An Introduction to Mechanisms

1 Cams

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A mechanism is a device that takes an input motion or force and outputs a different motion or force.
Gears trains, for instance, are a type of mechanism.

This gear train takes rotary motion as input, and outputs rotary motion. The difference between the input and output is the speed and direction of the motion.
In this project you're going to be looking at different type mechanism called a Cam Mechanism.

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Cam mechanisms turn rotary motion (round and round) into reciprocating motion (up and down)

Learn It

A cam mechanism is made up of three main parts: cam, slide and follower. In the image below, the slide (or guide) is the red ring.

The cam rotates continually. The follower is a rod that rests on the edge of the turning cam.
The follower moves up and down, but can't move to the side because of the slide or guide.
This means the cam follower can only:
- Rise
- Fall
- Dwell

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We can draw what are know as displacement graphs for any cam mechanism.
A displacement graph shows how the follower moves as the cam rotates.
Follow these steps to create your own displacement graphs. This one is for a pear cam.

Badge It - Silver

Click on the following link to complete the quiz on different types of cams and displacement graphs.

Try It

Let's try and make one of the Cams in SolidWorks
We'll make a pear-shaped Cam.
If you've forgotten how to get started in SolidWorks, then ask your teacher for some help.
First we'll need a couple of circles, as shown below

Notice the little symbol between the circles like this.

This means they have a tangential relationship (look up the word tangent if you don't know what that means)
You can give sketch elements a tangential relationship by shift-clicking both elements and choosing tangent from the menu on the left

The centre of the two circles also have a horizontal relationship
Now draw two straight lines as shown below. Don't let them touch the circles yet.

We can now give the lines a tangential relationship with each of the circles.

-Then use the trim tool to cut away the lines you don't want

Lastly you can add a small circle in the cam, where doweling would go.

Once completed, you can extrude the sketch.
Note that this is just practice and not your actual cam, which will need to have a different center cut-out.
Here is a video tutorial, explaining how to design the cam above.

Badge It - Gold

Using SolidWorks, produce either a heart, drop, irregular or ratchet cam.
The Cam's diameter must not exceed 60mm.

Screenshot your finished sketches including the part where it states your sketch is fully defined.

Try It

We can animate cams in SolidWorks as well.
Create a new assembly and import in one of your cams.
The first part brought into the assembly is 'fixed' in place, we need to change this so the part can move. Right click on the part and select 'float'.
Now select New Motion Study from the tool bar.

Near the bottom of the screen, the motion study will appear. In it's tool bar is the symbol for a motor - click it.

Now you'll need to select the inner face of the cam, to choose what part the motor will turn.

You should see it populated in the menu on the left. You can make other changes here as well, such as the speed of rotation.

Once you're done, watch the animation using the play buttons. You may need to change this to 'Basic motion' to see the movement.

Badge It - Platinum

SolidWorks can be used to produce animations.
Independently (or with a little help from the instructions above), produce an animation of one of your cams rotating.
Take a screenshot of the motion study and upload this to the platinum badge.