Creating a Lead Screw Gear Pair
In this tutorial, you define a tooth profile from scratch using embedded profile generator.
The first step is to input all gear parameters in the shape definition step of Gear AT preprocessing which stores all geometrical data including profile in a gear property file (*.tlp) which is used as input for meshing and for trapezoidal lead spindle gear element definition. The *.tld file represents data sheet of a gear, so it summarizes all basic geometrical data required to define profile.
Next step is to generate FE meshes, run Nastran SOL 101 and extract stiffness matrix to a gear stiffness file (*.tls), which is then used for gear force definition.
The figure shows the gear pair that you are going to create.
Prepare your working directory
To prepare your working directory:
1. Navigate to your working directory in which you create new directory named gears to store all files related to gears.
2. Go back to your working directory and create new directory named WS_01_ls_gear_pair.
3. Start Adams either from desktop or Windows Start menu → All Programs → Adams 20xx.
Opening Start Model
To open an existing start model:
1. Under the Welcome dialog box, select New Model.
2. Under the Create New Model dialog box, click OK button.
Loading the Workshop Model
To load a Workshop Start Model:
1. Click the Machinery tab on the Adams View ribbon and from the Gear AT container, click the icon to pop up Gear AT menu.
2. In the Menu, select the Gear AT → Help → Getting started → Lead screw → Workshop Start Model.
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Creating nut tooth property file using Gear AT Shape Definition
At this point there are no gear property files (*.tlp) available, so we have to prepare them from scratch. In this step we define a property file and definition file name (instead of browsing for an existing definition file) and enter all geometrical parameters manually.
To create the nut tooth Property file:
1. In the Gear AT menu, select Leadscrew → Gear AT Preprocess → Gear AT Shape Definition Leadscrew.
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2. In the Property file, name with relative path: ../gears/nut_coefficients (name of definition file is automatically filled up).
3. Enter values in the General tab as shown in figure.
4. Select the Mass tab.
5. In the Define Mass By option menu, select User Input.
6. Enter values in the Input Data FE Model section as shown in figure.
7. Select the Profile tab.
8. Check the option menu, and make sure that the COEFFICIENTS is selected.
9. Enter values in all required fields as shown in dialog box.
10. Click the Preview Profile button to review the tooth profile.
11. Click the Generate button.
12. The nut_coefficients.tlp file is created in the ../gears directory. Click the Cancel button to close the Gear AT Shape Definition dialog box.
Meshing nut tooth using Gear AT Mesh
In this step we preprocess FE mesh of a flexible tooth based on profile stored in a *.tlp file and generate shell file for Adams geometrical representation. Hereafter the stiffness matrix of a flexible tooth is generated with the help of Nastran embedded solver in Adams which is stored in *.tls file located in the gears folder. It will be referenced for the gear pair contact force definition later on.
To create Nastran mesh and the geometry of the Nut:
1. In the Gear AT menu, select Leadscrew → Gear AT Preprocess → Gear AT Mesh.
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2. In the Property File, right click and Browse the ../gears directory for the: nut_coefficient.tlp.
3. Select the FE Data tab.
4. Select the option Moderate mesh.
5. Select the More toggle for more options.
6. Enter values in the FE Data tab as shown on figure.
7. In the display option, make sure to select All for the Number of teeth to display toggle.
8. Select the Preprocessor: External ViewFlex.
9. Select the Preprocessing Mode: Run Monitored.
10. Click the Generate button, and click YES to confirm the start of preprocessing and wait till the SOL101 is completed
Creating spindle tooth property file using Gear AT Shape Definition
To create the spindle tooth property file:
1. In the Gear AT menu, select Leadscrew → Gear AT Preprocess → Gear AT Shape Definition Leadscrew.
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2. Type in the Definition File name with relative path: ../gears/spindle_coefficients (name of property file is automatically filled up, but you can change this name as required).
3. Enter values in the General tab as shown in figure.
4. Select the Profile tab.
5. Check the option menu, and make sure that the “coefficients” is selected.
6. Enter values in all required fields as shown in dialog box.
7. Click the Preview Profile button to review the tooth profile.
8. Click the Generate button.
9. The spindle_coefficients.tlp file is created in the ../gears directory. Click the Cancel button to close the Gear AT Shape Definition dialog box.
Meshing spindle tooth using Gear AT Mesh
To create Nastran mesh and the geometry of the spindle:
1. In the Gear AT menu, select Leadscrew → Gear AT Preprocess → Gear AT Mesh.
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2. In the Property File, right click and Browse the ../gears directory for the: spindle_coefficients.tlp.
3. Select the FE Data tab.
4. Select the option Moderate mesh.
5. Select the More toggle for more options.
6. Enter values in the FE Data tab as shown in figure.
7. In the display option, make sure to select All for the Number of teeth to display toggle.
8. Select the Preprocessor: External ViewFlex.
9. Select the Preprocessing Mode: Run Monitored.
10. Click the Generate button, and click YES to confirm the start of preprocessing and wait till the SOL101 is completed.
Creating Nut Gear AT Element
To create Nut Gear AT Element:
1. In the Gear AT menu, select Leadscrew → Gear AT Element → Gear AT Nut Element → New.
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2. Enter the Gear Name: Nut.
3. In the Property File, right click and Browse the ../gears directory for the: nut_coefficients.tlp.
4. Right click in the Ring Gear Reference Marker field, go to Marker and Browse for the ref_nut, which belongs to the Nut_body part.
5. Click the Apply button.
6. The Nut Gear AT Element has been created.
Creating Spindle Gear AT Element
To create spindle Gear AT Element:
1. In the Gear AT menu, select Leadscrew → Gear AT Element → Gear AT Spindle Element → New.
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2. Enter the Gear Name: Spindle.
3. In the Property File, right click and Browse the ../gears directory for the: spindle_coefficient.tlp.
4. Right click in the Ring Gear Reference Marker field, go to Marker and Browse for the ref_spindle, which belongs to the Spindle_body part.
5. Click the OK button.
6. The Spindle Gear AT Element has been created.
Creating Gear AT Contact Force for Leadscrew gear pair
Theory – Damping Force
The function b defined by:
b = 1.0 - gap / (2*oil film thickness)
is used to smooth the damping.
There is no hydrodynamic damping, when b < 0:
F hyd = 0 for b<0
Hydrodynamic damping increases exponentially with decreasing oil film height. The introduction of the damping exponent d_exp:
F hyd = damp rate oil * squeeze vel * vel bd_exp for 0>b>1
is used for this purpose (see Figure 1)
Figure 1 Oil Film Thickness
The structural damping force is made proportional to the contact force as shown by:
F struc damp = F cnt * Damp structure * sign (squeeze vel)
A value of 0.01 means, that the structural damping force is 1.0 percent of the elastic contact force.
Theory – Friction Force
The static friction coefficient (
s) is usually somewhat higher than the dynamic friction (
d) coefficient. Step functions are used for smoothing the transitions (Figure 2). Parameter of slip velocity (Vs) limits the region of sign change of the sliding velocity.
s) is usually somewhat higher than the dynamic friction (d) coefficient. Step functions are used for smoothing the transitions (Figure 2). Parameter of slip velocity (Vs) limits the region of sign change of the sliding velocity.The combination of very small slip velocity (Vs) and high friction can reduce the performance of the integrator. You are advised to validate this selection through postprocessing of the sliding velocity.
Transition velocity (Vd) defines the start of the region, where the dynamic friction is constant. A small difference between slip velocity (Vs) and transition velocity could (Vd) also lead to numerical issues of the integrator.
Figure 2 Friction vs. Slip Velocity
To create gear contact force for the gear pair:
1. In Gear AT menu, select Leadscrew → Gear AT Force → New.
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2. Enter the Gear Force Name: leadscrew_gear_force.
3. Right click in the Nut field, go to gear_at_leadscrew_t_nut_element and Browse for the Nut.
4. Right click in the Nut field, go to gear_at_leadscrew_t_spindle_element and Browse for the Spindle.
5. In the Stiffness File Nut (tls), right click and Browse for TLS file of the Nut in the ../gears directory: nut_coefficients_004_02_06.tls.
6. In the Stiffness File Nut (tls), right click and Browse for TLS file of the Spindle in the ../gears directory: spindle_coefficients_003_02_06.tls.
7. Set Modeling Option to Flexible Tooth.
8. Set Contact Overlap to Normal.
9. Go to Friction tab.
10. Set the Friction Model to ON.
11. Go to Damping tab and enter the Damping Rate Oil: 10.0.
12. Click the OK button.
13. The Gear AT Force has been created.
Note: | The color of the Nut and Spindle Gear AT Element has changed. The color coding is set according to the role of a gear. |
Completed Leadscrew gear model
Setup Input motion and Output Torque
Before running simulation make sure that values of following testrig parameters are set as shown thus the driving motion function is constant at 200 RPM and the output force steps up from 50% to 100% of 9000.0N.
1. In the Gear AT menu, select Help → Getting Started → Setup Workshop Testrig.
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2. Go to Input speed tab and set the driving motion parameters as shown.
3. Go to Output force tab and set the loading force parameters as shown.
4. Click the Apply button.
Set the Solver Settings
To set the solver settings:
1. In the Menu, select Settings → Solver → Dynamics.
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2. Select the Integrator: HHT.
3. Enter the Error: 1.0E-06.
4. Enter the Hmax: 1.0E-04.
5. Change the Category to: Executable.
6. Set the Executable to: External.
7. Change the Category to: Display.
8. Set the Show Messages to: Yes.
9. select Category: Output.
10. Set the Save Files: YES.
11. Set the File prefix: Adams.
12. Set the Graphics File: NO.
13. Set the Request File: NO.
14. Set the Results File: YES.
15. Select Category: Equilibrium.
16. Select the More options.
17. Enter the Tlimit: 0.01.
18. Enter the Alimit: 0.01.
19. Enter the Maxit: 250.
Note: | Using default solver settings for static equilibrium could result in failure to reach convergence for static and quasi-static simulation. |
Verify simulation script and run the simulation
To verify the simulation script and run the dynamic simulation:
1. In the Model Browser double click on Simulations, right click on dyn_run and select Modify.
2. Verify the Solver Script and click OK button.
3. In the Simulation tab select Run a Scripted Simulation.
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4. In the Simulation Script Name, right click and go to Simulation_Script, and Browse for the: dyn_run.
5. Push the Play button to start the simulation. The simulation will take a few minutes to run.
Investigating simulation results
In the Adams Postprocessor you can investigate the simulation results.
Make plot of Spindle Nut Power:
1. Switch to Adams Postprocessor (press F8 on keyborad).
2. Select the Source: Requests.
3. Select the Request: Dyno_measurement.
4. Select the Component: Spindle_Power and click Add Curves button.
5. Select the Component: Nut_Power and click Add Curves button.
Make plot of Spindle and Nut Speed and Torque:
1. Create a new page
2. Select the Request: Dyno_measurement.
3. Select the Component: Nut_Ang_Speed, click Add Curves button.
4. Select the Component: Spindle_Tran_Speed, click Add Curves button.
5. Select the Component: Nut_Torque, click Add Curves button.
6. Select the Component: Spindle_Force, click Add Curves button.
Make plot of Nut axial force FZ exerted on screw and Nut torque applied around its rotational axes TZ:
Note: | The results are reported in so-called in element coordinate system denoted by “s” index for spindle (screw) and “n” index for nut on as shown on theFigure 3. In the Total Force and Torque request group the vectors represent sum of all components from contact stiffness, damping and friction. However, one can plot each component of total force or torque separately. For more information, refer Gear AT Results.  Figure 3 Gear_AT_LS_gear_contact_co-ord_sys |
1. Create a new page
2. Select the Request: leadscrew_gear_force_Total_Force_and_Torque.
3. Select the Components: FZ_Nut and click Add Curves button.
4. Select the Components: TZ_Nut and click Add Curves button.
Make plot of Spindle Nut Relative angular velocity WZ and Relative translational velocity VZ:
1. Create a new page
2. Select the Request: leadscrew_gear_force_Kinematics.
3. Select the Component: Relative_WZ and click Add Curves button.
4. Select the Component: Relative_VZ and click Add Curves button.
Make plot of Spindle Nut Friction:
1. Create a new page
2. Select the Request: leadscrew_gear_force_Friction.
3. Select the Component: TZ_Nut and click Add Curves button.
4. Select the Component: Tooth_0_Tz_Frict : Tooth_3_Tz_Frict, and click Add Curves button.
Theory – Teeth Numbering convention
To plot tooth force magnitude applied on all teeth in contact:
1. Create a new page
2. Select the Source: Requests.
3. Select the Request: leadscrew_gear_force_Total_Force_and_ Torque.
4. Select the Components: Tooth_0 : Tooth_3 and click Add Curves button.
5. Zoom in the plot as appropriate.
Save your Work
This concludes the workshop, save your work before exit.
To save your model:
1. Switch to Adams View (press F8 on keyboard).
2. In the File menu, and select Export....
3. Select the File Type: Adams View Command File.
4. Enter File Name as WS_01_LS_finished.
5. Click the OK button.
6. The CMD file is exported to your working directory. You can use it in the next workshop.
