Analysis of Joint and Hand Impedance During Teleoperation and Free-Hand Task Execution

Teleoperated robotic surgery allows filtering and scaling the hand motion to achieve high precision during the surgical interventions. Teleoperation represents a very complex sensory-motor task, mainly due to the kinematic and kinetic redundancies that characterize the human motor control. It requires an intensive training phase to acquire sufficient familiarity with the master-slave architecture. We estimated the hand stiffness modulation during the execution of a simulated suturing task in teleoperation, with two different master devices, and in free hand. Kinematic data of eight right-handed users were acquired, using electromagnetic and optical tracking systems, and analyzed using a musculoskeletal model. Through inverse dynamics, muscular activation was computed and used to obtain the joint torque and stiffness, leading to end-point stiffness estimation. The maximal stiffness value and its angular displacement with respect to the trajectory tangent were computed. The results show that there is a difference in how the main stiffness axis was modulated by using the two master devices with respect to free hand, with higher values and variability for the serial link manipulator. Moreover, a directional modulation of the hand stiffness through the trajectory was found, showing that the users were aligning the direction of the main stiffness axis perpendicularly to the trajectory.