﻿ Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves > Step 16.3: Blend-Curve and Motion-Path FB - Basic

# 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

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 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. 1.Part-Editor: Geometry toolbar > Add Blend-Curve 2.Part-Editor: Hover + Drag from the end-Point of the Line and ... 3.... Hover above end-Point of the Arc 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-Point •Angle = 90º vertically upwards.  Equal to the angle of the Line . •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.  <<< Blend-Curve Parameters End-Point •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 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

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 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. This is the new shape for the Blend-Curve.

#### Add a Motion Path FB  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 in the Command-Manager The graphic-area after STEP 1 Motion-Path FB 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. 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. 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 : Rotary 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. 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.

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