Sensor/actuator Asymmetries in Telemanipulators
ProQuest, 2009 - 199 pages
The use of robotic telemanipulators is increasing in many fields, but force reflection in telemanipulators is challenging and costly to implement; often prohibitively so for commercial applications. By feeding back forces to the operator in only a subset of degrees of freedom of the manipulator, the number of sensors and actuators used in the telemanipulator can be reduced. While this type of partial force feedback reduces the cost and complexity of the telemanipulator hardware, an imbalance, or asymmetry, in the number of sensors and actuators is created. This dissertation presents a method for modeling and classifying the different types of sensor/actuator asymmetries in telemanipulators. Asymmetries can result from the design of either the master or slave manipulator. Both asymmetry classes are accounted for in the model presented, while preserving the nuances of each. The impact of sensor/actuator asymmetries on several common telemanipulator control architectures is described. The model is used to show that conditions commonly used to ensure telemanipulator stability, such as passivity and unconditional stability, are not valid for telemanipulators with sensor/actuator asymmetries. Instabilities are observed in simple linear, time-invariant telemanipulators, even when discretization of the hardware and time-delay in the communication system are ignored. The effect on human performance of coupling in telemanipulators with sensor/actuator asymmetries is shown through two sets of experiments. Results show that performance with partial force feedback can approximate full force feedback performance, but only if the environment couples the dynamics of the degree of freedom missing feedback to the dynamics of a sensed degree of freedom. When forces are decoupled, partial force feedback significantly reduces the ability of users to control applied force in the degree of freedom missing feedback. A third experiment shows that performance during simple tasks like drawing and tracing with a 6-degree-of-freedom manipulator is not significantly affected by the reduction of feedback from 6 degrees of freedom (force and torque) to 3 degrees of freedom (force only). Collectively, this work demonstrates the potential of sensor/actuator asymmetries in telemanipulators based on the ability of humans to "fill-in" missing force information. However, instabilities in these systems exist and are problematic.
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2n-port actuators applied force asymmetry matrix Axial FF condition communication block control architecture coupled degrees of freedom DOFs dynamics eigenvalues Force & Torque force and torque force applied force displayed force feedback conditions force histogram force information force sensing force sensors frequency Full FF full force feedback gripper haptic device human and environment hybrid matrix impedance infimum instability interaction Intuitive Surgical Jacobian master and slave master asymmetry master device master manipulator maximum singular value mixed-mode controller motor saturation n-DOF Nikhil Chopra norm operator parameters partial force feedback passive performance position position-position control provide force feedback robot robustly stable robustness criterion satisfy the robustness scattering matrix Section sense forces sensor/actuator asymmetries significantly slave asymmetry slave device slave manipulator strain gauges tele telema telemanip telemanipulators with asymmetries telemanipulators with partial telemanipulators with sensor/actuator teleoperator torque feedback translational force velocity Vinci Surgical System virtual environment virtual pen virtual wall workspace