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Involute gear construction gear feature parameterization establishment process In the three-dimensional design, the process of creating a part is the process of shape analysis of the part. The filtering and extraction of solid features means that after a part is created, the basic body composed of the parts is separated to obtain the geometric data. Based on the establishment of the gear solid model, based on the basic features and their constraint relationships, the abstract shape features are extracted from the design feature information set, that is, the involute gear can be seen as composed of two parts: the gear blank part and other parts. On this basis, through the feature constraint relationship matching, editing and Boolean operations, gear parallel design in real time. The gear feature parameterization establishment process is as shown.
In the establishment of the three-dimensional model of the gear, the gear contour curve needs to be drawn first, that is, when the involute gear is established, the corresponding involute curve is first created in the selected reference plane, and the involute curve is established as shown in Fig. 2. The involute curve equation is: si=sri/r-2ri(invi-inv)(1) where: i=rb/ri, invi=tani-i, s=m/22xmtan.
In the process of gear machining and use, in order to meet the requirements of not being cut and strength, the gear is often deformed during the machining process, so that the tooth thickness on the gear index circle changes. When considering the model, the influence of the displacement coefficient must be considered.
At present, in the three-dimensional modeling of involute cylindrical spur gears, there are mainly two methods: one is to make a sketch tooth profile on the end face, scan along the vertical end face or directly stretch a tooth profile, and then along the circumferential array The second is to make a one-degree tooth profile on the end face, and then scan or cut directly in the direction of the vertical end face.
In the analysis of the displacement coefficient, the influence on the tooth thickness is mainly reflected in the change of the central angle corresponding to the tooth thickness on the index circle. The center angle corresponding to the indexing circle tooth thickness is:=2s/(mZ)(2) Then, the OC line is connected, and it is rotated /2 around its origin O in the direction of its curvature, and mirrored with reference thereto, so that the end faces of the teeth can be obtained, and then arrayed along the indexing circle direction, The end face of the entire gear is stretched to obtain the blank of the gear, and then the simple model of the gear is added to reduce the solid model of the gear.
The extraction of involute gear features is found by analyzing the characteristics of the gear and gear shaft. The establishment of the three-dimensional model of the gear mostly establishes the tooth profile curve in the selected plane, and establishes the end face of the entire gear by mirroring and array, and establishes the gear by stretching. The blank, finally, on the basis of the gear blank, by adding and subtracting the characteristics of other holes, grooves and shafts, the three-dimensional model of the gear can be obtained. Therefore, how to efficiently and accurately establish the gear blank model will establish the three-dimensional shape of the gear. The solid model plays an important role. To this end, the first task of establishing a three-dimensional solid model of the involute gear is the establishment of the gear blank feature.
The features generally include shape features, precision features, material features, positioning features and analysis features, while the establishment of solid three-dimensional geometric models is mainly related to shape features and positioning features. Therefore, the gear blank features are mainly represented by the involute shape. And the location is determined.
The parametric design of the gear feature determines the parameters of the feature including the shape parameters that determine its shape and the positioning parameters that determine its position and orientation. Shape parameters are further divided into two categories: one is the parameter input by the designer; the other is the parameter inherited from the superior feature. The former is input by the designer according to the functional requirements or assembly requirements of the part, and is subject to the constraints of the constraint equation, which is the variable in the constraint equation. The latter is inherited from the superior feature attached to the feature. It has a certain relationship with itself, but the parameters that cannot be automatically established by inheritance can be manually established by a relational expression or a dimensional chain, so that a control size can be modified. When you can achieve the linkage effect of the relevant size, improve the design efficiency.
In this paper, the involute gear is taken as an example. The geometric model of the displacement gear is established by using the feature-based parameter modeling technology. Since the displacement gear needs to consider the influence of the center distance, this paper takes a pair of gears as an example. The basic parameters of the pair of gears are: modulus m=8, number of teeth Z1=15, Z2=71, pressure angle=20 (the displacement is x1=0368, x2=1226, the actual center distance is A= 3556.
The gear geometry model extracts the gear blank feature on the Pro/E operating platform, inputs the gear parameters in the interactive input window, clicks on the regeneration, and the system will automatically update the 3D model of the gear blank. On this basis, add the step axis or subtract The hole-removing feature is the geometric model of the gear shaft and the large gear.
The conclusion is based on the Pro/E operating platform, which decomposes the gear into gear blank features and other simple features. On this basis, the parametric modeling technology is used to establish the gear blank characteristics, and the gears are serialized by parameter driving. When designing, only a part of the parameters need to be modified to obtain an accurate gear blank model, which greatly improves the design efficiency of the gear. When checking the interference problem of the gear motion, it can be assembled on the basis of the gear blank, and the motion interference problem during the gear meshing process can be quickly detected.
This paper mainly starts from the involute cylindrical gear, and other characteristic-based parametric design such as helical gear, bevel gear and worm gear drive will be discussed and studied in the subsequent work.