Mechanism Tutorial 5: CD-ROM Advanced Mechanism Connections

Objective: Use Mechanism Design to create kinematic gear pair connections. You create gear pairs by selecting joint axes, and the gear pair connections constrain the relative velocity of the joint axes. Because of this, the physical geometry of the gears has no impact on the kinematics. In the example below, a motor turns several gears, driving the position of the laser housing in a CD-ROM drive.

1. Download the CD-ROM parts from website 2. Open File cd_case.asm

Assemble the lift part that is used to raise and lower the laser housing when a disc is inserted. First create a Slider connection. Slider connection sis used to maintain the orientation of the part throughout the motion. The gray component is the slot for the slot/follower connection, and as it moves back and forth it raises and lowers the component you are about to assemble Part Lift Bracket Assembly 1. Select the lift_bracket.prt part in your model tree > RMB on the part > Select Hide Model. This will cleanup are workspace and hide unneeded parts for now. 2. Click on the Assemble Icon > Select lift.prt > Constraints a. Choose Slider Connection i. Assembly: Select slider_axis ii. Component: Select slider_axis b. Rotation i. Assembly: Slider_Ref ii. Part: Slider_Ref iii. RMB Flip Constraint

Slider: Select Axis lines

Rotation: Select Slider_Ref from both parts

c. Using the 3D Dragger (Tracker Ball) to move the part into the slots shown. Do not worry about making it perfect. We just want to create a starting point

Place approximately in the slots

d. Green Check to Accept the connection. (NOTE we will be editing this connection after hiding some features from the Model Tree) e. Hide the Following in the Model Tree i. Case.prt ii. Lift_Motor.asm f. Unhide the following in the Model Tree i. Lift_Bracket.prt g. RMB on Lift.prt > Edit Definition > Select Placement Tab > Select New > Select Slot Connection > Select the following NOTE: SET THE MODEL TO HIIDDEN LINES FOR BETTER VISUAL i. Assembly: HOLD CTRL KEY > Select the following three lines from the slot that represent the path for the slot sweep ii. Part: Select PNT 0 as shown below

Datum PNT 0

Slot Path (Hold CTRL Key to select all 3 lines)

h. Select Green Check to accept Connection i. Change View Display to Shading j. Unhide the Following from the Model Tree i. Case.prt ii. Lift_Motor.asm k. Use the Hand Grab to select the Bracket and drag to it to show the movement Notice the bracket is constrained to the area within the Slot.

Part Assembly: Gear Connections 1

Assemble the following objects. See example for placement of parts 1. Tray_Gear.prt: Use a Pin Connection with the center axis of the left post from the case_2.prt (Main Body). Pin Connection w/post from case.prt

Lift_Gear.prt Tray_Gear.prt

2. Lift_Gear.prt: Use a Pin Connection with the center axis of the left post from the case_2.prt (Main Body). Try to line gears up as best as possible with the Lift_Bracket.prt 3. Pulley_2.prt: Assemble to appropriate hole using the Pin Connection to the center axis of the post provided from case_2.prt (Main Body) NOTE: Be sure to have the motion pointing up. May have to flip the direction of motion.

Pulley_2.prt: Pin Connection with post. Gear Teeth face down to Case_2.prt

4. Belt.prt: Assemble using standard Coincident constraints to the Lift_Motor.asm to the Pulley_2.prt. When placing the height of the belt approximate the distance to fit the belt between the Lift_Motor.asm to the Pulley_2.prt.

5. Hide the Lift_Bracket.prt and the Lift.prt from the Model Tree > Select Applications Tab > Mechanism Icon > Choose to access the Gear Pair Definition dialog > Change name to Pulley_Gear

6. Select the following connection from the small side of the pulley (selection should be the Pin/axis of the pin connector shown. The system selects the Gear and Carrier bodies, and displays a purple arrow indicating the direction of rotation(place your right thumb in the direction of the arrow, and your fingers curl in the direction of rotation) a. Enter 4 for pitch circle diameter

Pitch Circle Diameter 4

Select this Pin Connection

7. Choose Gear 2 Tab > Choose the motion axis as shown (Part Pulley_2.prt axis line) > Flip the direction , so the direction of motion is the same as Gear 1 > Circle Pitch Diameter 14 > Click Apply

Flip Direction

Pitch Circle Diameter 14

Select Pin Connection from Pulley_2.prt

Note: The system displays a gear icon for each component, as well as a dashed line indicating the connection between them. You can change the location of the icon to make it more easily associated with the components. 8. Choose in the Icon Location area of the dialog > Select approximately in the location shown below > Click Apply

9. Choose Gear 1 Tab > Choose in the Icon Location area of the dialog > Select approximately in the location shown below > Click Apply > Click Ok

10. Use the drag components icon to drag the gears. The gears move as expected. Note that as the larger pulley turns, the teeth on the bottom interfere with the teeth of the adjacent gears. The system does not measure or use interference to drive the gears, they are only driven by the relative velocity of the gear pairs, which has not yet been established for the other gears in the system.

Part Assembly: Gear Connections 2: Pulley to Largest Gear 1. Select > Name: Large Gear >Select the Motion Axis as shown > Circle Pitch Diameter 7

2. Select Gear 2 Tab > Select the Motion Axis as shown > Circle Pitch Diameter 25 NOTE: Make sure the purple arrow is pointed in the same direction as Gear 1 selection (may have to flip direction) > Select OK

Part Assembly: Gear Connections 3: Pair Gear

1. Select > Name: Pinion Gear >Select the Motion Axis as shown > Circle Pitch Diameter 7

2. Select Gear 2 Tab > Select the Motion Axis as shown > Circle Pitch Diameter 22 NOTE: Make sure the purple arrow is pointed in the same direction as Gear 1 selection (may have to flip direction) > Select OK

Drag the components to see what happens. Notice how all the gears are moving together.

Part Assembly: Gear Connections 4: Rack and Pinion Gear

1. Unhide Lift_Bracket.asm and Lift.prt 2. Select > Name: Rack and Pinion Gear > Change Type to Rack & Pinion > Select the Motion Axis as shown > Circle Pitch Diameter 11

3. Choose in the Icon Location area of the dialog > Select the point approximately as shown below

4. Choose the Rack Tab > Select Slider Motion Axis Shown Below > Select Ok

Drag the components to see what happens. Show Mr Jourden Upon Completion