New colonoscopy simulator with improved haptic fidelity

Colonoscopy is a safe and effective procedure to diagnose and treat the large bowel with the help of the flexible endoscope. This paper presents a new colonoscopy training simulator to help trainees practice and acquire the necessary skills and experiences with no risk to the patients and possibly less cost. The simulator includes a specialized haptic interface to transfer force feedback through a long and flexible tube, and graphics algorithms to display the virtual colon realistically while managing the large number of polygons. A new 2-d.o.f. haptic device with folding guides is developed to transmit large decoupled forces of the colonoscopy simulation to the user. The physicians apply a jiggling motion to the colonoscopy tube to advance the scope. This jiggling is an important skill of colonoscopy and is incorporated for the first time by using the new sensor mechanism. A colonoscope handle that shares the look, feel and functions with an actual colonoscope is developed with the necessary electronics inside. The simulator contains controllers to compensate for the inertia and friction effects, and is evaluated by physicians. New graphics algorithms including polygon reduction, navigation and collision detection are developed to compute the deformation and the corresponding reflective force in real-time.     

Multi-Fingered Bimanual Haptic Interface Robot with Three-Directional Force Display

This paper introduces a bimanual haptic interface robot and presents results from its trial operation. Our aim in developing a bimanual haptic interface is to display high-precision three-directional forces at all 10 fingertips of both hands of the operator. By installing two five-fingered robot hands and two robot arms, we construct a bimanual haptic interface. A haptic interface that consists of robot hands and robot arms can provide multi-point contact between the operator and a virtual environment. However, there is the risk that robot hands and robot arms will collide while an operator is manipulating the haptic interface. To solve this problem, we also propose a collision avoidance control law for the multi-fingered bimanual haptic interface. Finally, to determine the validity of the proposed interface, we carry out several experiments. These results show the validity and great potential of the proposed bimanual haptic interface.     

Feeling a rigid virtual world through an impulsive haptic display

In this paper the first haptic display capable of applying a true impulse to the operator is presented. The applied impulse results in an immediate change of the user's momentum. Such a change is considered to be invaluable in making interactions with rigid virtual objects feel realistic. Conventional methods can only approximate impulses by outputting a constant force over a certain number of sample periods. The quality of these impulses is therefore limited by the maximum torque of the motor. At high interaction velocities these methods lose realism. The usage of large motors not only brings along safety issues, it also compromises the feeling of free motion. The new haptic display can generate an arbitrarily large impulse by continuously adapting the amount of momentum of a momentum wheel. At the predicted instant of contact with the virtual object, an electromagnetic tooth-clutch is engaged. The momentum wheel is mechanically connected to the handle of the haptic display and a real, but controlled, collision between the operator and momentum wheel is realized. The impulse generation part of the device is in fact the first 'generalized encountered haptic display'. Like typical encountered haptic displays its influence is not felt in free motion, but in contrast to them it is not limited to only static encounters, but effectively applicable to make encounters over a full velocity spectrum.     

Accurate force reflection method for a multi-d.o.f. haptic interface using instantaneous restriction space without a force sensor in an unstructured environment

This paper proposes an accurate force reflection method for a multi-d.o.f. haptic interface without a force sensor. Sensorless force reflection is possible using position–position (p–p) architecture. However, the conventional p–p architecture in the literature has limitations representing constraint space when it is applied to a multi-d.o.f. haptic interface in that it gives an inaccurate force direction. This paper demonstrates the limitation of the conventional p–p architecture through an example and proposes a novel force reflection method using the instantaneous restriction space (IRS) concept. The IRS can be calculated using the Jacobian and joint angle error of a slave manipulator. Since the proposed method has the form of an impedance two-port architecture in the sense of data flow, it can be easily combined with previous well-known results of two-port haptic display frameworks. The proposed method is especially useful when the slave manipulator collides with unexpected obstacles during motion, even though the slave does not have a force sensor. The performance of the proposed method is evaluated through experiments.     

Design and validation of a complete haptic system for manipulative tasks

The present work deals with the design, implementation and assessment of a new haptic system specifically conceived for manipulative tasks in virtual environments. Such a system was designed by taking into account specific issues related to fine manipulation, such as multipoint haptics, coherence, transparency and physical representation. The haptic system described herein is integrated with a virtual environment engine for the simulation of multifinger manipulation. A preliminary evaluation of the system was conducted by comparing human performance in the manipulation of virtual objects with respect to real objects, according to the data available in the literature. The experiments confirm how the most relevant relationships among physiological and physical parameters involved in manipulation are also preserved during virtual manipulation. However, an in-depth analysis of the results shows that simulation parameters affect the level of force control during virtual manipulation and the quality of the perceived force feedback.     

A haptic representation system for a virtual plain wall

The purpose of this study is to develop a virtual wall display system for a walk simulator to grope its way in an 'invisible' situation, such as in a building filled with dense smoke, etc. To reproduce the realistic haptic sense of a building wall, the implementation of the wideness and the rigidity of wall are essential. Wideness of a virtual wall was realized by a hand-tracking control combined with a small wall panel which is mounted on a three-axis Cartesian manipulator. A 6-d.o.f. magnetic tracking system was utilized for the hand position tracking in the non-contact situation of the hand and the panel. In the contact situation, high rigidity of the wall was attained as stiffness in the normal direction is provided to the wall panel to represent the haptic sense of a rigid wall. Force-based tracking provides the low stiffness in the tangential direction to make the wall panel move easily along the direction of hand movement to represent a wide plain wall. A three-axis force sensor is attached on the wall panel to detect the contact force. The realization of smooth switching between both tracking controls provides the user with the haptic feel of the presence and continuity of a virtual wall. In addition, the frictional sensation has the effect of giving the system more reality. Experimental results have shown the effectiveness of the hybrid tracking method for the virtual wall system.     

Development of a high-performance haptic telemanipulation system with dissimilar kinematics

This work addresses selected practical issues regarding the development of a telerobotic system for 6-d.o.f. tasks. The system consists of a hyper-redundant 10-d.o.f. haptic input device ViSHaRD10, a redundant 7-d.o.f. manipulator and a stereo vision system. The redundancy of the haptic input device is exploited to assure large convex workspaces and singularity-free operation. The anthropomorphic construction of the telemanipulator enables intuitive manipulation and increases the user-friendliness of the overall system. As a practical benchmark, an assembly experiment in 6 d.o.f. for the case of a negligible time delay was performed. Issues regarding inverse kinematics, spatial interaction control, transparency and intuitiveness of teleoperation are discussed.     

Haptic interface through wave transformation using delayed reflection: application to a passive haptic device

From the viewpoint of passivity, it is well known that wave variables are robust to transmission delay of a system. During wave transformation for the sampled-data system, a unit delay arises due to causality of the reflection wave. This delay makes the wave transformation in the sampled-data system different from the standard one in the continuous-time system. The unit delay on the reflection wave occasionally becomes a passive element. From the passivity condition of the sampled-data system, the wave impedance can be designed such that wave transformation using delayed reflection provides the effect of positive damping and thus a stable haptic interface is achieved in the sampled-data system. For a passive haptic device, although it is always considered stable because of its passive nature, the oscillatory motion appears during the wall-following task with force approximation. Various experiments for a two-linked passive haptic device show that a stable haptic interface can be accomplished for the wall-following task through wave transformation using delayed reflection.     

Robot-assisted evaluation of coordination between grasp and load forces in a power grasp in humans

A novel approach for evaluation of a grasp in humans is presented. The key novelty is combination of a haptic interface with force/torque transducers for measuring the grasp force. This paper presents results of grasp and load force coordination for quasi-static and dynamic external load force disturbances for a power grasp. An elevation of the grasp force is observed in a dynamic task. Elevation of the grasp force is needed for an additional safety margin to ensure a stable grasp.     

Force-guided motions of a 6-d.o.f. industrial robot with a joint space approach

This article deals with the interaction between humans and industrial robots, more specifically with the new design and implementation of an algorithm for force-guided motions of a 6-d.o.f. robot. It may be used to comfortably teach positions without using any teaching pendant or for some assistance tasks. For this purpose, from readings of the force/torque sensor mounted in the robot wrist, the gravity forces and torques first have to be eliminated. To control the robot in joint space, it is then convenient to transform the external force and torque values from Cartesian space into joint space using the manipulator transposed Jacobian. This is why with the present approach the Jacobian matrix of the robot used was calculated. Now, from the computed joint torques, suitable position commands of the robot arm can be generated to obtain the desired behavior. A suggestion for this desired behavior is also included in this article. It is based on the impedance control approach in joint space. The proposed algorithm was implemented with the standard Stäubli RX90B industrial robot.     

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.     

Image-based predictive display for high d.o.f. uncalibrated tele-manipulation using affine and intensity subspace models

The addition of immediate but estimated visual feedback, called predictive display, improves tele-manipulaton performance when the real video feedback is delayed. Current systems typically rely upon a previously calibrated camera and manipulator. We present a method where the motor-visual calibration is estimated on-line from motor commands and returned video images only. Predicted visual feedback is presented in two forms. As soon as a basic model has been estimated, a wire frame drawing of the predicted current pose is overlaid on the delayed video feedback. After some time when a rich model has been estimated, predicted intensity images are synthesized and these replace the delayed real video. In an intermediate situation where blurry synthesized images can be computed, the wireframe is overlaid on the synthesized images to show precisely the pose of the object. Experiments with a Utah/MIT robot hand and PUMA robot arm are shown.     

Dynamic Formulation and Performance Evaluation of the 6-d.o.f. Parallel Structure Seismic Simulator

This paper presents the dynamic formulation and performance evaluation of the 6-d.o.f. parallel structure seismic simulator. By means of the principle of virtual work and the concept of link Jacobian matrices, the inverse dynamic model of the seismic simulator is set up. Then, a series of new dynamic performance indices with obvious physical meanings have been proposed. The dynamic performance index combining the acceleration, velocity and gravity terms of the dynamic equations has been achieved by decoupling the inverse dynamics in an exhaustive way. By using the index, it is possible for us to evaluate the performance in different directions. The index has been applied to the dynamic characteristic evaluation of the 6-d.o.f. parallel structure seismic simulator in the numerical simulation. Conclusions and results are provided at the end of the paper.     

Workspace Determination of General 6-d.o.f. Cable Manipulators

This paper addresses workspace determination of general 6-d.o.f. cable-driven parallel manipulators with more than seven cables. The workspace under study is called force-closure workspace, which is defined as the set of end-effector poses satisfying the force-closure condition. Having force-closure in a specific end-effector pose means that any external wrench applied to the end-effector can be balanced through a set of non-negative cable forces under any motion condition of the end-effector. In other words, the inverse dynamics problem of the manipulator always has a feasible solution at any pose in the force-closure workspace. The workspace can be determined by the Jacobian matrix and, thus, it is consistent with the usual definition of workspace in the robotics literature. A systematic method of determining whether or not a given end-effector pose is in the workspace is proposed. Based on this method, the shape, boundary, dimensions and volume of the workspace of a 6-d.o.f., eight-cable manipulator are discussed.     

High-speed visual servoing of a 6-d.o.f. manipulator using multivariable predictive control

This paper presents a new approach to model and control high-speed 6-d.o.f. visual servo loops. The modeling and control strategy take into account the dynamics of the velocity-controlled 6-d.o.f. manipulator as well as a simplified model of the camera and acquisition system in order to significantly increase the bandwidth of the servo loop. Multi-input multi-output generalized predictive control (GPC) is used to optimally control the visual loop with respect to the proposed dynamical model. The predictive feature of the GPC is used for optimal trajectory following in Cartesian space. Experimental results on a 6-d.o.f. industrial robot are presented that validate the proposed model. The visual sensor used in the experiments is a high-speed camera that acquires 120 non-interlaced images. Using this camera, a sampling rate of 120 Hz is achieved for the visual loop. Furthermore, a precise synchronization method is used to reduce the delays due to image transfer and processing. The experiments show a drastic improvement of the loop performance with respect to more classical control strategies for 6-d.o.f. visual servo loops.     

TORSO: Development of a Telexistence Visual System Using a 6-d.o.f. Robot Head

In telexistence master–slave systems, it is important to transmit visual information from remote places to the operator. Conventional imaging devices in head-mounted displays (HMDs) can only express the three-axis rotation of the neck. However, humans can obtain broader visual fields and motion parallax information from the translational motion of their necks. We have proposed a system that can acquire natural and comfortable visual information, and can accurately track the head motion of a person. Our proposed device can express the head motion and the translation movements of the neck. We have developed a robot, called 'TORSO', and constructed a telexistence visual system with a display device, HMD. In this paper, by means of a broader field of view achieved by motion involving looking around, we demonstrate the advantage and novelty of our proposed system. In addition, we suggest the evolution of the TORSO–HMD system.     

Pneumatic impedance control of a 3-d.o.f. physiotherapy robot

Stroke is a common condition resulting in 30 000 people per annum left with significant disability. In patients with severe arm paresis after stroke, functional recovery in the affected arm is poor. Inadequate intensity of treatment is cited as one factor accounting for the lack arm recovery found in some studies. Given that physical therapy resource is limited, strategies to enhance the physiotherapists' efforts are needed. One approach is to use robotic techniques to augment movement therapy. A 3-d.o.f. pneumatic robot has been developed to apply physiotherapy to the upper limb. The robot has been designed with a workspace encompassing the reach-retrieve range of the average male. Slight non-linearities in the response of the pneumatic system are observed and explained. Building upon previous work that used an error-prone custom force sensor, a commercial 6-d.o.f. force sensor is used to apply impedance control in 3 d.o.f. on the robot.