Step 16.3: Blend-Curve and Motion-Path FB - Basic

<< Click to Display Table of Contents >>

Navigation:  Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves >

Step 16.3: Blend-Curve and Motion-Path FB - Basic

Blend-Curve sketch-element and Motion-Path FB

To guide a Motion-Point along an XY-Path, we will use a Blend-Point sketch-element. The Blend-Curve can provide curvature continuity with other sketch-elements. Curvature Continuity is important to prevent needless vibration of mechanism elements that are joined to Motion-Points that move along the sketch-elements.

The two basic steps are:

1.Edit a Part to add a sketch-path. Th sketch-path includes a Blend-Curve (in this example), to define the shape of a sketch-path.

2.Add a Motion-Path FB to the sketch-path.


Note: As with other sketch-elements:

A Blend-Curve can be one(1) sketch-element that is separate from other sketch-elements

- or -

Its start-Point and/or end-Point can be merged with other Blend-Curves

- and / or -  

Its start-Point and/or end-Point can be merged with different sketch-elements


Add a Blend-Curve

In this tutorial, we merge the start-Point of the Blend-Curve to a Line and its end-Point to an Arc. The sketch will be an open sketch-path

GST-16-3-GA-BlendCurveMotPath-01

STEP 1: Add the Line and Arc sketch-elements

1.Mechanism-Editor : Edit the Base-Part

2.Part-Editor: Geometry toolbar > Add Arc and Add Line

3.Part-Editor: Constraints toolbar > Add Horizontal | Click the Line ; Click the start-Point, center-Point, also end-Point of Arc , to be horizontal.

4.Part-Editor: Constraints toolbar > Add Horizontal | Click the end-Point of the Arc and end-Point of the Line to be Horizontal.

5.Part-Editor: Constraints toolbar > Add Dimension | Click the Arc - Enter 20, Click the end-Point of the Line and end-Point of the Arc - enter 50.

GST-16-3-GA-BlendCurveMotPath-02

STEP 2: Add the Blend-Curve

1.Part-Editor: Geometry toolbar > Add Blend-Curve

2.Part-Editor: Hover + Drag from the end-Point of the LineRed-14-1b and ...

3.... Hover above end-Point of the ArcRed-14-2  

4.Release your mouse-button.

The start-Point and end-Point of the Blend-Curve are merged with the end-Point of the Arc and Line.


NOTES: Default Blend-Curve Parameters at its start-Point and its end-Point:

Blend-Curve Parameters define its shape at its start-Point and end-Point.

The Default Blend-Curve Parameters will equal those of the sketch-element(s) with which you merge its start-Point and/or end-Point.


<<< Blend-Curve Parameters Start-PointRed-14-1b

Angle = 90º vertically upwards.  Equal to the angle of the LineRed-14-3.

Curvature = 0. Radius of a Line = ∞. Curvature = 1/ Radius = 1/∞ = 0

Curvature Rate = 0. The Curvature of the Line is constant. Therefore the Curvature-Rate = 0.

GST-16-3-GA-BlendCurveMotPath-03

GST-16-3-GA-BlendCurveMotPath-04

<<< Blend-Curve Parameters End-Point Red-14-2

Angle = –90º, vertically downwards. Equal to the angle of th Arc

Curvature  = 50 , Radius of a Arc = 20. Curvature = 1/ Radius = 1/0.02 = 50

Curvature Rate = 0. The Curvature of the Arc is constant. Therefore the Curvature-Rate = 0.

Edit the Blend-Curve

GST-16-3-Dialog-Blend-Curve

STEP 3: Open the Blend-Curve dialog-box

Note: You can edit the Blend-Curve in the Part-Editor and the Mechanism-Editor.

1.Part-Editor: Double-click the Blend-Curve

or

See How to open a dialog-Box

The Blend-Point dialog-box is now open.


Start-Point parameters  

Parameters are equal to our observations at the start-Point, above.

Blend is selected for each parameter. Thus, the parameters are Read-Only

The shape of the Blend-Curve is continuous with the sketch-elements to which it is merged:

Angle = 90 - and equal to the angle of the Line

Curvature = 0 - and equal to the Curvature of the Line Same Radius as the start-Point)

Curvature Rate = 0 and equal to the Curvature Rate of any other sketch-element in the Part-Editor

Velocity-Scaling - this parameter is a way of inflating the Blend-Curve

GST-16-3-Dialog-Blend-Curve-CR

STEP 4: Edit the Blend-Curve

You must click a Blend check-box to de-select it, before you can edit a Blend-Curve Parameter.

1.Blend-Curve dialog-box : start-Point : Curvature Rate -Click the Blend check box (to de-select it) of the

2.Blend-Curve dialog-box : Curvature Rate of the start-Point = 2400

3.Blend-Curve dialog-box : Click the Blend check box, for the Curvature Rate of the end-Point  

4.Blend-Curve dialog-box : Curvature Rate of the end-Point = -3000

5.Exit the Blend-Point dialog-box

The units of Curvature Rate are 1/m2.

Rather than calculate values for Curvature Rate, it is easier to observe the shape of the Blend-Curve as you use the Spin-Box.

What is the best Blend-Curve?

It is not possible to know unless you know the application of the Blend-Curve.

 

GST-16-3-GA-BlendCurveMotPath-05

This is the new shape for the Blend-Curve.

Add a Motion Path FB

GST-Icon-FB-MotionPath

GST-16-3-MotionPathFB-B

STEP 1: Add a Motion-Path FB

1.Mechanism-Editor: Kinematic-FB toolbar > Add Motion-Path FB

2.Mechanism-Editor: In the Graphic-area: lick the vertical Line

3.Click OK-tiny-11-15 in the Command-Manager

 

GST-16-3-MotionPathFB-A

The graphic-area after STEP 1

Red-14-1b Motion-Path FB

Red-14-2 Motion-Point at the start-Point of the Line sketch-element


Note: Where is the Motion-Point?

When the sketch-path is an open sketch-path, the Motion-Point finds the sketch-element that has a start-Point that is nearest to the sketch-element that you click.


GST-16-3-MotionPathFB-C

STEP 2: Add a Function-Blocks

1.Mechanism-Editor: Kinematic-FB toolbar > Add Linear-Motion FB

2.Mechanism-Editor: Kinematic-FB toolbar > Add Motion FB

3.Connect the Function-Blocks with wires, in the usual way.

 

GST-16-3-MotionPathFB-MotionFBRotary

STEP 3: Edit the Output Data-Type of the Motion-FB

1.Mechanism-Editor: Open the Motion FB dialog-box

2.Motion FB dialog-box: Motion-FB Parameters Output-Data-Type : RotaryRed-14-1


What are the different Output Data-Types in the Motion FB?

Motion (default) maps input to a Angular (degrees) or Linear (mm) for Motion-Parts

Linear - maps input to Literal Position on the sketch-path for Motion-Points

E.g. 90 maps the Motion-Point to 90mm on the sketch-path.

Rotary - maps input to Total-Length/360 of the sketch-path for Motion-Points

E.g. 90 maps the Motion-Point to (Total-Length/360)×90mm along the sketch-path.


 

Motion-Point - Click to Play

Motion-Point along 25% of Total-Length

GST-16-3-MotionPathFB-D

STEP 4: Observe the Motion-Point when you cycle the model

1.Mechanism-Editor: Press ALT+C keys on your keyboard to cycle and ALT+C again to stop the model (or Run toolbar > Cycle)


STEP 5: Motion MMA to 120

1.Feedback-Area: Drag (with your mouse-pointer in the MMA scale) to the left or tight to move the MMA to approximately 120

or

1.Feedback-Area: Enter 120 in the MMA Digital Read-Write box


<<< click to play video

STEP 6: Edit the Motion in MotionDesigner, to have a range of 0 to 360

Position of the Motion-Point = Total-Length/360) × INPUT

A input-range of 0-360 moves the Motion-Point from the start-point to the end-Point of the sketch-path.

Motion-Point along Total-Length

Motion-Point along Total-Length

STEP 7: Edit the Motion in MotionDesigner, to have a range of 0 to 359.99

Why 355.99?

When the motion-value is 360, the Motion-Point wraps to the start-Point of the sketch-Path

When the motion-value is 359.99, the Motion-Point will not wrap to the start-Point of the sketch-Path .

359.99 is extremely near to the end-Point of the sketch-Path.


<<< click to play video