Cam Speed and the Cam-Follower Contact Force.

The Cam-Follower Part (Rocker/Lever) and the Cam-Follower Roller have mass. As you increase the machine speed, you will also increase acceleration and inertia forces.

In this step, we will give the Cam-Follower a Motion - from MotionDesigner. We increase the machine speed until the Contact-Force between the Cam and Cam-Follower becomes zero or negative.

Add a Motion to the Cam-Follower.

MD-QST13-5-1

This motion will move the Cam-Follower ±5º – a total swing of 10º.

Use the tools in MotionDesigner to design the motion to the left.

 

MD-QST13-5-2
1.Add a Motion FB to the graphic-area .
2.Edit the Motion FB and select the Motion1 in drop-down box.
3.Connect the Linear-Motion FBRed-14-1b to the new Motion FBRed-14-2 and to the Motion-Dimension FBRed-14-3 for the Cam-Follower.

I have de-selected Display Force Vectors to make it easier to see the new shape of the 2D-Cam.

See, in the image:

•The 2D-CamRed-14-4
•The original Cam Profile element (Pink)Red-14-5.

Cam Contact Force

MD-QST13-5-3

We can show Contact-Force between the Cam and Cam-Roller in four ways:

•the force vector that ACTS-ON the Cam-Follower Part, and
•the force vector that ACTS-ON the Cam-Part

Note: YOU must determine whether the contact-force is active ON (towards)the cam or active OFF (away from) the cam.

2.Cam Display and Properties dialog > Cam Display Options > Contact-Force.
3.Force-Data FB with a cam and plot with a Graph FB.

Note: YOU must determine whether the contact-force is active ON (towards)the cam or active OFF (away from) the cam.

4.Use a Cam-Data FB . Use the Contact Force output-connector to plot with a Graph FB.

If the Contact Force < Zero,  then the Contact-Force is = zero. This is the preferred option for Cam Contact Force.

Dialog-R13.2-CamDisplay-CamDisplayOp

We will use the 2D-Cam dialog-box.

1.Double-click the 2D-Cam

The 2D-Cam dialog-box opens.

We want to show the contact force

In the Cam Display Options separator:

In the 'Display Cam Contour as...' box

Select 'Contact Force' radio-button

To see the colours of the  more clearly, make the:

Line Thickness of Cam: = 2 or 3

MD-QST13-5-5

In the graphic-area, the 2D-Cam shows the:

•Cam is Colour Coded
•Contact-Force at the contact point
•Colour-coded swatch and Force scale at the left of the display

Note: The contact is not a point. When the cam-follower is cylindrical or flat, the contact is a 'line' across the width of the cam-follower. The 'line' becomes a small rectangle area as the cam and roller deform. Thus, there is a contact stress.

If the cam-follower is barrel-shaped, then the contact is a small ellipse.

See Cam Analysis and Design Checklist.

MD-QST13-5-6

Drag the Master-Machine-Angle Slider until the Contact-Force is at a minimum.

For my motion, this is at a Machine Angle of 109º.

The minimum Contact-Force agrees, approximately, with the maximum deceleration of the Cam-Follower Arm.

MD-QST13-5-7

Open the Edit menu > Machine Settings dialog

Increase the Machine Speed until the Contact-Force becomes ~0N.

Again, drag the Master-Machine-Angle Slider until the Contact-Force is at a minimum. If the contact-force is a function of inertia, gravity, and springs, then the minimum will be at different machine-angles for different machine-speeds.

For my motion, the Contact-Force becomes ~0N when the cam-shaft rotates at ~91.5 Cycles per minute. (RPM)

The maximum speed is a function of:

•The motion
•The mass and mass distribution of the Cam-Follower Rocker

Are there ways to increase the speed of the cam-shaft, but use the same motion and the same mass distribution?

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd