Byung-Keun Song

Design of a New 4-DOF Haptic Master Featuring Magnetorheological Fluid

This work presents a novel 4-degree-of-freedom (4-DOF) haptic master using magnetorheological (MR) fluid which is applicable to a robot-assisted minimally invasive surgery (RMIS) system. By using MR fluid, the proposed haptic device can easily generate bidirectional repulsive torque along the directions of the required motions. The proposed master consists of two actuators: an MR bidirectional clutch associated with a planetary gear system and an MR clutch with a bevel gear system. After demonstrating the configuration, the torque models of MR actuators are mathematically derived based on the field-dependent Bingham model. An optimal design that accounts for spatial-limitation and the desired torque constraint is then undertaken. An optimization procedure based on finite element analysis is proposed to determine optimal geometric dimensions. Based on the design procedure, MR haptic master with the optimal parameters has been manufactured. In order to demonstrate the practical feasibility of the proposed haptic master, the field-dependent generating repulsive force is measured. In addition, a proportional-integral-derivative (PID) controller is empirically implemented to accomplish the desired torque trajectories. It has been shown that the proposed haptic master can track the desired torque trajectory without a significant error.

Design of tactile device for medical application using magnetorheological fluid

For the tactile recognition of human organ in minimally invasive surgery (MIS), this paper presents a novel tactile device that incorporates with magnetorheological (MR fluid). The MR fluid is contained by diaphragm and several pins. The operator for MIS can feel different force (or stiffness) from the proposed tactile device by applying different magnetic field or current. In order to generate required force from the device, the repulsive force from the human body is measured as reference data and an appropriate size of tactile device is designed and manufactured. It has been demonstrated via experiment that the repulsive force corresponding to the human body can be achieved by applying proper control input current. In addition, it has been shown that we can control the repulsive force by dividing the tactile device by several sections.

Repulsive torque control of a robot-assisted surgery system using a magnetorheological haptic master

In this work, a repulsive torque control of a robot-assisted surgery system using a 4-degree-of-freedom haptic master which is operated using the properties of magnetorheological fluid is undertaken. The proposed haptic master can generate a repulsive torque along 4-degree-of-freedom motion and provide command signals to the slave robot. This is possible due to controllability of the torque by applying the magnetic field (or current) to magnetorheological fluid domain of the clutch system. For the realization of the master-slave robot-assisted minimally invasive surgery system, an encoder is integrated with the haptic master, and the motion command of the haptic master is realized by the surgical slave robot in the robot-assisted minimally invasive surgery architecture. The haptic master–slave system is then established by incorporating the slave robot with the master device, in which the repulsive torque and position commands are transferred to each other. In order to demonstrate superior performance of the proposed haptic master in terms of torque-tracking controllability between the master and surgical positions, a sliding mode controller is designed and experimentally implemented. It is validated via tracking experiment that superior torque-tracking control performance can be achieved by commanding dynamic motions of the haptic master featured by the inherent characteristics of magnetorheological fluid.

The impact of bobbin material and design on magnetorheological brake performance

In this work, a new configuration of magnetorheological brakes (MRBs) is developed in order to improve the compactness, manufacturing accuracy and cost of conventional ones. In the conventional configuration of MRBs, the coil is normally wound on a nonmagnetic bobbin which is placed on the stationary housing. This causes difficulties in manufacturing and the bottle-neck problem of the magnetic circuit of the MRBs. In the proposed configuration, the nonmagnetic bobbin is eliminated and the coil is wound directly on a magnetic bobbin which is a part of the housing. In this case, the magnetic bobbin part should be designed with a contractive cross-section in order to prevent magnetic flux going through and thus forcing the magnetic flux across the MR fluid (MRF) duct. After proposing the new configurations of MRBs, the modelling of the MRBs is performed based on the Bingham rheological model of the MRF. An optimal design of the proposed MRBs and conventional MRBs is then performed based on finite element analysis of the magnetic circuit of the MRBs. A comparative work between the optimal parameters of the proposed MRBs and the conventional MRBs is conducted and the advanced performance characteristics of the proposed MRBs are then investigated. In addition, experiments on both the conventional and the proposed MRBs are performed to validate the advanced performance characteristics of the proposed MRBs.

A new congruency-based hysteresis modeling and compensating of a piezoactuator incorporating an adaptive neuron fuzzy inference system:

This paper proposes a new approach to modeling and compensating for a rate-independent hysteresis of a piezoactuator. The model—namely, congruency-based hysteresis—is developed based on two very important characteristics of the hysteresis. These are congruency and wipe-out. The proposed approach consists of two branches for cases of monotonic increase and monotonic decrease of input excitation. In order to realize this model, datasets of first-order minor-loop values should be determined in advance. This can be done using the adaptive neuron fuzzy system (ANFIS) technique and experimental data. With this technique, an input-output relationship of first-order minor-loop values is estimated effectively. In addition, the ANFIS technique is also used in constructing datasets of inverse first-order minor-loop values, which are essential parts of a congruency-based hysteresis compensator. Several experiments in modeling and open-loop control are conducted to show the effectiveness of the proposed approach. In addition, a comparative work between the proposed approach and one of previous works is undertaken to demonstrate the benefit of the proposed method.

Development of a novel diagonal-weighted Preisach model for rate-independent hysteresis

This article develops an alternative approach in modeling a hysteresis using Preisach model. A Preisach model is demonstrated geometrically by an inverted triangle, namely Preisach triangle, which contains an amount of fundamental operators. In a conventional Preisach model, these fundamental operators are ideal relays. Consequently, there exists an inherently discontinuous jump between two consecutive relays. To resolve this problem, in this work, a generalized linear operator is used as the fundamental elements. Correspondingly, its representative Preisach triangle consists of numerous discrete elements whose weight concentrates just along their diagonal. With such approach, it is possible to predict the response of the model according to any input without the aid of numerical interpolation tools. In addition, in this work, to determine the elements’ weights of the model, two accurate identification methods corresponding to two schemes of experimentally biased and unbiased dataset are developed. At last, several simulations and experiments are conducted to assess the effectiveness of the proposed approach showing comparative results with conventional Preisach model.

Design of a novel 6-DOF haptic master mechanism using MR clutches and gravity compensator

Abstract This work presents design and dynamic analysis results of a novel 6-degrees-of-freedom (6-DOF) haptic master mechanism featured by magneto-rheological (MR) devices and gravity compensator. The design target of the haptic master mechanism is determined on the basis of the possible application to the robotic-assisted minimally invasive surgery (RMIS) system in which a certain magnitude of the force or moment is required to feel by the surgeon. The dynamic torque/force models associated with MR clutches and brakes are derived considering the geometry and Bingham characteristics of MR Fluid. In the mechanism geometry, the wrist part is designed with a symmetrical structure such that the center of gravity is at the center of the handle. This makes the dynamic model of the proposed mechanism to be decoupled between the wrist motion and the translation motion. In addition, a gravity compensator is designed to enhance tracking performances of the desired repulsive forces/torques. It is demonstrated that the proposed 6-DOF MR haptic master can sufficiently generate desired rotational and translational forces/torques required in RMIS system.

Controllable Water Droplet for Microsystem Actuators: An Experimental Analysis

Dielectric liquids such as water exhibit significant displacement under a high electric field. Alike smart materials, oscillations of such dielectric liquids can be manipulated using controlled voltage. This study investigates basic actuation property of a water droplet by applying an electrical voltage across two parallel plate electrodes covered by a thin dielectric material. The dynamic characteristics of the water droplet response are evaluated using step input voltage. The sensitivity of the droplet response to a change in the system parameters is also analyzed. The procedure of analysis of variance is adopted to analyze the effectiveness and the combined effect of different parameters on the response. Accordingly, several parameters such as the relative permittivity of the dielectric substrate, thickness of the dielectric substrates, gap between the electrodes, relative permittivity of the dielectric fluid, and applied electric voltage are chosen as control factors. The steady-state response and damping ratio are considered as the output responses. The quadratic regression model associated with the response surface methodology is thereafter used to correlate the output response with the system parameters. It is shown that the gap between the electrodes is the dominant factor affecting the steady-state response whereas the thickness of the dielectric substrate is the dominant factor affecting the damping ratio. In addition, a good consistency is observed between the predicted and experimental responses.

A new hysteresis identification model using a diagonal-weighted Preisach model and recursive approach with application to piezostack actuators

This article presents a new hysteresis model of a piezostack actuator which is designed from the modification of the conventional Preisach hysteresis model. The proposed model which is called diagonal-weighted Preisach model is featured by weights of fundamental elements constituting triangles just along their own diagonal. With such an approach, there is no discontinuous jump at two consecutive elements in the Preisach triangle. Consequently, there is no need to adopt any further interpolation tool. In this work, a recursive approach with a simple computation associated with the proposed model is also developed. It is noted that in order to implement the proposed model, weights of fundamental elements must be obtained in prior. In order to demonstrate some characteristics of the proposed model, the prediction accuracy of the hysteresis is investigated based on the discretized number and compared with the conventional Preisach model. In addition, the proposed model is experimentally realized for the piezostack actuator and the identified displacement from the proposed model is compared with the actual one to validate the effectiveness.