<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves > Step 16.4: Compare XY Piggyback Sliders and Blend-Curve |
We will use the two ways to design a path that moves up and over an obstacle.
•Piggyback Sliders i9n the X-axis and Y-axis direction
•Sketch-Path and Motion-Path FB
STEP 1: Add an Obstacle to the Base-Part To see the obstacle, we will add a rectangle.
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STEP 2: Add Piggyback Sliders
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STEP 3: Design Motions for the X-axis Slider.
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STEP 4: Design Motions for the Y-axis Slider.
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STEP 5: Add Function-Blocks
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STEP 6: Add a Trace-Point to see the Path
<<< click to play video
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STEP 7: Open the Point Properties dialog-box
The Point Properties dialog-box is now open. STEP 8: Select the Vectors to show
Magnitude = √(X2 + Y2) STEP 9: Cycle the model
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The Maximum Vertical and Horizontal velocity and acceleration vectors will equal those of the X and Y Velocity and Acceleration graphs in MotionDesigner. This maximum acceleration Magnitude can be found by: •Moving the MMA until the Acceleration Vector is a maximum value - see left •Use a Point-Data FB and a Graph FB to measure and plot motion-values •Use a Stats FB to review the statistical data values |
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We will imagine that this motion is to guide a Pick and Place Robot. We may want the Robot to move more rapidly in the Pick direction (say from right-to-left) as compared with the Place direction (say from the left-to-right direction) STEP 9: Edit the Motions to Return more quickly.
It takes a while to create suitable motions with Piggyback Sliders. Small changes to the motion can give large changes to the Path. There is a different approach. You will notice that it is not very easy to make the 'Place' and 'Pick' paths the same. |
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Alternative, and easier strategy: |
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![]() Motion to modify the MMA |
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![]() Output of Motion FB is input to Motion FB |
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STEP 1: Add an Obstacle Draw a simple shape in the Base-Part and add a Profile to it. Use Visibility toolbar > Show Solids in Mechanism to see the Solid if you like.
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STEP 2: Add a sketch in the Base-Part to give the XY-Path a)Add a vertical Line b)Add a vertical Line c)Add a Blend-Curve d)Close the Part-Editor |
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STEP 3: Look in the Blend-Curve dialog-box Open the Blend-Curve dialog 1.Double-click Blend-Curve sketch-element In the Start Point separator and the End-Point separator, accept the values for the: •Angle: Start +90, End-90), •Curvature: Start 0,End 0 and •Curvature Rate: Start 0,End 0) The image shows the Start-Point separator expanded. |
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STEP 4: Add a Motion-Path FB to the sketch of the XY-Path. a)Click Function-Block menu (or Toolbar) > Motion-Path FB The Command-Manager selection-box will accept a sketch-element b)Click the Line c)Click 'OK' in the Command-Manager The Motion-Path FB shows in the graphic-area. The Motion-Point |
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STEP 5: Add a Motion FB and Linear-Motion FB a)Edit the Motion FB b)Connect the FBs c)Cycle the Mechanism. |
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STEP 6: Edit the Motion that is linked to the Motion FB There are two ways to make sure the Motion-Point moves along all of the XY-Path, and returns. a)Edit the Motion so it equals the projected length of the XY-Path, and returns to zero. The disadvantage to this approach is when you edit the XY-Path. The length of the XY-Path will change. We do not recommend you do this. Use Method b) |
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b)Edit the Motion so it changes from 0 to 360 (See Note) and returns to zero(0). In this case, a motion from 0 to 360 ALWAYS moves the Motion-Point along the complete length of a XY-Path. When you edit the XY-Path, the Motion-Point will always move from the start of the first sketch-element to the end of the last sketch-element. Note: Make the motion value equal to 359.999 (not 360) to make sure the Motion-Point does not, for an instant, appear at the start of the first sketch-element when it should be at the end of the last sketch-element. This is because it is possible that the motion-value that should be 360 is actually 360.000001. |
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STEP 7: Edit the Motion so the first segment is longer than the second segment. In this example, the first segment is 2x longer than the second segment. The segment types are the same. In this case: •The Velocity of the Motion-Point when moving in the 'forward' direction has 1/2 of the Velocity in the 'return' direction. •The Acceleration of the Motion-Point when moving in the 'forward' direction has 1/4 of the Acceleration in the 'return' direction. |