Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves > Step 16.1: About the Blend-Curve & Motion-Path FB

Difference between a Motion-Part and a Motion-Point

A Motion-Part and a Motion-Point are similar elements.

Motion-Path FB & Motion-Point

Motion-Path FB and Motion-Point

Function-Block menu > Motion-Path FB:

1.Click the Motion-Path FB command icon to add a Motion-Path FB

2.Click a sketch-element in a sketch-path*

3.Click in the Command-Manager.

The Motion-Point is at the start-Point of the sketch-element that you select.

We constrain the Motion-Point to the sketch-elements in the sketch-path

The Motion-Path FB controls the motion of the Motion-Point along the sketch-path.

Note: you can edit a parameter in the Motion-Point dialog to offset the starting position of the Motion-Point along the sketch-path - e.g 30 mm.

Motion-Path> Point-List & Data Display

To see the dimension near to the Motion-Point:

1.Open and edit the Motion-Path FB > Point Parameters >

2.Expand Point List and Data Display :

3.Select:

Nothing: do not show Displacement or Phase

Displacement: the absolute linear position of the Motion-Point along the sketch-path from the start-Point of sketch-path - see dimension (above)

Phase: the normalized phase-angle of the Motion-Point along the sketch-path. The length of the sketch-path is normalized to 360.

Motion-Dimension FB & Motion-Parts

Motion-Dimension Rocker and Slider

Function-Blocks menu > Add Motion-Dimension FB

1.Click the Motion-Dimension FB command icon to add a Motion-Path FB

2.Click a joint and two sketch-elements*

3.Click in the Command-Manager.

A Motion-Dimension FB controls the position of a sketch-element in a Part relative to a position of a sketch-element in a different Part -

The sketch-elements are Lines when you select a Pin-Joint - to give a Rocker.

The sketch-elements are Points when you select a Slide-Joint - to give a Slider.

When we control the Angular displacement of a Part we call it a Rocker.

When we control the Linear displacement of a Part we call it a Slider.

Why use a Blend-Curve?

A Blend-Curve is a sketch-element.

Use the Blend-Curve dialog to control (at its start-Point and at its end-Point) these parameters:

•Angle

•Curvature

•Rate-of-Change of Curvature

•Velocity-Scaling - a normalization parameter that controls the overall length and shape of the Blend-Curve.

The advantages of a Blend-Curve over Lines and Arcs, are its smoothness and how it blends with other sketch-elements at its start-point and end-Point.

Questions:

Question 1: Why do we need a Blend-Curve?

Answer 1: To eliminate a curvature-discontinuity.

Question 2: What is a curvature-discontinuity?

Answer 2: A curvature-discontinuity is a step in Radius-of-Curvature.

E.g. when you join an Arc to a Line (and vice versa), or join two Arcs with a different radii. Even if the sketch-elements are tangent with each other, there is a step in the Radius-of-Curvature.

Question 3: What is wrong with a curvature-discontinuity?

Answer 3: A machine element that moves along path with a curvature-discontinuity will vibrate. To reduce mechanical vibrations, you must eliminate the curvature-discontinuity.

The purpose of the Blend-Curve element is to eliminate curvature-discontinuities.