ME 3222 Design & Manufacturing II. Creating and Animating a Slider-Crank in Creo Elements (Version 2.0)

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1 ME 3222 Design & Manufacturing II Creating and Animating a Slider-Crank in Creo Elements (Version 2.0) Tom Chase February 18, 2016 Overview This document explains how to create a mechanism and animate it in Assembly mode of Creo. The procedure for a slider-crank is discussed in this example. However, a similar procedure can be used for four-bar linkages. Multi-loop mechanisms, multi-degree-of-freedom mechanisms, and spatial mechanisms can also be animated using similar methods. Preliminary Steps 1. We have created a series of model and sub-assembly files for you corresponding to the slider-crank example described here. Please go to the Discussion Sections link of the ME 3222 web site. Click on the link for Linkage Analysis Software. Download the following files to a folder of your CSElabs account that you can access from Creo: (a) coupler link.prt (b) coupler pin.prt (c) crank gnd pin.prt (d) crank link.prt (e) frame.prt (f) slider.prt (g) coupler asm.asm (h) crank asm.asm (i) frame assm.asm (j) slide assm.asm 2. Create an assembly model for the overall mechanism. Assemble the frame link sub-assembly (frame assm.asm) to the overall assembly using conventional assembly constraints 1. Adding and Animating the Crank Link 1. Adding the crank link: (a) Bring the crank model into the overall assembly model as follows. Select the Add a component to the assembly icon from the menu at the top of the graphics window (see Fig.1). Open the crank assembly file (crank assm.asm) 2. (b) Set the joint type as follows. Locate the field in the component placement dashboard that reads User Defined by default. Select Pin from the drop-down menu associated with this field. (c) Align the revolute joint axes as follows. Click on the Placement tab of the component placement dashboard. The Axis alignment constraint will be highlighted by default. Align the crank ground pivot joint axis with the corresponding axis on the frame link. (d) Set the z position of the crank relative to the frame as follows. The Translation constraint 1 The frame assembly should have an axis, F AXIS, visible on it. If it does not, open file FRAME ASSM.ASM. Then, choose Show -> Layer Tree from the model tree on the left of the screen. Right-click on DEF AXIS, then choose Unhide. 2 The crank assembly should display axes symbols at the pin joints. If it does not, temporarily cancel the addition of the crank component by selecting the red X at the right of the component placement dashboard. Open file CRANK ASSM.ASM. Then, choose Show -> Layer Tree from the model tree on the left of the screen. Right-click on DEF AXIS, then choose Unhide. Then, return to the main assembly model and re-start the procedure to add the crank link. 1

2 Add a component to the assembly Play current result set Regenerate Figure 1: Assembly icon menu. will now be highlighted by default. Select the center plane in the crank sub-assembly ( CRANK-C ) and the center plane in the frame link sub-assembly ( FRAME-C ). (e) Set the initial angle of the crank as follows. Click on the Rotation1 field of the Placement dialog box. Select plane CRANK-B in the crank assembly model and plane FRAME-A in the frame assembly model. Set the Current Position field to 60. The crank will then be oriented 60 relative to the frame. (f) Click on the green arrow of the component placement dashboard at the upper right of the screen to complete the placement of the crank. 2. Test your crank connection and set up the crank as a driver as follows: (a) Click on the Applications menu at the top of the screen, then select Mechanism. (b) Select the Define a servo motor from the menu at the top of the graphics window (see Fig. 2). (c) Enter a name for your servo motor, such as DriverMotor, in the Name field of the Servo Motor Definition dialogue box. (d) Select the arrow extending off the front of your first ground pin joint in the main work window. This step instructs Creo to rotate the crank about the frame link. (e) Select the Profile tab in the Servo Motor Definition dialogue box. Set the Specification to Velocity. Check the Current box in the Initial Position field to start the crank at the position where you placed it previously. Accept Constant as the Magnitude. Change A to 3.6 (for 3.6 crank increments). Figure 3: The Playback dialogue box. (f) Click the OK button to close the Servo Motor Definition dialogue box. (g) Select the Mechanism Analysis icon from the menu at the top of the graphics window (see Fig. 2). Enter a descriptive name for your analysis in the Name field of the Analysis Definition dialog box, such as cranktest. Select Position in the Type field. Be sure you have selected the Preferences tab in the Analysis Definition dialogue box. Select Length and Frame Count in the Graphical Display field. Set Frame Count to 101. Set End Time to 100. Select Current for the Initial Configuration. (h) Click on the Run button at the bottom of the Analysis Definition dialogue box. This will record an animation of your mechanism under the name defined in Step 2g. Click OK to close the Analysis Definition dialogue box. (i) Click on the Playback icon on the menu at the top of the graphics screen (see Fig. 2). Click on the Play current result set icon at the top of the Playback dialog box (see Fig. 3). This raises the Animate dialog box, which looks like a DVD control panel (see Fig. 4). (j) Click the Play button in the Animate dialogue box to start the animation (see Fig. 4). Click the Stop button to stop the animation. Note that you can vary the speed of the animation. You can also select whether you want the animation to continuously replay or stop after one cycle of the driving link. When you are done, click on the Reset the 2

3 Mechanism analysis Replay a previously run analysis Define a servo motor Close mechanism application Figure 2: Mechanism icon menu (abbreviated). Reset the animation to the beginning Stop Play Figure 4: The Animate dialogue box. animation to the beginning icon (see Fig. 4). Close the Playbacks dialog box. (k) Close the Mechanism dashboard by clicking on the Close icon at the top right of the graphics display (see Fig. 2). You will receive a warning that you will lose the motion results if you do not save them as a playback file before exiting. As we aren t done defining our slider-crank yet, choose Exit without saving. (l) Click on the Regenerate icon at the left of the menu at the top of the graphics display (see Fig. 1). Save your file to enable recalling your mechanism definition to this point. Closing the Loop 1. Assemble the slider link: (a) Select the Add component to the assembly icon. Open the slider link assembly file (slide assm.asm) 3. 3 The slider assembly should display two axes symbols, A 2 and (b) Set the joint type as follows. Locate the field in the component placement dashboard that reads User Defined by default. Select Slider from the drop-down menu associated with this field. (c) Align the sliding axes. Click on the Placement tab at the top of the dashboard. Align the direction of the sliding axis on the slider assembly ( S AXIS ) with the corresponding axis on the frame assembly ( F AXIS ). (d) Set the angular orientation of the slider as follows. The Rotation field will now be highlighted by default. Set the angle of the slider by aligning the center plane in the slider assembly ( SLIDE-C ) with the center plane in the frame assembly ( FRAME-C ). (e) Set a reasonable x-position for the slider. Click on Translation Axis in the Placement dialogue box. Select FRAME B as an assembly reference. Select SLIDE B as a component reference. Type 10 in the Current Position field. This should roughly center the slider in the slot in the frame. (f) Click the green checkmark to the right of the Component Placement dashboard to close it. 2. Assemble the coupler link: (a) Select the Add component to the assembly icon. Open the coupler link assembly file (coupler asm.asm) 4. S AXIS. If it does not, temporarily cancel the addition of the slider component by selecting the red X at the right of the component placement dashboard. Open file SLIDE ASSM.ASM. Then, choose Show -> Layer Tree from the model tree on the left of the screen. Rightclick on DEF AXIS, then choose Unhide. Then, return to the main assembly model and re-start the procedure to add the slider link. 4 The coupler assembly should display axes symbols at the pin joints. If it does not, temporarily cancel the addition of the coupler component by selecting the red X at the right of the component placement dashboard. Open file COUPLER ASM.ASM. Then, choose Show -> Layer Tree from the model tree on the left of the screen. Right-click on 3

4 (b) Set the joint type for connecting the coupler with the driver. Locate the field in the component placement dashboard that reads User Defined by default. Select Pin from the drop-down menu associated with this field. (c) Align the axes of the pin joint connecting the coupler with the driver as follows. Click on the Placement tab of the Component Placement dashboard. Align an axis of the left moving pivot of the coupler with an axis of the moving pivot of the crank link. Note: Be sure to choose an axis which is part of the crank assembly. (d) Set the z -position of the coupler by aligning the center plane of the coupler assembly ( COUPLER C ) with the center plane of the crank assembly ( CRANK C ). Note: Since the axis references a part in the crank assembly, the offset plane must also reference a plane in the crank assembly. In other words, if you try to reference a plane of the frame link or sliding link, the constraint will not be understood. (e) Specify that the coupler position is set by orienting it relative to the slider as well as the driver as follows. Click on New Set at the bottom left of the Placement dialogue box. Locate the field in the component placement dashboard that reads Pin. Choose Cylinder from the drop-down menu associated with that field. Align an axis on the right moving pivot of the coupler link with an axis of a pin joint on the slider. (f) Click the green checkmark to the right of the Component Placement dashboard to close it. 3. Animate your mechanism: (a) Select Mechanism from the Applications menu. (b) Select the Mechanism Analysis icon. (c) Enter a descriptive name for your analysis in the Name field, such as crankconstantomega. Select Position in the Type field. Be sure you have selected the Preferences tab in the Analysis Definition dialogue box. Select Length and Frame Count in the Graphical Display field. Set Frame Count to 101. Set End Time to 100. Select Current for the Initial Configuration. (d) Click on the Run button at the bottom of the Analysis Definition dialogue box. This will record an animation of your mechanism under the name defined in Step 2g. Click OK to close the Analysis Definition dialogue box. (e) Click on the OK button at the bottom of the Analysis Definition dialogue box to close it. 4. Playing your animation: (a) Select the Replay a previously run analysis icon (see Fig. 2). (b) Click on the Play current result set icon in the Playbacks dialogue box (see Fig. 3). (c) Use the Animate dialogue box to control your animation, just as was done with the crank in Step 2j. (d) If you would like to create a generic.mpg movie file to record your animation, click on the Capture button. (e) Close the Animate dialogue box. Close the Playbacks dialogue box. Close the Mechanism dashboard. Choose Save and exit from the Save Playbacks dialogue box. Select Regenerate from the menu at the top of the graphics display (see Fig. 1). Save your final assembly file. On Mechanism Constraints Note that the coupler link was assembled using a pin connection at one end and a cylinder connection at the other. A pin connection sets both a rotational axis and a Z -position. The cylinder connection sets only a rotational axis. Intuitively, you may be tempted to use a pin at each end of the coupler link. However, the Z -position is set by the first pin. Attempting to use a pin at the second end would introduce a conflicting Z -constraint! This, in turn, causes the mechanism assembly to fail. The same constraint logic would apply to a four bar linkage; i.e., the final link is assembled using one pin constraint and one cylinder constraint. DEF AXIS, then choose Unhide. Then, return to the main assembly model and re-start the procedure to add the coupler link. 4

5 Guidelines for Creating Links We provided you with the part and sub-assembly files for building the example slider-crank linkage. You can create your own links using standard part and assembly files by considering the following while creating each link: 1. Build a part or assembly model for each link in the mechanism. Creating a sub-assembly corresponding to each link is recommended, as it enables you to add parts to each link. For example, the crank link in our example, crank assm.asm, constructs the link out of five separate parts Define a cylindrical axis coincident with the axis of each pin joint in the part model of at least one of the links in each sub-assembly. 3. Define a datum axis along the direction of sliding in a part model that includes a sliding joint. Create a similar axis in the part model used in the mating part for the slider. 5 Only three part files are needed, crank link, coupler pin & crank gnd pin, since crank link and coupler pin are used twice in the assembly model. 5