Manikantan Nambi

On the Ability of Humans to Apply Controlled Forces to Admittance-Type Devices

Human–robot collaborative systems have the potential to dramatically change many aspects of surgery, manufacturing, hazardous-material handling, and other dextrous tasks. We are particularly interested in precise manipulation tasks, which are typically performed under an admittance-control regime, where the controlled velocity of a non-backdrivable robot is proportional to the sensed user-applied force. During fast movements, there is a noticeable degradation in control precision and prior results have indicated that system velocity, and not system admittance, is the factor that is most correlated with force control precision. In this paper, we report evidence that system admittance is more important than velocity in determining the users ability to control applied force and that both factors are less important than the force level itself, and we provide an explanation as to why prior results might have indicated otherwise. We find the conditions under which human force control performance is best when operating under admittance control. We also report the conditions under which human force control on a moving admittance-type device is indistinguishable from isometric force control, which can be used to design better device controllers.

Toward intuitive teleoperation of micro/nano-manipulators with piezoelectric stick-slip actuators

Commercial micro/nano-manipulators, which utilize piezoelectric stick-slip actuators to achieve high precision over a large workspace, are currently controlled by a human operator at the joint level, leading to unintuitive and time-consuming teleoperation. Prior work has considered the use of computer-vision-feedback to close a control loop for improved performance, but computer-vision-feedback is not a viable option for many end users. In this paper, we discuss how open-loop models of the micro/nano-manipulator can be used to achieve desired end-effector movements, and we explain the process of obtaining open-loop models. We propose a rate-control teleoperation method that utilizes the obtained model, and we experimentally quantify the effectiveness of the method using a common commercial manipulator (the Kleindiek MM3A).

A Compact Retinal-Surgery Telemanipulator that Uses Disposable Instruments

We present a retinal-surgery telemanipulation system with submicron precision that is compact enough to be head-mounted and that uses a full range of existing disposable instruments. Two actuation mechanisms are described that enable the use of actuated instruments, and an instrument adapter enables quick-change of instruments. Experiments on a phantom eye show that telemanipulated surgery results in reduction of maximum downward force on the retina as compared to manual surgery for experienced users.

A Compact Telemanipulated Retinal-Surgery System that Uses Commercially Available Instruments with a Quick-Change Adapter

We present a telemanipulation system for retinal surgery that uses a full range of unmodified commercially available instruments. The system is compact and light enough that it could reasonably be made head-mounted to passively compensate for head movements. Two mechanisms are presented that enable the system to use commercial actuated instruments, and an instrument adapter enables quick-change of instruments during surgery. A custom stylus for a haptic interface enables intuitive and ergonomic telemanipulation of actuated instruments. Experimental results with a force-sensitive phantom eye show that telemanipulated surgery results in reduced forces on the retina compared to manual surgery, and training with the system results in improved performance.

Human Velocity Control of Admittance-Type Robotic Devices With Scaled Visual Feedback of Device Motion

An admittance-type robotic manipulator is a nonbackdrivable device whose motion is controlled to move in response to a user-applied force, typically with velocity proportional to force. This study characterizes the ability of ten human subjects to accurately and precisely control the velocity of such a device, using force applied by the index finger, as the user is provided visual feedback of device motion and a target velocity on a display. The admittance, the velocity, and the visualization scale factor are varied in a full factorial design, with parameter levels representative of microsurgery/micromanipulation tasks. The results indicate that: visual scaling has no effect, for the levels tested; low velocity at high admittance results in reduced precision and accuracy; high velocity at low admittance results in reduced accuracy; and an admittance-dependent velocity exists at which accuracy is maximized. The results suggest that gain scheduling will result in improved performance.

An Empirical Study of Static Loading on Piezoelectric Stick-Slip Actuators of Micromanipulators

Piezoelectric stick-slip actuators have become the foundation of modern micromanipulation. Due to difficulty in closed-loop control with manipulators that use piezoelectric stick-slip actuators, methods for open-loop control with a human in the loop have been developed. The utility of such methods depends directly on the accuracy of the open-loop models of the manipulator. Prior research has shown that modeling of piezoelectric actuators is not a trivial task as they are known to suffer from nonlinearities that degrade their performance. In this paper, we study the effect of static (non-inertial) loads on a prismatic and a rotary piezoelectric stick-slip actuator, and obtain a model relating the step size of the actuator to the load. The actuator-specific parameters of the model are calibrated by taking measurements in specific configurations of the manipulator. Results comparing the obtained model to experimental data are presented.

Revisiting the effect of velocity on human force control

Human-robot collaborative systems (HRCS) have the potential to dramatically change many aspects of surgery, manufacturing, hazardous-material handling, and other dextrous tasks. We are particularly interested in precise manipulation tasks, which are typically performed under an admittance-control regime, where the controlled velocity is proportional to the user-applied force. During precise fast movements, there is a noticeable degradation in control precision, and prior results have indicated that system velocity, and not system admittance, is the factor that is correlated with force-control precision. In this paper, we report evidence that system admittance is more important than velocity in determining the users ability to control force, and we provide an explanation as to why prior results might have indicated otherwise.