Modeling of soft objects, measurement of elasticity, and real-time virtual system

一般来说，虚拟现实处理的对象是固体和坚硬的。然而，有许多物体既不是固体也不是硬的，即软的和可变形的物体。这项研究关注的是处理这类物体的方法。我们将定义柔软度并测量实际柔软的、可变形的物体的柔软度。研究的两个例子是人脸和硅胶立方体。软度被定义为力和位移之间的关系。为了表示软物体，我们采用弹簧网络模型，用弹簧连接两个相邻的节点。为了分配节点，我们使用气泡网格方法，在软区域放置等间距的气泡。通过Vornoi图确定气泡是否连通的标准。下一个问题是如何确定模型的弹簧常数。我们改变弹簧常数，直到在真实软物体和虚拟物体之间得到相同的力和位移关系。我们构建了一个专门设计的柔软度测量系统，该系统由激光位移装置和力测量装置组成。为了确定弹簧常数，我们让它在局部相等。我们在硅胶立方体上设置了5个测量点，在人脸上设置了9个测量点。在成功测量柔软度后，我们在PC上建立了一个带有力反馈装置PHANToM的虚拟现实系统。人们发现，这个系统能够给我们一种触摸硅胶立方体和人脸的错觉。预计该系统将为扩大虚拟现实领域对软物体的处理开辟一条新的途径。

Generally the objects that Virtual Reality deals with are solid and hard. However, there are many objects that are neither solid nor hard, i.e. soft and deformable objects. This research has been concerned with the approach to deal with such objects. We will define softness and measure the softness of actual soft, deformable objects. Two examples that were investigated are human face and a silicone cube. The softness has been defined as a relation between the force and displacement. To represent a soft object, we employed a spring network model which connects two adjacent nodes with a spring. In order to allocate nodes, we used a bubble mesh method which places equally spaced bubbles in a soft region. The criteria for deciding whether bubbles are connected or not was carried out through the Vornoi Diagram.Then the next problem is how to determine the spring constants of the model. We vary spring constants until the identical relation between force and displacement are obtainable between the real soft object and the virtual object. We constructed a specially designed system for measuring softness which consists of a laser displacement device and a force measurement device. To identify the spring constant, we set it to be identical locally. We set five measuring points on the silicone cube and nine points on a human face.After successful measurement of softness, we built a virtual reality system on a PC with a force feedback device, a PHANToM.It has been found that this system is able to give us an illusion of touching the silicone cube and the human face. It is expected that this system will open a new avenue for expanding the field of VR to treat soft objects.