Jinah Park

Real-time area-based haptic rendering and the augmented tactile display device for a palpation simulator

Although people usually contact a surface with some area rather than a point, most haptic devices allow a user to interact with a virtual object at one point at a time and likewise most haptic rendering algorithms deal with such situations only. In a palpation procedure, medical doctors push and rub the organs surface, and are provided the sensation of distributed pressure and contact force (reflecting force) for discerning doubtable areas of the organ. In this paper, we suggest real-time area-based haptic rendering to describe distributed pressure and contact force simultaneously, and present a haptic interface system to generate surface properties in accordance with the haptic rendering algorithm. We represent the haptic model using the shape-retaining chain link (S-chain) framework for a fast and stable computation of the contact force and distributed pressure from a volumetric virtual object. In addition, we developed a compact pin-array-type tactile display unit and attached it to the PHANToMTM haptic device to complement each other. For the evaluation, experiments were conducted with non-homogenous volumetric cubic objects consisting of approximately 500 000 volume elements. The experimental results show that compared to the point contact, the area contact provides the user with more precise perception of the shape and softness of the objects composition, and that our proposed system satisfies the real-time and realism constraints to be useful for a virtual reality application.

Shape retaining chain linked model for real-time volume haptic rendering

Haptic rendering is the process of computing and generating forces in response to user interactions with virtual objects. While we speak of real-time volume rendering for visualization, we are still very much limited to Surface models for manipulation due to overwhelming computational requirements for volumetric models. In this paper, we propose a new volumetric deformable model that is suitable for volume haptic interactions. The volume elements of our proposed model are linked to their nearest neighbors and their displacements are transformed into potential energy of the virtual object. The original 3D ChainMail algorithm does not account the fact that the residual energy left in the object after some interactions becomes a critical problem in haptic rendering. We present the shape-retaining chain linked model, which allows for fast and realistic deformation of elastic objects. Furthermore, we incorporate force-voltage analogy (duality) concepts into the proposed shape-retaining chain linked representation in order to develop a fast volumetric haptic model that is Suitable for realtime applications. We experimented with homogenous and non-homogenous virtual objects of size 75/spl times/75/spl times/75 volume elements, and we were able to verify real-time and realistic haptic interaction with a 3DOF PHANToM/spl trade/ haptic device.

The Real-Time Haptic Simulation of a Biomedical Volumetric Object with Shape-Retaining Chain Linked Model

This paper presents a new model which computes the deformation and the feedback force of high-resolution biomedical volumetric objects consisting of hundreds of thousands of volume elements. The main difficulty in the simulation of these high-resolution volumetric objects is to compute and generate stable feedback force from the objects within a haptic update time (1 msec). In our model, springs are used in order to represent material properties of volume elements and cylinders are used to activate corresponding springs according to the amount of deformation. Unlike in a mass-spring model, springs in our model have constraint conditions. In our model, the deformation is calculated locally and then is propagated outward through objects volume as if a chain is pulled or pushed. The deformed configuration is then used to compute the objects internal potential energy that is reflected to the user. The simple nature of our model allows the much faster calculation of the deformation and the feedback force from the volumetric deformable object than the conventional model (an FEM or a mass-spring model). Experiments are conducted with homogenous and non-homogenous volumetric cubic objects and a volumetric human liver model obtained from CT data at a haptic update rate of 1000 Hz and a graphic update rate of 100 Hz to show that our model can be utilized in the real-time volume haptic rendering. We verify that our model provides a realistic haptic feeling for the user in real time through comparative study.

Real-time haptic rendering of a high-resolution volumetric deformable object in a collaborative virtual environment

A collaborative virtual environment (CVE) is a shared environment that allows geographically separated users to watch and manipulate the same object at the same time. This paper presents a fast haptic rendering method when users interact with a virtual object at multiple points or multiple areas in a CVE. Previously, we proposed a new model (Shape-retaining Chain Linked Model) for real-time volume haptic rendering. The haptic rendering of an object represented by our model guarantees real-time performance because the deformation of the object is computed locally and is then propagated outward through its volume. However, this local computation approach presented us with a new issue for handling virtual deformable objects in a CVE, where interactions occur at multiple points or multiple areas. In order to overcome the limitation of the local computation, we construct a modeling framework that allows colliding interactions among geographically separated users. For the modeling framework, we vectorially sum forces generated at interaction points or areas. In order to inspect the behavior of objects modeled with our method, experiments are conducted with volumetric objects consisting of about 500 000 nodes at a haptic update rate of 1000 Hz. We perform a calculation time analysis to investigate real-time performance and conduct human factor studies to show that the feedback force from our model is realistic. Our experiments verify that our model provides realistic haptic feeling to participants in real-time under a CVE.

Area-contact haptic simulation

This paper presents the haptic interaction method when the interaction occurs at several points simultaneously. In many virtual training systems that interact with a virtual object, the haptic interface is modeled as a point. However, in the real world, the portion interacting with real material is not a point but rather multiple points, i.e., an area. In this paper, we address an area-based haptic rendering technique that enables the user to distinguish hard regions from softer ones by providing the distributed reflected force and the sensation of rotation at the boundary. We have used a shape retaining chain linked model that is suitable for real-time applications in order to develop a fast area-based volume haptic rendering method for volumetric objects. We experimented with homogeneous and non-homogeneous virtual objects consisting of 421,875 (75×75×75) volume elements.

Multiple-contact representation for the real-time volume haptic rendering of a non-rigid object

This paper presents a fast haptic rendering method providing the sense of touch from a virtual volumetric non-rigid object when a human operator interacts with the object at multiple points. Previously, we have proposed a fast volume haptic rendering method based on the shape-retaining chain linked model (or the S-chain model) that can handle the deformation of a volumetric non-rigid object and its haptic feedback in real time. One of the key differences between the S-chain model and a traditional FEM or mass-spring model is that the computation of the deformation and its reflected force is performed at a local level. When there are more than one interaction points with the object, it is necessary to consider a modeling framework that can handle human operators all inputs together. In this paper, we propose a modeling framework in which forces generated at interaction points are vectorially summed to deal with the multiple contact points. Our experiments demonstrate that our proposed method is suitable for the real-time volume haptic rendering of a volumetric non-rigid object with multiple-contact points.

Real-Time area-based haptic rendering for a palpation simulator

In palpation procedure, medical doctors push and rub the organs surface and they are provided the sensation of distributed pressure and contact force (reflecting force) for discerning doubtable portion. This paper suggests a real-time area-based haptic rendering model to describe distributed pressure and contact force simultaneously and present a haptic interface system to generate surface property in accordance with the haptic rendering algorithm. We represent the haptic model using the shape-retaining chain link (or S-Chain) framework for a fast and stable computation of the contact force and distributed pressure from a volumetric virtual object. In addition, we developed a compact pin-array type of tactile display unit and attached it to PHANToMTM haptic device to complement each other. In order to evaluate the performance of the proposed scheme, related experiments have been conducted with non-homogenous volumetric cubic objects consisting of approximately 500,000 volume elements at a haptic update rate of 1000 Hz. The experimental results show that compared to the point-contact the area-contact provides the users with more precise perception of the shape and softness of the objects composition, and that our proposed system satisfies the real-time and realism constraints to be useful for virtual reality applications

Mechanical Representation of Shape-Retaining Chain Linked Model for Real-Time Haptic Rendering

We have earlier proposed a voxel-based representation of an elastic object that can respond to a user’s input in real-time for haptic rendering. We called it shape-retaining chain-linked model or S-chain model. The S-chain model is constructed from the 3D voxel data of an object, where each voxel is a chain element that is linked to its six nearest neighbors. Its deformed configuration is computed, upon the user’s input, by propagating outward the unabsorbed input force from the interaction point as if a chain is pulled or pushed. The deformed configuration is then used to compute its disturbed internal energy that is reflected to the user. The basic idea of force rendering is that the reflected force is proportional to the number of chain elements that are displaced from its initial position. This simple nature of the model allows very fast deformation of a volumetric object so that it can be utilized in real-time applications. In this paper, we present a mechanical interpretation of the haptic model as to how the reflected forces are being computed by utilizing spring-and-cylinder units. Furthermore, we investigate the quality of the haptic feeling of the S-chain model by comparing with that of FEM against the human haptic perception. The result of our experiments demonstrates that S-chain model provides not only the real-time performance but also the quality of FEM with respect to our haptic sense.

Evaluation of Areal Touch Feedback for Palpation Simulation

The effectiveness of the areal contact versus the point contact was experimented. We created virtual 3D cubic volumetric objects consisting of approximately 500,000 nodes. The object is placed on a plane so that the nodes at the bottom of the object are constrained. A user can interact with the object by pushing and pulling at the top surface of the object as shown in Figure 2. Figure 2 (a) and (b) are the configurations of pulling up, and pushing down, respectively, in the middle of the top surface with the haptic interface. The square-shaped areal contact was made with the tactile display unit attached to the gimbals of Phantom TM haptic device. For a point-based contact, only the Phantom haptic device was used for interaction with the virtual object. We constructed two volumetric soft objects where four hard blocks, which represents tumors, are placed inside of each soft volume as illustrated in Figure 3. Figure 4 shows the top view of the test volume objects. The test object (a) is used for the experiment with the point haptic feedback only, while the test object (b) is used for the experiment with the area-based haptic feedback with the augmented tactile display. We asked 20 human subjects to explore the objects with the haptic interface device, one without the tactile display unit and the other with the tactile display unit. Their task was to locate the hard portions (i.e., tumors) inside the volume, and they were asked to draw the tumors they found on a piece of paper. Each subject drew what he/she visualized the tumor’s location and size solely with the touch feedback. All subjects did not have a pre-knowledge of the number of tumors that they can find. Figure 5 shows the representative drawings done by the subjects. We can observe that the area-based haptic interface gave a superior results compare to the one with the point-based interface. With the point-based interface, most subjects missed the tumor #4 which is relatively small in size. However, all of them were detected with the area-based haptic interface. In palpation, it is important to find not only the number of tumors but also a precise location and the size of the tumors. We defined the accuracy measures concerning the center location of the tumor and the actual size of the tumor. Table 2 and 3 shows the average errors computed against the accuracy measures. Although there seems to be an intrinsic source of error due to human perception, our results clearly demonstrates that areal haptic feedback provides a better visualization of the object.

Real-time Simulation of Seas and Swells for Ship Maneuvering Simulators

Seas and swells are basic wave types in ocean surface simulation and are very important elements in the simulation of ocean background. In this paper, we propose a real-time simulation method, for reproducing realistic seas and swells, to be used in real-time simulators such as ship maneuvering simulators. Seas and swells have different visual properties. Swells have relatively longer wavelengths and round crests compared with seas, therefore they are visualized globally with large meshes and procedural methods. Parameters to illustrate swells are extracted from ocean wave spectra. Conversely, seas have shorter wavelengths and their characteristics are only clearly apparent near to the observation point. Here, we present visualization of seas based on a statistical wave model using ocean wave spectra, which provides realistic results in a reactively small area.