Abstract: This paper introduces the composition of agile fixture system, expounds the hierarchical representation structure of agile fixture, and puts forward a feasible research method of computer-aided automatic configuration of agile fixture.
key words: agile fixture; Computer aided fixture design feature modeling; Automatic configuration design
fixture is an important basic component in manufacturing system and equipment. With the development of cad/cam technology, the traditional fixture design method can not meet the flexible and fast requirements of modern manufacturing system. Agile fixture is a new fixture concept and clamping system produced to meet this requirement. It is a traditional combined fixture The extension and development of flexible fixture. Agile fixture can improve the ability of manufacturing system to quickly respond to product changes, shorten product design and manufacturing cycle, increase the flexibility of manufacturing system, and reduce costs, Improving product quality is of great significance.
1 hierarchical representation of agile fixture
there are two kinds of quasi clamping systems commonly used now, including the clamping system based on T-groove and the clamping system based on pin structure. Because the pin fixture system is easier to realize the automatic assembly of fixture, so in the process of the current agile fixture research, The pin clamping system is selected as the research object. In the pin clamping system, all clamping components are positioned and connected to the base plate in a certain way, and the connecting holes with standard spacing are distributed on the base plate. In the pin clamp system, when the workpiece and components are fixed on the base plate, the specific structure of the whole clamp can be expressed in three levels: clamping unit layer, component layer Functional surface layer.
1.1 clamping unit layer
clamping unit is a collection of several interconnected fixture elements, in which at least one (usually only one) fixture element is in direct contact with the workpiece through the functional surface, playing the role of positioning, support or clamping. We define this functional surface as the action surface of the clamping unit. The action surface of the clamping unit has two kinds: plane and cylindrical. The plane uses the midpoint PC Unique identification of plane normal vector VC; The cylinder surface can be uniquely identified by a point PA on the central axis of the cylinder and the central axis vector va. the midpoint of the action surface of the clamping unit is called the action point of the clamping unit, and the distance from the action point to the base plate is defined as the action height H. the action height is an important parameter in the fixture configuration design, which will be discussed later in this paper.
1.2 fixture element layer
the configuration process of the agile fixture can be regarded as a selection element The process of assembling components. Fixture components are divided into four categories: base plate, positioning components, clamping components at the end of 2013, and support components. The latter three types of components form clamping units through assembly, The clamping unit is installed on the base plate to form a clamp that meets the design requirements. A component library containing a large number of standard fixture components and a component assembly relationship library are the premise and foundation of configuration design. Fixture component library and component assembly relationship library record three aspects of information: component geometry information, component assembly feature information, and assembly relationship between components. Component geometry information is obtained by reading component graphics directly by CAD platform; The component assembly information is obtained by defining and reading the surface parameters of each assembly function of the component; For the description of the assembly relationship between two components (including the assembly relationship between two identical components), first judge whether the two components can be assembled according to the assembly characteristics of the two components, The assembly relationship model of standard fixture components is shown in Figure 1 (V1, V2,... V8 in the figure all represent the clamping components in the agile fixture component library). If the assembly requirements are met, the assembly characteristics of the components and the assembly method between the two components are recorded in the clamping component assembly relationship library and stored. After traversing the assembly relationship between all components in the agile fixture component library, You can get the system's agile fixture component assembly relationship library.
Figure 1 standard fixture component assembly relationship model figure
1.3 functional surface layer
functional surface is the surface on the fixture component that contacts the workpiece and other components and plays the role of positioning, clamping or assembly.
2 system introduction
we have developed a computer-aided agile fixture design system, The system module is shown in Figure 2.
Figure 2. The structure diagram of the agile fixture computer-aided automatic configuration design system module
before the configuration design, the user rotates the upper collet handle in a human-computer interactive way to input the upper end of the wire into the clamping planning. The system automatically selects the appropriate positioning clamping components from the component library, and assembles the clamping units corresponding to each clamping point according to the component assembly relationship, At the same time, the position and direction of each positioning clamping element and clamping unit are automatically determined, and finally automatically assembled into the overall fixture assembly drawing and managed. Now the main modules are introduced as follows:
(1) clamping planning module, which provides a friendly user interface and allows users to input the clamping plan, which is used to determine the positioning clamping points on each positioning clamping surface and related surfaces of the workpiece to be processed.
(2) fixture component library, It is a database based on feature modeling, which adopts feature modeling technology to carry out parameter design, record the solid characteristics and assembly characteristics of fixture components.
(3) fixture component assembly relationship library, record the mutual assembly relationship between components.
(4) automatic configuration module, which automatically generates agile fixture assembly drawings based on fixture component library and component assembly relationship library according to fixture planning and workpiece information. This module includes component selection Three sub modules of fixture unit generation and fixture unit installation.
3 automatic configuration of agile fixture
agile fixture automatically generates agile fixture assembly drawings according to workpiece information and fixture planning based on the establishment of fixture component library and fixture component assembly relationship Library in the automatic configuration module. Its configuration process can be divided into the following two steps.
3.1 select fixture components and generate
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