<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 6: Cams: Flat, Barrel, Globoidal, 'Slot' > 6D: Slot-Cams > Step 6D3.1: Export Slot-Cam to SOLIDWORKS |
A standard rotating-cam is a closed Cam-Profile. The contact-point (XY-Points) between the Follower-Profile and the Cam-Profile steadily moves along the Cam-Profile as the MMA increases from 0 to 360. The Cam-Profile does self-intersect or repeat (unless there is undercutting). However, with a Slot-Cam*, the contact-point may not move along the Cam-Profile steadily. The contact-point of a Slot-Cam retraces the Cam-Profile as the Follower-Roller or the Cam-Part moves in the opposite direction. Thus, the Cam-Profile repeats itself. You cannot create a Curve feature 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-Profile. |
There are two possible complications: A.The motion of the Follower relative to the Cam changes direction, or dithers*. In MechDesigner, when the Follower changes its direction, the contact-point moves from one Cam-Flank to the other Cam-Flank. This happens even if the the change in direction is a short interval. * Dithers : small directional changes. B.The motion of the Follower is Stationary When the Follower is stationary relative to the cam - usually at each end of the Slot-Cam - the contact-point also becomes stationary (of course). As the MMA increases, when the contact-point is stationary, we continue to calculate for you the cam-coordinates. 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 the text file of the cam-coordinates before you import them into SolidWorks as a Curve feature. It is difficult, but possible. •In MechDesigner, linearize the motion between the Cam and Follower. Linearize is the best option. |
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Linearize the Independent Input to the Cam.We need two models - the Original-Model and a Dummy-Model. STEP 1: Measure the full motion 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 displacement range of the sliding-part - 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. For example: 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. |