Tutorial Template

Ptc: Mcad Solution Specialist

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• Publié par: Enno
• Nombre de lectures: 105
• Langue: English

Extrait

Title: Mechanism Design Option Date: 8/8/2002      

Mechanism Design Option    

          Table of Contents: 1) Objective   2) Overview   3) Tutorial   4) Tutorial Evaluation          

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Title: Mechanism Design Option Date: 8/8/2002   Objective:  At the end of this tutorial, you will be able to: • Explain why Mechanism is useful for design investigation. • Create assemblies with mechanism constraints and analyze its movement. • Identify a current project where this method can be applied.   Overview: The Pro/ENGINEER® Mechanism Design Extension enables designers to quickly and easily assemble Pro/ENGINEER parts and subassemblies using pre-defined connections (pin joints, ball joints, sliders, etc.) to create a mechanism assembly. These connections are intelligent Pro/ENGINEER features and can be used in conjunction (and are interchangeable with) the traditional assembly constraints like mate, align and insert. The mechanism can then be interactively dragged through its range of motion, or by using 'drivers', animations of pre-defined motion can be created, stored and replayed.      

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Title: Mechanism Design Option Date: 8/8/2002   Tutorial: This Suggested Technique will demonstrate how Mechanism Design can be used to assemble a mechanism using connections. Assemblies created using Mechanism Design may then be transfered to Pro/MECHANICA Motion for Motion Analyses. Within Mechanism Design, Drivers may be added and the mechanism motion may be simulated kinematically. Mechanism Design results may be used to check for possible interferences which may arise between moving parts. For the purposes of this document a piston and crank assembly will be used. This example mechanism contains five parts: Engine Block Bottom, Crank Shaft, Piston Connecting Rod, Connecting Rod Clamp, and the Piston Head.

  Table 1: Types of Connections Available in Mechanism Design and the Required References.     Connection References Required at Part Level  References Re L q e u v ir e e l  d at Assembly  - Axis - Axis Pin -  Point or Planar - Point or Planar Surface Surface Slider  - -    P A l x a i n s  a   r Surface  - -    P A l x a i n s  a   r Surface  Cylindrical - Axis - Axis Ball Point - Point - Planar - Planar Surface - Planar Surface Procedure    1. The engine block in this mechanism will serve as ground. All other components will be moving with respect to the Engine Block Bottom. Therefore, we need to assemble the Engine Block Bottom with fixed constraints. We will do this by selecting Component , Assemble and picking the .prt file for the Engine Block Bottom. Use the Automatic constraint to assemble this part.  

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Title: Mechanism Design Option Date: 8/8/2002  

Figure 1

 

 

  2. Next, the first moving part of the mechanism will be assembled. The Crank Shaft will assemble to the Engine Block Bottom and will be spinning about its axis with respect to the Engine Block Bottom. Therefore a pin joint is needed between the Crank Shaft and the Engine Block Bottom. To assemble the Crank Shaft, select Component , Assemble , and select the Crank Shaft part file. Then select "Connections" to expand the Component Placement dialogue box. Set the connection type to be "Pin." To create a pin joint two sets of constraints are necessary (See Table 1). Select an axis on the assembly and an axis on the part for the "Axis Alignment" constraints. You will then need to select a plane or surface in the assembly and a plane or surface in the part for the translation constraints. Mechanism Design uses the axes to line up the axis of rotation of the part to the axis in the assembly about which the part may spin. The datum planes are simply used for placement references (the datum planes are lined up). Once all the necessary constraints have been defined the part will be properly placed in the assembly and a pin connection icon displayed, as shown in Figure 2.

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Title: Mechanism Design Option Date: 8/8/2002  

Figure 2

 

 

 

3. With the Crank Shaft in the current orientation, it will be more difficult to place the next component. Prior to accepting the placement of the Crank Shaft it would be advisable to change the orientation of the Crank Shaft. To change the orientation of the part being assembled, select the "Move" tab from the "Component Placement" dialogue box. Make sure Rotate is selected and then using left mouse button click somewhere on the screen. After clicking on the screen the Crank Shaft may be spun about its axis of rotation simply by moving the mouse around. Once desired orientation is achieved click on the screen again to fix the orientation. Finally, select Ok from the "Component Placement" dialogue box to complete the assembly of the Crank Shaft. See Figure 3.

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Title: Mechanism Design Option Date: 8/8/2002  

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Figure 3

 

 

4. The Piston Connecting Rod will be assembled next using a pin connection between it and the Crank Shaft. As in step 2, select Component , Assemble , and select the Piston Connecting Rod part file. Select "Pin" for the connection type. As in step 2 select all the necessary references.

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Title: Mechanism Design Option Date: 8/8/2002  

Figure 4

 

 

5. Notice how in Figure 4, the connecting rod has assembled pointing down into the Engine Block Bottom. Just as in step 3 "Move" may be used to reorient the Connecting rod to point up. See Figure 5.

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Title: Mechanism Design Option Date: 8/8/2002  

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Figure 5

 

 

  6. Now that the Connecting Rod has been positioned and oriented correctly, we need to assemble the Connecting Rod Clamp. The Connecting Rod Clamp is fixed to the Connecting Rod and therefore will move with it. See Figure 6. To implement this the Connecting Rod Clamp needs to be assembled with Fixed constraints with respect to the connecting rod.

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Title: Mechanism Design Option Date: 8/8/2002  

Figure 6

 

 

    To assemble the Connecting Rod Clamp using Fixed constraints, select Component , Assemble , and select the Connecting Rod Clamp Part. Instead of selecting "Connections" to expand the dialogue box, use traditional Pro/ENGINEER Assembly constraints. In this case a mate constraint and a pair of align constraints may be used to properly assemble the Connecting Rod Clamp to the Connecting Rod. See Figure 7.

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Title: Mechanism Design Option Date: 8/8/2002  

   

Figure 7

 

 

7. The final part to be assembled is the Piston Head. The Piston Head will be assembled on to the Connecting Rod using a pin connection. The orientation of the Piston Head may be adjusted if necessary. See Figure 8.

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Title: Mechanism Design Option Date: 8/8/2002  

Figure 8

 

 

  8. Although the model is fully assembled now, it is still incomplete. The Piston Head has a pin connection to the Connecting Rod. However, as it is assembled the Piston Head is free to flop around rotating about its pin connection with the Connecting Rod. The model needs to be finished by adding another connection such that the Piston Head would move up and down as if it were inside a cylinder. To do this, a cylinder joint needs to be defined between the Piston Head and Ground which is the Engine Block Bottom in this model. If you still have the "Component Placement" dialogue box open, you may simply select Add and change the connection type to "cylinder". Otherwise select Component , Redefine , and pick the Piston Head. Select the Add button and change the type of the new connection to "cylinder". As shown in Table 1, a cylinder connection only needs an axis alignment constraint. Select the appropriate axes on the Engine Block Bottom and the Piston Head. Select Ok to complete the definition of the cylinder connection. A "slider" connection would also work in this model. Figure 9 and 10 show this model with a "slider" connection. If you use a "cylinder" connection your model will have a "cylinder" connection icon instead.

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