A standard rotating-cam is a closed shape. The contact-point between the follower and the cam-profile steadily moves along the cam-profile as the MMA increases from 0 to 360. The XYZ Points do not self-intersect or repeat (unless there is undercutting).
However, with a Slot-Cam* the contact-point may not move along the cam steadily. The contact-point will usually retrace its path as the roller moves in the opposite direction. Thus, the coordinates can repeat.
You cannot create a sketch in SolidWorks when the coordinates repeat.
This topic describes how to solve this problem.
* Any Cam in which the contact-point does not move steadily along the cam.
There are two possible complications:
A.The Cam-Follower changes its direction, or dithers*.
If the cam-follower changes its direction, the contact-point of 'Cam 1', as calculated by MechDesigner, moves from one cam-flank to the other cam-flank
*'Dithers' : small directional changes
B.The Cam-Follower becomes Stationary
If the cam-follower becomes stationary relative to the cam - usually at each end of the Slot-Cam - the contact-point also becomes stationary. While the contact-point is stationary, the cam-coordinates continue to be calculated as the MMA increases.
When the cam-coordinates have complications as described in A or B, or A and B, SOLIDWORKS cannot create the Curve feature.
Example of a cam with the two complications.
Refer to the image above and the VIDEO to the left.
The sliding-Part moves horizontally. A 'connecting-rod' joins the sliding-part to a point that has a complex 'looping' motion
Thus, the sliding-part moves to the right and left, then right again but with a complex motion, rather than move with a simple motion that is to the right and then to the left.
Each time the sliding-part changes its direction, the contact-point moves from one cam-flank to the other cam-flank
A line is drawn between the cam-flanks each time the contact moves across
SOLIDWORKS will NOT be able to create a Curve Feature with this Cam.
Before we export the cam to SolidWorks, we must remove the two 'complications'.
There are two ways:
•Manually edit a text file of the cam-coordinates - which can be difficult, but possible.
•Linearize the motion between the cam and cam-follower.
Linearize is the best option.
Linearize the Independent Input to the Cam.
We need two models - the Original-Model and a Dummy-Model.
STEP 1: Measure the full range of the sliding-part in the original-model.
Original Sliding Range = Maximum – Minimum
We can use a Measurement FB and a Graph FB to measure the Sliding-Part Range - just note the Minimum and Maximum values.
STEP 2: Build a Dummy-Model with a Dummy-Slider and a Dummy-Rocker.
Important: The input to the Dummy-Slider should increase at a constant rate ( Constant-Velocity ).
In one machine cycle, the Dummy-Slider should move the same distance and range as the Original-Slider
To do this:
1.Connect a Linear-Motion FB to the input of a Gearing FB. The output from the Gearing FB is connected to the input of the Motion-Dimension FB of the Dummy Slider.
2.Edit the Gearing FB and enter for the Gearing Ratio : Original Sliding Range (Maximum-Minimum) / 360 (the numerical sliding range, not the words!)
The output from the Gearing FB will increase steadily: From 0 to Real Sliding Range (mm) in one machine cycle.
If, with the original model, the Maximum Measurement is 340mm, and the Minimum Measurement is 20mm, then the Range is 340-20 = 320mm.
Thus enter the actual equation for the Gearing Ratio : 320/360 . The Gearing Ratio will equate to 0.88889. (You can also, if the Range is an integer value, use the Pulley Teeth parameters: Enter enter 320 as the output-pulley and the 360 as the input-pulley).
Connect wires from the output-connector of the Linear-Motion FB to the Gearing FB, and to the input-connectors of the Motion-Dimension FB.
Now the Dummy-Slider will move with Constant-velocity from 0 to 320mm
Now, the Cam-Coordinates will not change flanks.
When you export the cam, SolidWorks can create the Curve entity and the Cam feature.
Note: You may need to delete the last point in the saved cam-coordinate data or from the Curve feature in SolidWorks.
You can also save the Cam-Coordinates as a text file. and Manually edit the values.