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Accurate gear 3D model has important significance for all aspects of gear research and CNC machining of gear molds. At present, CADCAM software can generate three-dimensional models of involute gears, but because of the inconvenient treatment of the transition curve between the base circle and the root circle (the transition curve is not regular), the generated three-dimensional model of the gear has errors. The program is written in the AutoLISP language embedded in AutoCAD, and the three-dimensional model of the gear is generated by simulating the actual cutting, which ensures the consistency of the gear 3D model with the actual. In addition, the entire simulated cutting process is observable.
1 program design principles and methods In order to expand the scope of the program, can cover a variety of actual processing conditions, the program should meet the requirements of standard gears and non-standard gears. The program consists of two parts: one is the AutoLISP main program; the other is the DCL dialog file. The program process is as follows: 1.1 Calling the DCL dialog file for convenience, the program uses dialog form to input parameters.
After calling the DCL dialog file, the parameter input dialog box appears, and the required parameters are entered in the dialog box. It can be seen from the parameter item of the dialog box of the Natural Science Foundation of Jinggangshan College of Jiangxi Province (04LY07) that the program can input the parameters of standard gears and non-standard gears.
1.2 Program Simulation The gear cutting program simulates the same method as the actual machining gear to machine the gear and generate a three-dimensional model of the gear. Since the rack type tool is easy to draw with AutoCAD, the rack cutting tool is used for the analog cutting process.
The program should reflect the principle of Fancheng processing, and the contents are as follows: (1) Drawing a wheel blank and a rack-type tool map. The program calculates the coordinate values ​​of the graphic control points based on the input gear parameters, and calls the Auto2CAD command to draw the rack-type tool and the wheel blank.
(2) The program ensures the relative position of the rack-type cutter and the wheel blank, which is consistent with the actual engagement. That is, the center distance between the index line of the rack-type cutter and the wheel blank is: 0.5mz xm (m is the modulus, and x is the displacement coefficient).
(3) The program reflects Fan Cheng's processing movement. During the cutting process, the movement amount Δ of the rack-type cutter and the rotation angle β of the wheel blank are in accordance with the meshing motion relationship: Δ = β (π Π180) × (0.5 mz), and the β unit is (°).
(4) The essence of the simulated cutting is to call the difference command subtract to remove some of the entities from the wheel blank. The simulated cutting process is as shown.
(5) The program has a parameter prompt to prevent erroneous input. If the number of teeth is too small, the program reminds the user to generate an undercut; when the displacement coefficient x is too large, the user is reminded that the tip of the tooth will be sharpened; if the diameter of the inner hole is not properly entered, the user will be prompted to adjust the input parameters.
2 source program source program can be edited in Windows Notepad or VisualLISPEditor in AutoCAD. The main program is a LISP file, which is named gear.lsp.gear.lsp and saved in the C drive. The DCL dialog file is named dclgear.dcl.dclgear.dcl and is saved in the Support directory of Au2toCAD. The main program excerpt is as follows: (defunC:gear(Πdclfiledclnamedclflagokid); specify the main expression name gear(setqdclfile "dclgear"; specify the dialog DCL file name dclname "gear1"); specify the dialog name (setqdclflag(loaddialogdclfile)); Into the DCL file); the main expression ends defungearinput; specify the expression name (acquire input parameters) (setqz (atof (gettile "keyz"))); parameter conversion (setqm (atof (gettile "keym"))); parameter conversion ); expression end (defundogear (Πddadf); specify the expression name (simulated cut) (setqd (3mz)); calculate the value (setqda (d (32.0m) (32.0mx))); calculate the value (setqdf (- ( d(32.0mx))(32.5m))); calculate the value (setqgp0 (getpoint "insert reference point Basepoint:")); determine the input point on the screen (while(<=gdis(3( 1z)pim)); Start of the cycle (command "move" entgg "" gp6(list(cargp6)(cadrgp6)(-(caddrgp6)(32.0b))))(command "copy"entgg""gp6gp6)(s Etqentggg(entlast))(command "subtract"ent3dpp""entggg"")(command "move"entgg""gp6(list(cargp6)(cadrgp6)( (caddrgp6)(32.0b))))(command "rotate" Ent3dpp""gp0gaccur)(command "move"entgg""gp6(list(-(cargp6)(Π(3pimgaccur(30.5z)))))(cadrgp6)(caddrgp6)))(setqgdis( gdis(Π(3pimgaccur) (30.5z))-180)))); end of cycle); expression end 3 example gear tooth number z=20, modulus mn=12, displacement coefficient x=0, tooth angle α=22.5°, tip The high coefficient h3=1, the head clearance coefficient c3=0.25, the inner hole diameter D=130, the gear width B=60. It can be seen that the gear is a non-standard gear, and the modulus is large, limited by the machine tool and the tool. Gears are not convenient for conventional machining.
After entering AutoCAD, load the program: command: (load "c: gear") and press Enter. At this time, the gear is used like the original AutoCAD command.
Command:gear Enter the name of the program and press Enter to display the dialog box as shown. Enter the parameters in the above example in the dialog box, press the OK button, the program simulates cutting, the upper and lower movements of the rack-type tool, and finally the three-dimensional model of the gear as shown. The model is exactly the same as the actual one.
Gear 3D Module 4 Conclusion (1) In this way, a precise gear 3D model that is identical to the actual machining can be obtained.
(2) Using this method to obtain the three-dimensional model of the gear can be free from the limitation of whether the gear is a standard gear or not because the gear module is too large and is limited by the machine tool and the tool.
(3) The obtained precision gear model has a wide range of applications, such as accurate calculation of displacement of gear oil pumps, study of kinematics of gears, design and manufacture of gear molds.
(4) Further research on this method can be applied to the design and manufacture of some new gears, because most of the new gears are not standard gears, and it is difficult to obtain three-dimensional models of gears by conventional methods, such as the recent Logix gears.