From Telerobotics Lab

Research: Telemanipulation for Micromanipulation and Microsurgery

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Retinal Microsurgery

Selected Publications

M. Nambi, P. S. Bernstein, and J. J. Abbott, "A Compact Retinal-surgery Telemanipulator that uses Disposable Instruments," Int. Conf. Medical Image Computing and Computer-Assisted Intervention, 2015.


Dr. Paul Bernstein

Intuitive Tele-operation of Micromanipulators with Piezoelectric Stick-slip Actuators

Micro/Nano-manipulation deals with handling of extremely small objects on the order of 10-3 to 10-9m. Development of scanning and transmission electron microscopes (SEMs/TEMs) has enabled researchers to image and manipulate objects as small as 1\,nm in size. However, due to difficulties in simultaneous imaging and manipulating, micro/nano-manipulation is still a laborious task requiring great patience.

The goal of our research is to enable tele-operated rate control of micro/nano-manipulators without relying on any feedback from the vision system, other than the human user looking at the microscope image. This involves obtaining empirical models for the micro/nano-manipulator joints so that reliable position estimates can be obtained in the absence of feedback and development of control methods to move the end-effector using position estimates obtained from the open-loop models. Through intelligent algorithm development and drift compensation techniques we can greatly improve the efficiency with which such piezoelectric stick-slip actuators are operated.

Functional description of a piezoelectric stick-slip actuator.

Piezoelectric stick-slip actuators have become the foundation of modern micro/nano-manipulation due to their simple structure, high positional accuracy, unlimited movable distance, and high stability as they are supported by guiding surfaces. These actuators consist of a piezoelectric element and a sliding mass that moves relative to the piezoelectric element. A saw-tooth voltage is applied to the piezoelectric element. As the voltage slowly increases from 1 to 2, the piezoelectric element stretches by a distance D, and due to stick-slip friction between the piezoelectric element and the sliding mass, the sliding mass also advances (stick phase). When the voltage is quickly reduced from 2 to 3, the piezoelectric element quickly shrinks, but the inertia of the sliding mass prohibits it from moving backward as quickly, resulting in a net forward displacement of the sliding mass of d < D (slip phase). Typically, these actuators have no sensor feedback, and hence, the individual joints of the manipulators are controlled open-loop, using one knob per joint. It is not always clear what combination of joint commands will lead to a desired end-effector movement from only a microscope image. In addition, manipulators are often mounted on moving stages and on different surfaces at varying angles. The user observing the end-effector of such a manipulator under a microscope has to perform the difficult task of mapping the image frame to his/her egocentric frame of reference. Use of multiple manipulators further complicates the situation. Thus, micro/nano-manipulation is currently unintuitive and time consuming.

This video shows a Kleindiek MM3A micromanipulator being controlled using one knob per joint (on the left) vs. using coordinated rate control of the end-effector using a joystick (on the right). Direct joint control is unintuitive and time consuming, but is very common with this type of micromanipulator. More detail can be found in the paper "Toward Intuitive Teleoperation of Micro/Nano-Manipulators with Piezoelectric Stick-Slip Actuators", which appeared at IROS 2011.

This video shows a Kleindiek MM3A micromanipulator being controlled using coordinated rate control with a simulated human user that simply attempts to move the end-effector toward the goal. The developed algorithm chooses the correct number of steps commands to send to each joint to accomplish the goal. Both videos use an open-loop model of joint step size. In the video on the left, the estimate of the end-effector position is updated, although it can be seen that error in the estimate grows with each step. In the video on the right, the estimate of the end-effector's position is never updated from the starting point. It can been seen in both videos that control of the end-effector is robust to these errors. More detail can be found in the paper "Toward Intuitive Teleoperation of Micro/Nano-Manipulators with Piezoelectric Stick-Slip Actuators", which appeared at IROS 2011.

Selected Publications

A. Damani, M. Nambi, and J. J. Abbott, "An Empirical Study of Static Loading on Piezoelectric Stick-Slip Actuators of Micromanipulators," Int. Symp. Experimental Robotics, 2012.

M. Nambi, A. Damani, and J. J. Abbott, "Toward Intuitive Teleoperation of Micro/Nano-Manipulators with Piezoelectric Stick-Slip Actuators," IEEE/RSJ Int. Conf. Intelligent Robots and Systems, pp. 445-450, 2011.

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Page last modified on September 29, 2015, at 10:56 AM