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.
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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.
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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 FB 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-Cam •The original Cam Profile element (Pink) |
.Cam Contact Force
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We can show Contact-Force between the Cam and Cam-Roller in four ways: 1.Display Force Vectors to show •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. |
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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 colors of the more clearly, make the: Line Thickness of Cam: = 2 or 3 |
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In the graphic-area, the 2D-Cam shows the: •Cam is color Coded •Contact-Force at the contact point •color-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. |
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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. |
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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? |
