Solid wood furniture refers to furniture made from natural wood. Solid wood furniture is very different from the panel home in appearance. The design of the panel furniture is simple in structure. It can represent most of the modeling information by adding a thickness information to a two-dimensional view. The solid wood furniture is not standardized and has a complicated structure. In addition to the external shape, three basics are required. Outside the view, you usually need a secondary view.
Due to the rich and complex shape of solid wood furniture, in order to facilitate the furniture designers to fully exert their free thinking and imagination, and thus promote their innovative design, we are developing the solid wood furniture CAD system, considering the modeling method and technology of solid wood furniture, decided to adopt more The modeling methods (solid modeling technology, surface modeling technology, 3D parametric modeling technology, feature modeling technology, assembly modeling technology, etc.) are combined to complement each other to meet the different design needs of furniture designers. The following are some of the modeling techniques discussed below.
1 Feature-based 3D parametric solid modeling
Solid modeling is based on cubes, cylinders, spheres, cones, rings, and other basic elements. The set geometry (flat or Boolean operation) is used to generate the required geometry; the 3D parametric solid shape is Correlate the 3D solid model of the product with a set of parameters, and use the geometric constraints of the set of parameters to establish engineering equations and relationships to determine and describe the shape features of the product model, so as to quickly design a cluster of similarities in shape or function. Furniture products. In the solid wood furniture CAD system, a three-dimensional parametric solid modeling method based on features is adopted. The so-called feature is to separately extract the shape information and engineering information such as chamfer, hole and raft used for processing to meet the requirements of automatic production. And the collection of product information formed. In the solid wood furniture CAD system, the features of the parts are divided into two categories: work features and geometric features. As shown in Figure 1.
Working characteristics, also known as positioning features, auxiliary features, mainly refers to the working point, working axis and working plane, which provides a benchmark for design, solid modeling and assembly. Additional work features include structural features that refer to lines and circles that aid in constraining the 2D sketch of the part, and their use as auxiliary lines minimizes the number of geometric and dimensional constraints required for a 2D sketch of the part.
Geometric features are divided into sketch features and placement features. Sketch features are features generated from sketches (two-dimensional closed contours) that support multiple sketches and dynamic sketches to generate complex features at once. The sketch features are: stretch feature, which generates various features composed of columns and cones; rotation features to generate features composed of the body of revolution; sweep features, which generate complex features from sketches according to the sweep path, the path can be two The dimension can also be three-dimensional; the loft feature, which generates an entity with a more complex surface from multiple sketches of the space.
A placement feature is a feature that can be generated without the need for a sketch, given a position on other features. The placement features are: chamfer feature; fillet feature (fixed radius, variable radius); round hole feature (straight hole, counterbore, chamfer hole); pupil feature; raft feature; surface cutting feature, transform complex surface As part of the entity, the transformation of the surface to the entity is realized, and a complex entity with an outer surface is generated; the array of features changes a feature into a plurality of features arranged in a certain order through a rectangular array and a circular array; the feature of the part is divided into a whole The design is divided into multiple parts as needed; the part's Boolean operation feature combines multiple parts into one part, which can be used to decompose complex parts into simple parts and then merge them, providing another means for the generation of complex parts.
In the solid wood furniture CAD system, the solid parts of the solid wood furniture mainly adopts the feature-based three-dimensional parametric solid modeling technology, and is supplemented by the complex surface modeling technology based on NURBS. The shape of solid wood furniture adopts a bottom-up working style, and its design idea is:
First analyze the whole solid wood furniture parts and determine the simplest modeling method: determine how to break the parts into simple shapes, find the appropriate structural elements as the basic features, determine the order of creating additional features and the relationship and connection between the features. Form, determine the method of creating features; then start the specific shape of the part according to the previous analysis: Mr. into the basic features, and then generate other main features, complete the main shape, and then generate additional features to complete the overall shape of the part. Partially editable modifications can be made to the part at any time.
2 Surface modeling technology
In solid wood furniture design, it is often necessary to mix various simple and complex curves and surfaces to express the designer's design intent, which is not easy to achieve by solid modeling or feature modeling technology.
In the solid wood furniture CAD system, solid wood furniture parts can be generated by entities or by curved surfaces. Surface modeling can generate more complex parts than solid modeling, but parametric design is not as convenient as parametric solid modeling. The curved surface in the solid wood furniture CAD system is mainly used to cut the surface of the solid to complete the required geometric shape. Figure 3 shows the geometric shape of the solid wood chair leg surface by using the stretched surface to complete the geometric shape.
In the solid wood furniture CAD system, the surface is divided into basic surface, moving surface, skin surface and derived surface according to its generation method. Basic surfaces are elementary analytical surfaces, including cylindrical, conical, spherical, and toroidal surfaces. A moving surface is a curved surface formed by some curves moving in space according to a certain rule, including a rotating surface, an extruded surface, a swept surface, and a circular tube surface. A skin surface is a surface that overlays a wireframe model, including ruled surfaces, flat surfaces, U loft surfaces, and UV bidirectional loft surfaces. Derived surfaces are surfaces derived from known surfaces, including variable radius fillets, three-sided corner rounding, transition surfaces, and offset faces. In this system, functions such as comprehensive editing, breaking, merging and extension of surfaces, surface interception, stitching, simplification, repairing gaps, and replacing surface boundaries are provided.
The key to surface cutting is: 1. Create a surface, 2. Determine the position of the surface. The key to creating a surface is the creation of the section line and the sweep path (for the swept surface). There are several ways to create the section line and the sweep path, such as extracting the section outline of the solid, copying the solid boundary, drawing the user, etc. . The first two are suitable for the case where the section line or the sweeping path is complicated or the user draws a relatively complicated thing, such as the curved surface shown in Fig. 4, and the sweeping path is a part of the front end boundary of the front leg of the solid wood chair.
3 Constraint-based assembly modeling
There are two methods for assembly modeling, bottom-up modeling and top-down modeling. The former is that after the overall plan is determined, the designer uses the CAD tool to separately design the detailed structure of each part, and then defines the assembly relationship between these parts to form a product model. The latter first establishes the functional expression of the product and analyzes whether the expression meets the product requirements. Then the designer uses the CAD system to continuously refine the geometry of the part to ensure that the structure of the part meets the functional requirements of the product and establish a product model.
Solid wood furniture product modeling uses a combination of these two approaches. Because the actual solid wood furniture product design is not strictly top-down design, but the whole top-down, there is still a bottom-up work mode. At the same time, product functional requirements and scheme design restrict the structural design of the parts, and the detailed structural design of the parts in turn affects the assembly scheme of the products. The process of product design is actually the repeated function of product function and scheme design and detailed design of part structure. Process, so part modeling and assembly modeling need to be combined. The assembly model of the product is based on high-level semantic information, so the product assembly model needs to be modeled with features.
Solid wood furniture products are assembled from lower-level components, which are composed of lower-level parts and sub-components. The solid wood furniture CAD system uses assembly constraints to assemble these parts and components into furniture products according to a certain level. The overall assembly of solid wood furniture takes a top-down approach, and the assembly process is generally divided into two steps:
The first step is to build an assembly tree. Add the components that will establish the assembly constraint relationship to the assembly tree.
The second step is to add constraints to the components in the assembly tree to gradually reduce the freedom of the components and assemble them to form the furniture product according to the specified constraints. The assembly constraints of solid wood furniture CAD systems are divided into the following types: mating, surface flushing, alignment angle and insertion, which realize faces and faces, faces and lines, faces and points, lines and lines, lines and points, and points and points. The constraint between. The surface can be a plane or a cylindrical surface, the lines can be straight lines, axes, and vector directions, and the points can be solid vertices, endpoints, and centers.
4 Conclusion
The feature-based three-dimensional parametric solid modeling technology, surface modeling technology and constraint-based assembly modeling technology described in this paper are applied and realized in the solid wood furniture CAD system, which greatly improves the speed of solid wood furniture modeling. The system was used in Guangming Group Furniture Co., Ltd. and the effect was good. Figure 7-9 is a partial example of the design of solid wood furniture by Guangming Group Furniture Co., Ltd. using solid wood furniture CAD system.
references
1. Dong Renyang. 3D Mechanical Design Software MDT 4 Enhanced Training Course. Autodesk Western China University. 2000, 4
2. Yang Jiping. Research and development of solid wood furniture CAD system. [Master's thesis]. Chongqing: Chongqing University, 2000
Due to the rich and complex shape of solid wood furniture, in order to facilitate the furniture designers to fully exert their free thinking and imagination, and thus promote their innovative design, we are developing the solid wood furniture CAD system, considering the modeling method and technology of solid wood furniture, decided to adopt more The modeling methods (solid modeling technology, surface modeling technology, 3D parametric modeling technology, feature modeling technology, assembly modeling technology, etc.) are combined to complement each other to meet the different design needs of furniture designers. The following are some of the modeling techniques discussed below.
1 Feature-based 3D parametric solid modeling
Solid modeling is based on cubes, cylinders, spheres, cones, rings, and other basic elements. The set geometry (flat or Boolean operation) is used to generate the required geometry; the 3D parametric solid shape is Correlate the 3D solid model of the product with a set of parameters, and use the geometric constraints of the set of parameters to establish engineering equations and relationships to determine and describe the shape features of the product model, so as to quickly design a cluster of similarities in shape or function. Furniture products. In the solid wood furniture CAD system, a three-dimensional parametric solid modeling method based on features is adopted. The so-called feature is to separately extract the shape information and engineering information such as chamfer, hole and raft used for processing to meet the requirements of automatic production. And the collection of product information formed. In the solid wood furniture CAD system, the features of the parts are divided into two categories: work features and geometric features. As shown in Figure 1.
Working characteristics, also known as positioning features, auxiliary features, mainly refers to the working point, working axis and working plane, which provides a benchmark for design, solid modeling and assembly. Additional work features include structural features that refer to lines and circles that aid in constraining the 2D sketch of the part, and their use as auxiliary lines minimizes the number of geometric and dimensional constraints required for a 2D sketch of the part.
Geometric features are divided into sketch features and placement features. Sketch features are features generated from sketches (two-dimensional closed contours) that support multiple sketches and dynamic sketches to generate complex features at once. The sketch features are: stretch feature, which generates various features composed of columns and cones; rotation features to generate features composed of the body of revolution; sweep features, which generate complex features from sketches according to the sweep path, the path can be two The dimension can also be three-dimensional; the loft feature, which generates an entity with a more complex surface from multiple sketches of the space.
A placement feature is a feature that can be generated without the need for a sketch, given a position on other features. The placement features are: chamfer feature; fillet feature (fixed radius, variable radius); round hole feature (straight hole, counterbore, chamfer hole); pupil feature; raft feature; surface cutting feature, transform complex surface As part of the entity, the transformation of the surface to the entity is realized, and a complex entity with an outer surface is generated; the array of features changes a feature into a plurality of features arranged in a certain order through a rectangular array and a circular array; the feature of the part is divided into a whole The design is divided into multiple parts as needed; the part's Boolean operation feature combines multiple parts into one part, which can be used to decompose complex parts into simple parts and then merge them, providing another means for the generation of complex parts.
In the solid wood furniture CAD system, the solid parts of the solid wood furniture mainly adopts the feature-based three-dimensional parametric solid modeling technology, and is supplemented by the complex surface modeling technology based on NURBS. The shape of solid wood furniture adopts a bottom-up working style, and its design idea is:
First analyze the whole solid wood furniture parts and determine the simplest modeling method: determine how to break the parts into simple shapes, find the appropriate structural elements as the basic features, determine the order of creating additional features and the relationship and connection between the features. Form, determine the method of creating features; then start the specific shape of the part according to the previous analysis: Mr. into the basic features, and then generate other main features, complete the main shape, and then generate additional features to complete the overall shape of the part. Partially editable modifications can be made to the part at any time.
2 Surface modeling technology
In solid wood furniture design, it is often necessary to mix various simple and complex curves and surfaces to express the designer's design intent, which is not easy to achieve by solid modeling or feature modeling technology.
In the solid wood furniture CAD system, solid wood furniture parts can be generated by entities or by curved surfaces. Surface modeling can generate more complex parts than solid modeling, but parametric design is not as convenient as parametric solid modeling. The curved surface in the solid wood furniture CAD system is mainly used to cut the surface of the solid to complete the required geometric shape. Figure 3 shows the geometric shape of the solid wood chair leg surface by using the stretched surface to complete the geometric shape.
In the solid wood furniture CAD system, the surface is divided into basic surface, moving surface, skin surface and derived surface according to its generation method. Basic surfaces are elementary analytical surfaces, including cylindrical, conical, spherical, and toroidal surfaces. A moving surface is a curved surface formed by some curves moving in space according to a certain rule, including a rotating surface, an extruded surface, a swept surface, and a circular tube surface. A skin surface is a surface that overlays a wireframe model, including ruled surfaces, flat surfaces, U loft surfaces, and UV bidirectional loft surfaces. Derived surfaces are surfaces derived from known surfaces, including variable radius fillets, three-sided corner rounding, transition surfaces, and offset faces. In this system, functions such as comprehensive editing, breaking, merging and extension of surfaces, surface interception, stitching, simplification, repairing gaps, and replacing surface boundaries are provided.
The key to surface cutting is: 1. Create a surface, 2. Determine the position of the surface. The key to creating a surface is the creation of the section line and the sweep path (for the swept surface). There are several ways to create the section line and the sweep path, such as extracting the section outline of the solid, copying the solid boundary, drawing the user, etc. . The first two are suitable for the case where the section line or the sweeping path is complicated or the user draws a relatively complicated thing, such as the curved surface shown in Fig. 4, and the sweeping path is a part of the front end boundary of the front leg of the solid wood chair.
3 Constraint-based assembly modeling
There are two methods for assembly modeling, bottom-up modeling and top-down modeling. The former is that after the overall plan is determined, the designer uses the CAD tool to separately design the detailed structure of each part, and then defines the assembly relationship between these parts to form a product model. The latter first establishes the functional expression of the product and analyzes whether the expression meets the product requirements. Then the designer uses the CAD system to continuously refine the geometry of the part to ensure that the structure of the part meets the functional requirements of the product and establish a product model.
Solid wood furniture product modeling uses a combination of these two approaches. Because the actual solid wood furniture product design is not strictly top-down design, but the whole top-down, there is still a bottom-up work mode. At the same time, product functional requirements and scheme design restrict the structural design of the parts, and the detailed structural design of the parts in turn affects the assembly scheme of the products. The process of product design is actually the repeated function of product function and scheme design and detailed design of part structure. Process, so part modeling and assembly modeling need to be combined. The assembly model of the product is based on high-level semantic information, so the product assembly model needs to be modeled with features.
Solid wood furniture products are assembled from lower-level components, which are composed of lower-level parts and sub-components. The solid wood furniture CAD system uses assembly constraints to assemble these parts and components into furniture products according to a certain level. The overall assembly of solid wood furniture takes a top-down approach, and the assembly process is generally divided into two steps:
The first step is to build an assembly tree. Add the components that will establish the assembly constraint relationship to the assembly tree.
The second step is to add constraints to the components in the assembly tree to gradually reduce the freedom of the components and assemble them to form the furniture product according to the specified constraints. The assembly constraints of solid wood furniture CAD systems are divided into the following types: mating, surface flushing, alignment angle and insertion, which realize faces and faces, faces and lines, faces and points, lines and lines, lines and points, and points and points. The constraint between. The surface can be a plane or a cylindrical surface, the lines can be straight lines, axes, and vector directions, and the points can be solid vertices, endpoints, and centers.
4 Conclusion
The feature-based three-dimensional parametric solid modeling technology, surface modeling technology and constraint-based assembly modeling technology described in this paper are applied and realized in the solid wood furniture CAD system, which greatly improves the speed of solid wood furniture modeling. The system was used in Guangming Group Furniture Co., Ltd. and the effect was good. Figure 7-9 is a partial example of the design of solid wood furniture by Guangming Group Furniture Co., Ltd. using solid wood furniture CAD system.
references
1. Dong Renyang. 3D Mechanical Design Software MDT 4 Enhanced Training Course. Autodesk Western China University. 2000, 4
2. Yang Jiping. Research and development of solid wood furniture CAD system. [Master's thesis]. Chongqing: Chongqing University, 2000
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