Cam and Follower Mechanism

1. Cam: Rotating Driver

• Plate cam (disk) with profiled edge
• Rotates continuously at constant speed
• Profile shape programs the motion

2. Follower: Moving Output

• Translates or oscillates
• Maintains contact with cam surface
• Executes programmed motion

3. Frame: Fixed Reference

• Provides cam shaft bearing
• Guides follower motion
• Maintains alignment

Standard Cam Cycle:

A complete 360° rotation typically includes four phases:

Rise: Outward Motion

• Follower moves away from cam center
• Lift distance: L
• Rise angle: typically 90-120°

Dwell: High Position

• Follower remains stationary at maximum lift
• Cam continues rotating
• Constant radius circular arc

Return: Inward Motion

• Follower moves back toward cam center
• Return angle: typically 90-120°

Dwell: Low Position

• Follower remains at base position
• Ready for next cycle

Base Circle Radius (R_b)

• Minimum cam radius
• Determines minimum follower position
• Foundation of cam geometry

Lift (L)

• Maximum follower displacement
• Distance from base to peak position
• Critical design parameter

Prime Circle Radius (R_p)

• R_p = R_b + L
• Maximum cam radius
• Defines peak follower position

Rise Angle

• Angular duration of outward motion
• Typical: 90-120°
• Affects acceleration

Dwell Angles

• High dwell: follower at maximum lift
• Low dwell: follower at base position
• Total angles must sum to 360°

Return Angle

• Angular duration of inward motion
• Often mirrors rise angle
• Affects deceleration

Simple Harmonic Motion

• Smooth acceleration
• Good for moderate speeds
• Used in this lesson

Where:

• is the follower displacement
• is the cam rotation angle
• is the total lift
• is the cam angle over which the rise occurs

Cycloidal Motion

• Smoother acceleration than harmonic
• Ideal for high-speed cams
• More complex mathematics

Polynomial Motion

• Customizable acceleration profiles
• Advanced applications
• Requires numerical calculation

For this lesson, you’ll use:

Part Design

• Creating individual cam and follower parts
• Primary workbench for solid modeling

Sketcher

• Designing the cam profile curve
• Angular constraints and polar geometry

Spreadsheet

• Parameter control table
• Motion law calculations

Assembly

• Combining cam, follower, and frame
• Motion constraints

TechDraw

• Motion documentation
• Displacement diagrams

Essential Navigation Controls:

In the spreadsheet, create this parameter table:

Why Aliases?

Aliases let you reference cells by descriptive names instead of cell addresses like “B2”, making formulas readable and maintainable.

Create aliases for all parameter values:

1. Click cell B2

2. Right-click → Properties

3. In “Alias” field, type: BaseCircleRadius

4. Click OK

5. Repeat for each parameter value in column B:

   • B3: Lift
   • B4: PrimeCircleRadius
   • B5: RollerRadius
   • B6: CamThickness
   • B7: ShaftDiameter
   • B8: ShaftRadius
   • B9: RiseAngle
   • B10: DwellAngle1
   • B11: ReturnAngle
   • B12: DwellAngle2

Now you can use Spreadsheet.BaseCircleRadius anywhere in your model!

Notice the formulas in B4 and B8:

PrimeCircleRadius = BaseCircleRadius + Lift

• This ensures the maximum cam radius automatically updates when you change base radius or lift
• Central concept of parametric design: relationships, not fixed values

ShaftRadius = ShaftDiameter / 2

• Convenience calculation
• Changes to shaft diameter automatically propagate to shaft radius

Simple Harmonic Motion Rise:

For smooth acceleration during rise, we use simple harmonic motion:

Where:

• = follower displacement from base position
• = current cam angle from start of rise
• = total rise angle (120°)
• = total lift (20mm)

Cam Radius at Angle θ:

Where:

• = base circle radius

Key Points for 120° Rise:

Two Approaches:

Option A: B-Spline Through Calculated Points (Accurate)

• Calculate exact positions using motion law formulas
• Place points at key angles
• Connect with smooth B-spline curve
• Most accurate representation

Option B: Circular Arc Approximation (Simplified)

• Use circular arcs to approximate smooth curves
• Easier to construct and constrain
• Acceptable for demonstration and low-speed applications
• We’ll use this approach for simplicity

Cam Profile Construction:

Base Circle:

• Circle centered at origin
• Radius = BaseCircleRadius (40mm)
• Represents dwell at base position

Rise Section (0° to 120°):

• Smooth curve from 40mm to 60mm radius
• Approximate with arc or B-spline

High Dwell (120° to 180°):

• Circular arc at PrimeCircleRadius (60mm)
• Constant radius maintains follower at max lift

Return Section (180° to 300°):

• Mirror of rise section
• Smooth curve from 60mm back to 40mm

Low Dwell (300° to 360°):

• Circular arc at BaseCircleRadius (40mm)
• Completes the cycle

Shaft Hole:

• Circle at origin
• Radius = ShaftRadius (10mm)

We’ll use construction geometry to establish angular positions:

1. Draw horizontal reference line

   • Line tool (press L)
   • Draw from origin horizontally to the right
   • Press Escape

2. Make it construction geometry

   • Select the line
   • Press G key (toggles construction mode)
   • Line turns blue (construction)

3. Constrain it horizontal

   • Select the line
   • Press H key
   • Now it’s locked horizontal

4. Set the length

   • Distance constraint on line length
   • Type: 70 mm (extends beyond prime circle)

This horizontal line at 0° is our angular reference.

Simplified approach using a single arc:

1. Draw arc from base to prime circle

   • Arc tool (or press A)
   • Click at angle 0°, radius 40mm (on base circle, at horizontal line)
   • Click at angle 120°, radius 60mm (estimate position)
   • Click a third point to define arc curvature
   • Press Escape

2. Constrain start point

   • Coincident constraint
   • Arc start point → Base circle
   • Arc start point → Horizontal reference line
   • This locks it at 0°, 40mm radius

3. Constrain end point angle

   • Draw construction line from origin at 120° angle
   • Angle constraint: 120° relative to horizontal
   • Coincident: Arc end point → this 120° line

4. Constrain end point radius

   • Distance constraint from origin to arc endpoint
   • Click ƒx button
   • Type: Spreadsheet.PrimeCircleRadius
   • Press Enter

The rise section is now constrained!

For more accurate harmonic motion (optional):

1. Calculate and place points

   Using the table from earlier:

   • Point 1: 0°, 40mm radius
   • Point 2: 30°, 42.68mm radius
   • Point 3: 60°, 50mm radius
   • Point 4: 90°, 57.32mm radius
   • Point 5: 120°, 60mm radius

2. Use Point tool

   Place points at each calculated position

3. Constrain each point

   • Distance from origin (radius)
   • Angle from horizontal (use construction lines)

4. Connect with B-spline

   • B-spline tool (press S)
   • Click each point in sequence
   • Press Escape when complete

This creates a smooth curve matching the harmonic motion law exactly.

Easiest method: Mirror the rise section

1. Create symmetry axis

   • Draw vertical construction line through origin
   • Make it vertical (press V)

2. Select rise geometry

   • Select the rise arc (or spline and all points if using advanced method)

3. Apply symmetry constraint

   • Symmetry constraint tool
   • Select rise geometry
   • Create mirrored copy about vertical axis

4. Position correctly

   The mirrored section should span 180° to 300°

Alternative: Draw return section manually

1. Draw return arc

   • Arc from 180° position (60mm radius) to 300° position (40mm radius)

2. Constrain endpoints

   • Start: Coincident to high dwell end
   • End: Use construction line at 300° angle

3. Constrain radii

   • Start radius: Spreadsheet.PrimeCircleRadius
   • End radius: Spreadsheet.BaseCircleRadius

1. Select the roller sketch in the tree

2. Click Revolve tool in Part Design toolbar

3. In the Revolve panel:

   • Axis: Select Vertical or Z-axis
   • Angle: 360° (full rotation)
   • Symmetric to plane: Off

4. Click OK

You now have a cylindrical roller!

For this lesson, we’ll position roller and stem together in assembly without a physical pin connection. This keeps the focus on cam motion.

For more realism:

1. Create another Body: RollerPin

2. Sketch a circle (pin cross-section) on appropriate plane

3. Revolve to create cylindrical pin

4. Position to connect roller to stem in assembly

1. Switch to Assembly workbench

   Use workbench dropdown (may be labeled “Assembly 3” or “Assembly 4” depending on version)

2. Create new assembly

   Assembly → Create Assembly

   An assembly container appears in the tree

3. Add parts

   Drag parts from tree into assembly or use “Add Part” button:

   • Frame
   • Cam
   • FollowerStem
   • Roller

1. Select Frame in assembly tree

2. Apply Fixed constraint

   Click Fixed or Lock constraint button

3. Frame is now locked in place

   This serves as the ground reference for all motion

Allow cam to rotate about shaft:

1. Select cam shaft hole axis

   Click on the circular edge or use the References panel

2. Select frame shaft hole axis

3. Apply Axial Align constraint

   This aligns the axes and allows rotation about that axis

Test: Try rotating the cam manually in the assembly view - it should spin about the Z-axis!

Constrain follower to vertical motion only:

1. Select follower stem body

2. Select frame guide surfaces

   You may need to select the parallel guide rails or frame top surface

3. Apply constraints for vertical sliding:

   • Plane constraint: Aligns stem face to frame reference
   • Linear motion constraint: Allows only Z-direction movement

   The exact constraint type depends on your Assembly workbench version

Goal: Follower can slide up and down (Z-axis) but cannot move sideways or rotate

Position roller at bottom of stem:

1. Select roller and follower stem

2. Apply constraints:

   • Coincident or Attachment: Position roller at stem bottom
   • Align axes if needed

3. Adjust height so roller just touches cam base circle

Manual motion verification:

1. Rotate cam slowly in the assembly

   Grab the cam and rotate it incrementally

2. Manually adjust follower height to maintain roller contact with cam

   As cam rotates through rise, move follower up During dwell, keep follower stationary During return, move follower down

3. Observe the cycle:

   • 0° to 120°: Follower rises
   • 120° to 180°: Follower stays high (dwell)
   • 180° to 300°: Follower descends
   • 300° to 360°: Follower stays low (dwell)

1. Add angular dimension tool

   Select angular dimension from toolbar

2. Dimension each motion zone

   • 0° to 120°: Rise zone
   • 120° to 180°: High dwell
   • 180° to 300°: Return zone
   • 300° to 360°: Low dwell

3. Add text annotations

   Use Text tool to label:

   RISE (120°)

   • Lift: 20mm
   • Motion: Simple Harmonic

   DWELL (60°)

   • Position: Maximum Lift

   RETURN (120°)

   • Motion: Simple Harmonic

   DWELL (60°)

   • Position: Base Circle

Add critical dimensions:

1. Base circle radius

   Radial dimension: 40mm

2. Prime circle radius

   Radial dimension: 60mm

3. Lift

   Linear dimension showing 20mm difference

4. Shaft hole

   Diameter dimension: 20mm

5. Cam thickness

   Side view dimension: 15mm

1. Create sketch on drawing page

   Use TechDraw → Insert Sketch

2. Draw axes

   • Horizontal axis: 360 units (degrees)
   • Vertical axis: 20 units (mm)

3. Plot the profile

   • Use Line and Arc tools to trace motion profile
   • Mark key points: 0°, 120°, 180°, 300°, 360°

4. Label axes and zones

For more accurate diagram:

Use the motion law formulas to calculate displacement at multiple angles, then plot:

Plot these points and connect smoothly.

1. Open Spreadsheet

   Double-click Spreadsheet in tree

2. Change Lift parameter

   • Click cell B3
   • Type: 30
   • Press Enter

3. Recompute

   Press Ctrl+R or click Recompute button

4. Observe changes:

   • Cam profile grows! Prime circle is now 70mm radius
   • Rise and return sections steeper
   • Follower stroke increases to 30mm
   • All constraints maintain!

✅ Success! Your lift is parametric!

1. Change BaseCircleRadius

   • Cell B2: Type 50
   • Enter

2. Recompute (Ctrl+R)

3. Verify:

   • Entire cam scales up!
   • Base circle now 50mm
   • Prime circle automatically becomes 70mm (50 + 20)
   • Shaft hole remains centered
   • Profile proportions maintain

✅ Your cam scales parametrically!

1. Change CamThickness

   • Cell B6: Type 25
   • Enter

2. Recompute

3. Verify:

   • Cam becomes thicker (25mm instead of 15mm)
   • Profile shape unchanged
   • Assembly still aligns

✅ Thickness updates correctly!

Try these configurations:

Watch how the cam profile adapts!

1. Add return spring

   Model a compression spring that keeps follower in contact with cam

2. Create cam with different dwell timing

   Try 90° rise, 90° dwell, 90° return, 90° dwell

3. Add more parameters

   Control rise angle, dwell angles via spreadsheet

1. Design cycloidal motion cam

   Use cycloidal equations for smoother acceleration

2. Create flat-faced follower

   Replace roller with flat contact surface

3. Add manufacturing features

   Keyway in shaft hole, mounting bolt holes

1. Calculate and plot velocity/acceleration

   Derive velocity and acceleration from displacement curve

2. Design conjugate cam

   Two cams on same shaft for balanced forces

3. Create positive-drive cam

   Groove cam that drives follower in both directions

4. FEA stress analysis

   Analyze contact stresses using FEM workbench

“Cam profile has sharp corners”

“Profile doesn’t close properly”

“Follower motion is jerky”

“Roller doesn’t maintain contact”

“Cam profile breaks when changing parameters”

“Cannot create B-spline smoothly”