Figure 1 - Delta Theta Input Selection

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1 Creating Cams in Pro/Engineer Wildfire Using DYNACAM Mechanical Engineering Mechanical Design Created by: David E. Yamartino M.S. Mechanical Engineering May 2004 April 12, 2004 Objective: The objective of this supplement is to aid students working on projects and MQP s in creating cams for use in motion analyses in Pro/Engineer Wildfire from cams created using Professor Norton s professional version of DYNACAM. This supplement will cover exporting surface points in DYNACAM, importing these points into Wildfire for creation of a cam, defining cam-follower connections in the motion modeling portion of Pro/Engineer, Mechanism, and running an analysis. Assumptions: The following assumptions were undertaken when writing this paper: 1. Readers are familiar with the DYNACAM cam modeling software to create cam input motion profiles (s, v, a, j profiles), size the cam properly using either a translating or oscillating rocker follower, and running dynamic and vibrational analyses for the particular cam operating speed. 2. Readers are currently using the Professional Edition of DYNACAM (not the student versions in the lab). 3. Readers are familiar with basic Microsoft Excel operations and usage. 4. The CAD model is developed with ground bodies and joints between the moving and non-moving components. The linkage system should have the following components before the cam connection is added: Ground bodies Linkage system and joints defined A roller-follower with a pin joint between the roller and lever arm A cam shaft that is either stationary or can rotate due to a pin joint with a ground body 1

2 5. CAD modeling techniques and connections will not be discussed in this document except for the connection between the cam and follower. 6. The figures in this supplement are from the author s thesis project and may not represent the reader s physical situation or layout. Components and techniques present in this supplement may have to be adapted for certain situations. Exporting DYNACAM Information: The reader must first ensure that the current cam is completed and fully analyzed for kinematic performance using the professional DYNACAM software package. Users must input the appropriate follower pivot location, length and follower diameter information into the Sizecam tab in DYNACAM. DYNACAM has the ability to change the angular calculation rate for any cam project, i.e. the step size of the cam. These settings can be changed in the S-V-A-J button when DYNACAM opens and can be seen in Figure 1 below. Figure 1 - Delta Theta Input Selection The Delta Theta pull down menu allows the user to change calculation step sizes to produce a more accurate cam solution. For example, if 1.0 is selected, there will be one 2

3 step or calculation for every degree (360 data points when outputting surface files). If 0.25 is selected, the computer will produce 1440 data points. The author of this supplement suggests calculating cams for use in Pro/E for every degrees that would result in 2880 data points. This is done to allow a very accurate spline curve to be drawn into Pro/Engineer, and less error is produced when the CAD software interpolates between data points. Once this is selected, you will need to Calc All through the input and size cam screens in DYNACAM. In the Size Cam Screen, pay careful attention to the Keyway At pulldown menu. You will need to select 12, 3, 6, or 9 o clock as dictated on the cam drawing. Figure 2 shows the Keyway screen shot from DYNACAM. Figure 2 - DYNACAM Size Cam Screen After the cam has been designed and sized, the surface profile must be exported so it can be imported in Pro/E. Use the following commands in DYNACAM after the Draw Cam screen is finished: 3

4 File>Export>Profile>Cam Surface X-Y Coordinates Vs. Machine Zero. Save the file to your computer. The name will be *.pts Creating a Cam in Pro/E: Once the x-y surface point file has been created, it must be slightly modified in Excel before it can be input into Pro/E. Open the *.pts file in Excel (select Excel if a dialog box appears asking you to choose an application with which to open the file). Delete rows 1-6. (Figure 3) Figure 3 - Cam Coordinates in Excel before Editing When you are finished, you should have 2880 data points with x, y, and z coordinates for the cam as in Figure 4. Figure 4 - Cam Coordinates in Excel after Editing 4

5 Click on the Disk Icon (save) in Excel and you will be prompted with the dialog box in Figure 5. Figure 5 - Excel Save Dialog Box Click on Yes. Then exit out of Excel and click No to any other save dialog boxes. The file is now ready to be imported into Pro/Engineer. Creating a Cam in Pro/E: Now the cam from the surface points can be modeled in the CAD software. Create a new part and title it with the name of the cam. The methodology for cam creation in Pro/Engineer Wildfire is to first sketch a datum spline curve that contains the output data file from the designed cam. Once the datum curve has the cam profile, a protrusion will be extruded and then the keyway and shaft hole can be cut along with any other features need to be included on the cam part. Once the new file is open, click on the sketched datum curve icon ( ). Pick the datum planes you would like for a reference (generally Front and then Top for the right plane). Before any sketching can be done, a sketcher coordinate system must be inserted at the intersection of the two reference planes. From the sketch menu, choose Coordinate system and place the coordinate system at the intersection of the two planes (it should snap in the center). 5

6 Use the spline icon ( ) to draw an arbitrary egg shape spline curve around the newly created coordinate system with three or four data points as shown in Figure 6. Generic Spline Coordinate System Figure 6 - Generic Spline Sketch in Pro/E A generic spline is then edited and the three or four data points are replaced with the 2880 (or other increment) exported from DYNACAM. Double click on the spline curve to bring up the spline edit dashboard below the sketcher screen. Clicking on the File menu in the spline dashboard should bring up the following screen: 6

7 DYNACAM exports Cartesian points, so this can be left with the radio button checked. Pro/E is prompting the user for a coordinate system. Click on the black arrow to activate this selection box and then click on your newly created coordinate system IN THE SKETCHER. DO NOT USE THE MODEL TREE. The sketcher coordinate system must be selected. Once this is completed, the Open, Save and Info buttons will light up. Now click on the yellow folder icon to open an import dialog box: Select the file you created with DYNACAM and Excel (note: if the file is not in the same working directory as your parts, you will have to use the navigation buttons to locate the file and open it). Once the file is open, you will get the following message from Wildfire: You should select yes. This question is asking the user to replace the three or four original data points with the 2880 from the DYNACAM file. This is OK. Your cam profile will now be shown on the screen with the spline. Remember that your keyway will always be pointing towards the top of the screen, depending on what you selected in DYNACAM. Be prepared to rotate the part in the assembly if the keyway is at 3, 6 or 9 o clock. 7

8 A spline curve has been created on a datum plane that follows the cam surface profile. You may also use the roller center or other export options in DYNACAM, but must compensate by extruding differently in Pro than as follows. Create a new extruded feature and select the same datum planes as the sketched spline. In the sketcher, you must click on the use edge icon ( ) and select the spline profile. The spline cam surface should be highlighted in cyan and edge will be selected as a reference. That s all that needs to be done in the extrusion sketcher. You may extrude your sketch to the appropriate running thickness (consult your engineering drawing and it is recommended to use both sides so the spline curve is in the center of the cam running surface). Now you can cut the shaft hole, keyway, add the flange and any other features such as rotation direction and cam name. The cam is now completed in Pro/E and should look something like Figure 7. Figure 7 - Pro/Engineer CAD Cam Setting Up and Running an Analysis: Before a cam-follower motion analysis can be conducted, the new cam part must be imported into the assembly and two connections made: The rotation joint between the cam and a stationary object 8

9 The cam joint between the cam running surface and the follower running surface. It is recommended that the cam be the last component brought into the assembly. It is suggested that all ground bodies be inserted and offset using the appropriate dimensions and references. Next, start with one end of the linkage system, bringing in each rotating part and then adding the appropriate joints (pin, cylinder, slider, etc.). Work your way back through the linkage system (i.e. adding upper rocker arm first and then connecting rod, then cam lever etc for a typical industrial cam-follower system). Then finally add the cam rotational joint and then set up the cam-follower interface. Cam Rotational Joint There are two methods for attaching the cam to the assembly; first, all require a rotational connection between the cam s central axis and a non-moving ground component. A pin joint may be placed using the cam s axis and a grounded axis and then the translational portion can be added to a surface or datum plane. For this case, you will need to know the exact distances the cam s face or center is from another reference. Optional Connection Method If the distance between the cam and some other grounded object or distance along the camshaft is not known, a second method of rotational joint may be applied. To conduct this, add a cylinder joint between the cam s rotational axis and the grounded rotational axis. Then in essence, create a pin joint by adding a slider joint between the cam s side surface and the flat face of the follower as shown in Figure 8. This will produce a pin joint with the same DOF and allows the cam face to snap up against the follower face. Again, there are a variety of options for inserting the cam s rotational joint. 9

10 Figure 8 - Alternate Cam Rotational Joint Connection Location Cam-Follower Connection To create the cam-follower joint enter the Mechanism Application: Applications>Mechanism We will now need to add a cam-follower connection to join the cam and follower. The cam-follower connections in Mechanism require two surfaces on different parts. Cam1 is the full surface of the cam and Cam2 is the full surface of the roller-follower. Note that you must select the surface the cam and follower will run against. 10

11 Click the cams icon on the right toolbar ( ) and open a cam dialog box. Click on New to add a new connection. You may rename the cam-follower connection if desired. The cam dialog box should look something like below: Figure 9- Cam-Follower Interface Dialog Box To choose the face of the cam, click on Autoselect and choose one of the faces the follower will run against. If Autoselect works correctly, the entire running surface of the cam should be highlighted in red. If this is fine, click on the OK box in the small select dialog (this may be hidden) and the cam running surface should be highlighted in cyan. Click on the Cam2 tab and use the same procedure to select the other running surface of the roller. Make sure you get both sides of the roller because Pro/E divides all round objects into 2 parts. If Autoselect does not work, choose each face by selecting a face, holding Ctrl and selecting the other face. Make sure to always select OK in the small select dialog box. Figure 10 shows the faces that should be selected for the cam. 11

12 Roller Follower Surface Cam Running Surface Figure 10 - Cam and Follower Selection Surfaces Congratulations, you have successfully created a cam from DYNACAM and imported it into a CAD assembly. For the motion analysis, remember to setup a snapshot in the Drag box that has the cam at Machine Zero for starting. Determine the time for one complete revolution of the cam and this becomes the time increment. Select a frame rate that will produce around 100 time steps (more steps if a more in depth analysis is required). The cam can then be moved using the Drag hand and the motion of the linkage system will follow. To motorize the cam, add a driver with the appropriate angular velocity to the rotational cam joint between the axis of revolution of the cam and ground body. 12

13 Conclusions: This supplement should assist a student in producing a cam in Pro/Engineer from a DYNACAM design. Experience with cam design, program DYNACAM, CAD modeling and motion analysis are all required for the successful completion of the cam system. The cam can be analyzed kinematicaly and dynamically in DYNACAM and then a motion analysis can be conducted in Pro/E to determine similar parameters for comparison, tooling clearance or follower motion. References: Ault, H.K. and D.E. Yamartino. ES 3323 C04 Cam Lab. Worcester Polytechnic Institute, ES 3323 Advanced Computer Aided Design, Norton, R. L. DYNACAM Cam Simulation Software Program, Yamartino, D.E. Analysis, Modeling and Redesign of Cam-Follower Systems to Increase Operating Speed. Worcester Polytechnic Institute, MS Thesis, April