Virtual Tissue Cutting With Haptic Feedback Using a Hybrid Actuator With DC Servomotor and Magnetorheological Brake

[+] Author and Article Information
Berk Gonenc

Department of Mechanical Engineering,
Johns Hopkins University,
Baltimore, MD 21211

Hakan Gurocak

School of Engineering and Computer Science,
Washington State University,
Vancouver, WA 98686

Contributed by the Computers and Information Division of ASME for publication in the JOURNAL OF COMPUTING AND INFORMATION SCIENCE IN ENGINEERING. Manuscript received December 22, 2015; final manuscript received March 5, 2016; published online June 30, 2016. Assoc. Editor: Francesco Ferrise.

J. Comput. Inf. Sci. Eng 16(3), 030902 (Jun 30, 2016) (8 pages) Paper No: JCISE-15-1430; doi: 10.1115/1.4033046 History: Received December 22, 2015; Revised March 05, 2016

Surgical training is an important and recent application where haptic interfaces are used to enhance the realism of virtual training simulators. Tissue cutting with surgical scissors is a common interaction mode in the simulations. The haptic interface needs to render a wide range of tissue properties and resistance forces accurately. In this research, we developed a hybrid haptic device made of a DC servomotor and a magnetorheological (MR) brake. The motor can provide fast dynamic response and compensate for inertia and friction effects of the device. But alone, it cannot supply high force levels and the sensation of stiff interaction with hard tissues such as tendons. On the other hand, the MR-brake can provide very stiff interaction forces yet cannot reflect fast dynamics that are encountered as the virtual scissors go through the tissue. The hybrid actuator developed in this work combines the two based on a control scheme that decomposes the actuator command signal into two branches considering each actuator's capabilities. It is implemented on a compact single degree-of-freedom (DOF) interface to simulate virtual tissue cutting with three different scissor types (Mayo, Metzenbaum, Iris) and four types of rat tissue (liver, muscle, skin, tendon). Results have shown close tracking of the desired force profile in all cases. Compared to just using a DC motor, the hybrid actuator provided a wider range of forces (up to 18 N) with fast response to render quick force variations without any instability for all simulated tissue and scissor types.

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Fig. 1

(a) Sectional view and components of the brake: the size of critical sections needs to be optimized to allow for maximal magnetic flux, (b) serpentine magnetic flux path weaving through the drum, the MR fluid and the stator, and the main design parameters (R1−5, L1), and (c) equivalent magnetic circuit of the MR-brake

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Fig. 2

The serpentine magnetic flux using FEM analysis (for input current of 1 A) and the variation of magnetic flux density in the fluid gap (for input current of 0.1 A and 1 A)

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Fig. 3

Torque output of the MR-brake versus input current: The theoretical response curve based on the FEM analysis is within the major hysteresis loop of the actual response

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Fig. 4

Haptic interface with the hybrid actuator

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Fig. 5

Hybrid actuator control scheme with force feedback. Based on the measured and desired force levels, the manipulation module decides on two actuator input signals.

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Fig. 6

(a) Virtual tissue cutting experiment setup AND (b) Simulated scissor types

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Fig. 7

Virtual tissue cutting experiment results with Mayo scissors

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Fig. 8

Cutting liver with Mayo scissors: (a) the desired force profile versus the measured forces using only the MR brake and the hybrid actuator; (b) the brake is commanded to provide a smooth force profile; (c) the motor is commanded to make instantaneous injections on this profile to correct errors quickly; (d) hybrid actuator causes significantly less force tracking error compared to the single use of the brake; (e) and (f) the angle between the scissor blades and corresponding angular velocity; and (g) the product of measured force and velocity, which is always negative proving passivity of the interface.

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Fig. 9

Virtual tissue cutting experiment results with Metzenbaum scissors

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Fig. 10

Virtual tissue cutting experiment results with Iris scissors




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