Bongsoo Kang

Dynamic modeling of structurally-flexible planar parallel manipulator

This paper presents a dynamic model of a planar parallel manipulator including structural flexibility of several linkages. The equations of motion are formulated using the Lagrangian equations of the first type and Lagrangian multipliers are introduced to represent the geometry of multiple closed loop chains. Then, an active damping approach using a PZT actuator is described to attenuate structural vibration of the linkages. Overall dynamic behavior of the manipulator, induced from structural flexibility of the linkage, is well illustrated through simulations. This analysis will be used to develop a prototype parallel manipulator.

Dynamic modeling of Mckibben pneumatic artificial muscles for antagonistic actuation

This paper presents the dynamic modeling of Mckibben pneumatic artificial muscles. The air flow model of a valve orifice and the air volume model of a pneumatic muscle are incorporated into the proposed dynamic model to estimate precisely the pressure variance of a pneumatic muscle when Mckibben muscles are in inflating and deflating. Coefficient parameters of the proposed model are determined optimally through well-coordinated experiments. Frequency response test is performed on an antagonistic structure consisting of Mckibben muscles manufactured in our laboratory and a pneumatic circuit with fast pneumatic control valves. Comparing with experimental results, simulations revealed that the proposed model gave good performance in estimating motions of the antagonistic actuation as well as the pressure variance of the Mckibben muscles.

Design of high speed planar parallel manipulator and multiple simultaneous specification control

This paper presents a planar parallel mechanism which can achieve very rapid motion due to the low inertia of its moving parts and the use of multiple simultaneous specification (MSS) control. The proposed parallel manipulator was designed based on a prismatic-revolute-revolute kinematic structure. The proximal prismatic joints were realized using a linear slider with a ball screw mechanism. All actuators remain stationary resulting in a reduction of the inertia of moving parts. Since coupling terms between multiple chains of the parallel manipulator were significant, the MSS control scheme was implemented to satisfy multiple conflicting closed-loop performance specifications. Simulation and experimental results show that the proposed planar parallel manipulator yields better dynamic performance than a conventional X-Y table and has great potential in application to high speed assembly.

Architecture Selection and Singularity Analysis of a Three-Degree-of-Freedom Planar Parallel Manipulator

A three degree-of-freedom planar parallel manipulator, intended for high-speed, high-precision wire-bonding and electronic-component placement tasks, has been developed in our laboratory. In this paper, the work related to the kinematic manipulator-architecture selection is presented. The reachable workspace and “effective base area” metrics of the parallel manipulator were utilized for selecting the best possible architecture amongst six potential configurations. Constant platform-orientation regions, within the reachable workspace of the selected manipulator, were identified based on the manipulator task requirements. Simulation results for the workspace analyses (reachable workspace, effective base areas, and constant-orientation regions) are presented in this paper. Once the optimal-workspace architecture was selected, both workspace-boundary and internal singularities were further investigated in order to have a clear view of the set of uncontrollable poses of the manipulator. Singularity analyses examples are also included herein.

Vibration Control of a Planar Parallel Manipulator Using Piezoelectric Actuators

Abstract This paper presents an active damping control approach applied to piezoelectric actuators attached to flexible linkages of a planar parallel manipulator for the purpose of attenuation of unwanted mechanical vibrations. Lightweight linkages of parallel manipulators deform under high acceleration and deceleration, inducing unwanted vibration of linkages. Such vibration must be damped quickly to reduce settling time of the manipulator platform position and orientation. An integrated control system for a parallel manipulator is proposed to achieve precise path tracking of the platform while damping the undesirable manipulator linkage vibration. The proposed control system consists of a PD feedback control scheme for rigid body motion of the platform, and a linear velocity feedback control scheme applied to piezoelectric actuators to damp unwanted linkage vibrations. In this paper, we apply the proposed vibration suppression algorithm to two different types of piezoelectric actuators and evaluate their respective performances. The two piezoelectric actuators are (i) a PVDF layer applied to the flexible linkage and (ii) PZT actuator segments also applied to the linkage. Simulation results show that both piezoelectric actuators achieve good performance in vibration attenuation of the planar parallel manipulator. The dynamics of the planar parallel platform are selected such that the linkages have considerable flexibility, to better exhibit the effects of the vibration damping control system proposed.

UWB-Aided Inertial Motion Capture for Lower Body 3-D Dynamic Activity and Trajectory Tracking

This paper introduces a novel method for simultaneous 3-D trajectory tracking and lower body motion capture (MoCap) under various dynamic activities such as walking and jumping. The proposed method uses wearable inertial sensors fused with an ultrawideband localization system using a cascaded Kalman filter-based sensor fusion algorithm, which consists of a separate orientation filter cascaded with a position/velocity filter. In addition, to further improve the joint angle tracking accuracy, anatomical constraints are applied to the knee joint. Currently, available self-contained inertial tracking methods are not only drift-prone over time but also their accuracy is degraded under fast movements with unstable ground contact states due to the lack of external references. However, our experimental results, which benchmark the system against a reference camera-based motion tracking system, show that the proposed fusion method can accurately capture the dynamic activities of a subject without drift. The results show that the proposed system can maintain similar accuracies between fast and slow motions in lower body MoCap and 3-D trajectory tracking. The obtained accuracies of the system for 3-D body localization and knee joint angle tracking for fast motions were less than 5 cm and 2.1°, respectively.

Dynamic modeling and vibration control of high speed planar parallel manipulator

Presents dynamic formulations of a planar parallel manipulator including structural flexibility of several linkages. The equations of motion are formulated using the Lagrangian equations of the first type. To avoid complexity in calculating passive coordinates of the parallel manipulator, we introduce Lagrangian multipliers, which combine with constraint equations representing the geometry of multiple closed loop chains. Then, an approach for active damping using a PZT actuator is described to attenuate structural vibration of the linkage. Attached on the linkage, the PZT actuator produces a bending moment according to a linear velocity feedback control scheme. Overall dynamic behavior of the manipulator, induced from structural flexibility of the linkage, is well illustrated through simulations. This analysis is used to develop the prototype parallel manipulator.

Two-time scale controller design for a high speed planar parallel manipulator with structural flexibility

Planar parallel manipulators, with potential applications in high speed, high acceleration tasks such as electronic component placement, would be subject to mechanical vibration due to high inertial forces acting on the linkages and other components. To achieve high throughput capability, such motion induced vibration would have to be damped quickly, to reduce settling time of the platform position and orientation. This paper develops a two-time scale dynamic model of a three-degree-of-freedom planar parallel manipulator with structurally flexible linkages. Based on the two-time scale model, a composite controller, consisting of a computed torque controller for the slow time-scale or rigid body subsystem dynamics, and a linear-quadratic state-feedback regulator for the fast time-scale flexible dynamic subsystem, is designed. Simulation results show that the composite control scheme permits the parallel manipulator platform to follow a given desired trajectory, while damping structural vibration arising due to excitation from inertial forces.

Robust Tracking Control of a Direct Drive Robot

This paper presents a robust controller for tracking control of a direct-drive robot. The proposed controller consists of two portions: a computed torque method which precompensates for dynamics of the modeled plant and an H∞ controller which postcompensates for residual errors which are not completely removed by the computed torque method. Experimental methods for identifying appropriate model structure and parameters are presented, and three specific controller types are compared. Using the robot designed in our laboratory, the combined controller reduced tracking errors by one half compared to computed torque control alone, and by one sixth compared to conventional independent joint control.

Robust Biomechanical Model-Based 3-D Indoor Localization and Tracking Method Using UWB and IMU

This paper proposes a robust sensor fusion algorithm to accurately track the spatial location and motion of a human under various dynamic activities, such as walking, running, and jumping. The position accuracy of the indoor wireless positioning systems frequently suffers from non-line-of-sight and multipath effects, resulting in heavy-tailed outliers and signal outages. We address this problem by integrating the estimates from an ultra-wideband (UWB) system and inertial measurement units, but also taking advantage of the estimated velocity and height obtained from an aiding lower body biomechanical model. The proposed method is a cascaded Kalman filter-based algorithm where the orientation filter is cascaded with the robust position/velocity filter. The outliers are detected for individual measurements using the normalized innovation squared, where the measurement noise covariance is softly scaled to reduce its weight. The positioning accuracy is further improved with the Rauch–Tung–Striebel smoother. The proposed algorithm was validated against an optical motion tracking system for both slow (walking) and dynamic (running and jumping) activities performed in laboratory experiments. The results show that the proposed algorithm can maintain high accuracy for tracking the location of a subject in the presence of the outliers and UWB signal outages with a combined 3-D positioning error of less than 13 cm.