Jeha Ryu

New dimensionally homogeneous Jacobian matrix formulation by three end-effector points for optimal design of parallel manipulators

Development of optimal design methods for parallel manipulators is important in obtaining an optimal architecture or pose for the best kinetostatic performance. The use of performance indexes such as the condition number of the conventional Jacobian matrix that is composed of nonhomogeneous physical units, however, may lack in physical significance. In order to avoid the unit inconsistency problem in the conventional Jacobian matrix, we present a new formulation of a dimensionally homogeneous Jacobian matrix for parallel manipulators with a planar mobile platform by using three end-effector points that are coplanar with the mobile platform joints. The condition number of the new Jacobian matrix is then used to design an optimal architecture or pose of parallel manipulators for the best dexterity. An illustrative design example with a six-degree-of-freedom Gough-Stewart platform parallel manipulator by using the proposed formulation is shown to generate the same optimal configurations as those from using the other existing dimensionally homogenous Jacobian formulation methods.

A geometrical method for computing the constant-orientation workspace of 6-PRRS parallel manipulators

This paper presents a geometrical method for the workspace analysis of 6-PRRS parallel manipulators. A geometric algorithm is described for the computation of the constant-orientation workspace, which was implemented in the CAD/CAM system CATIA. The influence of the different design parameters on the workspace, as well as on other properties of the manipulator, is discussed. In addition, a new representation of the mobile platform orientation is presented for easier interpretation of the orientation. Finally, examples are provided to demonstrate the usefulness of the method.

Design, fabrication, and evaluation of a new haptic device using a parallel mechanism

This paper presents design, fabrication, and evaluation of a new 6-DOF haptic device for interfacing with virtual reality by using a parallel mechanism. The mechanism is composed of three pantograph mechanisms that are driven by ground-fixed servomotors, three spherical joints between the top of the pantograph mechanisms and the connecting bars, and three revolute joints between the connecting bars and a mobile joystick handle. Forward and inverse kinematic analyses are performed and the Jacobian matrix is derived. Performance indexes such as global payload index, global conditioning index, translation and orientation workspaces, and sensitivity are evaluated to find optimal parameters in the design stage. The proposed haptic mechanism has better load capability than those of the pre-existing haptic mechanisms due to the fact that the motors are fixed at the base. It has also a wider orientation workspace mainly due to a RRR-type spherical joint. A control method is presented with gravity compensation and force feedback by a force/torque sensor to compensate for the effects of unmodeled dynamics such as friction and inertia. Also, the dynamic performance is evaluated for force characteristics. Virtual wall simulation with the developed haptic device is demonstrated.

Robustly Stable Haptic Interaction Control using an Energy-bounding Algorithm

Stability is a challenging issue when controlling haptic interaction systems because unstable behavior may injure human operators or deteriorate the realism of the provided cues. Based on the passivity condition for sampled-data haptic systems, we propose a novel energy-bounding algorithm to ensure robustly stable haptic interactions. The proposed algorithm limits the energy generated by a sample-and-hold operator within the energy consumable by the effective damping elements in the haptic system. The algorithm also ensures that the VE and controller are passive. This guarantees robustly stable haptic interactions, regardless of the sampling frequency and its variations, but compromises the displayable impedance range of the VE. Simulations and experiments using a commercial haptic device are used to demonstrate the effectiveness of the proposed algorithm.

Determining the Feasibility of Forearm Mounted Vibrotactile Displays

At first glance, multi-element forearm mounted vibrotactile displays would appear to have considerable potential as an output device for mobile computing. The devices are small, robust and discrete, and the body site both easily accessible and socially acceptable for such a purpose. However, due to the absence of a thorough account of vibrotactile perception, it is hard to determine their feasibility, or even what might form an appropriate arrangement of vibrating elements or tactors. We describe two studies intended to shed light on these issues. The first extends the localization literature relating to the forearm, and its results indicate that different spatial arrangements of tactors can result in substantially different levels of performance. The second study examines the influence of adjusting the size of the area of the skin experiencing a vibration with its perceived intensity. The results indicate a positive relationship between increased size and increased perceived intensity. Finally, the implications of these studies for the design of vibrotactile arrays are discussed.

Volumetric error analysis and architecture optimization for accuracy of HexaSlide type parallel manipulators

Abstract This paper presents a volumetric error analysis and an architecture optimization method for accuracy of parallel manipulators. A comprehensive volumetric kinematic error model that relates all kinematic error sources in the manipulator’s architecture to the pose errors of the end-effector is derived for HexaSlide ( P US) type parallel manipulators. The error model results in the total error transformation matrix from which three error amplification factors are derived and used as design criteria for accuracy in the optimum design formulation with constraints on workspace and design variable limits. Then, design optimization for accuracy has been performed by using a nonlinear optimization technique. Optimization results have been validated by Monte Carlo statistical simulation technique.

Experimental results on kinematic calibration of parallel manipulators using a partial pose measurement device

This paper presents kinematic calibration of parallel manipulators with partial pose measurements, using a device that measures a rotation of the end-effect or along with its position. The device contains a linear variable differential transformer, a biaxial inclinometer, and a rotary sensor. The device is designed in a modular fashion, and links of different lengths can be used. Two additional kinematic parameters required for the measurement device are discussed, kinematic relations are derived, and cost function is established to perform calibration with the proposed device. The study is performed for a six-degree-of-freedom fully parallel HexaSlide mechanism (HSM). Experimental results show significant improvement in the accuracy of the HSM.

A closed-form solution to the direct kinematics of nearly general parallel manipulators with optimally located three linear extra sensors

This paper presents a new closed-form solution of the direct kinematic problem of nearly general parallel manipulators by using three linear extra sensors. The sensors are disposed at optimal location, connecting the planar base and the planar mobile platform at distinct points. The basic idea is to use the coordinates of the three distinct anchor points of the extra sensors on the mobile platform to represent the pose of the mobile platform. Thus, the extra sensory data enable one to reduce the problem to the solution of a system of six linear equations in six of the nine generalized coordinates. The other three coordinates are obtained directly from the extra sensory data. In addition, an optimal location of the extra sensors is sought by minimizing the condition number of the linear equations for the least sensitivity to sensor measurement errors. A numerical example is presented for optimal sensor location and the error behavior of the proposed solution scheme by computer simulation.

A tactile glove design and authoring system for immersive multimedia

Viewer expectations for rich, immersive interaction with multimedia are driving new technologies- such as high-definition 3D displays and multichannel audio systems-to greater levels of sophistication. While researchers continue to study ways to develop new capabilities for visual and audio sensory channels, improvements in haptic channels could lead to even more immersive experiences.

A Novel Reconfigurable Ankle/Foot Rehabilitation Robot

This paper presents a novel reconfigurable ankle rehabilitation robot to cover various rehabilitation exercise modes. The designed robot can allow desired ankle and foot motions including toe and heel raising as well as traditional ankle rotations since the mechanism can generate relative rotation between the fore and rear platforms as well as pitch and roll motions. In addition, the robotic device can be reconfigured from a range of motion (ROM)/strengthening exercise device to a balance/proprioception exercise device by simply incorporating additional plate. Further, the action of the device is two folded in the sense that while a patient’s foot is fastened firmly to the ROM/strengthening device for task specific training, s/he can also stand on the balance/proproception device. The suggested ankle rehabilitation robot is expected to substitute not only the traditional therapy in various exercise modes but also supply the advanced functional exercises.