 Cam Surface Mesh Density
 Rims along the Cam-Flanks (Purple), the Top and Bottom (Orange), and Points along each Rim. |
Preamble:
| • | We specify 3D-Cams with four(4) cam faces. |
| • | There are a number of lines, that we call Rims, along each cam face. |
| • | There are a number of points along each Rim. |
The four (4) cam faces are the:
| • | Two working faces.They are the Cam-Flanks. |
The Cam Flanks are in continuous contact with the Cam-Follower Roller. There must be some clearance between the roller and the actual cam.
| • | Two non-working faces. The Root-Face and the Top-Face. |
The Root-Face is at the 'floor' of the cam. It should not contact the actual Cam-Follower Roller at any time.
The Top Face is 'outside' the cam diameter. It does not have a function in the actual cam. We use the Top-Face to close the 3D-Cam, when we export the data to SolidWorks, or save it as a STEP file.
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Parameters:
# Points along Rims:
Number-of-points along each Rim: '360' in dialog to left
# Rims along Flanks:
Number-of-rims across each flank (working faces) of the Cam: '6' in dialog to left
# Rims along Top & Bottom:
Number-of-Rims across the Root and Top (non working faces) of the Cam: '4' in dialog to left
# Hoops (data for CAD only)
Number-of-hoops that wrap around the 3D-Cam and connect the same Point along each Rim: '10' in dialog to left
The hoops help SolidWorks to keep the shape of the surfaces.
| • | There is a minimum of 4 hoops if the Cam-Follower oscillates or reciprocates. That is, it is continuous. |
| • | If the Cam-Follower indexes, then Hoops are generated for you at the end-caps. There are 2. |
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Roller Parameters
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Preamble: Note: the equation: V = r ω [Linear Velocity = Radius × Angular Velocity]
The Roller-Parameter is the 'Taper-Angle' of the Cam-Follower Roller.
Why use a Taper-Roller with a Barrel and Globoidal Cam?
Different points on the cam-flank surface are at different radii from the cam's rotational axis. The tangential velocity of points on the flank of a 3D-Cam are not the same. A point that is at a large radius from the Cam's rotational-axis has a greater tangential velocity than a point that is at a small radius.
Points on the surface of a cam-follower have identical radii from its 's rotational-axis. Thus, the tangential velocities of all points on the surface of a cylindrical roller are identical.
The surface speed of the cam and the surface speed of the follower can only be the same at one contact points. The follower must be skidding at all other points!
If you use a a tapered-roller, with an apex that is coincident with the rotational-axis of the cam, then pure rolling can occur during the dwell periods, and nearly pure rolling during the motion periods.
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Nevertheless, cylindrical rollers are most often used as they are readily available, cheap, and can take high loads when they have needle-rollers.
What is the Roller Diameter of a Taper-Roller?
We cannot consider this until we understand the Extrusion-Offset and Extrusion-Depth parameters that define the Profile Extrusion of the Cam-Follower Roller.
In MechDesigner, to model a 3D-Cam, we sketch a circle to represent the diameter of the roller. We add a Profile to the circle to represent the cylindrical sides of the Cam-Follower. We use Extrusion dialog-box to make the parameter equal to the 'Length/Width' of the Cam-Follower [usually given as the 'B' parameter in bearing catalogues].
Extrusion dialog-box:
Extrusion-Offset [mm]: Positive or Negative value
| • | A dimension, that may be positive or negative. |
| • | Equals the position of the Primary-Contour [when the Part-Offset parameter = 0mm]. |
Extrusion-Depth [mm]: ONLY a positive value.
Extrusion-Offset [mm] + Extrusion-Depth [mm]= the position of the Secondary-Contour.
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Note: In image to the left, +Z-axis direction is down.\/
Parameters
Taper-Angle [degrees] inclines the Flanks of the 3D-Cam. The taper angle pivots about the Secondary-Contour. This is not as convenient as the the Primary Contour, for which we apologise.
With reference to the image to the left, we can see the
| • | Positive Taper Angle increases the diameter in the +Z-axis direction. |
| • | Negative Taper Angle [shown in image] decreases the diameter in the +Z-axis direction. |
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Recommendation , if you are going to use the Taper-Roller parameter.
Below, we assume you have made sure the Mechanism Plane of the Cam-Follower is half way through the width of the Cam-Follower. It if is not, then change the dimension below to suit your model.
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STEP 1
| 1. | Edit the Cam-Follower Extrusion with the Extrusion dialog-box |
Enter these parameters:
| • | Extrusion-Depth[mm] = 0.5 × Actual Roller Width[mm] |
| • | Extrusion-Offset [mm] = — Extrusion-Depth[mm], |
The Extrusion-Offset is the negative of the Extrusion-Depth. The Secondary Profile is now on the Mechanism-Plane.
Now, the Taper-Angle parameter will rotate the cam flanks, pivoting on the Mechanism-Plane.
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STEP 2:
In the Clearances separator [in the 3D-CAM dialog, see below], enter:
 Root-Clearance = a minimum of 0.5 × Actual Roller Width[mm]
 You will need to add further Root-Clearance and Top-Clearance to extend the flanks as required of the 3D-Cam, to suit your design.
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Clearances
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Preamble:
Clearances are practical considerations.
Clearance assumes the Cam is a Groove/Track Cam.
Positive Clearance values move the 3D-Cam faces away from the Cam-Follower Roller.
Parameters:
Radial-Clearance
| • | A positive value 'pushes' the working cam-faces [flanks] outwards, to be outside of the cam-follower roller. |
| • | A negative value 'pulls' the working cam-faces [cam-flanks] inwards, to be inside the cam-follower roller. |
Note: Total Clearance = 2 × Radial Clearance.
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Note: the Top-Clearance may be the Root-Clearance and Vice Versa.
Root-Clearance: This is intended to be the at the 'floor' of the cam-groove/track.
| • | Use this parameter so that the Cam-Follower Roller does not touch the floor/root of the Cam Groove. A positive value extends the bottom, non-working face, nearer to the Centre of the Cam. |
If the Extrusion Depth of the Cam-Follower Roller is the same as the width (B dimension) of the Cam-Follower Roller that you intend to use in your machine, then you should add Root-Clearance to give clearance between the bottom of the roller and the cam floor/root.
Top-Clearance: This is intended to be the an imaginary surface outside the working diameter of the Cam. We use it in SolidWorks to create a closed form.
| • | A positive value moves the top, non-working face, further from the Centre of the Cam. |
Make sure the top, non-working face is outside the maximum radius of the Cam-Blank.
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Practically, the Radial Clearance is necessary to make sure that the Cam-Follower Roller does not jam as it slides along the Cam Groove in the Barrel or Globoidal Cam. My guide for Radial Clearance is approximately 1 ∕ 1000 of the Roller Diameter for accurately built machines.
As you increase the Radial Clearance there is more 'Play'. The motion of the machine will not be exactly the same as your motion design. Impacts and vibration occur each time the Cam-Follower Roller traverses the Radial Clearance. The greater the clearance, the longer the roller will skid before it reaches the rolling speed again.
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To check the Cam-Follower-Roller does not show outside the four faces of the cam.
| 1. | Increase the Number-of-Points to ~1 Point per 0.1º of cam rotation. Experiment for different size cams. |
| 2. | Rebuild the cam with the Rebuild button at the top of the dialog |
| 3. | Edit the Roller Extrusion. In the Edit Extrusion dialog-box, increase the Image Quality to High - the maximum Quality. |
| 5. | Step through the machine cycle with the F or B key. Or use the MMA spin box for smaller steps. |
| 6. | Inspect the Cam in the graphic-area to make sure the Cam-Follower does not break through the cam flanks and the Root of the Cam. |
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Flank Length
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Preamble:
Flank Length parameters apply to Indexing Cams.
When you add a 3D-Cam, we calculate the coordinates for the cam over a complete machine cycle of the MMA, 0 – 360. However, cam-follower rollers of indexing cams do not stay in contact with the cam for a complete machine cycle 0 – 360. The cam-follower rollers progressively engage, then disengage with the cam, in a similar way to gear teeth.
We use the 'Flank-Length' separator to calculate the cam coordinates for the period only when one of the cam-followers is engaged with the cam. To do this we reduce the 'Flank Length' from a machine period of 0 and 360, to a period between two other machine angles.
Parameters:
You may need to edit the 'Flank Length' to calculate the cam for angles that are not from 0 and 360.
To edit the Flank-Length:
Enter a 'Cam Start Angle' and a 'Cam End Angle'.
As you edit the Start-Angle and End Angle, you will notice the Cam becomes shorter in length.
The Number-of-Points that we calculate along each 'rim' in the cam does not change. Thus, the points along each rim become nearer to each other.
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