A Parametric Model of EPS Worm and Worm Gear Transmission Pair and a Method for Generating Tool Edge Lines

Abstract

The present invention discloses a parametric model of an EPS worm and worm gear transmission pair and a method for generating a tool edge line, which is a method for generating a parametric model of a worm and worm gear and a tool edge line based on CATIA parametric design, motion simulation and secondary development technologies, and a corresponding custom dialogue window is developed for inputting the basic parameters of the worm and worm gear and implementing specific functions. It includes: creating a parametric model of the worm, creating a machining tool model for the worm, creating a machining tool model for the worm gear, creating a worm gear model, worm and worm gear motion simulation and meshing state analysis, etc. The implementation of this method optimizes the meshing tooth profile, reduces repetitive work, shortens the design and development cycle, is efficient and time-saving, and has strong versatility.

Description

Technical Field

[0001] The present invention relates to the design of a worm and worm gear transmission pair in an electric power steering device for an automotive steering system, specifically to a parametric model of a worm and worm gear and a method for generating a cutting edge line of a cutting tool. Background Art

[0002] In an electric power steering device (EPS) of an automotive steering system, a worm and worm gear is a key transmission pair. As the first-stage transmission connecting the assist motor, it has been maturely used in column-type C-EPS, recirculating ball-type B-EPS, and pinion-type P-EPS. The worm and worm gear transmission is stable, has a large transmission ratio, and is structurally compact. In order to adapt to the application environment in EPS, optimize tooth profile meshing, be easy to machine, improve efficiency, reduce wear, extend service life, resist wear and reduce noise, etc., a worm gear made of nylon plus a metal skeleton composite material is generally matched with a metal worm. The tooth profiles of the worm and worm gear adopt non-conjugate surface design, and the tooth thicknesses of the worm and worm gear are unevenly distributed. In addition, methods such as worm gear modification machining or tooth profile modification are also used to improve the meshing state. Moreover, when matching different vehicle models and transmitting different torques and rotational speeds, the parameters of the worm and worm gear need to be adjusted. If recalculating, optimizing the design, generating a digital model, designing the cutting edge line of the cutting tool, and manufacturing the cutting tool, the development cycle is long, the repetitive workload is large, and the project progress is affected.

[0003] In order to shorten the design and development cycle of a worm and worm gear with new parameters, reduce repetitive work, and optimize tooth profile meshing, based on CATIA parametric design, motion simulation, and secondary development technologies, combined with the company's existing technologies, a "parametric model of a worm and worm gear transmission pair and a template for generating a cutting edge line of a cutting tool" has been developed. It can quickly generate a worm and worm gear model after inputting the basic parameters of the worm and worm gear. After determining the machining method, it can quickly obtain the cutting edge line of the cutting tool, output the point coordinate values, and generate a cutting tool model, directly guiding the design and manufacturing of the cutting tool, which is efficient, time-saving, and has strong versatility.

[0004] Due to the different processing conditions of each production company, different types of worms are selected. According to the shape of the worm tooth profile, they can be divided into Archimedes ZA worms (axial straight tooth profile), normal straight profile ZN worms, involute ZI worms (straight tooth profile tangent to the base circle section), and other section-formed worms. The processing technologies of each production enterprise are different. For the processing of worms, some use straight-edge turning tools, which are arranged axially, normally, or tangent to the base cylinder surface; some use disc milling cutters or finger milling cutters, and the tool shapes change with the tooth profile; some use whirling milling, which has high batch production efficiency; some use grinding to improve the processing accuracy. When creating the worm processing tool model, the worm processing tool model is created according to the structure and installation form of the tool on the processing equipment. When machining with a straight-edge tool, the tool forming is simple and easy to implement, and there is no need to intercept the worm tooth profile line; when machining with a non-standard curve cutting edge, it is easier to intercept the corresponding worm tooth profile line. The processing of nylon worm wheels mainly includes hobbing and fly cutter machining. Hobbing has high efficiency. The fly cutter is equivalent to a single tooth of the hob, with low efficiency. Fly cutter cutting is often used for single-piece or small-batch production, and worm wheel hobs are often used for batch production. The matching worm wheel tooth profile is complex. When hobbing with the worm as the tool, the conjugate tooth profile formed by machining is the ideal worm wheel tooth, but the EPS worm has few heads and a small bottom diameter, making it difficult to be converted into a tool. According to the deformation situation of the meshing of metal worms and nylon worm wheels, based on the theory of elastic meshing of mismatched involute worms, and considering simple processing technology and cost reduction, the use of nylon helical gears to replace worm wheels in EPS has been widely used. Helical gear hobs with multiple heads are used to machine worm wheels, or worm wheels machined with large-diameter hobs, and some also use tooth profile modification methods to improve the meshing state. No matter which method is selected, as long as the cross-section position can be defined, the tool edge line and point coordinates can be extracted to guide the tool design and manufacturing. Summary of the Invention

[0005] The present invention mainly solves the technical problems in the prior art that the matching worm wheel tooth profile is complex, when hobbing with the worm as the tool, the conjugate tooth profile formed by machining is the ideal worm wheel tooth, but the EPS worm has few heads and a small bottom diameter, making it difficult to be converted into a tool, etc., and proposes an EPS worm and worm wheel transmission pair parametric model and a tool edge line generation method.

[0006] An EPS worm and worm wheel transmission pair parametric model and a tool edge line generation method provided by the present invention are a worm and worm wheel parametric model and a tool edge line generation method based on CATIA parametric design, motion simulation, and secondary development technologies, and a corresponding custom dialogue window is developed for inputting the basic parameters of the worm and worm wheel and realizing specific functions.

[0007] It mainly includes the following parts: creating a worm parametric model, creating a worm processing tool model, creating a worm wheel processing tool model, creating a worm wheel model, worm and worm wheel motion simulation and meshing state analysis. The overall technical solution process (see Figure 1 Overall technical solution flow chart) is as follows:

[0008] First, create a parametric model of the worm, including creating the basic parameters of the worm, other geometric parameters, relations, reference benchmarks, and the worm geometry. Create the worm geometry with reference to the parameters and benchmarks. Modify the parameters, refresh the model, and verify whether the followability of the parametric model is correct. If it is unqualified, modify the parameters, benchmarks, relations, dimensions, etc., and then refresh the model until it is qualified to realize the parametric model of the worm.

[0009] Secondly, extract the tool edge line (tooth profile line on the section) and the coordinate values of the points on the line from the worm model according to the actual processing method, which are used to generate the model of the machining tool for the worm and the worm gear. Check whether the tool edge line of the machining tool matches the corresponding machining process method by arranging several relative positions between the worm machining tool and the worm model. If it is unqualified, analyze the reasons and modify it. If it is qualified, the coordinate values of the points on the tool edge line of the worm machining tool can be output to guide the design and manufacture of the worm machining tool. If the worm gear is machined with a hob, the model generated by inputting the parameters of the worm gear machining tool in the parametric model of the worm can directly replace the hob (the difference from the actual hob is the lack of tooth segmentation and the rake angle and clearance angle at the cutting edge, etc.).

[0010] Then, create a worm gear model, including creating the basic parameters of the worm gear, other geometric parameters, relations, reference benchmarks, the blank geometry of the worm gear, and the formation of the worm gear teeth. Create the blank geometry of the worm gear with reference to each parameter and benchmark.

[0011] The models of the above worm gear machining tool (worm gear hob) and the worm gear blank have been completed. Next, generate the worm gear teeth by simulating the generating machining process. Assemble the worm gear model and the worm model according to the product structure, simulate their relative motion, observe the continuity of the meshing of the worm and the worm gear, the position of the meshing spot, the ratio of the meshing length to the tooth width, the interference situation during the motion, etc. Analyze the observation results and preliminarily determine whether the worm gear model generated by the worm gear machining tool in this state meets the matching requirements (is qualified) with the theoretical worm model. If the requirements cannot be met (unqualified), it is necessary to modify the basic parameters of the worm and the worm gear, or the forming section of the worm, or the tool edge line of the worm gear machining tool, etc. After modification, refresh the model, regenerate the worm gear model, and re-check the meshing state until the meshing state meets the requirements (qualified), then the parameters of the worm gear machining tool (hobbing) or the coordinate values of the points on the tool edge line (turning or profiling milling) can be output to guide the design and manufacture of the worm gear machining tool.

[0012] Furthermore, there are four methods for forming the worm gear teeth: Method 1: Full tooth Boolean subtraction; Method 2: Single tooth Boolean subtraction array; Method 3: Full tooth segmentation; Method 4: Single tooth segmentation array. Method 1 and Method 2 use the Boolean subtraction loop to form the tooth groove profile, and Method 3 and Method 4 use the segmentation loop method to form the tooth groove profile. Any one of the above four methods can be used to realize the formation of the worm gear teeth, thus completing the worm gear model.

[0013] Method 1: Full-tooth Boolean subtraction. The process of machining a worm gear with a worm gear cutting tool is simulated by means of a Boolean subtraction loop to generate all the teeth. The specific process is as follows: First, copy the worm gear cutting tool and rename it as "Worm Gear Cutting Tool 00". Worm Gear Cutting Tool 00 rotates around its own axis by i * Si * 360 / Angle, and the rotation is named after the value of i * Si * 360 / ; Then, Worm Gear Cutting Tool 00 rotates around the axis of the worm gear blank by -i * 360 / Angle, and the rotation is named after the value of -i * 360 / , noting the reverse rotation. Next, the geometry of the "Worm Gear Cutting Tool 00" obtained by rotation is used as the item to be removed in the Boolean subtraction and removed from the geometry of the worm gear blank. The Boolean subtraction is named after the value of -i * 360 / , and a random color is set for the cutting surface generated by the Boolean subtraction; If an abnormal problem is encountered during the execution of the above operations, the program sets different handling methods for different problems and then enters the next loop; Repeat the above operation loop until all the teeth are completed. The loop count i ranges from n1 to n2, and generally n1 = 1 and n2 = N; Finally, hide the worm gear cutting tool; In this method, in each loop, "Worm Gear Cutting Tool 00" starts from the starting position, first rotates around its own axis, and then rotates around the axis of the worm gear blank. The entire loop completes all the teeth.

[0014] The second method, the single-tooth Boolean subtraction array. Similar to the full-tooth Boolean subtraction, it uses the Boolean subtraction loop to simulate the process of machining a worm gear with a worm gear cutting tool. Only a single tooth groove of the worm gear is generated first, then the single-tooth groove surface is extracted, and then the tooth groove surfaces are merged. The merged tooth groove surfaces are arrayed, and finally the surplus material of the worm gear blank is removed by dividing the arrayed surface to generate all the teeth. The specific process is as follows: First, copy the worm gear cutting tool geometry and rename it as "worm gear cutting tool 00". The worm gear cutting tool 00 rotates around its own axis by i*Si*360 / angle, and the rotation is named with the value of i*Si*360 / . Then, the worm gear cutting tool 00 rotates around the axis of the worm gear blank by -i*360 / angle, and the rotation is named with the value of -i*360 / , note the reverse rotation. Then, the "worm gear cutting tool 00" geometry obtained by rotation is used as the item to be removed in the Boolean subtraction and removed from the worm gear blank geometry. The Boolean subtraction is named with the value of -i*360 / , and a random color is set for the cutting surface generated by the Boolean subtraction. If an abnormal problem is encountered during the execution of the above operations, the program sets different handling methods for different problems and then enters the next loop. Repeat the above operation loop until a single tooth groove is completed. The loop count i ranges from n1 to n2. Generally, n1 = 0 and n2 = N / Z2, where Z2 is the number of teeth of the worm gear. Subsequently, hide the worm gear cutting tool, and then extract the formed surface in each loop of the single-tooth groove profile surface and merge it. Before merging, it is necessary to process the formed tooth groove surface. Especially during the Boolean subtraction loop, the cutting of the tooth tip of the worm gear cutting tool is complex and cannot form a smooth surface. The more loops there are, the more complicated the processing process is, and it can only be processed manually, which affects the forming efficiency of the teeth. Extend the boundary of the merged overall single-tooth groove surface, and then array the extended single-tooth groove profile surface according to the number of teeth. Finally, use the split feature to remove the surplus material of the worm gear blank with the arrayed tooth profile surface, complete all the teeth of the worm gear, and hide the tooth profile surface. In each loop, the "worm gear cutting tool 00" starts from the starting position, first rotates around its own axis, and then rotates around the axis of the worm gear blank. The whole loop completes a single tooth groove, then arrays the single-tooth groove surface, and finally forms the split.

[0015] Method 3: Full tooth segmentation. Use the tooth profile surface to perform cyclic segmentation, simulate the process of the worm wheel machining tool cutting the worm wheel, and generate all teeth. The specific process is as follows: First, extract each group of tooth profile surfaces of the worm wheel machining tool, merge each group of tooth profile surfaces into an overall surface respectively, name it as "the j-th group of tooth profile surfaces", and hide the worm wheel machining tool. Then, enter the loop of selecting the first-layer tooth profile surface. Select the j-th group of tooth profile surfaces. If a problem is encountered, the program jumps out and waits for processing. If there is no problem, enter the second-layer loop. Start the segmentation loop of the j-th group of tooth profile surfaces. Copy the j-th group of tooth profile surfaces and rename it as "the j-th group of tooth profile surfaces 00". Rotate the j-th group of tooth profile surfaces 00 around its worm axis by i * Si * 360 / angle, and the rotation is named with the value of i - Si * 360 / . Then rotate the j-th group of tooth profile surfaces 00 around the worm wheel blank axis by -i * 360 / angle, and the rotation is named with the value of -i * 360 / , note the reverse rotation. Then, use the rotated "the j-th group of tooth profile surfaces 00" as the segmentation element of the segmentation feature, remove the tooth groove part from the worm wheel blank geometry, note that the retention direction is set to the outside, and the segmentation is named with the value of -i - 360 / . Then, randomly set the color for the cutting surface generated by the segmentation. If insufficient memory is encountered during the loop, save the data and exit the program. Repeat the above operations until all teeth of the j-th group of tooth profile surfaces are segmented. Hide the j-th group of tooth profile surfaces 00. The second-layer loop is completed. The loop times i range from n1 to n2, where n1 = 1 and n2 = N. The loop times j of the first-layer loop range from 1 to Z 刀 , Z 刀 is the number of starts of the worm hob; Repeat selecting the tooth profile surface and the second-layer segmentation loop until all teeth are completed; In this method, the "tooth profile surface" is used to replace the worm wheel machining tool entity in each loop, and all teeth are completed through two-layer loops.

[0016] Method 4: Single-tooth segmentation array. Similar to the full-tooth segmentation, the tooth profile surface is cyclically segmented to simulate the process of a worm gear machining tool cutting a worm gear. Only a single tooth slot of the worm gear is generated first, then the single-tooth slot surface is extracted, and then the tooth slot surfaces are merged. The merged tooth slot surfaces are arrayed, and finally the surplus material of the worm gear blank is removed by array surface segmentation to generate all the teeth. The specific process is as follows: First, extract a group of tooth profile surfaces of the worm gear machining tool, merge them into an overall surface, and hide the worm gear machining tool. Then, enter the tooth profile surface segmentation loop. Copy the tooth profile surface and rename it as "tooth profile surface 00". The tooth profile surface 00 rotates around its worm axis by i - Si * 360 / angle, and the rotation is named by the value of i - Si - 360 / . The tooth profile surface 00 then rotates around the worm gear blank axis by -i - 360 / angle, and the rotation is named by the value of -i - 360 / , noting the reverse rotation. Then, use the rotated "tooth profile surface 00" as the segmentation element of the segmentation feature to remove the tooth slot part from the worm gear blank geometry, noting that the retention direction is set to the outside, and the segmentation is named by the value of -i - 360 / . Then, randomly set a color for the cutting surface generated by the segmentation. If insufficient memory is encountered during the loop, save the data and exit the program. Repeat the above operations until a single tooth slot is completed. The loop count i ranges from n1 to n2, where n1 = 0 and n2 = N / Z2. Subsequently, hide the tooth profile surface 00. The tooth slot profile surfaces formed by the single-tooth slot segmentation loop are not flat and need to be processed. The more loops there are, the more complicated the processing process is, and it can only be processed manually, affecting the tooth forming efficiency. Extract the formed single-tooth slot profile surface after processing, merge the sub-surfaces into an overall surface, then extend the surface boundary, and then array the extended single-tooth slot tooth profile surfaces according to the number of teeth. Finally, use the segmentation feature to cut the surplus material of the worm gear blank with the arrayed tooth slot tooth profile surfaces to complete all the teeth of the worm gear. In this method, the "tooth profile surface" is used to replace the worm gear machining tool entity in each loop. First, a single tooth slot is completed, then the single-tooth slot surface is arrayed, and finally all the teeth are segmented and completed.

[0017] Further, to implement the parametric model of the worm and worm gear and the method for generating the tool edge line, two custom windows are created, the worm model dialogue window and the generated worm gear dialogue window. The worm model dialogue window (such as Figure 3 the worm model dialogue window) can select the type of the worm, input the basic parameters of the worm, and click the "Refresh Model" button to synchronously update the model according to the selected type and the set basic parameters. In the worm model dialogue window, a "tool cutting-in profile" is set to select the profile option where different worm machining tools may extract the profile line. The "Point and Coordinate Extraction" function button can extract points and the coordinate values of the points on the intercepted tooth slot profile according to the selected profile, and the "Number of Points Extracted" can be set. The generated worm gear window (such as Figure 4Generate a worm gear dialogue window) for inputting the basic parameters of the worm gear, setting the loop parameters. The "Boolean subtraction loop" function button realizes the first or second method of Boolean subtraction forming of the worm gear teeth. The "Segmentation loop" function button realizes the third or fourth method of segmented forming of the worm gear teeth. The previous method and the latter method are distinguished by setting the loop parameter of "from n1 to n2". The "Take points and coordinates" function button is the same as the "Take points and coordinates" function in the worm model window, except that the profile section for intercepting is not set in advance.

[0018] Furthermore, perform basic parameter settings in the worm model dialogue window. As input parameters, directly control the corresponding basic parameters of the worm model. Cylindrical worm gears are divided into ZA, ZN, ZI and other forming types, which are set in the type option bar in the upper left corner of the worm model dialogue window. The worm type is determined by the form of the tooth groove section and its layout position. When the ZA worm is selected, the tooth profile is straight in the axial section. When the ZN worm is selected, the tooth profile is straight in the normal section and a single slotting feature is required. When the involute ZI worm is selected, the tooth profile is straight on one side in the section tangent to the base circle. Since a single blade can only machine the tooth profile on one side, the left and right blades are arranged in the upper and lower base circle tangent planes respectively, and two slotting features need to be added. When the root circle is smaller than the base circle, a root slotting feature also needs to be added. After creating the worm model, adjust the basic parameters, click the "Refresh model" function button in the worm model dialogue window, automatically update the corresponding parameters in the model, recalculate other geometric parameters, update the reference datum and the worm forming features, check the corresponding changed parameters and dimensions, and verify whether the followability of the parametric model is qualified. If it is not qualified, find the problem point and modify the corresponding position of the model, then click the "Refresh model" function button again to verify the followability of the parametric model until it is qualified to achieve the creation of the worm parametric model.

[0019] Furthermore, select the section where the tool cuts in the drop-down combo box of "Tool cutting-in section" in the lower left corner of the worm model dialogue window, and associate these sections with the corresponding sections in the worm model. The normal section of the tooth groove, the normal section of the tooth tip, the axial section, the middle section parallel to the end face, the section tangent to the upper base circle, and the section tangent to the lower base circle are initially set, and the tool cutting-in section and the corresponding sections in the model can be expanded as needed. Click the "Take points and coordinates" function button, a manual selection profile dialogue window will pop up. After manually selecting the tooth profile line and clicking the OK button in the dialogue window, continue to execute the program to take points on the tooth groove profile line, and then output the absolute coordinate values of each point, save them in the specified name and format (.xlsx), and store them in the specified location. The number of points N to be taken is set in the "Number of points to be taken" text box in the lower right corner of the dialogue box.

[0020] Furthermore, the reference coordinate system in the model is default set with the direction parallel to the axis of the worm gear as the X-axis, the direction parallel to the axis of the worm as the Y-axis, and the common normal direction of the worm axis and the worm gear axis as the Z-axis (Figure 2 (Reference coordinate system). The worm model uses the X1Y1Z1 coordinate system with the midpoint of the worm shaft as the origin, and the worm gear model uses the X2Y2Z2 coordinate system with the midpoint of the worm gear shaft as the origin.

[0021] Furthermore, points are taken on the combined tooth groove profile. The process of taking points is a cyclic process of defining point features on the curve according to a ratio. The cyclic variable is i, with a range from 0 to N, where N is the number of points taken and is set in the "Worm Model" dialog box. Each time a point is taken, it is taken at a distance ratio of i / N from the starting point of the curve. Then, the GetCoordinates Coord statement is used to extract the absolute coordinate values of each point in the X1Y1Z1 coordinate system and save them to an EXCEL document, stored at a specified location with a set name and format (.xlsx). At this time, the absolute coordinate values (Coord / X1, Coord / Y1, Coord / Z1) need to be converted into the plane relative coordinate values (Coord / Y1’, Coord / Z1’) in the normal section of the tooth groove. The projection of the worm axis in the section is taken as the Y1’ axis, and the median line of the tooth groove is taken as the Z1’ axis. The corresponding conversion formula is:

[0022]

[0023] In this invention, taking the normal tooth groove profile of the worm machining tool and the hobbing machining of the worm gear machining tool as examples, the model function is not limited to this and can be expanded according to actual needs.

[0024] The beneficial effects provided by this invention: This invention can realize the rapid generation of worm and worm gear models after inputting the basic parameters of the worm and worm gear, shorten the design and development cycle of new products, quickly obtain the optimized tool edge line, output point coordinate values, and guide the design and manufacture of tools. The implementation of this method optimizes the meshing profile, reduces repetitive work, shortens the design and development cycle, is efficient and time-saving, and has strong versatility. Brief Description of the Drawings

[0025] Figure 1 Flow chart of the overall technical solution;

[0026] Figure 2 Reference coordinate system;

[0027] Figure 3 Worm model dialog window;

[0028] Figure 4 Generated worm gear dialog window;

[0029] Figure 5 Model structure tree;

[0030] Figure 6 Process for obtaining the tool edge line and point coordinate values;

[0031] Figure 7 Profile Selection Dialog Box

[0032] Figure 8 Output Point Coordinate Values and Data Processing

[0033] Figure 9 Flow Chart for Creating Worm Gear Model

[0034] Figure 10 Full Tooth Boolean Subtraction Array Process

[0035] Figure 11 Single Tooth Boolean Subtraction Array Process

[0036] Figure 12 Full Tooth Division Array Process

[0037] Figure 13 Single Tooth Division Array Process

[0038] Figure 14 Worm Gear Model

[0039] Figure 15 Worm and Worm Gear Mechanical Device

[0040] Figure 16 Flow Chart for Creating Worm and Worm Gear Motion Simulation

[0041] Reference Numerals in the Drawings: 1. Worm; 2. Worm Gear; 3. Support Base Detailed Implementation Manner

[0042] To make the technical problems solved by the present invention, the technical solutions adopted, and the achieved technical effects clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Additionally, it should be noted that for the sake of description, only parts related to the present invention are shown in the drawings rather than all the content.

[0043] The parametric modeling of the worm includes creating parameters, relations, reference benchmarks, and the worm geometry (such as Figure 1 ). First, create parameters, which include basic parameters and other geometric parameters. The basic parameters include: normal module m n , number of starts of the worm Z1, normal tooth profile angle α n , lead angle γ of the pitch cylinder, backlash coefficient c, addendum coefficient ha*, width b1 of the worm tooth, tooth space width coefficient s, and other geometric parameters are mainly the axial module m deduced from the basic parameters according to the standard formula a, the diameter coefficient q, addendum height ha1, dedendum height hf1, total tooth height h1, base circle diameter db1, pitch circle diameter d1, addendum circle diameter da1, and dedendum circle diameter df1. The deduced formulas are placed in the relationship. Then, create reference benchmarks, which are used to arrange the position of the worm and control key points, lines, and surfaces of the worm, such as the origin, reference coordinate system, theoretical central axis, intermediate perpendicular line, pitch circle, base circle, addendum circle, dedendum circle, tooth groove section, starting point of the helix, helix (helical tooth section trajectory line), etc. The constraints and dimensions of these benchmarks are controlled by basic parameters and other geometric parameters. Finally, create the worm geometry with reference to geometric parameters and reference benchmarks. The worm geometry is realized by features such as external cylinder extrusion, tooth profile grooving, and cylindrical array. The central curve and profile of the tooth profile grooving are the key to controlling the worm forming. The reference benchmarks are selected from the reference benchmarks such as the sketch pitch circle, tooth groove section, helix, etc.

[0044] Set the basic parameters in the worm model dialogue window (such as Figure 3 ), which are used as input parameters to directly control the corresponding basic parameters of the worm model. Cylindrical worms are divided into ZA, ZN, ZI, and other forming types, which are set in the type option bar in the upper left corner of the worm model dialogue window. The worm type is determined by the form and layout position of the tooth groove section. When the ZA worm is selected, the tooth profile is straight in the axial section. When the ZN worm is selected, the tooth profile is straight in the normal section, and a single grooving feature is required (such as Figure 5 (a) and (b) therein); when the involute ZI worm is selected, the tooth profile is straight on one side in the section tangent to the base circle. Since a single blade can only machine the tooth profile on one side, the left and right blades are respectively arranged in the upper and lower base circle tangent planes, and two grooving features need to be added. When the dedendum circle is smaller than the base circle, a dedendum grooving feature also needs to be added (such as Figure 5 (c) therein). After completing the creation of the worm model, adjust the basic parameters, click the "Refresh Model" function button in the worm model dialogue window, automatically update the corresponding parameters in the model, recalculate other geometric parameters, update the reference benchmarks and worm forming features, check the corresponding changed parameters and dimensions, and verify whether the followability of the parametric model is qualified. If it is unqualified, find the problem point and modify the corresponding position of the model, then click the "Refresh Model" function button again to verify the followability of the parametric model again until it is qualified to realize the creation of the worm parametric model.

[0045] After completing the qualified worm parametric model, start creating the worm machining tool model. Here, taking the machining of the ZI worm by a whirling milling cutter as an example, the cutting edge line of the blade is taken from the tooth groove normal section. The specific process of obtaining the point coordinate values (see Figure 6 ) is as follows:

[0046] First, according to the actual situation of machining ZI involute worm by whirling milling, create the normal plane of the tooth groove as the section for the tool to cut in, that is, along the normal direction of the worm tooth, the plane passing through the intersection point of the median line of the tooth groove (the axis that makes the tooth groove symmetrical left and right) and the worm axis. Select the normal plane of the tooth groove to create a section for the worm, and the intercepted middle tooth groove is the profile tooth groove. Different machining processes correspond to different sections, and the profile positions are different. Several sections are created in the worm model dialog box for selection. Then, select the tooth groove profile, merge the tooth groove profiles (the profiles are generally segmented), extract the overall profile as the cutting edge line of the whirling milling cutter blade, and generate the whirling cutter blade model. Generate the cutter head model according to the tool structure and installation form of the machining equipment, and assemble the cutter blade model onto the whirling milling cutter head model to complete the overall model of the worm machining tool. Take points on the merged tooth groove profile. The process of taking points is a cyclic process of defining point features on the curve at a ratio. The cyclic variable is i, and the range is from 0 to N, where N is the number of points taken, which is set in the worm model dialog box. Each time a point is taken, it starts from the starting point of the curve and takes a point at a distance ratio of i / N. Then, use the GetCoordinates Coord statement to extract the absolute coordinate values of each point (in the X1Y1Z1 coordinate system) and save them to an EXCEL document, which is stored at the specified location in the set name and format (.xlsx). The absolute coordinate values at this time (Coord / X1, Coord / Y1, Coord / Z1) need to be converted into the plane relative coordinate values (Coord / Y1’, Coord / Z1’) in the normal section of the tooth groove. Take the projection of the worm axis in the section as the Y1’ axis and the median line of the tooth groove as the Z1’ axis. The corresponding conversion formula is:

[0047]

[0048] Finally, if necessary, the curve formed by connecting the relative coordinate points can be fitted with an equation to generate the cutting edge line equation of the whirling milling cutter blade for use in the design, machining, and inspection of the worm machining cutter blade.

[0049] In the drop-down combo box of "Tool Cutting-in Section" in the lower left corner of the worm model dialog window, select the section for the tool to cut in, and associate these sections with the corresponding sections in the worm model. The normal section of the tooth groove, the normal section of the tooth tip, the axial section, the middle section parallel to the end face, the section tangent to the base circle above, and the section tangent to the base circle below are initially set. The tool cutting-in section and the corresponding sections in the model can be expanded according to needs. Click the "Take Points and Coordinates" function button to pop up a manual selection profile dialog window (such as Figure 7 ). After manually selecting the tooth profile, click the OK button in the dialog window to continue executing the program, realize taking points on the tooth groove profile, and then output the absolute coordinate values of each point (such as Figure 8) Save it with the set name and format (.xlsx) and store it in the specified location. The number of sampling points N is set in the "Number of Sampling Points" text box in the lower right corner of the dialog box. The more points, the higher the accuracy, but the greater the computational effort.

[0050] It is possible to check whether the cutting edge line of the machining tool matches the corresponding machining process method by arranging several relative positions between the worm machining tool and the worm model. If it is unqualified, analyze the reasons and modify it. If it is qualified, the coordinate points on the cutting edge line of the worm machining tool can be output.

[0051] Next, based on the completed parametric model of the worm, complete the model of the worm gear machining tool. Here, a multi-head large-diameter worm gear hob is used to machine the worm gear. The difference between the multi-head large-diameter worm model and the actual worm gear hob with the same parameters lies in the lack of tooth segmentation and the rake angle and relief angle at the cutting edge. The worm model can be fully used to replace the worm gear hob for subsequent simulation generating machining. Input the basic parameters of the worm gear hob, including the normal module m n 、number of heads Z 刀 、normal tooth profile angle α n 、lead angle γ of the pitch cylinder 刀 、tool mounting angle θ (i.e., the angle θ between the worm gear blank and the hob axis), clearance coefficient c 刀 、addendum coefficient ha* 刀 、tooth width b 刀 、tooth space width coefficient s 刀 , where the normal module m n and the normal tooth profile angle α n are the same as the worm parameters. The setting of the tool mounting angle θ is due to the fact that the axis intersection angle between the worm gear hob and the worm gear blank is not the same as the axis intersection angle between the worm and the worm gear. Therefore, set the angle θ between the worm gear and the tool axis (i.e., the tool mounting angle θ), and the axis of the hob is defined as the "rotatable central axis". The tooth profile modification of the worm gear is modified in the tooth space section according to the test conclusions or experience to modify the section sketch. After adjusting all the parameters and the tooth profile shape, refresh the model to generate a multi-head large-diameter worm model similar to the worm gear hob for subsequent simulated hobbing machining. This model can guide the design and manufacture of the worm gear hob.

[0052] In the dialog window of the worm model (such as Figure 3 ), input the basic parameters of the worm gear hob. When there is tooth profile modification of the worm gear, it is necessary to adjust the section sketch of the tooth space. Then, click the "Refresh Model" function button in the dialog window to generate the worm gear hob model.

[0053] Next, start creating the worm gear model. The specific creation process (see Figure 9) includes creating basic parameters, other geometric parameters, relations, reference datums, worm wheel blanks, and worm wheel gear forming. First, create the parameters of the worm wheel, including basic parameters and other geometric parameters. The basic parameters of the worm wheel include: number of teeth z2, angle θ between the worm wheel and the worm wheel machining tool axis (i.e. tool installation angle θ), displacement coefficient x2, center distance a, tooth top height coefficient ha2*, number of cycles i. Other geometric parameters of the worm wheel are mainly the pitch circle helix angle β2, tooth width b2, tooth top height ha2, tooth root height hf2, full tooth height h2, center circle diameter dm2, pitch circle diameter d2, tooth top circle (throat circle) diameter da2, tooth root circle diameter df2, outer circle diameter de2, which are calculated from the basic parameters according to the standard formula. The basic parameters and other geometric parameters are placed in the parameters, and the calculated formulas are placed in the relations. Secondly, create the reference datum. The reference datum for the worm wheel blank includes the origin, the reference coordinate system, the worm wheel axis point, and the axis line. Then, create the stretching feature of the worm wheel blank geometry. The stretching feature forming parameters include: outer diameter de2, tooth width b2, angle θ between the worm wheel and the worm wheel machining tool axis, and center distance a. Other geometric parameters are used as reference parameters and are not used to generate the worm wheel model. Finally, perform the worm wheel tooth forming operation. The worm wheel tooth profile that matches the worm is complex and difficult to accurately express according to the theoretical tooth profile line generation. Here, the generated worm wheel hob is used to simulate the machining forming process to create the worm wheel teeth.

[0054] The basic parameters of the worm gear are set in the Generate Worm Gear dialog window (such as Figure 4 ) as input parameters to directly control the corresponding basic parameters of the worm gear blank model. Click the "Refresh Model" function button to synchronously refresh other geometric parameters, as well as the datums and features in the worm gear blank model. Every time you change the basic parameters, you need to click "Refresh Model", but the features and entities in the subsequent Boolean subtraction and split operations of the generated gear teeth will not be updated and need to be deleted and regenerated.

[0055] The models of the worm gear machining tool (worm gear hob) and worm gear blank have been completed. Now, the worm gear teeth are generated by simulating the development process. There are four methods to realize the worm gear tooth forming: full tooth Boolean subtraction, single tooth Boolean subtraction array, full tooth segmentation, single tooth segmentation array, and you can choose any one of them. Before starting the worm gear tooth forming, you need to make the following preparations in the part module: arrange the accurate relative position of the worm gear machining tool and the worm gear blank geometry, determine the center distance and installation angle, prepare the Boolean subtraction cycle program, and set the basic parameters in the model. The basic parameters include: i number of cycles, Si worm gear transmission ratio, N total number of cycles (i.e., the full tooth 360° is completed in several cycles), n1 cycle starting point, n2 cycle end point, and "from n1 to n2" sets the start point to the end point of the cycle.

[0056] Method 1: Full-tooth Boolean Subtraction (Remove). Use a Boolean subtraction loop to simulate the process of a worm gear machining tool machining a worm gear, generating all teeth. The specific process (see Figure 10 ) is as follows:

[0057] First, copy the worm gear machining tool and rename it to "Worm Gear Machining Tool 00". Worm Gear Machining Tool 00 rotates around its own axis by i - Si * 360 / angle, and the rotation is named with the value of i * Si - 360 / . Then, Worm Gear Machining Tool 00 rotates around the axis of the worm gear blank by -i * 360 / angle, and the rotation is named with the value of -i * 360 / . Note the reverse rotation. Then, use the "Worm Gear Machining Tool 00" geometry obtained by rotation as the item to be removed in the Boolean subtraction, and remove it from the worm gear blank geometry. The Boolean subtraction is named with

[0058] the value of -i - 360 / , and randomly set the color for the cutting surface generated by the Boolean subtraction. If an abnormal problem is encountered during the execution of the above operations, the program sets different handling methods for different problems, and then enters the next loop. Repeat the above operations in a loop until all teeth are completed. The loop count i ranges from n1 to n2, generally n1 = 1 and n2 = N. Finally, hide the worm gear machining tool. In this method, in each loop, "Worm Gear Machining Tool 00" starts from the starting position, first rotates around its own axis, and then rotates around the axis of the worm gear blank. The entire loop completes all teeth, so it is defined as full-tooth Boolean subtraction.

[0059] Method 2: Single-tooth Boolean Subtraction (Remove) Array. Similar to full-tooth Boolean subtraction, use a Boolean subtraction loop to simulate the process of a worm gear machining tool machining a worm gear. First, generate a single tooth groove of the worm gear, then extract the single-tooth groove surface, then merge the tooth groove surfaces, array the merged tooth groove surfaces, and finally use the arrayed surface to divide and remove the surplus material of the worm gear blank to generate all teeth. The specific process (see Figure 11 ) is as follows:

[0060] First, copy the worm gear machining tool geometry and rename it as "Worm Gear Machining Tool 00". Worm Gear Machining Tool 00 rotates around its own axis by i - Si - 360 / Angle, and the rotation is named after the value of i - Si - 360 / . Then, Worm Gear Machining Tool 00 rotates around the axis of the worm gear blank by -i * 360 / Angle, and the rotation is named after the value of -i * 360 / , note the reverse rotation. Then, use the "Worm Gear Machining Tool 00" geometry obtained by rotation as the item to be removed in the Boolean subtraction, and remove it from the worm gear blank geometry. The Boolean subtraction is named after the value of -i * 360 / , and randomly set the color for the cutting surface generated by the Boolean subtraction. If abnormal problems are encountered during the execution of the above operations, the program sets different handling methods for different problems, and then enters the next loop. Repeat the above operation loop until a single tooth groove is completed. The loop count i ranges from n1 to n2, generally n1 = 0, n2 = N / Z2 (Z2 is the number of teeth of the worm gear). Subsequently, hide the worm gear machining tool, then extract the formed surface in each loop of the single tooth groove profile surface, and merge them. Before merging, it is necessary to process the formed tooth groove surface. Especially during the Boolean subtraction cycle, the cutting of the tooth tip of the worm gear tool is complex and cannot form a smooth surface. The more loops there are, the more complicated the processing process is, and it can only be processed manually, which affects the forming efficiency of the gear teeth. Extend the boundary of the merged overall single tooth groove surface, and then array the extended single tooth groove profile surface according to the number of teeth. Finally, use the split feature to cut the remaining material of the worm gear blank with the arrayed tooth profile surface, complete all the gear teeth of the worm gear, and hide the tooth profile surface. Currently, the automatic program can only achieve the completion of a single tooth groove in the Boolean subtraction cycle. The subsequent processing, merging, arraying, and splitting of the tooth groove surface need to be manually operated (except for the processing of the tooth groove surface, all other operations can be automated). In this method, in each loop, "Worm Gear Machining Tool 00" starts from the starting position, first rotates around its own axis, and then rotates around the axis of the worm gear blank. The whole loop completes a single tooth groove, then arrays the single tooth groove surface, and finally splits and forms. Therefore, it is defined as single tooth Boolean subtraction array.

[0061] Method 3: Full tooth splitting (Split), use the tooth profile surface to split in a loop to simulate the process of the worm gear machining tool cutting the worm gear and generate all the gear teeth. The specific process (see Figure 12 ) is as follows:

[0062] First, extract the profile surfaces of each group (head) of the worm wheel machining tool, merge each group of profile surfaces into an overall surface respectively, name it as the "profile surface of the j-th group", and hide the worm wheel machining tool. Then, enter the loop for selecting the first-layer profile surface. Select the profile surface of the j-th group. If a problem is encountered, the program jumps out and waits for processing (set loop protection). If there is no problem, enter the second-layer loop. Start the loop for splitting the profile surface of the j-th group. Copy the profile surface of the j-th group and rename it as the "profile surface of the j-th group 00". Rotate the profile surface of the j-th group 00 around its worm axis by i * Si * 360 / angle, and name the rotation by the value of i * Si * 360 / . Then rotate the profile surface of the j-th group 00 around the axis of the worm wheel blank by -i * 360 / angle, and name the rotation by the value of -i * 360 / , noting the reverse rotation direction. Then, use the rotated "profile surface of the j-th group 00" as the splitting element of the splitting feature to remove the tooth groove part from the worm wheel blank geometry, noting that the retention direction is set to the outside, and name the splitting by the value of -i * 360 / . Then, randomly set the color for the cutting surface generated by the splitting. If insufficient memory is encountered during the loop, save the data and exit the program. Repeat the above operations until all the teeth of the profile surface of the j-th group are split. Hide the profile surface of the j-th group 00. The second-layer loop is completed, and the loop count i ranges from n1 to n2 (generally n1 = 1, n2 = N). The loop count j of the first-layer loop ranges from 1 to Z 刀 , (Z 刀 is the number of heads of the worm hob) Repeat the selection of the profile surface and the second-layer splitting loop until all the teeth are completed. In this method, the worm wheel machining tool entity is replaced by the "profile surface" in each loop, and all the teeth are completed through two-layer loops, so it is defined as full-tooth splitting.

[0063] Method 4, single-tooth splitting (Split) array. Similar to full-tooth splitting, it uses the profile surface to perform loop splitting to simulate the process of the worm wheel machining tool cutting the worm wheel. First, generate a single tooth groove of the worm wheel, then extract the single-tooth groove surface, then merge the tooth groove surfaces, array the merged tooth groove surfaces, and finally use the array surface to split and remove the remaining material of the worm wheel blank to generate all the teeth. The specific process (see Figure 13 ) is as follows:

[0064] First, extract a set of tooth profile surfaces of the worm wheel machining tool, merge them into an overall surface, and hide the worm wheel machining tool. Then, enter the tooth profile surface segmentation loop. Copy the tooth profile surface and rename it as "Tooth Profile Surface 00". The Tooth Profile Surface 00 rotates around its worm axis by i * Si * 360 / Angle, and the rotation is named by the value of i * Si * 360 / . The Tooth Profile Surface 00 then rotates around the worm wheel blank axis by -i - 360 / Angle, and the rotation is named by the value of -i * 360 / , noting the reverse rotation. Then, use the rotated "Tooth Profile Surface 00" as the segmentation element of the segmentation feature to remove the tooth space part from the worm wheel blank geometry, noting that the retention direction is set to the outside, and the segmentation is named by the value of -i * 360 / . Then, randomly set the color for the cutting surface generated by the segmentation. If insufficient memory is encountered during the loop, save the data and exit the program. Repeat the above operations until a single tooth space is completed. The loop count i ranges from n1 to n2 (generally n1 = 0, n2 = N / Z2). Subsequently, hide the Tooth Profile Surface 00. The tooth space profile surfaces formed by the single tooth space segmentation loop are not flat and need to be processed. The more loops there are, the more complicated the processing process is, and it can only be processed manually, which affects the forming efficiency of the gear teeth. Extract the formed single tooth space profile surface after processing, merge the sub-surfaces into an overall surface, then extend the surface boundary, and then array the extended single tooth space tooth profile surfaces according to the number of teeth. Finally, use the segmentation feature to cut the remaining material of the worm wheel blank with the arrayed tooth space tooth profile surfaces to complete all the gear teeth of the worm wheel. Currently, the automatic program can only achieve the completion of a single tooth space in the segmentation loop, and subsequent manual operations such as tooth space surface processing, merging, arraying, and segmentation (except for tooth space surface processing, all other operations can be automated). This method replaces the worm wheel machining tool entity with the "Tooth Profile Surface" in each loop, first completes a single tooth space, then arrays the single tooth space surfaces, and finally segments to complete all the gear teeth. Therefore, it is defined as single tooth segmentation array.

[0065] Method 1 and Method 2 use the method of Boolean subtraction loop of the worm wheel machining tool entity. Method 3 and Method 4 use the method of segmentation with tooth profile surfaces. In Method 1 and Method 3, the loop completes all the teeth, and the large amount of data requires a computer with strong performance and large memory. In Method 2 and Method 4, the loop completes a single tooth, and then arrays the single tooth space surfaces, which requires relatively less computer memory. The loop step can be reduced to improve the tooth profile accuracy. However, the single tooth space surfaces need to be processed before they can be used for merging, arraying, and segmentation, and the surface processing process is complicated and time-consuming. In Method 1, Method 2, and Method 4, only one layer of loop is required in the loop, while two layers of loop are required in Method 3, making the logical operation complex.

[0066] If method one and method two encounter abnormal problems during the loop execution, the program sets different handling methods for corresponding problems. For example, when "a geometric body does not correctly cut another geometric body: unable to calculate the division" or "unable to cut the highlighted element: check its tangent contact point" appears, "deactivate" is performed; "failed to allocate bytes for the model" or "fatal error, unable to save, failed to allocate bytes, insufficient memory, store data, exit the program". When the computer performance is insufficient, it is necessary to appropriately reduce the number of loops or segment the loop. Method three and method four use the splitting feature of the surface. The splitting of the surface will not encounter problems such as "not correctly cut" and "unable to cut the highlighted element" in the Boolean subtraction. Even if the solid is not cut, there will be no error, and the amount of surface data is small, which will improve the running speed.

[0067] In the generated worm gear dialogue window (such as Figure 4 ), set the total number of loop steps "N" and the loop starting point to the ending point "from n1 to n2". "From n1 to n2" is set to "from 1 to N" in method one and method three to complete the full tooth cutting loop, or divided into several continuous segments to gradually complete the full tooth; in method two and method four, it is set to "from 0 to N / Z2" to complete the single tooth cutting loop. Click the "Boolean subtraction loop" function button to execute method one or method two; click the "splitting loop" function button to execute method three or method four. Comparing the advantages and disadvantages of each method, select any one way to generate the worm gear model (such as Figure 14 ), and the corresponding features are also added to the worm gear geometric body in the model structure tree (such as Figure 5 in (d)).

[0068] So far, the worm gear model with corresponding set parameters is created. Whether it meets the design requirements and product usage requirements needs to be verified and tested. Next, assemble the completed worm model and the worm gear model (such as Figure 15 ), create a transmission model, simulate the meshing motion, and observe and analyze the meshing state during the motion. The specific process (such as Figure 16 ) is as follows:

[0069] First, create a support base model so that the worm and the worm gear can be installed on the support base according to their relative positions. Then, assemble the worm model, the worm gear model and the support base. The support base is fixed, and the worm and the worm gear are arranged vertically and crosswise according to the center distance requirement. The worm gear can rotate around the axis on the support base, and the worm can rotate around its own axis. Create a mechanical device.1 (worm and worm gear mechanical device) in the DMU Kinematics mechanism module, set the joints, including the cylindrical joint between the worm gear and the support base and the cylindrical joint between the worm and the support base. Set the support base as a fixed part, add drive commands for the two cylindrical joints, and configure the relationship between the two commands according to the transmission ratio. For example, for the rotation of the worm gear, `Command.1\Angle = Mechanical Device.1\KINTime` / 1s * 6 deg; for the rotation of the worm, `Command.2\Angle = Mechanical Device.1\Command\Command.1\Angle` * 16.5, and the transmission ratio is 16.5 at this time. Simulate the movement of the worm and worm gear mechanical device.1, set the relevant parameters, and set the collision detection open state to "continue the collision movement". Play the simulation, mainly observe the continuity of meshing, the position of the meshing spot, the ratio of the meshing length to the tooth width, and the interference situation during the meshing movement of the worm and worm gear. Then analyze the observation results to preliminarily determine whether the generated worm gear model and the theoretical worm model meet the requirements (are qualified) in this state. If the meshing state does not meet the requirements (is unqualified), it is necessary to modify the basic parameters of the worm and worm gear, or the forming section of the worm, or the cutting edge line of the worm gear machining tool, etc. The basic parameters of the worm are modified in the "Worm Model" dialogue window; the basic parameters of the worm gear are modified in the "Generate Worm Gear" dialogue window; the forming section of the worm (the part not determined by the basic parameters, such as tooth profile modification) is modified in the sketch; the selection of the cutting edge line of the worm gear machining tool, the section setting, etc. need to be modified during the operation, and specific problems need to be analyzed and adjusted specifically. After modification, refresh the model, extract the cutting edge lines of the worm and the worm gear machining tool again, generate the worm gear model again, and re-check the meshing state until the meshing state meets the requirements (is qualified), indicating that the worm and worm gear match qualified under these parameters and tool cutting edge lines. The parameters of the worm gear machining tool (hob) or the absolute coordinate values of the points on the cutting edge line (turning or forming milling) can be output (in the X2Y2Z2 coordinate system), which need to be converted into the relative coordinate values in the cross-section plane. An approximate curve equation can also be fitted according to the point coordinates. The specific method is the same as the method for extracting the cutting edge line and coordinate values of the worm machining tool (whirling insert), and the output results are used to guide the design, manufacture and inspection of the worm gear machining tool.

[0070] Regarding the specific criteria and inspection methods for judging whether the conditions of the contact surface during movement (elastic deformation amount / interference), the shape and position of the meshing spot, and the ratio of the meshing length to the tooth width meet the requirements, they will not be described in detail here.

[0071] Set the "Point Picking and Coordinates" function button in the worm gear dialogue window. Its functions include creating points on a line and extracting point coordinates, which are the same as those of the "Point Picking and Coordinates" in the worm model window, except that the section for intercepting the profile is not set in advance. When it is necessary to obtain the tooth profile line from the worm gear, such as comparing the front and rear tooth profile lines of the cutting tool edge line when changing the machining method, or comparing the theoretical profile lines at the meshing position of the worm gear and the worm, create a section and extract the profile line according to the actual situation.

[0072] Up to this point, all processes are completed. When changing parameters or optimizing the matching of the EPS worm and worm gear, use this method to quickly generate the worm and worm gear models, quickly obtain the cutting tool edge line, and output the point coordinate values. The implementation of this method optimizes the meshing profile, reduces repetitive work, shortens the design and development cycle, is efficient and time-saving, and has strong versatility.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: modifying the technical solutions recorded in the foregoing embodiments, or equivalently replacing some or all of the technical features therein, does not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A parametric model of an EPS worm and worm gear transmission pair and a method for generating a cutting edge line of a tool, characterized in that, The steps include the following: First, create a worm model, including creating the basic parameters, other geometric parameters, relationships, reference benchmarks, and worm geometry of the worm; refresh the worm model to verify whether the followability of the worm model is correct. If it is unqualified, modify the basic parameters, other geometric parameters, relationships, reference benchmarks, and worm geometry, and then refresh the worm model until it is qualified to achieve the parameterization of the worm model; Second, extract the tool edge line, i.e., the tooth profile line on the section, and the coordinate values of the points on the line from the worm model according to the actual machining method for generating the model of the machining tool for the worm and the worm gear; check whether the tool edge line of the machining tool matches the corresponding machining process method by arranging several relative positions between the worm machining tool and the worm model. If it is unqualified, analyze the reasons and modify it. If it is qualified, output the coordinate values of the points on the tool edge line of the worm machining tool; Then, create a worm gear model, including creating the basic parameters, other geometric parameters, relationships, reference benchmarks, the blank geometry of the worm gear, and the formation of the worm gear teeth; Finally, assemble the worm gear model and the worm model according to the product structure, simulate the relative movement, observe the continuity of the meshing of the worm and the worm gear, the position of the meshing spot, the ratio of the meshing length to the tooth width, and the interference situation during the movement, analyze the observation results, and initially determine whether the worm gear model generated by the worm gear machining tool and the theoretical worm model meet the matching requirements. If the requirements are not met, modify the basic parameters of the worm and the worm gear, or the forming section of the worm, or the tool edge line of the worm gear machining tool; after modification, refresh the model, regenerate the worm gear model, and recheck the meshing state until the meshing state meets the requirements, and then output the parameters of the worm gear machining tool, i.e., hobbing, or the coordinate values of the points on the tool edge line, i.e., turning or profiling milling, to guide the design and manufacturing of the worm gear machining tool; The formation of the worm gear teeth includes the full-tooth segmentation of Method 3 and the single-tooth segmentation array of Method 4, both of which use the method of segmentation and circulation to form the tooth groove profile surface to achieve the formation of the worm gear teeth, thus completing the worm gear model; For Method 3, full-tooth segmentation, use the tooth profile surface to cycle and segment, simulate the process of the worm gear machining tool cutting the worm gear, and generate all the teeth. The specific process is as follows: First, extract each group of tooth profile surfaces of the worm wheel machining tool, merge each group of tooth profile surfaces into an overall surface respectively, name it as the "jth group of tooth profile surfaces", and hide the worm wheel machining tool; then, enter the loop for selecting the first-layer tooth profile surfaces. Select the jth group of tooth profile surfaces. If a problem is encountered, the program jumps out and waits for processing. If there is no problem, enter the second-layer loop; start the loop for dividing the jth group of tooth profile surfaces. Copy the jth group of tooth profile surfaces and rename it as the "jth group of tooth profile surfaces 00". Rotate the jth group of tooth profile surfaces 00 around the worm axis by an angle of i * Si * 360 / N, and name the rotation with the value of i * Si * 360 / N. Si represents the transmission ratio of the worm and worm wheel; then rotate the jth group of tooth profile surfaces 00 around the axis of the worm wheel blank by an angle of -i * 360 / N, and name the rotation with the value of -i * 360 / N, rotating in the reverse direction; then use the rotated "jth group of tooth profile surfaces 00" as the dividing element of the dividing feature to remove the tooth space part from the worm wheel blank geometry, set the retention direction to the outside, and name the division with the value of -i * 360 / N; then, randomly set the color for the cutting surface generated by the division. If insufficient memory is encountered in the loop, save the data and exit the program; repeat the operation until all the teeth of the jth group of tooth profile surfaces are divided. Hide the jth group of tooth profile surfaces 00. The second-layer loop is completed. The loop times i range from n1 to n2, where n1 = 1 and n2 = N; the loop times j of the first-layer loop range from 1 to Z 刀 , Z 刀 is the number of heads of the worm hob; repeat the selection of the tooth profile surfaces and the second-layer division loop until all the teeth are completed; For Method 4, single-tooth segmentation array, similar to full-tooth segmentation, use the tooth profile surface to cycle and segment, simulate the process of the worm gear machining tool cutting the worm gear, first generate a single tooth groove of the worm gear, then extract the single-tooth groove surface, then merge the tooth groove surfaces, array the merged tooth groove surfaces, and finally use the array surface to segment and remove the surplus material of the worm gear blank to generate all the teeth. The specific process is as follows: First, extract a set of tooth profile surfaces of the worm gear machining tool, merge them into an overall surface, and hide the worm gear machining tool. Then, enter the tooth profile surface segmentation loop. Duplicate the tooth profile surface and rename it as "Tooth Profile Surface 00". Rotate Tooth Profile Surface 00 by an angle of i * Si * 360 / N around its worm axis, and name the rotation with the value of i * Si * 360 / N. Then rotate Tooth Profile Surface 00 by an angle of -i * 360 / N around the worm gear blank axis, and name the rotation with the value of -i * 360 / N, rotating in the opposite direction. Then, use the rotated "Tooth Profile Surface 00" as the segmentation element of the segmentation feature to remove the tooth space part from the worm gear blank geometry, set the retention direction to the outside, and name the segmentation with the value of -i * 360 / N. Then, randomly set the color for the cutting surface generated by the segmentation. If insufficient memory is encountered during the loop, save the data and exit the program. Repeat the operation until a single tooth space is completed. The loop variable i ranges from p1 to p2, where p1 = 0 and p2 = N / Z2, and Z2 is the number of teeth of the worm gear. Subsequently, hide Tooth Profile Surface 00. Extract the formed single tooth space profile surface after processing and merge the sub-surfaces into an overall surface. Then, extend the surface boundary and array the extended single tooth space tooth profile surfaces according to the number of teeth. Finally, use the segmentation feature to cut off the surplus material of the worm gear blank with the arrayed tooth space tooth profile surfaces to complete all the teeth of the worm gear. In the steps of implementing the parametric model of the worm and worm gear and the tool edge line generation method, two custom windows are created: the worm model dialogue window and the generated worm gear dialogue window. Select the worm type through the worm model dialogue window, input the basic parameters of the worm, and click the "Refresh Model" button to synchronously update the model according to the selected type and set basic parameters. In the worm model dialogue window, set the "Tool Cutting Profile" to select the profile option for extracting the profile line of different worm machining tools. The "Get Points and Coordinates" function button realizes the function of extracting points and the coordinate values of the extracted points on the intercepted tooth space profile according to the selected profile, and set the "Number of Points to Get". The generated worm gear dialogue window is used to input the basic parameters of the worm gear and set the loop parameters. The "Segmentation Loop" function button realizes Method 3 or Method 4 of the worm gear tooth segmentation forming method, and distinguishes the previous method from the latter method by setting the loop parameters. The "Get Points and Coordinates" function button is the same as the "Get Points and Coordinates" function in the worm model dialogue window.

2. The parametric model of an EPS worm and worm gear transmission pair and the tool edge line generation method according to claim 1, wherein Set the basic parameters in the worm model dialogue window. As input parameters, they directly control the corresponding basic parameters of the worm model. Cylindrical worms are divided into ZA, ZN, ZI and other forming types, which are set in the type option bar in the upper left corner of the worm model dialogue window. The worm type is determined by the form of the tooth groove section and its layout position. When the ZA worm is selected, the tooth profile is straight in the axial section. When the ZN worm is selected, the tooth profile is straight in the normal section and a single slotting feature is required. When the involute ZI worm is selected, the tooth profile is straight on one side in the section tangent to the base circle. Since a single blade can only machine the tooth profile on one side, the left and right blades are arranged in the upper and lower base circle tangent planes respectively, and two slotting features need to be added. When the root circle is smaller than the base circle, the root slotting feature also needs to be added. After creating the worm model, adjust the basic parameters, click the "Refresh Model" function button in the worm model dialogue window, automatically update the corresponding parameters in the worm model, recalculate other geometric parameters, update the reference datum and the worm forming features, check the corresponding changed parameters and dimensions, and verify whether the followability of the worm model is qualified. If it is not qualified, find the problem point and modify the corresponding position of the worm model, then click the "Refresh Model" function button again to verify the followability of the worm model until it is qualified to complete the creation of the worm model.

3. The parametric model of an EPS worm and worm gear transmission pair and the tool edge line generation method according to claim 1, characterized in that, Select the profile where the tool cuts in the drop-down combo box of "Tool Cutting-in Profile" in the lower left corner of the worm model dialogue window, and associate the profile with the corresponding section in the worm model. The normal profile of the tooth groove, the normal profile of the tooth tip, the axial profile, the middle profile parallel to the end face, the profile tangent to the upper base circle, and the profile tangent to the lower base circle are initially set. Expand the tool cutting-in profile and the corresponding section in the worm model as needed. Click the "Get Points and Coordinates" function button, and a dialogue window for selecting the profile line will pop up. After manually selecting the tooth profile line and clicking the OK button in the dialogue window for selecting the profile line, continue to execute the program to obtain points on the tooth groove profile line, and then output the absolute coordinate values of each point, save them in the specified name and in the ".xlsx" format, and store them in the specified location. The number of points N is set in the "Number of Points" text box in the lower right corner of the dialogue box.

4. The parametric model of an EPS worm and worm wheel transmission pair and the tool edge line generation method according to claim 1, characterized in that, The reference coordinate system in the worm model and the worm gear model is default set with the direction parallel to the axis of the worm gear as the X-axis, the direction parallel to the axis of the worm as the Y-axis, and the common normal direction of the worm axis and the worm gear axis as the Z-axis. The worm model uses the X1Y1Z1 coordinate system with the midpoint of the worm axis as the origin, and the worm gear model uses the X2Y2Z2 coordinate system with the midpoint of the worm gear axis as the origin.

5. A parametric model of an EPS worm and worm gear transmission pair and a tool edge line generation method according to claim 4, characterized in that, Points are taken on the merged tooth groove profile. The process of taking points is a cyclic process of defining point features on the curve at a ratio. The cyclic variable is i, ranging from 0 to N, where N is the number of points taken and is set in the "worm model" dialog box. Each time a point is taken, it is taken at a distance ratio of i / N from the starting point of the curve. Then, the GetCoordinatesCoord statement is used to extract the absolute coordinate values of each point in the X1Y1Z1 coordinate system and save them to an EXCEL document, which is stored in a specified location with a set name and in the ".xlsx" format. The absolute coordinate values (Coord / X1, Coord / Y1, Coord / Z1) are converted into the plane relative coordinate values (Coord / Y1’, Coord / Z1’) in the normal section of the tooth groove. The projection of the worm axis in the section is taken as the Y1’ axis, and the median line of the tooth groove is taken as the Z1’ axis. The corresponding conversion formula is: Coord / Z1’ = Coord / Z1.

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