Background- A 'Standard Rotating Cam'

Example Cam

When we export cam-coordinates to SolidWorks, the coordinates of the cam in SolidWorks becomes the XYZ table of a Curve feature.

After the transfer is finished, we must use the Convert Entities sketch tool to convert the Curve feature to a Spline sketch-element. We extrude, or cut, the Spline to become the cam surface.

A 'standard rotating-cam' is a closed shape. The contact-point between the cam and the cam-follower moves around the cam continuously as the MMA increases from 0 to 360.

It is easy to export and extrude these cams to SolidWorks.

However, with a 'Slot-Cam*', the contact-point may not move along the cam steadily. SolidWorks may not be able to create the Curve feature.

This topic describes how to solve this problem.


* Any cam in which the contact-point does not move steadily along the cam.


tog_minus'Complications' when exporting coordinates of a Slot-Cam to SOLIDWORKS

If the contact-point does not continually move along a cam's surface, 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 changes in direction

B.The Cam-Follower becomes Stationary

If the cam-follower becomes stationary relative to the cam, the contact-point also becomes stationary. While the contact-point is stationary, the cam-coordinates become the same values, even as the MMA increases.

When the cam-coordinates have complications as described in A or B, or the two, SOLIDWORKS cannot create the Curve feature.

SlotCam-reciprocating2

Example of a cam with the two complications.

Refer to the image to the left:

Sliding-part1s-red moves horizontally. A 'connecting-rod'2s joins the sliding-part to a point that has a complex 'looping' motion' as identified by the Trace-Point3s.

Thus, the sliding-part1s-red moves to the right and to the left, 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-flank4s.

Because MechDesigner draws the cam from cam-point to cam-point, a line is drawn across from one cam-flank to the other cam-flank4s.

tog_minusLinearize the input to the Cam.

SlotCam-reciprocating4

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, or
'linearize' the motion between the cam and cam-follower.

To do this, we need to add a new mechanism with a Slider and a Rocker.

The Slider1s-red should:

move at constant velocity in one direction, and
move the same distance as the Sliding-Part in the original model

The Rocker2s* must:

rotate with the same motion as the original model, coordinated to the linear position of the Sliding-Part.

* Or Slider.

Steps to 'Linearize' the Independent Input to the Cam.

STEP 1: Measure the full stroke of the sliding-part in the 'original model'

The full stroke of the sliding-part in the original model is the 'Sliding-Part Range'.

There are number of ways to measure the Sliding-Part Range.  For example, connect the output of the Measurement FB* to a Graph FB, or a Statistics FB, and scrutinize those values.

* We use a Measurement FB to measure the position of the Sliding-Part in the original model. Thus, this FB is already available.

STEP 2: Build a new model to replace the Sliding-Part and Rocker of the original model with a Slider1s-red and Rocker2s.

Note: the difference between a Sliding-Part and a Slider.

The input to the Slider and the Motion FB for the Rocker should increase linearly with a displacement range equal to the Sliding-Part's displacement range.

Add a Linear-Motion and a Gearing FB3s and connect them with wires to the Motion-Dimension for the Slider.

We need the motion-values at the output-connector of the Gearing FB to have a range equal to Sliding-Part Range. Thus the Gearing Ratio in the Gearing FB dialog-box should be:

Gearing Ratio = Sliding-Part Range/360.

STEP 3: Edit the Gearing FB
STEP 4: Enter a Gearing Ratio = Sliding-Part Range/360

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 the Gearing Ratio = 320/360 = 0.88889.  Enter this, as an equation, [that is, enter exactly 320/360] in the Gearing Ration in the Gearing FB dialog-box.

Connect wires from the output-connector of the Linear-Motion FB to the Gearing FB to the input-connectors of the Motion FB and the Motion-Dimension FB.

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.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd