Boolean operations are classic procedures in computer-aided design, and allow the creation of complex objects by combining simple objects. Although Boolean operations are trivial in implicit surface representations, they are problematic in polygonal meshes. Methods that directly use meshes to compute Boolean operations consistently consider the intersections between two faces without taking into account coplanar collisions. Thus, they either perturb the input meshes when colliding faces are coplanar or simply ignore this kind of collision. Most existing approaches for Boolean operations convert input meshes to volumetric representations such as binary space partitioning (BSP) and voxel grids. The output mesh is obtained by remeshing the resulting volumetric model. We propose a robust, exact, and simple method to manage Boolean operations between colliding shells without conversion and use a pure surface approach. The proposed method consists of three steps: (1) Calculating the intersections of input shells for both non-coplanar and coplanar collisions, (2) Decomposing the whole new mesh into its manifold components, and (3) Preserving only the components related to the requested operation (union or intersection). Subtraction operations are considered by reversing the surface orientation of the subtracted shell using the intersection operation. The output preserves the exact geometry of the input mesh while adding vertices for the remeshed colliding faces. In comparison with existing methods that use the mesh directly, the main advantage of the proposed method is that it processes coplanar collisions without geometrical modification, which avoids creating many small shells when two objects share the same part of the surface. Compared with methods using volumetric representation, the proposed method is faster and does not require input meshes without a boundary. We demonstrated the effectiveness of our method using synthetic models and real-world objects.
In the milling simulation of a large stamping die for an automobile part, a workpiece solid model is necessary as an input data. The initial shape of the workpiece is generally equivalent to an offset shape of the stamping die CAD model. Accurate offset shape is not a requirement on the workpiece solid model for the milling simulation. In this paper, we propose a novel method named “Simple Offset” for fast and stable generation of a simplified offset shape of a polyhedral solid model. In this method, surface points of the offset shape are sampled using 3 mutually perpendicular grids in the model space. The final offset shape is obtained by properly connecting the sampled points. Simplification level of the offset shape can be controlled by changing the resolution of the grids for sampling the surface points. An experimental system is implemented and some computation results are demonstrated.
Digital Signage has been evolved continuously over the years, and it has shown the potential in application of navigation recently. Comparing to conventional usage of advertisement and broadcasting, the interacting with digital signage has gained great interest for researchers due to hot issue of Internet of Thing. In these days, the ubiquity of smartphone and the development of sensor make it possible to apply more intuitive interaction with digital signage. A new navigation system which combined UHD (Ultra High Definition) display with personal smartphone is proposed. User is allowed to control Web-based 3D model instead of 2D subway map through smartphone's gyroscope sensor. In this paper, multi user access approach is proposed by applying multi sub-screen in UHD Signage system with BLE (Bluetooth Low Energy) tech and a novel WebSocket server design. Different from one-to-one control, this approach provides multi-to-multi accessibility that allows multiple users to access the navigation system simultaneously. A novel WebSocket server design reduces the delay and provides better control experience for multiple users' accession. This technology makes user able to access system sequentially, according to the access time and the distance between user and signage. The distance information is provided by iBeacon which attached to the UHD display. The result shows better feasibility when applied this navigation system to solve wayfinding problem inside complex subway station.
Asymptote is widely used in astronomy, mechanics, architecture and relevant subjects. In this paper, by analyzing the Frenet frame and the Darboux frame of a curve on the surface, the necessary and sufficient conditions for a quadrilateral boundary being asymptotic of a surface are derived. This quadrilateral is called asymptotic quadrilateral. Given corner data including positions, tangents and curvatures of a cubic B-spline quadrilateral with six control points in each boundary, a family of asymptotic quadrilaterals are constructed after solving the identification conditions of the control points. An optimized one is obtained by minimizing the strain energy of the boundary curves. Then, the transverse tangent vectors along the boundaries of the B-spline surface can be obtained by the asymptotic conditions and the resulting B-spline surface is of bi-quintic degree. Two arrays of control points of the surface along the quadrilateral are obtained from combinations transverse tangent vectors and the boundaries which are elevated from the cubic B-spline curves. For the given inner control points, B-spline surface of bi-quintic degree interpolating the cubic B-spline asymptotic quadrilateral is constructed. The optimized surface is the one with the minimized thin plate spline energy. The method is verified by some representative examples including the boundary curves with lines and inflections. Such interpolation scheme for the construction of the tensor-product B-spline surfaces is compatible with the CAD systems.
In current product design, CAE based on FEA has become absolutely imperative for developing high quality products. In some analyses of assembly models with movable parts such as electro-magnetic field analyses of motors, conformal tetrahedral meshes including meshes both of objects (parts) and space (called “object mesh” and “space mesh” in this paper) are needed. In general CAE processes, poses of moving parts of CAD models are first modified, then conformal meshes of the modified CAD models are generated, and FEAs are finally performed at each pose of the object in motion. However, simultaneous conformal meshing for objects and spaces is unstable and time-consuming. To reduce the frequency of the meshing, many mesh adaptation methods have been proposed. Although they can generate the conformal mesh of each object pose by modifying the mesh connectivity and vertex positions depending on the object motion, they are inefficient because the mesh topology and geometry are globally adapted even if the differences in poses of the objects in motion are very small. In addition, they do not deal with contacts of the object meshes. In this paper, we propose a new efficient tetrahedral mesh adaptation method for moving objects with contact. For efficient mesh adaptation, the mesh adaptation process is applied to only a set of space mesh elements around the moving object based on a distance field. In addition, to keep mesh conformity on the contact regions between object meshes, the topology and geometry of surface triangular meshes of contacted object meshes are adapted by vertex repositioning and local topological operations. The proposed method is demonstrated using three samples. In an experimental result where a cylinder is translated toward a half tube, the conformal tetrahedral meshes with 160k tetrahedra were generated without any inverted elements for about 5 seconds in each motion step.
Image-based surgical techniques can support minimally invasive keyhole neurosurgery through the segmentation of computed tomography or magnetic resonance imaging, optimal surgical planning, and surgical guidance. Keyhole neurosurgery requires automatic surgical planning and accuracy guidance for a target of the non-invasive or minimally invasive treatment of an anatomical structure. For supporting these requirements, we propose a markerless surgical robotic guidance system for keyhole neurosurgery. Our proposed robotic system consists of a six-degree of freedom (DoF) robotic arm, a needle guidance device, a mobile cart, a control workstation, and a 3D surface scanner. A 3D surface scanner is used for markerless registration between a preoperative reference image and a patient’s face in the operating room. This system configuration has merits of minimally invasive surgery. Traditional frame-based registration requires a stereotactic frame onto the patient’s head. Also, it requires an additional CT/MRI scanning to identify the coordinate system of the frame. However, the proposed markerless system can register without an additional CT scan by using a surface scanner. First, we show the system configuration to perform robotic-assisted surgery precisely. Next, we analyze subcomponents and calibrations such as the repeatability of the robotic arm, hand-tool calibration error for the relationship between needle guidance device and flange of the robotic arm, 3D scanning accuracy of the surface scanner, and hand-eye calibration error for the relationship between the surface scanner and the flange of the robotic arm. After calibrating each component of proposed system, the system accuracy is affected by the propagation of small errors. We sampled 15 paths located in the working space to check and compensate the residual transformation. We also test the total system accuracy with a phantom model; the proposed system allows us to obtain translation error (0.75 ± 0.38 mm) and rotation error (0.85 ± 0.16°) as a residual median error, which satisfies a surgical requirement (< 1 mm). With placements of medical devices to the planned pathway, it is crucial to automatically calculate a surgical path for keyhole neurosurgery. Thus, we proposed a path-planning algorithm that can support surgical decision-making process for keyhole neurosurgery. In the proposed algorithm, a possible trajectory is defined by a pair of a possible entry point on skull surface and a target point inside of target region. Then, the surgical paths are evaluated to satisfy the surgical rules such as the avoidance of vital organs, the maximization of the coverage of the target volume, and orthogonal insertion into the scalp surface.
(Bi)harmonic field has wide applications in geometry processing. Traditionally, to locally control the influence region of a (bi)harmonic field, users usually need to determine the range of its support, regions with non-zero scalar values, by prescribing appropriate boundary conditions. However, this way is non-intuitive and inconvenient. We proposed localized quasi-(bi)harmonic field, which is achieved through a ℓ1-norm regularized convex optimization. It can conveniently control the local support of the scalar field while still keeping some nice properties of the (bi)harmonic field. We applied the localized quasi-(bi)harmonic field in applications such as shape deformation and shape merging, and the experiment results show its benefits.
In machining, hole-making process takes up large part of the manufacturing processes. In previous hole-making processes optimization researches, researcher considered machine tools to have movement control on 3-axis. Thus, it is difficult to apply the result of the researches to 5-axis machining. In addition, in these studies, it is assumed that tool needed to make a hole are always available or only a single tool is needed to make a hole. However in a real working environment, number of the tools available are limited and also single tool cannot make a required hole diameter and tolerance in the most cases. Thus, the result of past researches is difficult to apply in real working environment. This research investigated hole-making optimization that can be applied to 5-axis machining, and considering the tool movement, tool switching, and limitation in the tool. Also tolerances of the holes were considered as a machining accuracy. Optimization can be done using brute-force approach and method solving traveling salesman problem (TSP). However, brute-force approach will be difficult to apply due to the longer time for calculation, when number of the hole pattern increases. For optimization, Genetic Algorithm (GA) was used to create optimization system. System was compared against the brute-force approach to check its validity by comparing the result and calculation time. After validity check, system was applied to the engine block model to obtain optimized hole-making processes.
In order to perform accurately scheduling of machining using a machine tool, it is necessary to estimate the actual machining time. The machining time is generally estimated by CAM systems. However, the error between the estimated and real cutting times is considerable because the systems do not consider the control and functional characteristics of the machine tool. In addition, control functions are installed in machine tools to achieve high precision and high speed motion while optimizing the tool paths and control parameters. The functions significantly affect the machining time. However, estimating machining time is difficult, thereby complicating optimization process. In this study, a method to identify the control characteristics and actual tool paths and a system to estimate the cutting time were developed. Furthermore, an estimation system using a deep neural network (DNN) was constructed to incorporate a control function. Finally, verification experiments were conducted wherein the estimation accuracy of the machining time was found to be within 5%.
This paper presents a case study of product architecture design for industrial robots, which extends the scope of conventional product architecture. Industrial robots are required to meet a wide range of customer needs depending on the end-use environment. While modularization with various options can effectively meet customer needs, the selection of options is often planned in a haphazard way, which may cause consumer confusion and result in non-optimal solutions. This research attempts to solve this issue by refining product architecture design with consideration of not only relationships between physical functions and entity structure, but also their relationships to customer needs. This study uses design structure matrixes (DSM) which represent the interactions between these three aspects (i.e. customer needs, physical functions, and entity structure), and domain mapping matrixes (DMM) which integrate the three DSMs. A function to evaluate the rationality and integrity of the module architecture is formulated with those DSMs and DMMs. A simulated annealing-based method is then used to explore optimal modular architectures. The case study shows that an industrial robot can be modularized to reflect customer needs, including those related to maintenance and productivity.