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Human motor control in robot-assisted tasks

When grasping and manipulating hand-held objects, people naturally modulate their grip force with the load force applied by the object, ensuring that the object does not slip from their hand. When performing minimally invasive robot-assisted surgery with a teleoperation system, surgeons use a master robot to control the patient-side device, which directly interacts with the tissue. However, surgeons cannot feel any load forces (e.g., elasticity while retracting tissue), due to the lack of haptic feedback. While using excessive amounts of grip force may prevent tissue from slipping from the surgeon's grasp, it can also potentially damage the tissue or cause the surgeon's hand to become fatigued. This project is focused on studying grip force modulation during indirect object manipulation via robotic devices, both with and without haptic feedback.

Grip force control during virtual object interaction: Effect of force feedback, accuracy demands, and training

This study examines the effects of force feedback, accuracy demands, and training on grip force control during object interaction in a virtual environment. The task required subjects to use a haptic device to grasp and move a virtual object while tracking a target. When feedback of the spring force in the virtual environment was not provided, subjects failed to couple grip and load force, a capability fundamental to direct object interaction. Subjects also exerted larger grip force without force feedback and when accuracy demands of the tracking task were high. In addition, the presence or absence of force feedback during training affected subsequent performance, even when the feedback condition was switched. Subjects’ grip force control remained reminiscent of their employed grip during the initial training. These results motivate the use of force feedback during telemanipulation and highlight the effect of force feedback during training.


T. L. Gibo, A. J. Bastian, and A. M. Okamura.
Grip force control during virtual object interaction: effect of force feedback, accuracy demands, and training
IEEE Transactions on Haptics, 7(1):37-47, 2013.

Case study on a custom version of the da Vinci Surgical System

This preliminary study was performed in order to extend the above results to an actual surgical teleoperation system. We used a custom research version of the da Vinci Surgical System to study the control of grip force of an expert surgeon during teleoperated manipulation. The surgeon used the da Vinci to grasp and stretch a rubber band with and without feedback of the patient-side load forces. Coupling between the grip and load force was greater with force feedback, akin to our previous results, although a higher grip force was used with load force feedback. This preliminary study motivates future experiments with the addition of different levels of user experience and the incorporation of grip force feedback.

T. L. Gibo, D. R. Deo, Z. F. Quek, and A. M. Okamura.
Effect of load force feedback on grip force control: A preliminary study
Haptics Symposium, 2014