 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. See image to the left. |
The four (4) cam faces are the:
| • | Two working faces or the Cam-Flanks. |
Cam-Flanks: the two faces along which the Cam-Roller will roll or slide.
| • | Two non-working faces. These are called the Root-Face and the Top-Face. |
Root-Face: the 'floor' of the cam. It should not contact the actual Cam-Roller at any time.
Top Face: 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.
Each Face is specified by: Rims and Points
| • | There are a number of lines, that we call Rims, along each cam face. We can specify how many Rims - see below. |
| • | There are a Points along each Rim. We can specify how many Points - see below. |
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Parameters:
Number-of-Points along each Rim
Number-of-rims across each flank (working faces) of the Cam
Number-of-Rims across the Root and Top (non-working faces) of the Cam:
Number-of-hoops that wrap around the 3D-Cam and connect the same Point along each Rim:
The hoops help SolidWorks to keep the shape of the surfaces.
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Preamble:
Note: the equation: V = r ω (Linear Velocity = Radius × Angular Velocity)
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 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 Cam-Roller. We add a Profile to the circle to represent the cylindrical sides of the Cam-Roller. We use Extrusion dialog-box to make the parameter equal to the 'Length/Width' of the Cam-Roller bearing (Typically, '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
of the Cam-Follower Roller.
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 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 (mid-)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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 C = Actual Roller Width |
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) (Dimension 'C' in image to the left (thank you SKF) |
| • | Extrusion-Offset (mm) = — Extrusion-Depth(mm) (Equal to –C) |
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 and pivot on the Mechanism-Plane.
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STEP 2:
In the Clearances separator (see below ):
 Root-Clearance = a minimum of 0.5 × Actual Roller Width(mm)
 You need to add more Root-Clearance and Top-Clearance to extend the flanks as required of the 3D-Cam, to suit your design.
Typical Root-Clearance = 0.6 x Actual Roller Width
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Preamble:
Clearances are practical considerations.
Clearance assumes the Cam is a Groove/Track Cam.
Parameters:
| • | 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-Face may be the Root-Face of the Cam - Vice-Versa. It is a function of your actual model.
To find out which face is which face, enter values and Rebuild the model, to see which faces actually moves.
We will assume that the Extrusion-Depth of the Cam-Follower Roller (in the model) is equal to the Actual Cam-Follower Width (Dimension C)
A positive value extends the Root/Floor and non-working face more into cam, and usually nearer to the centre of the Cam.
You will not normally need to use this parameter. However, edit this parameter when the Top-Face is actually the Root-Face.
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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.
As you edit the Start-Angle and End Angle, you will notice the Cam becomes shorter in length.
The 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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