An Introduction to Mechanisms

1 Cams

Learn It

  • 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.

Gears_animation.gif

  • 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.

Learn It

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

Nockenwelle_ani.gif

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.

Slide_identifier.jpg

  • 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

Learn It

  • 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.

IMG_0922.jpg IMG_0923.jpg IMG_0925.jpg IMG_0926.jpg IMG_0927.jpg IMG_0928.jpg

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

pear1.PNG

  • Notice the little symbol between the circles like this.

pear2.PNG

  • 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

pear1a.PNG

  • 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.

pear3.PNG

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

pear4.PNG -Then use thew trim tool to cut away the lines you don't want pear5.PNG

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

pear6.PNG

  • 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.

Badge It - Gold

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

cams.jpg

  • 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.
  • Now select New Motion Study from the tool bar.

pear7.PNG

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

pear8.PNG

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

pear9.PNG

  • 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.

pear10.PNG

  • Once you're done, watch the animation using the play buttons.

Pear11.PNG

Badge It - Platinum

  • SolidWorks can be used to produce animations.
  • Independently (or with a little help from your teacher), produce an animation of one of your cams rotating.
  • Using the save icon, you can produce a video of you cam moving.