Pyung-Hun Chang

Design of learning input shaping technique for residual vibration suppression in an industrial robot

In this paper, a practical method is proposed to suppress residual vibrations of industrial robots without a real-time estimation of vibration frequencies. Through theoretical analysis and experiments, we designed an input shaping technique (IST) for the first three axes of a six-degrees-of-freedom industrial robot. Iterative learning IST (LIST) is applied to the first axis to suppress its time-varying nonlinear residual vibration, while conventional IST is applied to the second and third axes. Experimental results show that LIST can suppress residual vibrations to a level similar to that of a time-varying IST which requires complicated real-time estimation of a dynamic model. The LIST is an attractive method for suppression of nonlinear and time-varying residual vibrations in industrial robots which perform repetitive tasks because most industrial robots have limited computing power and memory space in their controllers.

Robust force/position control of a robot manipulator using time-delay control

Abstract Robot hybrid control has been noted for its difficulty due to the so-called dynamic stability problem, and consequently demands robust control algorithms that can overcome this difficulty, yet with accuracy. In this paper, a control law based on time-delay control has been derived for hybrid control, with a condition for closed-loop stability. In addition, its relationship with the disturbance observer has been investigated. It turned out that the disturbance observer is very similar to the proposed control. Throughout the simulations and experiments, this control law was observed to outperform PD or PID control, thereby proposing itself as promising for hybrid control purposes.

Development of a wheelchair-based rehabilitation robotic system (KARES II) with various human-robot interaction interfaces for the disabled

This paper describes our ongoing project about a new wheelchair-based rehabilitation robotic system for the disabled, called KARES II (KAIST Rehabilitation Engineering Service system II). We shall concentrate on the issues of design and visual servoing of the robotic arm with three human-robot interaction subsystems: an eye-mouse, an EMG interface, and a haptic suit interface. First, the specific required tasks of the robotic arm system are defined according to extensive surveys and interviews with the potential users, i.e., the people with spinal cord injury. In order to design the robotic arm for the predefined tasks effectively, a target-oriented design procedure is adopted. Next, a visual servoing subsystem for the robotic arm is designed and is integrated to perform the predefined tasks in an uncertain/time-varying environment. Finally, various human-robot interaction devices are proposed as interface for diverse users with physical disability. One or more of these interfaces may be selected on the basis of each users need. These diverse input devices can be used in a complementary way according to the users preference and to the degree of disability. Experimental results show that all subsystems can perform the defined tasks through the robotic arm in an integrated way.

Sliding mode control with perturbation estimation: application to motion control of parallel manipulator

Abstract Sliding mode control (SMC) incorporated with perturbation compensation is developed here to reduce the low-frequency tracking error in the presence of wide-band frequency perturbations for a nonlinear dynamic system. The control scheme is then applied to the motion control of a two-degree-of-freedom (DOF) parallel manipulator, utilizing its reduced dynamics for real-time implementation. It is shown that the SMC with perturbation compensation is far superior to the conventional SMC in tracking control of the manipulator under large payload and external disturbance conditions.

Neural tracts injuries in patients with hypoxic ischemic brain injury: Diffusion tensor imaging study

Many studies have reported on vulnerable areas of the brain in hypoxic ischemic brain injury (HI-BI). However, little is known about the involvement of neural tracts following HI-BI. We investigated neural tract injuries in adult patients with HI-BI, using diffusion tensor tractography (DTT). Twelve consecutive patients with HI-BI and 12 control subjects were recruited for this study. We classified the patients into two subgroups according to the preservation of alertness: subgroup A-5 patients who had intact alertness and subgroup B-7 patients who had impaired alertness. DTI-Studio software was used for evaluation of seven neural tracts: corticospinal, cingulum, fornix, superior longitudinal fasciculus, inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and optic radiation. We measured the DTT parameters (fractional anisotropy, apparent diffusion coefficient and voxel number) of each neural tract. In the individual analysis, all 12 patients showed injuries in all 24 neural tracts in terms of both DTT parameters and integrity, except for the corticospinal tract (75.0% injury). In the group analysis, the patient group showed neural injuries in all 24 neural tracts. In comparison of subgroups A and B, subgroup B showed more severe injuries: subgroup B showed a higher rate of disruption (39.8%) than subgroup A (12.9%) on individual DTTs and subgroup B had more severe injuries in both the cingulum and superior longitudinal fasciculus. In conclusion, we found that extensive injuries in the neural tracts were accompanied by HI-BI. Patients with impaired alertness appeared to show more severe injuries of neural tracts.

Learning input shaping technique for non-LTI systems

It is well known that a conventional input shaping technique is not very effective in suppressing residual vibrations for non-LTI systems, such as substantially nonlinear or time-varying systems. In an effort to increase the effectiveness for such systems, this paper presents a learning input shaping technique (LIST), which iteratively updates the parameters of the IST from the previous trials. Simulations are presented for 4 different cases: 1) when the natural frequency or damping of a system does not estimated well; 2) when a system has time varying vibration; 3) when a system has nonlinear flexibility; and 4) when a closed loop system includes the saturation limit in the loop. The experiments are made by using a 6-DOF industrial robot to evaluate the method. Results of both the simulations and experiments show that the residual vibrations become considerably smaller as iteration goes on, thereby demonstrating the effectiveness of the LIST.

The cortical activation pattern by a rehabilitation robotic hand: a functional NIRS study

Introduction: Clarification of the relationship between external stimuli and brain response has been an important topic in neuroscience and brain rehabilitation. In the current study, using functional near infrared spectroscopy (fNIRS), we attempted to investigate cortical activation patterns generated during execution of a rehabilitation robotic hand. Methods: Ten normal subjects were recruited for this study. Passive movements of the right fingers were performed using a rehabilitation robotic hand at a frequency of 0.5 Hz. We measured values of oxy-hemoglobin (HbO), deoxy-hemoglobin (HbR) and total-hemoglobin (HbT) in five regions of interest: the primary sensory-motor cortex (SM1), hand somatotopy of the contralateral SM1, supplementary motor area (SMA), premotor cortex (PMC), and prefrontal cortex (PFC). Results: HbO and HbT values indicated significant activation in the left SM1, left SMA, left PMC, and left PFC during execution of the rehabilitation robotic hand (uncorrected, p < 0.01). By contrast, HbR value indicated significant activation only in the hand somatotopic area of the left SM1 (uncorrected, p < 0.01). Conclusions: Our results appear to indicate that execution of the rehabilitation robotic hand could induce cortical activation.

Control Architecture Design for a Fire Searching Robot using Task Oriented Design Methodology

Recently, there has been an increase in the development of fire searching robots for indoor spaces such as the basements of buildings. This paper presents the control architecture for a fire searching robot using task oriented design (TOD) methodology. TOD is the systematic methodology used to design a system which follows a purpose closely by specifying a target clearly. As indoor spaces are blocked by walls, dangerous fires with smoke, high temperatures, and the possibility of explosions make it difficult for fire fighters to gain access to the fire. For this reason, a fire searching robot is developed in this study. It takes the place of fire fighters by means of an analysis of the properties of the environment of a fire, as well as the tasks demanded by the situation. For a stable operation, the fire searching robot is controlled by remote control. The control system is divided into three parts. The first is the robot controller, the second is a controller for the remote operating device, and the third is a wireless communication system. The appropriate hardware and software was developed for each part of the control system, and the fire search robot was tested in a test environment. The tests validated the performance and usefulness of the proposed control architecture

Anatomical location of the corticospinal tract according to somatotopies in the centrum semiovale.

Little is known about the somatotopic location of the corticospinal tract (CST) in the centrum semiovale (CS). We investigated the somatotopic location of the CST in the CS in the human brain using diffusion tensor tractography (DTT). Fifty-two healthy volunteers were recruited for this study. Diffusion tensor images (DTIs) were obtained at 1.5T, and CSTs for the hand and leg were obtained using FMRIB software. Normalized DTT images were reconstructed using the Montreal Neurological Institute echo-planar imaging template supplied with the SPM. Individual DTI data were calculated as number of pixels in the CS. In the mediolateral direction, average distances of the highest probabilistic locations for hand and leg somatotopies were 25.57 mm and 21.72 mm from the midline between the right and left hemispheres, respectively. For the anteroposterior direction, the average distance of the highest probabilistic locations for hand and leg somatotopies were 0.4 mm and 5.2 mm behind the horizontal line between the medial end of the central sulcus and midline, respectively. In conclusion, hand somatotopy of the CST was found to be located at about 26 mm lateral to the midline almost along the horizon line between the medial end of central sulcus and midline, and leg somatotopy of the CST was found to be located medioposteriorly to the hand somatotopy of the CST.

Robust Trajectory Control of Robot Manipulators Using Time Delay Estimation and Internal Model Concept

This paper proposes an enhanced controller, using Time Delay Estimation(TDE) and Internal Model Control(IMC) concept for robot manipulators. The proposed controller has a compensator based on IMC to improve robustness of Time Delay Control (TDC) against friction; it is effective enough to handle bad effect of friction, moreover, simple and efficient as to match positive attribute of TDC. The controller with TDE, does not need whole model of plants, thus, it is easily applicable. The analysis and experimental results show the effectiveness of the proposed controller against the friction effects of the robot manipulators.