6 To create an assembly.

Transcription

1 6 To create an assembly. Contents. 6.1 Introduction. 6.2 Pre-requisites. 6.3 Creating an assembly The base component. 6.4 To assemble the LUG.prt to STARTPART.prt The surface normal vector The Mate constraint The Align constraint The Align offset constraint. 6.5 Assembling the BOLT component. 6.6 Mechanisms. Pro/ENGINEER: To create an assembly. Page 1 of 18

2 6.1 Introduction. You will now produce a new model called an Assembly. This model will comprise the three parts, STARTPART.prt, LUG.prt and BOLT1.prt that you have already created. You will learn how to use the Mate and Align placement constraints to join or position components relative to each other. 6.2 Pre-requisites. You must have successfully completed: Pro/ENGINEER: 4 The starter part. 5 To create additional parts. 6.3 Creating an assembly. Create a new object. In the New window select Assembly as the type. Enter the name: assm1 Click OK. A new assembly type file is created in your working directory. You are presented with assembly base features, the three datum planes, similar to a new part. Pro/ENGINEER: To create an assembly. Page 2 of 18

3 6.3.1 The Base component. You begin the assembly with a Base component. This will be a component you are unlikely to want to remove later on. From the Menu Manager: Component > Assemble In the Open window, select the STARTPART.prt model as the component. Click on Open. The Component Placement window appears. In this instance the default Constraints between the assembly base features (the datum planes) and the STARTPART are OK, so click OK. Pro/ENGINEER will automatically place the component on the assembly base features. 6.4 To assemble the LUG.prt to STARTPART.prt. Again, from the Menu Manager: Component > Assemble Click on to select and Open the LUG.prt file. To simplify the display you may wish to switch off the datum planes. You will see the LUG.prt in the display along with the STARTPART.prt. Initially Pro/ENGINEER arbitrarily places the component automatically. In section you will explicitly specify how you want the LUG placed, relative to the STARTPART. Do not click anything at this point in time. Pro/ENGINEER: To create an assembly. Page 3 of 18

4 6.4.1 The surface normal vector. Before you start to use constraints you should be aware of the surface normal vector. It is an imaginary vector, or arrow, perpendicular to the model surface, pointing from the inside to the outside of the solid. The surface normal vector concept can help when visualising and defining your Align and Mate constraints. Aligned. Aligned coincident. Aligned offset. Aligned components have their surface normal vectors pointing in the same direction, as shown above. Below are two mated components, where the surface normal vectors point in opposite directions. Mated. Mated coincident. Mated offset. Pro/ENGINEER: To create an assembly. Page 4 of 18

5 6.4.2 The Mate constraint. You are going to mate the large top surface of STARTPART.prt with the narrow bottom surface of LUG.prt. In the Component Placement window, display the Constraints Type pull-down sub-menu and select Mate.! Note: Remember that Pro/E can distinguish between the inside and the outside of your model. When mating two surfaces, imagine that they are to be parallel (if flat) and facing each other. (In other words the surface normal vectors of those surfaces will be in opposite directions.) " Tip: Read the message. So now you have to select the surfaces that are to be mated, or joined face to face. Select the surfaces indicated below. " Tip: Develop the habit of using Query Select whenever you have to select an entity in an Assembly! See section Pro/E automatically distinguishes between the Assembly Reference and the Component Reference. Assembly Reference (on the base component). Component Reference, don't forget to use Query Select, bottom hidden surface (on the new unplaced component). Observe how the component moves to reflect it's placement constraint and that the Placement Status changes to Partially Constrained. Pro/ENGINEER: To create an assembly. Page 5 of 18

6 6.4.3 The Align constraint. You are going to align side surfaces of the two parts. In the Component Placement window, display the Constraints Type pull-down sub-menu and select Align.! Note: Align is similar to mate, the difference being that the flat surfaces to be aligned face the same direction. The surface normal vectors point in the same direction. Using Query Select select the two surfaces indicated below. On successful selection the component moves to reflect the new constraints placed. Select the side surface......and this surface. New position with extra constraint. Pro/ENGINEER: To create an assembly. Page 6 of 18

7 6.4.4 The Align offset constraint. Pro/ENGINEER will automatically make the mated or aligned surfaces coincident, which means that they touch. You can change the distance between these surfaces by specifying an Offset when defining your constraints.! Note: Be aware that making the surfaces touch by specifying an offset of zero is different to specifying coincidence. In a coincident constraint no dimension exists in the assembly to specify the separation between the surfaces, whereas in an offset constraint one does. (When the offset value is set to zero, which makes the surfaces touch, a constraint dimension with a value of zero will exist in the assembly.) So, finally you will Align the end faces and offset them. In the Component Placement window, display the Constraints Type pull-down submenu and select Align. Select the two surfaces indicated below. This surface......and this surface. To specify an Offset, click on the Coincident text in the Offset column and display the pull-down menu. Click on the 0.0 to enable an Offset value to be entered. To display the direction of the offset, press Return. Observe the Red arrow direction. To enter your offset value, click on the value in the box and then enter 100 as your new value and press Return. Observe the new placement of the LUG.prt. Because of the negative value entered, it should have been offset 100mm in the opposite direction to the default direction indicated by the RED arrow. The LUG.prt is fully constrained. To complete the assembly of the LUG click OK. Pro/ENGINEER: To create an assembly. Page 7 of 18

8 6.5 Assembling the BOLT component. Using the procedures introduced in section 6.4, add your BOLT1.prt or BOLT2.prt component to the assembly to make it fully constrained. Use the constraints detailed below. Spin, zoom/refit the model and use Query Select as required. Save the assembly when finished and then close the window. First, Mate this flat shoulder surface... Secondly, use the Insert constraint to place the bolt shank......in the lug hole....with this flat surface. Pro/ENGINEER: To create an assembly. Page 8 of 18

9 6.6 Mechanisms. Assemblies of parts can be created so that they are free to move in a controlled way. This allows the modelling of working assemblies, comprising components that rotate or slide relative to each other. Within Pro/ENGINEER these assemblies are referred to as mechanisms. You create a mechanism assembly as you would a normal assembly, only you use connection placement constraints rather than the usual placement constraints when bringing a component into the assembly. In this tutorial you will create and animate the working mechanism shown below: Mechanism terminology. The model: The mechanism comprises two crank shafts, rotating in a base block. These shafts are connected by the two links. Each shaft is driven independently by its own servo motor, indicated by the spiral line around the individual rotation axes. Each shaft and link here is assembled using a connection. The connections used here are called Pin joints and are indicated by the black arrows in the above picture. A Pin joint allows freedom of rotation about axes and has a position constraint along this rotational axis, preventing components from moving axially. The analysis: Once the model has been completed, you will define what is called a kinematic analysis. This will run the servomotors for a defined period of time, allowing you to visualise the motion and examine interferences and general kinematics of the mechanism. Pro/ENGINEER: To create an assembly. Page 9 of 18

10 6.6.1 The ground or base part. The assembly requires a grounded base part that does not move. Before we start modeling, copy the folder called mechanism to your home directory (U:\ drive?) and set your current working directory to it. This folder contains the following part files you will need for this exercise: BODY.PRT LINK.PRT SHAFT_1.PRT SHAFT_2.PRT Create a new Pro/E assembly file called mechanism. (Make sure that it is an assembly file and not a part file!) From the Menu Manager: Component > Assemble In the Open window, select the body.prt model as the component. Click on Open. The Component Placement window appears. In this instance the default Constraints between the assembly base features (the datum planes) and the body.prt are acceptable, so click on this button and then OK. Pro/ENGINEER will automatically place the component on the assembly datum planes (base features). You will now assemble the remaining components onto this body component using connections, in order to create the mechanism. Pro/ENGINEER: To create an assembly. Page 10 of 18

11 6.6.2 To create a Pin Connection. Using the same procedure, begin to add the shaft_1.prt component to the assembly. When the Component Placement window appears you need to enable the connections commands by clicking on the Connections bar as shown here: Note how the contents of the window changes. The connection type has defaulted to Pin, which is the type we will use here. A Pin connection requires two Constraints to be defined. (A Pin connection, remember, allows rotation about an axis but no axial movement.) To define both the axes from the assembly and the component to be used, use Query Select and pick the two axes shown below: Assembly Reference axis. Component Reference axis. Pro/ENGINEER: To create an assembly. Page 11 of 18

12 When the shaft_1 component jumps into the block hole, the axes are now aligned, you need to define the Translation Constraint in order to position the shaft somewhere along this axis. Using the usual procedures select these two surfaces to align the shaft to the block. (Note that the shaft will be in the located axially with the hole at this stage.) You should now see the shaft_1 component located as shown here. Observe that the placement Status window now reports: Connection Definition Complete Click on OK. Save your work. Pro/ENGINEER: To create an assembly. Page 12 of 18

13 6.6.4 To create a Servo Motor. The component shaft_1 is now connected to the block. It is free to rotate but it cannot slide out of the hole. The next step is to define a driver, or a Servo Motor, for the shaft. The Servo Motor simply provides a means of driving the rotation of the shaft in a precise and controlled way. To work with the motion properties of a mechanism from the Menu Manager ASSEMBLY click on Mechanism. Observe the new buttons on the right hand side of the display. Start defining a new servo motor by clicking this button: The Servo Motors window appears: To create a new motor click on New. The Servo Motor Definition window appears: Use the default Name of ServoMotor1. From the display select the Pin Joint Axis you have just created for shaft_1. Next, click on the Profile tab. Pro/ENGINEER: To create an assembly. Page 13 of 18

14 This profile defines the motion, in this case the rotation, characteristics of the servo motor. For this example use the settings shown here. They give a rotational Velocity of a Constant magnitude of 36 (deg/sec). Click on OK. You should now have a servo motor symbol in the display, it looks like a tapering spiral around the Pin joint. Save the model To define an analysis. For this example we will set up and run a simple kinematic analysis, which basically will run the servo motor for a set period of time, at 36 deg/sec. Once the analysis has been run it can be played back and viewed at our leisure. So, select: Menu Manager ASSEMBLY Analyses In the resultant Analyses window click on New. In the resultant Analysis Definition window we will use the default set up as shown here. Note that the start time is 0 and the end time is 10. This means that the display of the analysis will calculate for 10 seconds with the servo motor running at 36 degrees per second, giving one whole revolution of the shaft. The Frame count is the number of frames or snapshots taken each second. Click on OK. Pro/ENGINEER: To create an assembly. Page 14 of 18

15 6.6.5 To run and replay analyses. To run this analysis simply click on this button. Select the analysis you wish to run in the Analyses window, and click on Run. To play back a previously run analysis use this button. Save the model again To assemble the second shaft using connections. We will now continue to build the mechanism. From MENU MANAGER click on: ASSEMBLY Component Assemble Assemble the other shaft, shaft_2.prt, using a Pin connection, using the same procedures as for shaft_1 in section Define a new servo motor for its Pin joint connection, giving it a Profile of Constant Velocity again, only with a magnitude of 72 deg/sec (twice as fast as shaft_1). Accept the default name, such as ServoMotor To add a new servo motor to the Analysis. From the MENU MANAGER, click on: Mechanism Analyses Within the Analyses window select the first analysis we set up and click on Edit. Click on the Motors tab and add a row. Click on the new Motor and pull down the selection menu. Select the new motor. Click on OK. Run the analysis to check it. Pro/ENGINEER: To create an assembly. Page 15 of 18

16 6.6.8 To add the two links. First assemble an instance of the link.prt to each shaft, as shown below, using Pin connections: Link.prt connected to shaft_1.prt, through the hole in the link. Link.prt connected to shaft_2.prt, by it s spigot, through the hole in the shaft_2.prt web. Note the symbols for the pin connections and the servo motors. Ensure that these surfaces are used for the translation constraints for the links. (Flip the constraints if the link appears on the wrong side of the component. Pro/ENGINEER: To create an assembly. Page 16 of 18

17 6.6.9 To connect the two links. At the moment each link can freely rotate around its own Pin connection axis. As the links are already constrained axially, by their Pin connections, we will complete the mechanism by connecting their free ends using a Cylinder connection. (A cylinder connection is similar to a Pin connection, only it does not require a translation constraint.) Ensure that you are displaying the model tree: Observe the components in the assembly. You should have a model tree like this one: We will Redefine the assembly of the last link to be assembled. Select and Right hand Mouse button click on the last link to be assembled. Click on Redefine. You should now have the Component Placement window back up. Add a new connection to this link by clicking on the + button. In the Connection Type region, click on the Pin window and pull down the menu. Select Cylinder. Using the Query Select command, as usual, select the axes on the free ends of the links to connect with the Cylinder connection. The links should connect up. Click OK. Save your work. Pro/ENGINEER: To create an assembly. Page 17 of 18

18 Run the analysis again, observing the motion of the links. You can view the model during playback using the normal keyboard/mouse combinations Extension work. You may wish to experiment with different servo motor profiles or different link center distances. Create a model, using your own components, of a reciprocating mechanism using Slider or Cylinder connections. Pro/ENGINEER: To create an assembly. Page 18 of 18