillations in output with conventionally controlled backhoes and excavators, and it is even more of a problem with this advanced user interface. Results indicate that the coordinated control provides more intuitive operation, and the haptic feedback relays meaningful information back to the user. But the biodynamic feedthrough problem must be overcome in order for this improved interface to be applicable. For the purposes of reducing model complexity, the system is limited to a single degree of freedom, using fore-aft motion only. This paper investigates what types of controller-based methods of compensation for biodynamic feedthrough are most effective in backhoe operation, and how they can be implemented and tested with human operators.
(Georgia Institute of Technology, 2002-11)
George, Lynnane E.; Book, Wayne J.
A rigid (micro) robot mounted serially to the tip of a long, flexible (macro) manipulator is often used to increase reach capability, but flexibility in the macromanipulator can interfere with positioning accuracy. A rigid manipulator attached to a flexible but un actuated base was used to study a scheme to achieve positioning of the micromanipulator combined with enhanced vibration damping of the base. Ineltial interaction forces and torques acting between the robot and its base were modeled and studied to determine how to use them to damp the vibration. One issue is that there are locations in the workspace where the rigid robot loses its ability to create interactions in one or more degrees of freedom. These "ineltial singularities" are functions of the rigid robot's joint variables. A performance index was developed to predict the ability of the rigid robot to damp vibrations and will help ensure the robot is operating in joint space configurations favorable for inertial damping. It is shown that when the performance index is used along with the appropriate choice of feedback gains, the inertia effects, or those directly due to accelerating the robot's links, have the greatest influence on the interactions. By commanding the robot link's accelerations propOitional to the base velocity, vibration energy will be removed from the system. This signal is then added to the rigid robot's position control signal. Simulations of a three-degree of freedom anthropomorphic rigid robot mounted on a flexible base were developed and show the effectiveness of the control scheme. In addition, results from two degree of freedom vibration damping are included.