Research outline
1. The VCAD System

Unlike conventional CAD, VCAD (=Volume CAD) is an integrated software system designed to handle not only the shape of objects, but also volume information, such as internal structure, defects, etc., aiming to support complex manufacturing. Here, "Integrated" means the integration of the Design, Measurement, Modeling, Simulation, Visualization, and Machining processes. In this way, VCAD transcends the framework of CAD.

The ability of VCAD to build models with complicated internal structures makes it suitable for applications not only to manufacturing, but also to some fields of medicine and biosciences.

The VCAD Program was launched in 2001 as a RIKEN project and ended in March 2011. However, software applications that have been developed within VCAD are expected to be both expanded and upgraded. Maintenance will also be continued.

2. Structure of VCAD System

Figure 1 shows the structure of the VCAD system. It consists of four processes: Input, Modeling, Simulation, and Machining. Data that can be input into the VCAD system includes not only design data (like conventional CAD), but also "surface shape data" acquired from 3D shape measurement devices, as well as data obtained by measurement of internal structures and defects of objects, e.g. by using X-ray CT, 3D internal structure microscope, confocal laser microscope, etc.

VCADシステムの全体像

Figure 1. Structure of the VCAD System

Shape data imported into the VCAD system is made up of discretized point groups, while structure data is composed of 3D image data. These types of data are converted to implicit function shape expressions in the Modeling process or to shape and structure models using a method for extracting the region of interest.

In the Modeling process, shape and structure models are further converted into analysis models for thermal fluid analysis, structural analysis, optical path analysis, etc., after which the data is sent to the Simulation process.

In the Simulation process, simulation is carried out on the behavior of thermofluid systems, deformation and fracture, optical path, biomechanical systems, and cellular biology, while the results are visualized. The aim of VCAD is to ensure smooth data flow between these processes. We also developed CAM functions for precision machining, such as Nagata patches, which are able to handle highly precise shape expression data unique to VCAD.

3. Research and Development Activities of VCAD Program

The Integrated Volume-CAD System Research Program launched in 2001 in RIKEN aimed to realize a method which can directly express complicated internal structures and physical attributes of objects on the computer, in other words, a method that can express "Volumetric Objects" and use the data acquired to integrate design (CAD), measurement (CAT), simulation (CAE), and machining (CAM). We thus named this approach "Volume-CAD System" to mean a technique capable of expressing the volume information of objects.

"Volume Data Structure" is a simple and clear method for representing "Volumetric Objects", which is realized by dividing the solid and fluid spaces into an equally distance grid (each unit of the divided space is called cell), and the object boundary information is explicitly assigned to the cell, and if necessary, the cell can be divided into octree sub-cells.

VCADシステムの全体像

Figure 2 Expression of Kitta Cube Expressing Space and Boundary

We called each of these cells "Kitta Cube" and named the software application used to generate such cell data "VCAD Framework". With this framework, it was thought that the surfaces and internal spaces can be discretized in the same manner using the cells as the unit of space, and that the structured data can also be directly used for analysis. This seemed easy at first, but we encountered numerous difficulties. One was the limited freedom of the shape expression. For instance, we were not able to express ridges and pyramidal points of object surfaces as desired. We were also not able to control the shape and the size of finite elements at boundary cells when conducting finite element structural analyzes. Furthermore, in fluid analyzes, numerous types of boundary shape appeared inside the cells, rendering their analysis quite difficult.

Therefore, we improved the Kitta Cube cells and developed two additional expression methods. One method is based on signed-distance functions for expressing fluid space, by using octree cell structures similar to the Kitta Cube, which however does not express the boundary face explicitly.

The other method is designed for structural analysis, generating finite elements whose size and shape are controlled along the boundary, taking cell structure focusing on the surface and boundary face of objects as its template.

As important fundamental technologies of the VCAD system, we finally developed two new three-dimensional shape expression methods. One, named SLIM, is designed to express shape boundaries using implicit functions, and the other, called Nagata patch, can explicitly and accurately describe faces as piecewise quadratic triangles. The first method is suitable for generating boundary faces from measured surface point data, and the second method is an excellent expression capable of preventing C0-dicontinuities across neighboring patches, a problem which has been difficult to solve with conventional CADs.

Based on the results of such fundamental research, we launched the "VCAD System Research Program" from April 2006. The goal of the second phase project was to sophisticate and integrate the technologies developed in the first phase, and develop a system which can be applied to real product designs and manufacturing.

It is worth noting that in this second phase, we also added bioscience fields to the applications of the VCAD system, and undertook two research and development themes in this area. The aim of the first theme, targeting cellular biology, was to eliminate noise from three-dimensional data along the time axis within a fully four-dimensional dataset obtained by confocal laser microscope, etc., extract areas of interest, quantify the properties, and model them. The other theme was to model the behavior of actin filaments of moving cells in multi-scale dynamics based on measurement results, with the aim to understand the behavior of living cells both mechanically and biochemically.

4. VCAD Software Released to the Public

Figure 3 shows the software programs released to public, and specifically illustrates the basic structure of VCAD shown in Figure 1. The Modeling process consists of the block generating shape models [1] and the block creating structure models [2]. From the modeling to simulation processes, there are five horizontally long blocks from [3] to [7]. Each block consists of a series of software applications for generating analysis models, for dynamical and optical analyses, and for visualization of the results.

VCADシステムの全体像 「形」の離散モデル作成 「もの」の構造/欠陥の離散モデル作成 VCAD Framewordベースの構造・流体解析 ボクセルベースの熱流体解析 有限要素法による非線形構造解析" 超精密光学素子の光路解析 細胞のモデル化、シミュレーション 精密加工

Figure 3. VCAD software released to public

Clicking a block jumps to its detailed explanation.