Dong-Soo Kwon

Modeling of a magnetorheological actuator including magnetic hysteresis

Magnetorheological (MR) actuators provide controlled torque through control of an applied magnetic field. Therefore knowledge of the relationship between the applied current and output torque is required. This paper presents a new nonlinear modeling of MR actuators considering magnetic hysteresis to determine the torque-current nonlinear relationship. Equations for transmitted torque are derived according to mechanical shear configurations of the MR actuator. Hodgdons hysteresis model is used to capture the characteristics of hysteresis nonlinearity in the MR actuators. An MR actuator test setup has been constructed using a commercial MR brake to evaluate the proposed model. The measured torque shows hysteresis effects as the current increases and decreases. Using Hodgdons hysteresis model of the magnetic circuit and Bingham model of the MR fluid, a novel nonlinear model of the MR actuator is obtained as a torque estimator for practical torque control purpose. The validity of the theoretical results is verified by comparison between experiments and simulations. Furthermore, the current versus torque frequency response of the MR actuator is examined to evaluate its applicability to torque control. The bandwidth of the MR actuator is high enough for especially haptic applications.

Mobile robots at your fingertip: Bezier curve on-line trajectory generation for supervisory control

A new interfacing method is presented to control mobile robot(s) in a supervised manner. Mobile robots often provide global position information to an operator. This research describes a method whereby the operator controls a mobile robot(s) using his finger or stylus via a touchpad or touch screen interface. Using a mapping between the robots operational site and the input device, a human user can provide routing information for the mobile robot. Two algorithms have been developed to create the robot trajectory from the operators input. Information regarding numerous path points is generated when the operator moves his finger/stylus. To prune away meaningless point information, a simple but powerful significant points extracting algorithm is developed. The resulting significant points are used as waypoints. An on-line piecewise cubic Bezier curves (PCBC) trajectory generation algorithm is presented to create a smooth trajectory for these significant points. As the method is based on distance and not on time, the velocity of mobile robot can be controlled easily within its allowable dynamic range. The PCBC trajectory can also be modified on the fly. Simulation results are presented to verify these newly developed methods.

Microsurgical telerobot system

A microsurgical telerobot system has been developed according to the results of the microsurgery task analysis. Several fields of the microsurgery have been investigated and the surgery tasks and tool motions are analyzed to acquire guidelines for specifications of a microsurgical telerobot system. A slave robot system consists of a 6-DOF parallel micromanipulator, that is our own modified Stewart platform type, and a 6-DOF macro-motion industrial robot that mounts the parallel micromanipulator at the end. A 6-DOF force-reflecting master device has also been developed using five-bar parallel mechanisms driven by harmonic DC servomotors. A bilateral control algorithm has been proposed based on the force-position loop, and the local position controller for the master has been developed to minimize the effect of gravity, friction, and inertia.

Control of a flexible manipulator with noncollocated feedback: time-domain passivity approach

A new method to control a flexible manipulator with noncollocated feedback is proposed. We introduce a method to implement the time-domain passivity-control approach to a flexible manipulator with noncollocated feedback, which could not be treated with the previous time-domain passivity-control framework due to a possible active transfer function from the input to the noncollocated output. The proposed method is simulated with a single-link flexible manipulator, and a good control performance is obtained.

Integration of a Rehabilitation Robotic System (KARES II) with Human-Friendly Man-Machine Interaction Units

In this paper, we report some important results of design and evaluation of a wheelchair-based robotic arm system, named as KARES II (KAIST Rehabilitation Engineering Service System II), which is newly developed for the disabled. KARES II is designed in consideration of surveyed necessary tasks for the target users (that is, people with spinal cord injury). At first, we predefined twelve important tasks according to extensive interviews and questionnaires. Next, based on these tasks, all subsystems are designed, simulated and developed. A robotic arm with active compliance and intelligent visual servoing capability is developed by using cable-driven mechanism. Various kinds of human-robot interfaces are developed to provide broad range of services according to the levels of disability. Eye-mouse, shoulder/head interface, EMG signal-based control subsystems are used for this purpose. Besides, we describe the process of integration of our rehabilitation robotic system KARES II, and discuss about user trials. A mobile platform and a wheelchair platform are two main platforms in which various subsystems are installed. For a real-world application of KARES II system, we have performed user trials with six selected potential end-users (with spinal cord injury).

Haptic control of the master hand controller for a microsurgical telerobot system

A microsurgical telerobot system has been developed based on the results of the operation task analysis. The telerobot system is composed of a 6-DOF parallel micromanipulator attached to the macro-motion industrial robot and a 6-DOF force-reflecting haptic master device. The master device uses five-bar parallel mechanisms driven by harmonic DC servomotors. The proposed 6-DOF master hand controller has nonlinear coupled dynamics and friction. Since the disturbance force due to friction, gravity and coupled inertia can distort the operators perception, a disturbance observer is introduced in the operational space and implemented in the microsurgery master hand controller.

Development of a miniature pin-array tactile module using elastic and electromagnetic force for mobile devices

In these days, tactile sensation using a vibration motor is recently receiving attention for immersive interaction with mobile devices. However, the vibration motor is not enough to provide detailed texture or small-scale shape. In order to generate various and exiting tactile sensation, this paper presents a new tactile actuator with a solenoid, a permanent magnet and an elastic spring. This paper also proposes a miniature tactile module with the proposed actuators. On constructing a miniature tactile module, we separate the elastic springs in the actuators into several layers to minimize the contactors gap without decreasing the performance of the tactile module. We conduct experiments to investigate each contactors output force and the frequency response of the proposed tactile module. Each contactor can generate enough output force to stimulate humans mechanoreceptors. Moreover, since the contactors are actuated in a wide range of frequency, the proposed tactile module can generate various tactile sensations.

Real-time area-based haptic rendering and the augmented tactile display device for a palpation simulator

Although people usually contact a surface with some area rather than a point, most haptic devices allow a user to interact with a virtual object at one point at a time and likewise most haptic rendering algorithms deal with such situations only. In a palpation procedure, medical doctors push and rub the organs surface, and are provided the sensation of distributed pressure and contact force (reflecting force) for discerning doubtable areas of the organ. In this paper, we suggest real-time area-based haptic rendering to describe distributed pressure and contact force simultaneously, and present a haptic interface system to generate surface properties in accordance with the haptic rendering algorithm. We represent the haptic model using the shape-retaining chain link (S-chain) framework for a fast and stable computation of the contact force and distributed pressure from a volumetric virtual object. In addition, we developed a compact pin-array-type tactile display unit and attached it to the PHANToMTM haptic device to complement each other. For the evaluation, experiments were conducted with non-homogenous volumetric cubic objects consisting of approximately 500 000 volume elements. The experimental results show that compared to the point contact, the area contact provides the user with more precise perception of the shape and softness of the objects composition, and that our proposed system satisfies the real-time and realism constraints to be useful for a virtual reality application.

Evolutionary programming-based univector field navigation method for past mobile robots

Most of navigation techniques with obstacle avoidance do not consider the robot orientation at the target position. These techniques deal with the robot position only and are independent of its orientation and velocity. To solve these problems this paper proposes a novel univector field method for fast mobile robot navigation which introduces a normalized two dimensional vector field. The method provides fast moving robots with the desired posture at the target position and obstacle avoidance. To obtain the sub-optimal vector field, a function approximator is used and trained by evolutionary programming. Two kinds of vector fields are trained, one for the final posture acquisition and the other for obstacle avoidance. Computer simulations and real experiments are carried out for a fast moving mobile robot to demonstrate the effectiveness of the proposed scheme.

Quantitative tactile display device with pin-array type tactile feedback and thermal feedback

This paper proposes a tactile display device providing pin-array type tactile feedback and thermal feedback. The pin-array type tactile display is composed of a 6times5 pin-array that is actuated by 30 piezoelectric bimorphs. Micro shape and vibrotactile feedback can be generated by the device, and various planar distributed patterns can be displayed as can braille cell patterns. The thermal feedback device is composed of a thin film resistance temperature detector (RTD), a Peltier thermoelectric heat pump and a water cooling jacket. Users can discriminate among different materials by considering the temperature variation that can be sensed as they touch an objects surface. This paper also includes an experimental evaluation of the device to prove effectiveness of displaying textures. Material property discriminating evaluation was conducted using thermal feedback device that displays simulated temperature profile. To determine the relation between stimulated area and thermal perception sensitivity, a thermal perception experimental setup is developed and the experimental method is described