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Example Problems
AutoCAD Modeler:
Stacked blocks, an introduction to the multi-loop problem
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Few assembly models will require only one vector loop because of the complexity of real problems. The multi-loop generation will be introduced using a characteristic three part assembly.

CREATING THE ASSEMBLY DRAWING

The drawing with its dimensions and tolerances is given below in Figure 5-1. This drawing may be either created by hand or loaded by calling up the drawing stkblks.dwg in AutoCAD, again found in directory c:\autocad\cats\drawings.

Figure 5-1. Dimensioned Stack Blocks.

DEFINING PARAMETERS

SetUp

The steps for the multi-loop problem will parallel those for creating the single loop problem. The only difference is that more loops are created (three in this example) and so the process is slightly longer.

Enter CATS at AutoCAD's command line.
Select SETUP from the CATS menu.
Select 1.0 for the text and symbol height.

Remember that this value may be either keyed in, selected from the pop-up menu, or selected from two points 1.0 units vertical distance apart.

Enter 0.0001 as the parallel factor.
Enter No to implement the pop-up menus.

If you are not yet familiar with the different joint types and datums the icon menus may still be used.

DEFINING PARTS

Creating the Cylinder

Now that the parameters have been set individual parts will be identified with their datum reference frames (DRFs).

Select PARTS from the main CATS menu.
Select NEW_P from the PARTS menu to begin creating DRFs.
Select the CENter of the circle, or a cylinder's face.
Enter cylinder to enter the part name for PART 1.
Select Cylindri from the datum pop-up menu.

The datum type may also be keyed in as c, or cylindrical.

Enter Return to continue creating parts.

Creating the Block

The second part in the assembly drawing will now be created.

Select the INTersection of the lower left corner of the block.
Enter block for the part name.
Select Rectangu from the datum pop-up menu.
Select the positive x-axis using NEArest as shown on the block in figure 5-2.
Enter Yes to continue creating new parts.

Creating the Ground

The final part will now be created.

Select the INTersection of the lower left inside corner of the ground.
Enter ground for the second part's name.
Select Rectangu from the datum pop-up menu.
Select the positive x-axis (see Fig. 5-2 for axis definitions on the ground).
Enter No to stop creating new parts.

The stack blocks should now appear as Figure 5-2 below without the axis definitions.

Figure 5-2. The Stack Blocks with Parts defined.

DEFINING JOINTS

The second step will be to locate the contact joints between each part.
Cylindrical Slider joint between the Cylinder and the Ground.

Select JOINTS from the CATS menu.
Select NEW_J to begin creating new joints.
Select the INTersection point where the CYLINDER is tangent to the GROUND.

see Figure 5-3 a at point O).

Select CYLSLI from the joint pop-up menu.

A cylindrical slider joint is a contact location where a cylinder is allowed to slide along a plane or flat surface.

Select a point NEArest to the ground where the CYLINDER is tangent to the ground.

See Figure 5-3 a at point X. This is the plane which the cylinder may slide along. It does not matter if the sliding plane is on one side or the other of the joint, although symbols may be oriented different.

First DRF path back to first part, the CYLINDER.

Select the CYLINDER's DRF for the first part's DRF.
Enter Return to default directly to the DRF from the contact joint.
Enter Yes to verify the correct path back to the DRF.

Second DRF path back to second part, the GROUND.

Select the GROUND's DRF for the second part's DRF.
Enter Return to default directly to the DRF from the contact joint.
Enter Yes to verify the correct path back to the DRF.
Enter Yes to continue creating new joints.
Select Redraw from the side menu to redraw the model.

By selecting redraw rather than entering redraw on the command line the joints function is not interrupted.

The assembly drawing should now appear as in Figure 5-3 b without axis definitions.


Figure 5-3 (a) Sliding plane


Figure 5-3 (b) DRF paths for Joint 4.

Edge Slider joint between the Block and the Ground

Select the INTersection of the BLOCK and the GROUND's vertical face.
Enter EDGSLI from the joint pop-up menu.

An edge slider joint is where an edge of one part is in contact with a plane surface of another part.

Select a point NEArest the same sliding plane as the Cylindrical Slider's plane.

Refer to Figure 5-3a.

First DRF path back to first part, the BLOCK.

Select the DRF on the first part, the BLOCK.
Enter Return to default directly to the DRF from the contact joint.
Enter Return to verify the correct path back to the DRF.

Second DRF path back to second part, the GROUND.

Select the DRF on the second part, the GROUND.

Enter Return to default directly to the DRF from the contact joint.
Enter Return to verify the correct path back to the DRF.
Enter Return to continue creating new joints.

Cylindrical Slider joint between the Cylinder and the Block.

Select the INTersection point where the CYLINDER is tangent to the BLOCK.
Select CYLSLI from the pop-up joint menu.
Select a point NEArest the BLOCK's plane surface where the CYLINDER may slide.

Refer to Figure 5-5a at X nearest to the joint location.

First DRF path back to first part, the CYLINDER.

Select the DRF on the first part, the CYLINDER.
Enter Return to default directly to the DRF from the contact joint.
Enter Return to verify the correct path back to the DRF.

Creating the second DRF path to the BLOCK.

Select the DRF on the second part, the BLOCK.
Select the INTersection of the BLOCK and GROUND where joint 5 is located.

This is where the first feature datum will be created. Zoom In to select the INTersection of the ground and the Block and not the intersection of the joint symbol and the Ground.

Enter Return to select a rectangular feature datum.

Select Zoom Out.
Enter Return to default directly to the DRF from the feature datum.
Enter Return to verify the correct path back to the DRF.
Enter Return to create another joint.

Edge Slider joint between the Block and the Ground (Joint 9, Fig 5-5b).

Select the INTersection of the BLOCK and the GROUND on the first 'step.'
Select EDGSLI from the joint pop-up menu.
Select a point NEArest to the bottom surface of the BLOCK.

Refer to the X nearest joint 9 in Figure 5-5a.

First DRF path back to the first part, the BLOCK.

Select the DRF on the first part, the BLOCK.
Enter Return to default directly to the DRF from the contact joint.
Enter Return to verify the correct path back to the DRF.

Creating the second DRF path, the GROUND.

Select the DRF on the second part, the GROUND.
Select the INTersection of the lower inside right corner, directly below the joint.

A feature datum will be created at this point.

Enter Return to select a rectangular feature datum.
Enter Return to default directly to the DRF from the feature datum.
Enter Return to verify the correct path back to the DRF.
Enter Return to create another joint.

Edge Slider joint between the Block and the Ground (Joint 11, Fig. 5-5b).

Select the INTersection of the BLOCK and GROUND on the second 'step.'
Select EDGSLI from the joint pop-up menu.
Select a point NEArest to the same plane as the last joint created

Refer to the X nearest joint 11 in Figure 5-5a.

First DRF path back to the first part, the BLOCK.

Select the DRF on the first part, the BLOCK.
Enter Return to default directly to the DRF from the contact joint.
Enter Return to verify the correct path back to the DRF.

Creating the second DRF path, the GROUND.

Select the DRF on the second part, the GROUND.

Many DRF paths may be created. Depending on how the assembly drawing was dimensioned the DRF path will vary. For example, if the assembly was dimensioned one way the DRF path with datums would appear as in Figure 5-4a. With the dimensioning of this example as shown in Figure 5-1 the DRF path will appear as in Figure 5-4b.


Figure 5-4 (a) One DRF path

Figure 5-4 (b). Different DRF path.

Enter .X
Select a point NEAr the vertical line extending downward from the joint's location.
Select the INTersection at DATUM8.
Enter Return to create a rectangular feature datum at this point.
Enter Return to go directly back to the DRF.
Enter Yes to verify the correct path.
Enter No to stop creating joints, you may also redraw at this point.

The assembly should now appear as in Figure 5-5b below:


Figure 5-5 (a). Sliding planes

Figure 5-5 (b). Joint assembly.

DEFINING LOOPS

The three different loops for the stackblocks will now be created. We will generate the first loop manually and the other two loops automatically. Refer to figure 4-1 for tolerances and figure 4-6 for correct loops.

LOOP 1

Select LOOPS from the CATS menu.
Select NEW_L from the Loops menu.
Enter Closed or Return for the loop type.
Select Joint 11 for the first joint in the loop.
Select Joint 9 to be the next joint.
Select the GROUND's DRF to be the common part.

Since the two joints share the same parts CATS needs to know which contact you would like.

Select Joint 11 to end the loop.

By selecting the joint you started on the closed loop is completed.

Enter Yes, the first loop was created correctly.
Enter 0.125 for the tolerance on the nominal length of 10.6750.
Enter Return for the nominal angle tolerance of 0.00 for 90deg..

This enters a 0.00 tolerance for the angle since no tolerance was specified.

Enter 0.35 for the tolerance on the nominal length of 28.125.
Enter 0.125 for the tolerance on the nominal length of 3.905.
Enter Return for the nominal angle tolerance default of 0.00 for 90deg..
Enter 0.15 for the tolerance on the nominal length of 4.0600.
Select a point to begin text for the loop name, LOOP_1 (24,10).
Enter No to stop creating loops manually.

LOOP 2

The first loop has now been completed, the program will automatically generate the next two loops.

Select AUTOLOOP from the LOOPS main menu.
Enter Return , the second loop was created correctly.
Enter Return for the nominal angle tolerance
Enter 0.075 for the tolerance on the nominal length of 6.8050.
Enter Return for the nominal angle tolerance.
Enter 0.125 for the tolerance on the nominal length of 3.9050 .
Enter Return for the nominal angle tolerance.
Enter 0.15 for the tolerance on the nominal length of 4.0600
Select a point to begin text for the loop name, LOOP_2 (7,12).

LOOP 3

Enter Return , the third loop was created correctly.
Enter 0.075 for the tolerance on the nominal length of 6.8050.
Enter Return for the tolerance on the nominal length of 6.8050.
Enter Return for the nominal angle tolerance.
Enter 0.2 for the nominal length on the radius of 6.6200.
Enter Return for the nominal length on the radius of 6.6200 default.
Select a point to begin text for the loop name, LOOP_3 (10,25).

The three loops are now complete and should appear as in Figure 5-6.

Figure 5-6. Complete Loops for the Stackblocks Problem.


DEFINING FEATURE CONTROLS

ANSI Y14.5 feature controls should also be included for this problem. These feature controls allow an engineer to account for machining surface variations such as flatness, circularity and perpendicularity.

Flatness feature controls on the Ground

The first feature control will be flatness on the Ground:

Select FEATURES from the CATS menu.
Select NEW_F to begin adding feature controls to the drawing.
Select FLATNESS feature control from the feature control icon menu.

Flatness may vary on a part because of machining or rolling. The part may still be considered flat within a certain tolerance zone. This tolerance is specified by using feature controls.

Select the GROUND's DRF.

This will select the part on which the flatness feature control will apply.

Select Joint 4

This is the contact point where the feature control applies. Joints may only be selected by their symbol, not their number. For example, the text 4 will not select joint 4, only the cylindrical slider symbol of joint 4.

Select a point for the feature control symbol location (see Figure 5-7).
Enter 0.080 to be the flatness tolerance band for that feature.
Enter Yes to continue creating feature controls.
Select FLATNESS feature control from the feature control icon menu.
Select the GROUND's DRF.

This will select the part on which the flatness feature control will apply.

Select Joint 5
Select a point for the feature control symbol location (see Figure 5-7).
Enter 0.080 to be the flatness tolerance band for that feature.
Enter Yes to continue creating feature controls.

Flatness feature controls on Block

Select FEATURES from the CATS menu.
Select NEW_F to begin adding feature controls to the drawing.
Select FLATNESS feature control from the feature control icon menu.
Select the BLOCK's DRF.

This will select the part on which the flatness feature control will apply.

Select Joint 7
Select a point for the feature control symbol location (see Figure 5-7).
Enter 0.050 to be the flatness tolerance band for that feature.
Enter Yes to continue creating feature controls.
Select FLATNESS feature control from the feature control icon menu.
Select the BLOCK's DRF.

This will select the part on which the flatness feature control will apply.

Select Joint 9
Select a point for the feature control symbol location (see Figure 5-7).
Enter 0.050 to be the flatness tolerance band for that feature.
Enter Yes to continue creating feature controls.
Select FLATNESS feature control from the feature control icon menu.
Select the BLOCK's DRF.

This will select the part on which the flatness feature control will apply.

Select Joint 11
Select a point for the feature control symbol location (see Figure 5-7).
Enter 0.050 to be the flatness tolerance band for that feature.
Enter Yes to continue creating feature controls.

Roundness feature control for the Cylinder

Select the ROUNDNESS feature control from the icon menu.

Roundness measures the amount a circle varies from being a circle. For example, the cylinder may actually be an ellipse.

Select the CYLINDER's DRF.

This will select the part on which the roundness feature control will apply.

Select Joint 4
Select a point for the feature control symbol location (see Figure 5-7).
Enter 0.02 to be the roundness tolerance band at that point.
Enter Yes or Return to continue creating feature controls.
Select the ROUNDNESS feature control from the icon menu.

Roundness measures the amount a circle varies from being a circle. For example, the cylinder may actually be an ellipse.

Select the CYLINDER's DRF.

This will select the part on which the roundness feature control will apply.

Select Joint 7
Select a point for the feature control symbol location (see Figure 5-7).
Enter 0.02 to be the roundness tolerance band at that point.
Enter No to discontinue creating feature controls.

The assembly drawing should now look like Figure 5-7.

Figure 5-7. Feature Controls for the Stackblocks Problem.

DEFINING DESIGN SPECIFICATIONS

A dependent length specification will be applied between the Cylinder and Ground. This specification provides for a tolerance on the point of contact between two parts.

Select SPECS from the CATS menu.
Select NEW_S to begin creating a design specification.
Select DepLEN from the specification pop-up menu.
Select the vector extending from joint 4 to the DRF of the ground.
Enter 0.3 as the symmetric tolerance on the dependent length of 18.7182.
Enter -2.7,18 as the specification symbol location.

Figure 5-8. Dependent Length Specification for the Stackblocks Problem.

CREATING A NEUTRAL FILE

A neutral file will now be created using the current model information.

Select CATSFILE from the main or sub-menu.
Select WRITE_NF to create the neutral file.
Enter Return to default the file's name to be stkblks.nf

A file will be created called stkblks.nf and will be located in the current directory. This file should resemble the neutral file located in Appendix A. To view the neutral file, use a text editor. The model is now ready for analysis by the CATS Analyzer.


PRO-E

Modeler: Clutch | Stack Blocks | Remote Positioner
Analyzer: Clutch | Stack Blocks | Remote Positioner
Verification: Clutch | Stack Blocks | Remote Positioner | Bike Crank | Parallel Blocks | NFOV

AutoCAD

Modeler: Clutch | Stack Blocks | Remote Positioner
Analyzer: Clutch | Stack Blocks | Remote Positioner
Verification: Clutch | Stack Blocks | Remote Positioner | Bike Crank | Ratchet | Parallel Blocks | NFOV

CATIA

Modeler: Crank Slider

 

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