Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves > Step 16.4: Compare XY Piggyback Sliders and Blend-Curve

Compare 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

Piggyback Sliders

GST-16-4-Motion-Path-A

STEP 1: Add an Obstacle to the Base-Part

To see the obstacle, we will add a rectangle.

1.Part-Editor: Geometry toolbar > Add 4 × Lines

2.Part-Editor: Constraints toolbar > Add 3 × Perpendicular

3.Part-Editor: Geometry toolbar > Add 1 × Horizontal to a Line

4.Part-Editor: Geometry toolbar > Add Dimension (70mm wide, 50mm tall )

5.Exit Part-Editor

GST-16-4-Motion-Path-B

STEP 2: Add Piggyback Sliders

1.Edit Base-Part: Geometry toolbar > Add Line, Vertical Constraint, Dimension

2.Exit Part-Editor

3.Mechanism-Editor: Kinematic elements toolbar, Add Part, Add Slide-Joint

4.Mechanism-Editor: Kinematic FB toolbar, Add Motion-Dimension FB (Y-axis)

5.Edit Sliding-Part: Add vertical Line (Horizontal in Mechanism-Plane),

6.Exit Part-Editor

7.Mechanism-Editor: Kinematic elements toolbar, Add Part, Add Slide-Joint

8.Mechanism-Editor: Kinematic FB toolbar, Add Motion-Dimension FB (X-axis)

X-axis motion

STEP 3: Design Motions for the X-axis Slider.

1.Motion-Designer: Right-Click the motion graph. Rename to X

2.Motion-Designer: Blend-Point Editor. All Blend-Point Position=0,

3.Motion-Designer: Close Blend-Point Editor

4.Motion-Designer: Insert Blend-Point: Click the Motion graph

5.Motion-Designer: Blend-Point Editor. Edit X-axis values of all Blend-Points.

6.Motion-Designer: Blend-Point Editor. Edit Y-axis values of all Blend-Points.

Y-axis motion

STEP 4: Design Motions for the Y-axis Slider.

1.Motion-Designer: File toolbar > Add new Motion

2.Motion-Designer: Right-click the motion graph Rename to Y

3.Motion-Designer: Blend-Point Editor. Edit X-axis values of all Blend-Points.

4.Motion-Designer: Blend-Point Editor. Edit Y-axis values of all Blend-Points.

GST16-4-Motion-Path-E

STEP 5: Add Function-Blocks

1.Mechanism-Editor: Kinematic FB toolbar, Linear-Motion FB, Click Graphic-area

2.Mechanism-Editor: Kinematic FB toolbar, Motion FB, Click Graphic-area

3.Mechanism-Editor: Kinematic FB toolbar, Add Motion FB AGAIN, Click Graphic-area

4.Mechanism-Editor: Edit a Motion FB - select Y in Select-Motion drop-down.

5.Mechanism-Editor : Drag wires to connect FBs to the Motion-Dimension FBs

STEP 6: Add a Trace-Point to see the Path

1.Mechanism-Editor: Kinematic elements toolbar > Add Trace-Point

2.Graphic-area: Click a Point on the X-axis Slider.

3.Command-Manager: Click to close

<<< click to play video

GST-16-4-Motion-Path-G-Point-Properties

STEP 7: Open the Point Properties dialog-box

1.Mechanism-Editor: Filters toolbar > Filter for Points

2.Mechanism-Editor: Double-Click the Point with the Trace-Point

The Point Properties dialog-box is now open.

STEP 8: Select the Vectors to show

1.Click Show Velocity Vector

2.Click Show Acceleration Vector

3.Click Velocity Vector Options: Mag. (Magnitude)

4.Click to close the Point Properties dialog-box

Magnitude = √(X2 + Y2)

STEP 9: Cycle the model

1.Click Run toolbar > Cycle

1.Press ALT+C on your keyboard

GST-16-4-Motion-Path-H

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

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.

1.Try to edit the X and Y motions to move the Sliders quickly in the Pick direction as compared to the Place direction

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.

Alternative, and easier strategy:

Motion to modify the MMA

When you want a fast Pick and slow Place, it is easier change the input function to the X-Y-axis Slider motions.

In the standard motion strategy - as above - the output from the Linear-Motion FB is the input-function to the X-Y-axis motions. Its output mirrors the MMA.

This is motion-function is indicated in the image with the Linear-Motion FB motion (in the top image, left)

The alternative motion increases slowly until its output reaches 180, and then increases rapidly until its output reaches 360.

See again, the top image, left, with the Blue then Orange segments

The output of this motion is connected to the X and Y-axis Motion FBs in exactly the same way as the output from a Linear-Motion FB in the examples above - see middle image, left

With this technique, XY-path does not change, buy you change the speed along it - this is often the best strategy.

Output of Motion FB is input to Motion FB

A Motion-Path FB.

	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.
	STEP 2: Add a sketch in the Base-Part to give the XY-Path a)Add a vertical Line to the right of the rectangle/obstacle. Make sure you 'Drag upwards' from the start-Point to the end-Point. b)Add a vertical Line to the left of the rectangle/obstacle Make sure you 'Drag downwards' from the start-Point to the end-Point. c)Add a Blend-Curve Drag from the top of the Line in the right side, to the top of the Line on the Left side. Make sure you Hover+Drag to make the start and end-Points merge. d)Close the Part-Editor
	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.
	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 on the right of the XY-Path c)Click 'OK' in the Command-Manager The Motion-Path FB shows in the graphic-area. The Motion-Point shows at the start-Point of the Line.
	STEP 5: Add a Motion FB and Linear-Motion FB a)Edit the Motion FB Change the Output Data Type to Linear b)Connect the FBs c)Cycle the Mechanism. You will see that Motion-Point does not move all the way along the XY-Path.
	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. Keep the Output Data Type in the Motion FB as Linear. 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)
	b)Edit the Motion so it changes from 0 to 360 (See Note) and returns to zero(0). In the Motion FB, change the Output Data Type to Rotary. 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.
	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.