Design and analysis of an fMRI compatible haptic robot

Magnetic resonance (MR) compatible haptic devices have certain specific structural and operational properties, which are due to the magnetic field, and haptic requirements. Through the development of a haptic mechanism, which is compatible with a magnetic resonance environment, certain problems were solved, which are common to all robotic devices operating in an MR tunnel. This paper deals with the manipulability problem of a novel 3 DOF MR compatible haptic mechanism, considering limited space and its visualisation. An appropriate 3D visualisation method has been developed for analysing the manipulability characteristics of a haptic mechanism within an MR environment. Choosing a suitable driving system is one of the crucial design attributes for quality force transmission in haptic interfaces. This paper introduces certain adaptations, which have been done to enable the MR compatibility of a cable drive driven by an electric motor. It also presents the theoretical modelling of a cable drive for a 3 DOF MR compatible haptic mechanism, focusing on the hysteretic behaviour of polymeric cables.     

Design and control of a planar haptic device with passive actuators based on passive force manipulability ellipsoid (FME) analysis

In this paper, we propose an optimal design for a passive haptic device with brakes and its control method. The inability of a brake to generate torque significantly affects the performance of a multi‐DOF haptic device, in that a desired force can be generated only approximately in some workspace and, in some cases, the device may become stuck contrary to the user's intention. In this research, these limitations are analyzed by means of the so‐called passive force manipulability ellipsoid. Through the analysis, performance indices are developed for evaluating the limitations associated with passive haptic devices. Optimization is conducted for a 5‐bar mechanism with redundant actuation, and a coercive force approximation scheme is developed to avoid unsmooth motion during the wall‐following task along the virtual wall. It is experimentally shown that the performance in relation to the limitations is greatly improved for the optimized mechanism. © 2005 Wiley Periodicals, Inc.     

Development of a single-master multi-slave tele-micromanipulation system

This paper proposes the development of a human–robot cooperative tele-micromanipulation system through a network. We have developed a novel single-master (PHANToM haptic device) multi-slave (6-d.o.f. parallel manipulator) scaled tele-micromanipulation system which enables human operators to perform meso or small-size object manipulation such as assembly or manufacturing with sufficient telepresence. It is expected to improve the human's operability and the overall dexterity of conventional tele-micromanipulation systems. To overcome the problems of the multiple parallel mechanism manipulator, virtual kinematic mapping is considered, based on the manipulability analysis of the workspace. The pick-and-place experiment results prove the validity of the developed single-master multi-slave system.     

A new desk-top encounter-type haptic device with an actively driven pen-tablet LCD panel

In conventional haptic devices for virtual reality (VR) systems, a user interacts with a scene by handling a tool (such as a pen) using a mechanical device (i.e. an end-effector-type haptic device). In the case that the device can ‘mimic’ a VR object, the user can interact directly with the VR object without the mechanical constraint of a device (i.e. an encounter-type haptic device). A new challenge of an encounter-type haptic device is displaying the visuals and haptic information simultaneously on a single device. We are proposing a new desk-top encounter-type haptic device with an actively driven pen-tablet LCD panel. The proposed device is capable of providing pseudo-3D visuals and haptic information on a single device. As the result, the system provides to the user a sense of interaction with a real object. To develop a proof-of-concept prototype, a compact parallel mechanism was developed and implemented. The aim of this research is to propose a new concept in haptic research. In this paper, the concept, the prototype, and some preliminary evaluation tests with the proposed system are presented.     

Design and Control of Five-Fingered Haptic Interface Opposite to Human Hand

This paper presents the design and control of a newly developed five-fingered haptic interface robot named HIRO II. The developed haptic interface can present force and tactile feeling to the five fingertips of the human hand. Its mechanism consists of a 6 degree of freedom (DOF) arm and a 15 DOF hand. The interface is placed opposite the human hand, which ensures safety and freedom of movement, but this arrangement leads to difficulty in designing and controlling the haptic interface, which should accurately track the fingertip positions of the operator. A design concept and optimum haptic finger layout, which maximizes the design performance index is presented. The design performance index consists of the product space between the operator's finger and the hapic finger, and the opposability of the thumb and fingers. Moreover, in order to reduce the feeling of uneasiness in the operator, a mixed control method consisting of a finger-force control and an arm position control intended to maximize the control performance index, which consists of the hand manipulability measure and the norm of the arm-joint angle vector is proposed. The experimental results demonstrate the high potential of the multifingered haptic interface robot HIRO II⁺ utilizing the mixed control method.     

New Multi-d.o.f. Haptic Device Using a Parallel Mechanism with a Wide Rotational Working Area

A parallel mechanism is a multi-legged kinematic structure with actuators fixed on the base. In recent years, parallel mechanisms have been implemented in haptic devices due to their benefits, such as high rigidity, high output force, high accuracy and high backdrivability. Multi-d.o.f. haptic devices with rotational motion have become increasingly important as haptic applications have become diversified (e.g., in surgical training). However, typical multi-d.o.f. parallel mechanisms (e.g., Stewart platform and HEXA) have limitations on the working area for rotational motions. A multi-d.o.f. haptic device can be designed by stacking the translational and rotational mechanisms by decoupling these motions. However, this dedoupling can have an adverse effect on inertia because of the weight of the stacking mechanism. Eventually, the operability of the device deteriorates. Therefore, a parallel mechanism with both a translational and rotational multi-d.o.f. structure can effectively apply the full advantages of a parallel mechanism to a multi-d.o.f. haptic device. In this paper, a 6-d.o.f. (five active: three translations, two rotations and one passive rotation) parallel mechanism, called the D-8, is presented. In the D-8, a new redundant parallel mechanism is introduced to overcome the problem of operability.     

A geometric constraint-based approach to force and motion coupling between real and virtual mechanisms

This paper presents a new stable controller design for use with a general 6-d.o.f. robotic haptic device. A virtual manipulator concept is developed that couples the haptic device kinematics with the constraints of a simulated manipulator. Using impedance-based constraints, the haptic device is controlled to oppose applied forces in directions orthogonal to the motions of the virtual manipulator. The virtual manipulator kinematics constrains the haptic device motion, allowing motion to simulate specific virtual mechanisms. The implementation is illustrated using experimental simulations.     

A Survey of Haptic Rendering Techniques

Computer Graphics technologies have developed considerably over the past decades. Realistic virtual environments can be produced incorporating complex geometry for graphical objects and utilising hardware acceleration for per pixel effects. To enhance these environments, in terms of the immersive experience perceived by users, the human's sense of touch, or haptic system, can be exploited. To this end haptic feedback devices capable of exerting forces on the user are incorporated. The process of determining a reaction force for a given position of the haptic device is known as haptic rendering. For over a decade users have been able to interact with a virtual environment with a haptic device. This paper focuses on the haptic rendering algorithms which have been developed to compute forces as users manipulate the haptic device in the virtual environment.     

Stable haptic interaction using a damping model to implement a realistic tooth-cutting simulation for dental training

It is difficult to implement a stable and realistic haptic simulation for cutting rigid objects that is based on a damping model because of an inevitable conflict between stability and high output force. This paper presents passivity techniques to show that an excessive damping coefficient causes the output stiffness to exceed the maximum output stiffness of the haptic device, leading to instability. By analysing the damping model of a haptic dental-training simulator, we construct a relationship among the damping coefficient, position resolution, sampling frequency, human operation, and the maximum achievable device stiffness that will still maintain device stability. A method is also provided to restrict the output stiffness of the haptic device to ensure stability while enabling the realistic haptic simulation of cutting rigid objects (teeth) that is based in a damping model. Our analysis and conclusions are verified by a damping model that is constructed for a dental-training haptic display. Three types of haptic devices are used in our analysis and experiments.     

Haptic display of micro surface undulation based on discrete mechanical stimuli to whole fingers

Humans can perceive a wide and small surface undulation that is hundreds micrometers in height and hundreds millimeters in width by scanning the surface with their whole fingers and palm in the distal and proximal directions. We developed a wearable haptic device that presents a surface undulation to the hand. The device is composed of nine independent stimulator units that control the heights of nine finger pads of the index finger, the middle finger, and the ring finger (three units on each finger) according to the virtual surface. Three experiments are carried out to evaluate the haptic perception by the haptic device. A first experiment shows that the perceived dimensions are diminished as compared to the dimensions applied by the haptic device. On the basis of this result, the applied dimensions are calibrated to match the virtual surface undulation to the real surface undulation. A second experiment shows that the shape of gently-curved surfaces can be estimated with the haptic display. A third experiment shows that the discrimination threshold is not different between the virtual surface undulation and the real surface undulation. These experimental results show the applicability of the haptic device as a haptic interface.     

基于力觉交互的高速率精准操作技能训练方法

介绍了用力觉交互技术进行手眼协调高速率精准操作的动作技能训练方法。提出了记录播放和轨迹智能导引两种培训模式。在记录培训模式中,采用PD控制的方法使学员被动感受专家的运动信息。在智能导引纠正模式中,学员主动操作交互设备,计算机根据学员的操作情况控制交互设备输出导引力或纠正力。最后,采用Omega 3DOF建立了具备触觉显示和图形显示功能的“信封靶”描绘技能训练系统样机平台,分析了力模型参数对系统稳定性的影响。实验结果证明了培训方法的可行性。     

Effects of using a force feedback haptic augmented simulation on the attitudes of the gifted students towards studying chemical bonds in virtual reality environment

The aim of this study is to identify the effects of force feedback haptic applications developed in virtual reality environments (VREs), which is an important field of study in computer science and engineering, on gifted students’ attitudes towards chemistry education in learning process. A 3D 6 DOF (Degree of Freedom) haptik device (Phantom Omni?) has been used to develop the algorithm in this study. It can be used to transmit force and motion using a haptic device. Visual C++ was choosen as the software development environment. OpenGL? and Haptic Device Application Programming Interface have been used for rendering graphics. At the 3D image creation state Wrap 1200?, which is a kind of head-mounted display, has been chosen. The sample of this study consists of 52 students identified as gifted and are attending 6th and 7th grades at the Istanbul Science &; Art Center in Istanbul. The experimental group studied chemical bonds using an application developed by using a force feedback haptic device in VRE and the control group studied it by traditional teaching methods. The study reveals that there is a relation between using force feedback haptic applications which are developed in VREs and gifted students’ attitudes towards educational programs.     

力反馈主手研究现状及其力控制方法研究

力觉主手作为主从遥操作机器人系统的关键部件,其机构特性和力控制性能直接关系到整个遥操作系统能否完成预期的任务要求。近年来,关于力觉主手及其力控制方法的研究已成为机器人遥操作领域的研究热点。文中详细介绍了力觉主手在机构设计和力控制算法方面研究现状和发展趋势。     

虚拟装配中基于导纳控制的力觉渲染技术

传统的力触觉渲染多采用阻抗控制,不能很好地满足虚拟装配的应用要求,相比之下导纳控制模式更适用这一领域.为此提出一种基于导纳控制的双线程力觉渲染构架,并给出相应的力觉渲染算法.首先建立用于导纳控制的动力学模型,并讨论了碰撞和约束这2个状态下的力觉渲染;为了使用力觉交互接口进行虚拟装配中的小间隙装配,提出物理约束与几何约束结合的力觉渲染方法;最后针对物理计算和力反馈循环2个线程刷新频率不匹配的问题,利用二次拉格朗日多项式进行数值插值,实现了力觉交互接口的平稳输出.通过力反馈设备与自主开发的虚拟装配原型系统VAPP的连接与应用,验证了所提出的算法满足虚拟装配系统中力觉交互的应用要求.     

Energy-based control of a haptic device using brakes.

This paper proposes an energy-based control method of a haptic device with electric brakes. Unsmooth motion is frequently observed in a haptic system using brakes during a wall-following task. Since it is generally known that a haptic system using brakes is passive due to brake's characteristics, its energy behavior has seldom been investigated. However, force distribution at the end effector reveals that the unsmooth motion of a haptic system using brakes represents active behavior of the system in the specific direction. A force control scheme is proposed that computes the gain for smooth motion by considering the energy behavior of a system. Experiments show that smooth wall following is possible with a proposed force control scheme.     

Haptic teleoperation of a multirotor aerial robot using path planning with human intention estimation

Classical haptic teleoperation systems heavily rely on operators’ intelligence and efforts in aerial robot navigation tasks, thereby posing significantly users’ workloads. In this paper, a novel shared control scheme is presented facilitating a multirotor aerial robot haptic teleoperation system that exhibits autonomous navigation capability. A hidden Markov model filter is proposed to identify the intention state of operator based on human inputs from haptic master device, which is subsequently adopted to derive goal position for a heuristic sampling based local path planner. The human inputs are considered as commanded velocity for a trajectory servo controller to drive the robot along the planned path. In addition, vehicle velocity is perceived by the user via haptic feedback on master device to enhance situation awareness and navigation safety of the user. An experimental study was conducted in a simulated and a physical environment, and the results verify the effectiveness of the novel scheme in safe navigation of aerial robots. A user study was carried out between a classical haptic teleoperation system and the proposed approach in the identical simulated complex environment. The flight data and task load index (TLX) are acquired and analyzed. Compared with the conventional haptic teleoperation scheme, the proposed scheme exhibits superior performance in safe and fast navigation of the multirotor vehicle, and is also of low task and cognitive loads.

     

On the role of dissipation in haptic systems

Passivity theory has been used for the past decade to derive stability conditions for human/machine interface applications. Demonstrating passivity of the haptic display implies stable and safe interaction for the human user. At the heart of the stability analysis is the physical dissipation provided by the haptic device, as it plays a key role in the design process for all components. This paper will derive the condition that the haptic device must satisfy in order to achieve passivity of the haptic display. These results will be used to investigate a general nonlinear device model.     

A haptic-rendering technique based on hybrid surface representation

A novel haptic rendering technique using a hybrid surface representation addresses conventional limitations in haptic displays. A haptic interface lets the user touch, explore, paint, and manipulate virtual 3D models in a natural way using a haptic display device. A haptic rendering algorithm must generate a force field to simulate the presence of these virtual objects and their surface properties (such as friction and texture), or to guide the user along a specific trajectory. We can roughly classify haptic rendering algorithms according to the surface representation they use: geometric haptic algorithms for surface data, and volumetric haptic algorithms based on volumetric data including implicit surface representation. Our algorithm is based on a hybrid surface representation - a combination of geometric (B-rep) and implicit (V-rep) surface representations for a given 3D object, which takes advantage of both surface representations.     

柔顺性触觉再现技术的研究

柔顺性触觉再现的研究难点主要集中在对触觉机理了解不深入、动态的感知过程、装置性能有限等方面.介绍了当前几种有代表性的柔顺性触觉再现装置:基于电流变液的触觉再现装置、气囊触觉再现装置、气动阵列触觉再现装置和基于弹性梁触觉再现装置.在此基础上讨论了这些装置的优缺点,并进行了比较.最后总结了柔顺性触觉再现技术的发展思路.     

Rendering stiffer walls: a hybrid haptic system using continuous and discrete time feedback

Instability in conventional haptic rendering destroys the perception of rigid objects in virtual environments. Inherent limitations in the conventional haptic loop restrict the maximum stiffness that can be rendered. In this paper we present a method to render virtual walls that are much stiffer than those achieved by conventional techniques. By removing the conventional digital haptic loop and replacing it with a part-continuous and part-discrete time hybrid haptic loop, we were able to render stiffer walls. The control loop is implemented as a combinational logic circuit on an field-programmable gate array. We compared the performance of the conventional haptic loop and our hybrid haptic loop on the same haptic device, and present mathematical analysis to show the limit of stability of our device. Our hybrid method removes the computer-intensive haptic loop from the CPU—this can free a significant amount of resources that can be used for other purposes such as graphical rendering and physics modeling. It is our hope that, in the future, similar designs will lead to a haptics processing unit (HPU).