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 as the MMA increases from 0 to 360.

It is easy to export and extrude these cams to SolidWorks as Points do not self-intersect or interfere with a different point.

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

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 Calculations with Slot Cams

Example Calculations with Slot Cams

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_minusSolution to the Complications : LINEARISE the MOTION 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 - which can be very difficult
Linearise the motion between the cam and cam-follower.

Linearize is the best option.

 

Linearise the Independent Input to the Cam.

STEP 1: Measure the full range of the sliding-part in the 'Real model'

The full range of the sliding-part in the real model is : Real Sliding Range = Maximum – Minimum

Use a Measurement FB to measure the Sliding-Part Range, and connect to a Graph FB, and take a note of the Minimum and Maximum values.

STEP 2: Build a dummy model with the same kinematic-elements as the Real Model - with a Dummy Slider1s-red and a Dummy Rocker2s.

Important: The input to the Dummy Slider should increase at a constant rate with a range equal to Sliding-Part-Range in the 'Real Model'

To do this: connect a Linear-Motion FB to the input of a Gearing FB3s . The output from the Gearing FB is connected to the input of the Motion-Dimension FB to the Dummy Slider.

Edit the Gearing FB to set the Gearing Ratio parameter = Real Sliding Range / 360.

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 the Gearing Ratio = 320/360 = 0.88889.  Enter this, as an equation - that is, enter 320/360 in the Gearing Ratio parameter box of 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-Dimension FB.

Now the 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.

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