Step 6D1.3: Add the Stationary 2D-Cam
Contents
Add the Cam
In this Step, we add a 2D-Cam. We add the Cam to the Base-Part (Machine Frame).
First: What do we want the Cam to look like?
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We have prepared a motion for the Rocker. See image to the left. IMPORTANT NOTE: Imagine that the units along the X-axis of the Motion are not degrees, but 'unit-less'. That is, they are 'numbers'. |
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The Stationary 2D-Cam We will look at four methods to get the Stationary 2D-Cam we want. We explain the problems and advantages of each.
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Method 1: Add the 2D Cam as normal
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For convenience, we name the Part the Cam-Follower and the Profile the Cam-Follower Roller. |
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The image to the left shows the Pitch-Curve of the 'Stationary 2D-Cam'. The only good thing is the Stationary 2D-Cam is 'Stationary'! Q: What is the problem? A: It does not look like the Rocker motion! Do you need more explanation? |
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The motion for the Rocker is specified in MotionDesigner - see Step 6D.2. We have connected a Linear-Motion FB to the Motion FB. Therefore, the input to the Motion FB increases continuously from 0 to 360 Hence, the Motion FB follows the Motion Design in MotionDesigner for each complete cycle of the Master-Machine-Angle – this is what we know and love! Why is this design so different? |
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Imagine the Slider is Stationary while we cycle the machine. The Rocker will still continue through its motion design because the output from the Linear-Motion FB always 'feeds' the wire with the Master-Machine-Angle. We must synchronize the motion of the Rocker with the Motion of the Slider, NOT the Master-Machine-Angle! This is an important concept. |
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Method 2: Use the MMA at the input to the Slider Motion and the Rocker Motion
Method 2 will synchronize the Motion of the Slider and Rocker with the Master-Machine-Angle. This is easy! Drive the two with a Linear-Motion FB (the MMA). |
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Method 2:
The image to the left shows the Stationary 2D-Cam after Step3. We use the top 2 FBs to move the Slider. We use the bottom 3 FBs to move the Rocker (That is opposite to what they look like!) The Slider moves with the MMA, or constant velocity, for 360mm. It then 'jumps' back to the Base-Value of the Motion-Dimension FB. |
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Question 1: Why is this no good? The Stationary 2D-Cam 'looks' like the Rocker Motion designed for the Rocker. Answer 1: The Slider moves 360mm not 100mm the original Slider Motion. A Gearing FB can reduce the output from the Linear-Motion FB from 360 to 100mm.
The Stationary Cam now is 'perfect'. |
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Notes:
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Question 2: Why is this still not a good result? Answer 2: The Stationary Cam is 'perfect'. However, when we add the 2D-Cam for the Slider, it looks like a 'Snail'! The method is not useful to synchronize the motion of Cam-Follower Rocker with the motion of a different motion axis. MechDesigner is 'software for complete machine design', NOT 'software for single motion axis design'! The 2D-Cam is like a snail because the slider moves at constant velocity to the right and then jumps back. We want a 2D-Cam for the Slider and the Stationary 2D-Cams. |
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Method 3: Use the output from the Slider motion as the input to the Rocker FB
As stated above. We want the Slider Cam AND the Stationary Cam for the Rocker. Re-connect the input to Slider Motion-Dimension FB to give the Slider 2D-Cam again. Then, we can use the output from the Slider as the input to the Rocker. |
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Method 3:
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The image above shows the Stationary 2D-Cam. There are 5 FBs joined end to end. The values at the output of each connector is as follows
Note: You will get a message in the Feedback area: '1 Mechanism dependencies detected'. It is advisable to rebuild the model when the number of dependencies becomes more than 1. |
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The black arrows in the image to the left indicate the range of the input to the Motion FB that defines Rocker Motion. The input cycles between a Minimum to Maximum range of 30 and 130 (units) The 2D-Cam looks a lot nearer to the cam we want. But it is not complete. Q: Why is the stationary 2D-Cam not complete? A: The X-axis of the Rocker motion in MotionDesigner has a 'range' of 0 to 360. However, the input to the Motion FB is not 0 to 360. It is 30 to 130. Thus, the Y-axis output of the Rocker motion are those between 0 and 10. |
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Add a Gearing FB to increase the 'Range' of the Motion out of the Slider Motion-Dimension FB
The range of values at the output-connector of the Gearing FB is now 360, not 100. |
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The image above shows the Stationary 2D-Cam. The Stationary 2D has a step in it! Why is this?
We can see why in the image below. |
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In MechDesigner, when, or if, the input motion value extends more than the maximum value X-axis value of the Motion in MotionDesigner, the input 'wraps' around the X-axis to start at 0 again. This means when the input is 108 to 468, the output from the Motion FB
Question: What do we do to make the input from 0 to 360, not 108 to 468? A: Edit the Gearing FB to subtract 108 from all of the input values that are at the input-connector. |
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Two parameters do this. Edit one of them.
[The input is 30–130. The Gear Ratio changes it to 108–468. This parameter changes it to 0–360. Perfect]. - or -
[The input was originally 30–130. This parameter changes it to 0–100. The Gear Ratio changes it to 0–360]. The two options give the output from the Gearing FB as 0–360. You can see we have the Slider Cam and the Rocker Cams Success! |
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Method 4: Edit the Rocker Motion 'X Range' to match the Slider Motion 'Y Range'
The 'Y Range' of the Slider is 100mm. We edit the 'X Range' of the Rocker Motion to be 100 units. We will design the Rocker Motion with an X Range of 100, not 360. This is a reduction ratio of 100/360. We must also edit the position of each Blend-Point along the X-axis by the same proportion of 100/360. |
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Method 4:
Reduce the X-Values of each Blend-Point. The last Point should be at 100 'degrees'.
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Q: Why does the Cam have a step? A: Because the output from the Slider Motion-Dimension FB is actually 30 to 130 not 0 to 100mm Q: How do you correct that? There are a number of ways to correct it. Pick one: Answer 1: Add a Segment of width '30' to the start of the Motion. Answer 2: Edit the Motion Start with the Active Motion Settings - Generally not recommended. See MotionDesigner help. Answer 3: Use a Gearing FB and shift the output by 30 - same as Method 3. We will look A1. |
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This Rocker Motion has a new segment. The segment moves the motion to the 'left'. The motion now has an X-axis total range of 0 to 130. The input from the Slider Motion-Dimension FB to the Motion FB has a range between 30 and 130. |
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Here is the result. You can see the Slider Cam and the Rocker Cams Success! What do we do if the Slider is not a Slider? What? It is possible that the Slider (a Motion-Part) is a sliding-part. A sliding-part is a Part joined to a different Part with a Slide-Joint. It does not use a Motion-Dimension to get its motion. See Tutorial 6D2.0. |
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