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?

MD-QST5D-3-00

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'.

MD-QST5D-3-0

The Stationary 2D-Cam1s-red, looks like the Rocker motion.

We will look at four methods to get the Stationary 2D-Cam we want. We explain the problems and advantages of each.

Method 1: Do 6D1.2 again: Fail
Method 2: Fail, but better
Method 3: Success for Single-axis Machines
Method 4: Success for Multi-axis Machines

tog_minusMethod 1: Add the 2D Cam as normal

Icon-AddProfile

STEP 1: Click the Solids toolbar > Add Profile

MD-QST5D-2-8

STEP 2: Click the Circle sketch-element in the 'Rocker'

For convenience, we name the Part the Cam-Follower and the Profile the Cam-Follower Roller.

Icon-Add2DCam

STEP 3: Click 2D-Cam

MD-QST5D-2-9

STEP 4: Click the Base-Part Part-Outline.
STEP 5: The 2D-Cam is stationary. Therefore, we add it to the Base-Part.
STEP 6: Click the new Cam-Roller
STEP 7: The 2D-Cam is a bird's nest*.
STEP 8: To help us untangle the bird's nest, hide Cam 1 and Cam 2 and leave the Pitch-Circle-Path.
STEP 9: Click the 2D-Cam – see image to the left - then 'Double-click it in the Selection-Window'
STEP 10: In the 2D-Cam Properties Display dialog-box, select the Pitch-Curve check box and clear the Cam 1 and Cam 2 check boxes.

MD-QST5D-2-10

STEP 11: You can also select the 'Open Cam' option in the dialog-box.

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?

MD-QST5D-3-2

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?

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.

tog_minusMethod 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).

Click to Expand / Collapse
Click to Expand / Collapse

Method 2:

STEP 1: Delete the wire that connect the Motion (Slider) FB to the Slider Motion-Dimension FB from the Motion FB
STEP 2: Delete the wire that connects the Linear-Motion FB to the Motion (Slider) FB
STEP 3: Connect a Linear-Motion FB directly to the Slider Motion-Dimension FB

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.

Click to Expand / Collapse
Click to Expand / Collapse

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.

STEP 1: Add a Gearing FB to the graphic-area. Delete the existing wires. Connect the FBs to include the Gearing FB
STEP 2: Double-click the Gearing FB to open the Gearing dialog-box.
STEP 3: Select 'Use Ratio of Pulley Teeth' check box. Enter 10 and 30 for the 'Input Pulley' and 'Output Pulley', respectively.

The Stationary Cam now is 'perfect'.

Notes:

We could also design a motion with a constant velocity of 100mm/cycle and use a Motion FB, as an alternative to the Gearing FB.
I took the opportunity to reduce the diameter of the Cam-Follower Roller. The 2D-Cam started to 'undercut'.
Click to Expand / Collapse
Click to Expand / Collapse

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.

tog_minusMethod 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.

Click to Expand / Collapse
Click to Expand / Collapse

Method 3:

STEP 1: Delete the wire to input-connector of the Slider Motion-Dimension FB
STEP 2: Connect the Motion FB (with the Slider Motion) to the Slider Motion-Dimension FB.
STEP 3: Disconnect the Linear-Motion FB that is connected to the input-connector of the Motion FB (with the Rocker Motion)
STEP 4: Connect Slider Motion-Dimension FB to the Rocker Motion-Dimension FB.

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

The Output from the Linear-Motion FB is 0 to 360.
The Output from the 'Slider' Motion FB is 0-100. It is a motion 'function', see DRRD.
The Output from the Slider Motion-Dimension FB is 30 to 130, (the Base-Value is 30mm and hence 0-100 becomes 30-130).
The Output from the Rocker Motion FB is 0 to approximately 10º.
The Output from the Rocker Motion-Dimension FB is -10º to approximately 0º, because the Base-Value -10º.
This is connected to the input-connector of the Rocker Motion-Dimension FB.

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.

MD-QST5D-3-10

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.

Click to Expand / Collapse
Click to Expand / Collapse

Add a Gearing FB to increase the 'Range' of the Motion out of the Slider Motion-Dimension FB

STEP 1: Add a Gearing FB.
STEP 2: Connect the output from the Slider Motion-Dimension FB to the input of the Gearing FB.
STEP 3: Connect the output from the Gearing FB to the Motion FB.
STEP 4: Double-click the Gearing FB to open the Gearing FB dialog-box. Select 'Use Ratio of Pulley Teeth' check box.
STEP 5: Enter 360 (or 36) and 100 (or 10) for the Input Pulley and Output Pulley.

The range of values at the output-connector of the Gearing FB is now 360, not 100.

The image above shows the Stationary 2D-Cam. The Stationary 2D has a step in it! Why is this?

The Output from the Slider Motion-Dimension FB is 30–130, (the Base-Value is 30mm).
The Output from the Gearing FB is 108–468. When we look at the numbers:
30 * 36/10 = 108
130 *36/10 = 468.
Therefore, the input to the Motion FB varies from 108 to 468, not from 0 to 360.
It needs to be 0–360, not 108–468.

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

start where the X-axis is 108,
follow the motion from 108 to 360,
continues from 0 to 108.

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.

Click to Expand / Collapse
Click to Expand / Collapse

Two parameters do this. Edit one of them.

Edit the 'After Gear Ratio' to subtract 108 from the output values. This is AFTER the FB applies the Gear Ratio to the motion at the input-connector.

[The input is 30–130. The Gear Ratio changes it to 108–468. This parameter changes it to 0–360. Perfect].

- or -

Edit the 'Before Gear Ratio' to subtract 30 from the input values. This is BEFORE the FB applies the Gear Ratio to the motion at the input-connector.

[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!

tog_minusMethod 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.

MD-QST5D-3-14

Method 4:

STEP 1: Edit the Rocker Motion in MotionDesigner.

Reduce the X-Values of each Blend-Point.

The last Point should be at 100 'degrees'.

STEP 2: Delete the Gearing FB
STEP 3: Connect the Slider output to the Rocker input.
Click to Expand or Collapse
Click to Expand or Collapse

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.

MD-QST5D-3-16

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.

Click to Expand / Collapse
Click to Expand / Collapse

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.

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