Constraint-based technique for haptic volume exploration

Journal ArticleWe present a haptic rendering technique that uses directional constraints to facilitate enhanced exploration modes for volumetric datasets. The algorithm restricts user motion in certain directions by incrementally moving a proxy point along the axes of a local reference frame. Reaction forces are generated by a spring coupler between the proxy and the data probe, which can be tuned to the capabilities of the haptic interface. Secondary haptic effects including field forces, friction, and texture can be easily incorporated to convey information about additional characteristics of the data. We illustrate the technique with two examples: displaying fiber orientation in heart muscle layers and exploring diffusion tensor fiber tracts in brain white matter tissue. Initial evaluation of the approach indicates that haptic constraints provide an intuitive means for displaying directional information in volume data

Haptic interface control-design issues and experiments with a planar device

Describes the haptic rendering of a virtual environment by drawing upon concepts developed in the area of teleoperation. A four-channel teleoperation architecture is shown to be an effective means of coordinating the control of a 3-DOF haptic interface with the simulation of a virtual dynamic environmen

Expanding Haptic Workspace for Coupled-Object Manipulation

Haptic force-feedback offers a valuable cue in exploration and manipulation of virtual environments. However, grounding of many commercial kinesthetic haptic devices limits the workspace accessible using a purely position-control scheme. The bubble technique has been recently presented as a method for expanding the user’s haptic workspace. The bubble technique is a hybrid position-rate control system in which a volume, or “bubble,” is defined entirely within the physical workspace of the haptic device. When the device’s end effector is within this bubble, interaction is through position control. When exiting this volume, an elastic restoring force is rendered, and a rate is applied that moves the virtual accessible workspace. Existing work on the bubble technique focuses on point-based touching tasks. When the bubble technique is applied to simulations where the user is grasping virtual objects with part-part collision detection, unforeseen interaction problems surface. This paper discusses three details of the user experience of coupled-object manipulation with the bubble technique. A few preliminary methods of addressing these interaction challenges are introduced

On the passivity of interaction control with series elastic actuation

Regulating the mechanical interaction between robot and environment is a fundamentally important problem in robotics. Many applications such as manipulation and assembly tasks necessitate interaction control. Applications in which the robots are expected to collaborate and share the workspace with humans also require interaction control. Therefore, interaction controllers are quintessential to physical human-robot interaction (pHRI) applications. Passivity paradigm provides powerful design tools to ensure the safety of interaction. It relies on the idea that passive systems do not generate energy that can potentially destabilize the system. Thus, coupled stability is guaranteed if the controller and the environment are passive. Fortunately, passive environments constitute an extensive and useful set, including all combinations of linear or nonlinear masses, springs, and dampers. Moreover, a human operator may also be treated as a passive network element. Passivity paradigm is appealing for pHRI applications as it ensures stability robustness and provides ease-of-control design. However, passivity is a conservative framework which imposes stringent limits on control gains that deteriorate the performance. Therefore, it is of paramount importance to obtain the most relaxed passivity bounds for the control design problem. Series Elastic Actuation (SEA) has become prevalent in pHRI applications as it provides considerable advantages over traditional sti actuators in terms of stability robustness and delity of force control, thanks to deliberately introduced compliance between the actuator and the load. Several impedance control architectures have been proposed for SEA. Among the alternatives, the cascaded controller with an inner-most velocity loop, an intermediate torque loop and an outer-most impedance loop is particularly favoured for its simplicity, robustness, and performance. In this thesis, we derive the necessary and su cient conditions to ensure the passivity of the cascade-controller architecture for rendering two classical linear impedance models of null impedance and pure spring. Based on the newly established passivity conditions, we provide non-conservative design guidelines to haptically display free-space and virtual spring while ensuring coupled stability, thus the safety of interaction. We demonstrate the validity of these conditions through simulation studies as well as physical experiments. We demonstrate the importance of including physical damping in the actuator model during derivation of passivity conditions, when integral controllers are utilized. We note the unintuitive adversary e ect of actuator damping on system passivity. More precisely, we establish that the damping term imposes an extra bound on controller gains to preserve passivity. We further study an extension to the cascaded SEA control architecture and discover that series elastic damping actuation (SEDA) can passively render impedances that are out of the range of SEA. In particular, we demonstrate that SEDA can passively render Voigt model and impedances higher than the physical spring-damper pair in SEDA. The mathematical analyses of SEDA are veri ed through simulations

근전도 신호를 통한 굴신예측을 이용한 1자유도 무릎관절용 외골격 로봇의 안정한 자유운동 구현

학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2016. 2. 조규진.Control system design of exoskeleton type robots is basically different to that of conventional or industrial robots which requires robust motion control. Exoskeleton type robots always interact with human during achieving its own goal, so designing control system of exoskeleton type robot must encounter important issues such as ensuring safety, adaptive and robust performance. Exoskeleton type robots can roughly classified into three categories according to its purpose or target performance, assistance, rehabilitation and human-power augmentation. If attention is narrowed on powered-exoskeleton which has at least one actuator, the common requirement of the each types of exoskeleton to achieving its target performance is to make the exoskeleton interacts with human as if the exoskeleton system acts like desired virtual environment. For example, exoskeleton for assistance of raising arm should have environment which push the human arm upward so that it can assist desired raising motion of human arm. The virtual environment which the exoskeleton simulates could be combination of realistic mechanical system, or any virtual characteristics which actually do not exist in real world. This requirement of rendering virtual environment is common issue on haptics technology which has purpose on transparently simulating virtual environment to human operator. Haptic display have a limitation about rendering virtual environment on two extremes, high impedance and low impedance environments. For given haptic device, when haptic display render hard surface or free motion, It is impossible to render complete hard surface or free motion. It is previously investigated by many researchers that its higher and lower boundary can be written in relatively simple formula which includes system characteristics. This range of rendering is important indicator of evaluation of haptic display performance. Exoskeleton type robots have advantage in gathering extra information from biosignal which enable the system to estimate or predict human movement because exoskeleton usually rigidly bind to human. This paper proposes triggering algorithm using surface electromyography(sEMG) signal for improving performance of haptic display during free motion on admittance-controlled 1DOF exoskeleton. Within the framework of haptics, The purpose of this research is expanding lower impedance boundary of virtual environment by implementing triggering algorithm using sEMG signal. For avoiding complexity caused by including human model, this triggering algorithm is driven by simple pattern-recognition of sEMG signal, not by quantitative evaluation of the signal. Two-port absolute stability criteria is considered for designing the exoskeleton control system so that it guarantees stability with arbitrary characteristics of human operator and virtual environment. The limitations of conventional haptic display to implement free motion and the concept of the triggering algorithm is illustrated. The performance of proposed algorithm is presented by simulation results and experimental results.1.Introduction 1 2.Device Design and Properties 4 2.1 System Description. 4 2.2 Dynamic Characteristics Estimation 6 3.Control System Design 7 3.1 Network Model of Haptic Display 7 3.2 Passivity and Llewellyns Stability Criteria 8 3.3 sEMG Prediction Model and Processing. 10 3.4 Design of Control Algorithm using sEMG 11 4.Simulation and Experiment Results 16 4.1 Control Algorithm Validation with Simulation 16 4.2 Control Algorithm Validation with Experiment 20 5.Conclusion 24 Bibliography 27 국문 초록 29Maste