PRE-RELEASE sec - SolidWorks Motion Tutorials

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24 Spring force.

Create a new plot.

Define the plot using Forces, Reaction Force and Magnitude. Select the Linear Spring as the simulation element.

Click OK. 25 Warning.

Similarly to Lesson 2, we will receive a warning about redundant constraints. Redundant constraints may have significant impact on the mate forces (forces in the mechanical connections, mates, defined by the mates) and will be discussed later in the course. The resulting force obtained for this mechanism is, however, correct.

Click No.

26 Review the plot.

From the plot we can see that the maximum spring force is 1 N.

We can see that the spring only pushes the projectile for about 0.1 seconds.

Analysis with Friction

(Optional)

In this part we will study the effect of contact friction on the motion of the projectile. We will use the study we have just done and add friction between the projectile and the projectile holder.

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27 Duplicate the study.

Duplicate the existing motion study and name it Larger Friction. 28 Add friction.

Edit the group contact set containing the projectile and projectile holder. Activate Friction with the default values for Steel (Dry). 29 Motion study properties.

Under Motion study Properties set Number of Frames to 100. Click the Advanced Options button and change the Integrator Type to WSTIFF.

Note Integrators are discussed in detail in Lesson 4.

30 Run the simulation.

31 Animate results.

Animate the results and notice that the projectile would not slide onto the arm due to the added friction.

32 Save and close the file.

Summary In this lesson we analyzed a catapult assembly. The main objective was to rotate the arm to the position where a projectile can be loaded, then release the arm and eject the projectile. The following features were used and explained in detail: interference check through the computed time steps, definition of the spring and damper and the specification of the solid body contact with the contact groups. Because the parameters of the contact setup are subject of Lesson 4, this lesson only introduced the procedure to define the contacts with friction. Both static and kinematic friction types were introduced and shown. This assembly also features multiple gear mates.

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Exercise 4:

The Bug

In this exercise, we will use a mechanical bug with an oscillating motor to demonstrate the effects of friction on the movement of parts. We will run the study twice, first without friction and then with friction.

This exercise reinforces the following skills:

I Contact Friction on page 84.

1 Open an assembly file.

Open Bug Assembly file from the Lesson03\Exercises folder.

The assembly consists of a flat plate and a two piece mechanical bug.

The intent is to have the movement of the leg move the bug along the plate. There is a Coincident mate between central planes on the Base and Plate to keep the Bug moving down the middle of the Plate. 2 Verify the document units.

Click Tools, Options, Document Properties, Units.

Verify that MMGS (millimeter, gram, second) is selected for the Unit system.

3 New study.

Crate a new motion study. Make sure you select Motion Analysis. 4 Add gravity.

Add gravity in the negative Y direction.

5 Add contact.

Using contact groups, add solid body contact between the Plane and the two parts of the bug (Leg and Base).

Select Rubber (Dry) for the material.

Clear Friction.

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6 Add a motor.

Add an oscillating Rotary Motor to the Leg. Attach the motor to the edge shown and set the motor to move 30 degrees at 5 Hz.

7 Calculate.

Calculate the analysis for 2 seconds.

While the motor oscillates properly, without friction, the bug does not move.

8 Add friction.

Edit the two contacts and select Friction. The dynamic friction coefficient will be set to that of the specified material (Rubber (Dry)).

Select static friction and use the default values.

9 Re-calculate.

Run the analysis for 20 seconds.

With friction added, the bug will move along the plate.

10 Save and close the file.

Summary In this exercise you analyzed a small assembly called bug. The main objective was to see the effect of the friction model in the contact specification. While in the model without friction the bug assembly does not move, addition of the friction come close to reality – the bugs moves along the base plane.

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Exercise 5:

Door Closer

In public buildings such as schools or offices, door closers are often added to non-motorized swing doors to ensure that the doors automatically close after use. To ensure that the doors do not close too quickly and slam, a spring damper is added to the interior of the door closer.

Door Closer Analysis

In this exercise, we will use the Motion Manager to add an internal spring and damper to the door closer. We will then use SolidWorks Motion to plot the effect of the spring and damper on the door's behavior and adjust the parameters to achieve the desired result.

This exercise reinforces the following skills:

I Translational Spring on page 85.

I Translational Damper on page 87.

Procedure Open the existing assembly from the Exercises folder.

1 Open an assembly file.

Open door from the Lesson03\Exercises folder.

2 Verify the document units.

Click Tools, Options, Document Properties, Units.

Verify that MMGS (millimeter, gram, second) is selected for the Unit system.

3 New study.

Crate a new motion study. Make sure you select Motion Analysis.

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4 Create a linear spring.

Define a Linear Spring between the gas-piston and gas-cylinder. Use the circular edges as indicated in the figure. You must select the edges and not the faces or else the software does not use the center. The spring must be aligned with the cylinder.

Use 1 N/mm and 180 mm for the Spring Constant and the Free Length, respectively.

Use 5 N/(mm/s) for the Damping constant. Input appropriate values in the Display PropertyManager.

Note It may be necessary to change the transparency of the door closer's gas cylinder in order to select the interior parts necessary to define the linear spring.

Click OK.

Note The damper is used to prevent doors from slamming shut due to the force of the spring.

5 Run the Motion Analysis.

Run the analysis for 40 seconds.

Edges for the spring definition

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6 Plot door velocity.

Create a plot of the door (center of mass) velocity magnitude.

Notice that the door closes too quickly (within approximately 24 seconds) and passes through the door frame before coming to a complete stop.

We do not wish to close the door so quickly. Furthermore, we do not want the door to actually pass through the door frame and open on the opposite side. To solve this, we need to redefine the spring and damper constants.

7 Duplicate the study.

Note It is possible to simply change the constants in the Motion Study we just created. However, we want to be able to compare results from the two constant settings. Therefore, we will duplicate the initial Motion Study and make modifications to the duplicate study.

8 Redefine the spring with damper.

Increase the Spring Constant value from 1.00 N/mm to 2.00 N/mm. Increase the Damping Constant value from 5.00 N/(mm/s) to 10.00 N/(mm/s).

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9 Calculate the Motion Analysis.

Calculate and plot the door velocity.

10 Compare results.

Clicking either of the motion studies we just completed will enable you to compare the results from both studies. You can observe that in the second study, the door closes slower and comes to a complete stop without actually passing through the frame.

Conclusion From the data in the two simulations, we can determine the appropriate spring and damper constants for the door to close as desired and without slamming.

Summary In this exercise you analyzed a door assembly. The main objective was to practice the definition of the spring and damper to model the door closer and to find an optimum spring and damper parameters to close the door slowly without it passing through the frame.