Humans can localize lumps in soft tissue using the distributed tactile feedback and processing afforded by the fingers and brain. This task becomes extremely difficult when the fingers are not in direct contact with the tissue, such as in laparoscopic or robot-assisted procedures. Tactile sensors have been proposed to characterize and detect lumps in robot-assisted palpation. In this work, we compare the performance of a capacitive tactile sensor with that of the human finger. We evaluate the response of the sensor as it pertains to robot-assisted palpation and compare the sensor performance to that of human subjects performing an equivalent task on the same set of artificial tissue models. Furthermore, we investigate the effects of various tissue parameters (lump size, lump depth, and surrounding tissue stiffness) on the performance of both the human finger and the tactile sensor. Using signal detection theory for determining tactile sensor lump detection thresholds, the tactile sensor outperforms the human finger in a palpation task.

Direct haptic feedback and graphical force feedback have both been hypothesized to improve the performance of robot-assisted surgery. In this study we evaluate the benefits of haptic and graphical force feedback on surgeon performance and tissue exploration behavior during a teleoperated palpation task of artificial tissues. Seven surgeon subjects (four experienced in robot-assisted surgery) used a 7-degree-offreedom teleoperated surgical robot to identify a comparatively rigid rigid target object (representing a calcified artery) in phantom heart models using the following feedback conditions: (1) direct haptic and graphical feedback, (2) direct haptic only, (3) graphical feedback only, and (4) no feedback. To avoid the problems of force sensing in a minimally invasive surgical environment, we use a position-exchange controller with dynamics compensation for direct haptic feedback and a force estimator displayed via tool-tip tracking bar graph for graphical force feedback. Although the transparency of the system is limited with this approach, results show that direct haptic force feedback minimizes applied forces to the tissue, while coupled haptic and graphical force feedback minimizes subject task error. For experienced surgeons, haptic force feedback substantially reduced task error independent of graphical feedback.

In this paper, we develop and test a 6-degree-of-freedom surgical teleoperator that has four possible modes of operation: (1) direct force feedback, (2) graphical force feedback, (3) direct and graphical force feedback together, and (4) no force feedback. In all cases, visual feedback of the environment is provided via a head-mounted display. A position-position controller with local dynamic compensators provides the direct force feedback. The graphical force feedback is overlaid on the environment image, and displays a bar whose height and color is related to the environment force estimated using the current applied to the actuators of the patient-side arm. We evaluate the performance of the teleoperator modes in assisting a user to find the location of stiff objects hidden inside a soft material, similar to a calcified artery hidden in heart tissue and a tumor in the prostate. Seven people used the teleoperator to perform palpation in these materials. Results showed that direct force feedback mode minimizes palpation task error for the heart model.

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