SangJoo Kwon

A discrete-time design and analysis of perturbation observer for motion control applications

A discrete perturbation observer (DPO) is suggested in state-space form for motion control applications. In existing disturbance observer design methods, the low-pass filter (so-called Q-filter) is central. However, the effect of the Q-filter on performance and robustness has not been clarified, specifically in the discrete-time domain. Considering the discrete Q-filter, with general order and inertia perturbations as a structured model uncertainty, we clarify how the performance and robustness of the perturbation observer are changed according to the variation of the Q-filter parameters and model parameter (i.e., inertia) perturbations in discrete control systems. Experimental results show the validity of the analysis and the effectiveness of the DPO.

On the coarse/fine dual-stage manipulators with robust perturbation compensator

A dual-stage, fast and fine robotic manipulator is presented. By adopting merits of both coarse and fine actuator, a desirable system having the capacity of large workspace with high resolution of motion is enabled. We constructed an ultra precision XY-manipulator with dual-stage structure where the PZT driven fine stage is mounted on the motor driven XY positioner and applied it to fine tracking controls and micro-teleoperations as a slave manipulator. We describe essential merits of the compound actuation mechanism and the control strategy to successfully utilize it with a proper servo system design. Through experimental results, the effectiveness of the coarse/fine manipulation by the dual stage manipulator is shown.

RIC (robust internal-loop compensator) based flight control of a quad-rotor type UAV

A QRT (quad-rotor type) hovering robot system is developed for quick detection and observation of the circumstances under calamity environment such as indoor fire spots. The UAV (unmanned aerial vehicle) is equipped with four propellers driven by each electric motor, an embedded controller, an INS (inertial navigation system) using three rate gyros and accelerometers, a CCD (charge coupled device) camera with wireless communication transmitter for observation, and an ultrasonic range sensor for height control. The developed hovering robot shows stable flying performances under the adoption of RIC (robust internal-loop compensator) based disturbance compensation and the vision based localization method. Although a model is incorrect, RIC method can design a controller by regarding the inaccurate part of the model and sensor noises as disturbances. The UAV can also avoid obstacles using eight IRs (infrareds) and four ultrasonic range sensors. This kind of micro UAV can be widely used in various calamity observation fields without danger of human beings under harmful environment.

Combined Synthesis of State Estimator and Perturbation Observer

A combined observer is synthesized bv unifying the conventional linear state estimator and the perturbation observer to estimate plant uncertainties and disturbances. It enables robust state estimation for uncertain dynamical systems and simultaneously, provides full-stateto the perturbation observer under output feedback conditions. The proposed combined observer is very practical since it is given as a recursive discrete-time form with minimal tuning parameters, and it requires no knowledge of the plant uncertainty. A coupled estimation error dynamics is derived, and the related technical issues such as stability and noise sensitivity are addressed. The combined observer setting is also extended to stochastic systems, and the discrete Kalman filter is reformulated by including the perturbation estimate update process. Numerical examples and experimental results validate the proposed schemes.

Robust performance of the multiloop perturbation compensator

A novel perturbation attenuation method is proposed for robust performance of mechanical systems. First, we give a unified view on a class of existing perturbation observers and define the residual perturbation. In terms of the view and the definition, a new perturbation compensator with multiloop structure is developed. It effectively compensates the perturbation (i.e., model uncertainty and external disturbance) to the plant in a hierarchical and recursive fashion. In the multiloop perturbation compensator (MPEC) proposed, as the number of loops increases, the external disturbance condition for system stability is greatly relaxed and the perturbation attenuation performance is gradually enhanced but the robust stability margin on the modeling error becomes more strict. A recursive algorithm for general n-loop case of the MPEC is derived. By combining the developed robust perturbation compensator with a nominal feedback controller, a robust motion controller is synthesized. Experimental results for XY positioner and 2-DOF robot arms demonstrate the excellent robust tracking performance in spite of arbitrary large perturbation inputs.

Cellular force measurement for force reflected biomanipulation

In biological cell manipulations, manual thrust or a skilled operator, relying only on the visual feedback information only, usually performs penetration of injection pipette into single cells. Accurately measuring cellular force is a requirement for minimally invasive cell injection and it is essential in investigating biomechanical properties of cell membranes. We have fabricated an end effector with microforce sensing capability for biocell injections using PVDF piezoelectric polymer and measured several mN level injection force for zebrafish egg cell. Experimental results show that the cellular force level is changed as the injection pipette penetrates yolk and chorion sequentially. As well, the experimental setup with haptic interface suggests that a more reliable biomanipulation can be achieved by supplying real-time cellular force feedback to the operator.

An Effective Kalman Filter Localization Method for Mobile Robots

An effective Kalman filter localization method for mobile robots is investigated in terms of the robust Kalman filter with perturbation estimator. In the recursive algorithm, the perturbation estimator produces equivalent perturbations with respect to the nominal state equation and the action model of a mobile robot is adaptively modified with the perturbation estimates. The integral control property of the perturbation estimator enables a great reduction of the localization error, specifically when the odometric disturbance is large. The Kalman filter recursive equations including predictor, corrector, perturbation estimator, and the corresponding covariance propagation equations are formulated systematically. The effectiveness of the proposed scheme is verified through simulation and experimental results for a wheeled mobile robot

Identification and control of a sensorized microgripper for micromanipulation

This paper presents the design and control of a sensorized microgripper using a voice coil motor and a flexure mechanism. To increase the gripping sensitivity, shape design and determination of sensor attachment position are performed using finite element analysis. Empirical models of the microgripper are acquired for the design of position control and gripping force control. By using the identified models, both the perfect tracking controller for position control and the adaptive zero-phase error tracking controller for force control are implemented. The effectiveness of the proposed model-based control methods is verified by experimental studies.

General Algorithm for Automatic Generation of the Workspace for n-link Planar Redundant Manipulators

An efficient algorithm to simulate the workspace for a n-link redundant manipulator with rotating base is developed. The unique feature of the algorithm is its ability to automatically generate the binary angle selection code for the given manipulator. This code system makes it possible to avoid repetitions in calculating positions and plotting arcs for the workspace and thus saves considerable computing and graphic time. Two types of workspace are possible using this algorithm. Numerical examples including the workspace of human arm motion and that of a 20-link system are demonstrated to illustrate the effectiveness of the algorithm.

Tilting-Type Balancing Mobile Robot Platform for Enhancing Lateral Stability

In this paper, a tilting-type balancing mobile robot platform is investigated for enhancing lateral stability. In addition to pitch, yaw, and straight motion by the conventional two-wheeled inverted pendulum mechanism, it can generate roll and vertical motion by an additional tilting mechanism. The static force analysis shows that body separation tilting is more advantageous in power consumption than single body tilting, specifically when the payload to body weight is relatively small. Some design considerations are given for the determination of body structure and actuator powers. For the dynamic modeling, the titling balancing platform is assumed as a three-dimensional inverted pendulum with moving base and the nonlinear equation of motion is derived in terms of Kanes method. Then, a velocity/posture control loop is constructed, where the tilt angle reference is naturally generated according to the centrifugal force variation in following a circular path. Experimental results are given to validate the proposed mobile platform with the tilting control strategy.